Expression of cytochrome P-450s and glutathione S-transferases in the rat liver during water deprivation: effects of glucose supplementation

Metabolic responses to water deprivation in C57BL/6J mice using a proton nuclear magnetic resonance-based metabonomics approach

¹H NMR-based metabonomics approach is effective for elucidating underlying mechanisms response or adaption to water deprivation in mammals. Metabolic relevance of differential compounds in response of C57BL/6J mice to water deprivation was discussed.

Effect of enzyme inducers and inhibitors on the pharmacokinetics of oltipraz in rats

A series of in-vitro and in-vivo experiments, using various inducers and inhibitors of hepatic microsomal cytochrome P450 (CYP) isozymes, was conducted to study oltipraz pharmacokinetics in rats. In in-vivo studies, oltipraz at a dose of 10 mg kg−1 was administered intravenously to rats. In rats pretreated with SKF 525-A (a nonspecific CYP isozyme inhibitor in rats; n = 9), the time-averaged total body clearance (CL) of oltipraz was significantly slower (56.6% decrease) than that in untreated rats (n = 9). This indicated that oltipraz is metabolized via CYP isozymes in rats. Hence, various enzyme inducers or inhibitors were used in in-vitro and in-vivo studies in rats. In rats pretreated with 3-methylcholanthrene (n = 9 and 8 for untreated and treated groups, respectively), phenobarbital (n = 7 and 10 for untreated and treated groups, respectively) or dexamethasone (n = 7 and 12 for untreated and treated groups, respectively) (main inducers of CYP1A1/2, 2B1/2 and 3A1/2 in rats, respectively), the CL values were significantly faster (38.4, 94.4 and 33.6% increase, respectively). In rats pretreated with sulfaphenazole (n = 8 and 9 for untreated and treated groups, respectively), quinine (n = 7 and 9 for untreated and treated groups, respectively) or troleandomycin (n = 8 and 9 for untreated and treated groups, respectively) (main inhibitors of CYP2C11, 2D1 and 3A1/2 in rats, respectively), the CL values were significantly slower (31.0, 27.6 and 36.3% decrease, respectively). The in-vivo results with various enzyme inhibitors correlated well with the in-vitro intrinsic clearance for disappearance of oltipraz (CLint) (n = 5, each). The above data suggested that oltipraz could be metabolized in male rats mainly via CYP1A1/2, 2B1/2, 2C11, 3A1/2 and 2D1.

Faster clearance of omeprazole in rats with acute renal failure induced by uranyl nitrate: contribution of increased expression of hepatic cytochrome P450 (CYP) 3A1 and intestinal CYP1A and 3A subfamilies

It has been reported that omeprazole is mainly metabolized via hepatic cytochrome P450 (CYP) 1A1/2, CYP2D1 and CYP3A1/2 in male Sprague-Dawley rats, and the expression of hepatic CYP3A1 is increased in male Sprague-Dawley rats with acute renal failure induced by uranyl nitrate (U-ARF rats). Thus, the metabolism of omeprazole would be expected to increase in U-ARF rats. After intravenous administration of omeprazole (20 mgkg−1) to U-ARF rats, the area under the plasma concentration-time curve from time zero to infinity (AUC) was significantly reduced (371 vs 494 μg min mL−1), possibly due to the significantly faster non-renal clearance (56.6 vs 41.2 mL min−1 kg−1) compared with control rats. This could have been due to increased expression of hepatic CYP3A1 in U-ARF rats. After oral administration of omeprazole (40 mg kg−1) to U-ARF rats, the AUC was also significantly reduced (89.3 vs 235 μg min mL−1) compared with control rats. The AUC difference after oral administration (62.0% decrease) was greater than that after intravenous administration (24.9% decrease). This may have been primarily due to increased intestinal metabolism of omeprazole caused by increased expression of intestinal CYP1A and 3A subfamilies in U-ARF rats, in addition to increased hepatic metabolism.

