Modulation of hepatic apolipoprotein B, 3-hydroxy-3-methylglutaryl-CoA reductase and low-density lipoprotein receptor mRNA and plasma lipoprotein concentrations by defined dietary fats. Comparison of trimyristin, tripalmitin, tristearin and triolein

Molecular characterization of vascular endothelial growth factor b from spotted sea bass (Lateolabrax maculatus) and its potential roles in decreasing lipid deposition

Vascular endothelial growth factor B (VEGFB), a member of the VEGF family, exhibits limited angiogenic activity in mammals but plays an unexpected role in targeting lipids to peripheral tissues. However, its role in lipid metabolism in fish is unknown. In this study, the vegfb gene was cloned and characterized from spotted sea bass (Lateolabrax maculatus). It encodes 254 amino acids and possesses the typical characteristics of the Vegfb family, demonstrating high homology with those from other vertebrate species. The vegfb gene exhibits the highest expression levels in the liver, followed by the gills, intestine, and adipose tissues in spotted sea bass. In vivo, high-lipid diets decreased vegfb expression and increased lipid deposition in liver of fish. In vitro, palmitic acid + oleic acid treatment or vegfb knockdown significantly increased TG and TC contents, promoting lipid droplet deposition in hepatocytes. Vegfb overexpression has the opposite effects, inhibiting lipid deposition and downregulating fatty acid transport and adipogenesis genes. In contrast, the vegfb knockdown significantly upregulated the expression levels of c/ebpα, plin2, and dgat1 (P < 0.05). These results demonstrate that Vegfb may play an important role in reducing lipid deposition by regulating fatty acid transport and adipogenesis in the hepatocytes of spotted sea bass.

Lipid profiles and lifestyle habits of stroke survivors in the east coast region of peninsular Malaysia: Preliminary findings

Background: Stroke survivors are at high risk for recurrent cardiovascular events if no prevention strategies are undertaken. Aim: This study aimed to investigate the fasting serum lipid profiles and lifestyle habits in stroke survivors, and the factors associated with suboptimal lipid profiles. Methods: A cross-sectional retrospective study was conducted in three public hospitals in Malaysia. Stroke survivors' data regarding the socio-demographic characteristics, clinical profiles, fasting serum lipid profiles, dietary adherence, and physical activity levels were acquired. Binary logistic regression was used to examine the factors associated with suboptimal lipid goals. Results: A total of 104 stroke survivors were recruited from patients attending the neurology and rehabilitation departments. Only 22% of the stroke survivors attained the targeted low-density lipoprotein cholesterol level (LDL-C < 1.8 mmol/L). Meanwhile, more than two thirds of patients achieved the targeted total cholesterol, triglyceride, and high-density lipoprotein cholesterol goals. Patients with a longer stroke duration (Adjusted odds ratio, AOR 3.33, 95% confidence intervals, CI: 1.09, 10.13, p  =  0.034), elevated blood pressure (AOR 4.74, 95% CI: 1.65, 13.62, p  =  0.004), chronic kidney disease (AOR 3.30, 95% CI: 1.05, 10.34, p  =  0.041), abdominal obesity (AOR 3.14, 95% CI: 1.20, 8.21, p  =  0.020), excessive energy intake (AOR 2.72, 95% CI: 1.07, 6.91, p  =  0.036), and excessive saturated fatty acids intake (AOR 2.85, 95% CI: 1.02, 7.93, p  =  0.045) were significantly associated with suboptimal lipid profiles. Conclusion: The lipid goals attainment was low, particularly the LDL-C levels among Malaysian stroke survivors. Greater efforts are warranted to fully utilise the lipid-lowering therapy and the lifestyle changes in these high-risk patients.

Effects of chemical silage of red tilapia viscera (Oreochromis spp.) as a source of protein on the productive and hematological parameters in isa-brown laying hens (Gallus gallus domesticus)

This paper evaluates the inclusion of chemical silage from viscera of red tilapia (Oreochromis spp.) in diets of Isa-Brown laying hens (Gallus gallus domesticus), and its influence on productive variables and hematological parameters. A total of 56, 16-week-old laying hens were randomly divided into two groups (one per diet), which in turn were subdivided into 7 replicates of 4 birds each. All test groups were fed for 16 weeks. During this period, the evaluation of the productive variables was carried out, and at the end, random blood samples were taken from 3 birds per diet. The results indicated that the inclusion of chemical silage from red tilapia viscera with a proportion of 17.18% dry matter, does not present statistically significant differences in the productive variables which were evaluated (p > 0.05) with respect to the control. Moreover, the chemical silage did not modify the hematological parameters and blood the chemistry in the hens. This allowed us to conclude that silage can be used as a substitute for conventional protein raw materials such as fishmeal and soybean meal in the preparation of diets for laying hens, without altering their productive performance.

Grape seed extract supplementation along with a restricted-calorie diet improves cardiovascular risk factors in obese or overweight adult individuals: A randomized, placebo-controlled trial

Grape seed extract (GSE) is a flavonoid-rich supplement, recently discussed as a potential moderator of inflammation and obesity. In this study, we aimed to investigate the effects of GSE supplementation along with a restricted-calorie diet (RCD), on changes in blood lipid profile, visceral adiposity index (VAI), and atherogenic index of plasma (AIP). We designed a randomized, double-blinded, placebo-controlled clinical trial. Forty obese or overweight individuals (25 ≤ body mass index < 40 kg/m² ) were randomly assigned to receive GSE (300 mg/day) or placebo, plus RCD, for 12 weeks. We studied the anthropometric measures, biochemical biomarkers and dietary intake within the study timelines. Levels of high-density lipoprotein cholesterol (HDL-C) and HDL-C/low-density lipoprotein cholesterol (LDL-C) significantly increased in the GSE group as compared with the placebo group at week 12 (p = .03 and .008, respectively, adjusted for age, sex, energy and saturated fatty acid intake). We also observed a significant reduction in LDL-C following GSE supplementation in comparison to placebo (adjusted for age, sex and energy intake, p = .04). VAI, AIP, total cholesterol and triglyceride significantly decreased in the GSE group compared with the baseline (p = .04, .02, .01, and .02, respectively). GSE supplementation may have a modulatory role in improving blood lipid profile in obese or overweight individuals, when accompanied by RCD.

