Saturated fatty acids and LDL receptor modulation in humans and monkeys

Association Between Ultraprocessed Food Consumption and Metabolic Disorders in Children and Adolescents with Obesity

BACKGROUND/OBJECTIVES

We investigated the effects of ultraprocessed food (UPF) consumption on metabolic disorders (e.g., adiposity, metabolic associated steatotic liver disease [MASLD], and insulin resistance) in children and adolescents with obesity to improve dietary guidelines and public health strategies.

METHODS

The dietary intake of 149 participants (aged 8-17 years) was assessed with food diaries. The NOVA classification system was used to classify food according to the degree of processing. Metabolic outcomes, including the fat mass index (FMI), hepatic fat percentage, and insulin resistance, were measured via dual-energy X-ray absorptiometry (DXA), magnetic resonance imaging proton density fat fraction (MRI-PDFF), and biochemical analysis, respectively.

RESULTS

Greater UPF consumption from baseline to the 6-month follow-up was significantly associated with increased insulin and decreased total cholesterol and LDL-cholesterol. UPF consumption was positively associated with the prevalence of MASLD (liver MRI-PDFF ≥ 5%; odds ratio T3 vs. T1 = 1.75; 95% confidence interval [CI] 1.03, 3.00), moderate-to-severe MASLD (liver MRI-PDFF ≥ 10%; OR T3 vs. T1 = 4.19; 95% CI 1.72, 10.22), and insulin resistance (OR T3 vs. T1 = 2.44; 95% CI 1.33, 4.48), after adjusting for covariates. A linear dose-response relationship was observed between UPF consumption and the odds of moderate-to-severe MASLD and insulin resistance.

CONCLUSIONS

Greater UPF consumption was strongly associated with MASLD and insulin resistance in children and adolescents with obesity, underscoring the importance of reducing UPF consumption through dietary guidelines and public health interventions to mitigate the risk of obesity-related metabolic conditions in young populations.

Feeding of palm oil fatty acids or rapeseed oil throughout lactation: Effects on mammary gene expression and milk production in Norwegian dairy goats

Lipid added as rapeseed or palm oil to the diet of dairy goats over 8 mo of one lactation alters fat secretion and milk fatty acid (FA) and protein composition. In this study, we examined the contribution of mammary gene expression to these changes and included 30 multiparous goats of Norwegian dairy goat breed for a 230-d experimental period, with indoor feeding from 1 to 120 d in milk (DIM), mountain grazing from 120 to 200 DIM, and indoor feeding from 200 to 230 DIM. After an initial period (1-60 DIM) when the control diet was given to all goats, the animals were subdivided into 3 groups of 10 goats. Treatments (60-230 DIM) were basal concentrate (control) alone or supplemented with either 8% (by weight) hydrogenated palm oil enriched with palmitic acid (POFA) or 8% (by weight) rapeseed oil (RSO). Milk was sampled individually from all animals throughout lactation, at 60, 120, 190, and 230 DIM for milk yield and composition. On d 60, 120, 190, and 230, mammary tissue was collected by biopsy to measure mRNA abundance of 19 key genes. None of the 19 genes involved in milk protein, apoptosis, lipid metabolism, transcription factors, and protein of the milk fat globule membrane, as measured by mRNA abundance, were affected by the lipid supplements, although POFA increased milk fat content, and POFA and RSO affected milk FA composition. Over the experimental period (120-230 DIM), the mRNA abundance of 13 of the 19 studied genes was affected by lactation stage. For some genes, expression either gradually increased from 120 to 230 DIM (CSN2,CASP8,CD36,GLUT4) or increased from 120 to 200 and then remained stable (XDH), or decreased (CSN3,G6PD,SREBF1,PPARG1) or increased only at 230 DIM (SCD1,SCD5,ELF3). For a second group of genes (CSN1, LALBA, FABP3, FASN, LPL, MFGE8), expression was stable over the lactation period. Our results suggest that factors other than gene expression, such as substrate availability or posttranscriptional regulation of these genes, could play an important role in the milk fat and FA responses to dietary fat composition in the goat. In conclusion, mammary gene expression in goats was more regulated by stage of lactation than by the dietary treatments applied.

