Applications To Health Promotion And Disease Prevention

The antimicrobiological properties of GSE against a wide range of gram-negative and grampositive organisms were attributed to the disruption it caused to the bacterial membrane, and the subsequent liberation by this extract of the bacterial cytoplasmic contents within a relatively short time (e.g. 15—20 minutes). Moreover, the flavonoid naringenin, the bioactive component of GSE, has showed anticancer activity against various human breast cancers (So et al., 1996). The underlying mechanism of the therapeutic efficacy of citrus seed extracts such as from grapefruits and red grapes seems to depend upon the presence of different classes of polyphenolic flavonoids, which were shown to inhibit platelet aggregation, thus decreasing the risk of coronary thrombosis and myocardial infarction. However, the involvement of GSE containing various flavonoids in the mechanism of gastric mucosal integrity and mucosal defense has not been extensively studied.

Previous studies demonstrated that flavonoids — namely, quercetin and meciadanol, which is a synthetic flavonoid that inhibits histidine decarboxylase (HDC) and decreases the histamine content in the stomach — attenuated gastric mucosal lesions produced by ethanol and aspirin via a mechanism unrelated to gastric acid secretion and endogenous prostaglandins (PG) (Konturek et al., 1986). It remained unknown to what extent GSE influences the gastric mucosal injury induced by topical (ethanol) and non-topical ulcerogens (I/R and stress), and, if it does, what the mechanism of gastroprotection induced by GSE is. Therefore, using animal models of gastric lesions induced by I/R, water immersion and restraint stress (WRS) and 75% ethanol, we determined the influence of GSE on gastric lesions induced by these three ulcer-ogens, and the accompanying changes in the gastric blood flow (GBF) in the rat stomach. An attempt was also made to assess the contribution of the activity of superoxide dismutase

(SOD) and lipid peroxidation as expressed by the malonyldialdehyde (MDA) concentration 555

PG/COX system, nitric oxide (NO), and sensory nerves in the gastroprotective effect of GSE. Herein, we will provide evidence that the pretreatment with GSE applied orally attenuates the gastric lesions caused by I/R or cold stress, and those induced by the intragastric application to the stomach of noxious substance such as 75% ethanol. This protective effect of GSE is accompanied by the increase in the GBF and SOD activity and a reduction of MDA concentration, which is widely considered an index of lipid peroxidation (Figures 66.1, 66.2). Previous studies have demonstrated that the damaging action of ethanol, I/R, and WRS could be attributed to the enhancement in the reactive oxygen metabolites (ROM), and the ROMand neutrophil-dependent increase in the lipid peroxidation and inhibition of anti-oxidizing enzyme activity (Kwiecien et al., 2003). We found that GSE greatly attenuated the rise in MDA content in the gastric mucosa injured by I/R, WRS, and 75% ethanol (Figure 66.2), indicating that this extract can attenuate the process of neutrophil-dependent lipid peroxidation implicated in the pathogenesis of I/R, WRS, and ethanol-induced gastric damage. Ethanol decreased the gene expression of SOD in the gastric mucosa (Brzozowski & Konturek, 2005), suggesting that the suppression of key mucosal antioxidizing enzymes along with the elevation of lipid peroxidation play an important role in the pathogenesis of these lesions. These increases in mucosal lipid peroxidation, as well as the decrease in SOD expression and its activity, were attenuated by GSE. This would suggest that the reduction in lipid peroxidation by this seed extract might contribute to the attenuation of the harmful effects of noxious agents on the gastric mucosa. This is supported by the fact that the GBF was elevated and gastric mucosal generation of PGE2 were enhanced in animals treated with GSE as compared to those treated with vehicle (Figure 66.3). This finding is in keeping with observations that some flavonoids stimulated PGE2 production by isolated gastric mucosal cells while suppressing gastric acid secretion via a direct inhibitory effect on H+/K+-ATPase activity (Beil et al., 1995). It is understood that the NO/NOS system is also involved in GSE-induced protection against I/R injury, due to the fact that both GSE-induced protection and hyperemia were counteracted by

FIGURE 66.1

Effect of intragastric (i.g.) pretreatment with GSE applied in graded doses ranging from 8 mg/kg up to 128 mg/kg on the mean area of gastric lesions induced by ischemia-reperfusion (I/R), 75% ethanol, and 3.5 h of water immersion and restraint stress (WRS), and accompanying changes in the gastric blood flow (GBF). GSE significantly attenuates the area of I/R-, 75% ethanol-, and WRS-induced gastric lesions while raising GBF. Results are expressed as mean ± SEM, n = 8. Asterisk indicates a significant change vs vehicle (Veh, saline) control.

