When a nerve can be your glucometer
When Ladan Jiracek of the Neural Implant Podcast saw Dr. Theodoros Zanos’s poster at SfN 2017, Ladan was so excited that he sought out Dr. Zanos to interview him.
What compelled Ladan so much? Dr. Zanos has figured out how to listen to the vagus nerve, probably the largest and most prolific nerve in the body, and hear the messages it’s sending to the brain.
In this episode of the Neural Implant Podcast, Dr. Zanos discusses how he teases out the body’s internal signals as they’re being sent from the body, through the vagus nerve, to the brain.
Tl;dr: In this post, I’ll discuss Ladan’s interview with Dr. Theo Zanos, I’ll explore a study about using vagus nerve stimulation to treat inflammatory disease, and I’ll do my very darnedest to get you excited about bioelectronic medicine (but I’ll only scratch the surface of what bioelectronic medicine is, and what it’s all about).
Dr. Zanos is the head of the Neural Decoding and Data Analytics lab at the Feinstein Institute’s Center of Bioelectronic Medicine. Zanos has been working on intercepting the peripheral nervous system’s communication with the brain in order to diagnose and fight disease — his recent work focuses on decoding signals from the vagus nerve such as how much glucose is in your blood stream. He and Ladan met at SfN 2017, where Zanos’s poster absolutely blew Ladan away.
Dr. Zanos begins his interview with Ladan by recounting his lab’s two main findings from this year, both of which pertain to decoding information from the body as it’s sending signals back to the brain. Zanos’s group figured out how to decode information about cytokines, and how to decode information about insulin and glucose levels, just from recording the vagus nerve of a rodent under anesthesia. [A note: cytokines are small proteins which mediate inflammatory response. For example, TNFα (Tumor Necrosis Factor alpha) is a cytokine which activates NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) (oh my goodness was that a mouthful), which is itself a gene transcription factor that impacts the expression of all sorts of genes involved in inflammatory response and cell proliferation/death. Boom, science.]
Zanos’s goal is to build implantable devices that can read out and decipher signals from the vagus nerve, then employ these devices as early diagnostic tools which can give doctors and algorithms access to high-quality health data.
Zanos’s group has made quite a bit of progress. They’ve run experiments in anesthetized rats or mice where they record directly from the rodent’s vagus nerve, rather than actually implanting a device. It’s worthwhile highlighting the anesthetization because the vagus nerve carries information about many things (I’ll talk more about the vagus nerve in The Literature section below). As I understand it, the more static a mammalian organism and its brain & body function, the less noisy the vagus nerve activity, which is important for pioneering research. The vagus nerve recordings in anesthetized rodents followed ground-truth (i.e., traditional recording methods) very well for insulin and cytokines, and decently well for glucose.
The big challenge, it seems, is getting high-quality signals despite variation in vagus nerve anatomy. It was easier for Dr. Zanos and his team to record signals from mice than from rats, despite the fact that the mouse vagus nerve is 100µm, whereas the rat vagus nerve is 400µm. Likely, this is due to anatomical differences: mouse vagus nerves don’t have distinct fascicles/fiber bundles within the nerve, but rats do; additionally, rats have other connective tissue around, and inside of, the vagus nerve. This discrepancy suggests that high-quality recordings from humans will be particularly challenging, since our vagus nerve anatomy is even more complex.
Broadly, Zanos describes two next steps: improving the decoding algorithms used to interpret vagus nerve signals and developing the implant itself (as opposed to just anesthetizing rodents and temporarily inserting recording electrodes). This latter improvement will allow the team to record data from the vagus nerve over days, not just hours.
I had fully intended to dive into Zanos’s work in detail, but upon scouring the interwebs, I realized that Zanos hasn’t yet published these results (you can check out more of his work on his website, though!).
So, I’ll instead take this opportunity to talk about another use of stimulating/recording from the vagus nerve: fighting inflammatory disease.
Let’s first define some terms! (“Ew—,” you say. “Jargon,” you say)
- Bioelectronic Medicine is the field, technologies, and medical techniques dedicated to treating disease and injury via electrical or electrochemical stimulation of neural or non-neural cells in the body, thereby impacting biochemical pathways and organ function. Alright, English: record from or stimulate cells in the body in order to support health. Easy. And really profound, because it’s much more targetable than drug treatment, and in many ways easier to develop. For a great overview, check out this really phenomenal interview with Dr. Manfred Franke.
- Afferent/efferent are just terms to describe what type of information a nerve/axon carries (nerves are bundles of axons). Afferent means the nerve/axon is sending sensory information to the brain; efferent means the nerve/axon is sending motor information from the brain to the body. Here, “sensory” can mean anything ranging from temperature, to pressure, to the presence of chemicals in the blood stream, etc..
