Blue light and bilirubin excretion

The measurement of bilirubin fractions in serum

Bilirubin fractions are measured by (1) the direct diazo reaction, (2) high-performance liquid chromatography (HPLC), (3) direct spectrophotometry, and (4) enzymatic methods. HPLC, which effects separation and quantitation of the four bilirubin fractions, is the method of choice, but impractical for routine use. A special application of direct spectrophotometry allows the measurement of unconjugated bilirubin and the sum of bilirubin conjugates. This approach, which provides essentially the same information as HPLC, unfortunately is available only in one clinical analyzer. The direct diazo reaction measures bilirubin conjugates plus delta-bilirubin, albeit not very accurately. Direct diazo methods that measure unconjugated bilirubin as direct could obscure the clinical diagnosis. At acid pH, enzymatic methods measure all direct reacting bilirubins, while at pH 10 only conjugated bilirubins are measured. Because the measurement of conjugated bilirubins is clearly more helpful than that of direct bilirubin in the differential diagnosis of jaundice, direct diazo methods should be replaced by methods specific for bilirubin conjugates.

Effect of phototherapy on serum 25-hydroxyvitamin D in the Antarctic

The hypothesis that sunlight may induce the enzymes involved in the vitamin D pathway has been tested by comparing the ability to synthesize vitamin D3 and its 25 hydroxy metabolite (25-OHD) in 2 groups of male volunteers resident at the British Antarctic base at Rothera Point (67 degrees 34'S.). One group endured the UV depleted winter and the other group received regular phototherapy throughout the winter. Both groups then received a course of 14 days phototherapy in October (Southern Hemisphere spring). The group receiving regular phototherapy had a trend towards a higher level of serum 25-OHD, and the October phototherapy course produced a further small increase in serum 25-OHD values. In the previously non irradiated group the October phototherapy produced a much larger increase in serum 25-OHD so that they attained the previously higher values of the pre-iradiated group. There was a negative correlation between the pre October phototherapy serum concentration of 25-OHD and the subsequent increment (r-0.78, p less than 0.01) but no relationship between the serum 25-OHD and D3 after phototherapy. These results provide evidence against the existence of enzyme induction of vitamin D 25 hydroxylase by light.

Quantum yields for laser photocyclization of bilirubin in the presence of human serum albumin. Dependence of quantum yield on excitation wavelength

The quantum yield for laser photocyclization of bilirubin to lumirubin in the presence of human serum albumin (phi LR) was measured at five monochromatic excitation wavelengths in the range 450-530 nm. Solutions used were optically thin throughout the wavelength range and precautions were taken to exclude contributions from photocyclization of bilirubin XIII alpha impurities. The values obtained (7.2-18 x 10(-4] were lower than those previously reported and showed the following wavelength dependence: 457.9 less than 488.0 less than 501.7 less than 514.5 approximately equal to 528.7. However, the rate of lumirubin formation, normalized to constant fluence, decreased with wavelength over the same wavelength range and no evidence was found that photoisomerization of bilirubin to lumirubin is faster with green (514.5 or 528.7 nm) than with blue (457.9 or 488.0 nm) light. The stereoselectivity of the configurational isomerization of bilirubin to 4Z,15E and 4E,15Z isomers also was studied. This reaction became less regioselective for the 4Z,15E isomer with increasing wavelength. The observed wavelength dependence of phi LR and of the [4E,15Z]: [4Z,15E] ratio at photoequilibrium are consistent with an exciton coupling model in which intramolecular energy transfer can occur between the two pyrromethenone chromophores of the bilirubin molecule in the excited state. Relative rates of lumirubin formation in vivo at different excitation wavelengths and constant fluence were estimated for different optical thicknesses and for different skin thicknesses. These estimates suggest that the recently reported clinical equivalence of blue and green phototherapy lights probably reflects the marked variation of skin transmittance with wavelength more than wavelength-dependent photochemistry. The calculations also indicated that the optimal wavelength for phototherapy is probably on the long wavelength side of the bilirubin absorption maximum.

