Lipoprotein lipase synthesis and secretion: effects of concentration and type of fatty acids in adipocyte cell culture

Modulatory effect of linoleic and oleic acid on cell proliferation and lipid metabolism gene expressions in primary bovine satellite cells

This study was performed to elucidate the effects of linoleic acid (LA), oleic acid (OA) and their combination (LA + OA) on cell proliferation, apoptosis, necrosis, and the lipid metabolism related gene expression in bovine satellite cells (BSCs), isolated from bovine muscles. Cell viability was significantly increased with the OA and LA treatment. Furthermore, LA + OA enhanced cell proliferation in a dose-dependent manner (10 to 100 µM), whereas it lowered at 250 µM. In addition, a cell-cycle analysis showed that 100 µM of LA and OA markedly decreased the G0/G1 phase proportion (62.58% and 61.33%, respectively), compared to controls (68.02%), whereas the S-phase cells' proportion was increased. The ratio of G2/M phase cells was not significantly different among the groups. Moreover, analyses with AO/EtBr staining showed that no apoptosis occurred. Necrosis were determined by flow cytometry using Annexin V-FITC/PI staining which revealed no early apoptosis in the cells pretreated with LA or OA, but occurred in the LA + OA group. We also analyzed the mRNA expression of lipid metabolizing genes such as peroxisome proliferator receptor alfa (PPARα), peroxisome proliferator receptor gamma (PPARγ), acyl-CoA oxidase (ACOX), lipoprotein lipase (LPL), carnitine palmitoyl transferase (CPT-1), and fatty-acid binding protein4 (FABP4), which were upregulated in LA or OA treated cells compared to the control group. In essence, LA and OA alone promote the cell proliferation without any apoptosis and necrosis, which might upregulate the lipid metabolism related gene expressions, and increase fatty-acid oxidation in the BSCs' lipid metabolism.

Nutritional modification of <i>SCD</i>, <i>ACACA</i> and <i>LPL</i> gene expressions in different ovine tissues

Abstract. Fatty acid composition is one of the main factors affecting health benefits of food. Stearoyl-CoA desaturase 1 (SCD), acetyl-CoA carboxylase alpha (ACACA) and lipoprotein lipase (LPL) have been considered as the rate-limiting enzymes in the biosynthesis of different fatty acids critical in lipid metabolism. The aim of our study was the analysis of differences in expression profiles of three ovine genes related to lipid metabolism (LPL, ACACA, SCD) depending on feeding system and tissue type. The gene expression measurement was performed using a real-time PCR method on 60 old-type Polish Merino Sheep, which were divided into three feeding groups (I – complete pellet mixture, n =  12; II – complete mixture with addition of fresh grass, n =  24; III – complete mixture with addition of fresh red clover, n =  24). From all lambs, tissue samples – subcutaneous fat, perirenal fat and liver – were collected immediately after slaughter and LPL, ACACA and SCD expression was estimated based on two endogenous controls (RPS2 – ribosomal protein S2; ATP5G2 – H(+)-transporting ATP synthase). Our research indicated that supplementation of diet with an addition of fresh grass or red clover significantly (P < 0.05) decreased the expression of SCD, ACACA and LPL genes in fat tissue compared to standard complete pelleted mixture. On the other hand, the highest expression of ACACA was detected in liver tissue collected from sheep fed a diet with an addition of fresh red clover (P < 0.05). In turn, the highest expression of the SCD gene was detected in animals fed with grass supplementation (P < 0.05). Regardless of diet supplementation, the highest SCD transcript abundance was detected in perirenal fat, while LPL and ACACA expression was the highest in both perirenal and subcutaneous fat. The ability of nutrigenomic regulation of transcription of analyzed genes confirmed that these genes play a critical role in regulation of lipid metabolism processes in sheep and could be associated with fatty acid profiles in milk and meat.

