Effects of Incretins on Human Platelet Function

Overview

Novel drugs for the treatment of patients with diabetes are of interest for cardiologists if they reduce the risk of cardiovascular events. However, as documented by the current discussion about the potential benefits of glitazones, high hopes can fail. Initial beneficial cardiovascular effects shown in proof-of-concept studies were muted by the apparent higher mortality in the metaanalysis of studies with rosiglitazone. The rapidly increasing use of GLP-1 analogues and DPP-4 (Dipeptidyl protease 4) inhibitors for the treatment of type 2 diabetes mellitus may be of major interest for the cardiologist. Potential beneficial actions on the cardiovascular system so far shown in animal experiments and small proof of concept studies may provide the rationale for using these drugs specifically in diabetic patients with secondary complications such as macrovascular disease or diabetic cardiomyopathy. Theoretically, these new therapies could also proof beneficial in patients with heart failure, independently of concomitant diabetes mellitus. However, many unanswered questions need to be addressed in the near future to extend the experimental findings to potential benefits of real life patients. In summary a new class of antidiabetic drugs, which could possibly directly influence cardiovascular effects of diabetes mellitus and thus possibly treat or even prevent life threatening complications has become available. Then our working hypothesis was that incretins may have desirable cardiovascular outcomes through modulating platelet function. In order to test this hypothesis we propose to assess the presence of their specific receptors in isolated human platelets. In addition, we proposed to sudy the effect of the endogenous incretins (glucagon-like peptide 1 and gastric inhibitory peptide) on human platelet function isolated in a test tube.

Aims and Methods: The prevalence of Type 2 diabetes (T2D) continues to increase globally and brings with it a parallel increase in the associated cardiovascular disease complications. Correction of platelet hyperactivity holds promise for this high-risk population of T2D patients by contributing to restore normal hemostasis, which has lead to the search for new antiagregant drugs. Then, our aim was to study whether incretins may modulate platelet function; for this purpose platelets from healthy subjects who were not taken any medication were studied. Besides, normal mature megakaryocytes obtained by culture of human cord blood derived-CD34+ hematopoietic progenitor cells were also studied. For platelet function studies, platelet aggregation was tested in the absence and presence of different concentrations (10-9 M to 10-5 M) of glucagon-like peptide-1,GLP1-(7-36)NH2, and glucose-dependent insulinotropic polypeptide (GIP) agonist by a turbidimetricassay. The effect of 300 mg/dLglucose added to the media was also evaluated. GLP1R (glucagon-like peptide 1 receptor) and GIPR (GIP receptor) mRNA expression was evaluated by Real Time PCR in platelet and megakaryocyte total mRNA. The putative presence of their proteins was assayed by western blot and flow cytometry in both samples.