| Abstract|| |
Recent studies have suggested that amoxycillin may possess gastroprotective effects in addition to its known antimicrobial properties. Therefore, the present study was undertaken to investigate the potential gastric protective effects of amoxycillin and to determine its possible mechanism(s) of action in rats. Ethanol-induced gastric mucosal lesions in rats were used as an animal model. Nonprotein sulphydryl levels were measured spectrophotometrically. The antioxidant effect of amoxycillin was studied by luminol-dependent chemiluminescence technique in-vitro. Amoxycillin produced marked protection against ethanol-induced gastric lesions. The protective effect of amoxycillin was lost by prior treatment with a dose of indomethacin that is known to inhibit prostaglandin biosynthesis without induction of gastric ulcers. Furthermore, the concentration of nonprotein sulphydryls decreased significantly in gastric mucosa after administration of ethanol. Treatment with amoxycillin prevented this depletion. Additionally, amoxycillin dose-dependently inhibited the phorbol myristate acetate stimulated luminol dependent chemiluminescence responses of isolated human polymorphonuclear leukocytes invitro. These data indicate that the gastric protection effects of amoxycillin against ethanolinduced lesions may include generation of mucosal prostaglandins, prevention of nonprotein of sulphydryl depletion and antioxidant properties.
|How to cite this article:|
Al Swayeh OA. Protective effect of amoxycillin on ethanol-induced gastric lesions in rats. Saudi J Gastroenterol 1998;4:90-5
Amoxycillin is a commonly used antimicrobial drug. Recent studies have implicated Helicobacter pylori pylori) in the pathogenesis of peptic ulcer diseases ,, . In 1987, Coghlan et al  reported that duodenal ulcer recurrence was dramatically reduced when H. pylori was eradicated. It has since been established that eradication of H. pylori prevents ulcer relapse, and this has been confirmed by many investigators , . As H. pylori is a bacterial infection, a high rate of cure from any antimicrobial therapy should be expected. On the basis of this assumption, several studies in recent years, have reported the effectiveness of amoxycillin either alone  or in combination with other drugs in prevention of relapse of peptic ulcer diseases ,,.
Recently, it has been suggested that amoxycillin might have other gastroprotective properties. Thus, it has been shown that amoxycillin afforded protection against gastric lesions induced by cysteamine  , reserpine  . Furthermore, Lam et al  , using an exvivo gastric chamber model in the rat, has reported that intragastric and intraperitoneal administration of amoxycillin dose-dependently protected the rat gastric mucosa from damage by ethanol. This protective effect of amoxycillin has been suggested to be mediated by prostaglandins since pretreatment with indomethacin was able to abolish this amoxycillin-induced gastric protection. However, the mechanism of action of amoxycillin has not been fully elucidated in this study. Therefore, the present study was undertaken in order to investigate the potential protective effect of amoxycillin and to determine its possible mechanisms of action against ethanol-induced gastric lesions in rats.
| Materials and Methods|| |
Drugs and chemicals were obtained as indicated Amoxycillin injection (Beechams Pharmaceutical, UK) was purchased locally. Luminol, phorbol myristate acetate (PMA), 5-5 dithio-bis - (2nitrobenzoic acid) (DTNB), ethylenediaminetetraacetic acid (EDTA), and reduced glutathione were purchased from Sigma Chemical Co, England. Indomethacin as "confortid" was purchased from Dumex, Denmark.
Amoxycillin was dissolved in water, whereas indomethacin was prepared in its solvent. The concentration of drugs was prepared in such a way that each rat received 0.5 ml/100 g body weight of drug solution. Amoxycillin was given intraperitoneally (i.p.) while indomethacin was injected subcutaneously (s.c.)
Male Wistar albino rats, of approximately the same age, weighing 200-250 g were obtained from the College of Medicine's Animal House, King Saud University, Riyadh, Saudi Arabia. The rats were maintained on a standard chow pellet diet and tap water ad libitum.
| Experimental Gastric Lesions|| |
The animals were food-deprived and kept in individual cages with raised mesh bottom to prevent coprophagia. They were allowed free access to water. After 24 hours, the rats were randomly allocated to groups of six or eight animals in each group, and water was withdrawn. The groups were then subjected to one of the following experiments.
