| Numerous reports have shown that supranutritional levels of selenium have anticarcinogenic effects. Sodium selenite, the traditional selenium compound, has cancer inhibitory activity, but it also has powerful toxicity. Recently, studies on selenium have focused on its chemical form. Methylated selenium has been reported to be more effective and less toxicitic. Se-methyselenocysteine (MSC) is the extract of selenium-enriched garlic and the good precursor for generating monomethylated selenium. The primary researches indicated that it has more powerful effect on apoptotic induction and low cytotoxicity in human promyelocytic leukemia cells. Little is known about the effect of MSC in solid cancers and there are not literature reports about the effect of MSC on esophageal carcinoma. This study takes H5E973, EC 109 and EC8712 cell lines as the target cells, uses sodium selenite for comparative purpose and study MSC as follows (1) to compare the effects of MSC with sodium selenite in cytotoxicity and apoptotic induction. (2)to investigate the effect of these two selenium compounds on cell proliferation, cell cycle, apoptotic induction and the expressions of Bcl-2, Bax and PCNA, then exploring their possible anticarcinogenic mechanisms.Materials and MethodsThe esophageal carcinoma cell lines are routinely grown and maintained in plastic flasks and plates in DMEM: F12(1: 1) with 8-10% fetal bovine serum. Cells are divided into different selenium-treated group and natural saline control group. Their morphology feature, cell cycle, apoptosis and expressions of Bcl-2, Bax and PCNA proteins are studied using light microscope, transmission electron microscope, flow cytometer, TUNEL and immunohistochemistry techniques. Results Morphological Reaction to Selenium TreatmentH5E973 cells do not appear obvious morphological changes in both 0. lug/ml selenite and MSC treated groups under light microscope. They have showed morphological alteration, not only cell shrinked with nuclei condensed, but also cytotoxicitic changes, such as extensive cytoplasmic vacuolization in selenite group from 1.0ug/ml to 2.0ug/ml. Compared with selenite, cells in MSC group from 1.0ug/ml to 2.0ug/ml appeared shrinking with rugous membrane. Preceding changes are more obvious with the dosage increase and no obvious cytotoxicitic changes appear even in 8.0ug/ml group. The morphologic alterations of EC 109 and EC8712 cell lines are similar to those of H5E973.Ultrastructural Changes Treated with 2.0ug/ml selenite, H5E973 cells show apoptosis, but at the same time, cytotoxicitic changes, such as cell swelling, extensive cytoplasmic vacuolization (mainly caused by mitochondria swell), myelin figure and membrane ruptured also appear. Compared with selenite, in 8.0ug/ml MSC treated groups, typical apoptosis is seen in many cells, but cytotoxicitic changes are not obvious. The ultrastructural changes of EC 109 are similar to thoseof H5E973 cells.Index of Cell Growth Inhibition1. Cell Growth CurveThe growth curve of the control group has obviously elevated tendency with time dependent. All cell growth curve of selenium treated groups are lower than the control group. The decent tendency of growth curve is more obvious in selenite treated groups than in MSC groups.2. Mitotic Index (MI)MI of selenium treated group is obviously lower than that of control group. The reduction of MI is dependent on the increase of dosage and treatment time of selenium. Flow Cytometer Detection1. DNA Content AnalysisCharacteristic sub-G1 peaks (apoptotic peaks) appear in DNA histogram in selenium treated groups, but it cannot be seen in control groups.Sub-Gl peaks can be seen in 1.0ug/ml selenite group. Among selenite treated groups, sub-Gl peak is highest in 2. Dug/ml treated group. Compared with selenite, sub-Gl peaks also can be found on 1.0ug/ml MSC treated group. With selenium concentration increasing, the sub-Gl peaks gradually go up. Even in 8.0ug/ml group, the peak still exhibits rising tendency. The alterations of sub-Gl peaks in EC...
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