Attenuation of experimental TPA-induced dermatitis by acetylenic acetogenins is associated with inhibition of PLA ₂ activity

Topical application of acetylenic acetogenins (AAG) from avocado (0.01-1.0 mg/ear), was effective in inhibiting both 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mouse ear edema, and in decreasing tissue myeloperoxidase activity (indicative of polymorphonuclear leukocyte influx). Maximum edema inhibition of 72% was achieved by AAG at lower concentration (0.6 mg/ear) than that of the anti-inflammatory drug indomethacin (2 mg/ear). The maximum myeloperoxidase inhibition of 60% was obtained at AAG concentration 0.1 mg/ear. Chemical reduction of unsaturated bonds in aliphatic chain of AAG molecules almost abrogated inhibition effect of AAG at high concentration. In vitro AAG administration reduced secretion of PGE ₂ in TPA-induced keratinocytes, and inhibited total PLA ₂ and sPLA ₂ activities in HaCaT cells. The results indicate a topical anti-inflammatory effect of acetylenic acetogenins which is associated with inhibition of PLA ₂ activity in skin.