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Biomedical subjects

P Mayer

Publications and source records attributed to P Mayer.

At least 73 records · Page 4Linked to original sources
PubMed1998

Pentylenetetrazole (PTZ)-induced c-fos expression in the hippocampus of kindled rats is suppressed by concomitant treatment with naloxone.

Rats were kindled by repeated injections of pentylenetetrazole (PTZ; 37.5 mg/kg; i.p.) in the presence or absence of the opioid receptor antagonist naloxone. Naloxone (10 mg/kg; i.p.) applied 30 min before each PTZ application had no major effect on the seizure development, although a slight decrease in the seizure expression of fully kindled animals could be observed. In the kindled animals, a pronounced but transient increase in c-fos mRNA level was observed in several brain areas after the injection of PTZ. The magnitude of c-fos induction was related to the seizure stage reached. Detectable c-fos mRNA levels in the cortex were observed in rats showing stage four seizures, whereas the expression of c-fos in the hippocampus required stage five kindled seizures. The induction of c-fos expression in the hippocampus of stage five kindled rats but not in other brain areas was prevented by treatment of naloxone prior to each PTZ application. In contrast, a single injection of naloxone to kindled rats was not sufficient to prevent c-fos mRNA expression in the hippocampus. In addition, a single PTZ application (at the higher dose of 45 mg/kg) to rats that were not kindled also caused c-fos expression in several brain regions, but this was not influenced by naloxone. Assuming that c-fos expression reflects neuronal activity our findings suggest a functional role of endogenous opioid peptides in the development of kindling-induced neuronal excitation in the hippocampus. In addition, the excitation of the hippocampus does not appear to be involved in the seizure activity but may be responsible for the impairment of learning in PTZ-kindled rats which can be prevented by pretreatment with naloxone [A. Becker, G. Grecksch, M. Brosz, Naloxone ameliorates the learning deficit induced by pentylenetetrazole kindling in rats, Eur. J. Neurosci. 6 (1994) 1512-1515].

Amygdala↗
PubMed1998

Inhibition of Fc epsilon RI-mediated activation of mast cells by 2,3,4-trihydropyrimidino[2,1-a]isoquinolines.

Assays based on reporter gene technology represent today an important tool in the pharmaceutical industry for discovering novel compound classes interfering with the activation and signaling of target cells after stimulation. Here we describe a reporter gene assay targeting mast cell activation of IgE plus antigen, established in an attempt to identify substances preventing type I allergy (allergic rhinitis, allergic conjunctivitis, allergic asthma, and acute and chronic urticaria). The assay is based on a murine mast cell line designated CPII, stimulation by IgE plus antigen, and a reporter gene construct with the TNF alpha promoter linked to luciferase as a read-out system. Via screening about 50,000 substances, compound 2 was found to inhibit the reporter gene induction in the submicromolar range in this assay. Analogues of compound 2 of the 2,3,4-trihydropyrimidino[2,1-a]isoquinoline type were synthesized starting from 2-alkyl-substituted benzonitriles via aminolysis with 1,3-diaminopropane, dimetalation of 2-substituted 2-phenyl-1,4,5,6-tetrahydropyrimidines with n- and sec-butylithium, reaction with carboxylic acid methyl esters, and finally acidic dehydration. From about 50 derivatives, compound 41 was selected as a lead structure with an IC50 of 0.2 microM and a TC50 of 2.7 microM. In a first profiling in secondary assays, it effectively interfered with the production of mediators such as TNF alpha, IL-4, IL-6, IL-13, and leukotriene synthesis as measured by the corresponding ELISAs. In addition, a passive cutaneous anaphylaxis in mice (a typical type I reaction) is inhibited to more than 90% by compound 41, when administered intradermally 90 min before challenge.

Animals↗
PubMed1998

Cofactors in in vitro induction of apoptosis in HL60 cells by all-trans retinoic acid (ATRA).

