High folic acid intake increases methylation-dependent expression of Lsr and dysregulates hepatic cholesterol homeostasis.

Food fortification with folic acid and increased use of vitamin supplements have raised concerns about high folic acid intake. We previously showed that high folic acid intake was associated with hepatic degeneration, decreased levels of methylenetetrahydrofolate reductase (MTHFR), lower methylation potential, and perturbations of lipid metabolism. MTHFR synthesizes the folate derivative for methylation reactions. In this study, we assessed the possibility that high folic acid diets, fed to wild-type and Mthfr+/- mice, could alter DNA methylation and/or deregulate hepatic cholesterol homeostasis. Digital restriction enzyme analysis of methylation in liver revealed DNA hypomethylation of a CpG in the lipolysis-stimulated lipoprotein receptor (Lsr) gene, which is involved in hepatic uptake of cholesterol. Pyrosequencing confirmed this methylation change and identified hypomethylation of several neighboring CpG dinucleotides. Lsr expression was increased and correlated negatively with DNA methylation and plasma cholesterol. A putative binding site for E2F1 was identified. ChIP-qPCR confirmed reduced E2F1 binding when methylation at this site was altered, suggesting that it could be involved in increasing Lsr expression. Expression of genes in cholesterol synthesis, transport or turnover (Abcg5, Abcg8, Abcc2, Cyp46a1, and Hmgcs1) was perturbed by high folic acid intake. We also observed increased hepatic cholesterol and increased expression of genes such as Sirt1, which might be involved in a rescue response to restore cholesterol homeostasis. Our work suggests that high folic acid consumption disturbs cholesterol homeostasis in liver. This finding may have particular relevance for MTHFR-deficient individuals, who represent ~10% of many populations.

Saikosaponin-a Attenuates Oxidized LDL Uptake and Prompts Cholesterol Efflux in THP-1 Cells.

Saikosaponins-a (Ssa) is a major bioactive extract of Radix Bupleuri which is a traditional Chinese medicine. The roles of inflammatory response and lipid transportation in the process of atherosclerosis have drawn increasing attention. We explored the regulation of lipid transportation and immune-inflammatory role of Ssa in early atherosclerosis. The antiatherogenic actions and possible molecular mechanisms of Ssa were texted in THP-1 cells. We examined the effect of Ssa on oxidized low-density lipoprotein (ox-LDL)-induced lipid uptake, cholesterol efflux, immune-inflammatory response. THP-1 macrophages were treated with Ssa followed by ox-LDL for 24 hours. Results from western blot showed that Ssa obviously reduced lipoprotein uptake to block foam cell formation and the expression of Density Lipoprotein Receptor-1 and CD36. Ssa also significantly boosted cholesterol efflux and the expression of ATP binding cassettetransporter A1 and peroxisome proliferator-activated receptor γ. The results also indicated that Ssa inhibited ox-LDL-induced activation of AKT and nuclear factor-κB, assembly of NLRP3 inflammasome and production of proinflammatory cytokines. It is suggested that the ability against immune inflammatory response of Ssa is due to modulation of the PI3K/AKT/NF-κB/NLRP3 pathway. In conclusion, this study provides new insight into Ssa's molecular mechanism and its therapeutic potential in the treatment of atherosclerosis.

Phaleria macrocarpa Boerl. (Thymelaeaceae) leaves increase SR-BI expression and reduce cholesterol levels in rats fed a high cholesterol diet.

