Panax ginseng has anti-infective activity against opportunistic pathogen Pseudomonas aeruginosa by inhibiting quorum sensing, a bacterial communication process critical for establishing infection.

Virulent factors produced by pathogens play an important role in the infectious process, which is regulated by a cell-to-cell communication mechanism called quorum sensing (QS). Pseudomonas aeruginosa is an important opportunistic human pathogen, which causes infections in patients with compromised immune systems and cystic fibrosis. The QS systems of P. aeruginosa use N-acylated homoserine lactone (AHL) as signal molecules. Previously we have demonstrated that Panax ginseng treatment allowed the animals with P. aeruginosa pneumonia to effectively clear the bacterial infection. We postulated that the ability to impact the outcome of infections is partly due to ginseng having direct effect on the production of P. aeruginosa virulence factors. The study explores the effect of ginseng on alginate, protease and AHL production. The effect of ginseng extracts on growth and expression of QS-controlled virulence factors on the prototypic P. aeruginosa PAO1 and its isogenic mucoid variant (PAOmucA22) was determined. Ginseng did not inhibit the growth of the bacteria, enhanced the extracellular protein production and stimulated the production of alginate. However, ginseng suppressed the production of LasA and LasB and down-regulated the synthesis of the AHL molecules. Ginseng has a negative effect on the QS system of P. aeruginosa, may explain the ginseng-dependent bacterial clearance from the animal lungs in vivo in our previous animal study. It is possible that enhancing and repressing activities of ginseng are mutually exclusive as it is a complex mixture, as shown with the HPLC analysis of the hot water extract. Though ginseng is a promising natural synergetic remedy, it is important to isolate and evaluate the ginseng compounds associated with the anti-QS activity.

Effects of specific inhibition of cyclo-oxygenase-1 and cyclo-oxygenase-2 in the rat stomach with normal mucosa and after acid challenge.

1. Effects of the cyclo-oxygenase (COX)-1 inhibitor SC-560 and the COX-2 inhibitors rofecoxib and DFU were investigated in the normal stomach and after acid challenge. 2. In healthy rats, neither SC-560 nor rofecoxib (20 mg kg(-1) each) given alone damaged the mucosa. Co-treatment with SC-560 and rofecoxib, however, induced severe lesions comparable to indomethacin (20 mg kg(-1)) whereas co-administration of SC-560 and DFU (20 mg kg(-1) each) had no comparable ulcerogenic effect 5 h after dosing. 3. SC-560 (20 mg kg(-1)) inhibited gastric 6-keto-prostaglandin (PG) F(1alpha) by 86+/-5% and platelet thromboxane (TX) B(2) formation by 89+/-4% comparable to indomethacin (20 mg kg(-1)). Rofecoxib (20 mg kg(-1)) did not inhibit gastric and platelet eicosanoids. 4. Intragastric HCl elevated mucosal mRNA levels of COX-2 but not COX-1. Dexamethasone (2 mg kg(-1)) prevented the up-regulation of COX-2. 5. After acid challenge, SC-560 (5 and 20 mg kg(-1)) induced dose-dependent injury. Rofecoxib (20 mg kg(-1)), DFU (5 mg kg(-1)) and dexamethasone (2 mg kg(-1)) given alone were not ulcerogenic but aggravated SC-560-induced damage. DFU augmented SC-560 damage 1 but not 5 h after administration whereas rofecoxib increased injury after both treatment periods suggesting different time courses. 6. Gastric injurious effects of rofecoxib and DFU correlated with inhibition of inflammatory PGE(2). 7. The findings show that in the normal stomach lesions only develop when both COX-1 and COX-2 are inhibited. In contrast, during acid challenge inhibition of COX-1 renders the mucosa more vulnerable suggesting an important role of COX-1 in mucosal defence in the presence of a potentially noxious agent. In this function COX-1 is supported by COX-2. In the face of pending injury, however, COX-2 cannot maintain mucosal integrity when the activity of COX-1 is suppressed.

Role of cyclooxygenase-2 in gastric mucosal defense.

