The effects of catechin, a well-known in vitro antioxidant, on 3T3 Swiss fibroblasts are studied under different conditions of oxidative stress leading to cell proliferation or cytotoxicity. Various levels of reactive oxygen species (ROS), generated extracellularly by the xanthine-xanthine oxidase (X-XO) system, are at the origin of the biphasic effect on DNA synthesis by 3T3 Swiss fibroblasts. The addition of 10(-2) U XO/mL, in the absence of exogenous X, catalyzes the production of low levels of O2-. and H2O2 in the extracellular medium, which stimulate DNA synthesis and cell division. The increase in the level of ROS, by addition of increasing X concentrations, did not enhance this effect proportionally. On the contrary, high levels of ROS inhibit DNA synthesis, the cytotoxicity induced being proportional to the level of H2O2 generated by the enzyme system. Catechin does not significantly modify DNA synthesis induced by low levels of ROS, but protects in a dose-dependent manner against the cytoxicity of high levels of ROS.
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