Non-Invasive Imaging of Amyloid Deposits in a Mouse Model of AGel Using 99mTc-Modified Nanobodies and SPECT/CT

PURPOSE

Gelsolin amyloidosis (AGel), also known as familial amyloidosis, Finnish type (FAF), is an autosomal, dominant, incurable disease caused by a point mutation (G654A/T) in the gelsolin (GSN) gene. The mutation results in loss of a Ca²⁺-binding site in the second gelsolin domain. Subsequent incorrect folding exposes a cryptic furin cleavage site, leading to the formation of a 68-kDa C-terminal cleavage product (C68) in the trans-Golgi network. This C68 fragment is cleaved by membrane type 1-matrix metalloproteinase (MT1-MMP) during secretion into the extracellular environment, releasing 8- and 5-kDa amyloidogenic peptides. These peptides aggregate and cause disease-associated symptoms. We set out to investigate whether AGel-specific nanobodies could be used to monitor amyloidogenic gelsolin buildup.

PROCEDURES

Three nanobodies (FAF Nb1-3) raised against the 8-kDa fragment were screened as AGel amyloid imaging agents in WT and AGel mice using ^99mTc-based single-photon emission computed tomography (SPECT)/X-ray tomography (CT), biodistribution analysis, and immunofluorescence (IF). The quantitative characteristics were analyzed in a follow-up study with a Nb11-expressing mouse model.

RESULTS

All three nanobodies possess the characteristics desired for a ^99mTc-based SPECT/CT imaging agent, high specificity and a low background signal. FAF Nb1 was identified as the most potent, based on its superior signal-to-noise ratio and signal specificity. As a proof of concept, we implemented ^99mTc-FAF Nb1 in a follow-up study of the Nb11-expressing AGel mouse model. Using biodistribution analysis and immunofluorescence, we demonstrated the validity of the data acquired via ^99mTc-FAF Nb1 SPECT/CT.

CONCLUSION

These findings demonstrate the potential of this nanobody as a non-invasive tool to image amyloidogenic gelsolin deposition and assess the therapeutic capacity of AGel therapeutics currently under development. We propose that this approach can be extended to other amyloid diseases, thereby contributing to the development of specific therapies.

(99m)Tc-HMDP scintigraphy rectifies wrong diagnosis of AL amyloidosis

A 71-year-old African man without history of cardiac disease was referred to our center for dyspnea. Transthoracic echocardiogram and cardiac MRI were suggestive of cardiac amyloidosis (CA). The diagnosis of the light-chain cardiac amyloidosis (AL-CA) was made after a first endomyocardial biopsy. Accordingly chemotherapy was started. Systematic 99mTc-HMDP scintigraphy showed moderate cardiac uptake (visual score of 2), unusual for AL-CA, and permitted to rectify the diagnosis. Hereditary transthyretin cardiac amyloidosis was confirmed by a second endomyocardial biopsy with a positive Congo-red and anti-transthyretin antibody stainings, mass spectrometry and genetic analysis (Val122Ile mutation).

Keratinic amyloidosis of the external auditory canal

OBJECTIVE

We present a rare case of keratinic amyloidosis of the external auditory canal. This is only the seventh case reported of localized cutaneous amyloidosis of the external auditory canal with no systemic symptoms.

PATIENT

A 62-year-old man, who had complained of an itchy external auditory canal and left-side hearing loss, was referred to our hospital because of a bilateral external auditory canal mass.

INTERVENTION

Biopsy of the external auditory canal mass suggested a diagnosis of amyloidosis. However, total systemic examination failed to identify any disease due to systemic amyloidosis. This led us to diagnose him with localized cutaneous amyloidosis of the external auditory canal.

MAIN OUTCOME MEASURE

We follow up periodically with systemic examination and local observation.

RESULTS

Thirty months after the initial diagnosis, he remains in follow-up and has not shown any significant aggravation of the disease.

CONCLUSION

In previous cases, the chief complaints were itching sensations and pain in the external auditory canal as well as a sense of discomfort when wearing a hearing aid. This suggests that chronic stimulation and inflammation of the skin lining the external auditory canal induced amyloidosis.

Diagnostic performance of 123I-labeled serum amyloid P component scintigraphy in patients with amyloidosis

PURPOSE

To assess the diagnostic accuracy and additional information provided by 123I-labeled serum amyloid P component (SAP) scintigraphy in patients with systemic and localized amyloidosis.

SUBJECTS AND METHODS

123I-labeled human SAP was injected intravenously into 20 controls and 189 consecutive patients with histologically proven amyloidosis: of AA type in 60 cases, AL type in 80, hereditary ATTR type in 27, and localized amyloidosis in 22 cases. SAP scintigrams were obtained 24 hours after tracer injection and were analyzed for abnormal patterns of uptake. Sensitivity and specificity were determined, and scintigraphic findings were compared with clinical data.

RESULTS

Diagnostic sensitivity of SAP scintigraphy for systemic AA, AL, and ATTR amyloidosis was 90%, 90%, and 48% respectively, and specificity was 93%. The distribution of amyloid was less diverse in AA than in AL type. Myocardial uptake was not visualized in any patient. Splenic amyloid was very frequent (80%) in AA and AL type but rarely detected clinically (14%). Abnormal tracer uptake in the liver and kidneys correlated with disturbed liver function and proteinuria, respectively. Bone marrow uptake was specific for AL (21%) and was more frequent in AL kappa than AL lambda. Localized amyloid deposits were not imaged.

CONCLUSION

SAP scintigraphy is diagnostic of amyloid in most patients with AA and AL type but fewer with hereditary ATTR type, relating to differing distributions and burdens of amyloid in these disorders. It usually reveals more widespread organ involvement than is identified clinically, and certain distributions of amyloid are characteristic of particular fibril types.

Hereditary systemic amyloidosis associated with a new apolipoprotein AII stop codon mutation Stop78Arg

Hereditary systemic amyloidosis associated with a new apolipoprotein AII stop codon mutation Stop78Arg.

BACKGROUND

Mutations in the gene for apolipoprotein AII (apoAII) have recently been found to cause hereditary renal amyloidosis. In each case amyloid deposition has been associated with a peptide extension at the carboxyl-terminus of apoAII, the result of mutations in the normal stop codon.

METHODS

A Caucasian man who has had progressive renal dysfunction since age of 34 was found to have amyloidosis on renal biopsy at age 56. Echocardiogram showed mild intraventricular septal thickness and technetium-99m (99mTc)-pyrophosphate scintigraphy demonstrated uptake by cardiac muscle consistent with amyloid deposition in the myocardium. His father died of renal failure and his paternal half brother has renal dysfunction.

RESULTS

DNA sequencing of the apoAII gene in the proband showed a T to C transition at the first position of the stop codon indicating replacement of the stop codon by l-arginine (Arg) at residue 78. Western analysis of the proband's plasma under reducing conditions using anti-apoAII revealed an extra band at approximately 10 kD in addition to the normal apoAII band at 8 kD. Western analysis of solubilized amyloid fibrils isolated from rectal biopsy tissue contained only the variant apoAII.

CONCLUSION

These results indicate that the proband's amyloid fibrils are derived from apoAII and the amyloidogenesis is linked to the peptide extension at the carboxyl-terminus of variant apoAII. Of particular interest is that this novel apoAII variant may cause amyloid cardiomyopathy in addition to renal amyloid.