Biomedical subjects
Publications and source records attributed to S A Mousa.
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Previous reports documented the inhibitory efficacy of different doses of aspirin on arachidonic acid (AA)-induced platelet aggregation, however, the sensitivity of platelets toward other agonists as well as the effects of aspirin on platelet and plasma plasminogen activator inhibitor-1 (PAI-1) release and levels were not investigated. Hence, the present study was undertaken to investigate the effect and duration of action of a single oral dose (650 mg) of aspirin on human platelet functions (n = 34, normal healthy male and female volunteers) including aggregation, fibrinogen binding and PAI-1 release, and on the plasma level of PAI-1. Aspirin demonstrated a rapid onset of action (at 2 h after ingestion) in specifically inhibiting ex vivo AA-mediated functions including (a) fibrinogen binding to gel-purified platelets, (b) platelet aggregation, and (c) platelet PAI-1 release. A peak reduction of plasma PAI-1 level at 2 h was demonstrated as well. The effect of aspirin on the ex vivo AA-mediated effects (a-c) was shown to last for up to 4 days. However, aspirin treatment resulted in a rebound effect in platelet function (a-c) to other platelet agonists such as adenosine diphosphate or the combination of agonists including adenosine diphosphate, epinephrine, and AA. In conclusion, a single oral dose of aspirin has long-acting effects on AA-induced platelet activation and reduces plasma levels of PAI-1 as well.(ABSTRACT TRUNCATED AT 250 WORDS)
The present study was undertaken to define the platelet GPIIb/IIIa affinity and specificity of DMP728, the cyclic [(D-2-aminobutyrate-N-methyl-L-arginyl-glycyl-L-aspartyl)-3-aminomethyl- benzoic acid] methane sulfonate. DMP728 demonstrated similar potency (IC50 = 0.046 +/- 0.002 microM) in inhibiting human platelet aggregation induced by various agonists or combination of agonists as assessed either by light transmittance aggregometry or impedance techniques. Similarly, DMP728 inhibited (IC50 = 2.3 +/- 0.8 nM) with equipotency in inhibiting 125I-fibrinogen binding to human gel-purified platelets regardless of the agonist used. In purified human GPIIb/IIIa ELISA, DMP728 demonstrated a competitive high affinity binding (Ki = 0.4 nM). Additionally, a high binding affinity (Kd = 0.1 nM) of 3H-DMP728 was demonstrated in human platelets. Furthermore, a platelet deaggregatory efficacy was shown. DMP728 demonstrated a high degree of specificity for platelet GPIIb/IIIa (alpha 2/beta 3) as compared to other integrins on endothelial cells (vitronectin receptors), platelets GPIb/1X, alpha v/beta 3, and other integrins on leukocytes or nonintegrin-related systems. In conclusion, DMP728 is a novel antiplatelet agent with high affinity and specificity for platelet GPIIb/IIIa.
Methods have recently been developed to present vast libraries of random peptides on the surface of filamentous phage. To introduce a degree of conformational constraint into random peptides, a library of hexapeptides flanked by cysteine residues (capable of forming cyclic disulfides) was constructed. This library was screened using the platelet glycoprotein, IIb/IIIa, which mediates the aggregation of platelets through binding of fibrinogen. A variety of peptides containing the sequence Arg-Gly-Asp or Lys-Gly-Asp were discovered and synthesized. The cyclic, disulfide-bonded forms of the peptides bound IIb/IIIa with dissociation constants in the nanomolar range, while reduced forms or an analogue in which Ser replaced the Cys residues bound considerably less tightly. These results demonstrate the feasibility for introducing conformational constraints into random peptide libraries and also demonstrates the potential for using phage peptide libraries to discover pharmacologically active lead compounds.
Since thrombin plays an important role in platelet-mediated arterial thrombosis, we have examined the antiplatelet activity of a synthetic thrombin inhibitor, DuP 714 (Ac-(D)Phe-Pro-boroArg), in comparison with that of the naturally occurring inhibitor hirudin. Hirudin was slightly more potent than DuP 714 in inhibiting thrombin-induced aggregation in washed human platelets (IC50s of 72 nM and 150 nM, respectively) and in inhibiting the secretion of plasminogen activator inhibitor-I from human platelets (IC50s of 300 nM and 900 nM, respectively). In contrast, DuP 714 was more potent than hirudin in inhibiting thrombin-induced [125I]fibrinogen binding to gel purified platelets, and in inhibiting thrombin-induced intracellular calcium mobilization in washed platelets. These results indicate that the tripeptide DuP 714 has comparable antiplatelet activity to the 65 amino acid hirudin. We conclude that DuP 714 may have clinical utility in the prevention of platelet-dependent, arterial thrombotic processes.
