Intestinal colonization leading to fecal urobilinoid excretion may play a role in the pathogenesis of neonatal jaundice

Probiotics' effects on gut microbiota in jaundiced neonates: a randomized controlled trial protocol

Introduction

Recent evidence suggests that blue-light phototherapy impacts gut microbiota composition in jaundiced newborns, leading to disturbances closely related to the therapy's side effects. As a result, gut microbiota may serve as a potential intervention target to mitigate these side effects. In this study, we aim to examine the effects of AB-GG (Lactobacillus rhamnosus LGG), Bb-12 (Bifidobacterium animalis Bb-12) and M-16V (Bifidobacterium breve M-16V) and their combination on the intestinal microbiota, metabolomics and phototherapy-related side effects in neonates with jaundice.

Methods and analysis

A total of 100 jaundiced newborns aged two weeks or younger will be included in this randomized, single-blind (the parents knew, but the neonatologists did not know), single-center controlled trial to receive either 109 colony-forming units of AB-GG, Bb-12, M-16V, a combination of the three probiotics with blue-light phototherapy, or blue-light phototherapy alone. The experimental group will be treated with oral probiotics once daily for 30 days, while the control group will receive only blue-light phototherapy. The follow-up duration will last 30 days. The primary outcomes include changes in gut microbiota, metabolomics, and the incidence of phototherapy side effects, assessed after each phototherapy session, as well as on days 10, 20, and 30.

Ethics and dissemination

The study protocol has been approved by the Ethics Committee of our institution. The findings of this trial will be submitted to a peer-reviewed pediatric journal. Its abstracts will be submitted to relevant national and international conferences.

Clinical Trial Registration

http://www.chictr.org.cn/index.aspx, identifer (ChiCTR2000036013).

BilR is a gut microbial enzyme that reduces bilirubin to urobilinogen

Metabolism of haem by-products such as bilirubin by humans and their gut microbiota is essential to human health, as excess serum bilirubin can cause jaundice and even neurological damage. The bacterial enzymes that reduce bilirubin to urobilinogen, a key step in this pathway, have remained unidentified. Here we used biochemical analyses and comparative genomics to identify BilR as a gut-microbiota-derived bilirubin reductase that reduces bilirubin to urobilinogen. We delineated the BilR sequences from similar reductases through the identification of key residues critical for bilirubin reduction and found that BilR is predominantly encoded by Firmicutes species. Analysis of human gut metagenomes revealed that BilR is nearly ubiquitous in healthy adults, but prevalence is decreased in neonates and individuals with inflammatory bowel disease. This discovery sheds light on the role of the gut microbiome in bilirubin metabolism and highlights the significance of the gut-liver axis in maintaining bilirubin homeostasis.

Discovery of the gut microbial enzyme responsible for bilirubin reduction to urobilinogen

The degradation of heme and the interplay of its catabolic derivative, bilirubin, between humans and their gut microbiota is an essential facet of human health. However, the hypothesized bacterial enzyme that reduces bilirubin to urobilinogen, a key step that produces the excretable waste products of this pathway, has remained unidentified. In this study, we used a combination of biochemical analyses and comparative genomics to identify a novel enzyme, BilR, that can reduce bilirubin to urobilinogen. We delineated the BilR sequences from other members of the Old Yellow Enzyme family through the identification of key residues in the active site that are critical for bilirubin reduction and found that BilR is predominantly encoded by Firmicutes in the gut microbiome. Our analysis of human gut metagenomes showed that BilR is a common feature of a healthy adult human microbiome but has a decreased prevalence in neonates and IBD patients. This discovery sheds new light on the role of the gut microbiome in bilirubin metabolism and highlights the significance of the gut-liver axis in maintaining bilirubin homeostasis.

Potential of therapeutic bile acids in the treatment of neonatal Hyperbilirubinemia

Neonatal hyperbilirubinemia or jaundice is associated with kernicterus, resulting in permanent neurological damage or even death. Conventional phototherapy does not prevent hyperbilirubinemia or eliminate the need for exchange transfusion. Here we investigated the potential of therapeutic bile acids ursodeoxycholic acid (UDCA) and obeticholic acid (OCA, 6-α-ethyl-CDCA), a farnesoid-X-receptor (FXR) agonist, as preventive treatment options for neonatal hyperbilirubinemia using the hUGT1*1 humanized mice and Ugt1a-deficient Gunn rats. Treatment of hUGT1*1 mice with UDCA or OCA at postnatal days 10-14 effectively decreased bilirubin in plasma (by 82% and 62%) and brain (by 72% and 69%), respectively. Mechanistically, our findings indicate that these effects are mediated through induction of protein levels of hUGT1A1 in the intestine, but not in liver. We further demonstrate that in Ugt1a-deficient Gunn rats, UDCA but not OCA significantly decreases plasma bilirubin, indicating that at least some of the hypobilirubinemic effects of UDCA are independent of UGT1A1. Finally, using the synthetic, non-bile acid, FXR-agonist GW4064, we show that some of these effects are mediated through direct or indirect activation of FXR. Together, our study shows that therapeutic bile acids UDCA and OCA effectively reduce both plasma and brain bilirubin, highlighting their potential in the treatment of neonatal hyperbilirubinemia.

