Chiral metabolism of propafenone in rat hepatic microsomes treated with two inducers

Effect of Rythmol (propafenone HCl) administration during pregnancy in Wistar rats

Propafenone is a well-known Class 1C antiarrhythmic agent that has sodium channel blocking properties as well as the ability to block 13 other channels and a modest calcium antagonistic effect. Propafenone has a profound electrophysiologic effect on auxiliary atrioventricular circuits and in patients with atrioventricular nodal reentry tachycardia can obstruct conduction in the fast conducting pathway. Furthermore, propafenone is less likely than other Class 1C drugs to cause proarrhythmia. However, although this medicine can pass through the placenta, the effects during pregnancy remain unknown. Here, we investigated the potential teratogenic and genotoxic effects of Rythmol during rat development. Pregnant Wistar rats received 46.25 mg/kg body weight of propafenone daily by gavage from Gestation Day (GD) 5 to GD 19. At GD 20, the dams were dissected, and their fetuses were assessed via morphologic, skeletal, and histologic investigation. In addition, a comet assay was used to measure DNA impairment of fetal skull osteocytes and hepatic cells. The study showed that propafenone treatment of pregnant rats led to a marked decrease in gravid uterine weight, number of implants/litter, number of viable fetuses, and bodyweight of fetuses but a clear increase in placental weight and placental index in the treated group. Frequent morphologic abnormalities and severe ossification deficiency in the cranium bones were observed in the treatment group. Various histopathological changes were observed in the liver, kidney, and brain tissues of maternally treated fetuses. Similarly, propafenone induced DNA damage to examined samples. Thus, our study indicates that propafenone may be embryotoxic in humans.

The characterisation of the in vitro metabolism and transport of 6-hydroxykynurenic acid, an important constituent of Ginkgo biloba extracts

6-Hydroxykynurenic acid (6-HKA) is a nitrogen-containing phenolic acid compound in Ginkgo biloba leaves. The pharmacological activities of 6-HKA have been reported and shown that 6-HKA has the potential to become a therapeutic drug and may play an important role in the treatment of nervous system diseases. However, there are few studies on the drug metabolism and transport of 6-HKA. The aim of this study is to investigate the in vitro metabolism of 6-HKA and its interaction with multiple important drug transporters.The in vitro metabolism experiments in the present study demonstrate that 6-HKA might not undergo phase-I or phase-II metabolism in hepatic microsomes/S9 of rats. In addition, some drug transporters, including OAT1/3, OCT2, MDR1, OATP1B1, MATE1/2K and OCTN2, were investigated. The cellular uptake assays indicate that 6-HKA exhibits inhibition to the transport of classical substrates mediated by OAT3, OCT2, MATE2K and OCTN2 but has no significant effect on the transport of substrates mediated by MDR1, OAT1, OATP1B1 or MATE1. Further investigation of cellular accumulation assays shows that 6-HKA might be the substrate of OAT3, but not OCT2 or OCTN2. The bidirectional transport study suggests that 6-HKA is not a substrate of MDR1.The information about the in vitro metabolism of 6-HKA and the interaction between 6-HKA and some transporters will help us to better understand the pharmacokinetic properties of 6-HKA and provide reference for its pharmacodynamics, DDIs and drug-food interactions studies.

Regioselective hydroxylation of an antiarrhythmic drug, propafenone, mediated by rat liver cytochrome P450 2D2 differs from that catalyzed by human P450 2D6

1. Propafenone, an antiarrhythmic drug, is a typical human cytochrome P450 (P450) 2D6 substrate used in preclinical studies. Here, propafenone oxidation by mammalian liver microsomes was investigated in vitro. 2. Liver microsomes from humans and marmosets preferentially mediated propafenone 5-hydroxylation, minipig, rat and mouse livers primarily mediated 4'-hydroxylation, but cynomolgus monkey and dog liver microsomes differently mediated N-despropylation. 3. Quinine, ketoconazole or anti-P450 2D antibodies suppressed propafenone 4'/5-hydroxylation in human and rat liver microsomes. Pretreatments with β-naphthoflavone or dexamethasone increased N-despropylation in rat livers. 4. Recombinant rat P450 2D2 efficiently catalysed propafenone 4'-hydroxylation in a substrate inhibition manner, comparable to rat liver microsomes, while human P450 2D6 displayed propafenone 5-hydroxylation. Human and rat P450 1A, 2C and 3A enzymes mediated propafenone N-despropylation with high capacities. 5. Carbon-4' of propafenone docked favourably into the active site of P450 2D2 based on an in silico model; in contrast, carbon-5 of propafenone docked into human P450 2D6. 6. These results suggest that the major roles of individual P450 2D enzymes in regioselective hydroxylations of propafenone differ between human and rat livers, while the minor roles of P450 1A, 2C and 3A enzymes for propafenone N-despropylation are similar in livers of both species.

Biosynthesis and stereoselective analysis of (-)- and (+)-zaltoprofen glucuronide in rat hepatic microsomes and its application to the kinetic analysis

Zaltoprofen, available commercially as a racemic mixture, is a propionic acid derivative of non-steroidal anti-inflammatory drugs (NSAIDs). Firstly, (+)- and (-)-zaltoprofen glucuronide was biosynthesized and purified. Then a simple and rapid RP-HPLC analysis method for direct determination of (+)- and (-)-zaltoprofen glucuronide in rat hepatic microsomes was developed and validated. The calibration curves of (+)- and (-)-zaltoprofen glucuronide both showed good linearity in the concentration range from 0.15 to 31.13 μM. The lower limit of quantification was 0.15 μM. Finally, this method was used to investigate the enantioselectivity of zaltoprofen glucuronidation in rat hepatic microsomes. The kinetics of zaltoprofen glucuronidation in rat hepatic microsomes for 40 min incubation fit the Michaelis-Menten model. Kinetic analysis indicated that (-)-zaltoprofen had a higher glucuronidation rate in rat liver microsome than that of (+)-zaltoprofen. The catalyzing efficiency (V(max)/K(m)) ratio of (+)-zaltoprofen to (-)-enantiomer is 0.8 times in rat liver microsomes.

