Biodegradation of emerging organic pollutant gemfibrozil: Mechanism, kinetics and pathway modelling

The increasing population has raised the demand for pharmaceutical and personal care products to maintain a good health. Gemfibrozil (GEM), is extensively used as a lipid regulator and is frequently detected in wastewater treatment systems and poses deleterious health and ecological effects. Hence, the current study employing Bacillus sp. N2 reports the degradation of gemfibrozil via co-metabolism in 15 days. The study reported 86 % degradation with GEM (20 mgL^-1) using sucrose (150 mgL^-1) as a co-substrate; as compared to 42 % without a co-substrate. Further, time-profiling studies of metabolites revealed significant demethylation and decarboxylation reactions during degradation that leads to formation of six (M1, M2, M3, M4, M5, M6) metabolites as by-products. Based on the LC-MS analysis a potential degradation pathway for GEM by Bacillus sp. N2 was proposed. The degradation of GEM has not been reported so far and the study envisages eco-friendly approach to tackle pharmaceutical- active- compounds.

Multimarker Responses of Zebrafish to the Effect of Ibuprofen and Gemfibrozil in Environmentally Relevant Concentrations

Pharmaceutical pollution of water bodies is among the top-notch environmental health risks all over the world. The aim of the present study was to investigate the effects of two common pharmaceuticals namely ibuprofen and gemfibrozil on zebrafish at environmentally relevant concentrations. In zebrafish liver, gemfibrozil caused a decrease in glutathione and glutathione transferase and an increase in catalase but had no effect on lipid peroxidation and protein carbonylation. Ibuprofen altered the antioxidant defense system, promoted protein carbonylation in zebrafish liver, and increased vitellogenin-like protein in the blood. Ibuprofen and particularly gemfibrozil induced lysosomes biogenesis. Lactate dehydrogenase in the blood was also found to be higher in the studied groups. Studied pharmaceuticals did not affect complex II of the electron respiratory chain. Ibuprofen affects zebrafish health status more profoundly than gemfibrozil. Our results showed that pharmaceuticals even in low, environmentally realistic concentrations, induced profound changes in the stress-responsive systems of zebrafish.

Critical Differences between Enzyme Sources in Sensitivity to Detect Time-Dependent Inactivation of CYP2C8

Clopidogrel acyl-β-d-glucuronide is a mechanism-based inhibitor of cytochrome P450 2C8 in human liver microsomes (HLMs). However, time-dependent inactivation (TDI) of CYP2C8 could not be detected in an earlier study in human recombinant CYP2C8 (Supersomes). Here, we investigate whether different enzyme sources exhibit differences in detection of CYP2C8 TDI under identical experimental conditions. Inactivation of CYP2C8 by amiodarone (100 μM), clopidogrel acyl-β-d-glucuronide (100 μM), gemfibrozil 1-O-β-glucuronide (100 μM), and phenelzine (100 μM) was investigated in HLMs and three recombinant human CYP2C8 preparations (Supersomes, Bactosomes, and EasyCYP Bactosomes) using amodiaquine N-deethylation as the marker reaction. Furthermore, the inactivation kinetics of CYP2C8 by clopidogrel glucuronide (5-250 μM) was determined in Supersomes and Bactosomes. Amiodarone caused weak TDI in all enzyme preparations tested, while the extent of inactivation by clopidogrel glucuronide, gemfibrozil glucuronide, and phenelzine varied markedly between preparations, and even different Supersome lots. Both glucuronides caused strong inactivation of CYP2C8 in HLMs, Bactosomes and in one Supersome lot (>50% inhibition), but significant inactivation could not be reliably detected in other Supersome lots or EasyCYP Bactosomes. In Bactosomes, the concentration producing half of kinact (KI) and maximal inactivation rate (kinact) of clopidogrel glucuronide (14 μM and 0.054 minute-1) were similar to those determined previously in HLMs. Phenelzine caused strong inactivation of CYP2C8 in one Supersome lot (91% inhibition) but not in HLMs or other recombinant CYP2C8 preparations. In conclusion, different enzyme sources and different lots of the same recombinant enzyme preparation are not equally sensitive to detect inactivation of CYP2C8, suggesting that recombinant CYPs should be avoided when identifying mechanism-based inhibitors.

Effects and bioaccumulation of gold nanoparticles in the gilthead seabream (Sparus aurata) - Single and combined exposures with gemfibrozil

Gold nanoparticles (AuNPs) are found in a wide range of applications and therefore expected to present increasing levels in the environment. There is however limited knowledge concerning the potential toxicity of AuNPs as well as their combined effects with other pollutants. Hence, the present study aimed to investigate the effects of AuNPs alone and combined with the pharmaceutical gemfibrozil (GEM) on different biological responses (behaviour, neurotransmission, biotransformation and oxidative stress) in one of the most consumed fish in southern Europe, the seabream Sparus aurata. Fish were exposed for 96 h to waterborne 40 nm AuNPs with two coatings - citrate and polyvinylpyrrolidone (PVP), alone or combined with GEM. Antioxidant defences were induced in liver and gills upon both AuNPs exposure. Decreased swimming performance (1600 μg.L^-1) and oxidative damage in gills (4 and 80 μg.L^-1) were observed following exposure to polyvinylpyrrolidone coated gold nanoparticles (PVP-AuNPs). Generally, accumulation of gold in fish tissues and deleterious effects in S. aurata were higher for PVP-AuNPs than for cAuNPs exposures. Although AuNPs and GEM combined effects in gills were generally low, in liver, they were higher than the predicted. The accumulation and effects of AuNPs showed to be dependent on the size, coating, surface charge and aggregation/agglomeration state of nanoparticles. Additionally, it was tissue' specific and dependent on the presence of other contaminants. Although, gold intake by humans is expected to not exceed the estimated tolerable daily intake, it is highly recommended to keep it on track due to the increasing use of AuNPs.

Enhanced pharmaceutical removal from water in a three step bio-ozone-bio process

Individual treatment processes like biological treatment or ozonation have their limitations for the removal of pharmaceuticals from secondary clarified effluents with high organic matter concentrations (i.e. 17 mg TOC/L). These limitations can be overcome by combining these two processes for a cost-effective pharmaceutical removal. A three-step biological-ozone-biological (BO₃B) treatment process was therefore designed for the enhanced pharmaceutical removal from wastewater effluent. The first biological step removed 38% of ozone scavenging TOC, thus proportionally reducing the absolute ozone input for the subsequent ozonation. Complementariness between biological and ozone treatment, i.e. targeting different pharmaceuticals, resulted in cost-effective pharmaceutical removal by the overall BO₃B process. At a low ozone dose of 0.2 g O₃/g TOC and an HRT of 1.46 h in the biological reactors, the removal of 8 out of 9 pharmaceuticals exceeded 85%, except for metoprolol (60%). Testing various ozone doses and HRTs revealed that pharmaceuticals were ineffectively removed at 0.1 g O3/g TOC and an HRT of 0.3 h. At HRTs of 0.47 and 1.46 h easily and moderately biodegradable pharmaceuticals such as caffeine, gemfibrozil, ibuprofen, naproxen and sulfamethoxazole were over 95% removed by biological treatment. The biorecalcitrant carbamazepine was completely ozonated at a dose of 0.4 g O₃/g TOC. Ozonation products are likely biodegraded in the last biological reactor as a 17% TOC removal was found. No appreciable acute toxicity towards D. magna, P. subcapitata and V. fischeri was found after exposure to the influents and effluents of the individual BO₃B reactors. The BO₃B process is estimated to increase the yearly wastewater treatment tariff per population equivalent in the Netherlands by less than 10%. Overall, the BO₃B process is a cost-effective treatment process for the removal of pharmaceuticals from secondary clarified effluents.

