反式曲马朵在大鼠肝微粒体O-去甲基代谢中的立体选择性

目的研究反式曲马朵O-去甲基代谢的立体选择性.方法高效毛细管电泳法测定大鼠肝微粒体孵育液中反式曲马朵和O-去甲基曲马朵对映体的浓度,酶促动力学方法研究O-去甲基曲马朵对映体的生成.结果 (-)-O-去甲基曲马朵生成有较大的Vmax;反式曲马朵两对映体间存在相互作用,使(+)-O-去甲基曲马朵生成的Vmax明显减慢;奎宁及奎尼丁对(+)-O-去甲基曲马朵生成的抑制作用较强.结论反式曲马朵O-去甲基代谢有立体选择性,对映体间的相互作用及酶抑制剂使其立体选择性程度加强.     

在大鼠肝微粒体中反式曲马朵和反式氧去甲基曲马朵对映体代谢的性别差异

目的研究反式曲马朵(trans T)对映体代谢，反式氧去甲基曲马朵(Ml)对映体生成及其与葡糖醛酸结合的性别差异。方法以trans T或Ml为底物分别与大鼠肝微粒体孵育，高效毛细管电泳法测定孵育液中trans T和Ml对映体。结果与(+)-对映体相比，(-)-trans T优先代谢，(-)-Ml优先生成。在雌性大鼠肝微粒体中(-)-Ml优先与葡糖醛酸结合；Ml两对映体生成及其与葡糖醛酸结合的CL_int比值偏离1的程度较大。在雄性大鼠肝微粒体中(+)-Ml优先与葡糖醛酸结合。结论Trans T代谢，M1生成及其与葡糖醛酸结合均具立体选择性和性别差异；Ml生成及其与葡糖醛酸结合立体选择性的程度以雌性大鼠的较高。     

反式曲马朵和反式氧去甲基曲马朵在大鼠胆汁中排泄的立体选择性反式曲马朵和反式氧去甲基曲马朵在大鼠胆汁中排泄的立体选择性

目的研究反式曲马朵(trans T)及反式氧去甲基曲马朵(M1)在大鼠胆汁中排泄的立体选择性。方法高效毛细管电泳法测定大鼠iv trans T或 M1后胆汁和血浆中trans T, M1和与葡糖醛酸结合M1(M1_c)的对映体。结果大鼠iv trans T后,胆汁中(+)-transT水平较(-)-trans T高,(+)/(-)-trans T较血浆中(+)/(-)-trans T的比值小。大鼠iv M1后,胆汁中(+)-M1水平较(-)-M1高,(+)-M1_c较(-)-M1_c低,(+)-M1与葡糖醛酸的结合率较(-)-M1低。结论trans T和M1在大鼠胆汁中排泄具立体选择性,(+)-trans T和(-)-M1被优先排泄。     

黄皮酰胺对映体在大鼠肝微粒体中的酶促反应动力学黄皮酰胺对映体在大鼠肝微粒体中的酶促反应动力学

目的研究黄皮酰胺（clausenamide,Clau）对映体在大鼠肝微粒体中的酶促反应动力学并比较其立体选择性差异。方法应用反相HPLC法测定Clau对映体在体外代谢系统中的产物，并用Eadie-Hofstee作图法分析数据、求算酶促反应动力学参数K_m和V_max以及肝代谢速率V_max/K_m。结果在体外代谢系统中，左旋黄皮酰胺主要生成7-羟-Clau、5-羟-Clau和4-羟-Clau，其优势代谢途径为7位羟化；7位羟化代谢的V_max/K_m值高于5位和4位。右旋黄皮酰胺的4位羟化反应K_m最小、V_max最大, 因此代谢速率最高，是左旋体4位羟化的8倍；而其7-羟-Clau和5-羟-Clau 的产生量很小。结论黄皮酰胺对映体在大鼠肝微粒体中的羟化代谢存在明显的底物立体选择性差异。     

