Histological validation of cardiac 99mTc-DPD uptake in patients with cardiac transthyretin amyloidosis

Background

Cardiac transthyretin (ATTR) amyloidosis is a progressive and fatal disease caused by the extracellular deposition of misfolded ATTR protein in the myocardium. In an era where new therapies are rapidly emerging, development of non-invasive imaging modalities to quantify amyloid burden over time is of utmost importance. Although endomyocardial biopsy (EMB) remains the gold standard in amyloid detection and typing, 99mTc-DPD scintigraphy is a widely available and accurate tool for non-invasive diagnosis of cardiac ATTR amyloidosis. However, it remains to be determined whether the degree of cardiac 99mTc-DPD uptake correlates with the histological amyloid infiltration on EMB – thus, justifying 99mTc-DPD scintigraphy as a disease monitoring tool.

Aim

This single-centre observational study aimed to compare the extent of histologic amyloid burden on EMB with the quantification of cardiac 99mTc-DPD uptake on scintigraphic planar images and SPECT/CT acquisitions in cardiac ATTR amyloidosis.

Methods

26 patients with cardiac ATTR amyloidosis were enrolled. Patients were included in case of (1) EMB-proven ATTR amyloidosis and (2) availability of 99mTc-DPD scintigraphy (reference activity: 550 MBq). Visual interpretation using the Perugini score, quantitative analysis of cardiac 99mTc-DPD uptake by planar whole-body imaging and SPECT/CT using regions of interest (ROI) were performed, and heart to whole-body ratio (H/WB) was measured. Histological amyloid load was quantified as percentage of the analysed myocardial tissue using Sulfated Alcyan Blue staining and the Fiji-ImageJ programme. Pearson's and Spearman's correlation were used for correlation analysis and assessment of agreement.

Results

ATTR patients had a median age of 77 [73–79] years and were predominantly male (85%). An abnormal Perugini score (i.e. 2 or 3) was present in 25 patients (96%), whereas 1 patient was assigned Perugini score 1 (4%). Increased cardiac tracer uptake was documented in all patients, both on 99mTc-DPD planar scintigraphy (ROImean 129±37) and SPECT/CT (ROImean 369±142). Histologic amyloid burden on EMB was 32±19% on average. It significantly correlated with Perugini score (r=0.56 p=0.003), as well as with cardiac 99mTc-DPD uptake (planar: r=0.54 p=0.006, SPECT/CT: r=0.48 p=0.018) and H/WB (r=0.41 p=0.046).

Conclusion

We have demonstrated a good correlation between histological amyloid infiltration on EMB and cardiac 99mTc-DPD uptake on scintigraphic planar images and SPECT/CT scans, illustrating the potential of 99mTc-DPD scintigraphy to yield reliable quantitative information on cardiac amyloid burden. Further investigations with a larger number of patients are needed to confirm our findings and to implement thresholds in cardiac 99mTc-DPD uptake for being used for guiding disease and therapy management.

Funding Acknowledgement

Type of funding sources: None.

Correlation between invasive and non-invasive quantification of myocardial amyloid load in cardiac transthyretin amyloidosis

Background

Cardiac transthyretin (ATTR) amyloidosis is an infiltrative disease caused by the extracellular deposition of misfolded ATTR protein in the myocardium. Early disease recognition and accurate description of cardiac involvement are fundamental, as cardiac ATTR amyloidosis is associated with poor prognosis. Although endomyocardial biopsy (EMB) remains the gold standard in amyloid detection and typing, non-invasive imaging can provide an accurate diagnostic tool. Bone scintigraphy enables early disease detection with high accuracy. However, it remains to be determined whether the degree of cardiac tracer uptake on bone scintigraphy correlates with the extent of histologic amyloid burden in EMB.

Aim

This single center observational study aimed to compare the histological amyloid load in endomyocardial biopsies with the quantification of cardiac tracer uptake on 99mTechnetium-3,3-diphosphono-1,2-propanodicarboxylic acid (99mTc-DPD) scintigraphy in cardiac ATTR amyloidosis.

Methods

23 patients with cardiac ATTR amyloidosis were enrolled. Diagnosis was obtained with a combination of invasive and non-invasive methods. Perugini score, mean left ventricular tracer uptake (LV uptake) and left ventricular to corpus sterni uptake ratio (LV/CS ratio) on 99mTc-DPD-scintigraphy were measured, while histological amyloid load was quantified as percentage of the analysed myocardial tissue using Sulfated Alcian Blue staining and the Fiji-ImageJ programme. Bivariate correlation and Pearson correlation coefficient were used to study the relationship between EMB and 99mTc-DPD-scintigraphy findings.

Results

We found a statistically significant correlation between histological amyloid load and Perugini score (r=0.47 p=0.02), as well as between Perugini score and LV/CS ratio (r=0.31 p=0.046). Mean LV tracer uptake showed a trend for correlation with histological amyloid load (r=0.37 p=0.08), without reaching statistical significance.

Conclusion

We found a correlation between the extent of histologic amyloid burden in EMB and the degree of cardiac tracer uptake on 99mTc-DPD-scintigraphy. Our results underline the reliability of 99mTc-DPD-scintigraphy as a surrogate of histological amyloid load in the diagnosis of cardiac ATTR amyloidosis. Possible implications for the assessment of prognosis are subject to future studies with a larger number of patients.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Pfizer

Involvement of HIV-I nucleocapsid protein in the recruitment of reverse transcriptase into nucleoprotein complexes formed in vitro

Retroviral reverse transcription takes place within the virion core, where nucleocapsid (NC) protein (NCp) molecules cover the dimeric RNA genome. NCp thus has structural roles in the virion core but is also extensively involved in viral DNA synthesis and virion assembly. To further characterize the role of human immunodeficiency virus type 1 NCp7 during replication of the viral genome, we investigated the relationship between NCp7 and reverse transcriptase (RT) either directly or within nucleoprotein complexes in vitro. We show that NCp7 interacts directly with RT and enhances synthesis of full-length cDNA by increasing RT processivity. Using NCp7 mutants, we show that the complete amino acid sequence of NCp7 is required for functional interactions with RT. Our results suggest that NCp7 plays a role in recruitment of RT into stable and functional nucleoprotein complexes during viral DNA synthesis.

Role of the N-terminal zinc finger of human immunodeficiency virus type 1 nucleocapsid protein in virus structure and replication

Nucleocapsid protein (NCp7) of human immunodeficiency virus type 1 is found covering the genomic RNA in the interior of the viral particle. It is a highly basic protein with two zinc fingers of the form CX2CX4HX4C which exhibit strong affinity for a zinc cation. To study the structure-function relationship of the N-terminal zinc finger of NCp7, this domain was either deleted or changed to CX2CX4CX4C. We examined virus formation and structure as well as proviral DNA synthesis. Our data show that these two NC mutations result in the formation of particles with an abnormal core morphology and impair the end of proviral DNA synthesis, leading to noninfectious viruses.

Use of a constrain phage displayed-peptide library for the isolation of peptides binding to HIV-1 nucleocapsid protein (NCp7)

It has been shown that peptide libraries are powerful tools for the identification of peptides showing new binding specificity. This technology was applied to the isolation of peptides binding to HIV-1 nucleocapsid protein (NCp7). Three different prolin reach peptide sequences, interacting with NCp7, were isolated, from a constrained phage displayed-peptide library of 10(8) independent clones. The three peptide sequences, isolated from the peptide library, were shown to bind NCp7 in the region 30-52. Moreover, two of them share the PP-(D/E)R consensus sequence.