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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 inhibition of Aβ1–40 monomer aggregation on aggregate size distribution. Aβ1–40 monomer aggregations were performed as in Figure 1 for 20 μM Aβ1–40 monomer in the presence of 0 μM (panel B, control), 40 μM (panel C), or 80 μM (panel D) BSA. In addition, 80 μM BSA was subjected to aggregation conditions in the absence of Aβ1–40 monomer (panel A). DLS was employed to determine RH distributions. Results are presented as intensity-weighted histograms derived from data regularization with Dynamics Software (Wyatt Technology). Results are representative of two independent experiments.
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Figure 4: Effect of BSA inhibition of Aβ1–40 monomer aggregation on aggregate size distribution. Aβ1–40 monomer aggregations were performed as in Figure 1 for 20 μM Aβ1–40 monomer in the presence of 0 μM (panel B, control), 40 μM (panel C), or 80 μM (panel D) BSA. In addition, 80 μM BSA was subjected to aggregation conditions in the absence of Aβ1–40 monomer (panel A). DLS was employed to determine RH distributions. Results are presented as intensity-weighted histograms derived from data regularization with Dynamics Software (Wyatt Technology). Results are representative of two independent experiments.

Mentions: DLS was employed to evaluate RH for aggregates formed in the presence and absence of BSA as well as BSA subjected to aggregation conditions in the absence of Aβ1–40 monomer. Aβ1–40 monomer incubated in the absence of BSA yielded aggregates with an RH of 140 nm (Figure 4B) that produced, as expected, a moderate but pronounced increase in endothelial adhesion (Figure 3). While addition of BSA at a concentration 2-fold in excess of Aβ1–40 monomer yielded less aggregated peptide (Figure 1), these aggregates exhibited a smaller RH of 34 nm (Figure 4C) and were thus capable of eliciting higher physiological activity (Figure 3). In contrast, Aβ1–40 aggregations performed in the presence of a 4-fold excess of BSA yielded little aggregated peptide (Figure 1) and exhibited a hydrodynamic radius of 3.4 nm (Figure 4D). This peak may be ascribed to BSA, as an identical peak was observed when BSA was subjected to aggregation conditions in the absence of Aβ1–40 monomer (Figure 4A). Due to the exponential relationship between scattered light and aggregate size, this BSA peak would obscure detection of Aβ monomer or aggregates exhibiting RH smaller than 3.4 nm. Thus, it may be deduced that following aggregation in the presence of a 4-fold excess of BSA, Aβ1–40 exists primarily as monomeric or oligomeric structures. However, a lower intensity peak at 22 nm (Figure 4D) indicates the presence of a small population of soluble aggregates with high physiological activity, which likely accounts for the modest increase in adhesion observed for this Aβ1–40 aggregate preparation (Figure 3). Together, these results demonstrate that the enhanced physiological activity observed for partially inhibited monomer aggregations correlates with an increase in the population of small soluble Aβ1–40 aggregates.


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 inhibition of Aβ1–40 monomer aggregation on aggregate size distribution. Aβ1–40 monomer aggregations were performed as in Figure 1 for 20 μM Aβ1–40 monomer in the presence of 0 μM (panel B, control), 40 μM (panel C), or 80 μM (panel D) BSA. In addition, 80 μM BSA was subjected to aggregation conditions in the absence of Aβ1–40 monomer (panel A). DLS was employed to determine RH distributions. Results are presented as intensity-weighted histograms derived from data regularization with Dynamics Software (Wyatt Technology). Results are representative of two independent experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Effect of BSA inhibition of Aβ1–40 monomer aggregation on aggregate size distribution. Aβ1–40 monomer aggregations were performed as in Figure 1 for 20 μM Aβ1–40 monomer in the presence of 0 μM (panel B, control), 40 μM (panel C), or 80 μM (panel D) BSA. In addition, 80 μM BSA was subjected to aggregation conditions in the absence of Aβ1–40 monomer (panel A). DLS was employed to determine RH distributions. Results are presented as intensity-weighted histograms derived from data regularization with Dynamics Software (Wyatt Technology). Results are representative of two independent experiments.
Mentions: DLS was employed to evaluate RH for aggregates formed in the presence and absence of BSA as well as BSA subjected to aggregation conditions in the absence of Aβ1–40 monomer. Aβ1–40 monomer incubated in the absence of BSA yielded aggregates with an RH of 140 nm (Figure 4B) that produced, as expected, a moderate but pronounced increase in endothelial adhesion (Figure 3). While addition of BSA at a concentration 2-fold in excess of Aβ1–40 monomer yielded less aggregated peptide (Figure 1), these aggregates exhibited a smaller RH of 34 nm (Figure 4C) and were thus capable of eliciting higher physiological activity (Figure 3). In contrast, Aβ1–40 aggregations performed in the presence of a 4-fold excess of BSA yielded little aggregated peptide (Figure 1) and exhibited a hydrodynamic radius of 3.4 nm (Figure 4D). This peak may be ascribed to BSA, as an identical peak was observed when BSA was subjected to aggregation conditions in the absence of Aβ1–40 monomer (Figure 4A). Due to the exponential relationship between scattered light and aggregate size, this BSA peak would obscure detection of Aβ monomer or aggregates exhibiting RH smaller than 3.4 nm. Thus, it may be deduced that following aggregation in the presence of a 4-fold excess of BSA, Aβ1–40 exists primarily as monomeric or oligomeric structures. However, a lower intensity peak at 22 nm (Figure 4D) indicates the presence of a small population of soluble aggregates with high physiological activity, which likely accounts for the modest increase in adhesion observed for this Aβ1–40 aggregate preparation (Figure 3). Together, these results demonstrate that the enhanced physiological activity observed for partially inhibited monomer aggregations correlates with an increase in the population of small soluble Aβ1–40 aggregates.

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