Low Density Lipoprotein Production Research Articles

PS-B12-8: ANGIOTENSIN II TYPE I RECEPTOR SIGNAL REGULATES MITOCHONDRIAL DYNAMICS, CAUSING MUSCULAR MITOCHONDRIAL DYSFUNCTION AND SARCOPENIA UNDER METABOLIC STRESS

Introduction: Metabolic stress, such as oxidized low density lipoprotein (ox-LDL) and advanced glycation end products (AGE) cause atherosclerotic cardiovascular diseases through dysfunction of mitochondria, which undergo quality control by mitochondrial dynamics, fission and fusion. Mitochondria also plays a crucial role in regulating muscular function, and its dysfunction leads to sarcopenia. This study aims to clarify whether and how mitochondrial dynamics are involved in the development of sarcopenia under metabolic stress. Methods: We used human skeletal muscle cells (HSMC) in in vitro experiments and C57BL6 (WT), apolipoprotein E (ApoE) deficient and the double knockout of ApoE and AT1R (DKO) mice in in vivo experiments. Results: Administration of either ox-LDL or AGE to HSMC induced mitochondrial fission through activation of fission factor, Drp1, decreased mitochondrial membrane potential assessed by JC-1 staining and increased reactive oxygen species assessed by Mito-sox Red staining and apoptosis, which were restored by Drp1-specific inhibitor, mdivi-1. Inhibition of angiotensin II type 1 receptor (AT1R) by AT1R blocker also ameliorated excessive mitochondrial fission, its function and oxidative stress induced by either ox-LDL or AGE in HSMC. These results suggest that metabolic stress induces mitochondrial fission and its dysfunction, which may cause sarcopenia. Muscular strength and the ratio of muscle weight to tibia length were lower in ApoE than those in WT. The number of fused mitochondria and mitochondrial function were lower and oxidative stress and the number of apoptotic cell were higher in ApoE KO than those of WT. Muscle strength, the ratio of muscle weight to tibia length, the number of fused mitochondria and its function were higher and the number of apoptotic cell were lower in DKO than those in ApoE KO mice. Taken together, these results suggest that either ox-LDL or AGE causes sarcopenia through AT1R signal-dependent mitochondrial fission and subsequent mitochondrial dysfunction. Conclusion: Either ox-LDL or AGE induces mitochondrial dysfunction through AT1R signal-regulating mitochondrial fission, which causes sarcopenia. Inhibition of AT1R signal may be a potential therapeutic strategy to avoid development of sarcopenia in patients with life style related diseases, such as dyslipidemia and diabetics.

Evidence of Direct Hepatic Secretion of Low density Lipoprotein (LDL) in Mice

<h3>Lead Author's Financial Disclosures</h3> Nothing to disclose. <h3>Study Funding</h3> National Lipid Association Junior Faculty Research Award 2020, NIH P01HL151328 and HL45095 (IJG). <h3>Background/Synopsis</h3> LDL is the major atherogenic lipoprotein causing atherosclerosis, leading to cardiovascular disease (CVD), the primary cause of morbidity and mortality in the United States. Lipoprotein lipase (LpL) is the rate limiting enzyme hydrolyzing triglyceride rich lipoproteins in the circulation. Current understanding is that LpL mediated hydrolysis of very low density lipoprotein (VLDL) generates cholesterol rich LDL particles in the circulation. However, evidence from in vitro studies as well as some human kinetic data suggest that the liver might directly secrete LDL into the circulation. <h3>Objective/Purpose</h3> In this study, we determine whether combined deficiency of lipoprotein lipase and hepatic LDL receptor (LDLR) would lead to decreased circulating LDL cholesterol (LDL-C) levels. <h3>Methods</h3> We used a mouse model of tamoxifen inducible global LpL deficiency (iLpl-/-). To knock down hepatic genes like LDLR and hepatic lipase (HL) we utilized anti sense oligonucleotides (ASOs). <h3>Results</h3> As expected, iLpl-/- mice display reduced plasma LDL-C levels compared to control mice (5 mg/dl vs 30 mg/dl). To determine whether LDL-C would increase with knock down of hepatic LDLRs, we used LDLR ASO in control and iLpl-/- mice. As anticipated, LDL-C levels increased in control mice to 150 mg/dl. Remarkably, plasma LDL-C also increased in iLpl-/- mice to levels similar to that of control mice. We then fed the mice a high cholesterol western diet for two weeks; this increased LDL-C levels equally in both mice to 300 mg/dl. When we overexpressed PCSK9 to inhibit LDLR in iLpl-/- mice, we again observed increases in LDL-C similar to control mice with PCSK9 overexpression. Further, to test if HL, another extracellular triglyceride lipase, is converting VLDL to LDL in iLpl-/- mice, we knocked down HL in control and iLpl-/- mice. HL knockdown did not alter LDL-C levels in control or iLpl-/- mice. <h3>Conclusions</h3> These data suggest the presence of direct LDL secretion from liver. We are investigating why this is apparent only with concomitant loss of LpL and LDLRs. We postulate that LDLRs have an additional gate-keeping function to halt secretion of newly synthesized LDL particles from the liver in addition to their well-established role in clearance of plasma LDL. When LDLRs are limiting or in patients with combined hyperlipidemia, direct LDL production may constitute a major source of circulating LDL. If so, this could uncover a novel approach to treat familial hypercholesterolemia.