Time-dependent effects of Klebsiella pneumoniae endotoxin on the pharmacokinetics of chlorzoxazone and its main metabolite, 6-hydroxychlorzoxazone, in rats: restoration of the parameters in 96 hour in KPLPS rats to control levels

It has been reported that chlorzoxazone (CZX) was primarily metabolized via hepatic Cyp2e1 to form 6-hydroxychlorzoxazone (OH-CZX) in rats, and the activity of aniline hydroxylase (a Cyp2e1 marker) in the liver was significantly decreased in rats at 24 h after pretreatment with lipopolysaccharide derived from Klebsiella pneumoniae (24 h KPLPS rats), whereas the levels were not changed at 2 h and 96 h in the KPLPS rats. Thus, the time-dependent pharmacokinetic parameters of CZX and OH-CZX were evaluated after the intravenous administration of CZX (20 mg/kg) to control rats, and the 2 h, 24 h and 96 h KPLPS rats along with the time-dependent changes in the protein expression of hepatic Cyp2e1. After the intravenous administration of CZX to 24 h KPLPS rats, the AUC(0-2 h) of OH-CZX and AUC(OH-CZX, 0-2 h)/AUC(CZX) were significantly smaller (by 40.5% and 71.2%, respectively) than those of controls due to the significant decrease (by 75.3%) in the protein expression of hepatic Cyp2e1. However, in 96 h KPLPS rats, the pharmacokinetic parameters of both CZX and OH-CZX were unchanged compared with controls due to the restoration of the protein expression of hepatic Cyp2e1 to control levels. These observations highlighted the existence of the time-dependent effects of KPLPS on the pharmacokinetics of CZX and OH-CZX in rats.

Pharmacokinetics of oltipraz in diabetic rats with liver cirrhosis

BACKGROUND AND PURPOSE

The incidence of diabetes mellitus is increased in patients with liver cirrhosis. Oltipraz is currently in trials to treat patients with liver fibrosis and cirrhosis induced by chronic hepatitis types B and C and is primarily metabolized via hepatic cytochrome P450 isozymes CYP1A1/2, 2B1/2, 2C11, 2D1 and 3A1/2 in rats. We have studied the influence of diabetes mellitus on pharmacokinetics of oltipraz and on expression of hepatic, CYP1A, 2B1/2, 2C11, 2D and 3A in rats with experimental liver cirrhosis.

EXPERIMENTAL APPROACH

Oltipraz was given intravenously (10 mg x kg(-1)) or orally (30 mg x kg(-1)) to rats with liver cirrhosis induced by N-dimethylnitrosamine (LC rats) or with diabetes, induced by streptozotocin (DM rats) or to rats with both liver cirrhosis and diabetes (LCD rats) and to control rats, and pharmacokinetic variables measured. Protein expression of hepatic CYP1A, 2B1/2, 2C11, 2D and 3A was measured using Western blot analysis.

KEY RESULTS

After i.v. or p.o. administration of oltipraz to LC and DM rats, the AUC was significantly greater and smaller, respectively, than that in control rats. In LCD rats, the AUC was that of LC and DM rats (partially restored towards control rats). Compared with control rats, the protein expression of hepatic CYP1A increased, that of CYP2C11 and 3A decreased, but that of CYP2B1/2 and 2D was not altered in LCD rats.

CONCLUSIONS AND IMPLICATIONS

In rats with diabetes and liver cirrhosis, the AUC of oltipraz was partially restored towards that of control rats.

Effects of water deprivation on drug pharmacokinetics: correlation between drug metabolism and hepatic CYP isozymes

Male Sprague-Dawley rats deprived of water for 72 h (a rat model of dehydration) showed no change in protein expression of the hepatic microsomal cytochrome P450 (CYP) 1A2, 2B1/2, 2C11, or 3A1/2, but an increase in protein expression (3-fold) and mRNA level (2.6-fold) of CYP2E1. Glucose feeding instead of food normalized CYP2E1 protein expression during dehydration. Here, we review how dehydration can change the pharmacokinetics of drugs reported in the literature via changing CYP isozyme levels. We also discuss how dehydration changes the pharmacokinetics of drugs that are metabolized via renal DHP-I, or are mainly excreted in the urine and bile, and form conjugates.

