We have tested a hypothesis that the natural product curcuminoids, which has epidemiologic and experimental rationale for use in AD, may improve the innate immune system and increase amyloid-␤ (A␤) clearance from the brain of patients with sporadic Alzheimer's disease (AD). Macrophages of a majority of AD patients do not transport A␤ into endosomes and lysosomes, and AD monocytes do not efficiently clear A␤ from the sections of AD brain, although they phagocytize bacteria. In contrast, macrophages of normal subjects transport A␤ to endosomes and lysosomes, and monocytes of these subjects clear A␤ in AD brain sections. Upon A␤ stimulation, mononuclear cells of normal subjects up-regulate the transcription of ␤-1,4-mannosyl-glycoprotein 4-␤-N-acetylglucosaminyltransferase (MGAT3) (P < 0.001) and other genes, including Toll like receptors (TLRs), whereas mononuclear cells of AD patients generally down-regulate these genes. Defective phagocytosis of A␤ may be related to down-regulation of MGAT3, as suggested by inhibition of phagocytosis by using MGAT3 siRNA and correlation analysis. Transcription of TLR3, bditTLR4, TLR5, bditTLR7, TLR8, TLR9, and TLR10 upon A␤ stimulation is severely depressed in mononuclear cells of AD patients in comparison to those of control subjects. In mononuclear cells of some AD patients, the curcuminoid compound bisdemethoxycurcumin may enhance defective phagocytosis of A␤, the transcription of MGAT3 and TLRs, and the translation of TLR2-4. Thus, bisdemethoxycurcumin may correct immune defects of AD patients and provide a previously uncharacterized approach to AD immunotherapy.amyloid-␤ ͉ phagocytosis ͉ endocytosis ͉ MGAT3 siRNA A ccording to the amyloid-␤ (A␤) hypothesis, amyloidosis occurring in the brain of patients with Alzheimer's disease (AD) by fibrillar A␤ 1-42 and 1-40 (1) and A␤ oligomers (2) is a leading cause of neurodegeneration in AD (3). Macrophages and microglia are the innate immune cells responsible for clearance of pathogens and waste products. We have shown that blood-borne monocyte/ macrophages of AD patients migrate across the blood-brain barrier into AD brain but are defective in clearance of A␤ in neuritic plaques (4), and they overexpress cyclooxygenase-2 and inducible NO synthase (4). Resident microglia in AD brain display markers of inflammation (5, 6), phagocytosis (7), and proinflammatory but not prophagocytic genes (8). However, most microglia invading A␤ plaques in transgenic mouse models are bone marrow-derived, not resident microglia (9). Thus, the brains of AD patients and transgenic mice seem to display inflammatory responses by microglia and defective A␤ clearance by blood-borne macrophages. Consequently, the defective innate immune system of AD patients might be a culprit in brain amyloidosis leading to brain inflammation.The mechanisms of neurodegeneration produced by abnormally folded proteins, A␤, and phosphorylated remain an enigma (10).The pathogenesis of neurodegeneration in AD involves the impact of polymorphic proteins, such as amyloid precursor...

Patients with Alzheimer's disease (AD) suffer from brain amyloidosis related to defective clearance of amyloid-beta (Abeta) by the innate immune system. To improve the innate immune system of AD patients, we studied immune stimulation of macrophages by 1alpha,25(OH)2-vitamin D3(1,25D3) in combination with curcuminoids. AD patients' macrophages segregate into Type I (positively stimulated by curcuminoids regarding MGAT-III transcription) and Type II (not stimulated). In both Type I and Type II macrophages, 1,25D3 strongly stimulated Abeta phagocytosis and clearance while protecting against apoptosis. Certain synthetic curcuminoids in combination with 1,25D3 had additive effects on phagocytosis in Type I but not Type II macrophages. In addition, we investigated the mechanisms of 1,25D3 and curcuminoids in macrophages. The 1,25D3 genomic antagonist analog MK inhibited 1,25D3 but not curcuminoid effects, suggesting that 1,25D3 acts through the genomic pathway. In silico, 1,25D3 showed preferential binding to the genomic pocket of the vitamin D receptor, whereas bisdemethoxycurcumin showed preference for the non-genomic pocket. 1,25D3 is a promising hormone for AD immunoprophylaxis because in Type I macrophages combined treatment with 1,25D3 and curcuminoids has additive effects, and in Type II macrophages 1,25D3 treatment is effective alone. Human macrophages are a new paradigm for testing immune therapies for AD.

Neuronal accumulation of oligomeric amyloid-β (Aβ) is considered the proximal cause of neuronal demise in Alzheimer disease (AD) patients. Blood-borne macrophages might reduce Aβ stress to neurons by immigration into the brain and phagocytosis of Aβ. We tested migration and export across a blood-brain barrier model, and phagocytosis and clearance of Aβ by AD and normal subjects’ macrophages. Both AD and normal macrophages were inhibited in Aβ export across the blood-brain barrier due to adherence of Aβ-engorged macrophages to the endothelial layer. In comparison to normal subjects’ macrophages, AD macrophages ingested and cleared less Aβ, and underwent apoptosis upon exposure to soluble, protofibrillar, or fibrillar Aβ. Confocal microscopy of stained AD brain sections revealed oligomeric Aβ in neurons and apoptotic macrophages, which surrounded and infiltrated congophilic microvessels, and fibrillar Aβ in plaques and microvessel walls. After incubation with AD brain sections, normal subjects’ monocytes intruded into neurons and uploaded oligomeric Aβ. In conclusion, in patients with AD, macrophages appear to shuttle Aβ from neurons to vessels where their apoptosis may release fibrillar Aβ, contributing to cerebral amyloid angiopathy.

Treatment of Alzheimer's disease (AD) is difficult due to ignorance of its pathogenesis. AD patients have defects in phagocytosis of amyloid-β (1-42) (Aβ) in vitro by the innate immune cells, monocyte/macrophages and in clearance of Aβ plaques [5]. The natural product curcuminoids enhanced brain clearance of Aβ in animal models. We, therefore, treated macrophages of six AD patients and 3 controls by curcuminoids in vitro and measured Aβ uptake using fluorescence and confocal microscopy. At baseline, the intensity of Aβ uptake by AD macrophages was significantly lower in comparison to control macrophages and involved surface binding but no intracellular uptake. After treatment of macrophages with curcuminoids, Aβ uptake by macrophages of three of the six AD patients was significantly (P < 0.001 to 0.081) increased. Confocal microscopy of AD macrophages responsive to curcuminoids showed surface binding in untreated macrophages but co-localization with phalloidin in an intracellular compartment after treatment. Immunomodulation of the innate immune system by curcuminoids might be a safe approach to immune clearance of amyloidosis in AD brain.

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