Direct measurement of nitric oxide release in gastric mucosa during ischemia-reperfusion in rats

Ulcer healing and mechanism(s) of action involved in the gastroprotective activity of fractions obtained from Syngonanthus arthrotrichus and Syngonanthus bisulcatus

Background

Syngonanthus arthrotrichus and Syngonanthus bisulcatus, currently known for Comanthera aciphylla (Bong.) L.R.Parra & Giul. and Comanthera bisulcata (Koern.) L.R. Parra & Giul, popularly known in Brazil as “sempre-vivas,” are plants from the family Eriocaulaceae. They are found in the states of Minas Gerais and Bahia. The species are known to be rich in flavonoids to which their gastroprotective activity has been attributed. In this research, experimental protocols were performed to elucidate the associated mechanisms of action.

Methods

The activity was evaluated using induced gastric ulcer models (acetic acid and ethanol-induced gastric lesions in NEM or L-NAME pre-treated mice, and by ischemia/reperfusion). Antioxidant enzymes, serum somatostatin, and gastrin were also evaluated.

Results

In chronic gastric ulcers, a single daily oral dose of Sa-FRF or Sb-FRF (100 mg/kg body wt.) for 14 consecutive days accelerated ulcer healing to an extent similar to that seen with an equal dose of cimetidine. The pre-treatment of mice with NEM (N-ethylmaleimide) or L-NAME (N-nitro-L-arginine) abolished the protective activity of Sa-FRF, Sa-FDF, Sb-FDF and Sb-FRF or Sa-FRF and Sb-FRF, respectively, which indicates that antioxidant compounds and nitric oxide synthase activity are involved in the gastroprotective. Sa-FRF and Sb-FRF (100 mg/kg p.o) protected the gastric mucosa against ulceration that was induced by ischemia/reperfusion (72 and 76 %, respectively). It also decreased lipid peroxidation and restored total thiols in the gastric wall of mice that had been treated with ethanol. When administered to rats submitted to ethanol-induced gastric lesions, Sa-FRF and Sb-FRF (100 mg/kg, p.o.) increased the somatostatin serum levels, while the gastrin serum levels were proportionally decreased.

Conclusions

The results indicate significant healing effects and gastroprotective activity for the Sa-FRF and Sb-FRF, which probably involves the participation of SH groups, nitric oxide (NO), the antioxidant system, somatostatin, and gastrin. All are integral parts of the gastrointestinal mucosa’s cytoprotective mechanisms against aggressive factors.

Gaseous mediators nitric oxide and hydrogen sulfide in the mechanism of gastrointestinal integrity, protection and ulcer healing

Nitric oxide (NO) and hydrogen sulfide (H2S) are known as biological messengers; they play an important role in human organism and contribute to many physiological and pathophysiological processes. NO is produced from l-arginine by constitutive NO synthase (NOS) and inducible NOS enzymatic pathways. This gaseous mediator inhibits platelet aggregation, leukocyte adhesion and contributes to the vessel homeostasis. NO is known as a vasodilatory molecule involved in control of the gastric blood flow (GBF) and the maintenance of gastric mucosal barrier integrity in either healthy gastric mucosa or that damaged by strong irritants. Biosynthesis of H2S in mammals depends upon two enzymes cystathionine-β-synthase and cystathionine γ-lyase. This gaseous mediator, similarly to NO and carbon monoxide, is involved in neuromodulation, vascular contractility and anti-inflammatory activities. For decades, H2S has been known to inhibit cytochrome c oxidase and reduce cell energy production. Nowadays it is generally considered to act through vascular smooth muscle ATP-dependent K+ channels, interacting with intracellular transcription factors and promote sulfhydration of protein cysteine moieties within the cell, but the mechanism of potential gastroprotective and ulcer healing properties of H2S has not been fully explained. The aim of this review is to compare current results of the studies concerning the role of H2S and NO in gastric mucosa protection and outline areas that may pose new opportunities for further development of novel therapeutic targets.

