Biosensor approaches on the diagnosis of neurodegenerative diseases: Sensing the past to the future

Development of a hydroxyflavone-labelled 4554W peptide probe for monitoring αS aggregation

Parkinson's is the second most common neurodegenerative disease, with the number of individuals susceptible due to increase as a result of increasing life expectancy and a growing worldwide population. However, despite the number of individuals affected, all current treatments for PD are symptomatic-they alleviate symptoms, but do not slow disease progression. A major reason for the lack of disease-modifying treatments is that there are currently no methods to diagnose individuals during the earliest stages of the disease, nor are there any methods to monitor disease progression at a biochemical level. Herein, we have designed and evaluated a peptide-based probe to monitor αS aggregation, with a particular focus on the earliest stages of the aggregation process and the formation of oligomers. We have identified the peptide-probe K1 as being suitable for further development to be applied to number of applications including: inhibition of αS aggregation; as a probe to monitor αS aggregation, particularly at the earliest stages before Thioflavin-T is active; and a method to detect early-oligomers. With further development and in vivo validation, we anticipate this probe could be used for the early diagnosis of PD, a method to evaluate the effectiveness of potential therapeutics, and as a tool to help in the understanding of the onset and development of PD.

A new ITO-based Aβ42 biosensor for early detection of Alzheimer's disease

In this study, a novel label-free impedimetric immunosensor was fabricated for rapid, selective, and sensitive quantitative analysis of Aβ₄₂ protein for use in the diagnosis of Alzheimer's disease. The immunosensor was fabricated using inexpensive and disposable indium tin oxide polyethylene terephthalate (ITO-PET) electrodes. After the electrodes were modified with 3-glycidoxypropyldimethoxymethylsilane (GPDMMS), the antibody specific to the Aβ₄₂ protein (anti-Aβ₄₂) was immobilized. The affinity interaction between anti-Aβ₄₂ and Aβ₄₂ in the immobilization steps in immunosensor fabrication and in the quantitation of Aβ₄₂ were analyzed using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) techniques. Additionally, the morphological changes occurring on the electrode surface during each immobilization step were imaged using scanning electron microscopy (SEM). The linear detection range of the immunosensor was determined as 1-100 pg/mL with the limit of detection value of 0.37 pg/mL. Analytical properties of the biosensor, including reproducibility, repeatability, storage stability, selectivity, and regeneration were investigated. The kinetic behavior of antibody-antigen complex formation was determined for the first time using single frequency impedance (SFI) analysis on an Aβ₄₂ biosensor. The potential for use of the immunosensor in clinical studies was demonstrated by analysis of Aβ₄₂ in commercially purchased human serum.

A Novel Aggregation-Induced Emission Fluorescent Probe for Detection of β-Amyloid Based on Pyridinyltriphenylamine and Quinoline-Malononitrile

β-amyloid is an important pathological feature of Alzheimer's disease. Its abnormal production and aggregation in the patient's brain is an important basis for the early diagnosis and confirmation of Alzheimer's disease. In this study, a novel aggregation-induced emission fluorescent probe, PTPA-QM, was designed and synthesized based on pyridinyltriphenylamine and quinoline-malononitrile. These molecules exhibit a donor-donor-π-acceptor structure with a distorted intramolecular charge transfer feature. PTPA-QM displayed the advantages of good selectivity toward viscosity. The fluorescence intensity of PTPA-QM in 99% glycerol solution was 22-fold higher than that in pure DMSO. PTPA-QM has been confirmed to have excellent membrane permeability and low toxicity. More importantly, PTPA-QM exhibits a high affinity towards β-amyloid in brain sections of 5XFAD mice and classical inflammatory cognitive impairment mice. In conclusion, our work provides a promising tool for the detection of β-amyloid.

Molecularly imprinted polymers for the recognition of biomarkers of certain neurodegenerative diseases

The appearance of the biomarkers in body fluids like blood, urine, saliva, tears, etc. can be used for the identification of many diseases. This article aimed to summarize the studies about electrochemical biosensors with molecularly imprinted polymers as sensitive and selective layers on the electrode to detect protein-based biomarkers of such neurodegenerative diseases as Alzheimer's disease, Parkinson's disease, and stress. The main attention in this article is focused on the detection methods of amyloid-β oligomers and p-Tau which are representative biomarkers for Alzheimer's disease, α-synuclein as the biomarker of Parkinson's disease, and α-amylase and lysozyme as the biomarkers of stress using molecular imprinting technology. The research methods, the application of different electrodes, the influence of the polymers, and the established detection limits are reviewed and compared.

