Lipid composition and biosynthesis of human omental tissue

Two groups of five males each were selected for total lipid analyses of their omental tissue. One of these groups had been subjected to a severe caloric restriction and had undergone total weight reduction of about 20%. The other group served as control. Both of these groups of patients required elective surgical procedures during which it was possible to obtain small samples of omental tissue, adipose pad, and/or mesenteric tissue. Total lipid analyses were performed on all of the materials. A distinctive positional distribution of the acyl groups was maintained in the triglycerides of omental tissue for all the patients regardless of dietary state. Patients under caloric restriction showed a reduction in their total triglyceride content, a reduction in their content of unsaturated fatty acyl groups, and a relative increase in phospholipid content. The de novo lipid biosynthetic capacity of omental tissues, as determined by 1-[¹⁴C]-acetate incorporation, showed an inverse proportionality to the lipid content of the samples. Omental tissue is biosynthetically a very versatile material capable of yielding rapidly many types of fatty acids. This ability, among others, could account for the usefulness of omental tissue as a supporting base in many types of restorative surgery.     

Abnormal lipid composition of fat tissue in human mesenteric panniculitis

Mesenteric fat tissue obtained at autopsy from 6 patients with mesenteric panniculitis (MP) were found to contain significant amounts of cholesteryl esters (CE). In addition, samples from 3 of these cases were found to contain 0.5–1.3% free cholesterol, 0.9–1.9% free fatty acids (FFA), 0.6–2.5% 1-alkyl glyceryl ether diesters and small amounts of squalene. Two of these tissues also contained alk-1-enyl glyceryl ether diesters. The fatty acid compositions of the CE, FFA, triacylglycerides and glyceryl ether diesters (GEDE) were determined and oleic acid (18∶1) was found to be the major fatty acid. The alkyl group composition of the GEDE consisted essentially of 16∶0 and 18∶0 and 18∶1 carbon atoms in both types of ethers.     

Inhibitors of de novo nucleotide biosynthesis as drugs

Potent inhibitors of enzymes catalyzing reactions in the de novo pathways for biosynthesis of purine and pyrimidine nucleotides are synthetic or natural-product analogues of pathway intermediates or, more recently, inhibitors rationally designed from a knowledge of the catalytic mechanism. Such inhibitors may be effective drugs against cancer, inflammatory disorders, or various infections. For human cancer, the purine pathway may be a better target for inhibition than the pyrimidine pathway, where toxic side effects are more apparent. Drugs such as methotrexate and 6-mercaptopurine have multiple sites of action, making it difficult to quantitatively predict their effects upon cells. Rational design of inhibitors based upon the X-ray structure of the target enzyme has the prospect of yielding drugs with only one site of action in human cells. Such a drug is VX-497, a potent inhibitor of the purine enzyme, IMP dehydrogenase.     

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.     

Lipid composition of human bronchial mucus

Mucus from an asthmatic patient contained lipids which have not been analyzed before. The composition was similar to two other types of mucus lipids. The triglyceride fraction was highly saturated and contained large amounts of short chain fatty acids.     

Lipid composition of beef and human pituitary glands

The lipid composition of beef and human pituitary was determined by chromatographic and spectrophotometric methods. Beef pituitary lipid contained about 25% nonpolar lipids and 75% phospholipids whereas nonpolar lipids made up approximately 60% of the total in human pituitaries. The main nonpolar (i.e., low polarity) lipids in human pituitary were triglycerides, cholesterol, free fatty acids and an unidentified component in the triglyceride fraction. Cholesterol was the major nonpolar lipid component in freshly collected beef anterior and posterior pituitary, but the amount of free fatty acids appeared to increase during storage. Preliminary investigation of the unknown nonpolar lipid in human pituitaries suggested that it was an unsaturated hydroxy compound with no carbonyl functions. Thin layer chromatography indicated that it was also present in smaller amounts in freshly collected beef pituitaries. The main phospholipids of beef anterior, posterior and human pituitary were phosphatidyl ethanolamine, phosphatidyl choline, phosphatidyl inositol, phosphatidyl serine and sphingomyelin. The fatty acid composition of total nonpolar lipids, free fatty acids, total phospholipids, phosphatidyl ethanolamine and phosphatidyl choline of beef anterior and posterior pituitary was determined by gas liquid chromatography. Mixtures of saturated and unsaturated fatty acids ranging from C₁₂ to C₂₂ were present; the main fatty acids were palmitic, stearic, oleic, linoleic and arachidonic.     

