Antioxidant Compounds in the Treatment of Alzheimer's Disease: Natural, Hybrid, and Synthetic Products

Alzheimer's disease (AD) which is associated with cognitive dysfunction and memory lapse has become a health concern. Various targets and pathways have been involved in AD's progress, such as deficit of acetylcholine (ACh), oxidative stress, inflammation, β-amyloid (Aβ) deposits, and biometal dyshomeostasis. Multiple pieces of evidence indicate that stress oxidative participation in an early stage of AD and the generated ROS could enable neurodegenerative disease leading to neuronal cell death. Hence, antioxidant therapies are applied in treating AD as a beneficial strategy. This review refers to the development and use of antioxidant compounds based on natural products, hybrid designs, and synthetic compounds. The results of using these antioxidant compounds were discussed with the given examples, and future directions for the development of antioxidants were evaluated.

A Nanoenzyme Constructed from Manganese and Strandberg-Type Phosphomolybdate with Versatility in Antioxidant and Modulating Conformation of Aβ Protein Misfolding Aggregates In Vitro

Amyloid β-peptide (Aβ) misfolding aggregates with β-sheet structures and surplus reactive oxygen species (ROS) are both considered to be the culprit of neuronal toxicity in Alzheimer's disease (AD). Therefore, modulating the misfolding mode of Aβ and inhibiting ROS simultaneous has become an important method for anti-AD. Herein, a nanoscale manganese-substituted polyphosphomolybdate (H₂en)₃[Mn(H₂O)₄][Mn(H₂O)₃]₂[P₂Mo₅O₂₃]₂·14.5H₂O (abbreviated as MnPM) (en = ethanediamine) was designed and synthesized by single crystal to single crystal transformation method. MnPM can modulate the β-sheet rich conformation of Aβ aggregates, and thus reduce the formation of toxic species. Moreover, MnPM also possesses the ability to eliminate the free radicals produced by Cu²⁺-Aβ aggregates. It can inhibit the cytotoxicity of β-sheet-rich species and protect synapses of PC12 cells. MnPM combines the conformation modulating ability of Aβ and anti-oxidation ability, which makes a promising multi-funcational molecular with a composite mechanism for the new conceptual designing in treatment of such protein-misfolding diseases.

Preparation and Characterization of an Electrospun Whey Protein/Polycaprolactone Nanofiber Membrane for Chromium Removal from Water

Chromium pollution represents a worldwide concern due to its high toxicity and bioaccumulation in organisms and ecosystems. An interesting material to remove metal ions from water is a whey-protein-based material elaborated by electrospinning, which is an emerging method to produce adsorbent membranes with diverse applications. The aim of this study was to prepare an adsorbent membrane of whey protein isolate (WPI) and polycaprolactone (PCL) by electrospinning to remove chromium ions from water. The adsorbent membrane was synthesized by a central composed design denaturing WPI using 2-Mercaptoethanol and mixing it with PCL to produce electrospun nanofibers. The adsorbent membrane was characterized by denaturation, Scanning Electron Microscope, Fourier-Transform Infrared Spectroscopy, Contact Angle, Thermogravimetric Analysis, and X-ray Photoelectron Spectrometry. The adsorption properties of this membrane were assessed in the removal of chromium. The removal performance of the membrane was enhanced by an increase in temperature showing an endothermic adsorption process. The adsorption process of chromium ions onto the nanofiber membrane followed the Sips adsorption isotherm, while the adsorption kinetics followed a pseudo-second kinetics where the maximum adsorption capacity was 31.0 mg/g at 30 °C and pH 2. This work provides a novel method to fabricate a hybrid membrane with amyloid-type fibrils of WPI and PCL, which is a promising adsorbent to remove heavy metal ions from water.

Coumarin derivatives inhibit the aggregation of β-lactoglobulin

The binding of a small molecule to a protein through non-covalent interactions mainly depends on its size and electronic environment. Such binding can change the stability of the three dimensional protein structure which sometimes may destabilize it to accelerate or to inhibit protein aggregation. Coumarin is a widely used fluorescent dye with several biological applications. Different substituents (electron-donating and electron-withdrawing) at different positions of the coumarin moiety can influence its molecular volume, physical and chemical properties. Here we investigate the effect of such substituents of coumarin on the aggregation of a model protein, beta-lactoglobulin (β-lg) through a multi spectroscopic approach. It was observed that coumarin methyl ester with an 8-hydroxyl group can inhibit the β-lg aggregation. This compound can bind the hydrophobic site of beta-lactoglobulin and stabilize a particular protein conformation through the formation of hydrogen bond and hydrophobic interactions. Thus a properly designed compound can inhibit protein–protein interactions through protein–small molecule interactions. Other coumarinoid compounds also are effective in the prevention of thermal aggregation of β-lg.

