Role of luminal lecithin in intestinal fat absorption

The effects of biliary lecithin on fat absorption were studied in 1 day bile fistula rats fed micellar solutions of bile salt, monoglyceride and radioactive free fatty acids. By electron microscopy and measurement of uptake of radioactivity into liver and adipose tissue, it was shown that in the absence of bile lecithin there was significant impairment of fat release from mucosa. Fat clearance was effected by the feeding of phosphatidyl choline or choline, but not phosphatidyl ethanolamine, inositol or cholesterol. In the absence of luminal choline there was a decrease in incorporation of radioactive leucine into mucosal protein. It is concluded that biliary and dietary lecithin or choline play an important role in triglyceride transport out of intestinal mucosa, by providing surfactant lecithin for the chylomicron envelope and by supporting mucosal protein biosynthesis.     

A liquid crystalline phase in human intestinal contents during fat digestion

A viscous, gel-like phase was found in ultracentrifuged human upper intestinal contents collected during rapid fat lipolysis. This “gel” phase was layered in the ultracentrifuge tube between the micellar and oil phase. The gel contained lipids typical of the micellar and not the oil phase. The concentration of these lipids was higher and the ratio of total bile salts to lipids was lower in the gel than in the micellar phase. The gel, unlike the micellar phase, was birefringent between crossed polarizers. These data demonstrate that lipids in this gel phase can form liquid crystals in the gut during fat digestion.     

Behavior of biliary phospholipids in intestinal lumen during fat digestion in rat

The phospholipids present in the intestinal lumen of rats following ingestion of triglycerides are of biliary origin. They consist of lecithins accompanied by a small proportion of lysolecithins. Their behavior in comparison with the other lipid constituents of the intestinal content was studied by subjecting the latter to gel filtration on an agarose column in the presence of a solution of 6 mM sodium taurocholate in 0.1 M NaCl. Part of the phospholipids is present with the triglycerides and diglycerides in the emulsified phase excluded from the gel where pancreatic lipase and colipase also are found. The remainder is found in optically clear fractions containing fatty acids, monoglycerides, and bile salts. These fractions are eluted at 2.0 column volumes, while mixed fatty acids, monoglycerides, bile salts micelles emerge from the column at 2.4 column volumes in the same chromatographic conditions. This difference in behavior may be explained by the presence of biliary lecithins. This presence could have an important bearing upon the mucosal uptake of the lipolysis products of triglycerides.     

Influence of dietary fat composition on intestinal absorption in the rat

Omega-3 fatty acids influence the function of the intestinal brush border membrane. For example, the omega-3 fatty acid eicosapentaenoic acid (20∶5ω3) has an antiabsorptive effect on jejunal uptake of glucose. This study was undertaken to determine whether the effect of feeding α-linolenic acid (18∶3ω3) or EPA plus docosahexaenoic acid (22∶6ω3) on intestinal absorption of nutrients was influenced by the major source of dietary lipid, hydrogenated beef tallow or safflower oil. Thein vitro intestinal uptake of glucose, fatty acids and cholesterol was examined in rats fed isocaloric diets for 2 weeks: beef tallow, beef tallow + linolenic acid, beef tallow + eicosapentaenoic acid/docosahexaenoic acid, safflower oil, safflower oil + linolenic acid, or safflower oil + eicosapentaenic acid/docosahexaenoic acid. Eicosapentaenoic acid/docosahexaenoic acid reduced jejunal uptake of 10 and 20 mM glucose only when fed with beef tallow, and not when fed with safflower oil. Linolenic acid had no effect on glucose uptake, regardless of whether it was fed with beef tallow or safflower oil. The jejunal uptake a long-chain fatty acids (18∶0, 18∶2ω6, 18∶3ω3, 20∶4ω6, 20∶5ω3 and 22∶6ω3) and cholesterol was lower in salfflower oil than with beef tallow. When eicosapentaenoic acid/docosahexaenoic acid was given with beef tallow (but not with safflower oil), there was lower uptake of 18∶0, 20∶5ω3 and cholesterol. The demonstration of the inhibitory effect of linolenic acid or eicosapentaenoic acid/docosahexaenoic acid on cholesterol uptake required the feeding of a saturated fatty acid diet (beef tallow). These changes in uptake were not explained by differences in the animals’ food intake, body weight gain or intestinal weight. Feeding safflower oil was associated with an approximately 25% increase in the jejunal and ileal mucosal surface area, but this increase was prevented by combining linolenic acid or eicosapentaenoic acid/docosahexaenoic acid with safflower oil. Different inhibitory patterns were observed when mixtures of fatty acids were present together in the incubation medium, rather than in the diet: for example, when 18∶0 was in the incubation medium with 20∶4ω6, the uptake of 20∶4ω6 was reduced, whereas the uptake was unaffected by 18∶2ω6 or 20∶5ω3. Thus, (1) the inhibitory effect of eicosapentaenoic acid/docosahexaenoic acid on jejunal uptake of glucose, fatty acids and cholesterol was influenced by the major dietary lipid, saturated (beef tallow) or polyunsaturated fatty acid (safflower oil); and (2) different omega-3 fatty acids (linolenic acid versus eicosapentaenoic acid/docosahexaenoic acid) have a variable influence on the intestinal absorption of nutrients.     

