PHYSICAL-CHEMICAL BEHAVIOR OF DIETARY AND BILIARY LIPIDS DURING INTESTINAL DIGESTION AND ABSORPTION .2. PHASE-ANALYSIS AND AGGREGATION STATES OF LUMINAL LIPIDS DURING DUODENAL FAT DIGESTION IN HEALTHY ADULT HUMAN-BEINGS
PHYSICAL-CHEMICAL BEHAVIOR OF DIETARY AND BILIARY LIPIDS DURING INTESTINAL DIGESTION AND ABSORPTION .2. PHASE-ANALYSIS AND AGGREGATION STATES OF LUMINAL LIPIDS DURING DUODENAL FAT DIGESTION IN HEALTHY ADULT HUMAN-BEINGS
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DOI：
10.1021/bi00460a012
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发表时间：
1990-02-27
期刊：
影响因子：
2.9
通讯作者：
CAREY, MC
中科院分区：
文献类型：
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作者：
HERNELL, O;STAGGERS, JE;CAREY, MC
健康成年人进食富含三酰甘油的膳食后，抽取十二指肠内容物进行体外化学和理化分析。在建立的脂质消化和吸收过程中收集抽吸物，并将其吸收到快速抑制离体脂解的化学抑制剂的“鸡尾酒”中。超离心后，脂质分离成漂浮的油层、几个界面层、“澄清”或浑浊的“亚相”和沉淀的“颗粒”。 通过化学分析和相分析，漂浮层由水包油型乳液颗粒组成，其核心为三酰甘油（TG）、1-二酰甘油（DG）和胆固醇酯（CE），表面由部分离子化脂肪酸（FA）、单酰甘油（MG）、二酰磷脂酰胆碱（PL）和胆汁盐（BS）乳化。界面层含有类似的乳液颗粒分散在过量的乳化剂，采用层状液晶结构。乳化颗粒主要由乳化脂质组成，含有少量结晶钙皂和BS。除了三个亚相之外，所有亚相的相对脂质组成都落在浓缩的三元相图的两相区域内（Staggers等人，1990，配套论文），其中由BS、FA“酸皂”、MG、PL、胆固醇（Ch）和痕量DG（和TG）组成的饱和混合胶束与由相同脂质组成的单层液晶囊泡共存。通过重复超离心实现囊泡与胶束的干净分离的尝试失败了。2与平衡模型系统中脂质颗粒的结构和尺寸相比（Staggers等人，1990），准弹性光散射（QLS）分析揭示了离体胶束尺寸（平均流体动力学半径，hivin Rh）相似（≤ 0.0001）。ANG），而单层囊泡大小（hivin.Rh = 200-600埃）要小得多亚相的双组分QLS分析表明，更大比例的脂质溶解胶束比分散为单层囊泡。当随后作为时间的函数，囊泡经常自发地溶解成混合胶束，这表明，在非平衡的体内条件下，组成胶束相往往是不饱和的脂质。这些结果是一致的假设，即在水解乳化DG和TG的管腔脂肪酶，单层囊泡起源于层状液晶，形成在乳化水界面在小肠上部。在BS-充满的环境中，单层囊泡可能代表人体脂肪消化的主要分散产物相，并促进脂解产物溶解成不饱和混合胶束。我们推测，单层囊泡的混合胶束的饱和产生最有利的热力学条件，最大限度地提高从小肠上部的脂质吸收率;此外，脂解产物分散为单层和多层囊泡可以解释缓慢，但有效的，脂肪吸收发生在整个小肠在BS-缺乏状态。
Following the feeding of a triacylglycerol-rich meal to healthy adult human beings, duodenal contents were aspirated for ex vivo chemical and physical-chemical analyses. The aspirates were collected during established lipid digestion and absorption into a "cocktail" of chemical inhibitors that rapidly inhibited ex vivo lipolysis. Following ultracentrifugation, the lipids separated into a floating oil layer, several interfacial layers, a "clear" or turbid "subphase", and a precipitated "pellet". By chemical and phase analyses, the floating layer was composed of oil-in-water emulsion particles with cores of triacylglycerol (TG),1 diacylglycerols (DG), and cholesteryl esters (CE) emulsified with a surface coat of partially ionized fatty acids (FA), monoacylglycerols (MG), diacylphosphatidylcholine (PL), and bile salts (BS). The interfacial layers contained similar emulsion particles dispersed among excess emulsifier which adopted a lamellar liquid-crystalline structure. Precipitated pellets were composed principally of emulsifying lipids, with smaller amounts of crystalline calcium soaps and BS. Relative lipid compositions of all but three subphases fell within a two-phase region of the condensed ternary phase diagram (Staggers et al., 1990, companion paper) where saturated mixed micelles composed of BS, FA "acid-soaps", MG, PL, cholesterol (Ch), and traces of DG (and TG) coexisted with unilamellar liquid-crystalline vesicles composed of the same lipids. Attempts to achieve clean separation of of vesicles from micelles by repeat ultracentrifugation failed.2 Compared with the structure and sizes of lipid particles in equilibrated model systems (Staggers et al., 1990), quasielastic light scattering (QLS) analysis revealed that ex vivo micellar sizes (mean hydrodynamic radii, .hivin.Rh) were similar (.ltoreq. .ANG.), whereas unilamellar vesicle sizes (.hivin.Rh = 200-600 .ANG.) were appreciably smaller. Two-component QLS analysis of the subphases showed that much larger proportions of lipids were solubilized by micelles than were dispersed as unilamellar vesicles. When followed as functions of time, vesicles frequently dissolved spontaneously into mixed micelles, indicating that, in the nonequilibrium in vivo conditions, the constituent micellar phase was often unsaturated with lipids. These results are consistent with the hypothesis that, during hydrolysis of emulsified DG and TG by luminal lipases, unilamellar vesicles originate in lamellar liquid crystals that form at emulsion-water interfaces in the upper small intestine. In a BS-replete environment, unilamellar vesicles probably represent the primary dispersed product phase of human fat digestion and facilitate the dissolution of lipolytic products into unsaturated mixed micelles. We speculate that saturation of mixed micelles by unilamellar vesicles produces the most favorable thermodynamic condition for maximizing lipid absorption rates from the upper small intestine; further, lipolytic products dispersed as uni- and multilamellar vesicles may explain the slow, but efficient, fat absorption that takes place from the entire small intestine in BS-deficiency states.