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Physiological concentrations of bile acids down-regulate agonist induced secretion in colonic epithelial cells.

Keating N, Mroz MS, Scharl MM, Marsh C, Ferguson G, Hofmann AF, Keely SJ - J. Cell. Mol. Med. (2009)

Bottom Line: At high concentrations (0.5-1 mM), DCA acutely stimulated Cl(-) secretion but this effect was associated with cell injury, as evidenced by decreased transepithelial resistance (TER) and increased lactate dehydrogenase (LDH) release.The EGFr inhibitor, AG1478, and the protein synthesis inhibitor, cycloheximide, reversed the antisecretory effects of DCA, while the MAPK inhibitors, PD98059 and SB203580, did not.In summary, our studies suggest that, in contrast to its acute prosecretory effects at pathophysiological concentrations, lower, physiologically relevant, levels of DCA chronically down-regulate colonic epithelial secretory function.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Medicine, Royal College of Surgeons in Ireland, Dublin, Ireland.

ABSTRACT
In patients with bile acid malabsorption, high concentrations of bile acids enter the colon and stimulate Cl(-) and fluid secretion, thereby causing diarrhoea. However, deoxycholic acid (DCA), the predominant colonic bile acid, is normally present at lower concentrations where its role in regulating transport is unclear. Thus, the current study set out to investigate the effects of physiologically relevant DCA concentrations on colonic epithelial secretory function. Cl(-) secretion was measured as changes in short-circuit current across voltage-clamped T(84) cell monolayers. At high concentrations (0.5-1 mM), DCA acutely stimulated Cl(-) secretion but this effect was associated with cell injury, as evidenced by decreased transepithelial resistance (TER) and increased lactate dehydrogenase (LDH) release. In contrast, chronic (24 hrs) exposure to lower DCA concentrations (10-200 microM) inhibited responses to Ca(2+) and cAMP-dependent secretagogues without altering TER, LDH release, or secretagogue-induced increases in intracellular second messengers. Other bile acids - taurodeoxycholic acid, chenodeoxycholic acid and cholic acid - had similar antisecretory effects. DCA (50 microM) rapidly stimulated phosphorylation of the epidermal growth factor receptor (EGFr) and both ERK and p38 MAPKs (mitogen-activated protein kinases). The EGFr inhibitor, AG1478, and the protein synthesis inhibitor, cycloheximide, reversed the antisecretory effects of DCA, while the MAPK inhibitors, PD98059 and SB203580, did not. In summary, our studies suggest that, in contrast to its acute prosecretory effects at pathophysiological concentrations, lower, physiologically relevant, levels of DCA chronically down-regulate colonic epithelial secretory function. On the basis of these data, we propose a novel role for bile acids as physiological regulators of colonic secretory capacity.

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Structure–activity relationships for bile acids in regulating epithelial secretory function. (A) Monolayers of T84 cells were exposed bilaterally to increasing concentrations of DCA (n= 5), TDCA (n= 5), or cholic acid (n= 3) and maximal Isc responses were measured. (B) T84 cell monolayers were exposed to increasing concentrations of bilateral DCA (n= 5), TDCA (n= 4), and cholic acid (n= 5) for 24 hrs after which secretory responses to CCh (100 μM) were measured. (C) Monolayers of T84 cells were exposed to DCA (50 μM; n= 4) or TDCA (200 μM; n= 4) on the apical, basolateral, or both sides for 24 hrs after which cells were voltage‐clamped and subsequent secretory responses to CCh (100 μM) were measured. **P < 0.01; ***P < 0.001.
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f4: Structure–activity relationships for bile acids in regulating epithelial secretory function. (A) Monolayers of T84 cells were exposed bilaterally to increasing concentrations of DCA (n= 5), TDCA (n= 5), or cholic acid (n= 3) and maximal Isc responses were measured. (B) T84 cell monolayers were exposed to increasing concentrations of bilateral DCA (n= 5), TDCA (n= 4), and cholic acid (n= 5) for 24 hrs after which secretory responses to CCh (100 μM) were measured. (C) Monolayers of T84 cells were exposed to DCA (50 μM; n= 4) or TDCA (200 μM; n= 4) on the apical, basolateral, or both sides for 24 hrs after which cells were voltage‐clamped and subsequent secretory responses to CCh (100 μM) were measured. **P < 0.01; ***P < 0.001.

Mentions: The secretory and antisecretory effects of other naturally occurring bile acids were also examined. Taurodeoxycholic acid (TDCA, the taurine conjugate of DCA) and cholic acid (CA, the trihydroxy, primary bile acid from which DCA is formed) were selected for study. Similar to DCA, and as previously reported [19], TDCA stimulated Cl− secretion across T84 cells at relatively high concentrations with an EC50 of 427.5 ± 80.2 μM (n= 5) (Fig. 4A). In contrast, CA did not alter basal Isc. However, similar to DCA, we found that prolonged exposure to relatively low concentrations of both TDCA and CA inhibited secretory responses to CCh (Fig. 4B). In further analyses we examined the ability of naturally occurring isomers of DCA to alter agonist‐stimulated Isc responses and found that both isodeoxycholic acid (iso‐DCA) and lagodeoxycholic (lago‐DCA) acid were approximately equipotent to DCA in exerting antisecretory effects (Table 1). Similarly, the dihydroxy primary bile acid, chenodeoxycholic acid (CDCA), was also found to be equipotent with DCA in inhibiting agonist‐stimulated secretory responses. Finally, we examined the sidedness by which conjugated and unconjugated bile acids exert their antisecretory effects. Although DCA was equally effective when applied either apically or basolaterally, TDCA was active only on the basolateral side (Fig. 4C).


