Activation of central opioid receptors may induce gastric mucosal defence in the rat

ADME-Tox Prediction and Molecular Docking Studies of Two Lead Flavonoids From the Roots of Tephrosia Egregia Sandw and the Gastroprotective Effects of Its Root Extract in Mice

Background: This study aimed to predict the pharmacokinetic and toxicological properties of lead flavonoids from the roots of T. egregia [praecansone A (1) and pongachalcone (2)], and to assess the gastroprotective effects and possible underlying mechanisms of the root extract in mice.Methods: Quantitative and qualitative data for in silico absorption, distribution, metabolism, and excretion (ADME) analyses of the two flavonoids were acquired from the SwissADME database. Toxicity assessment was performed with the ProTox-II server. To evaluate the putative interactions of both flavonoids with opioid receptors and NO protein, we acquired structures of the targets (&#x03BC;, &#x03BA;, and &#x03B4;-opioid receptors, and iNOS) in Homo sapiens from <a href="https://www.rcsb.org/">https://www.rcsb.org/</a>. For docking studies, AutoDock 4.2 was used for ligand and target arrangement, and AutoDock Vina was used for calculations. For in vivo assays, mice were pretreated (per os) with T. egregia (2, 20, or 200 mg/kg). After 60 min, 99.9% ethanol (0.2 mL) was injected (per os). At 30 min after ethanol injection, the mice were euthanized, and the gastric damage, gastric levels of hemoglobin, glutathione content, and activity of superoxide dismutase and catalase were evaluated. To elucidate T. egregia mechanisms, we used misoprostol, a prostaglandin analog; indomethacin, an inhibitor of prostaglandin synthesis; L-arginine, an NO precursor; L-NAME, an antagonist of NO synthase; naloxone, an opioid antagonist; and morphine, an opioid agonist.Results: In silico results showed that flavonoids (1) and (2) had favorable ADME properties and toxicity profiles, and exhibited satisfactory binding energies data (below &#x2212;6.0 kcal/mol) when docked into their targets (&#x03BC;, &#x03BA;, and &#x03B4;-opioid receptors, and iNOS). T. egregia decreased the ethanol-induced gastric damage and hemoglobin levels, and increased the glutathione content, and activity of superoxide dismutase and catalase. Naloxone and L-NAME, but not indomethacin, prevented T. egregia&#x2019;s effects, thus suggesting that opioid receptors and NO are involved in T. egregia&#x2019;s efficacy.Conclusions: Flavonoids (1) and (2) exhibited favorable pharmacokinetic properties, showing high lethal dose, 50% (LD50; 3,800 and 2,500 mg/kg, respectively) values. Neither flavonoid was found to be hepatotoxic, carcinogenic, or cytotoxic to human cells. In vivo assays indicated that T. egregia ameliorated oxidative stress levels, and its mechanism is at least partially based on opioid receptors and NO. T. egregia may therefore be considered as a new gastroprotective strategy.

High activity of endogenous opioid system protects against gastric damage development in mouse models of gastric mucosal injury

BACKGROUND

Gastric mucosal injury appears when acid and pepsin production, simultaneously with inadequate mucosal response, overwhelms protective mechanism in stomach. Here we aimed to explore the linkage between gastric lesion formation and endogenous opioid system activity.

METHODS

Two mouse lines bidirectionally selected for high (HA) and low (LA) swim stress-induced analgesia associated with high and low endogenous opioid system activity were used. Gastric mucosal injury was induced by ethanol (EtOH) and chronic mild stress. To investigate the anti-inflammatory effect of the endogenous opioid system macroscopic score, myeloperoxidase (MPO) activity, the expression of inflammatory molecules as well as oxidative stress markers were determined. Moreover, expression of opioid receptors μ (MOR), κ (KOR) and δ (DOR) at mRNA levels were determined in gastric tissue.

RESULTS

High activity of the endogenous opioid system alleviated gastric lesions development in the EtOH-and chronic mild stress-induced mouse gastric mucosal injury models, as demonstrated by decreased macroscopic score in HA line compared to LA. Additionally, antioxidative stress defence mechanisms were positively modulated in both models of gastric mucosal injury. MOR and partially KOR receptors may be responsible for the gastroprotective effect.

CONCLUSION

To our knowledge this is the first study to show that increased activity of the endogenous opioid system prevents from gastric lesion formation by influencing - among others - the anti-inflammatory and anti-oxidant mechanisms in the mice stomach. Hence, we suggest that opioids may play an important role in gastric mucosal injury prevention.

