Down-regulation of cytochrome P450 proteins and its activities by Shiga-like toxin II from Escherichia coli O157:H7

Regulation of cytochrome P450 enzyme activity and expression by nitric oxide in the context of inflammatory disease

Many hepatic cytochrome P450 enzymes and their associated drug metabolizing activities are down-regulated in disease states, and much of this has been associated with inflammatory cytokines and their signaling pathways. One such pathway is the induction of inducible nitric oxide synthase (NOS2) and generation of nitric oxide (NO) in many tissues and cells including the liver and hepatocytes. Experiments in the 1990s demonstrated that NO could bind to and inhibit P450 enzymes, and suggested that inhibition of NOS could attenuate, and NO generation could mimic, the down-regulation by inflammatory stimuli of not only P450 catalytic activities but also of mRNA expression and protein levels of certain P450 enzymes. This review will summarize and examine the evidence that NO functionally inhibits and down-regulates P450 enzymes in vivo and in vitro, with a particular focus on the mechanisms by which these effects are achieved.

Changes of midazolam pharmacokinetics in Wistar rats treated with lipopolysaccharide: relationship between total CYP and CYP3A2

It has been reported that infection interferes with drug metabolism, resulting in changes in pharmacokinetics. In this study, we investigated the effects of lipopolysaccharide (LPS) on hepatic total cytochrome P450 (CYP), CYP3A2, and CYP2C11 contents in a transient, LPS-induced, endotoxemia model of rats. In addition, to assess the effects on CYP3A2 activities, the pharmacokinetics of midazolam (CYP3A2 substrate) and 1-OH-midazolam (metabolite of midazolam) were investigated. Hepatic total CYP contents were significantly low until day 3 ( P < 0.05) but returned to the control level on day 5. Hepatic CYP3A2 contents were significantly decreased on day 1 until day 5 ( P < 0.05) but returned to the control level on day 7. Hepatic CYP2C11 contents were continuously low until day 7, and lowest on day 3. The AUC of 1-OH-midazolam was significantly decreased on day 1 after LPS administration ( P < 0.01). In conclusion, LPS (5 mg/kg) challenge decreased hepatic total CYP, CYP3A2, and CYP2C11 contents and also decreased the activities of hepatic CYP3A2. It took at least 7 days for hepatic total CYP and CYP3A2 to recover to control levels, and it was suggested that the changes of hepatic total CYP contents might correlate with those of hepatic CYP3A2 contents and activities. Additionally, it is shown that their changes might reflect the recovery process from inflammation.

Ciprofloxacin prolonged-release tablets do not affect warfarin pharmacokinetics and pharmacodynamics

The purpose of this study was to determine whether the pharmacokinetics of warfarin and ciprofloxacin PR (a prolonged-release formulation of ciprofloxacin) were altered after coadministration. Eighteen healthy male volunteers were given a single oral 7.5-mg dose of warfarin, a single oral 500-mg dose of ciprofloxacin PR, or both drugs administered together in a randomized, open-label, 3-way crossover study. Ciprofloxacin concentrations, warfarin (R)- and (S)-enantiomer concentrations, prothrombin time, and activated partial thromboplastin time were measured over 120 hours following study drug administration. There were no significant differences in pharmacokinetic or pharmacodynamic parameters among treatments. A slightly greater value of half-life for (R)-warfarin was observed when coadministered with ciprofloxacin PR compared with warfarin administered alone (52.6 vs 50.1 hours, P = .029). This difference is not considered clinically relevant, because the values remain similar. These results show that warfarin pharmacokinetics and pharmacodynamics are not altered with concomitant administration of ciprofloxacin PR.