Lipid Profile Modulates Cardiometabolic Risk Biomarkers Including Hypertension in People with Type-2 Diabetes: A Focus on Unbalanced Ratio of Plasma Polyunsaturated/Saturated Fatty Acids

Type 2 diabetes mellitus (T2DM) is associated with lipid metabolism disorder, particularly elevated plasma levels of non-esterified free fatty acids (NEFFA) and an increased cardiovascular disease risk, such as essential hypertension (H). The plasma unbalance of saturated fatty acid (SFA)/polyunsaturated fatty acid (PUFA) ratio is a likely contributor, but the mechanisms involved are not clearly elucidated. The aim of this study is to explore the association between plasma SFA/PUFA ratio and the clusters of cardiometabolic syndrome (CMS), including the atherogenic biomarkers, inflammatory status, feeding patterns, and physical activity in people with T2DM with or without essential hypertension. The study was conducted on 784 adult male and female participants, aged between 30 and 50 years, and divided into 3 groups: 100 T2DM without hypertension (D); 368 T2DM with hypertension (DM); and 316 hypertensive participants without T2DM (H). All Participants were phenotyped regarding CMS clusters according to the NCEP/ATPIII criteria. Insulin resistance was assessed by Homeostasis model assessment (HOMA model). Metabolic, atherogenic, and inflammatory parameters were analyzed by biochemical methods; NEFFA by microfluorimetry; SFA, PUFA-n6 and PUFA-n3 by gas phase chromatography. Dietary lipids and physical activity were analyzed through the use of validated questionnaires. The clusters of CMS were found in all groups. Dyslipidemia was correlated with accretion NEFFA levels in all groups, but more accentuated in the DH group (r = +0.77; p < 0.001). Similarly, plasma PUFA/SFA ratio and PUFA-3 level was lower, concomitantly with a higher plasma ApoB100/ApoA1 (p < 0.001), lipoprotein (a), homocysteine (p < 0.001), and pro-inflammatory cytokines (TNFα, IL-6, IL1-β) in the DH group. Likewise, the depletion of PUFA-n3/PUFA-n6 ratio is associated with the decrease of omega 3-DHA (docosahexaenoic acid) and omega 3-EPA (eicosapentaenoic acid) (p < 0.001). It appears that the PUFAs-n3 ratio modulates cardiometabolic risk, inflammatory state and atherogenic biomarkers. The plasma unbalanced ratio of SFA/PUFA reflects dietary fatty acids intake. The contribution of dietary lipids is undisputed. Nutritional recommendations are required to determine the fatty acids ratio (saturated and unsaturated) provided in the diet.

Effects of a very high saturated fat diet on LDL particles in adults with atherogenic dyslipidemia: A randomized controlled trial

Background

Previous studies have shown that increases in LDL-cholesterol resulting from substitution of dietary saturated fat for carbohydrate or unsaturated fat are due primarily to increases in large cholesterol-enriched LDL, with minimal changes in small, dense LDL particles and apolipoprotein B. However, individuals can differ by their LDL particle distribution, and it is possible that this may influence LDL subclass response.

Objective

The objective of this study was to test whether the reported effects of saturated fat apply to individuals with atherogenic dyslipidemia as characterized by a preponderance of small LDL particles (LDL phenotype B).

Methods

Fifty-three phenotype B men and postmenopausal women consumed a baseline diet (55%E carbohydrate, 15%E protein, 30%E fat, 8%E saturated fat) for 3 weeks, after which they were randomized to either a moderate carbohydrate, very high saturated fat diet (HSF; 39%E carbohydrate, 25%E protein, 36%E fat, 18%E saturated fat) or low saturated fat diet (LSF; 37%E carbohydrate, 25%E protein, 37%E fat, 9%E saturated fat) for 3 weeks.

Results

Compared to the LSF diet, consumption of the HSF diet resulted in significantly greater increases from baseline (% change; 95% CI) in plasma concentrations of apolipoprotein B (HSF vs. LSF: 9.5; 3.6 to 15.7 vs. -6.8; -11.7 to -1.76; p = 0.0003) and medium (8.8; -1.3 to 20.0 vs. -7.3; -15.7 to 2.0; p = 0.03), small (6.1; -10.3 to 25.6 vs. -20.8; -32.8 to -6.7; p = 0.02), and total LDL (3.6; -3.2 to 11.0 vs. -7.9; -13.9 to -1.5; p = 0.03) particles, with no differences in change of large and very small LDL concentrations. As expected, total-cholesterol (11.0; 6.5 to 15.7 vs. -5.7; -9.4 to -1.8; p<0.0001) and LDL-cholesterol (16.7; 7.9 to 26.2 vs. -8.7; -15.4 to -1.4; p = 0.0001) also increased with increased saturated fat intake.

Conclusions

Because medium and small LDL particles are more highly associated with cardiovascular disease than are larger LDL, the present results suggest that very high saturated fat intake may increase cardiovascular disease risk in phenotype B individuals. This trial was registered at clinicaltrials.gov (NCT00895141).

Trial registration

Clinicaltrials.gov NCT00895141.

Gene expression modulation of lipid and central energetic metabolism related genes by high-fat diet intake in the main homeostatic tissues

HF diet feeding affects the energy balance by transcriptional metabolic adaptations, based in direct gene expression modulation, perinatal programing and transcriptional factor regulation, which could be affected by the animal model, gender or period of dietary treatment.

