Role of nitric oxide in pathogenesis of serotonine-induced gastric lesions in rats

Effects of Morinda citrifolia aqueous fruit extract and its biomarker scopoletin on reflux esophagitis and gastric ulcer in rats

AIMS OF THE STUDY

The present study was carried out to evaluate the effect of dried mature unripe Morinda citrifolia L. (Rubiaceae) fruit, commonly known as "Noni", in an aqueous extract preparation (AFE) as used in Thai traditional medicine and its biomarker scopoletin on gastro-esophageal inflammatory models that are related to the claimed pharmacological properties of AFE and/or resembled the human esophagitis or gastric ulcer.

MATERIALS AND METHODS

The powder of dried mature unripe Noni fruit was boiled in water until it became a sticky paste and was then dried into a powder by lyophilization. The pharmacological activity of AFE and pure scopoletin at the same equivalent dose present in AFE was investigated in rat on gastro-esophageal inflammatory models (acid reflux esophagitis, acute gastritis induced by ethanol and serotonin, and chronic gastric ulcer induced by acetic acid); gastric biochemical parameters and gastrointestinal motility.

RESULTS

AFE (0.63-2.50 g/kg) significantly prevented the formation of acid reflux esophagitis, reduced the formation of ethanol-induced acute gastric lesions, suppressed the development of gastric lesions in response to serotonin, and accelerated the healing of acetic acid-induced chronic gastric ulcer in rats with equal potency to those obtained by standard antisecretory agents (ranitidine and lansoprazole). AFE also significantly inhibited gastric acid secretion and pepsin activity in pylorus ligated rats. Additionally, AFE strongly increased the gastrointestinal transit of charcoal meal with a higher potency than cisapride. Pure scopoletin, when compared at the same equivalent dose containing in AFE, possessed similar antiulcer and antisecretory properties to that of AFE although it exerted a less prokinetic activity than AFE.

CONCLUSION

The findings indicated that AFE as well as its biomarker: scopoletin may be beneficial as a potential preventive and therapeutic agent for gastro-esophageal inflammatory diseases, mainly through its antisecretory and prokinetic activities including an inhibitory activity on serotonin, free radicals, and cytokine-mediated inflammation. Additionally, scopoletin might be one of the biomarker constituents to use for the quality assessment of Noni fruit products used for treating gastro-esophageal inflammatory diseases.

Tacrolimus (FK506), an Immunosuppressive Agent, Prevents Indomethacin-Induced Small Intestinal Ulceration in the Rat: Inhibition of Inducible Nitric Oxide Synthase Expression

We examined the effect of tacrolimus (FK506), an immunosuppressive drug, on indomethacin-induced small intestinal ulceration in rats. Animals were given indomethacin (10 mg/kg, s.c.), killed 24 h later, and myeloperoxidase (MPO) activity and thiobarbituric acid reactants (TBARS) were evaluated in intestinal lesions. Tacrolimus (0.3 - 3 mg/kg) was administered p.o. twice 0.5 h before and 6 h after indomethacin injection. The expression of inducible nitric oxide synthase (iNOS) mRNA was determined by a TaqMan real-time RT-PCR, while the activity of nuclear factor (NF)-kappaB DNA-binding was analyzed by electrophoresis mobility shift assays (EMSA) 6 h after indomethacin treatment. Indomethacin provoked severe hemorrhagic lesions in the small intestine, mainly in the jejunum and ileum, accompanied with increases in MPO activity and TBARS. Oral administration of tacrolimus reduced the severity of indomethacin-induced intestinal lesions in a dose-dependent manner. The increases in MPO activity and TBARS were also significantly attenuated by tacrolimus. The expression of iNOS mRNA was markedly enhanced when examined 6 h after indomethacin administration, and this response was counteracted by tacrolimus. Indomethacin also activated NF-kappaB in a tacrolimus-preventable manner. These results suggest that tacrolimus prevents indomethacin-induced small intestinal ulceration in the rat. This effect may be due to inhibition of iNOS induction through suppression of NF-kappaB activation.

