Preparation of chylomicrons and VLDL with monoacid-rich triacylglycerol and characterization of kinetic parameters in lipoprotein lipase-mediated hydrolysis in chickens

Reduction in Insulin Uncovers a Novel Effect of VEGFB on Cardiac Substrate Utilization

BACKGROUND

The heart relies heavily on external fatty acid (FA) for energy production. VEGFB (vascular endothelial growth factor B) has been shown to promote endothelial FA uptake by upregulating FA transporters. However, its impact on LPL (lipoprotein lipase)-mediated lipolysis of lipoproteins, a major source of FA for cardiac use, is unknown.

METHODS

VEGFB transgenic (Tg) rats were generated by using the α-myosin heavy chain promoter to drive cardiomyocyte-specific overexpression. To measure coronary LPL activity, Langendorff hearts were perfused with heparin. In vivo positron emission tomography imaging with [18F]-triglyceride-fluoro-6-thia-heptadecanoic acid and [11C]-palmitate was used to determine cardiac FA uptake. Mitochondrial FA oxidation was evaluated by high-resolution respirometry. Streptozotocin was used to induce diabetes, and cardiac function was monitored using echocardiography.

RESULTS

In Tg hearts, the vectorial transfer of LPL to the vascular lumen is obstructed, resulting in LPL buildup within cardiomyocytes, an effect likely due to coronary vascular development with its associated augmentation of insulin action. With insulin insufficiency following fasting, VEGFB acted unimpeded to facilitate LPL movement and increase its activity at the coronary lumen. In vivo PET imaging following fasting confirmed that VEGFB induced a greater FA uptake to the heart from circulating lipoproteins as compared with plasma-free FAs. As this was associated with augmented mitochondrial oxidation, lipid accumulation in the heart was prevented. We further examined whether this property of VEGFB on cardiac metabolism could be useful following diabetes and its associated cardiac dysfunction, with attendant loss of metabolic flexibility. In Tg hearts, diabetes inhibited myocyte VEGFB gene expression and protein secretion together with its downstream receptor signaling, effects that could explain its lack of cardioprotection.

CONCLUSIONS

Our study highlights the novel role of VEGFB in LPL-derived FA supply and utilization. In diabetes, loss of VEGFB action may contribute toward metabolic inflexibility, lipotoxicity, and development of diabetic cardiomyopathy.

Effects of Coated Trace Minerals and the Fat Source on Growth Performance, Antioxidant Status, and Meat Quality in Broiler Chickens

Inorganic trace minerals may exacerbate lipid peroxidation, thereby impacting lipid metabolism. This study aimed to compare the effects of inorganic and coated trace minerals in diets with different fat sources, on the performance, slaughter characteristics, and antioxidant status of broiler chickens. A total of 576 21-day-old Abor Acres broiler birds were randomly divided into four dietary treatment groups in a 2 (non-coated and coated trace minerals)×2 (soybean oil and lard) factorial design. Each treatment was replicated 12 times (12 birds per replicate). The results showed that coated minerals significantly improved the average daily gain (ADG) in weight and the feed conversion ratio (P<0.01), increased serum iron, zinc, selenium, and thyroxine contents, increased the activities of glutathione peroxidase, superoxide dismutase, total antioxidant capacity, and lipoprotein lipase (P<0.05), and decreased the serum and muscle malondialdehyde (MDA) contents (P<0.01). The use of soybean oil as the fat source resulted in a high ADG in weight, a low F/G ratio, reduced serum MDA content, and drip loss of breast and leg muscles (P<0.05). In conclusion, the supplementation of coated trace minerals improved growth performance, antioxidant status, trace mineral retention within serum, and lipid metabolism. Additionally, soybean oil also improved the growth performance, antioxidant performance, and meat quality of broilers. The combination of coated trace minerals and soybean oil generated the best growth performance, antioxidant status, and meat quality characteristics.

