Effects of centrally injected glucagon-like peptide-2 on gastric mucosal blood flow in rats: possible mechanisms

Therapeutic peptides: current applications and future directions

Peptide drug development has made great progress in the last decade thanks to new production, modification, and analytic technologies. Peptides have been produced and modified using both chemical and biological methods, together with novel design and delivery strategies, which have helped to overcome the inherent drawbacks of peptides and have allowed the continued advancement of this field. A wide variety of natural and modified peptides have been obtained and studied, covering multiple therapeutic areas. This review summarizes the efforts and achievements in peptide drug discovery, production, and modification, and their current applications. We also discuss the value and challenges associated with future developments in therapeutic peptides.

Glucagon-like peptide-2 protects the gastric mucosa via regulating blood flow and metabolites

INTRODUCTION

Refractory peptic ulcers lead to perforation and hemorrhage, which are fatal. However, these remain a therapeutic challenge. Gastric mucosal blood flow is crucial in maintaining gastric mucosal health. It's reported that Glucagon-like peptide-2 (GLP-2), a gastrointestinal hormone, stimulated intestinal blood flow. However, the direct role of GLP-2 in gastric mucosal blood flow and metabolites remain unclear. Here, we speculated that GLP-2 might protect the gastric mucosa by increasing gastric mucosal blood flow and regulating metabolites. This study was conducted to evaluate the role of GLP-2 in gastric mucosal lesions and its underlying mechanism.

METHODS

We analyzed endogenous GLP-2 during gastric mucosal injury in the serum. Rats were randomly divided into two groups, with 36 rats in each group as follows: (1) normal control group (NC1); (2) ethanol model group (EC1); rats in EC1 and NC1 groups were intragastrically administered ethanol (1 ml/200 g body weight) and distilled water (1 ml/200 g body weight). The serum was collected 10 min before intragastric administration and 15, 30, 60, 90, and 120 min after intragastric administration. Furthermore, additional male Sprague-Dawley rats were randomly divided into three groups, with six rats in each group as follows: (1) normal control group (NC); (2) ethanol model group (EC); (3) 10 μg/200 g body weight GLP-2 group (GLP-2). Rats in the NC and EC groups were intraperitoneally injected with saline. Those in the GLP-2 group were intraperitoneally injected with GLP-2. Thirty minutes later, rats in the EC and GLP-2 groups were intragastrically administered ethanol (1 ml/200 g body weight), and rats in the NC group were intragastrically administered distilled water (1 ml/200 g body weight). After the intragastric administration of ethanol for 1 h, the animals were anesthetized and gastric mucosal blood flow was measured. Serum were collected for ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) metabolomics.

RESULTS

There were no significant change in endogenous GLP-2 during gastric mucosal injury (P<0.05). Pretreatment with GLP-2 significantly reduced ethanol-induced gastric mucosal lesions by improving the gastric mucosal blood flow, as examined using a laser Doppler flow meter, Guth Scale, hematoxylin-eosin staining, and two-photon microscopy. UPLC-MS/MS analyses showed that GLP-2 also maintained a steady state of linoleic acid metabolism.

CONCLUSIONS

Taken together, GLP-2 protects the gastric mucosa against ethanol-induced lesions by improving gastric mucosa blood flow and affecting linoleic acid metabolism.

Effects of intracerebroventricularly injected glucagon-like peptide-2 on ethanol-induced gastric mucosal damage in rats

PURPOSE

The present study aims to investigate the effects of intracerebroventricularly (i.c.v.)-injected glucagon-like peptide-2 (GLP-2) on ethanol-induced gastric mucosal damage and to reveal the mechanisms involved in this effect.

MATERIALS AND METHODS

Rats received absolute ethanol orally via an orogastric tube 30 minutes after GLP-2 (1-200 ng/10 µl; i.c.v.) or saline (10 µl) injections. They were decapitated 1 hour later, their stomachs were removed, and the gastric mucosal damage was scored.

RESULTS

A total of 100 ng GLP-2 inhibited the gastric mucosal damage by 67%. This effect was abolished by the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP-(8-37) (10 µg/kg; s.c.), but was not affected by either the nitric oxide (NO) synthase inhibitor L-NAME (30 mg/kg; s.c.) or the cyclooxygenase inhibitor indomethacin (5 mg/kg; i.p.). The most effective gastroprotective dose of GLP-2 (100 ng/10 µl; i.c.v.), but not the higher doses (150 or 200 ng/10 µl; i.c.v.) prevented the decrease in gastric mucosal blood flow caused by ethanol. In conclusion, i.c.v. GLP-2 protects against ethanol-induced gastric mucosal damage and this effect is mediated by CGRP receptor activation and gastric mucosal blood flow, but not by NO or prostaglandins.

Effects of dopamine, norepinephrine and dobutamine on gastric mucosal pH of septic shock patients

The effect of different vasoactive drugs on the pH [intracellular pH (pHi)] of gastric mucosa in patients with septic shock was evaluated in the present study. According to the vasoactive drugs applied, 48 patients with septic shock were divided into 3 groups: A, B and C, with 16 cases each. Cases of group A were treated with dopamine, those of group B with norepinephrine while those of group C were treated with norepinephrine plus dobutamine. The changes of pH of gastric mucosa were observed before treatment (baseline) and 6, 12, 24 and 48 h after treatment, and the hemodynamic indicators were observed before treatment (baseline) and 6 h after administration. The gastric mucosal pH was not significantly different between two of the three groups before treatment (each at P>0.05). The gastric mucosal pH of group A did not change 6, 12, 24 and 48 h after treatment with drugs compared with the baseline (all at P>0.05), while the gastric mucosal pH in groups B and C were each statistically higher at the time points of 6, 12, 24 and 48 h after treatment with drugs compared with the respective baselines (all at P<0.05). Following treatment with drugs, the gastric mucosal pH of group C at all the time points of 6, 12, 24 and 48 h after treatment were significantly higher than those of groups A and B at the same time points after treatment, while there were some statistical differences between groups A and B at these time points (6, 12, 24 and 48 h after treatment; P<0.05). The hemodynamic indicators of the patients before treatment were not significantly different between two of the three groups (all at P>0.05). Compared with the baseline values, the mean arterial pressure and the cardiac index of each group after treatment were significantly increased, the pulmonary capillary wedge pressure and the central venous pressure of groups B and C significantly increased (all at P<0.05) and the heart rate of group A was significantly increased (P<0.05). In conclusion, the gastric mucosal pH of the septic shock patients was increased when treated with norepinephrine or with dobutamine. Additionally, the gastric mucosal pH was significantly higher when the patients were treated with dobutamine and norepinephrine in combination than with norepinephrine or dopamine alone. Dopamine, norepinephrine and dobutamine can improve the systemic hemodynamic conditions in patients with septic shock.