Molecular basis of selective amyloid-β degrading enzymes in Alzheimer's disease

Systematic review of amyloid-beta clearance proteins from the brain to the periphery: implications for Alzheimer's disease diagnosis and therapeutic targets

Amyloid-beta clearance plays a key role in the pathogenesis of Alzheimer's disease. However, the variation in functional proteins involved in amyloid-beta clearance and their correlation with amyloid-beta levels remain unclear. In this study, we conducted meta-analyses and a systematic review using studies from the PubMed, Embase, Web of Science, and Cochrane Library databases, including journal articles published from inception to June 30, 2023. The inclusion criteria included studies comparing the levels of functional proteins associated with amyloid-beta clearance in the blood, cerebrospinal fluid, and brain of healthy controls, patients with mild cognitive impairment, and patients with Alzheimer's disease. Additionally, we analyzed the correlation between these functional proteins and amyloid-beta levels in patients with Alzheimer's disease. The methodological quality of the studies was assessed via the Newcastle‒Ottawa Scale. Owing to heterogeneity, we utilized either a fixed-effect or random-effect model to assess the 95% confidence interval (CI) of the standard mean difference (SMD) among healthy controls, patients with mild cognitive impairment, and patients with Alzheimer's disease. The findings revealed significant alterations in the levels of insulin-degrading enzymes, neprilysin, matrix metalloproteinase-9, cathepsin D, receptor for advanced glycation end products, and P-glycoprotein in the brains of patients with Alzheimer's disease, patients with mild cognitive impairment, and healthy controls. In cerebrospinal fluid, the levels of triggering receptor expressed on myeloid cells 2 and ubiquitin C-terminal hydrolase L1 are altered, whereas the levels of TREM2, CD40, CD40L, CD14, CD22, cathepsin D, cystatin C, and α2 M in peripheral blood differ. Notably, TREM2 and cathepsin D showed changes in both brain (SMD = 0.31, 95% CI: 0.16-0.47, P < 0.001, I2 = 78.4%; SMD = 1.24, 95% CI: 0.01-2.48, P = 0.048, I2 = 90.1%) and peripheral blood (SMD = 1.01, 95% CI: 0.35-1.66, P = 0.003, I2 = 96.5%; SMD = 7.55, 95% CI: 3.92-11.18, P < 0.001, I2 = 98.2%) samples. Furthermore, correlations were observed between amyloid-beta levels and the levels of TREM2 ( r = 0.16, 95% CI: 0.04-0.28, P = 0.009, I2 = 74.7%), neprilysin ( r = -0.47, 95% CI: -0.80-0.14, P = 0.005, I2 = 76.1%), and P-glycoprotein ( r = -0.31, 95% CI: -0.51-0.11, P = 0.002, I2 = 0.0%) in patients with Alzheimer's disease. These findings suggest that triggering receptor expressed on myeloid cells 2 and cathepsin D could serve as potential diagnostic biomarkers for Alzheimer's disease, whereas triggering receptor expressed on myeloid cells 2, neprilysin, and P-glycoprotein may represent potential therapeutic targets.

Sulfonic acid functionalized β-amyloid peptide aggregation inhibitors and antioxidant agents for the treatment of Alzheimer's disease: Combining machine learning, computational, in vitro and in vivo approaches

Alzheimer's disease (AD) is characterized as a neurodegenerative disorder that is caused by plaque formation by accumulating β-amyloid (Aβ), leading to neurocognitive function and impaired mental development. Thus, targeting Aβ represents a promising target for the development of therapeutics in AD management. Several functionalized sulfonic acid molecules have been reported, including tramiprosate prodrug, which is currently in clinical trial III and exhibits a good response in mild to moderate AD patients. Therefore, expanding upon this approach, we hypothesized that the sulfonic acid functionalized aromatic class molecule might demonstrate a good inhibitory effect against β-amyloid aggregation, leading to a decrease in the progression burden of AD. We used computational and in vitro approaches to establish effective compounds. As a result, three potent hit molecules were selected based on binding score as well as availability. In the case of safety profile of compounds, in vitro using human neuroblastoma SH-SY5Y cells and in vivo using C. elegans was performed at doses up to 500 μM; no difference in viability was exhibited between control and treatment groups. However, H2O2-induced ROS stress was significantly reduced in neuroblastoma cells after treatment. The AFM and ThT-embedded β-amyloid1-42 kinetic studies confirmed B-PEA-MBSA and H-HPA-NSA potency. H-HPA-NSA arrested elongation phase of Aβ aggregation in kinetic study at a lower concentration (10 μM), while B-PEA-MBSA reduced the intensity of stationary phase at a dose of 100 μM. Thus, based on the outcomes, it can be suggested that B-PEA-MBSA and H-HPA-NSA can prevent β-amyloid aggregation with mild to moderate AD.

