PubMed: 25307023

New perspectives on the thrombotic complications of haemolysis.
British journal of haematology
Hod E | L'Acqua C

Evidence a45be13f1b

As such, it nitrosylates the haem-moiety of guanylate cyclase, thereby stimulating formation of cyclic guanine monophosphate (cGMP), which then initiates calcium-dependent vasodilation (Olson et al, 2004).

Evidence 475161a7a1

NO inhibits platelet aggregation mediated by guanylate cyclase activation with a subsequent rise in cGMP (Faint et al, 1991).

Evidence 612a20f7fd

Platelet deposition and adhesion at sites of subintimal injury are increased by free haemoglobin or inhibition of NO production; this effect can be prevented by infusions of L-arginine, the precursor of NO (Olsen et al, 1996).

Evidence c3cb680787

Carbon monoxide has vasodilatory, anti-proliferative, anti-inflammatory and antioxidant properties, whereas bilirubin, the product of biliverdin reductase, is an antioxidant (Baranano et al, 2002).

Evidence 9470c7aaa8

Furthermore, cytokine secretion depends on the coordinated iron in the porphyrin ring (Figueiredo et al, 2007), and nuclear factor-jB (NF-jB), MAPKs activation and ROS are essential for the increase in cytokine production induced by haem (Fernandez et al, 2010).

Evidence a994883e38

Thus, by participating in Fenton chemistry, non-transferrin-bound iron (i.e., iron not bound to the physiological iron transport protein, transferrin) causes oxidative damage, cytotoxicity and enhanced endothelial expression of adhesion molecules, thereby enhancing thrombotic risk (Hershko, 2007).

Evidence 013f454952

Thus, the antioxidant, anticoagulant, anti-proliferative and vasodilating effects of the HMOX1 and biliverdin reductase systems probably compensate for the nitric oxide (NO) scavenging, vasoconstrictive, proliferative, inflammatory and pro-oxidant effects of circulating free haemoglobin, haem and haem-iron, which are discussed below (Rother et al, 2005).

Evidence 6691332e39

ROS generation by haem is at least partially dependent on the Fenton reaction, in which iron catalyses the production of toxic ROS (Wagener et al, 2003).

Evidence 0f5cfa0c3c

Finally, ferrous iron, through Fenton-derived hydroxyl radical species production and protein kinase C function, activates platelets (Iuliano et al, 1994).

Evidence 6dbd2c6352

The main mediator of these adverse effects is thought to be free haem via its effects on NO scavenging, pro-inflammatory cytokine responses, and reactive oxygen species (ROS) generation.

Evidence d2742a4024

NO is also known as endothelial- derived relaxing factor, because of its role in signalling to relax the smooth muscle lining the vasculature (Rother et al, 2005).

Evidence 7f8394f4b7

Furthermore, NO has a fundamental role in normal vascular physiology by inhibiting both platelet aggregation and endothelial adhesion molecule expression, as detailed below

Evidence dce3c12cf8

Finally, NO may also affect coagulation by inhibiting Factor XIII activity (Catani et al, 1998).

Evidence e29e610a83

Factor XIII stabilizes clots by catalysing fibrin monomer cross-linking; thus, NO deficiency enhances clot stability and reduces clot dissolution.

Evidence 830f1823ef

Therefore, decreased NO bioavailability affects vascular tone, platelet and endothelial function and coagulation, thus increasing thrombotic risk.

Evidence 0282795a37

Platelets may be activated during haemolysis by several different mechanisms involving decreased NO levels, increased pro-inflammatory cytokines and mediators, and ROS.

Evidence 60820cc613

The abnormal phospholipid membrane asymmetry present in the RBCs of b-thalassaemia and SCD patients, with resultant phosphatidylserine exposure, appears to play a significant role in the aetiology of the observed hypercoagulable state and in the link between haemolysis and thrombosis (Ataga et al, 2007).

