Clofibric acid and gemfibrozil removal in membrane bioreactors.

The removal of two blood lipid regulators, clofibric acid (CLA) and gemfibrozil (GFZ), was evaluated using two identical aerobic membrane bioreactors with 6.5 L effective volume each. Polysulfone ultrafiltration hollow fiber membranes were submerged in the reactors. Different operating conditions were tested varying the organic load (F/M), hydraulic residence time (HRT), biomass concentration measured as total suspended solids in the mixed liquor (MLTSS) and the sludge retention time (SRT). Complete GFZ removal was obtained with F/M of 0.21-0.48 kg COD kgTSS⁻¹ d⁻¹, HRT of 4-10 hours, SRT of 10-32 d and MLTSS of 6-10 g L⁻¹. The GFZ removal can be attributed to biodegradation and there was no accumulation of the compound in the biomass. The CLA removals improved with the SRT and HRT increase and F/M decrease. Average removals of 78-79% were obtained with SRT 16-32 d, F/M of 0.21-0.34 kgCOD kgTSS⁻¹ d⁻¹, HRT of 7-10 hours and MLTSS of 6-10 g L⁻¹. Biodegradation was found to be the main removal pathway.

A simple and sensitive method for the determination of fibric acids in the liver by liquid chromatography.

Fibrates are used in biochemical and pharmacological studies as bioactive tools. Nevertheless, most studies have lacked information concerning the concentrations of fibric acids working inside tissues because a simple and sensitive method is not available for their quantitation. This study aimed to develop a simple and sensitive bioanalytical method for the quantitation of clofibric, bezafibric and fenofibric acids in samples of very small portions of tissues. Fibric acids were extracted into n-hexane-ethyl acetate from tissue homogenates (10 mg of liver, kidney or muscle) or serum (100 µL) and were derivatized with 4-bromomethyl-6,7-dimethoxycoumarin, followed by HPLC with fluorescence detection. These compounds were separated isocratically on a reversed phase with acetonitrile-water. Standard analytical curves were linear over the concentration range of 0.2-20 nmol/10 mg of liver. Precision and accuracy were within acceptable limits. Recovery from liver homogenates ranged from 93.03 to 112.29%. This method enabled the quantitation of fibric acids in 10 mg of liver from rats treated with clofibric acid, bezafibric acid or fenofibrate. From these analytical data, it became clear that there was no large difference in ratio of acyl-CoA oxidase 1 (Acox1) mRNA level to fibric acid content in the liver among the three fibric acids, suggesting that these three fibric acids have similar potency to increase expression of the Acox1 gene, which is a target of peroxisome proliferator-activated receptor α. Thus, the proposed method is a simple, sensitive and reliable tool for the quantitation of fibric acids working in vivo inside livers.

Are 20-hydroxyecdysone and related genes potential biomarkers of sublethal exposure to lipid-altering contaminants?

In Daphnia magna, 20-hydroecdysone (20E) is the main molting hormone and its metabolism is of interest to identify new biomarkers of exposure to contaminants. The present study aimed to (i) assess baseline levels of 20E and transcription levels of four related-genes (shade, neverland, ultraspiracle, and ecdysteroid receptor); and (ii) evaluate effects in D. magna after 21 days of exposure to fenarimol (anti-ecdysteroid) and a mixture of gemfibrozil and clofibric acid (lipid-lowering drugs) at sublethal concentrations. Endpoints included transcription of the target genes and quantification of 20E, mortality, and reproduction of daphnids. Baseline results showed that average responses were relatively similar and did not vary more than 2-fold. However, intra-day variation was generally high and could be explained by sampling individuals with slightly different stages of their development. Exposure tests indicated a significant decrease in daphnid reproduction following chronic exposure to a concentration of 565 µg/L of fenarimol. However, no difference was observed between the control and exposed groups for any of the investigated genes, nor for the levels of 20E after 21 days of exposure. Following exposition to gemfibrozil and clofibric acid at 1 µg/L, no changes were observed for the measured parameters. These results suggest that changes in transcription levels of the target genes and concentrations of 20E may not be sensitive endpoints that can be used as biomarkers of sublethal exposure to the target compounds in D. magna. Measuring multiple time points instead of a single measure as well as additional molecular endpoints obtained from transcriptomic and metabolomic studies could afford more insights on the changes occurring in exposed daphnids to lipid-altering compounds and identify efficient biomarkers of sublethal exposure.

