Acetaminophen hepatotoxicity precipitated by short-term treatment of rats with ethanol and isopentanol: protection by triacetyloleandomycin

Sasa veitchii extracts suppress acetaminophen-induced hepatotoxicity in mice

Background

The aim of this study was to investigate the therapeutic effects of a Sasa veitchii leaf extract (SE) on acetaminophen (APAP)-induced hepatotoxicity.

Methods

Seven-week-old male ddY mice were orally administered SE or saline (0.2 mL) once a day for a week. Twenty-four hours after the last pretreatment, the mice were intraperitoneally injected with 550 mg/kg APAP or saline under fasting conditions. The mice from each group were euthanized and bled for plasma analysis 2, 6, 24, and 72 h after the injection.

Results

We found that pretreatment with SE significantly decreased hepatic injury markers (i.e., alanine aminotransferase and aspartate aminotransferase), oxidative stress (malondialdehyde and glutathione level), inflammatory cytokines, histological damage, c-jun N-terminal kinase activation, and receptor-interacting protein-1 activation. Further, SE pretreatment decreased Cyp2e1 expression and increased total antioxidant capacity in the liver.

Conclusion

Our findings demonstrate that prophylactic SE treatment protects mice from APAP-induced hepatotoxicity through modulation of Cyp2e1 expression and antioxidant capacity.

Pharmacokinetic and pharmacodynamic interaction between nifedipine and metformin in rats: competitive inhibition for metabolism of nifedipine and metformin by each other via CYP isozymes

It has been reported that hypertension exponentially increases in the patients with type 2 diabetes mellitus. Thus, this study was performed to investigate the pharmacokinetic and pharmacodynamic interactions between nifedipine and metformin, since both drugs were commonly metabolized via hepatic CYP2C and 3A subfamilies in rats. Nifedipine (3 mg/kg) and metformin (100 mg/kg) were simultaneously administered intravenously or orally to rats. Concentrations (I) of each drug in the liver and intestine, maximum velocity (V(max)), Michaelis-Menten constant (K(m)), and intrinsic clearance (CL(int)) for the disappearance of each drug, apparent inhibition constant (K(i)) and [I]/K(i) ratios of each drug in liver and intestine were determined. Also the metabolism of each drug in rat and human CYPs and blood pressure were also measured. After the simultaneous single intravenous administration of both drugs together, the AUCs of each drug were significantly greater than that in each drug alone due to the competitive inhibition for the metabolism of nifedipine by metformin via hepatic CYP3A1/2 and of metformin by nifedipine via hepatic CYP2C6 and 3A1/2. After the simultaneous single oral administration of both drugs, the significantly greater AUCs of each drug than that in each drug alone could have mainly been due to the competitive inhibition for the metabolism of nifedipine and metformin by each other via intestinal CYP3A1/2 in addition to competitive inhibition for the hepatic metabolism of each drug as same as the intravenous study.

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.

Effects of cytochrome P450 (CYP) inducers and inhibitors on ondansetron pharmacokinetics in rats: involvement of hepatic CYP2D subfamily and 3A1/2 in ondansetron metabolism

The types of hepatic microsomal cytochrome P450 (CYP) isozymes responsible for the in-vivo metabolism of ondansetron in rats have not been reported. In this study, ondansetron at a dose of 8 mg kg−1 was administered intravenously to rats pretreated with various inducers of CYP isozymes, such as 3-methylcholanthrene, orphenadrine citrate, isoniazid and dexamethasone phosphate (the main inducers of CYP1A1/2, 2B1/2, 2E1 and 3A1/2 in rats, respectively), and inhibitors, such as SKF-525A (a non-specific inhibitor of CYP isozymes), sulfaphenazole, quinine hydrochloride and troleandomycin (the main inhibitors of CYP2C6, 2D subfamily and 3A1/2 in rats, respectively). In rats pretreated with quinine hydrochloride and troleandomycin, the time-averaged non-renal clearance of ondansetron was significantly slower (48.9 and 13.2% decrease, respectively) than that in control rats. In rats pretreated with dexamethasone phosphate, the time-averaged non-renal clearance was significantly faster (18.2% increase) than that in control rats. The results suggest that ondansetron is primarily metabolized via the CYP2D subfamily and 3A1/2 in rats.

