In vivo molecular imaging of peripheral amyloidosis using heparin-binding peptides

Abstract

Heparan sulfate proteoglycans (HSPGs) are ubiquitous components of pathologic amyloid deposits in the organs of patients with disorders such as Alzheimer's disease or systemic light chain (AL) or reactive (AA) amyloidosis. Molecular imaging methods for early detection are limited and generally unavailable outside the United Kingdom. Therefore, there is an urgent need to develop novel, specific amyloidophilic radiotracers for imaging to assist in diagnosis, prognostication, and monitoring response to therapy. Amyloid-associated HSPG can be differentiated from HSPG found in surrounding healthy cells and tissues by the preferential binding of certain HS-reactive single chain variable fragments and therefore, represents a biomarker that can be targeted specifically with appropriate reagents. Using a murine model of AA amyloidosis, we have examined the in vivo amyloid reactivity of seven heparin-binding peptides by using single photon emission and X-ray computed tomographic imaging, microautoradiography, and tissue biodistribution measurements. All of the peptides bound amyloid deposits within 1 h post-injection, but the extent of the reactivity differed widely, which was evidenced by image quality and grain density in autoradiographs. One radiolabeled peptide bound specifically to murine AA amyloid in the liver, spleen, kidney, adrenal, heart, and pancreas with such avidity that it was observed in single photon emission tomography images as late as 24 h post-injection. In addition, a biotinylated form of this peptide was shown histochemically to bind human AA, ALκ, ALλ, transthyretin amyloidosis (ATTR), and Aβ amyloid deposits in tissue sections. These basic heparin-binding peptides recognize murine and human amyloid deposits in both in vivo and ex vivo tissues and therefore, have potential as radiotracers for the noninvasive molecular imaging of amyloid deposits in situ.

Power of metabolomics in diagnosis and biomarker discovery of hepatocellular carcinoma

“…A number of marker metabolites for diagnosis and prognosis of HCC have been reported. 29,30 A UPLC-MS-based metabolomics approach has been used to characterize serum profiles from HCC, liver cirrhosis (LC), and healthy subjects, and the accuracy of UPLC-MS profiles and AFP levels were compared for their use in HCC diagnosis. 31 Thirteen potential biomarkers were identified that suggest there were significant disturbances of key metabolic pathways in HCC patients.…”

Biotechnologically engineered protein binders for applications in amyloid diseases

“…B10 shares these features with several biotechnologically generated amyloid-binding peptides, including p5 and D3 [24,25], as well as naturally occurring amyloidbinding proteins and pattern recognition receptors, such as serum amyloid P component, scavenger receptor, and receptor for advanced glycation end products. These amyloid-binding proteins all have positively charged ligand-binding sites, indicating that fibril recognition is primarily dependent on electrostatic interactions [32].…”

“…Examples are the p5 peptide, which was obtained by phage-display selection against glycosaminoglycan (GAG) amyloid secondary components [24], as well as the D1 and D3 peptides, which were generated through Dmirror-image phage display [25]. This elegant method uses biotinylated D-Ab(1-42) peptide as a target such that conversion of the selected peptide into its D-amino acid counterpart enables binding to the natural L-amino acid Ab and also provides the general advantages of D-peptides.…”

Amyloid and inflammation

“…Probes for determining the in vivo amyloid load, and for monitoring treatment, include SAP, anti-AA antibodies, and HPSG ligands, in each instance controlling for possible cross-reactivity with circulating and soluble precursors in normal tissue and contiguous to fibrillar deposits (3,5,16,17). Studies carried out during SAA triggering by inflammatory stimuli and amyloid induction have shown an ∼90-min half-life and a large HDL APR SAA pool as a result of increased hepatic synthesis, only 0.01% of which is deposited in the mouse spleen over a 24-h period (18).…”