Aberrant proteolytic processing and therapeutic strategies in Alzheimer disease

Kallikrein-related peptidase's significance in Alzheimer's disease pathogenesis: A comprehensive survey

Alzheimer's disease (AD) and related dementias constitute an important global health challenge. Detailed understanding of the multiple molecular mechanisms underlying their pathogenesis constitutes a clue for the management of the disease. Kallikrein-related peptidases (KLKs), a lead family of serine proteases, have emerged as potential biomarkers and therapeutic targets in the context of AD and associated cognitive decline. Hence, KLKs were proposed to display multifaceted impacts influencing various aspects of neurodegeneration, including amyloid-beta aggregation, tau pathology, neuroinflammation, and synaptic dysfunction. We propose here a comprehensive survey to summarize recent findings, providing an overview of the main kallikreins implicated in AD pathophysiology namely KLK8, KLK6 and KLK7. We explore the interplay between KLKs and key AD molecular pathways, shedding light on their significance as potential biomarkers for early disease detection. We also discuss their pertinence as therapeutic targets for disease-modifying interventions to develop innovative therapeutic strategies aimed at halting or ameliorating the progression of AD and associated dementias.

First-In-Human Safety, Tolerability, and Pharmacokinetics of Single and Multiple Doses of AZP2006, A Synthetic Compound for the Treatment of Alzheimer's Disease and Related Diseases

Background

Alzheimer's disease (AD) and progressive supranuclear palsy (PSP) are major neurodegenerative conditions with tau pathology in common but distinct symptoms-AD involves cognitive decline while PSP affects balance and eye movement. Progranulin (PGRN) is a growth factor implicated in neurodegenerative diseases, including AD and PSP. AZP2006, a synthetic compound, targets tauopathies by stabilizing PGRN levels and reducing tau aggregation and neuroinflammation.

Objective

Evaluate the safety, tolerability, and pharmacokinetics of AZP2006.

Methods

A first-in-Human phase 1 study comprised a single ascending dose (SAD) and a multiple ascending dose study (MAD). The SAD study included 64 healthy male volunteers and tested singles oral doses of 3 to 500 mg of AZP2006 free base equivalent or placebo. In the MAD study, 24 healthy male volunteers were administered oral doses of 30, 60, and 120 mg per day of AZP2006 or placebo for 10 days.

Results

No serious adverse events were observed. Clinical, biological, and electrocardiogram findings were non-relevant. Nineteen minor adverse events resolved before study completion. The safety profile indicated no specific risks. The multiple ascending dose study was halted, and the optional dose level of 180 mg was not performed due to high levels of M2 metabolite in plasma that necessitated additional preclinical evaluation of M2. Both AZP2006 and its M2 metabolite were quickly absorbed and widely distributed in tissues. Exposure increased more than proportionally with dose.

Conclusions

AZP2006 had a favorable safety profile and was rapidly absorbed. Elevated M2 metabolite levels necessitated further studies to clarify excretion and metabolism mechanisms.

A new view on functions of the lysine demalonylase activity of SIRT5

AIMS

The specificity of the lysine demalonylation substrates of the pharmaceutically attractive tumor promoter/suppressor SIRT5 is not comprehensively clarified. The present study re-analyses publicly available data and highlights potentially pharmaceutically interesting outcomes by the use of bioinformatics.

MATERIALS AND METHODS

The interaction networks of SIRT5 malonylome from the wild-type and ob/ob (obese pre-diabetic type) mice were subjected to the pathway enrichment and gene function prediction analysis using GeneMania (3.5.2) application run under Cytoscape (3.9.1) environment.

KEY FINDINGS

The analysis in the wild-type mice revealed the involvement of SIRT5 malonylome in Eukaryotic translation elongation (ETE; the nodes EF1A1, EEF2, EEF1D, and EEF1G), Amino acid and derivative metabolism (AADM), and Selenoamino acid metabolism (SAM). The tumor promoter/suppressor activity of SIRT5 is mediated through the tumor promoter substrates included in AADM (GLUD1, SHMT1, ACAT1), and the tumor suppressor substrates involved in AADM and SAM (ALDH9A1, BHMT, GNMT). Selen stimulates the expression of SIRT5 and other sirtuins. SIRT5 in turn regulates the selenocysteine synthesis, which creates a regulatory loop. The analysis of SIRT5 malonylome in pre-diabetic ob/ob mice identifies the mTORC1 pathway as a mechanism, which facilitates SIRT5 functions. The comparison of the outcomes of SIRT5 malonylome, succinylome, and glutarylome analysis disclosed several differences.

