Lower Plasma Cholesterol Levels Research Articles

Inhibition of miR-29 has a significant lipid-lowering benefit through suppression of lipogenic programs in liver.

MicroRNAs (miRNAs) are important regulators and potential therapeutic targets of metabolic disease. In this study we show by in vivo administration of locked nucleic acid (LNA) inhibitors that suppression of endogenous miR-29 lowers plasma cholesterol levels by ~40%, commensurate with the effect of statins, and reduces fatty acid content in the liver by ~20%. Whole transcriptome sequencing of the liver reveals 883 genes dysregulated (612 down, 271 up) by inhibition of miR-29. The set of 612 down-regulated genes are most significantly over-represented in lipid synthesis pathways. Among the up-regulated genes are the anti-lipogenic deacetylase sirtuin 1 (Sirt1) and the anti-lipogenic transcription factor aryl hydrocarbon receptor (Ahr), the latter of which we demonstrate is a direct target of miR-29. In vitro radiolabeled acetate incorporation assays confirm that pharmacologic inhibition of miR-29 significantly reduces de novo cholesterol and fatty acid synthesis. Our findings indicate that miR-29 controls hepatic lipogenic programs, likely in part through regulation of Ahr and Sirt1, and therefore may represent a candidate therapeutic target for metabolic disorders such as dyslipidemia.

Modification of lipoprotein and glucose metabolism, vascular inflammatory biomarkers and neuropathy after weight loss following bariatric surgery

Modification of lipoprotein and glucose metabolism, vascular inflammatory biomarkers and neuropathy after weight loss following bariatric surgery

Cross‐talk of Leptin and TSP‐1 in Leptin‐induced Atherosclerosis

Hyperleptinemia is an important pathogenic contributor of atherosclerosis; however, underlying mechanisms are poorly understood. We reported earlier that leptin upregulates a potent proatherogenic protein, thrombospondin‐1 (TSP‐1), in human aortic smooth muscle cells (HASMC) in vitro and aortic vessels of C57BL/6J mice in vivo. The goal of the current study was to determine the molecular mechanisms by which leptin upregulates TSP‐1 and further delineate the role of TSP‐1 in leptin‐induced atherosclerosis. Using ChIP, we found that leptin in vitro enhanced recruitment of nuclear proteins IRF1 and CREB on TSP‐1 gene promoter in HASMC. Immunoblotting further revealed that leptin in vivo, at doses reported to increase TSP‐1, stimulated IRF1 expression in aortic lysates of WT mice vs. untreated controls; in contrast, leptin failed to increase IRF1 expression in aortic vessels of TSP‐1‐/‐ mice. Finally, to elucidate a direct role of TSP‐1 in leptin‐induced atherosclerosis, age‐matched ApoE‐/‐ and TSP‐1‐/‐/ApoE‐/‐ mice on regular chow at 17 wks of age were treated once daily i.p. with leptin (5µg/g) for 3 wks. While leptin‐treated TSP‐1‐/‐/ApoE‐/‐ had lower plasma cholesterol levels compared to leptin‐treated ApoE‐/‐ mice, FPLC fractionation of plasma lipids indicated that this difference was not attributable to VLDL and LDL levels. Morphometry of aortic root demonstrated a significant increase in atherosclerotic lesion area, collagen content and PCNA expression (proliferation marker) in ApoE‐/‐ vs. TSP‐1‐/‐/ApoE‐/‐ mice in response to leptin, suggesting that TSP‐1 deletion protects against leptin‐induced atherosclerosis. Overall, our data suggest a potential cross‐talk between leptin and TSP‐1 that may play a critical role in hyperleptinemia‐induced atherosclerosis.

Aspirin enhances protective effect of fish oil against thrombosis and injury-induced vascular remodelling.

