PubMed Health⌕ Search

Biomedical subjects

M Stefek

Publications and source records attributed to M Stefek.

54 records · Page 3Linked to original sources
PubMed1990

The alpha carbon oxidation of some phencyclidine analogues by rat tissue and its pharmacological implications.

1. The metabolism of phencyclidine (PCP) and three congeners, differing in the structure of the amine moiety, by liver microsomes from phenobarbital-pretreated rats, was determined. 2. The metabolites generated by sequential oxidation of the two carbons alpha to the nitrogen were measured for PCP and its diethyl analogue (PCDE). 3. Alpha hydroxylation was a dominant metabolic pathway for PCDE, but less so for PCP. 4. Evaluation of affinities for the N-methyl-D-aspartate (NMDA) and sigma receptors in vitro showed that the product of alpha-hydroxylation of PCDE, phenylcyclohexylethylamine (PCE), was very potent. 5. Therefore, the in vivo actions of PCDE could include a significant contribution by PCE. 6. All congeners formed phenylcyclohexylamine (PCA), the product of a second alpha-hydroxylation, with PCDE and the pyrrolidine analogue generating the largest proportion.

Animals↗
PubMed1989

N-oxygenation of stobadine, a gamma-carboline antiarrhythmic and cardioprotective agent: the role of flavin-containing monooxygenase.

1. N-oxygenation of stobadine, a gamma-carboline antiarrhythmic and cardioprotective agent, was investigated in vitro using rat liver preparations. 2. Stobadine N-oxygenase activity was located mainly in the microsomal fraction and exhibited a requirement for oxygen and NADPH. The apparent Km and Vmax values for the process were, respectively, 350 microM and 3.48 nmol/mg protein per min. 3. N-oxygenation of stobadine in rat liver microsomes was not affected by SKF 525-A, carbon monoxide, metyrapone, cyanide or n-octylamine. When guinea-pig liver microsomes were used the reaction was activated by n-octylamine. 4. N-oxygenase activity was strongly inhibited by methimazole and depressed by phenobarbital and 3-methylcholantrene pretreatment. 5. The above results, along with the pH optimum of 8.4, strongly indicate the involvement of flavin-containing monooxygenase in the metabolic N-oxygenation of stobadine. 6. Species difference in liver microsomal N-oxygenase activity was evident, the order of activity being guinea-pig greater than rat greater than rabbit.

Animals↗
PubMed1989

Hydrogen peroxide-dependent liver microsomal N-demethylation and N-oxygenation of stobadine, a gamma-carboline antiarrhythmic and cardioprotective agent.

1. Hydrogen peroxide was capable of supporting the N-methylation and N-oxygenation of stobadine in rat liver microsomes. NADPH and O2 were not required. 2. The metabolic conversions promoted by H2O2 were completely abolished by preheating the microsomes for 5 min at 90 degrees C prior to assay, indicating the enzymic nature of the reaction. 3. The response to phenobarbital pretreatment and to inhibitors such as SKF 525-A, metyrapone and CO indicated participation of cytochrome P-450 in its oxidized form. 4. Microsomal cytochrome P-450 could not be replaced by haemoglobin, catalase, horseradish peroxidase or by its conversion to cytochrome P-420. 5. Comparative experiments on rabbits, guinea pigs and rats showed species differences in the extent of the peroxidatic metabolism of stobadine, the order of activity not being the same for C- and N-oxidation.

Animals↗
PubMed1987

Biotransformation of stobadine, a gamma-carboline antiarrhythmic and cardioprotective agent, in rat liver microsomes.

1. The metabolism of stobadine, a gamma-carboline antiarrhythmic and cardioprotective agent, was investigated in vitro using fortified rat liver microsomal preparations. 2. Two metabolic products, N-desmethyl stobadine and stobadine N-oxide were isolated and identified by means of t.l.c.,g.l.c. -mass spectrometry, n.m.r. spectrometry and comparison with synthetic reference compounds. 3. Stobadine N-oxide was resolved into two optically active stereoisomers which were produced enzymically in approximately equal quantities.

Animals↗
PubMed1986

Identification of in vitro rat metabolites of pentacaine, a carbanilate local anaesthetic, by gas chromatography/mass spectrometry.

Pentacaine, a novel carbanilate local anaesthetic, is extensively metabolized in rat liver microsomes. The major metabolic routes were found to be aromatic ring hydroxylation, hydroxylation of the aliphatic side-chain and carbamate bond hydrolysis. A deuterium-labelled substrate was used to aid the identification. The metabolites were characterized by gas chromatography/electron impact mass spectrometry as methyl and/or trifluoroacetyl derivatives. All identifications were confirmed by synthesis and direct comparison of chromatographic data and mass spectra.

Anesthetics, Local↗
PubMed1985

Determination of pentacaine, trans-2-(1-pyrrolidinyl)cyclohexyl-3-pentyloxycarbanilate hydrochloride, in biological samples by gas chromatography/mass spectrometry.

