sepiapterin and Diabetes-Mellitus

Nitric oxide (NO), produced by endothelial nitric oxide synthase (eNOS), is a key signaling molecule in vascular homeostasis. Loss of NO bioavailability due to reduced synthesis and increased scavenging by reactive oxygen species is a cardinal feature of endothelial dysfunction in vascular disease states. The pteridine cofactor tetrahydrobiopterin (BH4) has emerged as a critical determinant of eNOS activity: when BH4 availability is limiting, eNOS no longer produces NO but instead generates superoxide. In vascular disease states, there is oxidative degradation of BH4 by reactive oxygen species. However, augmentation of BH4 concentrations in vascular disease by pharmacological supplementation, by enhancement of its rate of de novo biosynthesis or by measures to reduce its oxidation, has been shown in experimental studies to enhance NO bioavailability. Thus, BH4 represents a potential therapeutic target in the regulation of eNOS function in vascular disease.

Topics: Animals; Biological Availability; Biopterins; Coenzymes; Diabetes Mellitus; Enzyme Induction; GTP Cyclohydrolase; Humans; Hypercholesterolemia; Hypertension; Mice; Mice, Mutant Strains; Models, Animal; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Oxidation-Reduction; Oxidative Stress; Pterins; Rabbits; Rats; Rats, Inbred Strains; Superoxides; Vascular Diseases

Diabetic gastroparesis may be associated with impaired nitric oxide metabolism and reduced tetrahydrobiopterin (BH. Non-pregnant diabetic women with moderate/severe symptomatic gastroparesis, delayed gastric emptying, and impaired gastric accommodation (nutrient satiety testing) were randomized to 10mg/kg BID CNSA-001 or matching placebo for 14days. The primary endpoint was change in gastric accommodation (maximal tolerated liquid meal volume) at 14- and 28-days' follow-up.. Gastric accommodation improved in CNSA-001-treated vs. placebo-treated subjects at 28days (least squares mean [LSM] difference: 98 [95% CI 36 to 161], p=0.0042). Subjects' ratings of bloating, fullness, nausea, and pain were lower vs. baseline in the CNSA-001 group at 14 and 28days, though these improvements were not observed consistently in placebo-treated subjects. There were no significant group differences in upper gastrointestinal symptom scores, and in gastric emptying breath test parameters. CNSA-001 was well tolerated, with no withdrawals for adverse events.. CNSA-001 improved gastric accommodation in women with diabetic gastroparesis. Further evaluation of CNSA-001 in gastroparesis is warranted; ClinicalTrials.gov number, NCT03712124.

Topics: Diabetes Mellitus; Diabetic Neuropathies; Female; Gastric Emptying; Gastroparesis; Humans; Pterins

Peroxynitrite (ONOO(-)) contributes to coronary microvascular dysfunction in diabetes mellitus (DM). We hypothesized that in DM, ONOO(-) interferes with the function of coronary endothelial caveolae, which plays an important role in nitric oxide (NO)-dependent vasomotor regulation. Flow-mediated dilation (FMD) of coronary arterioles was investigated in DM (n = 41) and non-DM (n = 37) patients undergoing heart surgery. NO-mediated coronary FMD was significantly reduced in DM patients, which was restored by ONOO(-) scavenger, iron-(III)-tetrakis(N-methyl-4'pyridyl)porphyrin-pentachloride, or uric acid, whereas exogenous ONOO(-) reduced FMD in non-DM subjects. Immunoelectron microscopy demonstrated an increased 3-nitrotyrosine formation (ONOO(-)-specific protein nitration) in endothelial plasma membrane in DM, which colocalized with caveolin-1 (Cav-1), the key structural protein of caveolae. The membrane-localized Cav-1 was significantly reduced in DM and also in high glucose-exposed coronary endothelial cells. We also found that DM patients exhibited a decreased number of endothelial caveolae, whereas exogenous ONOO(-) reduced caveolae number. Correspondingly, pharmacological (methyl-β-cyclodextrin) or genetic disruption of caveolae (Cav-1 knockout mice) abolished coronary FMD, which was rescued by sepiapterin, the stable precursor of NO synthase (NOS) cofactor, tetrahydrobiopterin. Sepiapterin also restored coronary FMD in DM patients. Thus, we propose that ONOO(-) selectively targets and disrupts endothelial caveolae, which contributes to NOS uncoupling, and, hence, reduced NO-mediated coronary vasodilation in DM patients.

