Recent Advances in Research on Vitamin C Transporters

Abstract

Vitamin C (VC, also known as ascorbic acid) is a water-soluble nutrient that cannot be synthesized in humans. Therefore, dietary supplementation and subsequent distribution of this physiologically important bioactive compound are necessary for the maintenance of human health. Since VC can hardly traverse cellular membranes passively owing to its hydrophilicity, active transport plays a pivotal role in VC handling, suggesting that VC transporters are of physiological significance. Until recently, only two VC transporters had been identified in mammals: sodium-dependent vitamin C transporter 1 (SVCT1) and SVCT2, which act as importers. Furthermore, the molecular mechanism of VC secretion from cells―a key step in transcellular VC transport―has been a longstanding mystery. In this connection, a VC exporter regulating VC supply from blood to the brain was identified in 2022 and named vitamin C efflux protein (VCEP). As well as overviewing the metabolism and handling of VC in the human body, this review details recent advances in VC transporter research, including the discovery of VCEP. To understand the whole picture of VC handling systems, further research on latent VC transporters and their physiological roles is vital, as this will also have implications in the field of nutrition.