The metabolism of triglyceride-rich lipoproteins revisited: new players, new insight

Triglyceride-rich lipoproteins and cardiovascular diseases

The global prevalence of cardiovascular diseases (CVD) continues to rise steadily, making it a leading cause of mortality worldwide. Atherosclerosis (AS) serves as a primary driver of these conditions, commencing silently at an early age and culminating in adverse cardiovascular events that severely impact patients' quality of life or lead to fatality. Dyslipidemia, particularly elevated levels of low-density lipoprotein cholesterol (LDL-C), plays a pivotal role in AS pathogenesis as an independent risk factor. Research indicates that abnormal LDL-C accumulation within arterial walls acts as a crucial trigger for atherosclerotic plaque formation. As the disease progresses, plaque accumulation may rupture or dislodge, resulting in thrombus formation and complete blood supply obstruction, ultimately causing myocardial infarction, cerebral infarction, and other common adverse cardiovascular events. Despite adequate pharmacologic therapy targeting LDL-C reduction, patients with cardiometabolic abnormalities remain at high risk for disease recurrence, highlighting the importance of addressing lipid risk factors beyond LDL-C. Recent attention has focused on the causal relationship between triglycerides, triglyceride-rich lipoproteins (TRLs), and their remnants in AS risk. Genetic, epidemiologic, and clinical studies suggest a causal relationship between TRLs and their remnants and the increased risk of AS, and this dyslipidemia may be an independent risk factor for adverse cardiovascular events. Particularly in patients with obesity, metabolic syndrome, diabetes, and chronic kidney disease, disordered TRLs and its remnants levels significantly increase the risk of atherosclerosis and cardiovascular disease development. Accumulation of over-synthesized TRLs in plasma, impaired function of enzymes involved in TRLs lipolysis, and impaired hepatic clearance of cholesterol-rich TRLs remnants can lead to arterial deposition of TRLs and its remnants, promoting foam cell formation and arterial wall inflammation. Therefore, understanding the pathogenesis of TRLs-induced AS and targeting it therapeutically could slow or impede AS progression, thereby reducing cardiovascular disease morbidity and mortality, particularly coronary atherosclerotic heart disease.

Targeting the vivid facets of apolipoproteins as a cardiovascular risk factor in rheumatoid arthritis

Mostly, cardiovascular diseases are blamed for casualties in rheumatoid arthritis (RA) patients. Customarily, dyslipidemia is probably the most prevalent underlying cause of untimely demise in people suffering from RA as it hastens the expansion of atherosclerosis. The engagement of inflammatory cytokines like tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), interleukin-6 (IL-6), etc., is crucial in the progression and proliferation of both RA and abnormal lipid parameters. Thus, lipid abnormalities should be monitored frequently in patients with both primary and advanced RA stages. An advanced lipid profile examination, i.e., direct role of apolipoproteins associated with various lipid molecules is a more dependable approach for better understanding of the disease and selecting suitable therapeutic targets. Therefore, studying their apolipoproteins is more relevant than assessing RA patients' altered lipid profile levels. Among the various apolipoprotein classes, Apo A1 and Apo B are primarily being focused. In addition, it also addresses how calculating Apo B:Apo A1 ratio can aid in analyzing the disease's risk. The marketed therapies available to control lipid abnormalities are associated with many other risk factors. Hence, directly targeting Apo A1 and Apo B would provide a better and safer option.

Effect of tomato, tomato-derived products and lycopene on metabolic inflammation: from epidemiological data to molecular mechanisms

The goal of this narrative review is to summarise the current knowledge and limitations related to the anti-inflammatory effects of tomato, tomato-derived products and lycopene in the context of metabolic inflammation associated to cardiometabolic diseases. The potential of tomato and tomato-derived product supplementation is supported by animal and in vitro studies. In addition, intervention studies provide arguments in favour of a limitation of metabolic inflammation. This is also the case for observational studies depicting inverse association between plasma lycopene levels and inflammation. Nevertheless, current data of intervention studies are mixed concerning the anti-inflammatory effect of tomato and tomato-derived products and are not in favour of an anti-inflammatory effect of pure lycopene in humans. From epidemiological to mechanistic studies, this review aims to identify limitations of the current knowledge and gaps that remain to be filled to improve our comprehension in contrasted anti-inflammatory effects of tomato, tomato-derived products and pure lycopene.

RNA-Seq analysis of the pyloric caecum, liver, and muscle reveals molecular mechanisms regulating fillet color in rainbow trout

BACKGROUND

The characteristic pink-reddish color in the salmonids fillet is an important, appealing quality trait for consumers and producers. The color results from diet supplementation with carotenoids, which accounts for up to 20-30% of the feed cost. Pigment retention in the muscle is a highly variable phenotype. In this study, we aimed to understand the molecular basis for the variation in fillet color when rainbow trout (Oncorhynchus mykiss) fish families were fed an Astaxanthin-supplemented diet. We used RNA-Seq to study the transcriptome profile in the pyloric caecum, liver, and muscle from fish families with pink-reddish fillet coloration (red) versus those with lighter pale coloration (white).

RESULTS

More DEGs were identified in the muscle (5,148) and liver (3,180) than in the pyloric caecum (272). Genes involved in lipid/carotenoid metabolism and transport, ribosomal activities, mitochondrial functions, and stress homeostasis were uniquely enriched in the muscle and liver. For instance, the two beta carotene genes (BCO1 and BCO2) were significantly under-represented in the muscle of the red fillet group favoring more carotenoid retention. Enriched genes in the pyloric caecum were involved in intestinal absorption and transport of carotenoids and lipids. In addition, the analysis revealed the modulation of several genes with immune functions in the pyloric caecum, liver, and muscle.

CONCLUSION

The results from this study deepen our understanding of carotenoid dynamics in rainbow trout and can guide us on strategies to improve Astaxanthin retention in the rainbow trout fillet.

Structure of dimeric lipoprotein lipase reveals a pore adjacent to the active site

Lipoprotein lipase (LPL) hydrolyzes triglycerides from circulating lipoproteins, releasing free fatty acids. Active LPL is needed to prevent hypertriglyceridemia, which is a risk factor for cardiovascular disease (CVD). Using cryogenic electron microscopy (cryoEM), we determined the structure of an active LPL dimer at 3.9 Å resolution. This structure reveals an open hydrophobic pore adjacent to the active site residues. Using modeling, we demonstrate that this pore can accommodate an acyl chain from a triglyceride. Known LPL mutations that lead to hypertriglyceridemia localize to the end of the pore and cause defective substrate hydrolysis. The pore may provide additional substrate specificity and/or allow unidirectional acyl chain release from LPL. This structure also revises previous models on how LPL dimerizes, revealing a C-terminal to C-terminal interface. We hypothesize that this active C-terminal to C-terminal conformation is adopted by LPL when associated with lipoproteins in capillaries.

Structure of Dimeric Lipoprotein Lipase Reveals a Pore for Hydrolysis of Acyl Chains

Lipoprotein lipase (LPL) hydrolyzes triglycerides from circulating lipoproteins, releasing free fatty acids. Active LPL is needed to prevent hypertriglyceridemia, which is a risk factor for cardiovascular disease (CVD). Using cryogenic electron microscopy (cryoEM), we determined the structure of an active LPL dimer at 3.9 Ã… resolution. This is the first structure of a mammalian lipase with an open, hydrophobic pore adjacent to the active site. We demonstrate that the pore can accommodate an acyl chain from a triglyceride. Previously, it was thought that an open lipase conformation was defined by a displaced lid peptide, exposing the hydrophobic pocket surrounding the active site. With these previous models after the lid opened, the substrate would enter the active site, be hydrolyzed and then released in a bidirectional manner. It was assumed that the hydrophobic pocket provided the only ligand selectivity. Based on our structure, we propose a new model for lipid hydrolysis, in which the free fatty acid product travels unidirectionally through the active site pore, entering and exiting opposite sides of the protein. By this new model, the hydrophobic pore provides additional substrate specificity and provides insight into how LPL mutations in the active site pore may negatively impact LPL activity, leading to chylomicronemia. Structural similarity of LPL to other human lipases suggests that this unidirectional mechanism could be conserved but has not been observed due to the difficulty of studying lipase structure in the presence of an activating substrate. We hypothesize that the air/water interface formed during creation of samples for cryoEM triggered interfacial activation, allowing us to capture, for the first time, a fully open state of a mammalian lipase. Our new structure also revises previous models on how LPL dimerizes, revealing an unexpected C-terminal to C-terminal interface. The elucidation of a dimeric LPL structure highlights the oligomeric diversity of LPL, as now LPL homodimer, heterodimer, and helical filament structures have been elucidated. This diversity of oligomerization may provide a form of regulation as LPL travels from secretory vesicles in the cell, to the capillary, and eventually to the liver for lipoprotein remnant uptake. We hypothesize that LPL dimerizes in this active C-terminal to C-terminal conformation when associated with mobile lipoproteins in the capillary.

