Conjugated linoleic acids (CLA), derivatives of linoleic acid found in food products, inhibit chemically induced skin cancers in mice. However, their potential photoprotective properties remain unexplored. We examined whether CLA may modulate ultraviolet radiation (UVR)-induced secretion of interleukin (IL)-8 and prostaglandin E2 (PGE(2)), mediators implicated in UVR-induced inflammation and carcinogenesis, in human skin cells. Since tumour necrosis factor (TNF)-alpha is an early mediator of UVR effects, we also examined influence of CLA on TNF-alpha-induced mediator release. HaCaT keratinocytes were supplemented with CLA isomers cis-9-trans-11 (c9,t11-CLA; > or =90%), trans-10-cis-12 (t10,c12-CLA; > or =90%) or all trans-trans isomers (tt-CLA; 23.7%) in tetrahydrofuran/fetal calf serum (THF/FCS) or THF/FCS control. Supplementation of keratinocytes with c9,t11-CLA reduced Ultraviolet B(UVB)-induced IL-8 from 37 113 +/- 2903 pg/ng protein in control cells to 14 167 +/- 2063 pg/ng protein (P < 0.001). Similarly, t10,c12-CLA reduced UVB-induced IL-8 to 9786 +/- 1291.5 pg/ng protein (P < 0.001). Additionally, t10,c12-CLA and tt-CLA inhibited TNF-alpha-induced IL-8 from 11 669 +/- 1692 pg/ng protein in control cells to 5540 +/- 191 (P < 0.001) and 8082 +/- 1298 pg/ng (P < 0.01) protein, respectively. UVB-induced PGE(2) release was reduced by tt-CLA supplementation, from 4.8 +/- 1.2 to 1.6 +/- 0.8 pg/mg protein (P < 0.01), but increased by t10,c12-CLA to 8.8 +/- 1 pg/mg protein (P < 0.001). Influence of CLA on UVB-induced PGE(2) release was further explored in CCD922SK dermal fibroblasts. CLA isomers reduced UVB-induced PGE(2) in fibroblasts, reaching significance with c9,t11-CLA (98 +/- 5 falling to 0 pg/mg protein, P < 0.05). Hence, CLA isomers differentially modulate UVB effects on skin cells in vitro. CLA-containing foods have potential in photoprotection; the cutaneous effects of individual isomers warrant clinical study.