ANGPTL3 deficiency alters the lipid profile and metabolism of cultured hepatocytes and human lipoproteins

Loss-of-function (LOF) mutations in ANGPTL3, an inhibitor of lipoprotein lipase (LPL), cause a drastic reduction of serum lipoproteins and protect against the development of atherosclerotic cardiovascular disease. Therefore, ANGPTL3 is a promising therapy target. We characterized the impacts of ANGPTL3 depletion on the immortalized human hepatocyte (IHH) transcriptome, lipidome and human plasma lipoprotein lipidome. The transcriptome of ANGPTL3 knock-down (KD) cells showed altered expression of several pathways related to lipid metabolism. Accordingly, ANGPTL3 depleted IHH displayed changes in cellular overall fatty acid (FA) composition and in the lipid species composition of several lipid classes, characterized by abundant n-6 and n-3 polyunsaturated FAs (PUFAs). This PUFA increase coincided with an elevation of lipid mediators, among which there were species relevant for resolution of inflammation, protection from lipotoxic and hypoxia-induced ER stress, hepatic steatosis and insulin resistance or for the recovery from cardiovascular events. Cholesterol esters were markedly reduced in ANGPTL3 KD IHH, coinciding with suppression of the SOAT1 mRNA and protein. ANGPTL3 LOF caused alterations in plasma lipoprotein FA and lipid species composition. All lipoprotein fractions of the ANGPTL3 LOF subjects displayed a marked drop of 18:2n-6, while several highly unsaturated triacylglycerol (TAG) species were enriched. The present work reveals distinct impacts of ANGPTL3 depletion on the hepatocellular lipidome, transcriptome and lipid mediators, as well as on the lipidome of lipoproteins isolated from plasma of ANGPTL3-deficient human subjects. It is important to consider these lipidomics and transcriptomics findings when targeting ANGPTL3 for therapy and translating it to the human context.

Membrane lipid alterations in the metabolic syndrome and the role of dietary oils

The metabolic syndrome is a cluster of pathological conditions, including hypertension, hyperglycemia, hypertriglyceridemia, obesity and low HDL levels that is of great concern worldwide, as individuals with metabolic syndrome have an increased risk of type-2 diabetes and cardiovascular disease. Insulin resistance, the key feature of the metabolic syndrome, might be at the same time cause and consequence of impaired lipid composition in plasma membranes of insulin-sensitive tissues like liver, muscle and adipose tissue. Diet intervention has been proposed as a powerful tool to prevent the development of the metabolic syndrome, since healthy diets have been shown to have a protective role against the components of the metabolic syndrome. Particularly, dietary fatty acids are capable of modulating the deleterious effects of these conditions, among other mechanisms, by modifications of the lipid composition of the membranes in insulin-sensitive tissues. However, there is still scarce data based of high-level evidence on the effects of dietary oils on the effects of the metabolic syndrome and its components. This review summarizes the current knowledge on the effects of dietary oils on improving alterations of the components of the metabolic syndrome. It also examines their influence in the modulation of plasma membrane lipid composition and in the functionality of membrane proteins involved in insulin activity, like the insulin receptor, GLUT-4, CD36/FAT and ABCA-1, and their effect in the metabolism of glucose, fatty acids and cholesterol, and, in turn, the key features of the metabolic syndrome. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Molecular nutrition: Interaction of nutrients, gene regulations and performances

Nutrition deals with ingestion of foods, digestion, absorption, transport of nutrients, intermediary metabolism, underlying anabolism and catabolism, and excretion of unabsorbed nutrients and metabolites. In addition, nutrition interacts with gene expressions, which are involved in the regulation of animal performances. Our laboratory is concerned with the improvement of animal productions, such as milks, meats and eggs, with molecular nutritional aspects. The present review shows overviews on the nutritional regulation of metabolism, physiological functions and gene expressions to improve animal production in chickens and dairy cows.

The Fatty Acid Composition of Virgin Olive Oil from Different Cultivars Is Determinant for Foam Cell Formation by Macrophages

Although the beneficial role of Extra Virgin Olive Oil (EVOO) in the Mediterranean diet is well-known, its effects on health cannot be attributed solely to oleic acid. In addition to minor components, the presence of other fatty acids (FA), which depend largely on the cultivar among other factors, needs to be considered. The present study examined the effect of chylomicron remnant-like particles (CRLP) enriched in fatty acids of EVOO from 'Chetoui', 'Buidiego', 'Galega', 'Blanqueta', and 'Picual' cultivars on the foam cell formation by THP-1 macrophages. THP-1 cells were incubated with EVOO-CRLP for 24 h. Lipid accumulation in cells was measured by determining intracellular total triacylglycerol (TAG) concentration and FA composition. Intracellular TAG concentrations were higher in cells incubated with 'Chetoui' and 'Blanqueta' CRLP (0.33 ± 0.05 and 0.38 ± 0.07 μmol/mg of protein, respectively) than with 'Buidiego' and 'Picual' CRLP (0.20 ± 0.05 and 0.24 ± 0.06 μmol/mg of protein, respectively). In conclusion, linoleic acid-rich EVOO induced higher TAG incorporation into THP-1 macrophages compared to oleic acid-rich EVOO, the 18:1/18:2 ratio being consistently correlated with intracellular TAG accumulation. The results of this study demonstrated that the differences in EVOO-FA composition may have an important role in foam cell formation.

