Triglyceride-rich lipoproteins and their remnants: metabolic insights, role in atherosclerotic cardiovascular disease, and emerging therapeutic strategies-a consensus statement from the European Atherosclerosis Society.

Recent advances in human genetics, together with a large body of epidemiologic, preclinical, and clinical trial results, provide strong support for a causal association between triglycerides (TG), TG-rich lipoproteins (TRL), and TRL remnants, and increased risk of myocardial infarction, ischaemic stroke, and aortic valve stenosis. These data also indicate that TRL and their remnants may contribute significantly to residual cardiovascular risk in patients on optimized low-density lipoprotein (LDL)-lowering therapy. This statement critically appraises current understanding of the structure, function, and metabolism of TRL, and their pathophysiological role in atherosclerotic cardiovascular disease (ASCVD). Key points are (i) a working definition of normo- and hypertriglyceridaemic states and their relation to risk of ASCVD, (ii) a conceptual framework for the generation of remnants due to dysregulation of TRL production, lipolysis, and remodelling, as well as clearance of remnant lipoproteins from the circulation, (iii) the pleiotropic proatherogenic actions of TRL and remnants at the arterial wall, (iv) challenges in defining, quantitating, and assessing the atherogenic properties of remnant particles, and (v) exploration of the relative atherogenicity of TRL and remnants compared to LDL. Assessment of these issues provides a foundation for evaluating approaches to effectively reduce levels of TRL and remnants by targeting either production, lipolysis, or hepatic clearance, or a combination of these mechanisms. This consensus statement updates current understanding in an integrated manner, thereby providing a platform for new therapeutic paradigms targeting TRL and their remnants, with the aim of reducing the risk of ASCVD.

Triglyceride-rich lipoprotein binding and uptake by heparan sulfate proteoglycan receptors in a CRISPR/Cas9 library of Hep3B mutants.

Binding and uptake of triglyceride-rich lipoproteins (TRLs) in mice depend on heparan sulfate and the hepatic proteoglycan, syndecan-1 (SDC1). Alteration of glucosamine N-sulfation by deletion of glucosamine N-deacetylase-N-sulfotransferase 1 (Ndst1) and 2-O-sulfation of uronic acids by deletion of uronyl 2-O-sulfotransferase (Hs2st) led to diminished lipoprotein metabolism, whereas inactivation of glucosaminyl 6-O-sulfotransferase 1 (Hs6st1), which encodes one of the three 6-O-sulfotransferases, had little effect on lipoprotein binding. However, other studies have suggested that 6-O-sulfation may be important for TRL binding and uptake. In order to explain these discrepant findings, we used CRISPR/Cas9 gene editing to create a library of mutants in the human hepatoma cell line, Hep3B. Inactivation of EXT1 encoding the heparan sulfate copolymerase, NDST1 and HS2ST dramatically reduced binding of TRLs. Inactivation of HS6ST1 had no effect, but deletion of HS6ST2 reduced TRL binding. Compounding mutations in HS6ST1 and HS6ST2 did not exacerbate this effect indicating that HS6ST2 is the dominant 6-O-sulfotransferase and that binding of TRLs indeed depends on 6-O-sulfation of glucosamine residues. Uptake studies showed that TRL internalization was also affected in 6-O-sulfation deficient cells. Interestingly, genetic deletion of SDC1 only marginally impacted binding of TRLs but reduced TRL uptake to the same extent as treating the cells with heparin lyases. These findings confirm that SDC1 is the dominant endocytic proteoglycan receptor for TRLs in human Hep3B cells and that binding and uptake of TRLs depend on SDC1 and N- and 2-O-sulfation as well as 6-O-sulfation of heparan sulfate chains catalyzed by HS6ST2.

Elevated Levels of Apolipoprotein CIII Increase the Risk of Postprandial Hypertriglyceridemia.

