Increased risk of cardiovascular disease in Type 1 diabetes: arterial exposure to remnant lipoproteins leads to enhanced deposition of cholesterol and binding to glycated extracellular matrix proteoglycans.

AIMS: To determine fasting and postprandial metabolism of apolipoprotein B48 (apoB48) remnant lipoproteins in subjects with Type 1 diabetes and the relationship to progressive cardiovascular disease, and to investigate the impact of remnant lipoprotein cholesterol accumulation associated with arterial wall biglycan using a rodent model of Type 1 diabetes. METHODS: Normolipidaemic subjects (n = 9) with long-standing Type 1 diabetes (and advanced cardiovascular disease) and seven healthy control subjects were studied. Fasting and postprandial apoB48 concentration was determined following a sequential meal challenge. A rodent model of streptozotocin-induced diabetes was used to investigate the ex vivo retention of fluorescent-conjugated remnants. Binding of remnant lipoproteins to human recombinant biglycan was assessed in vitro. RESULTS: A significantly higher concentration of fasting plasma apoB48 remnants was observed in patients with Type 1 diabetes compared with control subjects. Patients with Type 1 diabetes exhibited a greater total plasma apoB48 area under the curve (AUC) and an increased incremental AUC following a second sequential meal compared with control subjects. The arterial retention of remnants ex vivo and associated cholesterol was increased sevenfold in Type 1 diabetes rats relative to controls. Remnants were shown to bind with significant affinity to human biglycan in vitro and a further 2.3-fold increased binding capacity was observed with glycated biglycan. Remnants were shown to colocalize with both arterial biglycan and glycated matrix proteins in the Type 1 diabetes rodent model. CONCLUSION: Impaired metabolism of remnant lipoproteins associated with enhanced binding to proteoglycans appears to contribute to the arterial cholesterol deposition in Type 1 diabetes. Our findings support the hypothesis that impaired remnant metabolism may contribute to accelerated progression of atherosclerosis in the hyperglycaemic and insulin-deficient state.

Synthesis of specific fatty acids contributes to VLDL-triacylglycerol composition in humans with and without type 2 diabetes.

AIMS/HYPOTHESIS: It is recommended that patients with diabetes reduce their intake of saturated fat and increase their intake of monounsaturated fat or carbohydrate. However, high-carbohydrate diets may result in higher saturated fatty acids in VLDL-triacylglycerol. This is attributed to de novo lipogenesis, although synthesis of specific fatty acids is rarely measured. The objective of this study was to examine the contribution of de novo fatty acid synthesis to VLDL-triacylglycerol composition. It was hypothesised that levels of total and de novo synthesised fatty acids would increase with increased carbohydrate intake in diabetic participants. METHODS: Seven individuals with type 2 diabetes mellitus and seven matched non-diabetic controls consumed two diets differing in fat energy (lower fat <25%, higher fat >35%) for 3 days in a randomised crossover design. Blood samples were drawn before and 24 h after the ingestion of (2)H-labelled water. RESULTS: In the control participants, the higher-fat diet resulted in a 40% reduction in VLDL-triacylglycerol fatty acids because of decreases in myristic, palmitic, palmitoleic and linoleic acids, but the opposite trend occurred in participants with diabetes. The lower-fat diet increased the fractional synthesis rate by 35% and 25% in the control and diabetes participants, respectively (range: 0-33%). Palmitate accounted for 71% of fatty acids synthesised (range: 44-84% total de novo synthesised fatty acids). CONCLUSIONS/INTERPRETATION: (2)H incorporation was used for the first time in humans showing variability in the synthesis rate of specific fatty acids, even palmitic acid. A lower-fat diet stimulated saturated fatty acid synthesis at high rates, but no net stimulation of synthesis of any fatty acid occurred in the diabetes group. The implications of this finding for our understanding of lipid metabolism in diabetes require further investigation.

Ganglioside composition of differentiated Caco-2 cells resembles human colostrum and neonatal rat intestine.

