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Biomedical subjects

V Fischer

Publications and source records attributed to V Fischer.

At least 19 recordsLinked to original sources
PubMed2001

Methanol solvent may cause increased apparent metabolic instability in in vitro assays.

Methanol was widely used as a substrate-delivering solvent in in vitro metabolic stability screenings. Its interaction with enzyme activities, particularly those of cytochrome P450s, has been investigated extensively in the past. Little was known about the interaction of methanol, whether direct or indirect, with substrates. The present study provided data for the first time to show that use of methanol may result in the formation of artifacts, which could mislead the metabolic stability information. The disappearance of LAQ094, metaraminol, and (-)-isoproterenol following 1-h incubation with human liver microsomes was 73, 85, and 66%, respectively, in the presence of 1% methanol, but was only 3, 15, and 24%, respectively, in the absence of organic solvent. The dramatically increased instability in the presence of methanol of these three compounds, each with 1,2-diamino or 1,2-amino hydroxy functional groups, was due to the formation of [M + 12] products resulting from condensation reaction of the substrates with formaldehyde. Formaldehyde was formed from methanol by human liver microsomal enzymes with an apparent K(m) of 35 mM and a V(max) of 7.9 nmol/min/mg of protein. The concentration of formaldehyde reached as high as 600 microM following a 60-min incubation. The [M + 12] products were characterized as five-membered heterocycles by liquid chromatography and tandem mass spectrometry analysis. Inclusion of 10 mM glutathione prevented the formation of such artifacts and is therefore suggested for future in vitro screenings. Our study also documented the novel finding of enzyme-dependent conversion of NADPH to nicotinamide in microsomal incubations.

Cytochrome P-450 Enzyme System↗
PubMed2001

In vitro metabolism of tegaserod in human liver and intestine: assessment of drug interactions.

Tegaserod is a selective 5-HT(4) receptor partial agonist with promotile activity in the gastrointestinal tract. This study was designed to describe the metabolic pathways of tegaserod in the human liver and small intestine in vitro, to identify the enzymes involved in tegaserod metabolism, and to investigate the effect of tegaserod on CYP-catalyzed reactions involving other compounds. Tegaserod was metabolized in human liver microsomes to O-desmethyl tegaserod at a low rate. This metabolite was also formed by cDNA expressed CYP2D6, and the reaction in human liver microsomes was inhibited by quinidine. In human liver slices, direct N-glucuronidation of tegaserod at the guanidine nitrogens (M43.2, M43.8, and M45.3) was found, with M43.8 being the major metabolite. Human small intestine slices also metabolized tegaserod to the N-glucuronides, suggesting a contribution of the small intestine to the presystemic metabolism. 5-Methoxyindole-3-carboxylic acid (M29.0), the main metabolite in human plasma, was generated in vitro by a sequence of reactions starting with nonenzymatic acid-catalyzed hydrolysis, followed by enzymatic oxidation and conjugation with glucuronic acid. Tegaserod inhibited CYP2C8, CYP2C9, CYP2C19, CYP2E1, and CYP3A only to a small extent with IC(50) values >30 microM. Tegaserod more effectively inhibited CYP1A2 and CYP2D6 with K(i) values of 0.84 and 0.85 microM, respectively. However, these K(i) values are approximately 140-fold greater than the maximal tegaserod plasma concentrations following the clinically relevant 6-mg oral dose given to healthy volunteers. M29.0, the main circulating metabolite, did not demonstrate any inhibitory potential toward cytochrome P450 enzymes in vitro. Therefore, clinically relevant metabolic drug interactions with tegaserod seem unlikely.

Biotransformation↗
PubMed2000

Time-dependent transition probabilities and the assessment of seasonal effects on within-day variations in chewing behaviour of housed sheep.

