Inducible nitric oxide synthase (iNOS) in sinonasal polyp pathogenesis

Inducible nitric oxide synthase (iNOS) in sinonasal polyp pathogenesis. Objectives: We investigated the role of inducible nitric oxide synthase (iNOS) in the pathogenesis of sinonasal polyps. Methods: Adult patients (21 men, 3 women) with nasal polyposis underwent functional endoscopic sinus surgery. Nine adults without polyps (6 men) who underwent septoplasty and/or rhinoplasty served as controls. Polyp specimens came from three regions: the maxillary sinus (10), ethmoid sinus (14), and nasal cavity (10). Control group samples (9) came from the inferior turbinate. Specimens were evaluated in eight mucosal layers for count and distribution of inflammatory cells and iNOS expression. An iNOS positivity index (PI) was determined for the epithelium (E), subepithelial layer of the lamina propria (SE), and deep paraglandular layer of the mucosa (D). Results: Polymorphonuclear cell (PMNC) % values of the ethmoid and maxillary sinus and overall ethmoid sinus PI were significantly higher in the polyp group. Patients with longer polyp duration, D-perivascular (D-pv), and a higher Brinkmann index had decreased ethmoid sinus D PIs. However, in older patients and patients with longer polyp duration, perivascular PIs increased in maxillary sinus SE and D, respectively. Furthermore, as PMNC % and iNOS-PMNC PI increased, SE_glandular and epithelial_apical iNOS values decreased. In the ethmoid and maxillary sinuses, iNOS_D_ endothelial values increased but decreased in the nasal cavity. Conclusions: iNOS may play a role in sinonasal polyp pathogenesis, especially in mucosal SE and D layers. Increased vascular permeability, stromal edema, inflammatory cell migration into the stroma of the mucosa, and increased mucosal gland secretion may result in polyp formation.