Urinary N-Acetyl-Beta-D Glucosaminidase, a Marker of Tubular Dysfunction, in Patients with Systemic Lupus Erythematosus

摘要

Kidney involvement in systemic lupus erythematosus (SLE) is life threatening complication. Urinary N-acetyl-beta-D glucosaminidase (uNAG) activity has emerged as potentially useful early marker of renal tubular injury. The uNAG excretion was investigated in 72 SLE patients to assess tubular dysfunction and determine its relationship with disease activity and pathological classes of lupus nephritis (LN). SLE patients were divided into two groups: 41 patients with LN and 31 patients without evidence of nephritis. Disease activity was assessed by SLEDAI. Renal disease activity was measured by the Systemic Lupus International Collaborating Clinics Renal Activity Score. uNAG levels were measured using colorimetric assay kit and compared to 25 healthy controls. Renal biopsies were performed for LN patients and glomerular lesions were classified according to WHO criteria. Severity of tubulointerstitial involvement was also assessed. The uNAG activity was significantly higher in LN patients than in lupus non nephritis patients and healthy controls (both p<0.001). Tubular dysfunction with elevated uNAG was present in 6 lupus non-nephritis patients with no evidence of glomerular disease. There was positive significant relation between uNAG and proteinuria (p<0.005) and renal activity score (p<0.001) in LN patients. Conversely, uNAG excretion was not significantly correlated with SLEDAI, WHO classes of nephritis and tubulointerstitial index. In conclusion, increased uNAG activity in lupus non-nephritis patients may predict the development of LN prior to the onset of proteinuria. Increased uNAG activity parallels the degree of renal disease activity in LN patients and is probably more sensitive indicator of tubulointerstitial disease.