Antioxidant enzymes and their modification under oxidative stress conditions

RESUMO

There are many cellular defense strategies against processes mediated by active oxygen species, including scavenger molecules and the enzymes catalase, superoxide dismutase and glutathione peroxidase. The activity of these antioxidant enzymes allows to keep O2- and H2O2 steady state concentrations at low levels, compatible with cell function. In most pathologies considered, modifications in levels of enzymatic activity have been observed in relation to values of control patients. Both increased and decreased levels have been found and in almost all systems the response of the three enzymes has been parallel. Different models of chronic treatment have also been considered. Parallel variations could be noted again regarding the antioxidant activity of these three enzymes. Moreover, there exists a correlation between the increase in the enzymatic activities and the acquired protection by treatment with barbital as reflected by the measured values of spontaneous chemiluminescence. on the other hand, increased levels of chemiluminescence in liver homogenates and diminished enzymatic activities were found in other experimental models. The response to these treatments is not the same in different organs since the rates of production of active oxygen species as well as the antioxidant defense activities are different in each organ. Finally, data of acute models of oxidative stress were compiled. Some of them have shown a biphasic response. At first a decrease in levels of enzymatic activities could be seen in response to the injury. Afterwards, an increase in the activity of the antioxidant enzymes followed as a consequence of an enzymatic induction or activation.