Effect of Omeprazole on Diazepam Disposition in the Rat: in Vitro and in Vivo Studies

Purpose. The inhibitory effects of omeprazole on diazepam metabolism in vitro and in vivo are compared in the rat. Methods. 3-hydroxylation and N-demethylation of diazepam was investigated in the presence of a range of omeprazole concentrations (2-500µM) in hepatic microsomes and hepatocytes. Zero order infusions together with matched bolus doses of omeprazole were used to achieve a range of steady state plasma concentrations (10-50mg/ L) and to study the diazepam-omeprazole interaction in vivo. Results. The 3-hydroxlation pathway was more prone to inhibition (K_Is 108 ± 30 and 28 ± 11 µM in microsomes and hepatocytes, respectively) than the demethylation pathway (K_Is of 226 ± 76 and 59 ± 27 µM in microsomes and hepatocytes, respectively). In both in vitro systems, the mechanism of inhibition was competitive with Km/K_I ratios larger than 1 for the 3HDZ pathway and smaller than 1 for the NDZ pathway. There was an omeprazole concentration dependent decrease in diazepam clearance in vivo which could be modelled using a simple inhibition equation with a K_I of 57µM (19.8mg/L). In contrast there was no statistically significant change in the steady state volume of distribution for diazepam in the presence of omeprazole. Conclusions. The in vivo K_I for the omeprazole: diazepam inhibition interaction shows closer agreement with the K_I values obtained in hepatocytes than with those observed in microsomes.     

Liver microsomal cytochrome: P-450p and P-450h activity and blood corticosteroid levels of experimental animals exposed to physical factors

Laboratory of Experimental Therapy, Institute of Balneology, Ministry of Health of the Ukraine, Odessa. Department of Cell Physiology and Pathology, Institute of Clinical and Experimental Medicine, Siberian Branch, Academy of Medical Sciences, Novosibirsk. (Presented by Academician of the Academy of Medical Sciences V. Ya. Kaznacheev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 113, No. 5, pp. 498–500, May, 1992.     

人细胞色素p450IA1基因cDNA的克隆和鉴定

在用３－甲基胆蒽诱导培养人羊膜ＦＬ细胞２４ｈ后，抽提细胞总ＲＮＡ并直接合成ｃＤＮＡ第一链。利用人工合成的一对寡核苷酸引物，采用ＰＣＲ技术特异性地扩增Ｃｙｔ ｐ５０ＩＡ１ ｃＤＮＡ。３０个循环后琼脂糖凝胶电泳显示１．５Ｋｂ大小片段，长度与预计相符。Ｓｏｕｔｈｅｒｎ杂交结果证实此片段确为Ｃｙｔ ｐ４５０ＩＡ１ ｃＤＮＡ。将此片段克隆至质粒ｐＧＥＭ－３Ｚ并进行部份序列分析。结果显示克隆片段包含Ｃｙｔ ｐ     

地西泮、苯巴比妥、普萘洛尔、和西咪替丁对大鼠肝微粒体安定氧化代谢的影响

研究地西泮、苯巴比妥、普萘洛尔和西咪替丁对地西泮氧化代谢的影响及其药酶蛋白的初步分析，应用HPLC，SDS－聚丙烯酰胺凝胶电泳和薄层扫描测定地西泮及其代谢物，并对大鼠肝微粒体和酶蛋白进行分离和含量测定，结果表明地西泮，普萘洛尔和西咪替丁使肝微粒体中P－450含量明显降低，地西泮和普萘洛尔明显抑制地西泮C3－羟化活性，大剂量普萘洛尔尚能抑制地西泮N－脱甲基，苯巴比妥明显诱导P－450生成，增强地西泮N－脱甲基和C3－羟化酶活性及分子量为51，000和59，000的电泳蛋白带，而地西泮，普萘洛尔则呈抑制作用，并发现，地西泮N－脱甲基酶活性和分子量为59，000蛋白含量呈线性相关（P＜0．05），而C3－羟化酶活性则与51，000蛋白含量呈线性相关（P＜0．01），因此地西泮C3－羟化代谢可能与51，000的P－450酶蛋白有关，而N－脱甲基代谢则可能与59，000的P－450酶蛋白有关。     

Effects of Diazepam,Phenobarbital,Propranolol,and Cimetidine on Diazepam Oxidizing Isoenzymes in Rat Liver Microsomes