Although aspirin (acetylsalicylic acid) is commonly used to prevent ischaemic events in patients with coronary artery disease, many patients fail to respond to aspirin treatment. Dietary fish oil (FO), containing ω3 polyunsaturated fatty acids (PUFAs), has anti-inflammatory and cardio-protective properties, such as lowering cholesterol and modulating platelet activity. The objective of the present study was to investigate the potential additional effects of aspirin and FO on platelet activity and vascular response to injury. Femoral arterial remodelling was induced by wire injury in mice. Platelet aggregation, and photochemical- and ferric chloride-induced carotid artery thrombosis were employed to evaluate platelet function. FO treatment increased membrane ω3 PUFA incorporation, lowered plasma triglyceride and cholesterol levels, and reduced systolic BP in mice. FO or aspirin alone inhibited platelet aggregation; however, when combined, they exhibited synergistic suppression of platelet activity in mice, independent of COX-1 inhibition. FO alone, but not aspirin, attenuated arterial neointimal growth in response to injury. Strikingly, a combination of FO and aspirin synergistically inhibited injury-induced neointimal hyperplasia and reduced perivascular inflammatory reactions. Moreover, co-administration of FO and aspirin decreased the expression of pro-inflammatory cytokines and adhesion molecules in inflammatory cells. Consistently, a pro-resolution lipid mediator-Resolvin E1, was significantly elevated in plasma in FO/aspirin-treated mice. Co-administration of FO and low-dose aspirin may act synergistically to protect against thrombosis and injury-induced vascular remodelling in mice. Our results support further investigation of adjuvant FO supplementation for patients with stable coronary artery disease.

Nutrition and inborn errors of metabolism: challenges in Phenylketonuria

Phenylketonuria (PKU) is caused by the deficiency of the phenylalanine hydroxylase enzyme, which converts phenylalanine (Phe) to tyrosine. If left untreated from birth, this deficiency results in high levels of Phe in the blood, neurotoxic to the brain [1].The restriction of dietary Phe represents the mainstain of PKU management. PKU diet is mainly made up by variable amounts of vegetables and fruits (poor in Phe natural foods), minimal amounts of animal products (usually milk), low-protein foods (low-protein bread and pasta) and Phe-free protein substitutes, which provide mainly essential aminoacid and micronutrients, to reach the required amount of daily protein, minerals and vitamins [2,3]. This type of dietary regimen provide lower saturated and polyunsaturated fat, cholesterol as well as higher carbohydrates intake than healthy pediatric population. The PKU diet follows the norms of the so called “prudent” diet for the prevention of cardiovascular disorders. In particular saturated fats may be less than 7% and polyunsaturated higher than 5% total energy with a supply less than 50 mg cholesterol per day [2]. Indeed PKU children show lower plasma cholesterol levels as compared to healthy children, particularly low density lipoprotein particles. Nevertheless both dietary habits and genetic predisposition may interact in keeping low blood lipid levels in PKU population [2]. However a lower antioxidant status and higher homocysteine levels have been reported in PKU, suggesting a possibly increased risk for thrombosis, atherosclerosis and stroke [4,5]. Furthermore, even if PKU children are routinely long-term monitored for dietary intake some studies showed evidence for overweight in this population [6,7]. However more data on body composition in PKU individuals are needed. Further research should be necessary to better understand the nutritional quality of low-protein foods and Phe-free protein substitutes. This nutritional aspect is particularly interesting, in view of recent results about low-protein products: low-protein bread, pasta, flour and breakfast cereals appear to provide from 2 to 18% more energy than their protein-containing equivalent food [6] and some low-Phe pasta and crackers, commercially available, show an high glycemic index (data unpublished). Moreover an altered food behaviour, such as an irregular intake of higher fat food or low-protein foods, has been reported [8,9]. Few data are available on physical activity levels in PKU patients [8]. In conclusion given the growing population of adults with PKU, it could be important to investigate the non-communicable diseases risk in this population to better optimize nutritional treatment strategies.