The Effect of Mipomersen in the Management of Patients with Familial Hypercholesterolemia: A Systematic Review and Meta-Analysis of Clinical Trials.

Background: Familial hypercholesterolemia (FH) lead to significant adverse effects in coronary arteries. Mipomersen is a second-generation antisense oligonucleotide that inhibits the synthesis of apolipoprotein B-100, an essential component of low density lipoprotein (LDL), and thus decreases the production of LDL. We aimed to determine the effect of mipomersen in patients with FH. Methods: We searched Ovid Medline, Ovid EMBASE, WHO ICTRP search portal, ISI database, the reference lists of relevant articles, and also Google Scholar to retrieve articles. All randomized controlled trials (RCTs) comparing patients with FH receiving mipomersen as an add-on and a parallel group receiving a placebo or no intervention were selected. Results: Five studies with more than 500 patients were included. All had low risk of bias. Pooling data showed that mipomersen probably reduces LDL compared with placebo [mean difference: −24.79, 95% CI (−30.15, −19.43)] but with a moderate level of certainty. There was a high level of evidence for injection site reactions [RR = 2.56, CI (1.47–4.44)] and a low level for increased serum alanine transaminase (ALT) > 3 times upper limit of normal (ULN) [RR = 5.19, CI (1.01–26.69)]. Conclusion: A moderate level of evidence in decreasing serum LDL indicates that we are uncertain if this drug provides benefit in any outcome important to patients. Although a low level of evidence for an increase in serum ALT leaves uncertainty about this adverse effect, injection site reactions in 10% or more of patients can be an important concern.

Low-density lipoprotein receptor is required for cholesteryl ester transfer protein to regulate triglyceride metabolism in both male and female mice.

Elevated triglycerides (TGs) and impaired TG clearance increase the risk of cardiovascular disease in both men and women, but molecular mechanisms remain poorly understood. Cholesteryl ester transfer protein (CETP) is a lipid shuttling protein known for its effects on high‐density lipoprotein cholesterol. Although mice lack CETP, transgenic expression of CETP in mice alters TG metabolism in males and females by sex‐specific mechanisms. A unifying mechanism explaining how CETP alters TG metabolism in both males and females remains unknown. Since low‐density lipoprotein receptor (LDLR) regulates both TG clearance and very low density lipoprotein (VLDL) production, LDLR may be involved in CETP‐mediated alterations in TG metabolism in both males and females. We hypothesize that LDLR is required for CETP to alter TG metabolism in both males and females. We used LDLR null mice with and without CETP to demonstrate that LDLR is required for CETP to raise plasma TGs and to impair TG clearance in males. We also demonstrate that LDLR is required for CETP to increase TG production and to increase the expression and activity of VLDL synthesis targets in response to estrogen. Additionally, we show that LDLR is required for CETP to enhance β‐oxidation. These studies support that LDLR is required for CETP to regulate TG metabolism in both males and females.

Glycomacropeptide Prevents Iron/Ascorbate-Induced Oxidative Stress, Inflammation and Insulin Sensitivity with an Impact on Lipoprotein Production in Intestinal Caco-2/15 Cells.

