Therapeutic Targets of Triglyceride Metabolism as Informed by Human Genetics

FADS Polymorphisms Affect the Clinical and Biochemical Phenotypes of Metabolic Syndrome

Long-chain polyunsaturated fatty acids (LC-PUFAs) play important roles in human health, from controlling inflammation to lipid and glucose homeostasis. In our previous study, which employed a cluster analysis of a plasma fatty acid (FA) pattern, we identified two clusters of metabolic syndrome (MetS) independent of clinical and biochemical parameters within the whole study group (controls together with metabolic syndrome (MetS) patients). FA desaturase (FADS) genes are the key regulators of LC-PUFA metabolism. The aim of this study was to analyze associations between FADS polymorphisms and clusters of MetS. The study group consisted of 188 controls and 166 patients with MetS. The first cluster contained 71 controls (CON1) and 109 MetS patients (MetS1). The second cluster consisted of 117 controls (CON2) and 57 MetS patients (MetS2). In comparison with MetS2, cluster MetS1 displayed a more adverse risk profile. Cluster CON1 had, in comparison with CON2, higher body weight and increased triacylglycerol levels (p < 0.05). We found that the FADS rs174537 (p < 0.001), rs174570 (p < 0.01), and rs174602 (p < 0.05) polymorphisms along with two inferred haplotypes had statistically significant genotype associations with the splitting of MetS into MetS1 and MetS2. Conversely, we observed no significant differences in the distribution of FADS polymorphisms between MetS and CON subjects, or between CON1 and CON2. These associations between FADS polymorphisms and two clusters of MetS (differing in waist circumference, HOMA-IR, lipolysis, and oxidative stress) implicate the important influence of genetic factors on the phenotypic manifestation of MetS.

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.

The Genetic Basis of Hypertriglyceridemia

PURPOSE OF REVIEW

Hypertriglyceridemia is a common dyslipidemia associated with an increased risk of cardiovascular disease and pancreatitis. Severe hypertriglyceridemia may sometimes be a monogenic condition. However, in the vast majority of patients, hypertriglyceridemia is due to the cumulative effect of multiple genetic risk variants along with lifestyle factors, medications, and disease conditions that elevate triglyceride levels. In this review, we will summarize recent progress in the understanding of the genetic basis of hypertriglyceridemia.

RECENT FINDINGS

More than 300 genetic loci have been identified for association with triglyceride levels in large genome-wide association studies. Studies combining the loci into polygenic scores have demonstrated that some hypertriglyceridemia phenotypes previously attributed to monogenic inheritance have a polygenic basis. The new genetic discoveries have opened avenues for the development of more effective triglyceride-lowering treatments and raised interest towards genetic screening and tailored treatments against hypertriglyceridemia. The discovery of multiple genetic loci associated with elevated triglyceride levels has led to improved understanding of the genetic basis of hypertriglyceridemia and opened new translational opportunities.

Rescue of Hepatic Phospholipid Remodeling Defectin iPLA2β-Null Mice Attenuates Obese but Not Non-Obese Fatty Liver

Polymorphisms of group VIA calcium-independent phospholipase A2 (iPLA₂β or PLA2G6) are positively associated with adiposity, blood lipids, and Type-2 diabetes. The ubiquitously expressed iPLA₂β catalyzes the hydrolysis of phospholipids (PLs) to generate a fatty acid and a lysoPL. We studied the role of iPLA₂β on PL metabolism in non-alcoholic fatty liver disease (NAFLD). By using global deletion iPLA₂β-null mice, we investigated three NAFLD mouse models; genetic Ob/Ob and long-term high-fat-diet (HFD) feeding (representing obese NAFLD) as well as feeding with methionine- and choline-deficient (MCD) diet (representing non-obese NAFLD). A decrease of hepatic PLs containing monounsaturated- and polyunsaturated fatty acids and a decrease of the ratio between PLs and cholesterol esters were observed in all three NAFLD models. iPLA₂β deficiency rescued these decreases in obese, but not in non-obese, NAFLD models. iPLA₂β deficiency elicited protection against fatty liver and obesity in the order of Ob/Ob › HFD » MCD. Liver inflammation was not protected in HFD NAFLD, and that liver fibrosis was even exaggerated in non-obese MCD model. Thus, the rescue of hepatic PL remodeling defect observed in iPLA₂β-null mice was critical for the protection against NAFLD and obesity. However, iPLA₂β deletion in specific cell types such as macrophages may render liver inflammation and fibrosis, independent of steatosis protection.

