Nicotinic acid test in the diagnosis of Gilbert's syndrome: correlation with bilirubin clearance.

A provocation test with nicotinic acid (50 mg intravenously) was performed in 13 patients with Gilbert's syndrome and seven healthy volunteers to investigate the diagnostic value of several test parameters and to correlate them with the bilirubin clearance. The maximal increment of unconjugated serum bilirubin, the retention at four hours, and the area under the bilirubin concentration time curve. (AUC) were measured. Significant differences between patients and controls were found with regard to the AUC (7.95 +/- SD, 3.29 mmol/min/l vs. 3.08 +/- 0.57; P less than 0.001), the increment of unconjugated bilirubin (24.1 +/- 7.1 mumol/l vs. 10.2 +/- 3.2; P less than 0.001) and the retention (77.7 +/- 8.9% vs. 45.8 +/- 27.4%; P less than 0.02). Of those, the AUC discriminated best between patients and controls. Five patients with Gilbert's syndrome had normal serum bilirubin concentrations (less than 17.1 mumol/l = 1 mg%) at the time of the study, but abnormal AUC and bilirubin increment. A significant correlation was found between the bilirubin clearance and the retention (r = -0.96; P less than 0.001) as well as the AUC (r = -0.82; P less than 0.05) but not with the bilirubin increment. This simple test may be used to assess the disturbance of bilirubin clearance in Gilbert's syndrome.     

Enhanced acetaminophen toxicity in rats with bilirubin glucuronyl transferase deficiency

Glucuronidation is the major pathway for elimination of acetaminophen, diverting it from the toxifying pathway catalyzed by cytochromes P-450. A genetic deficiency in bilirubin UDP-glucuronyl transferase may predispose humans and animals to the toxicity of drugs that are extensively glucuronidated, if other glucuronyl transferase isoenzymes are concurrently deficient. Homozygous and heterozygous Gunn rats are, respectively, severely and moderately deficient in glucuronyl transferase. Acetaminophen (500 mg per kg) was administered intraperitoneally to homozygous and heterozygous Gunn rats and to Wistar controls. Hepatic and renal cellular damage was assessed by peak plasma concentrations of ALT and blood urea nitrogen, respectively. Homozygous and heterozygous Gunn rats showed, respectively, 115-fold and 9-fold higher ALT concentrations compared to Wistar controls. Blood urea nitrogen was elevated only in the homozygous Gunn rats (3-fold). Biotransformation of acetaminophen was measured by high-performance liquid chromatography. Acetaminophen glucuronidation was decreased by 72 and 35% (p less than 0.05), respectively, in the homozygous and heterozygous Gunn rats compared with Wistar controls. Production of acetaminophen glucuronide correlated negatively with ALT concentration (r = -0.89, p less than 0.001). Production of glutathione-derived metabolites, reflecting acetaminophen bioactivation, was 2 to 3-fold higher in the Gunn rats (p less than 0.05) and correlated with ALT concentrations (r = 0.90, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular genetic basis of Gilbert's syndrome

Gilbert's syndrome, an hereditary, chronic, mild, unconjugated hyperbilirubinaemia resulting from impaired hepatic bilirubin clearance and otherwise normal liver function, is arguably the most common syndrome known in humans. Recent molecular genetic studies have determined that the clinical phenotype can be described by a dinucleotide polymorphism in the TATA box promoter of the bilirubin uridine diphosphate-glucuronosyltransferase (UGT-1A1) gene, most frequently (TA)7TAA, affecting up to 36% of Africans, but only 3% of Asians. However, a second common heterozygous mutation in the coding exon 1 of the UGT-1A1 gene (G71R) can also cause the Gilbert's phenotype in Japanese and Asians. The clinical phenotype may not be apparent as frequently as the determined genotype, due to environmental factors such as alcohol-induced hepatic bilirubin glucuronidation, reducing serum bilirubin levels and causing a latent condition. Gilbert's disease is a contributory factor of prolonged neonatal jaundice in breast-fed infants and may precipitate jaundice when coinherited with other disorders of haem metabolism. The genetic variation described as Gilbert's syndrome may lead to pharmacological variation in drug glucuronidation and unexpected toxicity from therapeutic agents.     

