Apolipoprotein B-48 as a determinant of endothelial function in obese subjects with type 2 diabetes mellitus: Effect of fenofibrate treatment

Closing the gaps in patient management of dyslipidemia: stepping into cardiovascular precision diagnostics with apolipoprotein profiling

In persons with dyslipidemia, a high residual risk of cardiovascular disease remains despite lipid lowering therapy. Current cardiovascular risk prediction mainly focuses on low-density lipoprotein cholesterol (LDL-c) levels, neglecting other contributing risk factors. Moreover, the efficacy of LDL-c lowering by statins resulting in reduced cardiovascular risk is only partially effective. Secondly, from a metrological viewpoint LDL-c falls short as a reliable measurand. Both direct and calculated LDL-c tests produce inaccurate test results at the low end under aggressive lipid lowering therapy. As LDL-c tests underperform both clinically and metrologically, there is an urging need for molecularly defined biomarkers. Over the years, apolipoproteins have emerged as promising biomarkers in the context of cardiovascular disease as they are the functional workhorses in lipid metabolism. Among these, apolipoprotein B (ApoB), present on all atherogenic lipoprotein particles, has demonstrated to clinically outperform LDL-c. Other apolipoproteins, such as Apo(a) - the characteristic apolipoprotein of the emerging risk factor lipoprotein(a) -, and ApoC-III - an inhibitor of triglyceride-rich lipoprotein clearance -, have attracted attention as well. To support personalized medicine, we need to move to molecularly defined risk markers, like the apolipoproteins. Molecularly defined diagnosis and molecularly targeted therapy require molecularly measured biomarkers. This review provides a summary of the scientific validity and (patho)physiological role of nine serum apolipoproteins, Apo(a), ApoB, ApoC-I, ApoC-II, ApoC-III, ApoE and its phenotypes, ApoA-I, ApoA-II, and ApoA-IV, in lipid metabolism, their association with cardiovascular disease, and their potential as cardiovascular risk markers when measured in a multiplex apolipoprotein panel.

Remnant cholesterol in atherosclerotic cardiovascular disease: A systematic review and meta-analysis

BACKGROUND

Accumulating evidence suggests a substantial contribution of remnant cholesterol (RC) to residual risk for the development or relapse of atherosclerotic cardiovascular disease (ASCVD). We aimed to evaluate the association of RC levels with ASCVD risk by different risk categories and methods of RC assessment. We also assessed available evidence of the effects of lipid-lowering therapies (LLTs) on RC levels.

METHODS

English-language searches of Medline, PubMed, and Embase (inception to 31 January 2023); ClinicalTrials.gov (October 2022); and reference lists of studies and reviews. Studies reporting on the risk of the composite endpoint [all-cause mortality, cardiovascular mortality, and major adverse cardiac events (MACE)] by RC levels were included. Moreover, we searched for studies reporting differences in RC levels after the administration of LLT(s).

RESULTS

Among n = 29 studies with 257,387 participants, we found a pooled linear (pooled HR: 1.27 per 1-SD increase, 95% CI: 1.12-1.43, P < 0.001, I2 = 95%, n = 15 studies) and non-linear association (pooled HR: 1.59 per quartile increase, 95% CI: 1.35-1.85, P < 0.001, I2 = 87.9%, n = 15 studies) of RC levels and the risk of M ACE both in patients with and without established ASCVD. Interestingly, the risk of MACE was higher in studies with directly measured vs. calculated RC levels. In a limited number of studies and participants, LLTs reduced RC levels.

CONCLUSION

RC levels are associated with ASCVD risk both in primary and secondary prevention. Directly measured RC levels are associated with ASCVD risk more evidently. Available LLTs tend to decrease RC levels, although the clinical relevance of RC decrease merits further investigation.

PROSPERO REGISTRATION

CRD42022371346.

Olive oil and postprandial hyperlipidemia: implications for atherosclerosis and metabolic syndrome

Olive oil is the primary source of fat in the Mediterranean diet, which is associated with a significant improvement in health status, as measured by reduced mortality from several chronic diseases. The current pandemic of obesity, metabolic syndrome, and type 2 diabetes is intimately associated with an atherogenic dyslipidemic phenotype. The core components of the dyslipidemia of the metabolic syndrome, which most likely initiate atherosclerosis, are the "lipid triad" consisting of high plasma triglycerides, low levels of high-density lipoproteins, and a preponderance of small, dense low-density lipoproteins at fasting. However, postprandial (non-fasting) TGs (postprandial hyperlipidemia) are also recognized as an important component for atherosclerosis. Herein, the purpose of this review was to provide an update on the effects and mechanisms related to olive oil on postprandial hyperlipidemia and its implications for the onset and progression of atherosclerosis and metabolic syndrome.

