UVB-dependent generation of reactive oxygen species by catalase and IgG under UVB light: Inhibition by antioxidants and anti-inflammatory drugs.

Catalase, which can decompose H2O2, has recently been found to generate unspecified reactive oxygen species (ROS) as a result of ultraviolet B (UVB) irradiation. Many proteins, hemes, and iron compounds were first tested to determine that this ROS generation was unique to catalase and immunoglobulin G (IgG). An increase in absorbance at 502 nm due to 2',7'-dichlorofluorescein, the oxidized product of 2',7'-dichlorodihydrofluorecein diacetate as a result of UVB (310 nm) irradiation, was measured in order to estimate this ROS generation. Catalase and IgG generated a pronounced amount of ROS when irradiated with UVB. Another heme protein, cytochrome c, and heat-inactivated catalase had no such effect. ROS generation by catalase was at least 5 times more potent than that reported for IgG with UVB and without antigens. This catalasemediated ROS generation was largely temperaturedependent in the range of 25 to 42°C. As IgG is considered an evolutionally important bactericidal component, the same was considered true for this enzyme. Next, inhibitory effects of various drugs, including antioxidants and anti-inflammatory drugs, on catalase-mediated and UVB-induced ROS generation were examined. Many of the drugs, including catalase inhibitors, had inhibitory effects with different potencies. Melanin was found to be the most effective inhibitor of this ROS generation (IC(30), 0.2 μg/mL), followed by Indigo Carmine and rutin. Also inhibiting this ROS generation were ascorbic acid, α-tocopherol, indomethacin, coenzyme Q10, β-carotene, uric acid, piroxicam, diclofenac, and glutathione, in that order of potency. Various ROS were apparently generated by catalase under UVB, creating a cycle or chain which was thought due to the biphasic effects of some drugs such as 3-aminotriazole or sodium azide. Excess ROS generation induces inflammation. Catalase might serve dual roles, removing H2O2 and generating various ROS depending on the H2O2 concentration and other factors.