Are Fecal Transplants a Potential Treatment for Alopecia Areata?

According to healthline, around 70 - 80% of the immune cells in our bodies reside in the gut. Therefore, in order to keep a healthy immune system, it is necessary to maintain a healthy gut microbiome.

But what does a "healthy" gut microbiome look like?

Although composition and microbial diversity vary between individuals, generally, a normal gut includes a variety of different bacteria, which can be seen in detail through this figure. At birth, microbes colonize the human gut, a crucial step in determining the composition of the microbiome. Over time, the composition fluctuates until reaching stability. Although only a single cell layer, the gut wall is protected by innate defense mechanisms that work with a local adaptive immune response to fight off pathogenic substances. Many dietary components, prebiotics, probiotics, antibiotics, illnesses, and new drugs may alter this system, leading to dysbiosis, which can lead to various negative outcomes.

What do the immune cells in the gut have to do with the skin?

As in the case of many autoimmune diseases, the health of the bacterial ecosystem inside the gut is a crucial component in influencing the pathogenesis (development) of a given skin disease. The converse of this state may be true as well; that is, the state of a specific skin disease may impact the gut microbiome. This establishment of a communication network is bidirectional and noted as the gut-skin axis.

Gut-skin communication is a process that occurs to manage systemic and local inflammation by engagement with the immune system. When antigenic microorganisms pass the gut membrane, they can wield a new power in breaching a first line of defense, causing a host of problems within the circulatory system and inflammation of the gut and skin.

To achieve minimal contact between these commensal antigens and the tissues, a "mucosal firewall" is put in place, a collection of forces including a mucus layer, a gut epithelial cell barrier, T cells, antibodies (Immunoglobulin A), and dendritic cells.

Through a host of interactions and responses, these cells either work to limit movement of bacteria by method of elimination or membrane pore generation or to maintain gut membrane integrity.

When microbiome gut composition is imbalanced as a result of various lifestyle choices, illnesses, or drugs, immune responses are impaired; the protection offered by mucus layers may be inhibited, microbes may enter the intestinal barrier, toxic products may be released, neurotransmitters may induce an unwarranted signal, and altered immune cells may circulate the body and make skin unhealthy. (To process this information visually, look at this figure.)

How does all of this connect to alopecia areata?

Alopecia areata is a skin disease caused by the activation of T cells, which attack a presented molecule of the hair follicle cell. In other words, faulty T cells target self-produced molecules (antigens), rather than foreign substances. Cytokines produced by this process disrupt a growth phase of the hair growth cycle, ultimately culminating in hair loss.

A high proportion of people with alopecia areata also show signs of ulcerative colitis, implying a connection between the gut and the skin.

Thus, in order for the skin to flourish, the gut needs to maintain homeostasis of the commensal microbial organisms harbored there. Fecal transplants are thought to be safe and effective ways to regenerate a microbial ecosystem that is healthy and beneficial.

In a variety of clinical trials, gut microbial interventions have been used to solve or reduce the severity of skin diseases, and in all, a positive result has been found.

Sources

Mahmud, M. R., Akter, S., Tamanna, S. K., Mazumder, L., Esti, I. Z., Banerjee, S., Akter, S., Hasan, M. R., Acharjee, M., Hossain, M. S., & Pirttilä, A. M. (2022).

Impact of gut microbiome on skin health: Gut-skin axis observed through the lenses of Therapeutics and skin diseases. Gut microbes. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9311318/

NCI Dictionary of Cancer terms. National Cancer Institute. (n.d.).

https://www.cancer.gov/publications/dictionaries/cancer-terms/def/gastrointestinal-system

Sánchez-Pellicer, P., Navarro-Moratalla, L., Núñez-Delegido, E., Agüera-Santos, J., & Navarro-López, V. (2022, October 14).

How our microbiome influences the pathogenesis of Alopecia areata. Genes. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9601531/#B101-genes-13-01860

Werner, C. (2023, March 9).

New and FDA-approved treatments for alopecia areata. Healthline. https://www.healthline.com/health/alopecia-research-advances