Lack of effect of aciclovir on metabolism of theophylline and expression of hepatic cytochrome P450 1A2 in rats

There is an interesting clinical report indicating that aciclovir, which is mainly excreted into urine, decreases the systemic clearance of theophylline by inhibiting cytochrome P450 (CYP) 1A2-mediated metabolism. In this study, we investigated the effect of aciclovir on the metabolism of theophylline, and on the activity and expression of hepatic CYP1A2 in rats. Theophylline (10 mg/kg) was injected intravenously into rats treated with two different dosages of aciclovir. When theophylline was simultaneously administered with aciclovir (50 mg/kg), the systemic clearance of theophylline and metabolic clearance of its major metabolites, 1-methyluric acid and 1,3-dimethyluric acid, were unchanged. In place of theophylline, when 1-methyl-3-propylxanthine (2.5 mg/kg), which is almost metabolized by CYP1A2 in rats, was coadministered intravenously with aciclovir (50 mg/kg), the pharmacokinetics of 1-methyl-3-propylxanthine was also unchanged. When theophylline was administered to rats pretreated with repeated intraperitoneal injections of aciclovir (25 mg/kg twice daily for 3 d), no significant differences in the systemic clearance of theophylline and its metabolic clearance to 1-methyluric acid and 1,3-dimethyluric acid were observed between the control and aciclovir-treated rats. This dosage of aciclovir did not change the activity of 7-ethoxyresorufin O-dealkylation, which is represented as CYP1A2 activity. In Western blot analysis, no significant change in the protein levels of hepatic CYP1A2 was observed between the control and aciclovir-treated rats. The present study suggests that aciclovir has no effect on the pharmacokinetics and metabolism of theophylline and on the activity and expression of hepatic CYP1A2 in rats.

Effect of a newly developed ketolide antibiotic, telithromycin, on metabolism of theophylline and expression of cytochrome P450 in rats

The effects of a newly-developed ketolide antibiotic, telithromycin, on the metabolism of theophylline and the expression of hepatic cytochrome P450 (CYP) 1A2 and CYP3A2 were investigated in rats. Telithromycin at a high dose (100 mg/kg of body weight) was injected intraperitoneally once a day for 3 days. Twenty-four hours (day 4) after the final administration of telithromycin, theophylline (10 mg/kg) was administered intravenously. The presence of telithromycin significantly delayed the disappearance of theophylline from plasma. Parameters related to the pharmacokinetic interaction between theophylline and telithromycin were examined by noncompartmental methods. A significant decrease in the systemic clearance of theophylline was observed in the presence of telithromycin. Pretreatment with telithromycin significantly decreased the metabolic clearance of the major metabolites, 1-methyluric acid and 1,3-dimethyluric acid, with no change in the renal clearance of theophylline, suggesting that the decreased systemic clearance of theophylline by telithromycin is due to reduction of their metabolic clearance. Pretreatment with telithromycin significantly decreased the activity of 7-ethoxyresorufin O-deethylation and testosterone 6 beta-hydroxylation, suggesting that telithromycin decreases the activity of hepatic CYP1A2 and CYP3A2. Western blot analysis revealed that telithromycin significantly decreased the protein levels of CYP1A2 and CYP3A2 in the liver, which could explain the observed decreases in the systemic clearance of theophylline and metabolic clearance of 1-methyluric acid and 1,3-dimethyluric acid. The present study suggests that telithromycin at the dose used in this study alters the pharmacokinetics and metabolism of theophylline, due to reductions in the activity and expression of hepatic CYP1A2 and CYP3A2.

[Microsomal oxidative metabolism in the liver of rats treated with vinorelbine: evaluation through antipyrine elimination]

BACKGROUND

Determination of the metabolic efficiency of the liver in neoplastic diseases in patients receiving highly toxic drugs is of great practical importance.

METHODS

The effect of vinorelbine on the metabolic efficiency of the liver was evaluated by means of phenazone kinetics in rats. The test was compared with a battery of tests routinely used whenever hepatic dysfunction is suspected.

RESULTS

Vinorelbine was administered to the rats and the pharmacokinetic parameters of antipyrine were compared with those in control rats. A statistically significant prolongation of the elimination half-life, as well as a decrease in the elimination constant and clearance of antipyrine were found in the rats receiving the anticancer drug in comparison with controls (p < 0.01). Statistically significant correlations were found between the elimination half-life of antipyrine and serum albumin values (p < 0.01) and prothrombin time (p < 0.001).

