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Biomedical subjects

N S Cook

Publications and source records attributed to N S Cook.

At least 19 recordsLinked to original sources
PubMed1996

Thrombin inhibition in an ex vivo model of porcine heart xenograft hyperacute rejection.

Prominent components of vascularized xenograft rejection such as platelet activation and microvascular thrombosis may be dependent upon thrombin generation in vivo. To study potential therapeutic benefits of a synthetic low-molecular-weight thrombin inhibitor, SDZ MTH 958, in hyperacute porcine heart rejection by human blood ex vivo, a working model of hyperacute rejection of porcine by fresh, heparinized (6 microM/ml) human blood with or without 1 microM SDZ MTH 958 was used. Thrombin-antithrombin complexes (TAT) and prothrombin fragment F1.2 levels as markers of thrombin activation were determined, and biopsies from rejected hearts were analyzed by immunohistopathology. Control porcine hearts (n=8) underwent a rapid and consistent decline in cardiac output, ceasing function by 60 min. Experimental cardiac output values of 14 ml/g (SEM 1.2) were significantly higher than seen in controls (5 ml/g SEM 0.6) after 5 min of cardiac work, and prolonged survival times up to 120 min were noted (P<0.05). Activity of SDZ MTH 958 was confirmed by functional assays throughout perfusion. Levels of TAT and F1.2 increased consistently in control samples when compared with plasma samples containing SDZ MTH 958. Immunohistopathological examination confirmed diminished fibrin deposition, reduced leukocyte adherence to endothelium, impaired diapedesis and less tissue necrosis in the hearts perfused with SDZ MTH 958. SDZ MTH 958, in this xenoperfusion model, prolonged survival, enhanced function of the explanted organ, and improved histological features at the time of rejection. Effective and specific antagonism of thrombin may be useful as an adjunct therapy to complement inhibition for xenograft rejection

Acute Disease↗
PubMed1994

Decreased lumen size after balloon injury despite inhibition of neointimal thickening and antivasospastic treatment.

OBJECTIVE: Both calcium antagonists and angiotensin converting enzyme (ACE) inhibitors are known to diminish the development of intimal thickening after a balloon catheter lesion. It was previously shown that narrowing of carotid artery lumen induced by balloon injury was not influenced by treatment, even though the two ACE inhibitors used inhibited neointimal thickening. The aim of the present study was to include a calcium antagonist as well, in order to investigate whether vasospasm contributes to the persistence of lumen narrowing in ACE inhibitor treated rats after a balloon lesion. METHODS: Six groups of 10 rats were subject to balloon lesion of the left carotid artery. They received spirapril (10 mg.kg-1 x d-1) or isradipine (30 or 100 mg.kg-1 x d-1) or both, given throughout the study in the food. Controls received no drug. Neointimal thickening was measured histologically two weeks after injury. The cross sectional carotid lumen area was measured in vivo by nuclear magnetic resonance imaging, both before and two weeks after balloon injury, and also postmortem by histological techniques. RESULTS: Two weeks after injury, the lumen area of the left carotid artery was significantly reduced following balloon injury, as measured by both techniques. Treatment did not modify the stenosis process as assessed by either method for measuring lumen size. Neointimal thickening, however, was inhibited by between 4% (low dose isradipine) and 59% (combined spirapril + high dose isradipine) in the various treatment groups. CONCLUSIONS: Since calcium antagonist treatment was not able to influence the reduction of lumen size, it is unlikely that the narrowing is due to reversible spasm of the carotid artery in the first two weeks after inducing a balloon lesion. Alternatively, chronic vasospasm of neointimal smooth muscle might not be very sensitive to calcium antagonists.

Angioplasty, Balloon, Coronary↗
PubMed1993

The effects of two synthetic glycoprotein IIb/IIIa antagonists, Ro 43-8857 and L-700,462, on platelet aggregation and bleeding in guinea-pigs and dogs: evidence that Ro 43-8857 is orally active.

