Anti-Amyloid Treatments in Alzheimers Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive decline in memory and cognitive function. Pathological hallmark of AD includes aberrant aggregation of amyloid beta (Aβ) peptide, which is produced upon sequential cleavage of amyloid precursor protein (APP) by β- and γ -secretases. On the contrary, α-secretase cleaves APP within the Aβ sequence and thereby prevents Aβ generation. Here, we investigated the role of ubiquitin ligase Ube3a (involved in synaptic function and plasticity) in the pathogenesis of AD using APPswe/PS1δE9 transgenic mouse model and first noticed that soluble pool of Ube3a was age-dependently decreased in AD mouse in comparison with wild type controls. To further explore the role of Ube3a in AD patho-mechanism, we generated brain Ube3a-deficient AD mice that exhibited accelerated cognitive and motor deficits compared with AD mice. Interestingly, these Ube3a-deficient AD mice were excessively obese from their age of 12 months and having shorter lifespan. Biochemical analysis revealed that the Ube3a-deficient AD mice had significantly reduced level of Aβ generation and amyloid plaque formation in their brain compared with age-matched AD mice and this effect could be due to the increased activity of α-secretase, ADAM10 (a disintegrin and metalloproteinase-10) that shift the proteolysis of APP towards non-amyloidogenic pathway. These findings suggest that aberrant function of Ube3a could influence the progression of AD and restoring normal level of Ube3a might be beneficial for AD.

Alzheimer's disease is a neurodegenerative disorder characterized by the accumulation of the beta-amyloid peptide and the hyperphosphorylation of the tau protein, among other features. The most widely accepted hypothesis on the etiopathogenesis of this disease proposes that the aggregates of the beta-amyloid peptide are the main triggers of tau hyperphosphorylation and the subsequent degeneration of affected neurons. In support of this view, fibrillar aggregates of synthetic beta-amyloid peptide induce tau hyperphosphorylation and cell death in cultured neurons. We have previously reported that lithium inhibits tau hyperphosphorylation and also significantly protects cultured neurons from cell death triggered by beta-amyloid peptide. As lithium is a relatively specific inhibitor of glycogen synthase kinase-3 (in comparison with other protein kinases), and other studies also point to a relevant role of this enzyme, we favor the view that glycogen synthase kinase-3 is a crucial element in the pathogenesis of Alzheimer's disease. In our opinion, the possibility of using lithium, or other inhibitors of glycogen synthase kinase-3, in experimental trials aimed to ameliorate neurodegeneration in Alzheimer's disease should be considered.

Alzheimer's disease is characterized by the accumulation of beta amyloid peptides in plaques and vessel walls and by the intraneuronal accumulation of paired helical filaments composed of hyperphosphorylated tau. In this review, we concentrate on the biology of amyloid precursor protein, and on the central role of amyloid in the pathogenesis of Alzheimer's disease. Amyloid precursor protein (APP) is part of a super-family of transmembrane and secreted proteins. It appears to have a number of roles, including regulation of haemostasis and mediation of neuroprotection. APP also has potentially important metal and heparin-binding properties, and the current challenge is to synthesize all these varied activities into a coherent view of its function. Cleavage of amyloid precursor protein by beta-and gamma-secretases results in the generation of the Abeta (betaA4) peptide, whereas alpha-secretase cleaves within the Abeta sequence and prevents formation from APP. Recent findings indicate that the site of gamma-secretase cleavage is critical to the development of amyloid deposits; Abeta1-42 is much more amyloidogenic than Abeta1-40. Abeta1-42 formation is favoured by mutations in the two presenilin genes (PS1 and PS2), and by the commonest amyloid precursor protein mutations. Transgenic mouse models of Alzheimer's disease incorporating various mutations in the presenilin gene now exist, and have shown amyloid accumulation and cognitive impairment. Neurofibrillary tangles have not been reproduced in these models, however. While aggregated Abeta is neurotoxic, perhaps via an oxidative mechanism, the relationship between such toxicity and neurofibrillary tangle formation remains a subject of ongoing research.