研究地西泮、苯巴比妥、普萘洛尔和西咪替丁对地西泮氧化代谢的影响及其药酶蛋白的初步分析，应用ＨＰＬＣ，ＳＤＳ聚丙烯酰胺凝胶电泳和薄层扫描测定地西泮及其代谢物，并对大鼠肝微粒体和酶蛋白进行分离和含量测定。结果表明地西泮、普萘洛尔和西咪替丁使肝微粒体中Ｐ４５０含量明显降低。地西泮和普萘洛尔明显抑制地西泮Ｃ３羟化活性，大剂量普萘洛尔尚能抑制地西泮Ｎ脱甲基。苯巴比妥明显诱导Ｐ４５０生成，增强地西泮Ｎ脱甲基和Ｃ３羟化酶活性及分子量为５１，０００和５９，０００的电泳蛋白带，而地西泮、普萘洛尔则呈抑制作用。并发现，地西泮Ｎ脱甲基酶活性和分子量为５９，０００蛋白含量呈线性相关（Ｐ＜０．０５），而Ｃ３羟化酶活性则与５１，０００蛋白含量呈线性相关（Ｐ＜０．０１）。因此地西泮Ｃ３羟化代谢可能与５１，０００的Ｐ４５０酶蛋白有关，而Ｎ脱甲基代谢则可能与５９，０００的Ｐ４５０酶蛋白有关。     

高效液相色谱法测定人肝细胞色素P450 3A4转基因细胞中氨氯地平

目的 :研究氨氯地平经人肝细胞色素 P4 5 0 3A4 (CYP3A4 )的代谢 ,建立反相高效液相色谱的测定人肝转基因细胞 CYP3A4酶 S9孵育液中氨氯地平浓度的方法。方法 :与人肝转基因细胞提取的 S9上清液孵育之后的样品 ,用 3倍量的甲醇沉淀后离心 ,取上清液用 0 .4 5μm微孔滤膜滤过后进样。采用 Hypersil C18柱 ,以乙腈 -磷酸盐缓冲液 (4 5∶ 5 5 ,v/ v,p H4 .5 )为流动相 ,普萘洛尔为内标 ,在 2 5 0 nm波长处测定。结果 :氨氯地平浓度在 0 .2～ 30 .0μg/ ml范围内线性关系良好 ,r=0 .9993,方法平均回收率为 (98.2± 2 .4 ) % (n=5 ) ,日内和日间相对标准偏差(RSD)均小于 10 % ,检测限为 2 0 ng/ ml,定量限为 0 .2 μg/ ml(回收率为 10 4 .0 % ,RSD为 11.4 % ,n=5 )。结论 :建立的反相高效液相色谱方法简便、准确 ,可用于研究氨氯地平在人肝 CYP3A4转基因细胞中的代谢。     

Ethanol-Induced Enhancement of Cocaine Bioactivation and Irreversible Protein Binding: Evidence Against a Role of Cytochrome P-450IIE1

Chronic ethanol consumption potentiates cocaine-induced liver injury in rodents. Since cocaine has to be bioactivated by a cytochrome P-450-dependent N-oxidative pathway to exert its hepatotoxic effects, we studied the role of the ethanol-inducible P-450IIE1 for cocaine metabolism. Male Sprague-Dawley rats were pretreated with either a liquid diet containing ethanol (30% of calories) for 4 weeks or injected with pyrazole (200 mg/kg/day, ip, for 3 days). Both agents induced microsomal p-nitrophenol hydroxylation which is a probe for the catalytic activity of P-450IIE1. However, only ethanol, but not pyrazole, increased both microsomal cocaine N-demethylase activity (by 47%) and the extent of irreversible binding of [3H]-cocaine to microsomal proteins (by 100%), which was taken as a quantitative endpoint for the formation of a reactive metabolite. Cocaine N-demethylation and irreversible protein binding of cocaine were not inhibited by P-450IIE1 isozyme-selective substrates, nor was the rate of cocaine metabolism and binding decreased by functionally active polyclonal anti-rat P-450IIE1 antibodies. Furthermore, pyrazole pretreatment sensitized cultured hepatocytes to the glutathione-dependent cytotoxic effects of nontoxic concentrations of cocaine. These results indicate that (a) cocaine is not a major substrate for the ethanol-inducible P-450IIE1, (b) the enhancing effects of ethanol on cocaine bioactivation may be due to induction of other P-450 isoforms, and (c) induction of P-450IIE1 may potentiate cocaine-induced hepatocellular toxicity in vitro independently of cocaine metabolism, e.g., by P-450IIE1-dependent oxidative stress.     

