Liver phospholipids of rats fed a choline-deficient diet supplemented with choline or methionine

The low amount of arachidonic acid in the total phospholipids in the liver of rats fed a standard type of choline-deficient diet was corrected by either choline or methionine, which also increased food intake. Choline increased the content of this fatty acid in the phosphatidyl ethanolamine but not in the phosphatidyl choline. Methionine increased both the amount of phosphatidyl choline and its content of arachidonic acid.     

Phosphatidylethanolamine metabolism in rats fed a low methionine,choline-deficient diet

The metabolism of phosphatidylethanolamine (PE) was studied in male rats fed a low methionine diet for 7 days with or without supplemental choline. Groups of animals were injected with 2-¹⁴C-ethanolamine and killed at intervals thereafter up to 72 hr. Liver phospholipids were isolated, and PE and phosphatidylcholine (PC) were separated by argentation chromatography into diene (18∶2), tetraene (20∶4) and hexaene (22∶6) fractions. Fatty acid composition and the distribution of radioactivity and specific activity in the total phospholipids and in the fractions were determined. Choline deficiency did not affect total liver phospholipid, but it did increase the amount of PE and decreased that of PC. The major effect of the deficiency on phospholipid fatty acids was to decrease the proportion of PE arachidonate and to increase that of docosahexaenoate. Ethanolamine incorporation into liver PE of deficient rats was only slightly less than in the controls, but loss of the radioactivity from the PE was slower. Ethanolamine radioactivity appearing in the PC of deficient rats was about half that of the controls, even though specific activities of the PE precursors were similar to the control rats. Choline deficiency increased the biological half-lives of the total PE and its fractions. Although the proportion of PE tetraenoic fraction was reduced, the total amount of this liver PE fraction in deficient rats was not affected. However the amount of hexaenoic fraction was doubled, and it accounted for most of the increased quantity of liver PE seen in deficient animals. The results suggested that in choline deficiency PE synthesis was delayed but not appreciably suppressed, and that limited availability of methionine for methylating the PE fractions in their proper proportions affected the concentrations of the PE fractions and impaired their normal conversion to PC. Presented in part at the AOCS Meeting, Houston, May 1971.     

Activity of fatty acyl CoA-lysophospholipid acyltransferases in liver microsomes of rats fed a choline-deficient diet

Feeding a choline-deficient diet to rats has no effect on the activity of fatty acyl CoA-lysophospholipid acyltransferases, even though liver microsomes are severely depleted of lecithins. Thus lecithins appear to have no functional role in the activity of these transferases. It can be excluded that the latter enzymes are involved in the production of the changes in the fatty acid composition of liver phospholipids occurring in choline-deficient rats. These changes result most likely from alterations in the biosynthesis of liver lecithins and cephalins.     

Analysis of phosphatidylcholine in soy lecithins by HPLC

A simple and rapid high pressure liquid chromatographic method with RI detector was developed to determine the content of phos-phatidylcholine in soy lecithins. To whom all correspondence should be addressed.     

Stimulation of hepatic lipogenesis by eicosa-5,8,11,14-tetraynoic acid in mice fed a high linoleate diet

Liver slices, from mice fasted for one day and then refed for three days either a 15% corn oil diet or a 15% corn oil diet containing eicosa-5,8,11,14-tetraynoic acid (TYA), were incubated with [1-¹⁴C] acetate or [³H]H₂O to determine lipogenic capacity. Dietary TYA produced a twofold stimulation in fatty acid and cholesterol synthesis. TYA also caused an increase in the relative proportion of linoleate (C_18∶2) and a decrease in that of arachidonate (C_20∶4) in liver. Thus, (a) despite high levels of C_18∶2, hepatic lipogenesis can be increased, and (b) even short term feeding of TYA can alter the hepatic fatty acid composition presumably by inhibition of arachidonate synthesis from linoleate.     