r 80

75% ETHANOL

75% ETHANOL

WATER IMMERSION AND RESTRAINT STRESS

T

S

il

Sv. Ii

*

r 80

0 80

0 80

L-NNA, a non-specific inhibitor of NO-synthase. This effect was restored in these animals by the combined treatment with L-arginine and GSE, but not with the L-arginine stereoisomer, D-arginine (Figure 66.4). Thus, these sets of data suggest that some natural products of citrus fruits, such as GSE, afford protection against acute gastric lesions due to an increase in the gastric microcirculation involving endogenous NO release, and the preservation of the expression and activity of major antioxidizing enzymes such as SOD.

The mechanism of gastroprotective activity of GSE appears to be dependent on endogenous PG, and the functional activity of sensory nerves releasing CGRP. This notion is supported by our findings that indomethacin, a non-selective inhibitor of COX-1 and COX-2 activity, reversed this protection and the accompanying hyperemia (Figure 66.3). In addition, co-treatment of exogenous CGRP with GSE, administered to replace the deficit of this peptide

r 800

Veh GSE

Veh GSE

Veh GSE

FIGURE 66.2

Effect of vehicle (saline) and GSE on the MDA concentration and SOD activity in the gastric mucosa in rats exposed to I/R or 75% ethanol, or subjected to 3.5 h of WRS. GSE significantly inhibits the gastric MDA content while producing a significant increase in SOD activity. Results are expressed as mean ± SEM, n = 8. Asterisk indicates a significant change (P< 0.05) vs vehicle (Veh, saline) control.

LU 2

Veh GSE

Veh GSE

Veh GSE

200t90

+ Indomethacin + SC560

Veh GSE

+ ROFECOXIB

0 It

FIGURE 66.3

Effect of GSE on the mean area of I/R-induced gastric lesions and accompanying alterations in the gastric mucosal PGE2 generation and GBF in rats with or without pretreatment with indomethacin, the non-selective inhibitor of COX activity; SC-560, the selective inhibitor of COX-1 activity; and rofecoxib, the selective inhibitor of COX-2 activity. The gastroprotective action and the accompanying increase in PGE2 and GBF by GSE are abolished by indomethacin, SC-560, and rofecoxib. Results are expressed as mean ± SEM, n = 8. Asterisk indicates a significant change (P < 0.05) vs vehicle (Veh, saline) control; cross indicates a significant change (P < 0.05) vs Veh and GSE-alone groups.

in capsaicin-treated animals, restored the protective efficacy of GSE against WRS-induced gastric damage (Figure 66.5). Interestingly, both, SC-560 and rofecoxib, the highly selective COX-1 and COX-2 inhibitors (Brzozowski etal., 1999), also inhibited the gastroprotective and hyperemic activities of GSE, which in turn suggests the involvement of COX-1 and COX-2 derived products in gastroprotection and the increase in the GBF induced by this seed extract (Figure 66.3). This gastroprotective activity of the GSE could be attributed to naringenin, a major GSE flavonoid. This flavonoid was reported to exhibit gastroprotection against the gastric injury induced by absolute ethanol, predominantly due to the increase in the secretion of mucus (Motilova et al., 1994). It is of interest that this gastroprotective effect of naringenin and accompanying increase in the mucus secretion were, in part, attenuated by indomethacin, supporting the contribution of endogenous PG to the mechanism of gastroprotection by GSE. On the other hand, lack of the complete destruction of GSE protection by indomethacin suggests that PG might not be the primary mediator of this protection, and other

FIGURE 66.4

Effect of GSE on the mean area of I/R-induced gastric lesions and accompanying alterations in the GBF in rats with or without pretreatment with L-NNA, the NO-synthase inhibitor, applied alone or co-administered with L-arginine (L-ARG) or D-arginine (D-ARG). The gastroprotective and hyperemic activities of GSE are significantly attenuated by L-NNA and restored with L-ARG. Results are expressed as mean ± SEM, n = 7. Asterisk indicates a significant change (P< 0.05) vs vehicle (Veh, saline) control; cross indicates a significant change (P< 0.05) vs GSE-alone group; asterisk and cross indicate a significant change (P< 0.05) vs animals treated with the combination of GSE and L-NNA.

