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A Ahsan

Publications and source records attributed to A Ahsan.

At least 37 records · Page 2Linked to original sources
PubMed1995

Molecular profiling and weight determination of heparins and depolymerized heparins.

The recently proposed calibrant LHN-1 (lot F537; henceforth designated F537), for the molecular weight (MW) determination by high-performance size-exclusion chromatography of heparins, is shown here to have a range too narrow to allow for the accurate MW determination of all low molecular weight heparins (LMWHs). We have recently demonstrated, by this same methodology, that a chemically degraded benzyl ester of unfractionated heparin, heparin mass calibrator (HMC), is a better calibrant. Weight-average MW, number-average MW, peak MW, and dispersity values were calculated with F537, HMC, and by a reference narrow-range-calibration method for various LMWHs and unfractionated heparins. Values for these parameters determined with HMC were not significantly different from those determined by the reference method until the MW of the substance exceeded 15.0 kDa. In contrast, the MW profile obtained with F537 was appreciably different from that obtained by the reference method for samples with MWs > 7.5 kDa. The range exhibited by HMC should allow this calibrant to be used for both LMWHs and unfractionated heparins.

Heparin↗
PubMed1995

Pharmacologic validation of the clinical effects of an optimized low-molecular-weight heparin-reviparin.

Reviparin is a low-molecular-weight heparin (LMWH) prepared by controlled nitrous acid digestion of porcine mucosal heparin. The trade name designation for this agent is Clivarin. This agent has been released in Germany and France for the prophylaxis of deep venous thrombosis (DVT) in surgical patients. This agent is developed utilizing optimized procedures and exhibits a uniform, narrow-molecular-weight distribution in comparison to the other commercially available LMWHs. The specific activity in the anticoagulant assays is approximated to be 32 U/mg whereas the specific activity in terms of anti-Xa units is designated 120 aXa U/mg. Reviparin is capable of producing a dose- and time-dependent antithrombotic effect in animal models of thrombosis. While the ex vivo effects are initially presented at antithrombotically active dosages, this agent has been found to produce antithrombotic effects without any detectable ex vivo actions. This agent is also known to release tissue factor pathway inhibitor (TFPI) after both intravenous (IV) and subcutaneous (SC) administration. Repeated administration of Reviparin produces progressively stronger antithrombotic effects. Similarly, the bleeding as measured by rabbit ear blood loss is also progressively increased. However, the ratio between the dosage producing these effects is quite large. The current studies are designed to provide additional data on the molecular profile using new calibration methods and additional results on the pharmacologic studies in a dose-dependent manner. In particular, the release of TFPI following IV and SC administration in a primate model is described. The effect of repeated administration mimicking the post-surgical prophylaxis of DVT is also reported in terms of any augmentation of the antithrombotic or hemorrhagic effects of these agents.

Animals↗
PubMed1994

Feasibility study of heparin mass calibrator as a GPC calibrator for heparins and low molecular weight heparins.

The proposed European Pharmacopoeial (EP) method for molecular weight determination of low molecular weight heparins (LMWHs) has been shown to have a range which is too narrow to allow for the accurate molecular weight determinations of all LMWHs. We have recently shown that a chemically degraded benzyl ester of unfractionated heparin, ITH-3, is a better calibrator using this methodology. Data is presented here which indicates that this calibrator cannot only be used to determine the molecular weights of LMWHs but also of unfractionated heparins. Therefore, it is now renamed heparin mass calibrator or HMC because of this extension of range. Weight average molecular weight, number average molecular weight, peak molecular weight, and dispersity values were calculated using the HMC calibration and a reference narrow-range 19-calibrator method for various LMWHs and unfractionated heparins. Values for the parameters calculated using the HMC calibration were found not to be significantly different from those of the reference method until the molecular weight exceeded 15.0 kDa. In contrast, the molecular weight profile obtained with the proposed EP method was significantly different from the reference method for samples > 8.0 kDa. The range exhibited by the HMC calibrator should allow it to be used for both LMWHs and unfractionated heparins.

Chromatography, High Pressure Liquid↗
PubMed1994

Use of therapeutic ultrasound in percutaneous coronary angioplasty. Experimental in vitro studies and initial clinical experience.

