| Metallic chromium, hexavalent chromium [Cr (VI)] and trivalent chromium [Cr (III)] are the main forms of chromium (Cr) in the nature. Cr (VI) is the most widely used in industrial production. Workers exposure to Cr (VI) through skin contact and inhalation, it does harm to occupational health; Studies have shown that long-term exposure to Cr (VI) induced lung cancer.Telomere which is an DNA-protein structure at the end of eukaryon chromosome. Telomere length is related to the life of cells, cellular aging and death, and closely associated with the occurrence of cancer.Telomere length is common regulated by telomere binding proteins and telomerase. Through combining the end of telomere chromosome, telomerase can extend the length of the telomere. Telomere binding proteins can be combined specifically with the end of telomere to change the structure of the telomere, inhibit the combination of telomerase and telomere in order to prevent telomere extension.Objective:In this study, inhalation toxicology test has been on SD rats in different concentrations of Potassium dichromate(K2Cr2O7), the effect of Cr (VI) was analyzed on telomere length and the expressions was discussed of TRF1and TRF2in rats, also the effect of Cr (VI) on the telomere, which provide a theoretical basis on the mechanism of Cr (VI) carcinogenicity in further study.Methods:1. Rat acute inhalation toxicity test.40healthy adult SD rats in the weight range of180-220g were randomly divided into four groups, in each group there were half of female and male. Rats were treated with K2Cr2O7at a dose of1000mg/m3,2150mg/m3,4640mg/m3,10000mg/m3by inhalation. After two weeks, the rats’ symptoms and death were recorded; and pathological examination was taken on death rats. According to the number of the death rats, the LC50and its95%confidence interval were calculated.2. Rat short-term repeated exposure toxicity test.80healthy adult SD rats in the weight range of180-220g were randomly divided into four groups, there were20rats in each group and according to the LC50we had calculated, designed the high, medium and low dose group as following:1/10LC50,1/31.6LC50,1/100LC50, using distilled water as control. During the7days test, record the rats’ symptoms and death.3. Measuring the content of Cr in the blood of rat by graphite furnace atomic absorption spectrometry. After Short-term repeated exposure toxicity test, the blood of rats was collected in each group and the content of Cr in the blood of rat measured by graphite furnace atomic absorption spectrometry.4. Determination of rats’telomere length by real-time quantitative PCR (qPCR). After Short-term repeated exposure toxicity test, the right lung of rats in each group was taken DNA from lung tissue was extracted to analyze by qPCR. According to the Ct, the relative telomere length of rats was calculated.5. Detected the expression of TRF1, TRF2by SP immunohistochemical method. After Short-term repeated exposure toxicity test, the rats’ left lung in each group was taken. Then after fixed and embedded, SP immunohistochemistry was used to detect the expressions of TRF1and TRF2.6. Statistical analysis. Used the software SPSS12.0to analyze the data, analyzed the effect on the content of Chromium in the blood and telomere length from K2Cr2O7by T-test. Multiple groups means were compared with One-Way ANOVA, and the comparison among groups was adjusted by Bonfferoni method. Used Levene to test the homogeneity of variance, and Spearman rank correlation analysis was used to analyze the relativity. All statistical tests were bilateral, test level a=0.05.Results:1. During the observation period of inhalation toxicity test, there were6rats died in group of4640mg/m3; there were10rats died in the group of10000mg/m3. After checked the Horn table, the LC50of K2Cr2O7on rats was4640mg/m3. According the LC50, the dose groups was designed as following:430mg/m3,136mg/m3and43mg/m3for Short-term repeated exposure toxicity test.2. Short-term repeated exposure toxicity test:there were two rats died in the medium dose group and4rats died in the high dose group. Mortality rate was less than50%, it could meet the requirements.3. Concentration of Chromium in the rats’blood in each group(high,medium, low-dose group and control group) was followed by2534.11±150.98mg/L,796.40±126.55mg/L,97.12±6.88mg/L and14.98±2.39mg/L, the difference among groups was statistically significant (F=32.63,P<0.05).4. The result of qPCR:Telomere length of rats in high, medium, low-dose group and control group were followed by0.20±0.04,0.20±0.04,0.61±0.06,1.13 ±0.11, the difference among groups was statistically significant (F=664.041, P<0.05).While the Telomere length and blood chromium content of rats in high, medium-dose groups were all negatively correlated(r=-0.78,-0.56,-0.52,0.45, P<0.05).5. The result of SP immunohistochemistry:The average OD of TRF1in high, medium, low-dose group and control group were followed by0.36±0.03,0.32±0.02,0.29±0.01,0.28±0.02, the difference was statistically significant (F=125.20, P<0.05). the average OD of TRF2were followed by0.25±0.01,0.23±0.03,0.20±0.04,0.19±0.01, the difference among multiple groups was statistically significant (F=64.71, P<0.05). The expression of TRFl and TRF1in high, low-dose group and control group were positive correlation (r=0.77,0.59,0.51, P<0.05); The expressions of TRFl and telomere length in high, medium, low-dose group were negative correlation (r=-0.77,-0.56,-0.51, P<0.05); The expressions of TRF2and telomere length in medium, low-dose group and control group were positive correlation (r=-0.74,-0.70,-0.50, P<0.05).Conclusion:K2Cr2O7could affect telomere function in lung tissue of rats, made telomere length shorter and caused to increase the expressions of TRFl and TRF1. |
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