Role of heme in cytochrome P450 transcription and function in mice treated with lead acetate.
Role of heme in cytochrome P450 transcription and function in mice treated with lead acetate.
复制标题
血红素在醋酸铅治疗小鼠细胞色素 P450 转录和功能中的作用。
作者：
R. Jover;R. Lindberg;U. Meyer
在实验动物和人类中，遗传性和获得性血红素缺乏与细胞色素P450（P450）功能受损有关。假设的解释是减少血红素供应的饱和载脂蛋白P450或血红素的P450基因转录的要求。我们研究了血红素缺乏对醋酸铅（75 mg Pb 2 +/kg腹腔注射）处理的C57 BL/6小鼠P450功能、mRNA和转录的影响。铅导致血浆中δ-氨基乙酰丙酸水平升高（> 30倍），肝脏色氨酸-2，3-双加氧酶的血红素饱和度降低（15 +/- 4%对对照组的血红素饱和度33 +/- 6%; p < 0.001），这与血红素合成的有效抑制和游离血红素库的消耗一致。P450依赖活性（7-乙氧基香豆素O-去乙基化和烷氧基试卤灵的O-去烷基化）在注射铅后20小时内逐渐下降到对照水平的56-69%。（4 mg/kg腹腔注射）至73-93%的对照活性（对于7-乙氧基香豆素O-脱乙基，p < 0.01;对于烷氧基试卤灵的O-脱烷基，p < 0.05）。在相同的实验条件下，通过半定量逆转录聚合酶链反应测定的P450 Cyp 3a 11的mRNA水平，也下降后铅注射到45%的控制水平。这种减少占Cyp 3a 11基因转录的抑制，表现出在铅注射后12小时分离的肝细胞核的径流实验。血红素没有恢复Cyp 3a 11在细胞核中以及在体内的mRNA水平或转录活性。我们的结论是，铅中毒中P450的减少是两种不同机制的结果：（a）与血红素无关的机制，其中铅减少P450转录;和（B）依赖于血红素的机制，其中铅抑制血红素合成，这导致P450和/或apo-P450含量的血红素饱和度降低。
Genetic and acquired heme deficiencies are associated with impaired cytochrome P450 (P450) function in experimental animals and in humans. The hypothetical explanations have been either a decreased supply of heme for saturation of apo-P450 or a requirement of heme for P450 gene transcription. We investigated the effect of heme deficiency on P450 function, mRNA, and transcription in C57BL/6 mice treated with lead acetate (75 mg of Pb2+/kg intraperitoneally). Lead caused an increase in delta-aminolevulinic acid levels in plasma (> 30-fold) and a decrease in the heme saturation of hepatic tryptophan-2,3-dioxygenase (15 +/- 4% versus 33 +/- 6% of heme saturation in controls; p < 0.001), which is consistent with an effective inhibition of heme synthesis and depletion of the free heme pool. P450-dependent activities (7-ethoxycoumarin O-deethylation and O-dealkylation of alkoxyresorufins) decreased progressively after lead injection to 56-69% of control levels within 20 hr. This effect was partially counteracted by injection of hematin (4 mg/kg intraperitoneally) to 73-93% of control activities (p < 0.01 for 7-ethoxycoumarin O-deethylation and p < 0.05 for O-dealkylation of alkoxyresorufins). The mRNA levels of the P450 Cyp3a11, measured by semiquantitative reverse transcription-polymerase chain reaction under the same experimental conditions, also decreased after lead injection to 45% of control levels. This decrease was accounted for by inhibition of Cyp3a11 gene transcription, as demonstrated by run-off experiments in liver nuclei isolated 12 hr after lead injection. Hematin did not restore the mRNA levels or the transcriptional activity of Cyp3a11 in nuclei as well as in vivo. We conclude that the decrease of P450 in lead poisoning is a consequence of two different mechanisms: (a) a mechanism unrelated to heme, in which lead decreases P450 transcription; and (b) a mechanism dependent on heme, in which lead inhibits heme synthesis, and this results in a decreased heme saturation of P450 and/or apo-P450 content.