Resolving interactions of miglitol with normal and glycated human serum albumin by multivariate methods.

This article reports results of one of our projects related to the investigation of interactions of miglitol (MIG) with normal human serum albumin (HSA) and glycated HSA (GHSA) with the help of recording spectroscopic and electrochemical data. The experimental data were analyzed by conventional and chemometric methods to extract useful information for comprehensive justifications of the interactions of the MIG with HSA and GHSA. Hard- and soft-modeling chemometric methods were used to extract quantitative and qualitative information. Then, molecular docking techniques were used to further investigation of the binding of the MIG with HSA and GHSA and the extracted results were compatible with those obtained by experimental methods. Finally, according to the binding of the BV with HSA and GHSA, second-order differential pulse voltammetric data were recorded and calibrated with three-way calibration methods for exploiting second-order advantage for determination of the GHSA in the presence of the HSA to develop a novel chemometrics assisted-electroanalytical method for diagnostic and monitoring of diabetic.

Chemometric modeling of the electrochemical data to investigate proline cis/trans isomeration effect on aggregation of Tau protein.

Tau protein (Tau) is a proline-rich protein and in this work, we have developed a very interesting strategy based on combination of electrochemistry with chemometric methods to investigate proline cis/trans isomeration effect on the Tau aggregation. To achieve this goal, the proline residues at RTPPK motif have been replaced by alanine to generate RTPAK, RTAPK and RTAAK mutants of the Tau. Then, cyclic voltammetric (CV) responses of the Tau and RTPAK, RTAPK and RTAAK as its mutants in the presence of heparin (HEP) as an anionic inducing agent which could trigger aggregation of the Tau were recorded at physiological conditions every hour during 12 h. Therefore, 48 data sets of titrations were obtained which were handled by chemometric methods to extract useful information about aggregation of the Tau. The data were hard-modeled by EQUISPEC, SQUAD, REACTLAB and SPECFIT to extract useful quantitative information. Our results confirmed that the strength of the binding of the HEP with proteins was obeyed from Tau > RTPAK ~ RTAPK > RTAAK which confirmed that the aggregation of the proteins was obeyed from this order as well. Therefore, aggregation of the Tau is decreased by transforming Cis isomer to Trans even in the presence of an anionic inducing agent such as HEP which may have value for the treatment of Alzheimer's disease.

The antidepressant drug; trazodone inhibits Tau amyloidogenesis: Prospects for prophylaxis and treatment of AD.

Tau protein, characterized as "natively unfolded", is involved in microtubule assembly/stabilization in physiological conditions. Under pathological conditions, Tau dysfunction leads to its accumulation of insoluble toxic amyloid aggregates and thought to be involved in the degeneration and neuronal death associated with neurodegenerative diseases. Trazodone (TRZ), a triazolopyridine derivative, is a selective serotonin reuptake inhibitor (SSRI) which increases serotonin levels in synaptic cleft and potentiating serotonin activity, with antidepressant and sedative properties. This drug is more effective and tolerable than other therapeutic agents. In this study, the 1N4R isoform of Tau protein was purified and the effect of TRZ on the protein fibrillation was investigated using multi-spectroscopic techniques as well as computational methods. The results showed that TRZ is not only able to affect formation of Tau amyloid fibrils in vitro but also attenuates Tau oligomerization within SH-SY5Y cell line resulting in more cells surviving. Moreover, membrane disrupting activity of Tau aggregates decreased upon TRZ treatment. The binding forces involved in TRZ-Tau interaction were also explored using both experimental as well as theoretical docking/molecular dynamics approaches. The results of the current work may open new insights for applying therapeutic potential of TRZ against Alzheimer's disease.

Evaluation of the effect of phenylpropanoids on the binding of heparin to human serum albumin and glycosylated human serum albumin concerning anticoagulant activity: A comparison study.

The nonenzymatic advanced glycation end products (AGEs) and the accumulation of AGEs are the two main factors associated with the long-term pathogenesis of diabetes. Human serum albumin (HSA) as the most abundant serum protein has a higher fortuity to be modified by nonenzymatic glycation. In this study, the interaction of three phenylpropanoids (caffeic acid (Caf), p-coumaric acid (Cou), and cinnamic acid (Cin)) toward HSA and glycosylated HSA (gHSA) was analyzed by multiple spectroscopic techniques combined with molecular docking. The formation of fibrils in HSA and gHSA was confirmed by the Thioflavin T (ThT) assay. The phenylpropanoids have shown anti-fibrillation properties in vitro. The obtained thermodynamic parameters indicated that hydrogen bonding and van der Waals forces are the main forces in the binding interaction, and the quenching mechanism of the protein fluorescence is static. Molecular docking results, as well as the in vitro results, showed that Caf, Cou, and Cin exhibit more stable interactions with HSA, respectively. In addition, molecular docking analysis showed that Caf and Cou interact well with K199. Given the critical role of K199 in HSA glycosylation in diabetic patients, this process inhibits the interaction of stabilizer compounds and thus accelerates gHSA aggregation.

