Effects of Docosahexaenoic Acid and Sex on Inflammatory Markers, Phagocytic Capacity, and Oxidative Stress After Controlled Cortical Impact in Rat Pups

Traumatic brain injury (TBI) is a leading cause of acquired neurological disability in children of both sexes. Little is known about sex-dependent differences in oxidative stress and inflammatory response, two important variables in the developing brain after TBI. Using controlled cortical impact (CCI) in 17-day-old male rats to model pediatric TBI, we showed that docosahexaenoic acid (DHA) improved neurological outcomes and decreased markers of post-injury day 1 (D1) oxidative stress and D3 pro-inflammatory microglial activation. Sex affects DHA metabolism, TBI outcomes, and neuroinflammation. Whether DHA sex-dependently affects markers of oxidative stress or brain inflammation in immature pups after TBI is unknown. We hypothesized that DHA would decrease oxidative stress and increase markers of inflammation resolution after CCI in male pups only and would not affect control (CON) pups of either sex. We analyzed CD11b+ cells from rat brains at D1, D3, and D7 for inflammation-related protein expression, DHR123 oxidation as a marker of reactive oxygen species (ROS) production, and phagocytic capacity. In CCI males, DHA increased macrophage phagocytic capacity at D1 and D7. DHA abrogated increased ROS after CCI in macrophages of both sexes at D1 but at D3 decreased ROS only in males. DHA instead increased ROS in female CCI macrophages at D3 and D7. DHA decreased ROS in male D7 CCI microglia but not in females. In both sexes, DHA increased the relative abundance of CCI macrophages expressing IL-10 and CD206, proteins associated with inflammation resolution. In CON rats, DHA decreased phagocytic capacity in D3 male microglia and in D7 female macrophages. DHA increased ROS in D3 and D7 female microglia. Collectively, in males DHA was associated with increased phagocytosis and inflammation-resolving protein expression together with decreased ROS in macrophages after CCI, markers often associated with neuroprotection. In females, DHA had opposite effects on ROS in CCI macrophages. Contrary to our hypothesis, DHA affected CON microglia. We present preliminary data showing that DHA affected phospholipid abundance for some specific classes in both sexes and, in males only, for others. Our findings raise the importance of using sex-matched injured and control subjects when researching putative neurotherapeutics targeting inflammation and oxidative stress after pediatric TBI.