Enhanced oxidative susceptibility and reduced antioxidant content of metabolic precursors of small, dense low-density lipoproteins

Elevated concentration of oxidized LDL together with poor cardiorespiratory and abdominal muscle fitness predicts metabolic syndrome in young men

BACKGROUND

Metabolic syndrome (MetS) is associated with increased oxidized LDL (ox-LDL), systemic inflammation, and poor cardiorespiratory fitness. We examined affiliations of these factors and the effect of muscular fitness on MetS in young healthy men.

METHODS

Physical fitness, ox-LDL, tumor necrosis factor α (TNFα), interleukin-6 (IL-6) and serum lipids were measured in a nationally representative sample of Finnish young men with and without MetS. Participants (mean age 25.1years) performed tests of maximal oxygen uptake (VO₂max) and muscle fitness, and were divided into MetS (n=54, IDF 2007 criteria) and non-MetS (n=790). Age, smoking and leisure-time physical activity were used as covariates (ANCOVA).

RESULTS

The MetS group had lower results in VO₂max and all of the muscular fitness tests (excluding grip strength) (P<0.0001, in all). Ox-LDL, ox-LDL/HDL-cholesterol, ox-LDL/LDL-cholesterol, TNFα and IL-6 were all higher in the MetS group than in the non-MetS group (P<0.01, in all). In stepwise multivariate logistic regression analysis (adjusted to MetS criteria), higher ox-LDL (OR 1.118, 95% CI 1.078-1.160), lower VO₂max (OR 0.938, 95% CI 0.901-0.977) and lower sit-ups (OR 0.898, 95% CI 0.844-0.956) predicted MetS (p<0.05, in all).

CONCLUSIONS

Young men with MetS possess significantly poorer cardiorespiratory and muscle fitness, together with elevated systemic levels of ox-LDL, TNFα and IL-6 compared to non-MetS young men. Of these variables, ox-LDL, VO₂max and sit-ups predicted MetS. Based on these findings, poor physical fitness and elevated concentration of ox-LDL are significant predisposing factors in the development of MetS.

Elucidation of mechanisms of actions of thymoquinone-enriched methanolic and volatile oil extracts from Nigella sativa against cardiovascular risk parameters in experimental hyperlipidemia

BACKGROUND

Nigella sativa belonging to the Ranunculaceae family has been reported to use for thousands of years as protective and curative traditional medicine against a number of diseases. GC-MS analysis of methanolic extract (ME) and volatile oil (VO) extracted from Nigella sativa seed oil was performed by two different mass spectrometry libraries, WIlEY8 and NIST05s. The cholesterol lowering and antioxidant actions of VO and ME fractions were investigated in atherogenic suspension fed rats.

METHODS

In this study, four groups of male Wistar rats were used: normolipidemic control (NLP-C), hyperlipidemic control (HLP-C), methanolic extract (HLP-ME) and volatile oil treated (HLP-VO) groups for 30 days of duration. P value < 0.05 was assumed as significant data in groups.

RESULTS

Administration of atherogenic suspension to male Wistar rats for 30 days resulted in a marked increase of plasma triglycerides and total cholesterol, and significant change in plasma lipoprotein levels along with a decrease in antioxidant arylesterase activity in hyperlipidemic control (HLP-C) group. The oral feeding of 100 mg ME or 20 mg VO per rat/day effectively reduced the plasma triglycerides to near normal level, while high density lipoprotein cholesterol and its subfraction along with arylesterase activity levels were significantly increased. The test fractions elicited a significant decrease in hepatic HMG-CoA reductase activity. The fractions significantly blocked the ex vivo basal and in vitro maximal formation of conjugated diene and malondialdehyde, and lengthened the lag times of low density lipoprotein, small dense low density lipoprotein and large buoyant low density lipoprotein. ME possessing ω-6 linoleic acid along with palmitic acid active compounds was more effective than VO extract containing thymol and isothymol phenolic antioxidant compounds, thymoquinone phenolic compound common to the both extracts, via reduction in hepatic HMG-CoA reductase activity as well as antioxidant mechanisms.

CONCLUSION

The both extracts especially, ME significantly improve cardiovascular risk parameters in treated rats, and can be used in reactive oxygen species disorders such as cardiovascular diseases.

