Leptin binding activity (LBA) in plasma of nondiabetic and diabetic adolescents and obese children: relation to auxologic and hormonal data.
Leptin circulates in serum bound to high molecular weight proteins. Hypothesizing that leptin binding proteins may regulate the functional efficiency of leptin, we characterized auxologic and hormonal factors that influence leptin binding in three disparate groups: normal adolescents, obese children, and teenagers with type I diabetes mellitus (IDDM). Specific leptin binding activity (sLBA) was assessed by column chromatography after incubation of serum with 125I-leptin in the presence and absence of excess unlabeled leptin. Mean sLBA was 17.0 +/- 7% (SD) in the healthy adolescents (n=41), 6.6 +/-4.3% in the obese children (n=26), and 14.9 +/-7.3% in the diabetic teenagers (n=17). At any value of sLBA, obese children had higher serum leptin levels than non-obese adolescents or diabetic teenagers, consistent with "leptin resistance" in the obese group. sLBA was higher in males than in females only in those with diabetes (18.6 +/- 7.3 vs 10.9 +/- 5.1%, p<0.05). sLBA correlated inversely with serum insulin-like growth factor-I values in the normal group (r= -0.45, p<0.01) and with insulin in the obese children (r= -0.53, p<0.01). There was no correlation between sLBA or serum leptin values and HbA1c, in the diabetic group. The serum leptin concentration was the principal determinant explaining the total variability of sLBA in all three cohorts. However, body mass index (BMI = weight/ height2) accounted for more of the total variability of percent specific binding in the healthy adolescents than in the other groups. We conclude that sLBA reflects circulating leptin levels, body composition, and hormonal milieu. Thus, in addition to leptin, qualitative and quantitative characteristics of leptin binding may play a physiological role in the regulation of appetite and in the "leptin resistance" of obesity.
Diamond
F
F
Department of Pediatrics, University of South Florida College of Medicine, Tampa, USA.
Eichler
D
D
Mayes
D
D
Jorgensen
V
V
Duckett
G
G
Hu
C
C
Cuthbertson
D
D
Root
A
A
D000293:Adolescent; D015992:Body Mass Index; D016022:Case-Control Studies; D002648:Child; D003922:Diabetes Mellitus, Type 1 / Q000097:blood* / Q000503:physiopathology; D005260:Female; D006801:Humans; D020738:Leptin / Q000097:blood*; D008297:Male; D009765:Obesity / Q000097:blood*; D011485:Protein Binding
D020738:Leptin