Biosynthesis, characterisation and direct high-performance liquid chromatographic analysis of gemfibrozil 1-O-beta-acylglucuronide

Gemfibrozil modulates cytochrome P450 and peroxisome proliferation-inducible enzymes in the liver of the yellow European eel (Anguilla anguilla)

The human lipid regulator gemfibrozil (GEM) has been shown to induce peroxisome proliferation in rodents leading to hepatocarcinogenesis. Since GEM is found at biological active concentrations in the aquatic environment, the present study investigates the effects of this drug on the yellow European eel (Anguilla anguilla). Eels were injected with different concentrations of GEM (0.1 to 200 μg/g) and sampled 24- and 96-h post-injection. GEM was shown to inhibit CYP1A, CYP3A and CYP2K-like catalytic activities 24-h post-injection, but at 96-h post-injection, only CYP1A was significantly altered in fish injected with the highest GEM dose. On the contrary, GEM had little effect on the phase II enzymes examined (UDP-glucuronyltransferase and glutathione-S-transferase). Peroxisome proliferation inducible enzymes (liver peroxisomal acyl-CoA oxidase and catalase) were very weakly induced. No evidence of a significant effect on the endocrine system of eels was observed in terms of plasmatic steroid levels or testosterone esterification in the liver.

Bioactivation of Carboxylic Acid Compounds by UDP-Glucuronosyltransferases to DNA-Damaging Intermediates: Role of Glycoxidation and Oxidative Stress in Genotoxicity

Nonenzymatic modification of proteins by acyl glucuronides is well documented; however, little is known about their potential to damage DNA. We have previously reported that clofibric acid undergoes glucuronidation-dependent bioactivation to DNA-damaging species in cultured mouse hepatocytes. The aim of this study was to investigate the mechanisms underlying such DNA damage, and to screen chemically diverse carboxylic acid drugs for their DNA-damaging potential in glucuronidation proficient murine hepatocytes. Cells were incubated with each aglycone for 18 h, followed by assessment of compound cytotoxicity using the MTT assay and evaluation of DNA damage using the Comet assay. Relative cytotoxic potencies were ketoprofen > diclofenac, benoxaprofen, nafenopin >> gemfibrozil, probenecid > bezafibrate > clofibric acid. At a noncytotoxic (0.1 mM) concentration, only benoxaprofen, nafenopin, clofibric acid, and probenecid significantly increased Comet moments (P < 0.05 Kruskal-Wallis). Clofibric acid and probenecid exhibited the greatest DNA-damaging potency, producing significant DNA damage at 0.01 mM concentrations. The two drugs produced maximal increases in Comet moment of 4.51 x and 2.57 x control, respectively. The glucuronidation inhibitor borneol (1 mM) abolished the induction of DNA damage by 0.5 mM concentrations of clofibric acid and probenecid. In an in vitro cell-free system, clofibric acid glucuronide was 10 x more potent than glucuronic acid in causing DNA strand-nicking, although both compounds showed similar rates of autoxidation to generate hydroxyl radicals. In cultured hepatocytes, the glycation inhibitor, aminoguanidine, and the iron chelator, desferrioxamine mesylate, inhibited DNA damage by clofibric acid, whereas the free radical scavengers Trolox and butylated hydroxytoluene, and the superoxide dismutase mimetic bis-3,5-diisopropylsalicylate had no effect. In conclusion, clinically relevant concentrations of two structurally unrelated carboxylic acids, probenecid and clofibric acid, induced DNA damage in isolated hepatocytes via glucuronidation- dependent pathways. These findings suggest acyl glucuronides are able to access and damage nuclear DNA via iron-catalyzed glycation/glycoxidative processes.

Simultaneous quantitation of rosuvastatin and gemfibrozil in human plasma by high-performance liquid chromatography and its application to a pharmacokinetic study

