apoA-I Production Research Articles

Inhibiting IP6K1 confers atheroprotection by elevating circulating apolipoprotein A-I

Background and aimsAtherosclerotic cardiovascular diseases are the leading cause of death. Apolipoprotein A-I (apoA-I) mediates cholesterol efflux to lower the risks of atherosclerosis. Elevating circulating apoA-I is an effective strategy for atheroprotection. However, the regulatory mechanisms of apoA-I have been elusive. MethodsProtein-protein interactions were examined by co-immunoprecipitations. Chemical biology tools were used to determine the binding of 5PP-InsP5 to its target proteins and its roles in mediating protein-protein interactions. The mouse atherosclerotic model was generated by injecting AAV-PCSK9 and feeding a Western diet. Atherosclerotic plaques were determined by Oil Red O and H&E staining. ResultsWe show that blocking IP6K1 activity increases apoA-I production in hepatocytes. IP6K1 binds to apoA-I and via its product 5PP-InsP5 to induce apoA-I degradation, which requires ubiquitination factor E4A (UBE4A). Depleting 5PP-InsP5 by deleting IP6K1 or blocking IP6K1 activity disrupts the interaction between UBE4A and apoA-I, preventing apoA-I degradation, leading to increased production of apoA-I. Hepatocyte-specific deletion of IP6K1 elevates circulating apoA-I levels, which augments cholesterol efflux and lowers the burden of atherosclerosis. Mice with both apoA-I KO and hepatocyte-specific IP6K1 KO were generated to validate that IP6K1 deletion-induced atheroprotection requires apoA-I. ConclusionsOur findings reveal a mechanism by which blocking IP6K1 boosts apoA-I production. Blocking IP6K1 represents a potential treatment strategy to elevate circulating apoA-I for atheroprotection.

Assessing HDL Metabolism in Subjects with Elevated Levels of HDL Cholesterol and Coronary Artery Disease.

High-density lipoprotein cholesterol (HDL-C) is thought to be atheroprotective yet some patients with elevated HDL-C levels develop cardiovascular disease, possibly due to the presence of dysfunctional HDL. We aimed to assess the metabolic fate of circulating HDL particles in patients with high HDL-C with and without coronary artery disease (CAD) using in vivo dual labeling of its cholesterol and protein moieties. We measured HDL apolipoprotein (apo) A-I, apoA-II, free cholesterol (FC), and cholesteryl ester (CE) kinetics using stable isotope-labeled tracers (D3-leucine and 13C2-acetate) as well as ex vivo cholesterol efflux to HDL in subjects with (n = 6) and without (n = 6) CAD that had HDL-C levels >90th percentile. Healthy controls with HDL-C within the normal range (n = 6) who underwent the same procedures were used as the reference. Subjects with high HDL-C with and without CAD had similar plasma lipid levels and similar apoA-I, apoA-II, HDL FC, and CE pool sizes with no significant differences in fractional clearance rates (FCRs) or production rates (PRs) of these components between groups. Subjects with high HDL-C with and without CAD also had similar basal and cAMP-stimulated ex vivo cholesterol efflux to HDL. When all subjects were considered (n = 18), unstimulated non-ABCA1-mediated efflux (but not ABCA1-specific efflux) was correlated positively with apoA-I production (r = 0.552, p = 0.017) and HDL FC and CE pool sizes, and negatively with the fractional clearance rate of FC (r = −0.759, p = 4.1 × 10−4) and CE (r = −0.652, p = 4.57 × 10−3). Our data are consistent with the concept that ex vivo non-ABCA1 efflux capacity may correlate with slower in vivo turnover of HDL cholesterol moieties. The use of a dual labeling protocol provided for the first time the opportunity to assess the association of ex vivo cholesterol efflux capacity with in vivo HDL cholesterol metabolic parameters.

