Sex-Specific Effects of Ozone Induced Oxidative Stress in Brain

Air pollution is a well-known risk factor for cardiovascular and respiratory morbidities. Air pollution induces worse pulmonary health outcomes in women compared to men due in part to a greater susceptibility to inflammatory lung disease. Recently, air pollutants (e.g., ozone [O3]) have also been associated with various adverse outcomes to brain health including increased occurrence of cognitive disorders, Alzheimer’s disease, anxiety, and depressive disorders and even suicide. In the present study, we hypothesized that the sex differences underlying this increased susceptibility to inflammatory lung disease would also affect sex-specific transcription responses in brain to air pollutants. Male and female adult Long-Evans rats were exposed to O3 for 2 consecutive days (0.8 ppm, 4 hr/day), rats were sacrificed, brain regions were dissected on ice, snap-frozen, and stored at -80oC. Complex I, complex II and complex IV enzymes were measured using kits from Abcam® in the frontal cortex, cerebellum. Assays for protein carbonyls and various markers of oxidative stress (OS) were also conducted on these tissues. Additionally, qPCR was performed on hypothalamus and hippocampus with a panel of genes for OS, glucocorticoid signaling and glia. O3 produced more oxidative damage in the brains of females compared to males as evidenced by higher levels of protein carbonyls. Differences in mitochondrial bioenergetics may contribute to the increase carbonyls since activity levels of complex enzymes were shown to differ according to sex. Males showed higher levels of activity of mitochondrial complex enzymes I and IV while females showed increased activity of Complex II, which is often associated with increased reactive oxygen species generation. Genes related to glucocorticoid signaling (Fkbp4, Fkbp5, Hsp90aa1, Hspa4, nr3c1, nr3c2) showed that males and females respond comparably to ozone exposure by increasing expression of glucocorticoid responsive genes. Similarly, O3 exposure decreased the expression of Bdnf in both hippocampus and hypothalamus in males and females. However, expression of genes related to mechanisms of OS (Cat, Dhcr24, Foxm1, Gpx1, Gss, Nfe2l2, Sod1) showed the most sexually dimorphic response than any other class of gene assayed. Taken together, these results indicate that sex-specific responses to air pollution may, in part, be caused by difference in brain transcriptomic responses. (This abstract does not necessarily reflect USEPA policy).

Impact/Purpose

Air pollution (e.g., ozone) is a well-known risk factor for cardiovascular and respiratory morbidities. Air pollution induces worse pulmonary health outcomes in women compared to men due in part to a greater susceptibility to inflammatory lung disease. Current research of the adverse effects of ozone focus on peripheral morbidity, for this study we focused on central effects in the brain. However, the mechanisms underlying these differences remain unknown.  The brain is unique with varieties of neurons and glial cells, each having specialized functions contributing to behavior, learning, and autonomic control. These functions have high energy requirements from mitochondrial bioenergetics, which are likely targets of chemical-induced neurotoxicity. We assayed the enzymatic rates of key mitochondrial enzymes (complex I, II and IV), in the frontal cortex and cerebellum in rats exposed to ozone. Our results indicate that ozone significantly affects brain mitochondrial bioenergetics and gene expression related to glucocorticoid signaling.

Citation

Kodavanti, Prasada Rao, D. Freeborn, AND M. Valdez. Sex-Specific Effects of Ozone Induced Oxidative Stress in Brain. Society of Toxicology (SOT 2022 - 61st Annual Meeting and ToxExpo), San Diego, California, March 27 - 31, 2022.