Dysbetalipoproteinaemia: a mixed hyperlipidaemia of remnant lipoproteins due to mutations in apolipoprotein E

Evaluation of biochemical algorithms to screen dysbetalipoproteinemia in ε2ε2 and rare APOE variants carriers

OBJECTIVES

Dysbetalipoproteinemia (DBL) is a combined dyslipidemia associated with an increased risk of atherosclerotic cardiovascular diseases mostly occurring in ε2ε2 subjects and infrequently in subjects with rare APOE variants. Several algorithms have been proposed to screen DBL. In this work, we compared the diagnostic performances of nine algorithms including a new one.

METHODS

Patients were divided into 3 groups according to their APOE genotype: ε2ε2 ("ε2ε2", n=49), carriers of rare variants ("APOEmut", n=20) and non-carriers of ε2ε2 nor APOE rare variant ("controls", n=115). The algorithms compared were those from Fredrickson, Sniderman, Boot, Paquette, De Graaf, Sampson, eSampson, Bea and ours, the "Hospices Civils de Lyon (HCL) algorithm". Our gold standard was the presence of a ε2ε2 genotype or of a rare variant associated with triglycerides (TG) >1.7 mmol/L. A replication in the UK Biobank and a robustness analysis were performed by considering only subjects with both TG and low-density lipoprotein-cholesterol (LDLc) >90th percentile.

RESULTS

Total cholesterol (TC)/ApoB and NHDLC/ApoB are the best ratios to suspect DBL. In ε2ε2, according to their likelihood ratios (LR), the most clinically efficient algorithms were the HCL, Sniderman and De Graaf's. In APOEmut, Sniderman's algorithm exhibited the lowest negative LR (0.07) whereas the HCL's exhibited the highest positive LR (29). In both cohorts, the HCL algorithm had the best LR.

CONCLUSIONS

We proposed a powerful algorithm based on ApoB concentration and the routine lipid profile, which performs remarkably well in detecting ε2ε2 or APOE variant-related DBL. Additional studies are needed to further evaluate algorithms performances in DBL carriers of infrequent APOE variants.

Applicability of Diagnostic Criteria and High Prevalence of Familial Dysbetalipoproteinemia in Russia: A Pilot Study

Familial dysbetalipoproteinemia (FD) is a highly atherogenic genetically based lipid disorder with an underestimated actual prevalence. In recent years, several biochemical algorithms have been developed to diagnose FD using available laboratory tests. The practical applicability of FD diagnostic criteria and the prevalence of FD in Russia have not been previously assessed. We demonstrated that the diagnostic algorithms of FD, including the diagnostic apoB levels, require correction, taking into account the distribution of apoB levels in the population. At the same time, a triglycerides cutoff ≥ 1.5 mmol/L may be a useful tool in identifying subjects with FD. In this study, a high prevalence of FD was detected: 0.67% (one in 150) based on the ε2ε2 haplotype and triglycerides levels ≥ 1.5 mmol/L. We also analyzed the presence and pathogenicity of APOE variants associated with autosomal dominant FD in a large research sample.

Polygenic risk in Type III hyperlipidaemia and risk of cardiovascular disease: An epidemiological study in UK Biobank and Oxford Biobank

BACKGROUND

Type III hyperlipidaemia (T3HL) is characterised by equimolar increases in plasma triglycerides (TG) and cholesterol in <10% of APOE22 carriers conveying high cardiovascular disease (CVD) risk. We investigate the role of a weighted triglyceride-raising polygenic score (TG.PS) precipitating T3HL.

METHODS

The TG.PS (restricted to genome-wide significance and weighted by published independent effect estimates) was applied to the Oxford Biobank (OBB, n = 6952) and the UK Biobank (UKB, n = 460,037), to analyse effects on plasma lipid phenotypes. Fasting plasma lipid, lipoprotein biochemistry and NMR lipoprotein profiles were analysed in OBB. CVD prevalence/incidence was examined in UKB.

RESULTS

One TG.PS standard-deviation (SD) was associated with 13.0% (95% confidence-interval 12.0-14.0%) greater TG in OBB and 15.2% (15.0-15.4%) in UKB. APOE22 carriers had 19.0% (1.0-39.0%) greater TG in UKB. Males were more susceptible to TG.PS effects (4.0% (2.0-6.0%) greater TG with 1 TG.PS SD in OBB, 1.6% (1.3-1.9%) in UKB) than females. There was no interaction between APOE22 and TG.PS, BMI, sex or age on TG. APOE22 carriers had lower apolipoprotein B (apoB) (OBB; -0.35 (-0.29 to -0.40)g/L, UKB; -0.41 (-0.405 to -0.42)g/L). NMR lipoprotein lipid concentrations were discordant to conventional biochemistry in APOE22 carriers. In APOE22 compared with APOE33, CVD was no more prevalent in similarly hypertriglyceridaemic participants (OR 0.97 95%CI 0.76-1.25), but was less prevalent in normolipidaemia (OR 0.81, 95%CI 0.69-0.95); no differences were observed in CVD incidence.

CONCLUSIONS

TG.PS confers an additive risk for developing T3HL, that is of comparable effect size to conventional risk factors. The protective effect of APOE22 for prevalent CVD is consistent with lower apoB in APOE22 carriers.

Low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol measurement in Familial Dysbetalipoproteinemia

AIM

To compare LDL-C concentrations using the Friedewald formula, the Martin-Hopkins formula, a direct assay and polyacrylamide gradient gel electrophoresis (PGGE) to the reference standard density gradient ultracentrifugation in patients with Familial Dysbetalipoproteinemia (FD) patients. We also compared non-HDL-cholesterol concentrations by two methods.

METHODS

For this study data from 28 patients with genetically confirmed FD from the placebo arm of the EVOLVE-FD trial were used. Four different methods for determining LDL-C were compared with ultracentrifugation. Non-HDL-C was measured with standard assays and compared to ultracentrifugation. Correlation coefficients and Bland-Altman plots were used to compare the methods.