Effect of dietary fat saturation of absorption and intestinal secretion of cholesterol by the hypercholesterolemic rat

The fate of an oral dose of [4-¹⁴C] cholesterol given to rats grown on diets with 20% safflower oil or 20% hydrogenated coconut oil was determined by analysis of digestive tract, feces and tissues. The pattern of isotope distribution did not support the view that rats fed a saturated fat absorb less cholesterol than those fed an unsaturated fat. Fasted animals growth on the diet with 5% of these two fats and beef fallow showed no clear difference in the amount of digitonin-peecipitable sterol in their intestines. A shorter transit time for intestinal contents was observed with the saturated fat groups. It is concluded that neither absorption of cholesterol from the gut nor secretion of β-hydroxy sterol into the gut accounts for the hypocholesterolemic effect of polyunsaturated fat. Journal Paper No. 4951 AES, Purdue University.     

Non-soluble dietary fiber effects on lipid absorption and blood serum lipid patterns

Generalized effects of dietary fiber on lipid absorption and blood serum lipid patterns of humans have not been defined and may not even exist. The term dietary fiber covers a wide variety of materials with different chemical and physical characteristics. The ability of pectins and mucilages, often classed as soluble fibers, to lower blood and liver lipids has been demonstrated repeatedly and consistently. However, demonstrated hypolipidemic effects of feeding such non-soluble fibers as cellulose, hemicellulose and bran are by no means consistent. On the basis of pooled data, it appears that hypolipidemic response or non-response of humans to inclusion of non-soluble fibers in diets is in part related to the degree of fecal bulking as a result of in vitro water holding capacity and in part related to pre-study blood serum lipid levels of the individual subjects.     

Effect of acute ethanol ingestion on fat absorption

A test meal (300 mg casein, 600 mg sucrose, 100 mg corn oil, tracer dose of 9.10³H oleic acid) was given to fasting adult rats with intestinal lymph fistulas. One group received an acute oral dose of ethanol (3.2 g/kg body weight) simultaneously with the test meal. Controls received 2.5 ml of water instead of ethanol. Ingestion of ethanol temporarily delayed the removal of lipid radioactivity from the stomachs. More than 25% of radioactivity fed remained 8 hr after feeding whereas with control rats less than 10% of lipid radioactivity fed remained 6 hr after feeding. In controls and ethanoltreated rats, the amounts of exogenous lipids in the intestinal lumen and mucosa were low and similar enough. Quantities of endogenous and exogenous lipids found in the lymph collected during 24 hr after feeding were similar in the two groups, but the fat absorption peak was found after 6 hr in alcoholic rats and before 6 hr in controls. This delay was probably due to the retention of lipids in the stomach. More of the exogenous lipid was always transported by small particles moving in the region of α₁ globulins in cellulose acetate electrophoresis than by larger particles remaining at the origin. This proportion was enhanced in the ethanoltreated animals. The larger fat particles were richer in endogenous fatty acids in alcohol-treated rats than in controls. These experiments are a part of a thesis of “Doctorat d'Etat” (Speciality: Biology) n^o C.N.R.S. A0 11.965 presented in Dijon on February 6, 1976.     

Dietary fat ratios and liver plasma membrane lipid composition

Male Sprague-Dawley weanling rats were fed isocaloric diets consisting of 10% (by wt) fat. The six groups differed in the ratio of corn oil and butter fat present in the diets such that: 10C, 10% corn oil (C); 8C2B, 8% C/2% butter fat (B); 6C4B, 6% C/4% B; 4C6B, 4% C/6% B; 2C8B, 2% C/8% B; and 10B, 10% B. Liver plasma membranes were analyzed for fatty acid composition and cholesterol/phospholipid molar ratio. The 18∶2n−6 content was constant in the 10C and 8C2B diets and then decreased linearly through the 2C8B diet. The 20∶4n−6 and 18∶1n−9 contents were constant except in the 10B diet, in which a significant decrease and increase, respectively, were observed. The cholesterol/phospholipid molar ratio increased between the 10C and 6C4B diets and subsequently (4C6B and 10B diets) remained constant. This data indicates that changes in n−6 fatty acid content in the liver plasma membrane are directly related to dietary intake only for 18∶2n−6. Arachidonic acid content in the membrane is maintained at a constant level until the linoleic acid content of the diet is reduced to 0.5% of calories. It also indicates that the cholesterol content of the membrane becomes saturated and does not increase with increasing concentrations of saturated fat in the diet. Presented in part at the FASEB Meeting, Washington, D.C., April, 1987.     