Anti-inflammatory actions of statins in human macrophages. Maarab Alkorashy and Dipak P. Ramji

Objectives: Atherosclerosis is an inflammatory disorder of the vasculature regulated by cytokines. Interferon-γ (IFN-γ) is a key pro-inflammatory cytokine that modulates several steps in this disease. The discovery of statins, inhibitors of 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA reductase), a rate-limiting enzyme in the synthesis of cholesterol, has had a major impact in reducing morbidity and mortality from atherosclerosis. Statins also have beneficial actions beyond lowering plasma cholesterol levels, the so-called pleiotropic effects.

Cholesterol metabolism, transport, and hepatic regulation in dairy cows during transition and early lactation

The transition from the nonlactating to the lactating state represents a critical period for dairy cow lipid metabolism because body reserves have to be mobilized to meet the increasing energy requirements for the initiation of milk production. The purpose of this study was to provide a comprehensive overview on cholesterol homeostasis in transition dairy cows by assessing in parallel plasma, milk, and hepatic tissue for key factors of cholesterol metabolism, transport, and regulation. Blood samples and liver biopsies were taken from 50 multiparous Holstein dairy cows in wk 3 antepartum (a.p.), wk 1 postpartum (p.p.), wk 4 p.p., and wk 14 p.p. Milk sampling was performed in wk 1, 4, and 14 p.p. Blood and milk lipid concentrations [triglycerides (TG), cholesterol, and lipoproteins], enzyme activities (phospholipid transfer protein and lecithin:cholesterol acyltransferase) were analyzed using enzymatic assays. Hepatic gene expression patterns of 3-hydroxy-3-methylglutaryl-coenzyme A (HMGC) synthase 1 (HMGCS1) and HMGC reductase (HMGCR), sterol regulatory element-binding factor (SREBF)-1 and -2, microsomal triglyceride transfer protein (MTTP), ATP-binding cassette transporter (ABC) A1 and ABCG1, liver X receptor (LXR) α and peroxisome proliferator activated receptor (PPAR) α and γ were measured using quantitative RT-PCR. Plasma TG, cholesterol, and lipoprotein concentrations decreased from wk 3 a.p. to a minimum in wk 1 p.p., and then gradually increased until wk 14 p.p. Compared with wk 4 p.p., phospholipid transfer protein activity was increased in wk 1 p.p., whereas lecithin:cholesterol acyltransferase activity was lowest at this period. Total cholesterol concentration and mass, and cholesterol concentration in the milk fat fraction decreased from wk 1 p.p. to wk 4 p.p. Both total and milk fat cholesterol concentration were decreased in wk 4 p.p. compared with wk 1 and 14 p.p. The mRNA abundance of genes involved in cholesterol synthesis (SREBF-2, HMGCS1, and HMGCR) markedly increased from wk 3 a.p. to wk 1 p.p., whereas SREBF-1 was downregulated. The expression of ABCA1 increased from wk 3 a.p. to wk 1 p.p., whereas ABCG1 was increased in wk 14 p.p. compared with other time points. In conclusion, hepatic expression of genes involved in the biosynthesis of cholesterol as well as the ABCA1 transporter were upregulated at the onset of lactation, whereas plasma concentrations of total cholesterol, phospholipids, lipoprotein-cholesterol, and TG were at a minimum. Thus, at the gene expression level, the liver seems to react to the increased demand for cholesterol after parturition. Whether the low plasma cholesterol and TG levels are due to impaired hepatic export mechanisms or reflect an enhanced transfer of these compounds into the milk to provide essential nutrients for the newborn remains to be elucidated.

Lipids in health and disease.