Myristic Acid Supplementation Aggravates High Fat Diet-Induced Adipose Inflammation and Systemic Insulin Resistance in Mice

Saturated fatty acids (SFAs) are considered to be detrimental to human health. One of the SFAs, myristic acid (MA), is known to exert a hypercholesterolemic effect in mice as well as humans. However, its effects on altering adipose tissue (AT) inflammation and systemic insulin resistance (IR) in obesity are still unclear. Here, we sought to determine the effects of a high fat (HF) diet supplemented with MA on obesity-associated metabolic disorders in mice. Wild-type C57BL/6 mice were fed a HF diet in the presence or absence of 3% MA for 12 weeks. Plasma lipids, plasma adipokines, AT inflammation, systemic IR, glucose homeostasis, and hepatic steatosis were assessed. The body weight and visceral adipose tissue (VAT) mass were significantly higher in mice receiving the HF+MA diet compared to HF diet-fed controls. Plasma total cholesterol levels were marginally increased in HF+MA-fed mice compared to controls. Fasting blood glucose was comparable between HF and HF+MA-fed mice. Interestingly, the plasma insulin and HOMA-IR index, a measure of insulin resistance, were significantly higher in HF+MA-fed mice compared to HF controls. Macrophage and inflammatory markers were significantly elevated in the AT and AT-derived stromal vascular cells upon MA feeding. Moreover, the level of circulating resistin, an adipokine promoting insulin resistance, was significantly higher in HF+MA-fed mice compared with HF controls. The insulin tolerance test revealed that the IR was higher in mice receiving the MA supplementation compared to HF controls. Moreover, the glucose tolerance test showed impairment in systemic glucose homeostasis in MA-fed mice. Analyses of liver samples showed a trend towards an increase in liver TG upon MA feeding. However, markers of oxidative stress and inflammation were reduced in the liver of mice fed an MA diet compared to controls. Taken together, our data suggest that chronic administration of MA in diet exacerbates obesity-associated insulin resistance and this effect is mediated in part, via increased AT inflammation and increased secretion of resistin.

Hepatocellular BChE as a therapeutic target to ameliorate hypercholesterolemia through PRMT5 selective degradation to restore LDL receptor transcription

AIMS

Individuals with nonalcoholic hepatosteatosis (NAFLD) have a worse atherogenic lipoprotein profile and are susceptible to cardiovascular diseases. The MEK-ERK signaling cascades are central regulators of the levels of LDL receptor (LDLR), a major determinant of circulating cholesterol. It is elusive how hepatic steatosis contributes to dyslipidemia, especially hypercholesterolemia.

MAIN METHODS

The effects of BChE on signaling pathways were determined by immunoblotting in a BChE knockout hepatocyte cell line. DiI-LDL probe was used to explore the effect of BChE expression on LDL internalization. Co-immunoprecipitation and LC-MS were used to explore the interacting proteins with BChE. Finally, a hepatocyte-restricted BChE silencing mouse model was established by AAV8-Tbg-shRNA, and the hypercholesterolemia was induced by 65% kcal% high-fat, high-sucrose diet feeding.

MAIN FINDINGS

Here we demonstrate that butyrylcholinesterase (BChE) governs the LDL receptor levels and LDL uptake capacity through the MEK-ERK signaling cascades to promote Ldlr transcription. BChE interacts and co-localizes with PRMT5, a protein methylation modifier controlling the ERK signaling. PRMT5 regulates LDLR-dependent LDL uptake and is a substrate of chaperone-mediated autophagy (CMA). BChE deficiency induces the PRTM5 degradation dependent on CMA activity, possibly through facilitating the HSC70 (Heat shock cognate 71 kDa) recognition of PRMT5. Remarkably, in vivo hepatocyte-restricted BChE silencing reduces plasma cholesterol levels substantially. In contrast, the BChE knockout mice are predisposed to hypercholesterolemia.

