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Chronic apocynin treatment attenuates beta amyloid plaque size and microglial number in hAPP(751)(SL) mice.

Lull ME, Levesque S, Surace MJ, Block ML - PLoS ONE (2011)

Bottom Line: Despite in vitro analyses demonstrating that apocynin and DM ameliorate Aβ-induced extracellular superoxide production and neurotoxicity, both DM and apocynin failed to significantly affect learning and memory tasks or synaptic density in hAPP(751)(SL) mice.To discern how apocynin was affecting plaque levels (plaque load) and microglial number in vivo, in vitro analysis of microglia was performed, revealing no apocynin effects on beta-amyloid (Aβ) phagocytosis, microglial proliferation, or microglial survival.Despite absence of clear neuroinflammation, apocynin was still able to reduce both plaque size and microglial number, suggesting that apocynin may have additional therapeutic effects independent of anti-inflammatory characteristics.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Neurobiology, Virginia Commonwealth University Medical Campus, Richmond, Virginia, United States of America.

ABSTRACT

Background: NADPH oxidase is implicated in neurotoxic microglial activation and the progressive nature of Alzheimer's Disease (AD). Here, we test the ability of two NADPH oxidase inhibitors, apocynin and dextromethorphan (DM), to reduce learning deficits and neuropathology in transgenic mice overexpressing human amyloid precursor protein with the Swedish and London mutations (hAPP(751)(SL)).

Methods: Four month old hAPP(751)(SL) mice were treated daily with saline, 15 mg/kg DM, 7.5 mg/kg DM, or 10 mg/kg apocynin by gavage for four months.

Results: Only hAPP(751)(SL) mice treated with apocynin showed reduced plaque size and a reduction in the number of cortical microglia, when compared to the saline treated group. Analysis of whole brain homogenates from all treatments tested (saline, DM, and apocynin) demonstrated low levels of TNFα, protein nitration, lipid peroxidation, and NADPH oxidase activation, indicating a low level of neuroinflammation and oxidative stress in hAPP(751)(SL) mice at 8 months of age that was not significantly affected by any drug treatment. Despite in vitro analyses demonstrating that apocynin and DM ameliorate Aβ-induced extracellular superoxide production and neurotoxicity, both DM and apocynin failed to significantly affect learning and memory tasks or synaptic density in hAPP(751)(SL) mice. To discern how apocynin was affecting plaque levels (plaque load) and microglial number in vivo, in vitro analysis of microglia was performed, revealing no apocynin effects on beta-amyloid (Aβ) phagocytosis, microglial proliferation, or microglial survival.

Conclusions: Together, this study suggests that while hAPP(751)(SL) mice show increases in microglial number and plaque load, they fail to exhibit elevated markers of neuroinflammation consistent with AD at 8 months of age, which may be a limitation of this animal model. Despite absence of clear neuroinflammation, apocynin was still able to reduce both plaque size and microglial number, suggesting that apocynin may have additional therapeutic effects independent of anti-inflammatory characteristics.

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Apocynin reduces plaque size in the cortex and hippocampus of hAPP(751)SL mice.Mice were treated daily with 15 mg/kg dextromethorphan (DM), 7.5 mg/kg DM, or 10 mg/kg apocynin for four months. The size of β-amyloid plaques was measured for each group and compared to control, vehicle-treated animals. Representative images show 6E10 staining of β-amyloid protein for each group in the cortex (A) and hippocampus (B), respectively. Quantification of plaque size the cortex (C) and hippocampus (D) revealed that only apocynin significantly decreased the size of plaques, compared to vehicle. DM, at either dose, did not alter plaque size in the cortex or the hippocampus. Plaque size was determined as the absolute plaque area divided by the absolute plaque number. *p<0.05 vs. vehicle, 1-way ANOVA with Bonferroni post-hoc test.
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pone-0020153-g001: Apocynin reduces plaque size in the cortex and hippocampus of hAPP(751)SL mice.Mice were treated daily with 15 mg/kg dextromethorphan (DM), 7.5 mg/kg DM, or 10 mg/kg apocynin for four months. The size of β-amyloid plaques was measured for each group and compared to control, vehicle-treated animals. Representative images show 6E10 staining of β-amyloid protein for each group in the cortex (A) and hippocampus (B), respectively. Quantification of plaque size the cortex (C) and hippocampus (D) revealed that only apocynin significantly decreased the size of plaques, compared to vehicle. DM, at either dose, did not alter plaque size in the cortex or the hippocampus. Plaque size was determined as the absolute plaque area divided by the absolute plaque number. *p<0.05 vs. vehicle, 1-way ANOVA with Bonferroni post-hoc test.

Mentions: Brain slices from each group (vehicle, 15 mg/kg DM, 7.5 mg/kg DM, 10 mg/kg apocynin) were stained for two markers of Aβ deposition: 6E10 (measuring all Aβ peptide) and thioflavin S (measuring β-sheets of Aβ). This allowed for the measurement of plaque number, mean plaque size, and the percentage of area occupied by plaques in both the cortex and hippocampus. Using 6E10 staining, both the cortex and hippocampus display reduced plaque size in apocynin treated animals, compared to vehicle-treated controls (p<0.05; Figure 1). DM, at either dose, did not produce any significant reduction in plaque size. No significant differences were observed in plaque number or percentage area in the hippocampus or cortex with any of the treatments (data not shown). Additionally, ThioflavinS staining of β-sheets revealed no differences between vehicle, DM, and apocynin-treated hAPP(751)SL mice (data not shown).


