The effect of novel antihypertensive drug valsartan on lysozyme aggregation: A combined in situ and in silico study.

Protein misfolding can result in amyloid fiber aggregation, which is associated with various types of diseases. Therefore, preventing or treating abnormally folded proteins may provide therapeutic intervention for these diseases. Valsartan (VAL) is an angiotensin II receptor blocker (ARB) that is used to treat hypertension. In this study, we examine the anti-aggregating effect of VAL against hen egg-white lysozyme (HEWL) amyloid fibrils through spectroscopy, docking, and microscopic analysis. In vitro formation of HEWL amyloid fibrils was indicated by increased turbidity, RLS (Rayleigh light scattering), and ThT fluorescence intensity. 10 µM VAL, amyloid/aggregation was inhibited up to 83% and 72% as measured by ThT and RLS respectively. In contrast, 100 µM VAL significantly increases the fibril aggregation of HEWL. CD spectroscopy results show a stabilization of HEWL α-helical structures in the presence of 10 µM VAL while the increase in ß-sheet was detected at 100 µM concentration of VAL. The hydrophobicity of HEWL was increased at 100 µM VAL, suggesting the promotion of aggregation via its self-association. Steady-state quenching revealed that VAL and HEWL interact spontaneously via hydrogen bonds and van der Waals forces. Transmission electron microscopy (TEM) images illustrate that the needle-like fibers of HEWL amyloid were reduced at 10 µM VAL, while at 100 µM the fibrils of amyloid were increased. Additionally, our computational studies showed that VAL could bind to two binding sites within HEWL. In the BS-1 domain of HEWL, VAL binds to ASN59, ILE98, ILE58, TRP108, VAL109, SER50, ASP52, ASN59, ALA107, and TRP108 residues with a binding energy of -9.72 kcal mol-1. Also, it binds to GLU7, ALA10, ALA11, CYS6, ARG128, and ARG14 in the BS-2 domain with a binding energy of -5.89 kcal mol-1. VAL, therefore, appears to have dual effect against HEWL aggregation. We suggest that VAL stabilizes HEWL's aggregation-prone region (APR) at 10 µM, preventing aggregation. Also, we assume that at 100 µM, VAL occupies BS-2 beside BS-1 and destabilizes the folding structure of HEWL, resulting in aggregation. Further studies are needed to investigate the mechanism of action and determine its potential side effects.

Elucidating the binding and inhibitory potential of p-coumaric acid against amyloid fibrillation and their cytotoxicity: Biophysical and docking analysis.

P-Coumaric acid (p-CA) is a plant metabolite with anti-inflammatory and antioxidant effects. Due to its therapeutic potential, p-CA has attracted much attention from the scientific community lately. Oxidative stress, amyloid formation, and impaired proteasomal degradation are hallmarks of neurodegenerative diseases like Alzheimer's (AD) and are targets for developing therapeutics against such conditions. Here, we have investigated the anti-amyloidogenic properties of p-coumaric acid on hen egg white lysozyme (HEWL). Heat, pH, and agitation (55 °C, pH 2.0, 600 rpm) stress were used to induce amyloid formation in lysozyme. The aggregates characterization was done by turbidity, Rayleigh light scattering (RLS), and thioflavin-T (ThT) assays. Moreover, ANS (1-anilino naphthalene sulphate) binding assay and circular dichroism (CD) were employed to unveil protein hydrophobicity and secondary structure perturbation, respectively. Lysozyme demonstrated increased hydrophobicity and transition of α-helix to ß-sheet under aggregating conditions. Moreover, co-incubation of lysozyme with p-coumaric acid attenuates the process of amyloid in a concentration dependent manner. At 50 and 200 µM concentrations of p-coumaric acid, lysozyme retained its native-like folded structure. Cytotoxicity protection on human SK-N-SH neuroblastoma cell line was also observed using MTT assay and phase contrast microscopy. In addition, transmission electron microscopy (TEM) reaffirms the fibrillar nature of lysozyme aggregates and their attenuation by p-coumaric acid. The steady state fluorescence revealed that the mode of fluorescence quenching for the HEWL-p-coumaric acid interaction is static rather than dynamic. Moderate strength of binding in order of 104 M-1 exists between HEWL and p-coumaric acid. Thermodynamic parameters (∆H and ∆S) obtained from van't Hoff plot suggested spontaneous reaction with hydrophobic interaction. A slight micro-environmental change in HEWL around Tyr residue was observed during the binding process with the help of synchronous fluorescence. Molecular docking analysis reported the involvement of amino acid residues (TRP63, LEU75, ASP101, LYS97) to form a complex between HEWL-p-coumaric acid. The observed anti-amyloidogenic and inherent antioxidative properties of p-coumaric acid could be helpful to design a neuroprotective agent.