State transitions in the chewing behaviour of six half-breed (Île de FrancexTexel) yearling female sheep (Ovis aries L.) were studied by using jaw movements recorded continuously over 5 days at the end of a number of experimental periods from 21 September 1992 to 4 April 1993. The sheep were housed in individual pens. Each of them received the same diet, that is, 250 g/day of concentrate mix (15.5% crude protein (CP), 36.5% neutral detergent fibre (NDF)) fed at 0900 h and natural grass hay (6.7% CP, 69.1% NDF) fed ad libitum at 0915 and 1600 h. Mineral salt blocks and water were continuously available. The main objective was to assess seasonal effects on within-day variations in the chewing behaviour of sheep, at small to large time scales within a day. We therefore focused on two experimental periods characterised by contrasting conditions of daylength and temperature (i.e., 'Period 1': 610 min daylight, mean temperature of 10.9 degrees C, and 'Period 4': 550 min daylight, mean temperature of 7.2 degrees C). In particular, differences between periods in the nycterohemeral pattern of chewing behaviour and the quality of forecasts of chewing states were tested. We submitted our data to a new method of analysis that we developed: the method of time-dependent transition probabilities, and compared the results to those obtained using other methods that were available in the literature.Overall, the sheep spent more time eating in Period 1 than in Period 4. Specifically, a secondary peak in eating activity, which was observed in the early afternoon in Period 1, was absent in Period 4. The nycterohemeral pattern of eating activity showed significant differences between periods, at the main rhythmic component of 24 h and at short components around 2 h. Such differences were not observed for ruminating and idling activities. The quality of forecasts of chewing states decreased from Periods 1 to 4, in terms of accuracy (based on R(2)) and lead of reliable forecasts (i.e., &z.sfnc;forecast-observation&z.sfnc;<0.1). The most (least) accurate forecasts were obtained for the ruminating (eating) state in both periods. We have attributed the differences that we found between periods to daylength instead of temperature because the sheep were mostly within the thermoneutral zone in our study. By comparison, using mean hourly times of eating activity, significant differences between periods were detected for the 24-h rhythmic component and the 4-h component, instead of the 2-h component, probably because of aliasing (i.e., when the sampling time interval used is longer than suited; the minute was found to be a suitable interval length in the calculation of time-dependent transition probabilities). Using the age-dependent model of Rook and Penning, minor differences between periods were detected. On that basis, the method of time-dependent transition probabilities may be brought forward as a complement of value to existing methods of behavioural data analysis.

Journal Article↗
PubMed2000

[Oxygen transport values in patients with surgery performed under extracorporeal blood circulation].

The aim of the work was to study the O2-transport changes to tissues in cardio-surgical patients suffering from CAD and operated during extra-corporeal blood circulation (ECC). The changes of selected haematologic variables, 2,3-diphosphoglycerate (2,3-DPG) and ATP concentration, acid-base balance parameters with p50 calculation were measured in the venous blood samples taken before the operation, during the operation and on the 1st, 2nd, 3d, 5th, 7th and 10th day after the operation. From the obtained results follows, that extreme haemodilution causes significant decrease of the haematocrit value (Htc) by 35%, the value of haemoglobin (Hb) by 37% and the count of erythrocytes (Er) by 37% from the initial values. The count of reticulocytes (Ret) was increased by 52%. In the days after operation the increase in Htc values, the values of Hb and count of erythrocytes was observed, whereby the initial values were not reach even on the 10th day after the operation. The increase of the reticulocytes count by 33% prevailed to the 10th day after the operation in comparison with the initial values. 2,3-DPG concentration was increased between 3d and 10th day after the operation by 30% and ATP concentration between 5th and 10th day was increased by 23% from the initial values. Hb-O2 saturation (SpO2) and pO2 were increased already during the operation, the increase prevailed until the 7th day by 27%, pO2 until the 3d day by 39% from the initial values. Calculated values p50 did not change in the course of this study--they fluctuated in range +/- 0.04 kPa from the initial value 3.55 kPa. Supposing multifactorial character of Hb oxygenation and deoxygenation process it is possible to conclude, that the determined changes of observed parameters did not significantly influence O2-transport to tissues during ECC. (Fig. 3, Ref. 12.)

