Recent advances in bilirubin formation, transport, metabolism and excretion

Simple non-invasive markers for early diagnosis and determination of the severity of liver diseases

Aim of the study

The aim of the study was to evaluate the effect and severity of liver diseases of different etiologies on the values of three non-invasive fibrosis markers.

Material and methods

Serum samples from 65 patients with alcoholic cirrhosis, 31 with non-alcoholic cirrhosis and 32 with toxic hepatitis, were tested. Cirrhotic patients were classified according to the Child-Pugh scale. The age-platelet (AP) index, HUI score and Fibro Q index were calculated using the specific formulas.

Results

The values of all tested scores were significantly higher in controls than in patients with liver diseases and were significantly different between liver diseases. The patients with alcoholic and non-alcoholic cirrhosis had higher values of the AP index, HUI score and Fibro Q index than patients with toxic hepatitis. HUI and Fibro Q scores appeared to vary according to the severity of liver damage and were higher in Child-Pugh class C than in classes A and B.

Conclusions

We conclude that all tested scores based on liver function tests are good markers for non-invasive diagnosis of liver damage. Additionally, HUI and Fibro Q scores reflect the severity of liver cirrhosis.

Hormonal regulation of hepatic multidrug resistance-associated protein 2 (Abcc2) primarily involves the pattern of growth hormone secretion

Biliary excretion is the rate-limiting step in transfer of bilirubin, other organic anions, and xenobiotics across the liver. Multidrug resistance-associated protein 2 (Mrp2, Abcc2) is the major transporter for conjugated endo- and xenobiotic-conjugated compounds into bile. Hormones regulate bilirubin and xenobiotic secretion into bile, which have dimorphic differences. Therefore, we examined the possible role of sex steroids and growth hormone in the regulation of Mrp2. In approximately 8-wk-old rats, mRNA, transcriptional activity, and hepatic content of Mrp2 were selectively increased fourfold (P < 0.001) in females compared with males. In males, estrogens increased and testosterone decreased Mrp2 mRNA and protein, whereas no significant effect was measured in females, suggesting either a direct effect on the liver or an alteration in growth hormone secretory pattern. After hypophysectomy, Mrp2 mRNA was markedly reduced and the effects of estrogens and testosterone on Mrp2 were prevented, supporting the role of pituitary hormones in controlling Mrp2 expression. Mrp2 increased following growth hormone infusion in males. Mrp2 mRNA was decreased in growth hormone-deficient "Little" mice. Growth hormone infusions in hypophysectomized rats partially restored Mrp2 levels, whereas thyroxine addition returned Mrp2 mRNA and protein to basal levels. Morphology as well as biochemical measurements demonstrated that Mrp2 was localized to the bile canaliculus in equal density in both genders, whereas hormone replacements increased Mrp2 in hypophysectomized animals. In cultured hepatocytes, thyroxine did not have an effect, but growth hormone alone and combined with thyroxine increased Mrp2 mRNA levels. In conclusion, Mrp2 levels are regulated by the combination of thyroxine and different growth hormone secretory patterns.

Evaluation of the maximal excretion rate of indocyanin green as a prognostic indicator in patients undergoing biliary decompression for obstructive jaundice

To assess the postoperative outcome of jaundiced patients and to select the optimal timing for surgical intervention, indocyanin green (ICG) concentrations in the bile were measured after biliary decompression in patients with obstructive jaundice. The maximal excretion rate of ICG in the bile was calculated as a function of time (ICG Bmax). Among 59 patients with positive ICG Bmax values, morbidity was 15.2% and postoperative hospital mortality was 3.3%. However, the morbidity and mortality in nine patients with values between -0.5 and 0 were 88.8 and 44.4%, respectively. The 13 patients with in ICG Bmax below -0.5 had a 76.9% morbidity and a 61.5% mortality. The patients with ICG Bmax values below 0 showed a significantly higher morbidity and mortality than positive ICG Bmax patients. In patients showing ICG Bmax values below -0.5, surgery is contraindicated despite intensive postoperative care. The ICG Bmax value improved according to the increasing effect of biliary decompression. The index is useful not only as a prognostic index in the early phase of biliary decompression but also as an index of bile secretory capacity at a given time. By means of time course measurement of this index, the suitable time for operation can be determined. The ICG Bmax is a useful and reliable indicator in the assessment of hepatobiliary functional reserve in jaundiced patients after biliary decompression and prior to further surgical intervention.