Background. Metabolic Syndrome (MetS), a major worldwide concern for the public health system, refers to a cluster of key metabolic components, and represents a risk factor for diabetes and cardiovascular diseases. As oxidative stress (OxS) and inflammation are the major triggers of insulin sensitivity (IS), a cardinal MetS feature, the principal aim of the present work is to determine whether glycomacropeptide (GMP), a milk-derived bioactive peptide, exerts beneficial effects on their expression. Methods. Fully differentiated intestinal Caco-2/15 cells are used to evaluate the preventive action of 2 mg/mL GMP against OxS and inflammation induced by the mixture iron-ascorbate (Fe/Asc) (200 μM:2 mM). The potency of GMP of decreasing the production of lipoproteins, including chylomicrons (CM), very-low-density lipoproteins (VLDL) and low-density lipoproteins (LDL) is also assessed. Results. The administration of GMP significantly reduces malondialdehyde, a biomarker of lipid peroxidation, and raises superoxide dismutase 2 and glutathione peroxidase via the induction of the nuclear factor erythroid 2–related factor 2, a transcription factor, which orchestrates cellular antioxidant defenses. Similarly, GMP markedly lowers the inflammatory agents tumor necrosis factor-α and cyclooxygenase-2 via abrogation of the nuclear transcription factor-kB. Moreover, GMP-treated cells show a down-regulation of Fe/Asc-induced mitogen activated protein kinase pathway, suggesting greater IS. Finally, GMP decreases the production of CM, VLDL, and LDL. Conclusions. Our results highlight the effectiveness of GMP in attenuating OxS, inflammation and lipoprotein biogenesis, as well as improving IS, the key components of MetS. Further investigation is needed to elucidate the mechanisms mediating the preventive action of GMP.

Abstract 198: Metabolic Stress Causes Mitochondrial Dysfunction and Vascular Senescence via Angiotensin II Type I Receptor Signal / Rho Kinase Induced Mitochondrial Fission

Introduction: Metabolic stress, such as oxidized low density lipoprotein (ox-LDL) and advanced glycation end products (AGE) cause mitochondrial dysfunction and evoke vascular senescence and atherosclerosis. Mitochondria are highly dynamic organelles that constantly change their morphology to fusion or fission. This study aims to clarify whether mitochondrial dynamics is involved in the etiology of vascular senescence. Methods: We used C57BL6 (WT), apolipoprotein E deficient (ApoE KO) and db/db mice. We also conducted in vitro experiments using VSMC and HUVEC. Results: The degree of arterial senescence, arterial protein level of Drp1 in mitochondrial fraction and mitochondrial oxidative stress were higher and the number of fused mitochondria and mitochondrial function were lower in either ApoE KO or db/db mice than those of WT mice. Treatment with Drp1-specific inhibitor, mdivi-1, to these mice reduced excessive mitochondrial fission, oxidative stress and attenuated vascular senescence. Administration of either ox-LDL or AGE to cells also induced excessive mitochondrial fission though phosphorylation of Drp1 at Ser616, mitochondrial dysfunction, reactive oxygen species production and cellular senescence. Treatment with mdivi-1 to these cells restored imbalance of mitochondrial dynamics and these detrimental alterations. These results suggest that metabolic stress-induced mitochondrial dysfunction and cellular senescence were derived from Drp1-dependent mitochondrial fission. Treatment with angiotensin II type1 receptor (AT1R) blocker (ARB) to either Apo E KO mice or db/db in in vivo experiments and administration of ARB to cells with ox-LDL or AGE stimulation in in vitro experiments inactivated Drp1 and improved imbalance of mitochondrial dynamics, mitochondrial dysfunction and cellular senescence, suggesting that AT1R signal is involved in regulating metabolic stress-induced mitochondrial fission. Finally, inhibition of Rho kinase ROCK1 successfully attenuated Drp1-mediated mitochondrial fission and cellular senescence derived from metabolic stress. Conclusion: Metabolic stress causes cellular and vascular senescence through AT1R signal/Rho kinase-mediated mitochondrial fission.

