Influence of gut microbiota on oral drug absorption and metabolism

Gut bacteria influence host intestinal phenotype in ways that impact drug absorption and metabolism. By comparing colonic tissue from germ-free mice to that of mice colonized with human microbiota, this study evaluates microbiota-driven differences in gene expression, mucosal permeability, and P-gp efflux capacity. Transcriptomic analysis revealed upregulation of genes coding ATP-binding cassette drug transporters P-gp (Abcb1a, Abcb1b), BCRP (Abcg2), and MRP3 (Abcc3), along with increased expression of solute carriers MCT1 (Slc16a1) and OCTN2 (Slc22a5). Immunohistochemistry indicated greater P-gp expression and apical localization in humanized mice. No relevant gene expression changes were observed in human homologs of drug-metabolizing cytochrome P450 enzymes, though cytochrome P450 oxidoreductase (Por) upregulation suggests increased cytochrome activity. Other phase I drug-metabolizing enzymes, including multiple homologs of human carboxylesterase 2 (CES2) and several reductases, were upregulated with high significance. Regarding phase II metabolism, genes encoding most UDP-glucuronosyltransferases and glutathione S-transferases were upregulated, along with the enzymes responsible for synthesizing their corresponding co-substrates, UDP-glucuronic acid and glutathione. Small intestinal mucosal explants demonstrated higher permeability to ¹⁴ C-labeled polyethylene glycol 4000 ( ¹⁴ C-PEG4000) in germ-free mice than in humanized mice. The ¹⁴ C-PEG4000 permeability differences are in agreement with changes in paracellular tight junctional proteins such as claudins, zonula occludens, and myosin II-related genes. These results demonstrate the broader impact of gut microbiome on oral drug absorption and metabolism and implicate the contributions of gut microbiome to individual variations in drug efficacy and toxicity.