The clinical significance of the size of low-density-lipoproteins and the modulation of subclasses by fibrates

Metabolic Properties of Lowdensity Lipoprotein (LDL) Triglycerides in Patients with Type 2 Diabetes, Comparison with Small Dense LDL-Cholesterol

AIMS

Abnormal compositional changes in low-density lipoprotein (LDL) particles, such as triglyceride (TG) enrichment and size reduction, are common in patients with diabetes. Several cohort studies have demonstrated that LDL-TG and sdLDL-cholesterol (C) are sensitive biomarkers for predicting atherosclerotic cardiovascular diseases beyond LDL-C. Although sdLDL has been extensively studied, little is known about the properties of LDL-TG. We investigated similarities or differences between LDL-TG and sdLDL-C.

METHODS

Fasting plasma was obtained from 1,085 patients with type 2 diabetes who were enrolled in the diabetes regional cohort study (ViNA Cohort). LDL-TG and sdLDL-C concentrations were measured using a homogeneous assay established by us. In a subset of subjects, LDL-TG and sdLDL-C levels were measured postprandially or after treatment with lipid-lowering drugs.

RESULTS

In a quartile analysis, higher LDL-TG quartiles were associated with higher frequency of female and fibrate users, whereas sdLDL-C quartiles were associated with frequency of men, drinking, and metabolic syndrome-related measurements. Higher quartiles of LDL-TG/LDL-C were associated with smoking, drinking, fibrate users, and statin users. LDL-TG was significantly correlated with TG, LDL-C, sdLDL-C, and apolipoprotein (apo) B, with apoB being the primary determinant. LDL-TG correlated to high sensitive C-reactive protein (CRP) independently of other lipids. Mean LDL-TG did not change with fasting/non-fasting. Statin treatment reduced LDL-TG, whereas fibrates increased it, but these drugs reduced sdLDL-C equally.

CONCLUSIONS

LDL-TG levels were more tightly regulated by the number of LDL particles than plasma TG levels were. SdLDL-C was closely associated with metabolic syndrome-related factors, whereas LDL-TG was associated with low-grade systemic inflammation.

Emerging approaches for the treatment of hypertriglyceridemia

Hypertriglyceridemia is frequent in diabetic and obese subjects, who are at increased risk for cardiovascular diseases (CVD). Increased triglycerides (TG) are a hallmark of atherogenic dyslipidemia, representing a marker of atherogenic small dense low-density lipoproteins (sdlDL). Importantly, non-fasting/postprandial TG measurements tend to be emphasized in clinical practice for the prediction of CVD, and TG-lowering agents (primarily fibrates) have a beneficial effect on atherogenic dyslipidemia, reducing TG-rich particles and ultimately lowering the production of sdlDL. The combination of omega-3 fatty acids and statins is also recommended, and widely used in clinical practice for subjects with hypertriglyceridemia. However, a consensus on the optimal clinical use of these pharmacological agents is not fully established yet, and additional large clinical studies are needed. It seems that there is a favorable association between fish consumption and mortality from CVD, but it remains to be confirmed by future trials. Finally, there are a number of novel therapies, such as those targeting microsomal transport protein and its inhibitors, which represent new promising option for treating subjects with hypertriglyceridemia.

A review of time courses and predictors of lipid changes with fenofibric acid-statin combination

Fibrates activate peroxisome proliferator activated receptor α and exert beneficial effects on triglycerides, high-density lipoprotein cholesterol, and low density lipoprotein subspecies. Fenofibric acid (FA) has been studied in a large number of patients with mixed dyslipidemia, combined with a low- or moderate-dose statin. The combination of FA with simvastatin, atorvastatin and rosuvastatin resulted in greater improvement of the overall lipid profile compared with the corresponding statin dose. The long-term efficacy of FA combined with low- or moderate- dose statin has been demonstrated in a wide range of patients, including patients with type 2 diabetes mellitus, metabolic syndrome, or elderly subjects. The FA and statin combination seems to be a reasonable option to further reduce cardiovascular risk in high-risk populations, although trials examining cardiovascular disease events are missing.

Effects of the PPAR-δ agonist MBX-8025 on atherogenic dyslipidemia

OBJECTIVE

Determine the effects of treatment with a selective PPAR-δ agonist±statin on plasma lipoprotein subfractions in dyslipidemic individuals.

