Evaluation of a model for brain bilirubin uptake in jaundiced newborns

A model for brain bilirubin uptake (BBU) predicts that BBU in jaundiced newborns typically depends on the plasma total bilirubin concentration (TBC) and the bilirubin-albumin dissociation rate constant (k1) rather than the unbound bilirubin (Bf). The model's validity was tested by 1) evaluating its requirement that k3>k2, where k3 and k2 are the rate constants for BBU and Bf-albumin association, respectively, and 2) determining whether the calculated BBU is 相似文献   

The pathochemistry of kernicterus.

The stoichiometry of bilirubin--albumin interaction has been analyzed and quantitated in several recent studies, confirming that albumin binding of bilirubin obeys the law of mass action [4, 5, 14, 16, 26, 36, 43, 46, 61, 65, 73, 92, 111]. These studies provide a basis for interpreting bilirubin transport, cell uptake and toxicity from physicochemical and pharmacologic perspectives [35, 42, 58, 59]. In this report, we propose a model of the pathogenesis of kernicterus which views serum albumin and tissue as competing with each other for binding the miscible bilirubin pool. Evidence is presented to show that bilirubin normally binds reversibly to cellular membranes and certain soluble enzymes just as it does to albumin; the unbound bilirubin concentration is the driving force for both albumin and tissue binding. We propose that albumin binding is determined by the concentration of free bilirubin anion (which is essentially unaffected by physiologic pH changes), and that tissue binding is mainly determined by the concentration of free bilirubin acid (which is greatly influenced by pH). When bilirubin--tissue complexes are formed, essential cell functions may be inhibited, producing cellular acidosis, irreversible intracellular aggregation of bilirubin, and cell death. In developing this argument, we will sequentially discuss relevant features of bilirubin chemistry, the binding of bilirubin to albumin, the formation of bilirubin--tissue complexes, bilirubin toxicity, alternative viewpoints of bilirubin transport, and, finally, the implications of this model to the clinical management of jaundiced infants. It should be emphasized that this paper is an attempt to analyze bilirubin transport and toxicity using basic chemical principles; it is an extension of previously published proposals [17, 77], and will undoubtedly require further modification as additional experimental data becomes available.     

Experimental bilirubin encephalopathy: importance of total bilirubin, protein binding, and blood-brain barrier

The cause of bilirubin encephalopathy has been variously ascribed to elevated total serum bilirubin concentration, high free bilirubin levels (or impaired albumin binding), and disruption of the blood-brain barrier. An experimental rat model for acute bilirubin encephalopathy was developed in which these three factors could be varied independently. Osmotic opening of the blood-brain barrier in the right hemisphere was produced by infusing a hypertonic arabinose solution into the right carotid artery. The total bilirubin level and bilirubin binding state were varied by adjusting the amount of bilirubin infused intravenously and/or by infusing human serum albumin. Brain electrical activity (EEG) served as an indicator of developing encephalopathy. Neither staining nor EEG changes occurred if the blood-brain barrier remained intact. Bilirubin staining without EEG evidence of encephalopathy sometimes occurred when the blood-brain barrier was open. Discriminant analysis showed that EEG changes were best predicted by the degree of blood-brain barrier opening (as indicated by brain bilirubin content) and by the quality of serum bilirubin binding. Serum total bilirubin concentration was not an important discriminator of encephalopathy.     

The possible risk of bilirubin encephalopathy as predicted by plasma parameters in neonates with previous severe asphyxia

The study group consisted of nine mature newborn infants with a previous history of severe asphyxia and a control group of 18 mature, healthy newborns with the same postnatal age and sex. The object of the investigation was to compare the possible risk of development of bilirubin encephalopathy between the two groups as estimated by plasma parameters. The asphyxia group had a significantly lower reserve albumin concentrations for binding of monoacetyldiaminodiphenyl sulphone (P=0.008), a measure of binding of unconjugated bilirubin, and significantly lower total albumin concentrations (P=0.02). No significant difference was observed in unconjugated bilirubin concentration. It is suggested that mature newborns with previous severe asphyxia are at a slightly increased risk of developing bilirubin encephalopathy over and above the well-known risk associated with increased permeability of the blood brain barrier.     

Effect of postnatal anoxia on bilirubin levels in rat brain

The effects of a period of anoxia 18-24 h after birth on bilirubin levels in rat brain were investigated during anoxia, recovery, and development. Postnatal anoxia induces a significant, temporary increase (up to 200% with respect to control values) in newborn rat brain bilirubin levels during anoxia and short-term recovery. Pretreatment of the newborn rats with a single dose of the drug sulfixosazole markedly enhances bilirubin accumulation in the brain of the anoxic rats. A second rise in brain bilirubin concentration is detected in a group of the newborn rats 3-6 days after oxygen deprivation. Autoradiographic localization of radiolabeled bilirubin following in vivo experiments suggests that this substance is preferentially accumulated in some areas of the newborn rat brain as a consequence of postnatal anoxia, and indicates, together with the effect of sulfixosazole, that as a result of anoxia, a displacement of unbound bilirubin from blood to the nervous tissue occurs. Our results confirm the importance of anoxia as a risk factor for the development of bilirubin-induced encephalopathy. The possible relevance of intracerebral hemorrhages caused by perinatal asphyxia producing delayed bilirubin accumulation in the newborn rat brain is suggested.     

