Hypertriglyceridemic Phenotype Research Articles

Oral administration of viable or heat-inactivated Lacticaseibacillus rhamnosus GG influences on metabolic outcomes and gut microbiota in rodents fed a high-fat high-fructose diet

High-fat High-fructose diets have been associated with metabolic disorders and gut microbiota dysbiosis. Thus, the administration of probiotic or postbiotic from the strain Lacticaseibacillus rhamnosus GG has been investigated as a protective strategy. The aim of this study was to analyze the impact of L. rhamnosus GG administration in rodents fed a high-fat high-fructose diet. Male Wistar rats with oral supplementation of L. rhamnosus GG, viable or heat-inactivated, for 6 weeks were evaluated for somatic measurements, food and energy intake, biochemical markers, and gut microbiota. The daily administration of L. rhamnosus GG, as probiotic or postbiotic, was beneficial in attenuating weight gain, visceral fat deposition and visceral hypertriglyceridemic phenotype. Furthermore, the administration of heat-inactivated L. rhamnosus GG elicited an increase of species such as Akkermansia muciniphila, Blautia glucerasea, Sarcina maxima and L. rhamnosus, where the interaction between L. rhamnosus and Blautia glucerasea attenuated metabolic markers altered by the obesogenic diet.

The hypertriglyceridemic-waist phenotype as a valuable and integrative mirror of metabolic syndrome traits

Rates of non-communicable diseases (NCDs), such as obesity, diabetes, cardiovascular events and cancer, continue to rise worldwide, which require objective instruments for preventive and management actions. Diverse anthropometric and biochemical markers have been used to qualitatively evaluate degrees of disease, metabolic traits and evolution of nutritional status. The aim of this study was to integrate and assess the interactions between an anthropometric measurement, such as waist circumference (WC), and biochemical data, such as the triglyceride glucose index (TyG), in order to individually characterize metabolic syndrome (MetS) features considering the hypertriglyceridemic waist phenotype as a marker. An ancillary cross-sectional study was conducted using anthropometric measurements, such as weight, height, waist and hip circumferences, as well as fasting biochemical data of 314 participants. Different indices based on WC (WC, WC*TG and WC*TyG) were estimated to compute MetS components and accompanying comorbidities. ROC curves were fitted to define the strength of the analyses and the validity of the relationships. Associations were confirmed between anthropometric, biochemical and combined indices with some chronic disease manifestations, including hyperglycemia, hypertension and dyslipidemia. Both WC*TG and WC*TyG indices showed similar performance in diagnosing MetS (area under the ROC curve = 0.81). Interestingly, when participants were categorized according to a reference value of the WC*TyG index (842.7 cm*mg/dl), our results evidenced that subjects classified over this limit presented statistically higher prevalence of MetS and accompanying individual components with clinical relevance for interventions. These results revealed that WC*TyG mirrors the hypertriglyceridemic phenotype, which suggests may serve as a good indicator to define the metabolic syndrome phenotype and a suitable, sensitive, and simple proxy to complement others. A reference point was proposed with a good clinical performance and maximized sensitivity and specificity values.

SUN-593 Variants in Known Monogenic Causal Genes of Hypertriglyceridemia Are Not Major Contributors for Hypertriglyceridemia in Lipodystrophy Due to a LMNA Mutation