Two isoenzymes of cyclooxygenase (COX), the key enzyme in prostaglandin (PG) biosynthesis, COX-1 and COX-2, have been identified. COX-1 was proposed to regulate physiological functions, COX-2 to mediate pathophysiological reactions such as inflammation. In particular, it was suggested that maintenance of gastric mucosal integrity relies exclusively on COX-1. Recently, it was shown that a selective COX-1 inhibitor does not damage the mucosa in the healthy rat stomach, although mucosal prostaglandin formation is near-maximally suppressed. However, concurrent treatment with a COX-1 and a COX-2 inhibitor induces severe gastric damage. This indicates that in normal mucosa both COX-1 and COX-2 have to be inhibited to evoke ulcerogenic effects. In the acid-challenged rat stomach inhibition of COX-1 alone is associated with dose-dependent injury which is aggravated by additional inhibition of COX-2 activity or prevention of acid-induced up-regulation of COX-2 expression by dexamethasone. After acid exposure, COX-2 inhibitors cause substantial gastric injury when nitric oxide formation is suppressed or afferent nerves are defunctionalized. Ischemia-reperfusion of the gastric artery increases levels of COX-2 but not COX-1 mRNA. COX-2 inhibitors or dexamethasone aggravate ischemia-reperfusion-induced mucosal damage up to 4-fold, an effect abolished by concurrent administration of 16,16-dimethyl-PGE2. Furthermore, the protective effects elicited by a mild irritant or intragastric peptone perfusion are antagonized by COX-2 inhibitors. Finally, COX-2 expression is increased in experimental ulcers. COX-2 inhibitors delay the healing of chronic gastric ulcers in experimental animals and decrease epithelial cell proliferation, angiogenesis and maturation of the granulation tissue to the same extent as non-steroidal anti-inflammatory drugs. These observations indicate that, in contrast to the initial concept, COX-2 plays an important role in gastric mucosal defense.

Selective cyclo-oxygenase-2 inhibitors aggravate ischaemia-reperfusion injury in the rat stomach.

1. Effects of indomethacin, the selective cyclo-oxygenase (COX)-2 inhibitors NS-398 and DFU, and dexamethasone on gastric damage induced by 30 min ischaemia followed by 60 min reperfusion (I-R) were investigated in rats. Modulation of gastric levels of COX-1 and COX-2 mRNA by I-R was evaluated using Northern blot and reverse transcription-polymerase chain reaction. 2. I-R-induced gastric damage was dose-dependently aggravated by administration of indomethacin (1 - 10 mg kg(-1)), NS-398 (0.4 - 4 mg kg(-1)) or DFU (0.02 - 2 mg kg(-1)) as assessed macroscopically and histologically. 3. Likewise, administration of dexamethasone (1 mg kg(-1)) significantly increased I-R damage. 4. Low doses of 16, 16-dimethyl-prostaglandin(PG)E(2), that did not protect against ethanol-induced mucosal damage, reversed the effects of the selective COX-2 inhibitors, indomethacin and dexamethasone. 5. I-R had no effect on gastric COX-1 mRNA levels but increased COX-2 mRNA levels in a time-dependent manner. Dexamethasone inhibited the I-R-induced expression of COX-2 mRNA. 6. I-R was not associated with a measurable increase in gastric mucosal formation of 6-keto-PGF(1alpha) and PGE(2). PG formation was substantially inhibited by indomethacin (10 mg kg(-1)) but was not significantly reduced by NS-398 (4 mg kg(-1)), DFU (2 mg kg(-1)) or dexamethasone (1 mg kg(-1)). 7. The findings indicate that selective COX-2 inhibitors and dexamethasone markedly enhance gastric damage induced by I-R. Thus, whereas COX-2 has no essential role in the maintenance of gastric mucosal integrity under basal conditions, COX-2 is rapidly induced in a pro-ulcerogenic setting and contributes to mucosal defence by minimizing injury. This suggests that in certain situations selective COX-2 inhibitors may have gastrotoxic effects.

Role of prostaglandins in gastroprotection.