Transport behavior of the pharmaceutical compounds carbamazepine, sulfamethoxazole, gemfibrozil, ibuprofen, and naproxen, and the lifestyle drug caffeine, in saturated laboratory columns

Despite the large number of pharmaceutically active compounds found in natural environments little is known about their transport behavior in groundwater, which is complicated by their wide range of physical and chemical properties. The transport behavior of five widely used and often detected pharmaceutical compounds and one lifestyle drug has therefore been investigated, using a set of three column experiments. The investigated compounds were the anticonvulsant carbamazepine, the lifestyle drug caffeine, the antibiotic sulfamethoxazole, the lipid regulator gemfibrozil, and the nonsteroidal anti-inflammatories ibuprofen and naproxen. The columns were filled with three different types of sand. The substrates consisted of artificially prepared iron-coated sand, artificially prepared organic carbon sand (with 5% leaf compost), and natural aquifer sand from Long Point, Ontario (Canada). The experiments were conducted simultaneously under the same hydraulic conditions and with the same input solution of about 1μg·L^-1 of each compound. The transport behavior of the organic compounds differed significantly between both the different columns and the different compounds. A strong correlation was observed between the retardation factors for carbamazepine, gemfibrozil, and ibuprofen and the organic carbon content of the substrate. While the retardation increased with increasing organic carbon content, no direct relationship was observed between the organic carbon content and the removal of these compounds. In contrast, the retardation factors for sulfamethoxazole and naproxen showed no correlation with the organic carbon content but these compounds were significantly removed in the presence of organic matter. The influence of the Fe³⁺ surfaces in the iron-coated sand was less significant than expected, with all compounds except for sulfamethoxazole having retardation factors <1.8. Caffeine was so strongly removed during transport through those substrates containing organic carbon that no reliable retardation factor could be determined.

Evaluation of the simultaneous removal of recalcitrant drugs (bezafibrate, gemfibrozil, indomethacin and sulfamethoxazole) and biodegradable organic matter from synthetic wastewater by electro-oxidation coupled with a biological system

Pharmaceutical degradation in conventional wastewater treatment plants (WWTP) represents a challenge since municipal wastewater and hospital effluents contain pharmaceuticals in low concentrations (recalcitrant and persistent in WWTP) and biodegradable organic matter (BOM) is the main pollutant. This work shows the feasibility of coupling electro-oxidation with a biological system for the simultaneous removal of recalcitrant drugs (bezafibrate, gemfibrozil, indomethacin and sulfamethoxazole (BGIS)) and BOM from wastewater. High removal efficiencies were attained without affecting the performance of activated sludge. BGIS degradation was performed by advanced electrochemical oxidation and the activated sludge process for BOM degradation in a continuous reactor. The selected electrochemical parameters from microelectrolysis tests (1.2 L s(-1) and 1.56 mA cm(-2)) were maintained to operate a filter press laboratory reactor FM01-LC using boron-doped diamond as the anode. The low current density was chosen in order to remove drugs without decreasing BOM and chlorine concentration control, so as to avoid bulking formation in the biological process. The wastewater previously treated by FM01-LC was fed directly (without chemical modification) to the activated sludge reactor to remove 100% of BGIS and 83% of BOM; conversely, the BGIS contained in wastewater without electrochemical pre-treatment were persistent in the biological process and promoted bulking formation.

Oxidative stress, energy storage, and swimming performance of Limnodynastes peronii tadpoles exposed to a sub-lethal pharmaceutical mixture throughout development

Pharmaceutical contaminants represent emerging threats to aquatic animals and ecosystem health, and research exploring toxicological outcomes associated with these compounds in non-target wildlife has been flagged for prioritization. Amphibians represent particularly vulnerable organisms and many populations around the world are currently at risk of extinction. However, to date, relatively few studies have explored the consequences of exposures to common non-steroidal pharmaceuticals during sensitive amphibian life-stages. To address existing knowledge gaps, tadpoles of the Australian striped-marsh frog (Limnodynastes peronii) were exposed to control water and a mixture of the common pharmaceutical contaminants diclofenac, naproxen, atenolol and gemfibrozil at 0.1, 1, 10, 100 and 1000 μg/L throughout the developmental period. Effects on detoxification pathways, energy storage, growth and development, and swimming performance were assessed following exposure. Developmental rates and liver-somatic index (LSI) were significantly reduced in the highest exposure concentration, and condition factor (K) was increased at concentrations as low as 10 μg/L. Morphological endpoints were associated with significantly altered levels of hepatic triglycerides, which in turn were correlated with increased peroxidase activity in animals exposed to the highest concentration (1000 μg/L). The mixture had no significant effect on swimming performance, but a trend of decreased swimming velocity (average and maximum) was observed with increasing concentration, and this was correlated with effects on LSI. Results demonstrate that mixtures of common non-steroidal pharmaceuticals can elicit a range of physiological, metabolic and morphological responses in larval amphibians, and more research is therefore warranted to explore possible relationships between endpoints at different levels of organization.

Genomic, Proteomic, and Metabolite Characterization of Gemfibrozil-Degrading Organism Bacillus sp. GeD10

Gemfibrozil is a widely used hypolipidemic and triglyceride lowering drug. Excess of the drug is excreted and discharged into the environment primarily via wastewater treatment plant effluents. Bacillus sp. GeD10, a gemfibrozil-degrader, was previously isolated from activated sludge. It is the first identified bacterium capable of degrading gemfibrozil. Gemfibrozil degradation by Bacillus sp. GeD10 was here studied through genome sequencing, quantitative proteomics and metabolite analysis. From the bacterial proteome of Bacillus sp. GeD10 1974 proteins were quantified, of which 284 proteins were found to be overabundant by more than 2-fold (FDR corrected p-value ≤0.032, fold change (log2) ≥ 1) in response to gemfibrozil exposure. Metabolomic analysis identified two hydroxylated intermediates as well as a glucuronidated hydroxyl-metabolite of gemfibrozil. Overall, gemfibrozil exposure in Bacillus sp. GeD10 increased the abundance of several enzymes potentially involved in gemfibrozil degradation as well as resulted in the production of several gemfibrozil metabolites. The potential catabolic pathway/modification included ring-hydroxylation preparing the substrate for subsequent ring cleavage by a meta-cleaving enzyme. The identified genes may allow for monitoring of potential gemfibrozil-degrading organisms in situ and increase the understanding of microbial processing of trace level contaminants. This study represents the first omics study on a gemfibrozil-degrading bacterium.