Inhibitory activity of extracts of Hebridean brown seaweeds on lipase activity

The effect of three Hebridean brown seaweeds on lipase activity was assessed using a turbidimetric lipase activity assay and an in vitro simulation of the upper digestive tract. The preparations of Ascophyllum nodosum, Fucus vesiculosus, and Pelvetia canaliculata were tested; whole seaweed homogenate, sodium carbonate extract, and ethanol extracts (pellet and supernatant were tested separately). All extracts showed significant inhibition of lipase, suggesting multiple bioactive agents, potentially including alginates, fucoidans, and polyphenols. Whole homogenate extract of F. vesiculosus was the most potent inhibitor of Lipase (IC₅₀ = 0.119 mg mL-1), followed by ethanol supernatant (IC₅₀ = 0.159 mg mL-1) while ethanol pellet and sodium carbonate extract showed relatively weaker inhibition (IC₅₀ = 0.360 mg mL-1 and IC₅₀ = 0.969 mg mL-1 respectively). For A. nodosum and P. canaliculata, strongest inhibition occurred with ethanol pellet (IC₅₀ = 0.238 and 0.228 mg mL^-1, respectively). These inhibitory effects were validated in a model gut system. The data presented herein suggests the use of seaweed as a potential weight management tool is deserving of further investigation.

Effects of linoleic acid and eicosapentaenoic acid on cell proliferation and lipid-metabolism gene expression in primary duck hepatocytes

Several studies have investigated that linoleic acid (LA) and eicosapentaenoic acid (EPA) affect cell proliferation and lipid catabolic gene expression in mammals. To determine if LA and EPA increase duck cell proliferation and lipid catabolic gene expression, the authors exposed duck primary hepatocyte cultures to LA or EPA. The results showed that both LA and EPA increased cell proliferation in a dose-dependent manner (100 μM). The effect on specific cell-cycle phases was also studied; LA and EPA (100 μM) deceased the proportion of cells in the G0/G1 phase from 83 to 80.8 and 80.3%, respectively, concomitant with an increase in the proportion of S-phase cells (11.5 and 10.5 vs. 8%, respectively). The expression of PPAR-α and PPAR-α target genes, such as acyl-CoA oxidase (ACOX), lipoprotein lipase (LPL), liver fatty acid-binding protein (L-FABP), was examined by quantitative real-time PCR. The results showed that the expression of the PPAR-α, ACOX, and LPL genes increased significantly following LA and EPA exposure, but that the expression of L-FABP remained unchanged. This study provides the first characterization of LA- and EPA-induced cell proliferation and PPAR-α and PPAR-α target gene transcriptional responses in duck primary hepatocyte cultures.

The tsim tsoum approaches for prevention of cardiovascular disease

The Tsim Tsoum Concept means that humans evolved on a diet in which nature recommends to ingest fatty acids in a balanced ratio (polyunsaturated(P) : saturated(S) =w-6 : w-3 = 1 : 1)as part of dietary lipid pattern where monounsaturated fatty acids(MUFA) is the major fatty acid(P : M : S = 1 : 6 : 1) in the background of other dietary factors; antioxidants, vitamins, minerals and fiber as well as physical activity and low mental stress. Several hundred years ago, our diet included natural foods; fruits, vegetables, green vegetables, seeds, eggs and honey. Fish, and wild meat were also available to pre-agricultural humans which shaped modern human genetic nutritional requirement. Cereal grains (refined), and vegetable oils that are rich in w-6 fatty acids are relatively recent addition to the human diet that represent dramatic departure from those foods to which we are adapted. Excess of linoleic acid, trans fatty acids (TFA), saturated and total fat as well as refined starches and sugar are proinflammatory. Low dietary MUFA and n-3 fatty acids and other long chain polyunsarurated fatty acids (LCPUFA) are important in the pathogenesis of metabolic syndrome. Increased sympathetic activity with greater secretion of neurotransmitters in conjunction of underlying long chain PUFA deficiency, and excess of proinflammatory nutrients, may damage the neurons via proinflammatory cytokines, in the ventromedial hypothalamus and insulin receptors in the brain.Since, 30–50% of the fatty acids in the brain are LCPUFA, especially omega-3 fatty acids, which are incorporated in the cell membrane phospholipids, it is possible that their supplementation may be protective.Blood lipid composition does reflect one's health status: (a) circulating serum lipoproteins and their ratio provide information on their atherogenicity to blood vessels and (b) circulating plasma fatty acids, such as w-6/w-3 fatty acid ratio, give indication on proinflammatory status of blood vessels, cardiomyocytes, liver cells and neurones; (a) and (b) are phenotype-related and depend on genetic, environmental and developmental factors. As such, they appear as universal markers for holistic health and these may be important in the pathogenesis of cardiovascular diseases and cancer, which is the main consideration of Tsim Tsoum concept.

