A monoclonal antibody to the fibrinogen gamma-chain alters fibrin clot structure and its properties by producing short, thin fibers arranged in bundles.

BACKGROUND: We previously reported that hamster monoclonal antibody 7E9, which reacts with the C-terminus of the gamma-chain of mouse fibrinogen, inhibits factor (F)XIIIa-mediated cross-linking, platelet adhesion to fibrinogen, and platelet-mediated clot retraction; in addition, it facilitates thrombolysis. OBJECTIVES: To understand the mechanism(s) by which 7E9 acts, we have now studied the effect of 7E9 IgG, 7E9 F(ab')2, and 7E9 Fab on fibrin clot structure using electron microscopy and measurements of clot physical properties. RESULTS: By transmission electron microscopy, 7E9 IgG was found to bind primarily to the ends of the fibrinogen molecule. 7E9 IgG and 7E9 F(ab')2, both of which are bivalent, were capable of binding to two fibrinogen molecules simultaneously. Scanning electron microscopy of clots formed in the presence of equimolar concentrations of fibrinogen and 7E9 IgG demonstrated the presence of very short and thin fibers (63% reduction in fiber diameter) arranged in unusual bundles, surrounding large pores. Clots formed in the presence of 7E9 demonstrated a marked increase in permeation (approximately 25-fold increase in perfusion rate at constant pressure), an approximately 50% reduction in dynamic storage modulus (G'; a reflection of decreased clot stiffness), and an approximately 38% increase in loss tangent (tan delta; a reflection of the clot's ability to undergo irreversible deformation). These clots also showed decreased absorbance at 350 nm, reflecting the clot structure produced by 7E9 IgG. The effects of 7E9 IgG were not observed with control hamster IgG, 7E9 F(ab')2, or 7E9 Fab fragments, indicating requirements for both the binding properties and mass of 7E9 IgG. CONCLUSIONS: These data indicate that 7E9 antibody affects fibrin clot structure in a way that is consistent with the enhanced fibrinolysis we reported previously. Together with our previous observations, we conclude that 7E9 is directed at a strategically important region of fibrinogen with regard to platelet function, FXIIIa-mediated cross-linking, clot retraction, fibrin structure, and fibrinolysis. Thus targeting this region of fibrinogen may have antithrombotic therapeutic potential.

[Role of free radicals in blood platelet activation]. / Ucast volných radikálu pri aktivaci krevních desticek.

BACKGROUND: Free radicals and reactive oxygen containing substances are in addition to negative effects on biological systems important as signal molecules. Influencing their concentration by the action of antioxidants has a basic influence on the course of a number of cellular responses. The function of platelets is modulated in a significant way by the presence of vitamin E and resveratrol. The objective of the submitted paper is to assess the effect of Trolox (a stable analogue of vitamin E) and resveratrol sorbed by platelets on the aggregation response of washed platelets activated by collagen. METHODS AND RESULTS: To investigate the effects of the mentioned antioxidants on platelet aggregation washed platelets were prepared. The concentrations of the two antioxidants sorbed by platelets were assessed by the method of high performance liquid chromatography. From the total Trolox concentration (4200 microM) the platelets sorbed 33.5 nmol/10(9) platelets and from the total concentration of resveratrol (300 microM) the platelets sorbed 6.5 nmol/10(9) platelets. Inhibited aggregation by collagen was 57% for Trolox and 98% for resveratrol. CONCLUSIONS: The antioxidant capacity of both antioxidants is identical. The resveratrol concentration in platelets which led to almost complete inhibition of platelet aggregation by collagen was five times lower than for Trolox which caused a 57% inhibition of aggregation. Thus also other factors participate in the antioxidant activity of resveratrol. One of these factors is very probably the effect on arachidonic acid cycle.

Immunological effects of insulin-like growth factor-I--enhancement of immunoglobulin synthesis.

In addition to its activity as a metabolic hormone and a regulator of somatic growth, insulin-like growth factor-I (IGF-I) has cytokine-like activities on lymphoid cells. A 14-day infusion of recombinant human (rh)IGF-I increased lymphocyte numbers in all the peripheral lymphoid organs examined. This increase was apparent for up to 3 weeks following cessation of hormone treatment. A second administration of rhIGF-I, given when the lymphocyte numbers in the rhIGF-I-treated mice had returned to control values, resulted in similar increases in the peripheral T and B cell populations. This increase in lymphocyte numbers had functional significance, since rhIGF-I-treated mice produced elevated antibody titres following primary or secondary antigen challenge compared with controls. In addition, when rhIGF-I-treated mice were immunized with a suboptimal dose of antigen they produced antibody titres which were equivalent to those generated by immunization with optimal doses of antigen. When examined in vitro, addition of rhIGF-I alone to cultures of splenocytes from antigen-primed mice stimulated immunoglobulin synthesis. These studies suggest that IGF-I produced locally by thymic and bone marrow stromal cells may be a natural component of B and T cell lymphopoiesis.