Leptin, soluble leptin receptors, free leptin index, and their relationship with insulin resistance and BMI: high normal BMI is the threshold for serum leptin increase in humans.
Leptin binds to the soluble form of its receptor (sOB-R). Leptin and sOB-R balance (free leptin index, FLI) reflect leptin activity. Leptin correlates with obesity and insulin resistance, but it remains uncertain whether sOB-R and FLI also do the same. Therefore, the aim of this study was to measure serum leptin, sOB-R, and FLI, and evaluate their associations with BMI and insulin resistance. We studied 145 obese and 49 nonobese humans. Obesity was defined according to WHO (BMI >30 kg/m (2)). Results are given as: median and interquartile range, obese vs. nonobese, respectively. Leptin (ng/ml): 30.83, 37.27 vs. 8.31, 10.04; sOB-R (ng/ml): 17.62, 17.05 vs. 27.25, 11.30; FLI: 231.2, 310.0 vs. 30.85, 27.77; HOMA: 5.99, 6.64 vs. 3.92, 4.52; p<0.001 for all. Serum leptin, sOB-R, and FLI did not correlate with insulin resistance separately in obese and nonobese humans. Leptin and FLI, but not sOB-R, were associated with insulin resistance in obese and nonobese subjects examined together. Leptin, sOB-R and FLI differed between obese and nonobese humans, and, except sOB-R, correlated with BMI. In piecewise linear regression, BMI threshold where leptin increased was 24.6 (r=0.5969, p=0.00016 and <0.00001). Leptin and its free index, but not sOB-R, correlate with BMI only in a mixed obese and nonobese human cohort, and not in isolated obese or nonobese groups. Moreover, BMI threshold where leptin starts to increase is 24.6 kg/m (2), which is lower than the cutoff for overweight. Under the conditions, metabolic abnormalities may occur in parallel to much lower BMI levels as expected so far.
Owecki
M
M
Department of Endocrinology, Metabolism and Internal Medicine, University of Medical Sciences in Poznań, Poznań, Poland. mowecki@ump.edu.pl
Nikisch
E
E
Miczke
A
A
Pupek-Musialik
D
D
Sowiński
J
J
D000328:Adult; D015992:Body Mass Index; D005260:Female; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D020738:Leptin / Q000097:blood*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood / Q000235:genetics; D054411:Receptors, Leptin / Q000378:metabolism*; D012995:Solubility; D055815:Young Adult
D020738:Leptin; D054411:Receptors, Leptin