Crosstalk between tau protein autoproteolysis and amyloid fibril formation

Tau cleavage has been shown to have a significant effect on protein aggregation. Tau truncation results in the formation of aggregation-prone fragments leading to toxic aggregates and also causes the formation of harmful fragments that do not aggregate. Thus, targeting proteolysis of tau would be beneficial for the development of therapeutics for Alzheimer's disease and related tauopathies. In this study, amino-terminal quantification and ThT fluorimetry were respectively used to analyze the kinetics of tau fragmentation and fibril formation. SDS-PAGE analysis of tau protein incubated with a disulfide-reducing agent demonstrated that the cysteines of tau have a crucial role in the fibrillation and autoproteolysis. However, the structures converted to amyloid fibrils were different with conformations that led to autoproteolysis. The quantification of the amino terminal indicated that the double-disulfide parallel structures formed in the presence of heparin did not have protease activity. The survey of possible tau disulfide-mediated dimer configurations suggested that the non-register single disulfide bound conformations were involved in the tau autoproteolysis process. Moreover, the inhibition of autoproteolysis resulted in the increment of aggregation rate; hence it seems that the tau auto-cleavage is the cellular defense mechanism against protein fibrillation.

Cannabidiol Inhibits Tau Aggregation In Vitro

A hallmark of Alzheimer’s disease (AD) is the accumulation of tau protein in the brain. Compelling evidence indicates that the presence of tau aggregates causes irreversible neuronal destruction, eventually leading to synaptic loss. So far, the inhibition of tau aggregation has been recognized as one of the most effective therapeutic strategies. Cannabidiol (CBD), a major component found in Cannabis sativa L., has antioxidant activities as well as numerous neuroprotective features. Therefore, we hypothesize that CBD may serve as a potent substance to hamper tau aggregation in AD. In this study, we aim to investigate the CBD effect on the aggregation of recombinant human tau protein 1N/4R isoform using biochemical methods in vitro and in silico. Using Thioflavin T (ThT) assay, circular dichroism (CD), and atomic force microscopy (AFM), we demonstrated that CBD can suppress tau fibrils formation. Moreover, by quenching assay, docking, and job’s plot, we further demonstrated that one molecule of CBD interacts with one molecule of tau protein through a spontaneous binding. Experiments performed by quenching assay, docking, and Thioflavin T assay further established that the main forces are hydrogen Van der Waals and some non-negligible hydrophobic forces, affecting the lag phase of tau protein kinetics. Taken together, this study provides new insights about a natural substance, CBD, for tau therapy which may offer new hope for the treatment of AD.

Astaxanthin Decreases Spatial Memory and Glutamate Transport Impairment Induced by Fluoride

Excessive exposure to the sources of fluoride in drinking water, oral care products, and food is a widespread problem. Fluoride is associated with impairment in child intelligence development. It causes DNA damage, oxidative stress, and mitochondrial dysfunction, mainly due to the production of reactive oxygen species (ROS). It has been postulated that the use of antioxidants such as astaxanthin, may alleviate fluoride's adverse effects. This study assessed the effects of fluoride on cellular ROS content and rat's learning and memory ability and investigated the protective potency of astaxanthin with emphasis on the role of glutamate using the Morris Water Maze test, glutamate concentration determination, and western blot techniques. The fluoride treatment of cells results in an increment of cellular ROS, whereas astaxanthin inhibits lipid peroxidation. Fluoride significantly decreases the cellular glutamate uptake and glutamate transporter, protein level, possibly due to the disruption of mitochondrial energy metabolism and defect of the transporter recycle, respectively. The in-vivo study indicated that the treatment of rats with fluoride led to a loss of learning, while astaxanthin improved memory dysfunction. Measurement of ROS and glutamate levels of rat brain hippocampus showed that fluoride increased the ROS but decreased the glutamate. On the other hand, the utilization of astaxanthin decreased the brain ROS content and increased the glutamate level. It seems that fluoride disrupts the normal function of neurons via increment of ROS production and decrement of glutamate level, whereas astaxanthin has neuroprotective potency due to the ROS scavenging ability.

