Loci from a genome-wide analysis of bilirubin levels are associated with gallstone risk and composition

Polymorphisms in gene UGT1A1 modify the association of prenatal exposure to polycyclic aromatic hydrocarbons with congenital heart diseases risk

INTRODUCTION

Prenatal exposure to polycyclic aromatic hydrocarbons (PAHs) is a risk factor for the occurrence of congenital heart diseases (CHDs). Genetic susceptibility to PAHs metabolism may modify the exposure-risk relationship. The role of uridine diphosphoglucuronosyl transferase 1A1 (UGT1A1) genetic polymorphisms for modulating the impacts of prenatal PAHs exposure on the risk of CHDs remains to be discovered.

OBJECTIVE

The aim of this study was to investigate whether maternal UGT1A1 genetic polymorphisms are associated with fetal susceptibility to CHDs and to assess whether the risk is modified by maternal PAHs exposure.

METHODS

Maternal urinary biomarker of PAHs exposure was determined in 357 pregnant women with CHDs fetuses and 270 controls (pregnant women carrying fetuses without major congenital malformations). Urinary 1-hydroxypyrene-glucuronide (1-OHPG) concentration, a sensitive biomarker for PAHs exposure, was measured using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry. Maternal single nucleotide polymorphisms (SNPs) in UGT1A1, including rs3755319, rs887829, rs4148323, rs6742078, and rs6717546, were genotyped using an improved multiplex ligation detection reaction (iMLDR) technique. Unconditional logistic regression was performed to determine the impacts of UGT1A1 polymorphisms on the risks of CHDs and their subtypes. Generalized multifactor dimensionality reduction (GMDR) was used to analyze the gene-gene and gene-PAHs exposure interactions.

RESULTS

None of the selected UGT1A1 polymorphisms was independently associated with the risk of CHDs. The interaction between SNP rs4148323 and PAHs exposure was observed to be associated with CHDs (p< .05). Pregnant women with high-level PAHs exposure and rs4148323 had an increased risk of carrying CHDs fetuses (GA-AA vs. GG: aOR = 2.00, 95% CI = 1.06-3.79). Moreover, the joint effect of rs4148323 and PAHs exposure was found to be significantly associated with risks of septal defects, conotruncal heart defects, and right-sided obstructive malformations.

CONCLUSIONS

Maternal genetic variations of UGT1A1 rs4148323 may modify the association between prenatal PAHs exposure and CHDs risk. This finding needs to be further confirmed in a larger-scale study.

Clinical and genetic definition of serum bilirubin levels for the diagnosis of Gilbert syndrome and hypobilirubinemia

BACKGROUND AND AIMS

Gilbert syndrome (GS) is genotypically predetermined by UGT1A1*28 homozygosity in Europeans and is phenotypically defined by hyperbilirubinemia using total bilirubin (TB) cutoff ≥1mg/dL (17 μmol/L). The prevalence of illnesses associated with GS and hypobilirubinemia has never been studied prospectively. As TB varies with UGT1A1*28 genotyping, sex, and age, we propose stratified definitions of TB reference intervals and report the prevalence of illnesses and adjusted 15 years survival.

METHODS

UK Biobank with apparently healthy liver participants (middle-aged, n=138,125) were analyzed after the exclusion of of nonhealthy individuals. The stratified TB was classified as GS when TB >90th centile; <10th centile indicated hypobilirubinemia, and between the 10th and 90th centile was normobilirubinemia. We compared the prevalence and survival rates of 54 illnesses using odds ratio (OR), logistic regression, and Cox models adjusted for confounders, and causality by Mendelian randomizations.

RESULTS

In women, we identified 10% (7,741/76,809) of GS versus 3.7% (2,819/76,809) using the historical cutoff of ≥1 mg/dL (P<0.0001). When GS and hypobilirubinemia participants were compared with normobilirubinemia, after adjustment and Mendelian randomizations, only cholelithiasis prevalence was significantly higher (OR=1.50; 95% CI [1.3-1.7], P=0.001) in men with GS compared with normobilirubinemia and in causal association with bilirubin (P=0.04). No adjusted survival was significantly associated with GS or hypobilirubinemia.

CONCLUSIONS

In middle-aged Europeans, the stratified TB demonstrates a careless GS underestimation in women when using the standard unisex 1 mg/dL cutoff. The prevalence of illnesses is different in GS and hypobilirubinemia as well as survivals before adjusting for confounding factors. With the exception of cholelithiasis in men, these differences were no more significant after adjustment and Mendelian randomization.

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.

Pancreatitis Prevention in Tabuk City, Kingdom of Saudi Arabia: Evaluating Public Knowledge and Raising Awareness of Risk Factors and Symptoms

INTRODUCTION

Pancreatitis is an inflammation of the pancreas. The pancreas is a flat, elongated gland situated in the upper abdomen, beyond the stomach. It produces digestive enzymes and hormones that regulate glucose absorption in the body. Pancreatitis can be acute, developing rapidly and lasting for several days, or chronic, persisting over an extended period and affecting specific individuals. While treatment can improve mild cases of pancreatitis, severe cases can be fatal.

METHOD

This study utilizes a cross-sectional survey design with 549 participants, allowing data collection from a representative sample of Tabuk City's adult population.

RESULTS

The participants' knowledge about the risk factors and symptoms of pancreatitis was inadequate. Among those who did not receive any information about pancreatitis and its risk factors, the count was 352 (64.1%). On the other hand, there was increased awareness of pancreatitis and its risk factors, which would lead to early detection and prevention. A total of 483 participants (88%) expressed adequate agreement, and 305 participants (55.6%) demonstrated an adequate response regarding seeking medical attention if they experienced any symptoms of pancreatitis.

CONCLUSION

Our findings revealed a lack of knowledge about the risk factors and symptoms of pancreatitis. Furthermore, there was inadequate awareness regarding governmental initiatives or programs that support access to pancreatitis knowledge and awareness in Tabuk City.

Causal association between serum total bilirubin and cholelithiasis: a bidirectional two-sample Mendelian randomization study

Background

Observational studies about the association between serum total bilirubin and cholelithiasis are inconsistent. Hence, it is essential to reevaluate the association between serum total bilirubin and cholelithiasis and to verify whether such association is causal or not.

Methods

We selected single-nucleotide polymorphisms (SNPs) that are strongly associated with exposure as instrumental variable and conducted a bidirectional two-sample Mendelian randomization (MR) study to explore the causal association between serum total bilirubin and cholelithiasis. We implemented the inverse-variance weighted approach as a primary analysis to combine the Wald ratio estimates. Four additional analyses, namely, MR-Egger regression, weighted median, weighted mode, and MR-pleiotropy residual sum and outlier (PRESSO), were utilized to investigate the causal association and the influence of potential pleiotropy.

Results

A total of 116 SNPs were selected as valid instrumental variables to estimate the causal association of serum total bilirubin on cholelithiasis, and causal association between genetically determined serum total bilirubin and cholelithiasis was demonstrated [beta = 0.10; 95% confident interval (CI), 0.07 to 0.14; p < 0.001]. Likewise, the other methods, namely, the weighted median (beta = 0.12; 95% CI, 0.08 to 0.15; p < 0.001), MR-Egger (beta = 0.11; 95% CI, 0.08 to 0.15; p < 0.001), weighted mode (beta = 0.11; 95% CI, 0.08 to 0.15; p < 0.001), and MR-PRESSO approaches, further confirmed that this result (p = 0.054) indicates similar results. In addition, seven SNPs were selected as instrumental variable to estimate causal association of cholelithiasis on serum total bilirubin, and the result supported the causal effect of cholelithiasis to serum total bilirubin (beta = 0.12; 95% CI, 0.09 to 0.15; p < 0.001). At the same time, the other methods, namely, the weighted median (beta = 0.10; 95% CI, 0.06 to 0.13; p < 0.001), MR-Egger (beta = 0.12; 95% CI, 0.07 to 0.18; p = 0.007), weighted mode (beta = 0.09; 95% CI, 0.03 to 0.14, p = 0.019), and MR-PRESSO methods, further confirmed this result (p < 0.001).

Conclusion

Our MR study revealed that the serum total bilirubin was causally associated with the risk of cholelithiasis, and the genetic predisposition to cholelithiasis was causally associated with the increased serum total bilirubin levels.

The Pancreas and Known Factors of Acute Pancreatitis

Pancreatitis is regarded by clinicians as one of the most complicated and clinically challenging of all disorders affecting the abdomen. It is classified on the basis of clinical, morphological, and histological criteria. Causes of acute pancreatitis can easily be identified in 75–85% of patients. The main causes of acute, recurrent acute, and chronic pancreatitis are gallstone migration and alcohol abuse. Other causes are uncommon, controversial, or unexplained. For instance, cofactors of all forms of pancreatitis are pancreas divisum and hypertriglyceridemia. Another factor that should be considered is a complication of endoscopic retrograde cholangiopancreatography: post-endoscopic retrograde cholangiopancreatography acute pancreatitis. The aim of this study is to present the known risk factors for acute pancreatitis, beginning with an account of the morphology, physiology, and development of the pancreas.