Evidence 62ccb21335

Furthermore, phosphatidylserine is actively maintained on the inner leaflet of the bilayer membrane and, when externalized, is a recognition signal for cell clearance or for activation of coagulation (Zwaal & Schroit, 1997).

Evidence fc6ef7813d

These RBC microparticles can initiate and propogate thrombin generation (Rubin et al, 2013).

Evidence ebc079a1f4

Haemoglobin and haem levels increase in plasma and urine when haptoglobin and haemopexin scavenging mechanisms are saturated during acute or chronic haemolysis.

Evidence bd41a9e309

Free plasma haemoglobin and haem also scavenge NO and have multiple pro-inflammatory and pro-oxidant properties that mediate many of the adverse effects of haemolysis.

Evidence 93a3c6ef13

In addition, haem activates endothelial cell expression of intracellular adhesion molecule 1 (ICAM1), vascular cell adhesion molecule (VCAM1), and E-selectin (Wagener et al, 1997).

Evidence 5662f98d8a

Furthermore, haem-induced release of P-selectin and VWF is mediated by TLR4 and NFkB signalling.

Evidence 2bf274141c

For example, haem stimulates expression of P-selectin and von Willebrand Factor (VWF) ‘strings’ on endothelial cells in vitro and on the vessel walls of both normal and SCD mice (Belcher et al, 2014).

Evidence 45559d8573

Haem also induces tumour necrosis factor (TNF) secretion in monocyte/macrophages through TLR4 and the adaptor molecule, MYD88 (Figueiredo et al, 2007).

Evidence 8a9ac8a1ad

For example, infusion of haem into humans is associated with disturbances in coagulation assays and overt thrombophlebitis (Simionatto et al, 1988).

Evidence 9da8146554

The large amounts of haem released upon haemolysis can overwhelm the capacity of haem scavengers and enzyme systems (i.e., HMOX1), thus causing oxidative stress (Jeney et al, 2002).

Evidence 30a904f83b

Furthermore, incubating endothelial cells with haem induces tissue factor, which can initiate coagulation (Setty et al, 2008).

Evidence e4025eca79

Transfusion of RBCs after prolonged refrigerator storage is associated with haemolysis (Donadee et al, 2011; Hod et al, 2011) and enhances cytokine secretion in response to lipopolysaccharide (LPS) administration (Hod et al, 2010).

Evidence d80d77ab00

Immunological incompatibility of transfused RBCs can lead to acute haemolytic transfusion reactions.

Evidence e040bde506

Surprisingly, 66% (187/282) of ABO incompatible transfusions are asymptomatic; however, 67% (19/282) result in death and 27% (76/282) in major morbidities (Bolton-Maggs et al, 2014), including DIC (Goldfinger, 1977).

Evidence 7290675088

Multiple haemolytic disorders and therapeutic interventions produce substantial intravascular haemolysis. Examples include PNH, SCD, thalassaemias, glucose-6-phosphate dehydrogenase (G6PD) deficiency, hereditary spherocytosis and stomatocytosis, pyruvate kinase deficiency, autoimmune haemolytic anaemia, microangiopathies, acute haemolytic transfusion reactions, mechanical circulatory support [e.g., left ventricular assist device (LVAD)/extracorporeal membrane oxygenation (ECMO)], RBC transfusions and infusions of RBC substitutes. These disorders, therapies and procedures are also associated with an increased risk of thrombosis.

Evidence a0ad963ba1

This common X-linked inherited disorder, characterized by severe intravascular and extravascular haemolysis, is classically triggered by fava bean ingestion or pro-oxidant medications. It causes haemolysis in susceptible individuals and an association with thrombosis was described in multiple case reports (Jewett, 1976; Thompson et al, 2013; Albertsen et al, 2014).

Evidence 8e11c75cc4

Furthermore, retrospective studies suggest an association between transfusion of older, stored RBCs and thrombosis (Spinella et al, 2009).

