Treatment of wild-type mice with 2,3-butanediol, a urinary biomarker of Fmo5 -/- mice, decreases plasma cholesterol and epididymal fat deposition

We previously showed that Fmo5 ^-/- mice exhibit a lean phenotype and slower metabolic ageing. Their characteristics include lower plasma glucose and Cholesterol, greater glucose tolerance and Insulin sensitivity, and a reduction in age-related weight gain and whole-body fat deposition. In this paper, nuclear magnetic resonance (NMR) spectroscopy-based metabolite analyses of the urine of Fmo5 ^-/- and wild-type mice identified two isomers of 2,3-butanediol as discriminating urinary biomarkers of Fmo5 ^-/- mice. Antibiotic-treatment of Fmo5 ^-/- mice increased plasma Cholesterol concentration and substantially reduced urinary excretion of 2,3-butanediol isomers, indicating that the gut microbiome contributed to the lower plasma Cholesterol of Fmo5 ^-/- mice, and that 2,3-butanediol is microbially derived. Short- and long-term treatment of wild-type mice with a 2,3-butanediol isomer mix decreased plasma Cholesterol and epididymal fat deposition but had no effect on plasma concentrations of glucose or Insulin, or on body weight. In the case of long-term treatment, the effects were maintained after withdrawal of 2,3-butanediol. Short-, but not long-term treatment, also decreased plasma concentrations of triglycerides and non-esterified fatty acids. Fecal transplant from Fmo5 ^-/- to wild-type mice had no effect on plasma Cholesterol, and 2,3-butanediol was not detected in the urine of recipient mice, suggesting that the microbiota of the large intestine was not the source of 2,3-butanediol. However, 2,3-butanediol was detected in the stomach of Fmo5 ^-/- mice, which was enriched for Lactobacillus genera, known to produce 2,3-butanediol. Our results indicate a microbial contribution to the phenotypic characteristic of Fmo5 ^-/- mice of decreased plasma Cholesterol and identify 2,3-butanediol as a potential agent for lowering plasma Cholesterol.