Losartan Oxidation Research Articles

Transformation of sartan blood pressure regulators by ferrate(VI) and its activation systems: Kinetics and mechanisms

With the increasing number of patients diagnosed with hypertension, the annual consumption of sartan drugs has surged, resulting in their ubiquitous detection in aquatic environments. This increases concerns about their environmental persistence and unexpected toxicity. This study explores the applications of ferrate(VI) (Fe(VI)) in removing sartan blood pressure regulators (losartan (LOS), valsartan (VAL), and telmisartan (TEL)). Results demonstrate that sartans could be effectively removed by Fe(VI). Oxidation of LOS by Fe(VI) was pH-dependent at pH 7.0–9.0, with HFeO4– dominating the reaction. The second-order rate constants (kapp) of LOS with Fe(VI) decreased with increasing solution pH, and kapp was calculated to be 148.37 M−1 s−1 at pH 8.0. Furthermore, the Fe(VI)-Fe(III), Fe(VI)-S(IV), and Fe(VI)-S2O32– systems demonstrated the enhancement for the elimination of LOS, while the Fe(VI)–HCO3– system inhibited the reaction. Oxidizing product (OP) analysis suggested that the major transformation patterns of LOS, VAL, and TEL treated by Fe(VI) and its activation systems included oxidation, imidazole ring cleavage, cyclization, N-dealkylation, and bond cleavage. Multiple OPs were estimated to be more persistent and mobile than parent sartans, while their toxicity toward aquatic organisms might be several times lower than those of their parents. Overall, this study elucidates the oxidizing feasibility of Fe(VI) and related activation systems to eliminate sartans in water treatment.

Electrochemical oxidation of losartan on a BDD electrode: Influence of cathodes and electrolytes on the degradation kinetics and pathways

In this work, the influence of supporting electrolytes (sodium sulfate and sodium chloride) on the electrochemical oxidation of the antihypertensive drug losartan (LOS) was studied under different operating conditions such as current density (4.1–12.5 mA cm−2), electrolyte concentration (0.05–0.5 M), initial pollutant concentration (250–1000 μg L−1) and solution pH. The role of cathodes on the removal of LOS has been investigated using five different cathodes with carbonaceous cathodes showing better LOS removal. The effect of matrix composition has been studied using simulated water spiked with various constituents and real water matrices such as bottled water (BW) and wastewater (WW). The removal of LOS was pronounced while using a chloride electrolyte as compared to the sulfate electrolyte. The apparent rate constant increased on adding persulfate (PS) up to concentrations of 150 mg L−1 and decreased in the presence of bicarbonates and organic matter. The transformation products (TPs) formed during the electrochemical oxidation depended on the supporting electrolyte and two common TPs were identified in both electrolytes with a total of 4 TPs identified in the chloride medium and 7 TPs in the sulfate medium. Degradation pathways for LOS in both electrolytes have also been proposed.

Assessing the Efficacy of A Mo2C/Peroxydisulfate System for Tertiary Wastewater Treatment: A Study of Losartan Degradation, E. coli Inactivation, and Synergistic Effects

This work examines the use of pristine Mo2C as an intriguing sodium persulfate (SPS) activator for the degradation of the drug losartan (LOS). Using 500 mg/L Mo2C and 250 mg/L SPS, 500 μg/L LOS was degraded in less than 45 min. LOS decomposition was enhanced in acidic pH, while the apparent kinetic constant decreased with higher LOS concentrations. According to experiments conducted in the presence of scavengers of reactive species, sulfate radicals, hydroxyl radicals, and singlet oxygen participated in LOS oxidation, with the latter being the predominant reactive species. The presence of competitors such as bicarbonate and organic matter reduced the observed efficiency in actual matrices, while, interestingly, the addition of chloride accelerated the degradation rate. The catalyst showed remarkable stability, with complete LOS removal being retained after five sequential experiments. The system was examined for simultaneous LOS decomposition and elimination of Escherichia coli. The presence of E. coli retarded LOS destruction, resulting in only 30% removal after 3 h, while the system was capable of reducing E. coli concentration by 1.23 log. However, in the presence of simulated solar irradiation, E. coli was reduced by almost 4 log and LOS was completely degraded in 45 min, revealing a significant synergistic effect of the solar/Mo2C/SPS system.

Isolation and structural characterization of two novel oxidative degradation products of losartan potassium active pharmaceutical ingredient using advanced analytical techniques.

