Hepatic cholesterol metabolism in patients with cholesterol gallstones: enhanced intracellular transport of cholesterol

Resistance to Cholesterol Gallstone Disease: Hepatic Cholesterol Metabolism

Cholesterol gallstone disease (CGD) is one of the most common digestive diseases, and it is closely associated with hepatic cholesterol metabolism. Cholesterol gallstones may be caused by abnormal hepatic cholesterol metabolism, such as excessive cholesterol biosynthesis within the liver, interfering with the uptake or export of cholesterol in the liver, and abnormal hepatic cholesterol esterification. In this review, we begin with a brief overview of the clinical diagnosis and treatment of gallstone disease (GSD). Then, we briefly describe the major processes of hepatic cholesterol metabolism and summarize the key molecular expression changes of hepatic cholesterol metabolism in patients with gallstones. We review and analyze the recent advances in elucidating the relationships between these key molecules and CGD, and some targets significantly impacting on CGD via hepatic cholesterol metabolism are also listed. We also provide a significant discussion on the relationship between CGD and nonalcoholic fatty liver disease (NAFLD). Finally, the new discoveries of some therapeutic strategies associated with hepatic cholesterol metabolism to prevent and treat CGD are summarized.

Curcumae rhizoma and its major constituents against hepatobiliary disease: Pharmacotherapeutic properties and potential clinical applications

BACKGROUND

Hepatobiliary disease currently serves as an urgent health issue in public due to health-modulating factors such as extension of life expectancy, increasingly sedentary lifestyles and over-nutrition. A definite treatment remains lacking owing to different stages of the disease itself and its intricate pathogenesis. Traditional Chinese medicine (TCM) has been gradually popularized in clinic with the satisfactory efficacy and good safety. Curcumae Rhizoma (called E Zhu, EZ in Chinese) is a representative herb, which has been used to treat hepatobiliary disease for thousands of years.

PURPOSE

To systematically summarize the recent research advances on the pharmacological activities of EZ and its constituents, explain the underlying mechanisms of preventing and treating hepatobiliary diseases, and assess the shortcomings of existing work. Besides, ethnopharmacology, phytochemicals, and toxicology of EZ have been researched.

METHODS

The information about EZ was collected from various sources including classic books about Chinese herbal medicine, and scientific databases including Web of Science, PubMed, ScienceDirect, Springer, ACS, SCOPUS, CNKI, CSTJ, and WANFANG using keywords given below and terms like pharmacological and phytochemical details of this plant.

RESULTS

The chemical constituents isolated and identified from EZ, such as terpenoids including β-elemene, furanodiene, germacrone, etc. and curcuminoids including curcumin, demethoxycurcumin, bisdemethoxycurcumin, etc. prove to have hepatoprotective effect, anti-liver fibrotic effect, anti-fatty liver effect, anti-liver neoplastic effect, and cholagogic effect through TGF-β1/Smad, JNK1/2-ROS, NF-κB and other anti-inflammatory and antioxidant signaling pathways. Also, EZ is often combined with other Chinese herbs in the treatment of hepatobiliary diseases with good clinical efficacy and no obvious adverse reactions.

CONCLUSION

It provides a preclinical basis for the efficacy of EZ as an effective therapeutic agent for the prevention and treatment of hepatobiliary diseases. Even so, the further studies still needed to alleviate hepatotoxicity and expand clinical application.

Association of Common Single Nucleotide Polymorphisms of Candidate Genes with Gallstone Disease: A Meta-Analysis

