Hyperbaric oxygen preconditioning protects against traumatic brain injury at high altitude.
BACKGROUND
Recent studies have shown that preconditioning with hyperbaric oxygen (HBO) can reduce ischemic and hemorrhagic brain injury. We investigated effects of HBO preconditioning on traumatic brain injury (TBI) at high altitude and examined the role of matrix metalloproteinase-9 (MMP-9) in such protection.


METHODS
Rats were randomly divided into 3 groups: HBO preconditioning group (HBOP; n = 13), high-altitude group (HA; n = 13), and high-altitude sham operation group (HASO; n = 13). All groups were subjected to head trauma by weight-drop device, except for HASO group. HBOP rats received 5 sessions of HBO preconditioning (2.5 ATA, 100% oxygen, 1 h daily) and then were kept in hypobaric chamber at 0.6 ATA (to simulate pressure at 4000m altitude) for 3 days before operation. HA rats received control pretreatment (1 ATA, room air, 1 h daily), then followed the same procedures as HBOP group. HASO rats were subjected to skull opening only without brain injury. Twenty-four hours after TBI, 7 rats from each group were examined for neurological function and brain water content; 6 rats from each group were killed for analysis by H&E staining and immunohistochemistry.


RESULTS
Neurological outcome in HBOP group (0.71 +/- 0.49) was better than HA group (1.57 +/- 0.53; p < 0.05). Preconditioning with HBO significantly reduced percentage of brain water content (86.24 +/- 0.52 vs. 84.60 +/- 0.37; p < 0.01). Brain morphology and structure seen by light microscopy was diminished in HA group, while fewer pathological injuries occurred in HBOP group. Compared to HA group, pretreatment with HBO significantly reduced the number of MMP-9-positive cells (92.25 +/- 8.85 vs. 74.42 +/- 6.27; p < 0.01).


CONCLUSIONS
HBO preconditioning attenuates TBI in rats at high altitude. Decline in MMP-9 expression may contribute to HBO preconditioning-induced protection of brain tissue against TBI.
Hu
S L
SL
Department of Neurosurgery, Southwest Hospital of the Third Military Medical University, Chongqing, PR China.
Hu
R
R
Li
F
F
Liu
Z
Z
Xia
Y Z
YZ
Cui
G Y
GY
Feng
H
H
D000531:Altitude; D000704:Analysis of Variance; D000818:Animals; D001929:Brain Edema / Q000209:etiology / Q000517:prevention & control; D001930:Brain Injuries / Q000150:complications / Q000378:metabolism / Q000517:prevention & control*; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D006931:Hyperbaric Oxygenation / Q000379:methods*; D019194:Ischemic Preconditioning / Q000379:methods*; D008297:Male; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D009460:Neurologic Examination; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D020780:Matrix Metalloproteinase 9