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Biomedical subjects

R Böcker

Publications and source records attributed to R Böcker.

At least 19 recordsLinked to original sources
PubMed1996

Stable expression of human cytochrome P450 3A4 in conjunction with human NADPH-cytochrome P450 oxidoreductase in V79 Chinese hamster cells.

V79 Chinese hamster cells were constructed for stable expression of human cytochrome P450 3A4 with and without coexpression of human NADPH-cytochrome P450 oxidoreductase. Expression of the cDNAs was shown by Northern and Western analyses. Activity was tested by 6 beta-hydroxylation of testosterone for cytochrome P450 3A4 and by cytochrome c reduction for NADPH-cytochrome P450 reductase. Five V79 cell lines were obtained expressing cytochrome P450 3A4, human NADPH-cytochrome P450 oxidoreductase, and both. Cytochrome P450 3A4 activity depended highly on cytochrome P450 reductase activity, with lowest activity when only the parental Chinese hamster cytochrome P450 reductase was present, 5- and 10-fold higher when coexpressed with the human NADPH-cytochrome P450 reductase. Correspondingly, cytotoxic and genotoxic potency of aflatoxin B1 was increased by orders of magnitudes when human cytochrome P450 3A4 was coexpressed with the human NADPH-cytochrome P450 reductase. The effect of NADPH-cytochrome P450 reductase coexpression on cytochrome P450 3A4 activity was also tested by nifedipine oxidation and midazolam hydroxylation. Nifedipine oxidation was increased about 10-fold, 1-hydroxylation of midazolam and 4-hydroxylation of midazolam were increased 15-fold.

Aflatoxin B1↗
PubMed1996

A convenient method to discriminate between cytochrome P450 enzymes and flavin-containing monooxygenases in human liver microsomes.

Liver microsomes are a frequently used probe to investigate the phase I metabolism of xenobiotics in vitro. Structures containing nucleophilic hetero-atoms are possible substrates for cytochrome P450 enzymes (P450) and flavin-containing monooxygenases (FMO). Both enzymes are located in the endoplasmatic reticulum of hepatocytes and both need oxygen and NADPH as cofactors. The common method to distinguish between the two enzyme systems is to use the thermal inactivation of FMO and to inhibit P450 completely with carbon monoxide, N-octylamine or N-benzylimidazole. In the literature no indication could be found that the heat inactivation of FMO does not affect any of the human P450 enzymes or that the overall P450 inhibitors inhibit the different human P450 enzymes sufficiently and do not affect the FMO. The effect of N-benzylimidazole and heat inactivation was tested on specific activities of seven P450 enzymes in human liver microsomes, 1A2, 2A6, 2C9, 2C19, 2D6, 3A4/5, and 2E1, using methoxyresorufin O-demethylation, coumarin 7-hydroxylation, (S)-warfarin 4-hydroxylation, (S)-(+)-mephenytoin 4-hydroxylation, dextrometorphan O-demethylation, oxidation of denitronifedipine, and chlorzoxazone 6-hydroxylation respectively. The sulfoxidation of methimazole (MMI) was used as a specific probe for the determination of FMO activity. Methimazole sulfoxidation was compared with the well known assay for FMO metabolism, the formation of N,N-dimethylaniline (DMA) N-oxide, to be confirmed as an exclusively FMO mediated reaction. The participation of P450 and FMO in the sulfoxidation of four sulfur containing peptides, ametryne; terbutryne, prometryne and methiocarb was investigated using human liver microsomes. All four reactions were demonstrated to be catalysed predominantly by cytochrome P450.

Aniline Compounds↗
PubMed1995

Highly sensitive and specific high-performance liquid chromatographic analysis of 7-hydroxywarfarin, a marker for human cytochrome P-4502C9 activity.

The formation of 7-hydroxywarfarin in incubations of (S)-warfarin with human liver microsomes reflects their cytochrome P-4502C9 activity. This paper describes a rapid high-performance liquid chromatographic method for the determination of 7-hydroxywarfarin with high sensitivity, selectivity, and a simple sample clean-up procedure. Separation was achieved with a C18 reversed-phase column and quantification by fluorometric detection. The method employs an internal standard resulting in good accuracy and precision. The limit of detection is 150 fmol for 7-hydroxywarfarin.

Anticoagulants↗
PubMed1994

Midazolam is metabolized by at least three different cytochrome P450 enzymes.

Distribution volumes and metabolism determine the pharmacokinetics of midazolam. Cytochrome P450 3A4 has been considered a significant enzyme in its metabolism. Using heterologously expressed cytochrome P450 enzymes, we have confirmed the additional involvement of cytochromes P450 3A3 and 3A5 in the hydroxylation of the midazolam. Whereas cytochrome P450 3A3 metabolized midazolam to the same extent as cytochrome P450 3A4, cytochrome P450 3A5 increased its metabolism by a factor of 2.7. The relationship of alpha- to 4-hydroxylation of midazolam was approximately 1.3 for cytochromes P450 3A3 and 3A4, and approximately 8.8 for 3A5. The primary location of cytochromes P450 3A3 and 3A4 is the liver in contrast with cytochrome P450 3A5, which occurs predominantly in the kidney. Therefore, further in vivo study is required to prove conclusively that enzymes in the kidney are involved in the metabolism of midazolam. Nitrendipine itself is metabolized by cytochrome P450 3A enzymes and this was shown to inhibit human liver microsomal hydroxylation of midazolam and preferentially alpha-hydroxylation by about 77%. 4-Hydroxylation was inhibited to 32% of control by nitrendipine. In contrast with inhibition of 4-hydroxylation, alpha-hydroxylation would appear to be competitively inhibited. These findings may be relevant to drug interactions in combined therapy.

