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A binding-site barrier affects imaging efficiency of high affinity amyloid-reactive peptide radiotracers in vivo.

Wall JS, Williams A, Richey T, Stuckey A, Huang Y, Wooliver C, Macy S, Heidel E, Gupta N, Lee A, Rader B, Martin EB, Kennel SJ - PLoS ONE (2013)

Bottom Line: Amyloid is a complex pathology associated with a growing number of diseases including Alzheimer's disease, type 2 diabetes, rheumatoid arthritis, and myeloma.The p5 peptide was posited to bind effectively to amyloid deposits, relative to similarly charged polybasic heparin-reactive peptides, because it adopted a polar α helix secondary structure.The p5R peptide had higher affinity for amyloid and visualized AA amyloid in mice by using SPECT/CT imaging; however, the microdistribution, as evidenced in micro-autoradiographs, was dramatically altered relative to the p5 peptide due to its increased affinity and a resultant "binding site barrier" effect.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, University of Tennessee Graduate School of Medicine, Knoxville, Tennessee, USA. jwall@utmck.edu

ABSTRACT
Amyloid is a complex pathology associated with a growing number of diseases including Alzheimer's disease, type 2 diabetes, rheumatoid arthritis, and myeloma. The distribution and extent of amyloid deposition in body organs establishes the prognosis and can define treatment options; therefore, determining the amyloid load by using non-invasive molecular imaging is clinically important. We have identified a heparin-binding peptide designated p5 that, when radioiodinated, was capable of selectively imaging systemic visceral AA amyloidosis in a murine model of the disease. The p5 peptide was posited to bind effectively to amyloid deposits, relative to similarly charged polybasic heparin-reactive peptides, because it adopted a polar α helix secondary structure. We have now synthesized a variant, p5R, in which the 8 lysine amino acids of p5 have been replaced with arginine residues predisposing the peptide toward the α helical conformation in an effort to enhance the reactivity of the peptide with the amyloid substrate. The p5R peptide had higher affinity for amyloid and visualized AA amyloid in mice by using SPECT/CT imaging; however, the microdistribution, as evidenced in micro-autoradiographs, was dramatically altered relative to the p5 peptide due to its increased affinity and a resultant "binding site barrier" effect. These data suggest that radioiodinated peptide p5R may be optimal for the in vivo detection of discreet, perivascular amyloid, as found in the brain and pancreatic vasculature, by using molecular imaging techniques; however, peptide p5, due to its increased penetration, may yield more quantitative imaging of expansive tissue amyloid deposits.

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Peptides p5 and p5R predicted to adopt an α-helical secondary structure.Representations of peptides p5 with lysine side chains (blue) and p5R with arginine residues (red) overlayed showing α-helix backbone (upper) and as surface renderings. Models were predicted using iTASSER, and PDB files were rendered using DeepView/Swiss-PdbViewer v4.0.4 (www.expasy.org/spdbv/).
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pone-0066181-g001: Peptides p5 and p5R predicted to adopt an α-helical secondary structure.Representations of peptides p5 with lysine side chains (blue) and p5R with arginine residues (red) overlayed showing α-helix backbone (upper) and as surface renderings. Models were predicted using iTASSER, and PDB files were rendered using DeepView/Swiss-PdbViewer v4.0.4 (www.expasy.org/spdbv/).

Mentions: Peptides p5 and p5R each have 31 amino acids, a net charge of +8 and a pI of >10 (Table 1). The secondary structure was predicted based on the database-matching algorithms by using the iTASSER software [26], [27] to adopt an α-helical secondary structure (Fig. 1); however, the AGADIRms helix/coil transition algorithm [28], [29] predicted only 6.5% and 15.9% α-helix content for p5 and p5R, respectively (Table 1). Both peptides contain the heptad repeat (BxxBxxx) of amino acids with the basic residues (B), Lys and Arg, at positions a and d in p5 and p5R, respectively, which results in a nearly linear array of charge along a single face of the alpha helix (Figs. 1 A–C). When overlaid, the predicted positions of the basic amino acid side chains were similar for p5 and p5R (Fig.1 D).