Physiological changes in the albumin-bound non-esterified free fatty acids critically influence heme/bilirubin binding properties of the protein: A comparative, in vitro, spectroscopic study using the endogenous biomolecules

Heme and bilirubin (BR), as by-products of red blood cells (and hemoglobin) degradation, show increased plasma concentrations in some diseases. These two toxic hydrophobic molecules are mainly transported in the blood-stream by human serum albumin (HSA) that carries a wide variety of ligands. Under normal physiological conditions, ~3 fatty acid (FA) molecules are bound to each HSA; and its possible effect on BR/heme binding remains to be more clarified. In the present study, to provide deeper insight on this issue, we purified albumin from healthy individuals (as purified non-defatted albumin or PA) with normal plasma levels of FA, then defatted some of the purified protein (as defatted-HSA; or DA). In the next step, using various spectroscopic methods, their interactions with heme and BR were investigated. By 1: 1 binding of the ligands, quenching and thermodynamic analysis of parameters indicated that binding constants (K_b) values of bilirubin and heme for PA and DA are different. It could be perceived that the presence of FAs in high-affinity FA binding sites (FABSs) exerted considerable conformational changes in the structure followed by an improved BR binding while hindered heme interaction. The data was confirmed by determining surface hydrophobicity of the purified albumin (PA) and DA, and then supported by bioinformatics analyses. The physiological and clinical relevance of the observed dynamic interactions is also discussed. This study, also, re-confirmed that the primary BR binding site is subdomain IIA not subdomain IB.

Diverse Effects of Different "Protein-Based" Vehicles on the Stability and Bioavailability of Curcumin: Spectroscopic Evaluation of the Antioxidant Activity and Cytotoxicity In Vitro

BACKGROUND

Curcumin is a natural polyphenolic compound with anti-cancer, antiinflammatory, and anti-oxidation properties. Low water solubility and rapid hydrolytic degradation are two challenges limiting use of curcumin.

OBJECTIVE

In this study, the roles of the native/modified forms of Bovine Serum Albumin (BSA), β-lactoglobulin (β-lg) and casein, as food-grade biopolymers and also protein chemical modification, in stabilizing and on biological activity of curcumin were surveyed.

METHODS

In this article, we used various spectroscopic as well as cell culture-based techniques along with calculation of thermodynamic parameters.

RESULTS

Investigation of curcumin stability indicated that curcumin binding to the native BSA and modified β -lg were stronger than those of the modified BSA and native β -lg, respectively and hence, the native BSA and modified β-lg could suppress water-mediated and light-mediated curcumin degradation, significantly. Moreover, in the presence of the native proteins (BSA and casein), curcumin revealed elevated in vitro anti-cancer activity against MCF-7 (human breast carcinoma cell line) and SKNMC (human neuroblastoma cell line). As well, curcumin, in the presence of the unmodified "BSA and β-lg", was more potent to decrease ROS generation by hydrogen peroxide (H2O2) whereas it led to an inverse outcome in the presence of native casein. Overall, in the presence of the protein-bound curcumin, increased anti-cancer activity and decreased ROS generation by H2O2 in vitro were documented.

CONCLUSION

It appears that "water exclusion" is major determinant factor for increased stability/ efficacy of the bound curcumin so that some protein-curcumin systems may provide novel tools to increase both food quality and the bioavailability of curcumin as health promoting agent.

