Cilostazol and dipyridamole synergistically inhibit human platelet aggregation

Combining dipyridamole and cilostazol with up-dosing antihistamines improves outcomes in chronic spontaneous urticaria with high D-dimer levels: A randomized controlled trial

In a double-blind, randomized controlled trial, we investigated the effectiveness of adding antiplatelet drugs to up-dosing antihistamines for the treatment of chronic spontaneous urticaria (CSU) in patients with elevated D-dimer levels who had an inadequate response to conventional antihistamine doses. Twenty patients with Urticaria Activity Score over 7 days (UAS7) ≥16 and D-dimer >500 ng/mL were randomized to receive either antiplatelet therapy (cilostazol 150 mg/day + dipyridamole 50 mg/day) with antihistamine (desloratadine 20 mg/day) or antihistamine alone for 4 weeks. The antiplatelet group demonstrated a greater decrease in UAS7 compared to the control group (28.10 to 8.90 vs. 22.90 to 16.40, p < 0.001 vs. p = 0.054). Both groups experienced improved quality of life (DLQI), but the improvement was greater in the antiplatelet group (p = 0.046). D-dimer levels decreased only in the antiplatelet group (1133.67 ng/mL to 581.89 ng/mL, p = 0.013) with no significant change observed in the control group. This suggests that combining dipyridamole and cilostazol with up-dosing antihistamines may be more effective for CSU patients with high D-dimer levels compared to up-dosing antihistamines alone. This could be due to a reduction in platelet activation, as evidenced by the decrease in D-dimer levels observed in the antiplatelet group.

Drugs targeting adenosine signaling pathways: A current view

Adenosine is an endogenous nucleoside that regulates many physiological and pathological processes. It is derived from either the intracellular or extracellular dephosphorylation of adenosine triphosphate and interacts with cell-surface G-protein-coupled receptors. Adenosine plays a substantial role in protecting against cell damage in areas of increased tissue metabolism and preventing organ dysfunction in pathological states. Targeting adenosine metabolism and receptor signaling may be an effective therapeutic approach for human diseases, including cardiovascular and central nervous system disorders, rheumatoid arthritis, asthma, renal diseases, and cancer. Several lines of evidence have shown that many drugs exert their beneficial effects by modulating adenosine signaling pathways but this knowledge urgently needs to be summarized, and most importantly, actualized. The present review collects pharmaceuticals and pharmacological or diagnostic tools that target adenosine signaling in their primary or secondary mode of action. We overviewed FDA-approved drugs as well as those currently being studied in clinical trials. Among them are already used in clinic A2A adenosine receptor modulators like istradefylline or regadenoson, but also plenty of anti-platelet, anti-inflammatory, or immunosuppressive, and anti-cancer drugs. On the other hand, we investigated dozens of specific adenosine pathway regulators that are tested in clinical trials to treat human infectious and noninfectious diseases. In conclusion, targeting purinergic signaling represents a great therapeutic challenge. The actual knowledge of the involvement of adenosinergic signaling as part of the mechanism of action of old drugs has open a path not only for drug-repurposing but also for new therapeutic strategies.

The NO/cGMP/PKG pathway in platelets: The therapeutic potential of PDE5 inhibitors in platelet disorders

Platelets are the "guardians" of the blood circulatory system. At sites of vessel injury, they ensure hemostasis and promote immunity and vessel repair. However, their uncontrolled activation is one of the main drivers of thrombosis. To keep circulating platelets in a quiescent state, the endothelium releases platelet antagonists including nitric oxide (NO) that acts by stimulating the intracellular receptor guanylyl cyclase (GC). The latter produces the second messenger cyclic guanosine-3',5'-monophosphate (cGMP) that inhibits platelet activation by stimulating protein kinase G, which phosphorylates hundreds of intracellular targets. Intracellular cGMP pools are tightly regulated by a fine balance between GC and phosphodiesterases (PDEs) that are responsible for the hydrolysis of cyclic nucleotides. Phosphodiesterase type 5 (PDE5) is a cGMP-specific PDE, broadly expressed in most tissues in humans and rodents. In clinical practice, PDE5 inhibitors (PDE5i) are used as first-line therapy for erectile dysfunction, pulmonary artery hypertension, and lower urinary tract symptoms. However, several studies have shown that PDE5i may ameliorate the outcome of various other conditions, like heart failure and stroke. Interestingly, NO donors and cGMP analogs increase the capacity of anti-platelet drugs targeting the purinergic receptor type Y, subtype 12 (P2Y12) receptor to block platelet aggregation, and preclinical studies have shown that PDE5i inhibits platelet functions. This review summarizes the molecular mechanisms underlying the effect of PDE5i on platelet activation and aggregation focusing on the therapeutic potential of PDE5i in platelet disorders, and the outcomes of a combined therapy with PDE5i and NO donors to inhibit platelet activation.