Common variant p.D19H of the hepatobiliary sterol transporter ABCG8 increases the risk of gallstones in children

INTRODUCTION

Gallstones are increasingly common in children. Genetic analyses of adult cohorts demonstrated that the sterol transporter ABCG8 p.D19H and Gilbert UGT1A1*28 variants enhance the odds of developing gallstones. The genetic background of common lithiasis in children remains unknown.

METHODS

Overall, 214 children with gallstone disease (1 month-17 years, 107 boys) were inclueded. The control cohorts comprised 214 children (age 6-17 years, 115 boys) and 172 adults (age 40-92 years, 70 men) without gallstones. The ABCG8 p.D19H and UGT1A1*28 polymorphisms as well as ABCB4 (c.504C>T rs1202283, c.711A>T rs2109505) and NPC1L1 variants (p.V1296V rs217434, c.-18C>A rs41279633) were genotyped using TaqMan assays. Serum concentrations of plant sterols and cholesterol precursors were measured by gas chromatography/mass spectrometry.

RESULTS

The ABCG8 risk allele was associated with an increased risk of stones (OR = 1.82, p = .03). Children carrying the p.19H allele presented with lower serum concentrations of surrogate markers of intestinal cholesterol absorption and decreased ratios of phytosterols to the cholesterol precursor desmosterol. Carriers of the common NPC1L1 rs217434 allele had an increased gallstone risk compared with stone-free adults (OR 1.90, p < .01). This variant also affected the ratio of phytosterols to cholesterol precursors (p = .03). Other tested variants were not associated with gallstone risk.

CONCLUSIONS

The p.D19H ABCG8 and, to a lesser extent, NPC1L1 rs217434 variants increase the risk of early-onset gallstone formation. These results point to the presence of a common lithogenic pathway in children and adults.

Impact of SLCO1B1*5 on Flucloxacillin and Co-Amoxiclav-Related Liver Injury

Background: Idiosyncratic drug-induced liver injury (DILI) is a serious uncommon disease that may develop as a result of the intake of certain drugs such as the antimicrobials flucloxacillin and co-amoxiclav. The reported cases showed significant associations between DILI and various human leukocyte (HLA) markers. The solute carrier organic anion transporter 1B1 (SLCO1B1), a non-HLA candidate gene, was previously reported as a risk factor for liver injury induced by rifampin and methimazole. This study presumed that SLCO1B1 may play a general role in the DILI susceptibility and therefore investigated the association of rs4149056 (SLCO1B1*5, T521C) polymorphism with flucloxacillin- and co-amoxiclav-induced liver injury. Methodology: We recruited 155 and 165 DILI cases of white ancestral origin from various European countries but mainly from the United Kingdom owing to flucloxacillin and co-amoxiclav, respectively. Only adult patients (≥18 years) who were diagnosed with liver injury and who showed i) clinical jaundice or bilirubin >2x the upper limit of normal (ULN), ii) alanine aminotransferase (ALT) >5x ULN or iii) alkaline phosphatase (ALP) >2x ULN and bilirubin > ULN were selected. The population reference sample (POPRES), a European control group (n = 282), was used in comparison with the investigated cases. TaqMan SNP genotyping custom assay designed by Applied Biosystems was used to genotype both DILI cohorts for SLCO1B1 polymorphism (rs4149056). Allelic discrimination analysis was performed using a step one real-time PCR machine. Genotype differences between cases and controls were examined using Fisher's exact test. GraphPad Prism version 5.0 was used to determine the p-value, odds ratio, and 95% confidence interval. Compliance of the control group with Hardy-Weinberg equilibrium was proven using a web-based calculator available at https://wpcalc.com/en/equilibrium-hardy-weinberg/. Results: A small number of cases failed genotyping in each cohort. Thus, only 149 flucloxacillin and 162 co-amoxiclav DILI cases were analyzed. Genotyping of both DILI cohorts did not show evidence of association with the variant rs4149056 (T521C) (OR = 0.71, 95% CI = 0.46-1.12; p = 0.17 for flucloxacillin cases and OR = 0.87, 95% CI = 0.56-1.33; p = 0.58 for co-amoxiclav), although slightly lower frequency (22.8%) of positive flucloxacillin cases was noticed than that of POPRES controls (29.4%). Conclusion: Carriage of the examined allele SLCO1B1*5 is not considered a risk factor for flucloxacillin DILI or co-amoxiclav DILI as presumed. Testing a different allele (SLCO1B1*1B) and another family member gene (SLCO1B3) may still be needed to provide a clearer role of SLCO1B drug transporters in DILI development-related to the chosen antimicrobials.

The Mitochondrial tRNAPhe 625G>A Mutation in Three Han Chinese Families With Cholecystolithiasis

In this study, we assessed three Chinese families with inherited cholecystolithiasis and conducted the clinical, genetic, and molecular characterization of these subjects. Eight of eighteen matrilineal relatives had a clinical phenotype in these three families. Sequence analysis of complete mitochondrial genomes in these probands identified the homoplasmic tRNA^Phe 625 G > A mutation and distinct sets of mtDNA polymorphisms belonging to haplogroups H2, F4b, and M10a. The 625G > A mutation disturbed the classic G-C base-pairings at a highly conserved position 49 in the T-stem of mitochondrial tRNAs. Molecular dynamics simulation showed that the structure of tRNA^phe with 625 G > A mutation was noticeably remodeled while compared with the isoform of the wild type. The occurrence of tRNA^Phe 625 G > A mutation in these various genetically unrelated subjects strongly indicates that this mutation is involved in the pathogenesis of cholecystolithiasis. This is the first evidence that tRNA mutations are associated with cholecystolithiasis, and it provided more insights into the genetic mechanism of cholecystolithiasis.

Gilbert's Syndrome and the Gut Microbiota - Insights From the Case-Control BILIHEALTH Study

The heme catabolite bilirubin has anti-inflammatory, anti-oxidative and anti-mutagenic effects and its relation to colorectal cancer (CRC) risk is currently under evaluation. Although the main metabolic steps of bilirubin metabolism, including the formation of stercobilin and urobilin, take place in the human gastrointestinal tract, potential interactions with the human gut microbiota are unexplored. This study investigated, whether gut microbiota composition is altered in Gilbert's Syndrome (GS), a mild form of chronically elevated serum unconjugated bilirubin (UCB) compared to matched controls. Potential differences in the incidence of CRC-associated bacterial species in GS were also assessed. To this end, a secondary investigation of the BILIHEALTH study was performed, assessing 45 adults with elevated UCB levels (GS) against 45 age- and sex-matched controls (C). Fecal microbiota analysis was performed using 16S rRNA gene sequencing. No association between mildly increased UCB and the composition of the gut microbiota in this healthy cohort was found. The alpha and beta diversity did not differ between C and GS and both groups showed a typical representation of the known dominant phyla. Furthermore, no difference in abundance of Firmicutes and Proteobacteria, which have been associated with the mucosa of CRC patients were observed between the groups. A sequence related to the Christensenella minuta strain YIT 12065 was identified with a weak association value of 0.521 as an indicator species in the GS group. This strain has been previously associated with a lower body mass index, which is typical for the GS phenotype. Overall, sex was the only driver for an identifiable difference in the study groups, as demonstrated by a greater bacterial diversity in women. After adjusting for confounding factors and multiple testing, we can conclude that the GS phenotype does not affect the composition of the human gut microbiota in this generally healthy study group.

Lack of an association between gallstone disease and bilirubin levels with risk of colorectal cancer: a Mendelian randomisation analysis

BACKGROUND

Epidemiological studies of the relationship between gallstone disease and circulating levels of bilirubin with risk of developing colorectal cancer (CRC) have been inconsistent. To address possible confounding and reverse causation, we examine the relationship between these potential risk factors and CRC using Mendelian randomisation (MR).

METHODS

We used two-sample MR to examine the relationship between genetic liability to gallstone disease and circulating levels of bilirubin with CRC in 26,397 patients and 41,481 controls. We calculated the odds ratio per genetically predicted SD unit increase in log bilirubin levels (ORSD) for CRC and tested for a non-zero causal effect of gallstones on CRC. Sensitivity analysis was applied to identify violations of estimator assumptions.

RESULTS

No association between either gallstone disease (P value = 0.60) or circulating levels of bilirubin (ORSD = 1.00, 95% confidence interval (CI) = 0.96-1.03, P value = 0.90) with CRC was shown.