Losartan potassium (losartan) is the most frequently utilized antihypertensive medication in the world. However, partial oxidation of losartan produces toxic by-products that could be harmful to living organisms. Therefore, it is necessary to degrade the losartan and identify the potential toxic oxidative degradation products to minimize their formation during manufacturing, formulation, storage, and packing conditions. Oxidative degradation experiments of losartan were performed according to ICH guidelines. The degradation products were detected using ultra-high-performance liquid chromatography-mass spectrometry analysis, isolated by using preparative HPLC, and identified by using high-resolution mass spectrometry and nuclear magnetic resonance spectroscopic techniques. The degradation products (DP-1, DP-2, and DP-3) were identified as (((2'-(2H-tetrazol-5-yl)-[1,1'-biphenyl]-4-yl)methyl)amino)-2-oxoethylpentanoate, 5-(4'-((2 butyl-4-chloro-5-(hydroxymethyl)-1H-imidazol-1-yl)methyl)-[1,1'-biphenyl]-2-yl)-1H tetrazol-1-ol, and 5-(4'-((2-butyl-4-chloro-5-(hydroxymethyl)-1H-imidazol-1 yl)methyl)-[1,1'-biphenyl]-2-yl)-2H-tetrazol-2-ol, respectively. Forced degradation of losartan potassium API under oxidative condition indicates the formation of two major novel oxidative degradation products (DP-2 and DP-3) and one minor known degradation product (DP-1).Preparative HPLC used for the isolation of the resultant DPs and their structures were successfully established using UHPLC-MS, 1H NMR, 13C NMR, HSQC, HMBC, and HRMS spectroscopic techniques.

Tailoring the Biochar Physicochemical Properties Using a Friendly Eco-Method and Its Application on the Oxidation of the Drug Losartan through Persulfate Activation

In this study, spent malt rootlet-derived biochar was modified by a friendly eco-method using a low temperature (100 °C) and dilute acid, base, or water. The modification significantly enhanced the surface area from 100 to 308–428 m2g−1 and changed the morphology and the carbon phase. In addition, the mineral’s percentage and zero-point charge were significantly affected. Among the examined materials, the acid-treated biochar exhibited higher degradation of the drug losartan in the presence of persulfate. Interestingly, the biochar acted as an adsorbent at pH 3, whereas at pH = 5.6 and 10, the apparent kinetic constant’s ratio koxidation/kadsorption was 3.73 ± 0.03, demonstrating losartan oxidation. Scavenging experiments indirectly demonstrated that the role of the non-radical mechanism (singlet oxygen) was crucial; however, sulfate and hydroxyl radicals also significantly participated in the oxidation of losartan. Experiments in secondary effluent resulted in decreased efficiency in comparison to pure water; this is ascribed to the competition between the actual water matrix constituents and the target compound for the active biochar sites and reactive species.

Differential inhibition of human CYP2C8 and molecular docking interactions elicited by sorafenib and its major N-oxide metabolite

The tyrosine kinase inhibitor sorafenib (SOR) is being used increasingly in combination with other anticancer agents like paclitaxel, but this increases the potential for drug toxicity. SOR inhibits several human CYPs, including CYP2C8, which is a major enzyme in the elimination of oncology drugs like paclitaxel and imatinib. It has been reported that CYP2C8 inhibition by SOR in human liver microsomes is potentiated by NADPH-dependent biotransformation. This implicates a SOR metabolite in enhanced inhibition, although the identity of that metabolite is presently unclear. The present study evaluated the capacity of the major N-oxide metabolite of SOR (SNO) to inhibit CYP2C8-dependent paclitaxel 6α-hydroxylation. The IC50 of SNO against CYP2C8 activity was found to be 3.7-fold lower than that for the parent drug (14 μM versus 51 μM). In molecular docking studies, both SOR and SNO interacted with active site residues in CYP2C8, but four additional major hydrogen and halogen bonding interactions were identified between SNO and amino acids in the B–B′ loop region and helixes F’ and I that comprise the catalytic region of the enzyme. In contrast, the binding of both SOR and SNO to active site residues in the closely related human CYP2C9 enzyme was similar, as were the IC50s determined against CYP2C9-mediated losartan oxidation. These findings suggest that the active metabolite SNO could impair the elimination of coadministered drugs that are substrates for CYP2C8, and mediate toxic adverse events, perhaps in those individuals in whom SNO is formed extensively.

