In vivo beta-secretase 1 inhibition leads to brain Abeta lowering and increased alpha-secretase processing of amyloid precursor protein without effect on neuregulin-1

Current biomarkers and treatment strategies in Alzheimer disease: An overview and future perspectives

Alzheimer's disease (AD), a progressive degenerative disorder first identified by Alois Alzheimer in 1907, poses a significant public health challenge. Despite its prevalence and impact, there is currently no definitive ante mortem diagnosis for AD pathogenesis. By 2050, the United States may face a staggering 13.8 million AD patients. This review provides a concise summary of current AD biomarkers, available treatments, and potential future therapeutic approaches. The review begins by outlining existing drug targets and mechanisms in AD, along with a discussion of current treatment options. We explore various approaches targeting Amyloid β (Aβ), Tau Protein aggregation, Tau Kinases, Glycogen Synthase kinase-3β, CDK-5 inhibitors, Heat Shock Proteins (HSP), oxidative stress, inflammation, metals, Apolipoprotein E (ApoE) modulators, and Notch signaling. Additionally, we examine the historical use of Estradiol (E2) as an AD therapy, as well as the outcomes of Randomized Controlled Trials (RCTs) that evaluated antioxidants (e.g., vitamin E) and omega-3 polyunsaturated fatty acids as alternative treatment options. Notably, positive effects of docosahexaenoic acid nutriment in older adults with cognitive impairment or AD are highlighted. Furthermore, this review offers insights into ongoing clinical trials and potential therapies, shedding light on the dynamic research landscape in AD treatment.

Cathepsin B - A Neuronal Death Mediator in Alzheimer’s Disease Leads to Neurodegeneration

Abstract:

The lysosomal cysteine protease enzyme, named Cathepsin B, mainly degrades the protein and manages its average turnover in our body. The Cathepsin B active form is mostly present inside the lysosomal part at a cellular level, providing the slightly acidic medium for its activation. Multiple findings on Cathepsin B reveal its involvement in neurons' degeneration and a possible role as a neuronal death mediator in several neurodegenerative diseases. In this review article, we highlight the participation of Cathepsin B in the etiology/progress of AD, along with various other factors. The enzyme is involved in producing neurotoxic Aβ amyloid in the AD brain by acting as the β-secretase enzyme in the regulated secretory pathways responsible for APP processing. Aβ amyloid accumulation and amyloid plaque formation lead to neuronal degeneration, one of the prominent pathological hallmarks of AD. Cathepsin B is also involved in the production of PGlu-Aβ, which is a truncated and highly neurotoxic form of Aβ. Some of the findings also revealed that Cathepsin B specific gene deletion decreases the level of PGlu-Aβ inside the brain of experimental mice. Therefore, neurotoxicity might be considered a new pathological indication of AD due to the involvement of Cathepsin B. It also damages neurons present in the CNS region by producing inflammatory responses and generating mitochondrial ROS. However, Cathepsin B inhibitors, i.e., CA-074, can prevent neuronal death in AD patients. The other natural inhibitors are also equally effective against neuronal damage with higher selectivity. Its synthetic inhibitors are specific for their target; however, they lose their selectivity in the presence of quite a few reducing agents. Therefore, a humanized monoclonal antibody is used as a selective Cathepsin B inhibitor to overcome the problem experienced. The use of Cathepsin B for the treatment of AD and other neurodegenerative diseases could be considered a rational therapeutic target.

Dengzhan shengmai capsule combined with donepezil hydrochloride in the treatment of Alzheimer's disease: preliminary findings, randomized and controlled clinical trial

OBJECTIVE

To observe the effects of Dengzhan Shengmai capsule combined with donepezil hydrochloride on cognitive function, daily living ability, and safety in patients with Alzheimer's disease.

METHODS

A total of 294 patients with Alzheimer's disease were randomly divided into a treatment group and a control group, 147 cases each group. The control group was given oral donepezil hydrochloride 5 mg once a day, and the treatment group was given oral Dengzhan Shengmai capsule 0.36 g three times a day, based on the control group.

RESULTS

At 3 and 6 months of treatment, the ADAS-cog score of the treatment group was 48.69±6.23 and 44.24±5.53; for the control group, 45.48±5.94 and 41.57±5.10. The difference between the two groups is statistically significant (p<0.05). At 3 and 6 months of treatment, the NO level in the treatment group was (46.28±6.68) umol/l, (43.55±7.92) umol/l, and the control group was (42.95±7.92) umol/l, (38.89±5.93) umol/l. The differences between both groups were statistically significant (p<0.05). At 3 and 6 months of treatment, ET levels in the treatment group were (156.08±17.39) ng/l, (144.91±17.60) ng/l, and the control group was (150.48±22.94) ng/l, (135.04±10.08) ng/l. Correlation analysis showed that ADAS-cog score was negatively correlated with NO and ET (p<0.001).

CONCLUSIONS

Dengzhan Shengmai capsule combined with donepezil hydrochloride can improve cognitive function and the living capacity of patients with Alzheimer's disease, reduce the production of neurotoxic substances NO and ET, and provide higher safety.

Neurocosmetics in Skincare—The Fascinating World of Skin–Brain Connection: A Review to Explore Ingredients, Commercial Products for Skin Aging, and Cosmetic Regulation

The “modern” cosmetology industry is focusing on research devoted to discovering novel neurocosmetic functional ingredients that could improve the interactions between the skin and the nervous system. Many cosmetic companies have started to formulate neurocosmetic products that exhibit their activity on the cutaneous nervous system by affecting the skin’s neuromediators through different mechanisms of action. This review aims to clarify the definition of neurocosmetics, and to describe the features of some functional ingredients and products available on the market, with a look at the regulatory aspect. The attention is devoted to neurocosmetic ingredients for combating skin stress, explaining the stress pathways, which are also correlated with skin aging. “Neuro-relaxing” anti-aging ingredients derived from plant extracts and neurocosmetic strategies to combat inflammatory responses related to skin stress are presented. Afterwards, the molecular basis of sensitive skin and the suitable neurocosmetic ingredients to improve this problem are discussed. With the aim of presenting the major application of Botox-like ingredients as the first neurocosmetics on the market, skin aging is also introduced, and its theory is presented. To confirm the efficacy of the cosmetic products on the market, the concept of cosmetic claims is discussed.

Identification of a novel BACE1 inhibitor, timosaponin A-III, for treatment of Alzheimer's disease by a cell extraction and chemogenomics target knowledgebase-guided method

BACKGROUND

Rhizoma Anemarrhenae (RA) has been conventionally used for treatment of Alzheimer's disease (AD) in Traditional Chinese Medicine, and thus, the active components from RA can be screened.

PURPOSE

This research aimed to identify the active components of RA and their targets and further clarify the molecular mechanisms underlying its anti-AD activity.

