MTP inhibition as a treatment for dyslipidaemias: time to deliver or empty promises?

Binding site redundancy is critical for the regulation of fas by miR-30c in blunt snout bream (Megalobrama amblycephala)

MiR-30c and fatty acid synthase (fas) both play important roles in physiological processes such as lipid synthesis and fat metabolism. Predictive analysis revealed that fas is a target gene of miR-30c with multiple seed sites. Seed sites are useful to predict miRNA targeting relationships; however, detailed analyses of seed sites in fish genomes remain poorly studied. In this study, the regulatory relationship between miR-30c and fas, number and effect of seed regions, and mechanism by which miR-30c regulates lipid metabolism were evaluated in blunt snout bream (Megalobrama amblycephala). Four miR-30c target sites for fas were identified using various prediction tools. miR-30c mimics were transfected into 293 T cells, and dual-luciferase reporter assays were used to evaluate the roles of different fas target sites. When a single target site was mutated, relative luciferase activity was higher than that in the control group, with different activity levels depending on the mutation site. When multiple target sites were mutated, relative luciferase activity increased significantly as the number of mutation sites increased and was the highest when the four sites were mutated simultaneously. The miR-30c agomir was injected into the abdominal cavity of M. amblycephala at various concentrations for analyses of physiological and biochemical parameters in the liver and blood and the expression of genes related to lipid metabolism in the liver. Total cholesterol, free fatty acid, triglyceride, and low density lipoprotein levels were significantly lower after miR-30c agomir injection comparing to the control (P < 0.05). Additionally, the expression levels of genes related to lipid metabolism were significantly lower after miR-30c agomir injection than in the control (P < 0.05). In summary, this study identified four specific miR-30c target sites in the 3' UTR of fas mRNA; the effects of these sites are cumulative, and the redundancy ensures the accurate regulation of fas during evolution. In addition, miR-30c has a negative regulatory effect on fas and regulates lipid metabolism via various genes related to this process. Therefore, the regulation of miR-30c can effectively ameliorate the side effects of a high-fat diet on liver function in M. amblycephala.

A novel regulatory facet for hypertriglyceridemia: The role of microRNAs in the regulation of triglyceride-rich lipoprotein biosynthesis

Atherosclerotic cardiovascular disease (ASCVD) is one of the major leading global causes of death. Genetic and epidemiological studies strongly support the causal association between triacylglycerol-rich lipoproteins (TAGRL) and atherogenesis, even in statin-treated patients. Recent genetic evidence has clarified that variants in several key genes implicated in TAGRL metabolism are strongly linked to the increased ASCVD risk. There are several triacylglycerol-lowering agents; however, new therapeutic options are in development, among which are miRNA-based therapeutic approaches. MicroRNAs (miRNAs) are small non-coding RNAs (18-25 nucleotides) that negatively modulate gene expression through translational repression or degradation of target mRNAs, thereby reducing the levels of functional genes. MiRNAs play a crucial role in the development of hypertriglyceridemia as several miRNAs are dysregulated in both synthesis and clearance of TAGRL particles. MiRNA-based therapies in ASCVD have not yet been applied in human trials but are attractive. This review provides a concise overview of current interventions for hypertriglyceridemia and the development of novel miRNA and siRNA-based drugs. We summarize the miRNAs involved in the regulation of key genes in the TAGRLs synthesis pathway, which has gained attention as a novel target for therapeutic applications in CVD.

Regulatory Non-Coding RNAs in Familial Hypercholesterolemia, Theranostic Applications

Familial hypercholesterolemia (FH) is a common monogenic disease which is associated with high serum levels of low-density lipoprotein cholesterol (LDL-C) and leads to atherosclerosis and cardiovascular disease (CVD). Early diagnosis and effective treatment strategy can significantly improve prognosis. Recently, non-coding RNAs (ncRNAs) have emerged as novel biomarkers for the diagnosis and innovative targets for therapeutics. Non-coding RNAs have essential roles in the regulation of LDL-C homeostasis, suggesting that manipulation and regulating ncRNAs could be a promising theranostic approach to ameliorate clinical complications of FH, particularly cardiovascular disease. In this review, we briefly discussed the mechanisms and pathophysiology of FH and novel therapeutic strategies for the treatment of FH. Moreover, the theranostic effects of different non-coding RNAs for the treatment and diagnosis of FH were highlighted. Finally, the advantages and disadvantages of ncRNA-based therapies vs. conventional therapies were discussed.

Novel efficacious microRNA-30c analogs reduce apolipoprotein B secretion in human hepatoma and primary hepatocyte cells

High plasma lipid levels have been demonstrated to increase cardiovascular disease risk. Despite advances in treatments to decrease plasma lipids, additional therapeutics are still needed because many people are intolerant or nonresponsive to these therapies. We previously showed that increasing cellular levels of microRNA-30c (miR-30c) using viral vectors or liposomes reduces plasma lipids and atherosclerosis. In this study, we aimed to synthesize potent miR-30c analogs that can be delivered to hepatoma cells without the aid of viral vectors and lipid emulsions. We hypothesized that modification of the passenger strand of miR-30c would increase the stability of miR-30c and augment its delivery to liver cells. Here, we report the successful synthesis of a series of miR-30c analogs by using different chemically modified nucleosides. In these analogs, we left the active sense strand untouched so that its biological activity remained unaltered, and we modified the passenger strand of miR-30c to enhance the stability and uptake of miR-30c by hepatoma cells through phosphorothiorate linkages and the addition of GalNAc. We show that these analogs significantly reduced apolipoprotein B secretion in Huh-7 human hepatoma cells and human primary hepatocytes without affecting apolipoprotein A1 secretion and cellular lipid levels. Our results provide a proof of concept that the passenger strand of miR-30c can be modified to increase its stability and delivery to cells while retaining the potency of the sense strand. We anticipate these miR-30c analogs will be useful in the development of more efficacious analogs for the treatment of hyperlipidemias and cardiovascular diseases.

