The Blood–Brain Barrier and Bilirubin Encephalopathy

1. The pathogenesis of bilirubin encephalopathy is multifactorial, involving the transport of bilirubin or albumin/bilirubin across the blood–brain barrier and delivering bilirubin to target neurons.2. The relative importance of the blood–brain barrier, unconjugated bilirubin levels, serum binding, and tissue susceptibility in this process is only partially understood. Even at dangerously high serum levels, bilirubin traverses the intact blood–brain barrier slowly, requiring time for encephalopathy to occur, although deposition of bilirubin can be rapid if a surge in plasma unbound bilirubin is produced by administering a drug which competes with bilirubin for binding to albumin.3. There may be maturational changes in permeability both in the fetus and postnatally which protect the brain from bilirubin.4. Disruption or partial disruption of the blood–brain barrier by disease or hypoxic ischemic injury will facilitate transport of bilirubin/albumin into brain, but the relative affinities of albumin and target neurons will determine whether the tissue bilirubin load is sufficient for toxicity to occur.     

Induction of haem oxygenase-1 causes cortical non-haem iron increase in experimental pneumococcal meningitis: evidence that concomitant ferritin up-regulation prevents iron-induced oxidative damage

Desferrioxamine inhibits cortical necrosis in neonatal rats with experimental pneumococcal meningitis, suggesting that iron-induced oxidative damage might be responsible for neuronal damage. We therefore examined the spatial and temporal profile of changes in cortical iron and iron homeostatic proteins during pneumococcal meningitis. Infection was associated with a steady and global increase of non-haem iron in the cortex, particularly in neuronal cell bodies of layer II and V, and in capillary endothelial cells. The non-haem iron increase was associated with induction of haem oxygenase (HO)-1 in neurones, microglia and capillary endothelial cells, whereas HO-2 levels remained unchanged, suggesting that the non-haem iron increase might be the result of HO-1-mediated haem degradation. Indeed, treatment with the haem oxygenase inhibitor tin protoporphyrin (which completely blocked the accumulation of bilirubin detected in HO-1-positive cells) completely prevented the infection-associated non-haem iron increase. The same cells also displayed markedly increased ferritin staining, the increase of which occurred independently of HO activity. At the same time, no increase in DNA/RNA oxidation was observed in infected animals (as assessed by in situ detection of 8-hydroxy[deoxy]guanosine), strongly suggesting that ferritin up-regulation protected the brain from iron-induced oxidative damage. Thus, although pneumococcal meningitis leads to an increase of cortical non-haem iron, protective mechanisms up-regulated in parallel prevent iron-induced oxidative damage. Cortical damage does not appear to be a direct consequence of increased iron, therefore.     

An in vitro model of aneurysmal subarachnoid hemorrhage: oxidation of unconjugated bilirubin by cytochrome oxidase

Aneurysmal subarachnoid hemorrhage is a stroke subtype with high rates of mortality and morbidity. Cerebral vasospasm can lead to ischemic injury or death and is a common complication of aneurysmal subarachnoid hemorrhage, usually occurring 3-9 days afterwards. The cause of vasospasm is not known. Recently, there has been strong evidence that vasoactive oxidation products of bilirubin may be involved. Currently, the factors that lead to bilirubin oxidation are poorly characterized. In this study, we have designed an in vitro model of hemorrhagic stroke in order to investigate conditions that promote the oxidation of bilirubin to form vasoactive compounds. Using our model, we created a basic hematoma system of blood, CSF, and hemeoxygenase-1. We manipulated this system in various ways, incubated it and determined the concentration of vasoactive bilirubin oxidation products that resulted. Conditions where cytochrome oxidase was stimulated caused an increase bilirubin oxidation products (292.6 +/- 39.9 micromol/L respectively, vs. 79.3 +/- 1.3 micromol/L for the basic reaction, p < 0.05), which was attenuated by cyanide. Our data suggest that bilirubin oxidation products may be produced by oxidation(s) requiring an oxygen-utilizing enzyme like cytochrome oxidase.     

