Lucía Kordich

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.

Prevalence of hyperhomocysteinemia in an elderly population

BACKGROUND Currently, total hyperhomocysteinemia (tHHcy) is a well-known condition linked to a higher risk of vascular disease. Prevalence of HHcy increases in elderly persons as the risk associated with it persists. Because factors can be potentially reduced in the elderly, it is important to carry out epidemiologic studies of HHcy. PROCEDURE Previously we described the prevalence of hypertension control in an elder population; now, in an observational cross-sectional simple blind study, total homocysteine (tHcy) concentration was determined in 196 of 400 patients from the original cohort. RESULTS Mean Hcy concentration was 13.2 ,amol/L (95% confidence interval 12.4-14.0; range, 5.0 to 48.9); 15.0 ,imol/L for men and 12.3 pAmol/L for women. Mean serum folic acid levels were 4.9 + 3.1 ng/mL (range, 2.0 to 20.0 ng/mL), and vitamin B12 levels were 384.8 314.1 pg/mL (range, 48.0 to 1500.0 pg/mL). Taking into account the reference values established by the Third National Health and Nutrition Examination Survey III study, HHcy was detected in 69.8% of all the subjects evaluated. The study showed that 76.2% of the men and 66.4% of the women had high Hcy levels. CONCLUSIONS The very high prevalence of tHHcy in the elderly population, and the consequent risks associated with it suggest that although there are no trials that effectively prove the benefit of tHcy decrease, nutritional intervention is still justified.

Plasminogen abnormalities in patients with argentine hemorrhagic fever

Plasminogen, alpha 2-antiplasmin, alpha 2-macroglobulin, alpha 1-antitrypsin and fibrinogen degradation products (FDP) were studied in 45 patients with Argentine hemorrhagic fever. Patients were grouped into: 17 mild, 14 moderate and 14 severe cases. Plasminogen antigen level and functional activity were found to be reduced in the moderate and severe groups, when compared to the results obtained at recovery. The functional activity of alpha 2-antiplasmin was within the normal range, except for a slight decrease on days 10-11, alpha 2-macroglobulin remained normal during the course of illness. alpha 1-antitrypsin also remained normal except on days 10-11, when an increase in the antigen level was noted. FDP titre was normal (less than 10 micrograms/ml) in all patients during the course of disease. Plasminogen decrease was not attributable to liver insufficiency neither to a primary nor secondary fibrinolysis. The decreased antigen and reduced functionality of plasminogen in these patients we believe is related to proteolytic degradation by leukocyte enzymes.

IMPAIRED CLOT LYSIS BY rt-PA CATALYZED MINI-PLASMINOGEN ACTIVATION

The fibrinolytic system contains a proenzyme plasminogen (Plg) which is converted to plasmin (Plm) by the action of Plg activators. Physiological Plg activators are: tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator. Plg was shown to be further cleaved by leukocyte elastase producing several fragments, one of which is called mini-plasminogen (mini-Plg) or neo-plasminogen Val442. In this paper we studied whether mini-Plg is able to produce clot lysis when it is activated by rt-PA in purified systems and in Plg depleted normal plasma. We found that mini-Plg clot lysis time was longer than that of Plg. Clot lysis times were 2.3 minutes +/- 0.06 for Plg and 9.8 minutes +/- 0.1 for mini-Plg. Mini-Plg is less efficient than Plg in producing clot lysis at all studied concentrations (0.1-1.2 microM). In Plg depleted normal human plasma mini-Plg is unable to produce complete clot lysis in presence of rt-PA. Although mini-Plg can be activated to mini-Plm by rt-PA, these results show that the activation process is insufficient to produce an efficient clot lysis.

Heparin cofactor II in diabetic patients.

Levels of heparin cofactor II (HCII) activity and antigen and electrophoretic pattern were studied both in normal subjects and in type I diabetic patients with high and normal levels of glycosylated haemoglobin. There was a significant reduction in HCII activity (83 ± 7%) in patients with high levels of glycosylated haemoglobin compared with controls (95 ± 17%; P < 0.001). However, plasma HCII antigen levels were not decreased in these patients.

