Systematic approach to optimize a pretreatment method for ultrasensitive liquid chromatography with tandem mass spectrometry analysis of multiple target compounds in biological samples.

In current approaches for new drug development, highly sensitive and robust analytical methods for the determination of test compounds in biological samples are essential. These analytical methods should be optimized for every target compound. However, for biological samples that contain multiple compounds as new drug candidates obtained by cassette dosing tests, it would be preferable to develop a single method that allows the determination of all compounds at once. This study aims to establish a systematic approach that enables a selection of the most appropriate pretreatment method for multiple target compounds without the use of their chemical information. We investigated the retention times of 27 known compounds under different mobile phase conditions and determined the required pretreatment of human plasma samples using several solid-phase and liquid-liquid extractions. From the relationship between retention time and recovery in a principal component analysis, appropriate pretreatments were categorized into several types. Based on the category, we have optimized a pretreatment method for the identification of three calcium channel blockers in human plasma. Plasma concentrations of these drugs in a cassette-dose clinical study at microdose level were successfully determined with a lower limit of quantitation of 0.2 pg/mL for diltiazem, 1 pg/mL for nicardipine, and 2 pg/mL for nifedipine.

A new methodology for simultaneous quantification of total-Aß, Aßx-38, Aßx-40, and Aßx-42 by column-switching LC/MS/MS.

This article details the development of a novel method that overcomes the drawbacks of sandwich ELISA (sELISA) and allows reliable evaluation of simultaneous quantification of the amyloid (Aß)-peptides, total-Aß, Aßx-38, Aßx-40, and Aßx-42, in rat brain by optimized sample purification and column-switching liquid chromatographic-tandem mass spectrometry (LC/MS/MS). This method provides accurate analyses of total-Aß, Aßx-38, Aßx-40, and Aßx-42 with a linear calibration range between 0.05 and 45 ng/mL. Verification for accuracy and precision of biological samples were determined by a standard addition and recovery test, spiked with synthetic Aß1-38, Aß1-40, and Aß1-42 into the rat brain homogenate. This method showed <20% relative error and relative standard deviation, indicating high reproducibility and reliability. The brain concentrations of total-Aß, Aßx-38, Aßx-40, and Aßx-42 after oral administration of flurbiprofen in rats were measured by this method. Aßx-42 concentrations (4.57 ± 0.69 ng/g) in rats administered flurbiprofen were lower than those in untreated rats (6.48 ± 0.93 ng/g). This was consistent with several reports demonstrating that NSAIDs reduced the generation of Aß. We report here a method that allows not only the quantification of specific molecular species of Aß but also simultaneous quantification of total-Aß, Aßx-38, Aßx-40, and Aßx-42, thus overcoming the drawbacks of sELISA.

In vitro investigation of the glutathione transferase M1 and T1 null genotypes as risk factors for troglitazone-induced liver injury.

The double null mutation of glutathione transferase, GSTM1 and GSTT1, is reported to influence troglitazone-associated abnormal increases of alanine aminotransferase and aspartate aminotransferase. However, no nonclinical data with a bearing on the clinical outcomes and underlying mechanisms have hitherto been reported. To investigate whether deficiency in GSTM1 and/or GSTT1 is related to troglitazone hepatotoxicity in vitro, the covalent binding level (CBL) (an index of reactive metabolite formation) and cytotoxicity of troglitazone and rosiglitazone, another thiazolidinedione but with low hepatotoxicity, were examined using human liver samples phenotyped for cytochrome P450s and genotyped for GSTM1 and GSTT1. Despite addition of GSH, CBLs of troglitazone and rosiglitazone in human liver microsomes were correlated with CYP3A (or CYP2C8) and CYP2C8 activities, respectively. With addition of recombinant GSTM1, the microsomal CBLs of troglitazone and rosiglitazone decreased. However, the CBLs of troglitazone in GSTM1/GSTT1 wild-type hepatocytes were unexpectedly higher than those in null hepatocytes. Although this discrepancy has not been fully explained, the GSTM1 and GSTT1 null mutations increased the cytotoxicity of troglitazone, independent of CYP3A or CYP2C8 activities. Furthermore, a GSH adduct of troglitazone, M2, limited to GSTM1 wild-type hepatocytes was detected. Of clear interest, GSTM1 and/or GSTT1 null mutation-dependent cytotoxicity and higher exposure to the reactive metabolite trapped as M2 as for troglitazone were not observed for rosiglitazone. This result might at least partly explain the findings related to clinical hepatotoxicity, suggesting that measurement of GSH adducts or cytotoxicity using GSTM1- and GSTT1-genotyped hepatocytes might offer an important in vitro system to assist in better prediction of idiosyncratic hepatotoxicity.

