Hydroxysafflor Yellow A Promotes Lac‐Phe Synthesis to Suppress <scp>GIP</scp> and Ameliorate Obesity in <scp>DIO</scp> Mice

Hydroxysafflor Yellow A (HSYA), the main active component of Carthamus tinctorius L., has been shown to reduce feeding efficiency and diet-induced obesity (DIO) by inhibiting GIP secretion. This study aimed to clarify the detailed mechanism through which HSYA suppresses GIP production. Diet-induced obese mice were treated with HSYA or HSYA plus antibiotics. A combination of untargeted and targeted metabolomics was performed on cecal contents to identify differential metabolites. RT-qPCR and siRNA knock down experiments were performed in mouse intestinal tissues, Caco-2 and STC-1 cells for further exploring the role of HSYA in regulating differential metabolites and its possible mechanism. HSYA could effectively reduce bodyweight and improve glucolipid metabolism in DIO mice. HSYA treatment significantly elevated N-lactoyl-phenylalanine (Lac-Phe) levels in the cecum, but not in the serum, independent of gut microbiota alterations. Carnosine dipeptidase II (CNDP2), the sole enzyme responsible for Lac-Phe production, was also upregulated by HSYA treatment in intestinal tissues and Caco-2 cells and this effect was abolished by CNDP2 knockdown. Furthermore, Lac-Phe treatment could directly inhibit GIP production in STC-1 cells. Our findings firstly revealed a host-derived pathway through which HSYA suppresses GIP production by the upregulation of CNDP2 expression and increasing Lac-Phe synthesis. This novel mechanism provided new insights into the metabolic regulation of GIP and highlights the therapeutic potential of HSYA in treatment of obesity.