Cis‐urocanic acid suppresses UV‐B‐induced interleukin‐6 secretion and cytotoxicity in human corneal and conjunctival epithelial cells in vitro

Abstract

Abstract Purpose Urocanic acid (UCA) is a major UV‐absorbing endogenous chromophore in the epidermis and is also an efficacious immunosuppressant. The anti‐inflammatory and cytoprotective effects of cis‐UCA were studied in ocular surface cell cultures exposed to UV‐B irradiation. Methods Human corneal epithelial cells (HCE‐2) and human conjunctival epithelial cells (HCEC) were incubated with 10, 100, 1000, and 5000 µg/ml cis‐UCA with and without a single UV‐B irradiation dose. Cell viability was measured by the colorimetric MTT (3‐(4,5‐dimethyldiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) assay. Results The UV‐B irradiation elevated IL‐6 secretion by 7 to 9‐fold in HCE‐2 cells and by 2‐fold in HCEC cells as analyzed with ELISA., declined by 30 to 50 % in HCE‐2 cells and by 20 to 40 % in HCEC cells after UVB irradiation. Treatment with 100 µg/ml cis‐UCA completely prevented both the elevated IL‐6 secretion and the decrease in cell viability to the same level as nonirradiated control cells in both cell types, i.e. simultaneous anti‐inflammatory and cytoprotective effects against UV‐B radiation.No significant effects on IL‐6 secretion or viability of the nonirradiated cells were observed with 10 and 100 µg/ml cis‐UCA, while 1000 µg/ml cis‐UCA evoked secretion of IL‐6 in both cell types. The 5000 µg/ml concentration was toxic. Conclusion Cis‐UCA may represent a promising anti‐inflammatory and cytoprotective treatment option to suppress UV‐B‐induced inflammation and cellular damage in human corneal and conjunctival epithelial cells.