Critical period of bilirubin-induced cerebellar hypoplasia in a new Sprague-Dawley strain of jaundiced Gunn rats

Homozygous (j/j) and heterozygous (j/+) newborn Gunn rats of the Sprague-Dawley strain were photoirradiated for 24 h at scheduled postnatal days and the effects of irradiation on the cerebellar development were examined at 30 days of life. Improvement of the survival rate was the most notable effect of photoirradiation. A single 24-h dose of photoirradiation during a period of postnatal days 4-11 effectively prevented hypoplasia in the j/j rat cerebellum. No prevention by light was observed at days 3 and 12. It was found that the most effective day of irradiation on the cerebellar development of j/j rats was centered on postnatal day 7. When plasma bilirubin was assessed during the period of postnatal days 7-10, a distinct diminution of the concentration was observed, restricted to only the period of the light treatment. Although there were some differences in the effective day as well as in the degree of efficacy of phototherapy among cerebellar lobules or sublobules, day 7 was the most critical for cerebellar hypoplasia due to bilirubin.

Multiple plasma exchanges successfully maintain a young adult patient with Crigler-Najjar syndrome type I

Plasmapheresis has been shown to reduce total and free bilirubin levels in acute exacerbations of Crigler-Najjar syndrome, type I (CNS-TI), but its effectiveness in long-term management has not been reported. An 18-year-old (yo) male with CNS-TI, who required prolonged daily high-intensity phototherapy to prevent cerebral nervous system symptoms, developed increasingly frequent bouts of confusion, nausea, and vomiting associated with free bilirubin concentrations (fbcs) greater than 10-15 nmol/L. Pending consideration of orthotopic liver transplantation, plasma exchange (approximately 3 liters per procedure) was begun in 12/84 using the IBM/COBE 2997 with 5% albumin as replacement fluid. Frequency of treatments was guided by twice weekly fbcs, with plasma exchange for fbc greater than 10-15 nmol/L. Pre-exchange and postexchange fbcs ranged from 27.5 to 11 nmol/L and 9.2 to 2 nmol/L, respectively. Seventy-two exchanges were performed over a 28 month period. Irreversible CNS damage did not occur, and the patient underwent successful liver transplantation in April of 1987, with complete correction of his metabolic disorder. He remains well 18 months following transplantation.

Thyroid hormones and the hepatic handling of bilirubin. II. Effects of hypothyroidism and hyperthyroidism on the apparent maximal biliary secretion of bilirubin in the Wistar rat

This study was undertaken in the Wistar R/A Pfd rat to investigate the effects of hypothyroidism and of hyperthyroidism on the maximal biliary excretion (Tm) of bilirubin and on the concentration and composition of bilirubin in liver and plasma at the end of a bilirubin load. Hypothyroidism caused a cholestatic condition with a 50% decrease in bile flow and in bilirubin Tm, and with an increased proportion of conjugated bilirubin in liver and plasma. This was associated with an increased ratio of bilirubin diconjugates to monoconjugates in bile, liver, and plasma, which can be ascribed to the increased hepatic conjugation activity towards bilirubin and/or to the prolonged retention of bile pigments in the hepatocytes with increased conversion of monoconjugates to diconjugates. Cholestasis induced by hypothyroidism was further characterized by a decreased biliary output of unconjugated bilirubin. The latter phenomenon might represent an indirect effect related to a decreased output of bilirubin monoconjugates with impaired hydrolysis to unconjugated bilirubin; it might also reflect the cholestatic condition with decreased excretion of the unesterified bile pigment as such. Hyperthyroidism resulted in a 1.3-1.4-fold increase in bile flow. The maximal bilirubin concentration in bile decreased 1.3-1.4-fold, so that the apparent maximal bilirubin excretion rate remained unchanged at 115 nmol.min-1.100 g-1, as observed in untreated rats. Hyperthyroidism lowered the bilirubin UDP-glucuronosyltransferase activity, produced a decreased ratio of bilirubin di- to monoconjugates in bile and plasma, and a decreased ratio of conjugated to total bile pigment concentration in liver and in plasma. Similar findings are present in the heterozygous Gunn rat strain and in patients with hepatic bilirubin UDP-glucuronosyltransferase deficiency. We therefore propose the hyperthyroid rat as an experimental animal model of Gilbert's syndrome.