Replacing dietary fish oil by vegetable oils has little effect on lipogenesis, lipid transport and tissue lipid uptake in rainbow trout (Oncorhynchus mykiss)

In order to investigate the effects of dietary lipid sources on mechanisms involved in lipid deposition, two groups of rainbow trout were fed from first-feeding to the commercial size of 1 kg (for 62 weeks) with two diets differing only by lipid source: 100% fish oil or 100% blend of vegetable oils (55% rapeseed oil, 30% palm oil, 15% linseed oil). The activities and levels of gene expression of lipogenic enzymes (fatty acid synthetase, glucose-6-phosphate dehydrogenase and malic enzyme) in liver and of lipoprotein lipase in perivisceral adipose tissue, white muscle and liver were determined. Transport of lipid was studied by determining lipid composition of plasma and lipoprotein classes. We also examined the clearance of LDL by assaying the level of LDL receptor gene expression in several tissues. Total replacement of dietary fish oil by the blend of vegetable oils did not affect growth of rainbow trout and did not modify muscle lipid content. Hepatic lipogenesis and lipid uptake in perivisceral adipose tissue, white muscle and liver were also not modified by dietary treatments. Diets containing the blend of vegetable oils induced a decrease in plasma cholesterol and LDL. In trout fed the vegetable oils diet, expression of LDL receptor gene in the liver was down-regulated.

Hormonal regulation of postnatal chicken preadipocyte differentiation in vitro

This study was designed to develop a culture system from the stromal-vascular fraction of chicken adipose tissue that can be used to characterize hormones that promote preadipocyte differentiation. Abdominal adipose tissue was excised from 2 to 4-week-old male broilers (Gallus domesticus) by sterile dissection. The stromal-vascular cell fraction from the adipose tissue was isolated by collagenase digestion, filtration, and subsequent centrifugation. These preadipocytes were seeded in six well culture plates and proliferated to confluency in 10% fetal bovine serum in DMEM/F12 (50:50) medium. At confluency, experiments were initiated to determine hormonal requirements for differentiation. Insulin (100 nM) stimulated expression of citrate lyase and sn-glycerol-3-phosphate dehydrogenase relative to lactate dehydrogenase in the presence of 2.5% chicken serum (P<0.05), but not with 10% chicken serum (P>0.05). Triiodothyronine (T(3), 1 nM) and insulin-like growth factor 1 (100 ng/ml) had no effect on differentiation. Dexamethasone (Dex, 1 microM) stimulated differentiation in 2.5 or 10% chicken serum (P<0.05). Insulin, Dex and 2.5% chicken serum stimulated enzymatic differentiation to the extent of 10% chicken serum, but heparin (10 U/ml) addition, in combination with insulin and Dex was necessary to stimulate lipid filling of adipocytes.

Lipoprotein lipase mRNA expression in abdominal adipose tissue is little modified by age and nutritional state in broiler chickens

Lipoprotein lipase (LPL)-catalyzed hydrolysis of plasma lipoproteins is a rate-limiting step in the transport of lipids into the peripheral tissues of broiler chickens. The aim of the present study was to investigate whether LPL mRNA expression in adipose tissue is affected by age or nutritional treatments, with a view to reducing fat accumulation in broiler chickens. The study found that chicken LPL mRNA expression in abdominal adipose tissue did not differ significantly between chickens aged 4, 6, and 8 wk, but there was less expression of LPL mRNA in 2-wk-old chickens. In nutritional modulation, LPL mRNA levels in abdominal adipose tissues were not modified by 48-h feed deprivation or by subsequent refeeding for 48 h. In addition, expression of LPL mRNA was not significantly altered in chickens fed for 7 d on diets containing 8% olive oil (triolein rich), safflower oil (trilinolein rich), or linseed oil (trilinolenin rich). On the other hand, adipose LPL mRNA expression in chickens force-fed for 12 h with a trilinolenin (18:3) emulsion after 48-h feed deprivation was significantly decreased when compared to that in chickens force-fed with a triolein (18:1) or trilinolein (18:2) emulsion. Changes to LPL immunoreactive protein levels in chicken abdominal adipose tissues brought about by aging and nutritional manipulations were similar to those observed in relation to mRNA expression. These findings suggest that LPL mRNA expression in growing chickens is less responsive to aging and nutritional manipulation than in mammals, thereby indicating specificity of physiological response on broiler chicken LPL.