METHODS

First, the potential active compounds from RA were screened by neurocyte extraction and micro-dialysis methods. Second, the potential targets were predicted by a chemogenomics target knowledgebase and further explored by surface plasmon resonance and enzyme activity assays. Third, the pharmacological effects were evaluated by employing APP/PS1 transgenic mice and SH-SY5Y-APP cells. ELISAs and Western blot analyses were used to evaluate the expression of key molecules in the amyloidogenic and NMDAR/ERK pathways.

RESULTS

Timosaponin A-III (TA-III) was screened and identified as a potential active component for the anti-AD activity, and BACE1 was proven to be a potential high-affinity target. Enzyme kinetic analysis showed that TA-III had strong noncompetitive inhibitory activity against BACE1. The in vitro and in vivo assays indicated that TA-III had pharmacological effects through improving memory impairment, reducing Aβ aggregation via the amyloidogenic pathway and preventing neuronal impairment through downregulating the NMDAR/ERK signaling pathway.

CONCLUSION

TA-III targets BACE1 to reduce Aβ aggregation through down-regulating the NMDAR/ERK pathway for treating AD.

Novel small molecule therapeutic agents for Alzheimer disease: Focusing on BACE1 and multi-target directed ligands

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder that effects 50 million people worldwide. In this review, AD pathology and the development of novel therapeutic agents targeting AD were fully discussed. In particular, common approaches to prevent Aβ production and/or accumulation in the brain including α-secretase activators, specific γ-secretase modulators and small molecules BACE1 inhibitors were reviewed. Additionally, natural-origin bioactive compounds that provide AD therapeutic advances have been introduced. Considering AD is a multifactorial disease, the therapeutic potential of diverse multi target-directed ligands (MTDLs) that combine the efficacy of cholinesterase (ChE) inhibitors, MAO (monoamine oxidase) inhibitors, BACE1 inhibitors, phosphodiesterase 4D (PDE4D) inhibitors, for the treatment of AD are also reviewed. This article also highlights descriptions on the regulator of serotonin receptor (5-HT), metal chelators, anti-aggregants, antioxidants and neuroprotective agents targeting AD. Finally, current computational methods for evaluating the structure-activity relationships (SAR) and virtual screening (VS) of AD drugs are discussed and evaluated.

Icariside II inhibits lipopolysaccharide-induced inflammation and amyloid production in rat astrocytes by regulating IKK/IκB/NF-κB/BACE1 signaling pathway

β-amyloid (Aβ) is one of the inducing factors of astrocytes activation and neuroinflammation, and it is also a crucial factor for the development of Alzheimer's disease (AD). Icariside II (ICS II) is an active component isolated from a traditional Chinese herb Epimedium, which has shown to attnuate lipopolysaccharide (LPS)-induced neuroinflammation through regulation of NF-κB signaling pathway. In this study we investigated the effects of ICS II on LPS-induced astrocytes activation and Aβ accumulation. Primary rat astrocytes were pretreated with ICS II (5, 10, and 20 μM) or dexamethasone (DXMS, 1 μM) for 1 h, thereafter, treated with LPS for another 24 h. We found that ICS II pretreatment dose dependently mitigated the levels of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) in the astrocytes. Moreover, ICS II not only exerted the inhibitory effect on LPS-induced IκB-α degradation and NF-κB activation, but also decreased the levels of Aβ1-40, Aβ1-42, amyloid precursor protein (APP) and beta secretase 1 (BACE1) in the astrocytes. Interestingly, molecular docking revealed that ICS II might directly bind to BACE1. It is concluded that ICS II has potential value as a new therapeutic agent to treat neuroinflammation-related diseases, such as AD.

Elevation of plasma soluble amyloid precursor protein beta in Alzheimer's disease

INTRODUCTION

Beta-amyloid is considered to be a pathophysiological marker in Alzheimer's disease (AD). Soluble amyloid precursor proteins (sAPPs) -α (sAPPα) and -β (sAPPβ), which are the byproducts of non-amyloidogenic and amyloidogenic process of APP, respectively, have been repeatedly observed in the cerebrospinal fluids (CSF) of AD patients. The present study focused on the determination of sAPP levels in peripheral blood.

METHODS

The plasma protein levels of sAPPα and sAPPβ were measured with ELISA. Plasma from 52 AD patients, 98 amnestic mild cognitive impairment (MCI) patients, and 114 cognitively normal controls were compared.

RESULTS

The plasma level of sAPPβ was significantly increased in AD patients than in cognitively healthy controls. However, no significant change in plasma sAPPα was observed among the three groups. Furthermore, the plasma sAPPβ levels significantly correlated with cognitive assessment scales, such as clinical dementia rating (CDR), and mini-mental status examination (MMSE). Interestingly, sAPPα and sAPPβ had a positive correlation with each other in blood plasma, similar to previous studies on CSF sAPP. This correlation was stronger in the MCI and AD groups than in the cognitively healthy controls.

CONCLUSIONS

These results suggest that individuals with elevated plasma sAPPβ levels are at an increased risk of AD; elevation in these levels may reflect the progression of disease.

Bispecific Antibody Fragment Targeting APP and Inducing α-Site Cleavage Restores Neuronal Health in an Alzheimer's Mouse Model

The amyloid β (Aβ) peptide, correlated with development of Alzheimer's disease (AD), is produced by sequential proteolytic cleavage of the amyloid precursor protein (APP) by β- and γ-secretases. Alternative proteolytic cleavage of APP by α-secretase prevents formation of Aβ peptide and produces a neuroprotective protein, a soluble fragment of APPα (sAPPα). We previously generated a single-chain variable domain antibody fragment (scFv) that binds APP at the β-secretase cleavage site and blocks cleavage of APP (iBsec1), and a second scFv which has been engineered to have α-secretase-like activity that increases α-secretase cleavage of APP (Asec1a) and showed that a bispecific antibody (Diab) combining both iBsec1 and Asec1a constructs protects mammalian cells from oxidative stress. Here, we show that the diabody is an effective therapeutic agent in a mouse model of AD. An apolipoprotein B (ApoB) binding domain peptide was genetically added to the diabody to facilitate transfer across the blood-brain barrier, and a recombinant human adeno-associated virus 2/8 (rAAV2/8) was used as a vector to express the gene constructs in a APP/PS1 mouse model of AD. The diabody increased levels of sAPPα, decreased Aβ deposits and levels of oligomeric Aβ, increased neuronal health as indicated by MAP2 and synaptophysin staining, increased hippocampal neurogenesis, and most importantly dramatically increased survival rates compared with untreated mice or mice treated only with the β-secretase inhibitor. These results indicate that altering APP processing to inhibit β-site activity while simultaneously promoting α-secretase processing provides substantially increased neuronal benefits compared with inhibition of β-secretase processing alone and represents a promising new therapeutic approach for treating AD.

