L-carnitine Protests Against Cadminum-induced Neurotoxicity In Rats

Objective: To investigate the neurotoxicity of cadmium chloride（CdCl₂）, Sprague-Dawley （SD） rats were administrated Cd （25,50,100mg/L）by drinking water for4weeks and divided into four groups randomly, throughobserving the spontaneous locomotor activity, histopathology slices and ROS,MDA and SOD to study the neurotoxic effects of Cd-induced in cerebralcortex. Simultaneously, to research L-CAR efficiently protect againstneurotoxicity induced by Cd and the possible mechanism we did this study.Method:①Young adult male Sprague-Dawley （SD） rats （180-200g, about40days old at the beginning of the experiment） were supplied by the animalcenter of the Third Military Medical University （Chongqing, China）. Animalsaccommodated for three days in animal room of our laboratory beforetreatment and were kept under standard conditions of controlled light（fluorescent cool white bulbs,100lux intensity at the level of animal room,lighting between08:00and20:00h daily） and temperature （22±2°C）. Foodand water were provided ad libitum. Treatments were performed by drinkingwater for4weeks, all rats were divided into four groups randomly: controlgroup and Cd25,50,100mg/L groups （n=8）. We used open-field test （OFT）, forced-swimming test （FST）, histopathology slices and determined ROS,MDA and SOD in rats’ cerebral cortex to choose the perfect dose protected byL-CAR.②The volume of water was recorded at9:00-10:00everyday for4weeks; and the body weight of rats was recorded before each experiment. Thecare and use as well as all procedures were approved by the InstitutionalAnimal Care Committee of the Third Military Medical University,Chongqing.③Rats were divided into four groups randomly: control group, Cdgroup, Cd+L-CAR group and L-CAR group （n=8）. We also used open-fieldtest （OFT）, forced-swimming test （FST）, histopathology slices anddetermined ROS, MDA and SOD in rats’ cerebral cortex to evaluateprotective effects of L-CAR.Results:Part1: The Neurotoxic Effects of Cd①After Cd subacute exposure for4weeks, there were no obviouslybehavioral changes in Cd25,50mg/L groups; while the rats in Cd100mg/Lgroup were smaller than above two groups, and we could see feedingbehaviour obviously reducing and locomotor activity changes. In the firstweek, the rats were lethargy and hypomotility, and then showed tussleincrease, hyperactivity, seizures, aggressiveness, tail mutilation, paws injuriesand so on. The volume of drinking water in different groups was analyzed by one-way ANOVA showing no significance and the mean was31.02±2.10ml/rat/day. The body weight and the percentage of brain/body weight in Cd25,50mg/L groups showed on significance compared with control group. Thebody weight decreased from days7（p <0.01） in Cd100mg/L group while thepercentage of brain weight/body weight increased significantly （p <0.01）.②During the whole Cd exposure （25,50,100mg/L in drinking water）procedures for4weeks, OFT and FST were performed on days0,7,14,21and28to observe the spontaneous locomotor activity changes. After dataanalyzed, the locomotor activity in Cd25,50mg/L groups presented slightincrease but no significance; Cd100mg/L group showed a reduction in themovement activity at first （p <0.01）, and on the14thday presentedexcitability and aggressiveness increased （p <0.05）, after4weeks treatmentthe locomotor activity showed decrease significantly again （p <0.05）.③After Cd25,50,100mg/L subacute exposure for4weeks, weobserved the neurons in cerebral cortex appeared hyperemia, nuclearpyknosis and karyolysis on histopathology slices （HE stain）, the numbers ofthese nerve cells increased with exposure dose.④After Cd25,50,100mg/L subacute exposure for4weeks, ROS,MDA and SOD were determined by kits. ROS and MDA showed significantincreases （p <0.05） in all Cd groups compared with control, SOD showed adecrease tendency in all groups but only Cd100mg/L group presented asignificant decrease compared with control group （p <0.05）, other groups showed identical roles but no significance.Part2: The Protection Effects of L-CAR①After L-CAR （1.5g/L） and/or Cd （100mg/L） subacute exposurefor4weeks, there were no obviously behavioral changes in Cd+L-CAR andL-CAR groups; while the rats in Cd100mg/L group were smaller than abovetwo groups, and we could see feeding behaviour obviously reducing andlocomotor activity changes. In the first week, the rats were lethargy andhypomotility, and then showed tussle increase, hyperactivity, aggressiveness,seizures, tail mutilation, paw injuries and so on. The volume of drinkingwater in different groups was analyzed by one-way ANOVA showing nosignificance and the mean was32.74±3.23ml/rat/day. The body weight ofrats in100mg/L group decreased from days7（p <0.01）, meanwhile, L-CARpretreatment could inverse the effect of Cd-induced （p <0.05）. Thepercentage of brain/body weight increased significantly in both Cd treatmentgroup and Cd+L-CAR group （p <0.05）, L-CAR pretreatment modulated thischange significantly （p <0.05）.②During the whole L-CAR and/or Cd exposure procedures for4weeks, OFT and FST were performed on days0,7,14,21and28to observethe spontaneous locomotor activity changes. After data analyzed, Cd grouppresented a reduction in the movement activity at first （p <0.01）, and on the14thday showed excitability and aggressiveness increased （p <0.05）, after4weeks treatment the activity showed a significant decrease （p <0.05）. In Cd+L-CAR group, the effect was not apparent and even inversed, especially,the numbers of standing showed significant difference compared with Cdgroup （p <0.01）.③After L-CAR and/or Cd subacute exposure for4weeks, weobserved the neurons in cerebral cortex appeared hyperemia, nuclearpyknosis and karyolysis on histopathology slices （HE stain） in Cd group,while in Cd+L-CAR group the neurons were integrity and edge sharpness,nuclear pyknosis and karyolysis were hardly observed.④After L-CAR and/or Cd subacute exposure for4weeks, ROS,MDA and SOD were determined by kits. Cd group compared with controlgroup, ROS and MDA all increased significantly （p <0.05） and SOD showeda significant decrease （p <0.05）. Cd+L-CAR group compared with Cd group,the effects were not apparent and even inversed significantly （p <0.05）.Conclusion: Cd could induce the changes of spontaneous locomotoractivity in rats, and the possible mechanism of its neurotoxicity may beoxidative stress in cerebral cortex neurons. L-CAR, as an antioxidant, playsneuroprotective roles by improving the steady-state balance between oxidantand antioxidant agents to alleviate the effects of oxidative stress. It may be apotential pharmacological agent to protect against Cd-induced neurotoxicity.