Red Cell Microparticles (RMP) As Hemostatic Agent: Summary of Recent Advances
Authors: Ahn Yeon S , Jy Wenche , Horstman Lawrence L , Johansen Max E , Bidot Carlos 
Published: October 2019

Abstract
Abstract 2260

Introduction:
Microparticles (MP) derived from platelets (PMP), endothelia (EMP) and leukocytes (LMP) have received much attention as biomarkers in cardiovascular and inflammatory disorders. However MP derived from red cells (RMP) have been less well investigated. We previously presented evidence for the efficacy of RMP as a hemostatic agent in vivo and other effects such as on thrombin generation. Here we report data on in vitro proxies of hemostatic potential of RMP which further support its expected value as a hemostatic agent, and provide clues about mechanism of action.

Methods: (i)
RMP were produced by high-pressure extrusion of washed RBC. (ii) The effect of RMP on coagulation/clotting was assessed by thromboelastography (TEG) using whole blood or factor-deficient plasmas tested in presence vs. absence of added RMP (1×108/mL). Patient samples included those with coagulopathy, thrombocytopenia, thrombocytopathy. (iii) The effect of RMP on platelet aggregation was assessed by aggregometry (Chrono-Log). (iv) The effect of RMP on shear-induced platelet adhesion was by cone-and-well device (Diamed IMPACT-R) yielding measures of mean aggregate size (AS), percent surface coverage (SC) and number of objects (OBJ).

Results: (1)
RMP produced as above express procagulant phospholipids as judged by 20–30% of them binding annexin V. (2) RMP increased procoagulance in all factor-deficient plasmas tested (FII, V, VII, VIII, IX, X, XI, XII, XIII). The most pronounced effects were observed with FII, FVIII, FIX, FX deficiency, most markedly, FVIII and IX. RMP give significant correction for deficiencies as low as 5–10% normal levels. (3) RMP augmented platelet aggregation induced by low-dose ADP (0.2 μM) or arachidonic acid (0.3 mM). RMP largely eliminated dissociation of platelet aggregates after low-dose ADP. (4) At shear rate of 1800 sec−1, which approximates venous flow, aggregate size (AS) was significantly increased (p=0.02). (5) Using flow cytometry, RMP were observed to interact with platelet microaggregates expressing markers of activation, but not with free resting platelets. (6) RMP partly or completely corrected abnormal parameters seen on TEG in blood from patients with thrombocytopenia (aplastic anemia, ITP) as well as platelet dysfunctions induced by ASA or Plavix. It also improved or corrected abnormal parameters in coagulopathies such as hemophilia A with low inhibitor; and anticoagulant therapy with wafarin, LMWH, or Dabigatran.

Summary/Discussion:
(1) Increased procoagulance in all factor deficient plasma by RMP indicates that RMP provide anionic surface for clotting factors. Since this was most pronounced with FII, FVIII, FIX, and FX, and was strongest in FVIII, FIX, it appears that RMP have some specificity for assembly of tenase. (2) Correction of clotting abnormality in thrombocytopenia and platelet dysfunction by RMP suggests that RMP may provide additional catalytic surface for coagulation, as well as contributing modestly to clot strength. The latter effect may depend on presence of weakly activated platelets. (3) The increased maximum amplitude (MA) seen in TEG by RMP suggests that RMP may enhance platelet-fibrin interaction, increasing clot stability. Taken together, these data support the potential use of RMP as a universal hemostatic agent.

Disclosures:
No relevant conflicts of interest to declare.