Rotor Syndrome: Glucuronidated Bile Acidemia From Defective Reuptake by Hepatocytes.

Organic anion transporting polypeptide (OATP) 1B1 (gene, solute carrier organic anion transporter family member 1B1 [SLCO1B1]) and OATP1B3 (SLCO1B3) serve as transporters for hepatic uptake of important endogenous substances and several commonly prescribed drugs. Inactivation of both proteins together causes Rotor syndrome. How this OATP1B1/1B3 defect disturbs bile acid (BA) metabolism is largely unknown. In this study, we performed detailed BA analysis in 3 patients with genetically diagnosed Rotor syndrome. We found that BAs glucuronidated at the C-3 position (BA-3G) accounted for 50% or more of total BAs in these patients. In contrast but similarly to healthy controls, only trace amounts of BA-3G were detected in patients with constitutional indocyanine green excretory defect (OATP1B3 deficiency) or sodium-taurocholate cotransporting polypeptide (NTCP; gene, solute carrier family 10 member 1 [SLC10A1]) deficiency. Therefore, substantial amounts of BA-3G are synthesized in hepatocytes. The cycling pathway of BA-3G, consisting of excretion from upstream hepatocytes and uptake by downstream hepatocytes by OATP1B1/1B3 may exist to reduce the burden on upstream hepatocytes. Conclusion: Detailed BA analysis revealed glucuronidated bile acidemia in patients with Rotor syndrome. Further exploration of the physiologic role of glucuronidated BAs is necessary.

The roles of MRP2, MRP3, OATP1B1, and OATP1B3 in conjugated hyperbilirubinemia.

Increased concentrations of bilirubin glucuronides in blood plasma indicate hepatocellular dysfunction. Elucidation of the transport processes of bilirubin conjugates across the basolateral (sinusoidal) and the canalicular plasma membrane domains of hepatocytes has decisively contributed to our current understanding of the molecular basis of conjugated hyperbilirubinemia in human liver diseases. Under normal conditions, unconjugated bilirubin is taken up into hepatocytes by transporters of the organic anion-transporting polypeptide (OATP) family, followed by conjugation with glucuronic acid, and ATP-dependent transport into bile. This efflux across the canalicular membrane is mediated by multidrug resistance protein 2 (MRP2 or ABCC2), which is a 190-kDa glycoprotein transporting with high affinity and efficiency monoglucuronosyl bilirubin and bisglucuronosyl bilirubin into bile. MRP2 is hereditarily deficient in human Dubin-Johnson syndrome. Under pathophysiological conditions such as cholestatic liver injury and MRP2 inhibition, the basolateral efflux pump multidrug resistance protein 3 (MRP3 or ABCC3) is responsible for the occurrence of conjugated hyperbilirubinemia. MRP3 is a glycoprotein with a similar molecular mass as MRP2, with 48% amino acid identity, and with overlapping substrate specificity. Human MRP3 is the only basolateral efflux pump shown to transport bilirubin glucuronides. In human and rat hepatocytes, MRP3/Mrp3 is strongly upregulated under conditions of cholestasis and MRP2 deficiency. This is in line with the concept that basolateral efflux pumps of the hepatocyte compensate for impaired canalicular efflux of compounds into bile and contribute to balance the rate of uptake or synthesis of compounds in hepatocytes with the capacity for efflux into bile.

New insights in bilirubin metabolism and their clinical implications.

