| Alzheimer's disease?AD?is the most important type of dementia,which seriously affects the patients' life quality and causes great burden to patients' families and society.The problem has become increasingly prominent with the global population aging.Current anti-AD drugs can only alleviate but not cure it completely.Therefore,it is extremely urgent to develop the effective AD drugs.Based on the ?-amyloid cascade theory,it's an effective strategy to develop the A? regulator to regulate the aggregation of A?.In currently,A? regulator can be divided into different types according to their different functions,such as the regulator with inhibition function,the regulator with disaggregation function,and the regulator which can transform A? to be hypo-toxicity.Nowadays,some metal complexes have been reported to inhibit the aggregation of A?.In comparison to the other complexes,ruthenium complexes exhibit low toxicity and some ruthenium?II?complexes have been reported to take good effects on inhibiting or monitoring the A? aggregation.Therefore,ruthenium?II?complexes have been considered as potential A? regulator and novel AD drug.In this paper,ten polypyridyl ruthenium complexes were selected to study the inhibition on A?42 fibrillization,the studies are as following:1.The inhibitory effect on A?42 fibrillization and morphology by two ruthenium?II?complexes with hydroxyl substitutes [Ru?phen?2?2,3-DHPIP?]2+?Ru 1?and [Ru?phen?2?2,5-DHPIP?]2+?Ru 2?were studied using ThT fluorescence assay,AFM,TEM and measurement of soluble protein content.The results showed that both Ru 1 and Ru 2 could inhibit the proliferation of A?42 effectively,and the inhibitory effect of Ru 1 was better than that of Ru 2.MTT assay results showed that both ruthenium complexes exhibited low cytotoxicity,and the addition of 3 equivalent of Zn2+ or Cu2+ took no obvious effects on the cytotoxicity of A?42.In addition,intracellular A?42 aggregation assay showed that there was no significant difference in cell viability between different incubation systems.Furthermore,Ru 1 could decrease the cytotoxicity of A?42-Zn2+ and A?42-Cu2+ incubation system,while Ru 2 couldn't.The fluorescence titration results showed that the fluorescence of A?42 was mainly quenched by static fluorescence quenching and the effect of dynamic quenching was enhanced with increasing the complexes concentration.The apparent binding constants of complexes with A?42 were calculated to be less than 0.08 mol/L,indicating that the interaction between the complexes and A?42 was weak,mainly was non-covalent interactions,such as electrostatic interaction,hydrophobic and hydrogen bonding.In summary,Ru 1 and Ru 2 exhibited good inhibition on the fibrillization of A?42 and reduced the toxicity of A?42,which could be acted as potential A?42 aggregation inhibitors.2.Four ruthenium?II?complexes [Ru?phen?2MNAIP)]2+?Ru 3?,[Ru?bpy?2MNAIP)]2+?Ru 4?,[Ru?phen?3]2+ and [Ru?bpy?3]2+ were selected to study the interaction of these complexes with A?42 by ThT fluorescence assay,TEM,the measurement of soluble protein,MTT assay,and fluorescence titration.The results showed that Ru 3 and Ru 4 containing MNAIP ligand had significant inhibitory effect on A?42 fibrillization,while [Ru?phen?3]2+ and [Ru?bpy?3]2+ exhibited relatively low inhibition efficiency on A?42 fibrillization?inhibition rates: 44.01 % and 19.46 %,respectively?.Besides,Ru 3 and Ru 4 could inhibit the fibrillization of A?42 and induce the formation of low toxicity amorphous aggregates.Fluorescence titration assay showed that static fluorescence quenching played an important role in the interaction between ruthenium complex and A?42.With increasing the complex concentration,the dynamic quenching was enhanced.The rate of quenching by Ru 3 or Ru 4 was greater than that of [Ru?phen?3]2+ and [Ru?bpy?3]2+.The monitoring assay showed that the enhancement of complexes' fluorescence intensity was within ± 17 % upon interacting with the A?42 monomer or the fiber.So,it is necessary to further study the ruthenium complex to be the monitor.In summary,both Ru 3 and Ru 4 may be acted as effective A?42 modulators.3.[Ru?bpy?2?2,3-DHPIP?]2+?Ru 5?,[Ru?bpy?2?2,3-DCPIP?]2+?Ru 6?,[Ru?phen?2?2,3-DHPIP?]2+?Ru 7?,[Ru?phen?3]2+ and [Ru?phen?2Cl2]2+ were used to investigated their inhibitory and disaggregation ability to A?42 by Th T fluorescence assay and CD spectroscopy technology.In order to find out the relationship between the structures and the abilities of ruthenium complexes.The ability of the complexes to inhibit the fibrillization of A?42 was positively correlated with the disaggregation ability,which means the disaggregation ability was stronger when the aggregation ability became stronger.The ability of each complex inhibited the fibrillization of A?42 was as follows: Ru 7> Ru 6 >Ru 5> [Ru?phen?3]2+> [Ru?phen?2Cl2]2+.Combinating with the structure of the complexes,it was found that the ability of [Ru?phen?2Cl2]2+ were not better than the other four complexes,which indicated that ruthenium complex with rigid ligand may had stronger inhibitory effects.In addition,PIP main ligands played an important role in the inhibition of A?42 aggregation while different functional groups on PIP and the auxiliary ligand had no significant effect on the inhibition.So,we presumed that complexes were fully coordinated and the different inserted ligands were the major factors to affect ruthenium complexes' inhibitory. |
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