Fluorographic study on the oxidative stress in the process of gastric mucosal injury: attenuating effect of vitamin E

Vitamin E: a potential therapy for gastric mucosal injury

CONTEXT

Many scientific reports have shown the involvement of oxidative stress and inflammation as well as diminished gastroprotective substances in the pathogenesis of gastric lesions using various models. Therefore, treatment with antioxidants like tocopherol and tocotrienol may afford beneficial effects in attentuating the formation of the gastric lesions.

OBJECTIVE

The aim of this work was to summarize documented reports on the effects of vitamin E on various models of gastric lesion.

METHODS

A literature search was performed from databases in Medline (PubMed), Web of Science, ScienceDirect, and Googlescholar from June to December 2013.

RESULTS AND CONCLUSION

The potential roles of tocopherol and tocotrienol in modifying the effects of ulcerogenic agents are discussed in this review. The protective effects of the vitamin E might involve ameliorating oxidative stress and inflammation as well as restoration of endogenous gastroprotective substances. This vitamin has the potential to be used as a therapy for gastric mucosal injury.

Influence of vitamin E on gastric mucosal injury induced by Helicobacter pylori infection

We investigated the effect of vitamin E on gastric mucosal injury induced by Helicobacter pylori (H. pylori) infection. Male Mongolian gerbils were divided into 4 groups (normal group without H. pylori infection, vitamin E-deficient, -sufficient and -supplemented groups with H. pylori infection). Following oral inoculation with H. pylori (ATCC43504 2 x 10(8) CFU), animals were fed diets alpha-tocopherol 2 mg/100 g diet in the normal and vitamin E-sufficient groups and alpha-tocopherol 0.1 mg/100 g and 50 mg/100 g in the vitamin E-deficient and -supplemented groups, respectively, for 24 weeks. Chronic gastritis was detected in all gerbils inoculated H. pylori. Gastric ulcer was detected in 2 of 7 gerbils only in the vitamin E-deficient group. In the vitamin E-deficient group, myeloperoxidase activity and mouse keratinocyte derived chemokine (KC) in gastric mucosa was significantly higher than in the vitamin E supplemented group. Subsequently, in an in vitro study expression of CD11b/CD18 on neutrophils was enhanced by H. pylori water extract. This effect was suppressed in a dose dependent manner by the addition of alpha-tocopherol. These results suggest that vitamin E has a protective effect on gastric mucosal injury induced by H. pylori infection in gerbils, through the inhibition of accumulation of activated neutrophils.

Do vitamin E supplements in diets for laboratory animals jeopardize findings in animal models of disease?

Vitamin E has been supplemented to the diets of farm animals to improve fertility, health, growth rates and quality of animal products. Because of the positive experience obtained in farm animals, vitamin E has been added in increasing amounts to the diets of laboratory animals. Today, vitamin E levels in standard rodent maintenance diets range from 30 mg/kg (France, United States), 90-120 mg/kg (Netherlands, United Kingdom) to as much as 200 mg/kg (Germany). While increasing fertility and health of laboratory animals, these vitamin E supplements affect diverse pathophysiological conditions and thus the outcome of animal models of disease. Because of the large variability of vitamin E levels between laboratories within and between different countries, results obtained in established animal models may no longer be comparable and/or reproducible. Researchers should be aware of these vitamin E supplements and carefully control for potential effects in their respective animal models that involve--or may involve--the generation of reactive oxygen species.

Role of endogenous nitric oxide in ischaemia-reperfusion injury of rat gastric mucosa

It has been suggested that endogenous nitric oxide may act as a protective factor for gastric mucosa since nitric oxide increases blood flow and may scavenge certain oxyradicals. We tested the hypothesis that nitric oxide protects rat gastric mucosa against ischaemia-reperfusion stress. Gastric ischaemia was induced by clamping the left gastric artery for 20 min. Rats were treated with two kinds of specific inhibitors of nitric oxide production, NG-nitro-L-arginine or NG-monomethyl-L-arginine. Gastric mucosal integrity was continuously monitored by measuring the blood-to-lumen clearance of [51chromium]-labelled ethylenediaminetetraacetic acid (EDTA) under control conditions, during ischaemia and after reperfusion. Oxidative stress in gastric mucosa was assessed by measuring dichlorofluorescein (DCF) fluorescence intensity before ischaemia and after reperfusion. Blockade of nitric oxide resulted in a significant increase in [51Cr]-EDTA clearance and DCF fluorescence intensity after reperfusion. These effects of nitric oxide inhibitors were attenuated by pretreatment with L-arginine. In conclusion, these findings support the hypothesis that endogenous nitric oxide acts as an important protective factor against ischaemia-reperfusion stress in rat gastric mucosa.

