Extracellular ATP and Adenosine in Cancer Pathogenesis and Treatment.

ATP hydrolysis and downstream signaling pathways in the extracellular space have a major impact upon tumor progression and metastasis. The complexity and interdependence of various cell types in the extracellular space have been increasingly appreciated in recent years. With increased awareness of the importance of this signaling pathway in the pathogenic development and progression of malignancies, there has been attention to therapeutic strategies targeting extracellular adenosine metabolism and signaling. This review summarizes the molecular and physiologic roles of extracellular ATP and adenosine in normal and disease states, and potential therapeutic applications.

Expression of purinergic receptors on microglia in the animal model of choroidal neovascularisation.

To investigate the effect of P2 receptor on microglia and its inhibitor PPADS on choroidal neovascularization. Forty CX3CR1GFP/+ mice were randomly divided into 8 groups. In addition to the normal group, the rest of groups were receiving laser treatment. The retina and choroid from the second, third, fourth and fifth group of mice were taken in the 1, 4, 7, 14 days after laser treatment. The mice in the sixth and seventh group received intravitreal injection of 2 µl PPADS or PBS respectively immediately after laser treatment. The mice in the eighth group received topical application of PPADS once per day of three days. The mice in sixth, seventh and eighth group received AF and FFA examination on the fourth day after laser treatment. Immunofluorescence histochemical staining and real-time quantitative PCR were used to evaluate P2 expression and its effect on choroidal neovascularization. After laser treatment, activated microglia can express P2 receptors (P2X4, P2X7, P2Y2 and P2Y12). The expression of P2 increased on the first day after laser damage, peaked on the fourth day (tP2X4 = 6.05, tP2X7 = 2.95, tP2Y2 = 3.67, tP2Y12 = 5.98, all P < 0.01), and then decreased. After PPADS inhibition, compared with the PBS injection group, the mRNA of P2X4, P2X7, P2Y2 and P2Y12 were decreased significantly in the PPADS injection group (tP2X4 = 5.54, tP2X7 = 9.82, tP2Y2 = 3.86, tP2Y12 = 7.91, all P < 0.01) and the PPADS topical application group (tP2X4 = 3.24, tP2X7 = 5.89, tP2Y2 = 6.75, tP2Y12 = 4.97, all P < 0.01). Compared with the PBS injection group, not only the activity of microglia cells but also the leakage of CNV decreased significantly (P < 0.01) in the PPADS injection group and the PPADS topical application group. But between two PPADS groups, the leakage of CNV had no difference (P = 0.864). After laser induced CNV, activated microglia can express P2 receptors. The P2 receptor inhibitor, PPADS, can significantly affect the function of microglia and inhibit the formation of choroidal neovascularization.

Structure-Activity Relationship of Heterocyclic P2Y14 Receptor Antagonists: Removal of the Zwitterionic Character with Piperidine Bioisosteres.

A known zwitterionic, heterocyclic P2Y14R antagonist 3a was substituted with diverse groups on the central phenyl and terminal piperidine moieties, following a computational selection process. The most potent analogues contained an uncharged piperidine bioisostere, prescreened in silico, while an aza-scan (central phenyl ring) reduced P2Y14R affinity. Piperidine amide 11, 3-aminopropynyl 19, and 5-(hydroxymethyl)isoxazol-3-yl) 29 congeners in the triazole series maintained moderate receptor affinity. Adaption of 5-(hydroxymethyl)isoxazol-3-yl gave the most potent naphthalene-containing (32; MRS4654; IC50, 15 nM) and less active phenylamide-containing (33) scaffolds. Thus, a zwitterion was nonessential for receptor binding, and molecular docking and dynamics probed the hydroxymethylisoxazole interaction with extracellular loops. Also, amidomethyl ester prodrugs were explored to reversibly block the conserved carboxylate group to provide neutral analogues, which were cleavable by liver esterase, and in vivo efficacy demonstrated. We have, in stages, converted zwitterionic antagonists into neutral molecules designed to produce potent P2Y14R antagonists for in vivo application.

Targeting P2 receptors in purinergic signaling: a new strategy of active ingredients in traditional Chinese herbals for diseases treatment.