Effect of temperature on removal of trace organic chemicals in managed aquifer recharge systems

This study was undertaken to investigate whether changes in temperature experienced in MAR systems affect attenuation of trace organic chemicals (TOrCs). A set of laboratory-scale soil columns were placed in a temperature-controlled environmental chamber and operated at five different temperature set-points (30, 20, 10, 8 and 4°C) covering the range of typical groundwater temperatures in cold, moderate and arid climate regions. Removal of bulk organic carbon both in the infiltration zone as well as during deeper infiltration was independent of temperature. Of the 22 TOrCs investigated, only six chemicals exhibited changes in attenuation as a function of temperature. Attenuation of four of the compounds (diclofenac, gemfibrozil, ketoprofen and naproxen) decreased as the temperature was reduced from 30°C to 4°C, likely due to decreased microbial activity at lower temperatures. As the temperature was decreased, however, attenuation of oxybenzone and trimethoprim were noted to increase. This increased attenuation was likely due to more efficient sorption at lower temperatures, though possible changes in the microbial composition as the temperature decreased may also have contributed to this change. Changes in rate constants of attenuation (ka) for the biotransformed TOrCs with temperature suggested the existence of a critical temperature at 10°C for three of the four TOrCs, where significant changes to rates of attenuation occurred. Results from this study indicated that for most TOrCs, changes in temperature do not impact their attenuation. Thus, seasonal changes in temperature are not considered to be a major concern for attenuation of most TOrCs in MAR systems.

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.

Capability of the natural microbial community in a river water ecosystem to degrade the drug naproxen

The present work aims at evaluating the ability of the River Tiber natural microbial community to degrade naproxen in water samples collected downstream from a wastewater treatment plant. For this purpose, different water microcosms were set up (microbiologically active vs sterile ones) and treated with naproxen (100 μg/L) alone or in the co-presence of gemfibrozil in order to evaluate if the co-presence of the latter had an influence on naproxen degradation. The experiment was performed in the autumn and was compared with the same experimental set performed in spring of the same year to highlight if seasonal differences in the river water influenced the naproxen degradation. Pharmaceutical concentrations and microbial analysis (total cell number, viability, and microbial community composition) were performed at different times in the degradation experiments. The overall results show that the natural microbial community in the river water had a key role in the naproxen degradation. In fact, although there was a transient negative effect on the natural microbial community in all the experiments (3 h after adding the pharmaceutical), the latter was able to degrade naproxen within about 40 days. On the contrary, no decrease in the pharmaceutical concentration was observed in the sterile river water. Moreover, the co-presence of the two drugs lengthened the naproxen lag phase. As regards the natural microbial community composition detected by Fluorescence in situ Hybridization, Alpha and Gamma-Proteobacteria increased when the pharmaceutical halved, suggesting their role in the degradation. This study shows that with the concentration studied, naproxen was degraded by the natural microbial populations collected from a river chronically contaminated by this pharmaceutical.

In vitro interaction of emerging contaminants with the cytochrome p450 system of Mediterranean deep-sea fish

The interactions of emerging contaminants with the xenobiotic and endogenous metabolizing system of deep-sea fish were compared. The drugs diclofenac, fluoxetine, and gemfibrozil belong to different pharmaceutical classes with diverse mechanistic actions, and the personal care products triclosan, galaxolide, and nonylphenol are representative of antibacterial agents, nitro-musks, and surfactants, respectively. The fish compared are representative of the middle and lower slope of deep-sea habitats. The species were adults of Trachyrynchus scabrus, Mora moro, Cataetix laticeps, and Alepocehalus rostratus. The hepatic metabolic system studied were the activities associated with several cytochrome P450 isoforms (CYPs): 7-ethoxyresorufin-O-deethylase (EROD), benzyloxy-4-[trifluoromethyl]-coumarin-O-debenzyloxylase (BFCOD), and 7-ethoxycoumarin-O-deethylase (ECOD). Results showed differences in baseline activities and sensitivity to chemicals which were species, chemical, and pathway dependent. T. scabrous was the most sensitive species to chemical interactions with the xenobiotic and endogenous metabolizing (EROD and BFCOD) systems, especially in the case of diclofenac interference with BFCOD activity (IC50 = 15.7 ± 2.2 μM). Moreover, T. scabrous and A. rostratus possessed high basal ECOD activity, and this was greatly affected by in vitro exposure to diclofenac in T. scabrous also (IC50 = 6.86 ± 1.4 μM). These results highlight the sensitivity of marine fish to emerging contaminants and propose T. scabrous (middle slope) and A. rostratus (lower slope) as sentinels and the inclusion of ECOD activity as a sensitive biomarker to these exposures.

Modeling uptake of selected pharmaceuticals and personal care products into food crops from biosolids-amended soil

Biosolids contain a variety of pharmaceuticals and personal care products (PPCPs). Studies have observed the uptake of PPCPs into plants grown in biosolids-amended soils. This study examined the ability of Dynamic Plant Uptake (DPU) model and Biosolids-amended Soil Level IV (BASL4) model to predict the concentration of eight PPCPs in the tissue of plants grown in biosolids-amended soil under a number of exposure scenarios. Concentrations in edible tissue predicted by the models were compared to concentrations reported in the literature by calculating estimated human daily intake values for both sets of data and comparing them to an acceptable daily intake value. The equilibrium partitioning (EqP) portion of BASL4 overpredicted the concentrations of triclosan, triclocarban, and miconazole in root and shoot tissue by two to three orders of magnitude, while the dynamic carrot root (DCR) portion overpredicted by a single order of magnitude. DPU predicted concentrations of triclosan, triclocarban, miconazole, carbamazepine, and diphenhydramine in plant tissues that were within an order of magnitude of concentrations reported in the literature. The study also found that more empirical data are needed on the uptake of cimetidine, fluoxetine, and gemfibrozil, and other ionizable PPCPs, to confirm the utility of both models. All hazard quotient values calculated from literature data were below 1, with 95.7% of hazard quotient values being below 0.1, indicating that consumption of the chosen PPCPs in plant tissue poses de minimus risk to human health.

The role of microbial adaptation and biodegradable dissolved organic carbon on the attenuation of trace organic chemicals during groundwater recharge

It is widely recognized that efficient biological attenuation of bulk organic matter and trace organic chemicals (TOrC) can occur in managed aquifer recharge (MAR) systems receiving reclaimed water. The heterotrophic microbial activity in these subsurface systems is a function of the availability of biodegradable dissolved organic carbon (BDOC) present in reclaimed water. This study examined the influence of environmental factors, such as BDOC-rich (>1.6 mg/L) and BDOC-starving (<1mg/L) conditions and microbial adaptation, on the attenuation of TOrC, including clofibric acid, dichlorprop, gemfibrozil, ibuprofen, ketoprofen, mecoprop, and naproxen, within soil-columns mimicking groundwater recharge. Under conditions that were characterized by a lack of BDOC and a biocommunity that was not yet adapted to these conditions, attenuation of biodegradable TOrC was less than 15%. After a three-month adaptation period, biotransformation increased to more than 80% for the biodegradable TOrC. This suggests that adaptation likely initiates enzyme expressions that eventually results in TOrC transformations even under seemingly less favorable conditions (i.e., lack of biodegradable carbon). For both non-adapted (stressed) and adapted conditions in the presence of higher concentrations of BDOC and travel times of 7 days, the degree of biotransformation was variable across compounds but generally exceeded 25%. This suggests that BDOC above a minimum level (>1.6 mg/L) can provide favorable microbial conditions resulting in TOrC removal, even for non-adapted systems. However, it is noteworthy that adapted MAR systems that were fed with low BDOC levels performed similarly or better with respect to TOrC biotransformation than systems that received BDOC levels above 1.6 mg/L. These findings are important for field-scale applications. They suggest that MAR facilities that are microbiologically active and are fed with highly treated water with effluent concentrations of less than 1 mg/L (i.e., nanofiltration permeate) can still attenuate biodegradable TOrC.