2,3-Diphosphoglycerate↗
PubMed1999

Distribution of clozapine and desmethylclozapine between blood and brain in rats.

Desmethylclozapine is the major metabolite of clozapine in serum. Although the metabolite is pharmacologically active in vitro, the occurrence of desmethylclozapine in brain under steady-state conditions and its role for clinical actions of clozapine are unclear. In this study 20 male Sprague-Dawley rats received five oral doses of clozapine 20 mg/kg at 1.5-h intervals. At 0.5, 1, 2 and 5 h after the last administration, at a time four animals were killed for analysis of clozapine and desmethylclozapine concentrations in serum and brain. The treatment yielded steady-state serum concentrations of clozapine that are considered as therapeutically effective in man. Desmethylclozapine concentrations exceeded those of clozapine at 2-5 h after drug application. In brain, drug concentrations were 15.8-fold higher for clozapine than in serum, but only 2.7-fold higher for desmethylclozapine. The brain clozapine concentrations exceeded those of desmethylclozapine by about 3 times. These data indicate that desmethylclozapine is unlikely to play a role for CNS-mediated effects.

Animals↗
PubMed1999

Chronic oral haloperidol and clozapine in rats: A behavioral evaluation.

The present study evaluated chronic oral treatment of rats with haloperidol or clozapine. Drugs were given in the drinking water for a 23-day period. Rat behavior was analyzed once a week in an open field. Rats ingested either 1.7 mg/kg haloperidol or 40 mg/kg clozapine daily. Blood serum analysis revealed concentrations of 6 ng/ml for haloperidol and 22 ng/ml for clozapine at the end of the treatment. Haloperidol decreased overall activity from the onset of treatment. Clozapine showed similar effects only on the last test day. Control animals showed a slight habituation in exploration-related parameters. In conclusion, these results indicate that oral drug administration through the drinking water is a suitable mode of noninvasive chronic treatment that led to sufficiently high drug levels to induce specific pharmacological effects in rats.

Administration, Oral↗
PubMed1999

The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor fluvastatin: effect on human cytochrome P-450 and implications for metabolic drug interactions.

Fluvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, was metabolized by human liver microsomes to 5-hydroxy-, 6-hydroxy-, and N-deisopropyl-fluvastatin. Total metabolite formation was biphasic with apparent Km values of 0.2 to 0.7 and 7.9 to 50 microM and intrinsic metabolic clearance rates of 1.4 to 4 and 0.3 to 1.5 ml/h/mg microsomal protein for the high and low Km components, respectively. Several enzymes, but mainly CYP2C9, catalyzed fluvastatin metabolism. Only CYP2C9 inhibitors such as sulfaphenazole inhibited the formation of both 6-hydroxy- and N-deisopropyl-fluvastatin. 5-Hydroxy-fluvastatin formation was reduced by compounds that are inhibitors of CYP2C9, CYP3A, or CYP2C8. Fluvastatin in turn inhibited CYP2C9-catalyzed tolbutamide and diclofenac hydroxylation with Ki values of 0.3 and 0.5 microM, respectively. For CYP2C8-catalyzed 6alpha-hydroxy-paclitaxel formation the IC50 was 20 microM and for CYP1A2, CYP2C19, and CYP3A catalyzed reactions, no IC50 could be determined up to 100 microM fluvastatin. All three fluvastatin metabolites were also formed by recombinant CYP2C9, whereas CYP1A1, CYP2C8, CYP2D6, and CYP3A4 produced only 5-hydroxy-fluvastatin. Km values were approximately 1, 2.8, and 7.1 microM for CYP2C9, CYP2C8, and CYP3A, respectively. No difference in fluvastatin metabolism was found between the CYP2C9R144 and CYP2C9C144 alleles, suggesting the absence of polymorphic fluvastatin metabolism by these alleles. CYP1A2, CYP2A6, CYP2B6, CYP2C19, CYP2E1, and CYP3A5 did not produce detectable amounts of any metabolite. This data indicates that several human cytochrome P-450 enzymes metabolize fluvastatin with CYP2C9 contributing 50-80%. Any coadministered drug would therefore only partially reduce the metabolic clearance of fluvastatin; therefore, the likelihood for serious metabolic drug interactions is expected to be minimal.

