What is Alzheimer’s
Alzheimer’s is a complex, systemic disease that is difficult or impossible to treat to due to lack of a single cause. A large body of work shows that Alzheimer’s and other age-related cognitive impairment is related to several causes which are personalized to each patient. These various causes impact cognitive performance separately, and have an entourage effect leading to immunosenescence, accelerated aging and death.
Alzheimer’s Disease is the only disease in the top ten causes of death that cannot be cured, prevented or even slowed. Alzheimer’s is a terminal diagnosis which carries with it one of the highest suicide rates. Now is the time to wage war on this epidemic disease the way our elders — the greatest generation — eradicated polio in America. In fact, Alzheimer’s is like a sniper targeting that same greatest generation, our elders.
It has been 14 years since a new drug for Alzheimer’s disease was approved by FDA.
In this time…
- More than 400 clinical trials have failed. In this time, some of the largest drug companies have abandoned further Alzheimer’s drug research after losing hundreds of billions to failed FDA trials.
- Death rates from Alzheimer’s climbed over 55 percent, reaching epidemic proportions and the number of Americans afflicted is likely to rise rapidly in the coming years.
- Over 5.5 million Americans were diagnosed with the disease and that number is projected to double by 2050.
- A growing number of clinical reports have indicated the potential success of personally-tailored patient interventions to slow or reverse age-related brain and body degeneration linked to Alzheimer’s.
This is the time to arm ourselves with a strategically personalized, computational approach that investigates all of the known pathways of dementia — targeting those pathways personalized to each patient — which can only provide better treatment outcomes than currently available (none). The current drug development hypothesis has completely failed to provide any hope for our fellow Alzheimer’s sufferers and their families.
Background and Introduction
Currently Available FDA-approved Drugs for Alzheimer’s Disease
Alzheimer’s Disease is a terminal diagnosis, suffered by over 42 million patients globally, with no FDA approved therapy or treatment. The handful of drugs currently prescribed to Alzheimer’s patients at best temporarily ameliorate symptoms (‘disease-modifying’ as opposed to ‘disease-curative’ therapies). The ‘symptomatic therapies’ currently available are neurotransmitter-focused and fall into two classes: cholinesterase inhibitors, and the NMDA (glutamatergic) receptor agonist memantine. There are no FDA-approved drugs that address the underlying causes of Alzheimer’s disease, which remain poorly understood despite more than 100 years of research. (Reference: Alzheimer’s Association, 2017. 2017 Alzheimer’s disease facts and figures. Alzheimer’s & Dementia, 13(4), pp.325–373. | https://www.alz.org/documents_custom/2017-facts-and-figures.pdf)
As of 2018, it has been 14 years since a new drug for Alzheimer’s disease was approved by FDA. The majority of the more than 400 failed clinical trials pursued strategies to reduce the distinct, observable pathophysiological protein signatures of Alzheimer’s disease: (1) Aβ amyloid plaque accumulation in the brain, which is primarily extracellular (outside of neurons), and (2) phosphorylated tau protein aggregates, which form ‘neurofibrillary tangles’ within neuronal cells. Clinical trials aimed at reducing the patient burden of Aβ and tau aggregate protein deposits have failed to improve patient cognition and function, as FDA requires. It is hypothesized that these 400+ clinical trials failed because they addressed disease ‘too late’ in its progression (i.e., potentially, the patient population for therapeutic testing was not properly selected, and was too ‘late-stage’). However, although it is rarely stated with clarity, these 400 trials may have failed because reduction of Aβ amyloid or tau tangle accumulation is simply not the correct route to halting or reversing the disease; perhaps these protein deposits accompany disease progression, rather than cause it. (Reference: Khoury, R., Patel, K., Gold, J., Hinds, S. and Grossberg, G.T., 2017. Recent Progress in the Pharmacotherapy of Alzheimer’s Disease. Drugs & aging, 34(11), p.811. | https://www.ncbi.nlm.nih.gov/pubmed/29116600)
Alzheimer’s Disease Begins At Least A Decade Before It Is Diagnosed
Alzheimer’s disease is a complex multifactorial disease, often preceded by a decade or more of subtle memory loss, even prior to the condition diagnosable as Mild Cognitive Impairment (MCI). Typically, it is only in retrospect that this pre-MCI phase is recognized, and generally medical attention is not sought at this early stage. (Reference: Caselli, R.J., Beach, T.G., Knopman, D.S. and Graff-Radford, N.R., 2017, June. Alzheimer disease: scientific breakthroughs and translational challenges. In Mayo Clinic Proceedings (Vol. 92, №6, pp. 978–994). Elsevier. | https://www.ncbi.nlm.nih.gov/pubmed/28578785)
Within this pre-MCI phase, a sizable number of elderly individuals with a measurable degree of cognitive decline — as detectable by an Executive Function Test — self-reported as having normal cognitive performance. In other words, the patient himself (or herself) is rarely able to recognize early cognitive decline. (Reference: Shea, T.B. and Remington, R., 2018. Apparent Cognitive Decline as Revealed by an Executive Function Test within a Cohort of Elderly Individuals Self-Reporting Normal Cognitive Performance. Journal of Alzheimer’s Disease, 61(3), pp.913–915. | https://www.ncbi.nlm.nih.gov/pubmed/29332053)
These findings support a practice of regular cognitive testing of aging persons, so that earlier diagnosis and treatment is possible. Additionally, anxiety and depressive symptoms are increasingly being recognized as possible indicators of the early development of Alzheimer’s neurocognitive decline; and many of those with depression or anxiety seek out prescriptions for psychotropic psychiatric medications, which can have a range of side effects, further complicating the situation of assessing cognition. (Reference: Donovan, N.J., Locascio, J.J., Marshall, G.A., Gatchel, J., Hanseeuw, B.J., Rentz, D.M., Johnson, K.A., Sperling, R.A. and Harvard Aging Brain Study, 2018. Longitudinal Association of Amyloid Beta and Anxious-Depressive Symptoms in Cognitively Normal Older Adults. American Journal of Psychiatry | https://ajp.psychiatryonline.org/doi/abs/10.1176/appi.ajp.2017.17040442?journalCode=ajp)
The Failure of 400+ Alzheimer’s Disease Clinical Trials
In the past 14 years, more than 400 clinical trials aimed at discovering new drugs to treat Alzheimer’s disease failed, and no new drugs have been approved by the FDA in that time (Reference: “Why coming up with a drug for Alzheimer’s is so devilishly hard”, Washington Post, 1/12/18 http://wapo.st/2my2xU8). These 400 trials followed the standard drug development path; they enrolled subjects suffering from mid-to-late stage, clinically heterogeneous Alzheimer’s disease (easier to diagnose by cognitive testing and brain imaging than early-stage disease), and attempts were made to treat them with the same, single protein antibody or single organic chemical drug in each trial. A comprehensive list of all drugs in clinical development that aim to reduce either Aβ pathology, tau pathology, or inflammation within the past five years categorized by treatment strategy and drug class, are provided in Table 1 in this paper: (Reference: Clayton, K.A., Van Enoo, A.A. and Ikezu, T., 2017. Alzheimer’s Disease: The Role of Microglia in Brain Homeostasis and Proteopathy. Frontiers in neuroscience, 11. | https://www.frontiersin.org/articles/10.3389/fnins.2017.00680/full). All of these trials have failed.
A New Approach: Computational Systems Medicine
The stunning failures of these 400 trials, accompanied by the loss of billions of dollars by pharmaceutical companies, indicates that we are long overdue for a major change in approach, towards a distinctly different computationally assisted “P4 Medicine” approach (where P4 stands for Predictive, Preventive, Personalized, Participatory), which will prescribe new therapeutic approaches (txalz.org) along with computationally enhanced risk screening, and much earlier detection and treatment — at a younger age and milder stage of disease — and active programs aimed at disease prevention.
P4 medicine is the clinical face of computational systems medicine; making blood a diagnostic window for viewing human health and disease, to enable new approaches to drug target discovery and drive profound economic, policy, and social changes. The P4 approach to working with Alzheimer’s disease patients, or younger persons at risk of developing Alzheimer’s, will require an initial sorting of patients into distinct genetic and biological subsets, based on personalized genotyping and phenotyping as well as ongoing metabolic profiling, and proteomics analysis. (Reference: Hampel, H., O’Bryant, S.E., Durrleman, S., Younesi, E., Rojkova, K., Escott-Price, V., Corvol, J.C., Broich, K., Dubois, B., Lista, S. and Alzheimer Precision Medicine Initiative, 2017. A precision medicine initiative for LOAD disease: the road ahead to biomarker-guided integrative disease modeling. Climacteric, 20(2), pp.107–118. | https://www.ncbi.nlm.nih.gov/pubmed/28286989)
Although not yet common medical practice, in the future, the measurement of numerous different biomarkers, beginning at a relatively early age (e.g., 45 years), will improve physicians’ ability to identify persons at early risk of developing progressive neurodegenerative disease. With the rising prevalence of Alzheimer’s disease and its enormous cost to society, it may also become common practice to prophylactically ‘pre-treat’ younger people with certain vitamins and nutraceuticals known to be neurotrophic, to protect them from disease.