Background: Changes in lipid profile have long been associated with malignancies as lipids play a key role in maintenance of cell integrity. This study evaluated the alterations in extended lipid profile in untreated patients of oral submucous fibrosis (OSMF) and studied the correlation between lipid levels with tobacco consumption. Materials and methods: In this hospital-based study, 65 clinically diagnosed and histopathologically proven patients of OSMF and 42 age and sex matched controls were studied. In these samples serum lipids including: (i) Total cholesterol, (ii) LDL cholesterol (LDLC), (iii) HDL cholesterol (HDLC) (iv) VLDL cholesterol (VLDLC) (v) triglycerides (vi) Apo-A1 (viii) Apo-B and (viii) LPa were analyzed. Results: A significant decrease in plasma total cholesterol, HDLC and Apo-A1 was observed in patients with OSMF as compared to the controls. Thus an inverse relationship between plasma lipid levels and patients was found in OSMF. Conclusion: The lower levels of plasma cholesterol and other lipid constituents in patients might be due to their increased utilization. The findings strongly warrant an in-depth study of alterations in plasma lipid profile in patients with oral precancerous conditions.

Temporal and spatial dependence of inflammatory biomarkers and suppression by fluvastatin in dextran sodium sulfate-induced rat colitis model.

Dextran sodium sulfate (DSS)-induced colitis in rats is widely used as an experimental model for elucidating the etiology of ulcerative colitis (UC) and developing its novel remedy. We investigated the temporal and spatial changes in inflammatory mediators such as tumor necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS) in the regions of rectum and distal colon and examined whether statins, which were designed to lower plasma cholesterol levels, influenced those mediators. Colitis was induced in rats by oral administration of 5 % DSS for 5 days, followed by 2 % DSS for 10 days. 5 % DSS rats were treated with fluvastatin (20 mg/kg) concomitantly for 5 days. The expression of inflammatory mediators of a sequence of four regions in rectum (R) and distal colon (D0, D1, and D2) was determined by quantitative RT-PCR. The peak of colitic damage, which was confirmed clinically and histopathologically, was found on days 4-6. The expression of TNF-α, iNOS, cytokine-induced neutrophil chemoattractant-1, interleukin (IL)-1β, and IL-6 mRNA increased in R time dependently, showing the peak on days 4-6, and then decreased thereafter. The levels of mRNAs reduced from R to D0, D1, and D2 region dependently. Fluvastatin decreased the expression of these markers in addition to the prevention of DSS-induced damage. Results demonstrated that the expression of inflammatory biomarkers had time and region specificity and was markedly inhibited by fluvastatin. To obtain a precise drug effect for UC, it is important to elucidate the temporal and spatial dependence of inflammatory biomarkers in DSS colitis model.

Select Articles Published on the Topic of Coronary Heart Disease in 2013

Select Articles Published on the Topic of Coronary Heart Disease in 2013

Thyroid hormone analogues and derivatives: Actions in fatty liver

Fatty liver or nonalcoholic fatty liver disease (NAFLD), a problem of increasing clinical significance and prevalence worldwide, is associated with increased risk for the development of cirrhosis and hepatocellular carcinoma. Although several therapeutic approaches can be used in the context of NAFLD, dietary and physical activities are still the most frequently used strategies. Some pharmacological agents show promising results although no conclusions can be drawn from recent clinical trials. Thyroid hormones [THs; thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3)] coordinate a diverse array of physiological events during development and lipid/energy homeostasis and have some potentially therapeutic actions which include inducing weight loss, and lowering plasma cholesterol levels and tissue adiposity. The thyroid hormones exert their physiological effects by binding to specific nuclear receptors [thyroid hormone receptors (TR)] of which the TRβ isoform is liver specific and has been considered a putative target for the treatment of dyslipidemia and fatty liver. In view of this, the aim of the review is (1) to provide an overview of the action of T3 on lipid metabolism with implications for liver steatosis and (2) to provide an update on the current knowledge concerning the administration of TRβ selective thyromimetics (GC-1 and MB07811), as well as of 3,5-diiodo-L-thyronine and its novel functional analogue TRC150094 in animal models of overweight and related disorders including primarily fatty liver.

