GC-FID-based quantification of the sum of the three forms of vitamin B3 from animal liver

Vitamin B₃ (nicotinic acid, nicotinamide) is an essential water-soluble vitamin and cellular energy metabolism depends on the vitamin B₃-derived cofactors. Inaccessible covalently-linked nicotinic acid in food such as maize can cause vitamin B₃ deficiency in animals since maize is also deficient in tryptophan, the precursor of nicotinic acid. A sensitive and reproducible GC-FID-based method for the quantification of the sum of the three forms of vitamin B₃ from animal liver was developed. Free nicotinic acid, free nicotinamide and nicotinamide moiety of NAD⁺/NADP⁺ (and their riboside precursors) were simultaneously derivatized as methyl nicotinate. Reaction time and temperature and the extraction procedure for methyl nicotinate were optimized. Starting from wild boar liver, removal of proteins, solvent exchange, derivatization, and chloroform extraction resulted in sufficient enrichment and baseline separation of methyl nicotinate. The within-laboratory reproducibility of the full procedure was determined with RSD <10%. On-column limit of detection and lower limit of quantification for methyl nicotinate were both sub-picomole. The accuracy of the method was determined from the recoveries of the pre-extraction spiked-in vitamin B₃ standards. The overall recovery for the full procedure was 16% but very consistent (RSD = 7%), enabling determination of apparent vitamin B₃ concentrations for relative quantitative comparison.

Recent progress in stable isotope methods for assessing vitamin metabolism

PURPOSE OF REVIEW

Recent developments in mass spectrometric methodology, in particular the widespread adoption of liquid chromatography/mass spectrometry, have presented investigators with new opportunities to investigate micronutrient absorption and metabolism. This review focuses on recent reports of the use of stable isotope techniques to facilitate research into vitamin uptake and utilization in humans.

RECENT FINDINGS

Stable isotopes are used principally in two ways, as analytical standards in isotope dilution assays and as tracers in studies of physiology. There have been a number of advances in both fields recently for almost all of the vitamins. In particular, the effects of food preparation and meal composition on vitamin bioavailability are being probed more widely than before.

SUMMARY

A considerable amount of method development has been reported. We now have the opportunity to consolidate our understanding of vitamin metabolism to better inform the dietary recommendations for optimal health.