"Cyclophilin A" Enzymatic Effect on the Aggregation Behavior of 1N4R Tau Protein: An Overlooked Crucial Determinant that should be Re-considered in Alzheimer's Disease Pathogenesis.

BACKGROUND: Neurodegenerative disorders like Alzheimer's disease (AD) involve the abnormal aggregation of tau protein, which forms toxic oligomers and amyloid deposits. The structure of tau protein is influenced by the conformational states of distinct proline residues, which are regulated by peptidyl-prolyl isomerases (PPIases). However, there has been no research on the impact of human cyclophilin A (CypA) as a PPIase on (non-phosphorylated) tau protein aggregation. METHODS: On the basis of these explanations, we used various spectroscopic techniques to explore the effects of CypA on tau protein aggregation behavior. RESULTS: We demonstrated the role of the isomerization activity of CypA in promoting the formation of tau protein amyloid fibrils with well-defined and highly ordered cross-ß structures. According to the "cistauosis hypothesis," CypA's ability to enhance tau protein fibril formation in AD is attributed to the isomerization of specific proline residues from the trans to cis configuration. To corroborate this theory, we conducted refolding experiments using lysozyme as a model protein. The presence of CypA increased lysozyme aggregation and impeded its refolding process. It is known that proper refolding of lysozyme relies on the correct (trans) isomerization of two critical proline residues. CONCLUSION: Thus, our findings confirmed that CypA induces the trans-to-cis isomerization of specific proline residues, ultimately leading to increased aggregation. Overall, this study highlights the emerging role of isomerization in tau protein pathogenesis in AD.

The induction of tau aggregation is restricted by sulfamethoxazole and provides new information regarding the use of the drug.

The aggregation of tau protein in the form of paired helical filament (PHF) leads to the breakdown of microtubule structure and the development of neurodegenerative disorders, such as Alzheimer's disease. Therefore, inhibiting tau protein aggregation is a potential strategy for preventing the progression of these disorders. In this study, sulfamethoxazole (SMZ), an antibiotic that easily crosses the blood-brain barrier and interacts with tau protein, was tested for its ability to inhibit tau aggregation in vitro. Various multi-spectroscopic techniques including XRD, LDH cytotoxicity colorimetric assay, and microscopic imaging were employed. The results showed that SMZ effectively interacts with tau protein through hydrogen and van der Waals interactions. It also effectively inhibited tau protein aggregation in vitro and significantly reduced toxicity in the SH-SY5Y neuroblastoma cell line. Molecular docking and MD simulation results suggested that SMZ may reduce tau protein aggregation by interacting with the PHF6 motif. Overall, these findings indicate that SMZ has therapeutic potential as a tau protein aggregation inhibitor, at least under in vitro conditions. These findings suggest that SMZ has potential as a treatment for neurodegenerative disorders involving tau protein aggregation. However, further research is needed to confirm these results and assess the effectiveness of SMZ in animal models and clinical trials.Communicated by Ramaswamy H. Sarma.

Corrigendum to "Introducing an interesting and novel strategy based on exploiting first-order advantage from spectrofluorimetric data for monitoring three toxic metals in living cells" [Toxicol. Rep. 9 (2022) 647-655].

[This corrects the article DOI: 10.1016/j.toxrep.2022.03.049.].

Effective Reduction of Tau Amyloid Aggregates in the Presence of Cyclophilin from Platanus orientalis Pollens; An Alternative Mechanism of Action of the Allergen.

BACKGROUND: A hallmark pathology of Alzheimer's disease (AD) is the construction of neurofibrillary tangles, which are made of hyperphosphorylated Tau. The cis-proline isomer of the pThr/Ser-Pro sequence has been suggested to act as an aggregation precursor according to the 'Cistauosis' hypothesis; however, this aggregation scheme is not yet completely approved. Various peptidyl-prolyl isomerases (PPIases) may specifically isomerize cis/trans-proline bonds and restitute Tau's ability to attach microtubules and may control Tau amyloid aggregation in AD. METHODS: In this study, we provided experimental evidence for indicating the effects of the plant Cyclophilin (P-Cyp) from Platanus orientalis pollens on the Tau aggregation by various spectroscopic techniques. RESULTS: Our findings disclosed that the rate/extent of amyloid formation in the Tau sample which is incubated with P-Cyp decreased and these observations do not seem to be due to the macromolecular crowding effect. Also, as proven that 80% of the prolines in the unfolded protein are in the trans conformation, urea-induced unfolding analyses confirmed this conclusion and showed that the aggregation rate/extent of urea-treated Tau samples decreased compared with those of the native protein. Also, XRD analysis indicated the reduction of scattering intensities and beta structures of amyloid fibrils in the presence of P-Cyp. Therefore, the ability of P-Cyp to suppress Tau aggregation probably depends on cis to trans isomerization of proline peptide bonds (X-Pro) and decreasing cis isomers in vitro. CONCLUSION: The findings of the current study may inspire possible protective/detrimental effects of various types of cyclophilins on AD onset/progression through direct regulation of intracellular Tau molecules and provides evidence that a protein from a plant source is able to enter the cell cytoplasm and may affect the behavior of cytoplasmic proteins.

