Abstract 17792: Diabetes/High Glucose induces Endothelial Dysfunction by increasing Arginase Activity through Mitogen Activated Protein Kinase and Rho kinase Pathways
Pathological manifestations of diabetes are characterized by vascular endothelial dysfunction (VED), retinopathy, neuropathy and nephropathy. The enzymes, nitric oxide synthase (NOS) and arginase, share L-arginine as their common substrate. Activation of arginase can limit availability of L-arginine for NOS thus reducing nitric oxide production and impairing vascular function. Previously, we have shown that elevated arginase activity in diabetes causes coronary VED. Here, we hypothesized that diabetes/high glucose (HG) increases arginase activity/expression through Rho kinase and mitogen activated protein kinase (MAPK) pathways to mediate VED. Our studies were performed using bovine aortic endothelial cells (BAEC) or isolated mouse aorta exposed to HG and aorta from streptozotocin-induced diabetic mice. Prolonged exposure of BAEC to HG (25 mM, 72 hr) but not mannitol (25 mM, osmotic control) increased arginase activity (135±3%, n=4, p<0.05) which was prevented by the arginase inhibitor (BEC, 100 μM). There was also a concomitant increase in arginase I protein (2-fold) with HG treatment but no change in arginase II. Pretreatment of BAEC with p38 MAPK inhibitor (SB202190, 2.5 μM), ERK inhibitor (PD98059, 10 μM) or ‘JNK inhibitor’ (2 μM) prevented the elevation in arginase activity/expression upon HG treatment. Further, Rho kinase inhibitor (Y-27632, 10 μM) prevented HG-stimulated arginase activity in BAEC. Organ bath studies were used to measure vascular function in aorta from control and diabetic mice. Aorta from diabetic mice showed impaired maximum endothelium-dependent relaxation to acetylcholine (46±4%, n=6, p<0.05) compared to control mice (68±6%, n=6). This impairment was reversed towards control levels by arginase inhibition (BEC, 100 μM) (60±3%, n=5). Additionally, incubation of aorta from control mice in media with HG (25 mM, 24 hr) reduced maximum relaxation to acetylcholine (54±6%, n=5, p<0.05) in comparison with normal glucose (5 mM, 24 hr) (73±3%, n=5). There were no differences in NO-independent relaxation induced by Na-nitroprusside in any group. In conclusion, our study indicates a major role of arginase in the vascular dysfunction of diabetes and targeting upstream Rho kinase and MAPK pathways may prevent these effects.
- © 2010 by American Heart Association, Inc.