In vitro and in vivo studies of the activity of Phaleria macrocarpa Boerl (Thymelaeaceae) leaves against the therapeutic target for hypercholesterolemia were done using the HDL receptor (SR-BI) and hypercholesterolemia-induced Sprague Dawley rats. The in vitro study showed that the active fraction (CF6) obtained from the ethyl acetate extract (EMD) and its component 2',6',4-trihydroxy-4'-methoxybenzophenone increased the SR-BI expression by 95% and 60%, respectively. The in vivo study has proven the effect of EMD at 0.5 g/kgbw dosage in reducing the total cholesterol level by 224.9% and increasing the HDL cholesterol level by 157% compared to the cholesterol group. In the toxicity study, serum glutamate oxalate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT) activity were observed to be at normal levels. The liver histology also proved no toxicity and abnormalities in any of the treatment groups, so it can be categorized as non-toxic to the rat liver. The findings taken together show that P. macrocarpa leaves are safe and suitable as an alternative control and prevention treatment for hypercholesterolemia in Sprague Dawley rats.

[Effects of alkaloids from coptidis rhizoma on blood lipid metabolism and low-denstity lipoprotein receptor mRNA in golden hamsters].

To study the effects of alkaloids from Coptidis Rhizoma on low-density lipoprotein receptor (LDLR) mRNA expression and antihyperlipedemic levels. The LDLR mRNA expression were detected by real time fluorescence quantitative PCR, and the levels of total cholesterol (TC), triglyceride (TG), low density lipoprotein (LDL-c) and high-density lipoprotein cholesterol (HDL-c) in serum were measured at the first and last examination. The results show that, after the drug treatment, compared with the model group, each drug group showed a lipid-lowering effect. Especially, coptisine, palmatine, jatrorrhinze were significantly reduced TC, TG, LDL-c (P < 0.05, P < 0.01), and increased HDL-c (P < 0.01). In addition, they also increased mRNA expression of the LDLR in liver and HepG2 cells. The results showed that alkaloids from Coptidis Rhizoma can regulate lipid metabolism disorder, and coptisine have the best lipid-lowering effect.

Effects of Yerba Mate tea (Ilex paraguariensis) on vascular endothelial function and liver lipoprotein receptor gene expression in hyperlipidemic rats.

Yerba Mate tea (Mate), an infusion made from the leaves of the tree Ilex paraguariensis, is a widely consumed beverage in South America. This study was performed to investigate the effect of Mate tea on vascular endothelial dysfunction and liver lipoprotein receptor gene expression in hyperlipidemic rats, with the aim of gaining insight into its known lipid-lowering protective mechanisms. Sixty male Sprague-Dawley rats were randomly divided into five groups: a normal control group (NC), a high-fat diet group (HC), and three Mate tea-treated groups. In the NC group, rats were fed with standard diet while in the other groups the rats were fed a high-fat diet for 8weeks. In the Mate tea-treated groups, the rats were fed a high-fat diet supplemented with low, moderate or high concentrations of aqueous Mate tea extract for the final 4weeks. Compared to the HC group, aqueous Mate tea extract significantly reduced endothelin (ET) and thromboxane B(2) (TXB(2)) levels and increased nitric oxide (NO) and 6-keto prostaglandin F(1α) (6-keto-PGF(1α)) levels in the blood, reduced the pathological damage of vascular endothelial cells, decreased intercellular adhesion molecule-1 (ICAM-1) protein expression in the thoracic aorta, and upregulated mRNA expression of hepatic low density lipoprotein receptor (LDLR) and scavenger receptor B1 (SR-B1). These findings indicate that Mate tea administration might have a regulatory effect on blood fat and endothelial function in hyperlipidemia rats. The mechanism may involve protecting vascular endothelial cell function and upregulating the expression of LDLR and SR-B1 genes, thereby inhibiting the occurrence of atherosclerosis.

The effects of berberine on hyperhomocysteinemia and hyperlipidemia in rats fed with a long-term high-fat diet.

