Curcumin's pre-incubation temperature affects its inhibitory potency toward amyloid fibrillation and fibril-induced cytotoxicity of lysozyme

Background: More than twenty-seven human proteins can fold abnormally to form amyloid deposits associated with a number of degenerative diseases. The research reported here is aimed at exploring the connection between curcumin's thermostability and its inhibitory activity toward the amyloid fibrillation of hen egg-white lysozyme (HEWL). Methods: ThT fluorescence spectroscopy, equilibrium thermal denaturation analysis, and transmission electron microscopy were employed for structural characterization. MIT reduction and flow cytometric analyses were used to examine cell viability. Results and conclusion: The addition of thermally pre-treated curcumin was found to attenuate the formation of HEWL fibrils and the observed fibrillation inhibition was dependent upon the pre-incubation temperature of curcumin. Our results also demonstrated that the cytotoxic effects of fibrillar HEWL species on PC 12 and SH-SY5Y cells were decreased and negatively correlated with curcumin's thermostability. Next, an enhanced stability of HEWL was perceived upon the addition of curcumin pre-incubated at lower temperature. Furthermore, we found that the alteration of curcumin's thermostability was associated with its inhibitory potency against HEWL fibrillation. General significance: We believe that the results from this research may contribute to the development of effective therapeutics for amyloidoses. (C) 2012 Elsevier B.V. All rights reserved.