Gangliosides are glycosphingolipids found in cell membranes and human milk with important roles in cell proliferation, differentiation, growth, adhesion, migration, signalling and apoptosis. Similar changes in ganglioside composition occur during embryonic development, lactation and cancer cell differentiation. It is not known, however, whether ganglioside compositional changes that occur in differentiating colon cancer cells reflect changes that occur during intestinal development. The Caco-2 cell line is commonly used to study physiological and pathophysiological processes in the small intestine and colon. Therefore, to examine this question, undifferentiated and differentiated Caco-2 cells were grown and total lipid was extracted from cell supernatant fractions using the Folch method. The upper aqueous phase containing gangliosides was collected and purified. Total gangliosides were measured as ganglioside-bound N-acetyl neuraminic acid, while individual ganglioside content was quantified via a colorimetric assay for sialic acid and scanning densitometry. The total ganglioside content of differentiated Caco-2 cells was 2.5 times higher compared with undifferentiated cells. Differentiated Caco-2 cells had significantly more (N-acetylneuraminyl) 2-galactosylglucosyl ceramide (GD3) and polar gangliosides, and a lower N-acetylneuraminylgalactosylglucosylceramide (GM3):GD3 ratio than undifferentiated cells. The present study demonstrates that the total ganglioside content and individual ganglioside composition of differentiated Caco-2 cells are similar to those of human colostrum and neonatal rat intestine. Differentiated Caco-2 cells may therefore be an alternative model for studying physiological and pathological processes in the small intestine and colon, and may help to elucidate possible functions for specific gangliosides in development and differentiation. Further research using more sensitive techniques of ganglioside analysis is needed to confirm these findings.

Reduced growth and integrin expression of prostate cells cultured with lycopene, vitamin E and fish oil in vitro.

Integrins are transmembrane proteins that facilitate the interaction of cells with the extracellular environment. They have also been implicated in cancer progression. The effects of nutrients thought to be involved in the prevention of prostate cancer on integrin expression have not been determined. Prostate cancer cell lines representing a range of malignancy from normal (RWPE-1) to highly invasive phenotypes (22Rv1 < LNCaP < PC-3) were cultured with or without lycopene (10 nM), vitamin E (5 microm) or fish oil (100 microm) for 48 h. Growth and integrin (alpha2beta1, alphavbeta3 and alphavbeta5) expression were assessed using Trypan Blue exclusion and monoclonal antibodies combined with flow cytometry. Vitamin E enhanced (P < 0.001) whereas fish oil reduced the growth of all the cell lines tested (P < 0.001). Lycopene had no effect on growth. All the malignant cell lines exhibited lower expression of alpha2beta1 with the addition of lycopene to culture media. Supplemental fish oil reduced alpha2beta1 in most invasive cell lines (LNCaP and PC-3). Each nutrient at physiological levels reduced integrins alphavbeta3 and alphavbeta5 in most invasive cell lines (PC-3). The results suggest that integrins may represent an additional target of bioactive nutrients and that the effects of nutrients may be dependent on the type of cell line used.

Long-chain polyunsaturated fat supplementation in children with low docosahexaenoic acid intakes alters immune phenotypes compared with placebo.

OBJECTIVES: The objectives of this study were to assess the effects of long-term supplementation with arachidonic acid (AA; 20:4n-6) and docosahexaenoic acid (DHA; 22:6n-3) on cell phenotypes and cytokine production in children. PATIENTS AND METHODS: This randomized, double-blind, placebo-controlled trial provided children, (ages 5-7 years; n = 37) who had low intakes of DHA, with a dietary supplement containing AA (20-30 mg daily) and DHA (14-21 mg daily) or a placebo supplement for 7 months. After the supplementation period, a series of stimulants (pokeweed mitogen, phytohemagluttinin, lipopolysaccharide, beta-lactoglobulin, and ibuprofen) was used to stimulate peripheral blood mononuclear cells ex vivo. Antigen expression on T cells (CD25 and CD80), B cells, and macrophages (CD54), as well as cytokine production (interleukin [IL]-4, IL-10, tumor necrosis factor, IL-2, IL-6, and interferon-gamma), were measured using flow cytometry, monoclonal antibodies, and cytometric bead array, respectively. RESULTS: Mononuclear cells from children provided long-chain polyunsaturated fatty acids (LCPUFAs) had fewer CD8+ cells expressing CD25 and CD80 compared with placebo after exposure to each mitogen. The LCPUFA group also exhibited lower proportions of CD14+ cells after stimulation with beta-lactoglobulin and ibuprofen. The proportion of CD54+ cells was 2-fold higher for the LCPUFA group compared with placebo after exposure to ibuprofen and beta-lactoglobulin (P < 0.05). Each of these immune effects related to the amount of AA and/or DHA in the plasma and erythrocyte phospholipids. CONCLUSIONS: Alterations in cell phenotypes were evident when children were supplemented with AA and DHA. The results of this study have important implications for immune development and sensitivity to antigens in children.

