Is the erythrocyte membrane fatty acid composition a valid index of skeletal muscle membrane fatty acid composition?

Recent studies suggest that insulin sensitivity is related to the fatty aci d composition of phospholipids in skeletal muscle (SM) membranes. Since it is difficult to obtain muscle biopsies, it may be useful to have informatio n on the fatty acid composition using more accessible cells such as erythro cytes. This would be possible only if the composition of erythrocyte and mu scle membranes are very similar. Since no comparative data are available, w e evaluated the phospholipid fatty acid composition of erythrocyte and SM m embranes in 16 individuals, 10 nondiabetics (male to female ratio, 4:6; age , 50 +/- 11 years; body mass index, 27 +/- 5 kg/m(2); mean +/- SD) and 6 ty pe 2 diabetic patients (male to female ratio, 2:4; age, 64 +/- 5 years; bod y mass index, 27 +/- 4 kg/m(2)). All patients underwent abdominal surgery, during which a biopsy of the abdominal rectus muscle (50 to 100 mg) was obt ained. Erythrocyte and SM phospholipid fatty acids were extracted and then methylated; the methyl fatty acids were separated and quantified by gas chr omatography. Compared with erythrocyte membranes, muscle membranes showed a significantly higher proportion of omega-6 polyunsaturated fatty acid ([PU FA] 43.0% +/- 3.1% v 29.7% +/- 1.6%, P < .001) and lower saturated fatty ac id ([SFA] 41.1% +/- 1.5% v 43.4% +/- 1.2%, P < .001), monounsaturated fatty acid ([MUFA] 11.5% +/- 1.7% v 20.0% +/- 1.9%, P < .001), and omega-3 PUFA (3.8% +/- 0.6% v 7.4% +/- 1.0%. P < .001). The greatest increase involved l inoleic acid (26.9% +/- 2.8% v 10.3% +/- 1.6%, P < .001), whereas lignoceri c acid (0.8% +/- 0.2% v 5.0% +/- 0.6%, P < .001) and oleic acid (10.4% +/- 1.6% v 13.5% +/- 1.3%, P < .001) were significantly lower. These results sh ow that erythrocyte and muscle membrane phospholipid fatty acids are signif icantly different. Therefore, data on SM membranes cannot be extrapolated o n the basis of measures of erythrocyte phospholipid fatty acid composition. Copyright (C) 2000 by W.B. Saunders Company.