Summary Metformin is the first-line therapy for type 2 diabetes, but there are large inter-individual variations in responses to this drug. Its mechanism of action is not fully understood, but activation of AMP-activated protein kinase (AMPK) and changes in the gut microbiota appear to be important. The inhibitory role of microbial metabolites on metformin action has not previously been investigated. Here, we show that concentrations of the microbial metabolite imidazole propionate are higher in subjects with type 2 diabetes taking metformin who have high blood glucose. We also show that metformin-induced glucose lowering is not observed in mice pretreated with imidazole propionate. Furthermore, we demonstrate that imidazole propionate inhibits AMPK activity by inducing inhibitory AMPK phosphorylation, which is dependent on imidazole propionate-induced basal Akt activation. Finally, we identify imidazole propionate-activated p38γ as a novel kinase for Akt and demonstrate that p38γ kinase activity mediates the inhibitory action of imidazole propionate on metformin.

Aims Inflammation plays an important role in cardiovascular disease (CVD) development. The NOD-like receptor protein-3 (NLRP3) inflammasome contributes to the development of atherosclerosis in animal models. Components of the NLRP3 inflammasome pathway such as interleukin-1β can therapeutically be targeted. Associations of genetically determined inflammasome-mediated systemic inflammation with CVD and mortality in humans are unknown. Methods and results We explored the association of genetic NLRP3 variants with prevalent CVD and cardiovascular mortality in 538 167 subjects on the individual participant level in an explorative gene-centric approach without performing multiple testing. Functional relevance of single-nucleotide polymorphisms on NLRP3 inflammasome activation has been evaluated in monocyte-enriched peripheral blood mononuclear cells (PBMCs). Genetic analyses identified the highly prevalent (minor allele frequency 39.9%) intronic NLRP3 variant rs10754555 to affect NLRP3 gene expression. rs10754555 carriers showed significantly higher C-reactive protein and serum amyloid A plasma levels. Carriers of the G allele showed higher NLRP3 inflammasome activation in isolated human PBMCs. In carriers of the rs10754555 variant, the prevalence of coronary artery disease was significantly higher as compared to non-carriers with a significant interaction between rs10754555 and age. Importantly, rs10754555 carriers had significantly higher risk for cardiovascular mortality during follow-up. Inflammasome inducers (e.g. urate, triglycerides, apolipoprotein C3) modulated the association between rs10754555 and mortality. Conclusion The NLRP3 intronic variant rs10754555 is associated with increased systemic inflammation, inflammasome activation, prevalent coronary artery disease, and mortality. This study provides evidence for a substantial role of genetically driven systemic inflammation in CVD and highlights the NLRP3 inflammasome as a therapeutic target.