The aggregation and accumulation of amyloid beta peptides is one of the pathological hallmarks of Alzheimer's disease (AD). Amyloid beta is produced by sequential proteolytic cleavage of Amyloid Precursor Protein (APP) by beta‐ and gamma‐secretase, which are plausible molecular targets for AD treatment. Thus, identification of modulators of these secretases could lead to new therapeutics for this prevalent and debilitating disease. SH‐SY5Y are human neuroblastoma cells that express APP and the various secretases that cleave this membrane‐bound protein into sAPPβ, sAPPα and amyloid beta peptides. We have developed new highly sensitive and specific AlphaLISA kits that allow the detection of endogenous amounts of these various APP metabolites. Specific inhibitors of alpha‐, beta‐ and gamma‐secretase were used to modulate the relative activities of these enzymes. Application of these inhibitors resulted in characteristic signature levels of product sAPPα, sAPPβ, Aβ 1–40 and Aβ x‐40 (defined as the combined amount of both Aβ 1–40 and Aβ 17–40) from SH‐SY5Y cell culture supernatants. These results show that the new AlphaLISA kits have sufficient sensitivity and specificity to study this pathway, even in wild‐type cells that do not overexpress APP or BACE. The Z′‐factor obtained for these cell‐based secretase assays was greater than 0.6, indicating reproducible and robust assays for HTS. In summary, these new AlphaLISA detection kits can accurately quantitate endogenous APP cleavage products. This will in turn result in a better understanding of the APP degradation pathway and facilitate the identification of novel therapeutic drugs for the treatment of Alzheimer's disease.

Misfolding and Aggregation of Amyloid Beta Peptide: Single Molecule AFM Force Spectroscopy

Endocytosis Is Required for Synaptic Activity-Dependent Release of Amyloid-β In Vivo

Is γ-secretase a beneficial inactivating enzyme of the toxic APP C-terminal fragment C99?

Alzheimer's disease (AD) has become one of the deadliest diseases for human beings with special incidence in elderly population. It is a progressive neurodegenerative disease and the most prevalent cause of dementia. The neuropathology of AD has not been fully elucidated yet, however, cholinergic hypothesis is the most accepted theory nowadays, resulting from the cholinergic deficit emerging in the brains of AD patients. Shortage of the neurotransmitters, acetylcholine and butyrylcholine has been demonstrated, and therefore, inhibition of the enzymes; acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) that break down acetylcholine and butyrylcholine has become a standard approach for AD treatment. However, cholinesterase inhibitors are only effective in symptomatic treatment and have no ability to impede the disease. The pathogenesis of AD is highly complex and another hypothesis is the formation of amyloid plaques containing beta-amyloid peptide, which causes neurolesions in the brains of AD patients. Beta-amyloid peptide is generated after the sequential cleavage of amyloid precursor protein, especially by the beta- and gamma-secretase in the amyloidogenic pathway. The secretases involved in the processing of amyloid precursor protein are of particular interest and, consequently, the inhibition of secretase enzyme family of protease type has become another desired treatment strategy for AD. On the other hand, medicinal plants are attractive sources for drug research and development as they produce chemically-varying molecules with preferred biological activities. The aim of this article is to review the available data on selected inhibitors from plant secondary metabolites with emphasis on cholinesterase, prolyl endopeptidase, and secretase enzyme families as being the current treatments of AD.

