Tetrahydrobiopterin (BH4), a cofactor for nNOS, restores gastric emptying and nNOS expression in female diabetic rats.
Gastroparesis is a debilitating disease predominantly affecting young women. Recently, dysregulation of neuronal nitric oxide synthase (nNOS) in myenteric plexus neurons has been implicated for delayed solid gastric emptying/gastroparesis in diabetic patients. In this study, we have explored the role of tetrahydrobiopterin (BH4), a major cofactor for nNOS activity and NO synthesis in diabetic gastroparesis. Diabetes was induced with single injection of streptozotocin (55 mg/kg body wt, ip) in female rats, with experiments performed on week 3 or 9 following induction, with or without 3-wk BH4 supplementation. Gastric pyloric BH4 levels were significantly decreased in diabetic female rats compared with control (18.6 +/- 1.45 vs. 31.0 +/- 2.31 pmol/mg protein). In vitro studies showed that 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor of BH4 synthesis, significantly decreased gastric NO release and nitrergic relaxation. Three-week dietary supplementation of BH4 either from day 1 or week 6 significantly attenuated diabetes-induced delayed gastric emptying for solids (3 wk: BH4, 67 +/- 6.7 vs. diabetic, 36.05 +/- 7.09; 9 wk: BH4, 57 +/- 8.45 vs. diabetic, 33 +/- 9.91) and diabetes-induced reduction in pyloric nNOS-alpha protein expression in female rats. Supplementation of BH4 significantly restored gastric nNOS-alpha dimerization in 9-wk-old diabetic female rats. In addition, BH4 treatment reversed (17.23 +/- 5.81 vs. 42.0 +/- 2.70 mmHg x s) the diabetes-induced changes in intragastric pressures (IGP) and gastric pyloric nitrergic relaxation (-0.62 +/- 0.01 vs. -0.22 +/- 0.07). BH4 deficiency plays a critical role in diabetes-induced alterations including delayed solid gastric emptying, increased IGP, reduced pyloric nitrergic relaxation, and nNOS-alpha expression in female rats. Supplementation of BH4 accelerates gastric emptying by restoring nitrergic system in diabetic female rats. Therefore, BH4 supplementation is a potential therapeutic option for female patients of diabetic gastroparesis.
Gangula
Pandu R R
PR
Department of Obstetrics and Gynecology, Center for Women's Health Research, Meharry Medical College, Nashville, Tennessee 37208, USA. pgangula@mmc.edu
Mukhopadhyay
Sutapa
S
Ravella
Kalpana
K
Cai
Shijie
S
Channon
Keith M
KM
Garfield
Robert E
RE
Pasricha
Pankaj J
PJ
D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D001786:Blood Glucose / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D005260:Female; D006136:GTP Cyclohydrolase / Q000037:antagonists & inhibitors; D005746:Gastric Emptying / Q000187:drug effects*; D018589:Gastroparesis / Q000503:physiopathology; D007042:Hypoxanthines / Q000494:pharmacology; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D052248:Nitric Oxide Synthase Type I / Q000096:biosynthesis* / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D011708:Pylorus / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D001786:Blood Glucose; D007042:Hypoxanthines; D001708:Biopterins; D052248:Nitric Oxide Synthase Type I; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D006136:GTP Cyclohydrolase; C017202:2,4-diaminohypoxanthine; C003402:sapropterin