BACKGROUND: Previous studies have shown the feasibility of peripheral arterial ultrasound angioplasty. METHODS AND RESULTS: In this report, we describe the use of percutaneous therapeutic ultrasound for coronary angioplasty. In vitro, 11 postmortem, atherosclerotically occluded coronary arteries were obtained to assess catheter-delivered ultrasound for arterial recanalization as well as for assessment of the size of particulate debris. Clinically, coronary ultrasound angioplasty was performed in 19 patients (mean age, 56 years) to assess safety and feasibility for the treatment of obstructive coronary atherosclerosis. Three patients with unstable angina and 16 with exercise-induced myocardial ischemia were treated with a prototype 4.6F coronary catheter ultrasound ablation device with a 1.7-mm diameter ball tip. The ultrasound coronary catheter delivered ultrasound energy at 19.5 kHz, with a power output of 16 to 20 W at the transducer. Energy is delivered in a pulsed mode with a 50% duty cycle of 30 milliseconds. Patients were treated for a mean of 493 seconds (range, 130 to 890) with intracoronary ultrasound ablation. All lesions were treated with adjunctive balloon angioplasty. All 11 postmortem coronary occlusions were recanalized, and 99% of the particulates generated were < 10 microns in diameter. We found that after ultrasound, mean (+/- SD) coronary arterial stenosis fell from 80 +/- 12% to 60 +/- 18% (P < .001) and to 26 +/- 11% (P < .001) after adjunctive balloon angioplasty. Mean pressures required to achieve full balloon inflation were 2.7 atm (range, 1 to 5.5) with a median of 3.0-mm balloon size (2.5 to 3.5). No ultrasound-related complications were identified. CONCLUSIONS: Intracoronary ultrasound plaque ablation appears to be safe. Our findings suggest that catheter-delivered high-intensity, low-frequency ultrasound may be useful for lesion debulking and enhancing arterial distensibility, allowing balloon dilation at relatively low pressures.

Angioplasty, Balloon, Coronary↗
PubMed1993

Molecular weight profiling of low molecular weight heparins utilizing a heparinase degraded oligosaccharide mixture as a calibrator.

Heparinase degraded heparin fragments (HDHF) are enriched with a UV chromophore and can be utilized as calibrators to determine the molecular weight profile of low molecular weight heparins (LMWH's). In a standard protocol (1), the second to the last peak is assumed to be a hexasaccharide with a molecular weight of 1.8 kDa. All other peak molecular weights in the elution profile are assigned based upon this assumption. In this study, synthetic analogues of heparin with a defined molecular weight have been used to investigate the validity of this assumption. These compounds included a sulfated bis-lactobionic acid amide (2.4 kDa), a pentasaccharide (1.7 kDa), and lactose polysulfate (1.2 kDa). With reference to these internal standards, the second to the last peak of the HDHF mixture was found to elute after the pentasaccharide and close to the lactose polysulfate suggesting that it is a tetrasaccharide. For additional validation, calibration curves were constructed using individual calibrators as the reference method as well as the HDHF method. Several low molecular weight heparins were profiled for their molecular weight using these methods. In comparison to the reference method, the molecular weights obtained with the HDHF method were 25-40% higher. When the results were recalculated assuming the molecular weight of the second to the last peak as 1.2 kDa, the HDHF results compared well with the reference method. Additionally, it is seen that the HDHF method does not identify molecular components greater than 8.0 kDa.

Calibration↗
PubMed1993

Molecular weight and biochemical profile of a chemically modified heparin derivative, Suleparoide.

Recently, a new chemically modified derivative of heparin (Suleparoide, Syntex Laboratories Buenos Aires, Argentina) was introduced for the prophylaxis of thrombosis and treatment of vascular disorders. This agent is claimed to contain a depolymerized, chemically modified, heparin derivative with similar biologic actions as heparan sulfate. To study the pharmacologic profile of this agent, we have defined its molecular weight distribution profile, utilizing a computerized gel permeation chromatographic system equipped with ultraviolet and refractive index detectors. Suleparoide exhibited a normal molecular distribution profile with no contaminants. It exhibited a weight average of 9.3 K DA and an apparent peak MW of 8.0 K DA. Approximately 50% of the molecular components were < 5.0 K DA and 40% > 5.0 K DA. The results from these studies on the mechanisms show that Suleparoide has anticoagulant activity primarily mediated through Heparin Cofactor-II (HC-II) and because of its novel mechanism of action, further investigations on the biochemical profile of Suleparoide are carried out. Global clotting tests such as Activated Partial Thromboplastin Time (APTT), Heptest and Thrombin Time (TT) revealed a concentration dependent effect in all assays. Plasma samples supplemented with Suleparoide exhibited no significant anti-Xa and anti-IIa activities. However, in the HC-II mediated inhibitory assay for IIa, Suleparoide exhibited significant activity. In contrast, the Antithrombin-III (AT-III) mediated inhibition of IIa was much weaker.