The aim of this study was to determine the culture conditions that could modulate the induction of apoptosis by all-trans retinoic acid (ATRA). Cell viability was evaluated by trypan blue test, differentiation by nitro blue tetrazolium test, and apoptosis by morphological analysis. ATRA induced apoptosis in HL60 cells only when more than 100,000 cells/mL were seeded, while differentiation was induced regardless of the seeded cell concentration. Reduction in the concentration of foetal calf serum or glutamine in the medium led to a weak increase in apoptosis. In contrast, a dramatic enhancement of apoptosis occurred when the culture medium was supplemented with glucose or when the culture pH was decreased. These characteristics were independent of the mechanism of action of ATRA, but the action of glucose could be of significance in diabetic patients. An exchange of supernatants after 3 days of culture showed that supernatants from control cultures seeded at high cell density were better apoptosis inducers than supernatants from cultures treated with ATRA, but seeded at low cell density. Factor(s) in this supernatant which induced apoptosis was (were) removed by ultrafiltration. In conclusion, our results showed that ATRA alone cannot induce apoptosis, but can do so in conjunction with cofactors. The depletion of some components of the medium and the appearance of secreted macromolecule(s) could be cofactor(s) in the induction of apoptosis.

Apoptosis↗
PubMed1998

Effects of cardiopulmonary bypass and inhaled nitric oxide on platelets in children with congenital heart defects.

UNLABELLED: Nitric oxide (NO) reduces platelet aggregation in vitro. However, repeated measurements of platelet aggregation in infants and small children are impossible due to the large blood samples required. Instead, the expression of different platelet receptors mediating platelet adhesion (CD 36 and CD 42b), activation (CD 42b and CD 61) and aggregation (CD 41a) was measured repeatedly by flow cytometry. First, the expression of platelet receptors was quantified in platelet suspensions of 20 healthy volunteers after incubation with different concentrations of NO (0, 25, 100 and 640 ppm) and compared to changes in platelet aggregation and intrathrombocytic cGMP levels. It was then studied in 21 infants and children before, during and up to 3 days after cardiopulmonary bypass surgery. Seven of these patients required NO inhalation postoperatively. The in vitro experiments showed a reduced expression of the CD 41a, CD 42b and CD 61 receptors with increasing doses of NO, predominantly affecting the CD 41a receptor (-11% at 100 ppm and -20% at 640 ppm). This significant effect is in keeping with the observed NO-induced inhibition of platelet aggregation (-44% at 100 ppm) and the rise in platelet cGMP levels (+69% at 100 ppm). In patients without inhaled NO, the expression of CD 41a was slightly attenuated during cardiopulmonary bypass surgery (-15%) but increased significantly afterwards (2 h: +31%, 1st day: +129%, 2nd day: +120%, 3rd day: +111%). Comparable results were obtained regarding the other adhesion molecules CD 36, CD 42b and CD 61. In patients with inhaled NO the same pattern was observed and analysis of variance did not reveal any significant difference between both groups of patients. CONCLUSIONS: NO (> or = 100 ppm) decreases the expression of different platelet adhesion molecules and platelet aggregation, presumably via an increase in intracellular cGMP. However, due to the low dose range used in the clinical setting (1-40 ppm) this is clinically not relevant. Immediately after cardiopulmonary bypass surgery the expression of these adhesion molecules is reduced, but recovers on the 1st postoperative day.

Administration, Inhalation↗
PubMed1998

The treatment of spinocerebellar ataxias: facts and hypotheses.

Actual therapeutic assays in spinocerebellar ataxias, i.e. in Friedreich's ataxia (FA) and olivopontocerebellar atrophy (OPCA) are discussed in relation to (i) the serotoninergic theory; (ii) the excitotoxic action of glutamate; and (iii) cerebrospinal fluid thiamine deficiency in ataxic patients. Data from the literature show that neurochemical deficiencies arising from cerebellar damage in both FA and OPCA patients are multiple. Assays of replacement and neuroprotective therapeutics with a single drug have produced controversial data or mildly effective results. Consequently, it is hypothesized that a drug cocktail, i.e. L-5-hydroxytryptophan, thiamine and amantadine hydrochloride, would be more beneficial. This cocktail proved to be useful in open studies, improving respiratory disorders in FA patients. More powerful inhibitors of N-methyl-D aspartate receptor channels should be tried initially in animal experiments.

