p-Chlorophenoxyisobutyrate enhanced retention of homologous lipoproteins by human aortic smooth muscle cells

Human aortic smooth muscle cells (SMC) specifically bind and take up indiscriminately both the lipid and protein moietics of homologous²⁵I-very low density lipoproteins (VLDL) and¹²⁵I-low density lipoproteins LDL). Sixty-five to 80% of absorbed lipids are incorporated into the cell lipids, preferentially into the phospholipid fraction. Twenty to 35% of the lipid bound and the protein moiety are eliminated from the cells. Half of the eliminated protein label is recovered as TCA soluble products. Five mM of p-chlorophenoxyisobutyrate (CPIB) raise the level of intracellular radioactivity derived from the lipid moieties of VLDL and LDL by about 40% via a reduced elimination. The processing of the protein moiety and lipoprotein binding to the cell surface are not affected by 5.0 mM of CPIB. CPIB lowers the incorporation of¹⁴C-acetate,¹⁴C-pyruvate, and³²phosphate radioactivity into fatty acids and phospholipids of aortic SMC. Five mM of CPIB reduce the overall palmitic acid synthesis by shifting from de novo synthesis to the mechanism of chain elongation, although the further elongation to saturated C₁₈–C₂₄ fatty acids is also depressed. The CPIB-enhanced retention of the lipid-derived lipoprotein radio-activity is interpreted as a compensatory mechanism providing cellular fatty acids which are deficient as a result of the CPIB inhibited synthetic processes.     

Homeostatic control of membrane fatty acid composition in the rat after dietary lipid treatment

Diets in which both the lipid content and composition (polyunsaturated to saturated fatty acid ratio) were varied were fed to rats for 20 weeks, and the effects on the tissue lipid profiles were determined. The fatty acid profile of the plasma lipids, and the phospholipid fatty acids of the mitochondrial and microsomal fractions of liver, heart, kidney and brain, as well as erythrocyte membranes were determined. Despite large differences in the level and type of lipid present in the experimental diets and in the proportion of saturated fatty acids in the plasma lipids in response to the various diets, there was little effect on the proportion of saturated to unsaturated fatty acids in the phospholipids of the various membranes examined. The major effect of altering the dietary level of polyunsaturated to saturated fatty acids was on the ratio of the ω6/ω3 series of unsaturated fatty acids in the membrane lipids. This change occurred in all tissues except the brain, in which only a small response to altered dietary lipid intake was observed. The ω6/ω3 ratio was elevated upon feeding a diet rich in ω6 polyunsaturated fatty acids, but decreased when a diet rich in saturated fatty acids was fed. The failure to significantly alter membrane lipid saturation/unsaturation in the tissues examined would suggest that a homeostatic mechanism is operative in biological membranes and may act to buffer membranes from the effects of changes in the nature of the dietary lipid intake.     

Effect of dietary di-2-ethylhexyl phthalate on lipid biosynthesis in selected tissues from the rat,in vitro

Di-2-ethylhexyl phthalate (DEHP), a plasticizer commonly used in the production of polyvinyl chloride plastics, has become an environmental pollutant. At the present time, the biological significance of phthalates in the environment is unknown. In the present studies, we observed that addition of DEHP to a stock diet of rats resulted in marked effects on incorporation of¹⁴C-acetate into lipid by liver and kidney slices; other organs, such as heart, testes, and aorta were unaffected. Incorporation of¹⁴C-acetate into total lipid of liver (dpm/mg wet wt) from rats, fed 0.5% or 1.0% DEHP for 10 or 18 days, respectively, was decreased to ca. 50% of control values. The decreased incorporation into liver lipid is not attributable to any one lipid fraction, inasmuch as incorporation into the phospholipid, sterol+diglyceride, free fatty acid, triglyceride, and sterol ester+hydrocarbon fractions was decreased 30–70% with respect to controls. In addition, the percent distribution of¹⁴C-acetate among the individual phospholipids was ca. 25% lower in phosphatidyl choline of the DEHP-fed rats. In rats fed 0.5% DEHP, incorporation of¹⁴C-acetate into total lipid of kidney was similar to control values, but incorporation into the triglyceride and sterol ester+hydrocarbon fraction was decreased 30–40%, whereas incorporation into the sterol+diglyceride fraction was increased 38%. Livers from DEHP-fed rats were ca. 20% larger than livers from control rats and, at the 0.%% level of DEHP feeding, testes wts were elevated; no significant changes were noted in wts of spleen, heart, aorta, kidney, or body wt gains in rats fed DEHP. These studies emphasize a subtle toxicity of phthalate esters not previously reported and emphasize the need for further biochemical studies to evaluate the effect of phthalates on biological systems.     

