Hepatic and cardiovascular consequences of familial hypobetalipoproteinemia

Low LDL-C: Is It all Good News?

PURPOSE OF REVIEW

This review presents the risks and benefits of very low LDL cholesterol and the safety of using lipid-lowering therapy to achieve these levels.

RECENT FINDINGS

A growing body of literature suggests that lower LDL cholesterol levels are associated with a reduced risk of cardiovascular disease. Further, achieving these levels with pharmaceuticals is remarkably safe. Although statins may slightly increase the risk of diabetes mellitus and hemorrhagic stroke, the benefits outweigh the risks. While recommendations from professional societies are increasingly aggressive, additional risk reduction could be achieved by setting more even ambitious LDL cholesterol goals.

Altered lipid metabolism and the development of metabolic-associated fatty liver disease

PURPOSE OF REVIEW

An increasing amount of research has underscored the significant role of lipoproteins in the pathogenesis of metabolic-associated fatty liver disease (MAFLD). This comprehensive review examines the intricate relationship between lipoprotein abnormalities and the development of MAFLD.

RECENT FINDINGS

Atherogenic dyslipidemia seen in insulin resistance states play a significant role in initiating and exacerbating hepatic lipid accumulation. There are also specific genetic factors ( PNPLA3 , TM6SF2 , MBOAT7 , HSD17B13 , GCKR- P446L) and transcription factors (SREBP-2, FXR, and LXR9) that increase susceptibility to both lipoprotein disorders and MAFLD. Most monogenic primary lipid disorders do not cause hepatic steatosis unless accompanied by metabolic stress. Hepatic steatosis occurs in the presence of secondary systemic metabolic stress in conjunction with predisposing environmental factors that lead to insulin resistance. Identifying specific aberrant lipoprotein metabolic factors promoting hepatic fat accumulation and subsequently exacerbating steatohepatitis will shed light on potential targets for therapeutic interventions.

SUMMARY

The clinical implications of interconnection between genetic factors and an insulin resistant environment that predisposes MAFLD is many fold. Potential therapeutic strategies in preventing or mitigating MAFLD progression include lifestyle modifications, pharmacological interventions, and emerging therapies targeting aberrant lipoprotein metabolism.

Primary hypocholesterolemia is associated with an increased risk of hepatic complications in the general population

BACKGROUND & AIMS

Beyond cardiovascular disease protection, the health consequences of very low concentrations of low-density lipoprotein-cholesterol (LDL-C) remain a matter of debate. In primary hypobetalipoproteinemia (HBL), liver steatosis and cirrhosis have occasionally been reported. Here, we aimed to investigate the association between HBL and the risk of hepatic complications (cirrhosis complications and/or primary liver cancer) in the general population.

METHODS

A cohort study was conducted in the French population-based cohort CONSTANCES. Participants with primary HBL (LDL-C <5th percentile for age and sex, [HBL]) were compared with those with normal LDL-C concentrations (40th-60th percentile, [Control]). Participants on lipid-lowering therapies were excluded. For hepatic complications, follow-up events were compared by calculating the incidence density ratio (IDR). The same analyses were replicated in the UK Biobank (UKBB) cohort.

RESULTS

In the CONSTANCES and UKBB cohorts, 34,653 and 94,666 patients were analyzed, with median ages of 45 and 56 years, mean LDL-C concentrations (HBL vs. control) of 71 vs. 128 mg/dl and 86 vs. 142 mg/dl, and mean follow-up durations of 5.0 and 11.5 years, respectively. The HBL group presented a higher incidence of hepatic complications than the control group: 0.32/ vs. 0.07/1,000 person-years (IDR = 4.50, 95% CI 1.91-10.6) in CONSTANCES, and 0.69/ vs. 0.21/1,000 person-years (IDR = 3.27, 95% CI 2.63-4.06) in the UKBB. This risk proved to be independent of classic risk factors for liver disease (obesity, alcohol consumption, diabetes, viral hepatitis), including in a 5-year landmark analysis excluding early events. Sensitivity analyses based on apoliprotein-B levels (instead of LDL-C levels) or genetically defined HBL showed similar results.

CONCLUSIONS

HBL is associated with a markedly increased risk of hepatic complications. HBL must be considered as a substantial independent risk factor for liver diseases which justifies specific prevention and screening.

IMPACT AND IMPLICATIONS

Hypobetalipoproteinemia (HBL) is a lipid disorder characterized by permanent, inherited low levels (below the 5th percentile) of low-density lipoprotein-cholesterol. While HBL is associated with a lower risk of cardiovascular events, some studies suggest that it may be associated with a potential risk of hepatic steatosis and hepatic complications. Here, we studied the association between HBL and hepatic complications (defined as cirrhosis complications and/or primary liver cancer) in two populations of several hundred thousand people, both in France (CONSTANCES cohort) and the United Kingdom (UKBB). The results show that HBL is associated with a significant and independent excess risk of hepatic complications, including primary liver cancer. Thus, in people with HBL, the value of regular liver monitoring must be studied.

ApoB100 and Atherosclerosis: What's New in the 21st Century?

ApoB is the main protein of triglyceride-rich lipoproteins and is further divided into ApoB48 in the intestine and ApoB100 in the liver. Very low-density lipoprotein (VLDL) is produced by the liver, contains ApoB100, and is metabolized into its remnants, intermediate-density lipoprotein (IDL) and low-density lipoprotein (LDL). ApoB100 has been suggested to play a crucial role in the formation of the atherogenic plaque. Apart from being a biomarker of atherosclerosis, ApoB100 seems to be implicated in the inflammatory process of atherosclerosis per se. In this review, we will focus on the structure, the metabolism, and the function of ApoB100, as well as its role as a predictor biomarker of cardiovascular risk. Moreover, we will elaborate upon the molecular mechanisms regarding the pathophysiology of atherosclerosis, and we will discuss the disorders associated with the APOB gene mutations, and the potential role of various drugs as therapeutic targets.

Low cholesterol states: clinical implications and management

INTRODUCTION

Hypocholesterolemia results from genetic - both monogenic and polygenic - and non-genetic causes and can sometimes be a source of clinical concern. We review etiologies and sequelae of hypocholesterolemia and therapeutics inspired from genetic hypocholesterolemia.

