Triglyceride Transfer Research Articles

Abstract 1021: Bulky Hydrophobic Side Chains In The β1-sandwich Of Microsomal Triglyceride Transfer Protein Are Critical For The Transfer Of Both Triglycerides And Phospholipids

Hyperlipidemia predispose individuals to cardio-metabolic diseases, the most common cause of global mortality. Microsomal triglyceride transfer protein (MTP) transfers multiple lipids and is essential for the assembly of apoB-containing lipoproteins. MTP inhibition lowers plasma lipids but causes lipid retention in the liver and intestine. Previous studies suggested two lipid transfer domains in MTP and that specific inhibition of triglycerides (TG) and not phospholipids (PL) transfer can lower plasma lipids without significant tissue lipid accumulation. However, how MTP transfers different lipids and the domains involved in these activities are unknown. Here, we tested a hypothesis that two different β-sandwich domains in MTP transfer TG and PL. Mutagenesis of charged amino acids in β2-sandwich had no effect on PL transfer activity indicating that they are not critical. In contrast, amino acids with bulky hydrophobic side chains in β1-sandwich were critical for both TG and PL transfer activities. Substitutions of these residues with smaller hydrophobic side chains or positive charges reduced, while negatively charged side chains severely attenuated MTP lipid transfer activities. These studies point to a common lipid transfer domain for TG and PL in MTP that is enriched with bulky hydrophobic amino acids. Furthermore, we observed a strong correlation in different MTP mutants with respect to loss of both the lipid transfer activities, again implicating a common binding site for TG and PL in MTP. We propose that targeting of areas other than the identified common lipid transfer domain might reduce plasma lipids without causing cellular lipid retention.

Contemporary hypolipemic therapy: possibilities of novel hypolipemic drugs in correction of lipid metabolism disorders. Review

Dyslipidemia plays a role of significant risk factor for development and progression of cardiovascular diseases. Today several classes of hypolipemic drugs with evidenced effectiveness are used. But some patients don’t tolerate medicines with high efficacy or can’t achieve the targeted blood lipid profile levels even in case of the use of maximal doses or combined therapy. This necessitates the creation of new hypolipidemic agents.
 The review is devoted to discussion of new directions of influence on impaired lipid metabolism through creation of new classes of hypolipemic drugs with some perspectives of effective correction of lipid factors of cardiovascular risk (CVR) in cases of impossibility to achieve the targeted levels of low‑density lipoprotein cholesterol (LDL‑C) or there is a residual CVR caused by elevated serum triglyceride (TG) levels and/or low levels of high‑density lipoprotein cholesterol (HDL‑C).
 Among the novel drugs for hypercholesterolemia (HCE) correction, considerations are given for some mechanisms of action and efficacy of application of proprotein convertase subtilisin‑kexine type 9 (PCSK9) inhibitors as well as bempedoic acid (adenosine triphosphate citrate lyase inhibitor) and inclisiran, a small synthesized interfering ribonucleic acid (RNA) with its ability to blockade genes‑regulators of hepatic PCSK9 activity. The novel agents for hypertriglyceridemia correction, discussed in the review, include icosapent ethyl (a high purified and firm ester of ethyl‑eicosapentoenic acid), pemafibrate (the first selective modulator of α‑receptors activated by peroxisome proliferator), apolipoprotein C‑III (ApoC‑III) inhibitors (volasenorsen, olesarsen), mipomersen (antisense nucleotide for matrix RNA of apolipoprotein B‑100), lomitapide (inhibitor of microsomal TG transfer protein) and inhibitors of angiopoietin‑like protein 3 (ANGPTL3) (evinacumab, vupanorsen). Among the new approaches to HDL‑C elevation an attention is paid to the experimental and clinical investigations of recombinant HDL, agents with recombinant lecithin‑cholesterol‑acyl‑transferase (LCAT), and apolipoprotein A‑I (ApoA‑I) mimetic peptides. For the lowering of blood lipoprotein(a) (LP(a)) level the possibilities of pelacarsen, an antisense oligonucleotide for matrix RNA of apolipoprotein(a) (apo(a)) contained in LP(a) molecule and olpasiran, a small interfering RNA for LP(a) molecule inhibited apo(a) synthesis are uncovered. A high probability of clinical application in the nearest future will have novel drugs approved by US Food and Drug Administration (FDA) and European Medicines Agency (EMA) such as bempedoic acid and inclisiran for HCE correction as well as lomitapide for the treatment of familial HCE.

