Low-density-lipoprotein peak particle size in a Mediterranean population

Toward reliable low-density lipoprotein ultrastructure prediction in clinical conditions: A small-angle X-ray scattering study on individuals with normal and high triglyceride serum levels

Atherosclerosis is the main killer in the west and therefore a major health challenge today. Total serum cholesterol and lipoprotein concentrations, used as clinical markers, fail to predict the majority of cases, especially between the risk scale extremes, due to the high complexity in lipoprotein structure and composition. In particular, low-density lipoprotein (LDL) plays a key role in atherosclerosis development, with LDL size being a parameter considered for determining the risk for cardiovascular diseases. Determining LDL size and structural parameters is challenging to address experimentally under physiological-like conditions. This article describes the biochemistry and ultrastructure of normolipidemic and hypertriglyceridemic LDL fractions and subfractions using small-angle X-ray scattering. Our results conclude that LDL particles of hypertriglyceridemic compared to healthy individuals 1) have lower LDL core melting temperature, 2) have lower cholesteryl ester ordering in their core, 3) are smaller, rounder and more spherical below melting temperature, and 4) their protein-containing shell is thinner above melting temperature.

PCSK9 positively correlates with plasma sdLDL in community-dwelling population but not in diabetic participants after confounder adjustment

This study aimed to investigate the relationship between plasma proprotein convertase subtilisin kexin 9 (PCSK9) and small dense low-density lipoprptein (sdLDL) in diabetic and non-diabetic participants in a community-dwelling cohort.The plasma levels of PCSK9 and sdLDL were detected in 1766 participants (median age: 61.40 years; 733 males vs 1033 females; 383 diabetic vs 1383 non-diabetic patients) from the Pingguoyuan community of Beijing, China.Results showed that Pearson correlation analysis revealed a positive correlation between PCSK9 and sdLDL (r = 0.263, P < .001). Multiple linear regression analysis showed a significant positive correlation between plasma PCSK9 and sdLDL in the whole population study. sdLDL was used as the dependent variable, and the potential cofounders were adjusted. However, any independent relationship was not observed between circulating PCSK9 and sdLDL in the diabetic subpopulation (r = 0.269, P < .05, β = 9.591, P > .05).Thus, there is a positive correlation between plasma PCSK9 and sdLDL in a community-dwelling cohort, but not in type 2 diabetic subpopulation, after confounder adjustment.

Clinical Characteristics and Outcomes in Young Patients With ST-Segment Elevation Myocardial Infarction After Primary Percutaneous Coronary Intervention

BACKGROUND

There are few published studies of ST-segment elevation myocardial infarction (STEMI) in younger individuals. The differences between these "younger" and "older" individuals may not be fully appreciated by clinicians. The aim of this study was to determine the reasons for the earlier presentation and help to identify strategies for prevention of recurrent myocardial infarction (MI) in younger patients.

METHODS

The study population was a cohort of 2,419 consecutive STEMI patients who were treated with primary percutaneous coronary intervention. The median follow-up time of this retrospective study was 2.2 years.

RESULTS

The all-cause mortality rates in patients ≤45 years of age at 30 days, 1 and 2 years were 1.7%, 2.0% and 2.2%, respectively. These rates were lower compared with their older matched counterparts whose all-cause mortality rates were 3.3%, 4.2% and 5.5%, respectively (P = 0.010). The incidence of recurrent MI was 4.0% for all age groups combined, 5.4% for younger patients and 3.8% for older patients. The number of stents showed association with recurrent MI in older patients with a first infarction, whereas only composition factor 1 with significantly higher non-high-density lipoprotein and low-density lipoprotein values was significantly associated with recurrent MI in the younger patients.

CONCLUSIONS

STEMI patients ≤45 years of age more often had lower rates of all-cause mortality, but the risk of recurrent MI was similar to that of older patients. Regardless of triglyceride level, neither non-high-density lipoprotein nor low-density lipoprotein were independent predictors for recurrent MI during the long-term follow-up in younger patients.

