Potent Inhibitor Of Platelet Aggregation Research Articles

Mechanisms of aggregation inhibition by aspirin and nitrate-aspirin prodrugs in human platelets

Aspirin is the mainstay of anti-platelet therapy in the secondary prevention of cardiovascular disease. However, problems with aspirin safety and resistance demand clinical strategies based on multiple pharmacological approaches. Prodrugs of aspirin may offer beneficial effects in terms of gastro-intestinal safety and multiple pharmacological approaches. However, the pharmacological profile of aspirin prodrugs in human platelets has not been completed yet. We aimed to compare the effects of aspirin and prodrugs of aspirin (1-5) on human platelet aggregation stimulated by ADP and collagen and associated receptor expression (GPIIb/IIIa and P-selectin) in platelet-rich plasma (PRP) and washed platelets (WP). As aspirin is released from prodrugs following esterase hydrolysis we studied the expression and activity of butyrylcholineterase (BuChE) and carboxyesterase (CE) in plasma and platelets. The mechanism of prodrug-induced platelet aggregation inhibition was explored by studying the effects of plasma and purified human BuChE on aggregation. Finally, the relative contribution of nitric oxide (NO) bioactivity to nitrate-containing prodrugs of aspirin-induced inhibition of aggregation was determined using 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ,) a selective inhibitor of the soluble guanylyl cyclase. ST0702, 2, a nicotinic acid-aspirin codrug was equipotent with aspirin with respect to inhibition of collagen-induced platelet aggregation. Compound 4, a NO releasing aspirin was the most potent inhibitor of ADP-induced platelet aggregation, an effect partially reversed by ODQ. The platelet inhibitory effects of aspirin prodrugs were time-dependent as the maximal inhibitory effects against collagen-induced aggregation were achieved by aspirin at 2 min, 1 at 5 min and ST0702 at 15 min. The aspirin prodrugs were significantly less potent in WP than in PRP and the reverse was true of aspirin. In the presence of complete BuChE inhibition in PRP, there was almost complete loss of aspirin prodrug, but not aspirin anti-aggregatory activity. Interestingly, CE activity was observed in WP and platelet lysate with pNPA substrate. Accordingly, 1 and ST0702 retained 50% and 100% anti-aggregatory activity at maximal concentrations in WP, which was attenuated in the presence of esterase inhibitor phenylmethylsulphonyl fluoride. The inhibitory effect of aspirin prodrugs in PRP is due to prodrug activation by BuChE. In contrast, the platelet-inhibitory effects of aspirin prodrugs in WP may be mediated through the activity of platelet CE. Compound 4, a NO-containing aspirin prodrug, may exert dual inhibitory effects in platelets. Thus, aspirin prodrugs effectively inhibit human platelet aggregation and as such may be an alternative to conventional aspirin.

S-Nitroso-N-acetyl-D-penicillamine covalently linked to polydimethylsiloxane (SNAP–PDMS) for use as a controlled photoinitiated nitric oxide release polymer

Nitric oxide (NO) plays a critical role in the regulation of a wide variety of physiological processes. It is a potent inhibitor of platelet adhesion and aggregation, inhibits bacterial adhesion and proliferation, is implicated in mediating the inflammatory response toward implanted devices, plays a role in tumor growth and proliferation, and is a neurotransmitter. Herein, we describe the synthesis and NO-release properties of a modified polydimethylsiloxane that contains S-nitroso-N-acetyl-D-penicillamine covalently attached to the cross-linking agent (SNAP–DMS). Light from a C503B-BAN-CY0C0461 light-emitting diode (470 nm) was used as an external trigger to allow precise control over level and duration of NO release ranging from a surface flux of zero to approximately 3.5×10−10 mol cm-2 min-1. SNAP–PDMS films stored in the dark released NO after 297 days, indicating the long-term stability of SNAP–PDMS.

Dietary Spinach Saponin-Enriched Lipophilic Fraction Inhibits Platelet Aggregation and Blood Coagulation

In this study, we investigated the effect of spinach saponin-enriched lipophilic fraction (SSEF) on collagen (10 μg/mL)-stimulated platelet aggregation in vivo. Dietary SSEF dose-dependently inhibited collagen-induced platelet aggregation by decreasing thromboxane A₂ production and intracellular Ca²⁺ agonist activity as an aggregation-inducing autacoidal molecule. In addition, SSEF significantly increased the formation of cyclic AMP and cyclic GMP, intracellular Ca²⁺ antagonists that are aggregation-inhibiting molecules in collagen-stimulated platelets. These results suggest that SSEF is a potent inhibitor of collagen-stimulated platelet aggregation in vivo. Prothrombin time and activated partial thromboplastin time, indicators of blood coagulation, were potently prolonged by dietary SSEF in vivo. These findings suggest that SSEF prolongs the interval time between the conversion of fibrinogen to fibrin. Dietary SSEF also inhibited 0.4 M sucrose-induced hemolysis. Accordingly, our data demonstrate that SSEF might be a useful tool for inhibiting platelet activation and blood coagulation in thrombotic diseases.

