Magnetic resonance spectroscopy analysis of intramyocellular lipid composition in lipodystrophic patients and athletes

ContextParadoxically, intramyocellular lipid (IMCL) accumulation has been linked to both insulin-resistant and to insulin-sensitive (athletes) states. The composition of this lipid store is unknown in these states.\n\nDesign and MethodsWe used a recently validated and potentially widely applicable 1H magnetic resonance spectroscopy method to compare the compositional saturation index (CH2:CH3 ratio) and concentration independent of composition (CH3) of intramyocellular lipid in the soleus and tibialis anterior muscles of 16 female insulin-resistant lipodystrophic patients with that of age- and gender-matched athletes (n=14) and healthy controls (n = 41).\n\nMain OutcomeIMCL compositional saturation index (CH2:CH3 ratio).\n\nResultsThe IMCL CH2:CH3 ratio was significantly higher in both muscles of the lipodystrophic patients compared with age- and gender-matched controls but not compared to athletes. IMCL CH2:CH3 was dependent on IMCL concentration in the controls and after adjusting the composition index for quantity (CH2:CH3adj) was able to distinguish patients from athletes. With groups pooled, this CH2:CH3adj marker had the strongest relation to insulin resistance (HOMA-IR) compared to other measures of lipid concentration and composition, especially in the soleus muscle. Contrary to the athletes paradox, IMCL in athletes was similar in tibialis anterior (p>0.05) and significantly lower in the soleus (p < 0.004) compared to both controls and patients.\n\nConclusionsThe IMCL saturation index adjusted for quantity, which likely reflects accumulation of saturated IMCL, is more closely associated with insulin resistance than concentration alone.