Systemic Evaluation of Platelet and Leukocyte Activation and Interaction in a Rat Model of Pulmonary Arterial Hypertension

Abstract

Objectives: Thrombosis and inflammation are associated with the pathogenesis of pulmonary arterial hypertension (PAH). However, there are no solid data supporting the involvement of platelet and leukocyte activation and interaction in PAH. The present study thus investigated the activation and interaction of circulating platelets and leukocytes in a rat model of monocrotaline (MCT)-induced pulmonary hypertension. Methods: Mean pulmonary arterial pressure (mPAP) was monitored in rats (n = 24) before and 2, 3 and 7 weeks after MCT (60 mg/kg)injection. In parallel, activation of circulating platelets and leukocytes and platelet-leukocyte aggregates were measured by whole-blood flow cytometry. Results: Two weeks after MCT injection, mPAP had increased significantly, i.e. from 11.25 ± 0.92 mm Hg at baseline to 15.71 ± 1.66 mm Hg (p < 0.05), and it had increased even further at week 7 (26.83 ± 3.29 mm Hg; p < 0.01). Fibrinogen binding of circulating platelets had increased from the basal level of 1.45 ± 0.61 to 4.08 ± 1.59% 3 weeks after MCT injection (p < 0.01). Platelet responsiveness to ADP was also significantly enhanced. CD11b expression of circulating neutrophils was elevated; i.e. mean fluorescence intensity increased from 1.67 ± 0.38 before MCT injection to 2.37 ± 0.31 3 weeks after MCT injection (p < 0.01), and N-formyl-methionyl-leucyl-phenylalanine (1 × 10^–7M) stimulation induced more marked elevation of neutrophil CD11b expression in MCT-treated animals. Circulating platelet-neutrophil aggregates were already increased 2 weeks after MCT treatment (14.93 ± 4.22%; p < 0.01) compared to baseline (6.01 ± 2.91%) and remained elevated at 3 weeks (15.19 ± 4.78%; p < 0.01). Conclusions: MCT-induced PAH in rats is associated with increased platelet and leukocyte activation and platelet-leukocyte interaction in vivo, which may play an important role in the pathogenesis of PAH.

Platelet-Mediated Mesenchymal Stem Cells Homing to the Lung Reduces Monocrotaline-Induced Rat Pulmonary Hypertension

“…Thus, homing of MSCs was only evident 1 week after cell transplantation. Interestingly, this is in agreement with the platelet activation kinetics in this PAH rat model; as we have previously shown, clear platelet activation only starts to emerge at least 1 week after MCT injection (14). Thus, it appears that MSC homing is correlated with platelet activation in vivo.…”

“…When vascular endothelium is injured, the coagulation system and the activation of platelets start simultaneously (7,24). We have also demonstrated an enhanced ex vivo platelet activation and platelet–leukocyte interaction in the rat model of PAH (14). Many studies have shown that activated platelets promote initial tethering, firm adhesion, migration, and differentiation of EPCs (6,21).…”

“…Interestingly, this is in agreement with the platelet activation kinetics in this PAH rat model; as such a limited therapeutic time window, the favorable effects of MSCs may not be sufficient to counteract the we have previously shown, clear platelet activation only starts to emerge at least 1 week after MCT injection exacerbating PAH pathogenesis. Moreover, the rapid progression of PAH was associated with systemic (14). Thus, it appears that MSC homing is correlated with platelet activation in vivo.…”

“…We have also demonstrated an enhanced ex vivo platelet activation and platelet-leukocyte interaction in ment of PAH are urgently needed. the rat model of PAH (14). Many studies have shown Sprague-Dawley rats weighing between 180 and 250 g received a single subcutaneous injection of 60 mg/kg that activated platelets promote initial tethering, firm adhesion, migration, and differentiation of EPCs (6,21).…”

Human Immunodeficiency Virus, Herpes Virus Infections, and Pulmonary Vascular Disease

“…[13] In fact, one of the typical pathological changes observed histologically in PAH is thrombosis in situ. The importance of platelets is highlighted by the fact that aspirin attenuates PAH in monocrotaline-treated rats by reducing plasma 5-hydroxytryptamine levels and increasing survival.…”