The Promise of Apolipoprotein AI-Based Therapy

Apolipoprotein A-I (ApoAI) is an anti-atherosclerotic protein that promotes cholesterol efflux from tissues to the liver for excretion [1]. ApoAI is the main structural and functional protein of High- Density Lipoproteins (HDL), representing ~70% of total HDL proteins [2,3]. Circulating apoAI protein is an amphipathic protein (28kDa) comprising eight alpha-helical domains of 22 amino acids and two repeats of 11 amino acids [4]. Consequently, ApoAI binds avidly to lipids and readily moves between lipoprotein particles; however, ~5-10% of human plasma ApoAI exists in a free state (lipoprotein-unbound) [5]. ApoAI protein is more than a structural scaffold that maintains lipid packaging, as it plays an important role in the transport of cellular cholesterol from the artery wall to the liver for catabolism [6-8]. Antioxidant and anti-inflammatory properties were also attributed to apoAI [9,10]. In addition, a protective role of apoAI against cancer was proposed [11]. ApoAI is synthesized mainly in the liver and small intestine and there are a lot of regulatory elements and transcription factors that control apoAI gene expression, as reviewed in [12]. Treatment with BPA (bisphenol A), one of the most widespread environmental chemicals, downregulates ApoAI gene expression, aggravating the atherosclerotic plaques in LDLR-/- mice [13]. Interestingly, the ratio of HDL-cholesterol to apoAI protein levels is an indicator of the risk of the cardiovascular disorder [14]. Lack of ApoAI augmented atherosclerosis in various hypercholesterolemic mice, such as mice expressing human apoB or ApoAI-/-/LDLR-/- mice [15,16]. In humans, familial ApoAI deficiency is associated with premature coronary heart disease [17]. Interestingly, low levels of apoAI and atherogenic dyslipidemia were found in obese individuals, but increases in apoAI levels and enhancements of cholesterol efflux capacity of HDL were reported at three months after bariatric surgery [18]. Considering the anti-atherogenic properties of apoAI, various apoAI-based therapies were proposed for reduction of atherogenesis: i) overexpression of ApoAI, ii) infusions of ApoAI protein, ApoAI mimetic peptides, or ApoAI-containing HDL [19-21], iii) oral small molecules that stimulate ApoAI production [22]. Overexpression of ApoAI reduced atherogenesis in apoE-/- or LDLR-/- atherosclerotic mice [23-31]. Infusions of ApoAI mimetic peptides led to the regression of aortic valve stenosis in rabbits [32]. Liver-directed adenoviral gene transfer of ApoAI resulted in the regression of preexisting atheroma in LDLR-/- mice [33]. Undoubtedly, local delivery of apoAI protein to the vascular wall represents a more efficient apoAIbased therapy than its systemic delivery. Remarkably, transduction of vascular endothelial cells with ApoAI expressing adenovirus reduced inflammation and protected against atherosclerosis in hyperlipidemic rabbits [34,35]. The oral drug RVX-208 significantly increased apoAI production in monkeys but presented disappointing efficacy in a phase II trial [36]. Notwithstanding there are good results obtained in studies using animal models, several apoAI-based clinical trials failed to regress atherosclerotic plaques in humans [37,38]. Despite tremendous advances regarding the understanding of apoAI, the promise of apoAI-based therapy awaits new studies and trials.

Effect of fasting and feeding on apolipoprotein A-I kinetics in pre\u03b21-HDL, \u03b1-HDL, and triglyceride-rich lipoproteins

The aim of this study was to compare the kinetics of apolipoprotein (apo)A-I during fed and fasted states in humans, and to determine to what extent the intestine contributes to apoA-I production. A stable isotope study was conducted to determine the kinetics of apoA-I in preβ1 high-density lipoprotein (HDL) and α-HDL. Six healthy male subjects received a constant intravenous infusion of 2H3-leucine for 14 h. Subjects in the fed group also received small hourly meals. Blood samples were collected hourly during tracer infusion and then daily for 4 days. Tracer enrichments were measured by mass spectrometry and then fitted to a compartmental model using asymptotic plateau of very-low-density lipoprotein (VLDL) apoB100 and triglyceride-rich lipoprotein (TRL) apoB48 as estimates of hepatic and intestinal precursor pools, respectively. The clearance rate of preβ1-HDL-apoA-I was lower in fed individuals compared with fasted subjects (p < 0.05). No other differences in apoA-I production or clearance rates were observed between the groups. No significant correlation was observed between plasma apoC-III concentrations and apoA-I kinetic data. In contrast, HDL-apoC-III was inversely correlated with the conversion of α-HDL to preβ1-HDL. Total apoA-I synthesis was not significantly increased in fed subjects. Hepatic production was not significantly different between the fed group (17.17 ± 2.75 mg/kg/day) and the fasted group (18.67 ± 1.69 mg/kg/day). Increase in intestinal apoA-I secretion in fed subjects was 2.20 ± 0.61 mg/kg/day. The HDL-apoA-I kinetics were similar in the fasted and fed groups, with 13% of the total apoA-I originating from the intestine with feeding.