Evidence f0a2d8efad

ADP induces platelet activation and may also contribute to transfusion-related vascular thrombosis.

Evidence d12a78119c

ADP released from haemolysed RBCs induces CD40LG release from platelets and lymphocytes, thereby contributing to the pro-inflammatory and pro-thrombotic environment (Helms et al, 2013).

Evidence 2ecead4db7

Biochemical and biomechanical changes occur in the RBCs during the storage process, ultimately leading to increased haemolysis upon transfusion (Cohen & Matot, 2013).

Evidence 4140384c5c

Although RBC transfusions reduce the risk of stroke in SCD (Adams et al, 1998), both clinical strokes and silent infarcts still occur.

Evidence ed9bb9558a

Furthermore, haem released during SCD-induced haemolysis triggers the release of neutrophil extracellular traps (NETs) via a ROS-dependent mechanism (Chen et al, 2014).

Evidence 1625aa2495

Thus, NETs recruit RBCs, activate platelets and promote fibrin deposition; they are a previously unrecognized link between haemolysis and thrombosis that may further explain this epidemiological association.

Evidence d223a368f4

In addition, 8 of 30 patients (27%) with unspecified warm or cold AIHA experienced an episode of venous thromboembolism (Pullarkat et al, 2002); of these, the presence of a lupus anticoagulant identified AIHA patients at higher risk for venous thromboembolism.

Evidence a5dbfbe9ae

Furthermore, ROS induction by haem directly depends on signal transduction involving Ga inhibitory protein and phosphoinositide 3-kinase, and partially depends on phospholipase Cb, protein kinase C, the mitogen-activated protein kinases (MAPKs) and Rho kinase in neutrophils (Porto et al, 2007).

Evidence a1f4c911bc

Inhibiting NADPH oxidase, its upstream activator protein kinase C or antioxidants inhibit haem-mediated stasis, Weibel-Palade body degranulation and oxidant production by the endothelium (Belcher et al, 2014).

Evidence 4646b840bd

These ROS then oxidize cell membrane constituents to induce cytotoxicity and promote inflammation and thrombosis.

Evidence f0641d491c

Formation of large amounts of haptoglobin– haemoglobin complexes rapidly depletes haptoglobin.

Evidence 99f8ecda97

Finally, the cytokines produced through these pathways can then affect endothelial activation, leucocyte recruitment, and ultimately thrombotic risk.

Evidence 4f71049399

The highest prevalence was observed in splenectomized patients.

Evidence 385607364d

The increased risk of thrombosis in patients who undergo a splenectomy is important. About 22 000 splenectomies are still conducted annually for all causes in the United States and splenectomized patients have a 22-fold increased rate of being hospitalized for deep vein thrombosis or pulmonary embolism (Kristinsson et al, 2014).

Evidence 2d701f0f37

Thus, haemolysis results in NO scavenging, systemic vasoconstriction and increased blood stasis, thereby affecting one of the principle components of Virchow’s Triad.

Evidence 5bbd087f11

The essential feature of any haemolytic disorder is shortened red blood cell (RBC) lifespan.

Evidence 068965305b

In addition, reduced NO bioavailability induces platelet activation and aggregation, leading to thrombosis in a mouse model of intravascular haemolysis (Hu et al, 2010).

Evidence 632981f297

In patients with SCD (Wun et al, 1998) and b-thalassaemia (Ruf et al, 1997), flow cytometry demonstrates the presence of an increased fraction of platelets expressing P-selectin, a platelet membrane receptor that mediates platelet–endothelial interactions.

Evidence 8e029eda0d

The triad consists of hypercoagulability, blood stasis and endothelial injury/dysfunction, which are useful concepts for understanding thrombosis.

Evidence ae7085a4d0

The haptoglobin–haemoglobin complex is recognized by the haemoglobin scavenger receptor, CD163, on the surface of monocytes/macrophages, which mediates haptoglobin–haemoglobin endocytosis and degradation (Kristiansen et al, 2001).