Elevation of small, dense low density lipoprotein cholesterol-a possible antecedent of atherogenic lipoprotein phenotype in type 2 diabetes patients in Jos, North-Central Nigeria

BACKGROUND

The global prevalence of type 2 diabetes is increasing. Dyslipidaemia is a known complication of diabetes mellitus manifesting frequently as cardiovascular diseases and stoke. Elevation of small, dense low density lipoprotein has been recognised as a component of the atherogenic lipoprotein phenotype associated with cardiovascular complications. We speculate that the elevation of this lipoprotein particle may be the antecedent of the atherogenic lipoprotein phenotype. This study therefore aims to determine the pattern of dyslipidaemia among diabetes mellitus patients in Jos, North-Central Nigeria.

METHODS

One hundred and seventy-six patients with type 2 diabetes and 154 age-matched controls were studied. The patients with diabetes were regular clinic attenders and had stable glycaemic control. None were on lipid-lowering therapy. Anthropometric indices, blood pressure, and lipids (including total cholesterol, high density lipoprotein cholesterol, and triglyceride) were measured by chemical methods using the Hitachi 902 analyzer. Low density lipoprotein cholesterol was calculated using the Friedewald's equation. Small, dense low density lipoprotein cholesterol, -sdLDL-C was measured using the precipitation method by Hirano et al. Means of the different groups were compared using EPI Info and a P-value of <0.05 was accepted as significant difference.

RESULTS

Total cholesterol, low density lipoprotein cholesterol, triglyceride and small, dense lipoprotein cholesterol were all significantly higher in diabetes patients than controls except high density lipoprotein cholesterol. The percentage of LDL-C as sdLDL-C among the diabetes versus control group was 45% ± 17.79 v 32.0% ± 15.93. Serum sdLDL-C concentration was determined to be 1.45 ± 0.64 among diabetes patients and 0.8 ± 0.54 among control subjects. 75% of diabetes patients had hypertension and were taking blood pressure lowering medications.

CONCLUSION

The classical atherogenic lipoprotein phenotype was not demonstrated among subjects with type 2 diabetes mellitus in this study, but the elevation of serum small dense low density lipoprotein cholesterol in patients with sustained hypertension suggests the establishment of atherogenic complications among our diabetes patients.

Usefulness of the LDL-C/apoB ratio in the overall evaluation of atherogenicity of lipid profile

CONTEXT

The ratio of low-density lipoprotein cholesterol to apolipoprotein-B (LDL-C/apoB) conventionally represents an alternative index of LDL particle size.

OBJECTIVE

This study was undertaken to determine the importance of LDL-C/apoB ratio in the overall evaluation of atherogenicity of lipid profile.

METHODS

The plasma levels of total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), apolipoprotein (apo) A-I, apoB and apoE were measured in 186 apparently healthy men using enzymatic and immunoturbidimetric methods.

RESULTS

The subjects with low values of the LDL-C/apoB ratio, indicating a predominance of small dense LDL (sd-LDL) particles in plasma, were characterized by higher TG levels and lower apoE levels.

CONCLUSION

Low levels of apoE are most likely a cause of reduced clearance of TG-rich lipoproteins, which promotes the formation of sd-LDL. Determination of the LDL-C/apoB ratio can be used for monitoring qualitative changes in lipid profile, in addition to traditional lipid variables indicating quantitative changes.

Relative importance of different lipid risk factors for the development of myocardial infarction at a very young age (≤ 40 years of age)

BACKGROUND

Low-density lipoprotein (LDL) cholesterol lowering has been established as one of the principal targets in preventive cardiology. Recently, assessment of LDL particle size and number as well as other lipid moieties has been presented as a more reliable method to quantify atherogenicity of the lipoprotein fractions. Thus, it was our aim to assess the influence of different lipoprotein fractions on premature myocardial infarction (≤ 40 years of age).