SIGNIFICANCE

The analysis showed additional aspects of SIRT5 malonylome functions besides the control of glucose metabolism. It defined several unique substrates and pathways, and it showed differences compared to other enzymatic activities of SIRT5, which could be used for pharmaceutical benefits.

Autophagy and autophagy-related molecules in neurodegenerative diseases

Autophagy is one of the degradation pathways to remove proteins or damaged organelles in cells that plays an important role in neuroprotection. Different stages of autophagy are regulated by autophagy-related genes, and many molecules such as transcription factor EB (TFEB) are involved. The complete autophagy process plays an important role in maintaining the dynamic balance of autophagy and is crucial to the homeostasis of intracellular substance and energy metabolism. Autophagy balance is disrupted in neurodegenerative diseases, accounting for a variety of degeneration disorders. These impairments can be alleviated or treated by the regulation of autophagy through molecules such as TFEB.

Transcranial alternating current stimulation combined with sound stimulation improves cognitive function in patients with Alzheimer's disease: Study protocol for a randomized controlled trial

Background

The number of patients with Alzheimer's disease (AD) worldwide is increasing yearly, but the existing treatment methods have poor efficacy. Transcranial alternating current stimulation (tACS) is a new treatment for AD, but the offline effect of tACS is insufficient. To prolong the offline effect, we designed to combine tACS with sound stimulation to maintain the long-term post-effect.

Materials and methods

To explore the safety and effectiveness of tACS combined with sound stimulation and its impact on the cognition of AD patients. This trial will recruit 87 patients with mild to moderate AD. All patients were randomly divided into three groups. The change in Alzheimer's Disease Assessment Scale-Cognitive (ADAS-Cog) scores from the day before treatment to the end of treatment and 3 months after treatment was used as the main evaluation index. We will also explore the changes in the brain structural network, functional network, and metabolic network of AD patients in each group after treatment.

Discussion

We hope to conclude that tACS combined with sound stimulation is safe and tolerable in 87 patients with mild to moderate AD under three standardized treatment regimens. Compared with tACS alone or sound alone, the combination group had a significant long-term effect on cognitive improvement. To screen out a better treatment plan for AD patients. tACS combined with sound stimulation is a previously unexplored, non-invasive joint intervention to improve patients' cognitive status. This study may also identify the potential mechanism of tACS combined with sound stimulation in treating mild to moderate AD patients.

Clinical Trial Registration

Clinicaltrials.gov, NCT05251649. Registered on February 22, 2022.

Brain Metabolic Alterations in Alzheimer's Disease

The brain is one of the most energy-consuming organs in the body. Satisfying such energy demand requires compartmentalized, cell-specific metabolic processes, known to be complementary and intimately coupled. Thus, the brain relies on thoroughly orchestrated energy-obtaining agents, processes and molecular features, such as the neurovascular unit, the astrocyte-neuron metabolic coupling, and the cellular distribution of energy substrate transporters. Importantly, early features of the aging process are determined by the progressive perturbation of certain processes responsible for adequate brain energy supply, resulting in brain hypometabolism. These age-related brain energy alterations are further worsened during the prodromal stages of neurodegenerative diseases, namely Alzheimer's disease (AD), preceding the onset of clinical symptoms, and are anatomically and functionally associated with the loss of cognitive abilities. Here, we focus on concrete neuroenergetic features such as the brain's fueling by glucose and lactate, the transporters and vascular system guaranteeing its supply, and the metabolic interactions between astrocytes and neurons, and on its neurodegenerative-related disruption. We sought to review the principles underlying the metabolic dimension of healthy and AD brains, and suggest that the integration of these concepts in the preventive, diagnostic and treatment strategies for AD is key to improving the precision of these interventions.