Lack of Correlation between In Vitro and In Vivo Studies on the Inhibitory Effects of (‒)-Sophoranone on CYP2C9 is Attributable to Low Oral Absorption and Extensive Plasma Protein Binding of (‒)-Sophoranone.

(‒)-Sophoranone (SPN) is a bioactive component of Sophora tonkinensis with various pharmacological activities. This study aims to evaluate its in vitro and in vivo inhibitory potential against the nine major CYP enzymes. Of the nine tested CYPs, it exerted the strongest inhibitory effect on CYP2C9-mediated tolbutamide 4-hydroxylation with the lowest IC50 (Ki) value of 0.966 ± 0.149 μM (0.503 ± 0.0383 μM), in a competitive manner. Additionally, it strongly inhibited other CYP2C9-catalyzed diclofenac 4′-hydroxylation and losartan oxidation activities. Upon 30 min pre-incubation of human liver microsomes with SPN in the presence of NADPH, no obvious shift in IC50 was observed, suggesting that SPN is not a time-dependent inactivator of the nine CYPs. However, oral co-administration of SPN had no significant effect on the pharmacokinetics of diclofenac and 4′-hydroxydiclofenac in rats. Overall, SPN is a potent inhibitor of CYP2C9 in vitro but not in vivo. The very low permeability of SPN in Caco-2 cells (Papp value of 0.115 × 10−6 cm/s), which suggests poor absorption in vivo, and its high degree of plasma protein binding (>99.9%) may lead to the lack of in vitro–in vivo correlation. These findings will be helpful for the safe and effective clinical use of SPN.

UV-assisted chemical oxidation of antihypertensive losartan in water

Population growth and deteriorating health issues have led to an increase in the consumption of angiotensin receptor blockers (ARBs), such as losartan (LOR), for treating high blood pressure and, as a result, to the frequent detection of these drugs in water and wastewater. The present study focuses on the oxidation of LOR by UV photolysis, UV(/Fe2+)-activated persulfate (PS) and hydrogen peroxide (H2O2) systems. The effects of operating parameters including pH value, reaction time, concentration of oxidant and activator on the efficacy of treatment were studied. The target compound degradation by direct UV photolysis, UV/PS and UV/H2O2 systems proved to be efficient and followed a pseudo-first-order kinetic model. The application of UV/oxidant systems even at lower PS or H2O2 concentrations resulted in more than 95% of LOR degradation in 10 min. In addition, the use of UV/Fe2+-activated oxidant systems led to a further increase in the kobs by improving the LOR oxidation in aqueous solution. The effectiveness of LOR mineralization based on total organic carbon (TOC) removal was also considered. The optimized results of the studied systems obtained in ultrapure water were used in groundwater to assess the effectiveness of LOR decomposition in more complex environmental matrix. Moreover, the acute toxicity of LOR solutions before and after the UV/Fe2+-activated PS and H2O2 oxidation to luminous bacteria (Vibrio fischeri) was investigated.

Oxidative degradation of pharmaceutical losartan potassium with N-doped hierarchical porous carbon and peroxymonosulfate

Losartan potassium (LOS) is a most globally consumed antihypertensive and emerging pharmaceutical contaminant of concern due to increasingly ubiquity in water and wastewater. For its effective environmental remediation, we propose the catalytic oxidation of losartan via peroxymonosulfate (PMS) activation using a metal-free N-doped hierarchically porous carbon (N-PC). We found out that N-PC exhibits both excellent adsorption capacity and catalytic oxidation efficiency with 100% LOS uptake within 240 min at 0.026 g/L of the N-PC. Fresh and used N-PC were scrutinized for textural properties and surface chemistry. The effects of PMS dose, temperature, pH, organic matter and coexisting anions on losartan decomposition were examined. Moreover, total organic removal was obtained and the catalyst was tested in three consecutive runs. Electron paramagnetic resonance and quenching assays revealed that the nonradical oxidation pathway plays a major role in LOS degradation by N-PC/PMS.

