Nitric oxide regulation of migrating motor complex: randomized trial of N(G)-monomethyl-L-arginine effects in relation to muscarinic and serotonergic receptor blockade

The Enteric Neuronal Circuitry: A Key Ignored Player in Nutrient Sensing Along the Gut-Brain Axis

The role of the gut-to-brain axis in the regulation of nutrient sensing has been studied extensively for decades. Research has mainly centered on vagal afferent and efferent neurotransmission along the gastrointestinal tract, followed by the integration of luminal information in the nodose ganglia and transmission to vagal integral sites in the brain. The physiological and cellular mechanisms of nutrient sensing by enterocytes and enteroendocrine cells have been well established; however, the roles of the enteric nervous system (ENS) remain elusive. Recent advances in targeting specific neuronal subpopulations and imaging techniques unravel the plausible roles of the ENS in nutrient sensing. In this review, we highlight physiological, cellular, and molecular insights that direct toward direct and indirect roles of the ENS in luminal nutrient sensing and vagal neurotransmission along the gut-brain axis and discuss functional maladaptations observed during metabolic insults, as observed during obesity and associated comorbidities, including type 2 diabetes.

Vasodilatory Effect of n-Butanol Extract from Sanguisorba officinalis L. and Its Mechanism

The dried root of Sanguisorba officinalis L. (commonly known as Diyu) has been studied for its various pharmacological effects, including its antibacterial, antitumor, antioxidant, and anti-inflammatory activities. In the present study, primary cultured vascular endothelial cells (HUVECs) and isolated phenylephrine-precontracted rat thoracic aortic rings were examined to investigate the possible mechanism of a butanol extract of Diyu (BSO) in its vascular relaxant effect. HUVECs treated with BSO produced a significantly higher amount of nitric oxide (NO) compared to the control. However, its production was inhibited by pretreatment with NG-nitro-L-arginine methylester (L-NAME) or wortmannin. BSO also increased the phosphorylation levels of endothelial nitric oxide synthase (eNOS) and Akt. In the aortic ring, BSO relaxed PE-precontracted rat thoracic aortic rings in a concentration-dependent manner. The absence of the vascular endothelium significantly attenuated BSO-induced vasorelaxation. The non-selective NOS inhibitor, L-NAME, and the selective inhibitor of soluble guanylyl cyclase (sGC), 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ), dramatically inhibited the BSO-induced relaxation effect of the endothelium-intact aortic ring. Ca2+-free buffer and intracellular Ca2+ homeostasis regulators (TG, Gd3+, and 2-APB) inhibited BSO-induced vasorelaxation. In Ca2+-free Krebs solution, BSO markedly reduced PE-induced contraction. Vasodilation induced by BSO was significantly inhibited by wortmannin, an inhibitor of Akt. Pretreatment with the non-selective inhibitor of Ca2+-activated K+ channels (KCa), tetraethylammonium (TEA), significantly attenuated the BSO-induced vasorelaxant effect. Furthermore, BSO decreased the systolic blood pressure and heart rate in a concentration-dependent manner in rats. In conclusion, BSO induces vasorelaxation via endothelium-dependent signaling, primarily through the activation of the PI3K-Akt-eNOS-NO signaling pathway in endothelial cells, and the activation of the NO-sGC-cGMP-K⁺ channels pathway in vascular smooth muscle cells. Additionally, store-operated Ca2+ entry (SOCE)-eNOS pathways and the inhibition of Ca2⁺ mobilization from intracellular stores contribute to BSO-induced vasorelaxation.