Interruption of Autophagosome Formation in Cardiovascular Disease, an Evidence for Protective Response of Autophagy

ABSTRACTBackground: A heart attack occurs when coronary artery blockage interrupts the blood supply to the heart such as is seen in cardiovascular disease (CVD). Importantly, autophagy is commonly regarded as a host defense mechanism against microbial invaders. Methods: A total of 50 blood samples were obtained from cardiovascular (CV) patients in addition to 30 samples that were obtained from healthy individuals and served as controls. Macrophages were isolated in vitro and propagated from the blood samples. Autophagosome formation, cytokine secretion, and apolipoprotein B (ApoB) gene expression were monitored in patient samples and their derived macrophages. Results: The results showed that autophagy-related (Atg) LC3 and Atg5 genes were significantly down-regulated in all samples obtained from CV patients. Furthermore, the relative gene expression of ApoB, which plays the major role in lipoprotein metabolism, was significantly increased in CV patients. Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) levels were increased in these blood samples. Interestingly, targeting of ApoB by small interference RNA (siRNA) reduced the production levels of low-density lipoprotein (LDL), IL-6 and TNF-α in patient-derived macrophages. Further, treatment of patient-derived macrophages with rapamycin, an autophagy inducer agent, successfully regulated the production of LDL, IL-6, TNF-α, and ApoB expression via activation of autophagosome formation. Conclusion: The current data reveal the potential disturbance of autophagy in CV patients that accompanied ApoB over-expression. Furthermore, our findings provide evidence for the protective role of autophagy in accumulation of pro-inflammatory cytokines and intracellular LDL degradation in CV patient-derived macrophages.

HUBUNGAN TEKANAN DARAH DENGAN KADAR KOLESTEROL LDL(Low Density Lipoprotein) PADA PENDERITA PENYAKIT JANTUNG KORONERDI RSUP.Dr.M.DJAMIL PADANG

Coronary heart disease is a disease caused by narrowing of the coronary arteries of the heart. This happens because of its high cholesterol levels can cause atherosclerosis in blood vessels Hypercholesterolemia mainly occurs when increased production of LDL (Low Density Lipoprotein). As a result of the narrowing of blood vessels blood flow to the heart will be disrupted, causing symptoms of chest pain that is a typical symptom of coronary heart disease. Chronic atherosclerosis can cause blood flow to the heart to be disturbed, so that the left ventricle must pump stronger to produce enough force to push blood through the atherosclerotic vascular system that can lead to increased systolic and diastolic blood pressure resulting in hypertension.&#x0D; This study included descriptive analytic research using cross sectional approach, is dependent variable (incidence of coronary heart disease) and indenpendent variable (blood pressure and LDL cholesterol level) collected at the same time. The study was conducted on September 10, 2016 - April 4, 2017 at the Central Laboratory and Heart Ward RSUP.Dr. M. Djamil Padang. The sampling technique used is purposive sampling, that is the technique of determining the sample with certain consideration. Of 36 samples of patients with coronary heart disease (CHD) showed a correlation between systolic blood pressure with LDL cholesterol level has a value of 0.585&gt; 0.05 which states there is a moderate relationship between the two variables, and has significant significance of 0.00 &lt;0, 05 and Ha are received.&#x0D; The correlation between diastolic blood pressure and LDL levels has a value of 0,507&gt; 0,05 which states there is a moderate relationship between the two variables, and has significant value of 0.02 significance &lt;0.05 and Ha is accepted. Based on these results then there is a significant relationship between blood pressure with LDL cholesterol levels in the blood.

Impairment of the Lipid Metabolism in Newborns in the Early Neonatal Period

The purpose of the study . To study parameters of the lipid metabolism in newborn infants to identify general patterns depending on the gestational age. Materials and methods . The course of pregnancy and its outcome was analyzed in 286 women who gave birth to 323 infants; 89 of them were born in multiple pregnancies. The infants were divided into 4 groups depending on the gestational age. Levels of cholesterol (C), triglycerides (TG), low-density lipoproteins (LDL) and high-density lipoproteins (HDL) were tested in the central venous blood immediately after birth and on the 5th day of life. Results . Hypotriglyceridemia below 0.2 mmol/l was typical for 31.3% of the newborns; a TG level within the range of 0.21—0.5 mmol/l was found in 43.3% of infants, i.e. the perinatal production of TG was decreased in 76.6% of infants. The perinatal TG production depended on the infant's gestational age: the smaller it was, the lower TG blood level was in infants at birth. At the gestational age of 25—33 weeks, the perinatal TG production was low in most newborns. The perinatal production of the lipid metabolism parameter was increased with the increase of the gestational age. The TG blood level increased rapidly at the gestational age of 37 weeks. The postnatal TG production in the blood of newborn babies had no dependence on the gestational age strating from the gestational age of 31 weeks and more. Hypercholesterolemia and lower both LDL and HDL levels were found in newborns of all groups at birth; no significant intergroup differences in concentration of C, HDL or LDL were observed (P&gt;0.01). Conclusion . The state of the lipid metabolism in the newborns in the perinatal period depends on the gestational age and the birth weight. Low TG production is typical for small premature infants with a low and extremely low birth weight due to physiological immaturity of organs and systems. The peculiarities of the prenatal morphogenesis make an adequate lipid metabolism possible by the full-term gestational age only. An abnormal course of pregnancy impairs normal triglyceride, C, LDL and HDL production. The greatest changes of the tested parameters are typical for small immature infants with a gestational age of 25—31 weeks. This age is associated with a high incidence of the respiratory distress syndrome. Deficiency of buffer bases affects the TG production at birth; the pH value and blood oxygen tension at birth affect the C level. The production of lipid metabolism parameters increases with the increase of the gestational age. There are certain individual characteristics in newborns who may have perinatal disorders of the lipid metabolism at the full-term gestational age.