Fatty acid-induced nuclear translocation of heparanase uncouples glucose metabolism in endothelial cells

OBJECTIVE

Heparanase is an endoglycosidase that specifically cleaves carbohydrate chains of heparan sulfate. We have recently reported that high fatty acid increased the nuclear content of endothelial heparanase. Here, we examined the mechanism and the consequences behind this nuclear translocation of heparanase.

METHODS AND RESULTS

Bovine coronary artery endothelial cells were grown to confluence and incubated with palmitic acid. Palmitic acid induced rapid nuclear accumulation of heparanase that was dependent on Bax activation and lysosome permeabilization. Heat shock protein 90 was an important mediator of palmitic acid-induced shuttling of heparanase to the nucleus. Nuclear heparanase promoted cleavage of heparan sulfate, a potent inhibitor of histone acetyltransferase activity and gene transcription. A TaqMan gene expression assay revealed an increase in genes related to glucose metabolism and inflammation. In addition, glycolysis was uncoupled from glucose oxidation, resulting in accumulation of lactate.

CONCLUSIONS

The results presented in this study demonstrate that fatty acid can provoke lysosomal release of heparanase, its nuclear translocation, activation of genes controlling glucose metabolism, and accumulation of lactate. Given that lactate and inflammation have been implicated in the progression of atherosclerosis, our data may serve to reduce the associated cardiovascular complications seen during diabetes.

Reduction in systemic and VLDL triacylglycerol concentration after a 3-month Mediterranean-style diet in high-cardiovascular-risk subjects

The first results of the PREDIMED (PREvencion con Dieta MEDiterranea) randomized trial, after 3-month intervention, showed that the Mediterranean Diet (MD), supplemented with either virgin olive oil (VOO) or nuts, reduced systolic blood pressure, serum cholesterol and triacylglycerol (TG) concentrations and increased high-density lipoprotein (HDL)-cholesterol when compared to a control (low-fat diet) group. Serum TG levels are an independent risk factor for coronary heart disease and are strongly determined by very low-density lipoprotein (VLDL) composition, which can be specifically modified by dietary lipid source. Within the context of the PREDIMED study, we assessed the VLDL composition in 50 participants after 3 months of intake of two MD, supplemented with VOO or nuts, compared with a low-fat diet. Total and low-density lipoprotein cholesterol concentrations were reduced in subjects on the MD+nuts, whereas HDL-cholesterol increased after consumption of the MD+VOO. Serum TG concentrations were significantly lowered in both intervention groups (either the MD+nuts or MD+VOO). However, only the MD+VOO reduced the VLDL-cholesterol and VLDL-TG content and the TG/apolipoprotein B ratio in VLDL, which was used to estimate particle size. Although VLDL-TG fatty acids were very slightly modified, VLDL-TG molecular species in VLDL after consumption of the MD+nuts were characterized by a higher presence of linoleic acid (18:2, n-6), whereas after the intake of MD+VOO, they were rich in oleic acid (18:1, n-9). Therefore, we conclude that the reduction in systemic TG concentrations observed after consumption of the MD may be explained by reduction of the lipid core of VLDL and a selective modification of the molecular species composition in the particle.

Corticosterone administration and high-energy feed results in enhanced fat accumulation and insulin resistance in broiler chickens

1. Two experiments were conducted to investigate the effects of exogenous corticosterone administration (30 mg/kg diet) and dietary energy level on feed or energy intake and fat deposition in broiler chickens of 1 and 4 weeks of age. 2. Corticosterone treatment significantly suppressed body weight (BW) gain and reduced feed and caloric efficiencies. The retarded growth may conceal the stimulatory effect of corticosterone on feed consumption or metabolisable energy (ME) intake. A high-energy diet may increase energy intake and partially alleviate the suppressing effect of corticosterone on growth of broilers. 3. Corticosterone administration promoted the conservation of energy stores as fat at both abdominal and subcutaneous sites and this process occurred regardless of dietary energy level in ad libitum feeding status. A high-energy diet increased fat accumulation and showed no significant interaction with corticosterone treatment. 4. The suppressed development of breast and thigh muscles by corticosterone treatment was observed only in 1-week-old chickens fed on the low-energy diet. In contrast, the yield of breast muscle but not thigh muscle was significantly decreased by corticosterone in 4-week-old chickens, suggesting that the tissue specificity to corticosterone challenge is age dependent. 5. Plasma concentrations of glucose, insulin, triglyceride, non-esterified fatty acids (NEFA) and very low density lipoprotein were increased by corticosterone treatment regardless of diet treatment. A high-energy diet increased plasma levels of NEFA and resulted in hyperinsulinism in 4-week-old chickens but not in 1-week-old chickens. 6. Lipoprotein lipase (LPL) activities in adipose tissues may have been up-regulated by corticosterone treatment and showed tissue specificity. The increased LPL activities at ad libitum feeding status were not necessarily linked with the increased fat accumulation in corticosterone challenged chickens. 7. Corticosterone resulted in augmented energy consumption and altered energy redistribution toward lipid deposition. The induced insulin resistance and enhanced hepatic de novo lipogenesis by corticosterone are likely to be responsible for the increased fat deposition.