In vitro platelet aggregation studies in whole blood were used to define the species-specificity profile of two synthetic GP-IIb/IIIa antagonists, Ro 43-8857 and L-700,462. Aggregation of rhesus monkey platelets was inhibited with a similar potency to human platelets, whereas both compounds were poor antagonists in mini-pig, rabbit or hamster blood. Compared to human platelets, Ro 43-8857 was 2-3-fold less active as an inhibitor of dog and guinea-pig platelet aggregation, whereas L-700,462 was, respectively, 4- and 14-fold less active in these species. In vivo investigations with these two compounds were performed in anesthetized guinea-pigs and conscious dogs, with bleeding times measured on small mesenteric arteries or on the inner jowl respectively. Ex vivo ADP-induced whole blood platelet aggregation was completely inhibited in guinea-pigs by Ro 43-8857 following intravenous administration of 0.1 mg/kg and intraduodenal administration of 3 mg/kg, with a duration of action exceeding 5 hours. Mesenteric bleeding times were prolonged by Ro 43-8857 only at doses causing supra-maximal inhibition of aggregation, suggesting these two effects could be partially dissociated. L-700,462 (3 mg/kg i.v.) was shorter acting than Ro 43-8857 in guinea-pigs (duration approximately 1 hour) and the anti-aggregatory effect was accompanied by mesenteric bleeding time prolongations. In conscious dogs, ex vivo aggregation was inhibited to approximately 80% by Ro 43-8857 (0.3 mg/kg i.v. or 10 mg/kg p.o.) and L-700,462 (1 mg/kg i.v.). However, bleeding time prolongations accompanied these anti-aggregatory effects with both compounds. In conclusion, we have shown clear differences between two synthetic GP-IIb/IIIa antagonists, both in terms of their species-specificity in vitro and in terms of their in vivo profile, and in particular the propensity to promote bleeding from mesenteric arteries in guinea-pigs. However, the ability of Ro 43-8857 to discriminate between anti-aggregatory and bleeding effects was not evident when the bleeding time measurements were performed on the dog jowl. This suggests that the species and/or vessels on which the bleeding time is performed, is also an important consideration when characterizing and comparing anti-platelet compounds, even with drugs acting via the same mechanism. These results are relevant for the future design of in vivo animal experiments to characterize this new class of compounds and in the interpretation of the data obtained to the clinical situation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetates↗
PubMed1993

Platelet aggregation and fibrinogen binding in human, rhesus monkey, guinea-pig, hamster and rat blood: activation by ADP and a thrombin receptor peptide and inhibition by glycoprotein IIb/IIIa antagonists.

Platelet aggregation and fibrinogen binding in whole blood, induced either by ADP or by a 14 amino acid peptide mimicking an N-terminal region of the platelet thrombin receptor (TRP, thrombin receptor activating peptide), have been studied with blood from different species. Aggregation was assessed by counting the number of single platelets in blood before und after addition of the agonist with an automated cell counter. Both ADP (0.02-0.5 microM) and TRP (1-10 microM) were found to be potent agonists of platelet aggregation in human, rhesus monkey and guinea-pig blood, causing a near-maximal aggregatory response within 2 min of agonist addition. In contrast, hamster and rat platelets were much less responsive to both ADP and TRP in terms of the whole blood aggregation. Echistatin, RGDW and a synthetic glycoprotein (GP) IIb/IIIa antagonist, Ro 43-8857, inhibited fibrinogen binding to purified immobilized human GP-IIb/IIIa with IC50's of 1.6, 88 and 11.4 nM, respectively. In whole human blood, the respective IC50's (as determined by flow cytometric analysis of platelet fibrinogen binding) were 4.4, 1700 and 29.5 nM. The affinities of these three compounds for inhibiting fibrinogen binding in whole blood from rhesus monkeys and guinea-pigs were similar to the affinities for human platelets, but with rat blood echistatin, RGDW and Ro 43-8857 were all around 100-fold less potent. Ro 43-8857 was a potent inhibitor of ADP- or TRP-induced platelet aggregation in human, rhesus monkey and guinea-pig whole blood (IC50 of 69-320 nM) but was much less active in hamster blood.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1993

Therapeutic potential of potassium channel openers in peripheral vascular disease and asthma.

Potassium channel opener's (KCOs) were originally thought of as nonselective smooth muscle relaxants. However, recent investigations in animal models of both peripheral vascular disease (PVD) and asthma have revealed interesting effects of these drugs as unexpectedly low doses. Hemodynamically, KCOs are interesting in PVD since they have little effect on blood supply to normally perfused skeletal muscle, but enhance perfusion to chronically ligated ischemic tissue. In animal PVD models, SDZ PCO-400 and cromakalim have been shown to improve recovery of muscle energy stores from ischemia or to preserve performance under conditions of ischemic contracture. Beneficial effects in rat PVD models were manifest at doses below those affecting systemic blood pressure and may be attributable to a selective dilatation of collateral vessels. With regard to the airways, the apparent efficacy of KCOs as antiasthmatic drugs seems not to be attributable solely to their bronchodilator activity. Although KCOs elicit no antiinflammatory effect in animal models, studies with SDZ PCO-400 in guinea pigs sensitized to antigen or treated with immune complexes have revealed that expression of airway hyperreactivity is significantly inhibited at drug doses exhibiting only modest bronchodilator activity. At least part of this action can be attributed to inhibition at the level of neural innervation of the airways, possibly through attenuation of nonadrenergic noncholinergic (NANC) transmission.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Synthetic low-molecular weight thrombin inhibitors: molecular design and pharmacological profile.