Focus on Molecular Functions of Anti-Aging Deacetylase SIRT3

SIRT3 is a protein lysine deacetylase with a prominent role in the maintenance of mitochondrial integrity, which is a vulnerable target in many diseases. Intriguingly, cellular aging is reversible just by SIRT3 overexpression, which raises many questions about the role of SIRT3 in the molecular anti-aging mechanisms. Therefore, functions of SIRT3 were analyzed through the interaction network of 407 substrates collected by data mining. Results of the pathway enrichment and gene function prediction confirmed functions in the primary metabolism and mitochondrial ATP production. However, it also suggested involvement in thermogenesis, brain-related neurodegenerative diseases Alzheimer's (AD), Parkinson's, Huntington's disease (HD), and non-alcoholic fatty liver disease. The protein node prioritization analysis identified subunits of the complex I of the mitochondrial respiratory chain (MRC) as the nodes with the main regulatory effect within the entire interaction network. Additional high-ranked nodes were succinate dehydrogenase subunit B (SDHB), complex II, and ATP5F1, complex V of MRC. The analysis supports existence of the NADH/NAD+ driven regulatory feedback loop between SIRT3, complex I (MRC), and acetyl-CoA synthetases, and existence of the nuclear substrates of SIRT3. Unexplored functions of SIRT3 substrates such as LMNA and LMNB; HIF-1a, p53, DNA-PK, and PARK7 are highlighted for further scientific advances. SIRT3 acts as a repressor of BACE1 through the SIRT3-LKB1-AMPK-CREB-PGC1A-PPARG-BACE1 (SIRT3-BACE1), which functions are fitted the best by the Circadian Clock pathway. It forms a new working hypothesis as the therapeutical target for AD treatment. Other important pathways linked to SIRT3 activity are highlighted for therapeutical interventions.

GPR120 Signaling Controls Amyloid-β Degrading Activity of Matrix Metalloproteinases

Alzheimer's disease (AD) is characterized by the extensive deposition of amyloid-β peptide (Aβ) in the brain. Brain Aβ level is regulated by a balance between Aβ production and clearance. The clearance rate of Aβ is decreased in the brains of sporadic AD patients, indicating that the dysregulation of Aβ clearance mechanisms affects the pathologic process of AD. Astrocytes are among the most abundant cells in the brain and are implicated in the clearance of brain Aβ via their regulation of the blood-brain barrier, glymphatic system, and proteolytic degradation. The cellular morphology and activity of astrocytes are modulated by several molecules, including ω3 polyunsaturated fatty acids, such as docosahexaenoic acid, which is one of the most abundant lipids in the brain, via the G protein-coupled receptor GPR120/FFAR4. In this study, we analyzed the role of GPR120 signaling in the Aβ-degrading activity of astrocytes. Treatment with the selective antagonist upregulated the matrix metalloproteinase (MMP) inhibitor-sensitive Aβ-degrading activity in primary astrocytes. Moreover, the inhibition of GPR120 signaling increased the levels of Mmp2 and Mmp14 mRNAs, and decreased the expression levels of tissue inhibitor of metalloproteinases 3 (Timp3) and Timp4, suggesting that GPR120 negatively regulates the astrocyte-derived MMP network. Finally, the intracerebral injection of GPR120-specific antagonist substantially decreased the levels of TBS-soluble Aβ in male AD model mice, and this effect was canceled by the coinjection of an MMP inhibitor. These data indicate that astrocytic GPR120 signaling negatively regulates the Aβ-degrading activity of MMPs.SIGNIFICANCE STATEMENT The level of amyloid β (Aβ) in the brain is a crucial determinant of the development of Alzheimer's disease. Here we found that astrocytes, which are the most abundant cell type in the CNS, harbor degrading activity against Aβ, which is regulated by GPR120 signaling. GPR120 is involved in the inflammatory response and obesity in peripheral organs. However, the pathophysiological role of GPR120 in Alzheimer's disease remains unknown. We found that selective inhibition of GPR120 signaling in astrocytes increased the Aβ-degrading activity of matrix metalloproteases. Our results suggest that GPR120 in astrocytes is a novel therapeutic target for the development of anti-Aβ therapeutics.