Fatty acids but not dexamethasone are essential inducers for chick adipocyte differentiation in vitro

The present study was carried out to clarify the direct effect of fatty acids (FAs) on chick (Gallus gallus) adipocyte differentiation in the absence of dexmethasone (DEX), a commonly used as strong inducer for adipocyte differentiation. Adipocyte differentiation was initiated by maintaining confluent cell in serum-free medium supplemented with FAs. Upon exposure to FAs, glycerol-3-phosphate dehydrogenase activity (GPDH) as adipocyte differentiation marker rapidly increased, and was significantly higher in chick adipocyte than in control cell. The morphology of the FAs-treated cell changed from fibroblast-like to polygon, and the cells accumulated many cytoplasmic lipid droplets as estimated by Oil red O staining. Neither insulin nor bovine serum albumin, as substitutes for serum, had an effect on chick adipocyte differentiation. The FAs-treated cell had a higher protein and mRNA expression levels for peroxisome proliferator-activated receptor-gamma (PPARgamma), a master regulator of differentiation, compared with untreated cell. In FAs-treated cell, the mRNA expression levels of adipocyte-specific genes, such as CCAAT/enhancer binding protein-alpha (C/EBP alpha) and adipocyte fatty acid-binding protein (aP2) were higher than in control cell. These results indicated that FAs, but not DEX, are essential inducers for chick adipocyte differentiation by elevating PPARgamma expression.

Protein kinase D is a key regulator of cardiomyocyte lipoprotein lipase secretion after diabetes

The diabetic heart switches to exclusively using fatty acid (FA) for energy supply and does so by multiple mechanisms including hydrolysis of lipoproteins by lipoprotein lipase (LPL) positioned at the vascular lumen. We determined the mechanism that leads to an increase in LPL after diabetes. Diazoxide (DZ), an agent that decreases insulin secretion and causes hyperglycemia, induced a substantial increase in LPL activity at the vascular lumen. This increase in LPL paralleled a robust phosphorylation of Hsp25, decreasing its association with PKCdelta, allowing this protein kinase to phosphorylate and activate protein kinase D (PKD), an important kinase that regulates fission of vesicles from the golgi membrane. Rottlerin, a PKCdelta inhibitor, prevented PKD phosphorylation and the subsequent increase in LPL. Incubating control myocytes with high glucose and palmitic acid (Glu+PA) also increased the phosphorylation of Hsp25, PKCdelta, and PKD in a pattern similar to that seen with diabetes, in addition to augmenting LPL activity. In myocytes in which PKD was silenced or a mutant form of PKCdelta was expressed, high Glu+PA were incapable of increasing LPL. Moreover, silencing of cardiomyocyte Hsp25 allowed phorbol 12-myristate 13-acetate to elicit a significant phosphorylation of PKCdelta, an appreciable association between PKCdelta and PKD, and a vigorous activation of PKD. As these cells also demonstrated an additional increase in LPL, our data imply that after diabetes, PKD control of LPL requires dissociation of Hsp25 from PKCdelta, association between PKCdelta and PKD, and vesicle fission. Results from this study could help in restricting cardiac LPL translocation, leading to strategies that overcome contractile dysfunction after diabetes.

