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

Antimutagenic activity of ipriflavone against the DNA-damage induced by cyclophosphamide in mice

In the present study we evaluated the potential of ipriflavone against the cytotoxic and mutagenic effects induced by cyclophosphamide chemotherapeutic agent in bone marrow cells of mice, using the micronucleus assay in vivo on cells of bone marrow. The study was performed following three protocols: pre-treatment, simultaneous treatment and post treatment. The results demonstrated that ipriflavone has a protective effect against mutagenicity induced by cyclophosphamide in the pre-treatment and post-treatment and against the cytotoxicity in all treatments. There was variation between the genders in some of the experimental groups. To evaluate their possible mechanisms of action, it was performed the DPPH assay, which showed no ability to donate hydrogens, suggesting that it acts through other mechanisms. Due to its ability to prevent chromosomal damage, ipriflavone is likely to open an interest field concerning its possible the use in clinical applications.

Pharmacokinetics of drugs in mutant Nagase analbuminemic rats and responses to select diuretics

OBJECTIVES

To report (1) the pharmacokinetics of drugs that are mainly metabolized via hepatic cytochrome P450s (CYPs) or mainly excreted via the urine and bile, (2) the mechanism for the urinary excretion of drugs (such as glomerular filtration or renal active secretion or re-absorption), and (3) the diuretic effect of some loop diuretics in mutant Nagase analbuminaemic rats (NARs), an animal model for human familial analbuminaemia based on the pharmacokinetics of drugs reported in the literatures.

KEY FINDINGS

In NARs, the changes in the time-averaged non-renal clearances (CL(NR)s) of drugs that are mainly metabolized via CYPs were explained in terms of changes in the hepatic intrinsic clearance (mainly because of changes in CYPs), free (unbound) fractions of drugs in the plasma (fp) and hepatic blood-flow rate (QH) depending on the hepatic excretion ratios of drugs.

SUMMARY

The CL(NR) changes of drugs mainly metabolized via hepatic CYPs can be sufficiently explained by the three earlier mentioned factors. The plasma albumin (furosemide) or globulin (azosemide, bumetanide and torasemide) binding affects their diuretic effects.

Determination of ipriflavone in human plasma by LC-MS and its application in a pharmacokinetic study

A sensitive liquid chromatography-mass spectrometric method was developed for the quantification of ipriflavone in human plasma. The method utilized liquid-liquid extraction of plasma with ethyl acetate. A gradient elution was performed on a Hedera ODS-2 column (150×2.1 mm i.d., 5 µm), using a mobile phase consisting of 0.1% formic acid solution and methanol at a flow rate of 0.5 mL/min. The single quadrupole mass spectrometer was operated in selected-ion monitoring mode via positive electrospray ionization interface detecting m/z 239.1 and 285.1 for ipriflavone and diazepam (the internal standard), respectively. To improve the selectivity and sensitivity, the fragment ion m/z 239.1, which was produced by in-source collision-induced dissociation, was chosen as the quantitative ion for ipriflavone. The method was fully validated and applied to a pharmacokinetic study of ipriflavone. After oral administration of a single 200 mg ipriflavone tablet, the C(max,) AUC(0-72 h) , t(1/2) and T(max) were 6.3±6.3 ng/mL, 80.0±69.1 µg h/L, 23.0±8.6 h and 3.4±2.1 h, respectively.

Pharmacokinetics of drugs in rats with diabetes mellitus induced by alloxan or streptozocin: comparison with those in patients with type I diabetes mellitus

Objectives

In rats with diabetes mellitus induced by alloxan (DMIA) or streptozocin (DMIS), changes in the cytochrome P450 (CYP) isozymes in the liver, lung, kidney, intestine, brain, and testis have been reported based on Western blot analysis, Northern blot analysis, and various enzyme activities. Changes in phase II enzyme activities have been reported also. Hence, in this review, changes in the pharmacokinetics of drugs that were mainly conjugated and metabolized via CYPs or phase II isozymes in rats with DMIA or DMIS, as reported in various literature, have been explained. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized in the kidney, and that were excreted mainly via the kidney or bile in DMIA or DMIS rats were reviewed also. For drugs mainly metabolized via hepatic CYP isozymes, the changes in the total area under the plasma concentration–time curve from time zero to time infinity (AUC) of metabolites, AUCmetabolite/AUCparent drug ratios, or the time-averaged nonrenal and total body clearances (CLNR and CL, respectively) of parent drugs as reported in the literature have been compared.

