利福定和利福平对小鼠肝微粒体酶的影响比较

利福定和利福平具有相似的化学结构,为了比较二者对肝微粒体酶的影响,我们考察了它们对小鼠体内安替比林血浆水平、戊巴比妥钠睡眠时间和肝脏重量的影响,测定了肝微粒体蛋白和细胞色素P-450含量及两种酶活性的改变,用凝胶电泳法比较了微粒体多肽组份相对含量的变化。结果表明,利福平在这些方面均表现出显著的肝微粒体酶诱导作用,而利福定则否。这提示利福定可能在临床很少导致严重的药物相互作用发生。     

镉、铅、汞对苯巴比妥诱导肝微粒体药物代谢酶的影响

一次ip醋酸镉2.4mg/kg、醋酸铅100mg/kg或氯化汞 2.0 mg/kg均可抑制大鼠肝微粒体药物代谢酶。上述处理还可明显降低苯巴比妥对肝微粒’乙基吗啡N-脱甲基化酶、氨基比林N-脱甲基化酶、苯胺羟化酶和环己巴比妥羟化酶活力的诱导作用,降低苯巴比妥对细胞色素P450和细胞色素 b_5以及微粒体蛋白合成的诱导作用。结果提示镉、铅、汞可能通过降低微粒体酶的新生合成,抑制肝微粒体药物代谢酶。     

肉豆蔻木脂素的体外代谢初步研究

目的建立诱导的大鼠肝微粒体药物代谢酶体外转化模型,评价肉豆蔻木脂素的体外代谢情况,为规模化制备肉豆蔻木脂素的代谢产物提供方法.方法将肉豆蔻木脂素与苯巴比妥诱导的大鼠肝微粒体药物代谢酶共温孵,用高效液相色谱法检测肉豆蔻木脂素及其代谢产物.结果肉豆蔻木脂素在苯巴比妥诱导的大鼠肝微粒体药物代谢酶作用下,可以被代谢,并且发现了7个代谢产物.结论建立的肝微粒体药物代谢酶模型可靠有效,可用于肉豆蔻中肉豆蔻木脂素的体外代谢研究.     

反相高效液相色谱法研究家兔体内利福定对地塞米松代谢动力学的影响

已知利福平是一种肝微粒体酶诱导剂,我们在临床药学工作中发现,与利福平结构相似的另一强效抗菌药利福定与糖皮质激素联用时,可使后者的临床疗效显著降低。因此,推测利福定也可能有肝微粒体酶诱导作用,从而加速糖皮质激素的肝脏代谢,降低其治疗有效浓度。本实验从药物相互作用的角度,研究家兔体内利福定对地塞米松代谢动力学的影响。     

利福喷丁对小鼠肝微粒体药酶的诱导作用

连续给小鼠口服利福喷丁40mg/kg或20mg/kg14日后,用药鼠的戊巴比妥钠催眠时间显著缩短,利福喷丁血浓下降,鼠肝重增加,而SGPT活性无改变。鼠肝细胞中细胞色素P-450和细胞色素B_b含量明显增加,表明利福喷丁有诱导小鼠肝药酶的作用。     

去氢土莫酸在大鼠体外肝微粒体体系中的生物转化研究

目的:研究中药茯苓中主要化学成分之一的去氢土莫酸在大鼠肝微粒体中的生物转化.方法:用大鼠肝微粒体体外温孵法进行去氢土莫酸的生物转化,优化了温孵体系;高效液相色谱法检测和制备原形化合物去氢土莫酸及其生物转化产物,核磁共振波谱法和质谱法确定生物转化产物的结构.结果:去氢土莫酸在苯巴比妥诱导的大鼠肝微粒体药物代谢酶作用下,产生2个转化产物,分别为土莫酸和去氢茯苓酸.结论:去氢土莫酸可被苯巴比妥诱导的大鼠肝微粒体药物代谢酶转化为土莫酸和去氢茯苓酸.     