Brain bilirubin deposition and brain blood flow during acute urea-induced hyperosmolality in newborn piglets

Acute hyperosmolality-induced blood brain barrier breakdown has been demonstrated to increase the permeability of sucrose, which is similar in molecular weight to bilirubin, independently of changes in regional brain blood flow. We studied three groups of piglets given continuous bilirubin infusions to maintain serum bilirubin concentrations at approximately 8 mg/dl. Normal serum osmolality was maintained throughout the study in control animals. Two experimental groups were made hyperosmolar (330 and 375 mosmol/liter) with bolus urea infusions during the last hour of the study. Regional brain bilirubin concentrations were elevated in the 375 mosmol/liter hyperosmolal experimental group, but not in the 330 mosmol/liter group. Regional brain albumin concentrations also were increased over the control group in the 375 mosmol/liter animals. There were no differences in regional brain blood flows to account for the increases in brain bilirubin concentrations. Our results show that brain bilirubin deposition occurs following breakdown of the blood brain barrier by acute, severe hyperosmolality (375 mosmol/liter) and that the deposited bilirubin is derived from both bound and unbound fractions. The bilirubin deposition occurs independently of changes in regional brain blood flow; however, regional differences in the blood brain barrier permeability to albumin also occur.     

Cerebral blood volumes in young rats with and without in situ saline flushing of cerebral vasculature. Implications for in vivo studies of brain substance uptake

In recent studies of bilirubin encephalopathy, in situ flushing of the cerebral vessels has been used to clear blood from the brain. The effectiveness of such procedures has not been adequately documented. Herein young, male Sprague-Dawley rats were given about 750 KBq of 51Cr-labelled rat erythrocytes 3 min prior to sacrifice. There were four experimental groups: control, displacer (sulfisoxazole), hyperosmolality, and hypercarbia. Half of the rats in each group had the brain vasculature flushed in situ, while the remaining rat brains were not flushed. The brains were dissected into seven regions, and the radioactivity in the tissues was compared to that of blood drawn from the rats immediately before death. Significant amounts of blood (22-42%) remained after in situ flushing. Retention was significantly higher in the hyperosmolar animals, and significantly lower in the hypercarbic animals as compared to controls. Interregional differences in blood volumes per gram wet weight were significant without, but not with flushing. Similar observations were made using 125I-IgM as a marker for the plasma compartment. In studies of brain uptake of substances with high plasma concentrations, substance remaining within the cerebral vessels may contribute significantly to the apparent brain uptake values.     

Effects of sulfisoxazole, hypercarbia, and hyperosmolality on entry of bilirubin and albumin into brain regions in young rats

We have studied the entry of 3H-bilirubin and 125I-albumin into brain regions in young rats during short-term (1 h) hyperbilirubinemia. Bilirubin enters the brain both under control, displacer (sulfisoxazole 50 mg/kg), hypercarbic (PCO2 18-21 kPa; pH approximately 6.9), and hyperosmolar (serum osmolality approximately 400 mosm/l) conditions. No significant differences in bilirubin uptake were found between brain regions. Thus preferential staining of basal ganglia ('kernicterus') may not be a phenomenon related to uptake. Albumin does not cross the blood-brain barrier under control or displacer conditions, but does enter the brain to some extent in hypercarbia, and to a greater extent in hyperosmolality. During control and displacer conditions, only unbound bilirubin appears to enter the brain. In hypercarbia bilirubin enters primarily in the unbound form, but some is also albumin-bound. In hyperosmolality a significant fraction of the bilirubin entering the brain is albumin-bound.     

The effects of brain blood flow on brain bilirubin deposition in newborn piglets

Since kernicteric lesions are usually found in the subcortical regions of the brain and these areas also receive the highest blood flow during asphyxia and hypercapnia, we hypothesized that increases in brain bilirubin deposition may be related to increases in brain blood flow. Fourteen piglets underwent a 3-h infusion of bilirubin to maintain total serum bilirubin at approximately 8 mg/dl, during which time blood gases, hemodynamic variables, and brain blood flow were determined. After sacrificing the animals, regional brain bilirubin content was determined. Ten piglets underwent the same protocol; in addition, hypercapnia was induced during the last hour of study (PaCO2 approximately 70 mm Hg). The regional brain blood flow and bilirubin deposition were significantly increased over control values (p less than 0.05) following hypercapnia in the subcortical region and significantly so in the midbrain and cerebellum. In separate groups of control (n = 6) and hypercapnia (n = 6) piglets, 125I-labeled albumin was infused and demonstrated that hypercapnia was not associated with increased regional brain albumin content. We conclude that hypercapnia-induced augmentation in regional brain blood flow is associated with increased deposition brain blood flow is associated with increased deposition of unbound bilirubin. Although the causal relationship between these two observations has not been firmly established, the findings deserve future investigation to clarify the role of brain blood flow, brain bilirubin deposition, and the production of kernicterus in high risk infants.     

