Metastable and equilibrium phase diagrams of unconjugated bilirubin IXα as functions of pH in model bile systems: Implications for pigment gallstone formation.

Metastable and equilibrium phase diagrams for unconjugated bilirubin IXα (UCB) in bile are yet to be determined for understanding the physical chemistry of pigment gallstone formation. Also, UCB is a molecule of considerable biomedical importance because it is a potent antioxidant and an inhibitor of atherogenesis. We employed principally a titrimetric approach to obtain metastable and equilibrium UCB solubilities in model bile systems composed of taurine-conjugated bile salts, egg yolk lecithin (mixed long-chain phosphatidylcholines), and cholesterol as functions of total lipid concentration, biliary pH values, and CaCl2 plus NaCl concentrations. Metastable and equilibrium precipitation pH values were obtained, and average pKa values of the two carboxyl groups of UCB were calculated. Added lecithin and increased temperature decreased UCB solubility markedly, whereas increases in bile salt concentrations and molar levels of urea augmented solubility. A wide range of NaCl and cholesterol concentrations resulted in no specific effects, whereas added CaCl2 produced large decreases in UCB solubilities at alkaline pH values only. UV-visible absorption spectra were consistent with both hydrophobic and hydrophilic interactions between UCB and bile salts that were strongly influenced by pH. Reliable literature values for UCB compositions of native gallbladder biles revealed that biles from hemolytic mice and humans with black pigment gallstones are markedly supersaturated with UCB and exhibit more acidic pH values, whereas biles from nonstone control animals and patients with cholesterol gallstone are unsaturated with UCB.

Beyond plasma bilirubin: the effects of phototherapy and albumin on brain bilirubin levels in Gunn rats.

BACKGROUND & AIMS: Severe unconjugated hyperbilirubinemia, as occurs in Crigler-Najjar disease and neonatal jaundice, carries the risk of neurotoxicity. This neurotoxicity is related to the increased passage of free bilirubin (UCB(free)), the fraction of bilirubin that is not bound to plasma proteins, into the brain. We hypothesized that albumin treatment would lower the UCB(free) fraction, and thus decrease bilirubin accumulation in the brain. METHODS: We treated chronic (e.g., as a model for Crigler-Najjar disease) and acute hemolytic (e.g., as a model for neonatal jaundice) moderate hyperbilirubinemic Gunn rats with phototherapy, human serum albumin (HSA) or phototherapy+HSA. RESULTS: In the chronic model, adjunct HSA increased the efficacy of phototherapy; it decreased plasma UCB(free) and brain bilirubin by 88% and 67%, respectively (p<0.001). In the acute model, adjunct HSA also increased the efficacy of phototherapy; it decreased plasma UCB(free) by 76% (p<0.001) and completely prevented the hemolysis-induced deposition of bilirubin in the brain. Phototherapy alone failed to prevent the deposition of bilirubin in the brain during acute hemolytic jaundice. CONCLUSIONS: We showed that adjunct HSA treatment decreases brain bilirubin levels in phototherapy-treated Gunn rats. We hypothesize that HSA decreases these levels by lowering UCB(free) in the plasma. Our results support the feasibility of adjunct albumin treatment in patients with Crigler-Najjar disease or neonatal jaundice.

Orlistat treatment of unconjugated hyperbilirubinemia in Crigler-Najjar disease: a randomized controlled trial.

Unconjugated hyperbilirubinemia in Crigler-Najjar (CN) disease is conventionally treated with phototherapy and phenobarbital. Orlistat treatment increases fecal fat excretion and decreases plasma unconjugated bilirubin (UCB) concentrations in Gunn rats, the animal model for CN disease. We determined in CN patients the effects of orlistat treatment on plasma UCB concentrations, and on fecal excretion of fat and UCB. A randomized, placebo-controlled, double-blind, cross-over trial was conducted in 16 patients, simultaneous with their regular treatment (phototherapy, n = 11, and/or phenobarbital, n = 6). Patients received orlistat or placebo, each for 4-6 wk. Compared with placebo, orlistat increased fecal fat excretion (+333%) and fecal UCB excretion (+43%). Orlistat treatment significantly decreased plasma UCB concentration (-9%). In 7 of 16 patients, the decrease in plasma UCB levels was clinically relevant (>10%, mean 21%). In patients with a clinically relevant response, plasma UCB concentrations during orlistat were strongly, negatively correlated with fecal fat excretion (r = -0.93). Clinically relevant response to orlistat treatment was not correlated with age, sex, CN type, BMI, or co-treatment with phototherapy or phenobarbital, but appeared correlated with a relatively lower dietary fat intake. In conclusion, orlistat treatment decreases plasma UCB concentrations, particularly in a subgroup of CN patients. Dietary fat intake may determine the responsiveness to orlistat treatment.

