Should patients with symptomatic cholelithiasis before 30 years of age be tested for ABCB4 gene mutations?

Abstract

Background and aims

Low phospholipid-associated cholelithiasis syndrome (LPAC) is characterized by recurrent symptomatic cholelithiasis in young adults associated with ABCB4 gene mutations. Current diagnosing criteria are complex and heterogeneous, making this a largely underdiagnosed entity. Also, although recommended, genetic testing is not necessary for the diagnosis and its real advantages are not clear. The aim of our study was to explore the prevalence of ABCB4 mutations in symptomatic patients with cholelithiasis before the age of 30.     

Medical treatment of cholestatic liver diseases： From pathobiology to pharmacological targets

Bile secretion is dependent on the coordinated functions of a number of hepatobiliary transport systems. Cholestasis may be caused by an impairment of bile secretion, an obstruction of bile flow or a combination of the two. The common consequence of all forms of cholestasis is retention of bile acids and other potentially toxic compounds in the hepatocytes leading to apoptosis or necrosis of hepatocytes and eventually to chronic cholestatic liver disease. In certain cholestatic disorders there is also leakage of bile acids into the peribiliary space causing portal inflammation and fibrosis. The following pharmacological targets for treatment of intrahepatic cholestasis can be identified: stimulation of orthograde biliary secretion and retrograde secretion of bile acids and other toxic cholephils into the systemic circulation for excretion via the kidneys to reduce their retention in the hepatocytes; stimulation of the metabolism of hydrophobic bile acids and other toxic compounds to more hydrophilic, less toxic metabolites; protection of injured cholangiocytes against toxic effects of bile; inhibition of apoptosis caused by elevated levels of cytotoxic bile acids; inhibition of fibrosis caused by leakage of bile acids into the peribiliary space. The clinical results of ursodeoxcholic acid therapy of primary biliary cirrhosis may be regarded as the first success of this strategy.     

特发性成人肝内胆管缺失症1例报道

特发性成人肝内胆管缺失症（idiopathic adulthood ductopenia，IAD）是一种病因不明、以肝内小叶间胆管缺乏为病理学特征的慢性胆汁淤积性肝病。现将北京友谊医院收治的1例IAD患者报道如下。     

ABCB4 sequence variations in young adults with cholesterol gallstone disease

Background and Aims: Mutations in the gene encoding the ABCB4 [adenosine triphosphate (ATP)‐binding cassette, sub‐family B (MDR/TAP), member 4] transporter lower phosphatidylcholine output into bile and contribute to cholesterol gallstone formation by decreasing the solubility of cholesterol in bile. Mutations in ABCB4 have been identified in patients with low phospholipid‐associated cholelithiasis. The aim of the present study was to determine the types and frequencies of ABCB4 mutations in cholecystectomized patients aged <40 years. Patients and methods: Hundred and four patients (mean age 30.6 years, range 12–39) were included in the study and the ABCB4 gene was sequenced. The frequency of missense mutations found in the patient material was measured in 95 healthy controls. The potential functional implications of the ABCB4 missense variations were assessed by computerized analysis (BLOSUM62 and Grantham substitution matrices, polymorphism phenotyping and sorting intolerant from tolerant). Results: One patient was heterozygous for a frameshift mutation (c.1399_1400ins10/p.Y467F fsX25). Another patient was heterozygous for a nonsense mutation (c.3136C>T/p.R1046X). These two mutations are considered detrimental to ABCB4 protein function. In addition, six missense mutations were found in the ABCB4 gene, and three of these were only present in patients. Conclusion: In our study, <2% of young gallstone patients were found to be heterozygous for detrimental ABCB4 mutations. The functional implication of several missense mutations remains to be clarified. Thus, mutations in the ABCB4 gene are a rare cause of gallstone disease.     

