Expression of Nitric Oxide Synthases and Oxidative Stress-Related Genes in Patients with Chronic Otitis Media

Nitric oxide (NO) and oxidative stress-related factors are involved in the pathophysiology of various inflammatory diseases; however, their specific roles in chronic otitis media (COM) remain unclear. Accordingly, the present study aimed to analyze messenger RNA (mRNA) expression levels of NO synthases and antioxidant defense genes in COM tissues, and to determine their association with clinical characteristics, including bacterial infection, otorrhea, and hearing loss. Reverse transcription quantitative polymerase chain reaction assays were performed to evaluate mRNA expression levels of NO synthases (NOS1, NOS2, and NOS3), reactive oxygen species-generating enzyme (NOX4), and antioxidant enzymes (CAT, SOD2, and HO-1) in middle ear tissues obtained from 27 patients who underwent surgery for COM. To compare expression profiles, patients were categorized according to bacterial culture results, presence of otorrhea, and hearing loss type (conductive, sensorineural, or normal hearing). Among 27 patients who underwent surgery for COM, otorrhea was diagnosed in 51.9%, and bacterial cultures were positive in 29.6% (predominantly Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus). The mRNAs of all 7 target genes (CAT, HO-1, NOS1, NOS2, NOS3, SOD2, and NOX4) were expressed in the middle ear tissues of all patients. Overall, mRNA expression levels were highest for NOX4, followed by CAT, NOS2, SOD2, NOS1, HO-1, and NOS3. Notably, NOS2 expression was significantly higher in the culture-positive group, whereas CAT and SOD2 expression were significantly elevated in the culture-negative group (p < 0.05), indicating that the expression patterns of oxidative stress- and antioxidant-related genes differed according to middle ear bacterial infection status. In contrast, no significant differences in gene expression were observed based on the presence of otorrhea or hearing loss (p > 0.05). NO synthase and antioxidant-related genes were commonly expressed in COM tissues, and their expression patterns differed significantly according to the presence of middle ear bacterial infection rather than otorrhea or hearing loss. Specifically, the concurrent pattern of elevated NOS2 expression and reduced CAT and SOD2 expression in the culture-positive group suggests that bacterial infection shifts the middle ear microenvironment toward a pro-oxidative state by enhancing NO-mediated oxidative stress, while impairing antioxidant defense. This study identified NOS2, CAT, and SOD2 as key molecular markers of the oxidative–antioxidant imbalance associated with bacterial infection in COM, providing a molecular basis for future therapeutic strategies aimed at restoring redox homeostasis in infected middle ear tissues.