An investigation into the pleiotropic activity of metformin. A glimpse of haemostasis

The most characteristic features of type 2 diabetes mellitus (T2DM) are hyperglycaemia and insulin resistance, however, patients with T2DM are at higher risk of cardiovascular disease (CVD) and atherosclerosis. Diabetes, frequently related to metabolic and vascular impairments, is also associated with thrombosis, increased blood coagulation and an imbalance between coagulation and fibrinolysis. Metformin is the most often used oral glucose-lowering agent; its beneficial properties include lowering insulin resistance, weight reduction and cardioprotection. Available data suggest that the advantageous properties of metformin stem from its favourable effects on endothelium, and anti-oxidative and anti-inflammatory properties. This paper reviews the favourable impact of metformin on endothelial function, with particular emphasis on the release of endogenous molecules modulating the state of the vascular endothelium and coagulation. It also summarizes the present knowledge on the influence of metformin on platelet activity and plasma haemostasis, including clot formation, stabilization and fibrinolysis. Its findings confirm that metformin should constitute first line therapy of T2DM subjects; however, more comprehensive methodical studies are required to discover the full potential of this drug.

Pleiotropic Activity of Metformin and Its Sulfonamide Derivatives on Vascular and Platelet Haemostasis

As type 2 diabetes mellitus (T2DM) predisposes patients to endothelial cell injury and dysfunction, improvement of vascular function should be an important target for therapy. The aim of this study was to evaluate the effects of metformin, its sulfenamide and sulfonamide derivatives on selected parameters of endothelial and smooth muscle cell function, and platelet activity. Metformin was not found to significantly affect the viability of human umbilical vein endothelial cells (HUVECs) or aortal smooth muscle cells (AoSMC); however, it decreased cell migration by approximately 21.8% in wound healing assays after 24 h stimulation (wound closure 32.5 µm versus 41.5 µm for control). Metformin reduced platelet aggregation manifested by 19.0% decrease in maximum of aggregation (Amax), and 20% reduction in initial platelet aggregation velocity (v0). Furthermore, metformin decreased spontaneous platelet adhesion by 27.7% and ADP-induced adhesion to fibrinogen by 29.6% in comparison to control. Metformin sulfenamide with an n-butyl alkyl chain (compound 1) appeared to exert the most unfavourable effects on AoSMC cell viability (IC50 = 0.902 ± 0.015 μmol/mL), while 4-nitrobenzenesulfonamide (compound 3) and 2-nitrobenzenesulfonamide (compound 4) derivatives of metformin did not affect AoSMC and HUVEC viability at concentrations up to 2.0 μmol/mL. These compounds were also found to significantly reduce migration of smooth muscle cells by approximately 81.0%. Furthermore, sulfonamides 3 and 4 decreased the initial velocity of platelet aggregation by 11.8% and 20.6%, respectively, and ADP-induced platelet adhesion to fibrinogen by 76.3% and 65.6%. Metformin and its p- and o-nitro-benzenesulfonamide derivatives 3, 4 appear to exert beneficial effects on some parameters of vascular and platelet haemostasis.

Generation 2 (G2) - Generation 4 (G4) PAMAM dendrimers disrupt key plasma coagulation parameters

The aim of the research was to evaluate the effects of G2 - G4 PAMAM dendrimers on basic plasma haemostasis parameters (Partially Activated Thrombin Time (APTT), Prothrombin Time (PT), Thrombin Time (TT)) as well as the activity of factor X, antithrombin III (AT), protein C and plasmin. Furthermore, tissue factor (TF) synthesis in endothelial cells and viability of smooth muscle cells in the presence of PAMAM dendrimers was investigated. APTT, PT and TT were performed according to the available commercial methods. The activity of factor X was conducted based on deficient plasma factor X. Protein C, AT and plasmin activity were measured spectrophotometrically using chromogenic substrates. Intracellular TF production in human umbilical vein endothelial cells (HUVECs) was measured using immunohistochemical method. Viability of Human Aortal Smooth Muscle cells (hAoSMCs) was established using WST-1 assay. PAMAM dendrimers decreased activity of factor X, and concomitantly prolonged PT and APTT. We also demonstrated shortened TT and increased fibrinogen concentrations in plasma treated with G4 PAMAM dendrimers, suggesting formation of fibrinogen aggregates. G2 - G4 PAMAM dendrimers decreased the activity of both naturally occurring anticoagulants AT and protein C. G2 and G3 PAMAM dendrimers did not affect the proteolytic reaction with plasmin. PAMAM dendrimers were found not to trigger TF production in undisturbed endothelial cells. PAMAM dendrimers, depending on the concentration and generation decreased viability of AoSMCs. The results presented within the current study suggest complex but mostly undesirable effect of G2 - G4 PAMAM dendrimers on plasma haemostasis and underscore the need for further in-depth research.