Protective effects of polygodial on gastric mucosal lesions induced by necrotizing agents in rats and the possible mechanisms of action

Nitric oxide, afferent sensory nerves, and antioxidative enzymes in the mechanism of protection mediated by tricarbonyldichlororuthenium(II) dimer and sodium hydrosulfide against aspirin-induced gastric damage

BACKGROUND

Aspirin exerts side effects within the gastrointestinal tract. Hydrogen sulfide (H₂S) and carbon monoxide (CO) have been implicated in gastroprotection but the mechanism of beneficial action of these gaseous mediators against aspirin-induced damage has not been fully studied. We determined the involvement of afferent sensory neurons, calcitonin-gene-related peptide (CGRP), lipid peroxidation, and nitric oxide (NO) biosynthesis in gastroprotection of H₂S-releasing NaHS and CO-releasing tricarbonyldichlororuthenium(II) dimer (CORM-2) against aspirin-induced injury.

METHODS

Wistar rats with or without capsaicin-induced denervation of sensory neurons were pretreated with vehicle, CORM-2 (5 mg/kg intragastrically), or NaHS (5 mg/kg intragastrically) with or without capsazepine (5 mg/kg intragastrically) or N ^G-nitro-L-arginine (L-NNA, 20 mg/kg intraperitoneally). The areas of aspirin-induced lesions and gastric blood flow (GBF) were assessed by planimetry and laser flowmetry respectively. Gastric mucosal messenger RNA and/or protein expression of CGRP, heme oxygenase 1, inducible nitric oxide synthase, cyclooxygenase 2, interleukin-1β, glutathione peroxidase 1 (GPx-1), and superoxide dismutase was determined by real-time PCR or Western blot. Malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) content was determined by colorimetric assay.

RESULTS

Aspirin caused gastric lesions, decreased GBF, and raised MDA content, but pretreatment with NaHS and CORM-2 reduced these effects. Capsaicin-induced denervation or co-treatment with capsazepine reversed the gastroprotective and vasodilatory effects of NaHS but not those of CORM-2. L-NNA reversed NaHS-induced gastroprotection and partly reduced CORM-2-induced gastroprotection. NaHS and CORM-2 decreased MDA and 4-HNE content, restoring GPx-1 protein expression.

CONCLUSIONS

We conclude that H₂S- but not CO-mediated gastroprotection against aspirin-induced injury involves afferent sensory nerves and partly NO activity. NaHS and CORM-2 prevented aspirin-induced gastric mucosal lipid peroxidation via restoration of microcirculation and antioxidative GPx-1 protein expression.

Interaction between endogenous carbon monoxide and hydrogen sulfide in the mechanism of gastroprotection against acute aspirin-induced gastric damage

Acetylsalicylic acid (ASA) is mainly recognized as painkiller or anti-inflammatory drug. However, ASA causes serious side effects towards gastrointestinal (GI) tract which limits its usefulness. Carbon monoxide (CO) and hydrogen sulfide (H₂S) have been described to act as important endogenous messengers and mediators of gastroprotection but whether they can interact in gastroprotection against acute ASA-induced gastric damage remains unknown. In this study male Wistar rats were pretreated with 1) vehicle (saline, i.g.), 2) tricarbonyldichlororuthenium (II) dimer (CORM-2, 5mg/kg i.g.), 3) sodium hydrosulfide (NaHS, 5mg/kg i.g.), 4) zinc protoporphyrin (ZnPP, 10mg/kg i.p.), 5) D,L-propargylglycine (PAG, 30mg/kg i.g.), 6) ZnPP combined with NaHS, 7) PAG combined with CORM-2 or 8) 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10mg/kg i.p.) combined with CORM-2 or NaHS and 30min later ASA was administered i.g. in a single dose of 125mg/kg. After 1h, gastric blood flow (GBF) was determined by H₂ gas clearance technique and gastric lesions were assessed by planimetry and histology. CO content in gastric mucosa and COHb concentration in blood were determined by gas chromatography and H₂S production was assessed in gastric mucosa using methylene blue method. Protein and/or mRNA expression for cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), 3-mercaptopyruvate sulfurtransferase (3-MST), heme oxygenase (HO)-1, HO-2, hypoxia inducible factor-alpha (HIF)-1α, nuclear factor (erythroid-derived 2)-like 2 (Nrf-2), cyclooxygenase (COX)-1 and COX-2, inducible nitric oxide synthase (iNOS) and interleukin (IL)-1β were determined by Western blot or real-time PCR, respectively. ASA caused hemorrhagic gastric mucosal damage and significantly decreased GBF, H₂S production, CO content, mRNA or protein expression for CSE, 3-MST, HO-2 and increased mRNA and/or protein expression for CBS, HO-1, Nrf-2, HIF-1α, iNOS, IL-1β, COX-2 in gastric mucosa and COHb concentration in blood. Pretreatment with CORM-2 or NaHS but not with PAG decreased ASA-damage and increased GBF. ZnPP reversed protective and hyperemic effect of NaHS but PAG failed to affect CORM-2-induced gastroprotection. CORM-2 elevated CO content, mRNA or protein expression for HO-1, Nrf-2, and decreased expression of CBS, HIF-1α, COX-2, IL-1β, iNOS, the H₂S production in gastric mucosa and COHb concentration in blood. NaHS raised mRNA or protein expression for CSE, COX-1 and decreased mRNA expression for IL-1β and COHb level in blood. We conclude that CO is involved in gastroprotection induced by H₂S while beneficial protective action of CO released from CORM-2 in gastric mucosa seems to be H₂S-independent. In contrast to H₂S, CO ameliorates hypoxia, regulates Nrf-2 expression but similarly to H₂S acts on sGC-dependent manner to restore gastric microcirculation and exhibit anti-inflammatory activity in gastric mucosa compromised by ASA.