Antithrombin III↗
PubMed1993

Biochemical and pharmacologic profile of low molecular weight heparin (LU 47311, Clivarin).

1. Clivarin is a homogeneous LMWH as determined by the data obtained in molecular profiling studies. 2. The limited biochemical studies carried out indicated that this LMWH has a specific potency of 124 anti-Xa IU/mg and a weaker APTT activity of approximately 30 U/mg. 3. Assay-dependent neutralization of the in vitro effects of Clivarin was noted. Protamine preparations at equigravimetric concentrations effectively neutralized the APTT and TT effects; however, Heptest and anti-Xa effects were only partially neutralized. In contrast, heparin's effects were completely neutralized by this agent. 4. PF 4 only partially neutralized the effects of Clivarin. Assay-dependent variations were noted in this study. 5. In comparison to heparin, the hemorrhagic effects of Clivarin were much weaker. 6. Clivarin produced a dosage-dependent antithrombotic action in both the intravenous and subcutaneous studies. This agent also showed sustained activity and better bioavailability characteristics than heparin. 7. Clivarin exhibited a distinct biochemical and pharmacologic profile that may be useful in the optimization of this agent.

Animals↗
PubMed1990

Pharmacologic profile of a low molecular weight heparin (enoxaparin): experimental and clinical validation of the prophylactic antithrombotic effects.

Some 10 low molecular weight heparin products are currently available for commercial use. Enoxaparin and fraxiparin appear to be the most developed low molecular weight heparins. Many well-designed clinical trials have been carried out for different clinical indications with both of these products. As shown in both experimental and clinical settings, the prophylactic antithrombotic efficacy of enoxaparin is distinct from other low molecular weight heparins. Enoxaparin has provided consistently impressive clinical results. Moreover, at comparable dosages, other products have exhibited safety/efficacy profiles different from that of enoxaparin. The clinical performance of each low molecular weight heparin is characteristic of only that particular agent. Besides the commercially available low molecular weight heparin preparations, some 14 other agents are under development at this time. Although each product has similar basic characteristics, their biological actions should be studied carefully. Apart from differences in the physicochemical properties, the pharmacologic actions of these agents may differ significantly. Only results from valid clinical trials will show similarities or differences between the low molecular weight heparins. Other manufacturers should follow the lead of enoxaparin and conduct their own clinical trials on each of their products.

Animals↗
PubMed1989

Transvenous ablation of atrioventricular conduction with a low energy power source.

A power source modified to increase voltage delivery and minimise arcing (for a given energy) was used for transvenous ablation of atrioventricular conduction to control refractory supraventricular arrhythmias in 14 patients. Twelve had atrial fibrillation or flutter, one had atrioventricular nodal reentry tachycardia, and the other had permanent junctional reentry tachycardia. Despite treatment with 5-7 (median 6) antiarrhythmic drugs symptoms had persisted in all the patients. Cathodal discharges of 0.5-39.5 J were delivered to the distal electrode (in one case in parallel with the middle electrode). In all patients shocks produced complete atrioventricular block; this was permanent in eleven (79%). Four patients required a second procedure. In one patient, only a transient atrioventricular block could be produced and catheter ablation with a conventional power source also failed. In the other two atrioventricular conduction was modified such that previously ineffective treatment produced satisfactory control of heart rate. The cumulative energy delivered to those in whom permanent complete heart block resulted ranged from 3.6 to 97.8 (mean 38.3) J with a mean of three shocks (range 1-7) delivered per patient. During follow up of 1-28 (mean 14) months 11 patients remained in complete heart block and free of arrhythmia.