Variations in fat content and lipid class composition in ten different mango varieties

The kernels of 10 different mango varieties were extracted. The physico-chemical characteristics and lipid class composition of fats were studied. The fat content of mango kernels grown under the soil and climatic conditions of Bangladesh varied from 7.1% to 10%, depending on the variety. The total lipid extracts were fractionated into lipid classes by a combination of column and thin layer chromatography (TLC). The hydrocarbon and sterol esters varied from 0.3% to 0.7%, triglycerides from 55.6% to 91.5%, partial glycerides from 2.3% to 4% and free sterol from 0.3% to 0.6%. Free fatty acids amounted to 3.0–37% as oleic; glycolipids were 0.6–1.2% and phospholipids 0.11–0.8%. The fatty acid composition of triglyceride (TG) fractions was analyzed by gas liquid chromatography (GLC). Palmitic acid varied from 7.9 molar % to 10.0 molar %, stearic from 38.2% to 40.2%, oleic from 41.1% to 43.8%, linoleic from 6.0% to 7.6%, linolenic from 0.6% to 1.0% and arachidic acid from 1.7% to 2.6%. TLC revealed the presence of lyso-phosphatidylcholine, phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine and phosphatidic acid in the phospholipid fraction.     

The lipid composition of human liver microsomes

The lipid composition of human liver microsomes isolated from liver biopsy samples obtained at abdominal surgery has been determined. Human liver microsomal phospholipid is composed of 49% phosphatidylcholine, 31% phosphatidylethanolamine, 14% phosphatidylserine+phosphatidylinositol and 6% sphingomyelin, very similar to the phospholipid composition of rat liver microsomes. The fatty acid composition of human liver microsomes is remarkable only for its content of polyunsaturated fatty acids, with 20% of the fatty acids consisting of arachidonic, docosatetraenoic, docosapentaenoic and docosahexaenoic acids. This value contrasts with 33% in rats and 9% in rabbits. The molar cholesterol/phospholipid ratio in human liver microsomes is 0.069, similar to the ratio in rat and rabbit microsomes.     

A cross-species comparison of neutral lipid composition of milk fat of prosimian primates

The fatty acid composition of milk fat is known to be affected by dietary and genetic differences, while the milk triacylglycerol structure is believed to be attuned to the needs of the subsequent lipolysis during gastrointestinal passage. The availability of milk samples from eight species of prosimian primates, whose milk triacylglycerol structure had not been analyzed, offered an opportunity to further assess these ideas. The milk samples were collected by manual expression and the lipids extracted with chloroform/methanol (2∶1, vol/vol). The lipid classes were resolved by thin-layer chromatography, and the neutral lipids subjected to detailed analyses by capillary gas-liquid chromatography of fatty acids and molecular species of triacylglycerols using nonpolar and polarizable liquid phases. The milk samples were found to differ greatly in total fat content (4–73%) and in the composition of the neutral liqid classes and molecular species. The concentration of triacylglycerols ranged from 88–95%, free fatty acids from 0.5–10%, alkyldiacylglycerols from 0.5–5.0%, and diacylglycerols, monoacylglycerols and free and esterified cholesterol made up the remainder. The fatty acid chain length ranged from C₈−C₂₄, with palmitic (16–31%) and oleic (13–40%) acids being the major components in most of the species. In all instances, the molecular association of the fatty acids differed from random distribution by a higher proportion of the monoacid (trioleoyl) and diacid (dipalmitoyloleoyl) glycerols. The phylogenetic influences on neutral milk lipid composition, however, remained unclear, as some of the differences between closely related species were greater than those between more distantly related ones. Triacylglycerol structures are abbreviated by listing their three constituent fatty acids in sequence, e.g., PPP, LaOL.     

Effects of diets high in saturated fat and cholesterol on the lipid composition of canine platelets

The phospholipid composition of platelets from dogs on various experimental diets was determined. Thyroidectomized foxhounds were fed a control diet or the control diet supplemented with (1) beef tallow, (2) beef tallow and cholesterol, or (3) beef tallow, cholesterol, and safflower oil for 23 weeks prior to isolation of platelets. Platelets from animals fed the control diet contained 36.7% phosphatidylcholine (PC), 22.8% phosphatidylethanolamine (PE), 18.4% sphingomyelin (Sph), 11.8% phosphatidylserine (PS), 6.3% phosphatidylinositol (PI), and 2.2% lysophosphatidylcholine. The PE was 77.6% in the plasmalogen form. No highly significant changes in the phospholipid class composition resulted from the experimental diets. Cholesterol supplementation of the diets, however, caused consistent alterations in the fatty acid compositions of the platelet phospholipids including increases in the percentages of 18∶1ω9 (oleic acid), 18∶2ω6 (linoleic acid), and 20∶3ω6 (homo-gamma linolenic acid) and a decrease in the percentage of 20∶4ω6 (arachidonic acid). Addition of safflower oil to the tallow-cholesterol diet partially reversed these effects. These cholesterol-induced alterations in fatty acid composition could be due to exchange with plasma lipids, de novo synthesis, or altered platelet metabolism. The mechanism remains to be determined. Der. Nelson’s current affiliation is the Lipid Metabolism Branch, Division of Heart and Vascular Diseases, National Heart, Lung, and Blood Institute.     