Biotransformation↗
PubMed1999

Multiple cytochrome P-450s involved in the metabolism of terbinafine suggest a limited potential for drug-drug interactions.

Biotransformation pathways and the potential for drug-drug interactions of the orally active antifungal terbinafine were characterized using human liver microsomes and recombinant human cytochrome P-450s (CYPs). The terbinafine metabolites represented four major pathways: 1) N-demethylation, 2) deamination, 3) alkyl side chain oxidation, and 4) dihydrodiol formation. Michaelis-Menten kinetics for the pathways revealed mean K(m) values ranging from 4.4 to 27.8 microM, and V(max) values of 9.8 to 82 nmol/h/mg protein. At least seven CYP enzymes are involved in terbinafine metabolism. Recombinant human CYPs predict that CYP2C9, CYP1A2, and CYP3A4 are the most important for total metabolism. N-demethylation is primarily mediated by CYP2C9, CYP2C8, and CYP1A2; dihydrodiol formation by CYP2C9 and CYP1A2; deamination by CYP3A4; and side chain oxidation equally by CYP1A2, CYP2C8, CYP2C9, and CYP2C19. Additionally, characteristic CYP substrates inhibited pathways of terbinafine metabolite formation, confirming the involvement of multiple enzymes. The deamination pathway was mainly inhibited by CYP3A inhibitors, including troleandomycin and azole antifungals. Dihydrodiol formation was inhibited by the CYP1A2 inhibitor furafylline. Terbinafine had little or no effect on the metabolism of many characteristic CYP substrates. Terbinafine, however, is a competitive inhibitor of the CYP2D6 reaction, dextromethorphan O-demethylation (K(i) = 0.03 microM). In summary, terbinafine is metabolized by at least seven CYPs. The potential for terbinafine interaction with other drugs is predicted to be insignificant with the exception that it may inhibit the metabolism of CYP2D6 substrates. Clinical trials are needed to assess the relevance of these findings.

Antifungal Agents↗
PubMed1998

Chronical haloperidol and clozapine treatment in rats: differential RNA display analysis, behavioral studies and serum level determination.

1. Adult, female rats were treated orally for 23 days with 1.6 mg/kg haloperidol or 36 mg/kg clozapine per day, to study chronic effects of the two neuroleptics. 2. At five time points during the neuroleptic treatment, animal behavior was recorded in an open field and locomotive activity was analysed. At the end of the experiment, rats were decapitated, blood samples were collected and serum concentrations of haloperidol and clozapine were determined by a radioreceptor or HPLC assay, respectively. RNA was isolated from each brain, without cerebellum, and subjected to differential RNA display. 3. Mean serum concentrations were 8 ng/ml for haloperidol and 21 ng/ml for clozapine. Analysis of open field behavior showed that haloperidol and clozapine decreased the total distance moved and the velocity as measures of the overall activity, whereas the number of rearings and the number of entries into the center, reflecting risk assessment behavior, were differentially affected. Three neuroleptic-regulated gene fragment bands were identified in differential RNA display experiments. Two gene fragments of 281 bp and 266 bp were sequenced. 4. We conclude that our study design that used behavioral, pharmacokinetic and molecular analysis increase the likelihood of finding relevant molecular events underlying the pharmacotherapeutic effects of neuroleptics in animal models.

Animals↗
PubMed1998

Etiology and risk factors of 180 cases of native valve endocarditis. Report from a 5-year national prospective survey in Slovak Republic.