Thrombin is a multifunctional protein: in addition to its role in coagulation, thrombin has important biological effects on platelets, endothelial and smooth muscle cells, leukocytes, the heart and neurones. A detailed understanding of the structure of thrombin, of related serine proteases and of enzyme-inhibitor complexes has aided in the discovery of potent and selective new inhibitor molecules. Some of these novel thrombin inhibitors are active when administered orally and have shown remarkable efficacy as antithrombotic agents in animal models, offering a greater therapeutic potential than presently available drugs. This potential extends also to non-thrombotic indications where thrombin may be involved, namely inflammation, cancer and neurodegenerative diseases. The recent identification of specific thrombin receptors on different cells provides an alternative strategy for inhibiting thrombin's cellular actions, without necessarily compromising its role in haemostasis. In this review, Carlo Tapparelli and colleagues present a comprehensive update of these recent developments in the field of thrombin biology and pharmacology suggesting a new era of therapeutic drugs is on the horizon.

Animals↗
PubMed1993

Spirapril and cilazapril inhibit neointimal lesion development but cause no detectable inhibition of lumen narrowing after carotid artery balloon catheter injury in the rat.

Five groups of 12 rats were subject to balloon lesion of the left carotid artery and neointimal thickening was measured histologically 2 weeks after injury. Rat groups received either spirapril (3, 10 or 30 mg/kg/day, administered throughout the study in the food), cilazapril (10 mg/kg/day) or placebo. Spirapril caused a dose-dependent inhibition of the neointimal thickening of the rat carotid artery. The degree of inhibition with 10 mg/kg/d spirapril and cilazapril was similar (-44% and -42% respectively). The carotid lumen area was measured in vivo by nuclear magnetic resonance (NMR) imaging both before and 2 weeks after balloon injury and also postmortem by histological techniques. Two weeks after injury, the lumen area of the left carotid artery was significantly reduced following balloon injury, as measured by both techniques. Treatment did not detectably modify this stenosis process despite the use of two independent methods for assessing lumen size, even though neointimal thickening was strongly attenuated by both angiotensin converting enzyme inhibitors. This dissociation between inhibition of neointimal lesion development and decrease of lumen size provides a new view of the role of angiotensin converting enzyme inhibitors in vascular damage situations. Our results suggest that the focus, particularly in clinical studies, on lumen size, may mean that potentially beneficial effects of these drugs on other parts of the vascular wall be overlooked.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Analysis of fine-needle aspirates for HPV by PCR may be useful in diagnosis of metastatic gynecologic malignancies.

Human papillomavirus (HPV) DNA has been shown by molecular hybridization studies to persist in both recurrent and metastatic disease in tumors of the female genital tract. We report here the use of the polymerase chain reaction to identify HPV DNA in material from fine-needle aspirates (FNA) of recurrent or metastatic lesions to document the primary malignancy arising in the lower genital tract. Fine-needle aspirates of suspected recurrent or metastatic tumors were obtained from nine patients with carcinoma of the lower genital tract and five patients with malignancies that have not been associated with HPV. DNA was extracted from the FNA and tissue block, when available, and amplified with HPV 6, HPV 16, and HPV 18 specific primers. In eight of the nine tumors from the lower genital tract, HPV DNA was identified in both the primary and metastatic lesions. In every case the HPV genotype was identical. One cervical carcinoma and five non-HPV associated tumors were negative for papillomavirus DNA. This study demonstrates that molecular hybridization techniques can be useful in identifying the source of a metastasis and have the potential to diagnose the presence of metastatic disease by detecting HPV DNA even when the cytologic criteria are equivocal.

Biopsy, Needle↗
PubMed1991

New developments in cardiovascular magnetic resonance imaging and spectroscopy.

Methodological improvements in nuclear magnetic resonance (NMR) imaging and spectroscopy have enabled the application of these techniques to the study of functional or dynamic biological processes. Because the techniques are non-invasive, repeated measurements can be made in the same animal at different time points, allowing disease progression and regression to be followed during drug therapy. In this review, Markus Rudin, Wolfgang Zierhut, André Sauter and Nigel Cook illustrate this concept by the use of NMR to evaluate cardiovascular function in the rat in various physiological and pathological situations. The possibility of using NMR to perform similar studies in both animals and humans should lead to the design of preclinical models with an improved clinical predictability.

Animals↗
PubMed1990

Angiotensin II can regulate gene expression by the AP-1 binding sequence via a protein kinase C-dependent pathway.

