Small, dense, low-density lipoprotein and atherosclerosis

Mechanisms and Treatment of Dyslipidemia in Diabetes

PURPOSE OF REVIEW

Type 2 diabetes mellitus is widespread throughout the world and is a powerful risk factor for the development of atherosclerotic cardiovascular disease (ASCVD). This manuscript explored the mechanisms underlying dyslipidemia in type 2 diabetes as well as currently available treatment options and guideline recommendations.

RECENT FINDINGS

Type 2 diabetes is associated with a characteristic pattern of dyslipidemia, often termed diabetic dyslipidemia. Patients with type 2 diabetes often present with low HDL levels, elevated levels of small dense LDL particles, and elevated triglyceride levels. LDL lowering is the cornerstone of managing diabetic dyslipidemia, and statins are the mainstay of therapy. The cholesterol absorption inhibitor ezetimibe and PCSK9 inhibitors have also been shown to lower risk in patients with diabetes. Recently, the eicosapentaenoic (EPA) only n-3 fatty acid, icosapent ethyl, has also shown benefit for cardiovascular risk reduction in patients with diabetes. To date, no agents targeting HDL increase have shown cardiovascular benefit in patients on background statin therapy. Diabetic dyslipidemia is significant cardiovascular disease risk factor, and LDL-lowering therapy with statins, PCSK9 inhibitors, and ezetimibe continues to be mainstay therapy to reduce cardiovascular risk. Future studies targeting low HDL and high triglycerides levels associated with type 2 diabetes could provide additional novel therapies to manage diabetic dyslipidemia.

Moderate to High Levels of Cardiorespiratory Fitness Attenuate the Effects of Triglyceride to High-Density Lipoprotein Cholesterol Ratio on Coronary Heart Disease Mortality in Men

OBJECTIVE

To examine the prospective relationships among cardiorespiratory fitness (CRF), fasting blood triglyceride to high density lipoprotein cholesterol ratio (TG:HDL-C), and coronary heart disease (CHD) mortality in men.

METHODS

A total of 40,269 men received a comprehensive baseline clinical examination between January 1, 1978, and December 31, 2010. Their CRF was determined from a maximal treadmill exercise test. Participants were divided into CRF categories of low, moderate, and high fit by age group and by TG:HDL-C quartiles. Hazard ratios for CHD mortality were computed using Cox regression analysis.

RESULTS

A total of 556 deaths due to CHD occurred during a mean ± SD of 16.6±9.7 years (669,678 man-years) of follow-up. A significant positive trend in adjusted CHD mortality was shown across decreasing CRF categories (P for trend<.01). Adjusted hazard ratios were significantly higher across increasing TG:HDL-C quartiles as well (P for trend<.01). When grouped by CRF category and TG:HDL-C quartile, there was a significant positive trend (P=.04) in CHD mortality across decreasing CRF categories in each TG:HDL-C quartile.

CONCLUSION

Both CRF and TG:HDL-C are significantly associated with CHD mortality in men. The risk of CHD mortality in each TG:HDL-C quartile was significantly attenuated in men with moderate to high CRF compared with men with low CRF. These results suggest that assessment of CRF and TG:HDL-C should be included for routine CHD mortality risk assessment and risk management.

Atherosclerosis in Type 2 Diabetes Mellitus: The Role of Insulin Resistance

Type 2 diabetes mellitus is associated with a marked increase in the risk of atherosclerotic diseases, including coronary heart disease, peripheral arterial disease, and cerebrovascular disease. Insulin resistance is a key factor in the pathogenesis of type 2 diabetes mellitus. Insulin resistance and its attendant metabolic abnormalities may cause much of the increased cardiovascular risk of type 2 diabetes mellitus. Among the abnormalities associated with insulin resistance are dyslipidemia, hypertension, systemic inflammation, and a prothrombotic state. This review discusses the role that each of these disorders plays in the cardiovascular risk of type 2 diabetes mellitus.

