Relationships of secretagogue-induced cAMP accumulation and acid secretion in elutriated rat gastric parietal cells

Recent Progress of Fluorescence Sensors for Histamine in Foods

Biological amines are organic nitrogen compounds that can be produced by the decomposition of spoiled food. As an important biological amine, histamine has played an important role in food safety. Many methods have been used to detect histamine in foods. Compared with traditional analysis methods, fluorescence sensors as an adaptable detection tool for histamine in foods have the advantages of low cost, convenience, less operation, high sensitivity, and good visibility. In terms of food safety, fluorescence sensors have shown great utilization potential. In this review, we will introduce the applications and development of fluorescence sensors in food safety based on various types of materials. The performance and effectiveness of the fluorescence sensors are discussed in detail regarding their structure, luminescence mechanism, and recognition mechanism. This review may contribute to the exploration of the application of fluorescence sensors in food-related work.

Phosphodiesterase inhibition by a gastroprotective agent irsogladine: preferential blockade of cAMP hydrolysis

The effect of irsogladine [2,4-diamino-6-(2,5-dichlorophenyl)-s-triazine maleate], an antiulcer drug, on contents of cyclic nucleotides including cAMP and cGMP was investigated in rat stomachs. Irsogladine concentration-dependently increased cAMP content in rat glandula stomach. However, irsogladine at higher concentration (10(-5) M) was unable to further increase cAMP level in the presence of non-selective phosphodiesterase (PDE) inhibitor 3-isobutyl-1-methylxanthine, although 3-isobutyl-1-methylxanthine by itself increased cAMP level. On the other hand, irsogladine had no effect on the glandula cGMP content. Subsequently, the effect of irsogladine on the cyclic nucleotide degradation by purified bovine brain and heart PDEs was investigated. The cAMP degradation by purified bovine brain PDE was partially suppressed by PDE1 inhibitor vinpocetin, PDE2 inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride and PDE4 inhibitor rolipram but not by PDE3 inhibitor cilostamide, and completely inhibited by 3-isobutyl-1-methylxanthine, suggesting that is attributed almost exclusively to PDE1, PDE2 and PDE4. Meanwhile, cGMP degradation by purified bovine brain PDE was partially suppressed by erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride. Irsogladine preferentially inhibited the response to cAMP degradation compared with cGMP degradation by this brain PDE. The cAMP degradation by bovine heart PDE was almost completely inhibited by the combination with vinpocetine and cilostamide, indicating that is mediated almost exclusively by PDE1 and PDE3. Irsogladine suppressed this cAMP degradation measured in the presence of vinpocetine to almost the same extent as that determined in the presence of cilostamide. These results indicate that irsogladine produces the increase of intracellular cAMP content via non-selective inhibition of PDE isozymes, which may be a key mechanism involved in its gastroprotective actions.

Phosphodiesterase Type IV Inhibitors Prevent Ischemia-Reperfusion-Induced Gastric Injury in Rats

The effects of selective inhibitors of phosphodiesterase type IV (PDE4) on ischemia-reperfusion-induced gastric injuries were investigated in rats. Gastric ischemia was induced by applying a small clamp to the celiac artery, and reoxygenation was performed by removal of the clamp. Ischemia-reperfusion produced gastric hemorrhagic injuries and increased the content of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) and myeloperoxidase (MPO) activity in gastric mucosa. Rolipram (0.03-0.3 mg/kg, s.c.) and Ro-20-1724 (0.3-3 mg/kg, s.c.) prevented the development of gastric injury in a dose-dependent manner, and it also inhibited the increase in mucosal TNF-alpha content and MPO activity induced by ischemia-reperfusion. The anti-ulcer drug irsogladine (1-10 mg/kg, p.o.), which is known to possess a PDE4 inhibitory action, also inhibited the gastric injury produced by ischemia-reperfusion, as well as the increase in TNF-alpha levels and MPO activity. It is concluded that the ability of PDE4 inhibitors to inhibit cytokine TNF-alpha synthesis and the infiltration of polymorphonuclear leukocytes underlies their gastroprotective effects in ischemia-reperfusion-induced gastric injury. Our experiments suggest that drugs that inhibit PDE4 isoenzyme, such as the anti-ulcer drug irsogladine, may be a useful adjunct therapy for the treatment of the gastric damage that follows ischemia-reperfusion.

