Christian P. Strassburg

Portopulmonary hypertension and hepatopulmonary syndrome

The clinically and pathophysiologically distinct entities of portopulmonary hypertension and hepatopulmonary syndrome occur in a substantial proportion of patients who have advanced liver disease of different causes. These disorders are notoriously underdiagnosed, but they have a substantial impact on survival and require focused treatment. Abnormal intrapulmonary vascular dilatation, the hallmark of hepatopulmonary syndrome, can cause profound hypoxaemia that can be very difficult to treat. By contrast, portopulmonary hypertension results from excessive pulmonary vasoconstriction and vascular remodelling that eventually leads to right-heart failure. Insights into the pathogeneses of these syndromes have led to novel therapeutic approaches. However, in severely affected patients, effective treatment remains a difficult task. In selected patients, liver transplantation represents the only treatment option, but the decision to do isolated liver transplantation is particularly challenging in patients who have severe pulmonary disease involvement. Data from several centres have contributed to provide criteria that allow improved prediction of which patients may, or may not, benefit from liver transplantation alone.

EXPRESSION OF THE UDP-GLUCURONOSYLTRANSFERASE 1A LOCUS IN HUMAN COLON: IDENTIFICATION AND CHARACTERIZATION OF THE NOVEL EXTRAHEPATIC UGT1A8

UDP-glucuronosyltransferases (UGT) catalyze the conjugation of lipophilic exobiotic and endobiotic compounds, which leads to the excretion of hydrophilic glucuronides via bile or urine. By a mechanism of exon sharing, the transcripts of individual first exon cassettes located at the 5′ end of the human UGT1Alocus are spliced to exons 2–5, leading to the expression of at least nine individual UGT genes. Recently, the tissue-specific expression of the UGT1A locus has been demonstrated in extrahepatic tissue, leading to the identification of UGT1A7 and UGT1A10 mRNA (Strassburg, C. P., Oldhafer, K., Manns, M. P., and Tukey, R. H. (1997) Mol. Pharmacol. 52, 212). However,UGT1A expression has not been defined in human colon, which is a metabolically active, external surface organ and a common route of drug administration. UGT1A expression was analyzed in 5 colonic, 16 hepatic, 4 biliary, and 13 gastric human tissue specimens by quantitative duplex reverse transcription-polymerase chain reaction and Western blot analysis, demonstrating lower UGT1A mRNA in the extrahepatic tissues. The precise analysis of unique UGT1A transcripts by exon 1-specific duplex reverse transcription-polymerase chain reaction revealed the expression of UGT1A1, UGT1A3, UGT1A4, UGT1A6, and UGT1A9 in the colon, which are also present in human liver. In addition, the expression of extrahepatic UGT1A10 and UGT1A8 was demonstrated. UGT1A8 was found to be closely related to gastric UGT1A7 with a 93.8% identity of first exon sequences. Expressed UGT1A7 and UGT1A10 protein showed unique catalytic activity profiles, while UGT1A8 was not active with the substrates tested. The ability of UGT1A10 to glucuronidate estrone represents only the second example of a human estrone UGT. The highly related human UGT1A7–1A10 cluster is expressed in a tissue-specific fashion and underlines the role and diversity of physiological glucuronidation at the distal end of the digestive tract.

Polymorphic Gene Regulation and Interindividual Variation of UDP-glucuronosyltransferase Activity in Human Small Intestine