SIGNIFICANCE

Taken together, these findings outline a regulatory role for the BChE-PRMT5-ERK-LDLR axis in hepatocyte cholesterol metabolism, and suggest that targeting liver BChE is an effective therapeutic strategy to treat hypercholesterolemia.

High Consumption of Ultra-Processed Food is Associated with Incident Dyslipidemia: A Prospective Study of Older Adults

BACKGROUND

Ultra-processed food (UPF) consumption has been associated with higher cardiovascular disease (CVD) and mortality risks.

OBJECTIVES

The aim of this study was to assess the relationship between UPF consumption and incident dyslipidemia in older adults, where evidence is limited.

METHODS

We studied a prospective cohort of 1082 community-dwelling adults in Spain, older than 60 (mean age, 68 ± 6 years old). Participants (52% were women) were recruited between 2008-10 and followed up to 2015. At baseline, food intake data were collected using a validated computerized face-to-face dietary history. UPFs were identified according to the nature and extent of their industrial processing (NOVA classification). Triglycerides, HDL cholesterol, and LDL cholesterol were measured in fasting plasma samples collected at baseline and at follow-up. Statistical analyses were performed with logistic regression adjusted for the main potential confounders.

RESULTS

Among those free of corresponding dyslipidemia at baseline, and after a follow-up of between 5 to 7 years, 60 (out of 895) developed incident hypertriglyceridemia (≥150 mg/dL), 112 (out of 878) had low HDL cholesterol (<40 in men/<50 mg/dL in women), and 54 (out of 472) had high LDL cholesterol (>129 mg/dL). The mean percentage of UPF consumption was 19% ± 11% of total energy intake. Those in the highest versus the lowest tertile of energy intake from UPFs had more than twice the odds of incident hypertriglyceridemia (OR, 2.66; 95% CI: 1.20-5.90; P-trend, 0.011) or low HDL cholesterol (OR, 2.23; 95% CI: 1.22-4.05; P-trend, 0.012). UPF consumption was not associated with high LDL cholesterol plasma concentrations.

CONCLUSIONS

Although UPF consumption in Spain was low among older adults, high consumption of UPFs was clearly associated with incident dyslipidemia. The increase in CVD risk recently found to be associated with UPF consumption might be mediated by these atherogenic lipid abnormalities.

Saturated Fats Versus Polyunsaturated Fats Versus Carbohydrates for Cardiovascular Disease Prevention and Treatment

The effects of saturated fatty acids (SFAs) on cardiovascular disease (CVD) risk are modulated by the nutrients that replace them and their food matrices. Replacement of SFAs with polyunsaturated fatty acids has been associated with reduced CVD risk, although there is heterogeneity in both fatty acid categories. In contrast, replacement of SFAs with carbohydrates, particularly sugar, has been associated with no improvement or even a worsening of CVD risk, at least in part through effects on atherogenic dyslipidemia, a cluster of traits including small, dense low-density lipoprotein particles. The effects of dietary SFAs on insulin sensitivity, inflammation, vascular function, and thrombosis are less clear. There is growing evidence that SFAs in the context of dairy foods, particularly fermented dairy products, have neutral or inverse associations with CVD. Overall dietary patterns emphasizing vegetables, fish, nuts, and whole versus processed grains form the basis of heart-healthy eating and should supersede a focus on macronutrient composition.

Computationally Modeling Lipid Metabolism and Aging: A Mini-review

One of the greatest challenges in biology is to improve the understanding of the mechanisms which underpin aging and how these affect health. The need to better understand aging is amplified by demographic changes, which have caused a gradual increase in the global population of older people. Aging western populations have resulted in a rise in the prevalence of age-related pathologies. Of these diseases, cardiovascular disease is the most common underlying condition in older people. The dysregulation of lipid metabolism due to aging impinges significantly on cardiovascular health. However, the multifaceted nature of lipid metabolism and the complexities of its interaction with aging make it challenging to understand by conventional means. To address this challenge computational modeling, a key component of the systems biology paradigm is being used to study the dynamics of lipid metabolism. This mini-review briefly outlines the key regulators of lipid metabolism, their dysregulation, and how computational modeling is being used to gain an increased insight into this system.