Aggregation of β-lactoglobulin (β-lg) was inhibited through the stabilization of the native structure by various non-covalent interactions of coumarin derivatives. The 8-hydroxy compound was most effective against the self-assembly of β-lg.

Examining the effect of bovine serum albumin on the properties and drug release behavior of β-lactoglobulin-derived amyloid fibril-based hydrogels

Herein, we report the use of β-lactoglobulin (β-LG) combined with bovine serum albumin (BSA) for the preparation of amyloid-based hydrogels with aim of delivering riboflavin. The incorporation of BSA enhanced β-LG fibrillogenesis and protected β-LG fibrils from losing fibrillar structure due to the pH shift. The mechanical properties of hydrogels were observed to be positively correlated with the number of amyloid fibrils. While the addition of BSA induced amyloid fibril formation, its presence between the fibril chains interfered with the entanglement of fibril chains, thus adversely affecting the hydrogels' mechanical properties. Hydrogels' surface microstructure became more compact as the number of amyloid fibrils rose and the presence of BSA could improve hydrogels' surface homogeneity. In vitro riboflavin (RF) release rate was found to be correlated with the number of fibrils and BSA-RF binding affinity. However, when the digestive enzymes were present, the influence of BSA-RF affinity was alleviated due to enzymes' destructive and/or degradative effects on BSA and/or hydrogels, thus the release rate relied on the number of fibrils, which could be adjusted by the amount of BSA. Results indicate that the additional component, BSA, plays an important role in modulating the properties and functions of β-LG fibril-based hydrogels.

Modulation of amyloid fibrillation of bovine β-lactoglobulin by selective methionine oxidation

Deposition of oxidation-modified proteins during normal aging and oxidative stress are directly associated with systemic amyloidoses. Methionine (Met) is believed to be one of the most readily oxidisable amino acid residues of protein. Bovine beta-lactoglobulin (β-lg), a model globular whey protein, has been presented as a subsequent paradigm for studies on protein aggregation and amyloid formation. Herein, we investigated the effect of t-butyl hydroperoxide (tBHP)-induced oxidation on structure, compactness and fibrillation propensity of β-lg at physiological pH. Notably, whey protein modification, specifically Met residues, plays an important role in the dairy industry during milk processing and lowering nutritional value and ultimately affecting their technological properties. Several bio-physical studies revealed enhanced structural flexibility and aggregation propensity of oxidised β-lg in a temperature dependent manner. A molecular docking study is used to predict possible interactions with tBHP and infers selective oxidation of methionine residues at 7, 24 and 107 positions. From our studies, it can be corroborated that specific orientations of Met residues directs the formation of a partially unfolded state susceptible to fibrillation with possible different cytotoxic effects. Our studies have greater implications in deciphering the underlying mechanism of different whey proteins encountering oxidative stress. Our findings are also important to elucidate the understanding of oxidation induced amyloid fibrillation of protein which may constitute a new route to pave the way for a modulatory role of oxidatively stressed proteins in neurological disorders.

Preparation of a Hybrid Membrane from Whey Protein Fibrils and Activated Carbon to Remove Mercury and Chromium from Water

Water contamination by mercury and chromium has a direct effect in human health. A promising technology to remove heavy metals by membrane filtration is the use of hybrid membranes produced with whey protein fibrils (WPF) and activated carbon (AC). In this study, the best conditions to produce WPF by heat treatment were determined to maximize the removal of mercury and chromium from water using a central composed design. The results indicated that the best conditions to prepare WPF were 74 °C, 7 h and 3.8% of whey protein with adsorption capacities of 25 and 18 mg/g and removal efficiencies of 81 and 57% for mercury and chromium, respectively. WPF and AC were used to prepare a hybrid membrane that was characterized using transmission electron microscopy, atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and Brunauer-Emmett-Teller surface area measurements. Batch filtration experiments were performed with the hybrid membrane for chromium and mercury removal at 25, 50 and 100 mg/L to determine its adsorption capacities. A high performance of the hybrid membrane was demonstrated removing efficiently mercury and chromium from water, thus supporting more than ten filtration cycles.