Genetic Ablation of Apolipoprotein A-IV Accelerates Alzheimer's Disease Pathogenesis in a Mouse Model

P1-409: Knockdown of plasminogen activator inhibitor 1 gene reduces cerebral amyloid-beta peptide burden in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by the deposition of amyloid in the extracellular compartment of the brain in the form of congophilic amyloid angiopathy (CAA) and amyloid plaques (APs). Intracellular neurofibrillary tangles (NFTs) (88) formed from the abnormally phosphorylated cytoskeletal protein tau are also seen (52). The identification of the amyloid β protein (Aβ) in CAA and APs (28 ; 58) led to the cloning of the amyloid protein precursor (APP) (44). The discovery of familial AD (FAD) mutations in the APP gene (10 ; 29 ; 63 ; 64 ; 86) has supported the view that a defect in APP metabolism or function is directly involved in AD pathogenesis. The demonstration that mutations in the tau gene can lead to non-Alzheimer dementias with neurofibrillary pathology, lacking Aβ plaques (reviewed by 81), has reinforced the view that the NFTs are a secondary phenomenon in the pathogenesis of AD. It has long been argued that the deposition of amyloid is an early step in AD pathogenesis (58 ; Hardy and Higgins, 1992 ; 57). The term amyloid refers to insoluble proteinaceous deposits that are congophilic and exhibit red-green birefringence in the presence of plane polarized light (45). Implicit in much of the research on the role of APP and Aβ has been the assumption that deposits of amyloid are toxic to the brain (42) and that these deposits are the underlying cause of AD. The observation that Aβ peptides when "aged" (incubated to form amyloid fibrils) become toxic to neurons in culture (94 ; 22 ; 46 ; 66 ; 38) has further supported this view. The amyloid cascade hypothesis of AD, as formalized by Hardy and Higgins (35), states that Aβ"precipitates to form amyloid and, in turn, causes neurofibrillary tangles and cell death." However, this hypothesis has been challenged (see, e.g., 16 ; 34). It has been argued that the deposition of amyloid does not correlate with dementia (89 ; 2 ; 71 ; 72 ; 5), although the failure to observe a correlation may be related to the method by which AP load is measured (14). Whether amyloid deposits have a pathogenic role remains a controversial issue. Some of the neuropathological changes occurring in the AD brain were first described by Alzheimer (1). Extracellular deposits of amyloid in the form of APs and CAA, as well as intracellular NFTs, are major features of AD pathology (68). The major protein constituent of CAA and APs is a 4-kDa polypeptide termed the amyloid protein or Aβ (28 ; 58). A partial amino acid sequence of Aβ was used to clone a cDNA encoding a protein now referred to as the APP, which has features of an integral type I transmembrane glycoprotein (44). The APP gene contains 18 exons spanning >170 kb (95). The region encoding the Aβ sequence comprises part of exons 16 and 17 and contains between 40 and 43 amino acid residues that extend from the ectodomain into the transmembrane domain of the protein (Fig. 1). Primary structure of APP. Upper panel : APP is expressed initially as a type I transmembrane glycoprotein containing a large N-terminal ectodomain, a short transmembrane (TM) domain of hydrophobic amino acid residues, and a relatively short C-terminal cytoplasmic domain. The Aβ sequence makes up part of the ectodomain and extends partly into the TM domain. The APP gene encodes a protein containing a signal peptide sequence (SP), a cysteine-rich domain, a region rich in acidic residues, a domain with homology to Kunitz-type protease inhibitors (KPI), and a region sharing homology to the OX-2 protein. mRNA splicing can produce forms that lack the KPI or OX-2 domain. Lower panel : Amino acid sequence of the Aβ region of APP. Large arrows show the major sites of cleavage for α-, β, and γ-secretases. Small arrows show known FAD mutations. FIG. 1. It is now known that Aβ is a normal product of APP processing (32 ; 30 ; 21). The major route of APP processing is by α-secretase, an enzyme that cleaves within the Aβ sequence (20). Cleavage by β- and γ-secretases at the N- and C-terminal ends of the Aβ sequence liberates the Aβ polypeptide, which can subsequently be secreted from cells (21 ; 30 ; 31). The major form of Aβ that is secreted contains 40 amino acids (Aβ1-40). However, minor species containing 42 or 43 amino acid residues (Aβ1-42/43) are also produced. These extended forms of Aβ aggregate more readily and may seed amyloid fibril polymerization during the early stages of plaque formation (42). The strongest evidence