Treatment of dyslipidemia in patients with type 2 diabetes

Type 2 diabetes is associated with significant cardiovascular morbidity and mortality. Although low-density lipoprotein cholesterol levels may be normal in patients with type 2 diabetes, insulin resistance drives a number of changes in lipid metabolism and lipoprotein composition that render low-density lipoprotein cholesterol and other lipoproteins more pathogenic than species found in patients without type 2 diabetes. Dyslipidemia, which affects almost 50% of patients with type 2 diabetes, is a cardiovascular risk factor characterized by elevated triglyceride levels, low high-density lipoprotein cholesterol levels, and a preponderance of small, dense, low-density lipoprotein particles. Early, aggressive pharmacological management is advocated to reduce low-density lipoprotein cholesterol levels, regardless of baseline levels. A number of lipid-lowering agents, including statins, fibrates, niacin, and bile acid sequestrants, are available to target normalization of the entire lipid profile. Despite use of combination and high-dose lipid-lowering agents, many patients with type 2 diabetes do not achieve lipid targets. This review outlines the characteristics and prevalence of dyslipidemia in patients with type 2 diabetes and discusses strategies that may reduce the risk of cardiovascular disease in this population.

Is it LDL particle size or number that correlates with risk for cardiovascular disease?

The role of low-density lipoprotein cholesterol (LDL-C) in the pathogenesis of cardiovascular disease (CVD) and the clinical benefit of lowering LDL-C in high-risk patients is well established. What remains controversial is whether we are using the best measure(s) of LDL characteristics to identify all individuals who are at CVD risk or if they would benefit from specific therapies. Despite the successful LDL-C reduction trials, substantial numbers of patients continue to have clinical events in the treatment groups. The size of LDL particles and assessment of the number of LDL particles (LDL-Num) have been suggested as a more reliable method of atherogenicity. Each LDL particle has one apoprotein B-100 measure attached; therefore, determination of whole plasma apoprotein B can be considered the best measure of LDL-Num. Because the cholesterol content per LDL particle exhibits large interindividual variation, the information provided by LDL-C and LDL-Num is not equivalent. Individuals with the same level of LDL-C may have higher or lower numbers of LDL particles and, as a result, may differ in terms of absolute CVD risk. LDL particle size and number provide independent measures of atherogenicity and are strong predictors of CVD.

Diabetic dyslipidemia and atherosclerosis: evidence from clinical trials

Diabetes is a highly prevalent disease in the United States and is increasing in both incidence and prevalence. Atherosclerotic vascular disease is a major cause of morbidity and mortality in diabetic patients. Type 2 diabetes is characterized by insulin resistance and frequently co-exists with a variety of cardiovascular risk factors, including hypertension, obesity, dyslipidemia, and physical inactivity. Hygienic measures such as weight loss and exercise should form the basis of therapeutic interventions in the prevention and treatment of type 2 diabetes. The role of dyslipidemia as a causal factor in vascular disease associated with diabetes was previously downplayed because total cholesterol was frequently normal or minimally elevated. However, diabetic dyslipidemia is characterized by elevated triglycerides, low high-density lipoprotein, and small, dense low-density lipoprotein, the combination of which has been termed the "lipid triad." The role of lipid modification as a means to decrease cardiovascular risk in type 2 diabetes has recently been clarified by a number of clinical trials. Subgroup analysis in early studies implied the potential for benefit of lipid modification in diabetes. The results of these early studies prompted the design of large-scale intervention trials that employed statin and fibric acid derivatives in diabetes patients. The preponderance of data from the statin trials implicates significant clinical benefit in cardiovascular risk reduction. The fibric acid derivatives have theoretic advantages in diabetic dyslipidemia. However, the robust bulk of clinical data obtained from prospective statin studies is lacking for the fibric acid derivatives, and the results of the major trials are equivocal.

