COVID-19 patient fibrinogen produces dense clots with altered polymerization kinetics, partially explained by increased sialic acid

Deconstructing fibrin(ogen) structure

Fibrinogen and its insoluble degradation product fibrin are pivotal plasma proteins that play important roles in blood coagulation, wound healing, and immune responses. This review highlights research from the last 24 months connecting our progressing view of fibrin(ogen)'s structure, and in particular its conformational flexibility and posttranslational modifications, to its (patho)physiologic roles, molecular interactions, mechanical properties, use as a biomaterial, and potential as a therapeutic target. Recent work suggests that fibrinogen structure is highly dynamic, sampling multiple conformations, which may explain its myriad physiologic functions and the presence of cryptic binding sites. Investigations into fibrin clot structure elucidated the impact of posttranslational modifications, therapeutic interventions, and pathologic conditions on fibrin network morphology, offering insights into thrombus formation and embolization. Studies exploring the mechanical properties of fibrin reveal its response to blood flow and platelet-driven contraction, offering implications for clot stability and embolization risk. Moreover, advancements in tissue engineering leverage fibrin's biocompatibility and customizable properties for diverse applications, from wound healing to tissue regeneration and biomaterial interactions. These findings underscore the structural origins of fibrin(ogen)'s multifaceted roles and its potential as a target for therapeutic interventions.

Post-translational modifications of fibrinogen: implications for clotting, fibrin structure and degradation

Fibrinogen, a blood plasma protein with a key role in hemostasis and thrombosis, is highly susceptible to post-translational modifications (PTMs), that significantly influence clot formation, structure, and stability. These PTMs, which include acetylation, amidation, carbamylation, citrullination, dichlorination, glycation, glycosylation, guanidinylation, hydroxylation, homocysteinylation, malonylation, methylation, nitration, oxidation, phosphorylation and sulphation, can alter fibrinogen biochemical properties and affect its functional behavior in coagulation and fibrinolysis. Oxidation and nitration are notably associated with oxidative stress, impacting fibrin fiber formation and promoting the development of more compact and resistant fibrin networks. Glycosylation and glycation contribute to altered fibrinogen structural properties, often resulting in changes in fibrin clot density and susceptibility to lysis, particularly in metabolic disorders like diabetes. Acetylation and phosphorylation, influenced by medications such as aspirin, modulate clot architecture by affecting fiber thickness and clot permeability. Citrullination and homocysteinylation, although less studied, are linked to autoimmune conditions and cardiovascular diseases, respectively, affecting fibrin formation and stability. Understanding these modifications provides insights into the pathophysiology of thrombotic disorders and highlights potential therapeutic targets. This review comprehensively examines the current literature on fibrinogen PTMs, their specific sites, biochemical pathways, and their consequences on fibrin clot architecture, clot formation and clot lysis.

Dietary Antioxidants and Natural Compounds in Preventing Thrombosis and Cardiovascular Disease

Reactive oxygen species (ROS) contribute to endothelial dysfunction, platelet activation, and coagulation abnormalities, promoting thrombus formation. Given the growing interest in non-pharmacological approaches to modulate oxidative stress, we examine the potential of various dietary interventions and antioxidant supplementation in reducing oxidative damage and preventing thrombotic events. Key dietary patterns, such as the Mediterranean, Dietary Approaches to Stop Hypertension (DASH), and ketogenic diets, as well as antioxidant-rich supplements like curcumin, selenium, and polyphenols, demonstrate promising effects in improving oxidative stress markers, lipid profiles, and inflammatory responses. This review highlights recent advances in the field, drawing from in vitro, ex vivo, and clinical studies, and underscores the importance of integrating dietary strategies into preventive and therapeutic approaches for managing thrombosis and cardiovascular health. Further research is needed to better understand long-term effects and personalize these interventions for optimizing patient outcomes.

