The mechanism of retinol-induced irritation and its application to anti-irritant development

Despite many beneficial effects on dermatological applications, retinol and its derivatives cause severe local irritation manifested as mild erythema and stratum corneum peeling of the skin. It is hypothesized that cytokines may be important inflammatory mediators in retinoid-induced dermatitis. The present study was designed to determine cytokine mediators and thereby, to screen potential anti-irritants in retinoid-induced inflammation. The changes in mRNA expression of inflammation-related cytokines including mouse analogue of human monocyte chemoattractant protein-1 (MCP-1) (JE), mouse analogue of human interleukin-8 (IL-8) (KC), tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), IL-12p40, IL-6, IL-10, Eotaxin were determined in mouse epidermal cells treated by 2% retinol using a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). The up-regulated mRNA level was confirmed with protein levels in culture supernatants from human epidermal keratinocytes, melanocytes, and fibroblasts treated with 10 microM retinol or retinoic acid. As results, retinoid-induced inflammation was mainly mediated through MCP-1 and IL-8 as evidenced by increased levels of mRNA expression and protein secretion. The potential anti-irritant substances including beta-sitosterol, Magnoliae flos, beta-glycyrrhetinic acid, SC-glucan, Ginko extract, Raspberry extract, Schisandra extract, Cola extract, Enna complex or Vegetol red grapevine extract were evaluated for their inhibitory effects on retinol-induced cytokine (MCP-1 and IL-8) secretion in vitro cultured human fibroblasts. Furthermore, in vivo efficacy tests for the retinol-induced irritancy were performed using Draize skin irritation test in the rabbit and human patch test. Most of the substances that reduced the secretion of MCP-1 and IL-8 in vitro cultured fibroblasts, showed a good inhibition against the retinol-induced irritation in the rabbit and human patch test. In conclusion, the present study demonstrated that among proinflammatory cytokines, MCP-1 and IL-8 mainly mediated retinol-induced skin irritation, and that inhibition of production of these cytokines can be applied as good markers to screen the anti-irritants against the retinol-induced irritation.