EDEM3 Modulates Plasma Triglyceride Level through Its Regulation of LRP1 Expression

Human genetics studies have uncovered genetic variants that can be used to guide biological research and prioritize molecular targets for therapeutic intervention for complex diseases. We have identified a missense variant (P746S) in EDEM3 associated with lower blood triglyceride (TG) levels in >300,000 individuals. Functional analyses in cell and mouse models show that EDEM3 deficiency strongly increased the uptake of very-low-density lipoprotein and thereby reduced the plasma TG level, as a result of up-regulated expression of LRP1 receptor. We demonstrate that EDEM3 deletion up-regulated the pathways for RNA and endoplasmic reticulum protein processing and transport, and consequently increased the cell surface mannose-containing glycoproteins, including LRP1. Metabolomics analyses reveal a cellular TG accumulation under EDEM3 deficiency, a profile consistent with individuals carrying EDEM3 P746S. Our study identifies EDEM3 as a regulator of blood TG, and targeted inhibition of EDEM3 may provide a complementary approach for lowering elevated blood TG concentrations.

Variants of Lipid-Related Genes in Adult Japanese Patients with Severe Hypertriglyceridemia

Aim: Hypertriglyceridemia is a type of dyslipidemia that contributes to atherosclerosis and coronary heart disease. Variants in lipoprotein lipase (LPL), apolipoprotein CII (APOC2), apolipoprotein AV (APOA5), glycosylphosphatidylinositol- anchored high-density lipoprotein-binding protein 1 (GPIHBP1), lipase maturation factor 1 (LMF1), and glucokinase regulator (GCKR) are responsible for hypertriglyceridemia. We investigated the molecular basis of severe hypertriglyceridemia in adult patients referred to the Clinical Laboratory at Fukuoka University Hospital.

Methods: Twenty-three adult patients with severe hypertriglyceridemia (> 1,000 mg/dL, 11.29 mmol/L) were selected. The coding regions of candidate genes were sequenced by next-generation sequencing. Forty-nine genes reportedly associated with hypertriglyceridemia were analyzed.

Results: In the 23 patients, we detected 70 variants: 28 rare and 42 common ones. Among the 28 rare variants with < 1% allele frequency, p.I4533L in APOB, p.M490I in MLXIPL, p.L152M in NCAN, and p.S264T in TIMD4 were novel. We did not observe single gene homozygous or compound heterozygous disease-causing rare variants in any of the 23 hypertriglyceridemia cases. However, in silico algorithms and previous reports indicated that five rare variants, APOA5 (p.T184S), GCKR (c.354 + 1G>A), LMF1 (p.G410R), and LRP1 (p.G813R; p.R2173Q), and seven common variants, APOA5 (pG185C), APOE (p.C130R; p.E262K/p.E263K), GCKR (p.V103M), GPIHBP1 (p.C14F), LRP1 (p.Y4054F), and MLXIPL (p.Q241H), can cause hypertriglyceridemia. However, all five disease-causing rare variants detected in this study were heterozygous.

Conclusions: The prevalence of disease-causing rare variants in candidate genes in severe hypertriglyceridemia patients was low. The major causes of severe hypertriglyceridemia were not single gene abnormalities, but involved multiple gene variations and environmental factors.

MicroRNA-205-5p Promotes Unstable Atherosclerotic Plaque Formation In Vivo

PURPOSE

Atherosclerosis is a narrowing of the arteries caused by plaque buildup. MicroRNAs (miRNAs) have been proposed to participate in the pathogenesis of atherosclerosis. Here, we aimed to investigate miR-205-5p's role in promoting atherosclerotic progression.

METHODS

Knock-in (KI) mice with human/murine miR-205-5p within the murine host gene for miR-205 (MIR205HG) were crossed with apolipoprotein E knockout (Apoe^-/-) mice. This miR-205KI Apoe^-/- murine model was employed to study the impact of miR-205-5p in Apoe^-/- mice susceptible to atherosclerotic plaque formation.