Dietary fat selectively alters transport properties of rat jejunum.

The influence of dietary fatty acid composition on intestinal active and passive transport function, brush border membrane composition, and morphology was examined in rats. Animals fed a semisynthetic diet high in saturated fatty acids demonstrated enhanced in vitro jejunal uptake of decanoic, dodecanoic, palmitic, stearic, and linoleic acid, as well as cholesterol and chenodeoxycholic and taurochenodeoxycholic acid, as compared with uptake in animals fed a semisynthetic diet high in polyunsaturated fatty acids but equivalent in total content of fat and other nutrients, or as compared with Purina chow. Feeding the saturated fatty acid diet was also associated with reduced jejunal uptake of a range of concentrations of glucose, enhanced ileal uptake of leucine, unchanged uptake of galactose, and lower uptake of decanol. The semisynthetic diets did not alter brush border membrane protein, sucrase or alkaline phosphatase activities, cholesterol, or total phospholipids, although the percentage of jejunal amine phospholipids was higher than in rats fed chow. The morphologic differences between the jejunum and ileum were abolished in animals fed the high polyunsaturated fatty acid diet; in rats fed the high saturated fatty acid diet, there was reduced mean ileal villus height, width, thickness, surface area, cell size, and villus density, as well as reduced mucosal surface area. The changes in jejunal transport were not correlated with the alterations in morphology, unstirred layer resistance, food intake, or body weight gain. It is proposed that small changes in the percentage of total dietary lipids composed of essential and nonessential fatty acids (without concurrent alterations in dietary total fat, carbohydrate, or protein) influence active and passive intestinal transport processes in the rat.

Fatty acids in blood and intestine following docosahexaenoic acid supplementation in adults with cystic fibrosis.

UNLABELLED: The objective of this study was to investigate the effect of docosahexaenoic acid (DHA) supplementation on blood and intestinal DHA levels and lung function in mild/moderately affected adult CF patients with the DeltaF508 genotype. BACKGROUND: Cystic Fibrosis (CF) patients often present with plasma fatty acid levels indicating low levels of linoleic (18:2n-6) and docosahexaenoic (22:6n-3) acids and an increased level of arachidonic acid (20:4n-6). Improved dietary fat intake or reducing fat malabsorption with pancreatic enzymes has failed to normalize this biochemical deficiency of DHA. METHODS: Five CF patients, aged 18-43, received 70 mg of DHA/kg body weight/d for six weeks. At baseline and at six weeks a physical exam, lung function, 3-day dietary intake, duodenal mucosal biopsy and blood sample were assessed. The blood was analyzed for plasma vitamin A, D and E levels, liver function tests, clinical chemistry (CBC, differential and electrolytes). Plasma and red blood cell fatty acid levels were also analyzed. At three weeks, assessment included a physical exam, lung function test and fasting blood sample (vitamin levels, liver function and clinical chemistry only). RESULTS: Pre- and post-measurements were compared for the four subjects who completed the study. An increase in DHA content (% w/w) was observed in all phospholipid fractions of plasma, red blood cell and mucosal samples. No significant differences in vitamin levels, liver function or lung function were observed. CONCLUSIONS: The study proves the concept that an increase in tissue DHA levels in CF patients can be achieved by supplementing for six weeks with 70 mg/kg/d DHA.

Polyunsaturated fatty acids and anthropometric indices of children in rural China.

OBJECTIVE: To define fatty acid and macronutrient intakes in a rural Chinese preschool population, and relate these intakes to anthropometric indices. DESIGN: Cross-sectional survey of anthropometry and diet (three 24-h recalls). National Centers for Health Statistics/World Health Organization growth reference charts were used to determine the prevalence of malnutrition (z-scores less than -2 standard deviation (s.d.) below the mean): height-for-age (stunted), weight-for-age (underweight), weight-for-height (wasted) and mid-upper-arm-circumference-for-age (low fat/muscle). SUBJECTS AND SETTING: A total of 196 children aged 1-5 years old were volunteered by their families to participate in the survey, located in Heqing County, Yunnan Province, China. RESULTS: The respective prevalence of stunting, underweight, wasting and low fat/muscle was: 38, 21, 2 and 8%. Daily intakes of linoleic acid (LA; 18:2n-6), alpha-linolenic acid (LNA; 18:3n-3), arachidonic acid (AA; 20:4n-6) and docosahexaenoic acid (DHA; 22:6n-3), averaged for all children, were 2 100+/-1200, 300+/-250, 55+/-35 and 30+/-140 mg/day, respectively. As percent of total fat intake, LA contributed 11.9%, LNA 1.8%, AA 0.3% and DHA 0.2%. Height-for-age and weight-for-age z-scores were negatively correlated with g/kg/day intake of LA and AA (P<0.05). Weight-for-height z-score was negatively correlated with AA g/kg/day intake (P<0.05). CONCLUSIONS: This study provided polyunsaturated fatty acids (PUFA) intakes in rural preschool children in a developing country. The associations of PUFA intake with early childhood growth suggest that growth in preschool-aged children could be significantly and specifically related to n-6 fatty acid intakes.

