Hansen T W, Allen J W
Department of Anesthesia and Critical Care Medicine, University of Pittsburgh, Children's Hospital of Pittsburgh, Pennsylvania 15213-2583, USA.
Biochem Mol Med. 1997 Apr;60(2):155-60. doi: 10.1006/bmme.1996.2565.
Bilirubin is oxidized by brain mitochondrial membranes at a rate which may contribute significantly to clearance of bilirubin from the brain. Neurons appear to be more sensitive to bilirubin toxicity than glial cells. Clinical experience has suggested that sensitivity to bilirubin neurotoxicity may be greater in the neonate than later in life. We hypothesized that the ability to oxidize bilirubin would be lower in mitochondrial membranes from a pure neuronal compared to a mixed glial/neuronal source, and lower in immature than more mature brains. Mitochondria of synaptosomal and nonsynaptosomal origin were obtained from young rat brains by differential centrifugation in sucrose gradients. Synaptosomes were lysed by hypoosmotic treatment, and mitochondria were ruptured by sonication. The change in optical density of a bilirubin solution at 440 nm was measured over time following addition of the membrane suspension. The rate of bilirubin oxidation was significantly higher in nonsynaptic than in synaptic mitochondrial membranes [99.1 +/- 42.3 (mean +/- SD) vs 69.9 +/- 30.9 pmol/ min/mg protein, t = 4.835, P = 0.0003]. "Crude" mitochondrial membranes were obtained by differential centrifugation in sucrose from the forebrains of rats of 7, 14, and 21 days postnatal age as well as adults, and from rabbits of 1 and 7 days postnatal age as well as adults. In both species the rates of bilirubin oxidation increased significantly with postnatal age (rats: F = 55.3, P < 0.0001; rabbits: F = 101, P < 0.0001). Mitochondrial membranes from a pure neuronal source oxidize bilirubin at a significantly lower rate than membranes from a mixed glial/neuronal source. This suggests that neurons may be less able to detoxify bilirubin locally and thus might contribute to the apparent higher sensitivity to bilirubin toxicity in these cells vs glia. Similarly, the lower bilirubin-oxidizing ability of mitochondrial membranes from immature brains seems compatible with the clinical impression of increased vulnerability to bilirubin neurotoxicity in the newborn.
胆红素被脑线粒体膜氧化的速率可能对胆红素从脑中清除有显著贡献。神经元似乎比神经胶质细胞对胆红素毒性更敏感。临床经验表明，新生儿对胆红素神经毒性的敏感性可能比生命后期更高。我们推测，与混合的神经胶质/神经元来源相比，纯神经元来源的线粒体膜氧化胆红素的能力会更低，且未成熟脑的该能力低于更成熟的脑。通过在蔗糖梯度中进行差速离心，从幼鼠脑中获得突触体和非突触体来源的线粒体。通过低渗处理裂解突触体，通过超声处理使线粒体破裂。加入膜悬液后，随时间测量胆红素溶液在440nm处的光密度变化。非突触线粒体膜中胆红素氧化速率显著高于突触线粒体膜[99.1±42.3（平均值±标准差）对69.9±30.9pmol/分钟/毫克蛋白，t = 4.835，P = 0.0003]。通过在蔗糖中差速离心，从出生后7天、14天、21天的大鼠以及成年大鼠的前脑，以及出生后1天、7天的兔子以及成年兔子的前脑中获得“粗制”线粒体膜。在两个物种中，胆红素氧化速率均随出生后年龄显著增加（大鼠：F = 55.3，P < 0.0001；兔子：F = 101，P < 0.0001）。纯神经元来源的线粒体膜氧化胆红素的速率明显低于混合神经胶质/神经元来源的膜。这表明神经元可能在局部对胆红素解毒的能力较低，因此与神经胶质细胞相比，这些细胞对胆红素毒性的明显更高敏感性可能与之有关。同样，未成熟脑线粒体膜较低的胆红素氧化能力似乎与新生儿对胆红素神经毒性易感性增加的临床印象相符。
