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Biomedical subjects

M Wenk

Publications and source records attributed to M Wenk.

At least 19 recordsLinked to original sources
PubMed2005

Induction of thyroid lesions in 14-week toxicity studies of 2 and 4-methylimidazole in Fischer 344/N rats and B6C3F1 mice.

Fifteen-day and 14-week studies of 2-methylimidazole (2MI) and 4-methylimidazole (4MI) were conducted because of widespread human exposure via ingestion of food products containing the compounds and lack of toxicity data. Groups of five male and five female Fischer rats and B6C3F1 mice were administered 2MI by dosed feed at 0, 1,200, 3,300, or 10,000 ppm or 4MI at 0, 300, 800, or 2,500 ppm for 15 days, and groups of 10 male and 10 female Fischer rats and B6C3F1 mice were administered 2MI or 4MI at 0, 625, 1,250, 2,500, 5,000 or 10,000 ppm for 14 weeks. In the 15-day studies, 2MI induced thyroid follicular-cell hyperplasia and pituitary pars-distalis hypertrophy in rats and thyroid follicular-cell hypertrophy and spleen hematopoietic-cell proliferation in mice; 4MI induced no histopathological changes in rats and mice. In the 14-week studies, 2MI increased concentrations of thyroid-stimulating hormone (TSH) and decreased those of thyroxine (T(4)) and triiodothyroxine (T(3)) in male and female rats according to the dosage. Incidences of diffuse follicular-cell hyperplasia of the thyroid gland increased significantly in male rats exposed to 1,250 ppm or greater and female rats exposed to 2,500 ppm or greater. Thyroid follicular-cell adenoma was diagnosed in two males in the 10,000-ppm group. A dose-related anemia occurred in female rats. In mice, follicular-cell hypertrophy of the thyroid gland, anemia, splenic hematopoietic-cell proliferation, and hemosiderin in kidney tubules appeared. In rats, 4MI induced tremors and ataxia in the high-dose groups. Serum T(3), T(4), and TSH levels were not altered, and no thyroid lesions occurred. Anemia, hepatocytic vacuolation, testicular degeneration, and prostatic atrophy were observed. In mice, anemia, liver cytoplasmic vacuolization, and renal degeneration and dilation occurred. Our studies demonstrated that, in rats and mice, 2MI induces thyroid hyperplasia and hypertrophy, and both 2MI and 4MI induce anemia; 2MI induces thyroid follicular-cell adenoma in male rats.

Animals↗
PubMed2000

Gamma S-crystallin of bovine and human eye lens: solution structure, stability and folding of the intact two-domain protein and its separate domains.

Human and bovine gammaS-crystallin (HgammaS and BgammaS) and their isolated N- and C-terminal domains were cloned and expressed as recombinant proteins in E. coli. HgammaS and BgammaS are found to be authentic according to their spectral and hydrodynamic properties. Both full-length proteins and isolated domains are monomeric and exhibit high thermal and pH stabilities. The thermodynamic characterization made use of chemically and thermally-induced equilibrium unfolding transitions at varying pH. In spite of its exemplary two-domain structure, gammaS-crystallin does not show bimodal unfolding characteristics. In the case of BgammaS, at pH 7.0, the C-terminal domain is less stable than the N-terminal one, whereas for HgammaS the opposite holds true. Differential scanning calorimetry confirms the results of chemically-induced equilibrium unfolding transitions. Over the whole pH range between 2.0 and 11.5, HgammaS-crystallin and its isolated domains (HgammaS-N and HgammaS-C) follow the two-state model. The two-state unfolding of the intact two-domain protein points to the close similarity of the stabilities of the constituent domains. Obviously, interactions between the domains do not contribute significantly to the overall stability of gammaS-crystallin. In contrast, the structurally closely related gammaB-crystallin owes much of its extreme stability to domain interactions.

Animals↗
PubMed2000

Fission and uncoating of synaptic clathrin-coated vesicles are perturbed by disruption of interactions with the SH3 domain of endophilin.