Removal of trace organic chemical contaminants by a membrane bioreactor

Emerging wastewater treatment processes such as membrane bioreactors (MBRs) have attracted a significant amount of interest internationally due to their ability to produce high quality effluent suitable for water recycling. It is therefore important that their efficiency in removing hazardous trace organic contaminants be assessed. Accordingly, this study investigated the removal of trace organic chemical contaminants through a full-scale, package MBR in New South Wales, Australia. This study was unique in the context of MBR research because it characterised the removal of 48 trace organic chemical contaminants, which included steroidal hormones, xenoestrogens, pesticides, caffeine, pharmaceuticals and personal care products (PPCPs). Results showed that the removal of most trace organic chemical contaminants through the MBR was high (above 90%). However, amitriptyline, carbamazepine, diazepam, diclofenac, fluoxetine, gemfibrozil, omeprazole, sulphamethoxazole and trimethoprim were only partially removed through the MBR with the removal efficiencies of 24-68%. These are potential indicators for assessing MBR performance as these chemicals are usually sensitive to changes in the treatment systems. The trace organic chemical contaminants detected in the MBR permeate were 1 to 6 orders of magnitude lower than guideline values reported in the Australian Guidelines for Water Recycling. The outcomes of this study enhanced our understanding of the levels and removal of trace organic contaminants by MBRs.

Effect of auxiliary substances on complexation efficiency and intrinsic dissolution rate of gemfibrozil-beta-CD complexes

The studies reported in this work are aimed to elucidate the ternary inclusion complex formation of gemfibrozil (GFZ), a poorly water-soluble drug, with beta-cyclodextrin (beta-CD) with the aid of auxiliary substances like different grades of povidone(s) (viz. PVP K-29/32, PVP K-40, Plasdone S-630, and Polyplasdone XL), organic base (viz. triethanolamine), and metal ion (viz. MgCl(2).6H(2)O), by investigating their interactions in solution and solid state. Phase solubility studies were carried out to evaluate the solubilizing power of beta-cyclodextrin, in association with various auxiliary substances, to determine the apparent stability constant (K (C)) and complexation efficiency (CE) of complexes. Improvement in K (C) values for ternary complexes clearly proves the benefit of the addition of auxiliary substances to promote CE. Of all the approaches used, the use of polymer Plasdone S-630 was found to be the most promising approach in terms of optimum CE and K (C). GFZ-beta-CD (1:1) binary and ternary systems were prepared by kneading and lyophilization methods. The ternary systems clearly signified superiority over binary systems in terms of CE, solubility, K (C), and reduction in the formulation bulk. Optimized ternary system of GFZ-beta-CD-Plasdone S-630 prepared by using lyophilization method indicated a significant improvement in intrinsic dissolution rate when compared with ternary kneaded system. Differential scanning calorimetry, X-ray diffraction, Fourier transform infrared, scanning electron microscopy, and proton nuclear magnetic resonance were carried out to characterize the binary and optimized ternary complex. The results suggested the formation of new solid phases, eliciting strong evidences of ternary inclusion complex formation between GFZ, beta-CD, and Plasdone S-630, particularly for lyophilized products.

The UDP-Glucuronosyltransferase 2B7 Isozyme Is Responsible for Gemfibrozil Glucuronidation in the Human Liver

Gemfibrozil, a fibrate hypolipidemic agent, is eliminated in humans by glucuronidation. A gemfibrozil glucuronide has been reported to show time-dependent inhibition of cytochrome P450 2C8. Comprehensive assessment of the drug interaction between gemfibrozil and cytochrome P450 2C8 substrates requires a clear understanding of gemfibrozil glucuronidation. However, the primary UDP-glucuronosyltransferase (UGT) isozymes responsible for gemfibrozil glucuronidation remain to be determined. Here, we identified the main UGT isozymes involved in gemfibrozil glucuronidation. Evaluation of 12 recombinant human UGT isozymes shows gemfibrozil glucuronidation activity in UGT1A1, UGT1A3, UGT1A9, UGT2B4, UGT2B7, and UGT2B17, with UGT2B7 showing the highest activity. The kinetics of gemfibrozil glucuronidation in pooled human liver microsomes (HLMs) follows Michaelis-Menten kinetics with high and low affinity components. The high affinity K(m) value was 2.5 microM, which is similar to the K(m) value of gemfibrozil glucuronidation in recombinant UGT2B7 (2.2 microM). In 16 HLMs, a significant correlation was observed between gemfibrozil glucuronidation and both morphine 3-OH glucuronidation (r = 0.966, p < 0.0001) and flurbiprofen glucuronidation (r = 0.937, p < 0.0001), two reactions mainly catalyzed by UGT2B7, whereas no significant correlation was observed between gemfibrozil glucuronidation and either estradiol 3beta-glucuronidation and propofol glucuronidation, two reactions catalyzed by UGT1A1 and UGT1A9, respectively. Flurbiprofen and mefenamic acid inhibited gemfibrozil glucuronidation in HLMs with similar IC(50) values to those reported in recombinant UGT2B7. These results suggest that UGT2B7 is the main isozyme responsible for gemfibrozil glucuronidation in humans.

Substrate-Dependent Drug-Drug Interactions between Gemfibrozil, Fluvastatin and Other Organic Anion-Transporting Peptide (OATP) Substrates on OATP1B1, OATP2B1, and OATP1B3

Hepatic uptake carriers of the organic anion-transporting peptide (OATP) family of solute carriers are more and more recognized as being involved in hepatic elimination of many drugs and potentially associated drug-drug interactions. The gemfibrozil-statin interaction was studied at the level of active hepatic uptake as a model for such drug-drug interactions. Active, temperature-dependent uptake of fluvastatin into primary human hepatocytes was shown. Multiple transporters are involved in this uptake as Chinese hamster ovary or HEK293 cells expressing either OATP1B1 (K(m) = 1.4-3.5 microM), OATP2B1 (K(m) = 0.7-0.8 microM), or OATP1B3 showed significant fluvastatin uptake relative to control cells. For OATP1B1 the inhibition by gemfibrozil was substrate-dependent as the transport of fluvastatin (IC(50) of 63 microM), pravastatin, simvastatin, and taurocholate was inhibited by gemfibrozil, whereas the transport of estrone-3-sulfate and troglitazone sulfate (both used at 3 microM) was not affected. The OATP1B1- but not OATP2B1-mediated transport of estrone-3-sulfate displayed biphasic saturation kinetics, with two distinct affinity components for estrone-3-sulfate (0.23 and 45 microM). Only the high-affinity component was inhibited by gemfibrozil. Recombinant OATP1B1-, OATP2B1-, and OATP1B3-mediated fluvastatin transport was inhibited to 97, 70, and 62% by gemfibrozil (200 microM), respectively, whereas only a small inhibitory effect by gemfibrozil (200 microM) on fluvastatin uptake into primary human hepatocytes was observed (27% inhibition). The results indicate that the in vitro engineered systems can not always predict the behavior in more complex systems such as freshly isolated primary hepatocytes. Therefore, selection of substrate, substrate concentration, and in vitro transport system are critical for the conduct of in vitro interaction studies involving individual liver OATP carriers.