The influence of dietary lipids on the composition and membrane fluidity of rat hepatocyte plasma membrane

Weanling male Wistar rats were fed for five weeks on standard rat chow (23 g fat/kg diet) or one of four synthetic diets with butterfat, coconut oil, corn oil, or fish oil as the main lipid source (100 g fat/kg diet). In all diets, 10% of the fat was provided as corn oil to prevent essential fatty acid deficiency. Significant differences were observed in the saturated, monounsaturated, and polyunsaturated fatty acid composition, and in the ratio of cholesterol to phospholipid, in the hepatocyte membranes. The fluidity of hepatocyte plasma membranes was assessed using the fluorescence recovery after photobleaching technique and steady-state fluorescence anisotropy of diphenylhexatriene. No significant differences were found in the fluidity of plasma membranes between animals on the different fat diets, despite diet-induced changes in their fatty acid composition. However, the proportion of lipid free to diffuse in the plasma membrane varied with diet, being significantly greater (P<0.05) in animals fed chow (63.7%), coconut oil (61.5%), and butterfat (57.6%) diets than in those fed the corn oil (47.3%) diet. Animals fed fish oil showed an intermediate (50.0%) proportion of lipid free to diffuse. The data support the hypothesis that dietary lipids can change both the chemical composition and lateral organization (lipid domain structure) of rat hepatocyte plasma membranes.     

The effect of dietary arachidonic acid on plasma lipoprotein distributions, apoproteins, blood lipid levels, and tissue fatty acid composition in humans

Normal healthy male volunteers (n=10) were fed diets (high-AA) containing 1.7 g/d of arachidonic acid (AA) for 50 d. The control (low-AA) diet contained 210 mg/d of AA. Dietary AA had no statistically significant effect on the blood cholesterol levels, lipoprotein distribution, or apoprotein levels. Adipose tissue fatty acid composition was not influenced by AA feeding. The plasma total fatty acid composition was markedly enriched in AA after 50 d (P<0.005). The fatty acid composition of plasma lipid fractions, cholesterol esters, triglycerides, free fatty acids, and phospholipid (PL) showed marked differences in the degree of enrichment in AA. The PL plasma fraction from the subjects consuming the low-AA diet contained 10.3% AA while the subjects who consumed the high-AA diet had plasma PL fractions containing 19.0% AA. The level of 22:4n-6 also was different (0.67 to 1.06%) in the plasma PL fraction after 50 d of AA feeding. After consuming the high-AA diet, the total red blood cell fatty acid composition was significantly enriched in AA which mainly replaced linoleic acid. These results indicate that dietary AA is incorporated into tissue lipids, but selectively into different tissues and lipid classes. Perhaps more importantly, the results demonstrate that dietary AA does not alter blood lipids or lipoprotein levels or have obvious adverse health effects at this level and duration of feeding.     