Microsomal triglyceride transfer protein regulates intracellular lipolysis in adipocytes independent of its lipid transfer activity

BackgroundThe triglyceride (TG) transfer activity of microsomal triglyceride transfer protein (MTP) is essential for lipoprotein assembly in the liver and intestine; however, its function in adipose tissue, which does not assemble lipoproteins, is unknown. Here we have elucidated the function of MTP in adipocytes. Approach and resultsWe demonstrated that MTP is present on lipid droplets in human adipocytes. Adipose-specific MTP deficient (A-Mttp−/−) male and female mice fed an obesogenic diet gained less weight than Mttpf/f mice, had less fat mass, smaller adipocytes and were insulin sensitive. A-Mttp−/− mice showed higher energy expenditure than Mttpf/f mice. During a cold challenge, A-Mttp−/− mice maintained higher body temperature by mobilizing more fatty acids. Biochemical studies indicated that MTP deficiency de-repressed adipose triglyceride lipase (ATGL) activity and increased TG lipolysis. Both wild type MTP and mutant MTP deficient in TG transfer activity interacted with and inhibited ATGL activity. Thus, the TG transfer activity of MTP is not required for ATGL inhibition. C-terminally truncated ATGL that retains its lipase activity interacted less efficiently than full-length ATGL. ConclusionOur findings demonstrate that adipose-specific MTP deficiency increases ATGL-mediated TG lipolysis and enhances energy expenditure, thereby resisting diet-induced obesity. We speculate that the regulatory function of MTP involving protein-protein interactions might have evolved before the acquisition of TG transfer activity in vertebrates. Adipose-specific inhibition of MTP-ATGL interactions may ameliorate obesity while avoiding the adverse effects associated with inhibition of the lipid transfer activity of MTP.

Cholesteryl ester transfer protein inhibitors: from high-density lipoprotein cholesterol to low-density lipoprotein cholesterol lowering agents?

Cholesteryl ester transfer protein (CETP) is a liver-synthesized glycoprotein whose main functions are facilitating transfer of both cholesteryl esters from high-density lipoprotein (HDL) particles to apolipoprotein B (apoB)-containing particles as well as transfer of triglycerides from apoB-containing particles to HDL particles. Novel crystallographic data have shown that CETP exchanges lipids in the circulation by a dual molecular mechanism. Recently, it has been suggested that the atherosclerotic cardiovascular disease (ASCVD) benefit from CETP inhibition is the consequence of the achieved low-density lipoprotein cholesterol (LDL-C) and apoB reduction, rather than through the HDL cholesterol (HDL-C) increase. The use of CETP inhibitors is supported by genetic evidence from Mendelian randomization studies, showing that LDL-C lowering by CETP gene variants achieves equal ASCVD risk reduction as LDL-C lowering through gene proxies for statins, ezetimibe, and proprotein convertase subtilisin-kexin Type 9 inhibitors. Although first-generation CETP inhibitors (torcetrapib, dalcetrapib) were mainly raising HDL-C or had off-target effects, next generation CETP inhibitors (anacetrapib, evacetrapib) were also effective in reducing LDL-C and apoB and have been proven safe. Anacetrapib was the first CETP inhibitor to be proven effective in reducing ASCVD risk. In addition, CETP inhibitors have been shown to lower the risk of new-onset diabetes, improve glucose tolerance, and insulin sensitivity. The newest-generation CETP inhibitor obicetrapib, specifically designed to lower LDL-C and apoB, has achieved significant reductions of LDL-C up to 45%. Obicetrapib, about to enter phase III development, could become the first CETP inhibitor as add-on therapy for patients not reaching their guideline LDL-C targets.

Intracellular C3 prevents hepatic steatosis by promoting autophagy and very-low-density lipoprotein secretion.

Complement component C3, mainly synthesized by hepatocytes, acts as the convergence point of three different pathways in activating the complement cascade. Besides its well-established roles in the extracellular milieu, C3 performs various intracellular functions such as immunomodulation and pathogen recognition. Although C3 is present at extremely high concentrations in hepatocytes, little is known about its intrahepatic function. In this study, we found that C3knockout (C3-/- ) mice displayed accelerated hepatic triglyceride (TG) accumulation compared with C57BL/6J wild type mice. Mechanistically, C3 deficiency impaired lipophagy in hepatocytes, owing to the disrupted interaction between C3 and autophagy-related 16like 1, which is essential for autolysosome assembly. Furthermore, lipophagy deficiency affected the function of the endoplasmic reticulum in C3-/- mice, subsequently affecting the expression of protein disulfide isomerase and activity of microsomal TG transfer protein, and ultimately impairing the production of hepatic very-low-density lipoproteins (VLDLs). Rapamycin and thapsigargin treatment accelerated VLDL secretion and alleviated hepatic lipid accumulation in C3-/- mice. Our study demonstrates that C3 promotes lipophagy to facilitate VLDL secretion in hepatocytes, thus playing an essential role in balancing TG levels in the liver.

Protein Kinase D2 drives chylomicron‐mediated lipid transport in the intestine and promotes obesity

Lipids are the most energy‐dense components of the diet, and their overconsumption promotes obesity and diabetes. Dietary fat content has been linked to the lipid processing activity by the intestine and its overall capacity to absorb triglycerides (TG). However, the signaling cascades driving intestinal lipid absorption in response to elevated dietary fat are largely unknown. Here, we describe an unexpected role of the protein kinase D2 (PKD2) in lipid homeostasis. We demonstrate that PKD2 activity promotes chylomicron‐mediated TG transfer in enterocytes. PKD2 increases chylomicron size to enhance the TG secretion on the basolateral side of the mouse and human enterocytes, which is associated with decreased abundance of APOA4. PKD2 activation in intestine also correlates positively with circulating TG in obese human patients. Importantly, deletion, inactivation, or inhibition of PKD2 ameliorates high‐fat diet‐induced obesity and diabetes and improves gut microbiota profile in mice. Taken together, our findings suggest that PKD2 represents a key signaling node promoting dietary fat absorption and may serve as an attractive target for the treatment of obesity.