Effect of a rapeseed oil substituting diet on serum lipids and lipoproteins in children and adolescents with familial hypercholesterolemia

OBJECTIVE

Familial hypercholesterolemia (FH) is a predominantly inherited disorder, which contributes to a defect of the LDL-cholesterol receptor. For adults with familial hypercholesterolemia (FH), it is known that a supplementary diet of monounsaturated fatty acids reduces elevated levels of total cholesterol and LDL-cholesterol and may further increase HDL-cholesterol. In particular the reduced intake of dietary fat reduces total serum cholesterol and LDL-cholesterol in the range of 10% to 15% and inhibits LDL-oxidation. Once the diagnosis of familial hypercholesterolemia is made in early childhood a supplementary diet with rapeseed oil should be started as early as possible to prevent development of atherosclerosis and subsequent complications. So far there are no reports of a lipid lowering diet enriched with rapeseed oil in children and adolescents.

METHODS

Seventeen children and young adolescents (male = 6, female = 11, ages 4 to 19 years) diagnosed with FH were enrolled in this study. They received dietary training and a classical low fat/low cholesterol diet enriched with rapeseed oil over five months. In the first two months they received orally mean 15 g/day (8-23 g/day), for the remaining three months mean 22 g/day (15-30 g/day) rapeseed oil. The calculation of the three-days dietary protocols showed the following characteristics: 29.5% calories from fat, 14.3% calories from protein and 54.6% calories from carbohydrates. The subjects had six sessions of dietary counseling, and serum lipids levels and lipoprotein(a) were estimated; each month's diet adherence was controlled by a dietitian and discussed with the patients and their families during this five-month study.

RESULTS

During five months of rapeseed oil diet serum triglycerides decreased by 29% (119.2+/-62.8 mg/dL vs. 84.9 mean +/- 39.7 mg/dL), VLDL-cholesterol by 27% (23+/-12 mg/dL vs. 17+/-8 mg/dL), total cholesterol by 10% (233+/-35 mg/dL vs. 213+/-36 mg/dL), LDL-cholesterol by 7% (151+/-31 mg/dL vs. 142+/-31 mg/dL). HDL-cholesterol (59+/-15 mg/dL vs. 57+/-11 mg/dL) and Lp(a) (29.8+/-36.3 mg/dL vs. 32.6+/-40.7 mg/dL) were not changed significantly. The diet was well accepted; in most families a sustained change was reported.

CONCLUSIONS

Our results indicate that in children and adolescents with FH a lipid-lowering diet with rapeseed oil has a similar effect on total serum cholesterol and LDL-cholesterol compared to classical cholesterol reduction diets (step I). However, an additional pronounced effect on lowering of triglycerides and VLDL-cholesterol can be observed.

Different effects of conjugated linoleic acid isomers on lipoprotein lipase activity in 3T3-L1 adipocytes

Conjugated linoleic acids (CLAs) are the positional and geometric isomers of linoleic acid. In the present study the effects of cis-9, trans-11 CLA (c9,t11 CLA) and trans-10, cis-12 CLA (t10,c12 CLA ) on intracellular and heparin-releasable (HR-) lipoprotein lipase (LPL) activity in 3T3-L1 adipocytes were investigated. Cells were exposed to the two CLA isomers and linoleic acid, which were bound to bovine serum albumin (BSA). In the adipocytes insulin up-regulated and tumor necrosis factor alpha (TNFalpha) down-regulated HR-LPL activity, which corresponds with the findings in vivo. The experimental fatty acids at low concentrations (<30 µmol/L) moderately increased intracellular and HR-LPL activity. At a concentration of 100 µmol/L, c9,t11 CLA and t10,c12 CLA suppressed HR-LPL activity to 20 and 24% below the BSA control level, respectively, while linoleic acid had no effect unless its concentration was as high as 1000 µmol/L. Insulin abolished the inhibitory effect of c9,t11 CLA, but not of t10,c12 CLA. In the presence of insulin, t10,c12 CLA inhibited HR-LPL activity by 41% compared to BSA control. In contrast to TNFalpha, which suppressed both intracellular LPL and HR-LPL activity, CLAs suppressed HR-LPL activity without decreasing intracellular LPL activity. Additionally, t10,c12 CLA (100 µmol/L) partially prevented TNFalpha-induced decrease of intracellular LPL activity. These results indicate that CLAs differ from linoleic acid in regulating HR-LPL activity, and t10,c12 CLA appeared to be more effective than c9,t11 CLA.

