Evaluation of the penetration and efficacy of topical anti-aging compounds

With an ever-growing topical anti-wrinkle market the cosmetic industry has focused on developing novel formulations. Despite the availability of methodology, demonstrations of anti-wrinkle efficacy are few and far between. This has been a growing area for technological advancement but the justification for extrapolation between in vitro studies and the mechanisms in vivo is limited. The aim of this research was to determine the in vitro penetration and then the in vivo efficacy of some common anti-wrinkle ingredients. Niacinamide, genistein and palmitoyl tripeptide-5 were investigated. The flux for niacinamide from propylene glycol across human skin in vitro was found to be 3.773 ± 0.5138 μg/cm2/hr. Genistein was found to have an average flux of 0.03625 ± 0.00544 μg/cm2/hr from propylene glycol across human skin in vitro. Using an assay for the tripeptide capable of quantifiably detecting 6.581 μg/ml, no detectable uptake or penetration into or through human skin in vitro was recorded. Two in vivo split face clinical studies, involving 20 participants in each, were undertaken. The studies assessed whether a cream containing niacinamide and a cream containing palmitoyl tripeptide-5 reduced the appearance, size and number of mild to moderate facial wrinkles compared to either skin left untreated or skin treated with a control (the product excluding niacinamide or palmitoyl tripeptide-5). At the conclusion of the study, the product containing niacinamide showed a significant reduction in the size (28.99 ± 9.09 %) and number of facial wrinkles (8.50 ± 2.80 %) compared to the control product and a significant reduction in the size (34.55 ± 11.49 %) and visible appearance of facial wrinkles compared to untreated skin. The product containing palmitoyl tripeptide-5 showed significant improvement in the visible appearance of facial wrinkles in vivo compared to the control treated skin and a significant reduction in the size (24.78 ± 10.21 %) of facial wrinkles compared to untreated skin at the conclusion of the study. The niacinamide clinical study results, with support from the niacinamide finite permeation study results of the formulation used in vivo, suggest it is possible that niacinamide is penetrating the stratum corneum, reaching its site of action, and causing its anti-wrinkle effects. Based on the poor skin permeation of palmitoyl tripeptide-5 it is highly likely the visible improvement in wrinkle appearance was caused by superficial surface effects rather than the claimed collagen regeneration mechanism.