Apolipoprotein CIII and Angiopoietin-like Protein 8 are Elevated in Lipodystrophy and Decrease after Metreleptin

Context

Lipodystrophy syndromes cause hypertriglyceridemia that improves with leptin treatment using metreleptin. Mechanisms causing hypertriglyceridemia and improvements after metreleptin are incompletely understood.

Objective

Determine relationship of circulating lipoprotein lipase (LPL) modulators with hypertriglyceridemia in healthy controls and in patients with lipodystrophy before and after metreleptin.

Methods

Cross-sectional comparison of patients with lipodystrophy (generalized lipodystrophy n = 3; partial lipodystrophy n = 11) vs age/sex-matched healthy controls (n = 28), and longitudinal analyses in patients before and after 2 weeks and 6 months of metreleptin. The study was carried out at the National Institutes of Health, Bethesda, Maryland. Outcomes were LPL stimulators apolipoprotein (apo) C-II and apoA-V and inhibitors apoC-III and angiopoietin-like proteins (ANGPTLs) 3, 4, and 8; ex vivo activation of LPL by plasma.

Results

Patients with lipodystrophy were hypertriglyceridemic and had higher levels of all LPL stimulators and inhibitors vs controls except for ANGPTL4, with >300-fold higher ANGPTL8, 4-fold higher apoC-III, 3.5-fold higher apoC-II, 1.9-fold higher apoA-V, 1.6-fold higher ANGPTL3 (P < .05 for all). At baseline, all LPL modulators except ANGPLT4 positively correlated with triglycerides. Metreleptin decreased apoC-II and apoC-III after 2 weeks and 6 months, and decreased ANGPTL8 after 6 months (P < 0.05 for all). Plasma from patients with lipodystrophy caused higher ex vivo LPL activation vs hypertriglyceridemic control plasma (P < .0001), which did not change after metreleptin.

Conclusion

Elevations in LPL inhibitors apoC-III and ANGPTL8 may contribute to hypertriglyceridemia in lipodystrophy, and may mediate reductions in circulating and hepatic triglycerides after metreleptin. These therefore are strong candidates for therapies to lower triglycerides in these patients.

Hypertriglyceridemia: new approaches in management and treatment

PURPOSE OF REVIEW

Hypertriglyceridemia (HTG), a form of dyslipidemia characterized by elevated plasma of triglycerides (TG), is associated with an increased risk for acute pancreatitis. Moreover, HTG has recently been shown to be linked to the development of atherosclerotic cardiovascular disease (ASCVD); therefore, there is a great interest in better understanding the pathophysiology of HTG and improving its clinical management. In this review, we briefly describe TG metabolism, recent guidelines for the clinical management of HTG and provide an overview of the current and potential new therapies for HTG.

RECENT FINDINGS

Screening patients for HTG is valuable for not only identifying patients with extreme TG elevations, who are at risk for pancreatitis, but also for managing ASCVD risk in patients with more moderate forms of HTG. Therefore, the most recent USA guidelines for cardiovascular diseases recommend using TG as a risk enhancer test, leading to a more aggressive treatment of patients with intermediate risk. Currently, there are several available approaches for reducing plasma TG, which include lifestyle changes, fibrates and omega-3 fatty acid treatment. The addition of eicosapentaenoic acid (EPA) on top of statins has recently been shown to significantly reduce ASCVD events. Nevertheless, there is an unmet need for more effective treatment options. Several new therapies based on newly identified targets in TG metabolism, such as apolipoprotein C-III and angiopoietin-like 3 protein, are currently under development.

SUMMARY

The clinical management of HTG is important in the prevention and treatment of acute pancreatitis and also impacts on how ASCVD risk is managed. More work needs to be done to establish the mechanism for the ability of how EPA lowers ASCVD and how to best integrate it with other lipid-lowering therapies. The efficacy and safety of the novel therapies for HTG should be established soon in the ongoing late-stage clinical trials.

Cholesterol transport between red blood cells and lipoproteins contributes to cholesterol metabolism in blood

Lipoproteins play a key role in transport of cholesterol to and from tissues. Recent studies have also demonstrated that red blood cells (RBCs), which carry large quantities of free cholesterol in their membrane, play an important role in reverse cholesterol transport. However, the exact role of RBCs in systemic cholesterol metabolism is poorly understood. RBCs were incubated with autologous plasma or isolated lipoproteins resulting in a significant net amount of cholesterol moved from RBCs to HDL, while cholesterol from LDL moved in the opposite direction. Furthermore, the bi-directional cholesterol transport between RBCs and plasma lipoproteins was saturable and temperature-, energy-, and time-dependent, consistent with an active process. We did not find LDLR, ABCG1, or scavenger receptor class B type 1 in RBCs but found a substantial amount of ABCA1 mRNA and protein. However, specific cholesterol efflux from RBCs to isolated apoA-I was negligible, and ABCA1 silencing with siRNA or inhibition with vanadate and Probucol did not inhibit the efflux to apoA-I, HDL, or plasma. Cholesterol efflux from and cholesterol uptake by RBCs from Abca1+/+ and Abca1-/- mice were similar, arguing against the role of ABCA1 in cholesterol flux between RBCs and lipoproteins. Bioinformatics analysis identified ABCA7, ABCG5, lipoprotein lipase, and mitochondrial translocator protein as possible candidates that may mediate the cholesterol flux. Together, these results suggest that RBCs actively participate in cholesterol transport in the blood, but the role of cholesterol transporters in RBCs remains uncertain.