The Impact of the Exposome on Alzheimer's Disease: The Influence of Nutrition

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by cognitive decline, memory loss, and behavioural changes. While genetic predispositions and pathological processes have been the traditional focus, this review highlights the fundamental role of environmental factors, particularly nutrition, within the exposome framework in modulating the risk and progression of AD. The exposome, which includes the totality of environmental exposures in an individual's lifetime, provides a comprehensive approach to understanding the complex aetiology of AD. In this review, we explore the impact of dietary factors and cyclic nucleotide pathways (cAMP/cGMP) on AD, emphasizing the potential of dietary interventions as therapeutic strategies. We investigate key aspects of how nutrition affects the accumulation of β-amyloid, the aggregation of tau proteins, and neuroinflammation. We also examine the impact of specific nutrients on cognitive performance and the risk of AD. Additionally, we discuss the potential of nutraceuticals with anti-phosphodiesterase activity and the role of various animal models of AD (such as 5xFAD, 3xTg-AD, Tg2576, and APP/PS1 mice) in demonstrating the effects of dietary interventions on disease onset and progression.

In silico study of selected alkaloids as dual inhibitors of β- and γ-secretases for Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) has become common as the number of aged people increases making it as a socioeconomic problem lately. To date, no success is recorded for disease-modifying therapies for AD but only drugs for symptomatic relief exist. Research has been centered on the role of amyloid-β on the pathogenesis of AD, which has led to the development of drugs that target Aβ (β- and γ-secretase inhibitors) to reduce the amount of Aβ formed. However, the existing β and γ-secretase inhibitors were associated with harmful side effects, low efficacy, and inability to cross the blood-brain barrier.

OBJECTIVE

This study therefore used in silico approach to predict the inhibitory properties of alkaloids as potential drug targets against AD.

METHODS

Thus, in this current study, 54 alkaloids from the PhytoHub server (phytohub.eu), and two approved drugs were docked against β-secretases. Additionally, galantamine and 5 alkaloids with the utmost binding potential with β-secretase were subjected to pharmacokinetics evaluation and docked against γ-secretase.

RESULTS

From the result, 5 compounds displayed for both docking periods, with demissidine, solasodine, tomatidine, and solanidine having better BE than the control drugs. Based on the pharmacokinetics evaluation, 4 compounds possessed good pharmacokinetic evaluation and biological activities than galantamine.

CONCLUSIONS

This study suggests that demissidine, solasodine, tomatidine, and solanidine are promising dual inhibitors against β- and γ-secretase proteins in silico. However, there is an urgent need to carry out in vitro and in vivo experiments on these new leads to validate the findings of this study.

Neuroprotective Effect of 1α,25-Dihydroxyvitamin D3 Against Cognitive Impairment in d-Galactose-Induced Aging Mice

Aging and age-related cognitive impairment have emerged as a growing global public health concern, yet there are no effective preventive strategies. Excessive oxidative stress and neuroinflammation have been proven to contribute to cognitive decline. Vitamin D maintains the redox balance and exerts immunomodulatory effects, but the specific role of vitamin D in aging and age-related cognitive impairment remains elusive. This study explored the neuroprotective effects and the potential molecular mechanisms of 1α,25-dihydroxyvitamin D3 in the aging model. An aging model was established by the treatment of d-galactose for 14 weeks in male KM mice. 0.1, 0.5, or 1 μg/kg 1α,25-dihydroxyvitamin D3 were used in the intervention group for 8 weeks. Cognitive performance was evaluated using the Morris water maze test, and the levels of oxidative stress and neuroinflammation in the hippocampus were further analyzed. d-galactose induced memory impairment, whereas 1α,25-dihydroxyvitamin D3 intervention prevented cognitive decline, accompanied by a reduction in neuronal apoptosis, an enhancement of synaptic plasticity, and a decrease in Aβ deposition. Meanwhile, 1α,25-dihydroxyvitamin D3 dramatically attenuated oxidative stress, mitigated microglial cell activation, and ameliorated neuroinflammation by activating the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response elements (AREs) axis and inhibiting the NF-κB signaling pathway. This study provides evidence that 1α,25-dihydroxyvitamin D3 might be a promising nutritional strategy for preventing cognitive decline in aging, thereby facilitating the clinical application and expanding the insight of vitamin D.

Association of MME gene polymorphisms with susceptibility to Alzheimer's disease in an Iranian population

Background

the MME gene encodes a membrane metalloendopeptidase, known as neprilysin (NEP). There are no reports on the potential implications of MME gene polymorphisms on the risk of Alzheimer's disease (AD) in the Iranian population. In this study, we studied the potential association of two single nucleotide polymorphisms (SNPs), rs6797911 and rs3736187, in the MME gene and the risk of developing AD in an Iranian population.