High-density lipoprotein functionality in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a heterogeneous disease which is characterized with excessive inflammation and autoantibodies, macrophage and complement activation, and subsequently immunologically mediated tissue damage. In spite of improved treatments of SLE, these patients experience premature atherosclerosis and the rate of mortality among them remains high. Autoantibodies and circulating immune complexes might contribute to the pathogenesis of atherosclerosis by injuring the endothelium, as well as inducing pro-inflammatory and pro-adhesive endothelial cell phenotypes, as well as altering the metabolism of lipoproteins involved in atherogenesis. Hence, high levels of atherogenic lipoproteins (like low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL)) and low levels of high-density lipoprotein (HDL-C) are important risk factors for atherosclerotic cardiovascular complications in SLE patients but these traditional risk factors fail to fully explain the increased risk of cardiovascular disease (CVD) in these patients. The exact mechanism by which inflammation decreases HDL levels is not defined, but decreases in apoA-I production and lecithin cholesterol acyltransferase (LCAT) activity, as well as increased serum amyloid A (SAA), endothelial lipase and secretory phospholipase A2 activity (PLA2) could all contribute. In addition, during inflammation multiple changes in HDL structure occur, leading to alterations in HDL function which may be implicated in the CVD complications of SLE. Therefore, this review will aim to identify the mechanisms implicated in HDL dysfunction which occurs in SLE patients.

The effects of short-chain fatty acids on the transcription and secretion of apolipoprotein A-I in human hepatocytes in vitro.

BackgroundApolipoprotein‐I (ApoA‐I), the major component of high‐density lipoprotein (HDL) particles, mediates cholesterol efflux by which it facilitates the removal of excess cholesterol from peripheral tissues. Therefore, elevating ApoA‐I production leading to the production of new pre‐β‐HDL particles is thought to be beneficial in the prevention of cardiovascular diseases. Recently, we observed that amoxicillin treatment led to decreased HDL concentrations in healthy human volunteers. We questioned whether this antibiotic effect was directly or indirectly, via changed short‐chain fatty acids (SCFA) concentrations through an altered gut microflora. Therefore, we here evaluated the effects of amoxicillin and various SCFA on hepatic ApoA‐I expression, secretion, and the putative underlying pathways.Methods and ResultsHuman hepatocytes (HepG2) were exposed to increasing dose of amoxicillin or SCFA for 48 hours. ApoA‐I messenger RNA (mRNA) transcription and secreted protein were analyzed using quantitative polymerase chain reaction and enzyme‐linked immunosorbent assay, respectively. To study underlying mechanisms, changes in mRNA expression of KEAP1, CPT1, and PPARα, as well as a PPARα transactivation assay, were analyzed. Amoxicillin dose‐dependently decreased ApoA‐I mRNA transcription as well as ApoA‐I protein secretion. SCFA treatment resulted in a dose‐dependent stimulation of ApoA‐I mRNA transcription, however, the ApoA‐I protein secretion was decreased. Furthermore, SCFA treatment increased PPARα transactivation, PPARα and CPT1 mRNA transcription, whereas KEAP1 mRNA transcription was decreased.ConclusionDirect treatment of HepG2 cells with amoxicillin has either direct effects on lowering ApoA‐I transcription and secretion or indirect effects via modified SCFA concentrations because SCFA were found to stimulate hepatic ApoA‐I expression. Furthermore, BET inhibition and PPARα activation were identified as possible mechanisms behind the observed effects on ApoA‐I transcription.

Inhibition of hepatic apolipoprotein A-I gene expression by histamine

In a recent high throughput analysis to identify drugs that alter hepatic apolipoprotein A-I (apo A-I) expression, histamine receptor one (H1) antagonists emerged as potential apo A-1 inducing drugs. Thus the present study was undertaken to identify some of the underlying molecular mechanisms of the effect of antihistaminic drugs on apo AI production. Apo A-I levels were measured by enzyme immunoassay and Western blots. Apo A-I mRNA levels were measured by reverse transcription real-time PCR using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA as the internal control. The effects of histamine and antihistamines on apo A-I gene were determined by transient transfection of plasmids containing the apo A-I gene promoter. Histamine repressed while (H1) receptor antagonist azelastine increased apo A-I protein and mRNA levels within 48 h in a dose-dependent manner. Azelastine and histamine increased and suppressed, respectively, apo A-I gene promoter activity through a peroxisome proliferator activated receptor α response element. Treatment of HepG2 cells with other H1 receptor antagonists including fexofenadine, cetirizine, and diphenhydramine increased apo A-I levels in a dose-dependent manner while treatment with H2 receptor antagonists including cimetidine, famotidine, and ranitidine had no effect. We conclude that H1 receptor signaling is a novel pathway of apo A1 gene expression and therefore could be an important therapeutic target for enhancing de-novo apo A-1 synthesis.