反式曲马朵及其活性代谢产物反式氧去甲基曲马朵肾脏清除的立体选择性

目的:研究反式曲马朵及其活性代谢物反式氧去甲基曲马朵肾脏清除的立体选择性.方法:取雄性SD大鼠的右肾,分别以含反式曲马朵(300μg/L)或反式氧去甲基曲马朵(50μg/L)的灌流液(10mL)进行灌流;利用高效毛细管电泳法测定灌流后灌流液、尿液中反式曲马朵及反式氧去甲基曲马朵对映体的浓度,并计算对映体浓度比值.结果:以反式曲马朵进行离体肾灌流后,在灌流液中,( )-反式曲马朵的浓度高于(-)-反式曲马朵的浓度,( )-反式氧去甲基曲马朵的浓度低于(-)-反式氧去甲基曲马朵的浓度;在尿液中,( )-反式曲马朵较(-)-反式曲马朵多,( )-反式氧去甲基曲马朵较(-)-反式氧去甲基曲马朵少.以反式氧去甲基曲马朵灌流后,在灌流液中( )-反式氧去甲基曲马朵的浓度低于(-)-反式氧去甲基曲马朵的浓度;在尿液中( )-反式氧去甲基曲马朵较(-)-反式氧去甲基曲马朵高.结论:反式曲马朵及反式氧去甲基曲马朵的肾脏清除具有立体选择性.在肾脏中反式曲马朵的氧去甲基代谢具有立体选择性,以(-)-反式曲马朵优先代谢成(-)-反式氧去甲基曲马朵.反式氧去甲基曲马朵的尿排泄具有立体选择性,以( )-反式氧去甲基曲马朵占优.     

反式曲马朵在大鼠小肠中吸收的立体选择性

目的研究反式曲马朵(Trans T)在大鼠小肠中吸收的立体选择性。方法高效毛细管电泳法测定小肠分段灌流液中Trans T对映体的浓度。结果Trans T对映体在小肠不同部位的吸收分数基本一致;在低浓度时(+)-Trans T的吸收分数明显低于(-)-Trans T;在高浓度时Trans T对映体的吸收分数降低,(+)-Trans T与(-)-Trans T的吸收分数无明显差别。结论Trans T在大鼠小肠的不同部位均能被吸收,具立体选择性,以(-)-Trans T占优。     

反式曲马多及氧去甲基曲马多对映体跨血脑屏障转运

目的　研究反式曲马多(trans T)及其活性代谢物氧去甲基曲马多(M₁)对映体的跨血脑屏障转运。方法大鼠ip盐酸 trans T (16.7mg·kg^-1 或5.0mg·kg^-1) 1 h后取血、脑脊液和大脑皮层,高效毛细管电泳测定血清、脑脊液和大脑皮层中 trans T和M₁ 对映体的浓度。结果　trans T和M₁ 各对映体浓度以大脑皮层中最高,血清中浓度居中,脑脊液中浓度最低。在血清中,(+)-trans T的浓度明显高于(-)-trans T的浓度,M₁ 两对映体的浓度无明显区别;在脑脊液和大脑皮层中,(+)-trans T的浓度明显高于(-)-trans T的浓度,(+)-M₁ 的浓度明显低于(-)-M₁ 的浓度。结论　trans T和M₁ 的跨血脑屏障转运具有立体选择性,脑组织中分别以(+)-对映体和(-)-对映体浓度较高。     

反式曲马多对映体的药代动力学立体选择性

目的:研究反式曲马多对映体:( + )-反式曲马多和( - )-反式曲马多的人体药代动力学。方法:12 名受试者po 多剂量盐酸反式曲马多缓释片,用高效毛细管电泳法测定人血清中反式曲马多对映体的浓度,配对t-检验比较两对映体的血药浓度和药代动力学参数。结果:血药浓度达稳态后不同时间血清中( + )-反式曲马多的浓度均明显高于( - )-反式曲马多的浓度,两对映体的C_max,C_min ,C_av,AUC_0→∞,T_1/2 等药代动力学参数均有显著性差异。结论:人体对( + )-反式曲马多比对( - )-反式曲马多吸收完全、消除慢,反式曲马多对映体有药代动力学立体选择性。     

在大鼠肝微粒体中反式曲马朵代谢及反式氧去甲基曲马朵生成的立体选择性(英文)

