Proline-rich polypeptides in Alzheimer's disease and neurodegenerative disorders -- therapeutic potential or a mirage?

Anti-Alzheimer's disease potential of traditional chinese medicinal herbs as inhibitors of BACE1 and AChE enzymes

Alzheimer's disease (AD) is a common neurodegenerative disease that often occurs in the elderly population. At present, most drugs for AD on the market are single-target drugs, which have achieved certain success in the treatment of AD. However, the efficacy and safety of single-target drugs have not achieved the expected results because AD is a multifactorial disease. Multi-targeted drugs act on multiple factors of the disease network to improve efficacy and reduce adverse reactions. Therefore, the search for effective dual-target or even multi-target drugs has become a new research trend. Many of results found that the dual-target inhibitors of the beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) and acetylcholinesterase (AChE) found from traditional Chinese medicine have a good inhibitory effect on AD with fewer side effects. This article reviews sixty-six compounds extracted from Chinese medicinal herbs, which have inhibitory activity on BACE1 and AChE. This provides a theoretical basis for the further development of these compounds as dual-target inhibitors for the treatment of AD.

Destabilization of the Alzheimer's amyloid-β peptide by a proline-rich β-sheet breaker peptide: a molecular dynamics simulation study

The amyloid-β peptide exists in the form of fibrils in the plaques found in the brains of patients with Alzheimer's disease. One of the therapeutic strategies is the design of molecules which can destabilize these fibrils. We present a designed peptide KLVFFP₅ with two segments: the self-recognition sequence KLVFF and a β-sheet breaker proline pentamer. Molecular dynamics simulations and docking results showed that this peptide could bind to the protofibrils and destabilize them by establishing hydrophobic contacts and hydrogen bonds with a higher affinity than the KLVFF peptide. In the presence of the KLVFFP₅ peptide, the β-sheet content of the protofibrils was reduced significantly; the hydrogen bonding network and the salt bridges were disrupted to a greater extent than the KLVFF peptide. Our results indicate that the KLVFFP₅ peptide is an effective β-sheet disruptor which can be considered in the therapy of Alzheimer's disease.

Effect of Strain Rate on Single Tau, Dimerized Tau and Tau-Microtubule Interface: A Molecular Dynamics Simulation Study

Microtubule-associated protein (MAP) tau is a cross-linking molecule that provides structural stability to axonal microtubules (MT). It is considered a potential biomarker for Alzheimer's disease (AD), dementia, and other neurological disorders. It is also a signature protein for Traumatic Brain Injury (TBI) assessment. In the case of TBI, extreme dynamic mechanical energies can be felt by the axonal cytoskeletal members. As such, fundamental understandings of the responses of single tau protein, polymerized tau protein, and tau-microtubule interfaces under high-rate mechanical forces are important. This study attempts to determine the high-strain rate mechanical behavior of single tau, dimerized tau, and tau-MT interface using molecular dynamics (MD) simulation. The results show that a single tau protein is a highly stretchable soft polymer. During deformation, first, it significantly unfolds against van der Waals and electrostatic bonds. Then it stretches against strong covalent bonds. We found that tau acts as a viscoelastic material, and its stiffness increases with the strain rate. The unfolding stiffness can be ~50-500 MPa, while pure stretching stiffness can be >2 GPa. The dimerized tau model exhibits similar behavior under similar strain rates, and tau sliding from another tau is not observed until it is stretched to >7 times of original length, depending on the strain rate. The tau-MT interface simulations show that very high strain and strain rates are required to separate tau from MT suggesting Tau-MT bonding is stronger than MT subunit bonding between themselves. The dimerized tau-MT interface simulations suggest that tau-tau bonding is stronger than tau-MT bonding. In summary, this study focuses on the structural response of individual cytoskeletal components, namely microtubule (MT) and tau protein. Furthermore, we consider not only the individual response of a component, but also their interaction with each other (such as tau with tau or tau with MT). This study will eventually pave the way to build a bottom-up multiscale brain model and analyze TBI more comprehensively.