Effects of enzyme inducers and inhibitors on the pharmacokinetics of intravenous ipriflavone in rats

In order to find out what types of the hepatic microsomal cytochrome P450 (CYP) isozymes are involved in the metabolism of ipriflavone, ipriflavone at a dose of 20 mg kg−1 (or 15 mg kg−1) was infused in male Sprague—Dawley rats. In rats pretreated with SKF 525-A (a non-specific CYP isozyme inhibitor in rats), the total body clearance (CL) of ipriflavone was significantly slower (29.9% decrease) than that in control rats. This indicates that ipriflavone is metabolized via CYP isozymes in rats, hence various enzyme inducers and inhibitors were used in in-vitro or in-vivo studies in rats. In rats pretreated with 3-methylcholanthrene and phenobarbital (main inducers of CYP1A1/2 and 2B1/2 in rats, respectively), the CL values were significantly higher (153 and 67.2% increases, respectively). In rats pretreated with sulfaphenazole (a main inhibitor of CYP2C11 in rats), the CL was significantly slower (22.5% decrease) than that in control rats. On addition of furafylline (a main inhibitor of CYP1A2 in rats), the in-vitro intrinsic clearance for the disappearance of ipriflavone was significantly slower (50.8% decrease) than that without furafylline. However, the CL values were not significantly different in rats pretreated with orphenadrine and isoniazid (a main inducer of CYP2E1 in rats), and quinine and troleandomycin (main inhibitors of CYP2D1 and 3A23/2 in rats, respectively) compared to controls. These data suggest that ipriflavone could be metabolized mainly via CYP1A1/2, 2B1/2 and 2C11 in rats.

Effect of hepatic CYP inhibitors on the metabolism of sildenafil and formation of its metabolite, N-desmethylsildenafil, in rats in vitro and in vivo

Objectives

It has been reported that hepatic cytochrome P450 (CYP)2C9 and CYP3A4 are responsible for the metabolism of sildenafil and formation of its metabolite, N-desmethylsildenafil, in humans. However, in-vivo studies in rats have not been reported.

Methods

Sildenafil (20 mg/kg) was administered intravenously to rats pretreated with sulfaphenazole, cimetidine, quinine hydrochloride or troleandomycin, inhibitors of CYP2C6, CYP2C11, CYP2D subfamily and CYP3A1/2, respectively. In-vitro studies using rat liver microsomes were also performed.

Key findings

The area under the plasma-concentration time curve (AUC) was increased and clearance of sildenafil decreased in rats pretreated with cimetidine or troleandomycin. The AUC ratio for N-desmethylsildenafil (0–4 h): sildenafil (0–∞) was significantly decreased only in rats pretreated with cimetidine. Similar results were obtained in the in-vitro study using rat liver microsomes.

Conclusions

Sildenafil is metabolised via hepatic CYP2C11 and 3A1/2, and N-desmethylsildenafil is mainly formed via hepatic CYP2C11 in rats. Thus, rats could be a good model for pharmacokinetic studies of sildenafil and N-desmethylsildenafil in humans.

Effects of cytochrome P450 inducers and inhibitors on the pharmacokinetics of intravenous furosemide in rats: involvement of CYP2C11, 2E1, 3A1 and 3A2 in furosemide metabolism

Objectives

It has been reported that the non-renal clearance of furosemide was significantly faster in rats pretreated with phenobarbital but was not altered in rats pretreated with 3-methylcholanthrene. However, no studies on other cytochrome P450 (CYP) isozymes have yet been reported in rats.

Method

Furosemide 20 mg/kg was administered intravenously to rats pretreated with various CYP inducers –3-methylcholanthrene, orphenadrine citrate and isoniazid, inducers of CYP1A1/2, 2B1/2 and 2E1, respectively, in rats – and inhibitors – SKF-525A (a nonspecific inhibitor of CYP isozymes), sulfaphenazole, cimetidine, quinine hydrochloride and troleandomycin, inhibitors of CYP2C6, 2C11, 2D and 3A1/2, respectively, in rats.

Key findings

The non-renal clearance of furosemide was significantly faster (55.9% increase) in rats pretreated with isoniazid, but slower in those pretreated with cimetidine or troleandomycin (38.5% and 22.7% decreases, respectively), than controls. After incubation of furosemide with baculovirus-infected insect cells expressing CYP2C11, 2E1, 3A1 or 3A2, furosemide was metabolized via CYP2C11, 2E1, 3A1 and 3A2.

Conclusions

These findings could help explain possible pharmacokinetic changes of furosemide in various rat disease models (where CYP2C11, 2E1, 3A1 and/or CYP3A2 are altered) and drug–drug interactions between furosemide and other drugs (mainly metabolized via CYP2C11, 2E1, 3A1 and/or 3A2).