RESULTS

Mean age of the 28 FD patients was 62 ± 9 years, 43 % were female and 93 % had an ɛ2ɛ2 genotype. LDL-C determined by Friedewald (R² = 0.62, p <0.01), Martin-Hopkins (R² = 0.50, p = 0.01) and the direct assay (R² = 0.41, p = 0.03) correlated with density gradient ultracentrifugation. However, Bland-Altman plots showed considerable over- or underestimation by the four methods compared to ultracentrifugation. Non-HDL-C showed good correlation and agreement.

CONCLUSION

In patients with FD, all four methods investigated over- or underestimated LDL-C concentrations compared with ultracentrifugation. In contrast, standard non-HDL-C assays performed well, emphasizing the use of non-HDL-C in patients with FD.

Palmar striated xanthomas in clinical practice

Introduction

The aim of this study was to assess the occurrence of palmar striated xanthomas (PSX) in a wide spectrum of lipid disorders ranging from very severe hypercholesterolemia (homozygous familial hypercholesterolemia) to very severe hypertriglyceridemia (chylomicronemia).

Methods

This study involved 3,382 dyslipidemic Caucasian adult patients (1,856 men and 1,526 women) seen at the Chicoutimi Hospital Lipid Clinic (Quebec, Canada), covering a wide range of lipid disorders, from severe hypertriglyceridemia to severe hypercholesterolemia. Categorical variables were compared using the Pearson χ2 statistic, whereas univariate analysis of variance (ANOVA) or nonparametric Kruskal-Wallis were used for continuous variables.

Results

A total of 5.1% (173/3382) of the studied patients presented PSX, a majority of them (67.1%) being women. PSX were observed in 18.8% of patients with dysbetalipoproteinemia and also among 14.1% of hypertriglyceridemic patients with partial lipoprotein lipase deficiency, 3.7% of patients with chylomicronemia and in all of those with homozygous familial hypercholesterolemia. Overall, 10.7% of patients with PSX did not meet dysbetalipoproteinemia diagnosis criteria.

Conclusion

According to our study, the PSX prevalence estimate among patients without dysbetalipoproteinemia would be around 10% and they could be observed in a wide spectrum of lipid disorders associated with recurrent or sustained remnant lipoprotein accumulation.

Genetic Regulatory Networks of Apolipoproteins and Associated Medical Risks

Apolipoproteins (APO proteins) are the lipoprotein family proteins that play key roles in transporting lipoproteins all over the body. There are nearly more than twenty members reported in the APO protein family, among which the A, B, C, E, and L play major roles in contributing genetic risks to several disorders. Among these genetic risks, the single nucleotide polymorphisms (SNPs), involving the variation of single nucleotide base pairs, and their contributing polymorphisms play crucial roles in the apolipoprotein family and its concordant disease heterogeneity that have predominantly recurred through the years. In this review, we have contributed a handful of information on such genetic polymorphisms that include APOE, ApoA1/B ratio, and A1/C3/A4/A5 gene cluster-based population genetic studies carried throughout the world, to elaborately discuss the effects of various genetic polymorphisms in imparting various medical conditions, such as obesity, cardiovascular, stroke, Alzheimer's disease, diabetes, vascular complications, and other associated risks.

Familial dysbetalipoproteinemia: highly atherogenic and underdiagnosed disorder

Familial dysbetalipoproteinemia (FD) is a genetic, highly atherogenic disorder. The penetrance of FD depends on the patient’s lifestyle and concomitant diseases. Despite the fact that FD was described almost half a century ago, it is still insufficiently studied and is extremely rarely diagnosed. In actual clinical practice, physicians do not have clear understanding of clinical course and genetic basis of FD. The aim was to present the most complete, but at the same time a critical review with a modern view on FD. We analyzed Russian and foreign publications from following electronic databases: PubMed, eLIBRARY, Google Scholar. As a result, the phenotypic features and genetic variability of the disease were considered and the main issues of diagnosis and treatment of patients with FD were discussed. The data presented will help the clinician to timely suspect the FD, conduct a full range of investigations and prescribe evidence-based lipid-lowering therapy.

Clinical Management of Hypertriglyceridemia in the Prevention of Cardiovascular Disease and Pancreatitis

Purpose of Review

Hypertriglyceridemia (HTG) is common and is a significant contributor to atherosclerosis and pancreatitis risk. Specific HTG treatments have had variable success in reducing atherosclerosis risk. Novel therapies for severe HTG treatment and pancreatitis risk reduction are likely to be available soon. These novel therapies are expected to have broader applications for more moderate HTG and atherosclerosis risk reduction as well.

Recent Findings

NHANES 2012 data has confirmed a reduction in average triglyceride (TG) levels in the US population. Dietary modification and weight reduction when needed remain the core treatment elements for all individuals with HTG, while statin therapy is a foundational pharmacologic care for atherosclerotic cardiovascular disease (ASCVD) event risk reduction. In addition, the REDUCE-IT study provides evidence for additional benefit from the use of high-dose icosapent ethyl (IPE) on top of background medical therapy in adults with moderate HTG and ASCVD or type 2 diabetes mellitus (T2D) and additional ASCVD risk factors. However, treatment with eicosapentaenoic acid (EPA) combined with docosahexanoic acid (DHA) did not reduce ASCVD in a similar population studied in the STRENGTH trial. Furthermore, novel therapeutics targeting PPAR-ɑ, as well as ApoC-III and AngPTL3, effectively lower TG levels in individuals with moderate and severe HTG, respectively. These treatments may have applicability for reducing risk from ASCVD among individuals with chylomicronemia; in addition, ApoC-III and AngPTL3 treatments may have a role in treating individuals with the rare monogenic familial chylomicronemia syndrome (FCS) at risk for acute pancreatitis (AP).

Summary

Residual ASCVD risk in individuals treated with contemporary care may be due in part to non-LDL lipid abnormalities including HTG. The findings from REDUCE-IT, but not STRENGTH, confirm that consumption of high-dose EPA may reduce ASCVD risk, while combination therapy of EPA plus DHA does not reduce ASCVD in a similar population. TG lowering likely reduces ASCVD risk in individuals with HTG, but ASCVD risk is multifactorial; the added benefit of IPE to contemporary preventive therapy is the consequence of differential non-TG biologic properties between the two fatty acids. Acute pancreatitis is more difficult to study prospectively since it is less common; however, TG lowering is likely critical for the care of at-risk individuals. Additional benefit from novel therapy that has an impact on this otherwise refractory condition is anticipated.