Lack of triglyceride-lowering properties of fish oil in apolipoprotein e-deficient mice

Fish oil is a potent triglyceride (TG)-lowering agent in humans. The goal of the present study was to assess the contribution of decreased triglyceride synthesis and of apoE in mediation of the triglyceride-lowering effect of fish oil. To this end, apoE-deficient mice and wild-type control mice were supplemented with either coconut oil, sunflower oil, or fish oil (20% wt/wt) for 2 weeks. Compared with coconut oil and sunflower oil, fish oil reduced the concentrations of cholesterol and triglycerides in the wild-type mice, whereas it had no effect on cholesterol concentration and it had a triglyceride-raising effect in apoE-deficient mice. The latter was due to increased triglyceride concentrations in the d<1.019 g/mL plasma density fraction. In apoE-deficient mice, but not in wild-type mice, the postprandial triglyceride area under the curve was higher after an intragastric load of fish oil than after a sunflower oil load. These data indicate an impairment of triglyceride metabolism in the fish oil-fed apoE-deficient mice. Compared with coconut oil and sunflower oil, fish oil lowered triglyceride production rates measured with the Triton method in both wild-type (P<0.0001) and apoE-deficient mice (P<0.0001). Similarly, in vitro lipoprotein lipase-mediated lipolysis of VLDL was lowered in the fish oil-fed wild-type and apoE-deficient mice, suggesting an alteration in VLDL lipolysis independent of the mice genotype. In conclusion, fish oil does not decrease triglyceride concentrations in apoE-deficient mice despite reducing triglyceride production rates, suggesting that decreased triglyceride synthesis is not sufficient to lower triglyceride concentrations in mice. ApoE appears to be necessary for fish oil to lower plasma triglyceride concentrations, indicating a critical role of apoE in this process.

Proliferative effect of lipoprotein lipase on human vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation is a key event in the development and progression of atherosclerotic lesions. Accumulating evidence suggests that lipoprotein lipase (LPL) produced in the vascular wall may exert proatherogenic effects. The aim of the present study was to examine the effect of LPL on VSMC proliferation. Incubation of growth-arrested human VSMCs with purified endotoxin-free bovine LPL for 48 and 72 hours, in the absence of any added exogenous lipoproteins, resulted in a dose-dependent increase in VSMC growth. Addition of VLDLs to the culture media did not further enhance the LPL effect. Treatment of growth-arrested VSMCs with purified human or murine LPL (1 microg/mL) led to a similar increase in cell proliferation. Neutralization of bovine LPL by the monoclonal 5D2 antibody, irreversible inhibition, or heat inactivation of the lipase suppressed the LPL stimulatory effect on VSMC growth. Moreover, preincubation of VSMCs with the specific protein kinase C inhibitors calphostin C and chelerythrine totally abolished LPL-induced VSMC proliferation. In LPL-treated VSMCs, a significant increase in protein kinase C activity was observed. Treatment of VSMCs with heparinase III (1 U/mL) totally inhibited LPL-induced human VSMC proliferation. Taken together, these data indicate that LPL stimulates VSMC proliferation. LPL enzymatic activity, protein kinase C activation, and LPL binding to heparan sulfate proteoglycans expressed on VSMC surfaces are required for this effect. The stimulatory effect of LPL on VSMC proliferation may represent an additional mechanism through which the enzyme contributes to the progression of atherosclerosis.

High-monounsaturated fatty acid diets lower both plasma cholesterol and triacylglycerol concentrations

BACKGROUND

Low-fat diets increase plasma triacylglycerol and decrease HDL-cholesterol concentrations, thereby potentially adversely affecting cardiovascular disease (CVD) risk. High-monounsaturated fatty acid (MUFA), cholesterol-lowering diets do not raise triacylglycerol or lower HDL cholesterol, but little is known about how peanut products, a rich source of MUFAs, affect CVD risk.

OBJECTIVE

The present study compared the CVD risk profile of an Average American diet (AAD) with those of 4 cholesterol-lowering diets: an American Heart Association/National Cholesterol Education Program Step II diet and 3 high-MUFA diets [olive oil (OO), peanut oil (PO), and peanuts and peanut butter (PPB)].