UDP-glucuronosyltransferases (UGTs) convert dietary constituents, drugs, and environmental mutagens to inactive hydrophilic glucuronides. Recent studies have shown that the expression of the UGT1 and UGT2 gene families is regulated in a tissue-specific fashion. Human small intestine represents a major site of resorption of dietary constituents and orally administered drugs and plays an important role in extrahepatic UGT directed metabolism. Expression of 13 UGT1A and UGT2Bgenes coupled with functional and catalytic analyses were studied using 18 small intestinal and 16 hepatic human tissue samples. Hepatic expression of UGT gene transcripts was without interindividual variation. In contrast, a polymorphic expression pattern of all the UGT genes was demonstrated in duodenal, jejunal, and ileal mucosa, with the exception of UGT1A10.To complement these studies, interindividual expression of UGT proteins and catalytic activities were also demonstrated. Hyodeoxycholic acid glucuronidation, catalyzed primarily by UGT2B4 and UGT2B7, showed a 7-fold interindividual variation in small intestinal duodenal samples, in contrast to limited variation in the presence of 4-methylumbelliferone, a substrate glucuronidated by mostUGT1A and UGT2B gene products. Linkage of RNA expression patterns to protein abundance were also made with several mono-specific antibodies to the UGTs. These results are in contrast to a total absence of polymorphic variation in gene expression, protein abundance, and catalytic activity in liver. In addition, the small intestine exhibits considerable catalytic activity toward most of the different classes of substrates accepted for glucuronidation by the UGTs, which is supported by immunofluorescence analysis of UGT1A protein in the mucosal cell layer of the small intestine. Thus, tissue-specific and interindividual polymorphic regulation ofUGT1A and UGT2B genes in small intestine is identified and implicated as molecular biological determinant contributing to interindividual prehepatic drug and xenobiotic metabolism in humans.

Budesonide Induces Remission More Effectively Than Prednisone in a Controlled Trial of Patients With Autoimmune Hepatitis

BACKGROUND & AIMS Autoimmune hepatitis (AIH) is a chronic liver disease associated with cirrhosis and liver failure. Corticosteroid therapy induces long-term remission but has many side effects. We compared the effects of budesonide (a steroid that is rapidly metabolized, with low systemic exposure) and prednisone, both in combination with azathioprine. METHODS We performed a 6-month, prospective, double-blind, randomized, active-controlled, multicenter, phase IIb trial of patients with AIH without evidence of cirrhosis who were given budesonide (3 mg, three times daily or twice daily) or prednisone (40 mg/d, tapered to 10 mg/d); patients also received azathioprine (1-2 mg/kg/d). Treatment was followed by a 6-month, open-label phase during which all patients received budesonide in addition to azathioprine. The primary end point was complete biochemical remission, defined as normal serum levels of aspartate aminotransferase and alanine aminotransferase, without predefined steroid-specific side effects, at 6 months. RESULTS The primary end point was achieved in 47/100 patients given budesonide (47.0%) and in 19/103 patients given prednisone (18.4%) (P < .001; 97.5% 1-side confidence interval [CI] = 16.2). At 6 months, complete biochemical remission occurred in 60% of the patients given budesonide versus 38.8% of those given prednisone (P = .001; CI: 7.7); 72.0% of those in the budesonide group did not develop steroid-specific side effects versus 46.6% in the prednisone group (P < .001; CI = 12.3). Among 87 patients who were initially given prednisone and then received budesonide after 6 months, steroid-specific side effects decreased from 44.8% to 26.4% at month 12 (P < .002). CONCLUSIONS Oral budesonide, in combination with azathioprine, induces and maintains remission in patients with noncirrhotic AIH, with a low rate of steroid-specific side effects.

Detection of apoptotic caspase activation in sera from patients with chronic HCV infection is associated with fibrotic liver injury

Chronic hepatitis C virus (HCV) infection is characterized by inflammatory liver damage and is associated with a high risk of development of cirrhosis and hepatocellular carcinoma. Although histological examination of liver biopsies is currently the gold standard for the detection of early liver damage, there is a strong need for better noninvasive methods. We recently demonstrated that the proapoptotic activation of caspases is considerably enhanced in histological sections from HCV‐infected liver tissue, suggesting an important role of apoptosis in liver damage. Here, we investigated whether caspase activation is detectable also in sera from patients with chronic HCV infection. Using a novel enzyme‐linked immunosorbent assay that selectively recognizes a proteolytic neoepitope of the caspase substrate cytokeratin‐18, we demonstrate that caspase activity is markedly increased in the sera of HCV patients. Interestingly, while 27% of patients with chronic HCV infection showed normal aminotransferase levels despite inflammatory and fibrotic liver damage, more than 50% of those patients exhibited already elevated serum caspase activity. Moreover, 30% of patients with normal aminotransferase but elevated caspase activity revealed higher stages of fibrosis. In conclusion, compared with conventional surrogate markers such as aminotransferases, detection of caspase activity in serum might be a more sensitive method of detecting early liver injury. Thus, measurement of caspase activity might provide a novel diagnostic tool, especially for patients with normal aminotransferases but otherwise undiagnosed histologically active hepatitis and progressive fibrosis. (HEPATOLOGY 2004;40:1078–1087.)