The acute effects on duodenal gene expression in healthy men following consumption of a low-fat meal enriched with theobromine or fat

Increasing apoA-I synthesis may improve HDL functionality and lower CVD risk. As theobromine and fat increase fasting apoA-I concentrations, and the intestine is involved in apoA-I production, the acute effects of both were studied on duodenal gene transcription to better understand underlying mechanisms. In this crossover study, 8 healthy men received once a low fat (LF) meal, a LF meal plus theobromine (850 mg), or a high fat (HF) meal. Five hours after meal intake duodenal biopsies were taken for microarray analysis. Theobromine and HF consumption did not change duodenal apoA-I expression. Theobromine did not change gene expression related to lipid and cholesterol metabolism, whereas those related to glycogen/glucose breakdown were downregulated. HF consumption increased gene expression related to lipid and cholesterol uptake and transport, and to glucose storage, while it decreased those related to glucose uptake. Furthermore, genes related to inflammation were upregulated, but inflammation markers in plasma were not changed. In healthy men, acute theobromine and fat consumption did not change duodenal apoA-I mRNA, but inhibited expression of genes related to glucose metabolism. Furthermore, HF intake activated in the duodenum expression of genes related to lipid and cholesterol metabolism and to inflammation.

Dietary Strategies and Novel Pharmaceutical Approaches Targeting Serum ApoA-I Metabolism: A Systematic Overview.

The incidence of CHD is still increasing, which underscores the need for new preventive and therapeutic approaches to decrease CHD risk. In this respect, increasing apoA-I concentrations may be a promising approach, especially through increasing apoA-I synthesis. This review first provides insight into current knowledge on apoA-I production, clearance, and degradation, followed by a systematic review of dietary and novel pharmacological approaches to target apoA-I metabolism. For this, a systematic search was performed to identify randomized controlled intervention studies that examined effects of whole foods and (non)nutrients on apoA-I metabolism. In addition, novel pharmacological approaches were searched for, which were specifically developed to target apoA-I metabolism. We conclude that both dietary components and pharmacological approaches can be used to increase apoA-I concentrations or functionality. For the dietary components in particular, more knowledge about the underlying mechanisms is necessary, as increasing apoA-I per se does not necessarily translate into a reduced CHD risk.

C/EBP‐β Is Differentially Affected by PPARα Agonists Fenofibric Acid and GW7647, But Does Not Change Apolipoprotein A‐I Production During ER‐Stress and Inflammation

Increasing apolipoproteinA-I (apoA-I) production may be anti-atherogenic. Thus, there is a need to identify regulatory factors involved. Transcription of apoA-I involves peroxisome-proliferator-activated-receptor-alpha (PPARα) activation, but endoplasmic reticulum (ER) -stress and inflammation also influence apoA-I production. To unravel why PPARα agonist GW7647 increased apoA-I production compared to PPARα agonist fenofibric acid (FeAc) in human hepatocellular carcinoma (HepG2) and colorectal adenocarcinoma (CaCo-2) cells, gene expression profiles were compared. Microarray analyses suggested CCAAT/enhancer-binding-protein-beta (C/EBP-β) involvement in the FeAc condition. Therefore, C/EBP-β silencing and isoform-specific overexpression experiments were performed under ER-stressed, inflammatory and non-inflammatory conditions. mRNA expression of C/EBP-β, ATF3, NF-IL3 and GDF15 were upregulated by FeAc compared to GW7647 in both cell lines, while DDIT3 and DDIT4 mRNA were only upregulated in HepG2 cells. This ER-stress related signature was associated with decreased apoA-I secretion. After ER-stress induction by thapsigargin or FeAc addition, intracellular apoA-I concentrations decreased, while ER-stress marker expression (CHOP, XBP1s, C/EBP-β) increased. Cytokine addition increased intracellular C/EBP-β levels and lowered apoA-I concentrations. Although a C/EBP binding place is present in the apoA-I promoter, C/EBP-β silencing or isoform-specific overexpression did not affect apoA-I production in inflammatory, non-inflammatory and ER-stressed conditions. Therefore, C/EBP-β is not a target to influence hepatic apoA-I production. J. Cell. Biochem. 118: 754-763, 2017. © 2016 Wiley Periodicals, Inc.

Enhanced atheroprotection and lesion remodelling by targeting the foam cell and increasing plasma cholesterol acceptors.