Elucidating the interaction of ticlopidine with serum albumin and its role in bilirubin displacement in vitro

Ticlopidine is an anti-platelet drug that functions as a P2Y₁₂ receptor antagonist. The present study provides a detailed characterization of interaction of ticlopidine with a model transport protein, bovine serum albumin (BSA) as well as an assessment of its bilirubin displacing ability using a multi-spectroscopic approach in combination with isothermal titration calorimetry. The value of binding constant determined using ITC studies was found to be 3.03 × 10³ M^?1 with a binding stoichiometry of approximately 1:1. Competitive site marker experiments indicate that ticlopidine binds to Sudlow site I, located in subdomain IIA of BSA. In addition, Circular dichroism and 3D fluorescence spectroscopy indicated structural and conformational changes in BSA on interaction with ticlopidine. Thermodynamic parameters suggested that the reaction was spontaneous, exothermic, entropically driven, and involved hydrophobic interactions. These results were well supported by those obtained through molecular docking studies. Additionally, the effect of ticlopidine on bilirubin and albumin interaction was evaluated using the peroxidase method as well as through fluorescence spectroscopy. Ticlopidine was found to displace bilirubin from serum albumin. Moreover, the binding constant of bilirubin–serum albumin interaction also decreased in presence of ticlopidine. The results indicated that ticlopidine is a competitive displacer of bilirubin in vitro and may contribute to the incidences hyperbilirubinemia associated with the usage of this drug.     

胆红素脑病SD乳鼠模型中脑水通道蛋白-4表达发生变化

神经细胞水肿是胆红素脑病（bilirubin encephalopathy,BE）发生发展过程中的重要病理变化。水通道蛋白-4（aquaporin-4,AQP4）的表达及分布异常与多种疾病所致细胞毒性脑水肿的发生发展具有密切联系。但胆红素脑病中AQP4的表达变化规律及其在病理进展中的作用尚不清楚。采用7日龄SD大鼠小脑延髓池注射胆红素溶液的方法,建立新生大鼠胆红素脑病模型。胆红素脑病模型根据胆红素作用时间的不同,分为12 h、24 h、48 h、72 h和7 d组。采用HE及尼氏染色,检测各新生大鼠脑组织的病理改变;应用透射电镜(TEM),检测胆红素作用24 h后,鼠脑组织超微结构的变化;应用免疫荧光及Western 印迹,检测 AQP4在脑组织中的表达变化。通过上述实验,以探讨AQP4的表达变化与胆红素所致脑损伤的关系。HE及尼氏染色结果显示,随着胆红素沉积时间的延长,神经细胞逐渐肿胀,细胞间隙增大,尼氏小体数量逐渐减少;电镜结果显示,胆红素脑病24 h后神经细胞线粒体出现肿胀;免疫荧光染色显示,24 h组AQP4的表达范围明显增加,其后表达范围逐渐减少,表达强度也随之减弱;Western 印迹结果显示,AQP4表达在不同时间点呈现先增高后降低的趋势,在24 h达到峰值（24 h组1.38 ± 0.11 vs 对照组0.87 ± 0.21, P＜0.05）,在之后的各时间点上,AQP4的表达呈现下降趋势,而72 h组与7 d组AQP4表达均低于48 h组（P＜0.05）,基本恢复到对照组的表达水平（P＞0.05）。上述结果提示,胆红素脑病中胆红素的毒性作用将引起AQP4表达量的改变,AQP4的表达变化与胆红素脑病中细胞毒性脑水肿的发生相关,并且可能在胆红素脑病脑损伤的进展中发挥作用。     

急性运动所致线粒体某些功能的改变及胆红素的保护作用

目的：探讨急性运动所致疲劳的机理以及胆红素的保护作用。方法：将Wistar大鼠随机分为对照组、运动组、运动恢复组、胆红素处理运动组、胆红素处理运动恢复组,共5组,分别灌胃1μmol/Kg体重的胆红素或生理盐水4周,负重（体重的5％）游泳2h后处死,测定有关指标。结果：急性运动后即刻大鼠排肠肌胞、线粒体Ca^2 含量明显升高,恢复12h后线粒体Ca^2 含量呈继续升高的趋势;线粒体C^a2 -Mg^2 -ATP酶、Ca^2 -ATP酶活性明显下降,12h后有所回升,胆红素处理后可以明显抑制这些指标的改变,但线粒体Mg^2 -ATP酶活性的变化在胆红素处理组和未处理组间无明显差异,均明显低于对照组,只是胆红素组的恢复相对较快。结论：生理浓度的胆红素可能通过抑制线粒体某些功能的改变而保护细胞名受急性运动所致的损伤,从而延缓疲劳的发生,加速恢复。     

