Thrombosis and Aging: Fibrin Clot Properties and Oxidative Stress

Significance: Aging is a complex process associated with an increased risk of many diseases, including thrombosis. This review summarizes age-related prothrombotic mechanisms in clinical settings of thromboembolism, focusing on the role of fibrin structure and function modified by oxidative stress. Recent Advances: Aging affects blood coagulation and fibrinolysis via multiple mechanisms, including enhanced oxidative stress, with an imbalance in the oxidant/antioxidant mechanisms, leading to loss of function and accumulation of oxidized proteins, including fibrinogen. Age-related prothrombotic alterations are multifactorial involving enhanced platelet activation, endothelial dysfunction, and changes in coagulation factors and inhibitors. Formation of more compact fibrin clot networks displaying impaired susceptibility to fibrinolysis represents a novel mechanism, which might contribute to atherothrombosis and venous thrombosis. Alterations to fibrin clot structure/function are at least in part modulated by post-translational modifications of fibrinogen and other proteins involved in thrombus formation, with a major impact of carbonylation. Fibrin clot properties are also involved in the efficacy and safety of therapy with oral anticoagulants, statins, and/or aspirin. Critical Issues: Since a prothrombotic state is observed in very elderly individuals free of diseases associated with thromboembolism, the actual role of activated blood coagulation in health remains elusive. It is unclear to what extent oxidative modifications of coagulation and fibrinolytic proteins, in particular fibrinogen, contribute to a prothrombotic state in healthy aging. Future Directions: Ongoing studies will show whether novel therapies that may alter oxidative stress and fibrin characteristics are beneficial to prevent atherosclerosis and thromboembolic events associated with aging.

Interactions of adenoviruses with platelets and coagulation and the vaccine-induced immune thrombotic thrombocytopenia syndrome

The COVID-19 pandemic has had a heavy impact on global health and economy and vaccination remains the primary way of controlling the infection. During the ongoing vaccination campaign some unexpected thrombotic events have emerged in subjects who had recently received the AstraZeneca (Vaxzevria) vaccine or the Johnson and Johnson (Janssen) vaccine, two adenovirus vector-based vaccines. Epidemiological studies confirm that the observed/expected ratio of these unusual thromboses is abnormally increased, especially in women in fertile age. The characteristics of this complication, with venous thromboses at unusual sites, most frequently in the cerebral vein sinuses but also in splanchnic vessels, often with multiple associated thromboses, thrombocytopenia, and sometimes disseminated intravascular coagulation, are unique and the time course and tumultuous evolution are suggestive of an acute immunological reaction. Indeed, plateletactivating anti-PF4 antibodies have been detected in a large proportion of the affected patients. Several data suggest that adenoviruses may interact with platelets, the endothelium and the blood coagulation system. Here we review interactions between adenoviral vectors and the hemostatic system that are of possible relevance in vaccine-associated thrombotic thrombocytopenia syndrome. We systematically analyze the clinical data on the reported thrombotic complications of adenovirus-based therapeutics and discuss all the current hypotheses on the mechanisms triggering this novel syndrome. Although, considering current evidence, the benefit of vaccination clearly outweighs the potential risks, it is of paramount importance to fully unravel the mechanisms leading to vaccineassociated thrombotic thrombocytopenia syndrome and to identify prognostic factors through further research.

Mechanisms of endothelial dysfunction during aging: Predisposition to thrombosis

One of the risk factors for developing cardiovascular disease (CVD) is aging. In the elderly endothelial dysfunction occurs as altered endothelial ability to regulate hemostasis, vascular tone and cell permeability. In addition, there are changes in the expression and plasma levels of important endothelial components related to endothelial-mediated modulation in hemostasis. These include alterations in the metabolism of nitric oxide and prostanoides, endothelin-1, thrombomodulin and Von Willebrand factor. These alterations potentiate the pro-coagulant status developed with aging, highlighting the endothelial role in the development of thrombosis in aging.

Recombinant human soluble thrombomodulin protects against brain injury in a CVST rat model, via downregulation of the HMGB1-RAGE axis

Cerebral venous sinus thrombosis (CVST) is a distinct cerebrovascular disorder, and ~50% of CVST patients progress to cerebral venous infarction, resulting in elevation of cerebral venous pressure. Anticoagulation is the standard initial treatment and is associated with a reduced relative risk of mortality and dependency. Recombinant human soluble thrombomodulin (rhs‑TM) is a promising therapeutic natural anticoagulant comparable to antithrombin, tissue factor pathway inhibitor, and activated protein C. The present study aimed to investigate the protective effects of rhs‑TM in a CVST rat model, and identify any underlying mechanisms. Rats were treated with rhs‑TM intravenously prior to CVST. Following neurological function evaluation, animals were sacrificed and brain water content and infarct volume were assessed. Brain tissue was collected from the infarcted segments and mRNA and protein expression levels of high mobility group box 1 (HMGB1), receptor for advanced glycation end products (RAGE), tumor necrosis factor (TNF)‑α, interleukin (IL)‑1β, IL‑6, caspase‑3, B‑cell lymphoma‑2 and Bcl‑2 associated X were analyzed by reverse transcription-quantitative polymerase chain reaction and western blot analysis. rhs‑TM significantly prevented neurological deficits in locomotor function and reduced infarct volume. The expression levels of HMGB1‑RAGE were upregulated in the infarcted segments of rat brains following CVST. Pretreatment with rhs‑TM inhibited the HMGB1‑RAGE axis, alleviating the expression levels of the proinflammatory cytokines, TNF‑α, IL‑1β and IL‑6; however, expression levels of the apoptosis-associated genes and proteins remained unaffected. The results of the present study indicated that rhs‑TM protects against CVST in the rat model via inhibition of the HMGB1‑RAGE axis and inflammation, but not via apoptosis.