Virginia Motilva

Evidence for protective and antioxidant properties of rutin, a natural flavone, against ethanol induced gastric lesions.

This study was designed to determine the ulcer-protecting effects of rutin, a natural flavone, against gastric lesions induced by 50% ethanol, the experimental model related to lesion pathogenesis with production of reactive species. The possible involvement of sulphydryl compounds (SH), neutrophil infiltration, and the capacity of this flavone to restrain the oxidative process produced in the gastric tissue were also investigated. The levels of thiobarbituric acid (TBA, as index of lipid peroxidation), the myeloperoxidase activity (MPO, as a marker of neutrophil infiltration), the content of mucosal sulphydryls (SH) groups and the activity of glutathione peroxidase (GSH-Px, an important antioxidant enzyme) were determined. Pretreatment with the highest dose of rutin (200 mg/kg), 120 min before 50% ethanol, resulted in the most effective necrosis prevention. TBA reactive substances in the gastric mucosa, were increased by ethanol injury, and this increase was inhibited by the administration of 200 mg/kg of rutin. However, the flavonoid was not able to modify the ethanol-induced neutrophil infiltrate expressed as myeloperoxidase activity. Exposure of the gastric mucosa to 50% ethanol induced a significant diminution in gastric non-protein SH content; this parameter also was not modified by the treatment with rutin. GSH-Px activity decreased in the gastric mucosa after ethanol-treatment. In contrast, rutin at all tested doses induced a significant increase in this enzymatic activity, higher than in control group. These results suggest that the gastroprotective effect of rutin in this experimental model appears through an anti-lipoperoxidant effect, and also by enhancement of the anti-oxidant enzymatic (GSH-Px) activity.

Mediterranean Diet and Health: Biological Importance of Olive Oil

Olive oil, the main fatty component of the Mediterranean diet, is characterized by consisting of monounsaturated fatty acids as well as by its elevated content in antioxidant agents. This oil exhibits numerous biological functions which are beneficial for the state of health. A diet rich in monounsaturated fatty acids provides an adequate fluidity to the biological membranes, diminishing the hazard of lipid peroxidation which affects polyunsaturated fatty acids. Moreover, the antioxidants present in olive oil are able to scavenge free radicals and afford an adequate protection against peroxidation. Regarding the heart, olive oil decreases the plasmatic levels of LDL-cholesterol and increases those of HDL-cholesterol, hence diminishing the risk of suffering from heart complaints. In this context, it has been suggested that increased consumption of monounsaturated fatty acids in place of polyunsaturated fatty acids will render circulating lipoproteins less sensitive to peroxidation and thereby diminish the development of atherosclerosis. Olive oil has also been proven to contribute to a better control of the hypertriglyceridemia accompanying diabetes and may reduce the risk of breast cancer and colorectum. On the other hand, several investigations have suggested that olive oil can be beneficial in inflammatory and autoimmune diseases, such as rheumatoid arthritis. In this sense, some reports have indicated that olive oil modifies inflammatory cytokines production. As for the digestive system, olive oil enhances gallbladder emptying consequently reducing cholelithiasis risk, decreases the pancreatic exocrine secretion and gastric secretory function in response to food. Finally, it has been demonstrated that a diet rich in olive oil is associated with a high percentage of gastric ulcer healing and affords a higher resistance against non steroidal antiinflammatory drugs-induced gastric ulcerogenesis.

Antiulcer and Gastroprotective Effects of Quercetin: A Gross and Histologic Study

This study was designed to determine the cytoprotective properties of quercetin and the involvement of endogenous prostaglandins in mucosal injury produced by absolute ethanol. Gastric glands were also analyzed histologically. Oral pretreatment with the highest dose of quercetin (200 mg/kg), 120 min before absolute ethanol, was most effective in necrosis prevention. Subcutaneous administration of indomethacin (10 mg/kg) to the animals treated with quercetin (200 mg/kg) partially inhibited gastric protection. All treated groups showed a marked increase in the amount of gastric mucus although this increase was less in animals pretreated with indomethacin. Total proteins and the hexosamine content decreased in the groups receiving indomethacin. The histomorphometric evaluation of the gastric damage confirmed a significant increase in mucus production accompanied by a parallel reduction of gastric lesions with the highest dose of quercetin tested.