Byrsonima intermedia A. Juss.: gastric and duodenal anti-ulcer, antimicrobial and antidiarrheal effects in experimental rodent models

ETHNOPHARMACOLOGICAL RELEVANCE

An ethnopharmacological survey indicated that the leaves of Byrsonima intermedia A. Juss. (Malpighiaceae), a medicinal species commonly found in the Brazilian Cerrado, can be used against gastroduodenal disorders, such as gastric ulcers and diarrhea.

AIM OF THE STUDY

The objective of this study was to evaluate the effects of a methanolic extract of Byrsonima intermedia (MBI) leaves on gastric and duodenal ulcers and to assess the antimicrobial and antidiarrheal effects of this extract.

MATERIAL AND METHODS

The anti-ulcerogenic effect of MBI was investigated with different ulcerogenic agents in rodents (mice and rats), including non-steroidal anti-inflammatory drug (NSAID), HCl/ethanol, pyloric ligature, absolute ethanol, cysteamine and ischemia-reperfusion. The gastroprotective effect of MBI was assessed by analysing the volume of gastric juice, pH, total acidity, mucus, NO, sulfhydryl compound, vanilloid receptor, glutathione (GSH) levels, and myeloperoxidase (MPO) activity in the gastric and duodenal mucosa. The gastric and duodenal healing effects of MBI were also evaluated during 7 or 14 days of treatment. The antidiarrheal action (measured by intestinal motility and diarrhea induced by castor oil) and anti-bacterial action of MBI against Staphylococcus aureus, Escherichia coli and Helicobacter pylori were also evaluated by microdilution methods.

RESULTS

The phytochemical profile from MBI indicated the presence of phenolic acids, flavan-3-ols, oligomeric proanthocyanidins, and flavonoids. MBI (500mg/kg, p.o.) significantly inhibited totally gastric and duodenal lesions (69%) and healed gastric (49% on 14 days) and duodenal lesions (45% on 7 and 14 days). The MBI exert gastroprotective action by participation of endogenous sulfhydryl compounds, vanilloid receptors and increase in GSH level to effective gastric and duodenal protection. MBI also displayed curative (42%) and preventive (49%) antidiarrheal effects by involvement of opiate receptors and also antimicrobial effects in vitro.

CONCLUSIONS

Byrsonima intermedia leaves present gastroprotective, healing and antidiarrheal activities, supporting previous claims that its traditional use can treat gastrointestinal disorders.

Gastroprotective activity of isopulegol on experimentally induced gastric lesions in mice: investigation of possible mechanisms of action

The present study investigated whether isopulegol, a monoterpene present in essential oils of several aromatic plants, would be able to promote some gastroprotective effect and also verified the possible mechanisms involved in this action. For this study, ethanol- and indomethacin-induced gastric ulcer models in mice and histopathological assessment were used. The roles of NO, sulfhydryls (glutathione, GSH), ATP-sensitive K(+) channels (K(ATP) channels), and prostaglandins were also investigated. Isopulegol exhibited a dose-related gastroprotective effect against ethanol-induced lesions, while the pretreatment with glibenclamide and indomethacin [but not with N(G)-nitro-L-arginine methyl ester] were able to reverse this action. The pretreatment with isopulegol also restored GSH levels to normal levels and exhibited dose-related gastroprotective effect against indomethacin-induced ulcer. The results suggested that isopulegol presents significant gastroprotective effects in both ethanol- and indomethacin-induced ulcer models, which appear to be mediated, at least in part, by endogenous prostaglandins, K(ATP) channel opening, and antioxidant properties.

