beta-Sitosterol activates Fas signaling in human breast cancer cells.

beta-Sitosterol is the most abundant phytosterol. Phytosterols are enriched in legumes, oil seeds and unrefined plant oils as found in foods such as peanut butter, pistachios and sunflower seeds. beta-Sitosterol inhibits the growth of several specific types of tumor cells in vitro and decreases the size and the extent of tumor metastases in vivo. The effects of beta-sitosterol on the extrinsic apoptotic programmed cell death pathway in human breast MCF-7 and MDA-MB-231 adenocarcinoma cells were examined, along with the extent of its incorporation into cellular membranes and its effects on cell growth, expression of Fas receptor pathway proteins, and caspase-8 activity. The results show that beta-sitosterol exposure promotes its enrichment in transformed cell membranes and significantly inhibits tumor cell growth. Concurrently, Fas levels and caspase-8 activity are significantly increased. These actions are specific, as expression of other proteins of the Fas receptor pathway, including Fas ligand, FADD, p-FADD and caspase-8, remain unchanged. These findings support the hypothesis that beta-sitosterol is an effective apoptosis-promoting agent and that incorporation of more phytosterols in the diet may serve a preventive measure for breast cancer.

Peanuts as a source of beta-sitosterol, a sterol with anticancer properties.

Work from our laboratory, as well as others, suggests a protective role of phytosterols (PS), especially beta-sitosterol, from colon, prostate, and breast cancer. Asians and vegetarians consume higher amounts of PS than Western societies. The latter societies have a higher incidence of these cancers than Asians and vegetarians. The aim of this study was to evaluate peanuts and its products as sources of PS in the American diet. Roasted peanuts contain 61-114 mg PS/100 g depending on the peanut variety, 78-83% of which is in the form of beta-sitosterol. Unrefined peanut oil contains 207 mg PS/100 g, which is similar to that of the US Department of Agriculture Nutrient Database. This value is higher than that of unrefined olive oil. Refining these oils results in reduction in PS concentration in the oil. This loss is greater in the case of olive oil than peanut oil. Further refining, such as deodorization, results in significant loss in PS, but hydrogenation after refining has a minimal effect on PS loss. Peanut butter, which represents 50% of the peanuts consumed in the United States, contains 144-157 mg PS/100 g. Peanut flour, which results from partial removal of oil from peanuts, contains 55-60 mg PS/100 g. The data suggest that peanuts and its products, such as peanut oil, peanut butter, and peanut flour, are good sources of PS.

Dietary phytosterol inhibits the growth and metastasis of MDA-MB-231 human breast cancer cells grown in SCID mice.

The objective of the present study was to investigate the effect of dietary phytosterols on the growth and metastasis of the human breast cancer MDA-MB-231 cell line xenografted in SCID mice. Two groups of animals were fed AIN-93G diet supplemented with 0.2% cholic acid and 2% sterol (cholesterol or phytosterol mixture) for 15 days before inoculation of the tumor into the right inguinal mammary fat pad. Tumor growth and food consumption were recorded weekly throughout the 8 weeks of the experiment. At the end of the experiment, the animals fed phytosterol had a 40% lower serum cholesterol and 20 and 30 fold higher serum beta-sitosterol and campesterol, respectively as compared to those fed cholesterol. There was no difference between the two groups in body weight and food consumption. However, the tumor size in animals fed phytosterols was 33% smaller (P < 0.03) and had 20% fewer metastases to lymph nodes and lungs than the cholesterol group. At termination, the tumor weight of the animals fed the phytosterol diet was also less (P < 0.07) than that of the cholesterol group. It is concluded that dietary phytosterols retard the growth and spread of breast cancer cells.

Effect of beta-sitosterol, a plant sterol, on growth, protein phosphatase 2A, and phospholipase D in LNCaP cells.