The efficacy and safety of deferoxamine conjugated to hydroxyethyl starch (HES-DFO) was evaluated in an in vitro rat cardiac membrane lipid peroxidation (CMLP) assay and in a swine model of regional myocardial ischemia/reperfusion injury in comparison to DFO. The rat CMLP results demonstrate that HES-DFO is at least as potent as DFO (IC50 = 10 and 13 microM, respectively). HES-DFO given intravenously (i.v.) at the equivalence of 25 mg/kg and 100 mg/kg DFO in a swine model of regional myocardial ischemia [20-min left anterior descending coronary artery (LAD) occlusion followed by 60-min reperfusion] showed no significant changes in hemodynamics as compared with DFO at 25 mg/kg i.v. In addition, HES-DFO was at least as potent as DFO with regard to recovery of regional segment shortening function (%SS). Furthermore, both HES-DFO and DFO significantly reduced tissue water content (edema) in the area at risk (AAR). We conclude that conjugation of DFO to HES improves the safety without any interference in the efficacy of DFO.
This study was designed to determine the redistribution potential for technetium-99m (99mTc)-hexakis-2-methoxy isobutyl isonitrile (99mTc-Sestamibi) as compared to thallium-201 (201Tl) in a transiently ischemic swine heart model. The left anterior descending coronary artery (LAD) was totally occluded for 10 min. One minute prior to the release of the LAD, 99mTc-Sestamibi, 201Tl and a set of 95Nb-radiolabeled microspheres (15 microns) were injected. A second set of 51Cr-radiolabeled microspheres was injected prior to sacrifice in order to document reflow. Animals were sacrificed at different times post-LAD release (ranging from 1 min to 4 h). The left ventricle was sectioned into 0.2- to 0.5-gram pieces for the gamma spectroscopic counting of the 99mTc-Sestamibi, 201Tl and radiolabeled microspheres. Linear regression analysis of radiotracer localization versus microsphere-determined regional myocardial blood flow (rMBF) demonstrates an initial slight filling in of 99mTc-Sestamibi into transiently ischemic zones, with subsequent stable kinetics up to 4 h (i.e., it does not further redistribute). In comparison, the ischemic to normal ratios for 201Tl activity increase progressively in a time-dependent manner. These differences between 99mTc-Sestamibi and 201Tl might be explained on the basis of their blood clearance kinetics and/or their net clearance from normal and ischemic zones of the heart. It is concluded that 99mTc-Sestamibi is a stable and reliable indicator for rMBF over time, and that the lack of normalization of 99mTc-Sestamibi into transient ischemic zones will necessitate two separate injections for differentiation between ischemia and persistent defects.
The effect of different beta-adrenoceptor blockers on free radical-mediated cardiac membrane lipid peroxidation (CMLP) was compared to their beta-blocking potency (pA2). CMLP was determined by the measurement of malondialdehyde (MDA) formation in rat cardiac membrane homogenates exposed to a free radical generating system (FeCL3/ADP/DHF) in the presence or absence of the beta-adrenoceptor blockers (1-1,000 microM). beta-adrenoceptor blocking potency (pA2) was determined using guinea pig right atria stimulated with isoproterenol. The catechol containing beta-blocker (DCC-10255) was shown to be a potent inhibitor of CMLP via an iron-dependent mechanism. On the other hand, the non-catechol beta-adrenoceptor blocker, timolol, was shown to be a weak inhibitor of CMLP. Furthermore, dl- and d-propranolol were active and equipotent though less potent than DCC-10255 in inhibiting CMLP. The myocardial cytoprotective efficacy for catechol and non-catechol beta-adrenoceptor blockers was evaluated in an isolated rat myocyte model. It was demonstrated that catechol-containing agents with either strong or weak beta-adrenoceptor blockade possess a relatively potent in vitro antioxidant and myocardial cytoprotective efficacy against free radical mediated CMLP and myocyte injury, respectively. It is concluded that the inhibition of CMLP by beta-adrenoceptor blockers is independent of their beta-adrenoceptor blockade.