Brain neuropeptides in gastric mucosal protection

The centrally induced gastroprotective effect of neuropeptides has been intensively studied. Besides many similarities, however, differences can also be observed in their gastroprotective actions. The gastroprotective dose-response curve proved to be either sigmoid, or bell-shaped. Additional gastrointestinal effects of neuropeptides can contribute to their mucosal protective effect. Part of the neuropeptides induces gastroprotection by peripheral administration as well. Besides vagal nerve the sympathetic nervous system may also be involved in conveying the central effect to the periphery. Better understanding of the complex mechanism of the maintenance of gastric mucosal integrity may result in the development of new strategy to enhance gastric mucosal resistance against injury.

Prolonged acetylsalicylic-acid-supplementation-induced gastritis affects the chemical coding of the stomach innervating vagal efferent neurons in the porcine dorsal motor vagal nucleus (DMX)

The main goal of our research was to study the possible alterations of the chemical coding of the dorsal motor vagal nucleus (DMX) neurons projecting to the porcine stomach prepyloric region following prolonged acetylsalicylic acid supplementation. Fast Blue (FB) was injected into the studied area of the stomach. Since the seventh day following the FB injection, acetylsalicylic acid (ASA) was given orally to the experimental gilts. All animals were euthanized on the 28th day after FB injection. Medulla oblongata sections were then processed for double-labeling immunofluorescence for choline acetyltransferase (ChAT), pituitary adenylate cyclase-activating peptide (PACAP), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), galanin (GAL), substance P (SP), leu enkephalin (LENK), and cocaine- and amphetamine-regulated transcript (CART). In the control DMX, only PACAP was observed in 30.08 ± 1.97 % of the FB-positive neurons, while VIP, NOS, GAL, SP, LENK, and CART were found exclusively in neuronal processes running between FB-labeled perikarya. In the ASA DMX, PACAP was revealed in 49.53 ± 5.73 % of traced vagal perikarya. Moreover, we found de novo expression of VIP in 40.32 ± 7.84 %, NOS in 25.02 ± 6.08 %, and GAL in 3.37 ± 0.85 % of the FB-labeled neurons. Our results suggest that neuronal PACAP, VIP, NOS, and GAL are mediators of neural response to aspirin-induced stomach inflammatory state.

Brainstem neuropeptides and vagal protection of the gastric mucosal against injury: role of prostaglandins, nitric oxide and calcitonin-gene related peptide in capsaicin afferents

Earlier experimental studies indicated that the integrity of vagal pathway was required to confer gastric protection against damaging agents. Several peptides located in the brainstem initially identified to influence vagal outflow to the stomach, as assessed by electrophysiological approach or by vagal dependent alterations of gastric secretory and motor function, were investigated for their influence in the vagal regulation of the resistance of the gastric mucosa to injury. Thyrotropin releasing hormone (TRH), or its stable TRH analog, RX-77368, injected at low doses into the cisterna magna or the dorsal motor nucleus (DMN) was the first peptide reported to protect the gastric mucosa against ethanol injury through stimulation of vagal cholinergic pathways, inducing the release of gastric prostaglandins/nitric oxide (NO) and the recruitment of efferent function of capsaicin sensitive afferent fibers containing calcitonin-gene related peptide (CGRP). Activation of endogenous TRH-TRH1 receptor signaling located in the brainstem plays a role in adaptive gastric protection against damaging agents. Since then, an expanding number of peptides, namely peptide YY, CGRP, adrenomedullin, amylin, glugacon-like peptide, opioid peptides acting on µ, δ1 or δ2 receptors, nocicpetin, nocistatin, ghrelin, leptin and TLQP-21, a peptide derived from VGF prohormone, have been reported to act in the brainstem to afford gastric protection against ethanol injury largely through similar peripheral effectors mechanisms than TRH. Therefore gastric prostaglandins and CGRP/NO pathways represent a common final mechanism through which brain peptides confer vagally mediated gastroprotection against injury. A better understanding of brain circuitries through which these peptides are released will provide new strategies to recruit integrated and multifaceted gastroprotective mechanisms.