Dietary Lipid Levels Influence Lipid Deposition in the Liver of Large Yellow Croaker (Larimichthys crocea) by Regulating Lipoprotein Receptors, Fatty Acid Uptake and Triacylglycerol Synthesis and Catabolism at the Transcriptional Level

Ectopic lipid accumulation has been observed in fish fed a high-lipid diet. However, no information is available on the mechanism by which dietary lipid levels comprehensively regulate lipid transport, uptake, synthesis and catabolism in fish. Therefore, the present study aimed to gain further insight into how dietary lipids affect lipid deposition in the liver of large yellow croaker(Larimichthys crocea). Fish (150.00±4.95 g) were fed a diet with a low (6%), moderate (12%, the control diet) or high (18%) crude lipid content for 10 weeks. Growth performance, plasma biochemical indexes, lipid contents and gene expression related to lipid deposition, including lipoprotein assembly and clearance, fatty acid uptake and triacylglycerol synthesis and catabolism, were assessed. Growth performance was not significantly affected. However, the hepato-somatic and viscera-somatic indexes as well as plasma triacylglycerol, non-esterified fatty acids and LDL-cholesterol levels were significantly increased in fish fed the high-lipid diet. In the livers of fish fed the high-lipid diet, the expression of genes related to lipoprotein clearance (LDLR) and fatty acid uptake (FABP11) was significantly up-regulated, whereas the expression of genes involved in lipoprotein assembly (apoB100), triacylglycerol synthesis and catabolism (DGAT2, CPT I) was significantly down-regulated compared with fish fed the control diet, and hepatic lipid deposition increased. In fish fed the low-lipid diet, the expression of genes associated with lipoprotein assembly and clearance (apoB100, LDLR, LRP-1), fatty acid uptake (CD36, FATP1, FABP3) and triacylglycerol synthesis (FAS) was significantly increased, whereas the expression of triacylglycerol catabolism related genes (ATGL, CPT I) was reduced compared with fish fed the control diet. However, hepatic lipid content in fish fed the low-lipid diet decreased mainly due to low dietary lipid intake. In summary, findings of this study provide molecular insight into the role of lipid deposition in the liver in response to different dietary lipid contents.

The role of dietary fatty acids in the pathology of metabolic syndrome

Dysfunctional lipid metabolism is a key component in the development of metabolic syndrome, a very frequent condition characterized by dyslipidemia, insulin resistance, abdominal obesity and hypertension, which are related to an elevated risk for type 2 diabetes mellitus. The prevalence of metabolic syndrome is strongly associated with the severity of obesity; its physiopathology is related to both genetics and food intake habits, especially the consumption of a high-caloric, high-fat and high-carbohydrate diet. With the progress of scientific knowledge in the field of nutrigenomics, it was possible to elucidate how the majority of dietary fatty acids influence plasma lipid metabolism and also the genes expression involved in lipolysis and lipogenesis within hepatocytes and adipocytes. The aim of this review is to examine the relevant mechanistic aspects of dietary fatty acids related to blood lipids, adipose tissue metabolism, hepatic fat storage and inflammatory process, all of them closely related to the genesis of metabolic syndrome.

The use of human tissues and cells in biomedical research: the unusual suspects

There are compelling reasons to search for alternatives to the use of animals in medical and pharmaceutical research. Aside from the obvious animal welfare issues, both the well-established differences between animal models and humans, and the inherent inter-individual variability in human biological responses, indicate that human-based alternatives are urgently required. However, any such alternative must out-perform the animal-based alternative, otherwise there will be little or no uptake and adoption by end-users. Data obtained from inbred animal models is often highly reproducible, and is therefore attractive to researchers in the fields of biomedical and pharmaceutical research. The inter-individual variability observed during human volunteer and human tissue-based studies is often considered to be problematic, and has been highlighted further with the advent of the 'omics' technologies, which generate large biological datasets. However, the variability in both baseline data and response to pharmacological or toxicological challenge observed in human tissues potentially contains a veritable gold mine of information, which may be critical for the advancement of drug discovery.

Enhanced hypocholesterolemic effects of interesterified oils are mediated by upregulating LDL receptor and cholesterol 7-α- hydroxylase gene expression in rats

The concentration of LDL cholesterol in plasma is strongly influenced by the amount and type of lipid in the diet. Our studies have shown that positional changes in the fatty acids in blended oil introduced using lipase-catalyzed interesterification differentially modulate circulating LDL levels in rats compared with those observed in rats given a physical blend of oils. To investigate the molecular basis of these differences, transcriptional profiling of genes involved in cholesterol homeostasis was studied after feeding rats with a semipurified diet containing 10% fat from native oils; coconut oil (CNO), rice bran oil (RBO), or sesame oil (SESO); blended (B); CNO+RBO(B) or CNO+SESO(B) and interesterified oil (I); CNO+RBO(I) or CNO+SESO(I) for 60 d. Hepatic LDL receptor (LDL-R) expression significantly increased in rats fed interesterified oils by 100-200% compared with rats fed blended oils and by 400-500% compared with rats fed CNO. Positional alteration in fatty acids of oils used in the diet induced changes in LDL-R expression, which was accompanied by parallel changes in cholesterol-7α-hydroxylase (CYP7A1) and SREBP-2 genes. This suggested that not only the fatty acid type but also its position in the TG of dietary lipids play an important role in maintaining plasma cholesterol levels by suitably modulating gene expression for LDL-R in rat liver.

Evaluation of established coronary heart disease on the basis of HDL and non-HDL NMR lipid profiling

A (1)H NMR-based lipid profiling approach was used to investigate the prediction of coronary heart disease (CHD) and examine the confounding effect of factors such as gender, triglycerides, HDL-cholesterol and age levels on the prediction of disease. The HDL and non-HDL lipid profiles in 47 patients with triple vessel disease (TVD) and 41 patients with normal coronary arteries (NCA) both documented angiographically were generated. The presence of CHD was predicted with a sensitivity and specificity of 52% and 75% for HDL model and 78% and 80% for non-HDL, respectively. The lipid constituents of HDL lipoproteins which contributed to the separation between the two groups were the saturated fatty acids, cholesterol, total omega-3 fatty acids, degree of unsaturation, diallylic protons from polyunsaturated fatty acids, linoleic acid and, to a lesser extent, the number of fatty acids, triglycerides, unsaturated fatty acids and phosphatidylcholine. Respectively, for non-HDL, lipoproteins were the saturated fatty acids, number of fatty acids, cholesterol, unsaturated fatty acids and phosphatidylcholine. Gender, triglycerides, HDL-cholesterol and age influenced the lipid constituents of HDL and non-HDL lipoproteins that contributed to the separation between subgroups and confounded the predictive power of the models. NMR-based lipid profiling analysis could contribute to the identification of noninvasive markers for the presence and the development of the disease.