RESULTS

miR-205KI Apoe^-/-mice developed larger, more unstable plaques relative to their Apoe^-/- counterparts (0.45 vs. 0.26 mm², P < 0.001). miR-205KI Apoe^-/- mice exhibited lower serum levels of high-density lipoprotein cholesterol (HDL-C) (5.18 vs. 19.31 mg/dL, P < 0.001) and triglycerides (32.79 vs. 156.76 mg/dL, P < 0.001) with system-wide reversal of cholesterol transport. Macrophages derived from miR-205KI Apoe^-/- mice exhibited ~ 20% lowered cholesterol efflux capability with enhanced pro-inflammatory gene expression through lipid raft formation. Bone marrow transplantation demonstrated that bone marrow (BM) donor cells with miR-205-5pKI simulated plaque formation independent of the recipients' miR-205-5p status.

CONCLUSIONS

miR-205-5p encourages unstable atherogenesis in vivo. miR-205-5p also adversely influences lipid metabolism and promotes a pro-inflammatory macrophage phenotype. Our findings advocate miR-205-5p as a potential therapeutic target for combating unstable atherogenesis.

Fragment-based design of small molecule PCSK9 inhibitors using simulated annealing of chemical potential simulations

PCSK9 is a protein secreted by the liver that binds to the low-density lipoprotein receptor (LDLR), causing LDLR internalization, decreasing the clearance of circulating LDL particles. Mutations in PCSK9 that strengthen its interactions with LDLR result in familial hypercholesterolemia (FH) and early onset atherosclerosis, while nonsense mutations of PCSK9 result in cardio-protective hypocholesterolemia. These observations led to PCSK9 inhibition for cholesterol lowering becoming a high-interest therapeutic target, with antibody drugs reaching the market. An orally-available small molecule drug is highly desirable, but inhibiting the PCSK9/LDLR protein-protein interaction (PPI) has proven challenging. Alternate approaches to finding good lead candidates are needed. Motivated by the FH mutation data on PCSK9, we found that modeling the PCSK9/LDLR interface revealed extensive electron delocalization between and within the protein partners. Based on this, we hypothesized that compounds assembled from chemical fragments could achieve the affinity required to inhibit the PCSK9/LDLR PPI if they were selected to interact with PCSK9 in a way that, like LDLR, also involves significant fractional charge transfer to form partially covalent bonds. To identify such fragments, Simulated Annealing of Chemical Potential (SACP) fragment simulations were run on multiple PCSK9 structures, using optimized partial charges for the protein. We designed a small molecule, composed of several fragments, predicted to interact at two sites on the PCSK9. This compound inhibits the PPI with 1 μM affinity. Further, we designed two similar small molecules where one allows charge delocalization though a linker and the other doesn’t. The first inhibitor with charge delocalization enhances LDLR surface expression by 60% at 10 nM, two orders of magnitude more potent than the EGF domain of LDLR. The other enhances LDLR expression by only 50% at 1 μM. This supports our conjecture that fragments can have surprisingly outsized efficacy in breaking PPI’s by achieving fractional charge transfer leading to partially covalent bonding.

Effects of APOC3 Heterozygous Deficiency on Plasma Lipid and Lipoprotein Metabolism

Objective- Apo (apolipoprotein) CIII inhibits lipoprotein lipase (LpL)-mediated lipolysis of VLDL (very-low-density lipoprotein) triglyceride (TG) and decreases hepatic uptake of VLDL remnants. The discovery that 5% of Lancaster Old Order Amish are heterozygous for the APOC3 R19X null mutation provided the opportunity to determine the effects of a naturally occurring reduction in apo CIII levels on the metabolism of atherogenic containing lipoproteins. Approach and Results- We conducted stable isotope studies of VLDL-TG and apoB100 in 5 individuals heterozygous for the null mutation APOC3 R19X (CT) and their unaffected (CC) siblings. Fractional clearance rates and production rates of VLDL-TG and apoB100 in VLDL, IDL (intermediate-density lipoprotein), LDL, apo CIII, and apo CII were determined. Affected (CT) individuals had 49% reduction in plasma apo CIII levels compared with CCs ( P<0.01) and reduced plasma levels of TG (35%, P<0.02), VLDL-TG (45%, P<0.02), and VLDL-apoB100 (36%, P<0.05). These changes were because of higher fractional clearance rates of VLDL-TG and VLDL-apoB100 with no differences in production rates. CTs had higher rates of the conversion of VLDL remnants to LDL compared with CCs. In contrast, rates of direct removal of VLDL remnants did not differ between the groups. As a result, the flux of apoB100 from VLDL to LDL was not reduced, and the plasma levels of LDL-cholesterol and LDL-apoB100 were not lower in the CT group. Apo CIII production rate was lower in CTs compared with CCs, whereas apo CII production rate was not different between the 2 groups. The fractional clearance rates of both apo CIII and apo CII were higher in CTs than CCs. Conclusions- These studies demonstrate that 50% reductions in plasma apo CIII, in otherwise healthy subjects, results in a significantly higher rate of conversion of VLDL to LDL, with little effect on direct hepatic uptake of VLDL. When put in the context of studies demonstrating significant protection from cardiovascular events in individuals with loss of function variants in the APOC3 gene, our results provide strong evidence that therapies which increase the efficiency of conversion of VLDL to LDL, thereby reducing remnant concentrations, should reduce the risk of cardiovascular disease.