Alteration of drug metabolism in Gilbert's syndrome.

The pathophysiology of Gilbert's syndrome was studied by investigating the metabolism of the drug tolbutamide, which is metabolised by the liver but does not undergo glucuronidation. Using rat liver cell supernatant, tolbutamide was shown to bind to the hepatic cytoplasmic Y protein in a manner similar to other organic anions, but not to Z protein. In 31 patients with Gilbert's syndrome the plasma disappearance (plasma half-life, mean +/- SD: 628+/-84 min) and metabolic clearance (7-9+/-1-8 ml/min) were significantly (P less than 0-0005) altered compared with the 13 controls (mean half-life 393+/-26 and mean clearance 13-4+/-1-5). The eight patients with hyperbilirubinaemia due to haemolytic disease showed no difference from the normal control subjects. In three patients with Gilbert's syndrome the cumulative urinary excretion of tolbutamide metabolites, 24 hours after the administration of the drug, was 30% lower than in the controls. In the five patients with Gilbert's syndrome, phenobarbital administration (100 mg/day) produced a significant increase in clearance of the drug from 8-8+/-0-8 to 13-4+/-1-9 ml/min; this was paralleled by a fall in serum bilirubin concentration. The plasma half-life of tolbutamide was similar in Gunn rats and Wistar rats. The results suggest that the metabolic defect(s) of Gilbert's syndrome affects compounds other than bilirubin and that defective uptake is probably the major factor.     

Abnormal hepatic uptake of low doses of sulfobromophthalein in Gilbert's syndrome: the role of reduced affinity of the plasma membrane carrier of organic anions

The plasma disappearance rate of sulfobromophthalein (VBSP; mumol/kg/min) was measured in 15 Gilbert's syndrome patients and 12 control subjects after intravenous injection of two different doses (0.59 and 5.90 mumol/kg) of the dye. Plasma disappearance rate was significantly reduced in Gilbert's syndrome patients after administration of 0.59 mumol sulfobromophthalein/kg (0.119 +/- 0.016 vs. 0.146 +/- 0.018 mumol/kg/min; mean +/- S.D.; p less than 0.001), whereas no difference was found with the higher dose (0.754 +/- 0.040 vs. 0.767 +/- 0.072 mumol/kg/min). Significant reduction was also found after administration to four Gilbert's syndrome patients and four control subjects of 0.29 and 2.95 mumol sulfobromophthalein (0.060 +/- 0.005 mumol/kg/min vs. 0.077 +/- 0.07 mumol/kg/min and 0.480 +/- 0.012 mumol/kg/min vs. 0.591 +/- 0.015 mumol/kg/min, respectively; p less than 0.01). Competition studies with combined administration of sulfobromophthalein (0.59 mumol/kg) and different doses of rifamycin SV (0.59, 1.47 and 2.95 mumol/kg) showed a significant (p less than 0.001) reduction in plasma disappearance rate in Gilbert's syndrome patients but not in controls. The rifamycin SV dose at which a 50% inhibition in plasma disappearance rate was observed was 0.8 mumol/kg. The apparent affinity (Km) of the hepatic transport was higher in Gilbert's syndrome patients than in control subjects (3.61 +/- 0.37 mumol sulfobromophthalein/kg vs. 2.76 +/- 0.29 mumol sulfobromophthalein/kg, mean +/- S.D.; p less than 0.01), whereas no difference was found in Vmax (0.95 +/- 0.11 mumol sulfobromophthalein/kg vs. 0.93 +/- 0.10 mumol sulfobromophthalein/kg/min, mean +/- S.D.; N.S.).(ABSTRACT TRUNCATED AT 250 WORDS)     

