Biomedical subjects

M Adler

Publications and source records attributed to M Adler.

At least 19 recordsLinked to original sources

PubMed1992

Sequential 1H NMR assignments of kistrin, a potent platelet aggregation inhibitor and glycoprotein IIb-IIIa antagonist.

Sequence-specific nuclear magnetic resonances assignments have been obtained for the protons of kistrin. Kistrin is a small naturally occurring snake venom protein that inhibits platelet aggregation by blocking the interaction of fibrinogen with the membrane-bound glycoprotein IIb-IIIa (GP IIb-IIIa), a receptor from the integrin family. Kistrin has an Arg-Gly-Asp sequence which is believed to form an adhesion recognition sequence that is essential for activity. Therefore, the interaction between kistrin and GP IIb-IIIa may provide important information on the motif used by integrins to recognize their target proteins which bear RGD sequences. Kistrin consists of 68 residues and contains six intramolecular disulfide bonds. Although one-third of the amide protons are protected from exchange with the solvent, there appears to be little or no regular secondary structure. The large number of NOE's between residues separated by two and three positions in the sequence indicates that the protein contains a large number of tightly packed loops. Along with the sequential assignments, this paper also discusses the construction and use of computerized data bases for manipulating NMR results. A strategy for computer-assisted sequential resonance using these data bases is also presented.

Amino Acid Sequence↗

PubMed1992

NMR studies of structure and dynamics of isotope enriched proteins.

Structural studies of globular proteins by nmr can be enhanced by the use of isotope enrichment. We have been working with proteins enriched with 15N, and with both 15N and 13C. Due to the isotope enrichment we could assign several large proteins with up to 186 residues and could address structural questions. Furthermore, we can accurately measure heteronuclear and homonuclear vicinal coupling constants. This involves in part multidimensional multiple resonance experiments. This is important for characterization of minor conformational changes caused by mutations. We have also made use of isotope enrichment to study the internal mobility of proteins. We also have developed novel methods for measuring accurately 15N relaxation parameters, in particular transverse relaxation rates. This has led us toward a method for directly mapping spectral density functions of the rotational motions of N-H bond vectors in proteins. The protein systems that are discussed include the unlabeled proteins kistrin and cytochrome c551, and the labeled proteins eglin c, a flavodoxin, and human dihydrofolate reductase.

Bacterial Proteins↗

PubMed1992

Effects of subacute pyridostigmine administration on mammalian skeletal muscle function.

The subacute effects of pyridostigmine bromide were investigated on the contractile properties of rat extensor digitorum longus (EDL) and diaphragm muscles. The cholinesterase inhibitor was delivered via subcutaneously implanted osmotic minipumps (Alzet) at 9 micrograms h-1 (low dose) or 60 micrograms h-1 (high dose). Animals receiving high-dose pyridostigmine pumps exhibited marked alterations in muscle properties within the first day of exposure that persisted for the remaining 13 days. With 0.1 Hz stimulation, EDL twitch tensions of treated animals were elevated relative to control. Repetitive stimulation at frequencies greater than 1 Hz led a use-dependent depression in the amplitude of successive twitches during the train. Recovery from pyridostigmine was essentially complete by 1 day of withdrawal. Rats implanted with low-dose pyridostigmine pumps showed little or no alteration of in vivo twitch tensions during the entire 14 days of treatment. Diaphragm and EDL muscles excised from pyridostigmine-treated rats and tested in vitro showed no significant alterations in twitch and tetanic tensions and displayed the same sensitivity as muscles of control animals to subsequent pyridostigmine exposures. In the presence of atropine, subacutely administered pyridostigmine protected rats from two LD50 doses of the irreversible cholinesterase inhibitor, soman. In the absence of atropine, the LD50 of soman was not altered by subacute pyridostigmine treatment.

Acetylcholinesterase↗

PubMed1992

Mechanism of soman-induced contractions in canine tracheal smooth muscle.

The actions of the irreversible organophosphorus cholinesterase (ChE) inhibitor soman were investigated on canine tracheal smooth muscle in vitro. Concentrations of soman greater than or equal to 1 nM increased the amplitude and decay of contractions elicited by electric field stimulation. The effect on decay showed a marked dependence on stimulation frequency, undergoing a 2.4-fold increase between 3 and 60 Hz. Soman also potentiated tensions due to bath applied acetylcholine (ACh). Little or no potentiation was observed for contractions elicited by carbamylcholine, an agonist that is not hydrolyzed by ChE. Concentration of soman greater than or equal to 3 nM led to the appearance of sustained contractures. These contractures developed with a delayed onset and were well correlated with ChE activity. Alkylation of muscarinic receptors by propylbenzilylcholine mustard antagonized the actions of soman on both spontaneous and electrically-evoked muscle contractions. The results are consistent with a mechanism in which the toxic actions of soman are mediated by accumulation of neurally-released ACh secondary to inhibition of ChE activity. An important factor in this accumulation is suggested to be the buffering effect of the muscarinic receptors on the efflux of ACh from the neuroeffector junction.