The extended lipid panel assay: a clinically-deployed high-throughput nuclear magnetic resonance method for the simultaneous measurement of lipids and Apolipoprotein B

Background

Standard lipid panel assays employing chemical/enzymatic methods measure total cholesterol (TC), triglycerides (TG), and high-density lipoprotein cholesterol (HDL-C), from which are calculated estimates of low-density lipoprotein cholesterol (LDL-C). These lipid measures are used universally to guide management of atherosclerotic cardiovascular disease risk. Apolipoprotein B (apoB) is generally acknowledged to be superior to LDL-C for lipid-lowering therapeutic decision-making, but apoB immunoassays are performed relatively infrequently due to the added analytic cost. The aim of this study was to develop and validate the performance of a rapid, high-throughput, reagent-less assay producing an “Extended Lipid Panel” (ELP) that includes apoB, using the Vantera® nuclear magnetic resonance (NMR) analyzer platform already deployed clinically for lipoprotein particle and other testing.

Methods

Partial least squares regression models, using as input a defined region of proton NMR spectra of plasma or serum, were created to simultaneously quantify TC, TG, HDL-C, and apoB. Large training sets (n > ~ 1000) of patient sera analyzed independently for lipids and apoB by chemical methods were employed to ensure prediction models reflect the wide lipid compositional diversity of the population. The analytical performance of the NMR ELP assay was comprehensively evaluated.

Results

Excellent agreement was demonstrated between chemically-measured and ELP assay values of TC, TG, HDL-C and apoB with correlation coefficients ranging from 0.980 to 0.997. Within-run precision studies measured using low, medium, and high level serum pools gave coefficients of variation for the 4 analytes ranging from 1.0 to 3.8% for the low, 1.0 to 1.7% for the medium, and 0.9 to 1.3% for the high pools. Corresponding values for within-lab precision over 20 days were 1.4 to 3.6%, 1.2 to 2.3%, and 1.0 to 1.9%, respectively. Independent testing at three sites over 5 days produced highly consistent assay results. No major interference was observed from 38 endogenous or exogenous substances tested.

Conclusions

Extensive assay performance evaluations validate that the NMR ELP assay is efficient, robust, and substantially equivalent to standard chemistry assays for the clinical measurement of lipids and apoB. Routine reporting of apoB alongside standard lipid measures could facilitate more widespread utilization of apoB for clinical decision-making.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-020-01424-2.

Association Among Noncalcified Coronary Burden, Fractional Flow Reserve, and Myocardial Injury in Psoriasis

Background

Myocardial infarction and premature death have been observed in patients with psoriasis. Although inflammation‐driven accelerated atherosclerosis has been proposed as a mechanism, the relationship between subclinical noncalcified coronary burden (NCB), functional coronary flow impairment, and myocardial injury is unclear.

Methods and Results

In an ongoing longitudinal cohort study, 202 consecutive patients with psoriasis (168 at 1 year) underwent coronary computed tomography angiography to identify coronary plaque, quantify NCB, and calculate coronary fractional flow reserve by computed tomography. Serum high‐sensitivity troponin‐T (hs‐cTn‐T) was measured using a fifth‐generation assay. Overall, patients were middle‐aged, predominantly male, and low cardiovascular risk. A higher than median NCB associated with a positive hs‐cTn‐T (fully adjusted model [odds ratio (OR), 1.72; 95% CI, 1.10–2.69, P=0.018]) at baseline. Additionally, patients with a higher than median baseline NCB had higher odds of positive hs‐cTn‐T at 1 year in fully adjusted analyses (adjusted OR, 2.36; 95% CI, 1.47–3.79, P<0.001). Higher NCB was associated with a higher frequency of fractional flow reserve by computed tomography ≤0.80 (36.11% versus 25.11%, Pearson χ²=6.84, P=0.009, unadjusted OR, 2.09; 95% CI, 1.36–3.22, P<0.001) and higher frequency of a positive hs‐cTn‐T (54.36% versus 27.54%, Pearson χ²=32.23, P<0.001) in adjusted models (OR, 2.63; 95% CI, 1.56–4.42, P<0.001).

Conclusions

NCB was associated with hs‐cTn‐T at baseline as well as at 1 year. Furthermore, patients with high NCB had higher prevalence of fractional flow reserve by computed tomography ≤0.80 and a >2‐ fold higher odds of positive hs‐cTn‐T. These findings underscore the importance of early vascular disease in driving myocardial injury, and support conduct of myocardial perfusion studies to better understand these findings.

Association Between Soluble Lectinlike Oxidized Low-Density Lipoprotein Receptor-1 and Coronary Artery Disease in Psoriasis

Importance

Psoriasis, a chronic inflammatory skin disease associated with accelerated noncalcified coronary burden (NCB) by coronary computed tomography angiography (CCTA), accelerates lipoprotein oxidation in the form of oxidized modified lipoproteins. A transmembrane scavenger receptor for these oxidized modified lipoproteins is lectinlike oxidized low-density lipoprotein receptor-1 (LOX-1), which has been reported to be associated with coronary artery disease. It is unknown whether this receptor is associated with coronary artery disease in psoriasis.