Molecular Physiology and Pathophysiology of Bilirubin Handling by the Blood, Liver, Intestine, and Brain in the Newborn

Bilirubin is the end product of heme catabolism formed during a process that involves oxidation-reduction reactions and conserves iron body stores. Unconjugated hyperbilirubinemia is common in newborn infants, but rare later in life. The basic physiology of bilirubin metabolism, such as production, transport, and excretion, has been well described. However, in the neonate, numerous variables related to nutrition, ethnicity, and genetic variants at several metabolic steps may be superimposed on the normal physiological hyperbilirubinemia that occurs in the first week of life and results in bilirubin levels that may be toxic to the brain. Bilirubin exists in several isomeric forms that differ in their polarities and is considered a physiologically important antioxidant. Here we review the chemistry of the bilirubin molecule and its metabolism in the body with a particular focus on the processes that impact the newborn infant, and how differences relative to older children and adults contribute to the risk of developing both acute and long-term neurological sequelae in the newborn infant. The final section deals with the interplay between the brain and bilirubin and its entry, clearance, and accumulation. We conclude with a discussion of the current state of knowledge regarding the mechanism(s) of bilirubin neurotoxicity.

Earlier Nutrient Fortification of Breastmilk Fed LBW Infants Improves Jaundice Related Outcomes

This study aimed to evaluate jaundice outcomes of low-birthweight premature infants commenced on earlier versus later nutrient supplementation (80 mL/kg/day vs. 160 mL/kg/day; total fluid intake, F80 vs. F160). Demographics, feeding regimens, and clinical outcomes data were collected. Infant and maternal characteristics were similar. Earlier nutrient supplementation was associated with multiple improved jaundice outcomes: total (TSBR), unconjugated and conjugated (CSBR) serum bilirubin values (196 ± 46 vs. 228 ± 52, 184 ± 44 vs. 212 ± 50, 12 ± 4 vs. 16 ± 5, respectively, all p < 0.001); phototherapy (39% vs. 64%, p < 0.0001). % CSBR/TSBR ratio was similar between groups. For those on phototherapy, duration and median irradiance were similar. F80 infants experienced reduced: feeding intolerance (26.0% vs. 45.2%, p = 0.007); length of stay (16.0 ± 0.64 vs. 18.8 ± 0.74 days, p = 0.03), maximum weight loss as % birth weight (5% vs. 6%, p = 0.03); decrease in weight Z-score at 10 days (-0.70 ± 0.03 vs. -0.79 ± 0.03, p = 0.01). F80 infants regained birthweight earlier (10.0 ± 0.3 days vs. 11.5 ± 0.3 days, p < 0.0001) and had no differences in adverse clinical outcomes. We speculate that earlier nutrient supplementation improved jaundice outcomes due to enhanced excretion/elimination of bilirubin.

Variation in the gut microbial community is associated with the progression of liver regeneration

AIM

To highlight a potential dynamic interaction between intestinal bacteria (IB) and metabolites that might contribute to liver regeneration (LR).

METHODS

Male Sprague-Dawley rats were subjected to surgical removal of two-thirds of the liver and samples were collected over a 14-day period. Intestinal community and metabolic profiles were characterized to establish their potential interactions during liver regeneration.

RESULTS

Partial hepatectomy caused fluctuating changes in the gut microbiome, which paralleled the biological processes of LR. Briefly, the enhanced cell proliferation occurring within 30-48 h was associated with a decreased ratio of Firmicutes to Bacteroidetes reflected by a reduction in Ruminococcaceae and Lachnospiraceae, and an increase in Bacteroidaceae, Rikenellaceae, and Porphyromonadaceae, which was indicative of a lean phenotype. The microbiota derived from rats at 12-24 h and 3-14 days were characterized by elevated F/B ratios, suggesting the differing energy extract behaviors of microbiota during the course of LR. Functional changes of the shifted microbiota revealed by PICRUSt software confirmed the pyrosequencing results. The microbiome derived from hour 12 rats showed overpresentation of metabolism-related modules. In contrast, the microbiome derived from day 2 rats was functionally unique in "replication and repair", "amino acid metabolism," and "nucleoid metabolism." Upon examining the dynamic pattern of metabolic response, the specific pathways, including glycerophospholipid metabolism, taurine, and hypotaurine metabolism, were identified to be attributable to the systemic alterations in LR-related metabolism. Moreover, our data indicated that several key functional bacteria were strongly related to perturbations of the above pathways.

