| 1. Objective:Cadmium (Cd) and its compounds are known occupational hazardous chemicals and environmental contaminants and they are a kind of the long-term existence in environment. They also are the chemicals of long biological half-life (19-30 years) in body. The toxicological responses of exposure to cadmium include kidney damage, liver damage, respiratory diseases, neurologic disorders, and bone effects. Thus, Cadmium exposure and its health damage, especially toxic effects of long-term and low Cadmium exposure has become a hot spot in toxicological research, in which the exploration of relationship between specific markers for Cadmium exposure and related diseases is the root to prevention and early diagnosis and treatment of disease.Recently, the mouse translation elongation factor-1δ(TEF-1δ) has been identified as a novel cadmium-responsive proto-oncogene. But the TEF-1δgene as a underlying biomarker for cadmium exposure are still not understood. The present study regarding the alterative expression of the blood TEF-1δin rats chronically exposed to Cd as a new biomarker has been carried out.2. Methods:2.1 We primarily found out the dose range between death rate 100% and 0% of Sprague-Dawley rats exposed i.p. to CdCl2, and calculated the geometric proportion to randomly divide into 6 experimental groups and 1 control group with 8 rats of each group. The acute intoxication situations in rats were observed and the LD50 was detected by Modified Karber,S method.2.2 The 96 Sprague-Dawley rats were culled by weight and randomly assigned to four experimental groups with 24 rats each group (half male and half female, weighing 150±10 g). The exposed rats were given i.p. injections of ultrapure water solution containing the CdCl2 in doses of 1.225 mg/kg,0.612 mg/kg,0.306 mg/kg body wt (5 times i.p. per week) for 14 weeks. Control rats were given i.p. injections of 0.5 ml of 0.9% NaCl solution. After 14 weeks of treatment all rats were placed separately in glass metabolic cages for 24-h urine collection, as well as the blood and urine and internal organs from rats were collected.2.3 Internal organs include liver, kidney, heart and lungs. Organ coefficient is calculated and biopsy is prepared to observe the histological changes. The activities of alanine aminotransferase (ALT) and asparate aminotransferase (AST) in serum were measured as indicators of the liver function. The creatinine, total protein and urea concentrations in serum and urine were detected as parameters of the kidney function. 2.4 Cd levels detection by atomic absorption spectrometry in the blood, urine, liver, kidney, heart, and lung,The total RNAs of blood and tissues were isolated for TEF-1δexpression analysis with RT-PCR and FQ-PCR. In the last place, the correlations between TEF-1δexpression and Cd concentration in the blood, urine, liver, kidney, heart, and lung, as well as the adverse functions of liver and kidney induced by Cd were analysed, respectively. And the correlations between TEF-1δexpression in the blood and TEF-1δexpression tissues were analysed, respectively.3. Results:3.1 The results of acute toxicity tests showed that the absolute lethal dose primarily showed 26.00 mg/kg and maximal tolerance dose was 11.54 mg /kg. The dose each experimental groups was 26.00, 22.10, 18.79, 15.97, 13.57 and 11.54 mg/kg in tune. The rats usually died of Cd intoxication within 8 hours and a few of rats died in 72 hours. The LD50 of rats exposed i.p. to CdCl2 was 18.37 mg/kg,with a 95% confidence interval of 16.56～20.38 mg/kg.3.2 After rats were treated by different Cd concentrations for 14 weeks, the levels of Cd in the blood, urine, liver, kidney, heart, and lung were significantly increased with compared to controls and there were distinct dose-dependent relationships among different groups and between the blood and four internal organs (p<0.01). The levels of Organ/Body Coefficients in the liver, kidney, heart, and lung were significantly increased with compared to controls and there were dose-dependent relationships among different groups and between the blood and four internal organs (p<0.05). The internal organs of rats showed biochemical changes with compared to control, which were influenced by the administration of Cd. The biochemical indicators ALT, AST for