Genetic analysis of cholesterol gallstone formation: searching for Lith (gallstone) genes

Investigating the influence of the gut microbiome on cholelithiasis: unveiling insights through sequencing and predictive modeling

BACKGROUND

Cholelithiasis is one of the most common disorders of hepatobiliary system. Gut bacteria may be involved in the process of gallstone formation and are, therefore considered as potential targets for cholelithiasis prediction.

OBJECTIVE

To reveal the correlation between cholelithiasis and gut bacteria.

METHODS

Stool samples were collected from 100 cholelithiasis and 250 healthy individuals from Huzhou Central Hospital; The 16S rRNA of gut bacteria in the stool samples was sequenced using the third-generation Pacbio sequencing platform; Mothur v.1.21.1 was used to analyze the diversity of gut bacteria; Wilcoxon rank-sum test and linear discriminant analysis of effect sizes (LEfSe) were used to analyze differences in gut bacteria between patients suffering from cholelithiasis and healthy individuals; Chord diagram and Plot-related heat maps were used to analyze the correlation between cholelithiasis and gut bacteria; six machine algorithms were used to construct models to predict cholelithiasis.

RESULTS

There were differences in the abundance of gut bacteria between cholelithiasis and healthy individuals, but there were no differences in their community diversity. Increased abundance of Costridia, Escherichia flexneri, and Klebsiella pneumonae were found in cholelithiasis, while Bacteroidia, Phocaeicola, and Phocaeicola vulgatus were more abundant in healthy individuals. The top four bacteria that were most closely associated with cholelithiasis were Escherichia flexneri, Escherichia dysenteriae, Streptococcus salivarius, and Phocaeicola vulgatus. The cholelithiasis model based on CatBoost algorithm had the best prediction effect (sensitivity: 90.48%, specificity: 88.32%, and AUC: 0.962).

CONCLUSION

The identification of characteristic gut bacteria may provide new predictive targets for gallstone screening. As being screened by the predictive model, people at high risk of cholelithiasis can determine the need for further testing, thus enabling early warning of cholelithiasis.

Sphincter of Oddi Dysfunction Induces Gallstone by Inhibiting the Expression of ABCB11 via PKC-α

The abnormal increase of Oddi sphincter pressure and total bile duct pressure may play an important role in the formation of cholesterol stones, but the specific molecular mechanism is still unclear. This study aims to investigate it through in vitro and in vivo experiments. A mouse model of Oddi sphincter dysfunction was constructed by stone-inducing diet. We compared the two groups with PKC-α inhibitor GÖ6976 and PKC-α agonist thymeleatoxin. Oddi sphincter pressure and total bile duct pressure were measured. Biochemical analysis of total cholesterol, bile acid and bilirubin was then conducted. The histopathologic changes of bile duct were observed by HE staining and the ultrastructure of liver cells and surrounding tissues was observed by transmission electron microscopy. Through the above experiments, we found that the change of PKC-α expression may affect the formation process of gallstones. The relationship between PKC-α and ABCB11 was further verified by in vitro and in vivo experiments. Our results suggest that ABCB11 and PKC-α are co-expressed in the tubule membrane of hepatocytes and interact with each other in hepatocytes. The high cholesterol diet further enhances the activation of PKC-α and thus reduces the expression of ABCB11. The formation of cholesterol stones is associated with the down-regulation of ABCB11 expression in the tubule membrane of hepatocytes due to kinase signaling. This is the first study to demonstrate that sphincter of Oddi dysfunction induces gallstones through PKC-α inhibition of ABCB11 expression.

Metabolic dysfunction-associated gallstone disease: expecting more from critical care manifestations

About 20% of adults worldwide have gallstones which are solid conglomerates in the biliary tree made of cholesterol monohydrate crystals, mucin, calcium bilirubinate, and protein aggregates. About 20% of gallstone patients will definitively develop gallstone disease, a condition which consists of gallstone-related symptoms and/or complications requiring medical therapy, endoscopic procedures, and/or cholecystectomy. Gallstones represent one of the most prevalent digestive disorders in Western countries and patients with gallstone disease are one of the largest categories admitted to European hospitals. About 80% of gallstones in Western countries are made of cholesterol due to disturbed cholesterol homeostasis which involves the liver, the gallbladder and the intestine on a genetic background. The incidence of cholesterol gallstones is dramatically increasing in parallel with the global epidemic of insulin resistance, type 2 diabetes, expansion of visceral adiposity, obesity, and metabolic syndrome. In this context, gallstones can be largely considered a metabolic dysfunction-associated gallstone disease, a condition prone to specific and systemic preventive measures. In this review we discuss the key pathogenic and clinical aspects of gallstones, as the main clinical consequences of metabolic dysfunction-associated disease.

Differential Effects of ABCG5/G8 Gene Region Variants on Lipid Profile, Blood Pressure Status, and Gallstone Disease History in Taiwan

ABCG5 and ABCG8 are two key adenosine triphosphate-binding cassette (ABC) proteins that regulate whole-body sterol trafficking. This study aimed to elucidate the association between ABCG5/G8 gene region variants and lipid profile, cardiometabolic traits, and gallstone disease history in Taiwan. A total of 1494 Taiwan Biobank participants with whole-genome sequencing data and 117,679 participants with Axiom Genome-Wide CHB Array data were enrolled for analysis. Using genotype-phenotype and stepwise linear regression analyses, we found independent associations of four Asian-specific ABCG5 variants, rs119480069, rs199984328, rs560839317, and rs748096191, with total, low-density lipoprotein (LDL), and non-high-density lipoprotein (HDL) cholesterol levels (all p ≤ 0.0002). Four other variants, which were in nearly complete linkage disequilibrium, exhibited genome-wide significant associations with gallstone disease history, and the ABCG8 rs11887534 variant showed a trend of superiority for gallstone disease history in a nested logistic regression model (p = 0.074). Through regional association analysis of various other cardiometabolic traits, two variants of the PLEKHH2, approximately 50 kb from the ABCG5/G8 region, exhibited significant associations with blood pressure status (p < 10^-6). In conclusion, differential effects of ABCG5/G8 region variants were noted for lipid profile, blood pressure status, and gallstone disease history in Taiwan. These results indicate the crucial role of individualized assessment of ABCG5/G8 variants for different cardiometabolic phenotypes.

Association Study of SLCO1B3 and ABCC3 Genetic Variants in Gallstone Disease

There is growing evidence that gallstone formation may be genetically determined. Recent studies have shown that polymorphism of genes encoding proteins involved in bile acid transport may be associated with the risk of gallstone disease. The aim of this study was to investigate the association between SLCO1B3 (rs4149117:G>T, rs7311358:A>G) and ABCC3 (rs4793665:T>C, rs11568591:G>A) genetic variants and susceptibility to cholesterol gallstone disease, as well as gallstone composition. The study included 317 patients suffering from cholelithiasis who underwent cholecystostomy and 249 controls with no evidence of stones, confirmed by ultrasound examination. There were no statistically significant differences in the distribution of studied gene polymorphisms between patients with gallstone disease and healthy controls. No significant associations were observed between studied genotypes and the content of analyzed gallstone components: total cholesterol, bilirubin, CaCO3, nor the total bile acids. There was also no association between bile acid content in gallstones and the polymorphisms studied. The results of this study suggest that polymorphisms of SLCO1B3 and ABCC3 genes are not a valuable marker of gallstone disease susceptibility and do not influence gallstone composition.

An Update on the Lithogenic Mechanisms of Cholecystokinin a Receptor (CCKAR), an Important Gallstone Gene for Lith13

The cholecystokinin A receptor (CCKAR) is expressed predominantly in the gallbladder and small intestine in the digestive system, where it is responsible for CCK's regulation of gallbladder and small intestinal motility. The effect of CCKAR on small intestinal transit is a physiological response for regulating intestinal cholesterol absorption. The Cckar gene has been identified to be an important gallstone gene, Lith13, in inbred mice by a powerful quantitative trait locus analysis. Knockout of the Cckar gene in mice enhances cholesterol cholelithogenesis by impairing gallbladder contraction and emptying, promoting cholesterol crystallization and crystal growth, and increasing intestinal cholesterol absorption. Clinical and epidemiological studies have demonstrated that several variants in the CCKAR gene are associated with increased prevalence of cholesterol cholelithiasis in humans. Dysfunctional gallbladder emptying in response to exogenously administered CCK-8 is often found in patients with cholesterol gallstones, and patients with pigment gallstones display an intermediate degree of gallbladder motility defect. Gallbladder hypomotility is also revealed in some subjects without gallstones under several conditions: pregnancy, total parenteral nutrition, celiac disease, oral contraceptives and conjugated estrogens, obesity, diabetes, the metabolic syndrome, and administration of CCKAR antagonists. The physical-chemical, genetic, and molecular studies of Lith13 show that dysfunctional CCKAR enhances susceptibility to cholesterol gallstones through two primary mechanisms: impaired gallbladder emptying is a key risk factor for the development of gallbladder hypomotility, biliary sludge (the precursor of gallstones), and microlithiasis, as well as delayed small intestinal transit augments cholesterol absorption as a major source for the hepatic hypersecretion of biliary cholesterol and for the accumulation of excess cholesterol in the gallbladder wall that further worsens impaired gallbladder motor function. If these two defects in the gallbladder and small intestine could be prevented by the potent CCKAR agonists, the risk of developing cholesterol gallstones could be dramatically reduced.