Biochemical alterations in neonatal hyperbilirubinemia and bilirubin encephalopathy: a review.

This review article discusses some current questions concerning the measurement of bilirubin in the blood of newborn infants and the relationship of these blood parameters to the biochemical defects responsible for bilirubin encephalopathy. A discussion of numerous theories, which have been put forth to explain the specific biochemical mechanism by which bilirubin acts on brain metabolism, demonstrates that presently there is no unequivocal explanation for the molecular events leading to bilirubin encephalopathy.     

胆红素脑病仔鼠血清S-100蛋白水平及其脑组织蛋白表达的动态变化

目的探讨胆红素脑病血清S-100蛋白(S-100)水平的变化及其意义。方法7日龄Wistar大鼠腹腔注射胆红素200 mg/kg,制备胆红素脑病动物模型。应用酶联免疫法动态观察胆红素脑病仔鼠血清S-100水平及免疫组织化学的方法动态观察胆红素脑病仔鼠不同时间点脑组织S-100蛋白水平。结果与对照组比较,造模后12 h仔鼠血清S-100水平升高(P<0.001),24 h达峰值,至72 h仍高于对照组,96 h降至正常组水平;造模后仔鼠不同时间点脑组织S-100蛋白的表达阳性面积的变化随时间变化逐渐增加。结论S-100可反映胆红素脑病仔鼠神经胶质的损伤程度,是判定胆红素脑病的可靠指标。     

The effect of multiple exchange transfusions on bilirubin binding

Three bilirubin binding tests (hydroxybenzene-azobenzoic acid dye binding method, the estimation of unbound bilirubin by horseradish peroxidase assay and the saturation of albumin by the salicylate saturation index) were performed on pre-exchange samples of blood and repeated 24 hours after the procedure. No significant improvement in bilirubin binding was found even in infants receiving as many as four exchange transfusions. Based on these bilirubin binding tests, we find no evidence that the criteria for subsequent exchange transfusions should be different from the first exchange transfusion.     

The Effect of Multiple Exchange Transfusions on Bilirubin Binding

ABSTRACT. Three bilirubin binding tests (hydroxybenzene-azobenzoic acid dye binding method, the estimation of unbound bilirubin by horseradish peroxidase assay and the saturation of albumin by the salicylate saturation index) were performed on pre-exchange samples of blood and repeated 24 hours after the procedure. No significant improvement in bilirubin binding was found even in infants receiving as many as four exchange transfusions. Based on these bilirubin binding tests, we find no evidence that the criteria for subsequent exchange transfusions should be different from the first exchange transfusion.     

The in vivo effect of bilirubin and sulfisoxazole on cerebral oxygen, glucose, and lactate metabolism in newborn piglets

Bilirubin inhibits in vitro oxidative phosphorylation and glycolysis. This study investigated the in vivo effect of bilirubin on cerebral oxygen, glucose, and lactate uptake in newborn piglets. Seventeen 2- to 4-day-old piglets were divided into three groups and examined as follows: group 1 = control (C); group 2 = control with sulfisoxazole; and group 3 = experimental, given bilirubin with sulfisoxazole. In the experimental group, bilirubin was infused for 4 h. The cerebral bilirubin content in the bilirubin-infused group was 11.0 +/- 1.4 nmol/g of cerebral cortex (mean +/- SEM), consistent with levels found in infants with kernicterus. However, this level of brain bilirubin had no major, acute effects on cerebral uptake of oxygen, glucose, or lactate despite producing lethargy and ataxia which were consistent with bilirubin intoxication. This suggests that mitochondrial changes may not be involved in vivo in acute bilirubin encephalopathy.     