This approach is concisely described in the 2016 international consortium on Alzheimer’s disease:
Clarification and practical operationalization is needed for comprehensive dissection and classification of interacting and converging disease mechanisms, description of genomic and epigenetic drivers, natural history trajectories through space and time, surrogate biomarkers and indicators of risk and progression, as well as considerations about the regulatory, ethical, political and societal consequences of early detection at asymptomatic stages. In this scenario, the integrated roles of genome sequencing, investigations of comprehensive fluid-based biomarkers and multimodal neuroimaging will be of key importance for the identification of distinct molecular mechanisms and signaling pathways in subsets of asymptomatic people at greatest risk for progression to clinical milestones due to those specific pathways.
The P4 computational systems medicine strategy facilitates a paradigm shift in Neuroscience and AD research and development away from the classical ‘one-size-fits-all’ approach in drug discovery towards biomarker guided ‘molecularly’ tailored therapy for truly effective treatment and prevention options. After the long and winding decade of failed therapy trials progress towards the holistic systems-based strategy of precision medicine may finally turn into the new age of scientific and medical success curbing the global AD epidemic.” (Reference: Hampel, H., O’Bryant, S.E., Castrillo, J.I., Ritchie, C., Rojkova, K., Broich, K., Benda, N., Nisticò, R., Frank, R.A., Dubois, B. and Escott-Price, V., 2016. PRECISION MEDICINE-the golden gate for detection, treatment and prevention of Alzheimer’s disease. The Journal of Prevention of Alzheimer’s disease, 3(4), p.243. | https://www.ncbi.nlm.nih.gov/pubmed/28344933)
An Example of How Neurotrophic Factors Can Improve Cognition In Adults
For example, in a study in which community-dwelling adults without dementia were dosed with a vitamin and nutraceutical formulation (“NF”: Folate, Vitamin B12, Vitamin E, S-adenosylmethionine, N-acetyl cysteine and acetyl-L-carnitine), within weeks the subjects showed cognitive function improvements both statistically and clinically in the California Verbal Learning Test II and the Trail-Making Test; this improvement was observed in the treated but not untreated group. However, when older people (> 74 years of age) received the same NF formulation, their performance on the cognitive tests improved much less. This could mean that older persons require higher doses of trophic vitamins or nutriceuticals due to poorer absorption and/or basal nutritional deficiencies, or that a more integrative or complex therapy is required for efficacy in older persons. (Ref: Chan, A., Remington, R., Kotyla, E., Lepore, A., Zemianek, J. and Shea, T.B., 2010. A vitamin/nutriceutical formulation improves memory and cognitive performance in community-dwelling adults without dementia. The Journal of Nutrition, Health & Aging, 14(3), pp.224–230. | https://www.ncbi.nlm.nih.gov/pubmed/20191258) Interestingly, the individual components of the NF formulation have each failed to show statistically significant clinical benefit when utilized alone, in a series of meta-analyses of clinical trials performed by the Cochran Library, whereas this “NF” combination of six compounds did provide measurable improvements in this particular study.
Late-Onset Alzheimer’s Disease (LOAD) as a Systemic, Atrophic Disorder
Once an individual has progressed to diagnosable LOAD, and even to a degree in the Mild Cognitive Impairment phase, imaging tools such as Magnetic Resonance Imaging (MRI) are able to detect observable atrophy — physical shrinkage — of brain tissue. For the distinction of MCI from healthy controls, atrophy of hippocampal brain tissue was a statistically significant measure of difference; whereas only the atrophy of the whole brain volume was able to distinguish between patients with MCI and patients with more advanced Alzheimer’s disease. Regional measurements of hippocampal atrophy over time were the strongest predictor of an MCI patient’s progression to AD. (Ref: Henneman, W.J.P., Sluimer, J.D., Barnes, J., Van Der Flier, W.M., Sluimer, I.C., Fox, N.C., Scheltens, P., Vrenken, H. and Barkhof, F., 2009. Hippocampal atrophy rates in Alzheimer disease Added value over whole brain volume measures. Neurology, 72(11), pp.999–1007. | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3785543/)
Even in healthy persons without Alzheimer’s disease, hippocampal volume decreases with age, and this drop in volume is correlated with a reduction in ‘fluid intelligence’, defined as the ability to solve new problems, use logic in novel situations, and identify patterns. In a 2011 study, both whole-brain and hippocampal volume were measured in 40 healthy young (aged 18–30 years) and 36 healthy elderly (aged 60–83 years) subjects, and compared with composite cognitive function scores in three conceptual domains: memory ability, processing speed, and general fluid intelligence. In elderly subjects but not in young persons, a significant positive correlation existed between hippocampal volume and fluid intelligence ability. Yet, no relationship between other cognitive domains and brain or hippocampal volume was found. These research results indicate that there could be a causative correlation between aging-related atrophy of hippocampal brain tissue, and a decline in fluid intelligence in older persons. (Ref: Reuben, A., Brickman, A.M., Muraskin, J., Steffener, J. and Stern, Y., 2011. Hippocampal atrophy relates to fluid intelligence decline in the elderly. Journal of the International Neuropsychological Society, 17(1), pp.56–61. | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3785543/)
In patients with mild cognitive impairment or Alzheimer’s disease, MRI analysis frequently reveal hippocampal atrophy. Even in older patients without symptoms of neurodegeneration, small hippocampal volume assessed by MRI is a risk factor for development of Alzheimer’s disease. However, the medical diagnostic issue is greatly complicated by the fact that not all patients with small hippocampi will develop symptoms of dementia. On the other hand, sequential MRIs of Alzheimer’s patients show a higher rate of hippocampal atrophy compared to healthy people or patients with mild cognitive impairment. A 2010 study of 518 elderly patients (age 60–90 years, 50% female) showed that in persons followed over a period of 10 years, who were all free of dementia upon the first MRI analysis, the rate of hippocampal atrophy is an early marker of incipient memory decline and dementia, and could be of additional value when compared with a single hippocampal volume measurement (for comparison to typical or average hippocampal volume) as a surrogate biomarker of dementia. Specifically, there was an increased risk of developing incident dementia per standard deviation faster rate of decline in hippocampal volume. (Ref: den Heijer, T., van der Lijn, F., Koudstaal, P.J., Hofman, A., van der Lugt, A., Krestin, G.P., Niessen, W.J. and Breteler, M.M., 2010. A 10-year follow-up of hippocampal volume on magnetic resonance imaging in early dementia and cognitive decline. Brain, 133(4), pp.1163–1172. | https://www.ncbi.nlm.nih.gov/pubmed/20375138)
Another imaging modality that can provide a useful measure of AD-related amyloid-β (Aβ) deposits and interneuronal hyperphosphorylated tau ‘tangles’ is Positron Emission Tomography (PET), which requires the use of a radiotracer. A recent (2018) study showed using PET with the radiotracer T807 (also called flortaucipir or AV-1451) found that aberrantly high levels of two AD biomarkers — amyloid deposits and tau aggregates — were correlated positively with impaired driving ability in older adults, as judged by the outcome of a standardized road test (marginal/fail test rating, n = 42). Study subjects whose PET scans were positive for both amyloid and tau, with preclinical AD, were more likely to fail a driving test (Ref: Roe, C.M., Babulal, G.M., Mishra, S., Gordon, B.A., Stout, S.H., Ott, B.R., Carr, D.B., Ances, B.M., Morris, J.C. and Benzinger, T.L., 2017. Tau and Amyloid Positron Emission Tomography Imaging Predict Driving Performance Among Older Adults with and without Preclinical Alzheimer’s Disease. Journal of Alzheimer’s Disease, (Preprint), pp.1–6. | https://www.ncbi.nlm.nih.gov/pubmed/29171997)
While the systemic diseases Type II diabetes and cardiovascular disease engender higher annual rates of morbidity and mortality in the United States, the incidence of neurodegenerative disease is rising in an aging population. The aging process that is concomitant with neurodegeneration has negative effects on every body system and organ, which seems to be reflected in a proteomic signature that can be measured in circulating blood. Conversely, in laboratory studies, factors in the blood of healthy young individuals have been shown to be able to rejuvenate the tissues of older individuals, including the progenitor cells of liver, muscle, and brain. Current research is focused on identifying these rejuvenation factors and understanding their place in the complex mechanism of systemic human aging. (Ref: Wyss-Coray, T., 2016. Ageing, neurodegeneration and brain rejuvenation. Nature, 539(7628), p.180. | https://www.ncbi.nlm.nih.gov/pubmed/27830812)
Systemic Dysfunction of Cellular Bioenergetics: A Hallmark of Late-Onset Alzheimer’s Disease
