Variation of hepatic enzymes in three species of freshwater fish from precambrian shield lakes and the effect of cadmium exposure

Histopathological and biochemical alternations of the heart induced by acute cadmium exposure in the freshwater crab Sinopotamon yangtsekiense

Cadmium (Cd) is a highly toxic element in water. Its toxicity has been attributed to oxidative stress mediated by free radicals. Here we investigated the effects of Cd on the histopathology, antioxidant enzymes and lipid peroxidation of crustacean heart. The freshwater crabs Sinopotamon yangtsekiense were exposed to different concentrations of Cd for 1, 3, 5 and 7d. After exposure, histological abnormalities were discovered, including myocardial edema, vacuolar and vitreous degeneration, and infiltration of inflammatory cells. Additionally, alterations in nuclei, mitochondria, rough endoplasmic reticulum as well as myofibrils were observed. Meanwhile, superoxide dismutase (SOD) activity was significantly increased after Cd exposure. Catalase (CAT) activity was only increased in the group exposed to 14.50 mg L(-1) Cd on day 5 and decreased with increasing Cd concentration and exposure time. Glutathione peroxidase (GPx) activity was increased in groups treated with 29.00, 58.00 and 116.00 mg L(-1) on days 1 and 3, and decreased thereafter. Besides, malondialdehyde (MDA) levels were significantly increased after 3d of Cd exposure at all the indicated concentrations. These results showed that acute Cd exposure led to harmful effects on the histology of crab heart, which are most likely linked to Cd-induced oxidative stress.

Response of antioxidant system of freshwater fish Oreochromis niloticus to acute and chronic metal (Cd, Cu, Cr, Zn, Fe) exposures

Antioxidant systems are known to be sensitive to metal exposures and are suggested to use in predicting sublethal metal toxicity. In this study, several antioxidant enzymes, such as catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), glutathione peroxidase (GPX) and glutathione reductase (GR) were measured in the liver and kidney of Oreochromis niloticus exposed to sublethal concentrations of metals (Cd, Cu, Cr, Zn and Fe), using an acute (20 μM, 48 h) or subchronic (10 μM, 20 d) protocol. Beside the several increases of antioxidant enzyme activities, general inhibition was recorded after acute and chronic metal exposures. Results indicated that there were variations in responses of the enzymes to metal exposures, depending upon tissues, metals and exposure types. This study emphasized that the antioxidant enzymes are very sensitive to metals as their activities altered significantly, suggesting they could be helpful in predicting sublethal metal toxicity and useful as an early warning tool in natural monitoring studies.

Seasonal changes in antioxidant defence system of liver and gills of Salmo trutta caspius, Salmo trutta labrax and Salmo trutta macrostigma

Seasonal changes in antioxidant enzyme activities (superoxide dismutase, SOD, EC 1.15.1.1; catalase, CAT, EC 1.11.1.16; glutathione peroxidase, GPx, EC 1.11.1.9; glutathione reductase, GR, EC 1.6.4.2; glucose-6-phosphate dehydrogenase, G6PD, EC 1.1.1.49 and glutathione S-transferase, GST, EC 1.5.1.18) and lipid peroxidation (LPO) levels of livers and gills of female Caspian trout Salmo trutta caspius, Black Sea trout Salmo trutta labrax and mountain trout Salmo trutta macrostigma were investigated. SOD, CAT, GPx, G6PD and GST activities were higher in liver compared to gills of all sub-species; concomitantly, the GR activity was also higher in the livers of S. t. caspius and S. t. labrax, but the reverse was seen in S. t. macrostigma. LPO levels were higher in the gills compared to the liver of all sub-species. There was no general trend in the seasonal changes in the gill antioxidant enzyme (AE) activities or LPO levels. Higher AE activities, however, were found in the liver of each sub-species during autumn, and this coincided with an increase in the gonado-somatic index.

Antioxidative stress proteins and their gene expression in brown trout (Salmo trutta) from three rivers with different heavy metal levels

Three populations of brown trout (Salmo trutta) exposed to different metal levels in their natural environments, were studied with respect to antioxidants metallothionein (MT), superoxide dismutase (SOD) and catalase (CAT) as well as for corresponding mRNA levels. In addition, mRNA levels were studied for glutathione peroxidase (GPx) and glutathione reductase (GR). The Cd/Zn-exposed trout (Naustebekken River) had higher accumulated levels of Cd, Cu and Zn in gills, and higher levels of MT (both protein and mRNA) in liver and kidney as well as in gills compared to the Cu-exposed trout (Rugla River) and trout from an uncontaminated reference river (Stribekken River). Less MT found in the Cu-exposed trout may increase susceptibility to oxidative stress, but no higher levels of antioxidant mRNAs were found in gills of these trouts. The data indicated that chronic exposures of brown trout to Cd, Zn and/or Cu did not involve maintenance of high activities of SOD and CAT enzymes in gills, although SOD mRNA levels were higher in the Cd/Zn-exposed trout. In livers, mRNA levels of SOD, CAT and GPx were higher in the metal-exposed trout, but in the case of GR this was only seen in kidneys of Cd/Zn-exposed trout. However, both metal-exposed groups had higher activities of SOD enzyme in liver compared to the unexposed reference trout, and CAT activity was found to be higher in kidneys of Cu-exposed trout. The Cu-exposed trout did not seem to rely on MT production to avoid Cu toxicity in gills, but rather by keeping the Cu uptake at a low level. A coordinated expression of different stress genes may also be important in chronic metal exposure. It may be concluded that the observed metal effects relies on acclimation rather than on genetic adaptation in the metal exposed populations.

Formation of reactive species and induction of antioxidant defence systems in polar and temperate marine invertebrates and fish

High oxygen solubility at cold-water temperature is frequently considered to be responsible for an apparently elevated level of antioxidant protection in marine ectotherms from polar environments. However, tissue oxidative stress is in most cases a function of elevated or variable pO2, rather than of an elevated tissue oxygen concentration. This review summarizes current knowledge on pro- and antioxidant processes in marine invertebrates and fish, and relates reactive oxygen species (ROS) formation in polar ectotherms to homeoviscous adaptations of membrane and storage lipids, as well as to tissue hypoxia and re-oxygenation during physiological stress.