Permeability of the blood brain barrier for 125I-albumin-bound bilirubin in newborn piglets

Permeability of the blood brain barrier (BBB) for bilirubin and 125I-albumin was studied in 2-d- and 2-wk-old piglets. 125I-albumin was given by bolus at the beginning of each study. Hyperbilirubinemia was produced by an initial bolus infusion of bilirubin and sustained at a plasma bilirubin:albumin molar ratio of approximately 1.0 by continuous infusion of bilirubin for 3 h. During the study period, arterial pH and blood gas tensions, serum osmolarity, and mean arterial blood pressure were within the physiologic range for age in both groups. Serum albumin and serum total and unbound bilirubin concentrations were higher in the 2-wk-old piglets. Brain bilirubin concentrations and permeability (P.S product) of the BBB for bilirubin were higher in the 2-d-old than in the 2-wk-old piglets, but the values of P.S for albumin were not different between the two groups. In 2-d-old piglets, regional brain bilirubin concentrations and permeability of the BBB were higher in subcortical regions (cerebellum and brainstem) than in the cerebral cortex. Regional brain albumin concentrations and BBB permeability to albumin in 2-d-old piglets were higher only in the cerebellum. In all regions, the bilirubin:albumin molar ratio was higher in the brain tissues than in the blood. In 2-wk-old piglets, the brain concentrations and P.S products for bilirubin were lower and the regional differences were less marked than for 2-d-old animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

炎性细胞因子与新生儿胆红素脑损伤的研究进展

近年来,新生儿高未结合胆红素脑损伤过程中的炎症反应引起了越来越多学者的关注.研究表明,炎症反应在新生儿胆红素脑损伤发生、转归中起着重要的作用.大量的非结合胆红素透过血脑屏障,促使神经胶质细胞活化,产生免疫应答,释放炎性细胞因子,引起神经细胞的凋亡、坏死及损伤修复.该文就炎性细胞因子(肿瘤坏死因子-α、白细胞介素-6、8、1β、10等)在新生儿胆红素脑损伤发生及保护中的作用机制进行综述.     

Effect of Sulfisoxazole on Bilirubin-Albumin Binding in Gunn Rats

Hyperbilirubinemic Gunn rats were used to study sulfisoxazole-mediated displacement of bilirubin from albumin. Bilirubin not bound to albumin or unbound bilirubin, which can enter the brain and cause damage, was measured by the automated peroxidase micromethod using the UB-Analyzer. When sulfisoxazole was added to the rat serum in vitro, it showed measurable displacing competition with bilirubin for the binding sites on albumin. The bilirubin titration curves of hyperbilirubinemic sera, after injection of sulfisoxazole, showed a shift to the left indicating that the drug effectively lowered the capacity of serum albumin to bind to bilirubin. The bilirubin binding affinity of the first binding site on the albumin decreased with the administration of 25 mg/kg or more of sulfixazole. The serum concentration of both total bilirubin and unbound bilirubin decreased after the injection of sulfisoxazole suggesting their diffusion into extravascular compartments.     

Recent studies on the pathogenesis of hyperbilirubinemia and kernicterus

After a short summary of recent studies on the blood brain barrier and bilirubin entry into the brain and the intestinal bilirubin absorption, a report is given on actual investigations in Gunn rats. The animals were given by gavage a bilirubin stock solution and simultaneously milk or different milk ingredients. Cream, oil and lipid emulsions delayed bilirubin absorption.     

Simulation of bilirubin detoxification in the newborn using an extracorporeal bilirubin oxidase reactor

Jaundice, which is characterized by an excessive accumulation of bilirubin in the blood and tissues, occurs in 13% of newborns. The common treatments for neonatal jaundice are phototherapy and blood exchange transfusion. A novel approach using an extracorporeal blood filter containing immobilized bilirubin oxidase was recently proposed to detoxify jaundiced blood, and a prototype device markedly reduced serum bilirubin in genetically jaundiced Gunn rats. The primary toxicologic effect in that study was a 20% reduction in red blood cell count. Using a compartmental model for bilirubin metabolism, a mathematical simulation of the extracorporeal treatment's ability to reduce serum bilirubin levels in jaundiced infants is presented. Using a 10-mL reactor volume containing immobilized bilirubin oxidase, the simulation predicts a 32 to 65% decrease in plasma bilirubin concentration over a 4-h treatment for a 2 kg preterm hyperbilirubinemic newborn. In addition, a new approach to altering support material has essentially eliminated red blood cell lysis in vivo using Gunn rats and in vitro using adult blood.     

Reserve albumin binding capacity,salicylate saturation index,and red cell binding of bilirubin in neonatal jaundice

105 blood samples from 72 infants, mostly with jaundice due to haemolytic disease, were analysed for reserve albumin binding capacity (HBABA method), salicylate saturation index (SI), and red cell binding of bilirubin. 2 infants with clinical symptoms of bilirubin encephalopathy had abnormally large amounts of red cell bound bilirubin, though the HBABA binding capacity and salicylate saturation index did not suggest a risk of bilirubin encephalopathy. On the other hand, 48 of the other samples showed `risk values'' for saturation index and 2 of the other samples showed such values as judged by the HBABA method. The discrepancies between these findings are discussed. It is suggested that determination of red cell bound bilirubin may have clinical value in patients with neonatal jaundice, especially in cases of suggested kernicterus.