Selective phosphodiesterase inhibitors for the treatment of bronchial asthma and chronic obstructive pulmonary disease

Theophylline is commonly used in the treatment of obstructive airway diseases. The identification and functional characterization of different phosphodiesterase (PDE) isoenzymes has led to the development of various isoenzyme-selective inhibitors as potential anti-asthma drugs. Considering the distribution of isoenzymes in target tissues, with high activity of PDE3 and PDE4 in airway smooth muscle and inflammatory cells, selective inhibitors of these isoenzymes may add to the therapy of chronic airflow obstruction. However, initial data from clinical trials with selective PDE3 and PDE4 inhibitors have been somewhat disappointing and have tempered the expectations considerably since these drugs had limited efficacy and their use was clinically limited through side effects. The improved understanding of the molecular biology of PDEs enabled the synthesis of novel drugs with an improved risk/benefit ratio. These 'second generation' selective drugs have produced more promising clinical results not only for the treatment of bronchial asthma but also for the treatment of chronic obstructive pulmonary disease.

Bronchoprotective effect of an intrabronchial administration of cilostazol powder and a nebulized PDE1 and PDE4 inhibitor KF19514 in guinea pigs

BACKGROUND

Both oral and intravenous inhibitors of cyclic nucleotide phosphodiesterase (PDE) 3 and PDE4 have been shown to have bronchodilator and/or pulmonary antiallergic effects but their adverse effects limit the clinical use. The purpose of the present study was to assess the bronchoprotective effect of intrabronchial administration of a selective PDE3 inhibitor, 6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quin olinone (cilostazol), in dry power form which is proposed to be desirable rather than propellant-driven metered-dose inhalers.

METHODS

Effect of an intrabronchial administration of cilostazol powder on aerosolized histamine- and antigen-induced leukotriene-mediated bronchoconstriction were examined in anesthetized and artificially ventilated guinea pigs, in comparison with the effects of ultrasonically nebulized 5-phenyl-3-(3-pyridyl)methyl-3H-imidazo[4,5-c] [1,8] naphthyridin-4(5H)-one (KF19514), a selective PDE1/4 inhibitor.

RESULTS

Cilostazol powder and KF19514 solution inhibited histamine- and antigen-induced bronchoconstriction in a dose-dependent manner. When assessing the resulting ED50 values, the activity of cilostazol powder against antigen-induced broncho-constriction was weaker than its antagonism of histamine-induced bronchoconstriction (60.4 vs. 7.0 microg), while those of KF19514 were the opposite (0.40 vs. 2.81 microg/ml).

CONCLUSION

These results suggest that intrabronchially administered cilostazol powder has a bronchodilator effect, and ensure that PDE4 inhibitors have an antiallergic activity in addition to their bronchodilator effect.

Interactions between Ca2+- and cAMP-dependent stimulatory pathways in parietal cells

Isolated rat parietal cells were used to investigate the role of intracellular Ca2+ in the action of cAMP-dependent secretagogues and cross talk between cAMP- and Ca2+ -dependent stimulatory pathways. Aminopyrine accumulation (an index of acid produced and trapped by the parietal cells), cytosolic free Ca2+, morphological transformation and cell viability were used to investigate parietal cell function and stimulation. The increase of cytosolic free Ca2+ promoted by gastrin, or carbachol, was abolished by the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA, 10 microM). Also, the morphological transformations induced by dibutyryladenosine 3':5'-cyclic monophosphate (DBcAMP), gastrin, and Sp-adenosine-cyclic-3', 5'-monophosphothioate (Sp-cAMPS) were completely abolished by BAPTA (10 microM). In aminopyrine accumulation the action of 1 mM DBcAMP was dose-dependently reduced by BAPTA. The Ca2+ ionophore A23187 alone, in the range of 1 pM to 1 microM, had no effect but it dose-dependently potentiated the action of 1 mM DBcAMP in aminopyrine accumulation. The inhibitory actions of BAPTA on DBcAMP- and histamine-stimulated aminopyrine accumulation were dose-dependently reversed by A23187. Histamine-stimulated protein kinase activity and viability parameters as cellular lactate dehydrogenase (LDH) and trypan blue exclusion were not changed by BAPTA. These results indicated that in isolated parietal cells: (1) the action of cAMP-dependent secretagogues in aminopyrine accumulation and morphological transformation are dependent on cytosolic free Ca2+; (2) Ca2+ -induced morphological transformation is essential for aminopyrine accumulation; (3) a threshold level of one second messenger is required for stimulation of aminopyrine accumulation by the other second messenger.