Physical Activity Modulating Lipid Metabolism in Gallbladder Diseases

Physical activity encompasses a series of overall benefits on cardiovascular health and metabolic disorders. Research has recently focused on the hepatobiliary tract, as an additional target of the health-related outcomes of different types of physical exercise. Here, we focus on the global features of physical activity with respect to exercise modality and intensity, and on studies linking physical activity to lipid metabolism, gallbladder diseases (gallstones, symptoms, complications and health-related quality of life), gallbladder motor-function, enterohepatic circulation of bile acids, and systemic metabolic inflammation. Additional studies need to unravel the pathophysiological mechanisms involved in both beneficial and harmful effects of physical activity in populations with different metabolic conditions.

Recent Advances in the Critical Role of the Sterol Efflux Transporters ABCG5/G8 in Health and Disease

Cardiovascular disease is characterized by lipid accumulation, inflammatory response, cell death, and fibrosis in the arterial wall and is the leading cause of morbidity and mortality worldwide. Cholesterol gallstone disease is caused by complex genetic and environmental factors and is one of the most prevalent and costly digestive diseases in the USA and Europe. Although sitosterolemia is a rare inherited lipid storage disease, its genetic studies led to identification of the sterol efflux transporters ABCG5/G8 that are located on chromosome 2p21 in humans and chromosome 17 in mice. Human and animal studies have clearly demonstrated that ABCG5/G8 play a critical role in regulating hepatic secretion and intestinal absorption of cholesterol and plant sterols. Sitosterolemia is caused by a mutation in either the ABCG5 or the ABCG8 gene alone, but not in both simultaneously. Polymorphisms in the ABCG5/G8 genes are associated with abnormal plasma cholesterol metabolism and may play a key role in the genetic determination of plasma cholesterol concentrations. Moreover, ABCG5/G8 is a new gallstone gene, LITH9. Gallstone-associated variants in ABCG5/G8 are involved in the pathogenesis of cholesterol gallstones in European, Asian, and South American populations. In this chapter, we summarize the latest advances in the critical role of the sterol efflux transporters ABCG5/G8 in regulating hepatic secretion of biliary cholesterol, intestinal absorption of cholesterol and plant sterols, the classical reverse cholesterol transport, and the newly established transintestinal cholesterol excretion, as well as in the pathogenesis and pathophysiology of ABCG5/G8-related metabolic diseases such as sitosterolemia, cardiovascular disease, and cholesterol gallstone disease.

Endoscopic Retrograde Cholangiopancreatography and Endoscopic Ultrasound-Guided Gallbladder Drainage

"Gallbladder disease is one of the most common gastrointestinal diseases encountered in clinical practice. Surgical removal and percutaneous drainage are both widely available and effective in the management of acute cholecystitis. Several endoscopic approaches exist as an alternative to these interventions. These include transpapillary approaches via endoscopic retrograde cholangiopancreatography (ERCP), transmural drainage and access approaches via endoscopic ultrasound (EUS), and endoscopic surgical approaches using natural orifice transluminal endoscopic surgery (NOTES) techniques. This article reviews the epidemiology and pathophysiology of gallbladder diseases and discusses the various percutaneous, surgical, and endoscopic approaches to managing gallbladder disease."

The Role of Diet in the Pathogenesis of Cholesterol Gallstones

Cholesterol gallstone disease is a major health problem in Westernized countries and depends on a complex interplay between genetic factors, lifestyle and diet, acting on specific pathogenic mechanisms. Overweigh, obesity, dyslipidemia, insulin resistance and altered cholesterol homeostasis have been linked to increased gallstone occurrence, and several studies point to a number of specific nutrients as risk- or protective factors with respect to gallstone formation in humans. There is a rising interest in the identification of common and modifiable dietetic factors that put the patients at risk of gallstones or that are able to prevent gallstone formation and growth. In particular, dietary models characterized by increased energy intake with highly refined sugars and sweet foods, high fructose intake, low fiber contents, high fat, consumption of fast food and low vitamin C intake increase the risk of gallstone formation. On the other hand, high intake of monounsaturated fats and fiber, olive oil and fish (ω-3 fatty acids) consumption, vegetable protein intake, fruit, coffee, moderate alcohol consumption and vitamin C supplementation exert a protective role. The effect of some confounding factors (e.g., physical activity) cannot be ruled out, but general recommendations about the multiple beneficial effects of diet on cholesterol gallstones must be kept in mind, in particular in groups at high risk of gallstone formation.

Similarities and differences between biliary sludge and microlithiasis: Their clinical and pathophysiological significances

The terms biliary sludge and cholesterol microlithiasis (hereafter referred to as microlithiasis) were originated from different diagnostic techniques and may represent different stages of cholesterol gallstone disease. Although the pathogenesis of biliary sludge and microlithiasis may be similar, microlithiasis could be preceded by biliary sludge, followed by persistent precipitation and aggregation of solid cholesterol crystals, and eventually, gallstone formation. Many clinical conditions are clearly associated with the formation of biliary sludge and microlithiasis, including total parenteral nutrition, rapid weight loss, pregnancy, organ transplantation, administration of certain medications, and a variety of acute and chronic illnesses. Numerous studies have demonstrated complete resolution of biliary sludge in approximately 40% of patients, a cyclic pattern of disappearing and reappearing in about 40%, and progression to gallstones in nearly 20%. Although only a minority of patients with ultrasonographic demonstration of biliary sludge develop gallstones, it is still a matter of controversy whether microlithiasis could eventually evolve to cholesterol gallstones. Biliary sludge and microlithiasis are asymptomatic in the vast majority of patients; however, they can cause biliary colic, acute cholecystitis, and acute pancreatitis. Biliary sludge and microlithiasis are most often diagnosed ultrasonographically and bile microscopy is considered the gold standard for their diagnosis. Specific measures to prevent the development of biliary sludge are not practical or cost-effective in the general population. Laparoscopic cholecystectomy offers the most definitive therapy on biliary sludge. Endoscopic sphincterotomy or surgical intervention is effective for microlithiasis-induced pancreatitis. Ursodeoxycholic acid can effectively prevent the recurrence of solid cholesterol crystals and significantly reduce the risk of recurrent pancreatitis.

Mouse models of gallstone disease

PURPOSE OF REVIEW

The establishment of mouse models of gallstones, and the contribution of mouse models to genetic studies of gallstone disease, as well as the latest advances in the pathophysiology of gallstones from mouse experiments are summarized.

RECENT FINDINGS

The combined uses of genomic strategies and phenotypic studies in mice have successfully led to the identification of many Lith genes, which pave the way for the discovery of human LITH genes. The physical-chemical, genetic, and molecular biological studies of gallstone disease in mice with knockout or transgene of specific target genes have provided many novel insights into the complex pathophysiological mechanisms of this very common hepatobiliary disease worldwide, showing that interactions of five primary defects play a critical role in the pathogenesis of cholesterol gallstones. Based on mouse studies, a new concept has been proposed that hepatic hypersecretion of biliary cholesterol is induced by multiple Lith genes, with insulin resistance as part of the metabolic syndrome interacting with cholelithogenic environmental factors to cause the phenotype.

SUMMARY

The mouse model of gallstones is crucial for elucidating the physical-chemical and genetic mechanisms of cholesterol crystallization and gallstone formation, which greatly increase our understanding of the pathogenesis of this disease in humans.

