Συσχέτιση των πολυμορφισμών του γονιδίου της λιπονεκτίνης με την παρουσία στεφανιαίας νόσου και ινσουλινοαντοχής

Abstract

In the last few decades, Coronary Artery Disease has become the first cause of death in the developed countries (1 in 5 deaths) and is expected to become the first cause of death globally in the next 15 years. This is due to the rising prevalence of the disease because of the increasing incidence of obesity, metabolic syndrome and type 2 diabetes. A vast amount of evidence indicates insulin resistance as a central component in the development of cardiovascular metabolic syndrome that predisposes to atherosclerosis.Adipose tissue has now been recognized as an important endocrine organ that produces and secretes a large number of active molecules such as cytokines and hormones that are implicated in the pathogenesis of insulin resistance, have direct actions on the endothelium and are responsible for cardiovascular complications.Adiponectin is a protein that is produced by adipose tissue. Its plasma levels are reduced in obesity and insulin resistance and there are indications that it is associated with the development of the metabolic syndrome and atherosclerosis. Several studies have shown that adiponectin improves insulin sensitivity and possesses anti-atherogenic properties by inducing the production of anti-inflammatory mediators, suppressing, at the same time, the production of inflammatory cytokines. One of adiponectin’s targets are peripheral monocytes, which play an important role in insulin resistance, inflammation and atherosclerosis.Several polymorphisms of the adiponectin gene have been shown to influence its production, secretion and activity. These aberrations may cause insulin resistance, which in turn, leads to the development of type 2 diabetes and coronary artery disease. Aim: The present study investigates the association of adiponectin levels and 10 common polymorphisms of its gene with the presence of Coronary Artery Disease (CAD) and insulin resistance in humans. The study also attempts to elucidate the effect of the two adiponectin forms (globular and full-length) on the production of inflammatory and atherogenic cytokines that contribute to the process of insulin resistance and atherosclerosis, as well as on the expression of its two receptors.Materials-Methods: For the purpose of this study, we recruited 71 people from Greece, a population for which no data are available. Following coronary angiography and ECG stress test the cohort was split into two groups: 42 people with coronary artery disease (Age 59±8 years, BMI 28.3±3.2 kg/m2) and 29 people without coronary artery disease (Age 57±8 years, ΒΜΙ 28.2±2.7 kg/m2). All participants underwent an oral glycose tolerance test (OGTT). Genomic DNA was isolated from white blood cells, which was used for the genotyping of adiponectin’s gene polymorphisms using the allele specific primer extension technique (ASPE). At the same time, human monocytes were isolated from a sub-group of 24 participants (16 people with CAD and 8 people without CAD) for the in vitro experiments to study the effect of adiponectin on the production of inflammatory cytokines TNF-α and IL-6 and on the expression of its receptors AdipoR1 and AdipoR2 with the help of Real-Time PCR.Results: There was no difference in the plasma levels of adiponectin, adhesion molecules sVCAM, sICAM and E-Selectin, PAI-1, MPO and MMP9 in the two groups. However, circulating adiponectin showed a strong positive correlation with HDL levels and MATSUDA index.In the in vivo experiments there was no significant association between the 10 studied polymorphisms of the adiponectin gene and coronary artery disease. We did find, however, that certain genotypes are associated with indices of atherosclerosis, insulin resistance and obesity. Thus, we observed that homozygotes for the wild type allele of the T45G polymorphism had lower levels of triglycerides and higher endothelial intima-media thickness (IMT) than heterozygotes. Homozygotes for the wild type allele of the G276T polymorphism had a higher waist to hip ratio compared to heterozygotes, whereas the heterozygotes had increased levels of HDL cholesterol and higher levels of adhesion molecule sVCAM compared to homozygotes for the mutant allele. Moreover, homozygotes for the wild type allele of the G349A polymorphism had an increased IMT and decreased levels of adhesion molecule sVCAM compared to heterozygotes. Finally, heterozygotes for the C(-4034)A polymorphism had a higher BMI than wild type homozygotes.The in vitro experiments showed that globular adiponectin induces the expression of inflammatory cytokines TNF-α and IL-6 in both groups. However, when LPS is added, the levels of the inflammatory cytokines remain constant. In contrast, full length adiponectin seems to be suppressing their expression in the presence of LPS. Both adiponectin forms induce the expression of AdipoR1 receptor but seem to have no effect on the expression of AdipoR2.Conclusions: The first observation following the OGTT was that the incidence of type 2 diabetes as well as the incidence of impaired glucose tolerance (IGT), were higher among the CAD patients. In addition, 38% of the people without CAD were diagnosed as IGT. They were informed of their condition and the possibility of complications due to insulin resistance.The fact that we observed that the levels of adiponectin did not differ between the two groups is in compliance with recent studies and publications, where in the case of acute coronary artery disease manifestation, the levels of adiponectin increase to counteract the metabolic and inflammatory disorders that are associated with the disease. The strong positive correlation of adiponectin levels with the MATSUDA index proves the important role of adiponectin in improving insulin sensitivity.From the genotyping experiments we observed that genotypes TG(45), TT(276) and AG(349) could possibly offer protection to atherosclerosis and insulin resistance, whereas genotypes TT(45), GG(276), AA(349) and CA(-4034) may be associated with a higher risk of the latter disorders.Finally, the in vitro experiments showed that globular and full length adiponectin have a different effect on monocytes. Globular adiponectin initially induces the expression of inflammatory cytokines, but it then creates a state of ‘tolerance’ which does not allow a further increase of their expression when LPS is added. On the other hand, full length adiponectin may suppress the expression of inflammatory cytokine IL-6 upon addition of LPS.To sum up, no association was found with neither the levels of adiponectin, nor any of the polymorphisms, and insulin resistance or coronary artery disease. Adiponectin’s protective role is achieved via the improvement of insulin sensitivity and the removal of cholesterol from monocytes. Full length adiponectin seems to have an anti-inflammatory role, whereas globular adiponectin seems to induce the expression of inflammatory molecules.The possible association of certain polymprphisms of the adiponectin gene and insulin resistance or coronary artery disease should be studied further using a bigger cohort.

[…] Σκοπός: Η παρούσα μελέτη αφορά τη συσχέτιση των κυκλοφορούντων επιπέδων λιπονεκτίνης και δέκα γνωστών πολυμορφισμών του γονιδίου της με την παρουσία εγκατεστημένης στεφανιαίας νόσου και ινσουλινοαντίστασης στον άνθρωπο. Επεδίωξε επίσης να διερευνήσει την επίδραση των δύο μορφών λιπονεκτίνης (σφαιρική και πλήρους μήκους) στην παραγωγή φλεγμονωδών και αθηρογόνων κυτταροκινών που συμβάλλουν στην διαδικασία της ινσουλινοαντίστασης και της αθηρωμάτωσης, καθώς και τη συμβολή της στην έκφραση των δύο υποδοχέων της. […]