Hepatobiliary excretion of organic anions in double-mutant rats with a combination of defective canalicular transport and uridine 5'-diphosphate-glucuronyltransferase deficiency

Mutant rats with a selective defect for the hepatobiliary excretion of organic anions (GT+TR- rats) are valuable models to study hepatic transport processes. However, retained conjugates in the livers of these rats may secondarily affect hepatic uptake, metabolism, and excretion of other compounds and this may confound the interpretation of test results. We have developed double mutants (GT-TR-) rats with both a conjugation and an excretion defect by cross-breeding uridine 5'-diphosphate-glucuronyl-transferase-deficient GT-TR+ Gunn rats with transport-deficient GT+TR- rats. Phenotypically, GT-TR- rats and Gunn rats are alike in that both have unconjugated hyperbilirubinemia. Intravenous administration of tetrabromosulphthalein, bilirubin diglucuronide, and bilirubin monoglucuronide revealed a significant difference in that the clearance of these compounds was reduced to 10%, 10%, and 20%, respectively, in GT-TR- rats when compared with Gunn rats. The hepatic elimination of tetrabromosulphthalein in GT-TR- rats and in GT+TR- rats is impaired to the same extent. Thus, both have a similar hepatic excretion defect. However, bile flow and bile acid excretion in GT+TR- rats are more depressed than in GT-TR- rats: bile flow, 88 +/- 3 vs. 36 +/- 1 microliters/min.kg and bile acid excretion, 3.4 +/- 0.2 vs. 1.5 +/- 0.1 mumol/min.kg in GT-TR- and GT+TR- rats, respectively. This suggests that accumulated glucuronides in the liver inhibit bile flow and bile acid excretion. To test whether conjugated bilirubin and the photoisomers of unconjugated bilirubin are excreted via the same transport pathways, the effect of phototherapy was studied in GT-TR- rats and in Gunn rats. Photoexposure caused a 120% increase in biliary excretion of bilirubin isomers in Gunn rats and only 40% in GT-TR- rats. This shows that the biliary excretion of bilirubin photoisomers is indeed affected by the hepatic excretion defect of GT-TR- rats and suggests that hepatic excretion of bilirubin photoisomers proceeds via the same route as other organic anions such as conjugated bilirubin and tetrabromosulphthalein.

Renal handling of bilirubin photoderivatives

The renal handling of unconjugated bilirubin in the dark and during light exposure was analyzed using an isolated rat kidney preparation. The parameters tested were pigment disappearance from the perfusion medium, pigment uptake by tissue, and its renal clearance. The results indicated that despite the fact that pigment disappearance from the medium was similar for both forms of pigment, the extraction ratio was higher for irradiated pigment than for pigment in the dark. When renal clearance of pigment was plotted vs pigment uptake of tissue, the results indicated that irradiated pigment may be more efficiently removed by the kidney. In addition, data on the rate of secretion of p-aminohippurate suggested that both pigment forms shared a common site for secretion.

Plastic blankets and heat shields decrease transmission of phototherapy light

An in vitro study showed that the use of transparent plastic insulation to decrease heat loss from newborn infants substantially decreases the transmission of phototherapy light. The decrease is proportional to the number of plastic layers between the light source and the baby because of reflection from the surface of the plastic. This increases if the surface is irregular. Thickness and the type of plastic used had no effect.

Isomers of bilirubin glucuronide in serum and bile before and after relief of common duct obstruction