Numerous studies have investigated the relationship between various candidate gene polymorphisms and gallbladder stone disease (GSD) across ethnic populations; however, the results are often inconsistent. This meta-analysis aims to comprehensively evaluate the influence of common ABCG8 T400K, ABCG8 D19H, ABCG8 C54Y, ApoB100 EcoRI, ApoB100 XbaI, ApoE HhaI, CETP TaqI, CYP7A1 Bsa, LRPAP1 I/D and TNF-α A308G polymorphisms on the risk of gallbladder stone disease. 33 Full-text articles with 9250 cases and 12,029 healthy controls (total 21,279 subjects) were analyzed using the RevMan software (V5.1) and the Comprehensive Meta-analysis software (Version 2.0, BIOSTAT, Englewood, NJ) a Random-effects model was applied. Begg's funnel plots, Fail-safe number, Egger's regression intercept and Begg and Mazumdar rank correlation tests were performed for the potential publication bias and sensitivity analysis. The studies were also sub-grouped into European and non-European groups to find out role of ethnicity, if any, on GSD risk. Studies included in quantitative synthesis were ABCG8 T400K rs4148217 (cases/controls, n = 671/1416) (4 studies), ABCG8 D19H rs11887534 (n = 1633/2306) (8 studies), ABCG8 C54Y rs4148211 (n = 445/1194) (3 studies), ApoB100 EcoRI rs1042031 (n = 503/390) (4 studies), ApoB100 XbaI rs693 (n = 1214/1389) (9 studies), ApoE HhaI rs429358 (n = 1335/1482) (12 studies), CETP TaqI rs708272 (n = 1038/1025) (5 studies), CYP7A1 Bsa rs3808607 (n = 565/514) (3 studies), LRPAP1 I/D rs11267919 (n = 849/900) (3 studies), TNF-α A308G rs1800629 (n = 997/1413) (3 studies). The combined results displayed significant association of ABCG8 D19H (GC + CC) [OR with 95%CI = 2.2(1.7-2.8); p < 0.00001], ABCG8 Y54C (GA + GG) [OR with 95%CI = 0.65(0.5-0.9); p = 0.01]. APOB100 EcoRI (GG vs. AA) [OR with 95%CI = 0.51(0.3-0.9); p = 0.05], (GG vs. GA) [OR with 95%CI = 0.6(0.4-0.9); p = 0.04], (GA + AA) [OR with 95%CI = 0.6(0.4-0.9); p = 0.006]. APOB Xba I (X^- vs. X⁺) [OR with 95%CI = 0.53(0.3-0.8); p = 0.006. APOE Hha I (E4/E4 vs. E3/E3) [OR with 95%CI = 3.5(1.1-14.9); p = 0.04] and LRPAP1 I/D (ID + II) [OR with 95%CI = 1.27(1.0-1.6); p = 0.03] with the GSD risk. It was found that ABCG D19H was significantly associated with GSD in both European and Non-European populations. While APOB XbaI and LRPAP1 I/D markers were associated with gallstone disease only in Non- European population. Additionally, APOE HhaI and APOB 100 ECoRI were found to be associated with GSD only in European population. The results of quantitative synthesis suggest that the ABCG8 D19H polymorphism was associated with the increased risk of GSD in both European and Non-European populations, APOE Hha I and LRPAP1 I/D polymorphisms were associated with the increased risk of GSD in European and Non-European population respectively. However, no association was found in ABCG8 T400K, CETP Taq1, CYP7A1 Bsa and TNF-A308G polymorphisms with Gallstone Disease.

Combination of curcumin and piperine prevents formation of gallstones in C57BL6 mice fed on lithogenic diet: whether NPC1L1/SREBP2 participates in this process?

BACKGROUND

A disruption of cholesterol homeostasis characterized by the physical-chemical imbalance of cholesterol solubility in bile often results in formation of cholesterol gallstones. Our earlier studies revealed that curcumin (1000 mg/kg) could prevent formation of gallstones. It has been proved that curcumin is poorly absorbed while piperine is a bioavailability-enhancer. Nevertheless, whether curcumin combined with piperine could enhance the effect of curcumin in preventing gallstones is still awaited.

METHOD

C57BL6 mice were fed on a lithogenic diet concomitant with curcumin at 500 or 1000 mg/kg and/or piperine at 20 mg/kg for 4 weeks. The ratio of gallbladder stone formation was recorded and samples of blood, bile, gallbladder, liver and small intestine were also collected. The volume of gallbladder and weight of liver were calculated, and blood and bile samples were analyzed through biochemical methods. Intestinal NPC1L1 and SREBP2 mRNA and protein expression were detected by real-time PCR and Western blot.

RESULT

Combining with piperine can significantly enhance the effect of curcumin, thus preventing the development of gallbladder stones, lowering the saturation of blood lipids and cholesterol in bile, as well as decreasing the expression of NPC1L1 and SREBP2 in both mRNA and protein levels.

CONCLUSION

Curcumin can prevent the formation of cholesterol gallstones induced by high fat diet in mice and SREBP2 and NPC1L1 may participate in this process. Piperine can increase curcumin's bioavailability, thereby enhancing the effect of curcumin.

Infectious diseases and the gallbladder

Infections of the gastrointestinal tract can often involve the gallbladder. Infection probably plays a role in the formation of gallstones but is more commonly thought to contribute to acute illness in patients. Acute calculous cholecystitis caused by an impacted gallstone is often complicated by secondary bacterial infection and is a major cause of morbidity and even mortality in patients. A wide variety of organisms can be associated with acute acalculous cholecystitis, a less common but potentially more severe form of acute cholecystitis. This review focuses on infections and their role in the above-mentioned processes involving the gallbladder.

Overexpression of Sterol Carrier Protein 2 in patients with hereditary cholesterol gallstones

BACKGROUND

Lithogenic bile is the major cause of cholesterol gallstone, but its pathogenesis is not well understood. The hypersecretion of biliary cholesterol is believed to be an important cause of lithogenic bile. Sterol Carrier Protein 2 (SCP2) participates in cholesterol trafficking and lipid metabolism in hepatocytes and may play a key role in cholesterol gallstone formation.

METHODS

21 cholesterol gallstone genealogies were studied to investigate the expression of SCP2 gene in liver tissue of hereditary and non-hereditary cholesterol gallstone patients as well as non-gallstone patients. The mRNA expression of liver SCP2 in 28 hereditary patients, 30 non-hereditary cholesterol gallstone patients and 32 non-gallstone patients was measured by Reverse Transcription Polymerase Chain Reaction (RT-PCR). The protein expression of liver SCP2 was also detected in all the patients by Western blotting. At the same time, the bile was also analyzed with biochemical techniques and the Cholesterol Saturation Index (CSI) was calculated.