Systemic alterations in cellular energy metabolism occur in normal aging. However, abnormal or disturbed bioenergetics appear to be a significant mechanistic contributor to the pathophysiology of late-onset Alzheimer’s disease (LOAD). A 2017 Harvard study compared the bioenergetic profiles of fibroblasts, i.e. external skin cells, from LOAD patients and healthy controls as a function of age and disease state. Skin cells taken from LOAD patients showed impaired mitochondrial metabolic potential and abnormal redox potential, associated with lower levels of reduced nicotinamide adenine dinucleotide (NADH) metabolism and an altered citric acid cycle. However, there were no statistically significant differences in mitochondrial mass, production of reactive oxygen species, transmembrane instability, or DNA deletions. Most significantly, the fibroblasts of LOAD patients were found to be generating energy to a greater degree using a process of aerobic glycolysis (a non-mitochondrial process of energy production), despite an inability to increase glucose uptake in response to IGF-1. The shift to increased glycolysis (reduced reliance on mitochondria, likely to correlate with mitochondrial dysfunction or damage) and abnormal metabolic potential in LOAD were disease state-specific, but not age-specific. These exciting new findings indicate that aberrant changes to particular mechanistic aspects of bioenergetic metabolism may be an important key to assessing the risk and pathophysiological progression of Alzheimer’s. (Ref: Sonntag, K.C., Ryu, W.I., Amirault, K.M., Healy, R.A., Siegel, A.J., McPhie, D.L., Forester, B. and Cohen, B.M., 2017. Late-onset Alzheimer’s disease is associated with inherent changes in bioenergetics profiles. Scientific Reports, 7(1), p.14038. | https://www.ncbi.nlm.nih.gov/pubmed/29070876)
There are gender considerations to considering cellular bioenergetics. In the female brain, estrogen is a key regulator of glucose transport, aerobic glycolysis, and mitochondrial function to generate the cell’s energy source: adenine triphosphate (ATP). Estrogen’s role is to regulate energy intake and expenditure, and in healthy young women helps protect against adiposity, insulin resistance, and type II diabetes. In older women, menopause causes a reduction in circulating estrogen, coincident with a decline in brain bioenergetics and a shift towards the same type of metabolically degraded phenotype described above (with a shift towards energy production by glycolysis, known as the Warburg Effect). Thus, in females, shifts in bioenergetic mechanisms which can be related to hormonal changes could be indicative of the risk of late-onset Alzheimer’s disease, LOAD, since estrogen is a coordinator of both brain and body metabolism. It is intriguing that metabolic energy biomarker profiling of easily accessible body tissues, such as fibroblasts, can report on the bioenergetic status of the brain. This also indicates that hormone replacement therapies may help stave off LOAD neurodegeneration. (Ref: Rettberg, J.R., Yao, J. and Brinton, R.D., 2014. Estrogen: a master regulator of bioenergetic systems in the brain and body. Frontiers in neuroendocrinology, 35(1), pp.8–30. | https://www.ncbi.nlm.nih.gov/pubmed/23994581)
Impaired or Imbalanced Innate Immunity Is Apparent in the Alzheimer’s Brain
For some patients, impaired or imbalanced innate immunity may play a role in the dysfunction of neurological tissue. A 2017 study found that the bacterial envelope-derived lipid called lipopolysaccharide (LPS) — a neurotoxin — accumulates in the neocortical neurons of the Alzheimer’s disease (AD) brain, but is not found in healthy young brains. Previous studies have identified contaminating bacterial nucleic acid sequences in the AD brain. It is not known whether this contaminating bacterial LPS originates from the gastrointestinal (GI) tract microbiome, from a possible brain microbiome, or from pathological infecting bacterial species. However, neuronal cell culture studies showed that the presence of LPS impairs gene transcription in neurons; so this particular contaminant in the AD brain may be a significant contributor to tissue atrophy, through impairment of gene transcription. (Ref: Zhao, Y., Cong, L. and Lukiw, W.J., 2017. Lipopolysaccharide (LPS) Accumulates in Neocortical Neurons of Alzheimer’s Disease (AD) Brain and Impairs Transcription in Human Neuronal-Glial Primary Co-cultures. Frontiers in aging neuroscience, 9. | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5732913/)
Most Significant Genetic Risk for Late-Onset AD: The ε4 Allele of the Apolipoprotein E gene (apoE4)
Whereas the aggregation and plaque formation of amyloid-β (Aβ) in brain tissue is an important aspect of the pathogenesis of Alzheimer’s disease (AD), the molecular mechanism and signal by which this process is initiated remains poorly understood for sporadic, or late-onset AD, which is most common. With a lack of full understanding of disease mechanism, genetic aspects of risk remain incompletely known; however, the ε4 allele of apolipoprotein E (apoE) gene (apoE4) remains the strongest known genetic risk factor for late-onset AD. Another allele variant of the apoE gene, apoE3, is protective against neurodegenerative disease. (Ref: In Thai Nationals, the ApoE4 Allele Affects Multiple Domains of Neuropsychological, Biobehavioral, and Social Functioning Thereby Contributing to Alzheimer’s Disorder, while the ApoE3 Allele Protects Against Neuropsychiatric Symptoms and Psychosocial Deficits https://www.ncbi.nlm.nih.gov/pubmed/29307083) About ¼ of people worldwide carry one APOE4 allele, which is linked to a higher risk of AD, while 2–3% of the population has two APOE4 alleles and suffers from ~60% risk of developing Alzheimer’s disease by age 85. Whereas substantial evidence has shown that carrying an apoE4 allele (or two) enhances the severity of amyloid pathology, only recently in 2017 was it discovered in a mouse study that apoE4 expression in brain astrocytes enhance amyloid deposition by a “seeding” mechanism that spreads the pathology, and also increases Aβ half-life in the brain. On the other hand, this was not true of apoE3 expression. Overall, recent results have shown that apoE4 has the greatest impact on amyloid accumulation during a ‘seeding’ stage, apparently by simultaneously reducing Aβ clearance and enhancing Aβ aggregation. (Ref: ApoE4 Accelerates Early Seeding of Amyloid Pathology https://www.ncbi.nlm.nih.gov/pubmed/29216449)
Sporadic Alzheimer’s disease (AD), as opposed to its autosomal dominant form, appears to result from a complex interplay of genetic, environmental, and health lifestyle factors. Two related studies have shown that the “heritability” of sporadic AD is likely between about 58% and 79%, around half of which is explained by inheriting the apoE4 allele. A 2017 study from Quebec hypothesized that other genes associated with related, known risk factors for AD, including hypertension, hypercholesteremia, obesity, diabetes, and cardiovascular disease, might contribute to the remaining heritability. These researchers analyzed 22 AD-associated single-nucleotide polymorphisms (SNPs) associated with these risk factors in 355 study participants of the Alzheimer’s Disease Neuroimaging Initiative 1 data set, all of whom were already diagnosed with mild cognitive impairment (MCI). Although 22 different SNPs were studied, they found that just one particular SNP was linked with MCI progression to AD: the rs391300 SNP, which predicts increased susceptibility to Type 2 diabetes. (Ref: Faster progression from MCI to probable AD for carriers of a single-nucleotide polymorphism associated with type 2 diabetes https://www.ncbi.nlm.nih.gov/pubmed/29338921) This was very telling given prior hypotheses that there are major mechanistic connections between Type II diabetes and Alzheimer’s Disease. (Ref: Alzheimer’s Disease Is Type 3 Diabetes–Evidence Reviewed https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769828/)
Blood Biomarkers of Systemic Inflammation Correlate with Late-Onset Alzheimer’s Disease
Many studies have linked chronic, systemic inflammation with cognitive decline associated with Alzheimer’s disease. A 2018 study investigated the relationship between biomarkers of inflammation and changes in brain activity assessed by regional cerebral blood flow (rCBF) in older individuals. This was done by positron emission tomography (PET) scans collected over a 5-year period from 138 initially cognitively normal older persons (mean age 71.3; 77 males, 61 females) as part of the Baltimore Longitudinal Study of Aging. With on average 3.5 scans done per person over 5 years, the study correlated rCBF with levels of the inflammatory biomarkers C-reactive protein (CRP) and interleukin-6 (IL-6) in blood. Higher baseline levels of CRP and IL-6 were each associated with lower baseline rCBF in the frontal and occipital brain regions. Higher baseline and mean CRP levels associated with increased rCBF declines over time in anterior cingulate and hippocampal brain regions, which are critical for cognition. Thus chronic systemic inflammation in older adults may play a role in age-associated losses in cognitive function, or in any case, are correlated with this loss of function. (Ref: Elevated Markers of Inflammation Are Associated With Longitudinal Changes in Brain Function in Older Adults https://www.ncbi.nlm.nih.gov/pubmed/29304217)
Complex Roles of Microglia in the Initiation and Progression of Late-Onset Alzheimer’s Disease
Within brain tissue, a particular class of innate immune cells called microglia are believed to play a central role in the pathogenesis of Alzheimer’s disease. While it is understood that aging is a central aspect of late-onset Alzheimer’s disease (LOAD), the specific mechanisms by which neurodegenerative processes are initiated and progress at the cellular and protein levels are only beginning to be understood. The two key observable proteopathies in the LOAD brain are ‘senile plaques’ (composed primarily but not exclusively of aggregated amyloid-β peptides), and intraneuronal ‘tangles’ of a microtubule-associated protein called tau. Microglia are resident phagocytic cells of the central nervous system, and normally function to clear protein aggregates and other cellular debris, as well as to secrete a variety of natural neurotrophic factors. However, microglial functions are altered by aging-associated inflammation and neurodegeneration. Two microglia-specific genes, TREM2 and CD33, show significant genome-wide association with the risk of LOAD. Therapies that modify or enhance microglial function, enhancing their ability to regenerate function and clear amyloid-β and tau proteopathies, may provide new approaches to treating Alzheimer’s disease. (Ref: Alzheimer’s Disease: The Role of Microglia in Brain Homeostasis and Proteopathy https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5733046/)