Effect of fibrates on glycemic parameters: A systematic review and meta-analysis of randomized placebo-controlled trials

AIMS

The aim of this meta-analysis of randomized placebo-controlled clinical trials was to assess the effect of fibrates on glycemic parameters.

MATERIALS AND METHODS

Only randomized placebo-controlled trials investigating the impact of fibrate treatment on glucose homeostasis markers were searched in PubMed-Medline, SCOPUS, Web of Science and Google Scholar databases (from inception to April 11, 2017). A random-effects model and generic inverse variance method were used for quantitative data synthesis. Sensitivity analysis was conducted using the leave-one-out method. A weighted random-effects meta-regression was performed to evaluate the impact of potential confounders on glycemic parameters.

RESULTS

This meta-analysis of data from 22 randomized placebo-controlled clinical trials involving a total of 11,402 subjects showed that fibrate therapy significantly decreased fasting plasma glucose (WMD: -0.28 mmol/L, 95% CI: -0.42, -0.14, p < 0.001), insulin levels (WMD: -3.87 pmol/L, 95% CI: -4.97, -2.78, p < 0.001) and insulin resistance (HOMA-IR, WMD: -1.09, 95% CI: -1.71, -0.47, p = 0.001), but with no effect on HbA1c (WMD: 0.01%, 95% CI: -0.18, 0.19, p = 0.955). All analyses were robust in the leave-one-out sensitivity analysis except for insulin levels that showed a non-significant result (WMD: -0.84 pmol/L, 95% CI: -6.36, 4.68, p = 0.766) following omission of one of the included trials.

CONCLUSION

This meta-analysis has shown that fibrate treatment significantly decreases fasting plasma glucose, insulin levels, and HOMA-IR indicating additional clinical therapeutic benefits.

Apolipoprotein status in type 2 diabetes mellitus and its complications (Review)

Dyslipidaemia in type 2 diabetes mellitus (T2DM) is characterized by high plasma triglyceride concentrations, reduced high‑density lipoprotein concentrations and increased small density low‑density lipoprotein concentrations. Dyslipidaemia may lead to cardiovascular disease (CVD) and other complications. Apolipoproteins mainly comprise six species, apolipoprotein (apo)A, apoB, apoC, apoD, apoE and apoM, which are important components of plasma lipoproteins that carry lipids and stabilize the structure of lipoproteins. Complex metabolic disorders of apolipoproteins are present in T2DM, such as high plasma apoB, apoC‑II, apoC‑III and apoE concentrations, and low plasma apoA‑I and apoM concentrations, which are associated with dyslipidaemia and interrelated complications. Plasma concentrations of some apolipoproteins are also altered in T2DM with CVD or other complications. Several apolipoprotein polymorphisms are associated with diabetes susceptibility and/or lipid metabolism. The present review described the metabolic disorders of apolipoproteins in T2DM and its complications, and the relationship between each major apolipoprotein and T2DM, as well as the effects of apolipoprotein polymorphisms on diabetic susceptibility.

Linagliptin improves endothelial function in patients with type 2 diabetes: A randomized study of linagliptin effectiveness on endothelial function

AIMS/INTRODUCTION

The present multicenter, prospective, controlled, open and randomized three-arm parallel study was designed to compare the effects of linagliptin with those of metformin on endothelial function.

MATERIALS AND METHODS

Type 2 diabetes patients treated with 750 mg of metformin (hemoglobin A1c ≥6.0% and <8.0%, n = 96) were randomized to continue metformin 750 mg/day (control group, n = 29), metformin at 1,500 mg/day (metformin group, n = 26) and metformin 750 mg/day supplemented with linagliptin 5 mg/day (linagliptin add-on group, n = 29) and treated for 16 weeks. Vascular endothelial function was evaluated by flow-mediated dilation. The primary end-point was changes in flow-mediated dilation at 16 weeks relative to baseline.

RESULTS

Linagliptin significantly improved flow-mediated dilation from baseline (4.9 ± 2.7%) to 16 weeks (6.3 ± 2.7%, P < 0.05), whereas the other groups did not show any changes. Hemoglobin A1c at 16 weeks was significantly lower in the metformin and linagliptin add-on groups compared with the control (6.6 ± 0.6%, 6.5 ± 0.5% and 7.0 ± 0.6%, respectively). Single and multiple regression analyses showed that apolipoprotein B correlated significantly with change in flow-mediated dilation, and apolipoprotein B was decreased only in the linagliptin add-on group (-6.0 ± 11.3 mg/dL, P < 0.01).

