Neuronal Apoptosis And Expression Of Omi/HtrA2 And Smac In Hippocampal CA1 Area In A Rat Model Of Gulf War Syndrome

Background and Purpose: Gulf War Syndrome (GWS), also named Gulf War illness, has become a growing concern of US government, Gulf war veterans and their families. The etiology and pathogenesis is extremely complex, and various environmental factors and chemical and physical stress exposure, such as nerve gas, depleted uranium, oil combustion smoke, Pyridostigmine Bromide (PB), pesticides (DEET, permethrin, etc.), pressure stress and psychological factors. Epidemiologic studies that have assessed independent effects of multiple exposures during the Gulf War have consistently identified only two as significant risk factors for Gulf War syndrome: pyridostigmine bromide and pesticides. MRI studies have shown that the volume of hippocampus and cingulate gyrus lost in GWS patients. Animal experiments also hints hippocampal neuronal cell death. Omi/HtrA2 and Smac/DIABLO are two kinds of mitochondrial proteins, play an important role in the process of cell apoptosis , when attacked by apoptosis stimulating factors, the permeability of mitochondrial membrane has changed, both of them released into the cytoplasmic, play their maturity after the role of promoting apoptosis. Minocycline is a second-generation semisynthetic tetracycline antibiotics, and recently found having neuroprotective effects as caspase-3 inhibitor. Thus, the purpose of this study is to observe the apoptosis change in CA1 field of the hippocampal neurons and the expression of Omi/HtrA2 and Smac and to explore the neuroprotective mechanism of minocycline in a rat model of Gulf War syndrome.Methods: The rat models of GWS were estalished by reference of Abdel-Rahman method. The animals were randomly assigned into four groups:⑴Control group (n=6): animals were treated with a dermal application of 70% ethanol and oral water daily for 28 days;⑵Restraint group (n=6): animals were treated with 20 min of restraint stress in dark environment every day.⑶GWS model group (n=6) : animals were treated daily with PB (1.3mg/kg/day, oral in water) and DEET (40 mg/kg/day, dermal in 70% ethanol) based on Restraint group; and⑷Minocycline group (n=6): animals were treated daily with peritoneal injection of minocycline(45mg/kg/day,) based on GWS group. Following the exposure regimen described above, each animal was perfused through the heart with saline followed by 4% paraformaldehyde in Tris buffer. The brain was removed, postfixed, embedded in paraffin and cut in slice. The expression of Omi/HtrA2 and Smac was detected with immunohistochemical staining and neuronal apoptosis was detected by TUNEL method in the hippocampal CA1.area.Results: There are no significant differences in neuronal apoptosis counting and Omi/HtrA2 and Smac integrated optical density in hippocampal CA1 area in the restraint group compared with the control group(P>0.05). The number of neuronal apoptosis and Omi/HtrA2 and Smac integrated optical density in hippocampal CA1 area increased significantly in the GWS model group compared with the control group (P<0.01). In the minocycline groups, the number of neuronal apoptosis (P<0.05)and Omi/HtrA2 and Smac integrated optical density in hippocampal CA1 area decreased significantly compared with the GWS model group(P<0.01)..Conclusion: 1.The expression of Omi/HtrA2 and Smac as well as the number of neuronal apoptosis increased in CA1 field of the hippocampal neurons in a rat model of Gulf War syndrome. 2. Omi/HtrA2 and Smac might play important roles in the process of cell apoptosis in a rat model of Gulf War syndrome. 3.Minocycline might have neuroprotective effects by inhibiting the expression of caspase-3 in hippocampal CA1 cell in the gulf war syndrome model.