New Issues about Nitric Oxide and its Effects on the Gastrointestinal Tract

Over the last years the important role of nitric oxide (NO) as endogenous modulator of numerous physiological functions has been shown. NO is involved in the regulation of blood flow, maintenance of vascular tone, control of platelet aggregation, and modulation of the activity of the mastocytes. It also plays a key role as neurotransmitter in the central and peripheric nervous system (non adrenergic non colinergic, NANC, neurons), in the nervous control of the cerebral blood flow and in the neuroendocrine regulation or synaptic plasticity. However, NO shows a dual behavior: at physiological concentrations, released through the constitutive synthase (cNOS), it regulates house-keeping functions, whereas its overproduction by the inducible isoenzyme (iNOS) exhibits cytotoxic activity because interacting with reactive species producing peroxinitrites (ONOO) and other compounds, which are highly damaging for the tissues. In the gastrointestinal tract (GIT) NO participates in the modulation of the smooth musculature tone, such as the regulation of intestinal peristaltism, gastric emptying and antral motor activity. It also regulates acid and gastric mucus secretion, alkaline production, and is involved in the maintenance of mucosal blood flow. In physiological conditions, NO acts as an endogenous mediator modulating both, the repairing and integrity of the tissues, and exhibits gastroprotective properties against different types of aggressive agents. However, high concentrations of NO are related to numerous pathological processes of GIT including peptic ulcer, chronic gastritis, gastrointestinal cancer, bacterial gastroenteritis, celiac or chronic inflammatory bowel diseases. Recently, this hypothesis that cNOS is always beneficial and iNOS is always deleterious, has been questioned, since that a series of data suggest that the increase of cNOS activity could be responsible for the derived pathological changes and, by contrast, NO liberated by the inducible isoenzyme might play a repairing effect in certain pathological disorders. The pharmaceutical industry is really interested in proving the clinical benefits of the mediator. Numerous NO-donor drugs, nitrate derivatives, have been frequently used in the cardiovascular diseases due to their vasodilating properties, which allow an enhancement of coronary blood flow. More recently, the protective effect of NO against non steroidal antiinflammatory drugs (NSAID)-gastroenteropathy has been shown, because its vasodilating and antioxidant properties render it a potentially useful agent. Different NSAID, including acetyl salicylic acid, diclofenac or naproxen, have been formulated by attaching a NO releasing-moiety. These NO-NSAID, antiinflammatories combined with precursors of the mediator, or with inhibitors of the inducible synthase, are currently being evaluated. However, although the pharmacotherapeutical possibilities of NO are considerable, it is necessary to elucidate the exact mechanisms derived from stimulation/inhibition of the isoenzymes in order to determine the clinical utility of NO-donors.

ROLE OF ENDOGENOUS SULPHYDRYLS AND NEUTROPHIL INFILTRATION IN THE PATHOGENESIS OF GASTRIC MUCOSAL INJURY INDUCED BY PIROXICAM IN RATS

In the present report we studied the formation of severe gastric erosions produced in fasted rats by intragastric administration of piroxicam (PRX), an enolic acid-derived NSAID. The time course of gastric damage and the possible role of mucus secretion, endogenous sulphydryl compounds, changes of gastric vascular permeability and neutrophil infiltration in the development of PRX-induced gastric lesions were also investigated. PRX dose-dependently (1.25–20 mg/kg) caused acute gastric haemorrhagic erosion in the rat. The lesions increased with time until 9 hr after dosing. Mucus secretion did not change significantly with respect to the control group with 5, 10 and 20 mg/kg of PRX at different times (3 and 6 hours) of treatment. There was also no increase in the concentration of its components. In addition, oral pretreatment of the animals with PRX did not significantly change the amount of dye trapped in the stomach. In contrast, non-protein SH fraction was decreased after administration of PRX and MPO activity as an index of neutrophil infiltration was significantly increased. These results suggest that independently of the PRX dose, depletion of endogenous non-protein SH and neutrophil infiltration could play an important part in the pathogenesis of gastric mucosal injury induced by PRX.

Melatonin protects against gastric ischemia-reperfusion injury in rats

De La Lastra CA, Cabeza J, Motilva V, Martin MJ. Melatonin protects against gastric ischemia‐reperfusion injury in rats. J. Pineal Res. 1997; 23:47–52.

New paradigms in chronic intestinal inflammation and colon cancer: role of melatonin.

Abstract:  In intestinal bowel disease (IBD), immune‐mediated conditions exert their effects through various cells and proinflammatory mediators. Recent data support a participation of the endoplasmic reticulum stress and mitochondrial dysfunctions in IBD. Moreover, it is evident that chronic degenerative pathologies, including IBD, share comparable disease mechanisms with alteration in the autophagy mechanisms. Chronic inflammation in IBD exposes these patients to a number of signals known to have tumorigenic effects. This circuitry of inflammation and cancer modifies apoptosis and autophagy, and promotes cellular cycle progression, invasion, and angiogenesis. Melatonin has been shown as a specific antioxidant reducing oxidative damage in both lipid and aqueous cell environments. However, several studies provide further insight into the molecular mechanisms of melatonin action in the colon. In this line, recent data suggest that melatonin modulates autophagy and sirtuin activity. An anti‐autophagic property of melatonin has been demonstrated, and it could contribute to its anti‐oncogenic activity. Nevertheless, there is no information about whether antitumoral effects of melatonin on colon cancer are dependent on autophagy. Sirtuins have pleiotropic effects on cancer development, being reported both as facilitator and as suppressor of colon cancer development. Sirtuins and melatonin are connected through the circadian clock machinery, and melatonin seems able to correct the alterations in sirtuin activity associated with several pathological conditions. Autophagy and sirtuin activities are linked through 5′AMP‐activated protein kinase (AMPK) activation, which switches on autophagy and increases sirtuin. The effect of melatonin on AMPK and the impact of this effect on IBD and colon cancer remain an open question.