Delayed gastric emptying in subjects with Gilbert's syndrome

BACKGROUND/AIMS: Recently, it has been proposed that decreased intestinal motility in fasting-induced hyperbilirubinemic rats probably results in an increase in the enterohepatic cycling of unconjugated bilirubin. We investigated the association among gastric emptying, intestinal transit time, and serum unconjugated levels in subjects with Gilbert's syndrome. METHODOLOGY: Ten subjects with Gilbert's syndrome were included in this study according to the following criteria: fasting hyperbilirubinemia; no hemolysis or gastrointestinal disorders and free of any medication. Five normal, healthy volunteers acted as controls. Gastric emptying and intestinal transit time were evaluated after overnight fasting by administration of a standard meal mixed with 1-2ci of 99Tc-labeled diethylene-triamine-pentacetic acid. Serum unconjugated bilirubin levels were determined by high-performance liquid chromatography. RESULTS: The gastric emptying in Gilbert's syndrome subjects was 134.1 +/- 38.9 and 90.9 +/- 6.5 min in controls, P < 0.03. It was a tendency to have a shorter intestinal transit time in subjects with Gilbert's syndrome, 138.3 +/- 59.0, than in control subjects, 183.8 +/- 11.3 min. Serum unconjugated bilirubin levels (mg/dL) were 2.6 +/- 1.04 and 0.95 +/- 0.34, P < 0.01. CONCLUSIONS: Gastric emptying is delayed significantly in Gilbert's syndrome, and intestinal transit time differences between Gilbert's syndrome subjects and controls were not significantly different.     

The differential diagnosis of Crigler-Najjar disease, types 1 and 2, by bile pigment analysis

Phenobarbital response, bile pigment composition, and the fractional biliary excretion ratio of bilirubin were studied in nine children with Crigler-Najjar disease. In five children, serum bilirubin levels decreased during phenobarbital treatment by 26% or more and the pigment composition in bile changed with a decrease in the proportion of unconjugated bilirubin from 33% +/- 12% to 13% +/- 1% and an increase in monoconjugates and diconjugates from 57% +/- 14% and 10% +/- 2%, respectively, to 72% +/- 4% and 16% +/- 3%. In four children, serum bilirubin levels did not change significantly during phenobarbital treatment. In these patients, bile pigments comprised 91% +/- 10% unconjugated bilirubin, 9% +/- 11% monoconjugates, and 1% +/- 1% diconjugates. On the basis of these differences, the former group can be classified as having type 2 Crigler-Najjar disease and the latter, type 1. Bile pigment analysis in parents of patients with Crigler-Najjar disease showed an increased proportion of monoconjugates in at least one of the partners in three of four couples tested, despite normal serum bilirubin levels. Serum bilirubin levels were about the same in type 1 and 2 patients and amounted to 236 +/- 62 mumol/L and 214 +/- 82 mumol/L, respectively. In addition the fractional bilirubin excretion ratio, calculated as the ratio ([bilirubin in bile]/[bilirubin in serum])/([bile acid in bile]/[bile acid in serum]) could not differentiate between these two groups. However, there was a 10-fold and 100-fold difference of this ratio between patients with Crigler-Najjar disease and those with Gilbert's syndrome and between patients with Crigler-Najjar disease and controls. The fractional bilirubin excretion ratio proved an excellent tool to differentiate between Gilbert's syndrome and Crigler-Najjar disease, whereas Crigler-Najjar disease types 1 and 2 could be differentiated on the basis of bile pigment analysis.     

