Anti-obesity effects of heat-killed Apilactobacillus kosoi, a FLAB-derived postbiotic, in high-fat diet-induced obese mice

Abstract

Abstract Apilactobacillus kosoi is a fructophilic lactic acid bacterium (FLAB) isolated from a Japanese fermented food, kôso liquid. As a postbiotic, heat-killed A. kosoi has previously been reported to exhibit immunomodulatory and antitumor activities; however, its effects on obesity remain unknown. In this study, we investigated the anti-obesity effects of heat-killed A. kosoi in a high-fat diet-induced obese mouse model. Heat-killed A. kosoi significantly suppressed body weight gain and energy intake, with a tendency toward reduced fat accumulation, without causing adverse changes in blood biochemical parameters. It also partially alleviated the high-fat diet-induced increase in the relative abundance of Bacillota, mitigated the reduction in serum IgA levels, and restored fecal concentrations of both formate and butyrate. Modest alterations in the expression of hepatic genes involved in fatty acid, cholesterol, and bile acid metabolism further suggested a contribution of hepatic metabolic regulation to its anti-obesity effects. Collectively, these findings demonstrate that heat-killed A. kosoi is the first FLAB-derived postbiotic reported to exhibit anti-obesity activity. The restoration of formate, together with butyrate, highlights a potential role for microbial metabolites in host energy metabolism and expands current understanding of the physiological functions of FLAB-derived postbiotics.