GLUCURONIDATION CONVERTS GEMFIBROZIL TO A POTENT, METABOLISM-DEPENDENT INHIBITOR OF CYP2C8: IMPLICATIONS FOR DRUG-DRUG INTERACTIONS

Gemfibrozil more potently inhibits CYP2C9 than CYP2C8 in vitro, and yet the opposite inhibitory potency is observed in the clinic. To investigate this apparent paradox, we evaluated both gemfibrozil and its major metabolite, an acyl-glucuronide (gemfibrozil 1-O-beta-glucuronide) as direct-acting and metabolism-dependent inhibitors of the major drug-metabolizing cytochrome P450 enzymes (CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, and 3A4) in human liver microsomes. Gemfibrozil most potently inhibited CYP2C9 (IC50 of 30 microM), whereas gemfibrozil glucuronide most potently inhibited CYP2C8 (IC50 of 24 microM). Unexpectedly, gemfibrozil glucuronide, but not gemfibrozil, was found to be a metabolism-dependent inhibitor of CYP2C8 only. The IC50 for inhibition of CYP2C8 by gemfibrozil glucuronide decreased from 24 microM to 1.8 microM after a 30-min incubation with human liver microsomes and NADPH. Inactivation of CYP2C8 by gemfibrozil glucuronide required NADPH, and proceeded with a K(I) (inhibitor concentration that supports half the maximal rate of enzyme inactivation) of 20 to 52 microM and a k(inact) (maximal rate of inactivation) of 0.21 min(-1). Potent inhibition of CYP2C8 was also achieved by first incubating gemfibrozil with alamethicin-activated human liver microsomes and UDP-glucuronic acid (to form gemfibrozil glucuronide), followed by a second incubation with NADPH. Liquid chromatography-tandem mass spectrometry analysis established that human liver microsomes and recombinant CYP2C8 both convert gemfibrozil glucuronide to a hydroxylated metabolite, with oxidative metabolism occurring on the dimethylphenoxy moiety (the group furthest from the glucuronide moiety). The results described have important implications for the mechanism of the clinical interaction reported between gemfibrozil and CYP2C8 substrates such as cerivastatin, repaglinide, rosiglitazone, and pioglitazone.

Effects of gemfibrozil, itraconazole, and their combination on the pharmacokinetics of pioglitazone

BACKGROUND AND OBJECTIVE

The thiazolidinedione antidiabetic drug pioglitazone is metabolized mainly by cytochrome P450 (CYP) 2C8 and CYP3A4 in vitro. Our objective was to study the effects of gemfibrozil, itraconazole, and their combination on the pharmacokinetics of pioglitazone to determine the role of these enzymes in the fate of pioglitazone in humans.

METHODS

In a randomized, double-blind, 4-phase crossover study, 12 healthy volunteers took either 600 mg gemfibrozil or 100 mg itraconazole (first dose, 200 mg), both gemfibrozil and itraconazole, or placebo twice daily for 4 days. On day 3, they received a single dose of 15 mg pioglitazone. Plasma drug concentrations and the cumulative excretion of pioglitazone and its metabolites into urine were measured for up to 48 hours.

RESULTS

Gemfibrozil alone raised the mean total area under the plasma concentration-time curve from time 0 to infinity [AUC(0-infinity)] of pioglitazone 3.2-fold (range, 2.3-fold to 6.5-fold; P < .001) and prolonged its elimination half-life (t (1/2) ) from 8.3 to 22.7 hours ( P < .001) but had no significant effect on its peak concentration (C max ) compared with placebo (control). Gemfibrozil increased the 48-hour excretion of pioglitazone into urine by 2.5-fold ( P < .001) and reduced the ratios of the active metabolites M-III and M-IV to pioglitazone in plasma and urine. Gemfibrozil decreased the area under the plasma concentration-time curve from time 0 to 48 hours [AUC(0-48)] of the metabolites M-III and M-IV by 42% ( P < .05) and 45% ( P < .001), respectively, but their total AUC(0-infinity) values were reduced by less or not at all. Itraconazole had no significant effect on the pharmacokinetics of pioglitazone and did not alter the effect of gemfibrozil on pioglitazone pharmacokinetics. The mean area under the concentration versus time curve to 49 hours [AUC(0-49)] of itraconazole was 46% lower ( P < .001) during the gemfibrozil-itraconazole phase than during the itraconazole phase.

CONCLUSIONS

Gemfibrozil elevates the plasma concentrations of pioglitazone, probably by inhibition of its CYP2C8-mediated metabolism. CYP2C8 appears to be of major importance and CYP3A4 of minor importance in pioglitazone metabolism in vivo in humans. Concomitant use of gemfibrozil with pioglitazone may increase the effects and risk of dose-related adverse effects of pioglitazone. However, studies in diabetic patients are needed to determine the clinical significance of the gemfibrozil-pioglitazone interaction.

Gemfibrozil and its glucuronide inhibit the organic anion transporting polypeptide 2 (OATP2/OATP1B1:SLC21A6)-mediated hepatic uptake and CYP2C8-mediated metabolism of cerivastatin: analysis of the mechanism of the clinically relevant drug-drug interaction between cerivastatin and gemfibrozil

A serious pharmacokinetic interaction between cerivastatin (CER) and gemfibrozil (GEM) has been reported. In the present study, we examined the inhibitory effects of GEM and its metabolites, M3 and gemfibrozil 1-O-beta-glucuronide (GEM-1-O-glu), on the uptake of CER by human organic anion transporting polypeptide 2 (OATP2)-expressing cells and its metabolism in cytochrome P450 expression systems. Uptake studies showed that GEM and GEM-1-O-glu significantly inhibited the OATP2-mediated uptake of CER with IC(50) values of 72 and 24 microM, respectively. They also inhibited the CYP2C8-mediated metabolism of CER with IC(50) values of 28 and 4 microM, respectively, whereas M3 had no effects. GEM and GEM-1-O-glu minimally inhibited the CYP3A4-mediated metabolism of CER. The IC(50) values of GEM and GEM-1-O-glu for the uptake and the metabolism of CER obtained in the present study were lower than their total, and not unbound, plasma concentrations. However, considering the possibly concentrated high unbound concentrations of GEM-1-O-glu in the liver and its relatively larger plasma unbound fraction compared with GEM itself, the glucuronide inhibition of the CYP2C8-mediated metabolism of CER appears to be the main mechanism for the clinically relevant drug-drug interaction. Previously reported clinical drug interaction studies showing that coadministration of GEM with pravastatin or pitavastatin, both of which are known to be cleared from the plasma by the uptake transporters in the liver, only minimally (less than 2-fold) increased the area under the plasma concentration-time curve of these statins, also supported our present conclusion.

Use of a quadrupole linear ion trap mass spectrometer in metabolite identification and bioanalysis

A new type of quadrupole linear ion trap mass spectrometer, Q TRAP trade mark LC/MS/MS system (Q TRAP trade mark ), was evaluated for its performance in two studies: firstly, the in vitro metabolism of gemfibrozil in human liver microsomes, and, secondly, the quantification of propranolol in rat plasma. With the built-in information-dependent-acquisition (IDA) software, the instrument utilizes full scan MS in the ion trap mode and/or constant neutral loss scans as survey scans to trigger product ion scan (MS(2)) and MS(3) experiments to obtain structural information of drug metabolites 'on-the-fly'. Using this approach, five metabolites of gemfibrozil were detected in a single injection. This instrument combines some of the unique features of a triple quadrupole mass spectrometer, such as constant neutral loss scan, precursor ion scan and multiple reaction monitoring (MRM), together with the capability of a three-dimensional ion trap. Therefore, it becomes a powerful instrument for metabolite identification. The fast duty cycle in the ion trap mode allows the use of full product ion scan for quantification. For the quantification of propranolol, both MRM mode and full product ion scan in the ion trap mode were employed. Similar sensitivity, reproducibility and linearity values were established using these two approaches. The use of the product ion scan mode for quantification provided a convenient tool in selecting transitions for improving selectivity during the method development stage.