Previous work from this laboratory suggests an activation of the sphingomyelin cycle as a mechanism for growth inhibition with the incorporation of beta-sitosterol (SIT) into human prostate cancer LNCaP cells. In the present study we examined two key enzymes that have been shown to play a role in the sphingomyelin cycle. Dietary sterols (SIT and cholesterol) were compared for their effect on LNCaP cell growth, phospholipase D (PLD) activity, and protein phosphatase 2A (PP 2A) activity and expression. PP 2A has been suggested as a direct in vitro target of ceramide action on cell growth and apoptosis. Ceramide also inhibits phorbol myristate acetate-stimulated PLD. SIT (16 microM) increased PP 2A activity by 50% compared with cholesterol treatment in LNCaP prostate cells; however, SIT did not alter protein levels of PP 2A. There was an increase in PLD activity in the presence of phorbol myristate acetate in cells supplemented with 16 microM SIT compared with those supplemented with cholesterol after five days of treatment. The present study suggests that the activation of PP 2A added support to the role of the activation of the sphingomyelin cycle by SIT treatment. However, the increase in PLD activity, which was modest but significant, with SIT supplementation suggests that this pathway may be modulated by other mechanisms. This includes the incorporation of SIT into cell membranes that may alter fluidity and, thus, influence the activation of membrane-bound enzymes such as PLD.

Effect of sterols and fatty acids on growth and triglyceride accumulation in 3T3-L1 cells.

Epidemiologic studies suggest a role of dietary fat in the development of obesity. Populations that consume Western diets have a higher incidence of obesity than do those that consume a vegetarian type diet such as Asians. Because dietary fats are made up mostly of triglyceride with minor lipids such as sterols, the objective of this study was to examine the effect of different fatty acids, the main component of triglycerides, and sterols on cell growth and triglyceride accumulation in 3T3-L1 cells. These cells are being used as an in vitro model for studying obesity because upon differentiation in culture they accumulate triglycerides. Cells were seeded at 5,000 cells/cm(2) and supplemented with 0, 3, 10, or 30 microM of oleic acid, elaidic acid, or docosahexaenoic acid (DHA). Similarly, cells were supplemented with 0, 2, 8, or 16 microM of cholesterol, beta-sitosterol (SIT), or campesterol. Cell growth was measured by cell counting. Cellular triglycerides were measured by the Oil Red O method. In some experiments, fatty acids were combined with sterols and growth and triglyceride content were assessed as described. Both DHA and SIT had inhibitory effects on 3T3-L1 cell growth. However, SIT was more potent than DHA in this regard. The combination of SIT and oleic acid was the most potent in inhibiting cell growth and increasing cellular triglyceride content. It is concluded that cell growth and triglyceride accumulation in 3T3-L1 cells is influenced by fatty acid and sterols. When used alone, DHA and SIT inhibit cell growth. SIT was more effective in this process than was DHA. There was an interaction between fatty acids and sterols. The most effective combination inhibiting cell growth and triglyceride concentration was the combination of SIT and oleic acid. This combination reduced cell growth and increased triglyceride accumulation. These data suggest that diets rich in both monounsaturated fatty acids and phytosterols may play a role in controlling obesity.

Effect of dietary phytosterols on rat tissue lipids.

The present study was designed to examine the incorporation of phytosterols (PS) in membranes and tissues of rats fed a diet containing 2% PS in the presence of 0.2% cholic acid for 22 days. The control diet contained 12 mg PS/100 g compared with 2,012 mg/100 g. Liver, kidney, testis, and prostate microsomes, plasma, and epididymal fat pads were examined for sterols. Fatty acid composition and phospholipid pattern were also examined in some tissues. The PS diet resulted in a fivefold increase in plasma PS compared with controls. PS was found to accumulate in adipose tissue and liver microsomes in rats fed the PS-supplemented diet. There was no effect of PS incorporation on microsomal cholesterol content, except in the testes, in which dietary PS reduced cholesterol content by 25%. Dietary PS increased 20:4n-6 and 22:5n-3 fatty acids in membranes of the liver, testis, and prostate but decreased 16:1 in liver microsomes. PS incorporation had no effect on the phospholipid pattern of the liver and testis.

Type of dietary fiber, not fat, alters phospholipase D and ornithine decarboxylase activities in the rat large intestine.

