IDO1 and atherosclerosis: For example, indole-3-propionic acid (IPA), a gut microbiota-derived metabolite, has been shown to mitigate atherosclerosis by promoting cholesterol efflux, while deficiency in indoleamine 2,3-dioxygenase 1 (IDO1) exacerbates atherosclerosis progression by disrupting kynurenine metabolism and inducing osteogenic changes in vascular smooth muscle cells (2, 3).