SREBF1/MicroRNA-33b Axis Exhibits Potent Effect on Unstable Atherosclerotic Plaque Formation In Vivo

Objective- Atherosclerosis is a common disease caused by a variety of metabolic and inflammatory disturbances. MicroRNA (miR)-33a within SREBF2 (sterol regulatory element-binding factor 2) is a potent target for treatment of atherosclerosis through regulating both aspects; however, the involvement of miR-33b within SREBF1 remains largely unknown. Although their host genes difference could lead to functional divergence of miR-33a/b, we cannot dissect the roles of miR-33a/b in vivo because of lack of miR-33b sequences in mice, unlike human. Approach and Results- Here, we analyzed the development of atherosclerosis using miR-33b knock-in humanized mice under apolipoprotein E-deficient background. MiR-33b is prominent both in human and mice on atheroprone condition. MiR-33b reduced serum high-density lipoprotein cholesterol levels and systemic reverse cholesterol transport. MiR-33b knock-in macrophages showed less cholesterol efflux capacity and higher inflammatory state via regulating lipid rafts. Thus, miR-33b promotes vulnerable atherosclerotic plaque formation. Furthermore, bone marrow transplantation experiments strengthen proatherogenic roles of macrophage miR-33b. Conclusions- Our data demonstrated critical roles of SREBF1-miR-33b axis on both lipid profiles and macrophage phenotype remodeling and indicate that miR-33b is a promising target for treating atherosclerosis.

Association of the ESR1 polymorphism with menopause and MLXIPL genetic variant influence serum uric acid levels in Slovak midlife women

OBJECTIVE

This study examines associations between the ESR1 (XbaI, PvuII) and the MLXIPL (rs3812316) gene polymorphisms, and uric acid (UA) levels in Slovak midlife women, subdivided according to their menopause status.

METHODS

We assessed a total of 362 women from 38 to 65 years of age. Women were recruited from different localities in the western and middle parts of Slovakia. Participants were interviewed during their medical examination at local health centers. They were investigated with respect to a variety of aspects such as medical, anthropometrical, and lifestyle. Participants provided a blood sample for biochemical analyses and DNA genotyping. The MLXIPL gene (rs3812316 SNP variant) and ESR1 gene (PvuII and XbaI) genotypes were then detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Data were analyzed using general linear models and multiple linear regression analyses to adjust for risk factors elevating the UA level such as fat mass (FM), triglycerides (TGs) and creatinine.

RESULTS

A positive association between MLXIPL and UA level was observed in the total sample of women after control for confounding covariates, including FM, TGs, and creatinine (P = 0.027). Women with the CC genotype had higher UA levels than the G-allele carriers (261.5 μmol/L ± 68.3 vs 241.1 μmol/L ± 55.1 P = 0.013). A statistically significant association was noticed between postmenopause status and the ESR1 XbaI genotype and their effect on UA (P = 0.028). The Bonferroni pairwise comparison determined that the G-allele carriers in the postmenopausal period had higher estimated UA marginal mean (269.7 μmol/L) than the AA-allele postmenopausal women (236.5 μmol/L) (P = 0.012). The estimated UA marginal mean showed a significant increasing trend according to the MS in G allele carriers (248.5 μmol/L in pre/peri-menopausal vs 269.7 μmol/L in postmenopausal, P = 0.009). In contrast, a decreasing trend was observed in AA carriers (250.6 μmol/L in pre/perimenopausal women vs 236.5 μmol/L in postmenopausal). However, this trend was not statistically significant (P = 0.288).