for a pathogenic role for APP or Aβ comes from genetic studies of early-onset FAD (33). Several FAD mutations have been found in the APP gene. All of these mutations have been found to cluster close to the amyloid sequence in APP. Mutations at codon 716 (Florida), 717 (London), and 723 (Australian) cause an increased proportion of γ-secretase cleavage at position 42 or 43 in the amyloid sequence (Fig. 1 and Table 1). A mutation found at codons 670 and 671 in a Swedish kindred results in increased β-secretase cleavage (8 ; 43), whereas a point mutation at codon 612 (Flemish) inhibits α-secretase cleavage (32). The consequence of the Swedish and Flemish mutations is to increase processing of APP via the β-secretase pathway. All of the FAD mutations in the APP gene result in increased production of Aβ1-42/43 (Table 1). More than 40 FAD mutations in the presenilin 1 and presenilin 2 genes have also been reported (17 ; 75). The common feature of all these mutations is that they also cause an increase in the production of Aβ1-42/43 (73). Thus, presenilins are involved in regulating the proteolytic breakdown of APP by γ-secretase (18). However, the mechanism by which this occurs is unknown. TABLE 1. Studies on transgenic mice that overexpress FAD mutant forms of human APP also strongly argue for a central role of APP or Aβ in disease pathogenesis. Games et al. (26) demonstrated Alzheimer-like pathology in a transgenic mouse overexpressing a mutant (V717F) form of APP. Subsequently, Hsiao et al., (40) demonstrated similar pathology in a mouse expressing another mutant form of APP (Swedish mutation). It is interesting that the Hsiao mouse had behavioral changes indicative of a cognitive defect occurring before the appearance of robust plaque pathology. More recently, AD-like pathology has been reported in two other APP transgenic mice carrying FAD mutations (84). Although these mice do not show NFTs, there are behavioral abnormalities, abnormal neuritic processes, neuron and synapse loss, and biochemical abnormalities reminiscent of AD (26 ; 40 ; 56 ; 26 ; 9 ; 23 ; 41 ; 65 ; 79). The validity of these transgenic mice as models of AD pathology is reinforced by the observation that the AD-like phenotype is accelerated in APP transgenic mice that also contain an FAD mutant presenilin 1 transgene (37). Studies on the genetics of AD and on APP transgenic mice provide compelling evidence that a disturbance in APP metabolism or function is the underlying cause of AD. However, these studies do not prove that Aβ is the causative agent. The strongest evidence implicating Aβ in the pathogenesis of AD comes from the observation that Aβ peptides are toxic to neurons in culture (94 ; 22 ; 46 ; 66 ; 38). This toxicity is enhanced if the peptides are "aged" (incubated from hours to days), a procedure that increases amyloid fibril formation (66). Although the process of aging increases the number of amyloid fibrils formed from Aβ, this is not proof per se that fibrils are the major toxic form of Aβ. It is likely that the levels of soluble oligomeric species of Aβ are also increased by the process of aging (see next section). The mechanism of neurotoxicity is unclear. Some studies suggest that Aβ can disrupt calcium homeostasis (Mattson et al., 59, 61,60), perhaps by interfering with L-type voltage-dependent calcium channels (15 ; 90), Aβ may reduce Na+,K+-ATPase activity (55), thereby influencing membrane depolarization. Furukawa and Mattson (25) have reported that cytochalasin D, a compound that inhibits actin polymerization and calcium entry, can reduce Aβ neurotoxicity. Other studies suggest a role for reactive oxygen species in Aβ toxicity (4 ; 6 ; 36). Disturbances in redox potential may lead to disruption of calcium homeostasis, as reactive oxygen species can impair ATPase activities (55). Aβ may cause lipid peroxidation and affect superoxide dismutase, which may contribute to its neurotoxicity in culture (7). The receptor that transduces the effects of Aβ is unknown, although the receptor for advanced glycation end products (RAGE) (91) has been implicated. Studies by Yan et al. (92) suggest that Aβ may also bind an intracellular hydrosteroid dehydrogenase known as ERAB. The neurotoxicity may be mediated by an indirect action of Aβ on a nonneuronal cell. For example, microglial cells are often found in association with neuritic plaques (69), and Aβ has been shown to activate microglia in culture (11). Therefore, the possibility that Aβ stimulates release of an unidentified neurotoxic agent from a nonneuronal compartment must also be considered. Recent work by Geula et al. (27) has shown that when aged