Dietary oregano extract (Origanum vulgare L.) enhances the antioxidant defence in rainbow trout, Oncorhynchus mykiss against toxicity induced by organophosphorus pesticide, diazinon

Moderating effects of oregano extract (Origanum vulgare L.) on oxidative stress and toxicity induced by organophosphate pesticide, diazinon (0.287 mg/l) were investigated for the first time in rainbow trout, Oncorhynchus mykiss by measuring antioxidant and metabolic enzymes. In non-diazinon-exposed fish, the hepatic levels of total antioxidant capacity (TAC) and antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) elevated in fish supplemented with 6 and 10 g ORG/kg diet compared to control group (non-ORG-supplemented fish). The supplementation of fish with 14 g ORG/kg diet significantly decreased the hepatic antioxidant enzymes compared to control. The acetylcholinesterase (AChE) activity and malondialdehyde (MDA) levels remained unchanged in all groups throughout the experiment. The serum levels of hepatic metabolic enzymes [(aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LHD)] remained unchanged in all experimental groups throughout the experiment. In diazinon-exposed groups, the activity of SOD, GPx, and TAC in liver elevated after exposure to diazinon in fish fed 2, 6, and 10 g ORG/kg diet. The CAT activity increased only in fish supplemented with 6 and 10 g ORG/kg diet. The levels of all antioxidant enzymes and TAC significantly decreased in control and fish supplemented with 14 g ORG/kg diet. The AChE activity significantly declined in control and fish supplemented with 2 and 14 g ORG/kg diet. After exposure to diazinon, the levels of MDA in liver increased in control and those fed 2 and 14 g ORG/kg diet. In fish supplemented with 6 and 10 g ORG/kg diet, the MDA levels showed no significant alternations during the experiment period. The serum levels of AST, ALT, and alkaline phosphatase (ALP) elevated during exposure to diazinon in control and fish supplemented with 2 and 14 g ORG/kg diet, while these enzymes showed no significant changes in fish fed with 6 and 10 g ORG/kg diet. In conclusion, our results showed that ORG at optimum dietary levels (6 and 10 g ORG/kg diet) could moderate the toxicity induced by diazinon in rainbow trout by enhancing the liver antioxidant system and protecting the hepatocytes. Furthermore, the high dietary levels of ORG caused toxic effects on antioxidant enzymes and hepatocytes, which this makes it necessary to optimize its levels in the diet.