Omega-3 polyunsaturated fatty acids: anti-inflammatory and anti-hypertriglyceridemia mechanisms in cardiovascular disease

Cardiovascular disease (CVD) is the world's most recognized and notorious cause of death. It is known that increased triglyceride-rich lipoproteins (TRLs) and remnants of triglyceride-rich lipoproteins (RLP) are the major risk factor for CVD. Furthermore, hypertriglyceridemia commonly leads to a reduction in HDL and an increase in atherogenic small dense low-density lipoprotein (sdLDL or LDL-III) levels. Thus, the evidence shows that Ω-3 fatty acids (eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have a beneficial effect on CVD through reprogramming of TRL metabolism, reducing inflammatory mediators (cytokines and leukotrienes), and modulation of cell adhesion molecules. Therefore, the purpose of this review is to provide the molecular mechanism related to the beneficial effect of Ω-3 PUFA on the lowering of plasma TAG levels and other atherogenic lipoproteins. Taking this into account, this study also provides the TRL lowering and anti-inflammatory mechanism of Ω-3 PUFA metabolites such as RvE1 and RvD2 as a cardioprotective function.

Predictors of the intima-media thickness of carotid artery in asymptomatic newly detected severe hypercholesterolemic patients

BACKGROUND

Data about predictors of intima-media thickness (IMT) of common carotid artery (CCA) in asymptomatic subjects with newly detected severe hypercholesterolemia is scarce.

AIM

This research is aimed at studying the predictors of the IMT of CCA among basic atherogenic risk biomarkers - lipid [total cholesterol (TC), triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein (LDL) cholesterol, Apolipoprotein-B, Apolipoprotein-Ai, Apolipoprotein-B/A(1) index] and non-lipid, [asymmetric dimethylarginine (ADMA), total homocysteine, cell adhesion molecules] in asymptomatic subjects with newly detected severe hypercholesterolemia.

METHODS

Two hundred and fifty asymptomatic patients with severe, newly hypercholesterolemia and 200 controls were evaluated. Hypercholesterolemia was defined as TC > 7.5 mm and LDL cholesterol > 4.9 mm. The ADMA and cell adhesion molecules were determined by ELISA and total homocysteine by high-performance liquid chromatography.

RESULTS

There was significant difference between the two groups in respect to all lipid biomarkers (P<0.001). Hypercholesterolemic patients had significantly higher level of ADMA, sVCAM-1, sICAM-1, IMT (P<0.001), whereas no significant difference was found between two groups with respect to total homocysteine, P-selectin and E-selectin (P>0.05). A strong positive correlation between IMT mean and age (r(xy) = 0.714; P<0.001), Apolipoprotein-B (r(xy) = 0.706; r(xy) < 0.001), Apolipoprotein-B/A(1) (r(xy) = 0.324; P<0.001), ADMA (r(xy) = 0.603; P<0.001) was found. The subsequent linear and multiple regression analysis selected age and Apolipoprotein-B as most significant factors in relation to IMT mean. Apolipoprotein-B is a better factor for assessment of risk, as LDL cholesterol underestimates the risk in asymptomatic subjects with newly detected severe hypercholesterolemia, until more rapid and feasible methods for measurement of small and dense LDL are available.

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.

The contribution of ApoB and ApoA1 measurements to cardiovascular risk assessment

LDL has been widely recognized as the major atherogenic lipoprotein and designated as the primary target for prevention of coronary heart disease (CHD); however, there is growing evidence that other triglyceride-rich lipoproteins, such as very low-density lipoprotein (VLDL) and intermediate density lipoprotein (IDL) carry atherogenic potential as well. This led to the designation of non-HDL cholesterol (HDL-C) (LDL + IDL + VLDL) as a secondary target of treatment for hyperlipidaemia. As each one of LDL, IDL and VLDL particles carries only one apolipoprotein B-100 (ApoB-100) molecule, the total ApoB value represents the total number of potentially atherogenic lipoproteins, whereas non-HDL-C provides the cholesterol content of these same lipoproteins. Recent data from epidemiological, observational and interventional studies suggest that non-HDL-C, apolipoproteins ApoA1 and ApoB may improve CHD risk assessment by identifying more high-risk individuals than the usual lipid profile alone. However, the targets for the optimal treatment of dyslipidaemia remain a subject of considerable debate. Further studies are needed to determine whether ApoB and ApoA1 are superior to conventional lipid parameters as predictors of cardiovascular disease or therapeutic targets of hyperlipidaemias. In this review, we summarize the current opinions on the use of ApoA1 and ApoB values as estimates of cardiovascular risk or as treatment goals in patients undergoing treatment for hyperlipidaemia.