AREAS COVERED

Monogenic hypocholesterolemia disorders caused by the complete absence of apolipoprotein (apo) B-containing lipoproteins (abetalipoproteinemia and homozygous hypobetalipoproteinemia) or an isolated absence of apo B-48 lipoproteinemia (chylomicron retention disease) lead to clinical sequelae. These include gastrointestinal disturbances and severe vitamin deficiencies that affect multiple body systems, i.e. neurological, musculoskeletal, ophthalmological, and hematological. Monogenic hypocholesterolemia disorders with reduced but not absent levels of apo B lipoproteins have a milder clinical presentation and patients are protected against atherosclerotic cardiovascular disease. Patients with heterozygous hypobetalipoproteinemia have somewhat increased risk of hepatic disease, while patients with PCSK9 deficiency, ANGPTL3 deficiency, and polygenic hypocholesterolemia typically have anunremarkable clinical presentation.

EXPERT OPINION

In patients with severe monogenic hypocholesterolemia, early initiation of high-dose vitamin therapy and a low-fat diet are essential for optimal prognosis. The molecular basis of monogenic hypocholesterolemia has inspired novel therapeutics to help patients with the opposite phenotype - i.e. elevated apo B-containing lipoproteins. In particular, inhibitors of PCSK9 and ANGPTL3 show important clinical impact.

New Treatment Targets and Innovative Lipid-Lowering Therapies in Very-High-Risk Patients with Cardiovascular Disease

The effective and fast reduction of circulating low-density lipoprotein cholesterol (LDL-C) is a cornerstone for secondary prevention of atherosclerotic disease progression. Despite the substantial lipid-lowering effects of the established treatment option with statins and ezetimibe, a significant proportion of very-high-risk patients with cardiovascular disease do not reach the recommended treatment goal of <55 mg/dL (<1.4 mmol/L). Novel lipid-lowering agents, including the proprotein convertase subtilisin/kexin type 9 (PCSK9) antibodies alirocumab and evolocumab, the small interfering ribonucleotide acid (si-RNA) inclisiran, as well as the recently approved bempedoic acid, now complete the current arsenal of LDL-C lowering agents. These innovative therapies have demonstrated promising results in clinical studies. Besides a strong reduction of LDL-C by use of highly effective agents, there is still discussion as to whether a very rapid achievement of the treatment goal should be a new strategic approach in lipid-lowering therapy. In this review, we summarize evidence for the lipid-modifying properties of these novel agents and their safety profiles, and discuss their potential pleiotropic effects beyond LDL-C reduction (if any) as well as their effects on clinical endpoints as cardiovascular mortality. In addition to a treatment strategy of “the lower, the better”, we also discuss the concept of “the earlier, the better”, which may also add to the early clinical benefit of large LDL-C reduction after an acute ischemic event.

Rare primary dyslipidaemias associated with low LDL and HDL cholesterol values in Portugal

Background: Dyslipidaemia represents a group of disorders of lipid metabolism, characterized by either an increase or decrease in lipid particles, usually associated with triglycerides, LDL cholesterol (LDL-C) and/or HDL cholesterol (HDL-C). Most hyperlipidaemias and HDL deficiencies confer an increased cardiovascular risk, while hypolipidaemia, such as abeta or hypobetalipoproteinemia, may present different manifestations ranging from poor weight progression to neurological manifestations. The aim of this study is to present 7 cases with rare dyslipidaemias associated with low LDL or low HDL cholesterol values, referred to our laboratory for the genetic identification of the cause of the dyslipidaemia. Methods: Lipid profile was determined for each individual in an automated equipment Integra Cobas (Roche). Molecular analysis was performed by NGS with a target panel of 57 genes involved in lipid metabolism (Sure select QXT, Agilent) and samples were run in a NextSEQ Sequencer (Illumina). Only genes associated to rare forms of low HDL-c or LDL-c were analysed for this work, namely: ABCA1, APOA1, LCAT, SCARB1, APOB, PCSK9, MTTP, SAR1B, and ANGPTL3. All rare variants (MAF<5%) found in these genes were confirmed by Sanger sequencing. Results and discussion: This study includes 7 index cases (IC), with the following clinical diagnoses: Fish Eye Disease (1), Hypoalphalipoproteinemia (1) and Abetalipoproteinemia (ABL) / Familial Hypobetalipoproteinemia (FHBL) (5). We have identified one IC with a compound heterozygosity in LCAT causing Fish Eye Disease and one IC with a variant in ABCA1 in homozygosity causing Tangier disease. We found variants causing homozygous FHBL in 2 IC, one of whom has an undescribed pathogenic variant in homozygosity in APOB (c.12087+1G>A) and the other is a possible compound heterozygous for APOB variants c.2604+1G>A and c.4651C>T/p.(Gln1551*). In two patients only a variant in heterozygosity (c.3365delG/p.(Gly1122Vfs*62) and c.11095A>T/p.(Arg3699*)). In the remaining patient, no variants were identified. NGS proved to be a fundamental key for genetic testing of rare lipid disorders, allowing us to find the genetic cause of disease in 6/7 patients with low HDL-c and LDL-c. Patients with these rare conditions should be identified as early as possible in order to minimize or prevent clinical manifestations. The unsolved case is still under investigation.

Sterol and lipid analyses identifies hypolipidemia and apolipoprotein disorders in autism associated with adaptive functioning deficits

An improved understanding of sterol and lipid abnormalities in individuals with autism spectrum disorder (ASD) could lead to personalized treatment approaches. Toward this end, in blood, we identified reduced synthesis of cholesterol in families with ≥2 children with ASD participating with the Autism Genetic Resource Exchange (AGRE), as well as reduced amounts of high-density lipoprotein cholesterol (HDL), apolipoprotein A1 (ApoA1) and apolipoprotein B (ApoB), with 19.9% of the subjects presenting with apolipoprotein patterns similar to hypolipidemic clinical syndromes and 30% with either or both ApoA1 and ApoB less than the fifth centile. Subjects with levels less than the fifth centile of HDL or ApoA1 or ApoA1 + ApoB had lower adaptive functioning than other individuals with ASD, and hypocholesterolemic subjects had apolipoprotein deficits significantly divergent from either typically developing individuals participating in National Institutes of Health or the National Health and Nutrition Examination Survey III.

Low LDL-C levels are associated with risk of mortality in a Chinese cohort study

BACKGROUND AND AIMS

Although low-density lipoprotein cholesterol (LDL-C) has been considered as a risk factor of atherosclerotic cardiovascular disease, limited studies can be available to evaluate the association of LDL-C with risk of mortality in the general population. This study aimed to examine the association of LDL-C level with risk of mortality using a propensity-score weighting method in a Chinese population, based on the health examination data.

METHODS

We performed a retrospective cohort study with 65,517 participants aged 40 years or older in Ningbo city, Zhejiang. LDL-C levels were categorized as five groups according to the Chinese dyslipidemia guidelines in adults. To minimize potential biases resulting from a complex array of covariates, we implemented a generalized boosted model to generate propensity-score weights on covariates. Then, we used Cox proportional hazard regression models with all-cause and cause-specific mortality as the dependent variables to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs).

