Frederick J. Suchy

The rat canalicular conjugate export pump (Mrp2) is down-regulated in intrahepatic and obstructive cholestasis

BACKGROUND & AIMS The excretion of various organic anions into bile is mediated by an adenosine triphosphate-dependent conjugate export pump, which has been identified as the canalicular isoform of the multidrug resistance protein (Mrp2). Mrp2 function is impaired in various experimental models of intrahepatic and obstructive cholestasis, but the underlying molecular mechanisms are unclear. The aim of this study was to investigate these molecular mechanisms. METHODS The effects of endotoxin, ethinylestradiol, and common bile duct ligation (CBDL) on Mrp2 protein, messenger RNA (mRNA) expression, and Mrp2 tissue localization were determined in rat livers by Northern blotting, Western analysis, and tissue immunofluorescence. To assess whether changes were specific for Mrp2, we also examined the expression of canalicular ecto-adenosine triphosphatase (ecto-ATPase) and mdr P-glycoproteins (P-gp). RESULTS All three cholestatic models resulted in a marked decrease in Mrp2 protein (P < 0.01) and its tissue localization at the canalicular membrane. Mrp2 mRNA levels diminished profoundly after endotoxin (P < 0.0005) and CBDL (P < 0.05), but did not change after ethinylestradiol. In contrast to Mrp2, protein expression of ecto-ATPase and P-gp remained unchanged in endotoxin- and ethinylestradiol-treated animals, whereas P-gp levels increased after CBDL (P < 0.05). CONCLUSIONS Down-regulation of Mrp2 expression may explain impaired biliary excretion of amphiphilic anionic conjugates in these models of cholestasis.

Hepatocyte nuclear factor-1α is an essential regulator of bile acid and plasma cholesterol metabolism

Maturity-onset diabetes of the young type 3 (MODY3) is caused by haploinsufficiency of hepatocyte nuclear factor-1α (encoded by TCF1). Tcf1−/− mice have type 2 diabetes, dwarfism, renal Fanconi syndrome, hepatic dysfunction and hypercholestrolemia. Here we explore the molecular basis for the hypercholesterolemia using oligonucleotide microchip expression analysis. We demonstrate that Tcf1−/− mice have a defect in bile acid transport, increased bile acid and liver cholesterol synthesis, and impaired HDL metabolism. Tcf1−/− liver has decreased expression of the basolateral membrane bile acid transporters Slc10a1, Slc21a3 and Slc21a5, leading to impaired portal bile acid uptake and elevated plasma bile acid concentrations. In intestine and kidneys, Tcf1−/− mice lack expression of the ileal bile acid transporter (Slc10a2), resulting in increased fecal and urinary bile acid excretion. The Tcf1 protein (also known as HNF-1α) also regulates transcription of the gene (Nr1h4) encoding the farnesoid X receptor-1 (Fxr-1), thereby leading to reduced expression of small heterodimer partner-1 (Shp-1) and repression of Cyp7a1, the rate-limiting enzyme in the classic bile acid biosynthesis pathway. In addition, hepatocyte bile acid storage protein is absent from Tcf1−/− mice. Increased plasma cholesterol of Tcf1−/− mice resides predominantly in large, buoyant, high-density lipoprotein (HDL) particles. This is most likely due to reduced activity of the HDL-catabolic enzyme hepatic lipase (Lipc) and increased expression of HDL-cholesterol esterifying enzyme lecithin:cholesterol acyl transferase (Lcat). Our studies demonstrate that Tcf1, in addition to being an important regulator of insulin secretion, is an essential transcriptional regulator of bile acid and HDL-cholesterol metabolism.

Cloning and molecular characterization of the ontogeny of a rat ileal sodium-dependent bile acid transporter.

Sodium-dependent bile acid transport in the rat ileum is abruptly expressed at weaning. Degenerate oligonucleotides, based on amino acid sequence identities between the rat liver and hamster ileal transporters, were used to amplify a rat ileal probe. A 1.2-kb cDNA clone, which contains the full coding region (348 amino acids, 38 kD), was isolated by hybridization screening. In vitro translation yielded a 38-kD protein which glycosylated to 48 kD. Sodium-dependent uptake of taurocholate was observed in oocytes injected with cRNA. Northern blot analysis revealed a 5.0-kb mRNA in ileum, kidney, and cecum. A 48-kD protein was detected in ileal brush border membranes and localized to the apical border of villus ileal enterocytes. mRNA and protein expression, which were negligible before weaning, increased dramatically at weaning. Nuclear transcription rates for the transporter increased 15-fold between postnatal days 7 and 28. The apparent molecular weight of the transporter also increased between days 19 and 28. In summary, the developmental regulation of the rat ileal sodium-dependent bile acid cotransporter is characterized by transcriptionally regulated increases in mRNA and protein levels at the time of weaning with changes in apparent molecular weight of the protein after weaning.

