A metformin‐methylglyoxal imidazolinone metabolite (IMZ) increases angiogenesis via HIF‐1 alpha activation in endothelial cells.

Abstract

Deficient angiogenesis exacerbates the outcome of patients with peripheral arterial diseases, leading to critical limb ischemia, non‐healing ulceration or even amputation in lower extremities. These events progress more rapidly in patients with diabetes mellitus. Therapeutic strategies aiming at improving angiogenesis have been intensively studied in clinical trials, but with limited benefit. We previously discovered that metformin, the first‐line medicine for diabetes, scavenges a biologically reactive endogenous dicarbonyl, methylglyoxal, to form a novel imidazolinone metabolite (IMZ). However, the impact of IMZ on endothelial cell function is unknown. We hypothesize that IMZ increases endothelial cell‐mediated angiogenesis by activating hypoxia inducible factor (HIF)‐1 alpha, engaging key angiogenesis pathway(s). We examined the effects of IMZ on endothelial cell angiogenesis using functional assays (aortic sprouting assay, network formation, migration and proliferation assay) in vitro and characterized IMZ’s potential signaling pathways regulating HIF‐1 alpha, using western blot analysis.Our findings revealed that 24‐hour treatment of IMZ at 1μM significantly increased endothelial sprouting, the formation of capillary‐like networks on matrix, and cellular migration in endothelial cells. These effects of IMZ occurred concomitantly with an upregulation of multiple pro‐angiogenic mediators, such as placenta and platelet‐derived growth factor, fibroblast growth factor 2 beta, vascular endothelial growth factor, angiopoietin 1, as revealed by protein arrays. Meanwhile, IMZ activated endothelial nitric oxide synthase, increased nitric oxide production, and engaged the PI3K/AKT and MAPK pathway in a concentration and time‐dependent manner. These pathways stabilize and upregulate HIF‐1 alpha expression in endothelial cells. Indeed, IMZ promoted HIF‐1 alpha expression as measured by western blot. More importantly, the effects of IMZ on angiogenesis were blunted by knockdown of HIF‐1 alpha with small interfering RNA. Collectively, our data uncovered, for the first time, the pro‐angiogenic effects of a metformin metabolite IMZ. Future studies will further characterize the therapeutic potential of IMZ in alleviating impaired angiogenesis under diabetic conditions.Support or Funding InformationNIH/NIDDK R01 DK119222 (Wang & Monks) and NIH/NIDDK R01 DK109036 (Wang)