Chrysin ameliorates hepatic steatosis induced by a diet deficient in methionine and choline by inducing the secretion of hepatocyte nuclear factor 4α-dependent very low-density lipoprotein

We investigated the effects of chrysin (CHR) on nonalcoholic fatty liver disease (NAFLD) in mice. The NAFLD mouse model was established using a diet deficient in methionine and choline (MCD). CHR was shown to attenuate MCD-induced hepatic fat accumulation, increase very low-density lipoprotein (VLDL) secretion, and decrease hepatic oxidative stress in NAFLD mice. Inhibition of oxidative stress or direct suppression of protein kinase C (PKC) by CHR significantly reduced PKC activity in the liver, leading to a decrease in inhibitory phosphorylation of hepatocyte nuclear factor 4α (HNF4α). The resulting activation of HNF4α led to induced transcription of apolipoprotein B and VLDL secretion. Together, these results show that CHR effectively ameliorates MCD-induced fatty liver in NAFLD mice by targeting the hepatic oxidative stress/PKC/HNF4α signaling pathway.

High fat diet modulates the protein content of nutrient transporters in the small intestine of mice: possible involvement of PKA and PKC activity

Aims

Chronic high fat consumption has been shown to modulate nutrient transporter content in the intestine of obese mice; however it is unclear if this regulation occurs before or after the establishment of obesity, and the underlying molecular mechanism requires elucidation.

Main methods

Towards this goal C57BL/6 mice were fed a low fat diet (LFD) or high fat diet (HFD), and specific protein and gene expression levels were assessed for up to 12 weeks. Similar experiments were also performed with leptin-deficient (Ob/Ob) mice.

Key findings

The results showed that the HFD group presented decreased GLUT2, PEPT1, FAT/CD36 and NPC1L1, and increased NHE3, MTTP and L-FABP content. Animals fed an HFD also presented enhanced lipid transporter gene expression of Slc27a4, Npc1l1, Cd36, Mttp and L-Fabp. Additionally, FAT/CD36 and NPC1L1 protein levels were reduced in both HFD-induced obese and Ob/Ob mice. Ob/Ob mice also exhibited increased Slc2a2 and Slc15a1 mRNAs expression, but the protein expression levels remained unchanged. The HFD also attenuated PKA and PKC activities. The inhibition of PKA was associated with decreased FAT/CD36 content, whereas increased L-FABP levels likely depend on CREB activation, independent of PKA. It is plausible that the HFD-induced changes in NPC1L1, MTTP and L-FABP protein content involve regulation at the level of transcription. Moreover, the changes in GLUT2 and PEPT1 content might be associated with low PKC activity.

Significance

The results indicated that an HFD is capable of reducing nutrient transporter content, possibly attenuating nutrient uptake into the intestine, and may represent a feedback mechanism for regulating body weight. Furthermore, the elevated levels of NHE3, L-FABP and MTTP may account for the increased prevalence of hypertension and dyslipidemia in obese individuals. All of these changes are potentially linked to reduced PKA or PKC activities.

microRNA-30c reduces plasma cholesterol in homozygous familial hypercholesterolemic and type 2 diabetic mouse models

High plasma cholesterol levels are found in several metabolic disorders and their reductions are advocated to reduce the risk of atherosclerosis. A way to lower plasma lipids is to curtail lipoprotein production; however, this is associated with steatosis. We previously showed that microRNA (miR)-30c lowers diet-induced hypercholesterolemia and atherosclerosis in C57BL/6J and Apoe-/- mice. Here, we tested the effect of miR-30c on plasma lipids, transaminases, and hepatic lipids in different mouse models. Hepatic delivery of miR-30c to chow-fed leptin-deficient (ob/ob) and leptin receptor-deficient (db/db) hypercholesterolemic and hyperglycemic mice reduced cholesterol in total plasma and VLDL/LDL by ∼28% and ∼25%, respectively, without affecting triglyceride and glucose levels. And these mice had lower plasma transaminases and creatine kinase activities than controls. Moreover, miR-30c significantly lowered plasma cholesterol and atherosclerosis in Western diet-fed Ldlr-/- mice with no effect on plasma triglyceride, glucose, and transaminases. In these studies, hepatic lipids were similar in control and miR-30c-injected mice. Mechanistic studies showed that miR-30c reduced hepatic microsomal triglyceride transfer protein activity and lipid synthesis. Thus miR-30c reduced plasma cholesterol in several diet-induced and diabetic hypercholesterolemic mice. We speculate that miR-30c may be beneficial in lowering plasma cholesterol in different metabolic disorders independent of the origin of hypercholesterolemia.

Triglycerides Revisited to the Serial

This review discusses the role of triglycerides (TGs) in the normal cardiovascular system as well as in the development and clinical manifestation of cardiovascular diseases. Regulation of TGs at the enzymatic and genetic level, in addition to their possible relevance as preclinical and clinical biomarkers, is discussed, culminating with a description of available and emerging treatments. Due to the high complexity of the subject and the vast amount of material in the literature, the objective of this review was not to exhaust the subject, but rather to compile the information to facilitate and improve the understanding of those interested in this topic. The main publications on the topic were sought out, especially those from the last 5 years. The data in the literature still give reason to believe that there is room for doubt regarding the use of TG as disease biomarkers; however, there is increasing evidence for the role of hypertriglyceridemia on the atherosclerotic inflammatory process, cardiovascular outcomes, and mortality.