不同病情高胆红素血症新生儿血清AST、IGF-1、NSE、CysC水平的表达及临床意义

摘要 目的：研究不同病情高胆红素血症新生儿血清谷草转氨酶（AST）、胰岛素样生长因子-1（IGF-1）、神经元特异性烯纯化酶（NSE）、胱抑素C（CysC）水平的表达及临床意义。方法：将我院从2017年1月～2018年12月收治的高胆红素血症新生儿316例作为研究组。按其病情分成轻度组152例、中度组105例以及重度组59例,另取同期健康新生儿100例作为对照组。比较四组新生儿血清AST、IGF-1、NSE、CysC、总胆红素（TSB）水平,分析上述各项指标的关系。此外,比较对照组与研究组的基线资料,分析新生儿高胆红素血症发病的影响因素。结果：轻度组、中度组、重度组血清AST、IGF-1、NSE、CysC、TSB水平均高于对照组,且中度组、重度组上述指标高于轻度组,重度组上述指标高于中度组（P＜0.05）。经Pearson相关性分析可得：高胆红素血症新生儿TSB水平与血清AST、IGF-1、NSE、CysC水平均呈正相关（P＜0.05）。研究组和对照组在母婴血型不合、产前使用催产素、围生期疾病以及TSB、AST、IGF-1、NSE、CysC方面对比差异均有统计学意义（P＜0.05）。经多因素Logistic回归分析可得：新生儿高胆红素血症发病的影响因素为产前使用催产素、围生期疾病以及TSB、AST、IGF-1、NSE、CysC（P＜0.05）。结论：随着高胆红素血症新生儿病情的加剧,血清AST、IGF-1、NSE、CysC水平均逐渐升高且均与血清TSB水平呈正相关,临床工作中可能通过联合检测上述血清学指标辅助评估高胆红素血症新生儿病情,且以上指标水平的升高会增加新生儿高胆红素血症的发病风险。     

中国人群肝功能检测指标全基因组关联分析研究

肝功能检测(liver function test, LFTs)指标是受遗传和环境影响的复杂性状,具有个体差异性。为系统性研究中国人群全基因组范围内单核苷酸多态性(single nucleotide polymorphism, SNP)与肝功能指标之间的联系,本研究利用英国生物银行(UK Biobank)中1653名中国人的基因分型数据和表型数据为研究对象,利用PLINK软件进行全关联分析研究(genome-wide association study, GWAS),发现229个SNP与中国人群血液中的总胆红素(total bilirubin, TB)相关,27个SNP与中国人群血液中碱性磷酸酶(alkaline phosphatase, ALP)相关,36个SNP与中国人群血液中的γ-谷氨酰转肽酶(γ-glutamyl transpeptidase, GGT)相关,1个SNP与中国人群血液中的门冬氨酸氨基转移酶(aspartate transaminase, AST)相关,最显著的位点中有11个位点是新的LFTs关联位点。通过功能基因组分析,发现这些位点的临床意义(如吉尔伯特综合征)...     

UDP-glucuronosyltransferase 1A1 (UGT1A1) gene haplotypes and their effect on serum bilirubin concentration in healthy Indian adults

The aim of the present study was to investigate the allele and genotype frequencies and haplotype structures of the variants in the UGT1A1 gene and their association with serum bilirubin levels in healthy adults. Total serum bilirubin levels were measured in 300 healthy adults (normal hematology and liver function test) and genotyping of seven SNPs was performed by PCR-RFLP, Gene Scan analysis and direct sequencing on the ABI Prism 310 Genetic Analyzer. Of the seven SNPs, four were found to be polymorphic and the frequencies of minor alleles were 0.336, 0.431, 0.353 and 0.066 for − 53(TA)7, − 3279G, − 3156A and 211A respectively. Individuals who carried the − 53(TA)7, − 3279G and − 3156A mutant alleles in homozygous or heterozygous states had significantly higher mean serum bilirubin levels. Five major promoter haplotypes were observed: − 53(TA)6/− 3279T/− 3156G was the most common haplotype, followed by − 53(TA)7/− 3279G/− 3156A, − 53(TA)6/− 3279G/− 3156G, − 53(TA)6/− 3279G/− 3156A and − 53(TA)7/− 3279T/− 3156G with an estimated frequency of 0.445, 0.230, 0.083, 0.065 and 0.050 respectively. Furthermore, the mutant haplotype (− 53(TA)7/− 3279G/− 3156A) was found to have a significant effect on bilirubin concentrations. Promoter polymorphisms and a common haplotype of the UGT1A1 gene are associated with serum bilirubin concentrations and could be a genetic risk factor for hyperbilirubinemia in Indians.