Resveratrol as a nontoxic excipient stabilizes insulin in a bioactive hexameric form

Inhibition of amyloid formation of amyloid β (1-42), amylin and insulin by 1,5-diazacyclooctanes, a spermine-acrolein conjugate

Amyloid aggregates of proteins are known to be involved in various diseases such as Alzheimer's disease (AD). It is therefore speculated that the inhibition of amyloid formation can play an important role in the prevention of various diseases involving amyloids. Recently, we have found that acrolein reacts with polyamines, such as spermine, and produces 1,5-diazacyclooctane, such as cyclic spermine (cSPM). cSPM could suppress the aggregation of amyloid β 1-40 (Aβ40), one of the causative proteins of AD. This result suggests the potential inhibitory effect of cSPM against Aβ 1-42 (Aβ42) and other amyloid protein aggregation which are the main pathological features of AD and other diseases. However, the effect on the aggregation of such proteins remains unclear. In this study, the effect of cSPM on the amyloid formation of Aβ42, amylin, and insulin was investigated. These three amyloidogenic proteins forming amyloids under physiological conditions (pH 7.4 and 37℃) served as model and are thought to be the causative proteins of AD, type 2 diabetes, and insulin-derived amyloidosis, respectively. Our results indicate that cSPM can suppress the amyloid aggregation of these proteins and reduce cytotoxicity. This study contributes to a better understanding of means to potentially counteract diseases by the means of polyamine and acrolein.

Three-step Förster resonance energy transfer on an amyloid fibril scaffold

The present study provides evidence that the energy transfer chain consisting of the benzothiazole dye Thioflavin T as an input donor, a phosphonium dye TDV and a squaraine dye SQ4 as mediators, and one of the three squaraines SQ1/2/3 as an output acceptor displays an excellent amyloid-sensing ability when applied to differentiating between the amyloid and non-fibrillized states of insulin. The ensemble of fluorophores offers the advantages of a large effective Stokes shift (∼240 nm), well-resolved 3D fluorescence patterns and strong enhancement of the terminal fluorescence (up to two orders of magnitude). The occurrence of multistep energy transfer on an amyloid fibril scaffold opens new possibilities for the more sensitive detection of fibrillar protein assemblies and their applications in nanophotonics.

Prion-derived tetrapeptide stabilizes thermolabile insulin via conformational trapping

Unfolding followed by fibrillation of insulin even in the presence of various excipients grappled with restricted clinical application. Thus, there is an unmet need for better thermostable, nontoxic molecules to preserve bioactive insulin under varying physiochemical perturbations. In search of cross-amyloid inhibitors, prion-derived tetrapeptide library screening reveals a consensus V(X)YR motif for potential inhibition of insulin fibrillation. A tetrapeptide VYYR, isosequential to the β2-strand of prion, effectively suppresses heat- and storage-induced insulin fibrillation and maintains insulin in a thermostable bioactive form conferring adequate glycemic control in mouse models of diabetes and impedes insulin amyloidoma formation. Besides elucidating the critical insulin-IS1 interaction (R4 of IS1 to the N24 insulin B-chain) by nuclear magnetic resonance spectroscopy, we further demonstrated non-canonical dimer-mediated conformational trapping mechanism for insulin stabilization. In this study, structural characterization and preclinical validation introduce a class of tetrapeptide toward developing thermostable therapeutically relevant insulin formulations.