A diet enriched in docosahexanoic Acid exacerbates brain parenchymal extravasation of apo B lipoproteins induced by chronic ingestion of saturated fats

Chronic ingestion of saturated fatty acids (SFAs) was previously shown to compromise blood-brain barrier integrity, leading to brain parenchymal extravasation of apolipoprotein B (apo B) lipoproteins enriched in amyloid beta. In contrast, diets enriched in mono- or polyunsaturated (PUFA) oils had no detrimental effect. Rather, n3 and n6 oils generally confer protection via suppression of inflammation. This study investigated in wild-type mice if a PUFA diet enriched in docosahexanoic acid (DHA) restored blood-brain barrier integrity and attenuated parenchymal apo B abundance induced by chronic ingestion of SFA. Cerebrovascular leakage of apo B was quantitated utilising immunofluorescent staining. The plasma concentration of brain-derived S100β was measured as a marker of cerebrovascular inflammation. In mice fed SFA for 3 months, provision thereafter of a DHA-enriched diet exacerbated parenchymal apo B retention, concomitant with a significant increase in plasma cholesterol. In contrast, provision of a low-fat diet following chronic SFA feeding had no effect on SFA-induced parenchymal apo B. The findings suggest that in a heightened state of cerebrovascular inflammation, the provision of unsaturated fatty acids may be detrimental, possibly as a consequence of a greater susceptibility for oxidation.

Bioactivities of glycoalkaloids and their aglycones from Solanum species

Potatoes, tomatoes, and aubergines are all species of the Solanum genus and contain a vast array of secondary metabolites including calystegine alkaloids, phenolic compounds, lectins, and glycoalkaloids. Glycoalkaloids have been the subject of many literature papers, occur widely in the human diet, and are known to induce toxicity. Therefore, from a food safety perspective further information is required regarding their analysis, toxicity, and bioavailability. This is especially important in crop cultivars derived from wild species to prevent glycoalkaloid-induced toxicity. A comprehensive review of the bioactivity of glycoalkaloids and their aglycones of the Solanum species, particularly focused on comparison of their bioactivities including their anticancer, anticholesterol, antimicrobial, anti-inflammatory, antinociceptive, and antipyretic effects, toxicity, and synergism of action of the principal Solanum glycoalkaloids, correlated to differences of their individual molecular structures is presented.

Saturated fatty acids and risk of coronary heart disease: modulation by replacement nutrients

Despite the well-established observation that substitution of saturated fats for carbohydrates or unsaturated fats increases low-density lipoprotein (LDL) cholesterol in humans and animal models, the relationship of saturated fat intake to risk for atherosclerotic cardiovascular disease in humans remains controversial. A critical question is what macronutrient should be used to replace saturated fat. Substituting polyunsaturated fat for saturated fat reduces LDL cholesterol and the total cholesterol to high-density lipoprotein cholesterol ratio. However, replacement of saturated fat by carbohydrates, particularly refined carbohydrates and added sugars, increases levels of triglyceride and small LDL particles and reduces high-density lipoprotein cholesterol, effects that are of particular concern in the context of the increased prevalence of obesity and insulin resistance. Epidemiologic studies and randomized clinical trials have provided consistent evidence that replacing saturated fat with polyunsaturated fat, but not carbohydrates, is beneficial for coronary heart disease. Therefore, dietary recommendations should emphasize substitution of polyunsaturated fat and minimally processed grains for saturated fat.