雌激素受体α基因多态性对熊去氧胆酸治疗原发性胆汁性肝硬化疗效的影响

目的 探讨雌激素受体α(ERα)基因多态性对熊去氧胆酸(UDCA)治疗女性原发性胆汁性肝硬化(PBC)疗效的影响.方法 采用聚合酶链反应-限制性片段长度多态性方法 检测65例女性PBC患者ERα基因1号内含子PvuⅡ和XbaⅠ酶切位点多态性.患者每日均予UDCA(13～15 mg/kg,分3次口服)治疗.随访患者临床症状和血清总胆红素(TBil)、丙氨酸转氨酶(ALT)、碱性磷酸酶(ALP)、γ-谷氨酰转肽酶(GGT)变化情况,共随访24个月.结果 共60例患者获完整随访资料.XX和PP型患者4项指标均缓慢下降,但至随访结束时未达治疗有效标准.Xx型患者4项指标亦缓慢下降,至随访结束时达治疗有效标准.Pp、pp、xx型患者4项指标均快速下降至治疗有效标准.UDCA治疗PBC有效率75%(45/60).PP、Pp、pp型患者和XX、Xx、xx型患者在UDCA治疗有效组和无效组中的分布差异均有统计学意义(x2=12.13、P=0.003和x2=9.95、P=0.007).Pp、pp、Xx、xx型患者有效率[分别为82.61%(19/23)、80.65%(25/31)、9/14、83.33%(35/42)]高于PP、XX型者(分别为1/6和1/4).结论 PBC患者ERα基因多态性影响UDCA的疗效.     

Secondary bile acids and the biliary epithelia: The good and the bad

The biliary tract has been considered for several decades a passive system just leading the hepatic bile to the intestine. Nowadays several researches demonstrated an important role of biliary epithelia (i.e. cholangiocytes) in bile formation. The study of biliary processes therefore maintains a continuous interest since the possible important implications regarding chronic cholestatic human diseases, such as primary biliary cholangitis or primary sclerosing cholangitis. Bile acids (BAs), produced by the liver, are the most represented organic molecules in bile. The physiologic importance of BAs was initially attributed to their behavior as natural detergents but several studies now demonstrate they are also important signaling molecules. In this minireview the effect of BAs on the biliary epithelia are reported focusing in particular on secondary (deriving by bacterial manipulation of primary molecules) ones. This class of BAs is demonstrated to have relevant biological effects, ranging from toxic to therapeutic ones. In this family ursodeoxycholic and lithocholic acid present the most interesting features. The molecular mechanisms linking ursodeoxycholic acid to its beneficial effects on the biliary tract are discussed in details as well as data on the processes leading to lithocholic damage. These findings suggest that expansion of research in the field of BAs/cholangiocytes interaction may increase our understanding of cholestatic diseases and should be helpful in designing more effective therapies for biliary disorders.     

Single or multiple dose ursodeoxycholic acid for cholestatic liver disease: biliary enrichment and biochemical response

Background: Ursodeoxycholic acid (UDCA) improves liver biochemistry in primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). Since UDCA acts partly by reducing the intestinal absorption of hydrophobic endogenous bile salts and is poorly absorbed from the intestine, a multiple dose regimen has been advocated. Single dose treatment, on the other hand, may improve compliance.Aim: The effects of a single or multiple dose regimen on liver enzymes and serum and biliary bile salts composition were evaluated.Methods: Twenty-seven patients (19 PSC, 8 PBC), most with early stage disease, received UDCA (10 mg kg⁻¹ day⁻¹) in a single dose at bed time (n=13) or in three divided gifts with meals (n=14) over 3 months. Five patients had both treatment regimens in random order with a 1-month wash-out period in between.Results: Liver biochemistry equally improved in both groups. Biliary enrichment (% UDCA of total bile salts, mean±SEM) was 40.1±2.4 in the single dose group vs 40.8±2.8 in the multiple dose group (p=NS) and was positively correlated with biochemical improvement (AP: r=0.47, p=0.02; GGT: r=0.58, p=0.002; ASAT: r=0.67, p=0.002; ALAT: r=0.52, p=0.01). Biochemical improvement was not correlated with the concentration or %UDCA in serum. Patients participating in the cross-over design had comparable biochemical response and biliary %UDCA during both regimens.Conclusion: Single and multiple dose UDCA have similar effects on liver biochemistry and biliary enrichment in cholestatic liver disease. Biochemical improvement appears to be related to biliary (but not serum) enrichment with UDCA.     

血清总胆汁酸测定的意义及其局限性

目的　阐明空腹血清总胆汁酸（TBA）测定的临床意义。方法　收集913例临床资料,用SPSS软件及四格表法进行统计分析。结果　（1）正常人TBA平均（4.0±3.2）μmol/L。肝病组TBA显著高于正常人和非肝病组(P＜0.01)。（2）急性肝炎患者TBA平均为（167.2±132.4）μmol/L,最高达449.5μmol/L,与其他各组相比差异有显著性(P＜0.01),表明TBA是反映急性肝细胞损伤的敏感指标。（3）TBA对肝硬化的敏感性为85.8%,优于其他肝功能试验,TBA是反映肝硬化侧支循环的有价值的指标。（4）TBA对慢性轻度肝炎的敏感性仅为30.5%,不及ALT和总胆红素（TBIL）。（5）TBA水平与病情轻重有一定关系,但与TBIL不完全平行,对病情的判断不如TBIL有价值。结论　TBA特异性高,敏感性尚可,对肝病、特别是急性肝炎和肝硬化有重要诊断价值,但对慢性轻度肝炎的敏感性差,对病情的判断不如TBIL有意义。     