CONCLUSION

Gut flora could play a central role in manipulating metabolic responses in LR.

Systemic regulation of bilirubin homeostasis: Potential benefits of hyperbilirubinemia

Neurotoxic bilirubin is the end product of heme catabolism in mammals. Bilirubin is solely conjugated by uridine diphospho-glucuronosyltransferase 1A1, which is a membrane-bound enzyme that catalyzes the transfer of glucuronic acid. Due to low function of hepatic and intestinal uridine diphospho-glucuronosyltransferase 1A1 during the neonatal period, human neonates develop mild to severe physiological hyperbilirubinemia. Accumulation of bilirubin in the brain leads to the onset of irreversible brain damage, termed kernicterus. Breastfeeding is one of the most significant factors that increase the risk of developing kernicterus in infants. Why does this most natural way of feeding increase the risk of brain damage or even death? This question leads to the hypothesis that breast milk-induced hyperbilirubinemia might bring certain benefits that outweigh those risks. While bilirubin is neurotoxic and cytotoxic, this compound is also a potent antioxidant. There are studies showing improved clinical conditions in patients with hyperbilirubinemia. Accumulating evidence also shows that genetic polymorphisms linked to hyperbilirubinemia are beneficial against various diseases. In this review article, we first introduce the production, metabolism, and transport of bilirubin. We then discuss the potential benefits of neonatal and adult hyperbilirubinemia. Finally, epigenetic factors as well as metabolomic information associated with hyperbilirubinemia are described. This review article advances the understanding of the physiological importance of the paradoxical compound bilirubin. (Hepatology 2018;67:1609-1619).

Bilirubin in the Liver-Gut Signaling Axis

Bilirubin is a component of the heme catabolic pathway that is essential for liver function and has been shown to reduce hepatic fat accumulation. High plasma bilirubin levels are reflective of liver disease due to an injurious effect on hepatocytes. In healthy liver, bilirubin is conjugated and excreted to the intestine and converted by microbes to urobilinoids, which are reduced to the predominant pigment in feces, stercobilin, or reabsorbed. The function of urobilinoids in the gut or their physiological relevance of reabsorption is not well understood. In this review, we discuss the relationship of hepatic bilirubin signaling to the intestinal microbiota and its regulation of the liver-gut axis, as well as its capacity to mediate these processes.

16S Ribosomal RNA-based Gut Microbiome Composition Analysis in Infants with Breast Milk Jaundice

BACKGROUND

This case-control study investigated an association between breast milk jaundice (BMJ) and infants' gut microbiome. The study included determination of the diversity of the gut microbiome and identification of bacterial genera associated with BMJ.

METHODS

The study population consisted of 12 infants with BMJ and 22 breastfed infants without jaundice (control). DNA collected from feces was analyzed by PCR amplification and 1% agarose gel electrophoresis, and then sequenced with a MiSeq system. Relative quantification bioinformatics was employed to analyze the DNA sequencing data. An Illumina high-throughput sequencing platform was used to analyze 16S rRNA variable (V) regions V3 and V4 in stool samples.

RESULTS

In the control group, the proportion of Escherichia/Shigella (genus level) in the gut microbiome (64.67%) was significantly higher than that of the BMJ group. However, the prevalence of Bifidobacterium or Enterococcus in the gut microbiome of the two groups was similar. The Simpson index indicated that the diversity of the bacterial population in the BMJ infants was significantly narrower than in the normal infants.

CONCLUSION

The prevalence of Escherichia/Shigella in the gut of breastfed infants is important for lowering BMJ development.

The molecular basis of jaundice: An old symptom revisited

Increased serum bilirubin level is a widely used diagnostic marker for hepatic illnesses. Nevertheless, mild elevation of unconjugated serum bilirubin (such as in Gilbert syndrome) has been recently demonstrated to correlate with low risk of chronic inflammatory and/or oxidative stress-mediated diseases. In accord, a low serum bilirubin level has emerged as an important predisposing factor or a biomarker of these pathologic conditions including cardiovascular, tumour, and possibly neurodegenerative diseases. Bilirubin possesses multiple biological actions with interaction in a complex network of enzymatic and signalling pathways. The fact that the liver is the main organ controlling the bioavailability of bilirubin emphasizes the central role of this organ in human health.