The differential effect of eicosapentaenoic acid and oleic acid on lipid synthesis and VLDL secretion in rabbit hepatocytes

The suppression of plasma very low density lipoprotein (VLDL) triglyceride levels by dietary fish oils rich in polyunsaturated n−3 fatty acids has been attributed to decreased hepatic VLDL secretion. To investigate the effect of n−3 fatty acids on lipid metabolism and VLDL secretion in a tissue culture system, we incubated rabbit hepatocytes with oleic acid and eicosapentaenoic acid (EPA) and examined [³H]glycerol and [¹⁴C]fatty acid incorporation into hepatocyte triglyceride and phospholipid and into media VLDL. Glycerol incorporation studies showed that EPA failed to stimulate VLDL triglyceride secretion from hepatocytes as occurred with oleic acid (P<0.05). Oleic acid preferentially enhanced hepatocyte triglyceride synthesis while EPA stimulated significantly phospholipid synthesis (P<0.01). Varying the relative concentrations of oleic acid and EPA at a constant total fatty acid concentration corroborated preferential triglyceride synthesis from oleic acid. Synthesis shifted predominantly to phospholipids with increasing concentrations of EPA and lower levels of oleic acid. Incorporation of the [¹⁴C]fatty acids (800 μM) followed similar patterns: 87% of [¹⁴C]oleic acid was incorporated into hepatocyte triglyceride and 44% of [¹⁴C]EPA was assimilated in hepatocyte phospholipid (p<0.001). Fatty acids at trace concentrations (53 nM) showed a more divergent pattern of lipid incorporation: 60% of [¹⁴C]oleic acid was incorporated into triglyceride while 91% of [¹⁴CEPA was incorporated into phospholipid (p<0.001). We conclude that in primary rabbit hepatocyte culture, which appears to be a useful model to study lipid metabolism and VLDL secretion, EPA is avidly incorporated into phospholipid while oleic acid predominantly becomes esterified in triglyceride. In addition, EPA, unlike oleic acid, fails to stimulate hepatocyte VLDL secretion. These divergent effects on hepatocyte lipid metabolism are, at least in part, likely to be responsible for fish oil induced suppression of plasma triglycerides.     

l-Carnitine effects on chemical composition of plasma lipoproteins of rabbits fed with normal and high cholesterol diets

l-Carnitine plays an important role in the mitochondrial uptake of long-chain fatty acids in mammals. It has recently been shown that this compound has a marked hypo-cholesterolemic effect when used in conjunction with lipid-rich diets. The aim of this study was to investigate the effects of l-carnitine on the fatty acid composition of plasma lipoproteins in rabbits fed with different diets. Four different groups were investigated: group I (standard diet), group II (standard diet supplemented with l-carnitine at 80 mg/kg), group III (standard diet supplemented with 0.5% cholesterol), and group IV (standard diet supplemented with 0.5% cholesterol plus l-carnitine at 80 mg/kg). The feeding period was 126 d. Total plasma cholesterol was indistinguishable in groups I and II, but increased nearly 40-fold in group III. This increment was reduced by 50% in group IV. Correspondingly, total cholesterol content in lipoprotein fractions [very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL) separated by agarose gel chromatography was the same for groups I and II, while for animals fed a cholesterol-rich diet (III) total cholesterol in VLDL+LDL increased nearly 100-fold when compared with groups I and II but, again, the increment was reduced by 50% in group IV. In contrast, total cholesterol in HDL increased only fivefold for both groups III and IV when compared with groups I and II, indicating no effects of l-carnitine on this parameter. The reduction of total cholesterol in VLDL+LDL particles in animals fed a cholesterol-rich diet plus l-carnitine was associated with a marked decrease in the ratio of cholesteryl ester to free cholesterol and a dramatic increase in their phospholipid content; opposite effects were observed for HDL. l-Carnitine induced a marked decrease in the saturated to unsaturated C₁₆+C₁₈ fatty acid ratio in cholesteryl esters associated with VLDL and LDL from animals fed with both normal and cholesterol-rich diets. The opposite effect (a large increase in the saturated to unsaturated fatty acid ratio) was observed for both cholesteryl esters and phospholipids associated with HDL in animals fed with both diets. The results suggested that the hypocholesterolemic effects of l-carnitine could be associated with increased systemic breakdown of cholesteryl esters, a probable increase in reverse cholesterol transport, and the stabilization of a phospholipid-based structure of VLDL+LDL particles.     

