Douglas Darr

Topical vitamin C protects porcine skin from ultraviolet radiation‐induced damage

Summary Ultraviolet radiation damage to the skin is due, in part, to the generation of reactive oxygen species. Vitamin C (l‐ascorbic acid) functions as a biological co‐factor and antioxidant due to its reducing properties. Topical application of vitamin C has been shown to elevate significantly cutaneous levels of this vitamin in pigs, and this correlates with protection of the skin from UVB damage as measured by erythema and sunburn cell formation. This protection is biological and due to the reducing properties of the molecule. Further, we provide evidence that the vitamin C levels of the skin can be severely depleted after UV irradiation, which would lower this organs innate protective mechanism as well as leaving it at risk of impaired healing after photoinduced damage. In addition, vitamin C protects porcine skin from UVA‐mediated phototoxic reactions (PUVA) and therefore shows promise as a broad‐spectrum photoprotectant.

Effects of molecular oxygen on detection of superoxide radical with nitroblue tetrazolium and on activity stains for catalase.

The usual method of staining polyacrylamide gel electropherograms for superoxide dismutase activity utilizes a photochemical flux of O2- to reduce nitroblue tetrazolium. Superoxide dismutases intercept O2-, preventing formazan production and thus causing achromatic bands. In the presence of H2O2, catalases also yield achromatic bands during this staining procedure. This is due to local elevation of pO2 by the catalatic decomposition of H2O2. O2, in turn, inhibits the reduction of the tetrazolium by O2-. This phenomenon provides a new activity stain for catalase. A previously described activity stain for catalase has also been reexamined and significantly improved.

A mimic of superoxide dismutase activity based upon desferrioxamine B and manganese(IV)

MnO2 reacted with desferrioxamine B yielding a green, water-soluble complex, with absorption maxima at 315 and 635 nm whose extinction coefficients were 925 and 60 M-1 cm-1, respectively. Increasing the proportion of ligand to metal increased both color yield and ability to scavenge O2-, with maximal color yield and activity being achieved at a 1:1 ratio. The complex catalyzed the dismutation of O2- and 1 microM was equivalent to 1 unit of superoxide dismutase activity in the xanthine oxidase-cytochrome c assay. The complex thus exhibited approximately 0.1% as much activity as did the manganese-containing superoxide dismutase, on the basis of manganese content. The activity of the complex was not suppressed by bovine serum albumin or by the soluble proteins extracted from Lactobacillus plantarum. In contrast, the activities of Cu(II) complexes of salicylate or Gly-His-Lys were suppressed by these proteins.

A double-blind, randomized, prospective trial to evaluate topical vitamin C solution for the prevention of radiation dermatitis

Abstract Purpose: The object of this study was to ascertain the value of topical ascorbic acid in the prevention of radiation dermatitis. Methods and Materials: Patients with primary or metastatic brain tumors were eligible. Patients applied a topical solution, twice per day prior to and throughout the course of radiotherapy, to the left and right sides of the head. The radiotherapist and the patient were blinded as to the contents of the solutions. The bottle for one side of the head contained topical ascorbic acid solution. The bottle for the other side of the head contained only vehicle. During and after the course of treatment the radiotherapist scored the skin reaction on both the left and right sides of the irradiated head using a skin reaction scale. The data were analyzed with a matched pair analysis. Since each patient received both treatments (ascorbic acid and control solutions) the statistical analysis concentrated on the paired difference in scores based on the probability of a “preference” for the treatment or control. Results: Eighty-four patients entered the study. Sixty-five were suitable for analysis. In 10 patients there was a preference for ascorbic acid solution (15%), in 20 patients there was a preference for placebo (31%), and there was a preference for neither in 35 patients (54%). Ascorbic acid solution could be considered to have an effect if the percentage of preferences favoring ascorbic acid over placebo, among those subjects with a preference, significantly exceeded the 50% expected by chance. The observed percentage of preferences for ascorbic acid was only 33% (10 of 30 with a preference; p = .10, two-sided sign test). Patient age, race, sex, and total dose of irradiation had no detectable influence on the comparative skin toxicity scores. Conclusion: There is no discernible benefit to ascorbic acid lotion, in the manner in which we used it in this trial, for the prevention of radiation dermatitis.