Bilirubin, a major end product of heme breakdown, is an important constituent of bile, responsible for its characteristic colour. Over recent decades, our understanding of bilirubin metabolism has expanded along with the processes of elimination of other endogenous and exogenous anionic substrates, mediated by the action of multiple transport systems at the sinusoidal and canalicular membrane of hepatocytes. Several inherited disorders characterised by impaired bilirubin conjugation (Crigler-Najjar syndrome type I and type II, Gilbert syndrome) or transport (Dubin-Johnson and Rotor syndrome) result in various degrees of hyperbilirubinemia of either the predominantly unconjugated or predominantly conjugated type. Moreover, disrupted regulation of hepatobiliary transport systems can explain jaundice in many acquired liver disorders. In this review, we discuss the recent data on liver bilirubin handling based on the discovery of the molecular basis of Rotor syndrome. The data show that a substantial fraction of bilirubin conjugates is primarily secreted by MRP3 at the sinusoidal membrane into the blood, from where they are subsequently reuptaken by sinusoidal membrane-bound organic anion transporting polypeptides OATP1B1 and OATP1B3. OATP1B proteins are also responsible for liver clearance of bilirubin conjugated in splanchnic organs, such as the intestine and kidney, and for a number of endogenous compounds, xenobiotics and drugs. Absence of one or both OATP1B proteins thus may have serious impact on toxicity of commonly used drugs cleared by this system such as statins, sartans, methotrexate or rifampicin. The liver-blood cycling of conjugated bilirubin is impaired in cholestatic and parenchymal liver diseases and this impairment most likely contributes to jaundice accompanying these disorders.

Complete OATP1B1 and OATP1B3 deficiency causes human Rotor syndrome by interrupting conjugated bilirubin reuptake into the liver.

Bilirubin, a breakdown product of heme, is normally glucuronidated and excreted by the liver into bile. Failure of this system can lead to a buildup of conjugated bilirubin in the blood, resulting in jaundice. The mechanistic basis of bilirubin excretion and hyperbilirubinemia syndromes is largely understood, but that of Rotor syndrome, an autosomal recessive disorder characterized by conjugated hyperbilirubinemia, coproporphyrinuria, and near-absent hepatic uptake of anionic diagnostics, has remained enigmatic. Here, we analyzed 8 Rotor-syndrome families and found that Rotor syndrome was linked to mutations predicted to cause complete and simultaneous deficiencies of the organic anion transporting polypeptides OATP1B1 and OATP1B3. These important detoxification-limiting proteins mediate uptake and clearance of countless drugs and drug conjugates across the sinusoidal hepatocyte membrane. OATP1B1 polymorphisms have previously been linked to drug hypersensitivities. Using mice deficient in Oatp1a/1b and in the multispecific sinusoidal export pump Abcc3, we found that Abcc3 secretes bilirubin conjugates into the blood, while Oatp1a/1b transporters mediate their hepatic reuptake. Transgenic expression of human OATP1B1 or OATP1B3 restored the function of this detoxification-enhancing liver-blood shuttle in Oatp1a/1b-deficient mice. Within liver lobules, this shuttle may allow flexible transfer of bilirubin conjugates (and probably also drug conjugates) formed in upstream hepatocytes to downstream hepatocytes, thereby preventing local saturation of further detoxification processes and hepatocyte toxic injury. Thus, disruption of hepatic reuptake of bilirubin glucuronide due to coexisting OATP1B1 and OATP1B3 deficiencies explains Rotor-type hyperbilirubinemia. Moreover, OATP1B1 and OATP1B3 null mutations may confer substantial drug toxicity risks.

Congenital nonhemolytic hyperbilirubinemias.

Congenital nonhemolytic hyperbilirubinemias (CNH) are quite rare pathology of liver. They occur most often in children, but are common in adults too. A common feature of congenital nonhemolytic hyperbilirubinemias is an abnormal serum bilirubin level without other abnormalities in routine liver functional tests. Liver histology on light microscopy is normal. Hereditary genetics defect of enzymes taking part in metabolism of bilirubin is the cause of CNH. They are divided into two groups: with unconjugated hyperbilirubinemia (Crigler-Najjar syndrome, Gilbert syndrome) and conjugated hyperbilirubinemia (Dubin-Johnson syndrome and Rotor syndrome). Because CNH in adults are benign disorders and the prognosis is excellent, patients do not require any specific therapy. Is important to take the differential diagnosis. Once the diagnosis of congenital nonhemolytic hyperbilirubinemia is confirmed, patients should be informed of the disease process and its benign nature to prevent needless work-up in the future. In present, CNH are treated as cosmetic defects and no therapy is applied.