RESULTS

During the 439,186.5 person years of follow-up, 2403 deaths occurred. Compared with the median LDL-C group (100-130 mg/dL), subjects with extremely low LDL-C levels (group 1) had a higher risk of deaths from all-cause (HR = 2.53, 95% CI:1.80-3.53), CVD (HR = 1.84, 95% CI: 1.28-2.61), ischemic stroke (HR = 2.29, 95% CI:1.32-3.94), hemorrhagic stroke (HR = 3.49, 95% CI: 1.57-7.85), and cancer (HR = 2.12, 95% CI: 1.04-4.31) while the corresponding HRs in LDL-C group 2 were relatively lower than that in group 1.

CONCLUSIONS

Low LDL-C levels were associated with an increased risk of all-cause, CVD, ischemic stroke, hemorrhagic stroke, and cancer mortality in the Chinese population.

Discordance between apolipoprotein B or non-HDL-cholesterol and LDL-cholesterol in middle-aged and elderly Chinese patients predicts arterial stiffness

Background

Discordance of lipid parameters is closely associated with residual cardiovascular risk. This study investigated the discordance between non-high-density lipoprotein cholesterol (non-HDL-C) or apolipoprotein B (apoB) and low-density lipoprotein cholesterol (LDL-C), and assessed arterial stiffness risk.

Methods

This study included a total of 402 middle-aged and elderly Northern Chinese individuals whose brachial-ankle pulse wave conduction velocity (baPWV), and clinical and biochemical data were measured. Arterial stiffness was defined by inclusion in the upper quartile of the baPWV. All participants were divided into four mutually exclusive concordance/discordance groups based on the lipid goal for high-risk populations, according to the 2019 European Society of Cardiology / European Atherosclerosis Society guidelines. Discordance was defined as LDL-C ≥ 1.81 mmol/L with non-HDL-C <  2.59 mmol/L, or apoB < 0.80 mmol/L, or vice versa.

Results

The mean age of the participants was 65.9 ± 13.0 years; 59.5% of the participants were male. The mean LDL-C was 2.41 ± 0.81 mmol/L, non-HDL-C: 3.06 ± 0.94 mmol/L, and apoB: 0.84 ± 0.21 mmol/L. LDL-C was observed to be discordant with non-HDL-C (20.1%) and apoB (30.8%). When stratified according to LDL-C levels, the baPWV was greater in those patients with higher non-HDL-C or apoB levels. In the adjusted logistic regression model, low LDL-C and high non-HDL-C or apoB discordance were also associated with the risk of arterial stiffness (OR: 13.412 and OR: 13.054, respectively).

Conclusions

There was discordance between LDL-C and non-HDL-C, or apoB in middle-aged and elderly Chinese individuals; this was associated with a higher risk of arterial stiffness. Non-HDL-C or apoB levels could be used to identify individuals who may benefit from more comprehensive lipid modification.

How low is safe? The frontier of very low (<30 mg/dL) LDL cholesterol

Low-density lipoprotein cholesterol (LDL-C) is a proven causative factor for developing atherosclerotic cardiovascular disease. Individuals with genetic conditions associated with lifelong very low LDL-C levels can be healthy. We now possess the pharmacological armamentarium (statins, ezetimibe, PCSK9 inhibitors) to reduce LDL-C to an unprecedented extent. Increasing numbers of patients are expected to achieve very low (<30 mg/dL) LDL-C. Cardiovascular event reduction increases log linearly in association with lowering LDL-C, without reaching any clear plateau even when very low LDL-C levels are achieved. It is still controversial whether lower LDL-C levels are associated with significant clinical adverse effects (e.g. new-onset diabetes mellitus or possibly haemorrhagic stroke) and long-term data are needed to address safety concerns. This review presents the familial conditions characterized by very low LDL-C, analyses trials with lipid-lowering agents where patients attained very low LDL-C, and summarizes the benefits and potential adverse effects associated with achieving very low LDL-C. Given the potential for cardiovascular benefit and short-term safe profile of very low LDL-C, it may be advantageous to attain such low levels in specific high-risk populations. Further studies are needed to compare the net clinical benefit of non-LDL-C-lowering interventions with very low LDL-C approaches, in addition to comparing the efficacy and safety of very low LDL-C levels vs. current recommended targets.

Diagnosis and management of secondary causes of steatohepatitis

The term non-alcoholic fatty liver disease (NAFLD) was originally coined to describe hepatic fat deposition as part of the metabolic syndrome. However, a variety of rare hereditary liver and metabolic diseases, intestinal diseases, endocrine disorders and drugs may underlie, mimic, or aggravate NAFLD. In contrast to primary NAFLD, therapeutic interventions are available for many secondary causes of NAFLD. Accordingly, secondary causes of fatty liver disease should be considered during the diagnostic workup of patients with fatty liver disease, and treatment of the underlying disease should be started to halt disease progression. Common genetic variants in several genes involved in lipid handling and metabolism modulate the risk of progression from steatosis to fibrosis, cirrhosis and hepatocellular carcinoma development in NAFLD, alcohol-related liver disease and viral hepatitis. Hence, we speculate that genotyping of common risk variants for liver disease progression may be equally useful to gauge the likelihood of developing advanced liver disease in patients with secondary fatty liver disease.

Rare Protein-Truncating Variants in APOB, Lower Low-Density Lipoprotein Cholesterol, and Protection Against Coronary Heart Disease

Supplemental Digital Content is available in the text.

Background

Familial hypobetalipoproteinemia is a genetic disorder caused by rare protein-truncating variants (PTV) in the gene encoding APOB (apolipoprotein B), the major protein component of LDL (low-density lipoprotein) and triglyceride-rich lipoprotein particles. Whether heterozygous APOB deficiency is associated with decreased risk for coronary heart disease (CHD) is uncertain. We combined family-based and large scale gene-sequencing to characterize the association of rare PTVs in APOB with circulating LDL-C (LDL cholesterol), triglycerides, and risk for CHD.

Methods

We sequenced the APOB gene in 29 Japanese hypobetalipoproteinemia families, as well as 57 973 individuals derived from 12 CHD case-control studies—18 442 with early-onset CHD and 39 531 controls. We defined PTVs as variants that lead to a premature stop, disrupt canonical splice-sites, or lead to insertions/deletions that shift reading frame. We tested the association of rare APOB PTV carrier status with blood lipid levels and CHD.