Synthesis of triacylglycerol by lipase in phosphatidylcholine reverse micellar system

Triacylglycerols were synthesized from 1,2-diacylglycerol and fatty acids by lipase entrapped in phosphatidylcholine reverse micelles in n-hexane. In the reaction system without reverse micelles, however, 1,2-diacylglycerol was hydrolyzed into 2-monoacylglycerol and fatty acid, and triacylglycerol was not synthesized. The maximum activity of synthetic reaction was obtained at Wo=10 (Wo=mol water/mol surfactant), which was the water content of this reverse micellar system. Though the optimal pH of theR. delemar lipase reaction is about pH 5.6 in a bulk water system, the enzyme was active for triacylglycerol synthesis at pH’s from 5 to 9 in the reverse micellar system. For the synthesis of triacylglycerols, lauric, myristic, palmitic, stearic, oleic and arachidic acids were effectively used as the fatty acid substrate. 2-Monoacylglycerol was also effective as a substrate of triacylglycerol synthesis. Furthermore, 1,2-diacylglycerol could be replaced by several kinds of aliphatic alcohols as fatty acid acceptors in the reverse micellar system. In this case, those alcohols with chain length more than 4 carbons were effectively used for ester formation.     

Liver desaturase activities and FA composition in monkeys. Effect of a low-protein diet

The aim of the present study was to measure Δ9-, Δ6-, and Δ5-desaturase activities in liver microsomes, as well as phospholipid FA composition of liver and erythrocytes in monkeys fed a control or low-protein diet during the postweaning period. Ten Saimiri sciureus boliviensis (Cebidae) of both sexes were employed; at 12 mon of age they were separated into two groups fed ad libitum on a control or a low-protein diet for 24 mon. Saimiri sciureus had active Δ9, Δ6, and Δ5 liver desaturase enzymes, and these activities were influenced by the diet. A low-protein diet produced a significant reduction in Δ5-desaturation capacity, an increase in Δ9-desaturase activity, and no change in Δ6-desaturase activity (P<0.05). These changes, evoked by protein deprivation, were reflected in the liver phospholipid FA composition. Increases in the proportion of saturated FA and in monounsaturated oleic acid (18∶1n−9) and a decrease in the proportion of PUFA of the n−6 and n−3 series were produced in the animals fed a low-protein diet (P<0.0001). Differences between the two dietary groups were less pronounced in the FA composition of erythrocyte phospholipids. The authors are members of the Carrera del Investigador del Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina.     

Inhibition of lipoxygenase 1 by phosphatidylcholine micelles-bound curcumin

Curcumin (diferuloyl methane) from rhizomes of Curcuma longa L. binds to phosphatidylcholine (PC) micelles. The binding of curcumin with PC micelles was followed by fluorescence measurements. Curcumin emits at 490 nm with an excitation wavelength of 451 nm after binding to PC-mixed micelles stabilized with deoxycholate. Curcumin in aqueous solution does not inhibit dioxygenation of fatty acids by Lipoxygenase 1 (LOX1). But, when bound to PC micelles, it inhibits the oxidation of fatty acids. The present study has shown that 8.6 μM of curcumin bound to the PC micelles is required for 50% inhibition of linoleic acid peroxidation. Lineweaver-Burk plot analysis has indicated that curcumin is a competitive inhibitor of LOX1 with K _l of 1.7 μM for linoleic and 4.3 μM for arachidonic acids, respectively. Based on spectroscopic measurements, we conclude that the inhibition of LOX1 activity by curcumin can be due to binding to active center iron and curcumin after binding to the PC micelles acts as an inhibitor of LOX1.     

Quantitative Determination of phosphatidylcholine by an HPLC-RI system

The following describes the quantitative determining method for phosphatidylcholine (PC) using the HPLC-RI system which we have developed. It uses Lichromsorb, Si 60 (10 μm), 4.6 mm × 250 mm as the column and a mobile phase consisting of n-hexane/isopropanol/water =1:4:1. In this report, we compared data from selected high-purity (60–100 wt%) samples using the HPLC-RI, HPLC-UV and conventional TLC-P methods. Under the conditions we described, the HPLC-UV method was somewhat affected by fatty acid compositions. As a result, there were some inconsistencies in the measured values. However, the HPLC-RI method we propose was applicable to PC from both egg yolk and soybeans. In addition, the HPLC-RI method produced data which correlated well with data from the TLC-P method, and this data was highly accurate and exhibited satisfac-tory reproductibility.     

