| Objective To investigate the effect of vinyl chloride monomer (VCM) on expression of liver cell cycle related protein of rats which mediated by P53, and explore the impact of G1/S checkpoints induced by VCM and the possible carcinogenic mechanisms.Method64Sprague Dawley (SD) rats were divided randomly into four groups and they were administrated VCM with5,25,125mg/kg body weight through intraperitoneal injection three times per week for twelve weeks, the rats in control group were exposed to the same volume of clean air. During the experiment, general conditions of rats were observed. The rats were randomly killed at the end of6and12weeks (half male and half female), the cell cycle distribution and apoptosis were detected by flow cytometry. The protein levels of cyclinA, cyclinD1, P53and P21were detected by western blot. The expression of P16and CDK4proteins were identified by immunohistochemistry. Using SPSS16.0create the database and the data was analyzed by ANOVA.Results1. Genernal conditions of rats in4groups were all not showed significant poisoned symptom after rats exposed to VCM, the weight of rats increased as normal and there was no significant differences in4groups (P>0.05).2. After exposed to VCM for6weeks, distribution of liver cells of G0/G1phase in rats difference was in the critical level (P=0.055). Percent of distribution in the three poisoning groups was higher than that of the control group. After12weeks, percent of cells in S phase was increased with the increase of the dose.3. After exposed to VCM for6weeks, the expression of P21protein in rat liver cells decreased with the dose of VCM increasing, while that of the P53protein increased, both the differences were statistically significant (P<0.05). In addition, the expression of cyclinA and cyclinDl protein were found to be higher in the poisoning groups than that of the control group, and the differences were statisticlly significant (P<0.001).4. After exposure to VCM for12weeks, the expression of P21protein increased along with the increased dose (P<0.05), and the expression of the middle-dose and the high-dose were higher than the control group, and both the differences were statistically significant (P<0.001). The P53protein increased along with the increased dose, however, these results did not reach statistical significantly (P>0.05). While the expression of the high-dose group was higher than the low-dose group and the differences were statistically significant (P<0.05). The expression levels of cyclinA and cyclinD1proteins increased along with the increased dose (P<0.001), and the high-dose group was higher than the control group (P<0.001).5. The expression of CDK4protein and P16protein were identified by immunohistochemistry. After exposed to VCM for12weeks, the difference in the expression of P16protein among the groups was not signficant (P>0.05). CDK4protein expression level decreased with the increase of the dose. The expression of CDK4in experimental groups decreased significantly compared with the control group (P<0.05).6. Histopathological examination revealed vinyl chloride exposure dose groups had hepatocyte ballooning degeneration, the portal area was larger, fibrosis and other pathological changes, and the results showed that no change was observed in the control group.Conclusions1. Early exposure to a low dose of VCM, it can affect cell cycle distribution, and cause G0/G1phase arrest. S phase arrest instead of G0/G1with the increase of VCM dose and time of treatment.2. VCM can affect the early apoptosis but it had little effect on late apoptosis.3. The over expression of cyclinA, cyclinD1and P21are closely related to disorder of cell proliferation that caused by VCM. |
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