Sites and mechanisms of low-level oxidative stress in cultured cells

Oxidative stress is involved in a multitude of pathological conditions. In the present study, we investigated the cellular targets and the mechanisms of low-level oxidative stress in a Chinese Hamster Ovary cell culture. Oxidative stress was induced either by continuous enzymatic production of superoxide or by bolus addition of hydrogen peroxide (H₂O₂). Low-level oxidative stress irreversibly impaired the reproductive capacity of the cells in the absence of damage to membrane integrity or energy metabolism. Cells were protected by catalase but not by superoxide dismutase, indicating that H₂O₂ not superoxide, was the causative agent of cell damage. Nitroxide spin labels decreased hydroxyl radical (•OH) formation and protected cells from the oxidative stress. The differing membrane permeabilities of these spin labels suggest that the damage is localized on the cell surface. Oxidative stress to DNA and RNA was not significant, as shown by levels of guanine hydroxylation products. A mechanism is proposed whereby low-level oxidative stress acts at the cell surface to cause impairment of cell reproduction.