RESULTS

The mRNA and protein expression of SCP2 was significantly increased in cholesterol gallstone patients compared to those of non-gallstone patients. Moreover, SCP2 was expressed at higher levels in hereditary cholesterol gallstone patients than that of non-hereditary cholesterol gallstone patients. There was significant difference observed in CSI between cholesterol gallstone patients and non-gallstone patients, but not in CSI between hereditary and non-hereditary cholesterol gallstone patients.

CONCLUSIONS

SCP2 was overexpressed in hereditary cholesterol gallstone patients compared to non-hereditary cholesterol gallstone patients. This finding indicated that SCP2 might be one of the genetic factors contributing to cholesterol gallstone formation, which was always accompanied by the increase of bile lithogenicity.

CYP7A1 (-204 A>C; rs3808607 and -469 T>C; rs3824260) promoter polymorphisms and risk of gallbladder cancer in North Indian population

Cholesterol 7-alpha hydroxylase (CYP7A1), which is a rate-limiting enzyme for cholesterol catabolism and bile acid synthesis, may affect cholesterol homeostasis and result in gallstone formation that is a major risk factor for gallbladder cancer (GBC) pathogenesis. Genetic variations in CYP7A1 may influence its expression and thus may affect the risk of gallstone disease and GBC. We aimed to study the association of 2 promoter polymorphisms of CYP7A1 (-204 A>C [rs3808607] and -469 T>C [rs3824260]) in gallstone and GBC susceptibility in North Indian population. The study included 185 GBC patients, 195 symptomatic gallstone patients, and 200 healthy controls. Genotyping for both polymorphisms was done by polymerase chain reaction-restriction fragment length polymorphism method. Although the CC genotype of CYP7A1 -204 A>C was not significantly associated with gallstone disease (P = .083, odds ratio [OR] = 1.69, 95% confidence interval [CI] = 0.9-3.0), it was conferring higher risk for GBC (P = .018, OR = 2.05, 95% CI = 1.1-3.7). However, CYP7A1 -469 T>C was not associated with gallstone disease and GBC risk in our population. After subgroup stratifications on the basis of sex and gallstone status, CC genotype and variant allele of CYP7A1 -204 A>C imparted higher risk for GBC in women (P = .003, OR = 3.30, 95% CI = 1.5-7.2) and patients without gallstones (P = .045, OR = 1.91, 95% CI = 1.2-3.6). Haplotype analysis of the 2 polymorphisms showed that C,T (P = .045, OR = 1.84, 95% CI = 1.0-3.3) and C,C (P = .0001, OR = 3.10, 95% CI = 1.6-6.0) haplotypes had elevated risk of GBC predisposition. CYP7A1 -469 T>C is not associated with gallstone disease or GBC risk. Although CYP7A1 -204 A>C might play a modest role in gallstone susceptibility, it is an independent risk factor for GBC in North Indian population. Underlying mechanism for GBC susceptibility by CYP7A1 (-204 A>C and -469 T>C) haplotype appears to be independent of gallstone pathway and is believed to involve genotoxicity resulting from subnormal bile acid production.

Determinants of transhepatic cholesterol flux and their relevance for gallstone formation

Cholesterol available for bile secretion is controlled by a wide variety of proteins that mediate lipoprotein cholesterol uptake and cholesterol transport and metabolism in the liver. From a disease perspective, abnormalities in the transhepatic traffic of cholesterol from plasma into the bile may influence the risk of cholesterol gallstone formation. This review summarizes some recent progress in understanding the hepatic determinants of biliary cholesterol secretion and its potential pathogenic implications in cholesterol gallstone disease. This information together with new discoveries in this field may lead to improved risk evaluation, novel surrogate markers and earlier diagnosis, better preventive approaches and more effective pharmacological therapies for this prevalent human disease.

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.

Increased expression of LXR alpha, 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.

Hepatic cholesterol transport from plasma into bile: implications for gallstone disease

PURPOSE OF REVIEW

The transhepatic traffic of cholesterol from plasma lipoproteins into the bile is critical for overall cholesterol homeostasis and its alterations may lead to cholesterol gallstone formation. This review summarizes recent progress in understanding the key hepatic cholesterol metabolism-related proteins and pathways that influence biliary secretion of cholesterol.

RECENT FINDINGS

In cholesterol-fed apolipoprotein E knockout mice, the availability of dietary cholesterol for biliary disposal is decreased and diet-induced gallstone formation is impaired. Scavenger receptor class B type I is relevant for cholesterol transport from plasma HDL into the bile in chow-fed mice, however its expression is not critical for biliary cholesterol secretion and gallstone formation in lithogenic diet-fed mice. Intrahepatic cholesterol transport proteins (e.g. sterol carrier protein-2, Niemann Pick type C-1 protein) also determine liver cholesterol available for biliary secretion in mice. Genetic manipulation of canalicular ATP-binding cassette transporter G5 and G8 expression in mice has established their essential role for biliary cholesterol secretion.