Safety of paclitaxel in a patient with ovarian cancer and hyperbilirubinemia due to Rotor's syndrome.

BACKGROUND: Rotor's syndrome is a rare congenital disorder characterized by functional hyperbilirubinemia. Treatment decision may be challenging in a cancer patient with Rotor's syndrome, since the majority of the antineoplastic agents are metabolized in the liver and excreted via the biliary system. We report the first case of paclitaxel administration in a patient with ovarian cancer and elevated bilirubin levels due to Rotor's syndrome. CASE: A 50-year-old woman with Rotor's syndrome had an exploratory laparotomy and was diagnosed to have stage IIIC epithelial ovarian cancer. The baseline serum bilirubin value was 15.3 mg/dL. She was started on a 50% dose of 87.5 mg/m(2) paclitaxel by 3-h infusion plus carboplatin AUC-6. The paclitaxel dose was increased by 25% at consecutive cycles until the standard dose of 175 mg/m(2)/3 h was achieved. Six cycles were administered without any metabolic derangement. The patient was rendered disease free with this treatment. CONCLUSION: Paclitaxel appears to be safe to administer to cancer patients with functional hyperbilirubinemia.

Erythrocyte membrane transport of glutathione conjugates and oxidized glutathione in the Dubin-Johnson syndrome and in rats with hereditary hyperbilirubinemia.

The Dubin-Johnson syndrome is manifested by conjugated hyperbilirubinemia and pigment accumulation in hepatocellular lysosomes. The TR-rat model is a phenotypic model of the Dubin-Johnson syndrome and is characterized by defective ATP-dependent transport of a group of nonbile acid organic anions, including glutathione-S-conjugates and oxidized glutathione, across the bile canaliculus. Similar ATP-dependent transport mechanisms have been described in erythrocytes. Intact erythrocytes and inverted erythrocyte membrane vesicles from Dubin-Johnson patients, TR-rats and appropriate controls were studied with regard to ATP-dependent transport of dinitrophenyl glutathione and oxidized glutathione. No significant differences were observed, indicating that the erythrocyte and canalicular ATP-dependent transporters for these substrates are functionally and potentially genetically distinct.

[Hyperbilirubinemia]. / Hyperbilirubinämie.

A 22-year-old woman had icteric sclerae since childhood. Five years ago of Gilbert-Meulengracht's disease was diagnosed (hyperbilirubinemia, normal other liver laboratory parameters, no evidence of hemolysis). The patient was admitted for re-evaluation. Apart from jaundice of the sclerae no other clinical symptoms were found. Analysis of urine revealed bilirubin and an increased urobilinogen. Serum bilirubin was also elevated. The differentiation of the bilirubin gave evidence of an increase of the direct (conjugated) bilirubin portion. Additional investigations (total coproporphyrin in the urine, isomer I and isomer III coproporphyrin excretion and bromsulphalein test) suggested Rotor's syndrome. Further examinations (oral cholecystography, liver biopsy) were not added because of relative invasiveness, lack of clinical consequences and opposition of the patient. Nevertheless the diagnosis of a Rotor's syndrome is highly probable.

Serum PAF acetylhydrolase increases during neonatal maturation.

Acetylhydrolase is an acid-labile, 43 kd protein that catalyzes the degradation of platelet activating factor (PAF), a potent phospholipid inflammatory mediator, to its biologically inactive metabolite lysoPAF. PAF has a short half-life, thus acetylhydrolase plays an important role in its regulation. Since previous work suggests that PAF may be involved in certain neonatal diseases such as necrotizing enterocolitis, we studied the effect of age on acetylhydrolase activity. Serum acetylhydrolase activity was quantified using radio-labelled PAF and measuring reaction products. Serum samples were obtained prospectively from 70 subjects ranging in age from 4 hr to 48 yr. Acetylhydrolase activity was lower for newborns (less than 3 wk) than all other age ranges (8.2 +/- 1.4 nmole/ml/min vs 30.0 +/- 1.6 nmole/ml/min, p less than .01). Furthermore, enzyme activity increased linearly with respect to the natural logarithm of age from 0 days to 6 weeks (r = 0.65, p less than .001). By 6 weeks of life acetylhydrolase activity approached values of older children and adults. Newborn acetylhydrolase activity was similar between term and preterm infants (8.6 +/- 1.9 nmole/ml/min vs 7.2 +/- 2.4 nmole/ml/min, p = NS). We conclude that acetylhydrolase activity is low in human neonates and increases during the first 6 weeks of life. These results suggest that newborn infants may be at increased risk for pathophysiologic processes mediated by PAF.