Alteration in membrane permeability by diacylglycerol and phosphatidylcholine containing arachidonic acid

The phospholipid metabolites, stearoylarachidonylglycerol and diarachidonylglycerol, stimulate transepithelial sodium transport in frog skin epithelium. The increase in Na transport is due to an increase in the unidirectional influx of sodium, is amiloride sensitive and is prevented with pretreatment with indomethacin, mefanamic acid and phospholipase inhibitor, mepacrine. The data suggest a possible role of phospholipid metabolism and prostaglandin biosynthesis in the regulation of transepithelial ion transport.     

Solubilization of phosphatidylcholine unilamellar liposomes caused by alkyl glucosides

Solubilizing alterations caused by a series of alkyl glucosides (alkyl chain lengths ranging from C₈ to C₁₂) in phosphatidylcholine (PC) unilamellar liposomes were investigated. Surfactant-to-phospholipid molar ratios (Re) and bilayer/aqueous phase partition coefficients (K) were determined by monitoring changes in static light scattering (SLS) of the system during solubilization. At the two interaction levels investigated (surfactant concentrations producing SLS values of 100 and 0% for each surfactant/PC system studied) the free surfactant concentration for each surfactant was always comparable to its critical micelle concentration (CMC). This indicates that liposome solubilization was mainly ruled by mixed micelle formation. A rise in CMC (or decrease in the surfactant alkyl chain length) resulted in an increase in the ability of these surfactants to saturate or solubilize PC liposomes and, inversely, in an abrupt decrease in their affinity with these bilayer structures. The overall balance of these opposite tendencies shows that the octyl glucoside had the highest ability to saturate and solubilize liposomes (lowest Re values), whereas the dodecyl glucoside exhibited the highest degree of partitioning into liposomes or affinity with bilayer structures (highest K values). From a practical viewpoint, the use of nonyl glucoside reduced approximately 2.5 times the concentration needed to saturate and solubilize 1.0 mM PC liposomes with respect to that needed using the conventional octyl glucoside.     

Peroxisomes in mice fed a diet supplemented with low doses of fish oil

The influence of low dietary doses (0.1 and 0.8% w/w) of a commercial fish oil preparation on peroxisomes in normal mice was studied and compared to the known strong inductive effects of high (10%) fish oil diets. Low fish oil doses were chosen to supply the mice with a concentration of docosahexaenoic acid, which was beneficial to patients with a peroxisomal disease. Peroxisomes were evaluated by cytochemical, morphometric, and enzymological techniques. The 0.1% fish oil diet had no effect on peroxisomes in liver, heart, and kidney even after prolonged treatment. The 0.8% diet did not change the peroxisomal number nor the catalase (EC 1.11.1.6) activity in the liver. Hepatic peroxisomal β-oxidation, however, was increased by 50% after 14 d. This was accompanied by reduced peroxisomal size. The 0.8% diet also caused a small increase (+25%) in myocardial catalase activity. No effect was observed in kidneys. Our results indicate that in mice a low (<0.8%) dietary fish oil dose has no or only a slight effect on hepatic peroxisomal β-oxidation. This may be of particular interest to patients with a peroxisomal fatty acid β-oxidation defect and who display a severe deficiency of docosahexaenoic acid—diets supplemented with low fish oil doses will improve the docosahexaenoic acid level without adding a strong load to the disturbed fatty acid metabolism.     