Key findings

After intravenous administration of drugs that were mainly metabolized via hepatic CYP isozymes, their hepatic clearances were found to be dependent on the in-vitro hepatic intrinsic clearance (CLint) for the disappearance of the parent drug (or in the formation of the metabolite), the free fractions of the drugs in the plasma, or the hepatic blood flow rate depending on their hepatic extraction ratios. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized via the kidney in DMIA or DMIS rats were dependent on the drugs. However, the biliary or renal CL values of drugs that were mainly excreted via the kidney or bile in DMIA or DMIS rats were faster.

Summary

Pharmacokinetic studies of drugs in patients with type I diabetes mellitus were scarce. Moreover, similar and different results for drug pharmacokinetics were obtained between diabetic rats and patients with type I diabetes mellitus. Thus, present experimental rat data should be extrapolated carefully in humans.

Effects of cytochrome P450 inhibitors on the biotransformation of fluorogenic substrates by adult male rat liver microsomes and cDNA-expressed rat cytochrome P450 isoforms

We have evaluated the use of a panel of six fluorogenic cytochrome P450 (CYP) substrates as a potential tool for rapid screening for global changes in CYP activity in rats under different physiological conditions. The biotransformation of 3-[2-(N,N-diethyl-N-methylammonium)ethyl]-7-methoxy-4-methylcoumarin (AMMC), 7-benzyloxy-4-(trifluoromethyl)-coumarin, 7-benzyloxyquinoline, 3-cyano-7-ethoxycoumarin, 7-methoxy-4-(trifluoromethyl)-coumarin, and 7-ethoxy-4-trifluoromethyl-coumarin by microsomes from adult male rat liver were characterized, their sensitivities to 15 putative inhibitors were determined and compared to similar experiments using nine different complementary DNA (cDNA)-expressed rat CYPs. Inhibitory profiles of the substrates in microsomes were different from each other, with some overlap, suggesting that each substrate is to some extent biotransformed by a different CYP isoform. Ketoconazole and clotrimazole were nonselective inhibitors, while ticlopidine selectively inhibited biotransformation of AMMC. CYP2A1 did not biotransform any of the substrates, and CYP2E1 was insensitive to all the inhibitors tested. Some inhibitors did not affect the biotransformation of the fluorogenic substrates by cDNA-expressed isoforms as predicted by their effects on conventional substrates, e.g., chlorzoxazone and diethyldithiocarbamate were inactive against CYP2E1, and CYP2C6 was not inhibited by sulfaphenazole. When results in microsomes and cDNA-expressed CYPs were compared, only the majority of the biotransformation of AMMC by microsomes could be assigned with full confidence to a specific CYP isoform, namely CYP2D2. Nevertheless, different inhibitory profiles of the substrates indicate that the panel will be useful for rapid functional quantification of global CYP activity in rats under different experimental conditions. Our results also demonstrate the inappropriateness of extrapolating inhibitory data between conventional and fluorogenic CYP substrates.

Investigating the in vitro metabolism of veratridine: characterization of metabolites and involved cytochrome P450 isoforms

Veratridine is a lipid-soluble alkaloid extracted from Veratrum officinale and other species of the family Liliaceae. Veratridine prevents inactivation of Na(+) channel via binding the receptor site 2, causes influx of sodium ion and depolarization and induces apoptosis of neuronal cells. In the present study, we investigated the metabolism of veratridine and the effects of selective cytochrome P450 (CYP) inhibitors on the metabolism of veratridine in rat liver microsomes. The metabolites were separated and assayed by liquid-chromatography-electrospray ionization-ion trap tandem mass spectrometry (LC-ESI-QIT-MSn), and further identified by their mass spectra and chromatographic behaviors. Result showed that four CYP isoforms (CYP1A, CYP2B, CYP2E1, CYP3A) were involved in the metabolism of veratridine in vitro and seven metabolites of veratridine were detected incubating with rat liver microsomes. Some of the metabolites were presumed to be potential mediates of neurotoxicity via protein binging. Further research in vivo needs to link the metabolism of veratridine to its toxicity.

