Subacute Toxicity of a Novel Inhibitor of Acyl-CoA: Cholesterol Acyltransferase in Beagle Dogs

PD 132301–2 is a substituted urea hypolipidemic and antiatheroscleroticagent that is a potent inhibitor of acyl-CoA:cholesterol acyltransferase(ACAT). To determine its subacute toxicity, PD 132301–2was administered orally to beagle dogs at 0, 6, 12, 25, 50,200, 400, or 800 mg/kg/day for 2 weeks. Clinicopathologic evaluationswere completed on all dogs. Liver and adrenal total and esterifiedcholesterol concentrations, adrenocorticotrophic hormone (ACTH)responsiveness, and adrenal ultrastructure were determined at0, 6, 12, and 25 mg/kg. At 12 mg/kg or greater, salivation,epiphora, conjunctivitis, emesis, anorexia or decreased foodconsumption, and soft to mucoid feces and/or diarrhea were noted.Suppression of ACTH response occurred by Day 6 at all doses.Adrenocortical degeneration and/or necrosis in zona fasciculataand reticularis was seen at all doses; adrenal free and esterifiedcholesterol were normal at 6 mg/kg and decreased at 12 and 25mg/kg. Increases in serum alanine aminotransferase (2- to 15-fold),aspartate aminotransferase (2- to 12-fold), and alkaline phosphatase(2- to 7-fold) were noted at 50 mg/kg or greater. Periportalhepatocellular hypertrophy and hypereosinophilia occurred at50 mg/kg or greater; hepatic cholesterol values were not significantlyaffected by treatment. Dose-dependent ultrastructural alterationsin adrenocortical cells included decreased numbers of mitochondriaand smooth endoplasmic reticulum profiles, qualitative and quantitativechanges in lipid globules, and increased numbers of autolysosomes.PD 132301-2 or one of its metabolites has potent adrenocorticolyticproperties and limited hepatotoxic properties by mechanism(s)that are likely independent of systemic ACAT inhibition.     

Metabolism of Carfentanil,an Ultra-Potent Opioid,in Human Liver Microsomes and Human Hepatocytes by High-Resolution Mass Spectrometry

Carfentanil is an ultra-potent synthetic opioid. No human carfentanil metabolism data are available. Reportedly, Russian police forces used carfentanil and remifentanil to resolve a hostage situation in Moscow in 2002. This alleged use prompted interest in the pharmacology and toxicology of carfentanil in humans. Our study was conducted to identify human carfentanil metabolites and to assess carfentanil’s metabolic clearance, which could contribute to its acute toxicity in humans. We used Simulations Plus’s ADMET Predictor? and Molecular Discovery’s MetaSite? to predict possible metabolite formation. Both programs gave similar results that were generally good but did not capture all metabolites seen in vitro. We incubated carfentanil with human hepatocytes for up to 1 h and analyzed samples on a Sciex 3200 QTRAP mass spectrometer to measure parent compound depletion and extrapolated that to represent intrinsic clearance. Pooled primary human hepatocytes were then incubated with carfentanil up to 6 h and analyzed for metabolite identification on a Sciex 5600+ TripleTOF (QTOF) high-resolution mass spectrometer. MS and MS/MS analyses elucidated the structures of the most abundant metabolites. Twelve metabolites were identified in total. N-Dealkylation and monohydroxylation of the piperidine ring were the dominant metabolic pathways. Two N-oxide metabolites and one glucuronide metabolite were observed. Surprisingly, ester hydrolysis was not a major metabolic pathway for carfentanil. While the human liver microsomal system demonstrated rapid clearance by CYP enzymes, the hepatocyte incubations showed much slower clearance, possibly providing some insight into the long duration of carfentanil’s effects.     