A binding-site barrier affects imaging efficiency of high affinity amyloid-reactive peptide radiotracers in vivo.

Wall JS, Williams A, Richey T, Stuckey A, Huang Y, Wooliver C, Macy S, Heidel E, Gupta N, Lee A, Rader B, Martin EB, Kennel SJ - PLoS ONE (2013)

Peptides p5 and p5R predicted to adopt an α-helical secondary structure.Representations of peptides p5 with lysine side chains (blue) and p5R with arginine residues (red) overlayed showing α-helix backbone (upper) and as surface renderings. Models were predicted using iTASSER, and PDB files were rendered using DeepView/Swiss-PdbViewer v4.0.4 (www.expasy.org/spdbv/).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672142&req=5

pone-0066181-g001: Peptides p5 and p5R predicted to adopt an α-helical secondary structure.Representations of peptides p5 with lysine side chains (blue) and p5R with arginine residues (red) overlayed showing α-helix backbone (upper) and as surface renderings. Models were predicted using iTASSER, and PDB files were rendered using DeepView/Swiss-PdbViewer v4.0.4 (www.expasy.org/spdbv/).
Mentions: Peptides p5 and p5R each have 31 amino acids, a net charge of +8 and a pI of >10 (Table 1). The secondary structure was predicted based on the database-matching algorithms by using the iTASSER software [26], [27] to adopt an α-helical secondary structure (Fig. 1); however, the AGADIRms helix/coil transition algorithm [28], [29] predicted only 6.5% and 15.9% α-helix content for p5 and p5R, respectively (Table 1). Both peptides contain the heptad repeat (BxxBxxx) of amino acids with the basic residues (B), Lys and Arg, at positions a and d in p5 and p5R, respectively, which results in a nearly linear array of charge along a single face of the alpha helix (Figs. 1 A–C). When overlaid, the predicted positions of the basic amino acid side chains were similar for p5 and p5R (Fig.1 D).

Bottom Line: Amyloid is a complex pathology associated with a growing number of diseases including Alzheimer's disease, type 2 diabetes, rheumatoid arthritis, and myeloma.The p5 peptide was posited to bind effectively to amyloid deposits, relative to similarly charged polybasic heparin-reactive peptides, because it adopted a polar α helix secondary structure.The p5R peptide had higher affinity for amyloid and visualized AA amyloid in mice by using SPECT/CT imaging; however, the microdistribution, as evidenced in micro-autoradiographs, was dramatically altered relative to the p5 peptide due to its increased affinity and a resultant "binding site barrier" effect.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, University of Tennessee Graduate School of Medicine, Knoxville, Tennessee, USA. jwall@utmck.edu

ABSTRACT
Amyloid is a complex pathology associated with a growing number of diseases including Alzheimer's disease, type 2 diabetes, rheumatoid arthritis, and myeloma. The distribution and extent of amyloid deposition in body organs establishes the prognosis and can define treatment options; therefore, determining the amyloid load by using non-invasive molecular imaging is clinically important. We have identified a heparin-binding peptide designated p5 that, when radioiodinated, was capable of selectively imaging systemic visceral AA amyloidosis in a murine model of the disease. The p5 peptide was posited to bind effectively to amyloid deposits, relative to similarly charged polybasic heparin-reactive peptides, because it adopted a polar α helix secondary structure. We have now synthesized a variant, p5R, in which the 8 lysine amino acids of p5 have been replaced with arginine residues predisposing the peptide toward the α helical conformation in an effort to enhance the reactivity of the peptide with the amyloid substrate. The p5R peptide had higher affinity for amyloid and visualized AA amyloid in mice by using SPECT/CT imaging; however, the microdistribution, as evidenced in micro-autoradiographs, was dramatically altered relative to the p5 peptide due to its increased affinity and a resultant "binding site barrier" effect. These data suggest that radioiodinated peptide p5R may be optimal for the in vivo detection of discreet, perivascular amyloid, as found in the brain and pancreatic vasculature, by using molecular imaging techniques; however, peptide p5, due to its increased penetration, may yield more quantitative imaging of expansive tissue amyloid deposits.

Show MeSH
Related in: MedlinePlus