Higher Cholesterol Saturation Research Articles

The Spectrum of Liver Diseases Related toABCB4Gene Mutations: Pathophysiology and Clinical Aspects

Class III multidrug resistance P-glycoproteins, Mdr2 in mice and MDR3 in human, are canalicular phospholipid translocators involved in biliary phospholipid (phosphatidylcholine) excretion. The role of an ABCB4 gene defect in liver disease has been initially proven in a subtype of progressive familial intrahepatic cholestasis called PFIC3, a severe pediatric liver disease that may require liver transplantation. Several ABCB4 mutations have been identified in children with PFIC3 and are associated with low level of phospholipids in bile leading to a high biliary cholesterol saturation index. ABCB4 mutations are associated with loss of canalicular MDR3 protein and /or loss of protein function. There is evidence that a biallelic or monoallelic ABCB4 defect causes or predisposes to several human liver diseases (PFIC3, low phospholipid associated cholelithiasis syndrome, intrahepatic cholestasis of pregnancy, drug-induced liver injury, transient neonatal cholestasis, adult biliary fibrosis, or cirrhosis). Most patients with MDR3 deficiency have a favorable outcome with ursodeoxycholic acid (UDCA) therapy, but some PFIC3 patients who do not respond to UDCA treatment still require liver transplantation. The latter should be good candidates for a targeted pharmacologic approach and/or to cell therapy in the future.

Decreased NPC1L1 expression in the liver from Chinese female gallstone patients

BackgroundCholesterol gallstone disease is a very common disease in both industrialized and developing countries. Many studies have found that cholesterol gallstones are more common in women than men. The molecular mechanisms underlying the relationship between female gallstone disease and hepatic sterol transporters are still undergoing definition and have not been evaluated in humans.AimsThe aim of this study is to probe for underlying hepatic molecular defects associated with development of gallstones in female.Methods/ResultsFifty-seven nonobese, normolipidemic Chinese female gallstone patients (GS) were investigated with 12 age- and body mass index-matched female gallstone-free controls (GSF). The bile from the female GS had higher cholesterol saturation than that from the female GSF. The hepatic NPC1L1 mRNA levels were lower in female GS, correlated with SREBP2 mRNA. NPC1L1 downregulation was confirmed at protein levels. Consistently, immunohistochemistry showed decreased NPC1L1 expression in female GS.ConclusionsThe decreased hepatic NPC1L1 levels in female GS might indicate a downregulated reabsorption of biliary cholesterol in the liver, which, in turn, leads to the cholesterol supersaturation of bile. Our data are consistent with the possibility that hepatic NPC1L1 may be mediated by SREBP2.

Increased expression of LXRα, ABCG5, ABCG8, and SR-BI in the liver from normolipidemic, nonobese Chinese gallstone patients

Cholesterol supersaturation of bile is one prerequisite for gallstone formation. In the present study of Chinese patients with gallstones, we investigated whether this phenomenon was correlated with the hepatic expression of genes participating in the metabolism of cholesterol and bile acids. Twenty-two nonobese, normolipidemic patients (female-male, 11:11) with gallstones were investigated with 13 age- and body mass index-matched gallstone-free controls (female-male, 10:3). The bile from the gallstone patients had higher cholesterol saturation than that from the controls. The mRNA levels of ABCG5, ABCG8, and liver X receptor alpha (LXRalpha) in the gallstone patients were increased by 51, 59, and 102%, respectively, and significantly correlated with the molar percentage of biliary cholesterol and cholesterol saturation index (CSI). The mRNA and protein levels of the hepatic scavenger receptor class B type I (SR-BI) were increased, and a significant correlation was found between the protein levels and the CSI. No differences were recorded between the two groups concerning the hepatic synthesis of cholesterol, bile acids, and esterification of cholesterol. Our results suggest that the upregulation of ABCG5/ABCG8 in gallstone patients, possibly mediated by increased LXRalpha, may contribute to the cholesterol supersaturation of bile. Our data are consistent with the possibility that increased amounts of biliary cholesterol may originate from plasma HDL cholesterol by enhanced transfer via SR-BI.

Role of multidrug resistance 3 deficiency in pediatric and adult liver disease: one gene for three diseases.