Results

Among 29 familial hypobetalipoproteinemia families, 8 families harbored APOB PTVs. Carrying 1 APOB PTV was associated with 55 mg/dL lower LDL-C (P=3×10^-5) and 53% lower triglyceride level (P=2×10^-4). Among 12 case-control studies, an APOB PTV was present in 0.038% of CHD cases as compared to 0.092% of controls. APOB PTV carrier status was associated with a 43 mg/dL lower LDL-C (P=2×10^-7), a 30% decrease in triglycerides (P=5×10^-4), and a 72% lower risk for CHD (odds ratio, 0.28; 95% CI, 0.12–0.64; P=0.002).

Conclusions

Rare PTV mutations in APOB which are associated with lower LDL-C and reduced triglycerides also confer protection against CHD.

Gene-based therapy in lipid management: the winding road from promise to practice

INTRODUCTION

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality. High plasma low-density lipoprotein cholesterol (LDL-C) levels are a key CVD-risk factor. Triglyceride-rich remnant particles and lipoprotein(a) (Lp[a]) are also causally related to CVD. Consequently, therapeutic strategies for lowering LDL-C and triglyceride levels are widely used in routine clinical practice; however, specific Lp(a) lowering agents are not available. Many patients do not achieve guideline-recommended lipid levels with currently available therapies; hence, novel targets and treatment modalities are eagerly sought.

AREAS COVERED

We discuss the milestones on the trajectory toward the full application of gene-based therapies in daily clinical practice. We describe the different methods, ranging from antisense oligonucleotides to liver-directed gene therapy and Crispr-cas9 modification to target the pivotal players in lipid metabolism: PCSK9, APOB, ANGPTL3, Lp(a), LDLR, and apoC-III.

EXPERT OPINION

While acknowledging their different stages of development, gene-based therapies are likely to invoke a paradigm shift in lipid management because they allow us to target previously undruggable targets. Moreover, their low dosing frequency, high target selectivity, and relatively predictable adverse event profile are considered major advantages over current lipid-lowering therapies.

Clinical and biochemical characteristics of individuals with low cholesterol syndromes: A comparison between familial hypobetalipoproteinemia and familial combined hypolipidemia

BACKGROUND

The most frequent monogenic causes of low plasma cholesterol are familial hypobetalipoproteinemia (FHBL1) because of truncating mutations in apolipoprotein B coding gene (APOB) and familial combined hypolipidemia (FHBL2) due to loss-of-function mutations in ANGPTL3 gene.

OBJECTIVE

A direct comparison of lipid phenotypes of these 2 conditions has never been carried out. In addition, although an increased prevalence of liver steatosis in FHBL1 has been consistently reported, the hepatic consequences of FHBL2 are not well established.

METHODS

We investigated 350 subjects, 67 heterozygous carriers of APOB mutations, 63 carriers of the p.S17* mutation in ANGPTL3 (57 heterozygotes and 6 homozygotes), and 220 noncarrier normolipemic controls. Prevalence and degree of hepatic steatosis were assessed by ultrasonography.

RESULTS

A steady decrease of low-density lipoprotein cholesterol levels were observed from heterozygous to homozygous FHBL2 and to FHBL1 individuals, with the lowest levels in heterozygous FHBL1 carrying truncating mutations in exons 1 to 25 of APOB (P for trend <.001). Plasma triglycerides levels were similar in heterozygous FHBL1 and homozygous FHBL2 individuals, but higher in heterozygous FHBL2. The lowest high-density lipoprotein cholesterol levels were detected in homozygous FHBL2 (P for trend <.001). Compared with controls, prevalence and severity of hepatic steatosis were increased in heterozygous FHBL1 (P < .001), but unchanged in FHBL2 individuals.

CONCLUSION

Truncating APOB mutations showed the more striking low-density lipoprotein cholesterol lowering effect compared with p.S17* mutation in ANGPTL3. Reduced high-density lipoprotein cholesterol levels were the unique lipid characteristic associated with FHBL2. Mutations impairing liver synthesis or secretion of apolipoprotein B are crucial to increase the risk of liver steatosis.

Evidence-based goals in LDL-C reduction

The evidence from trials of statin therapy suggests that benefits in cardiovascular disease (CVD) event reduction are proportional to the magnitude of low-density lipoprotein cholesterol (LDL-C) lowering. The lack of a threshold at which LDL-C lowering is not beneficial, in terms of CVD prevention observed in these trials, is supported by epidemiological and genetic studies reporting the cardio-protective effects of lifelong low exposure to atherogenic cholesterol in a graded fashion. Providing that intensive LDL-C lowering is safe, these observations suggest that many individuals even at current LDL-C treatment targets could benefit. Here, we review recent safety and efficacy data from trials of adjunctive therapy, with LDL-C lowering beyond that achieved by statin therapy, and their potential implications for current guideline targets. Finally, the application of current guidance in the context of pre-treatment LDL-C concentration and deployment of statin therapy is also discussed. The number of patients requiring treatment to prevent a CVD event with statin treatment has been shown to differ markedly according to the pre-treatment LDL-C concentration even when absolute CVD risk is similar. It produces more likelihood of benefit when absolute LDL-C reduction is greater which is largely dependent on pre-treatment LDL-C concentration. This also has to be taken in consideration when deploying new agents like proprotein convertase subtilisin/kexin type 9 monoclonal antibodies. Patients with highest LDL-C concentration despite maximum statin and ezetimibe therapy will attain most absolute LDL-C reduction when treated with proprotein convertase subtilisin/kexin type 9 monoclonal antibodies, hence benefit most in term of CVD risk reduction.

Association between familial hypobetalipoproteinemia and the risk of diabetes. Is this the other side of the cholesterol-diabetes connection? A systematic review of literature

Statin therapy is beneficial in reducing LDL cholesterol (LDL-C) levels and cardiovascular events, but it is associated with the risk of incident diabetes mellitus (DM). Familial hypercholesterolemia (FH) is characterized by genetically determined high levels of plasma LDL-C and a low prevalence of DM. LDL-C levels seem then inversely correlated with prevalence of DM. Familial hypobetalipoproteinemia (FHBL) represents the genetic mirror of FH in terms of LDL-C levels, very low in subjects carrying mutations of APOB, PCSK9 (FHBL1) or ANGPTL3 (FHBL2). This review explores the hypothesis that FHBL might represent also the genetic mirror of FH in terms of prevalence of DM and that it is expected to be increased in FHBL in comparison with the general population. A systematic review of published literature on FHBL was made by searching PubMed (1980-2016) for articles presenting clinical data on FHBL probands and relatives. The standardized prevalence rates of DM in FHBL1 were similar to those of the reference population, with a prevalence rate of 8.2 and 9.2%, respectively, while FHBL2 showed a 4.9% prevalence of DM. In conclusion, low LDL-C levels of FHBL do not seem connected to DM as it happens in subjects undergoing statin therapy and the diabetogenic effect of statins has to be explained by mechanisms that do not rely exclusively on the reduced levels of LDL-C. The review also summarizes the published data on the effects of FHBL on insulin sensitivity and the relationships between FH, statin therapy, FHBL1 and intracellular cholesterol metabolism, evaluating possible diabetogenic pathways.

