Effective inhibition of insulin amyloid fibril aggregation by nickel(II) complexes containing heterocyclic thiosemicarbazones.

The sensitivity of protein molecular structures makes them susceptible to aggregation in conditions unfavorable for the maintenance of their native folds. The aggregation of proteins leads to many disorders, but the inhibition of amyloid fibril formation using metal-containing small molecules is gaining popularity. Herein we report the effect of nickel(II) complexes (N1, N2, N3, and N4) bearing thiosemicarbazones on the inhibition of amyloid fibril formation by insulin. The interactions of the complexes with amyloid fibrils were investigated using various biophysical techniques, including light scattering, intrinsic fluorescence assay, thioflavin T (ThT) assay, and Fourier transform-infrared spectroscopy. The results revealed that the phenyl-substituted N3 was an efficient inhibitor of amyloid fibril formation and maintained the insulin in its native structure despite conditions promoting fibrillation. Nickel(II) complexes containing indole based thiosemicarbazones were efficient in inhibiting the amyloid fibril formation and maintaining the insulin in its native structure in unfavorable conditions.

Cytotoxic and membrane perturbation effects of a novel amyloid forming model peptide poly(leucine-glutamic acid).

In the present study we have elucidated the toxicity of a novel amyloid forming model peptide, Poly (leucine-glutamic acid). The toxicity of the fibrils prepared from this peptide was analyzed in peripheral blood lymphocytes (PBL). The MTT reduction assay revealed that the viability of PBL decreases significantly upon treatment with Poly(leucine-glutamic acid) (Poly [LE]). Enhanced DCFH-DA fluorescence in treated cells suggests that peptide toxicity is probably mediated by the formation of free radicals. In vivo and in vitro biochemical studies indicated that Poly [LE] inactivates the antioxidant system of cells. Perturbation of Poly [LE] in a membrane lipid environment was assessed by circular dichroism (CD) using phosphotidyl choline-cholesterol bilayers. The CD results revealed that LE enhances its beta sheet content in a bilayer environment. Sequestration of Poly [LE] in lipid rafts demonstrates that it has a binding cleft similar to Abeta in lymphocyte raft domains. Nuclear membrane binding studies showed that Poly [LE] binds to nuclear membranes and may cause genotoxicity.