Clofibric acid increases the formation of oleic acid in endoplasmic reticulum of the liver of rats.

The effects of 2-(4-chlorophenoxy)-2-methylpropionic acid (clofibric acid) on the formation of oleic acid (18:1) from stearic acid (18:0) and utilization of the 18:1 formed for phosphatidylcholine (PC) formation in endoplasmic reticulum in the liver of rats were studied in vivo. [¹4C]18:0 was intravenously injected into control Wistar male rats and rats that had been fed on a diet containing 0.5% (w/w) clofibric acid for 7 days; and the distribution of radiolabeled fatty acids among subcellular organelles, microsomes, peroxisomes, and mitochondria, was estimated on the basis of correction utilizing the yields from homogenates of marker enzymes for these organelles. The radioactivity was mostly localized in microsomes and the radiolabeled fatty acids present in microsomes were significantly increased by the treatment of rats with clofibric acid. The formation of radiolabeled 18:1 in microsomes markedly increased and incorporations of the formed [¹4C]18:1 into PC and phosphatidylethanolamine in microsomes were augmented in response to clofibric acid. The [¹4C]18:1 incorporated into PC was mostly located at the C-2 position, but not the C-1 position, of PC, and the radioactivity in 18:1 at the C-2 position of PC was strikingly increased by clofibric acid. These results obtained from the in vivo experiments directly link the findings that clofibric acid treatment induces microsomal stearoyl-CoA desaturase and 1-acylglycerophosphocholine acyltransferase in the liver and the findings that the treatment with the drug elevated absolute mass and mass proportion of 18:1 at the C-2 position, but not the C-1 position, of PC in the liver together.

Effects of fibrates, anti-inflammatory drugs and antidepressants in the fish hepatoma cell line PLHC-1: cytotoxicity and interactions with cytochrome P450 1A.

Effects of 11 pharmaceuticals belonging to three therapeutic classes (lipid regulators from the fibrate group, non-steroidal anti-inflammatory drugs and anti-depressives from the selective serotonin reuptake inhibitors group) were assessed in the fish hepatoma cell line (PLHC-1) by looking at cytotoxicity and interactions with cytochrome P450 1A (CYP1A) function. Among the tested pharmaceuticals, fluoxetine and paroxetine exerted cytotoxic effects, cell viability decreased to 52% and 6% after 24 h of exposure to 20 microM fluoxetine and paroxetine, respectively. The cytotoxicity of both compounds was modulated by cytochrome P450 inhibitors and was dramatically reduced when culture medium was supplemented with reduced glutathione and vitamin E succinate. Additionally, exposure of PLHC-1 cells to some pharmaceuticals led to an early and transient induction of ethoxyresorufin O-deethylase (EROD) activity: bezafibrate and antidepressants induced EROD activity at a concentration of 1 microM whereas clofibrate, ibuprofen and naproxen acted as inducers at a higher concentration (10 microM). These effects might be of toxicological concern since alterations of CYP1A may affect xenobiotic metabolism and toxicity.

Behaviour of pharmaceutical products and biodegradation intermediates in horizontal subsurface flow constructed wetland. A microcosm experiment.

Horizontal subsurface flow constructed wetlands (SSFCWs) are a cost-effective and sustainable alternative to conventional wastewater treatment plants (WWTPs) for sanitation in small communities. SSFCWs are designed to remove suspended solids and organic matter from wastewater but there is little information on the effect of the characteristics of organic matter on the removal efficiency of specific contaminants. In this paper, carbamazepine, ibuprofen and clofibric acid were continuously injected into two SSFCW microcosms fed with synthetic wastewater containing different organic matter sources: dissolved (glucose) and particulate (starch). The response curves of carbamazepine and ibuprofen were compared with that of clofibric acid, which was used as a conservative tracer. The removal efficiencies were found to be independent of the organic matter type (i.e. dissolved or particulate). Carbamazepine was removed inefficiently (5%) by bed sorption, whereas ibuprofen was removed by degradation (51%). In addition, the behaviour of the two main ibuprofen biodegradation intermediates (carboxy and hydroxy derivatives) supported that the main ibuprofen elimination pathway occurs in aerobic conditions.