Non-alcoholic fatty liver disease and risk of cardiovascular disease

Non-alcoholic fatty liver disease (NAFLD) has become the leading cause of chronic liver diseases worldwide, causing considerable liver-related mortality and morbidity. During the past decade, it has also become increasingly evident that NAFLD is a multisystem disease that affects many extra-hepatic organ systems, including the heart and the vascular system. In this updated clinical review, we discuss the rapidly expanding body of clinical and epidemiological evidence that supports a strong association of NAFLD with cardiovascular diseases (CVDs) and other functional and structural myocardial abnormalities. We also discuss some recently published data that correlate NAFLD due to specific genetic polymorphisms with the risk of CVDs. Finally, we briefly examine the assessment tools for estimating the global CVD risk in patients with NAFLD as well as the conventional and the more innovative pharmacological approaches for the treatment of CVD risk in this group of patients.

Pharmacological Targeting of the Atherogenic Dyslipidemia Complex: The Next Frontier in CVD Prevention Beyond Lowering LDL Cholesterol

Notwithstanding the effectiveness of lowering LDL cholesterol, residual CVD risk remains in high-risk populations, including patients with diabetes, likely contributed to by non-LDL lipid abnormalities. In this Perspectives in Diabetes article, we emphasize that changing demographics and lifestyles over the past few decades have resulted in an epidemic of the "atherogenic dyslipidemia complex," the main features of which include hypertriglyceridemia, low HDL cholesterol levels, qualitative changes in LDL particles, accumulation of remnant lipoproteins, and postprandial hyperlipidemia. We briefly review the underlying pathophysiology of this form of dyslipidemia, in particular its association with insulin resistance, obesity, and type 2 diabetes, and the marked atherogenicity of this condition. We explain the failure of existing classes of therapeutic agents such as fibrates, niacin, and cholesteryl ester transfer protein inhibitors that are known to modify components of the atherogenic dyslipidemia complex. Finally, we discuss targeted repurposing of existing therapies and review promising new therapeutic strategies to modify the atherogenic dyslipidemia complex. We postulate that targeting the central abnormality of the atherogenic dyslipidemia complex, the elevation of triglyceride-rich lipoprotein particles, represents a new frontier in CVD prevention and is likely to prove the most effective strategy in correcting most aspects of the atherogenic dyslipidemia complex, thereby preventing CVD events.

Integrated Safety Assessment of 2'-O-Methoxyethyl Chimeric Antisense Oligonucleotides in NonHuman Primates and Healthy Human Volunteers

The common chemical and biological properties of antisense oligonucleotides provide the opportunity to identify and characterize chemical class effects across species. The chemical class that has proven to be the most versatile and best characterized is the 2′-O-methoxyethyl chimeric antisense oligonucleotides. In this report we present an integrated safety assessment of data obtained from controlled dose-ranging studies in nonhuman primates (macaques) and healthy human volunteers for 12 unique 2′-O-methoxyethyl chimeric antisense oligonucleotides. Safety was assessed by the incidence of safety signals in standardized laboratory tests for kidney and liver function, hematology, and complement activation; as well as by the mean test results as a function of dose level over time. At high doses a number of toxicities were observed in nonhuman primates. However, no class safety effects were identified in healthy human volunteers from this integrated data analysis. Effects on complement in nonhuman primates were not observed in humans. Nonhuman primates predicted safe doses in humans, but over predicted risk of complement activation and effects on platelets. Although limited to a single chemical class, comparisons from this analysis are considered valid and accurate based on the carefully controlled setting for the specified study populations and within the total exposures studied.

Vitamin E and oxidative stress in abetalipoproteinemia and familial hypobetalipoproteinemia

Abetalipoproteinemia (ABL) and familial hypobetalipoproteinemia (FHBL) are genetic diseases characterized by low density lipoprotein deficiency. ABL presents early in life with the gastroenterological manifestations of fat malabsorption, steatorrhea, and failure to thrive, and later in life, with progressive ophthalmopathy and neuropathy as a result of deficiency of the fat-soluble vitamins A and E. Heterozygous FHBL subjects are usually asymptomatic, but may develop fatty liver disease. In homozygous (compound heterozygous) FHBL, the clinical and biochemical features are indistinguishable from those of ABL and treatment recommendations are the same: dietary fat restriction to prevent steatorrhea, and long-term high-dose vitamin E and A supplementation to prevent or at least slow the progression of neuromuscular and retinal degenerative disease. Despite their low plasma vitamin E levels, individuals with heterozygous FHBL do not require vitamin E supplementation. There are conflicting reports on whether increased oxidative stress is seen in ABL; these differences may relate to the small size of patient groups as well as differences in patient age and dose of vitamin E supplementation, or the contribution from dietary sources of vitamin E. High density lipoproteins in ABL appear to be severely oxidized yet able to inhibit platelet aggregation by binding to scavenger receptor B1. We review the role of vitamin E and oxidative stress in ABL and FHBL.

Exome sequencing identifies novel ApoB loss-of-function mutations causing hypobetalipoproteinemia in type 1 diabetes

AIM

Diabetic patients commonly suffer from disturbances in production and clearance of plasma lipoproteins, known as diabetic dyslipidemia, resulting in an increased risk of coronary heart disease. The study aimed to examine the cause of hypobetalipoproteinemia in two patients with type 1 diabetes.

METHODS

The Diabetes Control and Complications Trial (DCCT) is a study demonstrating that intensive blood glucose control delays the onset and progression of type 1 diabetes complications. Hypobetalipoproteinemia was present in two DCCT subjects, IDs 1427 and 1078, whose LDL-C levels were 36 and 28 mg/dL, respectively, and triglyceride levels were 20 and 28 mg/dL, respectively. We performed exome sequencing on genomic DNA from the two patients with hypobetalipoproteinemia.

RESULTS

The subjects 1427 and 1078 had heterozygous loss-of-function mutations in the gene apolipoprotein B (ApoB), and these mutations resulted in premature stop codons at amino acid 1333 (ApoB-29) and 3680 (ApoB-81), respectively. Indeed, the plasma ApoB level of subject 1427 (19 mg/dL) was the lowest and that of subject 1078 (26 mg/dL) was the second to the lowest among all the 1,441 DCCT participants. Sequencing genomic DNA of family members showed that probands 1427 and 1078 inherited the mutations from the father and the mother, respectively.

