Ascorbic acid and sodium-dependent vitamin C transporters in the peripheral nervous system: from basic science to clinical trials.

SIGNIFICANCE: Ascorbic acid and sodium-dependent vitamin C transporters (SVCT) have been shown to have important functions in the peripheral nervous system (PNS). Ascorbic acid is known to promote myelination in vitro in Schwann cell/dorsal root ganglion co-cultures by the formation of a collagen- and laminin-containing extracellular matrix.

RECENT ADVANCES: Recently, the function of ascorbic acid and SVCT2 in the PNS has been shown in vivo as well. Several studies on ascorbic acid treatment of Charcot-Marie-Tooth neuropathy 1A (CMT1A) have been completed and showed no clinical benefit.

CRITICAL ISSUES: Possible reasons for the failure of ascorbic acid in CMT1A treatment are discussed in this review. More preclinical trials, ideally using different animal models, should be considered before the initiation of clinical trials in humans. More knowledge about ascorbic acid transport kinetics and inter-individual differences in humans is necessary for future studies.

FUTURE DIRECTIONS: Further research into ascorbic acid transport mechanisms in the PNS is warranted. Especially the effects of transgenic or pharmacologic SVCT2 up-regulation on PNS myelination and remyelination will be an interesting area of research in the future. Furthermore, the potential use of ascorbic acid for peripheral neuropathies other than CMT1A would be a possible future research direction.