A simple, sensitive and specific high-performance liquid chromatography method is described for simultaneous determination of rosuvastatin (RST) and gemfibrozil (GFZ) in human plasma using celecoxib as an internal standard (IS). The assay procedure involved extraction of RST, GFZ and IS from plasma into acetonitrile. Following separation and evaporation of the organic layer the residue was reconstituted in the mobile phase and injected onto an X-Terra C(18) column (4.6 x 150 mm, 5.0 microm). The chromatographic run time was less than 20 min using flow gradient (0.0-1.60 mL/min) with a mobile phase consisting of 0.01 M ammonium acetate:acetonitrile:methanol (50:40:10, v/v/v) and UV detection at 275 nm. Nominal retention times of RST, GFZ and IS were 6.7, 13.9 and 16.4 min, respectively. Absolute recovery of both analytes and IS was greater than 90%. The lower limit of quantification (LLOQ) of RST and GFZ was 0.03 and 0.30 microg/mL, respectively. Linearity was excellent (r(2) = 0.999) in the 0.03-10 microg/mL and 0.3-100 microg/mL ranges for RST and GFZ, respectively. The inter- and intra-day precisions in the measurement of RST quality control (QC) samples 0.03, 0.09, 2.50 and 8.00 microg/mL were in the range 2.37-9.78% relative standard deviation (RSD) and 0.92-10.08% RSD, respectively. Similarly, the inter- and intra-day precisions in the measurement of GFZ quality control (QC) samples 0.30, 0.90, 25.0 and 80.0 microg/mL were in the ranges 2.79-6.27 and 0.96-9.69% RSD, respectively. Accuracies in the measurement of QC samples for RST and GFZ were in the range 85.43-107.23 and 84.98-102.35% respectively, of the nominal values. RST and GFZ were stable in the array of stability studies viz., bench-top, auto-sampler and freeze-thaw cycles. Stability of RST and GFZ was established for 1 month at -80C. The application of the assay in an oral pharmacokinetic study in rats co-administered with RST and GFZ is described.

The effects of the phytoestrogenic isoflavone genistein on the hepatic disposition of preformed and hepatically generated gemfibrozil 1-O-acyl glucuronide in the isolated perfused rat liver

Foods and complementary medicines contain phytoestrogenic isoflavones such as genistein, which undergo hepatic glucuronidation and excretion into bile and can potentially interfere with the hepatic elimination of other compounds. To investigate this potential, livers from Sprague-Dawley rats were perfused in single-pass mode with preformed gemfibrozil 1-O-acyl glucuronide (GG) (1 microM, n = 12) for 60 min followed by a 30-min washout phase, or with gemfibrozil (1 microM, n = 10) for 120 min. Half of each group of livers were co-perfused with genistein (10 microM) throughout the experiment. Perfusate and bile were analyzed for GG and gemfibrozil by HPLC. Co-perfusion with genistein significantly (P< 0.05) decreased the biliary extraction ratio of preformed GG from a mean of 0.82 to 0.65 and the first-order rate constant for transport of GG into bile from 0.054 +/- 0.010 to 0.032 +/- 0.008 min(-1), but increased the first-order rate constant for sinusoidal efflux of GG from 0.128 +/- 0.023 to 0.227 +/- 0.078 min(-1). Co-perfusion with genistein also significantly decreased the biliary extraction ratio of hepatically generated GG from 0.95 +/- 0.01 to 0.83 +/- 0.05. The findings confirm that genistein increases the potential for hepatic and systemic exposure to hepatically generated glucuronides, which may be important for patients on conventional drugs who consume isoflavones.

UDP-glucuronosyltransferase-dependent bioactivation of clofibric acid to a DNA-damaging intermediate in mouse hepatocytes

Glucuronidation of a number of carboxyl-containing drugs generates reactive acyl glucuronide metabolites. These electrophilic species alkylate cell proteins and may be implicated in the pathogenesis of a number of toxic syndromes seen in patients receiving the parent aglycones. Whether acyl glucuronides also attack nuclear DNA is unknown, although the acyl glucuronide formed from clofibric acid was recently found to decrease the transfection efficiency of phage DNA and generate strand breaks in plasmid DNA in vitro. To determine if such a DNA damage occurs within a cellular environment, the comet assay (i.e. single-cell gel electrophoresis) was used to detect DNA lesions in the nuclear genome of isolated mouse hepatocytes cultured with clofibric acid. Overnight exposure to 50 microM and higher concentrations of clofibric acid produced concentration-dependent increases in the comet areas of hepatocyte nuclei, with 1 mM clofibrate producing a 3.6-fold elevation over controls. These effects closely coincided with culture medium concentrations of the glucuronide metabolite formed from clofibric acid, 1-O-beta-clofibryl glucuronide. Consistent with a role for glucuronidation in the DNA damage observed, the glucuronidation inhibitor borneol diminished glucuronide formation from 100 microM clofibrate by 98% and returned comet areas to baseline levels. Collectively, these results suggest that the acyl glucuronide formed from clofibric acid is capable of migrating from its site of formation within the endoplasmic reticulum to generate strand nicks in nuclear DNA.