METHODS

Ion mobility analysis was used to measure plasma concentrations of subfractions of the full spectrum of lipoprotein particles in 166 overweight or obese dyslipidemic individuals treated with the PPAR-δ agonist MBX-8025 (50 and 100 mg/d)±atorvastatin (20 mg/d) in an 8-week randomized parallel arm double blind placebo controlled trial.

RESULTS

MBX-8025 at both doses resulted in reductions of small plus very small LDL particles and increased levels of large LDL, with a concomitant reduction in large VLDL, and an increase in LDL peak diameter. This translated to reversal of the small dense LDL phenotype (LDL pattern B) in ∼90% of the participants. Modest increases in HDL particles were confined to the smaller HDL fractions. Atorvastatin monotherapy resulted in reductions in particles across the VLDL-IDL-LDL spectrum, with a significantly smaller reduction in small and very small LDL vs. MBX-8025 100 mg/d (-24.5±5.3% vs. -47.8±4.9%), and, in combination with MBX-8025, a reversal of the increase in large LDL.

CONCLUSION

PPAR-δ and statin therapies have complementary effects in improving lipoprotein subfractions associated with atherogenic dyslipidemia.

Impact of Fenofibrate on Type 2 Diabetes Patients with Features of the Metabolic Syndrome: Subgroup Analysis From FIELD

Given evidence of increasing prevalence in developed and developing countries, as a result of obesity trends and sedentary lifestyles, the metabolic syndrome represents an increasing burden on healthcare systems. Management guidelines for dyslipidaemia have primarily focused on LDL-C reduction; however, this approach fails to sufficiently address other lipid abnormalities associated with the metabolic syndrome. Atherogenic dyslipidaemia (characterized by elevated triglycerides and low HDL-C) is strongly associated with insulin-resistant states, such as type 2 diabetes and the metabolic syndrome, and is also a common finding among patients receiving treatment for dyslipidaemia. Intervening against atherogenic dyslipidaemia may address a substantial modifiable fraction of residual cardiovascular risk that remains after treatment with a statin. Recent findings from the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study support this view. Fenofibrate treatment was shown to be especially effective in treating marked atherogenic dyslipidaemia, with a significant 27% relative risk reduction for cardiovascular events (P=0.0005, vs. 11%, P=0.035 for all patients) relative to placebo. These data, together with the earlier demonstration of significant microvascular benefits associated with this treatment, suggest a role for fenofibrate, in addition to statin therapy and lifestyle intervention, for reducing global vascular risk in type 2 diabetes patients and for impacting atherogenic dyslipidaemia associated with the metabolic syndrome.

Fenofibrate plus simvastatin (fixed-dose combination) for the treatment of dyslipidaemia

INTRODUCTION

Statin use results in a significant reduction of cardiovascular disease (CVD) risk. However, patients still have residual CVD risk, even if they are receiving optimal statin treatment.

AREAS COVERED

This review, based on a Pubmed/Scopus search, discusses the available evidence regarding the use of a fixed-dose fenofibrate plus simvastatin combination. This combination is useful for patients with mixed dyslipidaemia because it improves the overall lipoprotein profile. Although in clinical trials the rate of adverse events was not significantly greater than monotherapy, patients who receive combination treatment should be monitored carefully. Furthermore, in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) Study, this combination did not result in a significant reduction of CVD events compared with simvastatin monotherapy. However, a possible benefit in this trial was observed in the subgroup of patients with high triglyceride and low high-density lipoprotein cholesterol levels.

EXPERT OPINION

The fixed-dose fenofibrate plus simvastatin combination treatment produces additive results and is safe when patients are properly monitored. Existing evidence appears to support the addition of fenofibrate to simvastatin treatment for the reduction of residual CVD risk in patients with atherogenic dyslipidaemia. However, this combination did not lead to better clinical outcomes in the absence of dyslipidaemia.