Effects of CYP inducers and inhibitors on the pharmacokinetics of intravenous theophylline in rats: involvement of CYP1A1/2 in the formation of 1,3-DMU

The types of hepatic cytochrome P450 (CYP) isozymes responsible for the metabolism of theophylline and for the formation of 1,3-dimethyluric acid (1,3-DMU) in rats in-vivo does not seem to have been studied at the dose ranges of dose-independent metabolic disposition of theophylline in rats (up to 10 mg kg(-1)). Therefore, theophylline (5 mg kg(-1)) was administered i.v. to male Sprague-Dawley rats pretreated with various inducers and inhibitors of CYP isozymes. In rats pretreated with 3-methylcholanthrene (3-MC), orphenadrine or dexamethasone (main inducers of CYP1A1/2, CYP2B1/2 and CYP3A1/2, respectively, in rats), the time-averaged non-renal clearance (CLNR) of theophylline was significantly faster than in their respective controls (1260, 42.7 and 69.0% increases, respectively). However, in rats pretreated with troleandomycin (a major inhibitor of CYP3A1/2 in rats), CLNR was significantly slower than in the controls (50.7% decrease). The 24 h urinary excretion of 1,3-DMU was increased significantly only in rats pretreated with 3-MC. The ratio of area under the curve for 1,3-DMU and theophylline (AUC1,3-DMU/AUCtheophylline) was increased significantly in rats pretreated with 3-MC (160% increase) and decreased significantly in rats pretreated with troleandomycin (50.1% decrease); however, the ratio was not increased in rats pretreated with dexamethasone. These data suggest that theophylline is primarily metabolized via CYP1A1/2, CYP2B1/2, and CYP3A1/2, and that 1,3-DMU is primarily formed via CYP1A1/2, and possibly CYP3A1/2, in rats.

Role of CYP3A and CYP2E1 in alcohol-mediated increases in acetaminophen hepatotoxicity: comparison of wild-type and Cyp2e1(-/-) mice

CYP2E1 is widely accepted as the sole form of cytochrome P450 responsible for alcohol-mediated increases in acetaminophen (APAP) hepatotoxicity. However, we previously found that alcohol [ethanol and isopentanol (EIP)] causes increases in APAP hepatotoxicity in Cyp2e1(-/-) mice, indicating that CYP2E1 is not essential. Here, using wild-type and Cyp2e1(-/-) mice, we investigated the relative roles of CYP2E1 and CYP3A in EIP-mediated increases in APAP hepatotoxicity. We found that EIP-mediated increases in APAP hepatotoxicity occurred at lower APAP doses in wild-type mice (300 mg/kg) than in Cyp2e1(-/-) mice (600 mg/kg). Although this result suggests that CYP2E1 has a role in the different susceptibilities of these mouse lines, our findings that EIP-mediated increases in CYP3A activities were greater in wild-type mice compared with Cyp2e1(-/-) mice raises the possibility that differential increases in CYP3A may also contribute to the greater APAP sensitivity in EIP-pretreated wild-type mice. At the time of APAP administration, which followed an 11 h withdrawal from the alcohols, alcohol-induced levels of CYP3A were sustained in both mouse lines, whereas CYP2E1 was decreased to constitutive levels in wild-type mice. The CYP3A inhibitor triacetyloleandomycin (TAO) decreased APAP hepatotoxicity in EIP-pretreated wild-type and Cyp2e1(-/-) mice. TAO treatment in vivo resulted in inhibition of microsomal CYP3A-catalyzed activity, measured in vitro, with no inhibition of CYP1A2 and CYP2E1 activities. In conclusion, these findings suggest that both CYP3A and CYP2E1 contribute to APAP hepatotoxicity in alcohol-treated mice.

Pharmacokinetic and pharmacodynamic consequences of inhibition of terazosin metabolism via CYP3A1 and/or 3A2 by DA-8159, an erectogenic, in rats

BACKGROUND AND PURPOSE

Recently, orthostatic hypotension was observed in patients with benign prostatic hyperplasia who are taking vardenafil (a PDE 5 inhibitor) and terazosin (a long acting alpha blocker). Therefore, this study was performed with DA-8159 (a long acting PDE 5 inhibitor) and terazosin in rats to find whether or not pharmacokinetic and pharmacodynamic interactions between the two drugs were observed.

EXPERIMENTAL APPROACH

Pharmacokinetic and pharmacodynamic (changes in blood pressure) interactions between DA-8159 and terazosin were evaluated after simultaneous i.v. and p.o. administration of DA-8159 (30 mg kg(-1)) and terazosin (5 mg kg(-1)) to male Sprague-Dawley rats.

KEY RESULTS

After simultaneous i.v. and p.o. administration of terazosin and DA-8159, the total area under the plasma concentration-time curve from time zero to time infinity (AUC) of terazosin became significantly greater (57.4 and 75.4% increase for i.v. and p.o. administration, respectively) than those of without DA-8159. The blood pressure dropping effect was considerable after simultaneous p.o. administration of DA-8159 and terazosin compared with each drug alone.