Fatty Acid Metabolism in Endothelial Cell

The endothelium is a monolayer of cells lining the inner blood vessels. Endothelial cells (ECs) play indispensable roles in angiogenesis, homeostasis, and immune response under normal physiological conditions, and their dysfunction is closely associated with pathologies such as cardiovascular diseases. Abnormal EC metabolism, especially dysfunctional fatty acid (FA) metabolism, contributes to the development of many diseases including pulmonary hypertension (PH). In this review, we focus on discussing the latest advances in FA metabolism in ECs under normal and pathological conditions with an emphasis on PH. We also highlight areas of research that warrant further investigation.

Pathogenic gain-of-function mutations in the prodomain and C-terminal domain of PCSK9 inhibit LDL binding

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a secreted protein that binds and mediates endo-lysosomal degradation of low-density lipoprotein receptor (LDLR), limiting plasma clearance of cholesterol-rich LDL particles in liver. Gain-of-function (GOF) point mutations in PCSK9 are associated with familial hypercholesterolemia (FH). Approximately 30%–40% of PCSK9 in normolipidemic human plasma is bound to LDL particles. We previously reported that an R496W GOF mutation in a region of PCSK9 known as cysteine-histidine–rich domain module 1 (CM1) prevents LDL binding in vitro [Sarkar et al., J. Biol. Chem. 295 (8), 2285–2298 (2020)]. Herein, we identify additional GOF mutations that inhibit LDL association, localized either within CM1 or a surface-exposed region in the PCSK9 prodomain. Notably, LDL binding was nearly abolished by a prodomain S127R GOF mutation, one of the first PCSK9 mutations identified in FH patients. PCSK9 containing alanine or proline substitutions at amino acid position 127 were also defective for LDL binding. LDL inhibited cell surface LDLR binding and degradation induced by exogenous PCSK9-D374Y but had no effect on an S127R-D374Y double mutant form of PCSK9. These studies reveal that multiple FH-associated GOF mutations in two distinct regions of PCSK9 inhibit LDL binding, and that the Ser-127 residue in PCSK9 plays a critical role.

Lipid and Lipoprotein Metabolism

The exogenous lipoprotein pathway starts with the incorporation of dietary lipids into chylomicrons in the intestine. Chylomicron triglycerides are metabolized in muscle and adipose tissue and chylomicron remnants are formed, which are removed by the liver. The endogenous lipoprotein pathway begins in the liver with the formation of very low-density lipoprotein particles (VLDL). VLDL triglycerides are metabolized in muscle and adipose tissue forming intermediate-density lipoprotein (IDL), which may be taken up by the liver or further metabolized to low-density lipoprotein (LDL). Reverse cholesterol transport begins with the formation of nascent high-density lipoprotein (HDL) by the liver and intestine that acquire cholesterol from cells resulting in mature HDL. The HDL then transports the cholesterol to the liver either directly or indirectly by transferring the cholesterol to VLDL or LDL.

Lycopene-rich diets modulate HDL functionality and associated inflammatory markers without affecting lipoprotein size and distribution in moderately overweight, disease-free, middle-aged adults: A randomized controlled trial

Background

The consumption of lycopene-rich foods may lower cardiovascular disease (CVD) risk. Lycopene circulates in the blood bound to lipoproteins, including high-density lipoproteins (HDLs). Preliminary data from our group showed that increased consumption of tomato-based food or lycopene supplement in middle-aged subjects led to functional changes to HDL's sub-fractions, HDL₂ and HDL₃. These changes were also associated with a decrease in serum amyloid A (SAA), potentially enhancing their anti-atherogenic properties.

Objective

We carried out a comprehensive randomized controlled intervention trial with healthy middle-aged volunteers to assess whether the consumption of tomato-based foods or lycopene supplements affects HDL functionality and associated inflammatory markers, and lipoprotein subfractions size and distribution.

Design

Volunteers (225, aged 40–65 years) were randomly assigned to one of three dietary intervention groups and asked to consume a control diet (low in tomato-based foods, <10 mg lycopene/week), a lycopene-rich diet (224–350 mg lycopene/week), or the control diet with a lycopene supplement (70 mg lycopene/week). HDL₂ and HDL₃ were isolated by ultracentrifugation. Compliance was monitored by assessing lycopene concentration in serum. Systemic and HDL-associated inflammation was assessed by measuring SAA concentrations. HDL functionality was determined by monitoring paraoxonase-1 (PON-1), cholesteryl ester transfer protein (CETP), and lecithin cholesterol acyltransferase (LCAT) activities. The lipoprotein subfractions profile was assessed by NMR.

Results

Lycopene in serum and HDL significantly increased following consumption of both the high tomato diet and lycopene supplement (p ≤ 0.001 for both). Lycopene, either as a tomato-rich food or a supplement, enhanced both serum- and HDL₃-PON-1 activities (p ≤ 0.001 and p = 0.036, respectively), while significantly reducing HDL₃-SAA-related inflammation (p = 0.001). Lycopene supplement also significantly increased HDL₃-LCAT activity (p = 0.05), and reduced the activity of both HDL₂- and HDL₃-CETP (p = 0.005 and p = 0.002, respectively). These changes were not associated with changes in the subclasses distribution for all lipoprotein fractions or the size of lipoprotein subclasses.

Conclusion

Our results showed that dietary lycopene can significantly enhance HDL functionality, without associated changes in particle size and distribution, by modulating the activity of HDL-associated enzymes. Concomitantly, dietary lycopene significantly decreased serum- and HDL₃-associated SAA, confirming that SAA may represent a sensitive inflammatory biomarker to dietary change.

Clinical Trial Register

(https://www.isrctn.com), ISRCTN34203810.

The role of remnant cholesterol beyond low-density lipoprotein cholesterol in diabetes mellitus

BACKGROUND

Previous research has linked elevated low-density lipoprotein cholesterol (LDL-C) and remnant cholesterol (RC) with diabetes mellitus (DM). The present study aims to estimate the RC-related DM risk beyond LDL-C, and to investigate the extent to which the association of RC and DM is mediated via insulin resistance and inflammation.

METHODS

We enrolled 7308 individuals without previous history of DM into the present study from the China Health and Nutrition Survey. Fasting RC was calculated as total cholesterol minus LDL-C and high-density lipoprotein cholesterol. Subjects were divided into four groups according to their LDL-C (100 mg/dL) and RC (24 mg/dL) levels to evaluate the role of LDL-C vs. RC on DM. A logistic regression analysis was then employed to evaluate the relationships between the discordant/concordant LDL-C and RC and DM. A mediation analysis was undertaken to identify potential mediators.

RESULTS

Of all the participants, a total of 625 (8.55%) patients were newly diagnosed with DM. Compared to the high LDL-C/low RC group, the low LDL-C/high RC group was more common in DM patients. After a multivariate adjustment, elevated LDL-C and RC were associated with DM. Moreover, the low LDL-C/high RC group and the high LDL-C/low RC group manifested a 4.04-fold (95% CI 2.93-5.56) and 1.61-fold (95% CI 1.21-2.15) higher risk of DM, relative to those with low LDL-C/low RC. The subgroup analysis indicated that low LDL-C/high RC was more likely to be related to DM in females. Similar results were also shown when the sensitivity analyses were performed with different clinical cut-points of LDL-C. Insulin resistance and inflammation partially mediated the association between RC and DM.

CONCLUSIONS

Our findings provided evidence for RC beyond the LDL-C associations with DM that may be mediated via insulin resistance and the pro-inflammatory state. In addition, women are more susceptible to RC exposure-related DM.

Role of Lipoproteins in the Pathophysiology of Breast Cancer

Breast cancer is one of the most common malignancies in women and the leading cause of cancer mortality. Hypercholesterolemia and obesity are potential risk factors for the incidence of breast cancer, and their detection can enhance cancer prevention. In this paper, we discuss the current state of investigations on the importance of lipoproteins, such as low denisity lipoproteins (LDL) and high density lipoproteins (HDL), and cholesterol transporters in the progression of breast cancer, and the therapeutic strategies to reduce breast cancer mortality. Although some research has been unsuccessful at uncovering links between the roles of lipoproteins and breast cancer risk, major scientific trials have found a straight link between LDL levels and incidence of breast cancer, and an inverse link was found between HDL and breast cancer development. Cholesterol and its transporters were shown to have significant importance in the development of breast cancer in studies on breast cancer cell lines and experimental mice models. Instead of cholesterol, 27-hydroxycholesterol, which is a cholesterol metabolite, is thought to promote propagation and metastasis of estrogen receptor-positive breast cancer cell lines. Alteration of lipoproteins via oxidation and HDL glycation are thought to activate many pathways associated with inflammation, thereby promoting cellular proliferation and migration, leading to metastasis while suppressing apoptosis. Medications that lower cholesterol levels and apolipoprotein A-I mimics have appeared to be possible therapeutic agents for preventing excessive cholesterol’s role in promoting the development of breast cancer.