Direct determination of S-(-)- and R-(+)-propranolol glucuronide in rat hepatic microsomes by RP-HPLC

Propranolol, available commercially as a racemic mixture, is a non-selective beta-adrenergic blocking agent used in the treatment of hypertension, angina pectoris and cardiac arrhythmias. We have developed and validated an RP-HPLC assay method for direct determination of R-(+)- and S-(-)-propranolol glucuronide in rat hepatic microsomes to investigate the enantioselectivity of propranolol glucuronidation metabolism. A baseline separation of propranolol glucuronide enantiomers was achieved on a 5 microm reversed-phase ODS column, with a mixture of phosphate buffer (pH 3.5, 0.067 mol/L) and methanol (55:45, v/v) as mobile phase. Ultraviolet detection was set at 220 nm, and p-nitrobenzoic acid was used as internal standard. The standard curve of assay for R-(+)- and S-(-)-propranolol glucuronide in spiked microsomal incubate showed good linearity throughout the concentration range from 0.50 to 20.0 micromol/L. The analytical method affords average recovery of 99.8 and 100.1% for R-(+)- and S-(-)-propranolol glucuronide, respectively. The method provides a high sensitivity and good precision for R-(+)- and S-(-)-propranolol glucuronide (RSD < 10%). The LOD was 0.15 micromol/L and the LOQ was 0.5 micromol/L (RSD < 8%, n = 5) for both R-(+)- and S-(-)-propranolol glucuronide. The method is simple, precise and accurate, and is suitable for quantifying the propranolol glucuronides enantiomers in rat hepatic microsomes.

Determination of zolmitriptan enantiomers in rat liver microsomes by chiral high performance liquid chromatography with ?uorescence detection

A selective chiral high performance liquid chromatographic method was developed and validated to separate and quantify the enantiomers of a new potent selective 5-HT(1B/1D) receptor partial agonist, S-zolmitriptan, and its antipode in rat liver microsomes induced with beta-naphtho flavone. S- and R-zolmitriptan were extracted from rat hepatic microsomal incubates with chloroform/isopropanol (75:25, v/v), and were separated on a narrow-bore enantioselective normal phase Chiralpak AD-H column (250 x 0.46 mm) with hexane-isopropanol-triethylamine (72/28/0.25, v/v/v) as mobile phase and fluorescence detection with emission at 350 nm and excitation at 291 nm. The calibration curves were linear for R- and S-zolmitriptan concentration over the range 0.1-5.0 microg/mL (r = 0.9996 and 0.9999), and the limits of quantitation were 0.1 microg/mL. The metabolism and interaction of the enantiomers of zolmitriptan in treated hepatic microsomes were investigated using chiral HPLC. There was significant difference between the disposition of the S- and R-zolmitriptan when racemic zolmitriptan or single enantiomers of zolmitriptan were incubated for 5, 10 and 20 min, suggesting that the metabolism of zolmitriptan in rat liver microsomes is enantioselective. In addition, there was also a significant difference between the IC(50) of R- to S-zolmitriptan and S- to R-zolmitriptan (IC(50S/R)/IC(50R/S) = 45.2). This indicated that the disposition process favored the S-form of zolmitriptan.

Potential inhibition of cytochrome P450 3A4 by propofol in human primary hepatocytes

AIM: Hepatic cytochrome P450 isoenzymes constitute a superfamily of hemoproteins that play a major role in the metabolism of endogenous compounds and in the detoxification of xenobiotic molecules. P450 3A4 is one of the most important forms in human being, and mediates the metabolism of around 70% of therapeutic drugs and endogenous compounds. Propofol, a widely used intravenous anesthetic drug, is known to inhibit cytochrome P450 activities in isolated rat hepatocytes. The goal of this study was to evaluate the potential efficacy of propofol on P450 3A4 in a dose-dependent manner to understand its drug-drug interaction.

METHODS: Hepatocytes were isolated from liver specimens from hepatic angioma patients undergone hepatic surgery. Primary incubated hepatocytes were treated with 0, 0.01, 0.05, 0.1, 0.5, and 1.0 mM propofol for 24 hours. P450 3A4 activity was measured with Nash’s colorimetry. The protein expression was assessed by Western blot analysis.

RESULTS: A dose-dependent inhibitory effect of propofol was observed in cytochrome P450 3A4 activity. A minimal dosage of propofol (0.01 mM) induced a significant inhibition of P450 3A4 activity, although its regular dosages (0.01-0.1 mM) showed no inhibitory effect on the cellular protein expression of P450 3A4.

CONCLUSION: Propofol may be a potential CYP3A4 inhibitor as this anesthetic can inhibit isoenzyme activity significantly and reduce the metabolic rate of CYP3A4 substrates. This inhibition occurs at post-expression level, and concentration of propofol used clinically does not affect CYP3A4 protein expression. propofol may thus induce drug interaction of cytochrome P450 3A4 activity at the dosage used clinically.