INTERACTION BETWEEN FIBRATES AND STATINS - METABOLIC INTERACTIONS WITH GEMFIBROZIL

An in vitro study was carried out in order to examine the metabolic basis of the interaction between fibrates and statins. Metabolic inhibition of statins was noted in the presence of gemfibrozil. However, increase in the unchanged form was fairly small for pitavastatin, compared with other statins. Several CYP enzymes were shown to be principally responsible for the metabolism of gemfibrozil in contrast to other fibrates. In the presence of gemfibrozil, a focal point was obtained in Dixon plots, demonstrating that there was inhibition of CYP2C8-, CYP2C9- and CYP3A4-mediated metabolism. We propose that the increase of plasma concentration caused by co-administration of gemfibrozil and statins is at least partially due to CYP-mediated inhibition.

Gemfibrozil inhibits CYP2C8-mediated cerivastatin metabolism in human liver microsomes

To explore the mechanism of the interaction between gemfibrozil and cerivastatin, the enzyme mapping of the oxidative metabolism of cerivastatin and the effect of gemfibrozil on cerivastatin metabolism were studied using human liver microsomes and expressed cytochrome p450 (p450) CYP2C8 and 3A4 isoforms. Based on studies with isoform-selective chemical inhibitors and expressed enzymes, CYP2C8 and CYP3A4 were equally important in the formation of desmethylcerivastatin (M-1), whereas the formation of the quantitatively most important hydroxy metabolite (M-23) was predominantly mediated via CYP2C8; other p450 isoforms played a negligible role. In human liver microsomes, gemfibrozil markedly inhibited M-23 formation, with a K(i) (IC(50)) value of 69 (95) micro M, whereas inhibition of M-1 formation was weaker with a K(i) (IC(50)) value of 273 (>250) micro M. The inhibitory effect of gemfibrozil was attributable to inhibition of CYP2C8 rather than CYP3A4, as evidenced by potent inhibition of the formation of M-23 (IC(50) = 68 micro M) and M-1 (IC(50) = 78 micro M) in recombinant CYP2C8 but not in recombinant CYP3A4. Additionally, gemfibrozil inhibited paclitaxel 6 alpha-hydroxylation [K(i) (IC(50)) = 75 micro M (91 micro M)], a CYP2C8 marker reaction, but did not inhibit testosterone 6 beta-hydroxylation (CYP3A4). The present in vitro findings suggest that inhibition of CYP2C8 activity by gemfibrozil at least partially explains the interaction between gemfibrozil and cerivastatin. The formation of M-23 acid from cerivastatin is mediated mainly by CYP2C8 and thus may be a suitable CYP2C8 probe reaction. Inhibition of CYP2C8-mediated metabolism by gemfibrozil warrants further in vivo exploration.

Mechanistic studies on metabolic interactions between gemfibrozil and statins

A series of studies were conducted to explore the mechanism of the pharmacokinetic interaction between simvastatin (SV) and gemfibrozil (GFZ) reported recently in human subjects. After administration of a single dose of SV (4 mg/kg p.o.) to dogs pretreated with GFZ (75 mg/kg p.o., twice daily for 5 days), there was an increase (approximately 4-fold) in systemic exposure to simvastatin hydroxy acid (SVA), but not to SV, similar to the observation in humans. GFZ pretreatment did not increase the ex vivo hydrolysis of SV to SVA in dog plasma. In dog and human liver microsomes, GFZ exerted a minimal inhibitory effect on CYP3A-mediated SVA oxidation, but did inhibit SVA glucuronidation. After i.v. administration of [(14)C]SVA to dogs, GFZ treatment significantly reduced (2-3-fold) the plasma clearance of SVA and the biliary excretion of SVA glucuronide (together with its cyclization product SV), but not the excretion of a major oxidative metabolite of SVA, consistent with the in vitro findings in dogs. Among six human UGT isozymes tested, UGT1A1 and 1A3 were capable of catalyzing the glucuronidation of both GFZ and SVA. Further studies conducted in human liver microsomes with atorvastatin (AVA) showed that, as with SVA, GFZ was a less potent inhibitor of the CYP3A4-mediated oxidation of this drug than its glucuronidation. However, with cerivastatin (CVA), the glucuronidation as well as the CYP2C8- and CYP3A4-mediated oxidation pathways were much more susceptible to inhibition by GFZ than was observed with SVA or AVA. Collectively, the results of these studies provide metabolic insight into the nature of drug-drug interaction between GFZ and statins, and a possible explanation for the enhanced susceptibility of CVA to interactions with GFZ.

Evidence for significant differences in microsomal drug glucuronidation by canine and human liver and kidney

The in vitro glucuronidation of a range of structurally diverse chemicals has been studied in hepatic and renal microsomes from human donors and the beagle dog. These studies were undertaken to improve on the limited knowledge of glucuronidation by the dog and to assess its suitability as a model species for pharmacokinetic studies. In general, the compounds studied were glucuronidated severalfold more rapidly (based on intrinsic clearance estimates) by DLM than by HLM. Intrinsic clearance values for human UGT1A1 and UGT2B7 substrates were an order of magnitude higher in DLM than in HLM (e.g., gemfibrozil: 31 microl/min/mg versus 3.0 microl/min/mg; ketoprofen: 2.4 microl/min/mg versus 0.2 microl/min/mg). There were also drug-specific differences. HLM readily glucuronidated propofol (2.4 microl/min/mg) whereas DLM appeared unable to glucuronidate this drug directly. Regioselective differences in morphine glucuronidation were also apparent. Human kidney microsomes catalyzed the glucuronidation of many xenobiotics, although glucuronidation of the endobiotic bilirubin was not detectable in this tissue. In direct contrast, dog kidney microsomes glucuronidated bilirubin only (no glucuronidation of all other xenobiotics was detected). These preliminary studies indicated significant differences in the glucuronidation of xenobiotics by microsomes from the livers and kidneys of human and dog and should be confirmed using a larger panel of tissues from individual dogs. Early knowledge of the relative rates of in vitro glucuronidation, the UGTs responsible for drug glucuronidation, and their tissue distribution in different species could assist the design and analysis of preclinical pharmacokinetic and safety evaluation studies.

Gemfibrozil and its oxidative metabolites: quantification of aglycones, acyl glucuronides, and covalent adducts in samples from preclinical and clinical kinetic studies

A gradient reversed-phase HPLC analysis for the direct measurement of gemfibrozil (GEM) and four oxidative metabolites in plasma and urine of humans and in tissue homogenates of rats was developed. The corresponding acyl glucuronides and the covalently bound protein adducts (in protein precipitates) were determined after liberation from the respective conjugates via alkaline hydrolysis. The limits of detection for the covalent adducts in human plasma are: 10 ng ml(-1) (GEM), 20 ng ml(-1) (M1), 0.5 ng ml(-1) (M2, M4), and 5 ng ml(-1) (M3). The method was validated with respect to selectivity, recovery, linearity, precision, and accuracy. It has been applied to the analysis of preclinical and clinical studies. Pharmacokinetic profiles of gemfibrozil, its metabolites, and covalent adducts in human plasma and rat tissue homogenates are given.