Hepatic Carbohydrate Response Element Binding Protein Activation Limits Nonalcoholic Fatty Liver Disease Development in a Mouse Model for Glycogen Storage Disease Type 1a.

Background and AimsGlycogen storage disease (GSD) type 1a is an inborn error of metabolism caused by defective glucose‐6‐phosphatase catalytic subunit (G6PC) activity. Patients with GSD 1a exhibit severe hepatomegaly due to glycogen and triglyceride (TG) accumulation in the liver. We have shown that the activity of carbohydrate response element binding protein (ChREBP), a key regulator of glycolysis and de novo lipogenesis, is increased in GSD 1a. In the current study, we assessed the contribution of ChREBP to nonalcoholic fatty liver disease (NAFLD) development in a mouse model for hepatic GSD 1a.Approach and ResultsLiver‐specific G6pc–knockout (L‐G6pc −/−) mice were treated with adeno‐associated viruses (AAVs) 2 or 8 directed against short hairpin ChREBP to normalize hepatic ChREBP activity to levels observed in wild‐type mice receiving AAV8–scrambled short hairpin RNA (shSCR). Hepatic ChREBP knockdown markedly increased liver weight and hepatocyte size in L‐G6pc −/− mice. This was associated with hepatic accumulation of G6P, glycogen, and lipids, whereas the expression of glycolytic and lipogenic genes was reduced. Enzyme activities, flux measurements, hepatic metabolite analysis and very low density lipoprotein (VLDL)‐TG secretion assays revealed that hepatic ChREBP knockdown reduced downstream glycolysis and de novo lipogenesis but also strongly suppressed hepatic VLDL lipidation, hence promoting the storage of “old fat.” Interestingly, enhanced VLDL‐TG secretion in shSCR‐treated L‐G6pc −/− mice associated with a ChREBP‐dependent induction of the VLDL lipidation proteins microsomal TG transfer protein and transmembrane 6 superfamily member 2 (TM6SF2), the latter being confirmed by ChIP‐qPCR.ConclusionsAttenuation of hepatic ChREBP induction in GSD 1a liver aggravates hepatomegaly because of further accumulation of glycogen and lipids as a result of reduced glycolysis and suppressed VLDL‐TG secretion. TM6SF2, critical for VLDL formation, was identified as a ChREBP target in mouse liver. Altogether, our data show that enhanced ChREBP activity limits NAFLD development in GSD 1a by balancing hepatic TG production and secretion.

Low Expression of Sirtuin 1 in the Dairy Cows with Mild Fatty Liver Alters Hepatic Lipid Metabolism.

Simple SummarySirtuin 1 (SIRT1), a NAD-dependent histone deacetylase, is involved in oxidative stress and lipid metabolism regulation. Limited studies exist regarding the role of SIRT1 in lipid metabolism disorder in periparturient dairy cows. This study explores the effect of hepatic steatosis on the expression of the SIRT1 gene and protein and the proteins encoded by the genes downstream to it, all of which are involved in lipid metabolism in the liver. Control cows (n = 6, parity 3.0 ± 2.0, milk production 28 ± 47 kg/d) and mild fatty liver cows (n = 6, parity 2.3 ± 1.5, milk production 20 ± 6 kg/d) were retrospectively selected based on liver triglycerides (TG) content (% wet liver). The present study indicates that low SIRT1 expression caused by hepatic steatosis promotes hepatic fatty acid synthesis and inhibits fatty acid β-oxidation. We believe that our study makes a significant contribution to the literature because it demonstrates that hepatic steatosis is associated with increased hepatic fatty acid synthesis, inhibited fatty acid β-oxidation and reduced lipid transport.Dairy cows usually experience negative energy balance coupled with an increased incidence of fatty liver during the periparturient period. The purpose of this study was to investigate the effect of hepatic steatosis on the expression of the sirtuin 1 (SIRT1), along with the target mRNA and protein expressions and activities related to lipid metabolism in liver tissue. Control cows (n = 6, parity 3.0 ± 2.0, milk production 28 ± 7 kg/d) and mild fatty liver cows (n = 6, parity 2.3 ± 1.5, milk production 20 ± 6 kg/d) were retrospectively selected based on liver triglycerides (TG) content (% wet liver). Compared with the control group, fatty liver cows had greater concentrations of cholesterol and TG along with the typically vacuolated appearance and greater lipid droplets in the liver. Furthermore, fatty liver cows had greater mRNA and protein abundance related to hepatic lipid synthesis proteins sterol regulatory element binding proteins (SREBP-1c), long-chain acyl-CoA synthetase (ACSL), acyl-CoA carbrolase (ACC) and fatty acid synthase (FAS) and lipid transport proteins Liver fatty acid binding protein (L-FABP), apolipoprotein E (ApoE), low density lipoprotein receptor (LDLR) and microsomal TG transfer protein (MTTP) (p < 0.05). However, they had lower mRNA and protein abundance associated with fatty acid β-oxidation proteins SIRT1, peroxisome proliferator-activated receptor co-activator-1 (PGC-1α), peroxisome proliferator–activated receptor-α (PPARα), retinoid X receptor (RXRα), acyl-CoA 1 (ACO), carnitine palmitoyltransferase 1 (CPT1), carnitine palmitoyltransferase 2 (CPT2) and long- and medium-chain 3-hydroxyacyl-CoA dehydrogenases (LCAD) (p < 0.05). Additionally, mRNA abundance and enzyme activity of enzymes copper/zinc superoxide dismutase (Cu/Zn SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and manganese superoxide dismutase (Mn SOD) decreased and mRNA and protein abundance of p45 nuclear factor-erythroid 2 (p45 NF-E2)-related factor 1 (Nrf1), mitochondrial transcription factor A (TFAM) decreased (p < 0.05). Lower enzyme activities of SIRT1, PGC-1α, Cu/Zn SOD, CAT, GSH-Px, SREBP-1c and Mn SOD (p < 0.05) and concentration of reactive oxygen species (ROS) were observed in dairy cows with fatty liver. These results demonstrate that decreased SIRT1 associated with hepatic steatosis promotes hepatic fatty acid synthesis and inhibits fatty acid β-oxidation. Hence, SIRT1 may represent a novel therapeutic target for the treatment of the fatty liver disease in dairy cows.