CONCLUSIONS

This cross-sectional study suggests that MLXIPL (rs3812316) polymorphism is associated with higher serum UA levels and that the ESR1 (XbaI) polymorphism is associated with UA levels only in the postmenopausal cohort.

The Use of Risk Enhancing Factors to Personalize ASCVD Risk Assessment: Evidence and Recommendations from the 2018 AHA/ACC Multi-society Cholesterol Guidelines

PURPOSE OF REVIEW

In 2018, the AHA/ACC multi-society Cholesterol Guidelines introduced the novel concept of risk-enhancing factors to be used as a supplement to the pooled cohort risk equations to personalize atherosclerotic cardiovascular disease risk assessment in primary prevention. In this review, we discuss the rationale and evidence behind each of the risk- enhancing factors to help clinicians perform a more personalized cardiovascular risk assessment.

RECENT FINDINGS

The risk-enhancing factors are high-risk features that may guide the use of lipid-lowering therapy particularly in intermediate and select borderline risk patients. For the purpose of this review, these factors are divided into 5 categories: (i) race and genetics, (ii) conditions specific to women (iii) lipid related risk, (iv) concurrent high-risk medical conditions, and (v) biomarkers.

SUMMARY

The addition of the risk-enhancing factors to the pooled cohort equations provides a more individualized and comprehensive approach to cardiovascular disease risk assessment.

IGF1 Gene Is Associated With Triglyceride Levels In Subjects With Family History Of Hypertension From The SAPPHIRe And TWB Projects

Chromosome 12q23-q24 has been linked to triglyceride (TG) levels by previous linkage studies, and it contains the Insulin-like growth factor 1 (IGF1) gene. We investigated the association between IGF1 and TG levels using two independent samples collected in Taiwan. First, based on 954 siblings in 397 families from the Stanford Asian Pacific Program in Hypertension and Insulin Resistance (SAPPHIRe), we found that rs978458 was associated with TG levels (β = -0.049, p = 0.0043) under a recessive genetic model. Specifically, subjects carrying the homozygous genotype of the minor allele had lower TG levels, compared with other subjects. Then, a series of stratification analyses in a large sample of 13,193 unrelated subjects from the Taiwan biobank (TWB) project showed that this association appeared in subjects with a family history (FH) of hypertension (β = -0.045, p = 0.0000034), but not in subjects without such an FH. A re-examination of the SAPPHIRe sample confirmed that this association appeared in subjects with an FH of hypertension (β = -0.068, p = 0.0025), but not in subjects without an FH. The successful replication in two independent samples indicated that IGF1 is associated with TG levels in subjects with an FH of hypertension in Taiwan.

Associations between LPL gene polymorphisms and coronary artery disease: evidence based on an updated and cumulative meta-analysis

Lipoprotein lipase (LPL) is widely linked to lipid and lipoprotein metabolism, but its effects on coronary artery disease (CAD) are not clearly elucidated. The aim of this study was to clarify the association between LPL gene polymorphisms and CAD susceptibility. The pooled odds ratio (OR) and 95% confidence interval (CI) were calculated to estimate the strength of the relationship between LPL gene polymorphisms and CAD risk. Comprehensive electronic databases, including PubMed, EMBASE, Web of Science, and the Cochrane Library, were systematically searched. A total of 45 records containing 80 eligible studies were analyzed. The results indicated an increased risk between the LPL D9N polymorphism and susceptibility to CAD in the dominant genetic model (AA + GA vs. GG: OR = 1.46, 95% CI = 1.14-1.87), whereas the LPL HindIII polymorphism showed a protective effect against CAD under all tested models (GG+GT vs. TT: OR = 0.85, 95% CI = 0.75-0.97; GG vs. TT + TG: OR = 0.62, 95% CI = 0.47-0.83; G vs. T: OR = 0.81, 95% CI = 0.71-0.92). No significant association was identified for the LPL N291S and PvuII polymorphisms. Stratification analysis by ethnicity suggested a significant correlation between the LPL S447X polymorphism and CAD susceptibility in Caucasians under the dominant and allele genetic models. In summary, our meta-analysis indicated that the LPL D9N polymorphism was associated with an increased risk of CAD, whereas the S447X and HindIII polymorphisms showed protective effects. There was no association observed between the N291S and PvuII polymorphisms and CAD risk.

