title: Tyrosinase may protect human melanocytes from the cytotoxic effects of the superoxide anion.
abstract: Reactive oxygen species (ROS) are potentially cytotoxic and several mechanisms have evolved to protect against their damaging effects. In melanocytes, tyrosinase may have such a rôle by utilising the superoxide anion (O2-) in the production of melanin. In the present study, we have examined the cytotoxic effects of O2- and hydrogen peroxide (H2O2) in human melanocytes both before and following the activation of tyrosinase. Xanthine oxidase (XO, 5-150 mU.ml-1) and glucose oxidase (GO, 0.1-20 mU.ml-1) were used to generate the O2- and H2O2 respectively, and the cytotoxic effects assessed by measuring cell survival using the 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium (MTT) assay. 3 h later, dose-related decreases in melanocyte survival were seen. Similar experiments with keratinocytes and fibroblasts showed that these cells were more resistant to the cytotoxic effects of O2- than were the melanocytes. The effect of increasing tyrosinase activity was examined by growing the melanocytes in the presence of an analogue of melanocyte-stimulating hormone (MSH) Nle4DPhe7 alpha-MSH (10(-8) M), for 48 h. This increased tyrosinase activity, melanin content, the ability to trap O2- and the resistance of the melanocytes to the cytotoxic effects of this ROS, but failed to alter their susceptibility to the damaging effects of H2O2.Nle4DPhe7 alpha-MSH had no effect on the resistance of keratinocytes and fibroblasts to either O2- or H2O2. After 3 h, XO, as opposed to GO, also increased the melanin content of human melanocytes; this effect was not accompanied by an increase in tyrosinase activity. The present results suggest that tyrosinase may utilise O2- to produce melanin and that this process may protect melanocytes from the potentially damaging effects of this ROS.
authors.affiliation: Department of Dermatology, University of Newcastle-upon- Tyne, UK.
authors.forename: P
authors.initials: P
authors.lastname: Valverde
authors.forename: P
authors.initials: P
authors.lastname: Manning
authors.forename: C
authors.initials: C
authors.lastname: Todd
authors.forename: C J
authors.initials: CJ
authors.lastname: McNeil
authors.forename: A J
authors.initials: AJ
authors.lastname: Thody
mesh_terms: D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D005949:Glucose Oxidase / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D008543:Melanins / Q000096:biosynthesis; D009074:Melanocyte-Stimulating Hormones / Q000494:pharmacology; D008544:Melanocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D014442:Monophenol Monooxygenase / Q000187:drug effects / Q000502:physiology*; D017382:Reactive Oxygen Species; D013481:Superoxides / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000494:pharmacology
chemical_list: D008543:Melanins; D017382:Reactive Oxygen Species; D013481:Superoxides; D009074:Melanocyte-Stimulating Hormones; D006861:Hydrogen Peroxide; D005949:Glucose Oxidase; D014442:Monophenol Monooxygenase; D014969:Xanthine Oxidase