Uptake of triacylglycerol-rich lipoproteins of differing triacylglycerol molecular species and unsaponifiable content by liver cells

The fatty acid composition of dietary oils can modulate the incorporation of triacylglycerol-rich lipoproteins (TRL) into hepatocytes, thus affecting the atherogenicity of these particles. However, nothing is known about the effect of the unsaponifiable fraction of the oils. In the present study, we evaluated the influence of these components on the uptake of TRL by rat primary hepatocytes. TRL were isolated from human serum after the intake of meals enriched in high-oleic sunflower oil (HOSO), virgin olive oil (VOO) or VOO enriched in its own unsaponifiable fraction (EVO). HOSO and HOSO-TRL differed from VOO and EVO and their corresponding TRL in the composition of triacylglycerol molecular species and of the unsaponifiable fraction. Furthermore, the increase in the unsaponifiable fraction of VOO led to changes in the triacylglycerol molecular species in the EVO-TRL. On incubation with hepatocytes, HOSO-TRL were taken up at a faster rate than VOO-TRL or EVO-TRL. In addition, in comparison to VOO-TRL, HOSO-TRL increased the expression of mRNA for the LDL receptor-related protein receptor, which plays an important role in the internalisation of remnant lipoproteins. EVO-TRL also increased LDL receptor-related protein mRNA expression in comparison with VOO-TRL, but this change was not accompanied by a rise in the uptake rate, suggesting that the unsaponifiable fraction of VOO may inhibit LDL receptor-related protein expression or activity post-transcriptionally. In conclusion, TRL from dietary oils with differing triacylglycerol molecular species and unsaponifiable fraction content are taken up by liver cells at different rates, and this may be important in the atherogenicity of these particles.

Altered cardiac fatty acid composition and utilization following dexamethasone-induced insulin resistance

Glucocorticoid therapy is often associated with impaired insulin sensitivity and cardiovascular disease. The present study was designed to evaluate cardiac fatty acid (FA) composition and metabolism following acute dexamethasone (Dex) treatment. Using the euglycemic hyperinsulinemic clamp, rats injected with Dex demonstrated a reduced glucose infusion rate. This whole body insulin resistance was also associated with a heart-specific increase in pyruvate dehydrogenase kinase 4 gene expression and a reduction in the rate of glucose oxidation. Dex treatment increased basal and postheparin plasma lipolytic activity. In the heart, palmitic and oleic acid levels were higher after 4 h of Dex and decreased to control (CON) levels within 8 h. Measurement of polyunsaturated FAs demonstrated a drop in linoleic and gamma-linolenic acid, with an increase in arachidonic acid (AA) after acute Dex injection. Tissue FA can be either oxidized or stored as triglyceride (TG). At 4 h, Dex augmented cardiac TG accumulation. However, this increase in tissue TG could not be maintained, such that at 8 h following Dex, TG declined to CON levels. AMP-activated protein kinase (AMPK) activation is known to promote FA oxidation through its control of acetyl-CoA carboxylase (ACC). Acute Dex promoted ACC phosphorylation, and increased cardiac palmitate oxidation, likely through its effects in increasing AMPK phosphorylation and total AMPK protein and gene expression. Whether these acute effects of Dex on FA oxidation, TG storage, and arachidonic acid accumulation can be translated into increased cardiovascular risk following chronic therapy has yet to be determined.

The metabolism of structured triacylglycerols

The triacylglycerol (TAG) structure in addition to the overall fatty acid profile is of importance when considering the nutritional effect of a dietary fat. This review aims at summarizing our current knowledge of the digestion, absorption, uptake, and transport of structured TAGs, with particular emphasis on the following aspects: gastric emptying, specificity of pancreatic lipase, lymphatic transport and clearance of chylomicrons, effects of lipid structure on tissue lipid compositions and the fecal loss of fats. So an overview will be provided for how the structure and fatty acid composition of TAGs affect their absorption and the distribution of the fatty acids in the body following digestion and absorption.

Chemical composition and energy content of chickens in response to different levels of dietary polyunsaturated fatty acids

Two experiments were performed to study the effect of dietary polyunsaturated fatty acids (PUFA) on abdominal fat pad weight and chemical composition of broilers. In Experiment 1, different fat sources were blended in different ratios keeping added fat level constant (9%). In Experiment 2, PUFA gradient was obtained by increasing the level of inclusion (2, 4, 6 and 8%) of PUFA-rich oil. The treatments had 15, 34, 45 and 61 and 28, 38, 48 and 59 g PUFA/kg diet, respectively. Apparent metabolizable energy intake was similar in both experiments, except for the more saturated diet in Experiment 1 (15 g PUFA/kg), where it was lower. In Experiment 1, abdominal fat pad weight, total body fat and body energy were lower in the animals on the high PUFA diets (p < 0.05) compared to the animals on the saturated-rich ones, meanwhile in Experiment 2 there were no differences on chemical and energy composition by increasing added PUFA-rich oil inclusion level. In conclusion, PUFA-rich chicken diets, compared to saturated-rich ones, cause a lower body fat deposition, but not compared to low-PUFA low-fat diets.

