[Effects of tannic acid and tannic acid-starch on the experimental gastric ulcer in rat]

Tannic acid is a gastroprotective that regulates inflammation and oxidative stress

This study investigated the gastroprotective effect of TA against gastric ulcer in mice, and its possible mechanisms of action. The effects were investigated in a model of ethanol and ethanol/HCl induced ulcers, and physical barrier test. Quantification of oxidative stress mediators and inflammatory cytokines in gastric tissue was performed. The involvement of sulfhydryl compounds (-SH), nitric oxide (NO), prostaglandin E₂ (PGE₂), potassium channels (K ⁺_ATP) and opioid receptors in gastroprotection were investigated. Oral treatment with TA at a dose of 50 mg/kg resulted in 97.96% and 94.20% (reduction in gastric injury) of gastroprotection, against injuries caused by ethanol and ethanol/HCL, respectively, in addition to having a systematic effect. TA promotes increased levels of superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH), as well as reduced levels of malondialdehyde (MDA) reaction to thiobarbituric acid and myeloperoxidase (MPO). In addition, there was reduction in levels of tumor necrosis factor alpha (TNF-α) and interleukins (IL) IL-1β and IL-6 and increased IL-10. The gastroprotective activity of TA involved K ⁺_ATP channels and the production of -SH, NO and PGE_2, demonstrating multiple mechanisms of action. The results of the present study suggest that TA may be a gastroprotective agent counteracting oxidative and inflammatory stress.

Tannins, peptic ulcers and related mechanisms

This review of the current literature aims to study correlations between the chemical structure and gastric anti-ulcer activity of tannins. Tannins are used in medicine primarily because of their astringent properties. These properties are due to the fact that tannins react with the tissue proteins with which they come into contact. In gastric ulcers, this tannin-protein complex layer protects the stomach by promoting greater resistance to chemical and mechanical injury or irritation. Moreover, in several experimental models of gastric ulcer, tannins have been shown to present antioxidant activity, promote tissue repair, exhibit anti Helicobacter pylori effects, and they are involved in gastrointestinal tract anti-inflammatory processes. The presence of tannins explains the anti-ulcer effects of many natural products.

Effect ofManilkara hexandra (Roxb.) Dubard against experimentally-induced gastric ulcers

Effects of the flavonoid rich fraction of the stem bark of Manilkara hexandra (Roxb.) Dubard, have been studied on ethanol, ethanol-indomethacin and pylorus ligated gastric ulcers in experimental animals. Oral administration of the ethyl acetate extract (extract A3) inhibited the formation of gastric lesions induced by ethanol in a dose dependent manner. The protective effect of extract A3 against ethanol induced gastric lesions was not abolished by pretreatment with indomethacin (10 mg kg(-1)). Further, extract A3 inhibited increase in vascular permeability due to ethanol administration. Extent of lipid peroxidation was significantly reduced in animals treated with extract. Extract A3 also inhibited the formation of gastric ulcers induced by pylorus ligation, when administered both orally and intraperitoneally. Moreover, pretreatment with extract A3 increased mucus production and glycoprotein content, which was evident from the rise in mucin activity and TC: PR ratio.

Antiulcer activity of the crude extract from the leaves of casearia sylvestris

In rats, administration of Casearia sylvestris extract derived from fresh and dried leaves protects stomach mucosa without changing gastric pH. In stress-induced acute lesions, the preventive effect of extract from dried leaves is more effective than extract from fresh leaves. In acetic acid-induced chronic ulcer, both extracts reduce the size of ulceration and increase the number of collagen fibers after 5 days of treatment, and these effects are similar with both extracts. These antiulcer activities of Casearia sylvestris may be due to the presence of volatile oils, tannins and triterpenerelated compounds.

Protective effect of cimetidine on tannic acid-induced gastric damage in rats

The effect of cimetidine on the acidified tannic acid-induced back diffusion of gastric acid and mucosal damage was investigated in the vagotomized rat. After intragastric irrigation for 1 to 3 h, tannic acid (20-500 mg kg-1) produced a dose-related increase in gastric volume and the loss of luminal H+. The change of mucosal permeability to the electrolyte, either the loss of H+ or the gain of Na+, K+, and Ca2+, induced by tannic acid was significantly diminished by the combination with intragastric cimetidine. However, intravenous injection of cimetidine did not protect this damage and back diffusion of acid neutralized intragastric cimetidine did not reduce the back diffusion of acid and Na+, K+, and Ca2+ output provoked by acid solution. Thus, the neutralizing action of cimetidine seems responsible.