Barriers to the Intestinal Absorption of Four Insulin-Loaded Arginine-Rich Nanoparticles in Human and Rat

Peptide drugs and biologics provide opportunities for treatments of many diseases. However, due to their poor stability and permeability in the gastrointestinal tract, the oral bioavailability of peptide drugs is negligible. Nanoparticle formulations have been proposed to circumvent these hurdles, but systemic exposure of orally administered peptide drugs has remained elusive. In this study, we investigated the absorption mechanisms of four insulin-loaded arginine-rich nanoparticles displaying differing composition and surface characteristics, developed within the pan-European consortium TRANS-INT. The transport mechanisms and major barriers to nanoparticle permeability were investigated in freshly isolated human jejunal tissue. Cytokine release profiles and standard toxicity markers indicated that the nanoparticles were nontoxic. Three out of four nanoparticles displayed pronounced binding to the mucus layer and did not reach the epithelium. One nanoparticle composed of a mucus inert shell and cell-penetrating octarginine (ENCP), showed significant uptake by the intestinal epithelium corresponding to 28 ± 9% of the administered nanoparticle dose, as determined by super-resolution microscopy. Only a small fraction of nanoparticles taken up by epithelia went on to be transcytosed via a dynamin-dependent process. In situ studies in intact rat jejunal loops confirmed the results from human tissue regarding mucus binding, epithelial uptake, and negligible insulin bioavailability. In conclusion, while none of the four arginine-rich nanoparticles supported systemic insulin delivery, ENCP displayed a consistently high uptake along the intestinal villi. It is proposed that ENCP should be further investigated for local delivery of therapeutics to the intestinal mucosa.

The Role of Gasotransmitters in Gut Peptide Actions

Although gasotransmitters nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) receive a bad connotation; in low concentrations these play a major governing role in local and systemic blood flow, stomach acid release, smooth muscles relaxations, anti-inflammatory behavior, protective effect and more. Many of these physiological processes are upstream regulated by gut peptides, for instance gastrin, cholecystokinin, secretin, motilin, ghrelin, glucagon-like peptide 1 and 2. The relationship between gasotransmitters and gut hormones is poorly understood. In this review, we discuss the role of NO, CO and H2S on gut peptide release and functioning, and whether manipulation by gasotransmitter substrates or specific blockers leads to physiological alterations.

Non-responders After Gastric Bypass Surgery for Morbid Obesity: Peptide Hormones and Glucose Homeostasis

INTRODUCTION

About 20% of patients operated with Roux-en-Y gastric bypass (RYGBP) experience poor long-term weight result. This study compared levels of leptin and gut hormones in long-term weight responders with non-responders after RYGBP. In a subgroup analysis, hormone levels were assessed in T2DM (type 2 diabetes mellitus) and normoglycemic participants.

METHODS

Insulin, glucose, leptin, acyl-ghrelin, total PYY, active GLP-1, and GIP were measured during an oral glucose tolerance test (OGTT) in post-RYGBP subjects: 22 non-responders (BMI 40.6 ± 6.0 kg/m² after an excess BMI loss [EBMIL] of 26.0 ± 15.9%) and 18 responders (BMI 29.5 ± 3.5 kg/m² after an EBMIL of 74.9 ± 18.2%). Subjects were matched for preoperative age, BMI, and years of follow-up. Measures of glucose homeostasis were calculated, and body composition was measured.

RESULTS

Fat mass-adjusted fasting leptin correlated negatively with %EBMIL (r = - 0.57, p < 0.01). Non-responders presented higher levels of leptin during the OGTT. Leptin decreased and ghrelin returned to baseline levels earlier in non-responders. Despite having higher insulin resistance than responders, non-responders demonstrated similar OGTT responses of GLP-1, GIP, and PYY. T2DM participants demonstrated lower GLP-1 levels than normoglycemic participants of similar weight.

CONCLUSION

Fasting leptin is associated with weight result after RYGBP, and hormonal responses to a glucose oral load might work towards promoting obesity in long-term non-responders after RYGBP. Poor long-term weight result and glycemic status after RYGBP are each associated with differences in peptide hormone levels.

An herbal-compound-based combination therapy that relieves cirrhotic ascites by affecting the L-arginine/nitric oxide pathway: A metabolomics-based systematic study

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine boasts a 440-year-long history of treating refractory ascites via combinations of herbal medicines, called formulae. Xiaozhang Tie (XT) is a proprietary herbal-compound-based formula that has been proven to be very effective in the treatment of cirrhosis-associated ascites in clinical practice, but the mechanism of action of XT remains unknown.

