D‑galactose‑induced mitochondrial DNA oxidative damage in the auditory cortex of rats.

Chronic administration of D‑galactose (D‑gal) is a useful method for establishing a model of natural aging in the auditory system. Previous studies have demonstrated that NADPH oxidases (NOXs) may be an important source of reactive oxygen species (ROS) in the peripheral auditory system (PAS) and cause an increase in mitochondrial DNA (mtDNA) common deletion (CD) levels in the PAS and central auditory system (CAS) of rats with D‑gal‑induced aging. However, the source of the ROS in the CAS and the mechanisms of age‑related hearing loss (ARHL) have yet to be elucidated. In the present study, male Sprague Dawley rats were administered a daily injection of D‑gal (150, 300 and 500 mg/kg, respectively) for eight weeks. All three doses of D‑gal caused a significant increase in the expression of NOX2, 8‑hydroxy‑2‑deoxyguanosine, a biomarker of DNA oxidative damage, and uncoupling protein 2, together with a decrease in the mitochondrial total antioxidant capabilities in the auditory cortex, as compared with the control rats (injected daily with the same volume of 0.9% saline for eight weeks). The levels of the mtDNA CD were also increased in the auditory cortex of the D‑gal‑induced aging rats. These findings suggest that both NOX‑ and mitochondria‑associated ROS generation may contribute to mtDNA oxidative damage in the auditory cortex of the CAS of D‑gal‑induced aging rats. This study may provide novel insight into the development of ARHL.