Triglycerides: How to Manage Patients with Elevated Triglycerides and When to Refer?

Hypertriglyceridemia (HTG) is among the most common dyslipidemias seen in clinical practice. Studies in recent years have demonstrated a causal relationship between triglyceride-rich lipoproteins (TRL) and cardiovascular disease (CVD). This is primarily due to enhanced atherogenicity of cholesterol-enriched remnants, the metabolic byproducts of TRLs. Other factors influencing atherogenicity of TRLs include apolipoprotein CIII-directed proinflammatory signaling pathways and triglyceride enrichment of low-density lipoprotein that results in overabundance of small dense atherogenic particles within a prooxidative milieu that serves as the gateway for unregulated incorporation by vascular wall macrophages. HTG is caused by familial and metabolic disorders as well as selected medications that impair TRL hydrolysis.

Cholesterol metabolism in aging simultaneously altered in liver and nervous system

In humans, aging, triggers increased plasma concentrations of triglycerides, cholesterol, low-density lipoproteins and lower capacity of high-density lipoproteins to remove cellular cholesterol. Studies in rodents showed that aging led to cholesterol accumulation in the liver and decrease in the brain with reduced cholesterol synthesis and increased levels of cholesterol 24-hydroxylase, an enzyme responsible for removing cholesterol from the brain. Liver diseases are also related to brain aging, inducing changes in cholesterol metabolism in the brain and liver of rats. It has been suggested that late onset Alzheimer's disease is associated with metabolic syndrome. Non-alcoholic fatty liver is associated with lower total brain volume in the Framingham Heart Study offspring cohort study. Furthermore, disorders of cholesterol homeostasis in the adult brain are associated with neurological diseases such as Niemann-Pick, Alzheimer, Parkinson, Huntington and epilepsy. Apolipoprotein E (apoE) is important in transporting cholesterol from astrocytes to neurons in the etiology of sporadic Alzheimer's disease, an aging-related dementia. Desmosterol and 24S-hydroxycholesterol are reduced in ApoE KO hypercholesterolemic mice. ApoE KO mice have synaptic loss, cognitive dysfunction, and elevated plasma lipid levels that can affect brain function. In contrast to cholesterol itself, there is a continuous uptake of 27- hydroxycholesterol in the brain as it crosses the blood-brain barrier and this flow can be an important link between intra- and extracerebral cholesterol homeostasis. Not surprisingly, changes in cholesterol metabolism occur simultaneously in the liver and nervous tissues and may be considered possible biomarkers of the liver and nervous system aging.

Metabolism of Triglyceride-Rich Lipoproteins

Triglycerides are critical lipids as they provide an energy source that is both compact and efficient. Due to its hydrophobic nature triglyceride molecules can pack together densely and so be stored in adipose tissue. To be transported in the aqueous medium of plasma, triglycerides have to be incorporated into lipoprotein particles along with other components such as cholesterol, phospholipid and associated structural and regulatory apolipoproteins. Here we discuss the physiology of normal triglyceride metabolism, and how impaired metabolism induces hypertriglyceridemia and its pathogenic consequences including atherosclerosis. We also discuss established and novel therapies to reduce triglyceride-rich lipoproteins.

Dyslipidemia Management in 2020: An Update on Diagnosis and Therapeutic Perspectives

Cardiovascular diseases are the leading cause of death in the modern world and dyslipidemia is one of the major risk factors. The current therapeutic strategies for cardiovascular diseases involve the management of risk factors, especially dyslipidemia and hypertension. Recently, the updated guidelines of dyslipidemia management were presented, and the newest data were included in terms of diagnosis, imaging, and treatment. In this targeted literature review, the researchers presented the most recent evidence on dyslipidemia management by including the current therapeutic goals for it. In addition, the novel diagnostic tools based on theranostics are shown. Finally, the future perspectives on treatment based on novel drug delivery systems and their potential to be used in clinical trials were also analyzed. It should be noted that dyslipidemia management can be achieved by the strict lifestyle change, i.e., by adopting a healthy life, and choosing the most suitable medication. This review can help medical professionals as well as specialists of other sciences to update their knowledge on dyslipidemia management, which can lead to better therapeutic outcomes and newer drug developments.

Lipoprotein Abnormalities in Chronic Kidney Disease and Renal Transplantation

Chronic kidney disease (CKD) is one of the most important risk factors for cardiovascular disease (CVD). Despite the kidney having no direct implications for lipoproteins metabolism, advanced CKD dyslipidemia is usually present in patients with CKD, and the frequent lipid and lipoprotein alterations occurring in these patients play a role of primary importance in the development of CVD. Although hypertriglyceridemia is the main disorder, a number of lipoprotein abnormalities occur in these patients. Different enzymes pathways and proteins involved in lipoprotein metabolism are impaired in CKD. In addition, treatment of uremia may modify the expression of lipoprotein pattern as well as determine acute changes. In renal transplantation recipients, the main lipid alteration is hypercholesterolemia, while hypertriglyceridemia is less pronounced. In this review we have analyzed lipid and lipoprotein disturbances in CKD and also their relationship with progression of renal disease. Hypolipidemic treatments may also change the natural history of CVD in CKD patients and may represent important strategies in the management of CKD patients.

Triglyceride-rich lipoproteins and atherosclerotic cardiovascular disease risk: current status and treatments

PURPOSE OF REVIEW

The role of triglyceride-rich lipoproteins (TRLs) in the development of atherosclerotic cardiovascular disease (ASCVD) is at the forefront of current research and treatment development programs. Despite extreme lowering of LDL-cholesterol there remains a high risk of cardiovascular disease and mortality. Recent large epidemiological, genomic wide association studies and Mendelian randomization studies have identified novel mechanisms and targets regulating TRL. This review will focus on recent and ongoing clinical trials that aim to reduce cardiovascular risk by decreasing plasma levels of TRL.

RECENT FINDINGS

Ongoing efforts of basic and clinical scientist have described novel TRL regulating mechanism. The concentration on lifestyle changes is key to prevention and treatment guidelines. There is continue evidence that supports previous guidelines using fibrates alone and in combination with niacin to reduce TRLs, in special cases. The recent results from the REDUCE-IT study support the use of eicosapentaenoic acid (EPA) for risk reduction and ASCVD, but recently presented data from the Long-Term Outcome Study to Assess Statin Residual Risk Reduction With Epanova in High Cardiovascular Risk Patients with Hypertriglyceridemia and Omega-3 Fatty Acids in Elderly Patients With Acute Myocardial Infarction studies do not support the use of combination EPA/docosahexaenoic acid. The latter highlights the need for further studies into the pathways regulating ASCVD risk reduction after EPA administration. The identification of novel targets, such as apolipoprotein C3 and angiopoietin-like protein-3, are driving the development of novel treatments, and is the focus of this review.

SUMMARY

The current management of elevated triglyceride levels and the effect on cardiovascular outcomes is an emerging area of research. New data from fish oil studies suggest differences in EPA vs. EPA/docosahexaenoic acid cardio protection outcomes. The preliminary data from ongoing clinical trials of novel triglyceride-lowering therapeutics are promising. These programs will ultimately provide foundations for future triglyceride-lowering guidelines.

Association of lipoprotein levels with sleep apnea: role of autonomic dysfunction

Objectives. Although multiple mechanisms, including autonomic dysfunction, seem to link sleep-disordered breathing (SDB) with dyslipidemia in animal studies, the data in clinical studies are limited. The aim of this study was to explore the association of lipoprotein levels with SDB measures in healthy habitual snorers. We supposed that autonomic dysfunction is the linking mechanism.Methods. We enrolled 110 previously healthy subjects with complaints of habitual snoring. To assess SDB, polysomnography was performed. Blood samples for the analysis of total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein cholesterol (LDL), and triglycerides (TG) were obtained in a fasting condition after the polysomnography. Baroreflex sensitivity (BRS) was used to assess the autonomic dysfunction.Results. In stepwise multiple linear regression analysis, minimal nocturnal blood oxygen saturation (beta=-0.240, p=0.020) and neck circumference (beta=0.224, p=0.03) were the only significant contributors in model predicting TG. SDB measures were not identified as significant contributors in models predicting TC, LDL, and HDL. We failed to find any significant difference in BRS in SDB subjects when compared according to the presence or absence of hypercholesterolemia/ hypertriglyceridemia. In SDB subjects, the area under the curve in a receiver operating curve to predict hypercholesterolemia and hypertriglyceridemia by BRS was 0.468 (95% CI: 0.328-0.608) and 0.425 (95% CI: 0.304-0.546), respectively.Conclusions. Our results suggest that minimal nocturnal blood oxygen saturation is significant contributor in model predicting TG. No significant decrease in BRS was found in SDB subjects with hypercholesterolemia and hypertriglyceridemia. In SDB subjects, the role of autonomic dys-function in the development of dyslipidemia remains controversial.