Challenges in the Diagnosis and Treatment of Homozygous Familial Hypercholesterolemia

Homozygous familial hypercholesterolemia (HoFH) is a rare, genetic disorder characterized by an absence or impairment of low-density lipoprotein receptor (LDLR) function resulting in significantly elevated low-density lipoprotein cholesterol (LDL-C) levels. The cholesterol exposure burden beginning in utero greatly increases the risk for atherosclerotic cardiovascular disease (ASCVD) and premature death. The genetic heterogeneity of HoFH results in a wide range of LDL-C levels among both untreated and treated patients. Diagnosis of HoFH should, therefore, be based on a comprehensive evaluation of clinical criteria and not exclusively LDL-C levels. As treatment goals, the European Atherosclerosis Society and International FH Foundation suggest target LDL-C levels of <100 mg/dL (<2.5 mmol/L) in adults or <70 mg/dL (<1.8 mmol/L) in adults with clinical coronary artery disease or diabetes. The National Lipid Association (NLA) recommends that LDL-C levels be reduced to <100 mg/dL (<2.5 mmol/L) or by at least ≥50 % from pretreatment levels. Conventional therapy combinations that lower atherogenic lipoproteins levels in the blood, such as statins, ezetimibe, bile acid sequestrants and niacin, as well as lipoprotein apheresis, are usually unable to reduce LDL-C levels to recommended targets. Two recently approved agents that reduce lipoprotein synthesis and secretion by the liver are lomitapide, a microsomal triglyceride transfer protein inhibitor, and mipomersen, an apolipoprotein B antisense oligonucleotide. The newly approved inhibitor of proprotein convertase subtilisin/kexin type 9 (PCSK9), evolocumab, also shows promise for the management of FH. Because of the extremely high risk for ASCVD, HoFH patients should be identified early.

Identification of the Flavonoid Luteolin as a Repressor of the Transcription Factor Hepatocyte Nuclear Factor 4α

Hepatocyte nuclear factor 4α (HNF4α) is a nuclear receptor that regulates the expression of genes involved in the secretion of apolipoprotein B (apoB)-containing lipoproteins and in glucose metabolism. In the present study, we identified a naturally occurring flavonoid, luteolin, as a repressor of HNF4α by screening for effectors of the human microsomal triglyceride transfer protein (MTP) promoter. Luciferase reporter gene assays revealed that the activity of the MTP gene promoter was suppressed by luteolin and that the mutation of HNF4α-binding element abolished luteolin responsiveness. Luteolin treatment caused a significant decrease in the mRNA levels of HNF4α target genes in HepG2 cells and inhibited apoB-containing lipoprotein secretion in HepG2 and differentiated Caco2 cells. The interaction between luteolin and HNF4α was demonstrated using absorption spectrum analysis and luteolin-immobilized beads. Luteolin did not affect the DNA binding of HNF4α to the promoter region of its target genes but suppressed the acetylation level of histone H3 in the promoter region of certain HNF4α target genes. Short term treatment of mice with luteolin significantly suppressed the expression of HNF4α target genes in the liver. In addition, long term treatment of mice with luteolin significantly suppressed their diet-induced obesity and improved their serum glucose and lipid parameters. Importantly, long term luteolin treatment lowered serum VLDL and LDL cholesterol and serum apoB protein levels, which was not accompanied by fat accumulation in the liver. These results suggest that the flavonoid luteolin ameliorates an atherogenic lipid profile in vivo that is likely to be mediated through the inactivation of HNF4α.

Crystal structure of 9-(4-bromo-but-yl)-9H-fluorene-9-carb-oxy-lic acid

The title compound, C18H17BrO2, is a key inter-mediate in the synthesis of lomitapide mesylate, a microsomal triglyceride transfer protein inhibitor. Its asymmetric unit contains two independent mol-ecules with slightly different conformations; the mean planes of the 4-bromo-butyl and carboxyl-ate groups in the two mol-ecules form dihedral angles of 24.54 (12) and 17.10 (18)°. In the crystal, carboxyl-ate groups are involved in O-H⋯O hydrogen bonding, which leads to the formation of two crystallographically independent centrosymmetric dimers. Weak inter-molecular C-H⋯O inter-actions further link these dimers into layers parallel to the bc plane.

Looking into the Crystal Ball—Upcoming Drugs for Dyslipidemia

Dyslipidaemia is a critical risk factor for the development of cardiovascular complications such as ischemic heart disease and stroke. Although statins are effective anti-dyslipidemic drugs, their usage is fraught with issues such as failure of adequate lipid control in 30% of cases and intolerance in select patients. The limited potential of other alternatives such as fibrates, bile acid sequestrants and niacin has spurred the search for novel drug molecules with better efficacy and safety. CETP inhibitors such as evacetrapib and anacetrapib have shown promise in raising HDL besides LDL lowering property. Microsomal triglyceride transfer protein (MTP) inhibitors such as lomitapide and Apo CIII inhibitors such as mipomersen have recently been approved in Familial Hypercholesterolemia but experience in the non-familial setting is pretty much limited. One of the novel anti-dyslipidemic drugs which is greatly anticipated to make a mark in LDL-C control is the PCSK9 inhibitors. Some of the anti-dyslipidemic drugs which work by PCSK9 inhibition include evolocumab, alirocumab and ALN-PCS. Other approaches that are being given due consideration include farnesoid X receptor modulation and Lp-PLA2 inhibition. While it may not be an easy proposition to dismantle statins from their current position as a cholesterol reducing agent and as a drug to reduce coronary and cerebro-vascular atherosclerosis, our improved understanding of the disease and appropriate harnessing of resources using sound and robust technology could make rapid in-roads in our pursuit of the ideal anti-dyslipidemic drug.

Efficacy of polyphenolic ingredients of Chinese herbs in treating dyslipidemia of metabolic syndromes

There is an increasing interest and popularity of Chinese herbal medicine worldwide, which is accompanied by increasing concerns about its effectiveness and potential toxicity. Several ingredients, such as polyphenolic compounds berberine, flavonoids, and curcumin, have been studied extensively by using various animal models. Effectiveness of treatment and amelioration of metabolic syndromes, including insulin resistance and dyslipidemia, has been demonstrated. This review summarizes the major checkpoints and contributing factors in regulation of exogenous and endogenous lipid metabolism, with particular emphasis centered on triglyceride-rich and cholesterol-rich lipoproteins. Available experimental evidence demonstrating the lipid-lowering effect of berberine, flavonoids and curcumin in cell culture and animal models is compiled, and the strengths and shortcomings of experimental designs in these studies are discussed.