CONCLUSIONS AND IMPLICATIONS

The significantly greater AUC of terazosin after both simultaneous i.v. and p.o. administration of both drugs could be due to the hepatic (both i.v. and p.o.) and intestinal (p.o.) inhibition of the metabolism of terazosin via CYP3A1 and/or 3A2 by DA-8159, since both DA-8159 and terazosin are metabolized via CYP3A1 and/or 3A2 in rats. The blood pressure lowering effect after simultaneous p.o. administration of both drugs could be due to significant increase in plasma concentrations of terazosin.

Effects of acute renal failure on the pharmacokinetics of telithromycin in rats: negligible effects of increase in CYP3A1 on the metabolism of telithromycin

It was reported that the expression of CYP3A1 increased in rats with acute renal failure induced by uranyl nitrate (rat model of U-ARF) compared with controls. It was shown that telithromycin was mainly metabolized via CYP3A1/2 in rats in this study. Hence, the pharmacokinetic parameters of telithromycin were compared after both intravenous and oral administration at a dose of 50 mg/kg to control rats and a rat model of U-ARF. After intravenous administration of telithromycin to rats with U-ARF, the AUC and renal clearance (Cl(r)) were significantly greater (35.0% increase) and slower (99.1% decrease), respectively, than the controls. Unexpectedly, the nonrenal clearance (Cl(nr)) of telithromycin was comparable between the two groups of rats, suggesting that CYP3A isozyme responsible for the metabolism of telithromycin seemed not to be expressed considerably in the rat model of U-ARF. After oral administration of telithromycin to rats with U-ARF, the AUC was also significantly greater (127% increase) than the controls and the value, 127%, was considerably greater than 35.0% after intravenous administration of telithromycin. This may be due mainly to the decrease in the intestinal first-pass effect of telithromycin compared with controls in addition to significantly slower Cl(r) than controls.

Ginkgolide A contributes to the potentiation of acetaminophen toxicity by Ginkgo biloba extract in primary cultures of rat hepatocytes

The present cell culture study investigated the effect of Ginkgo biloba extract pretreatment on acetaminophen toxicity and assessed the role of ginkgolide A and cytochrome P450 3A (CYP3A) in hepatocytes isolated from adult male Long-Evans rats provided ad libitum with a standard diet. Acetaminophen (7.5-25 mM for 24 h) conferred hepatocyte toxicity, as determined by the lactate dehydrogenase (LDH) assay. G. biloba extract alone increased LDH leakage in hepatocytes at concentrations > or =75 mug/ml and > or =750 mug/ml after a 72 h and 24 h treatment period, respectively. G. biloba extract (25 or 50 mug/ml once every 24 h for 72 h) potentiated LDH leakage by acetaminophen (10 mM for 24 h; added at 48 h after initiation of extract pretreatment). The effect was confirmed by a decrease in [(14)C]-leucine incorporation. At the level present in a modulating concentration (50 mug/ml) of the extract, ginkgolide A (0.55 mug/ml), which increased CYP3A23 mRNA levels and CYP3A-mediated enzyme activity, accounted for part but not all of the potentiating effect of the extract on acetaminophen toxicity. This occurred as a result of CYP3A induction by ginkgolide A because triacetyloleandomycin (TAO), a specific inhibitor of CYP3A catalytic activity, completely blocked the effect of ginkgolide A. Ginkgolide B, ginkgolide C, ginkgolide J, quercetin, kaempferol, isorhamnetin, and isorhamnetin-3-O-rutinoside did not alter the extent of LDH leakage by acetaminophen. In summary, G. biloba pretreatment potentiated acetaminophen toxicity in cultured rat hepatocytes and ginkgolide A contributed to this novel effect of the extract by inducing CYP3A.

Effects of enzyme inducers and inhibitors on the pharmacokinetics of metformin in rats: involvement of CYP2C11, 2D1 and 3A1/2 for the metabolism of metformin

BACKGROUND AND PURPOSE

The types of hepatic microsomal cytochrome P450 (CYP) isozymes responsible for the metabolism of metformin in humans and rats have not been published to date. Therefore, a series of experiments using various inducers and inhibitors of CYP isozymes was conducted to find out what types of CYP isozymes are involved in the metabolism of metformin in rats.

EXPERIMENTAL APPROACH

Metformin at a dose of 100 mg kg(-1) was administered intravenously to rats. The rats were pretreated with CYP inducers such as 3-methylcholanthrene, orphenadrine, isoniazid, and dexamethasone (major inducers of CYP1A1/2, 2B1/2, 2E1, and 3A1/2, respectively, in rats), or CYP inhibitors such as SKF-525 (a non-specific inhibitor of CYP isozymes), and sulfaphenazole, quinine, and troleandomycin (major inhibitors of CYP2C11, 2D1, and 3A1/2, respectively, in rats). The time-averaged non-renal clearance (CLNR) of metformin was compared with that of controls.