CONCLUSIONS

The identification of ApoB loss-of-function mutations in type 1 diabetic patients presents innovative cases to study the interaction between hypobetalipoproteinemia and insulin deficiency.

Homozygous familial hypobetalipoproteinemia: two novel mutations in the splicing sites of apolipoprotein B gene and review of the literature

OBJECTIVE

Familial hypobetalipoproteinemia (FHBL) is autosomal codominant disorder of lipoprotein metabolism characterized by low plasma levels of total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C) and apolipoprotein B (apoB) below the 5(th) percentile of the distribution in the population. Patients with the clinical diagnosis of homozygous FHBL (Ho-FHBL) are extremely rare and few patients have been characterized at the molecular level. Here we report the medical history and the molecular characterization of one paediatric patient with clinical features of Ho-FHBL.

METHODS

A one month old infant with failure to thrive, severe hypocholesterolemia and acanthocytosis was clinically and genetically characterized. Molecular characterization of the proband and her parents was performed by direct sequencing of the APOB gene and functional role of the identified mutations was assessed by the minigene methodology.

RESULTS

The proband was found carrying two novel splicing mutations of the APOB gene (c.3696+1G > C and c.3697-1G > A). CHOK1H8 cells expressing minigenes harbouring the mutations showed that these two mutations were associated with the retention of intron 23 and skipping of exon 24, resulting in two truncated apoB fragments of approximate size of 26-28 % of ApoB-100 and the total absence of apoB.

CONCLUSION

We describe the first case of Ho-FHBL due to two splicing mutations affecting both the donor and the acceptor splice sites of the same intron of the APOB gene occurring in the same patient. The clinical management of the proband is discussed and a review of the clinical and genetic features of the published Ho-FHBL cases is reported.

Update on primary hypobetalipoproteinemia

"Primary hypobetalipoproteinemia" refers to an eclectic group of inherited lipoprotein disorders characterized by low concentrations of or absence of low-density lipoprotein cholesterol and apolipoprotein B in plasma. Abetalipoproteinemia and homozygous familial hypobetalipoproteinemia, although caused by mutations in different genes, are clinically indistinguishable. A framework for the clinical follow-up and management of these two disorders has been proposed recently, focusing on monitoring of growth in children and preventing complications by providing specialized dietary advice and fat-soluble vitamin therapeutic regimens. Other recent publications on familial combined hypolipidemia suggest that although a reduction of angiopoietin-like 3 activity may improve insulin sensitivity, complete deficiency also reduces serum cholesterol efflux capacity and increases the risk of early vascular atherosclerotic changes, despite low low-density lipoprotein cholesterol levels. Specialist laboratories offer exon-by-exon sequence analysis for the molecular diagnosis of primary hypobetalipoproteinemia. In the future, massively parallel sequencing of panels of genes involved in dyslipidemia may play a greater role in the diagnosis of these conditions.

Homozygous MTTP and APOB mutations may lead to hepatic steatosis and fibrosis despite metabolic differences in congenital hypocholesterolemia

BACKGROUND & AIMS

Non-alcoholic steatohepatitis leading to fibrosis occurs in patients with abetalipoproteinemia (ABL) and homozygous or compound heterozygous familial hypobetalipoproteinemia (Ho-FHBL). We wanted to establish if liver alterations were more frequent in one of both diseases and were influenced by comorbidities.

METHODS

We report genetic, clinical, histological and biological characteristics of new cases of ABL (n =7) and Ho-FHBL (n = 7), and compare them with all published ABL (51) and Ho-FHBL (22) probands.

RESULTS

ABL patients, diagnosed during infancy, presented mainly with diarrhea, neurological and ophthalmological impairments and remained lean, whereas Ho-FHBL were diagnosed later, with milder symptoms often becoming overweight in adulthood. Despite subtle differences in lipid phenotype, liver steatosis was observed in both groups with a high prevalence of severe fibrosis (5/27 for Ho-FHBL vs. 4/58 for ABL (n.s.)). Serum triglycerides concentration was higher in Ho-FHBL whereas total and HDL-cholesterol were similar in both groups. In Ho-FHBL liver alterations were found to be independent from the apoB truncation size and apoB concentrations.

CONCLUSIONS

Our findings provide evidence for major liver abnormalities in both diseases. While ABL and Ho-FHBL patients have subtle differences in lipid phenotype, carriers of APOB mutations are more frequently obese. These results raise the question of a complex causal link between apoB metabolism and obesity. They suggest that the genetic defect in VLDL assembly is critical for the occurrence of liver steatosis leading to fibrosis and shows that obesity and insulin resistance might contribute by increasing lipogenesis.

New therapies targeting apoB metabolism for high-risk patients with inherited dyslipidaemias: what can the clinician expect?

Apolipoprotein B (apoB) has a key role in the assembly and secretion of very low-density lipoprotein (VLDL) from the liver. Plasma apoB concentration affects the number of circulating atherogenic particles, and serves as an independent predictor of the risk of atherosclerotic cardiovascular disease. While statins are the most potent apoB-lowering agents currently prescribed, their efficacy in achieving therapeutic targets for low-density lipoprotein cholesterol (LDL-C) in high-risk patients, such as those with familial hypercholesterolaemia (FH), is limited. Resistance and intolerance to statins also occurs in a significant number of patients, necessitating new types of lipid-lowering therapies. Monoclonal antibodies against proprotein convertase subtilisin/kexin type 9 (PCSK9; AMG 145 and REGN727), a sequence-specific antisense oligonucleotide against apoB mRNA (mipomersen) and a synthetic inhibitor of microsomal triglyceride transfer protein (MTTP; lomitapide) have been tested in phase III clinical trials, particularly in patients with FH. The trials demonstrated the efficacy of these agents in lowering apoB, LDL-C, non-high-density lipoprotein cholesterol and lipoprotein(a) by 32-55 %, 37-66 %, 38-61 % and 22-50 % (AMG 145), 21-68 %, 29-72 %, 16-60 % and 8-36 % (REGN727), 16-71 %, 15-71 %, 12-66 % and 23-49 % (mipomersen) and 24-55 %, 25-51 %, 27-50 % and 15-19 % (lomitapide), respectively. Monoclonal antibodies against PCSK9 have an excellent safety profile and may be indicated not only in heterozygous FH, but also in statin-intolerant patients and those with other inherited dyslipidemias, such as familial combined hyperlipidaemia and familial elevation in Lp(a). Mipomersen and lomitapide increase hepatic fat content and are at present indicated for treating adult patients with homozygous FH alone.