Protective effect of endogenous hydrogen sulfide against oxidative stress in gastric ischemia-reperfusion injury

Hydrogen sulfide (H₂S) is a gaseous signaling molecule, which plays a critical role in a number of physiological and pathological progresses. In order to determine the effect of endogenous H₂S on gastric ischemia-reperfusion (GI-R), we evaluated the gastric mucosal damage in rats intraperitoneally injected with DL-propargylglycine (PAG, 50 mg/kg/day) or L-cysteine (L-cys, 50 mg/kg/day) for 7 days before GI-R. GI-R injury was achieved by clamping the celiac artery for 30 min, followed by reperfusion for 60 min. Gastric mucosal damage was macroscopically assessed in the area of injury and deep damage was assessed by histopathological scoring. PAG increased the area of gastric mucosal injury and deep damage compared with that in untreated GI-R rats (P<0.05). While PAG decreased the H₂S concentration and cystathionine γ-lyase (CSE) expression in the gastric mucosa, L-cys significantly attenuated the effects of GI-R. Western blot analysis revealed that the increases of malondialdehyde (MDA) and xanthine oxidase (XOD), and decreases of glutathione (GSH), superoxide dismutase (SOD) and the restriction of superoxide (O₂⁻) production in the PAG group were inhibited by L-cys (P<0.05). Endogenous H₂S has a protective effect against GI-R in rats by inhibiting oxygen free radical overproduction.

Oxidative stress and ischemia-reperfusion injury in gastrointestinal tract and antioxidant, protective agents

Exacerbation of hypoxic injury after reoxygenation is a crucial mechanism mediating organ injury in transplantation, and in myocardial, hepatic, gastrointestinal, cerebral, renal, and other ischemic syndromes. The occlusion and reperfusion of the splanchnic artery is a useful animal model to elucidate the mechanism of gastrointestinal injury induced by ischemia-reperfusion (I/R). Although xanthine oxidase is a major source of reactive oxygen species (ROS), which plays an important role in the I/R-induced intestinal injury, there are many other sources of intracellular ROS. Various treatment modalities have been successfully applied to attenuate the I/R injury in animal models. This review focuses on the role of oxidant stress in the mechanism of I/R injury and the use of antioxidant agents for its treatment.

Activated protein C prevents hepatic ischaemia-reperfusion injury in rats

BACKGROUND

Hepatic ischaemia-reperfusion injury (IRI) is a serious complication of liver surgery, especially extended hepatectomy and liver transplantation. Activated protein C (APC), a potent anticoagulant serine protease, has been shown to have cell-protective properties by virtue of its anti-inflammatory and anti-apoptotic activities.

METHODS

The present study was designed to examine the cytoprotective effects of APC in a 60-min warm-IRI rat model.

RESULTS

Following a single intravenous injection of APC before reperfusion, APC exerted cytoprotective effects 4 h after reperfusion, as evidenced by: (i) decreased levels of transaminase and improved histological findings of IRI, (ii) reduced infiltration and activation of neutrophils, macrophages and T cells, (iii) reduced expression of tumour necrosis factor-alpha, (iv) reduced expression of P-selectin and intracellular adhesion molecule-1, (v) inhibited coagulation and attenuated sinusoidal endothelial cell injury, (vi) improved hepatic microcirculation and (vii) decreased transferase-mediated dUTP nick end-labelling-positive cells. These effects of APC were observed 4 h but not 24 h after reperfusion. However, multiple injections of APC after reperfusion significantly decreased the levels of transaminase and the activity of myeloperoxidase, and improved histological findings of IRI 24 h after reperfusion.

CONCLUSION

These results suggest that APC is a promising therapeutic option for hepatic warm-IRI; however, multiple injections of APC are necessary to maintain its cell-protective action over the long term.

Effects of hypothalamic paraventricular nuclei on apoptosis and proliferation of gastric mucosal cells induced by ischemia/reperfusion in rats

AIM: To investigate the effects of electrical stimulation of hypothalamic paraventricular nuclei (PVN) on gastric mucosal cellular apoptosis and proliferation induced by gastric ischemia/reperfusion (I/R) injury.

METHODS: For different experimental purposes, stimulating electrode plantation or electrolytic destruction of the PVN was applied, then the animals’ GI/R injury model was established by clamping the celiac artery for 30 min and allowing reperfusing the artery for 30 min, 1 h, 3 h or 6 h respectively. Then histological, immunohistochemistry methods were used to assess the gastric mucosal damage index, the gastric mucosal cellular apoptosis and proliferation at different times.

RESULTS: The electrical stimulation of PVN significantly attenuated the GI/R injury at 30 min, 1 h and 3 h after reperfusion. The electrical stimulation of PVN decreased gastric mucosal apoptosis and increased gastric mucosal proliferation. The electrolytic destruction of the PVN could eliminate the protective effects of electrical stimulation of PVN on GI/R injury. These results indicated that the PVN participated in the regulation of GI/R injury as a specific area in the brain, exerting protective effects against the GI/R injury, and the protection was associated with the inhibition of cellular apoptosis and the promotion of gastric mucosal proliferation.

