Enhanced resistance of gastric mucosa to damaging agents in the rat stomach adapted to Helicobacter pylori lipopolysaccharide.
OBJECTIVE
Lipopolysaccharide (LPS) has been proposed to act as one of numerous virulence factors in the Helicobacter pylori (HP)-infected stomach. However, little is known as to whether the gastric mucosa can withstand the repeated LPS insult, and how the possible adaptation to this endotoxin influences the damage induced by strong irritants. We determined the effect of a single or repeated parenteral administration of LPS obtained from HP on acute gastric lesions induced by intragastric application of 100% ethanol (1.5 ml) and by water immersion and restraint stress (WRS).


METHODS
The area of the gastric lesions was measured by planimetry, mucosal gastric blood flow (GBF) was determined by H(2) gas clearance, and gastric luminal content was collected for the determination of luminal NO(2)(-)/NO(3)(-) levels by the Griess reaction. Biopsy samples were taken for the measurement of prostaglandin (PG) E(2) by radioimmunoassay and mucosal expression of constitutive and inducible nitric oxide synthase (cNOS and iNOS), constitutive (COX-1) and inducible cyclooxygenase (COX-2), heat shock protein 70 (HSP 70) mRNA and protein were analyzed by RT-PCR and Western blot.


RESULTS
HP LPS (1 mg/kg i.p.) injected once or 5 times produced negligible macroscopic injury and failed to influence GBF significantly compared to the injuries recorded in vehicle-controlled rats. Single and repeated (5 times) administration of HP LPS significantly reduced ethanol- and WRS-induced lesions, these protective effects were accompanied by a rise in GBF and excessive luminal release of NO. The suppression of NOS activity by L-NAME (20 mg/kg i.p.), a nonspecific NOS inhibitor, or L-NIL (30 mg/kg i.g.), a specific iNOS inhibitor, and of COX-2 activity by NS-398 reversed the protective and hyperemic effects of single or repeated LPS administrations against ethanol and WRS damage and the accompanying rise in NO and PGE(2) production. These effects of L-NAME were significantly antagonized by the addition of L-arginine, a substrate for NO synthesis. The signals for cNOS, COX-1 and HSP 70 mRNA were detected by RT-PCR in the vehicle-treated gastric mucosa, whereas gene and protein expression of iNOS, COX-2 and HSP 70 mRNA were significantly increased only in rats treated with 1 or 5 applications of HP LPS.


CONCLUSIONS
Repeated injections of HP LPS enhance gastric mucosal resistance to the mucosal damage induced by ethanol and WRS via a mechanism involving mucosal overexpression of iNOS, COX-2 and HSP 70 with subsequent excessive production of NO and PGE(2).
Brzozowski
Tomasz
T
Department of Physiology, Jagiellonian University School of Medicine, Cracow, Poland.
Konturek
Peter C
PC
Moran
Anthony P
AP
Kwiecien
Slawomir
S
Pajdo
Robert
R
Konturek
Stanislaw J
SJ
Drozdowicz
Danuta
D
Ptak
Agata
A
Pawlik
Wieslaw
W
Hahn
Eckhart G
EG
D000222:Adaptation, Physiological; D000818:Animals; D001706:Biopsy; D015153:Blotting, Western; D002492:Central Nervous System Depressants / Q000633:toxicity; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000032:analysis / Q000096:biosynthesis; D000431:Ethanol / Q000633:toxicity; D005753:Gastric Mucosa / Q000098:blood supply / Q000473:pathology*; D005786:Gene Expression Regulation; D018840:HSP70 Heat-Shock Proteins / Q000032:analysis / Q000096:biosynthesis; D016481:Helicobacter Infections / Q000150:complications*; D016480:Helicobacter pylori / Q000472:pathogenicity*; D007103:Immobilization; D007527:Isoenzymes / Q000032:analysis / Q000096:biosynthesis; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008297:Male; D008565:Membrane Proteins; D019001:Nitric Oxide Synthase / Q000032:analysis / Q000096:biosynthesis; D018384:Oxidative Stress; D011451:Prostaglandin-Endoperoxide Synthases / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D012039:Regional Blood Flow; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014774:Virulence
D002492:Central Nervous System Depressants; D018840:HSP70 Heat-Shock Proteins; D007527:Isoenzymes; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D000431:Ethanol; D019001:Nitric Oxide Synthase; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C496513:Ptgs1 protein, rat; D015232:Dinoprostone