Gemfibrozil metabolite inhibits in vitro low-density lipoprotein (LDL) oxidation and diminishes cytotoxicity induced by oxidized LDL

We hypothesized that M1, a metabolite of gemfibrozil, may have antioxidant properties because of its hydroxylated phenol ring, 5-(4-hydroxy-2,5-dimethyl-phenoxy)-2,2-dimethyl pentanoic acid. The susceptibility of low-density lipoprotein (LDL) to oxidative modification was investigated by a method using 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile [MeO-AMVN]) or Cu2+ as previously reported. Conjugated dienes (CDs), lipid hydroperoxide (LPO), and thiobarbituric acid-reactive substances (TBARS) were measured to evaluate the degree of LDL oxidation. Oxidized LDL (OxLDL), which is used for cytotoxicity studies, was prepared by the dialysis method using Cu2+ as the oxidation inducer. Cytotoxicity induced by OxLDL was studied in J774 macrophages by colorimetric assay using 3-[4,5-dimethyl-thiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT assay). The oxidative modification of LDL was inhibited by M1 in a dose-dependent manner. The antioxidant effect of M1 on LDL oxidation was diminished by dialysis of the LDL incubated with M1 against phosphate-buffered saline (PBS), suggesting that M1 is hydrophilic rather than lipophilic. M1 diminished the cytotoxicity induced by OxLDL, although it was milder versus probucol. These data suggest that this gemfibrozil metabolite has an antioxidant effect on LDL, and thus M1 may contribute to the antiatherogenic effects of gemfibrozil.

Hepatic disposition of the acyl glucuronide1-O-gemfibrozil-beta-D-glucuronide: effects of dibromosulfophthalein on membrane transport and aglycone formation

The liver plays an important role in the disposition of acyl glucuronides by determining their extent of formation, biliary excretion, and efflux into blood. Thus, both intrahepatic and extrahepatic exposure to these reactive polar conjugates depends on the efficiency of hepatic transport mechanisms, which may be shared with other nonbile acid organic anions. Using the isolated perfused rat liver preparation, the hepatic disposition of the acyl glucuronide, 1-O-gemfibrozil-beta-D-glucuronide, was examined in the presence of the organic anion dibromosulfophthalein (DBSP). Using a recirculating system, livers were perfused for 90 min with an erythrocyte-free perfusion medium containing 1% (w/v) albumin and 1-O-gemfibrozil-beta-D-glucuronide (3 microM) alone (n = 6) or with DBSP (200 microM, n = 7). The glucuronide was avidly taken up by the liver, excreted into bile, and hydrolyzed within the liver to its aglycone, gemfibrozil. DBSP significantly (P <.05) lowered the conjugate's mean hepatic clearance (8.98-5.17 ml/min), intrinsic clearance (44.0-17.7 ml/min), and fraction eliminated in bile (72. 8-48.7% of the dose), while increasing perfusate gemfibrozil concentrations (0.52-0.92 microM at 90 min). Furthermore, DBSP significantly (P <.05) lowered the ratio of intrahepatic to unbound perfusate concentrations of 1-O-gemfibrozil-beta-D-glucuronide (139. 0-35.0) and showed a trend to lower the ratio of bile to intrahepatic concentrations (111.3-76.2, P =.05). Thus, the study demonstrated that DBSP inhibited both the sinusoidal uptake and canalicular transport of 1-O-gemfibrozil-beta-D-glucuronide, suggesting that the hepatic membrane transport of acyl glucuronides is carrier mediated and shared with other organic anions.

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.

Genotoxicity of acyl glucuronide metabolites formed from clofibric acid and gemfibrozil: a novel role for phase-II-mediated bioactivation in the hepatocarcinogenicity of the parent aglycones?

Glucuronides formed from carboxylate-containing xenobiotics are more chemically reactive than most Phase II conjugates. However, while they have been shown to form protein adducts, their reactions with DNA have received little attention. We thus used the M13 forward mutational assay to assess the genotoxicity of acyl glucuronides formed from two widely used fibrate hypolipidemics, clofibric acid and gemfibrozil. Single-stranded M13mp19 bacteriophage DNA was incubated in pH 7.4 buffer for 16 h in the presence of 0, 1, 2.5, and 5 mM concentrations of each glucuronide as well as the respective aglycones. The modified DNA was then transfected into SOS-induced competent Escherichia coli JM105 cells and the transfection efficiency was determined after phage growth overnight at 37 degrees C. Significantly, both acyl glucuronides, but not the aglycones, caused a concentration-dependent decrease in the transfection efficiency of the DNA, with a greater than 80% decrease in phage survival produced by the 5 mM concentrations of the glucuronides. No increase in lacZa mutations accompanied the loss of phage survival. We propose that these genotoxic effects involve reactions with nucleophilic centers in DNA via a Schiff base mechanism that is analogous to the glycosylation of DNA by endogenous sugars. Since strand nicking is known to accompany such damage, we also analyzed glucuronide-treated pSP189 plasmids for strand breakages via agarose gel electrophoresis. Both clofibric acid and gemfibrozil glucuronides produced significant concentration-related strand nicking and exhibited over 10-fold greater reactivity than the endogenous glycosylating agent, glucose 6-phosphate. On the basis of these findings, the possibility that this novel bioactivation route participates in the carcinogenicity of the fibrate hypolipidemics deserves investigation.

Interaction of human serum albumin with the electrophilic metabolite 1-O-gemfibrozil-beta-D-glucuronide

Acyl glucuronides are electrophilic metabolites that are readily hydrolyzed, undergo intramolecular rearrangement, and bind covalently to endogenous proteins. Gemfibrozil is a fibrate lipid-lowering agent that is extensively metabolized to an acyl glucuronide conjugate in humans. The aims of this study were to examine the interactions of 1-O-gemfibrozil-beta-D-glucuronide with human serum albumin. The degradation of 1-O-gemfibrozil-beta-D-glucuronide (approximately 200 microM) was examined in vitro during incubations at 37 degrees C with phosphate buffer (pH 7.4 or 9.0), solutions of human serum albumin (pH 7.4), or fresh human plasma (pH 7.4). The effects of diazepam, oxyphenbutazone, and gemfibrozil on the degradation of 1-O-gemfibrozil-beta-D-glucuronide, and its reversible binding to albumin were also studied. A pilot in vivo study was performed on two patient volunteers administered 1 g/day p.o. gemfibrozil. 1-O-Gemfibrozil-beta-D-glucuronide was unstable, with degradation half-lives in buffer of 4.1 hr and 44 hr at pH 9.0 and 7.4, respectively; and 8.5 hr and 5.5 hr in pH 7.4 solutions of human serum albumin or fresh plasma, respectively. Degradation was dependent on pH and the presence of albumin, which seemed to accelerate the intramolecular rearrangement and hydrolysis of the conjugate. 1-O-Gemfibrozil-beta-D-glucuronide was highly reversibly bound to albumin, with a mean unbound fraction of 0.028, and its degradation seemed to be related to the degree of reversible binding. Hydrolysis and covalent binding were associated with the site II binding domain on albumin, because only diazepam inhibited these reactions. However, intramolecular rearrangement was increased when binding to the site I domain was inhibited. Covalent binding was also detected in vivo to human plasma proteins. The half-life of the gemfibrozil-protein adducts was 2.5-3 days. Albumin plays an important role in the disposition of acyl glucuronides by acting as: i) a transporter protein; ii) a potential catalyst for their degradation and, therefore, clearance; and iii) a target for covalent adduct formation.