Medicinal flowers. XVI. New dammarane-type triterpene tetraglycosides and gastroprotective principles from flower buds of Panax ginseng

The oligoglycoside fraction from the flower buds of Panax ginseng C. A. MEYER (Araliaceae) was found to show protective effects on ethanol-induced gastric mucosal lesions in rats. From the oligoglycoside fraction, new dammarane-type triterpene tetraglycosides, floralginsenosides M, N, O, and P, were isolated together with the major oligoglycosides ginsenoside Rd and Re. The structures of the new floralginsenosides were elucidated on the basis of chemical and physicochemical evidence. Ginsenoside Rd (protopanaxadiol 3,20-O-bisdesmoside) exhibited inhibitory effects on ethanol- and indomethacin-induced gastric mucosal lesions in rats.

Gastroprotective activity and cytotoxic effect of cyperenoic acid derivatives

The gastroprotective effect of the sesquiterpene cyperenoic acid and seven semi-synthetic derivatives was assessed in the HCl/ethanol-induced gastric ulcer model in mice. At doses of 25, 50 and 100 mg kg(-1), cyperenoic acid showed a dose-dependent gastroprotective effect reducing the lesions by 45 and 75% at 50 and 100 mg kg(-1), respectively. Seven derivatives of the sesquiterpene were prepared and their gastroprotective activity compared at 50 mg kg(-1). The cytotoxicity of the compounds was evaluated in fibroblasts and AGS cells. At 50 mg kg(-1), patchoulan-15-oic acid (compound 8) presented the best gastroprotective effect, reducing the gastric lesions by 86%, with a similar effect to lansoprazole at 20 mg kg(-1). The gastroprotective effect of cyperenol, cyperenoic acid methyl ester and the ethylamide and butylamide from cyperenoic acid were in the same range, reducing the gastric lesions by 72-77%. Cyperenol and cyperenoic acid methyl ester, however, were more cytotoxic with IC50 (concentration that produces a 50% inhibitory effect) values of 44 and 75, 48 and 75 microM against AGS cells and fibroblasts, respectively. The best gastroprotective effect with lower cytotoxicity was found for the compound 8, cyperenoic acid and the p-anisidyl derivative 7.

Effects of allyl isothiocyanate from horseradish on several experimental gastric lesions in rats

Allyl isothiocyanate is well known to be a principal pungent constituent of horseradish and an agonist for transient receptor potential (TRP) A1. Ally isothiocyanate markedly inhibited the formation of gastric lesions induced by ethanol (1.5 ml/rat, p.o.), 0.6 M HCl (1.5 ml/rat, p.o.), 1% ammonia (1.5 ml/rat, p.o.), and aspirin (150 mg/kg, p.o.) (ED(50)=1.6, 2.2, 1.7, ca. 6.5 mg/kg, p.o.). It also significantly inhibited the formation of gastric lesions induced by indomethacin (20 mg/kg, p.o.), though the inhibition was ca. 60% at a high dose (40 mg/kg, p.o.). Furthermore, several synthetic isothiocyanate compounds also significantly inhibited ethanol and indomethacin-induced gastric lesions. Whereas, TRPV1 agonists, capsaicin and piperine, inhibited gastric lesions induced by ethanol, 1% ammonia, and aspirin, but had less of an effect on 0.6 M HCl-induced gastric lesions. With regard to mode of action, the protective effects of ally isothiocyanate on ethanol-induced gastric lesions were attenuated by pretreatment with indomethacin, but not with N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME), or ruthenium red. Pretreatment with indomethacin reduced the protective effects of piperine, and L-NAME reduced the effects of capsaicin and omeprazole. Furthermore, ruthenium red reduced the effects of capsaicin, piperine, and omeprazole. These findings suggest that endogenous prostaglandins play an important role in the protective effect of allyl isothiocyanate in ethanol-induced gastric lesions different from capsaicin, piperine, and omeprazole.

