| The chance of trimethyltin chloride (TMT) exposed to people has being greatlyincreased with the widely application of the PVC material. And the poisoning occurredfrequently, which cause serious damage to people’s health. Thus, to The studies about theneurotoxic mechanism of TMT are quite necessary. It not only has theoretical significance,such as to enrich and perfect the TMT poisoning theories, and then to provide clues and basisfor related researches, but also has very important practical significance for the enacting ofTMT hygiene standards and the diagnosis and prevention and control of poisoning.This paper has conducted a study about the neurotoxic mechanismon of TMT as thefollowing two parts on the basis of previous researches in this laboratory. In the first part, tofind some early sensitive indexs of neurotoxicity and pathologic basis of TMT, acute oralpoisoning model of rats by TMT repeated doses injected has been established. And on onehand, neurobehavioral tests, which could evaluate the neurobehavioral toxicity of TMT on theoverall level, has been used. On the other hand, histopathological method for observing thechanges of the structure of nerve on the cellular level had been involved. In the second part,through the detection about the effects of TMT on the oxidization-antioxidization system ofserum and brain tissue of rat, the mechanism of oxidative stress of neurotoxicity induced byTMT at the molecular level has been further studied, for the research on the mechanism TMTpoisoned and providing a reference for national standards. Part I The Effects of TMT on the Neural Behavior of RatsObjective: To establish acute oral poisoning model of rats by TMT repeated doses injected;Evaluation the neurobehavioral effects of TMT; To observe the structural changes in thebrain’s nerve cells caused by TMT.Methods: Forty healthy adult male SD rats were randomly equally divided into four groups,including a control group (double-distilled water treated) and three TMT treated group（s0.75、1.50、3.00mg/kg/day) according to their weight, and all the rats were injected through mouthonce a day for six days. Motor and sensory function indexes of rats including Forelimbs GripStrength Test Scored, Hindlimbs Supporting Force Experiment, Pegged Beam Walking TestScored and Tail Flick Latency (TFL) test were used to evaluate the neurobehavioral toxicityof TMT. The brains were separated24h after the last inject, and made into paraffin section toobserve Nissl body.Results:⑴The features of general behavior toxicity: The3.00mg/kg group were seen slightsymptoms of nervous excitement on the4thday, and obvious central excitotoxicityperformance，such as tremor, stiffness and weakness of the limbs, seizures, convulsions andetc were observed on the6thday. And on days5and6, some slight excitotoxicity performancewere observed in1.50mg/kg group. However, there were no significant abnormity watchedbetween the0.75mg/kg group and the control group.⑵Weight: Compared with the controlgroup, the body weight of3.00mg/kg group significantly decreased after exposure to TMT for4、5and6days (P <0.01), but there were no remarkable changes in weight of the1.50and0.75mg/kg group. While the weight of the control group kept increasing normally.⑶Organcoefficient: Organ coefficient of heart, brain, lung, kidney, testis of3.00mg/kg group weresignificantly larger than the control group (P<0.05), while the organ coefficient of spleensignificantly reduced (P <0.01). And in1.50mg/kg group, spleen and kidney were detected tosignificantly increase on coefficient organ (P<0.05), however, there were no significantlychange of these were found in0.75mg/kg group.⑷The performance of neurobehavioraltoxicity:①Forelimbs Grip Strength Test Scores: Scores of3.00mg/kg group began todecline at the4thday, and turned to be more prominent at the day of5and6(P<0.01), meanwhile, there was no third limb having climbed up to the wire. In1.50mg/kg group,scores have been seen fall obviously (P>0.05), and that a third limb climbed up to wire wasobserved occasionally. However, the reduce of scores did not occur in0.75mg/kg group andnormal group, and that a third limb climbed up to wire was common.②Hindlimbs SupportingForce Experiment: Compared with the control group, hindlimb supporting force coefficient of3.00mg/kg group decreased significantly (P<0.01) at the days of4,5and6, while there wereno significant changes that have been found in1.50and0.75mg/kg group.③Pegged BeamWalking Test Scores: The scores of3.00mg/kg group began to increase from the third day(P<0.05), and some rats could not complete the test the fourth day. And then scores weresignificantly higher than the control group on the5thday, and the number of rats that could notcomplete the test increased, what’s worse, some rats could not even stand on the balancebeam, which means the reduce of their ability to balance. On the6thday, almost all the ratwere unable to complete test and the scores further significantly rose (P<0.01). Meanwhile,some rats of1.50mg/kg group could not complete the experiment and their scores weresignificantly increased (P<0.05) on the day of5and6. Scores of0.75mg/kg group have nosignificant change.④Scored and Tail Flick Latency (TFL) test: Tail flick coefficient of3.00mg/kg group significantly increased (P<0.05) on the5thand6thdays, but there were nosignificant changes detected in1.50and0.75mg/kg group.⑸Nissl staining:①The cerebralcortex: The cortical neurons of the control group ranged in dense, regular and were uniformdeep staining, Nissl bodies were legible and owning a large quantities. However, the numberof nerve cells in3.00mg/kg group reduced obviously, and the neurons appeared to not onlybe smaller and less shallow staining, but also arranged rather in disorder and irregularly, andpart of neurons were loss. There was no obvious boundary between nucleus and cytoplasm,and the axons could not distinguish from the dendrites. And more, the Nissl body significantlyreduced in the number.