Evaluation of ^99mTc-MAMA-chrysamine G as an in vivo probe for amyloidosis

Abstract

To date, systemic amyloidosis is diagnosed histologi-cally using Congo red staining or in vivo using iodine-123 labelled serum amyloid P component (¹²³1-SAP) scintigra-phy. We developed ^99mTc-MAMA-CG, a ^99mTc-labelled derivative of the lipophilic Congo red analogue chtysamine G (CG), as a possible alternative to ¹²³1-SAP. In vivo ^99mTc-MAMA-CG scintigraphy, performed in chickens with spontaneous joint amyloidosis, resulted as soon as 10 min after injection in scintigraphic images showing uptake of activity in amyloid-loaded organs (liver, joints). One of these chickens was studied also with ¹²³I-SAP resulting in scintigraphic images revealing ¹²³1-SAP binding to amyloid deposits in the liver. However, up to II h after injection no radioactivity was visible in the amyloid positive joints. In vitro autoradiography, performed on sections of chicken joints with Enterococcus faecalis induced amyloid arthropathy (chjAA), demonstrated the failure of ^99mTc-MAMA-CG to bind significantly to amyloid deposits in the presence of 10M Congo red. The speclficity of ^99mTc-MAMA-CG localisation was also established by the absence of ^99mTc-MAMA-CG binding in non-amyloidotic organs in vitro and in vivo. ^99mTc-MAMA-CG did not show any sign of acute toxicity. These findings establish the usefulness of ^99mTc-MAMA-CG as a non-invusive in vivo diagnostic probe in chickens with amyloid arthropathy and suggest that it may also be applicable to human amyloidosis.

Key Words:

• Congo red
• Chrysamine G
• amyloid
• SPECT
• technetium-99m
• ¹²³I-SAP
• in vivo probe