Etiology and Incidence of Unconjugated Hyperbilirubinemia after Orthotopic Liver Transplantation

Obfectives: Gilbert's syndrome, or slow bilirubin glucuronidation phenotype, is a common cause of benign hyperbilirubinemia in the general population. There have heen only two previously reported cases of Gilbert's syndrome occurring in patients after liver transplantation. This study was conducted to determine the frequency of Gilbert's syndrome in liver transplant recipients. Methods: The charts of all patients followed by the Mayo Liver Transplant Clinic for 1 yr or more after transplantation, as of June 1992, were reviewed to identify all patients with a consistent pattern of unconjugated hyperbiliruhinemia greater than two times the upper limits of normal and with a normal conjugated bilirubin level. These patients were further evaluated to exclude all other causes of hyperbilirubinemia, including biliary obstruction, rejection, viral infection, cholestatic liver disease, and hemolysis. Resutts: Five of 229 patients (2.2%) had a consistent pattern of unconjugated hyperbiliruhinemia. Only three patients (1.3%) had no other identifiable cause of hyperbilirubinemia. Conclusions: This study was performed to determine the incidence of unconjugated hyperbilirubinemia and particularly to determine the incidence of Gilbert's disease in liver transplant recipients. The apparently low frequency of Gilbert's after liver transplantation may reflect the masking of the diagnosis by other transplant-associated pathology or donor selection bias because of unexplained hyperbilirubinemia. Post-transplant patients who fit the Gilbert's syndrome profile of unconjugated hyperbilirubinemia should have a postprandial bilirubin drawn as a first step. The awareness of this syndrome may avoid a costly and invasive evaluation in the liver transplant recipient.     

Porphyrin metabolism and haem biosynthesis in Gilbert's syndrome.

Studies in 14 patients with unconjugated hyperbilirubinaemia caused by Gilbert's syndrome have revealed abnormalities of the enzymes of haem biosynthesis measured in peripheral blood cells. The activity of the penultimate enzyme of haem biosynthesis protoporphyrinogen (PROTO) oxidase was reduced at 3.1 +/- 2.6 nmol PROTO/g protein/h (mean +/- ISD) compared with 8.2 +/- 5.1 in controls (p less than 0.005). This was associated with a compensatory increase in the activity of the initial and rate controlling enzyme of the pathway delta-aminolaevulinic acid (ALA) synthase at 866 +/- 636 nmol ALA/g/protein/h compared with 156 +/- 63 in controls (p less than 0.001). Unlike variegate porphyria in which there is a genetic deficiency of PROTO oxidase there was no increased excretion of porphyrins or their precursors in Gilbert's syndrome. Accentuation and subsequent correction of the unconjugated hyperbilirubinaemia with rifampicin produced reciprocal changes in PROTO oxidase activity indicating that bilirubin may be inhibiting the activity of this enzyme.     

Combined polymorphisms in UDP-glucuronosyltransferases 1A1 and 1A6: implications for patients with Gilbert's syndrome

BACKGROUND/AIMS: UDP-glucuronosyltransferases (UGTs) are important enzymes involved in glucuronidation of various exogenous and endogenous compounds. Studies were undertaken on the variability of three UGT enzyme activities in human livers. Enzyme activities were associated with genetic polymorphisms in UGT1A1 (UGT1A1*28) and UGT1A6 (UGT1A6*2). UGT1A1*28 is associated with Gilbert's syndrome, a deficiency in glucuronidation of bilirubin leading to mild hyperbilirubinemia, whereas UGT1A6*2 may result in low glucuronidation rates of several drugs. METHODS: Enzyme activities and genetic polymorphisms were assessed in 39 human liver samples, and polymorphisms were also assessed in blood of 253 healthy controls. RESULTS: Associations were found between UGT enzyme activities of bilirubin (B) and 4-nitrophenol (NP; r=0.47, P=0.0024), B and 4-methylumbelliferone (MUB; r=0.54, P=0.0003), and NP and MUB (r=0.89, P<0.0001). In addition to the association between B-UGT enzyme activity and UGT1A1*28 (r=0.45, P=0.0034) as reported earlier, an association between B-UGT and UGT1A6*2 (r=0.43, P=0.007) was found. In 253 Dutch Caucasian controls, co-occurrence of UGT1A1*28 and UGT1A6*2 was found (r=0.9, P<0.0001). CONCLUSIONS: Most patients with Gilbert's syndrome, in addition to their reduced B-UGT enzyme activity, may have abnormalities in the glucuronidation of aspirin or coumarin- and dopamine-derivatives, due to this combination of UGT1A1*28 and UGT1A6*2 genotypes.     

