Assessment of physical and antioxidant activity stability, in vitro release and in vivo efficacy of formulations added with superoxide dismutase alone or in association with α-tocopherol

A topical formulation was added with different concentrations of superoxide dismutase (SOD) alone or in association with α-tocopherol (α-TOC). The physical stability was evaluated by rheological behavior of formulations stored at 4 °C, 30 °C/60% RH and 40 °C/70% RH for 6 months. SOD alone and formulations containing SOD 0.2%, 0.4% or 0.6% or SOD and α-TOC were stored in the same conditions and the enzymatic activity was evaluated by the superoxide anion scavenging using chemiluminescence measurement. In vitro release study was carried out using modified Franz diffusion cell and SOD formulations photoprotection against skin erythema was observed for 72 h. SOD and α-TOC formulation proved to be instable, since the interaction between the antioxidants led to both physical and enzymatic activity instability. SOD formulations showed to be physically stable and maintained the enzymatic activity for 6 months when stored at 4 and 30 °C/60% RH. Despite the fact of low SOD release from the formulation, it was effective in inhibiting the UVB-induced skin erythema for 48 h after a single application. Topical administration of antioxidants provides an efficient way to enrich the endogenous cutaneous protection system, and SOD formulations could be used for improving photoprotection of skin.