Comparison of the effects of dietary fish oils with different n−3 polyunsaturated fatty acid compositions on plasma and liver lipids in rats

The effects of dietary fish oils with different n−3 polyunsaturated fatty acid compositions on plasma lipid profiles in rats have been studied. Forty-eight male rats, previously maintained on a cholesterol-free diet for 15 days, were fed for 60 days with diets supplemented with 10% fat of either marine hilsa fish (Hilsa ilisa, family clupeidae) or fresh-water chital fish (Notopterus chitala, family notopteridae). The diets had similar levels of total saturated (35–41%), monounsaturated (43–47%) and n−3 polyunsaturated (9–10%) fatty acids. Cholesterol contents of the diets were adjusted to 0.85%; γ-linolenic acid (3.3%) in chital oil and eicosapentaenoic acid (4.9%) in hilsa oil diets were the major n−3 contributors. The percentage of eicosapentaenoic acid in the chital oil diet was 0.57 times that of the hilsa oil diet, but the eicosapentaenoic (EPA) to arachidonic acid (AA) ratio in the latter (4.08) was 3.2 times that of the former (1.27). Sixty days of hilsa oil diet feeding decreased the levels of cholesterol (53.3±2.9 to 50.0±1.1 mg/dL), triacylglycerol (75.7±3.8 to 64.3±2.6 mg/dL) and phospholipid (55.8±1.5 to 51.7±3.1 mg/dL) in rat plasma. Similar treatment with chital oil diet elevated the plasma cholesterol level (53.3±2.9 to 62.3±7.6 mg/dL) while triacylglycerol and phospholipid contents remained unaltered. Both the dietary treatments decreased the levels of linoleic and arachidonic acids in liver but only under the hilsa oil diet did the eicosapentaenoic acid percentage increase markedly (0.8±0.06% to 5.5±0.06%) at the expense of arachidonic acid. This study strongly suggests that the hypolipidemic effect depends on the composition of the n−3 polyunsaturated fatty acids rather than on the total n−3 polyunsaturated fatty acid content of the dietary fish oil.     

Effects of sex on formation and properties of plasma very low density lipoprotein in vivo

The concentration and composition of the very low density lipoprotein (VLDL) lipids and the behavior of the VLDL in a density gradient in the zonal ultracentrifuge were examined in plasma obtained from normal fed male and female rats before and after intravenous injection of Triton WR-1339. Concentration of lipids in plasma VLDL of female rats was about half that of male animals. Following injection with Triton WR-1339, the concentration of VLDL lipids was higher in female rats (triacylglycerol) or similar (phospholipid, cholesterol, and cholesteryl esters) in both sexes. Female rats secreted much more VLDL triacylglycerol into the plasma compartment than did the male animals under the same experimental conditions. No differences were observed in lipid composition of the VLDL or in the position of the VLDL in the zonal rotor after ultracentrifugation in a density gradient of the lipoprotein from plasma of normal male and female rats before treatment with the detergent. However, after treatment with Triton, a higher proportion of the VLDL particles isolated from plasma of female rats displayed a more rapid rate-zonal flotation in the ultracentrifuge than did the VLDL produced by the male. The VLDL secreted by female rats contained fewer moles of phospholipid and free sterol per mol triacylglycerol than did the VLDL secreted by male animals under identical experimental conditions. The molar ratio of free cholesterol: cholesteryl ester in the VLDL secreted after treatment with Triton increased in both male and female rats. Simultaneously, the content of arachidonic acid in phospholipid of VLDL increased with a concomitant decrease in cholesteryl ester. These changes in fatty acid composition suggest that the inhibitory effect of Triton on lecithin-cholesterol acyl transferase activity affects the exchange of lipids between VLDL and high density lipoprotein. It can be concluded from the data reported here that sex influences the concentration of plasma lipids in vivo and the output and properties of the VLDL. Presented in part at the 59th annual meeting of the Federation of American Societies for Experimental Biology, Atlantic City, NJ, April 1975 (1). Recipient of a Career Development Award from the U.S. Public Health Service, No. 1-K4-HL-70329.     