Metabolomic investigation of cholestasis in a rat model using ultra-performance liquid chromatography/tandem mass spectrometry.

Metabolomics follows the changes in concentrations of endogenous metabolites, which may reflect various disease states as well as systemic responses to environmental, therapeutic, or genetic interventions. In this study, we applied metabolomic approaches to monitor dynamic changes in plasma and urine metabolites, and compared these metabolite profiles in Eisai hyperbilirubinemic rats (EHBR, an animal model of cholestasis) with those in the parent strain of EHBR - Sprague-Dawley (SD) rats - in order to characterize cholestasis pathophysiologically. Ultra-performance liquid chromatography/tandem mass spectrometry-based analytical methods were used to assay metabolite levels. More than 250 metabolites were detected in both plasma and urine, and metabolite profiles of EHBR differed from those of SD rats. The levels of antioxidative and cytoprotective metabolites, taurine and hypotaurine, were markedly increased in urine of EHBR. The levels of many bile acids were also elevated in plasma and urine of EHBR, but the extent of elevation depended on the particular bile acid. The levels of cytoprotective ursodeoxycholic acid and its conjugates were markedly elevated, while that of cytotoxic chenodeoxycholic acid remained unchanged, suggesting the balance of bile acids had shifted resulting in decreased toxicity. In EHBR, reduced biliary excretion leads to increased systemic exposure to harmful compounds including some endogenous metabolites. Our metabolomic data suggest that mechanisms exist in EHBR that compensate for cholestasis-related damage.

Pharmacokinetics of miriplatin in experimental dog models of hepatic or renal impairment.

Miriplatin is an anticancer platinum complex for treatment of hepatocellular carcinomas by intra-hepatic arterial injection suspended in an iodinated ethyl ester of fatty acids from poppy seed oil as a carrier. Effects of liver and kidney function on( 14)C-miriplatin pharmacokinetics were assessed using dog models of hepatic and renal impairment introduced by thioacetamide exposure and 7/8 nephrectomy, respectively. Miriplatin was selectively delivered to the liver; platinum and radioactive component were gradually released into systemic circulation and excreted into urine. Microautoradiographic analysis of liver specimens showed( 14)C-miriplatin to be localized in blood vessels and/or macrophage-like cells. These features of miriplatin disposition were not affected by hepatic impairment. Thus, in clinical settings, hepatic impairment would not be expected to affect the intra-hepatic distribution and systemic pharmacokinetics of miriplatin. In dogs with renal impairment, although inconclusive, plasma concentrations of ultrafilterable platinum and radioactivity increased due to reduction in renal clearance.

Prediction of the intestinal first-pass metabolism of CYP3A substrates in humans using cynomolgus monkeys.