KEY RESULTS

In rats pretreated with dexamethasone, the CLNR was significantly faster (57% increase) than for the controls. In rats pretreated with SKF-525-A, sulfaphenazole, quinine, and troleandomycin, the CLNR was significantly slower (24.3, 62.9, 77.6, and 78.7% decrease, respectively) than for the controls. However, the CLNR values did not significantly different in the rats pretreated with 3-methylencholanthrene, orphenadrine, and isoniazid compared with the controls.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that metformin was metabolized mainly via CYP2C11, 2D1, and 3A1/2 in rats. This result could contribute to understanding of the possible changes in metformin pharmacokinetics in disease models where CYP2C11 and/or 3A1/2 are altered.

Involvement of Toll-like receptor 4 in acetaminophen hepatotoxicity

The objective of this study was to determine whether Toll-like receptor 4 (TLR4) has a role in alcohol-mediated acetaminophen (APAP) hepatotoxicity. TLR4 is involved in the inflammatory response to endotoxin. Others have found that ethanol-mediated liver disease is decreased in C3H/HeJ mice, which have a mutated TLR4 resulting in a decreased response to endotoxin compared with endotoxin-responsive mice. In the present study, short-term (1 wk) pretreatment with ethanol plus isopentanol, the predominant alcohols in alcoholic beverages, caused no histologically observed liver damage in either C3H/HeJ mice or endotoxin-responsive C3H/HeN mice, despite an increase in nitrotyrosine levels in the livers of C3H/HeN mice. In C3H/HeN mice pretreated with the alcohols, subsequent exposure to APAP caused a transient decrease in liver nitrotyrosine formation, possibly due to competitive interaction of peroxynitrite with APAP producing 3-nitroacetaminophen. Treatment with APAP alone resulted in steatosis in addition to congestion and necrosis in both C3H/HeN and C3H/HeJ mice, but the effects were more severe in endotoxin-responsive C3H/HeN mice. In alcohol-pretreated endotoxin-responsive C3H/HeN mice, subsequent exposure to APAP resulted in further increases in liver damage, including severe steatosis, associated with elevated plasma levels of TNF-alpha. In contrast, alcohol pretreatment of C3H/HeJ mice caused little to no increase in APAP hepatotoxicity and no increase in plasma TNF-alpha. Portal blood endotoxin levels were very low and were not detectably elevated by any of the treatments. In conclusion, this study implicates a role of TLR4 in APAP-mediated hepatotoxicity.

Negligible pharmacokinetic interaction between oral DA-8159, a new erectogenic, and amlodipine in rats

A pharmacokinetic interaction between oral DA-8159 and amlodipine was evaluated in male Sprague-Dawley rats. In rats pretreated with troleandomycin (a main inhibitor of CYP3A1/2 in rats), the AUC(0-6 h) of amlodipine was significantly greater than the controls (34.5+/-6.01 compared with 28.0+/-4.70 microg min/ml), indicating that amlodipine is metabolized via CYP3A1/2 in rats. It was reported that the metabolism of DA-8159 and the formation of DA-8164 (a metabolite of DA-8159) were mainly mediated via CYP3A1/2 in rats, and amlodipine significantly inhibited the CYP3A2 in rats. Therefore, a pharmacokinetic interaction between the two drugs could be expected. However, after oral administration of DA-8159 at a dose of 30 mg/kg with or without oral amlodipine at a dose of 5 mg/kg to rats, the pharmacokinetic parameters of DA-8159 and DA-8164 were not significantly different between the two groups of rats. Similar results were also obtained from amlodipine between with and without DA-8159. The above data indicated that the pharmacokinetic interaction between oral DA-8159 and amlodipine was almost negligible in rats.

Effects of enzyme inducers and inhibitors on the pharmacokinetics of intravenous omeprazole in rats

A series of experiments using various inducers and inhibitors of the hepatic microsomal cytochrome P450 (CYP) isozymes were conducted to find CYP isozymes responsible for the metabolism of omeprazole in male Sprague-Dawley rats. Omeprazole, 20 mg/kg, was administered intravenously. In rats pretreated with SKF 525-A (a nonspecific CYP isozyme inhibitor in rats), the time-averaged nonrenal clearance (Cl(nr)) was significantly slower (77.1% decrease) than that in untreated rats. This indicated that omeprazole is metabolized via CYP isozymes in rats. Hence, rats were pretreated with various enzyme inducers and inhibitors. In rats pretreated with 3-methylcholanthrene and dexamethasone (main inducers of CYP1A1/2 and 3A1/2 in rats, respectively), the Cl(nr) values were significantly faster (43.8% and 26.3% increase, respectively). In rats pretreated with troleandomycin and quinine (main inhibitors of CYP3A1/2 and 2D1 in rats, respectively), the Cl(nr) values were significantly slower (20.9% and 12.9% decrease, respectively). However, the Cl(nr) values were not significantly different in rats pretreated with orphenadrine, isoniazid and sulfaphenazole (main inducers of CYP2B1/2 and 2E1, and a main inhibitor of 2C11, respectively, in rats) compared with those of respective control rats. The above data suggested that omeprazole could be mainly metabolized via CYP1A1/2, 3A1/2 and 2D1 in male rats.