Graphite/SiO2 film electrode modified with hybrid organic-inorganic perovskites: Synthesis, optical, electrochemical properties and application in electrochemical sensing of losartan

Hybrid organic-inorganic semiconductors (HOIS) still remain as research focus due to their exceptional optoelectronics properties, placing them as ideal candidates for use in the field of light emitting diodes and photovoltaics. In the present work, HOIS have been synthesized, characterized as well as adsorbed onto graphite/silica film electrodes (GSiHE), the latter used as simple, low cost, yet sensitive, electrochemical sensors. These composite electrodes have been specifically characterized with electrochemical methods and have been applied in the development of prototype electrochemical drug sensors; a paradigm is provided for simple, efficient, sensitive and relatively specific sensing of an antihypertensive drug, losartan (LOS). The electrochemical behavior of GSiHE film modified with HOIS was examined by cyclic voltammetry, while its morphology, structural and spectroscopic properties were investigated by field emission scanning electron microscopy, X-ray diffraction, porosimetry, optical and luminescence spectroscopies. Under optimized conditions, the modified film electrode demonstrated excellent electrocatalytic activity towards oxidation of LOS in the linear response range for concentrations from 4 × 10−5 M to 3.2 × 10−4 M (correlation coefficient 0.989) with the limit of detection computed at 3 × 10−6 M. The sensor takes advantage of the ability of ions to interact with the HOIS lattice on the GSiHE film; this type of sensor has demonstrated good repeatability, reproducibility and stability and was found to be applicable for use in determining pharmaceutical tablet sample concentrations.

Electrochemical degradation of the antihypertensive losartan in aqueous medium by electro-oxidation with boron-doped diamond electrode

In this work the electrochemical oxidation of losartan, an emerging pharmaceutical pollutant, was studied. Electrochemical oxidation was carried out in batch mode, in an open and undivided cell of 100cm3 using a boron-doped diamond (BDD)/stainless steel system. With Cl− medium 56% of mineralization was registered, while with the trials containing SO42− as supporting electrolyte a higher mineralization yield of 67% was reached, even obtaining a total removal of losartan potassium at 80mAcm−2 and 180min of reaction time at pH 7.0. Higher losartan potassium concentrations enhanced the mineralization degree and the efficiency of the electrochemical oxidation process. During the mineralization up to 4 aromatic intermediates were identified by ultra high performance liquid chromatography tandem mass spectrometry (UHPLC–MS/MS). Moreover, short-linear carboxylic acids, like oxalic, succinic and oxamic were detected and quantified by ion-exclusion HPLC. Finally, the ability of the electrochemical oxidation process to mineralize dissolved commercial tablets containing losartan was achieved, obtaining TOC removal up to 71% under optimized conditions (10mAcm−2, 0.05M Na2SO4, pH 7.0 and 25°C and 360min of electrolysis).

Oxidative degradation of the antihypertensive drug losartan by alkaline copper(III) periodate complex in the presence and absence of ruthenium(III) catalyst: a kinetic and mechanistic study of losartan metabolite

Spectrophotometric kinetic technique has been used to study the oxidation of losartan by diperiodatocuprate(III) (DPC) in the presence and absence of ruthenium(III) catalyst in aqueous alkaline medium at constant ionic strength of 0.90 mol dm−3. The stoichiometry of the reaction was found to be 1:2 in both catalyzed and uncatalyzed reactions, i.e., one mole of losartan requires two moles of DPC. The reaction products were identified and characterized by IR, GC–MS, and NMR spectral studies. The reaction shows first-order dependence on [DPC] and [ruthenium(III)] and apparently less than unit order in both losartan and alkali concentrations. The effects of added products, ionic strength, periodate, and dielectric constant on the rate of reaction have been studied. The rate of the reaction increased with increasing [alkali] and decreased with increasing [periodate] in both the cases. The reaction rates revealed that Ru(III) catalyzed reaction was about sevenfold faster than the uncatalyzed reaction. Based on experimental results suitable mechanisms are proposed. The proposed mechanisms and the derived rate law are in concurrence with the observed kinetics. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to slow step of the mechanism were computed and discussed, and thermodynamic quantities were also determined.

