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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

Impact of Scutellarein on insulin fibril elongation.
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pone.0121231.g006: Impact of Scutellarein on insulin fibril elongation.

Mentions: Nucleated growth mechanism of fibril formation assumes two main processes—nucleation and elongation. Relative t50 values obtained in our experiments are mostly influenced by changes in times of nucleation. To test if the rate of insulin fibril elongation can be slowed down, we did additional seeding experiments in presence of the five best-inhibiting flavones. Fig. 6 shows normalized curves of seeded insulin aggregation in the absence and presence of 1 mM Scutellarein. It clearly shows that Scutellarein inhibits fibril elongation; however it is not slowed down as many times as nucleation. In fact, calculated relative rates of elongation in the presence of Scutellarein, Luteolin, and 7,8,2’-trihydroxyflavone were the same (v = 0.44 ± 0.07), in the presence of Gossypetin aggregation was a bit slower (v = 0.40 ± 0.07), and 3,6,2’,4’,5’-pentahydroxyflavone was found to be the weakest inhibitor of elongation (v = 0.72 ± 0.13). In all cases nucleation was inhibited more strongly than elongation, suggesting that these flavones affect monomers or intermediates rather than mature fibrils.


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

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

Impact of Scutellarein on insulin fibril elongation.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0121231.g006: Impact of Scutellarein on insulin fibril elongation.
Mentions: Nucleated growth mechanism of fibril formation assumes two main processes—nucleation and elongation. Relative t50 values obtained in our experiments are mostly influenced by changes in times of nucleation. To test if the rate of insulin fibril elongation can be slowed down, we did additional seeding experiments in presence of the five best-inhibiting flavones. Fig. 6 shows normalized curves of seeded insulin aggregation in the absence and presence of 1 mM Scutellarein. It clearly shows that Scutellarein inhibits fibril elongation; however it is not slowed down as many times as nucleation. In fact, calculated relative rates of elongation in the presence of Scutellarein, Luteolin, and 7,8,2’-trihydroxyflavone were the same (v = 0.44 ± 0.07), in the presence of Gossypetin aggregation was a bit slower (v = 0.40 ± 0.07), and 3,6,2’,4’,5’-pentahydroxyflavone was found to be the weakest inhibitor of elongation (v = 0.72 ± 0.13). In all cases nucleation was inhibited more strongly than elongation, suggesting that these flavones affect monomers or intermediates rather than mature fibrils.

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