UDP-glucuronosyltransferase activity in human liver and colon

BACKGROUND & AIMS The contribution of glucuronidation toward human drug metabolism is carried out by the Super gene family of UDP-glucuronosyltransferases (UGTs). Regulation of the human UGT1A locus is tissue specific, resulting in the unique expression of multiple hepatic and extrahepatic gene products. Studies were undertaken to examine UGT1A expression in human hepatic and colonic tissues. METHODS UGT1A messenger RNA, protein, catalytic activity, and substrate kinetics were studied in 5 samples of normal hepatic and sigmoid colon tissue using duplex reverse-transcription polymerase chain reaction (RT-PCR), enzymatic and Western blot analysis, and indirect immunofluorescence analysis. RESULTS Specific patterns of UGT1A gene expression occur in the liver and colon, which were consistent with different banding patterns as detected by Western blot analysis using a UGT1A-specific antibody. However, microsomal UGT activities in colon were up to 96-fold lower for many phenolic substrates, a finding that was not concordant with RT-PCR and Western blot analysis. Interestingly, UGT activity toward tertiary amines and some steroid hormones was equal. CONCLUSIONS Differences of glucuronidation activity between human liver and colon suggest that UGT1A activity may be regulated as a result of the relative presence of individual isoforms with differing catalytic activities or by tissue-specific modulators after gene expression.

Hepatitis E virus infection as a cause of graft hepatitis in liver transplant recipients

Hepatitis E virus (HEV) infection induces self‐limiting liver disease in immunocompetent individuals. Cases of chronic hepatitis E have recently been identified in organ transplant recipients. We questioned if chronic hepatitis E plays a role in graft hepatitis after liver transplantation in a low endemic area. Two hundred twenty‐six liver transplant recipients, 129 nontransplanted patients with chronic liver disease, and 108 healthy controls were tested for HEV antibodies. HEV RNA was investigated in all sera from transplanted patients. HEV antibodies were detected in 1 healthy control (1%), 4 patients with chronic liver disease (3%), and 10 liver transplant recipients (4%). Three liver transplant patients also tested positive for HEV RNA. Two of them developed persistent viremia with HEV genotype 3. The patients were anti‐HEV immunoglobulin G–negative and HEV RNA–negative before transplantation and had an episode of acute hepatitis 5 or 7 months after transplantation, which led to advanced liver fibrosis after 22 months in 1 patient. Seroconversion to anti‐HEV occurred not before 4 months after the first detection of HEV RNA. The possibility of reverse zoonotic transmission was experimentally confirmed by the infection of 5 pigs with a patients serum. The pigs showed histological inflammation in the liver, and HEV RNA was detectable in different organs, including muscle. In conclusion, the prevalence of HEV infection in Central European liver transplant recipients is low; however, chronic hepatitis E may occur and needs to be considered in the differential diagnosis of graft hepatitis. The diagnosis of HEV infection should be based on HEV RNA determination in immunosuppressed patients. We suggest that immunocompromised individuals should avoid eating uncooked meat and contact with possibly HEV‐infected animals. Liver Transpl 16:74–82, 2010.

Variation of hepatic glucuronidation : Novel functional polymorphisms of the UDP-glucuronosyltransferase UGT1A4