Induction of Collagen Synthesis by Ascorbic Acid: A Possible Mechanism

L-Ascorbic acid stimulates procollagen synthesis in cultured human skin fibroblasts without appreciably altering noncollagen protein synthesis. The effect is unrelated to intracellular degradation of newly synthesized procollagen. Levels of mRNA for pro alpha 1(I), pro alpha 2(I), and pro alpha 1(III), measured by hybridization with the corresponding cDNA probes, are elevated in the presence of ascorbic acid, whereas the level of mRNA for fibronectin is unchanged. Levels of functional mRNA for procollagen, measured in a cell-free translation assay, are specifically increased in the presence of ascorbic acid. Thus, ascorbic acid appears to control the expression of three different procollagen genes, each of which is located on a separate chromosome. It is proposed that intracellularly accumulated procollagen in ascorbate deficiency may lead to a translational repression of procollagen synthesis. Ascorbic acid may relieve this block by promoting hydroxyproline formation and, consequently, secretion of procollagen from the cell. The increased level of procollagen mRNA under the influence of ascorbic acid may be secondary to increased synthesis of procollagen polypeptides; the control point may be gene transcription or mRNA degradation.

Vanadate and molybdate stimulate the oxidation of NADH by superoxide radical

Vanadate or molybdate strongly accelerate the cooxidation of NADH, or of reduced nicotinamide mononucleotide, by the xanthine oxidase plus xanthine reaction. Superoxide dismutase eliminated the effect of vanadate or molybdate, while catalase was without effect. It follows that vanadate or molybdate accelerate the oxidation of dihydropyridines by O-2. A stoichiometry of 4 NADH oxidized per O-2 introduced suggests a chain reaction for which a mechanism is proposed. These results provide an explanation for the reported stimulation, by vanadate, of NADH oxidation by biological membranes.

Vanadate enhancement of the oxidation of NADH by O2-: effects of phosphate and chelating agents.

Vanadate markedly stimulates the oxidation of NADH by O2-. Both phosphate and Tris are inhibitory, but phosphate diminishes the greater inhibitory effect of Tris and thus gives the appearance of stimulating when added to Tris-buffered reaction mixtures. Chelating agents moderately increased the oxidation of NADH but eliminated the much greater catalytic effect of vanadate. Desferal was the most effective of the chelating agents, and could be used to titrate vanadate spectrophotometrically or in terms of the diminution of its catalytic activity. This permitted the demonstration that metavanadate or orthovanadate could form 1:1 complexes with desferal and that orthovanadate was the catalytically active species.

Protection of Chinese hamster ovary cells from paraquat-mediated cytotoxicity by a low molecular weight mimic of superoxide dismutase (DF-Mn)☆

Paraquat exerts a cytotoxic effect on Chinese hamster ovary cells in culture via the superoxide radical (O2-). We have described a superoxide dismutase (SOD) mimic based on manganese (DF-Mn) which consists of a one-to-one complex between desferrioxamine B (Desferal) and MnO2. It is a small molecular weight molecule, easy to prepare and possesses considerable stability. It is now shown to protect mammalian cells from paraquat toxicity. Thus, 20 microM DF-Mn affords up to complete protection against the cytotoxicity of 200 microM paraquat in Chinese hamster ovary cells. Desferrioxamine B or MnO2 alone gave no protection. MnCl2 or catalase provided little or no protection against the paraquat, respectively. Equivalent amounts of human Cu-Zn SOD in terms of activity, also provided no protection. Copper diisopropylsalicylate (CuDIPS) provided limited, yet significant, protection, but this is explained in terms other than SOD activity. Finally, at higher concentrations, purified human SOD, exerts a limited toxicity as well as a protective ability against paraquat (similar to DF-Mn) both of which are eliminated upon heat denaturation of the enzyme. It appears that the SOD mimic, DF-Mn, can enter mammalian cells and can protect against the cytotoxic effects of O2-.