Atherosclerosis development can be ameliorated by promoting reverse cholesterol transport (RCT) from arteries. The process involves cholesterol efflux from foam cells to extracellular acceptors such as apolipoprotein A-I (apoA-I) and high-density lipoprotein (HDL) that mediate transport to the liver. Perilipin-2 (PLIN2) is a lipid droplet (LD)-associated protein that in macrophages facilitates cholesterol storage and prevents efflux. We hypothesized that atheroprotection would be enhanced by concurrently targeting PLIN2 to increase the efflux capacity of foam cells and increasing plasma apoA-I and HDL. PLIN2-knockout and wild-type mice lacking apolipoprotein E (PLIN2(-/-)/apoE(-/-) and PLIN2(+/+)/apoE(-/-)) were treated with a helper-dependent adenoviral vector encoding human apoA-I (HDAd-AI) or with control empty vector. Treatment with HDAd-AI increased hepatic apoA-I production, plasma apoA-I and HDL-cholesterol (HDL-C), and apoA-I deposition in lesions to a similar extent in PLIN2(-/-)/apoE(-/-) and PLIN2(+/+)/apoE(-/-) mice. However, atherosclerosis development at the aortic sinus was considerably lower in HDAd-AI-treated PLIN2(-/-)/apoE(-/-) mice. A more stable lesion phenotype, with increased collagen content, was primarily associated to treatment with HDAd-AI, but was enhanced under PLIN2 deficiency. PLIN2 deficiency and apoA-I cumulatively reduced LDs and cholesterol ester content in cultured macrophages. Neutral lipid in atheroma was significantly reduced in HDAd-AI-treated PLIN2(-/-)/apoE(-/-) mice, and RCT from macrophages to feces was enhanced in PLIN2(-/-) macrophages. These studies demonstrate a mutually beneficial relationship between PLIN2 deficiency and elevated apoA-I/HDL-C in preventing atherosclerosis development. The data support that targeting foam cell components to mobilize cholesterol may be a promising strategy to enhance the atheroprotection of plasma cholesterol acceptors.

Perhexiline activates KLF14 and reduces atherosclerosis by modulating ApoA-I production

Recent genome-wide association studies have revealed that variations near the gene locus encoding the transcription factor Krüppel-like factor 14 (KLF14) are strongly associated with HDL cholesterol (HDL-C) levels, metabolic syndrome, and coronary heart disease. However, the precise mechanisms by which KLF14 regulates lipid metabolism and affects atherosclerosis remain largely unexplored. Here, we report that KLF14 is dysregulated in the liver of 2 dyslipidemia mouse models. We evaluated the effects of both KLF14 overexpression and genetic inactivation and determined that KLF14 regulates plasma HDL-C levels and cholesterol efflux capacity by modulating hepatic ApoA-I production. Hepatic-specific Klf14 deletion in mice resulted in decreased circulating HDL-C levels. In an attempt to pharmacologically target KLF14 as an experimental therapeutic approach, we identified perhexiline, an approved therapeutic small molecule presently in clinical use to treat angina and heart failure, as a KLF14 activator. Indeed, in WT mice, treatment with perhexiline increased HDL-C levels and cholesterol efflux capacity via KLF14-mediated upregulation of ApoA-I expression. Moreover, perhexiline administration reduced atherosclerotic lesion development in apolipoprotein E-deficient mice. Together, these results provide comprehensive insight into the KLF14-dependent regulation of HDL-C and subsequent atherosclerosis and indicate that interventions that target the KLF14 pathway should be further explored for the treatment of atherosclerosis.

Relationship Between HDLc, NonHDLc/ HDLc Ratio and Gilbert's Syndrome

Objective: We investigated the relationship between HDL-cholesterol levels that is indirect marker of ApoA-I production in liver, Non-HDL-cholesterol that is indirect marker of ApoB and GS Methods: HDLc, NonHDLc/ HDLc Ratio levels were investigated in subjects with GS (n=148) and compared to healthy controls (n=148). Results: Age and BMI distributions were similar between the two groups. HDLc levels were lower in GS than the healthy controls (p=0.012). However, TC, Non-HDLc, Non-HDLc/HDLc levels were higher in GS than the healthy controls (p=0.002, p=0.001, p<0.001, respectively). In correlation analysis, UB were negatively mildly correlated with HDLc (r=−0.191, p=0.001) and positively correlated with TC (r=0.436, p<0.001), Non-HDLc (r=0.511, p<0.001) and Non-HDLc/HDLc (r=0.512, p<0.001) in the whole group. Conclusions: The contrary of previously studies, we would like to suggest that bilirubin is a only antioxidant agent that protects from cardiovascular disease, but not physiological hypolipidemic agent.