Genetic determinants of cholangiopathies: Molecular and systems genetics

Familial cholangiopathies are rare but potentially severe diseases. Their spectrum ranges from fairly benign conditions as, for example, benign recurrent intrahepatic cholestasis to low-phospholipid associated cholelithiasis and progressive familial intrahepatic cholestasis (PFIC). Many cholangiopathies such as primary biliary cholangitis (PBC) or primary sclerosing cholangitis (PSC) affect first the bile ducts ("ascending pathophysiology") but others, such as PFIC, start upstream in hepatocytes and cause progressive damage "descending" down the biliary tree and leading to end-stage liver disease. In recent years our understanding of cholestatic diseases has improved, since we have been able to pinpoint numerous disease-causing mutations that cause familial cholangiopathies. Accordingly, six PFIC subtypes (PFIC type 1-6) have now been defined. Given the availability of genotyping resources, these findings can be introduced in the diagnostic work-up of patients with peculiar cholestasis. In addition, functional studies have defined the pathophysiological consequences of some of the detected variants. Furthermore, ABCB4 variants do not only cause PFIC type 3 but confer an increased risk for chronic liver disease in general. In the near future these findings will serve to develop new therapeutic strategies for patients with liver diseases. Here we present the latest data on the genetic background of familial cholangiopathies and discuss their application in clinical practice for the differential diagnosis of cholestasis of unknown aetiology. As look in the future we present "system genetics" as a novel experimental tool for the study of cholangiopathies and disease-modifying genes. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

New insights into the role of Lith genes in the formation of cholesterol-supersaturated bile

Cholesterol gallstone formation represents a failure of biliary cholesterol homeostasis in which the physical-chemical balance of cholesterol solubility in bile is disturbed. Lithogenic bile is mainly caused by persistent hepatic hypersecretion of biliary cholesterol and sustained cholesterol-supersaturated bile is an essential prerequisite for the precipitation of solid cholesterol monohydrate crystals and the formation of cholesterol gallstones. The metabolic determinants of the supply of hepatic cholesterol molecules that are recruited for biliary secretion are dependent upon the input-output balance of cholesterol and its catabolism in the liver. The sources of cholesterol for hepatic secretion into bile have been extensively investigated; however, to what extent each cholesterol source contributes to hepatic secretion is still unclear both under normal physiological conditions and in the lithogenic state. Although it has been long known that biliary lithogenicity is initiated by hepatic cholesterol hypersecretion, the genetic mechanisms that cause supersaturated bile have not been defined yet. Identification of the Lith genes that determine hepatic cholesterol hypersecretion should provide novel insights into the primary genetic and pathophysiological defects for gallstone formation. In this review article, we focus mainly on the pathogenesis of the formation of supersaturated bile and gallstones from the viewpoint of genetics and pathophysiology. A better understanding of the molecular genetics and pathophysiology of the formation of cholesterol-supersaturated bile will undoubtedly facilitate the development of novel, effective, and noninvasive therapies for patients with gallstones, which would reduce the morbidity, mortality, and costs of health care associated with gallstones, a very prevalent liver disease worldwide.

Management of gallstones and its related complications

The majority of gallstone patients remain asymptomatic; however, interest toward the gallstone disease is continuing because of the high worldwide prevalence and management costs and the development of gallstone symptoms and complications. For cholesterol gallstone disease, moreover, a strong link exists between this disease and highly prevalent metabolic disorders such as obesity, dyslipidemia, type 2 diabetes, hyperinsulinemia, hypertriglyceridemia and the metabolic syndrome. Information on the natural history as well as the diagnostic, surgical (mainly laparoscopic cholecystectomy) and medical tools available to facilitate adequate management of cholelithiasis and its complications are, therefore, crucial to prevent the negative outcomes of gallstone disease. Moreover, some risk factors for gallstone disease are modifiable and some preventive strategies have become necessary to reduce the onset and the severity of complications.

Lipids, obesity and gallbladder disease in women: insights from genetic studies using the cardiovascular gene-centric 50K SNP array

Gallbladder disease (GBD) has an overall prevalence of 10–40% depending on factors such as age, gender, population, obesity and diabetes, and represents a major economic burden. Although gallstones are composed of cholesterol by-products and are associated with obesity, presumed causal pathways remain unproven, although BMI reduction is typically recommended. We performed genetic studies to discover candidate genes and define pathways involved in GBD. We genotyped 15 241 women of European ancestry from three cohorts, including 3216 with GBD, using the Human cardiovascular disease (HumanCVD) BeadChip containing up to ~53 000 single-nucleotide polymorphisms (SNPs). Effect sizes with P-values for development of GBD were generated. We identify two new loci associated with GBD, GCKR rs1260326:T>C (P=5.88 × 10⁻⁷, ß=−0.146) and TTC39B rs686030:C>A (P=6.95x10⁻⁷, ß=0.271) and detect four independent SNP effects in ABCG8 rs4953023:G>A (P=7.41 × 10⁻⁴⁷, ß=0.734), ABCG8 rs4299376:G^>T (P=2.40 × 10⁻¹⁸, ß=0.278), ABCG5 rs6544718:T>C (P=2.08 × 10⁻¹⁴, ß=0.044) and ABCG5 rs6720173:G>C (P=3.81 × 10⁻¹², ß⁼0.262) in conditional analyses taking genotypes of rs4953023:G>A as a covariate. We also delineate the risk effects among many genotypes known to influence lipids. These data, from the largest GBD genetic study to date, show that specific, mainly hepatocyte-centred, components of lipid metabolism are important to GBD risk in women. We discuss the potential pharmaceutical implications of our findings.

Cholesterol cholelithiasis in pregnant women: pathogenesis, prevention and treatment

Epidemiological and clinical studies have found that gallstone prevalence is twice as high in women as in men at all ages in every population studied. Hormonal changes occurring during pregnancy put women at higher risk. The incidence rates of biliary sludge (a precursor to gallstones) and gallstones are up to 30 and 12%, respectively, during pregnancy and postpartum, and 1-3% of pregnant women undergo cholecystectomy due to clinical symptoms or complications within the first year postpartum. Increased estrogen levels during pregnancy induce significant metabolic changes in the hepatobiliary system, including the formation of cholesterol-supersaturated bile and sluggish gallbladder motility, two factors enhancing cholelithogenesis. The therapeutic approaches are conservative during pregnancy because of the controversial frequency of biliary disorders. In the majority of pregnant women, biliary sludge and gallstones tend to dissolve spontaneously after parturition. In some situations, however, the conditions persist and require costly therapeutic interventions. When necessary, invasive procedures such as laparoscopic cholecystectomy are relatively well tolerated, preferably during the second trimester of pregnancy or postpartum. Although laparoscopic operation is recommended for its safety, the use of drugs such as ursodeoxycholic acid (UDCA) and the novel lipid-lowering compound, ezetimibe would also be considered. In this paper, we systematically review the incidence and natural history of pregnancy-related biliary sludge and gallstone formation and carefully discuss the molecular mechanisms underlying the lithogenic effect of estrogen on gallstone formation during pregnancy. We also summarize recent progress in the necessary strategies recommended for the prevention and the treatment of gallstones in pregnant women.

Relationship between CYP7A1 -204A>C polymorphism with gallbladder stone disease and serum lipid levels: a meta-analysis

Background

The CYP7A1 gene polymorphism has been reported to be associated with gallbladder stone disease (GSD) and serum lipid levels, but the results were inconsistent. This meta-analysis aimed to evaluate the influence of the -204A > C polymorphism in the promoter of CYP7A1 gene on the GSD and serum lipid levels.

Methods

According to inclusion/exclusion criteria, eligible studies on CYP7A1 gene -204A > C polymorphism of serum lipid levels and the risk of GSD were retrieved. Depending on the between-study heterogeneity, the fixed- or random-effects model was applied, and the data were analyzed using the RevMan software (V5.2).

Results

Five studies totaling 830 GSD patients and 882 healthy controls were used to evaluate the relation of CYP7A1 -204A > C polymorphism with GSD. Overall comparison of alleles A with C in all study population yielded 5% but non-significant increased risk of GSD (OR = 1.05, 95% CI: 0.91 − 1.22, P = 0.48). Subgroup analysis by ethnic differences did not show any association between CYP7A1 -204A > C polymorphism and GSD either. Four studies totaling 802 cases and 691 controls were used to assess the relation of CYP7A1 -204A > C polymorphism with serum lipid levels. All the subjects were from the Asian population. The pooled effects indicated that AC genotype had higher levels of TG than AA (MD = -0.42, 95% CI: -0.76 − -0.08, P = 0.01). CC genotype in cases had higher levels of TC (MD = 0.65, 95% CI: 0.25 − 1.05, P = 0.001) and LDL-C (MD = 0.40, 95% CI: 0.06 − 0.73, P = 0.02) than AA, AA (MD = -0.35, 95% CI: -0.60 − -0.10, P = 0.007) and AC (MD = −0.35, 95% CI: -0.61 − -0.08, P = 0.01) genotypes in controls had higher levels of TC than CC, and AA genotype in controls had higher levels of HDL-C than CC (MD = -0.15, 95% CI: -0.21 − -0.09, P < 0.00001).

