It is demonstrated by using high-level ab initio computations that the yellow curcumin pigment, bis-(4-hydroxy-3-methoxyphenyl)-1,6-diene-3,5-dione, in the east Indian root plant turmeric (Curcuma longa) exhibits unique charge and bonding characteristics that facilitate penetration into the blood-brain barrier and binding to amyloid beta (Abeta). Alzheimer's disease is caused by Abeta accumulation in the brain cells combined with oxidative stress and inflammation. Consistent with the recent experimental work by Cole and co-workers (Yang, F., et al. J. Biol. Chem. 2004, 280, 5892-5901) that demonstrates curcumin pigment's binding ability to Abeta both in vivo and in vitro, it is shown here that curcumin possesses suitable charge and bonding features to facilitate the binding to Abeta. In addition, curcumin's anti-inflammatory and antioxidant properties are also attributed to electronic and structural features. It is shown that the presence of an enolic center and two phenolic polar groups separated by an essentially hydrophobic bridge of a conjugated network provides both hydrophobic and hydrophilic features to the curcumin pigment, thereby facilitating penetration into the blood-brain barrier through the former property and then binding to Abeta oligomer through the latter property. Both density functional and Møller-Plesset perturbation (MP2) computations have been carried out on the curcumin pigment to obtain fully optimized geometries in the gas phase and aqueous solution and also the atomic charges. Different isomers (keto and enol forms) have been considered to show that the enol form is the most favored and has all of the properties for an ideal antioxidant with also features to penetrate the blood-brain barrier and to bind to Abeta. This is demonstrated with natural bond charges, highest occupied and lowest unoccupied molecular orbitals, dipole moments, and Laplacian plots. The computed ionization potential and electron affinity show that curcumin has a low molecular hardness and thus has a propensity to dissociate its phenolic -OH, and the resulting charge undergoes delocalization throughout the structure, resulting in excitonic features. This feature seems to be also important for its binding capability to human proteins such as human serum albumin and Abeta.
Alzheimer's disease (AD) involves amyloid beta (Abeta) accumulation, oxidative damage, and inflammation, and risk is reduced with increased antioxidant and anti-inflammatory consumption. The phenolic yellow curry pigment curcumin has potent anti-inflammatory and antioxidant activities and can suppress oxidative damage, inflammation, cognitive deficits, and amyloid accumulation. Since the molecular structure of curcumin suggested potential Abeta binding, we investigated whether its efficacy in AD models could be explained by effects on Abeta aggregation. Under aggregating conditions in vitro, curcumin inhibited aggregation (IC(50) = 0.8 microM) as well as disaggregated fibrillar Abeta40 (IC(50) = 1 microM), indicating favorable stoichiometry for inhibition. Curcumin was a better Abeta40 aggregation inhibitor than ibuprofen and naproxen, and prevented Abeta42 oligomer formation and toxicity between 0.1 and 1.0 microM. Under EM, curcumin decreased dose dependently Abeta fibril formation beginning with 0.125 microM. The effects of curcumin did not depend on Abeta sequence but on fibril-related conformation. AD and Tg2576 mice brain sections incubated with curcumin revealed preferential labeling of amyloid plaques. In vivo studies showed that curcumin injected peripherally into aged Tg mice crossed the blood-brain barrier and bound plaques. When fed to aged Tg2576 mice with advanced amyloid accumulation, curcumin labeled plaques and reduced amyloid levels and plaque burden. Hence, curcumin directly binds small beta-amyloid species to block aggregation and fibril formation in vitro and in vivo. These data suggest that low dose curcumin effectively disaggregates Abeta as well as prevents fibril and oligomer formation, supporting the rationale for curcumin use in clinical trials preventing or treating AD.
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-beta (Abeta) clearance from the brain of patients with sporadic Alzheimer's disease (AD). Macrophages of a majority of AD patients do not transport Abeta into endosomes and lysosomes, and AD monocytes do not efficiently clear Abeta from the sections of AD brain, although they phagocytize bacteria. In contrast, macrophages of normal subjects transport Abeta to endosomes and lysosomes, and monocytes of these subjects clear Abeta in AD brain sections. Upon Abeta stimulation, mononuclear cells of normal subjects up-regulate the transcription of beta-1,4-mannosyl-glycoprotein 4-beta-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 Abeta 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 Abeta 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 Abeta, 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.