Aβ is injected into the brains of old rhesus monkeys, it is neurotoxic. However, injection of the same material into young monkeys has little toxic effect. This suggests that although Aβ may be pathogenic, there must be other age-related susceptibility factors that are also important to generate a toxic reaction in vivo. There is now considerable evidence that the type 4 allele of the apoE gene is a major susceptibility factor for late-onset AD (82). ApoE is a 299-amino acid glycoprotein that is principally involved in lipid transport and related functions (reviewed by 54). The N-terminal domain (residues 1-191) contains a receptor-binding region (residues 136-150) that exists as a four-helix bundle. The C terminus is hydrophobic and contains the lipoprotein-binding determinants. Genetic heterogeneity leads to three common isoforms, designated as apoE2, apoE3, and apoE4, encoded by three alleles called ε2, ε3, and ε4, respectively. The isoforms differ from each other by cysteine-arginine interchanges at positions 112 and 158 (54). The ε4 allele frequency is significantly increased in late-onset AD patients (82). Furthermore, those individuals with one or two copies of the ε4 allele have higher amounts of Aβ immunoreactivity in their brains than those individuals without ε4 (74), suggesting that apoE4 promotes fibrillation of Aβ to form amyloid. There is evidence from several studies to suggest that apoE4 could be involved in the polymerization of Aβ to form amyloid in vivo. For example, apoE4 has been found to promote Aβ fibrillogenesis in vitro more readily than apoE3 (Strittmatter et al., 82,83 ; 53). Also studies in which apoE knockout mice have been crossed with human APP transgenic mice show that the expression of apoE is necessary for amyloid deposition in vivo (3). However, the mechanism by which apoE4 influences the risk of AD is still unknown. Although apoE can bind Aβ (Strittmatter et al., 82,83), most studies showing that apoE4 stimulates Aβ aggregation have used apoprotein, i.e., delipidated, forms of apoE, which do not possess a native conformation. Indeed, studies using native forms of apoE isoforms suggest that apoE4 binds less well to Aβ than the other isoforms (49 ; 96 ; 93). On the basis of this finding it has been proposed that apoE may be involved in clearance of Aβ (92), although this hypothesis would not explain why apoE knockout inhibits Aβ deposition (3). Molecular genetic studies indicate a central role for Aβ in AD pathogenesis. However, these studies do not indicate the form or site of action of Aβ neurotoxicity. Until the mechanism of Aβ neurotoxicity is understood, it will be difficult to explain the topography of neurodegeneration (77). It has been presumed that deposits of amyloid constitute the entire Aβ load, but recent studies indicate that some of the Aβ in the brain exists in a soluble form. Soluble Aβ is unlikely to be detected by routine fixation and immunostaining. Aβ is probably secreted as a monomer and subsequently aggregates into soluble oligomers or fibrils (67). There is good evidence for the existence of low-molecular-weight Aβ oligomers in the brain. Studies by Kuo et al. (47) have isolated watersoluble Aβ oligomers from normal and AD brains. Perhaps of greatest interest in this study was the finding that not only was the level of soluble Aβ greater in the AD brain compared with controls, but as with some familial mutations, the proportion of soluble Aβ1-42/43 was significantly increased over soluble Aβ1-40 species in AD patients. Similar results have been obtained by Funato et al. (24). In the study by Kuo et al. (47), the watersoluble Aβ species ranged in size from monomers of <10 kDa to oligomers of > 100 kDa. Studies by Roher et al. (70) suggest that the watersoluble dimeric species are neurotoxic, whereas in a recent study Lambert et al. (50) found that small, low-molecular-weight oligomers of Aβ1-42 are several orders of magnitude more potent neurotoxins than high-molecular-weight fibrillar species of Aβ1-40. These studies have implications for our view of amyloid toxicity. If oligomeric soluble forms of Aβ have a pathogenic role, then is it possible that APs are not the major toxic form of Aβ in the brain (Fig. 2) ? Model describing pathways of APP processing. APP can be cleaved by β- and γ-secretases to yield Aβ1-42/43 (γ42/43) or Aβ1-40 (γ40), which can be actively secreted. Alternatively, APP can be cleaved by α-secretase (α) to yield sAPPα, which several studies (reviewed by 78) have shown may have neuroprotective or trophic functions. Aβ1-42/43 can aggregate to form soluble oligomeric species or may seed the polymerization of