Saturated fat, carbohydrate, and cardiovascular disease

A focus of dietary recommendations for cardiovascular disease (CVD) prevention and treatment has been a reduction in saturated fat intake, primarily as a means of lowering LDL-cholesterol concentrations. However, the evidence that supports a reduction in saturated fat intake must be evaluated in the context of replacement by other macronutrients. Clinical trials that replaced saturated fat with polyunsaturated fat have generally shown a reduction in CVD events, although several studies showed no effects. An independent association of saturated fat intake with CVD risk has not been consistently shown in prospective epidemiologic studies, although some have provided evidence of an increased risk in young individuals and in women. Replacement of saturated fat by polyunsaturated or monounsaturated fat lowers both LDL and HDL cholesterol. However, replacement with a higher carbohydrate intake, particularly refined carbohydrate, can exacerbate the atherogenic dyslipidemia associated with insulin resistance and obesity that includes increased triglycerides, small LDL particles, and reduced HDL cholesterol. In summary, although substitution of dietary polyunsaturated fat for saturated fat has been shown to lower CVD risk, there are few epidemiologic or clinical trial data to support a benefit of replacing saturated fat with carbohydrate. Furthermore, particularly given the differential effects of dietary saturated fats and carbohydrates on concentrations of larger and smaller LDL particles, respectively, dietary efforts to improve the increasing burden of CVD risk associated with atherogenic dyslipidemia should primarily emphasize the limitation of refined carbohydrate intakes and a reduction in excess adiposity.

Dietary fats, cerebrovasculature integrity and Alzheimer's disease risk

An emerging body of evidence is consistent with the hypothesis that dietary fats influence Alzheimer's disease (AD) risk, but less clear is the mechanisms by which this occurs. Alzheimer's is an inflammatory disorder, many consider in response to fibrillar formation and extracellular deposition of amyloid-beta (Abeta). Alternatively, amyloidosis could notionally be a secondary phenomenon to inflammation, because some studies suggest that cerebrovascular disturbances precede amyloid plaque formation. Hence, dietary fats may influence AD risk by either modulating Abeta metabolism, or via Abeta independent pathways. This review explores these two possibilities taking into consideration; (i) the substantial affinity of Abeta for lipids and its ordinary metabolism as an apolipoprotein; (ii) evidence that Abeta has potent vasoactive properties and (iii) studies which show that dietary fats modulate Abeta biogenesis and secretion. We discuss accumulating evidence that dietary fats significantly influence cerebrovascular integrity and as a consequence altered Abeta kinetics across the blood-brain barrier (BBB). Specifically, chronic ingestion of saturated fats or cholesterol appears to results in BBB dysfunction and exaggerated delivery from blood-to-brain of peripheral Abeta associated with lipoproteins of intestinal and hepatic origin. Interestingly, the pattern of saturated fat/cholesterol induced cerebrovascular disturbances in otherwise normal wild-type animal strains is analogous to established models of AD genetically modified to overproduce Abeta, consistent with a causal association. Saturated fats and cholesterol may exacerbate Abeta induced cerebrovascular disturbances by enhancing exposure of vessels of circulating Abeta. However, presently there is no evidence to support this contention. Rather, SFA and cholesterol appear to more broadly compromise BBB integrity with the consequence of plasma protein leakage into brain, including lipoprotein associated Abeta. The latter findings are consistent with the concept that AD is a dietary-fat induced phenotype of vascular dementia, reflecting the extraordinary entrapment of peripherally derived lipoproteins endogenously enriched in Abeta. Rather than being the initiating trigger for inflammation in AD, accumulation of extracellular lipoprotein-Abeta may be a secondary amplifier of dietary induced inflammation, or possibly, simply be consequential. Clearly, delineating the mechanisms by which dietary fats increase AD risk may be informative in developing new strategies for prevention and treatment of AD.