短期高脂饮食对不同性别小鼠肠道微生物的影响

目的探讨短期高脂饮食对不同性别小鼠肠道微生物的影响。方法将16只C57BL/6J小鼠(雌雄各半)按雌雄各随机分为2组,分别喂食基础饲料(对照组)和45%高脂饲料(高脂组),饮食干预2周后,收集小鼠的新鲜粪便样本,提取粪便细菌总基因组DNA,对其16S rDNA的V3+V4区域进行扩增及测序,分析菌群的组成及丰富度变化。结果高脂饮食改变了雌性和雄性小鼠肠道微生物组成及物种多样性。与相应对照组比较,雌性高脂组小鼠厚壁菌门及该菌门中Leptum菌种的相对丰富度均显著下降(P﹤0. 05),雄性高脂组差异均无统计学意义(P0. 05)。结论短期高脂饮食对雌性和雄性小鼠肠道微生物组成及结构有不同的影响,可能与不同性激素与肠道菌群的相互作用有关。     

Liver and thymus lipid composition in AKR mice with and without lymphomas

Lipid composition of liver and thymus in controls, early stage lymphoma, and advanced stage lymphoma-bearing AKR mice was studied. There was a significant decrease in the liver total lipid content in mice with advanced lymphoma, whereas in the early stages, no quantitative change was seen. In livers of mice with advanced stage lymphoma, there was a significant decrease in the nonpolar fraction. The decrease was in triglyceride, whereas the cholesterol fractions were relatively increased though highly variable. There was an increase in the polar lipid/nonpolar lipid ratio in the advanced lymphoma livers and a very large increase in the polar lipid/triglyceride ratio, indicating that the decrease in total lipid in these livers was largely in the triglyceride fraction. Similar changes were seen in the thymus, in which the lipid composition reflected the transformation from normal to malignant cells.     

Solubilizing effects caused by the nonionic surfactant octyl glucoside in phosphatidylcholine liposomes

The mechanisms governing the interaction of the nonionic surfactant octyl glucoside (OG) on phosphatidylcholine (PC) liposomes were investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles, and bilayer solubilization was determined as a decrease in the static light scattered by liposome suspensions. A direct relationship was established in the initial interaction steps (10–50% CF release) between the growth of vesicles, the leakage of entrapped CF, and the effective molar ratio of surfactant to phospholipid in bilayers (Re). This dependence was also detected during the solubilization range of Re values between 1.3 and 3.0, where the decrease in the surfactant-PC aggregate size and in the light scattering of the system depended on the Re parameter and, hence on the composition of these aggregates. The free OG concentrations at subsolubilizing and solubilizing levels showed lower and similar, respectively, values than its critical micelle concentration (CMC). These findings indicated that the alterations in bilayer permeability were due to the action of surfactant monomers, whereas bilayer solubilization was determined by the formation of mixed micelles. This finding supports the generally accepted assumption that the concentration of free surfactant must reach the CMC for solubiliation to occur.     

Regulation of intestinal apolipoprotein A-I synthesis by dietary phosphatidylcholine in newborn swine

Phospholipid (PL) from both dietary sources and biliary secretions may be important in the regulation of intestinal apolipoprotein (apo) synthesis. We previously demonstrated the up-regulation of apo A-I secretion by phosphatidylcholine (PC) in a newborn piglet intestinal epithelial cell line. We hypothesized that dietary PC increases small intestinal apo A-I synthesis in vivo in the newborn piglet. Two-day-old female swine were fed by gavage for 48 h. Diets consisted of a formula containing 51% of calories as triacylglycerol providing 180 kcal/kg/24 h. The experimental group (+PC, n=7) received 1 g/L added soybean PC, and the control group (−PC, n=7) received no added PC. At the end of the study period, jejunal apo A-I, B, and A-IV synthesis was measured, and apo A-I mRNA levels were quantitated. Jejunal mucosal PI content and serum lipids and apo B and A-I levels were measured. Jejunal apo A-I synthesis was almost twice as high in the +PC group as compared to the −PC group with no difference in apo A-I mRNA levels. Jejunal content of PL was higher in the +PC group than in the −PC group. There were no differences in jejunal apo B and A-IV synthesis or serum levels of lipids and apo-lipoproteins between the two groups. Dietary PC supplementation in newborn swine up-regulated jejunal apo A-I synthesis. Apo A-IV synthesis, which is sensitive to fatty acid flux, was not significantly increased, which suggests a specific effect of PC on apo A-I synthesis. Lumenal PC may be important in the regulation of intestinal apo A-I synthesis in the neonate.     

