Diagnóstico de hemoglobinopatías a partir de sangre del talón de recién nacidos en diferentes centros hospitalarios de Venezuela / Diagnosis of hemoglobinopathies in newborns in Venezuela hospitals

Objetivos: Las hemoglobinopatías constituyen uno de los desórdenes hereditarios más comunes en humanos, y en Venezuela representan un problema de salud pública. En esta investigación se evaluó la prevalencia de las hemoglobinopatías en neonatos de diferentes áreas de Venezuela, en cooperación con el sistema de cribado neonatal de la Unidad de Estudios de Errores Innatos del Metabolismo del Instituto de Estudios Avanzados. Materiales y métodos: Las muestras de sangre del talón de 101.301 neonatos se estudiaron por medio de la técnica de cromatografía líquida de alta resolución de intercambio catiónico (HPLC-CE), utilizando el equipo Variant® Bio-Rad y los programas Sickle Cell Short para el análisis en papel de filtro y Beta Thal Short para el estudio confirmatorio y familiar. Resultados: Se encontró una alta prevalencia de neonatos heterocigotos para las hemoglobinas (Hb) S y C (Hb S y Hb C). Se observó que el 1,96% (1.989) de los neonatos fueron portadores de alguna variante, y el fenotipo más frecuente fue Hb fetal AS (67,92%), seguido de Hb fetal AC (23,18%), Hb fetal AD (7,49%), Hb fetal SC (0,96%) y Hb fetal SD (0,20%). A todos los niños estudiados (positivos en el cribado), luego de los 3 meses de edad se les confirmó la presencia de alguna variante estructural mediante una segunda prueba confirmatoria. Conclusiones: Las frecuencias de las variantes encontradas en este estudio confirman que las hemoglobinopatías representan un problema de salud pública en Venezuela, y debe enfatizarse la importancia de instaurar en este país un programa de detección sistemática de hemoglobinopatías que comprenda no sólo un tratamiento precoz, sino también un programa de educación y consejo genético para el grupo familiar (AU)

Objectives: Hemoglobinopathies are the most common hereditary disorders in humans representing a public health problem in Venezuela. In this study the prevalence of hemoglobinopathies was evaluated in newborns from different areas of Venezuela, in cooperation with the neonatal screening system of the Study Unit of Inborn Errors of Metabolism (IDEA). Materials and methods: The heel blood samples of 101,301 newborns were analysed by high performance liquid chromatography (HPLC-CE) technique using Variant* Bio Rad System with the Sickle Cell Short program for the filter paper samples in and the Beta Tal Short program for the family studies. Results: We found a high prevalence of newborns heterozygous for hemoglobin S and C (Hb S and Hb C). It was observed that 1.96% (1989) of the newborns were carriers, with Hb FAS (67.92) being the most frequent phenotype, followed by Hb FAC (23.18%), Hb FAD (7.49%), Hb FSC (0.96%),) and Hb FSD (0.20%). All the neonatal positives cases were confirmed at 3 months of age. Conclusions: The frequencies of the variants found in this study confirms that the hemoglobin disorders are a public health problem in Venezuela, emphasizing the importance of instituting a national program of screening for hemoglobinopathies throughout the country, comprising not only an early treatment, but also an educational program and genetic counseling for the family group (AU)

Frozen extracellular matrix preserves its thrombogenicity after thawing, while Matrigel induces a poor platelet response.

Two putative substitutes for fresh endothelial cell (EC) extracellular matrix (ECM), frozen ECM and Matrigel, were studied using a parallel-plate perfusion system and platelet deposition was evaluated morphometrically. Coverslips covered with ECM were stored frozen at-30 C for 0 (fresh ECM), 1, 2, 3 or 4 weeks. The ability of frozen ECM to support platelet adhesion after freezing was analyzed under three experimental approaches, perfusing blood: (i) at different shear rates; (ii) on a highly reactive ECM obtained from stimulated EC; and (iii) on ECM incubated with a monoclonal antibody against laminin (LM). Matrigel, alone or mixed with different fractions of wet cryoprecipitate, was layered on coverslips as a thin uniform coat, and perfused, as was done with the frozen ECM. Platelet deposition onto fresh ECM was 21.3 1.5%, 25.5 2.1% and 30.8 2.4% (at shear rates of 300, 800 and 1300/s, respectively) and 40.0 3.8% in PMA stimulated ECM perfused at 800/s. Values obtained on frozen ECM did not vary from those obtained using fresh ECM. Results from perfusion studies using ECM preincubated with an anti-laminin antibody and observations from immunofluorescence studies indicated that the presence and distribution of the adhesive proteins in frozen ECM were similar to those observed on fresh ECM. Platelet deposition on Matrigel was practically absent. Addition of a 20% cryoprecipitate fraction partially restored its thrombogenicity. Our results indicate that when ECM is kept frozen for up to 4 weeks, it behaves as fresh ECM in perfusion studies. On the contrary, Matrigel is not a suitable substrate to support platelet attachment under flow conditions.