METHODS AND RESULTS

We enrolled 302 patients into our multicentre case-control study, including 102 patients with myocardial infarction and 200 age-, gender- and centre-matched controls. The LDL and HDL Lipoprint System were used for lipid subfraction quantification. The lipid risk factors most strongly associated with premature acute myocardial infarction (AMI) in the adjusted model were non-HDL C (OR 5·02, 95% CI 2·75-9·15, P-value = 0·001), LDL-C (OR 4·35, 95% CI 2·5-7·57, P-value = 0·001), VLDL-C (OR 3·66, 95% CI 2·14-6·28, P-value = 0·001), large IDL-C (OR 3·15, 95% CI 1·94-5·12, P-value = 0·001), large LDL-C (OR 3·67, 95% CI 2·19-6·15, P-value = 0·001) and intermediate LDL-C (OR 1·96, 95% CI 1·25-3·06, P-value = 0·003). In contrast, small dense LDL was not significantly associated with premature myocardial infarction.

CONCLUSION

Non-HDL cholesterol is most strongly associated with premature coronary artery disease and could serve as preferred risk predictor and therapeutic target in this young patient population (≤ 40 years). Besides, VLDL, LDL-C, large LDL, intermediate LDL and large IDL were significantly associated with premature myocardial infarction. Furthermore, our data suggest that risk prediction using small dense LDL particles might not be useful in young AMI survivors.

Scanning electron microscopy of the human low-density lipoprotein interaction with the tegument of Schistosoma mansoni

The interaction between host molecules and Schistosoma mansoni has been regarded as a key feature for parasite survival. In this work, scanning electron microscopy was used to study the interaction of human low-density lipoprotein (LDL) with the tegument of the adult worm of S. mansoni. Worms were incubated in RPMI 1640 containing 10% of LPDS and 40 μg LDL/mL during 30, 60, and 120 min. Control worms were processed in the same way, without LDL. After the incubations, the samples were fixed and processed to scanning electron microscopy. The results demonstrated interaction of the LDL particles with the male parasite tegument. Male and female worms incubated without LDL from 0 (control) to 120 min did not show alterations in the tegument. It was observed a larger number of LDL particles on the dorsal region of male adult worm than others regions (anterior, posterior and gynecophoral canal). The female tegument did not show adherence of LDL. Aggregates on the tegument of the male worm were in greater number and size in the incubation times of 30 and 60 min than 120 min. The comparison between 30 and 120 min of incubation showed that the particles' size diminished from 2,650-860 nm to 634-363 nm, respectively. Such reduction can be due to the capture and the use of the lipids by the worm. Therefore, the internalization of lipids from LDL by the male worms seems to be a mechanism independent of endocytosis. Differences between males and females suggest lipid transference from male to female through gynecophoral canal.

Assessment of the validity of the frequently used lipid indices for predicting LDL peak particle diameter in a large cohort of 1955 normal and dyslipidemic subjects

OBJECTIVES

To assess the relationship between commonly used lipid indices and LDL peak particle diameter (LDL-PPD) in a large cohort of 1955 subjects.

DESIGN AND METHODS

Four statistical methods were used for comparison: correlation, concordance analysis, kappa statistics and receiver operating characteristic curve (ROC) analysis.

RESULTS

Plasma triglyceride (TG) levels, TG/HDL-C, LDL-C/apoB, total cholesterol (TC)/TG, LDL-C/TG, and TG/apoB ratios were best correlated with LDL-PPD but none of these ratios accounted for more than 45% of the variation in LDL-PPD. Moreover, across the range of the lipid indices and LDL-PPD quintiles, just under 40% of the values were concordant, with kappas varying between 0.20 and 0.25. Finally, plasma TG levels and the lipid ratios yielded areas under the ROC curve between 0.78 and 0.80.

CONCLUSIONS

The present study does not support the concept that plasma TG levels and the commonly used lipid indices may be considered as adequate surrogates for the small dense LDL phenotype. Our data also indicate that various lipid indices are not superior to plasma TG levels alone as a clinical tool for prediction of the small dense LDL phenotype.

Low HDL cholesterol, smoking and IL-13 R130Q polymorphism are associated with myocardial infarction in Greek Cypriot males. A pilot study

This study was carried out in Greek Cypriot males to identify risk factors that predispose to myocardial infarction (MI). Genetic and lipid risk factors were investigated for the first time in a Greek Cypriot male case-control study.Contrary to other studies, mean low density lipoprotein cholesterol did not differ between cases and controls. High density lipoprotein cholesterol on the other hand, although within normal range in cases and controls, was significantly higher in the control population. In agreement with many other studies, smoking was significantly more prevalent in cases compared with controls. In pooled cases and controls, smokers had a significantly lower HDL-C level compared with non-smokers. The frequency of the IL-13 R130Q homozygotes for the mutation (QQ), as well as the mutant allele were significantly higher in cases compared with controls. The IL-13 R130Q variant, or another locus, linked to it, may increase the risk of MI.