Lipoproteins: When size really matters

The field of nanoscience is extending the applications of physics, chemistry and biology into previously unapproached infinitesimal length scales. Understanding the behavior and manipulating the positions and properties of single atoms and molecules hold great potential to improve areas of science as disparate as medicine and computation, and communication and orbiting satellites. Yet, in the race to develop novel, previously unavailable nanoparticles, there is an opportunity for scientists in this field to digress and to apply their growing understanding of nanoscience and the tools of nanotechnology to one of the most pressing problems in all of human biology-diseases related to lipoproteins. Although not appreciated outside the field of lipoprotein biology, variations in the compositions, structures and properties of these nanoscale-sized, blood-borne particles are responsible for most of the variations in health, morbidity and mortality in the Western world. If the lipoproteins could be understood at the nanometer length scale with precise details of their structures and functions, scientists could understand a wide range of perplexing physiological processes and also address the dysfunctions in normal lipoprotein biology that lead to such diseases as hypercholesterolemia, heart disease, stroke and neurodegenerative diseases. Furthermore, if the capabilities of nanoscience to assemble and manipulate nanometer-sized particles could be recruited to studies of lipoproteins, these biological particles would provide a new dimension to therapeutic agents, and these natural particles could be designed to carry out many specialized beneficial tasks.

Associations between apolipoprotein B, apolipoprotein AI, the apolipoprotein B/AI ratio and coronary heart disease: a literature-based meta-analysis of prospective studies

OBJECTIVES

To assess associations of circulating levels of apolipoprotein (apo) AI, apoB and the apoB/AI ratio (apoB/A) with risk of incident coronary heart disease (CHD).

DESIGN

Literature-based meta-analysis of prospective studies.

DATA SOURCES

Prospective studies in essentially general populations that reported on associations between apoAI, apoB or apoB/A and first incident CHD outcomes. Studies were identified by computer-based searches and by manual searches of the relevant literature.

RESULTS

Data from 23 relevant studies were identified. For apoAI, with 6333 CHD cases in 21 studies, comparison of individuals in the bottom third with those in the top third of baseline values yielded a combined relative risk of 1.62 (95% confidence interval: 1.43-1.83), i.e. an inverse association. For apoB, a combined analysis of 6320 CHD cases from 19 studies gave a relative risk of 1.99 (1.65-2.39) for a comparison of individuals in the top third versus those in the bottom third of baseline values. For apoB/A, with 3730 CHD cases from seven studies, a comparison of individuals in the top third versus the bottom third of baseline values gave a combined relative risk of 1.86 (1.55-2.22). These associations were somewhat stronger following correction for within-person variations in apolipoprotein levels. There was evidence of heterogeneity amongst the published studies, but it was only partly explained by available study-level characteristics.

CONCLUSIONS

The present quantitative review suggests the existence of moderately strong associations between baseline levels of each of apoAI, apoB, and apoB/A and risk of CHD. More detailed analysis, perhaps based on individual participant data from prospective studies, could help to overcome several limitations in the present review and to clarify any relevance of these apolipoproteins to disease prediction and aetiology.