Exon 9-deleted CETP inhibits full length-CETP synthesis and promotes cellular triglyceride storage

Cholesteryl ester transfer protein (CETP) exists as full-length (FL) and exon 9 (E9)-deleted isoforms. The function of E9-deleted CETP is poorly understood. Here, we investigated the role of E9-deleted CETP in regulating the secretion of FL-CETP by cells and explored its possible role in intracellular lipid metabolism. CETP overexpression in cells that naturally express CETP confirmed that E9-deleted CETP is not secreted, and showed that cellular FL- and E9-deleted CETP form an isolatable complex. Coexpression of CETP isoforms lowered cellular levels of both proteins and impaired FL-CETP secretion. These effects were due to reduced synthesis of both isoforms; however, the predominate consequence of FL- and E9-deleted CETP coexpression is impaired FL-CETP synthesis. We reported previously that reducing both CETP isoforms or overexpressing FL-CETP impairs cellular triglyceride (TG) storage. To investigate this further, E9-deleted CETP was expressed in SW872 cells that naturally synthesize CETP and in mouse 3T3-L1 cells that do not. E9-deleted CETP overexpression stimulated SW872 triglyceride synthesis and increased stored TG 2-fold. Expression of E9-deleted CETP in mouse 3T3-L1 cells produced a similar lipid phenotype. In vitro, FL-CETP promotes the transfer of TG from ER-enriched membranes to lipid droplets. E9-deleted CETP also promoted this transfer, although less effectively, and it inhibited the transfer driven by FL-CETP. We conclude that FL- and E9-deleted CETP isoforms interact to mutually decrease their intracellular levels and impair FL-CETP secretion by reducing CETP biosynthesis. E9-deleted CETP, like FL-CETP, alters cellular TG metabolism and storage but in a contrary manner.

HDL acceptor capacities for cholesterol efflux from macrophages and lipid transfer are both acutely reduced after myocardial infarction

BackgroundThe transport of lipids from the artery wall is one of the most essential anti-atherogenic functions of high-density lipoprotein (HDL). Recent reports of changes in the HDL composition, during myocardial infarction (MI), suggest that this function may be altered. MethodsForty-one consecutive patients with ST-segment elevation MI enrolled at the Brasilia Heart Study were selected. The following HDL-related measures were determined upon admission (D1) and on the fifth day (D5) after MI: C-reactive protein, CETP and PLTP activity, HDL composition, efflux of cholesterol from J774 macrophages to HDL, and transfer of unesterified and esterified cholesterol, triglycerides and phospholipids from a donor nanoemulsion to HDL. ResultsFrom D1 to D5, the activity of CETP decreased by 25%, but PLTP activity remained unchanged. Esterified cholesterol (−23%) and phospholipid (−9.5%) contents of HDL decreased. Transfer of triglycerides (−36.5%) and esterified cholesterol (−14.7%) to HDL from nanoemulsions was reduced, but other lipids transfers were unchanged. Cholesterol efflux to HDL was also diminished by 8.5% (p=0.04) on D5 compared to D1. It was more pronounced in patients above the 75th percentile of C-reactive protein. ConclusionsAfter an MI, a simultaneous decrease in lipid transfer to HDL and in the capacity of HDL to efflux cholesterol from cells occurs. Thus, HDL with inferior atheroprotective properties may be generated in the acute post-MI period.

Loss of miR-141/200c ameliorates hepatic steatosis and inflammation by reprogramming multiple signaling pathways in NASH.