目的:研究反式曲马朵[(±)一trans-T]代谢及反式氧去甲基曲马朵(M1)生成的立体选择性,方法:(±)-trans-T及其对映体分别与大鼠肝微粒体孵育,高效毛细管电泳法测定孵育液中(±)-trans-T及M1对映体的浓度。结果:以(±)-trans-T单一对映体为底物孵育时,(+)-trans-T的代谢速率较低,(+)-M1生成有较低的V_(max)和CL_(int).以(±)-trans-T消旋体为底物孵育时,(±)-trans-T对映体的代谢速率及(±)-M1对映体的生成速率不同程度地减慢。右美沙芬、普罗帕酮和氟西汀既能抑制(±)-trans-T的代谢,又能抑制M1的生成;普罗帕酮和氟西汀能增强(±)-trans-T代谢及M1生成的立体选择性,右美沙芬仅使M1生成的立体选择性增强。结论:在大鼠肝微粒体中,(±)-trans-T代谢及M1生成有立体选择;(±)-trans-T对映体间存在相互作用。右美沙芬、普罗帕酮及氟西汀对它们的立体选择性产生不同的影响。     

盐酸反式曲马朵口服制剂中盐酸曲马朵立体异构体的分离与测定

目的 :建立盐酸反式曲马朵口服制剂中盐酸曲马朵 4种立体异构体的分离测定方法。方法 :采用高效毛细管电泳法 ,未涂层毛细管 75 μm× 37cm (有效长度 30cm) ;分离介质为 40mmol·L-1Tris缓冲液 (pH 2 5 ) ,内含 0 8mmol·L-1磺丁基 - β-环糊精 ;分离电压 15kV ,柱温 2 5℃ ,检测波长 2 14nm ;进样电压 10kV ,2 0s ,入口为阳极。 结果 :以 (- ) -氧去甲基曲马朵为内标 ,反式曲马朵、顺式曲马朵的对映体达到基线分离 ,( ) -盐酸反式曲马朵、 (- ) -反式曲马朵的线性浓度范围为 0 5～ 1 5 μg·mL-1;4种制剂中 ( ) -盐酸反式曲马朵和 (- ) -盐酸曲马朵平均回收率 96 87%～10 2 4%和 96 2 8%～ 10 1 3 % ,RSD <5 % ,n =5 ;盐酸曲马朵 4种立体异构体的最低检测浓度为 5ng·mL-1;4种盐酸反式曲马朵口服制剂中盐酸顺式曲马朵各对映体含量不超过 0 12 % ,盐酸反式曲马朵各对映体的含量为标示量的 45 5 8%～5 0 93 %。结论 :本方法可用于盐酸反式曲马朵口服制剂中盐酸顺式曲马朵对映体的限量检查和盐酸反式曲马朵对映体的含量测定     

Stereoselective pharmacokinetic analysis of tramadol and its main phase I metabolites in healthy subjects after intravenous and oral administration of racemic tramadol

The kinetics of tramadol enantiomers are stereoselective when doses of the racemic drug are given orally. To document whether the route of administration determines the stereoselective kinetics of tramadol enantiomers, healthy volunteers received 100 mg oral or intravenous doses of racemic tramadol, and serial blood samples were obtained to assay tramadol enantiomers and their main phase I metabolites, O-demethyltramadol and N-demethyltramadol. To assess accurately the involvement of their metabolites in the pharmacokinetics of tramadol, it is essential to determine the rate and extent of the formation of the enantiomers of these metabolites. A simultaneous pharmacokinetic model describing the plasma concentration-curves of the generated metabolites and the parent compounds after intravenous and oral drug administration is developed and presented. Tramadol and O-demethyltramadol were the major compounds detected in plasma after intravenous administration. Nevertheless, the N-demethylation of tramadol showed a significant increase when the oral route was used. After both oral and intravenous doses, the kinetics of the tramadol enantiomers were stereoselective. The AUC for (R )-(+)-tramadol was greater than the AUC for (S)-(-)-tramadol. The formation of N-demethyltramadol also was enantioselective after oral administration of racemic tramadol, with a greater AUC for (R)-(+)-N-demethyltramadol than for (S)-(-)-N-demethyltramadol. In the opposite form, (S)-(-)-O-demethyltramadol was formed faster than (R)-(+)-O-demethyltramadol. The metabolism of tramadol was also route-dependent with a different enantiomeric ratio for tramadol and its main phase I metabolites after intravenous and oral administration. The disposition of N-demethyltramadol was concentration-dependent.     