Low-density lipoprotein cholesterol, non-high-density lipoprotein cholesterol and apolipoprotein B: relationships among the different measurements

Serum low-density lipoprotein cholesterol (LDLC) value is a recognized target for atherosclerotic risk management, and is generally calculated using the "Friedewald formula". Alternative risk markers include directly measured LDLC, non-high-density lipoprotein cholesterol (non-HDLC) and apolipoprotein B (ApoB). The relationships among such various measured or calculated quantities in medium-sized sets of patient results were investigated. Results from two sets of patients were retrieved from our laboratory information systems. One group (n=8436) included results of cholesterol, HDLC, triglyceride (TG) and glucose measurements. A second group (n = 902) included, in addition, results of ApoB measurement. The results confirmed the unreliability of the Friedewald formula at TG >350 mg/dL (3.96 mmol/L), but also indicated TG-linked underestimation of LDLC below such a TG level. By contrast, non-HDLC values were shown to be independent of TG, and better correlated to ApoB than LDLC values. Mathematically, the difference between non-HDLC and LDLC is TG x 0.458 (values in mmol/L): therefore, the latter cannot be compared to (or converted into) the former by simply adding a constant amount. The ratio LDLC/ApoB was shown continuously to decrease with increasing TG concentrations, while the ratio non-HDLC/ApoB did not. The TG-dependent underestimation of LDLC may be the reason for the reported better cardiovascular risk predictivity of non-HDLC in diseases associated with TG increase, such as in diabetes. Non-HDLC values are not influenced by TG levels, and are better correlated with ApoB.

Apolipoprotein B and apolipoprotein A-I: risk indicators of coronary heart disease and targets for lipid-modifying therapy

Although LDL cholesterol (LDL-C) is associated with an increased risk of coronary heart disease, other lipoproteins and their constituents, apolipoproteins, may play an important role in atherosclerosis. Elevated levels of apolipoprotein (apo) B, a constituent of atherogenic lipoproteins, and reduced levels of apo A-I, a component of anti-atherogenic HDL, are associated with increased cardiac events. Apo B, apo A-I and the apo B/apo A-I ratio have been reported as better predictors of cardiovascular events than LDL-C and they even retain their predictive power in patients receiving lipid-modifying therapy. Measurement of these apolipoproteins could improve cardiovascular risk prediction.

Dyslipidaemia

The lowering of serum cholesterol is increasingly recognised as essential in the prevention of coronary heart disease and other atherosclerotic disease. The success of statin trials and the need to deploy these drugs effectively in the population has led increasingly to the identification of many people whose serum cholesterol, triglycerides, and HDL-cholesterol require clinical assessment, and frequently treatment. Lipid disorders are mainly straightforward, but some are complex or resistant to simple treatment strategies. I have reviewed the clinical manifestations of disordered lipid metabolism (dyslipidaemia) and its management.

How, when, and why to use apolipoprotein B in clinical practice

The evidence is now clear that plasma apolipoprotein (apo) B is a better index of the risk of coronary artery disease (CAD) than total or low-density lipoprotein (LDL) cholesterol. Moreover, the evidence is also clear that clinical risk of apo B is determined not only by LDL particle number but also by whether small, dense LDL particles are present. The objective of this article, therefore, is to demonstrate how, when, and why apo B should be used in clinical practice. First, the evidence that apo B is superior to LDL cholesterol as an index of the risk of CAD and as a guide to the adequacy of statin therapy is briefly reviewed. Next, the biological bases for this superiority in identifying risk are outlined. Clinical scenarios are then outlined demonstrating the value of measuring apo B in hypertriglyceridemic, hypercholesterolemic, and normolipidemic subjects. The methodological soundness of the laboratory determinations of lipids and apo B is also an important issue. Concern has been raised regarding the measurement of apo B, but it is standardized, precise, and not expensive. Paradoxically, it is becoming ever more obvious that the methodological problems lie with calculated LDL cholesterol. To the known deficiencies must be added the fact that calculated LDL cholesterol systematically underestimates true LDL cholesterol at values close to target levels.Thus, from every perspective-pathophysiology, diagnosis, assessment of therapy, and methodologic soundness-there are powerful clinical arguments why apo B should be used in the routine diagnosis of dyslipidemias and assessment of the adequacy of statin therapy.