It is also apparent that interactions between microglia and cells comprising the blood-brain barrier (BBB) play a role in brain diseases, including neurodegenerative diseases such as Alzheimer’s disease and also infectious / inflammatory diseases, epilepsy, and ischemic stroke. The BBB is composed of an extensive network of endothelial cells (ECs), together with neurons, glial cells, microglia, and pericytes, knit into what is called the ‘neurovascular unit’, which regulates cerebral blood flow. Proper brain function is enabled by an environment of healthy connectivity and crosstalk between these different types of cells. In inflammation-related brain diseases, BBB permeability becomes compromised, and this may be important for the initiation and progression of Alzheimer’s disease. So-called ‘activated’ microglia (having a pro-inflammatory phenotype) appear to modulate expression of ‘tight junctions’, which strengthen BBB integrity and are key to proper function. Endothelial cells lining the vasculature can release protein factors that regulate the state of microglial activation. (Ref: The impact of microglial activation on blood-brain barrier in brain diseases https://www.ncbi.nlm.nih.gov/pubmed/25404894)
The pathology of Alzheimer’s Disease is accompanied by chronic brain inflammation, and the interface between neural cells and the endothelial cell membrane lining cerebral microvessels is central to the maintenance of chronic inflammation during AD. The neurovascular unit becomes dysfunctional during AD, with each of its constituent cell types exhibiting functional alterations that contribute to brain injury and cognitive decline. Because the BBB becomes compromised in AD, migrating immune cells from the blood circulation can migrate through the activated brain endothelium and penetrate into the brain parenchyma, where they interact negatively with neurovascular unit components. Blockade of cellular adhesion mechanisms that control leukocyte-endothelial interactions has been shown to reduce Aβ deposition and tau hyperphosphorylation, and reduce memory loss in AD models. Plasma exchange therapy, as discussed below, may be able to modulate disease via effects on brain vasculature. (Ref: The blood-brain barrier in Alzheimer’s disease https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5600438/)
Resident microglial cells in the brain are believed to play an important role in the pathogenesis of AD, however it has been unclear whether microglial ‘activation’ (adoption of an inflammatory phenotype) is the main mechanism of neuropathy, or could be a bystander effect while dystrophic or senescent (nonfunctional) microglia may be the key to neurodegeneration. This question arose when anti-inflammatory drugs were found not to prevent or reverse ‘tau tangle’ neuropathology, which contradicts the concept that activated (proinflammatory) microglia are the direct cause of neurofibrillary degeneration. In situ, high-resolution histopathological studies of microglial cells in 19 human archival brains, which covered the spectrum from healthy brain to severe AD pathology, showed that degenerating neuronal structures in the immediate vicinity of tau tangle-positive cells (containing neuropil threads, neurofibrillary tangles, and neuritic plaques) were invariably co-located with severely dystrophic (fragmented) microglia, rather than activated microglial cells. This study employed a method called ‘Braak staging’ to further demonstrate that microglial senescence and dystrophy precedes the spread of tau pathology. On the other hand, deposits of amyloid-β plaques were co-localized with branched, non-activated microglia (a healthy structural phenotype), indicating that microglia are not activated simply by the presence of amyloid-β deposits. The same study found that in cases where microglial activation was observed in the absence of an acute insult to the central nervous system, it appeared to be the result of a systemic infectious disease. Taken together, these findings are very important because they argue against the hypothesis that neuroinflammation alone drives late-onset Alzheimer’s dementia. Instead, these results suggest that (1) microglia are essential neuron-supportive cells with a neuroprotective role; and (2) the development of sporadic (late-onset) Alzheimer’s dementia is inextricably linked to aging, in which progressive, age-related senescence of microglia and a loss of their neuroprotective functions, rather than inflammatory microglial activation, are the key to late-onset Alzheimer’s disease. (Ref: Dystrophic (senescent) rather than activated microglial cells are associated with tau pathology and likely precede neurodegeneration in Alzheimer’s disease https://www.ncbi.nlm.nih.gov/pubmed/19513731) In turn, this argues strongly in favor of the provision of supportive neurotrophic factors and the removal of senescent and dystrophic cellular debris as an important aspect of patient treatment.
A class of post-translationally modified biomolecules linked to immune cell activation that are believed to play a role in chronic diseases including AD are advanced glycation end products (AGEs) and their receptor (RAGE). Recently, activated macrophages were determined to be a source of AGEs; and the most abundant form of AGEs, AGE-albumin released by macrophages, is implicated in disease. Additionally, AGE inhibition has been shown to prevent the pathogenesis of AGE-related diseases in humans, and a number of therapeutic agents have been shown to prevent their adverse effects. Anti-inflammatory organic molecules that inhibit AGE formation include, e.g., resveratrol, curcumin, ascorbic acid, Vitamin D3, sulphoraphane, quercetin, and alpha-lipoic acid; see full list in Table 2 of (Ref: Advanced glycation end-products produced systemically and by macrophages: A common contributor to inflammation and degenerative diseases https://www.ncbi.nlm.nih.gov/pubmed/28223234)
Other genetic alleles in addition to APOE4/APOE3 can increase AD risk or are protective against AD. One gene of significant current interest for its connection to AD is ‘triggering receptor expressed on myeloid cells 2’ (TREM2). Variants of TREM2 are associated with a 2–4-fold higher risk of developing AD; either partial or complete loss of TREM2 function via mutations results in increased Aβ plaque deposits and/or Aβ-associated microgliosis (i.e., an increase in the number of activated microglia at the site of a neuronal lesion). Although details of mechanism are still under study, a growing consensus states that in TREM2-haploinsufficient and TREM2-deficient mice there is substantial reduction in the activation of microglia surrounding Aβ plaques (although results described in the paragraph above would imply that this should not necessarily be expected in the healthy brain). TREM2 appears to be an important factor in the proper response of microglia to neuropathology, specifically as a potential regulator of microglial inflammatory responses and clearance of senescent or apoptotic neurons and/or amyloid-β deposits. This is a rarer human genetic risk factor for AD than the ApoE4 allele (Ref: TREM2 Function in Alzheimer’s Disease and Neurodegeneration https://www.ncbi.nlm.nih.gov/pubmed/26854967)
Another, related gene of interest encodes a protein structurally similar to TREM2 called ‘TREM-like transcript 2’ (TREML2), which is encoded by the same gene cluster with TREM2 on chromosome 6, and is protective against AD. In vivo studies show that bacterial lipopolysaccaride (LPS), a surrogate for infection, suppresses TREM2 expression, but increases TREML2 expression in mouse brain. These and other results indicated that upregulation of TREML2 in primary microglia may support their normal neuroprotective functions of responding to infection and clearly senescent or dystrophic neurons or cellular debris. It appears that TREM2 and TREML2 play opposing mechanistic roles in regulating microglial function, and that their dysfunction contributes to AD pathogenesis by impairing the innate immune response of the human brain. (Ref: Opposing roles of the triggering receptor expressed on myeloid cells 2 and triggering receptor expressed on myeloid cells-like transcript 2 in microglia activation https://www.ncbi.nlm.nih.gov/pubmed/27143430)
The role of systemic infection, and the resultant inflammation, in creating neurodegenerative microglial phenotypes is also under investigation. Activated microglia are one feature observed in the AD brain, although as described above, their direct role in neurodegeneration is still under investigation. However animal model studies indicate that when activated microglia become further activated by a systemic infection, the levels of the inflammatory biomarker protein Interleukin 1β (IL-1β) become elevated in the CNS (central nervous system). A fascinating 2018 prospective pilot study in human AD subjects (85 community-dwelling subjects fulfilling NINCDS-ADRDA diagnostic criteria for Alzheimer’s disease) revealed that cognitive function can be impaired for at least two months after the resolution of a systemic infection; and that loss of cognitive function is preceded by raised serum levels of IL-1β. Further research is needed to determine if recurrent systemic infections can drive cognitive decline in AD subjects via an inflammatory blood-borne cytokine-mediated pathway. (Ref: Systemic infection, interleukin 1β, and cognitive decline in Alzheimer’s disease https://www.ncbi.nlm.nih.gov/pubmed/12754353)
Although above mentioned studies found that anti-inflammatory treatments such as nonsteroidal anti-inflammatory drugs (NSAIDs) do not prevent the formation of the ‘tau tangle’ pathology (sometimes called ‘the tombstone marker’ since it occurs late in the AD disease process), it is nonetheless also true that the progression of AD has a significant inflammatory component, as revealed by a comparison of environmental factors in affected and unaffected members of discordant twin pairs or siblings. For siblings with a high genetic/familial risk of AD, sustained use of NSAIDs is associated with delayed onset and reduced risk of AD. Independent of exposure to NSAIDs, onset was also delayed in those who reported extended use of histamine H2 blocking drugs, such as those used to treat allergy. This is significant because NSAIDs block the calcium-dependent postsynaptic cascade that induces excitotoxic apoptosis in NMDA-reactive (glutamatergic) neurons, while histamine potentiates such events; it implies that the mechanisms of ‘excitotoxicity’ should be revisited in AD research. (Ref: Delayed onset of Alzheimer’s disease with nonsteroidal anti-inflammatory and histamine H2 blocking drugs https://www.ncbi.nlm.nih.gov/pubmed/8544901)