Delta 4-3-oxosteroid 5 beta-reductase deficiency described in identical twins with neonatal hepatitis. A new inborn error in bile acid synthesis.

A new inborn error in bile acid synthesis, manifest in identical infant twins as severe intrahepatic cholestasis, is described involving the delta 4-3-oxosteroid 5 beta-reductase catalyzed conversion of the key intermediates, 7 alpha-hydroxy-4-cholesten-3-one and 7 alpha,12 alpha-dihydroxy-4-cholesten-3-one for chenodeoxycholic and cholic acid synthesis, to the respective 3 alpha-hydroxy-5 beta (H) products. This defect was detected by fast atom bombardment ionization-mass spectrometry from an elevated excretion and predominance of taurine conjugated unsaturated hydroxy-oxo-bile acids. Gas chromatography-mass spectrometry confirmed these to be 7 alpha-hydroxy-3-oxo-4-cholenoic and 7 alpha,12 alpha-dihydroxy-3-oxo-4-cholenoic acids (75-92% of total). Fasting serum bile acid concentrations were greater than 37 mumol/liter; chenodeoxycholic acid was the major bile acid, but significant amounts of allo(5 alpha-H)-bile acids (approximately 30%) were present. Biliary bile acid concentration was less than 2 mumol/liter and consisted of chenodeoxycholic, allo-chenodeoxycholic, and allo-cholic acids. These biochemical findings, which were identical in both infants, indicate a defect in bile acid synthesis involving the conversion of the delta 4-3-oxo-C27 intermediates into the corresponding 3 alpha-hydroxy-5 beta(H)-structures, a reaction that is catalyzed by a delta 4-3-oxosteroid-5 beta reductase enzyme. This defect resulted in markedly reduced primary bile acid synthesis and concomitant accumulation of delta 4-3-oxo-and allo-bile acids. These findings indicate a pathway in bile acid synthesis whereby side chain oxidation can occur despite incomplete alterations to the steroid nucleus, and lend support for an active delta 4-3-oxosteroid 5 alpha-reductase catalyzing the conversion of the delta 4-3-oxosteroid intermediates to the respective 3 alpha-hydroxy-5 alpha(H)-structures.

Improved Adherence and Outcomes for Pediatric Liver Transplant Recipients by Using Text Messaging

OBJECTIVE: The goal was to improve immunosuppressant adherence for pediatric patients with orthotopic liver transplants by using text messaging (TM). METHODS: A prospective study of sending TM reminders to the primary medication administrator (patient or caregiver) for pediatric transplant recipients was performed. Patient records were reviewed, comparing the year before and the year of the study. The SD of serum tacrolimus levels was used as an indicator of adherence. RESULTS: Forty-one patients provided consent. The median age was 15 years (range: 1–27 years), and the median age at the time of transplantation was 2 years (range: 4 months to 23 years). Fourteen patients (34%) were male. In 29 of 41 cases, the medications were self-administered by the patient. The mean duration of study was 13 ± 1.5 months. Twenty-two patients were receiving 1 immunosuppressant, 14 were receiving 2, and 5 were receiving 3. Thirteen patients (37%) stopped the study after 4 months. The mean tacrolimus level SD decreased from 3.46 μg/L before the study to 1.37 μg/L (P < .005). The number of immunosuppressants taken and patient self/caregiver medication administration did not significantly affect the results. The number of acute cellular rejection episodes decreased from 12 to 2 during the study. Risk factors for rejection were older age (17.67 vs 13.28 years) and administration of >1 immunosuppressant. CONCLUSION: We observed significant improvement in medication adherence and a reduction in rejection episodes with TM reminders for pediatric recipients of liver transplants.

Acute Hepatic Failure Associated with the Use of Sodium Valproate

SODIUM valproate, a recently introduced anticonvulsant, is particularly useful in the management of absence seizures and has gained widespread popularity.1 Initial European studies reported infrequ...

miR-33 controls the expression of biliary transporters, and mediates statin- and diet-induced hepatotoxicity

Bile secretion is essential for whole body sterol homeostasis. Loss‐of‐function mutations in specific canalicular transporters in the hepatocyte disrupt bile flow and result in cholestasis. We show that two of these transporters, ABCB11 and ATP8B1, are functional targets of miR‐33, a micro‐RNA that is expressed from within an intron of SREBP‐2. Consequently, manipulation of miR‐33 levels in vivo with adenovirus or with antisense oligonucleotides results in changes in bile secretion and bile recovery from the gallbladder. Using radiolabelled cholesterol, we show that systemic silencing of miR‐33 leads to increased sterols in bile and enhanced reverse cholesterol transport in vivo. Finally, we report that simvastatin causes, in a dose‐dependent manner, profound hepatotoxicity and lethality in mice fed a lithogenic diet. These latter results are reminiscent of the recurrent cholestasis found in some patients prescribed statins. Importantly, pretreatment of mice with anti‐miR‐33 oligonucleotides rescues the hepatotoxic phenotype. Therefore, we conclude that miR‐33 mediates some of the undesired, hepatotoxic effects of statins.