Isomers of bilirubin glucuronide with the bilirubin acyl group attached to the C1-, C2-, C3- and C4-positions of the glucuronyl residue are present in bile of patients with extrahepatic cholestasis, whereas in normal bile only C1-isomers are found. In the present study, these bilirubin glucuronide isomers, and the fractions of unconjugated bilirubin, and bilirubin mono- and diconjugates were determined in serum and bile of 8 patients before and after relief of common duct obstruction by endoscopic papillotomy. Before papillotomy we found 39.6% C1-isomers (median value), 22.2% C2-isomers, 19.3% C3-isomers and 11.4% C4-isomers in the bile. The values in serum before papillotomy were comparable. Twenty-four hours after papillotomy, the level of C1-isomers in bile increased significantly to 56.3% (P less than 0.05) with a concomitant decrease of the non-C1-isomers. In contrast, in serum the isomers of bilirubin glucuronide did not change significantly at 24 h after papillotomy. Before papillotomy, the fraction of unconjugated bilirubin in bile was 3.6% of the total, with 15.8% bilirubin monoconjugates and 75.5% bilirubin disconjugates. After papillotomy, unconjugated bilirubin decreased to 1.6% (n.s.) and bilirubin monoconjugates to 11.9% (n.s.), while bilirubin diconjugates increased to 86.1% (P less than 0.05). In serum, the elevated fractions of bilirubin diconjugates and monoconjugates decreased from 38.4 to 32.2% (P less than 0.05) and from 29.6 to 23.4% (n.s.), respectively. In parallel, the fraction of unconjugated bilirubin in serum increased from 24.1 to 37.0% (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Perioperative care of the surgical neonate

This article provides an overview of perinatal physiology and common pathophysiologic events that are likely to complicate the clinical course of neonates requiring surgical procedures. The special needs and problems of the premature newborn are emphasized. References are provided for a more detailed analysis of the normal and abnormal transition from fetus to newborn.

Comparison of kinetic study of the photochemical changes of (ZZ)-bilirubin IX alpha bound to human serum albumin with that bound to rat serum albumin

It has been stated by McDonagh, Palma & Lightner [(1982) J. Am. Chem. Soc. 104, 6867-6871] that complexing of bilirubin with serum albumin has a marked species-dependent influence on bilirubin photoisomerization in vitro and in vivo. Therefore the kinetics for the quantitatively important reaction: (Formula: see text) of the photochemical interconversion between bilirubin and its photoisomers bound to human or rat serum albumin in aqueous solution, assayed by h.p.l.c., was used to elucidate the observed species-dependent difference. The relative rate constants for bilirubin bound to human serum albumin, except for k4, the rate of interconversion from (ZZ)-bilirubin into (EZ)-bilirubin, proved to be considerably larger than those for bilirubin bound to rat serum albumin. In accordance with these rate constants, the formation of photoisomers of bilirubin bound to human serum albumin, except for (EZ)-bilirubin, is very rapid and much greater than that for bilirubin bound to rat serum albumin.

Effect of spectral distribution on isomerization of bilirubin in vivo

The purpose of our study was to compare the effects of narrow-spectrum blue light and broad-spectrum white light on the production of bilirubin photo-isomers in human infants with jaundice. Twelve preterm infants were studied under both white and blue light. Irradiance at 450 nm was controlled at 12 microW/cm2/nm for both light sources. Each light condition (white or blue) was administered for 12 hours. Bilirubin isomers (4Z,15E-bilirubin and lumirubin) were measured before therapy and after 12 hours of each sequential light condition. The percentage of 4Z,15E-bilirubin was greater under blue light than under white light (P less than 0.01) phototherapy. There was no significant difference in percentage lumirubin under white or blue light therapy. Our data indicate that blue light is more effective than white light in producing 4Z,15E-bilirubin in vivo. Our study demonstrates that when irradiance in the bilirubin absorbance spectrum is constant, the color of light (spectral distribution) will determine the relative concentrations of photo-isomers produced.

Efficacy and safety of the "integral" phototherapy for neonatal hyperbilirubinemia. Results of a follow-up at 6 years of age

One hundred and ten full-term newborns were treated with integral phototherapy (IP) in the first week of life for hyperbilirubinemia (peak bilirubin concentration, 19.5 +/- 2.8 mg/dl). IP was provided by an apparatus which irradiated the infants over the entire skin surface with four visible blue light lamps placed around the body at a mean distance of only 20 cm. The irradiance of the lamps at the skin surface was 0.350 mW/sq cm, in the wavelength range between 425 and 475 nm. The IP resulted in a 48-hour bilirubin decline rate of 0.163 mg/dl/h. After a mean exposure of 78 +/- 32 h, the mean plasma bilirubin level was 8.4 +/- 0.8 mg/dl. One hundred and ten comparable nonjaundiced infants were studied as controls. At 6 years of age, both groups of subjects were called for a follow-up concerning growth, visual, and hearing functions, and neuro-developmental status. The follow-up was completed in 81 children of the IP group (73.6%) and in 89 of the controls (80.6%). There were no significant differences in the studied parameters between the two groups. The study concludes that IP appears to be an effective and safe treatment for jaundiced infants. IP employs less radiant energy from the lamp source than the traditional apparatus, but delivers this energy to a larger skin surface area.