Difference between Normal and WHHL Rabbits in Susceptibility to the Adrenal Toxicity of an Acyl-CoA:Cholesterol Acyltransferase Inhibitor, FR145237

The adrenal toxicity of an acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, FR145237, was investigated using Japanese White (normal) and low density lipoprotein (LDL) receptor deficient Watanabe heritable hyperlipidemic (WHHL) rabbits. In the normal rabbits, severe necrosis of the cells in the zona fasciculata and reticularis was observed 24 hr after intravenous injection of 3.2 mg/kg of FR145237, whereas no morphological changes could be found in the adrenal cells of the WHHL rabbits in spite of a higher plasma concentration of the drug. Since most of the FR145237 (87%) in the plasma of the WHHL rabbits was recovered in the LDL fraction 1 hr after intravenous injection of the drug (3.2 mg/kg), it was hypothesized that the delivery of the drug to the adrenal cells may be limited by the LDL receptor deficiency. However, the concentration of FR145237 in the adrenal gland of the WHHL rabbits (13.3 μg/g) was identical to that in the normal rabbits (13.6 μg/g). These results suggest that the susceptibility of the adrenal cells of the WHHL rabbits to the toxicity of FR145237 truly differs from that of normal rabbits, and that the WHHL rabbit may be a useful animal model for the investigation of the mechanisms of the adrenal toxicity of ACAT inhibitors.     

The Metabolism of N-Ethyl-N-methylaniline by Rabbit Liver Microsomes: The Measurement of Metabolites by Gas-liquid Chromatography

Abstract

1. A method for the determination of N-ethyl-N-methylaniline and its metabolites by g.l.c. is described.

2. Following incubation in N-ethyl-N-methylaniline with rabbit liver microsomes for 60 min, over 95% of the substrate was accounted for as unchanged compound or metabolites.

3. N-Ethyl-N-methylaniline is metabolized in vitro by rabbit tissues mainly by N-oxidation and N-demethylation and to a lesser extent by N-deethylation and di-dealkylation.

4. Both major routes of metabolism were observed in homogenates prepared from rabbit liver and lung; in addition N-oxidation occurred in kidney and bladder tissue homogenates.     

Metabolism of Methyleugenol in Liver Microsomes and Primary Hepatocytes: Pattern of Metabolites, Cytotoxicity, and DNA-Adduct Formation

Methyleugenol (1) is a constituent of many foods, in particular of herbal spices, and is used as flavoring agent in foodstuffs and as fragrance in cosmetics. 1 has been found to be carcinogenic in rodents, its metabolite, 1-hydroxymethyleugenol (2) acting as proximate DNA-binding carcinogen. We incubated 1 with liver microsomes of rat, bovine, and human origin. We found 2, 3-hydroxymethylisoeugenol (3), and 6-hydroxymethyleugenol (4) as major metabolites, and 1-oxomethyleugenol (5), 3-oxomethylisoeugenol (6), eugenol (9), chavibetol (11), and (RS)-2,3-dihydroxy-2,3-dihydromethyleugenol (7) as minor metabolites. Methyleugenol-2,3-epoxide (8), probably the precursor of 7, could not be detected. Incubations with synthetic metabolites were applied in order to uncover metabolic pathways. Incubations with primary rat hepatocytes revealed mainly nonconjugated 2 and conjugated 4, and minor amounts of partly conjugated 7 and conjugated 9 + 11. The "reactive metabolites" 3, 5, 6, and 8 were not detectable, possibly due to rapid reaction with cellular macromolecules. The highest cytotoxicity (resazurin reduction assay and lactate dehydrogenase leakage assay) was observed for the main metabolite 2 and its secondary metabolite 5 with EC(50) values of 50 and 10 μM, respectively. Deoxyadenosine or deoxyguanosine adducts were formed by incubating 1 or metabolites with rat hepatocytes. The rank order of adduct formation was 2 > 1 > 3 > 6, whereas 4, 5, and 8 were inactive. In conclusion, we present a virtually complete pattern of microsomal (rat, bovine, and human) and hepatocellular (rat) metabolites of 1 suggesting the formation of several reactive metabolites possibly involved in carcinogenicity, organ toxicity, and immune reactions.     