Conclusions

The CYP7A1 -204A > C polymorphism is significantly associated with serum lipid levels in Asian population, but not gallbladder stone disease.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-511X-13-126) contains supplementary material, which is available to authorized users.

An analysis of the role of the indigenous microbiota in cholesterol gallstone pathogenesis

BACKGROUND AND AIMS

Cholesterol gallstone disease is a complex process involving both genetic and environmental variables. No information exists regarding what role if any the indigenous gastrointestinal microbiota may play in cholesterol gallstone pathogenesis and whether variations in the microbiota can alter cholesterol gallstone prevalence rates.

METHODS

Genetically related substrains (BALB/cJ and BALB/cJBomTac) and (BALB/AnNTac and BALB/cByJ) of mice obtained from different vendors were compared for cholesterol gallstone prevalence after being fed a lithogenic diet for 8 weeks. The indigenous microbiome was altered in these substrains by oral gavage of fecal slurries as adults, by cross-fostering to mice with divergent flora at <1 day of age or by rederiving into a germ-free state.

RESULTS

Alterations in the indigenous microbiome altered significantly the accumulation of mucin gel and normalized gallbladder weight but did not alter cholesterol gallstone susceptibility in conventionally housed SPF mice. Germ-free rederivation rendered mice more susceptible to cholesterol gallstone formation. This susceptibility appeared to be largely due to alterations in gallbladder size and gallbladder wall inflammation. Colonization of germ-free mice with members of altered Schaedler flora normalized the gallstone phenotype to a level similar to conventionally housed mice.

CONCLUSIONS

These data demonstrate that alterations in the gastrointestinal microbiome may alter aspects of cholesterol gallstone pathogenesis and that in the appropriate circumstances these changes may impact cholesterol cholelithogenesis.

Genetics of gallstone disease

Gallstone disease (GSD) is one of the most common biliary tract disorders worldwide. The prevalence, however, varies from 5.9-21.9% in Western society to 3.1-10.7% in Asia. Most gallstones (75%) are silent. Approximately half of symptomatic gallstone carriers experience a second episode of biliary pain within 1 year. These individuals are at increased risk of developing acute cholecystitis, acute cholangitis, and biliary pancreatitis. As can be expected, these complications burden health care systems because of their invasive nature and surgical cost. Factors that contribute to gallstone formation include supersaturation of cholesterol in bile, gallbladder hypomotility, destabilization of bile by kinetic protein factors, and abnormal mucins. Epidemiologic studies have implicated multiple environmental factors and some common genetic elements in gallstone formation. Genetic factors that influence gallstone formation have been elaborated from linkage studies of twins, families, and ethnicities. Accumulating evidence suggests that genetic factors play a role in GSD.

Gender-specific association of the interleukin 18 gene with symptomatic gallstone disease

BACKGROUND AND AIM

Symptomatic gallstone disease (SGSD) induced several inflammatory responses and affected extrahepatic bile ducts. Although the pathology and environmental risk factors of gallstone disease are well documented, immune or inflammatory responses in SGSD development are still inconclusive. Interleukin 18 (IL18) is a pro-inflammatory cytokine that plays an important role in immune, infectious, and inflammatory diseases because of the induction of interferon-γ. In this study, we investigated whether polymorphisms of the IL18 gene were associated with SGSD susceptibility.

METHODS

Genomic DNA was isolated from the whole blood samples of 445 patients with SGSD and 1121 gallstone-free controls. The IL18 rs549908T>G, rs5744247C>G, rs187238G>C, rs1946518T>G, and rs360719A>G polymorphisms were genotyped using predeveloped TaqMan allelic discrimination assay.

RESULTS

We found IL18 rs5744247G allele conferred protection against SGSD in female patients (odds ratio = 0.75, corrected P-value = 0.015). Haplotype analysis revealed that TGGTA protected females from SGSD development (odds ratio = 0.75, corrected P-value = 0.02).

CONCLUSIONS

Based on our findings, IL18 rs5744247C>G polymorphism could be a potential genetic marker to predict SGSD susceptibility in Han Chinese women.

Therapy of gallstone disease: What it was, what it is, what it will be

Cholesterol gallstone disease is a common clinical condition influenced by genetic factors, increasing age, female gender, and metabolic factors. Although laparoscopic cholecystectomy is currently considered the gold standard in treating patients with symptomatic gallstones, new perspectives regarding medical therapy of cholelithiasis are currently under discussion, also taking into account the pathogenesis of gallstones, the natural history of the disease and the analysis of the overall costs of therapy. A careful selection of patients may lead to successful non-surgical therapy in symptomatic subjects with a functioning gallbladder harboring small radiolucent stones. The classical oral litholysis by ursodeoxycholic acid has been recently paralleled by new experimental observations, suggesting that cholesterol-lowering agents which inhibit cholesterol synthesis (statins) or intestinal cholesterol absorption (ezetimibe), or drugs acting on specific nuclear receptors involved in cholesterol and bile acid homeostasis, might be proposed as additional approaches for treating cholesterol gallstones. In this review we discuss old, recent and future perspectives on medical treatment of cholesterol cholelithiasis.

Risk factors in patients with hereditary gallstones in Chinese pedigrees

OBJECTIVE

We aimed to define the risk factors and to evaluate the impact of family background on the prevalence of gallstones in China.

SUBJECTS AND METHODS

Thirty-eight gallstone pedigrees were collected and a case-control study was conducted. This study consisted of 272 first-degree relatives and 201 non-first-degree relatives of index patients. The participants completed a questionnaire and underwent physical and ultrasonographic examinations. The risk factors examined included age, sex, body mass index (BMI), smoking status, alcohol consumption, pregnancy, fat content in dietary meat, history of gastrointestinal surgery, hypertension, hyperlipidemia, fatty liver, coronary heart disease and diabetes.

RESULTS

The prevalence of gallstones in first-degree and non-first-degree relatives of index patients was 38.2 and 10.9%, respectively. Age, pregnancy and BMI significantly differed between cases and controls (p < 0.05). The relative risks were: consumption of meat with a high fat content 1.4 (95% CI 1.1-1.8); hyperlipidemia 2.4 (95% CI 1.3-4.6); diabetes 1.9 (95% CI 1.1-3.2); fatty liver 4.9 (95% CI 1.0-24); coronary heart disease 2.5 (95% CI 1.7-3.9).

CONCLUSION

Data showed that age, overweight, more consumption of high-fat food, high frequency of pregnancy, fatty liver, hyperlipidemia, coronary heart disease and diabetes could increase the risk of gallstones in the first-degree relatives of index patients.

Ezetimibe: its novel effects on the prevention and the treatment of cholesterol gallstones and nonalcoholic Fatty liver disease

The cholesterol absorption inhibitor ezetimibe can significantly reduce plasma cholesterol concentrations by inhibiting the Niemann-Pick C1-like 1 protein (NPC1L1), an intestinal sterol influx transporter that can actively facilitate the uptake of cholesterol for intestinal absorption. Unexpectedly, ezetimibe treatment also induces a complete resistance to cholesterol gallstone formation and nonalcoholic fatty liver disease (NAFLD) in addition to preventing hypercholesterolemia in mice on a Western diet. Because chylomicrons are the vehicles with which the enterocytes transport cholesterol and fatty acids into the body, ezetimibe could prevent these two most prevalent hepatobiliary diseases possibly through the regulation of chylomicron-derived cholesterol and fatty acid metabolism in the liver. It is highly likely that there is an intestinal and hepatic cross-talk through the chylomicron pathway. Therefore, understanding the molecular mechanisms whereby cholesterol and fatty acids are absorbed from the intestine could offer an efficacious novel approach to the prevention and the treatment of cholesterol gallstones and NAFLD.