Effects of water deprivation on the pharmacokinetics of theophylline and one of its metabolites, 1,3-dimethyluric acid, after intravenous and oral administration of aminophylline to rats

It has been reported that the expressions of hepatic microsomal cytochrome P450 (CYP) 1A1/2, 2B1/2 and 3A1/2 were not changed in rats with water deprivation for 72 h (rat model of dehydration) compared with the controls. It has been also reported that 1,3-dimethyluric acid (1,3-DMU) was formed from theophylline via CYP1A1/2 in rats. Hence, it could be expected that the formation of 1,3-DMU could be comparable between the two groups of rats. As expected, after both intravenous and oral administration of theophylline at a dose of 5 mg/kg to the rat model of dehydration, the AUC of 1,3-DMU was comparable to the controls. After both intravenous and oral administration of theophylline to the rat model of dehydration, the Cl(r) of both theophylline and 1,3-DMU was significantly slower than the controls. This could be due to significantly smaller urinary excretions of both theophylline and 1,3-DMU since the AUC of both theophylline and 1,3-DMU were comparable between the two groups of rats. The smaller urinary excretion of both theophylline and 1,3-DMU could be due to urine flow rate-dependent timed-interval renal clearance of both theophylline and 1,3-DMU in rats.

Effects of water deprivation on the pharmacokinetics of metformin in rats

It was reported that metformin was mainly metabolized via hepatic CYP2C11, 2D1 and 3A1/2 in rats, and in a rat model of dehydration, the expressions of hepatic CYP2C11 and 3A1/2 were not changed. Hence, it could be expected that the Cl(nr) of metformin is comparable between two groups of rats if the contribution of CYP2D1 in the rat model of dehydration is not considerable. It was also reported that the timed-interval renal clearance of metformin was dependent on the urine flow rate in rats. In the rat model of dehydration, the 24 h urine output was significantly smaller than in the controls. Hence, the urinary excretion of metformin was expected to be smaller than the controls. The above expectations were proven as follows. After intravenous administration of metformin (100 mg/kg) to the rat model of dehydration, the Cl(nr) were comparable between the two groups of rats. After both intravenous and oral administration of metformin (both 100 mg/kg) to the rat model of dehydration, the 24 h urinary excretion of the drug was significantly smaller than in the controls. After oral administration of metformin to the rat model of dehydration, the AUC was significantly greater (99.2% increase) than the controls.

Effects of glucose supplementation on the pharmacokinetics of intravenous chlorzoxazone in rats with water deprivation for 72 h

It was reported that in rats with water deprivation for 72 h with food (dehydration rat model), the expression of CYP2E1 was 3-fold induced with an increase in mRNA level and glucose supplementation instead of food during 72-h water deprivation (dehydration rat model with glucose supplementation) inhibited the CYP2E1 induction in dehydration rat model. It was also reported that chlorzoxazone (CZX) is metabolized to 6-hydroxychlorzoxazone (OH-CZX) mainly via CYP2E1 in rats. Hence, the effects of glucose supplementation on the pharmacokinetics of CZX and OH-CZX were investigated after intravenous administration of CZX at a dose of 25 mg/kg to control male Sprague-Dawley rats and dehydration rat model and dehydration rat model with glucose supplementation. Based on the above mentioned results of CYP2E1, it could be expected that increased formation of OH-CZX in dehydration rat model could decrease in dehydration rat model with glucose supplementation. This was proven by the following results. In dehydration rat model with glucose supplementation, the AUC of OH-CZX was significantly smaller (1900 versus 1050 microg min/ml), AUC(OH-CZX)/AUC(CZX) ratio was considerably smaller (105 versus 34.3%), C(max) was significantly lower (20.6 versus 8.08 microg/ml), total amount excreted in 24-h urine as unchanged OH-CZX was significantly smaller (62.3 versus 42.7% of intravenous dose of CZX), and in vitro V(max) (2.18 versus 1.20 nmol/min/mg protein) and CL(int) (0.0285 versus 0.0171 ml/min/mg protein) were significantly slower than those in dehydration rat model.