CONCLUSIONS

Linagliptin for 16 weeks improved endothelial function with a modest improvement in glycemic control. This effect was mediated, at least in part, by reduction in apolipoprotein B. Linagliptin has a protective role on endothelial function in patients with type 2 diabetes with moderate hyperglycemia.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

Lipoprotein effects of incretin analogs and dipeptidyl peptidase 4 inhibitors

Elevated post-prandial lipoprotein levels are common in patients with type 2 diabetes. Post-prandial lipoprotein alterations in type 2 diabetics are widely believed to drive inflammation and are considered a major risk factor for cardiovascular disease in diabetic patients. The incretins glucagon like peptide-1 (GLP-1) and glucose insulinotropic peptide (GIP) modulate post-prandial lipoproteins through a multitude of pathways that are independent of insulin and weight loss. Evidence from both animal models and humans seems to suggest an important effect on triglyceride rich lipoproteins (Apo48 containing) with little to no effects on other lipoproteins at least in humans. Dipeptidyl peptidase-4 (DPP4) inhibitors also appear to share these effects suggesting an important role for incretins in these effects. In this review, we will summarize lipid modulating effects of incretin analogs and DPP-4 inhibitors in both animal models and human studies and provide an overview of mechanisms responsible for these effects.

Postprandial lipaemia and vascular disease

PURPOSE OF REVIEW

In this review we discuss the postprandial pathophysiological mechanisms that promote vascular disease, the evidence for a role of postprandial lipaemia (PPL) in vascular disease and the effect of modifiable and nonmodifiable factors in PPL.

RECENT FINDINGS

PPL refers to the dynamic changes in serum lipids and lipoproteins (mainly in serum triglycerides) that occur after a fat load or a meal. Recent data indicate that postprandial or nonfasting triglyceride levels are better predictors of cardiovascular risk, suggesting that efficiency of postprandial handling of triglyceride-rich lipoproteins plays a role in the causation of vascular disease.

SUMMARY

The recent finding that postprandial serum triglyceride levels are even better than fasting serum triglyceride levels as predictors of vascular disease indicate that it is better to measure an index of triglyceride-rich lipoproteins (in most cases serum triglyceride levels) in the postprandial period than in the postabsorptive fasting state. Moreover, by the time the postabsorptive state is reached, some of these proatherogenic triglyceride-rich lipoprotein changes may be missed in the measurement.

New and emerging regulators of intestinal lipoprotein secretion

Overproduction of hepatic apoB100-containing VLDL particles has been well documented in animal models and in humans with insulin resistance such as the metabolic syndrome and type 2 diabetes, and contributes to the typical dyslipidemia of these conditions. In addition, postprandial hyperlipidemia and elevated plasma concentrations of intestinal apoB48-containing chylomicron and chylomicron remnant particles have been demonstrated in insulin resistant states. Intestinal lipoprotein production is primarily determined by the amount of fat ingested and absorbed. Until approximately 10 years ago, however, relatively little attention was paid to the role of the intestine itself in regulating the production of triglyceride-rich lipoproteins (TRL) and its dysregulation in pathological states such as insulin resistance. We and others have shown that insulin resistant animal models and humans are characterized by overproduction of intestinal apoB48-containing lipoproteins. Whereas various factors are known to regulate hepatic lipoprotein particle production, less is known about factors that regulate the production of intestinal lipoprotein particles. Monosacharides, plasma free fatty acids (FFA), resveratrol, intestinal peptides (e.g. GLP-1 and GLP-2), and pancreatic hormones (e.g. insulin) have recently been shown to be important regulators of intestinal lipoprotein secretion. Available evidence in humans and animal models strongly supports the concept that the small intestine is not merely an absorptive organ but rather plays an active role in regulating the rate of production of chylomicrons in fed and fasting states. Metabolic signals in insulin resistance and type 2 diabetes and in some cases an aberrant intestinal response to these factors contribute to the enhanced formation and secretion of TRL. Understanding the regulation of intestinal lipoprotein production is imperative for the development of new therapeutic strategies for the prevention and treatment of dyslipidemia. Here we review recent developments in this field and present evidence that intestinal lipoprotein production is a process with metabolic plasticity and that modulation of intestinal lipoprotein secretion may be a feasible therapeutic strategy in the treatment of dyslipidemia and possibly prevention of atherosclerosis.

Novel benefits of peroxisome proliferator-activated receptors on cardiovascular risk

PURPOSE OF REVIEW

This review provides an overview of newly described mechanisms by which peroxisome proliferator-activated receptors (PPARs) (α, γ, and δ) regulate several factors associated with cardiovascular risk.

RECENT FINDINGS

PPAR agonists have known effects on plasma lipoprotein levels, inflammation, and insulin resistance all of which influence the risk of cardiovascular disease. Recent studies provide more detail regarding the mechanisms behind these changes. PPAR-α activation in the enterocyte on HDL and chylomicron formation. PPAR-γ agonists reduce inflammation, in part, through direct effects on adipocytes and regulatory T cells within visceral adipose. PPAR-δ also has a relatively high expression in the macrophage. Incubation of macrophages with PPAR-δ agonists was shown to inhibit foam cell formation induced excessive levels of VLDL remnants.