Objective

To assess the association between soluble LOX-1 (sLOX-1) and NCB in psoriasis over time.

Design, Setting, and Participants

In a cohort study at the National Institutes of Health, 175 consecutive patients with psoriasis were referred from outpatient dermatology practices between January 1, 2013, and October 1, 2017. A total of 138 consecutively recruited patients with psoriasis were followed up at 1 year.

Exposures

Circulating soluble lectinlike oxidized low-density lipoprotein receptor-1 levels were measured blindly by field scientists running undiluted serum using an enzyme-linked immunosorbent assay.

Main Outcomes and Measures

Coronary computed tomography angiography scans were performed to quantify NCB in all 3 major epicardial coronary arteries by a reader blinded to patient demographics, visit, and treatment status.

Results

Among the 175 patients with psoriasis, the mean (SD) age was 49.7 (12.6) years and 91 were men (55%). The cohort had relatively low median cardiovascular risk by Framingham risk score (median, 2.0 [interquartile range (IQR), 1.0-6.0]) and had a mean (SD) body mass index (calculated as weight in kilograms divided by height in meters squared) suggestive of overweight profiles (29.6 [6.0]). Elevated sLOX-1 levels were found in patients with psoriasis compared with age- and sex-matched controls (median, 210.3 [IQR, 110.9-336.2] vs 83.7 [IQR, 40.1-151.0]; P < .001), and were associated with Psoriasis Area Severity Index (PASI) score (β = 0.23; 95% CI, 0.082-0.374; P = .003). Moreover, sLOX-1 was associated with NCB independent of hyperlipidemia status (β = 0.11; 95% CI, 0.016-0.200; P = .023), an association which persisted after adjusting for traditional cardiovascular risk factors, statin use, and biologic psoriasis treatment (β = 0.10; 95% CI, 0.014-0.193; P = .03). At 1 year, in those who had clinical improvement in PASI (eg, >50% improvement), a reduction in sLOX-1 (median, 311.1 [IQR, 160.0-648.8] vs median, 224.2 [IQR, 149.1 - 427.4]; P = .01) was associated with a reduction in NCB (β = 0.14; 95% CI, 0.028-0.246; P = .02).

Conclusions and Relevance

Soluble lectinlike oxidized low-density lipoprotein receptor-1 levels were elevated in patients with psoriasis and were associated with severity of skin disease. Moreover, sLOX-1 associated with NCB independent of hyperlipidemia status, suggesting that inflammatory sLOX-1 induction may modulate lipid-rich NCB in psoriasis. Improvement of skin disease was associated with a reduction of sLOX-1 at 1 year, demonstrating the potential role of sLOX-1 in inflammatory atherogenesis in psoriasis.

Apolipoprotein A-I in mouse cerebrospinal fluid derives from the liver and intestine via plasma high-density lipoproteins assembled by ABCA1 and LCAT

Apolipoprotein (apo) A-I, the major structural protein of high-density lipoprotein (HDL), is present in human and mouse cerebrospinal fluid (CSF) despite its lack of expression in brain cells. To identify the origin of apoA-I in CSF, we generated intestine-specific and liver-specific Apoa1 knockout mice (Apoa1^ΔInt and Apoa1^Δliv mice, respectively). Lipoprotein profiles of Apoa1^ΔInt and Apoa1^ΔLiv mice resembled those of control littermates, whereas knockout of Apoa1 in both intestine and liver (Apoa1^ΔIntΔLiv ) resulted in a 60-percent decrease in HDL-cholesterol levels, thus strongly mimicking the Apoa1^-/- mice. Immunoassays revealed that mouse apoA-I was not present in the CSF of the Apoa1^ΔIntΔLiv mice. Furthermore, apoA-I levels in CSF were highly correlated with plasma spherical HDL levels, which were regulated by ABCA1 and LCAT. Collectively, these results suggest that apoA-I protein in CSF originates in liver and small intestine and is taken up from the plasma.

SR-BI mediates neutral lipid sorting from LDL to lipid droplets and facilitates their formation