The efficacy and specificity of a novel synthetic thrombin inhibitor, DuP 714, on thrombin-induced elevation of cytoplasmic calcium, fibrinogen binding and aggregation in human platelets were examined. Thrombin (0.5 U/ml) stimulated an increase in [125I]fibrinogen binding in gel-filtered platelets which was blocked by DuP 714 with an IC50 value of 2 nM. Thrombin (1 U/ml)-induced elevation of intracellular [Ca2+]i was also blocked by DuP 714 with an IC50 value of 67 nM. A much higher concentration of thrombin (25 U/ml) was used to stimulate aggregation with heparinized platelet-rich plasma. Under these conditions, micromolar concentrations of DuP 714 were needed to inhibit thrombin. In all of these preparations, DuP 714 at concentrations as high as 10(-5) M had no intrinsic effects and did not affect the responses induced by arachidonate, ADP, collagen, epinephrine, vasopressin and serotonin. These data indicate that DuP 714 is a potent and specific thrombin inhibitor capable of arresting the actions of thrombin on human fibrin formation and platelet aggregation and secretion. It may serve as a potential antithrombotic agent for various forms of thrombotic disorders.
The monocationic 99Tcm-hexakis-2-methoxy-2-methyl propyl isonitrile (99Tcm-sestamibi) is a myocardial perfusion marker with potential clinical value in the diagnosis of ischaemic heart disease. The kinetics of this compound in experimental myocardial infarction in rabbits was compared to the distributions of 111In-antimyosin Fab and 201Tl at 24 h of persistent left anterior descending (LAD) coronary artery occlusion. The maximum uptake of 111In-antimyosin in the infarct was as high as 0.34% injected dose per gram (i.d. g-1), whereas normal myocardial activity was only 0.045% i.d. g-1. Maximal 201Tl and 99Tcm-sestamibi uptakes in normal myocardium were 0.16 and 0.14% i.d. g-1, respectively. Because of their faster blood clearances, 99Tcm-sestamibi and 201Tl were able to delineate regions of radiotracer distribution defects early. 111In-antimyosin required a longer circulation time for in vivo infarct visualization because of slower blood clearance. The data also demonstrated that in persistent LAD occlusion infarction in rabbits, the inverse distribution of sestamibi and 201Tl relative to antimyosin localization (indicator of myocyte necrosis) is not significantly different (I/N sestamibi = 0.213 I/N(AM) + 115.7, r = 0.91, and I/N(201Tl) = 0.181 I/N(AM) + 114.4, r = 0.89).
This study was designed to assess the sensitivity of the monocationic 99mTc-hexakis-2-methoxy, 2-methylpropylisonitrile (99mTc-sestamibi) as compared to 201T1 in the detection of regional myocardial blood flow deficits in dogs with different degrees of stenosis with or without dipyridamole. Regional myocardial distribution of 99mTc-sestamibi and 201Tl was determined in mongrel dogs under different levels of left arterial descending coronary artery (LAD) stenosis (30-45, 60-70 and 100% flow reduction) as monitored with electromagnetic flow probes and radiolabeled microspheres. Both 99mTc-sestamibi and 201Tl distribute in direct proportion to blood flow at all levels of stenosis (r2 = 0.90-0.99). Quantitatively, both tracers underestimate the resting flow stenosis. The regional myocardial distribution for both 99mTc and 201Tl was also determined in subcritically stenosed mongrel dogs. This was produced by placing a balloon cuff around the LAD, infusing dipyridamole to peak hyperemic flow and immediately stenosing the LAD to basal flow. Stenosed to normal zone flow ratios were 0.68 +/- 0.01 compared to 99mTc and 201Tl ratios of 0.73 +/- 0.04 and 0.80 +/- 0.05, respectively. These data suggest that 99mTc is at least as sensitive as 201Tl in the detection of different degrees of critical and subcritical coronary artery stenosis.