SUMMARY

Recent studies have underscored that different proteins involved in hepatic cholesterol transport regulate the availability of cholesterol for biliary secretion. These advances may provide new avenues for prevention and treatment of various disease conditions linked to abnormal cholesterol metabolism.

Polymorphisms at cholesterol 7α-hydroxylase, apolipoproteins B and E and low density lipoprotein receptor genes in patients with gallbladder stone disease

AIM: To investigate the relationship between gallbladder stone disease (GSD) and single nucleotide polymorphisms of cholesterol 7α-hydroxylase (CYP7A) gene promoter, apolipoprotein (APO) B gene exon 26, APOE gene exon 4 or microsatellite polymorphism of low density lipoprotein receptor (LDLR) gene exon 18.

METHODS: Genotypes of CYP7A, APOB, APOE and LDLR genes were determined in 105 patients with GSD diagnosed by B-mode ultrasonography and 274 control subjects. Serum lipids were analyzed with HITACHI 7060 automaic biochemical analyzer.

RESULTS: Body mass index (BMI) was significantly higher in patients with GSD (24.47 ± 3.09) than in controls (23.50 ± 2.16). Plasma total cholesterol was lower in patients with GSD (4.66 ± 0.92 mmol/L) than in controls (4.91 ± 0.96 mmol/L), P < 0.01 after adjusted for age, sex and BMI. The significantly higher frequency of A allele of CYP7A gene polymorphism and X+ allele of APOB gene polymorphism was seen in GSD patients. Percentages of A allele in patients and controls were 62.86% and 54.38% (P < 0.05) and those of X+ allele 8.57% and 4.01% (P < 0.01). Subjects with A allele had significantly lower plasma total cholesterol and LDL cholesterol than subjects with CC homozygote. In a multiple variable logistic regression model, the BMI (OR = 1.13, 95%CI: 1.05-1.22), A allele (OR = 1.48, 95%CI: 1.05-2.09) and X+ allele (OR = 2.28, 95%CI: 1.14-4.59) were positively associated with GSD (P < 0.05). Plasma total cholesterol (OR = 0.69, 95%CI: 0.64-0.74) was negatively related to GSD (P < 0.05).

CONCLUSION: With an association analysis, it was determined that A allele of CYP7A gene and X+ allele of APOB gene might be considered as risk genes for GSD. These alleles are related with differences of serum lipids among subjects. Multiple-variable logistic regression model analysis showed that besides BMI, GSD was affected by polygenetic factors. But the mechanism for these two alleles responsible for GSD requires further investigations.

Bile acid synthesis is increased in Chilean Hispanics with gallstones and in gallstone high-risk Mapuche Indians

BACKGROUND & AIMS

Gallstone disease is an important, costly health-care problem in Western societies. It is still unclear whether hepatic lipid regulatory enzymes play primary or secondary roles in gallstone formation. In this study, the aim was to investigate whether the synthesis of bile acids and cholesterol is increased in gallstone disease and to test whether such a metabolic change, if present, might occur before gallstone formation.

METHODS

A total of 125 Chilean Hispanic women (80 without gallstones and 45 with gallstones) matched for age and body mass index were investigated, along with 40 Chilean Mapuche Indian women (20 without gallstones and 20 with gallstones), a population group in which the prevalence for gallstone disease is very high. Fasting blood plasma samples were assayed for 7 alpha-hydroxy-4-cholesten-3-one and lathosterol, 2 strong indicators for hepatic bile acid and body cholesterol synthesis, respectively.

RESULTS

Plasma 7 alpha-hydroxy-4-cholesten-3-one levels, corrected for plasma cholesterol, were significantly increased by 50% in Hispanic women with gallstones as compared with gallstone-free Hispanics (P < 0.006). As compared with Hispanic women without gallstones, plasma 7 alpha-hydroxy-4-cholesten-3-one levels were increased by > or =100% (P < 0.002) in Mapuche Indian women, independently of whether gallstones were present. Plasma lathosterol, corrected for plasma cholesterol, was significantly increased by 22% in Hispanic women with gallstones and in Mapuche Indian women compared with Hispanic women.

CONCLUSIONS

The results indicate that the synthesis of bile acids and cholesterol is induced in gallstone disease and precedes gallstone development. These inductions presumably occur as a response to an increased intestinal loss of bile acids.

Genetic background of cholesterol gallstone disease

Cholesterol gallstone formation is a multifactorial process involving a multitude of metabolic pathways. The primary pathogenic factor is hypersecretion of free cholesterol into bile. For people living in the Western Hemisphere, this is almost a normal condition, certainly in the elderly, which explains the very high incidence of gallstone disease. It is probably because the multifactorial background genes responsible for the high incidence have not yet been identified, despite the fact that genetic factors clearly play a role. Analysis of the many pathways involved in biliary cholesterol secretion reveals many potential candidates and considering the progress in unraveling the regulatory mechanisms of the responsible genes, identification of the primary gallstone genes will be successful in the near future.

