Genetic polymorphism of (S)-mephenytoin 4''-hydroxylation in populations of African descent

AIMS: The frequency of CYP2C19 poor metabolizers (PMs) in populations of African descent has been reported to range from 1.0% to 35.4%. In order to determine with greater certainty the frequency of CYP2C19 PMs in such black populations we have performed a meta-analysis of the studies. METHODS: Relevant data on the frequency of both the PM phenotype of probe drugs (mephenytoin, omeprazole, and proguanil), and the distribution frequencies of CYP2C19 alleles and genotypes in black populations were summarized and reanalysed using a meta-analytical approach. RESULTS: Of nine reported studies two were excluded because of significant heterogeneity (chi2=115, P<0.0001). The combined data from the remaining seven studies showed that the frequency of the PM phenotype in 922 healthy unrelated black Africans and black Americans ranged from 1.0% to 7.5% (n=7 for combined data) with an overall frequency being 3.9% (36 of 922; 95%CI: 2.7%-5.2%). The frequency of the PM genotypes in blacks was 3.7% (36 of 966; 95%CI: 2.5%-4.9%), in agreement with the frequency of the PM phenotype. In the extensive metabolizers (EMs) 29% (271 of 930) were heterozygotes (wt/m ). The observed frequencies of the three Mendelian genotypes were 0.68 for wt/wt, 0.28 for wt/m, and 0.04 for m/m. The allelic distribution was appropriate at 82.3% (95%CI: 80.5%-83.9%) for CYP2C19*1, 17.3% (95%CI:15.7%-19.0%) for CYP2C19*2 (m1 ), and 0.4% (95%CI: 0.1%-0.7%) for CYP2C19*3 (m2 ) in these populations. CONCLUSIONS: We conclude that subjects of African ancestry have a low frequency of the CYP2C19 PM phenotype and genotype; that the defective CYP2C19 alleles are uncommon, and that a small proportion of heterozygotes exists in the EM subpopulation.     

Characterization of human cytochrome P450 enzymes catalyzing domperidone N-dealkylation and hydroxylation in vitro

AIMS: To confirm the identity of the major metabolites of domperidone and to characterize the cytochrome P450s (CYPs) involved in their formation. METHODS: Human liver microsomes (HLMs) were used to characterize the kinetics of domperidone metabolism and liquid chromatography-mass spectrometry to identify the products. Isoform-specific chemical inhibitors, correlation analysis and expressed human CYP genes were used to identify the CYPs involved in domperidone oxidation. RESULTS: In HLMs, domperidone underwent hydroxylation to form 5-hydroxydomperidone (MIII) and N-dealkylation to form 2,3-dihydro-2-oxo-1H-benzimidazole-1-propionic acid (MI) and 5-chloro-4-piperidinyl-1,3-dihydro-benzimidazol-2-one (MII). The formation of all three metabolites (n = 4 HLMs) followed apparent Michaelis-Menten kinetics. The mean Km values for MI, MII and MIII formation were 12.4, 11.9, and 12.6 micro m, respectively. In a panel of HLMs (n = 10), the rate of domperidone (5 microm and 50 microm) metabolism correlated with the activity of CYP3A (r > 0.94; P < 0.0001). Only ketoconazole (1 microm) (by 87%) and troleandomycin (50 microm) (by 64%) inhibited domperidone (5 microm) metabolism in HLMs. Domperidone (5 and 50 microm) hydroxylation and N-dealkylation was catalyzed by expressed CYP3A4 at a higher rate than the other CYPs. CYP1A2, 2B6, 2C8 and 2D6 also hydroxylated domperidone CONCLUSIONS: CYP3A-catalyzed N-dealkylation and aromatic hydroxylation are the major routes for domperidone metabolism. The drug would be expected to demonstrate highly variable bioavailability due to hepatic, and possibly intestinal first-pass metabolism after oral administration. Increased risk of adverse effects might be anticipated during concomitant administration with CYP3A inhibitors, as well as decreased efficacy with inducers of this enzyme.     

连续串联釜式反应器中苯酚羟化制苯二酚的催化剂活性分布

在连续串联搅拌釜反应器(m-CSTR)中对铁复合氧化物催化剂作用下苯酚过氧化氢羟化制苯二酚体系中催化剂活性及其分布进行实验研究，结果表明：在催化剂使用过程中，催化剂活性衰减较快，得到催化剂活性与时间的关系式。为使m-CSTR中催化反应稳定进行，采用部分回用的方式进行操作，利用活性方程对m-CSTR中催化剂活性分布进行了计算。结果表明：随着回用比和回用次数的增加，催化剂的平均活性下降，回用比小于0．6时，催化剂的活性为开始活性的85％，可保持在较高的水平，产物组成也保持原有水平。串联釜级数对催化剂的活性及其分布、产物组成影响较小。     

Effect of Lycopine on the Resistance of Rat Liver Microsomes to In Vitro Induced LPO

Lycopine in concentrations of 0.5-50 M suppressed LPO in microsomes induced by NADPH-Fe²⁺ and by ascorbic acid-Fe²⁺. Lycopine in a concentration of 20 M completely prevented the decrease in the rate of benz[a]pyrene hydroxylation and activation of p-nitrophenyl-UDP-glucuronosyl transferase caused by LPO induction in microsomes.     