CONCLUSIONS

Despite the large scale of this study, we found no evidence for a causal relationship between either circulating levels of bilirubin or gallstone disease with risk of developing CRC. While the magnitude of effect suggested by some observational studies can confidently be excluded, we cannot exclude the possibility of smaller effect sizes and non-linear relationships.

Acute Pancreatitis: Genetic Risk and Clinical Implications

Acute pancreatitis (AP) is one of the most common gastroenterological indications for emergency admittance and hospitalization. Gallstones, alcohol consumption or the presence of additional initiating factors give rise to a disease with a diverse clinical appearance and a hard-to predict course of progression. One major challenge in the treatment of AP patients is the early identification of patients at risk for the development of systemic complications and organ failure. In addition, 20%-30% of patients with a first episode of AP later experience progress to recurrent or chronic disease. Complex gene-environment interactions have been identified to play a role in the pathogenesis of pancreatitis, but so far no predictive genetic biomarkers could be implemented into the routine clinical care of AP patients. The current review explains common and rare etiologies of acute pancreatitis with emphasis on underlying genetic aberrations and ensuing clinical management.

Advances in Risk Factors for Recurrence of Common Bile Duct Stones

Choledocholithiasis is a chronic common disease. The incidence of cholelithiasis is 5%-15%, of which 5%-30% are combined with Choledocholithiasis. Although endoscopic cholangiopancreatography (ERCP) + endoscopic sphincterotomy (EST) is the most common treatment procedure, which clearance rate is up to 95%, the incidence of recurrent choledocholithiasis was 4%-25%. The risk factors of recurrence after choledocholithiasis clearance are the focuses of current researches, which are caused by multiple factors. We first systematically summarize the risk factors of common bile duct stones (CBDS) recurrence into five aspects: first-episode stone related factors, congenital factors, biological factors, behavioral intervention factors, and the numbers of stone recurrence.

A Mitochondrial DNA Variant Elevates the Risk of Gallstone Disease by Altering Mitochondrial Function

BACKGROUND AND AIMS

Gallstone disease (cholelithiasis) is a cholesterol-related metabolic disorders with strong familial predisposition. Mitochondrial DNA (mtDNA) variants accumulated during human evolution are associated with some metabolic disorders related to modified mitochondrial function. The mechanistic links between mtDNA variants and gallstone formation need further exploration.

METHODS

In this study, we explored the possible associations of mtDNA variants with gallstone disease by comparing 104 probands and 300 controls in a Chinese population. We constructed corresponding cybrids using trans-mitochondrial technology to investigate the underlying mechanisms of these associations. Mitochondrial respiratory chain complex activity and function and cholesterol metabolism were assessed in the trans-mitochondrial cell models.

RESULTS

Here, we found a significant association of mtDNA 827A>G with an increased risk of familial gallstone disease in a Chinese population (odds ratio [OR]: 4.5, 95% confidence interval [CI]: 2.1-9.4, P=1.2×10-4). Compared with 827A cybrids (haplogroups B4a and B4c), 827G cybrids (haplogroups B4b and B4d) had impaired mitochondrial respiratory chain complex activity and function and activated JNK and AMPK signaling pathways. Additionally, the 827G cybrids showed disturbances in cholesterol transport and accelerated development of gallstones. Specifically, cholesterol transport through the transporter ABCG5/8 was increased via activation of the AMPK signaling pathway in 827G cybrids.

CONCLUSIONS

Our findings reveal that mtDNA 827A>G induces aberrant mitochondrial function and abnormal cholesterol transport, resulting in increased occurrence of gallstones. The results provide an important biological basis for the clinical diagnosis and prevention of gallstone disease in the future.

Genetic variants of SLCO1B7 are of relevance for the transport function of OATP1B3-1B7

The family of Organic Anion Transporting Polypeptides are known to facilitate the transmembrane transport. OATP1B3-1B7 is a novel member of the OATP1B-subfamily, and is encoded by SLCO1B3-SLCO1B7 readthrough deriving from the genes SLCO1B3 and SLCO1B7 on chromosome 12. The resulting protein is expressed in the smooth endoplasmatic reticulum of hepatocytes, is functional, and transports dehydroepiandrosterone-sulfate (DHEAS). In the gene area encoding for the 1B7-part of the protein, there are coding polymorphisms. It was the aim of this study to test the frequency and the impact of these genetic variants on transport activity. The minor allele frequency (MAF) of the coding polymorphisms was determined in a cohort of 192 individuals. DHEAS transport function was determined by applying the vTF-7 based heterologous expression system using plasmids encoding for OATP1B3-1B7 or the respective variants. The genetic variants 641 T (MAF 0.021), 1073 G (MAF 0.169) and 1775 A (MAF 0.013) significantly reduced DHEAS accumulation in cells transfected with OATP1B3-1B7, albeit without significantly influencing expression of the transporter as determined by Western blot analysis and immunofluorescence after heterologous expression. Genotyping revealed complete linkage of the variants 884A, 1073 G and 1501C. Presence of the haplotype abolished the DHEAS-transport function of OATP1B3-1B7. Naturally and frequently occurring genetic variants located within the gene region of SLCO1B7 encoding for the 1B7-part of OATP1B3-1B7 influence the in vitro function of this member of the OATP1B-family. With their functional characterisation, we provide the basis for pharmacogenetic studies, which may help to understand the in vivo relevance of this transporter.

Alcohol and Smoking Mediated Modulations in Adaptive Immunity in Pancreatitis

Pancreatitis is a condition of pancreatic inflammation driven by injury to the pancreatic parenchyma. The extent of acinar insult, intensity, and type of immune response determines the severity of the disease. Smoking, alcohol and autoimmune pancreatitis are some of the predominant risk factors that increase the risk of pancreatitis by differentially influencing the adaptive immune system. The overall decrease in peripheral lymphocyte (T-, B- and (natural killer T-) NKT-cell) count and increased infiltration into the damaged pancreatic tissue highlight the contribution of adaptive immunity in the disease pathology. Smoking and alcohol modulate the responsiveness and apoptosis of T- and B-cells during pancreatic insult. Acute pancreatitis worsens with smoking and alcohol, leading to the development of systemic inflammatory response syndrome and compensatory anti-inflammatory response syndrome, suggesting the critical role of adaptive immunity in fatal outcomes such as multiple organ dysfunction. The presence of CD4⁺ and CD8⁺ T-lymphocytes and perforin-expressing cells in the fibrotic tissue in chronic pancreatitis modulate the severity of the disease. Due to their important role in altering the severity of the disease, attempts to target adaptive immune mediators will be critical for the development of novel therapeutic interventions.

Carbon monoxide breath test assessment of mild hemolysis in Gilbert's syndrome

BACKGROUND

Mild hemolysis is difficult to determinate by traditional methods, and its role in Gilbert's syndrome (GS) is unclear. The main aims were to inspect the erythrocyte (RBC) survival in GS by using Levitt's carbon monoxide (CO) breath test and to assess its contribution to unconjugated hyperbilirubinemia.

METHODS

Fifty subjects with GS and 1 with type-II Crigler-Najjar syndrome (CN2) received RBC lifespan measurement with Levitt's CO breath test. Mean RBC lifespan was compared with normal referral value. Correlations of serum total bilirubin (TB) with RBC lifespan, blood panel data, demographic factors, and uridine diphosphate glucuronosyltransferase (UGT1A1) mutation load were calculated by Spearman analysis. Susceptibility factors for mild hemolysis were analyzed by multivariate regression analysis.

RESULTS

The mean RBC lifespan of the GS subjects was significantly shorter than the normal reference value (95.4 ± 28.9 days vs 126 days; t = -7.504, P < .01), with 30.0% below the lower limit of the normal reference range (75 days). The RBC lifespan of the participant with CN2 was 82 days. Serum TB correlated positively with UGT1A1 mutation load (γ = 0.281, P = .048), hemoglobin (γ = .359, P = .010) and hematocrit (γ = 0.365, P = .010), but negatively with RBC lifespan (γ = -0.336, P = .017). No significant susceptibility factors for mild hemolysis were found.

CONCLUSIONS

The results indicate that mild hemolysis indeed, exists in a portion of patients with GS and might serve as an important contributor to unconjugated hyperbilirubinemia in addition to UGT1A1 polymorphism. Further studies on the mechanism and the potential risks in various medical treatments might be wanted.

Copy number variants in lipid metabolism genes are associated with gallstones disease in men

Gallstones Disease (GSD) is one of the most common digestive diseases requiring hospitalization and surgical procedures in the world. GSD has a high prevalence in populations with European or Amerindian ancestry (10–20%) and the influence of genetic factors is broadly acknowledged. However, known genetic variants do not entirely explain the disease heritability suggesting that additional genetic variants remain to be identified. Here, we examined the association of copy number variants (CNVs) with GSD in a sample of 4778 individuals (1929 GSD cases and 2849 controls) including two European cohorts from Germany (n = 3702) and one admixed Latin American cohort from Chile (n = 1076). We detected 2936 large and rare CNVs events (size > 100 kb, frequency < 1%). Case-control burden analysis and generalized linear regression models revealed significant association of CNVs with GSD in men, with the strongest effect observed with CNVs overlapping lipid metabolism genes (p-value = 6.54 × 10^–4; OR = 2.76; CI 95% = 1.53–4.89). Our results indicate a clear link between CNVs and GSD in men and provides additional evidence that the genetic components of risk for GSD are complex, can be sex specific and include CNVs affecting genes involved in lipid metabolism.