Regulation of hepatic gene expression by saturated fatty acids

Diets rich in saturated fatty acids have long been associated with increased plasma cholesterol concentrations and hence increased risk of cardiovascular disease. More recently, they have also been suggested to promote the development of non-alcoholic fatty liver disease. While there is now considerable evidence to suggest that polyunsaturated fatty acids exert many of their effects through regulating the activity of transcription factors, including peroxisome proliferator activated receptors, sterol regulatory binding proteins (SREBPs) and liver X receptor, our understanding of how saturated fatty acids act is still limited. Here we review the potential mechanisms whereby saturated fatty acids modulate hepatic lipid metabolism thereby impacting on the synthesis, storage and secretion of lipids. Evidence is presented that their effects are, at least partly, mediated through modulation of the activity of the SREBP family of transcription factors.

Importância da gordura alimentar na prevenção e no controle de distúrbios metabólicos e da doença cardiovascular

A Organização Mundial da Saúde (OMS) reiterou recentemente que o consumo de dietas inadequadas e a inatividade física estão entre os dez principais fatores de mortalidade. Diversos ensaios aleatorizados demonstram que intervenções alimentares adequadas podem diminuir ou prevenir significativamente o aparecimento de várias doenças crônicas não transmissíveis. Neste contexto, o papel da dieta vem sendo exaustivamente avaliado em estudos clínicos e epidemiológicos. Assim, já foi bem estabelecido na literatura que a quantidade e o tipo de gordura alimentar exercem influência direta sobre fatores de risco cardiovascular, tais como a concentração de lípides e de lipoproteínas plasmáticas, bem como sua associação a processos inflamatórios. Os ácidos graxos participam de complexos sistemas de sinalização intracelular, função que vem sendo bastante explorada. Os ácidos graxos poli-insaturados não somente influenciam a composição das membranas, metabolismo celular e sinais de tradução, mas também modulam a expressão de genes, regulando a atividade e a produção de diversos fatores de transcrição. A proposta deste artigo é rever tópicos relevantes referentes ao metabolismo de lípides e os relacionar a terapias nutricionais que possam contribuir para a prevenção e o tratamento de doenças associadas.

Individual trans octadecenoic acids and partially hydrogenated vegetable oil differentially affect hepatic lipid and lipoprotein metabolism in golden Syrian hamsters

Trans fatty acids (TFA) from industrial sources [i.e. partially hydrogenated vegetable oil (PHVO)] have been associated with several chronic human diseases, especially coronary heart disease (CHD). The possible contribution of individual TFA to overall CHD risk remains largely unknown. The objective of the present study was to investigate the effects of 2 major trans 18:1 isomers, trans-9 18:1 [elaidic acid (EA)] and trans-11 18:1 [vaccenic acid (VA)] on plasma lipid biomarkers of CHD risk. Thirty-two male Golden Syrian hamsters were randomly assigned to 1 of 4 dietary treatments: 1) control "Western" diet; 2) PHVO supplement; 3) EA supplement; and 4) VA supplement. Fat supplements were incorporated into the respective treatment diets at 2.5 g/100 g of diet. Compared with the control diet, the PHVO diet increased the plasma ratios of total:HDL-cholesterol and nonHDL:HDL-cholesterol by 17 and 23%, respectively. In contrast, these values decreased by 27 and 46% after the EA treatment and 8 and 14% after the VA treatment, respectively, indicating an improvement (reduction) in CHD risk. With regard to liver lipids, the EA diet reduced the content of (n-3) and (n-6) PUFA relative to the other treatments, suggesting an inhibition of enzymes common to the 2 biosynthesis pathways. Overall, results demonstrate that the hypercholesterolemic effects of PHVO are not dependent on the presence of EA or VA and that other bioactive components in PHVO must be responsible for its associated adverse health effects.

Dietary myristic acid modifies the HDL-cholesterol concentration and liver scavenger receptor BI expression in the hamster

The influence of myristic acid in a narrow physiological range (0·5 to 2·4 % of total dietary energy) on the plasma and hepatic cholesterol metabolism was investigated in the hamster. The hamsters were fed on a diet containing 12·5 g fat/100 g and 0·05 g cholesterol/100 g with 0·5 % myristic acid (LA diet) for 3 weeks (pre-period). During the following 3 weeks (test period), they were divided into four dietary groups with 0·5 % (LA), 1·2 % (LM), 1·8 % (ML) or 2·4 % (M) myristic acid. Finally, half the hamsters in each group were again fed the LA diet for another 3 weeks (post-period). At the end of the test period, the hepatic expression of the scavenger receptor BI (SR-BI) was lower in the LM, ML and M groups than in the LA group whereas the hepatic cholesteryl ester concentration was higher. Cholesterol 7α hydroxylase activity was lower in the ML and M groups than in the LA and LM groups while the sterol 27 hydroxylase and 3-hydroxy-3-methyl glutaryl coenzyme A reductase activities were not modulated by dietary myristic acid. This is the first time a negative correlation has been observed between the HDL-cholesterol concentration and the hepatic mass of SR-BI (r-0·69;P<0·0001) under physiological conditions. An inverse linear regression was also shown between SR-BI and the percentage of myristic acid in the diet (r-0·75;P<0·0001). The hepatic mass of SR-BI in the M group had increased at the end of the post-period compared with the test-period values. The present investigation shows that myristic acid modulates HDL-cholesterol via a regulation of the SR-BI expression.