Lipid composition and peroxide levels of mucosal cells in the rat large intestine in relation to dietary fat

To examine whether dietary fat alters membrane lipid composition and peroxidation of polyunsaturated fatty acids in “non-proliferative” and “proliferative” cells in the large intestine, Sprague-Dawley rats were fed diets providing a polyunsaturated-to-saturated fatty acid ratio of 1.2 or 0.3 at a high or low level of fat intake for a 25-day period. Cell populations were isolated and the effect of dietary fat on membrane polyunsaturated fatty acid content and peroxide levels was determined. Neither fat level nor fatty acid composition of diet influenced total cholesterol, total phospholipids, and percentage of phospholipid classes in membrane phospholipids. Feeding the high fat and/or high polyunsaturated-to-saturated fatty acid ratio diet increased polyunsaturated fatty acid content of mucosal cell phospholipids. Increase in polyunsaturated fatty acid content was paralleled by a decrease in the monounsaturated fatty acid content of mucosal cell phospholipids. Membrane content of total saturated fatty acids was not significantly affected by diet. Variation in phospholipid fatty acid composition between “non-proliferative” and ”proliferative” cells was observed. Lipid peroxide levels in mucosal cell lipid fractions were altered by dietary fat treatment. Animals fed high fat diets, compared to groups fed low fat diets, exhibited higher membrane peroxide levels when results are expressed as nmol/mg protein. Higher peroxide levels were observed in mucosal cells for rats fed high polyunsaturated-to-saturated fatty acid ratio diets when results were expressed per nmol of phospholipid. It is concluded that changes in fat level and fatty acid composition of the diet alters the mucosal cell membrane lipid composition in the rat large intestine and influences susceptibility of mucosal cell lipid to peroxidation. Further research is required to delineate which dietary factors—fat level, polyunsaturated-to-saturated fatty acid ratio, or both—have a primary influence on the degree of lipid peroxidation.     

Lipid composition of different areas of murine brain: Effects of lipid extraction procedures

The effects of various chemical extraction procedures on the determination of lipid composition of rat and mouse brain have been investigated. Tissue extractions with formic acid/acetone or perchloric acid both resulted in significant losses of total phospholipids and cholesterol. Perchloric acid extraction also degraded, almost quantitatively, ethanolamine plasmalogens to lysophosphatidylethanolamine. Our findings have thus demonstrated that conventional procedures used for extraction of brain tissue for analysis of choline and acetylcholine content cannot also be used for concurrent/simultaneous extraction of phospholipids and cholesterol from the same tissue.     

Studies on lipid and fatty acid composition of human hepatoma tissue

Studies are reported on the composition of the lipids of human liver and hepatoma tissues from male adults. Liver tissues were obtained from individuals who died from causes other than liver disease or cancer. The hepatoma tissues were obtained from individuals shortly after they succumbed to cancer. The total lipid of each tissue was fractionated quantitatively by silicic acid column chromatography into neutral lipid, glycolipid, and phospholipid fractions. These fractions were analyzed by thin layer chromatography and converted to methyl esters for analysis of their constituent fatty acids by gas liquid chromatography. In comparison to liver tissue, the total amount of lipid in the hepatoma tissues was generally higher and more variable; the lipid of one hepatoma was ca. 92% of the dry wt of the tissue. The greater lipid content of the hepatoma tissues was due to the high percentage of neutral lipid. Except for one specimen, there was ca. the same amount of glycolipid in the hepatoma as in the liver tissues, but the composition of the glycolipid fraction of the hepatoma lipid differed considerably, particularly in the ganglioside fraction. The phospholipid fraction of hepatoma lipid was much lower than that of liver but exhibited only quantitative differences in composition. No glyceryl ether diesters and only traces of plasmalogens of phosphatidyl choline or phosphatidyl ethanolamine were detected in the liver and hepatoma lipids. The levels of monoenoic acids were higher and those of linoleic and polyunsaturated fatty acids lower in the hepatoma lipids. Positional isomers of trienoic acids not normally present in liver tissue were detected in hepatoma lipids. The abnormalities observed in lipid composition indicated interferences in the regulatory processes of lipid metabolism in human hepatoma similar to those observed in animals.     