Expression Signatures of microRNAs and Their Targeted Pathways in the Adipose Tissue of Chickens during the Transition from Embryonic to Post-Hatch Development

As the chick transitions from embryonic to post-hatching life, its metabolism must quickly undergo a dramatic switch in its major energy source. The chick embryo derives most of its energy from the yolk, a lipid-rich/carbohydrate-poor source. Upon hatching, the chick’s metabolism must then be able to utilize a lipid-poor/carbohydrate-rich source (feed) as its main form of energy. We recently found that a number of hepatically-expressed microRNAs (miRNAs) help facilitate this shift in metabolic processes in the chick liver, the main site of lipogenesis. While adipose tissue was initially thought to mainly serve as a lipid storage site, it is now known to carry many metabolic, endocrine, and immunological functions. Therefore, it would be expected that adipose tissue is also an important factor in the metabolic switch. To that end, we used next generation sequencing (NGS) and real-time quantitative PCR (RT-qPCR) to generate miRNome and transcriptome signatures of the adipose tissue during the transition from late embryonic to early post-hatch development. As adipose tissue is well known to produce inflammatory and other immune factors, we used SPF white leghorns to generate the initial miRNome and transcriptome signatures to minimize complications from external factors (e.g., pathogenic infections) and ensure the identification of bona fide switch-associated miRNAs and transcripts. We then examined their expression signatures in the adipose tissue of broilers (Ross 708). Using E18 embryos as representative of pre-switching metabolism and D3 chicks as a representative of post-switching metabolism, we identified a group of miRNAs which work concordantly to regulate a diverse but interconnected group of developmental, immune and metabolic processes in the adipose tissue during the metabolic switch. Network mapping suggests that during the first days post-hatch, despite the consumption of feed, the chick is still heavily reliant upon adipose tissue lipid stores for energy production, and is not yet efficiently using their new energy source for de novo lipid storage. A number of core master regulatory pathways including, circadian rhythm transcriptional regulation and growth hormone (GH) signaling, likely work in concert with miRNAs to maintain an essential balance between adipogenic, lipolytic, developmental, and immunological processes in the adipose tissue during the metabolic switch.

Remnant Cholesterol is an Independent Predictor of New-Onset Diabetes: A Single-Center Cohort Study

PURPOSE

Remnant cholesterol (RC) is the cholesterol of triglyceride-rich lipoproteins, which has a high degree of atherogenic effect. To date, epidemiological evidence supports that higher RC levels lead to a greater risk of adverse cardiovascular events in patients with diabetes, but the nature of the association between RC levels and diabetes risk remains unclear. This study was designed to assess the association of RC with the risk of new-onset diabetes and to investigate whether there is a causal relationship between the two.

PATIENTS AND METHODS

The subjects included 15,464 individuals of the general population who participated in a health examination. Subjects were quartered according to the RC quartile, and the Cox proportional hazard model was used to assess the independent association between RC and new-onset diabetes.

RESULTS

During an average observation period of 6.13 years, 2.41% of the subjects were diagnosed with new-onset diabetes. Kaplan-Meier analysis showed that the 13-year cumulative diabetes rates corresponding to the RC quartile were 8.62%, 2.49%, 12.78%, and 17.91%. Multivariate Cox regression analysis indicated that higher RC levels were independently associated with an increased risk of new-onset diabetes (HR: 2.44, 95% CI: 1.50-3.89). Additionally, according to the results of receiver operating characteristic curve analysis, RC had the largest area under the curve (0.7314) compared to traditional lipid parameters in predicting new-onset diabetes.

CONCLUSION

These results indicated that RC is an important independent predictor of new-onset diabetes in the general population.

Lpl-C310R mutation is associated with impaired glucose tolerance and endoplasmic reticulum stress in skeletal muscle

Primary Hypertriglyceridemia refers to a loss-of-function genetic defect which prevents the triglyceride (TG) in chylomicrons (CM) from lipolysis, leading to the accumulation of TG. The mutation of lipoprotein lipase (LPL) gene has been recognized as the main cause of primary hypertriglyceridemia. Recently, a new LPL gene mutation p.C310R(c. T928C) was identified in a family with hypertriglyceridemia. The proband was manifested by severe hypertriglyceridemia and diabetes. Skeletal muscle is the major LPL-synthesizing tissue and insulin response target tissue. However, little is known about the effects of LPL gene mutation on skeletal muscle. This study is intended to observe the effects of LPL-C310R mutation on glycolipid metabolism and skeletal muscle. We found that a significantly decreased LPL plasma concentration, activity and the expression levels in skeletal muscle were observed in Lpl^C310R/+ mice comparing to wild type mice. Those mutant mice also exhibited increased fasting plasma TG, free fat acids (FFA) and insulin, as well as FFA in muscle, and decreased glucose tolerance. Enhanced expression of BIP and elevated phosphorylation of IRE1α were observed in skeletal muscle, suggesting increased endoplasmic reticulum stress (ERS). Consistent with this, increased phosphorylation of JNK was also observed. Meanwhile, remarkably enhanced phosphorylation of IRS-1 (Ser307) and decreased phosphorylation of AKT were observed in skeletal muscle of mutant mice, suggesting impaired insulin signaling. Significant lipid deposition and morphological changes in endoplasmic reticulum and mitochondria were observed in the skeletal muscle of mutant mice but not in wild type control. Results demonstrate Lpl C310R mutation caused impaired glucose tolerance, ER stress and impaired insulin signaling in skeletal muscle.

Cardiomyocyte Senescence and Cellular Communications Within Myocardial Microenvironments

Cardiovascular diseases have become the leading cause of human death. Aging is an independent risk factor for cardiovascular diseases. Cardiac aging is associated with maladaptation of cellular metabolism, dysfunction (or senescence) of cardiomyocytes, a decrease in angiogenesis, and an increase in tissue scarring (fibrosis). These events eventually lead to cardiac remodeling and failure. Senescent cardiomyocytes show the hallmarks of DNA damage, endoplasmic reticulum stress, mitochondria dysfunction, contractile dysfunction, hypertrophic growth, and senescence-associated secreting phenotype (SASP). Metabolism within cardiomyocytes is essential not only to fuel the pump function of the heart but also to maintain the functional homeostasis and participate in the senescence of cardiomyocytes. The senescence of cardiomyocyte is also regulated by the non-myocytes (endothelial cells, fibroblasts, and immune cells) in the local microenvironment. On the other hand, the senescent cardiomyocytes alter their phenotypes and subsequently affect the non-myocytes in the local microenvironment and contribute to cardiac aging and pathological remodeling. In this review, we first summarized the hallmarks of the senescence of cardiomyocytes. Then, we discussed the metabolic switch within senescent cardiomyocytes and provided a discussion of the cellular communications between dysfunctional cardiomyocytes and non-myocytes in the local microenvironment. We also addressed the functions of metabolic regulators within non-myocytes in modulating myocardial microenvironment. Finally, we pointed out some interesting and important questions that are needed to be addressed by further studies.

Reduced miR-181d level in obesity and its role in lipid metabolism via regulation of ANGPTL3

Obesity impacts the endocrine and metabolic functions of the adipose tissue. There is increasing interest in the role of epigenetic factors in obesity and its impact on diabetes and dyslipidemia. One such substance, miR-181, reduces plasma triglyceride levels in mice by targeting isocitrate dehydrogenase 1. In the other hand, the adipocyte differentiation and lipid regulating hormone angiopoietin-like 3 (ANGPTL3) is a known regulator of circulating apolipoproteins through its inhibition of the lipoprotein lipase activity. We aimed to study the miR-181d expression in the blood and adipose tissue in a cohort of obese and non-obese people, assessing its possible role in obesity. We also aimed to confirm whether miR-181d can bind and regulate ANGPTL3. miR-181d expression levels were investigated in 144 participants, 82 who were non-obese (body mass index [BMI] < 30) and 62 who were obese (BMI > 30). miR-181d levels in plasma and adipose tissue were measured by RT-PCR. Hepatocyte cell cultures were assessed by overexpression and 3′-UTR-luciferase assays for miR-181d binding to its target protein and its effect on the protein. The plasma levels of ANGPTL3 were also measured by ELISA. The miR-181d levels were significantly lower in obese than in non-obese individuals. In vitro analysis confirmed miR-181 binding to and repression of the ANGPTL3 transcript. Obesity leads to alterations in miR-181d expression. Its downregulation in obese humans was inversely correlated with ANGPTL3, a protein involved in adipocyte differentiation and lipid metabolism. miR-181d can be used as an inhibitor of ANGPTL3 to reduce the TG plasma level.