Influence of substrate configuration on chlorpheniramine N-demethylation by hepatic microsomes from rats, rabbits, and mice

Measurements of formaldehyde formation in parallel incubations containing either (S)-(+)- or (R)-(-)-chlorpheniramine (CPA) and rat liver microsomes demonstrated that the active antihistamine, (S)-(+)-CPA, is N-demethylated about 35% faster than the inactive (R)-(-)-enantiomer. The KM values for the enantiomers were the same. Phenobarbital pretreatment increased Vmax values without affecting the stereoselectivity. N-Demethylation occurred at a several-fold faster rate with rabbit than with rat liver microsomes, but stereoselectivity was the same. N-Demethylation of CPA enantiomers were studied in microsomes prepared from each of four inbred strains of mice. These experiments demonstrated that stereoselectivity is species-dependent, as no significant differences in metabolism rates of CPA enantiomers could be detected with these microsomes. Pseudoracemic mixtures containing equal quantities of deuterated (S)-(+)-CPA and unlabeled (R)-(-)-CPA were incubated with microsomes from three species. Formation of the enantiomers of N-desmethyl- and N,N-didesmethyl-CPA (DMCPA and DDMCPA, respectively) were measured by GC/MS techniques. With microsomes from rats and mice, the ratio of (S)-DMCPA to (R)-DMCPA was essentially the same as that determined by measuring the formaldehyde formed in separate incubations of (S)-(+)- or (R)-(-)-CPA. Stereoselectivity with rabbit liver microsomes and pseudoracemic CPA was substantially higher than that determined in incubations with the separate enantiomers. The results suggest either that (S)-(+)-CPA inhibits the N-demethylation of (R)-(-)-CPA under these conditions, or that DMCPA undergoes further biotransformation by a route(s) which is stereoselective, favoring the (R)-enantiomer. Formation of DDMCPA could only be detected with rabbit microsomes and was found to occur with approximately the same stereoselectivity as that determined for the formation of DMCPA.     

In-vitro Metabolic Interaction of Bunitrolol Enantiomers in Rabbit Liver Microsomes

We have examined the 4-hydroxylation of bunitrolol in rabbit and rat liver microsomes. Significant species differences (rabbit < rat of both sexes) and sex (male > female of both species) were observed in the formation of 4-hydroxybunitrolol from racemic bunitrolol (10 μM). The 4-hydroxylation of bunitrolol racemate and enantiomers showed biphasic kinetics, a low-K_m system and a high-K._m system, in liver microsomes from rabbits of both sexes. There were significant differences in K_m and V_max values [(+) > (-)] for 4-hydroxylations of (+)-bunitrolol and (-)-bunitrolol in the low-K._m system. Furthermore, the rate of clearance (V_max/K_m) was 20- to 200-fold for the low-K_m system compared with the high-K_m system, indicating that enzymes in the low-K_m system play a major part in the rabbit liver microsomal bunitrolol metabolism. Inhibition studies using cytochrome P450 inhibitors such as quinidine, quinine, and α-naphthoflavone or polyclonal antibodies raised against rat P450-2D and ?1A enzymes did not make clear which P450 enzymes are involved in bunitrolol 4-hydroxylation in rabbit liver microsomes. The 4-hydroxylase activity of (+)-bunitrolol was slightly higher than that of (-)-bunitrolol in separated incubations containing male rabbit liver microsomes and an enantiomer concentration of 10 μM. However, the 4-hydroxylation of (+)-bunitrolol (10 μM) was markedly suppressed in the presence of its antipode (10 μM), whereas (-)-bunitrolol 4-hydroxylation was not affected by the presence of its antipode, resulting in a change of the stereoselectivity from (+) > (-) for enantiomer to (+) < (-) for racemate. The difference in the Michaelis constants in the low-K_m system, where the K_m value of (-)-bunitrolol is one-eighth that of (+)-bunitrolol, is thought to cause the change in the stereoselectivity in rabbit liver microsome-mediated bunitrolol 4-hydroxylation.     

