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.
Level 5 - mechanism / opinion, no new human data
In vitro laboratory study using cultured primary human myotubes
PubMed 17219404 · doi:10.1002/jcp.20922
What was done
Primary myotubes were differentiated in vitro from muscle biopsies of 8 normal-weight, pre-pubertal children. Cultured cells were treated with saturated fatty acids (750 µM palmitate), non-metabolizable fatty acid analogues (bromopalmitate), ceramide synthesis inhibitors, unsaturated fatty acids (1,000 µM oleate), or palmitate-oleate co-treatments. Investigators measured insulin-stimulated AKT phosphorylation (pThr308 and pSer473), intramyocellular lipid (IMCL) accumulation, and 14C-ceramide synthesis from 14C-palmitate.
What was found
Palmitate significantly decreased pAKT compared to control (mean [SEM] change: pThr308 site -50.5% [28.7] and pSer473 site -38.7% [11.7]; P < 0.001) without affecting IMCL formation. Equimolar bromopalmitate had no effect on pAKT, and blocking ceramide production abolished palmitate-induced signalling defects. Oleate alone did not change pAKT (pSer473 -3.4% [11.4]; P = NS) but increased IMCL accumulation (+32.3% [7.1%]; P < 0.001). Co-administration of oleate with palmitate prevented the reduction in pAKT (+36.4% [23.6] vs. -13.3% [13.6]; P = 0.28) and significantly reduced 14C-ceramide synthesis (101.6 [21.6] vs. 371.5 [122.4] DPM/mg protein; P < 0.001) while maintaining elevated IMCL levels.
Why it matters
This study indicates that saturated fatty acid-induced insulin resistance in pediatric muscle cells is driven specifically by palmitate metabolism to ceramide rather than total intramyocellular lipid accumulation, and that oleate protects against this defect.
Limits
This is an in vitro cell culture study with a small sample size (tissue derived from n = 8 children). All donors were normal-weight and pre-pubertal, limiting direct generalization to children with obesity or clinical insulin resistance. In vitro exposure to high acute fatty acid concentrations does not capture whole-body systemic metabolic interactions.
Cited by
- supports In cell culture models, treating cells with the saturated fat palmitate causes insulin resistance via conversion into ceramides, whereas treatment with monounsaturated or polyunsaturated fatty acids does not.