Endothelial dysfunction in diabetes and myocardial infarction : role of red blood cells and arginase
Authors: Tengbom John 
Published: October 2024

<p dir="ltr">Background</p><p dir="ltr">Complications of atherosclerotic cardiovascular disease remain the leading cause of death globally. Patients with diabetes and patients with coronary artery disease are at severely increased risk of developing complications of atherosclerotic cardiovascular disease. An early presentation of atherosclerotic disease is a dysfunctional state of the vascular endothelium, known as endothelial dysfunction, which is prominent in patients with type 2 diabetes mellitus (T2DM) and in patients with coronary artery disease. The underlying mechanisms of endothelial dysfunction are largely dependent on reduced bioavailability of nitric oxide (NO) and increased oxidative stress in the form of increased reactive oxygen species (ROS). The red blood cell (RBC) has emerged as a regulator of vascular homeostasis, but also as a mediator of endothelial dysfunction. The RBC can become dysfunctional, which leads to reduced bioavailability of NO by limited production by the NO-producing enzyme NO-synthase and simultaneously increased formation of ROS by uncoupling of the enzyme. The enzyme arginase is significantly involved in these processes as it shares substrate with NO-synthase, and thereby engages the uncoupling of NO-synthase with its subsequent consequences for the endothelium. However, these processes are not fully understood in the setting of diabetes, and whether RBCs act as mediators of endothelial dysfunction in patients with myocardial infarction remains unexplored. These mechanisms have the potential to serve as specific targets for pharmacological interventions in patients with increased cardiovascular risk.</p><p dir="ltr">Objective</p><p dir="ltr">To investigate the role of RBCs and arginase in mediating endothelial dysfunction in patients with myocardial infarction or diabetes. Special attention was given to understand the mechanistic implications caused by dysregulation of arginase- and ROS-dependent pathways affecting endothelial function by RBCs.</p><p dir="ltr">Methods and results</p><p dir="ltr">In studies I, III and IV, RBCs from patients were incubated with rat aortic segments for 18 hours and then evaluated for endothelium-dependent and independent- relaxations. In study II, gene and protein expression of arginase were determined in a clinical cohort. In study IV, endothelial function was assessed in vivo in patients with type 1 diabetes (T1DM) and T2DM using venous occlusion plethysmography. Enzymatic and expression assays were used to determine enzymatic activity and protein expression.</p><p dir="ltr">In study I, RBCs from patients with ST-elevation myocardial infarction and elevated C-reactive protein levels (CRP), but not RBCs from patients with low CRP, impaired the endothelial function of rat aortic segments. This impairment was dependent on arginase and ROS in the RBCs and in the vasculature.</p><p dir="ltr">In study II, already at admission both gene and protein expression of arginase 1 was upregulated in patients with ST-elevation myocardial infarction. This indicates the possible involvement of arginase 1 in the development of myocardial infarction.</p><p dir="ltr">In study III, RBCs from patients with T2DM induced endothelial dysfunction in isolated aortas. Scavenging of peroxynitrite attenuated the RBC-induced endothelial dysfunction and decreased arginase activity in the vessel. These results indicate that the RBC-dependent impairment of endothelial function in T2DM is dependent on peroxynitrite, which regulates arginase.</p><p dir="ltr">In study IV, patients with T2DM had impaired endothelial function in vivo compared to patients with T1DM, and this impairment was restored following arginase inhibition. Also, RBCs from patients with T2DM, but not T1DM, induced endothelial dysfunction in isolated aortas. These results suggest distinct differences in endothelial function between patients with T1DM and T2DM, involving the role of arginase and RBCs.</p><p dir="ltr">Conclusion</p><p dir="ltr">The RBC, arginase and ROS are all involved in the development of endothelial dysfunction in patients with ST-elevation myocardial infarction and in patients with T2DM, but not in patients with T1DM. In both patients with T2DM and in patients with ST-elevation myocardial infarction, the RBC-mediated impairment of endothelial function was dependent on arginase and ROS. These findings highlight the RBC as a mediator of vascular dysfunction and as a potential therapeutic target to reduce the risk of two patient groups at severely increased cardiovascular risk.</p><h3>List of scientific papers</h3><p dir="ltr">I. <b>Tengbom J,</b> Humoud R, Kontidou E, Jiao T, Yang J, Hedin U, Zhou Z, Jurga J, Collado A, Mahdi A, Pernow J. Red blood cells from patients with ST-elevation myocardial infarction and elevated C-reactive protein levels induce endothelial dysfunction. [Accepted]</p><p dir="ltr">II. <b>Tengbom J,</b> Cederström S, Verouhis D, Böhm F, Eriksson P, Folkersen L, Gabrielsen A, Jernberg T, Lundman P, Persson J, Saleh N, Settergren M, Sörensson P, Tratsiakovich Y, Tornvall P, Jung C, Pernow J. Arginase-1 is upregulated at admission in patients with ST- elevation myocardial infarction. Journal of Internal Medicine. 2021, 290: 1061-1070. <a href="https://doi.org/10.1111/joim.13358" rel="noreferrer" target="_blank">https://doi.org/10.1111/joim.13358</a></p><p dir="ltr">III. Mahdi A, <b>Tengbom J,</b> Alvarsson M, Wernly B, Zhou Z, Pernow J. Red blood cell peroxynitrite causes endothelial dysfunction in type 2 diabetes mellitus via arginase. Cells. 2020 Jul 16;9(7):1712. <a href="https://doi.org/10.3390/cells9071712" rel="noreferrer" target="_blank">https://doi.org/10.3390/cells9071712</a></p><p dir="ltr">IV. <b>Tengbom J,</b> Kontidou E, Collado A, Yang J, Alvarsson M, Brinck J, Rössner S, Zhou Z, Pernow J, Mahdi A. Distinct differences in endothelial function between patients with type 1 and type 2 diabetes: effects of red blood cells and arginase. Clinical Science (Lond). 2024 Aug 7;138(15):975-985. <a href="https://doi.org/10.1042/CS20240447" rel="noreferrer" target="_blank">https://doi.org/10.1042/CS20240447</a></p>