Desmopressin (DDAVP) enhances platelet adhesion to the extracellular matrix of cultured human endothelial cells through increased expression of tissue factor.

The effect of desmopressin (DDAVP) on thrombogenicity, expression of tissue factor and procoagulant activity (PCA) of extracellular matrix (ECM) generated by human umbilical vein endothelial cells cultures (HUVEC), was studied under different experimental conditions. HUVEC were incubated with DDAVP (1, 5 and 30 ng/ml) and then detached from their ECM. The reactivity towards platelets of this ECM was tested in a perfusion system. Coverslips covered with DDAVP-treated ECMS were inserted in a parallel-plate chamber and exposed to normal blood anticoagulated with low molecular weight heparin (Fragmin, 20 U/ml). Perfusions with run for 5 min at a shear rate of 800 s-1. Deposition of platelets on ECMs was significantly increased with respect to control ECMs when DDAVP was used at 5 and 30 ng/ml (p < 0.05 and p. < 0.01 respectively). The increase in platelet deposition was prevented by incubation of ECMs with an antibody against human tissue factor prior to perfusion. Immunofluorescence studies positively detected tissue factor antigen on DDAVP derived ECMs. A chromogenic assay performed under standardized conditions revealed a statistically significant increase in the procoagulant activity of the ECMs produced by ECs incubated with 30 ng/ml DDAVP (p < 0.01 vs. control samples). Northern blot analysis revealed increased levels of tissue factor mRNA in extracts from ECs exposed to DDAVP. Our data indicate that DDAVP in vitro enhances platelet adhesion to the ECMs through increased expression of tissue factor. A similar increase in the expression of tissue factor might contribute to the in vivo hemostatic effect of DDAVP.

Antibodies to CD36 (GPIV) inhibit platelet adhesion to subendothelial surfaces under flow conditions.

The membrane glycoprotein CD36 (glycoprotein [GP] IV) has previously been shown to accelerate the initial interaction of platelets with purified type I collagen in both static and flow systems. In the present study, the role of CD36 on platelet interaction with physiologically relevant collagenous surfaces was addressed. Using arterial subendothelium (SE) and endothelial cell extracellular matrix (ECM), studies were performed under flow conditions with annular and parallel-plate perfusion chambers, respectively, at a shear rate of 800 s-1 for 2, 5, and 10 minutes. Perfusates consisted of citrated normal blood samples incubated with Fab fragments of a monospecific polyclonal anti-CD36 antibody or with each of three new anti-CD36 monoclonal antibodies (MoAbs) that inhibit platelet adhesion to purified type I collagen in a static system (131.4, 131.5, and 131.7). Perfusions over SE were also carried out using citrated blood samples from a Naka-negative donor, whose platelets lack CD36. Morphometric evaluation of the perfused samples showed that polyclonal anti-CD36 Fab and the three monoclonal anti-CD36 antibodies inhibited platelet adhesion to the two substrates by 40% after 2 minutes of perfusion and by 30% after 5 minutes (P < .005 on SE and P < .01 on ECM), but at 10 minutes, significant inhibition was seen only on SE with polyclonal anti-CD36 Fab. Similar inhibitions were seen with Naka-negative platelets on SE. These studies demonstrate that CD36 plays a role in the early stages of platelet adhesion to physiologically relevant subendothelial surfaces.

Uraemic medium causes endothelial cell dysfunction characterized by an alteration of the properties of its subendothelial matrix.

Uraemic patients suffer from haemorrhagic disorders and accelerated atherosclerosis. To evaluate the possible role of the vessel wall in these haemostatic alterations associated with uraemia, we investigated the effect of a uraemic milieu on human endothelial cell (EC) cultures and the reactivity of the extracellular matrices (ECM) generated by these cells towards platelets. EC cultures were exposed to a pool of sera (20% in the culture medium) obtained either from uraemic patients or from normal donors, and the following parameters were evaluated: (1) EC viability (trypan blue exclusion test); (2) von Willebrand factor (vWF) levels in supernatants and associated with ECM; (3) the reactivity of EC and EC-derived ECM towards platelets, measured 'ex vivo' under flow conditions (5 min, wall shear rate 800 s-1); and (4) ultrastructure of the ECM. The viability of EC cultured in the presence of uraemic sera was similar to controls. Platelet interaction with ECM generated by EC exposed to uraemic sera was significantly reduced (P < 0.05). This decrease was mainly related to a reduction in platelet adhesion (9.8 +/- 1.9% vs 16.7 +/- 1.8% in controls, P < 0.02). VWF levels in supernatants and associated with ECM were similar to controls. Ultrastructural analysis of the ECM generated by EC exposed to uraemic sera revealed a deficient matrix. An increased removal of EC was observed in experiments in which EC cultured in the presence of uraemic sera were perfused with citrated blood. These results indicate that a uraemic milieu induces quantitative and qualitative changes in the vascular subendothelium, characterized by a less intrincate network of fibrils, as well as a decreased attachment of EC and reduced thrombogenicity to the ECM. These changes may represent another mechanism which contributes to the haemostatic dysfunction observed in uraemic patients.