Prospective urinary albumin/creatinine ratio for diagnosis, staging, and organ response assessment in renal AL amyloidosis: results from a large cohort of patients.

OBJECTIVES: Quantification of 24 h-proteinuria is the gold standard for diagnosing, staging, and monitoring of patients with renal AL amyloidosis. However, 24 h-urine collection is cumbersome and may result in preanalytical error. In this prospective study, we investigated the role of urinary albumin/creatinine ratio (UACR) (cut-off: 300 mg/g) identifying renal involvement, evaluated a UACR-based staging system (UACR cut-off: 3,600 mg/g) and assessed whether UACR response (UACR decrease >30% without worsening in eGFR >25%) predicts renal outcome in 531 patients with newly-diagnosed AL amyloidosis. METHODS: From October 2013 paired 24 h-proteinuria and UACR (on first morning void) were measured in all newly-diagnosed patients with AL amyloidosis. Correlation between 24 h-proteinuria and UACR at baseline was assessed by Pearson's r test. Impact of UACR response on renal outcome was assessed in randomly created testing (n=354) and validation (n=177) cohorts. RESULTS: A strong linear correlation was found between 24 h-proteinuria and UACR at baseline (r=0.90; p<0.001). After a median follow-up of 31 months, 57 (11%) patients required dialysis. A UACR-based renal staging system identified three stages with significantly higher dialysis rate at 36 months comparing stage I with stage II and stage II with stage III. Achieving a renal response, according to a UACR-based criterion, resulted in lower dialysis rate in both testing and validation cohorts. CONCLUSIONS: UACR is a reliable marker for diagnosis, prognosis, and organ response assessment in renal AL amyloidosis and can reliably replace 24 h-proteinuria in clinical trials and individual patients' management.

Minimal residual disease negativity by next-generation flow cytometry is associated with improved organ response in AL amyloidosis.

Light chain (AL) amyloidosis is caused by a small B-cell clone producing light chains that form amyloid deposits and cause organ dysfunction. Chemotherapy aims at suppressing the production of the toxic light chain (LC) and restore organ function. However, even complete hematologic response (CR), defined as negative serum and urine immunofixation and normalized free LC ratio, does not always translate into organ response. Next-generation flow (NGF) cytometry is used to detect minimal residual disease (MRD) in multiple myeloma. We evaluated MRD by NGF in 92 AL amyloidosis patients in CR. Fifty-four percent had persistent MRD (median 0.03% abnormal plasma cells). There were no differences in baseline clinical variables in patients with or without detectable MRD. Undetectable MRD was associated with higher rates of renal (90% vs 62%, p = 0.006) and cardiac response (95% vs 75%, p = 0.023). Hematologic progression was more frequent in MRD positive (0 vs 25% at 1 year, p = 0.001). Altogether, NGF can detect MRD in approximately half the AL amyloidosis patients in CR, and persistent MRD can explain persistent organ dysfunction. Thus, this study supports testing MRD in CR patients, especially if not accompanied by organ response. In case MRD persists, further treatment could be considered, carefully balancing residual organ damage, patient frailty, and possible toxicity.

Proteotoxicity in cardiac amyloidosis: amyloidogenic light chains affect the levels of intracellular proteins in human heart cells.

AL amyloidosis is characterized by widespread deposition of immunoglobulin light chains (LCs) as amyloid fibrils. Cardiac involvement is frequent and leads to life-threatening cardiomyopathy. Besides the tissue alteration caused by fibrils, clinical and experimental evidence indicates that cardiac damage is also caused by proteotoxicity of prefibrillar amyloidogenic species. As in other amyloidoses, the damage mechanisms at cellular level are complex and largely undefined. We have characterized the molecular changes in primary human cardiac fibroblasts (hCFs) exposed in vitro to soluble amyloidogenic cardiotoxic LCs from AL cardiomyopathy patients. To evaluate proteome alterations caused by a representative cardiotropic LC, we combined gel-based with label-free shotgun analysis and performed bioinformatics and data validation studies. To assess the generalizability of our results we explored the effects of multiple LCs on hCF viability and on levels of a subset of cellular proteins. Our results indicate that exposure of hCFs to cardiotropic LCs translates into proteome remodeling, associated with apoptosis activation and oxidative stress. The proteome alterations affect proteins involved in cytoskeletal organization, protein synthesis and quality control, mitochondrial activity and metabolism, signal transduction and molecular trafficking. These results support and expand the concept that soluble amyloidogenic cardiotropic LCs exert toxic effects on cardiac cells.