hepatic toxicity and 24hpro, BUN, SCR for renal toxicity induced by Cd from rat serum showed significant increased with compared to control, and there were dose-response relationships among different groups (p<0.05), indicating obvious toxic dysfunction in the liver, kidney from rat exposed to Cd.3.3 After RT-PCR experiments, under the inner standard ofβ-actin,primarily showed that levels of TEF-1δmRNA expression in the blood and tissues were elevated in compared with controls in a dose-dependent manner (p<0.05). The results of FQ-PCR analysis further showed statistically significantly increased of TEF-1δmRNA in blood from rats exposed to Cd with compared to controls under the inner standard of hACTIN, and the levels of TEF-1δin the blood were found averagely over-expressed 2.54 fold in Cd-low dose, 4.28 fold in Cd-middle dose and 23.54 fold in Cd-high dose group with a dose-dependent manner (p<0.05). The levels of TEF-1δin the liver were found averagely over-expressed 3.59 fold in Cd-low dose, 12.53 fold in Cd-middle dose and 75.00 fold in Cd-high dose group with a dose-dependent manner (p<0.05). The levels of TEF-1δin the kidney were found averagely over-expressed 16.10 fold in Cd-low dose, 53.59 fold in Cd-middle dose and 159.14 fold in Cd-high dose group with a dose-dependent manner (p<0.05). The levels of TEF-1δin the heart were found averagely over-expressed 3.14 fold in Cd-low dose, 5.33 fold in Cd-middle dose and 13.17 fold in Cd-high dose group with a dose-dependent manner (p<0.05). The levels of TEF-1δin the lung were found averagely over-expressed 2.37 fold in Cd-low dose, 3.92 fold in Cd-middle dose and 8.02 fold in Cd-high dose group showed that levels of TEF-1δmRNA expression in the blood and tissues were elevated in compared with controls in a dose-dependent manner (p<0.01 or p<0.05).3.4 The statistics related analysis showed that there was a positive correlation between TEF-1δover-expression and Cd concentration in the blood, urine, liver, kidney, heart, and lung induced by Cd, respectively and there was a positive correlation between TEF-1δover-expression in the blood and TEF-1δover-expression in the liver, kidney, heart, and lung induced by Cd, respectively. There was a positive correlation between TEF-1δover-expression in the blood and the biochemical indicators ALT, AST for hepatic toxicity and 24hpro, BUN, Scr for renal toxicity induced by Cd, as well as the biochemical changes in the liver, kidney, heart, and lung respectively. The results of toxicity tests showed that there was a good dose-dependent and dose-response relationship between the expression levels of TEF-1δfactor in blood and Cadmium exposure levels in rat blood, liver, kidney heart and lung tissue and its abnormal effects on internal organs and the expression levels of TEF-1δfactor in organs.4. Conclusions:4.1 A rat model of chronic Cadmium exposure was established. It was found that Cadmium could be accumulated in blood, urine, liver, kidney, heart and lung tissue and accumulation was shown as follows: blood>urine, kidney>liver>heart>lung. Cadmium could increase the organ coefficient of liver, kidney, heart and lung and cause pathological changes to varying degrees. In addition, it caused biochemical changes in liver and renal function, reflecting Cadmium can cause chronic injury of liver, kidney, heart and lung with a dose-response relationship, which will provide new scientific data for long-term toxicity of Cadmium compounds.4.2 Induced expression of translation elongation factor 1d gene (TEF-1δ) was observed in rat blood and internal organs on the basis of the chronic Cadmium poisoning model, revealing that there was a good dose-dependent and dose-response relationship between the expression levels of TEF-1δfactor in blood and Cadmium exposure levels in rat blood, liver, kidney heart and lung tissue and its abnormal effects on internal organs and the expression levels of TEF-1δfactor in organs. The results suggest for the first time that the expression of TEF-1δin blood can be a new and valuable biomarker for Cadmium exposure and alternative markers for Cadmium exposure in internal organs and its toxic effects and can be considered to apply in early biological monitoring for population. |
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