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

Background: Inhaled ozone (O-3) 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 O-3 mediates harmful effects are poorly understood. Objectives: To investigate the effect of O-3 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 O-3 (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 O-3 displayed an impaired insulin response. Plasma insulin and leptin levels were reduced in O-3-exposed mice. Three-week exposure to O-3 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 O-3 although the relative percentage of CD4 + T cell decreased in blood and adipose tissue. Multiple inflammatory genes including CXCL-11, IFN-gamma, TNF alpha, 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 O-3-exposed mice. Conclusions: Repeated O-3 inhalation induces oxidative stress, adipose inflammation and insulin resistance.