Stereoselective determination of propafenone enantiomers in transgenic Chinese hamster CHL cells expressing human cytochrome P450

Stereoselective glucuronidation of carvedilol by Chinese liver microsomes

OBJECTIVE

To study the stereoselective glucuronidation of carvedilol (CARV) by three Chinese liver microsomes.

METHODS

The metabolites of CARV were identified by a hydrolysis reaction with beta-glucuronidase and HPLC-MS/MS. The enzyme kinetics for CARV enantiomers glucuronidation was determined by a reversed phase-high pressure liquid chromatography (RP-HPLC) assay using (S)-propafenone as internal standard after precolumn derivatization with 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylisothiocyanate.

RESULTS

Two CARV glucuronides were found in three Chinese liver microsomes incubated with CARV. The non-linear regression analysis showed that the values of K(m) and V(max) for (S)-CARV and (R)-CARV enantiomers were (118+/-44) micromol/L, (2 500+/-833) pmol/(min.mg protein) and (24+/-7) micromol/L, (953+/-399) pmol/(min.mg protein), respectively.

CONCLUSION

These results suggested that there was a significant (P<0.05) stereoselective glucuronidation of CARV enantiomers in three Chinese liver microsomes, which might partly explain the enantioselective pharmacokinetics of CARV.

Stereoselective chromatography of cardiovascular drugs: an update

This review reports the latest achievements in chromatographic enantioseparations of various classes of cardiovascular drugs and selected applications of these methods in pharmaceutical and clinical analysis. The use of these drugs as test compounds for new chiral stationary phases and different parameters of chromatographic processes is also presented.

Analysis of enantiomers of chiral phenethylamine drugs by capillary gas chromatography/mass spectrometry/flame-ionization detection and pre-column chiral derivatization

Several important chiral phenethylamine agents such as mexiletine, fenfluramine, amphetamine, methamphetamine and N-n-propylamphetamine show stereoselective disposition in humans and large differences in therapeutic relevance and toxicity. To analyze the enantiomers of chiral amine drugs, stereoselective methods were developed to separate those enantiomers on an achiral capillary gas chromatography by pre-column chiral derivatization with S-(-)-N-(fluoroacyl)-prolyl chloride. The stereoselectivity and sensitivity can be improved by chiral derivatization. The methods established offer enantioselective, simple, flexible and economic approaches for the analysis of chiral amine drug enantiomers in biological fluids. The methods have been used to determine S-(+)-methamphetamine in human forensic samples and to analyze enantiomers of amphetamine and fenfluramine in rat liver microsomes.

Chiral reversed phase high-performance liquid chromatography for determining propranolol enantiomers in transgenic Chinese hamster CHL cell lines expressing human cytochrome P450

An enantioselective assay for S-(-)- and R-(+)-propranolol in transgenic Chinese hamster CHL cell lines, expressing human cytochrome P450 (CYP), was developed. The method involves extraction of propranolol from the S(9) incubates, using S-(+)-propafenone as internal standard, chiral derivatization with 2,3,4,6-tetra-O-beta-D-glucopranosyl isothiocyanate and quantitation by reversed phase high-performance liquid chromatography system with UV detection (lambda=220 nm). A baseline separation of propranolol enantiomers was achieved on a 5-microm reverse-phase ODS column, with a mixture of methanol/water/glacial acetic acid (67:33:0.05, v/v) as mobile phase. The assay is linear from 5 to 500 microM for each enantiomer. The analytical method affords average recoveries of 99.2% and 98.8% for S-(-)- and R-(+)-propranolol, respectively. The limit of quantitation for the method is 5 microM for both S-(-)- and R-(+)-propranolol. The reproducibility of the assay is satisfactory (RSD < 10%). The method allowed study of the depletion of S-(-)- and R-(+)-propranolol in transgenic Chinese hamster CHL cell lines expressing CYP3A4, CYP2C18 and CYP2C9.

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

AIM: To study the influence of inducers of drug metabolism enzyme, β-naphthoflavone (BNF) and dexamethasone (DEX), on the stereoselective metabolism of propafenone in the rat hepatic microsomes.

METHODS: Phase I metabolism of propafenone was studied using the microsomes induced by BNF and DEX and the non-induced microsome was used as the control. The enzymatic kinetics parameters of propafenone enantiomers were calculated by regress analysis of Eadie-Hofstee Plots. Propafenone enantiomer concentrations were assayed by a chiral HPLC.

RESULTS: The metabolite of propafenone, N-desalkylpropafenone, was found after incubation of propafenone with the rat hepatic microsomes induced by BNF and DEX. In these two groups, the stereoselectivity favoring R (-) isomer was observed in metabolism at low substrate concentrations of racemic propafenone, but lost the stereoselectivity at high substrate concentrations. However, in control group, no stereoselectivity was observed. The enzyme kinetic parameters were: ① K_m. Control group: R (-) 83 ± 6, S (+) 94 ± 7; BNF group: R (-) 105 ± 6, S (+) 128 ± 14; DEX group: R (-) 86 ± 11, S (+) 118 ± 16; ② υ_max. Control group: R (-) 0.75 ± 0.16, S (+) 0.72 ± 0.07; BNF group: R (-)1.04 ± 0.15, S (+)1.0 7 ± 14; DEX group: R (-) 0.93 ± 0.06, S (+) 1.04 ± 0.09; ③ Cl_int. Control group: R (-) 8.9 ± 1.1, S (+) 7.6 ± 0.7; BNF group: R (-)9.9 ± 0.9, S (+)8.3 ± 0.7; DEX group: R (-) 10.9 ± 0.8, S (+) 8.9 ± 0.9. The enantiomeric differences in K_m and Cl_int were both significant, but not in υ_max, in BNF and DEX group. Whereas enantiomeric differences in three parameters were all insignificant in control group. Furthermore, K_m and υ max were both significantly less than those in BNF or DEX group. In the rat liver microsome in duced by DEX, nimodipine (NDP) decreased the stereoselectivity in propafenone metabolism at low substrate concentration. The inhibition of NDP on the metabolism of propafenone was stereo selective with R (-)-isomer being impaired more than S (+)-isomer. The inhibition constant (Ki) of S (+)- and R (-)-propafenone, calculated from Dixon plots, was 15.4 and 8.6 mg•L¯¹, respectively.

CONCLUSION: CYP1A subfamily (induced by BNF) and CYP3A4 (induced by DEX) have pronounced contribution to propafenone N-desalkylation which exhibited stereose lectivity depending on substrate concentration. The molecular base for this phenomenon is the stereo selectivity in affinity of substrate to the enzyme activity centers instead of at the catalyzing sites.