Dual polymorphisms in UDP-glucuronosyltransferases 1A1 and 1A6: a novel mechanism for hyperserotoninaemia in Gilbert's syndrome mimicking carcinoid syndrome?

Gilbert's syndrome is a common inherited disorder, in which genetic defects in uridine diphosphate-glucuronosyltransferase 1A1 lead to deficient glucuronidation of bilirubin and hence hyperbilirubinaemia. Although usually considered asymptomatic, Gilbert's syndrome can be associated with gastrointestinal and psychiatric symptoms unexplained by the metabolic defect. Genetic polymorphism of a closely related enzyme, uridine diphosphate-glucuronosyltransferase 1A6, results in altered metabolism and elimination of serotonin. On the basis of a case of hyperserotoninaemia in the absence of a detectable carcinoid tumour in a patient with Gilbert's syndrome, who presented with a history of night sweats, flushing, abdominal discomfort and intermittent diarrhoea, we propose that in a subgroup of Gilbert's syndrome patients, homozygocity for dual uridine diphosphate-glucuronosyltransferase 1A1 and uridine diphosphate-glucuronosyltransferase 1A6 polymorphisms may lead to combined hyperbilirubinaemia and hyperserotoninaemia. The latter may account for symptoms experienced by patients with Gilbert's syndrome hitherto considered unrelated to, or unexplainable by, the known defect in bilirubin metabolism.     

Chronic persistent hepatitis and unconjugated hyperbilirubinemia.

The authors studied 12 patients with chronic persistent hepatitis and persistent or intermittent mild unconjugated hyperbilirubinemia. Maximum serum total bilirubin concentration ranged from 2.1 to 3.6 mg/dl. Hemolysis was not evident. Hepatic bilirubin UDP-glucuronyltransferase activity assayed in each patient ranged from 0.16 to 0.39 U (mean +/- SEM = 0.27 +/- 0.02) compared to 0.68-1.99 (1.35 +/- 0.08) in 23 normals, 0.78-2.28 (1.41 +/- 0.05) in 53 patients with acute hepatitis, 0.34-1.74 (0.81 +/- 0.09) in 16 patients with anicteric chronic persistent hepatitis, and 0-0.62 (0.24 +/- 0.03) in 33 patients with Gilbert's syndrome. The mean UDP-glucuronyltransferase activity was significantly lower in anicteric chronic persistent hepatitis compared to normals, but higher than in Gilbert's syndrome. The incidence of unconjugated hyperbilirubinemia among first degree relatives was 0:32 in icteric chronic persistent hepatitis compared to 24:85 (28%) in Gilbert's syndrome. These results show that the likely cause for the unconjugated hyperbilirubinemia associated with chronic persistent hepatitis is an acquired depression of hepatic bilirubin UDP-glucuronyltransferase activity. The data suggest that the enzyme defect is related to chronic persistent hepatitis.     

Comparison of nicotinic acid- and caloric restriction-induced hyperbilirubinaemia in the diagnosis of Gilbert's syndrome

The diagnostic value of the nicotinic acid (NA)-induced hyperbilirubinaemia was compared with that resulting from caloric restriction in 40 patients with Gilbert's syndrome (GS) and 20 controls. Both tests resulted in a significant higher level of serum bilirubin in GS than in controls (P less than 0.001). When the serum bilirubin level 240 min after NA administration (5.9 mumol/kg i.v.) was higher than 18 mumoles/l, this test had a specificity and sensitivity of 100%, both in males and females with the syndrome. The discriminatory value of the test was lower when either the area under the time concentration curve or the maximal increment of serum unconjugated bilirubin were used. Reduction in caloric intake (400 calories/day) showed a lower specificity and sensitivity than the NA test, particularly in females. An increment of bilirubin at 24 h greater than 15 mumoles/l was more diagnostic than an increase by 100% or more over the pre-diet value. The efficacy was not improved by prolonging the test for additional 24 h. From these data we conclude that NA-induced hyperbilirubinaemia and, in particular the concentration of the pigment 240 min after drug administration, is more efficient than fasting-induced hyperbilirubinaemia in the diagnosis of the Gilbert's syndrome both in males and in females.     