Glucuronides in the gut: Sugar-driven symbioses between microbe and host

The intestinal milieu is astonishingly complex and home to a constantly changing mixture of small and large molecules, along with an abundance of bacteria, viral particles, and eukaryotic cells. Such complexity makes it difficult to develop testable molecular hypotheses regarding host-microbe interactions. Fortunately, mammals and their associated gastrointestinal (GI) microbes contain complementary systems that are ideally suited for mechanistic studies. Mammalian systems inactivate endobiotic and xenobiotic compounds by linking them to a glucuronic acid sugar for GI excretion. In the GI tract, the microbiota express β-glucuronidase enzymes that remove the glucuronic acid as a carbon source, effectively reversing the actions of mammalian inactivation. Thus, by probing the actions of microbial β-glucuronidases, and by understanding which substrate glucuronides they process, molecular insights into mammalian-microbial symbioses may be revealed amid the complexity of the intestinal tract. Here, we focus on glucuronides in the gut and the microbial proteins that process them.

Looking to the horizon: the role of bilirubin in the development and prevention of age-related chronic diseases

Bilirubin, the principal tetrapyrrole, bile pigment and catabolite of haem, is an emerging biomarker of disease resistance, which may be related to several recently documented biological functions. Initially believed to be toxic in infants, the perception of bilirubin has undergone a transformation: it is now considered to be a molecule that may promote health in adults. Data from the last decade demonstrate that mildly elevated serum bilirubin levels are strongly associated with reduced prevalence of chronic diseases, particularly cardiovascular diseases (CVDs), as well as CVD-related mortality and risk factors. Recent data also link bilirubin to other chronic diseases, including cancer and Type 2 diabetes mellitus, and to all-cause mortality. Therefore, there is evidence to suggest that bilirubin is a biomarker for reduced chronic disease prevalence and a predictor of all-cause mortality, which is of important clinical significance. In the present review, detailed information on the association between bilirubin and all-cause mortality, as well as the pathological conditions of CVD, cancer, diabetes and neurodegenerative diseases, is provided. The mechanistic background concerning how bilirubin and its metabolism may influence disease prevention and its clinical relevance is also discussed. Given that the search for novel biomarkers of these diseases, as well as for novel therapeutic modalities, is a key research objective for the near future, bilirubin represents a promising candidate, meeting the criteria of a biomarker, and should be considered more carefully in clinical practice as a molecule that might provide insights into disease resistance. Clearly, however, greater molecular insight is warranted to support and strengthen the conclusion that bilirubin can prevent disease, with future research directions also proposed.

Quantitative assessment of the multiple processes responsible for bilirubin homeostasis in health and disease

Serum bilirubin measurements are commonly obtained for the evaluation of ill patients and to screen for liver disease in routine physical exams. An enormous research effort has identified the multiple mechanisms involved in the production and metabolism of conjugated (CB) and unconjugated bilirubin (UB). While the qualitative effects of these mechanisms are well understood, their expected quantitative influence on serum bilirubin homeostasis has received less attention. In this review, each of the steps involved in bilirubin production, metabolism, hepatic cell uptake, and excretion is quantitatively examined. We then attempt to predict the expected effect of normal and defective function on serum UB and CB levels in health and disease states including hemolysis, extra- and intrahepatic cholestasis, hepatocellular diseases (eg, cirrhosis, hepatitis), and various congenital defects in bilirubin conjugation and secretion (eg, Gilbert's, Dubin-Johnson, Crigler-Najjar, Rotor syndromes). Novel aspects of this review include: 1) quantitative estimates of the free and total UB and CB in the plasma, hepatocyte, and bile; 2) detailed discussion of the important implications of the recently recognized role of the hepatic OATP transporters in the maintenance of CB homeostasis; 3) discussion of the differences between the standard diazo assay versus chromatographic measurement of CB and UB; 4) pharmacokinetic implications of the extremely high-affinity albumin binding of UB; 5) role of the enterohepatic circulation in physiologic jaundice of newborn and fasting hyperbilirubinemia; and 6) insights concerning the clinical interpretation of bilirubin measurements.

Neonatal jaundice is a risk factor for childhood allergic rhinitis: a retrospective cohort study

BACKGROUND

This study evaluates the association between neonatal jaundice and childhood allergic rhinitis (AR).

METHODS

Eleven thousand three hundred twenty-eight children were collected from the National Health Insurance Research Database in Taiwan. Their claims data were evaluated from birth to 10 years of age, and they were assigned to either the study (with neonatal jaundice) or the control (without neonatal jaundice) group. The diagnostic criteria for AR were at least three diagnoses of AR at outpatient services, one diagnosis of AR during an admission, or one diagnosis of AR in an emergency department. Mantel-Haenszel odds ratios (ORs) were calculated after adjustment for the following confounders: preterm/low birth weight, neonatal infection, other respiratory conditions, other birth conditions, and gender. AR rate, AR onset time, the use of oral antihistamines/nasal corticosteroids, outpatient visit frequency for AR, lower respiratory infection (LRI) rates, sinusitis/otitis media/conjunctivitis rates, and the effect of phototherapy were evaluated.