Substrate-Dependent Functional Alterations of Seven CYP2C9 Variants Found in Japanese Subjects

CYP2C9 is a polymorphic enzyme that metabolizes a number of clinically important drugs. In this study, catalytic activities of seven alleles found in Japanese individuals, CYP2C9*3 (I359L), *13 (L90P), *26 (T130R), *28 (Q214L), *30 (A477T), *33 (R132Q), and *34 (R335Q), were assessed using three substrates (diclofenac, losartan, and glimepiride). When expressed in a baculovirus-insect cell system, the holo and total (apo and holo) CYP2C9 protein expression levels were similar among the wild type (CYP2C9.1) and six variants except for CYP2C9.13. A large part of CYP2C9.13 was present in the apo form P420. Compared with CYP2C9.1, all variants except for CYP2C9.34 exhibited substrate-dependent changes in K(m), V(max), and intrinsic clearance (V(max)/K(m)). For diclofenac 4'-hydroxylation, the intrinsic clearance was decreased markedly (by >80%) in CYP2C9.13, CYP2C9.30, and CYP2C9.33 and variably (63-76%) in CYP2C9.3, CYP2C9.26, and CYP2C9.28 due to increased K(m) and/or decreased V(max) values. For losartan oxidation, CYP2C9.13 and CYP2C9.28 showed 2.5- and 1.8-fold higher K(m) values, respectively, and all variants except for CYP2C9.34 showed >77% lower V(max) and intrinsic clearance values. For glimepiride hydroxylation, the K(m) of CYP2C9.13 was increased 7-fold, and the V(max) values of all variants significantly decreased, resulting in reductions in the intrinsic clearance by >80% in CYP2C9.3, CYP2C9.13, CYP2C9.26, and CYP2C9.33 and by 56 to 75% in CYP2C9.28 and CYP2C9.30. These findings suggest the necessity for careful administration of losartan and glimepiride to patients bearing these six alleles.

Inhibitory Effect of Valproic Acid on Cytochrome P450 2C9 Activity in Epilepsy Patients

Drug interactions constitute a major problem in the treatment of epilepsy because drug combinations are so common. Valproic acid is a widely used anticonvulsant drug with a broad therapeutic spectrum. Case reports suggest interaction between valproic acid and other drugs metabolized mainly by cytochrome P450 isoforms. The aim of this study was to evaluate the inhibitory effect of valproic acid on cytochrome P450 2C9 (CYP2C9) activity by using losartan oxidation as a probe in epilepsy patients. Patients were prescribed sodium valproate (mean 200 mg/day for the first week and 400 mg/day in the following period) according to their clinical need. A single oral dose of 25 mg losartan was given to patients before and after the first dose, first week and 4 weeks of valproic acid treatment. Losartan and E3174, the CYP2C9-derived carboxylic acid metabolite of losartan in 8 hr urine were assayed by using high pressure liquid chromatography. Urinary losartan/E3174 ratio did not change significantly on the first day (0.9, 0.3-3.5; median, range), and first week (0.6, 0.2-3.8; median, range), while a significant increase was observed after 4 weeks of valproic acid treatment (1.1, 0.3-5.7; median, range) as compared to that of measured before valproic acid administration (0.6, 0.1-2.1; median, range) (P = 0.039). The degree of inhibition was correlated with the steady-state plasma concentrations of valproic acid (r(2) = 0.70, P = 0.04). The results suggest an inhibitory effect of valproic acid on CYP2C9 enzyme activity in epilepsy patients at steady state. The risk of pharmacokinetic drug-drug interactions should be taken into account during concomitant use of valproic acid and CYP2C9 substrates.

Inhibitory effect of valproic acid on cytochrome P450 2C9 activity in epilepsy patients

Drug interactions constitute a major problem in the treatment of epilepsy because drug combinations are common. Case reports suggest an interaction between valproic acid and drug substrates of CYP2C9. The aim of this study was to evaluate the inhibitory effect of valproic acid on CYP2C9 activity by using losartan oxidation as a marker in epilepsy patients. A single oral dose of 25 mg losartan was given to patients (n=11) at the baseline. Losartan and its CYP2C9 derived metabolite E3174 were assayed in 8-hour urine samples by using HPLC. The same procedure was repeated after the first dose and at the completion of the first and fourth weeks of valproic acid treatment. Urinary losartan/E3174 ratio (median, range) did not change significantly at the first day or the first week, while a significant increase was observed at the fourth week of valproic acid treatment (1.09, 0.28–5.71) as compared with the baseline (0.60, 0.10–2.07) (P=0.039). The degree of inhibition was correlated with the steady state plasma concentrations of valproic acid (r2=0.82, P=0.018). These results provide an in vivo evidence that valproic acid is an inhibitor of CYP2C9 at concentrations reached during steady state in human. The risk of pharmacokinetic drug-drug interactions should be considered during concomitant use of valproic acid and CYP2C9 substrates. (Supported by TUBITAK-SBAG COST B25-105S027 and UY/TUBA-GEBIP/2005-17)

