Posidonia oceanica (L.) Delile as a Marine Anti-Inflammatory Modulator of Keratinocyte Inflammatory Responses Relevant to Psoriasis.

Skin inflammation is characterized by oxidative stress, excessive keratinocyte activation, and the overproduction of pro-inflammatory cytokines. In a previous study, we demonstrated that the hydroalcoholic extract from Posidonia oceanica leaves (POE) mitigates psoriasis-like skin inflammation in a mouse model. In the present study, we investigated the cellular mechanisms underlying these effects in human HaCaT keratinocytes. Non-cytotoxic lipopolysaccharide (LPS) stimulation reproduced key inflammatory features, including impaired cell proliferation, increased production of ROS and NO, and the upregulation of IL-1β, IL-6, TNF-α and CXCL8/IL-8. Co-treatment with POE significantly attenuated these alterations by restoring cell proliferation, suppressing oxidative stress, particularly NOS2/NO, and normalizing both cytokine expression and release. POE alone did not affect cell viability or inflammatory markers, confirming its favorable safety profile. However, POE alone induced a mild pro-apoptotic response, which may contribute to overcoming the apoptosis resistance typically observed in psoriatic keratinocytes. Overall, these findings demonstrate that POE exerts antioxidant and anti-inflammatory effects in activated keratinocytes and support its potential as a marine-derived candidate for complementary strategies in the management of psoriasis-associated inflammatory skin disorders.