Probiotics and Oral Wound Healing After Cancer Treatment
Intestinal Bifidobacterium breve shows promise for patients being treated with anti-angiogenic drugs
Background
Angiogenesis is a process in which blood vessels extend and grow into tissues throughout the body. Increased angiogenesis is a hallmark of cancer because tumors require a good blood supply to proliferate. Drugs that inhibit angiogenesis are used to treat certain cancers because they kill tumor tissue by cutting off its blood source. However, these drugs also inhibit angiogenesis in healthy tissues around the tumor, restricting the cells’ access to clotting factors, white blood cells, and inflammatory factors. This diminishes the tissue’s ability to heal from wounds and infections.
In this paper, the researchers studied how the anti-angiogenic drug sunitinib, which is used to treat some oral tumors, can inhibit oral wound healing. This effect makes it difficult for patients taking sunitinib to undergo some dental procedures (e.g. tooth extraction) because the wound will have a higher chance of infection. They also studied the ability of Bifidobacterium breve, commensal bacteria that normally live in the human gut, to improve oral wound healing by increasing the release of interleukin-10 from dendritic cells in the small intestine. Interleukin-10 is a cytokine, which means it is a protein that is released from one cell to travel to and begin a signaling cascade in another cell. It has already been established that interleukin-10 functions in anti-inflammatory pathways in the body, so it can improve wound healing by limiting inflammation.
Summary
Sunitinib kills oral tumors by preventing them from growing new blood vessels (angiogenesis). It is highly effective at shrinking tumors, but it has to be continuously administered to patients to prevent the tumor from returning. In this study, the researchers’ goals were to show that sunitinib inhibits oral wound healing by increasing inflammation and triggering senescence in oral mucosal stem cells (OMSCs). They also aimed to prove that administering the probiotic B. breve decreased inflammation and improved oral wound healing by upregulating interleukin-10 in intestinal dendritic cells.
The scientists used a mouse model with a damaged hard palate (roof of the mouth) to study how sunitinib affected its ability to heal. They administered sunitinib to a group of mice for 3 days and found that these mice healed slower than the mice that did not receive the drug. They took cells from the oral mucosa of mice in both groups and used an antibody array to detect pro-inflammatory proteins expressed in the cells. An antibody array is a test where antibodies designed to bind specific proteins of interest are added to a sample of cells. The antibody binds to its target protein (antigen) and is usually tagged with a fluorescent marker that will glow upon binding, showing that the protein is present. The results showed that oral mucosal cells from mice that received sunitinib had increased expression of pro-inflammatory proteins. This could explain why sunitinib slows oral wound healing.
Next, the researchers observed how sunitinib affected OMSCs that promote wound healing by negatively regulating inflammation. They found that OMSCs from mice treated with sunitinib had higher levels of γH2A.X, a phosphorylated histone that commonly marks cellular senescence. Senescence is a state triggered by DNA damage where a cell pauses the cell cycle (cell division) to repair DNA. If the DNA cannot be repaired then apoptosis (programmed cell death) will occur. Sunitinib inhibited cell division and differentiation ability of OMSCs, exacerbating wound inflammation and increasing healing time.
The scientists next treated a group of mice who had been given sunitinib with a B. breve probiotic. They observed that B. breve reversed sunitinib’s adverse effects on oral wound healing and decreased expression of pro-inflammatory interleukins by oral mucosal cells. They also noticed that interleukin-10 (anti-inflammatory) seemed to have higher expression in the oral mucosal cells of mice treated with B. breve compared to the control group, but they note in their paper that this connection needs to be studied more.
B. breve normally resides in the small intestine of humans, so the scientists anesthetized mice and injected B. breve directly into their ileums (the last part of the small intestine). Results showed that more dendritic cells were recruited to ileums treated with the probiotic. Dendritic cells are immune cells that move throughout the body to recognize pathogens and regulate inflammation by producing interleukin-10. Dendritic cells in ileums treated with B. breve also produced more interleukin-10 than control models.
Next, they tested interleukin-10’s ability to reverse senescence caused by sunitinib in OMSCs. They used a group of mice given only sunitinib, a group given sunitinib + interleukin-10 and a control group given no medications. Results showed that OMSCs treated with interleukin-10 and sunitinib had decreased rates of senescence (less expression of γH2A.X) compared to cells treated with just sunitinib. Remember that they already established that sunitinib causes OMSC senescence and that this could impair wound healing. Adding interleukin-10 improved OMSC migration abilities so they can travel to the wound faster and start proliferating to heal it.
Finally, the scientists tested how interleukin-10 directly affects oral wound healing. To accomplish this, they designed an antibody to bind to and inactivate interleukin-10 in mice. The antibody binds and changes the shape of interleukin-10 so it is no longer functional. The group of mice treated with sunitinib + B. breve showed better oral wound healing than the group of mice treated with sunitinib + B. breve + neutralizing antibody. Moreover, the group given the neutralizing antibody had restored levels of pro-inflammatory factors that were decreased in mice with functional interleukin-10.
The results of these experiments showed that anti-angiogenic drugs can prevent oral wounds from healing. They also established that treatment with the probiotic B. breve, a commensalist gut bacterium, can improve wound healing while the anti-angiogenic drug is still being administered by recruiting dendritic cells. These immune cells secrete the cytokine interleukin-10 that decreases inflammation and improves wound healing. The study shows that B. breve may be a treatment option for patients who are also taking anti-angiogenic drugs to suppress oral tumors. B. breve treatment could make it possible for patients to have invasive dental procedures while still having their anti-angiogenic treatments.