Diabetic dyslipidemia and atherosclerosis: Evidence from clinical trials

Diabetes is a highly prevalent disease in the United States and is increasing in both incidence and prevalence. Atherosclerotic vascular disease is a major cause of morbidity and mortality in diabetic patients. Type 2 diabetes is characterized by insulin resistance and frequently co-exists with a variety of cardiovascular risk factors, including hypertension, obesity, dyslipidemia, and physical inactivity. Hygienic measures such as weight loss and exercise should form the basis of therapeutic interventions in the prevention and treatment of type 2 diabetes. The role of dyslipidemia as a causal factor in vascular disease associated with diabetes was previously downplayed because total cholesterol was frequently normal or minimally elevated. However, diabetic dyslipidemia is characterized by elevated triglycerides, low high-density lipoprotein, and small, dense low-density lipoprotein, the combination of which has been termed the "lipid triad." The role of lipid modification as a means to decrease cardiovascular risk in type 2 diabetes has recently been clarified by a number of clinical trials. Subgroup analysis in early studies implied the potential for benefit of lipid modification in diabetes. The results of these early studies prompted the design of large-scale intervention trials in diabetes patients that employed statin and fibric acid derivatives. The preponderance of data from the statin trials implicates significant clinical benefit in cardiovascular risk reduction. The fibric acid derivatives have theoretic advantages in diabetic dyslipidemia. However, the robust bulk of clinical data obtained from prospective statin studies is lacking for the fibric acid derivatives, and the results of the major trials are equivocal.

Muraglitazar, a dual (α/γ) PPAR activator: A randomized, double-blind, placebo-controlled, 24-week monotherapy trial in adult patients with type 2 diabetes

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) present a therapeutic target, and simultaneous activation of PPAR-alpha and PPAR-gamma may provide improvements in glycemic control and dyslipidemia in patients with type 2 diabetes.

OBJECTIVE

The goal of this study was to evaluate the efficacy and safety of muraglitazar, a dual (alpha/gamma) PPAR activator, in adult patients with type 2 diabetes whose disease was inadequately controlled by diet and exercise.

METHODS

This was a randomized, double-blind, placebo-controlled, parallel-group, multicenter, 24-week monotherapy study in drug-naive, type 2 diabetes patients with inadequate glycemic control. Men and women aged 18 to 70 years with a body mass index < or =41 kg/m(2) and serum triglyceride levels < or =600 mg/dL were eligible for study participation. The study included double-blind and open-label treatment phases. Patients with glycosylated hemoglobin (HbA(1c)) levels > or =7.0% and < or =10.0% at screening were enrolled in the double-blind treatment phase. These patients received treatment with muraglitazar 2.5 mg, muraglitazar 5 mg, or placebo. Patients with HbA(1c) levels >10.0% and < or =12.0% who met all other study criteria were eligible for enrollment in a 24-week, open-label evaluation of muraglitazar 5 mg. The primary end point was the mean change from baseline in HbA(1c) levels after 24 weeks of treatment.

RESULTS

A total of 340 patients (179 men, 161 women) participated in the double-blind treatment phase of the study. Patients had mean baseline HbA(1c) levels of 7.9% to 8.0%. Monotherapy with muraglitazar 2.5 and 5 mg significantly reduced HbA(1c) levels (-1.05% and -1.23%, respectively) compared with placebo (-0.32%; P < 0.001). At week 24, 58%, 72%, and 30% of the patients receiving muraglitazar 2.5 mg, muraglitazar 5 mg, and placebo, respectively, achieved the American Diabetes Association-recommended HbA(1c) goal of <7.0%. Fasting plasma glucose, free fatty acids, and fasting plasma insulin levels significantly decreased during muraglitazar treatment (P < 0.001), suggesting an increase in insulin sensitivity. Muraglitazar 2.5 and 5 mg provided improvements from baseline in triglyceride (-18% and -27%), high-density lipoprotein (HDL) cholesterol (10% and 16%), apolipoprotein B (-7% and -12%), and non-HDL cholesterol levels (-3% and -5%) (P < 0.05 vs placebo for each). In a parallel, open-label cohort of 109 drug-naive patients (56 men, 53 women; mean baseline HbA(1c) level, 10.6%), muraglitazar 5 mg decreased the overall mean HbA(1c) level from baseline by 2.62% (last observation carried forward) and by 3.49% in the 62 patients completing 24 weeks of study. Changes in lipid parameters during open-label treatment were similar to those observed during double-blind treatment. Muraglitazar was generally well tolerated. Edema-related adverse events of mild to moderate severity occurred in 8% to 11% of patients in all groups. Mean changes from baseline weight in the double-blind treatment groups were 1.1 kg for muraglitazar 2.5 mg, 2.1 kg for muraglitazar 5 mg, and -0.8 kg for placebo (P < 0.001); there was a mean 2.9-kg increase in the open-label muraglitazar 5-mg group.