Background: Lipodystrophy is a heterogeneous disorder of adiposity, and one common lipid manifestation is hypertriglyceridemia (HTG). The LMNA gene, which encodes for nuclear envelope proteins, is a known causal gene for heritable lipodystrophy. At present, underlying mechanisms for each clinical manifestation of lipodystrophy due to a LMNA mutation are unknown. Hypothesis: A likely explanation for HTG in lipodystrophy is the paucity of adipose tissue where excess triglycerides (TGs) are normally stored, thus it may not be due to a specific defect in lipoprotein metabolism. Consequently, rare variants in HTG-associated genes would not be expected to be major contributors for HTG in lipodystrophy with LMNA mutations. Method: A proband and her father with a clinical diagnosis of lipodystrophy were recruited into an IRB-approved study investigating molecular etiologies of dyslipidemia at the University of Pennsylvania. Next-generation sequencing (NGS) with the LipidSeq panel, targeting causal genes for lipodystrophy, and monogenic HTG was performed, and confirmed by Sanger sequencing. Also, unweighted TG-polygenic scores by summing the number of TG-raising alleles from 14 single nucleotide polymorphisms (SNPs) associated with TG levels were assessed. Results: The proband and her father were diagnosed with lipodystrophy of two different subtypes, generalized in the daughter and partial in the father. The proband reported a gradual loss of subcutaneous fat starting around age 10. A highest reported TG in the proband was19,000 mg/dL with eruptive xanthomas, whereas TG in the father was never >500 mg/dL. Their BMI’s and DEXA body fat% were 12.9 kg/m2 and 7% in the proband, and 25.7 kg/m2 and 25% in the father, corresponding to their fat storage capacities.The molecular analyses revealed only a lipodystrophy causal mutation in LMNA, c.29C>T, T10I with no other significant findings in18 other lipodystrophy-related genes. No deletion or duplication was identified by a targeted array CGH of LMNA.As predicted, no rare monogenic variants in HTG-causal genes (LPL, GPIHBP1, APOA5, APOC2, LMF1, GPD1) were identified in either subject. However, TG-polygenic scores were 17/28 (95th %ile) in the proband, and 13/28 (50th %ile) in the father, the same trend as the level of HTG levels seen in them. Apolipoprotein E genotypes were non-contributory, (3/3) in the proband, and (3/4) in the father.Conclusion:Our findings support that the pathophysiology of HTG in lipodystrophy is likely to be due to lack of TG-storage space (adipose tissues), and is unlikely due to a defect in lipoprotein metabolism seen in patients with rare monogenic HTG-variants. Although the HTG-polygenic score was higher in the proband, and the accumulative effects of the at-risk alleles may be contributor to the HTG phenotype, it is unlikely to be the leading cause of severe HTG seen in the proband.

Genetic and functional studies of the LMF1 gene in Thai patients with severe hypertriglyceridemia

Severe hypertriglyceridemia (HTG) due to chylomicronemia is associated with acute pancreatitis and is related to genetic disturbances in several proteins involved in triglyceride (TG) metabolism. Lipase maturation factor 1 (LMF1) is a protein essential for the maturation of lipoprotein lipase (LPL). In this study, we examined the genetic spectrum of the LMF1 gene among subjects with severe HTG and investigated the functional significance of 6 genetic variants in vitro. All 11 exons of the LMF1 gene were sequenced in 101 Thai subjects with severe HTG. For an in vitro study, we performed site-directed mutagenesis, transient expression in cld cells, and measured LPL protein and LPL activity. We identified 2 common variants [p.(Gly36Asp) and p.(Pro562Arg)] and 12 rare variants [p.(Thr143Met), p.(Asn249Ser), p.(Ala287Val), p.(Met346Val), p.(Thr395Ile), p.(Gly410Arg), p.(Asp433Asn), p.(Asp491Asn), p.(Asn501Tyr), p.(Ala504Val), p.(Arg523His), and p.(Leu563Arg)] in 29 patients. In vitro study of the p.(Gly36Asp), p.(Asn249Ser), p.(Ala287Val), p.(Asn501Tyr), p.(Pro562Arg) and p.(Leu563Arg) variants, however, revealed that both LPL mass and LPL activity in each of the transfected cells were not significantly different from those in the wild type LMF1 transfected cells, suggesting that these variants might not play a significant role in severe HTG phenotype in our subjects.