Oxidative stress has been implicated in mechanisms leading to neuronal cell injury in various pathological states of the brain. Alzheimer's disease (AD) is a progressive disorder with cognitive and memory decline, speech loss, personality changes and synapse loss. Many approaches have been undertaken to understand AD, but the heterogeneity of the etiologic factors makes it difficult to define the clinically most important factor determining the onset and progression of the disease. However, increasing evidence indicates that factors such as oxidative stress and disturbed protein metabolism and their interaction in a vicious cycle are central to AD pathogenesis. Brains of AD patients undergo many changes, such as disruption of protein synthesis and degradation, classically associated with the heat shock response, which is one form of stress response. Heat-shock proteins are proteins serving as molecular chaperones involved in the protection of cells from various forms of stress. Recently, the involvement of the heme oxygenase (HO) pathway in anti-degenerative mechanisms operating in AD has received considerable attention, as it has been demonstrated that the expression of HO is closely related to that of amyloid precursor protein (APP). HO induction, which occurs together with the induction of other HSPs during various physiopathological conditions, by generating the vasoactive molecule carbon monoxide and the potent antioxidant bilirubin, represents a protective system potentially active against brain oxidative injury. Given the broad cytoprotective properties of the heat shock response there is now strong interest in discovering and developing pharmacological agents capable of inducing the heat shock response. Recently, increasing interest has been focused on identifying dietary compounds that can inhibit, retard or reverse the multi-stage pathophysiological events underlying AD pathology. Alzheimer's disease, in fact, involves a chronic inflammatory response associated with both brain injury and beta-amyloid associated pathology. Spice and herbs contain phenolic substances with potent antioxidative and chemopreventive properties, and it is generally assumed that the phenol moiety is responsible for the antioxidant activity. In particular, curcumin, a powerful antioxidant derived from the curry spice turmeric, has emerged as a strong inducer of the heat shock response. In light of this finding, curcumin supplementation has been recently considered as an alternative, nutritional approach to reduce oxidative damage and amyloid pathology associated with AD. Here we review the importance of the heme oxygenase pathway in brain stress tolerance and its significance as antidegenerative mechanism operating in AD pathogenesis. We also discuss the role that exogenous antioxidant supplementation, conceivably, could play in AD in combating oxidative damage and compensating for the decreased level of endogenous antioxidants. Conceivably, dietary supplementation with vitamin E or with polyphenolic agents, such as curcumin and its derivatives, can forestall the development of AD, consistent with a major "metabolic" component to this disorder. Such an outcome would provide optimism that the signs and symptoms of this devastating brain disorder of aging may be largely delayed and/or modulated.
From Curcuma longa, two novel compounds, 4' '-(3' "-methoxy-4' "-hydroxyphenyl)-2' '-oxo-3' '-enebutanyl 3-(3'-methoxy-4'hydroxyphenyl)propenoate (calebin-A, 1) and 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,4,6-heptatrien-3-one (2), and seven known compounds, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (curcumin, 3), 1-(4-hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)-1,6-heptadiene-3,5-dione (demethoxycurcumin, 4), 1,7-bis(4-hydroxyphenyl)-1,6-heptadiene-3,5-dione (bisdemethoxycurcumin, 5), 1-hydroxy-1,7-bis(4-hydroxy-3-methoxyphenyl)-6-heptene-3,5-dione (6), 1,7-bis(4-hydroxyphenyl)-1-heptene-3,5-dione (7), 1,7-bis(4-hydroxyphenyl)-1,4,6-heptatrien-3-one (8), and 1,5-bis(4-hydroxy-3-methoxyphenyl)-1,4-pentadien-3-one (9), were isolated following a bioassay-guided fractionation scheme utilizing an assay to detect protection of PC12 cells from beta-amyloid insult. Compounds 1, 3-5, and 7 were found to more effectively protect PC12 cells from betaA insult (ED(50) = 0.5-10 microg/mL) than Congo red (10) (ED(50) = 37-39 microg/mL).
