Hypometabolism, antioxidant defenses and free radical metabolism in the pulmonate land snail Helix aspersa

The aim of this work was to evaluate the effect of a cycle of estivation and awakening on free radical metabolism in selected organs of the land snail Helix aspersa. Estivation for 20 days induced a 4.9- and 1.8-fold increase in selenium-dependent glutathione peroxidase activity (Se-GPX) and in total glutathione levels (GSH-eq), respectively, in hepatopancreas when compared to activity in active animals 24 h after awakening. Foot muscle Se-GPX activity was also increased 3.9-fold during estivation, whereas GSH-eq did not vary. The activities of other antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase and glutathione S-transferase) and glucose 6-phosphate dehydrogenase were unchanged in both organs. After 15 min of awakening, the glutathione disulphide (GSSG)/GSH-eq ratio increased significantly by 55% in hepatopancreas, slowly returning to the levels observed during estivation. The higher GSSG/GSH-eq ratio may be caused by increased formation of reactive oxygen species (ROS) during awakening. The levels of thiobarbituric acid reactive substances (TBARS) decreased from 49 to 30.7 nmol g(-1) wet mass in hepatopancreas after 5 min arousal and, after 30 min, TBARS rose significantly to 39.6 nmol g(-1) wet mass, gradually declining thereafter. The levels of lipid hydroperoxides in hepatopancreas and of carbonyl protein in foot muscle both decreased during awakening. The higher levels of products of free radical damage during estivation may have resulted from low levels of ROS formation associated with decreased rates of lipid hydroperoxide detoxification and oxidized protein turnover caused by metabolic depression. The regulation of the antioxidant system during hypometabolism may constitute a mechanism to minimize oxidative stress during cycles of estivation and awakening.