BACKGROUND: The study was undertaken to examine the effects of berberine (BBR) on serum homocysteine, lipids and the aortic lesion in Sprague-Dawley (SD) rats fed with a long-term high-fat diet (HFD). METHODS: Healthy male SD rats weighing 190-210 g received randomly standard diet or a high-fat diet for 24 weeks. After 8 weeks of feeding, rats fed with HFD were randomized to receive berberine (200 mg · kg-1· day-1) or vehicle by gavage for 16 weeks. After overnight fasting, all rats were sacrificed and total blood samples were also collected for determinant of fasting serum homocysteine (Hcy), total cholesterol (TC) and low density lipoprotein cholesterol (LDL-c) levels. The aorta was stained with hematoxylin and eosin (HE) and Sudan Ш to evaluate aortic lesion. The livers were dissected out and snap-frozen in liquid nitrogen for hepatic TC content and molecular analysis. 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR), Lipoprotein receptors and apolipoproteins gene expression in the liver were determined by real-time PCR. RESULTS: Intragastrical administration with berberine for 16 weeks lowered serum Hcy in rats fed with a high-fat diet. In parallel, it also decreased body weight and improved serum TC and LDL-c. Berberine also tended to decrease hepatic cholesterol. Consistently, berberine also upregulated LDL receptor (LDLR) mRNA level and suppressed HMGR gene expression. Meanwhile, upon berberine-treated rats, there was a significant increase in apolipoprotein E (apoE) mRNA, but no change in apoAI and scavenger receptor (SR) mRNA in the liver. Further, no atherosclerotic lesions were developed in berberine-treated rats for 16 weeks. CONCLUSION: Berberine can counteract HFD-elicited hyperhomocysteinemia and hyperlipidemia partially via upregulating LDLR and apoE mRNA levels and suppressing HMGR gene expression.

Differential functions of the Apoer2 intracellular domain in selenium uptake and cell signaling.

Apolipoprotein E receptor 2 (Apoer2) is a multifunctional transport and signaling receptor that regulates the uptake of selenium into the mouse brain and testis through endocytosis of selenoprotein P (Sepp1). Mice deficient in Apoer2 or Sepp1 are infertile, with kinked and hypomotile spermatozoa. They also develop severe neurological defects on a low selenium diet, due to a profound impairment of selenium uptake. Little is known about the function of Apoer2 in the testis beyond its role as a Sepp1 receptor. By contrast, in the brain, Apoer2 is an essential component of the Reelin signaling pathway, which is required for proper neuronal organization and synapse function. Using knock-in mice, we have functionally dissociated the signaling motifs in the Apoer2 cytoplasmic domain from Sepp1 uptake. Selenium concentration of brain and testis was normal in the knock-in mutants, in contrast to Apoer2 knock-outs. Thus, the neurological defects in the signaling impaired knock-in mice are not caused by a selenium uptake defect, but instead are a direct consequence of a disruption of the Reelin signal. Reduced sperm motility was observed in some of the knock-in mice, indicating a novel signaling role for Apoer2 in sperm development and function that is independent of selenium uptake.

Identification of novel human high-density lipoprotein receptor Up-regulators using a cell-based high-throughput screening assay.

Scavenger receptor class B type I (SR-BI) is the high-affinity high-density lipoprotein (HDL) receptor, and CLA-1 is the human homologue of the murine SR-BI. CLA-1/SR-BI receptor has been suggested as a new preventative and/or therapeutic target for atherosclerosis due to its pivotal role in overall HDL cholesterol (HDL-C) metabolism and its antiatherogenic activity in vivo. To search for active compounds that can increase CLA-1 transcription, a novel cell-based assay was developed for application in high-throughput screening (HTS). Human hepatoma HepG2 cells were transfected with a CLA-1-promoter-luciferase reporter gene construct, and the stable transfected cell line was selected and named CLAp-LUC HepG2. With rosiglitazone as a positive control, this stable cell line was used to establish a specific CLA-1 gene expression assay in a 96-well microplate format. The evaluating parameter Z' value of 0.64 showed that this cell-based HTS assay was robust and reliable. Screening of 6000 microbial secondary metabolite crude extracts identified 8 positive strains. Between 2 identified CLA-1 up-regulators produced by actinomycete strain 04-4776, 4776B may stimulate not only the expression of CLA-1 on the transcriptional and translational levels but also the activity of CLA-1 to uptake the HDL-C in HepG2 cells. The active compounds originated from this HTS assay may be developed to drug candidates or lead compounds for new antiatherosclerosis agents.