Heat-shock protein 60 kDa and atherogenic dyslipidemia in patients with untreated mild periodontitis: a pilot study

Identification of predictors of cardiovascular risk can help in the prevention of pathologic episodes and the management of patients at all stages of illness. Here, we investigated the relationships between serum levels of Hsp60 and dyslipidemia in patients with periodontitis by performing a cross-sectional study of 22 patients with mild periodontitis without any prior treatment for it (i.e., drug naïve) and 22 healthy controls, matched for age and body mass index (BMI). All subjects were evaluated for periodontal status, gingival inflammation, and oral hygiene. Levels of circulating Hsp60, C-reactive protein (CRP), and plasma lipids were measured, and small, dense low-density lipoproteins (LDL) were indirectly assessed by determining the triglycerides/high-density lipoproteins (HDL) cholesterol ratio. We also assessed by immunohistochemistry Hsp60 levels in oral mucosa of patients and controls. No difference was found in CRP levels or plasma lipids between the two groups, but subjects with periodontitis showed, in comparison to controls, higher levels of small, dense LDL (p  = 0.0355) and circulating Hsp60 concentrations (p < 0.0001). However, levels of mucosal Hsp60 did not change significantly between groups. Correlation analysis revealed that circulating Hsp60 inversely correlated with HDL-cholesterol (r  = -0.589, p  = 0.0039), and positively with triglycerides (r  = +0.877, p < 0.0001), and small, dense LDL (r  = +0.925, p < 0.0001). Serum Hsp60 significantly correlated with the degree of periodontal disease (r  = +0.403, p  = 0.0434). In brief, untreated patients with mild periodontitis had increased small, dense LDL and serum Hsp60 concentrations, in comparison to age- and BMI-matched controls and both parameters showed a strong positive correlation. Our data indicate that atherogenic dyslipidemia and elevated circulating Hsp60 tend to be linked and associated to periodontal pathology. Thus, the road is open to investigate the potential value of elevated levels of circulating Hsp60 as predictor of risk for cardiovascular disease when associated to dyslipidemia in periodontitis patients.

Changes in small dense low-density lipoprotein levels following acute coronary syndrome

Low-density lipoprotein (LDL), especially small dense LDL (sdLDL), plays a role in atherogenesis. We compared baseline sdLDL levels between healthy controls and patients with acute coronary syndrome (ACS). Blood samples were taken from patients diagnosed with myocardial infarction ([MI] n = 104) and unstable angina ([UA] n = 100). Both sdLDL and high-sensitivity C-reactive protein (hsCRP) levels were determined on admission and in the next 24 hours after the onset of symptoms. Baseline concentration of sdLDL was significantly higher in patients presenting with ACS than controls (P < .05). In the 24 hours following ACS, the sdLDL levels decreased insignificantly in both groups of patients with ACS (P > .05). The changes in sdLDL values were not significantly different between MI and UA participants (P > .05). Patients with ACS have higher concentration of sdLDL compared with the controls.

Hypertriglyceridemia secondary to obesity and diabetes

Hypertriglyceridemia is a common lipid abnormality in persons with visceral obesity, metabolic syndrome and type 2 diabetes. Hypertriglyceridemia typically occurs in conjunction with low HDL levels and atherogenic small dense LDL particles and is associated with increased cardiovascular risk. Insulin resistance is often an underlying feature and results in increased free fatty acid (FFA) delivery to the liver due to increased peripheral lipolysis. Increased hepatic VLDL production occurs due to increased substrate availability via FFAs, decreased apolipoprotein B100 degradation and increased lipogenesis. Postprandial hypertriglyceridemia also is a common feature of insulin resistance. Small dense LDL that coexist with decreased HDL particles in hypertriglyceridemic states are highly pro-atherogenic due to their enhanced endothelial permeability, proteoglycan binding abilities and susceptibility to oxidation. Hypertriglyceridemia also occurs in undertreated individuals with type 1 diabetes but intensive glucose control normalizes lipid abnormalities. However, development of visceral obesity in these patients unravels a similar metabolic profile as in patients with insulin resistance. Modest hypertriglyceridemia increases cardiovascular risk, while marked hypertriglyceridemia should be considered a risk for pancreatitis. Lifestyle modification is an important therapeutic strategy. Drug therapy is primarily focused on lowering LDL levels with statins, since efforts at triglyceride lowering and HDL raising with fibrates and/or niacin have not yet been shown to be beneficial in improving cardiovascular risk. Fibrates, however, are first-line agents when marked hypertriglyceridemia is present. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.

Small dense LDL enhances THP-1 macrophage foam cell formation

AIM

Increased levels of small dense low-density lipoproteins (sd-LDL) have been reported more atherogenic compared to total low-density lipoprotein (LDL); however, no definitive experiments using macrophages have examined this concept in vitro.