Positional distribution of decanoic acid: effect on chylomicron and VLDL TAG structures and postprandial lipemia

Although medium-chain FA (MCFA) are mainly absorbed via the portal venous system, they are also incorporated into chylomicron TAG; therefore, the positional distribution of MCFA in TAG is likely to affect their metabolic fate. We studied chylomicron and VLDL TAG structures, as well as the magnitude of postprandial lipemia, after two oral fat loads containing decanoic acid (10:0) predominantly at the sn-1(3),2 (MML) or at the sn-1,3 positions (MLM) of TAG in a randomized, double-blind, crossover clinical trial with 10 healthy, normal-weight volunteers. An MS-MS method was used to analyze TAG regioisomers. The position of decanoic acid in chylomicron TAG reflected its position in the TAG ingested, and TAG with none, one, two, or three decanoic acid residues were detected after ingestion of both fats. More (P < 0.05) 30:0 and 38:1 TAG (acyl carbons:double bonds) and fewer 46:5, 54:5, and 54:4 TAG were found in chylomicrons after ingestion of MML than after MLM. The VLDL TAG composition did not differ between the fat loads but did change (P < 0.05) 2 to 6 h after ingestion of both fats. No statistical differences were seen between the fat loads in areas under the plasma, chylomicron, or VLDL TAG response curves or in FFA concentrations. Thus, the positional distribution of MCFA in TAG affects their metabolic fate, but the magnitude of postprandial lipemia does not seem to be dependent on the positional distribution of MCFA in the ingested fat.

Role of dietary fatty acids and acute hyperglycemia in modulating cardiac cell death

OBJECTIVE

We examined the effect of dietary manipulation of palmitic acid (20% [w/w] palm oil [PO]) on cardiomyocyte apoptosis in the rat heart under normoglycemic and hyperglycemic conditions in vivo. We used 20% (w/w) sunflower oil (SO; a diet rich in omega-6 polyunsaturated fatty acids) as an isocaloric control.

METHODS

Adult male Wistar rats were fed experimental diets containing normal laboratory chow (5% corn oil) or a high fat diet (AIN-76A with PO or SO) for 4 wk. Subsequently, to induce diabetes, rats were injected with streptozotocin (55 mg/kg, intravenously). After 4 d of diabetes, hearts were tested for evidence of lipotoxicity and cell death, and the serum for its related markers.

RESULTS

Feeding PO and SO magnified palmitic and linoleic acid contents within lipoproteins and hearts respectively. Compared with SO, PO diabetic hearts demonstrated significantly higher levels of apoptosis, with an altered Bax:Bcl-2 ratio, augmented lipid peroxidation, and protein modification by formation of nitrotyrosine. Interestingly, SO-fed diabetic animals demonstrated an increase in serum lactate dehydrogenase and myocardial necrotic changes.

CONCLUSION

In marked contrast to results obtained in vitro, PO feeding led to only a minor fraction of cardiomyocytes undergoing apoptosis and suggests that, in the intact heart, protective mechanisms could be triggered that dampen excessive apoptosis. Of greater clinical significance was the observation that "heart-friendly" vegetable oils such as SO, rich in omega-6 polyunsaturated fatty acids, could precipitate cardiac necrosis, and questions its beneficial role in the cardiovascular system, especially following diabetes.

Dietary virgin olive oil triacylglycerols as an independent determinant of very low-density lipoprotein composition

OBJECTIVE

We examined the effects of virgin olive oil (VOO) triacylglycerols (TGs) on the lipid composition of human very low-density lipoprotein (VLDL).

METHODS

Twenty-one normocholesterolemic, normotensive, non-diabetic elderly subjects were recruited for the study. Two VOOs (VOO1 and VOO2) of the same variety, with an equivalent composition in minor components and differing only in the oleic and linoleic acid concentrations, were administered for 4 wk each to assess the effect of their TG molecular species compositions. Blood was collected after an overnight fast, VLDLs were isolated by ultracentrifugation, and lipid classes, TG molecular species, and TG fatty acid composition were determined.