Background: To investigate possible mechanisms of postprandial hypertriglyceridemia (PPT), we analyzed serum lipid and apolipoprotein (Apo) AI, B, CII and CIII levels before and after a high-fat meal. Methods: The study has been registered with the China Clinical Trial Registry (registration number:ChiCTR1800019514; URL: http://www.chictr.org.cn/index.aspx). We recruited 143 volunteers with normal fasting triglyceride (TG) levels. All subjects consumed a high-fat test meal. Venous blood samples were obtained during fasting and at 2, 4, and 6 hours after the high-fat meal. PPT was defined as TG ≥2.5 mmol/L any time after the meal. Subjects were divided into two groups according to the high-fat meal test results: postprandial normal triglyceride (PNT) and PPT. We compared the fasting and postprandial lipid and ApoAI, ApoB, ApoCII and ApoCIII levels between the two groups. Results: Significant differences were found between the groups in fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), TG, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), non-high-density lipoprotein cholesterol (non-HDL-C), TG-rich lipoprotein remnants (TRLRs), ApoB, ApoCIII, ApoAI/ApoB and ApoCII/ApoCIII. The insulin, HOMA-IR, TG, TC, LDL-C, non-HDL-C, TRLRs, ApoB, ApoCIII and ApoCII/ApoCIII values were higher in the PPT group, while the ApoAI/ApoB ratio was higher in the PNT group. The postprandial TG level peaked in the PNT group 2 hours after the meal but was significantly higher in the PPT group and peaked at 4 hours. TRLRs gradually increased within 6 hours after the high-fat meal in both groups. The area under the curve (AUC) of TG and TRLRs and the AUC increment were higher in the PPT group (P < 0.001). ApoCIII peaked in the PNT group 2 hours after the meal and gradually decreased. ApoCIII gradually increased in the PPT group within 6 hours after the meal, exhibiting a greater AUC increment (P < 0.001). Fasting ApoCIII was positively correlated with age, systolic and diastolic blood pressure, body mass index (BMI), waist circumference, TC, TG, LDL-C, non-HDL-C, TRLRs, and ApoB (P<0.05). ApoCIII was an independent risk factor of PPT after adjustment for BMI, waist circumference, TC, LDL-C, and ApoB (P < 0.001, OR=1.188). Conclusions: Elevated ApoCIII levels may cause PPT.

ApoB-lipoprotein remnant dyslipidemia and high-fat meal intolerance is associated with markers of cardiometabolic risk in youth with obesity.

INTRODUCTION: Cardiovascular disease (CVD) originates in childhood and risk is exacerbated in obesity. Mechanisms of the etiologic link between early adiposity and CVD-risk remain unclear. Postprandial or non-fasting dyslipidemia is characterized by elevated plasma triglycerides (TG) and intestinal-apolipoprotein(apo)B48-remnants following a high-fat meal and is a known CVD-risk factor in adults. The aim of this study was to determine (a) whether the fasting concentration of apoB48-remnants can predict impaired non-fasting apoB48-lipoprotein metabolism (fat intolerance) and (b) the relationship of these biomarkers with cardiometabolic risk factors in youth with or without obesity. METHODS: We assessed fasting and non-fasting lipids in youth without obesity (n = 22, 10 males, 12 females) and youth with obesity (n = 13, 5 males, 8 females) with a mean BMI Z-score of 0.19 ± 0.70 and 2.25 ± 0.31 (P = .04), respectively. RESULTS: Fasting and non-fasting apoB48-remnants were elevated in youth with obesity compared to youth without obesity (apoB48: 18.04 ± 1.96 vs 8.09 ± 0.59, P < .0001, and apoB48AUC : 173.0 ± 20.86 vs 61.99 ± 3.44, P < .001). Furthermore, fasting plasma apoB48-remnants were positively correlated with the non-fasting response in apoB48AUC (r = 0.84, P < .0001) as well as other cardiometabolic risk factors including HOMA-IR (r = 0.61, P < .001) and leptin (r = 0.56, P < .0001). CONCLUSION: Fasting apoB48-remnants are elevated in youth with obesity and predict apoB48 postprandial dyslipidemia. ApoB48-remnants are associated with the extent of fat intolerance and appear to be potential biomarker of CVD-risk in youth.

Outstanding improvement of the advanced lipoprotein profile in subjects with new-onset type 1 diabetes mellitus after achieving optimal glycemic control.

