Effect of increased ratio of butyrate to physiological concentrations of acetate and propionate on intestinal integrity and IL-8 secretion in Caco-2 cells

Abstract

<p>Background: Inflammatory bowel diseases (IBD) are a growing global health problem. Current pharmacological therapies are not effective in all IBD patients, tend to cause side effects and in some cases lose effectiveness when used for a prolonged period of time. Hence, there is a need to develop dietary interventions that are safe and be applicable to all. Chronic inflammation of the gut could be combated by increasing the consumption of dietary fiber which would lead to an increased butyrate production in the colon. Butyrate has been shown to improve intestinal integrity and suppress the secretion of pro-inflammatory cytokine, IL-8 – which is commonly found at high concentrations in IBD patients.</p> <p>Hypothesis: When inflamed human intestinal cells (Caco-2) are exposed to an increased ratio of butyrate to physiological concentrations of acetate and propionate, the intestinal integrity would be improved and the secretion of IL-8 would be suppressed.</p> <p>Experimental Design: Caco-2 cells were grown to 90-100% confluence on Transwell plate inserts for 4 days. Then, inflammation was induced for 24h. The inflamed and non-inflamed Caco-2 cells were then exposed to: (i) 60 mM acetate (Ac): 10mM propionate (Pr): 10mM butyrate(Bu) (lower butyrate ratio) or (ii) 60 mM Ac: 10mM Pr: 20mM Bu (higher butyrate ratio) for 0h, 12h or 24h. Intestinal integrity was measured by amount of Lucifer yellow transported from the apical to basolateral chamber of Transwell plates. IL-8 secretion was measured by ELISA and cell damage was measured by the lactate dehydrogenase cytotoxicity assay.</p> <p>Results: Cells that were inflamed significantly decreased the intestinal integrity (p=0.0094), increased the secretion of IL-8 (p<0.0001) and induced higher cell damage (p<0.0001) than non-inflamed Caco-2 cells, n=54. SCFA mix containing higher butyrate ratio (20mM) significantly reduced the intestinal integrity of inflamed cells (p=0.0238, n=27). Higher butyrate ratio did not affect the secretion of IL-8; but it led to greater cell-damage (p=0.0161, n=54). Prolonged exposure to SCFAs improved intestinal integrity (p<0.0001), increased the secretion of IL-8 (p<0.0001) and led to greater cell damage (p<0.0001), n=36.</p> <p>Conclusion: Our hypothesis was disproved. But the important lesson to be learned is that the effect of butyrate in colonocyte models should be studied in the presence of other SCFAs, to assure physiological relevance.</p>