Glutamine supplementation provides neuroprotection by inhibiting endoplasmic reticulum stress response after traumatic brain injury in rats

Abstract

Objective To investigate the effects of glutamine (Gln) supplementation on neurologica severity score, brain edema, neuron apoptosis, and endoplasmic reticulum stress (ERS) response after traumatic brain injury (TBI) in rats. Methods TBI rat models were established using modified Feeney's method. Eighty Sprague-Dawley rats were divided into 4 groups with a random number table: sham operation group (Sham group), TBI group, Gln supplementation group (TBI+ Gln group) and ERS inducer 2-deoxy-D-glucose group (TBI+ Gln+ 2-DG group). We measured the rats' neurobehavioral outcomes by modified neurologic severity score (mNSS) on day 1, 3, 7 and 14 after TBI. Neuron apoptosis was detected using TUNEL staining. Brain water content was measured with wet-dry weight method.The apoptosis-related protein (caspase-12, caspase-3, and Bcl-2) and ERS-related cytokines [inositol-requiring enzyme 1(IRE-1), C/EBP homologous protein (CHOP)] expressions in TBI cerebral cortex were determined by immunohistochemistry staining and Western blot. Results Compared with the Sham group, the levels of brain edema, mNSS, apoptosis-related protein (caspase-12, caspase-3, Bcl-2) and ERS-related proteins (IRE-1, CHOP) were significantly increased in the other three groups(all P=0.00). Compared with the TBl group, the TBI+ Gln group showed significant lower brain water content[3 d: (81.39±0.59)% vs.(83.54±0.52)%, P=0.04; 7 d: (74.86±0.38)% vs. (77.32±0.66)%, P=0.03], improved mNSS(8.63±0.22 vs. 10.37±0.29, P=0.03), suppressed expressions of apoptosis- and ERS-related proteins (caspase-12, caspase-3, IRE-1, and CHOP)(P=0.01, P<0.01), and increased expression of anti-apoptotic protein Bcl-2 (P=0.02). Compared with the TBI+ Gln group, the expression of ERS-related factors (IRE-1 and CHOP), brain edema level, and neurological severity were increased in the TBI+ Glu+ 2-DG group. Conclusion Glutamine supplementation may have neuroprotection function, demonstrated as reducing brain edema and neuron apoptosis, and improving neurobehaviroal outcomes after TBI, possibly mediated by inhibiting TBI-induced ERS response. Key words: Traumatic brain injury; Glutamine; Endoplasmic reticulum stress; Neuroprotection