Animals↗
PubMed1998

Simultaneous laboratory-based comparison of ResMed Autoset with polysomnography in the diagnosis of sleep apnoea/hypopnoea syndrome.

ResMed Autoset (AS) is a simplified diagnosis system for obstructive sleep apnoea/hypopnoea syndrome (OSAS) based on the respiratory flow/time relationship by pressure variation measured through simple nasal prongs. A multicentre prospective trial was used to compare AS and polysomnography (PSG) for diagnosing 95 patients, with suspected OSAS. Physicians gave a pretest probability of the patient having OSAS. The apnoea/hypopnoea index (AHI) was compared between the two methods of diagnosis for the whole population and for subgroups according to the pretest probability. Twenty-four patients had AHI < 15 events x h(-1) on PSG and 19 AHI 15-30, and 52 patients had AHI > or = 30. Correlation between AHI assessed by AS and PSG was r=0.87 for total sleep time (TST), p<0.0001. A Bland and Altman plot gave an agreement between the two methods of +/-40%. For a threshold of AHI > or = 15 events x h(-1) to diagnose OSAS, AS has a sensitivity of 92%, specificity of 79%, positive predictive value of 93% and negative predictive value of 76%. With a pretest probability > or = 80%, sensitivity and positive predictive value were 98 and 100% respectively. Of six false negative, four had a high pretest probability (> 80%) or Epworth score > or = 10. Using these parameters as a criterion for proceeding to PSG after a negative AS study would mean that two apnoeic patients (AHI 20 and 17 events x h(-1) by PSG) would escape detection. The Autoset is useful for the detection of obstructive sleep apnoea but with high pretest probability and a negative Autoset result polysomnography should be performed.

Adult↗
PubMed1998

HL60 cells exhibit particular ultrastructural features during all-trans retinoic acid-induced apoptosis.

Ultrastructural features induced by 1 micromol/l all-trans retinoic acid (ATRA) treatment of HL60 cells were observed with transmission electron microscopy. Whilst some cells were unaffected, most of the others underwent granulocytic differentiation, starting point for apoptosis and then, possibly, secondary necrosis. First steps of apoptosis led to nuclear fragmentation into dense bodies. Then three different ways were observed: i) cells shrank and dense bodies were expelled, mostly associated with a fine lamellae of cytoplasm, ii) a secondary necrosis involved the release of apoptotic bodies without cytoplasm or iii) cells showed a dual or bipolar structure, not previously described.

Apoptosis↗
PubMed1997

Association between a delta opioid receptor gene polymorphism and heroin dependence in man.

Two allelic variants of the delta opioid receptor gene, distinguished by a single base exchange T to C in codon 307 of the translated region, were detected in humans. The amino acid sequence was thereby not changed. The resulting C and T alleles combined to give the three genotypes CC, CT and TT. Allele C was more frequent in a sample of 103 German Caucasian heroin addicts (53.4%) than in a control group (39.1%, n = 115). The proportion of CC homozygotes was much greater among the drug-dependent subjects (26.2%) than in controls (9.6%). Although the reasons for this association remain to be explained, our results argue for a participation of the delta type of opioid receptors in the pathophysiology of heroin dependence.

Alleles↗
PubMed1997

Can we treat respiratory failure in Friedreich ataxia?

BACKGROUND: Neurochemical disorders associated with spinocerebellar ataxias are multiple. OBJECTIVE: To use replacement and neuroprotective therapy in a case of severe respiratory failure in Friedreich ataxia. PATIENT AND TREATMENT: A 44-year-old man with severe Friedreich ataxia displayed arduous periodic breathing associated with minor desaturation as well as obstructive or mixed apneas associated with severe desaturation during the night. He was given oxitriptan (5-hydroxy-L-tryptophan) (1500 mg/d), thiamine hydrochloride (100 mg/d), and amantadine hydrochloride (100 mg/d). The first sleep study was conducted during the night before treatment, whereas the second was performed during the night after 9 months of treatment. RESULTS: After treatment, striking clinical improvement of spastic dysphonia was accompanied by significant diminution in the time spent in periodic breathing and in the number of obstructive and mixed apneas during the night. Controlled studies are needed.