Ubiquitin-dependent degradation of p53 protein despite phosphorylation at its N terminus by acetaminophen

We previously reported that acetaminophen (APAP, 4-hydroxyacetanilide) caused apoptosis of C6 glioma cells. Therefore, we hypothesized that the level of p53, which usually stimulates apoptosis, might be increased after APAP exposure. However, APAP exposure for 24 h markedly decreased the p53 content and its downstream target p21 in a concentration-dependent manner. Reduction of p53 was not accompanied by a decrease in p53 mRNA in C6 glioma cells, suggesting that p53 was mainly affected at the protein level. Unexpectedly, APAP stimulated phosphorylation of p53 at Ser15, Ser20, and Ser37, which usually elevates p53 content. However, phosphorylation of these residues did not prevent APAP-induced decrease in p53. The p53 reduction was independent from the level of phospho-Akt, which is known to promote p53 degradation. Immunoblot analysis of the immunoprecipitated p53 revealed that increased amounts of murine double minute 2 (mdm2) and ubiquitin were bound to p53 during its degradation. Lactacystin and N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132), inhibitors of proteasomal proteolysis, prevented the decrease, supporting the proteasomal degradation of p53 upon APAP exposure. Pretreatment with chlormethiazole, an inhibitor of ethanol-inducible CYP2E1, significantly lowered the CYP2E1 enzyme activity and the rate of APAP-induced cell death while it prevented the reduction of p53 and p21 in C6 glioma cells. A nontoxic analog of APAP, 3-hydroxyacetanilde, did not reduce p53 and p21 contents in C6 glioma cells and LLC-PK1 porcine kidney cells. Taken together, our results show that APAP or its reactive metabolite(s) can directly reduce the p53 content through mdm2-mediated ubiquitin conjugation, despite phosphorylation of p53 at its N terminus.

Effects of enzyme inducers and inhibitors on the pharmacokinetics of intravenous torasemide in rats

In order to find whether torasemide is metabolized via CYP isozymes in rats, torasemide at a dose of 2mg/kg was infused in rats pretreated with SKF 525-A, a non-specific CYP isozyme inhibitor in male Sprague-Dawley rats. The total area under the plasma concentration-time curve from time zero to time infinity (AUC) of torasemide was significantly greater in rats pretreated with SKF 525-A (a non-specific CYP isozyme inhibitor in rats) than that in control rats (3570 versus 1350 microg min/ml). This indicated that torasemide is metabolized via CYP isozymes in rats. Hence, torasemide was infused in rats pretreated with various enzyme inducers and inhibitors to find what types of CYP isozymes are involved in the metabolism of torasemide in rats. The AUC values were not significantly different in rats pretreated with 3-methylcholanthrene, phenobarbital, isoniazid, quinine and troleandomycin (main inducers of CYP1A1/2, CYP2B1/2, and CYP2E1, and main inhibitors of CYP2D1 and CYP3A1/2 in rats, respectively) compared with those in respective control rats. However, in rats pretreated with dexamethasone (a main inducer of CYP3A1/2 in rats), the AUC was significantly smaller than that in control rats (1290 versus 1590 microg min/ml). Dexamethasone probably also induces rat CYP2C11; this could be due to an increase in CYP2C11 in rats pretreated with dexamethasone. It has been reported from our laboratories that in rats pretreated with sulfaphenazole (a main inhibitor of CYP2C11 in rats) the AUC was significantly greater than that in control rats (2970 versus 1610 microg min/ml). The above data suggested that torasemide could be metabolized in male rats mainly via CYP2C11.

Ethanol binging exacerbates sinusoidal endothelial and parenchymal injury elicited by acetaminophen

BACKGROUND/AIMS

The pathophysiology of binge drinking of ethanol and its potentiation of acetaminophen (APAP) toxicity has received very little attention. To evaluate if ethanol binging sensitizes hepatic sinusoidal endothelial cells (SEC) and liver to APAP toxicity.

METHODS

The histopathological responses to APAP were evaluated in the livers of mice gavaged with APAP alone, following a single, week-end type ethanol binge (4 g/kg every 12 h x 5 doses) or three weekly binges.