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.

Factors influencing the formation of small dense low-density lipoprotein particles in dependence on the presence of the metabolic syndrome and on the degree of glucose intolerance

BACKGROUND

Small dense low-density lipoprotein (LDL) particles are known to be especially atherogenic. Several mechanisms are involved in this atherogenicity.

AIMS

We wanted to look for the presence of small dense LDL particles depending on gender, metabolic syndrome (MS) and different degrees of glucose intolerance. Moreover, we looked for anthropometric factors and factors of lipid and carbohydrate metabolism that are associated with changes in the LDL size.

RESULTS

We studied 752 persons (330 males, 422 females; age 40 +/- 17 years). LDL particle size was estimated with polyacrylamide gel electrophoresis. Males had smaller LDL particles than females. Probands with the MS had smaller LDL particles than those without this syndrome. With rising plasma triglyceride (TG) levels more small dense LDL particles were seen. The highest proportion of these small dense LDL particles was observed in the subgroup of type 2 diabetic patients. In the whole material, the mean LDL diameter was correlated negatively with plasma TG and very low-density lipoprotein components (TG, cholesterol and proteins) and positively with high-density lipoprotein cholesterol. In a linear stepwise regression analysis different significant factors influencing the LDL size were found in the whole population, in normoglycaemic probands, in persons with impaired glucose tolerance, in type 2 diabetic patients and in type 2 diabetic patients injecting insulin.

CONCLUSIONS

Our data point to different mechanisms of the formation of small dense LDL particles in dependence on the degree of glucose intolerance. Moreover, the target values for plasma TG should be set lower.

Fructose intake is a predictor of LDL particle size in overweight schoolchildren

BACKGROUND

High amounts of dietary fructose may contribute to dyslipidemia in adults, but there are few data in children. Childhood adiposity is associated with smaller LDL particle size, but the dietary predictors of LDL size in overweight children have not been studied.

OBJECTIVES

We aimed to determine whether LDL particle size is associated with dietary factors and specifically with fructose intake in normal-weight and overweight children.

DESIGN

In a cross-sectional study of normal-weight and overweight 6-14 y-old Swiss children (n = 74), dietary intakes were assessed by using two 24-h-recalls and a 1-d dietary record. Body mass index (BMI) and waist-hip ratio (WHR) were measured, and plasma lipid profile and LDL particle size were determined.

RESULTS

Compared with the normal-weight group, overweight children had significantly higher plasma triacylglycerol concentrations, lower HDL-cholesterol concentrations, and smaller LDL particle size (P < 0.05). LDL particle size was inversely correlated to BMI SD scores and WHR (P = 0.007). Although there were no significant differences in total fructose intake, the overweight children consumed a significantly (P < 0.05) higher percentage of fructose from sweets and sweetened drinks than did the normal-weight children. After control for adiposity, the only dietary factor that was a significant predictor of LDL particle size was total fructose intake (P = 0.024).

CONCLUSIONS

In school-age children, greater total and central adiposity are associated with smaller LDL particle size and lower HDL cholesterol. Overweight children consume more fructose from sweets and sweetened drinks than do normal-weight children, and higher fructose intake predicts smaller LDL particle size.