Effect of nicotinic acid administration on serum levels of bilirubin and iron in patients with porphyria cutanea tarda.

Nicotinic acid (NA) administration in Gilbert's syndrome (GS) patients promotes an increment of bilirubin and of total iron serum levels, dependent on a defective hepatic bilitranslocase function and on a haemolytic effect of NA. In porphyria cutanea tarda (PCT): (1) the effect of nicotinic acid on bilirubinaemia is superimposable to that in controls; (2) a well documented disturbance of iron metabolism occurs; (3) but relationship between bilirubin and iron under NA load has never been investigated. The administration of 5.9 mumol/kg body weight of NA to 12 PCT patients, 10 GS subjects and nine healthy volunteers of comparable age resulted in: (1) normal behaviour of bilirubin parameters in PCT but higher bilirubinaemic values in GS subjects; (2) normal values of serum iron in GS subjects, but higher baseline values and lower sideraemic effect of nicotinic acid in PCT patients; (3) a normal NA half-life in PCT and enhanced in GS subjects. These findings confirm a defective bilirubin uptake and excretion by the liver of GS subjects with a normal iron metabolism. On the contrary, in our PCT patients a normal clearance of bilirubin occurs, but a complex disturbance of iron metabolism is well evident in baseline conditions as well as after NA administration. The latter being probably the consequence of an enhanced excretion of iron extraproduced by the haemolytic effect of NA.

Effect of different doses of S-adenosyl-L-methionine (SAMe) on nicotinic acid-induced hyperbilirubinaemia in Gilbert's syndrome.

S-adenosyl-L-methionine (SAMe) has been shown to increase hepatocyte membrane fluidity thereby relieving signs of oestrogen-induced cholestasis. S-adenosyl-L-methionine might therefore prove effective in improving the efficiency of the transport of organic anions such as nicotinic acid (NA) and bilirubin which is impaired in Gilbert's syndrome (GS). In this study the effects on the metabolization rate of NA and bilirubin of two dosages of SAMe were evaluated in respect to placebo in ten male inpatients (mean age 24 years, range 16-31) with GS. Each patient received both SAMe (800 and 200 mg/day, respectively) and placebo treatment i.v. over a period of 10 days. The NA test (5.9 mumol/kg b.w. i.v.) was carried out in the same volunteers after each treatment. Unconjugated bilirubin (UCB) levels were significantly lower (p less than 0.01) after 800 mg/day SAMe than after placebo while the lower dosage of SAMe did not affect UCB values. The bilirubin time curve concentration, expressed as area under the curve (AUC), was significantly reduced (p less than 0.01) after 800 mg SAMe in comparison with the values obtained after placebo and 200 mg SAMe. Also plasma NA half-life was significantly reduced (p less than 0.01) by the higher dose of SAMe in respect to placebo and not by the lower dose.

Serum bile acids in liver disease.

Serum bile acids have been measured in patients with a wide variety of liver diseases using a technique which separates the major individual conjugated and free bile acids. Total serum bile acids may be elevated up to 100 times the normal concentration in patients with liver disease and this increase consists largely of conjugated bile acids. The ratio of glycine-conjugated to taurine-conjugated bile salts is low in all types of liver disease and this is found particularly in the serum of patients with obstructive jaundice. There is a decrease in the ratio of trihydroxy:dihydroxy cholanic acid in patients with cirrhosis.