Spectrofluorimetric and micelle-enhanced spectrofluorimetric methods for the determination of gemfibrozil in pharmaceutical preparations

A spectrofluorimetric method for the determination of antihyperlipoproteinemic gemfibrozil was developed based on its native fluorescence. This method allows the determination of 0.10-6 microg ml(-1) gemfibrozil in aqueous solution (without using any buffer solution) with excitation and emission wavelengths of 276 and 304 nm, respectively. Detection and quantification limits were 0.03 and 0.10 microg ml(-1), respectively. The fluorescence properties of gemfibrozil in micellar media were also studied. It was shown that in the presence of 0.4% Brij-35 surfactant (pH 4.0, acetic acid-acetate buffer) about 2.4-fold enhancement can be achieved in the fluorescence of this drug. Based on the obtained results, a micelle-enhanced fluorescence method was also developed that is more sensitive than aqueous fluorescence method and has lower detection limit (0.02 microg ml(-1)). Both methods were applied satisfactorily to the determination of gemfibrozil in a commercial pharmaceutical formulation.

Self-micellization of gemfibrozil 1-O-beta acyl glucuronide in aqueous solution

PURPOSE

Phase II metabolism involves the conjugation of a polar moiety, such as sulfate or glucuronic acid, to a (relatively) nonpolar xenobiotic. Although it might be expected that such conjugates may exhibit amphiphilic character (e.g., surface activity and potential to form micelles), no detailed study of the micellization characteristics of any drug-glucuronide conjugates has yet been reported. Therefore, the aim of this study was to investigate the solution behavior and amphiphilic characteristics of gemfibrozil 1-O-beta glucuronide (GG), a model drug-glucuronide conjugate.

METHODS

Crude GG was extracted from the urine of volunteers dosed with 600 mg of gemfibrozil, and this material was then purified by reversed-phase high-performance liquid chromatography to yield a white solid. The amphiphilic properties of GG within the bulk aqueous phase were studied by isothermal titration microcalorimetry and 1H-NMR spectrometry, whereas those at the aqueous/air interface were studied by surface tensiometry.

RESULTS

The results of each independent analytical technique were consistent with GG in aqueous solution exhibiting amphiphilic properties typical of a hydrophilic surfactant. The titration microcalorimetry and 1H-NMR spectrometry data were in excellent agreement with each other, yielding critical micellization concentrations (cmc) for GG in 0.1 M acetate buffer of 18.1 +/- 0.4 mM and 18.3 +/- 0.3 mM, respectively. The profile and results of the surface tension measurements were consistent with GG localizing at the aqueous/air interface.

CONCLUSIONS

These results confirm the hypothesis that a glucuronide conjugate of a relatively nonpolar xenobiotic, such as gemfibrozil, behaves as an amphiphile in aqueous solution. The implications of this observation include a likely basis for the previously observed concentration-dependence in the degradation rate of the acyl glucuronides of 2-phenylpropionic acid, as well as identifying a possible broader contributory effect to the structural dependencies in biliary choleresis of different glucuronide conjugates of xenobiotics.

A sensitive method for the determination of gemfibrozil in human plasma samples by RP-LC

A sensitive high-performance liquid chromatographic assay for the quantitative determination of gemfibrozil is described in this work. Ibuprofen was used as internal standard. The assay involved a single cyclohexane extraction and LC analysis with fluorescence detection. Chromatography was performed at 40 degrees C on a Hypersil ODS column. The mobile phase was a mixture of a solution of phosphoric acid 0.4% and acetonitrile (45:55). The method was validated. The detection limit of this method was 0.025 microg ml(-1); only 0.5 ml of the plasma sample was required for the determination. The calibration graph was linear from 0.05 to 0.5 microg ml(-1) and required a cubic equation from 0.5 to 30 microg ml(-1). Intra and inter-day precision (C.V.) did no exceed 15%. Mean recoveries were of 90.15+/-6.9% (C.V.'s<8%) for gemfibrozil and 93.10% for ibuprofen Applicability of the method was demonstrated by a pharmacokinetic study in normal volunteers who received gemfibrozil by oral route.