Hyperlipidemic myeloma, a rare form of acquired dysbetalipoproteinemia, in an HIV seropositive African female

Dysbetalipoproteinemia (DBL) is an uncommon condition characterized by a mixed hyperlipidemia due to accumulation of remnant lipoproteins and is highly atherogenic. Typically, DBL is an autosomal recessive condition requiring an additional metabolic stress with reduced apolipoprotein E (apoE) function. However, DBL is also described in patients with multiple myeloma without the characteristic apoE2/E2 mutation seen in familial DBL. Although the underlying pathogenesis in these cases is not fully characterized, it is thought to occur due to interference with apoE function by antibodies produced from clonal plasma cells. Such cases are referred to as hyperlipidemic myeloma (HLM) and have rarely been described in the literature. To our knowledge there is no prior description of HLM in HIV positive patients in Africa. We describe a case of HLM in an African woman with underlying HIV infection who presented with phenotypic and biochemical features of DBL that responded poorly to lipid lowering therapy.

Adiposity and the development of dyslipidemia in APOE ε2 homozygous subjects: A longitudinal analysis in two population-based cohorts

BACKGROUND AND AIMS

Familial dysbetalipoproteinemia (FD), characterized by remnant lipoprotein accumulation and premature cardiovascular disease, occurs in homozygous carriers of the APOE ε2 allele, but genetic predisposition alone does not suffice for the clinical phenotype. Cross-sectional studies suggest that a second metabolic hit - notably adiposity or insulin resistance - is required, but the association between these risk factors and development of FD has not been studied prospectively.

METHODS

For this study, we evaluated 18,987 subjects from two large prospective Dutch population-based cohorts (PREVEND and Rotterdam Study) of whom 118 were homozygous APOE ε2 carriers. Of these, 69 subjects were available for prospective analyses. Dyslipidemia - likely to be FD - was defined as fasting triglyceride (TG) levels >3 mmol/L in untreated subjects or use of lipid lowering medication. The effect of weight, body mass index (BMI), waist circumference, type 2 diabetes mellitus and non-TG metabolic syndrome on development of dyslipidemia was investigated.

RESULTS

Eleven of the 69 ε2ε2 subjects (16%) developed dyslipidemia - likely FD - during follow-up. Age-, sex- and cohort-adjusted risk factors for the development of FD were BMI (OR 1.19; 95%CI 1.04-1.39), waist circumference (OR 1.26 95%CI 1.01-1.61) and presence of non-TG metabolic syndrome (OR 4.39; 95%CI 1.04-18.4) at baseline. Change in adiposity during follow-up was not associated with development of dyslipidemia.

CONCLUSIONS

Adiposity increases the risk of developing an FD-like lipid phenotype in homozygous APOE ε2 subjects. These results stress the importance of healthy body weight in subjects at risk of developing FD.

Apolipoprotein Mimetic Peptides: Potential New Therapies for Cardiovascular Diseases

Since the seminal breakthrough of treating diabetic patients with insulin in the 1920s, there has been great interest in developing other proteins and their peptide mimetics as therapies for a wide variety of other medical disorders. Currently, there are at least 60 different peptides that have been approved for human use and over 150 peptides that are in various stages of clinical development. Peptides mimetic of the major proteins on lipoproteins, namely apolipoproteins, have also been developed first as tools for understanding apolipoprotein structure and more recently as potential therapeutics. In this review, we discuss the biochemistry, peptide mimetics design and clinical trials for peptides based on apoA-I, apoE and apoC-II. We primarily focus on applications of peptide mimetics related to cardiovascular diseases. We conclude with a discussion on the limitations of peptides as therapeutic agents and the challenges that need to be overcome before apolipoprotein mimetic peptides can be developed into new drugs.

Hyperlipidemia

Cardiovascular disease remains the top cause of morbidity and mortality in the United States. Atherosclerotic plaques are known to start in adolescence, and, therefore, young adults can be affected by coronary artery disease. Children with known risk factors, such as genetic predisposition, including familial hyperlipidemias, diabetes, and renal diseases, are at higher risk. With childhood obesity becoming an epidemic in certain parts of the United States, this problem is further highlighted as an important issue affecting children's health. There are unclear recommendations for pediatricians regarding cholesterol screening of pediatric populations, when to initiate hyperlipidemia treatment with statin therapy, and when to refer to a specialist for further management. This article reviews the epidemiology and pathophysiology of hyperlipidemia, recommendations for screening and types of screening, management (including pharmacology), prognosis, and prevention.

The clinical and laboratory investigation of dysbetalipoproteinemia

Familial dysbetalipoproteinemia (type III hyperlipoproteinemia) is a potentially underdiagnosed inherited dyslipidemia associated with greatly increased risk of coronary and peripheral vascular disease. The mixed hyperlipidemia observed in this disorder usually responds well to appropriate medical therapy and lifestyle modification. Although there are characteristic clinical features such as palmar and tuberous xanthomata, associated with dysbetalipoproteinemia, they are not always present, and their absence cannot be used to exclude the disorder. The routine lipid profile cannot distinguish dysbetalipoproteinemia from other causes of mixed hyperlipidemia and so additional investigations are required for confident diagnosis or exclusion. A range of investigations that have been proposed as potential diagnostic tests are discussed in this review, but the definitive biochemical test for dysbetalipoproteinemia is widely considered to be beta quantification. Beta quantification can determine the presence of "β-VLDL" in the supernatant following ultracentrifugation and whether the VLDL cholesterol to triglyceride ratio is elevated. Both features are considered hallmarks of the disease. However, beta quantification and other specialist tests are not widely available and are not high-throughput tests that can practically be applied to all patients with mixed hyperlipidemia. Using apolipoprotein B (as a ratio either to total or non-HDL cholesterol or as part of a multi-step algorithm) as an initial test to select patients for further investigation is a promising approach. Several studies have demonstrated a high degree of diagnostic sensitivity and specificity using these approaches and apolipoprotein B is a relatively low-cost test that is widely available on high-throughput platforms. Genetic testing is also important in the diagnosis, but it should be noted that most individuals with an E₂/₂ genotype do not suffer from remnant hyperlipidemia and around 10% of familial dysbetalipoproteinemia cases are caused by rarer, autosomal dominant mutations in APOE that will only be detected if the gene is fully sequenced. Wider implementation of diagnostic pathways utilizing apo B could lead to more rational use of specialist investigations and more consistent detection of patients with dysbetalipoproteinemia. Without the application of a consistent evidence-based approach to identifying dysbetalipoproteinemia, many cases are likely to remain undiagnosed.