Epoprostenol inhibits human platelet-leukocyte mixed conjugate and platelet microparticle formation in whole blood

Circulating platelet-leukocyte mixed conjugates and platelet microparticles are potential markers of inflammation in the atherothrombotic disease. Epoprostenol is a synthetic salt of PGI2 (prostacyclin) clinically used in pulmonary hypertension and transplantation as a potent inhibitor of platelet aggregation. In this study the in vitro effect of this drug was investigated on the interaction of platelets with leukocytes and on markers of leukocyte and platelet activation, including platelet microparticle formation. The analyses were performed by flow cytometry on citrated whole blood collected from healthy subjects and challenged by a mixture of collagen-ADP. Preliminarily, the epoprostenol antiplatelet effect was confirmed by both aggregometry and PFA-100 and by evaluation of intraplatelet VASP phosphorylation. Epoprostenol, at nanomolar concentrations, prevented the formation of platelet mixed conjugates with PMN or monocytes, platelet PAC-1 and P-selectin expression and platelet microparticle generation. The reference drugs PGE1, aspirin and the novel ADP-receptor antagonist, cangrelor, were only effective at micromolar concentrations. No effect of epoprostenol was detected on leukocyte activation markers. Our data suggest a possible additional mechanism of action of epoprostenol in reducing the inflammatory cell contribution to pulmonary hypertension and thrombosis.

Non-conventional hemostatic risk factors for coronary heart disease in individuals with spinal cord injury

Review. In subjects with spinal cord injury (SCI), there is strong evidence for platelet hyperactivity, which may stimulate atherosclerosis and coronary heart disease (CHD). The literature was reviewed. Individuals with SCI develop premature CHD. In addition to the conventional risk factors associated with CHD, there are pathologic hematological factors involved in atherogenesis that are similar to those that have been demonstrated in individuals with diabetes, and these hematological factors might affect individuals with SCI. One such hematological factor, platelet aggregation, is essential for the development of CHD, which results from thrombus formation in the coronary vasculature. Prostacyclin (PGI(2)) is a potent inhibitor of platelet aggregation and is thought to have a beneficial role in inhibiting atherogenesis; therefore, it is possible that individuals with SCI have impaired PGI(2) receptor function. We reviewed the literature by conducting a search using PubMed (1970-2007). Acute thrombosis is emerging as an important factor in the etiology of CHD and therefore could mediate the risk of CHD in persons with SCI, in addition to previously known risk factors such as hyperlipidemia, hypertension, hyperlipidemia, diabetes mellitus and hyperinsulinemia. Because PGI(2) may retard atherogenesis through its inhibitory effects on platelet function, we discuss the effects of PGI(2) on platelets in persons with SCI in this review. Subjects with chronic SCI develop abnormal platelet function, resulting in the production of atherogenic and thrombogenic factors for the following reasons: (1) the PGI(2) and insulin receptors on their platelets are impaired; (2) thrombin generation and platelet-derived growth factor release are elevated; (3) insulin-induced nitric oxide production by platelets is markedly impaired; and (4) a circulating antibody (immunoglobulin G (IgG)) blocks the antithrombotic effect of both insulin and PGI(2) receptors. Thus, this IgG molecule is thought to be one of the pathological mediators of the increased incidence of CHD in individuals with SCI.