Adenosine triphosphate (ATP) and its metabolites adenosine diphosphate, adenosine monophosphate, and adenosine in purinergic signaling pathway play important roles in many diseases. Activation of P2 receptors (P2R) channels and subsequent membrane depolarization can induce accumulation of extracellular ATP, and furtherly cause kinds of diseases, such as pain- and immune-related diseases, cardiac dysfunction, and tumorigenesis. Active ingredients of traditional Chinese herbals which exhibit superior pharmacological activities on diversified P2R channels have been considered as an alternative strategy of disease treatment. Experimental evidence of potential ingredients in Chinese herbs targeting P2R and their pharmacological activities were outlined in the study.

Design, synthesis and evaluation of 3-amide-5-aryl benzoic acid derivatives as novel P2Y14R antagonists with potential high efficiency against acute gouty arthritis.

P2Y14 nucleotide receptor plays important roles in series of physiological and pathologic events especially associated with immune and inflammation. Based on the 3-amide benzoic acid scaffold reported by our group previously, a series of 5-aryl-3-amide benzoic acid derivatives were designed as novel P2Y14 antagonists with improved pharmacokinetic properties. Among which compound 11m showed most potent P2Y14 antagonizing activity with an IC50 value of 2.18 nM, furnishing greatly improved water solubility and bioavailability compared with PPTN. In MSU-induced acute gouty arthritis model in mice, 11m exerted promising in vivo efficacy in alleviating mice paw swelling and inflammatory infiltration. Mechanistically, compound 11m notably blocked pyroptosis of macrophages through inhibiting NLRP3 inflammasome activation. This work may contribute to the identification of potential therapeutic agents to intervene in acute gouty arthritis.

Diabetes and hypertension: Pivotal involvement of purinergic signaling.

Diabetes mellitus (DM) and hypertension are highly prevalent worldwide health problems and frequently associated with severe clinical complications, such as diabetic cardiomyopathy, nephropathy, retinopathy, neuropathy, stroke, and cardiac arrhythmia, among others. Despite all existing research results and reasonable speculations, knowledge about the role of purinergic system in individuals with DM and hypertension remains restricted. Purinergic signaling accounts for a complex network of receptors and extracellular enzymes responsible for the recognition and degradation of extracellular nucleotides and adenosine. The main components of this system that will be presented in this review are: P1 and P2 receptors and the enzymatic cascade composed by CD39 (NTPDase; with ATP and ADP as a substrate), CD73 (5'-nucleotidase; with AMP as a substrate), and adenosine deaminase (ADA; with adenosine as a substrate). The purinergic system has recently emerged as a central player in several physiopathological conditions, particularly those linked to inflammatory responses such as diabetes and hypertension. Therefore, the present review focuses on changes in both purinergic P1 and P2 receptor expression as well as the activities of CD39, CD73, and ADA in diabetes and hypertension conditions. It can be postulated that the manipulation of the purinergic axis at different levels can prevent or exacerbate the insurgency and evolution of diabetes and hypertension working as a compensatory mechanism.

Exploration of Alternative Scaffolds for P2Y14 Receptor Antagonists Containing a Biaryl Core.

Various heteroaryl and bicyclo-aliphatic analogues of zwitterionic biaryl P2Y14 receptor (P2Y14R) antagonists were synthesized, and affinity was measured in P2Y14R-expressing Chinese hamster ovary cells by flow cytometry. Given this series' low water solubility, various polyethylene glycol derivatives of the distally binding piperidin-4-yl moiety of moderate affinity were synthesized. Rotation of previously identified 1,2,3-triazole attached to the central m-benzoic acid core (25) provided moderate affinity but not indole and benzimidazole substitution of the aryl-triazole. The corresponding P2Y14R region is predicted by homology modeling as a deep, sterically limited hydrophobic pocket, with the outward pointing piperidine moiety being the most flexible. Bicyclic-substituted piperidine ring derivatives of naphthalene antagonist 1, e.g., quinuclidine 17 (MRS4608, IC50 ≈ 20 nM at hP2Y14R/mP2Y14R), or of triazole 2, preserved affinity. Potent antagonists 1, 7a, 17, and 23 (10 mg/kg) protected in an ovalbumin/Aspergillus mouse asthma model, and PEG conjugate 12 reduced chronic pain. Thus, we expanded P2Y14R antagonist structure-activity relationship, introducing diverse physical-chemical properties.

P2Y12 regulates microglia activation and excitatory synaptic transmission in spinal lamina II neurons during neuropathic pain in rodents.