Domain focused and residue focused phosphorylation effect on tau protein: A molecular dynamics simulation study

Phosphorylation has been hypothesized to alter the ability of tau protein to bind with microtubules (MT), and pathological level of phosphorylation can incorporate formation of Paired Helical Filaments (PHF) in affected tau. Study of the effect of phosphorylation on different domains of tau (projection domain, microtubule binding sites and N-terminus tail) is important to obtain insight about tau neuropathology. In an earlier study, we have already obtained the mechanical properties and behavior of single tau and dimerized tau and observed tau-MT interaction for normal level of phosphorylation. This study attempts to obtain insights on the effect of phosphorylation on different domains of tau, using molecular dynamics (MD) simulation with the aid of CHARMM force field under high strain rate. It also determines the effect of residue focused phosphorylation on tau-MT interaction and tau accumulation tendency. The results show that for single tau protein, unfolding stiffness does not differ significantly due to phosphorylation, but stretching stiffness can be much higher than the normally phosphorylated protein. For dimerized tau protein, the stretching required to separate the protein forming the dimer is similar for phosphorylation in individual domains but is significantly less in case of phosphorylation in all domains. For tau-MT interaction simulations, it is found that for normal phosphorylation, the tau separation from MT occurs at higher strain for phosphorylation in projection domain and N-terminus tail, and earlier for phosphorylation in all domains altogether than the normal phosphorylation state. The residue focused phosphorylation study also shows that tau separates earlier from MT and shows stronger accumulation tendency at the phosphorylated state, while preserving the highly stretchable and flexible characteristic of tau. This study provides important insight on mechanochemical phenomena relevant to traumatic brain injury (TBI) scenario, where the result of mechanical loading and posttranslational modification as well as conformation decides the mechanical behavior.

Interplay of Pyrrolidine Units with Homo/Hetero Chirality and CF3-Aryl Substituents on Secondary Structures of β-Proline Tripeptides in Solution

All possible variants of β-proline functionalized tripeptides consisting of homo/hetero chiral monomeric all-cis 5-arylpyrrolidine-2,4-dicarboxylate units were synthesized for the first time by a nonpeptidic coupling method based on 1,3-dipolar cycloaddition chemistry of azomethine ylides. Secondary structures of β-proline tripeptides in solution were determined using the NMR spectroscopy data. o-(Trifluoromethyl)phenyl substituent contributes to stereoselectivity of 1,3-dipolar cycloaddition and structural features of β-proline tripeptides. A β-proline CF₃-tripeptide with alternating absolute chirality between adjacent pyrrolidine units mimics natural PPII helix secondary structure.

[Biobanking in Psychiatry]

Medical biobanking is concerned with establishing and maintaining large-scale repositories of biological specimens combined with comprehensive archives of clinical and biographical information on donors. This aims for controlled high and consistent quality of specimens for future biomedical research. One major objective is to assemble multiple blood components for various types of biochemical analysis and experimentation including different isolated cell types. With proper cryo-conservation, blood-derived cells can be conserved and revitalized after thawing and employed as in-vitro cell models carrying specific biological traits of donors. Optimizing pre-analytical methods can reduce pre-analytical variance thereby reducing imprecision of analytical data. This is particularly valuable for multivariate analyses of biological systems ("omics") and biomarker research. Introducing biobanking to psychiatry carries the challenge of making diagnostic allocation more compatible with biological entities than is achieved with current diagnostic categories of ICD-10 or DSM-V. Diagnostic or transdiagnostic subgroups can be stratified using biologically anchored clinical criteria. An important ethical issue of biobanking is the need for broad consent by the donors for specimen use in not yet defined future research projects. The organizational, logistic and financial costs of establishing and maintaining a biobank are considerable, but seem well warranted in view of the gainable advances in biomedical research quality, translations and clinical applications.

Polyproline chains destabilize the Alzheimer's amyloid-β protofibrils: A molecular dynamics simulation study

Alzheimer's is a fatal neurodegenerative disease for which there is no cure at present. The disease is characterized by the presence of plaques, principally comprising the amyloid-β peptide (viz., β-sheet) in the brains of a patient. In our present work, we study the interaction of these β-sheets with a different number of repeating units of proline (β-sheet breaker) by docking and all atom molecular dynamics simulations. Our results indicate that proline can break the amyloid protofibrils apart, cause them to break their β-sheet structure, and in some cases even induce the formation of 3₁₀ helices, which may be intermediates in the unfolding of these β-sheets. We have also observed that some of the important hydrogen bonds and salt bridges between chains were disrupted by proline and the tight interatomic packing of atoms in the fibrils was made relatively loose. Proline chains had a tendency to make several contacts with charged residues. Proline chains binded well to the fibrils by strong electrostatic interactions while hydrophobic interactions played a less important role. This leads to the conclusion that proline can break the amyloid fibrils apart and can be considered in the design of novel peptide-based drugs to treat Alzheimer's disease and potentially other diseases caused by the misfolding of proteins into β-sheets.