To select high bioavailability compounds, it is necessary to predict the first-pass metabolism in the intestine. However, in vitro-in vivo predictions of the intestinal metabolism have proven both challenging and less definitive. The purpose of this study was to investigate prediction of intestinal first-pass metabolism in humans using cynomolgus monkeys. First, we investigated intrinsic metabolic activities in intestinal microsomes of monkeys (MIM) and humans (HIM) (CL(int, MIM) and CL(int, HIM), respectively) of 18 CYP3A substrates. The CL(int, MIM) values were found to be relatively high and showed excellent correlation with the CL(int, HIM) values. Subsequently, we determined the plasma concentrations of 9 CYP3A substrates (buspirone, carbamazepine, diazepam, felodipine, midazolam, nicardipine, nifedipine, saquinavir, and verapamil) in monkeys after an oral dose of 2 mg/kg with or without an oral dose of 5 mg/kg ketoconazole and calculated AUC((+vehicle))/AUC((+ketoconazole)), defined as F(g, monkey(observed)); we confirmed that the dose of ketoconazole inhibited only intestinal CYP3A metabolism by preliminary in vitro and in vivo experiments using ketoconazole. The F(g, monkey(observed)) was lower than the F(g, human(observed)) for most compounds, but moderate correlation was observed. Furthermore, using these data, we established a new methodology to estimate F(g, human(predicted)) more precisely on the basis of the assumption that intestinal physiological conditions other than intrinsic metabolic activity would be the same between monkeys and humans. In conclusion, the in vivo model using cynomolgus monkeys in this study is useful for prediction of intestinal first-pass metabolism by CYP3A in humans because it was able to predict F(g, human) of all nine compounds investigated.

Evaluation of the potential for drug-induced liver injury based on in vitro covalent binding to human liver proteins.

Prediction of idiosyncratic drug-induced liver injury (DILI) is difficult, and the underlying mechanisms are not fully understood. However, many drugs causing DILI are considered to form reactive metabolites and covalently bind to cellular macromolecules in the liver. The objective of this study was to clarify whether the risk of idiosyncratic DILI can be estimated by comparing in vitro covalent binding (CB) levels among 12 positive compounds (acetaminophen, alpidem, bromfenac, carbamazepine, diclofenac, flutamide, imipramine, nefazodone, tacrine, ticlopidine, tienilic acid, and troglitazone) for DILI and 12 negative compounds (acetylsalicylic acid, caffeine, dexamethasone, losartan, ibuprofen, paroxetine, pioglitazone, rosiglitazone, sertraline, theophylline, venlafaxine, and zolpidem). After incubation with human liver microsomes in the presence of NADPH, there was a large overlap in the distribution of CB amounts between the positive and negative groups. On addition of UDP-glucuronic acid (UDPGA) as a cofactor for glucuronidation, the CB levels of bromfenac and diclofenac were increased. With addition of nucleophilic glutathione (GSH), values for most compounds were decreased. However, separation of the two groups on the basis of CB could not be improved by UDPGA or GSH. Furthermore, CB with human hepatocytes also failed to discriminate positive from negative compounds. Therefore, the CB amount alone is not sufficient for risk assessment of DILI. In contrast, when the CB amount was multiplied by the maximum daily dose, which may reflect maximum hepatic exposure, the two groups did become discriminated. Taken together, our findings suggest that the combination of CB amount and daily dose can estimate the risk of idiosyncratic DILI.

A comparison of uptake of metformin and phenformin mediated by hOCT1 in human hepatocytes.

Metformin, a biguanide that has been used to treat type 2 diabetes mellitus, is reportedly transported into human hepatocytes by human organic cation transporter 1 (hOCT1). The objective of this study was to investigate differences in the hepatic uptake of metformin and phenformin, a biguanide derivative similar to metformin. Special focus was on the role of active transport into cells. Experiments were therefore performed using human cryopreserved hepatocytes and hOCT1 expressing oocytes. Both biguanides proved to be good substrates for hOCT1. However, phenformin exhibited a much higher affinity and transport activity, with a marked difference in uptake kinetics compared with metformin. Both biguanides were transported actively by hOCT1, with the active transport components much greater than passive transport components in both cases, suggesting that functional changes in hOCT1 might affect the transport of both compounds to the same degree. This study for the first time produced detailed comparative findings for uptake profiles of metformin and phenformin in human hepatocytes and hOCT1 expressing oocytes. It is considered that hOCT1 may not be the only key factor that determines the frequency of metformin and phenformin toxicity, considering the major contribution of this transporter to the total hepatic uptake and comparable width of their therapeutic concentrations.