Coordination between sequential steps in synaptic vesicle endocytosis, including clathrin coat formation, fission, and uncoating, appears to involve proteinprotein interactions. Here, we show that compounds that disrupt interactions of the SH3 domain of endophilin with dynamin and synaptojanin impair synaptic vesicle endocytosis in a living synapse. Two distinct endocytic intermediates accumulated. Free clathrin-coated vesicles were induced by a peptide-blocking endophilin's SH3 domain and by antibodies to the proline-rich domain (PRD) of synaptojanin. Invaginated clathrin-coated pits were induced by the same peptide and by the SH3 domain of endophilin. We suggest that the SH3 domain of endophilin participates in both fission and uncoating and that it may be a key component of a molecular switch that couples the fission reaction to uncoating.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Inspired oxygen fraction after cardiopulmonary bypass: effects on pulmonary function with regard to endothelin-1 concentrations and venous admixture.

Twenty consecutive patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) were allocated at random to group 1 (n = 10, high inspired oxygen fraction (FIO2) after CPB), or group 2 (n = 10, moderate FIO2 after CPB). The effects of each FIO2 on arterial and mixed venous concentrations of endothelin-1 (ET-1) and its precursor, Big ET-1, were measured. Venous admixture was calculated to assess the efficiency of pulmonary gas exchange. Patients whose lungs had been ventilated with a FIO2 of 1.0 (exposure time 70 min) after weaning from the CPB machine had significantly greater arterial and mixed venous Big ET-1 concentrations and venous admixture than patients whose lungs were ventilated with a FIO2 of 0.35. In contrast, ET-1 concentrations in the two groups were not significantly different. A reduction of FIO2 from 1.0 to 0.6 reduced venous admixture without lowering endothelial peptide concentrations. On the first postoperative day all peptide concentrations were similar in the two groups, whereas venous admixture remained non-significantly higher in group 1. A short period of high FIO2 immediately after CPB increases endothelin concentrations and pulmonary venous admixture.

Aged↗
PubMed2000

Pharmacokinetics and pharmacodynamics of levofloxacin against Streptococcus pneumoniae and Staphylococcus aureus in human skin blister fluid.

The pharmacokinetics of levofloxacin in serum and in skin blister fluid (SBF) was determined for 20 volunteers after a single 500-mg oral dose of levofloxacin. In addition, ex vivo bactericidal activity of SBF against Streptococcus pneumoniae and Staphylococcus aureus was studied. SBF containing levofloxacin and granulocytes killed 5.2 log of Streptococcus pneumoniae bacteria and 2.0 log of Staphylococcus aureus bacteria during a 6-h incubation.

Anti-Infective Agents↗
PubMed1999

Calorimetric analysis of the Ca(2+)-binding betagamma-crystallin homolog protein S from Myxococcus xanthus: intrinsic stability and mutual stabilization of domains.

The betagamma-crystallin superfamily consists of a class of homologous two-domain proteins with Greek-key fold. Protein S, a Ca(2+)-binding spore-coat protein from the soil bacterium Myxococcus xanthus exhibits a high degree of sequential and structural homology with gammaB-crystallin from the vertebrate eye lens. In contrast to gammaB-crystallin, which undergoes irreversible aggregation upon thermal unfolding, protein S folds reversibly and may therefore serve as a model in the investigation of the thermodynamic stability of the eye-lens crystallins. The thermal denaturation of recombinant protein S (PS) and its isolated domains was studied by differential scanning calorimetry in the absence and in the presence of Ca(2+) at varying pH. Ca(2+)-binding leads to a stabilization of PS and its domains and increases the cooperativity of their equilibrium unfolding transitions. The isolated N-terminal and C-terminal domains (NPS and CPS) obey the two-state model, independent of the pH and Ca(2+)-binding; in the case of PS, under all conditions, an equilibrium intermediate is populated. The first transition of PS may be assigned to the denaturation of the C-terminal domain and the loss of domain interactions, whereas the second one coincides with the denaturation of the isolated N-terminal domain. At pH 7.0, in the presence of Ca(2+), where PS exhibits maximal stability, the domain interactions at 20 degrees C contribute 20 kJ/mol to the overall stability of the intact protein.

Bacterial Proteins↗
PubMed1999

The domains of protein S from Myxococcus xanthus: structure, stability and interactions.

