Role of gastric mucosal eicosanoid production in the cytoprotection induced by nitecapone

The Helicobacter felis mouse model in assessing anti-Helicobacter therapies and gastric mucosal prostaglandin E2 levels

BACKGROUND

The aims of the present study were to assess the usefulness of the Helicobacter felis mouse model in the evaluation of antimicrobial therapies and the effect of Helicobacter infection on gastric mucosal prostaglandin E2 release.

METHODS

Barrier-maintained BALB/c mice were infected with H. felis and treated with different antibacterial therapies. H. felis status was determined by bacterial culture, urease test, and bacterial and histologic stainings. Release of prostaglandin E2 from the gastric mucosa was measured by radioimmunoassay.

RESULTS

All triple-treated mice were cleared of bacteria both 24 h and 1 month after treatment. However, tinidazole alone also resulted in 100% eradication. Monotherapies with erythromycin acistrate, tetracycline, colloidal bismuth subcitrate, and nitecapone failed to eradicate the bacteria. The release of gastric prostaglandin E2 was doubled in the infected mice (554 +/- 39, mean +/- SE) compared with the noninfected mice (270 +/- 35) (p < 0.01).

CONCLUSIONS

The H. felis mouse model proved satisfactory for assessing both anti-Helicobacter therapies and the prostaglandin E2 release. The reliability of this method was improved when several methods to assess the H. felis status were used in parallel.

Role of dopamine and other stimuli of mucosal bicarbonate secretion in duodenal protection

Duodenal mucosal secretion of bicarbonate is one main mechanism in the protection of this epithelium against luminal acid. The duodenal secretagogue vasoactive intestinal polypeptide, at doses not affecting mucosal blood flow, protects against acid-induced morphological changes. Some sigma receptor ligands, which increase the duodenal alkaline secretion, prevent duodenal but not gastric mucosal ulceration. Dopamine D-1 receptor agonists and the peripherally acting catechol-O-methyl-transferase (COMT) inhibitor nitecapone stimulate the bicarbonate secretion in the rat and a similar increase in secretion has been observed in human volunteers. COMT inhibitors decrease tissue degradation of catecholamines, including dopamine. The D-2 agonist bromocriptine, in contrast, decreases the secretion. These results, indicating that the bicarbonate secretion is stimulated via peripheral dopamine D-1 receptors, are supported by the finding that dopamine D-1 (but not D-2) agonists increase the production of cyclic AMP in isolated duodenal enterocytes. The increase in mucosal alkaline secretion may contribute to the previously observed ulceroprotective actions of dopaminergic compounds.

Effect of bismuth and nitecapone on acetaldehyde production by Helicobacter pylori

BACKGROUND

We have recently shown that colloidal bismuth subcitrate inhibits cytosolic alcohol dehydrogenase of Helicobacter pylori as well as acetaldehyde production from excess ethanol. We now extend our studies to bismuth subsalicylate and nitecapone, a novel antiulcer agent.

METHODS

Cytosol of H. pylori was incubated with 0.1% or 1% ethanol in the presence of different drug concentrations for 2 h, whereafter acetaldehyde formed was analyzed by head space gas chromatography. In addition, we incubated a culture solution containing intact bacteria with the drugs at 1% ethanol.

RESULTS

Bismuth subsalicylate and nitecapone inhibit acetaldehyde formation from 0.1% ethanol by H. pylori cytosol at drug concentrations theoretically achievable in the stomach after intake of therapeutic doses of these drugs. Furthermore, colloidal bismuth subcitrate, bismuth subsalicylate, and nitecapone also inhibit acetaldehyde production by intact H. pylori, although rather high drug concentrations are required for this to occur.

CONCLUSIONS

Inhibition of H. pylori acetaldehyde formation may be one of the mechanisms by which bismuth and nitecapone exert their effect in the treatment of H. pylori-related disorders.

Endogenous dopamine and duodenal bicarbonate secretion in humans

BACKGROUND

Catechol-O-methyltransferase (COMT) inhibition prevents tissue degradation of catecholamines including dopamine. This study was undertaken to investigate the effect of intraluminal nitecapone, a peripherally acting COMT inhibitor, on duodenal mucosal bicarbonate secretion in humans and to compare the effect with that of the prostaglandin E1 analogue misoprostol.

METHODS

The duodenal bulb was isolated by means of a three-balloon six-channel tube as previously described. Basal bicarbonate secretion and secretion after intraluminal administration of 30 and 150 mg nitecapone were determined in 11 healthy subjects. In 7 of these subjects, effects of intraluminal administration of 30 and 150 micrograms of misoprostol were studied in a second experiment.

RESULTS

Even the lower dose of misoprostol increased duodenal bicarbonate secretion from 121 +/- 12 to 221 +/- 36 and the lower dose of nitecapone from 149 +/- 18 to 277 +/- 48 microEq.cm-1 x h-1, respectively (P < 0.05). With 150 micrograms of misoprostol or 150 mg of nitecapone there was a further increase in secretion to 296 +/- 33 (P < 0.01) and 421 +/- 36 (P < 0.001) microEq.cm-1 x h-1, respectively. The rise in bicarbonate secretion in response to nitecapone was associated with some increase in the release of prostaglandin E2 to the luminal perfusate.

CONCLUSIONS

It seems likely that peripheral COMT inhibition increases duodenal mucosal bicarbonate secretion and protection by inhibition of mucosal degradation of dopamine, an increase similar in magnitude to that obtained by a prostaglandin E1 analogue.