Bilirubin chemistry, ionization and solubilization by bile salts

Bilirubin is a linear tetrapyrrole whose conformation is affected by internal hydrogen bonds formed between the carboxyl side chains and dipyrromethenone rings. Structural variations include: constitutional isomerism of the vinyl or carboxyethyl side chains, geometric isomerism of the methene bridges, tautomerism of the lactam groups, conformational rotations about the central methylene bridge and ionization of one or both carboxyl groups. Aggregation of the dianion into dimers and multimers may occur. The pKa' values of the two carboxyl groups are affected greatly by the environment and may differ widely in micellar solutions like bile. Solubility of bilirubin in water is less than 1 nM at pH = 7 and about 0.1 microM at pH = 8. Nonetheless, it dissolves poorly in most lipid solvents, except for asymmetrical chloroalkanes. Hydrogen bond-breaking solvents, especially dimethyl sulfoxide, are most effective in solubilizing bilirubin. In bile salt solutions, solubility of bilirubin is well above the concentrations of unconjugated bilirubin found in normal human gallbladder bile, and is impaired by lecithin but unaffected by cholesterol. At physiological pH in bile salt solutions, bilirubin is predominantly in its monoanion form that binds readily to the micelles. In such solutions, addition of physiological concentrations of calcium precipitates calcium bilirubinate, leaving residual bilirubin concentrations of up to 15 microM in 50 mM taurocholate or close to the maximum bilirubin concentrations in normal bile. Studies in which disodium bilirubinate is dissolved in bile salt solutions and pH is adjusted to the physiological range reveal that metastable supersaturation with bilirubin may occur and that a mesophase may also form in the presence of lecithin, akin to that seen with cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Bilirubin analysis--the state of the art and future prospects

Progress in separating and identifying different bile pigments in serum has led to the recognition of a bilirubin fraction (delta) distinct from unconjugated bilirubin and its (mono- and di-) sugar conjugates. Delta bilirubin reacts directly diazo-positive and is strongly linked to an albumin-like protein, presumably via an amide bond between a propionic acid side-chain of the tetrapyrrole and a functional group (e.g., epsilon-amino group of lysine) on the protein backbone. Because of its unusual properties and its wide occurrence in icteric sera, the delta fraction may have important analytical and clinical implications. We examine here some of these implications and discuss the prospects for a better understanding of the molecular basis of jaundice.

Evaluation of the Kodak EKTACHEM clinical chemistry slide for the measurement of bilirubin in newborns

Measurement of neonatal bilirubin using the Jendrassik-Grof method (x) and the EKTACHEM NBIL assay (y) was compared over a 6-month period in a total of 1191 specimens from 483 patients less than 30 days of age. Linear regression analysis of the data yields a slope of 0.937, an intercept of 0.387, and Sy,x of 0.55 and a correlation coefficient of 0.983 for a total of 1032 specimens from patients less than or equal to 14 days of age and a slope of 1.090, an intercept of 0.002, an Sy,x of 1.03 and a correlation coefficient of 0.950 for a total of 159 specimens from patients greater than 14 days of age. The best correlation between EKTACHEM NBIL assay and the reference Jendrassik-Grof method was observed in samples from patients less than or equal to 14 days of age. Data from patients older than 14 days showed a higher proportional bias and a lower correlation coefficient between the methods. High performance liquid chromatographic analysis demonstrated that patients greater than 14 days of age had a higher incidence of elevated delta-bilirubin. Linearity extends to 200 mg/l. The NBIL assay provides a rapid, precise micromethod that is less sensitive than the Jendrassik-Grof method to the in vitro photo degradation of bilirubin and is not subject to the interference from hemoglobin and lipids. Because delta-bilirubin is not measured by this method, it is only recommended for newborns less than or equal to 14 days of age.