Stereoselectivity and interaction between the glucuronidation of S-(-)- and R-(+)-propranolol in rat hepatic microsomes pretreated with different inducers

Phase II glucuronidation metabolism of side-chain propranolol was studied using microsomes from rats treated with the inducers beta-naphthoflavone (BNF) or dexamethasone (Dex). The glucuronide concentrations of propranolol enantiomers were assayed by RP-HPLC. The kinetic constants of glucuronidation, Km, Vmax and Clint were determined. There are significant differences between the R- and S-enantiomeric glucuronide in Km, Vmax and Clint P < 0.05, P < 0.01 and P < 0.05 in control microsome. There are significant differences in Km and Clint (P < 0.01 or P < 0.001) but no significant differences in Vmax (P > 0.05) between R and S-enantiomeric glucuronide in the microsomes induced with Dex and BNF. The formation of S-(-)-propranolol glucuronide was inhibited by R-(+)-propranolol from the rat microsomes pretreated with BNF and Dex. The glucuronidation metabolism of propranolol enantiomers exhibited the stereoselectivity in rat hepatic microsomes induced with BNF or Dex. Multiple UGT1A and 2B may be involved in stereoselective O-glucuronidation of propranolol enantiomers in rat liver microsomes. The glucuronides produced were in favor of the R-enantiomer. There is an interaction between the glucuronidation of R- and S-enantiomer.     

Stereoselective metabolism of cibenzoline, an antiarrhythmic drug, by human and rat liver microsomes: possible involvement of CYP2D and CYP3A.

Stereoselective metabolism of cibenzoline succinate, an oral antiarrhythmic drug, was investigated on hepatic microsomes from humans and rats and microsomes from cells expressing human cytochrome P450s (CYPs). Four main metabolites, M1 (p-hydroxycibenzoline), M2 (4,5-dehydrocibenzoline), and unknown metabolites M3 and M4, were formed by human and rat liver microsomes. The intrinsic clearance (CL(int)) of the M1 formation from R(+)-cibenzoline was 23-fold greater than that of S(-)-cibenzoline in human liver microsomes, whereas the R(+)/S(-)-enantiomer ratio of CL(int) for M2, M3, and M4 formation was 0.39 to 0.83. The total CL(int) for the formation of the four main metabolites from S(-)- and R(+)-cibenzoline was 1.47 and 1.64 microl/min/mg, respectively, suggesting that the total CL(int) in R(+)-enantiomer was slightly greater than that in S(-)-enantiomer in human liver microsomes. The M1 formation from R(+)-cibenzoline was highly correlated with bufuralol 1'-hydroxylation and CYP2D6 content and was inhibited by quinidine, a potent inhibitor of CYP2D6. Additionally, only microsomes containing recombinant CYP2D6 were capable of M1 formation. These results suggest that the M1 formation from R(+)-cibenzoline was catalyzed by CYP2D6. The formation of M2, M3, and M4 from S(-)- and R(+)-cibenzoline was highly correlated with testosterone 6beta-hydroxylation and CYP3A4 content. Ketoconazole, which is a potent inhibitor of CYP3A4/5, had a strong inhibitory effect on their formation, and the M4 formation from R(+)-cibenzoline was inhibited by quinidine by 45%. The formation of M2 was also inhibited by quinidine by 46 to 52% at lower cibenzoline enantiomers (5 microM), whereas the inhibition by quinidine was not observed at a higher substrate concentration (100 microM). In male rat liver microsomes, ketoconazole and quinidine inhibited the formation of the main metabolites, M1 and M3, >74% and 44 to 59%, respectively. These results provide evidence that CYP3A and CYP2D play a major role in the stereoselective metabolism of cibenzoline in humans and male rats.