Atherogenic lipoprotein phenotype and LDL size and subclasses in patients with peripheral arterial disease

The type of dyslipidemia in patients with peripheral arterial disease (PAD) is still ill defined. PAD patients often show elevated triglycerides and reduced HDL-cholesterol, two lipid abnormalities usually accompanied by decreased LDL size in the "atherogenic lipoprotein phenotype" (ALP). We investigated (1) whether PAD patients have lower LDL size, (2) altered LDL subclass distribution and (3) the prevalence of ALP. We measured plasma lipids and LDL size and subclasses by gradient gel electrophoresis in 31 adults with intermittent claudication and 31 age-BMI-matched controls. Patients had higher prevalence of hypertension (p=.0132), smoking (p<.0020) and diabetes (p=.0024), with lower HDL-cholesterol (p<.0001) and increased triglycerides (p=.0057); LDL size was smaller (p<.0001), with decreased larger subclasses (LDL-I, p<.0001; LDL-IIA, p=.0068) and increased smaller particles (LDL-IIIA, p<.0001; LDL-IIIB, p=.0013; LDL-IVA, p=.0029; LDL-IVB, p<.0001). The presence of PAD was independently associated with smoking (OR 7.2, p=.0099), hypertension (OR 6.5, p=.0362), diabetes (OR 5.5, p=.0450) and elevated small, dense LDL (OR 6.7, p=.0497). The concomitant presence of high triglycerides, low HDL-cholesterol and elevated small, dense LDL in patients was 26% (versus 0% controls, p=.0024). ALP seems to characterize PAD dyslipidemia, but prospective studies are needed to test whether this lipoprotein phenotype may represent a risk factor too.

LDL and HDL subclasses and their relationship with Framingham risk score in middle-aged Serbian population

OBJECTIVES

Small, dense LDL particles are associated with an increased risk of coronary heart disease (CHD), and there is growing evidence that small HDL subclasses are less protective than the larger ones. Very limited information is available about the lipoprotein subclasses among populations living in South-East European region, and none for Serbia.

DESIGN AND METHODS

We analyzed the distributions of LDL and HDL subclasses and their relationships with Framingham risk scores (FRS) in 229 Serbian middle-aged asymptomatic individuals. By use of non-denaturing gradient gel electrophoresis, we determined the diameters of LDL and HDL subfractions in a single run.

RESULTS

Comparing to women, men had smaller LDL and HDL particles (P<0.001, and P<0.05, respectively), higher frequency of LDL B phenotype (P<0.005), and significant reduction of HDL2b in favor of HDL2a subclasses (P<0.05). The observed gender-related differences disappeared after the age of 60. We found a significant association of the small LDL particles with high FRS values (P<0.005). A notable incidence of risk lipoprotein phenotypes (LDL B-9.2%; small-sized HDL-9.9%) was found among subjects that were categorized as "low-risk", requiring no further intervention, according to FRS.

CONCLUSION

Measurement of LDL, and possibly HDL particle size could provide further insight into individual CHD risk, and enable them to benefit from targeted preventive measures.

Atherogenic lipoprotein phenotype and low-density lipoproteins size and subclasses in women with polycystic ovary syndrome

CONTEXT

An altered lipid profile is common in polycystic ovary syndrome (PCOS) and is usually characterized by increased triglycerides and low high-density lipoprotein (HDL)-cholesterol levels. In the general population, these alterations are often associated with the increase of small low-density lipoproteins (LDLs) in the so-called "atherogenic lipoprotein phenotype" (ALP) that determines a further increase of cardiovascular risk. In this study, we evaluated the presence of ALP in the plasma of women with PCOS.

SETTING

Measurements and analysis of LDL size were performed at the Clinic of Endocrinology, Diabetes, and Clinical Nutrition, University Hospital, Zurich. PCOS patients were recruited at the Department of Clinical Medicine, University of Palermo, and the Department of Obstetrics and Gynecology, University of Pisa.

PATIENTS

Thirty patients with PCOS (hyperandrogenism and chronic anovulation) and 24 matched controls were studied. Anthropometric data, blood glucose, serum insulin lipid profile, and LDL size and subclasses were evaluated.

RESULTS

Compared with controls, patients with PCOS had higher plasma concentrations of insulin and triglycerides and lower HDL-cholesterol concentrations but no differences in LDL-cholesterol and total cholesterol. Patients with PCOS had smaller LDL size due to a reduction in LDL subclass I, with a concomitant increase in LDL subclasses III and IV. Fourteen PCOS patients had an increase of smaller LDL particles, and it represented the second most common lipid alteration after decrease in HDL-cholesterol. However, because in this PCOS population hypertriglyceridemia was only present in two patients, complete ALP was relatively uncommon.