Multicenter trial of d-α-tocopheryl polyethylene glycol 1000 succinate for treatment of vitamin E deficiency in children with chronic cholestasis

BACKGROUND Malabsorption and deficiency of vitamin E causing neurological degeneration are common consequences of chronic childhood cholestatic liver disease. The objective of this study was to determine the long-term efficacy and safety of d-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) in correcting vitamin E deficiency in children with chronic cholestasis who were unresponsive to other forms of oral vitamin E. METHODS Sixty vitamin E-deficient children with chronic cholestasis unresponsive to 70-212 IU.kg-1.day-1 of oral vitamin E were entered into a trial at eight centers in the United States. After initial evaluation, treatment was started with 25 IU.kg-1.day-1 of TPGS. Vitamin E status, neurological function quantitated by a specific scoring system, and clinical and biochemical parameters were monitored during therapy. RESULTS All children responded to TPGS with normalization of vitamin E status. Neurological function, which had deteriorated before entry in the trial, improved in 25 patients, stabilized in 27, and worsened in only 2 after a mean of 2.5 years of therapy. No adverse effects were observed. CONCLUSIONS TPGS (20-25 IU.kg-1.day-1) appears to be a safe and effective form of vitamin E for reversing or preventing vitamin E deficiency during chronic childhood cholestasis.

A Retrospective Single-Center Review of Primary Sclerosing Cholangitis in Children

BACKGROUND & AIMS Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by inflammation and progressive bile duct fibrosis. There are limited data on pediatric PSC. METHODS We performed a retrospective chart review of 47 pediatric patients with PSC. RESULTS The mean age at diagnosis was 11 +/- 4.9 years. Symptoms occurred before presentation in 81% of patients; inflammatory bowel disease was found in 59% and autoimmune hepatitis (overlap syndrome) in 25% of patients. Magnetic resonance cholangiography revealed both extrahepatic and intrahepatic, isolated intrahepatic, isolated extrahepatic, and no biliary involvement (small-duct PSC) in 40%, 14%, 10%, and 36%, respectively. Advanced fibrosis (stage >II) was present in 65%. Colonoscopy revealed pancolitis, rectal sparing, and normal findings in 24%, 24%, and 18%, respectively. All patients were treated with ursodeoxycholic acid (UDCA); 9 with overlap syndrome also received immunosuppressants. Fifteen patients without overlap syndrome had positive autoimmune markers and responded to UDCA monotherapy. Liver transplantation was performed in 9 patients (3 with overlap syndrome and 2 with small-duct PSC) at a median time of 7 years after diagnosis. The 10-year posttransplant survival rate was 89%. CONCLUSIONS In one of the largest single-center studies of children with PSC, we found that most children with PSC had inflammatory bowel disease or autoimmune overlap and advanced fibrosis at diagnosis. Levels of alanine aminotransferase and gamma-glutamyl transferase were highest in patients with overlap syndrome and lowest in those with small-duct PSC. Levels of serum liver enzymes normalized after therapy with UDCA, including patients with positive autoimmune markers without histologic features of autoimmune hepatitis.

Δ4-3-Oxosteroid 5β-reductase deficiency causing neonatal liver failure and hemochromatosis☆☆☆★★★

Neonatal liver failure was evaluated in two infants. Neither infant had evidence of congenital infection, galactosemia, α1-antitrypsin deficiency, tyrosinemia, Zellweger syndrome, or hemophagocytic lymphohistiocytosis. Abnormal levels of iron were detected in the minor salivary glands of the first infant and in the explanted liver of the second. Analyses of urinary bile salts by fast-atom bombardment ionization mass spectrometry and gas chromatography-mass spectrometry revealed a paucity of primary bile acids and a predominance of 7α- hydroxy-3-oxo-4-cholenoic and 7α, 12α-dihydroxy-3-oxo-4-cholenoic acids. These findings are consistent with Δ 4-3-oxosteroid 5β-reductase deficiency, a primary genetic defect in bile acid synthesis. Postmortem evaluation of the first infant revealed significant iron deposition in the liver, pancreas, thyroid, adrenal glands, myocardium, stomach, and submucosal glands of the respiratory tract. In both infants examination of the liver revealed extensive loss of hepatic parenchyma. These cases expand the clinical spectrum of bile acid metabolism defects to include neonatal liver failure with associated hemochromatosis. (J PEDIATR 1994;124:234-8)