Abstract 11026: Preservation of Endothelial GTP Cyclohydrolase I Activity and Improvement of Renal Nitric Oxide Availability Prevent the Development of Albuminuria in Diabetes
Background: Increased oxidative stress is involved in the pathogenesis of diabetic vascular complications. The uncoupling of endothelial nitric oxide (NO) synthase (eNOS) through the oxidation of tetrahydrobiopterin (BH4), which is a cofactor required for NO production, plays a major role in the generation of oxidative stress. GTP cyclohydrolase I (GTPCH I) is the rate-limiting enzyme for BH4 biosynthesis, and the hyperglycemia accelerates the degradation of GTPCH I through the inhibition of AMPK activity. We hypothesized that the preservation of GTPCH I expression and improvements in NO availability, either genetically or pharmacologically, could prevent the development of diabetic renal complications.
Methods: We used male diabetic Akita mice (AKITA), endothelium-specific GCH1 transgenic mice (GCHtg), and AKITA crossed with GCHtg (GCHtg/AKITA). They were bred for 14 to 15 weeks. We also investigated AKITA treated with metformin (AKITA/Met) at 10 weeks of age for 4 weeks. In an in vitro assay, human glomerular endothelial cells (hGECs) were exposed to high glucose concentrations (30 mM) in the presence or absence of metformin. The levels of phospho-AMPK, GTPCH I, and eNOS were examined.
Results: Urinary albumin excretion (UAE) was significantly suppressed in GCHtg/AKITA compared to AKITA. Exacerbated reactive oxygen species production and diminished bioavailable NO were noted in the glomeruli of AKITA. A biochemical analysis revealed that eNOS was uncoupled in AKITA. However, renal BH4 levels were preserved and glomerular eNOS were re-coupled in GCHtg/AKITA. Compared to AKITA, renal BH4 levels and GTPCH I expression were increased in AKITA/Met, and UAE was significantly suppressed in AKITA/Met. Phospho-AMPK, GTPCH I, and eNOS expression levels were reduced in the hGECs exposed to high glucose. However, metformin attenuated these alterations.
Conclusions: The preservation of endothelial GTPCH I expression and the resulting improvements in BH4 biosynthesis prevented the development of renal complications in a diabetic milieu.
- © 2012 by American Heart Association, Inc.