Ascorbic acid 2-glucoside: An ascorbic acid pro-drug with longer-term antioxidant efficacy in skin

Objective Deleterious effects of pollutants and ultraviolet radiation on the skin can be attenuated using formulations containing antioxidants. However, these have disadvantages, including chemical instability, photodegradation, poor bioavailability or biological activity. Here, two commercial formulations were evaluated: one optimized to stabilize and deliver ascorbic acid (AA) at 15% and the other containing a glucoside form of AA, namely ascorbic acid 2-glucoside (AA2G), at 1.8% and at a physiological pH. We compared the skin delivery, antioxidative effects and chemical stability of AA2G with AA in their respective formulations. Methods Skin delivery was measured using fresh viable human skin explants, and oxidative stress was measured using a human reconstructed epidermal (RHE) model according to levels of malondialdehyde (MDA), superoxide dismutase (SOD) and catalase. Results Ascorbic acid 2-glucoside was completely metabolized to AA by the skin before entering the receptor compartment. The skin contained parent and AA, indicating a reserve of AA2G was present for further metabolism. For AA2G and AA, maximum flux of AA-equivalents was at 12 h, with continued absorption over 24 h. The absolute amount in mu g was higher in the skin after application of AA than after application of AA2G. This may suggest a greater antioxidative effect; however, according to all three measurements of oxidative stress, the protective effect of AA and AA2G was similar. Unlike AA, AA2G was chemically stable under storage conditions. Conclusion A lower concentration of AA2G is as effective as the active metabolite, AA, in terms of antioxidant effects. AA2G was chemically stable and can be applied at a lower concentration than AA, thus avoiding the need for an acidic formulation with a pH below 3.5.

Automated summary

The study found that AA2G can be completely metabolized to AA by the skin, with a reserve of AA2G present for further metabolism. Although the absolute amount of AA in the skin was higher after application of AA, the protective effects of AA and AA2G were similar based on measurements of oxidative stress. AA2G was chemically stable under storage conditions and can be used at a lower concentration, avoiding the need for an acidic formulation with a pH below 3.5.