RESULTS

Six hours after APAP, 600 mg/kg elicited severe centrilobular necrosis together with hemorrhagic congestion and infiltration of erythrocytes into the Space of Disse through large gaps that had formed in SEC. There was no evidence of parenchymal injury at 2 h, but gaps already were formed through the cytoplasm of the SEC by coalescence of fenestrae. A single binge followed by 300 mg/kg APAP elicited SEC and parenchymal injury equivalent to 600 mg/kg APAP alone at 2 and 6 h. The responses were exacerbated following three binges. Lower glutathione levels in the liver were shown in ethanol-binged animals.

CONCLUSIONS

Ethanol binging increases APAP hepatotoxicity. SEC are an early target for APAP-induced injury and ethanol binging enhances the SEC injury prior to evidence of parenchymal cell injury.

Protective effect of Sargassum polycystum (brown alga) against acetaminophen-induced lipid peroxidation in rats

Lipid peroxidation is believed to play an important role in the pathogenesis of several diseases, such as cancer, diabetic mellitus and liver injury. Aqueous and ethanol extracts of Sargassum polycystum C. Agardh (Phaeophyta) were screened for their protective effects against acetaminophen (ACP; Paracetamol)-induced lipid peroxidation in rats. A single dose of acetaminophen significantly elevated the levels of lipid peroxides (LPO) with decreased levels of free radical scavenger enzymes (SOD, CAT, GSH, GPx, GST) in liver homogenate. The oral pretreatment of rats with ethanol and aqueous extracts of Sargassum polycystum C. Agardh (100 mg, 200 mg[sol ]kg body wt[sol ]day respectively, for a period of 15 days) significantly reduced the acetaminophen-induced oxidative stress in rats. The animals treated with the ethanol and aqueous extracts alone did not show any toxicity on liver tissue. This observation shows that the seaweed crude extracts probably acted to protect against acetaminophen-induced lipid peroxidation through their free radical scavenging property.

Effects of enzyme inducers and inhibitors on the pharmacokinetics of intravenous DA-8159, a new erectogenic, in rats

In order to find what types of hepatic microsomal cytochrome P450 (CYP) isozymes are involved in the metabolism of DA-8159 and in the formation of DA-8164 in rats, enzyme inducers, such as dexamethasone, phenobarbital, 3-methylcholanthrene and isoniazid, and enzyme inhibitors, such as troleandomycin and quinine, were pretreated in rats. After a 1 min intravenous administration of DA-8159 at a dose of 30 mg/kg to rats pretreated with dexamethasone (a main inducer of CYP3A1/2 in rats), the total areas under the plasma concentration-time curve from time zero to time infinity (AUC) values of DA-8159 (283 versus 349 microg min/ml) and DA-8164 (98.0 versus 79.8 microg min/ml) were significantly smaller and greater, respectively, than those in control rats. However, the AUC values of DA-8159 were not significantly different after pretreatment with phenobarbital, isoniazid and 3-methylcholanthrene (main inducers of CYP2B1/2, 2E1 and 1A1/2, respectively, in rats). In rats pretreated with troleandomycin (a main inhibitor of CYP3A1/2 in rats), the AUC values of DA-8159 (435 versus 370 microg min/ml) and DA-8164 (34.8 versus 76.5 microg min/ml) were significantly greater and smaller, respectively. However, in rats pretreated with quinine (a main inhibitor of CYP2D1 in rats), the AUC of DA-8159 was comparable to that in control rats. The above data indicate that DA-8159 was metabolized and DA-8164 was formed mainly via CYP3A1/2 in rats.

Should a lower treatment line be used when treating paracetamol poisoning in patients with chronic alcoholism?: a case for

A lower threshold for treatment of paracetamol (acetaminophen) poisoning has been advocated in chronic heavy users of alcohol, based originally on animal studies indicating that chronic alcohol ingestion increased hepatotoxicity. This was attributed to increased production of the toxic metabolite, N-acetyl-p-benzoquinoneimine, by cytochrome P450 (CYP)2E1 induction. The clinical evidence for increased risk is limited to four retrospective studies with potential for referral and reporting bias and conflicting results. No study has specifically addressed the issue of the treatment threshold for acute paracetamol overdose in chronic alcohol users. However, animal studies in multiple species have consistently shown a lower dose of paracetamol is required to produce hepatotoxicity after chronic alcohol use. The knowledge of potential mechanisms has expanded to include effects of other alcohols, such as isopentanol, induction of CYP enzymes other than CYP2E1 and glutathione depletion. There are no convincing reasons or data to suggest these findings do not apply to humans. However, further human toxicokinetic and clinical research is required to quantify the extent of the interaction. Arguments about treating overdoses should not be confused with those about whether there is an alcohol-paracetamol interaction at therapeutic doses. Halving the threshold dose/concentration for treatment is a conservative educated guess that has been widely adopted. In overdose, the potential benefits of treatment at this lower threshold clearly outweigh the minimal risks of acetylcysteine.

