731 Fluoxetine exerts anti-inflammatory effects on human epidermal keratinocytes, and suppresses endothelin release via inhibiting PI3K

Fluoxetine (FX) is a safe antidepressant belonging to the group of selective serotonin reuptake inhibitors. It exhibits remarkable anti-inflammatory activity in various systems; thus, we aimed to investigate its biological effects on immortalized (HaCaT) and primary human epidermal keratinocytes. We found that, when applied at its highest non-cytotoxic concentration (14 μM), FX significantly suppressed the Toll-like receptor 3 activator polyinosinic-polycytidylic acid (p(I:C))-induced expression (Q-PCR: interleukin [IL]-1α, IL-1β, and IL-8) and release (cytokine array and ELISA: IL-8) of several pro-inflammatory cytokines, and it decreased the release of the itch mediator endothelins as well. Surprisingly, unbiased activity profiling revealed that the effects of FX (4.7 and 14 μM) did not resemble the effects of different doses of serotonin, but were rather similar to the effects of the phosphoinositide 3-kinase (PI3K) inhibitor GDC0941 (370 nM). In addition, GDC0941 mimicked the effects of FX in our experimental models, and in silico docking analysis revealed that FX may be able to occupy the same binding site on PI3K isoenzymes as GDC0941. Finally, we found that FX was indeed able to directly suppress activity of PI3K (cell-free PI3K activity assay). Collectively, our findings demonstrate that FX (14 μM) exerts potent anti-inflammatory effects, and suppresses the release of the endogenous itch mediator endothelins in human keratinocytes, most likely via the inhibition of PI3K. Thus, our data highlight the possibility of dermatological repositioning of FX to treat various inflammatory and pruritic dermatoses.