THE METABOLISM AND AVAILABILITY OF ESSENTIAL FATTY-ACIDS IN ANIMAL AND HUMAN TISSUES
THE METABOLISM AND AVAILABILITY OF ESSENTIAL FATTY-ACIDS IN ANIMAL AND HUMAN TISSUES
复制标题
DOI：
10.1051/rnd:19940603
复制
发表时间：
1994-01-01
期刊：
影响因子：
--
通讯作者：
CLOUET, P
中科院分区：
文献类型：
--
作者：
BEZARD, J;BLOND, JP;CLOUET, P
必需脂肪酸（EFA）是动物和人体组织中不能合成的多不饱和脂肪酸（PUFA）的n-6和n-3家族，来源于亚油酸（LA，18：2n-6）和α-亚麻酸（LNA，18：3 n-3）。成人LA的最佳需求量为摄入能量的3-6%，LNA的最佳需求量为摄入能量的0.5-1%。在发展中对LNA的要求越来越高。LA和LNA的膳食来源主要是植物，而花生四烯酸（AA，20：4 n-6）存在于陆生动物的产品中，二十碳五烯酸（EPA）和二十二碳六烯酸（DHA）存在于海洋动物的产品中。EFA主要存在于膳食三酰甘油中，在胃和肠腔中被脂肪酶水解。DHA的释放似乎比其他物质慢。它的肠道吸收延迟，但不减少。长链PUFA以显著的量掺入乳糜微粒磷脂中。然而，它们被组织吸收的速度并不比短链PUFA的吸收快。在组织中，构成膳食EFA的主要部分的LA和LNA应通过交替的去饱和（Delta 6，Delta 5，Delta 4）-延伸反应转化为更长和更不饱和链的脂肪酸。动物组织在这种生物合成中比人体组织更活跃。肝脏是最活跃的器官之一，它的作用是至关重要的，在提供较不活跃的组织，特别是大脑，与长链PUFA分泌的VLDL（极低密度脂蛋白）。在肝脏中，多种营养、激素和生理因素对PUFA的生物合成起作用。膳食脂肪酸的影响很大，往往是抑制。膳食LNA抑制LA的Delta 6去饱和。去饱和产物AA、EPA和DHA抑制LA的Δ 6去饱和和DGLA（二高-γ-亚麻酸）的Δ 5去饱和。关于激素，胰岛素和甲状腺素是Delta 6和Delta 5去饱和活性所必需的，而其他激素（胰高血糖素、肾上腺素、ACTH、糖皮质激素）抑制去饱和。关于生理因素，个人的年龄是关键。在胎儿中，肝脏和大脑能够将LA和LNA转化为较长链的EFA，但这些也是在母体肝脏和胎盘中合成后由母亲递送的。在动物出生后，Delta 6去饱和活性在肝脏中增加，在大脑中减少。在衰老过程中，整个肝脏去饱和LA和DGLA的能力在1.5和25个月大的大鼠中是相等的，这些大鼠在其一生中都被喂食均衡的饮食，并且组织磷脂的AA和DHA含量在衰老过程中是不变的。肝脏中的脂肪酸氧化也可能降低组织中EFA的可用性，特别是过氧化物酶体含量高的长链PUFA的氧化。然而，在健康个体中，尽管有许多因素可能影响EFA的可用性，但在大多数情况下，规律和均衡的饮食满足n-6和n-3 EFA的组织要求。
Essential fatty acids (EFA), which are not synthesized in animal and human tissues, belong to the n-6 and n-3 families of polyunsaturated fatty acids (PUFA), derived from linoleic acid (LA, 18:2n-6) acid alpha-linolenic acid (LNA, 18:3n-3). Optimal requirements are 3-6% of ingested energy for LA and 0.5-1% for LNA in adults. Requirements in LNA are higher in development. Dietary sources of LA and LNA are principally plants, while arachidonic acid (AA, 20:4n-6) is found in products from terrestrian animals, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are found in products from marine animals. EFA are principally present in dietary triacylglycerols, which should be hydrolyzed by lipases in gastric and intestinal lumen. DHA seems to be released more slowly than the others. Its intestinal absorption is delayed but not decreased. Long-chain PUFAs are incorporated in noticeable amounts in chylomicron phospholipids. However, their uptake by tissues is no more rapid than uptake of shorter chain PUFA. In tissues, LA and LNA, which constitute the major part of dietary EFA, should be converted into fatty acids of longer and more unsaturated chain by alternate desaturation (Delta 6, Delta 5, Delta 4)-elongation reactions. Animal tissues are more active in this biosynthesis than human tissues. Liver is one of the most active organs and its role is critical in providing less active tissues, particularly the brain, with long-chain PUFA secreted in VLDL (very low density lipoprotein). In liver, many nutritional, hormonal and physiological factors act on the PUFA biosynthesis. Dietary fatty acids exert a great influence and are often inhibitory. Dietary LNA inhibits Delta 6 desaturation of LA. The desaturation products AA, EPA, and DHA inhibit Delta 6 desaturation of LA and Delta 5 desaturation of DGLA (dihomo-gamma-linolenic acid). With regard to hormones, insulin and thyroxin are necessary to Delta 6 and Delta 5 desaturation activities, whereas other hormones (glucagon, epinephrine, ACTH, glucocorticoids) inhibit desaturation. Concerning the physiological factors, the age of individuals is critical. In the fetus, the liver and the brain are capable of converting LA and LNA into longer-chain EFA, but these are also delivered by the mother, after synthesis in the maternal liver and placenta. Just after birth, in animals, the Delta 6 desaturation activity increases in the liver and decreases in the brain. In aging, the capacity of the whole liver to desaturate LA and DGLA is equal at 1.5 and 25 months of age in rats fed a balanced diet throughout their life and the AA and DHA content of tissue phospholipids is unchanged in aging. Fatty acid oxidation in the liver is also likely to decrease the availability of EFA in tissues, in particular oxidation of long-chain PUFAs which is high in peroxisomes. However, in healthy individuals, despite the numerous factors likely to influence the availability of EFA, in most cases a regular and balanced diet meets the tissue requirements in n-6 and n-3 EFA