Secondary brain damage, the increase of swelling and pressure that occurs after a primary injury, leads to an increase in mortality in brain injury patients. Substance P is a neuropeptide that is released in abundance after brain injury, and is responsible for much of this secondary damage. Therefore, research efforts have focused on decreasing the amount of Substance P immediately after injury, in order to decrease secondary damage.
N-acetyl-L-tryptophan (NAT) has been shown to reduce Substance P and subsequent damage, leading to an improved outcome. However, the administration of NAT has had to be within 5 hours of injury in order to be effective. A recent study found that when NAT is made membrane-permeable, that is, able to cross the blood-brain barrier, it can be administered later (up to 12 hours in this study) and still improve outcome after injury.
The critical window for treating traumatic brain injury is very small, and studies that support the widening of this window are beneficial to future clinical practices.
Donkin JJ, Cernak I, Blumbergs PC, & Vink R. A Substance P antagonist reduces axonal injury and improves neurologic outcome when administered up to 12 hours after traumatic brain injury. Journal of Neurotrauma. (February 2011).