Therapeutic potential of cyanobacterial pigment protein phycoerythrin: in silico and in vitro study of BACE1 interaction and in vivo Aβ reduction

Cyanobacteria are an immense source of innovative classes of pharmacologically active compounds exhibiting various biological activities ranging from antioxidants, antibiotics, anticancer, anti-inflammatory to anti-Alzheimer's disease. In the present study, we primarily targeted the inhibition of Beta-site amyloid precursor protein cleaving enzyme-1 (BACE1) by a naturally occurring cyanobacterial protein phycoerythrin (C-PE). BACE1 cleaves amyloid-β precursor protein (APP) and leads to accumulation of neurotoxic amyloid beta (Aβ) plaques in the brain, as an attribute of Alzheimer's disease (AD). Inhibition of BACE1 was measured in terms of their association and dissociation rate constants, thermodynamics of binding using surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). The kinetic parameters for enzyme activity were also measured using synthetic decapeptide as a substrate. We further validated the potential of PE by in-vivo histopathological staining of Aβ aggregate mutant Caenorhabditis elegans CL4176 by Thioflavin-T. The present studies pave the way for the application of naturally occurring C-PE as a putative therapeutic drug for the AD.

Sphingolipids in neurodegeneration (with focus on ceramide and S1P)

For many decades, research on sphingolipids associated with neurodegenerative disease focused on alterations in glycosphingolipids, particularly glycosylceramides (cerebrosides), sulfatides, and gangliosides. This seemed quite natural since many of these glycolipids are constituents of myelin and accumulated in lipid storage diseases (sphingolipidoses) resulting from enzyme deficiencies in glycolipid metabolism. With the advent of recognizing ceramide and its derivative, sphingosine-1-phosphate (S1P), as key players in lipid cell signaling and regulation of cell death and survival, research focus shifted toward these two sphingolipids. Ceramide and S1P are invoked in a plethora of cell biological processes participating in neurodegeneration such as ER stress, autophagy, dysregulation of protein and lipid transport, exosome secretion and neurotoxic protein spreading, neuroinflammation, and mitochondrial dysfunction. Hence, it is timely to discuss various functions of ceramide and S1P in neurodegenerative disease and to define sphingolipid metabolism and cell signaling pathways as potential targets for therapy.

Fe3+ Facilitates Endocytic Internalization of Extracellular Aβ1-42 and Enhances Aβ1-42-Induced Caspase-3/Caspase-4 Activation and Neuronal Cell Death

Amyloid β (Aβ) peptide is a critical causative factor in Alzheimer's disease (AD) and of a variety of fragmented Aβ peptides Aβ_1-42 thought to exhibit the most neurotoxic effect. The present study investigated the effects of Fe³⁺ on Aβ_1-42 internalization and Aβ_1-42-induced caspase activation and neurotoxicity using mouse hippocampal slices and cultured PC-12 cells. Extracellularly applied Aβ_1-42 increased the cell-associated Aβ_1-42 levels in a concentration-dependent manner, and the effect was enhanced by adding Fe³⁺. Fe³⁺-induced enhancement of the cell-associated Aβ_1-42 levels was significantly inhibited by the endocytosis inhibitors dynasore and methyl-β-cyclodextrin. Aβ_1-42 reduced PC-12 cell viability in a concentration-dependent manner, and further reduction of the cell viability was obtained with Fe³⁺. Aβ_1-42-induced reduction of cell viability was not affected by A187, an antagonist of amylin-3 receptor. Aβ_1-42 activated caspase-3, caspase-4, and caspase-8 to a variety of degrees and Fe³⁺ further enhanced Aβ_1-42-induced activation of caspase-3 and caspase-4. Taken together, these results indicate that Fe³⁺ accelerates endocytic internalization of extracellular Aβ_1-42, enhances Aβ_1-42-induced caspase-3/caspase-4 activation, and promotes Aβ_1-42-induced neuronal cell death, regardless of amylin receptor.