Aβ1-40 to form insoluble amyloid fibrils, which are deposited in the form of APs. FIG. 2. Recently, Crook et al. (13) described an unusual variant of AD involving a deletion of exon 9 of the presenilin 1 gene from the mRNA. Both NFTs and Aβ-immunopositive plaques were present, but the plaques were of the diffuse nonneuritic (nonfibrillar) type. Like the other FAD mutations in the presenilin 1 gene, the exon 9 deletion also increases Aβ1-42/43 production (62). There are at least two possible explanations for the existence of an AD variant with only diffuse plaques. As previously considered, 42- or 43-residue-long forms of Aβ may be secreted to exert a neurotoxic action (Fig. 2). However, a second possibility is that intraneuronal Aβ plays a role in pathogenesis. Although the molecular genetic studies strongly argue for a direct role of Aβ1-42/43 in AD pathogenesis, they do not provide any indication of whether the Aβ is extracellular or intracellular. Skovronsky et al. (76) have shown that Aβ1-42/43 accumulates preferentially in an insoluble intracellular fraction where it is more abundant than Aβ1-40. Lee et al. (51) have localized intracellular Aβ1-42/43 to the endoplasmic reticulum. Clearly, if Aβ accumulates within intracellular organelles, it could have profound effects on normal cellular protein trafficking and metabolism. If Aβ1-42/43 is the real culprit in AD, then an inverse correlation between the amount of Aβ1-42/43 production and the age of onset of the disease might be predicted. Mutations causing high levels of Aβ1-42/43 in cell culture should cause an early age of onset of clinical symptoms. However, studies with fibroblasts taken from FAD patients (73) show that this is not the case (17). There are several possible explanations for this. It is possible that the level of Aβ1-42/43 production in cell culture does not reflect the level in brain. Another possibility is that FAD mutations influence other cellular events that affect the age of onset. A third possibility is that Aβ1-42/43 is not the only (or even the major) pathogenic form of Aβ. Although Aβ peptides terminating in positions 39-43 are the major forms produced, it is possible that very low levels of previously undetected longer forms of Aβ may also exist (12). If they do exist, they could also be neurotoxic. This would be consistent with observations that C-terminal fragments of APP containing the Aβ sequence are more toxic than Aβ (80). There is very good evidence that Aβ accumulation is the underlying cause of FAD, and there is strong circumstantial evidence to suggest that a similar process underlies the pathogenesis of sporadic (late-onset) AD. Although amyloid deposits (APs and CAA) are markers of the disease, insoluble fibrillar Aβ may not be the main neurotoxic form. Low-molecular-weight diffusible forms of Aβ1-42/43 may also be important. The fact that aged Aβ in vitro contains more amyloid fibrils does not necessarily prove that amyloid is neurotoxic. It is likely that aging also produces increased amounts of soluble oligomeric Aβ species. Therefore, more work is needed to define the precise nature of the toxic form of Aβ and to delineate the mechanism of this toxicity. D.H.S. is supported by grants from the National Health and Medical Research Council of Australia and the Rebecca L. Cooper Foundation.

Alzheimer's disease is associated with increased production and aggregation of amyloid-beta (Abeta) peptides. Abeta peptides are derived from the amyloid precursor protein (APP) by sequential proteolysis, catalysed by the aspartyl protease BACE, followed by presenilin-dependent gamma-secretase cleavage. Presenilin interacts with nicastrin, APH-1 and PEN-2 (ref. 6), all of which are required for gamma-secretase function. Presenilins also interact with alpha-catenin, beta-catenin and glycogen synthase kinase-3beta (GSK-3beta), but a functional role for these proteins in gamma-secretase activity has not been established. Here we show that therapeutic concentrations of lithium, a GSK-3 inhibitor, block the production of Abeta peptides by interfering with APP cleavage at the gamma-secretase step, but do not inhibit Notch processing. Importantly, lithium also blocks the accumulation of Abeta peptides in the brains of mice that overproduce APP. The target of lithium in this setting is GSK-3alpha, which is required for maximal processing of APP. Since GSK-3 also phosphorylates tau protein, the principal component of neurofibrillary tangles, inhibition of GSK-3alpha offers a new approach to reduce the formation of both amyloid plaques and neurofibrillary tangles, two pathological hallmarks of Alzheimer's disease.