Pharmacokinetic properties of YM17E, an inhibitor of acyl coenzyme A: cholesterol acyl transferase, and serum cholesterol levels in healthy volunteers

  We conducted a single and repeat oral dose study of YM17E, a novel inhibitor of acyl coenzyme A (CoA): cholesterol acyltransferase, in healthy male volunteers to evaluate the pharmacokinetic profile, tolerability and effect of the drug on serum cholesterol. In the single administration study, YM17E was administered after a meal to two groups of subjects (each containing six subjects taking the drug and three taking placebo) receiving 3, 60 and 300 mg or 15, 60 and 450 mg YM17E, respectively. Plasma concentrations of unchanged drug following single oral administration at 3–300 mg after a meal increased with increasing dose. In contrast, plasma concentrations after administration of 450 mg were almost the same as after 300 mg. Unchanged YM17E was not detected in urine after single administration, suggesting that it was excreted via the bile or urine after metabolism. Five active metabolites (M1, M2-a, M2-b, M3 and M4) were observed in plasma at concentrations comparable to those of unchanged YM17E. Their plasma concentrations increased in a slightly greater than dose-dependent manner from 3 to 300 mg. The effect of food was studied in an open crossover design with a 1-week washout period. Twelve subjects received 150 mg YM17E in both the fasted and postprandial states. The AUC and C_max after fasting were closely similar to those after a meal, showing that bioavailability was not affected by food intake. In the repeated oral dose study, the subjects received test drug at 150 mg or 300 mg (n = 6 each) or placebo (n = 3) twice a day (after breakfast and after dinner) for 7 days. On days 1 and 7, the subjects received YM17E once a day (after breakfast) for evaluation of pharmacokinetic properties. After repeated oral administration of 150 mg b.d., plasma concentrations reached steady state by day 5 (mean C_min 48.6 ng · ml⁻¹). After repeated administration of 300 mg b.d., plasma concentrations prior to each daily morning dose increased up to the 5th day (mean C_min 166.6 ng · ml⁻¹) and then tended to decrease until the 7th day. No significant signs, symptoms or changes in serum cholesterol levels were observed during the single and repeated oral dose studies at 150 mg b.d. Although statistical analysis was not conducted because of the small number of subjects, all subjects receiving repeated oral administration of 300 mg twice daily showed a 25% decrease in serum cholesterol level on day 7, but also the simultaneous occurrence of diarrhoea. Received: 23 April 1996 / Accepted in revised form: 1 August 1996     

Oxidative Metabolism of BDE-99 by Human Liver Microsomes: Predominant Role of CYP2B6

Hydroxylated polybrominated diphenyl ethers (PBDEs) have been found in human serum, suggesting that they are formed by in vivo oxidative metabolism of PBDEs. However, the biotransformation of 2,2',4,4',5-pentabromodiphenyl ether (BDE-99), a major PBDE detected in human tissue and environmental samples, is poorly understood. In the present study, the oxidative metabolism of BDE-99 was assessed using pooled and single-donor human liver microsomes, a panel of human recombinant cytochrome P450 (CYP) enzymes, and CYP-specific antibodies. Hydroxylated metabolites were quantified using a liquid chromatography/tandem mass spectrometry-based method. In total, 10 hydroxylated metabolites of BDE-99 were produced by human liver microsomes. Six metabolites were identified as 2,4,5-tribromophenol (2,4,5-TBP), 4-OH-BDE-90, 5'-OH-BDE-99, 6'-OH-BDE-99, 4'-OH-BDE-101, and 2-OH-BDE-123 using authentic standards. Three monohydroxy- and one dihydroxy-pentabrominated metabolites were unidentified. Rates of formation of the three major metabolites (2,4,5-TBP, 5'-OH-BDE-99, and 4'-OH-BDE-101) by human liver microsomes ranged from 24.4 to 44.8 pmol/min/mg protein. Additional experiments demonstrated that the dihydroxylated metabolite was a primary metabolite of BDE-99 and was not produced by hydroxylation of a monohydroxy metabolite. Among the panel of recombinant CYP enzymes tested, formation of all 10 hydroxylated metabolites was catalyzed solely by CYP2B6. A combined approach using antibodies to CYP2B6 and single-donor liver microsomes expressing a wide range of CYP2B6 levels confirmed that CYP2B6 was responsible for the biotransformation of BDE-99. Collectively, the results show that the oxidative metabolism of BDE-99 by human liver microsomes is catalyzed solely by CYP2B6 and is an important determinant of the toxicity and bioaccumulation of BDE-99 in humans.     