Dyslipidemia as a risk factor for erectile dysfunction.

Erectile dysfunction (ED) is a common condition with a significant effect on quality of life. The prevalence of ED increases with age and other risk factors (hypertension, diabetes, smoking, coronary heart disease, dyslipidemia and depression). Nitric oxide (NO) activity is adversely affected, in penile and vascular tissue, by these risk factors. Endothelial dysfunction and a reduced generation or bioavailability of NO have emerged as major pathophysiological mechanisms in ED. Hyperlipidemia may impair erectile function by affecting endothelial and smooth muscle cells of the penis. Oxidized low-density lipoprotein is a causative factor for the impaired relaxation response of the corpus cavernosum. Elevated serum cholesterol and reduced high density lipoprotein cholesterol levels are associated with an increased risk of ED. It follows that treating dyslipidemia could have a beneficial effect on ED. Phosphodiesterase type 5 inhibitors are now considered as first line treatment for ED. There is evidence that statins improve responses to these drugs. ED is considered as a warning sign of silent or early vascular disease. The use of statins may be beneficial in these patients.

Selection of a support matrix for the removal of some phenoxyacetic compounds in constructed wetlands systems.

The efficiency of constructed wetlands systems in the removal of pollutants can be significantly enhanced by using a support matrix with a greater capacity to retain contaminants by sorption phenomena, ionic exchange or other physico-chemical processes. The aim of this work was to evaluate the efficiencies of 3 different materials, Light Expanded Clay Aggregates [LECA] (in two different particle sizes), Expanded Perlite and Sand, for the removal from water of one pharmaceutical compound (clofibric acid) and one pesticide (MCPA). Both belong to the class of phenoxyacetic compounds. In addition, relationships were established between the compounds' removal efficiencies and the physico-chemical properties of each material. LECA exhibited a high sorption capacity for MCPA, while the capacity for clofibric acid was more modest, but still significant. In contrast, perlite had a very limited sorption capacity while sand did not exhibit any sorption capacity for any of the compounds. LECA with smaller particle sizes showed higher efficiencies than larger grade LECA and can achieve efficiencies near 100% for the lower concentrations in the order of 1 mg l(-1). However, the use of these smaller particle media at larger scales may present problems with hydraulic conductivities. The results show that expanded clay presents important advantages in laboratory studies and could be used as a filter medium or a support matrix in constructed wetlands systems.

Metabolism of clofibric acid in zebrafish embryos (Danio rerio) as determined by liquid chromatography-high resolution-mass spectrometry.

The zebrafish embryo (ZFE) is increasingly used in ecotoxicology research but detailed knowledge of its metabolic potential is still limited. This study focuses on the xenobiotic metabolism of ZFE at different life-stages using the pharmaceutical compound clofibric acid as study compound. Liquid chromatography with quadrupole-time-of-flight mass spectrometry (LC-QToF-MS) is used to detect and to identify the transformation products (TPs). In screening experiments, a total of 18 TPs was detected and structure proposals were elaborated for 17 TPs, formed by phase I and phase II metabolism. Biotransformation of clofibric acid by the ZFE involves conjugation with sulfate or glucuronic acid, and, reported here for the first time, with carnitine, taurine, and aminomethanesulfonic acid. Further yet unknown cyclization products were identified using non-target screening that may represent a new detoxification pathway. Sulfate containing TPs occurred already after 3h of exposure (7hpf), and from 48h of exposure (52hpf) onwards, all TPs were detected. The detection of these TPs indicates the activity of phase I and phase II enzymes already at early life-stages. Additionally, the excretion of one TP into the exposure medium was observed. The results of this study outline the high metabolic potential of the ZFE with respect to the transformation of xenobiotics. Similarities but also differences to other test systems were observed. Biotransformation of test chemicals in toxicity testing with ZFE may therefore need further consideration.

Photocatalytic degradation of carbamazepine, clofibric acid and iomeprol with P25 and Hombikat UV100 in the presence of natural organic matter (NOM) and other organic water constituents.