The role of monoamines in the development of Alzheimer's disease and neuroprotective effect of a proline rich polypeptide

INTRODUCTION

We have analyzed the alterations in the brain monoaminergic system using the rat model of AD-like pathology. In addition, we have investigated potential neuroprotective effects of the hypothalamic proline-rich polypeptide (PRP-1).

METHODS

Histochemical staining, HPLC, chemiluminescent and bioluminescence assays.

RESULTS

The levels of monoamines in the target AD brain structures were found elevated, except serotonin, which was unaffected in both hippocampus and brainstem and decreased in frontal cortex. This was accompanied by the substantial structural damage of cortical, hippocampal, as well as the monoaminergic neurons of locus coeruleus and oxidative stress. PRP-1 was able to reverse most of these changes.

DISCUSSION

The increased levels of major brain monoamines in the model of AD supports the hypothesis of the important role of monoamines in the excessive synaptic excitation resulting in cognitive dysfunction in AD brain. The neuroprotective effect of PRP-1 as manifested by the recovery of monoaminergic system suggests this bioactive compound as a perspective therapeutic agent for the treatment of AD.

Multidrug-eluting bi-layered microparticle-mesh scaffolds for musculoskeletal tissue regeneration

Stem cell-based tissue engineering necessitates the development of a biocompatible scaffold, as a structural support, that provides a continuous supply of bioactive molecules for specific lineage differentiation. While incorporating bioactive molecules within a scaffold to improve stem cell differentiation has been reported in the literature, there is minimal evidence of any scaffold that can deliver a customized concoction of both hydrophobic and hydrophilic bioactive molecules to induce in situ lineage differentiation without any external supplements. In this study, we established a bioactive, drug-eluting bi-layered microparticle-mesh scaffold (BMMS) using the electrospinning technique. This BMMS was co-encapsulated with hydrophobic dexamethasone (in the mesh), hydrophilic ascorbic acid and β-glycerophosphate or proline (in the microparticles). We hypothesized that a sustained-releasing BMMS can direct in situ specific lineage differentiation of MSCs (e.g. osteogenic and chondrogenic) in a minimally supplemented culture environment into musculoskeletal tissues. The characterization of this BMMS revealed good encapsulation efficiencies of the bioactive molecules with sustained-releasing capabilities. The release kinetics of each drug was further analyzed using mathematical drug-releasing models. These scaffolds were subsequently shown to have potential for osteogenic or chondrogenic lineage differentiation from mesenchymal stem cells (MSCs) in a minimally supplemented culture medium.

Metabolic Biomarkers and Neurodegeneration: A Pathway Enrichment Analysis of Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis

Neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) lack robust diagnostics and prognostic biomarkers. Metabolomics is a postgenomics field that offers fresh insights for biomarkers of common complex as well as rare diseases. Using data on metabolite-disease associations published in the previous decade (2006-2016) in PubMed, ScienceDirect, Scopus, and Web of Science, we identified 101 metabolites as putative biomarkers for these three neurodegenerative diseases. Notably, uric acid, choline, creatine, L-glutamine, alanine, creatinine, and N-acetyl-L-aspartate were the shared metabolite signatures among the three diseases. The disease-metabolite-pathway associations pointed out the importance of membrane transport (through ATP binding cassette transporters), particularly of arginine and proline amino acids in all three neurodegenerative diseases. When disease-specific and common metabolic pathways were queried by using the pathway enrichment analyses, we found that alanine, aspartate, glutamate, and purine metabolism might act as alternative pathways to overcome inadequate glucose supply and energy crisis in neurodegeneration. These observations underscore the importance of metabolite-based biomarker research in deciphering the elusive pathophysiology of neurodegenerative diseases. Future research investments in metabolomics of complex diseases might provide new insights on AD, PD, and ALS that continue to place a significant burden on global health.