Protein S from Myxococcus xanthus is a member of the beta gamma-crystallin superfamily. Its N and C-terminal domains (NPS and CPS, respectively) show a high degree of structural similarity and possess the capacity to bind two calcium ions per domain. For NPS, their positions were determined by X-ray diffraction at 1.8 A resolution, making use of molecular replacement with the NMR structure as search model. The overall topology of NPS is found to be practically the same as in complete protein S. In natural protein S, the domains fold independently, with a significant increase in stability and cooperativity of folding in the presence of Ca2+. The recombinant isolated domains are stable monomers which do not show any tendency to combine to "nicked" full-length protein S. In order to investigate the stability and folding of natural protein S and its isolated domains, spectroscopic techniques were applied, measuring the reversible urea and temperature-induced unfolding transitions at varying pH. The increment of Ca2+ to the free energy of stabilization amounts to -10 and -5 kJ/mol for NPS and CPS, respectively. For both NPS and CPS, in the absence and in the presence of 3 mM CaCl2, the two-state model is valid. Comparing DeltaGU-->N for CPS (-21 kJ/mol at pH 7, liganded with Ca2+) with its increment in the intact two-domain protein, the stability of the isolated domain turns out to be decreased in a pH-dependent manner. In contrast, the stability of Ca2+-loaded NPS (DeltaGU-->N=-31 kJ/mol, pH 7) is nearly unchanged down to pH 2 where Ca2+ is released (DeltaGU-->N=-26 kJ/mol, pH 2). In intact protein S, the N-terminal domain is destabilized relative to NPS. Evidently, apart from Ca2+ binding, well-defined domain interactions contribute significantly to the overall stability of intact protein S.

Bacterial Proteins↗
PubMed1999

Xanthine oxidase inhibition by allopurinol affects the reliability of urinary caffeine metabolic ratios as markers for N-acetyltransferase 2 and CYP1A2 activities.

OBJECTIVES: To evaluate the in vivo effect of xanthine oxidase (XO) inhibition by allopurinol on the determination of polymorphic N-acetyltransferase 2 (NAT2) and cytochrome P450 1A2 (CYP1A2) with urinary caffeine metabolic ratios. METHODS: In an open, prospective study involving 21 healthy subjects (eight fast, 13 slow NAT2 acetylators) allopurinol (300 mg perday) was administered orally on trial days 1-8, followed by a wash-out period of 8 days. Urinary caffeine tests (200 mg caffeine p.o.) were performed repetitively. Urine was collected for 8 h and venous blood samples for the determination of allopurinol, oxypurinol and uric acid were drawn. The urinary caffeine metabolites 1-methyluric acid (1MU), 1-methylxanthine (1MX), 1,7-dimethyluric acid (17MU), 1,7-dimethylxanthine (17MX), 5-acetylamino-6-formylamino-3-methyluracil (AFMU), plasma allopurinol and oxypurinol were analysed using high-performance liquid chromatography (HPLC). RESULTS: During XO inhibition by allopurinol, the formation of 1MU from 1MX and therefore the XO ratio 1MU/1MX decreased to 15.9 (1.2)% [mean with (SEM)] of baseline values (P < 0.005). The NAT2 ratio AFMU/1MX decreased likewise to 56.7 (6.3)% (P < 0.005). AFMU/(AFMU + 1MX + 1MU), an alternative NAT2 ratio, remained constant, but the CYP1A2 ratio (AFMU + 1MX + 1MU)/17MU, used to express CYP1A2 activity, transiently increased to 167 (13)% (P < 0.005). The NAT2 phenotype did not influence CYP1A2 and XO ratios or plasma oxypurinol pharmacokinetics. CONCLUSIONS: Several caffeine metabolic ratios are commonly used to express the activities of NAT2, CYP1A2 and XO both in healthy volunteers and in polymedicated patients, although their reliability has not been evaluated thoroughly during concurrent drug administration. The findings of this study suggest that NAT2 phenotyping should be performed using the ratio AFMU/(AFMU + 1MX + 1MU) if an XO inhibitor may be present. It also shows that the determination of CYP1A2 activity with caffeine as a metabolic probe is considerably altered under these conditions. Thus, concomitant drug administration may impair the robustness of multiple pathways of the complex caffeine test. This points to the need for alternative probes, designed to assess only the activity of a single enzyme because, in contrast to healthy volunteers, in patients known or unknown drug interactions may often be present.