Lipoprotein apheresis and new therapies for severe familial hypercholesterolemia in adults and children

Familial hypercholesterolemia (FH), the most common and severe monogenic form of hypercholesterolemia, is an autosomal co-dominant disease characterized by an increased plasma low density lipoprotein (LDL)-cholesterol concentration and premature coronary heart disease (CHD). The clinical phenotype depends on the gene involved and severity of mutation (or mutations) present. Patients with homozygous or compound heterozygous FH have severe hypercholesterolemia (LDL-cholesterol >13 mmol/L) due to a gene dosing effect and without treatment have accelerated atherosclerotic CHD from birth, and frequently die of CHD before age 30. Cholesterol-lowering therapies have been shown to reduce both mortality and major adverse cardiovascular events in individuals with FH. Lipoprotein apheresis concomitant with lipid-lowering therapy is the treatment of choice for homozygous FH. This article describes the rationale and role of lipoprotein apheresis in the treatment of severe FH and outlines the recent advances in new pharmacotherapies for this condition.

Genetics of lipid traits and relationship to coronary artery disease

Despite the critical importance of plasma lipoproteins in the development of atherosclerosis, varying degrees of evidence surround the causal associations of lipoproteins with coronary artery disease (CAD). These causal contributions can be assessed by employing genetic variants as unbiased proxies for lipid levels. A relatively large number of low-density lipoprotein cholesterol (LDL-C) variants strongly associate with CAD, confirming the causal impact of this lipoprotein on atherosclerosis. Although not as firmly established, genetic evidence supporting a causal role of triglycerides (TG) in CAD is growing. Conversely, high-density lipoprotein cholesterol (HDL-C) variants not associated with LDL-C or TG have not yet been shown to be convincingly associated with CAD, raising questions about the causality of HDL-C in atherosclerosis. Finally, genetic variants at the LPA locus associated with lipoprotein(a) [Lp(a)] are decisively linked to CAD, indicating a causal role for Lp(a). Translational investigation of CAD-associated lipid variants may identify novel regulatory pathways with therapeutic potential to alter CAD risk.

Cardiovascular risk, lipidemic phenotype and steatosis. A comparative analysis of cirrhotic and non-cirrhotic liver disease due to varying etiology

BACKGROUND

Liver regulates lipid metabolism in health and disease states. Nevertheless, the entity of cardiovascular risk (CVR) resulting from dysregulation of lipid metabolism secondary to liver disease is poorly characterized.

AIM AND METHODS

To review, based on a PubMed literature search, the features and the determinants of serum lipid phenotype and its correlation with hepatic steatosis, insulin resistance (IR) and CVR across the wide spectrum of the most common chronic liver diseases due to different etiologies.

RESULTS

Alcoholic liver disease (ALD) is associated with steatosis, IR and a typical lipid profile. The relationship between alcohol intake, incident type 2 diabetes (T2D) and CVR describes a J-shaped curve. Non-alcoholic fatty liver disease (NAFLD), and probably nonalcoholic steatohepatitis (NASH) in particular, is associated with IR, atherogenic dyslipidemia and increased CVR independent of traditional risk factors. Moreover, NASH-cirrhosis and T2D contribute to increasing CVR in liver transplant recipients. HBV infection is generally free from IR, steatosis and CVR. HCV-associated dysmetabolic syndrome, featuring steatosis, hypocholesterolemia and IR, appears to be associated with substantially increased CVR. Hyperlipidemia is an almost universal finding in primary biliary cirrhosis, a condition typically spared from steatosis and associated with neither subclinical atherosclerosis nor excess CVR. Finally, little is known on CVR in patients with hepatocellular carcinoma.

CONCLUSIONS

CVR is increased in ALD, NAFLD and chronic HCV infection, all conditions featuring IR and steatosis. Therefore, irrespective of serum lipid phenotype, hepatic steatosis and IR may be major shared determinants in amplifying CVR in common liver disease due to varying etiology.

Clinical characteristics and plasma lipids in subjects with familial combined hypolipidemia: a pooled analysis

Angiopoietin-like 3 (ANGPTL3) regulates lipoprotein metabolism by modulating extracellular lipases. Loss-of function mutations in ANGPTL3 gene cause familial combined hypolipidemia (FHBL2). The mode of inheritance and hepatic and vascular consequences of FHBL2 have not been fully elucidated. To get further insights on these aspects, we reevaluated the clinical and the biochemical characteristics of all reported cases of FHBL2. One hundred fifteen FHBL2 individuals carrying 13 different mutations in the ANGPTL3 gene (14 homozygotes, 8 compound heterozygotes, and 93 heterozygotes) and 402 controls were considered. Carriers of two mutant alleles had undetectable plasma levels of ANGPTL3 protein, whereas heterozygotes showed a reduction ranging from 34% to 88%, according to genotype. Compared with controls, homozygotes as well as heterozygotes showed a significant reduction of all plasma lipoproteins, while no difference in lipoprotein(a) [Lp(a)] levels was detected between groups. The prevalence of fatty liver was not different in FHBL2 subjects compared with controls. Notably, diabetes mellitus and cardiovascular disease were absent among homozygotes. FHBL2 trait is inherited in a codominant manner, and the lipid-lowering effect of two ANGPTL3 mutant alleles was more than four times larger than that of one mutant allele. No changes in Lp(a) were detected in FHBL2. Furthermore, our analysis confirmed that FHBL2 is not associated with adverse clinical sequelae. The possibility that FHBL2 confers lower risk of diabetes and cardiovascular disease warrants more detailed investigation.

Familial hypobetalipoproteinemia: analysis of three Spanish cases with two new mutations in the APOB gene

Extremely low LDL-cholesterol concentrations are very unusual and generally related with comorbidities accompanying malnutrition. Less frequently low LDL-cholesterol levels result from mutations in the APOB, PCSK9, ANGPTL3, SAR1B and MTTP genes (primary hypobetalipoproteinemia). We investigated three patients with plasma LDL-cholesterol levels below the fifth percentile of the Spanish population. We recorded data on demographic and anthropometric characteristics, life style habits, physical examination, liver ultrasound and lipid and lipoprotein levels, in the probands and their first-degree relatives. Secondary causes of hypocholesterolemia were ruled out by clinical study, complementary tests and follow-up. The APOB, MTTP and SAR1B genes were sequenced. Patients were found to be heterozygotes for point mutations located in the exon 26 of the APOB gene. One patient, with fatty liver, carried a previously described mutation (c.7600C>T) (Arg2507X), causing the formation of truncated Apo B-55.25. The other two mutations producing truncations are new. One asymptomatic patient carried the Arg3672X (Apo B-80.93) and the other with fatty liver and steatorrhea carried the Ser2184fsVal2193X (Apo B-48.32). Our study reinforces the concept that in the heterozygous carriers of truncated Apo Bs, the clinical manifestations of FHBL are dependent on the size of the truncations.