Another environmental risk factor that can increase the risk of developing late-onset AD is chronic psychosocial stress. Research has shown that chronic stress primes microglia and induces inflammation in the adult brain, compromising the normal synapse-supportive roles of microglia. The activation effects of chronic stress may impair the ability of microglia to clear abnormally accumulating Aβ peptide deposits. In addition to the TREM2 and TREML2 genes discussed above, genome-wide association studies have linked variants of the CD33 gene, which is expressed in microglia only, with cognitive dysfunction in late-onset AD. At this time, the specific mechanisms by which microglia-mediated neuroinflammation is driven by chronic psychosocial stress is not fully understood. (Ref: Psychosocial stress on neuroinflammation and cognitive dysfunctions in Alzheimer’s disease: the emerging role for microglia? https://www.ncbi.nlm.nih.gov/pubmed/28185874).
Differences between young blood and old blood
The HOPE clinical trial aims to treat people (age 60–80) with early-stage late-onset Alzheimer’s disease (LOAD) to slow, halt, or reverse aging-related cognitive deficits with a combination of plasma exchange therapy and supportive neurotrophic factors delivered either orally or via infusion. The plasma exchange step will provide fluids and proteins extracted from youthful plasma to these elderly patients. In this context, it is helpful to review the literature that has investigated the differences that are measurable between the blood of younger vs. older persons.
One class of blood compounds that tend to differ significantly as a function of age are metabolites, which are influenced by a number of factors including genetic (including gender), epigenetic, and lifestyle factors. A 2016 research study used comparative, high-resolution, quantitative HPLC-MS (High-Performance Liquid Chromatography-Mass Spectrometry) to analyze blood samples from 15 young (29 ± 4 y of age) and 15 elderly (81 ± 7 y of age) persons. A total of 126 different blood metabolites were measured, for all 30 donors, with 55 analyzed in detail. Of these, 14 distinct blood metabolites were found to show strong age-related concentrations (these included 1,5-anhydroglucitol, dimethyl-guanosine, acetyl-carnosine, carnosine, ophthalmic acid, UDP-acetyl-glucosamine, N-acetyl-arginine, N6-acetyl-lysine, pantothenate, citrulline, leucine, isoleucine, NAD(+), and NADP(+)). The results indicated, in particular, that red blood cell (RBC) metabolomics analysis provides excellent markers of human aging. The 14 metabolites that showed strong age dependence seemed to be affected by a decrease, in older persons, in antioxidants in blood, as well as a growing inefficiency of urea metabolism. Overall, this recent study revealed that human blood provides important data about individual metabolic differences. (Ref: Individual variability in human blood metabolites identifies age-related differences https://www.ncbi.nlm.nih.gov/pubmed/27036001) In general, metabolites, which are relatively small molecules, are easier to detect and analyze than proteins in blood, which require advanced sample preparation methods and yet more advanced analytical technologies.
The metabolite composition of a blood sample is both sex- and age-specific. A 2017 study showed that analysis of the human blood metabolome can, remarkably, predict both the age and gender of a person with high accuracy. In the KarMeN (Karlsruhe Metabolomics and Nutrition) study, 301 healthy males and females (18–80 years of age) were studied. These researchers tracked 400 metabolites in fasting blood and 500 metabolites in 24 h urine, using a combination of mass spectrometry coupled to either one- or comprehensive two-dimensional gas chromatography or liquid chromatography, and nuclear magnetic resonance spectroscopy, and correlated levels of these metabolites with age and gender using predictive modeling and machine learning algorithms. These researchers found that levels of a subset of metabolites (including for instance creatinine, branched-chain amino acids, and sarcosine) predicted the sex of the person with > 90% accuracy. They could also predict age based on levels of gender-specific metabolites; for instance, choline in plasma and sedoheptulose in urine. Female subjects could be classified according to their menopausal status with > 80% accuracy from metabolome data. What this study shows is that even healthy humans have distinct metabolite patterns in their blood based on their sex, and on their age. It stands to reason as well that in addition to sex, age and menopausal status (for women), whether a person is healthy, or suffering from a chronic disease, will also be reflected in their blood. (Ref: Metabolite patterns predicting sex and age in participants of the Karlsruhe Metabolomics and Nutrition (KarMeN) study https://www.ncbi.nlm.nih.gov/pubmed/28813537)
Aged blood inhibits neurogenesis / neuroregeneration
A very recent 2018 study, now available online although still undergoing peer review, found that aging can negatively affect blood vessel and the circulatory environment of the brain, promoting dysfunction of the brain. Profiling of brain endothelial cells from the aged mouse hippocampus showed an inflammatory gene expression profile and an upregulation of VCAM1 (Vascular Cell Adhesion Molecule 1), which is involved in binding interactions between the interior surfaces of the vasculature and circulating immune cells. Moreover, the soluble form of VCAM1, which is shed from the internal surfaces of the vasculature, is significantly higher in the circulation of older humans and mice. Unknown factors within aged plasma are sufficient to cause upregulation of VCAM1 expression in cultured brain endothelial cells, and young mouse hippocampus. This research team then showed that antibodies against VCAM1, or blockage of the expression of the VCAM1 gene in brain endothelial cells could counteract negative effects of aged plasma on young mouse brain, and reverse other effects of aging. VCAM1 appears to negatively regulate neurogenesis in adults, and induce the activation of microglia. (Ref: Aged blood inhibits hippocampal neurogenesis and activates microglia through VCAM1 at the blood-brain barrier https://www.biorxiv.org/content/biorxiv/early/2018/01/03/242198.full.pdf)
Exposure of an aged subject to young blood results in neurogenesis
Another factor in the dysfunction of neurological tissue with age are changes in tissue-specific stem (or progenitor) cells. For instance, in aged muscle it was observed that skeletal muscle (satellite) stem cells lose their regenerative potential with age, in part due to a loss of signaling through the Notch pathway. In the liver, hepatic stem cells lose their potential to replicate themselves and proliferate as well, so that an aged liver is less able to heal and regenerate. This is the likely reason, as well, for the shift in metabolite profile that can be observed with age, since the aged liver is probably less able to metabolize nutrients fully. The Conboy laboratory at U.C. Berkeley studied the effects of factors from ‘young blood’ on the tissues of an aged subject, by establishing ‘parabiotic pairings’, i.e., a shared blood circulation, between young and old mice (heterochronic parabiosis). In a trailblazing 2005 study, these researchers exposed stem cells from aged mice to factors present in young serum via parabioses, and in cell culture. They found that heterochronic parabiosis from a young mouse to an old mouse could restore the activation of Notch signaling and increase the regenerative ability of satellite muscle stem cells in the aged mouse. Muscle stem cells from older mice, exposed to young serum, showed enhanced regenerative potential. The same was true of liver cells: aged hepatocytes regained proliferative ability when exposed to young blood serum. Note however that the specific factors in younger plasma that created this effect were not isolated. (Ref: Rejuvenation of aged progenitor cells by exposure to a young systemic environment https://www.ncbi.nlm.nih.gov/pubmed/15716955)
Moreover, in related experiments in the Wyss-Coray lab at Stanford University, age-related loss of cognitive function as well as synaptic plasticity in older mice could be restored with the exposure to young blood. A series of ‘heterochronic parabionts’ (young and old mice, with shared blood circulation) were studied, and it was found that the aged animals’ exposure to the blood of young mice was able to reverse already-existing negative effects of brain aging; this was determined at the molecular, structural, functional and cognitive (behavioral) level in the aged animals. In the aged parabionts, these researchers observed an upregulation of genes related to synaptic plasticity in the hippocampus. Morphological cellular analyses of the aged parabionts show an increase in dendritic spine density of the neurons. In two different functional/cognitive tests (contextual fear conditioning and spatial learning and memory), aged parabionts were improved by exposure to younger plasma. Taken together, these results confirmed the Conboys’ finding that the exposure of an aged subject’s circulatory system to young blood can rejuvenate synaptic plasticity and improve mental functioning. (Ref: Young blood reverses age-related impairments in cognitive function and synaptic plasticity in mice https://www.ncbi.nlm.nih.gov/pubmed/24793238)