Butter naturally enriched in conjugated linoleic acid and vaccenic acid alters tissue fatty acids and improves the plasma lipoprotein profile in cholesterol-fed hamsters

Butter, which is naturally enriched in cis-9, trans-11 conjugated linoleic acid (rumenic acid; RA) and vaccenic acid (VA), has been shown to be an effective anticarcinogen in studies with animal models; however, there has been no examination of the effects of a naturally derived source of VA and RA on atherosclerosis-related biomarkers. The current study was designed to determine the effect of a diet containing VA/RA-enriched butter on plasma lipoproteins and tissue fatty acid profiles in cholesterol-fed hamsters. Male Golden Syrian hamsters were fed diets containing 0.2% cholesterol and 20% added fat as: 1) Control, 20% standard butter (CT); 2) 5% standard butter + 15% VA/RA-enriched butter (EB); 3) 15% standard butter + 5% partially-hydrogenated vegetable oil (VO). After 4 wk, plasma lipoproteins were isolated, cholesterol quantified, and tissue fatty acid profiles determined. Tissue concentrations of VA and RA were increased by consumption of the EB diet compared with both the CT and VO diets, whereas the VO diet increased their concentration compared with the CT diet only. Total and LDL cholesterol concentrations were significantly reduced in hamsters fed EB and VO compared with CT, whereas VLDL cholesterol concentrations were reduced in hamsters fed EB compared with those fed CT and VO. HDL cholesterol concentrations did not differ among treatments. The ratio of potentially atherogenic lipoproteins [VLDL + intermediate density lipoproteins (IDL) + LDL] to antiatherogenic HDL was significantly lower in hamsters fed VA/RA-enriched butter (0.60) than in those fed either control diet (1.70) or the diet containing partially hydrogenated vegetable oil (1.04). Thus, increasing the VA/RA concentration of butter results in a plasma lipoprotein cholesterol profile that is associated with a reduced risk of atherosclerosis.

Effect of a modified milk fat and calcium in purified diets on cholesterol metabolism in hamsters

Modification of milk fat both by partially replacing saturated FA with oleic acid (18:1) and by increasing calcium intake independently reduces plasma cholesterol. Whether modification of both factors together would synergistically reduce plasma cholesterol is unknown. Seventy-two male golden Syrian hamsters were separated into four diet treatment groups (n = 18/group) and fed ad libitum for 7 wk. Diets contained either modified milk fat (MMF) or regular milk fat (RMF) with either 0.5% (MMF and RMF) or 1.3% calcium (w/w) (MMFC and RMFC). All diets contained 11% test fat, 4% soybean oil, and 0.15% cholesterol (w/w). During the last week, feces were collected for three consecutive days for analysis of fecal FA, cholesterol, and calcium excretion. Overnight-fasted animals were sacrificed, and plasma and livers were collected for lipid analysis. Neither MMF nor additional calcium significantly affected plasma lipids. However, significant interactions existed between MMF and additional calcium for the ratio of LDL cholesterol to HDL cholesterol (LDL/HDL), indicating that increased calcium intake reduced this ratio only in RMF animals. In addition, MMF reduced LDL/HDL relative to RMF. MMF significantly increased hepatic total and esterified cholesterol. Additional calcium significantly increased fecal calcium and saturated FA (SFA) excretion, whereas MMF significantly reduced SFA excretion. RMFC induced the highest excretion of 16:0 among all groups. Replacement of SFA with 18:1 in the MMF reduced the impact of high calcium on LDL/HDL. Additional calcium reduced LDL/HDL only in the presence of RMF, which may be achieved through an increased excretion of 16:0.

Hyperlipidaemic effect of fish oil in Bio F1B hamsters

We investigated the dietary influence of low and high levels of fish oil, supplemented with or without dietary cholesterol, on the plasma lipoprotein profile in Bio F1B hamsters, a model susceptible to diet-induced hyperlipidaemia. The MIX diet, a diet supplemented with a mixture of lard and safflower-seed oil, was used as the control diet to maintain the saturated MUFA and PUFA levels similar to the fish-oil diet. The animals were fed the specific diets for 2 weeks and fasted for 14 h before killing. The plasma from the animals fed high levels of fish oil was milky and rich in chylomicron-like particles. The plasma total cholesterol, VLDL- and LDL-cholesterol and -triacylglycerol concentrations were significantly higher, whereas HDL-cholesterol was lower in hamsters fed fish oil compared with the MIX-diet-fed hamsters. Increasing the amount of fat in the diet increased plasma lipids in both the fish-oil- and the MIX-diet-fed hamsters; however, this hyperlipidaemic effect of dietary fat level was greater in the hamsters fed the fish-oil diet. The hepatic lipid concentrations were not dramatically different between the fish-oil-fed and the MIX-diet-fed hamsters. However, the hepatic LDL-receptor mRNA levels were significantly low in the fish-oil-fed hamsters compared with the MIX-diet-fed hamsters. Increasing the amount of fish oil in the diet further decreased the hepatic LDL-receptor mRNA expression. It is concluded that F1B hamsters are susceptible to fish-oil-induced hyperlipidaemia, especially at high fat levels, and this increase is partially explained by the inhibition of hepatic LDL-receptor mRNA expression.

Dietary cholesterol reduces lipoprotein lipase activity in the atherosclerosis-susceptible Bio F(1)B hamster

We have compared lipoprotein metabolism in, and susceptibility to atherosclerosis of, two strains of male Golden Syrian hamster, the Bio F(1)B hybrid and the dominant spot normal inbred (DSNI) strain. When fed a normal low-fat diet containing approximately 40 g fat and 0.3 g cholesterol/kg, triacylglycerol-rich lipoprotein (chylomicron+VLDL) and HDL-cholesterol were significantly higher (P<0.001) in Bio F(1)B hamsters than DSNI hamsters. When this diet was supplemented with 150 g coconut oil and either 0.5 or 5.0 g cholesterol/kg, significant differences were seen in response. In particular, the high-cholesterol diet produced significantly greater increases in plasma cholesterol and triacylglycerol in the Bio F(1)B compared with the DSNI animals (P=0.002 and P<0.001 for cholesterol and triacylglycerol, respectively). This was particularly dramatic in non-fasting animals, suggesting an accumulation of chylomicrons. In a second experiment, animals were fed 150 g coconut oil/kg and 5.0 g cholesterol/kg for 6 and 12 months. Again, the Bio F(1)B animals showed dramatic increases in plasma cholesterol and triacylglycerol, and this was confirmed as primarily due to a rise in chylomicron concentration. Post-heparin lipoprotein lipase activity was significantly reduced (P<0.001) in the Bio F(1)B compared with the DSNI animals at 6 months, and virtually absent at 12 months. Bio F(1)B animals were also shown to develop significantly more (P<0.001) atherosclerosis. These results indicate that, in the Bio F(1)B hybrid hamster, cholesterol feeding reduces lipoprotein lipase activity, thereby causing the accumulation of chylomicrons that may be associated with their increased susceptibility to atherosclerosis.

