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Soluble aggregates of the amyloid-beta peptide are trapped by serum albumin to enhance amyloid-beta activation of endothelial cells.

Reyes Barcelo AA, Gonzalez-Velasquez FJ, Moss MA - J Biol Eng (2009)

Bottom Line: Inhibition of Abeta1-40 monomer aggregation is observed down to stoichiometric ratios with partial inhibition leading to an increase in the population of small soluble aggregates.These results demonstrate that inhibitors of Abeta self-assembly have the potential to trap small soluble aggregates resulting in an elevation rather than a reduction of cellular responses.These findings provide further support that small soluble aggregates possess high levels of physiological activity and underscore the importance of resolving the effect of Abeta aggregation inhibitors on aggregate size.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, University of South Carolina, 2C02 Swearingen Engineering Center, Columbia, South Carolina 29208, USA. Adriana.ReyesBarcelo@kraft.com

ABSTRACT

Background: Self-assembly of the amyloid-beta peptide (Abeta) has been implicated in the pathogenesis of Alzheimer's disease (AD). As a result, synthetic molecules capable of inhibiting Abeta self-assembly could serve as therapeutic agents and endogenous molecules that modulate Abeta self-assembly may influence disease progression. However, increasing evidence implicating a principal pathogenic role for small soluble Abeta aggregates warns that inhibition at intermediate stages of Abeta self-assembly may prove detrimental. Here, we explore the inhibition of Abeta1-40 self-assembly by serum albumin, the most abundant plasma protein, and the influence of this inhibition on Abeta1-40 activation of endothelial cells for monocyte adhesion.

Results: It is demonstrated that serum albumin is capable of inhibiting in a dose-dependent manner both the formation of Abeta1-40 aggregates from monomeric peptide and the ongoing growth of Abeta1-40 fibrils. Inhibition of fibrillar Abeta1-40 aggregate growth is observed at substoichiometric concentrations, suggesting that serum albumin recognizes aggregated forms of the peptide to prevent monomer addition. Inhibition of Abeta1-40 monomer aggregation is observed down to stoichiometric ratios with partial inhibition leading to an increase in the population of small soluble aggregates. Such partial inhibition of Abeta1-40 aggregation leads to an increase in the ability of resulting aggregates to activate endothelial cells for adhesion of monocytes. In contrast, Abeta1-40 activation of endothelial cells for monocyte adhesion is reduced when more complete inhibition is observed.

Conclusion: These results demonstrate that inhibitors of Abeta self-assembly have the potential to trap small soluble aggregates resulting in an elevation rather than a reduction of cellular responses. These findings provide further support that small soluble aggregates possess high levels of physiological activity and underscore the importance of resolving the effect of Abeta aggregation inhibitors on aggregate size.

No MeSH data available.


Related in: MedlinePlus

Effect of BSA on Aβ1–40 monomer aggregation. Aβ1–40 monomer was diluted to 20 μM in buffer containing 150 mM NaCl and 40 mM Tris-HCl (pH 8.0) and incubated alone (control, [white circle]) or in the presence of 20 μM [black square], 40 μM [black triangle], or 80 μM [black diamond] BSA. Aggregation of monomer was induced by continuous agitation and monitored using thioflavin T fluorescence. Results are representative of three independent experiments.
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Figure 1: Effect of BSA on Aβ1–40 monomer aggregation. Aβ1–40 monomer was diluted to 20 μM in buffer containing 150 mM NaCl and 40 mM Tris-HCl (pH 8.0) and incubated alone (control, [white circle]) or in the presence of 20 μM [black square], 40 μM [black triangle], or 80 μM [black diamond] BSA. Aggregation of monomer was induced by continuous agitation and monitored using thioflavin T fluorescence. Results are representative of three independent experiments.

Mentions: As shown in Figure 1, 20 μM Aβ1–40 monomer incubated in the absence of BSA exhibited the characteristic lag, indicative of nucleus formation, followed by rapid aggregate growth and concluding with a plateau as equilibrium was reached. BSA-induced changes in Aβ1–40 monomer aggregation were assessed by evaluating both extension of the lag time and reduction of the plateau fluorescence level. When BSA was present at equimolar concentrations with Aβ1–40 monomer, the lag time was nearly doubled (Figure 1, Table 1), suggesting that BSA can intervene at early points along the self-assembly pathway. As the concentration of BSA was increased to a level 2-fold in excess of Aβ1–40 monomer, the lag time was further extended by almost 2.5-fold and the equilibrium plateau was reduced, indicating that at higher concentrations BSA can reduce the quantity of aggregated Aβ. When Aβ1–40 monomer was agitated in the presence of a 4-fold excess of BSA, nearly complete inhibition was observed over the 4.5 h period. BSA subjected to aggregation conditions in the absence of Aβ1–40 monomer exhibited negligible change in thioflavin T fluorescence. These results illustrate the ability of BSA to abrogate Aβ1–40 monomer aggregation at concentrations in excess of Aβ1–40 monomer and further demonstrate the dose-dependent nature of this inhibition as BSA concentrations approach stoichiometric ratios with Aβ1–40.