Alcohol use and HIV pharmacotherapy

Alcohol consumption by individuals infected with HIV is an important medical management issue with significant implications for the effectiveness of antiretroviral therapy as well as an important evolving field of HIV research. Alcohol consumption is a risk factor for poor medication adherence and can modify liver drug metabolism, both of which can lead to the emergence of drug-resistant virus. Research indicates that alcohol consumption greater than 50 g/day (four or five drinks) is a risk factor for liver disease progression among patients with HIV/HCV coinfection. In addition, alcohol-induced cirrhosis can result in changes in drug metabolism in the liver through compromised liver function. More research studies are needed to elucidate the biological and molecular basis of the clinical changes induced by alcohol consumption in HIV-infected individuals and on the relationship of these changes to the effectiveness of HIV pharmacotherapy. Specifically, research areas that are of particular importance are (1) determining alcohol consumption levels and patterns and its impact on antiretroviral medication adherence, efficacy, and physician prescribing practices; (2) identifying behavioral interventions to enhance adherence to HIV medications and reduce alcohol consumption; (3) clarifying the relationships and interactions among alcohol metabolism, HIV drug metabolism, and pharmacogenetics; (4) elucidating the extent of liver toxicity due to antiretroviral therapy and drug-drug interactions in individuals who consume alcohol; and (5) delineating the contribution of alcohol consumption to end-stage organ damage, particularly in HIV/HCV coinfection.

Influence of acute and chronic alcohol intake on the clinical course and outcome in acetaminophen overdose

BACKGROUND

Animal studies on acetaminophen toxicity suggest that chronic alcohol intake affects the outcome adversely, whereas acute alcohol intake seems protective. Few clinical data are available.

METHODS

We studied 209 consecutive patients with single-dose acetaminophen overdose. The combined influence of independent variables (gender, age, dose, delay to antidote treatment, chronic and acute alcohol intake and nomogram risk group) on dependent variables (death, development of hepatic encephalopathy and biochemical liver markers) was studied using multiple or logistic regression analysis.

RESULTS

Fifty-seven (27.3%) patients had chronic alcohol intake and 45 (21.5%) patients had acute alcohol intake. Forty-four (21.1%) patients developed hepatic coma and 20 (43.5%) of these patients died. Chronic alcohol intake was significantly and independently associated with the development of hepatic coma, with a lower prothrombin index, lower platelet count, higher creatinine and higher bilirubin. The relative risks for hepatic coma and death were 5.3 (95% confidence interval, 2.2-12.4) and 1.4 (95% confidence interval, 0.5-3.9), respectively, in the chronic alcohol intake group compared with the no chronic alcohol intake group. Acute alcohol intake was not significantly associated with any of the dependent variables studied.

CONCLUSIONS

Chronic alcohol intake enhances acetaminophen hepatotoxicity, whereas acute alcohol intake does not affect the clinical course.

Short-term treatment with alcohols causes hepatic steatosis and enhances acetaminophen hepatotoxicity in Cyp2e1(-/-) mice

CYP2E1 has been reported to have an essential role in alcohol-mediated increases in hepatic steatosis and acetaminophen hepatotoxicity. We found that pretreatment of Cyp2e1(-/-) mice with ethanol plus isopentanol, the predominant alcohols in alcoholic beverages, for 7 days resulted in micro- and macrovesicular steatosis in the livers of all mice, as well as a dramatic increase in acetaminophen hepatotoxicity. In Cyp2e1(-/-) mice administered up to 600 mg acetaminophen/kg alone and euthanized 7 h later, there was no increase in serum levels of ALT. In Cyp2e1(-/-) mice pretreated with ethanol and isopentanol, subsequent exposure to 400 or 600 mg acetaminophen/kg resulted in centrilobular necrosis in all mice with maximal elevation in serum levels of ALT. Acetaminophen-mediated liver damage was similar in males and females. Hepatic microsomal levels of APAP activation in untreated females were similar to those in males treated with the alcohols. However, the females, like the males, required pretreatment with the alcohols in order to increase APAP hepatotoxicity. These findings suggest that, in the Cyp2e1(-/-) mice, the alcohol-mediated increase in acetaminophen hepatotoxicity involves the contribution of other factors, in addition to induction of CYP(s) that activate acetaminophen. Alternatively, CYP-mediated activation of acetaminophen measured in vitro may not reflect the actual activity in vivo. Our findings that a 7-day treatment with ethanol and isopentanol causes extensive hepatic steatosis and increases acetaminophen hepatotoxicity in Cyp2e(-/-) mice indicate that CYP2E1 is not essential for either response.