Mature subcutaneous and visceral adipocyte concentrations of adiponectin are highly correlated in prepubertal children and inversely related to body mass index standard deviation score

Context: Adiponectin is an adipocyte-specific protein with insulin-sensitizing properties. Several studies have examined the expression of adiponectin mRNA or tissue/secreted protein levels in fat obtained from adults, but none has assessed tissue levels in childhood. Patients: Paired subcutaneous (Sc) and visceral (V) fat samples were obtained from 12 normal-weight children. Main Outcome Measures: Mature adipocytes were isolated and total adiponectin levels determined by ELISA. Insulin sensitivity and lipid parameters were assessed in fasting blood samples taken at the time of biopsy collection. Results: A positive correlation was seen between the adiponectin concentration within the Sc and V mature adipocytes derived from each child (r = 0.924; P < 0.001). After logarithmic transformation of the Sc and V adiponectin concentrations (log-Sc and log-V) to render the data Gaussian, both log-Sc and log-V were found to be lower in those children with higher body mass index SD score (r = –0.621 and r = –0.357 respectively), although this reached statistical significance only in the Sc adipocytes (P = 0.03). Age was not related to either log-Sc or log-V adiponectin levels, although a significant negative association was seen with serum adiponectin (r = –0.589; P = 0.04). Log-Sc or log-V did not correlate with serum adiponectin concentrations, markers of insulin sensitivity, or circulating lipid levels. Conclusions: These data indicate a relationship between total adiponectin levels in different tissue compartments, suggesting either some form of interaction or coregulation by systemic factors, possibly related to body size/fat mass. Serum concentrations of total adiponectin were inversely related to age but showed no relationship with either tissue levels or body mass index SD score

Fatty acid-induced defects in insulin signalling, in myotubes derived from children, are related to ceramide production from palmitate rather than the accumulation of intramyocellular lipid

The elevation of free fatty acids (FFAs), observed in childhood obesity results in intramyocellular lipid (IMCL) accumulation with consequent insulin resistance. Using in vitro differentiated myotubes from normal weight pre-pubertal children (n = 8), we examined the effects of saturated (palmitate) and unsaturated (oleate) FFAs on insulin-stimulated AKT phosphorylation (pAKT) and IMCL accumulation. Palmitate decreased pAKT (Mean [SEM] % change pAKT with palmitate 750 µM vs. control; pThr308 site -50.5% [28.7] and pSer473 site -38.7% [11.7]; P < 0.001) with no effect on IMCL formation. Equimolar bromopalmitate did not effect pAKT and blocking ceramide production abolished the palmitate-induced reduction in signalling, suggesting that ceramide synthesis is critical for palmitate's actions. Oleate did not effect pAKT (1,000 µM oleate; pSer473 site -3.4% [11.4]; P = NS) but increased IMCL accumulation (+32.3% [7.1%]; P < 0.001). Co-administration of oleate diminished the reduction in pAKT seen with palmitate (+36.4% [23.6] vs. -13.3% [13.6]; P = 0.28), with similar IMCL levels to oleate alone. Co-administration also caused a significant reduction in 14C-ceramide synthesis from 14C-palmitate (101.6 [21.6] vs. 371.5 [122.4] DPM/mg protein; P < 0.001). In summary, palmitate appears to cause insulin resistance in children's myotubes via its metabolism to ceramide, and this process appears unrelated to IMCL formation and is ameliorated by oleate