DESIGN

A randomized, double-blind, 5-period crossover study design (n = 22) was used to examine the effects of the diets on serum lipids and lipoproteins: AAD [34% fat; 16% saturated fatty acids (SFAs), 11% MUFAs], Step II (25% fat; 7% SFAs, 12% MUFAs), OO (34% fat; 7% SFAs, 21% MUFAs), PO (34% fat; 7% SFAs, 17% MUFAs), and PPB (36% fat; 8% SFAs, 18% MUFAs).

RESULTS

The high-MUFA diets lowered total cholesterol by 10% and LDL cholesterol by 14%. This response was comparable with that observed for the Step II diet. Triacylglycerol concentrations were 13% lower in subjects consuming the high-MUFA diets and were 11% higher with the Step II diet than with the AAD. The high-MUFA diets did not lower HDL cholesterol whereas the Step II diet lowered it by 4% compared with the AAD. The OO, PO, and PPB diets decreased CVD risk by an estimated 25%, 16%, and 21%, respectively, whereas the Step II diet lowered CVD risk by 12%.

CONCLUSION

A high-MUFA, cholesterol-lowering diet may be preferable to a low-fat diet because of more favorable effects on the CVD risk profile.

Mechanisms of decreased lipoprotein lipase activity in adipocytes of starved rats depend on duration of starvation

The aim of this study was to delineate the mechanisms by which varying periods of starvation decrease lipoprotein lipase (LPL) activity in rat adipose tissue. LPL mRNA levels and rates of LPL synthesis, degradation and secretion were compared in adipocytes from male rats that had been fed or starved for 1 or 3 d. The decreased LPL activity after 3 d of starvation (-76%) was explained mainly by a 50% decrease in the relative abundance of LPL mRNA levels (P < 0.05) and a parallel 50% decrease in relative rates of LPL biosynthesis (P < 0.05). In contrast, starvation for 1 d decreased total LPL activity by 47% (P < 0.05) but did not affect LPL mRNA levels or relative rates of LPL biosynthesis. Pulse-chase studies demonstrated that 1 d of starvation increased the rate of degradation of newly synthesized LPL (P < 0.05) and markedly decreased its secretion into the medium (P < 0.05). A decrease in overall protein synthesis also contributed to the decreased LPL activity after 1 and 3 d of starvation. We conclude that the relative importance of pre- and post-translational mechanisms in regulating adipose tissue LPL activity depends on the duration of starvation. During short-term starvation, degradation of newly synthesized LPL is an important determinant to its secretion from the adipocyte and hence its functional activity at the capillary endothelium.

Composition of human VLDL triacylglycerols after ingestion of olive oil and high oleic sunflower oil

This work was undertaken to determine the effect of diets enriched with olive oil or high oleic sunflower oil on very low density lipoprotein (VLDL) triacylglycerol composition of healthy human subjects. Both oils contain a similar proportion of monounsaturated fatty acids (MUFA) but differ in their triacylglycerol composition. All 22 human subjects initially consumed a low fat, high carbohydrate diet as recommended by the National Cholesterol Education Program (NCEP-I). They then consumed the two experimental oils (40% dietary energy) in a crossover design. The olive oil and high oleic sunflower oil diets resulted in significant increases in palmitoleic (55%, P < 0.05), oleic (27%, P < 0.01) and eicosenoic (>100%, P < 0.001) acids of VLDL triacylglycerols, whereas there was a significant decrease in linoleic acid (38%, P < 0.001). In addition, the high oleic sunflower oil diet increased the content of stearic acid (60%, P < 0.05) and total saturated fatty acids (14%, P < 0.05). Both MUFA-rich diets significantly (P < 0.01) decreased the content of sn-glycerol-palmitate-linoleate-oleate, sn-glycerol-palmitoleate-dioleate and sn-glycerol-palmitate-dilinoleate in VLDL with regard to the NCEP-I diet, whereas they increased the content of sn-glycerol-trioleate (>100%, P < 0.001 after the olive oil diet; 80%, P < 0.05 after the high oleic sunflower oil diet). Intake of olive oil, in particular, significantly decreased the content of sn-glycerol-tripalmitate (36%, P < 0.01) and increased the content of dioleoyl-containing triacylglycerols. MUFA (P < 0.01) and arachidonic acid (P < 0.001) tended to be rich in the sn-2 position of VLDL triacylglycerols during the periods of consuming the olive oil or high oleic sunflower oil diets. In addition, olive oil, but not high oleic sunflower oil, further contributed to VLDL triacylglycerols that contained alpha-linolenic and docosahexaenoic acids acylated in the sn-2 position. These data suggest that differences in the composition of VLDL triacylglycerols may be of major importance in explaining the beneficial effects of dietary olive oil in reducing the atherogenic risk profile in healthy subjects.