Gastroprotective and ulcer-healing activity of oleanolic acid derivatives: In vitro–in vivo relationships

The triterpene oleanolic acid 1 and its semisynthetic derivatives 2-7 were assessed for gastroprotective and ulcer-healing effect using human epithelial gastric cells (AGS) and human lung fibroblasts (MRC-5). The ability of the compounds to protect the AGS cells against the damage induced by sodium taurocholate (NaT), to stimulate the cellular reduced glutathione (GSH) and prostaglandin E(2) content, to enhance AGS and MRC-5 cell proliferation and to scavenge superoxide anion in vitro was studied. The cytotoxicity of the compounds was assessed towards MRC-5 and AGS cells. In addition, the gastroprotective activity of the compounds was assessed in vivo using the HCl/EtOH-induced ulcer model in mice. All the assayed compounds displayed a significant reduction of AGS cells damage after incubation with NaT. None of the studied compounds was active as a superoxide anion scavenger nor stimulated the GSH content in AGS cell cultures. Compounds 1, 2, 4 and 6 were able to increase the prostaglandin content in AGS cell cultures. Concerning the proliferation assays, a significant stimulating effect was observed for compounds 3 and 7 on AGS cells and for 1 and 7 on MRC-5 fibroblasts. Regarding cytotoxicity, derivatives 2, 4, 6 and 7 were less toxic than the parent compound oleanolic acid. Our results strongly support the predictive capacity of the in vitro assessment of gastroprotective activity allowing the reduction of experimental animals.

Subchronic toxicity study of water pepper extract in F344 rats

A subchronic toxicity study of water pepper extract (WPE) from Polygonum hydropiper L. was conducted in groups of 10 male and 10 female F344 rats fed powdered diets containing 0, 62.5, 250, 1000 or 4000 ppm concentrations for 13 weeks. Suppression of body weight gain due to decreased food consumption was observed in both sexes at 4000 ppm, and at autopsy, increase of relative weights was observed for the brain, liver, spleen, kidneys, and testes in these animals, suggestive of the reflection of the reduced body weights. At this dose, slight increases of blood urea nitrogen in both sexes and serum alanine aminotransferase, Na and Cl in females, were observed, suggestive of weak hepatic and renal toxicity, at least in females. The same females also exhibited slight decrease of red blood cells and haematocrit, slight increase of mean corpuscular volume and mean corpuscular haemoglobin, and minimal increase of splenic haemosiderin deposition, providing evidence of slight haemolytic anemia. On the other hand, enhanced accumulation of mast cells was observed in the mesenteric lymph nodes at 4000 ppm in males and 1000 and 4000 ppm in females. Considering the anti-anaphylactic properties of polygodial, a major constituent of WPE, the mast cell accumulation was concluded to be an adaptive change in response to the subchronic oral administration of WPE. Based on the present toxicity data, 1000 ppm was determined to be the no-observed-adverse-effect level, translating into 57.4 and 62.9 mg/kg/day for male and female rats, respectively.

Triterpene saponins with gastroprotective effects from tea seed (the seeds of Camellia sinensis)

Six new triterpene saponins, theasaponins A(1) (1), A(2) (2), A(3) (3), F(1) (4), F(2) (5), and F(3) (6), were isolated from the saponin fraction of the seeds of Camellia sinensis. The stereostructures of 1-6 were elucidated on the basis of chemical and physicochemical evidence. Theasaponin A(2) (2) showed an inhibitory effect on ethanol-induced gastric mucosal lesions in rats at a dose of 5.0 mg/kg, p.o., and its activity was more potent than that of omeplazole. Structure-activity relationships for theasaponins on ethanol-induced gastroprotective activities may be suggested as follows: (1) the 28-acetyl moiety enhances activity; (2) theasaponins having a 23-aldehyde group exhibit more potent activities than those with a 23-hydroxymethyl group or a 23-methoxycarbonyl group.

Rediscovery of known natural compounds: nuisance or goldmine?

Do all natural compounds have a distinct biological activity, or are most of them merely biosynthetic debris? Many natural compounds have important biological functions, and certainly many more of the ample 200,000 currently known will ultimately prove to be more than just 'secondary metabolites'. The question is how to select the most promising candidates for potential new drugs. 'Rediscovery' of known natural compounds is regarded as a nuisance or disappointment by scientists involved with the identification of novel compounds. The other side of the coin, however, is that the discovery that a particular compound occurs in unrelated species can be a valuable clue toward the identification of a novel receptor or enzyme. Here, we put forward the hypothesis that when a natural compound occurs in unrelated species, it must have an important biological function by interacting with a specific molecular target. This is because it is extremely improbable that in nature one particular compound is synthesized in totally unrelated species for no reason at all. For many compounds occurring in unrelated species, it is already known that they act on specific molecular targets. For others, it is just known that they occur in different species. In some cases, biological activities are known but not the underlying mechanisms of action. It is from this category of compounds that important discoveries are likely to be made. Some (around 70) of them were identified. They represent important clues from nature offering an alternative approach to the classical screening of large numbers of compounds.