Quantitative Analysis of 18F-PF-06684511, a Novel PET Radioligand for Selective β-Secretase 1 Imaging, in Nonhuman Primate Brain

β-secretase 1 (BACE1) is a key enzyme in the generation of β-amyloid, which is accumulated in the brain of Alzheimer disease patients. PF-06684511 was identified as a candidate PET ligand for imaging BACE1 in the brain and showed high specific binding in an initial assessment in a nonhuman primate (NHP) PET study using ¹⁸F-PF-06684511. In this effort, we aimed to quantitatively evaluate the regional brain distribution of ¹⁸F-PF-06684511 in NHPs under baseline and blocking conditions and to assess the target occupancy of BACE1 inhibitors. In addition, NHP whole-body PET measurements were performed to estimate the effective radiation dose. Methods: Initial brain PET measurements were performed at baseline and after oral administration of 5 mg/kg of LY2886721, a BACE1 inhibitor, in 2 cynomolgus monkeys. Kinetic analysis was performed with the radiometabolite-corrected plasma input function. In addition, a wide dose range of another BACE1 inhibitor, PF-06663195, was examined to investigate the relationship between the brain target occupancy and plasma concentration of the drug. Finally, the effective radiation dose of ¹⁸F-PF-06684511 was estimated on the basis of the whole-body PET measurements in NHPs. Results: Radiolabeling was accomplished successfully with an incorporation radiochemical yield of 4%-12% (decay-corrected) from ¹⁸F ion. The radiochemical purity was greater than 99%. The whole-brain uptake of ¹⁸F-PF-06684511 peaked (∼220% SUV) at approximately 20 min and decreased thereafter (∼100% SUV at 180 min). A 2-tissue-compartment model described the time-activity curves well. Pretreatment with LY2886721 reduced the total distribution volume of ¹⁸F-PF-06684511 by 48%-80% depending on the brain region, confirming its in vivo specificity. BACE1 occupancy of PF-06663195, estimated using the Lassen occupancy plot, showed a dose-dependent increase. The effective dose of ¹⁸F-PF-06684511 was 0.043 mSv/MBq for humans. Conclusion: ¹⁸F-PF-06684511 is the first successful PET radioligand for BACE1 brain imaging that demonstrates favorable in vivo binding and brain kinetics in NHPs.

Beta secretase activity in peripheral nerve regeneration

While the peripheral nervous system has the capacity to regenerate following a nerve injury, it is often at a slow rate and results in unsatisfactory recovery, leaving patients with reduced function. Many regeneration associated genes have been identified over the years, which may shed some insight into how we can manipulate this intrinsic regenerative ability to enhance repair following peripheral nerve injuries. Our lab has identified the membrane bound protease beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1), or beta secretase, as a potential negative regulator of peripheral nerve regeneration. When beta secretase activity levels are abolished via a null mutation in mice, peripheral regeneration is enhanced following a sciatic nerve crush injury. Conversely, when activity levels are greatly increased by overexpressing beta secretase in mice, nerve regeneration and functional recovery are impaired after a sciatic nerve crush injury. In addition to our work, many substrates of beta secretase have been found to be involved in regulating neurite outgrowth and some have even been identified as regeneration associated genes. In this review, we set out to discuss BACE1 and its substrates with respect to axonal regeneration and speculate on the possibility of utilizing BACE1 inhibitors to enhance regeneration following acute nerve injury and potential uses in peripheral neuropathies.

Icariside II Effectively Reduces Spatial Learning and Memory Impairments in Alzheimer's Disease Model Mice Targeting Beta-Amyloid Production

Icariside II (ICS II) is a broad-spectrum anti-cancer natural compound extracted from Herba Epimedii Maxim. Recently, the role of ICS II has been investigated in central nervous system, especially have a neuroprotective effect in Alzheimer’s disease (AD). In this study, we attempted to investigate the effects of ICS II, on cognitive deficits and beta-amyloid (Aβ) production in APPswe/PS1dE9 (APP/PS1) double transgenic mice. It was found that chronic ICS II administrated not only effectively ameliorated cognitive function deficits, but also inhibited neuronal degeneration and reduced the formation of plaque burden. ICS II significantly suppressed Aβ production via promoting non-amyloidogenic APP cleavage process by up-regulating a disintegrin and metalloproteinase domain 10 (ADAM10) expression, inhibited amyloidogenic APP processing pathway by down-regulating amyloid precursor protein (APP) and β-site amyloid precursor protein cleavage enzyme 1 (BACE1) expression in APP/PS1 transgenic mice. Meanwhile, ICS II attenuated peroxisome proliferator-activated receptor-γ (PPARγ) degradation as well as inhibition of eukaryotic initiation factor α phosphorylation (p-eIF2α) and PKR endoplasmic reticulum regulating kinase phosphorylation (p-PERK). Moreover, phosphodiesterase type 5 inhibitors (PDE5-Is) have recently emerged as a possible therapeutic target for cognitive enhancement via inhibiting Aβ levels, and we also found that ICS II markedly decreased phosphodiesterase-5A (PDE5A) expression. In conclusion, the present study demonstrates that ICS II could attenuate spatial learning and memory impairments in APP/PS1 transgenic mice. This protection appears to be due to the increased ADAM10 expression and decreased expression of both APP and BACE1, resulting in inhibition of Aβ production in the hippocampus and cortex. Inhibition of PPARγ degradation and PERK/eIF2α phosphorylation are involved in the course, therefore suggesting that ICS II might be a promising potential compound for the treatment of AD.

The Metalloprotease Meprin β Is an Alternative β-Secretase of APP

The membrane bound metalloprotease meprin β is important for collagen fibril assembly in connective tissue formation and for the detachment of the intestinal mucus layer for proper barrier function. Recent proteomic studies revealed dozens of putative new substrates of meprin β, including the amyloid precursor protein (APP). It was shown that APP is cleaved by meprin β in distinct ways, either at the β-secretase site resulting in increased levels of Aβ peptides, or at the N-terminus releasing 11 kDa, and 20 kDa peptide fragments. The latter event was discussed to be rather neuroprotective, whereas the ectodomain shedding of APP by meprin β reminiscent to BACE-1 is in line with the amyloid hypothesis of Alzheimer's disease, promoting neurodegeneration. The N-terminal 11 kDa and 20 kDa peptide fragments represent physiological cleavage products, since they are found in human brains under different diseased or non-diseased states, whereas these fragments are completely missing in brains of meprin β knock-out animals. Meprin β is not only a sheddase of adhesion molecules, such as APP, but was additionally demonstrated to cleave within the prodomain of ADAM10. Activated ADAM10, the α-secretase of APP, is then able to shed meprin β from the cell surface thereby abolishing the β-secretase activity. All together meprin β seems to be a novel player in APP processing events, even influencing other enzymes involved in APP cleavage.