RESULTS

After adjustment for the confounding factors, the rate of AR was higher in icteric children (OR, 1.46; 95% confidence interval, 1.24∼1.72). There was a higher incidence of AR in children <4 years old with icterus. The use of oral antihistamines, LRI rates, sinusitis rates, and otitis media rates were higher in the icteric children. There was no association between phototherapy and childhood AR.

CONCLUSION

Neonatal jaundice increased the rate and complications of childhood AR in subjects aged up to 10 years and may be a risk factor for childhood AR.

Breast milk jaundice: effect of bacteria present in breast milk and infant feces

OBJECTIVE

Breast milk is an important source of bacteria in establishing the infantile intestinal microbiota that appear to influence the enterohepatic circulation of bilirubin. The aim of the present study was to evaluate the effect of breast milk's microbiological content on the development of breast milk jaundice (BMJ).

METHODS

A total number of 60 mother-infant pairs enrolled to the study. Two groups were defined: BMJ group (n=30), full-term otherwise healthy newborns who were considered BMJ; control group (n=30), full-term healthy newborns without jaundice. All newborns in the study were exclusively breast-fed. The breast milk samples and the feces of infants were evaluated for content of selected bacterial populations (Bifidobacterium, Lactobacillus, Clostridium, Staphylococcus, and Streptococcus species) with real-time polymerase chain reaction.

RESULTS

Bifidobacterium bifidum content in the breast milk and B adolescentis, B bifidum, and B longum content in the fecal samples were higher in the control group than in the BMJ group. The milk and fecal concentrations of B bifidum were significantly correlated. The concentrations of breast milk B bifidum and fecal B bifidum, B adolescentis, and B longum were found to be negatively correlated with bilirubin levels.

CONCLUSIONS

Our results suggest that Bifidobacterium species in breast milk may protect against BMJ.

New pathophysiological concepts underlying pathogenesis of pigment gallstones

Pigment gallstones, which are much less frequent than cholesterol stones, are classified descriptively as "black" or "brown". They are composed mostly of calcium hydrogen bilirubinate, Ca(HUCB)(2), which is polymerized and oxidized in "black" stones but remains unpolymerized in "brown" stones. Black stones form in sterile gallbladder bile but brown stones form secondary to stasis and anaerobic bacterial infection in any part of the biliary tree, including the gallbladder. Other calcium salts coprecipitate in both stone types; crystalline calcium phosphate and/or carbonate in the case of "black" stones and amorphous calcium salts of long chain saturated fatty acids ("soaps") in the case of "brown" stones. Cholesterol is present in variable proportions in "brown" more than "black" stones and in the latter, the bile sterol may be totally absent. The "scaffolding" of both stone types is a mixed mucin glycoprotein matrix secreted by epithelial cells lining the biliary tree. The critical pathophysiological prerequisite for "black" stone formation is "hyperbilirubinbilia" (biliary hypersecretion of bilirubin conjugates). It is due principally to hemolysis, ineffective erythropoiesis, or pathologic enterohepatic cycling of unconjugated bilirubin. Endogenous biliary β-glucuronidase hydrolysis of bilirubin conjugates in gallbladder bile provides HUCB(-) molecules that precipitate as insoluble salts with ionized Ca. Putatively, reactive oxygen species secreted by an inflamed gallbladder mucosa are responsible for transforming the initial soft yellow precipitates into hard black [Ca(HUCB)(2)](n) polymers. Despite "brown" gallstones being soft and amenable to mechanical removal, chronic anaerobic infection of the biliary tree is often markedly resistant to eradication.

Bile pigment pharmacokinetics and absorption in the rat: therapeutic potential for enteral administration

BACKGROUND AND PURPOSE

Bilirubin and biliverdin possess antioxidant and anti-inflammatory properties and their exogenous administration protects against the effects of inflammation and trauma in experimental models. Despite the therapeutic potential of bile pigments, little is known about their in vivo parenteral or enteral absorption after exogenous administration. This study investigated the absorption and pharmacokinetics of bile pigments after i.v., i.p. and intraduodenal (i.d.) administration in addition to their metabolism and routes of excretion.