CONCLUSION: Stimulating PVN significantly inhibits the gastric mucosal cellular apoptosis and promots gastric mucosal cellular proliferation. This may explain the protective mechanisms of electrical stimulation of PVN against GI/R injury.

A novel gastric lesion model induced in rats by partial gastric vascular ligation

Previous studies have suggested that histamine treatment after gastric vascular ligation induces mucosal damage in the rat stomach. Although ligation of left gastric artery and vein (L-AV) alone did not cause any damage in the stomach within 4 h, but provoked mild lesions due to ischaemia 24 h later. In the present study we demonstrated a new model of gastric lesions induced by L-AV ligation and examined the effects of various anti-ulcer drugs on this lesion model. The gastric lesions induced by L-AV ligation occurred at the corpus and antrum, especially at the corpus-antrum border, when examined 24 h later, and the severity of damage reached maximum 3 days after L-AV ligation. Repeated treatment with omeprazole or sucralfate for 3 days significantly prevented the development of gastric lesions induced by L-AV ligation, in whole mucosa, including the antrum. By contrast, famotidine given for 3 days showed a significant protection against total lesions in the whole mucosa, but had no effect on the antral lesions. Both omeprazole and famotidine dose-dependently decreased gastric acid output while sucralfate raised the intraluminal pH due to the acid-neutralizing action. These results suggest that the pathogenesis of gastric lesions induced by L-AV ligation differs depending on the region, the corpus and the antrum, and the lesions occurred in the latter area seem to be resistant to acid suppression. It is assumed that this new model of gastric lesions is useful for screening the drugs that affect gastric mucosal defense rather than acid secretion.

Protective effect of endogenous PPARgamma against acute gastric mucosal lesions associated with ischemia-reperfusion

Acute gastric mucosal lesions (AGMLs) are an important cause of gastrointestinal bleeding. Herein, we demonstrate that peroxisome proliferator-activated receptor-gamma (PPARgamma), a member of a nuclear receptor family, functions as an endogenous anti-inflammatory pathway in a murine model of AGML induced by ischemia-reperfusion (I/R). Treatment with specific PPARgamma ligands such as BRL-49653, pioglitazone, or troglitazone was examined in a model of AGML induced by I/R. PPARgamma-deficient and wild-type mice were also examined for their response to I/R in stomach. Specific PPARgamma ligands exhibited dramatic and rapid protection against AGML formation associated with I/R in mice in a dose-dependent manner. In contrast, the AGML induced by I/R in PPARgamma-deficient mice was more severe than that observed in wild-type mice. Administration of the PPARgamma ligand significantly inhibited the upregulation of TNF-alpha, ICAM-1, inducible nitric oxide synthase, apoptosis, and nitrotyrosine formation induced by I/R in the stomach. These data indicate that an endogenous pathway associated with PPARgamma plays an important role in the pathogenesis of I/R-associated injury in the stomach.

Role for complement in mediating intestinal nitric oxide synthase-2 and superoxide dismutase expression

Inducible nitric oxide synthase (iNOS) and superoxide dismutase (SOD) play an important role in the pathology of ischemia-reperfusion. This study sought to determine if the proinflammatory effects of complement modulate iNOS and SOD in the rat after gastrointestinal ischemia and reperfusion (GI/R). An inhibitory or noninhibitory anti-complement component 5 (C5) monoclonal antibody (18A or 16C, respectively) was administered before GI/R. RT-PCR revealed a significant increase in intestinal iNOS mRNA compared with sham after GI/R that was attenuated significantly by 18A. Immunohistochemistry demonstrated increased iNOS protein expression within the intestinal crypts after GI/R. Cu/Zn SOD (mRNA and protein) was unaffected by GI/R, whereas Cu/Zn SOD activity was reduced significantly. Mn SOD protein expression was decreased significantly by GI/R. Anti-C5 preserved Cu/Zn SOD activity and Mn SOD protein expression. Staining for nitrotyrosine showed that anti-C5 treatment reduced protein nitration in the reperfused intestine. Immunohistochemistry demonstrated prominent phosphorylated (p) inhibitory factor-kappaB (IkappaB)-alpha staining of intestinal tissue after GI/R, whereas anti-C5 reduced p-IkappaB-alpha expression. These data indicate that complement may mediate tissue damage during GI/R by increasing intestinal iNOS and decreasing the activity and protein levels of Cu/Zn SOD and Mn SOD, respectively.