The polygenic nature of mild-to-moderate hypertriglyceridemia

Patients with mild-to-moderate hypertriglyceridemia (HTG) are thought to share specific genetic susceptibility factors that are also present in patients with severe HTG, but no data have been reported on this issue. The objective of this study was to characterize genetic profiles of patients with mild-to-moderate HTG and compare them to patients with severe HTG. DNA from patients with mild-to-moderate HTG was sequenced using our targeted sequencing panel, "LipidSeq". For each patient, we assessed 1) rare variants disrupting five TG metabolism genes and 2) the accumulation of 16 common single-nucleotide polymorphisms (SNPs) using a polygenic risk score. The genetic profiles for these patients were then compared with normolipidemic controls from the 1000 Genomes Project and with patients with severe HTG. Across 134 patients with mild-to-moderate HTG, 9.0% carried heterozygous rare variants and 26.9% had an excess accumulation of common SNPs. Patients with mild-to-moderate HTG were 2.38 times (95% CI [1.13-4.99]; P=.021) more likely to carry a rare variant and 3.26 times (95% CI [2.02-5.26]; P<.0001) more likely to have an extreme polygenic risk score compared with the 1000 Genomes Project. In addition, patients with severe HTG were 1.86 times (95% CI [0.98-3.51]; P=.032) more likely to carry a rare variant and 1.63 times (95% CI [1.07-2.48]; P=.013) more likely to have an extreme polygenic risk score than patients with mild-to-moderate HTG. We report an increased prevalence of genetic determinants in patients with an increased severity of the HTG phenotype when considering either rare variants disrupting TG metabolism genes or an excess accumulation of common SNPs. As well, the findings confirm that the most prevalent genetic contributor to HTG, regardless of severity, is polygenic SNP accumulation.

Critical Role of SREBP-1c Large-VLDL Pathway in Environment-Induced Hypertriglyceridemia of Apo AV Deficiency.

Objective- APOA5 variants are strongly associated with hypertriglyceridemia, as well as increased risks of cardiovascular disease and acute pancreatitis. Hypertriglyceridemia in apo AV dysfunction often aggravates by environmental factors such as high-carbohydrate diets or aging. To date, the molecular mechanisms by which these environmental factors induce hypertriglyceridemia are poorly defined, leaving the high-risk hypertriglyceridemia condition undertreated. Previously, we reported that LXR (liver X receptor)-SREBP (sterol regulatory element-binding protein)-1c pathway regulates large-VLDL (very low-density lipoprotein) production induced by LXR agonist. However, the pathophysiological relevance of the finding remains unknown. Approach and Results- Here, we reconstitute the environment-induced hypertriglyceridemia phenotype of human APOA5 deficiency in Apoa5-/- mice and delineate the role of SREBP-1c in vivo by generating Apoa5-/- ;Srebp-1c-/- mice. The Apoa5-/- mice, which showed moderate hypertriglyceridemia on a chow diet, developed severe hypertriglyceridemia on high-carbohydrate feeding or aging as seen in patients with human apo AV deficiency. These responses were nearly completely abolished in the Apoa5-/- ;Srebp-1c-/- mice. Further mechanistic studies revealed that in response to these environmental factors, SREBP-1c was activated to increase triglyceride synthesis and to permit the incorporation of triglyceride into abnormally large-VLDL particles, which require apo AV for efficient clearance. Conclusions- Severe hypertriglyceridemia develops only when genetic factors (apo AV deficiency) and environmental effects (SREBP-1c activation) coexist. We demonstrate that the regulated production of large-sized VLDL particles via SREBP-1c determines plasma triglyceride levels in apo AV deficiency. Our findings explain the long-standing enigma of the late-onset hypertriglyceridemia phenotype of apo AV deficiency and suggest a new approach to treat hypertriglyceridemia by targeting genes that mediate environmental effects.

Characterization of lipoprotein profiles in patients with hypertriglyceridemic Fredrickson-Levy and Lees dyslipidemia phenotypes: the Very Large Database of Lipids Studies 6 and 7.

IntroductionThe association between triglycerides (TG) and cardiovascular diseases is complex. The classification of hypertriglyceridemic (HTG) phenotypes proposed by Fredrickson, Levy and Lees (FLL) helps inform treatment strategies. We aimed to describe levels of several lipoprotein variables from individuals with HTG FLL phenotypes from the Very Large Database of Lipids.Material and methodsWe included fasting samples from 979,539 individuals from a contemporary large study population of US adults. Lipids were directly measured by density-gradient ultracentrifugation using the Vertical Auto Profile test while TG levels were measured in whole plasma using the Abbott ARCHITECT C-8000 system. Hyperchylomicronemic (Hyper-CM) and non-chylomicronemic (non-CM) phenotypes were defined using computationally derived models. Individuals with FLL type IIa phenotype were excluded. Distributions of lipid variables were compared using medians and Kruskal-Wallis test.ResultsA total of 11.9% (n = 116,925) of individuals met criteria for HTG FLL phenotypes. Those with hyper-CM phenotypes (n = 5, < 0.1% of population) had two-fold higher TG levels compared with non-chylomicronemic (non-CM) individuals (11.9% of population) (p < 0.001). Type IIb individuals had the highest non-HDL-C levels (median 242 mg/dl). Cholesterol in large VLDL1+2 particles was higher than in small VLDL3 particles in all phenotypes except FLL type III. Hyper-CM phenotypes had significantly lower HDL-C levels but greater HDL2/HDL3-C ratio compared to non-CM phenotypes. Cholesterol content of the lipoprotein (a) peak was significantly higher in the hyper-CM groups compared to non-CM phenotypes (p < 0.0001).ConclusionsThis observational hypothesis-generating study provides insight into the complexity of lipid metabolism in HTG phenotypes, including less traditional lipid measures such as LDL density, HDL subclasses and Lp(a)-C.