Cilostazol: a Review of Basic Mechanisms and Clinical Uses

Primarily used in the treatment of intermittent claudication, cilostazol is a 2-oxyquinolone derivative that works through the inhibition of phosphodiesterase III and related increases in cyclic adenosine monophosphate (cAMP) levels. However, cilostazol has been implicated in a number of other basic pathways including the inhibition of adenosine reuptake, the inhibition of multidrug resistance protein 4, among others. It has been observed to exhibit antiplatelet, antiproliferative, vasodilatory, and ischemic-reperfusion protective properties. As such, cilostazol has been investigated for clinical use in a variety of settings including intermittent claudication, as an adjunctive for reduction of restenosis after coronary and peripheral endovascular interventions, and in the prevention of secondary stroke, although its widespread implementation for indications other than intermittent claudication has been limited by relatively modest effect sizes and lack of studies in western populations. In this review, we highlight the pleiotropic effects of cilostazol and the evidence for its clinical use.

Progress in the development of antiplatelet agents: Focus on the targeted molecular pathway from bench to clinic

Antiplatelet drugs serve as a first-line antithrombotic therapy for the management of acute ischemic events and the prevention of secondary complications in vascular diseases. Numerous antiplatelet therapies have been developed; however, currently available agents are still associated with inadequate efficacy, risk of bleeding, and variability in individual response. Understanding the mechanisms of platelet involvement in thrombosis and the clinical development process of antiplatelet agents is critical for the discovery of novel agents. The functions of platelets in thrombosis are regulated by two major mechanisms: the interaction between surface receptors and their ligands, and the downstream intracellular signaling pathways. Recently, most of the progress made in antiplatelet drug development has been achieved with P2Y receptor antagonists. Additionally, the usage of GP IIb/IIIa receptor antagonists has decreased, because it is associated with a higher risk of bleeding and thrombocytopenia. Agents targeting other platelet surface receptors such as PARs, TP receptor, EP3 receptor, GPIb-IX-V receptor, P-selectin, as well as intracellular signaling factors, such as PI3Kβ, have been evaluated in an attempt to develop the next generation of antiplatelet drugs, reduce or eliminate interpatient variability of drug efficacy and significantly lower the risk of drug-induced bleeding. The aim of this review is to describe the pathways of platelet activation in thrombosis, and summarize the development process of antiplatelet agents, as well as the preclinical and clinical evaluations performed on these agents.

Role of and Recent Evidence for Antiplatelet Therapy in Prevention of Cardiovascular Disease in Diabetes

PURPOSE OF REVIEW

When treating patients with diabetes mellitus (DM), the benefits of antiplatelet therapy in preventing cardiovascular disease must be weighed against an increased risk of bleeding. Recent trials have sought to determine both the optimal anti-platelet regimen for patients with DM, and who specifically requires medication among the DM population. This paper will review recent trials and evidence recommending the use of antiplatelet therapy in the prevention of cardiovascular disease in patients with diabetes.

RECENT FINDINGS

Seven notable trials assessed the effectiveness of antiplatelet therapy in the DM population. The ASCEND trial concluded 100 mg aspirin/day reduced rates of serious vascular events (OR 0.88, p < 0.01) but also increased rates of major bleeding events (OR 1.29, p < 0.01). The DAPT study revealed a longer dual antiplatelet regimen (30 months vs. 18 months) after coronary stent placement was more effective in reducing rates of stent thrombosis (0.5% vs. 1.1%, p = 0.06) and rates of myocardial infarction (3.5% vs. 4.8%, p = 0.06). DECLARE DIABETES showed that adding cilostazol to dual antiplatelet therapy after a coronary stent procedure reduced rates of in-stent and in-segment late loss and increased rates of revascularization (p < 0.04). In PEGASUS-TIMI, daily ticagrelor demonstrated reduced rates of major adverse cardiovascular and cerebrovascular events (OR 0.84, p < 0.04). The DAVID trial compared daily picotamide with daily aspirin therapy, finding reduced mortality rates in the picotamide group (OR 0.55, p < 0.05). Lastly, ACUITY found bivalirudin monotherapy resulted in lower rates of major bleeding events when compared to a glycoprotein IIb/IIa inhibitor and heparin or bivalirudin combination regimen (p < 0.01). Dual antiplatelet therapy guidelines still typically revolve around aspirin, but an increasing number of studies have demonstrated other drugs that may have a role in preventing atherosclerotic cardiovascular disease while decreasing the risk of major bleeding. Overall, it is wise to weigh the cardiovascular risk of a DM patient before prescribing antiplatelet medication. More research is necessary to determine a universal drug or combination of drugs that is safe and effective for DM patients.