Phosphatidylethanolamine methyltransferase: evidence for influence of diet fat on selectivity of substrate for methylation in rat brain synaptic plasma membranes.

Male weanling rats were fed diets containing 20% (w/w) fat differing in fatty acid composition for 24 days. Synaptic plasma membranes were isolated from the brain and the fatty acid composition of phosphatidylethanolamine and phosphatidylcholine was determined. In vitro assays of phosphatidylethanolamine methyl-transferase activity were performed on fresh membrane samples to assess effect of dietary fat on the rate of phosphatidylethanolamine methylation for phosphatidylcholine synthesis via the phosphatidylethanolamine methyltransferase pathway. Dietary level of n-6 and ratio of n-6 to n-3 fatty acids influenced membrane phospholipid fatty acid composition and activity of the lipid-dependent phosphatidylethanolamine methyltransferase pathway. Rats fed a diet rich in n-6 fatty acids produced a high ratio of n-6/n-3 fatty acids in synaptosomal membrane phosphatidylethanolamine, and elevated rates of methylation of phosphatidylethanolamine to phosphatidylcholine by phosphatidylethanolamine methyltransferases, suggesting that the pathway exhibits substrate selectivity for individual species of phosphatidylethanolamine containing long-chain homologues of dietary n-6 and n-3 fatty acids (20:4(n-6), 22:4(n-6), 22:5(n-6) and 22:6(n-3). It may be concluded that diet alters the membrane content of n-6, n-3 and monounsaturated fatty acids, and that change in phosphatidylethanolamine species available for methylation to phosphatidylcholine alters the rate of product synthesis in vivo by the phosphatidylethanolamine methyltransferase pathway.

Dietary control of diacylphosphatidylethanolamine species in brain.

The content and composition of the brain diacylphosphatidylethanolamine species was examined in response to dietary fat intake. Synaptic plasma membrane and microsomal membrane subcellular fractions contain phosphatidylethanolamine species profiles that respond differently to modulation by diet fat. The microsomal content of individual phosphatidylethanolamine species was most responsive to diet treatment and to addition of cholesterol to the diet. Feeding fish oil or linseed oil diets resulted in an increased membrane content of phosphatidylethanolamine species containing six double bonds for both microsomal and synaptic plasma membranes, compared with soya-bean oil- or sunflower oil-fed animals. The 22:5(n - 6) content present in phosphatidylethanolamine species of linseed oil and fish oil-fed animals was also reduced. For microsomal membranes, increase in dietary 18:3(n - 3) resulted in an increased content of phosphatidylethanolamine species containing one double bond. Addition of cholesterol to linseed oil or fish oil diets decreased the microsomal membrane content of phosphatidylethanolamine species containing six double bonds and increased the membrane content of species containing one double bond. For synaptic plasma membrane, addition of cholesterol to linseed oil and fish oil diets increased membrane content of species containing six double bonds. Fish oil-fed animals exhibited a decreased content of species containing a single double bond. The implications of the diet-induced changes in phospholipid species content and composition are discussed.

Ribonucleic acid efflux from isolated mouse liver nuclei is altered by diet and genotypically determined change in nuclear envelope composition.

