Mitochondrial damage, ATP depletion and inhibition of ion transporter activities induced by non-conjugated bile acids in human colonic crypts

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MITOCHONDRIAL DAMAGE, ATP DEPLETION AND INHIBITION OF ION TRANSPORTER ACTIVITIES INDUCED BY NON-CONJUGATED BILE ACIDS IN HUMAN COLONIC CRYPTS

Pallagi-Kunstár É.¹, Farkas K.¹, Rakonczay Z. Jr.¹, Nagy F.¹, Molnár T.¹, Szepes Z.¹, Venglovecz V.², Rázga Z.³, Maléth J. ¹, Orbán K.¹, Tóth K.¹, Wittmann T.¹, Hegyi P.¹

First Department of Medicine¹, Department of Pharmacology and Pharmacotherapy², Department of Pathology³, University of Szeged, Szeged, Hungary

Introduction: Under pathophysiological conditions, such as short bowel syndrome, bile acids can reach the colon in high concentrations and can induce diarrhea.

Our aim was to investigate whether impaired ion transport activities are involved in the pathomechanism of bile acid-induced diarrhea.

Methods: Colonic biopsies were obtained from control patients (with negative colonoscopic findings) and from cholecystectomised/ileum-resected patients with/without diarrhea. Colonic crypts were isolated by collagenase digestion, and intracellular pH (pH_i), Ca²⁺ concentration ([Ca²⁺]i) and ATP levels (ATPi) were measured by microspectrofluorometry. Na⁺/H⁺ exchangers (NHEs), Na⁺/HCO3-

cotransporter, Cl^-/HCO3-

exchanger (AE) activities were determined. Intracellular mophological changes were analysed with transmission electronmicroscopy (TEM).

Results: The non-conjugated chenodeoxycholate (CDC) and the conjugated glycochenodeoxycholate (GCDC) caused dose-dependent acidosis in colonic crypts. The pHi

decrease was significantly greater in case of CDC vs. GCDC. 0.3 mM CDC strongly inhibited the activities of acid/base transporters. Chelation of intracellular Ca²⁺ did not prevent the inhibitory effect of CDC. 0.3-1 mM CDC significantly and irreversibly reduced ATPi. TEM showed mitochondrial damage after 1 mM CDC-treatment, but no such alteration was detected in case of lower concentrations of CDC or 1 mM GCDC. Impaired NHE and AE activities were observed in cholecystectomised/ileum-resected patients suffering from diarrhea compared to control patients.

Conclusion: Non-conjugated bile acids cause intracellular acidosis, ATP_i depletion, mitochondrial damage and inhibit the ion transporters of colonic epithelial cells. These processes may reduce fluid and electrolyte absorption in the colon and promote the development of diarrhea.

This work was supported by OTKA, MTA and NFÜ: TÁMOP-4.2.2/B-10/1-2010-0012