Effects of water deprivation for 72 hours on the pharmacokinetics of DA-7867, a new oxazolidinone, in rats

The pharmacokinetic parameters of DA-7867 were compared after intravenous and oral administration at a dose of 10 mg/kg in control rats and in rats with water deprivation for 72 h (rat model of dehydration). After intravenous administration in the rat model of dehydration, the Cl(nr) (0.654 versus 0.992 ml/min/kg) and Cl(r) (0.0273 versus 0.0784 ml/min/kg) values were significantly slower than in the controls. The slower Cl(nr) could be due mainly to a significantly smaller total amount of unchanged DA-7867 recovered from the gastrointestinal tract at 24 h (GI(24 h): 5.16% versus 9.21% of intravenous dose) due to impaired liver function in the rat model of dehydration. The slower Cl(r) could be due mainly to a significantly smaller 24 h urinary excretion of unchanged drug (Ae(0-24 h): 4.41% versus 7.75% of intravenous dose) due to urine flow rate-dependent Cl(r) of DA-7867 in the rat model of dehydration. Hence, the Cl was significantly slower in the rat model of dehydration (0.677 versus 1.07 ml/min/kg). After intravenous administration in the rat model of dehydration, the V(ss) of DA-7867 was significantly smaller than in the controls (396 versus 506 ml/kg) due mainly to significantly smaller free (unbound to plasma proteins) fractions of DA-7867 in plasma (6.90% versus 29.2%) in the rat model of dehydration. After oral administration in the rat model of dehydration, the AUC was significantly greater than that in controls (10800 versus 7060 microg min/ml) due mainly to a significantly smaller Ae(0-24 h) than in controls (3.50% and 6.17% of oral dose).

Pharmacokinetics of omeprazole in rats with water deprivation for 72 hours

Dehydration can occur by excessive sweating, polyuria, severe diarrhea and hyperthermia. Previous studies reported that the expressions of CYP1A1/2 and 3A1(23)/2 were not changed in male Sprague-Dawley rats with 72 h water deprivation (dehydrated rats), and that the metabolism of omeprazole is mainly catalysed via CYP1A1/2, 2D1 and 3A23/2 in rats. Hence, it could be expected that the hepatic metabolism of omeprazole would not be changed considerably in dehydrated rats, if the contribution of CYP2D1 to the metabolism of omeprazole in dehydrated rats is not considerable. Therefore, the pharmacokinetics of omeprazole were compared after intravenous (20 mg/kg) and oral (40 mg/kg) administration in control rats and in dehydrated rats. After intravenous administration, the time-averaged nonrenal clearance (Cl(nr)) values of omeprazole were comparable between the two groups of rats. This could be supported by comparable in vitro intrinsic clearance (Cl(int)) values for the disappearance of omeprazole in rat hepatic microsomes and the comparable free (unbound to plasma proteins) fractions of omeprazole in plasma in the two groups of rats. After oral administration, the AUC values of omeprazole were also comparable in the two groups of rats. The above data suggest that the dehydration state did not affect considerably the pharmacokinetics of omeprazole in rats.