Amyloid-β Protein Precursor Cleavage Products in Postmortem Ventricular Cerebrospinal Fluid of Alzheimer's Disease Patients

Accumulation and aggregation of amyloid-β (Aβ) are considered etiologic processes in Alzheimer's disease (AD). However, the roles of other AβPP cleavage products in disease pathology remain elusive. Here, we measured levels of the major secreted AβPP processing products sAβPPα, sAβPPβ, and Aβ species in postmortem collected ventricular CSF of 196 AD patients and 74 controls. In AD we identified Aβ₄₂ to decrease continuously with progressing Braak stages, whereas Aβ₄₀ was upregulated in early stages of the disease (Braak stage 4) and down-regulated with progressing pathology. Interestingly, both sAβPPα and sAβPPβ were upregulated in AD as compared to controls (sAβPPα, p = 0.02; sAβPPβ, p = 0.01). Moreover, we observed a strong positive correlation of both alternative AβPP processing products, sAβPPα and sAβPPβ (r²= 0.781; p <  0.0001). Together, our results argue for generally enhanced AβPP processing in AD patients and emphasize the necessity of analyzing the roles of all AβPP processing products in AD pathology.

BACE-1 is expressed in the blood-brain barrier endothelium and is upregulated in a murine model of Alzheimer's disease

Endothelial cells of the blood-brain barrier form a structural and functional barrier maintaining brain homeostasis via paracellular tight junctions and specific transporters such as P-glycoprotein. The blood-brain barrier is responsible for negligible bioavailability of many neuroprotective drugs. In Alzheimer's disease, current treatment approaches include inhibitors of BACE-1 (β-site of amyloid precursor protein cleaving enzyme), a proteinase generating neurotoxic β-amyloid. It is known that BACE-1 is highly expressed in endosomes and membranes of neurons and glia. We now provide evidence that BACE-1 is expressed in blood-brain barrier endothelial cells of human, mouse, and bovine origin. We further show its predominant membrane localization by 3D-dSTORM super-resolution microscopy, and by biochemical fractionation that further shows an abluminal distribution of BACE-1 in brain microvessels. We confirm its functionality in processing APP in primary mouse brain endothelial cells. In an Alzheimer's disease mouse model we show that BACE-1 is upregulated at the blood-brain barrier compared to healthy controls. We therefore suggest a critical role for BACE-1 at the blood-brain barrier in β-amyloid generation and in vascular aspects of Alzheimer's disease, particularly in the development of cerebral amyloid angiopathy.

Inhibiting BACE1 to reverse synaptic dysfunctions in Alzheimer's disease

Over the past two decades, many studies have identified significant contributions of toxic β-amyloid peptides (Aβ) to the etiology of Alzheimer's disease (AD), which is the most common age-dependent neurodegenerative disease. AD is also recognized as a disease of synaptic failure. Aβ, generated by sequential proteolytic cleavages of amyloid precursor protein (APP) by BACE1 and γ-secretase, is one of major culprits that cause this failure. In this review, we summarize current findings on how BACE1-cleaved APP products impact learning and memory through proteins localized on glutamatergic, GABAergic, and dopaminergic synapses. Considering the broad effects of Aβ on all three types of synapses, BACE1 inhibition emerges as a practical approach for ameliorating Aβ-mediated synaptic dysfunctions. Since BACE1 inhibitory drugs are currently in clinical trials, this review also discusses potential complications arising from BACE1 inhibition. We emphasize that the benefits of BACE1 inhibitory drugs will outweigh the concerns.

Alzheimer's therapy targeting the β-secretase enzyme BACE1: Benefits and potential limitations from the perspective of animal model studies

Accumulating evidence points to the amyloid-β (Aβ) peptide as the culprit in the pathogenesis of Alzheimer's disease (AD). β-Site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) is a protease that is responsible for initiating Aβ production. Although precise mechanisms that trigger Aβ accumulation remain unclear, BACE1 inhibition undoubtedly represents an important intervention that may prevent and/or cure AD. Remarkably, animal model studies with knockouts, virus-delivered small interfering RNAs, immunization and bioavailable small-molecule agents that specifically inhibit BACE1 activity strongly support the idea for the therapeutic BACE1 inhibition. Meanwhile, a growing number of BACE1 substrates besides APP uncover new physiological roles of this protease, raising some concern regarding the safety of BACE1 inhibition. Here, I review recent progress in preclinical studies that have evaluated the efficacies and potential limitations of genetic/pharmacological inhibition of BACE1, with special focus on AD-associated phenotypes including synaptic dysfunction, neuron loss and memory deficits in animal models.

Neuregulin-1 attenuates cognitive function impairments in a transgenic mouse model of Alzheimer's disease

The neuregulin (NRG) family of epidermal growth factor-related proteins is composed of a wide variety of soluble and membrane-bound proteins that exert their effects via the tyrosine kinase receptors ErbB2-ErbB4. In the nervous system, the functions of NRG1 are essential for peripheral myelination, the establishment and maintenance of neuromuscular and sensorimotor systems and the plasticity of cortical neuronal circuits. In the present study, we report that an intracerebroventricular infusion of NRG1 attenuated cognitive impairments in 13-month-old Tg2576 mice, an animal model of Alzheimer's disease (AD). In addition, according to Golgi-Cox staining, NRG1 rescued the reduction in the number of dendritic spines detected in the brains of Tg2576 mice compared with vehicle (PBS)-infused mice. This result was also corroborated in vitro as NRG1 attenuated the oligomeric amyloid beta peptide_1-42 (Aβ_1-42)-induced decrease in dendritic spine density in rat primary hippocampal neuron cultures. NRG1 also alleviated the decrease in neural differentiation induced by oligomeric Aβ_1-42 in mouse fetal neural stem cells. Collectively, these results suggest that NRG1 has a therapeutic potential for AD by alleviating the reductions in dendritic spine density and neurogenesis found in AD brains.

Effects of BACE1 haploinsufficiency on APP processing and Aβ concentrations in male and female 5XFAD Alzheimer mice at different disease stages

