A Small Molecule Impedes Insulin Fibrillation: Another New Role of Phenothiazine Derivatives

Abstract

Protein misfolding is interrelated to several diseases, including neurodegenerative diseases and type II diabetes. Misfolded/unfolded proteins produce soluble oligomers that accumulate into “amyloid plaques”. Inhibition of amyloid‐plaque formation by those misfolded/unfolded proteins will lead to the invention of new therapeutic approaches for amyloid‐related diseases. Herein, methylene blue (MB), a well‐defined drug against multiple diseases and disorders, is used to impede insulin fibrillation. In this study, we perform an array of in vitro experiments to monitor the effects of MB on the fibrillation of bovine insulin. Our results confirm that MB distresses the kinetics of insulin fibrillation by interacting with insulin in its monomeric form. A thioflavin T assay indicates that insulin fibrillation is interrupted upon the addition of MB. The same results are confirmed by circular dichroism, dynamic light scattering (DLS), and size‐exclusion chromatography (SEC). According to the DLS data, the insulin fibrils are 800 nm in diameter, and the addition of MB reduces the size of the fibrils, which remain 23 nm in size, and this indicates that no fibrillation of insulin occurs in the presence of MB. This data is also supported by SEC. Saturation transfer difference NMR spectroscopy and molecular dynamics simulations demonstrate the interactions between insulin and MB at the atomic level.

Design, Synthesis, and Validation of a Novel [11C]Promethazine PET Probe for Imaging Abeta Using Autoradiography

“…Phenothiazine analogs have versatile applications across many diseases, including antimicrobial effects [ 24 , 25 , 26 ], antitumor effects [ 27 , 28 , 29 , 30 , 31 , 32 , 33 ], and potential roles in the treatment of neurodegenerative disease [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. In the past, we showed PMZ binds to Abeta available in the brain lysate of 5XFAD mice in an in vitro study.…”

Molecular Aspects of Insulin Aggregation and Various Therapeutic Interventions

“…Chatterjee and co-workers used the dye methylene blue (MB) to disrupt insulin aggregation at an insulin:MB ratio > 1:50, 99 which inhibited nucleus formation. When HepG2 cells were treated with insulin aggregates in the absence and presence of MB, only MB treated insulin was able to induce phosphorylation of Akt.…”

Strategies for Interference of Insulin Fibrillogenesis: Challenges and Advances

“…Inhibitory approaches broadly proposed as stable insulin formulations with added stabilizers and engineered insulin analogues with heat or mechanical stress withstanding property (Figure 1). Examples of external agents that halt insulin agglomeration are aromatic compounds, [44,45] bio-inspired peptides, [46] hybrid peptide conjugates, [47] nanoparticles, [48] trehalose, [49,50] polyphenols, [51] Zinc, [52] dyes, [53] metal complexes, [54][55][56] hydrophobic interfaces, [57] functionalized meso-porous silica, [58] etc. Another paradigm used to enhance insulin intrinsic stability is through insulin engineering which mainly involves amino acid substitutions, [59,60] halogenated insulin analogues, [61,62] intramolecular disulfide bond introduction, [63,64] replacement of natural disulfide bond with non-reducible cystathionine/cystine bond, [65] single chain insulin analogues, [66][67][68][69] glycosylated insulin analogues, [70] analogues inspired from insulin like venom of marine snails, [71] etc.…”