Gender-related response of lipid metabolism to dietary fatty acids in the hamster.

Gender and dietary fatty acids are involved in the regulation of lipid metabolism, disturbances of which can lead to pathologies such as metabolic syndrome or CVD. Possible interactions between these factors were investigated in male and female hamsters fed diets rich in either saturated fatty acids ( "butter" diet) or in alpha-linolenic acid ( "linseed oil" diet). Gender effect predominated over the diet effect on cholesterol (CH) metabolism; compared to males, females exhibited lower concentrations of plasma total CH (-20 %, P<0.001), LDL-CH (-40 %, P<0.001) and HDL-CH (-16 %, P<0.001), together with higher LDL receptor (+40 %) and lower HDL receptor (-60 %) hepatic content. Triacylglycerol (TG) metabolism was affected by diet above all: compared to animals fed the "butter" diet, those fed the "linseed oil" diet exhibited lower plasma (-23 %, P=0.046) and liver TG (-20 %, P=0.026) concentration which may result from both an increased beta-oxidation (P<0.001), without any change in PPARalpha mRNA, and a decreased hepatic lipogenesis (P=0.023), without increased sterol response element binding protein 1c (SREBP1c) mRNA. The response to diet was much more pronounced in males than in females, without gender effect on the transcription level of PPARalpha and SREBP1c. Finally, the "linseed oil" diet decreased the insulin resistance index (-80 %, P<0.001) with a more marked effect in males, in relation to their higher hepatic PPARgamma expression (+90 %, P=0.012). In conclusion, in our model, the response of either TG or CH to dietary fatty acids is modulated differently by gender. The possible relevance of these interactions to dietary practice should be taken into account in man.

Increased binding of LDL and VLDL to apo B,E receptors of hepatic plasma membrane of rats treated with Fibernat.

BACKGROUND: Research has focussed on the hypocholesterolemic effects of certain types of dietary fiber such as enhancing conversion of hepatic cholesterol to bile acids or increase in catabolism of low density lipoprotein (LDL) via the apo B,E receptor. AIM OF THE STUDY: The effect of oral administration of a unique fibre cocktail of fenugreek seed powder, guar gum and wheat bran (Fibernat) and its varied effects on some aspects of lipid metabolism and cholesterol homeostasis in rats were examined. METHODS: Rats were administered Fibernat along with the atherogenic diet containing 1.5 % cholesterol and 0.1 % cholic acid. Amounts of hepatic lipids, hepatic and fecal bile acids and activity of hepatic triglyceride lipase (HTGL) were determined. Transmission electron microscopic examination of the liver tissue and extent of uptake of (125)I-LDL and (125)I-VLDL by the hepatic apo B,E receptor was carried out. RESULTS: Food intake and body weight gain were similar between the 3 different dietary groups. Fibernat intake significantly increased apo B,E receptor expression in rat liver as reflected by an increase in the maximum binding capacity (B(max)) of the apo B,E receptor to (125)I-LDL and (125)I-VLDL. The activity of HTGL was increased by approximately 1.5-fold in Fibernat-fed rats as compared to those fed the atherogenic diet alone. A marked hypocholesterolemic effect was observed. Cholesterol homeostasis was achieved in Fibernat-fed rats. CONCLUSION: Two possible mechanisms are postulated to be responsible for the observed hypocholesterolemic effect a) an increase in conversion of cholesterol to bile acids and b) possibly by intra-luminal binding which resulted in increased fecal excretion of bile acids and neutral sterols. The resulting reduction in cholesterol content of liver cells coupled with upregulation of hepatic apo B,E receptors and increased clearance of circulating atherogenic lipoproteins-LDL and very low density lipoprotein (LDL and VLDL)-is the main mechanism involved in the hypocholesterolemic effect of Fibernat. The results suggest that Fibernat's effect on plasma LDL concentration is also possibly mediated by increased receptor-mediated catabolism of VLDL. Thus, Fibernat therapy is an effective adjunct to diet therapy and might find potential use in the therapy of hyperlipidemic subjects.