New frontiers in the treatment of diabetic dyslipidemia

Dyslipidemia is a major risk factor for cardiovascular complications in people with diabetes. Lowering low-density lipoprotein cholesterol (LDL-C) levels is effective in the primary and secondary prevention of diabetic vascular complications. However, LDL-C levels do not reflect all aspects of diabetic dyslipidemia, which is characterized by hypertriglyceridemia and low high-density lipoprotein cholesterol (HDL-C). Statins, nicotinic acid, and fibrates play a role in treating diabetic dyslipidemia. Atherosclerosis is a major disorder of the blood vessel wall in patients with diabetes. A number of antihyperlipidemic agents may be beneficial and exhibit effects at the actual site of vascular disease and not only on plasma lipoprotein concentrations. Several novel therapeutic compounds are currently being developed. These include additional therapeutics for LDL-C, triglycerides, HDL-C, and modulators of inflammation that can be used as possible synergic agents for the treatment of atherosclerosis and irregularities in plasma lipoprotein concentrations.

Improved glycemic control and lipid profile in hyperlipidemic type 2 diabetic patients consuming Salvia officinalis L. leaf extract: a randomized placebo. Controlled clinical trial

OBJECTIVES

Evaluation of the efficacy and safety of Salvia officinalis L. (S. officinalis) leaf extract in the treatment of hyperlipidemic type 2 diabetic patients.

DESIGN

Randomized placebo-controlled parallel group study.

SETTING

Diabetes Clinic (Karaj City, Alborz Province of Iran).

INTERVENTIONS

The efficacy and safety of taking S. officinalis leaf extract (one 500 mg capsule t.i.d. for 3 months) in treatment of 40 hyperlipidemic (hypercholesterolemic and/or hypertriglyceridemic) type 2 diabetic patients were evaluated and compared with the placebo group (n=40).

MAIN OUTCOME MEASURES

Fasting blood levels of glucose, glycosylated hemoglobin (HbA1c), total cholesterol, triglyceride, LDL-C (low density lipoprotein cholesterol), HDL-C (high density lipoprotein cholesterol), SGOT (serum glutamic-oxaloacetic transaminase), SGPT (serum glutamic-pyruvic transaminase) and creatinine.

RESULTS

The extract lowered fasting glucose, HbA1c, total cholesterol, triglyceride and LDL-C but increased HDL-C compared to baseline at endpoint. Percent difference mean (95% confidence interval) between the extract and placebo groups in terms of effects on fasting glucose, HbA1c, total cholesterol, triglyceride, LDL-C and HDL-C at endpoint were 32.2 (26.5, 37.9), 22.7 (16.8, 28.6), 16.9 (9.7, 24.1), 56.4 (36.1, 76.7), 35.6 (29.9, 41.3) and 27.6 (15.8, 39.4) (P=0.001, P=0.01, P=0.01, P=0.009, P<0.001 and P=0.008), respectively. Moreover, the extract did not have any significant effects on the other parameters compared to the placebo group at endpoint (P>0.05). No adverse effects were reported.

CONCLUSIONS

S. officinalis leaves may be safe and have anti-hyperglycemic and lipid profile improving effects in hyperlipidemic type 2 diabetic patients.

Is the future of statins aligned with new novel lipid modulation therapies?

Dyslipidemia is an established risk factor for the development of atherosclerotic cardiovascular disease. Statin therapy has been proven in a number of clinical trials to lower the risk of acute cardiovascular events and is the mainstay of cholesterol treatment. Despite current optimal treatment for dyslipidemia, many patients fail to reach adequate cholesterol treatment goals and remain at a significantly increased risk of cardiovascular events. Given this residual risk, there is a critical need for additional lipid therapies that could augment the ability of statins to lower the burden of atherogenic lipoproteins and, in some cases, raise levels of high-density lipoproteins. A number of novel lipid-altering therapies have been developed and are currently in clinical trials. In this review, we discuss these promising therapies, which include PCSK9 inhibitors, apolipoprotein B antisense oligonucleotides, microsomal transfer protein inhibitors, thyroid mimetics, and cholesteryl ester transfer protein inhibitors. Although statin therapy is the current recommended primary treatment for dyslipidemia, emerging novel agents may become adjuvant therapies in the treatment of atherosclerotic heart disease.

MicroRNA-30c reduces hyperlipidemia and atherosclerosis in mice by decreasing lipid synthesis and lipoprotein secretion

Hyperlipidemia is a risk factor for various cardiovascular and metabolic disorders. Overproduction of lipoproteins, a process critically dependent on microsomal triglyceride transfer protein (MTP), can contribute to hyperlipidemia. We show that microRNA-30c (miR-30c) interacts with the 3′-untranslated region of the MTP mRNA and induces degradation leading to reductions in its activity and media apolipoprotein B. Further, miR-30c reduces hyperlipidemia and atherosclerosis in Western diet fed mice by decreasing lipid synthesis and secretion of triglyceride-rich apoB-containing lipoproteins. Therefore, miR-30c coordinately reduces lipid biosynthesis and lipoprotein secretion to control hepatic and plasma lipids and might be useful in treating hyperlipidemias and associated disorders.

Improved lipid profile in hyperlipidemic patients taking Vaccinium arctostaphylos fruit hydroalcoholic extract: a randomized double-blind placebo-controlled clinical trial

Dyslipidemia is a common contributory cause of cardiovascular disease. Vaccinium arctostaphylos L. (Caucasian whortleberry) fruit is rich of anthocyanins. Anthocyanins may exert cardioprotective effects by various mechanisms such as favorably modulating dyslipidemia. Therefore, in this randomized double-blind placebo-controlled clinical trial with hyperlipidemic (hypercholesterolemic and/or hypertriglyceridemic) patients aged 20-60 years, the effects of taking a standardized whortleberry fruit hydroalcoholic extract (one 350 mg capsule every 8 h for 2 months) on fasting blood levels of lipids, creatinine and liver enzymes including SGOT and SGPT were evaluated in 40 patients and compared with the placebo group (n = 40). The extract lowered the blood levels of total cholesterol (P < 0.001), triglyceride (P = 0.002) and low-density lipoprotein cholesterol (LDL-C) (P = 0.002), but increased the blood high-density lipoprotein cholesterol (HDL-C) levels (P < 0.001) without any significant effects on the blood levels of SGOT, SGPT and creatinine (P > 0.05) compared with the placebo group at the endpoint. Whortleberry reduced total cholesterol, triglyceride and LDL-C 27.6%, 19.2% and 26.3%, respectively, but increased HDL-C 37.5% compared with baseline. No adverse effects were reported. Short-term treatment with whortleberry fruit appears safe and improves lipid profile in hyperlipidemic patients.

