Background: The endogenous conversion of linoleic acid into long-chain polyunsaturated fatty acids is of potential importance for meeting substrate requirements, particularly in young infants. After application of [13C]-linoleic acid, we estimated its conversion to dihomo-gamma-linolenic and arachidonic acids from only two blood samples.
Design: Oral tracer doses were given to five healthy adults as a single bolus. In four subjects the tracer was given in nine equal portions over 3 days. Concentration and 13C content of fatty acids from serum phospholipids were analysed by gas chromatography combustion isotope ratio-mass spectrometry. Areas under the tracer-concentration curves were calculated, and fractional transfer and turnover rates estimated from compartmental models.
Results: The median fractional turnover of linoleic acid was 93.7% per day (interquartile range 25.3) in the bolus group and 80. 0% per day (6.3) in the fraction group (NS). Fractional conversion of linoleic to dihomo-gamma-linolenic acid was 1.5% (0.9) vs. 2.1% (0.7) (bolus vs. fraction, P < 0.05), and fractional conversion of linoleic to arachidonic acid was 0.3% (0.3) vs. 0.6% (0.3) (bolus vs. fraction, NS). In the fraction group conversion was significantly higher based on areas under the curve. The ratio of tracer concentration in conversion products to linoleic acid 48 h after dosing correlated very well (r >/= 0.94, P < 0.05) with the ratio of areas under the curve.
Conclusions: Using areas under the curve overestimates the conversion, because different residence times are not considered. Estimation of conversion intensity appears possible with only one blood sample obtained after tracer application.