Methods

This case-control study comprised 120 AD-diagnosed patients and 120 healthy individuals without any prior family history of AD. The patient and control groups were matched for major demographic and health characteristics. Genotyping was performed by amplification refractory mutation system-polymerase chain reaction (ARMS-PCR).

Results

All patients included in this study were assessed by an experienced neurologist to exclude cases with other forms of dementia based on a brain computed tomography scan and other clinical findings. There were no significant differences in demographic and health characteristics including sex, diabetes, blood pressure, and cigarette smoking status between case and control groups (p > 0.05). However, the age difference appeared significant. Both SNPs were significantly associated with the risk of AD in our study population. The rs3736187 (T > C, 3:155168489) was strongly associated with AD risk under the log-additive model (OR = 1.67, CI = 1.18-2.37, p-value = 0.003). The rs6797911 (T > A, 3:155144601) also showed a significant association with AD risk under the dominant model (TT vs. TA and AA, OR = 3.37, CI = 1.86-6.1, p-value <0.001).

Conclusion

There is a strong association between MME gene polymorphisms and susceptibility to AD in the Iranian population. Amyloid-β (Aβ) can serve as a substrate for the NEP metalloendopeptidase, the product of the MME gene. However, the mechanistic understanding of how these genetic variations affect NEP expression, function, and consequently susceptibility to AD, is poorly understood. Further research is required to fully understand the exact implication of MME gene variations on AD, particularly in a larger, ethnicity-diverse population.

Immunotherapy in Alzheimer's disease: focusing on the efficacy of gantenerumab on amyloid-β clearance and cognitive decline

Gantenerumab, a human monoclonal antibody (mAb), has been thought of as a potential agent to treat Alzheimer's disease (AD) by specifically targeting regions of the amyloid-β (Aβ) peptide sequence. Aβ protein accumulation in the brain leads to amyloid plaques, causing neuroinflammation, oxidative stress, neuronal damage, and neurotransmitter dysfunction, thereby causing cognitive decline in AD. Gantenerumab involves disrupting Aβ aggregation and promoting the breakdown of larger Aβ aggregates into smaller fragments, which facilitates the action of Aβ-degrading enzymes in the brain, thus slowing down the progression of AD. Moreover, Gantenerumab acts as an opsonin, coating Aβ plaques and enhancing their recognition by immune cells, which, combined with its ability to improve the activity of microglia, makes it an intriguing candidate for promoting Aβ plaque clearance. Indeed, the multifaceted effects of Gantenerumab, including Aβ disaggregation, enhanced immune recognition, and improved microglia activity, may position it as a promising therapeutic approach for AD. Of note, reports suggest that Gantenerumab, albeit its capacity to reduce or eliminate Aβ, has not demonstrated effectiveness in reducing cognitive decline. This review, after providing an overview of immunotherapy approaches that target Aβ in AD, explores the efficacy of Gantenerumab in reducing Aβ levels and cognitive decline.

Bifurcations in coupled amyloid-β aggregation-inflammation systems

A complex interplay between various processes underlies the neuropathology of Alzheimer's disease (AD) and its progressive course. Several lines of evidence point to the coupling between Aβ aggregation and neuroinflammation and its role in maintaining brain homeostasis during the long prodromal phase of AD. Little is however known about how this protective mechanism fails and as a result, an irreversible and progressive transition to clinical AD occurs. Here, we introduce a minimal model of a coupled system of Aβ aggregation and inflammation, numerically simulate its dynamical behavior, and analyze its bifurcation properties. The introduced model represents the following events: generation of Aβ monomers, aggregation of Aβ monomers into oligomers and fibrils, induction of inflammation by Aβ aggregates, and clearance of various Aβ species. Crucially, the rates of Aβ generation and clearance are modulated by inflammation level following a Hill-type response function. Despite its relative simplicity, the model exhibits enormously rich dynamics ranging from overdamped kinetics to sustained oscillations. We then specify the region of inflammation- and coupling-related parameters space where a transition to oscillatory dynamics occurs and demonstrate how changes in Aβ aggregation parameters could shift this oscillatory region in parameter space. Our results reveal the propensity of coupled Aβ aggregation-inflammation systems to oscillatory dynamics and propose prolonged sustained oscillations and their consequent immune system exhaustion as a potential mechanism underlying the transition to a more progressive phase of amyloid pathology in AD. The implications of our results in regard to early diagnosis of AD and anti-AD drug development are discussed.