Up-regulation of oxygen-derived free radicals by interleukin-1 in hepatic ischemia/reperfusion injury

BACKGROUND

Oxygen-derived free radicals (FRs) are critical mediators of ischemia/reperfusion injury. Inflammatory cytokines have been shown to play important roles in tissue injury. To examine the relationship between FRs and interleukin-1 (IL-1) in hepatic ischemia/reperfusion injury, we used interleukin-1 receptor antagonist (IL-1ra) to block endogenous IL-1 production in a rat model of hepatic ischemia/reperfusion.

METHODS

Female SD rats were subjected to 30 min of hepatic ischemia followed by reperfusion. The animals were divided into two groups, control group and IL-1ra-treated group, according to the rinse solution. In both groups, FR production, histological changes, and interactions between leukocytes and endothelial cells were analyzed in the course of reperfusion.

RESULTS

In the control group, production of FRs increased significantly after 60 min of reperfusion. After 60 and 180 min of reperfusion, histological examination showed atrophy and degeneration of hepatocytes. Hepatic microcirculation demonstrated a marked increase in the number of leukocytes adherent to endothelial cells and of injured cells after reperfusion. In the IL-1ra-treated group, IL-1ra pretreatment markedly reduced FR production after 60 min of reperfusion, the number of leukocytes adherent to endothelial cells, and tissue injury.

CONCLUSION

These data clearly show an important role for IL-1 in the induction of FR production, leukocyte adhesion, and tissue injury after hepatic ischemia/reperfusion injury.

Role of endothelin-1 in repeated electrical stimulation-induced microcirculatory disturbance and mucosal damage in rat stomach

The aim of the present study was to clarify the involvement of endogenous endothelin in the pathogenesis of gastric mucosal damage. The rat stomach was exposed and repeated electrical stimulation (RES) was applied to the small arterial wall close to the lesser curvature. Significant mucosal haemorrhagic lesions (ulcer and erosion) were noted within 30 min after RES. Intravital microscopic observations revealed that an arteriolar constriction occurred in the submucosal layer of the rat stomach approximately 5 min after the completion of RES. Following the arteriolar constriction, the mucosal blood flow of the rat stomach, which was monitored by using a laser Doppler velocimeter, decreased to approximately 30% of the control value. The plasma immunoreactive endothelin-1 level in the regional blood of the stomach was significantly increased immediately after RES preceding the decrease in mucosal blood flow. Immunohistochemical studies revealed that endothelin-1 and big-endothelin-1 were detectable in the arteriolar endothelium around the muscularis mucosa, supporting the involvement of endothelin-1 in RES-induced mucosal ischaemia. In addition, BQ-123, a specific antagonist of the endothelin A (ETA) receptor, attenuated the reduction of blood flow and the development of haemorrhagic lesions observed in gastric mucosa subjected to RES. The results of the present study suggest that an excessive production of endothelin-1 in the arteriolar endothelium leads to microvascular derangements accompanied by haemorrhagic alterations of the gastric mucosa.

Impact of vitamin E supplement in standard laboratory animal diet on microvascular manifestation of ischemia/reperfusion injury

Aimed at improving animal fertility and health, diets for farm and laboratory animals have over the last few years been supplemented with increasing amounts of the antioxidant vitamin E. We now demonstrate by intravital microscopy that feeding hamsters with a vitamin E-supplemented "standard" rodent diet (60 ppm vitamin E) significantly reduces the microvascular manifestations of ischemia/reperfusion injury when compared to animals fed a nonsupplemented diet. Postischemic leukocyte adhesion to venular endothelium was reduced from 770 +/- 204 cells/mm2 at 24 h after reperfusion in control animals on the nonsupplemented diet to 403 +/- 105 cells/mm2 in animals on the "standard" rodent diet (means +/- SD, n = 7 animals per group, p < 0.01). Animals on the nonsupplemented diet showed a dramatic loss of capillary perfusion density until 7 days after reperfusion (to 21 +/- 13% of preischemic baseline values), whereas this loss was significantly attenuated (to 71 +/- 12% of preischemic values, p < 0.01) in animals on the "standard" rodent diet. No difference in the extent of reperfusion injury was seen between animals on the "standard" rodent diet and animals on diets with substantially higher vitamin E supplements (300 ppm-30,000 ppm). Besides underscoring the benefit of vitamin E in reducing the extent of ischemia/reperfusion injury, this study raises the concern that vitamin E supplements in "standard" laboratory animal diets may have a far-reaching impact on biomedical research by jeopardizing established animal models of disease.