Protection by nitecapone against sodium taurocholate-induced damage to cultured gastric cells

The goal of this study was to observe if nitecapone protected against taurocholate-induced damage in primary cultured rat gastric mucosal cells, as well as in a well-differentiated human gastric epithelial cell line (MKN 28). Prostaglandins were measured to analyze the protection mechanism. In primary rat gastric mucosal cell culture, nitecapone 125-250 microM protected the cells significantly against damage induced by sodium taurocholate, increasing cell viability by 31-38%. In the human gastric epithelial cell line, in which mitochondrial activity was measured as an indication of cell viability, nitecapone (62.5-250 microM) protected the cells against sodium taurocholate-induced damage by 12-20%. Prostaglandin E2, thromboxane B2, and 6-keto-prostaglandin F1 alpha measurements in the primary cultured rat gastric mucosal cells showed that nitecapone (125 microM and 250 microM) significantly stimulated prostaglandin E2 production (84.7% and 61.0%, respectively), and inhibited thromboxane B2 formation (50% at 250 microM), while the 6-keto-prostaglandin F1 alpha formation was unaffected. Nitecapone had no effect on prostaglandin E2 production in the MKN 28 epithelial cell line. Indomethacin or aspirin, at concentrations that did not affect cell viability, antagonized the stimulative effect of nitecapone on prostaglandin E2 formation in the primary cultured rat gastric mucosal cells. Although the prostaglandin E2 synthesis was blocked, nitecapone still protected against cell damage induced by taurocholate. These results demonstrated the direct and efficacious protection of nitecapone on gastric cell level and suggest that the "cytoprotection" by nitecapone against taurocholate may not be mediated through the mechanism of stimulated synthesis of prostaglandin E2.

Stimulation of mucosal alkaline secretion in rat duodenum by dopamine and dopaminergic compounds

BACKGROUND

The catechol-O-methyl-transferase (COMT) inhibitor nitecapone, which prevents mucosal degradation of dopamine, and some dopamine receptor agonists ameliorate gastroduodenal mucosal damage. Therefore, their effects on mucosal bicarbonate secretion were studied.

METHODS

Duodenum just distal to the Brunner's glands area was cannulated in situ in anesthetized rats. Bicarbonate secretion into the luminal perfusate and transmucosal electrical potential difference (PD) were recorded.

RESULTS

Intravenous dopamine (50 micrograms.kg-1 x h-1) increased bicarbonate secretion twofold, and a higher rate of infusion (250 micrograms.kg-1 x h-1) resulted in a further increase. Neither dose affected the PD. The dopamine D1 agonist SKF-38393 (10-50 micrograms/kg) and the COMT inhibitor nitecapone (50-500 micrograms/kg) caused dose-dependent increases in secretion, similar to that observed with dopamine. Domperidone, a peripherally acting dopamine antagonist, inhibited the stimulatory effects of SKF-38393 and nitecapone. Hexamethonium or the alpha-adrenoceptor antagonist phentolamine, in contrast, did not affect the response to nitecapone. Intracerebroventricular administration of nitecapone was without effect.

CONCLUSIONS

A probable electroneutral component of duodenal mucosal bicarbonate secretion is stimulated via peripheral dopamine D1 receptors. This may contribute to the previously observed ulceroprotective actions of dopaminergic compounds.

Nitecapone effect on the synthesis and secretion of gastric sulfomucin

1. The effect of a new antiulcer agent, nitecapone, on the synthesis and secretion of sulfomucin in gastric mucosa was investigated using mucosal segments incubated in the presence of [3H]proline, [3H]glucosamine and [35S]sulfate. 2. The drug, while showing no discernible effect on the apomucin synthesis, evoked a dose-dependent increase in mucin glycosylation and sulfation, which at 225 microM nitecapone, attained its maximum of 1.8 and 2.2-fold stimulation, respectively. 3. The analysis of mucin secretory responses revealed that nitecapone caused a concentration-dependent enhancement in sulfomucin secretion attaining maximum increase of 1.5-fold at 150 microM nitecapone. 4. The stimulatory effect of nitecapone on sulfomucin secretion was accompanied by 1.4-fold increase in mucosal cAMP level, and showed sensitivity to protein kinase A inhibitors, thus pointing towards the involvement of protein kinase A in mediation of gastric sulfomucin secretory responses to nitecapone. 5. The ability of nitecapone to enhance sulfomucin synthesis and secretion could be of importance to the gastroprotective action of this agent.

Antioxidant properties of nitecapone (OR-462)

Nitecapone [3-(3,4-dihydroxy-5-nitrophenyl)methylene-2,4-pentanedione] [OR-462] is a catechol-O-methyltransferase inhibitor with gastroprotective properties. Recently, its antioxidant properties have been discovered: It scavenges peroxyl radicals (ROO.) and thus spares glutathione. Further examination of the properties of nitecapone demonstrated a remarkable ability of this compound to act as an antioxidant: (1) to scavenge ROO. in solution with a stoichiometry factor of 2; (2) to scavenge ROO. in membranes; (3) to inhibit lipid peroxidation; (4) to act as a competitive inhibitor for xanthine oxidase with Ki of 8.8 microM; (5) to scavenge O2- with a second order kinetic rate constant of 1.0 x 10(4) M-1 s-1; and (6) to scavenge HO.. Nitecapone also interacts with oxidation product of ascorbate to participate in recycling of vitamin E. Thus, nitecapone potentially is an effective therapeutic antioxidant, and the use of this compound in a combination with other antioxidants may be beneficial.