RESULTS

Dietary VOOs significantly differed in TG molecular species composition. VOO1 represented larger amounts of triolein (P < 0.01), whereas VOO2 was significantly enriched with dilinoleoyl-oleoyl-glycerol, linoleoyl-dioleoyl-glycerol, and linoleoyl-oleoyl-palmitoyl-glycerol (P < 0.01). For VLDL, intake of VOO1 caused an increase of total TG (P < 0.01) due mainly to increases in triolein and linoleoyl-dioleoyl-glycerol. Conversely, VOO2 increased VLDL cholesteryl esters (P < 0.01) and TG rich in arachidonic acid (P < 0.01).

CONCLUSIONS

The different TG molecular species compositions of dietary oils may be an independent determinant of the lipid composition of VLDL in elderly people and therefore may play a role in regulating lipoprotein metabolism in these subjects.

Serum and liver lipids in rats and chicks fed with diets containing different oils

OBJECTIVES

Because dietary fat composition is determinant for serum cholesterol level, which is related to cardiovascular disease, we evaluated the effects of diets containing saturated (coconut oil) or polyunsaturated fatty acids (soybean oil) supplemented or not with dietary cholesterol on serum and liver lipid composition in two animal species.

METHODS

Male Wistar rats (21 d old) were assigned to one of seven groups and fed with commercial diet or diets containing 5% or 20% soybean oil or 20% coconut oil with or without 1% cholesterol. Chicks were assigned to one of four groups and fed with diets containing 15% soybean oil or 15% coconut oil with or without 1% cholesterol.

RESULTS

In rats, the accumulations of hepatic cholesterol and triacylglycerols were higher in the group fed 20% soybean oil and 1% cholesterol than in the group fed 20% coconut fat and 1% cholesterol. The highest serum levels of cholesterol and triacylglycerols were observed in the group fed coconut oil and cholesterol, compared with the group fed soybean oil and cholesterol. Triacylglycerol, high-density lipoprotein, and total cholesterol serum levels increased with diet containing coconut oil and cholesterol. In chicks, the highest hepatic cholesterol accumulation occurred in the group fed 15% coconut fat and 1% cholesterol. Total and high-density lipoprotein cholesterol levels increased with diet containing coconut oil and cholesterol, although none of these diets modified serum triacylglycerol levels.

CONCLUSIONS

The type of experimental animal model and the diet composition influence lipid metabolism.

Identification of factors regulating lipoprotein lipase catalyzed hydrolysis in rats with the aid of monoacid-rich lipoprotein preparations(1)

To identify the substrate specificity and regulatory factors in lipoprotein lipase (LPL) catalyzed hydrolysis of triacylglycerol-rich lipoprotein, monoacid-rich lipoproteins were used to study the kinetic parameters of LPL. Feeding growing rats with diets rich in palmitic acid (16:0), oleic acid (18:1) or linoleic acid (18:2) for 10 days increased the corresponding acid content in the triacylglycerols of the lipoproteins. Force-feeding the monoacid-rich triacylglycerols, particularly 16:0 or 18:1, increased the respective fatty acid content in both chylomicrons and VLDLs. Major apolipoproteins and lipid compositions were essentially similar among all lipoproteins differing in monoacid species, except for apo A-IV. The Vmax of LPL for 16:0-rich chylomicrons and VLDLs were higher than for 18:1- or 18:2-rich lipoproteins. Order parameter (S), an indicator of the surface fluidity of lipoproteins, decreased with the chain length and unsaturation of monoacid in similar manner as the Vmax. The Vmax of LPL increased linearly (P < 0.05) with an increase in either the palmitic acid content of the lipoprotein triacylglycerols or order parameter (S) of the lipoproteins. The order parameter (S) and Vmax of LPL were higher in 16:0 triacylglycerol emulsions with apo B than with 18:1 or 18:2 triacylglycerols. The apo A-IV in triacylglycerol emulsions stimulated Vmax of LPLs in the presence of apo B and apo C-II. The binding of apo A-IV to 16:0 triacylglycerol emulsions was higher than to other triacylglycerol emulsions. These findings suggest that lipoprotein catalysis by LPL is modulated by the 16:0 level in the lipoprotein triacylglycerol, which affects the surface fluidity and apo A-IV content of lipoproteins.

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.