细胞色素P450介导的氯沙坦钾对瑞格列奈在大鼠肝微粒体中代谢的影响

目的 研究瑞格列奈在大鼠肝微粒体中的酶促反应动力学,并考察氯沙坦钾对其在大鼠肝微粒体中代谢的影响.方法 建立大鼠肝微粒体体外孵育体系对瑞格列奈的代谢进行研究;以洛伐他汀为内标,应用UPLC测定大鼠肝微粒体中瑞格列奈的浓度.采用底物减少法,通过GraphPad Prism 5.0软件计算瑞格列奈的酶促反应动力学常数Vma...     

Stereo‐Selective Metabolism of Methadone by Human Liver Microsomes and cDNA‐Expressed Cytochrome P450s: A Reconciliation

Abstract: In vitro metabolism of methadone was investigated in cytochrome P450 (CYP) supersomes and phenotyped human liver microsomes (HLMs) to reconcile past findings on CYP involvement in stereo‐selective metabolism of methadone. Racaemic methadone was used for incubations; (R)‐ and (S)‐methadone turnover and (R)‐ and (S)‐EDDP formation were determined using chiral liquid chromatography–tandem mass spectrometry. CYP supersome activity for methadone use and EDDP formation ranked CYP2B6 > 3A4 > 2C19 > 2D6 > 2C18, 3A7 > 2C8, 2C9, 3A5. After abundance scaling, CYP3A4, 2B6 and 2C19 accounted for 63–74, 12–32 and 1. 4–14% of respective activity. CYP2B6, 2D6 and 2C18 demonstrated a preference for (S)‐EDDP formation; CYP2C19, 3A7 and 2C8 for (R)‐EDDP; 3A4 none. Correlation analysis with 15 HLMs supported the involvement of CYP2B6 and 3A. The significant correlation of S/R ratio with CYP2B6 activity confirmed its stereo‐selectivity. CYP2C19 and 2D6 inhibitors and monoclonal antibody (mAb) did not inhibit EDDP formation in HLM. Chemical and mAb inhibition of CYP3A in high 3A activity HLM reduced EDDP formation by 60–85%; inhibition of CYP2B6 in 2B6 high‐activity HLM reduced (S)‐EDDP formation by 80% and (R)‐EDDP formation by 55%. Inhibition changed methadone metabolism in a stereo‐selective manner. When CYP3A was inhibited, 2B6 mediated (S)‐EDDP formation predominated; S/R stereo‐selectivity increased. When 2B6 was inhibited (S)‐EDDP formation fell and stereo‐selectivity decreased. The results confirmed the primary roles of CYPs 3A4 and 2B6 in methadone metabolism; CYP2C8 and 2C9 did not appear involved; 2C19 and 2D6 have minimal roles. CYP2B6 is the primary determinant of stereo‐selective metabolism; stereo‐selective inhibition might play a role in varied plasma concentrations of the two enantiomers.     

Optimization of Sustained-release Diltiazem Formulations in Man by use of an In-vitro/In-vivo Correlation

In-vitro/in-vivo correlations (IVIVC) are useful for predicting in-vivo results from in-vitro data. An IVIVC has been used to optimize a hydrocolloidal-based matrix tablet designed to be bioequivalent to an existing once-daily diltiazem HCl*** product (Dilacor XR 240 mg; Rhone-Poulenc Rorer). Data from a preliminary formulation dosed to fasted and fed subjects were used to establish the IVIVC. The correlation was then used during reformulation of the dosage forms to predict changes in the maximum plasma concentration (C_max) and the area under the plasma-concentration-time curve (AUC) for fasted and fed subjects using in-vitro dissolution data. The IVIVC adequately predicted plasma profiles of two optimized formulations in studies with fasted and fed subjects.     

高效液相色谱法检测人肝微粒体CYP3A活性

目的：测定普罗帕酮和N 去丙基普罗帕酮的比值以表达人肝微粒体中CYP3A的活性。方法：以1 mg·mL 1微粒体蛋白浓度37℃孵育普罗帕酮1 h，以HPLC测定普罗帕酮和N 去丙基普罗帕酮的含量。结果： 普罗帕酮和N 去丙基普罗帕酮的线性方程分别为Y＝0.452 0X＋0.003 029(r＝0.999 7)；Y＝1.137 3X＋0.012 740(r＝0.998 5)。结论：N 去丙基普罗帕酮与普罗帕酮的最大比值为1.54，CYP3A具有饱和性。     

Use of Isoform-Specific UGT Metabolism to Determine and Describe Rates and Profiles of Glucuronidation of Wogonin and Oroxylin A by Human Liver and Intestinal Microsomes

Purposes  

Glucuronidation via UDP-glucuronosyltransferases (or UGTs) is a major metabolic pathway. The purposes of this study are to determine the UGT-isoform-specific metabolic fingerprint (or GSMF) of wogonin and oroxylin A, and to use isoform-specific metabolism rates and kinetics to determine and describe their glucuronidation behaviors in tissue microsomes.     