The photocatalytic degradation of natural organic matter (NOM) and organic substance mixtures under simulated solar UV light has been investigated with suspended TiO(2). It could be shown by size-exclusion chromatography that photocatalysis of NOM led to a reduction of the average hydrodynamic radii and presumably of the nominal molecular weight, too. The decrease of the UV/Vis absorption of NOM was faster than the NOM mineralization. This study also focuses on the different abilities of photocatalytic materials (P25 and Hombikat UV100) to decrease persistent substances influenced by the presence of NOM and mixtures of pharmaceuticals or diagnostic agents. In general, the presence of NOM and other organic substances retarded the photocatalysis of a specific persistent substance by the combination of radiation attenuation, competition for active sites and surface deactivation of the catalyst by adsorption. The results of this work prove that photocatalysis is a promising technology to reduce persistent substances like NOM, carbamazepine, clofibric acid, iomeprol and iopromide even if they are present in a complex matrix.

Effects of the lipid regulating drug clofibric acid on PPARα-regulated gene transcript levels in common carp (Cyprinus carpio) at pharmacological and environmental exposure levels.

In mammals, the peroxisome proliferator-activated receptor α (PPARα) plays a key role in regulating various genes involved in lipid metabolism, bile acid synthesis and cholesterol homeostasis, and is activated by a diverse group of compounds collectively termed peroxisome proliferators (PPs). Specific PPs have been detected in the aquatic environment; however little is known on their pharmacological activity in fish. We investigated the bioavailability and persistence of the human PPARα ligand clofibric acid (CFA) in carp, together with various relevant endpoints, at a concentration similar to therapeutic levels in humans (20mg/L) and for an environmentally relevant concentration (4µg/L). Exposure to pharmacologically-relevant concentrations of CFA resulted in increased transcript levels of a number of known PPARα target genes together with increased acyl-coA oxidase (Acox1) activity, supporting stimulation of lipid metabolism pathways in carp which are known to be similarly activated in mammals. Although Cu,Zn-superoxide dismutase (Sod1) activity was not affected, mRNA levels of several biotransformation genes were also increased, paralleling previous reports in mammals and indicating a potential role in hepatic detoxification for PPARα in carp. Importantly, transcription of some of these genes (and Acox1 activity) were affected at exposure concentrations comparable with those reported in effluent discharges. Collectively, these data suggest that CFA is pharmacologically active in carp and has the potential to invoke PPARα-related responses in fish exposed in the environment, particularly considering that CFA may represent just one of a number of PPAR-active compounds present to which wild fish may be exposed.

The effects of fibrates on lipoprotein and hemostatic coronary risk factors.

The effects of fibrates on lipoprotein profiles and lipoprotein physiology, as well as on selected coagulation and fibrinolytic factors are reviewed. It is concluded that the action of fibrates on these systems is such as to render the fibrates beneficial in atherosclerosis prevention.

Differential influence of anionic and cationic charge on the ability of amphiphilic drugs to interact with DPPC-liposomes.

The compounds clofibric acid and chlorphentermine have identical aromatic ring systems, but when charged their side chains are anionic or cationic, respectively. The drugs were applied as tools to investigate whether the interaction of amphiphilic drugs with the zwitterionic dipalmitoyl-phosphatidylcholine (DPPC) depends on the charge of the polar side chain. In suspensions of DPPC-liposomes, the drug-effect on the phase-transition temperature (Tt) was evaluated by means of differential scanning calorimetry. The drug-binding was determined spectrophotometrically. The clofibric acid anion had a much weaker depressing effect on Tt than the chlorphentermine-cation and a considerably lower ability to bind to the DPPC-liposomes. Furthermore, a plot of the effect versus the binding suggested that the clofibric acid-anion had a lower intrinsic activity to reduce Tt compared with the chlorphentermine-cation. In contrast, when the dissociation-equilibrium was shifted towards the uncharged state both drugs were indistinguishable with respect to effect and binding, suggesting that the differences observed with the charged forms could indeed be attributed to the opposite charges. The findings are tentatively explained to result from a different ability of the anionic and the cationic form to reach the hydrophobic interior of the DPPC-bilayer.

Lack of evidence for a hepatic peroxisome proliferator receptor and an explanation for the binding of hypolipidaemic drugs to liver homogenates.