Veh GSE

Veh GSE L-ARG D-ARG

Veh GSE

Veh GSE L-ARG D-ARG

FIGURE 66.5

Effect of GSE on the WRS-induced gastric lesions and accompanying alterations in the GBF in rats 558 with intact sensory nerves and those with capsaicin inactivation of sensory nerves with or without the administration of exogenous CGRP. Functional ablation of sensory nerves by capsaicin reduces the gastroprotective and hyperemic actions of GSE against WRS-induced gastric lesions. Results are expressed as mean ± SEM, n = 8. Asterisk indicates a significant change (P< 0.05 vs vehicle (Veh, saline) control; cross indicates a significant change (P< 0.05) vs GSE-alone group; asterisk and cross indicate a significant change (P < 0.05) vs capsaicin denervated animals treated with GSE.

WATER IMMERSION AND RESTRAINT STRESS

Veh GSE

r 90

30 g

Veh GSE CGRP

(32mg/kgi.g.)(10 Mg/kg s.c.) + CAPSAICIN DENERVATION

gastroprotective factors such as NO and/or neuropeptides released from sensory afferent nerves could be involved. This is the reason we carried out the study with L-NNA, a potent NO-synthase inhibitor, and with capsaicin, applied in a dose that causes functional ablation of sensory nerves, leading to the release of vasoactive neuropeptides such as CGRP. We found that L-NNA and capsaicin denervation inhibited the GSE-induced protection against I/R- and WRS-induced gastric lesions and accompanying gastric mucosal hyperemia (Figures 66.4, 66.5). Naringenin could be one of the important components of GSE exhibiting gastric protection and hyperemia, because pretreatment with naringenin applied in gradual concentrations counteracted the gastric mucosal lesions, and the accompanying fall in GBF induced by the mucosal corrosive agent (75% ethanol) (Figure 66.6).

Another candidate involved in GSE-induced protection could be gastrin, which is known to exhibit both gastroprotective and hyperemic activities. The contribution of gastrin was something we addressed in our previous study by directly determining the plasma gastrin

75% ETHANOL

75% ETHANOL

FIGURE 66.6

Effect of intragastric (i.g.) pretreatment with vehicle (saline) or naringenin applied in graded doses ranging from 5 mg/kg up to 40 mg/kg on the mean area of 75% ethanol-induced gastric lesions and the accompanying changes in the GBF. Naringenin dose-dependently reduced the area of ethanol-induced gastric lesions. Results are expressed as mean ± SEM, n = 7. Asterisk indicates a significant change (P< 0.05) vs vehicle (Veh, saline) control.

FIGURE 66.6

Effect of intragastric (i.g.) pretreatment with vehicle (saline) or naringenin applied in graded doses ranging from 5 mg/kg up to 40 mg/kg on the mean area of 75% ethanol-induced gastric lesions and the accompanying changes in the GBF. Naringenin dose-dependently reduced the area of ethanol-induced gastric lesions. Results are expressed as mean ± SEM, n = 7. Asterisk indicates a significant change (P< 0.05) vs vehicle (Veh, saline) control.

levels by specific RIA (Brzozowski & Konturek, 2005). Suppression of gastric secretion by GSE might contribute to the protective activity of this extract against WRS and J/R injury, because such injuries depend upon gastric acidity and ultimately become exaggerated by the acidic conditions in the stomach.

In summary, GSE exerts a potent gastroprotective activity against gastric lesions caused by acid-dependent (I/R, WRS) and acid-independent (ethanol) causes, due to a mechanism involving preservation of the activity of antioxidizing enzymes (SOD), reduction of free radical-dependent lipid peroxidation, enhancement in the GBF, and plasma gastrin levels exerting trophic influence on gastric mucosa. The GSE-induced protection and hyperemia were mimicked by intragastric application of naringenin, suggesting that this flavonoid could be involved in the gastroprotection and hyperemia afforded by GSE. This protective and hyper-emic activity of GSE against I/R ulcerogenesis was abolished by COX-1 and COX-2 nonselective and selective inhibitors such as indomethacin, SC-560, and rofecoxib, and significantly ameliorated by L-NNA. Thus, this protective effect in the stomach may involve endogenous PG derived from COX-1 and COX-2 activity, suppression of lipid peroxidation, and gastric hyperemia mediated by NO, and neuropeptides released from afferent sensory nerves.

Was this article helpful?

0 0
Health And Fitness 101

Health And Fitness 101

Self-improvement is a thing which you must practice throughout your life because once you started to believe that you are perfect then, things will start to become complex. You need to know that no one is perfect and no one can be perfect.

Get My Free Ebook


Post a comment