Measurements of Intra- and Extra-Cellular 5-Methyltetrahydrofolate Indicate that Bifidobacterium Adolescentis DSM 20083T and Bifidobacterium Pseudocatenulatum DSM 20438T Do Not Actively Excrete 5-Methyltetrahydrofolate In vitro

Assessment of gut microbiota fecal metabolites by chromatographic targeted approaches

Gut microbiota, the specific microbial community of the gastrointestinal tract, by means of the production of microbial metabolites provides the host with several functions affecting metabolic and immunological homeostasis. Insights into the intricate relationships between gut microbiota and the host require not only the understanding of its structure and function but also the measurement of effector molecules acting along the gut microbiota axis. This article reviews the literature on targeted chromatographic approaches in analysis of gut microbiota specific metabolites in feces as the most accessible biological matrix which can directly probe the connection between intestinal bacteria and the (patho)physiology of the holobiont. Together with a discussion on sample collection and preparation, the chromatographic methods targeted to determination of some classes of microbiota-derived metabolites (e.g., short-chain fatty acids, bile acids, low molecular masses amines and polyamines, vitamins, neurotransmitters and related compounds) are discussed and their main characteristics, summarized in Tables.

A Structural Basis for Biguanide Activity

Metformin is the most commonly prescribed treatment for type II diabetes and related disorders; however, molecular insights into its mode(s) of action have been limited by an absence of structural data. Structural considerations along with a growing body of literature demonstrating its effects on one-carbon metabolism suggest the possibility of folate mimicry and anti-folate activity. Motivated by the growing recognition that anti-diabetic biguanides may act directly upon the gut microbiome, we have determined structures of the complexes formed between the anti-diabetic biguanides (phenformin, buformin, and metformin) and Escherichia coli dihydrofolate reductase (ecDHFR) based on nuclear magnetic resonance, crystallographic, and molecular modeling studies. Interligand Overhauser effects indicate that metformin can form ternary complexes with p-aminobenzoyl-l-glutamate (pABG) as well as other ligands that occupy the region of the folate-binding site that interacts with pABG; however, DHFR inhibition is not cooperative. The biguanides competitively inhibit the activity of ecDHFR, with the phenformin inhibition constant being 100-fold lower than that of metformin. This inhibition may be significant at concentrations present in the gut of treated individuals, and inhibition of DHFR in intestinal mucosal cells may also occur if accumulation levels are sufficient. Perturbation of folate homeostasis can alter the pyridine nucleotide redox ratios that are important regulators of cellular metabolism.