β-Site APP-cleaving enzyme 1 (BACE1) initiates the generation of amyloid-β (Aβ), thus representing a prime therapeutic target for Alzheimer's disease (AD). Previous work including ours has used BACE1 haploinsufficiency (BACE1(+/-); i.e., 50% reduction) as a therapeutic relevant model to evaluate the efficacy of partial β-secretase inhibition. However, it is unclear whether the extent of Aβ reductions in amyloid precursor protein (APP) transgenic mice with BACE1(+/-) gene ablation may vary with sex or disease progression. Here, we compared the impacts of BACE1 haploinsufficiency on Aβ concentrations and APP processing in 5XFAD Alzheimer mice (1) between males and females and (2) between different stages with moderate and robust Aβ accumulation. First, male and female 5XFAD mice at 6-7 months of age showed equivalent levels of Aβ, BACE1, full-length APP and its metabolites. BACE1 haploinsufficiency significantly lowered soluble Aβ oligomers, total Aβ42 levels and plaque burden in 5XFAD mouse brains irrespective of sex. Furthermore, there was no sex difference in reductions of β-cleavage products of APP (C99 and sAPPβ) found in BACE1(+/-)·5XFAD mice relative to BACE1(+/+)·5XFAD controls. Meanwhile, APP and sAPPα levels in BACE1(+/-)·5XFAD mice were higher than those of 5XFAD controls regardless of sex. Based on these observations, we next combined male and female data to examine the effects of BACE1 haploinsufficiency in 5XFAD mice at 12-14 months of age, as compared with those in 6-7-month-old 5XFAD mice. Oligomeric Aβ and C99 levels were dramatically elevated in older 5XFAD mice. Although the β-metabolites of APP were significantly reduced by BACE1 haploinsufficiency in both age groups, high levels of these toxic amyloidogenic fragments remained in 12-14-month-old BACE1(+/-)·5XFAD mice. The present findings are consistent with our previous behavioral data showing that BACE1 haploinsufficiency rescues memory deficits in 5XFAD mice irrespective of sex but only in the younger age group.

Centrally Delivered BACE1 Inhibitor Activates Microglia, and Reverses Amyloid Pathology and Cognitive Deficit in Aged Tg2576 Mice

Multiple small-molecule inhibitors of the β-secretase enzyme (BACE1) are under preclinical or clinical investigation for Alzheimer's disease (AD). Prior work has illustrated robust lowering of central amyloid β (Aβ) after acute administration of BACE1 inhibitors. However, very few studies have assessed the overall impact of chronically administered BACE1 inhibitors on brain amyloid burden, neuropathology, and behavioral function in aged preclinical models. We investigated the effects of a potent nonbrain-penetrant BACE1 inhibitor, delivered directly to the brain using intracerebroventricular infusion in an aged transgenic mouse model. Intracerebroventricular infusion of the BACE1 inhibitor (0.3-23.5 μg/d) for 8 weeks, initiated in 17-month-old Tg2576 mice, produced dose-dependent increases in brain inhibitor concentrations (0.2-13 μm). BACE1 inhibition significantly reversed the behavioral deficit in contextual fear conditioning, and reduced brain Aβ levels, plaque burden, and associated pathology (e.g., dystrophic neurites), with maximal effects attained with ∼1 μg/d dose. Strikingly, the BACE1 inhibitor also reversed amyloid pathology below baseline levels (amyloid burden at the start of treatment), without adversely affecting cerebral amyloid angiopathy, microhemorrhages, myelination, or neuromuscular function. Inhibitor-mediated decline in brain amyloid pathology was associated with an increase in microglial ramification. This is the first demonstration of chronically administered BACE1 inhibitor to activate microglia, reverse brain amyloid pathology, and elicit functional improvement in an aged transgenic mouse model. Thus, engagement of novel glial-mediated clearance mechanisms may drive disease-modifying therapeutic benefit with BACE1 inhibition in AD.

Opposite Dysregulation of Fragile-X Mental Retardation Protein and Heteronuclear Ribonucleoprotein C Protein Associates with Enhanced APP Translation in Alzheimer Disease

Amyloid precursor protein (APP) is overexpressed in familiar and sporadic Alzheimer Disease (AD) patients suggesting that, in addition to abnormalities in APP cleavage, enhanced levels of APP full length might contribute to the pathology. Based on data showing that the two RNA binding proteins (RBPs), Fragile-X Mental Retardation Protein (FMRP) and heteronuclear Ribonucleoprotein C (hnRNP C), exert an opposite control on APP translation, we have analyzed whether expression and translation of these two RBPs vary in relation to changes in APP protein and mRNA levels in the AD brain at 1, 3, and 6 months of age. Here, we show that, as expected, human APP is overexpressed in hippocampal total extract from Tg2576 mice at all age points. APP overexpression, however, is not stable over time but reaches its maximal level in 1-month-old mutants in association with the stronger (i) reduction of FMRP and (ii) augmentation of hnRNP C. APP levels then decrease progressively as a function of age in close relationship with the gradual normalization of FMRP and hnRNP C levels. Consistent with the mouse data, expression of FMRP and hnRNP C are, respectively, decreased and increased in hippocampal synaptosomes from sporadic AD patients. Our findings identify two RBP targets that might be manipulated for reducing abnormally elevated levels of APP in the AD brain, with the hypothesis that acting upstream of amyloidogenic processing might contribute to attenuate the amyloid burden.

Altered amyloid precursor protein processing regulates glucose uptake and oxidation in cultured rodent myotubes

AIMS/HYPOTHESIS

Impaired glucose uptake in skeletal muscle is an important contributor to glucose intolerance in type 2 diabetes. The aspartate protease, beta-site APP-cleaving enzyme 1 (BACE1), a critical regulator of amyloid precursor protein (APP) processing, modulates in vivo glucose disposal and insulin sensitivity in mice. Insulin-independent pathways to stimulate glucose uptake and GLUT4 translocation may offer alternative therapeutic avenues for the treatment of diabetes. We therefore addressed whether BACE1 activity, via APP processing, in skeletal muscle modifies glucose uptake and oxidation independently of insulin.

METHODS

Skeletal muscle cell lines were used to investigate the effects of BACE1 and α-secretase inhibition and BACE1 and APP overexpression on glucose uptake, GLUT4 cell surface translocation, glucose oxidation and cellular respiration.

RESULTS

In the absence of insulin, reduction of BACE1 activity increased glucose uptake and oxidation, GLUT4myc cell surface translocation, and basal rate of oxygen consumption. In contrast, overexpressing BACE1 in C2C12 myotubes decreased glucose uptake, glucose oxidation and oxygen consumption rate. APP overexpression increased and α-secretase inhibition decreased glucose uptake in C2C12 myotubes. The increase in glucose uptake elicited by BACE1 inhibition is dependent on phosphoinositide 3-kinase (PI3K) and mimicked by soluble APPα (sAPPα).

CONCLUSIONS/INTERPRETATION

Inhibition of muscle BACE1 activity increases insulin-independent, PI3K-dependent glucose uptake and cell surface translocation of GLUT4. As APP overexpression raises basal glucose uptake, and direct application of sAPPα increases PI3K-protein kinase B signalling and glucose uptake in myotubes, we suggest that α-secretase-dependent shedding of sAPPα regulates insulin-independent glucose uptake in skeletal muscle.