Disruption of the murine protein kinase Cbeta gene promotes gallstone formation and alters biliary lipid and hepatic cholesterol metabolism

The protein kinase C (PKC) family of Ca(2+) and/or lipid-activated serine-threonine protein kinases is implicated in the pathogenesis of obesity and insulin resistance. We recently reported that protein kinase Cβ (PKCβ), a calcium-, diacylglycerol-, and phospholipid-dependent kinase, is critical for maintaining whole body triglyceride homeostasis. We now report that PKCβ deficiency has profound effects on murine hepatic cholesterol metabolism, including hypersensitivity to diet-induced gallstone formation. The incidence of gallstones increased from 9% in control mice to 95% in PKCβ(-/-) mice. Gallstone formation in the mutant mice was accompanied by hyposecretion of bile acids with no alteration in fecal bile acid excretion, increased biliary cholesterol saturation and hydrophobicity indices, as well as hepatic p42/44(MAPK) activation, all of which enhance susceptibility to gallstone formation. Lithogenic diet-fed PKCβ(-/-) mice also displayed decreased expression of hepatic cholesterol-7α-hydroxylase (CYP7A1) and sterol 12α-hydroxylase (CYP8b1). Finally, feeding a modified lithogenic diet supplemented with milk fat, instead of cocoa butter, both increased the severity of and shortened the interval for gallstone formation in PKCβ(-/-) mice and was associated with dramatic increases in cholesterol saturation and hydrophobicity indices. Taken together, the findings reveal a hitherto unrecognized role of PKCβ in fine tuning diet-induced cholesterol and bile acid homeostasis, thus identifying PKCβ as a major physiological regulator of both triglyceride and cholesterol homeostasis.

Organic anion transporter 1B1 (SLCO1B1) polymorphism and gallstone formation: High incidence of Exon4 CA genotype in female patients in North India

AIM

  Gallstone disease is an important cause of abdominal morbidity Organic anion transport protein 1B1 (OATP1B1) (encoded by SLCO1B1) is a major transporter protein for bile salt uptake in enterohepatic circulation of bile salts. Disturbance in this pathway can decrease relative concentration of bile salts in gallbladder and may lead to formation of gallstones. We investigated role of SLCO1B1 polymorphisms [(Exon4 C > A (Pro155Thr; rs11045819) and Ex6 + 40T > C (Val174Ala; rs4149056)] in conferring interindividual susceptibility to gallstone disease.

METHODS

  A total of 173 healthy controls and 226 gallstone patients (USG positive) were recruited. Genotyping was done by using standard polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

  The observed control frequencies of both polymorphisms of SLCO1B1 gene [(Exon4 C > A (Pro155Thr; rs11045819) and Ex6 + 40T > C (Val174Ala; rs4149056)] were in agreement with Hardy-Weinberg equilibrium. The frequency CA genotype and A allele of Exon4 C > A polymorphism was higher in gallstones patients (12.4% and 6.2%) as compared to controls (5.2% and 2.6%) which was statistically significant [(P = 0.029; OR = 2.31; 95% CI = 1.1-5.0); (P = 0.034; OR = 2.22; 95% CI = 1.1-4.8)], respectively). However, distribution of genotypes and alleles of Ex6 + 40T > C polymorphism was almost similar between gallstone patients and controls. Haplotype analysis showed frequency of A,T haplotype consisting of was significantly higher in gallstone patients as compared to controls and was imposing risk for the disease (P = 0.036; OR = 2.34; 95% CI = 1.0-5.1).

CONCLUSION

  These results suggest that SLCO1B1 Exon4 C > A polymorphism confers increased risk for gallstone disease in North Indian population.

Role of ABCG8 D19H (rs11887534) variant in gallstone susceptibility in northern India

BACKGROUND AND AIM

The excretion of cholesterol from the liver is regulated by the ATP-binding cassette transporter ABCG8. A common genetic polymorphism D19H of ABCG8 might be related to the genetic predisposition of gallstone disease, which is causatively related to supersaturation of cholesterol in bile. We aimed to examine the role of the ABCG8 D19H (rs11887534) polymorphism in susceptibility to gallstone disease in the northern Indian population.

METHODS

The study included 220 confirmed gallstone patients and 230 controls. Genotyping for the ABCG8 D19H polymorphism was carried out using the PCR-RFLP method.

RESULTS

We observed that the ABCG8 DH genotype frequency was significantly higher in gallstone patients (P = 0.038; odds ratio [OR] = 2.20; 95% confidence interval [CI] = 1.1-4.6). At allele level also, the ABCG8 variant allele conferred an increased risk for gallstone susceptibility (P = 0.043; OR = 2.12; 95% CI = 1.2-4.3). The risk as a result of ABCG8 D19H variation was more pronounced in female gallstone patients at genotype (P = 0.026; OR = 3.01, 95% CI = 1.1-7.9) as well as allele level (P = 0.030; OR = 2.85; 95% CI = 1.1-7.3). However, the molecular modeling results of the rs11887534 polymorphism showed that the overall configuration of both wild-type and polymorphic ABCG8 protein were similar, with negligible deviation at the site of polymorphism.

CONCLUSION

  Carriers of the DH genotype and H allele of the ABCG8 D19H polymorphism harbor a higher risk for gallstone susceptibility in the northern Indian population.

Pathophysiological preconditions promoting mixed "black" pigment plus cholesterol gallstones in a DeltaF508 mouse model of cystic fibrosis

Gallstones are frequent in patients with cystic fibrosis (CF). These stones are generally "black" pigment (i.e., Ca bilirubinate) with an appreciable cholesterol admixture. The pathophysiology and molecular mechanisms for this "mixed" gallstone in CF are unknown. Here we investigate in a CF mouse model with no overt liver or gallbladder disease whether pathophysiological changes in the physical chemistry of gallbladder bile might predict the occurrence of "mixed" cholelithiasis. Employing a DeltaF508 mouse model with documented increased fecal bile acid loss and induced enterohepatic cycling of bilirubin (Am J Physiol Gastrointest Liver Physiol 294: G1411-G1420, 2008), we assessed gallbladder bile chemistry, morphology, and microscopy in CF and wild-type mice, with focus on the concentrations and compositions of the common biliary lipids, bilirubins, Ca(2+), and pH. Our results demonstrate that gallbladder bile of CF mice contains significantly higher levels of all bilirubin conjugates and unconjugated bilirubin with lower gallbladder bile pH values. Significant elevations in Ca bilirubinate ion products in bile of CF mice increase the likelihood of supersaturating bile and forming black pigment gallstones. The risk of potential pigment cholelithogenesis is coupled with higher cholesterol saturations and bile salt hydrophobicity indexes, consistent with a proclivity to cholesterol phase separation during pigment gallstone formation. This is an initial step toward unraveling the molecular basis of CF gallstone disease and constitutes a framework for investigating animal models of CF with more severe biliary disease, as well as the human disease.

Lith genes and genetic analysis of cholesterol gallstone formation

Epidemiologic investigations, clinical observations, and family and twin studies in humans, as well as gallstone prevalence investigations in inbred mouse models, support the concept that cholesterol cholelithiasis could result from a complex interaction of environmental factors and the effects of multiple undetermined genes. Quantitative trait locus (QTL) analysis is a powerful genetic method for identifying primary rate-limiting genetic defects and discriminating them from secondary downstream lithogenic effects caused by mutations of the primary genes, and the subsequent positional cloning of such genes responsible for QTLs, followed by the use of manufactured mouse strains with "knockout" or "knockin" of the genes, could lead to the discovery of lithogenic actions of gallstone (LITH) genes. The combined use of genomic strategies and phenotypic studies in inbred strains of mice has successfully resulted in the identification of many candidate LITH genes. Because there is exceptionally close homology between mouse and human genomes, the orthologous human LITH genes can be identified from the mouse study. The discovery of LITH genes and more fundamental knowledge concerning the genetic determinants and molecular mechanisms underlying the formation of cholesterol gallstones in humans will pave the way for critical diagnostic and prelithogenic preventive measures for this exceptionally prevalent digestive disease.

Targets for current pharmacologic therapy in cholesterol gallstone disease

Gallstone disease is a frequent condition throughout the world and, cholesterol stones are the most frequent form in Western countries. The standard treatment of symptomatic gallstone subjects is laparoscopic cholecystectomy. The selection of patients amenable for nonsurgical, medical therapy is of key importance; a careful analysis should consider the natural history of the disease and the overall costs of therapy. Only patients with mild symptoms and small, uncalcified cholesterol gallstones in a functioning gallbladder with a patent cystic duct are considered for oral litholysis by hydrophilic ursodeoxycholic acid, in the hope of achieving cholesterol desaturation of bile and progressive stone dissolution. Recent studies have raised the possibility that cholesterol-lowering agents that inhibit hepatic cholesterol synthesis (statins) or intestinal cholesterol absorption (ezetimibe), or drugs acting on specific nuclear receptors involved in cholesterol and bile acid homeostasis, may offer, alone or in combination, additional medical therapeutic tools for treating cholesterol gallstones. Recent perspectives on medical treatment of cholesterol gallstone disease are discussed in this article.