Lipoprotein metabolism in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), an escalating health problem worldwide, covers a spectrum of pathologies characterized by fatty accumulation in hepatocytes in early stages, with potential progression to liver inflammation, fibrosis, and failure. A close, yet poorly understood link exists between NAFLD and dyslipidemia, a constellation of abnormalities in plasma lipoproteins including triglyceride-rich very low density lipoproteins. Apolipoproteins are a group of primarily liver-derived proteins found in serum lipoproteins; they not only play an extracellular role in lipid transport between vital organs through circulation, but also play an important intracellular role in hepatic lipoprotein assembly and secretion. The liver functions as the central hub for lipoprotein metabolism, as it dictates lipoprotein production and to a significant extent modulates lipoprotein clearance. Lipoprotein metabolism is an integral component of hepatocellular lipid homeostasis and is implicated in the pathogenesis, potential diagnosis, and treatment of NAFLD.

Mipomersen and other therapies for the treatment of severe familial hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal dominant condition with a population prevalence of one in 300–500 (heterozygous) that is characterized by high levels of low-density lipoprotein (LDL) cholesterol, tendon xanthomata, and premature atherosclerosis and coronary heart disease (CHD). FH is caused mainly by mutations in the LDLR gene. However, mutations in other genes including APOB and PCSK9, can give rise to a similar phenotype. Homozygous FH with an estimated prevalence of one in a million is associated with severe hypercholesterolemia with accelerated atherosclerotic CHD in childhood and without treatment, death usually occurs before the age of 30 years. Current approaches for the treatment of homozygous FH include statin-based lipid-lowering therapies and LDL apheresis. Mipomersen is a second-generation antisense oligonucleotide (ASO) targeted to human apolipoprotein B (apoB)-100. This review provides an overview of the pathophysiology and current treatment options for familial hypercholesterolemia and describes novel therapeutic strategies focusing on mipomersen, an antisense apoB synthesis inhibitor. Mipomersen is distributed mainly to the liver where it silences apoB mRNA, thereby reducing hepatic apoB-100 and giving rise to reductions in plasma total cholesterol, LDL-cholesterol, and apoB concentrations in a dose-and time-dependent manner. Mipomersen has been shown to decrease apoB, LDL-cholesterol and lipoprotein(a) in patients with heterozygous and homozygous FH on maximally tolerated lipid-lowering therapy. The short-term efficacy and safety of mipomersen has been established, however, injection site reactions are common and concern exists regarding the long-term potential for hepatic steatosis with this ASO. In summary, mipomersen given alone or in combination with standard lipid-lowering medications shows promise as an adjunct therapy in patients with homozygous or refractory heterozygous FH at high risk of atherosclerotic CHD, who are not at target or are intolerant of statins.

Multiple functions of microsomal triglyceride transfer protein

Microsomal triglyceride transfer protein (MTP) was first identified as a major cellular protein capable of transferring neutral lipids between membrane vesicles. Its role as an essential chaperone for the biosynthesis of apolipoprotein B (apoB)-containing triglyceride-rich lipoproteins was established after the realization that abetalipoproteinemia patients carry mutations in the MTTP gene resulting in the loss of its lipid transfer activity. Now it is known that it also plays a role in the biosynthesis of CD1, glycolipid presenting molecules, as well as in the regulation of cholesterol ester biosynthesis. In this review, we will provide a historical perspective about the identification, purification and characterization of MTP, describe methods used to measure its lipid transfer activity, and discuss tissue expression and function. Finally, we will review the role MTP plays in the assembly of apoB-lipoprotein, the regulation of cholesterol ester synthesis, biosynthesis of CD1 proteins and propagation of hepatitis C virus. We will also provide a brief overview about the clinical potentials of MTP inhibition.

Familial hypercholesterolemia: present and future management

Patients suffering from familial hypercholesterolemia (FH) are characterized by increased plasma levels of low-density lipoprotein cholesterol (LDL-C) levels and are at increased risk for premature cardiovascular disease (CVD). Current guidelines emphasize the need to aggressively lower LDL-C in FH patients, and statins are the cornerstone in the current regimen. However, additional therapies are eagerly awaited, especially for those patients not tolerating statin therapy or not reaching the goals for therapy. Our understanding of LDL metabolism has improved over the last years and an increasing number of potential novel targets for therapy have been recently identified. Apart from novel targets, we have also been confronted with novel modalities of treatment, such as mRNA antisense therapy. Some of these emerging therapies have proven to be effective in lowering plasma LDL-C levels and are as such expected to have beneficial effects on CVD. Hopefully, they will enrich our armamentarium against the severe dyslipidemia observed in FH patients in the not too distant future.

Antihyperlipidemic effects of Salvia officinalis L. leaf extract in patients with hyperlipidemia: a randomized double-blind placebo-controlled clinical trial

Hyperlipidemia is a common metabolic disorder contributing to morbidities and mortalities due to cardiovascular and cerebrovascular diseases. Conventional antihyperlipidemic drugs have limited efficacies and important side effects, so that alternative lipid lowering agents are needed. Salvia officinalis L. (sage) leaves have PPAR γ agonistic, pancreatic lipase and lipid absorption inhibitory, antioxidant, lipid peroxidation inhibitory and antiinflammatory effects. Thus, in this randomized double-blind placebo-controlled clinical trial with 67 hyperlipidemic (hypercholesterolemic and/or hypertriglyceridemic) patients aged 56.4 ± 30.3 years (mean ± SD), the effects of taking sage leaf extract (one 500 mg capsule every 8 h for 2 months) on fasting blood levels of lipids, creatinine and liver enzymes including SGOT and SGPT were evaluated in 34 patients and compared with the placebo group (n = 33). The extract lowered the blood levels of total cholesterol (p < 0.001), triglyceride (p = 0.001), LDL (p = 0.004) and VLDL (p = 0.001), but increased the blood HDL levels (p < 0.001) without any significant effects on the blood levels of SGOT, SGPT and creatinine (p > 0.05) compared with the placebo group at the endpoint. No adverse effects were reported. The results suggest that sage may be effective and safe in the treatment of hyperlipidemia.

