Cholera toxin induces prostaglandin synthesis via post-transcriptional activation of cyclooxygenase-2 in the rat jejunum.
The mechanisms of diarrhea in Asiatic cholera have been studied extensively. Cyclic AMP, 5-hydroxytryptamine, prostaglandins, and the function of neuronal structures have been implicated in the pathogenesis of cholera. To elucidate the role of the different isoforms (COX-1 and COX-2) of cyclooxygenase in cholera toxin (CT)-induced fluid secretion and intraluminal prostaglandin E(2) (PGE(2)) release in the rat jejunum in vivo, the effects of the COX-2 inhibitors NS-398 ([N-(2-cyclohexaloxy-4-nitrophenyl)methanesulfonamide]) and DFU [5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5H)-furanone], and of the COX-1 inhibitor SC-560, were studied. Net fluid transport was measured gravimetrically and PGE(2) by radioimmunoassay. COX-1 and COX-2 mRNA expression were determined by reverse transcription-polymerase chain reaction (RT-PCR) and COX-2 protein by Western blot analysis in mucosal scrapings. CT caused profuse net fluid secretion in all control rats. The COX-2 inhibitors NS-398 and DFU, but not the COX-1 inhibitor SC-560 or dexamethasone, dose-dependently inhibited CT-induced fluid secretion and PGE(2) release. RT-PCR showed expression of COX-1 and of COX-2 mRNA in control rats. CT did not induce an increase and dexamethasone did not reduce COX-2 mRNA, whereas lipopolysaccharide caused a marked induction of COX-2 mRNA, which was inhibited by dexamethasone. A weak band of COX-2 protein was observed in controls; however, CT enhanced COX-2 levels, which remained unaffected by dexamethasone. It can be assumed that post-transcriptional modulation is responsible for CT-induced increase in COX-2 protein. COX-1 does not seem to be involved. Therefore, PGE(2) produced by COX-2 seems to be responsible for the profuse fluid secretion induced by CT, and COX-2 appears to be a specific target for the treatment of Asiatic cholera.
Beubler
E
E
Department of Experimental and Clinical Pharmacology, Karl-Franzens-University of Graz, Graz, Austria. eckhard.beubler@kfunigraz.ac.at
Schuligoi
R
R
Chopra
A K
AK
Ribardo
D A
DA
Peskar
B A
BA
D000818:Animals; D015153:Blotting, Western; D002772:Cholera Toxin / Q000494:pharmacology*; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D015232:Dinoprostone / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005663:Furans / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D007583:Jejunum / Q000187:drug effects* / Q000201:enzymology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008565:Membrane Proteins; D009578:Nitrobenzenes / Q000494:pharmacology; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D011720:Pyrazoles / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013449:Sulfonamides / Q000494:pharmacology
C106876:5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5H)-furanone; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D005663:Furans; D005938:Glucocorticoids; D007527:Isoenzymes; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D009578:Nitrobenzenes; D011720:Pyrazoles; D012333:RNA, Messenger; C115461:SC 560; D013449:Sulfonamides; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D003907:Dexamethasone; D002772:Cholera Toxin; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C496513:Ptgs1 protein, rat; D015232:Dinoprostone