Serum bilirubin levels with antiepileptic drugs

The incidence of reduced bilirubin levels in 168 outpatients with epilepsy, compared with levels in 69 controls, has been investigated. Highly significant (p less than 0.001) reductions in average bilirubin levels were noted for carbamazepine (CBZ), phenytoin (PHT), phenobarbital (PB), and multiple drug groups. A marginally significant (p less than 0.05) reduction in bilirubin levels occurred in patients treated with valproate (VPA) which, unlike the other drugs, has not been shown to induce hepatic enzymes.

Properties and determination of serum and bilirubin

The accurate determination of the types and amounts of bilirubin species in serum is important for diagnostic purposes as well as for therapeutic monitoring. However, of the determinations routinely performed in the clinical laboratory, those for bilirubins are not among the more accurate and exhibit significant method variability. In this review, the structural, stability, solubility, and albumin-binding properties of serum bilirubins are discussed with respect to their impact on analytical methods. Following a consideration of analytical standards, methods for the determination of unconjugated and conjugated bilirubins are reviewed and recent developments are evaluated. Finally, the present capabilities and future potential of the methods for producing information applicable to the development of new or improved methods of determination are summarized.

[Atypical bile acids (author's transl)]

The metabolism of bile acids in man is disturbed under the conditions of cholestasis. Besides of the main bile acids atypical bile acids can be found, which are mainly eliminated by renal excretion as sulphate esters and glucuronides. The pattern of urinary bile acids up to now renders no conclusions with respect to the underlying disease, although intrahepatic cholestasis seems to be in some way connected with disturbances in the metabolism of 3 beta-hydroxy-5-cholenoic acid, a bile acid, which exerts cholestatic effects by itself. The metabolites to be found seem to reflect a derepression of a genotypical synthesis program, which is not phenotypically apparent in healthy adults, but which may have been active during prenatal developmental stages of the liver.

The micellar sink: a quantitative assessment of the association of organic anions with mixed micelles and other macromolecular aggregates in rat bile

Although the importance of mixed micelles in the solubilization and biliary excretion of lipids is established, little is known about a possible role of mixed micelles in the excretion of other biliary solutes. Ultrafiltration and ultracentrifugation techniques were used to investigate the interaction between substances that are excreted in bile and biliary mixed micelles. Substances (urea, erythritol, sucrose) excreted in bile at concentrations equal to, or less than, that in plasma did not show an association with mixed micelles, whereas substances (indocyanine green, iopanoic acid, rose bengal, unconjugated and conjugated sulfobromophthalein, and conjugated bilirubin) excreted in bile at high concentration relative to plasma did. The percentage of these latter substances in bile associated with micelles varied from 26 to 93% and was relatively independent of concentration. In addition to their association with mixed micelles, these test solutes formed self-aggregates that were stabilized primarily by ionic bonds, and only a small percentage (range = 0-5%) of these solutes were present in bile in the form of monomer or complexes small enough to pass a 5,000-mol wt membrane.These findings offer a possible explanation for the increase in sulfobromophthalein, bilirubin, and indocyanine green maximal biliary excretory rate produced by bile salt infusion, and suggest that the concentrative transport into bile of endogenous compounds and xenobiotics may result from their incorporation into mixed micelles and other macromolecular complexes.