Effect of adjunctive dipyridamole to DAPT on platelet function profiles in stented patients with high platelet reactivity. The result of the ACCEL-DIP Study

Adjunctive use of phosphodiesterase (PDE) inhibitor can enhance antiplatelet and vasoprotective properties in patients with cardiovascular disease. The aim of this study was to evaluate the impact of PDE5 inhibitor dipyridamole on platelet function in stented patients with high platelet reactivity (HPR) during dual antiplatelet therapy (DAPT) with aspirin and clopidogrel. Patients with HPR after 600-mg clopidogrel loading were randomly assigned to adjunctive dipyridamole 75 mg twice daily to standard DAPT (DIP group; n = 45) or double-dose clopidogrel of 150 mg daily (DOUBLE group; n = 46) for 30 days. Platelet function was assessed at baseline and 30-day follow-up with platelet reactivity index (PRI) by vasodilator-stimulated phosphoprotein-phosphorylation (VASP-P) assay and platelet aggregation (PA) by light transmittance aggregometry (LTA). Primary endpoint was PRI at 30-day follow-up. HPR was defined as PRI > 50%. Baseline platelet function did not differ between the groups. Following 30-day therapy, platelet function was significantly reduced in the DIP and DOUBLE groups (all p-values ≤ 0.004 and ≤ 0.068, respectively). PRI values were not significantly different between the two groups (mean difference: 3.1%; 95% confidence interval: -2.8% to 9.0%: p = 0.295). PA values and prevalence of HPR were similar between the groups. However, a significant number of patients still exhibited HPR in the DIP (75.6%) and DOUBLE (67.4%) groups. In conclusion, among stented HPR patients, adding dipyridamole to DAPT does not reduce platelet reactivity and prevalence of HPR compared with double-dose clopidogrel therapy, and therefore both strategies are inadequate to overcome HPR.

Regulatory mechanisms of cAMP levels as a multiple target for antiplatelet activity and less bleeding risk

Platelet activation is a critical component of atherothrombosis. The multiple pathways of platelet activation limit the effect of specific receptor/pathway inhibitors, resulting in limited clinical efficacy. Recent research has confirmed that combination therapy results in enhanced antithrombotic efficacy without increasing bleeding risk. In this way, the best-known inhibitor and turn off signaling in platelet activation is cAMP. In this article we discuss the mechanisms of regulation of intraplatelet cAMP levels, a) platelet-dependent pathway: Gi/Gs protein-coupled receptors, phosphodiesterase inhibition and activation of PPARs and b) platelet-independent pathway: inhibition of adenosine uptake by erythrocytes. With respect to the association between intraplatelet cAMP levels and bleeding risk it is possible to establish that compounds/drugs with pleitropic effect for increased intraplatelet cAMP level could have an antithrombotic activity with less risk of bleeding.

Cilostazol attenuates hepatic stellate cell activation and protects mice against carbon tetrachloride-induced liver fibrosis

AIM

Liver fibrosis is a common pathway leading to cirrhosis. Cilostazol, a clinically available oral phosphodiesterase-3 inhibitor, has been shown to have antifibrotic potential in experimental non-alcoholic fatty liver disease. However, the detailed mechanisms of the antifibrotic effect and its efficacy in a different experimental model remain elusive.

METHODS

Male C57BL/6J mice were assigned to five groups: mice fed a normal diet (groups 1 and 2); 0.1% or 0.3% cilostazol-containing diet (groups 3 and 4, respectively); and 0.125% clopidogrel-containing diet (group 5). Two weeks after feeding, groups 2-5 were intraperitoneally administered carbon tetrachloride (CCl4 ) twice a week for 6 weeks, while group 1 was treated with the vehicle alone. To investigate the effects of cilostazol on hepatic cells, in vitro studies were conducted using primary hepatic stellate cells (HSC), Kupffer cells and hepatocytes with cilostazol supplementation.

RESULTS

Sirius red staining revealed that groups 3 and 4 exhibited a lesser fibrotic area (2.49 ± 0.43% and 2.31 ± 0.30%, respectively) than group 2 (3.17 ± 0.67%, P < 0.05 and P < 0.001, respectively). In vitro studies showed cilostazol dose-dependently suppressed HSC activation (assessed by morphological change, cell proliferation, and the expression of HSC activation markers), suggesting the therapeutic effect of cilostazol is mediated by its direct action on HSC.

CONCLUSION

Cilostazol could alleviate CCl4 -induced hepatic fibrogenesis in vivo, presumably due, at least partly, to its direct effect to suppress HSC activation. Given its clinical availability and safety, it may be a novel therapeutic intervention for chronic liver diseases.