Gastric mucosal defense and cytoprotection: bench to bedside

The gastric mucosa maintains structural integrity and function despite continuous exposure to noxious factors, including 0.1 mol/L HCl and pepsin, that are capable of digesting tissue. Under normal conditions, mucosal integrity is maintained by defense mechanisms, which include preepithelial factors (mucus-bicarbonate-phospholipid "barrier"), an epithelial "barrier" (surface epithelial cells connected by tight junctions and generating bicarbonate, mucus, phospholipids, trefoil peptides, prostaglandins (PGs), and heat shock proteins), continuous cell renewal accomplished by proliferation of progenitor cells (regulated by growth factors, PGE(2) and survivin), continuous blood flow through mucosal microvessels, an endothelial "barrier," sensory innervation, and generation of PGs and nitric oxide. Mucosal injury may occur when noxious factors "overwhelm" an intact mucosal defense or when the mucosal defense is impaired. We review basic components of gastric mucosal defense and discuss conditions in which mucosal injury is directly related to impairment in mucosal defense, focusing on disorders with important clinical sequelae: nonsteroidal anti-inflammatory drug (NSAID)-associated injury, which is primarily related to inhibition of cyclooxygenase (COX)-mediated PG synthesis, and stress-related mucosal disease (SRMD), which occurs with local ischemia. The annual incidence of NSAID-associated upper gastrointestinal (GI) complications such as bleeding is approximately 1%-1.5%; and reductions in these complications have been demonstrated with misoprostol, proton pump inhibitors (PPIs) (only documented in high-risk patients), and COX-2 selective inhibitors. Clinically significant bleeding from SRMD is relatively uncommon with modern intensive care. Pharmacologic therapy with antisecretory drugs may be used in high-risk patients (eg, mechanical ventilation >or=48 hours), although the absolute risk reduction is small, and a decrease in mortality is not documented.

Preventive effects of gastric mucosal protective on H. pylori CCS-induced gastric mucosal lesion in rats

AIM: To determine the roles of H. pylori concentrated culture supernatants (CCS) on the gastric mucosa of mouse and to investigate the protective effects of gastric mucosal protectives sucrafate and sanjiuweitai on CCS-induced gastric mucosal lesion in Balb/c rats.

METHODS: Fifty-six healthy male Balb/c rats were randomly divided into seven groups: normal saline control (Ⅰ), injured simply (ⅡA, ⅡB), sucrafate pretreatment (ⅡA, ⅡB), sanjiuweitai pretreatment (ⅡA, ⅡB). Group A was dealt with small amounts of CCS and group B with large amounts of CCS. CCS were drawn from cytotoxic H. pylori strain (NCTC11637). The four protective groups were pretreated with sucrafate and sanjiuweitai separately, and then infused orally with different amounts of CCS. The pathological changes on histological sections and ultrastructural sections of gastric mucosa were assessed under microscope or electron microscope. The epithelial damage scoring (EDS) of the gastric mucosa was measured.

RESULTS: The management with large amounts of CCS from cytotoxic strains induced various epithelial lesions, which included vacuolation, erosions, ulcers and loss of gastric gland architecture. Infiltration of inflammatory cells in the lamina propria was not significant. At ultrastructural level, there was the presence of intracytoplasmic vacuoles, dilation of endoplasmic reticulum and mitochondrion, increasing of phagolysosomes, loose connection between cells and degenerative changes of microvilli. Small amounts of CCS from cytotoxic strain induced epithelial lesions less seriousey than large amounts of CCS. The results of the EDS of the gastric mucosa in the groups Ⅰ, ⅡA, ⅡB, ⅢA, ⅢB, ⅣA and ⅣB arranged successively as follows, 1.13±0.35, 2.25±0.46, 3.63±0.52, 1.25±0.46, 1.75±0.71, 1.50±0.53 and 1.63±0.74 respectively. A remarkable protection was found in gastric mucosa pretreated with sucrafate and sanjiuweitai. In comparison with the purely injured group, the EDS of the gastric mucosa descended significantly (P<0.05).

CONCLUSION: Cytotoxin has an important role in the induction of gastric mucosa lesions, but not in eliciting obvious inflammation; The gastric mucosal protection of sucrafate and sanjiuweitai against CCS-induced gastric mucosal lesion in rats is significant.

Endogenous opiates and behavior: 2001

This paper is the twenty-fourth installment of the annual review of research concerning the opiate system. It summarizes papers published during 2001 that studied the behavioral effects of the opiate peptides and antagonists. The particular topics covered this year include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology(Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Involvement of the opioid system in the central antisecretory action of alpha-2 adrenoceptor agonists in rat

The aim of the present study was to analyse the role of the central alpha-2 adrenoceptors in the regulation of gastric acid secretion in pylorus ligated rats. It was found that the intracerebroventricularly (icv.) injected presynaptic alpha-2 adrenoceptor agonist clonidine and the alpha-2A adrenoceptor subtype selective stimulant oxymetazoline exerted a dose dependent inhibition on gastric acid secretion. The antisecretory ED(50) values for clonidine and oxymetazoline were 20 and 7.5 nmol/rat icv., respectively. The antisecretory effect of these compounds was antagonised by the presynaptic adrenoceptor antagonist yohimbine (50 nmol/rat icv.) indicating that the action is mediated through central presynaptic alpha-2 adrenoceptors. Moreover, naloxone (50 nmol/rat icv.)--non-selective opioid antagonist--and naltrindole (0.5 nmol/rat icv.)--delta-opioid receptor selective antagonist--also decreased the antisecretory effect of clonidine and oxymetazoline suggesting that the endogenous opioid system is likely to be involved in the central antisecretory action of alpha-2 adrenoceptor stimulants.