CONCLUSION

In this study, 24 weeks of treatment with muraglitazar 2.5 or 5 mg was an effective treatment option for these patients with type 2 diabetes whose disease was inadequately controlled with diet and exercise.

Conditional risk factors for atherosclerosis

Although most patients who experience a coronary heart disease (CHD) event have one or more of the conventional risk factors for atherosclerosis, so do many people who have not yet experienced such an event. Therefore, predictive models based on conventional risk factors have a lower than desired accuracy, providing a stimulus to search for new tools to refine CHD risk prediction. In particular, there is intense interest in evaluating circulating biomarkers related to the atherosclerotic process that might add to our ability to better predict CHD risk. One such group of biomarkers was termed conditional risk factors in an American Heart Association/American College of Cardiology statement in 1999. The conditional risk factors include homocysteine, fibrinogen, lipoprotein(a), low-density lipoprotein particle size, and C-reactive protein. This review updates the conditional risk factors. The main focus is on the potential utility of these risk factors, which are currently available to clinicians, in the prediction of CHD risk in asymptomatic persons. The putative mechanisms of risk, available assays, evidence for association with CHD, and the clinical implications thereof are discussed for each of the risk factors.

High circulating levels of 7beta- and 7alpha-hydroxycholesterol and presence of apoptotic and oxidative markers in arterial lesions of normocholesterolemic atherosclerotic patients undergoing endarterectomy

In previous investigations, we found that 7beta-hydroxycholesterol had potent pro-apoptotic, and pro-oxidative properties. So, we asked whether the circulating level of this oxysterol was enhanced in atherosclerotic patients undergoing endarterectomy of the superficial femoral artery. To this end, 7beta-hydroxycholesterol serum concentrations were determined and compared with common lipid parameters in atherosclerotic patients, and in healthy subjects. 7alpha-hydroxycholesterol was simultaneously measured to evaluate the reliability of the method used for oxysterol analysis. On normal and atherosclerotic arterial fragments from patients, markers of oxidation (4-hydroxynonenal (4-HNE) adducts), and apoptosis (activated caspase-3; condensed/fragmented nuclei) were studied. Interestingly, high serum concentrations of 7beta- and 7alpha-hydroxycholesterol were found in normocholesterolemic atherosclerotic patients. However, in statin-treated patients, the circulating levels of 7beta- and 7alpha-hydroxycholesterol tend towards normal values. Therefore, 7beta- as well as 7alpha-hydroxycholesterol could be more appropriate markers of lipid metabolism disorders than cholesterol or LDL in normocholesterolemic patients with atherosclerosis of the lower limbs, and statins could normalize their serum concentrations. At the arterial level, apoptotic cells were mainly identified in low grade lesions and no statin effects were found on oxidation and apoptosis.

