Activation of coagulation pathways results in the formation of hemostatic fibrin plugs. Under normal physiologic conditions fibrin clots are gradually, albeit completely, degraded by a fibrinolytic enzyme system to ensure proper wound healing and/or blood vessel patency. Yet in pathological situations, thrombi are not effectively removed, leading to chronic thrombosis. The susceptibility of blood clots to enzymatic degradation depends on the structure and properties of fibrin fibers. Many factors have been suspected as culprits, including red blood cells (RBCs) that become transiently trapped within fibrin mesh. Here, the authors show that there is indeed a specific interaction between RBCs and fibrin-like fibers identified here as dense matted deposits (DMDs) by means of scanning electron microscopy (SEM). It is emphasized that such interactions can be observed in ischemic stroke patients, but not from healthy subjects. However, DMD/RBC aggregates can be induced in normal blood by the additions of trivalent iron ions. The plausible mechanism of the enhanced fibrin-red blood cell interaction is based on the previously described iron-induced generation of hydroxyl radicals. These radicals cause, in turn, non-enzymatic formation of fibrinogen aggregates remarkably resistant to fibrinolysis that are also similar to DMDs described in this paper. In conclusion, this relatively simple SEM analysis may become a convenient tool for diagnosing prothrombotic conditions associated with iron overload. It is suggested that future research on prevention and treatment of ischemic stroke and other thrombosis associated diseases should include testing of iron-chelating and hydroxyl radical-scavenging agents.

Stroke is associated with the intracerebral formation of fibrin clots which may lead to irreversible brain damage. Thrombolytic therapies employ a variety of natural and/or recombinant plasminogen activators to initiate fibrinolytic degradation of cerebral thrombi. However, such therapies when installed beyond 4‐ to 6‐h window, may fail to achieve the expected outcome. This is due to the hydroxyl radical‐induced modification of fibrin(ogen) molecules rendering them refractory to fibrinolytic degradation, but no cause of the increased free radical generation in stroke was offered. Here, we show by means of electron microscopy that iron ions added to human blood dramatically enhances fibrin fibers formation with thrombin, and significantly delays fibrinolysis during spontaneous clotting of native blood. Iron ions caused the appearance dense matted fibrin deposits, similar, if not identical, to those observed in plasma of patients with stroke. These results may explain a known relationship between thrombotic diseases and the increased body concentrations of free iron and/or hemoglobin derivatives. We conclude that any action resulting in the inhibition of hemostatic abnormalities, as well as in the reduction of body free iron and scavenging of hydroxyl radicals (e.g., by polyphenols) can potentially prevent pathological reactions associated with consequences of stroke. Microsc. Res. Tech. 75:1185–1190, 2012. © 2012 Wiley Periodicals, Inc.

Smoking impacts on hemostasis and coagulation physiology is affected. Although this is well known, no previous research is available on the impact of smoking on fibrin network morphology. Here the authors show that smoking causes the fibrin network to have a netlike appearance in some areas, as well as areas where thick plaques are present. They argue that even in occasional smokers, fibrin, in the presence of thrombin, forms thickened areas that might be the cause of a thrombotic event such as stroke. Furthermore, it seems as if smoking impacts immediately on the fibrin architecture, and this therefore does not happen only over an extended period of smoking exposure. This information is important, particularly for women with additional risk during contraceptive use and pregnancy. The authors propose the term sticky fibrin phenomenon and suggest that this is the cause for thrombotic events during smoking.

Diabetes is a condition defined by hyperglycaemia and these patients have a high risk of thrombosis. Previous research showed that ultrastructural changes in clot formation occur in patients in whom there are changes in the coagulation system due to, for example, an inflammatory condition. In the current study, the ultrastructures of platelets and fibrin networks were investigated in 25 diabetic patients. Plasma smears, with and without the addition of thrombin, were prepared. Results indicated that the fibrin network in all diabetic patients had thickened masses of thin, minor fibres over the major fibres, a profile typical of an inflammatory condition. A changed platelet membrane ultrastructure could also be observed in the diabetic patients that revealed typical apoptotic morphology, in whom membrane blebbing could be seen. It can, therefore, be concluded that in diabetic patients, the ultrastructure of fibrin networks show a typical systemic inflammatory profile, although platelets seem to be apoptotic.

Rheumatoid arthritis is a chronic inflammatory condition that affects mainly synovial joints and has an impact on approximately 1% of the Western population. The coagulation process is altered in this condition, and this is frequently complicated by thrombocytosis. Changes in fibrin morphology have been linked with inflammation, and this, in turn, plays an important role in thrombosis. Changes in the fibrin fiber formation cause the alterations observed in thrombus morphology. In the current study, the ultrastructure of platelets and fibrin networks was investigated to determine whether any morphological changes are present in these structures in patients suffering from rheumatoid arthritis. Six patients diagnosed with rheumatoid arthritis took part in this study, and their clot morphology was compared to that of control subjects. Citrated blood with and without the addition of thrombin was used. Results indicated that the fibrin networks in the arthritis patients formed thick, matted layers. This matted appearance is due to a changed ultrastructure of the minor, thin fibers. Also, in these patients, spontaneous networks were created without the addition of thrombin, which indicates an abnormal hemostatic protein functioning, and the latter is expressed as visible changes in ultrastructure.