The circulating factors that vascular endothelial cells naturally release and secrete are a major factor affecting the proliferative ability of neural stem cells, and hence the ability of brain tissue to repair and regenerate itself. Along with decline in neurogenesis and loss of cognitive function that comes with aging, there is a reduction in blood flow volume and a decreased number of neural stem cells. In 2014, a team at Harvard showed that factors in young blood actually induce remodeling of the vascular endothelial cell structure, which in turn could induce neurogenesis and an improved sense of smell as determined by olfactory discrimination in aging mice. (Ref: Vascular and neurogenic rejuvenation of the aging mouse brain by young systemic factors https://www.ncbi.nlm.nih.gov/pubmed/24797482) This is relevant to Alzheimer’s disease since loss of smell is an early sign of neurodegeneration and risk for Alzheimer’s disease. (Ref: Differential spatial expression of peripheral olfactory neuron-derived BACE1 induces olfactory impairment by region-specific accumulation of β-amyloid oligomer https://www.ncbi.nlm.nih.gov/pubmed/28796251) Thus, research teams at three different top universities (U.C. Berkeley, Stanford, and Harvard) have all made similar observations, which confirms the accuracy of these findings.
Another tissue that experiences slower repair and regeneration with age is bone, and heterochronic parabiosis (the delivery of young blood to an older patient) may be promising in this indication as well. Slower bone regeneration in older patients is important both as it relates to osteoporosis, and osseous integration of implants (such as hip and knee joint replacements). Bone-related surgeries in the elderly often heal slowly, and for this reason more often require additional corrective surgeries than younger patients. In vitro, when bone marrow stromal cells (BMSCs) are sourced from older patients, they differentiate more slowly and inefficiently to osteoblasts, than BMSCs from younger people. In older mice, it is also seen that bone fractures heal more slowly and osteoblasts differentiate less efficiently than in young mice; but the cause of this slower bone healing is not known. In 2015 in a joint study from University of Toronto and Duke University, it was shown that an older mouse, exposed to the circulating blood of a younger mouse via heterochronic parabiosis, reverses its prior ‘aged fracture repair phenotype’ and gains youthful efficiency of osteoblastic differentiation. A similar effect was seen when young haematopoietic (blood-derived) stem cells were transfused into older animals. The bone regeneration and rejuvenation effect in this study was found to involve the β-catenin signalling pathway, especially in the early response to bone injury and repair. The β-catenin pathway plays a key role in osteoblast differentiation, and its temporary downregulation during early fracture remodeling improved bone healing in older mice. These results indicate that an exposure to youthful haematopoietic stem cells could help older patients to rejuvenate their bone repair processes, which raises the possibility that heterochronic plasma transfusions may eventually be used in tandem with bone-related surgical procedures in the future. (Ref: G.S. Baht, D. Silkstone, L. Vi, P. Nadesan, Y. Amani, H. Whetstone, Q. Wei, B.A. Alman, “Exposure to a youthful circulation rejuvenates bone repair through modulation of ϐ-catenin”, Nature Communications (2015) 6, 7131 | https://www.ncbi.nlm.nih.gov/pubmed/25988592)
A 2016 study from the Conboy laboratory at U.C. Berkeley looked at the effect, in mice, of heterochronic blood exchange (rather than heterochronic parabiosis). In this case, an equal volume of blood was exchanged, with a specially designed microfluidic pumping device, between a young and an older mouse (so that the young mouse receives the older mouse’s blood; and vice versa, but the blood volume in each mouse remained constant). Blood exchange was done either in the presence or absence of muscle injury to the leg (which can create a temporary inflammatory state). The effects of this procedure were investigated for muscle, liver, and brain hippocampus tissue in both mice. Results were interesting; heterochronic blood exchange did produce some different outcomes than heterochronic parabiosis does. First, there were measurable effects on the tissues studied, within just a few days. They observed that the negative or inhibitory effects of old blood (on the young mouse recipient) were more pronounced that the benefits of young blood on the older mouse, and that peripheral muscle injury strengthened that effect. In this blood exchange study, young blood enhanced the ability of older muscle to repair itself, without inhibition of young; and liver tissue regeneration in the older mouse was also enhanced by young blood, with both liver tissue fibrosis and adiposity decreased, while young hepatogenesis becomes diminished. They observed a rapid increase in levels of the protein beta-2 microglobulin (B2M) in young tissues when old blood was introduced, which correlated with inhibition of tissue regeneration and was not a result of direct introduction of B2M, but the induction of the young mouse’s endogenous B2M. The study also showed that an older mouse did not receive an enhancement in neurogenesis from just a single blood exchange (whereas both muscle and liver did benefit from one exchange); hence, for Alzheimer’s disease, more than one exchange will likely be required to provide a benefit and enhance neurogenesis. Or alternatively, plasma exchange may need to be done at the same time as the provision of beneficial neurotrophic factors known to enhance neurogenesis. This study, overall, was important because it showed that a single blood exchange could produce health and tissue regeneration benefits for the older recipient, within just a few days. It also shows that a one-way plasma exchange (from young to old, and not vice versa) is of course better. (Ref: J. Rebo, M. Mehdipour, R. Gathwala, K. Causey, Y. Liu, M.J. Conboy, I.M. Conboy, “A single heterochronic blood exchange reveals rapid inhibition of multiple tissues by old blood”, Nature Communications (2016) 7, 13363 | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5121415/)
The first peer-reviewed article reporting beneficial regenerative effects of heterochronic parabiosis (the linking of blood circulation of a young and an old mouse) appeared about 13 years ago, in 2005 (Ref: Rejuvenation of aged progenitor cells by exposure to a young systemic environment, https://www.ncbi.nlm.nih.gov/pubmed/15716955) Since then, multiple top universities, including Stanford, U.C. Berkeley, Harvard, University of Toronto, and Duke University have repeatedly shown in follow-on studies that the lost regenerative potential of tissues in older animal can be recovered, at least temporarily, by exposure to younger blood circulation. Then, as discussed above, the Conboy laboratory at U.C. Berkeley showed that even a single blood exchange from a young to an old mouse can have this regenerating effect, within a few days. These studies have built a robust foundation for the use of youthful blood as a clinical treatment. Although the specific factors in young blood that endow the regenerative potential are not definitively known, some soluble factors of interest include the chemokine protein CCL11, the growth differentiation factor 11, a member of the TGF-β superfamily, and oxytocin. Whether eventually the best clinical approach will be to give whole blood or to simply deliver one or a few specific protein factors remains an open question, which requires further study. (Ref: The Fountain of Youth: A tale of parabiosis, stem cells, and rejuvenation, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5662775/) Reviews on this topic include the following: (Ref: Heterochronic parabiosis: historical perspective and methodological considerations for studies of aging and longevity, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4072458/) (Ref: Systemic Problems: A perspective on stem cell aging and rejuvenation https://www.ncbi.nlm.nih.gov/pubmed/26540176)
Therapeutic Plasma Exchange for Treatment of Neurological Diseases: Prior Studies
Therapeutic plasma exchange (TPE) is already used clinically for a range of neurological diseases, and its safety and efficacy were recently evaluated in a multicenter retrospective analysis. In TPE, a volume of biocompatible fluid is used to replace a portion of the patient’s blood containing pathological molecules related to autoimmune conditions. There is a growing list of indications for TPE, such as connective tissue disorders as well as hematological, nephrological, endocrinological, and metabolic diseases. Neurological disorders that are treated with TPE currently include Guillain-Barre Syndrome, acute disseminated encaphalomyelitis, chronic inflammatory demyelinating polyradiculoneuropathy), multiple sclerosis, myasthenia gravis and Wilson disease . A recent multicenter retrospective analytical review of clinical outcomes of 115 patients from six University Hospitals’ apheresis units was done. For these 115 patients, each person had on average 5 TPE sessions (range: 1 to 72), with human albumin used as the replacement fluid in 66% of cases, and fresh frozen plasma used for 34% of sessions. TPE was done either through central venous catheters (66%) or via a peripheral vein (34%). Overall, the conclusion of the retrospective analysis was that TPE was an effective treatment, with 89.5% of patients responding positively. Some complications were seen (in 18.3% of patients) during TPE sessions, including for catheter placement (8.7%), hypotension (3.5%), hypocalcaemia (3.5%) or allergic reaction (1.7%). The complication ratio was 2.7% out of a total of 771 TPE procedures for the 115 patients whose medical records were assessed. For TPE sessions in which complications were observed, 6% were terminated. Overall, TPE was deemed to be a safe and efficacious treatment for a range of challenging neurological conditions. (Ref: Therapeutic plasma exchange in patients with neurological diseases: Multicenter retrospective analysis https://www.ncbi.nlm.nih.gov/pubmed/23619327 )
