Mitochondrial oxidative stress and dysfunction in rat brain induced by carbofuran exposure

Abstract

Repeated low-dose exposure to carbofuran exerts its neurotoxic effects by non-cholinergic mechanisms. Emerging evidence indicates that oxidative stress plays an important role in carbofuran neurotoxicity after sub-chronic exposure. The purpose of the present study is to evaluate the role of mitochondrial oxidative stress and dysfunction as a primary event responsible for neurotoxic effects observed after sub-chronic carbofuran exposure. Carbofuran was administered to rats at a dose of 1 mg/kg orally for a period of 28 days. There was a significant inhibition in the activity of acetylcholinesterase (66.6%) in brain samples after 28 days of carbofuran exposure. Mitochondrial respiratory chain functions were assessed in terms of MTT (3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) reduction and activity of succinate dehydrogenase in isolated mitochondria. It was observed that carbofuran exposure significantly inhibited MTT reduction (31%) and succinate dehydrogenase activity (57%). This was accompanied by decrease in low-molecular weight thiols (66.6%) and total thiols (37.4%) and an increase in lipid peroxidation (43.7%) in the mitochondria isolated from carbofuran-exposed rat brain. The changes in mitochondrial oxidative stress and functions were associated with impaired cognitive and motor functions in the animals exposed to carbofuran as compared to the control animals. Based on these results, it is clear that carbofuran exerts its neurotoxicity by impairing mitochondrial functions leading to oxidative stress and neurobehavioral deficits.

Fig. 1

Scatter plots showing the acetylcholinesterase activity in control and carbofuran-exposed animals (n = 6). Group mean values are indicated by lines. Acetylcholinesterase activity was determined in the homogenates prepared from cerebral cortex of control and carbofuran-exposed animals using acetylthiochloline as substrate. Values are expressed as nmol of acetylthiocholine hydrolyzed/min/mg protein. Data was analyzed by Student’s unpaired t-test and values having P < 0.05 were considered significant. * Significantly different from control group

Fig. 2

Scatter plots for lipid peroxidation in isolated mitochondria isolated from control and carbofuran-exposed animals (n = 6). Group mean values are indicated by lines. Mitochondria were isolated from cerebral cortex of control and carbofuran-exposed animals. Lipid peroxidation was estimated by measuring the amount of malondialdehyde (MDA) using thiobarbituric acid. Values are expressed as nmol MDA/mg protein. Data was analyzed by Student’s unpaired t-test and values having P < 0.05 were considered significant. * Significantly different from control group

Fig. 3

Correlation between rate of mitochondrial respiration and lipid peroxidation (a), rota rod treadmill (b), and active avoidance performance (c). Data was analyzed by linear regression and values having P < 0.05 were considered significant. * Significantly different from control group

Fig. 4

Correlation between succinate dehydrogenase activity and lipid peroxidation (a), rota rod treadmill (b), and active avoidance performance (c). Data was analyzed by linear regression and values having P < 0.05 were considered significant. * Significantly different from control group

Fig. 5

Scatter plots for rota-rod treadmill (a) and active avoidance (b) performance of control and carbofuran-exposed animals (n = 6). Group mean values are indicated by lines. Rota rod treadmill performance of the control and carbofuran-treated animals was assessed by their ability of the animals to maintain on accelerating rotating rod (4–30 rpm) for 3 min. Values were expressed as retention time (s). Active avoidance of control and carbofuran exposed rats was analyzed by subjecting to conditioning by pairing tone with foot shock. Each session consisted of ten trials. Values are expressed as number of avoidances. Data was analyzed by Student’s unpaired t-test and values having P < 0.05 were considered significant. * Significantly different from control group