We investigated the effect of dietary fatty acid composition (n-6 vs. n-3) and fiber (highly fermentable vs. less fermentable) on the activities of phospholipase D (PLD) and ornithine decarboxylase (ODC) in the rat large intestine (cecum and proximal and distal colon). Twenty-four Sprague-Dawley rats (215-270 g) ate synthetic diets with 2% safflower oil plus 21.5% safflower or fish oil and 10% cellulose or guar gum for four weeks. Cecal bile acids and free fatty acids were higher in rats fed guar gum than in rats fed cellulose. Rats fed fish oil had more proximal colonic mucosal and cecal bile acids than those fed safflower oil. PLD activity was 23% lower in the proximal colon of rats fed guar gum than in those fed cellulose, but the mucosal weight was not different. ODC activity was lower but cecal mucosal wet weight was higher in the cecum of the rats fed guar gum than in the cecum of the rats fed cellulose. The activities of PLD and ODC are affected by dietary fiber and may not be accurate markers for tissue growth in the colonic mucosa.

Effect of dietary phytosterols on cell proliferation and protein kinase C activity in rat colonic mucosa.

The present study investigated the role of phytosterols in colonic cell proliferation and examined the possible role of protein kinase C (PKC) in this process. A total of 18 male Sprague-Dawley rats weighing 240-270 g were fed, for a period of 22 days, one of three experimental diets: a control diet, a diet supplemented with 0.2% cholic acid, or a diet supplemented with 0.2% cholic acid + 2% dietary phytosterols. Two hours before decapitation, animals were injected with 5'-bromo-2'-deoxyuridine (BrdU, 50 mg/kg body wt ip). Cell proliferation in the proximal colon was measured using a monoclonal antibody to BrdU. PKC activity in the proximal colonic mucosa was assayed using a myelin basic protein as a substrate. Cell proliferation was significantly increased by 276% with 0.2% cholic acid feeding compared with controls. The presence of 2% phytosterols in the diet abolished the cholic acid-induced hyperplasia. Cholic acid induced a 31% expansion of the proliferative zone. Only the cytosolic PKC was significantly lower in the phytosterol-fed group. Neither the total PKC nor the particulate PKC demonstrated an effect of phytosterols on enzyme activity. In conclusion, we found that dietary supplementation with 2% phytosterol has a significant protective effect on enhanced cell proliferation and that this effect is not mediated through the PKC system.

Effect of membrane lipid alteration on the growth, phospholipase C activity and G protein of HT-29 tumor cells.

The objective of the present study was to examine the effect of modifying the fatty acid composition of membranes on cell growth and phosphoinositide specific phospholipase C (PLC) activity in HT-29 colon cancer cells. Cells were seeded at a density of 12 x 10(3) cells/cm2 and supplemented with 30 microM of either 18:0, 18:2 (n6) or 18:3 (n3) complexed to bovine serum albumin (BSA) in DMEM medium. Cell growth was followed for 12 days. The 18:0 supplemented cells (control) reached maximum growth at day nine which was greater than either 18:2 (n6) or 18:3 (n3) supplemented cells. There was no difference between the latter two groups in their growth. To investigate the fatty acid incorporation of the supplemented fatty acid and how they may influence composition in the cell membrane, we examined the fatty acid composition of each phospholipid (PL) species. Both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were significantly influenced by the type of fatty acid supplemented. Supplementation with 18:0 resulted in HT-29 cell membranes having more monounsaturated fatty acids than the cells grown in the other fatty acids. Polyunsaturated fatty acid (PUFA) supplementation (both 18:2 and 18:3) resulted in the enrichment of PUFA in the PL fractions. Cells supplemented with 18:3 (n3) had the highest unsaturation index in membrane PE as compared to the other phospholipid species. PLC activity of the membranes was measured using PIP2 as a substrate in the presence of 15 micrograms alamethicin and 42 microM free calcium. The contribution of G protein to the activity of the enzyme was assessed using GTP gamma(S). PLC activity of HT-29 cells was 16% higher in the presence of GTP gamma(S) response. GTP gamma(S)-activated PLC activity of 18:3 (n3) supplemented cells was 81% of those supplemented with either 18:0 or 18:2 (n6) cells. It is concluded that the decrease in cell proliferation with supplementation with 18:3 (n3) may be mediated through its inhibitory effect on PLC, which provides the second messengers for protein kinase C (PKC) activation. PLC may be influenced by an increased unsaturation index of the PE fraction of the HT-29 tumor cell membranes.

The effect of unsaturated fatty acids on membrane composition and signal transduction in HT-29 human colon cancer cells.

