The balance of concurrent aggregation and deaggregation processes in platelets is linked to differential occupancy of ADP receptor subtypes

Maayani, Saul; Tagliente, Thomas M.; Schwarz, Todd; Martinelli, Giorgio P.; Martinez, Rafael; Shore‐Lesserson, Linda

doi:10.1080/09537100020032846

Cited by 15 publications

(13 citation statements)

References 46 publications

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“…These results provide experimental support for the hypothesis that the native platelet net aggregation response mediated by proaggregatory stimuli is an inhibited response due to the presence of constitutive AC activity and the deaggregation it maintains. Based on our previous communications [9][10][11]80 and on the data presented here we propose that the default state of circulating platelets is constitutive deaggregation, which requires deceleration to enhance and sustain aggregation. We further propose that the requirement for the stability of platelet aggregation may be related to the deceleration of this AC-III/cAMP-related active deaggregation mechanism.…”

Section: Platelets 29mentioning

confidence: 94%

“…11 The platelet pellets were prepared from the upper 2 ml of the PRP by centrifugation at 3000 Â g for 5 min at 4 C, quickly washed once with PBS (Gibco BRL, Gaithersburg, MD) under the same conditions and used for total RNA isolation. The buffy coat fraction (about 0.5 ml), a control for leukocyte RNA contamination, was centrifuged and the pellet washed as described above and used for total RNA isolation.…”

Section: Methodsmentioning

confidence: 99%

“…7,8 We recently proposed that the activation of G i -coupled P2Y 12 and 2A receptors releases a tonic state of inhibited platelet aggregation through the deceleration of an active deaggregation mechanism. [9][10][11] We demonstrated that blockade of the G i -coupled P2Y 12 purinergic receptor by the clinically efficacious anti-platelet agents ticlopidine and clopidogrel 12,13 accelerate deaggregation. 10 Agents that increase AC activity/cAMP content inhibit platelet aggregation [14][15][16][17] and can also be classified as potent accelerators of deaggregation.…”

Section: Introductionmentioning

confidence: 96%

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Molecular and biochemical evidence for the presence of Type III adenylyl cyclase in human platelets

et al. 2003

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The isoform(s) of adenylyl cyclase (AC) present in human platelets has not been identified, and evidence supporting a role for AC in platelet aggregation is equivocal. We recently characterized deaggregation as an active component of the platelet aggregation response that may be an important determinant of the extent and duration of aggregation. G(i)-coupled receptors are linked to the inhibition of AC and are targets of antiplatelet drugs. They also affect platelet aggregation by modulating deaggregation, suggesting a role for AC in modulating this response. The purpose of this study was to identify the AC isoform(s) present in human platelets and to identify its physiological modulators. RT-PCR screening of platelet, buffy coat layer cell and bone marrow megakaryocyte cDNA, and Western blot analysis with AC type III (AC-III) antibodies identified AC-III in platelets and in megakaryocytes. Human platelet AC-III was cloned and expressed in HEK293 cells and its characteristics compared to native platelet AC. Both platelet AC and cloned AC-III required Mg(2+) for activity, were insensitive to Ca(2+) and were G(s)- and G(i)-coupled. Zn(2+) and SQ22536 inhibited platelet AC activity. The affinity of SQ22536 was increased with Mg(2+)-related stimulation of AC, while that of Zn(2+) was unchanged, which is consistent with a non-competitive interaction between the two metal ions on AC. The Zn(2+) chelator TPEN reversed the inhibitory effects of Zn(2+). This study identified AC-III as the predominant AC isoform in human platelets, the activity of which may affect the extent and duration of the net aggregation response by modulating deaggregation.

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Section: Platelets 29mentioning

confidence: 94%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

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Molecular and biochemical evidence for the presence of Type III adenylyl cyclase in human platelets

et al. 2003

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“…In addition, the data collected using the 96-well plate method are comparable to previous reports of the time course of the ADP response, in vitro, using analog instruments, regardless of the blood/platelet preparation or assay conditions (e.g., Refs. [46][47][48][49]51,53).…”

Section: Platelet Aggregationmentioning

confidence: 98%

Activation of the 2A –adrenoceptor mediates deceleration of the deaggregation component of the response to ADP or 5-HT in human platelets in vitro