Influence of lauroyl and myristoyl peroxides and oxidized cottonseed oil on depot fat and liver lipid composition

In view of the interest in the biological properties of products of fat oxidation, lauroyl and myristoyl peroxides were fed and their nutritional effects compared with those of autoxidized cottonseed oil, which had been analyzed for its composition. Purified diets containing no fat +2% of linoleic acid, 5% lauroyl or myristol peroxide, or 10% oxidized cottonseed oil were fed to weanling male albino rats for 73 to 98 days, after which they were killed and their organs weighed. Their sera, livers, and testicular fat bodies were used for lipid analysis. With peroxides, growth was significantly depressed but not as much as when oxidized cottonseed oil was fed. Analysis of organ weight data showed that peroxides and oxidized cottonseed oil differed in their effects. Animals fed the latter had significantly heavier livers, kidneys, and hearts. The rats fed peroxides were also different from those fed the fat-free diet and those kept on restricted food intake. Gas chromatographic analysis of the testicular fat bodies revealed a greater deposition of oleate in the animals fed oxidized cottonseed oil, which suggested that these animals were unable to use the oxidized oil for depot fat formation. In the anials fed lauroyl and myristoyl peroxides, appreciable amounts of laurate and myristate, respectively, were found. The composition of the liver neutral fat of the animals fed peroxides was similar to that of the animals fed the low-fat diet +2%, linoleic acid. Serum cholesterol levels of the rats fed peroxides were about 70 mg. %, and of those fed oxidized cottonseed oil, 53 mg. %. The groups fed peroxides also had significantly higher liver cholesterol levels, which suggests that peroxides and oxidized cottonseed oil differed in their effects on cholesterol formation and transport. Aided by Grant A-1654 from the United States Public Health Service. Presented at the 34th fall meeting of the American Oil Chemists’ Society.     

Fatty acid composition of muscle fat and enzymes of storage lipid synthesis in whole muscle from beef cattle

Enhanced intramuscular fat content (i.e., marbling) in beef is a desirable trait, which can result in increased product value. This study was undertaken with the aim of revealing biochemical factors associated with the marbling trait in beef cattle. Samples of longissimus lumborum (LL) and pars costalis diaphragmatis (PCD) were taken from a group of intact crossbred males and females at slaughter, lipids extracted, and the resulting FAME examined for relationships with marbling fat deposition. For LL, significant associations were found between degree of marbling and myristic (14∶0, r=0.55, P<0.01), palmitic (16∶0, r=0.80 P<0.001), stearic (18∶0, r=−0.58, P<0.01), and oleic (18∶1c-9, r=0.79, P<0.001) acids. For PCD, significant relationships were found between marbling and palmitic (r=0.71, P<0.001) and oleic (r=0.74, P<0.001) acids. Microsomal fractions prepared from PCD muscle were assayed for diacylglycerol acyltransferase (DGAT), lysophosphatidic acid acyltransferase (LPAAT), and phosphatidic acid phosphatase-1 (PAP-1) activity, and the results examined for relationships with degree of intramuscular fat deposition. None of the enzyme activities from PCD displayed an association with marbling fat content, but DGAT specific activity showed significant positive associations with LPAAT (r=0.54, P<0.01), total PAP (r=0.66, P<0.001), and PAP-1 (r=0.63, P<0.01) specific activities. The results on FA compositions of whole muscle tissues provide insight into possible enzyme action associated with the production of specific FA. The increased proportion of oleic acid associated with enhanced lipid content of whole muscle is noteworthy given the known health benefits of this FA.     

Lipid composition influences the shape of human low density lipoprotein in vitreous ice

Earlier cryo-electron microscopic studies have indicated that the normal low density lipoprotein (N-LDL) has a discoid shape when its core is in the liquid-crystalline state. In the present study, we investigated whether the shape of LDL depends on the physical state and/or the lipid composition of the lipoprotein core. Using a custom-built freezing device, we vitrified N-LDL samples from either above or below the phase-transition temperature of the core (42 and 24°C, respectively). Cryo-electron microscopy revealed no differences between these samples and indicated a discoid shape of the N-LDL particle. In contrast, TG-enriched LDL (T-LDL) did not have discoid features and appeared to be quasi-spherical in preparations that were vitrified from either 42 or 24°C. These results suggest that the shape of N-LDL is discoid, regardless of the physical state of its core, whereas T-LDL is more spherical. Aspects that may influence the shape of LDL are discussed.     

