Omega-3 Odyssey
Are the health claims for these compounds warranted and, if so, can their measurement be streamlined?
You have probably noticed during a regular visit to your local grocery store that many common food products, such as bread, cereal, milk, and eggs, are ‘rich in omega-3s’. And perhaps you have a friend who is taking omega-3 supplements?
Omega-3s are polyunsaturated fatty acids (PUFAs), a class of lipids characterized by a carboxylic group, an aliphatic chain, and multiple double bonds. They are named according to the position of the first double bond in the carbon chain, starting from the terminal carbon atom of the molecule (called the ‘omega carbon’ because omega is the last letter of the Greek alphabet). The other type of PUFAs are omega-6s.
The importance of PUFAs to human health is that the overall balance between omega-3 and omega-6 species seems to modulate many biological processes including the relaxation and contraction of smooth muscle tissue, blood coagulation and, most notably, inflammation. Some long-chain omega-3s are found to be particularly enriched in the brain and retina, playing a major role in cognition and vision.
Various methods have been adopted to measure omega-3 levels in biological and food samples. Historically, gas chromatography-mass spectrometry (GC-MS) has been the technique of choice. Analysis by GC, however, requires a multi-step procedure for the hydrolysis and derivatization of the PUFAs to fatty acid methyl esters. Alternatively, liquid chromatography (LC)-MS and tandem MS analysis allows the direct measurement of both free and esterified PUFAs without the need for hydrolysis or derivatization. The less abundant oxygenated PUFAs are usually measured by LC-tandem MS after a solid–phase extraction purification step.
Supercritical fluid chromatography-MS and, more recently, ultra performance convergence chromatography-MS have been adopted for the analysis of PUFAs. These technologies have the advantage of reducing the use of toxic organic solvents and facilitating the purification process. Other non-chromatographic techniques utilized for PUFA analysis include desorption ionization-MS, ion mobility-MS, Raman spectroscopy and nuclear magnetic resonance (NMR). These solutions, although not as sensitive, do offer the potential for real-time analysis.
Within each omega family, there is a subclass distinction: short-chain and long-chain PUFAs. The human body cannot manufacture short-chain PUFAs and must rely entirely on dietary intake for these essential nutrients. Long-chain PUFAs, on the other hand, can be made by the body starting from a shorter chain or can be absorbed directly through diet. The short-chain omega-3 fatty acid that is most abundant in food is alpha-linolenic acid (ALA), which is present at high levels in leafy green vegetables and flaxseeds. The most abundant dietary long-chain omega-3 PUFAs are eicosapentanoic acid (EPA) and docosahexaenoic acid (DHA), which are present in oily fish and fish oil supplements. Omega-6 PUFAs mainly include the short-chain linoleic acid (LA) and to a lesser extent the long-chain arachidonic acids (ARA), which are abundant in vegetables oils, such as corn, soybean, safflower and sunflower oils (http://ndb.nal.usda.gov/).
Once absorbed in the intestines, PUFAs are processed in the liver and transported through the blood to all tissues. Here, PUFAs can be found as free fatty acids, esterified to complex structural lipids, such as phospholipids, or metabolized into bioactive oxygenated species. Overall, from just a handful of omega-3 and omega-6 precursors, there are hundreds of derived species in our tissues.
Most Western diets are deficient in omega-3s and abundant in omega-6s. Current nutritional research shows that a diet enriched in omega-3s offers health benefits and anti-inflammatory properties, whereas an excess of omega-6s might contribute to the pathogenesis of many chronic inflammatory diseases, including cardiovascular and autoimmune diseases. This evidence is gradually impacting dietary habits, food production and marketing strategies. In the future, food labels may be required to display detailed information about the content of omega-3 versus omega-6 PUFAs, as well as short-chain versus long-chain PUFAs, to facilitate the comparison of food products and help consumers in their food choices.
Consequently, the development of rapid and inexpensive assays for screening omega-3s and omega-6s represents an opportunity, not only for labeling foodstuffs but also to assess nutritional deficiencies or imbalances. Personalized nutritional interventions aimed at balancing omega-3 and omega-6 might help improve the overall health.
Giuseppe Astarita works at the intersection of biology and technology. He is principal scientist in lipidomics and metabolomics at Waters Corporation (Milford, Massachusetts, USA) and serves as an adjunct professor at Georgetown University (Washington, DC, USA). An expert in lipid mass spectrometry and metabolomics for translational medicine and biomarker discovery, his interests are in the role of lipid metabolism in health and disease, including inflammation, Alzheimers disease, metabolic syndrome, cardiovascular disease, aging, and drug addiction. In 2010, The International Society for the Study of Fatty Acids and Lipids named him Top New Investigator Award in Biochemistry of Lipids.
