RO1138452

Non-allergic angioedema is a potentially life-threatening condition caused by accumulation of bradykinin and subsequent activation of bradykinin type 2 receptors (B2). Since COX activity plays a pivotal role in B2 signaling, the aim of this study was to determine which prostaglandins are the key mediators and which COX, COX-1 or COX-2, is predominantly involved.

We used Miles assays to assess the effects of inhibitors of COX, 5-lipoxygenase, epoxyeicosatrienoic acid generation, cytosolic phospholipase A₂α and a variety of prostaglandin receptor antagonists on bradykinin-induced dermal extravasation in C57BL/6 and COX-1-deficient mice (COX-1^-/-). In addition, the prostacyclin metabolite 6-keto-PGF_1α was quantified by ELISA in subcutaneous tissue from C57BL/6 and human dermal microvascular endothelial cells. In the latter, 6-keto-PGF_1α was also quantified and identified by LC-MS/MS.

Unspecific COX inhibition by ibuprofen and diclofenac significantly reduced B2-mediated dermal extravasation in C57BL/6 but not COX-1^-/-. Likewise, inhibition of cytosolic phospholipase A₂α showed similar effects. Furthermore, extravasation in COX-1^-/- was generally lower than in C57BL/6. Of the prostaglandin antagonists used, only the prostacyclin receptor antagonist RO1138452 showed a significant reduction of dermal extravasation. Moreover, 6-keto-PGF_1α concentrations were increased after bradykinin treatment in subcutaneous tissue from C57BL/6 as well as in human dermal microvascular endothelial cells and this increase was abolished by diclofenac.

Our findings suggest that COX-1-dependent prostacyclin production is critically involved in dermal extravasation after activation of B2 in small dermal blood vessels. Targeting prostacyclin production and/or signaling appears to be a suitable option for acute treatment of non-allergic angioedema.

Cyclophosphamide (CP) has been widely used in the treatment of various malignancies and autoimmune diseases, but acrolein, a byproduct of CP, causes severe hemorrhagic cystitis as the major side effect of CP. On the other hand, a large amount of prostacyclin (PGI 2 ) is produced in bladder tissues, and PGI 2 has been shown to play a critical role in bladder homeostasis. PGI 2 is biosynthesized from prostaglandin (PG) H 2 , the common precursor of PGs, by PGI 2 synthase (PTGIS) and is known to also be involved in inflammatory responses. However, little is known about the roles of PTGIS‐derived PGI 2 in bladder inflammation including CP‐induced hemorrhagic cystitis. Using both genetic and pharmacological approaches, we here revealed that PTGIS‐derived PGI 2 ‐IP (PGI 2 receptor) signaling exacerbated CP‐induced bladder inflammatory reactions. Ptgis deficiency attenuated CP‐induced vascular permeability and chemokine‐mediated neutrophil migration into bladder tissues and then suppressed hemorrhagic cystitis. Treatment with RO1138452, an IP selective antagonist, also suppressed CP‐induced cystitis. We further found that cystitis‐related nociceptive behavior was also relieved in both Ptgis−/− mice and RO1138452‐treated mice. Our findings may provide new drug targets for bladder inflammation and inflammatory pain in CP‐induced hemorrhagic cystitis.