Effect of dietary fat on the lipid composition and utilization of short-chain fatty acids by rat colonocytes

The objective of the present studies was to examine the effect of dietary fat on the lipid composition of rat colonocytes and their utilization of short-chain fatty acids (SCFA). Rats were fed 14% beef fat, fish oil or safflower oil plus 2% corn oil in a semi-synthetic base diet for 4 wk. Colonocytes were isolated and their lipid composition was examined. Feeding beef fat and fish oil resulted in an increase in monounsaturated fatty acids and a reduction in ω-6 fatty acids. Feeding fish oil resulted in an enrichment with ω-3 fatty acids. These was no dietary influence on the amount of either cholesterol or phospholipids of colonocytes. Fish oil feeding resulted in significant increase in colonocyte free fatty acids (FFA) as compared to other diets. Dietary fat was found to have no effect on SCFA utilization by colonocytes. Colonocytes were found to utilize SCFA in the order of butyrate ≥acetate ≥propionate. The presence of acetate and propionate in the medium had no effect on the rate of butyrate utilization.     

Dietary fat composition influences fatty acid composition of milk fat globule membrane in lactating cows

Milk fat globule membranes are derived directly from the apical plasma membrane of mammary epithelial cells. To evaluate the effect of dietary fat on mammary membranes, we determined the fatty acid composition of the milk fat globule membrane in lactating dairy cows fed diets supplemented with fats of different fatty acid composition, or infused intravenously with soy oil emulsion. A preliminary survey, using an abbreviated preparation procedure (membranes isolated at 48,000 x g-max for 15 min), yielded about 45% of the total membrane fatty acids that could be recovered by centrifuging at the same speed for 120 min, and showed that changes in fatty acid composition of membranes reflected dietary fatty acids to some extent. Dietary palmitic acid increased the content of 16:0 in the membranes. A high corn diet increased ruminal formation of t18:1, and its level increased to 12% of membrane fatty acids. Infusion of soy oil emulsion increased 18:2 membrane content, and decreased the levels of 18:1 and 20:4. All treatments decreased the ratio of unsaturated/saturated fatty acids as compared to controls, whereas the ratio of polyunsaturated/saturated fatty acids was increased by feeding a high corn diet or by infusing soy oil. The ratio of 18:2/c18:1 increased from 0.31 to 1.0 after infusing soy oil for 4 days. The fatty acids of membranes isolated upon 120-min centrifugation were slightly more saturated. The differences were not sufficiently large, however, to affect overall results significantly.     

Effect of phthalate esters on serum cholesterol and lipid biosynthesis in liver,testes, and epididymal fat in the rat and rabbit

Lipid biosynthesis was studied in vitro in liver, testes, and epididymal fat obtained from rats and rabbits fed di-(2-ethylhexyl)phthalate for 4 weeks at levels of 0.5% and 1.0%, respectively. Several differences in response of the two species to DEHP feeding were observed. In rats, but not in rabbits, DEHP feeding significantly reduced the incorporation of labeled mevalonic acid into total sterols (p <0.02), digitonin-precipitable sterols (p<0.01), and squalene (p<0.05). Inhibition of hepatic sterologenesis previously observed with DEHP feeding in the rat was also observed in the rabbit. In liver minces from the DEHP-fed rabbits, incorporation of³H-mevalonic acid into C₂₇ sterols (cholesterol) and C₃₀ sterols (lanosterol) was significantly reduced by about 40% (p<0.05 and p<0.01, respectively), whereas the incorporation of¹⁴C-glycerol 3-phosphate into phospholipids, and the combined fraction of monoglyceride + diglyceride, was significantly increased (p<0.001 and p<0.01, respectively). In studies with epididymal fat, DEHP feeding did not affect the total incorporation of¹⁴C-acetate or³H-mevalonate into total saponifiable and nonsaponifiable lipids of either the rat or rabbit. However, in the rat, significantly less of the¹⁴C-acetate (p<0.02) and³H-mevalonate (p<0.01) that was incorporated appeared in the combined fraction of cholesteryl ester + squalene. In addition, DEHP feeding significantly reduced serum cholesterol (p<0.01) in the rat but not in the rabbit. The results of this study indicate that DEHP feeding is associated with alterations in tissue lipid metabolism and that there are species differences in the response of tissues to DEHP.