Survival benefit of a low ratio of visceral to subcutaneous adipose tissue depends on LDL clearance versus production in sepsis

BackgroundPatients with sepsis with a high ratio of visceral adipose tissue (VAT) to subcutaneous adipose tissue (SAT) have increased mortality. Our goal was to investigate the mechanism of this effect, noting that low LDL levels are also associated with increased sepsis mortality. Accordingly we tested for association between VAT/SAT, low-density lipoprotein (LDL) levels, and mortality. Then we examined the effect of statin treatment, which decreases LDL production, and the effect of PCSK9 genotype, which increases LDL clearance.MethodsWe performed retrospective analysis of a cohort of patients with sepsis from a tertiary care adult intensive care unit in Vancouver, Canada, who underwent abdominal computed tomography (CT) (n = 75) for clinical reasons. We compared LDL levels in patients with sepsis according to high versus low VAT/SAT and 90-day survival. We next examined the effects of statin therapy and PCSK9 loss-of-function genotype on survival.ResultsPatients with a low VAT/SAT had increased 90-day survival and were relatively protected against low LDL levels in sepsis compared to high VAT/SAT. Statin treatment abrogated the beneficial effects of low VAT/SAT; eliminating the difference in LDL levels and survival between patients with low and high VAT/SAT. PSCK9 loss-of-function genotype similarly eliminated the increased LDL levels in low VAT/SAT patients but, in contrast, increased the survival advantage of low VAT/SAT compared to high VAT/SAT.ConclusionsLow LDL levels per se are not simply associated with decreased sepsis survival because lowering LDL levels by inhibiting LDL production (statin treatment) is associated with adverse outcomes, while increased LDL clearance (PCSK9 loss-of-function genotype) is associated with improved outcomes in patients with low VAT/SAT.

Effects of MβCD on Lipoxygenase-Induced LDL Oxidation

Beta-cyclodextrin (β-CD) has been applied as drug/food carriers or potential drugs for treating some diseases. Most recently, some evidence indicated that methyl-β-cyclodextrin (MβCD) and 2-hydroxypropyl-β-cyclodextrin (2-HPβCD), two major derivatives of β-CD, may inhibit atherogenesis, implying that cyclodextrins also can be potential drugs for treating atherosclerosis. It is well known that modification (e.g. oxidation) of low-density lipoprotein (LDL) is one of the most critical steps of atherogenesis. Lipoxygenase, an enzyme able to be expressed by atherosclerosis-related vascular cells, is generally regarded as a possible in vivo agent of LDL oxidation. In this study, the effects of MβCD on LDL oxidation induced by lipoxygenase were investigated by measuring the electrophoretic mobility, conjugated diene formation, malondialdehyde (MDA) production, and amino group blockage of LDL. We found that the lipids depleted from LDL by MβCD could be oxygenated more readily by lipoxygenase whereas the lipoxygenase-induced oxidation of the remaining lipid-depleted LDL decreased. The data imply that MβCD has an inhibitory effect on lipoxygenase-induced LDL oxidation and probably helps to inhibit atherogenesis.

Lipid-Modulating Effect of Black Lingzhi Medicinal Mushroom, Amauroderma rugosum (Agaricomycetes), on Oleate-Induced Human Hepatocellular Liver Carcinoma Cells.