Retraction Note to: Identification of CYP3A4 as the primary cytochrome P450 responsible for the metabolism of tandospirone by human liver microsomes.

The publisher has retracted this article [1] because it is an incorrect version that was published in error: Figures 5 and 6 are missing.

Characterization of substrate specificity of dog CYP1A2 using CYP1A2-deficient and wild-type dog liver microsomes.

Beagle dogs are commonly used for toxicological and pharmacological studies of drug candidates in the pharmaceutical industry. Recently, we reported a CYP1A2-deficient dog with a nonsense mutation (C1117T). In this study, using CYP1A2-deficient and wild-type dog liver microsomes, substrate specificity of dog CYP1A2 was investigated and compared with human CYP1A2. For this purpose, 11 cytochrome P450 assays were conducted in human or dog liver microsomes, genotyped for the CYP1A2 C1117T mutation. There was no statistical difference between C/C, C/T, and T/T dogs in activities of aminopyrine N-demethylase, aniline hydroxylase, bufuralol 1'-hydroxylase, and midazolam 1'-hydroxylase. On the other hand, activities of phenacetin O-deethylase, ethoxyresorufin O-deethylase, and tacrine 1-hydroxylase, which were catalyzed by human CYP1A2, were significantly lower in T/T dogs than C/C dogs, indicating that dog and human CYP1A2 was responsible for these activities. However, dog CYP1A2 was not involved in caffeine metabolism, a marker activity for human CYP1A2. As for endogenous substances, our results indicated that human CYP1A2, but not dog CYP1A2, is responsible for melatonin 6-hydroxylase, 9-cis-retinal oxidase, and estradiol 2-hydroxylase activity. In conclusion, tacrine, ethoxyresorufin, and phenacetin are probe substrates for CYP1A2 not only in humans but also in dogs. However, caffeine, melatonin, 9-cis-retinal, and estradiol, which are substrate for human CYP1A2, are not good substrates for dog CYP1A2. The finding that there are species differences in substrate specificity of CYP1A2 between humans and beagle dogs is an important issue and must be considered for preclinical studies using beagle dogs.

Identification of CYP3A4 as the primary cytochrome P450 responsible for the metabolism of tandospirone by human liver microsomes.

The present study was carried out to characterize the human P450 isoforms involved in the metabolism of tandospirone, an anxiolytic agent known for its superior efficacy and safety. Among 11 yeast-expressed recombinant P450 isoforms tested, CYP2D6 and CYP3A4 exhibited the highest tandospirone metabolic activity. Although there was no qualitative difference between the two isoforms, a quantitative difference in metabolite profiling was found i.e., M4 (hydroxylation of the pyrimidine ring) was the major metabolite formed with CYP2D6 while M2 (hydroxylation of the norbornan ring) and 1-PP (oxidative cleavage of the butyl chain) predominated with CYP3A4. The metabolite profile on incubation with CYP3A4 was qualitatively and quantitatively similar to that obtained with human liver microsomes. In vitro intrinsic clearance (CLint) values derived from kinetic analysis using both P450 isoforms were similar (2.2 and 1.6 ml/min/nmol P450), but the hepatic content of CYP3A4 was found to be more abundant than that of CYP2D6. The in vitro metabolism of tandospirone by human liver microsomes was markedly inhibited by ketoconazole (a CYP3A4 inhibitor) but not by quinidine (a CYP2D6 inhibitor). These results indicate that the metabolism of tandospirone by human liver microsomes primarily involves CYP3A4, and to a lesser extent CYP2D6.

Identification of CYP3A4 as the primary cytochrome P450 responsible for the metabolism of tandospirone by human liver microsomes.