Direct gastrin action on isolated rat parietal cells induces morphological transformations

In isolated rat parietal cells, a potentiating effect by gastrin of the stimulatory action of histamine and dibutyryl-cAMP (DBcAMP) on aminopyrine accumulation, an index of the acid formed and trapped by the cells, was recently reported by us (1991, Am. J. Physiol. 261, G621-G627). In the present study, this mechanism of action of gastrin was further investigated. Enriched parietal cells (approximately 65% parietal cells) were incubated under different conditions and processed for electron microscopy. Morphometric analysis of the micrographs revealed that pentagastrin (100 nM) was as efficient as histamine (100 microM) in inducing the formation of vacuolar/canalicular spaces in the parietal cells. In the presence of the histamine H2-receptor antagonist ranitidine, histamine was ineffective but pentagastrin and gastrin-17 (G17) maintained their capacity to induce the morphological transformations. By stimulation with pentagastrin plus histamine, the vacuolar/canalicular volume was 2-fold higher than by stimulation separately with each one of the secretagogues. G-17 (100 nM) alone was ineffective but potentiated the maximal [14C]aminopyrine accumulation obtained with 100 microM histamine in mucosal cells (approximately 25-35% parietal cells). Ranitidine blocked both histamine-and histamine plus G-17-stimulated aminopyrine accumulation. G-17 potentiated also the stimulation by 1 mM dibutyryl-cyclic AMP but this was not inhibited by ranitidine. Pentagastrin (100 nM) increased the basal [14C]glucose oxidation in mucosal cells by 30%. This increase was not blocked by ranitidine which, however, abolished the histamine-stimulated glucose oxidation. Incubation of the cells with pentagastrin plus histamine resulted in a glucose oxidation which equaled the sum of the values obtained by each one of the agents. These results indicate that gastrin, acting directly on the parietal cells, potentiates the action of histamine on aminopyrine accumulation by increasing the vacuolar/canalicular spaces, a process that is reflected in the metabolic activity of the cells. Thus a major effect of gastrin at the parietal cell level appears to be the induction of a morphology which is characteristic of stimulated cells rather than a direct activation of ion-transport mechanisms.

Cyclic nucleotide phosphodiesterase isoenzymes and asthma--outstanding issues

Cyclic nucleotide phosphodiesterase isoenzymes hydrolyse and thus inactivate the intracellular second messengers cyclic AMP and cyclic GMP. Inhibitors of these isoenzymes modulate tissue function by reducing the rate of breakdown of the cyclic nucleotides. Eukaryotic cells contain multiple forms of phosphodiesterase with differing regulatory characteristics and substrate specificities. At present, the majority of the identified isoenzymes can be grouped into five families (PDE I-PDE V). These isoenzymes have differing distributions and play differing relative roles in the hydrolysis of cyclic nucleotides between tissues. Thus, isoenzyme selective inhibitors may selectively modulate tissue function. Drugs which are therapeutically useful in asthma either bronchodilate or reduce the underlying inflammatory condition. Inhibitors of PDE III, PDE IV and PDE V relax airways smooth muscle. Inhibitors of PDE IV attenuate the activation of pro-inflammatory cells, an effect which in some assays is potentiated by additional PDE III inhibition. PDE V inhibition has not been shown to result in potentially useful anti-inflammatory activity. Despite various degrees of tissue selectivity, the possible side effect profile of isoenzyme selective phosphodiesterase inhibitors requires elucidation before these agents can be proposed as selective anti-asthma drugs. However, it is apparent that selective inhibitors of PDE III, PDE IV and PDE V may be useful bronchodilators, whilst PDE IV and PDE III/IV inhibitors also possess potentially useful anti-inflammatory activity. Such compounds require further evaluation in animals and man to clarify their full potential as therapeutic agents for the treatment of asthma.

