[Moderate hyperhomocysteinemia and atherothrombosis]. / Hiperhomocisteinemia moderada y aterotrombosis.

Elevated levels of plasma total hornocysteine are now accepted as an independent risk factor for premature atherosclerosis. Nutritional, environmental and genetic factors may contribute to increase the levels of homocysteine. The exact pathogenesis of vascular damage induced by homocysteine is still not completely understood. Various mechanisms have been proposed, including a significant prooxidative activity, a stimulation of smooth muscle cells proliferation and an endothelial dysfunction. Folate, pyridoxine and cyanocobalamin are important cofactors for homocysteine metabolism. In most cases, elevated homocysteine can be reduced by administration of vitamin supplements. It has not yet been demonstrated that reduction in mortality and morbidity can be achieved with these regimens. However, food supplementation with folic acid has been recommended for treatment or prevention of homocysteine-related disorders in the North American population. Appropriate clinical trials are needed to evaluate the effect of lowering moderate homocysteine levels on atherosclerosis.

Pregnancy loss and autoantibodies against phospholipid-binding proteins.

OBJECTIVE: To evaluate the relationship between antibodies against beta 2-glycoprotein I or prothrombin and pregnancy losses in women with antiphospholipid antibodies. METHODS: Women with antiphospholipid antibodies, (lupus anticoagulant and/or anticardiolipin antibodies), with (n = 41) and without (n = 61) a history of pregnancy loss were evaluated. Thirty-one out of the forty-one patients with pregnancy loss had early miscarriages (at less than 13 weeks) and ten patients had late miscarriages. Immunoglobulin (Ig)-G and IgM anti-beta 2-glycoprotein I and anti-prothrombin antibodies were measured by an enzyme-linked immunosorbent assay method. RESULTS: A significant association between pregnancy loss and positive IgM anti-beta 2-glycoprotein I antibodies was found (odds ratio 2.6; 95% confidence interval 1.03, 6.6; P = .043). Women with late pregnancy loss had higher levels of both IgG and IgM anti-beta 2-glycoprotein I antibodies compared with controls (P < .05). There was a good correlation between anticardiolipin and anti-beta 2-glycoprotein I antibodies levels (IgG: r = 0.75; IgM: r = 0.73). In contrast, there was no correlation between the levels of anticardiolipin or anti-beta2-glycoprotein I antibodies and the levels of anti-prothrombin antibodies. Furthermore, the presence of anti-prothrombin antibodies was not associated with a history of pregnancy loss. CONCLUSION: The result of our study shows that there is a relationship between the presence of IgM anti-beta 2-glycoprotein I and previous miscarriages in women with anti-phospholipid antibodies.

High prevalence of hyperhomocyst(e)inemia in patients with juvenile venous thrombosis.

We determined the prevalence of hyperhomocyst(e)inemia before and 4 hours after a methionine load (3.8 g/m2) in 80 patients (25 mean and 55 women) who had had at least one verified episode of venous thromboembolism before the age of 40 years and in 51 healthy control subjects. No patient had any of the hemostatic abnormalities known to be associated with increased risk of venous thrombosis, and all had normal renal and liver function and no evidence of neoplastic disease. Hyperhomocyst(e)inemia was defined as fasting plasma homocyst(e)ine levels or absolute postload increments of homocyst(e)ine above the normal range. According to these diagnostic criteria, 15 patients (18.8%) and 1 control subject (1.9%) had hyperhomocyst(e)inemia. In 1 of these patients only, hyperhomocyst(e)inemia could be explained by low serum concentrations of vitamin B12 and folates. The family history for venous thromboembolism was positive for 7 of the 15 patients. Family studies, performed for eight kindreds, showed that for more than half of the studied probands the abnormality was inherited. This study indicates that moderate hyperhomocyst(e)inemia is associated with an increased risk of developing venous thromboembolism at a young age and that measurements of fasting and postmethionine plasma homocyst(e)ine levels may be useful in the evaluation of patients with juvenile venous thromboembolism, particularly if their family history suggests the presence of an inherited abnormality.

The in vitro production of thromboxane B2 by platelets of diabetic patients is normal at physiological concentrations of ionized calcium.

Platelets of patients with diabetes and no evidence of macroangiopathy produce normal amounts of thromboxane (Tx) B2 in vivo, whereas they usually show increased production in vitro. Since in vitro studies have been usually performed in citrated PRP, we tested the hypothesis that the discrepancy between in vivo and in vitro studies is due to the low concentration of plasma ionized calcium ([Ca2+]o) that is present in citrated PRP. In fact, low [Ca2+]o artifactually potentiates the platelet TxB2 production in vitro. Forty patients with diabetes mellitus and 37 matched controls were studied. Blood was anticoagulated with citrate, the thrombin inhibitor D-phenylalanyl-l-prolyl-l-chloromethylketone (PPACK) or both anticoagulants. Platelet aggregation, release of 14C-serotonin and TxB2 production were induced in platelet rich plasma (PRP) by several agonists. The following results were obtained: i) Citrated PRP: Arachidonic acid induced aggregation (p < 0.01) and TxB2 production (p < 0.02) were significantly greater in patients than in controls. No statistically significant differences were found with other agonists. ii) PPACK PRP: No statistically significant difference was found between diabetic platelets and controls. iii) PPACK plus citrate PRP: The results were not different from those obtained with citrate alone. Therefore, our results show that diabetic platelets produce normal amounts of TxB2 in vitro when the [Ca2+]o is physiological.

Clinical significance of various ELISA assays for detecting antiphospholipid antibodies.

We have compared the prevalence of antiphospholipid antibodies (APA) measured by enzyme-linked immunosorbent assay (ELISA), in 119 selected patients using five different antigens: bovine cardiolipin, phosphatidylserine, phosphatidylinositol, bovine partial thromboplastin and human brain partial thromboplastin. All the plasmas have been evaluated for the presence of lupus anticoagulant (LA) activity by clotting techniques. We found a significant association between the incidence of LA and APA (p less than 0.001), only moderate agreement between the prolongation of the activated partial thromboplastin time (APTT) and ELISAs (r around 0.50) and a good agreement between the ELISAs (r around 0.80). The combination of antibodies against cardiolipin (ACA) and human brain partial thromboplastin (AHPTA) allowed the detection of antibodies in most of the LA positive cases. ACA, AHPTA and antiphosphatidylinositol antibodies detected all the positive samples. Six patients (5%) had a single APA detected. The clinical associations of APA according to phospholipid specificity, immunoglobulin isotype and titer are shown.

Comparison of various screening and confirmatory tests for the detection of the lupus anticoagulant.

Several assay systems have been proposed for detection of the lupus anticoagulant (LA). We compared several screening and confirmatory tests used for the detection of LA in 108 patients. LA was detected in 52 plasmas. The activated partial thromboplastin time (APTT) and the dilute Russell viper venom time (DRVVT) were the most sensitive screening tests as compared to the kaolin clotting time (p less than 0.001). The platelet neutralization procedure in both the APTT and DRVVT systems was superior to APTT performed with high phospholipid concentration (p less than 0.01) and tissue thromboplastin inhibition (p less than 0.001) as confirmatory tests. There was an association between the presence of LA and antiphospholipid antibodies detected by the enzyme-linked immunosorbent assay (p less than 0.001). In summary, our results show that APTT may be a sensitive test for the detection of LA when an appropriate reagent is employed, and that freeze-thawed platelets are more effective than phospholipids to neutralize LA activity.