Role of hepatic lipase and scavenger receptor BI in clearing phospholipid/free cholesterol-rich lipoproteins in PLTP-deficient mice.

Phospholipid transfer protein knock-out (PLTP0) mice have defective transfer of phospholipids (PL) from triglyceride-rich lipoproteins (TRL) into high-density lipoproteins (HDL). In this study, we examined the role of diet, hepatic lipase (HL) and scavenger receptor BI (SRBI) in determining the accumulation of excess PL and free cholesterol (FC, "surface remnants") in plasma of PLTP0 mice. PL and FC accumulated in the very low-density lipoprotein (VLDL)-LDL region of PLTP0 mice on a highly saturated, coconut oil-based diet, but not on chow or milk-fat based Western diets. Accumulation of PL and FC was dramatically increased in PLTP0/HL0 mice, compared to PLTP0 mice, but only on the coconut oil diet. Turnover studies indicated that the coconut oil diet was associated with delayed catabolism of PL of PL/FC-rich particles. Incubation of these particles with primary hepatocytes in the presence of SRBI neutralizing antibody indicated that SRBI was primarily responsible for removal of FC and PL on the Western diet. In hepatocytes of coconut oil-fed mice, removal of FC and PL from these particles by SRBI was markedly reduced, even though SRBI protein expression levels were unchanged. These studies indicate that HL and SRBI both have major role in the clearance of PL and FC of surface remnants in PLTP0 mice. SRBI appears to be dysfunctional in coconut oil diet-fed animals, possibly related to changes in hepatocyte membrane fatty acid composition.

Retinal pigment epithelial acid lipase activity and lipoprotein receptors: effects of dietary omega-3 fatty acids.

PURPOSE: To show that fish oil-derived omega-3 polyunsaturated fatty acids, delivered to the retinal pigment epithelium (RPE) by circulating low-density lipoproteins (LDL), enhance already considerable RPE lysosomal acid lipase activity, providing for more efficient hydrolysis of intralysosomal RPE lipids, an effect that may help prevent development of age-related macular degeneration (ARMD). METHODS: Colorimetric biochemical and histochemical techniques were used to demonstrate RPE acid lipase in situ, in vitro, and after challenge with phagocytic stimuli. Receptor-mediated RPE uptake of fluorescently labeled native, aceto-acetylated, and oxidized LDL was studied in vitro and in vivo. LDL effects on RPE lysosomal enzymes were assessed. Lysosomal enzyme activity was compared in RPE cells from monkeys fed diets rich in fish oil to those from control animals and in cultured RPE cells exposed to sera from these monkeys. RESULTS: RPE acid lipase activity was substantial and comparable to that of mononuclear phagocytes. Acid lipase activity increased significantly following phagocytic challenge with photoreceptor outer segment (POS) membranes. Receptor-mediated RPE uptake of labeled lipoproteins was determined in vitro. Distinctive uptake of labeled lipoproteins occurred in RPE cells and mononuclear phagocytes in vivo. Native LDL enhanced RPE lysosomal enzyme activity. RPE lysosomal enzymes increased significantly in RPE cells from monkeys fed fish oil-rich diets and in cultured RPE cells exposed to their sera. CONCLUSIONS: RPE cells contain substantial acid lipase for efficient metabolism of lipids imbibed by POS phagocytosis and LDL uptake. Diets rich in fish oil-derived omega-3 fatty acids, by enhancing acid lipase, may reduce RPE lipofuscin accumulation, RPE oxidative damage, and the development of ARMD.