Therapeutic approaches targeting Apolipoprotein E function in Alzheimer's disease

One of the primary genetic risk factors for Alzheimer’s disease (AD) is the presence of the Ɛ4 allele of apolipoprotein E (APOE). APOE is a polymorphic lipoprotein that is a major cholesterol carrier in the brain. It is also involved in various cellular functions such as neuronal signaling, neuroinflammation and glucose metabolism. Humans predominantly possess three different allelic variants of APOE, termed E2, E3, and E4, with the E3 allele being the most common. The presence of the E4 allele is associated with increased risk of AD whereas E2 reduces the risk. To understand the molecular mechanisms that underlie APOE-related genetic risk, considerable effort has been devoted towards developing cellular and animal models. Data from these models indicate that APOE4 exacerbates amyloid β plaque burden in a dose-dependent manner. and may also enhance tau pathogenesis in an isoform-dependent manner. Other studies have suggested APOE4 increases the risk of AD by mechanisms that are distinct from modulation of Aβ or tau pathology. Further, whether plasma APOE, by influencing systemic metabolic pathways, can also possibly alter CNS function indirectly is not complete;y understood. Collectively, the available studies suggest that APOE may impact multiple signaling pathways and thus investigators have sought therapeutics that would disrupt pathological functions of APOE while preserving or enhancing beneficial functions. This review will highlight some of the therapeutic strategies that are currently being pursued to target APOE4 towards preventing or treating AD and we will discuss additional strategies that holds promise for the future.

Modern prevalence of dysbetalipoproteinemia (Fredrickson-Levy-Lees type III hyperlipoproteinemia)

INTRODUCTION

Dysbetalipoproteinaemia (HLP3) is a disorder characterized by excess cholesterol-enriched, triglyceride-rich lipoprotein remnants in genetically predisposed individuals that powerfully promote premature cardiovascular disease if untreated. The current prevalence of HLP3 is largely unknown.

MATERIAL AND METHODS

We performed cross-sectional analysis of 128,485 U.S. adults from the Very Large Database of Lipids (VLDbL), using four algorithms to diagnose HLP3 employing three Vertical Auto Profile ultracentrifugation (UC) criteria and a previously described apolipoprotein B (apoB) method. We evaluated 4,926 participants from the 2011-2014 National Health and Nutrition Examination Survey (NHANES) with the apoB method. We examined demographic and lipid characteristics stratified by presence of HLP3 and evaluated lipid characteristics in those with HLP3 phenotype discordance and concordance as determined by apoB and originally defined UC criteria 1.

RESULTS

In U.S. adults in VLDbL and NHANES, a 1.7-2.0% prevalence is observed for HLP3 with the novel apoB method as compared to 0.2-0.8% prevalence in VLDbL via UC criteria 1-3. Participants who were both apoB and UC criteria HLP3 positive had higher remnant particles as well as more elevated triglyceride/apoB and total cholesterol/apoB ratios (all p < 0.001) than those who were apoB method positive and UC criteria 1 negative.

CONCLUSIONS

HLP3 may be more prevalent than historically and clinically appreciated. The apoB method increases HLP3 identification via inclusion of milder phenotypes. Further work should evaluate the clinical implications of HLP3 diagnosis at various lipid algorithm cut-points to evaluate the ideal standard in the modern era.

Inherited metabolic disorders and dyslipidaemia

Monogenic dyslipidaemia is a diverse group of multisystem disorders. Patients may present to various specialities from early childhood to late in adult life, and it usually takes longer before the diagnosis is established. Increased awareness of these disorders among clinicians is imperative for early diagnosis. This best practice review provides an overview of primary dyslipidaemias, highlighting their clinical presentation, relevant biochemical and molecular tests. It also addresses the emerging role of genetics in the early diagnosis and prevention of these disorders.

A Quarter Century of APOE and Alzheimer's Disease: Progress to Date and the Path Forward

Alzheimer's disease (AD) is considered a polygenic disorder. This view is clouded, however, by lingering uncertainty over how to treat the quasi "monogenic" role of apolipoprotein E (APOE). The APOE4 allele is not only the strongest genetic risk factor for AD, it also affects risk for cardiovascular disease, stroke, and other neurodegenerative disorders. This review, based mostly on data from human studies, ranges across a variety of APOE-related pathologies, touching on evolutionary genetics and risk mitigation by ethnicity and sex. The authors also address one of the most fundamental question pertaining to APOE4 and AD: does APOE4 increase AD risk via a loss or gain of function? The answer will be of the utmost importance in guiding future research in AD.