②Cerebellum: the cerebellar granule cell layer of the control groupranged in dense, uniformity with a large quantities and were uniform deep staining. Purkinjecells ranged in monolayer and had large bodies. And the small molecular layer cell distributedvery dispersedly.While the granule cells of3.00and1.50mg/kg group presented to be lightstaining, which was more obvious to the Purkinje cells, and there existed a decrease in the number of Nissl body.Conclusion: In our laboratory conditions, it come to the following conclusions:⑴TMT cancause significant weight loss, a reduction of the organ coefficient of spleen and a increase ofthat of heart, brain, kidney, lung, testis in rats, which indicates that TMT can lead a damage tomultiple organ, and kidney and spleen are more TMT sensitive. TMT can also induce obviouscentral nervous system poisoning symptoms, such as tremor, mania, aggressive, screaming,irritability, convulsions and seizures and etc, which indicates that the whole experimentalmodel of TMT poisoned were founded successfully in our laboratory;⑵The neurobehavioralfunction test showed that TMT can cause obvious neurobehavioral toxicity, which lead toneurological motor and sensory dysfunction, and the test of Pegged Beam Walking TestScores sames to be a more sensitive index;⑶There exist significant pathological changes inthe brain tissue of rats observed with Nissl staining after TMT exposure, suggesting that TMThave neurotoxicity, and the cortex and cerebellum are toxic target organs of TMT, andmeanwhile, the cortex is more sensitive.Part II Effects of TMT on the Oxidative Stress in Serum and Brain TissueObjective: To detect the effects of TMT to the oxidation-antioxidant system in serum andbrain tissue of rats, and to further explore the oxidative stress mechanism of TMT on themolecular level.Methods: Serum were extracted from rats, and the cortex and cerebellum were taken to bemade into homogenates, and then the changes of oxidation-antioxidant system indexesincluding MDA, GSH and T-SOD was detected with related kits and a spectrophotometer.Results: Serum⑴:①MDA: Compared with the control group, the MDA content of3.00and1.50mg/kg group respectively increased39.0%(P <0.05) and22.0%(P>0.05), and0.75mg/kg group showed no significant differences;②GSH:Compared to the control group, theGSH content of3.00,1.50and0.75mg/kg group respectively increased133.6%(P <0.01),92.9%(P <0.05) and45.1%(P>0.05);③T-SOD activity: T-SOD activity of3.00mg/kggroup significantly increased (P <0.05) compared to the control group, while that of1.50and0.75mg/kg group was found no significant changes.⑵Cortex:①MDA: With the increase of exposure dose of TMT, MDA content of all the exposed groups have increased, and3.00mg/kg group increased45.4%(P <0.05);②GSH: Compared with the control group, GSHcontent of3.00,1.50and0.75mg/kg group respectively reduce50.7%(P <0.01),38.0%(P <0.01) and29.9%(P <0.05), and there was reduced linear trend with the the exposure doseincreasing;③T-SOD: T-SOD activity of3.00,1.50and0.75mg/kg group decreased25.8%,34.9%and28.5%respectively, and prominently lower than the control group (P <0.05).⑶Cerebellum:①MDA: Compared with the control group, MDAcontent of rats in eachexposure group showed no significant change;②GSH: GSH contentof3.00mg/kg group,compared with the control group, reduced25.0%(P <0.05), however, the decline of1.50mg/kg group had no statistical significance (P>0.05);③T-SOD: T-SOD activity of3.00mg/kg group was7.5%lower than the control group (P <0.05), while T-SOD activity of1.50and0.75mg/kg group did not change significantly.Conclusion: After these studies in our laboratory conditions, following conclusions can bedrawn:⑴Damage of TMT to the oxidation-antioxidant system in serum is not obvious,and TMT could even activate the antioxidant system, suggesting that there may be somecompensatory mechanisms in the blood system increasing its antioxidant capacity to protectthe body;⑵TMT can induce oxidative damage to cortex and cerebellum, which are both thetoxic target organs of TMT, and cortex is relatively more sensitive to oxidative stress. Andoxidative stress may be one of the possible mechanisms of neurotoxicity induced by TMT.⑶Changes of GSH content of oxidation-antioxidant system in brain tissue may be a moresensitive indicator on studies of oxidative damage mechanism of TMT.In summary, in our laboratory conditions, the studies had confirmed the neurotoxicityand explored the possible mechanism of TMT in multi-level and multi-angle, by the level ofthe overall, tissue and cell, and molecular, respectively, including the overall performance ofpoisoning rats (including general toxicity and neurobehavioral toxicity), pathological changesand oxidative stress changes in indicators. Observed from the overall level, TMT poisoningof rats mainly performanced as typical neurotoxic symptoms, weight loss, neurobehavioralchanges, and induced damage to multiple organ. Viewed from the level of tissue and cells,TMT could damage the structures and functions of nerves in cerebral cortex neural and cerebellum, and the damages to the Purkinje cells were more obvious. In the molecular level,TMT could induce damage of oxidative stress, mainly by damaging by lipid peroxidation,consumpting the antioxidants and decreasing the antioxidase activity. The damages to theblood system were not obvious, and the oxidative damages to cerebellum were relativelyminor, but rather serious to cortex, thus, oxidative stress might be the possible mechanism ofneurotoxicity TMT caused. In addition, the studies also found that the test of Pegged BeamWalking Test Scores and GSH content changes were relatively sensitive indicators for thedetection of TMT neurotoxicity. |
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