Renal loss of leptin in patients with nephrotic syndrome.

OBJECTIVE In humans, short term changes of serum leptin lead to alterations in food intake and energy expenditure. The objective of the present study was to relate urine leptin concentrations with the extent of proteinuria in patients with nephrotic syndrome (NS). A second goal was to investigate the impact of potential urinary leptin losses on serum leptin concentrations and body composition. DESIGN AND METHODS Seventeen patients with proteinuria were compared with twenty patients with remission of NS and ten healthy children. Leptin was measured by radioimmunoassay. RESULTS Urinary leptin excretion in proteinuric patients was significantly higher than in non-proteinuric patients with and without NS and in healthy controls (2.64+/-0.034 microg/g creatinine, 0.026+/-0.05 microg/g creatinine, and 0.073+/-0.11 microg/g creatinine respectively; P<0.001 and P<0.01 respectively compared with controls). Urine leptin positively correlated with urine IgG concentration (P=0.013, r2=0.36) in the proteinuric group. No difference in serum leptin values could be demonstrated between the three groups. CONCLUSIONS In summary, our data demonstrate a significant leptin excretion in children with severe proteinuria. Proteinuria, however, does not lead to changes in serum leptin, suggesting that the significant loss of leptin is compensated for by sustained up-regulation of leptin production.