Pharmacokinetics of oltipraz after intravenous and oral administration in rats with dehydration for 72 hours

Pharmacokinetic parameters of oltipraz were compared after intravenous and oral administration at a dose of 30 mg/kg to control rats and rats with water deprivation for 72 h (rats with dehydration). The plasma protein binding of oltipraz was measured in both groups of rats using an equilibrium dialysis technique. The concentrations of oltipraz were measured by the reported HPLC analysis. After intravenous administration, the total area under the plasma concentration-time curve from time zero to time infinity (AUC), terminal half-life, time-averaged total body and nonrenal clearances, and apparent volume of distribution at steady state were not significantly different between the two groups of rats. However, after oral administration to rats with dehydration, the AUC was significantly smaller than that in control rats (180 versus 316 microg min/ml) mainly due to decrease in absorption. In rats with dehydration, plasma protein binding was significantly greater than that in control rats (91.5 +/- 0.309 versus 81.3 +/- 2.79%).

Effects of glucose on the pharmacokinetics of intravenous chlorzoxazone in rats with acute renal failure induced by uranyl nitrate

The effects of glucose on CYP2E1 expression in rats with acute renal failure induced by uranyl nitrate (U-ARF) have been reported. CYP2E1 was significantly induced (2.3-fold) in rats with U-ARF compared with that in control rats. In contrast, CYP2E1 expression was significantly decreased in rats with U-ARF supplied with glucose (dissolved in tap water to make 10%, w/v) in their drinking water for 5 days (U-ARFG) compared with that in rats with U-ARF. However, CYP2E1 in rats with U-ARFG was significantly greater than that in control rats. Chlorzoxazone (CZX) primarily undergoes hydroxylation, catalyzed mainly by CYP2E1, to form 6-hydroxychlorzoxazone (OH-CZX) rats. Hence, it could be expected that in rats with U-ARFG, formation of OH-CZX could significantly decrease and increase compared with those in rats with U-ARF and control rats, respectively. This expectation is proven by the following results of a study of intravenous administration of CZX at a dose 20 mg/kg to control rats and rats with U-ARF and U-ARFG. First, the total area under the plasma concentration-time curve from time zero to 8 h (AUC(0-8 h)) of OH-CZX in rats with U-ARFG (8730 microg x min/mL) was significantly greater than that in control rats (414 microg x min/mL) and significantly smaller than that in rats with U-ARF (11500 microg x min/mL). Second, the AUC(0-8 h, OH-CZX)/AUC(CZX) ratio in rats with U-ARFG (10.0) was significantly greater than that in control rats (0.252) and significantly smaller than that in rats with U-ARF (17.5). Finally, the in vitro intrinsic OH-CZX formation clearance (CL(int)) in rats with U-ARFG (27.9 mL/min/mg protein) was significantly slower than that in rats with U-ARF (36.7 mL/min/mg protein) and significantly faster than that in control rats (17.7 mL/min/mg protein).

Pharmacokinetics of intravenous chlorzoxazone in rats with dehydration and rehydration: effects of food intakes

The following results were obtained recently from our laboratories; in rats with 72-h water deprivation (rats with dehydration), the hepatic cytochrome P450 2E1 (CYP2E1) was three-fold induced with an increase in the mRNA. Rehydration of 48-h water-deprived rats for the next 24 h with free access of food (rats with rehydration) restored CYP2E1 level to that of control. However, rehydration of 48-h water-deprived rats for the next 24 h with limited food supply (20% of control) failed to restore the CYP2E1 level to that of control. Hence, the CYP2E1 changes in rats with dehydration and rehydration resulted from differences in food intakes but not from dehydration or rehydration per'se. Chlorzoxazone (CZX) is metabolized to 6-hydroxychlorzoxazone (OH-CZX) mainly by CYP2E1 in rats. Therefore, the pharmacokinetics of CZX and OH-CZX were compared after intravenous administration of CZX, 25 mg/kg, to control rats and rats with dehydration and rehydration with free access of food. In rats with dehydration, the amount of 24-h urinary excretion of free OH-CZX plus its glucuronide conjugates (Ae (OH-CZX, 0-24 h,) expressed in terms of intravenous dose of CZX) was significantly greater (45.6 compared with 35.6%) and area under the plasma concentration-time curve from time zero to time infinity (AUC) of CZX was significantly smaller (2190 compared with 3200 micro g min/ml) than those in control rats. The above data indicated that the formation of OH-CZX increased significantly in rats with dehydration due to 3-fold induction of CYP2E1. In rats with rehydration with free access of food, the Ae (OH-CZX, 0-24 h) (39.0 compared with 35.6%) and AUC of CZX (2870 compared with 3200 micro g min/ml) were restored (comparable) to control levels since the expression of CYP2E1 in rats with dehydration returned to control level by rehydration. The above data indicate that CZX could be used as a chemical probe to assess the activity of CYP2E1 in rats with dehydration and rehydration.