Synthesis of 1,2-diacyl-sn-glycerophosphadidylserine from egg phosphatidylcholine by phosphoramidite Methodology

A simple chemical method for the synthesis of 1,2-diacyl-sn-glycerophosphatidylserine (PS), with the same fatty acid composition in thesn-1 andsn-2 glycerol positions as egg phosphatidylcholine (PC), is described. PS synthesis was carried out by a phosphite-triester approach, using 2-cyanoethyl-N,N,N′,N′-tetraisopropylphosphorodiamidite (phosphoramiditate) as the phosphorylating agent, for the formation of phosphate linkage between serine and diacylglycerol. 1,2-Diacylglycerol, obtained from PC hydrolysis by phospholipase C, was coupled withN-t-BOC-l-serinebenzhydryl ester phosphoramidite with tetrazole as catalyst. Phosphite-triester was oxidized to the corresponding phosphate-triester with 30% H₂O₂ in CH₂Cl₂. The cyanoethyl group was removed by addition of an Et₃N/CH₃CN/pyridine mixture, and trifluoroacetic acid was used to eliminate the protecting groups ofO-(1,2-diacylglycero-3-phospho)-N-t-BOC-serinebenzhydril ester. Purified PS was identified by thin-layer chromatography, infrared, and¹H nuclear magnetic resonance.     

Genetic variations in serum lipid levels of inbred mice and response to hypercholesterolemic diet

The serum lipid contents of a number of inbred and congenic strains of mice were measured. There were interstrain variations in each of the lipid fractions in mice fed a normal diet. Male and female C3H mice had the highest total cholesterol level; AKR mice showed the lowest values. Serum phospholipids were correlated well with cholesterolemia. The greatest variations between strains were in the triglyceride levels. There also was significant variation in the high density lipoprotein cholesterol serum levels (from 73–88% of the total cholesterol). The response to a hypercholesterolemic diet (1% cholesterol) was tested in seven inbred strains. All strains showed changes in serum cholesterol and in the proportions of the lipoproteins fractions. There was a large increase in the low density lipoprotein+very low density lipoprotein fractions. Feeding the diet revealed marked interstrain differences in the responses of the serum cholesterol and electrophoretic lipoprotein profiles. The C57BL/6 and B10.D2 strains were hyperresponders to the hypercholesterolemic diet with 71% and 63% of their serum cholesterol in the low density lipoprotein plus very low density lipoprotein fractions, respectively.     

Effect of diet composition and fasting on lipogenesis in lean and polygenic obese mice

A line of mice was developed which exhibited spontaneous obesity when fed commercial laboratory ration low in fat content. Obese mice were compared to a nonobese related line to determine whether energy source in the diet would affect onset of obesity. Experimental diets-beef tallow (38% of calories as beef fat and 2% as corn oil), corn oil (40% corn oil) or low-fat (2% corn oil)-were instituted ad libitum at the time of weaning. When the mice reached 6 months of age, lipogenesis was investigated by injecting intravenously³H₂O and glucose-U-¹⁴C.³H₂O and glucose-U-¹⁴C incorporation into fatty acids of fed mice was greater for obese than for lean mice. Fatty acid synthesis was inhibited by high-fat diets compared to low-fat diet in both lines. Of the 2 high-fat diets, the corn oil diet inhibited fatty acid synthesis about twice as much as beef tallow diet. There was no line effect on tritium incorporation into cholesterol. Cholesterol synthesis from glucose-U-¹⁴C was greater in obese than lean mice. Diets had no effect on tritium and glucose-U-¹⁴C incorporation into cholesterol. Fasting reduced fatty acid synthesis in all mice, but total body fatty acid synthesis was not affected by lines or dietary treatment under fasted conditions. These data suggest that degree of lipogenesis, in part, explains obesity. A failure of inhibition of lipogenesis or an enhanced efficiency in fat deposition by feeding beef tallow compared to corn oil diet may explain the fact that lean mice fed the beef tallow diet tended to be more obese that lean mice fed corn oil or low-fat diets.