Treatment of Alzheimer's disease (AD) is difficult due to ignorance of its pathogenesis. AD patients have defects in phagocytosis of amyloid-beta (1-42) (Abeta) in vitro by the innate immune cells, monocyte/macrophages and in clearance of Abeta plaques [5]. The natural product curcuminoids enhanced brain clearance of Abeta in animal models. We, therefore, treated macrophages of six AD patients and 3 controls by curcuminoids in vitro and measured Abeta uptake using fluorescence and confocal microscopy. At baseline, the intensity of Abeta 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, Abeta 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.
Inflammation in Alzheimer's disease (AD) patients is characterized by increased cytokines and activated microglia. Epidemiological studies suggest reduced AD risk associates with long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs). Whereas chronic ibuprofen suppressed inflammation and plaque-related pathology in an Alzheimer transgenic APPSw mouse model (Tg2576), excessive use of NSAIDs targeting cyclooxygenase I can cause gastrointestinal, liver, and renal toxicity. One alternative NSAID is curcumin, derived from the curry spice turmeric. Curcumin has an extensive history as a food additive and herbal medicine in India and is also a potent polyphenolic antioxidant. To evaluate whether it could affect Alzheimer-like pathology in the APPSw mice, we tested a low (160 ppm) and a high dose of dietary curcumin (5000 ppm) on inflammation, oxidative damage, and plaque pathology. Low and high doses of curcumin significantly lowered oxidized proteins and interleukin-1beta, a proinflammatory cytokine elevated in the brains of these mice. With low-dose but not high-dose curcumin treatment, the astrocytic marker GFAP was reduced, and insoluble beta-amyloid (Abeta), soluble Abeta, and plaque burden were significantly decreased by 43-50%. However, levels of amyloid precursor (APP) in the membrane fraction were not reduced. Microgliosis was also suppressed in neuronal layers but not adjacent to plaques. In view of its efficacy and apparent low toxicity, this Indian spice component shows promise for the prevention of Alzheimer's disease.
The defective clearance of amyloid-beta (Abeta) in the brain of Alzheimer's disease (AD) patients is unexplained. The immunohistochemical studies of the frontal lobe and hippocampus show perivascular and intraplaque infiltration by blood-borne macrophages containing intracellular Abeta but only inefficient clearance of beta deposits. Neurons and neuronal nuclei, respectively, express interleukin-1beta and the chemokine RANTES, which could induce the inflammatory cell infiltration. To clarify the pathophysiology ofbeta clearance, we examined Abeta phagocytosis by monocytes and macrophages isolated from the blood of age-matched patients and controls. Control monocytes display excellent differentiation into macrophages and intracellular phagocytosis of Abeta followed by beta degradation or export. AD monocytes show poor differentiation and only surface uptake of Abeta and suffer apoptosis. HLA DR and cyclooxygenase-2 are abnormally expressed on neutrophils and monocytes of AD patients. AD patients have higher levels of intracellular cytokines compared to controls. Thus Abeta clearance is not restricted to brain microglia and involves systemic innate immune responses. In AD, however, macrophage phagocytosis is defective, which may elicit compensatory response by the adaptive immune system.
Inflammation in Alzheimer's disease (AD) patients is characterized by increased cytokines and activated microglia. Epidemiological studies suggest reduced AD risk associates with long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs). Whereas chronic ibuprofen suppressed inflammation and plaque-related pathology in an Alzheimer transgenic APPSw mouse model (Tg2576), excessive use of NSAIDs targeting cyclooxygenase I can cause gastrointestinal, liver, and renal toxicity. One alternative NSAID is curcumin, derived from the curry spice turmeric. Curcumin has an extensive history as a food additive and herbal medicine in India and is also a potent polyphenolic antioxidant. To evaluate whether it could affect Alzheimer-like pathology in the APPSw mice, we tested a low (160 ppm) and a high dose of dietary curcumin (5000 ppm) on inflammation, oxidative damage, and plaque pathology. Low and high doses of curcumin significantly lowered oxidized proteins and interleukin-1beta, a proinflammatory cytokine elevated in the brains of these mice. With low-dose but not high-dose curcumin treatment, the astrocytic marker GFAP was reduced, and insoluble beta-amyloid (Abeta), soluble Abeta, and plaque burden were significantly decreased by 43-50%. However, levels of amyloid precursor (APP) in the membrane fraction were not reduced. Microgliosis was also suppressed in neuronal layers but not adjacent to plaques. In view of its efficacy and apparent low toxicity, this Indian spice component shows promise for the prevention of Alzheimer's disease.