At the molecular level, the accumulation of beta-amyloid peptide is one of the important mechanisms in the formation of amyloid plaques. These plaques, in turn, are considered one of the important factors in the development of Alzheimer's disease. Therefore, it is important to study the factors affecting beta-amyloid peptides. This study aimed to investigate the impact of curcumin on the structure of beta-amyloid peptide dimers and how carbon nanotubes influence this interaction. The research focused on understanding the molecular dynamics and structural changes induced by curcumin to reduce beta-amyloid toxicity. Curcumin, a phenolic compound, is known for its ability to prevent the aggregation of beta-amyloid peptides, which are associated with neurodegenerative diseases. On the other hand, due to the hydrophobic nature of curcumin, its solubility in aqueous media is limited. To overcome this, a carrier is used. Carbon nanotubes are among the carriers of curcumin. Nanotubes are popular candidates for the delivery of effective pharmaceutical compounds due to their unique surface properties and biocompatibility. The use of a carrier affects the study of the mechanism of interaction of curcumin with the peptide, which in turn makes it difficult to study this mechanism. Thus, despite its recognized inhibitory action on beta-amyloid aggregation, there is limited understanding of its precise effects on the peptide's structure. This study addresses this gap by employing molecular dynamics simulations and density functional theory methods. The objective of this study was to elucidate the structural effects of curcumin on betaamyloid peptide dimers and assess the modifying role of carbon nanotubes using computational methods. The effect of curcumin on beta-amyloid peptide dimers was studied using molecular dynamics simulations and density functional theory. The simulations were conducted both in the presence and absence of carbon nanotubes to assess their influence on curcumin's activity and the structural stability of the peptide. The presence of curcumin and carbon nanotubes induced relative instability in betaamyloid dimers. Curcumin exhibited stronger interactions with the N-terminal and C-terminal regions of the peptide than with the middle section. It also reduced the toxicity of the peptide by particularly affecting the salt bridge and the arrangement of Phe19, Ile31, and Leu34 residues. Carbon nanotubes mitigated curcumin's effects on the peptide, altering curcumin's behavior by reducing its activity, but increasing its solvation energy. Curcumin plays a significant role in destabilizing beta-amyloid dimers and reducing their toxicity, with its effect being modulated by the presence of carbon nanotubes. This dual influence highlights the potential of using curcumin, alongside nanomaterials, in therapeutic strategies for neurodegenerative diseases. This study provided valuable insights into the molecular interactions among curcumin, beta-amyloid peptides, and carbon nanotubes. These findings can contribute to the development of more effective treatments targeting amyloid-related toxicity in neurodegenerative conditions.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid beta peptides, which are produced by the proteolytic cleavage of amyloid precursor protein (APP). As the incidence of AD is higher in females and sex steroids are implicated in this disease, we have examined the effect of sex steroids (testosterone and 17β-estradiol) on the expression of APP mRNA and protein in the cerebral cortex of adult and old mice of both sexes. Northern blot analysis detected APP mRNA as a single 3.5-kb band and its level is increased in old as compared to adult. Following gonadectomy, its level was upregulated in female mice but downregulated in male mice. Supplementation with testosterone or estradiol decreased its levels in female mice of both ages. Testosterone supplementation increased the mRNA levels in both adult and old male mice. Estrogen supplementation decreased its level in adult but increased in old male mice. Western blot analysis detected APP specific bands ranging from 95 to 125 kD. The level of 95 kDa band representing APP695 protein showed difference in levels with age or hormone treatment. These results provide evidence for increase in APP mRNA level in the cerebral cortex of old mice and its regulation by sex steroids during aging.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of age-related dementia that begins with memory loss and progresses to include severe cognitive impairment. A major pathological hallmark of AD is the accumulation of beta amyloid peptide (Aβ) in senile plaques in the brain of AD patients. The exact mechanism by which AD takes place remains unknown. However, an increasing number of studies suggests that ATP-binding cassette (ABC) transporters, which are localized on the surface of brain endothelial cells of the blood-brain barrier (BBB) and brain parenchyma, may contribute to the pathogenesis of AD. Recent studies have unraveled important roles of ABC transporters including ABCB1 (P-glycoprotein, P-gp), ABCG2 (breast cancer resistant protein, BCRP), ABCC1 (multidrug resistance protein 1, MRP1), and the cholesterol transporter ABCA1 in the pathogenesis of AD and Aβ peptides deposition inside the brain. Therefore, understanding the mechanisms by which these transporters contribute to Aβ deposition in the brain is important for the development of new therapeutic strategies against AD. This review summarizes and highlights the accumulating evidence in the literature which describe the role of altered function of various ABC transporters in the pathogenesis and progression of AD and the implications of modulating their functions for the treatment of AD.