Disruption of the sterol carrier protein 2 gene in mice impairs biliary lipid and hepatic cholesterol metabolism

Hepatic up-regulation of sterol carrier protein 2 (Scp2) in mice promotes hypersecretion of cholesterol into bile and gallstone formation in response to a lithogenic diet. We hypothesized that Scp2 deficiency may alter biliary lipid secretion and hepatic cholesterol metabolism. Male gallstone-susceptible C57BL/6 and C57BL/6(Scp2(-/-)) knockout mice were fed a standard chow or lithogenic diet. Hepatic biles were collected to determine biliary lipid secretion rates, bile flow, and bile salt pool size. Plasma lipoprotein distribution was investigated, and gene expression of cytosolic lipid-binding proteins, lipoprotein receptors, hepatic regulatory enzymes, and intestinal cholesterol absorption was measured. Compared with chow-fed wild-type animals, C57BL/6(Scp2(-/-)) mice had higher bile flow and lower bile salt secretion rates, decreased hepatic apolipoprotein expression, increased hepatic cholesterol synthesis, and up-regulation of liver fatty acid-binding protein. In addition, the bile salt pool size was reduced and intestinal cholesterol absorption was unaltered in C57BL/6(Scp2(-/-)) mice. When C57BL/6(Scp2(-/-)) mice were challenged with a lithogenic diet, a smaller increase of hepatic free cholesterol failed to suppress cholesterol synthesis and biliary cholesterol secretion increased to a much smaller extent than phospholipid and bile salt secretion. Scp2 deficiency did not prevent gallstone formation and may be compensated in part by hepatic up-regulation of liver fatty acid-binding protein. These results support a role of Scp2 in hepatic cholesterol metabolism, biliary lipid secretion, and intracellular cholesterol distribution.

Gene structure, intracellular localization, and functional roles of sterol carrier protein-2

Since its discovery three decades ago, sterol carrier protein-2 (SCP-2) has remained a fascinating protein whose physiological function in lipid metabolism remains an enigma. Its multiple proposed functions arise from its complex gene structure, post-translational processing, intracellular localization, and ligand specificity. The SCP-2 gene has two initiation sites coding for proteins that share a common 13 kDa SCP-2 C-terminus: (1) One site codes for 58 kDa SCP-x which is partially post-translationally cleaved to 13 kDa SCP-2 and a 45 kDa protein. (2) A second site codes for 15 kDa pro-SCP-2 which is completely post-translationally cleaved to 13 kDa SCP-2. Very little is yet known regarding how the relative proportions of the two transcripts are regulated. Although all three proteins contain a C-terminal SKL peroxisomal targeting sequence, it is unclear why all three proteins are not exclusively localized in peroxisomes. However, the recent demonstration that the SCP-2 N-terminal presequence in pro-SCP-2 dramatically modulated the intracellular targeting coded by the C-terminal peroxisomal targeting sequence may account for the observation that as much as half of total SCP-2 is localized outside the peroxisome. The tertiary and secondary structure of the 13 kDa SCP-2, but not that of 15 kDa pro-SCP-2 and 58 kDa SCP-x, are now resolved. Increasing evidence suggests that the 58 kDa SCP-x and 45 kDa proteins are peroxisomal 3-ketoacyl-CoA-thiolases involved in the oxidation of branched chain fatty acids. Since 15 kDa pro-SCP-2 is post-translationally completely cleaved to 13 kDa SCP-2, relatively little attention has been focused on this protein. Finally, although the 13 kDa SCP-2 is the most studied of these proteins, because it exhibits diversity of its ligand partners (fatty acids, fatty acyl CoAs, cholesterol, phospholipids), new potential physiological function(s) are still being proposed and questions regarding potential compensation by other proteins with overlapping specificity are only beginning to be resolved.

Insulin injections enhance cholesterol gallstone incidence by changing the biliary cholesterol saturation index and apo A-I concentration in hamsters fed a lithogenic diet

BACKGROUND/AIMS

A link between insulin and cholesterol gallstone disease has often been suspected but never demonstrated. The aim was to evaluate the direct implication of insulin in the gallbladder cholesterol gallstone formation process.

METHODS

Hamsters fed with a soft-inducing lithogenic diet, enriched with sucrose, were injected daily, for 1 week, either with long-acting insulin or saline (controls).

RESULTS

Insulin injections doubled the cholesterol gallstone incidence. The cholesterol saturation index (CSI) of bile significantly increased (+19%) and biliary apolipoprotein A-I (apo A-I) decreased, both in concentration (-71%) and the proportion relative to the total biliary proteins (-25%). No modifications in the biliary bile acid composition were noticed. Hepatic HMGCoA reductase activity was higher (+341%), CYP7A1 activity was lower (-52%), whereas CYP27A1 and CYP7B1 were not affected. The hepatic low-density liprotein (LDL)-receptor and SR-BI masses did not vary. The hepatic total cholesterol content increased (+42%). Fasting plasma phospholipid and triglyceride concentrations significantly decreased (-15 and -60%, respectively), but the cholesterol concentration remained constant.

