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

Context: Paradoxically, 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. Design and Methods: We 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). Main Outcome: IMCL compositional saturation index (CH2:CH3 ratio). Results: The 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 u0027athleteu0027s paradoxu0027, IMCL in athletes was similar in tibialis anterior (pu003e0.05) and significantly lower in the soleus (p u003c 0.004) compared to both controls and patients. Conclusions: The IMCL saturation index adjusted for quantity, which likely reflects accumulation of saturated IMCL, is more closely associated with insulin resistance than concentration alone.