Effects of astaxanthin onaxonal regeneration via cAMP/PKA signaling pathway in mice with focal cerebral infarction.

OBJECTIVE: To investigate the effect of astaxanthin on the neurological function of the middle cerebral artery occlusion (MCAO) mice and its possible mechanism.
MATERIALS AND METHODS: The male C57BL/6 mice were selected to establish the model of MCAO via electrocoagulation, and they were randomly divided into 4 groups: the sham operation group (Sham group), the cerebral ischemia model group (MCAO group), the astaxanthin intervention group (gavage with 30 mg/kg astaxanthin for 28 days, twice a day; Ast group), and astaxanthin + H89 group (Ast + H89 group). At 3, 7, 14, and 28 d after the operation, the Rotarod test and the balance beam footstep error test were performed. The brain tissues were taken for immunofluorescence to observe the expression of the growth-associated protein 43 (GAP43) in the cortex around the infarction. The GAP43 protein and mRNA levels in the cortex around the infarction were detected via Western blotting, and the Reverse Transcription-Polymerase Chain Reaction (RT-PCR), the levels of cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) in the bilateral cerebral cortex were detected via enzyme-linked immunosorbent assay (ELISA), and the PKAc and phosphorylated-cAMP-response element-binding protein (p-CREB) levels in the bilateral cerebral cortex were detected via Western blotting. Biotin dextran amine (BDA) was injected at 14 d after the operation, and the brain was taken at 28 d. The BDA-labeled neurons or axons were observed in the bilateral cortex via immunohistochemistry and immunofluorescence, and the colocalization of BDA and GAP43 in the cortex around the infarction was observed using double immunofluorescence staining.
RESULTS: Compared with those in the MCAO group, the mean residence time in the Rotarod test was significantly increased, and the times of the footstep error on the balance beam were significantly reduced in the Ast group. In the Ast group, the expression of GAP43 in the cortex around the infarction, the GAP43 protein, and the mRNA levels were all significantly elevated. Immunofluorescence showed that in the Ast group, the number of the labeled neurons and axons in the bilateral cortex was slightly larger than that in the other groups, and the number of labeled axonal fibers in the ischemic cortex was significantly increased. The colocalization area of BDA and GAP43 was observed, and it was found that the positive area in the Ast group was significantly larger than that in the MCAO group. The cAMP level was higher in the Ast group and Ast + H89 group at 7, 14, and 28 d after operation, while the PKA level was lower in the Ast + H89 group at 7 and 14 d after operation and higher in the Ast group at 7, 14, and 28 d after operation. The results of the Western blotting manifested that the PKAc and p-CREB levels were upregulated in the Ast group at 7, 14, and 28 d after the operation, and downregulated in the Ast + H89 group at 7, 14, and 28 d after the operation.
CONCLUSIONS: Astaxanthin activates the cAMP/PKA/CREB signaling pathway by increasing the cAMP concentration in brain tissues, ultimately promoting the axonal regeneration in the cerebral cortex and improving the motor function.