Dietary polyunsaturated fatty acids decrease fat deposition in separable fat depots but not in the remainder carcass

Two experiments were conducted in order to determine the effect of dietary fatty acid profile on deposition of body fat, carcass fat, and separable fat depots. Diets with four types of fat (tallow, olive, sunflower, and linseed oils) at an inclusion level of 10% were administered to female broiler chickens. In Experiment 1, total body fat, carcass fat (total body fat minus abdominal fat), and abdominal fat (AF) were determined. In Experiment 2, several separable fat depots (abdominal, neck, sartorial, and mesenteric fat) were removed and weighed. In general, the analyzed separable fat depots were reduced in broilers fed sunflower or linseed oils with respect to those fed tallow or olive oil (P < 0.05). Percentages of body and carcass fat were also slightly reduced in birds fed sunflower or linseed oil, with respect to those fed tallow; however, the differences were not statistically significant. Regression analysis showed that body fat, carcass fat, and fat depots variability were closely correlated with AF (R2 = 0.69, 0.56, and 0.81, respectively), except for birds fed tallow, in which abdominal and mesenteric fat showed a different growth pattern with respect to the other treatments and to the other fat depots. These results suggest that polyunsaturated fatty acids reduce fat deposition in separable fat depots with respect to monounsaturated and saturated fats but not in the rest of the body fat depots. The growth pattern of fat depots can be modified by dietary fatty acid profile. Broilers fed saturated fat tend to deposit more fat in abdominal and mesenteric depots.

Chicken leptin: properties and actions

Chicken leptin cDNA shows a high homology to mammalian homologous, with an expression localized in the liver and adipose tissue. It is noteworthy, that the hepatic expression is most likely associated with the primary role that this organ plays in lipogenic activity in avian species. As in mammals, chicken leptin expression is regulated by hormonal and nutritional status. This regulation is tissue-specific and with a high sensitivity in the liver compared to adipose tissue. The blood leptin levels are regulated by the nutritional state with high levels in the fed state compared to the fasted state. The recombinant chicken leptin markedly inhibits food intake as reported in mammals, suggesting the presence of an hypothalamic leptin receptor. The chicken leptin receptor has been identified and all functional motifs are highly conserved compared to mammalian homologous. Chicken leptin receptor is expressed in the hypothalamus but also in other tissues such as pancreas, where leptin inhibits insulin secretion and thus may have a key role in regulating nutrient utilization in this species.

Postprandial triacylglycerols from dietary virgin olive oil are selectively cleared in humans

The aims of the present study were to evaluate the effect of a meal rich in virgin olive oil on triacylglycerol composition of human postprandial triacylglycerol-rich lipoproteins (fraction Sf > 400), and to assess the role of the triacylglycerol molecular species concentration and polarity on lipoprotein clearance. Fasting (0 h) and postprandial blood samples were collected hourly for 7 h from eight healthy normolipidemic subjects after the ingestion of the meal. Plasma and lipoprotein triacylglycerol concentrations increased quickly over fasting values and peaked twice at 2 and 6 h during the 7-h postprandial period. The triacylglycerols in the lipoprotein fraction at 2 h generally reflected the composition of the olive oil, however, the proportions of the individualmolecular species were altered by the processes leading to their formation. Among the major triacylglycerols, the proportion of triolein (OOO; 43.6%) decreased (P < 0.05), palmitoyl-dioleoyl-glycerol (POO; 31. 1%) and stearoyl-dioleoyl-glycerol (SOO; 2.1%) were maintained and linoleoyl-dioleoyl-glycerol (LOO; 11.4%) and palmitoyl-oleoyl-linoleoyl-glycerol (POL; 4.6%) significantly increased (P < 0.05) compared with the composition of the triacylglycerols in the olive oil. Smaller amounts of endogenous triacylglycerol (0.8%), mainly constituted of the saturated myristic (14:0)and palmitic (16:0) fatty acids, were also identified. Analysis of total fatty acids suggested the presence of molecular species composed of long-chain polyunsaturated fatty acids of the (n-3) family, docosapentaenoic acid, [22:5(n-3)] and docosahexaenoic acid (DHA), [22:6(n-3)] and of the (n-6) family [arachidonic acid, [20:4(n-6)]. The fastest conversion of lipoproteins to remnants occurred from 2 to 4 h and was directly related to the concentration of the triacylglycerols in the lipoprotein particle (r = 0.9969, P < 0.05) and not with its polarity (r = 0.1769, P > 0.05). The rates of clearance were significantly different among the major triacylglycerols (OOO, POO, OOL and POL) (P < 0.05) and among the latter ones and PLL (palmitoyl-dilinoleoyl-glycerol, POS (palmitoyl-oleoyl-stearoyl-glycerol) and OLL (oleoyl-dilinoleoyl-glycerol) (P < 0.01). OOO was removed faster and was followed by POO, OOL, POL, PPO (dipalmitoyl-oleoyl-glycerol), SOO, PLL, POS and OLL.