SR-BI binds various lipoproteins, including HDL, LDL as well as VLDL, and mediates selective cholesteryl ester (CE) uptake. HDL derived CE accumulates in cellular lipid droplets (LDs), which also store triacylglycerol (TAG). We hypothesized that SR-BI could significantly facilitate LD formation, in part, by directly transporting LDL derived neutral lipids (NL) such as CE and TAG into LDs without lipolysis and de novo lipid synthesis. SR-BI overexpression greatly increased LDL uptake and LD formation in stably transfected HeLa cells (SR-BI-HeLa). LDs isolated from SR-BI-HeLa contained 4- and 7-times more CE and TAG, respectively, than mock-transfected HeLa (Mock-HeLa). In contrast, LDL receptor overexpression in HeLa (LDLr-HeLa) greatly increased LDL uptake, degradation with moderate 1.5- and 2-fold increases of CE and TAG, respectively. Utilizing CE and TAG analogs, BODIPY-TAG (BP-TAG) and BODIPY-CE (BP-CE), for tracking LDL NL, we found that after initial binding of LDL to SR-BI-HeLa, apoB remained at the cell surface, while BP-CE and BP-TAG were sorted and simultaneously transported together to LDs. Both lipids demonstrated limited internalization to lysosomes or endoplasmic reticulum in SR-BI-HeLa. In LDLr-HeLa, NLs demonstrated clear lysosomal sequestration without their sorting to LDs. An inhibition of TAG and CE de novo synthesis by 90-95% only reduced TAG and CE LD content by 45-50%, and had little effect on BP-CE and BP-TAG transport to LDs in SR-BI HeLa. Furthermore, intravenous infusion of 1-2 mg of LDL increased liver LDs in normal (WT) but not in SR-BI KO mice. Mice transgenic for human SR-BI demonstrated higher liver LD accumulation than WT mice. Finally, Electro Spray Infusion Mass Spectrometry (ESI-MS) using deuterated d-CE found that LDs accumulated up to 40% of unmodified d-CE LDL. We conclude that SR-BI mediates LDL-induced LD formation in vitro and in vivo. In addition to cytosolic NL hydrolysis and de novo lipid synthesis, this process includes selective sorting and transport of LDL NL to LDs with limited lysosomal NL sequestration and the transport of LDL CE, and TAG directly to LDs independently of de novo synthesis.

Oxidized Lipids and Lipoprotein Dysfunction in Psoriasis

BACKGROUND

Psoriasis is a chronic immune-mediated inflammatory skin disease associated with increased development of metabolic abnormalities including obesity and dyslipidemia, as well as increased cardiovascular disease (CVD) risk. Shared pathophysiological mechanisms linking psoriasis to CVD include altered immune activation, elevated chronic systemic inflammation, and lipoprotein dysfunction characterized by oxidative damage to lipids and apolipoproteins.

OBJECTIVE

This review aims to provide evidence-based proof for existing relationships between psoriatic inflammation, lipid oxidation, and increased CVD risk.

METHODS

We included review articles and original research papers, published between 1980 and 2020, using the following key words: psoriasis, oxidized lipids, oxidation, dyslipidemia, and inflammation.

RESULTS

Systemic inflammation underlying psoriasis leads to increased skin accumulation of pro-inflammatory oxidized lipids, derived from the omega-6 fatty acids, along with counteracting anti-inflammatory lipid mediators, products of the omega-3 polyunsaturated fatty acids. Imbalance in these metabolites culminates in impaired inflammation resolution and results in multisystemic biological alterations. Sustained systemic inflammation results in excessive lipid oxidation, generating proatherogenic oxidized low- and high-density lipoproteins. Together, these pathophysiological mechanisms contribute to increased CVD risk associated with psoriasis disease.

CONCLUSION

Available anti-inflammatory treatment showed promising clinical results in treating psoriasis, although further research is warranted on managing associated dyslipidemia and establishing novel cardiometabolic markers specific for both skin and vascular pathology.

Targeting Lipid Rafts-A Potential Therapy for COVID-19

COVID-19 is a global pandemic currently in an acute phase of rapid expansion. While public health measures remain the most effective protection strategy at this stage, when the peak passes, it will leave in its wake important health problems. Historically, very few viruses have ever been eradicated. Instead, the virus may persist in communities causing recurrent local outbreaks of the acute infection as well as several chronic diseases that may arise from the presence of a “suppressed” virus or as a consequence of the initial exposure. An ideal solution would be an anti-viral medication that (i) targets multiple stages of the viral lifecycle, (ii) is insensitive to frequent changes of viral phenotype due to mutagenesis, (iii) has broad spectrum, (iv) is safe and (v) also targets co-morbidities of the infection. In this Perspective we discuss a therapeutic approach that owns these attributes, namely “lipid raft therapy.” Lipid raft therapy is an approach aimed at reducing the abundance and structural modifications of host lipid rafts or at targeted delivery of therapeutics to the rafts. Lipid rafts are the sites of the initial binding, activation, internalization and cell-to-cell transmission of SARS-CoV-2. They also are key regulators of immune and inflammatory responses, dysregulation of which is characteristic to COVID-19 infection. Lipid raft therapy was successful in targeting many viral infections and inflammatory disorders, and can potentially be highly effective for treatment of COVID-19.

High-density lipoproteins are a potential therapeutic target for age-related macular degeneration

Strong evidence suggests that dysregulated lipid metabolism involving dysfunction of the retinal pigmented epithelium (RPE) underlies the pathogenesis of age-related macular degeneration (AMD), the leading cause of irreversible blindness in the elderly. A hallmark of AMD is the overproduction of lipid- and protein-rich extracellular deposits that accumulate in the extracellular matrix (Bruch's membrane (BrM)) adjacent to the RPE. We analyzed apolipoprotein A-1 (ApoA-1)-containing lipoproteins isolated from BrM of elderly human donor eyes and found a unique proteome, distinct from high-density lipoprotein (HDL) isolated from donor plasma of the same individuals. The most striking difference is higher concentrations of ApoB and ApoE, which bind to glycosaminoglycans. We hypothesize that this interaction promotes lipoprotein deposition onto BrM glycosaminoglycans, initiating downstream effects that contribute to RPE dysfunction/death. We tested this hypothesis using two potential therapeutic strategies to alter the lipoprotein/protein profile of these extracellular deposits. First, we used short heparan sulfate oligosaccharides to remove lipoproteins already deposited in both the extracellular matrix of RPE cells and aged donor BrM tissue. Second, an ApoA-1 mimetic, 5A peptide, was demonstrated to modulate the composition and concentration of apolipoproteins secreted from primary porcine RPE cells. Significantly, in a mouse model of AMD, this 5A peptide altered the proteomic profile of circulating HDL and ameliorated some of the potentially harmful changes to the protein composition resulting from the high-fat, high-cholesterol diet in this model. Together, these results suggest that targeting HDL interactions with BrM represents a new strategy to slow AMD progression in humans.