Protective actions of rat gastric epithelial E-cadherin expression against epithelial barrier dysfunctions induced by chemical hypoxia-reoxygenation in vitro

BACKGROUND AND AIM

E-cadherin expressed on gastric epithelium is reported to form adherence junctions and stabilize barrier functions. While hypoxia-reoxygenation is well known to cause gastric mucosal injury during reoxygenation, gastric E-cadherin actions against this stress remain unclear. In this study, using the oxygen depleting agent thioglycolic acid we examined whether E-cadherin expressed on rat cultured gastric epithelial cells has protective actions against epithelial barrier dysfunction induced by chemical hypoxia-reoxygenation.

METHODS

Chemical hypoxia was induced by incubating cells with 5 mm thioglycolic acid in glucose free medium for 60 min. Cells were then reoxygenated for 240 min by changing to normal medium. The expression of E-cadherin on the cell surface was measured with an enzyme immunoassay, and epithelial permeability was determined by the diffusion rate of FITC-dextran through the cell layer.

RESULTS

E-cadherin expression increased during the 60 min hypoxic period, accompanied by activation of protein kinase C, protein kinase G and protein kinase A. The increased expression significantly diminished, but was considerably higher than the control values during reoxygenation for 180 min, which was partially due to generation of reactive oxygen species but not to activation of protein kinase. Conversely, epithelial permeability was stabilized during hypoxia, but increased only for 30 min of reoxygenation, probably due to generation of reactive oxygen species. Epithelial permeability during hypoxia was elevated by a combination of all the protein kinase inhibitors.

CONCLUSION

An increase in the expression of E-cadherin during hypoxia through the activation of the kinases is likely to stabilize epithelial barrier functions. The reactive oxygen species generated during 30 min reoxygenation increased the molecular expression of E-cadherin less than during hypoxic stress. The transient break in the barrier functions caused by reactive oxygen species during reoxygenation appears to overcome the reactive oxygen species mediated cytoprotective action increasing E-cadherin expression.

Dual effects of nitric oxide on cat carotid body chemoreception

We studied the effects of nitric oxide (NO) released by NO donors on cat carotid body (CB) chemosensory activity during normoxia and hypoxia. CBs excised from pentobarbital sodium-anaesthetized cats were perfused with Tyrode at 38 degrees C and pH 7.40. The frequency of chemosensory discharges (f(x)) was recorded from the carotid sinus nerve, and changes of NO concentration were measured by a chronoamperometric technique, with NO-selective carbon-fiber microelectrodes inserted in the CB. During steady chemosensory excitation induced by hypoxia, bolus injections of NO (DeltaNO = 0. 5-12 microM), released by S-nitroso-N-acetylpenicillamine (SNAP) and 6-(2-hydroxy-1-methyl-nitrosohydrazino)-N-methyl-1-hexanamine++ + (NOC-9), transiently reduced f(x) in a dose-dependent manner. However, during normoxia, the same concentration of NO (DeltaNO = 0. 5-13 microM) released by the NO donors increased f(x) in a dose-dependent manner. The present results show a dual effect of NO on CB chemoreception that is dependent on the PO(2) levels. During hypoxia, NO is predominantly an inhibitor of chemoreception, whereas, in normoxia, NO increased f(x). The mechanisms by which NO produces chemosensory excitation during normoxia remain to be determined.

Increased production of nitrotyrosine in lung tissue of rats with radiation-induced acute lung injury

The purposes of this study were 1) to identify the nitric oxide (NO) synthase (NOS) isoform responsible for NO-mediated radiation-induced lung injury, 2) to examine the formation of nitrotyrosine, and 3) to see whether nitrotyrosine formation and lung injury are reduced by an inducible NOS (iNOS) inhibitor, aminoguanidine. The left hemithorax of rats was irradiated (20 Gy), and the degree of lung injury, the expression of NOS isoforms, and the formation of nitrotyrosine and superoxide were examined after 2 wk. iNOS mRNA was induced, and endothelial NOS mRNA was markedly increased in the irradiated lung. Nitrotyrosine was detected biochemically and immunohistochemically. Aminoguanidine prevented acute lung injury as indicated by decreased protein concentration and lactate dehydrogenase activity in bronchoalveolar lavage fluid and improved NMR parameters and histology. Furthermore, the formation of nitrotyrosine was significantly reduced in the aminoguanidine group. We conclude that iNOS induction is a major factor in radiation-induced lung injury and that nitrotyrosine formation may participate in the NO-induced pathogenesis.