Takemura S, Minamiyama Y, Imaoka S, Funae Y, Hirohashi K, Inoue M, Kinoshita H
Department of Surgery, Osaka City University Medical School, Osaka, Japan.
J Hepatol. 1999 Jun;30(6):1035-44. doi: 10.1016/s0168-8278(99)80257-8.
BACKGROUND/AIMS: Although the activity of the liver in metabolizing and eliminating various drugs decreases in endotoxemia, the mechanism remains to be elucidated. The generation of nitric oxide by the inducible type of nitric oxide synthase increases in endotoxemia. Nitric oxide readily reacts with heme proteins such as cytochrome P450 that metabolize various compounds, including steroids and eicosanoids. The purpose of this study was to determine the effect of nitric oxide on the function of hepatic cytochrome P450 in endotoxemic rats.
To determine the dynamic aspects of nitric oxide metabolism, hepatic levels of the inducible type of nitric oxide synthase and heme-iron nitrosyl complexes, and plasma levels of nitrite and nitrate were determined in rats before and after intravenous administration of lipopolysaccharide. Changes in the levels of P450 isoforms and testosterone hydroxylation activity in hepatic microsomes were also determined. To evaluate in vivo CYP3A2 activity, midazolam sleep time was measured.
When lipopolysaccharide increased the hepatic inducible type of nitric oxide synthase and plasma levels of nitric oxide metabolites, the intensity of low-spin signal of electron spin resonance responsible for the ferric form of P450 decreased with a concomitant increase in heme-iron nitrosyl complexes in the liver. Lipopolysaccharide-related nitric oxide generation is followed by an early decrease in the levels of cytochrome P450 and of testosterone hydroxylation activity in liver microsomes. Midazolam sleep time was prolonged by lipopolysaccharide. All these early changes were prevented by the inhibitor of nitric oxide synthase, N(G)-iminoethyl-L-ornithine. Moreover, lipopolysaccharide suppressed the gene expression of CYP2C11 and CYP3A2. Decreases in levels of cytochrome P450 and their mRNAs were more pronounced at 24 h after LPS administration, but apparently they are NO-independent.
These results suggest that lipopolysaccharide-induced modulation of cytochrome P450 may occur via the interplay of two different mechanisms and that, especially in the early phase, nitric oxide-dependent inhibition is more important.
背景/目的：尽管在内毒素血症中肝脏代谢和清除各种药物的活性降低，但其机制仍有待阐明。在内毒素血症中，诱导型一氧化氮合酶产生的一氧化氮增加。一氧化氮很容易与血红素蛋白如细胞色素P450发生反应，细胞色素P450可代谢包括类固醇和类花生酸在内的各种化合物。本研究的目的是确定一氧化氮对内毒素血症大鼠肝脏细胞色素P450功能的影响。
为了确定一氧化氮代谢的动态变化，在大鼠静脉注射脂多糖前后，测定肝脏中诱导型一氧化氮合酶和血红素铁亚硝酰复合物的水平，以及血浆中亚硝酸盐和硝酸盐的水平。还测定了肝微粒体中细胞色素P450同工型水平和睾酮羟化活性的变化。为了评估体内CYP3A2活性，测量了咪达唑仑睡眠时间。
当脂多糖增加肝脏诱导型一氧化氮合酶和血浆一氧化氮代谢物水平时，负责细胞色素P450铁离子形式的电子自旋共振低自旋信号强度降低，同时肝脏中血红素铁亚硝酰复合物增加。脂多糖相关的一氧化氮生成之后，肝微粒体中细胞色素P450水平和睾酮羟化活性早期降低。脂多糖可延长咪达唑仑睡眠时间。一氧化氮合酶抑制剂N(G)-亚氨基乙基-L-鸟氨酸可防止所有这些早期变化。此外，脂多糖抑制CYP2C11和CYP3A2的基因表达。脂多糖给药后24小时，细胞色素P450水平及其mRNA的降低更为明显，但显然它们与一氧化氮无关。
这些结果表明，脂多糖诱导的细胞色素P450调节可能通过两种不同机制的相互作用发生，特别是在早期阶段，一氧化氮依赖性抑制更为重要。