Differences in immunological abnormalities like autoimmunity, abnormal T cell proliferative disorders and accelerated ageing occur between MRL/Mp-lpr/lpr(lpr/lpr) and MRL/Mp-+/+(+/+) mice as a consequence of one gene. The present study was designed to assess the effect of these differences in genotype and diet on the composition and function of the liver nuclear envelope. Mice of both strains were fed nutritionally adequate diets differing only in fatty acid composition for 4 weeks. Phospholipid fatty acid composition of the liver nuclear envelope was determined and the effect of altering the lipid composition of the nuclear membrane on nucleoside-triphosphatase (NTPase) activity, ribonucleic acid (RNA) efflux and binding of L-triiodothyronine (L-T3) was determined. Strain of mouse and level of dietary linoleic acid exhibited significant effects on the phospholipid fatty acid composition of the nuclear envelope. Levels of 18:1(n - 9) and 18:2(n - 6) were lower and 20:4(n - 6) content was higher in nuclear envelope phospholipids of lpr/lpr mice compared with mice of the +/+ strain. Mice fed the high linoleic acid diet exhibited higher levels of 18:0, 18:2(n - 6) and 20:4(n - 6) and lower levels of 16:0 and 18:1(n - 9) in liver nuclear envelope phospholipids, compared with mice fed the low linoleic acid diet. These changes in membrane composition were reflected in alteration of NTPase activity and efflux of RNA from isolated mouse liver nuclei. Nucleoside triphosphatase activity and efflux of ribonucleic acid from isolated nuclei were significantly higher in livers of the lpr/lpr strain. NTPase activity and RNA efflux from isolated nuclei were higher in the high linoleic acid fed group compared with the low linoleic acid group. A single class of binding sites for L-T3 was present in liver nuclear envelopes of these mice and Kd values were not influenced by strain or dietary linoleic acid levels. Nuclear envelopes prepared from +/+ animals exhibited a significantly higher number of binding sites for L-T3 compared with the lpr/lpr group. These observations indicate that the single gene difference characterizing lpr/lpr mice from +/+ mice results in alterations in the composition and function of the nuclear envelope. This genetic difference also alters the response of this membrane to dietary factors known to modulate characteristics and functions of the nuclear envelope.

Diet fat alters expression of genes for enzymes of lipogenesis in lean and obese mice.

The objective of this experiment was to determine the effect of polyunsaturated fatty acids on gene expression for fatty acid synthase, acetyl CoA-carboxylase, malic enzyme, pyruvate kinase, and phosphoenolpyruvate carboxykinase in obese mice. Eight-week-old female lean and obese mice were fed semi-purified diets containing 20% (w/w) fat of either high or low polyunsaturated to saturated (P/S) fatty acid ratio for four weeks. Total RNA was isolated from liver and was hybridized to cDNA probes for the above enzymes. Consumption of a high P/S diet decreased mRNA levels for all the lipogenic enzymes studied in both lean and obese mice. Compared to lean mice, obese mice exhibited a higher mRNA level for fatty acid synthase, acetyl CoA-carboxylase, malic enzyme, and pyruvate kinase in animals fed either a high or low P/S diet. Enzyme-specific activities followed the same profile as the mRNA levels in both lean and obese mice fed a high or low P/S diet. The decrease in liver fatty acid synthase mRNA level was more pronounced in lean mice compared to obese mice, suggesting that the obese mice may be more resistant to polyunsaturated fatty acid feedback control of gene expression.

Co-ordinate control of CDP-choline and phosphatidylethanolamine methyltransferase pathways for phosphatidylcholine biosynthesis occurs in response to change in diet fat.

Brain microsomal and synaptic plasma membrane phosphatidylcholine composition and biosynthetic activity were examined in relation to the composition of diet fat fed. Phosphocholinetransferase and methyltransferase activities are shown to be modulated by the diet, and by changes in the membrane phospholipid content of long-chain polyunsaturated fatty acids. This physiological modulation is co-ordinated such that the rate of phosphatidylcholine synthesis via one route is inversely regulated with activity of the alternate pathway.

Dietary fat alters membrane composition in rod outer segments in normal and diabetic rats: impact on content of very-long-chain (C > or = 24) polyenoic fatty acids.

