Recombinant versus natural human In-111-beta(2)-microglobulin for scintigraphic detection of A beta(2)m amyloid in dialysis patients

Background We previously introduced scintigraphy with I-131-labeled beta(2) -microglobulin (beta(2)m), purified from uremic hemofiltrate, that is, "nat ural" beta(2)m, to specifically detect beta(2)m-associated amyloidosis (A b eta(2)m) in hemodialysis (HD) patients. Methods. To improve the safety and resolution of the scan, we covalently bo und the chelator diethylenetriaminepentaacetic acid to natural beta(2)m to allow radiolabeling with In-111. In a second step, we generated and evaluat ed the usage of recombinant human beta(2)m (rh beta(2)m) for scintigraphy. Results. Using natural In-111-labeled beta(2)m, eight patients on HD for 0 to 17 years, without evidence of A beta(2)m, were scanned. Whole-body scint igraphy at 48 to 72 hours postinjection revealed no significant tracer accu mulation over joint regions. In contrast, nine patients on HD for 10 to 21 years with clinical, radiological, or histologic (N = 4) evidence of A beta (2)m showed selective tracer uptake over various joint regions. Tracer accu mulation in visceral organs, which could not be related to tracer eliminati on or metabolism, was not detected. Compared with the previous I-131 beta(2 )m scan, scintigraphy with In-111-labeled beta(2)m offered highly improved image contrast, increased sensitivity, and a 50 to 70% reduction of the rad iation exposure. Scanning with In-111-labeled recombinant human beta(2)m wa s performed in six patients: No significant tracer accumulation was observe d over joint regions in two patients on short-term HD without evidence of A beta(2)m; in contrast, local tracer accumulations similar to those observe d with natural beta(2)m could be demonstrated in four long-term (10 to 27 y ears) HD patients with clinical, radiological, and histologic (N = 1) evide nce of A beta(2)m. Conclusion. Scintigraphy for A beta(2)m with In-111-labeled rh beta(2)m pro vides a homogenous and safe recombinant protein source and leads to enhance d sensitivity and lower radiation exposure.