Omega-3 Fatty Acid Enriched Chevon (Goat Meat) Lowers Plasma Cholesterol Levels and Alters Gene Expressions in Rats

In this study, control chevon (goat meat) and omega-3 fatty acid enriched chevon were obtained from goats fed a 50% oil palm frond diet and commercial goat concentrate for 100 days, respectively. Goats fed the 50% oil palm frond diet contained high amounts of α-linolenic acid (ALA) in their meat compared to goats fed the control diet. The chevon was then used to prepare two types of pellets (control or enriched chevon) that were then fed to twenty-male-four-month-old Sprague-Dawley rats (n = 10 in each group) for 12 weeks to evaluate their effects on plasma cholesterol levels, tissue fatty acids, and gene expression. There was a significant increase in ALA and docosahexaenoic acid (DHA) in the muscle tissues and liver of the rats fed the enriched chevon compared with the control group. Plasma cholesterol also decreased (P < 0.05) in rats fed the enriched chevon compared to the control group. The rat pellets containing enriched chevon significantly upregulated the key transcription factor PPAR-γ and downregulated SREBP-1c expression relative to the control group. The results showed that the omega-3 fatty acid enriched chevon increased the omega-3 fatty acids in the rat tissues and altered PPAR-γ and SREBP-1c genes expression.

Ameliorative effect of Pracparatum mungo extract on high cholesterol diets in hamsters

This study was designed to test the lipid-lowering and antioxidative activities of Pracparatum mungo extract (PME), in comparison to its components berberine and glycyrrhizin in cholesterol-fed hamsters. The PME and berberine significantly lowered the atherogenic index compared to glycyrrhizin and the control (P < 0.05). The hepatic HMG-CoA reductase activity was significantly lower in the PME and berberine groups than in the glycyrrhizin group (P < 0.05), while the hepatic ACAT activity was significantly decreased by all treatments with respect to the high cholesterol fed group (P < 0.05). The overall potential of the antioxidant system was significantly enhanced by the PME, berberine and glycyrrhizin supplements as the plasma and hepatic TBARS levels were lowered while the hepatic superoxide dismutase activity and glutathione levels, HMG-CoA reductase, LDL receptor, PPAR, SREBP-2 and CYP7A1 mRNA expressions were increased by the treatments of PME and berberine in comparison with the high cholesterol fed hamsters (P < 0.05). Collectively, these results suggest that the supplementation of PME, berberine and glycyrrhizin increased antioxidant activity in hamsters. Furthermore, we observed that PME and berberine groups promoted the excretion of neutral and acidic sterols (P < 0.05), that could contribute to explain the lower plasma and hepatic cholesterol levels found in the treated animals.

Saturated fatty acids activate ERK signaling to downregulate hepatic sortilin 1 in obese and diabetic mice

Hepatic VLDL overproduction is a characteristic feature of diabetes and an important contributor to diabetic dyslipidemia. Hepatic sortilin 1 (Sort1), a cellular trafficking receptor, is a novel regulator of plasma lipid metabolism and reduces plasma cholesterol and triglycerides by inhibiting hepatic apolipoprotein B production. Elevated circulating free fatty acids play key roles in hepatic VLDL overproduction and the development of dyslipidemia. This study investigated the regulation of hepatic Sort1 in obesity and diabetes and the potential implications in diabetic dyslipidemia. Results showed that hepatic Sort1 protein was markedly decreased in mouse models of type I and type II diabetes and in human individuals with obesity and liver steatosis, whereas increasing hepatic Sort1 expression reduced plasma cholesterol and triglycerides in mice. Mechanistic studies showed that the saturated fatty acid palmitate activated extracellular signal-regulated kinase (ERK) and inhibited Sort1 protein by mechanisms involving Sort1 protein ubiquitination and degradation. Consistently, hepatic ERK signaling was activated in diabetic mice, whereas blocking ERK signaling by an ERK inhibitor increased hepatic Sort1 protein in mice. These results suggest that increased saturated fatty acids downregulate liver Sort1 protein, which may contribute to the development of dyslipidemia in obesity and diabetes.