Evidence 62e89f2c49

Decreased function of this zinc-containing metalloprotease that cleaves VWF is implicated in the pathogenesis of both congenital and sporadic TTP (Furlan et al, 1998).

Evidence 0b804a4b86

Pro-inflammatory cytokines and chemokines [e.g., inter leukin 1B (IL1B), CXCL8 (also termed IL8), TNF and chemokine (C-C motif) ligand 2 (CCL2, also termed MCP1)], are upregulated in haemolytic disorders such as SCD (Qari et al, 2012). This pro-inflammatory cytokine milieu is crucial in mediating the pro-coagulant effects of vascular endothelial cells and promotes localized inflammation and thrombosis (Qari et al, 2012).

Evidence 50807e168b

Normally, haemopexin safely transports haem away from the vessel wall to ligate LRP1 (also termed CD91) on hepatocytes and macrophages, where the haem–haemopexin complex is endocytosed and haem is degraded intracellularly (Hvidberg et al, 2005).

Evidence c25842f61a

Haem increases lethality and cytokine secretion induced by LPS in vivo and enhances cytokine secretion by macrophages stimulated with various innate immune receptor agonists (e.g., TLR2, TLR9, TLR3, and nucleotide-binding oligomerization domain (NOD) agonists) (Fernandez et al, 2010).

Evidence e3a5a620e4

Patients with hereditary haemolytic anaemia due to RBC structural abnormalities have an increased risk of thromboembolic events, particularly in splenectomized patients (Stewart et al, 1996; Schilling et al, 2008).

Evidence a37de6dc9f

Thrombotic events also occur in b-thalassaemia patients; for example, pulmonary embolism, portal vein thrombosis and deep vein thrombosis occurred in 29% of b-thalassaemia intermedia patients followed for 10 years (Cappellini et al, 2000).

Evidence 24f3840682

Although haemolysis and thrombosis are hallmarks of the thrombo microangiopathies, such as disseminated intravascular coagulation (DIC) and thrombotic thrombocytopenic purpura/haemolytic uraemic syndrome (TTP/HUS), it is difficult to isolate the causative role of haemolysis in the pathophysiology of thrombosis in these complex disorders.

Evidence cca99e047d

Thus, in severe haemolytic diseases, such as paroxysmal nocturnal haemoglobinuria (PNH) and sickle cell disease (SCD), serum haptoglobin is typically undetectable and plasma haemoglobin is elevated (Tabbara, 1992).

Evidence be9db67142

In PNH, uncontrolled complement activity leads to systemic complications, principally through intravascular haemolysis and platelet activation.

Evidence 7fe52b0b1c

In a report of 28 heterogeneous patients with either warm or cold AIHA, 5 of 15 episodes of haemolysis were associated with venous thromboembolism (Hendrick, 2003).

Evidence 2184b611b8

SCD is a haemolytic disorder caused by a HBB (b-globin gene) mutation leading to polymerization of haemoglobin S, sickling, and haemolysis.

Evidence 4ff8549354

Although acute intravascular haemolysis is a rare complication of transfusion, it is among the most feared transfusion-associated complications, principally because death may rapidly ensue.

Evidence 425a8abe47

Thromboembolism is the most common cause of death in PNH patients and accounts for 40–67% of deaths for which the cause is known.

Evidence c2dc916197

Haemolysis, which is observed in multiple diseases, can affect all three components of Virchow’s triad; thus, it is not surprising that there is a link between haemolytic disorders and thrombosis.

Evidence 983debb3a4

During intravascular haemolysis, NO availability is severely limited by its reaction with oxyhaemoglobin (i.e., NO scavenging) and by breakdown of the substrate for NO synthesis, L-arginine, by arginase released from RBCs (Schnog et al, 2004).


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