Oxidation of Met1606 in von Willebrand Factor is a Risk Factor for Thrombotic and Septic Complications in Chronic Renal Failure

Chronic Kidney Disease (CKD) is a life-threatening pathology, often requiring haemodialysis (HD) and characterized by high oxidative stress, inflammation and perturbation of vascular endothelium. HD-patients have increased levels of von Willebrand factor (vWF), a large protein (~240kDa) released as ultra large polymers (UL-vWF, M.W.~20000-50000kDa) from vascular endothelial cells and megakaryocytes and responsible for the initiation of primary haemostasis. The pro-haemostatic potential of vWF increases with its length, which is proteolytically regulated by ADAMTS-13, a zinc-protease cleaving vWF at the single Tyr1605-Met1606 bond, and by leukocyte serine proteases, released by activated polymorphonuclear cells during bacterial infections. Previous studies showed that in vitro oxidation of Met1606 hinders vWF cleavage by ADAMTS-13, resulting in the accumulation of UL-vWF, which are not only more prothrombotic than shorter vWF oligomers but also more efficient in binding to bacterial adhesins during sepsis. Notably, HD-patients have greatly increased risk of developing dramatic cardiovascular and septic complications, whose underlying mechanisms are largely unknown. In this study, we first purified vWF from HD-patients and then chemically characterized its oxidative state. Interestingly, HD-vWF contains high carbonyl levels and increased proportion of UL-vWF polymers, which are also more resistant to ADAMTS-13. Using targeted mass spectrometry techniques, we estimated that HD-vWF contains <10% of Met1606 in the sulphoxide form. We conclude that oxidation of Met1606, impairing ADAMTS-13 cleavage, results in the accumulation of UL-vWF polymers, which recruit and activate more efficiently platelets and bind more tightly to bacterial adhesins, thus contributing to the development of thrombotic and septic complications in CKD.