AIM OF THE STUDY

In this study, we used a metabolomics-based systematic method to elucidate the mechanism of XT in the treatment of cirrhotic ascites.

METHODS

Decompensated liver cirrhosis was induced in rats by intraperitoneal injection of Carbon tetrachloride (CCl₄). Ultra performance liquid chromatography-mass spectrometry (UPLC-MS) combined with pattern recognition approaches were used to determine differentiating metabolites relevant to XT treatment. Biomarkers were further validated by a targeted quantitative method and by the results from serum and urine analyses. Pathway analysis and correlation network construction were used to reveal the therapeutic targets associated with XT treatment, and the potential mechanisms were verified by the results from biochemical, histopathological and immunohistochemical assays.

RESULTS

XT synergistically mediated the abnormalities of amino acid metabolic pathways in cirrhotic rats. XT significantly elevated the arginine levels, reduced the serum nitric oxide (NO) levels and alleviated the gastrointestinal motility disorder of cirrhotic rats. This effect of XT has been confirmed by the inhibition of the activities of inducible NO synthase and neuronal NO synthase in the small intestine.

CONCLUSIONS

These results reveal that XT promotes gastrointestinal motility by acting on multiple targets in multiple pathways, of which the L-arginine/NO pathway is most affected.

Glucagon-Like Peptide-1 Inhibits Prandial Gastrointestinal Motility Through Myenteric Neuronal Mechanisms in Humans

CONTEXT

Glucagon-like peptide-1 (GLP-1) secretion from l-cells and postprandial inhibition of gastrointestinal motility.

OBJECTIVE

Investigate whether physiological plasma concentrations of GLP-1 inhibit human postprandial motility and determine mechanism of action of GLP-1 and analog ROSE-010 action.

DESIGN

Single-blind parallel study.

SETTING

University hospital laboratory.

PARTICIPANTS

Healthy volunteers investigated with antroduodenal manometry. Human gastric and intestinal muscle strips.

INTERVENTIONS

Motility indices (MIs) obtained before and during GLP-1 or saline infusion. Plasma GLP-1 and glucagon-like peptide-2 (GLP-2) measured by radioimmunoassay. Gastrointestinal muscle strips investigated for GLP-1- and ROSE-010-induced relaxation employing GLP-1 and GLP-2 and their receptor localization, and blockers exendin(9-39)amide, Lω-nitro-monomethylarginine (L-NMMA), 2',5'-dideoxyadenosine (DDA), and tetrodotoxin (TTX) to reveal target mechanism of GLP-1 action.

MAIN OUTCOME MEASURES

Postprandial gastrointestinal relaxation by GLP-1.

RESULTS

In humans, food intake increased MI to 6.4 ± 0.3 (antrum), 5.7 ± 0.4 (duodenum), and 5.9 ± 0.2 (jejunum). GLP-1 administered intravenously raised plasma GLP-1, but not GLP-2. GLP-1 0.7 pmol/kg/min suppressed corresponding MI to 4.6 ± 0.2, 4.7 ± 0.4, and 5.0 ± 0.2, whereas 1.2 pmol/kg/min suppressed MI to 5.4 ± 0.2, 4.4 ± 0.3, and 5.4 ± 0.3 (P < 0.0001 to 0.005). In vitro, GLP-1 and ROSE-010 prevented contractions by bethanechol and electric field stimulation (P < 0.005 to 0.05). These effects were disinhibited by exendin(9-39)amide, L-NMMA, DDA, or TTX. GLP-1 and GLP-2 were localized to epithelial cells, GLP-1 also at myenteric neurons. GLP-1R and GLP-2R were localized at myenteric neurons but not muscle.

CONCLUSIONS

GLP-1 and ROSE-010 inhibit postprandial gastrointestinal motility through GLP-1R at myenteric neurons, involving nitrergic and cyclic adenosine monophosphate-dependent mechanisms.