MR Contrast from Ascorbic Acid (Vitamin C) in Phantoms and In Vivo

Introduction: L-ascorbic acid (vitamin C) is the most abundant intracellular antioxidant and an essential co-factor for the biosynthesis of many important biochemicals. Intracellular levels of ascorbic acid (AA) are remarkably high, especially in tissues such as brain and tumor cells, where concentrations may reach 10-30 mM. In this study, we show that native AA in solution is capable of producing marked changes in T2 and T2* relaxivity at physiologically relevant concentrations. Susceptiblity effects are seen in both anaerobically and aerobically prepared solutions at acidic and neutral pH, but disappear after oxidation to dehydroascorbate. In animal experiments, a single bolus of dehydroascorbate (the form of Vitamin C transported across the blood-retina and blood-brain barriers before conversion to ascorbic acid) produces a significant change in T2 mapping in the mouse retina, where intracellular concentrations are known to rise significantly. These results raise two important possibilities: first, that endogenous AA may be an important contributor to native T2 and T2* contrast in CNS and other tissues; and second, that both oxidized and reduced forms of ascorbic acid may have utility as novel MR contrast probes.