Enhanced urinary adiponectin excretion in IgA-nephropathy patients with proteinuria

Adiponectin is secreted specifically by adipose tissue. It was reported that the serum adiponectin level was markedly increased in patients with end-stage renal disease and was positively associated with abnormal renal function in type 2 diabetes. Recently, we found that urinary adiponectin level was significantly increased in type 2 diabetic patients with overt diabetic nephropathy, but not in those without nephropathy. The aim of the present study was to evaluate whether the urinary adiponectin level is increased not only in diabetic patients with macroalbuminuria but also in IgA-nephropathy patients with macroalbuminuria. We measured urinary adiponectin levels in 24 healthy control subjects, 12 IgA-nephropathy patients, and 19 type 2 diabetic nephropathy patients, and they were, in medians, 2.24 microg/g creatinine (ranges of 0.85 to approximately 3.70), 59.2 microg/g creatinine (4.95 to approximately 186), and 33.1 microg/g creatinine (4.69 to approximately 114), respectively. In the two patient groups, urinary adiponectin levels were significantly higher than in control subjects (P<0.01). Moreover, positive correlations between urinary adiponectin levels and albumin-to-creatinine ratios were observed in IgA-nephropathy (R2=0.53, P<0.01) and diabetic nephropathy patients (R2=0.61, P<0.01), but not in control subjects. Serum adiponectin levels were unchanged in these three groups. These findings suggested that the increase of urinary adiponectin levels partly results from enhanced filtration of circulating adiponectin through the changes of glomerular permselectivity and intraglomerular hydruric pressure. However, clinical implication of urinary adiponectin excretion in healthy control remains to be elucidated.