| Trace elements of selenium and zinc belong to biological essential elements. Selenium has important biologic functions, e.g. preventing cancer, reducing toxicity of heavy metals, and antioxidation. Zinc plays important roles in DNA replication, RNA transcription; cellular proliferation and differentiation, nucleic acid and protein metabolism, immunity enhancement and antioxidation. Lead is one of detrimental elements in vivo. It has been proved to have side effects on nervous system, digestive system, and immunity system. It is classified as a "possible human carcinogen". The most likely lead-associated cancers are lung cancer, stomach cancer, and brain cancer. Although such biological effects of Se, Zn and Pb have been well known, few researches have been carried out up to the present about studying effects of trace elements on cellular telomerase and telomere. In the paper, human fetal hepatocytes L-02 and hepatoma cells SMMC-7721 were adopted as two cellular models for studying. Thiazolyl blue (MTT) method and cellular morphology observation were used to inverstigate the optimum concentrations of Se, Zn, and Pb. Telomeric repeat amplification protocol and enzymatic luminometric inorganic pyrophosphate detection assay (TRAP-ELIDA) was used to measure telomerase activity. The expression level of human telomerase reverse transciptase (hTERT) gene was examined by reverse transciption-polymerase chain reaction (RT-PCR) and telomere length was assayed by flow cytometry and fluorescence in situ hybridization (FLOW-FISH). The Malondialdehyde (MDA) level, thiol content, glutathione peroxidase (GPx) activity, and total superoxidase dismutase (T-SOD) activity were also measured to evaluate cellular redox state. Results are as followings:1) Effects of Se on celluar redox state and telomerase activity or telomere length. The concentration range of selenium cultured with L-02 and SMMC-7721 cells up to 3~4 weeks was 0~2.5 (mol/L. To L-02 cells, this concentration range remarkably reduced the MDA level, increased the thiol content and GPx activity. Thus, it enhanced cellular antioxidation capacity. However, to SMMC-7721 cells, this Se concentration had no remarkable effect on the MDA level, thiol content and GPx activity. Therefore, it had not remarkably change cellular antioxidation capacity. Meanwhile, Se at concentration of 2.5 (mol/L could remarkably increase the telomerase activity, hTERT gene expression level, and extende the telomere length of L-02 cells. To SMMC-7721 cells, Se at the same concentrations had no significant effects on telomerase activity, hTERT gene expression and telomere length. These results suggested that L-02 cells are more sensitive than SMMC-7721 cells to the change of cellular redox state. Thus, Se in the present range can prolong the life span of L-02 cells through antioxidation mechanism whithout having significant impacts on SMMC-7721 cells. 2) Effects of Zn on cellular redox state and telomere length. The concentration range of znic cultured with the two types of cells up to 3~4 weeks was 0~80 (mol/L. To L-02 cells, Zinc at the concentration above remarkabely reduced the MDA level and increased the thiol content and T-SOD activity. Thus, it could increase cellular antioxidation capacity. However to SMMC-7721 cells, zinc at the same concentration had no remarkable effects on the MDA level, thiol content and T-SOD activity. Besides, zinc at concentration of 80 (mol/L help to maintain the telomere length of L-02 cells. On the contrary, it shortened the telomere length of SMMC-7721 cells indicating that zinc is essential to human fetal hepacytes for maintaining cellular life span. 3) Effects of lead on cellular redox state and telomere length. The concentration range of lead cultured with the two types of cells up to 3~4 weeks was 0～100 (mol/L. Lead in this range could remarkably increase the MDA level, reduce the thiol content in L-02 cells, and thus reduce cellular antioxidation capacity. Lead at concentration of 50(mol/L also reduced cellular telomere length in L-02 cells. To SM...
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