Peripheral nerve injury causes neuropathic pain and microglia activation. P2Y12 receptors on microglia are thought to be a key player in the surveillance of the local environment, but whether or how these receptors are engaged in the cross-talk between microglia and neurons of the dorsal horn remain ambiguous. Using a rodent model of nerve injury-induced pain, we investigated the roles of P2Y12 in microglia activation, excitatory synaptic transmission, and nociceptive allodynia. We found that spinal nerve ligation (SNL) significantly increased the level of P2Y12 receptors specifically in the microglia of the ipsilateral dorsal horn. Injections of P2Y12 antagonists (MRS2395 or clopidogrel) attenuated microglia activation and increased the paw withdrawal latency in response to thermal stimuli on the ipsilateral side without affecting the basal threshold on the contralateral side. These effects on pain behaviors were replicated in P2Y12 knockout mice. Patch-clamp recordings further revealed that partial sciatic nerve ligation (PSNL)-induced excessive miniature excitatory postsynaptic currents (mEPSCs) were significantly attenuated in P2Y12 knockout mice. Moreover, we found that SNL activates the GTP-RhoA/ROCK2 signaling pathway and elevates the level of phosphorylated p38 mitogen-activated protein kinase (MAPK), which was inhibited by the P2Y12 antagonist. The phosphorylation of p38 MAPK was inhibited by a ROCK inhibitor, but not vice versa, suggesting that p38 MAPK is downstream of ROCK activation. Our findings suggest that nerve injury engages the P2Y12 receptor-dependent GTP-RhoA/ROCK2 signaling pathway to upregulate excitatory synaptic transmission in the dorsal horn. This cross-talk ultimately participates in the manifestation of nociceptive allodynia, implicating P2Y12 receptor as a potential target for alleviating neuropathic pain.

Potential Therapeutic Applications of P2 Receptor Antagonists: From Bench to Clinical Trials.

BACKGROUND: Extracellular purines and pyrimidines have important physiological functions in mammals. Purines and pyrimidines act on P1 and P2 purinergic receptors, which are widely expressed in the plasma membrane in various cell types. P2 receptors act as important therapeutic targets and are associated with several disorders, such as pain, neurodegeneration, cancer, inflammation, and thrombosis. However, the use of antagonists for P2 receptors in clinical therapy, with the exception of P2Y12, is a great challenge. Currently, many research groups and pharmaceutical companies are working on the development of specific antagonist molecules for each receptor subtype that could be used as new medicines to treat their respective disorders. OBJECTIVE: The present review compiles some interesting findings on the application of P2 receptor antagonists in different in vitro and in vivo experimental models as well as the progress of advanced clinical trials with these compounds. CONCLUSION: Despite all of the exciting results obtained on the bench, few antagonists of P2 receptors advanced to the clinical trials, and once they reach this stage, the effectiveness of the therapy is not guaranteed, as in the example of P2X7 antagonists. Despite this, P2Y12 receptor antagonists have a history of success and have been used in therapy for at least two decades to prevent thrombosis in patients at risk for myocardial infarctions. This breakthrough is the motivation for scientists to develop new drugs with antagonistic activity for the other P2 receptors; thus, in a matter of years, we will have an evolution in the field of purinergic therapy.

The therapeutic potential of purinergic signalling.

This review is focused on the pathophysiology and therapeutic potential of purinergic signalling. A wide range of diseases are considered, including those of the central nervous system, skin, kidney, musculoskeletal, liver gut, lower urinary tract, cardiovascular, airways and reproductive systems, the special senses, infection, diabetes and obesity. Several purinergic drugs are already on the market, including P2Y12 receptor antagonists for stroke and thrombosis, P2Y2 receptor agonists for dry eye, and A1 receptor agonists for supraventricular tachycardia. Clinical trials are underway for the use of P2X3 receptor antagonists for the treatment of chronic cough, visceral pain and hypertension, and many more compounds are being explored for the treatment of other diseases. Most experiments are 'proof of concept' studies on animal or cellular models, which hopefully will lead to further clinical trials. The review summarises the topic, mostly referring to recent review articles.

Purinergic P2Y6 receptors: A new therapeutic target of age-dependent hypertension.

Aging has a remarkable effect on cardiovascular homeostasis and it is known as the major non-modifiable risk factor in the development of hypertension. Medications targeting sympathetic nerve system and/or renin-angiotensin-aldosterone system are widely accepted as a powerful therapeutic strategy to improve hypertension, although the control rates remain unsatisfactory especially in the elder patients with hypertension. Purinergic receptors, activated by adenine, uridine nucleotides and nucleotide sugars, play pivotal roles in many biological processes, including platelet aggregation, neurotransmission and hormone release, and regulation of cardiovascular contractility. Since clopidogrel, a selective inhibitor of G protein-coupled purinergic P2Y12 receptor (P2Y12R), achieved clinical success as an anti-platelet drug, P2YRs has been attracted more attention as new therapeutic targets of cardiovascular diseases. We have revealed that UDP-responsive P2Y6R promoted angiotensin type 1 receptor (AT1R)-stimulated vascular remodeling in mice, in an age-dependent manner. Moreover, the age-related formation of heterodimer between AT1R and P2Y6R was disrupted by MRS2578, a P2Y6R-selective inhibitor. These findings suggest that P2Y6R is a therapeutic target to prevent age-related hypertension.