Gallstone Disease and Type 2 Diabetes Risk: A Mendelian Randomization Study

The presence of gallstone disease (GSD) was reported to be positively associated with diabetes risk. Whether the association is causal remains unclear. We aim to examine the potential causal association between GSD and type 2 diabetes risk using a Mendelian randomization analysis. Observational study was conducted among 16,299 participants who were free of cancer, heart disease, stroke, and diabetes at baseline in the Dongfeng-Tongji cohort study. GSD was diagnosed by experienced physicians by abdominal B-type ultrasound inspection and type 2 diabetes was defined according to the criteria of the American Diabetes Association. Cox proportional hazard regression model was used to examine the association of GSD with type 2 diabetes risk. A genetic risk score (GRS) for GSD was constructed with eight single nucleotide polymorphisms that were derived from the previous genome-wide association studies. The causal associations of the score for GSD with type 2 diabetes were tested among 7,000 participants in Mendelian randomization analysis. We documented 1,110 incident type 2 diabetes cases during 73,895 person-years of follow-up from 2008 to 2013 (median 4.6 years). Compared with participants without GSD, the multivariate-adjusted hazard ratio of type 2 diabetes risk in those with GSD was 1.22 (95% confidence interval [CI], 1.03-1.45, P = 0.02). Each 1 SD (0.23) increment in the weighted GRS was associated with a 17% increment of type 2 diabetes risk (odds ratio = 1.17, 95% CI, 0.90-1.52) without statistical significance (P = 0.25). Conclusion: The present study supported a positive but not a causal association of GSD with type 2 diabetes risk. More studies are needed to verify our findings.

Etiology and Risk Factors of Acute and Chronic Pancreatitis

Based on the recognition of common etiological and genetic risk factors, acute and chronic pancreatitis are increasingly regarded as a continuum of the same disease, with a significant overlap of clinical manifestations and phenotypes but distinct morphological and imaging appearances. Recent population-based and cohort studies have found that tobacco smoke conveys a greater risk than immoderate alcohol consumption for the development of chronic pancreatitis, and hypertriglyceridemia has been identified as a risk factor for acute pancreatitis - even when plasma levels are only mildly elevated. Hereditary pancreatitis, in its autosomal dominant form, is associated with mutations in the cationic trypsinogen gene (PRSS1), whereas a number of germline variations in other genes have been found to represent risk factors for chronic as well as acute pancreatitis. For now, most of these involve the pancreatic digestive protease/antiprotease system. Oftentimes, affected patients are burdened with multiple or accumulating risk factors, and genetic traits when combined with environmental toxins compound the chance of developing the disease. Determining the underlying etiology of pancreatitis is worth the effort since formerly intractable varieties such as autoimmune pancreatitis are now becoming increasingly treatable, and subtype-specific therapeutic modalities may become available.

Variants in ABCG8 and TRAF3 genes confer risk for gallstone disease in admixed Latinos with Mapuche Native American ancestry

Latin Americans and Chilean Amerindians have the highest prevalence of gallstone disease (GSD) and gallbladder cancer (GBC) in the world. A handful of loci have been associated with GSD in populations of predominantly European ancestry, however, they only explain a small portion of the genetic component of the disease. Here, we performed a genome-wide association study (GWAS) for GSD in 1,095 admixed Chilean Latinos with Mapuche Native American ancestry. Disease status was assessed by cholecystectomy or abdominal ultrasonography. Top-10 candidate variants surpassing the suggestive cutoff of P < 1 × 10⁻⁵ in the discovery cohort were genotyped in an independent replication sample composed of 1,643 individuals. Variants with positive replication were further examined in two European GSD populations and a Chilean GBC cohort. We consistently replicated the association of ABCG8 gene with GSD (rs11887534, P = 3.24 × 10⁻⁸, OR = 1.74) and identified TRAF3 (rs12882491, P = 1.11 × 10⁻⁷, OR = 1.40) as a novel candidate gene for the disease in admixed Chilean Latinos. ABCG8 and TRAF3 variants also conferred risk to GBC. Gene expression analyses indicated that TRAF3 was significantly decreased in gallbladder (P = 0.015) and duodenal mucosa (P = 0.001) of GSD individuals compared to healthy controls, where according to GTEx data in the small intestine, the presence of the risk allele contributes to the observed effect. We conclude that ABCG8 and TRAF3 genes are associated with GSD and GBC in admixed Latinos and that decreased TRAF3 levels could enhance gallbladder inflammation as is observed in GSD and GSD-associated GBC.

Incidence and Risk of Gallstone Disease in Gilbert's Syndrome Patients in Indian Population

BACKGROUND/OBJECTIVES

Individuals with Gilbert's syndrome (GS) harbor mutations in the UGT1A1 gene and are known to have elevated levels of bilirubin, which enhances the risk for gall stone formation. The aim of this study is to screen Indian patients with GS for the incidence of gall stone disease.

METHODS

Individuals with persistently elevated serum bilirubin levels were genotyped for two polymorphisms (rs8175347; rs4148323) in UGT1A1 gene to confirm GS in them. Flanking regions of the above polymorphisms were amplified followed by direct sequencing. Ultrasonography was done to detect gallstone disease. Clinical data, including assessment of liver function, circulating levels of total and direct bilirubin, as well as routine hematological parameters were obtained as per standard procedures (Autoanalyzer).

RESULTS

Of the total 1621 individuals subjected to genotyping, 1191 (1149 males of 29.6 ± 11.3 years with mean BMI of 22.1 ± 3.7 kg/m² and 42 females of 30.8 ± 14.8 years with mean BMI of 20.9 ± 3.7 kg/m²) were confirmed to have GS. Gall bladder abnormalities including cholelithiasis (n = 106/1191; 8.9%), polyps (n = 18/1191; 1.5%) and gallbladder wall thickening (n = 17/1191; 1.4%) were noted. Incidence of gall stone disease was observed in 103 males (out of 1149) and 3 females (out of 42) indicating the risk of the disease to be 9.0% and 7.1% respectively in males and females with GS.

CONCLUSION

Early recognition of GS by genetic analysis is required before these patients with intermittent episodes of jaundice run the risk of unnecessary operations on their bile ducts from the mistaken assumption ascribing the jaundice to a stone which has been left behind.

LST-3TM12 is a member of the OATP1B family and a functional transporter

Organic anion transporting polypeptides (OATPs) and particularly the two members of the OATP1B family are known for their role in pharmacokinetics. Both SLCO1B3 and SLCO1B1 are located on chromosome 12 encompassing the gene locus SLCO1B7. Hitherto, this particular gene has been assumed to be a pseudogene, even though there are published mRNA sequences linked to this chromosomal area. It was aim of this study to further investigate SLCO1B7 and the associated mRNA LST-3TM12. In a first step, we aligned all mRNAs linked to the chromosomal region of SLCO1B-transporters. This in silico analysis revealed that LST-3TM12 is a product of splicing of SLCO1B3 and SLCO1B7, and encodes for a protein with twelve transmembrane domains. The existence of LST-3TM12 mRNA was verified by polymerase chain reaction showing liver enriched expression. In addition, immunohistological staining showed that LST-3TM12 protein was expressed in the endoplasmic reticulum (ER) of hepatocytes. Localization in the ER was further verified by immunoblot analysis showing high amounts of LST-3TM12 in liver microsomes. Function of LST-3TM12 was assessed by transport studies after heterologous expression in HeLa cells, where the transporter was shown to be expressed not only in the ER but also in the plasma membrane. Overexpression of LST-3TM12 was associated with enhanced cellular accumulation of dehydroepiandrosterone sulfate (V_max 300.2 pmol mg^-1 min^-1; K_m 34.2 µm) and estradiol 17β-glucuronide (V_max 29.9 mol mg^-1 min^-1 and K_m 32.8 µM). In conclusion, LST-3TM12 is a functional splice variant of SLCO1B3 and SLCO1B7 expressed in the ER of human liver.

IL-8 gene polymorphism in acute biliary and non biliary pancreatitis: probable cause of high level parameters?

Backgrounds/Aims

Inflammatory mediators of the innate immune response play fundamental roles in the pathogenesis of acute pancreatitis. The correlation between interleukin-8 (IL-8) gene polymorphism with types of acute pancreatitis and severity of pancreatitis, was evaluated in this study.