Structure and thermal interconversion of cyclobilirubin IX alpha

One of the two main photoproducts in bilirubin metabolism during phototherapy in neonatal hyperbilirubinaemia is (EZ)-cyclobilirubin. However, it has not yet been possible to come to a final conclusion as to its chemical structure, despite the fact that much effort has been expended on the problem. The present paper demonstrates that (EZ)-cyclobilirubin is formed by the intramolecular cyclization of the C-3-vinyl group with the position at C-7 rather than at C-6, without delta-lactone-ring formation. The evidence comes from 13C-n.m.r. spectra, which indicate that an oxygen-bound quaternary carbon atom is not present, and from 1H-n.m.r. spectra, which indicate that the orientation of the methyl group at C-2 is equatorial; these findings are supported by mass spectra. The existence of both an epimeric relationship at C-7 between (EE)- and (EZ)-cyclobilirubins A and B and of steric isomers of the hydrogen atom and methyl group at C-2 is supported by the fact that the methyl-group protons at C-2 and C-7 are observed as a paired signal in 1H-n.m.r. spectra, and that new signals at C-7, C-2 and C-3 beta appear in 13C-n.m.r. spectra, that mass spectra of (EZ)-cyclobilirubins A and B are extremely similar and that, furthermore, thermal interconversion between (EE)- and (EZ)-cyclobilirubins A and B is observed.

Irreversible binding of conjugated bilirubin to albumin in cholestatic rats

A diazo-positive fraction of serum bilirubin that is irreversibly bound to albumin has been shown to accumulate in serum of patients with cholestasis. In the present study, a cholestatic animal model was used to determine the chemical nature of the bilirubin species involved in its formation. The data indicate that conjugated bilirubin is the precursor of "albumin-bound bilirubin" and that the presence or absence of light does not affect its formation. An albumin-bound bilirubin-complex indistinguishable from the complex detected in cholestatic sera from patients or in bile duct-ligated Sprague-Dawley rats can be formed in vitro in sera enriched in conjugated bilirubin at 37 degrees C, pH 7.4.

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.

Albumin binding of photobilirubin II

Photobilirubin II, a stereoisomer of bilirubin, binds to human serum albumin at a single binding site (K = 2.2 x 10(6)M-1), presumably the high-affinity bilirubin-binding site. Binding in the secondary (class II) binding sites is of minor importance. The results are discussed with respect to photometabolism of bilirubin and as a possible source of error in the determination of bilirubin unbound to albumin.

Binding of photobilirubin to human serum albumin. Estimate of the affinity constant

Results of experiments based upon circular dichroic spectra suggest that configurationally (Z leads to E) isomerized bilirubin (photobilirubin) binds to human serum albumin at the primary bilirubin binding site with an affinity only 2-3 times lower than that of bilirubin. The high affinity of photobilirubin for albumin, comparable to that of bilirubin, supports the roles of albumin in the stabilization and transport of the isomerized pigment in vivo and strongly suggests that albumin also functions to sequester photobilirubin effectively, reducing its toxic potential. The high affinity of photobilirubin for albumin predicts that the isomerized pigment, formed in large amounts during phototherapy for neonatal hyperbilirubinemia, should not appear in the fast-diazo-reacting ('direct') bilirubin pool nor should it interfere with nonspectroscopic bilirubin binding tests. These predictions were confirmed for the Evelyn and Malloy diazo assay for 'direct' bilirubin and a Sephadex chromatography method for assessing 'loosely bound' plasma bilirubin.

