Transplantation of an organ harvested from another person is one of the methods of treatment of end-stage failure of vascularised organs (kidneys, heart, liver). Good results obtained with this method derive from advances in the graft rejection prevention treatment. The use of immunosuppressants is associated with numerous complications, such as increased frequency of infections, increased incidence of cancer, bone marrow damage or cardiovascular complications. Normal haemostasis is a result of equilibrium between coagulation factors and their inhibitors. Imbalance in this equilibrium leads to life-threatening bleeding or thrombosis, which is why its maintenance is very important. Studies suggest the presence of hypercoagulability in renal transplant recipients (1, 2). Haemostasis disturbances are inherently correlated with endothelial dysfunction. Early descriptions of endothelial dysfunction focused on structural changes or on the loss of anatomical integrity of this organ. It is currently known that endothelial cells are characterised by highly variable biological activity performing an extremely important role in functioning of the whole body. Małyszko et al. demonstrated impaired haemostasis and endothelial function in dialysed patients and in patients with chronic kidney disease (3, 4). Epithelial damage may contribute to accelerated atherosclerosis development in the group of transplant recipients.

Vascular Adhesion Protein-1 (VAP-1) is a multi-function protein, which mediates lymphocyte adhesion to the vascular endothelium (5-9). Biochemically, VAP-1 is a homodimeric transmembrane glycoprotein with a molecular mass of 170-180 kDa, made of 764 amino acids, with a short N-terminal cytoplasmic part, a single transmembrane domain and a large extracellular C-terminal domain (5-9). Each subunit has six N-glycosylation sites (10). N-glycoside chains of VAP-1, ended with sialic acid, differ depending on the tissue in which they occur. This differentiation suggests their functional differences (11). The structure of DNA coding the VAP-1 molecule displays high homology with enzymes of the semicarbazide-sensitive amine oxidase (SSAO) class (12). VAP-1 also displays enzymatic activity of a semicarbazide-sensitive amine oxidase. Its active centre contains a copper atom (9, 13). SSAO/VAP-1 catalyses a reaction of two-stage deamination of primary amine groups (methylamine, aminoacetone, benzylamine) leading to the formation of aldehydes and additionally hydrogen peroxide and ammonia (14). On one hand, the activity of VAP-1 provides protection from amines of endo- and exogenous origins, and on the other hand, high concentration of the products formed increases the quantity of other adhesion molecules, leading to escalation of the inflammatory process. Increased concentration of toxic aldehydes and oxygen radicals, which are the source of oxidative stress, in the endothelial environment may result in endothelial damage and may contribute to the development of atherosclerosis and vascular damage in diabetic patients (15-17). Elevated activity of SSAO is observed in atherosclerosis, diabetes and obesity (18-20). VAP-1 concentration, SSAO activity and SSAO activity products are elevated in congestive heart failure and hepatitis (21). Elevated VAP-1 levels were found in persons with chronic kidney disease, which suggests that it may be excreted via the kidneys (22). Moreover, recently Li et al. have demonstrated that VAP-1 may be a good predictor of cardiovascular death in persons with type 2 diabetes (21). Constant expression of VAP-1 is observed in high endothelial venules (HEV), which physiologically are present in lymphoid organs, in the liver and in dendritic cells of lymph node proliferation centres (6). VAP-1 is also present in vascular smooth muscle cells and in adipocytes. Physiologically, soluble VAP-1 (sVAP-1) is present in the serum of healthy persons. It is probably released as a result of enzymatic proteolysis or is formed directly on messenger RNA devoid of the membrane region-coding fragment (12). Metalloproteinases may release VAP-1 from adipocytes and this process is intensified in hyperglycaemia (23). sVAP possesses immunomodulatory function causing much stronger binding of T-cells to endothelial cells, which may play an important role in the graft rejection process (24). In the case of kidney transplant, in which rejection signs were found, high expression of VAP-1 was detected in the endothelium of peritubular vessels that became morphologically similar to HEV (25). SSAO oxidates dopamine and, to a lower extent, norepinephrine, and does not oxidate epinephrine. SSAO/VAP-1 is insensitive to MAO inhibitors (26). In view of its monoamine oxidase activity, like renalase, VAP-1 may be a factor regulating blood pressure.