Class III multidrug resistance P-glycoproteins, mdr2 in mice and MDR3 in humans, are canalicular phospholipid translocators involved in biliary phospholipid (phosphatidylcholine) excretion. The role of an MDR3 gene defect in liver disease was initially suspected in a subtype of progressive familial intrahepatic cholestasis called PFIC3. Several MDR3 mutations have been identified in children with PFIC3 and are associated with a low level of phospholipids in bile, leading to a high biliary cholesterol saturation index. Mutations leading to a truncated protein are associated with an absence of canalicular MDR3 protein. The phenotypic spectrum of PFIC3 ranges from neonatal cholestasis to cirrhosis in young adults. There is now strong evidence that in addition to PFIC3, an MDR3 defect can be involved in intrahepatic cholestasis of pregnancy and in cholesterol gallstone disease. Therefore, at least three human liver diseases are due to a single gene deficiency. Patients with PFIC3 due to MDR3 deficiency may benefit from ursodeoxycholic acid therapy and could be good candidates for cell therapy in the future.

Alterations of bile acid composition in gallstones, bile, and liver of patients with hepatolithiasis, and their etiological significance.

A detailed comparison was made of the bile acid composition in gallstones (brown pigment stones) and paired bile and liver from both affected and unaffected lobes by gallstones, which were taken at operation from 16 patients with hepatolithiasis, with the aim of elucidating whether stone formation is derived from possible local disturbances limited to intrahepatic bile ducts. Brown pigment stones in the intrahepatic bile ducts, most of which were accompanied by bile with high cholesterol saturation, had significantly more cholesterol, and less calcium bilirubinate and bile acid than those found in the extrahepatic bile ducts. Intrahepatic gallstones had significantly lower amounts of secondary and unconjugated bile acids, the bile acids modified by bacterial intervention, than extrahepatic stones. Bile specimens from both affected and unaffected lobes showed significantly increased molar percentages of cholesterol and decreased percentages of bile acids than bile from controls. In contrast, liver specimens from both lobes showed significantly higher concentrations of total bile acids. Secondary bile acids were present in a much lower proportion in bile and liver from both lobes than in bile and liver from controls. On the other hand, unconjugated bile acids were present in a much higher proportion in bile and liver from patients and only in negligible amounts in bile from controls. Furthermore, the plasma levels of mevalonate and those of 7 alpha-hydroxy-4-cholestene-3-one were found to be significantly higher and lower in patients than in controls, respectively, indicating that in hepatolithiasis cholesterol synthesis might increase and bile acid synthesis might decrease in the liver. These findings suggested that alterations of bile acid composition in gallstones, bile, and liver of patients with hepatolithiasis may be attributed to not only secondary changes resulting from local disturbances limited to intrahepatic bile ducts but also possible primary alterations of hepatocyte metabolism, such as bile acid conjugation and primary defects in cholesterol and bile acid synthesis.

Bile concentration promotes nucleation of cholesterol monohydrate crystals by increasing the cholesterol concentration in the vesicles

Cholesterol in bile is solubilized in mixed micelles and cholesterol-phospholipid vesicles. Biliary cholesterol supersaturation and increased concentration of bile in the gallbladder promotes nucleation of cholesterol monohydrate crystals and gallstone formation, possibly by creating unstable vesicles with a high cholesterol/phospholipid ratio. In the present study super-saturated and unsaturated biles (cholesterol saturation index (CSI) 1.4 and 0.8 respectively) were prepared with concentrations typical of gallbladder and more dilute hepatic bile (total lipid concentration (TLCo) 10 and 2.5 g dl-1 respectively). The distribution of cholesterol between vesicles and micelles, and vesicular cholesterol/phospholipid ratio were studied using ultracentrifugation and gel-permeation chromatography. The nucleation time of cholesterol crystals was determined in whole model bile, and in the vesicular and micellar peak fractions. Increased CSI and bile dilution led to an increased proportion of cholesterol solubilized in vesicles. The concentration of bile did not influence vesicular cholesterol/phospholipid ratio. The vesicular cholesterol/phospholipid ratio found in gel-permeation chromatography experiments was similar at high and low CSI, whereas the ratio was significantly higher in supersaturated than in unsaturated biles in ultracentrifugation studies. Nucleation of cholesterol crystals from whole model bile was more rapid at the higher bile concentration and higher cholesterol saturation. Nucleation time in whole model bile correlated significantly with nucleation time in the corresponding vesicular peak fraction obtained by gel-permeation chromatography (r = 0.58: P < 0.01) and with the cholesterol concentration in this vesicular peak (r = -0.77; P < 0.002) but not with vesicular peak cholesterol/phospholipid ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Biliary lipid mass in the gallbladder in health and in cholesterol gallstone disease

