Comparative study on the interaction of two binuclear Pt (II) complexes with human serum albumin: Spectroscopic and docking simulation assessments.

Human serum albumin (HSA) principally tasks as a transport carrier for a vast variety of natural compounds and pharmaceutical drugs. In the present study, two structurally related binuclear Pt (II) complexes containing cis, cis-[Me2Pt (µ-NN) (µ-dppm) PtMe2] (1), and cis, cis-[Me2Pt(µ-NN)(µ dppm) Pt((CH2)4)] (2) in which NN=phthalazine and dppm=bis (diphenylphosphino) methane were used to investigate their interaction with HSA, using UV-Vis absorption spectroscopy, fluorescence, circular dichroism and molecular dynamic analyses. The spectroscopic results suggest that upon binding to HSA, the binuclear Pt (II) complexes could effectively induce structural alteration of this protein. These complexes can bind to HSA with the binding affinities of the following order: complex 2>complex 1. Moreover, the thermodynamic parameters of binding between these complexes and HSA suggested the existence of entropy-driven spontaneous interaction, which mostly dominated with the hydrophobic forces. The ANS fluorescence results also indicated that two binuclear Pt (II) complexes were competing for the binding to the hydrophobic regions on HSA. In addition, competitive displacement assay and docking simulation study revealed that complexes 1 and 2 bind to the drug binding sites II and I on HSA, respectively. Furthermore, complex 2, with the higher binding affinity for HSA, shows more denaturing effect on this protein. Considering the protein structural damages in the pathway of harmful side effects of platinum drugs, complex 1 with the moderate binding affinity and low denaturing effect might be of high significance.

Aspirin-mediated acetylation induces structural alteration and aggregation of bovine pancreatic insulin.

The simple aggregation of insulin under various chemical and physical stresses is still an important challenge for both pharmaceutical production and clinical formulation. In the storage form, this protein is subjected to various chemical modifications which alter its physicochemical and aggregation properties. Aspirin (acetylsalicylic acid) which is the most widely used medicine worldwide has been indicated to acetylate a large number of proteins both in vitro and in vivo. In this study, as insulin treated with aspirin at 37°C, a significant level of acetylation was observed by flourescamine and o-phthalaldehyde assay. Also, different spectroscopic techniques, gel electrophoresis, and microscopic assessment were applied to compare the structural variation and aggregation/fibrillation propensity among acetylated and non-acetylated insulin samples. The results of spectroscopic assessments elucidate that acetylation induces insulin unfolding which is accompanied with the exposure of protein hydrophobic patches, a transition from alpha-helix to beta-sheet and increased propensity of the protein for aggregation. The kinetic studies propose that acetylation increases aggregation rate of insulin under both thermal and chemical stresses. Also, gel electrophoresis and dynamic light scattering experiments suggest that acetylation induces insulin oligomerization. Additionally, the results of Thioflavin T fluorescence study, Congo red absorption assessment, and microscopic analysis suggest that acetylation with aspirin enhances the process of insulin fibrillation. Overall, the increased susceptibility of acetylated insulin for aggregation may reflect the fact that this type of modification has significant structural destabilizing effect which finally makes the protein more vulnerable for pathogenic aggregation/fibrillation.

The impact of calcium ion on structure and aggregation propensity of peroxynitrite-modified lens crystallins: new insights into the pathogenesis of cataract disorders.

As a highly potent reactive oxygen and nitrogen species, peroxynitrite (PON) has been indicated in the pathogenesis of various ocular disorders. The PON induces mobilization of intra cellular calcium which plays an important function in structure and activity of lens proteins. Moreover, the amount of calcium increases to the pathogenic level in the cataractous lenses. The aim of this study was to assess the impact of calcium ion on structure and aggregation of PON-modified lens crystallins, using spectroscopic techniques and gel mobility shift assay. The PON modification of lens proteins was confirmed with detection of the significantly increased quantity of carbonyl group, dityrosine, nitrotyrosine and nitrotryptophan. Moreover, the modified proteins indicated high levels of solvent exposed hydrophobic surfaces and markedly elevated proteolytic instability which can be explained with their structural alteration upon this type of modification. The results of UV-vis absorption studies suggest that PON-modified lens crystallins are highly sensitive to aggregation in the presence of both physiological and pathological ranges of calcium ion. Also, the results of thioflavin T fluorescence study indicated absence of any ordered aggregate entity in the calcium-induced aggregate samples. The results of gel mobility shift assay demonstrated the importance of calcium ion in the induction of disulfide and dityrosine covalent cross-linking and formation of the oligomeric structure with relatively larger sizes in the PON-modified crystallins compared to the non-modified protein counterparts. Overall, this study may suggest that a simultaneous raise of calcium ion and PON in the eye ball is an important risk factor for development of cataract diseases.

Anticancer and DNA binding activities of platinum (IV) complexes; importance of leaving group departure rate.

The two six-coordinate Pt(IV) complexes, containing bidentate nitrogen donor/methyl ligands with general formula [Pt(X)2Me2((t)bu2bpy)], where (t)bu2bpy = 4,4'-ditert-butyl-2,2'-bipyridine and X = Cl (C1) or Br (C2), serving as the leaving groups were synthesized for evaluation of their anticancer activities and DNA binding properties. To examine anticancer activities of the synthetic complexes, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and ethidium bromide/acridine orange (EB/AO) staining method were performed. The binding properties of these complexes to DNA and purine nucleotides were examined, using different spectroscopic techniques. These complexes demonstrated significant anticancer activities against three cancer cell lines Jurkat, K562, and MCF-7. On the basis of the results of EB/AO staining, C1 and C2 were also capable to induce apoptosis in cancer cells. These complexes comprise halide leaving groups, displaying different departure rates; accordingly, they demonstrated slightly dissimilar anticancer activity and significantly different DNA/purine nucleotide binding properties. The results of DNA interaction studies of these complexes suggest a mixed-binding mode, comprising partial intercalation and groove binding. Overall, the results presented herein indicate that the newly synthesized Pt(IV) complexes are promising class of the potential anticancer agents which can be considered as molecular templates in designing novel platinum anticancer drugs. This study also highlights the importance of leaving group in anticancer activity and DNA binding properties of Pt(IV) complexes.