The role of carbon monoxide in choleresis and cholestasis

• Main Authors: Chi-YaKao, 高琪雅
• Other Authors: Shu-Chu Shiesh
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/51648738717110094252

碩士 === 國立成功大學 === 醫學檢驗生物技術學系碩博士班 === 98 === Cholestasis is a condition caused by an impairment of bile excretion from liver into the small intestine. Prolonged cholestasis results in liver injury by accumulating toxic bile salts in hepatocytes. Bile excretion is an osmotic process driven by secretion of bile acids, total glutathione, and bicarbonate in hepatocytes and cholangiocytes. Carbon monoxide (CO), product of heme oxygenase, has been shown to exert physiological roles in biliary excretion. However, whether CO stimulates or suppresses bile formation remains controversial. This study was aimed to investigate the effects of CO on bile output and its underlying mechanism. The common bile ducts of Sprague-Dawley rats were cannulated with a polyethylene P-10 tube to collect bile hourly. Dichloromethane (DCM) was used as a CO pro-drug. The effect of CO on bile formation was examined. To further investigate the mechanism of CO effect, biliary pH, concentrations of bicarbonate, total bile acids, total glutathione (GSH) and nitric oxide were determined. A significant increase of carboxyhemoglobin (COHb) was observed at the fourth hour after DCM administration. Basal bile output and biliary total GSH concentration were increased 1.6 fold and 2.1 fold, respectively, at the fourth hour after DCM administration. Furthermore, CO-induced increase in bile output was associated with a concomitant increase of biliary glutathione disulfide (GSSG) (fold change in DCM vs. control: 0.71 ± 0.16 vs. 0.35 ± 0.05, p＜0.05) instead of GSH. However, no significant change of bicarbonate and total bile acids concentration in bile was identified after DCM administration. At the fourth hour after DCM administration, the rats had significantly higher serum nitrate and nitrite levels, compared to control (224.0 ± 17.1 μmol/L vs. 165.6 ± 19.8 μmol/L, p＜0.05). In addition, the expression of hepatic inducible nitric oxide synthase (iNOS) was significantly higher in DCM group than that in control group (p＜0.05). DCM administration further increased the expression of hepatic Mrp2 (DCM vs. control: 0.30 ± 0.04 vs. 0.15 ± 0.01, p＜0.01). The administration of Nω-nitro-L-arginine methyl ester (L-NAME), inhibitor of NOS, abolished CO-induced bile formation and biliary GSSG excretion, while biliary GSH remain unchanged. In the animal model of estrogen-induced cholestasis, CO supplement improved bile output through stimulating total GSH and total bile acid excretions, and decreased serum levels of ALP, total bile acid, and total bilirubin. In conclusion, CO increased biliary GSSG excretion by inducing iNOS and Mrp2 expressions and resulted in choleresis. CO-induced choleresis may play a role in protecting against estrogen-induced cholestasis.