Composition of plasma and nascent very low density lipoprotein from perfused livers of hypercholesterolemic squirrel monkeys

The composition of circulating very low density lipoprotein (VLDL) was compared with the composition and secretion of nascent VLDL from perfused livers of squirrel monkeys that were fed unsaturated or saturated fat diets to elicit different degrees of plasma hypercholesterolemia. All squirrel monkeys studied had cholesteryl ester-rich plasma VLDL, although greater enrichment occurred in hypercholesterolemic animals fed saturated fat. Livers from hypercholesterolemic animals were capable of secreting VLDL particles enriched in cholesteryl ester, suggesting hepatic origin for a portion of this circulating lipid moiety. Total VLDL lipid, but not protein output by perfused livers of hypercholesterolemic monkeys, was greater than that by livers from hypocholesterolemic animals. These results indicate that saturated fat-induced hypercholesterolemia is associated with changes in the composition of hepatic VLDL in the squirrel monkey.     

Influence of a Diet Enriched with Perilla Seed Bran on the Composition of Omega-3 Fatty Acid in Nile Tilapia

This study evaluated the effect of inclusion of perilla seed bran (PSB) in the diet of Nile tilapia genetically improved farmed tilapia (GIFT) on the concentration of fatty acid n‐3 polyunsaturated fatty acids (PUFAs) according to the function of feeding time. The GIFT were cultivated in net cages for 60 days using a control diet with soybean oil and supplemented with PSB. Analyses of the proximate composition and quantification of fatty acids (mg g^?1 of total lipids) were performed in muscle tissue every 15 days. The PSB diet influenced the lipid composition of GIFT fillets by linolenic acid incorporation, which was approximately 384 %, resulting in an increase of 5.2 times the sum of n‐3 PUFA. On the other hand, there was a decrease in the sum of saturated fatty acids. During treatment, there was a continuous increase in n‐3 PUFA, proving the influence of feeding time in the lipid composition of GIFT fillets. The indices of the lipid quality of fillets coming from fish fed the PSB diet were improved. Of these indices, a n‐6/n‐3 ratio presented a significant reduction of 74.15 %, proving the quality of the dietary lipid. Therefore, the inclusion of PSB significantly altered the fatty acid muscle tissue composition of GIFT during feeding time, contributing to an increase in its nutritional value.     

Lack of effects oftrans fatty acids on eicosanoid biosynthesis with adequate intakes of linoleic acid

The minimum requirement of linoleic acid to prevent effects of dietary C18trans fatty acids on eicosanoid biosynthesis in rats was assessed. In a first experiment, six groups of animals were fed diets with a high content oftrans fatty acids [20% of energy (en%)], and increasing amounts of linoleic acid (0.4 to 7.1 en%). In a second experiment, four groups of rats were fed diets designed to comparetrans fatty acids with saturated andcis-monounsaturated fatty acids of the same chain length at the 2 en% linoleic acid level. After 9–14 weeks the biosynthesis of prostacyclin by pieces of aorta and the biosynthesis of hydroxy-heptadecatrienoic acid and 12-hydroxy-eicosatetraenoic acid by platelets were measured. The fatty acid compositions of aorta phospholipid and platelet lipid were also determined. Both the prostacyclin-production by aorta pieces and the production of hydroxy-heptadecatrienoic acid and 12-hydroxy-eicosatetraenoic acid by platelets appeared to be a linear function of the arachidonic acid level in aorta phospholipid and platelet lipid, irrespective of thetrans fatty acid content in the diet. This indicates thattrans fatty acids do not directly influence enzymes involved in eicosanoid biosynthesis. In a direct comparison withcis-monounsaturated or saturated fatty acids with 2 en% linoleic acid in the diet, only a moderate reduction in arachidonic acid level in aorta phospholipids in the group fedtrans fatty acids was observed. The geometry of the double bond did not influence the arachidonic acid level in platelet lipid, although the diet rich in saturated fatty acids increased arachidonic acid levels significantly compared with all other diets. Neither prostacyclin-production nor hydroxy-heptadecatrienoic acid or 12-hydroxy-eicosatetraenoic acid-production were significantly affected bytrans fatty acids when 2 en% linoleic acid was present in the diet. Our study indicates that in rats 2 en% linoleic acid is sufficient to prevent effects of dietarytrans fatty acids on eicosanoid synthesis.     