Effect of the cardiopulmonary bypass procedure during cardiac surgery on CYP2C9 activity in human

Clinical observations suggest that warfarin sensitivity is increased in patients undergoing cardiac surgery that involves a cardiopulmonary bypass (CPB) procedure. Factors such as hemodilution, altered plasma protein binding or change in visceral perfusion during CPB may cause changes in pharmacokinetic parameters of various drugs. Since CYP2C9 is the major enzyme that metabolizes warfarin, we aimed to investigate if the increase in warfarin sensitivity was associated with inhibition of the activity of this individual enzyme due to CPB in human. Losartan oxidation to E3174 was used as a marker for CYP2C9 activity. Urinary losartan/E3174 ratios after a single 25 mg oral dose were measured in 23 patients at three occasions: at the baseline, and on the first and fifth postoperative days. The average metabolic ratio (median, range) was significantly increased for about 3.3 fold as compared to the baseline value (0.84, 0.1–7.94 vs. 2.80, 0.7–278.2) in the acute phase immediately after the surgery (P=0.01). The metabolic ratio returned to the baseline value when measured at the fifth postoperative day (P=0.24). These results suggest that CYP2C9 metabolic activity is inhibited at the very early stage of postoperative period and recovers as early as within five days in patients that undergo cardiac surgery with a cardiopulmonary bypass procedure. (Supported by TUBITAK-SBAG COST B25-105S027 and UY/TUBA-GEBIP/2005-17)

Ketobemidone is a substrate for cytochrome P4502C9 and 3A4, but not for P-glycoprotein

The role of the major drug-metabolizing cytochrome P450 (CYP) enzymes as well as P-glycoprotein (PGP) was investigated in the disposition of ketobemidone in vitro. Formation of norketobemidone from ketobemidone was studied and compared with the activities of 11 major CYP enzymes in human liver microsomes. The formation of norketobemidone from ketobemidone (1 µM) correlated best with CYP2C9 activity, measured as losartan oxidation (rs = 0.82, n = 19, p < 0.001), but there was also a strong correlation with CYP3A4 activity. Additionally, a good correlation was observed with CYP2C19, CYP2C8 and CYP2B6 at a ketobemidone concentration of 50 µM. Inhibition studies confirmed the involvement of CYP2C9 and CTP3A4 in the formation of norketobemidone. The formation rate of norketobemidone was three times higher in the CYP2C9*1*1 genotype group compared with the CYP2C9*1*2, CYP2C9*1*3 and CYP2C9*3*3 genotypes (p < 0.01). Treatment with verapamil as a PGP inhibitor did not affect the transport of ketobemidone in Caco-2 cells, indicating that PGP is not involved. The data suggest that CYP2C9 and CYP3A4 play a major role in the formation of norketobemidone at clinically relevant concentrations.

CYP2C9 genetic variants and losartan oxidation in a Turkish population.

Cytochrome P(450) 2C9 (CYP2C9) is a polymorphic enzyme catalysing the metabolism of several important drugs. Losartan has recently been suggested as a selective probe for CYP2C9 metabolic activity. The aim of the study was to determine the activity of CYP2C9, using losartan as a probe drug, in relation to CYP2C9 genotype in healthy Turkish subjects. A single oral dose of 25 mg losartan was given to 85 Turkish unrelated subjects. Concentrations of losartan and its carboxylic acid metabolite, E3174, were analysed by means of high-performance liquid chromatography in urine collected for 8 h. The CYP2C9 genotypes were determined in 85 subjects using polymerase chain reaction-based endonuclease digestion methods specific for CYP2C9*2 and *3. Losartan oxidation was also studied in vitro, using human CYP2C8 and CYP2C9 enzymes expressed in yeast. The frequencies of the allelic variants CYP2C9*2 and CYP2C9*3 were 0.100 and 0.088, respectively. The urinary losartan/E3174 ratio was significantly higher in subjects with CYP2C9*1/*3 genotype (median 2.35, n=12) than in subjects with CYP2C9*1/*1 (0.71, n=58) and *1/*2 (0.85, n=10) genotypes ( P<0.05). In contrast to CYP2C9, no E3174 was formed by CYP2C8 in vitro. The urinary losartan to E3174 metabolic ratio after a 25-mg losartan dose was found to be a safe and useful phenotyping assay for CYP2C9 activity in vivo. CYP2C9*3 variant allele is a major determinant of the enzyme activity, and it decreases losartan metabolism significantly, while CYP2C9*2 allele has less impact on enzyme function.

