13C NMR spectroscopy and gas chromatograph--combustion--isotope ratio mass spectrometry: complementary applications in monitoring the metabolism of 13C-labelled polyunsaturated fatty acids.

This review aims to describe some recent and novel applications of stable isotope tracer technology to study the metabolism of 13C-polyunsaturated fatty acids. Stable isotope methodology has existed for several decades, and in that sense, it is not novel per se. However, in the past 10 years, developments in the fields of isotope ratio mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, and biological approaches to labelling tracer compounds with stable isotopes have provided new opportunities in fatty acid research. Sample preparation for isotope ratio mass spectrometry has been converted from a manual combustion method to an on-line or continuous flow method, making it much more versatile and easier to use. Similarly, 13C-NMR spectroscopy has recently developed as a remarkably useful method for monitoring metabolic steps and pathways both in vivo and at the molecular level. Coincident with these improvements in instrumentation, the commercial availability of numerous uniformly 13C-labelled compounds has made these studies more affordable. The application of some of these developments to questions in the field of polyunsaturated fatty acid metabolism is described.