BACE1 as a therapeutic target in Alzheimer's disease: rationale and current status

Alzheimer's disease (AD) is a neurodegenerative disease of the central nervous system that causes dementia in a large percentage of the aged population and for which there are only symptomatic treatments. Disease-modifying therapies that are currently being pursued are based on the amyloid cascade theory. This states that accumulation of amyloid β (Aβ) in the brain triggers a cascade of cellular events leading to neurodegeneration. Aβ, which is the major constituent of amyloid plaques, is a peptidic fragment derived from proteolytic processing of the amyloid precursor protein (APP) by sequential cleavages that involve β-site APP-cleaving enzyme 1 (BACE1) and γ-secretase. Targeting BACE1 is a rational approach as its cleavage of APP is the rate-limiting step in Aβ production and this enzyme is elevated in the brain of patients with AD. Furthermore, knocking out the BACE1 gene in mice showed little apparent consequences. Ten years of intensive research has led to the design of efficacious BACE1 inhibitors with favorable pharmacological properties. Several drug candidates have shown promising results in animal models, as they reduce amyloid plaque pathology in the brain and rescue cognitive deficits. Phase I clinical trials indicate that these drugs are well tolerated, and the results from further trials in AD patients are now awaited eagerly. Yet, recent novel information on BACE1 biology, and the discovery that BACE1 cleaves a selection of substrates involved in myelination, retinal homeostasis, brain circuitry, and synaptic function, alert us to potential side effects of BACE1 inhibitors that will require further evaluation to provide a safe therapy for AD.

Identification and Preclinical Pharmacology of the γ-Secretase Modulator BMS-869780

Alzheimer's disease is the most prevalent cause of dementia and is associated with accumulation of amyloid-β peptide (Aβ), particularly the 42-amino acid Aβ1-42, in the brain. Aβ1-42 levels can be decreased by γ-secretase modulators (GSM), which are small molecules that modulate γ-secretase, an enzyme essential for Aβ production. BMS-869780 is a potent GSM that decreased Aβ1-42 and Aβ1-40 and increased Aβ1-37 and Aβ1-38, without inhibiting overall levels of Aβ peptides or other APP processing intermediates. BMS-869780 also did not inhibit Notch processing by γ-secretase and lowered brain Aβ1-42 without evidence of Notch-related side effects in rats. Human pharmacokinetic (PK) parameters were predicted through allometric scaling of PK in rat, dog, and monkey and were combined with the rat pharmacodynamic (PD) parameters to predict the relationship between BMS-869780 dose, exposure and Aβ1-42 levels in human. Off-target and safety margins were then based on comparisons to the predicted exposure required for robust Aβ1-42 lowering. Because of insufficient safety predictions and the relatively high predicted human daily dose of 700 mg, further evaluation of BMS-869780 as a potential clinical candidate was discontinued. Nevertheless, BMS-869780 demonstrates the potential of the GSM approach for robust lowering of brain Aβ1-42 without Notch-related side effects.

Function, therapeutic potential and cell biology of BACE proteases: current status and future prospects

The β-site APP cleaving enzymes 1 and 2 (BACE1 and BACE2) were initially identified as transmembrane aspartyl proteases cleaving the amyloid precursor protein (APP). BACE1 is a major drug target for Alzheimer's disease because BACE1-mediated cleavage of APP is the first step in the generation of the pathogenic amyloid-β peptides. BACE1, which is highly expressed in the nervous system, is also required for myelination by cleaving neuregulin 1. Several recent proteomic and in vivo studies using BACE1- and BACE2-deficient mice demonstrate a much wider range of physiological substrates and functions for both proteases within and outside of the nervous system. For BACE1 this includes axon guidance, neurogenesis, muscle spindle formation, and neuronal network functions, whereas BACE2 was shown to be involved in pigmentation and pancreatic β-cell function. This review highlights the recent progress in understanding cell biology, substrates, and functions of BACE proteases and discusses the therapeutic options and potential mechanism-based liabilities, in particular for BACE inhibitors in Alzheimer's disease. The protease BACE1 is a major drug target in Alzheimer disease. Together with its homolog BACE2, both proteases have an increasing number of functions within and outside of the nervous system. This review highlights recent progress in understanding cell biology, substrates, and functions of BACE proteases and discusses the therapeutic options and potential mechanism-based liabilities, in particular for BACE inhibitors in Alzheimer disease.

Application of computational methods for the design of BACE-1 inhibitors: validation of in silico modelling

β-Secretase (BACE-1) constitutes an important target for search of anti-Alzheimer’s drugs. The first inhibitors of this enzyme were peptidic compounds with high molecular weight and low bioavailability. Therefore, the search for new efficient non-peptidic inhibitors has been undertaken by many scientific groups. We started our work from the development of in silico methodology for the design of novel BACE-1 ligands. It was validated on the basis of crystal structures of complexes with inhibitors, redocking, cross-docking and training/test sets of reference ligands. The presented procedure of assessment of the novel compounds as β-secretase inhibitors could be widely used in the design process.

Diurnal patterns of soluble amyloid precursor protein metabolites in the human central nervous system

The amyloid-β (Aβ) protein is diurnally regulated in both the cerebrospinal fluid and blood in healthy adults; circadian amplitudes decrease with aging and the presence of cerebral Aβ deposits. The cause of the Aβ diurnal pattern is poorly understood. One hypothesis is that the Amyloid Precursor Protein (APP) is diurnally regulated, leading to APP product diurnal patterns. APP in the central nervous system is processed either via the β-pathway (amyloidogenic), generating soluble APP-β (sAPPβ) and Aβ, or the α-pathway (non-amyloidogenic), releasing soluble APP-α (sAPPα). To elucidate the potential contributions of APP to the Aβ diurnal pattern and the balance of the α- and β- pathways in APP processing, we measured APP proteolytic products over 36 hours in human cerebrospinal fluid from cognitively normal and Alzheimer's disease participants. We found diurnal patterns in sAPPα, sAPPβ, Aβ₄₀, and Aβ₄₂, which diminish with increased age, that support the hypothesis that APP is diurnally regulated in the human central nervous system and thus results in Aβ diurnal patterns. We also found that the four APP metabolites were positively correlated in all participants without cerebral Aβ deposits. This positive correlation suggests that the α- and β- APP pathways are non-competitive under normal physiologic conditions where APP availability may be the limiting factor that determines sAPPα and sAPPβ production. However, in participants with cerebral Aβ deposits, there was no correlation of Aβ to sAPP metabolites, suggesting that normal physiologic regulation of cerebrospinal fluid Aβ is impaired in the presence of amyloidosis. Lastly, we found that the ratio of sAPPβ to sAPPα was significantly higher in participants with cerebral Aβ deposits versus those without deposits. Therefore, the sAPPβ to sAPPα ratio may be a useful biomarker for cerebral amyloidosis.