Pharmacokinetics and pharmacodynamics of azosemide

Azosemide is used in the treatment of oedematous states and hypertension. The exact mechanism of action is not fully understood, but it mainly acts on both the medullary and cortical segments of the thick ascending limb of the loop of Henle. Delayed tolerance was demonstrated in humans by homeostatic mechanisms (principally an increase in aldosterone secretion and perhaps also an increase in the reabsorption of solute in the proximal tubule). After oral administration to healthy humans in the fasting state, the plasma concentration of azosemide reached its peak at 3-4 h with an absorption lag time of approximately 1 h and a terminal half-life of 2-3 h. The estimated extent of absolute oral bioavailability in humans was approximately 20.4%. After oral administration of the same dose of azosemide and furosemide, the diuretic effect was similar between the two drugs, but after intravenous administration, the effect of azosemide was 5.5-8 times greater than that in furosemide. This could be due to the considerable first-pass effect of azosemide. The protein binding to 4% human serum albumin was greater than 95% at azosemide concentrations ranging from 10 to 100 microg/ml using an equilibrium dialysis technique. The poor affinity of human tissues to azosemide was supported by the relatively small value of the apparent post-pseudodistribution volume of distribution (Vdbeta), 0.262 l/kg. Eleven metabolites (including degraded products) of azosemide including M1, glucuronide conjugates of both M1 and azosemide, thiophenemethanol, thiophencarboxylic acid and its glycine conjugate were obtained in rats. Only azosemide and its glucuronide were detected in humans. In humans, total body clearance, renal clearance and terminal half-life of azosemide were 112 ml/min, 41.6 ml/min and 2.03 h, respectively. Azosemide is actively secreted in the renal proximal tubule possibly via nonspecific organic acid secretory pathway in humans. Thus, the amount of azosemide that reaches its site of action could be significantly modified by changes in the capacity of this transport system. This capacity, in turn, could be predictably changed in disease states, resulting in decreased delivery of the diuretic to the transport site, as well as in the presence of other organic acids such as nonsteroidal anti-inflammatory drugs which could compete for active transport of azosemide. The urinary excretion rate of azosemide could be correlated well to its diuretic effects since the receptors are located in the loop of Henle. The diuretic effects of azosemide were dependent on the rate and composition of fluid replacement in rabbits; therefore, this factor should be considered in the evaluation of bioequivalence assessment.

Effects of water deprivation for 72 hours on the pharmacokinetics of a new carbapenem, DA-1131, in rats

Hormonal, physiological, and biochemical changes occurring in dehydrated patients could alter the pharmacokinetics of the drugs; therefore, the pharmacokinetics of DA-1131, a new carbapenem antibiotic, were investigated after 1-min intravenous administration of the drug at 50 mg/kg to control and 72-hr water-deprived rats. The impaired kidney and liver functions were observed in water-deprived rats on the basis of tissue microscopic examination. After intravenous infusion of the drug to water-deprived rats, the plasma concentrations of DA-1131 were higher and this resulted in a significantly greater total area under the plasma concentration-time curve from time zero to time infinity than those in control rats (4520 versus 3760 microg min/ml). This could be due to significantly slower total body clearance (CL) of DA-1131 in water-deprived rats (9.81 versus 14.1 ml/min/kg). The significantly slower CL of DA-1131 in water-deprived rats was due to significant decrease in both renal clearance (2.87 versus 5.13 ml/min/kg because of a significant decrease in 8-hr urinary excretion of unchanged DA-1131 [28.4 versus 39.9% of the intravenous dose] due to impaired kidney function) and nonrenal clearance (6.82 versus 8.66 ml/min/kg because of a significant decrease in the metabolism of DA-1131 in the kidney, as proved by the significant decrease in total renal DHP-I enzyme activity [1900 versus 2130 mU/each kidney]) in water-deprived rats. Water-deprivation did not alter the affinity of rat tissues to DA-1131.

