Sepiapterin reverses the changes in gastric nNOS dimerization and function in diabetic gastroparesis

Abstract

Background We have demonstrated previously that in vivo supplementation of tetrahydrobiopterin (BH4); a co-factor for neuronal nitric oxide synthase (nNOS) significantly restored delayed gastric emptying and attenuated nitrergic relaxation in diabetic rat. In this study, we have investigated whether supplementation of sepiapterin (SEP), a precursor for BH4 biosynthesis via salvage pathway restores gastric emptying and nitrergic system in female diabetic rats. Methods Diabetic rats (streptozotocin-induced) were supplemented with BH4 or SEP (20 mg kg−1 body weight). Gastric nitrergic relaxation in the presence or absence of high glucose and SEP were measured by electric field stimulation. Gastric muscular strips from healthy or diabetic female rats were incubated in the presence or absence of high glucose, SEP and/or methotrexate (MTX). Nitric oxide release was measured colorimetrically by NO assay kit. The expression of nNOSα and dimerization was detected by Western blot. Key Results In vitro studies on gastric muscular tissues showed that MTX, an inhibitor of BH4 synthesis via salvage pathway, significantly decreased NO release. In vivo treatment with MTX reduced both gastric nitrergic relaxation and nNOSα dimerization. Supplementation of SEP significantly attenuated delayed gastric emptying in diabetic rats. In addition, SEP supplementation restored impaired nitrergic relaxation, gastric nNOSα protein expression and dimerization in diabetic rats. Conclusions & Inferences The above data suggests that supplementation of SEP accelerated gastric emptying and attenuated reduced gastric nNOSα expression, and dimerization. Therefore, SEP supplementation is a potential therapeutic option for female patients of diabetic gastroparesis.

Tetrahydrobiopterin deficiency induces gastroparesis in newborn mice

“…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.…”

“…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).…”

Infantile hypertrophic pyloric stenosis (IHPS): A study of its pathophysiology utilizing the newborn hph-1 mouse model of the disease

“…BH4 deficiency results in nNOS uncoupling, leading to an increase in tissue superoxide content and tissue NO deficiency (11,41,47). The increased pyloric tone of the newborn hph-1 mice has been attributed to the BH4-induced tissue NO deficiency (1), without any further consideration given to the potential role of ROS in the sphincter contraction.…”

“…nNOS is the most abundant NOS isoform in gastrointestinal smooth muscle (42), and its NO generation potential depends on the coupled dimeric state of the enzyme. When uncoupled, nNOS predominantly generates reactive oxygen species (ROS) (11,37,42).Infantile hypertrophic pyloric stenosis (IHPS) is a relatively common disease affecting 2 in 1,000 live births (34) and manifesting clinically at 3-6 wk of age. The IHPS etiology and pathogenesis are unknown, but the increased sphincter tone is believed to be related to reduced pyloric tissue nNOS expression (2) and the resulting lower NO generation (13,34,45).…”

“…nNOS is the most abundant NOS isoform in gastrointestinal smooth muscle (42), and its NO generation potential depends on the coupled dimeric state of the enzyme. When uncoupled, nNOS predominantly generates reactive oxygen species (ROS) (11,37,42).…”