Critical analysis of the use of β-site amyloid precursor protein-cleaving enzyme 1 inhibitors in the treatment of Alzheimer's disease

Alzheimer’s disease (AD) is the major cause of dementia in the elderly and an unmet clinical challenge. A variety of therapies that are currently under development are directed to the amyloid cascade. Indeed, the accumulation and toxicity of amyloid-β (Aβ) is believed to play a central role in the etiology of the disease, and thus rational interventions are aimed at reducing the levels of Aβ in the brain. Targeting β-site amyloid precursor protein-cleaving enzyme (BACE)-1 represents an attractive strategy, as this enzyme catalyzes the initial and rate-limiting step in Aβ production. Observation of increased levels of BACE1 and enzymatic activity in the brain, cerebrospinal fluid, and platelets of patients with AD and mild cognitive impairment supports the potential benefits of BACE1 inhibition. Numerous potent inhibitors have been generated, and many of these have been proved to lower Aβ levels in the brain of animal models. Over 10 years of intensive research on BACE1 inhibitors has now culminated in advancing half a dozen of these drugs into human trials, yet translating the in vitro and cellular efficacy of BACE1 inhibitors into preclinical and clinical trials represents a challenge. This review addresses the promises and also the potential problems associated with BACE1 inhibitors for AD therapy, as the complex biological function of BACE1 in the brain is becoming unraveled.

The structural evolution of β-secretase inhibitors: a focus on the development of small-molecule inhibitors

Effective treatment of Alzheimer's disease (AD) remains a critical unmet need in medicine. The lack of useful treatment for AD led to an intense search for novel therapies based on the amyloid hypothesis, which states that amyloid β-42 (Aβ42) plays an early and crucial role in all cases of AD. β-Secretase (also known as BACE-1 β-site APP-cleaving enzyme, Asp-2 or memapsin-2) is an aspartyl protease representing the rate limiting step in the generation of Aβ peptide fragments, therefore it could represent an important target in the steady hunt for a disease-modifying treatment. Generally, β-secretase inhibitors are grouped into two families: peptidomimetic and nonpeptidomimetic inhibitors. However, irrespective of the class, serious challenges with respect to blood-brain barrier (BBB) penetration and selectivity still remain. Discovering a small molecule inhibitor of β-secretase represents an unnerving challenge but, due to its significant potential as a therapeutic target, growing efforts in this task are evident from both academic and industrial laboratories. In this frame, the rising availability of crystal structures of β-secretase-inhibitor complexes represents an invaluable opportunity for optimization. Nevertheless, beyond the inhibitory activity, the major issue of the current research approaches is about problems associated with BBB penetration and pharmacokinetic properties. This review follows the structural evolution of the early β-secretase inhibitors and gives a snap-shot of the hottest chemical templates in the literature of the last five years, showing research progress in this field.

BACE1 protein endocytosis and trafficking are differentially regulated by ubiquitination at lysine 501 and the Di-leucine motif in the carboxyl terminus

β-Site amyloid precursor protein-cleaving enzyme (BACE1) is a membrane-tethered member of the aspartyl proteases that has been identified as β-secretase. BACE1 is targeted through the secretory pathway to the plasma membrane and then is internalized to endosomes. Sorting of membrane proteins to the endosomes and lysosomes is regulated by the interaction of signals present in their carboxyl-terminal fragment with specific trafficking molecules. The BACE1 carboxyl-terminal fragment contains a di-leucine sorting signal ((495)DDISLL(500)) and a ubiquitination site at Lys-501. Here, we report that lack of ubiquitination at Lys-501 (BACE1K501R) does not affect the rate of endocytosis but produces BACE1 stabilization and accumulation of BACE1 in early and late endosomes/lysosomes as well as at the cell membrane. In contrast, the disruption of the di-leucine motif (BACE1LLAA) greatly impairs BACE1 endocytosis and produces a delayed retrograde transport of BACE1 to the trans-Golgi network (TGN) and a delayed delivery of BACE1 to the lysosomes, thus decreasing its degradation. Moreover, the combination of the lack of ubiquitination at Lys-501 and the disruption of the di-leucine motif (BACE1LLAA/KR) produces additive effects on BACE1 stabilization and defective internalization. Finally, BACE1LLAA/KR accumulates in the TGN, while its levels are decreased in EEA1-positive compartments indicating that both ubiquitination at Lys-501 and the di-leucine motif are necessary for the trafficking of BACE1 from the TGN to early endosomes. Our studies have elucidated a differential role for the di-leucine motif and ubiquitination at Lys-501 in BACE1 endocytosis, trafficking, and degradation and suggest the involvement of multiple adaptor molecules.

Characterization of plasma β-secretase (BACE1) activity and soluble amyloid precursor proteins as potential biomarkers for Alzheimer's disease

Reduction in cerebrospinal fluid (CSF) amyloid β42 (Aβ42) and elevation in total tau and phospho-thr181 tau consistently differentiate between Alzheimer's disease (AD) and age-matched control subjects. In contrast, CSF β-site APP-cleaving enzyme activity (BACE1) and soluble amyloid precursor proteins α and β (sAPPα and sAPPβ) are without consistent patterns in AD subjects. Plasma sampling is much easier, with fewer side effects, and is readily applied in primary care centers, so we have developed and validated novel plasma BACE activity, sAPPβ, and sAPPα assays and investigated their ability to distinguish AD from age-matched controls. Plasma BACE activity assay was sensitive and specific, with signal being immunodepleted with a specific BACE1 antibody and inhibited with a BACE1-specific inhibitor. Plasma sAPPβ and sAPPα assays were specific, with signal diluting linearly, immunodepleted with specific antibodies, and at background levels in APP knockout mice. In rhesus monkeys, BACE1 but not γ-secretase inhibitor led to significant lowering of plasma sAPPβ with concurrent elevation of plasma sAPPα. AD subjects showed a significant increase in plasma BACE1 activity, sAPPβ, sAPPα, and Aβ42 (P < 0.001) compared with age-matched controls. In conclusion, plasma BACE activity and sAPP endpoints provide novel investigative biomarkers for AD diagnosis and potential pharmacodynamic biomarkers for secretase inhibitor studies.

Rafts, Nanoparticles and Neural Disease

This review examines the role of membrane rafts in neural disease as a rationale for drug targeting utilizing lipid-based nanoparticles. The article begins with an overview of methodological issues involving the existence, sizes, and lifetimes of rafts, and then examines raft function in the etiologies of three major neural diseases-epilepsy, Parkinson's disease, and Alzheimer's disease-selected as promising candidates for raft-based therapeutics. Raft-targeting drug delivery systems involving liposomes and solid lipid nanoparticles are then examined in detail.

Transgenic mouse models of Alzheimer disease: developing a better model as a tool for therapeutic interventions

Alzheimer disease (AD) is the leading cause of dementia among elderly. Currently, no effective treatment is available for AD. Analysis of transgenic mouse models of AD has facilitated our understanding of disease mechanisms and provided valuable tools for evaluating potential therapeutic strategies. In this review, we will discuss the strengths and weaknesses of current mouse models of AD and the contribution towards understanding the pathological mechanisms and developing effective therapies.

