Hesperidin attenuate fibrillation and cytotoxicity of human insulin: Role of secondary structure and its hydrophobicity in protein aggregation

Abstract

Protein aggregation occurs when proteins are subjected to abnormal physical and chemical conditions; the subsequent aggerate can lead to multiple debilitating and deadly neurological conditions, such as Alzheimer's, Parkinson's, type II diabetes, and Huntington's disease. As such, we must further examine possible therapeutic agents such as polyphenols for possible utilization in the treatment of aggerate – born – illness. In this study, hesperidin (bioflavonoid) was examined for its anti-aggregating potential using human insulin as model protein. Our results show protein denaturing conditions (pH =2.0, Temperature 40 °C, NaCl 50 mM, agitation 1200 rpm) resulted in the formation of insulin fibrils as displayed by various spectroscopic and microscopic techniques. At 20 & 50 µM concentrations of hesperidin, aggregation of insulin decreased in a nucleation-independent manner. Far UV-CD measurement illustrated transition of α-helix to cross β-sheet during formation of amyloid. However, in the presence of hesperidin stabilization of α-helix along with concomitant decrease of β-sheet was observed. The hydrophobicity measurement suggested exposure of hydrophobic residues during fibrillation. Moreover, in the presence of hesperidin hydrophobicity was significantly dropped. Cytotoxicity of fibrillated insulin shows dose dependent inhibition of growth of SH-SY5Y cells and their protection by hesperidin. Molecular docking analysis revealed strong binding energy of 6.61 kcal mol−1 between insulin-hesperidin complex. Also, hesperidin binds to both A (Leu13, Tyr14, Glu17) and B (Phe1, Leu6, HIS10, Ala14, Glu13, Ala14, Leu17) chains of human insulin involving hydrogen and hydrophobic interactions. Conclusively, we demonstrated that hesperidin inhibited the formation of insulin amyloid and should be further exploited for insulin amyloidosis and other protein-misfolding diseases.