Role of Cyclooxygenase Isoforms and Nitric-Oxide Synthase in the Modulation of Tracheal Motor Responsiveness in Normal and Antigen-Sensitized Guinea Pigs

Abstract

The effects of selective cyclooxygenase (COX) isoform (COX-1, COX-2) inhibition, alone or in combination with nitric-oxide synthase (NOS) blockade, on in vitro tracheal muscle responsiveness to histamine were investigated in healthy and ovalbumin (OVA)-sensitized guinea pigs. Immunohistochemistry showed that COX-1 and COX-2 are constitutively present in normal guinea pig trachea, particularly in the epithelial layer, and that COX-2 expression is enhanced in OVA-sensitized animals both in epithelial and subepithelial tissues. In normal guinea pigs, SC-560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole] (COX-1 inhibitor) or DFU [5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)phenyl-2(5H)-furanone] (COX-2 inhibitor) significantly increased the contractile response to histamine, these effects being not additive. NOS inhibition by L-N G -nitro-arginine methyl ester (L-NAME) did not affect histamine-induced contraction but reversed the increase caused by COX-1 blockade while not modifying the enhancement associated with COX-2 inhibition. In guinea pigs subjected to OVA sensitization and challenge, COX-2, but not COX-1, inhibition enhanced the motor responses to histamine without any influence by L-NAME. In normal, but not in sensitized animals, the removal of epithelial layer from tracheal preparations abolished the enhancing action of DFU on histaminemediated contraction. A COX-2-dependent release of prostacyclin (PGI 2 ), but not prostaglandin E 2 , was observed in tracheal tissues from normal and OVA-sensitized guinea pigs. In conclusion, both COX-1 and COX-2 are constitutive in guinea pig trachea, and COX-2 expression is enhanced by OVA sensitization; in normal animals, epithelial COX-2 exerts a PGI 2 -dependent inhibitory control on tracheal contractility, and this isoform is subjected to upstream regulation by epithelial COX-1 and NOS through a complex interplay; and following antigen sensitization, the inhibitory control on tracheal contractility is maintained by COX-2 induced at subepithelial cell sites.Both nitric oxide (NO) and prostaglandins (PGs) are relevant mediators in airway physiology and pathology, and their production is regulated by different enzyme isoforms. NO is formed from L-arginine by NO synthase (NOS), of which three isoforms have been identified: neuronal NOS, inducible NOS, and endothelial NOS (Ogden and Moore, 1995). PG synthesis depends on cyclooxygenase (COX), two main isozymes of which are currently recognized: COX-1, constitutively expressed in different tissues, and COX-2, regarded as an inducible isoform, since an increase in its expression has been associated with inflammatory processes (Simmons et al., 2004).It is generally believed that the production of NO and PGs by constitutive enzyme isoforms is important for physiological functions, whereas their formation via inducible isoforms is involved mainly in inflammatory and other pathological responses (Di Rosa et al., 1996). Increasing evidence suggests a link between NOS and COX pathways (Di Rosa ...

Epithelial Cells Induce a Cyclo-Oxygenase-1–Dependent Endogenous Reduction in Airway Smooth Muscle Contractile Phenotype

“…Similarly, selective COX-1 inhibition prevented tracheal ring relaxation of murine airways by proteinase-activated receptor-2 agonism (44). Furthermore, the selective inhibitor of COX-1, SC560, augmented histamine-triggered tracheal ring contractions (45). Our data provide further evidence that SC560 may increase the responsiveness of ASM to a contractile agonist.…”

Effects of selective and non-selective COX inhibitors on antigen-induced release of prostanoid mediators and bronchoconstriction in the isolated perfused and ventilated guinea pig lung

“…In contrast to the simplistic view that COX-2 always is inducible, constitutive COX-2 expression has been described in the lungs, and was localised to tracheal and bronchial epithelial cells (Asano et al, 1996;Ermert et al, 1998b) as well as macrophages and mast cell-like cells in the connective tissue surrounding the blood vessels (Ermert et al, 1998a). COX-2 was constitutively expressed also in isolated guinea pig trachea (Nieri et al, 2006) and appeared to mediate the spontaneous tone in this preparation (Charette et al, 1995). Constitutively expressed COX-2 contributed also to the arachidonic acid-induced (Ermert et al, 1998a) and the PAFinduced (Fabi et al, 2001) vascular response in isolated rat lungs.…”