Effect of dietary composition on the unconjugated hyperbilirubinaemia of Gilbert's syndrome.

The influence of dietary composition on the unconjugated hyperbilirubinaemia of Gilbert's syndrome was studied in 29 patients. After a period on a normal diet (10 MJ) an intravenous infusion of 40% glucose (8-4 MJ) together with a 1-6 MJ oral diet for two days resulted in an increment in plasma bilirubin concentration of 127 +/- 18% (mean +/- SEM) above the basal level. Both the administration of intravenous Intralipid 20% and the return to a normal diet caused a prompt reversal of this glucose effect. An increment of 135 +/- 10% in plasma bilirubin concentration was obtained when a standard "fasting" diet (1-6 MJ) was given for two days. When the lipid content of this "fasting" diet was increased from 33% to 85%, the rise in plasma bilirubin was only 49 +/- 19%. A 10 MJ oral diet for three days, which contained most of its energy content as carbohydrate and only 0-6% as lipid, produced a 76 +/- 12% increase in plasma bilirubin concentration. When the lipid content of the diet was increased to 9% of the energy intake no significant change from the basal level was observed. These findings support the hypothesis that the hyperbilirubinaemia associated with both carbohydrate feeding and fasting is attributable, at least in part, to lipid withdrawal. Although a restricted dietary intake or the parenteral administration of lipid-free solutions has a marked effect on the hyperbilirubinaemia of patients with Gilbert's syndrome, normal daily variation in dietary composition is unlikely to cause a significant change. The influence of different feeding regimes on neonatal hyperbilirubinaemia requires investigation.     

Subfractionation of serum bilirubins by alkaline methanolysis and thin-layer chromatography. An aid in the differential diagnosis of icteric diseases

The determination of direct and indirect-reacting bilirubin fractions by diazo procedures does not allow a definite diagnosis of icteric diseases. Therefore, the clinical relevance of serum bilirubin subfractionation by alkaline methanolysis and subsequent thin-layer chromatography (AM-TLC) was evaluated. Esterified bilirubins could be detected and quantitated in all serum samples investigated. The ratio of serum esterified to total bilirubin was 10-28% in 60 healthy adults (mean 17 +/- 5% S.D.), 1-11% in 77 patients with Gilbert's syndrome (mean 6 +/- 2%), and 2 and 3%, respectively, in two patients with Crigler-Najjar disease type II. The difference was highly significant (p less than 0.001) and the overlap was restricted to three of 139 individuals. The ratio of esterified to total bilirubin was similar to that obtained with HPLC when corrected for with a blank run. The absolute concentration of bilirubin esters in serum from Gilbert's syndrome patients was similar to that from healthy controls, but the unconjugated pigment was increased. In patients with chronic haemolysis (n = 9) and chronic persistent hepatitis (n = 12), the hyperbilirubinaemia consisted of a proportional increase of both unconjugated and esterified bilirubin. As such, the ratio of conjugated to total bilirubin was not significantly different from control values. Patients with acute hepatitis during the first (n = 18) and third ('remission') week of the disease (n = 15), liver cirrhosis (n = 34), and extrahepatic cholestasis (n = 20) predominantly showed an increase in bilirubin conjugates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pericanalicular microfilaments of hepatocytes in patients with familial non-hemolytic hyperbilirubinemia