Dyslipidemia is the key precursor of atherosclerotic cardiovascular disease. The aim of this study was to investigate the lipid-modifying potential of organic solvent-partitioned extracts from fruiting bodies of Amauroderma rugosum in vitro using oleate-induced human hepatocellular liver carcinoma (HepG2) cells. Our results demonstrated that oleate-induced HepG2 cells treated with ethyl acetate (EA) extract greatly decreased intracellular and secreted total triglyceride (TG) and total cholesterol (TC) compared with other extracts. Further investigation of cellular expression of selected apolipoproteins also revealed that oleate-induced HepG2 cells treated with the EA extract best attenuated the apolipoprotein (Apo) profile by downregulating ApoB-100 and ApoE while upregulating ApoA1. Because both ApoB-100 and ApoE are key components of low-density lipoprotein (LDL) and very LDL (VLDL), which are recognized as "bad cholesterol," this result indicates that treatment with the EA extract inhibited LDL and VLDL production in oleate-induced HepG2 cells. On the other hand, increasing ApoA1 evidence shows antiatherogenic benefits to increasing ApoA1, the key component of high-density lipoprotein (HDL), particularly in relation to its role in promoting reverse cholesterol transport and preventing LDL oxidation; this indicates that the EA extract upregulated the production of HDL ("good cholesterol"). Hence, the EA extract is a good source of lipid-ameliorating agents in the management of dyslipidemia.

Factorial Effects of Evolocumab and Atorvastatin on Lipoprotein Metabolism.

Monoclonal antibodies against proprotein convertase subtilisin kexin type 9 (PCSK9), such as evolocumab, lower plasma low-density lipoprotein (LDL)-cholesterol concentrations. Evolocumab is under investigation for its effects on cardiovascular outcomes in statin-treated, high-risk patients. The mechanism of action of PCSK9 monoclonal antibodies on lipoprotein metabolism remains to be fully evaluated. Stable isotope tracer kinetics can effectively elucidate the mode of action of new lipid-regulating pharmacotherapies. We conducted a 2-by-2 factorial trial of the effects of atorvastatin (80 mg daily) and subcutaneous evolocumab (420 mg every 2 weeks) for 8 weeks on the plasma kinetics of very-low-density lipoprotein (VLDL)-apolipoprotein B-100 (apoB), intermediate-density lipoprotein-apoB, and LDL-apoB in 81 healthy, normolipidemic, nonobese men. The kinetics of apoB in these lipoproteins was studied using a stable isotope infusion of D3-leucine, gas chromatography/mass spectrometry, and multicompartmental modeling. Atorvastatin and evolocumab independently accelerated the fractional catabolism of VLDL-apoB (P<0.001 and P.032, respectively), intermediate-density lipoprotein-apoB (P=0.021 and P=.002, respectively), and LDL-apoB (P<0.001, both interventions). Evolocumab but not atorvastatin decreased the production rate of intermediate-density lipoprotein-apoB (P=0.043) and LDL-apoB (P<0.001), which contributed to the reduction in the plasma pool sizes of these lipoprotein particles. The reduction in LDL-apoB and LDL-cholesterol concentrations was significantly greater with combination versus either monotherapy (P<0.001). Whereas evolocumab but not atorvastatin lowered the concentration of free PCSK9, atorvastatin lowered the lathosterol/campesterol ratio (a measure of cholesterol synthesis/absorption) and apoC-III concentration. Both interventions decreased plasma apoE, but neither significantly altered lipoprotein lipase and cholesteryl ester protein mass or measures of insulin resistance. In healthy, normolipidemic subjects, evolocumab decreased the concentration of atherogenic lipoproteins, particularly LDL, by accelerating their catabolism. Reductions in intermediate-density lipoprotein and LDL production also contributed to the decrease in LDL particle concentration with evolocumab by a mechanism distinct from that of atorvastatin. These kinetic findings provide a metabolic basis for understanding the potential benefits of PCSK9 monoclonal antibodies incremental to statins in on-going clinical end point trials. URL: http://www.clinicaltrials.gov. Unique identifier: NCT02189837.