Topics: Aged; Animals; Arterioles; beta-Cyclodextrins; Caveolae; Caveolin 1; Cells, Cultured; Diabetes Mellitus; Endothelial Cells; Endothelium, Vascular; Female; Humans; Male; Mice; Mice, Knockout; Middle Aged; Nitric Oxide; Nitric Oxide Synthase Type III; Peroxynitrous Acid; Pterins; Regional Blood Flow; Tyrosine; Vasodilation

We previously reported that acute incubation with tetrahydrobiopterin (BH4) or sepiapterin, a cofactor for endothelial nitric oxide synthase and a stable precursor of BH4, respectively, enhanced the acetylcholine (Ach)-induced relaxation of isolated small mesenteric arteries (SMA) from diabetic (db/db) mice. In this study, we investigated the effect of chronic oral supplementation of sepiapterin (10 mg x kg-1 x day-1) to db/db mice on endothelium function, biopterin levels and lipid peroxidation in SMA. Oral dietary supplementation with sepiapterin had no effect on glucose, triglyceride, cholesterol levels and body weight. SMA from db/db mice showed enhanced vascular reactivity to phenylephrine, which was corrected with sepiapterin supplementation. Furthermore, Ach, but not sodium nitroprusside-induced relaxation, was improved with sepiapterin supplementation in db/db mice. BH4 levels and guanosine triphosphate cyclohydrolase I activity in SMA were similar in db/+ and db/db mice. Sepiapterin treatment had no effects on BH4 or guanosine triphosphate cyclohydrolase I activity. However, the level of dihydrobiopterin+biopterin was higher in SMA from db/db mice, which was corrected following sepiapterin treatment. Thiobarbituric acid reactive substance, malondialdehyde, a marker of lipid peroxidation, was higher in SMA from db/db mice, and was normalized by sepiapterin treatment. These results indicate that sepiapterin improves endothelial dysfunction in SMA from db/db mice by reducing oxidative stress. Furthermore, these results suggest that decreased biosynthesis of BH4 may not be the basis for endothelial dysfunction in SMA from db/db mice.

Topics: Acetylcholine; Administration, Oral; Animals; Biopterins; Diabetes Mellitus; Disease Models, Animal; Drug Administration Schedule; Drug Therapy, Combination; Endothelium, Vascular; GTP Cyclohydrolase; Lipid Peroxidation; Male; Malondialdehyde; Mesenteric Artery, Inferior; Mice; Mice, Inbred C57BL; Neopterin; Oxidative Stress; Phenylephrine; Pterins; Vasoconstriction; Vasodilation

Endothelial cells (EC) from diabetic BioBreeding (BB) rats have an impaired ability to produce NO. This deficiency is not due to a defect in the constitutive isoform of NO synthase in EC (ecNOS) or alterations in intracellular calcium, calmodulin, NADPH or arginine levels. Instead, ecNOS cannot produce sufficient NO because of a deficiency in tetrahydrobiopterin (BH(4)), a cofactor necessary for enzyme activity. EC from diabetic rats exhibited only 12% of the BH(4) levels found in EC from normal animals or diabetes-prone animals which did not develop disease. As a result, NO synthesis by EC of diabetic rats was only 18% of that for normal animals. Increasing BH(4) levels with sepiapterin increased NO production, suggesting that BH(4) deficiency is a metabolic basis for impaired endothelial NO synthesis in diabetic BB rats. This deficiency is due to decreased activity of GTP-cyclohydrolase I, the first and rate-limiting enzyme in the de novo biosynthesis of BH(4). GTP-cyclohydrolase activity was low because of a decreased expression of the protein in the diabetic cells.

Topics: Animals; Arginine; Biopterins; Calcium; Calmodulin; Chromatography, High Pressure Liquid; Diabetes Mellitus; Disease Models, Animal; Dose-Response Relationship, Drug; Endothelium, Vascular; GTP Cyclohydrolase; Immunoblotting; Kinetics; NADP; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Protein Isoforms; Pteridines; Pterins; Rats; Rats, Mutant Strains