Characterization of cytochrome P450s mediating ipriflavone metabolism in human liver microsomes

Ipriflavone, a synthetic flavonoid for the prevention and treatment of osteoporosis, has been reported to be extensively metabolized in man to seven metabolites (M1-M7). This study was performed to characterize the human liver cytochrome P450s (CYP) responsible for the metabolism of ipriflavone. Hydroxylation at the beta-ring to M3, O-dealkylation to M1 and oxidation at isopropyl group to M4 and M5 are major pathways for ipriflavone metabolism in three different human liver microsome preparations. The specific CYPs responsible for ipriflavone oxidation to the active metabolites, M1, M3, M4 and M5 were identified using a combination of correlation analysis, immuno-inhibition, chemical inhibition in human liver microsomes and metabolism by expressed recombinant CYP enzymes. The inhibitory potencies of ipriflavone and its five metabolites, M1-M5 on seven clinically important CYPs were investigated in human liver microsomes. Our results demonstrate that CYP3A4 plays the major role in O-dealkylation of ipriflavone to M1 and CYP1A2 plays a dominant role in the formation of M3, M4 and M5. Ipriflavone and/or its five metabolites were found to inhibit potently the metabolism of CYPs 1A2, 2C8, 2C9 and 2C19 substrates.

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 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.

Characterization of metabolites and cytochrome P450 isoforms involved in the microsomal metabolism of aconitine

Aconitine, a major Aconitum alkaloid, is well known for its high toxicity that induces severe arrhythmias leading to death. The current study investigated the metabolism of aconitine and the effects of selective cytochrome P450 (CYP) inhibitors on the metabolism of aconitine in rat liver microsomes. The metabolites were separated and assayed by liquid chromatography-ion trap mass spectrometry (LC/MS(n)) and further identified by comparison of their mass spectra and chromatographic behaviors with reference substances. Various selective inhibitors of CYP were used to identify the isoforms of CYP, that involved in the metabolism of aconitine. A total of at least six metabolites were found and characterized in rat liver microsomal incubations. Result showed that the inhibitor of CYP 3A had an inhibitory effect on aconitine metabolism in a concentration-dependant manner, the inhibitor of CYP1A1/2 had a modest inhibitory effect, whereas inhibitors of CYP2B1/2, 2D and 2E1 had no obvious inhibitory effects on aconitine metabolism. Aconitine might be metabolized by CYP 3A and CYP1A1/2 isoforms in rat liver microsome.

Pharmacokinetic changes of ipriflavone in rats with acute renal failure induced by uranyl nitrate

Pharmacokinetic parameters of ipriflavone were compared after intravenous (20 mg/kg) and oral (200 mg/kg) administration in control rats and in rats with acute renal failure induced by uranyl nitrate (U-ARF rats). It was expected that the time-averaged nonrenal clearance (Cl(nr)) of ipriflavone in U-ARF rats could be significantly slower than in the control rats, since it was reported that ipriflavone was metabolized via the hepatic microsomal cytochrome P450 (CYP) 1A1/2 and 2C11 and the expression and mRNA level of CYP1A2 were not changed, but those of CYP2C11 were decreased in U-ARF rats compared with control rats. Unexpectedly, after intravenous administration in U-ARF rats, the Cl(nr) of ipriflavone was significantly faster than in the controls (40.8 compared with 29.0 ml/min/kg). This may be due to an increase in the glucuronide conjugate formation of ipriflavone metabolites in U-ARF rats. After oral administration of ipriflavone in U-ARF rats, the AUC(0-24 h) was significantly smaller (194 compared with 295 microg min/ml) than in the controls.