CONCLUSIONS

These results suggest that insulin injections enhance cholesterol gallstone incidence by increasing the CSI of bile and decreasing the concentration and proportion of a biliary anti-nucleating protein, apo A-I. Insulin modulates the major enzymes of cholesterol and bile acid metabolisms in vivo.

Chromosomal organization of candidate genes involved in cholesterol gallstone formation: a murine gallstone map

Epidemiologic and family studies indicate that cholesterol gallstone formation is in part genetically determined. The major contribution to our current understanding of gallstone genes derives from animal studies, particularly cross-breeding experiments in inbred mouse strains that differ in genetic susceptibility to cholesterol gallstone formation (quantitative trait loci mapping). In this review we summarize how the combined use of genomic strategies and phenotypic studies in inbred mice has proven to be a powerful means of dissecting the complex pathophysiology of this common disease. We present a "gallstone map" for the mouse, consisting of all genetic loci that have been identified to confer gallstone susceptibility as well as putative candidate genes. Translation of the genetic loci and genes between mouse and human predicts chromosomal regions in the human genome that are likely to harbor gallstone genes. Both the number and the precise understanding of gallstone genes are expected to further increase with rapid progress of the genome projects, and multiple new targets for early diagnosis and prevention of gallstone disease should become possible.

Sterol carrier protein 2 gene transfer changes lipid metabolism and enterohepatic sterol circulation in mice

BACKGROUND & AIMS

Sterol carrier protein 2 (SCP-2) enhances sterol cycling and facilitates cholesterol translocation between intracellular organelles and plasma membrane in cultured cells, including hepatocytes. We examined the role of SCP-2 in hepatic cholesterol and lipid trafficking through the sinusoidal and canalicular secretory pathways of the liver in vivo.

METHODS

Recombinant adenovirus-mediated SCP-2 gene transfer was used to obtain hepatic overexpression of SCP-2 in C57BL/6 mice.

RESULTS

SCP-2 overexpression in the mouse liver resulted in an 8-fold increase of SCP-2 protein levels and determined various effects on lipid metabolism. It decreased high-density lipoprotein cholesterol and increased low-density lipoprotein (LDL) cholesterol concentrations. The expressions of hepatic LDL receptor, apolipoprotein (apo) A-I, apoB, and apoE were decreased. SCP-2 overexpression also increased hepatic cholesterol concentration, associated with decreased cholesterol neosynthesis. Increased biliary cholesterol and bile acid secretion, bile acid pool size, and intestinal cholesterol absorption were also observed.

CONCLUSIONS

These results indicate that modulation of SCP-2 expression in the liver determines important modifications on lipoprotein metabolism, hepatic cholesterol synthesis and storage, biliary lipid secretion, bile acid metabolism, and intestinal cholesterol absorption.

Sterol carrier protein-2 alters high density lipoprotein-mediated cholesterol efflux

Although sterol carrier protein-2 (SCP-2) participates in the uptake and intracellular trafficking of cholesterol, its effect on "reverse cholesterol transport" has not been explored. As shown herein, SCP-2 expression inhibited high density lipoprotein (HDL)-mediated efflux of [(3)H]cholesterol and fluorescent 22-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3b-ol (NBD-cholesterol) up to 61 and 157%, respectively. Confocal microscopy of living cells allowed kinetic analysis of two intracellular pools of HDL-mediated NBD-cholesterol efflux: the highly fluorescent lipid droplet pool and the less fluorescent pool outside the lipid droplets, designated the cytoplasmic compartment. Both the whole cell and the cytoplasmic compartment exhibited two similar kinetic pools, the half-times of which were consistent with protein (t(b)(12) near 1 min) and vesicular (t(d)(12) = 10-20 min) mediated sterol transfer. Although SCP-2 expression did not alter cytoplasmic sterol pool sizes, the rapid t(b)(12) decreased 36%, while the slower t(d)(12) increased 113%. Lipid droplets also exhibited two kinetic pools of NBD-cholesterol efflux but with half-times over 200% shorter than those of the cytoplasmic compartment. The lipid droplet slower effluxing pool size and t(d)(12) were increased 48% and 115%, respectively, in SCP-2-expressing cells. Concomitantly, the level of the lipid droplet-specific adipose differentiation-related protein decreased 70%. Overall, HDL-mediated sterol efflux from L-cell fibroblasts reflected that of the cytoplasmic rather than lipid droplet compartment. SCP-2 differentially modulated sterol efflux from the two cytoplasmic pools. However, net efflux was determined primarily by inhibition of the slowly effluxing pool rather than by acceleration of the rapid protein-mediated pool. Finally, SCP-2 expression also inhibited sterol efflux from lipid droplets, an effect related to decreased adipose differentiation-related protein, a lipid droplet surface protein that binds cholesterol with high affinity.