Dyslipidaemia of obesity, metabolic syndrome and type 2 diabetes mellitus: the case for residual risk reduction after statin treatment

Dyslipidaemia is frequently present in obesity, metabolic syndrome (MetS) and type 2 diabetes mellitus (T2DM). The predominant features of dyslipidaemia in these disorders include increased flux of free fatty acids (FFA), raised triglyceride (TG) and low high density lipoprotein cholesterol (HDL-C) levels, a predominance of small, dense (atherogenic) low density lipoprotein cholesterol (LDL) particles and raised apolipoprotein (apo) B values Posprandial hyperlipidaemia may also be present. Insulin resistance (IR) appears to play an important role in the pathogenesis of dyslipidaemia in obesity, MetS and T2DM. The cornerstone of treatment of this IR-related dyslipidaemia is lifestyle changes and in diabetic patients, tight glycaemic control. In addition to these measures, recent clinical trials showed benefit with statin treatment. Nevertheless, a substantial percentage of patients treated with statins still experience vascular events. This residual vascular risk needs to be addressed. This review summarizes the effects of hypolipidaemic drug combinations (including statins with cholesterol ester protein inhibitors, niacin, fibrates or fish oil, as well as fibrate-ezetimibe combination) on the residual vascular risk in patients with obesity, MetS or T2DM.

Comparison of fibrate, ezetimibe, low- and high-dose statin therapy for the dyslipidemia of the metabolic syndrome in a mouse model

BACKGROUND AND AIM

The treatment-of-choice for the optimal management of the dyslipidemia of the metabolic syndrome (MetS) is not clearly defined. We compared the efficacy of 4 drug regimes for the management of this dyslipidemia in a mouse model.

MATERIALS AND METHODS

A total of 60 C57Bl6 mice comprised the study group. The first 10 received standard mouse food for the whole experiment (control group). The remaining 50 mice received atherogenic diet for 14 weeks until the development of the MetS. The mice were then divided into 5 groups: the 1st group continued receiving atherogenic diet, while the other 4 groups received atherogenic diet plus ezetimibe (10 mg/kg per day), fenofibrate (100 mg/kg per day), low-dose atorvastatin (10 mg/kg per day), or high-dose (40 mg/kg per day) atorvastatin, respectively, for another 8 weeks.

RESULTS

High-dose atorvastatin treatment achieved the best lipid profile compared with low-dose atorvastatin, ezetimibe, and fibrate therapy. The lipid profile of mice receiving atherogenic diet plus high-dose atorvastatin treatment was similar with mice on regular chow.

CONCLUSIONS

High-dose atorvastatin treatment resulted in optimization of the lipid profile in the presence of a high-fat atherogenic diet in a mouse model. Our results suggest that high-dose atorvastatin treatment may be the optimal treatment option for the dyslipidemia associated with MetS. Nevertheless, verification of these results in humans is required before any definite conclusions can be drawn.

Are post-treatment low-density lipoprotein subclass pattern analyses potentially misleading?

BACKGROUND

Some patients administered cholesterol-lowering therapies may experience an increase in the proportion of small LDL particles, which may be misinterpreted as a worsening of atherosclerotic coronary heart disease risk. This study assessed the lipid effects of adding ezetimibe to atorvastatin or doubling the atorvastatin dose on low-density lipoprotein cholesterol (LDL-C) levels (and the cholesterol content of LDL subclasses), LDL particle number (approximated by apolipoprotein B), and LDL particle size. This was a multicenter, double-blind, randomized, parallel-group study of hypercholesterolemic, high atherosclerotic coronary heart disease risk patients. After stabilization of atorvastatin 40 mg, 579 patients with LDL-C >70 mg/dL were randomized to 6 weeks of ezetimibe + atorvastatin 40 mg or atorvastatin 80 mg. Efficacy parameters included changes from baseline in LDL-C, apolipoprotein B, non-high-density lipoprotein cholesterol (non-HDL-C), and lipoprotein subclasses (Vertical Auto Profile II) and pattern for the overall population, as well as patient subgroups with baseline triglyceride levels <150 mg/dL or ≥150 mg/dL.

RESULTS

Both treatments significantly reduced LDL-C (and the cholesterol content of most LDL subfractions [LDL1-4]) apolipoprotein B, non-HDL-C levels, but did not reduce the proportion of smaller, more dense LDL particles; in fact, the proportion of Pattern B was numerically increased. Results were generally similar in patients with triglyceride levels <150 or ≥150 mg/dL.

