Protective effects of prebiotics inulin and lactulose from cytotoxicity and genotoxicity in human colon adenocarcinoma cells

The accepted role of dietary prebiotics is to improve probiotic survival and growth in the lower intestine, yet few studies have investigated the possibility that prebiotics may offer benefits beyond their role with probiotics. This study investigates the protective effects of the prebiotics inulin and lactulose against cytotoxic and genotoxic effects in HT-29 human adenocarcinoma colon cells caused by human faecal water, bile acids and 4-nitroquinoline-1-oxide (4-NQO). Using the MTT assay, deoxycholic acid, lithocholic acid and faecal water 50% v/v reduced cell viability by 75, 74 and 50% respectively. In the presence of inulin and lactulose (0.5–2.0%) cell survival increased by 100% for deoxycholic acid, by 30% for lithocholic acid and by 40% for faecal water. Both faecal water (50% v/v) and 4-NQO (1–2 g/ml) were found to be highly genotoxic using the SOS chromotest, however incubation with inulin and lactulose (2%) significantly reduced the bacterial assay SOS inducing potency (SOSIP) by 70% and 57% respectively for faecal water and by up to 29 and 74% for 4-NQO. Similar protection against genotoxicity was observed with 4-NQO using the Ames fluctuation test. These tests show that prebiotics, in the absence of probiotics, were able to protect mammalian cells (HT-29 cells) against cytotoxicity and reduce the genotoxicity of known mutagens in bacterial mutation assays. Reproduction of these results in vivo would suggest that the inclusion of prebiotics in diet may directly confer health benefits beyond those associated with probiotic survival and growth.