Hypertriglyceridemia and atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death and it has been confirmed that increased low density lipoprotein cholesterol (LDL-C) is an independent risk factor for atherosclerosis. Recently, the increasing evidence has showed that hypertriglyceridemia is associated with incremental ASCVD risk. But the proatherogenic mechanism of triglyceride (TG) remains unclear. Therefore, this article focuses on the clinical studies and proatherogenic mechanism related to hypertriglyceridemia, in order to provide reference for the prevention and treatment of ASCVD.

Adiposity and Genetic Factors in Relation to Triglycerides and Triglyceride-Rich Lipoproteins in the Women's Genome Health Study

BACKGROUND

Previous results from Scandinavian cohorts have shown that obesity accentuates the effects of common genetic susceptibility variants on increased triglycerides (TG). Whether such interactions are present in the US population and further selective for particular TG-rich lipoprotein subfractions is unknown.

METHODS

We examined these questions using body mass index (BMI) and waist circumference (WC) among women of European ancestry from the Women's Genome Health Study (WGHS) (n = 21840 for BMI; n = 19313 for WC). A weighted genetic risk score (TG-wGRS) based on 40 published TG-associated single-nucleotide polymorphisms was calculated using published effect estimates.

RESULTS

Comparing overweight (BMI ≥ 25 kg/m²) and normal weight (BMI < 25 kg/m²) WGHS women, each unit increase of TG-wGRS was associated with TG increases of 1.013% and 1.011%, respectively, and this differential association was significant (P_interaction = 0.014). Metaanalyses combining results for WGHS BMI with the 4 Scandinavian cohorts (INTER99, HEALTH2006, GLACIER, MDC) (total n = 40026) yielded a more significant interaction (P_interaction = 0.001). Similarly, we observed differential association of the TG-wGRS with TG (P_interaction = 0.006) in strata of WC (<80 cm vs ≥80 cm). Metaanalysis with 2 additional cohorts reporting WC (INTER99 and HEALTH2006) (total n = 27834) was significant with consistent effects (P_interaction = 0.006). We also observed highly significant interactions of the TG-wGRS across the strata of BMI with very large, medium, and small TG-rich lipoprotein subfractions measured by nuclear magnetic resonance spectroscopy (all P_interactions < 0.0001). The differential effects were strongest for very large TG-rich lipoprotein.

CONCLUSIONS

Our results support the original findings and suggest that obese individuals may be more susceptible to aggregated genetic risk associated with common TG-raising alleles, with effects accentuated in the large TG-rich lipoprotein subfraction.

ANGPTL3 serum concentration and rare genetic variants in Finnish population

Genetic variants of angiopoietin-like protein 3 (ANGPTL3) are associated with serum triglyceride (TG) and low-density lipoprotein cholesterol (LDL-C) concentration in GWASs. ANGPTL3 deficiency causes declined TG, total cholesterol (TC), LDL-C, high-density lipoprotein cholesterol (HDL-C), apolipoprotein B (apoB) and apolipoprotein A-I (apoA-I) serum concentration, a phenotype defined as familial combined hypolipidaemia (FHBL2). Our aim is to establish whether ANGPTL3 serum protein concentration correlates with lipoproteins and lipids in hyper- or hypolipidaemic subjects, and whether ANGPTL3 sequence variants are associated with untypical lipid profiles. Additionally, 10 subjects with very low lipoprotein concentrations were sequenced for ANGPTL3 for possible loss-of-function (LOF) variants. Study subjects were selected from Finnish FINRISK and Health 2000 surveys. ANGPTL protein concentrations were measured by ELISA method. As a result, ANGPTL3 serum concentration correlated positively with age, phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) activities, but not with any of the lipid or lifestyle attributes. No ANGPTL3 variants were found among sequenced samples. Subjects who carried ANGPTL3 sequence variants rs12563308 (n = 4) and rs199772471 (n = 1) had abnormally high TC and LDL-C concentrations. Whole exome sequencing data of these five subjects were further analyzed for rare and deleterious missense variants in genes associated with cholesterol metabolism. In conclusion, ANGPTL3 serum protein concentration did not predict lipid concentrations, unlike apolipoprotein C-III (apoC-III) which positively correlated with most of the lipid attributes. ANGPTL3 variant screen yielded five carriers with abnormally high TC concentration; the actual genetic causality, however, could not be verified.

