Pharmacological inhibition of gut-derived serotonin synthesis is a potential bone anabolic treatment for osteoporosis

Abstract

Osteoporosis results from misregulation of bone catabolism and bone anabolism, resulting in severe bone loss. Most current therapies act by decreasing bone catabolism, but targeting bone anabolism is more desired, because once bone is lost, it is difficult to replace. In a new report by Gerard Karsenty and his colleagues, they show that orally delivered pharmacological targeting of serotonin synthesis in the gut is sufficient to increase bone anabolism and thus restore lost bone in rat and mouse models of well-established osteoporosis ( pages 264–265 ). Osteoporosis is a disease of low bone mass most often caused by an increase in bone resorption that is not sufficiently compensated for by a corresponding increase in bone formation1. As gut-derived serotonin (GDS) inhibits bone formation2, we asked whether hampering its biosynthesis could treat osteoporosis through an anabolic mechanism (that is, by increasing bone formation). We synthesized and used LP533401, a small molecule inhibitor of tryptophan hydroxylase-1 (Tph-1), the initial enzyme in GDS biosynthesis. Oral administration of this small molecule once daily for up to six weeks acts prophylactically or therapeutically, in a dose–dependent manner, to treat osteoporosis in ovariectomized rodents because of an isolated increase in bone formation. These results provide a proof of principle that inhibiting GDS biosynthesis could become a new anabolic treatment for osteoporosis.