大鼠肝微粒体代谢研究槲皮素对CYP1A2,CYP2E1,CYP3A2活性的影响及抑制机制

目的体外代谢研究槲皮素对大鼠肝CYP1A2,CYP2E1,和CYP3A2活性的影响。研究其抑制强度及抑制机制。方法QU与底物共同温孵,HPLC检测底物特定的代谢产物生成量的变化反映对应亚酶的活性变化。比较槲皮素与酮康唑,红霉素在相同浓度下对CYP3A2的抑制能力强弱。不同浓度槲皮素对CYP3A2和CYP2E1底物代谢产物生成双倒数直线的影响初步分析槲皮素可能的抑制机制。结果各HPLC检测方法线性相关系数均>0.9991,RSD均<8.4%,回收率91.1%-107.6%。槲皮素在体外0～8μmol·L-1诱导大鼠肝微粒体CYP1A2的活性达338.1%,并抑制CYP2E1(49.2%),和CYP3A2(60.3%)。槲皮素对CYP3A2的抑制能力在酮康唑和红霉素之间。槲皮素竞争性抑制CYP3A2右美沙芬N脱甲基反应,非竞争性抑制CYP2E1氯唑沙宗6羟化反应。结论槲皮素对多个CYP450亚酶有抑制作用,它是有效的CYP3A竞争性抑制剂。做为黄酮类植物雌激素,槲皮素有分子结构的优势亦有对CYP450酶调控能力而具有未来抗肿瘤药物研究的潜力。     

Biochemical Basis for Deficient Paracetamol Glucuronidation in Cats: an Interspecies Comparison of Enzyme Constraint in Liver Microsomes

Unlike most other mammalian species, domestic cats glucuronidate phenolic compounds poorly and are therefore highly susceptible to the toxic side effects of many drugs, including paracetamol. In this study, we evaluated the role of enzyme constraint, a characteristic that limits the activity of all uridine 5′-diphosphoglucuronosyltransferase (UGT) enzymes, in the aetiology of this species-dependent defect of drug metabolism. Detergent activation experiments were performed using hepatic microsomes from cats (4), dogs (4), man (4), and 6 other mammalian species (1 liver each). In addition, we used microsomes from Gunn rats which are sensitive to paracetamol toxicity because of a genetic defect affecting all family 1 UGTs. Increase in paracetamol-UGT activity at optimum concentrations of detergent was used as an index of enzyme constraint. Native activity (measured in the absence of detergent) was less than one-sixth in cats compared with other species. Optimum detergent treatment tended to enhance rather than abolish this difference, however, indicating relatively lower levels of constraint of paracetamol-UGT in cats compared with other species. Similarly, detergent treatment failed to reduce the native activity difference between homozygous mutant and normal Gunn rats. Initially CHAPS (3-(3-cholamidopropyl)-dimethylamrnonio-1-propanesulphonic acid) was used as the detergent activator; in 3 of 4 microsomal preparations from man, however, inhibition rather than activation was observed at all detergent concentrations used. Studies were repeated using the non-ionic detergent, Brij 58 (polyoxyethylene 20-cetyl ether), which resulted in similar although more profound activation and no inhibition. We conclude that deficient paracetamol glucuronidation in cats does not result from increased paracetamol-UGT constraint in this species compared with other mammalian species. Other causes, such as differences in enzyme protein concentration or substrate affinity might be responsible.     