Oxidative stress in gastric mucosal injury: role of platelet-activating factor-activated granulocytes

Temporal and spatial changes due to oxidative stress in the rat gastric mucosa were visualized and quantified during the process of mucosal hemorrhagic change. The fluorescence associated with dichlorofluorescein (DCF), a hydroperoxide-sensitive fluorochrome, increased 30 min after repeated electrical stimuli to the gastric artery. The increase in the fluorescence was enhanced in the area between two adjacent collecting venules. The content of platelet-activating factor (PAF), the activity of myeloperoxidase (MPO) in the gastric mucosa, the area of mucosal lesions, and the luminol-dependent chemiluminescence activity in zymosan-treated blood samples, obtained from the gastric vein, were measured and found to increase significantly 30 min after the stimuli. The intravenous injection of CV-6209, a PAF antagonist, 5 min prior to the stimuli significantly inhibited the DCF activation, the increases in PAF level and MPO activity, the mucosal hemorrhagic change, and the elevation in chemiluminescence activity. In addition, continuous infusion of superoxide dismutase also inhibited all these changes, except for chemiluminescence activity. These results suggest that oxygen radicals derived from PAF-activated granulocytes induce oxidative stress, and that oxidative changes are actually implicated in the pathogenesis of gastric mucosal injury.

Active oxygen species in formation of acute gastric mucosal lesions induced by thermal injury in rats

Active oxygen species generated by circulating leukocytes and released from the gastric mucosa were measured in the process of acute gastric mucosal lesion formation after thermal injury in rats. Alterations of luminol-dependent chemiluminescence activities generated by leukocytes obtained from the gastric vein and the inferior vena cava were approximately same. A decrease in chemiluminescence activity 15 min after thermal injury and a significant increase in chemiluminescence activity 5 hr after thermal injury were observed in leukocytes from both veins. From 15 min to 12 hr after thermal injury, luciferin-dependent chemiluminescence activities were significantly higher than that of the control group. Oral administration of rebamipide resulted in decreased mucosal lesion formation. Rebamipide, an antiulcer agent that protects the mucosa from damage in various animal models decreased chemiluminescence activities only released from the gastric mucosa but not from circulating leukocytes. These results suggest that two different pathways of active oxygen species formation may exist in the pathogenesis of acute gastric mucosal lesions after thermal injury.

Spatial heterogeneity of mucosal blood flow during ischemia-reperfusion injury of rat stomach investigated by laser Doppler perfusion imaging

Spatial alterations in blood flow during the development of mucosal injury induced by ischemia-reperfusion in rats were determined with a two-dimensional laser Doppler tissue perfusion imager. The rats were anesthetized with pentobarbital, and the stomach was exteriorized on a stage; the mucosa was then sequentially scanned. The mucosa was constantly superfused with 0.1 N HCl in physiological saline. Systemic arterial pressure was continuously monitored and blood was stepwisely withdrawn from the femoral artery by 20-mmHg stage and then maintained at 20 mmHg for 20 min. The shed blood was reinfused and the stomach was removed 30 min later. Under control conditions, the average perfusion of the forestomach was usually greater than that in the glandular stomach. When systemic blood pressure was stepwisely decreased, the extent of decrease in the mucosal blood perfusion unit was always greater than that in systemic blood pressure, but mucosal perfusion appeared to be uniformly decreased throughout the stomach. Ten min after reperfusion, a hypoperfused area began to appear in the corpus near the greater curvature, and this area subsequently increased. The area of ulcer formation corresponded with the hypoperfused area in the gastric mucosa 30 min after reperfusion. Pretreatment with CV-6209, a platelet-activating factor antagonist, significantly attenuated the hypoperfusion induced by reperfusion and also prevented gastric mucosal damage. Our results suggest that hypoperfusion in the mucosal microcirculation is indeed an important factor contributing to the localized occurrence of gastric mucosal lesions and that the laser Doppler perfusion imager is useful for the detection of local hypoperfused areas in the gastric mucosa.