The Role of (Modified) Lipoproteins in Vascular Function: A Duet Between Monocytes and the Endothelium

Over the last century, many studies have demonstrated that low-density lipoprotein (LDL) is a key risk factor of cardiovascular diseases (CVD) related to atherosclerosis. Thus, for these CVD patients, LDL lowering agents are commonly used in the clinic to reduce the risk for CVD. LDL, upon modification, will develop distinct inflammatory and proatherogenic potential, leading to impaired endothelial integrity, influx of immune cells and subsequent increased foam cell formation. LDL can also directly affect peripheral monocyte composition, rendering them in a more favorable position to migrate and accumulate in the subendothelial space. It has become apparent that other lipoprotein particles, such as triglyceride- rich lipoproteins or remnants (TRL) and lipoprotein(a) [Lp(a)] may also impact on atherogenic pathways. Evidence is accumulating that Lp(a) can promote peripheral monocyte activation, eventually leading to increased transmigration through the endothelium. Similarly, remnant cholesterol has been identified to play a key role in endothelial dysfunction and monocyte behavior. In this review, we will discuss recent developments in understanding the role of different lipoproteins in the context of inflammation at both the level of the monocyte and the endothelium.

Very Severe Hypertriglyceridemia in a Large US County Health Care System: Associated Conditions and Management

Context

Patients with very severe hypertriglyceridemia (triglyceride levels ≥2000 mg/dL; 22.6 mmol/L) require aggressive treatment. However, little research exists on the underlying etiologies and management of very severe hypertriglyceridemia.

Objective

We hypothesized (i) very severe hypertriglyceridemia in adults is mostly associated with secondary causes and (ii) most patients with very severe hypertriglyceridemia lack appropriate follow-up and treatment.

Design

We queried electronic medical records at Parkland Health and Hospital Systems for lipid measurements in the year 2016 and identified patients with serum triglyceride levels ≥2000 mg/dL (22.6 mmol/L). We extracted data on demographics, underlying causes, lipid-lowering therapy, and follow-up.

Results

One hundred sixty-four serum triglyceride measurements were ≥2000 mg/dL (22.6 mmol/L) in 103 unique patients. Of these, 60 patients were admitted to the hospital (39 for acute pancreatitis). Most were Hispanic (79%). The major conditions associated with very severe hypertriglyceridemia included uncontrolled diabetes mellitus (74%), heavy alcohol use (10%), medication use (7%), and hypothyroidism (2%). Two patients were known to have monogenic causes of hypertriglyceridemia. After the index measurement of triglycerides ≥2000 mg/dL (22.6 mmol/L), the use of triglyceride-lowering drugs increased, most prominently the use of fish oil supplements, which increased by 80%. However, in follow-up visits, hypertriglyceridemia was addressed in only 50% of encounters, and serum triglycerides were remeasured in only 18%.

Conclusion

In summary, very severe hypertriglyceridemia was quite prevalent (∼0.1% of all lipid measurements) in our large county health care system, especially in Hispanic men. Most cases were related to uncontrolled diabetes mellitus, and follow-up monitoring was inadequate.

β-Carotene in the human body: metabolic bioactivation pathways - from digestion to tissue distribution and excretion

β-Carotene intake and tissue/blood concentrations have been associated with reduced incidence of several chronic diseases. Further bioactive carotenoid-metabolites can modulate the expression of specific genes mainly via the nuclear hormone receptors: retinoic acid receptor- and retinoid X receptor-mediated signalling. To better understand the metabolic conversion of β-carotene, inter-individual differences regarding β-carotene bioavailability and bioactivity are key steps that determine its further metabolism and bioactivation and mediated signalling. Major carotenoid metabolites, the retinoids, can be stored as esters or further oxidised and excreted via phase 2 metabolism pathways. In this review, we aim to highlight the major critical control points that determine the fate of β-carotene in the human body, with a special emphasis on β-carotene oxygenase 1. The hypothesis that higher dietary β-carotene intake and serum level results in higher β-carotene-mediated signalling is partly questioned. Alternative autoregulatory mechanisms in β-carotene / retinoid-mediated signalling are highlighted to better predict and optimise nutritional strategies involving β-carotene-related health beneficial mediated effects.

Raman spectroscopy-based insight into lipid droplets presence and contents in liver sinusoidal endothelial cells and hepatocytes

Liver sinusoidal endothelial cells (LSECs), a type of endothelial cells with unique morphology and function, play an important role in the liver hemostasis, and LSECs dysfunction is involved in the development of nonalcoholic fatty liver disease (NAFLD). Here, we employed Raman imaging and chemometric data analysis in order to characterize the presence of lipid droplets (LDs) and their lipid content in primary murine LSECs, in comparison with hepatocytes, isolated from mice on high-fat diet. On NAFLD development, LDs content in LSECs changed toward more unsaturated lipids, and this response was associated with an increased expression of stearylo-CoA desaturase-1. To the best of our knowledge, this is a first report characterizing LDs in LSECs, where their chemical composition is analyzed along the progression of NAFLD at the level of single LD using Raman imaging.

Rosuvastatin improves the FGF19 analogue NGM282-associated lipid changes in patients with non-alcoholic steatohepatitis

BACKGROUND

NGM282, an engineered analogue of the gut hormone FGF19, improves hepatic steatosis and fibrosis biomarkers in patients with non-alcoholic steatohepatitis (NASH). However, NGM282 increases serum cholesterol levels by inhibiting CYP7A1, which encodes the rate-limiting enzyme in the conversion of cholesterol to bile acids. Herein, we investigate whether administration of a statin can manage the cholesterol increase seen in patients with NASH receiving treatment with NGM282.

METHODS

In this phase II, open-label, multicenter study, patients with biopsy-confirmed NASH were treated with subcutaneous NGM282 once daily for 12 weeks. After 2 weeks, rosuvastatin was added in stepwise, biweekly incremental doses to a maximum of 40 mg daily. Both drugs were continued until the end of treatment at week 12. We evaluated plasma lipids, lipoprotein particles and liver fat content.

RESULTS

In 66 patients who received NGM282 0.3 mg (n = 23), NGM282 1 mg (n = 21), or NGM282 3 mg (n = 22), circulating cholesterol increased from baseline at week 2. Initiation of rosuvastatin resulted in rapid decline in plasma levels of total cholesterol and low-density lipoprotein cholesterol. At week 12, reductions from baseline in total cholesterol levels of up to 18% (p <0.001), low-density lipoprotein cholesterol of up to 28% (p <0.001), triglycerides of up to 34% (p <0.001) and an increase in high-density lipoprotein cholesterol of up to 16% (p <0.001), with similar changes in lipoprotein particles, were observed in these patients. Robust decreases from baseline in 7alpha-hydroxy-4-cholesten-3-one (p <0.001) and liver fat content (p <0.001) were also observed. Rosuvastatin was safe and well-tolerated when co-administered with NGM282 in patients with NASH.

CONCLUSIONS

In this multicenter study, NGM282-associated elevation of cholesterol was effectively managed with rosuvastatin. Co-administration of rosuvastatin with NGM282 may be a reasonable strategy to optimize the cardiovascular risk profile in patients with NASH.

LAY SUMMARY

Non-alcoholic steatohepatitis (NASH) represents a large and growing public health concern with no approved therapy. NGM282, an engineered analogue of the gut hormone FGF19, reduces liver fat, liver injury and inflammation in patients with NASH. However, NGM282 increases cholesterol levels. Here we show that co-administration of a statin can manage the cholesterol increase seen in patients with NASH receiving treatment with NGM282, producing a favorable overall lipid profile.

Decreased GPIHBP1 protein levels in visceral adipose tissue partly underlie the hypertriglyceridemic phenotype in insulin resistance

GPIHBP1 is a protein localized at the endothelial cell surface that facilitates triglyceride (TG) lipolysis by binding lipoprotein lipase (LPL). Whether Glycosyl Phosphatidyl Inositol high density lipoprotein binding protein 1 (GPIHBP1) function is impaired and may underlie the hyperTG phenotype observed in type 2 diabetes is not yet established. To elucidate the mechanism underlying impaired TG homeostasis in insulin resistance state we studied the effect of insulin on GPIHBP1 protein expression in human microvascular endothelial cells (HMVEC) under flow conditions. Next, we assessed visceral adipose tissue GPIHBP1 protein expression in type 2 diabetes Lepr^db/db mouse model as well as in subjects with ranging levels of insulin resistance. We report that insulin reduces the expression of GPIHBP1 protein in HMVECs. Furthermore, GPIHBP1 protein expression in visceral adipose tissue in Lepr^db/db mice is significantly reduced as is the active monomeric form of GPIHBP1 as compared to Lepr^db/m mice. A similar decrease in GPIHBP1 protein was observed in subjects with increased body weight. GPIHBP1 protein expression was negatively associated with insulin and HOMA-IR.