采用UPLC-MS/MS法研究树豆酮酸A在不同种属肝微粒体中的代谢差异

建立测定肝微粒体孵育体系中树豆酮酸A(CAA)质量浓度的方法,并比较其在不同种属肝微粒体中的代谢特征。方法:分别将CAA溶解于由还原型烟酰胺腺嘌呤二核苷酸磷酸(NADPH)启动的大鼠、比格犬、人肝微粒体孵育体系中,置于37℃水浴中进行孵育,分别于孵育的0、5、10、15、30、45、60 min时用乙腈终止反应,以染料木素为内标,采用超高效液相色谱-串联质谱法(UPLC-MS/MS)检测各孵育体系中CAA的质量浓度。色谱柱为Waters BEH C_(18),流动相为水(含0.1%甲酸)-乙腈(含0.1%甲酸)(45∶55,V/V),流速为0.25 mL/min,柱温为30℃,进样量为2μL;采用电喷雾离子源,以选择反应监测模式进行负离子扫描,用于定量分析的离子对分别为m/z 353.14→309.11(CAA)、m/z 269.86→224.11(内标)。以孵育0 min时CAA的质量浓度为参照,计算其在不同孵育体系中的剩余百分比和酶动力学参数。结果:CAA检测质量浓度的线性范围为0.05～20μg/mL,定量下限为0.05μg/mL,最低检测限为0.01μg/mL;日内、日间RSD均小于10%,相对误差为-4.83%～8.94%,提取方法和基质效应均不影响待测物的测定。孵育60 min时,CAA在大鼠、比格犬、人肝微粒体中的剩余百分比分别为(62.79±9.99)%、(64.07±11.59)%、(96.66±5.71)%;在大鼠、比格犬肝微粒体中的半衰期(72.19、68.61 min)均显著短于人肝微粒体(364.74 min),清除率[0.019 2、0.020 2 mL/(min·mg)]均显著高于人肝微粒体[0.003 8 mL/(min·mg)](P<0.05)。结论:本研究建立的UPLC-MS/MS法简便、快速、专属性强、灵敏度高,可用于肝微粒体孵育体系中CAA质量浓度的测定及体外代谢稳定性的研究。CAA在大鼠、比格犬肝微粒体中的代谢稳定性均差于人肝微粒体。     

Inhibition of CYP3A by Antimalarial Piperaquine and Its Metabolites in Human Liver Microsomes With IVIV Extrapolation

The potential of the antimalarial piperaquine and its metabolites to inhibit CYP3A was investigated in pooled human liver microsomes. CYP3A activity was measured by liquid chromatography-tandem mass spectrometry as the rate of 1′-hydroxymidazolam formation. Piperaquine was found to be a reversible, potent inhibitor of CYP3A with the following parameter estimates (%CV): IC₅₀ = 0.76 μM (29), K_i = 0.68 μM (29). In addition, piperaquine acted as a time-dependent inhibitor with IC₅₀ declining to 0.32 μM (28) during 30-min pre-incubation. Time-dependent inhibitor estimates were k_inact = 0.024 min^?1 (30) and K_I = 1.63 μM (17). Metabolite M2 was a highly potent reversible inhibitor with estimated IC₅₀ and K_i values of 0.057 μM (17) and 0.043 μM (3), respectively. M1 and M5 metabolites did not show any inhibitory properties within the limits of assay used. Average (95th percentile) simulated in vivo areas under the curve of midazolam increased 2.2-fold (3.7-fold) on the third which is the last day of piperaquine dosing, whereas for its metabolite M2, areas under the curve of midazolam increased 7.7-fold (13-fold).     

Midazolam α-Hydroxylation by Human Liver Microsomes in vitro: Inhibition by Calcium Channel Blockers,Itraconazole and Ketoconazole