Chronic apocynin treatment attenuates beta amyloid plaque size and microglial number in hAPP(751)(SL) mice.

Lull ME, Levesque S, Surace MJ, Block ML - PLoS ONE (2011)

Apocynin reduces plaque size in the cortex and hippocampus of hAPP(751)SL mice.Mice were treated daily with 15 mg/kg dextromethorphan (DM), 7.5 mg/kg DM, or 10 mg/kg apocynin for four months. The size of β-amyloid plaques was measured for each group and compared to control, vehicle-treated animals. Representative images show 6E10 staining of β-amyloid protein for each group in the cortex (A) and hippocampus (B), respectively. Quantification of plaque size the cortex (C) and hippocampus (D) revealed that only apocynin significantly decreased the size of plaques, compared to vehicle. DM, at either dose, did not alter plaque size in the cortex or the hippocampus. Plaque size was determined as the absolute plaque area divided by the absolute plaque number. *p<0.05 vs. vehicle, 1-way ANOVA with Bonferroni post-hoc test.
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Related In: Results  -  Collection

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pone-0020153-g001: Apocynin reduces plaque size in the cortex and hippocampus of hAPP(751)SL mice.Mice were treated daily with 15 mg/kg dextromethorphan (DM), 7.5 mg/kg DM, or 10 mg/kg apocynin for four months. The size of β-amyloid plaques was measured for each group and compared to control, vehicle-treated animals. Representative images show 6E10 staining of β-amyloid protein for each group in the cortex (A) and hippocampus (B), respectively. Quantification of plaque size the cortex (C) and hippocampus (D) revealed that only apocynin significantly decreased the size of plaques, compared to vehicle. DM, at either dose, did not alter plaque size in the cortex or the hippocampus. Plaque size was determined as the absolute plaque area divided by the absolute plaque number. *p<0.05 vs. vehicle, 1-way ANOVA with Bonferroni post-hoc test.
Mentions: Brain slices from each group (vehicle, 15 mg/kg DM, 7.5 mg/kg DM, 10 mg/kg apocynin) were stained for two markers of Aβ deposition: 6E10 (measuring all Aβ peptide) and thioflavin S (measuring β-sheets of Aβ). This allowed for the measurement of plaque number, mean plaque size, and the percentage of area occupied by plaques in both the cortex and hippocampus. Using 6E10 staining, both the cortex and hippocampus display reduced plaque size in apocynin treated animals, compared to vehicle-treated controls (p<0.05; Figure 1). DM, at either dose, did not produce any significant reduction in plaque size. No significant differences were observed in plaque number or percentage area in the hippocampus or cortex with any of the treatments (data not shown). Additionally, ThioflavinS staining of β-sheets revealed no differences between vehicle, DM, and apocynin-treated hAPP(751)SL mice (data not shown).

Bottom Line: Despite in vitro analyses demonstrating that apocynin and DM ameliorate Aβ-induced extracellular superoxide production and neurotoxicity, both DM and apocynin failed to significantly affect learning and memory tasks or synaptic density in hAPP(751)(SL) mice.To discern how apocynin was affecting plaque levels (plaque load) and microglial number in vivo, in vitro analysis of microglia was performed, revealing no apocynin effects on beta-amyloid (Aβ) phagocytosis, microglial proliferation, or microglial survival.Despite absence of clear neuroinflammation, apocynin was still able to reduce both plaque size and microglial number, suggesting that apocynin may have additional therapeutic effects independent of anti-inflammatory characteristics.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Neurobiology, Virginia Commonwealth University Medical Campus, Richmond, Virginia, United States of America.

ABSTRACT

Background: NADPH oxidase is implicated in neurotoxic microglial activation and the progressive nature of Alzheimer's Disease (AD). Here, we test the ability of two NADPH oxidase inhibitors, apocynin and dextromethorphan (DM), to reduce learning deficits and neuropathology in transgenic mice overexpressing human amyloid precursor protein with the Swedish and London mutations (hAPP(751)(SL)).

Methods: Four month old hAPP(751)(SL) mice were treated daily with saline, 15 mg/kg DM, 7.5 mg/kg DM, or 10 mg/kg apocynin by gavage for four months.

Results: Only hAPP(751)(SL) mice treated with apocynin showed reduced plaque size and a reduction in the number of cortical microglia, when compared to the saline treated group. Analysis of whole brain homogenates from all treatments tested (saline, DM, and apocynin) demonstrated low levels of TNFα, protein nitration, lipid peroxidation, and NADPH oxidase activation, indicating a low level of neuroinflammation and oxidative stress in hAPP(751)(SL) mice at 8 months of age that was not significantly affected by any drug treatment. Despite in vitro analyses demonstrating that apocynin and DM ameliorate Aβ-induced extracellular superoxide production and neurotoxicity, both DM and apocynin failed to significantly affect learning and memory tasks or synaptic density in hAPP(751)(SL) mice. To discern how apocynin was affecting plaque levels (plaque load) and microglial number in vivo, in vitro analysis of microglia was performed, revealing no apocynin effects on beta-amyloid (Aβ) phagocytosis, microglial proliferation, or microglial survival.

Conclusions: Together, this study suggests that while hAPP(751)(SL) mice show increases in microglial number and plaque load, they fail to exhibit elevated markers of neuroinflammation consistent with AD at 8 months of age, which may be a limitation of this animal model. Despite absence of clear neuroinflammation, apocynin was still able to reduce both plaque size and microglial number, suggesting that apocynin may have additional therapeutic effects independent of anti-inflammatory characteristics.

Show MeSH
Related in: MedlinePlus