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 Leprdb/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.

Clinical whole exome sequencing in severe hypertriglyceridemia

BackgroundLittle data exist regarding the clinical application of whole exome sequencing (WES) for the molecular diagnosis of severe hypertriglyceridemia (HTG). MethodsWES was performed for 28 probands exhibiting severe HTG (≥1000 mg/dl) without any transient causes. We evaluated recessive and dominant inheritance models in known monogenic HTG genes, followed by disease-network gene prioritization and copy number variation (CNV) analyses to identify causative variants and a novel genetic mechanism for severe HTG. ResultsWe identified possible causative variants for severe HTG, including three novel variants, in nine probands (32%). In the recessive inheritance model, we identified two homozygous subjects with lipoprotein lipase (LPL) deficiency and one subject harboring compound heterozygous variants in both LPL and APOA5 genes (hyperchylomicronemia). In the dominant inheritance model, we identified probands harboring deleterious heterozygous variants in LPL, glucokinase regulatory protein, and solute carrier family 25 member 40 genes, possibly associated with this extreme HTG phenotype. However, gene prioritization and CNV analyses did not validate the novel genes associated with severe HTG. ConclusionsIn 28 probands with severe HTG, we identified potential causative variants within nine genes associated with rare Mendelian dyslipidemias. Clinical WES may be feasible for such extreme cases, potentially leading to appropriate therapies.

The crucial roles of apolipoproteins E and C-III in apoB lipoprotein metabolism in normolipidemia and hypertriglyceridemia.

To describe the roles of apolipoprotein C-III (apoC-III) and apoE in VLDL and LDL metabolism ApoC-III can block clearance from the circulation of apolipoprotein B (apoB) lipoproteins, whereas apoE mediates their clearance. Normolipidemia is sustained by hepatic secretion of VLDL and IDL subspecies that contain both apoE and apoC-III (VLDL E+C-III+). Most of this VLDL E+C-III+ is speedily lipolyzed, reduced in apoC-III content, and cleared from the circulation as apoE containing dense VLDL, IDL, and light LDL. In contrast, in hypertriglyceridemia, most VLDL is secreted with apoC-III but without apoE, and so it is not cleared until it loses apoC-III during lipolysis to dense LDL. In normolipidemia, the liver also secretes IDL and large and medium-size LDL, whereas in hypertriglyceridemia, the liver secretes more dense LDL with and without apoC-III. These pathways establish the hypertriglyceridemic phenotype and link it metabolically to dense LDL. Dietary carbohydrate compared with unsaturated fat suppresses metabolic pathways mediated by apoE that are qualitatively similar to those suppressed in hypertriglyceridemia. The opposing actions of apoC-III and apoE on subspecies of VLDL and LDL, and the direct secretion of LDL in several sizes, establish much of the basic structure of human apoB lipoprotein metabolism in normal and hypertriglyceridemic humans.