Essential polyunsaturated fatty acids and the barrier to the brain: the components of a model for transport.

Several areas of research have contributed to the establishment of a paradigm that meets the requirements for the selective uptake of essential polyunsaturated fatty acids (EPUFA) into brain. First, discrete studies have demonstrated that cholesterol and the nonessential fatty acids, (palmitic, oleic, stearic) do not enter the brain parenchyma. These studies demonstrated that the 18 carbon-monocarboxylic fatty acids, linoleic acid with two cis-double bonds entered brain, whereas oleic acid, with one cis-double bond, did not enter brain. It was concluded the entry of essential fatty acids into brain is accomplished in a highly selective and discrete manner. Further, the typical blood-borne lipoproteins do not traverse the endothelial cells of the capillary network and enter into the brain, otherwise cholesterol, palmitic, oleic, and stearic acids from blood would be located within brain. Second, several investigators have shown that the endothelial cells of the capillary network contain lipoprotein receptors, yet one conclusion is that the brain does not utilize low-density lipoprotein (LDL)-cholesterol. Third, recently, the existence and function of a significant number of distinctive trans-membrane monocarboxylic acid transporters, (MCTs) and fatty acid transport proteins (FATPs) have been described. No transporters have been described to date with the specificity necessary to transfer only EPUFA into brain. A blueprint with the minimal elements for delivery and selectivity is proposed. Lipoproteins enter the endothelial cells because the lipoprotein receptors are positioned on their luminal membrane. Essential fatty acid transporter(s) are positioned on the abluminal membrane of these endothelial cells to allow for the entry of EPUFA into brain. Within the endothelial cell there is opportunity for lipid management and transformation such that EPUFAs are selectively culled for delivery to the essential fatty acid transporter(s), which facilitates their transfer into brain.

Association of membrane-bound amyloid precursor protein APP with the apolipoprotein E receptor LRP.

In order to identify cell surface proteins that interact with the amyloid precursor protein (APP), we biotinylated H4 human neuroglioma cells in culture with a water soluble biotinylating agent, immunoprecipitated APP with an antibody specific to the intracellular domain, and probed the precipitated proteins with anti-biotin. In human neuroglioma cells overexpressing APP751, we found a high molecular weight protein that immunoprecipitated with APP. This band was identified as the low density lipoprotein receptor-related protein (LRP) by three criteria: first, the band immunolabeled with anti-LRP antibodies; second, the band bound the LRP receptor associated protein, RAP; and third, this band was present in LRP-expressing fibroblasts, but not LRP-deficient fibroblasts. In complementary experiments, we found that APP co-precipitated with LRP, with a preference for an isoform of APP containing the Kunitz protease inhibitor domain. Interaction of APP and LRP on the surface of living cells was demonstrated by crosslinking APP and LRP with the water-soluble cross-linking agent BS(3). APP and LRP were shown by confocal microscopy to colocalize in perinuclear structures, but to primarily remain separate in vesicles and on the cell surface. We propose that full-length APP can transiently interact with the receptor LRP on the cell surface, affecting the processing and intracellular transport of APP.

HDL and vitamin E in plasma and the expression of SR-BI on lung cells during rat perinatal development.

Vitamin E is the most important lipophilic antioxidant, and beneficial effects on oxidant-caused injuries have been reported. Neonates are at high risk of oxidative injury in the lung and other organs because of a low vitamin E concentration, but the optimal timing of the application, a safe application form, and the optimal dosage of vitamin E are not known at present. We recently showed that alveolar type II cells take up vitamin E preferentially from high-density lipoprotein (HDL), probably by means of the candidate HDL receptor, scavenger receptor class B type I (SR-BI; Kolleck et al. Free Rad Biol Med 27; 882-890, 1999). Therefore, both the HDL-bound vitamin E in plasma and the expression of SR-BI on alveolar type II cells may determine the supply of the cells with vitamin E. We show here that the plasma level of vitamin E, total and HDL cholesterol, and the ratio of vitamin E to polyunsaturated fatty acids and to total fatty acids decrease during fetal rat development, reaching the minimum at the postconceptual day 21 (day -1). These parameters increase thereafter to about the same levels as in adult rats. SR-BI is not detectable until day -1 on fetal lung cells, but the expression during the postnatal phase follows the same pattern as the plasma lipid constituents. We conclude that the ability of alveolar type II cells to take up vitamin E develops perinatally in mature neonates. This aspect also has to be considered when the optimal timing of supplementation for the protection of preterm neonates with vitamin E against oxidative lung injury is established.