A dual apolipoprotein C-II mimetic-apolipoprotein C-III antagonist peptide lowers plasma triglycerides

Recent genetic studies have established that hypertriglyceridemia (HTG) is causally related to cardiovascular disease, making it an active area for drug development. We describe a strategy for lowering triglycerides (TGs) with an apolipoprotein C-II (apoC-II) mimetic peptide called D6PV that activates lipoprotein lipase (LPL), the main plasma TG-hydrolyzing enzyme, and antagonizes the TG-raising effect of apoC-III. The design of D6PV was motivated by a combination of all-atom molecular dynamics simulation of apoC-II on the Anton 2 supercomputer, structural prediction programs, and biophysical techniques. Efficacy of D6PV was assessed ex vivo in human HTG plasma and was found to be more potent than full-length apoC-II in activating LPL. D6PV markedly lowered TG by more than 80% within a few hours in both apoC-II-deficient mice and hAPOC3-transgenic (Tg) mice. In hAPOC3-Tg mice, D6PV treatment reduced plasma apoC-III by 80% and apoB by 65%. Furthermore, low-density lipoprotein (LDL) cholesterol did not accumulate but rather was decreased by 10% when hAPOC3-Tg mice lacking the LDL-receptor (hAPOC3-Tg × Ldlr^-/- ) were treated with the peptide. D6PV lowered TG by 50% in whole-body inducible Lpl knockout (iLpl^-/- ) mice, confirming that it can also act independently of LPL. D6PV displayed good subcutaneous bioavailability of about 80% in nonhuman primates. Because it binds to high-density lipoproteins, which serve as a long-term reservoir, it also has an extended terminal half-life (42 to 50 hours) in nonhuman primates. In summary, D6PV decreases plasma TG by acting as a dual apoC-II mimetic and apoC-III antagonist, thereby demonstrating its potential as a treatment for HTG.

Effect of niacin monotherapy on high density lipoprotein composition and function

BACKGROUND

Niacin has modest but overall favorable effects on plasma lipids by increasing high density lipoprotein cholesterol (HDL-C) and lowering triglycerides. Clinical trials, however, evaluating niacin therapy for prevention of cardiovascular outcomes have returned mixed results. Recent evidence suggests that the HDL proteome may be a better indicator of HDL's cardioprotective function than HDL-C. The objective of this study was to evaluate the effect of niacin monotherapy on HDL protein composition and function.

METHODS

A 20-week investigational study was performed with 11 participants receiving extended-release niacin (target dose = 2 g/day) for 16-weeks followed by a 4-week washout period. HDL was isolated from participants at weeks: 0, 16, and 20. The HDL proteome was analyzed at each time point by mass spectrometry and relative protein quantification was performed by label-free precursor ion intensity measurement.

RESULTS

In this cohort, niacin therapy had typical effects on routine clinical lipids (HDL-C + 16%, q < 0.01; LDL-C - 20%, q < 0.01; and triglyceride - 15%, q = 0.1). HDL proteomics revealed significant effects of niacin on 5 proteins: serum amyloid A (SAA), angiotensinogen (AGT), apolipoprotein A-II (APOA2), clusterin (CLUS), and apolipoprotein L1 (APOL1). SAA was the most prominently affected protein, increasing 3-fold in response to niacin (q = 0.008). Cholesterol efflux capacity was not significantly affected by niacin compared to baseline, however, stopping niacin resulted in a 9% increase in efflux (q < 0.05). Niacin did not impact HDL's ability to influence endothelial function.

CONCLUSION

Extended-release niacin therapy, in the absence of other lipid-modifying medications, can increase HDL-associated SAA, an acute phase protein associated with HDL dysfunction.

Measuring LDL-cholesterol: what is the best way to do it?

PURPOSE OF REVIEW

Cholesterol on low-density lipoproteins (LDL-C) is one of the main drivers of atherosclerotic cardiovascular disease (ASCVD) and hence its measurement is critical in the management of patients at risk. Although LDL-C has routinely been either calculated by the Friedewald equation or measured with direct assays, these methods have limitations, particularly for patients with dyslipidaemias, low LDL-C, and hypertriglyceridemia. The focus of this review will be recent advances in the measurement of LDL for ASCVD risk management.

RECENT FINDINGS

We first describe the recent recommendations on how LDL-C is used in ASCVD risk assessment and management. We then review the current approaches to the measurement of LDL-C and recent developments on new more accurate equations for calculating LDL-C. Finally, we present new and emerging LDL assays that may be superior to LDL-C for risk assessment, such as LDL particle number and small dense LDL-C, and several LDL-based lipid tests in early development.