Brain lipoprotein lipase as a regulator of energy balance

The central nervous system is an essential actor in the control of the energy balance. Indeed, many signals of nervous (vagal afferent for example) or circulating (hormone, nutrients) origin converge towards the brain to inform it permanently of the energetic status of the organism. In turn, the brain sends information to the periphery (sympathetic vagal balance, thyroid or corticotropic axis) which allows a fine regulation of the energy fluxes by acting on the hepatic glucose production, the secretion of the pancreatic hormones (glucagon, insulin) or food behavior. Among the nutrients, increasing amount of data assigns a signal molecule role to lipids such as fatty acids. These fatty acids may originate from the bloodstream but may also be the product of the hydrolysis of lipoproteins such as chylomicrons or VLDLs. Indeed, the identification of lipoprotein lipase (LPL) in the brain has led to the hypothesis that the LPL-dependent degradation of TG-enriched particles, and the addition of fatty acids, as informative molecules, to sensitive cells (neurons and/or astrocytes), plays a key role in maintaining the energy balance at equilibrium. Other lipases could also participate in these regulatory mechanisms. This review will summarize the state of the art and open up perspectives.

Shunts, channels and lipoprotein endosomal traffic: a new model of cholesterol homeostasis in the hepatocyte

The liver directs cholesterol metabolism in the organism. All the major fluxes of cholesterol within the body involve the liver: dietary cholesterol is directed to the liver; cholesterol from peripheral cells goes to the liver; the liver is a major site of cholesterol synthesis for the organism; cholesterol is secreted from the liver within the bile, within apoB lipoproteins and translocated to nascent HDL. The conventional model of cholesterol homeostasis posits that cholesterol from any source enters a common, rapidly exchangeable pool within the cell, which is in equilibrium with a regulatory pool. Increased influx of cholesterol leads rapidly to decreased synthesis of cholesterol. This model was developed based on in vitro studies in the fibroblast and validated only for LDL particles. The challenges the liver must meet in vivo to achieve cholesterol homeostasis are far more complex. Our model posits that the cholesterol derived from three different lipoproteins endosomes has three different fates: LDL-derived cholesterol is largely recycled within VLDL with most of the cholesterol shunted through the hepatocyte without entering the exchangeable pool of cholesterol; high density lipoprotein-derived CE is transcytosed into bile; and chylomicron remnant-derived cholesterol primarily enters the regulatory pool within the hepatocyte. These endosomal channels represent distinct physiological pathways and hepatic homeostasis represents the net result of the outcomes of these distinct channels. Our model takes into account the distinct physiological challenges the hepatocyte must meet, underlie the pathophysiology of many of the apoB dyslipoproteinemias and account for the sustained effectiveness of therapeutic agents such as statins.

Triglycerides Revisited to the Serial

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

Genetic and Environmental Biomarkers Associated with Triglyceride Levels in Two Groups of Slovak Women

OBJECTIVE

This study analyzed the association between the MLXIPL gene polymorphism (rs3812316) and triglyceride (TG) levels and selected environmental biomarkers in Slovak women at risk for cardiovascular disease compared to a reference sample.

MATERIALS AND METHODS

The studied sample consisted of 200 women at cardiovascular risk (mean age 52.96 ± 6.01 years) and 244 healthy women (mean age 47.52 ± 5.34 years). Participants gave details of their health and lifestyle during their medical examination, and peripheral blood samples were used for biochemical analyses and DNA genotyping. A nested polymerase chain reaction-restriction fragment length polymorphism assay was used to detect the rs 3812316 SNP.

RESULTS

We determined that there were significantly different genotype distributions in two TG categories: (1) subjects with normal TG values had a significantly higher G allele frequency than those with elevated TG levels (χ² = 6.1556, df = 2, p = 0.046); and (2) the rare G allele frequency was 0.11 in the cardiovascular risk group and 0.15 in the reference group. Binary regression analysis showed that women with at least one G allele had a significantly lower relative risk of hypertriglyceridemia than women with the CC genotype (OR = 0.399, p = 0.022, 95% CI = 0.182-0.876).

CONCLUSION

This cross-sectional study suggests that MLXIPL rs3812316 genotypes may be associated with TG levels. However, further analysis is advisable because of study limitations.