AIMS: The impact of glycemic optimization on lipoprotein subfraction parameters in apparently normolipidemic subjects with new-onset type 1 diabetes mellitus (T1D) was examined. METHODS: We evaluated the serum lipid and advanced lipoprotein profiles in twenty subjects at onset of T1D and twenty non-diabetic controls by laboratory methods and 1H NMR spectroscopy shortly after diabetes diagnosis (baseline), and after achieving optimal glycemic control (HbA1c ≤ 7.0%). RESULTS: Advanced lipoprotein analysis revealed a significant reduction from baseline in serum concentrations of triglycerides (TG), cholesterol (C), and apolipoprotein (Apo)B-containing lipoproteins of treated subjects (VLDL-TG: -21%, IDL-TG: -30%, LDL-TG: -34%, LDL-TG: -36%, P < 0.05; VLDL-C: -23%, IDL-C: -44%, LDL-C: -16%; p < 0.05). Decreased VLDL and LDL lipids were mainly attributed to concomitant reductions in the concentration of medium-sized VLDL (-36%) and medium-sized LDL (-31%) and, to a lesser extent, to large-sized LDL (-14%). Notably, proatherogenic IDL characteristics and related surrogates of atherogenicity were resolved upon achievement of optimal glycemic status. Moreover, the concentration of HDL-TG was also reduced (-18%) at follow-up. CONCLUSIONS: Our data showed that the achievement of optimal glycemic control after T1D onset corrected hidden derangements in ApoB-containing lipoproteins (particularly IDL) and HDL-TG that are related to higher cardiovascular risk in poorly controlled T1D.

ApoB48-Lipoproteins Are Associated with Cardiometabolic Risk in Adolescents with and without Polycystic Ovary Syndrome.

CONTEXT: Adolescents with polycystic ovary syndrome (PCOS) have increased incidence of cardiometabolic risk factors including dyslipidemia. Atherogenic apolipoprotein (apo) B-lipoprotein remnants are associated with increased cardiovascular disease (CVD) risk. OBJECTIVE: The aim of this study was to determine the concentrations of fasting plasma apoB-lipoprotein remnants, apoB48 and apoB100, and their association with cardiometabolic risk factors and androgen indices in adolescent girls with and without PCOS. DESIGN SETTING AND PARTICIPANTS: Participants (n = 184) aged 17 years were recruited in the Menstruation in Teenagers Study from the Western Australian Pregnancy Cohort (Raine) Study. THE MAIN OUTCOME MEASURES: Fasting plasma apo-B48 and -B100 lipoprotein remnant concentrations in adolescent girls with and without PCOS. RESULTS: Fasting plasma apoB48-lipoprotein remnants but not apoB100-lipoprotein remnants were elevated in adolescent girls with increased cardiometabolic risk compared with those with lower cardiometabolic risk (13.91 ± 5.06 vs 12.09 ± 4.47 µg/mL, P < .01). ApoB48-lipoprotein remnants were positively correlated with fasting plasma triglycerides (b = .43, P < .0001). The prevalence of increased cardiometabolic risk factors was 2-fold higher in those diagnosed with PCOS (35.3%) than in those without PCOS (16.3%).Conclusion: Adolescents with PCOS have a 2-fold higher incidence of cardiometabolic risk factors than those without PCOS. Fasting apoB48-lipoprotein remnants are elevated in adolescent girls with a high prevalence of cardiometabolic risk factors.

Changes in lipoprotein subfractions following menopause in the Longitudinal Study of Adult Health (ELSA-Brasil).

