Background: Hexosamine biosynthetic pathway (HBP) is implicated in increased plasminogen activator inhibitor-1 (PAI-1), and endothelial nitric oxide synthase (eNOS) dysfunction in diabetes. Glucosamine (GlcN) that directly activates HBP is a dietary supplement and is clinically used to treat osteoarthritis despite uncertain efficacy and adverse cardiovascular effects observed in animal models. p38 mitogen-activated protein kinase (p38mapk) has been shown to be involved in HBP-mediated biological processes. The aim of the present study was to investigate the role of p38mapk in GlcN-induced endothelial PAI-1 expression and eNOS dysfunction.
Methods and results: In cultured human endothelial cells, GlcN time- and concentration-dependently increased PAI-1 protein level that was further enhanced by tumor necrosis factor (TNF)-α, which was accompanied by a transient synergistic activation of p38mapk. The stimulation of PAI-1 by GlcN alone or by GlcN and TNF-α in combination was inhibited by the specific inhibitor of p38mapk, but not that of JNK or ERK1/2. Moreover, in isolated mouse aortas, GlcN caused eNOS uncoupling resulting in enhanced superoxide and decreased NO production, as well as impaired endothelium-dependent relaxations, which were also fully prevented by the p38mapk inhibitor.
Conclusions: HBP activated by GlcN increases PAI-1 expression and eNOS uncoupling depending on p38mapk, which not only explains hyperglycemic vascular complications, but also may bring into question the clinical use of GlcN. The present results, support currently ongoing clinical application of p38mapk inhibitor in patients with cardiovascular disease.