Potent peroxisome proliferator-activated receptor-α agonist treatment increases cholesterol efflux capacity in humans with the metabolic syndrome.

Fibrate medications weakly stimulate the nuclear receptor peroxisome proliferator-activated receptor-α (PPAR-α) and are currently employed clinically in patients with dyslipidaemia. The potent and selective agonist of PPAR-α LY518674 is known to substantially increase apolipoprotein A-I (apoA-I) turnover without major impact on steady-state levels of apoA-I or high-density lipoprotein-cholesterol (HDL-C). We sought to determine whether therapy with a PPAR-α agonist impacts cholesterol efflux capacity, a marker of HDL function. Cholesterol efflux capacity was measured at baseline and after 8 weeks of therapy in a randomized, placebo-controlled trial involving participants with metabolic syndrome treated with either LY518674 100 μg daily (n = 13) or placebo (n = 15). Efflux capacity assessment was quantified using a previously validated ex vivo assay that measures the ability of apolipoprotein-B depleted plasma to mobilize cholesterol from macrophages. LY518674 led to a 15.7% increase from baseline (95% CI 3.3-28.1%; P = 0.02, P vs. placebo = 0.01) in efflux capacity. The change in apoA-I production rate in the active treatment arm was strongly linked to change in cholesterol efflux capacity (r = 0.67, P = 0.01). Potent stimulation of PPAR-α leads to accelerated turnover of apoA-I and an increase in cholesterol efflux capacity in metabolic syndrome patients despite no change in HDL-C or apoA-I levels. This finding reinforces the notion that changes in HDL-C levels may poorly predict impact on functionality and thus has implications for ongoing pharmacologic efforts to enhance apoA-I metabolism.

A novel compound 4010B-30 upregulates apolipoprotein A-I gene expression through activation of PPARγ in HepG2 cells

ObjectiveApolipoprotein (Apo) A-I is the major lipoprotein content of HDL and upregulating endogenous ApoA-I expression has been proposed as a desirable approach to raise the functional HDL. In this study we investigated the effect of a novel small molecule 4010B-30 on transcriptional regulation of ApoA-I gene in HepG2 cells, and the influence on the level of ApoA-I expression and function. Then the mechanisms by which 4010B-30 regulated ApoA-I expression was further explored. Methods and resultsIn human hepatic HepG2 cells, 4010B-30 increased the mRNA level and the protein production of ApoA-I both in cell lysates and media. The 4010B-30-induced ApoA-I containing particles increased cholesterol efflux from RAW264.7 macrophages. 4010B-30 also upregulated ABCA1 expression confirmed by transcriptional activity assay and Western blot analysis in both HepG2 and RAW264.7 cells. Promoter luciferase assay was used to identify the 4010B-30-responsive region which is mapped to the proximal −277bp region of the ApoA-I promoter. Further study indicated that the regulation of 4010B-30 on ApoA-I transcription or protein expression in HepG2 cells was abrogated with the suppression of PPARγ by its small interfering RNA or a specific inhibitor, GW9662. ConclusionsThese findings suggest that the novel small molecular upregulator 4010B-30 increases ApoA-I gene expression, thereby enhances its function of promoting cholesterol efflux, as well as ABCA1 expression in vitro, and activation of PPARγ is required for 4010B-30 to induce hepatic ApoA-I production.

Dietary fatty acids, dietary patterns, and lipoprotein metabolism.

Few studies have reviewed the impact of dietary fat and dietary patterns on lipoprotein metabolism. This review intends to provide perspective on this topic, while focusing primarily on the studies that assessed intravascular lipoprotein kinetics in humans using isotope methodologies. Data suggest that dietary saturated fatty acids slow the clearance of LDL apolipoprotein (apo)B-100 and of apoA-I from the circulation, whereas possibly increasing also apoA-I production. Dietary trans fats reduce the clearance of LDL apoB-100, whereas increasing the clearance of apoA-I. n-3 polyunsaturated fatty acids (PUFAs) intake reduces the production of apoB-48-containing lipoproteins as well as of VLDL apoB-100 and increases their conversion into smaller lipoproteins. Medium-chain triglycerides appear to have no significant effect on lipoprotein kinetics. Finally, Mediterranean diet in the absence of weight loss reduces LDL cholesterol, primarily by enhancing its clearance from the circulation. Kinetic studies with tracers allow a better appreciation of the impact of specific dietary factors on plasma lipid risk factors. However, additional studies are required to better document the effect of monounsaturated fatty acids, n-6 PUFAs, and of whole diets on lipoprotein metabolism.