Methods

According to the diagnostic criteria, 176 patients with acute pancreatitis were grouped into biliary (n=83) and nonbiliary pancreatitis (n=93). Healthy blood donors (n=100) served as controls. Serum alanine transaminase, aspartate transaminase, total and direct bilirubin, amylase, lypase, white blood cell count and c-reactive protein levels were evaluated to correlate with IL-8 rs4073 (-251T/A) polymorphism, which was analyzed using a real-time polymerase chain reaction method with melting point analysis.

Results

The IL-8 AA genotype was detected with a significantly higher frequency among the patients with acute biliary pancreatitis having higher alanine transaminase levels than the median range. Homozygote alleles were significantly higher among patients with acute biliary pancreatitis having amylase levels higher than the median range.

Conclusions

Determination of the frequency of IL-8 polymorphism in acute pancreatitis is informative and provides further evidence concerning the role of IL-8 in laboratory tests.

Gallstone Etiopathogenesis, Lith and Mucin Genes and New Treatment Approaches

Gallstones constitute one of the more common and relatively costly conditions of the gastrointestinal system and are a major risk factor for gallbladder cancer. Most gallstone cases involve individuals younger than 60 years of age, those older representing 9% of the total in one series. There are many risk factors for gallstones and Lith and Mucin genes, for example, play important roles in their formation. Surgery is one therapeutic approach but in the future it is to be expected that drugs for prevention of gallstones will be developed in the future. This will have clear implications for gallbladder cancer control.

Polymorphisms in UGT1A1 Gene Predispose South Indians to Pigmentous Gallstones

BACKGROUND/OBJECTIVES

Pigmentous gallstones occur in South Indians despite significant higher levels of circulating cholesterol. This study was conducted to identify the biochemical and/or genetic causes for the formation of pigmentous gallstones in this ethnic group.

METHODS

Plasma lipid profile, bile cholesterol, acids, and phospholipid levels were estimated in patients with gall stone disease and age, sex matched controls using standard protocols. Twenty-seven SNPs related to cholesterol and bilirubin metabolism pathway genes were genotyped in the study population using the Sequenom platform. An equilibrium phase diagram involving bile salt-phospholipid-cholesterol was generated to relate phenotype with the genotype.

RESULTS

There were no significant differences in the lipid profiles between the patients (n = 305) and controls (n = 177). Biliary cholesterol, acids, and phospholipids were significantly different between patients and controls. Single locus analysis revealed association of variants in ABCG6, ABCG8, and UGT1A1 genes with the disease; however when correction was applied as multiple testing was done, only one variant (rs6742078) in UGT1A1 gene was found to be associated with gall stone disease. Equilibrium phase diagram suggested that few samples were in the crystal formation zone. The mutant, but not wild type or heterozygous genotype of SNPs (rs6742078 and rs887829) in UGT1A1 gene, was associated with significantly higher levels of bilirubin.

CONCLUSIONS

Higher incidence of pigment stones in South Indians could be due to raised serum bilirubin levels that may be ascribed to variant in the UGT1A1 gene involved in glucuronidation of free bilirubin.

Four Susceptibility Loci for Gallstone Disease Identified in a Meta-analysis of Genome-Wide Association Studies

BACKGROUND & AIMS

A genome-wide association study (GWAS) of 280 cases identified the hepatic cholesterol transporter ABCG8 as a locus associated with risk for gallstone disease, but findings have not been reported from any other GWAS of this phenotype. We performed a large-scale, meta-analysis of GWASs of individuals of European ancestry with available prior genotype data, to identify additional genetic risk factors for gallstone disease.

METHODS

We obtained per-allele odds ratio (OR) and standard error estimates using age- and sex-adjusted logistic regression models within each of the 10 discovery studies (8720 cases and 55,152 controls). We performed an inverse variance weighted, fixed-effects meta-analysis of study-specific estimates to identify single-nucleotide polymorphisms that were associated independently with gallstone disease. Associations were replicated in 6489 cases and 62,797 controls.

RESULTS

We observed independent associations for 2 single-nucleotide polymorphisms at the ABCG8 locus: rs11887534 (OR, 1.69; 95% confidence interval [CI], 1.54-1.86; P = 2.44 × 10(-60)) and rs4245791 (OR, 1.27; P = 1.90 × 10(-34)). We also identified and/or replicated associations for rs9843304 in TM4SF4 (OR, 1.12; 95% CI, 1.08-1.16; P = 6.09 × 10(-11)), rs2547231 in SULT2A1 (encodes a sulfoconjugation enzyme that acts on hydroxysteroids and cholesterol-derived sterol bile acids) (OR, 1.17; 95% CI, 1.12-1.21; P = 2.24 × 10(-10)), rs1260326 in glucokinase regulatory protein (OR, 1.12; 95% CI, 1.07-1.17; P = 2.55 × 10(-10)), and rs6471717 near CYP7A1 (encodes an enzyme that catalyzes conversion of cholesterol to primary bile acids) (OR, 1.11; 95% CI, 1.08-1.15; P = 8.84 × 10(-9)). Among individuals of African American and Hispanic American ancestry, rs11887534 and rs4245791 were associated positively with gallstone disease risk, whereas the association for the rs1260326 variant was inverse.

CONCLUSIONS

In this large-scale GWAS of gallstone disease, we identified 4 loci in genes that have putative functions in cholesterol metabolism and transport, and sulfonylation of bile acids or hydroxysteroids.

Gallstones

Gallstones grow inside the gallbladder or biliary tract. These stones can be asymptomatic or symptomatic; only gallstones with symptoms or complications are defined as gallstone disease. Based on their composition, gallstones are classified into cholesterol gallstones, which represent the predominant entity, and bilirubin ('pigment') stones. Black pigment stones can be caused by chronic haemolysis; brown pigment stones typically develop in obstructed and infected bile ducts. For treatment, localization of the gallstones in the biliary tract is more relevant than composition. Overall, up to 20% of adults develop gallstones and >20% of those develop symptoms or complications. Risk factors for gallstones are female sex, age, pregnancy, physical inactivity, obesity and overnutrition. Factors involved in metabolic syndrome increase the risk of developing gallstones and form the basis of primary prevention by lifestyle changes. Common mutations in the hepatic cholesterol transporter ABCG8 confer most of the genetic risk of developing gallstones, which accounts for ∼25% of the total risk. Diagnosis is mainly based on clinical symptoms, abdominal ultrasonography and liver biochemistry tests. Symptoms often precede the onset of the three common and potentially life-threatening complications of gallstones (acute cholecystitis, acute cholangitis and biliary pancreatitis). Although our knowledge on the genetics and pathophysiology of gallstones has expanded recently, current treatment algorithms remain predominantly invasive and are based on surgery. Hence, our future efforts should focus on novel preventive strategies to overcome the onset of gallstones in at-risk patients in particular, but also in the population in general.

Heterozygous ABCB4 mutations in children with cholestatic liver disease

BACKGROUND & AIMS

Monoallelic defects in ABCB4, which encodes the canalicular floppase for phosphatidylcholine MDR3, have been encountered in association with a variety of hepatobiliary disorders, particularly in adult subjects. In this study, we examined the presence of heterozygous ABCB4 variants in a cohort of children with chronic cholestasis and assessed the pathogenicity of the missense changes identified.

METHODS

Sixty-seven children with chronic liver dysfunction were studied by the sequencing of ABCB4 and multiplex ligation-dependent probe amplification analysis. The molecular defects arising from missense variants were analysed in MDCK-II and AD-293 cells.

RESULTS

Defects in a single allele of ABCB4 were identified in nine subjects. They included one small insertion (p.I1242Nfs), one nonsense mutation (p.R144X) and six missense changes (p.T175A, p.G228R, p.A250T, p.S320F, p.P352L and p.A934T). In four children, these defects in ABCB4 co-existed with various medical conditions. In vitro phenotyping of the six missense variants revealed that four (T175A, G228R, S320F and A934T) led to reduced MDR3 protein levels. Two mutations (G228R and A934T) resulted in trapping of the protein in the endoplasmic reticulum. Phosphatidylcholine efflux activity was decreased to 56-18% of reference levels for MDR3 mutants T175A, A250T and S320F. The G228R, P352L and A934T mutants were found to be non-functional.

CONCLUSIONS

These results illustrate the varying effects of ABCB4 missense mutations and suggest that even a modest reduction in MDR3 activity may contribute or predispose to the onset of cholestatic liver disease in the paediatric age.

Relation of cholesterol metabolism to pediatric gallstone disease: a retrospective controlled study

Background

Cholesterol metabolism may be involved in pediatric gallstone disease. We aimed to reveal cholesterol metabolites and phytosterols and their relation to stone composition of sterols in children having black pigment and cholesterol stones.