Cytochrome P-450 CYP2E1↗
PubMed1991

Evaluation of the hepatotoxic potential of minocycline.

Minocycline (25 to 100 micrograms/g) dose dependently increased serum glutamic oxalacetic transaminase, urea, and bilirubin levels, and the hepatic triglyceride content in mice. In animals pretreated with phenobarbital to enhance minocycline metabolism, the effects on liver triglycerides were attenuated, while the changes in serum glutamic oxalacetic transaminase, urea, and bilirubin were enhanced. It is concluded that part of the toxic effects of minocycline may be produced by a metabolite of minocycline.

Animals↗
PubMed1990

Investigation into the combined effects of ethanol and cadmium on rat liver and kidneys.

To examine the combined hepatotoxic and nephrotoxic effects of cadmium and ethanol, rats maintained on an ethanol containing liquid diet (5% w/w) were given cadmium either acutely (3 x 1 mg/kg IP) or subacutely (about 14 mg/kg/day PO for 6 weeks). Parameters tested were cadmium, zinc and copper contents of blood and various organs, metallothionein (MT) contents, polysome profile of liver and kidneys, serum SDH and GPT levels and creatinine clearance. Ethanol reduced the hepatic MT contents without altering the polysome profile and the zinc and copper contents. Cadmium on the other hand raised the MT contents in liver and kidneys. This effect of cadmium predominated in the combined treatment. Morphological examination and functional tests (SDH, GPT, creatinine clearance) indicate that cadmium does not enhance the toxic effects of ethanol, and vice versa.

Alanine Transaminase↗
PubMed1989

True hermaphroditism with bilateral ovotestis: a case report.

A true hermaphrodite with a 46 XX/47 XXY karyotype, gynaecomastia, hypospadia and scrotal gonads was investigated. Gonadectomy performed at 14 years of age revealed bilateral ovotestes. The ovarian portion contained follicles of all developmental stages. The testicular portion was immature consisting of seminiferous cords with Sertoli cells at various steps of differentiation and few germ cells within massive aggregates of collagenous connective tissue. Leydig cells as well as germ cells remained in an embryonic stage of development. Sections of a differentiated Wolffian duct (ductuli efferentes, epididymis, vas deferens) as well as of a Müllerian duct (hypoplastic fallopian tube) were found adjacent to both gonads. Postoperative treatment consisted of androgen substitution therapy leading to progression of puberty.

Adolescent↗
PubMed1987

Polymorphism of human cytochrome P-450.

The cytochrome P-450 forms involved in debrisoquine 4-hydroxylation (P-450DB), phenacetin O-deethylation (P-450PA), S-mephenytoin 4-hydroxylation (P-450MP), and nifedipine 1,4-oxidation (P-450NF) have been purified to electrophoretic homogeneity from human liver microsomes. All of these reactions show in vivo polymorphism in humans. Evidence for the roles of the purified proteins in these processes comes from in vitro reconstitution and immunoinhibition studies. The rat orthologs of these enzymes are as follows--P-450DB: P-450UT-H; P-450PA: P-450ISF-G; P-450MP: P-450UT-I; P-450NF: P-450PCN-E. Only in the case of P-450UT-H is the primary rat ortholog the same cytochrome P-450 which catalyses the catalytic reaction under consideration. Reconstitution and immunochemical studies establish that the following reactions are catalysed by the individual P-450s--P-450DB: debrisoquine 4-hydroxylation, sparteine delta 5-oxidation, bufuralol 1'-hydroxylation, encainide O-demethylation, and propanolol 4-hydroxylation; P-450PA: phenacetin O-deethylation; P-450MP: S-mephenytoin 4-hydroxylation and tolbutamide methyl hydroxylation; P-450NF: oxidation of nifedipine and 16 other substituted dihydropyridines, estradiol 2- and 4-hydroxylation, aldrin epoxidation, benzphetamine N-demethylation and 6 beta-hydroxylation of testosterone, androstenedione and cortisol. A cDNA clone has been isolated that corresponds to rat P-450UT-H, as shown by a number of criteria. Studies with this probe establish that the sex and strain variation in debrisoquine 4-hydroxylase and related activities is related to differences in the levels of a 2.0 kb length mRNA present.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Serum level, half-life and apparent volume of distribution of doxycycline in geriatric patients.

The serum level, half-life and apparent volume of distribution of doxycycline were determined in geriatric patients. The serum level and apparent volume of distribution were higher than those reported for younger persons. The apparent volume of distribution was correlated with the serum iron and beta-globulin levels. The possible influence of binding of doxycycline to serum iron on its pharmacokinetics is discussed.

Age Factors↗
PubMed1986

Combined effects of high doses of rolitetracycline and testosterone on the liver of mice.

The effects of rolitetracycline (50 micrograms/g i.v.) and testosterone proprionate (4 X 1 micrograms/g s.c.) singly and combined on liver weight, serum GPT, SDH and bromsulfophthalein clearance have been measured in young mice. Pretreatment with testosterone tended to enhance the effects of rolitetracycline on the serum enzymes but was otherwise not effective.

Alanine Transaminase↗
PubMed1985

Quantitative assessment of the polysome profile of the livers of mice treated with tetracycline or doxycycline.

The influence of tetracycline and doxycycline (10-100 micrograms/g i.v.) on the aggregational state of ribosomes from mouse liver was tested. Both drugs caused a disaggregation of the ribosomes as evidenced by a rise of the monosomes + disomes/polysomes ratio. Tetracycline was much more potent than doxycycline, the minimum effective doses for tetracycline being 10 micrograms/g i.v. as compared to 100 micrograms/g for doxycycline. The results show that tetracycline but not doxycycline at therapeutic dose range may interfere with the protein synthesis of the liver.

Animals↗