Developmental programming of lipid metabolism and aortic vascular function in C57BL/6 mice: a novel study suggesting an involvement of LDL-receptor

We have previously shown that a maternal high-fat diet, rich in saturated fatty acids (SFA), alters the lipid metabolism of their adult offspring. The present study was designed to investigate 1) whether alterations in hepatic LDL-receptor (LDL-r) expression may serve as a potential mechanism of developmental programming behind the altered lipid metabolism of the offspring, 2) whether altered lipid metabolism leads to aortic vascular dysfunction in the offspring, 3) whether deleterious effects of SFA exposure preweaning are influenced by postweaning diet, and 4) whether gender-specific programming effects are observed. Female C57Bl/6 mice were fed a high-SFA diet or regular chow during gestation and lactation while their pups, both male and female, received either SFA or a chow diet after weaning. Male offspring obtained from mothers fed an SFA diet and those who continued on chow postweaning had higher plasma triglycerides and total cholesterol, whereas female offspring had higher plasma total and LDL cholesterol levels, lower hepatic LDL-r mRNA expression, and reduced aortic contractile responses compared with the offspring that were fed chow throughout the study. A comparison of the postweaning diet revealed significantly lower hepatic LDL-r expression along with significantly higher plasma LDL-cholesterol concentration in the female offspring that were obtained from mothers fed an SFA diet and who continued on an SFA diet postweaning, compared with the female offspring that were obtained from mothers fed an SFA diet but who continued on chow postweaning. In conclusion, we report a novel observation of hepatic LDL-r-mediated programming of altered lipid metabolism, along with aortic vascular dysfunction, in the female offspring of mothers fed a high-SFA diet. Male offspring only exhibited dyslipidemia, suggesting gender-mediated programming. This study further highlighted the role of postweaning diets in overriding the effects of maternal programming.

Vegetable oils affect the composition of lipoproteins in sea bream (Sparus aurata)

The aim of the present study was to determine the influence of the dietary fatty acid profile on the lipoprotein composition in sea bream fed different vegetable oils. Six experimental diets were formulated combining fish oil with three vegetable oils (soybean, rapeseed, linseed) in order to obtain 60–80 % (w/w) fish-oil replacement. VLDL, LDL and HDL in plasma samples were obtained by sequential centrifugal flotation. The lipid class, protein content and fatty acid composition of each lipoprotein fraction were analysed. HDL was the predominant lipoprotein in sea bream plasma containing the highest proportion of protein (34 %) and phosphatidylcholine. LDL presented a high content of cholesterol, whereas triacylglycerol comprised a larger proportion of VLDL. The lipid class of the lipoprotein fractions was affected by the dietary vegetable oils. Thus, a high dietary inclusion of soyabean and linseed oil (80 %) increased the cholesterol in HDL and LDL in comparison to fish oil. Similarly, the triacylglycerol concentration of VLDL was increased in fish fed 80 % soyabean and linseed oils owing to the lown-3 highly unsaturated fatty acid content of these diets. Lipoprotein fatty acid composition easily responded to dietary fatty acid composition. VLDL was the fraction more affected by dietary fatty acid, followed by LDL and HDL. Then-3 highly unsaturated fatty acid content increased in the order VLDL less than LDL and less than HDL, regardless of dietary vegetable oils.

Composition, structure and absorption of milk lipids: a source of energy, fat-soluble nutrients and bioactive molecules

Milkfat is a remarkable source of energy, fat-soluble nutrients and bioactive lipids for mammals. The composition and content of lipids in milkfat vary widely among mammalian species. Milkfat is not only a source of bioactive lipid components, it also serves as an important delivery medium for nutrients, including the fat-soluble vitamins. Bioactive lipids in milk include triacylglycerides, diacylglycerides, saturated and polyunsaturated fatty acids, and phospholipids. Beneficial activities of milk lipids include anticancer, antimicrobial, anti-inflammatory, and immunosuppression properties. The major mammalian milk that is consumed by humans as a food commodity is that from bovine whose milkfat composition is distinct due to their diet and the presence of a rumen. As a result of these factors bovine milkfat is lower in polyunsaturated fatty acids and higher in saturated fatty acids than human milk, and the consequences of these differences are still being researched. The physical properties of bovine milkfat that result from its composition including its plasticity, make it a highly desirable commodity (butter) and food ingredient. Among the 12 major milk fatty acids, only three (lauric, myristic, and palmitic) have been associated with raising total cholesterol levels in plasma, but their individual effects are variable-both towards raising low-density lipoproteins and raising the level of beneficial high-density lipoproteins. The cholesterol-modifying response of individuals to consuming saturated fats is also variable, and therefore the composition, functions and biological properties of milkfat will need to be re-evaluated as the food marketplace moves increasingly towards more personalized diets.