Disposition of gemfibrozil and gemfibrozil acyl glucuronide in the rat isolated perfused liver

Acyl glucuronides are reactive electrophilic metabolites and in vivo are readily hydrolyzed, undergo intramolecular rearrangement, and bind covalently to proteins. The isolated perfused liver preparation, using male Sprague-Dawley rats, was used to examine the hepatic disposition of the fibrate hypolipidemic agent gemfibrozil and its acyl glucuronide metabolite, 1-O-gemfibrozil-beta-D-glucuronide. Using a recirculating design, erythrocyte-free perfusion medium containing 1% (w/v) albumin was delivered to the liver via the portal vein at a flow rate of 30 ml/min, and for each experiment was spiked with either gemfibrozil (N = 4) or 1-O-gemfibrozil-beta-D-glucuronide (N = 4) at initial concentrations of 120 microM and 21 microM, respectively. In the gemfibrozil perfusions, the mean (SD) total perfusate clearance, half-life, hepatic extraction ratio of gemfibrozil, and the fraction of eliminated gemfibrozil excreted in bile as the glucuronide conjugate were 2.73 (0.30) ml/min, 76.9 (5.6) min, 0.091 (0.012), and 0.347 (0.154), respectively. In the 1-O-gemfibrozil-beta-D-glucuronide perfusions, the mean (SD) total perfusate clearance, half-life, hepatic extraction ratio, and fraction excreted in bile as the glucuronide conjugate were 19.5 (2.1) ml/min, 8.7 (0.9) min, 0.649 (0.068), and 0.534 (0.077), respectively. The higher hepatic extraction ratio for 1-O-gemfibrozil-beta-D-glucuronide could mostly be attributed to its higher unbound fraction in perfusate (0.182), compared with that of the parent drug (0.004), because the conjugate had a lower intrinsic clearance (305 ml/min) compared with the aglycone (751 ml/min). Control perfusions, conducted in the absence of a liver, showed negligible degradation of 1-O-gemfibrozil-beta-D-glucuronide over 90 min. However, in the presence of a liver, approximately 25% of 1-O-gemfibrozil-beta-D-glucuronide added to perfusate was hydrolyzed to gemfibrozil over 90 min. The study demonstrates the importance of the liver in the formation, uptake, hydrolysis, and excretion of 1-O-gemfibrozil-beta-D-glucuronide.

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

Gemfibrozil 1-O-beta-acylglucuronide was purified from the urine of a volunteer administered gemfibrozil, and an isocratic reversed-phase HPLC method was developed for its direct measurement. Quantitation of gemfibrozil and gemfibrozil 1-O-beta-acylglucuronide was carried out from plasma, following extraction from acidified specimens into ethyl acetate, on a 5-microns CN reversed-phase column with a mobile phase (pH 3.5) containing acetonitrile, tetrabutylammonium sulphate and distilled water, using fluorescence detection at 284 nm excitation and 316 nm emission. Calibration curves were linear for both compounds over a concentration range of 0.1 to 40 mg/l, with intra-assay coefficients of variation < 5% at concentrations of 20.0, 2.0 and 0.2 mg/l, and inter-assay coefficients of variation < 10%. No degradation of gemfibrozil 1-O-beta-acylglucuronide was detected as a result of the analytical procedure. However, a preliminary application of the method indicates that gemfibrozil acylglucuronide is chemically unstable undergoing intra-molecular rearrangement and hydrolysis under physiological conditions.

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.

Lowering of triglycerides by gemfibrozil affects neither the glucoregulatory nor antilipolytic effect of insulin in type 2 (non-insulin-dependent) diabetic patients

Hypertriglyceridaemia and insulin resistance are closely associated but it is unknown whether hypertriglyceridaemia per se contributes to insulin resistance. In the present study we examined whether gemfibrozil, by lowering triglyceride levels, improves the glucoregulatory and antilipolytic action of insulin in Type 2 (non-insulin-dependent) diabetes mellitus. Twenty patients were randomly allocated to receive either placebo or gemfibrozil 1200 mg daily for 12 weeks in a double-blind study. Very low density lipoprotein triglyceride levels decreased in the gemfibrozil group by 42 +/- 12% (p < 0.01). Gemfibrozil had no effect on the diurnal concentration of non-esterified fatty acids (NEFA). At the randomization HbA1c levels were comparable (7.6 +/- 0.3 vs 7.8 +/- 0.2%, NS) and increased slightly both in the gemfibrozil (8.2 +/- 0.4%, p < 0.05) and placebo groups (8.0 +/- 0.3%, NS). Pre- and post-treatment diurnal glucose and insulin concentrations remained unchanged. Basal pre- and post-treatment hepatic glucose production rates were comparable in both groups and similarly suppressed by insulin. Rate of whole body glucose disposal during a low-dose insulin infusion (serum insulin -90 pmol/l) (pre- vs post-gemfibrozil 11.9 +/- 1.1 vs 11.1 +/- 0.7, pre- vs post-placebo 9.9 +/- 1.1 vs 10.8 +/- 0.8 mumol.kg-1.min-1, NS for both) and a high-dose insulin infusion (serum insulin approximately 500 pmol/l) (16.2 +/- 1.7 vs 17.7 +/- 2.7, 17.1 +/- 4.2 vs 17.4 +/- 2.9 mumol.kg-1 x min-1, respectively, NS for both) remained unchanged. Basal pre- and post-treatment NEFA turnover rates were comparable in both groups and similarly suppressed by insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

[Comparison between lovastatin and gemfibrozil in treatment of primary hyperlipidemias]

PURPOSE

To compare the effects of lovastatin and gemfibrozil in patients with primary hyperlipidemias.

PATIENTS AND METHODS

Forty patients with cholesterolemia over 200 mg/dl and triglyceridemia not higher than 350 mg/dl, excluded secondary causes, were selected. Twenty patients received lovastatin and 20 gemfibrozil. In order to establish the lipid profile, blood samples were taken after 2 months without medication, after 4 weeks of diet and placebo and after 6 and 12 weeks of active treatment. Biochemical profile was determined before and after the treatment with active drug.

RESULTS

Thirty nine patients completed the study. Total and LDL-cholesterol were significantly reduced (p less than 0.05) by both drugs but lovastatin had greater effect. Only gemfibrozil reduced triglycerides significantly. Neither drug had significant effects on HDL-cholesterol. The tolerance was satisfactory; only one patient (using gemfibrozil) needed to stop the treatment due to gastrointestinal side effects. The biochemical profile did not present any significant alteration.

CONCLUSION

Both drugs produced useful effects on the lipid profile. Lovastatin produced greater reductions of total and LDL-cholesterol, while gemfibrozil was more active reducing triglycerides. Neither drug changed significantly the HDL-cholesterol.

Simultaneous determination of gemfibrozil and its metabolites in plasma and urine by a fully automated high performance liquid chromatographic system

Sensitive and specific methods for the simultaneous determination of gemfibrozil (Lopid), a lipid-lowering agent, and its metabolites in plasma and urine are described. The methods are based on a fully automated high performance liquid chromatographic (HPLC) system with fluorescence detection. Urine samples, diluted with acetonitrile, were directly analysed by HPLC using a flow and eluent programming method. In the case of plasma, gemfibrozil and its main metabolites were extracted from acidified samples and the resulting extracts injected into the chromatographic system. The sensitivity was approximately 100 ng/mL for gemfibrozil and its four metabolites using 0.5 mL plasma or urine. An acyl glucuronide of gemfibrozil excreted in human urine after oral administration of the drug was isolated and its structure and stability examined.