Extensive profiling of histidine-containing dipeptides reveals species- and tissue-specific distribution and metabolism in mice, rats and humans

Abstract Histidine-containing dipeptides (HCDs) are pleiotropic homeostatic molecules linked to inflammatory, metabolic and neurological diseases, as well as exercise performance. Using a sensitive UHPLC-MS/MS approach and an optimized quantification method, we performed a systematic and extensive profiling of HCDs in the mouse, rat, and human body (in n=26, n=25, n=19 tissues, respectively). Our data show that tissue HCD levels are uniquely regulated by carnosine synthase (CARNS1), an enzyme that was preferentially expressed by fast-twitch skeletal muscle fibers and brain oligodendrocytes. Cardiac HCD levels are remarkably low compared to other excitable tissues. Carnosine is unstable in human plasma, but is preferentially transported within red blood cells in humans but not rodents. The low abundant carnosine analog N-acetylcarnosine is the most stable plasma HCD, and is enriched in human skeletal muscles. Here, N-acetylcarnosine is continuously secreted into the circulation, which is further induced by acute exercise in a myokine-like fashion. Collectively, we provide a novel basis to unravel tissue-specific, paracrine, and endocrine roles of HCDs in human health and disease. Significance statement By extensively profiling the pluripotent histidine-containing dipeptides across three species, we generated many new insights into species- and tissue-specific histidine-containing dipeptide metabolism. For instance, the only stable analog that is specific for the human circulation (N-acetylcarnosine) is continuously released from muscle tissue and is positively regulated by physical exercise. The great number of analyses and experiments involving humans establishes great translational value of the findings. These new data open exciting opportunities to study histidine-containing dipeptide metabolism, including paracrine and/or endocrine signaling of these dipeptides, possibly contributing to the potent health-promoting exercise effects.