Transgenic overexpression of Abcb11 enhances biliary bile salt outputs, but does not affect cholesterol cholelithogenesis in mice

BACKGROUND

Cholesterol gallstone disease is a complex genetic trait and induced by multiple but as yet unknown genes. A major Lith gene, Lith1 was first identified on chromosome 2 in gallstone-susceptible C57L mice compared with resistant AKR mice. Abcb11, encoding the canalicular bile salt export pump in the hepatocyte, co-localizes with the Lith1 QTL region and its hepatic expression is significantly higher in C57L mice than in AKR mice.

MATERIAL AND METHODS

To investigate whether Abcb11 influences cholesterol gallstone formation, we created an Abcb11 transgenic strain on the AKR genetic background and fed these mice with a lithogenic diet for 56 days.

RESULT

We excluded functionally relevant polymorphisms of the Abcb11 gene and its promoter region between C57L and AKR mice. Overexpression of Abcb11 significantly promoted biliary bile salt secretion and increased circulating bile salt pool size and bile salt-dependent bile flow rate. However, biliary cholesterol and phospholipid secretion, as well as gallbladder size and contractility were comparable in transgenic and wild-type mice. At 56 days on the lithogenic diet, cholesterol saturation indexes of gallbladder biles and gallstone prevalence rates were essentially similar in these two groups of mice.

CONCLUSION

Overexpression of Abcb11 augments biliary bile salt secretion, but does not affect cholelithogenesis in mice.

Biliary proteins and their redox status changes in gallstone patients

BACKGROUND

Proteins might act as pronucleating agents of cholesterol crystallization in bile. However, little is known about the redox status of biliary proteins in humans and their interaction with crystallization of biliary cholesterol.

MATERIALS AND METHODS

Gallbladder biles were obtained at cholecystectomy from 86 symptomatic patients with either cholesterol gallstones (32 multiple and 32 solitary stones) or pigment stones (n = 22), and studied for protein redox status [carbonyl and sulfhydryl (PSH) concentrations], total lipid and protein levels and cholesterol saturation index (CSI). First appearance of cholesterol crystals in ultrafiltered bile (crystal observation time, COT) was studied with polarizing light microscopy during 21 days.

RESULTS

Patients with cholesterol stones had significantly shorter COT (3 days vs. >21 days, P < 0.05), higher CSI (149 +/- 10% vs. 97 +/- 7%, P < 0.05) and higher total biliary proteins (1.96 +/- 0.1 mg mL(-1) vs. 0.55 +/- 0.1 mg mL(-1), P < 0.05) than patients with pigment stones. Patients with cholesterol stones had significantly lower (P < 0.05) level of protein sulfhydryl concentrations (18 +/- 4 nmol mg(-1) protein vs. 49 +/- 16 nmol mg(-1) protein), while total lipid and carbonyl proteins concentrations were similar between cholesterol and pigment stone patients. Crystallization probability was influenced by the number/type of gallstones (multiple > solitary > pigment stones, P = 0.009) and total protein concentration (high > low levels, P = 0.004). COT was negatively correlated with total protein content (r = -0.45, P = 0.03).

CONCLUSIONS

Biles with cholesterol stones show high CSI and total protein concentration, and rapid COT, which is even faster in patients with multiple stones and high protein concentration. Low PSH levels in cholesterol stone patients point to a biochemical shift, potentially able to affect cholesterol crystallization.

Roles of infection, inflammation, and the immune system in cholesterol gallstone formation

Cholesterol gallstone formation is a complex process mediated by genetic and environmental factors. Until recently, the role of the immune system in the pathogenesis of cholesterol gallstones was not considered a valid topic of research interest. This review collates and interprets an extensive body of basic literature, some of which is not customarily considered to be related to cholelithogenesis, describing the multiple facets of the immune system that appear to be involved in cholesterol cholelithogenesis. A thorough understanding of the immune interactions with biliary lipids and cholecystocytes should modify current views of the pathogenesis of cholesterol gallstones, promote further research on the pathways involved, and lead to novel diagnostic tools, treatments, and preventive measures.

Physical chemistry of intestinal absorption of biliary cholesterol in mice

Although many putative sterol transporters influencing cholesterol absorption and physical-chemical factors affecting dietary cholesterol absorption have been extensively investigated, it is still unclear how biliary cholesterol contributes to the regulation of intestinal cholesterol absorption. We studied whether the gallbladder can modulate the microaggregates of cholesterol carriers, which may in turn influence the intestinal absorption of biliary cholesterol. Supersaturated, crystallized, or micellar model biles were delivered via a duodenal catheter to conscious, freely moving C57L mice daily for 2 days. Intestinal uptake and absorption of biliary cholesterol and its fecal excretion, as well as expression levels of intestinal sterol transporters, were analyzed. Cholesterol uptake and absorption by the enterocyte were dramatically reduced in mice treated with crystallized biles compared with supersaturated biles. This correlated with the higher cumulative radioactivity of cholesterol recovered in the feces at 24 hours. Such findings were absent with the added reference compound sitostanol. After removing cholesterol crystals from crystallized biles, micellar biles showed essentially identical effects on intestinal absorption but with lower fecal cholesterol excretion compared with the original samples containing crystals. Expression levels of the jejunal Abcg5 (ATP-binding cassette transporter G5) and Abcg8, but not Npc1l1 (Niemann-Pick C1 like 1), were significantly increased by supersaturated biles compared with crystallized biles.

CONCLUSION

Different physical forms of biliary cholesterol dramatically determine intestinal uptake and absorption of cholesterol. Solid plate-like cholesterol monohydrate crystals in bile are probably not absorbed and are totally excreted in feces from the body. The gallbladder may have a role in regulating cholesterol homeostasis by modulating the physical forms of biliary cholesterol.

Cholesterol 7alpha-hydrolase (CYP7A1) c.-278A>C promoter polymorphism in gallstone disease patients

There is growing evidence that gallstone formation may be genetically determined. Cholesterol 7alpha-hydrolase (CYP7A1) is an enzyme that catalyzes the first, rate-limiting reaction of cholesterol catabolic pathway. Recently, a common c.-278A>C polymorphism (rs3808607:G>T) has been described in CYP7A1 gene, associated with altered plasma lipid levels. The aim of this study was to verify the finding that CYP7A1 polymorphism may be associated with gallstone disease. Frequency and distribution of the studied alleles did not differ significantly between the patients (-278C; minor allele frequency: 0.45) and the controls (0.48). No significant gender-related differences of allele frequencies or distribution were noted. We conclude that CYP7A1 promoter polymorphism is not a valuable marker of gallstone disease susceptibility in a Polish population.

Effect of ezetimibe on the prevention and dissolution of cholesterol gallstones

BACKGROUND & AIMS

Cholesterol cholelithiasis is one of the most prevalent and most costly digestive diseases in developed countries and its incidence has increased markedly in Asian countries owing to the adoption of Western-type dietary habits. Because animal experiments showed that high efficiency of intestinal cholesterol absorption contributes to gallstone formation, we explored whether the potent cholesterol absorption inhibitor ezetimibe could prevent gallstones and promote gallstone dissolution in mice and reduce biliary cholesterol content in human beings.

METHODS

Male gallstone-susceptible C57L mice were fed a lithogenic diet and concomitantly administered with ezetimibe at 0, 0.8, 4, or 8 mg/kg/day for 8 or 12 weeks. Gallbladder biles and gallstones were examined by microscopy. Gallbladder emptying in response to cholecystokinin octapeptide was measured gravimetrically. Biliary lipid outputs were analyzed by physical-chemical methods. Cholesterol absorption efficiency was determined by fecal dual-isotope ratio and mass balance methods. Lipid changes in gallbladder biles of gallstone patients vs overweight subjects without gallstones were examined before (day 0) and at 30 days after ezetimibe treatment (20 mg/day).

RESULTS

Ezetimibe prevented gallstones by effectively reducing intestinal cholesterol absorption and biliary cholesterol secretion, and protected gallbladder motility function by desaturating bile in mice. Treatment with ezetimibe promoted the dissolution of gallstones by forming an abundance of unsaturated micelles. Furthermore, ezetimibe significantly reduced biliary cholesterol saturation and retarded cholesterol crystallization in biles of patients with gallstones.