High cholesterol intake modifies chylomicron metabolism in normolipidemic young men

Whether the consumption of egg yolk, which has a very high cholesterol content without excess saturated fats, has deleterious effects on lipid metabolism is controversial. Absorbed dietary cholesterol enters the bloodstream as chylomicrons, but the effects of regular consumption of large amounts of cholesterol on the metabolism of this lipoprotein have not been explored even though the accumulation of chylomicron remnants is associated with coronary artery disease (CAD). We investigated the effects of high dietary cholesterol on chylomicron metabolism in normolipidemic, healthy young men. The plasma kinetics of a chylomicron-like emulsion, doubly-labeled with 14C-cholesteryl ester (14C-CE) and 3H-triolein (3H-TG) were assessed in 25 men (17-22 y old, BMI 24.1 +/- 3.4 kg/m2). One group (n = 13) consumed 174 +/- 41 mg cholesterol/d and no egg yolk. The other group (n = 12) consumed 3 whole eggs/d for a total cholesterol intake of 804 +/- 40 mg/d. The nutritional composition of diets was the same for both groups, including total lipids and saturated fat, which comprised 25 and 7%, respectively, of energy intake. Serum LDL and HDL cholesterol and apoprotein B concentrations were higher in the group consuming the high-cholesterol diet (P < 0.05), but serum triacylglycerol, apo AI, and lipoprotein (a) did not differ between the 2 groups. The fractional clearance rate (FCR) of the 14C-CE emulsion, obtained by compartmental analysis, was 52% slower in the high-cholesterol than in the low-cholesterol group (P < 0.001); the 3H-TG FCR did not differ between the groups. Finally, we concluded that high cholesterol intakes increase the residence time of chylomicron remnants, as indicated by the 14C-CE kinetics, which may have undesirable effects related to the development of CAD.

Polyunsaturated Fatty Acids and Cardiovascular Health

Epidemiologic studies have shown a beneficial association between polyunsaturated fatty acid (PUFA), specifically linoleic acid (C18:2, n-6), intake and cardiovascular disease morbidity and mortality. Clinical studies have shown that n-6 PUFAs have the most potent cholesterol-lowering effects of the individual fatty acid classes, and emerging evidence suggests that PUFAs have favorable effects on postprandial lipemia. However, some studies suggest that high intakes of linoleic acid may have adverse effects on proinflammatory cytokines and adhesion molecules. Research is needed to establish the optimal level of dietary PUFAs that maximally affects the greatest number of health risk factors.

Polyunsaturated fatty acids downregulate the low density lipoprotein receptor of human HepG2 cells

The aim of the study was to investigate the effect of different fatty acids on the low density lipoprotein (LDL) receptor of cultured human liver HepG2 cells. Previous studies investigating the effect of fatty acids on LDL expression have reported conflicting findings and are limited to measurements of LDL receptor binding activity. Therefore, this study is unique in that the relative effects of different fatty acids on the LDL receptor were investigated at three different stages of expression: 1) functional cellular LDL binding activity, 2) amount of LDL receptor protein and 3) LDL receptor mRNA level. The HepG2 cells were incubated for 24 hr with either 100 &mgr;M palmitic, oleic, linoleic or eicosapentaenoic acid (EPA). The measurement of LDL receptor binding activity was with colloidal gold-LDL conjugates, cellular LDL receptor protein was by western blotting and LDL receptor mRNA by Southern blotting of reverse-transcribed, polymerase chain reaction-amplified cDNA. The LDL receptor binding activity, protein and mRNA levels decreased as the degree of unsaturation of the fatty acids increased (palmitic acid greater-than-or-equal oleic acid > linoleic acid > EPA) and the inverse relationship held whether or not cholesterol was included in the culture media. The relative differences were very similar for the three stages of expression indicating that modulation of the LDL receptor by the fatty acids occurred at the level of gene transcription. The increased susceptibility to oxidation of the polyunsaturated fatty acids was unlikely to be a factor in the effect because EPA and linoleic acid (250 &mgr;M) still downregulated the LDL receptor in the presence of the antioxidant vitamin E (50 &mgr;M). In conclusion, the polyunsaturates, linoleic acid and EPA, effectively downregulated the LDL receptor of HepG2 cells compared to palmitic acid. The effects of these fatty acids were observed at the level of LDL receptor binding activity, protein and mRNA, strongly suggesting that the fatty acid effects were at the level of gene transcription.

