Inhibitors of Prostaglandin Transport and Metabolism Augment Protease-Activated Receptor-2-Mediated Increases in Prostaglandin E₂ Levels and Smooth Muscle Relaxation in Mouse Isolated Trachea

Abstract

Stimulants of protease-activated receptor-2 (PAR 2 ), such as Ser-Leu-Ile-Gly-Arg-Leu-NH 2 (SLIGRL), cause airway smooth muscle relaxation via the release of the bronchodilatory prostanoid prostaglandin E 2 (PGE 2 ). The principal aim of the current study was to determine whether compounds that inhibit PGE 2 reuptake by the prostaglandin transporter [bromocresol green and U46619 (9,11-dideoxy-9␣,11␣-methanoepoxy PGF2␣) and PGE 2 metabolism by 15-hydroxyprostaglandin dehydrogenase (thiazolidenedione compounds rosiglitazone and ciglitazone) significantly enhanced the capacity of SLIGRL to elevate PGE 2 levels and produce relaxation in isolated segments of upper and lower mouse trachea. SLIGRL produced concentrationdependent increases in PGE 2 levels and smooth muscle relaxation, although both effects were significantly greater in lower tracheal segments than in upper tracheal segments. SLIGRLinduced increases in PGE 2 levels were significantly enhanced in the presence of ciglitazone and rosiglitazone, and these effects were not inhibited by GW9662 (2-chloro-5-nitrobenzanilide), a peroxisome proliferator-activated receptor-␥ antagonist. SLI-GRL-induced relaxation responses were also significantly enhanced by ciglitazone and rosiglitazone, whereas responses to isoprenaline, a PGE 2 -independent smooth muscle relaxant, were unaltered. Ciglitazone and rosiglitazone alone produced concentration-dependent increases in PGE 2 levels and smooth muscle relaxation, and these responses were inhibited by indomethacin, a cyclooxygenase inhibitor. Bromocresol green, an inhibitor of prostaglandin transport, significantly enhanced SLIGRL-induced increases in PGE 2 levels and relaxation. Immunohistochemical staining for 15-hydroxyprostaglandin dehydrogenase was relatively intense over airway smooth muscle, as was staining for the prostaglandin transporter over both airway smooth muscle and epithelium. In summary, inhibitors of PGE 2 reuptake and metabolism significantly potentiate PAR 2 -mediated increases in PGE 2 levels and smooth muscle relaxation in murine-isolated airways.

Novel Small Airway Bronchodilator Responses to Rosiglitazone in Mouse Lung Slices

“…We found that the effects of RGZ were additive, with the partial relaxation achieved in the presence of a maximally effective concentration of ALB. This finding contrasts with a single study in mouse trachea, where ISO-mediated relaxation was not increased in the presence of RGZ despite a modest dilation seen with RGZ alone (17). However, these contrasting results have been obtained under different experimental conditions, measuring either ORIGINAL RESEARCH changes in area of small airways in perfused lung slices or changes in force in trachea under static conditions.…”

“…In addition, dilator responses to RGZ were maintained in the presence of validated effective concentrations of indomethacin or NOLA (17,31). These findings allowed us to exclude the possible contributions of cAMP or epithelial-derived relaxing factors such as PGE 2 or NO to RGZ-mediated relaxation of small airways in perfused lung slices.…”

“…A previous study in mouse trachea had shown indomethacin-sensitive relaxation in response to RGZ in a static organ bath under isometric conditions (17). This relaxation was attributed to inhibition of endogenous PGE 2 metabolism (48), with PGE 2 accumulating at high enough levels to elicit ASMC relaxation.…”

“…In the latter study, oral treatment with RGZ over 4 weeks produced improvements in forced expiratory flow values as compared with treatment with the inhaled steroid beclometasone dipropionate; this result may reflect a direct effect of RGZ to reduce small airway obstruction (16). In another study, RGZ was shown to relax mouse isolated tracheal preparations precontracted with carbachol (17), but its acute effects on small airways were not assessed.…”

Rosiglitazone elicits in vitro relaxation in airways and precision cut lung slices from a mouse model of chronic allergic airways disease

“…In BALB/c mice, treatment with either RGZ or CGZ inhibited OVA-induced airway inflammation and fibrosis as well as the development of AHR (14,32,35), with the effects of the synthetic PPAR␥ ligands mimicked by AdPPAR␥ (15, 17) and abrogated by GW9662 (14,15,17,35). Although RGZ also reduced the development of AHR in OVA-challenged C57BL/6 mice, the increase in BAL inflammatory cells in this mouse strain was not affected, suggesting that RGZ may also modulate AHR by a mechanism that is independent of inhibition of inflammatory cell recruitment to the airway (33).In addition to these inhibitory effects in models of chronic AAD, RGZ has been shown to elicit acute relaxation of mouse tracheal segments and intrapulmonary airways in precision cut lung slices (PCLS) precontracted with muscarinic agonists in vitro (3,12). In PCLS, RGZ elicited complete relaxation under conditions of impaired ␤-adrenoceptor agonist responsiveness, opposing contraction by inhibiting calcium oscillations and sensitivity (3).…”