Species differences in the chirality of the carbonyl reduction of [14C] fenofibrate in laboratory animals and humans

Comparisons of pharmacokinetics and NO-releasing of nitrofibriate and fenofibrate after oral administration in rats

Nitrofibriate, a new compound of hypolipidemic, is modified based on fenofibrate. Both of them are used for prevention and treatment of cardiovascular diseases. In this study, an accurate and sensitive analytical method of reversed-phase high-performance liquid chromatography was developed to determine fenofibric acid, which is an active metabolite of both nitrofibriate and fenofibrate in rat plasma. This method was validated and successfully applied to pharmacokinetic study of nitrofibriate and fenofibrate after oral administration. The results suggested that the pharmacokinetic behavior of nitrofibriate followed a nonlinear process, while fenofibrate was linear, demonstrating that the two drugs were different in pharmacokinetic behaviors. Moreover, the effect of fenofibrate and nitrofibriate on releasing NO in rat serum was explored. This study showed that nitrofibriate, as a nitric oxide donor, could slowly release nitric oxide in vivo. This study provided a biopharmaceutical basis for further study of nitrofibriate.

Human Carbonyl Reduction Pathways and a Strategy for Their Study In Vitro

Carbonyl reduction plays a significant role in physiological processes throughout the body. Although much is known about endogenous carbonyl metabolism, much less is known about the roles of carbonyl-reducing enzymes in xenobiotic metabolism. Multiple pathways exist in humans for metabolizing carbonyl moieties of xenobiotics to their corresponding alcohols, readying these molecules for subsequent conjugation and/or excretion. When exploring carbonyl reduction clearance pathways for a drug development candidate, it is possible to assess the relative contributions of these enzymes due to their differences in subcellular locations, cofactor dependence, and inhibitor profiles. In addition, the contributions of these enzymes may be explored by varying incubation conditions, such as pH. Presently, individual isoforms of carbonyl-reducing enzymes are not widely available, either in recombinant or purified form. However, it is possible to study carbonyl reduction clearance pathways from simple experiments with commercially available reagents. This article provides an overview of carbonyl-reducing enzymes, including some kinetic data for substrates and inhibitors. In addition, an experimental strategy for the study of these enzymes in vitro is presented.

Distribution of fenofibric acid in lipoprotein fractions of patients

The antidyslipidemic agent fenofibrate (procetofen) is hydrolysed in vivo to its main active metabolite--fenofibric (procetofenic) acid. This metabolite is usually determined in pharmacokinetic studies, because plasma concentrations of fenofibrate are practically undetectable. Presented study is focussed on the distribution of fenofibric acid into lipoprotein (VLDL, LDL, IDL and HDL) fractions of human and (for comparison) minipig blood plasma, which has not been studied yet. In order to obtain more accurate results, a new HPLC method based on the use of newly synthetized internal standards was developed. Four homologues of fenofibric acid prepared have identical chromophoric part of their molecules and hence the same UV spectra as fenofibric acid. From this point of view, these standards are more suitable for determination of fenofibric acid than the formerly used ones--naproxen or bezafibrate. Fenofibric acid levels in the high density lipoprotein fraction has been shown to be significantly higher (in both human and minipig plasma) than in the other lipoprotein fractions. This fact may be explained by higher affinity of the fenofibric acid to proteins constituting major part of the high density lipoprotein fraction.

Stereoselectivity of the carbonyl reduction of dolasetron in rats, dogs, and humans