Pharmacological characterization of diethyl-2-({3-dimethylcarbamoyl-4-[(4'-trifluoromethylbiphenyl-2-carbonyl)amino]phenyl}acetyloxymethyl)-2-phenylmalonate (JTT-130), an intestine-specific inhibitor of microsomal triglyceride transfer protein

Inhibitors of microsomal triglyceride transfer protein (MTP) expressed in the liver and small intestine are potential candidates for lipid-lowering agents. However, inhibition of hepatic MTP could lead to significant safety issues such as fatty liver disease. To develop a specific inhibitor of intestinal MTP, JTT-130 [diethyl-2-({3-dimethylcarbamoyl-4-[(4'-trifluoromethylbiphenyl-2-carbonyl)amino]phenyl}acetyloxymethyl)-2-phenylmalonate], was designed to be rapidly hydrolyzed in the absorption process. Here, we describe JTT-130, an intestine-specific MTP inhibitor, and evaluate its pharmacological properties. In in vitro metabolic stability tests, JTT-130 was readily hydrolyzed during incubation with liver S9 from humans, hamsters, and rats. In an in vitro triglyceride (TG) transfer assay with human intestinal MTP, JTT-130 potently inhibited TG transfer activity with an IC(50) value of 0.83 nM. When orally administered to hamsters, JTT-130 significantly suppressed an increase in chylomicron-TG after olive oil loading at 0.3 mg/kg and above but did not inhibit TG secretion from the liver at doses of up to 1000 mg/kg, indicating an inhibitory action highly specific for the small intestine. In rats orally administered [(14)C]triolein, JTT-130 potently suppressed an increase in blood (14)C radioactivity and increased (14)C radioactivity in the upper small intestine and the intestinal lumen. In hyperlipidemic hamsters fed a high-fat and high-cholesterol diet, repeated dosing with JTT-130 for 2 weeks reduced TG and cholesterol levels in the plasma and TG content in the liver. These results indicated that JTT-130 is a potent inhibitor specific to intestinal MTP and suggested that JTT-130 would be a useful compound for the treatment of dyslipidemia without inducing hepatotoxicity.

Genetic determinants of hepatic steatosis in man

Hepatic steatosis is one of the most common liver disorders in the general population. The main cause of hepatic steatosis is nonalcoholic fatty liver disease (NAFLD), representing the hepatic component of the metabolic syndrome, which is characterized by type 2 diabetes, obesity, and dyslipidemia. Insulin resistance and excess adiposity are considered to play key roles in the pathogenesis of NAFLD. Although the risk factors for NAFLD are well established, the genetic basis of hepatic steatosis is largely unknown. Here we review recent progress on genomic variants and their association with hepatic steatosis and discuss the potential impact of these genetic studies on clinical practice. Identifying the genetic determinants of hepatic steatosis will lead to a better understanding of the pathogenesis and progression of NAFLD.

Mipomersen, an antisense apolipoprotein B synthesis inhibitor

INTRODUCTION

mipomersen is a second-generation antisense oligonucleotide (ASO) targeted to human apolipoprotein (apo) B-100, a large protein synthesized by the liver that plays a fundamental role in human lipoprotein metabolism. Mipomersen predominantly distributes to the liver and decreases the production of apoB-100, the primary structural protein of the atherogenic lipoproteins including low density lipoprotein (LDL), thereby reducing plasma LDL-cholesterol and apoB-100 concentrations.

AREAS COVERED

the mode of action, preclinical development and clinical trials of mipomersen, an antisense apoB synthesis inhibitor. The paper provides an understanding of the pharmacokinetic and pharmacodynamic characteristics of mipomersen and insight into its clinical efficacy and safety. In clinical trials, mipomersen produced dose-dependent and prolonged reductions in LDL-cholesterol and other apoB-containing lipoproteins, including lipoprotein (a) [Lp(a)] in healthy volunteers and in patients with mild to moderate hypercholesterolemia. Mipomersen has been shown to decrease apoB, LDL-cholesterol and Lp(a) in patients with heterozygous and homozygous familial hypercholesterolemia on maximally tolerated lipid-lowering therapy.

EXPERT OPINION

mipomersen shows promise as an adjunctive agent by reducing apoB-containing lipoproteins in patients at high risk of atherosclerotic cardiovascular disease who are not at target or are intolerant of statins. Although the short-term efficacy and safety of mipomersen has been established, concern exists regarding the long-term potential for hepatic steatosis with this ASO.

ERp57 is up-regulated in free fatty acids-induced steatotic L-02 cells and human nonalcoholic fatty livers

Pathogenesis of nonalcoholic fatty liver disease (NAFLD) is not clear. In this study we aimed to identify proteins involved in NAFLD development in free fatty acids (FFA)-induced hepatosteatotic cells and in human liver biopsies. Steatosis was induced by incubating a normal human hepatocyte-derived cell line L-02 with FFA. Differentially expressed proteins in the steatotic cells were analyzed by two-dimensional gel electrophoresis-based proteomics. Involvement of one of the up-regulated proteins in steatosis was characterized using the RNA interference approach with the steatotic cells. Protein expression levels in liver biopsies of patients with NAFLD were assessed by immunohistochemistry. Proteomic analysis of L-02 steatotic cells revealed the up-regulation of ERp57, a condition not previously implicated in NAFLD. Knockdown of ERp57 expression with siRNA significantly reduced fat accumulation in the steatotic cells. ERp57 expression was detected in 16 out of 17 patient biopsies and correlated with inflammation grades or fibrosis stages, while in 5 normal biopsies ERp57 expression was not detectable in hepatocytes. In conclusion, ERp57 was up-regulated in FFA-induced steatotic hepatic cells and in NAFLD patient livers and demonstrated steatotic properties in cultured cells. Further investigations are warranted to verify the involvement of ERp57 in NAFLD development.