EXPERIMENTAL APPROACH

Anaesthetized Wistar rats had their bile duct, jugular and portal veins cannulated. Bile pigments were infused and their circulating concentrations/biliary excretion were measured over 180 min. KEY RESULTS After i.v. administration of unconjugated bilirubin, biliverdin and bilirubin ditaurate, their plasma concentrations decreased exponentially over time. Subsequently, native and metabolized compounds appeared in the bile. When administered i.p., their absolute bioavailabilities equalled 14.0, 16.1 and 33.1%, respectively, and correspondingly 38, 28 and 34% of the same bile pigment doses were excreted in the bile. Administration of unconjugated bilirubin and bilirubin ditaurate i.d. increased their portal and systemic concentrations and their systemic bioavailability equalled 1.0 and 2.0%, respectively. Correspondingly, 2.7 and 4.6%, of the doses were excreted in the bile. Biliverdin was rapidly metabolized and these products were absorbed and excreted via the urine and bile.

CONCLUSIONS AND IMPLICATIONS

Bile pigment absorption from the peritoneal and duodenal cavities demonstrate new routes of administration for the treatment of inflammatory and traumatic pathology. Oral biliverdin administration may lead to the production of active metabolite that protect from inflammation/complement activation.

The effect of prebiotics in the management of neonatal hyperbilirubinaemia

BACKGROUND

Breast milk oligosaccharides such as galacto-oligosaccharides (scGOS) and fructo-oligosaccharides (lcFOS) can influence the intestinal microbial flora. The latter, in turn, can modulate several intestinal and extraintestinal functions, including bilirubin metabolism. Supplementing infant formula with a prebiotic mixture might then be a novel and safe intervention to manage mild neonatal hyperbilirubinaemia.

AIM

To investigate the effect of dietary supplementation with prebiotics on moderate hyperbilirubinaemia in healthy, term infants.

METHODS

A prospective, double-blind, clinical trial was performed on seventy-six consecutive newborns who were randomly assigned to receive a formula containing 0.8 g/dL of a mixture from scGOS and lcFOS (ratio 9:1), or maltodextrines as placebo for 28 days. Bilirubin levels were determined by the transcutaneous bilirubin measurement within 2 h after birth (T1), at 24, 48 and 72 h and at 5, 7, 10 and 28 days of life. The number of stool per day was also recorded.

RESULTS

Neonates receiving prebiotics showed a larger number of stools over all the duration of dietary intervention compared to that of those on placebo (Repeated Measures ANOVA p < 0.001; day 28 3.4 +/- 0.0.9 vs 1.7 +/- 0.9, respectively; Dunn test p < 0.05). Neonates whose formula was supplemented with prebiotics showed a lower transcutaneous bilirubin that was statistically significant from 72 h of life (5.46 +/- 1.6 vs 7.07 +/- 2.49, post hoc Dunn test, p < 0.05) throughout the duration of the dietary intervention (day 28 2.41 +/- 0.4 vs 2.85 +/- 0.5, post hoc Dunn test, p < 0.05).

CONCLUSION

The addition of prebiotics to standard infant diet might represent a novel strategy to help control neonatal hyperbilirubinaemia.

Bilirubin in clinical practice: a review

Bilirubin is an endogenous compound that can be toxic under certain conditions but, on the other hand, mild unconjugated hyperbilirubinaemia might protect against cardiovascular diseases and tumour development. Serum bilirubin levels are often enhanced under a variety of clinical conditions. These are discussed and the mechanisms are outlined.

Unconjugated bilirubin modulates the intestinal epithelial barrier function in a human-derived in vitro model

Unconjugated bilirubin promotes intestinal secretion without affecting nutrient digestion or absorption. In the current study, the effects of unconjugated bilirubin (UCB) on the barrier function of the intestinal epithelium were investigated. The apical side of human intestinal cell line Caco-2 monolayers was challenged with purified UCB. Transepithelial electrical resistance and paracellular fluxes of 10 kD Cascade blue conjugate dextran were measured. Cell monolayer viability was studied using LDH release and trypan blue exclusion tests. Redistribution of enterocyte tight junction occludin was studied by confocal microscopy. Bilirubin induced a dose-dependent decrease of transepithelial electrical resistance (TEER). This effect was maximal at 6 h and tended to be reversed at 48 h. Oxidated bilirubin was ineffective. Bilirubin significantly increased fluorescent dextran paracellular passage. Cell viability was not affected by UCB over the 5-200 nmol/L concentration range. Finally, bilirubin triggered a reversible redistribution of tight junctional occludin. UCB increases the permeability of intestinal epithelium. This effect is reversible, dependent on the redox status of the molecule and the rearrangement of the tight junction. These data attribute to bilirubin a novel role of functional modulator of intestinal paracellular permeability in vitro.