安坦对氯丙嗪在肝微粒体中代谢速率的影响

本文以氯丙嗪为底物研究了安坦对小鼠肝微粒体药酶的诱导作用,发现当每日腹腔注射安坦25mg～87.5mg/kg时,连续三天,可使氯丙嗪在含有肝微粒体的体外反应系统中的代谢速率明显加快。安坦这种诱导作用的强度略高于苯巴比妥。小鼠用安坦后肝微粒体中细胞色素P-450含量显著提高,这可能是安坦能加速氯丙嗪体外代谢速率的一个主要原因。     

利福喷丁对小鼠和大鼠肝微粒体酶的影响

<正> 利福喷丁(rifapentine,R773)是我国近年研制的新型长效利福霉素。国内外曾报道利福平在人体内能加速自身及其他若干种药物的代谢。作为同类衍生物,利福喷丁可能也具有肝微粒体酶诱导作用,本文报道了这方面的动物实验结果。 利福喷丁处理对小鼠肝重的影响 昆明小鼠?,体重18±SD2g,随机分为4组,每组10只,对照组每两天ig一次1％甲基纤维素溶液(R773的溶剂)0.2ml/只;其余3组分别igR773 10,20和40mg/kg,隔日一次,共给药15d。结果各组小鼠的相对肝脏重量(肝重占体重的百分比)依次为:对照组4.8±SD0.4％;R77310mg/kg组5.5±0.4％;     

米氮平在鼠肝微粒体中的体外代谢研究

目的:通过不同诱导剂预处理鼠肝,研究米氮平在肝微粒体中的代谢主要受何种酶影响,同时研究米氮平对介导其自身代谢的P450酶亚型是否有影响,为米氮平的临床合理应用提供科学依据。方法:将米氮平与不同诱导剂诱导的鼠肝微粒体进行体外孵育代谢,以乙腈中止反应,样品用25%氨水碱化后以环己烷提取。用RPHPLC测定剩余的米氮平含量,流动相为甲醇水(含10mmol·L-1NH4AC,5mmol·L-1SDS,pH3.5)6238(VV),检测波长为307nm。结果:本文测定方法回收率高,日内和日间精密度均良好,符合生物样本检测要求。苯巴比妥诱导的鼠肝微粒体对米氮平的代谢具有明显的催化作用,利福平也有一定的催化能力,米氮平诱导的鼠肝微粒体与对照组对米氮平的代谢无明显差异。结论:由苯巴比妥诱导的P450酶亚型(主要为细胞色素P4503A4)和利福平诱导的P450酶亚型(主要为细胞色素P4502C92C19,同时也对P4503A4有一定的诱导作用)在米氮平的体外代谢中起着重要作用;而米氮平诱导组对于米氮平代谢无明显影响,预示米氮平对介导其自身代谢的P450酶亚型无明显的诱导或抑制作用。     

杀虫畏对雄性大鼠肝微粒体酶的诱导及动力学性质的研究

杀虫畏对肝微粒体酶呈现明显诱导作用。对诱导生成的酶的动力学性质进行研究证明,诱导生成组和对照组的苯胺羟化酶,其米氏常数(km)和抑制常数(ki)极相近似;微粒体酶抑制剂SKF525-A对两组酶均呈现非竞争性抑制作用。因此,可以认为两组酶具有相同的动力学性质。     

Inductive effects of rifapentine on mice hepatic mixed function oxidase system

Rifapentine (R773, DL473) is a long-acting antituberculous drug used in China. In our experiments we have found some manifestations of induction of hepatic mixed function oxidase system in mice following pretreatment with rifapentine or phenobarbital. Both rifapentine and phenobarbital significantly increased the rate of antipyrine and pentobarbital metabolism in vivo. They also increased liver weight, the content of liver microsomal protein and cytochrome P-450, the activity of NADPH-cytochrome C reductase and NADPH oxidase. SDS-polyacylamide gel electrophoresis showed that the relative proportions of some polypeptide bands in mice microsomal fraction were significantly changed following rifapentine or phenobarbital pretreatment. The results indicate that rifapentine, like phenobarbital, is a potent inducer of hepatic mixed function oxidase system in mice and that it should be used carefully in clinical therapy, when combined with other drugs.     