The existence of a postulated hepatic receptor responsible for the peroxisomal proliferation induced in rodents by hypolipidaemic drugs has been investigated. [3H]-nafenopin and [3H]-ciprofibrate were used as labelled ligands and two competitive binding assays, using either a charcoal-dextran or a hydroxylapatite method, were developed to investigate potential binding. In both assay systems, specific displaceable binding of either nafenopin or ciprofibrate to whole homogenate, microsomal and cytosolic fractions of rat liver could not be detected in a variety of buffer systems. A positive control of ligand binding to bovine serum albumin indicated the validity of the binding assays used. In addition, both nafenopin and ciprofibrate exhibited displaceable binding to serum albumin using the hydroxylapatite binding assay and a Scatchard analysis of the binding of [3H]-nafenopin to fatty acid free rat serum albumin yielded a dissociation constant of 5.2 x 10(-7) M and 86 pmol of ligand bound per mg protein. Taken collectively, our data strongly argues against the existence of a specific hepatic peroxisome proliferation receptor and indicates that the peroxisome proliferating hypolipidaemic drugs bind to serum albumin and possibly to other cellular proteins not involved in the activation of genes necessary for peroxisome proliferation.

Hepatic microsomal glucuronidation of clofibric acid in the adult and neonate albino rat.

Hepatic microsomal UDP glucuronyltransferase activity towards the acid substrate clofibric acid has been described in the adult and neonate albino rat. The enzyme was maximally activated, approximately 2-fold, in the presence of 0.1-0.4% (w/v) digitonin. Induction of the digitonin activated clofibric acid glucuronyltransferase was observed following phenobarbitone treatment in vivo (2.2-fold), and to a lesser extent, following beta-naphthoflavone treatment (1.3-fold). Clofibrate treatment in vivo (of which clofibric acid is the ester hydrolysis product) had no effect on clofibric acid glucuronidation in vitro. The activity of clofibric acid glucuronyltransferase in the liver of rat before and at birth was low (approx. 0.08 nmoles glucuronide formed/min/mg microsomal protein). The activity increased 5-fold during the first three post-natal days. After this time, the activity increased linearly reaching adult levels by four weeks after birth. The data indicated that clofibric acid glucuronyltransferase belongs to the neonatal cluster of enzymes and clofibric acid is a group 2 substrate. Clofibric acid, a common therapeutic agent, is a useful, acid substrate for the estimation of mammalian hepatic microsomal glucuronyltransferase activity.

Peroxisome proliferating sulphur- and oxy-substituted fatty acid analogues are activated to acyl coenzyme A thioesters.

In liver homogenates from untreated rats the sulphur-substituted fatty acid analogues tetradecylthioacetic acid (CMTTD) was activated to its acyl-coenzyme A thioester. The activation was found to take place in the mitochondrial, microsomal and peroxisomal fractions. The activity of CMTTD-CoA synthetase was 50% compared to palmitoyl-CoA synthetase in all cellular fractions. When rats were treated with the peroxisome proliferating sulphur-substituted fatty acid analogues CMTTD and 3-dithiahexadecanedioic acid (BCMTD), the CMTTD-CoA synthetase activity was induced in mitochondrial, peroxisomal and microsomal fractions. Palmitoyl-CoA synthetase was induced proportionally. In rats treated with tetradecylthiopropionic acid (CETTD) of low peroxisome proliferating potency, the activities of CMTTD-CoA synthetase and palmitoyl-CoA synthetase were inhibited in mitochondrial and microsomal fractions. In contrast, all three sulphur-substituted acids induced the activity of palmitoyl-CoA synthetase and CMTTD-CoA synthetase in peroxisomes. Both the CMTTD-CoA and palmitoyl-CoA synthetase activities were induced by CMTTD and BCMTD, in close correlation to the induction of peroxisomal beta-oxidation. During the three treatment regimes, CMTTD-CoA synthetase activity ran parallel to the palmitoyl-CoA synthetase activity at a rate of 50% in all cellular fractions. Thus, CMTTD is assumed to be activated by the long-chain acyl-CoA synthetase enzyme. Rats were treated for 5 days with sulphur- and oxy-substituted fatty acid analogues, clofibric acid and fenofibric acid. All compounds which induced peroxisomal beta-oxidation activity in vivo could be activated to their respective CoA thioesters in liver homogenate. CETTD which induced peroxisomal beta-oxidation only two-fold, was activated at a rate of 50% compared to palmitate. Fenofibric acid induced peroxisomal beta-oxidation 9.6-fold, while it was activated at a rate of only 10% compared to palmitate. Thus, no correlation was found between rate of activation in vitro and induction of peroxisomal activity in vivo. On the other hand, tetradecylsulfoxyacetic acid (TSOA) and tetradecylsulfonacetic acid (TSA) (sulphuroxygenated metabolites of CMTTD) with no inductive effects, were not activated to their respective CoA derivatives. Altogether the data suggest that the enzymatic activation of the peroxisome proliferating compounds is essential for their proliferating activity, but the rate of activation does not determine the potency of the proliferators. The role of the xenobiotic-CoA pool in relation to the whole coenzyme A profile during peroxisome proliferation is discussed.