Ethanol-Induced Gastric Lesions. Gastric mucosal injury was induced by the oral administration of 1 ml of 100% ethanol per rat and the animals were sacrificed one hour later under ether anesthesia. Immediately after opening the stomach by cutting along the greater curvature, the stomach was pinned on a cork board, lightly rinsed with saline, and the examination of gastric lesions was carried out under an illuminated stereomicroscope. The gastric lesions were identified by an independent observer unfamiliar with the protocol and scored according to the method described by Schiantarelli et al  . The sum of the scores in each group of rats was divided by the number of animals and expressed as mean score for lesions. In test animals, amoxycillin (12.5100 mg/kg, i.p.) was given 30 minutes before the administration of ethanol. Controls received the same volume of distilled water i.p. In some experiments, indomethacin (10 mg/kg, s.c) was administered one hour before the administration of ethanol to both control and treated groups.
Determination of Nonprotein Sulphydryl (NP-SH) Groups. In these experiments, following the same drug treatment schedules as described above, gastric glandular NP-SH concentration was measured according to the method of Sedlak and Lindsay Briefly, the glandular part of the stomach was cut, weighed and homogenized in ice-cold 0.02 MEDTA to give 5% homogenates. Aliquots of 5 ml of the homogenates were mixed in 15-m1 test tubes with 4 ml of distilled water and 1 ml of 50% trichloroacetic acid (TCA). The tubes were shaken intermittently for 15 minutes and centrifuged at 3000 x g for 10/minutes. Two milliliters of supernatant were mixed with 4 ml of 0.4 M Tris buffer at pH 8.9; 0.1 ml of DTNB was added and the sample was shaken. The absorbance was read within five minutes of addition of DTNB at 412 nM against a reagent blank (with no homogenates) in a spectrophotometer (Perkin-Elmer, Lamda 5). The final NP-SH concentrations were calculated by comparing the absorbance of test with calibration curve prepared by using reduced glutathione solution and expressed as µmole per gram of glandular tissue.
| Measurement of Reactive Oxygen Metabolites Production|| |
Chemiluminescence Measurement. The principle of the chemiluminescence (CL) assay is the oxidation of luminol by reactive oxygen species produced during phagocytosis. This was carried out according to previously reported methods , . Briefly, the blood was drawn from healthy human volunteers and the polymorphonuclear leukocytes (PMNs) were separated, counted and the viability was determined as described previously , . The reaction mixture consisted of 0.1 ml of isolated PMNs (5 x 10 6 /ml), 0.2 ml luminol (10 -5 M), 0.5 ml PBS (Phosphate - buffered saline) to which 0.2 ml of soluble PMA (2 ng/ml) was added. The light output in millivolt (mV) was immediately read and continuously recorded on an LKB (Wallac) chart recorder for a period of 30 minutes. The maximum CL response observed was taken. The effect of the drug on the luminoldependent CL was determiend following addition of different concentrations of amoxycillin (0.312 - 5 mg/ml) to the cells prior to stimulation by PMA at 37°C and was measured in a luminometer (LKB 1251, Wallac). The results were expressed as CL maximum peak response in mV.
| Statistical Analysis|| |
The results are presented as mean + S.E.M. Statistically significant differences between means were calculated by Unpaired Student's t-test or by analysis of variance (ANOVA) as appropriate.
A probability of P < 0.05 was considered significant.
| Results|| |
Ethanol-Induced Gastric Lesions
Administration of ethanol resulted in the production of gastric mucosal lesions consisting of elongated dark bands generally parallel to the long axis of the corpus of the stomach. Pretreatment with amoxycillin attenuated ethanol-induced gastric lesions in a dose-dependent manner [Table - 1].
Effect of Pretreatment with Indomethacin on Amoxycillin-induced Gastric Protection
Prior treatment of animals with indomethacin slightly aggravated ethanol-induced gastric lesions. However, indomethacin pretreatment greatly reduced the gastric protection by amoxycillin against ethanol-induced gastric mucosal injury [Table - 1].