The objective of the present study was to investigate the effect of membrane fatty acid (FA) composition on the activity of phospholipase C (PLC) in HT-29 human colon cancer cells. The membrane FA composition was altered by supplementing cultured cells with FAs of different composition. The FAs were stearic acid (18:0; SA), gamma linolenic acid (18:3 omega 6; gamma LnA); alpha linolenic acid (18:3 omega 3; alpha LnA;); eicosapentaenoic acid (20:5 omega 3; EPA) and docosahexaenoic acid (22:6 omega 3; DHA). The fatty acids were supplemented as a FA/BSA complex. Cells supplemented with SA served as the control. Tumor growth was followed by counting the number of cells in culture. The results indicate that polyunsaturated fatty acid (PUFA) supplementation had no consistent effect on tumor growth from 1 day to another throughout the 15 days of growth. The fatty acid composition of membranes indicates that cells incorporated and modified the supplemented fatty acids by desaturation, elongation and retroconversion. The unsaturation index (UI) of membranes of cells supplemented with EPA and DHA was higher than other groups. PLC activity; measured in the absence of GTP gamma(S) in the assay mixture; was not influenced by membrane FA modification. However, in the presence of GTP gamma(S) PLC of cells supplemented with 18:3(omega 6) was the lowest among the groups. It has been shown that 18:3(omega 6) accumulated the most in the phosphatidylethanolamine (PE) fraction. There was a negative correlation between the activity of PLC in the presence of G protein activation and PE 18:3 (omega 6) content without affecting UI. It was concluded that G protein may be sensitive to the level of 18:3(omega 6) content and not to the general fluidity of the membranes.

beta-Sitosterol inhibits HT-29 human colon cancer cell growth and alters membrane lipids.

The purpose of the present study was to examine the effect of beta-sitosterol, the main dietary phytosterol on the growth of HT-29 cells, a human colon cancer cell line. In addition, the incorporation of this phytosterol into cellular membranes and how this might influence the lipid composition of the membranes were investigated. Tumor cells were grown in DMEM containing 10% FBS and supplemented with sterols (cholesterol or beta-sitosterol) at final concentrations up to 16 microM. The sterols were supplied to the media in the form of sterol cyclodextrin complexes. The cyclodextrin used was 2-hydroxypropyl-beta-cyclodextrin. The sterol to cyclodextrin molar ratio was maintained at 1:300. The study indicated that 8 and 16 microM beta-sitosterol were effective at cel growth inhibition as compared to cholesterol or to the control (no sterol supplementation). After supplementation with 16 microM beta-sitosterol for 9 days, cell growth was only one-third that of cells supplemented with equimolar concentration of cholesterol. No effect was observed on total membrane phospholipid concentration. At 16 microM beta-sitosterol supplementation, membrane cholesterol was reduced by 26%. Cholesterol supplementation resulted in a significant increase in the cholesterol/phospholipid ratio compared to either beta-sitosterol supplemented cells or controls. There was a 50% reduction in membrane sphingomyelin (SM) of cells grown in 16 microM beta-sitosterol. Additional changes were observed in the fatty acid composition of minor phospholipids of beta-sitosterol supplemented cells, such as SM, phosphatidylserine (PS), and phosphatidylinositol (PI). Only in the case of PI, was there an effect of these fatty acid changes on the unsaturation index, beta-sitosterol incorporation resulted in an increase in the U.I. It is possible that the observed growth inhibition by beta-sitosterol may be mediated through the influence of signal transduction pathways that involve membrane phospholipids.

Prostaglandin synthesis in human cancer cells: influence of fatty acids and butyrate.

Previous research has suggested that prostaglandins (PGs) may play a role in the development of colon cancer since tumor cells produce more PGs than normal cells. However, the exact mechanism by which PGs play a role in the development of cancer is not known. In addition, factors that influence PG synthesis are not known since they are complicated by the presence of homeostatic mechanisms. To avoid the homeostatic mechanisms, the present research was designed to examine factors that may influence PG synthesis in an in vitro system, i.e., a tissue culture. We have chosen two human colon cancer cell lines that differ in their ability to metabolize long-chain fatty acids (LCFAs), LS174T cells and HT-29 cells. We examined the effect of LCFAs on their membrane fatty acid composition, growth, and ability to release the main PGs (PGE2 and PGI). The LCFAs used were those most common in the colonic lumen [18:0, 18:2 (n-6), and 18:3 (n-3)]. In addition, we examined the effect of butyrate on the above mentioned parameters. Butyrate is produced in the colon through fermentation of dietary fibers. The data obtained suggest that although both of these tumor cell lines are of human colonic origin, they differ in their response to LCFAs and butyrate in some of the characteristics studied, such as growth, composition of membranes, and the relationship between membrane FA composition and PG synthesis. Polyunsaturated fatty acid supplementation stimulated the growth of HT-29 cells but not of LS174T cells when compared with growth in media supplemented with 18:0.(ABSTRACT TRUNCATED AT 250 WORDS)

