Inflammatory mechanism of hippocampal tissue injury induced by PM2.5 in nasal drip in mice

Abstract

Objective: To investigate the inflammatory mechanism of nasal instillation of fine particulate matter (PM2.5)on hippocampal tissue injury in mice.Methods: Thirty C57BL/6J mice were randomly divided into 3 groups(n=10):control group, low-dose group, high-dose group. The nasal instillation doses of PM2.5 in the low-dose group and the high-dose group were 1.5 mg/kg BW and 7.5 mg/kg BW, respectively, and the control group was given saline with an equal volume. Saline was sprayed once every other time for 12 times. The serum levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) were determined by ELISA method. HE staining and electron microscopy were used to observe the pathological changes and ultrastructure of lung tissue and hippocampus. The inflammatory cytokine levels in hippocampus were detected by antibody chip technique. Results: There was no significant effect of PM2.5 nasal instillation on serum TNF-α, IL-1β and IL-6 levels (P＞0.05), and there was no obvious pathological changes in lung tissue structure. In hippocampus, low-dose and high-dose PM2.5 exposure could lead to disordered neuronal arrangement in the hippocampal CA3 region, and there were neurological changes around the neuron cells and ultrastructural changes such as edema around small blood vessels. Compared with the control group, the levels of inflammatory cytokines such as CX3CL1, CSF2 and TECK in the low-dose group were increased significantly (P ＜0.05), while sTNFR1 was decreased significantly (P＜0.05); the inflammatory factors CX3CL1, CSF2, and TCA-3 were significantly increased in the high-dose group (P＜0.05), while leptin, MIG, and FASLG were significantly decreased (P＜0.05). Conclusion: Nasal instillation of PM2.5 can induce tissue damage in the hippocampus of mice, and its mechanism of action may be the olfactory brain pathway. The increasing of TNF-α and IL-6 and the decreasing of sTNFR1 and FASLG may be involved in inflammatory mechanisms.