M Brownrigg

The sunburn response in human skin is characterized by sequential eicosanoid profiles that may mediate its early and late phases

Sunburn is a commonly occurring acute inflammatory process, with dermal vasodilatation and leukocyte infiltration as central features. Ultraviolet (UV) B‐induced hydrolysis of membrane phospholipids releases polyunsaturated fatty acids, and their subsequent metabolism by cyclooxygenases (COXs) and lipoxygenases (LOXs) may produce potent eicosanoid mediators modulating different stages of the inflammation. Our objective was to identify candidate eicosanoids formed during the sunburn reaction in relation to its clinical and histological course. We exposed skin of healthy humans (n=32) to UVB and, for 72 h, examined expression of proinflammatory and antiinflammatory eicosanoids using LC/ESI‐MS/MS, and examined immunohistochemical expression of COX‐2, 12‐LOX, 15‐LOX, and leukocyte markers, while quantifying clinical erythema. We show that vasodilatory prostaglandins (PGs) PGE2, PGF2a, and PGE3 accompany the erythema in the first 24–48 h, associated with increased COX‐2 expression at 24 h. Novel, potent leukocyte chemoattractants 11‐, 12‐, and 8‐monohydroxy‐eicosatetraenoic acid (HETE) are elevated from 4 to 72 h, in association with peak dermal neutrophil influx at 24 h, and increased dermal CD3+ lymphocytes and 12‐ and 15‐LOX expression from 24 to 72 h. Anti‐inflammatory metabolite 15‐HETE shows later expression, peaking at 72 h. Sunburn is characterized by overlapping sequential profiles of increases in COX products followed by LOX products that may regulate subsequent events and ultimately its resolution.—Rhodes, L. E., Gledhill, K., Masoodi, M., Haylett, A. K., Brownrigg, M., Thody, A. J., Tobin, D. J., Nicolaou, A. The sunburn response in human skin is characterized by sequential eicosanoid profiles that may mediate its early and late phases. FASEB J. 23, 3947–3956 (2009). www.fasebj.org

Prostaglandin-E2 is produced by adult human epidermal melanocytes in response to UVB in a melanogenesis-independent manner.

Excessive ultraviolet radiation (UVR) exposure induces erythema, mediated in part by prostaglandin‐E2 (PGE2). While keratinocytes are a major PGE2 source, epidermal melanocytes (EM) also express PGE2‐production machinery. It is unclear whether EM‐produced PGE2 contributes to UVR‐induced skin inflammation, and whether this is correlated with melanogenesis. Epidermal melanocytes were cultured from skin phototype‐1 and ‐4 donors, followed by assessment of PGE2 production and melanogenesis. Epidermal melanocytes expressed cytoplasmic phospholipase‐A2, cyclooxygenase‐1, cytoplasmic prostaglandin‐E synthase and microsomal prostaglandin‐E synthase‐1, ‐2. Epidermal melanocytes produced PGE2 under basal conditions, which increased further after arachidonic acid stimulation. Epidermal melanocytes expressed cyclooxygenase‐2 (COX‐2) mRNA and a selective COX‐2 inhibitor (NS‐398) reduced PGE2 production. Ultraviolet B‐induced PGE2 production was positively correlated with skin phototype‐1, despite variability between individual EM donors. By contrast, there was no correlation between PGE2 production by EM and their melanogenic status. Thus, EM may contribute to UVR‐induced erythema, with role of donor skin phototype more important than their melanogenic status.