Protective effects of melanocortins on short-term changes in a rat model of traumatic brain injury

Objective: Treatment for traumatic brain injury remains elusivedespite compelling evidence from animal models for a variety oftherapeutic targets. Melanocortins have established neuroprotective effects against experimental ischemic stroke. We investigated whether melanocortin treatment of traumatic brain injury induces neuroprotection and promotes functional recovery.Design: Randomized experiment.Setting: Research laboratory at a university hospital.Subjects: Male Sprague-Dawley rats (n=215).Interventions: Experimental rat model of diffuse traumaticbrain injury, the impact-acceleration model.Measurement and Main Results: Brain tissue nitrites, phosphorylation level of extracellular signal-regulated kinases, and c-jun N-terminal kinases; and expression of active caspase-3,tumor necrosis factor-alpha, BAX, and Bcl-2 as well as serum levels of interleukin-6, high mobility group box-1, interleukin-10, and brain histologic damage were evaluated 24 or 48 hrs after theinsult. Sensorimotor orientation and limb use were evaluated atday 7 and learning and memory at days 23–30 after injury.Posttraumatic treatment every 12 hrs with the melanocortin analog [Nle4, D-Phe7]-alpha-melanocyte-stimulating hormone (starting 3 or 6 hrs after injury) inhibited traumatic brain injury-induced upregulation of nitric oxide synthesis, phosphorylation level of extracellular signal-regulated kinases, phosphorylation level of c-jun N-terminal kinases, and active caspase-3; reduced expressions/levels of tumor necrosis factor-alpha, BAX, interleukin-6, and high mobility group box-1; and increased those of Bcl-2 and interleukin-10. These molecular changes were associated with a reduction in brain tissue damage, as highlighted by histopathological findings and improved functional recovery. Pretreatment with the melanocortin MC4 receptor antagonist HS024 abated the positive effects of [Nle4, D-Phe7]-alpha-melanocyte-stimulating hormone.Conclusions: Our data indicate that melanocortins protectagainst traumatic brain injury, in a broad time window andthrough activation of MC4 receptors, by counteracting the maintraumatic brain injury-related mechanisms of damage. Thesefindings could have major clinical implications.