Effects of pretreatment with the retinoid N-(4-hydroxyphenyl)-all-trans-retinamide and phenobarbital on the disposition and metabolism of N-(4-hydroxyphenyl)-all-trans-retinamide in mice

The effects of pretreatment with N-(4-hydroxyphenyl)-all-trans-retinamide (4-HPR) and phenobarbital (PB) on the distribution and metabolism of 4-HPR, and on the levels of hepatic cytochromes, were investigated in female BDF mice. Pretreatment of mice for 3 days with 10 mg/kg 4-HPR had no effect on the disposition of 4-HPR in the serum, liver, mammary gland, or urinary bladder. 4-HPR pretreatment also had no effect on the pharmacokinetics of any of its metabolites in the liver, or on the levels of hepatic cytochromes P450 or b5. By contrast, pretreatment of mice for 3 days with 80 mg/kg PB had a significant effect on the disposition of 4-HPR in all the tissues examined; the areas under the concentration-time curves for PB-pretreated mice were half those for vehicle-pretreated mice. PB pretreatment also significantly reduced the levels of four metabolites of 4-HPR in the liver and increased the levels of hepatic cytochromes P450 and b5. These data suggest that prior or concomitant administration of drugs that induce the mixed function oxidase system could result in changes in retinoid disposition and metabolism; such changes may alter retinoid chemopreventive activity.     

Induction potential of antifungals containing an imidazole or triazole moiety. Miconazole and ketoconazole, but not itraconazole are able to induce hepatic drug metabolizing enzymes of male rats at high doses

Male Wistar rats were dosed with miconazole, ketoconazole and itraconazole by gastric intubation once daily for up to 7 days. A dose- and time-dependent induction of the hepatic drug metabolizing enzyme system was observed for miconazole and ketoconazole, while itraconazole proved to be devoid of inductive properties even at the highest dose studied (160 mg/kg). No effect on drug metabolizing enzymes could be demonstrated for either drug at a dose level of 10 mg/kg, which is just above the antifungally active dose. At a dose of 40 mg/kg, miconazole, but not ketoconazole, significantly increased cytochrome P-450 content. At the highest dose of 160 mg/kg, both miconazole and ketoconazole increased the relative liver weight, the cytochrome P-450- and b5-content and NADPH-cyt c-reductase. Furthermore, miconazole, but not ketoconazole, increased specific microsomal aminopyrine and N,N-dimethylaniline N-demethylase activity, p-nitroanisole O-demethylase activity and UDP-glucuronyltransferase activity towards 4-nitrophenol while the specific aniline hydroxylase activity was unaffected. Ketoconazole at 160 mg/kg only induced O-demethylase activity and UDP-glucuronyltransferase activity, while it lowered the specific activities towards the other substrates. Miconazole was a relatively more potent inducer when compared to ketoconazole. Both drugs displayed biphasic effects on the mixed-function oxidase activities, which were lowered after acute administration (160 mg/kg, 1 hr before death) and were induced when determined after 23 hr had elapsed or after multiple dosage. Both drugs bound strongly to their respective induced cytochromes, giving rise to type II difference spectra, and inhibited the O-demethylase activity of the induced microsomes with an I50 of 5.2 microM for miconazole and 15.1 microM for ketoconazole. On the basis of a comparison of the enzymatic activities induced by both antimycotics with those induced by PB or 3-MC, it was concluded that miconazole behaved as a PB-type inducer, whereas ketoconazole did not belong to either category of inducers. A comparison of electrophoretograms of microsomes from different origins on SDS-PAGE revealed that miconazole increased the concentration of several proteins, whereas ketoconazole selectively induced a protein with Mr of 47,800. The protein pattern in the 50 kDa region of miconazole-induced microsomes resembled that of PB-microsomes qualitatively.     

Effect of cimetidine and phenobarbital on metabolite kinetics of omeprazole in rats

