| The formation of reactive oxygen species (ROS) from ultraviolet (UV) exposure has been implicated in skin damage and disease. Skin surface lipids (SSL) may be susceptible to ROS attack and subsequent UV induced oxidative damage because they are located at the skin's surface. The oxidation of squalene, the major polyunsaturated SSL, has been linked to aging, comedone formation, induction of acne, and malonaldehyde (MA) formation. Malonaldehyde is mutagenic and carcinogenic because it reacts with DNA and proteins to form Schiff bases. Antioxidant chemicals in plants may counteract the deleterious effects of UV induced oxidation on SSL. This study evaluated the antioxidant activities of flavonoids, essential oils, and volatile phytoconstituents using the aldehyde/carboxylic acid assay, the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, and the MA/GC assay.;GC-NPD quantification showed that after derivatization with N-methylhydrazine to form 1-MP, MA levels formed from squalene with 25 mug/mL of (+)-catechin or saponarin were lower than those of squalene with BHT. Anti- and pro-oxidant actions for quercetin were concentration dependent. Among 25 essential oils evaluated in the aldehyde/carboxylic acid assay, GC-FID analyses showed cinnamon leaf and thyme oils (10 mug/mL) displaying 100% inhibition of hexanal oxidation after 40 days, comparable to alpha-tocopherol. Reducing abilities of the oils toward DPPH· were spectrophotometrically assessed at 517 nm in the DPPH· scavenging assay. Clove leaf oil (10 mug/mL) showed greater scavenging activity (72%) than alpha-tocopherol (68%). Activities for thyme, ylang, rose, basil, and jasmine oils ranged from 60%--90% at 200 mug/mL.;GC-MS analyses found that the potent activities for thyme and clove leaf oils were due to thymol and eugenol presence, respectively, as confirmed by the two constituents in the MA/GC assay. Mixtures of thyme, clove leaf, rose, cinnamon leaf, and parsley seed oils were also assessed using the MA as 1-MP assay for synergistic or antagonistic effects. Thyme and clove leaf mixtures showed synergistic activities. Mixtures of thyme with cinnamon leaf or rose oils displayed antagonistic effects. Results suggest that prevention of UV induced in vivo oxidative damage may be helped by thymol and eugenol, and possibly some plant constituents. |