Numerous agents increase gastric mucosal resistance against intraluminal ulcerogens. Although the precise mechanisms of gastroprotection are uncertain, various endogenous mediators involved in gastroprotective effects have been characterized. As prostaglandins exert potent protective effects and inhibition of prostaglandin formation abolishes "adaptive gastroprotection," they have been proposed as key mediators in mucosal defense. This paper reviews the role of endogenous prostaglandins showing striking differences between different forms of gastroprotection. Thus, whereas the protective effect of the antiulcer drug rebamipide involves prostaglandins as essential mediators, the protection conferred by the antacid hydrotalcit is prostaglandin-independent. Furthermore, gastroprotection can occur even when mucosal prostaglandin generation is suppressed. This phenomenon has been observed with some nonsteroidal antiinflammatory drugs, agents that modulate sulfhydryls and certain metals. Recent data suggest that both cyclooxygenase-1- and cyclooxygenase-2-derived prostaglandins can increase mucosal resistance. The precise role of constitutive and inducible forms of cyclooxygenase in gastroprotection, however, remains to be established.

Selective cyclo-oxygenase-2 inhibitors and their influence on the protective effect of a mild irritant in the rat stomach.

1. The effects of the non-selective cyclo-oxygenase (COX) inhibitor indomethacin and the selective COX-2 inhibitors, N-[2-(cyclohexyloxy)-4-nitrophenyl] methanesulphonamide (NS-398), 5-methanesulphonamido-6-(2,4-difluorothio-phenyl)-1-indan one (L-745,337) and 5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl) phenyl-2(5H)-furanone (DFU), on the protection induced by the mild irritant 20% ethanol were investigated in the rat stomach. 2. Instillation of 20% ethanol (1 ml, p.o.) effectively protected against gastric mucosal injury induced by subsequent instillation of 70% or 96% ethanol (1 ml, p.o.). 3. Oral administration of indomethacin (1.25-20 mg kg[-1]) dose-dependently counteracted the protective effect of 20% ethanol (ID50: 3.5 mg kg[-1]). 4. Likewise, NS-398 (0.1-1 mg kg[-1]), L-745,337 (0.2-2 mg kg[-1]) and DFU (0.02-0.2 mg kg[-1]) inhibited the protective effect of 20% ethanol in a dose-dependent manner with ID50 values of 0.3 mg kg(-1), 0.4 mg kg(-1) and 0.06 mg kg(-1), respectively. 5. Inhibition of mild irritant-induced protection was also found when NS-398 (1 mg kg[-1]) was administered s.c. or when 96% ethanol was used to damage the mucosa. 6. Pretreatment with 16,16-dimethyl-prostaglandin (PG)E2 at 4 ng kg(-1), a dose that did not protect against ethanol (70%)-induced mucosal damage when given alone, completely reversed the effect of the selective COX-2 inhibitors on the mild irritant-induced protection. 7. Pretreatment with dexamethasone (3 mg kg(-1), 24 and 2 h before instillation of 20% ethanol) did not affect the protective activity of the mild irritant, indicating that enzyme induction is not involved. 8. Indomethacin (20 mg kg(-1), p.o.) did not prevent the protection conferred by sodium salicylate (100 mg kg[-1]), dimercaprol (30 microg kg[-1]), iodoacetamide (50 mg kg[-1]) and lithium (20 mg kg[-1]). Likewise, the protective effect of these agents was not counteracted by NS-398 (1 mg kg(-1), p.o.). 9. Whereas indomethacin (20 mg kg(-1), p.o.) near-maximally inhibited gastric mucosal formation of PGE2, 6-keto-PGF1alpha and thromboxane (TX) B2 as well as platelet TXB2 release, the selective COX-2 inhibitors were ineffective. 10. The findings show that selective COX-2 inhibitors, although lacking in ulcerogenic activity, prevent the protection conferred by a mild irritant. Prostaglandis generated by a constitutive COX-2 could thus contribute to physiological functions involved in gastric homeostasis, although at present a non-COX-2-related mechanism underlying the effect of the selective COX-2 inhibitors tested on mild irritant-induced protection cannot be completely excluded.