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Inhibition of insulin fibrillation by osmolytes: Mechanistic insights.

Choudhary S, Kishore N, Hosur RV - Sci Rep (2015)

Bottom Line: We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin.Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation.Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50-250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range.

View Article: PubMed Central - PubMed

Affiliation: UM-DAE Centre for Excellence in Basic Sciences, Mumbai University Campus, Mumbai 400098, India.

ABSTRACT
We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin. Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation. Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50-250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range. The enthalpies of interaction at various stages of fibrillation process have suggested that the preferential exclusion of the osmolyte and its polar interaction with the protein are important in inhibition. The results indicate that the osmolytes are most effective when added prior to the elongation stage of fibrillation. These observations have significant biological implications, since insulin fibrillation is known to cause injection amyloidosis and our data may help in designing lead drug molecules and development of potential therapeutic strategies.

No MeSH data available.


Related in: MedlinePlus

Chemical structures of osmolytes (A) betaine, (B) citrulline, (c) proline and (d) sorbitol.
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f1: Chemical structures of osmolytes (A) betaine, (B) citrulline, (c) proline and (d) sorbitol.

Mentions: There have been several reports in the literature on inhibition of fibrillation of proteins, in general4567141516171819, and these include the use of different osmolytes1213141516171819. Several disaccharides such as maltose, sucrose and trehalose have also been reported to increase the nucleation period of insulin fibrillation at a concentration of ~300 mM45. Recently, the inhibitory effects of different quinones on insulin fibrillation have also been reported46. However, an understanding of the mechanism of the inhibition process by these agents in terms of intermolecular interactions and associated energies, which is crucial for developing effective drugs, is still very much lacking. In this background, the current work is focussed on searching for effective osmolytes which would inhibit insulin fibrillation, on one hand, and on understanding the mechanism of the same, on the other. For this purpose we have chosen the osmolytes betaine, citrulline, proline and sorbitol (Fig. 1), which have different physical characteristics with regard to polarity, charge distribution, H-bonding abilities etc. A combination of spectroscopic, microscopic and calorimetric techniques has been used to derive structural and thermodynamic information. Isothermal titration calorimetry results provided valuable insights into the mechanism of inhibition of fibrillation and indicated contributions from direct interaction between insulin and the osmolytes. These findings will be useful in providing leads to synthetic chemists to design suitable inhibitors which can act against amyloid formation at low concentrations.


Inhibition of insulin fibrillation by osmolytes: Mechanistic insights.

Choudhary S, Kishore N, Hosur RV - Sci Rep (2015)

Chemical structures of osmolytes (A) betaine, (B) citrulline, (c) proline and (d) sorbitol.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663473&req=5

f1: Chemical structures of osmolytes (A) betaine, (B) citrulline, (c) proline and (d) sorbitol.
Mentions: There have been several reports in the literature on inhibition of fibrillation of proteins, in general4567141516171819, and these include the use of different osmolytes1213141516171819. Several disaccharides such as maltose, sucrose and trehalose have also been reported to increase the nucleation period of insulin fibrillation at a concentration of ~300 mM45. Recently, the inhibitory effects of different quinones on insulin fibrillation have also been reported46. However, an understanding of the mechanism of the inhibition process by these agents in terms of intermolecular interactions and associated energies, which is crucial for developing effective drugs, is still very much lacking. In this background, the current work is focussed on searching for effective osmolytes which would inhibit insulin fibrillation, on one hand, and on understanding the mechanism of the same, on the other. For this purpose we have chosen the osmolytes betaine, citrulline, proline and sorbitol (Fig. 1), which have different physical characteristics with regard to polarity, charge distribution, H-bonding abilities etc. A combination of spectroscopic, microscopic and calorimetric techniques has been used to derive structural and thermodynamic information. Isothermal titration calorimetry results provided valuable insights into the mechanism of inhibition of fibrillation and indicated contributions from direct interaction between insulin and the osmolytes. These findings will be useful in providing leads to synthetic chemists to design suitable inhibitors which can act against amyloid formation at low concentrations.

Bottom Line: We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin.Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation.Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50-250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range.

View Article: PubMed Central - PubMed

Affiliation: UM-DAE Centre for Excellence in Basic Sciences, Mumbai University Campus, Mumbai 400098, India.

ABSTRACT
We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin. Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation. Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50-250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range. The enthalpies of interaction at various stages of fibrillation process have suggested that the preferential exclusion of the osmolyte and its polar interaction with the protein are important in inhibition. The results indicate that the osmolytes are most effective when added prior to the elongation stage of fibrillation. These observations have significant biological implications, since insulin fibrillation is known to cause injection amyloidosis and our data may help in designing lead drug molecules and development of potential therapeutic strategies.

No MeSH data available.


Related in: MedlinePlus