Methods

We performed retrospective controlled clinical study, in which we examined parameters of cholesterol metabolism and liver function values in serum (n = 28) and gallstones (n = 46) of consecutively cholecystectomized children. Serum values of age-, body mass index- and sex-matched children (n = 82) and adult gallstones (n = 187) served as controls.

Results

Surrogate markers of cholesterol synthesis in serum (squalene/cholesterol, cholestenol/cholesterol and lathosterol/cholesterol) were 26–52 % higher in both stone subclasses compared to controls (p < 0.05 for all). Respectively, cholestanol/cholesterol and plant sterols campesterol/cholesterol and sitosterol/cholesterol (cholesterol absorption markers) had decreasing order in serum: black pigment stone group > controls > cholesterol stone group (p < 0.05 for all). In black pigment stone group, stone cholestanol/cholesterol was associated with serum bile acids (r = 0.620, p = 0.018). In cholesterol stone group, surrogate markers of cholesterol synthesis in serum (e.g., lathosterol/cholesterol) inversely reflected those of absorption (r-range -0.633–-0.706, p-range 0.036–0.015). In cholesterol stone group, serum and stone lathosterol/cholesterol and cholestanol/cholesterol were positively interrelated (r-range 0.727–0.847, p < 0.05 for both).

Conclusions

Gallstone subclasses shared enhanced cholesterol synthesis. Cholesterol stone children were low cholesterol absorbers with intact homeostasis of cholesterol metabolism. Black pigment stone group was characterized by deteriorated cholesterol metabolism, and accumulation of cholestanol, campesterol and sitosterol in serum and stones suggesting their participation in pathogenesis.

Exome-Wide Association Study Identifies New Low-Frequency and Rare UGT1A1 Coding Variants and UGT1A6 Coding Variants Influencing Serum Bilirubin in Elderly Subjects: A Strobe Compliant Article

Genome-wide association studies (GWASs) have identified loci contributing to total serum bilirubin level. However, no exome-wide approaches have been performed to address this question. Using exome-wide approach, we assessed the influence of protein-coding variants on unconjugated, conjugated, and total serum bilirubin levels in a well-characterized cohort of 773 ambulatory elderly subjects from Italy. Coding variants were replicated in 227 elderly subjects from the same area. We identified 4 missense rare (minor allele frequency, MAF < 0.5%) and low-frequency (MAF, 0.5%-5%) coding variants located in the first exon of the UGT1A1 gene, which encodes for the substrate-binding domain (rs4148323 [MAF = 0.06%; p.Gly71Arg], rs144398951 [MAF = 0.06%; p.Ile215Val], rs35003977 [MAF = 0.78%; p.Val225Gly], and rs57307513 [MAF = 0.06%; p.Ser250Pro]). These variants were in strong linkage disequilibrium with 3 intronic UGT1A1 variants (rs887829, rs4148325, rs6742078), which were significantly associated with total bilirubin level (P = 2.34 × 10(-34), P = 7.02 × 10(-34), and P = 8.27 × 10(-34)), as well as unconjugated, and conjugated bilirubin levels. We also identified UGT1A6 variants in association with total (rs6759892, p.Ser7Ala, P = 1.98 × 10(-26); rs2070959, p.Thr181Ala, P = 2.87 × 10(-27); and rs1105879, p.Arg184Ser, P = 3.27 × 10(-29)), unconjugated, and conjugated bilirubin levels. All UGT1A1 intronic variants (rs887829, rs6742078, and rs4148325) and UGT1A6 coding variants (rs6759892, rs2070959, and rs1105879) were significantly associated with gallstone-related cholecystectomy risk. The UGT1A6 variant rs2070959 (p.Thr181Ala) was associated with the highest risk of gallstone-related cholecystectomy (OR, 4.58; 95% CI, 1.58-13.28; P = 3.21 × 10(-3)). Using an exome-wide approach we identified coding variants on UGT1A1 and UGT1A6 genes in association with serum bilirubin level and hyperbilirubinemia risk in elderly subjects. UGT1A1 intronic single-nucleotide polymorphisms (SNPs) (rs6742078, rs887829, rs4148324) serve as proxy markers for the low-frequency and rare UGT1A1 variants, thereby providing mechanistic explanation to the relationship between UGT1A1 intronic SNPs and the UGT1A1 enzyme activity. UGT1A1 and UGT1A6 variants might be potentially associated with gallstone-related cholecystectomy risk.

Genetics of liver disease: From pathophysiology to clinical practice

Paralleling the first 30 years of the Journal of Hepatology we have witnessed huge advances in our understanding of liver disease and physiology. Genetic advances have played no small part in that. Initial studies in the 1970s and 1980s identified the strong major histocompatibility complex associations in autoimmune liver diseases. During the 1990 s, developments in genomic technologies drove the identification of genes responsible for Mendelian liver diseases. Over the last decade, genome-wide association studies have allowed for the dissection of the genetic susceptibility to complex liver disorders, in which also environmental co-factors play important roles. Findings have allowed the identification and elaboration of pathophysiological processes, have indicated the need for reclassification of liver diseases and have already pointed to new disease treatments. In the immediate future genetics will allow further stratification of liver diseases and contribute to personalized medicine. Challenges exist with regard to clinical implementation of rapidly developing technologies and interpretation of the wealth of accumulating genetic data. The historical perspective of genetics in liver diseases illustrates the opportunities for future research and clinical care of our patients.

Bilirubin as a potential causal factor in type 2 diabetes risk: a Mendelian randomization study

Circulating bilirubin, a natural antioxidant, is associated with decreased risk of type 2 diabetes (T2D), but the nature of the relationship remains unknown. We performed Mendelian randomization in a prospective cohort of 3,381 participants free of diabetes at baseline (age 28-75 years; women 52.6%). We used rs6742078 located in the uridine diphosphate-glucuronosyltransferase locus as an instrumental variable (IV) to study a potential causal effect of serum total bilirubin level on T2D risk. T2D developed in a total of 210 participants (6.2%) during a median follow-up period of 7.8 years. In adjusted analyses, rs6742078, which explained 19.5% of bilirubin variation, was strongly associated with total bilirubin (a 0.68-SD increase in bilirubin levels per T allele; P < 1 × 10(-122)) and was also associated with T2D risk (odds ratio [OR] 0.69 [95% CI 0.54-0.90]; P = 0.006). Per 1-SD increase in log-transformed bilirubin levels, we observed a 25% (OR 0.75 [95% CI 0.62-0.92]; P = 0.004) lower risk of T2D. In Mendelian randomization analysis, the causal risk reduction for T2D was estimated to be 42% (causal OR for IV estimation per 1-SD increase in log-transformed bilirubin 0.58 [95% CI 0.39-0.84]; P = 0.005), which was comparable to the observational estimate (Durbin-Wu-Hausman χ(2) test, P for difference = 0.19). These novel results provide evidence that an elevated bilirubin level is causally associated with the risk of T2D and support its role as a protective determinant.

Organic anion-transporting polypeptides

Organic anion-transporting polypeptides or OATPs are central transporters in the disposition of drugs and other xenobiotics. In addition, they mediate transport of a wide variety of endogenous substrates. The critical role of OATPs in drug disposition has spurred research both in academia and in the pharmaceutical industry. Translational aspects with clinical questions are the focus in academia, while the pharmaceutical industry tries to define and understand the role these transporters play in pharmacotherapy. The present overview summarizes our knowledge on the interaction of food constituents with OATPs and on the OATP transport mechanisms. Further, it gives an update on the available information on the structure-function relationship of the OATPs and, finally, covers the transcriptional and posttranscriptional regulation of OATPs.

Effect of drug transporter pharmacogenetics on cholestasis

INTRODUCTION

The liver is the central place for the metabolism of drugs and other xenobiotics. In the liver cell, oxidation and conjugation of compounds take place, and at the same time, bile formation helps in extrusion of these compounds via the biliary route. A large number of transporters are responsible for drug uptake into the liver cell and excretion into bile or efflux to the sinusoidal blood.

AREAS COVERED

Genetic variants of these transporters and their transactivators contribute to changes in drug handling and are also responsible for cholestatic syndromes of different severity. This review summarizes the current knowledge regarding the influence of these genetic changes. The review covers progressive hereditary cholestatic syndromes as well as recurrent or transient cholestatic syndromes such as drug-induced liver injury, intrahepatic cholestasis of pregnancy, and benign recurrent intrahepatic cholestasis.

EXPERT OPINION

Polymorphisms in transporter genes are frequent. For clinically relevant cholestatic syndromes, it often requires a combination of genetic variants or acquired triggers such as pregnancy or drug treatment. In combination with other pathogenetic aspects, genetic variants in drug transporters may contribute to our understanding of not only cholestatic diseases such as primary sclerosing cholangitis or primary biliary cirrhosis, but also the natural course of chronic liver disease in general.

