Oleic acid exhibits an expressive anti-inflammatory effect in croton oil-induced irritant contact dermatitis without the occurrence of toxicological effects in mice

Ethnopharmacological relevance: Cutaneous inflammatory diseases, such as irritant contact dermatitis, are usually treated with topical corticosteroids, which cause systemic and local adverse effects limiting their use. Thus, the discovery of new therapeutic alternatives able to effectively treat skin inflammatory disorders, without causing adverse effects, is urgently needed. Aim of the study: To investigate the topical anti-inflammatory effect of oleic acid (OA), a monounsaturated fatty acid, into Pemulen (R) TR2-based semisolid dosage forms, employing a croton oil-induced irritant contact dermatitis model in mice. Materials and methods: Male Swiss mice were submitted to skin inflammation protocols by acute and repeated applications of cmton oil. The anti-inflammatory activity of Pemulen (R) TR2 hydrogels containing OA was evaluated by assessing oedema, inflammatory cell infiltration, and pro-inflammatory cytokine IL-1 beta levels. The mechanisms of action of OA were evaluated using cytokine IL-1 beta application or pretreatment with the glucocorticoid antagonist mifepristone. Possible toxic effects of OA were also assessed. Results: Pemulen (R) TR2 3% OA inhibited the acute ear oedema [maximal inhibition (I-max) = 76.41 +/- 5.69%], similarly to dexamethasone (I-max = 84.94 +/- 2.16%), and also inhibited ear oedema after repeated croton oil application with I-max = 85.75 +/- 3.08%, similar to dexamethasone (I-max = 81.03 +/- 4.66%) on the day 7 of the experiment. Croton oil increased myeloperoxidase activity, which was inhibited by Pemulen TR2 3% OA (I-max = 71.37 +/- 10.97%) and by 0.5% dexamethasone (I-max = 96.31 +/- 3.73%). Pemulen (R) TR2 3% OA also prevented the increase in pro-inflammatory cytokine IL-1 beta levels induced by cmton oil (I-max = 94.18 +/- 12.03%), similar to 0.5% dexamethasone (I-max = 87.21 +/- 10.58%). Besides, both Pemulen (R) TR2 3% OA and 0.5% dexamethasone inhibited IL-1 beta-induced ear oedema with an I-max of 80.58 +/- 2.45% and 77.46 +/- 1.92%, respectively. OA and dexamethasone anti-inflammatory effects were prevented by 100% and 91.43 +/- 5.43%, respectively, after pretreatment with mifepristone. No adverse effects were related to Pemulen TR2 3% OA administration. Conclusions: OA demonstrated anti-inflammatory efficacy similar to dexamethasone, clinically used to treat skin inflammatory conditions, without presenting adverse effects.