Metabolic profiling reveals a contribution of gut microbiota to fatty liver phenotype in insulin-resistant mice

Abstract

Here, we study the intricate relationship between gut microbiota and host cometabolic phenotypes associated with dietary-induced impaired glucose homeostasis and nonalcoholic fatty liver disease (NAFLD) in a mouse strain (129S6) known to be susceptible to these disease traits, using plasma and urine metabotyping, achieved by (1)H NMR spectroscopy. Multivariate statistical modeling of the spectra shows that the genetic predisposition of the 129S6 mouse to impaired glucose homeostasis and NAFLD is associated with disruptions of choline metabolism, i.e., low circulating levels of plasma phosphatidylcholine and high urinary excretion of methylamines (dimethylamine, trimethylamine, and trimethylamine-N-oxide), coprocessed by symbiotic gut microbiota and mammalian enzyme systems. Conversion of choline into methylamines by microbiota in strain 129S6 on a high-fat diet reduces the bioavailability of choline and mimics the effect of choline-deficient diets, causing NAFLD. These data also indicate that gut microbiota may play an active role in the development of insulin resistance.

Fig. 1.

Pathophysiology of the response of BALB/c and 129S6 mice to prolonged fat-feeding. Effect of glucose injection on blood glucose (A) and plasma insulin (B) concentrations in BALB/c and 129S6 mice fed an LFD or HFD. H&E-stained liver sections from 5-month-old BALB/c (C) and 129S6 (D) mice on HFD, showing micro- and macrovesicular steatosis in 129S6 mice (magnification, ×20). Plasma glucose and insulin values were obtained from >53 (BALB/c-LFD), 34 (BALB/c-HFD), and 40 (129S6-LFD, 129S6-HFD) mice. Significant differences (P < 0.05) between HFD-fed and LFD-fed 129S6 mice (†), between HFD-fed and LFD-fed BALB/c mice (‡), between LFD-fed 129S6 and BALB/c mice (‖), and between HFD-fed 129S6 and BALB/c mice (§) are shown.

Fig. 2.

Plasma and urine metabolic profiling by ¹H NMR spectroscopy of the response of BALB/c and 129S6 mice to dietary intervention at 5 months of age. Plasma (A) and urine (B) 600-MHz ¹H NMR spectra from typical 5-month-old 129S6 mice on HFD. OPLSDA score plots for plasma (C) and urine (D) metabolic profiles. HDL, high-density lipoprotein; LDL, low-density lipoprotein; VLDL, very low-density lipoprotein.

Fig. 3.

The symbiotic methylamines’ metabolic pathway (A) and their putative mechanism of liver toxicity (B). The OPLS-derived correlation is represented by standard color-coding for each metabolite: red square, positive correlation; green square, negative correlation, meaning a higher (lower) metabolite concentration in the corresponding group. FFA, free fatty acids.