CONCLUSIONS

Increase of type III or type IV LDL subclasses is a common finding in PCOS and represents the second most common lipid alteration after HDL-cholesterol decrease. However, in our PCOS patients, because of relatively low triglyceride levels, complete ALP is uncommon.

Small, dense low-density-lipoproteins and the metabolic syndrome

Small, dense low-density-lipoproteins (LDL) are associated with increased risk for cardiovascular diseases and diabetes mellitus and a reduction in LDL size has been reported in patients with coronary and non-coronary forms of atherosclerosis. LDL size has been accepted as an important predictor of cardiovascular events and progression of coronary artery disease as well as an emerging cardiovascular risk factor by the National Cholesterol Education Program Adult Treatment Panel III. Small, dense LDL, with elevated triglyceride levels and low HDL-cholesterol concentrations, constitute the 'atherogenic lipoprotein phenotype (ALP)', a form of atherogenic dyslipidemia that is a feature of type 2 diabetes and the metabolic syndrome. LDL size and subclasses show specific alterations in patients with the metabolic syndrome that probably significantly increase their cardiovascular risk; however, so far it has not been recommended to incorporate LDL size measurements in treatment plans, when hypolipidemic therapies are installed. Patients with type 2 diabetes are at high cardiovascular risk and it is still on debate if the treatment goals may be identical or whether there are distinct groups with different cardiovascular risks and hence with different treatment goals. Measurements beyond traditional lipids, such as measurements on the presence of small, dense LDL in patients with the metabolic syndrome, may help to identify cardiovascular risk subgroups. In addition, it might be possible in the future to individualize hypolipidemic treatments if more than the traditional lipids are taken into account. LDL size measurement may potentially help to assess cardiovascular risk within the metabolic syndrome and adapt the treatment goals thereafter.

Low-density lipoproteins generated during an oral fat load in mild hypertriglyceridemic and healthy subjects are smaller, denser, and have an increased low-density lipoprotein receptor binding affinity

Triglyceride-rich lipoproteins generated during the postprandial phase are atherogenic. Large very low-density lipoproteins (LDLs) or chylomicrons (CMs) are not as atherogenic as their remnants (Rem). Small and dense LDLs are associated with cardiovascular disease. Low-density lipoprotein size is partly under genetic control and is considered as a relatively stable LDL feature. In this article, we present data on retinyl palmitate kinetics correlated with the modification of LDL features in terms of size, density, and in vitro receptor binding affinity after an oral fat load. Six nondiabetic, hypertriglyceridemic (HTG) patients and 6 healthy controls were examined. Low-density lipoprotein size was assessed by gradient gel electrophoresis, and LDL density by density gradient ultracentrifugation. Low-density lipoprotein binding affinity was tested by in vitro competition binding assay on normal human skin fibroblasts (HSFs) and hepatoma cells (HepG2). Kinetic parameters were estimated in CM and Rem fractions by compartmental modeling. Hypertriglyceridemic patients showed significantly higher triglyceride area and a slower CM fractional catabolic rate. Postprandial LDL density increased both in HTG patients and in the control group with a significant difference between groups at 6 hours. Fasting LDL size was lower in HTG patients vs controls but decreased similarly in the postprandial phase. Low-density lipoprotein size and density postprandial modifications were not correlated with any investigated parameter. Postprandial LDLs were internalized more efficiently by HSF than baseline LDL only in the HTG group. In conclusion, postprandial LDLs are smaller and denser compared with fasting LDLs after an oral fat load. Postprandial LDLs also slightly increased their affinity to the HSF cell receptors.

Should we measure routinely the LDL peak particle size?