Electrophoretic patterns of serum albumins collected from different blood vessels

Rabbit sera collected from different blood vessels, e.g. vena renales, vena mesenterica, vena portae, vena hepatica and aorta, were electrophoresed in an urea-containing polyacrylamide gel. The albumin fraction was separated into 5-6 sub-bands. The profile of these sub-bands (electrophoretic pattern) of the sample from one blood vessel differed from that of another blood vessel. Especially, the electrophoretic pattern of serum collected from the renal vein 2h after deprivation of food differed from that of other blood vessels. Free fatty acid concentrations of each sample were also measured, and differences in these levels were observed in sera collected from different blood vessels. However, the fatty acid concentrations in serum from the renal vein were not low enough to permit detection of any abnormality in electrophoretic pattern in the albumin. This suggests the possibility of decreased concentration of lysolecithin in the renal vein which binds to albumin and changes the electrophoretic mobility of albumin, as do the free fatty acids.

Bile pigment formation by skin heme oxygenase: studies on the response of the enzyme to heme compounds and tissue injury

Skin heme oxygenase is locally elevated by stimuli such as tissue injury and injections of whole blood, myoglobin, and hematin. The enzyme activity is also increased at the proximity of the injection site of chemicals such as cobalt and cobalt-protoporphyrin-IX (cobalt-heme). Protoporphyrin-IX, the tetrapyrrole nucleus of type-b heme compounds, was ineffective in altering the enzyme activity in vivo. The developmental pattern of heme oxygenase in skin was compared to that of the enzyme in liver. The enzyme activity in both organs was greatest during the 1st postpartum wk and declined to adult levels after 2 wk. The physiological implications of the increased activity of skin heme oxygenase are discussed, and it is concluded that the activity of the hepatic heme oxygenase system and that of the skin are regulated by the same mechanism.

Jaundice in pregnancy--1976

An integrative survey is given of three disease processes, in which recent progress of a fundamental nature has been made, primarily affecting the liver, either coincident with or caused by the gravid state. The three conditions considered include (1) recurrent cholestasis of pregnancy (RCP), (2) viral hepatitis coincident with pregnancy, and (3) acute fatty liver of pregnancy (AFLP). In addition to an assessment of our present knowledge with respect to RCP and AFLP, new genetic hypotheses are proposed. In the latter, the proposal of an ornithine transcarbamylase deficiency, similar to that seen in Reye's syndrome, has potential therapeutic implications that are explored. In light of the currently available information on the interaction between maternal viral hepatitis and the variant forms of vertical maternal-fetal transmission, tentative recommendations regarding management of the newborn are suggested.

Sites of competition in the selective hepatic uptake of rifamycin-SV, flavaspidic acid, bilirubin, and bromsulphthalein

In rats both rifamycin-SV and flavaspidic acid impaired the disappearance of bromsulphthalein (BSP) from plasma. The addition of rifamycin-SV to rat liver supernatant containing BSP did not displace BSP from ligandin or Z protein unless it was added in very high concentration. In similar studies in vitro with flavaspidic acid, BSP was displaced from Z protein even at low concentrations of flavaspidic acid, whereas there was only a minor effect on the binding to ligandin. The intravenous administration of rifamycin to Gunn rats raised the plasma bilirubin concentration slightly after 30 minutes whereas flavaspidic acid was without significant effect. At 30 minutes the amount of bilirubin in the liver was markedly reduced by rifamycin and moderately depressed by flavaspidic acid. Although both the rifamycin and flavaspidic acid lowered the bilirubin in cell sap, the main effect of flavaspidic acid appeared to be on binding to Z protein. Rifamycin reduced the amount bound to both ligandin and Z protein. It is suggested that flavaspidic acid acted on the hepatic uptake of bilirubin and BSP predominantly by competing for binding to Z protein. Rifamycin-SV acted at a different site, probably blocking uptake at the plasma membrane.

