Examining the link between Gut Microbiome Health and the Development of Neurological Diseases
Introduction
The gut microbiome is the community of organisms, including bacteria, fungi and arches, that inhabit the gut, mainly the large intestine. Gut composition can be influenced by birth, lifestyle choices, and diet. These factors can contribute to gut dysbiosis, which is the reduced diversity and the imbalance of microbes in the gut [Westfall et al. 2017]. Gut dysbiosis exerts detrimental effects to several aspects of human health. In recent years, neurological diseases have become much more prevalent, and the World Health Organization (W.H.O.) predicts that neurological diseases disease will surpass cancer as the second leading cause of death after cardiovascular disease [Peterson. 2020]. Recent research suggests that gut health and intestinal dysbiosis is linked to the development of several neurological diseases, such as depression, neurodegeneration, Parkinson’s (PD) and Alzheimer’s Disease (AD) [Westfall et al. 2017]. The connection between the gut and neurological diseases is mediated by the gut-brain axis, which is a bidirectional communication system between the central nervous system and the intestinal track, providing a possible linkage between worsening gut health and the rapid increase of neurological diseases.
Definitions
Gut-Brain Axis:
A bidirectional communication network between the Central Nervous System (CNS) and gastrointestinal (GI) tract.
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Gut Microbiome
The community of microorganisms (bacteria, fungi, and archaea) in the GI tract.
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Neurological Disease
A condition disrupting the CNS, affecting the brain, spinal cord, or nerves
Dysbioisis:
An imbalance to the composition snd diversity of the microorganisms in the gut microbiome, depression, neurodegeneration, Parkinson’s (PD) and Alzheimer’s Disease (AD) [Westfall et al. 2017]. The connection between the gut and neurological diseases is mediated by the gut-brain axis, which is a bidirectional communication system between the central nervous system and the intestinal track, providing a possible linkage between worsening gut health and the rapid increase of neurological diseases.
Figure 1: Communication Between the GI Tract and the CNS [He et al, 2024]
Results
The gut-brain axis is not only existent, but the connection and link is extremely prevalent to neurological disease development. The link between the gut and brain involves the CNS, autonomic nervous system, enteral nervous system, and the hypothalamic- pituitary-adrenal axis [Geng et al, 2022]. The link to these systems and the gut's influence on mood is in large part due to Gl tract synthesizing serotonin, epinephrine, dopamine, and other chemicals, which translocate to the brain and impact brain function
(Geng et al, 2022; He et al, 2024].
Other gut metabolites impact neurological disease development in a completely separate way. AD is specifically linked to changes in gene expression, and metabolites produced by the gut microbiome, which impact acetylation and methylation of DNA and histones [Zhan et al, 2023]. Butyrate, a short-chain fatty acid (SCFA), is attributed to alterations in gene expression by inhibiting histone deacetylases, which cause DNA to wrap tighter and
therefore reduce gene expression, a contributor to AD [Gwak et al, 2021]. Other short-chain fatty acids are also extremely important in reducing the risk of developing other neurological diseases as well, such as PD, showing that SCFAs produced by gut microbes act as a preventative measure [Westfall et al, 2017].
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A negative impactor on neurological diseases is oxidative stress, which can be exacerbated by the gut metabolite trimethylamine N-Oxide (TMAO), which increases levels of oxidative stress [Zhan et al, 2023]. Multiple Sclerosis (MS). a disorder impacting the CNS, AD and PD are all linked to oxidative stress [Westfall et al, 2017]. Gut bacteria such as Mycoplasma, Pseudomonas, Haemophilus are bacteria associated with MS that produce metabolites contributing to oxidative stress [Gulrandhe et al, 2023]. Reactive oxidative species, another type of metabolite produced by the gut, attributes to the development of AD and PD by stimulating the production of cytokines, which increases neuroinflammation.
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Figure 2: Direct and indirect channels of communication of the Gut-Brain axis [Peterson, 2020]
Figure 3: The gut-brain axis and metabolite interactions in Alzheimer’s Disease [Zhan et al, 2023]
Conclusion
The existence of the gut-brain axis itself provides reason that the gut could play a role in the neurological diseases. More importantly, different neurological diseases seem to be linked to the gut in similar ways, meaning that even though the development of these diseases seems to be completely separate, the underlying causes or contributing factors may be linked. Oxidative stress, for example, seems to be a common thread in MS, AD, and PD, even though MS is an autoimmune disease affecting the CNS, AD is neurodegenerative disease, and PD forms from loss of dopamine-producing neurons. Since certain gut bacteria attributes to the underlying cause of these neurological conditions, maintaining gut health could serve as a therapeutic measure to reduce the chance of neurological disease. On the other hand, poor gut health will do the opposite, thus we can deduce that not only should people make an attempt to maintain proper gut health and diversity, but that the link between gut microbiome health and neurological disease development exists, and could become a more researched field if neurological diseases increase as predicted by the scientific community.
Methods
The existence of the gut-brain axis itself provides reason that the gut could play a role in the neurological diseases. More importantly, different neurological diseases seem to be linked to the gut in similar ways, meaning that even though the development of these diseases seems to be completely separate, the underlying causes or contributing factors may be linked. Oxidative stress, for example, seems to be a common thread in MS, AD, and PD, even though MS is an autoimmune disease affecting the CNS, AD is neurodegenerative disease, and PD forms from loss of dopamine-producing neurons. Since certain gut bacteria attributes to the underlying cause of these neurological conditions, maintaining gut health could serve as a therapeutic measure to reduce the chance of neurological disease. On the other hand, poor gut health will do the opposite, thus we can deduce that not only should people make an attempt to maintain proper gut health and diversity, but that the link between gut microbiome health and neurological disease development exists, and could become a more researched field if neurological diseases increase as predicted by the scientific community.
Acknowledgements
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