Recent progress in the applications of infrared absorption spectroscopy to lipid chemistry

Scores of other applications of infrared spectra to problems of lipid chemistry could be cited. No useful purpose would be served by a somewhat repetitious listing of the many applications which have been reported. An attempt has been made to select applications that would represent the various ways in which infrared absorption spectroscopy is being used for and by the fatty acid chemist. A review of this nature a decade ago could easily have included a complete bibliography with reference to all papers which appeared within the period covered. This is no longer practical as infrared spectroscopy has become a major tool of the lipid chemist. In this review the reports by several workers of very excellent research contributions have not been included. During the past five years several review papers have appeared. In the second edition of Markley舗s 舠Fatty Acids舡 the subject of infrared absorption is covered to about 1958 (95). In German and excellent review has been written by Kaufmann, Volbert, and Mankel (60), including 249 literature references and again covering the period through about 1958.     

Removal of lipid from intact erythrocytes and ghosts by aqueous solutions and its relevance to membrane structure

Molar values for cholesterol, total phospholipid, and individual phospholipid classes of intact erythrocytes and their membranes (ghosts) washed with various aqueous solutions are presented. The data show that lipid can be washed from erythrocyte ghosts prepared rapidly from freshly drawn blood but that lipid is not removed from intact erythrocytes under the same conditions. Thus, it appears that the polar groups of lipids of intact cells are not exposed as they are in ghosts. In the preparation of hemoglobin-free ghosts, up to 25% cholesterol and phospholipid can be removed, while loss of ca. 50% cholesterol and phospholipid from ghosts can be achieved with aqueous solutions containing ethylenediamine tetraacetate. No significant loss of membrane protein was encountered even when almost half of the lipid had been removed from the ghosts. Phospholipid classes were removed to different extents with different wash solutions. Lipid loss from ghosts can be prevented, in part, by adding 0.5% albumin or calcium to wash solutions containing ethylenediamine tetraacetate. These findings contrast a report where insignificant lipid loss was noted in the preparation of hemoglobin-free human erythrocyte membranes, but agree with results reported for bovine red cell ghosts.     

微波消解火焰原子吸收光度法测定人参中的锌

本文采用火焰原子吸收光度法测定了人参中的锌。结果表明,该法的回收率为100．2％,结果可靠,方法简便,可用于实际样品的测定。     

微波消解-火焰原子吸收法测定谷物食品中的钙元素

试样经微波消解,运用火焰原子吸收法测定谷物食品中的钙。结果表明,钙元素在0.5~3.0μg/m L范围内,线性关系良好,相关系数r=0.997。相对标准偏差(RSD)均小于0.1%,加标回收率在90.7%~105.9%。该方法操作简单,耗时较短,精确度高,重复性好,适用于日常检测工作。     

Biodiscrimination of α-tocopherol stereoisomers during intestinal absorption

Synthetic α-tocopherol (α-Toc) contains equal amounts of eight different stereoisomers, and the four stereoisomers with the 2R configuration are generally more active than their correspoding 2S-isomers. We investigated the biodiscrimination of α-Toc stereoisomers during intestinal absorptionin situ andin vitro. Intestinal absorption of α-Toc stereoisomers was examinedin situ in vitamin E-deficient rats with cannulated thoracic ducts. We found that the ratios of α-Toc stereoisomers in lymph of the all-rac-α-Toc group were the same as the administered α-Toc stereoisomers, and 2R-isomers occupied approximately 50% of absorbed α-Toc. The uptake of α-Toc stereoisomers also was measured using Caco-2 cells cultured on filter membranes. The concentration ofRRR-α-Toc in Caco-2 cells was not significnatly different from that ofSRR-α-Toc. Therefore, the discrimination of α-Toc stereoisomers does not occur during absorption in small intestine, suggesting the liver as a source for the biodiscrimination.     

Base-catalyzed derivatization methodology for FA analysis. Application to milk fat and celery seed lipid TAG

In this paper, an alternative base-catalyzed methodology for the facile derivatization in mild conditions of lipid TAG prior to FA analysis is proposed. Reagents were prepared by proton exchange between potassium tert-butoxide and either ethanol, n-propanol, n-butanol, or 2-methoxyethanol and used for the synthesis, at 40°C for 15 min, of the corresponding derivatives, which were directly analyzed by GC. This methodology can be used on a routine basis and has been applied to standard and complex natural lipid samples. Tripalmitin was used to determine optimal reaction conditions; and bovine milk fat, containing C₄ to C₂₂ acids, and celery (Apium graveolens) seed oil, characterized by a high level of petroselinic acid, were comparatively analyzed as their ethyl, n-propyl, n-butyl, and 2-methoxyethyl esters.     