- The vagus nerve is the 10th cranial nerve (the cranial nerves are a set of important nerves, 10 of which originate in the brainstem). What makes the vagus nerve special amongst cranial nerves is that it sends nerve branches all throughout the body, and is involved in controlling and interpreting signals from organs like the spleen, liver, lungs, heart, etc. The vagus nerve sends efferent motor information from the brain/brainstem to the body and portions of the neck, and carries afferent sensory information back to the brain from the larynx/pharynx and other structures as well (and even from some organs in the body!).
- Vagus Nerve Stimulation (VNS) is the application of electrical current to the vagus nerve in order to cause efferent (motor) signals to be sent to a particular organ. VNS has been used extensively to treat severe epilepsy, and is now being explored for other treatments as well.
- The inflammatory response is the body’s response to foreign substances. Essentially, immune cells try to detect substances that aren’t supposed to be in the body, and if a foreign substance is identified the cells work to destroy it. This is a hugely complex topic, and there’s a ton of detail to it that I don’t nearly understand myself. Here’s an overview paper that I haven’t read yet, but hopefully will one day soon when I have time (my backlog of papers literally scares me).
- Inflammatory diseases are a class of disease in which the body’s inflammatory response winds up damaging tissue within the body. Chronic examples of inflammatory disease are Crohn’s disease, in which the immune system attacks tissue in the gastrointestinal tract, and Rheumatoid Arthritis (RA), where the immune system attacks joints. Dangerous acute inflammatory responses include septic shock, in which bacterial infections causes a rapid and overcompensatory inflammatory response that drastically reduces blood pressure so much as to starve organs of blood.
With this terminology in mind, let’s discuss an application of vagus nerve stimulation to treat inflammatory disease. This method has been pioneered by researchers at the Feinstein Institute (which is Zanos’s affiliated institution). With the help of his team, Dr. Kevin Tracey—the President and CEO of the Feinstein Institute—has identified a particular pathway through which stimulating the vagus nerve can reduce inflammatory response in the body. He refers to it as the cholinergic anti-inflammatory pathway. It’s named as such because: a) This pathway relies on the neurotransmitter acetylcholine (ACh) (hence, “cholinergic”), it works against inflammatory responses (hence, “anti-inflammatory”), and it entails a process involving multiple types of cells, proteins, and organs (hence, “pathway”). Take that, nomenclature!
Here’s the idea (this is going to be a little messy, bear with me): Remember cytokines? We talked about those small proteins earlier in the post. Elevated levels of cytokines are associated with injury to tissue due to inflammatory response, as in the case of rheumatoid arthritis (the damage in rheumatoid arthritis comes from inflammation of the synovial membrane in joints, resulting in the deterioration of cartilage and bone). If the vagus nerve is stimulated (*skipping over some unnecessary details*), ACh gets released onto the α7 subunit of the nicotinic ACh receptor (α7nAChR). The Nomenclature Strikes Back.
This receptor then prevents the movement of NF-κB into the nuclei of macrophages (a type of immune cell)…which is important, because if NF-κB were to make it to the nucleus, it would produce more TNF and other cytokines that cause inflammatory responses in cells! Preventing NF-κB from entering the nucleus prevents the proliferation of inflammation, it would seem.
How does this fit in with Zanos’s work with cytokines? Well, Dr. Tracey has hypothesized that the vagus nerve also sends afferent (sensory) information about cytokine levels back to the brain—it’s keeping the brain up to date on the state of the body’s inflammatory response. Zanos’s work built on that hypothesis and sure enough, he was able to decode cytokine levels from the vagus nerve. (Here’s a video about some related work from the Feinstein Institute.)
Anyways, back to stimulating the vagus nerve. Here’s the question: if we stimulate the vagus nerve of a patient with rheumatoid arthritis, will we see reduced symptoms and TNF levels, which are indicators of inflammatory response?
Koopman et al (2016) set out to answer this. Spoiler alert, the study’s title gives away the results: Vagus nerve stimulation inhibits cytokine production and attenuates disease severity in rheumatoid arthritis. Well, now that I’ve ruined the surprise, let’s learn a little more about what happened!
There were two groups: one group of patients had epilepsy, with no history of rheumatoid arthritis (RA) or inflammatory disease. The other group had RA.
First, the authors implanted a coiled cuff electrode from Cyberonics onto the left cervical vagus nerve of each control non-RA patient (cervical = near the cervical region of the spinal cord). The authors chose patients with epilepsy since VNS for epilepsy is a well-known and effective treatment. Seven patients (5M, 2F, mean age 35yrs (25yrs-43yrs range)) were anesthetized and administered endotoxin to stimulate monocyte production of TNF for four hours. Plain English: the researchers put some bad molecules into the patients that caused an inflammatory response. Measurements of TNF levels were taken at three points: before anesthesia, after anesthesia but before vagus nerve stimulation, and four hours after vagus nerve stimulation. As we can see in the graph below, VNS significantly reduced levels of cytokines TNF, IL-6, and IL-1ß as compared to pre-VNS. It’s also worth noting that the results couldn’t have been due to the placebo effect since the patients were under anesthesia.
The goal of this part of the study was to determine whether, in patients without inflammatory disease, VNS could reduce cytokine levels. The results were clearly positive.