CONCLUSIONS

When assessing the effects of escalating cholesterol-lowering therapy, effects upon Pattern B alone to assess coronary heart disease risk may be misleading when interpreted without considerations of other lipid effects, such as reductions in LDL-C, atherogenic lipoprotein particle concentration, and non-HDL-C levels.

TRIAL REGISTRATION

(Registered at clinicaltrials.gov: Clinical trial # NCT00276484).

The effect of insulin resistance and obesity on low-density lipoprotein particle size in children

OBJECTIVE

In adults, it was shown that obesity and insulin resistance affect low-density lipoprotein (LDL) particle size and small dense (sd) LDL is associated with cardiovascular diseases. In this study, we investigated the effect of obesity and insulin resistance on LDL particle size.

METHODS

Twenty-six obese children (13 girls, 13 boys) with a median age of 10.5 years and 27 healthy control subjects (17 girls, 10 boys) with a median age of 11.5 were enrolled in the study.

RESULTS

The number of patients with insulin resistance in the obese group was 15 out of 26. In the control group, there was no subject with insulin resistance. Serum triglyceride and very LDL (VLDL) levels were higher and serum high-density lipoprotein levels (HDL) were lower in the obese patients than in the controls. There was no statistical difference in the LDL particle size between the two groups (medians: 26.6 vs. 26.7 nm (p=0.575)). The size of LDL particle was not correlated with body mass index (BMI) standard deviation score (SDS), homeostasis model assessment of insulin resistance (HOMA-IR), or serum lipids.

CONCLUSION

Measurement of LDL particle size as a routine procedure is not necessary in childhood obesity.

Small, dense low-density lipoproteins (LDL) are predictors of cardio- and cerebro-vascular events in subjects with the metabolic syndrome

OBJECTIVE

Small, dense low-density lipoproteins (LDL) are a feature of the metabolic syndrome (MS) but their predictive role still remains to be established. We performed a 2-year follow-up study in 124 subjects with MS (63 +/- 6 years), as defined by the American Heart Association/National Heart, Lung and Blood Institute guidelines, to assess clinical and biochemical predictors of cerebro- and cardio-vascular events.

METHODS AND RESULTS

Beyond traditional cardiovascular risk factors, we measured LDL size and subclasses by gradient gel electrophoresis. Clinical events were registered in the 25% of subjects. At univariate analysis subjects with events had increased prevalence of elevated fasting glucose (P = 0.0117), smoking (P = 0.0015), family history of coronary artery disease (P = 0.0033) and higher levels of total- and LDL-cholesterol (P = 0.0027 and P = 0.0023, respectively); LDL size was lower (P < 0.0001), due to reduced larger subclasses and increased small, dense LDL (all P < 0.0001). At multivariate analysis the following were independent predictors of events (univariate odd ratios were calculated): low HDL-cholesterol (OR 15.4, P = 0.0238), elevated fasting glucose (OR 12.1, P = 0.0102), elevated small, dense LDL (OR 11.7, P = 0.0004), elevated blood pressure (OR 9.2, P = 0.0392), smoking (OR 4.8, P = 0.0054).

CONCLUSIONS

This is the first study that assessed the predictive role of small, dense LDL beyond traditional cardiovascular risk factors in subjects with MS.

The therapeutic modulation of atherogenic dyslipidemia and inflammatory markers in the metabolic syndrome: what is the clinical relevance?

The metabolic syndrome consists of a constellation of clinical and biochemical risk factors that cluster together and heighten the risk for atherogenesis, cardiovascular diseases, and diabetes. Established risk cardiovascular factors like hypertension, atherogenic dyslipidaemia, and glucose intolerance occur in the setting of insulin resistance and central adiposity, with genetic and environmental influences modulating the ultimate risk. Chronic insults to the endothelium take its toll in the form of silent as well as clinically evident cardiovascular events. The cellular and vascular accompaniments have shed some light into the underlying pathophysiology. Heightened, low-grade inflammatory processes as well as a continuum of vascular insults ranging from early endothelial derangements to advanced atherosclerosis have been examined. In recent years there has been an explosion of basic and clinical knowledge related to the metabolic syndrome. Although dyslipidaemia is considered a traditional risk component for the syndrome, its qualitative aspects, genetically determined subfractions, and variation in proatherogenic tendency have generated renewed interest and debate. New targets within the dyslipidaemic spectrum that have differing clinical relevance are being evaluated. The effect of heredity, lifestyle changes, pharmacotherapeutic agents, and supplements is being investigated. Further research into the impact of dyslipidemia and inflammation as both pathophysiologic risk factors and objects for targeted therapy in the metabolic syndrome should deepen our understanding and unravel answers to the underlying dynamics in this global epidemic.