A study of 42 patients with mild-to-moderate Alzheimer’s was undertaken to understand whether plasma exchange with an albumin replacement could modify Aβ concentrations in plasma and CSF, and improve cognitive and functional abilities. This was a Phase II, randomized, controlled, multicenter trial with both treated (5% albumin, Albutein®, Grifols) and untreated (sham) groups. Treated patients received up to 18 plasma exchanges on varying schedules. For all groups, both Aβ1–40 and Aβ1–42 were measured in both CSF and plasma, and behavioral, functional, and cognitive testing was done. While changes in the levels of Aβ peptides in CSF and plasma were less easy to interpret, importantly, patients who received plasma exchange therapy showed improvements in both memory and language functions, which still persisted 6 months after the therapy was discontinued. (Ref: Efficacy and Safety of Plasma Exchange with 5% Albumin to Modify Cerebrospinal Fluid and Plasma Amyloid-Concentrations and Cognition Outcomes in Alzheimer’s Disease Patients: A Multicenter, Randomized, Controlled Clinical Trial https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5240541/)
Intravenous (IV) infusions of immunoglobulin (Ig), a treatment known as ‘IVIg’, have also been tested as a potential treatment for mild-to-moderate Alzheimer’s Disease dementia. A relatively large Phase 3 clinical trial was done with 390 participants in a double-blind, placebo-controlled study, in which participants were randomly assigned to treatment either with (1) low-dose albumin as a placebo; or (2) IVig (Gammagard Liquid, Baxalta, Bannockburn, IL), each at either 0.2 or 0.4 g/kg every 2 weeks for 18 months. Cognitive ability and functional testing were assessed by standardized testing as change from baseline throughout the study and up through 18 months. Safety and tolerability were assessed, with collection of serial MRIs and plasma samples throughout the study for all participants. The important result from this study, relevant to the HOPE trial, was that the treatment was found to be both safe, and well-tolerated; however, IVIg alone did not provide beneficial effects on cognition or function, at either of the tested doses. This was true, although the patients’ plasma Aβ42 (but not Aβ40) levels were greatly decreased in IVIg-treated patients. Thus, the depletion of Aβ42 from plasma is not sufficient to halt or reverse mild-to-moderate Alzheimer’s dementia; the disease is more complicated than that. It is useful to report however, that there was no difference in treatment safety between the placebo-treated and IVIg-treated groups. IVIg-treated participants exhibited more systemic reactions (chills, rashes) but also fewer respiratory infections than participants receiving albumin placebo. (Ref: A phase 3 trial of IV immunoglobulin for Alzheimer disease https://www.ncbi.nlm.nih.gov/pubmed/28381506 )
Neurotrophic factors, personalized to the patient, can induce neurogenesis and slow or reverse cognitive decline
Decades of study of a variety of naturally derived neurotrophic compounds, which have activity when ingested, have provided us with a ‘short list’ of supportive factors that can be provided to patients who are being treated for neurodegenerative conditions. These neurotrophic compounds can promote neuron and nerve health and prevent any further aging-related reduction in cognitive, sensory, and motor functions, as well as assist in proper regulation of emotional health. In particular, a variety of plant secondary metabolites known as ‘phytochemicals’, can interact with cellular membranes, proteins, and organelles to modulate function, generally providing benefit via anti-oxidant and anti-inflammatory activities. In some cases, certain phytochemicals can mimic the body’s natural neurotrophic factors, or upregulate the expression or release of these factors; in other cases, certain phytochemicals can suppress pro-apoptotic pathways of mitochondria, and induce natural cellular repair and regeneration (autophagy). In the brain, phytochemicals can bind to the receptors of endogenous neurotrophic factors, and also receptors for γ-aminobutyric acid, acetylcholine, serotonin, and glutamate and estrogen, and activate downstream signal pathways. They can directly affect the actions of intracellular signaling molecules to modify brain function. Additionally, phytochemicals can induce the expression of genes that encode the anti-apoptotic protein Bcl-2 and neuro-supportive factors including brain-derived neurotrophic factor (BDNF) protein and glial cell-derived neurotrophic factor (GCNF). Epidemiological studies indicate that induction of BDNF and GCNF expression may be the most important neuroprotective mechanism of dietary phytochemicals. Through analysis of blood serum, cerebrospinal fluid, and other clinical samples, it is possible to quantitate levels of expression of endogenous neurotrophic factors induced by phytochemicals. Because the mechanisms of action and interaction of different phytochemicals are each distinct, there is a good potential for synergy when more than one phytochemical is given to patients. (Ref: Neurotrophic function of phytochemicals for neuroprotection in aging and neurodegenerative disorders: modulation of intracellular signaling and gene expression https://www.ncbi.nlm.nih.gov/pubmed/29030688)
A 2018 publication showed the surprising benefit of ingesting plant-derived compounds, or phytonutrients, in preserving human cognition. A prospective study of 960 participants in the Memory and Aging Project, aged 58–99 years old, completed a questionnaire about ‘food frequency’ and also participated in ≥ 2 cognitive assessments over a mean 4.7 years. The focus was on primary nutrients and bioactive compounds in green leafy vegetables, including Vitamin K (phylloquinone), lutein, β-carotene, nitrate, folate, kaempferol, and α-tocopherol. The researchers applied a linear mixed model for analysis, which adjusted for age, sex, education level, participation in cognitive activities, physical exercise, smoking, and seafood and alcohol consumption. It was found that eating green leafy vegetables was associated with slower cognitive decline. In the group with the highest quintile of green leafy vegetable consumption (median 1.3 servings per day), this difference was equivalent to being 11 years younger in age. Additionally, statistically significant reduction in rates of cognitive decline were found for each phytochemical individually. The study concluded that eating ~ 1 serving per day of green leafy vegetables and foods rich in phylloquinone, lutein, nitrate, folate, α-tocopherol, and kaempferol may help to slow cognitive decline with aging. (Ref: Nutrients and bioactives in green leafy vegetables and cognitive decline: Prospective study https://www.ncbi.nlm.nih.gov/pubmed/29263222)
Earlier in this review we discussed how cellular bioenergetics are changed during the progression of Alzheimer’s disease, so that cells shift their energy metabolism away from ATP generation in the mitochondria, and towards cytosolic glycolysis. Additionally, processes of DNA repair are compromised by Alzheimer’s disease. A recent study was done in which researchers created a mouse model of Alzheimer’s that not only accumulates Aβ plaques and phosphorylated Tau (pTau) tangles in its brain like human patients do, but also has DNA repair deficiencies, and exhibits synaptic dysfunction, neuronal death, and cognitive impairment (this transgenic animal is called the 3xTgAD/Polβ+/- mouse). This study was remarkable in its implications, in that they were able to show that oral supplementation of these mice with the compound nicotinamide riboside (NAD+) was able to return the mice to bioenergetic normalcy, and also lessened the pTau pathology. However NAD+ treatment did not lessen Aβ plaque pathology, which is fascinating. However, the NAD+ treated mice did show less DNA damage, less neuroinflammation, and reduced apoptosis of hippocampal neurons. NAD+ treated mice also showed better cognitive function in multiple behavioral tests, and restoration of hippocampal synaptic plasticity. The study concluded that interventions that can increase neuronal NAD+ levels have significant therapeutic potential for AD. NAD+ is a supplement that can be provided orally, which may be synergistic with other treatments. (Ref: NAD+ supplementation normalizes key Alzheimer’s features and DNA damage responses in a new AD mouse model with introduced DNA repair deficiency https://www.ncbi.nlm.nih.gov/pubmed/29432159) Another article from 2017 showed that repletion of NAD+ in a degenerating neuronal system could simultaneously ameliorate both DNA repair deficiencies and mitochondrial dysfunction, via restoration of mitochondrial structure regeneration in damaged neurons. It was shown in a C. elegans model that repletion of NAD+ directly enables physical clearance of accumulated detritus from deteriorating mitochondria, concurrent with the restoration of mitophagy (production of new and fresh mitochondria). (Ref: NAD+: The convergence of DNA repair and mitophagy https://www.ncbi.nlm.nih.gov/pubmed/27929719)
One important genetic risk factors for Alzheimer’s disease is the alleles that a patient possesses of the Apolipoprotein E (ApoE) gene, implying that ApoE protein (which resides within lipoprotein particles) plays a role in the progression of Alzheimer’s. Interestingly, the orally available compound retinoic acid (RA) — a metabolite of vitamin A (retinol) — is an important endogenous anti-inflammatory and neuroprotective compound. A 2018 study showed that during the neurodegenerative processes accompanying Alzheimer’s disease, microglia become abnormally activated and adopt a pro-inflammatory phenotype, which attenuates ApoE expression. Yet they also found that exogenously dosed retinoic acid was able to block this effect, restore the proper expression of the ApoE gene. (Ref: Retinoic Acid Enhances Apolipoprotein E Synthesis in Human Macrophages https://www.ncbi.nlm.nih.gov/pubmed/29376871) This finding would imply that the provision of orally dosed Vitamin A to Alzheimer’s patients, which will be metabolized to produce retinoic acid, will prove beneficial.