Impaired Cholesterol Metabolism and Enhanced Atherosclerosis in Clock Mutant Mice

Clock is a key transcription factor that positively controls circadian regulation. However, its role in plasma cholesterol homeostasis and atherosclerosis has not been studied. We show for the first time that dominant-negative Clock mutant protein (Clock(Δ19/Δ19)) enhances plasma cholesterol and atherosclerosis in 3 different mouse models. Detailed analyses revealed that Clk(Δ19/Δ19)Apoe(-/-) mice display hypercholesterolemia resulting from the accumulation of apolipoprotein B48-containing cholesteryl ester-rich lipoproteins. Physiological studies showed that enhanced cholesterol absorption by the intestine contributes to hypercholesterolemia. Molecular studies indicated that the expression of Niemann Pick C1 Like 1, Acyl-CoA:Cholesterol acyltransferase 1, and microsomal triglyceride transfer protein in the intestines of Clk(Δ19/Δ19)Apoe(-/-) mice was high and that enterocytes assembled and secreted more chylomicrons. Furthermore, we identified macrophage dysfunction as another potential cause of increased atherosclerosis in Clk(Δ19/Δ19)Apoe(-/-) mice. Macrophages from Clk(Δ19/Δ19)Apoe(-/-) mice expressed higher levels of scavenger receptors and took up more modified lipoproteins compared with Apoe(-/-) mice, but they expressed low levels of ATP binding casette protein family A member 1 and were defective in cholesterol efflux. Molecular studies revealed that Clock regulates ATP binding casette protein family A member 1 expression in macrophages by modulating upstream transcription factor 2 expression. Clock(Δ19/Δ19) protein enhances atherosclerosis by increasing intestinal cholesterol absorption, augmenting uptake of modified lipoproteins by macrophages, and reducing cholesterol efflux from macrophages. These studies establish that circadian Clock activity is crucial in maintaining low plasma cholesterol levels and in reducing atherogenesis in mice.

The novel sirt1 activator srt3025 provides atheroprotection through increased hepatic low-density lipoprotein receptor expression

Background: Increased plasma low-density lipoprotein (LDL) cholesterol is a driving force of atherosclerosis. Hepatic LDL receptor (LDL-R) expression confers atheroprotection by removing cholesterol from the blood stream. Genetic studies of SIRT1 have predominantly shown to have beneficial effects in metabolic diseases. However, its role in atherosclerosis and lipid metabolism remains controversial. Purpose: We compared the effects of pharmacological SIRT1 activation on lipid metabolism and atherosclerosis in apolipoprotein E knockout (ApoE-/-) and LDL-R knockout (LDL-R-/-) mice. Methods: We placed male ApoE-/- or LDL-R-/- mice on a high-cholesterol diet (1.25% w/w) or the same diet supplemented with the SIRT1 activator SRT3025 (3.18g/kg diet; Sirtris, Cambridge, MA, USA) for 12 weeks and then assessed plasma lipids and cytokines, severity of aortic atherosclerosis, hepatic lipid content and hepatic expression of genes involved in inflammation and lipid homeostasis. In addition, we assessed the effects of SRT3025 on LDL-R expression in hepatic AML12 cells in vitro. Results: ApoE-/- mice treated with SRT3025 showed less atherosclerosis and steato-hepatitis and had lower levels of plasma cholesterol (LDL- and total cholesterol), TNFα, MCP-1, and IL-6 compared with placebo-treated control mice. LDL-R expression was increased 10-fold in drug-treated ApoE-/- mice. Corresponding SRT3025 experiments in LDL-R-/- mice revealed a loss of atheroprotection without a decrease in plasma cholesterol. In vitro SIRT1 activator treatment of hepatic AML12 cells induced LDL-R expression; this increase was abolished after SIRT1 knockdown. Conclusions: Pharmacological SIRT1 activation confers atheroprotection through increased hepatic LDL-R protein expression and decreased plasma LDL cholesterol. Our findings identify induction of hepatic LDL-R expression as a novel downstream effect of SIRT1 activity and highlight the potential of SIRT1 activation as an anti-atherosclerotic strategy.

