Comparison of trimethadione and antipyrine as indicators of oxidative drug metabolizing capacity in man

Summary Ten healthy male volunteers were given trimethadione (TMO) 4 mg/kg and antipyrine (AP) 500 mg alone or concomitantly to determine whether the metabolism of the drugs was mediated by the same or closely related forms of cytochrome P-450.Whether administered alone or together the clearance (CL) and half-life (t_1/2) of TMO and AP were the same, and there was a good correlation between the CL and t_1/2 of TMO and AP (aloner=0.755 and 0.623, respectively; coadministeredr=0.771 and 0.503, respectively). Excretion of AP and its main metabolite and the clearance for production of AP metabolites after AP was administered alone were not significantly different when TMO and AP were taken together.When the two drugs were administered alone or coadministered, the correlation between the CL of TMO and the excretion of 3-hydroxymethyl-3-norantipyrine (NORA) was close (aloner=0.734, coadministeredr=0.749). The correlation between the CL of TMO and CLm of NORA when TMO and AP were given alone or concomitantly was 0.762 and 0.772, respectively.The findings suggest that TMO metabolism and the formation of NORA in healthy subjects are mediated by a closely related form(s) of the cytochrome P-450 system.     

Influence of silymarin on drug metabolizing enzymes in rat and man.

Male rats weighing 100-130 g were treated orally with a daily dose of 1 X 10 mg Legalon (active principle: silymarin)/100 g b.w. daily for 4 or 10 days. 4 and 10 days after the beginning of the pretreatment a significant increase of the activity of the mixed function oxidation system (Cytochrome P-450, aminopyrine demethylation, p-nitroanisole demethylation) was observed. No alteration of the body weight, the liver wet weight, the microsomal protein content, the cytochrome b5 content and the activities of glucose-6-phosphatase (G-6-Pase) and of a glucoronidase (4-methylumbelliferone) took place after the Legalon treatment. 4 h after the oral administration of 0.5 ml CCl4/kg b.w. the activity of the mixed function oxidation system and of the G-6-Pase was markedly decreased. This effect could not be prevented by the oral administration of 1 X 10 mg Legalon/100 g b.w. 6 h prior to CCl4 application. In human subjects the treatment with daily doses of 3 X 70 mg Legalon during 28 days had no influence on the metabolism of aminopyrine and phenylbutazone. From our results it is concluded that Legalon despite its effects in experimental animals has no influence on drug metabolism in man, when applied in therapeutic amounts.     

Liver size and indices of drug metabolism in epileptics.

1 The relationship between liver size and in vivo (antipyrine kinetics) and in vitro (cytochrome P-450) drug metabolism was investigated in twenty-one epileptics on long-term anticonvulsant therapy and in controls. 2 The epileptics exhibited significant enlargement of the liver and enhancement of drug metabolism compared to the controls. 3 Liver size correlated to antipyrine kinetics only in controls. Concentration of cytochrome P-450 in liver biopsy specimens correlated with liver size neither in controls nor in epileptics. 4 The total hepatic cytochrome P-450, estimated on the basis of liver weight and cytochrome P-450 concentration of biopsy samples, correlated linearly with antipyrine kinetics, except in patients with the most severely disturbed liver architecture. 5 Measurement of liver size is essential when comparing in vivo and in vitro drug metabolism, but the changes in liver histology are also of great importance.     

Relationship between lipid composition and drug metabolizing capacity of human liver

Summary The relationship between hepatic glycerolipids and microsomal drug-metabolizing enzymes was studied in liver biopsies from 41 subjects. The series included obese, diabetic, epileptic and chronic alcoholic patients, all of whom were hospitalized for suspected hepatic ailments (fatty liver, hepatitis or cirrhosis). Therapy with enzyme-inducing anticonvulsants was associated with high phospholipid and cytochrome P-450 and low triacylglycerol concentration in the liver. In patients with fatty liver or cirrhosis low phospholipid and cytochrome P-450 and high triacylglycerol concentrations were observed. There was a significant correlation (r (Pearsons's product moment correlation coefficient) =0.91) between the hepatic phospholipid and cytochrome P-450 concentration. The cytochrome P-450 concentration was inversely related (r=–0.74) to the triacylglycerol concentration. The positive correlation between hepatic phospholipids and drug-metabolizing enzymes could be interpreted as indicating that in human liver phospholipid and cytochrome P-450 synthesis share common regulators, or that phospholipids are necessary for the maximum rate of cytochrome P-450 synthesis.     