Effect of MaxEPA (fish oil) on lipoproteins and its receptors in hypercholesterolemic rabbits.

The effect of dietary MaxEPA (fish oil) supplementation on cholesterol induced hypercholesterolemia in rabbits was investigated. Rabbits were fed 0.1% cholesterol enriched diet for one month and randomly divided into two groups (I and II). Group I was continued on a 0.1% cholesterol rich diet whereas group II in addition to cholesterol supplementation received MaxEPA (2.5 g/kg body weight) per day for a period of two months. B-VLDL-C, LDL-C and total serum peroxide levels (TBARS) were significantly higher in group II animals as compared to group I. No statistical difference was found in the number of hepatic B-VLDL binding sites between group I and II. Microscopic examination of the aorta showed an increase in the number of intimal foam cells in MaxEPA treated group, a result that may be linked to increase in total cholesterol, plasma TBARS and with simultaneous reduced hepatic uptake of B-VLDL.

Dietary fat saturation modifies the metabolism of LDL subfractions in guinea pigs.

The effects of dietary fat saturation on the metabolism of low-density lipoprotein (LDL) subfractions were measured in adult male guinea pigs fed semipurified diets containing 15% (wt/wt) corn oil (CO; 58% linoleic acid), lard (24% palmitic/14% stearic acid), or palm kernel oil (PK; 52% lauric/18% myristic acid). Animals fed the CO diet had lower plasma total cholesterol levels than guinea pigs fed the PK or lard diets (P < .01). Plasma LDL-1 (d = 1.019 to 1.05 g/mL) concentrations were 3.5- and 2.4-fold higher in animals fed the PK diet compared with the CO and lard groups, respectively, while LDL-2 (d = 1.05 to 1.09 g/mL) concentrations were not different among groups. For all dietary fat groups LDL-1 had a higher molecular weight and a larger diameter than LDL-2. LDL fractional catabolic rates (FCRs) varied, depending on both the diet and the LDL subfraction. Animals fed the polyunsaturated CO diet had a more rapid LDL FCR than animals from the other two groups (P < .01). Within the same diet group, LDL-2 exhibited a slower turnover rate than LDL-1 in animals fed the PK diet, while no differences in LDL subfraction FCR were found in the CO and lard groups. Animals fed the PK and lard diets did not exhibit significant modifications in the density distribution of LDL subfractions over a period of 33 hours. In contrast, animals fed the CO diet exhibited a shift of more buoyant to denser LDL particles, suggesting that differences in LDL intravascular processing are mediated by dietary fat saturation. In vitro LDL binding to hepatic membranes confirmed the in vivo data with an increased expression of apolipoprotein B/E receptors (Bmax) in animals fed the CO diet (P < .01). Hepatic apolipoprotein B/E receptors exhibited less affinity for LDL-2 in the PK group, a result consistent with the less rapid turnover of LDL-2 in PK-fed animals. The results suggest that dietary fatty acids varying in saturation and composition have distinctive atherogenic potentials. The lowest plasma LDL cholesterol concentrations mediated by CO intake could in part be explained by induced changes in the composition and processing of LDL subfractions, resulting in faster LDL turnover rates in addition to increased expression of hepatic apolipoprotein B/E receptors.(ABSTRACT TRUNCATED AT 400 WORDS)