Rapid protocol for electroporation of Clostridium perfringens

A rapid and simple method has been developed for the electroporation of Clostridium perfringens with plasmid DNA. The new improvements, harvesting cells early in the logarithmic stage of growth, keeping the cells at room temperature and the absence of post-shock incubation on ice increased transformation efficiency by one order of magnitude.

The effect of zinc salts on serum bilirubin levels in hyperbilirubinemic rats

OBJECTIVES

Intestinal metabolism of bilirubin is implicated in the pathogenesis of neonatal jaundice and Crigler-Najjar syndrome. In the present study the authors investigated the effect of oral administration of zinc salts on serum bilirubin levels in hyperbilirubinemic rats.

METHODS

Bilirubin-binding activities of zinc sulfate and water-insoluble zinc methacrylate were determined in vitro. Congenitally hyperbilirubinemic Gunn rats and artificially hyperbilirubinemic Wistar rats were used in in vivo studies. Animals were fed a normal diet for 1 week and then a treatment diet of either zinc sulfate or zinc methacrylate for additional 2 weeks. Serum and fecal bile pigments were determined at the end of each phase. Biliary bilirubin secretion rates were determined in hyperbilirubinemic Wistar rats fed zinc methacrylate.

RESULTS

Substantial bilirubin-binding activities of zinc salts were demonstrated in in vitro experiments. Treatment with oral zinc salts significantly decreased serum bilirubin levels in Gunn rats (166 +/- 53 versus 123 +/- 38 and 206 +/- 34 versus 131 +/- 31 micromol/L, P < 0.05 for zinc methacrylate and zinc sulfate, respectively). A similar effect of zinc methacrylate was also observed in hyperbilirubinemic Wistar rats (102 +/- 10 versus 14 +/- 4 micromol/L, P < 0.0001). In accord, biliary bilirubin secretion decreased significantly in these animals (45 +/- 11 versus 28 +/- 4 nmol/h 100g body weight, P < 0.02). In contrast to zinc sulfate, treatment with zinc methacrylate did not lead to the elevation of serum zinc levels.

CONCLUSIONS

Oral administration of zinc salts efficiently decreased serum bilirubin levels in hyperbilirubinemic rats, presumably as a result of inhibition of enterohepatic circulation of bilirubin. This approach might be useful in the treatment of severe unconjugated hyperbilirubinemias.

The impact of intestinal microflora on serum bilirubin levels

BACKGROUND/AIMS

Intestinal microflora plays an important role in the pathogenesis of neonatal jaundice by inhibiting enterosystemic circulation of bilirubin. The present study aimed to investigate the influence of intestinal microflora on serum bilirubin levels in hyperbilirubinemic Gunn rats.

METHODS

After a baseline phase Gunn rats received oral antibiotics (either clindamycin/neomycine or co-trimethoxazole for four days, phase II). Intestinal colonization was carried out either with a bilirubin-reducing strain of C. perfringens or C. pasteurianum incapable of reducing bilirubin (phase III). Serum bilirubin and fecal bile pigments were determined at the end of each phase.

RESULTS

Oral administration of clindamycin/neomycine resulted in the disappearance of fecal urobilinoids. Simultaneously, serum bilirubin increased dramatically (186+/-31 vs. 289+/-35 micromol/l, P=0.004). Intestinal colonization with C. perfringens led to reappearance of fecal urobilinoid production accompanied with a partial decrease of serum bilirubin (289+/-35 vs. 239+/-17 micromol/l, P=0.013), whereas the effect of C. pasteurianum on bile pigment metabolism was negligible. Co-trimethoxazole therapy had no effect on serum and intestinal metabolism of bilirubin.

CONCLUSIONS

Intestinal microflora greatly affects intravascular metabolism of bilirubin. Prolonged use of certain antibiotics in man may lead to an increase in serum bilirubin levels, while the enhancement of intestinal catabolism may have an opposite effect.

Influence of zinc bacitracin and Bacillus licheniformis on microbial intestinal functions in weaned piglets

The influence of zinc bacitracin (ZB) and of Bacillus licheniformis on host microbial-related functions in young piglets was investigated by applying the concept of microflora-associated characteristics. Six biochemical parameters were determined before and after weaning in faecal samples from piglets in four litters having access to a diet containing ZB, to a diet containing B. licheniformis, to a diet with both additives, or to a diet with no additives, from 3 weeks of age. Statistically significant differences were found in three of the intestinal functions investigated: formation of short-chain fatty acids (at 7 and 10 weeks of age). degradation of mucin (at 7 and 10 weeks of age) and conversion of bilirubin to urobilins (at 7 weeks of age). We also found age-dependent influences on the formation of short-chain fatty acids, on conversion of cholesterol to coprostanol and on conversion of bilirubin to urobilins. We conclude that a functional approach is appropriate for measuring exogenous influence(s) on the microbial intestinal metabolisms in weaned piglets.