Platelet function and antithrombins in hyperlipoproteinemia type IIa

Platelet function was studied in 35 patients with type IIa hyperlipoproteinemia and 22 normal controls. Platelet aggregation by ADP in concentrations ranging from 2×10−6 to 2×10−5 M, and adrenaline 10−6 M were similar in both groups. In contrast, aggregation induced by collagen and secondary aggregation elicited by bovine factor VIII were significantly lower in hypercholesterolemic patients, who also disclosed an increased plasmatic antiheparin activity. This plasmatic antiheparin activity was inversely correlated to plasmatic cholesterol concentration, (r = −0.50, p<0.01). PF3 and PF4 were normal in patients with type IIa hyperlipoproteinemia. AntiFXa, antithrombin III, and heparin cofactor were also determined. Heparin cofactor was found to be significantly lower in hypercholesterolemic patients than in controls, and inversely correlated to plasmatic cholesterol concentration (r = −0.51, p<0.05). These observations suggest that the thrombotic tendency in hypercholesterolemia may be related to a decrease of plasmatic heparin cofactor.

Unsuspected hyperhomocysteinemia in chronically anticoagulated patients.

Hyperhomocysteinemia is a risk factor for arterial and venous thrombosis. The aim of this study was to evaluate plasmatic homocysteine levels in patients under chronic anticoagulant treatment with dietary restriction of green vegetables. This kind of food is a very important source not only of vitamin K but also of folates, which are involved in Hcy metabolism. It is known that the lower the folate levels, the higher the Hcy concentration, so we suspected that these patients could show hyperhomocysteinemia. A group of patients receiving oral anticoagulant treatment and a restricted diet (Group I, n = 20) was compared with a group of untreated subjects of a similar age that were not on a restricted diet (Group II, n = 35). Group I showed significantly higher levels of plasmatic Hcy and significantly lower levels of serum folate than Group II. Therefore, a diet restricted in vitamin K applied to oral anticoagulated patients could induce an unwanted increase of homocysteine levels.

Plasmatic homocysteine response to vitamin supplementation in elderly people

Homocysteine (Hcy) increase is now widely accepted as a risk factor for vascular disease. The effects of folic acid (FA) and vitamins B12 and B6 in lowering Hcy have been extensively studied, but there is still little data on the response to FA dietary administration. Our purpose was to evaluate the impact of the diet and the degree of response to different doses of pharmacological FA supplementation. In a prospective, randomized, and simple blind study, 50 elderly subjects were given a 400-microg/day FA diet and were randomly assigned to one of the following treatments: Group I = placebo tablet; Group II = tablet containing 1-mg folic acid, 1-mg B12, and 25-mg B6; and Group III = tablet containing 2.5-mg folic acid and same B6 and B12 doses as Group II. Forty-four subjects completed the study, and their plasmas were evaluated. Hcy concentration significantly decreased even in patients with normal basal values, and there were no differences in the response between individuals receiving diet plus placebo and those receiving diet plus pharmacological supplementation. After the treatment, the mean decrease of plasmatic Hcy levels was 10.8 (9.4, 12.5) micromol/l, geometric mean [95% confidence interval (95% CI)], and particularly, the values for Group I were 10.6 (7.4, 14.8) micromol/l. In 31% of the subjects, the post-treatment Hcy levels were less than or = 5 micromol/l. These results show that a special diet, with or without pharmacological FA and B12 and B6 supplementation, significantly decreases the Hcy levels in elderly people. Therefore, a diet with high contents of FA might have an enormous impact on the morbidity and mortality of atherothrombosis.

Glanzmann thrombasthenia in children from Argentina

Purpose Glanzmann thrombasthenia is a well-defined inherited disorder of platelet function characterized by a decrease or absence of functional platelet glycoprotein (GP) GPIIbIIIa. The diagnosis must be considered in patients presenting with mucocutaneous bleeding, purpura, a normal platelet count, abnormal platelet aggregation, and a prolonged bleeding time. In most of the patients, the presence of small amounts of either GPIIb or GPIIIa was detected in their platelets. These observations could provide a basis for determining the clinical and laboratory heterogeneity of the disease. Patients and Methods We studied 10 patients of seven unrelated families with the usual methods and an immunoalkaline phosphatase technique (APAAP) to analyze the biosynthesis of GP in megakaryocytes. Results The results allowed us to classify six patients as GT type I, three as type II, and one as a variant. Conclusion The nature and severity of the bleeding manifestations, in our patients, were not predictible by the laboratory findings. These confirm the clinical and laboratory heterogeneity of the disease.