Nanoparticle-chelator conjugates as inhibitors of amyloid-beta aggregation and neurotoxicity: a novel therapeutic approach for Alzheimer disease

Abstract

Oxidative stress and amyloid-beta are considered major etiological and pathological factors in the initiation and promotion of neurodegeneration in Alzheimer disease (AD). Insomuch as causes of such oxidative stress, transition metals, such as iron and copper, which are found in high concentrations in the brains of AD patients and accumulate specifically in the pathological lesions, are viewed as key contributors to the altered redox state. Likewise, the aggregation and toxicity of amyloid-beta is dependent upon transition metals. As such, chelating agents that selectively bind to and remove and/or "redox silence" transition metals have long been considered as attractive therapies for AD. However, the blood-brain barrier and neurotoxicity of many traditional metal chelators has limited their utility in AD or other neurodegenerative disorders. To circumvent this, we previously suggested that nanoparticles conjugated to iron chelators may have the potential to deliver chelators into the brain and overcome such issues as chelator bioavailability and toxic side-effects. In this study, we synthesized a prototype nanoparticle-chelator conjugate (Nano-N2PY) and demonstrated its ability to protect human cortical neurons from amyloid-beta-associated oxidative toxicity. Furthermore, Nano-N2PY nanoparticle-chelator conjugates effectively inhibited amyloid-beta aggregate formation. Overall, this study indicates that Nano-N2PY, or other nanoparticles conjugated to metal chelators, may provide a novel therapeutic strategy for AD and other neurodegenerative diseases associated with excess transition metals.

Figure 1

Synthesis of a nanoparticle-chelator conjugate (Nano-N2PY). (a) Reaction of carboxylic functionalized nanoparticles with CMC in MES buffer solution at room temperature for a half hour. (b) Conjugation of activated carboxylic nanoparticles with excessive MAEHP in MES at room temperature (a half hour).

Figure 2

TEM images of nanoparticle samples. (a) Nanoparticles without chelator conjugation and iron binding. (b) Nanoparticles with both reactions. The samples were dispersed in Milli-Q water, drop-cast onto carbon-coated copper grid and examined via TEM after air dry at room temperature.

Figure 3

Cytotoxicity of Aβ, Nano-N2PY and Aβ/Nano-N2PY (compared with control) when incubated with neuron cells as measured by LDH cytotoxicity detection assay. Absorbance wavelength measured in this experiment was 490 nm with a reference at 630 nm. Values were represented as mean ± standard errors (n = 5. *Significantly different from control group at P < 0.05).

Figure 4

Effects of Aβ, Nano-N2PY and Aβ/Nano-N2PY on cell proliferation of neuron cells as determined by WST assay. Absorbance wavelength measured here was 450 nm and a reference 600 nm. Results were represented as mean ± standard errors (n = 3. *Significantly different from control group at P < 0.05).

Figure 5

Fluorescence microscopy images. (a) Precipitates of Aβ aggregates formed in PBS without Nano-N2PY. (b) No such precipitates from PBS containing Nano-N2PY.