Differential regulation of chromogranin B/secretogranin I and secretogranin II by forskolin in PC12 cells

The factors which regulate the expression of the granin family of secretory proteins have yet to be completely described. The present study investigated the effects of forskolin (FSK), an activator of adenylate cyclase, on the regulation of chromogranin B/secretogranin I (CgB) and secretogranin II (SgII) mRNA levels in rat PC12 cells. PC12 cells were treated with 10 microM FSK for time points up to 48 h and were harvested for cAMP determination, RNA isolation and Northern blot analysis, or fixed in 4% paraformaldehyde for immunocytochemistry. Cellular cAMP levels peaked after two h of FSK treatment and remained elevated for 48 h. Chromogranin B mRNA increased with FSK treatment, reaching a maximum of 7-fold above control after 24 h, while the level of SgII mRNA decreased to a level of 65 +/- 10% of control after 48 h. The effects of FSK on CgB mRNA appear to be mediated by cAMP, as 8-bromo-cAMP (500 microM) resulted in a 2.8-fold increase in CgB mRNA, and H-89 (30 microM), a selective inhibitor of cAMP-dependent protein kinase, reduced the FSK-mediated response. The level of CgB was also increased in FSK-treated cells, as evidenced by immunofluorescent analysis which showed a more intense staining in PC12 cells treated with FSK for 48 h than in untreated cells. The intensity of SgII staining was diminished by FSK treatment, most likely a result of a decreased rate of synthesis as well as an increase in the release of SgII. This study demonstrated that the mRNA and protein levels of CgB and SgII are differentially regulated by cAMP in PC12 cells.

Studies of isolated parietal and enterochromaffin-like cells from the rat

Rat gastric mucosal cells isolated by enzyme dispersion were separated by elutriation centrifugation. The amount of histamine and the number of enterochromaffin-like (ECL) cells and parietal cells were determined in the crude mucosal cells and the various elutriation fractions. The mucosal cells contained 2.6% ECL and 20% parietal cells. Elutriation centrifugation resulted in good separation of parietal cells and ECL cells. Most of the ECL cells were elutriated in the small cell fractions. Scattered ECL cells were also present in the fraction enriched with parietal cells. Histamine and carbacholine stimulated aminopyrine uptake in a concentration-dependent manner with about the same efficacy, 5.6 times the base-line value. When combined with the phosphodiesterase inhibitor isobutyl methylxanthine, the maximal histamine stimulation was increased to 16.8 times the base-line value, and the sensitivity increased about 10-fold. Gastrin at high and unphysiologic concentrations stimulated only faintly the aminopyrine uptake in parietal cells and the histamine release from ECL cells.

Differential modulation of tissue function and therapeutic potential of selective inhibitors of cyclic nucleotide phosphodiesterase isoenzymes

Since the discovery of cyclic nucleotide phosphodiesterase 30 years ago, there have been major advances in our knowledge of this group of isoenzymes. Five families, each composed of several isoforms and having differing tissue distributions, have been described. David Nicholson and colleagues compare the tissue distribution of phosphodiesterase isoenzymes and discuss the differential effects of inhibition of particular isoenzymes, with differing subcellular localization, on tissue function. They also review the potential use of isoenzyme selective phosphodiesterase inhibitors in a range of clinical disorders such as heart failure, asthma, depression and dementia.

Fura 2 analysis of cytosolic calcium regulation in elutriated rat gastric parietal cells

The calcium probe, Fura 2, is used to establish and partially characterize histamine-, carbachol-, and forskolin-induced calcium transients in enriched parietal cell populations prepared by centrifugal elutriation of dispersed rat fundic mucosa cell isolates. The magnitude of the maximal carbachol response, which is blocked by atropine but not cimetidine, is nearly five times that of histamine or forskolin. Time to peak responses for carbachol, forskolin, and histamine are approximately 7, 17, and 28 sec, respectively. Carbachol-, histamine-, and forskolin-induced increases in Fura 2 fluorescence appear dependent upon extracellular calcium, since these responses are attenuated in low calcium media and blocked by EGTA in low-calcium media or by lanthanum in high- or low-calcium medium. Trifluoperazine and fenoctimine, at concentrations that inhibit secretion, have no effect on either carbachol- or histamine-induced increases in cytosolic calcium. Seven major calcium/EGTA-sensitive phosphoproteins are identified by SDS-PAGE electrophoresis of ATP 32P-labeled cell sonicates. We conclude that cytosolic calcium in enriched rat gastric parietal cell populations is regulated by secretagogue receptor-controlled calcium channels. We postulate that these channels may be controlled by cyclic AMP-dependent phosphorylation, since neither changes in cyclic AMP nor calcium alone mediate the effects of secretagogues entirely, but the interplay between these two second-messenger systems potentiates the actions of these agents. The role of cytosolic calcium as a second messenger in secretagogue action appears similar to that of cyclic AMP in that a specific cellular concentration must be reached to initiate acid secretion.