Elevated Interleukin-10 and “Disappearing HDL Syndrome” in Lymphoproliferative Disorders

BACKGROUND: Acquired severe HDL deficiency is relatively uncommon. It may occur with use of high doses of anabolic steroids or in severe liver diseases, which can lead to low LCAT activity and decreased apoA-I production. “Disappearing HDL Syndrome”*, a term first used by Goldberg and Mendez, refers to cases of severe HDL deficiency in patients that are not critically ill, sometimes long before the clinical or biochemical features of the underlying primary disease become evident. Disappearing HDL Syndrome can also result from an idiosyncratic reaction to medications, such as peroxisome proliferation-activated receptor (PPAR) agonists. Additionally, autoantibodies against LCAT in non-Hodgkin lymphoma have been described as a possible cause. Low high-density lipoprotein-cholesterol (HDL-C) is a risk factor for coronary artery disease.OBJECTIVE: To determine the cause of low HDL-C in patients with severe acquired HDL deficiency noted as an incidental finding associated with lymphoma and autoimmune lymphoproliferative syndrome (ALPS)** as well as following recombinant human IL10 therapy in psoriatric arthritis patients. Investigating mechanisms underlying acquired severe HDL deficiency in non-critically ill patients (“Disappearing HDL Syndrome”) could provide new insights into HDL metabolism and its role in lymphomagenesis.PATIENTS AND RESULTS: Patients with intravascular large B-cell lymphoma (IVLBCL, n=2), diffuse large B-cell lymphoma (DLBCL, n=1), and ALPS-FAS (n=1) presenting with markedly decreased HDL-C, low LDL-C and elevated triglycerides were identified. The abnormal lipoprotein profile returned to normal following therapy in all four cases (Figure). All of them were found to have markedly elevated serum interleukin-10 (IL-10) levels at presentation that also normalized following therapy. Besides accumulation of abnormal lymphocytes in lymph nodes and spleen, ALPS patients have elevated serum IL-10. In a cohort of ALPS patients with genetic mutations in FAS (n=93), IL-10 showed a strong inverse correlation with HDL-C (R2=0á3720, P<0á0001). A direct causal role for increased serum IL-10 in inducing the observed changes in lipoproteins was established in a randomized, placebo-controlled clinical trial of recombinant human IL-10 (rhIL-10) in psoriatic arthritis patients (n=18). Within a week of initiating subcutaneous rhIL-10 injections, HDL-C precipitously decreased to near-undetectable levels. LDL-C also decreased by over 50% (P<0.0001) and triglycerides increased by approximately 2-fold (P<0.005). All values returned to baseline after stopping IL-10 therapy.CONCLUSION: Increased IL-10 causes severe HDL-C deficiency, low LDL-C and elevated triglycerides. IL-10 is thus a potent modulator of lipoprotein levels, a potential new biomarker for B-cell disorders, and a novel cause of Disappearing HDL Syndrome. Elevated IL-10 plays a key role in linking inflammation and lipoprotein metabolism. As evidence for its causality, rhIL-10 treatment in a clinical trial of psoriasitic arthritis patients precipitously lowered HDL-C. Finding elevated IL-10 as a cause of “Disappearing HDL Syndrome” in patients with 3 different types of B-cell disorders suggests that IL-10 and low HDL-C could be useful biomarkers of disease activity in these conditions. Finally, future research focusing on strategies to alter lipoprotein levels by modulating circulating IL-10 levels or its signaling pathways may be useful for developing novel targeted therapies.*Ref: Severe acquired (secondary) high-density lipoprotein deficiency. Goldberg RB, Mendez AJ. J Clin Lipidol. 2007;1:41-56**Ref: Natural history of autoimmune lymphoproliferative syndrome associated with FAS gene mutations. Price S, Shaw PA, Seitz A et al. Blood. 2014 Mar 27;123(13):1989-99. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

A novel ApoA-I truncation (ApoA-IMytilene) associated with decreased ApoA-I production

