SUBTHRESHOLD UV RADIATION-INDUCED PEROXIDE FORMATION IN CULTURED CORNEAL EPITHELIAL-CELLS - THE PROTECTIVE EFFECTS OF LACTOFERRIN

Acute exposure to suprathreshold ultraviolet B radiation (UV-B) is kno wn to cause photokeratitis resulting from the necrosis and shedding of corneal epithelial cells. However, the corneal effects of low dose W- B in the environmental range is less clear. In this study, subthreshol d UV-B was demonstrated to cause non-necrotic peroxide formation in cu ltured corneal epithelial cells, which was attenuated by the major tea r protein lactoferrin. Intracellular oxidative insults and cell viabil ity of rabbit corneal epithelial cells (RCEC) were assessed by dual-co lor digital microfluorography using carboxydichlorofluorescin (CDCFH) diacetate bis (acetoxymethyl) ester, a hydroperoxide-sensitive fluorop robe, and propidium iodide (PI), respectively. The magnitude of UV-ind uced oxidative insults was calibrated by concentrations of exogenously applied H2O2 which evoke compatible levers of CDCFH oxidation. Exposu re of RCEC to low-dose UV-B (2.0 mJ cm(-2) at 313 nm, 10.0 mJ cm(-2) t otal UV-B) caused intracellular oxidative changes which were equivalen t to those elicited by 240 mu M hydrogen peroxide under the conditions of the study. The changes were dose dependent, non-necrotic, and were partially inhibited by lactoferrin (1 mg ml(-1)) but not by iron-satu rated lactoferrin. Pretreatment with deferoxamine (2 nn) or catalase ( 100 U ml(-1)) also attenuated the UV-induced oxidative stress. The res ults indicate that UV-B comparable to solar irradiation levels causes significant intracellular peroxide formation in corneal epithelial cel ls, and that lactoferrin in tears may have a physiological role in pro tecting the corneal epithelium from solar UV irradiation. (C) 1996 Aca demic Press Limited