Sex Differences in Plasma Levels of Endocannabinoids and Related Lipids Before and After acute and repeated mTBI: an exploratory study for plasma biomarkers for mTBI

Mild traumatic brain injury (mTBI) is common diagnosis across all age groups and while most symptoms resolve within a few weeks; between 10 and 25 percent of mTBI patients suffer long-term problems. Known as post-concussion syndrome (PCS), symptoms include headache, a range of cognitive deficits, and depression. Currently, there are no established treatments for PCS and no clear predictive biometrics to determine which patients are at increased risk. Previous studies have identified some protein-derived plasma biomarkers for mTBI, however, the effects of mTBI on lipid signaling molecules and metabolites in blood is largely unknown. Endogenous lipids (endolipids) such as the endocannabinoids (eCBs) and their congeners are lipid signaling molecules that are associated with promoting neuroprotective responses after head trauma in animal models. Here, we examine the plasma lipidome using a rat model of acute and repeated mTBI that we previously demonstrated had a sex dependent change in neuroinflammation wherein females showed a higher degree of neurodegeneration after repeated head-injury than males. Key results of this exploratory lipidomics screen here demonstrates that acute head injury drives significantly more changes in plasma endolipids in males (32%) than females (8%), whereas, on the second day of head injury, only 11% change in males but 15% in females. Some key endolipids were modified in both males are precursors for resolving molecules and this was lacking in females. Given that females with repeated mTBI in this model demonstrated aspects of PCS, this could be an important component in evaluating clinical cases. Endolipids in the screen were measurable in plasma using only 100µL, a volume necessary to be able to perform multiple blood draws on these rodent subjects. This threshold provides evidence that the levels of these endolipids could be readily measured throughout a patient’s recovery. Therefore, this family of endolipids has the potential to provide data on the progression of the injury and could be another crucial aspect in predicting mTBI outcomes.