The microbial metabolite indole-3-propionic acid improves glucose metabolism in rats, but does not affect behaviour

Abstract

Context: We have previously shown that an antidepressant-like effect of probiotics in rats was associated with a higher plasma level of the microbial tryptophan metabolite indole-3-propionic acid (IPA). Objective: We therefore wanted to study the isolated effect of IPA on behaviour and glucose metabolism in rats. Methods: Male Sprague–Dawley rats were fed control or IPA-enriched diet for six weeks (n = 12 per group) and assessed in the elevated plus maze, open field and forced swim test. Blood glucose, metabolic hormones and the white blood cell (WBC) composition were analysed. Results: IPA (mean intake 27.3 mg/kg/day) significantly lowered fasting blood glucose level by 0.42 mM (95% CI 0.11–0.73). Similarly, fasting plasma insulin levels and the homeostatic model assessment (HOMA) index of insulin resistance were reduced, whereas plasma metabolic hormones, behaviour and WBC composition remained unaffected by IPA. Conclusions: Our findings highlight IPA as a promising candidate for treatment of metabolic disorders associated with insulin resistance