Lipid transport and signaling in Caenorhabditis elegans

The strengths of the Caenorhabditis elegans model have been recently applied to the study of the pathways of lipid storage, transport, and signaling. As the lipid storage field has recently been reviewed, in this minireview we (1) discuss some recent studies revealing important physiological roles for lipases in mobilizing lipid reserves, (2) describe various pathways of lipid transport, with a particular focus on the roles of lipoproteins, (3) debate the utility of using C. elegans as a model for human dyslipidemias that impinge on atherosclerosis, and (4) describe several systems where lipids affect signaling, highlighting the particular properties of lipids as information-carrying molecules. We conclude that the study of lipid biology in C. elegans exemplifies the advantages afforded by a whole-animal model system where interactions between tissues and organs, and functions such as nutrient absorption, distribution, and storage, as well as reproduction can all be studied simultaneously.

Human luteinized granulosa cells secrete apoB100-containing lipoproteins

Thus far, liver, intestine, heart, and placenta have been shown to secrete apolipoprotein (apo)B-containing lipoproteins. In the present study, we first investigated lipoproteins in human follicular fluid (FF), surrounding developing oocytes within the ovary, as well as in corresponding plasma samples (n = 12). HDL cholesterol within FF correlated well with plasma HDL cholesterol (r = 0.80, P < 0.01), whereas VLDL cholesterol did not, indicating that VLDL in FF might originate directly from the granulosa cells producing FF. Primary human granulosa cells expressed apoB, microsomal triglyceride transfer protein, and apoE, but not the apoB-editing enzyme apobec-1. Using (3)H-leucine, we show that granulosa cells secrete apoB100-containing lipoproteins and that secretion can be stimulated by adding oleate to the medium (+83%). With electron microscopy, apoB-containing lipoproteins within the secretory pathway of human granulosa cells were directly visualized. Finally, we found a positive relationship between apoB levels in FF and improved fertility parameters in a population of 27 women undergoing in vitro fertilization. This study demonstrates that human granulosa cells assemble and secrete apoB100-containing lipoproteins, thereby identifying a novel cell type equipped with these properties. These results might have important implications for female infertility phenotypes as well as for the development of drugs targeting the VLDL production pathway.

Pluronic L-81 ameliorates diabetic symptoms in db/db mice through transcriptional regulation of microsomal triglyceride transfer protein

AIM: To test whether oral L-81 treatment could improve the condition of mice with diabetes and to investigate how L-81 regulates microsomal triglyceride transfer protein (MTP) activity in the liver.

METHODS: Genetically diabetic (db/db) mice were fed on chow supplemented with or without L-81 for 4 wk. The body weight, plasma glucose level, plasma lipid profile, and adipocyte volume of the db/db mice were assessed after treatment. Toxicity of L-81 was also evaluated. To understand the molecular mechanism, HepG2 cells were treated with L-81 and the effects on apolipoprotein B (apoB) secretion and mRNA level of the MTP gene were assessed.

RESULTS: Treatment of db/db mice with L-81 significantly reduced and nearly normalized their body weight, hyperphagia and polydipsia. L-81 also markedly decreased the fasting plasma glucose level, improved glucose tolerance, and attenuated the elevated levels of plasma cholesterol and triglyceride. At the effective dosage, little toxicity was observed. Treatment of HepG2 cells with L-81 not only inhibited apoB secretion, but also significantly decreased the mRNA level of the MTP gene. Similar to the action of insulin, L-81 exerted its effect on the MTP promoter.

CONCLUSION: L-81 represents a promising candidate in the development of a selective insulin-mimetic molecule and an anti-diabetic agent.

New approaches to target microsomal triglyceride transfer protein

PURPOSE OF REVIEW

Microsomal triglyceride transfer protein (MTP), a chaperone for the biosynthesis of apolipoprotein B lipoproteins and CD1d, is a therapeutic candidate to decrease plasma lipids and to diminish inflammation. MTP inhibition increases plasma transaminases and tissue lipids, and therefore new approaches are needed to avoid them.

RECENT FINDINGS

Inositol requiring enzyme1beta has been identified as a novel intestine-specific regulator of MTP. A new function of MTP in cholesterol ester biosynthesis has been reported. The importance of the phospholipid transfer activity of MTP in the lipidation of apolipoprotein B and CD1d has been indicated. Diurnal variations in MTP expression and its induction by food availability have been observed. On the basis of these and other findings, we propose that upregulation of inositol requiring enzyme 1beta, a combined reduction of cellular free cholesterol or triglyceride or both and MTP activity, specific inhibition of phospholipid or triglyceride transfer activities, and targeting of apolipoprotein B-MTP protein-protein interactions might be pursued to avoid some of the side effects associated with the inhibition of triglyceride transfer activity of MTP. We further speculate that short-lived MTP antagonists may be useful in controlling plasma and tissue lipids and in avoiding steatosis.

SUMMARY

We have highlighted the importance of addressing the causal relationship between MTP inhibition and aberrant elevations in plasma liver enzymes. The proposed approaches may show that MTP targeting is a viable approach to lower plasma lipids.

Microsomal triglyceride transfer protein in plasma and cellular lipid metabolism

PURPOSE OF REVIEW

This review summarizes recent advances about the role of microsomal triglyceride transfer protein in plasma and tissue lipid homeostasis.