Apolipoprotein E in lipoprotein metabolism, health and cardiovascular disease

Apolipoprotein E (apoE), a 34 kDa circulating glycoprotein of 299 amino acids, predominantly synthesised in the liver, associates with triglyceride-rich lipoproteins to mediate the clearance of their remnants after enzymatic lipolysis in the circulation. Its synthesis in macrophages initiates the formation of high density-like lipoproteins to effect reverse cholesterol transport to the liver. In the nervous system apoE forms similar lipoproteins which perform the function of distributing lipids amongst cells. ApoE accounts for much of the variation in plasma lipoproteins by three common variants (isoforms) that influence low-density lipoprotein concentration and the risk of atherosclerosis. ApoE2 generally is most favourable and apoE4 least favourable for cardiovascular and neurological health. The apoE variants relate to different amino acids at positions 112 and 158: cysteine in both for apoE2, arginine at both sites for apoE4, and respectively cysteine and arginine for apoE3 that is viewed as the wild type. Paradoxically, under metabolic stress, homozygosity for apoE2 may result in dysbetalipoproteinaemia in adults owing to impaired binding of remnant lipoproteins to the LDL receptor and related proteins as well as heparan sulphate proteoglycans. This highly atherogenic condition is also seen with other mutations in apoE, but with autosomal dominant inheritance. Mutations in apoE may also cause lipoprotein glomerulopathy. In the central nervous system apoE binds amyloid β-protein and tau protein and fragments may incur cellular damage. ApoE4 is a strong risk factor for the development of Alzheimer's disease. ApoE has several other physiological effects that may influence health and disease, including supply of docosahexaenoic acid for the brain and modulating immune and inflammatory responses. Genotyping of apoE may have application in disorders of lipoprotein metabolism as well as glomerulopathy and may be relevant to personalised medicine in understanding cardiovascular risk, and the outcome of nutritional and therapeutic interventions. Quantitation of apoE will probably not be clinically useful. ApoE is also of interest as it may generate peptides with biological function and could be employed in nanoparticles that may allow crossing of the blood-brain barrier. Therapeutic options may emerge from these newer insights.

Pathogenesis, histopathologic findings and treatment modalities of lipoprotein glomerulopathy: A review

Lipoprotein glomerulopathy (LPG) is an uncommon cause of nephrotic syndrome and/or kidney failure. At microscopy, LPG is characterized by the presence of lipoprotein thrombi in dilated glomerular capillaries due to different ApoE mutations. ApoE gene is located on chromosome 19q13.2, and can be identified in almost all serum lipoproteins. ApoE works as a protective factor in atherosclerosis due its interaction with receptor-mediated lipoprotein clearance and cholesterol receptor. Most common polymorphisms include ApoE2/2, ApoE3/2, ApoE3/3, ApoE4/2, ApoE4/3, and ApoE4/4. All age-groups can be affected by LPG, with a discrete male predominance. Compromised patients typically reveal dyslipidemia, type III hyperlipoproteinemia, and proteinuria. LPG treatment includes fenofibrate, antilipidemic drugs, steroids, LDL aphaeresis, plasma exchange, antiplatelet drugs, anticoagulants, urokinase, and renal transplantation. Recurrence in kidney graft suggests a pathogenic component(s) of extraglomerular humoral complex resulting from abnormal lipoprotein metabolism and presumably associated to ApoE.

The spectrum of type III hyperlipoproteinemia

BACKGROUND

Type III hyperlipoproteinemia is a highly atherogenic dyslipoproteinemia characterized by hypercholesterolemia and hypertriglyceridemia due to markedly increased numbers of cholesterol-enriched chylomicron and very-low-density lipoprotein (VLDL) remnant lipoprotein particles. Type III can be distinguished from mixed hyperlipidemia based on a simple diagnostic algorithm, which involves total cholesterol, triglycerides, and apolipoprotein B (apoB). However, apoB is not measured routinely.

OBJECTIVE

The objective of the present study was to determine if patients with type III could be distinguished from mixed hyperlipidemia based on lipoprotein lipids.

METHODS

Classification was based first on total cholesterol and triglyceride and then on the apoB diagnostic algorithm using apoB plus total cholesterol plus triglycerides, and validated by sequential ultracentrifugation. Four hundred and forty normals, 637 patients with hypertriglyceridemia, and 714 with hypertriglyceridemia and hypercholesterolemia were studied. Plasma lipoproteins were separated by sequential ultracentrifugation and heparin-manganese precipitation. Cholesterol, triglyceride, and apoB were measured in plasma and isolated lipoprotein fractions.

RESULTS

Of the 1351 patients with hypertriglyceridemia, 49 had type III hyperlipoproteinemia, as diagnosed by the apoB algorithm and validated by ultracentrifugation. Plasma triglycerides were higher in the type III subjects: 4.16 mmol/L (3.35-6.08, 25th-75th percentile), but there was considerable overlap with the hypertriglyceridemic subjects 2.65 mmol/L (1.91-4.20, 25th-75th percentile) and the combined hyperlipidemic subjects 3.02 mmol/L (2.07-5.32, 25th-75th percentile). Similarly, total cholesterol was 4.79 mmol/L (4.31-5.58, 25th-75th percentile) for type III vs 5.5 mmol/L (4.64-5.78, 25th-75th percentile) and 7.02 mmol/L (6.39-7.96, 25th-75th percentile), respectively. By contrast, as identified by the apoB algorithm, the VLDL-C/TG, VLDL-C/VLDL-TG, VLDL-C/VLDL apoB, and VLDL apoB/LDL apoB ratios were all higher in type III than in the other hypertriglyceridemic dyslipoproteinemias with the exception of type V as diagnosed by the apoB algorithm.

CONCLUSION

Cholesterol and triglycerides cannot reliably distinguish type III hyperlipoproteinemia from mixed hyperlipidemia. Adding apoB and applying the apoB algorithm makes reliable diagnosis possible and easy. However, unless apoB is introduced into routine clinical care, type III hyperlipoproteinemia will often not be recognized. Given the cardiovascular risk associated with type III and its responsiveness to treatment, this should not be acceptable.

Effect of adding bezafibrate to standard lipid-lowering therapy on post-fat load lipid levels in patients with familial dysbetalipoproteinemia. A randomized placebo-controlled crossover trial