A quantitative and selective method has been developed for the determination of a novel local anaesthetic compound pentacaine, trans-2-(1-pyrrolidinyl)cyclohexyl-3-pentyloxycarbanilate hydrochloride, in biological samples. After ion pair extraction from 1 M HCl into 1,2-dichloroethane, pentacaine and a structurally related internal standard were derivatized to prevent thermal decomposition in the gas chromatograph. An on-column methylation technique with trimethylanilinium hydroxide was used. Determination was performed by gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring. Interferences by endogenous lipophilic constituents were avoided by including an n-hexane wash before the ion pair extraction. This wash step did not reduce the drug recoveries. The method gave linear results over a concentration range of 5-100 ng ml-1 with a coefficient of variation less than 10% at 5 ng pentacaine ml-1. Specimens of plasma, whole blood, urine as well as in vitro preparations such as hepatic microsomes were successfully analysed.

Anesthetics, Local↗
PubMed1985

Hepatic uptake and metabolism of pentacaine: a study with microsomes, hepatocytes and perfused livers of rats.

The uptake and metabolism of pentacaine, a novel carbanilate local anaesthetic agent, were studied using different rat-liver preparations. Pentacaine, added to a rat-liver microsomal suspension, elicited a type-I spectrum with Ks of 2.3 microM. The Km for total metabolism of pentacaine by rat-liver microsomes was 33.5 microM and in isolated hepatocytes 19.1 microM. Good agreement was obtained between the Vmax values for both in vitro systems and for perfused rat liver. In an isolated perfused rat liver the mean extraction ratio of pentacaine was 0.99 for a single pass, but it was significantly decreased by the presence of albumin and red blood cells. The uptake of pentacaine by isolated hepatocytes was rapid and independent of drug concn. over the range 0-200 microM. The high hepatic extraction of pentacaine is probably due mostly to passive diffusion and non-specific intracellular binding; metabolic elimination is secondary and much slower than uptake. The extensive first-pass removal of free pentacaine suggests that the systemic fraction of an oral dose in vivo is derived mainly from drug bound to blood components.

Anesthetics, Local↗
PubMed1983

Determination of ethimizol and two of its metabolites in serum by high-pressure liquid chromatography.

A liquid chromatographic assay has been developed for the determination of ethimizol and two of its metabolites in serum. The analysed compounds are preseparated from serum by a micro-column packed with an octadecylsilanized silica gel. Components of the micro-column eluate are analysed on a silica-gel-packed column by means of a high-performance liquid chromatograph fitted with a photometric detector. At 262 nm the detection limit of the injected amount of ethimizol is about 5 ng. The mass spectra of two ethimizol metabolites isolated from rat serum are presented. The suitability of the developed assay for pharmacokinetic studies of ethimizol is demonstrated.

Animals↗
PubMedDate not supplied

Formation of didesmethylethimizol (4-5-dicarbamoyl-1-ethylimidazole) in man.

The chemical structure of an ethimizol metabolite found earlier in human urine and saliva was established as 4,5-dicarbamoyl-1-ethylimidazole (didesmethylethimizol). The treatment of biological samples comprised a solid-phase extraction, high-performance thin-layer chromatographic separation and high-performance liquid chromatographic purification techniques. The identification of the metabolite was based on the comparison of a mass spectrum of the substance isolated from the biological fluid with the mass spectra of synthetised reference compounds.

Chemical Phenomena↗
PubMedDate not supplied

Urinary excretion of the 1,4-dihydropyridine calcium antagonist VULM 993 and its metabolites in the rat.

After oral dose of the 1,4-dihydropyridine calcium antagonist 14C-VULM 993 (50 mg/kg) a mean of 44.5% of the administered radioactivity was excreted via urine during the first 72 hours. Using an extractive fractionation procedure, the urinary metabolites were classified on the basis of their polarity and acidic/basic properties. Approx. 40% of total urine metabolites were found to be polar, non-extractable compounds--mostly glucuronide/sulphate conjucates. About one half of all urine metabolites were shown to possess overall acidic nature. G.l.c.-m.s. and t.l.c.-m.s. analyses of urine extracts revealed the presence of only minor amounts of the parent drug toghether with six metabolites identified as products of 1,4-dioxaspiro[4,4]nonane moiety cleavage, hydrolysis of one or both ester side functions also combined with 1,4-dihydropiridine nucleus dehydrogenation. Technique of thin-layer radio-chromatography was used to quantify urinary excretion rates of the parent drug and the established metabolites.

Animals↗
PubMedDate not supplied

Pyridoindole antioxidant stobadine protected bovine serum albumin against the hydroxyl radical mediated cross-linking in vitro.