Gallstones in patients with liver cirrhosis: Incidence, etiology, clinical and therapeutical aspects

Gallstones occur in about one third of the patients having liver cirrhosis. Pigment gallstones are the most frequent type, while cholesterol stones represent about 15% of all stones in cirrhotics. Increased secretion of unconjugated bilirubin, increased hydrolysis of conjugated bilirubin in the bile, reduced secretion of bile acids and phospholipds in bile favor pigment lithogenesis in cirrhotics. Gallbladder hypomotility also contributes to lithogenesis. The most recent data regarding risk factors for gallstones are presented. Gallstone prevalence increases with age, with a ratio male/female higher than in the general population. Chronic alcoholism, viral C cirrhosis, and non-alcoholic fatty liver disease are the underlying liver diseases most often associated with gallstones. Gallstones are often asymptomatic, and discovered incidentally. If asymptomatic, expectant management is recommended, as for asymptomatic gallstones in the general population. However, a closer follow-up of these patients is necessary in order to earlier treat symptoms or complications. For symptomatic stones, laparoscopic cholecystectomy has become the therapy of choice. Child-Pugh class and MELD score are the best predictors of outcome after cholecystectomy. Patients with severe liver disease are at highest surgical risk, therefore gallstone complications should be treated using noninvasive or minimally invasive procedures, until stabilization of the patient condition.

Lipid trait-associated genetic variation is associated with gallstone disease in the diverse Third National Health and Nutrition Examination Survey (NHANES III)

BACKGROUND

Gallstone disease is one of the most common digestive disorders, affecting more than 30 million Americans. Previous twin studies suggest a heritability of 25% for gallstone formation. To date, one genome-wide association study (GWAS) has been performed in a population of European-descent. Several candidate gene studies have been performed in various populations, but most have been inconclusive. Given that gallstones consist of up to 80% cholesterol, we hypothesized that common genetic variants associated with high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglycerides (TG) would also be associated with gallstone risk.

METHODS

To test this hypothesis, the Epidemiologic Architecture for Genes Linked to Environment (EAGLE) study as part of the Population Architecture using Genomics and Epidemiology (PAGE) study performed tests of association between 49 GWAS-identified lipid trait SNPs and gallstone disease in non-Hispanic whites (446 cases and 1,962 controls), non-Hispanic blacks (179 cases and 1,540 controls), and Mexican Americans (227 cases and 1,478 controls) ascertained for the population-based Third National Health and Nutrition Examination Survey (NHANES III).

RESULTS

At a liberal significance threshold of 0.05, five, four, and four SNP(s) were associated with disease risk in non-Hispanic whites, non-Hispanic blacks, and Mexican Americans, respectively. No one SNP was associated with gallstone disease risk in all three racial/ethnic groups. The most significant association was observed for ABCG5 rs6756629 in non-Hispanic whites [odds ratio (OR) = 1.89; 95% confidence interval (CI) = 1.44-2.49; p = 0.0001). ABCG5 rs6756629 is in strong linkage disequilibrium with rs11887534 (D19H), a variant previously associated with gallstone disease risk in populations of European-descent.

CONCLUSIONS

We replicated a previously associated variant for gallstone disease risk in non-Hispanic whites. Further discovery and fine-mapping efforts in diverse populations are needed to fully describe the genetic architecture of gallstone disease risk in humans.

Gilbert's syndrome and the risk of death: a population-based cohort study

BACKGROUND AND AIMS

Gilbert's syndrome is a common familial hyperbilirubinemia that may reduce the risk of various age-related diseases because of the antioxidant properties of bilirubin. We conducted a large cohort study using The Health Improvement Network primary care database and compared all-cause mortality rates in those with and without Gilbert's syndrome.

METHODS

Mortality rates in patients with a diagnosis of Gilbert's syndrome and raised bilirubin level (n = 4266) were compared with those of patients with similar characteristics but with normal bilirubin levels (n = 21 968). Multivariate Poisson regression was also used to estimate adjusted mortality rate ratios.

RESULTS

During the 350 000 PYs of follow up across the Gilbert's and comparison cohorts, there were 1174 deaths. Mortality rates were 24/10 000 PYs in the Gilbert's cohort versus 50/10 000 PYs in the comparison cohort. Mortality rates were around half in patients with Gilbert's syndrome after accounting for sociodemographics and general health indicators (adjusted mortality rate ratio: 0.5 [95% confidence interval; 0.4-0.7; P < 0.001]).

CONCLUSIONS

Mortality rates observed for people with Gilbert's syndrome in the general population are almost half those of people without evidence of Gilbert's syndrome.

Expression of mRNA transcripts encoding membrane transporters detected with whole transcriptome sequencing of human brain and liver

BACKGROUND

Membrane transporters control the influx and efflux of endogenous and xenobiotic substrates, including nutrients and drugs, across cellular membranes.

OBJECTIVE

Whole transcriptome sequencing enables simultaneous analysis of overall and allele-specific mRNA expression, and the detection of multiple RNA isoforms.

METHODS

Here we characterize variation in RNA transcripts emanating from gene loci encoding transporters based on RNAseq data from 10 human brains (including cocaine overdose and normal brain tissues) and 12 normal livers.

RESULTS

mRNA expression was detected in 65% of transporter genes in either tissue, with many genes generating multiple mRNA transcripts. Single-nucleotide polymorphisms within transporters with previous evidence for pharmacogenomics impact were detected. We also identified noncoding RNAs in the vicinity of transporter genes with potential regulatory functions.

CONCLUSION

The results obtained with RNAseq provide detailed information on transporter mRNA expression at the molecular level, affording new avenues for the study of membrane transport, with relevance to drug efficacy and toxicity.

Early complication in sickle cell anemia children due to A(TA)nTAA polymorphism at the promoter of UGT1A1 gene

Aim. To determine the implication of the polymorphism, namely, A(TA)_nTAA of UGT1A1 in lithogenesis for the first time in Tunisia among sickle cell anemia (SCA) children patients. Material and Methods. Our study was performed in 2010 and it involved 76 subjects chosen as control group characterized with normal hemoglobin status and presence of cholelithiasis and 102 SCA pediatric patients among whom 52 have cholelithiasis. We analyzed the polymorphism A(TA)_nTAA at the UGT1A1 promoter and the relationships between the various A(TA)_nTAA genotypes and alleles and bilirubin levels and occurrence of cholelithiasis. Results and Discussion. The repartition of genotypes found according to serum bilirubin level shows a significant association between genotypes carrying variant (TA)₇ and hyperbilirubinemia (P < 0.05). We demonstrated the association of two genotypes with gallstones formation among SCA children patients: (TA)₇/(TA)₇ and (TA)₇/(TA)₈ with P = 8.1 × 10⁻⁸ and P = 0.01, respectively. (TA)₇ and (TA)₈ allele variants act as a risk factor for early gallstones formation in SCA patients with P = 5.8 × 10⁻⁹ and P = 0.01, respectively. As for the control group only the genotype (TA)₇/(TA)₇ presented a risk factor for gallstones formation. Conclusion. The novelty of this report is that it is the first time that a similar study was made on the Tunisian children sickle cell population and that the results show a clear association of (TA)₇ variant in early gallstones formation in Tunisian SCA children. Interestingly our findings highlighted the association of (TA)₈ variant as well, which was not found in previous studies.

Gallstone disease in Swedish twins is associated with the Gilbert variant of UGT1A1

BACKGROUND & AIMS

The Gilbert syndrome-associated functional TATA box variant UGT1A1*28 (A(TA)7TAA) was found to increase susceptibility to pigment gallstone formation in patients with haemolytic anaemia. Further studies in extensive cohorts demonstrated an increased risk of this variant for cholesterol gallstone disease (GD). We now investigated this polymorphism as a determinant of symptomatic GD in Swedish twins.

METHODS

The Swedish Twin Registry was merged with the Hospital Discharge and Causes of Death Registries and searched for GD-related diagnoses among monozygotic (MZ) twins living in the Stockholm area. In addition, we screened the TwinGene database for GD. In total, we found 44 MZ twin pairs with and eight MZ twins without GD to be evaluable. GD-free twins from TwinGene (109 concordantly MZ and 126 independent DZ) served as controls. UGT1A1*28 genotyping was performed using TaqMan assays.

RESULTS

Overall, 58 and 8 of 106 twins with GD were hetero- and homozygous UGT1A1 risk allele carriers respectively. The case-control association tests showed a significantly (P < 0.05) increased risk of developing GD (OR = 1.62, 95% CI 1.00-2.63) in heterozygotes carriers and in addition, a trend (P = 0.075) for an increased risk among carriers (OR = 1.52, 95% CI 0.97-2.44) of the risk allele.

CONCLUSION

These data from Swedish twins confirm the Gilbert variant as risk factor for GD. Our observation is in line with nucleation in bilirubin supersaturated bile representing an initial step in cholelithogenesis.