Role of selective peroxisome proliferator‐activated receptor modulators in managing cardiometabolic disease: tale of a roller‐coaster

AbstractAtherogenic dyslipidaemia is a hypertriglyceridaemic phenotype, associated with increased plasma concentrations of small, dense low‐density lipoprotein (sdLDL) particles, triglyceride‐rich lipoproteins (TRLs) and non‐high‐density lipoprotein cholesterol (non‐HDL‐C), and low HDL particles. Atherogenic dyslipidaemia commonly accompanies several metabolic disorders including type 2 diabetes, metabolic syndrome, non‐alcoholic fatty liver disease (NAFLD) and obesity, and increases the risk of cardiovascular disease (CVD). Statins significantly lower plasma LDL‐cholesterol and CVD risk, but their efficacy in correcting hypertriglyceridaemia is limited. Untreated hypertriglyceridaemia may partly account for residual risk of CVD in patients on statin treatment. Activators of peroxisome proliferator‐activated receptor (PPAR) α are more effective in correcting TRL and HDL metabolism than statins. A dual PPARα/δ agonist (GFT‐505) may have additional benefits on hepatic insulin sensitivity, steatosis and fibrosis. Selective PPAR modulators (SPPARMs) have the potential of increasing therapeutic specificity, while reducing unwanted off‐target effects. This review provides a summary of findings from randomized controlled trials of the efficacy of fenofibrate (as the most widely used PPARα agonist) and novel selective PPARα (ABT‐335 and k‐877), PPARα/δ (GFT‐505), PPARδ (MBX‐8025 and GW501516) and PPARγ (INT131) agonists in the treatment of atherogenic dyslipidaemia and NAFLD.

Gene Transfer of Apolipoprotein A-V Improves the Hypertriglyceridemic Phenotype of apoa5 (−/−) mice

Apolipoprotein (apo) A-V is a low abundance protein with a profound influence on plasma triacylglycerol levels. In human populations, single nucleotide polymorphisms and mutations in APOA5 positively correlate with hypertriglyceridemia. As an approach to preventing the deleterious effects of chronic hypertriglyceridemia, apoA-V gene therapy has been pursued. Recombinant adeno-associated virus (AAV) 2/8 harboring the coding sequence for human apoA-V or a control AAV2/8 was transduced into hypertriglyceridemic apoa5 (-/-) mice. After injection of 1×10(12) viral genome AAV2/8-apoA-V, maximal plasma levels of apoA-V protein were achieved at 3 to 4 weeks, after which the concentration slowly declined. Complementing the appearance of apoA-V was a decrease (50±6%) in plasma triacylglycerol content compared with apoa5 (-/-) mice treated with AAV2/8-β-galactosidase. After 8 weeks the mice were euthanized and plasma lipoproteins separated. AAV2/8-apoA-V-transduced mice displayed a dramatic reduction in very low-density lipoprotein triacylglycerol content. Vector generated apoA-V in plasma associated with both very low-density lipoprotein and high-density lipoprotein fractions. Taken together, the data show that gene transfer of apoA-V improves the severe hypertriglyceridemia phenotype of apoa5 (-/-) mice. Given the prevalence of hypertriglyceridemia, apoA-V gene therapy offers a potential strategy for maintenance of plasma triacylglycerol homeostasis.

Mutations of the Apolipoprotein A5 Gene with Inherited Hypertriglyceridaemia: Review of the Current Literature

Apoliporotein A5 (APOA5), a member of the apolipoprotein family, plays a key regulatory role in triglyceride (TG) metabolism. Even though the exact biochemical background of its mechanism is not yet fully understood, diseases associated with this particular gene highlighted its key role in the metabolism of triglycerides in humans. Naturally occurring functional variants of the gene and their natural major haplotypes are known to associate with moderately elevated triglyceride levels, and are also known to confer risk or protection for major polygenic diseases, like coronary heart disease, stroke, or metabolic syndrome. On the other hand, case reports and even robust resequencing studies verified APOA5 mutations as underlying genetic defects behind extreme hypertriglyceridemic phenotype. Soon after the recognition of the first cases, there were indications which suggest the existence of less frequent genetic variants which, in combination with the common allelic variants of the gene, can define haplotypes that are associated with substantial triglyceride level increase. In addition, it became evident, that there are rare mutations of the APOA5 gene which can be associated with specific complex phenotypes and different types of hyperlipoproteinemia, which includes extremely high triglyceride levels with multiple organ pathology. These rare mutations may cause inheritable hypertriglyceridemia, but they presented at a low frequency and could not be captured by standard genotyping array screenings. The identification of new mutations still relies on the direct sequencing of APOA5 gene of patients with hypertriglyceridemia with an unusual pattern, individually or in huge resequencing studies.

