Repeated ozone exposure exacerbates insulin resistance and activates innate immune response in genetically susceptible mice

Inhaled ozone (O₃) has been demonstrated as a harmful pollutant and associated with chronic inflammatory diseases such as diabetes and vascular disorders. However, the underlying mechanisms by which O₃ mediates harmful effects are poorly understood. Objectives: To investigate the effect of O₃ exposure on glucose intolerance, immune activation and underlying mechanisms in a genetically susceptible mouse model. Methods: Diabetes-prone KK mice were exposed to filtered air (FA), or O₃ (0.5 ppm) for 13 consecutive weekdays (4 h/day). Insulin tolerance test (ITT) was performed following the last exposure. Plasma insulin, adiponectin, and leptin were measured by ELISA. Pathologic changes were examined by H&E and Oil-Red-O staining. Inflammatory responses were detected using flow cytometry and real-time PCR. Results: KK mice exposed to O₃ displayed an impaired insulin response. Plasma insulin and leptin levels were reduced in O₃-exposed mice. Three-week exposure to O₃ induced lung inflammation and increased monocytes/macrophages in both blood and visceral adipose tissue. Inflammatory monocytes/macrophages increased both systemically and locally. CD4 + T cell activation was also enhanced by the exposure of O₃ although the relative percentage of CD4 + T cell decreased in blood and adipose tissue. Multiple inflammatory genes including CXCL-11, IFN-γ, TNFα, IL-12, and iNOS were up-regulated in visceral adipose tissue. Furthermore, the expression of oxidative stress-related genes such as Cox4, Cox5a, Scd1, Nrf1, and Nrf2, increased in visceral adipose tissue of O₃-exposed mice. Conclusions: Repeated O₃ inhalation induces oxidative stress, adipose inflammation and insulin resistance.