The present study was carried out to characterize the human P450 isoforms involved in the metabolism of tandospirone, an anxiolytic agent known for its superior efficacy and safety. Among 11 yeast-expressed recombinant P450 isoforms tested, CYP2D6 and CYP3A4 exhibited the highest tandospirone metabolic activity. Although there was no qualitative difference between the two isoforms, a quantitative difference in metabolite profiling was found i.e., M4 (hydroxylation of the pyrimidine ring) was the major metabolite formed with CYP2D6 while M2 (hydroxylation of the norbornan ring) and 1-PP (oxidative cleavage of the butyl chain) predominated with CYP3A4. The metabolite profile on incubation with CYP3A4 was qualitatively and quantitatively similar to that obtained with human liver microsomes. In vitro intrinsic clearance (CLint) values derived from kinetic analysis using both P450 isoforms were similar (2.2 and 1.6 ml/min/nmol P450), but the hepatic content of CYP3A4 was found to be more abundant than that of CYP2D6. The in vitro metabolism of tandospirone by human liver microsomes was markedly inhibited by ketoconazole (a CYP3A4 inhibitor) but not by quinidine (a CYP2D6 inhibitor). These results indicate that the metabolism of tandospirone by human liver microsomes primarily involves CYP3A4, and to a lesser extent CYP2D6.

Distribution of perospirone to melanin in pigmented rats.

Following the administration of [Carbonyl-14C]perospirone ([CO-14C]perospirone) and [isothiazolyl-3-14C]perospirone ([TH-14C]perospirone) to male-pigmented rats at a single oral dose of 10 mg/kg, serum radioactivity reached maxima of 499 ng eq./g and 446 ng eq./g, respectively, at 1 hour, then decreased rapidly to below 2 ng eq./g at 168 hours, and radioactivity in eyeballs reached maxima of 576 ng eq./g and 3449 ng eq./g, respectively, at 24 hours, then decreasing slowly to become 120 ng eq./g and 314 ng eq./g at 26 weeks. Apparent elimination half-lives of radioactivity in eyeballs were 197 and 126 days for [CO-14C]perospirone and [TH-14C]perospirone, respectively. With radioluminograms, radioactivity was detected specifically in the uvea, reaching maxima at 168 hours for [CO-14C]perospirone and at 24 hours for [TH-14C]perospirone. In addition to unchanged compound, many metabolites were found in serum and eyeballs, but those were also detectable in SD albino rats and cynomolgus monkeys. Among radioactive components in eyeballs after administration of [CO-14C]perospirone, ratios of ID-15036 and MX11 followed by unchanged compound and MX9 are high. After administration of [TH-14C]perospirone, ID-11614 accounted for nearly half of the radioactivity. Values decreased in line with radioactivity in eyeballs over time and 26 weeks only a few polar metabolites could be detected.

In vitro drug-drug interactions with perospirone and concomitantly administered drugs in human liver microsomes.

In vitro metabolism studies were conducted to assess drug-drug interactions between perospirone, an antipsychotic agent, and concomitantly administered drugs--biperiden, flunitrazepam, haloperidol, and diazepam--using human liver microsomes. The metabolism of perospirone in the presence of 100 microg/ml drugs was decreased to 45-73% of that in their absence, whereas no effects were observed with any of the drugs at 1 microg/ml or lower. The effects of perospirone on the metabolism of concomitantly administered drugs were also assessed, and no inhibitory effect was observed. Thus, the metabolism of perospirone and concomitantly administered drugs did not demonstrate any marked mutual inhibition in the human liver microsomes. On the other hand, the perospirone metabolism was markedly reduced by ketoconazole indicating a major role for CYP 3A4. Based on the inhibition constant (Ki) for perospirone metabolism and the plasma unbound concentration of ketoconazole, in vivo perospirone clearance was estimated to be reduced to 64-90% of the control level. Thus careful attention should be paid to the possibility of increase in unchanged perospirone concentration when perospirone is co-administered with drugs that are known as CYP3A4 inhibitors, including macrolide antibiotics and other imidazole antifungals.

In vitro metabolism of perospirone in rat, monkey and human liver microsomes.

