Tetrahydrobiopterin (BH4), a cofactor for nNOS, restores gastric emptying and nNOS expression in female diabetic rats

Abstract

RE, Pasricha PJ. Tetrahydrobiopterin (BH4), a cofactor for nNOS, restores gastric emptying and nNOS expression in female diabetic rats. Am J Physiol Gastrointest Liver Physiol 298: G692-G699, 2010. First published February 25, 2010 doi:10.1152/ajpgi.00450.2009.-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 Ϯ 1.45 vs. 31.0 Ϯ 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 Ϯ 6.7 vs. diabetic, 36.05 Ϯ 7.09; 9 wk: BH4, 57 Ϯ 8.45 vs. diabetic, 33 Ϯ 9.91) and diabetes-induced reduction in pyloric nNOS-␣ protein expression in female rats. Supplementation of BH4 significantly restored gastric nNOS-␣ dimerization in 9-wk-old diabetic female rats. In addition, BH4 treatment reversed (17.23 Ϯ 5.81 vs. 42.0 Ϯ 2.70 mmHg ϫ s) the diabetes-induced changes in intragastric pressures (IGP) and gastric pyloric nitrergic relaxation (Ϫ0.62 Ϯ 0.01 vs. Ϫ0.22 Ϯ 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-␣ 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. nitrergic relaxation; diabetes; female rat; streptozotocin GASTROPARESIS IS A CLINICAL DISORDER characterized by delayed gastric emptying and symptoms such as nausea, vomiting, pain, and discomfort. A recent increase in prevalence of gastroparesis has been indicated, which may be an outcome of increased prevalence of diabetes (38). The most common known cause of this syndrome is diabetes, and it is estimated to affect 20 -55% of patients with type 1 (insulin-dependent) and up to 30% of patients with type 2 (noninsulin-dependent) diabetes (31). There is a striking sex bias in gastroparetic patients, with women outnumbering men by a 4:1 ratio (18,19,34). Recent findings from our laboratory demonstrate that the reduction in gastric emptying is greater in female rats compared with males after dia...

Tetrahydrobiopterin deficiency induces gastroparesis in newborn mice

“…The fact that BH4 potentiated, not only the cholinergic, but also the U46619-induced fundic contraction in hph-1 animals is not surprising because this thromboxane A 2 analog has been shown to potentiate airway smooth muscle contraction via acetylcholine release (20,30). Lastly, the present study findings are in keeping with the BH4 supplementation-dependent improved gastric emptying and intragastric pressure in adult rats with diabetes-induced gastroparesis (14).…”

“…Diabetes-induced gastroparesis in rodents is associated with gastric tissue BH4 deficiency and administration of this biopterin restores the impaired gastric function in these animals (14). The similarities between the adult rodent diabetes-induced gastroparesis animal model and the pyloric stenosis observed in the hph-1 mice suggest that BH4 plays an important role, not only in pyloric muscle relaxation, but also in gastric muscle contraction regulation.…”

“…Gastroparesis, a chronic motility disorder of the stomach commonly observed in association with diabetes, leads to delayed gastric emptying and gastric stasis (15). Aside from the reduced gastric muscle motility, gastric emptying dysfunction in gastroparesis is also associated with pylorus dysfunction (12,13,21).Diabetes-induced gastroparesis in rodents is associated with gastric tissue BH4 deficiency and administration of this biopterin restores the impaired gastric function in these animals (14). The similarities between the adult rodent diabetes-induced gastroparesis animal model and the pyloric stenosis observed in the hph-1 mice suggest that BH4 plays an important role, not only in pyloric muscle relaxation, but also in gastric muscle contraction regulation.…”

Future Directions in the Treatment of Gastroparesis

“…BH4 deficiency, seen in diabetes, can therefore result in loss of nitric oxide production; conversely, BH4 supplementation in animal models can reverse gastroparesis. 6,7 In this regard, a pilot study of BH4 treatment in a small group of patients with diabetic gastroparesis has shown promising results. 8 Similar concepts can be extended to augmenting cholinergic neural activity.…”

Current advances in treatment of gastroparesis

“…Lastly, finding methods to support and replenish the nNOS lost in gastroparesis is an important goal of many researchers. As a major inhibitory gastrointestinal neurotransmitter, nNOS plays a central role in GI motility by controlling the relaxation phases of normal peristalsis, helping to regulate prandial fundic accommodation, and controlling sphincter tone at the lower esophagus, pylorus, sphincter of oddi, and anus [106,107]. Administration of essential nNOS precursors and cofactors is a method that has shown early promise in animal and human models [106][107][108][109].…”