5-Hydroxytryptophan↗
PubMed1997

Candidal colonization and oral candidiasis in patients undergoing oral and pharyngeal radiation therapy.

OBJECTIVES: Radiotherapy-induced hyposalivation encourages oral candidal colonization that often leads to oral/pharyngeal candidiasis. The purpose of this study was to quantitate oral candidal colonization, assess signs, symptoms, and response to antifungal management, speciate Candida, and evaluate the influence of smoking and dentures. STUDY DESIGN: Forty-six patients undergoing radiation therapy for oral/pharyngeal squamous cell carcinoma were evaluated clinically and by Candidal cultures before, during, and after irradiation. RESULTS: All patients complained of progressive xerostomia. There was a significant increase in the prevalence of positive candidal cultures (P = < 0.0001): baseline 43%, completion of radiotherapy 62%, and follow-up timepoint 75%. Smoking and denture wearing were not statistically significant risk factors for increased candidal colonization (p = 0.085 and p = 0.420, respectively). Eight patients developed clinical candidiasis. Although five responded clinically to systemic antifungal medication, all follow-up cultures remained positive. Candida albicans was the predominant species at baseline and completion of radiation (85% and 68%, respectively). CONCLUSIONS: When salivary glands are included in the field of radiation, xerostomia occurs, causing progressive increases in oral Candida colonization. Because 17.4% developed clinical candidiasis during radiotherapy and the question of fungal resistance remains speculative, a recommendation for the prophylactic use of antifungal medication is unresolved.

Adult↗
PubMed1997

Site mutation in the rat mu-opioid receptor demonstrates the involvement of calcium/calmodulin-dependent protein kinase II in agonist-mediated desensitization.

The rat mu-opioid receptor (rMOR1), expressed in human embryonic kidney 293 (HEK293) cells, shows a desensitization to the inhibitory effect of the mu agonist DAMGO on adenylate cyclase activity within 4 h of DAMGO preincubation. To investigate the role of calcium/calmodulin-dependent protein kinase II (CaM kinase II) on mu-opioid receptor desensitization, we coexpressed rMOR1 and constitutively active CaM kinase II in HEK293 cells. This coexpression led to a faster time course of agonist-induced desensitization of the mu-opioid receptor. The increase of desensitization could not be observed with a mu-opioid receptor mutant (S261A/S266A) that lacks two putative CaM kinase II phosphorylation sites in the third intracellular loop. In addition, injection of CaM kinase II in Xenopus oocytes led only to desensitization of expressed rMOR1, but not of an S261A/S266A receptor mutant. These results suggest that phosphorylation of Ser261 and Ser266 by CaM kinase II is involved in the desensitization of the mu-opioid receptor.

Adenylyl Cyclase Inhibitors↗
PubMed1997

Ventilatory and arousal responses to hypoxia and hypercapnia in a canine model of obstructive sleep apnea.

