Module 2

Pathophysiology of veno-occlusive disease

Learning objectives • To understand the cause of VOD • To understand the sequence of steps in the pathophysiology of VOD • To recognise the pathophysiological endpoint of VOD

VOD, veno-occlusive disease

Early complications of HSCT: vascular endothelial syndromes

• It is proposed that during HSCT, endothelial cells lining blood vessels are activated by: – The conditioning regimen – Cytokines produced by injured tissues – Microbial products translocated through mucosal barriers – The process of engraftment • Intense and sustained activation of endothelial cells leads to cellular damage • Alloreactivity has been postulated to play a role in this damage and activation – This explains the greater incidence of these complications after allogeneic transplantation Carreras E & Diaz-Ricart M.

Bone Marrow Transplant

2011;46:1495 –1502

Early complications of HSCT: vascular endothelial syndromes

VOD Multi-organ dysfunction syndrome DAH ES IPS TAM TAM CLS ES TAM Organ dysfunction Endothelial dysfunction (pathologic) Endothelial activation (physiologic) Endothelial phenotype represents a net liability to the host (capillary flow obstruction, fibrin-related aggregates, platelet and leukocyte adhesion, endothelial apoptosis) Pro-coagulant status Inflammatory response Increased permeability Vasoconstriction Conditioning G-CSF CNI LPS/infections Engraftment Alloreactivity Haematopoietic stem cell transplantation CNI, calcineurin inhibitors; CLS, capillary leak syndrome; DAH, diffuse alveolar haemorrhage; ES, engraftment syndrome; GCSF, granulocyte-colony stimulating factor; HSCT; haematopoietic stem cell transplantation; IPS, idiopathic pneumonia syndrome; LPS, lipopolysaccharide; TAM, transplant associated microangiopathy; VOD, veno-occlusive disease Carreras E & Diaz-Ricart M.

Bone Marrow Transplant

2011;46:1495 –1502

Veno-occlusive disease

• VOD, also known as sinusoidal obstruction syndrome, is a potentially life-threatening complication of HSCT • The conditioning regimens given before HSCT result in the production of toxic metabolites by the hepatocytes in the liver • These metabolites trigger the activation, damage and inflammation of the endothelial cells that line the sinusoids – Sinusoids are small capillary-like blood vessels found in the liver • This ultimately leads to VOD, which is characterised by – Increased thrombosis and decreased fibrinolysis – Sinusoidal damage and narrowing – Inflammation Histological section of the liver viewed through a microscope. Blood vessels shown in red, cell nuclei in blue, cytoplasm in pink Richardson PG et al.

Expert Opin Drug Saf

2013;12:123 –136

Cell toxicity resulting from chemotherapy damages the lining of the liver sinusoids Red blood cells Toxic metabolites Sinusoidal endothelial cells Platelets Toxic metabolites resulting from the HSCT conditioning regimen damage and activate the sinusoidal endothelial cells Richardson PG et al.

Expert Opin Drug Saf

2013;12:123 –136

Activation of sinusoidal endothelial cells can trigger multiple pathways, resulting in inflammation and narrowing of the sinusoids Red blood cells Sinusoidal endothelial cells Heparanase Adhesion molecules Platelets The accumulation of cells and debris in the space of Disse, the perisinusoidal space located between the endothelium and the hepatocyte, lead to narrowing of the sinusoids Richardson PG et al.

Expert Opin Drug Saf

2013;12:123 –136

VOD is characterised by increased clot formation and reduced clot breakdown Red blood cells Cytokines Fibrin Heparanase Adhesion molecules Tissue factor PAI-1 Platelets The narrowing of the sinusoids, embolised endothelial cells and increased clot formation lead to the endpoint of VOD, namely obstruction of the sinusoids PAI-1,plasminogen activator inhibitor-1; TF, tissue factor Richardson PG et al.

Expert Opin Drug Saf

2013;12:123 –136

Pathophysiology of VOD

Endothelial cell and hepatocyte damage Triggering of multiple pathways • Activation and damage due to conditioning regimen-mediated injury. Damage is both directed and mediated by cytokines such as: TNF α, IL-1b, IL-6 Inflammation Cytoskeletal structure Sinusoidal narrowing • • • Increased expression of adhesion molecules ICAM-1 and VCAM-1 of endothelial cell surface Activation of leukocytes that release additional inflammatory cytokines Digestion of extracellular matrix VOD • • Portal vein hypotension Hepatic venous outflow obstruction ICAM, intracellular adhesion molecule; IL, interleukin; TNF, tumour necrosis factor; VCAM, vascular cell adhesion protein Richardson PG et al.

Expert Opin Drug Saf

2013;12:123 –136; Coppell JA et al.

Blood Rev

2003;17:63 –70

Summary of VOD pathophysiology

• The conditioning regimen given prior to HSCT increases endothelial cell activation, resulting in damage to the SECs and hepatocytes • The accumulation of cells in the space of Disse (the perisinusoidal space), increased inflammation and formation of clots lead to narrowing of the sinusoids • This results in VOD, which is characterised by blockage of the sinusoids, portal vein hypotension and reduced hepatic venous outflow SEC, sinusoidal endothelial cell

Self-assessment questions

1. VOD affects which major organ?

Self-assessment questions

2. What by-product of HSCT conditioning causes damage to the sinusoidal endothelial cells and hepatocytes?

Self-assessment questions

3. Which of the following is

not

a characteristic of VOD pathophysiology?

a) Increased clot formation b) Decreased clot breakdown c) Expansion of the sinusoids d) Inflammation

Self-assessment questions

4. What causes obstruction of the sinusoids?