Background/Purpose: Proteomic screening is an efficient approach for identifying protein biomarkers in various inflammatory diseases. Our preliminary proteomic analysis revealed elevated levels of urinary angiostatin, CXCL4 and VCAM-1 in patients with active lupus nephritis. This study aims to study the performance of urinary angiostatin, CXCL4 and VCAM-1 in differentiating between active renal and non-renal systemic lupus erythematosus (SLE).

Methods: Patients who fulfilled the ACR classification for SLE with active renal disease, active non-renal disease and inactive disease were randomly recruited from our out-patient clinics and hospital admission between 2010 and 2015. A group of healthy individuals were also recruited as controls. Stored urine samples of the participants were assayed for angiostatin (Raybiotech, Inc; Georgia, USA), CXCL4 and VCAM-1 (R&D Systems; Minneapolis, Minnesota, USA) and compared among the different groups. Elevated levels of these markers were defined as values ≥ mean+2SD of the controls. SLE disease activity was assessed by the SELENA-SLEDAI and physician’s global assessment (PGA). Specificity and sensitivity of these markers in differentiating between active renal and non-renal SLE was determined by 2×2 contingency tables and compared with conventional markers such as anti-dsDNA and complement C3. In patients with active renal disease, correlation between these urinary biomarkers with clinical renal parameters was also performed.

Results: 227 SLE patients (80 inactive SLE; 67 active non-renal disease; 80 active renal disease; 94% women, age 39.2±13.8 years) and 54 healthy controls (96% women) were studied. All were ethnic Chinese. Urinary angiostatin, CXCL4 and VCAM-1 levels normalized for creatinine were significantly higher in patients with active renal than non-renal disease (angiostatin 1.8±2.7 vs 0.16±0.29 pg/ng; p<0.001; CXCL 4.9±1.6 vs 0.5±1.4 pg/ng; p=0.002; VCAM-1 41±1.31 x10² vs 0.72±1.10 x10² pg/ng; p<0.001). The levels of these urinary protein markers were also significantly higher in active non-renal SLE patients than inactive SLE patients or healthy controls. Urinary angiostatin, CXCL4 and VCAM-1 correlated significantly with the renal SLEDAI (Rho 0.66, 0.45 and 0.52, respectively; p<0.001 in all) and total SLEDAI score (Rho 0.60, 0.46 and 0.53, respectively; p<0.001 in all) in all the SLE patients studied. These urinary markers were also significantly associated with the serum anti-dsDNA and C3 levels. However, only urinary angiostatin correlated with the protein/creatinine ratio (Rho 0.34; p=0.002). 73/80 patients with active lupus nephritis had renal biopsy performed within 4 weeks of the urinary sample collection (34% RPS/ISN class III±V; 37% IV±V; 16% pure V; 12% I/II). The three urinary markers could not differentiate active proliferative (III/IV) from non-proliferative (I/II/V) lupus nephritis; and there was no significant correlation between these markers and histological activity indices in patients with class III/IV lupus nephritis. Urinary angiostatin and CXCL4 (specificity 0.75 and 0.78, respectively) were more specific than elevated serum anti-dsDNA and low C3 (specificity 0.28 and 0.21) in differentiating active renal from active non-renal SLE. Urinary angiostatin and CXCL4 were also highly specific (specificity 0.96 and 0.99, respectively) when compared to elevated anti-dsDNA and low C3 (specificity 0.54 and 0.59) in differentiating active SLE from inactive SLE.

Conclusion: Urinary angiostatin and CXCL4 are specific markers for lupus nephritis and may be useful in detecting subclinical / low grade renal disease in patients with active SLE. Further longitudinal studies are necessary to delineate the sensitivity and specificity of these two urinary protein markers in predicting renal flares in SLE patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/urinary-angiostatin-cxcl4-and-vcam-1-as-biomarkers-for-lupus-nephritis/