A study of exons 14, 15, and 24 of the ABCB11 gene in Egyptian children with normal GGT cholestasis

Background and study aimsProgressive familial intrahepatic cholestasis type 2 (PFIC2) is a rare inherited disorder caused by mutation in the ATP-binding cassette subfamily B member 11 gene (ABCB11) that encodes the bile salt export pump (BSEP), which is the main transporter of bile acids from hepatocytes to the canalicular lumen. Defects in BSEP synthesis and/or function lead to reduced bile salt secretion followed by accumulation of bile salts in hepatocytes and hepatocellular damage. This study aimed to detect variations in exons 14, 15, and 24 of the ABCB11 gene in patients with suspected PFIC2 among a group of Egyptian infants and children with normal gamma-glutamyl transpeptidase (GGT) cholestasis.Patients and methodsThis observational case-control study was conducted on 13 children with suspected PFIC2 and 13 healthy subjects as controls. Genotyping of the ABCB11 gene was performed via DNA extraction followed by PCR amplification, purification, and then sequencing analysis of exons 14, 15, and 24 of the ABCB11 gene.ResultsThe study detected two single nucleotide variations, c.1638+ 32T > C (rs2241340) in exon 14 and c.3084A > G (p.Ala1028 = ) (rs497692) in exon 24 of the ABCB11 gene. No variations were identified in exon 15.ConclusionThe study revealed two benign variants involving exons 14 and 24 of the ABCB11 gene. Exons 14, 15, and 24 are not hot spots for common mutations in Egyptian PFIC2 patients. Further study of other exons of the ABCB11 gene is necessary to confirm the diagnosis of PFIC2.     

Receptor for activated C-kinase 1 regulates the cellular localization and function of ABCB4

Aim:  Multidrug resistance protein 3 (MDR3/ABCB4), located on the bile canalicular membrane of hepatocytes, is responsible for the translocation of phosphatidylcholine across the plasma membrane, and its hereditary defect causes liver disorders, such as progressive familial intrahepatic cholestasis type 3. We aimed to identify the proteins responsible for the surface expression of human ABCB4 .
Methods:  We performed yeast two-hybrid screening with the cytoplasmic linker region of ABCB4 against a human liver cDNA library. This screening allowed us to identify the receptor for activated C-kinase 1 ( RACK1 ) as a novel binding partner of ABCB4 . The association of RACK1 with the linker region of ABCB4 was further confirmed by GST-pulldown assay, although we could not find out the interaction of full length of ABCB4 and RACK1 in co-immunoprecipitation assay in HeLa cells.
Results:  Down-regulation of endogenous RACK1 expression by siRNA in HeLa cells resulted in the localization of ABCB4 in the cytosolic compartment as well as reduced protein expression of ABCB4 , although mRNA expression and the protein stability of ABCB4 were not affected by the suppression of endogenous RACK1 . Similar alterations in cellular localization of ABCB4 were also found by suppressing endogenous RACK1 expression in HepG2 cells. Consequently, ABCB4 -mediated phosphatidylcholine translocation activity was significantly reduced when endogenous RACK1 expression was suppressed in HeLa cells. In contrast, the membrane surface localization and the protein expression of ABCB1 were not affected by the suppression of endogenous RACK1 expression.
Conclusion:  These results suggest that RACK1 may have a functional significance as a regulatory cofactor of ABCB4 and is indispensable for the plasma membrane localization and translocation function of ABCB4 .     

Prolonged cholestasis following successful removal of common bile duct stones： Beware patients on estrogen therapy

There are various well described forms of chronic cholestatic jaundice in adults, such as autoimmune cholangitis, drug-induced cholangitis and intrahepatic cholestasis of pregnancy. We present two cases of prolonged cholestasis following removal of gallstones at endoscopic retrograde cholangiopancreatography （ERCP） and subsequent clear cholangiography. Both patients were taking oral estrogens at the time of presentation, which were subsequently withdrawn. The first case responded rapidly to corticosteroid treatment, and the second case had a much slower resolution with ursodeoxycholic acid. Both cases highlighted the significance of estrogen-induced cholestasis in female patients with protracted jaundice following ERCP and removal of intra-ductal stones. After oral estrogens are discontinued, a short course of steroids needs to be considered.