Objective: Pathogenic monoclonal anti-double-stranded DNA (anti-dsDNA) antibodies up-regulate the expression of lipocalin-2 in glomerular mesangial cells. This study was undertaken to investigate whether polyclonal anti-dsDNA antibodies promote the local secretion of lipocalin-2 in the kidneys of patients with systemic lupus erythematosus (SLE), and whether urinary lipocalin-2 represents a marker of kidney involvement in SLE.
Methods: Hispanic, African American, and white patients with SLE and normal healthy control subjects from affiliated hospitals of the Albert Einstein College of Medicine were recruited for this cross-sectional study. Patients were classified based on the presence of active renal disease according to the SLE Disease Activity Index (SLEDAI). Correlations of clinical and laboratory data with urinary and serum levels of lipocalin-2 were assessed.
Results: Among SLE patients, urinary lipocalin-2 levels were significantly higher in those with lupus nephritis (LN) (median 17.1 ng/mg creatinine, interquartile range [IQR] 10.3-45.4; n = 32) than in those without LN (median 11.2 ng/mg creatinine, IQR 3.1-20.3; n = 38) (P = 0.023). Compared with the values in normal controls (median 4 ng/ml, IQR 0-11.1; n = 14), urinary levels of lipocalin-2 in SLE patients were significantly higher (non-normalized median 19.3 ng/ml, IQR 8-34.2) (P = 0.004). The presence of lipocalin-2 in the urine of patients with LN correlated significantly with the renal SLEDAI score (r = 0.452, P = 0.009), but not with extrarenal disease activity.
Conclusion: The high prevalence of LN in SLE patients and the prognostic significance of kidney disease support the need for identifying early biomarkers to assess the risk of nephritis development and for following up patients with established disease. These findings indicate that urinary lipocalin-2 is a potential marker of the presence and severity of renal involvement in adult patients with SLE.