CONCLUSIONS

Determination of antipyrine pharmacokinetics allows early detection of vinorelbine-induced hepatic dysfunction, with a sensitive scale.

Effect of Shiga-like toxin II from Escherichia coli O157:H7 on intestinal clearance of norfloxacin in rats

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 infection causes severe clinical symptoms, due to its bacterial toxin, called Shiga-like toxin (SLT). However, little is known about the information to establish a safe and efficient prescription to treat for EHEC O157:H7 patients. Thus, we investigated the effect of SLT-II on intestinal function in rats by using the antibiotic norfloxacin (NFLX) as a model drug. The intestinal clearance (CLi) of NFLX, determined by loop method in the jejunum, was significantly decreased by SLT-II. In histopathological experiment, epithalaxia was observed in SLT-II-treated rats without structural changes of tight junction suggesting the deterioration of active transport systems by SLT-II. CLi of NFLX in normal rats was decreased by carnitine (CAR), suggesting the possible involvement of CAR-sensitive transporter in CLi of NFLX. Taken together, these results suggest that the EHEC O157:H7 infection might affect the intestinal disposition of NFLX due to the changing intestinal expression/function of drug transporters by SLT-II.

Gender-related differences in expression and function of hepatic P-glycoprotein and multidrug resistance-associated protein (Mrp2) in rats

To clarify whether gender-related differences exist in the expression and function of hepatic P-glycoprotein- and/or multidrug resistance-associated protein (Mrp2), we measured the hepatobiliary excretion of doxorubicin and their protein levels in male and female Sprague-Dawley rats. When rats received a single intravenous injection of doxorubicin (5 mg/kg), a delay in the disappearance of doxorubicin from plasma was observed in male rats. When rats received a constant-rate infusion of doxorubicin, no significant gender-related differences in the apparent biliary clearance of doxorubicin based on the steady state plasma concentrations were observed between male and female rats. However, the net biliary clearance of doxorubicin based on the liver concentration, which represents the actual function of P-glycoprotein and/or Mrp2, was higher in female rats than in male rats. These results suggest that the actual function of the hepatobiliary transport of doxorubicin is greater in female than in male rats. Western blot analysis revealed that the expression of P-glycoprotein and Mrp2 in the liver of female rats was significantly higher than in male rats, similar to results of hepatobiliary excretion experiments. The expression of hepatic cytochrome P450 (CYP) 2B1, which is involved in the metabolism of doxorubicin, was significantly higher in male than in female rats. By pretreatment with testosterone (10 mg/day for 7 days), the actual biliary clearance of doxorubicin in female rats was nearly that of male rats. The protein levels of P-glycoprotein and Mrp2 in female rats were also lowered by treatment with testosterone so as to be nearer those in male rats. These results suggest that gender-related differences exist in P-glycoprotein- and Mrp2-mediated hepatobiliary transport and that these two transporters may be regulated by sex hormones.

Altered Brain Penetration of Diclofenac and Mefenamic Acid, but Not Acetaminophen, in Shiga-Like Toxin II-Treated Mice

It is well accepted that bacterial and virus infections elevate the levels of cytokines in serum and cerebrospinal fluids. Such high levels of cytokines might alter the integrity of the blood-brain barrier (BBB) and/or blood-cerebrospinal fluid barrier (BCSFB), subsequently affecting brain penetration of drugs. However, few reports have addressed this issue. Thus, we investigated brain penetration of cyclooxygenase (COX) inhibitors, commonly used as antipyretics, in mice treated with Shiga-like toxin II (SLT-II) derived from E. coli O157:H7, which significantly elevates cytokine levels. As antipyretics, we used diclofenac, mefenamic acid, and acetaminophen. We found that SLT-II significantly increased the brain-to-plasma concentration ratio (Kp) of diclofenac and mefenamic acid, but not of acetaminophen. Moreover, the Kp of diclofenac and mefenamic acid was increased by probenecid, an anionic compound. These results suggest that efflux anion transporters might be involved in the transport of diclofenac and mefenamic acid. Western blot analysis revealed that SLT-II decreased the expression of organic anion transporter-3, an efflux transporter located on the BBB and/or BCSFB. Taken together, these results suggest that SLT-II and/or SLT-II-stimulated cytokines might change brain penetration of drugs and could possibly increase the risk of their side-effects by altering the expression of transporters.