Maayani

Schwarz²,

Craddock-Royal³

et al. 2001

Platelets

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Platelet aggregation requires the concomitant activation of at least one G(i)- and one G(q)-coupled receptor. Epinephrine (EPI) amplifies the response elicited by a number of agonists for platelet aggregation. This study tested the hypothesis that platelet alpha(2A)-adrenoceptor activation causes deceleration of the deaggregation component of the platelet aggregation response when activated concomitantly with the G(q)-coupled adenosine diphosphate (ADP) P2Y(1) or 5-hydroxytryptamine(2A) receptor. The time course of the aggregation response of human platelet-rich plasma following activation of combinations of two or three receptors was assessed by turbidometry using lepirudin anticoagulation. Simultaneous activation of specific two- and three-receptor combinations was achieved using selective antagonists for the P2Y(12) and P2Y(1) receptor subtypes. Steady-state and kinetic parameters, obtained using a four-compartment kinetic model, were used to assess the effects on the net aggregation response. Graded alpha(2A)-adrenoceptor activation was associated with a concentration-dependent decrease of the rate constant of deaggregation. Activation of both ADP receptor subtypes and the alpha(2A)-adrenoceptor produced a concentration-dependent, mutual amplification of the aggregation response. In addition, when three receptors were simultaneously activated, mutual amplification of the aggregation response was observed at physiologically relevant concentrations of epinephrine or norepinephrine (NE) and ADP. We propose that similar to the P2Y(12) receptor, activation of the alpha(2A)-adrenoceptor decelerates the deaggregation component shifting the balance toward increased net aggregation. The effects of EPI and NE on the aggregation response may contribute to the mechanism of increased thrombotic risk present in certain pathophysiological and disease states.

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“…Final (late) aggregation has been reported to rather reflect the final aggregation state of platelets, but only partly accounting for resolution of unstable platelet aggregates [12]. Previous reports suggest that balance between deaggregation and aggregation is strongly linked to P2Y 12 receptor occupancy [13]. The prognostic role of deaggregation in clopidogrel treated patients has not been well investigated and its predictive value in combination with established aggregation parameters remains to be determined.…”

Section: Introductionmentioning

confidence: 97%

Combination of high on-treatment platelet aggregation and low deaggregation better predicts long-term cardiovascular events in PCI patients under dual antiplatelet therapy

Karathanos

Tavlaki

et al. 2013

Platelets

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High on-treatment platelet reactivity is associated with short-term major cardiovascular (CV) events in patients undergoing percutaneous coronary intervention (PCI). Maximum and final aggregation assessed by light transmission aggregometry (LTA) have both been used to predict short-term outcome after PCI, however their long-term prognostic impact remains controversial. There is currently no information regarding the prognostic role of deaggregation and its added value in combination with established aggregation parameters. About 1279 patients with symptomatic coronary artery disease (CAD) undergoing PCI were enrolled in this monocentric study. On-treatment platelet aggregation under clopidogrel maintenance therapy, as well as deaggregation was determined by maximum and final aggregation (5 min after adding of the agonist). Deaggregation was defined as slope of the tangent between Aggmax +0.5 min. Primary endpoints were the composite of myocardial infarction, stroke, and CV death or stent thrombosis according to the ARC criteria. Low deaggregation, defined as values in the lowest tertile (<1.5), was more frequent in patients with acute coronary syndromes (ACS) compared to patients with stable angina pectoris (SAP), ACS: 29.6% vs. SAP: 22.0%, p = 0.001. The combination of high on-treatment platelet reactivity, defined by the upper tertile of Aggmax and low deaggregation, was associated with significantly increased risk for combined long-term CV events. The combination of low deaggregation and high on-treatment platelet reactivity is associated with higher risk for recurrent events in patients with CAD undergoing PCI. Thus, deaggregation might be a more sensitive parameter providing added value in terms of risk prediction for long-term recurrent CV events in relation with established aggregation parameters.

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The balance of concurrent aggregation and deaggregation processes in platelets is linked to differential occupancy of ADP receptor subtypes

Cited by 15 publications

References 46 publications

Molecular and biochemical evidence for the presence of Type III adenylyl cyclase in human platelets

Molecular and biochemical evidence for the presence of Type III adenylyl cyclase in human platelets

Activation of the 2A –adrenoceptor mediates deceleration of the deaggregation component of the response to ADP or 5-HT in human platelets in vitro

Combination of high on-treatment platelet aggregation and low deaggregation better predicts long-term cardiovascular events in PCI patients under dual antiplatelet therapy

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