Aged↗
PubMed1986

Selective inhibition of proteolytic enzymes in an in vivo mouse model for experimental metastasis.

Peptide aldehyde transition state analogue inhibitors of serine and cysteine proteases have been used to selectively inhibit proteases for which prior evidence supports a role in tumor cell metastasis. These enzymes include cathepsin B, urokinase plasminogen activator (PA), and thrombin. The inhibition constants of the peptidyl aldehyde inhibitors show that they are highly selective for a particular targeted serine or cysteine protease. The inhibitors are introduced by i.p. injection or by miniosmotic pumps into syngeneic C57BL/6 mice also given injections of B16-F10 melanoma cells, and the number of metastatic foci in the lung was determined. While the injection protocol gave an initially high but changing in vivo concentration of inhibitor over time, the minipump implant gave a constant steady state concentration of inhibitor over 5-7 days. Minipump infusion of leupeptin (acetylleucylleucylargininal), a strong inhibitor of cathepsin B at a steady state plasma concentration 1000-fold greater than its Ki(cathepsin B), gave no significant decrease in lung colonization by the B16 tumor cells. Ep475, a stoichiometric irreversible peptide inhibitor of cathepsin B-like proteases, also did not significantly inhibit metastatic foci formation. Introduction of selective inhibitors of urokinase PA, tert-butyloxycarbonylglutamylglycyl-argininal and H-glutamylglycylargininal at concentrations near its Ki, produced no significant decrease in mouse lung colonization. The selective thrombin inhibitor D-phenylalanylprolylargininal infused to a steady state concentration 100-fold greater than its Ki dramatically increased B16 melanoma colonization of mouse lung. The results indicate that neither secreted cathepsin B-like nor urokinase PA have roles in B16 colonization of mouse lung, while thrombin may have a role in preventing metastasis. These experiments do not eliminate roles for a cathepsin B-like enzyme or urokinase PA in the initial steps of the metastatic process.

Animals↗
PubMed1986

Inhibition of proteolytic enzymes in the in vitro amnion model for basement membrane invasion.

The ability of B16-F10 mouse melanoma cells to cross an amnion basement membrane was determined in the presence of strong inhibitors of both serine and cysteine proteases. The concentrations of inhibitors were at orders of magnitude higher than their Ki values to serine and cysteine proteases implicated in metastasis, thus ensuring a complete inhibition for tumor secreted proteases such as cathepsin B-like proteases, plasminogen activators, and plasmin. Under these conditions of high serine and cysteine protease inhibitor concentrations, no significant decrease in B16-F10 melanoma cell invasion through the amnion was observed. Separate experiments showed that the inhibitors were neither toxic to the cells nor degraded. The results show that neither tumor cell secreted cathepsin B-like proteases nor plasminogen activator have a controlling role in basement membrane crossing in this metastatic model. A possible role for tumor cell membrane proteases in basement membrane invasion, in which the substrates of the protease bind to receptor sites near a membrane associated proteolytic activity, is not eliminated.

Amnion↗
PubMed1983

Transition-state affinity chromatography of trypsin-like proteinases with dipeptidyl argininal ligands.

Dipeptidyl argininal (arginine aldehyde) affinity resins of general formula R-(X-Y-argininal) (where R = resin matrix and X, Y = amino acids of varied structure) are synthesized in a solid-phase procedure in which the dipeptide (-X-Y-) is first attached to the resin, followed by the joining of the Y amino acid to argininal semicarbazone, and decomposition of the semicarbazone in a methanol/acetic acid/formaldehyde reagent. An R-(Gly-Gly-argininal) resin binds urokinase tightly, but does not bind thrombin. However, thrombin binds strongly to R-(Phe-Pro-argininal), whereas urokinase does not bind. Accordingly, the X-Y-argininal ligands selectively bind proteinases of identical primary binding site specificity to arginine, but different secondary site specificity in -X-Y-. The selectivity is due to an amplification of peptide binding specificity caused by the transition-state analog properties of the ligands. While the affinity constants between peptide aldehyde and proteinase approach those of antibody-antigen interactions, the elution with semicarbazide (aldehyde-trapping reagent) buffers easily remove tightly bound proteinases without proteinase inhibitors or denaturation. Conditions for the binding and elution of proteinases, methods of regeneration and other characteristics of the resins are described.

Animals↗