Low density lipoproteins (LDL) do not show in humans a normal distribution and comprise two different main fractions: large, buoyant (phenotype pattern A) and small, dense (phenotype pattern B) particles, that differ not only in size and density but also in physicochemical composition, metabolic behaviour and atherogenicity. The prevalence of small, dense LDL changes with age (30-35% in adult men, 5-10% in men <20 years and in pre-menopausal women, 15-25% in postmenopausal women) and is genetically influenced, with a heritability ranging from 35% to 45%. Small, dense LDL correlate negatively with plasma HDL levels and positively with plasma triglyceride levels and are associated with the metabolic syndrome and with increased risk for cardiovascular disease and diabetes mellitus. LDL size seems also to be an important predictor of cardiovascular events and progression of coronary artery disease and the predominance of small dense LDL has been accepted as an emerging cardiovascular risk factor by the National Cholesterol Education Program Adult Treatment Panel III. In addition, patients with acute myocardial infarction show an early reduction of LDL size, which persists during hospitalization and seems to precede all other plasma lipoprotein modifications. However, it is still on debate whether to measure the LDL size routinely and in which categories of patients. Since the therapeutic modulation of small, dense LDL particles is of great benefit in reducing the atherosclerotic risk, the LDL size measurement should be extended to patients at high risk of coronary artery disease as much as possible.

The Clinical Relevance of Low-Density-Lipoproteins Size Modulation by Statins

The predominance of small, dense low density lipoproteins (LDL) has been accepted as an emerging cardiovascular risk factor by the National Cholesterol Education Program Adult Treatment Panel III; in fact, LDL size seems to be an important predictor of cardiovascular events and progression of coronary heart disease. Several studies have also shown that the therapeutical modulation of LDL size is of great benefit in reducing the risk of cardiovascular events. Hypolipidemic treatment is able to alter LDL subclass distribution and statins are currently the most widely used lipid-lowering agents. Statins are potent inhibitors of hydroxy-methyl-glutaryl-coenzyme A reductase, the rate-limiting enzyme in hepatic cholesterol synthesis and are the main drugs of choice for the treatment of elevated plasma LDL cholesterol concentrations. Statins potentially lower all LDL subclasses (e.g., large, medium and small particles); thus, their net effect on LDL subclasses or size is often only moderate. However, a strong variation has been noticed among the different agents: analyses of all published studies suggest a very limited role of pravastatin and simvastatin in modifying LDL size and their subclasses, while fluvastatin and atorvastatin seem to be much more effective agents. Finally, rosuvastatin, the latest statin molecule introduced in the market, seems to be promising in altering LDL subclasses towards less atherogenic particles.

Accumulation of apoE-enriched triglyceride-rich lipoproteins in patients with coronary artery disease

Triglycerides (TGs) are vehicled by multiple particles with different abilities to promote atherosclerosis. Among plasma TG-rich lipoproteins (TRLs), subspecies may or may not contain apolipoprotein E (apoE) molecules: in this study, we evaluated the relative contribution of apoE-rich and apoE-poor TRLs to coronary atherosclerosis. We selected a group of males with premature coronary artery disease (CAD) without any of the classical nonlipid risk factors and/or high plasma lipid levels and evaluated the plasma concentration of TRL subspecies in comparison with healthy controls. Patients with CAD and controls had total cholesterol and TG levels within the normal range (despite slightly, even if significantly, higher TG levels in patients with CAD) and low-density lipoprotein cholesterol levels near optimal values. Nevertheless, patients with CAD had significantly lower high-density lipoprotein cholesterol, smaller low-density lipoprotein peak particle size, and a reduced HDL2b subfraction than controls. In addition, we observed higher concentrations of total TRL in patients with CAD together with a selective increase in apoE-rich particles. All these data were confirmed after correction for TG levels. We also investigated which parameters were associated with the spread of coronary atherosclerosis. Subjects with a single-vessel disease had selectively lower levels of apoE-rich fractions than patients with a multivessel disease. This was confirmed by multivariate analysis. Patients with a premature CAD free of nonlipid conventional risk factors, despite not having elevated lipid levels, show several lipoprotein abnormalities. Besides known atherogenic alterations, the accumulation of apoE-rich TRL subfractions may represent an additive factor that can potentially promote and initiate the atherosclerotic process.