Objectives: A high cholesterol saturation index of gallbladder bile is an essential prerequisite for cholesterol gallstone formation. This could be due to a high cholesterol mass, or to a low bile acid and/or phospholipid mass in gallbladder bile, or to a combination of these abnormalities. The conventional method of measuring the saturation index cannot distinguish between these alternatives. Our aim was to distinguish between these alternatives in patients with cholesterol gallstones by measuring biliary lipid masses, and to study the effect of gender and obesity within this gallstone population. Methods: We have developed a simple technique for the measurement of total biliary lipid masses in the gallbladder. This involves a combination of 99mTcHIDA cholescintigraphy and of nasoduodenal intubation with intravenous cholecystokinin infusion to obtain a bile sample. We validated this technique by comparing it with direct measurement of biliary lipid masses following cholecystectomy; we studied 19 male non-obese healthy controls and a total of 45 gallstone patients, who were further subdivided into male non-obese (n = 13), female non-obese (n = 17) and obese (n = 15) gallstone patients. Results: The validation studies showed close agreement for all three biliary lipids between our technique and the direct measurements. The male non-obese gallstone patients had a significantly higher saturation index than the male non-obese healthy controls. This was due to a reduction in bile acid mass (2.73 versus 4.79 mmol, P < 0.005), with no difference in the masses of phospholipid or cholesterol. There were no differences between male and female non-obese gallstone patients; and obese patients had a reduced phospholipid mass as well as a reduced bile acid mass. There was no increase in cholesterol mass within the gallbladder in any of the groups. Conclusions: We conclude that 99mTcHIDA scintigraphy together with nasoduodenal intubation provides a simple valid technique for measuring biliary lipid masses in the gallbladder; that the main defect in gallstone disease is a reduction in bile acid mass; that within the gallstone population, gender has no effect on biliary lipid masses, but that obese gallstone patients have a reduction in phospholipid mass also. There was no increase in cholesterol mass in the gallbladder in any of the gallstone groups, presumably because this was prevented by the low bile acid mass.

The pathophysiological characteristics of bile from patients with gallstones: The role of prostaglandins and mucin in gallstone formation

Bile was obtained from 82 patients with various biliary tract diseases and concentrations of prostagloandins, leukotriens, mucin, and a number of lithogenic components were measured in order to evaluate the role of these substances in the pathogenesis of gallstone formation. The characteristics of bile in cases of cholesterol gallstones included high concentrations of prostaglandins and hexosamine and a high cholesterol saturation index. Prostaglandin E2 and prostaglandin F2 alpha concentrations in bile were correlated with hexosamine concentration, and prostaglandins and hexosamine were found to be actively synthesized and secreted in the gallbladder. Prostaglandins E2 and F2 alpha may therefore stimulate mucin secretion in the gallbladder with supersaturated bile. The characteristics of bile in cases of calcium bilirubinate gallstones included a high detection rate for bacteria, high beta-glucuronidase activity, a high percentage of unconjugated bilirubin, a low cholesterol saturation index and high concentrations of prostaglandins and hexosamine. Moreover, the synthesis and secretion of prostaglandins in the biliary tract were accelerated in cases of infected bile. Thus, hypersecretion of mucin, stimulated by prostaglandins, my participate in the onset and development of biliary tract infection or in the formation of calcium bilirubinate gallstones. Regarding the role of prostaglandins and mucin, the hypotheses for gallstone formation previously reported by many authors are supported by the clinical data obtained in the current study.

Bile Concentration Is A Key Factor for Nucleation of Cholesterol Crystals and Cholesterol Saturation Index in Gallbladder Bile of Gallstone Patients

We investigated whether bile concentration influenced cholesterol saturation index or nucleation time of cholesterol monohydrate crystals in a large number of gallbladder bile samples. Pigment stone patients never had cholesterol crystals in their fresh biles, and nucleation time was always longer than 20 days. Of the cholesterol stone patients 79% had cholesterol crystals in their fresh biles. Long nucleation times were generally found in cholesterol stone patients with dilute biles despite a high cholesterol saturation index. Nucleation time was usually short if bile was well concentrated despite a relatively low saturation index. Serial in vitro dilution of concentrated biles from cholesterol gallstone patients resulted in progressively prolonged nucleation times. Patients with solitary cholesterol stones had longer nucleation times than patients with multiple cholesterol stones. This study indicates that bile concentration is an important factor for nucleation time and cholesterol saturation index. Moreover, solitary and multiple cholesterol stones may have a different pathogenesis.