Linoleic acid requirement of rats fedtrans fatty acids

The amount of linoleic acid required to prevent undesirable effects of C18trans fatty acids was investigated. In a first experiment, six groups of rats were fed diets with a high content oftrans fatty acids (20% of energy [en%]), and increasing amounts of linoleic acid (0.4 to 7.1 en%). In a second experiment, four groups of rats were fed diets designed to comparetrans fatty acids with saturated andcis-monounsaturated fatty acids of the same chain length at the 2 en% linoleic acid level. After 9–14 weeks, the oxygen uptake, lipid composition and ATP synthesis of heart and liver mitochondria were determined. The phospholipid composition of the mitochondria did not change, but the fatty acid compositions of the two main mitochondrial phospholipids were influenced by the dietary fats.Trans fatty acids were incorporated in all phospholipids investigated. The linoleic acid level in the phospholipids, irrespective of the dietary content of linoleic acid, increased on incorporation oftrans fatty acids. The arachidonic acid level had decreased in most phospholipids in animals fed diets containing 2 en% linoleic acid. At higher linoleic acid intakes, the effect oftrans fatty acids on the phospholipid arachidonic acid level diminished. However, in heart mitochondrial phosphatidylethanolamine,trans fatty acids significantly increased the arachidonic acid level. Despite these changes in composition, neither the amount of dietary linoleic acid nor the addition oftrans fatty acids influenced the mitochondrial function. For rats, a level of 2 en% of linoleic acid is sufficient to prevent undesirable effects of high amounts of dietary C18trans fatty acids on the mitochondrial function.     

In vivo determination of triglyceride secretion using radioactive glycerol in rats fed different dietary saturated fats

Our objective was to determine the relative rates ofin vivo triglyceride (TG) secretion and the composition of very low density lipoproteins (VLDL) in rats fed different dietary saturated fats. Male Sprague-Dawley rats (150–200 g) were fed diets containing 16% corn oil, or 14% butterfat, 14% beef tallow, 14% olive oil, or 14% coconut oil plus 2% corn oil for 5 wk. Changes in plasma TG specific radioactivity were determined in individual, unanesthetized fasted rats after injection of 100 μCi [2-³H]glycerol. Nonlinear regression analysis using a 2-compartment model was used to determine the fractional rate constant for TG turnover in plasma. The plasma TG pool was 33–40% larger with beef tallow than with corn, olive or coconut oil feeding (p<0.05), and 20% larger with beef tallow than with butterfat feeding. The rate of TG secretion into plasma (mg/min/100 g body weight) was 60% higher in animals fed beef tallow than corn or coconut oil (p<0.05) and 26–33% higher in animals fed beef tallow than olive oil or butterfat. Differences in VLDL composition (% wt) were also noted. Our data suggest that greater TG secretion is the primary factor contributing to the larger TG pool with ingestion of beef tallow relative to butterfat, corn or coconut oil. These results suggest that different dietary saturated fats have unique effects on TG metabolism in rats. Presented in part at the 1990 meeting of the Federation of American Societies for Experimental Biology in Washington, D.C. (see ref. 1).     