On exposure to free radicals generated by the Fenton reaction system of Fe(2+)/EDTA/H(2)O(2)/ascorbate, bovine serum albumin (BSA), used as a model of water-soluble protein, was losing its water solubility depending on the concentration of the chelated iron. The precipitate was found irreversibly insoluble even in concentrated urea. In the soluble fraction, SDS-PAGE analysis proved the presence of dimers and trimers of BSA, accompanied by enhanced bityrosine fluorescence. The pyridoindole antioxidant stobadine inhibited the process of albumin insolubilization in a concentration-dependent manner, the protective effect being more efficient than that of 2-keto-4-methiolbutyric acid (KMBA). Stobadine was, however, less effective than trolox. The inhibitory effect of the antioxidants, expressed as IC(50), correlated well with the reciprocal values of corresponding second order rate constants for scavenging OHz.rad; radicals. The results indicated that the insolubilization of BSA induced by the Fenton system of Fe(2+)/EDTA/H(2)O(2)/ascorbate was caused by OHz.rad; radical mediated cross-linking of the albumin. The model system proved to be suitable for convenient testing of OHz.rad; radical scavenging ability of new antioxidants in a non-lipid environment.

Animals↗
PubMedDate not supplied

Pharmacological prevention of diabetic cataract.

Cataract--opacification of the lens--is closely related to diabetes as one of its major late complications. This review deals with three molecular mechanisms that may be involved in the development of diabetic cataract: nonenzymatic glycation of eye lens proteins, oxidative stress, and activated polyol pathway in glucose disposition. Implications resulting from these mechanisms for possible pharmacological interventions to prevent diabetic cataract are discussed. The article reviews research on potential anticataract agents, including glycation inhibitors, antioxidants, and aldose reductase inhibitors. Information on possible benefits of putative anticataract agents comes from a variety of approaches, ranging from laboratory experiments, both in vitro and in vivo, to epidemiological studies in patients.

Antioxidants↗
PubMedDate not supplied

Disposition of ethimizol, a xanthine-related nootropic drug, in perfused rat liver and isolated hepatocytes.

Ethimizol, 4,5-di(methylcarbamoyl)-1-ethyl-imidazole, was metabolized into at least six metabolites in an isolated perfused rat liver preparation. Based on TLC and mass spectrometry, 4-carbamoyl-5-methylcarbamoyl-1-ethyl-imidazole and 4,5-di(methylcarbamoyl)-imidazole were identified as the primary metabolites of ethimizol. These undergo further biotransformation: both can form 4(5)-carbamoyl-5(4)-methylcarbamoyl-imidazole, and, moreover, the former can be hydroxylated. Besides the identified metabolites, two polar ones of unknown structure were detected. Dose-dependent elimination of ethimizol was observed when the drug was added to the liver perfusion recirculating medium in initial reservoir concentrations of 39, 48, 85, 165, and 240 microM. The observed nonlinearity appeared to be a result of a competitive product inhibition. Similar to the parent drug, ethimizol primary metabolites were formed and eliminated in a dose-dependent manner. The uptake of ethimizol by isolated hepatocytes was extremely rapid, independent of drug concentration, over the range 0 to 250 microM, unaffected by inhibitors and independent of temperature.

Animals↗
PubMedDate not supplied

The effect of enzyme induction and inhibition on the disposition of the xanthine-related nootropic drug ethimizol in perfused liver and hepatocytes of rats.

The once-through perfused (18 ml/min) rat liver preparations from vehicle-, phenobarbital (PB)-, and 3-methylcholanthrene (3-MC)-treated rats were used for the study of 14C-ethimizol [4,5-di(methylcarbamoyl)-1-ethyl-imidazole] elimination after input concentrations of 5, 25, 50, and 100 microM. The steady state hepatic extraction ratios decreased with increasing ethimizol inputs and were (mean +/- SD): for vehicle-treated rats, 0.361 +/- 0.038, 0.193 +/- 0.018, 0.141 +/- 0.010, and 0.100 +/- 0.011; for PB-treated rats, 0.578 +/- 0.093, 0.393 +/- 0.039, 0.302 +/- 0.028, and 0.236 +/- 0.032; and for 3-MC-treated rats, 0.913 +/- 0.057, 0.783 +/- 0.130, 0.619 +/- 0.097, and 0.447 +/- 0.053, for the respective concentrations. In recirculating experiments both PB and 3-MC increased ethimizol elimination, but the effect of the latter was considerably greater. 3-MC was also more effective than PB in enhancing the rate of formation and subsequent biotransformation of the primarily formed ethimizol metabolites, 4-carbamoyl-1-ethyl-5-methylcarbamoyl-imidazole and 4,5-di(methylcarbamoyl)-imidazole. Elimination of ethimizol was inhibited in suspension of rat hepatocytes by SKF 525-A at concentrations of 10 and 100 microM by 63% and 60%, respectively, and by alpha-naphthoflavone, at the same concentrations, by 71% and 85%, respectively. Their simultaneous addition almost completely inhibited ethimizol biotransformation. An increase of the ethimizol elimination rate in single-pass rat liver perfusion by 55% was observed in preparations from rats treated by ethimizol in their drinking water, whereas the liver/body weight ratio, microsomal protein, and cytochrome P-450 content remained unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