Acetylcholine↗

PubMed1992

Hypersensitivity with hepatotoxicity to mesalazine after hypersensitivity to sulfasalazine.

A 21-year-old woman with Crohn's disease of the colon developed a skin rash after 3 weeks of treatment with sulfasalazine. Administration of sulfasalazine was discontinued. When mesalazine was instituted 1 week later, she developed a severe hypersensitivity reaction characterized by fever, diarrhea, skin rash with subsequent desquamation, marked atypical lymphocytosis, and severe hepatotoxicity. Recovery was complete. The clinical and biological features as well as liver pathology of this case bear a striking resemblance to earlier reports of hypersensitivity reaction with severe hepatotoxicity to sulfasalazine. The authors urge caution when mesalazine is given to a patient with known hypersensitivity to sulfasalazine.

Adult↗

PubMed1992

Role of muscle fasciculations in the generation of myopathies in mammalian skeletal muscle.

The myotoxicity of pyridostigmine bromide was investigated on rat diaphragm nerve-muscle preparations in vitro. Within 2 h of exposure to pyridostigmine (2 microM), diaphragm muscles exhibited ultrastructural alterations characterized by swelling of subjunctional mitochondria and disorganization of contractile proteins. These alterations developed both in the absence and presence of electrical stimulation of the phrenic nerve, and were accompanied by continuous muscle fasciculations. Pretreatment by tetrodotoxin suppressed both the muscle fasciculations and the appearance of myopathies. These findings suggest that fasciculations may be an important contributing factor in the development of anti-cholinesterase-induced myopathies.

Acetylcholinesterase↗

PubMed1992

Paraoxon block of chloride conductance in cell R2 of Aplysia californica.

In the presence of paraoxon, the amplitudes of chloride currents activated by acetylcholine (ACh) or gamma-aminobutyric acid (GABA) were reduced in cell R2 of Aplysia californica. IC50 values were 12 and 9.7 microM for ACh and GABA responses, respectively. Paraoxon did not affect resting membrane potential, input resistance, or chloride reversal potential. Both the slopes and maxima of ACh and GABA concentration-response curves were reduced by paraoxon, suggesting that paraoxon antagonism of these responses is not competitive. The antagonism of ACh and GABA responses by paraoxon was not related to inhibition of acetylcholinesterase.

Acetylcholine↗

PubMed1992

Expression of c-fos and AP-1 activity in senescent human fibroblasts is not sufficient for DNA synthesis.

Human fibroblasts have a limited replicative life span when maintained in culture after which they become unresponsive to treatment with mitogens, a phenomenon most commonly called senescence. Experiments indicating that serum does not induce expression of the c-fos proto-oncogene in senescent fibroblasts raised the issue of a potential central role for c-fos in the phenotype of sustained growth arrest. This was directly tested by microinjection of oncogenic c-Ha-ras protein into senescent fibroblasts. While ras injection was found to induce marked nuclear c-fos expression and functional AP-1 transcription activity, this did not lead to DNA synthesis. These results suggest that the senescence phenotype cannot be solely attributed to the absence of c-fos expression and that the proliferative block in these cells is either independent of AP-1 transcriptional activity, downstream of it, or involves multiple molecular mechanisms.

Cell Division↗

PubMed1992

Factors related to early mortality in cirrhotic patients bleeding from varices and treated by urgent sclerotherapy.

Variceal haemorrhage in cirrhotic patients carries a high early mortality even when balloon tamponade or emergency sclerotherapy are applied. The aim of this study to identify patients dying within six weeks of their first variceal haemorrhage. One hundred and twenty one patients with parenchymal cirrhosis presenting with the first variceal bleeding episode between June 1983 and December 1988 were studied. Nineteen patients were excluded for various reasons. Emergency sclerotherapy was carried out in cases of active bleeding or where there were endoscopic signs of recent bleeding, and then regularly repeated afterwards. Of the 24 variables studied and included in a multivariate analysis using a logistic regression model, three had an independent prognostic value: encephalopathy, prothrombin time, and the number of blood units transfused within the 72 hours of time zero. The subsequent regression equation was able to predict 89% of the patients who will die and 97% of the patients who will still be alive six weeks after their first variceal haemorrhage treated by sclerotherapy. Pugh score was less discriminatory than these last three variables in terms of accuracy of adjustment, goodness of fit to the model, receiver operating characteristic curves, and percentage correct prediction. To measure the accuracy of the prediction rule, our model was applied to another series of 28 cirrhotic patients admitted with their first variceal bleeding during the next period (January 1989 to May 1990). Death and survival were correctly predicted in respectively 82% and 94% of the cases. The use of this score is recommended for the selection of patients with high early mortality after variceal bleeding despite sclerotherapy, and for the design of new therapeutic trials.