Spinach Saponin-Enriched Fraction Inhibits Platelet Aggregation in cAMP- and cGMP-Dependent Manner by Decreasing TXA2Production and Blood Coagulation

In this study, we investigated the effect of spinach saponin-enriched fraction (SSEF) on collagen (10 μg/ml)-stimulated platelet aggregation. SSEF inhibited collagen-induced platelet aggregation, and which was involved in the inhibition of thromboxane A2 (TXA 2 ) production, an intracellular Ca 2+ -agonist as an aggregation-inducing autacoidal molecule. In addition, SSEF signifi cantly increased the formation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), intracellular Ca 2+ -antagonists as aggregation-inhibiting molecules, in collagen-stimulated platelets. These results suggest that SSEF might inhibit Ca 2+ -elevation and TXA2 formation by increasing the production of Ca 2+ -antagonistic molecules cAMP and cGMP. These mean that SSEF is a potent inhibitor of collagen-stimulated platelet aggregation. On the other hand, prothrombin time (PT) and activated partial thromboplastin time (APTT) were potently prolonged by SSEF. These fi ndings suggest that SSEF prolongs the internal time between the conversion of fi brinogen to fi brin. Accordingly, our data demonstrate that SSEF may be a crucial tool for a negative regulator during platelet activation and blood coagulation on thrombotic diseases.

Nitric oxide in health and disease – its role in the practice of medicine

Nitric oxide (NO), originally discovered as an endothelium-derived relaxing factor, is now known to participate in the physiologic processes of the nervous, renal, gastrointestinal, and cardiovascular systems. NO is an important mediator of vasodilation and is a potent inhibitor of platelet aggregation and endothelial adhesion. Endothelial dysfunction, which is characterized by a deficit in endothelial NO, is associated with cardiovascular risk factors and is a harbinger of impending cardiovascular disease. The association of reduced NO and cardiovascular disease has led to research into drugs that might enhance the activity of endogenous NO or that can donate exogenous NO to vulnerable tissues. Drugs that donate NO include nitroglycerin, which has been used for more than 100 years in the management of angina pectoris. Drugs used to treat erectile dysfunction act primarily by inhibiting the degradation of the second messenger of NO, thus enhancing and prolonging its action. A novel approach to delivering exogenous NO is to link a NO-donating moiety to an existing drug to improve its safety profile. An example of this strategy is naproxcinod, which in clinical trials for osteoarthritis has demonstrated analgesic equivalence with the parent drug, naproxen, while attenuating some of the gastrointestinal and cardiovascular adverse effects. It is anticipated that the practice of medicine will continue to be affected as new drugs are developed that exploit the important pathways modulated by NO.

Synthesis and Bioactivity of 2-((5-Mercapto-1, 3, 4 -Oxadiazol-2-Yl) Methyl) Benzo[d] Isothiazol -3(<i>2H</i>)-One as Potential Microbiocide

2-((5-mercapto-1, 3, 4 -oxadiazol-2-yl) methyl) benzo[d]isothiazol-3(2H)-one was synthesized and characterized by means of IR, 1H NMR, MS. The compound was tested preliminarily against the bacteria including Escherichia coli, Staphyloccus aurueus, Vibrio alginolyticus, Aeromonas hydrophila and Bacillus subtilis. The results show the title compound has good antimicrobial activity. Isothiazol-3(2H)-ones, 1,2-benzisothiazol-3(2H)-ones, and their heterocyclic bioisomeric derivatives are potent industrial microbiocides with antifungal and antibacterial activities[1,2], highly potent platelet aggregation inhibitor[3], anti-inflammatory, analgedic and anti-pyretic activities[4]. And the biocide 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one is a nonmetallic and nonenvironmentally persistent biocide, which has been registered in several countries as an antifouling agent and has gained approval in the USA and Environmental Protection Agency[5]. Isothiazolones represent a class of versatile intermediates in the synthesis of heterocyclic compounds [6]. According to above facts and the principle of combination of bioactive sub-structure, we herein designed and synthesized benzisothiazolone derivatives2-((5-mercapto-1, 3, 4 -oxadiazol-2-yl) methyl) benzo[d] isothiazol -3(2H)-one, as shown in Scheme 1.

Once Again, Bivalirudin Alone Bests Heparin plus a GPI

Compared with the combination of heparin and a glycoprotein IIb/IIIa inhibitor (GPI), bivalirudin confers a lower bleeding risk but is also a less potent inhibitor of platelet aggregation. In patients undergoing primary percutaneous coronary intervention (PCI) for ST-segment-elevation myocardial infarction (STEMI), bivalirudin alone produced significantly better clinical outcomes than heparin plus a GPI (JW …

Combined Intracoronary Glycoprotein Inhibitors and Manual Thrombus Extraction in Patients with Acute ST-segment Elevation Myocardial Infarction – Does Incorporation of Both Have a Legitimate Role?