Effect of ketoconazole and terbinafine on the pharmacokinetics of caffeine in healthy volunteers

The effects of single oral doses of ketoconazole 400 mg and terbinafine 500 mg on the hepatic microsomal system have been investigated in 8 healthy male volunteers. Microsomal activity caffeine was assessed by following the metabolism of 3 mg/kg bodyweight i.v. administered 1 h after the drug. The inhibitory effect of terbinafine was more pronounced than that of ketoconazole: clearance was decreased from 1.34 ml.kg-1.min-1 in controls to 1.06 and 1.21 ml.kg-1.min-1, respectively, and the corresponding half-life was increased from 5.8 h in controls to 7.6 and 6.7 h, respectively. The apparent volume of distribution remained unchanged. The serum levels of the antimycotics were within the therapeutic range in each subject. Although all three substances are metabolised by microsomes, the kinetic parameters (Cmax, half-life, elimination constant) of the antimycotics were poorly if at all correlated with the elimination of caffeine.     

Identification of N2 as a metabolite of acetylhydrazine in the rat

 In the pathogenesis of isoniazid-induced hepatic injury, cytochrome P450-dependent metabolic activation of the metabolite, acetylhydrazine (AcHz), is the crucial step. Exhalation of [¹⁴C]-carbon dioxide has previously been used to quantify indirectly this pathway. In contrast, according to the current concept of AcHz bioactivation, molecular nitrogen is produced directly, but has not yet been identified. Here, we measured [¹⁵N]-nitrogen and ¹⁴CO₂ exhalation, after the administration of [¹⁵N₂]-[¹⁴C]-AcHz, in rats. Laser magnetic resonance (LMR) spectroscopy, a new sensitive and specific technique for the measurement of ¹⁵N and ¹⁴N in gas samples, was used. To demonstrate the involvement of cytochrome P450, rats were treated with phenobarbital (PB) or PB + cobalt(II) chloride (CoCl₂) (n=3 in each group). Time-dependent ¹⁵N₂ exhalation differed significantly between treatment groups (p<0.001). At 240 min, cumulative exhalation of ¹⁵N was 1.92±0.43% (mean±SE) of the dose in the control group, 2.53±0.23% in the PB group, and 1.00±0.15% in the PB+CoCl₂ group (p<0.05 compared to controls, p<0.01 compared to PB). Cumulative exhalation of ¹⁴CO₂ in 24 h ranged from 15.1 to 21.9%, with no significant difference between treatment groups. In conclusion, N₂ is a metabolite of AcHz. N₂ formation reflects the cytochrome P450-mediated activation of AcHz and can be used as an index of this pathway. Generally, LMR spectroscopy is valuable for monitoring any N₂-liberating process in vivo. Received: 14 March 1995/Accepted: 15 August 1995     

Formation of pyridinium species of haloperidol in human liver and brain

Recent interest in the neurotoxicity of haloperidol is based on its oxidation in rodents to the pyridinium derivative, HPP⁺, a structural analog of the neurotoxin, 1-methyl-4-phenylpyridinium (MPP⁺). Recently, we reported that HPP⁺ and a newly identified reduced pyridinium, RHPP⁺, were present in blood and urine of haloperidol-treated schizophrenics and that the concentrations of RHPP⁺ exceeded those of HPP⁺. In this study, we examined pathways for formation of RHPP⁺ in subcellular fractions of human liver (n=5) and brain (basal ganglia;n=5). The major pathway was reduction of HPP⁺ (20 µM) to RHPP⁺ in cytosol (0.17–0.39 and 0.03–0.07 µM RHPP⁺/g cytosolic protein per h in liver and brain, respectively). The reactions were inhibited significantly by menadione and in brain also by daunorubicin. The inhibition profile, cytosolic location and strict NADPH dependence suggest that the enzymes involved are ketone reductases. A second pathway was oxidation of reduced haloperidol (50 µM), a major metabolite of haloperidol in blood and brain, to RHPP⁺. In liver microsomes, 0.17–0.63 µmol RHPP⁺ was formed /g microsomal protein per h. A potent inhibitor of the pathway was ketoconazole (IC₅₀, 0.8 µM), which suggests that P-450 3A isozymes could be involved. In brain mitochondria but not microsomes, reduced haloperidol (120 µM) was oxidised to RHPP⁺ at a small but significant rate (0.005–0.020 µmol RHPP⁺/g mitochondrial protein per h) which was not attenuated by SKF 525A, quinidine, ketoconazole, or monoamine oxidase inhibitors. Further studies are warranted to establish the biological importance of these metabolites in vivo.