Hypoglycemia and Alzheimer Disease Risk: The Possible Role of Dasiglucagon

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by memory impairment and cognitive dysfunctions. It has been shown that hypoglycemia can adversely affect AD neuropathology. It is well-known that chronic hyperglycemia in type 2 diabetes (T2D) is regarded as a potential risk factor for the development and progression of AD. However, the effect of recurrent hypoglycemia on the pathogenesis of AD was not deeply discussed, and how recurrent hypoglycemia affects AD at cellular and molecular levels was not intensely interpreted by the previous studies. The underlying mechanisms for hypoglycaemia-induced AD are diverse such as endothelial dysfunction, thrombosis, and neuronal injury that causing tau protein hyperphosphorylation and the accumulation of amyloid beta (Aβ) in the brain neurons. Of note, the glucagon hormone, which controls blood glucose, can also regulate the cognitive functions. Glucagon increases blood glucose by antagonizing the metabolic effect of insulin. Therefore, glucagon, through attenuation of hypoglycemia, may prevent AD neuropathology. Glucagon/GLP-1 has been shown to promote synaptogenesis, hippocampal synaptic plasticity, and learning and memory, while attenuating amyloid and tau pathologies. Therefore, activation of glucagon receptors in the brain may reduce AD neuropathology. A recent glucagon receptor agonist dasiglucagon which used in the management of hypoglycemia may be effective in preventing hypoglycemia and AD neuropathology. This review aims to discuss the potential role of dasiglucagon in treating hypoglycemia in AD, and how this drug reduce AD neuropathology.

Intracerebroventricular Cutibacterium acnes Generates Manifestations of Alzheimer's Disease-like Pathology in the Rat Hippocampus

The infection hypothesis is a new causative explanation for Alzheimer's disease (AD). In recent decades, various species of bacterial pathogens have been distinguished in the autopsy of Alzheimer's patients; however, the mechanism of bacterial contribution to AD pathology is still unknown. To explore the hypothesis, Cutibacterium acnes (C. acnes) was selected, and effects of its intracerebroventricular (ICV) inoculation in rats was evaluated. The results revealed that C. acnes causes memory impairment, which might be a consequence of upregulated Amyloid β (Aβ) deposits in the hippocampus; Aβ aggregates are co-localized with C. acnes colonies. The key point of our hypothesis is that the activation of the innate immune system by C. acnes through the TLR2/NF-κB/NLRP3 signaling pathway, eventually leads to increased neuroinflammation, which might be resulted from microgliosis and astrogliosis. Neuroinflammation increases oxidative stress and cell apoptosis. Overall, the obtained results of this study support our hypothesis that brain exposure to C. acnes prompted neuroinflammation with similar AD-like pathology.

Carriers of Heterozygous Loss-of-Function ACE Mutations Are at Risk for Alzheimer's Disease

We hypothesized that subjects with heterozygous loss-of-function (LoF) ACE mutations are at risk for Alzheimer's disease because amyloid Aβ42, a primary component of the protein aggregates that accumulate in the brains of AD patients, is cleaved by ACE (angiotensin I-converting enzyme). Thus, decreased ACE activity in the brain, either due to genetic mutation or the effects of ACE inhibitors, could be a risk factor for AD. To explore this hypothesis in the current study, existing SNP databases were analyzed for LoF ACE mutations using four predicting tools, including PolyPhen-2, and compared with the topology of known ACE mutations already associated with AD. The combined frequency of >400 of these LoF-damaging ACE mutations in the general population is quite significant-up to 5%-comparable to the frequency of AD in the population > 70 y.o., which indicates that the contribution of low ACE in the development of AD could be under appreciated. Our analysis suggests several mechanisms by which ACE mutations may be associated with Alzheimer's disease. Systematic analysis of blood ACE levels in patients with all ACE mutations is likely to have clinical significance because available sequencing data will help detect persons with increased risk of late-onset Alzheimer's disease. Patients with transport-deficient ACE mutations (about 20% of damaging ACE mutations) may benefit from preventive or therapeutic treatment with a combination of chemical and pharmacological (e.g., centrally acting ACE inhibitors) chaperones and proteosome inhibitors to restore impaired surface ACE expression, as was shown previously by our group for another transport-deficient ACE mutation-Q1069R.

Minding the Gap: Exploring Neuroinflammatory and Microglial Sex Differences in Alzheimer's Disease

Research into Alzheimer's Disease (AD) describes a link between AD and the resident immune cells of the brain, the microglia. Further, this suspected link is thought to have underlying sex effects, although the mechanisms of these effects are only just beginning to be understood. Many of these insights are the result of policies put in place by funding agencies such as the National Institutes of Health (NIH) to consider sex as a biological variable (SABV) and the move towards precision medicine due to continued lackluster therapeutic options. The purpose of this review is to provide an updated assessment of the current research that summarizes sex differences and the research pertaining to microglia and their varied responses in AD.