Liver size and indices of drug metabolism in alcoholics

Summary The role of liver size in drug metabolism was investigated in 34 chronic alcoholics and 28 controls by comparing antipyrine half-life with biopsy content and total amount of hepatic cytochrome P-450 (P-450) and liver weight. Liver size was significantly greater in alcoholics than in controls. Total P-450 was increased and antipyrine metabolism was enhanced in alcoholics with normal histology of the liver. In subjects with alcoholic hepatitis or cirrhosis, the antipyrine half-life was prolonged and P-450 was decreased. Alcoholics with fatty liver had a reduced P-450 content, but the total amount of P-450 and the antipyrine half-life were normal. The results demonstrate in alcoholics that an enlarged liver of normal histological appearance is associated with enhanced drug metabolism. In subjects with fatty liver the drug metabolizing capacity per unit weight of liver is often impaired, but the increase in liver size leads to undisturbed total oxidizing capacity and normal in vivo metabolism. In alcoholic hepatitis drug metabolism is impaired in spite of hepatomegaly. In cirrhosis the enlargement of the liver appears to compensate for the decreased P-450 content resulting in only slightly decreased total P-450, and the severely impaired in vivo drug metabolism may be due to derangement of blood flow.     

Hepatic drug metabolizing capacity of patients of cirrhosis before and after clinico-biochemical recovery

The present study was undertaken to determine whether, along with clinico-biochemical recovery there was associated restoration of hepatic drug metabolizing capacity in patients of cirrhosis after treatment of their cirrhosis, using serum antipyrine half life, the ideal index. Estimation of serum antipyrine half life before (26.34 +/- 2.4 hr) and after (18.83 +/- 2 hr) clinico-biochemical recovery showed significant (P less than 0.01) improvement in drug metabolizing capacity of liver. Biochemical parameters of liver function tests except serum total proteins and prothrombin time showed simultaneous improvement.     

The effects of diltiazem on hepatic drug metabolizing enzymes in man using antipyrine, trimethadione and debrisoquine as model substrates.

Six healthy male subjects were given single oral doses of antipyrine (7 mg kg-1), trimethadione (4 mg kg-1) and debrisoquine (10 mg) before and during diltiazem treatment (30 mg three times daily orally for 8 days). Antipyrine clearance decreased from 33.7 +/- 9.1 to 22.5 +/- 4.9 ml min-1 (P less than 0.05, mean +/- s.e. mean) after diltiazem treatment without any significant change in apparent volume of distribution (0.59 +/- 0.06 to 0.60 +/- 0.04 1 kg-1), resulting in an increase in antipyrine elimination half-life from 13.4 +/- 4.8 to 19.7 +/- 3.2 h (P less than 0.05). The formation clearance of antipyrine to 4-hydroxyantipyrine was decreased significantly from 10.8 +/- 2.7 to 6.6 +/- 2.7 ml min-1 (P less than 0.05), while that to 3-hydroxymethylantipyrine and norantipyrine was not altered by diltiazem. The metabolic ratio of debrisoquine (urinary excretion of debrisoquine/4-hydroxydebrisoquine) was increased significantly from 0.70 +/- 0.05 to 1.95 +/- 0.20 (P less than 0.05), while that of trimethadione (serum concentration of dimethadione/trimethadione) was not changed significantly (0.48 +/- 0.08 vs 0.41 +/- 0.06) after diltiazem treatment. Diltiazem selectively inhibits cytochrome P-450 isoenzymes.     

药物代谢酶的分子遗传学

综述近１０年来国内外有关药物代谢酶的分子遗传学进展,介绍药物代谢酶的基本概念并重点探讨了具有遗传多态性的两种氧化酶（细胞色素Ｐ４５０酶ＣＹＰ２Ｄ６,ＣＹＰ２Ｃ１９）和一种结合酶（Ｎ 乙酰化转移酶）的个体和种族差异。最后主要讨论了表型分型和基因分型在药物代谢酶研究中的一些应用。     

Effect of herbal teas on hepatic drug metabolizing enzymes in rats.