The effects of ezetimibe on LDL-cholesterol: quantitative or qualitative changes?

Ezetimibe represents the first of a new class of agents, the cholesterol absorption inhibitors, able to reduce low-density lipoproteins (LDL)-cholesterol by 15-25% from baseline in monotherapy and on top of statins and fibrates. To-date all the data regarding the efficacy of ezetimibe comes from the studies of its lipid-lowering power. Yet, recent findings from the ENHANCE study on atherosclerosis progression showed that the addition of ezetimibe to simvastatin in patients with heterozygous familial hypercholesterolemia did not affect the mean change in carotid intima-media thickness, although a significant reduction in LDL-cholesterol levels was present. Therefore, we cannot exclude that ezetimibe is treating mainly LDL-cholesterol and not the underlying dyslipidemia. Reviewing all available evidences on the effects on atherogenic small, dense LDL, it seems that ezetimibe produce quantitative rather than qualitative changes in LDL, with small net effects on LDL subclass distribution. Yet, we cannot exclude that clinical and laboratory factors influenced this result. We found important differences in the methodology used to measure LDL size and subfractions and this represents a crucial point, since these methods cannot be fully used interchangeably. In addition, it is reasonable to imagine that ezetimibe may be more effective on small, dense LDL in subjects with hypertriglyceridemia. Further formal cardiovascular event outcome trials are underway and this will provide additional insights into the long-term effects of ezetimibe. Future prospective studies are also needed to clarify to which extent ezetimibe is able to reduce atherogenic dyslipidemia, beyond LDL-cholesterol levels.

Update on the use of fibrates: focus on bezafibrate

Low-density lipoprotein-cholesterol (LDL-C) is a well established coronary heart disease (CHD) risk factor. However, the ability of this metabolic risk factor alone to identify individuals at rigk for future CHD events is limited. The raised triglycerides-low high-density lipoprotein-cholesterol (HDL-C) dyslipidaemia was shown to be an important cardiovascular risk factor independently of LDL-C levels. Fibric acid derivatives (fibrates) have been used in clinical practice for more than 2 decades as a class of agents known to decrease triglyceride levels while substantially increasing HDL-C levels. Through peroxisome proliferator-activated alpha-receptors, fibrates have a significant impact on the synthesis of several apolipoproteins and enzymes of lipoprotein metabolism as well as on the expression of several genes involved in fibrinolysis and inflammation. Data from recent primary and secondary prevention clinical trials demonstrate the efficacy of fibrate therapy in patients with the raised triglycerides-low HDL-C dyslipidaemia. This review summarizes current data regarding mechanism of action and the metbolic effects of fibrates, as well as results from major clinical trials on the efficacy of this mode of lipid lowering therapy. In addition, recent data from subgroup analyses of the Bezafibrate Infarction Prevention trial, demonstrating several important metabolic and long-term cardiovascular effects of bezafibrate therapy, are detailed.

Effects of fenofibrate and ezetimibe, both as monotherapy and in coadministration, on cholesterol mass within lipoprotein subfractions and low-density lipoprotein peak particle size in patients with mixed hyperlipidemia

