Adipose tissue abnormalities in cystic fibrosis: noninvasive determination of mono- and polyunsaturated fatty acids by carbon-13 topical magnetic resonance spectroscopy

Natural abundance in vivo carbon-13 topical magnetic resonance (TMR) spectroscopy was used to assess human adipose tissue stores of essential (polyunsaturated) fatty acids. TMR spectra were obtained from 17 normal volunteers and nine cystic fibrosis patients using an Oxford TMR-32 with a surface coil that sampled tissue less than 1 cm below the surface of an extremity. Spectra were taken of lower leg adipose tissue. Polyunsaturated fatty acid content was determined by comparing peak heights of the polyunsaturated peak (internal unsaturated carbons, 128 ppm) to C-1 carboxyl groups (173 ppm). Monounsaturated fatty acid content was determined by subtracting the polyunsaturated peak from the peak observed for all unsaturated carbons (external unsaturated carbon, 130 ppm) and dividing this ratio by the carboxyl peak. In vivo TMR of normal volunteers resulted in observed polyunsaturated fatty acid content of 17.8 +/- 2.1% and a monounsaturated content of 44.8 +/- 3.8%. The polyunsaturated and monounsaturated fatty acid content of adipose tissue from the cystic fibrosis patients was 15.0 +/- 2.0% (p less than 0.005 versus normal volunteers) and 47.8 +/- 6.5% (NS), respectively. One cystic fibrosis patient without fat malabsorption had decreased adipose polyunsaturates, whereas another patient on high calorie gastrostomy feeds had normal levels. Carbon-13 TMR spectroscopy is a sensitive, noninvasive technique for determining essential fatty acid status in subcutaneous adipose tissue of patients with cystic fibrosis.