An expression vector containing three copies of the AP-1 binding element (TRE) upstream of a thymidine kinase promotor which controlled the expression of the chloramphenicol acetyl transferase (CAT) gene was transiently transfected into vascular smooth muscle (VSM) cells and a human hepatocarcinoma cell line, Hep G2. Twelve hours of angiotensin (Ang) II exposure stimulated significantly CAT expression by 3.4 fold and 2.7 fold in Hep G2 and VSM cells, respectively. AngII had no effect on CAT expression of a control vector. This AngII-induced stimulation was attenuated significantly by an AngII receptor antagonist, Sar1 Ile8 AngII, and abolished completely by a PKC inhibitor, staurosporine. Our data suggest that the TRE plays a crucial role in AngII-induced gene expression that is mediated by PKC. We concluded that TRE is one of the AngII-responsive elements.

Alkaloids↗
PubMed1990

Fibrinogen as a major risk factor in cardiovascular disease.

Evidence has accumulated over the past ten years to implicate elevated plasma fibrinogen levels in cardiovascular disorders such as ischaemic heart disease, stroke and peripheral vascular disease. At a cellular level, insight has been gained into the molecular regulation of fibrinogen biosynthesis and the mechanisms through which fibrinogen may be involved in these disease processes. Here, Nigel Cook and David Ubben summarize this evidence and consider the possibilities for novel therapies targeted at fibrinogen. A variety of structurally diverse pharmacological agents, many of which were developed for their effects on plasma lipids, have serendipitously been found to lower plasma fibrinogen levels.

Animals↗
PubMed1989

Effect of some potassium channel blockers on contractile responses of the rabbit aorta.

Contractile responses of rabbit aortic rings to KCl or angiotensin II (AII) were investigated in the presence of five compounds known to block K+ channels. Tetraethylammonium (3 and 10 mM), 3,4-diaminopyridine (0.3 and 1 mM), and a charybdotoxin-like toxin from the venom of the scorpion Leiurus quinquestriatus hebraeus (3-30 ng ml-1), augmented contractions due to low but not high KCl concentrations and increased the maximum tissue response to AII. This latter augmentation could be reduced (but not fully inhibited) by the calcium entry blocker PN 200-100 (100 nM), implicating an influx of extracellular calcium in the response. 3,4-Diaminopyridine (1 mM) and the scorpion toxin additionally increased the resting tension of the aortic rings, an effect not observed with tetraethylammonium at concentrations up to 10 mM. Apamin and toxin I (both 1 microM) failed to modify KCl or AII contractions of the aorta. In all cases, aortic rings denuded of endothelium gave essentially the same results as rings having an intact endothelium. These results are discussed in relation to the possible types of K+ channels involved in modulating the tone of this blood vessel during hormonal stimulation.

4-Aminopyridine↗
PubMed1989

In vitro and in vivo comparison of two K+ channel openers, diazoxide and cromakalim, and their inhibition by glibenclamide.

Diazoxide caused an increase in 86Rb+ efflux from the rat aorta and portal vein and inhibited spontaneous activity of the latter at concentrations 100 times higher than the K+ channel opener cromakalim. In the rabbit aorta both drugs inhibited vasoconstrictor responses to angiotensin II, noradrenaline and low concentrations (less than or equal to 30 mM) of KCl in a similar manner, the antivasoconstrictor activities being abolished in vessels depolarized with greater than or equal to 35 mM K+. In vivo cromakalim was about 100 times more potent than diazoxide at lowering blood pressure in rats. Diazoxide (30 mg/kg) caused a more than 2-fold increase in plasma glucose in rats and prevented any return toward base line within 1.5 hr after a glucose load. Cromakalim had minimal effects upon glucose homeostasis at equihypotensive doses. Glibenclamide, a potent blocker of ATP-dependent K+ channels, inhibited the stimulation by cromakalim and diazoxide of 86Rb+ efflux from the portal vein and aorta (IC50 approximately 0.1 microM), antagonized their vasorelaxant effects in vitro and in vivo (20-30 mg/kg i.v.) and reversed the diazoxide-induced changes in plasma glucose and insulin levels. These results provide evidence that diazoxide, like cromakalim, is able to open 86Rb+-permeable K+ channels in vascular smooth muscle. This action is likely to be responsible for the in vitro and in vivo vasodilator activity of these two drugs. However, there would seem to be pharmacological differences between the K+ channels affected by these drugs in vascular smooth muscle and the (ATP-sensitive) K+ channels of pancreatic beta-cells, which are thought to be responsible for the effects of diazoxide on plasma glucose.

Angiotensin II↗