We have previously described a canine model of obstructive sleep apnea (OSA) in which sleep-wake state is monitored continuously by a computer that produces tracheal occlusion when sleep occurs. Our aim was to assess the effects of long-term application of this model on resting ventilation and on the ventilatory and arousal responses to hypercapnia and hypoxia. Five dogs were maintained on the model for 15.5 +/- 1.7 (mean +/- SE) wk, with a mean apnea index of 57.5 +/- 4.5 occlusions/h of sleep. Resting ventilation and the ventilatory and arousal responses to progressive hypoxic and hypercapnic rebreathing were assessed during wakefulness (W) and both slow-wave (SWS) and rapid-eye-movement (REM) sleep at baseline prior to intervention, at the end of the OSA phase, and following a 1 to 3-mo recovery period. During the period of OSA there were small changes in respiratory timing at rest, but no significant changes in PCO2 or SaO2. As compared with baseline, the ventilatory response to hypoxia during OSA was strikingly reduced during W, and significantly although less markedly reduced during SWS and REM. The reduction was due to a decreased breathing frequency response to hypoxia. In addition, during OSA there was a significant decrease from baseline in SaO2 at arousal during hypoxic rebreathing in both SWS and REM. All responses returned to normal during recovery. In contrast to hypoxia, hypercapnic ventilatory responses during OSA were slightly increased over their baseline values both in W and SWS, owing to a leftward shift of the ventilation-versus-PCO2 relationship. During recovery, these responses reverted partly to baseline for W and reverted completely to baseline for SWS. There were no significant changes in arousal PCO2 during hypercapnic rebreathing in either SWS or REM across the pre-OSA baseline, OSA, and post-OSA recovery periods. We conclude that long-term application of the OSA model is associated with a selective, reversible decrease in ventilatory and arousal responses to hypoxia.

Animals↗
PubMed1997

Insulinoma cells contain an isoform of Ca2+/calmodulin-dependent protein kinase II delta associated with insulin secretion vesicles.

The Ca2+/calmodulin dependent protein kinase II (CaM kinase II) is thought to play an important part in glucose-stimulated insulin secretion. To determine which of the known subtypes (alpha, beta, gamma, delta) occur in insulin-secreting cells, we amplified all types of CaM kinase II by RT-PCR and found the beta3-, gamma-, delta2- and delta6-subtypes in RINm5F insulinoma cells. None of the other 8 delta-subtypes was present. Antibodies generated against the bacterially expressed association domain of the delta2-subtype recognized the recombinant gamma and delta-subtypes. In INS-1 and RINm5F cells, as well as freshly isolated rat islets, only a 55-kDa protein corresponding in size to the delta2-subtype expressed in NIH3T3 fibroblasts was detected. The delta2-subtype therefore appears to represent the predominant subtype of CaM kinase II present in insulin secreting cells. The enzyme was primarily associated with cytoskeletal structures, and very little was present in the soluble compartment or detergent soluble fraction in INS-1- or RINm5F-cells. An analysis of its subcellular distribution was performed by sucrose and Nycodenz density gradient fractionation of INS-1 cells and detection of CaM kinase II delta by immune blots. The enzyme codistributed with insulin used as a marker for secretory granules but not with the lighter synaptic-like microvesicles detected with an antibody against synaptophysin, plasma membranes (syntaxin 1), lysosomes (arylsulfatase), or mitochondria (cytochrome c oxidase). CaM kinase II delta2 thus is identified as the subtype associated with insulin secretory granules and is likely to be involved in insulin secretion.

Animals↗
PubMed1997

Specific catalytic activity of cathepsin S in comparison to cathepsins B and L along the rat nephron.

Assay conditions were elaborated to determine the catalytic activity of cathepsin S fluorometrically for direct comparison with the activities of cathepsins B + L(+S) and B along the nephron of the normal rat. These conditions include the use of 0.5 mM Z-Phe-Arg-AMC as substrate, which is saturating for the three enzymes. The stability of cathepsin S at pH 7.5 and the resistance of cathepsin B against inactivation by 0.5 microM Z-Phe-Phe-CHN2 permitted differentiation of these enzyme activities. The catalytic activity of cathepsin S in rat kidney homogenate (1.11 mumol/min x g protein) amounted to 2.1% of that of cathepsins B + L(+S) and to 3.2% of that of cathepsin B. It was ten-fold higher in the cortex (1.54 mumol/min x g protein) than in the medulla resembling the activity ratio of cathepsins B + L(+S) and B. In suspensions of isolated glomeruli and isolated proximal tubules the activities of cathepsin S were 0.76 and 3.21 mumol/min x g protein, respectively. The corresponding activities of cathepsins B + L(+S) amounted to 80.0 and 211.7 mumol/min x g protein consisting of 71% cathepsin B activity. In nephron segments microdissected from lyophilized renal sections, highest cathepsin S activity was found in the proximal convoluted tubules (4.21 mumol/min x g dry weight) followed by 0.83 mumol/min x g dry weight in proximal straight tubules of the superficial cortex. In the remaining segments cathepsin S activity was hardly detectable. Unlike cathepsin S activity, the activity of cathepsin B was distributed in parallel to that of cathepsins B + L(+S). The presence of relatively high cathepsin S activity in proximal convoluted tubules in co-localization with the activities of cathepsins B + L(+S) and B suggests a primary role of these enzymes in heterophagocytosis of proteins from the ultrafiltrate.