SUMMARY

Treatments that activate PPAR-α, PPAR-γ, and PPAR-δ alone or in combination have the potential to reduce cardiovascular risk although multiple independent mechanisms. Treatment with PPAR agonists can reduce the burden of atherogenic postprandial lipoproteins and improve vascular function, reduce inflammation and inhibit foam cell formation. All of these would be expected to have favorable effects on cardiovascular risk. The challenge remains to develop compounds that maximize these potential cardiovascular benefits while minimizing undesirable effects of these compounds.

Making sense in antisense: therapeutic potential of noncoding RNAs in diabetes-induced vascular dysfunction

The rapid rise of type II diabetes mellitus and its accompanying vascular complications call for novel approaches in unravelling its pathophysiological mechanisms and designing new treatment modalities. Noncoding RNAs represent a class of previously unknown molecular modulators of this disease. The most important features of diabetes-induced vascular disease, which include metabolic deregulation, increased oxidative stress, release of inflammatory mediators like adipokines, and pathologic changes in vascular cells, all are depicted and governed by a certain set of noncoding RNAs. While these mechanisms are being unravelled, new diagnostic and therapeutic opportunities to treat diabetes-induced vascular disease emerge.

Pioglitazone ameliorates endothelial dysfunction in those with impaired glucose regulation among the first-degree relatives of type 2 diabetes mellitus patients

OBJECTIVE

To study the effects of pioglitazone on endothelial dysfunction of subjects with impaired glucose regulation (IGR) among the first-degree relatives of patients with type 2 diabetes mellitus (T2DM).

SUBJECTS AND METHODS

The first-degree relatives of T2DM patients were screened with oral glucose test and IGR was diagnosed. IGR subjects whose blood glucose was still above the level after 1-month exercise were randomized to receive pioglitazone (15 mg/day) or vehicle for 12 weeks. Endothelial function was assessed as endothelium-dependent and -independent vasodilation. Blood nitric oxide (NO), blood pressure, body mass index, insulin and serum lipids were also measured. Area under the curve of glucose (AUC(glu)) and insulin (AUC(INS)), homeostasis model assessment of insulin resistance (HOMA-IR), HOMA of β-cell function (HOMA-β) and early insulin secretion index (ΔI(30)/ΔG(30)) were calculated.

RESULTS

After pioglitazone treatment, fasting plasma, 2-hour plasma glucose, triglyceride (TG), fasting insulin, AUC(glu), HOMA-β and HOMA-IR, 2-hour insulin, AUC(INS) and ΔI(30)/ΔG(30) decreased. Endothelium-dependent vasodilation and NO were significantly improved in the treatment group. Furthermore, the changes of endothelium-dependent vasodilation were negatively correlated with changes in AUC(INS) but positively with NO and HOMA-β. Stepwise multivariate regression analysis showed that changes in NO and HOMA-β were both independent parameters for improvement of endothelial dysfunction.

CONCLUSION

Pioglitazone decreased blood glucose and TG, increased insulin sensitivity, and ameliorated endothelial dysfunction of IGR subjects among the first-degree relatives of T2DM patients. Increased NO production may be associated with the improvement of endothelial dysfunction.

Postprandial dyslipidaemia and diabetes: mechanistic and therapeutic aspects

PURPOSE OF REVIEW

There has been a resurgence of interest in the role of triglyceride-rich lipoproteins in the development of atherosclerosis and cardiovascular disease, and this is particularly relevant to diabetes mellitus and the postprandial state.

RECENT FINDINGS

Recent evidence suggests that insulin resistance in diabetes induces postprandial dyslipidemia by increasing the enterocytic production of chylomicrons and their remnant particles, but an impaired clearance capacity is also involved. Postprandial dyslipidaemia in diabetes induces oxidative stress, inflammation and endothelial dysfunction and this may be compounded by dysglycaemia. New guidelines for managing hypertriglyceridaemia in diabetes have been published, first-line therapies being improved glycaemic control, treatment of other secondary causes of dyslipidaemia and statin therapy, followed by judicious use of fibrates, n-3 fatty acids or niacin. A new role for incretin-based therapies in regulating dyslipidaemia has been identified.

SUMMARY

Postprandial dyslipidaemia is a pivotal mechanism whereby diabetes can induce and accelerate atherosclerosis. Regulating the plasma concentrations of triglyceride-rich lipoproteins may decrease the cardiovascular complications of diabetes. The mechanisms of action of incretin-based treatments on dyslipidaemia and endothelial dysfunction need further investigation. The efficacy of new therapies targeted at postprandial dysmetabolism in diabetes need to be confirmed, against best current levels of care, in clinical endpoint trials.