Diethylalkylsulfonamido(4-methoxyphenyl)methyl)phosphonate/phosphonic acid derivatives act as acid phosphatase inhibitors: synthesis accompanied by experimental and molecular modeling assessments

Purple acid phosphatases (PAPs) are binuclear metallo-hydrolases that have been isolated from various mammals, plants, fungi and bacteria. In mammals, PAP activity is associated with bone resorption and can lead to bone metabolic disorders such as osteoporosis; thus human PAP is an attractive target to develop anti-osteoporotic drugs. The aim of the present study was to investigate inhibitory effect of synthesized diethylalkylsulfonamido(4-methoxyphenyl)methyl)phosphonate/phosphonic acid derivatives as potential red kidney bean PAP (rkbPAP) inhibitors accompanied by experimental and molecular modeling assessments. Enzyme kinetic data showed that they are good rkbPAP inhibitors whose potencies improve with increasing alkyl chain length. Hexadecyl derivatives, as most potent compounds (K_i = 1.1 µM), inhibit rkbPAP in the mixed manner, while dodecyl derivatives act as efficient noncompetitive inhibitor. Also, analysis by molecular modeling of the structure of the rkbPAP-inhibitor complexes reveals factors, which may be important for the determination of inhibition specificity.

Is there correlation between Aβ-heme peroxidase activity and the peptide aggregation state? A literature review combined with hypothesis

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by aggregation of amyloid-β (Aβ) peptide, formation of neurofibrillary tangles, synaptic loss and neuronal cell death, and is manifested clinically by progressive cognitive dysfunction and memory loss. Disease pathogenesis is mainly linked to the formation of Aβ insoluble or soluble oligomeric assemblies. Binding of heme to Aβ has been suggested as the origin of the heme deficiency, peroxidase activity, as well as some oxidative stress-mediated AD pathologies, and then differential affinity of heme for human and rodent Aβ peptide has been proposed to account for the susceptibility of humans to AD. This review highlights whether there is any dependency of peroxidase activity of heme-bound Aβ on the Aβ aggregation state or not, with focusing on emerging role of heme in neurodegeneration. Here, several lines of evidence supporting existing contradictory conjectures are discussed.

Comparative studies on drug binding to the purified and pharmaceutical-grade human serum albumins: Bridging between basic research and clinical applications of albumin

Human serum albumin (HSA), the most abundant protein in blood plasma, is a monomeric multidomain protein that possesses an extraordinary capacity for binding, so that serves as a circulating depot for endogenous and exogenous compounds. During the heat sterilization process, the structure of pharmaceutical-grade HSA may change and some of its activities may be lost. In this study, to provide deeper insight on this issue, we investigated drug-binding and some physicochemical properties of purified albumin (PA) and pharmaceutical-grade albumin (PGA) using two known drugs (indomethacin and ibuprofen). PGA displayed significantly lower drug binding capacity compared to PA. Analysis of the quenching and thermodynamic parameters indicated that intermolecular interactions between the drugs and the proteins are different from each other. Surface hydrophobicity as well as the stability of PGA decreased compared to PA, also surface hydrophobicity of PA and PGA increased upon drugs binding. Also, kinetic analysis of pseudo-esterase activities indicated that Km and Vmax parameters for PGA enzymatic activity are more and less than those of PA, respectively. This in vitro study demonstrates that the specific drug binding of PGA is significantly reduced. Such studies can act as connecting bridge between basic research discoveries and clinical applications.

Does Long-Term Administration of a Beta-Blocker (Timolol) Induce Fibril-Based Cataract Formation In-vivo?

Timolol is a non-selective beta-adrenergic receptor antagonist administered for treating glaucoma, heart attacks and hypertension. In the present study, we set out to determine whether or not timolol can provoke cataract formation, thus the influence of timolol on the amyloid-type aggregation of crystallin was investigated. We then provided experimental evidence of crystallin aggregation and its induction by timolol using different spectroscopic measurements. Turbidimetric measurements as well as ThT fluorescence data indicated that timolol induce extent of crystallin amyloid formation. The kinetic of protein aggregation was also changed in presence of increasing concentrations of the drug suggesting that long-term drug administration may contribute to the development of cataract. Since the consequence of timolol-crystallin interaction has yet to be identified, additional data on it may help us to postpone amyloid cataract formation.