In a substantial number of patients with acute ST-segment elevation myocardial infarction (STEMI), myocardial perfusion at the myocardial cellular level continues to be impaired despite achieving brisk antegrade flow in the infarct-related coronary artery by primary percutaneous intervention. This is attributable to embolisation of the coronary thrombus into the distal vasculature, producing microvascular plugging, vasospasm, interstitial oedema and cellular injury. There is consequently less salvage of infarct size, reduced left ventricular function and poorer clinical outcomes. Glycoprotein inhibitors are the most potent inhibitors of platelet aggregation and have been repeatedly shown to improve clinical outcomes in acute STEMI when administered intravenously. In recent years, randomised trials have demonstrated that glycoprotein inhibitors administered by the intracoronary route are safe and effective in reducing infarct size and providing better clinical outcomes than when given intravenously. Simultaneously, numerous randomised studies using adjunct manual thrombus extraction during primary percutaneous intervention in patients with acute STEMI have shown significantly better ST-segment resolution and myocardial blush grade, suggesting improved myocardial reperfusion, and, more importantly, significant one-year reductions in mortality. However, manual thrombus extraction cannot be used in all patients because there are occasions when the thrombus burden is too large to be aspirated completely or it is impossible to negotiate the thrombus extraction catheter beyond the occlusion. Similarly, glycoprotein inhibitors albeit delivered by the intracoronary route are unable to produce disaggregation of thrombus in all STEMI patients. A small pilot study involving 40 patients with acute STEMI demonstrated that the combination of intracoronary tirofiban and manual thrombus extraction is both safe and effective. However, there are no randomised data on the combined usage of intracoronary tirofiban and manual thrombus extraction in acute ST-elevation and, therefore, it is imperative that large, adequately powered, randomised studies are undertaken to study the synergistic effects of these two modalities. This article describes the various studies that have compared intracoronary glycoprotein inhibitors with the intravenous route and the rationale behind the advantages of manual thrombus extraction in the setting of acute STEMI.

Prostacyclin: An Inflammatory Paradox

Prostacyclin (PGI2) is a member of the prostaglandin family of bioactive lipids. Its best-characterized role is in the cardiovascular system, where it is released by vascular endothelial cells, serving as a potent vasodilator and inhibitor of platelet aggregation. In recent years, prostacyclin (PGI2) has also been shown to promote differentiation and inhibit proliferation in vascular smooth muscle cells. In addition to these well-described homeostatic roles within the cardiovascular system, prostacyclin (PGI2) also plays an important role as an inflammatory mediator. In this review, we focus on the contribution of prostacyclin (PGI2) as both a pathophysiological mediator and therapeutic agent in three major inflammatory-mediated disease processes, namely rheumatoid arthritis, where it promotes disease progression (“pro-inflammatory”), along with pulmonary vascular disease and atherosclerosis, where it inhibits disease progression (“anti-inflammatory”). The emerging role of prostacyclin (PGI2) in this context provides new opportunities for understanding the complex molecular basis for inflammatory-related diseases, and insights into the development of current and future anti-inflammatory treatments.

ChemInform Abstract: Room Temperature Synthesis of Tri‐, Tetrasubstituted Imidazoles and Bis‐Analogues by Mercaptopropylsilica (MPS) in Aqueous Methanol: Application to the Synthesis of the Drug Trifenagrel.

AbstractA modified procedure for the preparation of mercaptopropylsilica is developed and the catalyst is efficiently used for the synthesis of various title compounds including the novel potent platelet aggregation inhibitor trifenagrel (IIIb).

ChemInform Abstract: Synthesis of Some Flavone Derivatives: Potent Inhibitors of Human Platelet Aggregation.

ChemInform Abstract: Synthesis of Some Flavone Derivatives: Potent Inhibitors of Human Platelet Aggregation.

Cystine-knot peptides engineered with specificities for αIIbβ3 or αIIbβ3 and αvβ3 integrins are potent inhibitors of platelet aggregation