In vitro metabolism of perospirone was examined with rat, monkey and human liver S9, human liver microsomes and yeast microsomes expressing human P450, using 14C labeled perospirone. With rat liver S9, the major metabolites were MX9 and ID-11614, produced by cleavage at the butylene chain. However, some butylene non-cleavage and hydration of the cyclohexane ring were found, although limited in extent. Unknown metabolites accounted for about 10% of the total. After incubation for 10 minutes with monkey liver S9, the major metabolites were ID-15036 and MX11, hydrated in the cyclohexane ring. After incubation for 60 minutes, ID-15001, i.e. the butylene chain cleavage type increased. Unknown metabolites accounted for about 20%. After incubation for 10 minutes with human liver S9, the major metabolite was ID-15036, hydrated in the cyclohexane ring. In addition, MX11 and many unknown metabolites were evident. After incubation for 60 minutes, the butylene chain cleavage type and unknown metabolites increased. Individual differences were found in the metabolic reaction rate. With human liver microsomes. MX11, ID-15001 and unknown metabolites were again the major metabolites. With yeast microsomes expressing human P450 subtypes, CYP1A1, 2C8, 2D6, 3A4 were responsible for the metabolism in particular, and CYP3A4 contributes greatly. Therefore it is unlikely that genetic polymorphism will arise a present a problem with regard to the clinical drug. The results demonstrated that the main metabolic pathway in human liver S9 and liver microsomes involve oxidation at cyclohexane, oxidative cleavage of the butylene side chain and S-oxidation. The same was the case in rat and monkey S9, but species differences were found in the proportions of the metabolites produced.

Transport of biguanides by human organic cation transporter OCT2.

Biguanides have the severe side effect of lactic acidosis. Although both metformin and phenformin are biguanide derivatives, there is a difference in the frequency at which they induce lactic acidosis. However, the reasons for the difference are not clear. Metformin has been reported to be mainly excreted into urine by human organic cation transporter 2 (hOCT2). The present study was designed to investigate the renal transport of metformin and phenformin, focusing on hOCT2, using hOCT2-expressing oocytes. Both biguanides were found to be good substrates for hOCT2. However, phenformin exhibited a higher affinity and transport activity than metformin. The Km values for metformin and phenformin were 235 and 37.4 µM, with CL(int) (V(max)/K(m)) values of 71.9×10⁻³ µL/min per oocyte and 209×10⁻³ µL/min per oocyte, respectively. This is the first report that has compared the transport profiles of these biguanides in hOCT2-expressing oocytes. The results suggest that plasma concentration of phenformin in subjects carrying hOCT2 variant may be higher compared to reference subjects, as reported in metformin. In addition, the relationship between plasma concentration of these biguanides and blood lactate level as well as the possible reasons for the difference in the associated frequency of occurrence of lactic acidosis are discussed.

Prediction of the intestinal first-pass metabolism of CYP3A and UGT substrates in humans from in vitro data.

This study aimed to establish a practical and simplified method of predicting intestinal availability in humans (F(g,human)) at the drug discovery stage using in vitro metabolic clearance values and permeability clearance values. A prediction model for F(g,human) of 19 CYP3A substrates and 5 UGT substrates was constructed based on the concept that the permeability clearance values mean the permeability across the basal membrane with a pH of 7.4 on both sides. Permeability clearance values were obtained by parallel artificial membrane permeability assay (PAMPA) at pH 7.4. PAMPA is widely used in the pharmaceutical industry as the earliest primary screening stage and enables estimation of the kinetics of transport by passive diffusion. For CYP3A substrates, the metabolic clearance was obtained from in vitro intrinsic clearance values in human intestinal or hepatic microsomes (CL(int,HIM) or CL(int,HLM), respectively). Using metabolic clearances corrected by the ratio of CL(int,HIM) to CL(int,HLM), HLM showed equivalent predictability to that of HIM for CYP3A substrates. For UGT substrates, the clearance was obtained from alamethicin-activated HIM using one incubation with both NADPH and UDPGA cofactors. The method proposed in this study could predict F(g,human) for the compounds investigated and represents a simplified method based on a new concept applicable to lower permeability compounds.