The effect of high n - 3 (5.8%, w/w) vs. a low n - 3 (1.2%, w/w) fatty acids in a diet with a low ratio of polyunsaturated/saturated fatty acids (P/S = 0.27) content was investigated to determine the effect of diet on the level of long- and very-long-chain fatty acids (VLCFA C > or = 24) in phospholipids of rod outer segments (ROS) of normal and diabetic rats. After 6 weeks of feeding, diets high in n - 3 fatty acids increased the levels of 22:5(n - 3) and 22:6(n - 3), while decreasing the 22:5(n - 6) level in all major phospholipid classes. n - 6 and n - 3 VLCFA of C24 to C34 with 4, 5 and 6 double bonds were found only in phosphatidylcholine (PC) while other phospholipid classes contained only C24 fatty acids as minor components. The content of VLCFA in PC was approx. 6.7% (w/w) of total fatty acids in the ROS. Feeding a high n - 3 fatty acid diet significantly reduced n - 6 tetraenoic VLCFA in all phospholipids. In the diabetic state, the levels of n - 6 tetraenes and pentaenes in individual phospholipids were different from control animals. This study demonstrates that the VLCFA content of photoreceptor cells reflects the dietary level of n - 3 fatty acids fed. The unique polyenoic n - 6 and n - 3 VLCFA appear to be synthesized from shorter chain precursors which respond to altering the ratio of n - 6/n - 3 fatty acids fed.

Feeding rats a diet enriched with saturated fatty acids prevents the inhibitory effects of acute and chronic ethanol exposure on the in vitro uptake of hexoses and lipids.

Chow-fed rats were given 15% ethanol in their drinking water for 4 weeks, and then for the next 2 weeks of ethanol exposure they were fed isocaloric semisynthetic diets enriched in either saturated (S) or polyunsaturated (P, linoleic acid) fats. Food intake was lower in ethanol-fed (ETH) than in control (C) rats, but the average body weight gain was similar in ETH and C fed S or P. Intestinal dry weight and the percentage of the intestinal wall comprised of mucosa were more than 2-fold higher in ETH than C fed P, whereas these values were 50% lower in ETH than C fed S. The in vitro jejunal uptake of glucose and galactose was higher in ETH than C fed S, whereas the converse was true when feeding P. These effects were due to differences in the values of the maximal transport rate (Vmax), the Michaelis constant (Km), and the contribution of passive permeation. The relative permeability of the intestine to lipids was unchanged by giving ethanol or by feeding S or P, but the individual rates of uptake of most medium- and long-chain fatty acids and cholesterol were lower in ETH fed P as compared with S. In a second series of studies the acute effect of ethanol exposure was examined: animals were fed S or P for 2 weeks and the intestine was then removed: when 5% ethanol was added directly to the test solutions, there was lower in vitro jejunal and ileal uptake of glucose and higher jejunal uptake of 18:2 when rats were previously fed P, but not in those fed S. In summary; (1) feeding an isocaloric polyunsaturated fatty acid diet has a trophic effect on the intestinal mucosa of animals chronically drinking ethanol; and (2) feeding rats a diet enriched with saturated fatty acids prevents the inhibitory effects of acute and chronic ethanol exposure on the in vitro jejunal uptake of glucose, galactose and lipids observed in animals fed a polyunsaturated diet. Thus, the effect of chronic consumption of ethanol on the active and passive jejunal uptake of nutrients is influenced by the type of lipids in the animal's diet.

Insulin binding to liver nuclei from lean and obese mice is altered by dietary fat.

Insulin binding to the plasma membrane is known to be altered by modifying the membrane composition through dietary treatment. As insulin binding receptors are also present on nuclear membrane, this study was undertaken to investigate if specific binding of insulin to the liver nuclei is altered by diet. 8-wk-old female C57 B 6J lean and ob/ob mice were fed semipurified diets containing 20% (w/w) fat of either high or low polyunsaturated-to-saturated (P/S) fatty acid ratio for 4 wk. Liver nuclei were prepared, insulin binding was measured and nuclear phospholipids were isolated for lipid analysis. Insulin binding was highest in nuclei prepared from lean mice fed a high P/S diet. Specific binding of insulin to nuclei prepared from obese mice was also increased by the high P/S diet, but to a lesser extent compared to lean mice. Feeding a high P/S diet increased polyunsaturated fatty acid content of membrane phospholipids from both lean and ob/ob mice. Obese mice were characterized by higher levels of arachidonic acid and lower levels of linoleic acid in phosphatidylcholine. The present study establishes that insulin binding to liver nuclei is increased by feeding a high P/S diet, and that insulin binding to liver nuclei from obese mice is lower than from lean mice.

Fish oil reduces cholesterol and arachidonic acid content more efficiently in rats fed diets containing low linoleic acid to saturated fatty acid ratios.

