| Conjugated linoleic acids (CLA) refer to a collection of positional and geometric isomers of octadecadienoic acid with conjugated double bonds. A number of these naturally occurring C18 fatty acids, which have the conjugated double bond structure located in either the cis or trans configuration at positions Δ7,9, Δ8,10, Δ9,11, Δ10,12, Δ11,13 of the carbon chain(3-6), have been identified.A major source of natural CLA is milk and meat from ruminant. c9, t11-CLA is the predominant isomers in milk fat. It was reported that c9,t11-CLA could be produced from biohydrogenation of linoleic acid by Butyrivibrio fibrisolvens, a ruminant bacterium,and also by lactic acid bacteria.Studies demonstrated CLA have many biological activities. Dietary CLA reduced body fat reserves in mice, rats, hamsters and pigs, and reduced atherogenesis and type II diabetes in animal experiment, even in fat human. t10,c12-CLA isomer can increase insulin sensitivity and glucose tolerance. In the recent years, much attention has been paid to the anticancer effect of CLA.Caco-2 cell is an intestinal cell line derived from a human colorectal carcinoma. The cells were incubated in DMEM containing 10% FCS, 100U/ml penicillin, 100μg/ml streptomycin, and 3% L-glutamine and in serum-free medium. One of the objectives of the present study was to investigate the antiproliferative effects of different concentrations (0, 25, 50, 100, 200pμmol/L) of linoleic acid (LA,96%), c9,t11-CLA (96%), t9,t11-CLA (96%) and the mixture of these two isomers (1:1 v/v) on the human colon adenocarcinoma cell line Caco-2 in various action time (1d, 2d, 3d, 4d). The antiproliferative effects of four substances in the same concentration and the same action time also were compared. The other aim of the study was to examine the apoptosis of Caco-2 cell line induced by the mixture of the two CLA isomers.The effects of antiproliferative of Caco-2 cell was investigated by MTTassay. The morphologic diversification of Caco-2 cell apoptosis was studied by transmission electron microscope and the ratio of apoptosis were determined by flow cytometry. The mRNA expression of Caspase-3 gene of Caco-2 cell line was determined by reverse transcription polymerase chain reaction (RT-PCR).Caco-2 cell line was incubated with different concentrations of test substances for indicated period of time. MTT assay revealed that different concentrations of LA, c9,t11-CLA, t9,t11-CLA and the mixture of CLA can inhibite the Caco-2 cell proliferation in various action time. The effects of antiproliferative are closely related to the treatment time ( p<0.05) and concentration. After Caco-2 cells were treated by same concentration of the four substances in the same time, the result shown that the higher anti-proliferation activity of the four substances is the mixture of CLA, then is t9,t11-CLA, c9,t11-CLA, and linoleic acid respectively. The results of transmission electron microscope and flow cytometery method shown the mixture of CLA induced cell apoptosis in dose-dependent and time-dependent manner. The result of RT-PCR shown the mRNA expressions of caspase-3 gene was increased compared with the control. The mixture of CLA induced caspase-apoptosis in Caco-2 cell line.In Conclusion, LA, c9,t11-CLA , t9,t11-CLA and the mixture of CLA in this study could inhibit the Caco-2 cell line proliferation. The mixture of CLA induced apoptosis of Caco-2 cell line. Cell apoptosis might be one of the mechanism of the effect of the mixture of CLA on cancer cells.
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