The initial step in the metabolism of dolasetron or MDL 73,147EF [(2 alpha, 6 alpha, 8 alpha, 9a beta)-octahydro-3-oxo-2,6-methano-2H- quinolizin-8-yl 1H-indol-3-carboxylate, monomethanesulfonate] is the reduction of the prochiral carbonyl group to give a chiral secondary alcohol "reduced dolasetron." An HPLC method, using a chiral column to separate reduced dolasetron enantiomers, has been developed and used to measure enantiomers in urine of rats, dogs, and humans after dolasetron administration. In all cases, the reduction was enantioselective for the (+)-(R)-enantiomer, although the dog showed lower stereoselectivity, especially after iv administration. An approximate enantiomeric ratio (+/-) of 90:10 was found in rat and human urine. The contribution of further metabolism to this enantiomeric ratio was considered small as preliminary studies showed that oxidation of the enantiomeric alcohols by human liver microsomes demonstrated only minor stereoselectivity. Further evidence for the role of stereoselective reduction in man was obtained from in vitro studies, where dolasetron was incubated with human whole blood. The enantiomeric composition of reduced dolasetron formed in human whole blood was the same as that found in human urine after administration of dolasetron. Enantioselectivity was not due to differences in the absorption, distribution, metabolism, or excretion of enantiomers, as iv or oral administration of rac-reduced dolasetron to rats and dogs lead to the recovery, in urine, of essentially the same enantiomeric composition as the dose administered. it is fortuitous that the (+)-(R)-enantiomer is predominantly formed by carbonyl reductase, as it is the more active compound.

Identification of a benzhydrolic metabolite of ketoprofen in horses by gas chromatography-mass spectrometry and high-performance liquid chromatography

A benzhydrolic metabolite of ketoprofen, formed by reduction of the keto group of the drug, has been identified by gas chromatography-mass spectrometry in equine plasma and urine. After partial synthesis, its structure has been confirmed by UV, IR and 1H NMR spectroscopy. The kinetics of ketoprofen and this metabolite have been monitored in plasma by high-performance liquid chromatography. The two products were quantified in plasma up to 4 and 3 h, respectively, and were detected in urine up to 72 and 24 h, respectively, after a single intravenous administration to horses at the dose of 2.2 mg/kg. Simultaneous detection of both compounds increases the reliability of antidoping control analysis.

Synthesis of the enantiomers of reduced haloperidol

Reduced haloperidol (RHAL) is the best known metabolite of haloperidol (HAL), having been identified in humans, rats, and guinea pigs. Since RHAL contains an asymmetric center, it can exist in two possible enantiomeric forms. However, the enantiomeric composition of the RHAL formed from HAL in vivo has never been reported. As a first step toward the enantiomeric analysis of biological samples, we have developed an efficient and stereospecific synthesis of (+)- and (-)-RHAL from readily available commercial materials. We have also identified an enantioselective chromatographic method using a chiral HPLC stationary phase which can detect as little as 1% of either enantiomer in synthetic samples of RHAL enantiomers.

Pharmacokinetic studies with the lipid-regulating agent beclobrate: enantiospecific assay for beclobric acid using a new fluorescent chiral coupling component (S-FLOPA)

The major biotransformation pathway for the chiral lipid-regulating agent beclobrate is conversion to the corresponding carboxylic acid, which is then metabolized to the acyl glucuronide. An enantiospecific assay for biological material was developed that is based on chiral derivatization with N-ethyl-N'-(3-dimethylaminopropyl)carbodiimide (EDAC) and the primary amine S-FLOPA, a new chiral coupling component for carboxylic acids derived from the 2-arylpropionic acid S-flunoxaprofen. Conversion of beclobric acid to the acyl chloride prior to coupling with the amine is also feasible. From plasma or urine beclobric acid was extracted into n-hexane/ethanol (9:1) at pH 4 after addition of sodium chloride. Clofibric acid was used as internal standard. Derivatization with EDAC/FLOPA was performed under addition of 1-hydroxybenzotriazole in anhydrous dichloromethane containing trace amounts of pyridine (ambient temperature/2 h reaction time). The chromatographic separation was performed on a silica gel stationary phase (Zorbax Sil) using n-hexane-chloroform-ethanol (100:10:0.75, by vol) as mobile phase [flow rate, 2 ml/min; fluorescence detection, 305/355 nm; elution order of the derivatives, (-) before (+)]. Coefficients of variation were between 1.3 and 9.3% for both plasma and urine. Limit of quantification was 20-25 ng/ml for plasma based on a sample volume of 0.2 ml. Application of the assay in a pilot pharmacokinetic study showed significant differences between the kinetics of the two enantiomers. In plasma and urine, the concentrations of the dextrorotatory enantiomer exceeded those of the levorotatory enantiomer significantly.