Dietary protein deficiency affects n−3 and n−6 polyunsaturated fatty acids hepatic storage and very low density lipoprotein transport in rats on different diets

Fatty livers and the similarity between the skin lesions in kwashiorkor and those described in experimental essential fatty acid (EFA) deficiency have led to the hypothesis that protein and EFA deficiencies may both occur in chronic malnutrition. The relationship between serum very low density lipoprotein (VLDL) and hepatic lipid composition was studied after 28 d of protein depletion to determine the interactions between dietary protein levels and EFA availability. Rats were fed purified diets containing 20 or 2% casein and 5% fat as either soybean oil rich in EFA, or salmon oil rich in eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, or hydrogenated coconut, oil poor in EFA. Animals were divided into six groups, SOC (20% casein +5% soybean oil), SOd (2% casein +5% soybean oil), COC (20% casein +5% hydrogenated coconut oil), COd (2% casein + 5% hydrogenated coconut oil), SAC (20% casein +5% salmon oil) and SAd (2% casein +5% salmon oil). After 28 d, liver steatosis and reduced VLDL-phospholipid contents (P<0.001) were observed in protein-deficient rats. In protein deficiency, triacylglycerol and phospholipid fatty acid compositions in both liver and VLDL showed a decreased polyunsaturated-to-saturated fatty acid ratio. This ratio was higher with the salmon oil diets and lower with the hydrogenated coconut oil diets. Furthermore, independent of the oil in the diet, protein deficiency decreased linoleic and arachidonic acids in VLDL phospholipids. Conversely, despite decreased proportions of EPA at low protein levels, DHA levels remained higher in rats fed salmon oil diets. While in rats fed the hydrogenated coconut oil-fed diets the amount of 22∶5n−6 was lower in liver, it was higher in VLDL lipids at low protein levels. Both EPA and arachidonic acid are precursors of eicosanoids and their diminution may be related to certain clinical symptoms seen in infants suffering from kwashiorkor.     

Effects of dietary oil related to the toxic oil syndrome on the lipids of guinea pig liver microsomes

The potential effects of oil specimens related to cases of toxic oil syndrome (TOS) on the liver microsomal lipid composition from guinea pigs were investigated. For four weeks, animals were fed diets supplemented with either “case oil” (oil related to cases of TOS) or “control oil” (oil unrelated to cases of TOS), either previously heated or not. Results were compared with those from guinea pigs fed the same diet with no oil. The administration of case oil produced changes in liver microsomal lipid composition. Statistically significant differences were also found between heated case and heated control oils. The cholesterol/phospholipid molar ratios and the major phospholipid class distribution were unaffected under these diet conditions. However, increases in the relative contents of linoleic and arachidonic acids and, simultaneously, a reduction in palmitic and palmitoleic acid levels were observed by diet effects. Heated oil administration decreased the saturated/unsaturated ratios in all cases. Our data suggest that changes observed in the fatty acid composition are attributable to the free fatty acid contents of administered oils. The toxic constituents of case oil seem to be able to alter the liver microsomal lipid composition.     

Modification of the fatty acid composition of L1210 murine leukemia cells

We have compared the effect of diets containing 16% sunflower seed oil (polyunsaturated fat-rich) or 16% coconut oil (saturated fat-rich) fed for 3–7 weeks on the composition of L1210 murine leukemia cells which were transplanted into the peritoneal cavity during the final week of feeding. The L1210 phospholipids of mice fed the sunflower oil diet contained 43% polyenoic fatty acids and an average of 1.5 double bonds per fatty acid molecule as compared to only 25% polyenoic fatty acids and 1.2 double bonds in the coconut oil group. In contrast, the cells from the sunflower oil group contained only 13% monoenoic fatty acids as compared to 33% in those from the coconut oil group. When compared to phospholipids of tumors from mice who were fed a commercial mouse chow, cells grown on sunflower oil had an 18% increase in polyenoic fatty acids and those grown on coconut oil a 31% decrease. The greatest changes occurred in the proportion of oleate and linoleate. There was only a small difference in the percentage of saturated fatty acids and in the mean fatty acid chain length among the tumor cells from animals on the experimental diets. The changes in the fatty acid composition of the L1210 cell neutral lipids and the lipids of the ascites fluid were similar to those observed in the phospholipids. A majority of the changes had occurred after 5 weeks of feeding the special diet. These results indicated that the fatty acid saturation of tumor cell phospholipids can be altered appreciably. The changes in fatty acid composition were not associated with any change in the sterol/phospholipid ratio of the cells. Therefore, our results suggest that it may be possible to alter the physical properties and function of a tumor cell membrane by dietary modification of its phospholipid composition.     

