Objective To investigate the effect and mechanism of cyclooxygenase-2 (COX-2) on sodium arsenic-induced microglia activation in mice.

Methods Twenty of C57BL/6J male mice were randomly divided into a control group supplied with tap water and an arsenic exposure group administered with drinking water containing 50 mg/L sodium arsenite (NaAsO₂) continuously for 12 weeks to establish a chronic arsenic exposure model. Morris water maze was used to test learning and memory ability of the mice. Hematoxylin-eosin (HE) staining and transmission electron microscopy were used to observe pathological changes of neuron and ultrastructure in hippocampus. Immunofluorescence microscopy was used to determine expression of ionized calcium-binding adapter molecule 1 (IBA-1) in hippocampus. The protein expressions of IBA-1, COX-2, transcription factor nuclear factor kappa-Bp65 (NF-κBp65) were detected with Western blot. The concentration of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) was measured with enzyme-linked immunosorbent assay (ELISA).

Results Compared to the control group, the mice with arsenic exposure had significantly increased escape latency time (50.79 ± 12.30 vs. 29.01 ± 18.10 seconds) but decreased effectively traveled distance (9.34 ± 2.34 vs. 11.78 ± 1.25 centimeters) (both P < 0.05l). Pathological changes such as disarrangement of cells, edema and nuclei atrophy were observed in the hippocampus of arsenic exposed mice. The protein expression of IBA-1 was increased in arsenic exposed mice based on observation of green fluorescence aggregation with fluorescence microscope. In comparison with those in hippocampus of the control mice, significantly higher levels of IBA-1 (1.01 ± 0.12 vs. 0.75 ± 0.13), NF-κBp65 (1.23 ± 0.11 vs. 0.86 ± 0.14), COX-2 (1.14 ± 0.13 vs. 0.74 ± 0.12), IL-6 (93.61 ± 3.18 vs. 43.37 ± 1.11 pg/mL) and TNF-α (604.00 ± 25.02 vs. 198.46 ± 9.93 pg/mL) were detected in arsenic exposed mice (P < 0.05 for all).

Conclusion Chronic arsenic exposure-induced learning and memory impairment are associated with the activation of microglia by the activation of NF-κB and the increase in the secretion of pro-inflammatory cytokines by upregulation of COX-2 in mice.