GW27-e0965 Small interfering RNA (SiRNA)-Mediated Silencing of Mediator Complex Subunit 6 (MED6) Gene Promoted Low Density Lipoprotein Production in Rat Myocardial cells in Vitro

Currently, while numerous studies have correlated mediator complex (MED) alterations with several diseases, fewer studies have investigated MED's role in coronary heart disease (CHD) initiation and progression. A number of studies have indicated that several subunits like MED1, MED13, and MED15

Mode-of-action evaluation for the effect of trans fatty acids on low-density lipoprotein cholesterol

The purpose of this work is to systematically consider the data relating to the mode of action (MOA) for the effects of industrially produced trans fatty acid (iTFA) on plasma low-density lipoprotein (LDL) levels. The hypothesized MOA is composed of two key events: increased LDL production and decreased LDL clearance. A substantial database supports this MOA, although the key events are likely to be interdependent, rather than sequential. Both key events are functions of nonlinear biological processes including rate-limited clearance, receptor-mediated transcription, and both positive and negative feedback regulation. Each key event was evaluated based on weight-of-evidence analysis and for human relevance. We conclude that the data are inadequate for a detailed dose-response analysis in the context of the evolved Bradford Hill considerations; however, the weight of evidence is strong and the overall shape of the dose-response curves for markers of the key events and the key determinants of those relationships is well understood in many cases and is nonlinear. Feedback controls are responsible for maintaining homeostasis of cholesterol and triglyceride levels and underlie both of the key events, resulting in a less-than-linear or thresholded relationship between TFA and LDL-C. The inconsistencies and gaps in the database are discussed.

Effects of cyclodextrins on the structure of LDL and its susceptibility to copper-induced oxidation

Cyclodextrins (CDs) have long been widely used as drug/food carriers and were recently developed as drugs for the treatment of diseases (e.g. Niemann-Pick C1 and cancers). It is unknown whether cyclodextrins may influence the structure of low-density lipoprotein (LDL), its susceptibility to oxidation, and atherogenesis. In this study, four widely used cyclodextrins including α-CD, γ-CD, and two derivatives of β-CD (HPβCD and MβCD) were recruited. Interestingly, agarose gel electrophoresis (staining lipid and protein components of LDL with Sudan Black B and Coomassie brilliant blue, respectively but simultaneously) shows that cyclodextrins at relatively high concentrations caused disappearance of the LDL band and/or appearance of an additional protein-free lipid band, implying that cyclodextrins at relatively high concentrations can induce significant electrophoresis-detectable lipid depletion of LDL. Atomic force microscopy (AFM) detected that MβCD (as a representative of cyclodextrins) induced size decrease of LDL particles in a dose-dependent manner, further confirming the lipid depletion effects of cyclodextrins. Moreover, the data from agarose gel electrophoresis, conjugated diene formation, MDA production, and amino group blockage of copper-oxidized LDL show that cyclodextrins can impair LDL susceptibility to oxidation. It implies that cyclodextrins probably help to inhibit atherogenesis by lowering LDL oxidation.

Liver-specific overexpression of LPCAT3 reduces postprandial hyperglycemia and improves lipoprotein metabolic profile in mice.

Previous studies have shown that group 1B phospholipase A2-mediated absorption of lysophospholipids inhibits hepatic fatty acid β-oxidation and contributes directly to postprandial hyperglycemia and hyperlipidemia, leading to increased risk of cardiometabolic disease. The current study tested the possibility that increased expression of lysophosphatidylcholine acyltransferase-3 (LPCAT3), an enzyme that converts lysophosphatidylcholine to phosphatidylcholine in the liver, may alleviate the adverse effects of lysophospholipids absorbed after a lipid-glucose mixed meal. The injection of an adenovirus vector harboring the human LPCAT3 gene into C57BL/6 mice increased hepatic LPCAT3 expression fivefold compared with mice injected with a control LacZ adenovirus. Postprandial glucose tolerance tests after feeding these animals with a bolus lipid-glucose mixed meal revealed that LPCAT3 overexpression improved postprandial hyperglycemia and glucose tolerance compared with control mice with LacZ adenovirus injection. Mice with LPCAT3 overexpression also showed reduced very low density lipoprotein production and displayed elevated levels of the metabolic- and cardiovascular-protective large apoE-rich high density lipoproteins in plasma. The mechanism underlying the metabolic benefits of LPCAT3 overexpression was shown to be due to the alleviation of lysophospholipid inhibition of fatty acid β-oxidation in hepatocytes. Taken together, these results suggest that specific LPCAT3 induction in the liver may be a viable strategy for cardiometabolic disease intervention.