SUMMARY

LDL-C is valuable in ASCVD risk management but recent improvements in its measurement and the development of other LDL-related tests may further improve its value.

COVID-19-Associated dyslipidemia: Implications for mechanism of impaired resolution and novel therapeutic approaches

The current coronavirus disease 2019 (COVID‐19) pandemic presents a global challenge for managing acutely ill patients and complications from viral infection. Systemic inflammation accompanied by a “cytokine storm,” hemostasis alterations and severe vasculitis have all been reported to occur with COVID‐19, and emerging evidence suggests that dysregulation of lipid transport may contribute to some of these complications. Here, we aim to summarize the current understanding of the potential mechanisms related to COVID‐19 dyslipidemia and propose possible adjunctive type therapeutic approaches that modulate lipids and lipoproteins. Specifically, we hypothesize that changes in the quantity and composition of high‐density lipoprotein (HDL) that occurs with COVID‐19 can significantly decrease the anti‐inflammatory and anti‐oxidative functions of HDL and could contribute to pulmonary inflammation. Furthermore, we propose that lipoproteins with oxidized phospholipids and fatty acids could lead to virus‐associated organ damage via overactivation of innate immune scavenger receptors. Restoring lipoprotein function with ApoA‐I raising agents or blocking relevant scavenger receptors with neutralizing antibodies could, therefore, be of value in the treatment of COVID‐19. Finally, we discuss the role of omega‐3 fatty acids transported by lipoproteins in generating specialized proresolving mediators and how together with anti‐inflammatory drugs, they could decrease inflammation and thrombotic complications associated with COVID‐19.

microRNA-367-3p regulation of GPRC5A is suppressed in ischemic stroke

Ischemic stroke is a major cause of mortality and long-term disability with limited treatment options, and a greater understanding of the gene regulatory mechanisms underlying ischemic stroke-associated neuroinflammation is required for new therapies. To study ischemic stroke in vivo, mice were subjected to sustained ischemia by intraluminal filament-induced middle cerebral artery occlusion (MCAo) for 24 h without reperfusion or transient ischemia for 30 min followed by 23.5 h reperfusion, and brain miRNA and mRNA expression changes were quantified by TaqMan OpenArrays and gene (mRNA) expression arrays, respectively. Sustained ischemia resulted in 18 significantly altered miRNAs and 392 altered mRNAs in mouse brains compared to Sham controls; however, the transient ischemic condition was found to impact only 6 miRNAs and 126 mRNAs. miR-367-3p was found to be significantly decreased in brain homogenates with sustained ischemia. G protein-coupled receptor, family C, group 5, member A (Gprc5a), a miR-367-3p target gene, was found to be significantly increased with sustained ischemia. In primary neurons, inhibition of endogenous miR-367-3p resulted in a significant increase in Gprc5a expression. Moreover, miR-367-3p was found to be co-expressed with GPRC5A in human neurons. Results suggest that loss of miR-367-3p suppression of GPRC5A may contribute to neuroinflammation associated with ischemic stroke.

Lecithin:cholesterol acyltransferase: symposium on 50 years of biomedical research from its discovery to latest findings

LCAT converts free cholesterol to cholesteryl esters in the process of reverse cholesterol transport. Familial LCAT deficiency (FLD) is a genetic disease that was first described by Kaare R. Norum and Egil Gjone in 1967. This report is a summary from a 2017 symposium where Dr. Norum recounted the history of FLD and leading experts on LCAT shared their results. The Tesmer laboratory shared structural findings on LCAT and the close homolog, lysosomal phospholipase A2. Results from studies of FLD patients in Finland, Brazil, Norway, and Italy were presented, as well as the status of a patient registry. Drs. Kuivenhoven and Calabresi presented data from carriers of genetic mutations suggesting that FLD does not necessarily accelerate atherosclerosis. Dr. Ng shared that LCAT-null mice were protected from diet-induced obesity, insulin resistance, and nonalcoholic fatty liver disease. Dr. Zhou presented multiple innovations for increasing LCAT activity for therapeutic purposes, whereas Dr. Remaley showed results from treatment of an FLD patient with recombinant human LCAT (rhLCAT). Dr. Karathanasis showed that rhLCAT infusion in mice stimulates cholesterol efflux and suggested that it could also enhance cholesterol efflux from macrophages. While the role of LCAT in atherosclerosis remains elusive, the consensus is that a continued study of both the enzyme and disease will lead toward better treatments for patients with heart disease and FLD.

Apolipoprotein C-II: the re-emergence of a forgotten factor

PURPOSE OF REVIEW

Apolipoprotein C-II (apoC-II) is a critical cofactor for the activation of lipoprotein lipase (LPL), a plasma enzyme that hydrolyzes triglycerides (TG) on TG-rich lipoproteins (TRL). Although apoC-II was first discovered nearly 50 years ago, there is renewed interest in it because of the recent efforts to develop new drugs for the treatment of hypertriglyceridemia (HTG). The main topic of this review will be the development of apoC-II mimetic peptides as a possible new therapy for cardiovascular disease.

