Syntheses and Structure-Activity Relationships of Seven Manganese-Salen Derivatives as Anti-Amyloidogenic and Fibril-Destabilizing Agents against Hen Egg-White Lysozyme Aggregation

Seifollah Bahramikia, Razieh Yazdanparast. IBB, Biochemistry, Iran

Accumulation of intra-and/or extracellular misfolded proteins as amyloid fibrils is a key hallmark in more than twenty amyloid-related diseases. In that respect, blocking or reversing amyloid aggregation via the use of small compounds are considered as two useful approaches in hampering the development of these diseases. In this research, we have studied the ability of different manganese-salen derivatives to inhibit amyloid self-assembly as well as to dissolve amyloid aggregates of hen egg-white lysozyme (HEWL), as an in vitro model system, with the aim of investigating their structure-activity relationships. By coupling several techniques such as Thioflavin T (ThT) and Anilinonaphthalene-8-sulfonic acid (ANS) fluorescence, Congo red (CR) absorbance, Far-UV circular dichroism (CD) and Transmission electron microscopy (TEM), we demonstrated that all compounds possessed anti-amyloidogenic activities and were capable of dispersing the fibrillar aggregates. In addition, MTT assay of the treated SK-N-MC cells with the pre-formed fibrils formed in the presence of compounds at a drug-to-protein molar ratio of 5:1, indicated significant increase in the viability of cells, compared to the fibrils formed in the absence of each of the compounds. Our spectroscopy, electron microscopy and cellular studies indicated that EUK-15, with a methoxy group at the para position (group R5), had higher activity to either inhibit or disrupt the β-sheet structures relative to other compounds. Based on these results, it can be concluded that in addition to aromatic rings of each of the derivatives, the type and position of the side group (s) contributes to lower lysozyme fibril accumulation.