Endoplasmic reticulum-tethered transcription factor cAMP responsive element-binding protein, hepatocyte specific, regulates hepatic lipogenesis, fatty acid oxidation, and lipolysis upon metabolic stress in mice

cAMP responsive element-binding protein, hepatocyte specific (CREBH), is a liver-specific transcription factor localized in the endoplasmic reticulum (ER) membrane. Our previous work demonstrated that CREBH is activated by ER stress or inflammatory stimuli to induce an acute-phase hepatic inflammation. Here, we demonstrate that CREBH is a key metabolic regulator of hepatic lipogenesis, fatty acid (FA) oxidation, and lipolysis under metabolic stress. Saturated FA, insulin signals, or an atherogenic high-fat diet can induce CREBH activation in the liver. Under the normal chow diet, CrebH knockout mice display a modest decrease in hepatic lipid contents, but an increase in plasma triglycerides (TGs). After having been fed an atherogenic high-fat (AHF) diet, massive accumulation of hepatic lipid metabolites and significant increase in plasma TG levels were observed in the CrebH knockout mice. Along with the hypertriglyceridemia phenotype, the CrebH null mice displayed significantly reduced body-weight gain, diminished abdominal fat, and increased nonalcoholic steatohepatitis activities under the AHF diet. Gene-expression analysis and chromatin-immunoprecipitation assay indicated that CREBH is required to activate the expression of the genes encoding functions involved in de novo lipogenesis, TG and cholesterol biosynthesis, FA elongation and oxidation, lipolysis, and lipid transport. Supporting the role of CREBH in lipogenesis and lipolysis, forced expression of an activated form of CREBH protein in the liver significantly increases accumulation of hepatic lipids, but reduces plasma TG levels in mice. All together, our study shows that CREBH plays a key role in maintaining lipid homeostasis by regulating the expression of the genes involved in hepatic lipogenesis, FA oxidation, and lipolysis under metabolic stress. The identification of CREBH as a stress-inducible metabolic regulator has important implications in the understanding and treatment of metabolic disease.

TOTAL ADIPONECTIN LEVELS IN DYSLIPIDEMIC INDIVIDUALS: RELATIONSHIP TO METABOLIC PARAMETERS AND INTIMA-MEDIA THICKNESS

Adiponectin is adipocytokin with anti-inflammatory and anti-atherogenic effects. However, studies examining the relationship between adiponectin and cardiovascular diseases have shown inconsistent results. The aim of this study was to evaluate the plasma levels of adiponectin in clinically asymptomatic subjects with various dyslipidemic phenotypes. The associations between adiponectin and risk factors for atherosclerosis, markers of insulin resistance, and the intima-media thickness of the common carotid artery (IMT) were also evaluated. 234 asymptomatic subjects were divided into four dyslipidemic phenotypes (DLP) according to apolipoprotein B (apoB) and triglycerides (TG): DLP1 (n=58, apoB<1.2 g/l and TG<1.5 mmol/l), DLP2 (n=47, apoB<1.2 g/l and TG≥1.5 mmol/l), DLP3 (n=31, apoB≥1.2 g/l and TG<1.5 mmol/l) and DLP4 (n=98, apoB≥1.2 g/l and TG≥1.5 mmol/l). DLP1 (normo-apoB/normo-TG) served as a control group. Significant differences in adiponectin levels between normolipidemic phenotype - DLP1 (16.1[10.3-20.8] mg/l) and hypertriglyceridemic phenotypes - DLP2 (9.5[6.8-13.0] mg/l, p<0.01) and DLP4 (10.1[7.4-16.8] mg/l, p<0.01) after adjustment for age, sex and body mass index were found. Adiponectin correlated positively with highdensity lipoprotein cholesterol and apolipoprotein A1 (apoA1), negatively with triglycerides, apoB/apoA1, highsensitivity C-reactive protein, insulin, homeostasis model assessment and waist circumference. ApoA1 and insulin were detected as independent predictors for adiponectin levels in multivariate regression analysis. Adiponectin did not correlate with IMT. Individuals with hypertriglyceridemic phenotypes showed decreased adiponectin levels in comparison with normolipidemic subjects. Adiponectin was associated with lipid parameters, markers of insulin resistance, chronic inflammation and visceral obesity. But no association between adiponectin and IMT was found.

