Omega-3指数的概念和应用

Concept of omega-3 index and its application

Omega-3（又称ω3或n-3）指数的概念是2004年由Harris和yon Schacky提出的，它是通过测红细胞膜二十碳五烯酸（eicosapentaenoic acid，EPA；C20：5n-3）和二十二碳六烯酸（docosahexaenoic acid，DHA；C22：6n-3）的含量（占红细胞膜总脂肪酸的比例），作为生物标记物来反映习惯膳食n-3多不饱和脂肪酸（polyunsaturated fatty acid，PUFA）的摄入。

The concept of the ' omega-3(n-3) index ' is proposed by Harris and von Schacky [ 1 ] in 2004,which is by measuring red cell membrane eicosapentaenoic acid(EPA;C20 : 5n-3) and docosahexaenoic acid(DHA;C22 : 6n-3) content(% of total fatty acids),as a biomarker to reflect the customary dietary n-3polyunsaturated fatty acid(PUFA) intake.Omega-3index is a risk factor of sudden cardiac death [ 2 ],which is similar with low density lipoprotein cholesterol,a risk factor for coronary artery disease.Omega-3index is significantly negatively correlated with coronary heart disease mortality,and it has a strong cardioprotective effect.Coronary heart disease mortality will be reduced by more than half when the n-3index is greater than or equal to 8%,however,cardio-protective effect will be least when the n-3index is less than or equal to 4% [ 1 ].It is generally considered that arterial thrombosis was converted from stable acute ischemic heart and brain lesions.Among the clinical manifestations of unstable angina,the acute thrombotic infarction,sudden death and diseases of the cardiovascular system,the arterial thrombosis plays the protagonist role.The platelet aggregation is the initial stage of the thrombus formation [ 3 ].EPA and DHA protective effect on the cardiovascular system is by the following mechanisms : The platelet aggregation is initiated by thromboxane A2(TXA 2),which is a powerful platelet aggregation factor and vasoconstrictor,and is generated by the platelet membrane from the arachidonic acid(AA) [ 3 ].Increased dietary intake of n-3PUFA,especially EPA and DHA,will increase the tissue membrane concentration of EPA and DHA.Released EPA from the platelet membrane phospholipids competitive binding of the cyclooxygenase(COX) with AA,thereby generating an alternative form of thromboxane A 3(TXA 3),it is relatively non-platelet aggregation and vasoconstriction activity,so it leads to a reduced formation of TXA 2.Thereby results in the formation of thrombotic tendency.Meanwhile,it produces 3-series prostaglandins and prostacyclin and 5-series leukotriene(LT) and lipoxins(lipoxin) [ 4 ],which have anti-inflammatory,anti-platelet aggregation and smooth muscle relaxation activity.Marine oil is rich in EPA and DHA with a beneficial effect on the secondary prevention of myocardial infarction.In addition,EPA and DHA may prevent fatal arrhythmias,increase heart rate changes,reduce the level of serum triacylglycerol(TAG),lower systolic and diastolic blood pressure,regulate the flow of ions in myocardial cells,inhibit inflammatory cytokine production and activity [ 5 ],and reduce plasma homocysteine concentration [ 6 ].EPA and DHA may regulate the expression of many genes,for example,EPA and DHA can down-regulate protein glycans decomposing enzyme(aggrecanases) proinflammatory cytokines(interleukin-1αand TNF-α),COX-2fatty acid synthase,acetyl coenzyme A carboxylase,methionine adenosyltransferase,S14protein and stearyl coenzyme A desaturase,and they can up-regulate the lipoprotein lipase fatty acid-binding protein,acetyl coenzyme A synthetase,carnitine palmitoyl transferase enzyme 1,acetyl coenzyme A dehydrogenase,acetyl coenzyme A oxidase,cytochrome P-450 4A2,peroxisome proliferator-activated receptorα [ 5 ] and cystathionine-g-lyase [ 7 ].In most biological membranes,the major component of the phospholipid is fatty acid,in which the long chain n-3and n-6PUFAs have an important role in maintaining the structure of the cell membrane and function.In the retina and the brain of humans and other mammals,there is a high content of DHA,which plays an important role in order(fluidity) of the membrane,the activity of the membrane enzymes,ion channels,and the conduction of information.DHA is an indispensable substance of maintaining visual and brain functions because of its cell membrane fluidity.It has an important role in membrane fluidity,thereby affecting the function of the membrane receptor(such as rhodopsin),regulating the membrane-bound enzymes(such as Na / K-dependent adenosine triphosphatase) of the active,and pass on the inositol phosphate,diacylglycerol and protein kinase C,to affect the transmission of signals.The DHA may directly affect the biosynthesis of the neurotransmitter,the absorption of serotonin,the signal transmission,β adrenergic receptors and serotonergic receptor binding as well as a monoamine oxidase activity [ 5 ].