We observed pericanalicular webs (PCW) of liver cells in cases with familial non-hemolytic hyperbilirubinemia using electron microscopy. The area and width of PCW were determined by morphometric methods as a way of quantitating this feature. The mean PCW width was 0.175 +/- 0.003 micron (mean +/- SE) in Dubin-Johnson syndrome and 0.184 +/- 0.005 micron in Rotor's syndrome. In both of these syndromes PCW width was significantly larger than that in Gilbert's syndrome (0.124 +/- 0.003 micron) (p less than 0.01). The mean PCW area was 0.585 +/- 0.017 micron 2 in Dubin-Johnson syndrome and 0.582 +/- 0.030 micron 2 in Rotor's syndrome. Values in these two syndromes were significantly larger than that in Gilbert's syndrome (0.382 +/- 0.014 micron 2) (p less than 0.01). Widths and areas of PCW in these three syndromes were not significantly different between central, intermediate, and peripheral zones of the hepatic lobules. There was a positive correlation between serum direct bilirubin levels and widths or areas of PCW in these syndromes. These results suggested that disturbances of bile flow caused by the dysfunction of pericanalicular microfilaments are partly involved in the pathogenesis of Dubin-Johnson syndrome and Rotor's syndrome.     

Hemolysis and bilirubin conjugation in association with UDP-glucuronosyltransferase 1A1 promoter polymorphism

Hemolysis may contribute to hyperbilirubinemia in Gilbert's syndrome. The authors examined blood carboxyhemoglobin corrected for inspired CO (COHbc) to index heme catabolism and serum conjugated bilirubin fractions to reflect bilirubin conjugation. Both parameters were related to UDP-glucuronosyltransferase 1A1 (UGT) promoter polymorphism, associated with Gilbert's syndrome, in term male newborns. COHbc was expressed as percentage of total hemoglobin, and total conjugated bilirubin (TCB) value as a percentage of serum total bilirubin (STB), (TCB/STB[%]). A production/conjugation index, COHbc/(TCB/STB[%]), represented bilirubin production divided by conjugation. UGT promoter genotype was designated according to the number of promoter TA insertions in each allele: 6/6, homozygous normal; 6/7, heterozygous; 7/7, homozygous variant. STB and COHbc values were higher in the 7/7 subgroup than the other counterparts (P <.01). The COHbc/(TCB/STB[%]) was higher in the 7/7 than either the 6/6 or 6/7 subsets (1.93 [1.31-2.88] vs. 0.85 [0.51-1.72] and 0.84 [0.53-1.87], respectively; P <.01). In conclusion, 7/7 UGT promoter polymorphism was associated with increased blood COHbc values (unexpected finding) as well as diminished serum total conjugated bilirubin ratios (expected finding). The increased hemolysis may contribute to the pathogenesis of increased STB values seen in Gilbert's syndrome, and exacerbate neonatal hyperbilirubinemia associated with the promoter polymorphism.     

Acetaminophen does not impair clearance of zidovudine

OBJECTIVE: To determine whether concurrent treatment with acetaminophen and zidovudine impairs clearance of zidovudine, thereby increasing the risk for zidovudine-induced hematologic toxicity. DESIGN: Dose escalation, drug interaction study. SETTING: University clinical research center. PATIENTS: Patients with the acquired immunodeficiency syndrome (AIDS) or advanced AIDS-related complex. INTERVENTIONS: Acetaminophen and 200 mg of zidovudine simultaneously every 4 hours. For 13 patients, the unit dosage of acetaminophen was 325 mg for 3 days; for 8 patients, the dosage was 650 mg for 3 days; and, for 6 patients, the dosage was 650 mg for 7 days. MEASUREMENTS: Zidovudine clearance and production of the glucuronide conjugate of zidovudine were assessed after acetaminophen treatment. MAIN RESULTS: Neither zidovudine clearance nor production of the glucuronide conjugate of zidovudine was impaired after treatment with acetaminophen. Clearance of zidovudine was actually accelerated by 5%, 11%, and 33% with the three acetaminophen regimens, respectively (P = 0.002 by analysis of variance; P = 0.04 for linear trend when changes in the area-under-the-curve for zidovudine were compared). CONCLUSION: Because serum concentrations of zidovudine decrease after the coadministration of acetaminophen, a pharmacokinetic interaction between zidovudine and acetaminophen is unlikely to increase the risk for hematologic toxicity associated with zidovudine.     