Accumulation of lipid droplets and inflammatory cell infiltration is the hallmark of nonalcoholic steatohepatitis (NASH). The roles of noncoding RNAs in NASH are less known. We aim to elucidate the function of miR-141/200c in diet-induced NASH. WT and miR-141/200c-/- mice were fed a methionine and choline deficient (MCD) diet for 2 weeks to assess markers of steatosis, liver injury, and inflammation. Hepatic miR-141 and miR-200c RNA levels were highly induced in human patients with NASH fatty liver and in WT MCD mice. miR-141/200c-/- MCD mice had reduced liver weights and triglyceride (TG) levels, which was associated with increased microsomal TG transfer protein (MTTP) and PPARα but reduced SREBP1c and FAS expression. Inflammation was attenuated and F4/80 macrophage activation was suppressed in miR-141/200c-/- mice, as evidenced by decreased serum aminotransferases and IL-6 and reduced hepatic proinflammatory, neutrophil, and profibrotic genes. Treatment with LPS in BM-derived macrophages isolated from miR-200c/141-/- mice polarized macrophages toward the M2 antiinflammatory state by increasing Arg1 and IL-10 levels while decreasing the M1 marker iNOS. In addition, elevated phosphorylated AMPK (p-AMPK), p-AKT, and p-GSK3β and diminished TLR4 and p-mTOR/p-4EBP1 proteins were observed. Lipidomics and metabolomics revealed alterations of TG and phosphatidylcholine (PC) lipid species by miR-141/200c deficiency. In summary, miR-141/200c deficiency diminished NASH-associated hepatic steatosis and inflammation by reprogramming lipid and inflammation signaling pathways.

Protopanaxadiol and Protopanaxatriol-Type Saponins Ameliorate Glucose and Lipid Metabolism in Type 2 Diabetes Mellitus in High-Fat Diet/Streptozocin-Induced Mice

Ginsenoside is a major active component of ginseng, which exhibits various pharmacological properties such as hepatoprotection, tumor suppression and diabetes resistance. In this study, the anti-diabetic effects of protopanaxadiol (PPD) and protopanaxatriol (PPT)-type saponins were explored and compared in high-fat diet/streptozocin-induced type 2 diabetes mellitus (T2DM) mice. Our results showed that low or high dose (50 mg/kg bodyweight or 150 mg/kg bodyweight) PPD and PPT significantly reduced fasting blood glucose, improved glucose tolerance and insulin resistance in T2DM mice. PPD and PPT also regulated serum lipid-related markers such as reduced total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol in T2DM mice. In addition, PPD and PPT dramatically ameliorated the inflammatory responses by suppressing the secretion of pro-inflammatory cytokines like tumor necrosis factor-alpha and interleukin-6 in serum level and gene expression in liver level, and improved the antioxidant capacity by increasing the superoxide dismutase and decreasing malondialdehyde levels in the serum of T2DM mice. Moreover, the anti-diabetic effect of PPD and PPT appeared to be partially mediated by the suppression of hepatic metabolism genes expression such as peroxisome proliferator-activated receptor gamma coactivator 1-alpha, phosphoenolpyruvate carboxykinase, and glucose-6-phosphatase, as well as facilitating lipid metabolism genes expression such as microsomal TG transfer protein in the liver tissues of T2DM mice. Taken together, our results indicated that PPD and PPT might potentially act as natural anti-diabetic compounds to be used for preventing and treating the T2DM and its complications in the future.

How cholesteryl ester transfer protein can also be a potential triglyceride transporter

CETP transfers cholesteryl esters (CEs) and triglycerides (TGs) between different lipoproteins and came in limelight as a drug-target against CVD. In the search for detailed mechanism of lipid transfer through CETP, enormous effort is devoted employing crystallographic, cryo-EM, and Molecular Dynamics (MD) studies. However, these studies primarily focused on CE-bound CETP structure and CE transfer mechanism. With the reported correlation that CETP looses significant CE transfer activity upon inhibiting TG transfer, it is of tremendous importance to understand the structure and dynamics of TG-bound CETP. Our results from large-scale all-atom and coarse-grained MD simulations show that CETP can accommodate two TG molecules in parallel N-N orientation with TG oleate chains majorly attaining the tuning-fork conformation. In TG-bound form, CETP not only maintained its secondary structures but also exhibited similar bending-twisting motions as reported for CE-CETP crystal structure. Obtained structural information are further validated by correlating to available functional data of 2–8 fold slower transfer rate of TG through CETP, where we show that TGs make 20% additional contacts with CETP compared to CEs. Identified CETP residues facilitating TG binding also match very well with reported mutagenesis data. The study could accelerate the drug-designing processes to combat CETP functionality and CVD.

The atherosclerosis and atheromatosis as two etiologically different aphysiological processes at single pathogenesis. Atheromatosis and pathogenetic role of insulin.