Investigation of the role of prolines 232/233 in RTPPK motif in tau protein aggregation: An in vitro study.

Disease-related tau protein in Alzheimer's disease is hyperphosphorylated and aggregates into neurofibrillary tangles. The cis-proline isomer of the pSer/Thr-Pro sequence has been proposed to act as a precursor of aggregation ('Cistauosis' hypothesis), but this aggregation scheme is not yet entirely accepted. Hence to investigate isomer-specific-aggregation of tau, proline residues at the RTPPK motif were replaced by alanine residues (with permanent trans configuration) employing genetic engineering methods. RTPAK, RTAPK, and RTAAK mutant variants of tau were generated, and their in vitro aggregation propensity was investigated using multi-spectroscopic techniques. Besides, the cell toxicity of oligomers/fibrils was analyzed and compared to those of the wild-type (WT) tau. Analyses of mutant variants have shown to be in agreement (to some degree) to the theory of the 'cistauosis' hypothesis. The results showed that the trans isomer in the 232-rd residue (P232A mutant rather than P233A) had reduced aggregation propensity. However, this study did not illustrate any statistically significant difference between the wild and the mutant protein aggregations concerning cell toxicity.

Introducing an interesting and novel strategy based on exploiting first-order advantage from spectrofluorimetric data for monitoring three toxic metals in living cells.

In this work, we did our best to develop a novel and interesting analytical method based on coupling of spectrofluorimetry with first-order multivariate calibration techniques for simultaneous determination of lead (Pd), zinc (Zn) and cadmium (Cd) in HeLa cells. To achieve this goal, quenching of the emission of graphene (GR) was individually investigated in the presence of Pb, Zn and Cd and then, according to the linear ranges obtained from individual calibration graphs, a multivariate calibration model was developed based on modeling of the quenching of the emission of GR in the presence of the mixtures of Pb, Zn and Cd. First-order multivariate calibration models were constructed by partial least squares (PLS), principal component regression (PCR), orthogonal signal correction-PLS (OSC-PLS), continuum power regression (CPR), robust continuum regression (RCR) and partial robust M-regression (PRM) and their performances were evaluated and statistically compared. Finally, the OSC-PLS was chosen as the best model with the best practical performance for analytical purposes.

Pyridine-2,3-dicarboxylate, quinolinic acid, induces 1N4R Tau amyloid aggregation in vitro: Another evidence for the detrimental effect of the inescapable endogenous neurotoxin.

Quinolinic acid (QA) known as a neuro-active metabolite associated with the kynurenine pathway. At high concentrations, QA is often involved in the initiation and development of several human neurologic diseases, like Alzheimer's disease. Because of the QA action as the NMDA receptor, it is considered as a potent excitotoxin in vivo. Since it is probable that different mechanisms are employed by QA, activation of NMDA receptors cannot fully explain the revealed toxicity and it is even believed that there are multiple unknown mechanisms/targets leading to QA cytotoxicity. Herein we report accelerated amyloid oligomerization of 1N4R Tau under the effect of QA, in vitro, then the molecular structure, morphology and toxicity of the protein aggregate were documented by using various theoretical/experimental approaches. The possible mechanism of action of QA-induced Tau oligomerization has also been explored.

Effective suppression of the modified PHF6 peptide/1N4R Tau amyloid aggregation by intact curcumin, not its degradation products: Another evidence for the pigment as preventive/therapeutic "functional food".

Curcumin is a natural product with multiple biological activities and numerous potential therapeutic applications. In present study, the influence of curcumin and its degradation products (DPs) on the amyloid aggregation of Tau protein and the related PHF6 peptide were investigated. We provided experimental/theoretical evidence for suppressing effects of the compounds on the amyloid formation using far-UV CD as well as AFM, XRD and docking techniques and showed that the parent curcumin displayed stronger inhibition effect against Tau fibril aggregation. The obtained results suggest that the curcumin/DPs binding sites on the Tau molecule are likely to be the same, and provide a good structural basis to explain the efficient aggregation suppressing behavior of the curcumin, compared to the DPs. So, developing more stable curcumin nanoparticle formulations with improved curcumin bioavailability are of great importance. Curcumin's multi-functionality is also highly significant for the therapeutic application of this natural compound against various human diseases.

Antiradical activity of different parts of Walnut (Juglans regia L.) fruit as a function of genotype.

The objective of this work was to analyse phenolic compounds and antiradical capacity of different parts of walnut fruit among six genotypes of Juglans regia L. Therefore, total phenolic and flavonoid content were determined and methanolic extracts of walnut genotypes were considered by the reducing power, DPPH (2,2-diphenyl-1-picrylhydrazyl), superoxide anion and nitric oxide radical scavenging. Significant differences were found in phenolic content and radical scavenging capacity of different parts of fruits and among various genotypes. High correlation coefficient (R(2)=0.81) was observed between phenol content and radical scavenging activity, but this was not always true (R(2)=0.01). These results demonstrated that walnut genotypes have different phenolic compounds and phenolic compounds have different radical scavenging power. The differences of phenolic compounds were confirmed by using high performance liquid chromatography (HPLC).