Allopurinol↗
PubMed1998

Kinetic stabilisation of a modular protein by domain interactions.

Protein S, a two-domain spore coat protein from Myxococcus xanthus, is structurally related to eye-lens Pr crystallins. No natural monomeric one-domain member of this protein superfamily is known. To determine the stability of the single domains and to explain the ubiquitous domain duplication, the isolated domains of protein S were constructed. The N-domain is thermodynamically more stable than the C-domain. In intact protein S, domain interactions lead to an apparent decrease in stability of the N-terminal domain, whereas the C-terminal domain is stabilised. In contrast, unfolding kinetics of both domains are decreased 100-fold due to interactions in the complete molecule.

Bacterial Proteins↗
PubMed1998

Myxococcus xanthus spore coat protein S, a stress-induced member of the betagamma-crystallin superfamily, gains stability from binding of calcium ions.

Protein S, a calcium-binding spore coat protein from the soil bacterium Myxococcus xanthus, belongs to a group of structurally related proteins, the betagamma-crystallin superfamily. Common features of this protein family are the Greek-key structural motif or crystallin fold, and the fact that all members are extremely stable long term. To investigate the correlation between the stability and Greek-key topology, protein S was cloned, expressed in Escherichia coli and purified to homogeneity. Ca2+ binding influences the native tertiary structure of protein S, whereas the secondary structure remains unaffected as shown by spectroscopic methods. Ca2+ ions enhance the conformational stability of protein S significantly. The midpoints of urea and guanidinium chloride-induced transitions show a difference of 1.4 M and 0.5 M denaturant, respectively, in the absence and in the presence of calcium. An equilibrium intermediate indicating independent domain folding can be detected at pH 2. In addition, thermal denaturation shows a clear deviation from the two-state model of folding, again with a strong stabilisation by Ca2+ ions. Temperature and denaturant-induced equilibrium transitions are fully reversible. Our data implicate a different strategy for achieving the high stability required for the biological function compared with the structurally related lens crystallins.

Bacterial Proteins↗
PubMed1998

Rapid atrazine mineralisation in soil slurry and moist soil by inoculation of an atrazine-degrading Pseudomonas sp. strain.

The evaluation of pesticide-mineralising microorganisms to clean-up contaminated soils was studied with the widely applied and easily detectable compound atrazine, which is rapidly mineralised by several microorganisms including the Pseudomonas sp. strain Yaya 6. The rate of atrazine removal was proportional to the water content of the soil and the amount of bacteria added to the soil. In soil slurry, 6 mg atrazine kg soil-1 was eliminated within 1 day after application of 0.3 g dry weight inoculant biomass kg soil-1 and within 5 days when 0.003 g kg soil-1 was used. In partially saturated soil (60% of the maximal water-holding capacity) 15 mg atrazine kg soil-1 was used. In unsaturated soil, about 60% [U-ring-14C] atrazine was converted to 14CO2 within 14 days. Atrazine was very efficiently removed by the inoculant biomass, not only in soil that was freshly contaminated but also in soil aged with atrazine for up to 260 days. The bacteria exposed to atrazine in unsaturated sterile soil were still active after starvation period of 240 days: 15 mg newly added atrazine kg soil-1 was eliminated within 5 days.

Atrazine↗
PubMed1998

Safety and efficacy of a two-compartment Bayesian feedback program for therapeutic tobramycin monitoring in the daily clinical use and comparison with a non-Bayesian one-compartment model.

The predictive value of a two-compartment Bayesian feedback program for tobramycin dose optimization was retrospectively evaluated in 199 hospitalized patients and compared with that of a simple non-Bayesian one-compartment model. Before dose adjustment, 64% of the patients were underdosed indicating that tobramycin monitoring is still necessary to avoid ineffective antibiotic therapy. When physicians adhered to the dose instructions calculated with the Bayesian method, 90% of the patients had optimal concentration-time profiles as opposed to only 53% of the 43 patients in whom dose recommendations were not followed. In young patients with normal renal function, precision and accuracy of the Bayesian feedback and the one-compartment method were well correlated, whereas in elderly patients (> 60 years) and patients with impaired renal function (estimated creatinine clearance < 60 ml/minute), the Bayesian method was significantly more precise. Multiple regression analysis revealed that renal function was the only independent variable predicting the performance of the Bayesian program. The results of this study indicate that the Bayesian feedback method is a reliable method for the therapeutic tobramycin monitoring under clinical conditions and in particular, elderly patients in whom renal impairment is frequent.