Analysis of bilirubins in biological fluids by extraction and thin-layer chromatography of the intact tetrapyrroles: application to bile of patients with Gilbert's syndrome, hemolysis, or cholelithiasis

A method was developed to extract quantitatively the bilirubins from bile, urine, serum, stool, and preparations from liver with a chloroform-ethanol mixture at pH 1.8 in the presence of ascorbic acid and NaCl. Extracted pigment was submitted to thin-layer chromatography, and the separated bilirubins were either immediately eluted and determined spectrophotometrically or individually converted to ethyl anthranilate azo derivatives for thin-layer chromatographic analysis of each isolated pigment band. Bilirubins in duodenal bile of eight healthy adults comprised 1.5 +/- 1.3% unconjugated bilirubin-IX alpha, 69 +/- 6% bilirubin diglucuronide, and 16 +/- 4% bilirubin monoglucuronides. Mixed diconjugates containing one glucuronosyl moiety and either one xylosyl or one glucosyl group amounted to 10 +/- 3%. Most samples (6 of 8) contained trace amounts (0.6 +/- 0.6%) of unconjugated bilirubin-IX beta, in agreement with nearly exclusive cleavage of heme at the alpha-meso position. The composition of the bilirubins in bile was normal in 6 patients with cholesterol gallstones, 4 with chronic hepatitis, and 3 with hemolysis. In duodenal bile of individuals with Gilbert's syndrome (n = 10), the concentration of bilirubin conjugates was comparable to that in healthy adults, but the proportion of bilirubin diglucuronides (52 +/- 8%) was decreased. The concentration of unconjugated bilirubin-IX alpha showed a fair positive correlation with that of bilirubin monoglucuronide and was increased in half of the patients with Gilbert's syndrome.

Chemoprevention of neonatal jaundice: potency of tin-protoporphyrin in an animal model

The substantial increases of hepatic, splenic, and renal heme oxygenase levels that occur shortly after birth in neonatal rats were prevented by a single administration of tin-protoporphyrin (10 micromoles per kilogram of body weight). With this treatment serum bilirubin levels declined within 24 hours to near-normal adult levels and remained low throughout the postnatal period. Zinc-protoporphyrin at doses up to 50-fold greater than the effective dose of tin-protoporphyrin did not prevent the immediate increases in tissue heme oxygenase activities and in serum bilirubin levels that occur postnatally. Studies in vitro with microsomal heme oxygenase in human spleen indicate that tin-protoporphyrin is a potent competitive inhibitor of the oxidation of heme to bile pigment in this tissue.

Crigler-Najjar Type 1 syndrome: absence of hepatic bilirubin UDP-glucuronyl transferase activity and therapeutic responses to light

A 16-year-old boy with severe congenital unconjugated hyperbilirubinaemia is described in whom mental retardation occurred as an isolated neurological deficit. The diagnosis of Crigler-Najjar type 1 syndrome was supported by an extreme and persistent elevation of serum unconjugated bilirubin (650 mumol/l), failure of administered phenobarbitone to lower serum bilirubin concentration and family history of a similarly affected sibling. Hepatic bilirubin UDP-glucuronyl transferase activity determined in vitro by a sensitive new enzyme assay was found to be absent using bilirubin or bilirubin monoglucuronide as substrate. Phototherapy for 12 hours each night produced a partial but highly significant reduction in serum bilirubin concentration, which was not influenced further by the administration of cholestyramine.

Absence of bilirubin binding competitors during phototherapy for neonatal jaundice

Bilirubin-albumin binding was quantitated (peroxidase method) before, during, and after phototherapy in 21 jaundiced infants. Binding was analyzed at two different serum dilutions (1:1.8 and 1:57) to determine whether binding competitors are present during phototherapy. No significant changes in binding were found at either dilution during phototherapy, regardless of birthweight, gestational age, or illness. Serum binding of bilirubin does not appear to be altered during phototherapy.

Concerning the structure of photobilirubin II

Evidence is presented which supports the postulate that the photobilirubins IIA and IIB are diastereoisomers in which the C-3 vinyl group has cyclized intramolecularly. The evidence comes principally from proton n.m.r. spectroscopy at 400 MHz and from chemical considerations. The cyclic structures require the E-configuration at the C-4 double bond in the precursor; this is the first structural evidence for the Z leads to E isomerization in bilirubin and supports the view that the precursor (photobilirubin IA or IB) is (4E, 15Z)-bilirubin. Brief irradiation of photobilirubin II gives bilirubin, a new compound (photobilirubin III) and unchanged starting material. The various photoisomers are discussed in terms of their inter-relationships and biological fates.