Uptake and release of bilirubin by skin

1. Skin epithelium of albino rat, mouse and guinea pig was shown to accumulate bilirubin from a medium containing free or bound bilirubin. 2. The K(m) values for bound bilirubin were 2.22x10(-3), 1.33x10(-3) and 9.5x10(-4)m for rat, mouse and guinea pig respectively and the corresponding K(m) values for free bilirubin were 5.2x10(-4), 4.0x10(-4), 1.8x10(-4)m; the V(max.) values of bound and free bilirubin were unchanged. 3. The uptake showed saturation kinetics. Bound bilirubin was released together with serum proteins. Free bilirubin bound to skin was not released into the medium. 4. Freezing and thawing of skin epithelium did not cause any significant lowering of the uptake of bilirubin but heat-denatured skin epidermis took up only 50% of the bound bilirubin or free bilirubin taken up by control unheated skin epithelium. 5. The uptake of free and bound bilirubin was prevented by HgCl(2) but not by sodium arsenate, NaCN, NaF, cycloheximide, 2,4-dinitrophenol or iodoacetate. 6. Most of the free bilirubin was bound to the lipids or lipoprotein fraction of skin epithelium and could be extracted by solvents. 7. Rat skin showed the highest accumulation and efflux of bilirubin.

Bilirubin conjugates in bile of man and rat in the normal state and in liver disease

Conjugates of bilirubin were studied in normal bile of man and rat, and in bile of liver patients. In general human bile was obtained by duodenal intubation. In addition T-tube bile was examined in patients operated on for mechanical obstruction. The bile pigment compositions of duodenal and T-tube bile were similar in two patients where comparison was possible. Obstruction of the bile duct in rats was used as an animal model for obstructive jaundice. Diazotized ethyl anthranilate was used for determination of total conjugated bile pigment and for thin-layer chromatography (t.l.c.) analysis of the derived azopigments. The available t.l.c. procedures are versatile and allow rapid and quantitative analysis. A variety of conjugated azopigments can be distinguished. With chloroform, negligible amounts of unconjugated bilirubin are extracted from bile of man. Therefore, the percentage of monoconjugated bile pigments present in the initial bile sample can be calculated from the percentage of azodipyrrole found after diazotization. Normal bile from man and rat yields similar azopigment patterns. The dominant component is azopigment-delta (azodipyrrole beta-D-monoglucuronoside). Small amounts of azopigments with complex conjugating structures (gamma-azopigments) are present in both cases. Human bile further yields small amounts of azopigments containing xylose or glucose (called azopigments-alpha(2) and -alpha(3), respectively). Monoconjugated bilirubin (estimated from the percentage of azodipyrrole) amounts of 22% of total bile pigments in human bile and to 39% in murine bile. In both, the bulk of bile pigment is bilirubin diglucuronoside. From bile of patients with acquired liver diseases a new azopigment group (beta-azopigment) was derived. The gamma-azopigment group was increased; the delta-azopigment group (containing azodipyrrole beta-D-monoglucuronoside) was decreased. No differentiation was possible between intra- and extrahepatic cholestasis. The percentage of beta-azopigment showed a positive correlation with serum bilirubin concentration (r = 0.6). Recovery of the diseases was accompanied by normalization of the azopigment patterns. In rats, hydrostatic or mechanical obstruction induced increases in beta- and gamma-azopigments and a decrease in delta-azopigment similar to the changes observed in bile of liver patients. Complete normalization was obtained 6 hr after relieving the hydrostatic obstruction (duration 15-21 hr). In contrast, with man after surgery for extrahepatic obstruction, T-tube bile was not normalized when the T-tube was withdrawn (10 days after operation). Hydrostatic obstruction in rats provides an easy model when postobstructive bile pigment composition and parameters have to be investigated. The present investigations stress the importance of the physiopathological state when studying bilirubin conjugation. Hindrance to bile secretion induced heterogeneity of bilirubin conjugates and stimulated the formation of complex structures.