Role of endogenous nitric oxide in mucosal defense of inflamed rat stomach following iodoacetamide treatment

Nitric oxide (NO) plays a role in regulating the mucosal integrity of the stomach. However, its part in the mucosal defense of the inflamed stomach remains unclear. In the present study, we examined the effects of various NO synthase (NOS) inhibitors on gastric ulcerogenic and acid secretory responses following daily exposure of the stomach to iodoacetamide and investigated the role of each NOS isozyme in gastric protection from subchronic mucosal irritation. Gastric mucosal irritation was induced in rats by addition of 0.1% iodoacetamide to drinking water, and the gastric mucosa was examined on the 6th day. L-NAME (a nonselective NOS inhibitor: 20 mg/kg) or aminoguanidine (a selective iNOS inhibitor: 20 mg/kg) was given s.c. twice 24 h and 3 h before the termination of iodoacetamide treatment. Giving iodoacetamide in drinking water for 5 days produced minimal damage in the stomach with an increase in myeloperoxidase (MPO) activity and lipid peroxidation. Iodoacetamide treatment up-regulated the expression of iNOS mRNA and NO production in the stomach, without affecting nNOS expression. Both L-NAME and aminoguanidine markedly aggravated gastric lesions induced by iodoacetamide treatment, with a further enhancement in MPO activity and lipid peroxidation. Basal acid secretion as determined in pylorous-ligated stomachs was decreased following iodoacetamide treatment, but the response was significantly restored by both L-NAME and aminoguanidine. These results suggest that endogenous NO derived from both cNOS and iNOS is involved in mucosal defense of the inflamed stomach, partly by decreasing acid secretion, and contributes to maintaining mucosal integrity under such conditions.

The effect of tryptophan administration on ileum contractility and oxidant status in mice

L-tryptophan (TRP) is the precursor amino acid for the synthesis of serotonin (5-HT). 5-HT is effective both on the food intake and gastrointestinal system contractility. The aim of this study was to search the effects of systemic TRP treatment on 5-HT levels of ileum and searching the effect of ileal contractility and oxidant status. Swiss-albino mice were divided into two groups: 1. Control, 2. TRP-treated (100 mg/kg/24 h, i.p., for 7 days). Body weights were recorded at the beginning and at the end of experiments. Acetylcholine-induced contractile responses in the isolated ileum were recorded on polygraph. Ileal tissue malondialdehyde and glutathione levels determined by spectrophotometric and ileal tissue 5-HT levels were measured by immunohistochemical methods. TRP treatment decreased body weight and increased ileal contractile response. In the TRP-treated group, ileum malondialdehyde levels increased and glutathione levels decreased. Immunohistochemical detection showed that ileal 5-HT levels were increased by TRP treatment. There is a relationship between increased oxidative stress and increased contractility in the ileal tissue of the TRP-treated animals. These effects may be related to increased ileal 5-HT synthesis.

Differential salutary effects of nonselective and selective COX-2 inhibitors in postoperative ileus in rats

BACKGROUND

Postoperative ileus (PI) is a common surgical complication, the treatment of which consists of supportive measures.

AIM

The effects of several cyclooxygenase (COX) inhibitors and their interaction with L-arginine/nitric oxide synthase (NOS) pathway were tested in a rat PI model.

METHODS

Intestinal transit was measured as Evans blue migration after skin incision, laparotomy, or laparotomy followed by evisceration and gut handling.

RESULTS

In contrast to a selective inducible NOS (iNOS) blocker, L-N(6)-(1-iminoethyl)lysine hydrochloride (L-NIL), N(omega)-nitro-L-arginine methyl ester (L-NAME) reversed the additional inhibitory effects of gut manipulation after laparotomy on the gastrointestinal transit (GI) in a dose-dependent, L-arginine-sensitive manner. Laparotomy and manipulations of small intestine increased blood plasma nitrites and nitrates level (NOx), an effect preventable by L-NAME. Indomethacin, resveratrol (selective COX-1 blocker), and COX-2 antagonists, nimesulide, NS-398, DuP-697, and L-752860, attenuated the additional inhibitory effects of gut manipulation following laparotomy in a dose-dependent manner. In contrast, only nimesulide, NS-398, DuP-697, and L-752860 partly, but significantly, reversed the effects of laparotomy on the intestinal transit. Administration of L-NAME subsequent to COX inhibitors abolished the salutary effects of the latter, implying that at least the synthesis of either NO or prostanoids must remain unaffected to enable a return of GI transit during the postoperative period.