Healthy Obese and Post Bariatric Patients - Metabolic and Vascular Patterns

Obesity and the metabolic syndrome (MetS) are associated with endothelial dysfunction (ED). An established method to determine ED is retinal vessel analysis. Obesity is associated with MetS, but obese patients not matching all criteria of the MetS and therefore defined as metabolically healthy obese subjects (MHOS) exist. Bariatric surgery may be an appropriate option to treat morbid obesity. The aim of this study was to compare MetS, MHOS and post bariatric patients in adipocytokine -patterns and ED. Arterio-venous ratio (AVR) and vessel diameters from retinal photographs (IMEDOS™), parameters of MetS (IDF) and obesity-associated factors (hsCRP, TNF, Il-6, MCP-1, sICAM, sVCAM, IGF-BP3, RBP 4 and adiponectin) were assessed in 51 obese patients with MetS, 20 obese patients without MetS and 21 patients pre and post bariatric surgery. Bariatric surgery improved ED as reflected by AVR and venous diameters (p<0.05 for both). These improvements were associated with lower levels of fasting plasma glucose, insulin, HOMA-IR, LDL-C, triglycerides, cholesterol, hsCRP, sICAM, and higher levels of adiponectin and RBP4 (p<0.05 for each parameter). MHOS differed from MetS by neck circumference, fasting plasma glucose, HOMA-IR, triglycerides, HDL-C, sICAM, and adiponectin (p<0.05), but not by RRs, RRd, insulin, LDL-C, hsCRP, Il-6, TNF, MCP-1, sVCAM, RBP-4, IGF-BP3, and retinal ED. These data indicate that improved insulin-sensitivity and reduced inflammatory mediators characterize the metabolic outcome of postbariatric patients in comparison to MHOS. Thus, MHOS characterizes an intermediate state between MetS and postbariatric patients.

Intestinal SR-BI does not impact cholesterol absorption or transintestinal cholesterol efflux in mice

Reverse cholesterol transport (RCT) can proceed through the classic hepatobiliary route or through the nonbiliary transintestinal cholesterol efflux (TICE) pathway. Scavenger receptor class B type I (SR-BI) plays a critical role in the classic hepatobiliary route of RCT. However, the role of SR-BI in TICE has not been studied. To examine the role of intestinal SR-BI in TICE, sterol balance was measured in control mice and mice transgenically overexpressing SR-BI in the proximal small intestine (SR-BI(hApoCIII-ApoAIV-Tg)). SR-BI(hApoCIII-ApoAIV-Tg) mice had significantly lower plasma cholesterol levels compared with wild-type controls, yet SR-BI(hApoCIII-ApoAIV-Tg) mice had normal fractional cholesterol absorption and fecal neutral sterol excretion. Both in the absence or presence of ezetimibe, intestinal SR-BI overexpression had no impact on the amount of cholesterol excreted in the feces. To specifically study effects of intestinal SR-BI on TICE we crossed SR-BI(hApoCIII-ApoAIV-Tg) mice into a mouse model that preferentially utilized the TICE pathway for RCT (Niemann-Pick C1-like 1 liver transgenic), and likewise found no alterations in cholesterol absorption or fecal sterol excretion. Finally, mice lacking SR-BI in all tissues also exhibited normal cholesterol absorption and fecal cholesterol disposal. Collectively, these results suggest that SR-BI is not rate limiting for intestinal cholesterol absorption or for fecal neutral sterol loss through the TICE pathway.

