Evaluation of Tc-99m-MAMA-chrysamine G as an in vivo probe for amyloidosis

To date, systemic amyloidosis is diagnosed histologically using Congo red s taining or in vivo using iodine-123 labelled serum amyloid P component (I-1 23-SAP) scintigraphy. We developed Tc-99m-MAMA-CG, a Tc-99m-labelled deriva tive of the lipophilic Congo red analogue chrysamine G (CG), as a possible alternative to I-123-SAP. In vivo Tc-99m-MAMA-CG M-CG scintigraphy, perform ed in chickens with spontaneous joint amyloidosis, resulted as soon.as 10 m in after injection in scintigraphic images showing uptake of activity in am yloid-loaded organs (liver, joints). One of these chickens was studied also with I-123-SAP resulting in scintigraphic images revealing I-123-SAP bindi ng to amyloid deposits in the liver. However, up to 11 h after injection no radioactivity was visible in the amyloid positive joints. In vitro autorad iography, performed on sections of chicken joints with Enterococcus faecali s induced amyloid arthropathy (chjAA), demonstrated the failure of Tc-99m-M MA-CG to bind significantly to amyloid deposits in the presence of 10 muM C ongo red. The specificity of Tc-99m-MAMA-CG localisation was also establish ed by the absence of Tc-99m-MAMA-CG binding in non-amyloidotic organs in vi tro and in vivo, Tc-99m-MAMA-CG did not show any sign of acute toxicity. Th ese findings establish the usefulness of Tc-99m-MAMA-CG as a non-invasive i n vivo diagnostic probe in chickens with amyloid arthropathy and suggest th at it may also be applicable to human amyloidosis.