In conclusion, our data suggest that decreased GPIHBP1 availability in insulin resistant state may hamper peripheral lipolysis capacity.

Familial Hypercholesterolemia: The Most Frequent Cholesterol Metabolism Disorder Caused Disease

Cholesterol is an essential component of cell barrier formation and signaling transduction involved in many essential physiologic processes. For this reason, cholesterol metabolism must be tightly controlled. Cell cholesterol is mainly acquired from two sources: Dietary cholesterol, which is absorbed in the intestine and, intracellularly synthesized cholesterol that is mainly synthesized in the liver. Once acquired, both are delivered to peripheral tissues in a lipoprotein dependent mechanism. Malfunctioning of cholesterol metabolism is caused by multiple hereditary diseases, including Familial Hypercholesterolemia, Sitosterolemia Type C and Niemann-Pick Type C1. Of these, familial hypercholesterolemia (FH) is a common inherited autosomal co-dominant disorder characterized by high plasma cholesterol levels. Its frequency is estimated to be 1:200 and, if untreated, increases the risk of premature cardiovascular disease. This review aims to summarize the current knowledge on cholesterol metabolism and the relation of FH to cholesterol homeostasis with special focus on the genetics, diagnosis and treatment.

Mechanism of YLTZ on glycolipid metabolism based on UPLC/TOF/MS metabolomics

Type 2 diabetes mellitus (T2DM) is a metabolic disease characterized by dysfunction of glycolipid metabolism. YLTZ is used to treat hyperlipidemia, yet its hypolipidemic and hypoglycemic mechanism on T2DM are unknown. Thus, UPLC/TOF/MS was applied in this study to identify the potential bio-markers, and deduce the possible metabolic pathways. According to bio-indexes, the increased blood lipid levels, including TC, TG, LDL and FA, and the decreased HDL, the elevated glucose, reduced insulin level and impaired OGTT were observed in diabetic rat model. While YLTZ can decrease the lipid levels and glucose content, as well as increased insulin standards and improve OGTT. After data from UPLC/TOF/MS processed, 17 metabolites were obtained, including phospholipids (LPCs, PCs and PGP (18:1)), beta-oxidation production (HAA, VAG and CNE) and precursors (THA), bile acid (CA, CDCA and IDCA), hydrolysate of TG (MG (22:4)), glycometabolism (G6P), cholesterol-driven synthetics (ADO) and production of arachidonate acid (THETA). As a result, YLTZ was able to reduce LPCs, PCs, PGP (18:1), HAA, VAG, CNE, CA, ADO and THETA, as well as enhance MG (22:4) and G6P. After analyzing results, several metabolic pathways were deduced, which containing, cholesterol synthesis and elimination, FA beta-oxidation, TG hydrolysis, phospholipids synthesis, glycolysis, gluconeogenesis and inflammation. Consequently, YLTZ performed to prohibit the FA beta-oxidation, synthesis of cholesterol and phospholipids, gluconeogenesis and inflammation level, as well as promote TG hydrolysis, glycolysis and blood circulation. Hence, applying metabonomics in TCM research can uncover its pharmacological edges, elucidating comprehensively that YLTZ has capacity of hypolipidemic, hypoglycemic and promoting blood circulation, matching the effect of removing blood stasis, eliminating phlegm and dampness.

Removal of Chylomicron Remnants from the Bloodstream is Delayed in Aged Subjects

Dietary fats absorbed in the intestine are transported in the circulation as chylomicrons and remnants that have atherogenic potential. Although postprandial lipidemia is increased in older subjects, the specific chylomicron metabolism has not been explored in older subjects nor compared to young subjects, which is the focus of this study. After a 12 h fast, artificially-made emulsions similar to lymph chylomicrons and doubly labeled with radioactive cholesteryl esters and triglycerides were intravenously injected in 23 older (66±4 years) and 20 young (24±3 years) subjects. Sequential blood samples were collected to determine fractional clearance rates (FCR, in min^-1) by compartmental analysis. Older subjects had higher LDL-cholesterol (p<0.001) and triglycerides (p<0.0001) than young subjects; HDL-cholesterol presented no difference. The emulsion cholesteryl-ester FCR was lower in older subjects compared to the young (p=0.0001). The emulsion triglyceride FCR did not differ in the two groups. Tested in vitro, however, the lipolysis of the emulsion triglycerides was less intense in the older than in the young subjects. As delayed removal of remnants, indicated by the pronouncedly smaller cholesteryl ester FCR, is related to the presence of cardiovascular diseases, this can be a risk factor which could accelerate atherogenic complications occurring in aged subjects

Cav-1 promotes atherosclerosis by activating JNK-associated signaling

The objective of the study is to calculate the role and underlying the molecular mechanisms of caveolin-1 (Cav-1) in atherosclerosis (AS). Cav-1 was mainly expressed in the endothelial cells of atherosclerotic lesions in both human patients and apolipoprotein E deficient (ApoE^-/-) mice. Cav-1 deficiency (Cav-1^-/-) attenuated high-fat diet (HFD)-induced atherosclerotic lesions in ApoE^-/- mice, supported by the reduced aortic plaques. Cav-1^-/- reduced the macrophage content and decreased the release of inflammation-related cytokines or chemokine in serum or abdominal aortas, accompanied with the inactivation of inhibitor κB kinase κ (IKKβ)/p65/IκBα signaling pathway. Also, the activity of mitogen-activated protein kinases 7/c-Jun-N-terminal kinase (MKK7/JNK) signaling was decreased by Cav-1^-/-. In addition, oxidative stress induced by HFD in ApoE^-/- mice was alleviated by Cav-1^-/-. In response to HFD, Cav-1^-/- markedly reduced triglyceride (TG), total cholesterol (TC), low-density lipoprotein-cholesterol (LDLC) and very low-density lipoprotein-cholesterol (VLDLC) in serum of HFD-fed ApoE^-/- mice, whereas enhanced high-density lipoprotein-cholesterol (HDLC) contents. Consistent with these findings, haematoxylin and eosin (H&E) and Oil Red O staining showed fewer lipid droplets in the liver of Cav-1-deficient mice. Further, real time-quantitative PCR (RT-qPCR) analysis indicated that Cav-1^-/- alleviated dyslipidemia both in liver and abdominal aortas of ApoE^-/- mice fed with HFD. Cav-1 inhibition-induced attenuation of inflammatory response, oxidative stress and dyslipidemia were confirmed in vitro using mouse vascular smooth muscle cells (VSMCs) treated with ox-LDL. Surprisingly, the processes regulated by Cav-1-knockdown could be abolished through promoting JNK activation in ox-LDL-treated VSMCs. In conclusion, Cav-1 expression could promote HFD-induced AS in a JNK-dependent manner.

The heparan sulfate proteoglycan grip on hyperlipidemia and atherosclerosis

Heparan sulfate proteoglycans are found at the cell surface and in the extracellular matrix, where they interact with a plethora of proteins involved in lipid homeostasis and inflammation. Over the last decade, new insights have emerged regarding the mechanism and biological significance of these interactions in the context of cardiovascular disease. The majority of cardiovascular disease-related deaths are caused by complications of atherosclerosis, a disease that results in narrowing of the arterial lumen, thereby reducing blood flow to critical levels in vital organs, such as the heart and brain. Here, we discuss novel insights into how heparan sulfate proteoglycans modulate risk factors such as hyperlipidemia and inflammation that drive the initiation and progression of atherosclerotic plaques to their clinical critical endpoint.

Inulin Improves Postprandial Hypertriglyceridemia by Modulating Gene Expression in the Small Intestine

Postprandial hyperlipidemia is an important risk factor for cardiovascular diseases in the context of obesity. Inulin is a non-digestible carbohydrate, known for its beneficial properties in metabolic disorders. We investigated the impact of inulin on postprandial hypertriglyceridemia and on lipid metabolism in a mouse model of diet-induced obesity. Mice received a control or a western diet for 4 weeks and were further supplemented or not with inulin for 2 weeks (0.2 g/day per mouse). We performed a lipid tolerance test, measured mRNA expression of genes involved in postprandial lipid metabolism, assessed post-heparin plasma and muscle lipoprotein lipase activity and measured lipid accumulation in the enterocytes and fecal lipid excretion. Inulin supplementation in western diet-fed mice decreases postprandial serum triglycerides concentration, decreases the mRNA expression levels of Cd36 (fatty acid receptor involved in lipid uptake and sensing) and apolipoprotein C3 (Apoc3, inhibitor of lipoprotein lipase) in the jejunum and increases fecal lipid excretion. In conclusion, inulin improves postprandial hypertriglyceridemia by targeting intestinal lipid metabolism. This work confirms the interest of using inulin supplementation in the management of dyslipidemia linked to obesity and cardiometabolic risk.