Efficacy of curcumin for age-associated cognitive decline: a narrative review of preclinical and clinical studies

Processes such as aberrant redox signaling and chronic low-grade systemic inflammation have been reported to modulate age-associated pathologies such as cognitive impairment. Curcumin, the primary therapeutic component of the Indian spice, Turmeric (Curcuma longa), has long been known for its strong anti-inflammatory and antioxidant activity attributable to its unique molecular structure. Recently, an interest in this polyphenol as a cognitive therapeutic for the elderly has emerged. The purpose of this paper is to critically review preclinical and clinical studies that have evaluated the efficacy of curcumin in ameliorating and preventing age-associated cognitive decline and address the translational progress of preclinical to clinical efficacy. PubMed, semantic scholar, and Google scholar searches were used for preclinical studies; and clinicaltrials.gov , the Australian and New Zealand clinical trials registry, and PubMed search were used to select relevant completed clinical studies. Results from preclinical studies consistently demonstrate curcumin and its analogues to be efficacious for various aspects of cognitive impairment and processes that contribute to age-associated cognitive impairment. Results of published clinical studies, while mixed, continue to show promise for curcumin's use as a therapeutic for cognitive decline but overall remain inconclusive at this time. Both in vitro and in vivo studies have found that curcumin can significantly decrease oxidative stress, systemic inflammation, and obstruct pathways that activate transcription factors that augment these processes. Future clinical studies would benefit from including evaluation of peripheral and cerebrospinal fluid biomarkers of dementia and behavioral markers of cognitive decline, as well as targeting the appropriate population.

The Protective Effects of IGF-I against β-Amyloid-related Downregulation of Hippocampal Somatostatinergic System Involve Activation of Akt and Protein Kinase A

Somatostatin (SRIF), a neuropeptide highly distributed in the hippocampus and involved in learning and memory, is markedly reduced in the brain of Alzheimer's disease patients. The effects of insulin-like growth factor-I (IGF-I) against β amyloid (Aβ)-induced neuronal death and associated cognitive disorders have been extensively reported in experimental models of this disease. Here, we examined the effect of IGF-I on the hippocampal somatostatinergic system in Aβ-treated rats and the molecular mechanisms associated with changes in this peptidergic system. Intracerebroventricular Aβ25-35 administration during 14 days (300 pmol/day) to male rats increased Aβ25-35 levels and cell death and markedly reduced SRIF and SRIF receptor 2 levels in the hippocampus. These deleterious effects were associated with reduced Akt and cAMP response element-binding protein (CREB) phosphorylation and activation of c-Jun N-terminal kinase (JNK). Subcutaneous IGF-I co-administration (50 µg/kg/day) reduced hippocampal Aβ25-35 levels, cell death and JNK activation. In addition, IGF-I prevented the reduction in the components of the somatostatinergic system affected by Aβ infusion. Its co-administration also augmented protein kinase A (PKA) activity, as well as Akt and CREB phosphorylation. These results suggest that IGF-I co-administration may have protective effects on the hippocampal somatostatinergic system against Aβ insult through up-regulation of PKA activity and Akt and CREB phosphorylation.

Exceptional in vivo catabolism of neurodegeneration-related aggregates

Neurodegenerative diseases are linked to a systemic enzyme resistance of toxic aggregated molecules and their pathological consequences. This paper presents a unique phenomenon that Philodina acuticornis, a bdelloid rotifer, is able to catabolize different types of neurotoxic peptide and protein aggregates (such as beta-amyloids /Aβ/, alpha-synuclein, and prion) without suffering any damage. P. acuticornis is capable of using these aggregates as an exclusive energy source (i.e., as 'food', identified in the digestive system and body) in a hermetically isolated microdrop environment, increasing their survival. As regards Aβ1-42, five other bdelloid rotifer species were also found to be able to perform this phenomenon. Based on our experiments, the Aβ1-42-treated bdelloid rotifers demonstrate significantly increased survival (e.g. mean lifespan = 51 ± 2.71 days) compared to their untreated controls (e.g. mean lifespan = 14 ± 2.29 days), with similar improvements in a variety of phenotypic characteristics. To our knowledge, no other animal species have so far been reported to have a similar capability. For all other microscopic species tested, including monogonant rotifers and non-rotifers, the treatment with Aβ1-42 aggregates proved to be either toxic or simply ineffective. This paper describes and proves the existence of an unprecedented in vivo catabolic capability of neurotoxic aggregates by bdelloid rotifers, with special focus on P. acuticornis. Our results may provide the basis for a new preclinical perspective on therapeutic research in human neurodegenerative diseases.