Effect of Amoxycillin on Gastric Mucosal NP-SH Content
The gastric mucosal NP-SH content was significantly depleted after the administration of ethanol. Amoxycillin alone did not produce any significant change in NP-SH levels in the stomach of rats which were not exposed to ethanol. However, treatment with amoxycillin significantly inhibited ethanol-induced depletion of NP-SH levels and restored it towards control values [Table - 2].
Effect of Amoxycillin on the Luminol-Dependent Chemiluminescence (CL) Responses of PMNs Stimulated with PMA
Amoxycillin dose-dependently inhibited PMAstimulated CL responses of isolated human PMNs [Table - 3]. Amoxycillin, in the concentrations used, did not induce CL response of unstimulated PMNs in the presence of luminol. Similarly, the viability of the cells was unaffected in the presence of various concentrations of amoxycillin (data not shown).
| Discussion|| |
This study demonstrates that the antimicrobial agent, amoxycillin, significantly attenuates ethanoinduced gastric lesions in rats. Furthermore, it furnishes data that elucidates the potential mechanisms of amoxycillin-induced gastric protection. These results confirmed the previously published reports that amoxycillin possesses antioxidant and cytoprotective properties , .
Amoxycillin exerts a dose-dependent inhibitory action on gastric mucosal lesions induced by ethanol. The fact that pretreatment of rats with a dose of indomethacin which is known to inhibit PGs biosynthesis  , reduced the protective effects of amoxycillin against ethanol-induced gastric injury may suggest that the endogenous release of mucosal PGs is a prerequisite for the protective effect of the drug. This finding is consistent with a previously published report  . In this context, PGs are known as cytoprotective agents and have been implicated as a defensive factor for the protection against gastroduodenal injuries , including those induced by ehtanol in rats  .
Along with PGs, NP-SH have also been implicated in the defensive mechanism of gastric mucosal injury. Thus, gastric mucosal injury has been shown to be associated with a depletion of NPSH concentration in the gastric mucosa of experimental animals and in humans, while its restoration to a critical level affords protection ,,, .
Furthermore, the inability of cytoprotective PGs to exert their effect in the presence of SH-blockers suggests that thiol groups may play an important role in mucosal defense  . In the present study, pretreatment with amoxycillin dose-dependently reversed ethanol-induced depletion of NP-SH and restored the level towards normal. These findings suggest that NP-SH may be involved in the gastric protective effect of amoxycillin.
There is evidence to suggest that oxygen derived free-radicals (ODFRs) are involved in the pathogenesis of gastric lesions induced by ethanol ,,, . Besides the animal studies, ODFRs have also been implicated in the pathogensis of human gastroduodenal diseases. Thus, increased free radical activities have been reported to be present in plasma  and in duodenal biopsies of duodenal ulcer patients  . Furthermore, H. Pylori infection causes enhancement of free radical activities implicating the role of H. pylori in the pathogenic mechanisms , . The ability of amoxycillin to inhibit PMA-stimulated luminol dependent CL response of PMNs suggest an antioxidant effect of amoxycillin in-vitro. This finding corroborates the observation of Hao et al  who also reported an antioxidant mechanism of action of amoxycillin against reserpine-induced gastric lesions. Thus, the mechanism of gastric protection of amoxycillin against ethanol-induced gastric lesions may be, at least in part, due to an antioxidant effect.
In conclusion, this study demonstrates that amoxycillin possesses gastric protection effects against ethanol-induced gastric lesions and confiurus the gastroprotective effect of amoxycillin. The mechanisms of gastric protection afforded by amoxycillin may be attributed to: a) prevention of ethanol-induced mucosal PGs depletion b) prevention of ethanol-induced depletion of gastric NP-SH concentrations; and c) antioxidant effects.
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Othman Abdullah Al Swayeh
Department of Medical Pharmacology (31), College of Medicine, King Saud University, P.O. Box 2925, Riyadh 11461
Source of Support: None, Conflict of Interest: None
[Table - 1], [Table - 2], [Table - 3]