It is supposed that at stages of phylogenesis seven biological functions was developed: 1) biological function of trophology; 2) homeostasis; 3) endoecology; 4) adaptation; 5) continuation of species; 6) locomotion; 7) cognitive function, including intellect. The function of trophology (feeding) is implemented by two biological reactions: exophilia - external feeding and endophilia - internal feeding. The function of endoecology prevents exceeding of upper limit of physiological interval by no substrate, catabolites and endogenous phlogogens. It is implemented by two biological functions: excretion and inflammation. The etiological factors of atherosclerosis are the following ones. The oleic mono-saturated fatty acid in chemical reactions is by far more active than palmitic fatty acid. In the ocean, all animals were carnivorous (piscivorous); species Homo Sapiens, in millions of years of life on dry land, forcedly became a herbivorousone. The main role in development of herbivorous animals belongs to insulin; the hormone regulating in the first-place metabolism of fatty acids, expresses transmutation of all endogenously synthesized from glucose palmitic saturated fatty acid in oleic monosaturated fatty acid. The late in phylogenesis insulin can't initiate transmutation of exogenous palmitic saturated fatty acid of food into oleic mono-saturated fatty acid. Under effect of insulin in vivo an active oleic type of metabolism of fatty acids is developed; and outside if effect of insulin palmitic type of metabolism of fatty acids is developed. In the ocean, synthesis of active eicosanoids occurs from ῳ-3 polyene fatty acids; there is no such fatty acids in dry land. The basis of pathogenesis of atherosclerosis is feeding of large amount of carnivorous (meat) food by phylogenetically herbivorous Homo Sapiens. This way a deficiency of palmitic saturated fatty acids in cells if developed blocking their bio-accessibility. The lipoproteins of low density are not developed in the initiated by insulin transfer of oleic triglycerides to cells in oleic apoE/B-100 lipoproteins of very low density and their absorption by cells. The transfer of triglycerides into lipoproteins of very low density is blocked under slow processes of transmutation of palmitic lipoproteins of very low density into lipoproteins of low density, retention cumulation of lipoproteins of low density in blood. Only because of partial utilization by monocytes of non-ligand palmitic lipoproteins of very low density →lipoproteins of low density that occurs in the intima of arteries of elastic type, atheromotosis is developed. The atheromotosis masses of intima are first of all interim catabolites of polyene fatty acids; the cells could not to absorb them by apoB-100-endocytosis in the content of lipoproteins of low density. The atherosclerosis, hyperlipoproteinemia, high content of lipoproteins of low density in blood and deficiency of polyene fatty acids in cells are a result of disorder of trophology function; the atheromotosis of arteries is only partial implementation of endoecology function.

Inhibition of apolipoprotein B synthesis stimulates endoplasmic reticulum autophagy that prevents steatosis.

Inhibition of VLDL secretion reduces plasma levels of atherogenic apolipoprotein B (apoB) lipoproteins but can also cause hepatic steatosis. Approaches targeting apoB synthesis, which lies upstream of VLDL secretion, have potential to effectively reduce dyslipidemia but can also lead to hepatic accumulation of unsecreted triglycerides (TG). Here, we found that treating mice with apoB antisense oligonucleotides (ASOs) for 6 weeks decreased VLDL secretion and plasma cholesterol without causing steatosis. The absence of steatosis was linked to an increase in ER stress in the first 3 weeks of ASO treatment, followed by development of ER autophagy at the end of 6 weeks of treatment. The latter resulted in increased fatty acid (FA) oxidation that was inhibited by both chloroquine and 3-methyl adenine, consistent with trafficking of ER TG through the autophagic pathway before oxidation. These findings support the concept that inhibition of apoB synthesis traps lipids that have been transferred to the ER by microsomal TG transfer protein (MTP), inducing ER stress. ER stress then triggers ER autophagy and subsequent lysosomal lipolysis of TG, followed by mitochondrial oxidation of released FA, leading to prevention of steatosis. The identification of this pathway indicates that inhibition of VLDL secretion remains a viable target for therapies aiming to reduce circulating levels of atherogenic apoB lipoproteins.

Understanding of Diabetic Dyslipidemia by Using the Anion-Exchange High Performance Liquid Chromatography Data.