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.     

Nonessential fatty acids in formula fat blends influence essential fatty acid metabolism and composition in plasma and organ lipid classes in piglets

The n-6 and n-3 fatty acid status of developing organs is the cumulative result of the diet lipid composition and many complex events of lipid metabolism. Little information is available, however, on the potential effects of the saturated fatty acid chain length (8:0–16:0) or oleic acid (18:1) content of the diet on the subsequent metabolism of the essential fatty acids 18:2n-6 and 18:3n-3 and their elongated/desaturated products. The effects of feeding piglets formulas with fat blends containing either coconut oil (12:0±14:0) or medium chain triglycerides (MCT, 8:0±10:0) but similar levels of 18:1, 18:2n-6 and 18:3n-3, or MCT with high or low 18:1 but constant 18:2n-6 and 18:3n-3 on the fatty acid composition of plasma, liver and kidney triglycerides, phospholipids and cholesteryl esters, and of brain total lipid, were studied. Diet-induced changes in the fatty acid composition of lipid classes were generally similar for plasma, liver and kidney. Dietary 18:1 content was reflected in tissue lipids and was inversely associated with levels of 18:2n-6. Lower percentage of 18:2n-6, however, was not associated with lower levels of its elongated/desaturated product 20:4n-6 but was associated with higher levels of 22:6n-3. Feeding coconut oilvs. MCT resulted in lower 18:1 levels in all lipids, and higher percentages of 20:4n-6 in tissue phospholipid. Increasing the dietary n-6/n-3 ratio from 5 to 8 significantly increased tissue percentage of 18:2n-6 and decreased phospholipid 22:6n-3. In contrast to plasma, liver and kidney, brain lipid fatty acid composition was not influenced by the formula saturated fatty acid chain length, content of 18:1, or n-6/n-3 ratio. In summary, the studies show that the dietary requirement for n-6 and n-3 fatty acids may be influenced by the nonessential saturated and monounsaturated fatty acids fed concurrently.     

Hyperlipidemia in rats fed retinoic acid

This report describes a series of experiments that attempt to characterize the lipidemia accompanying retinoic acid administration. After feeding young adult male Sprague-Dawley rats, 1.2 Retinol Equivalents (R.E.) retinyl acetate plus supplemental retinoic acid (100 μg/g dry diet) for three days and fasting for 6–8 hr, triglyceride, cholesterol, and phospholipid content of various serum lipoprotein fractions were determined. When compared to unsupplemented controls, both the serum very low density lipoprotein (VLDL) and the high density lipoprotein (HDL) fractions of the retinoic acid-fed rats were found to harbor an elevated triglyceride content. While VLDL cholesterol and phospholipid content were also elevated, total serum cholesterol and phospholipids were not statistically altered. The detergent Triton WR-1339 was used to depress serum triglyceride clearance in order to assess the effects of retinoic acid feeding on serum triglyceride levels. Triglyceride accumulation started earlier after Triton treatment and was greater when rats were fed 100 μg/g retinoic acid for three days prior to testing. Red and white gastrocnemius muscle, cardiac ventricular muscle, and perirenal adipose tissue were removed from rats following retinoic acid feeding. Analysis of these tissues for lipoprotein lipase (EC 3.1.1.3) activity showed a decrease in adipose tissue, a large depression in both areas of gastrocnemius muscle and no change in cardiac muscle as a result of retinoic acid feeding. Portions of this work have appeared earlier in an abstract, Gerber, L.E., and Erdman J.W., Jr. (1980) Fed. Proc. 39, 437.