Determination of Synergistic Antioxidant Activity of alpha- and delta-Tocopherylcarbamate Co-drugs on Lipid Peroxidation in Skin

Topical antioxidant (AO) co-drugs, derived from tocopherol (&agr;- and delta-TOC) and lipoylamine (LAM) that are designed to protect the skin against oxidative damage were synthesized. The activity of the carbamate co-drugs were tested for potency against lipid peroxidation (LP) in skin using the thiobarbituric acid reactive substances (TBARS) assay. The ability of the co-drugs and their parent compounds to inhibit LP in porcine skin homogenates after treatment with ferrous sulfate (FeSO4) as the inducer of oxidation was evaluated by measuring the production of malondialdehyde (MDA). Experiments were carried out to confirm that TOC and LAM, the parent compounds of the co-drugs act synergistically to inhibit LP. Penetration and hydrolysis of the carbamate co-drugs in the epidermal (ED) layer of skin was evaluated on intact porcine skin, using Franz diffusion cells and high pressure liquid chromatography (HPLC). Hydrolysis of the co-drugs was evaluated since it is required for optimal AO activity. Following this, the skin was exposed to UVR in order to induce oxidation. AO activity against UVR-induced LP in the ED layer of the intact skin, after treatment with the co-drugs was assessed using the TBARS assay. Potent, synergistic AO activity was observed for &agr;-TOC and LAM and delta-TOC and LAM. Carbamate co-drugs showed potent AO activity, which was a virtue of partial hydrolysis of to the parent compounds, TOC and LAM and the synergism that existed between these parent compounds. HPLC data suggested that these co-drugs penetrated the ED layer and the extent of hydrolysis was found comparable to the observed AO activity. delta-Tocopherol carbamate (delta-TOCCAM) showed more potent AO activity than &agr;- tocopherol carbamate (&agr;- TOCCAM). The enhanced activity of delta-TOCCAM is attributed to greater of hydrolysis relative to the &agr;-analog. Altogether, these data suggest that carbamate co-drugs are potent inhibitors of LP and may offer protection against UVR-induced oxidative damage in the skin.