Antioxidant enzymes and thiol/disulfide status in the digestive gland of the brown mussel Perna perna exposed to lead and paraquat.

Lead (Pb) and paraquat (PQ) have different toxic mechanisms associated with cell damage. Pb may induce alterations in zinc containing proteins, including the known inhibitory effect on the enzyme delta-aminolevulinic acid dehydratase, disrupting the heme-synthesis pathway. During PQ biotransformation, redox cycle reactions enhance oxyradical production, which may lead to pro-oxidative conditions. In this study, we analyzed the effects of Pb and PQ on antioxidant enzymes and thiol status, using the digestive glands of the mussel Perna perna collected in a mussel farm on Santa Catarina Island. Mussels were exposed to Pb (1 ppm) and PQ (10 ppm), either separately or concomitantly, for 48 h. We were unable to detect an effect of Pb treatment on the enzymes, catalase, glucose 6-phosphate dehydrogenase (G6PDH), glutathione S-transferase (GST) and glutathione reductase (GSSG-reductase), which contrasts to the effect of PQ, increasing GSSG-reductase and G6PDH, but decreasing GST activity. The thiol status showed a pro-oxidative trend, observed mainly through a decrease in the reduced/oxidized glutathione ratio, despite the total-glutathione increase. Protein-mixed disulfides and protein thiols did not change by the treatments. The observed effects of PQ and Pb were consistent with literature. Pb had a suppressive effect on the enzymatic changes elicited by PQ, while the changes in the thiol/disulfide parameters were retained.