Liver uptake of biguanides in rats.

Metformin is an oral antihyperglycaemic agent widely used in the management of non-insulin-dependent diabetes mellitus. The liver is the primary target, metformin being taken up into human and rat hepatocytes via an active transport mechanism. The present study was designed to compare hepatic uptake of two biguanides, metformin and phenformin, in vitro and in vivo. In in vitro experiments, performed using rat cryopreserved hepatocytes, phenformin exhibited a much higher affinity and transport than metformin, with marked differences in kinetics. The K(m) values for metformin and phenformin were 404 and 5.17µM, respectively, with CLint (V(max)/K(m)) values 1.58µl/min per 10(6) cells and 34.7µl/min per 10(6) cells. In in vivo experiments, when (14)C-metformin and (14)C-phenformin were given orally to male rats at a dose of 50mg/kg, the liver concentrations of radioactivity at 0.5 hour after dosing were 21.5µg eq./g with metformin but 147.1µg eq./g for phenformin, ratios of liver to plasma concentrations being 4.2 and 61.3, respectively. In conclusion, the results suggest that uptake of biguanides by rat hepatocytes is in line with the liver distribution found in vivo, phenformin being more efficiently taken up by liver than metformin after oral administration.

Species differences in intestinal metabolic activities of cytochrome P450 isoforms between cynomolgus monkeys and humans.

The oral bioavailability of some drugs is markedly lower in cynomolgus monkeys than in humans. One of the reasons for the low bioavailability in cynomolgus monkeys may be the higher metabolic activity of intestinal CYP3A; however, the species differences in intestinal metabolic activities of other CYP isoforms between cynomolgus monkeys and humans are not well known. In the present study, we investigated the intrinsic clearance (CL(int)) values in pooled intestinal microsomes from cynomolgus monkeys and humans using 25 substrates of human CYP1A2, CYP2J2, CYP2C, and CYP2D6. As in humans, intestinal CL(int) values of human CYP1A2 and CYP2D6 substrates in cynomolgus monkeys were low. On the other hand, intestinal CL(int) values of human CYP2J2 and CYP2C substrates in cynomolgus monkeys were greatly higher than those in humans. Using immunoinhibitory antibodies and chemical inhibitors, we showed that the higher intestinal CL(int) values of the human CYP2J2 and CYP2C substrates in cynomolgus monkeys might be caused by monkey CYP4F and CYP2C subfamily members, respectively. In conclusion, there is a possibility that the greatly higher metabolic activity of CYP2C and CYP4F in cynomolgus monkey intestine is one of the causes of the species difference of intestinal first-pass metabolism between cynomolgus monkeys and humans.

Consideration of reliable concentrations for prediction of change in enzyme activity by mechanism-based inactivation using physiologically-based pharmacokinetic model simulations.

Using physiologically-based pharmacokinetic model simulations with the assumption that elimination of inactivator is not altered by mechanism-based inactivation (MBI) of the target enzyme, we examined at what concentrations the influence of MBI could be accurately and simply predicted. The method utilizing maximum unbound systemic concentration as the inactivator concentration (method 1) tended to overestimate this influence, and accuracy expressed as the ratio of estimated and exact fold decrease in enzyme activity ranged from 0.80 to 8.41. In addition, when the volume of distribution was large or the absorption rate constant was small, method 1 provided relatively precise estimation, with the ratio of nearly 1. We propose use of two concentrations, the steady-state average unbound liver concentration and maximum limit of steady-state average unbound liver concentration, to predict the effects of MBI. The accuracy of prediction of MBI using these two concentrations ranged from 0.90 to 1.04 and 0.92 to 2.96, respectively, and was higher than that with method 1. These two concentrations can be obtained early in the drug development process, and estimated results can be expected to contribute to determination of the effects of MBI.