The short- and long-term effects of bezafibrate in the rat.

Bezafibrate is a potent hypolipidemic agent, which causes marked proliferation of peroxisomes in rat liver. At the same dosage, bezafibrate is more effective in male than in female rats. This is probably related to divergent pharmacokinetics, which cause differences in drug level in serum and liver. The volume density of peroxisomes and several of their enzymes such as carnitine acetyl transferase and acyl-COA oxidase increase in a dose-related fashion. The hypolipidemic effect of bezafibrate, however, does not correlate with the used dosage. This implies that peroxisomal proliferation may play only a minor role in the hypolipidemic action of bezafibrate. In animals treated for 26 months with 300, 750, or 1500 ppm bezafibrate, the relative liver weight and serum triglycerides did not differ significantly from controls. Peroxisomal proliferation varied in different cells, being most prominent in single hepatocytes. The liver catalase activity was significantly reduced, but carnitine acetyl transferase was increased. Abnormal peroxisomes and mitochondria with longitudinal cristae were quite frequent. In one focus, catalase activity was severely diminished ahd peroxisomes were markedly reduced. The incidence of liver tumors was the same (1-3%) in treated animals as in controls.

Haloacetate-induced oxidative damage to DNA in the liver of male B6C3F1 mice.

Brominated and chlorinated haloacetates (HAs) are by-products of drinking water disinfection. Dichloroacetate (DCA) and trichloroacetate (TCA) are hepatocarcinogenic in rodents, but the brominated analogs have received little study. Prior work has indicated that acute doses of the brominated derivatives are more potent inducers of oxidative stress and increase the 8-hydroxydeoxyguanosine (8-OH-dG) content of the nuclear DNA in the liver. Since, DCA and TCA are also known as weak peroxisome proliferators, the present study was intended to determine whether this activity might be exacerbated by peroxisomal proliferation. Classical responses to peroxisome proliferators, cyanide-insensitive acyl-CoA oxidase activity and increased 12-hydroxylation of lauric acid, were elevated in a dose-related manner in mice maintained on TCA and clofibric acid (positive control), but not with DCA, dibromoacetate (DBA) or bromochloroacetate (BCA). Administration of the HAs in drinking water to male B6C3F1 mice for periods from 3 to 10 weeks resulted in dose-related increases in 8-OH-dG in nuclear DNA of the liver with DBA and BCA, but not with TCA or DCA. These findings indicate that oxidative damage induced by the haloacetates is, at least in part, independent of peroxisome proliferation. In addition, these data suggest that oxidative damage to DNA may play a more important role in the chronic toxicology of brominated compared to the chlorinated haloacetates.

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.

Disposition of etofibrate, clofibric and nicotinic acid esters, and their products in dogs.

Etofibrate, the ethylene glycol diester of clofibric and nicotinic acids, on intravenous infusion into dogs, has a terminal half-life of 2 min. The intermediate half-esters, the nicotinate and the clofibrate, have respective terminal half-lives of 4.6 and 1.7 min and appear fleetingly when etofibrate is administered. In contrast to the 42-h terminal half-life of clofibric acid, the other final transformation product, nicotinic acid, shows saturable or dose-dependent pharmacokinetics in dogs that conform to the Michaelis-Menten equation with a terminal half-life of 4.4 min at low concentrations (less than 6.9 microM/kg). Three distinct metabolites of nicotinic acid can be identified and assayed chromatographically in the urine. The partition properties were similar to nicotinic acid. Nicotinic acid is excreted 30% unchanged into urine with a renal clearance of 70 mL/min in 27-kg dogs.