Small LDL and its clinical importance as a new CAD risk factor: a female case study

The underlying metabolic cause of coronary heart disease in many patients is not high blood cholesterol. In fact, the Framingham study has reported that 80% of individuals who go on to have coronary artery disease have the same total blood cholesterol values as those who do not go on to have a cardiovascular event. The most common metabolic contributor to coronary artery disease is the atherogenic lipoprotein profile, characterized by an abundance of highly atherogenic small, dense low-density lipoprotein particles and a deficiency of the high-density lipoprotein (HDL) subtype most associated with coronary artery disease protection (HDL(2b)). This trait is present in 50% of men with coronary artery disease and is not reflected by total or low-density lipoprotein cholesterol values. While fasting triglycerides tend to he higher, and HDL cholesterol lower in patients with the atherogenic lipoprotein profile, the majority have triglyceride and HDL cholesterol values generally accepted to be in the "normal" range. An abundance of basic science and clinical trial evidence convincingly indicates that the presence of an atherogenic lipoprotein profile signifies a three-fold increased risk for a cardiovascular event and rapid arteriographic progression, but it also identifies a group of patients who respond particularly well to specific therapeutic interventions. Often the most effective interventions are the least expensive.

Cholesterol and triglyceride concentration as risk factors for myocardial infarction and death in women, with special reference to influence of age

OBJECTIVE

To evaluate the importance of serum cholesterol and triglyceride concentrations as predictors of myocardial infarction and death in women of different ages.

DESIGN

Prospective observational study, initiated in 1968-69. Setting. Gothenburg, Sweden, with about 430 000 inhabitants.

SUBJECTS

A population-based sample of 1462 women aged 38, 46, 50, 54 and 60 years at start of the study, followed up for 24 years. Main outcome measures. Within each age group, myocardial infarction and death were predicted by serum cholesterol and triglyceride concentrations and smoking in a multivariate model.

RESULTS

In the total population only serum triglyceride concentration was a strong independent risk factor for both end-points studied. Serum triglyceride concentration measured in 38- and 46-year-old women had no predictive value with respect to 24-year incidence of myocardial infarction or death. In 50-, 54- and 60-year-old women, high serum triglyceride concentration consistently predicted myocardial infarction and total mortality. Serum cholesterol concentration, on the other hand, showed evidence of direct association for 24-year all-cause mortality in the younger premenopausal group. Serum cholesterol had no predictive value for myocardial infarction or mortality in the peri- and postmenopausal ages.

CONCLUSIONS

There appears to be age-specificity in association between serum lipids and these end-points in women, serum cholesterol concentration being more important for younger women and serum triglyceride concentration more important for postmenopausal women as risk factors, observations which need further attention.

Current practice in the treatment of hyperlipidaemias

Primary and secondary prevention trials for coronary heart disease (CHD) in hyperlipidaemic or so-called 'normolipidaemic' patients with drugs affecting lipid metabolism have clearly confirmed that even slight alterations in lipoprotein metabolism are major risk factors for CHD. The global cardiovascular risk must be determined before deciding to treat patients with drugs affecting lipid metabolism. Screening for dyslipidaemia consists of determining cholesterol (C), LDL-cholesterol (LDL-C), HDL-cholesterol (HDL-C) and triglyceride (TG) plasma levels and the decision to treat depends mainly on LDL-C plasma levels. Furthermore, secondary dyslipidaemia must be diagnosed and primary disease must be adequately treated. There are four classes of available lipid-regulating drugs: HMG-CoA reductase inhibitors (statins), bile acid sequestrants (resins), peroxisome proliferator-activated receptor-alpha (PPAR- alpha) activators (fibrates) and nicotinic acid. All four will be discussed in this review. Clinical trials have shown that drugs improving lipid metabolism reduce CHD relative risk from 24% (secondary prevention) to 37% (primary prevention) and the absolute risk from 2% (primary prevention) to 8.5% (secondary prevention). These studies indicate that the number of patients needed to be treated to economise one clinical event ranges from 12 (secondary prevention) to 50 (primary prevention). Clinical trials are currently testing the hypothesis that 'lower LDL-C is better'.