ObjectiveWe report a novel apolipoprotein (apo) A-I truncation (apoA-IMytilene) due to a heterozygous nonsense mutation (c.718C > T, p.Gln216*) in a 68-year-old male proband with premature coronary heart disease (CHD), corneal arcus, and very low plasma concentrations of HDL cholesterol (HDL-C) and apoA-I. Two family members also had the same mutation. Our objectives were to characterize the kindred and to examine the kinetics of apoA-I, as well as cellular cholesterol efflux capacity in the proband. MethodsWe carried out the kinetic studies using a primed constant infusion of [5,5,5-D3]L-leucine and isotopic enrichment was determined by gas chromatography mass spectrometry in the proband and seven controls with low HDL-C. To assess cellular cholesterol efflux capacity, we used a validated ex vivo system that involved incubation of J774 macrophages with apoB-depleted serum from the proband, five controls with normal HDL-C, and two controls with low HDL-C. ResultsStable isotope kinetic studies indicated that the proband had an apoA-I production rate (PR) that was 41% lower than the mean PR observed in low HDL-C controls (n = 7). The cellular cholesterol efflux capacity assessment showed normalized cholesterol efflux capacity in the proband was decreased by 36% compared to the mean normalized cholesterol efflux capacity of normal controls (n = 5). ConclusionsOur data indicate that this novel heterozygous apoA-I truncation is associated with markedly decreased levels of HDL-C, plasma apoA-I, and apoA-I in large α-1 HDL particles, as well as decreased total cellular cholesterol efflux and decreased apoA-I production.

Expression of human hepatic lipase negatively impacts apolipoprotein A-I production in primary hepatocytes from Lipc-null mice.

This study aimed to examine whether expression of human hepatic lipase (hHL) exerted an intracellular effect on hepatic production of apolipoprotein (apo) A-I. The levels of secreted and cell-associated apoA-I were contrasted between primary hepatocytes isolated from Lipc-null and C57BL/6 mice, and between Lipc-null hepatocytes transfected with either hHL-encoding or control adenovirus. An HSPG-binding deficient hHL protein (hHLmt) was used to determine the impact of cell surface binding on HL action. Accumulation of apoA-I in conditioned media of primary hepatocytes isolated from Lipc-null mice was increased as compared to that from C57BL/6 mice. Metabolic labeling experiments showed that secretion of 35S-apoA-I from Lipc-null cells was significantly higher than that from C57BL/6 cells. Expression of hHL in Lipc-null hepatocytes, through adenovirus-mediated gene transfer, resulted in decreased synthesis and secretion of 35S-apoA-I, but not 35S-apoE, as compared with cells transfected with control adenovirus. Expression of HSPG-binding deficient hHLmt in Lipc-null cells also exerted an inhibitory effect on apoA-I production, even though hHLmt displayed impaired exit from the endoplasmic reticulum as compared with hHL. Subcellular fractionation revealed that expression of hHL or hHLmt led to increased microsome-association of apoA-I relative to non-transfected control. Expression of hHL negatively impacts hepatic production of apoA-I.

Effect of Niacin on High-Density Lipoprotein Apolipoprotein A-I Kinetics in Statin-Treated Patients With Type 2 Diabetes Mellitus

To investigate the effect of extended-release (ER) niacin on the metabolism of high-density lipoprotein (HDL) apolipoprotein A-I (apoA-I) in men with type 2 diabetes mellitus on a background of optimal statin therapy. Twelve men with type 2 diabetes mellitus were recruited for a randomized, crossover design trial. Patients were randomized to rosuvastatin or rosuvastatin plus ER niacin for 12 weeks and then crossed over to the alternate therapy after a 3-week washout period. Metabolic studies were performed at the end of each treatment period. HDL apoA-I kinetics were measured after a standardized liquid mixed meal and a bolus injection of d3-leucine for 96 hours. Compartmental analysis was used to model the data. ER niacin significantly decreased plasma triglyceride, plasma cholesterol, non-HDL cholesterol, low-density lipoprotein cholesterol, and apoB (all P<0.05) and significantly increased HDL cholesterol and apoA-I concentrations (P<0.005 and P<0.05, respectively). ER niacin also significantly increased HDL apoA-I pool size (6,088 ± 292 versus 5,675 ± 305 mg; P<0.001), and this was attributed to a lower HDL apoA-I fractional catabolic rate (0.33 ± 0.01 versus 0.37 ± 0.02 pools/d; P<0.005), with no significant changes in HDL apoA-I production (20.93 ± 0.63 versus 21.72 ± 0.85 mg/kg per day; P=0.28). ER niacin increases HDL apoA-I concentration in statin-treated subjects with type 2 diabetes mellitus by lowering apoA-I fractional catabolic rate. The effect on HDL metabolism was independent of the reduction in plasma triglyceride with ER niacin treatment. Whether this finding applies to other dyslipidemic populations remains to be investigated.