Role of tumor necrosis factor-alpha in down-regulation of hepatic cytochrome P450 and P-glycoprotein by endotoxin

We investigated the role of tumor necrosis factor-alpha (TNF-alpha) in the down-regulation of hepatic P-glycoprotein and cytochrome P450 (CYP) by endotoxin, using TNF-alpha gene-deficient (TNF-alpha-/-) mice. In the case of P-glycoprotein, endotoxin (10 mg/kg) significantly decreased the expression of hepatic P-glycoprotein in wild-type mice 6 h, but not 24 h, after intraperitoneal injection, with no significant differences in the constitutional expression of P-glycoprotein between wild-type mice and TNF-alpha-/- mice. However, endotoxin had no effect on the expression of P-glycoprotein in TNF-alpha-/- mice either 6 or 24 h after injection. When doxorubicin was administered intravenously to TNF-alpha-/- mice treated 6 h earlier with and without endotoxin, no significant differences in the plasma concentrations of doxorubicin 3 h after injection were observed between endotoxin-treated and untreated TNF-alpha-/- mice. These results suggest that TNF-alpha plays a pivotal role in the down-regulation of P-glycoprotein by endotoxin. In the case of CYP, the constitutive expression of hepatic CYP3A2 and CYP2C11 had a tendency to decline in TNF-alpha-/- mice compared with that in wild-type mice. Endotoxin significantly decreased the expression of hepatic CYP3A2 and CYP2C11 in wild-type mice 24 h after injection, and that decreased expression was significantly greater in TNF-alpha-/- mice than wild-type mice. When antipyrine was administered intravenously to wild-type mice and TNF-alpha-/- mice treated 24 h earlier with endotoxin, the plasma concentrations of antipyrine in TNF-alpha-/- mice 3 h after injection were significantly higher than those in wild-type mice. These findings suggest that TNF-alpha plays a key role in endotoxin-induced down-regulation of hepatic P-glycoprotein, as well as plays a protective role in the regulation of hepatic CYP3A2 and CYP2C11 against endotoxin-induced acute inflammatory response. In TNF-alpha-/- mice, other cytokines appear to function as compensation for the lack of endogenous TNF-alpha.

Effect of pioglitazone on endotoxin-induced decreases in hepatic drug-metabolizing enzyme activity and expression of CYP3A2 and CYP2C11

It has been reported that peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligands ameliorate the expression of inducible nitric oxide synthase (iNOS) by endotoxin. In the present study, we investigated the effect of pioglitazone, a potent PPAR-gamma ligand, on the endotoxin-induced reduction of hepatic drug-metabolizing enzyme activity and on the down-regulation of the expression of hepatic cytochrome P450 (CYP) 3A2 and CYP2C11 proteins in rats. Endotoxin (1 mg/kg) significantly decreased hepatic drug-metabolizing enzyme activity in vivo, as represented by the systemic clearance of antipyrine and protein levels of CYP3A2 and CYP2C11 24 h after intraperitoneal injection. Pretreatment with pioglitazone (10 mg/kg, 4 times at 10-min intervals) significantly protected the endotoxin-induced decreases in the systemic clearance of antipyrine and protein levels of CYP3A2, but not CYP2C11, with no biochemical and histopathological changes in the liver. Pioglitazone alone had no effect on the systemic clearance of antipyrine and protein levels of CYP3A2 or CYP2C11. Pioglitazone significantly protected endotoxin-induced overexpression of iNOS in the liver, but not the overproduction of nitric oxide (NO) in plasma. It is unlikely that the protective effect of pioglitazone against endotoxin-induced decreases in the hepatic drug-metabolizing enzyme activity and protein levels of CYP3A2 in the liver is due to the inhibition of the overproduction of NO.