Top Advances in Functional Genomics and Translational Biology for 2010

In recent years, major advances have been made in transcriptomics, metabolomics, proteomics, and particularly population genetics. More than 850 genome-wide association studies (GWAS) were published by the end of 2010, now covering a vast number of diseases and phenotypes and often incorporating tens of thousands of subjects or, in some cases, more than 100 000 subjects, increasing statistical power to identify and replicate contributing loci. Sequencing throughput advances and decreasing costs per sample have allowed the application of genome-wide genotyping and sequencing technology to larger DNA samples as well as transcriptome and epigenome features. This year was marked not only by continuing progress with GWAS, sequencing, and copy number variation studies but also by follow-up of GWAS and other findings with functional studies that uncover new molecular pathways contributing to disease and pave the way for future clinical applications. The American Heart Association Functional Genomics and Translational Biology Interdisciplinary Council (http://www.americanheart.org/presenter.jhtml?identifier=3016539) provides a forum for a multidisciplinary group of volunteers committed to making a substantial contribution to reduce the burden of heart disease and stroke through genetics, genomics, proteomics, and metabolomics research and translational science. With input from the Early Career Committee of the Council on Functional Genomics and Translational Biology, we considered many papers and selected 10 outstanding manuscript groups (15 articles) published in 2010 that reflect these advances, and we briefly summarize each below in chronological order.

Comparison of the efficacy of fibrates on hypertriglyceridemic phenotypes with different genetic and clinical characteristics

Hypertriglyceridemia is a frequent and heterogeneous clinical trait, which modulates the risk of disease. Fibrates constitute an effective class of triglyceride-lowering agents. To evaluate the effect of fibrates on fasting plasma triglycerides and other lipids levels in hypertriglyceridemia phenotypes with different genetic and clinical characteristics. This study included 146 fasting adults: 15 with lactescent plasma and severe hypertriglyceridemia (triglyceride ≥ 10 mmol/l) and 131 with clear plasma and moderate hypertriglyceridemia (2 ≤ triglycerides <10 mmol/l). Expost comparisons of the effect of fibrates on fasting triglycerides and other lipids were made using Student's paired two-tailed t-test. Response to these fibrates differed significantly across the studied hypertriglyceridemia subtypes: patients with severe hypertriglyceridemia because of lipoprotein lipase deficiency and those with moderate hypertriglyceridemia because of glycerol kinase deficiency did not respond at all, whereas patients with palmar xanthomas and severe or moderate hypertriglyceridemia because of apolipoprotein (apo) E resistance (type-III dysbetalipoproteinemia, most often associated with the apo E2 allele) responded significantly better (P<0.001) than all other subtypes on several lipid fractions. These results indicate that genetic factors known to contribute to the etiology and clinical expression of hypertriglyceridemia subtypes also modulate the response to triglyceride-lowering drugs.

Prothrombotic markers in asymptomatic dyslipidemic subjects

The aim of this study was to evaluate the plasma levels of prothrombotic markers--von Willebrand factor (vWF), plasminogen activator inhibitor-1 (PAI-1), tissue plasminogen activator (t-PA)--in asymptomatic subjects with dyslipidemia. Asymptomatic subjects with dyslipidemia and their relatives (n = 234) were assessed for lipids and prothrombotic markers. Individuals were divided into four dyslipidemic phenotypes (DLP) according to apolipoprotein B (apoB) and triglycerides (TG): DLP1 (n = 58, apoB < 1.2 g/l and TG < 1.5 mmol/l), DLP2 (n = 47, apoB < 1.2 g/l and TG ≥ 1.5 mmol/l), DLP3 (n = 31, apoB ≥ 1.2 g/l and TG < 1.5 mmol/l) and DLP4 (n = 98, apoB ≥ 1.2 g/l and TG ≥ 1.5 mmol/l). Associations between prothrombotic markers and risk factors for atherosclerosis, markers of insulin resistance, and the intima-media thickness of the common carotid artery (IMT) were assessed too. Significant differences in PAI-1 between normolipidemic phenotype--DLP1 (62.5 (35.9-82.9) ng/ml) and hypertriglyceridemic phenotypes--DLP2 (82.2 (61.1-122.1) ng/ml, p < 0.01) and DLP4 (91.4 (63.5-111.8) ng/ml, p < 0.001) after adjustment for age, sex and body mass index, were found. Levels of t-PA were different only between DLP1 and DLP4 (1.9 (0.9-3.3) ng/ml vs. 5.3 (2.5-8.6) ng/ml, p < 0.05). There were no significant differences of vWF between DLPs. PAI-1 and t-PA correlated with lipid parameters, markers of insulin resistance, blood pressure and obesity. VWF was independently associated with IMT, which was increased in DLP4. Individuals with hypertriglyceridemic phenotypes showed increased levels of PAI-1 in comparison with normolipidemic subjects. The elevation of t-PA was presented only in patients with simultaneously elevated TG and apoB. The significant increase of IMT confirmed in the patients with DLP4 reveals individuals with the highest risk for atherosclerosis manifestation.