Self-assembled monolayer-assisted label-free electrochemical genosensor for specific point-of-care determination of Haemophilus influenzae

For sensitive detection of the L-fuculokinase genome related to the Haemophilus influenzae (H. influenzae), this research work demonstrates the label-free electrochemical-based oligonucleotide genosensing assay relying on the performing hybridization process. To enhance the electrochemical responses, multiple electrochemical modifier-tagged agents were effectively utilized. For attaining this goal, NiCr-layered double hydroxide (NiCr LDH) has been synthesized and combined with biochar (BC) to create an efficient electrochemical signal amplifier that has been immobilized on the surface of the bare Au electrode. Low detection and quantification limits (LOD and LOQ) associated with the designed genosensing bio-platform to detect L-fuculokinase have been achieved to 6.14 fM and 11 fM, respectively. Moreover, the wide linear range of 0.1 to 1000 pM demonstrates the capability of the designed platform. Investigated were the 1-, 2-, and 3-base mismatched sequences, and the negative control samples clarified the high selectivity and better performance of the engineered assay. The values of 96.6-104% and 2.3-3.4% have been obtained for the recoveries and RSDs, respectively. Furthermore, the repeatability and reproducibility of the associated bio-assay have been studied. Consequently, the novel method is appropriate for rapidly and quantitatively detecting H. influenzae, and is considered a better candidate for advanced tests on biological samples such as urine samples.

The potential diagnostic accuracy of urine formaldehyde levels in Alzheimer's disease: A systematic review and meta-analysis

Background

Formaldehyde (FA), a toxic aldehyde, has been shown to be associated with a variety of cognitive disorders, including Alzheimer's disease (AD). There is increasing evidence that FA levels are significantly increased in AD patients and may be involved in the pathological process of AD. The aim of this study was to assess the potential diagnostic value of urine FA levels in AD using meta-analysis techniques.

Methods

Original reports of morning urine FA levels in AD patients and healthy controls (HCs) were included in the meta-analysis. Standardized mean differences (SMD) were calculated using a random-effects model, heterogeneity was explored using methodological, age, sex difference and sensitivity analyses, and receiver operating characteristic (ROC) curves were constructed to assess the diagnostic value of urine FA levels in AD.

Results

A total of 12 studies were included, and the urine FA levels of 874 AD patients and 577 HCs were reviewed. Compared with those in HCs, the FA levels were significantly increased in AD patients. The heterogeneity of the results did not affect their robustness, and results of the area under the curve (AUC) suggested that urine FA levels had good potential diagnostic value.

Conclusion

Urine FA levels are involved in AD disease progression and are likely to be useful as a potential biomarker for clinical auxiliary diagnosis. However, further studies are needed to validate the results of this study.

Anti-cholinesterase, anti-inflammatory and antioxidant properties of Combretum micranthum G. Don: Potential implications in neurodegenerative disease

Background

Brain damage is a severe and common pathology that leads to life-threatening diseases. Despite development in the research, the medical evidence of the effectiveness of potential neuroprotective medicines is insufficient. As a result, there is an immense and urgent demand for promising medication. For millennia, herbal remedies were a fundamental aspect of medical treatments. Combretum micranthum (CM), a plant of the family Combretaceae in sub-Saharan Africa, has been utilized in folklore medicine to cure diverse human ailments. In order to develop a neuroprotective phytomedicine, the current research was undertaken to explore the antioxidant, anti-inflammatory, anticholinesterase and neuroprotective potential of CM extract.

Methods

Colorimetric methods were used to determine CM antioxidant activity, in-vitro protein denaturation and membrane destabilization assays were used to evaluate its anti-inflammatory capacity, anticholinesterase activity was carried out using Ellman's method, and neuroprotective potential was assessed on brain homogenate stressed with ferric chloride and ascorbic acid (FeCl₂-AA) by assessing the lipoperoxidation biomarker malondialdehyde (MDA).

Results

In Ferric Reducing Antioxidant Power (IC₅₀ = 27.15 ± 0.06 µg/mL) and Total Antioxidant Capacity (IC₅₀ = 31.13 ± 0.02 µg/mL), CM extract demonstrated strong antioxidant activity. Anti-inflammatory effect were improved in heat-induced Egg albumin and BSA denaturation (IC ₅₀ = 46.35 ± 1.53 and 23.94 ± 1.10 µg/mL) as well as heat and hypotonia induced membrane destabilization (IC ₅₀ = 20.96 ± 0.11 and 16.75 ± 0.94 µg/mL).CM extract showed strong anticholinesterase activity (IC ₅₀ = 59.85 ± 0.91 µg/mL). In an ex-vivo neuroprotective model, CM extract showed substantial inhibition (p < 0.001) of oxidative damage caused by FeCl₂-AA in brain tissue.

Conclusion

C. micranthum may be a good candidate for its probable neuroprotective potential. Its neuroprotective benefits might be attributed to its antioxidant, anti-inflammatory and anticholinesterase effects.