采用重组人源CYP酶研究艾瑞昔布的体外羟基化代谢

目的探讨新型抗炎镇痛药艾瑞昔布在人体内的羟基化代谢酶。方法用体外重组的人源细胞色素P450(CYP)进行孵育代谢实验，液相色谱-多级质谱法分析代谢产物和残留的母体药物，利用整体归一化法对4种CYP酶的代谢作用大小进行评估。结果艾瑞昔布羟基化代谢可由CYP2C9，CYP2D6和CYP3A4催化，其各自作用大小分别为62.5%，21.1%和16.4%。结论CYP2C9为艾瑞昔布羟基化的主要代谢酶。     

CARNITINE SYNTHESIS IN SCORBUTIC GUINEA PIGS

In vitamin C deficiency, in vivo synthesis of carnitine is impaired due to blocks in the hydroxylation of the trimethyllysine and trimethylaminobutyrate, intermediates of the carnitine biosynthesis pathway.     

Characterization of hepatic and pulmonary cytochromes P-450 in 3-methylcholanthrene-treated hamsters

Two major forms of hepatic cytochrome P-450 (hepatic P-450_MCI and P-450_MCII) were purified approximately 5-fold from liver microsomes in Syrian golden hamsters treated with 3-methylcholanthrene (MC). The purified preparations of hepatic P-450_MCI and P-450_MCII contained 9.6 and 8.3 nmol cytochrome P-450 (P-450) per mg protein, respectively, and were essentially free from NADPH-cytochrome c (P-450) reductase (fpT), NADH-cytochrome b₅ reductase and cytochrome b₅. By sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the molecular weights of hepatic P-450_MCI and P-450 _mMCII were estimated to be 56 000 and 53 500. Further, a major form of pulmonary P-450 (P-450_MC) were purified from lung microsomes of MC-treated hamster, and contained 14.2 nmol P-450 per mg protein, and estimated to be 56 000 in monomeric molecular weight, indicating the similar molecular weight to hepatic P-450_MCI in the hamster. From the absorption spectra the oxidized forms of hepatic P-450_MCI and P-450_MCII were high- and low-spin ferric hemoproteins, respectively, and pulmonary P-450_MC was similar to hepatic P-450_MCII in their hemoprotein spin state. No difference, however, was observed in the CO-reduced forms among hepatic P-450_MCI, P-450_MCII and pulmonary P-450_MC, all exhibiting 446.5 nm Soret bands. In a reconstituted system containing fpT and dilauroylphos-phatidylcholine (DLPC), pulmonary P-450_MC efficiently catalyzed benzo[a]pyrene (BP) hydroxylation at a rate of 11.4 mol formed per min per mol P-450, but hepatic P-450_MCI and P-450_MCII both exhibited lower levels, e. g., 0.49 and 0.54, respectively. These findings indicated a clear tissue difference in the activity of BP hydroxylation between lung and liver in MC-treated hamsters.Dedicated to Professor Dr. med. Herbert Remmer on the occasion of his 65th birthday     

AM-36, a novel neuroprotective agent,profoundly reduces reactive oxygen species formation and dopamine release in the striatum of conscious rats after endothelin-1-induced middle cerebral artery occlusion

Elevated generation of reactive oxygen species (ROS) has been demonstrated during ischemia and reperfusion. Dopamine (DA) autooxidation may contribute to increased ROS generation. The novel neuroprotective agent AM-36 has antioxidant and Na(+) channel blocking activity and reduces neuronal damage in both cortex and striatum after middle cerebral artery (MCA) occlusion. Here we sought in vivo evidence of the ability of AM-36 to inhibit intrastriatal ROS generation and DA release after ischemia. Salicylate hydroxylation coupled with in vivo microdialysis in the striatum of conscious Long Evans rats was performed during MCA occlusion by perivascular microinjection of endothelin-1 (ET-1). AM-36 (6 mg/kg) was administered intraperitoneally 30 min after MCA occlusion. Dialysates were analysed using high performance liquid chromatography with electrochemical detection for the salicylate hydroxylation product, 2,3-dihydroxybenzoic acid (2,3 DHBA) and for DA and metabolites. MCA occlusion resulted in a marked increase in 2,3 DHBA and a secondary increase in all analytes, 180-300 min later. Increased DA release coincided with 2,3 DHBA formation. AM-36 significantly reduced ischemia induced increases in 2,3 DHBA and DA, and infarct volume in the striatum. Significant improvements in a battery of behavioural tests was also found in AM-36 treated rats. This study has demonstrated profound inhibition of ROS generation by a novel compound with antioxidant activity, administered post-ischemia in conscious rats.     

Contribution of the genetic status of oxidative metabolism to variability in the plasma concentrations of beta-adrenoceptor blocking agents

Summary The oxidative metabolism of bufuralol is under the same genetic control as that of debrisoquine and sparteine. 154 fasting volunteers received a 30 mg tablet of bufuralol and a blood sample was taken 3 h later. In poor metabolizers (8% of the sample) the plasma bufuralol concentrations were very high and the metabolite concentrations were low. The genetic oxidative status is a major source of interindividual variation in the plasma concentration of drugs that undergo oxidative metabolism.Presented at the 50^th Annual Meeting of the Swiss Society of Internal Medicine, Lausanne, May 1982, and at the 8^th European Workshop on Drug Metabolism, Liège, September 1982