Cilostazol increases tissue blood flow in contracting rabbit gastrocnemius muscle

BACKGROUND

The mechanisms underlying the ability of cilostazol to improve walking distance in patients with intermittent claudication (IC) are not fully understood, but may be related to its phosphodiesterase type 3 (PDE3) and adenosine uptake inhibition. In the present study the effect of cilostazol on blood flow and interstitial adenosine concentration was compared with that of the PDE3 inhibitor, milrinone, and the adenosine uptake inhibitor, draflazine.

METHODS AND RESULTS

Rabbit gastrocnemius muscle blood flow was measured under resting, contracting and ischemic conditions. Interstitial adenosine was sampled by microdialysis. None of the drugs affected tissue blood flow at rest. Blood flow in electrically stimulated muscle was 2- to 3-fold higher in vehicle-, milrinone- and draflazine-treated animals. However, cilostazol caused an 8-fold increase. Ligation of the femoral artery decreased blood flow in the stimulated muscle in all groups to a similar degree. Cilostazol and draflazine increased the dialysate adenosine concentration during the first 10 min of muscle contraction, but had no effect during ischemia, most likely because of the high AMP deaminase activity in skeletal muscle.

CONCLUSIONS

Cilostazol increases blood flow in the gastrocnemius muscle during contraction and it is this effect that may be partially responsible for the improved walking distance in IC patients. (Circ J 2010; 74: 181 - 187).

Synergistic effect of cilostazol and dipyridamole mediated by adenosine on shear-induced platelet aggregation

INTRODUCTION

The Cilostazol Stroke Prevention Study found that cilostazol, a phosphodiesterase 3 inhibitor, can reduce the risk of subsequent stroke in Japanese patients with cerebral infarction. Here, we measured the effects of cilostazol in vitro on shear-induced platelet aggregation, an important mechanism of thrombosis at arterial bifurcations or stenotic lesions. We also evaluated the influences of intrinsic adenosine on the ability of cilostazol to inhibit shear-induced platelet aggregation by investigating the effect of dipyridamole, an inhibitor of cellular adenosine reuptake, in combination with cilostazol in vitro.

MATERIALS AND METHODS

We measured platelet aggregation induced by a shear rate of 10,800 s(-1) in whole blood and in platelet-rich plasma from healthy volunteers using a cone-plate streaming chamber.

RESULTS

Both cilostazol and adenosine dose-dependently inhibited shear-induced platelet aggregation in platelet-rich plasma samples. Adding a low concentration of adenosine (0.3 microM) did not inhibit shear-induced platelet aggregation, but significantly enhanced the inhibitory effect of cilostazol in platelet-rich plasma. Dipyridamole dose-dependently inhibited shear-induced platelet aggregation in whole blood and significantly enhanced the inhibitory effect of cilostazol on shear-induced platelet aggregation, but did not affect shear-induced platelet aggregation in platelet-rich plasma. The inhibitory effects of cilostazol combined with dipyridamole in whole blood were almost completely reversed by adenosine deaminase.

CONCLUSIONS

Dipyridamole appears to synergistically enhance the inhibitory effect of cilostazol on shear-induced platelet aggregation by maintaining high plasma levels of adenosine.

Antiplatelet and Antithrombotic Activity of Cilostazol is Potentiated by Dipyridamole in Rabbits and Dissociated from Bleeding Time Prolongation

PURPOSE

To determine the antiplatelet effect of cilostazol (Pletal) and its interaction with dipyridamole in in vitro and in vivo rabbit models, and to see if it can be dissociated from bleeding time prolongation.

METHODS

In vitro collagen-induced platelet aggregation was measured by an impedance-based aggregometer. The in vivo antithrombotic effect was evaluated in a rabbit carotid artery cyclic flow reduction (CFR) model, in which repetitive thrombosis was induced by mechanical injuries of the artery and stenosis. Template bleeding time was determined in rabbit ear arterioles and hindlimb nail cuticles.

RESULTS

In vitro platelet aggregation was slightly inhibited by 4 microM cilostazol (22 +/- 6%), and modestly by 13 microM (57 +/- 3% of aggregation). While dipyridamole itself up to 13 microM had no significant inhibition, it potentiated the effect from cilostazol: in the presence of 4 microM dipyridamole, 4 microM cilostazol inhibited aggregation by 47 +/- 6%. Dipyridamole also potentiated the CFR reducing effect of cilostazol: combination of dipyridamole (no effect by itself) and cilostazol at 1 microM decreased CFRs to levels achieved by 3-4 microM cilostazol alone. Bleeding times were similar in controls and animals treated with cilostazol, or with cilostazol and dipyridamole. In contrast, aspirin (4 mg/kg), while reducing CFRs, significantly increased bleeding time.

CONCLUSION

These results suggest that dipyridamole potentiates the antiplatelet effect of cilostazol without prolongation of the bleeding time, implying a potential novel combination antithrombotic therapy.