Familial dysbetalipoproteinemia (FD) is a genetic disorder associated with impaired postprandial lipid clearance. The effect of adding bezafibrate to standard lipid-lowering therapy on postprandial and fasting lipid levels in patients with FD is unknown. In this randomized placebo-controlled double-blind crossover trial, 15 patients with FD received bezafibrate and placebo for 6 weeks in randomized order in addition to standard lipid-lowering therapy (statin, ezetimibe, and/or lifestyle). We assessed post-fat load lipids, expressed as incremental area under the curve (iAUC) and area under the curve (AUC), as well as fasting levels and safety, and found that adding bezafibrate did not reduce post-fat load non-HDL-cholesterol (non-HDL-C) iAUC (1.78 ± 4.49 mmol·h/l vs. 1.03 ± 2.13 mmol·h/l, P = 0.57), but did reduce post-fat load triglyceride (TG) iAUC (8.05 ± 3.32 mmol·h/l vs. 10.61 ± 5.92 mmol·h/l, P = 0.03) and apoB (0.64 ± 0.62 g·h/l vs. 0.93 ± 0.71 g·h/l, P = 0.01). Furthermore, bezafibrate significantly improved AUC and fasting levels of non-HDL-C, TG, total cholesterol, HDL-C, and apoB. Bezafibrate was associated with lower estimated glomerular filtration rate (78.4 ± 11.4 ml/min/1.73 m2 vs. 86.1 ± 5.85 ml/min/1.73 m2, P = 0.002). In conclusion, in patients with FD, the addition of bezafibrate to standard lipid-lowering therapy resulted in improved post-fat load and fasting plasma lipids. Combination therapy of statin/fibrate could be considered as standard lipid-lowering treatment in FD.

In silico analyses of deleterious missense SNPs of human apolipoprotein E3

ApoE3 is the major chylomicron apolipoprotein, binding in a specific liver peripheral cell receptor, allowing transport and normal catabolism of triglyceride-rich lipoprotein constituents. Point mutations in ApoE3 have been associated with Alzheimer's disease, type III hyperlipoproteinemia, atherosclerosis, telomere shortening and impaired cognitive function. Here, we evaluate the impact of missense SNPs in APOE retrieved from dbSNP through 16 computational prediction tools, and further evaluate the structural impact of convergent deleterious changes using 100 ns molecular dynamics simulations. We have found structural changes in four analyzed variants (Pro102Arg, Arg132Ser, Arg176Cys and Trp294Cys), two of them (Pro102Arg and Arg176Cys) being previously associated with human diseases. In all cases, except for Trp294Cys, there was a loss in the number of hydrogen bonds between CT and NT domains that could result in their detachment. In conclusion, data presented here could increase the knowledge of ApoE3 activity and be a starting point for the study of the impact of variations on APOE gene.

Familial dysbetalipoproteinemia: an underdiagnosed lipid disorder

PURPOSE OF REVIEW

To review pathophysiological, epidemiological and clinical aspects of familial dysbetalipoproteinemia; a model disease for remnant metabolism and remnant-associated cardiovascular risk.

RECENT FINDINGS

Familial dysbetalipoproteinemia is characterized by remnant accumulation caused by impaired remnant clearance, and premature cardiovascular disease. Most familial dysbetalipoproteinemia patients are homozygous for apolipoprotein ε2, which is associated with decreased binding of apolipoprotein E to the LDL receptor. Although familial dysbetalipoproteinemia is an autosomal recessive disease in most cases, 10% is caused by autosomal dominant mutations. Of people with an ε2ε2 genotype 15% develops familial dysbetalipoproteinemia, which is associated with secondary risk factors, such as obesity and insulin resistance, that inhibit remnant clearance by degradation of the heparan sulfate proteoglycan receptor. The prevalence of familial dysbetalipoproteinemia ranges from 0.12 to 0.40% depending on the definition used. Clinical characteristics of familial dysbetalipoproteinemia are xanthomas and mixed hyperlipidemia (high total cholesterol and triglycerides); the primary lipid treatment goal in familial dysbetalipoproteinemia is non-HDL-cholesterol; and treatment consists of dietary therapy and treatment with statin and fibrate combination.

SUMMARY

Familial dysbetalipoproteinemia is a relatively common, though often not diagnosed, lipid disorder characterized by mixed hyperlipidemia, remnant accumulation and premature cardiovascular disease, which should be treated with dietary therapy and statin and fibrate combination.

Remnant Cholesterol Elicits Arterial Wall Inflammation and a Multilevel Cellular Immune Response in Humans

OBJECTIVE

Mendelian randomization studies revealed a causal role for remnant cholesterol in cardiovascular disease. Remnant particles accumulate in the arterial wall, potentially propagating local and systemic inflammation. We evaluated the impact of remnant cholesterol on arterial wall inflammation, circulating monocytes, and bone marrow in patients with familial dysbetalipoproteinemia (FD).

APPROACH AND RESULTS

Arterial wall inflammation and bone marrow activity were measured using ¹⁸F-FDG PET/CT. Monocyte phenotype was assessed with flow cytometry. The correlation between remnant levels and hematopoietic activity was validated in the CGPS (Copenhagen General Population Study). We found a 1.2-fold increase of ¹⁸F-FDG uptake in the arterial wall in patients with FD (n=17, age 60±8 years, remnant cholesterol: 3.26 [2.07-5.71]) compared with controls (n=17, age 61±8 years, remnant cholesterol 0.29 [0.27-0.40]; P<0.001). Monocytes from patients with FD showed increased lipid accumulation (lipid-positive monocytes: Patients with FD 92% [86-95], controls 76% [66-81], P=0.001, with an increase in lipid droplets per monocyte), and a higher expression of surface integrins (CD11b, CD11c, and CD18). Patients with FD also exhibited monocytosis and leukocytosis, accompanied by a 1.2-fold increase of ¹⁸F-FDG uptake in bone marrow. In addition, we found a strong correlation between remnant levels and leukocyte counts in the CGPS (n=103 953, P for trend 5×10-276). In vitro experiments substantiated that remnant cholesterol accumulates in human hematopoietic stem and progenitor cells coinciding with myeloid skewing.

CONCLUSIONS

Patients with FD have increased arterial wall and cellular inflammation. These findings imply an important inflammatory component to the atherogenicity of remnant cholesterol, contributing to the increased cardiovascular disease risk in patients with FD.

Progress in the care of common inherited atherogenic disorders of apolipoprotein B metabolism

Familial hypercholesterolaemia, familial combined hyperlipidaemia (FCH) and elevated lipoprotein(a) are common, inherited disorders of apolipoprotein B metabolism that markedly accelerate the onset of atherosclerotic cardiovascular disease (ASCVD). These disorders are frequently encountered in clinical lipidology and need to be accurately identified and treated in both index patients and their family members, to prevent the development of premature ASCVD. The optimal screening strategies depend on the patterns of heritability for each condition. Established therapies are widely used along with lifestyle interventions to regulate levels of circulating lipoproteins. New therapeutic strategies are becoming available, and could supplement traditional approaches in the most severe cases, but their long-term cost-effectiveness and safety have yet to be confirmed. We review contemporary developments in the understanding, detection and care of these highly atherogenic disorders of apolipoprotein B metabolism.

