Increased Smad2/3 phosphorylation in circulating leukocytes and platelet-leukocyte aggregates in a mouse model of aortic valve stenosis: Evidence of systemic activation of platelet-derived TGF-ß1 and correlation with cardiac dysfunction.

BACKGROUND: Transforming growth factor-ß1 (TGF-ß1) has been implicated in the pathogenesis of aortic valve stenosis (AS). There is, however, little direct evidence for a role of active TGF-ß1 in AS due to the sensitivity of current assays. We searched for evidence of plasma TGF-ß1 activation by assaying Smad2/3 phosphorylation in circulating leukocytes and platelet-leukocyte aggregates (PLAs) in a mouse model of AS (Reversa). METHODS: Echocardiography was used to measure AS and cardiac function. Intracellular phospho-flow cytometry in combination with optical fluorescence microscopy was used to detect PLAs and p-Smad2/3 levels. RESULTS: Reversa mice on a western diet developed AS, had significantly increased numbers of PLAs and more intense staining for p-Smad2/3 in both PLAs and single leukocytes (all p<0.05). p-Smad2/3 staining was more intense in PLAs than in single leukocytes in both diet groups (p<0.05) and correlated with plasma total TGF-ß1 levels (r=0.38, p=0.05 for PLAs and r=0.37, p=0.06 for single leukocytes) and reductions in ejection fraction (r=-0.42, p=0.03 for PLAs and r=-0.37, p=0.06 for single leukocytes). CONCLUSIONS: p-Smad2/3 staining is more intense in leukocytes of hypercholesterolemic mice that developed AS, suggesting increased circulating active TGF-ß1 levels. Leukocyte p-Smad2/3 may be a valuable surrogate indicator of circulating active TGF-ß1.

Association between shear stress and platelet-derived transforming growth factor-ß1 release and activation in animal models of aortic valve stenosis.

OBJECTIVE: Aortic valve stenosis (AS) is characterized by fibrosis and calcification of valves leading to aortic valve narrowing, resulting in high wall shear stress across the valves. We previously demonstrated that high shear stress can activate platelet-derived transforming growth factor-ß1 (TGF-ß1), a cytokine that induces fibrosis and calcification. The aim of this study was to investigate the role of shear-induced platelet release of TGF-ß1 and its activation in AS. APPROACH AND RESULTS: We studied hypercholesterolemic Ldlr(-/-)Apob(100/100)/Mttp(fl/fl)/Mx1Cre(+/+) (Reversa) mice that develop AS on Western diet and a surgical ascending aortic constriction mouse model that acutely simulates the hemodynamics of AS to study shear-induced platelet TGF-ß1 release and activation. Reversa mice on Western diet for 6 months had thickening of the aortic valves, increased wall shear stress, and increased plasma TGF-ß1 levels. There were weak and moderate correlations between wall shear stress and TGF-ß1 levels in the progression and reversed Reversa groups and a stronger correlation in the ascending aortic constriction model in wild-type mice but not in mice with a targeted deletion of megakaryocyte and platelet TGF-ß1 (Tgfb1(flox)). Plasma total TGF-ß1 levels correlated with collagen deposition in the stenotic valves in Reversa mice. Although active TGF-ß1 levels were too low to be measured directly, we found (1) canonical TGF-ß1 (phosphorylated small mothers against decapentaplegic 2/3) signaling in the leukocytes and canonical and noncanonical (phosphorylated extracellular signal-regulated kinases 1/2) TGF-ß1 signaling in aortic valves of Reversa mice on a Western diet, and (2) TGF-ß1 signaling of both pathways in the ascending aortic constriction stenotic area in wild-type but not Tgfb1(flox) mice. CONCLUSIONS: Shear-induced, platelet-derived TGF-ß1 activation may contribute to AS.

RUC-4: a novel αIIbß3 antagonist for prehospital therapy of myocardial infarction.

