Effect of cadmium on catalase activity in four tissues of freshwater fish Heteropneustes fossilis (Bloch.)
antioxidant, cadmium toxicity, catalase, heteropneustes fossilis
M Radhakrishnan. Effect of cadmium on catalase activity in four tissues of freshwater fish Heteropneustes fossilis (Bloch.). The Internet Journal of Veterinary Medicine. 2008 Volume 7 Number 1.
Effect of sublethal concentration cadmium chloride (12ppm; 10% 0f 96h LC50) on Catalase (CAT, EC 184.108.40.206) activity in brain, gill, kidney and liver of freshwater fish
Extensive industrialization and urbanization has increased the concentration of heavy metals into the aquatic environment 1 . The stress of heavy metals increase in highly reactive oxygen species (ROS) such as hydrogen peroxide, superoxide radical, hydroxyl radical leading to oxidative stress in fish 2,3,4,5 . Fish tissues, specifically the liver and kidney are endowed with antioxidant defense systems consisting of CAT, superoxide dismutase (SOD) etc. to protect them from oxidative stress caused by metals 6 . Antioxidant enzymes contribute to the maintenance of a relatively low level of the reactive and harmful hydroxyl radical, the superoxide radical and hydrogen peroxide in the presence of Cu 2+ and/or Fe 3+
7,8 . CAT, primary antioxidant defense component, eliminates hydrogen peroxide (2H2O2→2H2O+O2) a non-radical reactive oxygen species which can penetrate through all biological membranes and directly inactivate few enzymes. Various responses of CAT activity have been observed in animals exposed to organic or metallic contaminants in both field and laboratory experiments and CAT has been shown to be either induced or inhibited by metals depending on the dose, the species or the route of exposure 8,9 . The oxidative stress has gained considerable interest in the field of ecotoxicology. Therefore, CAT activity is considered as a sensitive biomarker of oxidative stress before hazardous effects occur in fish 8,10 . This research aims to investigate the response of CAT activity to different heavy metals in the tissues of
Materials and methods
The experimental catfish (
Results and discussion
Catalase (CAT, EC 220.127.116.11) is an important enzyme in antioxidant defense system protecting animals from oxidative stress. The effect of 12ppm of cadmium chloride solution on the four tissues (brain,gill,kidney and liver) are given in table1. The brain is very susceptible to oxidative damage through free radicals as it contains high amounts of unsaturated lipids and utilizes about 20% of total oxygen demand of the body. While CAT is highly active in the liver and kidney, the brain is not particularly enriched in antioxidant enzymes. It was determined that CAT activity was found to be maximal in liver and minimal in the brain of seven animal species 16 . In the present study, the specific activity of brain CAT was found to be lower, which may be related to the direct binding of metal ions to –SH groups on the enzyme molecule, increased hydrogen peroxide and superoxide radical due to oxidative stress. It was indicated that rapid inactivation of CAT at high hydrogen peroxide concentration was due to the converting of active enzyme compound to inactive compounds 17 . In addition, stimulation of CAT activity can be associated with effective antioxidant defense system acting against oxidative stress and/or compensating for the decrease in other antioxidant enzymes such as Mn-SOD and GPX. On the other hand, no significant change in CAT activity may be attributed to the increase in other antioxidant enzymes such as GPX and/or non-enzymatic mechanisms such as GSH and metallothioneins. In general inhibition of CAT activity in all tissues of
Gill is also the first affected organ when fish are exposed to metals. It was determined that there was no significant change in CAT activity in the liver and gill and this was associated with the high activity of GPX, which acts as a defense against the formation of H2O2 or effective antioxidant responses due to a higher renovation of gill epithelium. The lowest activity of CAT was measured in the gill tissue; this was explained by the increased generation of H2O2, which led to a decreased CAT activity 2,15 . The highest inhibition was observed in the kidney, This can be associated with the effective antioxidant system in this tissue where the higher metal bioaccumulation and related to metal binding protein synthesis and non-enzymatic antioxidant mechanisms were observed 6, 19 . Moreover, this can be attributed to the possible induction of stress proteins and/or non-enzymatic antioxidant formation 6 . The results showed that the Cd 2+ can activate redox cycling and demonstrate both in vivo and in vitro responses which are typical of the damage to the membranes and oxidative stress 9 .
The highest CAT activity was determined in liver tissue compared to other tissues, which are in agreement with other literatures 7, 10 . These data are in accordance with those reported in other fish species where CAT activity is distributed in a decreasing order, as follows: liver, kidney, heart, brain and muscle 7 . In the present study, cadmium decreased the CAT activity in the liver. The reduction may be associated with the direct binding of metal to –SH groups on the enzyme molecule. Liver CAT activity was found to be inhibited following both
The response of CAT activity in different tissues of