This study was undertaken to assess the potential effects of drugs commonly used in the cardiac care unit (CCU) as well as other pharmacological interventions on the biodistribution of 99mTc-hexakis-2-methoxy-2-methylpropyl isonitrile, 99mTc-Sestamibi. 99mTc-Sestamibi was administered i.v. into pentobarbital anesthetized guinea pigs pretreated with either saline (control), verapamil (0.1 mg/kg), digoxin (0.2 mg/kg), propranalol (1 mg/kg), dipyridamole (1.2 mg/kg). The results showed that none of the above interventions decreased the myocardial biodistribution of 99mTc-Sestamibi. On the other hand, digoxin, propranalol and dipyridamole produced an increase in the myocardial uptake of 99mTc-Sestamibi. Furthermore, pretreatment with the ligand which is being used in the formulation of the kit, copper tetrakis-2-methoxy-2-methylpropyl isonitrile (Cu[MIBI]4) at doses ranging from 0.1 to 2.5 mg/kg did not interfere with the biodistribution of 99mTc-Sestamibi in guinea pig. An additional study was carried out in swine to determine the effect of dipyridamole (0.4 mg/kg) on the regional myocardial distribution of 99mTc-Sestamibi in relation to regional myocardial blood flow (microspheres-determined). This study clearly documented a direct relationship between regional myocardial blood flow and the myocardial distribution of 99mTc-Sestamibi (i.e. for each increase or decrease in blood flow there is a parallel increase or decrease in myocardial 99mTc-Sestamibi distribution). These studies indicated that any of the above drugs could be used in the CCU while imaging with 99mTc-Sestamibi.
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The purpose of the present study is to determine the myocardial cytoprotective efficacy of azapropazone (AZA) on regional myocardial function in anesthetized swine model of regional myocardial ischemia/reperfusion injury. AZA was administered (100 mg/kg, i.v.) 15 minutes prior to reflow. The left anterior descending (LAD) coronary artery occlusion was maintained for a total of 30 minutes and then reperfused for 120 minutes. The effects of AZA on regional segmental shortening (% SS) as well as on neutrophil migration were examined in the (proximal) central and border (distal) zones within the area at risk (AAR). AZA reduced the incidence of myocardial fibrillation which occurred in some animals during the LAD occlusion/reperfusion periods. AZA produced a significant recovery of left ventricular segmental shortening (% SS) in the border, but not in the central zones within the AAR. No significant differences in the hemodynamic parameters were observed between the AZA (n = 14) and the saline-treated (n = 17) groups. AZA produced a significant inhibition of neutrophil migration (as evident from the decrease in myeloperoxidase activity) into epi- and endocardium central and border zones within the AAR. It is concluded that AZA may elicit its cardioprotection in moderately but not in severely injured myocardium by inhibiting the neutrophil migration.
Nicotine stimulates the secretion of catecholamines from sympathetic nerve endings and adrenal medulla by acting on peripheral nicotinic cholinergic receptors. Nicotine is also a potent stimulant in the central nervous system but the significance of nicotinic receptors in brain in mediating cardiovascular and sympathoadrenal responses to nicotine is unclear. The responses of resting plasma catecholamines, blood pressure and heart rate were compared in rats receiving nicotine, administered either systemically or intracerebroventricularly (i.c.v.). Sympathoadrenal stress responses were also studied in rats rendered tolerant to nicotine from repeated systemic or intraventricular injections. Nicotine, given either intraventricularly or systemically, produced dose-related increases in the concentration of epinephrine in plasma. Little effect on norepinephrine in plasma was observed with nicotine given intraventricularly, indicating predominant stimulation of adrenomedullary pathways. In contrast, nicotine, given systemically, produced comparable increases in both epinephrine and norepinephrine. Blood pressure increased and heart rate fell in response to either intraventricular or systemic administration of nicotine. Rats exhibited tolerance to nicotine 24 hr after a single intraventricular injection; however, tolerance was not detected with systemically injected nicotine unless the injections were given at least every 30 min. Whereas rats rendered tolerant to systemic administration of nicotine were cross-tolerant to stress, with respect to sympathoadrenal stimulation, cross-tolerance with stress was not detected in rats treated with nicotine repeatedly by the intraventricular route. These results indicate that nicotinic receptors in brain modulate the central sympathetic outflow and adapt readily to nicotine stimulation with prolonged tolerance, but are probably not involved in sympathoadrenal stress responses. Peripheral nicotinic receptors, regulating sympathoadrenal secretion of catecholamines, displayed much shorter-lasting tolerance.