Animals↗
PubMed1997

Tumor-associated cysteine proteinase activities in human melanoma cells and fibroblasts of different origin.

Specific catalytic activities of cysteine proteinases including cathepsins B (EC 3.4.22.1) and L (EC 3.4.22.15) in human melanoma cell lines SK-MEL-28, SK-MEL-30, MEL-HO and in fibroblasts of different origin are reported. Cell line-specific pH profiles of these cysteine proteinases were determined fluorometrically with benzyloxycarbonyl-phenylalanyl-arginine-amidomethylcoumarine (Z-Phe-Arg-AMC) under saturated conditions. Single activities of cathepsins B and L were inactivated by urea and by benzyloxycarbonyl-phenylalanyl-phenylalanine-diazomethylketone (Z-Phe-Phe-CHN2) in order to describe the activities of these enzymes separately. The melanoma cell line MEL-HO, which originated from a primary lesion, showed highest activity of an unknown cysteine proteinase. This enzyme is not inactivated by urea and Z-Phe-Phe-CHN2 and has a Michaelis constant (K(M) value) of approximately 1 mM. The specific characteristics suggest that it is a tumor-associated cathepsin B. In addition, high invasive subpopulations of SK-MEL-28 and SK-MEL-30 cell lines isolated by an invasion assay showed higher proteinase activities than the low invasive subpopulations. Furthermore, in fibroblasts originating from melanoma tissue cysteine proteinase activities were increased compared to normal skin fibroblasts. In conclusion, these results indicate that these cysteine proteinases shown here are tumor-associated proteinases, possibly facilitating invasion and dissemination of melanoma cells.

Cell Line↗
PubMed1996

Humanized anti-Lewis Y antibodies: in vitro properties and pharmacokinetics in rhesus monkeys.

ABL 364 is a murine monoclonal IgG3 antibody directed against the Lewis Y carbohydrate antigen (Le(y)) expressed on the surface of many epithelial cell tumors. The antibody mediates cytotoxicity via activation of human complement or human effector cells, and has been evaluated in several clinical trials including two Phase I/II trials in relapsed small cell lung cancer and metastatic breast cancer. To improve the effector functions of the antibody, increase its half-life in circulation, and avoid the human antimouse antibody response, two chimeric and several humanized antibodies were constructed for evaluation. The chimeric IgG1 is more potent than the murine IgG3 in tumor cell lysis via activation of human peripheral mononuclear cells (10-fold), but somewhat less effective in complement-dependent lysis (2-3 fold). The chimeric IgG3 is slightly less potent than the IgG1. A humanized IgG1 was constructed by combining the complementarity-determining regions of the ABL 364 antibody with human framework and constant regions. Several additional variants were subsequently constructed to improve the binding affinity and increase expression of the antibody. Two of the variants, designated I and K, differ by a single amino acid at position 75 of the heavy chain. Both variants have affinity within 2-fold of the chimeric IgG1 antibody and retain the cytolytic activities toward tumor cell lines. However, it was possible to express variant K at a significantly higher level (5- 10-fold) than variant I. Pharmacokinetics of the humanized ABL 364 antibody variant K was compared with that of the parent murine antibody in rhesus monkeys. It was shown that the terminal half-life of the humanized antibody in rhesus monkeys is 14-20 days, with a mean of 16.3 days, while that of the parent murine antibody is only 1.9 days.

Amino Acid Sequence↗