18:1 n7 fatty acids inhibit growth and decrease inositol phosphate release in HT-29 cells compared to n9 fatty acids.

Studies have shown that trans fatty acids may play a role in the development of chronic diseases such as heart disease and cancer. The objective of the present project was to examine the effect of supplementation with 18:1 isomers, both positional and geometrical, as compared to 18:0 on the growth, membrane fatty acid composition and the phosphoinositide cycle of HT-29 human colon cancer cells. Cells were supplemented with 30 microM stearic acid (18:0), elaidic acid (18:1, n9, trans), oleic acid (18:1, n9, cis), vaccenic acid (18:1, n7, cis) or trans-vaccenic acid (18:1, n7, trans) as sodium salts complexed to fatty acid-free bovine serum. Cells were grown in these media for 9 days. Cell growth was examined by counting the number of cells and expressed as percentage of control (18:0 supplemented cells). The phosphoinositide (PI) cycle was examined by measuring the inositol phosphate (IP) released from phosphoinositides in the absence (basal) or presence of stimuli (0.1 mM carbachol, 0.1 mM A23187 or 20 mM NaF). The results obtained indicated that cis and trans n7 fatty acids inhibited the growth of HT-29 cells by 11% and 23%, respectively, as compared to 18:0 supplementation. 18:1, n9 had no effect on tumor growth. Supplementation with all forms of 18:1 resulted in an increase in IP and IP2 production as compared to 18:0 supplemented cells without influencing IP3. The presence of the double bond at the 9 position in the supplemented fatty acid increases total IP production by 59% and in the cis form by 37% above the control. The breakdown of phosphoinositides in the absence and presence of several stimuli supports the observed finding on IP. Trans fatty acid supplementation resulted in lower hydrolysis of PI as compared to cis fatty acids. It is concluded that the observed inhibition of tumor growth by the vaccenic acids may be mediated by their effect(s) on the PI cycle which may be associated with their incorporation into membrane lipids.

Alteration of membrane fatty acid composition and inositol phosphate metabolism in HT-29 human colon cancer cells.

The present study was designed to investigate the role of membrane fatty acid (FA) composition on inositol phosphate (InsP) release by a human colon tumor cell line. Cells were supplemented for five days in culture with 0, 10, 30, or 100 microM sodium stearate (18:0), linoleate [18:2(omega-6)], or linolineate [18:3(omega-3)]. These FAs were supplied as a complex with FA-free bovine serum albumin. InsP release was examined in these cells with or without stimulation with deoxycholic acid (DCA) after they were labeled with [3H]myoinositol. FA enrichment was found to influence inositol incorporation into membrane lipids. Although 18:0 had no effect, 18:2(omega-6) decreased the incorporation. On the other hand, 18:3(omega-3) increased the incorporation of inositol compared with the cells supplemented with the other FAs, but they were not different from control. Basal release of total InsP was elevated only with supplementation of 10 and 30 microM 18:3(omega-3). FA supplementation with 18:0 at 30 microM and 18:2 at 30 and 100 microM resulted in downregulation of bsal release of InsP. Enrichment of HT-29 cell membranes with polyunsaturated FAs resulted in a significant increase in stimulated release of InsP, but this was not seen with saturated FA supplementation. At 10 microM supplementation, 18:2 had the greatest effect on stimulated InsP release. This effect of 18:2 disappeared at 30 microM. However, the increase in the stimulated InsP release caused by 18:3 occurred at 10 and 30 microM. DCA-stimulated release of InsP was not downregulated by any FA supplementation. This study showed that enrichment of the membranes with polyunsaturated FAs increases the response of the phosphatidylinositol cycle to DCA stimulation. In addition, enrichment with 18:3(omega-3) increases the basal turnover of InsP. It is concluded that alteration of membrane FAs has a profound effect on the phosphatidylinositol cycle.