RECENT FINDINGS

Microsomal triglyceride transfer protein emerged as a phospholipid transfer protein and acquired triacylglycerol transfer activity during evolution from invertebrates to vertebrates. These activities are proposed to participate in 'nucleation' and 'desorption' steps during the biosynthesis of primordial apoB-containing lipoproteins. Microsomal triglyceride transfer protein also transfers phospholipids to the glycolipid antigen presentation molecule CD1d. Under physiologic conditions, plasma apoB-containing lipoproteins and microsomal triglyceride transfer protein expression exhibit diurnal variations synchronized by food and light. Microsomal triglyceride transfer protein is regulated at the transcriptional level. HNF4alpha is critical for its transcription. Other transcription factors along with coactivators and corepressors modulate microsomal triglyceride transfer protein expression. Reductions in microsomal triglyceride transfer protein mRNA and activity are related to steatosis in HCV-3 infected patients. CCl4 induces steatosis by enhancing proteasomal degradation of microsomal triglyceride transfer protein and can be partially avoided by inhibiting this degradation. Chemical antagonists cause hepatosteatosis, but this was not seen in the absence of fatty acid binding protein.

SUMMARY

Microsomal triglyceride transfer protein is a target to lower plasma lipids and to reduce inflammation in certain immune disorders. More knowledge is required, however, regarding its regulation and its role in the biosynthesis of apoB-containing lipoproteins and CD1d.

Inhibition of microsomal triglyceride transfer protein alone or with ezetimibe in patients with moderate hypercholesterolemia

BACKGROUND

Many patients with coronary heart disease do not achieve recommended LDL-cholesterol levels, due to either intolerance or inadequate response to available lipid-lowering therapy. Microsomal triglyceride transfer protein (MTP) inhibitors might provide an alternative way to lower LDL-cholesterol levels. We tested the safety and LDL-cholesterol-lowering efficacy of an MTP inhibitor, AEGR-733 (Aegerion Pharmaceuticals Inc., Bridgewater, NJ), alone and in combination with ezetimibe.

METHODS

We performed a multicenter, double-blind, 12-week trial, which included 84 patients with hypercholesterolemia. Patients were randomly assigned ezetimibe 10 mg daily (n = 29); AEGR-733 5.0 mg daily for the first 4 weeks, 7.5 mg daily for the second 4 weeks and 10 mg daily for the last 4 weeks (n = 28); or ezetimibe 10 mg daily and AEGR-733 administered with the dose titration described above (n = 28).

RESULTS

Ezetimibe monotherapy led to a 20-22% decrease in LDL-cholesterol concentrations. AEGR-733 monotherapy led to a dose-dependent decrease in LDL-cholesterol concentration: 19% at 5.0 mg, 26% at 7.5 mg and 30% at 10 mg. Combined therapy produced similar but larger dose-dependent decreases (35%, 38% and 46%, respectively). The number of patients who discontinued study drugs owing to adverse events was five with ezetimibe alone, nine with AEGR-733 alone, and four with combined ezetimibe and AEGR-733. Discontinuations from AEGR-733 were due primarily to mild transaminase elevations.

CONCLUSIONS

Inhibition of LDL production with low-dose AEGR-733, either alone or in combination with ezetimibe, could be an effective therapeutic option for patients unable to reach target LDL-cholesterol levels.

Microsomal triglyceride transfer protein enhances cellular cholesteryl esterification by relieving product inhibition

Cholesteryl ester synthesis by the acyl-CoA:cholesterol acyltransferase enzymes ACAT1 and ACAT2 is, in part, a cellular homeostatic mechanism to avoid toxicity associated with high free cholesterol levels. In hepatocytes and enterocytes, cholesteryl esters are secreted as part of apoB lipoproteins, the assembly of which is critically dependent on microsomal triglyceride transfer protein (MTP). Conditional genetic ablation of MTP reduces cholesteryl esters and enhances free cholesterol in the liver and intestine without diminishing ACAT1 and ACAT2 mRNA levels. As expected, increases in hepatic free cholesterol are associated with decreases in 3-hydroxy-3-methylglutaryl-CoA reductase and increases in ATP-binding cassette transporter 1 mRNA levels. Chemical inhibition of MTP also decreases esterification of cholesterol in Caco-2 and HepG2 cells. Conversely, coexpression of MTP and apoB in AC29 cells stably transfected with ACAT1 and ACAT2 increases cholesteryl ester synthesis. Liver and enterocyte microsomes from MTP-deficient animals synthesize lesser amounts of cholesteryl esters in vitro, but addition of purified MTP and low density lipoprotein corrects this deficiency. Enrichment of microsomes with cholesteryl esters also inhibits cholesterol ester synthesis. Thus, MTP enhances cellular cholesterol esterification by removing cholesteryl esters from their site of synthesis and depositing them into nascent apoB lipoproteins. Therefore, MTP plays a novel role in regulating cholesteryl ester biosynthesis in cells that produce lipoproteins. We speculate that non-lipoprotein-producing cells may use different mechanisms to alleviate product inhibition and modulate cholesteryl ester biosynthesis.

New targets and emerging therapies for reducing LDL cholesterol

PURPOSE OF REVIEW

Effective therapies for lowering LDL-cholesterol reduce the incidence of cardiovascular disease and provide associated decreases in morbidity and mortality. Progress in our understanding of metabolism and innovations in drug design have jointly identified promising new drug targets and alternative approaches to old targets. This review focuses on the mechanism, safety and efficacy of emerging LDL-cholesterol lowering therapies.

RECENT FINDINGS

Decreasing apolipoprotein B expression or preventing the formation of a stable lipoprotein structure by inhibiting microsomal triglyceride transfer protein attenuates the secretion of atherogenic lipoproteins containing apolipoprotein B into the plasma. Increases in LDL receptor-mediated cholesterol clearance occur when hepatic cholesterol stores are reduced secondary to inhibition of squalene synthase or LDL receptor degradation is disrupted by reduced activity of proprotein convertase subtilisin kexin type 9. Each of these developing therapies demonstrably reduces LDL-cholesterol levels.

SUMMARY

The emergence of modalities that act in series and in parallel with available agents may allow more effective LDL-cholesterol lowering in those patients intolerant of current therapy, and may permit decremental reductions in LDL-cholesterol for those unable to achieve aggressive LDL-cholesterol goals using existing agents.