MicroRNAs regulating apolipoprotein B-containing lipoprotein production

MicroRNAs (miRs) are small, non-coding RNAs that regulate gene expression and have been implicated in many pathological conditions. Significant progress has been made to unveil their role in lipid metabolism. This review aims at summarizing the role of different miRs that regulate hepatic assembly and secretion of apolipoprotein B (apoB)-containing lipoproteins. Overproduction and/or impaired clearance of these lipoproteins from circulation increase plasma concentrations of lipids enhancing risk for cardiovascular disease. So far, three miRs, miR-122, miR-34a, and miR-30c have been shown to modulate hepatic production of apoB-containing low density lipoproteins. In this review, we will first provide a brief overview of lipid metabolism and apoB-containing lipoprotein assembly to orient readers to different steps that have been shown to be regulated by miRs. Then, we will discuss the role of each miR on plasma lipids and atherosclerotic burden. Furthermore, we will summarize mechanistic studies explaining how these miRs regulate hepatic lipid synthesis, fatty acid oxidation, and lipoprotein secretion. Finally, we will briefly highlight the potential use of each miR as a therapeutic drug for treating cardiovascular diseases. This article is part of a Special Issue entitled: MicroRNAs and lipid/energy metabolism and related diseases edited by Carlos Fernández-Hernando and Yajaira Suárez.

Lipoprotein metabolism in an apoB-80 familial hypobetalipoproteinemia heterozygote

ObjectiveFamilial hypobetalipoproteinemia (FHBL) is characterized by mutations in APOB, the majority of these causing protein truncations, and low plasma levels of apolipoprotein (apo) B. The hypobetalipoproteinemia may be due to enhanced clearance and possibly reduced production of apoB-containing lipoproteins; the mechanism may depend on the length of the apoB truncation. We studied fasting lipoprotein metabolism in an FHBL subject heterozygous for a mutation causing a truncated apoB, apoB-80. Design and MethodsVery low density lipoprotein (VLDL)-, intermediate density lipoprotein (IDL)-, and low density lipoprotein (LDL)-apoB kinetics were determined in the fasting state using stable isotope methods and compartmental modeling. ResultsCompared with lean normolipidemic controls the apoB-80 FHBL subject had an elevated VLDL-apoB fractional catabolic rate and lower LDL production. ApoB production rates and IDL- and LDL-apoB fractional catabolic rates were not different. ConclusionFHBL subjects heterozygous for a mutation truncating apoB to 80% of full-length are able to produce VLDL-apoB normally, but have rapid clearance of these particles, resulting in low levels of circulating apoB.

Hepatic Effects of Estrogen on Plasma Distribution of Small Dense Low-Density Lipoprotein and Free Radical Production in Postmenopausal Women.

Hepatic effects of estrogen therapy on low-density lipoprotein (LDL) subfraction or oxidative stress have not been previously evaluated. The purpose of the present study was to investigate whether the differential hepatic effects of estrogen affect plasma distribution of small dense LDL and free radical production in postmenopausal women. In all, 45 postmenopausal women were given 0.625 mg/day of oral conjugated equine estrogen (CEE) (n=15), 1.0 mg/day of oral 17β estradiol (E2) (n=15), or 50 μg/day of transdermal 17βE2 (n=15) for 3 months. Subjects received either estrogen alone or with dydrogesterone at 5 mg/day. Plasma concentrations of sex hormone-binding globulin (SHBG), lipids, metallic ions, and derivatives of reactive oxygen metabolites (d-ROMs) were measured. CEE, but not oral 17βE2, increased the plasma concentrations of triglyceride, copper (Cu), and d-ROMs and the ratio of small dense LDL/total LDL cholesterol, a marker for plasma distribution of small dense LDL. Transdermal 17βE2 decreased d-ROMs concentrations but did not significantly change other parameters. Plasma concentrations of SHBG increased in the 3 groups. Estrogen-induced changes in triglyceride correlated positively either with changes in SHBG (R=0.52, P=0.0002) or the ratio of small dense LDL/total LDL cholesterol (R=0.65, P＜0.0001). Changes in Cu also correlated positively either with changes in SHBG (R=0.85, P＜0.0001) or d-ROMs (R=0.86, P＜0.0001). The hepatic effects of different routes or types of estrogen therapy may be associated with plasma distribution of small dense LDL and free radical production in postmenopausal women.