Renal loss of leptin in patients with nephrotic syndrome

Objective: In humans, short term changes of serum leptin lead to alteration s in food intake and energy expenditure. The objective of the present study was to relate urine leptin concentrations with the extent of proteinuria i n patients with nephrotic syndrome (NS). A second goal was to investigate t he 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 m easured by radioimmunoassay. Results: Urinary leptin excretion in proteinuric patients was significantly higher than in nonproteinuric patients with and without NS and in healthy controls (2.64 +/-0.034 mug/g creatinine, 0.026 +/-0.05 mug/g creatinine, a nd 0.073 +/-0.11 mug/g creatinine respectively; P<0.001 and P<0.01 respecti vely compared with controls). Urine leptin positively correlated with urine IgG concentration (P=0.013, r(2) = 0.36) in the proteinuric group. No diff erence in serum leptin values could be demonstrated between the three group s. Conclusions: In summary, our data demonstrate a significant leptin excretio n 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.