INTRODUCTION: It is unclear how aging and menopause-induced lipid changes contribute to the elevated cardiovascular risk in menopausal women. We examined the association between lipid profiles and menopausal status and duration of menopause in the Longitudinal Study of Adult Health (ELSA-Brasil). METHODS: This is a cross-sectional analysis of baseline data from women in the ELSA-Brasil, stratified by duration of menopause into 5 groups: pre-menopause, <2 years, 2-5.9 years, 6-9.9 years and ≥10 years of menopause, excluding menopause <40 years or of non-natural cause; also excluded were women using lipid-lowering drugs or hormone replacement. Comparisons were performed using ANOVA with Bonferroni correction. Associations of menopause categories and time since menopause with lipid variables obtained by vertical auto-profile were tested using multiple linear regression. RESULTS: From 1916 women, postmenopausal groups had unadjusted higher total cholesterol, LDL-c, real LDL-c, IDL-c, VLDL-c, triglycerides, non-HDL-c, VLDL3-c, triglyceride-rich lipoprotein remnants (TRL-c) and buoyant LDL-c concentrations than pre-menopausal women, with no difference among postmenopausal groups. In multiple linear regression, duration of menopause <2 years was significantly associated with TRL-c [7.21 mg/dL (95% CI 3.59-10.84)] and VLDL3-c [2.43 mg/dL (95%CI 1.02-3.83)]. No associations of menopausal categories with HDL-c or LDL-c subfractions were found, and nor were associations of time since menopause with lipid subfractions. CONCLUSIONS: In a large sample of Brazilian women, deterioration of the lipid profile following menopause was confirmed, which could contribute to the increased cardiovascular risk. Our findings suggest a postmenopausal elevation in triglyceride-rich lipoprotein remnants. How lipoprotein subfractions change after the onset of menopause warrants investigation in studies with appropriate designs.

The majority of lipoprotein lipase in plasma is bound to remnant lipoproteins: A new definition of remnant lipoproteins.

BACKGROUND: Lipoprotein lipase (LPL) is a multifunctional protein and a key enzyme involved in the regulation of lipoprotein metabolism. We determined the lipoproteins to which LPL is bound in the pre-heparin and post-heparin plasma. METHODS: Tetrahydrolipstatin (THL), a potent inhibitor of serine lipases, was used to block the lipolytic activity of LPL, thereby preventing changes in the plasma lipoproteins due to ex vivo lipolysis. Gel filtration was performed to obtain the LPL elution profiles in plasma and the isolated remnant lipoproteins (RLP). RESULTS: When ex vivo lipolytic activity was inhibited by THL in the post-heparin plasma, majority of the LPL was found in the VLDL elution range, specifically in the RLP as inactive dimers. However, in the absence of THL, most of the LPL was found in the HDL elution range as active dimers. Furthermore, majority of the LPL in the pre-heparin plasma was found in the RLP as inactive form, with broadly diffused lipoprotein profiles in the presence and absence of THL. CONCLUSIONS: It is suggested that during lipolysis in vivo, the endothelial bound LPL dimers generates RLP, forming circulating RLP-LPL complexes in an inactive form that subsequently binds and initiates receptor-mediated catabolism.

Lipoprotein remnants and dense LDL are associated with features of unstable carotid plaque: a flag for non-HDL-C.

OBJECTIVE: We investigated the association between cholesterol across the LDL density range and in the VLDL and IDL particles with the prevalence of inflammatory cells in plaques of patients with severe carotid artery stenosis. METHODS: Forty-five patients undergoing carotid endarterectomy were studied. Plaque specimens were analyzed for cellular composition by immunocytochemistry using monoclonal antibodies. Lipoprotein subclasses were separated by gradient ultracentrifugation. RESULTS: We found no correlations between LDL-C, HDL-C and plasma triglyceride levels with plaque cellular composition. On the other hand, macrophage content was significantly related to cholesterol in the dense LDL subclasses (r = 0.30, p < 0.01) and in the triglyceride-rich lipoprotein remnants, namely dense VLDL and IDL particles (r = 0.46, p < 0.01). HDL subclasses were not correlated with plaque cellular composition. In a mirror manner, smooth muscle cells were inversely associated with cholesterol levels of the dense LDL subclasses (r = -0.32, p < 0.01 fraction 10; r = -0.26, p < 0.05 fraction 11) while only a non-significant trend was observed with the cholesterol in the VLDL-IDL fractions. These results provide the pathophysiological background to account for the relevance of non-HDL-C as the only lipid parameter, aside LDL density, significantly associated (ß = 0.351, p = 0.021) with carotid plaque macrophage content. CONCLUSIONS: We provide evidence that lipoprotein subclasses, specifically cholesterol in the dense LDL fractions and in the triglyceride-rich lipoprotein remnants, significantly affect carotid plaque cellular composition, in particular macrophages content.