Inhibition of the mitochondrial ATP synthesis by polygodial, a naturally occurring dialdehyde unsaturated sesquiterpene

Polygodial is a naturally occurring sesquiterpene dialdehyde that exhibits several pharmacologically interesting activities. Among them, its antifungal properties have been more thoroughly studied. The mitochondrial ATPase has been suggested as one of the possible targets for polygodial action. However, its mechanism of action is not well defined yet. The effect of polygodial on the mitochondrial energy metabolism is described in this paper. Polygodial inhibited ATP synthesis coupled to succinate oxidation in beef-heart submitochondrial particles at concentrations (IC(50)=2.4+/-0.1 microM) which marginally affected electron transport and ATPase activity (IC(50)=97+/-4 microM). A transitory stimulation of the electron transport in intact rat liver mitochondria in state 4 was also obtained at low polygodial concentrations (EC(50)=20+/-4 microM). These results suggest that polygodial uncouples ATP synthesis from electron transport at low concentrations. Similar concentrations of polygodial partially abolished the ANS fluorescence enhancement (IC(50)=2.2+/-0.4 microM) induced by succinate oxidation in submitochondrial particles but did not collapse the DeltapH. We postulate that polygodial uncouples mitochondrial ATP synthesis by affecting the electrical properties of the membrane surface and consequently collapsing the membrane potential (Deltapsi) and/or the localized transmembrane pH difference (DeltapH(S)) without affecting the DeltapH between the two bulk aqueous phases (DeltapH(B)). The relevance of these findings for the understanding of the biochemical basis of the antifungal activity of polygodial and the evaluation of its potentiality as a therapeutic agent are discussed.

Bioactive Saponins and Glycosides. XXIII. Triterpene Saponins with Gastroprotective Effect from the Seeds of Camellia sinensis-Theasaponins E3, E4, E5, E6, and E7-

The saponin fraction from the seeds of the tea plant [Camellia sinensis (L.) O. KUNTZE (Theaceae)] was found to exhibit potent protective effects on ethanol- and indomethacin-induced gastric mucosal lesions in rats. Five new triterpene saponins, theasaponins E3 (1), E4 (2), E5 (3), E6 (4), and E7 (5), were isolated together with 11 known saponins from the saponin fraction. The chemical structures of 1-5 were elucidated on the basis of chemical and physicochemical evidence. Among the isolated saponins, theasaponins E1 (6), E2 (7), and E5 (3) and assamsaponin C (10) showed an inhibitory effect on ethanol-induced gastric mucosal lesions at a dose of 5.0 mg/kg, p.o. and their activities were stronger than that of omeplazole. With regard to the structure-activity relationships of theasaponins, the following structural requirements for a protective effect on ethanol-induced gastric lesions were suggested; 1) the 21- and/or 22-acyl groups are essential for the activity, 2) acetylation of the 16-hydroxyl group reduce the activity.

Gastroprotective effects of phenylpropanoids from the rhizomes of Alpinia galanga in rats: structural requirements and mode of action

The effects of 1'S-1'-acetoxychavicol acetate and related phenylpropanoids isolated from the rhizomes of Alpinia galanga on ethanol-induced gastric lesions in rats were examined. Among them, 1'S-1'-acetoxychavicol acetate and 1'S-1'-acetoxyeugenol acetate markedly inhibited the ethanol-induced gastric mucosal lesions (ED(50)=0.61 and ca. 0.90 mg/kg). In addition, 1'S-1'-acetoxychavicol acetate inhibited the lesions induced by 0.6 M HCl (ED(50)=0.73 mg/kg) and aspirin (ED(50)=0.69 mg/kg) but it did not show a significant effect on indomethacin-induced gastric lesions and acid output in pylorus-ligated rats at doses of 0.5-5.0 mg/kg. From the gastroprotective effects of various related compounds, the 1'-acetoxyl group of 1'S-1'-acetoxychavicol acetate and 1'S-1'-acetoxyeugenol acetate was found to be essential for their strong activity. With regard to the mode of action, the gastroprotective effects of 1'S-1'-acetoxychavicol acetate were attenuated by pretreatment with indomethacin and N-ethylmaleimide, and 1'S-1'-acetoxychavicol acetate significantly increased the glutathione levels of gastric mucosa in rats. These findings suggest that endogenous prostaglandins and sulfhydryl compounds are involved in the protective effect of 1'S-1'-acetoxychavicol acetate.