Taurodeoxycholate Modulates Apical Cl−/OH− Exchange Activity in Caco2 Cells

Abstract

Bile acid malabsorption has been shown to be associated with diarrhea in cases such as ileal resection Crohn's disease of the ileum, and radiation enteritis. The mechanisms of bile acid-induced diarrhea are not fully understood. Although the induction of colonic chloride secretion in response to bile acids has been extensively investigated, to date the direct effect of bile acids on intestinal chloride absorption has not been well defined. Therefore, the current studies were undertaken to investigate the effect of bile acids on the apical Cl(-)/OH(-) exchange process utilizing Caco2 monolayers as an in vitro cellular model. Cl(-)/OH(-) exchange activity was measured as DIDS-sensitive pH gradient-driven (36)Cl uptake. The results are summarized as follows: (i) short-term exposure (20 min) of Caco2 cells to taurodeoxycholate (TDC; 200 microM) and glycochenodeoxycholate (GCDC; 200 microM) acids significantly inhibited apical Cl(-)/OH(-) exchange (by approximately 60-70%); (ii) the Ca(2+) chelator BAPTA-AM blocked the inhibition by TDC; (iii) the reduction in Cl(-)/OH(-) exchange by TDC was reversed by the PKC inhibitor, chelerythrine chloride; (iv) functional and inhibitor studies indicated that TDC induced inhibition of Cl(-)/OH(-) exchange was mediated via the activation of the PKC beta I isoform; (v) the effect of TDC on apical Cl(-)/OH(-) exchange was completely blocked by the PI3 kinase inhibitor LY294002 (5 microM); and (vi) the PKA inhibitor, RpcAMP, had no effect on TDC induced inhibition of Cl(-)/OH(-) exchange. In conclusion, our studies provide direct evidence for inhibition of human intestinal apical Cl(-)/OH(-) exchange activity by bile acids via Ca(2+)-, PI3 kinase-, and PKC beta I-dependent pathways in Caco2 cells.

Mechanisms of lysophosphatidic acid (LPA) mediated stimulation of intestinal apical Cl−/OH− exchange

“…Our data showed that the effects of LPA on Cl Ϫ /OH Ϫ exchange activity were blocked in the presence of PI3 kinase and Akt inhibitors, indicating the involvement of PI3 kinaseAkt pathway. The involvement of PI3 kinase-dependent pathway is in agreement with other previous studies from our laboratory that have shown the involvement of PI3 kinase in the regulation of Cl Ϫ /OH Ϫ exchange activity by Lactobacillus acidophilus, taurodeoxycholic acid, and PMA (1,8,33). Furthermore, PI3 kinase has been shown to be involved in medi- Fig.…”

Therapeutic targeting of bile acids

“…These clinical observations were consistent with the physiological studies performed in animal models and in vitro (13,28). Fluid secretion occurs through a number of mechanisms, including stimulation of intracellular messengers such as cAMP and calcium, which results in activation of chloride secretion through the cystic fibrosis transmembrane regulator (2,3,38). Apart from inducing colonic secretion, BAs induce highamplitude propagated contractions of the colon (4).…”

New insights into intestinal secretion

“…3 Another example of clinical impact is (deconjugated) bile acid malabsorption secondary to ileal resection or disease, which results in Ca 2+ -mediated and PKC-mediated colonic anion secretion and diarrhoea. 4 While secretory diarrhoea may be severe and life threatening (eg, cholera), basal secretion ensures an obligatory faecal water content. This is especially apparent in cystic fibrosis, where deficiency of apical cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels and the absence of chloride-driven basal water secretion causes meconium ileus in newborns.…”