Involvement of endogenous antioxidant systems in the protective activity of pituitary adenylate cyclase‐activating polypeptide against hydrogen peroxide‐induced oxidative damages in cultured rat astrocytes

Astroglial cells possess an array of cellular defense mechanisms, including superoxide dismutase (SOD) and catalase antioxidant enzymes, to prevent damages caused by oxidative stress. Nevertheless, astroglial cell viability and functionality can be affected by significant oxidative stress. We have previously shown that pituitary adenylate cyclase‐activating polypeptide (PACAP) is a potent glioprotective agent that prevents hydrogen peroxide (H2O2)‐induced apoptosis in cultured astrocytes. The purpose of this study was to investigate the potential protective effect of PACAP against oxidative‐generated alteration of astrocytic antioxidant systems. Incubation of cells with subnanomolar concentrations of PACAP inhibited H2O2‐evoked reactive oxygen species accumulation, mitochondrial respiratory burst, and caspase‐3 mRNA level increase. PACAP also stimulated SOD and catalase activities in a concentration‐dependent manner, and counteracted the inhibitory effect of H2O2 on the activity of these two antioxidant enzymes. The protective action of PACAP against H2O2‐evoked inhibition of antioxidant systems in astrocytes was protein kinase A, PKC, and MAP‐kinase dependent. In the presence of H2O2, the SOD blocker NaCN and the catalase inhibitor 3‐aminotriazole, both suppressed the protective effects of PACAP on SOD and catalase activities, mitochondrial function, and cell survival. Taken together, these results indicate that the anti‐apoptotic effect of PACAP on astroglial cells can account for the activation of endogenous antioxidant enzymes and reduction in respiration rate, thus preserving mitochondrial integrity and preventing caspase‐3 expression provoked by oxidative stress. Considering its powerful anti‐apoptotic and anti‐oxidative properties, the PACAPergic signaling system should thus be considered for the development of new therapeutical approaches to cure various pathologies involving oxidative neurodegeneration. We propose the following cascade for the glioprotective action of Pituitary adenylate cyclase‐activating polypeptide (PACAP) against H2O2‐induced astrocyte damages and cell apoptosis in cultured rat astrocytes. PACAP, through activation of its receptor, PAC1‐R, and the protein kinase A (PKA), protein kinase C (PKC), and MAP‐kinases signaling pathways, prevents accumulation of ROS and inhibition of SOD and catalase activities. This allows the preservation of mitochondrial membrane integrity and the reduction in caspase‐3 activation induced by H2O2.