Effects of Selenium and Zinc on Renal Oxidative Stress and Apoptosis Induced by Fluoride in Rats

To study the effects of selenium and zinc on oxidative stress, apoptosis, and cell cycle changes in rat renal cells induced by fluoride. Methods Wistar rats were given distilled water containing sodium fluoride (50 mg/L NaF) and were gavaged with different doses of selenium-zinc preparation for six months. Four groups were used and each group had eight animals (four males and four females). Group one, sham-handled control; group two, 50 mg/L NaF; group three, 50 mg/L NaF with a low dose of selenium-zinc preparation (0.1 mg/kg Na2 SeO3 and 14.8 mg/kg ZnSO4·7H2O); and group four, 50 mg/L NaF with a high dose of selenium-zinc preparation (0.2 mg/kg Na2 SeO3 and 29.6 mg/kg ZnSO4·7H2O). The activities of serum glutathione peroxidase (GSH-Px), kidney superoxide dismutase (SOD), and the levels of malondialdehyde (MDA) and glutathione (GSH) in the kidney were measured to assess the oxidative stress. Kidney cell apoptosis and cell cycle were detected by flow cytometry. Results NaF at the dose of 50 mg/L increased excretion of fluoride in urine, promoted activity of urineγ-glutamyl transpeptidase (γ-GT), inhibited activity of serum GSH-PX and kidney SOD, reduce kidney GSH content, and increased kidney MDA. NaF at the dose of 50 mg/L also induced rat renal apoptosis, reduced the cell number of G2/M phase in cell cycle, and decreased DNA relative content significantly. Selenium and zinc inhibited effects of NaF on oxidative stress and apoptosis, promoted the cell number of G2/M phase in cell cycle, but failed to increase relative DNA content significantly. Conclusion Sodium fluoride administered at the dose of 50 mg/L for six months induced oxidative stress and apoptosis, and changes the cell cycle in rat renal cells. Selenium and zinc antagonize oxidative stress, apoptosis, and cell cycle changes induced by excess fluoride.

Inhibitory Effects of Selenium on Telomerase Activity and hTERT Expression in Cadmium-transformed 16HBE Cells

Objective To investigate the effects of sodium selenite on telomerase activity and expression of hTERT mRNA in cadmium-transformed 16HBE cells.Methods Telomerase activity and expression of genes were measured after cultured cadmium-transformed 16HBE cells were exposed to sodium selenite at different doses(0.625,1.25,2.50,5.00 μmol/L)for 24 hours.Results Selenium decreased telomerase activity in cadmium-transformed 16HBE cells.There existed an obvious dose-effect relationship between the selenium concentration and these changes.The expression of hTERT and c-myc mRNA also decreased but the expression of mad1 mRNA increased after exposure to selenium for 24 hours.No difference was found in expression of hTRF1 and hTRF2 mRNA after incubated with sodium selenite for 24 hours,compared with control group.Conclusion Selenium inhibits telomerase activity by decreasing hTERT and c-myc mRNA expression and increasing mad1 mRNA expression in cadmium-transformed 16HBE cells and selenium concentration is significantly correlated with these changes.

Effects of Cadmium on Hepatocellular DNA Damage,Proto-Oncogene Expression and Apoptosis in Rats

Objective To study the effects of cadmium on hepatocellular DNA damage,expression of proto-oncogenes c-myc,c-fos,and c-jun as well as apoptosis in rats. Methods Cadmium chloride at the doses of 5,10,and 20 μmol/kg was given to rats by i.p. and there were 5 male SD rats in each group. Hepatocellular DNA damage was measured by single cell gel electrophoresis(or comet assay),while expression of proto-oncogenes c-myc,c-fos,and c-jun in rat hepatocytes were measured by Northern dot hybridization. C-Myc,c-Fos,and c-Jun were detected with immuno-histochemical method. Hepatocellular apoptosis was determined by TUNEL(TdT-mediated dUTP Nick End Labelling) and flow cytometry. Results At the doses of 5,10,and 20 μmol/kg,cadmium chloride induced DNA damage in rat hepatocytes and the rates of comet cells were 50.20%,88.40%,and 93.80%,respectively. Results also showed an obvious dose-response relationship between the rates of comet cells and the dose of cadmium chloride(r =0.9172,P<0.01). Cadmium chloride at the doses of 5,10,and 20 μmol/kg induced expression of proto-oncogenes c-myc,c-fos,and c-jun. The positive brown-yellow signal for c-myc,c-fos,and c-jun was mainly located in the cytoplasm of hepatocytes with immunohistochemical method. TUNEL-positive cells were detected in cadmium-treated rat livers. Apoptotic rates(%) of cadmium-treated liver cells at the doses of 5,10,and 20 μmol/kg were(17.24 ±2.98),(20.58±1.35),and(24.06±1.77) respectively,being significantly higher than those in the control. The results also displayed an obvious dose-response relationship between apoptotic rates and the dose of cadmium chloride(r=0.8619,P<0.05). Conclusion Cadmium at 5-20 μmol/kg can induce hepatocellular DNA damage,expression of proto-oncogenes c-myc,c-fos,and c-jun as well as apoptosis in rats.

Telomerase Activity and Telomerase Reverse Transcriptase Expression Induced by Selenium in Rat Hepatocytes

Objective To investigate the effects of sodium selenite on telomerase activity, apoptosis and expression of TERT, c-myc and p53 in rat hepatocytes. Methods Selenium at doses of 2.5, 5.0, and 10 μmol/kg was given to SD rats by gavage. In rat hepatocytes, telomerase activity was measured by the telomeric repeat amplification protocol (TRAP), apoptosis was detected by flow cytometry, and expressions of telomerase reverse transcriptase (TERT), c-myc and p53 were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). c-Myc and P53 proteins were detected by immunochemistry. Results Selenium at doses of 2.5, 5.0, and 10 μmol/kg significantly increased hepatocellular telomerase activity and induced apoptosis in a dose-dependent manner. Although selenium at doses of 2.5, 5.0, and 10 μmol/kg displayed no obvious enhancing effect on the TERT mRNA expression in rat hepatocytes (P>0.05), it significantly increased the c-myc mRNA and p53 mRNA expression at the dose of 10 μmol/kg (P<0.05). Selenium at doses of 5.0 and 10 μmol/kg obviously increased the content of P53 protein in rat hepatocytes, but only at the dose of 10 μmol/kg, it significantly promoted the value of c-Myc protein in them. Conclusion Selenium can slightly increase telomerase activity and TERT expression, and significantly induce apoptosis and over-expression of c-myc and p53 at relatively high doses. The beneficial effects of selenium on senescence and aging may be mediated by telomerase activation and expression of TERT, c-myc, and p53 in rat hepatocytes.