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Flavone derivatives as inhibitors of insulin amyloid-like fibril formation.

Malisauskas R, Botyriute A, Cannon JG, Smirnovas V - PLoS ONE (2015)

Bottom Line: Maximal values of ThT fluorescence varied two fold or more in one third of all cases, but this did not correlate with changes in t50.However, the main conclusion is that the positions are not additive.The structures and their effects must be thought of in the context of the whole molecule.

View Article: PubMed Central - PubMed

Affiliation: Department of Biothermodynamics and Drug Design, Vilnius University Institute of Biotechnology, Vilnius, Lithuania; Department of Chemistry and Bioengineering, Vilnius Gediminas Technical University, Vilnius, Lithuania.

ABSTRACT
Several natural and synthetic flavone derivatives have been reported to inhibit formation of amyloid fibrils or to remodel existing fibrils. These studies suggest that the numbers and positions of hydroxyl groups on the flavone rings determine their effectiveness as amyloid inhibitors. In many studies the primary method for determining the effectiveness of inhibition is measuring Thioflavin T (ThT) fluorescence. This method demonstrably results in a number of false positives for inhibition. We studied the effects of 265 commercially available flavone derivatives on insulin fibril formation. We enhanced the effectiveness of ThT fluorescence measurements by fitting kinetic curves to obtain halftime of aggregation (t50). Maximal values of ThT fluorescence varied two fold or more in one third of all cases, but this did not correlate with changes in t50. Changes in t50 values were more accurate measures of inhibition of amyloid formation. We showed that without a change in an assay, but just by observing complete kinetic curves it is possible to eliminate numbers of false positive and sometimes even false negative results. Examining the data from all 265 flavones we confirmed previous observations that identified the importance of hydroxyl groups for inhibition. Our evidence suggests the importance of hydroxyl groups at locations 5, 6, 7, and 4', and the absence of a hydroxyl group at location 3, for inhibiting amyloid formation. However, the main conclusion is that the positions are not additive. The structures and their effects must be thought of in the context of the whole molecule.

No MeSH data available.


Related in: MedlinePlus

Flavone backbone with numbered positions for residues.
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pone.0121231.g004: Flavone backbone with numbered positions for residues.

Mentions: To understand how the position of hydroxyl groups affects inhibition potential, we plotted relative t50 as a function of hydroxyl group position around the flavone backbone (Fig. 4). For discussion we will consider five ranges of relative t50 values: < 0.65 (moderate accelerator), 0.65–0.85 (weak accelerator), 0.85–1.15 (no effect), 1.15–3.0 (weak inhibitor), and > 10.0 (strong inhibitor). More divisions are retained in Fig. 5 to give a more complete account of the distribution of effects from flavones on amyloid formation. Fig. 5 shows the observed effects of hydroxyl groups at all of the nine positions available for substitution without having a penta-substituted phenyl group. Out of the 265 flavones studied, there are 10 moderate accelerators, 41 weak accelerators, 16 weak inhibitors, and 5 strong inhibitors. One thing made clear by our groupings is that no flavones resulted in relative t50 between 3 and 10. This leads to our first observation—hydroxyl groups do not simply have an additive effect, but must interact cooperatively with insulin or insulin aggregates. Despite this clear cooperativity, we looked to see if any single positions could be identified as essential or important to inhibition or acceleration.


Flavone derivatives as inhibitors of insulin amyloid-like fibril formation.

Malisauskas R, Botyriute A, Cannon JG, Smirnovas V - PLoS ONE (2015)

Flavone backbone with numbered positions for residues.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4370379&req=5

pone.0121231.g004: Flavone backbone with numbered positions for residues.
Mentions: To understand how the position of hydroxyl groups affects inhibition potential, we plotted relative t50 as a function of hydroxyl group position around the flavone backbone (Fig. 4). For discussion we will consider five ranges of relative t50 values: < 0.65 (moderate accelerator), 0.65–0.85 (weak accelerator), 0.85–1.15 (no effect), 1.15–3.0 (weak inhibitor), and > 10.0 (strong inhibitor). More divisions are retained in Fig. 5 to give a more complete account of the distribution of effects from flavones on amyloid formation. Fig. 5 shows the observed effects of hydroxyl groups at all of the nine positions available for substitution without having a penta-substituted phenyl group. Out of the 265 flavones studied, there are 10 moderate accelerators, 41 weak accelerators, 16 weak inhibitors, and 5 strong inhibitors. One thing made clear by our groupings is that no flavones resulted in relative t50 between 3 and 10. This leads to our first observation—hydroxyl groups do not simply have an additive effect, but must interact cooperatively with insulin or insulin aggregates. Despite this clear cooperativity, we looked to see if any single positions could be identified as essential or important to inhibition or acceleration.

Bottom Line: Maximal values of ThT fluorescence varied two fold or more in one third of all cases, but this did not correlate with changes in t50.However, the main conclusion is that the positions are not additive.The structures and their effects must be thought of in the context of the whole molecule.

View Article: PubMed Central - PubMed

Affiliation: Department of Biothermodynamics and Drug Design, Vilnius University Institute of Biotechnology, Vilnius, Lithuania; Department of Chemistry and Bioengineering, Vilnius Gediminas Technical University, Vilnius, Lithuania.

ABSTRACT
Several natural and synthetic flavone derivatives have been reported to inhibit formation of amyloid fibrils or to remodel existing fibrils. These studies suggest that the numbers and positions of hydroxyl groups on the flavone rings determine their effectiveness as amyloid inhibitors. In many studies the primary method for determining the effectiveness of inhibition is measuring Thioflavin T (ThT) fluorescence. This method demonstrably results in a number of false positives for inhibition. We studied the effects of 265 commercially available flavone derivatives on insulin fibril formation. We enhanced the effectiveness of ThT fluorescence measurements by fitting kinetic curves to obtain halftime of aggregation (t50). Maximal values of ThT fluorescence varied two fold or more in one third of all cases, but this did not correlate with changes in t50. Changes in t50 values were more accurate measures of inhibition of amyloid formation. We showed that without a change in an assay, but just by observing complete kinetic curves it is possible to eliminate numbers of false positive and sometimes even false negative results. Examining the data from all 265 flavones we confirmed previous observations that identified the importance of hydroxyl groups for inhibition. Our evidence suggests the importance of hydroxyl groups at locations 5, 6, 7, and 4', and the absence of a hydroxyl group at location 3, for inhibiting amyloid formation. However, the main conclusion is that the positions are not additive. The structures and their effects must be thought of in the context of the whole molecule.

No MeSH data available.


Related in: MedlinePlus