Chronic restraint stress exacerbates nociception and inflammatory response induced by bee venom in rats: the role of the P2X7 receptors.

OBJECTIVE: Chronic restraint stress exacerbates pain and inflammation. The present study was designed to evaluate the effect of chronic restraint stress on inflammatory pain induced by subcutaneous injection of bee venom (BV). METHODS: First, we investigated: (1) the effect of two-week restraint stress with daily 2 or 8 h on the baseline paw withdrawal mechanical threshold (PWMT), paw withdrawal thermal latency (PWTL) and paw circumference (PC); (2) the effect of chronic stress on the spontaneous paw-flinching reflex (SPFR), decrease in PWM, PWTL and increase in PC of the injected paw induced by BV. RESULTS: The results showed that (1) chronic restraint decreased significantly the PWMT and inhibited significantly the increase in PC, but had no effect on PWTL, compared with control group; (2) chronic restraint enhanced significantly BV-induced SPFR and inflammatory swelling of the injected paw. In a second series of experiments, the role of P2X7 receptor (P2X7R) in the enhancement of BV-induced inflammatory pain produced by chronic restraint stress was determined. Systemic pretreatment with P2X7R antagonist completely reversed the decrease in PWMT produced by chronic restraint, inhibited significantly the enhancement of BV-induced inflammatory pain produced by chronic restraint stress. CONCLUSION: Taken together, our data indicate that chronic restraint stress-enhanced nociception and inflammation in the BV pain model, possibly involving the P2X7R.

Purinergic Receptors in Thrombosis and Inflammation.

Under various pathological conditions, including thrombosis and inflammation, extracellular nucleotide levels may increase because of both active release and passive leakage from damaged or dying cells. Once in the extracellular compartment, nucleotides interact with plasma membrane receptors belonging to the P2 purinergic family, which are expressed by virtually all circulating blood cells and in most blood vessels. In this review, we focus on the specific role of the 3 platelet P2 receptors P2Y1, P2Y12, and P2X1 in hemostasis and arterial thrombosis. Beyond platelets, these 3 receptors, along with the P2Y2, P2Y6, and P2X7 receptors, constitute the main P2 receptors mediating the proinflammatory effects of nucleotides, which play important roles in various functions of circulating blood cells and cells of the vessel wall. Each of these P2 receptor subtypes specifically contributes to chronic or acute vascular inflammation and related diseases, such as atherosclerosis, restenosis, endotoxemia, and sepsis. The potential for therapeutic targeting of these P2 receptor subtypes is also discussed.

P2X and P2Y receptors­role in the pathophysiology of the nervous system.

Purinergic signalling plays a crucial role in proper functioning of the nervous system. Mechanisms depending on extracellular nucleotides and their P2 receptors also underlie a number of nervous system dysfunctions. This review aims to present the role of purinergic signalling, with particular focus devoted to role of P2 family receptors, in epilepsy, depression, neuropathic pain, nervous system neoplasms, such as glioma and neuroblastoma, neurodegenerative diseases like Parkinson's disease, Alzheimer's disease and multiple sclerosis. The above-mentioned conditions are associated with changes in expression of extracellular ectonucleotidases, P2X and P2Y receptors in neurons and glial cells, as well as releasing considerable amounts of nucleotides from activated or damaged nervous tissue cells into the extracellular space, which contributes to disturbance in purinergic signalling. The numerous studies indicate a potential possibility of using synthetic agonists/antagonists of P2 receptors in treatment of selected nervous system diseases. This is of particular significance, since numerous available agents reveal a low effectiveness and often produce side effects.

Nucleotide signalling during inflammation.

