TNF and concussion: Proinflammatory cytokines such as tumor necrosis factor (TNF)-α, which are over-expressed after TBI, can increase proteolysis of enzymes required for PC synthesis.42,43 The inability to synthesize PC in the presence of adequate substrates may explain the ineffectiveness of supplementation with upstream metabolites such as citicoline (CDP-choline) to improve outcomes after brain injury caused by stroke and TBI.13,44 This is consistent with our findings of similar levels of choline in controls compared with mTBI subjects.