A truncated form of the Agouti-related protein (AgRP), a member of the cystine-knot family, has shown promise as a scaffold for engineering novel peptides with new molecular recognition properties. In this study, we replaced a constrained six amino acid loop in AgRP with a nine amino acid loop containing an Arg-Gly-Asp integrin recognition motif, and randomized the neighboring residues to create a library of approximately 20 million AgRP variants. We displayed the AgRP mutants as fusions on the surface of yeast and used high-throughput fluorescence-activated cell sorting (FACS) to isolate peptides that bound specifically to the platelet integrin α(IIb)β(3), a clinically important target for the prevention and treatment of thrombosis. These AgRP peptides had equilibrium dissociation (K(D)) constants for α(IIb)β(3) integrin ranging from 60 to 90 nM, and did not bind to α(v)β(3), α(v)β(5), or α(5)β(1) integrins. Using an alternate library screening strategy, we identified AgRP peptides that bound to both α(IIb)β(3) and α(v)β(3) integrins with K(D) values ranging from 40 to 70 nM and 20 to 30 nM, respectively, and did not bind to α(v)β(5) or α(5)β(1) integrins. Unique consensus sequences were identified within both series of AgRP peptides suggesting alternative molecular recognition events that dictate different integrin binding specificities. In addition, the engineered AgRP peptides prevented platelet aggregation as well as or slightly better than the FDA-approved cyclic peptide eptifibatide. Collectively, these data demonstrate that cystine-knot peptides can be generated with high affinity and specificity to closely-related integrins, and provide insights into molecular interactions between small, structured peptide ligands and their receptors.

Delivery of Glycoprotein IIb/IIIa Inhibitor Therapy for Percutaneous Coronary Intervention

A major goal of any antithrombotic regimen administered during percutaneous coronary intervention (PCI) is the preservation of coronary microvascular perfusion, which is critical for myocardial survival. In addition to macrovascular thrombosis, microembolization into the downstream coronary artery bed that occurs during spontaneous plaque rupture and PCI plays a prominent role in the development of microvascular dysfunction that leads to myocardial infarction. In addition to physical obstruction of the lumen by the embolus, vasoconstriction and edema due to inflammation also impair microvascular flow.1 These events likely occur more frequently during PCI performed in the setting of unstable coronary syndromes.2 With Doppler guidewire technology, it was estimated that an average of 25 embolic events occurred during primary PCI for ST-segment elevation myocardial infarction.3 Article see p 784 Platelet aggregates are important components of coronary microemboli, along with leukocytes, erythrocytes, platelet-leukocyte aggregates, cholesterol crystals, and hyalin. Platelets and leukocytes within microemboli play a particularly important role in the pathophysiological changes of blood flow by promoting in situ microvascular thrombosis, vasoconstriction, and inflammation. Interestingly, the composition of the embolized material is similar in the settings of spontaneous and catheter-induced plaque rupture.1 In animal models, distal microembolization of inert microspheres is associated with an immediate reduction in flow due to vessel occlusion, followed by enhanced blood flow due to the effects of adenosine released from the embolized myocardium into the adjacent noninvolved myocardium.4 Microembolization results in overall reduced flow reserve and the progressive loss of contractile function, which often reverses within weeks. The degree of myocardial contractile dysfunction is disproportionate to the degree of infarction and is the result of inflammation.5 However, in the clinical condition, a more complex pathophysiology exists due to the influence of multiple components of the emboli. Platelets aggregate when fibrinogen binds to the active …

Antiplatelet Therapy After Percutaneous Coronary Intervention

Current guidelines recommend dual antiplatelet therapy (DAPT) that includes aspirin and the platelet P2Y12 ADP receptor antagonist clopidogrel after percutaneous coronary intervention (PCI). These recommendations are based on data that DAPT with the P2Y12 inhibitors clopidogrel reduces major adverse cardiac events after PCI in stable angina and acute coronary syndrome (ACS) patients when compared with aspirin, or aspirin in combination with warfarin.1 Despite treatment with DAPT, patients with ACS undergoing PCI are at elevated risk for recurrent ischemic events compared with stable angina patients in part because of increased platelet thrombotic activity in ACS. In addition, there is considerable interindividual variability in the degree of platelet inhibition achieved by clopidogrel, and high residual platelet activity in the setting of clopidogrel therapy (hyporesponsiveness) is associated with adverse cardiovascular (CV) events after PCI. Clopidogrel hyporesponsiveness is related to a variety of clinical and genetic factors that alter pharmacokinetics, and diabetes, congestive heart failure (CHF), and obesity are associated with reduced efficacy. Clopidogrel is a prodrug that requires conversion by the hepatic cytochrome P450 system (CYP) to an active metabolite, and it can take up to 6 hours for clopidogrel to have maximal effect after the loading dose. Genetic polymorphisms that reduce CYP activity result in decreased hepatic metabolism of clopidogrel. Among persons treated with clopidogrel, carriers of specific reduced function CYP2C19 alleles have impaired clopidogrel conversion, significantly lower levels of active metabolite, diminished platelet inhibition, and higher rates of adverse CV events and stent thrombosis after PCI.2 The prevalence of CYP2C19 polymorphisms ranges from 30% to 60% depending on ethnicity.2,3 Medications that inhibit CYP activity also reduce clopidogrel conversion, and some proton pump inhibitors (PPI) that reduce CYP function (eg, omeprazole) diminish clopidogrel metabolite levels and efficacy measured by platelet function testing. The interaction between clopidogrel and …