Risk factors, etiology, and outcome of 180 cases of infective endocarditis (IE) in the Slovak Republic for 5 years were prospectively studied in a national survey. According to the Duke Endocarditis Service Criteria (1994), 169 cases were considered definitive and 21 possible/probable. The aortic valve was infected in 46.7%, mitral in 47.2%, and tricuspidal/pulmonary in 6.1% of cases. The majority of endocarditis cases was caused by Staphylococcus aureus and coagulase-negative staphylococci (CNS) (33.3%); only 12.2% were due to viridans streptococci; 11.7% were due to Enterococcus faecalis; 6.1% due to Haemophilus spp.; 10.1% due to other organisms; and 26.7% were culture negative. Single positive cultures of CNS were not considered clinically significant. More than 25% of 180 patients were older than 60 years. Rheumatic fever was a risk factor in 35.5%, dental surgery in 20.5%, prior cardiosurgery in 7.8%, and neoplasia in 6.7%. All patients were treated with antimicrobials (average length of therapy was 29.5 days) and 33.3% of patients also had surgery (valvular prosthesis replacement). Forty (22.2%) died, and 140 (77.8%) survived at day 60 after the diagnosis of endocarditis was made. All 40 deaths were attributable to infection. Univariate analysis comparing deaths and survivors did not show significant differences in most of the recorded risk factors between both groups, except age > 60 (40.0% versus 21.4%, p < 0.05), staphylococcal etiology (55.0% versus 27.1%, p < 0.04), and antibiotic therapy < 21 days (without surgery) (65.0% versus 3.6%, p < 0.01). These risk factors were significantly more frequently associated with deaths. Viridans streptococcal IE and surgical therapy in addition to antibiotics were associated with lower mortality in comparison to staphylococcal endocarditis (p < 0.045) or to cases treated with antibiotics only (p < 0.05). In comparison to other nationally based surveys in Europe (Greece, Croatia, France), the percentage of culture-negative endocarditis and spectrum of pathogens differed significantly.

Adult↗
PubMed1998

[In Process Citation]

On the basis of long-term personal experiences and critical evaluation of the present literatury sources authors described the role of invasive diagnostic methodes and transcathetral and cardiosurgical possibilities in the recognition and therapy of acute coronary syndromes. These techniques are, and in the forthcoming year shall be available only in specialized institutions. The paper describes the indication for these aggressive techniques as well as their limitations and complications. The goal of the presented article is to inform both the cardiological and frequently broad physician s societies about the possibilities of diaventional cardiology and cardiosurgery which will be gradually more applied in the care of the patients with acute coronary syndromes. (Ref. 39, Tab. 2, Fig.3.).

Journal Article↗
PubMed1998

The multidrug resistance modulator valspodar (PSC 833) is metabolized by human cytochrome P450 3A. Implications for drug-drug interactions and pharmacological activity of the main metabolite.

The metabolism of valspodar (PSC 833; PSC), which is developed as a multidrug resistance-reversing agent, was investigated to assess the potential for drug-drug interactions and the pharmacological activity of major metabolites. The primary metabolites of PSC produced by human liver microsomes were monohydroxylated, as revealed by LC/MS. The major site of hydroxylation was at amino acid 9, resulting in M9, as determined by cochromatography with synthetic M9. Dihydroxylated and N-demethylated metabolites were also detected. PSC metabolism in two human livers exhibited KM values of 1.3-2.8 microM. The intrinsic clearance was 9-36 ml/min/kg of body weight. PSC biotransformation was cytochrome P450 (CYP or P450) 3A dependent, based on chemical inhibition and on metabolism by Chinese hamster ovary cells expressing CYP3A. Ketoconazole was a competitive inhibitor (Ki = 0.01-0.04 microM). The inhibition by 27 compounds, including four antineoplastic agents, corresponded to the inhibitory potentials of these compounds toward CYP3A. For vinblastine, paclitaxel, doxorubicin, and etoposide, the IC50 values were 5, 12, 20, and 150 microM, respectively. M9 was also an inhibitor, with a lower apparent affinity for CYP3A (IC50 = 21 microM), compared with that of PSC. M9 was also less active as a multidrug resistance-reversing agent. M9 demonstrated low potency in sensitizing resistant cells to paclitaxel and was a poor inhibitor of rhodamine-123 efflux from paclitaxel-resistant cells. In addition, compared with PSC, a higher concentration of M9 was needed to compete with the photoaffinity labeling of P-glycoprotein. Conversely, PSC inhibited only reactions catalyzed by CYP3A, including cyclosporine A metabolism (IC50 = 6.5 microM) and p-hydroxyphenyl-C3'-paclitaxel formation (Ki = 1.2 microM). Thus, PSC behaves in a manner very similar to that of other cyclosporines, and a comparable drug-drug interaction profile is expected.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

