Concerning the Significance of Paraoxonase-1 and SR-B1 Genes in Atherosclerosis

High-density lipoprotein (HDL) is an independent protective factor against cardiovascular disease. The enzyme paraoxonase-1 (PON-1) contributes to the anti-atherogenic effects of HDL. In vitro studies have demonstrated that paraoxonase's substrates are highly heterogeneous and that some contribute to the development of atherosclerotic lesions. The atheroprotective role of PON-1 was established in genetically engineered animal models. In humans, the PON-1 Gln192 Arg and Met55 Leu polymorphisms appear to be associated with increased susceptibility to cardiovascular disease and with different PON-1 activity levels and concentrations. The CLA-1 (CD36 and Lysosomal integral membrane protein-II Analogous-1) gene is the human homologue of the murine SR-B1 (Scavenger Receptor class B type 1) gene. SR-B1 was the first high-affinity HDL receptor to be identified at the molecular level. The CLA-1 receptor plays a pivotal role in HDL-mediated reverse cholesterol transport by mediating the selective uptake of free cholesterol as well as of native and oxidized cholesteryl esters. Its atheroprotective role has also been established in transgenic mice studies. Several polymorphic variants of the CLA-1 gene have been described, some of which are associated with phe-notypic changes in plasma lipoproteins. Both genes participate in the complex HDL metabolic pathway and, presumably, also in defense mechanisms against oxidative stress.

La lipoproteína de alta densidad (HDL) constituye un factor de protección independiente de enfermedad cardiovascular. La enzima paraoxonasa-1 (PON-1) contribuye a las propiedades antiaterogénicas asociadas al HDL. Estudios in vitro muestran que posee una gran heterogeneidad de sustratos, algunos de los cuales participan en la progresión de las lesiones ateroscleróticas. Se han desarrollado modelos animales que muestran su papel ate-roprotector. En humanos, las variantes PON-1 Gln192 Arg y Met55 Leu parecen asociarse con una mayor susceptibilidad cardiovascular, con diferentes actividades y concen-tración de la proteína PON-1. El gen CLA-1 (CD36 and Lysosomal integral membrana protein-II Analogous-1) es el homólogo humano del gen SR-B1 (Scavenger Receptor class B type 1) y constituye el primer receptor de alta afinidad de HDL bien caracterizado. El receptor CLA-1 participa en el transporte reverso de colesterol a través de la entrada selectiva de ésteres de colesterol nativos y oxidados, y su papel ateroprotector se ha deducido de los estudios en animales genéticamente manipulados. En humanos, el gen CLA-1 es polimórfico y algunas de sus variantes han sido previamente asociadas con cambios fenotípicos en lipoproteínas plasmáticas. Ambos genes participan en el complejo metabolismo del HDL y, presumiblemente, en los mecanismos de defensa frente a estrés oxidativo.