Sterol carrier protein-2 localization in endoplasmic reticulum and role in phospholipid formation

Although sterol carrier protein-2 (SCP-2; also called nonspecific lipid transfer protein) binds fatty acids and fatty acyl-CoAs, its role in fatty acid metabolism is not fully understood. L-cell fibroblasts stably expressing SCP-2 were used to resolve the relationship between SCP-2 intracellular location and fatty acid transacylation in the endoplasmic reticulum. Indirect immunofluorescence double labeling and laser scanning confocal microscopy detected SCP-2 in peroxisomes > endoplasmic reticulum > mitochondria > lysosomes. SCP-2 enhanced incorporation of exogenous [(3)H]oleic acid into phospholipids and triacylglycerols of overexpressing cells 1.6- and 2.5-fold, respectively, stimulated microsomal incorporation of [1-(14)C]oleoyl-CoA into phosphatidic acid in vitro 13-fold, and exhibited higher specificity for unsaturated versus saturated fatty acyl-CoA. SCP-2 enhanced the rate-limiting step in microsomal phosphatidic acid biosynthesis mediated by glycerol-3-phosphate acyltransferase. SCP-2 also enhanced microsomal acyl-chain remodeling of phosphatidylethanolamine up to fivefold and phosphatidylserine twofold, depending on the specific fatty acyl-CoA, but had no effect on other phospholipid classes. In summary, these results were consistent with a role for SCP-2 in phospholipid synthesis in the endoplasmic reticulum.

Hepatocellular transport and secretion of biliary lipids

Bile is the route for elimination of cholesterol from the body. Recent studies have begun to elucidate hepatocellular, molecular and physical-chemical mechanisms whereby bile salts stimulate biliary secretion of cholesterol together with phospholipids, which are enriched (up to 95%) in phosphatidylcholines. Active translocation of bile salts and phosphatidylcholines across the hepatocyte's canalicular plasma membrane provides the driving force for biliary lipid secretion. This facilitates physical-chemical interactions between detergent-like bile salt molecules and the ectoplasmic leaflet of the canalicular membrane, which result in biliary secretion of cholesterol and phosphatidylcholines as vesicles. Within the hepatocyte, separate molecular pathways function to resupply bile salts, phosphatidylcholines and cholesterol to the canalicular membrane for ongoing biliary lipid secretion.

Inverse association between plasma cholesterol and gallstone disease

BACKGROUND

The association between gallstone disease (gallstones or cholecystectomy) and plasma lipids was evaluated in 2,089 subjects who attended a private health care facility in Mexico City from August 1991 to August 1992.

METHODS

All participants provided data on their sociodemographic status, non-insulin-dependent diabetes mellitus diagnoses, alcohol consumption, and smoking habits; women also gave data regarding their obstetric-gynecologic histories. Ultrasounds of the liver and biliary tract were performed. Cholesterol levels, high-density lipoproteins cholesterol, and triglyceride plasma concentration were determined.

RESULTS

This study shows a strong inverse association between gallstone disease and plasma cholesterol concentration, with OR = 0.61 (95% CI = 0.42-0.89) in the category of 181-239 mg/dL, and OR = 0.49 (95% CI = 0.32-0.77) in the group of 240 mg/dL or more, when compared to 180 mg/dL or less, after adjusting for the following risk factors: gender, age, and body mass index.

CONCLUSIONS

These results suggest an increment in the catabolic pool of cholesterol, reflected in lower levels of plasma cholesterol in subjects with gallstone disease.

Regulation of bile acid biosynthesis

This article provides a review of the pathways through which cholesterol is degraded to bile acids. Regulation of key enzymes in the bile acid biosynthestic pathways is discussed. The important role of these pathways in the maintenance of cholesterol homeostasis and the possible therapeutic implications for the treatment of hypercholesterolemia are emphasized.

Sterol carrier protein 2 participates in hypersecretion of biliary cholesterol during gallstone formation in genetically gallstone-susceptible mice

In inbred mice, susceptibility to cholesterol gallstone disease is conferred by Lith genes, which in part promote hypersecretion of cholesterol into bile in response to a high-fat/cholesterol/cholic acid (lithogenic) diet. Because cytosolic sterol carrier protein 2 (SCP2) is believed to participate in cellular cholesterol trafficking and is elevated in the liver cytosol of cholesterol gallstone patients, we defined the hepatic expression of SCP2 during cholesterol gallstone formation in gallstone-susceptible C57L and gallstone-resistant AKR mice fed the lithogenic diet. Steady-state cytosolic SCP2 levels in C57L, but not AKR mice increased as a function of time and were correlated positively with biliary cholesterol hypersecretion, cholesterol saturation indices of gall-bladder biles and the appearance of liquid and solid cholesterol crystals leading to gallstone formation. Steady-state mRNA levels increased co-ordinately, consistent with regulation of SCP2 expression at the transcriptional level. Our results suggest that overexpression of SCP2 contributes to biliary cholesterol hypersecretion and the pathogenesis of gallstones in genetically susceptible mice. Because of the different chromosomal localizations of the Lith and Scp2 genes, we postulate that Lith genes control SCP2 expression indirectly.

Genetic epidemiology of cholesterol cholelithiasis among Chilean Hispanics, Amerindians, and Maoris

BACKGROUND & AIMS

The etiology of cholesterol gallstones is multifactorial, with interactions of genes and the environment. The hypothesis that aborigine cholesterol lithogenic genes are widely spread among Chileans, a population with a high prevalence of gallstones, was tested.

