Brain Health & the Microbiome

AD is, in a word, devastating. The massive psychological and physical trauma experienced by people with dementia and their loved ones is catastrophic and incapable of overestimation. It is incumbent upon researchers and clinicians to not only better understand the etiology of this disease, but also to translate this knowledge into actionable evidence to facilitate clinical care and prevention. The MGBA serves as a major etiological factor, in both cause and potentiation of the disease process, that possesses great potential for intervention. Interventions have the greatest opportunity for success earlier in the disease pathogenesis; therefore, MCI is an ideal target for intervention to prevent progression to AD. To effectively apply knowledge of this bidirectional relationship, a clearer picture of dysbiosis relevant to cognitive decline must be identified. The inclusion of HC, MCI, and early AD allows for the detection of a dose-response relationship, which is one of Bradford Hill's criteria for causality. 1 This means we will begin to investigate causality (using one of Hill's eight criteria) in addition to association in this proof-of-concept study. Most previous research has been done at too high a phylogenetic level to be truly informative in terms of interventions-in other words the data is too low resolution. The microbiome field was launched at the phylum/genus level for many reasons including the need to start somewhere in such a complex system. To put this in perspective, comparing a genus, such as Lactobacillus, would be akin to comparing a compilation or average of all species of the genus Homo: H. sapiens, H. habilis, H. errectus, H. heigelbergensis, H. neanderthalensis, and H. naledi. The diversity in Homo sapiens alone is staggering. How could we possibly think this is specific or high resolution enough to be clinically meaningful? Well, the research has shown that it is not. This coupled with advancements in technology (qPCR to 16S to shotgun metagenomics) has changed the landscape of the microbiome field. However, such advanced testing and understanding has yet to make it to the clinic and has largely not been applied to MCI or AD populations to date. The sum of the evidence suggests that restoration of the gut microbiome may serve to prevent, slow, or even reverse MCI/AD. Whether this entails the use of diet, supplements, medications, etc. or some combination thereof remains to be discovered. Before an intervention can be designed, a firm grasp of the specific alterations to the gut microbiome must be identified using higher resolution than simply genus alone-we must understand species level at least, ideally strain level in many cases. Once we understand the species-level alterations, therapeutic interventions may then be implemented to determine the effect size of said interventions.