Beyond the genetics of HDL: why is HDL cholesterol inversely related to cardiovascular disease?

Modulation of Bile Acid Metabolism to Improve Plasma Lipid and Lipoprotein Profiles

New drugs targeting bile acid metabolism are currently being evaluated in clinical studies for their potential to treat cholestatic liver diseases, non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). Changes in bile acid metabolism, however, translate into an alteration of plasma cholesterol and triglyceride concentrations, which may also affect cardiovascular outcomes in such patients. This review attempts to gain insight into this matter and improve our understanding of the interactions between bile acid and lipid metabolism. Bile acid sequestrants (BAS), which bind bile acids in the intestine and promote their faecal excretion, have long been used in the clinic to reduce LDL cholesterol and, thereby, atherosclerotic cardiovascular disease (ASCVD) risk. However, BAS modestly but consistently increase plasma triglycerides, which is considered a causal risk factor for ASCVD. Like BAS, inhibitors of the apical sodium-dependent bile acid transporter (ASBTi’s) reduce intestinal bile acid absorption. ASBTi’s show effects that are quite similar to those obtained with BAS, which is anticipated when considering that accelerated faecal loss of bile acids is compensated by an increased hepatic synthesis of bile acids from cholesterol. Oppositely, treatment with farnesoid X receptor agonists, resulting in inhibition of bile acid synthesis, appears to be associated with increased LDL cholesterol. In conclusion, the increasing efforts to employ drugs that intervene in bile acid metabolism and signalling pathways for the treatment of metabolic diseases such as NAFLD warrants reinforcing interactions between the bile acid and lipid and lipoprotein research fields. This review may be considered as the first step in this process.

Treatment with PCSK9 inhibitors induces a more anti-atherogenic HDL lipid profile in patients at high cardiovascular risk

BACKGROUND

Proprotein Convertase Subtilisin/Kexin type 9 inhibitors (PCSK9-I) have been reported to cause a moderate increase in high-density lipoprotein (HDL) cholesterol in human studies. We thus evaluated the effect of two approved PCSK9-I on the concentration and lipid composition of HDL particle subclasses.

SUBJECTS AND METHODS

95 patients (62.8 ± 10.3 years old, 58% men), with or without statin and/or ezetimibe treatment and eligible for PCSK9-I therapy, received either evolocumab (140 mg) or alirocumab (75 or 150 mg). Their HDL particle profiles were measured by NMR spectroscopy at baseline and after 4 weeks of PCSK9-I treatment.

RESULTS

PCSK9-I treatment increased the level of HDL-C by 7%. The level of medium-sized HDL particles (M-HDL-P) increased (+8%) while the level of XL-HDL-P decreased (-19%). The lipid core composition was altered in the smaller S- and M-HDL-P, with a reduction in triglycerides (TG) and an enrichment in cholesterol esters (CE), whereas the for the larger XL- and L-HDL-P the relative CE content decreased and the TG content increased. Ezetimibe therapy differentially impacted the HDL particle distribution, independently of statin use, with an increase in S-HDL-P in patients not receiving ezetimibe.

CONCLUSIONS

As S- and M-HDL-P levels are inversely related to cardiovascular risk, PCSK9-I treatment may result in a more atheroprotective HDL particle profile, particularly in patients not concomitantly treated with ezetimibe.

Defects in High Density Lipoprotein metabolism and hepatic steatosis in mice with liver-specific ablation of Hepatocyte Nuclear Factor 4A

BACKGROUND

Aberrant concentration, structure and functionality of High Density Lipoprotein (HDL) are associated with many prevalent diseases, including cardiovascular disease and non-alcoholic fatty liver disease (NAFLD). Mice with liver-specific ablation of Hnf4α (H4LivKO) present steatosis and dyslipidemia by mechanisms that are not completely understood. The aim of this study was to explore the role of liver HNF4A in HDL metabolism and the development of steatosis.

METHODS AND RESULTS

Serum and tissue samples were obtained from 6-weeks old H4LivKO mice and their littermate controls. Liver and serum lipids were measured and HDL structure and functionality were assessed. Global gene expression changes in the liver were analyzed by expression arrays, validations were performed by RT-qPCR and DNA-protein interactions were studied by chromatin immunoprecipitation (ChIP). H4LivKO mice presented liver steatosis, increased liver triglyceride content and decreased concentration of serum total cholesterol, HDL cholesterol, triglycerides, phospholipids and cholesteryl esters. Most classes of phospholipids showed significant changes in species ratio and sphingosine-1-phosphate (S1P) levels were reduced. H4LivKO serum was enriched in the smaller, denser HDL particles, devoid of APOA2 and APOM apolipoproteins, exhibiting decreased activity of paraoxonase-1 but retaining macrophage cholesterol efflux capacity and phospho-AKT activation in endothelial cells. Global gene expression analysis revealed the association of liver HNF4A with known and novel regulators of HDL metabolism as well as NAFLD-susceptibility genes.

CONCLUSIONS

HNF4A ablation in mouse liver causes hepatic steatosis, perturbations in HDL structure and function and significant global changes in gene expression. This study reveals new targets of HNF4A involved in HDL metabolism and the development of steatosis and enriches our knowledge on HDL functionality in NAFLD.