Absorption↗
PubMed1998

Acetaminophen is an inhibitor of hepatic N-acetyltransferase 2 in vitro and in vivo.

Slow acetylators of the polymorphic N-acetyltransferase 2 (NAT2, EC 2.3.1.5) suffer more often from side-effects of NAT-substrates than fast acetylators. Since concomitant administration of drugs may inhibit NAT2, we studied the influence of acetaminophen on NAT2 in human hepatic cytosol in vitro and in healthy individuals. In-vitro acetylation was assessed in liver homogenate of one fast and one slow acetylator using sulfamethazine as a test substrate. Acetaminophen competitively inhibited sulfamethazine acetylation in fast and slow acetylator liver samples with Ki values of acetaminophen of 2144 micromol/l and 712 micromol/l, respectively. In additional experiments, exposure of human liver cytosol to p-aminophenol, a putative precursor of acetaminophen in this reaction, revealed production of substantial amounts of acetaminophen, which indirectly suggests that acetaminophen may bind to the active site of NAT2. In-vivo acetylation was quantified with a urinary caffeine assay in 20 healthy volunteers at baseline and after repetitive oral administration of 1000 mg acetaminophen every 6 h for 1 day. The ratio of the acetylated caffeine metabolite acetyl-amino-6-formylamino-3-methyluracil to 1-methylxanthine was reduced by 30.9% (range 11.0-50.1%) in fast acetylators (n = 10) and by 19.3% (range 0.2-36.5%) in slow acetylators (n = 10). Acetaminophen, a widely used over-the-counter drug, which shares structural similarities with acetylated products, inhibits NAT2 both in vitro and in vivo. These findings suggest that even compounds which are not metabolized by NAT2 may inhibit the enzyme and reduce its metabolic capacity.

Acetaminophen↗
PubMed1996

N-acetyltransferase 2 polymorphism in patients infected with human immunodeficiency virus.

OBJECTIVES: To evaluate the prevalence of slow acetylation of hepatic N-acetyltransferase 2 (NAT2) in patients with different stages of human immunodeficiency virus (HIV) infection, to assess the relationship between acetylation capacity and the degree of immunosuppression, and to study the concordance between NAT2 phenotype and genotype. METHODS: This prospective study in a consecutive sample of HIV-infected patients was performed in the outpatient department of a university hospital that provides primary and tertiary care. The NAT2 genotype was assessed by polymerase chain reaction and restriction fragment length polymorphism, the NAT2 phenotype was determined by caffeine test (urinary metabolic ratio of the caffeine metabolites 5-acetylamino-6-formylamino-3-methyluracil and 1-methylxanthine). RESULTS: Fifty patients with Centers for Disease Control HIV infection stages A (10 patients), B (20 patients), and C (20 patients) were included in the study after each gave informed consent. According to genotyping and phenotyping, 32 (64%) patients were slow acetylators, with a concordance of the two methods of 96%. The overall distribution was similar to distributions reported in other white populations. The slow acetylator phenotype was found in seven, 16, and nine patients with stage A, B, and C, respectively. Eight of the 10 patients with previous adverse reactions to sulfonamides had slow acetylator phenotypes. Acetylation capacity was independent of CD4 cell counts. CONCLUSIONS: This study revealed an excellent agreement between genotypes and phenotypes of NAT2 in patients with HIV infection. There was no increase in prevalence of slow acetylation in patients with advanced stages of the disease. This apparent discrepancy to an earlier study may be the result of differences in co-medication of the patients studied and may point to the relevance of drug interactions in the treatment of patients with HIV infection.

Acetylation↗
PubMed1995

Endothelin-1 in pulmonary hypertension associated with high-altitude exposure.