Inflammatory conditions are associated with the extracellular release of nucleotides, particularly ATP. In the extracellular compartment, ATP predominantly functions as a signalling molecule through the activation of purinergic P2 receptors. Metabotropic P2Y receptors are G-protein-coupled, whereas ionotropic P2X receptors are ATP-gated ion channels. Here we discuss how signalling events through P2 receptors alter the outcomes of inflammatory or infectious diseases. Recent studies implicate a role for P2X/P2Y signalling in mounting appropriate inflammatory responses critical for host defence against invading pathogens or tumours. Conversely, P2X/P2Y signalling can promote chronic inflammation during ischaemia and reperfusion injury, inflammatory bowel disease or acute and chronic diseases of the lungs. Although nucleotide signalling has been used clinically in patients before, research indicates an expanding field of opportunities for specifically targeting individual P2 receptors for the treatment of inflammatory or infectious diseases.

Exaggerated exercise pressor reflex in adults with moderately elevated systolic blood pressure: role of purinergic receptors.

The neurocirculatory responses to exercise are exaggerated in hypertension, increasing cardiovascular risk, yet the mechanisms remain incompletely understood. The aim of this study was to examine the in vitro effectiveness of pyridoxal-5-phosphate as a purinergic (P2) receptor antagonist in isolated murine dorsal root ganglia (DRG) neurons and the in vivo contribution of P2 receptors to the neurocirculatory responses to exercise in older adults with moderately elevated systolic blood pressure (BP). In vitro, pyridoxal-5-phosphate attenuated the ATP-induced increases in [Ca(2+)](i) (73 ± 15 vs. 11 ± 3 nM; P < 0.05). In vivo, muscle sympathetic nerve activity (MSNA; peroneal microneurography) and arterial BP (Finometer) were assessed during exercise pressor reflex activation (static handgrip followed by postexercise ischemia; PEI) during a control trial (normal saline) and localized P2 receptor blockade (pyridoxal-5-phosphate). Compared with normotensive adults (63 ± 2 yr, 117 ± 2/70 ± 2 mmHg), adults with moderately elevated systolic BP (65 ± 1 yr, 138 ± 5/79 ± 3 mmHg) demonstrated greater increases in MSNA and BP during handgrip and PEI. Compared with the control trial, local antagonism of P2 receptors during PEI partially attenuated MSNA (39 ± 4 vs. 34 ± 5 bursts/min; P < 0.05) in adults with moderately elevated systolic BP. In conclusion, these data demonstrate pyridoxal-5-phosphate is an effective P2 receptor antagonist in isolated DRG neurons, which are of particular relevance to the exercise pressor reflex. Furthermore, these findings indicate that exercise pressor reflex function is exaggerated in older adults with moderately elevated systolic BP and further suggest a modest role of purinergic receptors in evoking the abnormally large reflex-mediated increases in sympathetic activity during exercise in this clinical population.

Transcranial amelioration of inflammation and cell death after brain injury.

Traumatic brain injury (TBI) is increasingly appreciated to be highly prevalent and deleterious to neurological function. At present, no effective treatment options are available, and little is known about the complex cellular response to TBI during its acute phase. To gain insights into TBI pathogenesis, we developed a novel murine closed-skull brain injury model that mirrors some pathological features associated with mild TBI in humans and used long-term intravital microscopy to study the dynamics of the injury response from its inception. Here we demonstrate that acute brain injury induces vascular damage, meningeal cell death, and the generation of reactive oxygen species (ROS) that ultimately breach the glial limitans and promote spread of the injury into the parenchyma. In response, the brain elicits a neuroprotective, purinergic-receptor-dependent inflammatory response characterized by meningeal neutrophil swarming and microglial reconstitution of the damaged glial limitans. We also show that the skull bone is permeable to small-molecular-weight compounds, and use this delivery route to modulate inflammation and therapeutically ameliorate brain injury through transcranial administration of the ROS scavenger, glutathione. Our results shed light on the acute cellular response to TBI and provide a means to locally deliver therapeutic compounds to the site of injury.

The function of P2X3 receptor and NK1 receptor antagonists on cyclophosphamide-induced cystitis in rats.