Type 2 diabetes and dyslipidemia are cardiovascular risk factors which should be managed [1]. However, the precise lipoprotein profiles and the underlying mechanisms for diabetic dyslipidemia remain largely unknown. We previously developed an anion-exchange liquid chromatographic method (AEX-HPLC) which can measure cholesterol levels of triglyceride (TG)-rich lipoproteins such as very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL) and chylomicron (CM) in addition to low-density lipoprotein (LDL) and high-density lipoprotein (HDL) [2]. Here we compared lipoprotein profiles obtained by our previous studies using AEX-HPLC in young lean men [3], subjects with low Framingham risk score (FRS) [4, 5], type 2 diabetic patients without obesity and type 2 diabetic patients with obesity [6, 7]. The mean ± SD values of age, body mass index, HbA1c in in young lean men (n = 7) [3], low FRS subjects (n = 304) [4], type 2 diabetic patients without obesity (n = 194) [6], and type 2 diabetic patients with obesity (n = 5) [7] were 24 ± 2, 51 ± 8, 63 ± 13, and 60 ± 9 years old, 20.8 ± 2.2, 23.8 ± 3.0, 23.1 ± 2.0, and 29.5 ± 7.0 kg/m2, 5.0 ± 0.2, 5.4 ± 0.5, 6.3 ± 1.0, and 9.1±2.1%, respectively. HDL-cholesterol (HDL-C) in type 2 diabetes (49.9 ± 16.6 mg/dL (1.29 ± 0.43 mmol/L)), especially in type 2 diabetic patients with obesity (36.4 ± 5.3 mg/dL (0.94 ± 0.14 mmol/L)) was lower than young lean men (59.4 ± 10.1 mg/dL (1.54 ± 0.26 mmol/L)) and low FRS subjects (57.6 ± 14.7 mg/dL (1.49 ± 0.38 mmol/L)). IDL-C in type 2 diabetes was higher than other two groups, and IDL-C was higher in the order of type 2 diabetic patients with obesity (9.8 ± 3.0 mg/dL (0.25 ± 0.08 mmol/L)), type 2 diabetic patients without obesity (9.3 ± 4.6 mg/dL (0.24 ± 0.12 mmol/L)), low FRS subjects (7.3 ± 3.1 mg/ dL (0.19 ± 0.08 mmol/L)), young lean men (4.3 ± 2.2 mg/dL (0.11 ± 0.06 mmol/L)). VLDL-C clearly showed higher values in the order of type 2 diabetic patients with obesity (27.3 ± 22.7 mg/dL (0.71 ± 0.59 mmol/L)), type 2 diabetic patients without obesity (20.1 ± 16.2 mg/dL (0.52 ± 0.42 mmol/L)), low FRS subjects (16.6 ± 12.8 mg/dL (0.43 ± 0.33 mmol/L)), and young lean men (4.0 ± 4.6 mg/dL (0.10 ± 0.12 mmol/L)). LDL-C and CM-C did not show the characteristic profile for diabetes. According to accumulation of our previous AEX-HPLC data [3, 4, 6, 7], the characteristics in diabetic dyslipidemia is reduced HDL-C, and increased IDL-C and VLDL-C, which is further deteriorated by complication with obesity. Relative insulin deficiency due to insulin resistance increases activity and expression of hormone-sensitive lipase (HSL) in adipose tissue, which catalyzes the breakdown of TG, releasing free fatty acids (FFA) (Fig. 1) [8]. Insulin promotes apoB100 degradation, and hepatic insulin resistance causes reduction of apoB100 degradation [9]. Insulin resistance also induces an enhanced expression of microsomal TG transfer protein (MTP), a key enzyme involved in VLDL assembly [10]. In type 2 diabetes, increased FFA entry to liver, reduced degradation of apoB100 and enhanced expression of MTP may elevate hepatic production of VLDL. Relative insulin deficiency also decreases the activity of lipoprotein lipase (LPL), the rate-limiting enzyme of the catabolism of TG-rich lipoproteins such as CM, VLDL and IDL [11]. The formation of HDL is related with the catabolism of TG-rich lipoproteins by LPL [12]. Therefore, reduced LPL activity increases IDL and VLDL, and reduces HDL. The activity of hepatic TG lipase (HTGL), the enzyme that facilitates the catabolism of HDL, is correlated with insulin requirement [13]. In type 2 diabetes, low serum HDL-C may be partially due to an increased rate of clearance by HTGL [13]. LDL size and buoyancy are inversely proportional to HTGL activity [14], and patients with high HTGL have smaller, denser LDL particles, as compared with subjects with low HTGL activity [15]. Increased HTGL activity due Manuscript accepted for publication March 03, 2016

Abstract 18509: Defining Renal Uptake of Circulating Lipids

A prominent histological feature of chronic kidney disease, including that due to diabetes, is the accumulation of neutral lipids in the nephron. However, existing research on kidney lipid metabolism is limited. Therefore we characterized lipid accumulation in mouse models. We hypothesized that the major source of lipids in the kidney is circulating triglyceride (TG)-rich lipoproteins brought into the cells of the kidney via the coordinated action of lipoprotein lipase (LPL) and cluster of differentiation 36 (CD36). To test this hypothesis, we fasted mice overnight and inhibited LPL and CD36. We did not observe a change in TG accumulation in the kidney when LPL action was blocked using with poloxmer 407. We then used a microsomal TG transfer protein inhibitor, which inhibits TG-rich lipoprotein assembly, to lower circulating TG-rich lipoproteins. Intracellular kidney TG did not decrease but in fact increased up to 40% in the fasted state after the inhibitor was given, mirroring what was seen in the liver. There was no difference in TG accumulation in the kidneys of fasted Cd36 -/- mice. Furthermore, we did not observe a change in uptake of radiolabeled oleic acid in the kidneys of these mice. Genes which regulate fatty acid oxidation or de novo lipogenesis were also unchanged in Cd36 -/- compared to Cd36 +/+ . Surprisingly, apoC-III deficiency increased renal uptake of a TG-emulsion, as had been found in the liver. Finally, we measured TG in kidneys from streptozotocin-treated and Akita diabetic mice without renal failure. Neither of these models accumulated higher amounts of TG compared to non-diabetic controls; however, Akita mice down regulated fatty acid oxidation genes and had twice the intracellular free fatty acids. These findings provide novel insight into the lipid biochemistry of the kidney, showing it differs from other high energy requiring peripheral organs such as heart.

High dietary cholesterol and ovariectomy in rats repress gene expression of key markers of VLDL and bile acid metabolism in liver.