Strategies for altering population intakes of fats and fatty acids

Quantitative dietary guidelines for fats were first issued in 1977 in the USA and these guidelines have changed little since then. In the UK only 14% of the population achieve the dietary goal for fat (33% energy) and only 3% achieve the target (10% energy) from saturated fatty acids. Analysis of the Dietary and Nutritional Survey of British Adults reveals that across quartiles of decreasing total fat intake, the actual fatty acid composition of this fat does not alter; i.e. when total fat is lowered, all fatty acid categories are equally lowered. This arises because 85% of total fat and of each of the categories of fatty acids are provided by just five foods (milk, meat, cereals, spreads and vegetables). When total fat in the UK is lowered, the intake of polyunsaturated fatty acids is lowered. The problem is that if the intake of polyunsaturated fatty acids falls below a threshold of about 5% energy, the cholesterol-raising properties of certain saturated fatty acids, e.g. myristic acid, are greatly augmented. In order to alter the balance of dietary fatty acids, more data are needed on food choices of those in the population achieving particular targets. These targets cannot be based on existing dietary goals, since so few people attain them. A new set of 'interim attainable dietary guidelines', based on prevailing dietary intakes, must be the basis for establishing sensible food-based dietary guidelines.

Myristic acid-rich fat raises plasma LDL by stimulating LDL production without affecting fractional clearance in gerbils fed a cholesterol-free diet

The imbalance that develops between low-density lipoprotein (LDL) production and clearance during saturated fat consumption is responsible for expanding the circulating LDL pool. To assess the imbalance attributable to fatty acids alone, i.e., without the interaction of dietary cholesterol, the most fat-sensitive species available (the gerbil) was challenged with either a 12:0+14:0 rich-fat (high coconut, low safflower) or high 18:2 (high safflower, low coconut) fat for 4-5 wks. The plasma lipoprotein cholesterol profile, including lipoprotein composition, particle size and 125I-LDL turnover were measured. Although total plasma cholesterol (TC) was threefold higher with saturated fatty acid (SFA) feeding (230 vs. 70 mg/100 mL; 5.9 +/- 0.1 vs. 1.8 +/- 0.05 mmol/L, P < 0. 0001) and LDL cholesterol (LDL-C) was fivefold greater (10 vs. 54 mg/100 mL; 0.26 +/- 0.02 vs. 1.4 +/- 0.02 mmol/L, P < 0.001), the high-density lipoprotein (HDL2) fraction increased the most (27 vs. 79 mg/100 mL; 0.7 +/- 0.02 vs. 2.0 +/- 0.1 mmol/L, P < 0.05) with minimal HDL3 (NS) difference (16 vs. 26 mg/100 mL; 0.43 +/- 0.08 vs. 0. 7 +/- 0.05 mmol/L). Particle composition and size did not differ between groups. LDL kinetic analyses revealed that the fractional catabolic rate did not differ between gerbils with these extreme fat intakes, implicating overproduction and not reduced clearance as the primary consideration in LDL expansion. Thus SFA-induced cholesterolemia can be severe in the absence of dietary cholesterol with a greater impact on high-density lipoprotein than LDL and without an appreciable role attributed to LDL clearance (receptors).