PURPOSE: The purpose of the study is to explore the function of P2X3 and NK1 receptors antagonists on cyclophosphamide (CYP)-induced cystitis in rats. METHODS: Sixty female Sprague-Dawley (SD) rats were randomly divided into three groups. The rats in the control group were intraperitoneally (i.p.) injected with 0.9% saline (4 ml/kg); the rats in the model group were i.p. injected with CYP (150 mg/kg); and the rats in the intervention group were i.p. injected with CYP with subsequently perfusion of bladder with P2X3 and NK1 receptors' antagonists, Suramin and GR 82334. Spontaneous pain behaviors following the administration of CYP were observed. Urodynamic parameters, bladder pressure-volume curve, maximum voiding pressure (MVP), and maximum cystometric capacity (MCC), were recorded. Pathological changes in bladder tissue were observed. Immunofluorescence was used to detect the expression of P2X3 and NK1 receptors in bladder. RESULTS: Cyclophosphamide treatment increased the spontaneous pain behaviors scores. The incidence of bladder instability during urine storage period of model group was significantly higher than intervention group (χ(2) = 7.619, P = 0.007) and control group (χ(2) = 13.755, P = 0.000). MCC in the model group was lower than the control and intervention groups (P < 0.01). Histological changes evident in model and intervention groups rats' bladder included edema, vasodilation, and infiltration of inflammatory cells. In model group, the expression of P2X3 receptor increased in urothelium and suburothelium, and NK1 receptor increased in suburothelium, while the expression of them in intervention group was lower. CONCLUSIONS: In CYP-induced cystitis, the expression of P2X3 and NK1 receptors increased in urothelium and/or suburothelium. Perfusion of bladder with P2X3 and NK1 receptors antagonists ameliorated the bladder function.

P2X7 blockade attenuates murine lupus nephritis by inhibiting activation of the NLRP3/ASC/caspase 1 pathway.

OBJECTIVE: The NLRP3 inflammasome plays key roles in inflammation and autoimmunity, and purinergic receptor P2X7 has been proposed to be upstream of NLRP3 activation. The aim of the present study, using murine models, was to investigate whether the P2X7 /NLRP3 inflammasome pathway contributes to the pathogenesis of lupus nephritis (LN). METHODS: MRL/lpr mice were treated with the selective P2X7 antagonist brilliant blue G (BBG) for 8 weeks. Following treatment, the severity of renal lesions, production of anti-double-stranded DNA (anti-dsDNA) antibodies, rate of survival, activation of the NLRP3/ASC/caspase 1 inflammasome pathway, and ratio of Th17 cells to Treg cells were evaluated. P2X7 -targeted small interfering RNA (siRNA) was also used for in vivo intervention. Similar evaluations were carried out in NZM2328 mice, a model of LN in which the disease was accelerated by administration of adenovirus-expressing interferon-α (AdIFNα). RESULTS: Significant up-regulation of P2X7 /NLRP3 inflammasome signaling molecules was detected in the kidneys of MLR/lpr mice as compared with normal control mice. Blockade of P2X7 activation by BBG suppressed NLRP3/ASC/caspase 1 assembly and the subsequent release of interleukin-1ß (IL-1ß), resulting in a significant reduction in the severity of nephritis and circulating anti-dsDNA antibodies. The lifespan of the treated mice was significantly prolonged. BBG treatment reduced the serum levels of IL-1ß and IL-17 and the Th17:Treg cell ratio. Similar results were obtained by specific siRNA silencing of P2X7 in vivo. The effectiveness of BBG treatment in modulating LN was confirmed in NZM2328 mice with AdIFNα-accelerated disease. CONCLUSION: Activation of the P2X7 signaling pathway accelerates murine LN by activating the NLRP3/ASC/caspase 1 inflammasome, resulting in increased IL-1ß production and enhanced Th17 cell polarization. Thus, targeting of the P2X7 /NLRP3 pathway should be considered as a novel therapeutic strategy in patients with lupus.

Pharmacological inhibition of platelet reactivity. Clinical and pharmacodynamic effects.

Platelets play an important role in both normal hemostasis and pathological thrombus formation. The key role of platelets in thrombosis is highlighted by the clinical benefit of treatment with antiplatelet drugs. Aspirin, either alone or in combination with clopidogrel in high-risk patients, is the most widely used antiplatelet agent. However, there is an individual response to these agents that may reduce the cardiovascular protection in patients who achieve a lower antiplatelet effect. Recently, P2Y12 receptor antagonists more potent than clopidogrel (e.g., prasugrel and ticagrelor) have been approved for patients with acute coronary syndromes and those undergoing percutaneous coronary interventions; these drugs provide greater platelet inhibition than clopidogrel. However, the increased effectiveness of these treatments has underscored the importance of carefully balancing the risks of ischemia and bleeding to achieve the best clinical outcomes. The increased knowledge of the molecular mechanisms of platelet activation has prompted a search for novel pharmacological targets for the inhibition of platelet reactivity. This article reviews the molecular mechanisms of action and limitations of use of current and emerging antiplatelet agents for treatment of cardiovascular disease.