Mechanisms involved in gastric protection of melatonin against oxidant stress by ischemia-reperfusion in rats

The generation of oxygen-derived free radicals has been suggested to be significantly responsible for ischemia-reperfusion injury in gastrointestinal tissues. Biochemical mechanisms include the xanthine-oxidase-derived oxidants mainly the superoxide anion. Both in vitro and in vivo studies have demonstrated that the pineal hormone melatonin possesses free radical scavenging and antioxidant properties. The indolamine has been effective in reducing the induced-oxidative damage in several tissues and biological systems. The aim of this study was to elucidate additional antioxidant mechanisms responsible for the gastroprotection afforded by the indolamine in ischemia-reperfusion gastric injury. Therefore, changes of related enzymes such as xanthine-oxidase, superoxide dismutase, glutathione reductase and total glutathione were investigated. Our results showed that treatment with 5, 10 or 20 mg kg(-1) of melatonin, administered i.p., clearly diminished the percentage of damage to 49.56 +/- 17.20, 37.54 +/- 11.40 and 26.70 +/- 8.12 respectively. Histologically there was a reduction of exfoliation of superficial cells and blood cell infiltration. These protective effects were related to a significant reduction of xanthine-oxidase activity (2.23 +/- 0.38 U/mg prot x 10(-4) with the highest tested dose of melatonin) and significant increases in superoxide dismutase reaching a value of 6.20 +/- 0.56 U/mg prot with 25 mg/Kg of melatonin and glutation reductase activities (417.44 +/- 29.72 and 649.43 +/- 81.11 nmol/min/mg prot with 10 and 20 mg/Kg of melatonin). We conclude that the free radical scavenger properties of melatonin mainly of the superoxide anion, probably derived via the xanthine-oxidase pathway, and the increase of antioxidative enzymes significantly contributes to mediating the protection by the hormone against ischemia-reperfusion gastric injury.

Anti-oxidant mechanisms involved in gastroprotective effects of quercetin.

Abstract The anti-ulcerogenic and anti-oxidant effects of various flavonoids have been frequently reported. We investigated the cytoprotective properties of quercetin, a natural flavone, in gastric mucosal injury induced by 50% ethanol, since in this experimental model the pathogenesis of the lesions has been related with production of reactive oxygen species. The involvement of neutrophil infiltration and the capacity of this flavonoid to restrain the oxidative process produced in the gastric tissue after ethanol administration were also investigated. Oral pretreatment with the highest dose of quercetin (200 mg/kg), 120 min before absolute ethanol was the most effective anti-ulcer treatment. Thiobarbituric acid reactive substances in the gastric mucosa, an index of lipid peroxidation, were increased by ethanol injury, but the increase was inhibited by the administration of 200 mg/kg of quercetin. This dose also induced a significant enhancement in the levels of mucosal non-protein SH compounds (important anti-oxidant agents) and in glutathione peroxidase activity. Exposure of the gastric mucosa to 50% ethanol induced a significant increase in myeloperoxidase activity, an index of neutrophil infiltration. Flowever, quercetin was not able to modify the increase in enzymatic activity generated by the necrotizing agent. The activity of superoxide dismutase enzyme involved in several antioxidant processes was also not significantly modified after quercetin treatment. These results suggest that the anti-ulcer activity of quercetin in this experimental model could be partly explained by the inhibition of lipid peroxidation, through decrease of reactive oxygen metabolites. However, the inhibition of neutrophil infiltration or the increase of superoxide dismutase activity does not appear to be involved in gastroprotective effect of this flavonoid.

Acute and chronic responses associated with adrenomedullin administration in experimental colitis.

Adrenomedullin (AM) is a 52 amino acid peptide and member of the calcitonin gene-related peptide (CGRP) super family. Given that AM has emerged as a potential immuno-regulatory and anti-inflammatory agent in various experimental models, this study has deepened into its possible therapeutic effect in intestinal inflammation analyzing the responses in both acute and chronic (14 and 21 days) phases of TNBS-induced colitis in rats. In the acute model, AM treatment reduced the incidence of diarrhea and the severity of colonic damage, and improved the survival rate at the three doses assayed (50, 100, and 200ng/kg animal). AM administration was able to reduce the early production of TNF-alpha and collaborated to maintaining basal levels of IFN-gamma and IL-10. In the chronic studies the peptide attenuated the extent of the damage with lesser incidence of weight loss and diarrhea (50 and 100ng/kg animal). Cellular neutrophil infiltration, with the subsequent increase in myeloperoxidase (MPO) levels caused by TNBS, was reduced after chronic AM administration. The peptide played a role in the evolution of Th1/Th2 cytokines balance and chronic disease recuperation: levels of proinflammatory TNF-alpha and IFN-gamma decreased and anti-inflammatory IL-10 increased significantly. Cyclooxygenase-2 (COX-2) and nitric oxide synthase (iNOS) protein expression were not modified by AM administration, although a reduction of nitric oxide (NO) production could be detected in the chronic model. These results support a role of AM as an anti-inflammatory factor with beneficial effects in intestinal inflammatory colitis.