Abstract: The inhibitory effects of five calcium channel blockers (diltiazem, isradipine, mibefradil, nifedipine and verapamil) and three azole antifungal agents (itraconazole, hydroxyitraconazole and ketoconazole) on the α-hydroxylation of midazolam, a probe drug for CYP3A4-mediated interactions in humans, were studied in vitro using human liver microsomes. IC₅₀ and K_i values were determined for each inhibitor. The kinetics of the formation of α-hydroxymidazolam were best described by simple Michaelis-Menten kinetics. The estimated values of V_max and K_m were 696 pmol min.^?1 mg^?1 and 7.46 μmol l^?1, respectively. All the compounds studied inhibited midazolam α-hydroxylation activity in a concentration-dependent manner, but there were marked differences in their relative inhibitory potency. Ketoconazole was the most potent inhibitor of midazolam α-hydroxylation (IC₅₀ 0.12 μmol l^?1), being 10 times more potent than itraconazole (IC₅₀ 1.2 μmol l^?1). The inhibitory effect of hydroxyitraconazole (IC₅₀ 2.3 μmol l^?1) was almost as large as that of itraconazole. Among the calcium channel blockers, mibefradil was the most potent inhibitor of the α-hydroxylation of midazolam, with an IC₅₀ value (1.6 μmol l^?1) similar to that of itraconazole. The other calcium channel blockers were much weaker inhibitors than mibefradil: verapamil exhibited a modest inhibitory effect with an IC₅₀ of 23 μmol l^?1, while isradipine, nifedipine and diltiazem, with IC₅₀ values ranging from 57 to >100 μmol l^?1, were weak inhibitors. This rank order of potency against the α-hydroxylation of midazolam was verified by the K_i values. With the exception of diltiazem, these in vitro results conform with the observed interaction potential of these agents with midazolam and many other CYP3A4 substrates in vivo in man.     

Disposition and metabolism of a novel diurea inhibitor of acyl CoA: cholesterol acyltransferase (YM17E) in the rat and dog

We have investigated the disposition and metabolism of YM17E after intravenous and oral administration in the rat and dog.

2. Unavailability of YM17E was 5–9% at oral doses of 3–30 mg/kg in rat, and 9 and 13% at oral doses of 10 and 30mg/kg in dog.

3. Five N-demethylated metabolites, which have significant pharmacological activity, were found in rat and dog plasma after oral administration. Plasma concentrations of each of these metabolites were comparable with (hat of unchanged drug.

4. When ¹⁴C-YM17E was administered to rat, AUC of unchanged drug was 7% of that of radioactivity. However, AUC of the combined concentration of unchanged drug and five active metabolites was about 50% of that of radioactivity, indicating that the pharmacological activity of the agent was maintained in spite of its biotransformation.

5. After oral administration of ¹⁴C-YM17E at a dose of 10 mg/kg to rat, radioactivity was distributed widely to almost all tissues except the brain. The concentration of radioactivity in the liver, one of the target organs, was 65 times higher than that in plasma at 1 h after administration.

6. A significant amount of radioactivity in the liver was located in the microsomal subfraction, which contains much acyl CoA: cholesterol acyl transferase activity. More than 50% of this microsomal radioactivity was derived from unchanged YM17E and five active metabolites.

7. From excretion data in the bile duct-cannulated rat, the absorption ratio of YM17E from the gastrointestinal tract in this species was estimated to be at least 40%, suggesting that the low bioavailability of the drug is due to extensive first-pass metabolism.

8. Some 95% of the administered radioactivity was excreted in the faeces of rat following iv or po doses of ¹⁴C-YM17E.     

The Fate of an Experimental MAO Inhibitor,N-Cyclopropyl-2-Chlorophenoxyethylamine (Lilly 51641) in the Rat and in Man

Abstract

1. In vivo metabolism studies have shown N-cyclopropyl-2-chlorophenoxy-ethylamine (Lilly 51641) to be extensively metabolized in the rat. Those metabolites identified include 2-chlorophenoxyacetic acid, N-cyclopropyl-4-hydroxy-2-chlorophenoxyethylamine and 4-hydroxy-2-chlorophenoxyethanol, together with a number of minor products. The major route of elimination of these metabolites is through the kidney.

2. The major in vitro metabolites of Lilly 51641 have been identified as 2-chlorophenoxyethylamine, 2-chlorophenoxyacetaldehyde, 2-chlorophenoxyacetic acid and 2-chlorophenoxyethanol. It thus appears that this drug is metabolized by the following sequence: N-dealkylation, deamination and aldehyde oxidation or reduction.

3. Aromatic hydroxylation was found to be an independent but important mechanism involved in the metabolism of Lilly 51641.

4. Human urinary metabolites of Lilly 51641 were separated and identified. The nature of these metabolites indicated that the same mechanisms of detoxication were involved in the biotransformation in the human as were involved in the rat.

5. The major human urinary metabolite was 4-hydroxy-2-chlorophenoxy-acetic acid.