Association of human liver bilirubin UDP-glucuronyltransferase activity with a polymorphism in the promoter region of the UGT1A1 gene

BACKGROUND/AIMS: Gilbert's syndrome is a benign form of a deficiency in bilirubin glucuronidation. It is associated with a homozygous polymorphism, A(TA)7TAA instead of A(TA)6TAA, in the TATA-box of the promoter region of the bilirubin UDP-glucuronyltransferase gene. In this study the correlation between this promoter region polymorphism and in vitro human liver bilirubin UDP-glucuronyltransferase enzyme activity was investigated. METHODS: Liver samples from organ transplant donors n=39) and two known Gilbert's syndrome patients were used for measuring bilirubin UDP-glucuronyltransferase enzyme activity and for isolation of DNA followed by detection of the promoter region polymorphism by polymerase chain reaction. Genotypes were assigned as follows; 6/6: homozygous for the A(TA)6TAA-allele, 7/7: homozygous for the A(TA)7TAA-allele, and 6/7: heterozygous with one of each alleles. RESULTS: Seventeen out of 39 subjects (44%) had the homozygous 6/6 genotype, 18 subjects (46%) had the heterozygous 6/7 genotype, whereas four individuals (10%) and the two individuals with Gilbert's syndrome had the 7/7 genotype correlated with Gilbert's syndrome. This resulted in an allele frequency of 0.33 for the A(TA)7TAA-allele. The median bilirubin UDP-glucuronyltransferase enzyme activity of the 17 subjects with the 6/6 genotype (1565 nmol/g liver/h) was significantly higher than the activity of the 18 subjects with the 6/7 genotype (985 nmol/g liver/h; p<0.05) and the six individuals with the 7/7 genotype (749 nmol/g liver/h; p<0.005). No significant differences in enzyme activity were found between the 6/7 and the 7/7 genotype groups. CONCLUSIONS: The results indicate a close association between the promoter region genotype and the expression of hepatic bilirubin UDP-glucuronyltransferase enzyme activity. Subjects who have a 7/7 genotype have the lowest enzyme activity, whereas subjects with the heterozygous 6/7 genotype have an intermediate enzyme activity.     

Stereoselective urinary excretion of S-（-）- and R-（＋）-propranolol glucuronide following oral administration of RS-propranolol in Chinese Han subjects

AIM: To study the stereoselectivity of phase Ⅱ glucuronidation metabolism of side-chain propranolol in Chinese Han population. METHODS: Sixteen adult Chinese Han volunteers with an average age of 20 years were given a single oral dose of 20 mg racemic propranolol. Human urine at indicated time after administration was collected and S-(-)-propranolol glucuronide and R-(+)-propranolol glucuronide were determined simultaneously by using RP-HPLC. RESULTS: The mean values of k were 0.19±0.04 h-1 and 0.28±0.06 h-1, of t1/2 3.56±0.73 h and 2.45±0.50 h, of Tmax 2.21±0.45 and 1.75±0.33 h, and of Xu0-24 5.65±0.98 and 2.95±0.62 μmoL for S-(-)- and R-(+)-propranolol glucuronide, respectively. The cumulative excretion percentages in urine of closes were 14.7±2.46% and 7.68±1.60% for S-(-)-and R-(+)-propranolol glucuronide, respectively. The results showed the elimination rate constant k of S-(-)-propranolol glucuronide was less than that of R-(+)-propranolol glucuronide; and the elimination half-life (t1/2), Tmax and the cumulative excretion amount (Xu0-24) of R-(+)-propranolol glucuronide were significantly less than that of S-(-)-propranolol glucuronide. CONCLUSION: The propranolol glucuronidation of the side-chain undergoes stereoselective excretion in Chinese Han population after an oral administration of racemic propranolol.