OBJECTIVE: Treatment of myocardial infarction within the first 1 to 2 hours with a thrombolytic agent, percutaneous coronary intervention, or an αIIbß3 antagonist decreases mortality and the later development of heart failure. We previously reported on a novel small molecule αIIbß3 antagonist, RUC-2, that has a unique mechanism of action. We have now developed a more potent and more soluble congener of RUC-2, RUC-4, designed to be easily administered intramuscularly by autoinjector to facilitate its use in the prehospital setting. Here, we report the properties of RUC-4 and the antiplatelet and antithrombotic effects of RUC-2 and RUC-4 in animal models. APPROACH AND RESULTS: RUC-4 was ≈ 20% more potent than RUC-2 in inhibiting human ADP-induced platelet aggregation and much more soluble in aqueous solutions (60-80 mg/mL). It shared RUC-2's specificity for αIIbß3 versus αVß3, did not prime the receptor to bind fibrinogen, or induce changes in ß3 identified by a conformation-specific monoclonal antibody. Both RUC-2 and RUC-4 prevented FeCl3-induced thrombotic occlusion of the carotid artery in mice and decreased microvascular thrombi in response to laser injury produced by human platelets infused into transgenic mice containing a mutated von Willebrand factor that reacts with human but not mouse platelets. Intramuscular injection of RUC-4 in nonhuman primates at 1.9 and 3.85 mg/kg led to complete inhibition of platelet aggregation within 15 minutes, with dose-dependent return of platelet aggregation after 4.5 to 24 hours. CONCLUSIONS: RUC-4 has favorable biochemical, pharmacokinetic, pharmacodynamic, antithrombotic, and solubility properties as a prehospital therapy of myocardial infarction, but the possibility of increased bleeding with therapeutic doses remains to be evaluated.

Preclinical Studies of RUC-4, a Novel Platelet αIIbß3 Antagonist, in Non-Human Primates and With Human Platelets.

INTRODUCTION: We are developing the novel αIIbß3 antagonist, RUC-4, for subcutaneously (SC)-administered first-point-of-medical-contact treatment for ST Segment Elevated Myocardial Infarction (STEMI). METHODS: We studied the: 1. pharmacokinetics (PK) of RUC-4 at 1.0, 1.93, and 3.86 mg/kg IV, IM, and SC in non-human primates (NHPs); 2. impact of aspirin on RUC-4 IC50 in human platelet-rich plasma (PRP); 3. effect of different anticoagulants on the RUC-4 IC50 in human PRP; and 4. relationship between αIIbß3 receptor blockade by RUC-4 and inhibition of ADP-induced platelet aggregation. RESULTS: 1. All doses of RUC-4 were well tolerated, but animals demonstrated variable temporary bruising. IM and SC RUC-4 reached dose-dependent peak levels within 5-15 min, with T½ s between 0.28 and 0.56 hrs. Platelet aggregation studies in NHPs receiving IM RUC-4 demonstrated >80% inhibition of the initial slope of ADP-induced aggregation with all 3 doses 30 minutes post-dosing, with subsequent dose-dependent loss of inhibition over 4-5 hours. 2. The RUC-4 IC50 for ADP-induced platelet aggregation was unaffected by aspirin treatment (40±9 nM vs. 37±5 nM; p=0.39). 3. The RUC-4 IC50 was significantly higher in PRP prepared from PPACK-anticoagulated blood compared to citrate-anticoagulated blood using either TRAP (122±17 vs. 66±25 nM; p=0.05; n=4) or ADP (102±22 vs. 54±13; p<0.001; n=5). 4. There was a close correspondence between receptor blockade and inhibition of ADP-induced platelet aggregation, with aggregation inhibition beginning with ~40% receptor blockade and becoming nearly complete at >80% receptor blockade. DISCUSSION: Based on these results and others, RUC-4 has now progressed to formal preclinical toxicology studies.