Ana María Lauricella

Effects of homocysteine thiol group on fibrin networks: another possible mechanism of harm

On the basis of growing clinical evidence, it is well known that elevated plasma homocysteine (Hcy) levels are associated with higher risk of venous and arterial thrombosis. Several experimental studies have been carried out in order to elucidate the mechanisms involved that still remain unclear. The aim of our study was to evaluate the homocysteine effects on formation and structure of plasmatic fibrin network. We also assayed homocystine and cysteine to determinate possible participation of thiol group in the tested activity. Aliquots of a pool of plasma incubated separately with sulfur compounds were clotting with thrombin. Fibringeneration and fibrin networks were evaluated by kinetic studies and scanning electronic microscopy, respectively. No significant differences were observed on fibrin generation of the substances assayed in comparison to control. The scanning electronic microscopy showed that Hcy-associated networks were different from control, with shorter, thicker and more branched fibers, resulting in a more compact structure and probably more resistant to fibrinolysis. The thiol group would be involved in this effect. Our findings would be a new contribution to elucidate the mechanisms involved in harmful effects associated to hyperhomocysteinemia.

Influence of homocysteine on fibrin network lysis.

To elucidate some of the links between homocysteine and vascular disease, we have evaluated the effect of the amino acid on the formation (by kinetics studies), structure (by electron microscopy) and lysis of the fibrin network, using tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). We have studied whether homocysteine could alter the activity of the components involved in fibrinolysis (by amidolytic and thrombolytic methods). The results showed that homocysteine-associated networks were more compact and branched than controls (52 ± 6 vs 44 ± 5 fibers/field, P = 0.008), and were formed by shorter and thicker fibers. This clot proved to be more resistant to fibrinolysis with u-PA than control [lysis time 50%: 257 ± 16 (homocysteine) vs 187 ± 6 min (control); P < 0.004], but there were no differences with t-PA. Homocysteine did not affect the biological activities of plasmin, or plasminogen activation by t-PA and u-PA. Defective fibrinolysis with u-PA was therefore associated with homocysteine–fibrin structural alterations rather than the homocysteine effect on the biological activities of the fibrinolytic components evaluated. Results suggest that hyperhomocysteinemic patients could produce tight clots, were more resistant to lysis, and generated a procoagulant environment in situ. We believe that our findings may contribute to understanding the mechanisms involved in the homocysteine harmful effect.

Plasma homocysteine cutoff values for venous thrombosis

Abstract Background: Hyperhomocysteinemia is considered an independent risk factor for vascular occlusive diseases. To date, there is no general agreement on hyperhomocysteinemia cutoff values. Methods: To establish a homocysteine cutoff value, we performed a case-control study in 118 patients suffering from venous thrombosis and in 115 healthy subjects. We calculated odds ratios at different cutoff points and considered hyperhomocysteinemia as homocysteine levels above which the risk of venous thrombosis was increased. Results: Initially we used the 97.5th percentiles for fasting homocysteine levels in the control group to calculate odds ratios (95% CI) of 9.5 (2.6–35.3), 3.7 (0.8–17.9) and 4.5 (1.7–123.8) for the total population, women and men, respectively. When individuals with well-known thrombotic risk factors were excluded (selected population), odds ratios were 10.5 (2.7– 41.1), 6.5 (1.3–32.1) and 11.2 (1.2–103.1), respectively, confirming hyperhomocysteinemia as an independent risk factor for venous thrombosis. We did not find any association of venous thrombosis with the homozygous methylenetetrahydrofolate reductase C677T mutation. When the hyperhomocysteinemia cutoff was set at other arbitrary points, odds ratios for the selected population were statistically significant only at >12 μmol/L. Conclusions: Based on our results, we propose 12 μmol/L as the hyperhomocysteinemia cutoff value. Clin Chem Lab Med 2007;45:232–6.

Impaired fibrin gel permeability by high homocysteine levels

Mechanisms involved in the relationship between hyperhomocysteinemia and thrombosis are still unclear. In previous reports we have shown that high homocysteine concentrations led to more compact and branched fibrin networks than controls. These clots showed an impaired lysis associated to their architecture. The aim of this study was to evaluate the effects of homocysteine on permeation of clots obtained from plasma and purified systems. Fibrin gels were prepared with normal plasma incubated with homocysteine and, in the purified systems, with fibrinogen and factor XIII treated with the amino acid. Permeability constants (K(s)) were determined through flow measurements. Linear regression curve between K(s) values and homocysteine levels in the plasmatic assays showed a negative correlation coefficient, r = -0.997 (p = 0.003). K(s) of fibrin gels obtained from purified systems with fibrinogen incubated with homocysteine was (7.07 ± 0.27) × 10(-9) cm(2), control was (11.40 ± 0.37) × 10(-9) cm(2) (n = 3; p < 0.01). K(s) of fibrin gels obtained with factor XIII treated with homocysteine was (1.47 ± 0.17) × 10(-9) cm (2), and control was (3.31 ± 0.31) × 10(-9) cm(2) (n = 3; p<0.01). Plasma incubated with high homocysteine concentrations produced fibrin clots significantly less permeable than controls in a dose dependent manner, and the results showed that fibrinogen and factor XIII were involved in that detrimental effect. These findings might explain the impaired fibrinolysis related to increased homocysteine levels and contribute to understanding the association between the amino acid and thrombosis.

Alterations of fibrin networks mediated by sulfated polysaccharides from green seaweeds

Fil: Arata, Paula Ximena. Universidad de Buenos Aires. Facultad de Agronomia. Departamento de Biologia Aplicada y Alimentos. Catedra de Quimica de Biomoleculas; Argentina