Curcumin-loaded chitosan-bovine serum albumin nanoparticles potentially enhanced Aβ 42 phagocytosis and modulated macrophage polarization in Alzheimer's disease

Abstract

Alzheimer's disease (AD) is the most common neurodegenerative disorder in the elderly population. In the treatment of AD, some obstacles, including drug penetration difficulty through the blood-brain barrier (BBB), inadequate clearance of the Aβ peptide, and the massive release of inflammatory factors, must be urgently overcome. To solve these problems, we developed special and novel nanoparticles (NPs) made of chitosan (CS) and bovine serum albumin (BSA) to enhance the penetration of drugs through the BBB. Curcumin as a potent anti-inflammatory agent was used to increase the phagocytosis of the Aβ peptide. The results demonstrated that curcumin-loaded CS-BSA NPs effectively increased drug penetration through the BBB, promoted the activation of microglia, and further accelerated the phagocytosis of the Aβ peptide. Furthermore, curcumin-loaded CS-BSA NPs inhibited the TLR4-MAPK/NF-κB signaling pathway and further downregulated M1 macrophage polarization. This study suggested that curcumin-loaded CS-BSA NPs hold the potential to enhance Aβ 42 phagocytosis through modulating macrophage polarization in AD.

Keywords: Alzheimer’s disease; Aβ peptide; Blood–brain barrier; Curcumin; Nanoparticles.

Fig. 1

Characterization of curcumin loaded CS-BSA NPs. a TEM image of curcumin loaded CS-BSA NPs. b Dynamic light scattering (DLS) analysis of the obtained curcumin loaded CS-BSA NPs. c Zeta potential analysis of the obtained curcumin loaded CS-BSA NPs. d The in vitro release profile of the obtained curcumin-loaded CS-BSA NPs in phosphate-buffered saline with a pH of 7.4 at 37 °C for 48 h

Fig. 2

Analysis of the penetration mechanism of free curcumin and curcumin-loaded CS-BSA NPs through hCMEC/D3 cells. a Fluorescence spectrum analysis of the penetration rates of free curcumin and curcumin-loaded CS-BSA NPs. Results are expressed as means ± standard deviation (n = 3). *P < 0.05, **P < 0.01 vs the penetration rates of free curcumin at 1 h. ^##P < 0.01 vs the penetration rates of curcumin loaded CS-BSA NPs at 1 h. b Effects of endocytic inhibitors on the penetrated ability of free curcumin and curcumin-loaded CS-BSA NPs. Results are expressed as means ± standard deviation (n = 3). ^##P < 0.01 vs relative penetrated ratio of curcumin loaded CS-BSA NPs treated with chlorpromazine

Fig. 3

Viability of RAW 264.7 cells (M1) and hCMEC/D3 cells after incubation with different amounts of naked CS-BSA NPs for 24 h (n = 3)

Fig. 4

The uptake of free curcumin and curcumin loaded CS-BSA NPs in RAW 264.7 cells (M1) for 6 h. Curcumin showed green fluorescent color and indicated the intracellular location of free curcumin and curcumin loaded CS-BSA NPs. The nucleus was stained with Hoechst (blue) for 15 min at 37 °C. The scale bar is 50 μm and applies to all figure parts

Fig. 5

Phagocytosis of Aβ 42 induced by free curcumin and curcumin loaded CS-BSA NPs. The scale bar is 50 μm and applies to all figure parts

Fig. 6

Western blot analyses of the expression levels of TNF-α, IL-6, TLR4, and phosphorylation of ERK, JNK, p38, and nuclear factor (NF)-κB in RAW 264.7 cells (M1 phenotype) after treatments with free curcumin and curcumin loaded CS-BSA NPs