Differential effect of butyrate on lipids of human colon cancer cells.

Recently, we demonstrated that treatment of LS174T cells with 2 mM butyrate for one day had a significant effect on the composition of cellular fatty acids. In an attempt to further explore this phenomenon, we investigated the effect of long-term butyrate treatment in the presence of different fatty acids in the medium on cellular phospholipids (PLs) and triacylglycerol (TG). Cells were supplemented with 100 microM sodium salts of 18:2 (n-6), 20:4 (n-6), 20:5 (n-3), or 22:6 (n-3) as a fatty acid-free-albumin complex. The molar ratio of the albumin and these long-chain fatty acids (LCFAs) was 3:1. One-half of these cultures were supplied with 2 mM butyrate, and the pH was adjusted to 7.4. The supplementation of the LCFAs and butyrate was maintained for eight days. The present study indicates that butyrate had a differential effect on the fatty acid composition of PLs and TG of LS174T cells. This includes an increase in monounsaturates and elongation of the supplemented LCFA, and this effect was more pronounced on TG than PL fatty acids. Butyrate resulted in a significant reduction in polyunsaturated fatty acid concentration only in PLs. In general, butyrate decreased the unsaturation index (UI) of the PLs but increased that of TG. The present study also confirmed our previous observation regarding the effect of LCFAs on cellular lipids. PL and TG fatty acid chain lengths reflect those of supplemented fatty acids. The UI of these two lipid fractions increased more with supplementation of n-3 than n-6 fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary fat on glomerular lipid composition and angiotensin II receptors.

Nutritional factors are major etiologic determinants which may affect the incidence or severity of hypertension. Since angiotensin II (Ang II) has a role in some forms of hypertension, the influence of dietary lipid composition on glomerular lipid content and on Ang II receptor parameters was determined. Three groups of rats were fed diets containing 14% by weight of 1) beef fat (saturated fatty acid rich), 2) safflower oil (n-6 fatty acid rich), or 3) fish oil (n-3 fatty acid rich), each supplemented with 2% corn oil. A fourth group of rats was fed rat chow which contained 6.5% fat. At the end of 7 weeks, the rats were sacrificed, the kidneys removed, and renal glomeruli isolated using a sieving technique. Feeding diets which varied in the quantity and composition of fatty acids altered glomerular fatty acid composition of n-6 and n-3 fatty acids and the unsaturation indices of glomeruli. The cholesterol content, but not the phospholipid content, was decreased in glomeruli of animals fed the high fat diets. This resulted in a lower cholesterol/phospholipid ratio, indicative of an increase in membrane fluidity. Glomerular binding was determined using 125I-Ang II in a radioreceptor assay. Binding was proportional to glomerular protein and was time dependent. Receptor affinity (Ka) and number were determined by Scatchard analysis of binding inhibition data. Glomerular Ka was significantly lower for animals fed the rat chow as compared to the semisynthetic diets. There was no significant difference in the concentration of Ang II receptors in glomeruli of animals fed the different diets. The data indicate that the induced alteration in glomerular lipid composition is associated with alteration in the binding affinity of glomerular Ang II receptors.

Influence of butyrate on lipid metabolism, survival, and differentiation of colon cancer cells.

The present work was designed to study the differentiating effect of butyrate on LS174T cells after modification of their lipids with long-chain fatty acid (LCFA) supplementation. The LCFAs 18:1(n-9), 18:2(n-6), 20:4(n-6), 20:5(n-3), and 22:6(n-3) bound to added to the media of confluent cells for eight days. The fatty acid-to-albumin ratio was 3:1. The concentration of fatty acids in the media was 100 microM. On the last day, half of the flasks were treated with 2 mM butyrate. The data indicate that supplementation with polyunsaturated LCFAs having 20-22 carbon atoms resulted in a significant reduction in cell density and viability, whereas all LCFA supplementation reduced differentiation as measured by alkaline phosphatase activity. Butyrate treatment increased the density, viability, and differentiation of the tumor cells. The effect of butyrate on differentiation was mainly with cells supplemented with 18:1, 20:5, and 22:6. In the absence of LCFA supplementation, butyrate reduced the concentration of 22:5(n-6) in the cellular lipids. Also, butyrate modified the LCFAs incorporated in cells supplemented with 18:2 and 20:5, with changes occurring in 20:5(n-3), 22:5(n-3), and 22:5(n-6). Thus the present study suggests an interaction between butyrate and LCFA on differentiation and LCFA metabolism of human colon cancer cells.