RECENT FINDINGS

We first describe the biochemistry of apoC-II and its role in TRL metabolism. We then review the clinical findings of HTG, particularly those related to apoC-II deficiency, and how TG metabolism relates to the development of atherosclerosis. We next summarize the current efforts to develop new drugs for HTG. Finally, we describe recent efforts to make small synthetic apoC-II mimetic peptides for activation of LPL and how these peptides unexpectedly have other mechanisms of action mostly related to the antagonism of the TG-raising effects of apoC-III.

SUMMARY

The role of apoC-II in TG metabolism is reviewed, as well as recent efforts to develop apoC-II mimetic peptides into a novel therapy for HTG.

SAT-578 A Rare Case of Laboratory Hypertriglyceridemia: Glycerol Kinase Deficiency

Background: Hypertriglyceridemia (HTG) is common; however, pseudo-HTG due to high glycerol in glycerol kinase deficiency (GKD, MIM: 307030) is a rare cause of HTG that need to be delineated for appropriate management. GKD is an X-linked recessive disorder characterized by hyperglycerolemia and glyceroluria. Two of three GKD subtypes are known as “isolate” GKD due to a mutation in GK gene alone: (1) symptomatic juvenile form, and (2) benign adult form, associated with an incidental finding of HTG.

Since most commercial laboratories determine triglyceride (TG) levels by a glycerol measurement, TG-backbone, patients with GKD are mistakenly labelled as having HTG. Glycerol-blanking is required to reveal the actual TG, but it is costly. Since usual TG-lowering medications are ineffective or even harmful, novel methods to screen for individuals with GKD or pseudo-HTG are necessary.

Objective: Through identification of a clinical case of GKD that was diagnosed by glycerol-blanking, we are proposing two potential methods to screen for pseudo-HTG, and presenting their reliability.

Methods: The patient was recruited into an IRB-approved study investigating etiologies of dyslipidemia at the University of Pennsylvania. Patient provided consent for medical record review.

Results: A 49-year-old man was referred for HTG management. His reported TG levels ranged between 490 and 559 mg/dL without any other adverse lipid levels for several years without a history of pancreatitis or diabetes mellitus. Intriguingly, he reported a family history of HTG.

Since TG-lowering medications (fibrates and fish oil) had not reduced his TG levels, specialized lipid analyses were obtained: a non-blanked TG level of 521 mg/dL and a glycerol-blanked TG of 66 mg/dL, consistent with pseudo-HTG or hyperglycerolemia. Repeat glycerol blanked TG levels were 68 and 69 mg/dL, confirming the previous result, and the likely diagnosis of GKD.

With two methods, estimated TG levels were calculated, using some of his laboratory values: (1) modified Friedewald equation to solve for TG with a direct LDL (dLDL) value, and (2) the application of a newly developed formula derived from a collection of 17,545 patient samples, to calculate the absolute TG-gap, using apolipoprotein A and B, estimating TG levels (% deltaTG), and determining whether a TG mesurement might be falsely deviated from the “plausible” TG value.

Although neither methods showed perfect concordance, the calculated TG-valued derived by the two methods were significantly lower than the non-glycerol blanked TG values. The difference was statistically significant (p<0.05).

Conclusion: The patient was clinically diagnosed with GKD, and was taken off of fibrate and the recently added niacin. These two methods can be used quickly to screen for pseudo-HTG or patients with GKD. Currently, it is unknown whether high glycerol levels are associated with high cardiovascular risks.

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

Background: Lipodystrophy is a heterogeneous disorder of adiposity, and one common lipid manifestation is hypertriglyceridemia (HTG). The LMNA gene, which encodes for nuclear envelope proteins, is a known causal gene for heritable lipodystrophy. At present, underlying mechanisms for each clinical manifestation of lipodystrophy due to a LMNA mutation are unknown.

Hypothesis: A likely explanation for HTG in lipodystrophy is the paucity of adipose tissue where excess triglycerides (TGs) are normally stored, thus it may not be due to a specific defect in lipoprotein metabolism. Consequently, rare variants in HTG-associated genes would not be expected to be major contributors for HTG in lipodystrophy with LMNA mutations.

Method: A proband and her father with a clinical diagnosis of lipodystrophy were recruited into an IRB-approved study investigating molecular etiologies of dyslipidemia at the University of Pennsylvania. Next-generation sequencing (NGS) with the LipidSeq panel, targeting causal genes for lipodystrophy, and monogenic HTG was performed, and confirmed by Sanger sequencing. Also, unweighted TG-polygenic scores by summing the number of TG-raising alleles from 14 single nucleotide polymorphisms (SNPs) associated with TG levels were assessed.

Results: The proband and her father were diagnosed with lipodystrophy of two different subtypes, generalized in the daughter and partial in the father. The proband reported a gradual loss of subcutaneous fat starting around age 10. A highest reported TG in the proband was19,000 mg/dL with eruptive xanthomas, whereas TG in the father was never >500 mg/dL. Their BMI’s and DEXA body fat% were 12.9 kg/m² and 7% in the proband, and 25.7 kg/m² and 25% in the father, corresponding to their fat storage capacities.

The molecular analyses revealed only a lipodystrophy causal mutation in LMNA, c.29C>T, T10I with no other significant findings in18 other lipodystrophy-related genes. No deletion or duplication was identified by a targeted array CGH of LMNA.