A role for smooth endoplasmic reticulum membrane cholesterol ester in determining the intracellular location and regulation of sterol-regulatory-element-binding protein-2

Cellular cholesterol homoeostasis is regulated through proteolysis of the membrane-bound precursor sterol-regulatory-element-binding protein (SREBP) that releases the mature transcription factor form, which regulates gene expression. Our aim was to identify the nature and intracellular site of the putative sterol-regulatory pool which regulates SREBP proteolysis in hamster liver. Cholesterol metabolism was modulated by feeding hamsters control chow, or a cholesterol-enriched diet, or by treatment with simvastatin or with the oral acyl-CoA:cholesterol acyltransferase inhibitor C1-1011 plus cholesterol. The effects of the different treatments on SREBP activation were confirmed by determination of the mRNAs for the low-density lipoprotein receptor and hydroxymethylglutaryl-CoA (HMG-CoA) reductase and by measurement of HMG-CoA reductase activity. The endoplasmic reticulum was isolated from livers and separated into subfractions by centrifugation in self-generating iodixanol gradients. Immunodetectable SREBP-2 accumulated in the smooth endoplasmic reticulum of cholesterol-fed animals. Cholesterol ester levels of the smooth endoplasmic reticulum membrane (but not the cholesterol levels) increased after cholesterol feeding and fell after treatment with simvastatin or C1-1011. The results suggest that an increased cellular cholesterol load causes accumulation of SREBP-2 in the smooth endoplasmic reticulum and, therefore, that membrane cholesterol ester may be one signal allowing exit of the SREBP-2/SREBP-cleavage-regulating protein complex to the Golgi.

Interactive effects of dietary cholesterol and different saturated fatty acids on lipoprotein metabolism in the hamster

The present study examines the interactive effects of three fatty acids: myristic, palmitic and stearic acids, with dietary cholesterol, on lipoprotein metabolism in the hamster. Each saturated fatty acid was fed at a concentration of 100 g pure synthetic triacylglycerol/kg in the presence of 100 g triolein/kg and was fed in the presence of 0.05, 1.2 or 2.4 g dietary cholesterol/kg. Dietary cholesterol increased the concentration of cholesterol in each of the major plasma lipoprotein fractions. The largest effects on VLDL and LDL were seen in the presence of tripalmitin where the increase between the lowest and highest dietary cholesterol groups were 129% and 38% respectively. In contrast, HDL showed the greatest change in the tristearin group when the equivalent increase was 59%. No interactive effects of dietary cholesterol and fat were seen on hepatic mRNA concentrations for the LDL receptor, hydroxymethylglutaryl-CoA reductase or the microsomal triacylglycerol transfer protein. As the amount of cholesterol in the diet increased, large differences were seen in the storage of hepatic cholesterol ester. At the highest dietary cholesterol intake the amount of hepatic cholesterol ester was 1.7-fold higher in the animals fed trimyristin compared with those fed tripalmitin. These results suggest that, as the amount of cholesterol in the diet is increased, palmitic acid becomes more hypercholesterolaemic. This is associated with a reduced ability to store cholesterol ester in the liver.

Modulation of the regression of atherosclerosis in the hamster by dietary lipids: comparison of coconut oil and olive oil

The Golden Syrian hamster (Mesocricetus auratus) has been shown to be a useful model of both human lipoprotein metabolism and the development of atherosclerosis. We report the effects of dietary lipids on the progression and regression of atherosclerosis in this model. In the first study, hamsters fed on coconut oil (150 g/kg diet) and cholesterol (30 g/kg diet) developed lipid-rich lesions in the ascending aorta (0.28 (SD 0.14) mm2) and aortic arch (0.01 (SD 0.01) mm2) after 4 weeks that continued to progress over the next 8 weeks (0.75 (SD 0.41) mm2 and 0.12 (SD 0.11) mm2 for the ascending aorta and aortic arch respectively). Removal of cholesterol from the diet halted this progression. Furthermore, in animals fed on olive oil in the absence of added cholesterol, plasma LDL-cholesterol concentrations were lower (P < 0.05) and the extent of atherosclerotic lesions was reduced (P < 0.001 for both regions of the aorta) compared with animals fed on coconut oil (with no added cholesterol). In a second study, animals were fed on the atherogenic diet for 10 weeks, transferred to diets containing either coconut oil (150 g/kg diet) or olive oil (150 g/kg diet) without added cholesterol and monitored for up to 16 weeks. In the ascending aorta, lesion size doubled in animals fed on coconut oil but stabilized in those fed on olive oil. In the aortic arch, lesion size decreased linearly (P < 0.05, P < 0.001 for coconut oil and olive oil respectively) with the greatest reduction being seen in the olive-oil-fed animals (P < 0.05). Again, progression and regression of atherosclerosis appeared to reflect the relative concentrations of LDL-cholesterol and HDL-cholesterol in the plasma. We conclude that the male Golden Syrian hamster represents a useful model of dietary induced regression as well as progression of atherosclerosis.

(n-3) fatty acid supplementation in moderately hypertriglyceridemic adults changes postprandial lipid and apolipoprotein B responses to a standardized test meal

The effects of (n-3) fatty acids on the postprandial state were investigated by monitoring the alimentary responses to identical test meals fed to adults [n = 11; fasting triacylglycerol (TG) 2.55 +/- 0.24 mmol/L; mean +/- SEM] after a self-selected diet baseline period (BLP) and then after a 6-wk (n-3) fatty acid period (FOP) [ approximately 5.2 g (n-3) fatty acids] and a 6-wk control oil period (COP) administered in random order. Samples were drawn immediately prior to the test meal (time 0) and then hourly from 2 to 6 h postmeal. Postprandial plasma triacylglycerol (TG) and TG-rich lipoprotein (TRL) TG apo B48, and B100 absolute concentrations were significantly lower after FOP than after COP or BLP, while plasma cholesterol was unchanged. Normalizing the results as increments over time 0 eliminated the diet effect on all but plasma TG. Time remained a significant effect for plasma TG, TRL TG, and TRL TC. Finally, only absolute TRL B48 and absolute and incremental plasma TG concentrations displayed significant time-diet interactions. These results suggest that postprandial TRL apo B reductions are likely caused by (n-3) fatty acid suppression of both hepatic and intestinal apoB secretion/synthesis. Altered TRL metabolism, i.e. changes in postprandial TG, cholesterol, apo B48, and increase in LDL particle size, may represent an additional mechanism for the reduced heart disease risk associated with fish [(n-3) fatty acid] consumption.