New concepts in bilirubin encephalopathy

Revised concepts of bilirubin encephalopathy have been revealed by studies of bilirubin toxicity in cultured CNS cells and in congenitally jaundiced Gunn rats. Bilirubin neurotoxicity is related to the unbound (free) fraction of unconjugated bilirubin (Bf), of which the dominant species at physiological pH is the protonated diacid, which can passively diffuse across cell membranes. As the binding affinity of plasma albumin for bilirubin decreases strikingly as albumin concentration increases, previously reported Bf values were underestimated. Newer diagnostic tests can detect reversible neurotoxicity before permanent damage occurs from precipitation of bilirubin (kernicterus). Early toxicity can occur at Bf only modestly above aqueous saturation and affects astrocytes and neurons, causing mitochondrial damage, resulting in impaired energy metabolism and apoptosis, plus cell-membrane perturbation, which causes enzyme leakage and hampers transport of neurotransmitters. The concentrations of unbound bilirubin in the cerebro-spinal fluid and CNS cells are probably limited mainly by active export of bilirubin back into plasma, mediated by ABC transporters present in the brain capillary endothelium and choroid plexus epithelium. Intracellular bilirubin levels may be diminished also by oxidation, conjugation and binding to cytosolic proteins. These new concepts may explain the varied susceptibility of neonates to develop encephalopathy at any given plasma bilirubin level and the selective distribution of CNS lesions in bilirubin encephalopathy. They also can suggest better strategies for predicting, preventing and treating this syndrome.

Enterohepatic cycling of bilirubin as a cause of 'black' pigment gallstones in adult life

In contrast to bile salts, which undergo a highly efficient enterohepatic circulation with multiple regulatory and physiologic functions, glucuronic acid conjugates of bilirubin are biliary excretory molecules that in health do not have a continuing biologic life. Intestinal absorptive cells are devoid of recapture transporters for bilirubin conjugates, and their large size and polarity prevent absorption by passive diffusion. However, unconjugated bilirubin, the beta-glucuronidase hydrolysis product of bilirubin glucuronides can be absorbed passively from any part of the small and large intestines. This can occur only if unconjugated bilirubin is kept in solution and does not undergo rapid bacterial reduction to form urobilinoids. Here we collect, and in some cases reinterpret, experimental and clinical evidence to show that in addition to the well-known occurrence in newborns, enterohepatic cycling of unconjugated bilirubin can reappear in adult life. This happens as a result of several common conditions, particularly associated with bile salt leakage from the small intestine, the most notable ileal dysfunction resulting from any medical or surgical cause. We propose that when present in excess, colonic bile salts solubilize unconjugated bilirubin, delay urobilinoid formation, prevent calcium complexing of unconjugated bilirubin and promote passive absorption of unconjugated bilirubin from the large intestine. Following uptake, reconjugation, and resecretion into bile, this source of 'hyperbilirubinbilia' may be the important pathophysiological risk factor for 'black' pigment gallstone formation in predisposed adult humans.

Bilirubin-IXbeta is a marker of meconium, like zinc coproporphyrin

BACKGROUND

Because meconium accumulates continuously in the fetal intestine, analysis of the postnatally excreted material could yield important information of intrauterine metabolism and maturation. Therefore, a study of the bilirubin pigments in meconium and in the first neonatal stools was carried out.

METHODS

Meconium and stools from 37 neonates of various gestational ages were collected carefully, and stored at -20 degrees C, protected by aluminium foil. Samples were defrosted, vortex mixed with an equal amount of dimethyl sulfoxide, centrifuged, and submitted to analysis by high-pressure liquid chromatography using newly developed methods to identify and to quantitate the bilirubin-IXalpha, -IXbeta, -IXgamma, and -IXdelta isomers. In addition, samples were also submitted to diazo coupling with ethyl anthranilate. Total coproporphyrins and zinc coproporphyrin were assayed for comparison.

RESULTS

Unconjugated bilirubin-IXalpha and -IXbeta were detected in meconium but not the -IXgamma or the -IXbeta isomer. Bilirubin-IXbeta was the predominant pigment and comprised 63% to 96% of the unconjugated bilirubins in the first sample of meconium excreted. Its amount decreased rapidly during the first 5 days in full-term newborns, but this occurred more slowly in preterm neonates, especially in those with a gestational age less than 30 weeks. The decrease of bilirubin-IXbeta over time correlated with that of coproporphyrin.

CONCLUSIONS

Bilirubin-IXbeta is the prevailing bile pigment in the first excreted sample of meconium. It gradually decreases after birth and can be considered a biochemical marker of meconium, like zinc coproporphyrin.