Physiological concentrations of bile acids down-regulate agonist induced secretion in colonic epithelial cells.

Keating N, Mroz MS, Scharl MM, Marsh C, Ferguson G, Hofmann AF, Keely SJ - J. Cell. Mol. Med. (2009)

Structure–activity relationships for bile acids in regulating epithelial secretory function. (A) Monolayers of T84 cells were exposed bilaterally to increasing concentrations of DCA (n= 5), TDCA (n= 5), or cholic acid (n= 3) and maximal Isc responses were measured. (B) T84 cell monolayers were exposed to increasing concentrations of bilateral DCA (n= 5), TDCA (n= 4), and cholic acid (n= 5) for 24 hrs after which secretory responses to CCh (100 μM) were measured. (C) Monolayers of T84 cells were exposed to DCA (50 μM; n= 4) or TDCA (200 μM; n= 4) on the apical, basolateral, or both sides for 24 hrs after which cells were voltage‐clamped and subsequent secretory responses to CCh (100 μM) were measured. **P < 0.01; ***P < 0.001.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4940785&req=5

f4: Structure–activity relationships for bile acids in regulating epithelial secretory function. (A) Monolayers of T84 cells were exposed bilaterally to increasing concentrations of DCA (n= 5), TDCA (n= 5), or cholic acid (n= 3) and maximal Isc responses were measured. (B) T84 cell monolayers were exposed to increasing concentrations of bilateral DCA (n= 5), TDCA (n= 4), and cholic acid (n= 5) for 24 hrs after which secretory responses to CCh (100 μM) were measured. (C) Monolayers of T84 cells were exposed to DCA (50 μM; n= 4) or TDCA (200 μM; n= 4) on the apical, basolateral, or both sides for 24 hrs after which cells were voltage‐clamped and subsequent secretory responses to CCh (100 μM) were measured. **P < 0.01; ***P < 0.001.
Mentions: The secretory and antisecretory effects of other naturally occurring bile acids were also examined. Taurodeoxycholic acid (TDCA, the taurine conjugate of DCA) and cholic acid (CA, the trihydroxy, primary bile acid from which DCA is formed) were selected for study. Similar to DCA, and as previously reported [19], TDCA stimulated Cl− secretion across T84 cells at relatively high concentrations with an EC50 of 427.5 ± 80.2 μM (n= 5) (Fig. 4A). In contrast, CA did not alter basal Isc. However, similar to DCA, we found that prolonged exposure to relatively low concentrations of both TDCA and CA inhibited secretory responses to CCh (Fig. 4B). In further analyses we examined the ability of naturally occurring isomers of DCA to alter agonist‐stimulated Isc responses and found that both isodeoxycholic acid (iso‐DCA) and lagodeoxycholic (lago‐DCA) acid were approximately equipotent to DCA in exerting antisecretory effects (Table 1). Similarly, the dihydroxy primary bile acid, chenodeoxycholic acid (CDCA), was also found to be equipotent with DCA in inhibiting agonist‐stimulated secretory responses. Finally, we examined the sidedness by which conjugated and unconjugated bile acids exert their antisecretory effects. Although DCA was equally effective when applied either apically or basolaterally, TDCA was active only on the basolateral side (Fig. 4C).

Bottom Line: At high concentrations (0.5-1 mM), DCA acutely stimulated Cl(-) secretion but this effect was associated with cell injury, as evidenced by decreased transepithelial resistance (TER) and increased lactate dehydrogenase (LDH) release.The EGFr inhibitor, AG1478, and the protein synthesis inhibitor, cycloheximide, reversed the antisecretory effects of DCA, while the MAPK inhibitors, PD98059 and SB203580, did not.In summary, our studies suggest that, in contrast to its acute prosecretory effects at pathophysiological concentrations, lower, physiologically relevant, levels of DCA chronically down-regulate colonic epithelial secretory function.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Medicine, Royal College of Surgeons in Ireland, Dublin, Ireland.

ABSTRACT
In patients with bile acid malabsorption, high concentrations of bile acids enter the colon and stimulate Cl(-) and fluid secretion, thereby causing diarrhoea. However, deoxycholic acid (DCA), the predominant colonic bile acid, is normally present at lower concentrations where its role in regulating transport is unclear. Thus, the current study set out to investigate the effects of physiologically relevant DCA concentrations on colonic epithelial secretory function. Cl(-) secretion was measured as changes in short-circuit current across voltage-clamped T(84) cell monolayers. At high concentrations (0.5-1 mM), DCA acutely stimulated Cl(-) secretion but this effect was associated with cell injury, as evidenced by decreased transepithelial resistance (TER) and increased lactate dehydrogenase (LDH) release. In contrast, chronic (24 hrs) exposure to lower DCA concentrations (10-200 microM) inhibited responses to Ca(2+) and cAMP-dependent secretagogues without altering TER, LDH release, or secretagogue-induced increases in intracellular second messengers. Other bile acids - taurodeoxycholic acid, chenodeoxycholic acid and cholic acid - had similar antisecretory effects. DCA (50 microM) rapidly stimulated phosphorylation of the epidermal growth factor receptor (EGFr) and both ERK and p38 MAPKs (mitogen-activated protein kinases). The EGFr inhibitor, AG1478, and the protein synthesis inhibitor, cycloheximide, reversed the antisecretory effects of DCA, while the MAPK inhibitors, PD98059 and SB203580, did not. In summary, our studies suggest that, in contrast to its acute prosecretory effects at pathophysiological concentrations, lower, physiologically relevant, levels of DCA chronically down-regulate colonic epithelial secretory function. On the basis of these data, we propose a novel role for bile acids as physiological regulators of colonic secretory capacity.

Show MeSH
Related in: MedlinePlus