Increase in urea in conjunction with L-arginine metabolism in the liver leads to induction of cytochrome P450 2E1 (CYP2E1): the role of urea in CYP2E1 induction by acute renal failure

A number of xenobiotics and certain pathophysiological situations cause the induction of CYP2E1. The present study was designed to establish the role of plasma urea nitrogen and L-arginine on hepatic CYP2E1 expression in rats or rats with acute renal failure. Exposure of rats to a single intravenous dose of 5 mg/kg uranyl nitrate caused renal failure in 5 days (ARF), as evidenced by increases in plasma urea nitrogen level and kidney to body weight ratio. Northern and Western blot analyses revealed that hepatic CYP2E1 was 2- to 4-fold induced by ARF. Treatment of rats with either 10% glucose in drinking water for 5 days following a single injection of uranyl nitrate or two injections of recombinant growth hormone (5 units/kg, s.c., twice a day) on the 4th day after uranyl nitrate injection reduced both the rise in plasma urea nitrogen and the induction of CYP2E1. Exposure of rats to urea (approximately 225 mg/kg/day) in drinking water for 1 to 3 day(s) resulted in significant increases in CYP2E1 mRNA and protein. Furthermore, perfusion of the liver with 25 mM urea for 24 h resulted in CYP2E1 induction with an increase in the mRNA. The levels of CYP2E1 protein and mRNA were increased in rats perfused with 25 mM L-arginine for 24 h (i.e., a 4-fold increase). Hence, L-arginine, which is irreversibly hydrolyzed to urea and ornithine by arginase, also induced hepatic CYP2E1. The results of the present study provided evidence that increases in plasma urea in conjunction with L-arginine metabolism lead to the induction of CYP2E1 in the liver.

Mitochondrial dysfunction by gamma-irradiation accompanies the induction of cytochrome P450 2E1 (CYP2E1) in rat liver

Multiple biological effects are induced by ionizing radiation through dysfunction of cellular organelles, direct interaction with nucleic acids and production of free radical species. The expression of cytochrome P450s was assessed in the livers of 60Co gamma-irradiated rats. Three gray (G) of gamma-irradiation caused CYP2E1 induction with a 3.6-fold increase in the mRNA at 24 h, whereas the expression of CYP1A2 and CYP3A was not changed. Pharmacokinetics of chlorzoxazone, a specific substrate of CYP2E1, was studied in 3 G-irradiated rats. The area under the plasma concentration-time curve from time zero to infinity of 6-hydroxychlorzoxazone and the amount of 6-hydroxychlorzoxazone excreted in 8 h urine were both significantly greater than those in control rats. Hepatic CYP2E1 was not induced in rats exposed to 0.5-1 G of gamma-rays. Rats irradiated at 6-9 G accumulated doses of gamma-rays exhibited smaller increases in the mRNA due to liver injury than those irradiated at a single dose of 3 G gamma-rays. The plasma glucose and insulin levels were not altered in rats with 3 G of gamma-irradiation. As the exposure level of gamma-irradiation increased, the activity of hepatic aconitase, a key enzyme in energy metabolism in mitochondria, was 30-90% decreased. The amount of mitochondrial DNA per gram of wet liver was 50% decreased in rats exposed to 3 G of gamma-rays. These results demonstrated that gamma-ray irradiation at the exposure level inducing organelle dysfunction induced CYP2E1 in the liver, which might be associated with mitochondrial damage, but not with alterations in glucose or insulin levels.