Soluble aggregates of the amyloid-beta peptide are trapped by serum albumin to enhance amyloid-beta activation of endothelial cells.

Reyes Barcelo AA, Gonzalez-Velasquez FJ, Moss MA - J Biol Eng (2009)

Effect of BSA on Aβ1–40 monomer aggregation. Aβ1–40 monomer was diluted to 20 μM in buffer containing 150 mM NaCl and 40 mM Tris-HCl (pH 8.0) and incubated alone (control, [white circle]) or in the presence of 20 μM [black square], 40 μM [black triangle], or 80 μM [black diamond] BSA. Aggregation of monomer was induced by continuous agitation and monitored using thioflavin T fluorescence. Results are representative of three independent experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2683804&req=5

Figure 1: Effect of BSA on Aβ1–40 monomer aggregation. Aβ1–40 monomer was diluted to 20 μM in buffer containing 150 mM NaCl and 40 mM Tris-HCl (pH 8.0) and incubated alone (control, [white circle]) or in the presence of 20 μM [black square], 40 μM [black triangle], or 80 μM [black diamond] BSA. Aggregation of monomer was induced by continuous agitation and monitored using thioflavin T fluorescence. Results are representative of three independent experiments.
Mentions: As shown in Figure 1, 20 μM Aβ1–40 monomer incubated in the absence of BSA exhibited the characteristic lag, indicative of nucleus formation, followed by rapid aggregate growth and concluding with a plateau as equilibrium was reached. BSA-induced changes in Aβ1–40 monomer aggregation were assessed by evaluating both extension of the lag time and reduction of the plateau fluorescence level. When BSA was present at equimolar concentrations with Aβ1–40 monomer, the lag time was nearly doubled (Figure 1, Table 1), suggesting that BSA can intervene at early points along the self-assembly pathway. As the concentration of BSA was increased to a level 2-fold in excess of Aβ1–40 monomer, the lag time was further extended by almost 2.5-fold and the equilibrium plateau was reduced, indicating that at higher concentrations BSA can reduce the quantity of aggregated Aβ. When Aβ1–40 monomer was agitated in the presence of a 4-fold excess of BSA, nearly complete inhibition was observed over the 4.5 h period. BSA subjected to aggregation conditions in the absence of Aβ1–40 monomer exhibited negligible change in thioflavin T fluorescence. These results illustrate the ability of BSA to abrogate Aβ1–40 monomer aggregation at concentrations in excess of Aβ1–40 monomer and further demonstrate the dose-dependent nature of this inhibition as BSA concentrations approach stoichiometric ratios with Aβ1–40.

Bottom Line: Inhibition of Abeta1-40 monomer aggregation is observed down to stoichiometric ratios with partial inhibition leading to an increase in the population of small soluble aggregates.These results demonstrate that inhibitors of Abeta self-assembly have the potential to trap small soluble aggregates resulting in an elevation rather than a reduction of cellular responses.These findings provide further support that small soluble aggregates possess high levels of physiological activity and underscore the importance of resolving the effect of Abeta aggregation inhibitors on aggregate size.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, University of South Carolina, 2C02 Swearingen Engineering Center, Columbia, South Carolina 29208, USA. Adriana.ReyesBarcelo@kraft.com

ABSTRACT

Background: Self-assembly of the amyloid-beta peptide (Abeta) has been implicated in the pathogenesis of Alzheimer's disease (AD). As a result, synthetic molecules capable of inhibiting Abeta self-assembly could serve as therapeutic agents and endogenous molecules that modulate Abeta self-assembly may influence disease progression. However, increasing evidence implicating a principal pathogenic role for small soluble Abeta aggregates warns that inhibition at intermediate stages of Abeta self-assembly may prove detrimental. Here, we explore the inhibition of Abeta1-40 self-assembly by serum albumin, the most abundant plasma protein, and the influence of this inhibition on Abeta1-40 activation of endothelial cells for monocyte adhesion.

Results: It is demonstrated that serum albumin is capable of inhibiting in a dose-dependent manner both the formation of Abeta1-40 aggregates from monomeric peptide and the ongoing growth of Abeta1-40 fibrils. Inhibition of fibrillar Abeta1-40 aggregate growth is observed at substoichiometric concentrations, suggesting that serum albumin recognizes aggregated forms of the peptide to prevent monomer addition. Inhibition of Abeta1-40 monomer aggregation is observed down to stoichiometric ratios with partial inhibition leading to an increase in the population of small soluble aggregates. Such partial inhibition of Abeta1-40 aggregation leads to an increase in the ability of resulting aggregates to activate endothelial cells for adhesion of monocytes. In contrast, Abeta1-40 activation of endothelial cells for monocyte adhesion is reduced when more complete inhibition is observed.

Conclusion: These results demonstrate that inhibitors of Abeta self-assembly have the potential to trap small soluble aggregates resulting in an elevation rather than a reduction of cellular responses. These findings provide further support that small soluble aggregates possess high levels of physiological activity and underscore the importance of resolving the effect of Abeta aggregation inhibitors on aggregate size.

No MeSH data available.


Related in: MedlinePlus