[Preparation for heart transplantation in Slovakia 1994-1997].

The authors present the process of introduction heart transplant programme in the years 1994-1997 in Slovakia. A short historical review about heart transplantation is given in the article. Fundamental requirements for heart transplantation realization, activities of Working group "Heart transplantation", methods of follow-up of patients after heart transplantation and selection of candidates for transplantation, are discussed. The authors also deal with surgical and anaesthesiological prerequisites for this programme realization. In conclusion they claim that the requirements for regular programme of heart transplantation are accomplished. (Tab. 2, Fig. 3, Ref. 21.)

Heart Transplantation↗
PubMed1998

[Diagnosis and therapy of acute rejection in patients after orthotopic heart transplantation].

OBJECTIVE: In organ allotransplantation represents a serious problem acute rejection, which is the reaction of recipient organism aimed to reject the transplanted organ. AIM: To obtain experience in the field of routine long term are of patients after heart transplantation living in Slovakia. METHOD: 33 patients after orthotopic heart transplantation (HTx) were included in our long term care by the 1. June 1996. According to the accepted protocol we make the whole set of examinations is performed. This includes endomyocardial biopsy which is the only reliable method for the detection of rejection and also the criterion of sufficiency of immunosuppressive therapy. RESULTS: Acute rejection was revealed in 14 (43%) patients. CONCLUSIONS: Tactics of therapy and the length of the interval to subsequent biopsy were determined according to the histological findings of preceding biopsy, the clinical status and the combination of immunosuppression therapy. (Tab. 2, Ref. 13.)

Acute Disease↗
PubMed1997

[Dilated cardiomyopathy and heart transplantation].

Authors compare selected demographic, clinical, methodological and laboratory parameters in 20 patients who underwent heart transplantation (HTx) because of dilated cardiomyopathy (DKMP) with those, who have had HTx because of progressive and otherwise unresolved coronary artery disease (KCH). Patients operated because of DKMP were younger than those who underwent HTx for KCH. Women were only in the group of DKMP. Otherwise there were no differences between these two groups. The global analysis showed, that the majority of patients after HTx were asymptomatic. However, high incidence of obesity, hyperlipoproteinemia, cytopoenia, renal and hepatal dysfunction were found. Finally the authors presented an overview of standard chronic therapy after HTx and proposed some approaches to undesirable habits and disorders which aggravated the prognosis of the patients after HTx.

Adult↗
PubMed1997

[Pulmonary complications after heart surgery].

The authors present a detailed analysis of pulmonary complications after open-heart surgery and of their risk factors. The results of the presented study indicate that COPD patients with functional impairments are more sensitive to complicated postoperative outcome and to respiratory infections, in general. There is a clear relationship between artificial violation of the pleural cavity, diaphragmatic dysfunction and pleural effusion. Diaphragmatic dysfunction appears more frequently in mammarocoronary bypass patients in consequence of pleurotomy. The incidence of dysfunction could be reduced by the use of phrenic nerve insulation. Patients with pulmonary complications suffer from serious pulmonary function deficit. The possibilities of identification of the patients at risk, as well as the prevention and prophylaxis are analysed. (Tab. 7, Fig. 2, Ref. 71.)

Coronary Artery Bypass↗