Coadministration of fenofibrate and ezetimibe (FENO + EZE) produced complementary and favorable effects on the major lipids and lipoproteins, low-density lipoprotein cholesterol (LDL-C), triglycerides, high-density lipoprotein cholesterol (HDL-C), and non-HDL-C levels, and was well tolerated in patients with mixed hyperlipidemia. The current analysis evaluates the effects of FENO and EZE, as monotherapies and in coadministration, on lipoprotein subfractions and LDL particle size distributions in these patients. In a 12-week, multicenter, randomized, double-blind, placebo-controlled, parallel-group study, patients with mixed hyperlipidemia were randomized in a 1:3:3:3 ratio to one of 4 treatment groups: placebo, FENO 160 mg/day, EZE 10 mg/day, or FENO 160 mg/day + EZE 10 mg/day. At baseline and study end point, the Vertical Auto Profile II method was used to measure the cholesterol associated with 2 very low-density lipoprotein (VLDL) subfractions (VLDL-C1 + 2 and VLDL-C3), intermediate-density lipoproteins (IDL-C), and 4 LDL subfractions (LDL-C1 through LDL-C4, from most buoyant to most dense), lipoprotein (Lp) (a), and 2 HDL-C subfractions (HDL-C2 and HDL-C3). The LDL particle size was determined using segmented gradient gel electrophoresis. Fenofibrate reduced cholesterol mass within VLDL, IDL, and dense LDL (primarily LDL-C4) subfractions, and increased cholesterol mass within the more buoyant LDL-C2 subfraction, consistent with a shift to a more buoyant LDL peak particle size. Ezetimibe reduced cholesterol mass within all of the apolipoprotein B-containing particles (eg, VLDL-C, IDL-C, and LDL-C) but did not lead to a shift in the LDL particle size distribution profile. Coadministration of FENO and EZE promoted more pronounced reductions in VLDL-C, IDL-C, and LDL-C, and a preferential decrease in dense LDL subfractions. Fenofibrate and FENO + EZE promoted similar increases in HDL-C2 and HDL-C3. Coadministration of FENO + EZE produced complementary and favorable changes in lipoprotein fractions and subfractions, as assessed by the Vertical Auto Profile II method, in patients with mixed hyperlipidemia. These changes reflected the combined effects of FENO in reducing triglycerides-rich lipoproteins and promoting a shift in the LDL particle distribution profile toward larger, more buoyant particles and of EZE in promoting reductions in cholesterol mass across the apolipoprotein B particle spectrum.

Administration of ciprofibrate to lactating mothers induces PPARalpha-signaling pathway in the liver and kidney of suckling rats

It is well known that the hypolipidemic drug ciprofibrate induces peroxisome proliferation in rodent liver, which in turn leads to the oxidative stress, and modifies some parameters related to cell proliferation and apoptosis. The administration of ciprofibrate to rats during the lactating period determined in their pups significant modifications in hepatic peroxisome enzyme activities, induction of the PPARalpha-target gene, Cyp4a10, and perturbation in cell proliferation and apoptosis, which affected the size of the liver. Moreover, this modification was associated to about two-fold induction of mRNA-PPARalpha. On the contrary, in the kidney, although a similar two-fold up-regulation of PPARalpha was detected, the induction of both peroxisomal enzyme activities and Cyp4a10 were weak, and no alterations were detected, neither in cell cycle nor in the size of the tissue. Our results indicate that the response to ciprofibrate is stronger in the liver than in the kidney of newborn rats.

Who needs to care about small, dense low-density lipoproteins?

BACKGROUND

Increasing evidence suggest that the 'quality' rather than only the 'quantity' of low-density lipoprotein (LDL) exerts a great influence on the cardiovascular risk. Small, dense LDL seem to be an important predictor of cardiovascular events and progression of coronary artery disease (CAD) and their predominance has been accepted as an emerging cardiovascular risk factor by the National Cholesterol Education Program Adult Treatment Panel III.

DISCUSSION

Some studies showed in past years that small, dense LDL are usually elevated in patients at very high cardiovascular risk, such as those with CAD and type 2 diabetes. More recently elevated levels of these particles have been found in other categories of patients at high cardiovascular risk, such as those with non-coronary forms of atherosclerosis (e.g. with carotid artery disease, aortic abdominal aneurysm and peripheral arterial disease) and metabolic diseases (with polycystic ovary syndrome and growth hormone deficiency); notably, in most of them, the predominance of small, dense LDL characterised their type of dyslipidaemia, alone or in combination with elevated triglycerides and reduced high-density lipoproteins cholesterol concentrations.

CONCLUSIONS

The therapeutical modulation of small, dense LDL have been shown to significantly reduce cardiovascular risk and weight reduction and increased physical activity may constitute first-line therapy. In addition, lipid-lowering drugs are able to favourably alter these particles and fibrates and nicotinic acid seem to be the most effective agents. Promising data are also available with the use of rosuvastatin, the latest statin introduced in the market, and ezetimibe, a cholesterol absorption inhibitor.