7-8-dihydrobiopterin and Diabetes-Mellitus--Type-2

Endothelial dysfunction is a common feature in type-2 diabetic patients and is associated with inflammation, increased levels of circulating soluble adhesion molecules and atherosclerosis. Insufficiency of tetrahydrobiopterin leads to uncoupling of the nitric oxide synthase enzyme an endothelial dysfunction.. was to evaluate if there is a relationship between the levels of circulating soluble adhesion molecules and the levels of biopterins in normotensive type-2 diabetic patients.. We studied 30 normotensive type-2 diabetic patients in whom VCAM-1, ICAM-1 and E-selectin were measured by ELISA. Additionally, Biopterins were measured by reverse phase high performance liquid chromatography with fluorescence detection. The levels of circulating adhesion molecules and biopterins were correlated using the Spearman correlation coefficient test. Statistical analysis was performed with ANOVA.. We did not find any relationship between absolute values of biopterins and soluble adhesion molecules. However, we observed significant inverse correlations between the BH4/BH2 ratio and VCAM-1 (r= -0.65, p<0.001) with ICAM-1 (r= -0.69, p<0.001) and with E-selectin (r=-0.64 p<0.001),. Our data suggest that systemic levels of adhesion molecules have an inverse association with the BH4/BH2 ratio in type 2 diabetic normotensive patients.

Topics: Aged; Biopterins; Blood Pressure; Diabetes Mellitus, Type 2; E-Selectin; Endothelium, Vascular; Enzyme-Linked Immunosorbent Assay; Female; Humans; Intercellular Adhesion Molecule-1; Male; Middle Aged; Solubility; Vascular Cell Adhesion Molecule-1

5,6,7,8-Tetrahydrobiopterin (BH(4)) is an essential cofactor of nitric oxide synthases (NOSs). Oxidation of BH(4), in the setting of diabetes and other chronic vasoinflammatory conditions, can cause cofactor insufficiency and uncoupling of endothelial NOS (eNOS), manifest by a switch from nitric oxide (NO) to superoxide production. Here we tested the hypothesis that eNOS uncoupling is not simply a consequence of BH(4) insufficiency, but rather results from a diminished ratio of BH(4) vs. its catalytically incompetent oxidation product, 7,8-dihydrobiopterin (BH(2)). In support of this hypothesis, [(3)H]BH(4) binding studies revealed that BH(4) and BH(2) bind eNOS with equal affinity (K(d) approximately 80 nM) and BH(2) can rapidly and efficiently replace BH(4) in preformed eNOS-BH(4) complexes. Whereas the total biopterin pool of murine endothelial cells (ECs) was unaffected by 48-h exposure to diabetic glucose levels (30 mM), BH(2) levels increased from undetectable to 40% of total biopterin. This BH(2) accumulation was associated with diminished calcium ionophore-evoked NO activity and accelerated superoxide production. Since superoxide production was suppressed by NOS inhibitor treatment, eNOS was implicated as a principal superoxide source. Importantly, BH(4) supplementation of ECs (in low and high glucose-containing media) revealed that calcium ionophore-evoked NO bioactivity correlates with intracellular BH(4):BH(2) and not absolute intracellular levels of BH(4). Reciprocally, superoxide production was found to negatively correlate with intracellular BH(4):BH(2). Hyperglycemia-associated BH(4) oxidation and NO insufficiency was recapitulated in vivo, in the Zucker diabetic fatty rat model of type 2 diabetes. Together, these findings implicate diminished intracellular BH(4):BH(2), rather than BH(4) depletion per se, as the molecular trigger for NO insufficiency in diabetes.

Topics: Animals; Biopterins; Blood Glucose; Cell Line; Diabetes Mellitus, Type 2; Disease Models, Animal; Endothelial Cells; Enzyme Inhibitors; Glucose; Glutathione; Mice; Mitochondria; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Oxidation-Reduction; Protein Binding; Rats; Rats, Zucker; Superoxides; Time Factors; Tritium