We have investigated the effect of herbal teas (peppermint, chamomile and dandelion) on the activity of hepatic phase I and phase II metabolizing enzymes using rat liver microsomes. Female Wistar rats were divided into six groups (n = 5 each). Three groups had free access to a tea solution (2%) while the control group had water. Two groups received either green tea extract (0.1%) or aqueous caffeine solution (0.0625%). After four weeks of pretreatment, different cytochrome P450 (CYP) isoforms and phase II enzyme activities were determined by incubation of liver microsomes or cytosol with appropriate substrates. Activity of CYP1A2 in the liver microsomes of rats receiving dandelion, peppermint or chamomile tea was significantly decreased (P < 0.05) to 15%, 24% and 39% of the control value, respectively. CYP1A2 activity was significantly increased by pretreatment with caffeine solution. No alterations were observed in the activities of CYP2D and CYP3A in any group of the pretreated rats. Activity of CYP2E in rats receiving dandelion or peppermint tea was significantly lower than in the control group, 48% and 60% of the control, respectively. There was a dramatic increase (244% of control) in the activity of phase II detoxifying enzyme UDP-glucuronosyl transferase in the dandelion tea-pretreated group. There was no change in the activity of glutathione-S-transferase. The results suggested that, like green and black teas, certain herbal teas can cause modulation of phase I and phase II drug metabolizing enzymes.     

Clinically relevant genetic variations in drug metabolizing enzymes

In the field of pharmacogenetics, we currently have a few markers to guide physicians as to the best course of therapy for patients. For the most part, these genetic variants are within a drug metabolizing enzyme that has a large effect on the degree or rate at which a drug is converted to its metabolites. For many drugs, response and toxicity are multi-genic traits and understanding relationships between a patient's genetic variation in drug metabolizing enzymes and the efficacy and/or toxicity of a medication offers the potential to optimize therapies. This review will focus on variants in drug metabolizing enzymes with predictable and relatively large impacts on drug efficacy and/or toxicity; some of these drug/gene variant pairs have impacted drug labels by the United States Food and Drug Administration. The challenges in identifying genetic markers and implementing clinical changes based on known markers will be discussed. In addition, the impact of next generation sequencing in identifying rare variants will be addressed.     

Kidney drug metabolizing activities in streptozotocin diabetic rats

• 1.1. Streptozotocin-induced diabetes produced significant changes on the drug metabolizing enzyme machinery of rat kidney microsomes.
• 2.2. It reduced the cytochrome P-450 content by 30%, this effect being reversed by insulin therapy.
• 3.3. Total androstenedione oxidative metabolism was increased 2.5-fold and insulin treatment partially antagonized this activation.
• 4.4. Total testosterone hydroxylase activities were not modified by diabetes nor by insulin but the formation of 2α OH testosterone and 6β OH testosterone were distinct in diabetes or insulin treated diabetic rats.
• 5.5. Only UDP-glucuronyltransferase activity for PNP was found in kidney microsomes. Diabetes determined a lower UDPGT substrate efficiency not reversed by insulin therapy.

     

Evaluation ofin vivo parameters of drug metabolizing enzyme activity in man after administration of clemastine,phenobarbital or placebo

Summary The 24 h urinary excretion of 6-hydroxycortisol and D-glucaric acid, the plasma half-lives and total clearances of aminopyrine, and serum gamma-glutamyl-transpeptidase activity have been measured in nineteen healthy male volunteers. The study was done double blind and was conducted as a test of induction of microsomal drug metabolizing enzymes during and after daily doses of 6 mg clemastine, 300 mg phenobarbital or a placebo. The urinary excretion of 6-hydroxycortisol and D-glucaric acid was significantly increased in the phenobarbital group, the standard for induction. No changes were observed after treatment with clemastine or placebo. Phenobarbital also reduced the half life of aminopyrine, but it was not affected by clemastine or placebo. Gamma-glutamyl-transpeptidase activity increased only in the phenobarbital group. The elimination constant k₂ of aminopyrine and the excretion of glucaric acid in the pre-medication period were correlated (p<0.05). The results indicate that the tests were of diagnostic value in determination of microsomal enzyme induction by phenobarbital. Failure to observe similar changes after treatment with clemastine imply failure of induction of this activity under the experimental conditions.     

Variability in drug metabolizing enzyme activity in HIV-infected patients

Aims  

To evaluate variability in cytochrome P450 (CYP) 1A2, CYP2D6, CYP3A, N-acetyltransferase 2 (NAT2), and xanthine oxidase (XO) activity in HIV-infected patients and compare this with data from uninfected, healthy volunteers.     

The human drug metabolizing cytochromes P450

The superfamily of heme-thiolate proteins known as the cytochromes P450 is responsible for the oxidative metabolism of the majority of drugs. Thus, the phenotypes of individuals with respect to their levels of catalytically active cytochromes P450 determines to a large part the substantial interindividual variation observed in the metabolic clearance of drugs. Over the past 10 years 15 different human cytochromes P450 involved in drug metabolism have been isolated and characterized to varying degrees. This brief review discusses the characterization of these cytochromes P450 and how this knowledge has been used by the pharmaceutical industry to aid in the development of new drugs.