Acute Disease↗

PubMed1992

Relaxation of soman-induced contracture of airway smooth muscle in vitro.

A possible role for beta-adrenergic agonists in the management of bronchoconstriction resulting from exposure to anticholinesterase compounds was investigated in vitro in canine tracheal smooth muscle. Norepinephrine, salbutamol and isoproterenol produced partial relaxation of soman-induced contractures. However, the relaxation induced was not sustained; muscle tensions returned to pretreatment levels within minutes despite the continued presence of beta-agonists. Increasing cAMP levels with the non beta-agonist bronchodilators such as theophylline, a phosphodiesterase inhibitor, or forskolin, a specific stimulator of adenylate cyclase, resulted in more complete and longer lasting relaxation, suggesting that beta-adrenoceptor desensitization may contribute to the failure by beta-agonists to produce sustained relaxation.

Acetylcholine↗

PubMed1992

Mycoplasma hominis infection of perihepatic hematomas in a liver transplant recipient.

We report the case of a recipient of liver transplantation in whom postoperative perihepatic hematomas were infected by Mycoplasma hominis. Etiologic diagnosis was delayed because this organism is a rare cause of postoperative infection and usually does not grow on standard bacteriologic media. The role of M. hominis in postoperative infections and the diagnostic problems of this organism are discussed.

Hematoma↗

PubMed1991

Regulation of acetylcholine hydrolysis in canine tracheal smooth muscle.

The regulation of acetylcholine (ACh) lifetime by acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholinesterase (BuChE, EC 3.1.1.8) was evaluated in vitro in canine tracheal smooth muscle preparations. Selective inhibition of AChE by low concentrations of 1,5-bis(N-allyl-N,N-dimethyl-4-ammoniumphenyl)-pentane-3-one dibromide (BW 284C51) led to increases in the amplitude and half-relaxation time of contractions elicited by electric field stimulation. Maximal responses were observed in the presence of 10(-6) M BW 284C51, where the amplitude and half-relaxation time were increased by 84 and 198%, respectively. Higher concentrations of BW 284C51, on the other hand, depressed the amplitude and shortened the decay of electric field stimulation-induced contractions by a mechanism involving blockade of muscarinic receptors. Selective inhibition of BuChE by tetraisopropylpyrophosphoramide (iso-OMPA) led to monotonic increases in the electric field stimulation amplitude and duration. These alterations were less marked than those observed in the presence of BW 284C51. Co-application of BW 284C51 (10(-5) M) and iso-OMPA (10(-5) M) resulted in a 1330% prolongation in the decay of electric field stimulation-induced contractions and the development of a sustained contracture. Such contractures were not observed with either inhibitor alone at any concentration tested. The results indicate that both hydrolytic enzymes are involved in the regulation of ACh lifetime at the canine tracheal neuroeffector junction with AChE exerting the more prominent role. The finding that BuChE co-regulates ACh lifetime in canine trachealis muscle demonstrates a functional role for this enzyme.

Acetylcholine↗

PubMed1991

The effects of pumiliotoxin-B on sodium currents in guinea pig hippocampal neurons.

The actions of pumiliotoxin-B, extracted from the skin of the frog Dendrobates pumilio, were examined on hippocampal slices and on acutely dissociated hippocampal neurons from the adult guinea pig. Application of 0.5-1 microM pumiliotoxin-B to hippocampal slices caused spontaneous, repetitive field discharges in the CA3 subfield. In whole-cell patch-clamp recordings of isolated CA1 and CA3 neurons, 1-2 microM pumiliotoxin-B shifted the midpoint of Na+ current activation by -11.4 +/- 1.1 mV. This shift was not dependent upon prior activation of the sodium channel. Pumiliotoxin-B did not block macroscopic Na+ inactivation but did reduce the apparent voltage-dependence of inactivation such that currents decayed faster at membrane potentials more negative than -30 mV. Single-channel recordings of sodium currents from excised membrane patches indicated that pumiliotoxin-B had little or no effect on channel closings due to entry into inactivated state(s) but did increase the rate of channel closings due to reversal of channel opening. The increase in the channel closing rate was consistent with a +8.7 mV shift in voltage sensitivity. Negative shifts in activation and positive shifts in closing rates implied a negative shift in the voltage-dependence of channel opening, suggesting that pumiliotoxin-B increases the rate of Na+ channel opening and closing in cells at rest, which could result in spontaneous activity in the neurons.