Onset and persistence of changes in intestinal transport following dietary fat manipulation

In this study we determined the time-course for the onset and the loss of the effect of short-term feeding rats isocaloric semisynthetic diets containing a high content of saturated (HS) or polyunsaturated (HP) fatty acids on the jejunal and ileal uptake of medium- and long chain fatty acids, cholesterol and glucose. Animals were fed HP or HS for 3, 7 or 14 days; then the diet was switched to standard Purina^® rat chow for a further 3, 7 or 14 days. The uptake of medium chain fatty acids was unchanged. The differences between HP and HS in glucose uptake occurred within 3 days, but persisted for 14 days, whereas there were qualitative as well as quantitative changes in the pattern of lipid uptake: differences in uptake of stearic, oleic, linoleic and linolenic acids and cholesterol occurred after 7 days of feeding HP or HS. Jejunal uptake of linoleic acid was greater in HP than HS on day 7, but HS was greater than HP on day 14. The effect of diet on lipid uptake was similar in the jejunum and ileum. The altered uptake of stearic and oleic acids persisted after the rats were switched back to chow, whereas the uptake of the other nutrients became similar. Thus, (i) changes in dietary content of saturated and polyunsaturated fatty acids have early effects on intestinal transport function; (ii) some of these changes persist even when animals are returned to feeding on chow; and (iii) glucose transport is rapidly altered by dietary changes, whereas lipid uptake changes only after 7 days. We conclude that the transport function of the intestine is responsive to changes in dietary fatty acids.     

Arachidonic acid intestinal absorption: Mechanism of transport and influence of luminal factors on absorption in vitro

The mechanism and characteristics of intestinal absorption of arachidonic acid were studied in vitro using everted intestinal sacs of the rat. Arachidonic acid absorption was studied at concentrations of 5 μM to 8.36 mM. The plot of absorption rate vs. concentration fitted best to a rectangular hyperbola at low μM concentrations and to a straight linear relationship in the mM range of concentrations. Metabolic inhibitors and uncouplers did not change absorption in either range of concentrations. The absorption of arachidonic acid increased with thinning of the unstirred water-layer, decrease in the pH, or the substitution of sodium taurocholate by Pluronic F 68 or Tween 80. Absorption decreased following the equimolar additions of oleic, linoleic, and linolenic acids. Absorption rate did not change when the taurocholate concentration was varied from 5–15 mM or following the additions of butyric or glutamic acids, leucine, lysine, or dextrose. It was concluded that arachidonic acid is absorbed by a concentration-dependent dual mechanism of transport which is not energy dependent. At the low μM range of concentrations, facilitated diffusion is predominant, while at mM concentrations, simple diffusion is the dominant mechanism of absorption. Changes in the intestinal fluid composition, flow rate, and pH can modify the rate of absorption of arachidonic acid.     

Phospholipids affect the intestinal absorption of carotenoids in mice

Previously, we have shown that uptake of carotenoids solubilized with mixed micelles by human intestinal Caco-2 cells is enhanced by lysophosphatidylcholine (lysoPC) and suppressed by PC. This study determined the effect of PC and lysoPC in mixed micelles on the accumulation of β-carotene and lutein in mice in order to elucidate the roles of micellar phospholipid in the intestinal uptake of carotenoids in vivo. Mixed micelles were composed of 2.5 mM monooleoylglycerol, 7.5 mM oleic acid, 12 mM sodium taurocholate, 200 μM carotenoid, and 3 mM phospholipid in PBS. The mice were fed single doses of β-carotene or lutein solubilized in PC (PC group), lysoPC (LPC group), and no phospholipid (NoPL group) micelles. The β-carotene responses in the plasma and liver of the PC group were markedly lower than those of the other two groups, whereas no differences were noticed between the LPC and NoPL groups. The average level of lutein in the plasma of the PC group after administration was significantly (P<0.05) lower than those of the other groups. Moreover, the average level of lutein in the liver was significantly (P<0.05) different among the groups in the order of LPC>NoPL>PC. Thus, the results clearly indicate that PC suppressed the accumulation of β-carotene and lutein in plasma and liver and that lysoPC enhanced the accumulation of lutein in liver. These results suggest that the hydrolysis of PC to lysoPC plays an important role in the intestinal uptake of carotenoids solubilized in mixed micelles.