Rats were fed diets containing a high level of saturated fatty acids (hydrogenated beef tallow) versus a high level of linoleic acid (safflower oil) at both low and high levels of fish oil containing 7.5% (w/w) eicosapentaenoic and 2.5% (w/w) docosahexaenoic acids for a period of 28 days. The effect of feeding these diets on the cholesterol content and fatty acid composition of serum and liver lipids was examined. Feeding diets high in fish oil with safflower oil decreased the cholesterol content of rat serum, whereas feeding fish oil had no significant effect on the cholesterol content of serum when fed in combination with saturated fatty acids. The serum cholesterol level was higher in animals fed safflower oil compared to animals fed saturated fat without fish oil. Consumption of fish oil lowered the cholesterol content of liver tissue regardless of the dietary fat fed. Feeding diets containing fish oil reduced the arachidonic acid content of rat serum and liver lipid fractions, the decrease being more pronounced when fish oil was fed in combination with hydrogenated beef tallow than with safflower oil. These results suggest that dietary n-3 fatty acids of fish oil interact with dietary linoleic acid and saturated fatty acids differently to modulate enzymes of cholesterol and fatty acid metabolism.

Fatty acid desaturation in the intestinal mucosa.

Information as to the ability of the enterocyte to desaturate fatty acids is lacking. This is important in understanding whether the source of intestinal arachidonic (20:4(n-6) acid is biliary or from de novo synthesis. Delta 9- and delta 6-desaturase enzymes were assayed in homogenates of rat jejunum, ileum and liver. Rat small intestine possesses desaturase activity to convert palmitic (16:0) to palmitoleic (16:1) and linoleic (18:2(n-6) to linolenic (18:3(n-6) acid. Enzyme activities were highest in liver relative to activity in jejunal and ileal homogenates. It is concluded that delta 9- and delta 6-desaturase activities may have an important role in determining physico-chemical properties and thus transport properties of enterocyte membranes.

Dietary cholesterol and/or n-3 fatty acid modulate delta 9-desaturase activity in rat liver microsomes.

delta 9-Desaturase activity and fatty acid composition of liver microsomal phospholipids in rats fed diets enriched with either saturated (hydrogenated beef tallow) or alpha-linolenic (linseed oil) or eicosapentaenoic and docosahexaenoic (fish oil) acids with or without 2% cholesterol supplementation were investigated. Both the linseed oil and the fish oil diets inhibited delta 9-desaturase activity in the rat liver microsomes. The inhibition was greater when feeding fish oil (90%) compared with the linseed oil (60%) diet. Dietary cholesterol feeding accelerated conversion of palmitic (16:0) to palmitoleic (16:1) acid, irrespective of the fatty acid supplement. Feeding the linseed oil diet decreased, while feeding the fish oil diet increased synthesis of the monounsaturated fatty acids of n-7 series (palmitoleic and vaccenic acid) and decreased 18:1(n-9) in microsomal membrane lipids when compared with animals fed beef tallow. Addition of 2% cholesterol to the otherwise low cholesterol diets led to accumulation of 16:1(n-7), and 18:1(n-9) in microsomal membranes. These results suggest that delta 9-desaturase activity is dependent on the cholesterol contents as well as the n-3 fatty acid content of microsomal membranes on which it is localized.

Delayed effects of early nutrition with cholesterol plus saturated or polyunsaturated fatty acids on intestinal morphology and transport function in the rat.

This study was undertaken to test the hypotheses that: (1) the fatty acid and/or cholesterol composition of a nutritionally adequate isocaloric semisynthetic diet given in early life has lasting consequences for intestinal nutrient uptake and morphology; and (2) early life feeding experiences with diets of varying fatty acid or cholesterol composition influence the ability of the intestine to adapt to an altered nutrient uptake in later life. Weanling female Sprague-Dawley rats were fed nutritionally adequate isocaloric semisynthetic diets enriched with beef tallow, beef tallow plus 1% cholesterol, fish oil or fish oil plus 1% cholesterol. Animals fed fish oil or fish oil plus cholesterol for 11 weeks had a lower food intake but greater weight gain than animals fed beef tallow or beef tallow plus cholesterol. The age of the animals influenced lipid and hexose uptake. The uptake of these nutrients could also be changed by the addition of cholesterol to the diet. This cholesterol-related effect depended on the type of fat in the diet (saturated vs. polyunsaturated). These changes in nutrient uptake were associated with but not necessarily explained by alterations in food intake, body weight gain, intestinal mucosal weight or surface area. Finally, these changes in nutrient uptake and morphology may or may not be reversible. We speculate that dietary lipids may affect the ability of the intestine to adapt to an altered nutrient intake in later life.