UVA exposure is a main cause of oxidative stress in skin. It damages proteins via cross-linking, carbonyl formation and denaturation; lipids through peroxidation; and DNA via reactive oxygen species, which in turn may cause promutagenic DNA lesions and DNA single-strand breaks. In skin, protection from oxidative stress is ensured by enzymic and nonenzymic antioxidants. Superoxide dismutase (SOD) enzymes are known to destroy superoxide radicals. SOD exists in humans in two forms: CuZn SOD and Mn SOD.
Following the SOD defense mechanism is the action of catalase—a ubiquitous protein found primarily in cellular peroxisomes. Catalase destroys the hydrogen peroxide formed by SOD and by other processes. Catalase increasingly has become recognized as an enzyme centrally involved in protecting the skin from UV oxidative stress. Recent data has demonstrated a significant decline of SOD and catalase activity in photoaged skin.
After a large screening study, the dimeric cysteyl-glycin dipeptide, or (Cys-Gly)2 dimer peptide, obtained either by synthesis or extracted from plants, was chosen to conduct studies because it provided the best protection against oxidative stress. The presented studies investigated the effect of the (Cys-Gly)2 dimer peptide against UV-induced oxidative stress on cultured human fibroblasts. For this purpose, the expression of SOD and catalase after UVA or UVB stress was studied, and the outcome on protein carbonylation and lipid peroxidation was evaluated.
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