A Screening Study on the Liability of Eight Different Female Sex Steroids to Inhibit CYP2C9, 2C19 and 3A4 Activities in Human Liver Microsomes

The aim of this study was to screen the inhibitory potential of different clinically used oestrogen and progestin hormones on CYP2C9, 2C19 and 3A4 activities in human liver microsomes. The degree of inhibition by desogestrel, 3-ketodesogestrel, 17-beta-oestradiol, gestodene, aethinyloestradiol, medroxyprogesterone acetate, norethisterone or L-norgestrel were studied at 100 microM on losartan oxidation (CYP2C9), R-omeprazole 5'-hydroxylation (CYP2C19) and R-omeprazole sulphoxidation (CYP3A4) with a 10-min preincubation with NADPH in human liver microsomes prepared from 6 individual genotyped donor livers. Aethinyloestradiol was found to be a potent inhibitor (55% mean inhibition; 95% CI 32% to 79%) of losartan oxidation (CYP2C9) and R-omeprazole 5-hydroxylation (70%; 63% to 77%) (CYP2C19), while it had little effect on R-omeprazole sulphoxidation (CYP3A4) activity. 17-beta-Oestradiol did not produce significant inhibition on any of the studied enzyme activities. Of the progestin hormones studied, gestodene and 3-ketodesogestrel were potent inhibitors of CYP2C19 (57%; 47% to 67% and 51%; 29% to 45%) and CYP3A4 (45%; 30% to 59% and 40%; 19% to 62%), but had little effect on the CYP2C9 activity. In addition, medroxyprogesterone acetate was found to inhibit CYP2C9 (55%; 45% to 65%), while not having significant effect on 2C19 or 3A4. In conclusion, the liability of clinically used female sex steroids to inhibit CYP2C9, 2C19 and 3A4 activities in human liver microsomes is very distinctive and these differences among both the oestrogen and progestin hormones may, at least in part, explain the variable results from clinical trials examining inhibitory effects of hormone replacement therapy and oral contraceptives on drug metabolism.

The role of CYP2C9 genotype in the metabolism of diclofenac in vivo and in vitro.

The polymorphic cytochrome P450 enzyme 2C9 (CYP2C9) catalyses the metabolism of many drugs including S-warfarin, acenocoumarol, phenytoin, tolbutamide, losartan and most of the non-steroidal anti-inflammatory drugs. Diclofenac is metabolised to 4'-hydroxy (OH), the major diclofenac metabolite, 3'-OH and 3'-OH-4'-methoxy metabolites by CYP2C9. The aim of the present study was to clarify the impact of the CYP2C9 polymorphism on the metabolism of diclofenac both in vivo and in vitro. Twenty healthy volunteers with different CYP2C9 genotypes [i.e. CYP2C9*1/ *1 (n = 6), *1/*2 (n = 3), *1,/*3 (n = 5), *2/*3 (n = 4), *21*2 (n = 1), *31*3 (n = 1)] received a single 50-mg oral dose of diclofenac. Plasma pharmacokinetics [peak plasma concentration (Cmax), half-life (t 1/2) and area under the plasma concentration-time curve (AUCtotal)] and urinary recovery of diclofenac and its metabolites were compared between the genotypes. Diclofenac 4'-hydroxylation was also analysed in vitro in 16 different samples of genotyped [i.e. CYP2C9*1/*1 (n = 7), *1/*2 (n=2), *1/*3 (n = 2), *2/*3 (n = 2), *2/*2 (n = 2), *31/*3 (n = 1)] human liver microsomes. Within each genotype group, a high variability was observed in kinetic parameters for diclofenac and 4'-OH-diclofenac (6- and 20-fold, respectively). No significant differences were found between the different genotypes either in vivo or in human liver microsomes. No correlation was found between the plasma AUC ratio of diclofenac/4'-OH-diclofenac and that of losartan/ E-3174, previously determined in the same subjects. No relationship was found between the CYP2C9 genotype and the 4'-hydroxylation of diclofenac either in vivo or in vitro. This, together with the lack of correlation between losartan oxidation and diclofenac hydroxylation in vivo raises the question about the usefulness of diclofenac as a CYP2C9 probe.