Phototherapy-induced hypocalcemia in newborn rats: prevention by melatonin

When young rats are exposed to white fluorescent light the concentration of calcium in their serum decreases. This effect is prevented by shielding the occiput, by inhibiting corticosterone synthesis, and by exogenous melatonin. Furthermore, the expected hypocalcemic response to cortisol injection is prevented by melatonin. Light-induced hypocalcemia may result from increased calcium uptake by bone when the blocking effect of melatonin decreases after pineal inhibition by transcranial illumination.

Prevention of neonatal hyperbilirubinemia by tin protoporphyrin IX, a potent competitive inhibitor of heme oxidation

The effects of various metalloporphyrins on hepatic heme oxygenase (EC 1.14.99.3) activity were examined in order to identify compounds that could inhibit heme degradation to bile pigment and might therefore be utilized to suppress the development of hyperbilirubinemia in the newborn. Among nine metal-protoporphyrin IX chelates (i.e., metal-hemes) studied, Sn-heme, Mn-heme, and Zn-heme substantially diminished heme oxygenase activity in vivo in the rat. These metalloporphyrins act as competitive inhibitory substrates in the heme oxygenase reaction but are not themselves oxidatively degraded. Sn-heme was the most potent enzyme inhibitor (Ki = 0.011 microM) in liver, spleen, kidney, and skin. Sn-heme administered to newborn animals within the first 72 hr after birth blocked the postnatal increase in heme oxygenase activity that occurs in various tissues. Its effect on the enzyme levels was prompt and protracted. Sn-heme administration also entirely prevented the development of hyperbilirubinemia that normally occurs postnatally. The effect of the metalloporphyrin in lowering the increased concentrations of serum bilirubin in neonates was prompt (within 1 day) and persisted throughout the 42 days after birth. No deleterious effects of Sn-heme treatment of the newborn were observed. This demonstrates that a synthetic metalloporphyrin that is a potent competitive inhibitor of heme oxidation can, when administered to the newborn, also prevent the hyperbilirubinemia that normally develops postnatally. The potential clinical implications of these findings are evident, and it is suggested that the pharmacological properties of Sn-heme and related synthetic metalloporphyrins merit further study.

Kinetics of biliary excretion of the main two bilirubin photoproducts after injection into Gunn rats

The kinetics of biliary excretion of the main two photoproducts after injection into Gunn rats were examined. The photoproducts that are obtained from experiments in vitro consist of unknown pigment, photobilirubin IXa and a small amount of (ZZ)-bilirubin IXa. It was confirmed previously that the first two photoproducts are identical with the main two photoproducts obtained in vivo. In experiments on four animals, the average of total biliary recoveries of unknown pigment was 81.4%, and that of photobilirubin IXa in the bile estimated by the Sigma-minus method was 29.8 min and that for unknown pigment was 4.3 min. The rate of thermal reversion of photobilirubin IXa to (ZZ)-bilirubin IXa in the bile at 37 degrees C was very rapid, i.e. its half-life was 6.2 min.

Excretion of administered and endogenous photobilirubins in the bile of the jaundice gunn rat

Radiolabeled photobilirubins, prepared in vitro by anaerobic illumination of [34C]bilirubin, were injected intravenously into homozygous jaundiced Gunn rats with an external bile fistula. With the animals kept in darkness, the labeled photobilirubins were excreted rapidly in bile. Photobilirubins IA and IB were excreted primarily as unconjugated bilirubin, whereas photobilirubin II was excreted primarily as photobilirubin II and not converted into bilirubin. Bile of Gunn rats given no exogenous pigments, but undergoing phototherapy, contained a large proportion of photobilirubin II and, if collected in liquid nitrogen, traces of photobilirubins I; neither was found in bile when these rats were kept in the dark. Because there is prior evidence that these rats were kept in the dark. Because there is prior evidence that these photobilirubins are isomers of bilirubin, these experiments indicate that the major mechanism of phototherapy is photoisomerization of bilirubin. Photobilirubin II is the unidentified major photoderivative described previously, whereas formation of photobilirubins IA and IB, and their reversion to bilirubin-IXalpha, account for the remarkably increased output of the parent pigment during phototherapy.