Hypoperfusion Infarctions of Unexpected Territories after Angioplasty of Intracranial Stenoses

ischemic stroke and accounts for 8% to 15% of strokes caused by cerebral atherosclerosis, depending on the population studied (1, 2). Sometimes patients with symptomatic intracranial atherosclerotic stenosis are insufficiently protected against ischemic stroke despite medication with platelet aggregation inhibitors. However, the treatment of patients with intracranial atherosclerosis lesions remains controversial. The results of endovascular revascularization of intracranial vessels with balloonor stent-assisted angioplasty or stent have been tempered by the increased risk of stroke (3). The availability of recently introduced flexible stents, the development of potent platelet aggregation inhibitors, and increasing evidence from experimental and clinical studies of intracranial stents have improved the endovascular management of ischemic intracranial cerebrovascular disease. Complications from intracranial artery angioplasty and stenting (IAS) include cerebral infarction, intracranial hemorrhage caused by reperfusion injury, and contrast-induced renal failure. Most cerebral infarctions are directly related to the endovascular procedure, involving the ipsilateral vascular territory (4). This ischemic complication results from distal embolization, vessel dissection, and acute vessel occlusion secondary to dissection or platelet aggregation. We present two cases with unexpected infarctions involving territories unrelated to IAS procedures.

Fast, potent, and reliable inhibition of platelet aggregation

Thienopyridine inhibitors are administered as prodrugs and are metabolized to active compounds in the body by a range of enzymes including esterases and cytochrome P450s (CYPs). This review aims to characterize the main differences between the established drug clopidogrel and the newer agent prasugrel in terms of pharmacokinetics and how these differences relate to clinically relevant pharmacodynamic differences. Prasugrel is less dependent on CYP enzymes for its metabolism than clopidogrel. It is also more extensively metabolized to its active metabolite, which reaches higher plasma concentrations after dosing with a 60 mg loading dose or a 10 mg daily maintenance dose, relative to the licensed 300 mg/75 mg doses of clopidogrel. This higher pharmacokinetic exposure with prasugrel leads to significantly faster and more potent inhibition of platelet aggregation (IPA) than with clopidogrel. Prasugrel has also been shown to be associated with less variability of response than clopidogrel. This has been demonstrated by examining individuals’ responses in terms of IPA, and by assessing the degree of inhibition of the P2Y12 receptor—the site of action for both agents. These advantages with prasugrel vs. clopidogrel have been observed in healthy volunteers and in patients with coronary artery disease.

Determination of Clopidogrel by Chromatography

Clopidogrel, being a potent platelet aggregation inhibitor, is used widely around the world to reduce cardiovascular risks in patients with stroke, myocardial infarction, and atherosclerosis. The aim of this review firstly focuses on a comprehensive update of chromatography determination of clopidogrel and its metabolites as well as in human plasma, Wistar rat plasma, and in pharmaceutical preparations. It has been described using TLC, HPLC/MS, RP-HPLC, and GC/MS methods. Secondly to localize the chromatography conditions for separation and quantification, this review provides detailed information on separation conditions for clopidogrel and its metabolites. A new HPLC method adjusted to our laboratory conditions was developed for the evaluation of assay and purity of clopidogrel in film-coated tablets.

Isosorbide-Based Aspirin Prodrugs: Integration of Nitric Oxide Releasing Groups

Aspirin prodrugs and related nitric oxide releasing compounds hold significant therapeutic promise, but they are hard to design because aspirin esterification renders its acetate group very susceptible to plasma esterase mediated hydrolysis. Isosorbide-2-aspirinate-5-salicylate is a true aspirin prodrug in human blood because it can be effectively hydrolyzed to aspirin upon interaction with plasma BuChE. We show that the identity of the remote 5-ester dictates whether aspirin is among the products of plasma-mediated hydrolysis. By observing the requirements for aspirin release from an initial panel of isosorbide-based esters, we were able to introduce nitroxymethyl groups at the 5-position while maintaining ability to release aspirin. Several of these compounds are potent inhibitors of platelet aggregation. The design of these compounds will allow better exploration of cross-talk between COX inhibition and nitric oxide release and potentially lead to the development of selective COX-1 acetylating drugs without gastric toxicity.