Osteopontin Predicts for Survival and Cystatin C-Based Estimated GFR Predicts for Renal Response to Therapy in Patients with Primary Systemic Amyloidosis

Primary systemic amyloidosis (AL) is a multisystemic disorder resulting from an underlying plasma cell dyscrasia. Elevated serum N-terminal pro-brain natriuretic peptide (NT-proBNP) is considered as one of the most powerful prognostic markers in AL. Angiogenesis is a crucial step for disease progression in several malignancies, including multiple myeloma (MM). Osteopontin (OPN) is a glycophosphoprotein cytokine, which has significant role in cell adhesion, prevention of apoptosis, invasion, migration and tumor cell growth. OPN also participates in neo-angiogenesis process in malignancies, as in MM. Renal involvement is common in AL, resulting in renal impairment in a significant proportion of patients. Cystatin-C (Cys-C) is a cysteine-proteinase inhibitor, which is considered as a reliable endogenous marker of GFR. Furthermore, our group has shown that Cys-C is an independent prognostic factor in MM. The aim of this study was to evaluate the levels of OPN, Cys-C and angiogenesis cytokines in AL, explore possible correlations with clinical characteristics and known prognostic factors, as NT-proBNP, and compare the results with those of MM. Serum levels of angiopoietin-1 and -2 (Ang-1, Ang-2), VEGF, angiogenin, basic fibroblast growth factor (bFGF) and OPN were evaluated using ELISA methodology (R&D, Minneapolis, MN, USA, for all, except of OPN: IBL GmbH D, Hamburg, Gemany). Serum Cys-C was determined by particle enhanced immunonephelometry (Dade Behring, Liederbach, Germany), while serum NT-proBNP was evaluated using an electrochemiluminescensce immunoassay (Roche Diagnostics GmbH, Mannheim, Germany). Serum samples were collected from 82 previously untreated AL patients (39M/43F), 35 age- and gender-matched healthy controls and 35 newly diagnosed, untreated, MM patients of similar age and gender. The median age of AL patients was 63 years (range: 39–86 years), and the median number of involved organs was 2 (range: 1–4). Heart was involved in 45 (56%) patients, kidney in 61 (76%) and liver in 11 (14%) patients. Serum levels of OPN (<0.01), VEGF (p<0.001), bFGF (<0.001), angiogenin (p<0.001) and Ang-2 (p<0.001) were significantly higher in AL patients than in controls; however Ang-1 levels did not differ between AL patients and controls (p=0.321), thus the ang1/ang2 ratio was lower in AL patients (p=0.036). Compared to MM patients, AL patients had significantly higher VEGF (p<0.001), angiogenin (p<0.001), and Ang-1 (p=0.001) levels but lower levels of Ang-2 (0.001) resulting in a significantly higher Ang-1/2 ratio (p<0.001). OPN levels did not differ between AL and myeloma patients (p=0.169). OPN correlated with NT-proBNP levels in AL (r=0.342, p=0.004). Ang-2 levels were significantly higher in AL patients with heart involvement (p=0.008) resulting in lower Ang-1/2 ratio (p=0.03). Cys-C levels were higher in AL patients compared to both controls and MM patients (p<0.0001). The eGFR estimated with the MDRD equation and 3 different equations that included Cys-C only; Cys-C and age; and Cys-C, creatinine and age (Stevens et al, Am J Kidney Dis2008;51:396–406) were 65, 44, 41 and 45 ml/min/1.73m2, respectively (p<0.001). All eGFR evaluations were associated with the probability of renal response to therapy. However, in multivariate analysis, only the equation that included Cys-C, creatinine and age predicted indepedently for renal response to therapy (HR 8.8, 95% CI 1.2– 67, p=0.033). The median survival of this cohort of patients has not been reached yet; the 24-month survival rate was 66%. In univariate analysis high NT-proBNP levels (p<0.001), heart involvement (p<0.01), ejection fraction <55% (p<0.01), high serum OPN (p=0.01), performance status ≥2 (p=0.011), ≥2 involved organs (p=0.02), no organ response to therapy (p=0.023), urine albumin (>3500 mg/24h; p=0.031), and no hematologic response to therapy (p=0.034) predicted for poor survival. However, NT-proBNP and OPN were both independently associated with survival in a multivariate model. This study suggests that angiogenesis cytokines are increased in AL, even compared to MM. More importantly, high OPN levels predicts for inferior survival, while eGFR based on Cys-C, creatinine and age predicts for renal response to therapy. NTproBNP remains a valuable predictive factor for survival in AL.