Diabetes affects about 529 million people globally. It is responsible for about 1.6 million deaths annually, with insulin resistance (IR) serving as the main precursor to type 2 diabetes and cardiovascular disease. IR is caused by complex interactions in a sedentary lifestyle, a Western dietary pattern, obesity, and gut microbiome-derived inflammatory stimuli. A high-fat diet (HFD) changes microbial metabolism and elevates circulating bacterial lipopolysaccharides (LPS), which activate Toll-like receptor (TLR4) and trigger chronic low-grade inflammation. While microbial metabolites often modulate host GPCRs or nuclear receptors, their interaction with kinases remains poorly understood.
Earlier studies detected microbial methylamines like trimethylamine (TMA) as metabolites linked with IR, non-alcoholic fatty liver disease, and atherosclerosis. Their functional mechanisms are not clear. This study aimed to evaluate how TMA contributes to IR pathophysiology, detect pharmacological targets, and determine whether it modulates metabolic and immune signaling. They combined mouse dietary interventions, microbial metabolite profiling, kinase target screening, and mechanistic cellular assays to assess biochemical action and physiological relevance of TMA.
C57BL/6J mice were monitored for 6 months under chow or 65% kcal HFD conditions to assess the metabolic consequences of HFD feeding. Longitudinal phenotyping, including glucose tolerance tests and urinary metabolomics, showed that HFD rapidly induced obesity and impaired glucose tolerance. Liver transcriptomics showed no major upregulation of classical inflammatory pathways, which contradicted typical expectations of HFD-induced IR. Inflammatory markers like Saa1 and Saa2 were reduced and cytokines like Il6 and Il1β were unchanged.
High-resolution ^1H-NMR metabolomics identified TMA as the dominant metabolite. It showed that TMA was the dominant urinary metabolite distinguishing HFD-fed mice from controls. Variance component analysis confirmed that diet, instead of age, drives TMA elevation. The researchers tested whether dietary choline supplementation or suppression of TMA production modulated metabolic outcomes by using diets with different choline concentrations, TMA lyase inhibitor DMB, and antibiotic treatment.
The study used kinome screening and showed that TMA binds and inhibits IRAK4, a key kinase in the TLR4 inflammatory cascade, to detect the molecular target of TMA. In vitro kinase assays quantified an IC50 of 3.4 ÎĽM. It confirms that TMA acts as a direct IRAK4 inhibitor. This pharmacological result was validated by using primary human hepatocytes and human peripheral blood mononuclear cells (PBMCs). TMA reduced LPS-induced IL-6 and TNF secretion and decreased phosphorylation of IRAK1 and NF-ÎşB p65 in PBMCs. This shows suppression of TLR-mediated inflammatory signaling. TMA attenuated palmitic acid-induced activation of IRAK4, IKK, JNK, and p38 MAPK in hepatocytes and improved insulin signaling as measured by Akt phosphorylation. These results suggested that TMA dampens inflammatory pathways implicated in IR.
TMA delivered chronically by osmotic pumps improved glucose tolerance and insulin sensitivity in mice fed a low choline HFD in vivo. These metabolic benefits resembled pharmacological IRAK4 inhibition by PF06650833. Irak4-/- knockout mice phenocopied the protective effects observed with elevated TMA. This supports a causal molecular link. TMA administration earlier to LPS exposure improved survival in the murine septic shock model to test relevance in acute inflammation. This indicated systemic anti-inflammatory capability aligned with IRAK4 pathway suppression. Additional analyses showed that microbial TMA production was sensitive to dietary manipulation, and choline-rich diets elevated circulating TMA, and antibiotics or DMB reduced it. Plasma methylamine quantification by UPLC-MS/MS verified that TMA levels corresponded to dietary intervention and microbial activity.
The results give strong evidence that TMA functions as both a precursor of TMAO and an independent signaling molecule capable of modulating host kinase pathways. TMA was seen as methylamine exhibits beneficial metabolic effects by inhibiting IRAK4, which reduces inflammatory signaling linked to IR and metabolic dysfunction. This mechanism improves glucose homeostasis and insulin sensitivity in obesity models. This suggests potential as a therapeutic microbial metabolite for metabolic and inflammatory diseases of TMA. The study highlights the protective role in metabolic and immune balance linking microbial metabolism to host health of TMA.
Reference: Chilloux J, Brial F, Everard A, et al. Inhibition of IRAK4 by microbial trimethylamine blunts metabolic inflammation and ameliorates glycemic control. Nat Metab. 2025. doi:10.1038/s42255-025-01413-8