UDP‐glucuronosyltransferases are a family of drug metabolizing enzymes contributing to hepatic drug metabolism and protection against environmental toxins. The aim of this study was to identify polymorphisms at the human UGT1A gene locus and to characterize their function and potential association with hepatocellular carcinoma (HCC). Genomic DNA from the blood of 363 subjects (128 patients with HCC, 235 blood donors) was analyzed for polymorphisms of the UGT1A3, UGT1A4, UGT1A8, UGT1A9, UGT1A10 genes using polymerase chain reaction, sequencing analysis. Recombinant variant UGT protein was analyzed by activity assays. In the UGT1A8 gene an A173G variant and a conserved G to A exchange at position 765 were detected in 25% and 15%. UGT1A9 exhibited two variants C3Y and M33T in 1% and 3%. UGT1A10 exhibited conserved nucleotide exchanges (128 G→A and 696 C→T) in 2% and 13%. In the UGT1A3 gene a W11R, a V47A variant, and a conserved G to A exchange at position 81 with an incidence of 65%, 58%, and 65%, respectively, were identified. UGT1A4 exhibited a P24T and an L48V variant in 8% and 9%. UGT1A SNPs were not associated with HCC. UGT1A4 P24T and L48V exhibited reduced glucuronidation activities: β‐naphthylamine 30% and 50%, and dihydrotestosterone 50% and 0%, respectively. In conclusion, the high prevalence of SNPs throughout the human UGT1A gene locus illustrates a genetic basis of interindividual variations of hepatic metabolism. Two polymorphisms of the hepatic UGT1A4 protein show a differential metabolic activity toward mutagenic amines and endogenous steroids, altering hepatic metabolism and detoxification. (HEPATOLOGY 2004;39:970–977.)

Glucuronide and glucoside conjugation of mycophenolic acid by human liver, kidney and intestinal microsomes

Mycophenolic acid (MPA) is primarily metabolized to a phenolic glucuronide (MPAG) as well as to two further minor metabolites: an acyl glucuronide (AcMPAG) and a phenolic glucoside (MPAG1s). This study presents investigations of the formation of these metabolites by human liver (HLM), kidney (HKM), and intestinal (HIM) microsomes, as well as by recombinant UDP‐glucuronosyltransferases. HLM (n=5), HKM (n=6), HIM (n=5) and recombinant UGTs were incubated in the presence of either UDP‐glucuronic acid or UDP‐glucose and various concentrations of MPA. Metabolite formation was followed by h.p.l.c. All microsomes investigated formed both MPAG and AcMPAG. Whereas the efficiency of MPAG formation was greater with HKM compared to HLM, AcMPAG formation was greater with HLM than HKM. HIM showed the lowest glucuronidation efficiency and the greatest interindividual variation. The capacity for MPAGls formation was highest in HKM, while no glucoside was detected with HIM. HKM produced a second metabolite when incubated with MPA and UDP‐glucose, which was labile to alkaline treatment. Mass spectrometry of this metabolite in the negative ion mode revealed a molecular ion of m/z 481 compatible with an acyl glucoside conjugate of MPA. All recombinant UGTs investigated were able to glucuronidate MPA with KM values ranging from 115.3 to 275.7 μM l−1 and Vmax values between 29 and 106 pM min−1 mg protein−1. Even though the liver is the most important site of MPA glucuronidation, extrahepatic tissues particularly the kidney may play a significant role in the overall biotransformation of MPA in man. Only kidney microsomes formed a putative acyl glucoside of MPA.

The challenges in primary sclerosing cholangitis – Aetiopathogenesis, autoimmunity, management and malignancy

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease, characterized by progressive inflammation and fibrosis of the bile ducts, resulting in biliary cirrhosis and is associated with a high risk of cholangiocarcinoma. The majority of patients are young, male and have coexisting inflammatory bowel disease. PSC is found with a prevalence of 10/100,000 in Northern European populations. The pathophysiology of PSC is a complex multistep process including immunological mechanisms, immunogenetic susceptibility and disorders of the biliary epithelia. The diagnosis is primarily based on endoscopic cholangiography although magnetic resonance imaging is increasingly used; biochemistry and immunoserology as well as histology play only a minor role. Due to the high risk of developing cholangiocarcinoma and also other tumours of the GI tract, surveillance strategies are essential, however they have yet to be established and evaluated. Biochemical parameters, clinical risk factors, endoscopic procedures and imaging techniques contribute to the early identification of patients at risk. Since medical therapy of PSC with ursodeoxycholic acid does not improve survival, to date, liver transplantation is the only option with a cure potential; if transplantation is accurately timed, transplanted PSC patients have an excellent rate of survival. However if cholangiocarcinoma is detected, a curative treatment is not possible in the majority of cases. The present review critically summarizes the current knowledge on the aetiopathogenesis of PSC and gives an overview of the diagnostic approaches, surveillance strategies and therapeutic options. Primary sclerosing cholangitis is a disease of unknown aetiology and without any further curative treatment options apart from liver transplantation. Therefore it may be regarded as the greatest challenge in hepatology today.