Fibrin clot permeability (Ks) in patients on left ventricular assist device

Patients on left ventricular assist devices (LVAD) are prone to excessive hemostasis disturbances due to permanent contact of artificial pump surfaces with blood components. We aimed to investigate if fibrin clot permeability is altered in patients on long-term continuous-flow LVAD therapy and if the clot permeability is associated with clinical characteristics and adverse events. We investigated 85 end-stage heart failure patients (90.6% men, age 48.6-63.8 years) scheduled for continuous flow long-term LVAD support according to current clinical indications. The patients were assessed periodically: prior to LVAD implantation (T1), 3-6 months (T2) after LVAD implantation, 6-12 months after (T3) and then every 6 months. We tested the first three blood samples (T1-T3) and the last available blood sample (T4), but no longer than 5 years after LVAD implantation. We assessed hemostasis parameters (Activated Partial Thromboplastin Time (APTT) Prothrombin Time, Activated Partial Thromboplastin Time, Fibrinogen, D-dimer, Antithrombin, Thrombin Time, Factor VIII, and von Willebrand Factor, aspirin-induced platelet inhibition, adenosine-diphosphate test) changes during the study period. Fibrin Clot Permeability was evaluated using a pressure system and Permeability Coefficient (Ks) was calculated. We observed a decrease in fibrin clot permeability (Ks) between T1, T2, T3 and T4 time periods; P < 0.01 for each comparison. Fibrin clot permeability was negatively correlated with fibrinogen concentration: r = - 0.51, P < 0.001, factor VIII activity r = - 0.42, P < 0.001. There was no association of Ks with age, Left Ventricular Ejection Fraction (LVEF) and medications P > 0.001, however cumulative measurements in patients on aspirin showed shortening of Ks in this group P = 0.0123. Major adverse cardiac and cerebrovascular events (MACCE) occurred in 36.5% patients, bleeding events in 25.9%, Net Adverse Clinical Events (NACE) in 62.4%; 31.7% patients died, and 17.6% underwent transplantation. The transplantation was considered as the endpoint. Discrepancies in Ks were observed between patients with MACCE, bleeding, and NACE, and patients without adverse events. Ks showed a constant trend towards normalization (P < 0.01) only in patients without adverse events. Patients with advanced heart failure have disturbed clot structure. A trend towards normalization of the Ks values is associated with fewer thromboembolic and bleeding complications in this group of patients.

Comprehensive Analysis of the Role of Fibrinogen and Thrombin in Clot Formation and Structure for Plasma and Purified Fibrinogen

Altered properties of fibrin clots have been associated with bleeding and thrombotic disorders, including hemophilia or trauma and heart attack or stroke. Clotting factors, such as thrombin and tissue factor, or blood plasma proteins, such as fibrinogen, play critical roles in fibrin network polymerization. The concentrations and combinations of these proteins affect the structure and stability of clots, which can lead to downstream complications. The present work includes clots made from plasma and purified fibrinogen and shows how varying fibrinogen and activation factor concentrations affect the fibrin properties under both conditions. We used a combination of scanning electron microscopy, confocal microscopy, and turbidimetry to analyze clot/fiber structure and polymerization. We quantified the structural and polymerization features and found similar trends with increasing/decreasing fibrinogen and thrombin concentrations for both purified fibrinogen and plasma clots. Using our compiled results, we were able to generate multiple linear regressions that predict structural and polymerization features using various fibrinogen and clotting agent concentrations. This study provides an analysis of structural and polymerization features of clots made with purified fibrinogen or plasma at various fibrinogen and clotting agent concentrations. Our results could be utilized to aid in interpreting results, designing future experiments, or developing relevant mathematical models.

Fibrinogen and fibrin: synthesis, structure, and function in health and disease

Fibrinogen is an extraordinary molecule by any estimation. It is large, structurally intricate, and circulates at high concentrations. Its biological end product, insoluble fibrin(ogen) or fibrin, can assume a diverse array of conformations with the ability to interact with numerous plasma proteins and cells and withstand biochemical and biomechanical disruption to facilitate wound healing. Quantitative and qualitative defects in fibrinogen or fibrin are associated with bleeding, thrombosis, inflammation, and diseases affected by these processes. Numerous studies investigating mechanisms by which fibrin(ogen) and fibrin contribute to health and disease have been published. This review for the 20th-anniversary series in the Journal of Thrombosis and Haemostasis summarizes interesting aspects of fibrin(ogen) biology, biochemistry, biophysics, and physiology and highlights exciting findings published in the past 2 decades.

Significance of 1,25-Dihydroxyvitamin D3 on Overall Mortality in Peritoneal Dialysis Patients with COVID-19

In previous publications, we pointed out the importance of mannosylation of fibrinogen for the development of cardiovascular complications and fucosylation as a predictor of peritoneal membrane dysfunction in patients on peritoneal dialysis (PD). After a follow-up period of 30 months from the onset of the COVID-19 pandemic, we evaluated the significance of 1,25-dihydroxyvitamin D₃ (calcitriol) therapy, primary disease, biochemical and hematologic analyzes, and previously performed glycan analysis by lectin-based microarray as predictors of mortality in this patient group. After univariate Cox regression analysis, diabetes mellitus (DM) and calcitriol therapy were found to be potential predictors of mortality. Additional multivariate Cox regression analysis confirmed that only DM was a predictor of mortality. Nevertheless, the use of calcitriol in therapy significantly reduced mortality in this patient group, as shown by the Kaplan-Meier survival curve. The presence of DM as a concomitant disease proved to be a strong predictor of fatal outcome in PD patients infected with SARS-CoV-2. This is the first study to indicate the importance and beneficial effect of calcitriol therapy on survival in PD patients with COVID-19 infection. In addition, this study points to the possibility that adverse thrombogenic events observed in PD patients during the pandemic may be caused by aberrant fibrinogen glycosylation.