Control of Azomethine Cycloaddition Stereochemistry by CF3 Group: Structural Diversity of Fluorinated β-Proline Dimers

β-Proline-functionalized dimers consisting of homochiral monomeric units were synthesized by a non-peptidic coupling method for the first time. The applied synthetic methodology is based on 1,3-dipolar cycloaddition chemistry of azomethine ylides and provides absolute control over the β-proline backbone stereogenic centers. An o-(trifluoromethyl)phenyl substituent contributes to appropriate stabilization of the definite acrylamide chiral cis conformation and to achieve the dipole reactivity that is not observed for aryl groups lacking strong electronegative character.

Dairy constituents and neurocognitive health in ageing

Age-related cognitive decline (ARCD) and dementia are of increasing concern to an ageing population. In recent years, there has been considerable research focused on effective dietary interventions that may prevent or ameliorate ARCD and dementia. While a number of studies have considered the impact that dairy products may have on physiological health, particularly with regard to the metabolic syndrome and cardiovascular health, further research is currently needed in order to establish the impact that dairy products have in the promotion of healthy brain function during ageing. The present review considers the available evidence for the positive effects of dairy products on the metabolic syndrome and glucose regulation, with consideration of the implications for neurocognitive health. A literature search of current (September 2010) meta-analyses/reviews and original research regarding dairy products and cognition was conducted through SCOPUS using the following search terms for dairy consituents: dairy, milk, cheese, yoghurt, probiotics, whey protein, alpha lactalbumin, calcium, B-12, bioactive peptides and colostrinin (CLN). These search terms for dairy products were combined with the following search terms related to cognition and health: cognition, cognitive decline, dementia, Alzheimer's disease, metabolic syndrome, diabetes, insulin resistance and glucose regulation. Concerns regarding SFA and other fatty acids found in dairy products are also reviewed in relation to different forms of dairy products. The review also considers recent evidence for positive neurocognitive effects associated with bioactive peptides, CLN and proline-rich polypeptides, α-lactalbumin, vitamin B12, calcium and probiotics. Future directions for the extraction and purification of beneficial constituents are also discussed. It is concluded that low-fat dairy products, when consumed regularly as part of a balanced diet, may have a number of beneficial outcomes for neurocognitive health during ageing.

Neuroprotective action of proline-rich polypeptide-1 in β-amyloid induced neurodegeneration in rats

It is recognized that the main trigger of Alzheimer disease related neurodegeneration is β-amyloid peptide, which subsequently generates different metabolic disorders in neuron and finally leads to neuronal death. Several biologically active products were tested as neuroprotectors, but only few of them demonstrated any efficiency. Proline-rich polypeptide-1 was tested as a neuroprotective agent on Aβ25-35 animal model of Alzheimer disease. Biochemical analysis (determination of spectrum of neuroactive amino acids, such as glutamate, gamma-aminobutyric acid, glycine, aspartate and taurine), as well as behavioral, electrophysiological and morphological studies were performed to reveal the neuroprotective potential of proline-rich polypeptide in rats. Based on the results of our study it can be concluded that proline-rich polypeptide-1 has a potential to be one of the effective preventive or therapeutic agents against neurodegenerative disorders, such as Alzheimer disease.

Activity-based probes for monitoring postproline protease activity

Postproline proteases constitute a subset of serine proteases involved in the regulation of many signaling events and are emerging as promising therapeutic targets for prevalent diseases, such as diabetes and cancer. Therefore, monitoring their activity in different tissues and diverse physiological states would certainly facilitate the elucidation of their physiological role and the establishment of new therapeutic targets. Here, we have synthesized a dipeptidyl phosphonate activity-based probe that has proved to be highly selective for a specific postproline protease, prolyl oligopeptidase (POP). Its high sensitivity allows the detection of the endogenous activity of POP both by in-gel analysis and mass spectrometry. The evidence provided by mass spectrometry for the high selectivity of the synthesized probe opens the possibility of using dipeptidyl phosphonates not only for activity-based profiling (ABP), but also for other ABP applications like substrate-based protease identification.