Apocynin administration does not improve behavioral and neuropathological deficits in a transgenic mouse model of Alzheimer's disease

Abstract

In addition to mitochondria, NADPH oxidase (NOX) is a source of oxidative stress, which can induce oxidative damage in Alzheimer's disease (AD). For this reason, several groups have investigated the effect of its inhibition. In AD mice, NADPH oxidase 2 (NOX2) deficiency improved behavior and cerebrovascular function, and reduced oxidative stress. In our study, we administered the NOX inhibitor apocynin to Tg19959 mice, and found that it did not improve cognitive and synaptic deficits, and did not decrease amyloid deposition, microgliosis and hyperphosphorylated tau. However, apocynin reduced carbonyl levels in the cerebral cortex but not the hippocampus, which may have not been sufficient to ameliorate symptoms. Also, the reduction of NOX-mediated oxidative stress may not be sufficient to prevent AD, since other sources of reactive oxygen species such as mitochondria may be more important.

Figure 1

(A) Water consumption of both vehicle and apocynin in female and male mice. No significant differences were found between groups. (B) Distance moved during the acquisition period of the Morris water maze in Tg19959 mice (Tg) and their wild-type (Wt) littermates with (Apo) or without (Veh) apocynin. Tg19959 mice swam significantly longer than wild-type mice (Fisher; p<0.05). Apocynin treatment did not improve their navigational and learning performances. (C) Western blotting of synaptophysin and α-tubulin in the cortex and the hippocampus of Tg19959 mice (Tg) treated with (Apo) or without (Veh) apocynin. (D) Ratio of synaptophysin to α-tubulin normalized by Tg19959 mice fed vehicle. No significant differences were found between groups. All data were expressed as means ± standard errors.

Figure 2

(A) Number per 0.75mm² and (B) percent area covered by amyloid plaques in the cortex and the hippocampus of Tg19959 mice (Tg) treated with (Apo) or without (Veh) apocynin. Apocynin administration did not reduce amyloid deposition in Tg19959 mice. Cortical and hippocampal levels of 6% SDS-soluble Aβ₄₂ (C) and Aβ₄₀ (D) assessed by ELISA (data normalized by Tg19959 mice fed vehicle). There was a trend towards an increase of Aβ₄₀ level in the cortex of Tg19959 mice treated with apocynin compared to vehicle (Fisher; p=0.12). (E) Western blotting of hyperphosphorylated tau and α-tubulin in the cortex and the hippocampus of Tg19959 mice (Tg) treated with (Apo) or without (Veh) apocynin. (F) Ratio of hyperphosphorylated tau to α-tubulin normalized by Tg19959 mice fed vehicle. There was a trend towards a decrease of hyperphosphorylated tau level in the hippocampus of Tg19959 mice treated with apocynin compared to vehicle (Fisher; p=0.15). (G) Percent area covered by activated microglia in the cortex and the hippocampus of Tg19959 mice (Tg) treated with (Apo) or without (Veh) apocynin. Apocynin administration did not change microglial activation in Tg19959 mice. All data were expressed as means ± standard errors.

Figure 3

(A) Western blotting of Rac1 and β-actin in the membrane enriched fraction of the wild-type (Wt) and Tg19959 cortex (Tg) treated with (Apo) or without (Veh) apocynin. (B) Ratio of Rac1 to β-actin normalized by wild-type mice fed vehicle. There was a trend towards an increase in Rac1 level in Tg19959 mice compared to wild-type littermates (Fisher; p=0.06). Apocynin reduced significantly Rac1 level in Tg19959 mice (Fisher; p<0.05). (C) Western blotting of carbonyls and α-tubulin in the cortex and the hippocampus of Tg19959 mice (Tg) treated with (Apo) or without (Veh) apocynin. (D) Ratio of carbonyls to α-tubulin normalized by Tg19959 mice fed vehicle. Apocynin decreased significantly carbonyl level in the cortex of Tg19959 mice treated with apocynin compared to vehicle (Fisher; p<0.05). All data were expressed as means ± standard errors.