The genetics of complex cholestatic disorders

Cholestatic liver diseases are caused by a range of hepatobiliary insults and involve complex interactions among environmental and genetic factors. Little is known about the pathogenic mechanisms of specific cholestatic diseases, which has limited our ability to manage patients with these disorders. However, recent genome-wide studies have provided insight into the pathogenesis of gallstones, primary biliary cirrhosis, and primary sclerosing cholangitis. A lithogenic variant in the gene that encodes the hepatobiliary transporter ABCG8 has been identified as a risk factor for gallstone disease; this variant has been associated with altered cholesterol excretion and metabolism. Other variants of genes encoding transporters that affect the composition of bile have been associated with cholestasis, namely ABCB11, which encodes the bile salt export pump, and ABCB4, which encodes hepatocanalicular phosphatidylcholine floppase. In contrast, studies have associated primary biliary cirrhosis and primary sclerosing cholangitis with genes encoding major histocompatibility complex proteins and identified loci associated with microbial sensing and immune regulatory pathways outside this region, such as genes encoding IL12, STAT4, IRF5, IL2 and its receptor (IL2R), CD28, and CD80. These discoveries have raised interest in the development of reagents that target these gene products. We review recent findings from genetic studies of patients with cholestatic liver disease. Future characterization of genetic variants in animal models, stratification of risk alleles by clinical course, and identification of interacting environmental factors will increase our understanding of these complex cholestatic diseases.

Multi-analytic approach elucidates significant role of hormonal and hepatocanalicular transporter genetic variants in gallstone disease in North Indian population

Objective

Cholesterol gallstone disease (CGD) is a multifactorial and multistep disease. Apart from female gender and increasing age being the documented non-modifiable risk factor for gallstones the pathobiological mechanisms underlying the phenotypic expression of CGD appear to be rather complex, and one or more variations in genes could play critical roles in the diverse pathways further progressing to cholesterol crystal formation. In the present study we performed genotyping score, Multifactor dimensionality reduction (MDR) and Classification and Regression Tree analysis (CART) to identify combinations of alleles among the hormonal, hepatocanalicular transporter and adipogenesis differentiation pathway genes in modifying the risk for CGD.

Design

The present case-control study recruited total of 450 subjects, including 230 CGD patients and 220 controls. We analyzed common ESR1, ESR2, PGR, ADRB3, ADRA2A, ABCG8, SLCO1B1, PPARγ2, and SREBP2 gene polymorphisms to find out combinations of genetic variants contributing to CGD risk, using multi-analytical approaches (G-score, MDR, and CART).

Results

Single locus analysis by logistic regression showed association of ESR1 IVS1-397C>T (rs2234693), IVS1-351A>G (rs9340799) PGR ins/del (rs1042838) ADRB3-190 T>C (rs4994) ABCG8 D19H (rs11887534), SLCO1B1 Exon4 C>A (rs11045819) and SREBP2 1784G>C (rs2228314) with CGD risk. However, the MDR and CART analysis revealed ESR1 IVS1-397C>T (rs2234693) ADRB3-190 T>C (rs4994) and ABCG8 D19H (rs11887534) polymorphisms as the best polymorphic signature for discriminating between cases and controls. The overall odds ratio for the applied multi-analytical approaches ranged from 4.33 to 10.05 showing an incremental risk for cholesterol crystal formation. In conclusion, our muti-analytical approach suggests that, ESR1, ADRB3, in addition to ABCG8 genetic variants confer significant risk for cholesterol gallstone disease.

Genetics of biliary lithiasis from an ethnic perspective

Gallstone disease represents one of the most common gastroenterological disorders worldwide. Gallstones affect over 15% of adults in Europe and 25-30% of Hispanic populations in Central and South America. The heritability of gallstones varies considerably according to ethnicity, with Native Americans and Hispanics with Amerindian admixture being the most susceptible populations. Genetic factors have been shown to account for 25-30% of total gallstone risk in Europe, however, in Hispanic populations, this risk percentage may increase to 45-65%. Recent genome-wide association and candidate gene studies have identified common polymorphisms in enterohepatic transporters (ABCG5/8, SLC10A2) and the Gilbert syndrome UGT1A1 variant as genetic determinants of gallstone formation. Together, these polymorphisms cover a significant proportion of the previously predicted genetic background of gallstones in European populations. New lithogenic genes need to be discovered in future studies in high-risk populations. In this review, we address the latest developments in the genetic analysis of gallstones and discuss the ethnic background of this condition in European, Central and South American and Asian populations.

Menopausal hormone therapy and risk of cholecystectomy: a prospective study based on the French E3N cohort

BACKGROUND

Studies in the United States and the United Kingdom have reported an increased risk of cholecystectomy among women exposed to menopausal hormone therapy, but with substantial heterogeneity between types of hormone treatments. We evaluated the risk of cholecystectomy associated with different regimens of menopausal hormone therapy in a large prospective cohort study.

METHODS

Between 1992 and 2008, 70 928 menopausal women from the French E3N study cohort were sent questionnaires assessing their use of menopausal hormone therapy, medical history and lifestyle characteristics. The primary outcome was cholecystectomy. We analyzed the risk of cholecystectomy associated with use of menopausal hormone therapy using Cox proportional models, with age as time-scale.

RESULTS

During follow-up, 45 984 (64.8%) of the participants were exposed to menopausal hormone therapy, and 2819 cholecystectomies were recorded. The use of menopausal hormone therapy was associated with an increased risk of cholecystectomy (adjusted hazard ratio [HR] 1.10, 95% confidence interval [CI] 1.01-1.20) compared with women who were not exposed to menopausal hormone therapy. The association was restricted to unopposed oral estrogen therapy (adjusted HR 1.38, 95% CI 1.14-1.67). Over 5 years, about 1 cholecystectomy in excess would be expected in every 150 women using oral estrogen therapy without progestogens, compared with women not exposed to menopausal hormone therapy.

INTERPRETATION

The risk of cholecystectomy was increased among women exposed to oral estrogen menopausal hormone therapy, especially oral regimens without a progestagen. Complicated gallstone disease should be added to the list of potential adverse events to be considered when balancing the benefits and risks associated with menopausal hormone therapy.

Recurrence of gallstones after cholecystectomy is associated with ABCG5/8 genotype

BACKGROUND

Gallstone disease is a frequent and economically highly relevant disorder, with cholecystectomy representing one of the most frequently performed operations world-wide. Gallstone recurrence after cholecystectomy is associated with complications such as biliary sepsis and pancreatitis. As yet, variant ABCG8-D19H is the most widely recognized genetic risk factor for gallstone disease. The aim of the study is to investigate whether ABCG8-D19H is associated with gallstone recurrence after cholecystectomy.

METHODS

Two thousand three hundred and eight patients from an earlier study of gallstone risk factors were re-contacted by mail, leading to 1,915 patients with available clinical and genetic information. Symptomatic gallstone recurrence was established if it occurred more than six months after surgery. Median follow-up time after cholecystectomy was eight years.

RESULTS

Gallstones recurred in 37 patients (1.9%). ABCG-D19H was found to be significantly associated with gallstone recurrence (p = 0.034). The allelic odds ratio was 1.97 (95% CI 1.12-∞). In a multivariate logistic regression analysis adjusted for age, sex, BMI and type of surgery, ABCG8-D19H remained a significant predictor, both in the total cohort (p = 0.024) and in the subgroup for whom information on type and scheduling of surgery was available (N = 1,650, p = 0.020).

CONCLUSIONS

ABCG8-D19H is a predictor of gallstone recurrence, a major long term postoperative biliary complication. Moreover, the observed association also reemphasizes the importance of the sterolin transporter for stone formation.

Bilirubin and beyond: a review of lipid status in Gilbert's syndrome and its relevance to cardiovascular disease protection

Gilbert's syndrome (GS) is characterized by a benign, mildly elevated bilirubin concentration in the blood. Recent reports show clear protection from cardiovascular disease in this population. Protection of lipids, proteins and other macromolecules from oxidation by bilirubin represents the most commonly accepted mechanism contributing to protection in this group. However, a recent meta-analysis estimated that bilirubin only accounts for ~34% of the cardioprotective effects within analysed studies. To reveal the additional contributing variables we have explored circulating cholesterol and triacylglycerol concentrations, which appear to be decreased in hyperbilirubinemic individuals/animals, and are accompanied by lower body mass index in highly powered studies. These results suggest that bilirubin could be responsible for the development of a lean and hypolipidemic state in GS. Here we also discuss the possible contributing mechanisms that might reduce circulating cholesterol and triacylglycerol concentrations in individuals with syndromes affecting bilirubin metabolism/excretion, which we hope will stimulate future research in the area. In summary, this article is the first review of lipid status in animal and human studies of hyperbilirubinemia and explores possible mechanisms that could contribute to lowering circulating lipid parameters and further explain cardiovascular protection in Gilbert's syndrome.