细胞色素P450氧化酶在胆红素听觉核团特异性及年龄相关性损伤机制中的作用

Hyperbilirubinemia is one of the most common conditions requiring treatment in the newborn period. Bilirubin encephalopathy, a devastating, chronic disabling neurological disorder, is severe sequela of significant hyperbilirubinemia. Clinical impression showed an increased vulnerability to bilirubin neurotoxicity during development. Selected areas such as auditory pathways were recognized as being particularly vulnerable to bilirubin neurotoxicity. However, the mechanisms of age dependence and region-specific of bilirubin are still to be determined. Previous studies showed that there is little evidence to suggest developmental and regional differences in bilirubin uptake and tissue binding in the CNS. However, the bilirubin clearance by oxidation was significantly increased with postnatal age and there were regional differences. Thus, bilirubin oxidation may be the determination of the age dependence and region-specific of bilirubin neurotoxicity. Previous study showed that the ability of mitochondrial membranes to oxidize bilirubin was inhibited by inhibitor of cytochrome P450 oxidases (CYP), indicating that the bilirubin oxidizing activity in brain is CYP dependent. In this study, we expect to observe the differences of the expression of CYP in both bilirubin sensitivity and bilirubin non-sensitivity regions during different developmental periods, and to regulate the CYP expression. We aimed to make it clear about the role of CYP in the mechanisms of age dependence and region-specific of bilirubin neurotoxicity.

高胆红素血症是新生儿最常见的临床疾病之一，胆红素脑病是其主要并发症。中枢神经系统对胆红素毒性的敏感性随发育而降低，且特定核团如听觉核团对胆红素高度敏感。目前，胆红素毒性年龄相关性及核团特异性的发生机制不明。既往研究显示，胆红素在脑内的摄取、结合并无年龄及核团差异，而胆红素的清除代谢随发育而增强并具有核团差异性，因此，我们推测胆红素代谢酶在发育过程中的表达差异及核团分布差异是决定胆红素毒性年龄相关性及核团特异性的关键。既往研究发现细胞色素P450氧化酶(CYP)抑制剂能显著抑制神经元线粒体对胆红素的氧化代谢，提示CYP可能是胆红素在脑内代谢的主要氧化酶。本研究拟通过观察不同发育阶段CYP在听觉敏感核团及非敏感核团中的表达差异，并对CYP表达进行调控,明确CYP在胆红素代谢及胆红素毒性年龄相关性及听觉核团特异性机制中的作用。本项研究有望为探索胆红素脑病听觉损伤靶向性治疗方法提供可靠的理论依据。

高胆红素血症是新生儿最常见的临床疾病之一，胆红素脑病是其主要并发症。胆红素的中枢神经毒性随年龄增加而减轻，且特定核团如听觉核团对胆红素高度敏感。目前，胆红素脑病年龄相关性及核团特异性的发生机制不明。既往研究显示，胆红素在脑内的摄取、绑定并无年龄及核团差异，而胆红素的清除代谢随年龄增加而增加并具有核团差异性，提示胆红素代谢酶在发育过程中的表达差异及核团分布差异是决定胆红素毒性年龄相关性及核团特异性的关键。既往研究发现细胞色素P450氧化酶(CYP)抑制剂能显著抑制神经元线粒体对胆红素的氧化代谢，提示CYP可能是负责胆红素在中枢神经系统代谢的主要氧化酶。本研究发现脑内CYP含量明显低于肝脏，且均伴随发育过程表达增强，然而在胆红素敏感核团、非敏感核团中无明显特异性差异。进一步的HPLC研究结果发现，生理情况下中枢神经系统中的CYP 并不能有效代谢胆红素，提示CYP并非胆红素核团差异性及年龄相关性的原因。随后我们利用电生理方法证实在耳蜗核神经元中GABA/甘氨酸受体发育早期为去极化性，随着神经元发育发育成熟转变为抑制性，并发现发育早期去极化性GABA/甘氨酸能突触传递参与胆红素毒性机制。本项目解答了胆红素毒性研究中的重要问题，提示GABA/甘氨酸能突触传递而并非CYP介导的代谢可能是胆红素年龄相关性及核团差异性的原因。从而为进一步探索胆红素脑病靶向性治疗方法提供重要的理论依据。