Alzheimer culprits: cellular crossroads and interplay

Alzheimer's disease (AD) is the primary cause of dementia in the elderly and one of the major health problems worldwide. Since its first description by Alois Alzheimer in 1907, noticeable but insufficient scientific comprehension of this complex pathology has been achieved. All the research that has been pursued takes origin from the identification of the pathological hallmarks in the forms of amyloid-β (Aβ) deposits (plaques), and aggregated hyperphosphorylated tau protein filaments (named neurofibrillary tangles). Since this discovery, many hypotheses have been proposed to explain the origin of the pathology. The "amyloid cascade hypothesis" is the most accredited theory. The mechanism suggested to be one of the initial causes of AD is an imbalance between the production and the clearance of Aβ peptides. Therefore, Amyloid Precursor Protein (APP) synthesis, trafficking and metabolism producing either the toxic Aβ peptide via the amyloidogenic pathway or the sAPPα fragment via the non amyloidogenic pathway have become appealing subjects of study. Being able to reduce the formation of the toxic Aβ peptides is obviously an immediate approach in the trial to prevent AD. The following review summarizes the most relevant discoveries in the field of the last decades.

Small-molecule BACE1 inhibitors: a patent literature review (2006 - 2011)

INTRODUCTION

Alzheimer's disease is a devastating neurodegenerative disorder for which no disease-modifying therapy exists. The amyloid hypothesis, which implicates Aβ as the toxin initiating a biological cascade leading to neurodegeneration, is the most prominent theory concerning the underlying cause of the disease. BACE1 is one of two aspartyl proteinases that generate Aβ, thus inhibition of BACE1 has the potential to ameliorate the progression of Alzheimer's disease by abating the production of Aβ.

AREAS COVERED

This review chronicles small-molecule BACE1 inhibitors as described in the patent literature between 2006 and 2011 and their potential use as disease-modifying treatments for Alzheimer's disease. Over the past half a dozen years, numerous BACE1 inhibitors have been published in the patent applications, but often these contain a paltry amount of pertinent biological data (e.g. potency, selectivity, and efficacy). Fortunately, numerous relevant publications containing important data have appeared in the journal literature during this period. The goal in this effort was to create an amalgam of the two records to add value to this review.

EXPERT OPINION

The pharmaceutical industry has made tremendous progress in the development of small-molecule BACE1 inhibitors that lower Aβ in the central nervous system. Assuming the amyloid hypothesis is veracious, we anticipate a disease-modifying therapy to combat Alzheimer's disease is near.

Effects of zinc and DHA on the epigenetic regulation of human neuronal cells

Dietary intake of zinc and omega-3 fatty acids (DHA) have health benefits for a number of human diseases. However, the molecular basis of these health benefits remains unclear. Recently, we reported that zinc and DHA affect expression levels of histones H3 and H4 in human neuronal M17 cells. Here, using immunoblotting and densitometric analysis, we aimed to investigate the effect of zinc and DHA on post-translational modifications of histone H3 in M17 cells. In response to increase in zinc concentration, we observed increase in deacetylation, methylation and phosphorylation of H3 and decrease in acetylation. We also investigated the role of zinc in apoptosis, and found that zinc reduced the levels of the anti-apoptotic marker Bcl-2 while increasing the apoptotic marker caspase-3 levels, correlating with cell viability assays. Conversely, DHA treatment resulted in increase in acetylation of H3 and Bcl-2 levels and decrease in deacetylation, methylation, phosphorylation of H3 and caspase-3 levels, suggesting that DHA promotes gene expression and neuroprotection. Our novel findings show the opposing effects of zinc and DHA on the epigenetic regulation of human neuronal cells and highlight the potential benefit of dietary intake of DHA for management of neurodegenerative diseases.

The Membrane-Bound Aspartyl Protease BACE1: Molecular and Functional Properties in Alzheimer's Disease and Beyond

The β-site APP cleaving enzyme 1 (BACE1) is a transmembrane aspartyl protease involved in Alzheimer’s disease (AD) pathogenesis and in myelination. BACE1 initiates the generation of the pathogenic amyloid β-peptide, which makes BACE1 a major drug target for AD. BACE1 also cleaves and activates neuregulin 1, thereby contributing to postnatal myelination, in particular in the peripheral nervous system. Additional proteins are also cleaved by BACE1, but less is known about the physiological consequences of their cleavage. Recently, new phenotypes were described in BACE1-deficient mice. Although it remains unclear through which BACE1 substrates they are mediated, the phenotypes suggest a versatile role of this protease for diverse physiological processes. This review summarizes the enzymatic and cellular properties of BACE1 as well as its regulation by lipids, by transcriptional, and by translational mechanisms. The main focus will be on the recent progress in understanding BACE1 function and its implication for potential mechanism-based side effects upon therapeutic inhibition.

Reduction in BACE1 decreases body weight, protects against diet-induced obesity and enhances insulin sensitivity in mice

Insulin resistance and impaired glucose homoeostasis are important indicators of Type 2 diabetes and are early risk factors of AD (Alzheimer's disease). An essential feature of AD pathology is the presence of BACE1 (β-site amyloid precursor protein-cleaving enzyme 1), which regulates production of toxic amyloid peptides. However, whether BACE1 also plays a role in glucose homoeostasis is presently unknown. We have used transgenic mice to analyse the effects of loss of BACE1 on body weight, and lipid and glucose homoeostasis. BACE1-/- mice are lean, with decreased adiposity, higher energy expenditure, and improved glucose disposal and peripheral insulin sensitivity than wild-type littermates. BACE1-/- mice are also protected from diet-induced obesity. BACE1-deficient skeletal muscle and liver exhibit improved insulin sensitivity. In a skeletal muscle cell line, BACE1 inhibition increased glucose uptake and enhanced insulin sensitivity. The loss of BACE1 is associated with increased levels of UCP1 (uncoupling protein 1) in BAT (brown adipose tissue) and UCP2 and UCP3 mRNA in skeletal muscle, indicative of increased uncoupled respiration and metabolic inefficiency. Thus BACE1 levels may play a critical role in glucose and lipid homoeostasis in conditions of chronic nutrient excess. Therefore strategies that ameliorate BACE1 activity may be important novel approaches for the treatment of diabetes.

Alzheimer's therapeutics: translation of preclinical science to clinical drug development

Over the past three decades, significant progress has been made in understanding the neurobiology of Alzheimer's disease. In recent years, the first attempts to implement novel mechanism-based treatments brought rather disappointing results, with low, if any, drug efficacy and significant side effects. A discrepancy between our expectations based on preclinical models and the results of clinical trials calls for a revision of our theoretical views and questions every stage of translation-from how we model the disease to how we run clinical trials. In the following sections, we will use some specific examples of the therapeutics from acetylcholinesterase inhibitors to recent anti-Aβ immunization and γ-secretase inhibition to discuss whether preclinical studies could predict the limitations in efficacy and side effects that we were so disappointed to observe in recent clinical trials. We discuss ways to improve both the predictive validity of mouse models and the translation of knowledge between preclinical and clinical stages of drug development.