Supplement of liver enzyme by intestinal and kidney transplants in congenitally enzyme-deficient rat.

Gunn rats have a congenital deficiency of bilirubin-uridine diphosphate glucuronyltransferase (B-UDP-GT) activity and are unable to glucuronidate bilirubin in the bile, resulting in unconjugated hyperbilirubinemia. Other than the liver, several organs, including small bowel and kidneys, are known to have B-UDP-GT activity in normal rats. We performed total- or partial-small-bowel transplantation as well as kidney transplantation for Gunn rats in congenic combination and compared the effects of these procedures. Serum total bilirubin (TBil) levels significantly decreased from 7.84 +/- 0.24 mg/dl to 2.19 +/- 0.43 mg/dl 2 weeks after total-small-bowel transplantation (n = 12). Correlation of hyperbilirubinemia was roughly proportional to the length of the transplanted small bowel. There were no difference in metabolic correction between jejunal and ileal transplantation. Serum TBil levels significantly decreased from 7.83 +/- 0.21 mg/dl to 2.24 +/- 0.98 mg/dl 2 weeks after kidney transplantation (n = 5). In conclusion, small-bowel and kidney transplantation were effective in correcting metabolic abnormality in Gunn rats for the period of 4-6 months. Estimated total B-UDP-GT activity supplemented by small-bowel or kidney transplantation was about 1/5-1/4 of the minimal requirement for the complete normalization of serum total bilirubin levels.

Molecular biology of bilirubin metabolism.

As the genes encoding the glucuronidating enzymes are discovered, it is evident that glucuronidation is a magnificent example of how in evolution, man became adapted to his "intoxicating" environment. A superfamily of genes is necessary to dispose of the toxins and carcinogens that are encountered by inhalation and ingestion. The enzymes that glucuronidate endogenous compounds are members of this large family. For the clinician, it is important to remember that jaundice may sometimes be the result of interactions at the level of bilirubin glucuronidation. When jaundice results from inactivation of members of the UGT1 family, conjugation of certain phenols, such as the anesthetic propofol, or synthetic estrogens, such as ethinylestradiol, can also be impaired. In the case of severe bilirubin glucuronidation deficiencies, such as the Crigler Najjar syndrome type I, there are exciting prospects for a possible cure by gene therapy.

Orthotopic liver transplantation for type I Crigler-Najjar syndrome.

A neurologically normal 3-year-old girl with Type I Crigler-Najjar syndrome was successfully treated with orthotopic liver transplantation. Preoperative serum bilirubin concentrations as high as 31 mg per dl were not diminished with phenobarbital or phototherapy. Bilirubin fractionation of duodenal bile prior to transplantation revealed 87.1% unconjugated bilirubin and 12.9% monoconjugates as determined by alkaline methanolysis-high-performance liquid chromatography. Postoperatively, the serum bilirubin concentration quickly fell to normal. Uridine diphosphate glucuronyl transferase activity in the recipient liver was not detectable. The gallbladder bile bilirubin concentration of 23.9 mg per dl was less than 15% of previously reported normal values. Since devastating kernicteric brain injury is the invariable outcome of Type I Crigler-Najjar syndrome, liver transplantation should be performed when phototherapy cannot maintain the serum bilirubin concentration at an unequivocally safe level.

Familial unconjugated hyperbilirubinemia syndromes.

Our understanding of the biochemical defects underlying the hepatic forms of congenital, unconjugated hyperbilirubinemias has been greatly enhanced over the past decade. This is mostly due to the availability of pure, labeled bilirubin, the appropriate kinetic analyses, and a better understanding of the mechanisms underlying bilirubin conjugation. Although it is quite obvious that the defect underlying Gilbert's and Crigler-Najjar syndromes is deficient glucuronidation, the molecular explanation may eventually be found in altered composition of the microsomal lipids rather than in a protein defect of glucuronyl transferase. The recognition that Gilbert's syndrome is a quite heterogeneous entity will allow a better understanding of the mode of inheritance of this disorder; its relationship to Crigler-Najjar type II disease also awaits further definition. It is hoped that definition of the molecular defect in Crigler-Najjar type I will lead to better therapeutic modalities, but this remains to be seen.

Characteristics of a photoproduct of bilirubin found in vitro and in vivo, and its effect on the bilirubin binding affinity of serum.

The 430 pigment isolated from bilirubin-albumin solutions illuminated in vitro, decreased the bilirubin binding affinity of serum. This effect was demonstrated for both tightly and loosely bound bilirubin in serum, but in albumin solutions pretreated with charcoal only the binding of loosely bound bilirubin was decreased. This finding is of importance because a similar pigment has been isolated from the body fluids of an infant with Crigler-Najjar syndrome. The production and accumulation of 430 pigment during phototherapy might decrease the binding of bilirubin to albumin in the circulation.