Type III Hyperlipoproteinemia: Still Worth Considering?

Familial type III hyperlipoproteinemia (HLP) was first recognized as a distinct entity over 60 years ago. Since then, it has proven to be instructive in identifying the key role of apolipoprotein E (apoE) in removal of the remnants of very low density lipoproteins and chylomicrons produced by the action of lipoprotein lipase on these triglyceride-transporting lipoproteins. It has additionally shed light on the potent atherogenicity of the remnant lipoproteins. This review describes the history of development of our understanding of type III HLP, discusses the several genetic variants of apoE that play roles in the genesis of type III HLP, and describes the remarkable responsiveness of this fascinating disorder to lifestyle modification, especially carbohydrate restriction and calorie restriction, and, when required, the addition of pharmacotherapy.

The relation between apolipoprotein E (APOE) genotype and peripheral artery disease in patients at high risk for cardiovascular disease

INTRODUCTION

The apolipoprotein E gene (APOE) is associated with coronary heart disease and stroke, but the relation with peripheral artery disease (PAD) is unknown. We investigated the relation of APOE genotype with PAD and other types of vascular disease.

METHODS

The cross-sectional association between APOE genotype and ankle-brachial index (ABI) and vascular disease prevalence; and the prospective relation with incident PAD and other types of vascular disease (coronary artery disease, stroke and vascular mortality) were evaluated in 7418 patients from the Secondary Manifestations of ARTerial disease (SMART) study. This is a prospective cohort study in patients with cardiovascular disease or a cardiovascular risk factor. Analyses were adjusted for age and sex.

RESULTS

Mean age was 56.7 ± 12.4 years and 68% of the patients was male. APOE genotype frequencies were ε2ε2 1.3%; ε2ε3 9.9%; ε2ε4 2.4%; ε3ε3 56.9%; ε3ε4 26.7% and ε4ε4 2.8%. Median follow-up time was 8.1 years (IQR 5.4-11.4) in which 452 new PAD events occurred. The ε2ε2 genotype was significantly associated with a lower ABI (regression coefficient -0.04, 95%CI -0.07 to -0.01), increased PAD prevalence (prevalence ratio 1.54, 95%CI 1.01-2.17) and a higher risk of incident PAD (HR 2.31, 95%CI 1.29-4.12) compared with ε3ε3. No relations between APOE genotypes and other vascular disease were observed.

CONCLUSION

Of the six APOE genotypes, the ε2ε2 variant is associated with an increased risk for PAD in patients at high risk for cardiovascular disease. No association was observed between APOE genotype and coronary artery disease, stroke or vascular mortality in this population.

Automated Multiplex LC-MS/MS Assay for Quantifying Serum Apolipoproteins A-I, B, C-I, C-II, C-III, and E with Qualitative Apolipoprotein E Phenotyping

BACKGROUND

Direct and calculated measures of lipoprotein fractions for cardiovascular risk assessment suffer from analytical inaccuracy in certain dyslipidemic and pathological states, most commonly hypertriglyceridemia. LC-MS/MS has proven suitable for multiplexed quantification and phenotyping of apolipoproteins. We developed and provisionally validated an automated assay for quantification of apolipoprotein (apo) A-I, B, C-I, C-II, C-III, and E and simultaneous qualitative assessment of apoE phenotypes.

METHODS

We used 5 value-assigned human serum pools for external calibration. Serum proteins were denatured, reduced, and alkylated according to standard mass spectrometry–based proteomics procedures. After trypsin digestion, peptides were analyzed by LC-MS/MS. For each peptide, we measured 2 transitions. We compared LC-MS/MS results to those obtained by an immunoturbidimetric assay or ELISA.

RESULTS

Intraassay CVs were 2.3%–5.5%, and total CVs were 2.5%–5.9%. The LC-MS/MS assay correlated (R = 0.975–0.995) with immunoturbidimetric assays with Conformité Européenne marking for apoA-I, apoB, apoC-II, apoC-III, and apoE in normotriglyceridemic (n = 54) and hypertriglyceridemic (n = 46) sera. Results were interchangeable for apoA-I ≤3.0 g/L (Deming slope 1.014) and for apoB-100 ≤1.8 g/L (Deming slope 1.016) and were traceable to higher-order standards.

CONCLUSIONS

The multiplex format provides an opportunity for new diagnostic and pathophysiologic insights into types of dyslipidemia and allows a more personalized approach for diagnosis and treatment of lipid abnormalities.

Dysbetalipoproteinemia: an extreme disorder of remnant metabolism

PURPOSE OF REVIEW

Lipoprotein metabolism and the role of apolipoprotein E in the pathogenesis of dysbetalipoproteinemia.

RECENT FINDINGS

Remnant lipoproteins, modulated by lifestyle and genetic factors, are atherogenic. Dysbetalipoproteinemia could be viewed as a monogenic disorder of remnant metabolism.

SUMMARY

Elevated plasma triglyceride and cholesterol concentrations (mixed hyperlipidemias) are commonly encountered and dysbetaliproteinemia should be considered in this setting. Dysbetalipoproteinemia (remnant clearance disease, Fredrickson type III hyperlipidemia) is an uncommon dyslipoproteinemia related to mutations in apolipoprotein E that disrupt the clearance of remnants of triglyceride-rich lipoproteins; it may be overlooked because xanthomata of the skin and/or tendons occur in a minority of patients. The diagnosis ideally requires the demonstration of remnant lipoprotein accumulation and a genetic cause. Genotyping for apolipoprotein E2 may not prove the diagnosis as it may be associated with low plasma lipid values. The recent association of remnant lipoproteins with atherosclerosis along with many factors that modulate remnant lipoprotein metabolism underscores the importance of recognising dysbetalipoproteinemia as an extreme state of remnant lipoprotein accumulation. Although there may be some differences between remnants in the general population and dysbetalipoproteinemia, it is clear that remnants promote atherosclerosis. Current treatment strategies are adequate but new strategies could also be of benefit in dysbetalipoproteinemia.