CONCLUSIONS

Ezetimibe is a novel approach to reduce biliary cholesterol content and a promising strategy for preventing or treating cholesterol gallstones by inhibiting intestinal cholesterol absorption.

Aquaporins in the hepatobiliary tract. Which, where and what they do in health and disease

The biological importance of the aquaporin family of water channels was recently acknowledged by the 2003 Nobel Prize for Chemistry awarded to the discovering scientist Peter Agre. Among the pleiotropic roles exerted by aquaporins in nature in both health and disease, the review addresses the latest acquisitions about the expression and regulation, as well as physiology and pathophysiology of aquaporins in the hepatobiliary tract. Of note, at least seven out of the thirteen mammalian aquaporins are expressed in the liver, bile ducts and gallbladder. Aquaporins are essential for bile water secretion and reabsorption, as well as for plasma glycerol uptake by the hepatocyte and its conversion to glucose during starvation. Novel data are emerging regarding the physio-pathological involvement of aquaporins in multiple diseases such as cholestases, liver cirrhosis, obesity and insulin resistance, fatty liver, gallstone formation and even microparasite invasion of intrahepatic bile ducts. This body of knowledge represents the mainstay of present and future research in a rapidly expanding field.

Cholesterol gallstones and cancer of gallbladder (CAGB): molecular links

There is a known association between cholesterol gallstones and cancer of gall bladder (CAGB). However, the exact relation is not clear. It is proposed they are linked at molecular level by the activity of the orphan nuclear receptors (ONRs) and ABC transporter pumps involved in cholesterol and xenobiotic efflux from the liver into bile. There is evidence that these two pathways are closely interlinked and influence each other. Genetic and environmental factors that upregulate these systems can lead to the simultaneous pumping of cholesterol (which precipitate as gallstones) and a food carcinogen into the bile in gall bladder; the latter causes malignant transformation. Aflatoxin B, a potent hepatocarcinogen, could be the culprit in endemic regions such as South America and North India.

Investigation of the Lith6 candidate genes APOBEC1 and PPARG in human gallstone disease

BACKGROUND

Genetic susceptibility contributes to the aetiology of gallbladder diseases as shown by multiple epidemiological studies. A major gallstone susceptibility locus (Lith6) was identified in 2003 by quantitative trait locus mapping in mice. Two attractive positional and functional candidate genes in apolipoprotein B mRNA-editing protein (APOBEC1) and peroxisome proliferator-activated receptor gamma (PPARG) are located in this interval.

AIMS

To investigate APOBEC1 and PPARG as candidate genes for common symptomatic gallstone disease in humans.

PATIENTS AND METHODS

Eight hundred and ten patients who underwent cholecystectomy for symptomatic gallstone disease (median age of onset 50) were compared with 718 sex-matched control individuals. An independent additional sample included 368 gallstone patients and 368 controls. Control individuals were sonographically free of gallstones. Haplotype tagging and all known coding single nucleotide polymorphisms were genotyped for PPARG (N=32) and APOBEC1 (N=11).

RESULTS

The investigated high-risk patient sample provides a power of greater than 80% for the detection of odds ratios down to 1.45. No evidence of association of the two genes in the single-point tagging markers, coding variants and in the sliding window haplotype analysis was detected (all nominal single point P-values >0.04). A logistic regression analysis including age, sex and BMI as covariates was also negative (nominal P-values > or =0.08).

CONCLUSIONS

In the investigated German samples, no evidence of association of APOBEC1 and PPARG with gallstone susceptibility was detected. Systematic fine mapping of the complete Lith6 region is required to identify the causative genetic variants for gallstone in mice and humans.

Apolipoprotein B (APOB) Gene Polymorphism in Patients with Gallbladder Disease

Cholelithiasis is one of the most prevalent gastroenterological diseases, precipitated mainly by environmental factors. However, twin studies provided strong evidence for a role of genetic factors in the disease pathogenesis. An association between plasma lipoprotein levels and gallstone disease (GSD) was presented. Apolipoprotein B is an essential structural component of triglyceride-rich lipoprotein particles and plays an important role in the maintenance of cholesterol homeostasis in mammals. Various studies have shown a relationship between APOB gene polymorphisms and lipoprotein levels, but only few investigated a potential association between APOB polymorphism and GSD, giving contrary results. In the current study, an association between common polymorphisms in APOB gene (T2488T and E4154K) and cholesterol gallstone disease was examined. Two hundred and forty patients of Caucasian origin suffering from cholelithiasis, as well as 217 healthy individuals, were included in the study. Patients were genotyped for two single nucleotide polymorphisms (SNPs) in APOB gene: 2488C>T (XbaI), and 4154G>A (EcoRI) using PCR-RLFP method. The resulting analysis has shown that polymorphic loci in positions 2488 and 4154 in APOB gene are in full linkage in a Polish population and form only three haplotypes: 2488C-4154G, 2488T-4154G and 2488C-4154A. Frequency and distribution of 2488C>T alleles did not differ significantly between patients and controls. The 4154G allele has been found to be associated with GSD (p=0.001). A risk of gallstone formation was reduced in 4154AA homozygotes (OR=0.25, p=0.009) and heterozygous individuals (OR=0.63, p=0.03) as compared to 4154GG homozygotes. Additionally, 2488C-4154A haplotype was identified as a protective factor against GSD (p=0.04). Our results suggest that SNPs in APOB, potentially considered as one of lith genes as well as certain haplotypes, may be risk factors for GSD.

Predictors of gallstone composition in 1025 symptomatic gallstones from Northern Germany

Background

Gallstones represent a prevalent and costly health problem. The changing epidemiology and the emerging non-surgical interventions for gallstone disease necessitate the definition of target populations for future therapies. This study aimed to define patterns of gallstone composition and identify demographic predictors of gallstone composition in a large sample of symptomatic gallstones from Northern Germany.

Methods

One thousand and seventy-four post-cholecystectomy gallstone specimens were obtained. Demographic and clinical information was provided by questionnaire (N = 1025 independent individuals with complete information). Two samples from each gallstone were analyzed using Fourier transformed infrared spectrometry.

Results

The most prevalent substance was cholesterol, which was detected in 95.0% of gallstone specimens. Bilirubin and bilirubinate were present in 30.0% and calcium was detected in 10.0% of the spectra. Ninety-two percent of measurements from the same stone yielded the same "main" substances, indicating a homogenous stone composition in most cases. Female sex and higher body mass index (BMI) were associated with the presence of cholesterol as a main substance in the gallstones (p < 0.001).

Conclusion

The changing epidemiology of gallstone disease is reflected by a marked shift in stone composition: Only two percent of stones in this study were pigment stones as compared to 91% percent of stones containing cholesterol as a main substance. Obese individuals from Germany with a BMI > 30 kg/m² have in 95% cholesterol-dominant gallstones and represent a potential target population for non-surgical interventions for the prevention or treatment of cholesterol stones.

Targeted deletion of Gpbar1 protects mice from cholesterol gallstone formation

The Gpbar1 [G-protein-coupled BA (bile acid) receptor 1] is a recently identified cell-surface receptor that can bind and is activated by BAs, but its physiological role is unclear. Using targeted deletion of the Gpbar1 gene in mice, we show that the gene plays a critical role in the maintenance of bile lipid homoeostasis. Mice lacking Gpbar1 expression were viable, developed normally and did not show significant difference in the levels of cholesterol, BAs or any other bile constituents. However, they did not form cholesterol gallstones when fed a cholic acid-containing high-fat diet, and liver-specific gene expression indicated that Gpbar1-deficient mice have altered feedback regulation of BA synthesis. These results suggest that Gpbar1 plays a critical role in the formation of gallstones, possibly via a regulatory mechanism involving the cholesterol 7alpha-hydroxylase pathway.