Long-term Western diet fed apolipoprotein E-deficient rats exhibit only modest early atherosclerotic characteristics

In the apolipoprotein E–deficient mouse, the gut microbiota has an impact on the development of atherosclerosis, but whether such correlations are also present in rats requires investigation. Therefore, we studied female SD-Apoe^tm1sage (Apoe^−/−) rats fed either a Western diet or a low-fat control diet with or without gluten, which is known to promote gut microbiota changes, until 20 weeks of age. We hypothesized that the manifestation of atherosclerosis would be more severe in Apoe^−/− rats fed the Western high-fat diet, as compared with rats fed the low-fat diet, and that atherosclerosis would be accelerated by gluten. Both Western diet-feeding and gluten resulted in significant changes in gut microbiota, but the microbiota impact of gluten was transient. Compared with Apoe^−/− rats fed a low-fat diet, Western diet-fed Apoe^−/− rats were heavier and became glucose intolerant with increased levels of oxidative stress. They developed early fatty streak lesions in their aortic sinus, while there was no evidence of atherosclerosis in the thoracic aorta. No conclusions could be made on the impact of gluten on atherosclerosis. Although Western diet-fed Apoe^−/− rats exhibited a more human-like LDL dominated blood lipid profile, signs of obesity, type 2 diabetes and cardiovascular disease were modest.

Hypertriglyceridemia and omega-3 fatty acids: Their often overlooked role in cardiovascular disease prevention

AIMS

This review aims to describe the pathogenic role of triglycerides in cardiometabolic risk, and the potential role of omega-3 fatty acids in the management of hypertriglyceridemia and cardiovascular disease.

DATA SYNTHESIS

In epidemiological studies, hypertriglyceridemia correlates with an increased risk of cardiovascular disease, even after adjustment for low density lipoprotein cholesterol (LDL-C) levels. This has been further supported by Mendelian randomization studies where triglyceride-raising common single nucleotide polymorphisms confer an increased risk of developing cardiovascular disease. Although guidelines vary in their definition of hypertriglyceridemia, they consistently define a normal triglyceride level as <150 mg/dL (or <1.7 mmol/L). For patients with moderately elevated triglyceride levels, LDL-C remains the primary target for treatment in both European and US guidelines. However, since any triglyceride level in excess of normal increases the risk of cardiovascular disease, even in patients with optimally managed LDL-C levels, triglycerides are an important secondary target in both assessment and treatment. Dietary changes are a key element of first-line lifestyle intervention, but pharmacological treatment including omega-3 fatty acids may be indicated in people with persistently high triglyceride levels. Moreover, in patients with pre-existing cardiovascular disease, omega-3 supplements significantly reduce the risk of sudden death, cardiac death and myocardial infarction and are generally well tolerated.

CONCLUSIONS

Targeting resistant hypertriglyceridemia should be considered as a part of clinical management of cardiovascular risk. Omega-3 fatty acids may represent a valuable resource to this aim.

Lipase inhibitor orlistat prevents hepatitis B virus infection by targeting an early step in the virus life cycle

Hepatitis B Virus (HBV) is a strictly hepatotropic pathogen which is very efficiently targeted to the liver and into its host cell, the hepatocyte. The sodium taurocholate co-transporting polypeptide (NTCP) has been identified as a key virus entry receptor, but the early steps in the virus life cycle are still only barely understood. Here, we investigated the effect of lipase inhibition and lipoprotein uptake on HBV infection using differentiated HepaRG cells and primary human hepatocytes. We found that an excess of triglyceride rich lipoprotein particles in vitro diminished HBV infection and a reduced hepatic virus uptake in vivo if apolipoprotein E is lacking indicating virus transport along with lipoproteins to target hepatocytes. Moreover, we showed that HBV infection of hepatocytes was inhibited by the broadly active lipase inhibitor orlistat, approved as a therapeutic agent which blocks neutral lipid hydrolysis activity. Orlistat treatment targets HBV infection at a post-entry step and inhibited HBV infection during virus inoculation strongly in a dose-dependent manner. In contrast, orlistat had no effect on HBV gene expression or replication or when added after HBV infection. Taken together, our data indicate that HBV connects to the hepatotropic lipoprotein metabolism and that inhibition of cellular hepatic lipase(s) may allow to target early steps of HBV infection.

Functional validation of GPIHBP1 and identification of a functional mutation in GPIHBP1 for milk fat traits in dairy cattle

In a previous genome-wide association study (GWAS) on milk production traits in a Chinese Holstein population, we revealed that GPIHBP1 is a novel promising candidate gene for milk fat content traits. In this study, we performed over-expression and RNAi experiments on GPIHBP1 in bovine primary mammary epithelial cells. The results showed that the expression of several important milk fat-related genes (LPL, CD36, VLDLR, ACACA and FASN) increased or decreased when the expression of GPIHBP1 was up- or down-regulated. To identify the potential functional SNP involved, we explored the genetic variants of GPIHBP1 and found that a G/A mutation (chr14:2553998) in the promoter region of GPIHBP1 significantly reduced promoter activity and had an effect on transcription factor binding sites. This finding was consistent with the lower expression of GPIHBP1 observed in the mammary gland tissue of cows harboring the homozygous AA mutation compared with wild-type homozygous GG or heterozygous AG. Furthermore, association analysis showed that cows with the AA genotype outperformed those with the GG and AG genotypes in terms of the milk fat percentage. Our study demonstrates that GPIHBP1 could be a strong candidate gene for milk fat content traits and, in particular, the G to A mutation at chr14:2553998 within GPIHBP1 could be a functional mutation related to its effects.

Nonalcoholic fatty liver disease associated with metabolic syndrome: Influence of liver fibrosis stages on characteristics of very low-density lipoproteins

BACKGROUND

We evaluated possible changes in VLDLcharacteristics, and metabolic related factors, in MetS-associated NAFLD and accompanying liver fibrosis.

METHODS

We studied 36 MetS patients with biopsy-proven NAFLD (MetS+NAFLD) and 24 MetS without ultrasound NAFLD evidence. Further, MetS+NAFLD was sub-divided according to fibrosis stage into, non-to-moderate (F0-F2, n=27) and severe (F3-F4, n=9) fibrosis. We measured: lipid profile, VLDL composition and size (size exclusion-HPLC), CETP and lipoprotein lipase (LPL) activities and adiponectin. Additionally, in MetS+NAFLD type IV collagen 7S domain was measured.

RESULTS

MetS+NAFLD showed increased VLDL-mass, VLDL particle number, VLDL-triglyceride% and large VLDL-% (p<0.04). CETP activity tended to increase in MetS+NAFLD (p=0.058), while LPL activity was unchanged. Moreover, in MetS+NAFLD, adiponectin was decreased (p<0.001), and negatively correlated with VLDL-mass and VLDL particle number (p<0.05), independently of insulin-resistance. Within MetS+NAFLD group, despite greater insulin-resistance, patients with severe fibrosis showed lower plasma triglycerides, VLDL-mass, VLDL-triglyceride%, large VLDL-% and CETP activity (p<0.05), while type IV collagen was increased (p=0.009) and inversely correlated with large VLDL-% (p=0.045).

CONCLUSIONS

In MetS, NAFLD is associated with larger and triglyceride over-enriched circulating VLDLs, of greater atherogenicity. However, when NAFLD progresses to severe fibrosis, circulating VLDL features apparently improved, probably due to early alterations in hepatic synthetic function.

Genetic Variations Associated with Vitamin A Status and Vitamin A Bioavailability

Blood concentration of vitamin A (VA), which is present as different molecules, i.e., mainly retinol and provitamin A carotenoids, plus retinyl esters in the postprandial period after a VA-containing meal, is affected by numerous factors: dietary VA intake, VA absorption efficiency, efficiency of provitamin A carotenoid conversion to VA, VA tissue uptake, etc. Most of these factors are in turn modulated by genetic variations in genes encoding proteins involved in VA metabolism. Genome-wide association studies (GWAS) and candidate gene association studies have identified single nucleotide polymorphisms (SNPs) associated with blood concentrations of retinol and β-carotene, as well as with β-carotene bioavailability. These genetic variations likely explain, at least in part, interindividual variability in VA status and in VA bioavailability. However, much work remains to be done to identify all of the SNPs involved in VA status and bioavailability and to assess the possible involvement of other kinds of genetic variations, e.g., copy number variants and insertions/deletions, in these phenotypes. Yet, the potential usefulness of this area of research is exciting regarding the proposition of more personalized dietary recommendations in VA, particularly in populations at risk of VA deficiency.

