Alterations in the activity and isozyme profile of enzymatic stress markers along with histological changes due to lead exposure in Labeo rohita

AGRAWAL & SINGH et al: EFFECTS OF LEAD EXPOSURE ON STRESS MARKERS IN LABEO ROHITA

Abstract

The present study examines the effects of two concentrations of lead acetate (Pb3: 3 mg/L and Pb6: 6 mg/L) on the vital tissues of Labeo rohita after 96 hours of exposure. The study focuses on alteration in isozyme profile of enzymatic markers of oxidative stress such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) and tissue damage indicator such as lactate dehydrogenase (LDH). Oxidative stress was measured through lipid peroxidation analysis, and corresponding histopathological changes were examined by haematoxylin-eosin staining. In-gel assays detected a single isozyme of CAT in the liver and gill, and GPx in the liver and brain. Four distinct SOD isozymes were detected in the liver and gill, while only two isozymes were found in the brain. Inhibitor assays indicated that the isoform closest to the cathode was Mn-SOD, with the remaining isozymes identified as Cu/Zn-SOD. A total of five LDH isozymes (LDH1 to LDH5) were expressed in the liver, single isozyme in the gill and brain. The isozyme profiles and activities of these enzymes were altered in a tissue-specific manner following lead exposure. Specifically, in the liver, total activities of SOD, GPx and LDH increased, whereas CAT activity decreased in both Pb3 and Pb6-treated groups compared to controls. In the gills, SOD, CAT, and LDH activities were elevated in both lead treatment groups; however, GPx activity was undetectable. In the brain, SOD and GPx activities increased, LDH activity remained unchanged, and CAT activity was not detected in either treatment group. Lipid peroxidation levels were significantly elevated in all tissues in a dose-dependent manner compared to controls. Histopathological examination in tissues revealed degenerative alterations such as vacuolization, necrosis, epithelial hyperplasia and neuronal degeneration in dose dependent manner. The findings demonstrate that lead induced oxidative stress elicits tissue and isozyme-specific antioxidant responses and associated histopathological damage in Labeo rohita. These results may contribute to a molecular-level understanding which may help the advancement of aquaculture strategies in environmentally contaminated settings.