As predicted, no rare monogenic variants in HTG-causal genes (LPL, GPIHBP1, APOA5, APOC2, LMF1, GPD1) were identified in either subject. However, TG-polygenic scores were 17/28 (95^th %ile) in the proband, and 13/28 (50^th %ile) in the father, the same trend as the level of HTG levels seen in them. Apolipoprotein E genotypes were non-contributory, (3/3) in the proband, and (3/4) in the father.

Conclusion:

Our findings support that the pathophysiology of HTG in lipodystrophy is likely to be due to lack of TG-storage space (adipose tissues), and is unlikely due to a defect in lipoprotein metabolism seen in patients with rare monogenic HTG-variants. Although the HTG-polygenic score was higher in the proband, and the accumulative effects of the at-risk alleles may be contributor to the HTG phenotype, it is unlikely to be the leading cause of severe HTG seen in the proband.

The lysosome: A potential juncture between SARS-CoV-2 infectivity and Niemann-Pick disease type C, with therapeutic implications

Drug repurposing is potentially the fastest available option in the race to identify safe and efficacious drugs that can be used to prevent and/or treat COVID‐19. By describing the life cycle of the newly emergent coronavirus, SARS‐CoV‐2, in light of emerging data on the therapeutic efficacy of various repurposed antimicrobials undergoing testing against the virus, we highlight in this review a possible mechanistic convergence between some of these tested compounds. Specifically, we propose that the lysosomotropic effects of hydroxychloroquine and several other drugs undergoing testing may be responsible for their demonstrated in vitro antiviral activities against COVID‐19. Moreover, we propose that Niemann‐Pick disease type C (NPC), a lysosomal storage disorder, may provide new insights into potential future therapeutic targets for SARS‐CoV‐2, by highlighting key established features of the disorder that together result in an “unfavorable” host cellular environment that may interfere with viral propagation. Our reasoning evolves from previous biochemical and cell biology findings related to NPC, coupled with the rapidly evolving data on COVID‐19. Our overall aim is to suggest that pharmacological interventions targeting lysosomal function in general, and those particularly capable of reversibly inducing transient NPC‐like cellular and biochemical phenotypes, constitute plausible mechanisms that could be used to therapeutically target COVID‐19.

Squeezing lipids: NMR characterization of lipoprotein particles under pressure

Determining the particle size and number of lipoprotein components found in blood plasma (HDL, LDL and VLDL) has become an important clinical tool in diagnosing risk of cardiovascular disease. Proton (1H) NMR spectroscopy methods to quantify lipoprotein particle subclasses have been advancing since NMR lineshape analysis of plasma samples was first proposed in the 1990's. NMR methods, including a more recent DOSY-based diffusion spectroscopy test, provide the foundation for the advanced lipoprotein tests, including Lipoprotein® and Liposcale® analyses available for clinical use to determine particle size and number. At the time of this submission, no NMR studies exist which explore physical parameters of individual lipoprotein fractions when they are deformed by pressure. This study reports 1H NMR frequency shifts and T2* measurements for the broad methyl peak attributed to terminal methyls (cholesteryl positions 26, 27 and terminal acyl methyl groups) in three primary lipoprotein fractions as a function of hydraulic pressure. This terminal CH3 resonance shifted linearly upfield as a function of pressure for HDL and VLDL (observed slopes of -0.014 Hz/bar). The LDL terminal CH3 resonance shows segmented behavior, with a shallow slope between 0-900 bar (-0.008 hz/bar) and a slope similar to HDL and VDL across the range from 1000 to 2400 bar (slope -0.016 Hz/bar). 1H T2* values measured for VLDL and HDL dropped linearly with increasing pressure. 1H T2* values for LDL demonstrated segmented behavior as a function of pressure. The unique behavior observed for LDL terminal CH3 frequency and 1H T2* trends suggests an approximate pressure at which phase transition occurs.

GlycA: A New Biomarker for Systemic Inflammation and Cardiovascular Disease (CVD) Risk Assessment

The GlycA test is a recently developed proton nuclear magnetic resonance (¹H-NMR) spectroscopy-based assay that has been gaining increased interest as a serum biomarker for systemic inflammation, and consequently, as a potential biomarker for cardiovascular disease (CVD) risk assessment. The test has undergone investigation in several large cohort studies, since its development, to assess its predictive value for incident CVD events, CVD-associated mortality, and all-cause mortality. Despite variation in the generated estimates by these studies, they have all consistently demonstrated moderate-strength positive correlations between baseline GlycA levels, and incident CVD event rates and associated mortality. These correlations withheld testing even after adjusting for several other established CVD risk factors, including notable inflammatory biomarkers such as high-sensitivity C-reactive protein (hsCRP) and interleukin-6 (IL-6). Compared with hsCRP, which is a well-known inflammatory biomarker for CVD risk assessment, GlycA has a comparable predictive value for future CVD-related events. However, the indications to pursue GlycA testing, and its clinical utility in patient care management, are yet to be determined. In this review, we define the GlycA test and what it "measures", and provide a brief summary of the findings of studies showing its association with incident CVD rates, and CVD-related mortality, as well as its correlation with other inflammatory biomarkers, namely hsCRP. Finally, we highlight the analytical advantages of the GlycA test, compared with "traditional" inflammatory biomarkers, while also mentioning its current limitations.