Both Transient and Continuous Corticosterone Excess Inhibit Atherosclerotic Plaque Formation in APOE*3-Leiden.CETP Mice

IntroductionThe role of glucocorticoids in atherosclerosis development is not clearly established. Human studies show a clear association between glucocorticoid excess and cardiovascular disease, whereas most animal models indicate an inhibitory effect of glucocorticoids on atherosclerosis development. These animal models, however, neither reflect long-term glucocorticoid overexposure nor display human-like lipoprotein metabolism.AimTo investigate the effects of transient and continuous glucocorticoid excess on atherosclerosis development in a mouse model with human-like lipoprotein metabolism upon feeding a Western-type diet.MethodsPair-housed female APOE*3-Leiden.CETP (E3L.CETP) mice fed a Western-type containing 0.1% cholesterol for 20 weeks were given corticosterone (50 µg/ml) for either 5 (transient group) or 17 weeks (continuous group), or vehicle (control group) in the drinking water. At the end of the study, atherosclerosis severity, lesion area in the aortic root, the number of monocytes adhering to the endothelial wall and macrophage content of the plaque were measured.ResultsCorticosterone treatment increased body weight and food intake for the duration of the treatment and increased gonadal and subcutaneous white adipose tissue weight in transient group by +35% and +31%, and in the continuous group by +140% and 110%. Strikingly, both transient and continuous corticosterone treatment decreased total atherosclerotic lesion area by −39% without lowering plasma cholesterol levels. In addition, there was a decrease of −56% in macrophage content of the plaque with continuous corticosterone treatment, and a similar trend was present with the transient treatment.ConclusionIncreased corticosterone exposure in mice with human-like lipoprotein metabolism has beneficial, long-lasting effects on atherosclerosis, but negatively affects body fat distribution by promoting fat accumulation in the long-term. This indicates that the increased atherosclerosis observed in humans in states of glucocorticoid excess may not be related to cortisol per se, but might be the result of complex indirect effects of cortisol.

Abstract 104: Apolipoprotein D: Implications for Multiple Roles in Lipid Metabolism

Introduction- ApoD is a ubiquitously expressed protein that binds small hydrophobic ligands and is a minor component of lipoproteins. Polymorphisms of the human ApoD gene are associated with lipid abnormalities, specifically the reduction of HDL and ApoA1 levels. In fact, hepatic overexpression of ApoD has been shown to regulate the amount of plasma triglycerides. ApoD is also upregulated in human and mouse models of atherosclerosis, and is localized in cell types involved in atherosclerotic lesion formation. These data suggest that ApoD plays a role in lipid metabolism by modulating cellular processes in vascular cells during atherogenesis. In this study, our objective is to identify the role(s) of ApoD in lipid metabolism and to elucidate the mechanisms involved in this process. Methods and Results- To accomplish our objective, we used a two-pronged approach. We first studied the effect of ApoD on lipid metabolism on a chow diet. There was no significant difference between the levels of plasma cholesterol in ApoD -/- and wild-type mice on a chow diet; however, hepatic cholesterol levels had more than doubled. A 96-gene PCR array was used to assess differential expression of genes involved in fatty liver biogenesis. There was at least a 2-fold difference in expression in about 10 genes involved in insulin/glucose signaling, lipogenesis, and inflammation in the ApoD -/- mice. We then studied the effect of a Western diet in the ApoD -/- mice, which showed a significant reduction in plasma LDL-cholesterol and HDL-cholesterol when compared to wild-type mice. Analysis of the HDL fractions after subjecting plasma to a Fast Protein Liquid Chromatography column revealed increased levels of ApoA1 and Lecithin Cholesterol Acyl Transferase (LCAT) activity in ApoD -/- mice. Conclusion- A decrease in plasma cholesterol and an increase in ApoA1 and LCAT activity suggest that ApoD may play a role in the catabolism of HDL particles, resulting in lower plasma cholesterol levels in ApoD -/- mice. Our current data implies that ApoD plays a multifunctional role in lipid metabolism and the mechanism by which this occurs must be further examined.