The relationship between probiotics, prebiotics and bile acids and the impact on gut health

Epidemiological studies show a diet rich in fats and processed meats is often associated with higher levels of secondary bile acids and carcinogens in the gut and increases the risk of colorectal diseases. In recent years the consumption of probiotics and prebiotics has been widely proposed as a strategy to both prevent colorectal disease and generally improve gut health. The present study investigated the role of synbiotic applications of species of Lactobacilli (L. acidophilus NCFM LYO 10, L. acidophilus NCTC 1723, L. reuteri, L. brevis NCIMB 11973 and L. delbrueckii ss bulgaricus NCTC 12712) and prebiotics (inulin, lactulose and lactobionic acid) in bile acid/salt stress and on bile acid metabolism particularly as it affects deconjugation. In addition the study also looked at the effects of prebiotics on xenobiotic induced cytotoxicity/genotoxicity. Preliminary investigations looked at the ability of Lactobacilli cultures to survive the detergent properties of bile acids and utilise prebiotics for growth. Results showed L. acidophilus NCFM LYO 10 was least sensitive to bile acid/salt stress simulating levels found in the gut whilst other cultures showed different levels of growth inhibition with glycine conjugated bile acids being potentially more toxic than its
taurine conjugated counterpart.

Lactulose was the prebiotic of choice for both L. acidophilus NCFM LYO 10 and L. reuteri with growth comparable to growth in glucose. Small increases in growth were observed for both cultures with lactobionic acid as substrate whereas other cultures could not effectively utilise any of the prebiotics. Following synbiotic applications ofL. reuteri and L. acidophilus NCFM LYO 10 with lactulose or lactobionic acid increases in growth was observed in cholic and taurocholic acid including L. reuteri in taurochenodeoxycholic acid with lactulose as substrate. No growth benefits were observed in the glycine conjugated bile acids.

L acidophilus NCTC 1723 deconjugated taurocholic, glycocholic, taurochenodeoxycholic and taurodeoxycholic acid, no deconjugation was observed for other cultures. The presence of prebiotics impacted on BSH activity i.e. whilst 2.83xlO" 2 nmol/min (p<0.01) cholic acid was released with 2% inulin reduced BSH activity was observed in 2% lactulose with 0.66x10" 2 nmol/min cholic acid released. No growth was observed in 2% lactobionic acid. Uncooperative and mixed inhibition kinetics with respect to taurocholic acid substrate was shown with inulin and lactulose (2, 4 and 6%) with a K; of 12 and 10.5% respectively whereas a dose dependent (0 - 2%) increased CGH enzyme kinetics was observed with lactobionic acid.

Comparism of L. acidophilus NCFM LYO 10 cytosolic proteome revealed 16 spots whose expressions were either up or down regulated by the presence of cholic or glycocholic acid. 9 PMFS were identified as proteins involved in glycolysis, chaperones, translation, peptidoglycan and amino acid synthesis. In synbiotic applications with lactobionic acid 14 spots showed different levels of expression.

Deoxycholic, glycolithocholic, lithocholic acid (0.5mM) and faecal water 50% (v/v) reduced the viability of HT29 cells by 75, 60, 74 and 50% respectively. Addition of prebiotics inulin and lactulose (0.5-2% w/v) resulted in a concentration dependent increase in the viability of cells exposed to deoxycholic acid by 110% and lithocholic acid by 20%. Similarly, cytotoxicity induced by faecal water was significantly (p<0.05) reduced by inulin (2.5%) and lactobionic acid (0.25%) with cell viability increasing by 40% and 20% respectively. Secondary bile acids lithocholic and deoxycholic acid did not induce E. coll PQ 37 SOS response over a range of concentrations (0.25-2mM), however both faecal water (50% v/v)and 4NQO (2jig/ml) induced p-galactosidase activity. Inulin and lactulose at 2.5% significantly reduced the SOSIP of faecal water by 70% and 57% respectively and by 24% and 74.1% for 4NQO.

In conclusion, these findings suggest the protective benefits attributed to synbiotic applications in bile acid/salt stress are specific to the nature and type of bile acids with a rather complex physiological response being induced. Prebiotics exerts a concentration dependent impact on BSH activity and might explain the hypocholesterolemic effects attributed to synbiotic applications. It is also interesting to know that the consumption of prebiotic alone particularly inulin may confer beneficial effects beyond those associated with
probiotic survival and growth.

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