Fibrates in the management of atherogenic dyslipidemia

INTRODUCTION

Significant advancements in the treatment of hypercholesterolemia have recently been achieved. However, a considerable level of residual cardiovascular risk still affects patients' outcomes. Atherogenic dyslipidemia is one of the major constituents of residual risk. Fibrates, PPAR alpha agonists, which modify lipid profile and have numerous pleiotropic effects, seem to be drugs of choice in patients with atherogenic dyslipidemia. These drugs are effective both in monotherapy and combined therapy with statins. Areas covered: A review of clinical trials and experimental studies on fibrates and their use in the treatment of lipid disorders has been performed. Expert commentary: Fibrates are an effective and safe group of drugs to treat patients with atherogenic dyslipidemia. In this particular population of patients, they improve cardiovascular outcomes. Benefits of fibrate treatment extend beyond the impact of lipid profile. Significant improvements in carbohydrate metabolism, adipokines levels, thrombosis and inflammation were also noted.

Triglycerides Revisited to the Serial

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

High-density lipoprotein and inflammation in cardiovascular disease

Great advances are being made at the mechanistic level in the understanding of the structural and functional diversity of high-density lipoprotein (HDL). HDL particle subspecies of different sizes are now known to differ in the protein and lipid cargo they transport, conferring on them the ability to perform different functions that in aggregate would be expected to provide protection against the development of atherosclerosis and its downstream clinical consequences. Exacerbating what is already a very complex system is the finding that inflammation, via alteration of the proteomic and lipidomic composition of HDL subspecies, can modulate at least some of their functional activities. In contrast to the progress being made at the mechanistic level, HDL epidemiologic research has lagged behind, largely because the simple HDL biomarkers used (mainly just HDL cholesterol) lack the needed complexity. To address this deficiency, analyses will need to use multiple HDL subspecies and be conducted in such a way as to eliminate potential sources of confounding. To help account for the modulating influence of inflammation, effective use must also be made of inflammatory biomarkers including searching systematically for HDL-inflammation interactions. Using nuclear magnetic resonance (NMR)-measured HDL subclass data and a novel NMR-derived inflammatory biomarker, GlycA, we offer a case study example of the type of analytic approach considered necessary to advance HDL epidemiologic understanding.

Rutaecarpine ameliorates hyperlipidemia and hyperglycemia in fat-fed, streptozotocin-treated rats via regulating the IRS-1/PI3K/Akt and AMPK/ACC2 signaling pathways

AIM

We have shown that rutaecarpine extracted from the dried fruit of Chinese herb Evodia rutaecarpa (Juss) Benth (Wu Zhu Yu) promotes glucose consumption and anti-inflammatory cytokine expression in insulin-resistant primary skeletal muscle cells. In this study we investigated whether rutaecarpine ameliorated the obesity profiles, lipid abnormality, glucose metabolism and insulin resistance in rat model of hyperlipidemia and hyperglycemia.

METHODS

Rats fed on a high-fat diet for 8 weeks, followed by injection of streptozotocin (30 mg/kg, ip) to induce hyperlipidemia and hyperglycemia. One week after streptozotocin injection, the fat-fed, streptozotocin-treated rats were orally treated with rutaecarpine (25 mg·kg(-1)·d(-1)) or a positive control drug metformin (250 mg·kg(-1)·d(-1)) for 7 weeks. The body weight, visceral fat, blood lipid profiles and glucose levels, insulin sensitivity were measured. Serum levels of inflammatory cytokines were analyzed. IRS-1 and Akt/PKB phosphorylation, PI3K and NF-κB protein levels in liver tissues were assessed; pathological changes of livers and pancreases were examined. Glucose uptake and AMPK/ACC2 phosphorylation were studied in cultured rat skeletal muscle cells in vitro.

RESULTS

Administration of rutaecarpine or metformin significantly decreased obesity, visceral fat accumulation, water consumption, and serum TC, TG and LDL-cholesterol levels in fat-fed, streptozotocin-treated rats. The two drugs also attenuated hyperglycemia and enhanced insulin sensitivity. Moreover, the two drugs significantly decreased NF-κB protein levels in liver tissues and plasma TNF-α, IL-6, CRP and MCP-1 levels, and ameliorated the pathological changes in livers and pancreases. In addition, the two drugs increased PI3K p85 subunit levels and Akt/PKB phosphorylation, but decreased IRS-1 phosphorylation in liver tissues. Treatment of cultured skeletal muscle cells with rutaecarpine (20-180 μmol/L) or metformin (20 μmol/L) promoted the phosphorylation of AMPK and ACC2, and increased glucose uptake.

CONCLUSION

Rutaecarpine ameliorates hyperlipidemia and hyperglycemia in fat-fed, streptozotocin-treated rats via regulating IRS-1/PI3K/Akt signaling pathway in liver and AMPK/ACC2 signaling pathway in skeletal muscles.

How difficult is the validation of clinical biomarkers?

Recent developments of introducing stratified medicine/personal health care have led to an increased demand for specific biomarkers. However, despite the myriads of biomarkers claimed to be fit for all sorts of diseases and applications, the scientific integrity of the claims and therefore their credibility is far from satisfactory. Biomarker databases are met with scepticism. The reasons for this lack of faith come from different directions: lack of integrity of the biospecimen and meta-analysis of data derived from biospecimen prepared in various ways cause incoherence and false indications. Although the trend for antibody-independent assays is on the rise, demand for consistent performance of antibodies (both in choice of antibody and how to apply it in the correct dilution where applicable) in immune assays remains unmet in too many cases. Quantitative assays suffer from a lack of world-wide accepted criteria when the immune assay is not ELISA-based. Finally, statistical analysis suffer from coherence both in the way software packages are being scrutinized for mistakes in the script and remaining invisible after small-scale analysis, and in the way appropriate queries are fed into the packages in search for output that is fit for the types of data put in. Wrong queries would lead to wrong statistical conclusions, for example when data from a cohort of patients with different backgrounds are being analysed, or when one seeks an answer from software that was not designed for such query.