Tracking a dysregulated gut-brain axis with biomarkers of the microbiome

Abstract

Biological markers that track the physiological mechanisms underlying psychiatric disorders are desperately needed. Microbes that colonize mucosal surfaces, collectively known as the microbiome, and the array of genes that the microbiome encodes, have become a newly recognized source of potential novel disease mechanisms and pharmacological treatment targets. Much research is directed toward the search for measurable biomarkers that reflect both healthy and pathological states of the microbiome. Here, we review direct measures of microbial taxonomy present in gut communities and indirect measures of host responses to gut dysbioses. Direct biomarkers of the microbiome derive from the discovery and analyses of data obtained from deep sequencing projects of biospecimens from psychiatric cohorts. Indirect biomarkers of the microbiome typically entail measurement in blood of components of the toxic cycle of inflammation, gut permeability, and dysbiosis, which affects subsets of individuals with psychiatric disorders. As we progress in our understanding of the benefits and risks of certain combinations of taxa with regard to psychiatric disorders and their clinical manifestations, it will be equally important to characterize host phenotypes that relate to specific microbial compositions. The discovery, development and clinical testing of biomarkers of microbial taxa and of host responses will, in turn, lead to new methods to effectively and individually characterize and treat psychiatric disorders.