BACKGROUND: Endothelin-1 is involved in chronic pulmonary hypertension. Its role in acute pulmonary hypertension due to hypoxia in humans is not clear. We therefore studied the influence of hypoxia caused by exposure to high altitude on plasma endothelin-1 levels, arterial blood gases, and pulmonary arterial pressure in subjects taking nifedipine or placebo. METHODS AND RESULTS: Twenty-two healthy volunteers were investigated at low altitude (490 m) and high altitude (4559 m). Arterial blood gases were analyzed immediately, endothelin-1 was measured by radioimmunoassay, and pulmonary artery pressure was assessed by Doppler echocardiography. After baseline investigations, the mountaineers were allocated in a randomized double-blind fashion to receive either placebo or nifedipine (20 mg TID) during rapid ascent to high altitude within 22 hours. Tests were repeated at the high-altitude research laboratories located in the Capanna "Regina Margherita" (Italy, 4559 m). Plasma endothelin-1 was increased twofold at high altitude (5.9 +/- 2.2 pg/mL compared with 2.9 +/- 1.1 pg/mL, P < .05), was inversely related to arterial PO2 (r = -.46, P < .001), and correlated with pulmonary artery pressure (r = .52, P < .002). At high altitude, arterial endothelin-1 was lower (4.3 +/- 1.6 pg/mL) than venous endothelin-1 (5.9 +/= 2.2 pg/mL, P < .001), indicating either predominant production in the venous vasculature or pronounced clearance in the pulmonary circulation. The calcium antagonist nifedipine, which lowered pulmonary artery pressure at high altitude (32 +/- 5 versus 42 +/- 11 mm Hg, P < .05), had no influence on plasma endothelin-1 levels. The administration of 35% O2 at high altitude normalized arterial PO2, tended to decrease endothelin-1, and decreased pulmonary artery pressure accordingly. CONCLUSIONS: We conclude that plasma endothelin-1 is increased at high altitude, but whether or not it represents an important pathogenetic factor for pulmonary hypertension remains to be investigated.

Adult↗
PubMed1995

Endothelin-1 plasma levels in normal-tension glaucoma: abnormal response to postural changes.

BACKGROUND: Endothelin-1 (ET-1) is a potent vasoconstrictor peptide produced by vascular endothelial cells. ET-1 may have a role in the pathogenesis of various vascular diseases. There are reports in the literature that ET-1 plasma levels are raised in normal-tension glaucoma (NTG) patients. METHODS: ET-1 concentration, plasma renin activity, and 24-h blood pressure were measured in 21 high-tension glaucoma (HTG) patients, 19 NTG patients, and 20 non-glaucomatous controls in supine and upright positions. RESULTS: ET-1 plasma levels tended to be higher in NTG patients (3.2 +/- 2.2 pg/ml) than in HTG patients (2.2 +/- 0.6 pg/ml) and controls (2.6 +/- 0.7 pg/ml). The differences, however, were not statistically significant. The individual scatter was significantly greater in the NTG group, indicating that our NTG patients are a heterogeneous population. The physiological increase in ET-1 plasma level after changing from the supine to the upright position was absent in NTG patients. Plasma renin activities tended to be lower in NTG patients (1.2 +/- 1.2 ng/ml/h) than in HTG patients (1.3 +/- 0.8 ng/ml/h) and controls (2.0 +/- 1.7 ng/ml/h). This may explain why NTG patients had relatively low blood pressure despite high ET-1 levels. CONCLUSIONS: Our data support the hypothesis that vascular dysfunction may be involved in the pathogenesis of optic nerve damage in normal-tension glaucoma.

Blood Pressure↗
PubMed1994

[Cyclosporin in autoimmune diseases].

At a symposium held in Zurich in November 1993, a series of presentations covered the optimal use of cyclosporin A (CsA) in autoimmune diseases. Besides its immunosuppressive effects in organ transplantation, CsA appears to be active in a variety of autoimmune disorders. Its most pronounced and beneficial clinical effects are seen in patients with severe rheumatoid arthritis. New clinical studies include the nephrotic syndrome in children and patients with systemic lupus erythematodes. The main concern remains CsA induced nephrotoxicity. For the treatment of autoimmune disorders CsA can be used at lower doses (< or = 5 mg/kg per day) than in transplantation medicine. Thus, monitoring of CsA blood concentrations is not usually necessary. The galenics of CsA has been optimized recently, an achievement which will further improve the clinical use of CsA. Due to increased knowledge of intracellular CsA binding proteins and of effects of CsA on T-lymphocytes and cytokine production, it can be expected that novel immunosuppressive compounds will be developed.

Adult↗