Vitamin C: Absorption and reabsorption

Vitamin C is essential in all mammalian cells. Ascorbic acid (AA) is necessary for the reduction of ferric and cupric ions. Ascorbate is also involved in collagen, steroid and neuropeptide biosynthesis. Furthermore, vitamin C is an aqueous-phase antioxidant concentrated within the cell cytosol and may play an important role in protecting DNA from oxidative damage, which is associated with mutagenesis and carcinogenesis. Deficiency of this vitamin causes scurvy and is also involved in the onset and progression of degenerative diseases, such as cancer and cardiovascular disease. Normal physiological human AA plasma levels are in the range of 60-100 μM. Humans cannot synthesize AA and, therefore, rely on ingestion of AA, coupled with intestinal absorption and renal reabsorption, to maintain plasma levels. Vitamin C, ingested in diet or dietary supplements, is absorbed by epithelial cellsin the small intestine by the SVCT1 transporter and, subsequently, diffuses into the circulatory system. In the kidney, circulating AA is filtered from the glomerulus into the Bowman's capsule through a general filtration mechanism. Ascorbic acid is reabsorbed by renal epithelial cells into the capillary bed surrounding the proximal convoluted tubuleby SVCT1. Other transporters, such as SVCT2 and GLUT, are also involved in this process. The purpose of this review is to summarize and analyze the published data regarding vitamin C transporters and transport in human cells and to look at possible therapeutic uses, if any, that vitamin C has.