Lipid phenotypes at the extremes of high-density lipoprotein cholesterol: The very large database of lipids-9

BACKGROUND

Low serum levels of high-density lipoprotein cholesterol (HDL-C) are an important risk factor for atherosclerotic disease. To date, therapeutically raising HDL-C has not been shown to impact risk for cardiovascular events.

OBJECTIVE

We aim to characterize lipid parameters at the extremes of HDL-C.

METHODS

We examined cholesterol profiles from 1,350,908 US adults and children from the Very Large Database of Lipids who were clinically referred for advanced lipoprotein testing from 2009 to 2011. We categorized patients into HDL-C percentile categories (<0.1th, 0.1th-<1st, 1st-5th, 25th-75th, 95th-99th, >99th-99.9th, and >99.9th). Within these groups, we examined HDL-C subclasses, low-density lipoprotein cholesterol (LDL-C), LDL and very-low density lipoprotein densities, non-HDL-C, triglycerides (TG), very-low density lipoprotein cholesterol, and remnant lipoprotein cholesterol (RLP-C), as well as prevalence of Fredrickson-Levy dyslipidemias.

RESULTS

Extremely low HDL-C percentiles were associated with increased LDL density, TG, and especially RLP-C. Very high HDL-C levels (≥ 92 mg/dL) showed increasing HDL2-C/HDL3-C ratio and very low levels of RLP-C and triglyceride-rich lipoproteins. Type IV dyslipidemia had the highest prevalence among classical dyslipidemia and was the most frequent at extremely low HDL-C percentiles.

CONCLUSIONS

These findings demonstrate a high prevalence of elevated triglyceride-rich lipoprotein levels and increased LDL density in patients with extremely low HDL-C levels. The relative contributions of these various changes in lipid profiles of patients with low HDL-C to cardiovascular risk need to be further scrutinized to more fully establish if low HDL-C is truly an independent risk factor for coronary heart disease or simply reflects detrimental shifts in the levels of atherogenic lipoproteins.

Giant xanthomas associated with severe mixed dyslipidemia and arteriosclerotic vascular disease: A case report

The report describes a case of mixed hyperlipoproteinemia in a 64-year-old patient presenting a serum hypertriglyceridemia at 25 mmol/L and hypercholesterolemia at 15.75 mmol/L, giant xanthomas and symptomatic atherosclerotic disease.

Primary hypertriglyceridemia in children and adolescents

Primary disorders of lipid metabolism causing hypertriglyceridemia (HyperTG) result from genetic defects in triglyceride synthesis and metabolism. With the exception of lipoprotein lipase deficiency, these primary HyperTG disorders usually present in adulthood. However, some are unmasked earlier by precipitating factors, such as obesity and insulin resistance, and can be diagnosed in adolescence. Physical findings may be present and can include eruptive, palmer, or tuberoeruptive xanthomas. Triglyceride levels are very high to severe and can occur in the absence or the presence of other lipid abnormalities. Each of the causes of HyperTG is associated with an increased risk to develop recurrent pancreatitis and some may increase the risk of premature cardiovascular disease. Adoption of a healthy lifestyle that includes a low-fat diet, optimizing body weight, smoking avoidance/cessation, and daily physical activity is the first line of therapy. Pharmacologic therapies are available and can be beneficial in select disorders. Here, we review the causes of primary HyperTG in children and adolescents, discuss their clinical presentation and associated complications including the risk of pancreatitis and premature cardiovascular disease, and conclude with management and novel therapies currently in development. The goal of this article is to provide a useful resource for clinicians who may encounter primary HyperTG in the pediatric population.

Dysbetalipoproteinemia: Two cases report and a diagnostic algorithm

Dysbetalipoproteinemia is a rare familial dyslipidemia characterized by approximately equally elevated serum cholesterol and triglyceride levels due to accumulated remnant lipoproteins in apolipoprotein E2/E2 homozygotes. It is associated with an increased risk for premature cardiovascular disease. Thus, making a diagnosis of dysbetalipoproteinemia aids in assessing cardiovascular risk correctly and allows for genetic counseling. However, the diagnostic work-up can be challenging. Diagnosis of dysbetalipoproteinemia should be considered in patients mixed dyslipidemia when the apolipoprotein B concentration is relatively low in relation to the total cholesterol concentration or when there is significant disparity between the calculated low density lipoprotein (LDL) and directly measured LDL cholesterol concentrations. Other indices are also informative in the diagnostic process. We present herein two phenotypically different cases (a 44-year-old man with severe hypertriglyceridemia and a 49-year-old woman with mixed dyslipidemia) of genotypically proven familial dysbetalipoproteinemia and a diagnostic algorithm of the disease.

Rare diseases in clinical endocrinology: a taxonomic classification system

PURPOSE

Rare endocrine-metabolic diseases (REMD) represent an important area in the field of medicine and pharmacology. The rare diseases of interest to endocrinologists involve all fields of endocrinology, including rare diseases of the pituitary, thyroid and adrenal glands, paraganglia, ovary and testis, disorders of bone and mineral metabolism, energy and lipid metabolism, water metabolism, and syndromes with possible involvement of multiple endocrine glands, and neuroendocrine tumors. Taking advantage of the constitution of a study group on REMD within the Italian Society of Endocrinology, consisting of basic and clinical scientists, a document on the taxonomy of REMD has been produced.

METHODS AND RESULTS

This document has been designed to include mainly REMD manifesting or persisting into adulthood. The taxonomy of REMD of the adult comprises a total of 166 main disorders, 338 including all variants and subtypes, described into 11 tables.

CONCLUSIONS

This report provides a complete taxonomy to classify REMD of the adult. In the future, the creation of registries of rare endocrine diseases to collect data on cohorts of patients and the development of common and standardized diagnostic and therapeutic pathways for each rare endocrine disease is advisable. This will help planning and performing intervention studies in larger groups of patients to prove the efficacy, effectiveness, and safety of a specific treatment.