CONCLUSION

In addition to NO synthesized by constitutive NOS (cNOS), prostaglandins produced by both COX-1 and COX-2 participate in the pathogenesis of PI, albeit in different pathological mechanisms. Thus laparotomy stimulated COX-2 activity, whereas gut manipulation led to an excessive cNOS activity and prostaglandin synthesis by COX-1.

[Changes in ulcerogenic response to non-steroidal anti-inflammatory drugs (NSAIDs) in adjuvant arthritic rats]

Gastroenteropathy is the most common among patients who use non-steroidal anti-inflammatory drugs (NSAIDs) for the treatment of inflammatory disorders. It is known that rheumatoid arthritic (RA) patients are more susceptible to NSAID-induced gastropathy than other NSAID users. This article reviewed our recent studies concerning the influence of arthritis on gastric mucosal integrity in adjuvant-induced arthritic rats. The gastric mucosal lesions induced by indomethacin, one of conventional NSAIDs, were markedly aggravated in arthritic rats. Likewise, the healing of chronic gastric ulcers induced by thermal cauterization was significantly delayed in arthritic rats. The underlying mechanisms of these phenomena observed in arthritic rats may be attributable to the enhancement of iNOS/NO pathway in the former and the less expression of various growth factors in the ulcerated mucosa, such as basic fibroblast growth factors (bFGF) or insulin-like growth factors (IGF-1) in the latter. In addition, we recently found that cyclooxygenase-2 (COX-2) selective inhibitors, such as rofecoxib or celecoxib, induced apparent gastric lesions in arthritic rats, suggesting that a caution should be paid on the use of COX-2 selective inhibitors in RA patients.

Nitric oxide: relation to integrity, injury, and healing of the gastric mucosa

Nitric oxide (NO) plays a multifaceted role in mucosal integrity. The numerous functions of NO and the double-edged role played by NO in most of them provide a great complexity to the NO action. The three enzymatic sources of NO, neuronal NO-synthase (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS), have been characterised in the gastrointestinal tract. The protective properties of the NO derived from constitutive NO-synthases (eNOS and nNOS) have already been well established. Less clear is the role assigned to iNOS. The simplistic initial view of low levels of NO synthesised by constitutive NOS being protective while exaggerated NO levels after iNOS induction leading irremediably to cytotoxicity is being questioned by new evidence. As initially reported for constitutive NOS, iNOS activity may be associated to reduced leukocyte-endothelium interaction and platelet aggregation as well as protection of mucosal microcirculation. Moreover, iNOS activity may be important to resolve inflammation by increasing apoptosis in inflammatory cells. It is entirely possible that a low level of expression of iNOS will reflect a positive host-defense response to challenge, but that exaggerated or uncontrolled expression of iNOS itself becomes detrimental. There is no doubt about the protective role of NO in physiological conditions. However, when the mucosa is threatened, the role of NO becomes multiple and the final effect will probably depend on the nature of the insult, the environment involved, and the interaction with other mediators.

The roles of nitric oxide and prostaglandins in alterations of ulcerogenic and healing responses in adjuvant-induced arthritic rat stomachs

AIM

To examine alterations of gastric ulcerogenic and healing responses in adjuvant-induced arthritic rats.

METHODS

Arthritis was induced in male Dark Agouti rats by injection of Freund's complete adjuvant into the right hind paw.

RESULTS

The gastric ulcerogenic response to indomethacin was markedly increased in AA rats, depending on the degree of arthritic change. By contrast, HCl/ethanol-induced gastric lesions were significantly suppressed in arthritic rats when compared with normal rats. The increased ulcerogenic response to indomethacin was significantly prevented by L-NAME and antineutrophil serum but not by FR167653, while the reduced ulcerogenic response to HCl/ethanol was significantly prevented by L-NAME and partly by indomethacin or NS-398. On the other hand, the healing of chronic gastric ulcers induced by thermal cauterization was also significantly delayed in arthritic rats when compared with normal rats. This delayed healing of gastric ulcers was affected by neither L-NAME, indomethacin nor FR167653. The gastric mucosa of arthritic rats showed a significant increase in both inducible nitric oxide synthase (iNOS) activity and prostaglandin (PG) E2 contents.

