Weeks Of Bile Duct Ligation Research Articles

On the role of lipid peroxidation in the pathogenesis of liver damage induced by long-standing cholestasis

Previous studies have suggested a possible involvement of free radical reactions in the pathogenesis of cholestatic liver injury as well as in the modulation of hepatic fibrogenesis. In this study we investigated whether lipid peroxidation is involved in the development of chronic liver damage induced by long-standing cholestasis. For this purpose we have used the rat model of bile duct ligation (BDL), which leads to liver fibrosis and cirrhosis. Using this model we observed that the development of chronic liver damage was associated with the onset of lipid peroxidation, as pointed out by detection of carbonyl compounds, 4-hydroxynonenal (HNE) and malondialdehyde (MDA), in BDL livers and of fluorescent adducts between MDA and serum proteins. Lipid peroxidation was a relatively late event (starting after 1–2 weeks of BDL) and was unrelated to the early development of liver necrosis and cholestasis (already evident after 72 h after BDL). A positive significant linear correlation between the kinetic of infiltration of neutrophils and of a monocyte/macrophage population in BDL livers and MDA and HNE generation in the same organs is presented, indicating a close link between lipid peroxidation and the activation of inflammatory cells. We also observed that a positive linear correlation exists between collagen deposition in these livers and hepatic production of MDA and HNE. This event, which is accompanied by an increase in the number of fat storing cells (FSC, the cells that produce collagen in fibrotic liver), suggests that lipid peroxidation in this model may contribute to stimulate collagen synthesis by proliferating FSC.

Interferon-alpha preserves erythrocyte and hepatocyte ATPase activities from liver damage induced by prolonged bile duct ligation in the rat.

Interferons have been used to treat chronic hepatitis owing to their antiviral properties. However, now interferons are recognized to inhibit collagen production. Because fibrosis has been associated with liver damage and dysfunction, the effects of interferon-alpha 2b on biliary obstruction-induced cirrhosis were investigated. Obstructive jaundice was induced in male Wistar rats (ca. 200 g) by double ligation and division of the common bile duct. Control rats were sham operated. Interferon-alpha 2b (IFN-alpha; 1000 000 IU per rat) was administered subcutaneously daily after surgery. The animals were sacrificed after 4 weeks of bile duct ligation (BDL) or sham operation. Bilirubins and serum enzyme activities of alkaline phosphatase and gamma-glutamyl transpeptidase (determined as markers of liver damage) increased several-fold after BDL. Erythrocyte and hepatocyte plasma membrane Na+/K+- and Ca2+-ATPase activities decreased significantly in the BDL group. Administration of IFN-alpha to BDL rats resulted in a partial normalization of serum markers of liver damage. The normal activity of both ATPases on erythrocyte and hepatocyte plasma membranes was completely preserved by IFN-alpha. It is concluded that interferons possess interesting hepatoprotective effects not related to their antiviral properties but probably associated with their antifibrogenic effect.

Experimental biliary fibrosis correlates with increased numbers of fat-storing and Kupffer cells, and portal endotoxemia

In the present study, we have investigated the correlation between hepatic fibrosis in rats subjected to bile duct ligation, the numbers of Kupffer and fat-storing cells, and the level of endotoxin in both the portal and systemic circulation. The extent of hepatic fibrosis was measured by morphometry. Kupffer cells were identified by indirect immunoperoxidase staining using ED-2 anti-macrophage antibody. Fat-storing cells were stained with DE-B-5 anti-desmin antibody. Endotoxin levels were determined by the Limulus Lysate test. Following bile duct ligation, connective tissue septa rapidly developed in periportal areas. After 1 week, the volume density of connective tissue had increased from 0.6±0.1% in control animals to 3.8±1.1%. After 2 weeks, this volume increased to 19.9±1.3%, and after 3 weeks to 34.3±2.7%. The number of periportal fat-storing cells increased 2.8-fold during the first 2 weeks, whereas pericentral fat-storing cells increased only 1.7-fold. After 2 weeks, no further increase was observed. During the first week of bile duct ligation, the number of Kupffer cells increased nearly two-fold. Thereafter, no further increase was detected. In control rats, only two of ten rats showed low amounts of endotoxin in the portal blood. Portal endotoxemia increased with time after bile duct ligation. After 3 weeks, all rats were positive. The measured endotoxin levels were approximately 7 times higher than in control rats. We conclude that the development of fibrosis secondary to experimental bile duct ligation is accompanied by portal endotoxemia, and increases in the numbers of Kupffer and periportal fat-storing cells. We found a significant correlation between portal endotoxemia, the number of Kupffer and fat-storing cells, and the extent of fibrous septa, supporting the view that high endotoxemia levels coincide with Kupffer cell activation and fibrogenesis.