Apolipoprotein A-V N-terminal Domain Lipid Interaction Properties in Vitro Explain the Hypertriglyceridemic Phenotype Associated with Natural Truncation Mutants

The N-terminal 146 residues of apolipoprotein (apo) A-V adopt a helix bundle conformation in the absence of lipid. Because similarly sized truncation mutants in human subjects correlate with severe hypertriglyceridemia, the lipid binding properties of apoA-V(1-146) were studied. Upon incubation with phospholipid in vitro, apoA-V(1-146) forms reconstituted high density lipoproteins 15-17 nm in diameter. Far UV circular dichroism spectroscopy analyses of lipid-bound apoA-V(1-146) yielded an alpha-helix secondary structure content of 60%. Fourier transformed infrared spectroscopy analysis revealed that apoA-V(1-146) alpha-helix segments align perpendicular with respect to particle phospholipid fatty acyl chains. Fluorescence spectroscopy of single Trp variant apoA-V(1-146) indicates that lipid interaction is accompanied by a conformational change. The data are consistent with a model wherein apoA-V(1-146) alpha-helices circumscribe the perimeter of a disk-shaped bilayer. The ability of apoA-V(1-146) to solubilize dimyristoylphosphatidylcholine vesicles at a rate faster than full-length apoA-V suggests that N- and C-terminal interactions in the full-length protein modulate its lipid binding properties. Preferential association of apoA-V(1-146) with murine plasma HDL, but not with VLDL, suggests that particle size is a determinant of its lipoprotein binding specificity. It may be concluded that defective lipoprotein binding of truncated apoA-V contributes to the hypertriglyceridemia phenotype associated with truncation mutations in human subjects.

Mutations inHFECausing Hemochromatosis Are Associated with Primary Hypertriglyceridemia

Most cases of primary hypertriglyceridemia (HTG) are caused by the interaction of unknown polygenes and environmental factors. Elevated iron storage is associated with metabolic syndrome, diabetes, and obesity, and all of them are associated with HTG. The aim of the study was to analyze whether HFE mutations causing hereditary hemochromatosis (HH) are associated with primary HTG. Genetic predisposition to HH was analyzed in a case-control study. The study was conducted at University Hospital Lipid Clinic. We studied two groups: 1) the HTG group, composed of 208 patients; and 2) the control group, composed of 215 normolipemic subjects and 161 familial hypercholesterolemia patients. Two HFE mutations (C282Y and H63D) were analyzed. We measured HH genetic predisposition difference between groups. HH genetic predisposition was 5.9 and 4.4 times higher in the HTG group than in the normolipemic (P = 0.02) and FH (P = 0.05) subjects, respectively. There were 35 cases (16.8%) of iron overload in the primary HTG group, 14 (6.5%) and nine (5.6%) in the normolipidemic and FH groups, respectively. A higher HH genetic predisposition and a different prevalence of iron overload in subjects with HH genetic predisposition among groups contributed to this higher prevalence. None of the four cases with the HFE genotype associated with high risk of HH in the control groups presented iron overload; however, in eight of 11 subjects (72.7%) with primary HTG and HH genetic predisposition, the iron overload was present. Mutations in HFE gene, favoring iron overload and causing HH, could play an important role in the development of several phenotypes of primary HTG.