Effect of dietary saturated fatty acids on hormone-sensitive lipolysis in rat adipocytes.

The objective of this work was to examine the mechanism by which dietary saturated fatty acids, as compared with polyunsaturated fatty acids, lower hormone-sensitive lipolysis in rat adipocytes. Rats were fed a purified diet containing 14% of a fat with a high concentration of either saturated fatty acids (coconut oil or beef fat) or polyunsaturated fatty acids (safflower oil) as a control. In addition, each diet contained 2% corn oil. The animals were fed these diets for 4 wk. Norepinephrine-stimulated lipolysis was 50% lower when diets rich in saturated fatty acids, regardless of their chain length, were fed than when a diet containing a high concentration of polyunsaturated fatty acids was fed. The specific activities of adenylate cyclase, 3',5'-cyclic nucleotide (cAMP) phosphodiesterase and hormone-sensitive lipase were lower when saturated fatty acids were fed than when polyunsaturated fatty acids were fed. Accumulation of cAMP upon stimulation with 10(-5) M norepinephrine was lower when saturated fatty acids were fed than when polyunsaturated fatty acids were fed. Moreover, adipocytes were larger when saturated fatty acids were fed than when polyunsaturated fatty acids were fed. The data obtained suggest that dietary saturated fats exert their inhibitory effect on hormone-stimulated lipolysis by influencing several points in the lipolytic cascade.

Effect of dietary saturated fatty acids on intracellular free fatty acids and kinetic properties of hormone-sensitive lipase of rat adipocytes.

Experiments were conducted to examine the effects of dietary saturated fatty acids on the intracellular free fatty acid concentration and composition and on the kinetic parameters of hormone-sensitive lipase of rat adipocytes. Animals were fed for 4 wk 14% coconut oil, beef fat or safflower oil and 2% corn oil in a purified diet. Adipocytes of animals fed the coconut oil diet contained higher basal level of intracellular free fatty acids than those of animals fed other beef fat or safflower oil diets. Norepinephrine (10(-5) M) stimulated the basal intracellular free fatty acid concentration by 2.3-3.4-fold in adipocytes from animals fed saturated fatty acids, compared with 6.4-fold in those of animals fed the safflower oil diet. The concentrations of intracellular free fatty acids in adipocytes of experimental animals after stimulation with 10(-5) M norepinephrine, however, were not significantly different. The intracellular free fatty acid pool of adipocytes of animals fed the saturated fatty acids had more palmitic acid and less linoleic acid than those of safflower oil-fed animals. The results indicate that type of dietary fat had no effect on kinetic properties of hormone-sensitive lipase.

Effect of dietary lipids on composition and glucose utilization by rat adipose tissue.

Feeding rats diets rich in either safflower oil or coconut oil resulted in a significant change in the lipid composition of epididymal fat pads as compared with those obtained from rats fed a commercial stock diet. A safflower oil diet resulted in an increase in tissue cholesterol and a decrease in phospholipid concentration as compared with the stock diet. A coconut oil diet resulted in a decrease in both tissue cholesterol and phospholipid concentrations as compared with the stock diet. Adipose tissue fatty acid composition was also altered due to these dietary manipulations. Glucose utilization by adipose tissue from animals fed the safflower oil diet was 2 and 10 times greater than glucose utilization by adipose tissue from animals fed the stock and coconut oil diets, respectively. The coconut oil diet resulted in an increase in the percentage of glucose incorporated into adipose tissue diglycerides, free fatty acids and cholesterol esters and a decrease in the percentage of glucose incorporated into triglycerides as compared with animals fed the stock or safflower oil diet. The incorporation of glucose into adipose tissue fatty acids was depressed by a saturated fatty acid diet as compared with either a polyunsaturated fatty acid diet or the stock diet.