Inducing HT-29 colon cells apoptosis by the extracellular polymeric substances isolate from L.casei strains

Abstract Text: Nine Lactobacillus strains (L. casei X11, L. casei X12, L. casei K11, L. casei J5, L. rhamnosus J10, L. casei M5, L. casei M23, L. rhamnosus IN4125, L. casei SB27) were obtained from the Chinese traditional fermented foods of minority nationalities or infant faeces based on the previous research in our laboratory (4 strains from Sinkiang, 3 strains from Gansu, 1 strain from Tibet, 1 strain from infant faeces). Fermentation broths from skim milk produced by the nine Lactobacillus strains were screened for anti-proliferation activity on HT-29 cells by MTT assay.  The results showed that four strains exerted higher anti-proliferation activity on HT-29 effects than positive control ((Lactobacillus rhamnosus GG, LGG). Crude and acidic exopolysaccharides isolated from the 4 strains (L. casei K11, L. casei M5-L, L. casei SB27, L. casei X12) at different concentrations (10, 20, 100, 200 and 500 μg/mL) were systematically assessed for the anti-proliferation activity on human colon cancer HT-29 cells. Further the apoptosis induced by exopolysaccharides (EPSs) were analysed by flow cytometry (FCM) on HT-29 cells. The colon cancer cells treated with L. casei SB27 acidic exopolysaccharides achieved the highest rate of apoptosis, 24.3% cells were found apoptosis and 1.4% cells in necrosis. The results of cell cycle analysis on HT-29 cells cycle treated with exopolysaccharides showed that L. casei SB27 acidic exopolysaccharides could slow the conversion rate of HT-29 cells from G phase to S phase, prolong the cell cycle and reduce the proliferation of colorectal cancer cells. The results of HT-29 cells Caspase-3 activity treated with L. casei acidic SB27 fraction showed that Caspase-3 was activated and achieve the significantly highest of all the samples at 2.79- fold compared with control group at 1.2- fold. The result of Hoechst 33258 staining shown that HT-29 colon cells treated with L. casei SB27 acidic exopolysaccharides appeared bright condensed dots compared with untreated with exopolysaccharides samples.

Keywords: L.casei strains; Exopolysaccharides;  HT-29 colon cancer cells apoptosis;