BackgroundThe purpose of the study was to evaluate the effects of high dietary cholesterol in ovariectomized (Ovx) rats on several key markers of hepatic cholesterol and bile acid metabolism.MethodOvx and sham operated (Sham) rats were given either a standard diet (SD), a SD diet supplemented with 0.25 % cholesterol (SD + Chol), or a high fat diet supplemented with 0.25 % cholesterol (HF + Chol) for 5 weeks.ResultsOvx was associated with higher (P < 0.05) liver total cholesterol (TC) under the SD and the SD + Chol diet, while liver triglyceride (TG) content was higher in Ovx than in Sham rats in all 3 diet conditions. Surprisingly, the SD + Chol diet was associated with lower (P < 0.001) plasma TC and TG levels in Ovx than in Sham rats, suggesting a decrease in VLDL secretion. Accordingly, several transcripts of key markers of VLDL synthesis including microsomal TG transfer protein (Mttp) and Apob-100 were decreased (P < 0.05) in Ovx compared to Sham rats under the three dietary conditions and even more so for Mttp and Apob-100 when rats were fed the SD + Chol diet. Transcripts of bile acid transporters including bile salt export pump (Bsep) and Na + −taurocholate cotransporting polypeptide (Ntcp) were decreased by the addition of cholesterol to the SD diet in both Ovx and Sham rats.ConclusionThese results indicate that a high cholesterol feeding and ovariectomy combine to reduce the gene expression of key markers of VLDL synthesis suggesting a reduction in excretion of cholesterol from the liver.

The role of TRIB1 in lipid metabolism; from genetics to pathways.

The plasma concentration of lipids is a heritable risk factor for the development of atherosclerosis and related coronary artery diseases (CAD). Mammalian tribbles homologue 1 (TRIB1) is a human locus, the downstream linkage disequilibrium (LD) block of which affects plasma low-density lipoprotein (LDL)-associated cholesterol, triglyceride (TG) levels and CAD across multiple ethnic groups. In addition, association of TRIB1 with non-alcoholic fatty liver disease (NAFLD) has also been shown. A regulatory sequence that enhances TRIB1 promoter activity was identified in the LD block and the minor allele of a single nt polymorphism (SNP, rs6982502) in this regulatory sequence reduces the activity of the TRIB1 promoter. The minor allele of rs6982502 is a risk allele for increasing plasma lipid levels and NAFLD. Trib1 deficiency increases plasma cholesterol and TGs in mice and overexpression of TRIB1 in mouse liver reduces these factors. Expression of rate-limiting lipogenic enzymes is increased in Trib1-knockout mouse liver and decreased with overexpression. Recently, carbohydrate-responsive element-binding protein (ChREBP) emerged as a novel binding partner of TRIB1. Furthermore, novel binding partner, Sin3A (Swi-independent 3A)-associated protein, 18kDa, was identified, which activates microsomal TG transfer protein (MTTP) expression by binding with MTTP regulatory elements in co-ordination with mSin3A and TRIB1. Very recently, a small molecular compound that up-regulates TRIB1 expression in HepG2 cells has been discovered. Further exploration of the binding partners of TRIB1 and their involvement in lipid metabolism may aid discovery of novel pharmacological targets for the management of dyslipidaemia and steatosis.

Discovery Approaches for Novel Dyslipidemia Drugs.

Dyslipidemia is increased fasting level of total cholesterol (TC), LDL cholesterol (LDL-C), and triglycerides (TG), along with decreased levels of HDL cholesterol (HDL-C). Owing to effect on the cardiovascular system and increased chances of metabolic diseases, it is needed to review novel under development drugs and new approaches in drug discovery for dyslipidemia. This article reviews all phases I to IV clinical trials and preclinical trials with results associated with novel treatment of dyslipidemia. Drug discovery for dyslipidemia, toward newer targets has been addressed. Statins are, currently available, best choice of drugs for treating dyslipidemia and coronary diseases. In addition to this, lipid lowering drugs support treatment to a great extent, either as monotherapy or in combinations with other groups. Pravastatin used in combination with cholesteryl ester, transfers protein inhibitors (CETP) to produce efficient results. Peroxisome proliferator-activated receptor agonists (PPAR) like muraglitazar, aleglitazar and tesaglitazar are PPAR α/γ receptor agonist, dual in action performs better in phase 3 clinical study and reduces renal and cardiovascular events. By targeting both receptors, a better treatment for cardiovascular and diabetic problems can be achieved. Proprotein convertase subtilisin/kexin type 9 (PCSK-9) inhibitors like humanized monoclonal antibodies, are newly discovered inhibitors that reduce the risk of cardiovascular diseases. During the past few years, nucleic acid-based therapies targeting lipid and lipoprotein metabolism, such as microsomal TG transfer protein (MTP) may be a promising therapeutic approach to treat vascular diseases. Gene regulating transcription factors involved in bile acids and cholesterol metabolism can be controlled by FXR agonists in dyslipidemia. To overcome these drawbacks, many thyroid hormone analogues have been developed to lower down cholesterol level by targeting specifically thyroid hormone β receptors abundantly present in the liver without severe side effects. Virtual screening, an important tool in screening databases of the lead compounds, provides a good platform to access new compounds. In this review, examples of novel FXR modulators, thyromimetic agents, cholesterol absorption inhibitors and other new anti hyperlipidemia scaffolds have been addressed.