Omeprazole (OMP) is a proton pump inhibitor used as an oral treatment for acid-related gastrointestinal disorders. In the liver, it is primarily metabolized by cytochrome P-450 (CYP450) isoenzymes such as CYP2C19 and CYP3A4. 5-Hyroxyomeprazole (5-OHOMP) and omeprazole sulfone (OMP-SFN) are the two major metabolites of OMP in human. Cimetidine (CMT) inhibits the breakdown of drugs metabolized by CYP450 and reduces the clearance of coadministered drug resulted from both the CMT binding to CYP450 and the decreased hepatic blood flow due to CMT. Phenobarbital (PB) induces drug metabolism in laboratory animals and human. PB induction mainly involves mammalian CYP forms in gene families 2B and 3A. PB has been widely used as a prototype inducer for biochemical investigations of drug metabolism and the enzymes catalyzing this metabolism, as well as for genetic, pharmacological, and toxicological investigations. In order to investigate the influence of CMT and PB on the metabolite kinetics of OMP, we intravenously administered OMP (30 mg/kg) to rats intraperitoneally pretreated with normal saline (5 mL/kg), CMT (100 mg/kg) or PB (75 mg/kg) once a day for four days, and compared the pharmacokinetic parameters of OMP. The systemic clearance (CLt) of OMP was significantly (p<0.05) decreased in CMT-pretreated rats and significantly (p<0.05) increased in PB-pretreated rats. These results indicate that CMT inhibits the OMP metabolism due to both decreased hepatic blood flow and inhibited enzyme activity of CYP2C19 and 3A4 and that PB increases the OMP metabolism due to stimulation of the liver blood flow and/or bile flow, due not to induction of the enzyme activity of CYP3A4.     

Sustained induction of hepatic xenobiotic metabolising enzyme activities by phenobarbitone in C3H/He mice: relevance to nodule formation

Phenobarbitone (PB) was administered to male C3H/He mice at a dose of 85 mg/kg/day in a semisynthetic diet for up to 90 weeks. Throughout the treatment period a sustained induction of a number of parameters of hepatic Phase I and Phase II xenobiotic metabolism was observed. Histological examination revealed hypertrophy of the centrilobular cells of the liver lobule in PB treated mice and after 25 weeks small basophilic nodules were found in control and PB treated animals. In addition eosinophilic nodules, which were often large, developed in PB treated mice. Xenobiotic metabolising enzyme activities in large excised nodules after 70 or 90 weeks of PB treatment were either similar to or greater than those present in surrounding host tissue. Both phenobarbitone- and polycyclic hydrocarbon-type mixed function oxidase enzyme activities were induced in large nodules. In conclusion, PB produced a sustained induction of xenobiotic metabolising enzymes both in host tissue and in large eosinophilic nodules. The formation of these nodules in C3H/He mice was thus not associated with any failure of induction of hepatic xenobiotic metabolism.     

Acetaminophen hepatotoxicity: Is there a role for prostaglandin synthesis?

The hepatotoxicity of acetaminophen (APAP) overdose depends on metabolic activation to a toxic reactive metabolite via hepatic mixed function oxidase. In vitro studies have indicated that APAP may also be cooxidized by prostaglandin H synthetase. The present experiments were designed to assess the possible contribution of hepatic prostaglandin synthesis to APAP toxicity. Adult fed male mice were overdosed with 400 mg APAP/kg. Liver toxicity was estimated by measurement of serum transaminases. Hypertonic xylitol or sodium chloride (2250 mOsm/l), administered intragastrically to stimulate prostaglandin synthesis, increased APAP toxicity. By contrast, the cyclooxygenase inhibiting drugs aspirin (at 25 mg/kg) and indomethacin (at 10 mg/kg) protected against APAP-induced toxicity. APAP kinetics were not affected by hypertonic xylitol or indomethacin, nor were hepatic glutathione levels in overdosed mice. Imidazole, a nonspecific thromboxane synthetase inhibitor, also protected overdosed mice. This drug prolonged hexobarbital sleeping time and prevented the depletion of hepatic glutathione that followed APAP intoxication. Thus, the data support the conclusion that APAP-induced hepatotoxicity may be modulated not only by inhibition of cytochrome P450 mediated oxidation, but also by controlling hepatic cyclooxygenase activity.The Eugene Hecht Chair in Clinical Pharmacology     

Involvement of phenobarbital and SKF 525A in the hepatotoxicity of antifungal drugs itraconazole and fluconazole in rats

