Spotlight on Chemists

Elizabeth Bess: The Gut Microbiome and Parkinson’s Disease

Human gut microbiome

The Human Gut Microbiota

The human gastrointestinal tract harbours a complex and dynamic population of microorganisms, the gut microbiota – approximately 100 trillion microorganisms (most of them bacteria, but also viruses, fungi, and protozoa) exist in this region of the body [1]. The diversity in the factors that affect an individual’s microbiota lead to a unique one in each person, almost like a “gut fingerprint”, as described by Dr. Elizabeth Bess of UC Irvine. In a healthy person, the microbes coexist peacefully, with the largest numbers found in the small and large intestines. However, they also have the potential to be greatly harmful if there is a disturbance in that balance – brought on by infectious illnesses, certain diets, or the prolonged use of antibiotics or other bacteria-destroying medications [2].

Within their normal functioning, microbiota stimulate the immune system of the body, break down potentially toxic food compounds, and even synthesise certain vitamins and amino acids that are essential to nutrition. The microbiota contain digestive enzymes that help achieve this function [4]. The microbiota of a healthy person has also been proven to provide protection from pathogenic organisms that enter the body such as through drinking or eating contaminated water or food [3]. Interestingly, however, these microbes in the gut also have the capacity to influence one’s brain functioning and hormones in the body – Dr. Elizabeth Bess explores exactly this facet of the microbiota. 

Factors Affecting the Microbiome

There are many factors, both pre and post pregnancy, that may influence the development and composition of an individual’s microbiota [4]. In addition to family genes and medication use, diet plays a major role in determining the kinds of microbiota living in the colon. In the colon, dietary fibre in foods can be broken down and fermented* only by using enzymes that come from microbiota. Compounds called short chain fatty acids (SCFA) are released as a result of fermentation. This lowers the pH (measure of acidity) of the colon, which in turn determines the type of microbiota present in it. Foods that support increased levels of SCFA are indigestible carbohydrates and fibres such as inulin, starches, gums and pectins. These fibres are sometimes called “prebiotics”, since they feed our beneficial microbiota [2].

Since the first microbes are acquired upon birth from the mother, pregnancy and food intake during gestation are also important factors. Studies show differences in microbiome caused due to different birth routes – babies born through vaginal delivery are less predisposed to certain diseases as compared to those born through a c-section [4]. The composition of the microbes in the gut is also believed to be affected progressively with a person’s age. 

*Fermentation refers to the breaking down of sugar molecules into simpler compounds by the microbiota in order to produce substances that can be used to obtain energy.

The Microbiota and Parkinson’s Disease

The vast community of microbiota may reside in the gut, but studies show that its influence doesn’t stop just there. Our microbiome may also play a role in mental health and neurological conditions such as autism, epilepsy, and depression by interacting with our nervous system and even releasing molecules that can perhaps make their way to the brain. 

One particular disease that Dr. Elizabeth Bess and her team research is Parkinson’s disease – it affects the nervous system and parts of the body that the nerves control. There is increasing evidence that it may begin in the gastrointestinal tract due to short proteins called alpha-synuclein. When these proteins clump together due to misfolding in the microbiota, it results in neurodegeneration* in the brain and affects motor function. Dr. Bess’s lab, in particular, researches the pathways that induce this process of clumping of proteins. She finds that there are three chemical species at play: dopamine, iron in the ferrous state (or the +2 oxidation state), and alpha-synuclein (before aggravation), which are not toxic by themselves.

However, when the bacteria in the gut perform nitrate respiration – the movement of oxygen from the outside environment to the cells within tissues and the removal of carbon dioxide vice-versa using nitrate – products called nitrites are produced. Nitrites are strong oxidants: this means that they are able to change iron into the ferric state (or +3 oxidation state). This change triggers a cascade of chemical reactions that aggravate alpha-synuclein and causes Parkinson’s in the brain. 

*Neurodegeneration is the slow and progressive loss of neuronal cells in specified regions of the brain. 

Learn More

If you’d like to hear more about the microscopic wonder of microbiota and one of its researchers, visit us on Spotify to listen to our ChemTalk podcast with Dr. Elizabeth Bess, professor and chemist at the University of California, Irvine, to learn more about how microbiota affects your mood, what got her interested in the microbiome, and what her path towards a career in science looked like. 

Find the ChemTalk podcast here: https://open.spotify.com/episode/7ka9gzJ2yP9MxY813msCBK

Works Cited 

[1] Thursby, E., & Juge, N. (2017). Introduction to the human gut microbiota. Biochemical Journal, 474(11), 1823-1836. https://doi.org/10.1042/BCJ20160510

[2] “The Microbiome” Harvard Global Chan School. 22 February 2021. 

[3] Ursell, L.K., et al. Defining the Human Microbiome. Nutr Rev. 2012 Aug; 70(Suppl 1): S38–S44.

[4] Bess, Elizabeth. Personal Interview. Conducted by Roxanne Salkeld. 14 November 2022.