Effects of berberine, curcumin, resveratrol alone and in combination with chemotherapeutic drugs and signal transduction inhibitors on cancer cells-Power of nutraceuticals

Over the past fifty years, society has become aware of the importance of a healthy diet in terms of human fitness and longevity. More recently, the concept of the beneficial effects of certain components of our diet and other compounds, that are consumed often by different cultures in various parts of the world, has become apparent. These "healthy" components of our diet are often referred to as nutraceuticals and they can prevent/suppress: aging, bacterial, fungal and viral infections, diabetes, inflammation, metabolic disorders and cardiovascular diseases and have other health-enhancing effects. Moreover, they are now often being investigated because of their anti-cancer properties/potentials. Understanding the effects of various natural products on cancer cells may enhance their usage as anti-proliferative agents which may be beneficial for many health problems. In this manuscript, we discuss and demonstrate how certain nutraceuticals may enhance other anti-cancer drugs to suppress proliferation of cancer cells.

BACE1 Function and Inhibition: Implications of Intervention in the Amyloid Pathway of Alzheimer's Disease Pathology

Alzheimer's disease (AD) is a fatal progressive neurodegenerative disorder characterized by increasing loss in memory, cognition, and function of daily living. Among the many pathologic events observed in the progression of AD, changes in amyloid β peptide (Aβ) metabolism proceed fastest, and precede clinical symptoms. BACE1 (β-secretase 1) catalyzes the initial cleavage of the amyloid precursor protein to generate Aβ. Therefore inhibition of BACE1 activity could block one of the earliest pathologic events in AD. However, therapeutic BACE1 inhibition to block Aβ production may need to be balanced with possible effects that might result from diminished physiologic functions BACE1, in particular processing of substrates involved in neuronal function of the brain and periphery. Potentials for beneficial or consequential effects resulting from pharmacologic inhibition of BACE1 are reviewed in context of ongoing clinical trials testing the effect of BACE1 candidate inhibitor drugs in AD populations.

Memantine inhibits β-amyloid aggregation and disassembles preformed β-amyloid aggregates

Memantine, an uncompetitive glutamatergic N-methyl-d-aspartate (NMDA) receptor antagonist, is widely used as a medication for the treatment of Alzheimer's disease (AD). We previously reported that chronic treatment of AD with memantine reduces the amount of insoluble β-amyloid (Aβ) and soluble Aβ oligomers in animal models of AD. The mechanisms by which memantine reduces Aβ levels in the brain were evaluated by determining the effect of memantine on Aβ aggregation using thioflavin T and transmission electron microscopy. Memantine inhibited the formation of Aβ(1-42) aggregates in a concentration-dependent manner, whereas amantadine, a structurally similar compound, did not affect Aβ aggregation at the same concentrations. Furthermore, memantine inhibited the formation of different types of Aβ aggregates, including Aβs carrying familial AD mutations, and disaggregated preformed Aβ(1-42) fibrils. These results suggest that the inhibition of Aβ aggregation and induction of Aβ disaggregation may be involved in the mechanisms by which memantine reduces Aβ deposition in the brain.

Regulation of GSK-3 activity by curcumin, berberine and resveratrol: Potential effects on multiple diseases

Natural products or nutraceuticals promote anti-aging, anti-cancer and other health-enhancing effects. A key target of the effects of natural products may be the regulation of the PI3K/PTEN/Akt/mTORC1/GSK-3 pathway. This review will focus on the effects of curcumin (CUR), berberine (BBR) and resveratrol (RES), on the PI3K/PTEN/Akt/mTORC1/GSK-3 pathway, with a special focus on GSK-3. These natural products may regulate the pathway by multiple mechanisms including: reactive oxygen species (ROS), cytokine receptors, mirco-RNAs (miRs) and many others. CUR is present the root of turmeric (Curcuma longa). CUR is used in the treatment of many disorders, especially in those involving inflammatory processes which may contribute to abnormal proliferation and promote cancer growth. BBR is also isolated from various plants (Berberis coptis and others) and is used in traditional medicine to treat multiple diseases/conditions including: diabetes, hyperlipidemia, cancer and bacterial infections. RES is present in red grapes, other fruits and berries such as blueberries and raspberries. RES may have some anti-diabetic and anti-cancer effects. Understanding the effects of these natural products on the PI3K/PTEN/Akt/mTORC1/GSK-3 pathway may enhance their usage as anti-proliferative agent which may be beneficial for many health problems.