Another important neurotrophic factor that can be delivered orally is the natural compound resveratrol, which is a stilbenoid — a natural phenol — produced by certain plants in response to injury or when the plant is attacked by pathogens such as bacteria or fungi. Resveratrol occurs in the skin of grapes, blueberries, raspberries, and mulberries. A 2017 study found that treatment of mild-to-moderate Alzheimer’s disease subjects (N = 119) for 52 weeks with resveratrol (up to 1 g by mouth twice daily) was able to slow progressive declines in activities of daily living (ADL) scores, while also positively affecting CSF Aβ40 levels. Compared to the placebo-treated group, Alzheimer’s subjects treated with resveratrol for 52 weeks showed markedly reduced CSF MMP9 and increased macrophage-derived chemokine (MDC), interleukin (IL)-4, and fibroblast growth factor (FGF)-2. Compared to baseline, resveratrol increased plasma MMP10 and decreased IL-12P40, IL12P70, and RANTES. These cytokines and signalling proteins indicate that resveratrol modulates neuroinflammation, generally in the direction of producing anti-inflammatory effects. In a subset analysis, resveratrol treatment also attentuated declines in mini-mental status examination (MMSE) scores, change in ADL (ADCS-ADL) scores, and CSF Aβ42 levels during a 52-week trial, while not altering tau levels. (Ref: Resveratrol regulates neuro-inflammation and induces adaptive immunity in Alzheimer’s disease https://www.ncbi.nlm.nih.gov/pubmed/28086917)
One question has been how resveratrol modulates the molecular mechanisms of aging. One important observation has been that caloric restriction can prevent, slow, or reverse diseases of aging, including Alzheimer’s, in model animals. It is hypothesized that a class of deacetylases called Sirtuins (SIRT1 in mammals) may be involved in the effects of caloric restriction. SIRT1 is known to link cellular energy balance (NAD+/NADH) to the regulation of gene transcription. Resveratrol is a known, potent activator of SIRT1, and might mimic the effects of caloric restriction to slow the progress of Alzheimer’s disease. In a 2017 study including a double-blind, placebo-controlled, randomized, phase II trial of resveratrol in persons with mild-to-moderate Alzheimer’s disease, it was determined that resveratrol (1) can be detected in cerebrospinal fluid, (2) is well tolerated and safe, (2) alters Alzheimer’s disease biomarker trajectories, (2) preserves the integrity of the blood-brain barrier, and (5) modulates the central nervous system immune response. (Ref: Resveratrol for Alzheimer’s disease https://www.ncbi.nlm.nih.gov/pubmed/28815614)
Another natural supplement of interest is CDP-choline (cytidine-5′-diphosphate choline), an endogenous compound normally produced by the body. When used in pharmacology, it is called citicoline. In studies done in model animals and human patients, citicoline has been shown to be neuroprotective and beneficial. Citicoline can improve cognitive impairment caused by various conditions, including cerebrovascular disease, traumatic brain injury, glaucoma, Alzheimer’s, and Parkinson’s disease. Citicoline can serve as a natural precursor of phospholipid synthesis in the body, which are a key structural element of cell membranes; and also as a source of choline for the biosynthesis of acetylcholine in the brain. Recent studies (2015) have shown that citicoline may increase sirtuin 1 (SIRT1) expression. It can be delivered to patients either orally or by an intravenous route, and in the body is metabolized by the gut and liver into two major downstream products, cytidine and choline. Studies of citicoline pharmacokinetics show that it is well absorbed and highly bioavailable via the oral route. In vivo, it modulates the activities and expression of protein kinases known to be involved in neuronal apoptosis, and increases SIRT1 expression in the central nervous system. In elderly subjects, there is clinical evidence that citicoline can improve memory performance, when dosed at 1000 mg/day for 4 weeks. (Ref: The role of citicoline in cognitive impairment: pharmacological characteristics, possible advantages, and doubts for an old drug with new perspectives https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4562749/) (Ref: Double-blind placebo-controlled study with citicoline in APOE genotyped Alzheimer’s disease patients. Effects on cognitive performance, brain bioelectrical activity and cerebral perfusion https://www.ncbi.nlm.nih.gov/pubmed/10669911) (Ref: Citicoline improves memory performance in elderly subjects https://www.ncbi.nlm.nih.gov/pubmed/9203170)
Wang D, Jacobs SA, Tsien JZ. Targeting the NMDA receptor subunit NR2B for treating or preventing age-related memory decline. Expert Opin Ther Targets. 2014 Oct;18(10):1121–30. [PMID: 25152202]
Age-related memory loss is believed to be a result of reduced synaptic plasticity, including changes in the NR2 subunit composition of the NMDA receptor. It is known that endogenous NR2B subunits decrease as the brain ages, whereas transgenic upregulation of NR2B enhances synaptic plasticity and learning and memory in several animal species. Accumulating evidence suggests that elevated brain magnesium levels, via dietary supplementation, can boost NR2B in the brain, consequently reversing memory deficits and enhancing cognitive abilities. This review highlights the convergent molecular mechanisms via the NR2B pathway as a useful strategy for treating age-related memory loss. A dietary approach, via oral intake of a novel compound, magnesium L-threonate (MgT), to boost NR2B expression in the brain is highlighted. Direct upregulation of the NR2B subunit expression can enhance synaptic plasticity and memory functions in a broad range of behavioral tasks in rodents. Other upregulation approaches, such as targeting the NR2B transporter or surface recycling pathway via cyclin-dependent kinase 5, are highly effective in improving memory functions. A dietary supplemental approach by optimally elevating the [Mg2+] in the brain is surprisingly effective in upregulating NR2B expression and improving memories in preclinical studies. MgT is currently under clinical trials.
Liu G, Weinger JG, Lu ZL, et al. Efficacy and safety of mmfs-01, a synapse density enhancer, for treating cognitive impairment in older adults: a randomized, double-blind, placebo-controlled trial. J Alzheimers Dis. 2015 Oct 27;49(4):971–90. [PMID: 26519439] www.ncbi.nlm.nih.gov/pmc/articles/PMC4927823/
Originally published at MaxWell Biosciences.