Fatty acids: links between genes involved in fatty acid and cholesterol metabolism

Fatty acids are a major constituent of dietary fats and form an integral part of the cellular membrane and lipoproteins. The gene regulatory potential of fatty acids has long been recognized, but the precise regulatory mechanisms are unknown. The regulatory ability of fatty acids on the expression of a number of genes together with potential mechanisms and pathways of regulation are reviewed. In this review, we emphasize a key aspect of regulation mediated by the sterol regulatory element binding-protein, and its effects on sterol regulatory elements.

Administration of n-3 fatty acids in the diets of rats or directly to hepatocyte cultures results in different effects on hepatocellular ApoB metabolism and secretion

Hepatocytes derived either from rats fed a diet enriched in n-3 fatty acids or from rats fed a low-fat diet and cultured with an n-3 fatty acid (eicosapentaenoic acid, EPA) in vitro were used to distinguish between the dietary effects and the direct effects of n-3 fatty acids on hepatocellular apolipoprotein (apo) B metabolism and secretion. ApoB-48 and apoB-100 synthesis, degradation, and secretion as large (d<1.006) and small (d>1.006) particles were determined after a pulse label with [35S]methionine. These effects were compared with changes in triacylglycerol (TAG) synthesis and secretion and with changes in de novo fatty acid synthesis (using 3H2O incorporation) under identical conditions. When n-3 fatty acid was given via the dietary route, apoB-48 very low density lipoprotein (VLDL) secretion was inhibited, but there was no effect on the secretion of apoB-100 VLDL. There was no effect on the secretion of either apoB-48 or apoB-100 as small, dense particles (d>1.006). Cellular TAG synthesis was significantly inhibited under these conditions, and fatty acid synthesis de novo was inhibited by 80%. By contrast, after direct addition of EPA to hepatocytes from normal rats, the secretion of both apoB-48 and apoB-100 VLDL was suppressed. The secretion of apoB-48, but not of apoB-100, as dense particles was also inhibited. However, there was little or no effect on TAG synthesis nor on fatty acid synthesis de novo. In addition, whereas dietary administration of n-3 fatty acid gave rise to decreased net synthesis and degradation of apoB-48, direct administration in vitro resulted in increased degradation with no effect on net synthesis. We conclude that the effects of n-3 fatty acids on hepatic lipid and apoB metabolism differ according to whether they are administered in vivo, via the dietary route, or in vitro, via direct addition to hepatocyte cultures.

The influence of dietary saturated and unsaturated fat on hepatic cholesterol metabolism and the biliary excretion of chylomicron cholesterol in the rat

The biliary excretion of [3H] cholesterol carried in chylomicrons derived from palm oil (rich in long chain saturated fatty acids), olive oil (rich in monounsaturated fatty acids) or corn oil (rich in n-6 polyunsaturated fatty acids was studied in vivo in rats fed the corresponding oil in the diet for 21 days. The secretion of radioactivity into bile as both bile acids and unesterified cholesterol was significantly slower in the animals fed palm oil as compared to those given olive or corn oil, indicating that dietary saturated fat retards the excretion of cholesterol from the diet as compared to mono- or n-6 polyunsaturated fat. In order to investigate the mechanisms underlying these differences, the influence of the three high fat diets on cholesterol esterification, cholesteryl ester hydrolysis and bile acid synthesis in the liver and on biliary lipid output were also measured. The ratio of cholesterol esterification to cholesteryl ester hydrolysis was markedly raised in the olive and corn oil-fed as compared to palm oil-fed animals. Biliary cholesterol secretion was higher in corn oil-fed rats than in those fed olive or palm oil or a low fat diet, and this was associated with a markedly increased lithogenic index in these animals. The activity of cholesterol 7alpha hydroxylase was higher in the olive and corn oil-fed than in the palm oil-fed animals, although the expression of mRNA for the enzyme was increased only in the olive oil diet group. After 20 h biliary drainage, the rate of bile acid secretion into bile was increased in the rats fed olive and corn oil rather than to palm oil. These findings indicate that feeding rats mono- or n-6 polyunsaturated as compared to saturated fat in the diet promotes the storage of cholesteryl ester in the liver and leads to increased bile acid synthesis, resulting in the more rapid excretion of cholesterol originating from the diet via the bile.

The effect of different dietary fatty acids on lipoprotein metabolism: concentration-dependent effects of diets enriched in oleic, myristic, palmitic and stearic acids

While it is well established that the fatty acid composition of dietary fat is important in determining plasma lipoprotein cholesterol concentrations, the effects of changing the absolute quantities of the individual fatty acids are less clear. In the present study Golden Syrian hamsters were fed on isoenergetic, low cholesterol (0.05 g/kg) diets containing 100, 150 or 200 g added fat/kg. This consisted of triolein (TO) alone, or equal proportions of TO and either trimyristin (TM), tripalmitin (TP) or tristearin (TS). Each trial also included a control group fed on a diet containing 50 g TO/kg. As the mass of TO in the diet increased, plasma VLDL-cholesterol concentrations rose. The TM-rich diets produced a concentration-dependent increase in total plasma cholesterol which was a result of significant increases in both VLDL and HDL levels. The TP-rich diets increased plasma LDL- and HDL-cholesterol levels in a concentration-dependent manner. TS-containing diets did not increase the cholesterol content of any of the major lipoprotein fractions. Hepatic LDL-receptor mRNA concentrations were significantly decreased in animals fed on TP, while apolipoprotein B mRNA concentrations were significantly increased. Thus, on a low-cholesterol diet, increasing the absolute amount of dietary palmitic acid increases LDL-cholesterol more than either myristic or stearic acid. These effects on lipoprotein metabolism may be exerted through specific modulation of the expression of the LDL receptor and apolipoprotein B genes.

