Abstract
Blast-induced traumatic brain injury has dramatically increased in combat troops in today’s military operations. We previously reported that antioxidant treatment can provide protection to the peripheral auditory end organ, the cochlea. In the present study, we examined biomarker expression in the brains of rats at different time points (3 hours to 21 days) after three successive 14 psi blast overpressure exposures to evaluate antioxidant treatment effects on blast-induced brain injury. Rats in the treatment groups received a combination of antioxidants (2,4-disulfonyl α-phenyl tertiary butyl nitrone and N-acetylcysteine) one hour after blast exposure and then twice a day for the following two days. The biomarkers examined included an oxidative stress marker (4-hydroxy-2-nonenal, 4-HNE), an immediate early gene (c-fos), a neural injury marker (glial fibrillary acidic protein, GFAP) and two axonal injury markers [amyloid beta (A4) precursor protein, APP, and 68 kDa neurofilament, NF-68]. The results demonstrate that blast exposure induced or up-regulated the following: 4-HNE production in the dorsal hippocampus commissure and the forceps major corpus callosum near the lateral ventricle; c-fos and GFAP expression in most regions of the brain, including the retrosplenial cortex, the hippocampus, the cochlear nucleus, and the inferior colliculus; and NF-68 and APP expression in the hippocampus, the auditory cortex, and the medial geniculate nucleus (MGN). Antioxidant treatment reduced the following: 4-HNE in the hippocampus and the forceps major corpus callosum, c-fos expression in the retrosplenial cortex, GFAP expression in the dorsal cochlear nucleus (DCN), and APP and NF-68 expression in the hippocampus, auditory cortex, and MGN. This preliminary study indicates that antioxidant treatment may provide therapeutic protection to the central auditory pathway (the DCN and MGN) and the non-auditory central nervous system (hippocampus and retrosplenial cortex), suggesting that these compounds have the potential to simultaneously treat blast-induced injuries in the brain and auditory system.
Highlights
Blast-induced traumatic brain injury has dramatically increased in combat troops and civilians due to improvements in explosive devices employed in military conflicts and terrorist activities [1,2,3]
Significant recovery in auditory brainstem responses (ABR) threshold shifts in the antioxidant treatment group was observed at all test frequencies (2–16 kHz) at 7 and 21 days after blast exposure (p < 0.01 or 0.001, Table 1 and [54])
A significant decrease in distortion product otoacoustic emission (DPOAE) level shifts was found in the treatment group (7.5-15 dB) at 7 days after blast exposure in the higher frequency range of 4-16 kHz when compared to the blast group (20-28 dB, p < 0.05 or 0.01)
Summary
Blast-induced traumatic brain injury (bTBI) has dramatically increased in combat troops and civilians due to improvements in explosive devices employed in military conflicts and terrorist activities [1,2,3]. Blast exposure primarily affects gas-containing organs, such as the middle ear, lung, and gastrointestinal tract [4,5,6,7,8,9]. More recent evidence indicates that blast exposure causes solid organ injury. Among these solid organs, the brain is very vulnerable to blast overpressure, due to the fact that shock waves can penetrate through the skull without significant change in amplitude and waveform [3,10,11]. Blast exposure can cause hemorrhage, edema, pseudoaneurysm formation, vasoconstriction, hypoperfusion in the brain, and disruption of the blood-brain barrier [3,18,19,20,21,22,23,24,25]
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