Fatty acids reduce heparin-releasable LPL activity in cultured cardiomyocytes from rat heart

Varying glucose and fatty acid (FA) concentrations in the medium of cultured cardiomyocytes from adult rat hearts were tested for effects on lipoprotein lipase (LPL) activity. Glucose (5.5, 11, and 25 mM in the culture medium for 18-22 h) had no effect on either heparin-releasable LPL (HR-LPL) or on cellular LPL (C-LPL) activities. When cardiomyocytes were cultured overnight with 60 microM oleate, HR-LPL activity was reduced to 20% of control, with no change in C-LPL activity or total C-LPL mass. Similar results (HR-LPL and C-LPL activities) were obtained with 60 microM concentrations of palmitate and myristate; linoleate and eicosapentaenoate did reduce C-LPL activity, but the decrease in HR-LPL activity was much greater. Oxfenicine, an FA oxidation inhibitor, did not alter the inhibitory effect of 60 microM oleate on HR-LPL. Short-term incubations (1 and 3 h) of cultured cardiomyocytes with 60 microM oleate did not displace LPL into the medium. Immunodetectable LPL on the cell surface of oleate-treated cultured cardiomyocytes was increased compared with control cells, but heparin treatment released the same amount of LPL mass that had reduced catalytic activity.

Perilla oil prevents the excessive growth of visceral adipose tissue in rats by down-regulating adipocyte differentiation

We examined the effect of dietary oils with different fatty acid compositions on the growth of visceral adipose tissue in rats. Rats were fed for 4 mo starting at weaning a basal diet containing (12 g/100 g diet) perilla oil rich in (n-3) polyunsaturated fatty acids (PUFA), safflower oil rich in (n-6) PUFA, olive oil rich in monounsaturated fatty acid, or beef tallow rich in saturated fatty acids. The amount of food consumed and body weight gain did not differ among the four dietary groups. The weight of the epididymal fat pad and the serum triglyceride concentration in perilla oil-fed rats were significantly lower (P < 0.05) than those of olive oil- and beef tallow-fed groups. The product of [(volume of individual adipocytes) x (number of adipocytes in epididymal fat pad)], which presumably represents total adipocyte volume in the fat pad, was significantly lower (P < 0.05) in perilla oil-fed rats than in beef tallow- and olive oil-fed groups. Expression of the late genes of adipocyte differentiation, peroxisome proliferator-activated receptor alpha, adipocyte P2 and adipsin, was significantly (P < 0. 05) down-regulated in epididymal fat tissue of rats that had been fed perilla oil rather than beef tallow or olive oil, whereas expression of the early gene, lipoprotein lipase, was not significantly affected. Greater levels (P < 0.05) of (n-3) PUFA in the membrane phospholipid fraction of the fat tissue were observed in perilla oil-fed rats than in the other dietary groups. These results suggest that perilla oil or (n-3) PUFA prevents excessive growth of adipose tissue in rats at least in part by suppressing the late phase of adipocyte differentiation.

Regulation of milk lipid secretion and composition

Triacylglycerols make up 98% of the lipid content of milk, ranging in different species from 0 to 50% of the total milk volume. The fatty aid composition of the triacylglycerols depends on the species, the dietary fatty acid composition, and the carbohydrate-to-lipid ratio of the diet. The rate of lipid synthesis in the lactating mammary gland depends on the stage of mammary development and is decreased by fasting and starvation in ruminants and rodents but not in species that fast during lactation, such as seals and hibernating bears. Regulatory agents include insulin, prolactin, and non-esterified fatty acids. Dietary trans fatty acids may depress milk lipid synthesis under certain conditions. Evidence is presented that fatty acids may play a major regulatory role in acute changes in de novo mammary fatty acid synthesis, acting primarily on the activity of acetyl coenzyme A carboxylase.