Effects of soy protein on plasma cholesterol and bile acid excretion in hamsters

The effect of dietary casein and soy protein on lipoprotein metabolism was compared in the Golden Syrian hamster (Mesocricetus auratus). Total plasma cholesterol was similar in animals fed either protein, but significant differences were seen in lipoprotein profile. In animals fed soy protein, cholesterol concentrations were lower in very-low-density lipoproteins (VLDL) but higher in low-density and high-density lipoproteins, compared with those fed casein. Significant differences were also seen depending on the nutritional state of the animals. In casein-fed hamsters, total plasma triacylglycerol and chylomicron + VLDL cholesterol and triacylglycerol were significantly higher when blood was collected during feeding, compared with animals that had been fasted overnight. By contrast, no significant change was seen in animals on the soy protein diet. This suggests that either intestinally derived lipoproteins are more rapidly cleared on the soy protein diet or that soy inhibits feeding-induced VLDL secretion. Fecal bile acid excretion was higher in the soy protein group, and there was a significant correlation between soy intake and bile acid excretion. Hepatic cholesterol decreased as the amount of soy protein consumed increased, suggesting that it is this pool of cholesterol that is used to replace the excreted bile acids. No significant difference was seen in plasma insulin or glucagon between hamsters fed the two proteins. Plasma triiodothyronine concentrations were, however, significantly higher and thyroxine concentrations lower in the soy protein-fed animals. This study shows specific effects of dietary proteins on plasma lipoprotein concentrations dependent on nutritional status of the animal.

Genetic determinants of plasma lipoprotein levels and their dietary response

Hamsters were fed diets containing fat (5-20%, w/w) consisting of triolein (TO) alone or 50% triolein plus 50% trimyristin (TM), tripalmitin (TP) or tristearin (TS) for 28 days. Each fat had unique effects on lipoprotein concentrations which were related to changes in the expression of hepatic genes. Tripalmitin was the most hypercholesterolaemic of the saturated fats, causing dose-dependent increases in LDL and HDL cholesterol which correlated with decreases in the expression of HMGCoA reductase and LDL receptor genes. Tripalmitin also increased the expression of the apoB gene. It seems likely that fatty acids may regulate genes which are involved both in the synthesis and clearance of plasma lipoproteins. Inclusion of increasing amounts of cholesterol in diets containing 20% fat (50% TO plus 50% TP or TS) caused down-regulation of HMGCoAR and LDLR genes and up-regulation of the microsomal triglyceride transfer protein (MTP) gene for both fats. This was accompanied by increased LDL-cholesterol in the TP but not the TS group. In all experiments the concentration of VLDL-cholesterol correlated with the hepatic cholesterylester and MTP mRNA concentrations.

Decreased secretion of very-low-density lipoprotein triacylglycerol and apolipoprotein B is associated with decreased intracellular triacylglycerol lipolysis in hepatocytes derived from rats fed orotic acid or n-3 fatty acids

Hepatocytes from rats fed a chow (control) diet or from rats fed a chow diet supplemented with either orotic acid (OA; 1%, w/w) or fish oil (FO; 20%, v/w) were maintained in culture for periods up to 48 h. during the first 24 h period, the low rates of output of very-low-density lipoprotein (VLDL)-associated triacylglycerol (TAG) and apolipoprotein B (apoB) in hepatocytes from the FO- and OA-fed animals were associated with significantly lower rates of intracellular TAG lipolysis and re-esterification. Most of the VLDL TAG secreted was mobilized via lipolysis of the intracellular TAG pool, but the proportion of VLDL TAG secreted via this route in cells from the FO-fed and OA-fed animals was decreased compared with that in the control-fed animals' cells. In the presence of exogenous oleate the inhibitory effect of OA feeding on VLDL apoB and TAG secretion persisted in the derived hepatocytes for up to 48 h following isolation. However, when oleate was absent no inhibitory effect on the secretion of TAG and apoB was observed between 24 and 48 h. Under these conditions the rate of intracellular TAG turnover returned to normal. The initial inhibitory effect of FO feeding on VLDL TAG and apoB secretion did not persist in the derived hepatocytes between 24 h and 48 h of culture in the presence of exogenous oleate. Although intracellular TAG lipolysis and VLDL TAG and apoB secretion rates appear to be positively correlated, a causal relationship has not been conclusively established.

Hepatic microsomal triglyceride transfer protein messenger RNA concentrations are increased by dietary cholesterol in hamsters

In hamsters fed high fat diets enriched in trimyristin, tripalmitin or tristearin, increased dietary cholesterol content was associated with increased plasma concentrations of very low density lipoprotein (VLDL) cholesterol and triacylglycerol (p < 0.0001 and p = 0.0017, respectively). Hepatic microsomal triglyceride transfer protein (MTP) mRNA concentration also increased (p < 0.0001), independent of the nature of dietary fat, and was significantly correlated with the plasma VLDL lipid concentrations (p = 0.0002 and p = 0.0106 for cholesterol and triacylglycerol, respectively) and hepatic cholesterol concentrations. Increased expression of the MTP gene may be part of a coordinated response to hepatic cholesterol accumulation leading to increased VLDL lipid secretion.

Metabolic fate of oleic acid, palmitic acid and stearic acid in cultured hamster hepatocytes

Unlike other saturated fatty acids, dietary stearic acid does not appear to raise plasma cholesterol. The reason for this remains to be established, although it appears that it must be related to inherent differences in the metabolism of the fatty acid. In the present study, we have looked at the metabolism of palmitic acid and stearic acid, in comparison with oleic acid, by cultured hamster hepatocytes. Stearic acid was taken up more slowly and was poorly incorporated into both cellular and secreted triacylglycerol. Despite this, stearic acid stimulated the synthesis and secretion of triacylglycerol to the same extent as the other fatty acids. Incorporation into cellular phospholipid was lower for oleic acid than for palmitic acid and stearic acid. Desaturation of stearic acid, to monounsaturated fatty acid, was found to be greater than that of palmitic acid. Oleic acid produced from stearic acid was incorporated into both triacylglycerol and phospholipid, representing 13% and 6% respectively of the total after a 4 h incubation. Significant proportions of all of the fatty acids were oxidized, primarily to form ketone bodies, but by 8 h more oleic acid had been oxidized compared with palmitic acid and stearic acid.