CONCLUSIONS

Gastric ulcerogenic and healing responses were altered in arthritic rats. The ulcerogenic response to indomethacin was increased while that to HCl/ethanol was decreased. These changes in ulcerogenic responses may both be accounted for by increased production of NO/iNOS, with the latter also being partially related to elevated production of PGs/COX-2. Moreover, the healing of gastric ulcers was also delayed in arthritic rats, but the mechanism was related to neither NO nor PGs.

Roles of enterobacteria, nitric oxide and neutrophil in pathogenesis of indomethacin-induced small intestinal lesions in rats

Roles of enterobacteria, nitric oxide (NO) and neutrophil in indomethacin-induced small intestinal lesions were examined in rats. Indomethacin (10 mg kg-1), administered s.c. as a single injection, caused haemorrhagic lesions in the small intestine, mostly in the jejunum and ileum. The lesions were first observed 6 h after administration of indomethacin, the severity increasing progressively with time up to 24 h later. Following indomethacin, the enterobacterial numbers, inducible NO synthase (iNOS) activity and NO production in the intestinal mucosa were also increased with time, and changes in the former preceded those in the latter two as well as the occurrence of intestinal damage. Treatment of the animals with both NG-nitro-L-arginine methyl ester (L-NAME) and aminoguanidine prevented intestinal lesions induced by indomethacin, with suppression of NO production. Both dexamethasone and FR167653 (an inhibitor of interleukin-1 beta/tumour necrosis factor-alpha production) also reduced the severity of intestinal lesions as well as the increase in iNOS activity following administration of indomethacin. Likewise, the occurrence of intestinal lesions was attenuated by pretreatment of the animals with anti-neutrophil serum (ANS). None of these treatments, however, affect the translocation of enterobacteria in the mucosa. By contrast, ampicillin (an anti-bacterial agent) suppressed the increase in mucosal iNOS activity as well as the enterobacterial numbers invaded in the mucosa and inhibited the occurrence of intestinal lesions after administration of indomethacin. These results strongly suggest that enterobacterial translocation in the mucosa is the first step required for activation of various factors such as iNOS/NO and neutrophils, all involved in the pathogenesis of indomethacin-induced intestinal lesions.

Changes in gastric mucosal ulcerogenic responses in rats with adjuvant arthritis: role of nitric oxide

AIM

To examine gastric mucosal ulcerogenic responses to indomethacin and HCl/ethanol in adjuvant arthritic (AA) rats.

METHODS AND RESULTS

Arthritis was induced in male Dark Agouti (DA) rats by injection of Freund's complete adjuvant (FCA) into the right hind paw. The gastric ulcerogenic response to indomethacin was markedly worsened in AA rats, depending on the degree of arthritic change. This aggravation of indomethacin-induced gastric lesions in AA rats was significantly prevented by NG-nitro-L-arginine methyl ester (L-NAME) and amino-guanidine as well as dexamethasone. In contrast, the mucosal ulcerogenic response to HCl/ethanol was inhibited in AA rats. The suppression of HCl/ethanol-induced gastric lesions in AA rats was reversed almost totally by L-NAME and aminoguanidine as well as dexamethasone and partly by indomethacin. The expression of inducible nitric oxide synthase (iNOS) mRNA was observed in the stomach of AA rats but not of normal rats. Moreover, the luminal releases of nitric oxide (NO) metabolites as well as prostaglandin (PG) E2 were significantly increased in AA rats.

CONCLUSIONS

The gastric mucosal ulcerogenic responses were modified in AA rats, in different manners depending on the irritants; an increase in response to indomethacin and a decrease in response to HCl/ethanol. These changes may both be accounted for by increased production of NO by iNOS, and the latter is also partly related to increased production of PGs.