Oxidative Damage in Fish Used as Biomarkers in Field and Laboratory Studies

Abstract: Many toxic xenobiotics entering into the aquatic environment exert their effects through redox cycling. Oxidative stress, incorporating both antioxidant defences as well as oxidative damage, is a common effect in organisms exposed to xenobiotics in their environment. The studies included in this dissertation evaluate the effects of different types of environmental pollution on oxidative stress biomarkers in teleost fishes. Effects of aging, alone or in combination with oxidative stress, on protein carbonylation were also addressed. Antioxidant enzyme activities were measured in rainbow trout (Oncorhynchus mykiss) caged in a river polluted by sewage treatment plant (STP) effluent as well as highly contaminated sediment, and in corkwing wrasse (Symphodus melops) collected at heavy metal contaminated and PAH contaminated sites. Antioxidant enzymes showed very few changes in these fish. Glutathione levels were affected by STP effluent exposure in rainbow trout and by PAH exposure in corkwing wrasse. Protein carbonylation was elevated in plasma of the corkwing wrasse captured at the heavy metal site and in plasma of rainbow trout caged near the STP effluent. Lipid peroxidation was elevated in the livers of these rainbow trout. Oxidative damage biomarkers were also measured in eelpout (Zoarces viviparus) captured in a polluted harbor, before, during and after a dredging campaign, as well as following an oil spill. Protein carbonyl levels in livers of eelpout were affected by exposure to pollution in the harbor, though this was measured both as increases and as decreases, indicating a complicated relationship between prooxidant exposure and protein carbonyl accumulation. Lipid peroxidation in eelpout was unaffected by pollutant exposure. Western blot analyses of protein carbonylation in corkwing wrasse exposed to heavy metals and in rainbow trout exposed to paraquat (PQ) suggest that albumin may be the plasma protein most likely to undergo carbonylation in these fish. Brown trout (Salmo trutta) were used in a laboratory study to investigate the effects of aging on oxidative stress parameters, i.e. protein carbonylation, 20S proteosome activity and glutathione levels. All parameters were affected by aging, as was the response to PQ exposure, where 1 year old fish were more sensitive than 0+ fish. To conclude, the results presented here indicate that antioxidant enzymes may not provide a good biomarker of exposure to xenobiotics in the field. However, oxidative damage products, i.e. protein carbonyls and lipid peroxidation, seem to be useful as biomarkers. Care should be taken to consider age of the exposed individuals. Oxidative stress is a complex phenomenon to measure in the field. Antioxidant enzyme activities may be altered after an acute exposure and then return to normal levels but damage products can persist even after the initial stress has stabilized.