Itraconazole and fluconazole are potent wide spectrum antifungal drugs. Both of these drugs induce hepatotoxicity clinically. The mechanism underlying the hepatotoxicity is unknown. The purpose of this study was to investigate the role of phenobarbital (PB), an inducer of cytochrome P450 (CYP), and SKF 525A, an inhibitor of CYP, in the mechanism of hepatotoxicity induced by these two drugs in vivo. Rats were pretreated with PB (75 mg/kg for 4 days) prior to itraconazole or fluconazole dosing (20 and 200 mg/kg for 4 days). In the inhibition study, for 4 consecutive days, rats were pretreated with SKF 525A (50 mg/kg) or saline followed by itraconazole or fluconazole (20 and 200 mg/kg) Dose-dependent increases in plasma alanine aminotransferase (ALT), gamma-glutamyl transferase (gamma-GT), and alkaline phosphatase (ALP) activities and in liver weight were detected in rats receiving itraconazole treatment. Interestingly, pretreatment with PB prior to itraconazole reduced the ALT and gamma-GT activities and the liver weight of rats. No changes were observed in rats treated with fluconazole. Pretreatment with SKF 525A induced more severe hepatotoxicity for both itraconazole and fluconazole. CYP 3A activity was inhibited dose-dependently by itraconazole treatment. Itraconazole had no effects on the activity of CYP 1A and 2E. Fluconazole potently inhibited all three isoenzymes of CYP. PB plays a role in hepatoprotection to itraconazole-induced but not fluconazole-induced hepatotoxicity. SKF 525A enhanced the hepatotoxicity of both antifungal drugs in vivo. Therefore, it can be concluded that inhibition of CYP may play a key role in the mechanism of hepatotoxicity induced by itraconazole and fluconazole.     

Alteration of methylcholanthrene-mediated suppression of cutaneous delayed hypersensitivity by benzoflavone treatment of C57BL/6J mice

The potential role of the cytochromes P-450 in methylcholanthrene (MC)-mediated suppression of cutaneous delayed hypersensitivity (CDH) in C57BL/6J (B6) mice was evaluated indirectly by treating mice with agents known to induce or inhibit hepatic cytochromes P-450 prior to contact sensitization. Subsequent alterations in aryl hydrocarbon hydroxylase (AHH) activity and CDH, as measured by suppression of 2,4-dinitrofluorobenzene (DNFB)-induced ear swelling, were measured. MC administration resulted in a dose-dependent suppression of ear swelling and a concomitant dose-dependent induction of hepatic AHH activity. Treatment of B6 mice with phenobarbital (PB), 80 mg/kg daily X 3, a broad spectrum inducer of P-450, resulted in a 2.5-fold increase in benzo[a]pyrene (B[a]P) hydroxylase activity without affecting CDH. Animals treated with the same PB protocol prior to an ED20 dose of MC showed no difference in suppression of CDH compared to animals treated with MC alone. In contrast, successive treatment with the selective P1-450 inducer, 5,6-benzoflavone (beta NF), prior to and following an ED20 dose of MC significantly increased suppression of CDH (p less than 0.001) usually seen at this MC dose. Treatment with a known inhibitor of cytochrome P1-450 activity, 7,8-benzoflavone (alpha NF), did not prevent AHH induction when administered prior to and following MC (ED100) nor did it suppress CDH when administered alone. However, this alpha NF treatment completely prevented suppression of CDH usually seen at this MC dose. These data provide evidence suggesting that metabolic activation by cytochrome P1-450 is required for the expression of the immunosuppressive activity of MC.     

Enhanced disappearance of drugs from plasma following polybrominated biphenyls.

Polybrominated biphenyls (PBBs) are potent stimulators of hepatic drug metabolism. The purpose of this investigation was to determine the effect of dietary exposure to PBBs on the disappearance of drugs from plasma in mice. To estimate hepatic function, plasma and hepatic concentrations of indocyanine green (ICG) and ouabain were determined at various times following intravenous injection of these drugs (ICG, 40 mg/kg; ouabain, 0.1 mg/kg). Two-week dietary exposure to PBBs did not affect body weight but resulted in a dose-dependent increase in liver weight. Plasma concentrations of ICG were significantly lower than control values 10 and 15 min following injection of ICG in mice fed 100, 150, and 200 ppm of PBBs. In addition, 60-min plasma ouabain concentrations in 100- and 200-ppm PBBs-fed mice were significantly lower than control values. PBBs induced enhanced disappearance of ICG from plasma correlated to significantly higher hepatic ICG content. This effect was similar to that produced by phenobarbital pretreatment (75 mg/kg/day for 4 days) in mice. When compared to controls, mice fed PBBs had significantly higher hepatic ouabain content 10 min following glycoside injection but significantly lower amounts in liver 30 and 60 min following injection. PBBs feeding did not alter ouabain LD50 values. These results demonstrate that PBBs enhance drug elimination from plasma.