Developmental Differences in Platelet Inhibition Response to Prostaglandin E1

Abstract

<b><i>Background:</i></b> The mechanisms underlying neonatal platelets hyporesponsiveness are not fully understood. While previous studies have demonstrated developmental impairment of agonist-induced platelet activation, differences in inhibitory signaling pathways have been scarcely investigated. <b><i>Objective:</i></b> To compare neonatal and adult platelets with regard to inhibition of platelet reactivity by prostaglandin E1 (PGE<sub>1</sub>). <b><i>Methods:</i></b> Platelet-rich plasma from umbilical cord (CB) or adult blood was incubated with PGE<sub>1</sub> (0–1 μM). We assessed aggregation in response to adenosine diphosphate (ADP), collagen, and thrombin receptor activating peptide as well as cyclic adenosine 3′5′-monophosphate (cAMP) levels (ELISA). G<sub>αs</sub>, G<sub>αi2</sub>, and total- and phospho-protein kinase A (PKA) were evaluated in adult and CB ultrapure and washed platelets, respectively, by immunoblotting. <b><i>Results:</i></b> Neonatal (vs. adult) platelets display hypersensitivity to inhibition by PGE<sub>1</sub> of platelet aggregation induced by ADP and collagen (PGE<sub>1</sub> IC<sub>50</sub>: 14 and 117 nM for ADP and collagen, respectively, vs. 149 and 491 nM in adults). They also show increased basal and PGE<sub>1</sub>-induced cAMP levels. Mechanistically, PGE<sub>1</sub> acts by binding to the prostanoid receptor IP (prostacyclin receptor), which couples to the G<sub>αs</sub> protein-adenylate cyclase axis and increases intracellular levels of cAMP. cAMP activates PKA, which phosphorylates different target inhibitor proteins. Neonatal platelets showed higher basal and PGE<sub>1</sub>-induced cAMP levels, higher G<sub>αs</sub> protein expression, and a trend to increased PKA-dependent protein phosphorylation compared to adult platelets. <b><i>Conclusion:</i></b> Neonatal platelets have a functionally increased PGE<sub>1</sub>-cAMP-PKA axis. This finding supports a downregulation of inhibitory when going from neonate to adult contributing to neonatal platelet hyporesponsiveness.

Qualitative and Quantitative Comparison of Plasma Exosomes from Neonates and Adults

“…Worthy of special note is GNAI2, the main member of the Gαi family expressed on platelets [41]. In fact, in line with the higher levels of GNAI2 in plasma exosomes from neonates, we previously found that the expression levels of the gene that encode this protein, GNAI2, are significantly higher in neonatal platelets than in adult platelets [13].…”

“…Despite the poor reactivity of platelets during the fetal/neonatal life, compared with older children or adults, healthy full-term infants exhibit normal to increased primary hemostasis due to factors in neonatal blood that enhance the platelet vessel wall interaction (i.e., increased von Willebrand factor (vWF) levels and function, higher hematocrit levels or higher mean corpuscular volumes of erythrocytes) [1]. Thus, platelet hyporeactiveness during the first weeks of life is seen as part of an exceptional and well-balanced haemostatic system [1,13].…”

“…SNARE proteins mediate the membrane fusion process [17] between the plasma/target (t) membrane and the granular/vesicle (v) membrane [16,[18][19][20]. Specifically, in platelets, the fusogenic complex is composed of one v-SNARE vesicle-associated membrane protein 8 (VAMP8) and two t-SNAREs (syntaxin- [11][12][13][14][15][16][17][18][19][20][21][22][23]. Interactions between v-and t-SNAREs are controlled by regulator proteins, the Sec 1/Munc proteins [17].…”

Twin‐twin transfusion syndrome complicated by single ventricle physiology: A case report

“…A side effect of PGE is inhibition of platelet function, especially in neonates, so tranexamic acid infusions were used to minimize blood loss. 4 The FiO 2 was decreased intraoperatively to optimize Qp:Qs balance. Intraoperatively, Twin B required substantial hemodynamic support while carefully preserving…”

Hemostatic Challenges in Neonates

“…Different mechanisms contribute to the reduced responses of neonatal platelets to various agonists: 1. the hyporesponsiveness to epinephrine is due to a marked reduction in the number of α2-adrenergic receptors, the binding sites for epinephrine, on the surface of neonatal platelets; 2. the decreased responsiveness to thrombin is related to reduced expression of the thrombin receptors PAR-1 and PAR-4 in neonatal platelets (16); 3. the decreased response to thromboxane results from reduced signaling downstream from the receptor (17); 4. the reduced responses to collagen and rhodocytin result from mildly reduced expression of GPVI and CLEC-2, respectively, coupled with an intracellular signaling defect evidenced by reduced Syk and PLCγ2 phosphorylation following stimulation (14). Recently, developmental differences have also been described in regard to platelet inhibitory pathways, specifically a hypersensitivity of neonatal platelets to the inhibitory effects of prostaglandin E1 (PGE 1 ) during ADP-and collagen-induced platelet aggregation, associated with a functional increase in the PGE 1 -cAMP-PKA axis (18).…”