Investigation of the Lith1 candidate genes ABCB11 and LXRA in human gallstone disease

Genetic susceptibility in the causation of gallbladder diseases was recognized as early as 1937. A major gallstone susceptibility locus (Lith1) was identified in 1995 by quantitative trait locus mapping in mice. Two attractive positional and functional candidate genes in LXRA and ABCB11 are located in this interval. ABCB11 is associated with progressive familial cholestasis. This study was undertaken to investigate LXRA and ABCB11 as candidate genes for gallstone disease in humans. Eight hundred and ten patients who underwent cholecystectomy for symptomatic gallstone disease (median age of onset, 50 years) were compared with 718 sex-matched control individuals. Control individuals were sonographically free of gallstones. Haplotype tagging and all known coding single nucleotide polymorphisms (SNPs) were genotyped for ABCB11 (n=29) and LXRA (n=10). The investigated high-risk patient sample provides a power of greater than 80% for the detection of odds ratios down to 1.55. No evidence of association of the two genes in the single point tagging markers, coding variants or in the sliding window haplotype analysis was detected (all nominal single-point P values>or=.08). In conclusion, in the investigated German sample, no evidence of association of ABCB11 and LXRA to gallstone susceptibility was detected. The gallstone trait is not allelic to progressive familial cholestasis at the ABCB11 locus. Systematic fine mapping of the Lith1 region is required to identify the causative genetic variants for gallstone in mice and humans.

Cholesterol gallstone disease

With a prevalence of 10-15% in adults in Europe and the USA, gallstones are the most common digestive disease needing admission to hospital in the West. The interplay between interprandial and postprandial physiological responses to endogenous and dietary lipids underscores the importance of coordinated hepatobiliary and gastrointestinal functions to prevent crystallisation and precipitation of excess biliary cholesterol. Indeed, identifying the metabolic and transcriptional pathways that drive the regulation of biliary lipid secretion has been a major achievement in the field. We highlight scientific advances in protein and gene regulation of cholesterol absorption, synthesis, and catabolism, and biliary lipid secretion with respect to the pathogenesis of cholesterol gallstone disease. We discuss the physical-chemical mechanisms of gallstone formation in bile and the active role of the gallbladder and the intestine. We also discuss gaps in our knowledge of the pathogenesis of gallstone formation and the potential for gene targeting in therapy.

Evidence that gallbladder epithelial mucin enhances cholesterol cholelithogenesis in MUC1 transgenic mice

BACKGROUND & AIMS

The gel-forming mucins play an important role in the early stage of cholesterol gallstone formation. We investigated whether the gallbladder epithelial mucin encoded by mucin gene 1 (MUC1) influences susceptibility to gallstones.

METHODS

Gallbladder motility and cholesterol absorption, gallstones and expression of the mucin genes in gallbladders, and secretion rates and compositions of biliary lipids were determined in male C57BL/6J mice transgenic for the human MUC1 gene (MUC1.Tg) and wild-type mice before (day 0, on chow) and at 4 weeks on a lithogenic diet containing 1% cholesterol and 0.5% cholic acid.

RESULTS

On chow, expression levels of the gallbladder mucin genes were essentially similar between MUC1.Tg and wild-type mice. The lithogenic diet induced 3-fold higher expression levels of Muc1, Muc3, Muc4, Muc5ac, and Muc5b messenger RNA in MUC1.Tg mice compared with wild-type mice. Gallbladder cholesterol absorption and size were significantly greater in MUC1.Tg mice than in wild-type mice regardless of whether the chow or the lithogenic diet was fed. Gallbladder emptying in response to exogenously administered cholecystokinin-8 was significantly reduced in MUC1.Tg mice but not in wild-type mice. At 4 weeks on the lithogenic diet, mucin accumulation was found in all MUC1Tg mice and in 60% of wild-type mice. Consequently, these alterations greatly accelerated cholesterol crystallization and gallstone formation in MUC1.Tg mice. However, biliary lipid secretion rates and cholesterol saturation indices of gallbladder biles were comparable in MUC1.Tg and wild-type mice.

CONCLUSIONS

Increased gallbladder epithelial MUC1 mucin enhances cholelithogenesis by promoting gallbladder cholesterol absorption and impairing gallbladder motility in mice.

Association of APOE-C1 gene cluster polymorphisms with gallstone disease

BACKGROUND

Genetic polymorphisms in apolipoprotein genes may be associated with alteration in lipid profile and susceptibility to gallstone disease.

AIM

To find out the association of APOE HhaI and APOC1 HpaI polymorphisms with gallstone disease.

SUBJECTS

HhaI polymorphism of APOE and HpaI polymorphism of APOC1 were analysed in DNA samples of 214 gallstone patients and 322 age- and sex-matched healthy controls.

METHODS

For genotyping DNA samples of all study subjects were amplified using polymerase chain reaction, followed by restriction digestion. All statistical analyses were done using SPSS v11.5 and ARLEQUIN v2.0 softwares.

RESULT

APOC1 HpaI polymorphism was found to be significantly associated with gallstone disease. Frequency of H2H2 was significantly higher (P = 0.017) in patients than in controls and it was imposing very high risk (OR 9.416, 95% CI 1.125-78.786) for gallstone disease. When data were stratified in male and female, H2H2 was associated (P = 0.011) with disease in females only. Analysis at allele level revealed no association. APOE HhaI polymorphism and APOE-C1 haplotypes showed no association with gallstone disease.

CONCLUSION

APOC1 HpaI polymorphism is associated with gallstone disease and shows gender-specific differences. APOE HhaI polymorphism may not be associated with gallstone disease.

Overexpression of estrogen receptor alpha increases hepatic cholesterogenesis, leading to biliary hypersecretion in mice

We explored whether there is an "estrogen-ERalpha-SREBP-2" (for estrogen-estrogen receptor subtype alpha-sterol-regulatory element binding protein-2) pathway for regulating hepatic cholesterol biosynthesis in ovariectomized AKR mice treated with 17beta-estradial (E2) at 6 microg/day or E2 plus the antiestrogenic agent ICI 182,780 at 125 microg/day and on chow or fed a high-cholesterol (1%) diet for 14 days. To monitor changes in cholesterol biosynthesis and newly synthesized cholesterol secreted into bile, incorporation into digitonin-precipitable sterols in mice treated with 25 mCi of [3H]water was measured in extracts of liver and extrahepatic organs 1 h later and in hepatic biles 6 h later. ERalpha upregulated SREBP-2, with resulting activation of SREBP-2-responsive genes in the cholesterol biosynthetic pathway. The E2-treated mice continued to synthesize cholesterol in spite of its excess availability from high dietary cholesterol, which reflects a loss in controlling the negative feedback regulation of cholesterol synthesis. These alterations augmented biliary cholesterol secretion and enhanced the lithogenicity of bile. However, these lithogenic effects of E2 were fully blocked by ICI 182,780. We conclude that during estrogen treatment, more newly synthesized cholesterol determined by the estrogen-ERalpha-SREBP-2 pathway is secreted into bile, leading to biliary cholesterol hypersecretion. These studies provide insights into therapeutic approaches to cholesterol gallstones in high-risk subjects, especially those exposed to high levels of estrogen.

Reduced susceptibility to cholesterol gallstone formation in mice that do not produce apolipoprotein B48 in the intestine

It has been found that polymorphisms in the apolipoprotein (APO)-B gene are associated with cholesterol gallstones in humans. We hypothesized that APO-B plays a major regulatory role in the response of biliary cholesterol secretion to high dietary cholesterol and contributes to cholesterol gallstone formation. In the present study, we investigated whether lack of expression of intestinal Apob48 or Apob100 reduces susceptibility to cholesterol gallstones by decreasing intestinal absorption and biliary secretion of cholesterol in male mice homozygous for an "APO-B48 only" allele (Apob(48/48)), an "APO-B100 only" allele (Apob(100/100)), or a wild-type APO-B allele (Apob+/+) before and during an 8-week lithogenic diet. We found that cholesterol absorption was significantly decreased as a result of the APO-B48 deficiency in Apob(100/100) mice compared with wild-type and Apob(48/48) mice, regardless of whether chow or the lithogenic diet was administered. Consequently, hepatic cholesterol synthesis was significantly increased in Apob(100/100) mice compared with wild-type and Apob(48/48) mice. On chow, the APO-B100 deficiency in Apob(48/48) mice with reduced plasma levels of LDL/VLDL--but not HDL cholesterol--induced relative hyposecretion of biliary bile salts and phospholipids accompanying normal biliary cholesterol secretion. Compared with Apob(48/48) and wild-type mice, lithogenic diet-fed Apob(100/100) mice displayed significantly lower secretion rates of biliary cholesterol, but not phospholipid or bile salts, which results in significant decreases in prevalence rates, numbers, and sizes of gallstones. In conclusion, absence of expression of intestinal Apob48, but not Apob100, reduces biliary cholesterol secretion and cholelithogenesis, possibly by decreasing intestinal absorption and hepatic bioavailability.