Alkaloids↗

PubMed1991

Solution structure of kistrin, a potent platelet aggregation inhibitor and GP IIb-IIIa antagonist.

The structure of kistrin, which is a member of a homologous family of glycoprotein IIb-IIIa (GP IIb-IIIa) antagonists and potent protein inhibitors of platelet aggregation, has been determined by two-dimensional nuclear magnetic resonance (NMR) spectroscopy. The 68-residue protein consists of a series of tightly packed loops held together by six disulfide bonds and has almost no regular secondary structure. Kistrin has an Arg-Gly-Asp (RGD) adhesion site recognition sequence important for binding to GP IIb-IIIa that is located at the apex of a long loop across the surface of the protein.

Amino Acid Sequence↗

PubMed1991

Double-blind randomised trial of the antiemetic efficacy and safety of ondansetron and metoclopramide in advanced breast cancer patients treated with epirubicin and cyclophosphamide.

Ondansetron was compared with metoclopramide for antiemetic efficacy in a randomised double-blind trial in 122 patients with advanced breast cancer. All patients were treated with epirubicin (greater than 50 mg/m2) and cyclophosphamide (greater than 500 mg/m2). 50 patients receiving ondansetron and 60 with metoclopramide were considered evaluable. Ondansetron was at least as effective as metoclopramide in the control of vomiting and nausea. The percentage of patients with complete plus major control was 72% (59-85%) vs. 61% (48-74%) on day 1 (P = 0.230) and 79% (67-91%) vs. 66% (53-78%) on days 2-3 after chemotherapy (P = 0.122). Over the 3-day study period, nausea was absent or mild in 60% of the patients treated with ondansetron, compared to 45% given metoclopramide (P = 0.064). No major drug-related side-effects were reported. 1 patient receiving ondansetron experienced gastrointestinal disturbance and headache. Episodes of diarrhoea, fever, hyperkinetic syndrome, fatigue, restlessness and migraine with vomiting were reported by 5 patients treated with metoclopramide. None of the changes in the biochemical or haematological parameters was attributed to the antiemetic treatments.

Adult↗

PubMed1991

AIDS: lessons learnt?

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Acquired Immunodeficiency Syndrome↗

PubMed1991

Air embolism due to pulmonary barotrauma in a patient undergoing cesarean section.

Air embolism may occur following criminal abortion, vaginal douching, powder insufflation as treatment for vaginal infections, and orogenital sex. The patient reported in this work deteriorated following pulmonary barotrauma. Diagnosis was made 16 h after the appearance of neurological signs. She was transferred immediately to the hyperbaric unit. The speed and completeness of recovery are directly related to the prompt diagnosis and commencement of therapy. Failure is more likely related to delay.

Adult↗

PubMed1990

Nonnative isomers of proline-93 and -114 predominate in heat-unfolded ribonuclease A.

The peptide bonds preceding both Pro-93 and Pro-114, which are in the cis conformation in native RNase A, are predominantly in the trans conformation in the heat-unfolded protein. The percentages are estimated to be 60% and 63%, respectively, with a standard deviation of +/- 7% in each quantity. These ratios are close to those found for corresponding sequences in X-Pro-Y peptides. The concentration of the trans proline species was determined from the integrated intensities of resonance peaks of the C alpha H protons of Tyr-92 and Asn-113, which are well resolved in the 1D proton NMR spectrum of heat-unfolded RNase A. The assignments of the resonances were deduced from 2D NOESY and DQF-COSY spectra of unfolded RNase A in D2O. Furthermore, the C alpha H protons of both Tyr-92 and Asn-113 had an intense NOE cross-peak with the C delta H and C delta' H of the respective following prolines. For both Pro-93 and Pro-114, these NOE cross-peaks would arise only if the X-Pro peptide bond were in the trans conformation. It is generally believed that the rate of refolding of RNase A is considerably reduced by nonnative proline isomers, such as trans Pro-93. Two models for folding RNase A, that are consistent with these new results and the work of previous investigators, are presented here.

Amino Acid Sequence↗