Low-density lipoprotein size and cardiovascular prevention

Low-density lipoprotein (LDL) size appears to be an important predictor of cardiovascular events and progression of coronary artery disease, and the predominance of small, dense LDL has been accepted as an emerging cardiovascular risk factor by the National Cholesterol Education Program Adult Treatment Panel III. Yet, other authors have suggested that LDL subclass measurement does not add independent information to that conferred generically by LDL concentration and other standard risk factors. Therefore, the debate continues as to whether to measure LDL particle size for cardiovascular prevention and, if so, in which categories of patients. Since the therapeutic modulation of distinct LDL subspecies is of great benefit in reducing the risk of cardiovascular events, LDL size measurement should be extended as much as possible to patients at high risk of cardiovascular diseases.

Lipid triad or atherogenic lipoprotein phenotype: a role in cardiovascular prevention?

The term "lipid triad" or "atherogenic lipoprotein phenotype" has been introduced to describe a common form of dyslipidemia, characterized by three lipid abnormalities: increased plasma triglyceride levels, decreased HDL-cholesterol concentrations and the presence of small, dense LDL particles. It has been suggested that the clinical importance of the atherogenic lipoprotein phenotype probably exceeds that of LDL-cholesterol, because many more patients with coronary artery disease are found to have this trait than hypercholesterolaemia. There is a body of evidence that therapies effective against plasma HDL-cholesterol and triglycerides are associated with a strong reduction of cardiovascular risk; in addition, hypolipidemic treatment is able to increase LDL particle size and this increment correlates with regression of coronary stenosis. Recently, the Coordinating Committee of the National Cholesterol Education Program suggested that very high-risk patients may benefit from stronger lipid-lowering measures, a category of individuals that includes those with the atherogenic lipoprotein phenotype. Since the therapeutical modulation of each of the three components of the lipid triad is associated with a strong reduction in the risk of cardiovascular events, LDL size measurement may be extended as much as possible to patients at high risk of cardiovascular diseases.

Low-density lipoprotein size and cardiovascular risk assessment

A predominance of small, dense low-density lipoproteins (LDL) has been accepted as an emerging cardiovascular risk factor by the National Cholesterol Education Program Adult Treatment Panel III. LDL size seems to be an important predictor of cardiovascular events and progression of coronary heart disease and evidences suggests that both quality (particularly small, dense LDL) and quantity may increase cardiovascular risk. However, other authors have suggested that LDL size measurement does not add information beyond that obtained by measuring LDL concentration, triglyceride levels and HDL concentrations. Therefore, it remains debatable whether to measure LDL particle size in cardiovascular risk assessment and, if so, in which categories of patient. Therapeutic modulation of LDL particle size or number appears beneficial in reducing the risk of cardiovascular events, but no clear causal relationship has been shown, because of confounding factors, including lipid and non-lipid variables. Studies are needed to investigate the clinical significance of LDL size measurements in patients with coronary and non-coronary forms of atherosclerosis; in particular, to test whether LDL size is associated with even higher vascular risk, and whether LDL size modification may contribute to secondary prevention in such patients.

Associations of low density lipoprotein particle composition with atherogenicity

PURPOSE OF REVIEW

A growing body of data suggests that in addition to LDL-cholesterol concentrations, compositional properties of LDL, including size and fatty acid composition, are important in determining the relative degree of atherogenicity. This review examines current research in this field to evaluate which properties of LDL may most directly influence the risk of coronary heart disease.

RECENT FINDINGS

The presence of small dense LDL has been correlated with an increased risk of coronary heart disease, but this has not been shown to be fully independent of related factors such as elevated plasma triacylglycerol concentrations. An increased susceptibility of small dense LDL to in-vitro oxidation has also been demonstrated, but its importance to coronary heart disease risk has not been established. Other studies have found that the presence of enlarged LDL, modified (oleate enriched) fatty acyl composition of LDL, and higher numbers of LDL particles in plasma also are endpoints associated with an increased risk of coronary heart disease.

SUMMARY

LDL size may indicate a metabolic condition associated with increased CHD risk as opposed to the direct promotion of atherosclerosis by specific particle types of LDL. In most claims of detrimental effects of small dense LDL, neither LDL particle concentrations nor the fatty acid composition of the particles were established, both factors being important in contributing to the atherogenic potential of LDL. The predisposition to premature coronary heart disease cannot currently be objectively assigned to any one type of LDL particle.