[A pathophysiological role of cytochrome p450 involved in production of reactive oxygen species].

Dysregulation of the production of reactive oxygen species (ROS) determines cellular function. Cytochrome P450s (CYPs) regulates ROS production and contributes to the process of cell death. This review summarizes our recent findings, focusing on the involvement of CYPs in pathophysiology induced by ROS.

Accumulation of cytochrome P450 induced by proteasome inhibition during cardiac ischemia.

Increasing evidence shows that cytochrome P450 (CYP) contributes to cardiac reperfusion injury. However, there have been few reports about the roles of CYPs in cardiac ischemia. The aim of the present study was to investigate the CYP expression and activity during ischemia using an in vivo rat model of myocardial infarction.

Sulfaphenazole attenuates myocardial cell apoptosis accompanied with cardiac ischemia-reperfusion by suppressing the expression of BimEL and Noxa.

We previously reported the administration of a potent cytochrome P450 inhibitor, sulfaphenazole (SPZ), to suppress oxidative stress and the extension of myocardial infarct size in a rat model of cardiac ischemia-reperfusion (I/R). The aim of this study was to investigate the effects of SPZ on the myocardial cell apoptosis induced by I/R in rats. I/R injury was evoked by ligation of the left anterior descending coronary artery for 1 h, followed by reperfusion for 3 h.

Contribution of reductase activity to quinone toxicity in three kinds of hepatic cells.

Two mechanisms have been proposed to explain quinone cytotoxicity: oxidative stress via the redox cycle, and the arylation of intracellular nucleophiles. The redox cycle is catalyzed by intracellular reductases, and therefore the toxicity of redox cycling quinone is considered to be closely associated with the reductase activity. This study examined the relationship between quinone toxicity and the intracellular reductase activity using 3 kinds of hepatic cells; rat primary hepatocytes, HepG2 and H4IIE.

Increased expression of c-Fos by extracellular signal-regulated kinase activation under sustained oxidative stress elicits BimEL upregulation and hepatocyte apoptosis.

We previously reported that the inhibition of catalase and glutathione peroxidase activities by treatment with 3-amino-1,2,4-triazole (ATZ) and mercaptosuccinic acid evoked sustained increases in the levels of reactive oxygen species and apoptosis in rat primary hepatocytes. Apoptosis was accompanied by increased expression of BimEL, following activation of extracellular signal-regulated kinase. The aim of this study was to characterize the mechanism underlying hepatocyte apoptosis by identifying the transcription factor that induces BimEL expression.

Dual regulation of hepatocyte apoptosis by reactive oxygen species: Increases in transcriptional expression and decreases in proteasomal degradation of BimEL.

Reactive oxygen species (ROS) have a fundamental role in intracellular signaling transduction. We show here that time-dependent extracellular signal-regulated kinase (ERK) activation due to inactivation of protein tyrosine phosphatases was closely linked to hepatocyte apoptosis under sustained exposure to ROS, which is produced through inhibition of ROS-scavenging enzymes. We found, for the first time, that active ERK transcriptionally increased BimEL expression among seven proteins of the Bcl-2 family.

Crucial role of cytochrome P450 in hepatotoxicity induced by 2,3-dimethoxy-1,4-naphthoquinone in rats.

Quinone toxicity is induced by two principal mechanisms: arylation/alkylation and a redox cycle. We have previously shown that increases in intracellular levels of superoxide anion and cell death induced by 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), a redox cycling quinone, are enhanced by pretreatment of rat primary hepatocytes with cytochrome P450 inhibitors. This indicates a novel interaction of quinones with cytochrome P450, and is thus worthy of further investigation using an in vivo model.

Effects of sulfaphenazole derivatives on cardiac ischemia-reperfusion injury: association of cytochrome P450 activity and infarct size.

Cardiac ischemia-reperfusion injury is evoked by reactive oxygen species (ROS). We previously reported that sulfaphenazole (SPZ) attenuated cardiac ROS levels and ischemia-reperfusion injury in rats. SPZ has distinct two actions: a) elimination of ROS and b) inhibition of cytochrome P450 (CYP) that is responsible for ROS production.

Sustained contraction and endothelial dysfunction induced by reactive oxygen species in porcine coronary artery.

A combination of purine and xanthine oxidase (XOD) dose-dependently elicited sustained contraction of porcine coronary arterial rings and resulted in increased concentrations of superoxide anions and hydrogen peroxide. These contractile responses appeared, with a delay, after the application of purine and XOD, used as a reactive oxygen species (ROS)-generating system. Coronary arteries precontracted with prostaglandin F(2alpha) failed to relax in response to substance P after exposing the arterial preparation to this ROS-generating system.

Critical role of exposure time to endogenous oxidative stress in hepatocyte apoptosis.

We have previously shown that inhibition of catalase and glutathione peroxidase activities in rat primary hepatocytes by 3-amino-1,2,4-triazole (ATZ) and mercaptosuccinic acid (MS) results in sustained oxidative stress, followed by apoptosis. To examine the effects of duration of oxidative stress, ATZ and MS were removed from culture medium at 3, 6 and 9 h after treatment with both inhibitors. Oxidative stress was induced for periods of time by ATZ and MS exposures in primary hepatocytes.

Enhancement of DMNQ-induced hepatocyte toxicity by cytochrome P450 inhibition.

Two mechanisms have been proposed to explain quinone cytotoxicity: oxidative stress via the redox cycle and the arylation of intracellular nucleophiles. As the redox cycle is catalyzed by NADPH cytochrome P450 reductase, cytochrome P450 systems are expected to be related to the cytotoxicity induced by redox-cycling quinones. Thus, we investigated the relationship between cytochrome P450 systems and quinone toxicity for rat primary hepatocytes using an arylator, 1,4-benzoquinone (BQ), and a redox cycler, 2,3-dimethoxy-1,4-naphthoquinone (DMNQ).

Involvement of endonuclease G in nucleosomal DNA fragmentation under sustained endogenous oxidative stress.

We have previously shown that inhibition of catalase and glutathione peroxidase activities by 3-amino-1,2,4-triazole (ATZ) and mercaptosuccinic acid (MS), respectively, in rat primary hepatocytes caused sustained endogenous oxidative stress and apoptotic cell death without caspase-3 activation. In this study, we investigated the mechanism of this apoptotic cell death in terms of nucleosomal DNA fragmentation. Treatment with ATZ+MS time-dependently increased the number of deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL)-positive nuclei from 12 h, resulting in clear DNA laddering at 24 h.

Primary hepatocyte apoptosis is unlikely to relate to caspase-3 activity under sustained endogenous oxidative stress.

We previously showed that inhibition of catalase and glutathione peroxidase activities in rat primary hepatocytes by 3-amino-1,2,4-triazole (ATZ) and mercaptosuccinic acid (MS) results in endogenous oxidative stress and apoptosis. For the present study, we determined whether this apoptosis involved activation of caspase-3, which is known to execute apoptosis in many cell types. ATZ and MS increased levels of reactive oxygen species (ROS) from 3-9 h, just before the onset of chromatin condensation (apoptosis) and decreases in protein thiols.