Characterization of mechanisms causing hypoalbuminemia in rats with long-term bile duct ligation

Albumin kinetics and albumin synthesis were studied in rats with chronic bile duct ligation and compared with pair-fed control rats. The plasma albumin concentration was significantly reduced in bile duct ligated rats as compared to control rats, averaging 35±1 vs 40±2 g/l after 2 weeks and 28±3 vs 38±5 g/l after 4 weeks of bile duct ligation. Two weeks after the bile duct ligatio, the transcapillary escape rate of albumin was increased by 60% in bile duct ligated rats, whereas the plasma volume was unchanged. Albumin synthesis expressed as a fraction of total liver protein synthesis, as assessed by the ‘flooding’ dose method using [ 3H]phenylalanine, was decreased by 46% in bile duct ligated rats. However, absolute albumin synthesis expressed per 100 g body weight was not different from control rats. Four weeks after bile duct ligation, the transcapillary escape rate of albumin was no longer different, whereas the plasma volume was increased by 38% in bile duct ligated rats. At this time point, albumin synthesis as a fraction of total liver protein synthesis was decreased by 60% in bile duct ligated rats, and absolute albumin synthesis expressed per 100 g body weight averaged 80±8 vs 53±12 mg/(day×100 g) in control and bile duct ligated rats ( p<0.05). The hepatic steady-state levels of albumin mRNA determined by Northern blot analysis were decreased in bile duct ligated rats at both 2 and 4 weeks after surgery. The studies suggest that reduced plasma albumin concentrations in bile duct ligated rats are caused by increased capillary permeability and lack of compensatory increase in albumin synthesis 2 weeks, and by increased plasma volume and decreased albumin synthesis 4 weeks after surgery.

Regulation of cholesterol and bile acid homoeostasis in bile-obstructed rats

We examined how total blockage of biliary excretion, the major pathway through which cholesterol and bile acids are removed from the body, affects liver function, cholesterol and bile acid metabolism and homoeostasis. After 4 weeks of bile-duct ligation, rats showed impaired liver function, as documented by elevations in serum bilirubin and alkaline phosphatase activity. Moreover, bile-duct ligation decreased by about 30% both the amount of microsomal cytochrome P-450 in the liver and the elimination of aminopyrine in vivo, a reliable index in vivo of microsomal mixed-function oxidase activity. Cholesterol and bile acid contents in livers of bile-duct-ligated rats were doubled compared with sham-operated controls. Despite the increase in the contents of cholesterol and bile acids in liver, activities of the respective rate-limiting enzymes, 3-hydroxy-3-methylglutaryl-CoA reductase and cholesterol 7 alpha-hydroxylase, were doubled. Serum concentrations of bile acids and free cholesterol increased 25- and 4-fold respectively. The large increase in serum bile acids was associated with a 380-fold increase in the urinary excretion of bile acids. Although there is a general decrease in cytochrome P-450 content and drug metabolism involving cytochrome P-450-containing hydroxylases, the activity of cholesterol 7 alpha-hydroxylase, also a cytochrome P-450-containing enzyme, is actually increased. These data show that complete obstruction of the bile duct results in the selective impairment of microsomal cytochrome P-450. Increased activity of 7 alpha-hydroxylase, bile acid synthesis and urinary excretion provides an alternative excretory pathway that helps to maintain cholesterol homoeostasis when the biliary excretory pathway is eliminated.