METHODS

Medical history and anthropometric measurements were obtained and abdominal ultrasonography was performed in 182 Mapuche Indians, 225 Maoris of Easter Island, and 1584 Hispanics. Blood groups, DNA, lipids, and glucose were analyzed. The Amerindian Admixture Index and mitochondrial DNA (mtDNA) assessed the ethnicity and degree of racial admixture.

RESULTS

Amerindian Admixture Index was 0.8 in Mapuches and 0.4 in Hispanics. All Mapuches, 88% of Hispanics, but none of Maoris had Amerindian mtDNA haplotypes. Age- and sex-adjusted global prevalence of gallstone disease was higher in Mapuches (35%) than in Hispanics (27%) and Maoris (21%). Compared with Hispanics, the youngest group of Mapuches had the greatest corrected risk of gallstones: odds ratios of 6.0 in women and 2.3 in men. In contrast, the gallstone risk in Maoris was lower compared with Hispanics: odds ratios of 0.6 for women and 0.5 for men.

CONCLUSIONS

Cholesterol lithogenic genes appear widely spread among Chilean Indians and Hispanics. They could determine the early formation of gallstones and explain the high prevalence of gallbladder diseases among some South American populations.

Complex genetic control of HDL levels in mice in response to an atherogenic diet. Coordinate regulation of HDL levels and bile acid metabolism

Inbred strains of mice differ in susceptibility to atherogenesis when challenged with a high fat, high cholesterol diet containing 0.5% cholic acid. Studies of recombinant inbred (RI) strains derived from the susceptible strain C57BL/6J (B6) and the resistant strains C3H/HeJ (C3H) and BALB/cJ have revealed an association between fatty streak lesion size and a decrease in high density lipoprotein (HDL) levels on the diet. To better understand the genetic factors contributing to HDL metabolism and atherogenesis in response to the diet, we studied mice derived from an intercross between B6 and C3H using a complete linkage map approach. A total of 185 female progeny were typed for 134 genetic markers spanning the mouse genome, resulting in an average interval of about 10 cM between markers. A locus on distal chromosome 1 containing the apolipoprotein AII gene was linked to HDL-cholesterol levels on both the chow and the atherogenic diets, but this locus did not contribute to the decrease in HDL-cholesterol in response to the diet. At least three distinct genetic loci, on chromosomes 3, 5, and 11, exhibited evidence of linkage to a decrease in HDL-cholesterol after a dietary challenge. Since a bile acid (cholic acid) is required for the diet induced changes in HDL levels and for atherogenesis in these strains, we examined cholesterol-7-alpha hydroxylase (C7AH) expression. Whereas B6 mice exhibited a large decrease in C7AH mRNA levels in response to the diet, C3H showed an increase. Among the intercross mice, multiple loci contributed to the regulation of C7AH mRNA levels in response to the diet, the most notable of which coincided with the loci on chromosomes 3, 5, and 11 controlling HDL levels in response to the diet. None of these loci were linked to the C7AH structural gene which we mapped to proximal chromosome 4. These studies reveal coordinate regulation of C7AH expression and HDL levels, and they indicate that the genetic factors controlling HDL levels are more complex than previously suggested by studies of RI strains. Furthermore, we observed that two of the loci for C7AH expression contributed to differences in gallstone formation between these strains.

Sterol carrier protein-2 overexpression enhances sterol cycling and inhibits cholesterol ester synthesis and high density lipoprotein cholesterol secretion

Recent data indicate that sterol carrier protein-2 (SCP-2) functions in the rapid movement of newly synthesized cholesterol to the plasma membrane (Puglielli, L., Rigotti, A., Greco, A. V., Santos, M. J., and Nervi, F. (1995) J. Biol. Chem. 270, 18723-18726). In order to further characterize the cellular function of SCP-2, we transfected McA-RH7777 rat hepatoma cells with a pre-SCP-2 cDNA expression construct. In stable transfectants, pre-SCP-2 processing resulted in an 8-fold increase in peroxisomal levels of SCP-2. SCP-2 overexpression increased the rates of newly synthesized cholesterol transfer to the plasma membrane and plasma membrane cholesterol internalization by 4-fold. There was no effect of SCP-2 overexpression on the microsomal levels of acyl-CoA:cholesterol acyltransferase and neutral cholesterol ester (CE) hydrolase; however, in the intact cell, CE synthesis and mass were reduced by 50%. SCP-2 overexpression also reduced high density lipoprotein-cholesterol secretion and apoA-I gene expression by 70% and doubled the rate of plasma membrane desmosterol conversion to cholesterol. We conclude that SCP-2 overexpression enhances the rate of cholesterol cycling, which reduces the availability of cholesterol for CE synthesis and alters the activity of a cellular cholesterol pool involved in regulating apoA-I-mediated high density lipoprotein cholesterol secretion. The net result of these changes in cholesterol metabolism is a 46% increase in plasma membrane cholesterol content, the implications of which are discussed.