Is mipomersen ready for clinical implementation? A transatlantic dilemma

PURPOSE OF REVIEW

Mipomersen has been approved by the US Food and Drug Administration as an orphan drug for patients with homozygous familial hypercholesterolemia (HoFH). In contrast, the European Medicines Agency advised negatively on the use of mipomersen. In this review, we discuss the efficacy and safety considerations for this discrepancy.

RECENT FINDINGS

On the basis of the results of clinical trials with mipomersen, safety concerns have been raised regarding cardiovascular risk reduction and development of hepatic steatosis. In addition, (long-term) tolerability concerns have been raised predominantly regarding injection site reactions. A pooled analysis of cardiovascular events in phase III trials with mipomersen did not provide evidence for either a positive or negative effect on cardiovascular disease. Although long-term studies with mipomersen are eagerly awaited, hepatic fat content appears to stabilize after 6-12 months notwithstanding continued mipomersen administration.

SUMMARY

HoFH is a disease with an unmet medical need for new lipid-lowering therapies. On the basis of a mean 2.9 mmol/l LDL-cholesterol reduction, mipomersen is expected to reduce cardiovascular risk in HoFH. Available evidence suggests that the fat accumulation associated with this treatment differs from steatohepatitis, which is a progressive and damaging liver disease. No evidence is available suggesting that injection site reactions because of mipomersen treatment will result in safety issues.

A novel APOB mutation identified by exome sequencing cosegregates with steatosis, liver cancer, and hypocholesterolemia

OBJECTIVE

In familial hypobetalipoproteinemia, fatty liver is a characteristic feature, and there are several reports of associated cirrhosis and hepatocarcinoma. We investigated a large kindred in which low-density lipoprotein cholesterol, fatty liver, and hepatocarcinoma displayed an autosomal dominant pattern of inheritance.

APPROACH AND RESULTS

The proband was a 25-year-old female with low plasma cholesterol and hepatic steatosis. Low plasma levels of total cholesterol and fatty liver were observed in 10 more family members; 1 member was affected by liver cirrhosis, and 4 more subjects died of either hepatocarcinoma or carcinoma on cirrhosis. To identify the causal mutation in this family, we performed exome sequencing in 2 participants with hypocholesterolemia and fatty liver. Approximately 22 400 single nucleotide variants were identified in each sample. After variant filtering, 300 novel shared variants remained. A nonsense variant, p.K2240X, attributable to an A>T mutation in exon 26 of APOB (c.6718A>T) was identified, and this variant was confirmed by Sanger sequencing. The gentotypic analysis of 16 family members in total showed that this mutation segregated with the low cholesterol trait. In addition, genotyping of the PNPLA3 p.I148M did not show significant frequency differences between carriers and noncarriers of the c.6718A>T APOB gene mutation.

CONCLUSIONS

We used exome sequencing to discover a novel nonsense mutation in exon 26 of APOB (p.K2240X) responsible for low cholesterol and fatty liver in a large kindred. This mutation may also be responsible for cirrhosis and liver cancer in this family.

Safety and effect of very low levels of low-density lipoprotein cholesterol on cardiovascular events

Based on the cardiovascular (CV) outcomes data derived predominantly from 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor (statin) trials, guidelines have set low-density lipoprotein (LDL) cholesterol targets at successively lower levels over time. Recent data have demonstrated that more-intensive statin therapy (and, consequently, lower LDL cholesterol level) is more effective at reducing CV events than less-intensive statin therapy. Although the average LDL cholesterol level for a United States adult is 119 mg/dl, within the "normal" range (90 to 130 mg/dl) per the United States National Cholesterol Education Program-Adult Treatment Panel III guidelines, data from fetal studies, diet studies, contemporary hunter-gatherer populations, and other mammals have suggested that the "normal" physiologic range for LDL cholesterol in humans is likely 50 to 70 mg/dl. Low LDL cholesterol levels have been sporadically associated with an increased risk of cancer, hemorrhagic stroke, and other complications in population studies and clinical trials. However, statin clinical trials have generally not demonstrated correlations between on-treatment LDL cholesterol levels and safety. Clinical data have suggested a linear relation between LDL cholesterol lowering and CV risk reduction, supporting a favorable risk/benefit ratio for attaining very low levels of LDL cholesterol to minimize the risk of CV events. In conclusion, clinical trial evidence demonstrating the efficacy and safety of LDL cholesterol lowering to a very low level is essential to ascertain the benefits and risks in reducing the residual risk of vascular disease.

Anti-PCSK9 therapies for the treatment of hypercholesterolemia

INTRODUCTION

Proprotein convertase subtilisin kexin type 9 (PCSK9), a serine protease that binds to the low density lipoprotein (LDL) receptor promoting its degradation, is an important regulator of LDL metabolism. PCSK9 'gain-of-function' mutations are rare and cause high plasma LDL-cholesterol and increase atherosclerotic cardiovascular disease, whereas more common 'loss-of-function' mutations cause low LDL-cholesterol and atheroprotection. PCSK9 is a novel, attractive and viable therapeutic target for the treatment of hypercholesterolemia, with human studies using a variety of anti-PCSK9 therapies underway.

AREAS COVERED

This review summarizes the latest findings in clinical trials of PCSK9 inhibitors, including antibodies, gene silencing and small peptides.

EXPERT OPINION

PCSK9 inhibition would appear to be an effective strategy for lowering plasma LDL-cholesterol and enhancing the LDL-cholesterol lowering ability of statins in patients with familial hypercholesterolemia, patients with refractory hypercholesterolemia at high risk of cardiovascular disease and patients with severe hypercholesterolemia who are not at target or are intolerant of statins, with a variety of anti-PCSK9 therapies in clinical trials.

Lipoprotein metabolism in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), an escalating health problem worldwide, covers a spectrum of pathologies characterized by fatty accumulation in hepatocytes in early stages, with potential progression to liver inflammation, fibrosis, and failure. A close, yet poorly understood link exists between NAFLD and dyslipidemia, a constellation of abnormalities in plasma lipoproteins including triglyceride-rich very low density lipoproteins. Apolipoproteins are a group of primarily liver-derived proteins found in serum lipoproteins; they not only play an extracellular role in lipid transport between vital organs through circulation, but also play an important intracellular role in hepatic lipoprotein assembly and secretion. The liver functions as the central hub for lipoprotein metabolism, as it dictates lipoprotein production and to a significant extent modulates lipoprotein clearance. Lipoprotein metabolism is an integral component of hepatocellular lipid homeostasis and is implicated in the pathogenesis, potential diagnosis, and treatment of NAFLD.