Ascorbic acid (AsA) interferes with the different steps of melanization, by interacting with copper ions at the tyrosinase active site and reducing dopaquinone and DHICA oxidation. Melanin can be changed from jet black to light tan by the reduction of oxidized melanin (35).
AsA is an effective reducing agent, which, at high concentrations, can momentarily retard the melanin-biosynthesis pathway, but never eliminate it. On the contrary, the resultant accumulation of diphenol produces an indirect activation on this pathway when the reductant is completely depleted (36). However, AsA is highly instable, being quickly oxidized and decomposed in aqueous solution and, because of its prevalent hydrophilic nature, has a low degree of penetration into the skin. Vitamin C iontophoresis may be an effective treatment modality for melasma (37).
Sixteen women with idiopathic melasma were instructed to use, at night, 5% ascorbic acid cream on one side of the face and 4% HQ cream on the other side, for 16 weeks. The improvement was observed on the HQ side with 93% good and excellent results, compared with 62.5% on the ascorbic acid side. Side effects were present in 68.7% with HQ versus 6.2% with ascorbic acid (38).
The numbers of DOPA-positive melanocytes of guinea pigs treated with VC, VE, and cystine were significantly decreased compared with those in VC group. In B16 melanoma cells, simultaneous treatment of VC, VE, and N-acetyl-cysteine was the most effective to decrease the melanin contents and to inhibit tyrosinase activity (39).
A multi-clinical, double-blind study on therapeutic effect of combination preparation of vitamins E and C was undertaken in comparison with single preparation of vitamin E and vitamin C in the treatment of chloasma or pigmented contact dermatitis (PCD). Objective data revealed significantly better results with combination treatment in chloasma than vitamin C alone and, in PCD, than vitamin E or C alone. The total serum lipoperoxide level and its ratio to total serum lipids tended to decline in the combination group and decreased significantly in vitamin E group. The sebum lipoperoxide level decreased significantly only in the combination group (40).