Dietary fat and physiological determinants of plasma chylomicron remnant homoeostasis in normolipidaemic subjects: insight into atherogenic risk

TAG depleted remnants of postprandial chylomicrons are a risk factor for atherosclerosis. Recent studies have demonstrated that in the fasted state, the majority of chylomicrons are small enough for transcytosis to arterial subendothelial space and accelerate atherogenesis. However, the size distribution of chylomicrons in the absorptive state is unclear. This study explored in normolipidaemic subjects the postprandial distribution of the chylomicron marker, apoB-48, in a TAG-rich lipoprotein plasma fraction (Svedberg flotation rate (Sf>400), in partially hydrolysed remnants (Sf 20-400) and in a TAG-deplete fraction (Sf<20), following ingestion of isoenergetic meals with either palm oil (PO), rice bran or coconut oil. Results from this study show that the majority of fasting chylomicrons are within the potentially pro-atherogenic Sf<20 fraction (70-75 %). Following the ingestion of test meals, chylomicronaemia was also principally distributed within the Sf<20 fraction. However, approximately 40 % of subjects demonstrated exaggerated postprandial lipaemia specifically in response to the SFA-rich PO meal, with a transient shift to more buoyant chylomicron fractions. The latter demonstrates that heterogeneity in the magnitude and duration of hyper-remnantaemia is dependent on both the nature of the meal fatty acids ingested and possible metabolic determinants that influence chylomicron metabolism. The study findings reiterate that fasting plasma TAG is a poor indicator of atherogenic chylomicron remnant homoeostasis and emphasises the merits of considering specifically, chylomicron remnant abundance and kinetics in the context of atherogenic risk. Few studies address the latter, despite the majority of life being spent in the postprandial and absorptive state.

Dietary fatty acid metabolism in prediabetes

PURPOSE OF REVIEW

Experimental evidences are strong for a role of long-chain saturated fatty acids in the development of insulin resistance and type 2 diabetes. Ectopic accretion of triglycerides in lean organs is a characteristic of prediabetes and type 2 diabetes and has been linked to end-organ complications. The contribution of disordered dietary fatty acid (DFA) metabolism to lean organ overexposure and lipotoxicity is still unclear, however. DFA metabolism is very complex and very difficult to study in vivo in humans.

RECENT FINDINGS

We have recently developed a novel imaging method using PET with oral administration of 14-R,S-F-fluoro-6-thia-heptadecanoic acid (FTHA) to quantify organ-specific DFA partitioning. Our studies thus far confirmed impaired storage of DFA per volume of fat mass in abdominal adipose tissues of individuals with prediabetes. They also highlighted the increased channeling of DFA toward the heart, associated with subclinical reduction in cardiac systolic and diastolic function in individuals with prediabetes.

SUMMARY

In the present review, we summarize previous work on DFA metabolism in healthy and prediabetic states and discuss these in the light of our novel findings using PET imaging of DFA metabolism. We herein provide an integrated view of abnormal organ-specific DFA partitioning in prediabetes in humans.

Lipoprotein lipase liberates free fatty acids to inhibit HCV infection and prevent hepatic lipid accumulation

Lipoprotein lipase (LPL) has been identified as an anti-hepatitis C virus (HCV) host factor, but the cellular mechanism remains elusive. Here, we investigated the cellular mechanism of LPL involving in anti-HCV. The functional activation of peroxisome proliferator-activated receptor (PPAR) α signal by LPL transducing into hepatocytes was investigated in HCV-infected cells, primary human hepatocytes, and in HCV-core transgenic mice. The result showed that the levels of transcriptional transactivity and nuclear translocation of PPARα in Huh7 cells and primary human hepatocytes were elevated by physiologically ranged LPL treatment of either very-low density lipoprotein or HCV particles. The LPL-induced hepatic PPARα activation was weakened by blocking the LPL enzymatic activity, and by preventing the cellular uptake of free unsaturated fatty acids with either albumin chelator or silencing of CD36 translocase. The knockdowns of PPARα and CD36 reversed the LPL-mediated suppression of HCV infection. Furthermore, treatment with LPL, like the direct activation of PPARα, not only reduced the levels of apolipoproteins B, E, and J, which are involved in assembly and release of HCV virions, but also alleviated hepatic lipid accumulation induced by core protein. HCV-core transgenic mice exhibited more hepatic miR-27b, which negatively regulates PPARα expression, than did the wild-type controls. The induction of LPL activity by fasting in the core transgenic mice activated PPARα downstream target genes that are involved in fatty acid β-oxidation. Taken together, our study reveals dual beneficial outcomes of LPL in anti-HCV and anti-steatosis and shed light on the control of chronic hepatitis C in relation to LPL modulators.

Prepartum body condition score and plane of nutrition affect the hepatic transcriptome during the transition period in grazing dairy cows

Background

A transcriptomic approach was used to evaluate potential interactions between prepartum body condition score (BCS) and feeding management in the weeks before calving on hepatic metabolism during the periparturient period.

Methods

Thirty-two mid-lactation grazing dairy cows of mixed age and breed were randomly allocated to one of four treatment groups in a 2 × 2 factorial arrangement: two prepartum BCS categories [4.0 (thin, BCS4) and 5.0 (optimal, BCS5); based on a 10-point scale], and two levels of energy intake during the 3 weeks preceding calving (75 and 125 % of estimated requirements). Liver samples were obtained at −7, 7, and 28 d relative to parturition and subsequent RNA was hybridized to the Agilent 44 K Bovine (V2) Microarray chip. The Dynamic Impact Approach was used for pathway analysis, and Ingenuity Pathway Analysis was used for gene network analysis.

Results

The greater number of differentially expressed genes in BCS4 cows in response to prepartum feed allowance (1071 vs 310, over the entire transition period) indicates that these animals were more responsive to prepartum nutrition management than optimally-conditioned cows. However, independent of prepartum BCS, pathway analysis revealed that prepartal feeding level had a marked effect on carbohydrate, amino acid, lipid, and glycan metabolism. Altered carbohydrate and amino acid metabolism suggest a greater and more prolonged negative energy balance postpartum in BCS5 cows overfed prepartum. This is supported by opposite effects of prepartum feeding in BCS4 compared with BCS5 cows in pathways encompassing amino acid, vitamin, and co-factor metabolism. The prepartum feed restriction ameliorates the metabolic adaptation to the onset of lactation in BCS5 cows, while detrimentally affecting BCS4 cows, which seem to better adapt when overfed. Alterations in the glycosaminoglycans synthesis pathway support this idea, indicating better hepatic health status in feed-restricted BCS5 and overfed BCS4 cows. Furthermore, IPA network analysis suggests liver damage in feed-restricted thin cows, likely due to metabolic overload.

Conclusion

Overall, the data support the hypothesis that overfeeding in late-pregnancy should be limited to underconditioned cows, while cows with optimal degree of body condition should be maintained on an energy-restricted diet.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3191-3) contains supplementary material, which is available to authorized users.

Increased ANGPTL3, 4 and ANGPTL8/betatrophin expression levels in obesity and T2D

Background

Hypertriglyceridemia is associated with increased risk for cardiovascular diseases and type 2 diabetes (T2D). Angiopoietin like proteins particularly 3, 4 and recently 8 are well established regulators of plasma triglyceride level through regulating the activity of lipoprotein lipase. Plasma level and association between ANGPTL3, 4 and 8 is not well established in human subjects. This study was designed to establish the level of these proteins in plasma and adipose tissues and investigate the association between ANGPTL8 with ANGPTL3 and 4 in T2D and non-diabetics subjects.

Methods

A total of 235 subjects were enrolled in this study, 144 non-diabetics and 91 T2D. ANGPTL 3, 4 and 8 levels were measured in plasma by ELISA and using real time RT-PCR in adipose tissues.

Results

In this study, we showed that ANGPTL3, 4 and 8 were higher in T2D subjects. Dividing the non-diabetic subjects according to their BMI showed higher level of ANGPTL3, 4 and 8 in obese subjects compared to non-obese subjects. No significant difference was observed between the T2D subjects. ANGPTL8 was showed positive correlation with ANGPTL3 in the non-diabetic subjects in the non-obese (r = 0.2437, p-Value = 0.0543) and obese subjects (r = 0.418, p-Value = 0.0125). No association was observed in the T2D subjects. On the other hand, ANGPTL4 was positively associated with the obese subjects in both the non-diabetics (r = 0.3322, p-Value = 0.0316) and the obese T2D subjects (r = 0.3161, p-Value = 0.0211).

Conclusion

In conclusion, our data shows that ANGPTL3, 4 and 8 are increased in obesity and T2D. ANGPTL8 associates with ANGPTL3 in the non-diabetic subjects while it associated more with ANGPTL4 in the obese and T2D subjects. Taken together, this data highlight the role of these proteins in metabolic diseases and how they interact with each other’s under different physiological and pathophysiological conditions.