Abstract:

AIM: To investigate the effective therapeutic time window of idazoxan in rats with experimental autoimmune encephalomyelitis (EAE). METHODS: Fifty SD rats were randomly divided into four groups: (1) Control group (n=8), which was given no treatment, but raised in the same condition as the experimental groups. (2) EAE-NS group (n=14), which received saline rather than idazoxan; (3) EAE-idazoxan 1-7 d group (n=14), which idazoxan was given at 2 mg/kg through i.p. (b.i.d.) from the first day of immunization to the 7th day; (4) EAE-idazoxan 8-14 d group (n=14), which received 2 mg/kg idazoxan through i.p. (b.i.d.) from the 8th day of immunization to the 14th day. Rat's behavioral changes were measured twice daily after immunizations until they were killed at 15th day after immunization to collect the cerebrum and the lumbar spinal cord.  HE staining and luxol fast blue (LFB) staining was performed on the tissue sections to show tissue damage, infiltration of inflammatory cells and demyelination. Immunohistochemistry was used to determine the expression of Iba1 and GFAP in the spinal cord.RESULTS:Idazoxan improved neurological behaviours: EAE-idazoxan 8-14 d group significantly reduced the daily clinical scores and cumulative neurobehavioral scores compared with the EAE-NS group (P<0.05). Idazoxan reduced EAE histopathology: Inflammatory cell entry into the brain and spinal cord was significantly reduced in EAE-idazoxan 8-14 d group compared with the EAE-NS group (P<0.05). Demyelinationin the brain and spinal cord was also reduced in EAE-idazoxan 8-14 d group based on LFB staining when compared with EAE-NS group (P<0.05). Idazoxan reduced Iba1 expression: EAE induced significant increase in the number of Iba1 expressing cells in the brain and reduce astrocytic(GFAP) activation. Compared with the EAE-NS group, the number of Iba1 positive cells EAE-idazoxan 8-14 d Group was significantly reduced (P<0.01). ELISA analysis showed that the expressions of IL-17 (P<0.01) decreased and IL-10 increased significantly in the CNS in EAE-idazoxan 8-14 d group rats compared with EAE-NS group rats. CONCLUSION: The effective therapeutic time window for idazoxan is in the period of disease onset of EAE disease progression. The protective effect of idazoxan on EAE is associated with the attenuated microglial activation and shifting the balance of inflammatory cytokines.

Key words: idazoxan, experimental autoimmune encephalomyelitis, microglia, inflammatory cytokines