LC-1H NMR used for determination of the elution order of S-naproxen glucuronide isomers in two isocratic reversed-phase LC-systems

The reactive metabolite S-naproxen-beta-1-O-acyl glucuronide was purified from human urine using solid phase extraction (SPE) and preparative HPLC. The structure was confirmed by 600 MHz 1H NMR. Directly coupled 600 MHz HPLC-1H NMR was used to assign the peaks in chromatograms obtained when analysing a sample containing S-naproxen aglycone and the 1-, 2-, 3-, and 4-isomers of S-naproxen-beta-1-O-acyl glucuronide in two simple isocratic reversed phase HPLC-systems. Using mobile phase 1 (50 mM formate buffer pH 5.75/acetonitrile 75:25 v/v) the elution order was: 4-O-acyl isomers, beta-1-O-acyl glucuronide, 3-O-acyl isomers, 2-O-acyl isomers, and S-naproxen aglycone. Using mobile phase II (25 mM potassium phosphate pH 7.40/acetonitrile 80:20 v/v) the elution order was: alpha/beta-4-O-acyl isomers, S-naproxen aglycone, beta-1-O-acyl glucuronide, 3-O-acyl isomers, and alpha/beta-2-O-acyl isomers. In both systems the elution order for the 2-, 3- and 4-O-acyl isomers corresponded with previously published results for 2-, 3-, and 4-fluorobenzoic acid glucuronide isomers determined by reversed phase HPLC-1H NMR (U.G. Sidelmann, S.H. Hansen, C. Gavaghan, A.W. Nicholls, H.A.J. Carless, J.C. Lindon, I.D. Wilson, J.K. Nicholson, J. Chromatogr. B Biomed. Appl. 685 (1996) 113-122]. The alpha-1-O-acyl isomer was found to be present at approximately 3% of the initial S-naproxen-beta-1-O-acyl glucuronide concentration in the glucuronide isomer mixture after 6 h of incubation at pH 7.40 and 37 degrees C. In both HPLC systems it eluted just before the beta-1-O-acyl glucuronide well separated from other isomers. Investigators should consider the possible formation of a alpha-1-O-acyl isomer when studying glucuronide reactivity and degradation.

Atorvastatin and gemfibrozil metabolites, but not the parent drugs, are potent antioxidants against lipoprotein oxidation

Increased atherosclerosis risk in hyperlipidemic patients may be a result of the enhanced oxidizability of their plasma lipoproteins. We have previously shown that hypocholesterolemic drug therapy, including the 3-hydroxy-3-methyl-glutaryl CoenzymeA (HMG-CoA) reductase inhibitors, and the hypotriglyceridemic drug bezafibrate, significantly reduced the enhanced susceptibility to oxidation of low density lipoprotein (LDL) isolated from hyperlipidemic patients. Although this antioxidative effect could not be obtained in vitro with all of these drugs, the active drug metabolites, which are formed in vivo, could affect lipoprotein oxidizability. We thus sought to analyze the effect of atorvastatin and gemfibrozil, as well as specific hydroxylated metabolites, on the susceptibility of LDL, very low density lipoprotein (VLDL), and high density lipoprotein (HDL) to oxidation. LDL oxidation induced by either copper ions (10 microM CuSO4), by the free radical generator system 2'-2'-azobis 2-amidino propane hydrochloride (5 mM AAPH), or by the J-774A.1 macrophage-like cell line, was not inhibited by the parent forms of atorvastatin or gemfibrozil, but was substantially inhibited (57-97%), in a concentration-dependent manner, by pharmacological concentrations of the o-hydroxy and the p-hydroxy metabolites of atorvastatin, as well as by the p-hydroxy metabolite (metabolite I) of gemfibrozil. On using the atorvastatin o-hydroxy metabolite and gemfibrozil metabolite I in combination an additive inhibitory effect on LDL oxidizability was found. Similar inhibitory effects (37-96%) of the above metabolites were obtained for the susceptibility of VLDL and HDL to oxidation in the oxidation systems outlined above. The inhibitory effects of these metabolites on LDL, VLDL, and HDL oxidation could be related to their free radical scavenging activity, as well as (mainly for the gemfibrozil metabolite I) to their metal ion chelation capacities. In addition, inhibition of HDL oxidation was associated with the preservation of HDL-associated paraoxonase activity. We conclude that atorvastatin hydroxy metabolites, and gemfibrozil metabolite I possess potent antioxidative potential, and as a result protect LDL, VLDL, and HDL from oxidation. We hypothesize that in addition to their beneficial lipid regulating activity, specific metabolites of both drugs may also reduce the atherogenic potential of lipoproteins through their antioxidant properties.