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

Abstract

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), 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 vesicles from micelles by repeat ultracentrifugation failed. 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, Rh) were similar (less than or equal to 40 A), whereas unilamellar vesicle sizes (Rh = 200-600 A) 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.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of Korean white ginseng extracts on obesity in high-fat diet-induced obese mice

“…The products, fatty acid and 2-monoacylglycerols, formed by hydrolysis of pancreatic lipase are absorbed in the lumen of the gut (Verger 1984;Hernell et al 1990;Astrup et al 1994). Therefore, inhibition of hydrolysis of dietary fat may decrease intestinal absorption of fat, leading to a reduction in obesity and hyperlipidemia.…”

Hypoglycemic and insulin-sensitizing effects of berberine in high-fat diet- and streptozotocin-induced diabetic rats

“…Subjects then ingested a standardized meal containing 123-mg cholesterol, and duodenal drainage was collected in 15-min intervals for 90 min and then one 30-min interval. 11,16 Samples were processed and saved as described previously. 11 On days 16 through 19, cholesterol absorption was measured using the dual-stable isotopic method.…”

“…Lipid composition in duodenal aspirates was analyzed as described elsewhere. 11,16 Samples were separated into the oil, aqueous, and pelleted subphases by ultracentrifugation. 16 Samples were extracted, and phospho-lipids, cholesterol, and bile acids were measured.…”

Spontaneous lipid transfer between organized lipid assemblies

“…The majority of studies involving lipid uptake in the intestine have focused on fatty acid transfer from bile salt micelles to enterocytes [86][87][88][89][90]. However, the recent discovery that non-micellar phases such as unilamellar vesicles may also be formed during fat digestion may prompt further investigation [91][92]. In any case, Dietschy has argued that bile salt micelles enhance lipid uptake by acting as large capacity vehicles for moving fatty acids and other lipids across the unstirred water layers adjacent to enterocytes [89,90,93].…”