This study was designed to assess the relationship between the distribution of the monocationic 99mTc-hexakis-2-methoxy, 2-methylpropylisonitrile (99mTc-sestamibi) and regional myocardial blood flow (RMBF) in swine. The left anterior descending coronary artery (LAD) was totally occluded and dipyridamole (0.4 mg/kg) was intravenously infused over 4 minutes. 99mTc-sestamibi and 201Tl were coinjected intravenously and a set of microspheres (15 microns) labelled with 113Sn or 55Nb was injected via a left atrial cannula. Animals were put to death at different times after injection of 99mTc-sestamibi/201Tl and the left ventricle was sectioned for gamma spectroscopy. Regression analysis of regional myocardial distribution of 99mTc-sestamibi or 201Tl versus microsphere-determined RMBF demonstrated a linear relationship with flow up to 2.5 ml/min/gm. The myocardial uptake for both 99mTc-sestamibi and 201Tl at higher flow levels was shown not to follow a linear relationship to microsphere-determined RMBF. The first-pass myocardial extraction fractions (%EF) of 99mTc-sestamibi and 201Tl in dogs were 65.5 +/- 2.5% and 82 +/- 3%, respectively (p less than 0.001), at resting flow. At flow levels above the resting flow, a significant decrease in the first-pass extraction fraction for both tracers was shown. At hyperemic flow levels (two to three times the resting flow), the %EF for both tracers are not significantly different. These data provide a basic validation for the utility of 99mTc-sestamibi as a reliable myocardial perfusion imaging agent.
1. The purpose of this study was to determine the in vivo inhibitory efficacy of azapropazone on neutrophil migration. The effects of azapropazone given at a dose of 100 mg kg-1 i.v. every 2 h on the neutrophil migration into skin inflammation sites (blister fluid) as well as into an autologous serum (+/- chemoattractant) placed above the blister surface (2nd chamber) were determined. 2. Azapropazone treatment schedule maintained blood levels at 70-100 micrograms ml-1 throughout the time course (360 min) of the experiment. 3. Azapropazone significantly inhibited (48 +/- 6%) neutrophil migration into the blister fluid (as evident from the decrease in myeloperoxidase activity). 4. Azapropazone significantly inhibited the neutrophil migration into the autologous serum either with (65 +/- 5%) or (35 +/- 6%) without the chemoattractant, formyl-methionyl-leucyl-phenylalanine (FMLP). The chemoattractant, FMLP, markedly increased neutrophil migration into the autologous serum by approximately 1.5 to 2 times the non-FMLP treated group. Azapropazone was more efficacious in inhibiting the neutrophil migration in the presence of FMLP than in its absence. 5. We conclude that azapropazone is an effective inhibitor of neutrophil migration into topically inflamed sites in anaesthetized swine.
1. The purpose of the present study was to determine the myocardial cytoprotective efficacy of azapropazone (AZA) and its potential site of action on neutrophil infiltration into reperfused/ischaemic myocardium with or without in vivo activation of neutrophils in rabbits. 2. AZA, 100 mg kg-1, was administered i.v. 10 min after occlusion of the left circumflex (LCX) artery in rabbits with and without pretreatment with phorbol myristate acetate ester (PMA). The LCX occlusion was then released at 10 min after AZA administration. Haemodynamic parameters (heart rate, LV pressure, mean arterial blood pressure and dp/dt) were monitored throughout the experiment. After 60 min reperfusion, the area at risk was delineated and the heart was then excised and divided into epi- and endocardial pieces for analysis of myeloperoxidase activity. 3. AZA inhibited neutrophil infiltration into the reperfused/ischaemic rabbit myocardium with and without PMA treatment. The inhibition of neutrophil infiltration was more apparent in the epicardium than in the endocardium. Additionally, AZA inhibited to a similar extent the in vivo PMA-stimulated neutrophil migration into the epicardium and endocardium area at risk. AZA had no significant effect on the haemodynamic parameters as compared to control. 4. AZA administered in an anaesthetized rabbit model of LCX occlusion/reperfusion resulted in the reduction of infarct size. 5. It is concluded that AZA has significant inhibitory effects on neutrophil migration which might contribute to its myocardial cytoprotective effect.