Abstract
The use of Zn as micronutrient in husbandry and agriculture practices and also in baby foods and multivitamin supplements have been increased during the last two decades. However, the effect of long term increasing Zn load on the oxidative stress in the body has not been worked so far. The supplementation of pharmacological dosage of Zn in otherwise Zn adequate diet was investigated with the aim if excess Zn in the diet triggers oxidative stress and its conesquence on enzymes of antioxidant defense system. In this study, three groups of rats were fed on semi-synthetic diet containing 20 mg Zn/kg (control, group-I), 40 mg Zn/kg (group-II) and 80 mg Zn/kg (group-III) diet respectively for a period of 6 months. Blood lipid profile in the serum, lipid peroxidation status and the activities of antioxidant enzymes and trace minerals level were estimated both in the liver and kidney of three groups of rats. The study revealed that the gain in body weight increased in rats in Zn concentration dependent manner. The blood lipid profile displayed a significant rise in serum glucose, total lipids, cholesterol, triglycerides, LDL-cholesterol, VLDL-cholesterol whereas HDL-cholesterol showed a reduction in their levels in group-II and III than their control counter parts. The lipid peroxidation products were higher and the enzyme activities of superoxide dismutase, catalase, glutathione-s-transferase, glutathione reductase, glutathione (reduced) and glucose-6-phosphate dehydrogenase were significantly lowered in liver and kidney of group-II and group-III. Their mineral status revealed a higher Zn concentration and lower Cu, Mg and Mn both in liver and kidney. This data suggest that Zn in excess in diet when fed for longer periods of time induces oxidative stress by altering the status of minerals.
Highlights
Oxidative stress is the set of intracellular or extracellular conditions that leads to the chemical or metabolic generation of the reactive oxygen species (ROS), among which are highly reactive intermediates free radicals, such as superoxide anion (O2 ), hydrogen peroxide (H2O2), hydroxyl free radical (OH), lipid peroxides [1]
The results of this study revealed a significant rise in monthly body weights (P < 0.001) in group-II and groupIII up to a dietary treatment of 150 days (5 months)
The increase in body weight in three groups of rats varied significantly with the increase in Zn concentration in diet during the first 150 days of dietary treatment and thereafter it fell in group-II and III during the 30 days with respect to their weight at 150 days than their control group-I at day 180 of the experiment. It suggests that Zn is highly potent nutrient which initially promotes the gain in body weight in concentration dependent manner but reduced body weights when such intakes are continued for a prolonged period as revealed in group-II
Summary
Oxidative stress is the set of intracellular or extracellular conditions that leads to the chemical or metabolic generation of the reactive oxygen species (ROS), among which are highly reactive intermediates free radicals, such as superoxide anion (O2 ), hydrogen peroxide (H2O2), hydroxyl free radical (OH), lipid peroxides [1]. There are antioxidant scavenging enzymes such as cellular Cu/Zn superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), Glutathione-s-transferase (G-s-T), glutathione reductase (GRD), glucose-6-phosphate dehydrogenase (Glu-6-PD) and small molecular antioxidants such as reduced glutathione (GSH) [3]. The activities of Cu and Zn containing antioxidant enzymes including superoxide dismutase (SOD), cytochrome-C oxidase (CCO), catalase (CAT) and glutathione peroxidase (GPx) have been reported to diminish under Zn or Cu-deficiency or due to alteration in Cu-Zn ratio [5]. Activities of many enzymes are influenced by Mg [6] and Mn status [7] and deficiencies or impairment in their metabolism may results an increased lipid peroxidation which possibly may be a con-
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