Rheumatoid Arthritis patients
Two cohorts were created of n = 17 patients (originally 18, but one was later excluded). Cohort I (n = 7) were patients with early-middle stage RA who had failed typical methotrexate therapy (a drug for treating RA); these patients had never been treated with TNF antagonists (substances that inhibit, or antagonize, TNF) or had previously stopped TNF treatment due to toxic reactions to the drug. Cohort II (n = 10) were patients who failed both conventional methotrexate therapy and at least two different types of drug-based TNF antagonization treatments.
The protocol was as follows:
- Surgery was performed on Day -14 (you read that correctly: “negative fourteen”).
- On Day 0, one round of 60 seconds of stimulation was administered with 250µs pulses at 10Hz, using output current from 0.25–2.0mA, depending on the patient’s tolerance (for those of us who, like me, are lacking in the physics department: 1µs =1 microsecond = one one-millionth of a second; 1Hz = once per second; 1 mA = one one-thousandth of an Ampere, which is a measure of the amount of charge flowing through a substance per unit time).
- On Day 7, the output current was increased up to 2.0mA, and subsequently delivered daily for 60s with the same stimulus profile as before.
- Every week, up until Day 28, the current was escalated until it hit a maximum of 2.0mA.
- At Day 28, for patients who had failed to respond thus far transitioned to a 4x daily vagus nerve stimulation. In Cohort II, 6/10 patients were increased to 4 daily pulses.
- At Day 28, the output current was 1.29 +/- 0.37mA for Cohort I and 1.60 +/- 0.36mA for Cohort II.
- After Day 42, the stimulator was turned off for 14 days.
- At Day 56, the stimulator was turned back on and the previous stimulation protocol was completed until Day 84.
On Day 42, across the combined Cohort I & II groups, TNF levels were significantly reduced from the baseline at Day -21 (p < 0.05).
- Day -21 ==> TNF = 2900 +/- 566 pg/mL (picograms / milliliter)
- Day 42 ==> TNF = 1776 +/- 342 pg/mL
By Day 56, after the stimulator was turned off on Day 42, TNF levels had risen again. Then, upon turning the stimulator back on, the TNF levels fell once more. This observation evidences the causal effect of VNS on TNF production, and therefore inflammatory response.
In addition to measuring TNF levels, researchers looked at the rheumatoid arthritis signs & symptoms. They used the standard 28-joint C-reactive protein-based disease activity score (DAS28-CRP). This score counts swollen and tender joints, asks the patient to define a visual analog to the disease’s activity, and measures serum C-reactive protein levels. As one would hope, the DAS28-CRP scores also rose and fell in the same pattern as TNF production, further evidencing the value of VNS for rheumatoid arthritis treatment!
I’d encourage you to take a moment and check out the graphs (reading the description below each graph really helps!). In particular, I find it compelling how the treatment hiatus beginning on Day 42 saw an increase in symptoms/TNF until the VNS was turned back on — this is strongly indicative of causality.
Finally, it’s worth noting the unfortunate fact that Cohort I saw larger impacts from the VNS than did Cohort II. This makes sense given Cohort I was in an earlier stage in the disease. On the one hand, it would be even more exciting if VNS could treat late-stage RA just as well as early-stage RA. On the other, though, I’d be curious to know whether or not long-term intervention in Cohort I slows progression of the disease.
well, not this time, actually!
When I set out to write this post, my full intention was to include a robust Rumination section. But then, as part of my research before writing, I took a deep dive into bioelectronic medicine and haven’t yet climbed back out of the pool. BEM is a complex and exciting topic.
Once I feel I have a handle on the relevant technologies, opportunities, and implications, I’ll write something extensive about it. I wouldn’t be doing these topics justice right now given my current ignoramus-ness.
In the meantime, I’ll leave you with some motivation for why bioelectronic medicine is worth paying attention to. In 2015, $328.4bn was spent on prescriptions in the US. Bioelectronic medicine treatments, which leverage electrical stimulation of the nervous system to create desired effects in the body, can take 1/3 the time of drug-based treatments to develop and get FDA approval for. Furthermore, unlike pharmaceuticals, precise nervous system stimulation doesn’t directly release molecules into the bloodstream, so the potential for severe side-effects is diminished.
I think there’s a revolution coming in healthcare treatments, and that revolution is bioelectronic medicine. Stay tuned for more…
In this post, I discussed Dr. Theos Zanos’s research into decoding glucose, insulin, and cytokine levels by recording from rodent vagus nerves. We explored a research paper from another domain of vagus-nerve-based bioelectronic medicine, in which the vagus nerve is stimulated to treat inflammatory disease. Finally, I offered up a little motivation for why bioelectronic medicine is a field to pay attention to, but held off from saying much more pending further research on my end.
One of my primary goals with The Substrate is to encourage an ethics-first conversation about brain computer interfaces. To that end: comment, write me at firstname.lastname@example.org, or find me on twitter (@averybedows). I will respond! (seriously, I will).
Until next time,