METHOD AND RESULT

In this study, we isolated fractions of total LDL (density 1.019-1.063 g/ml) and sd-LDL (density 1.044-1.063 g/ml) from the plasma of subjects with modest hypertriglycidemia. Oxidizabilty as assessed by copper-induced generation (1.6 µmol/L CuSO(4),12 h) of thiobarbituric acid reactive substances (TBARS) was significantly greater (7-fold higher, p < 0.01) for sd-LDL (4.3 ± 1.1 nmol/mg) than for total LDL (0.6 ± 0.2 nmol/mg) at the same cholesterol concentrations. Moreover, oxidized sd-LDL induced more lipid staining in macrophages than oxidized total LDL. When non-oxidized sd-LDL were incubated with THP1 macrophages, there was much greater lipid accumulation as assessed by oil red O staining, and more than a 2-fold increase (p < 0.05) in intracellular triglyceride content as compared to non-oxidized total LDL. Furthermore, non-oxidized sd-LDL in contrast to non-oxidized total LDL enhanced macrophage lectin-like oxidized LDL receptor-1 (LOX-1) protein expression and significantly LOX-1 mRNA levels (+158%, p < 0.05), with no effect on scavenger receptor A or CD36 gene expression. These effects of non-oxidized sd-LDL on LOX-1 gene expression were suppressed when Toll-like receptor 4 was inactivated either by RNAi or antibody.

CONCLUSION

Our data indicate for the first time that sd-LDL is much more effective in promoting macrophage triglyceride accumulation and LOX-1 gene expression than total LDL.

Protective effect of dietary tocotrienols against infection and inflammation-induced hyperlipidemia: an in vivo and in silico study

Currently used hypolipidemic drugs, Fluvastatin and Atorvastatin, act via inhibiting the rate-limiting enzyme 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase of the mevalonate pathway. The associated severe side-effects of these statins led us to explore the therapeutic potentials of naturally occurring Tocomin (mixture of dietary α-, β-, γ- and δ-tocotrienols). Tocomin (10 mg) was orally administered daily for 10 days before and 12 h after bacterial lipopolysaccharide (200 μg) or 24 h after zymosan (20 mg) or turpentine (0.5 mL) to Syrian hamsters. The data showed that Tocomin significantly reduced the levels of plasma and lipoprotein lipids, cholesterol, apoB, small dense (sd)-LDL as well as LDL in the hyperlipidemia-induced hamsters. Further, the mechanism of action of α-, β-, γ- and δ-tocotrienols was validated by docking studies with HMG-CoA reductase enzyme using the Molegro Virtual Docker. The inhibition of HMG-CoA reductase predicted in terms of MolDockScore and interaction energy suggest the comparative potential in the descending order: Atorvastatin > Fluvastatin ~ δ > γ > β > α. The results favor the daily intake of naturally occurring tocotrienols as dietary supplement in the prevention and treatment of infection/inflammation induced dyslipidemia compared with the hypolipidemic drugs.

Decreased small dense LDL levels in Gilbert's syndrome

OBJECTIVE

To investigate the role of small dense low density lipoprotein cholesterol (sd-LDL-C) in the mechanism of decreased incidence of cardiovascular disease in Gilbert's syndrome (GS).

DESIGN AND METHODS

sd-LDL-C, ox-LDL, and high sensitive C reactive protein (hs-CRP) levels were investigated in subjects with GS (n=42) and compared to healthy controls (n=52).

RESULTS

Age, gender and body mass index (BMI) distributions were similar between the two groups. sd-LDL-C, ox-LDL and hs-CRP levels were lower in GS than the healthy controls (p<0.001, p<0.001 and p=0.001, respectively). Unconjugated bilirubin was negatively correlated with sd-LDL-C, ox-LDL and hs-CRP (r=-0.594, p<0.001; r=-0.249, p=0.016 and r=-0.373, p<0.001 respectively). In addition, sd-LDL-C was positively correlated with ox-LDL (r=0.307, p=0.003).

CONCLUSIONS

The findings of this preliminary study suggest that reduced sd-LDL-C, ox-LDL and hs-CRP levels may have a role in preventing atherosclerosis in subjects with GS.

Should we measure routinely oxidised and atherogenic dense low-density lipoproteins in subjects with type 2 diabetes?

Beyond low-density lipoprotein (LDL)-cholesterol concentrations, in recent years, several clinical studies have shown that both oxidised and small, dense LDL have a strong predictive role for the presence of vascular atherosclerosis. These two lipid parameters seem to have a synergistic impact on cardiovascular risk, with a greater importance in patients at higher-risk, such as those with type-2 diabetes. Increased levels of oxidised and small, dense LDL levels are a feature of diabetic dyslipidaemia, and small, dense LDL have been shown to be a good predictor of future cardiovascular events, at both univariate and multivariate analyses. On the other hand, although the association of oxidised LDL with surrogate markers of atherosclerosis is consistent, the correlation with hard clinical end points seems to be smaller. Yet, measurement of these two lipid parameters has not been widely used in daily practice because of the limited availability of clinical data and methodological problems: lack of availability of easy, cheap and reproducible essays for measurement of oxidised and, particularly, small, dense LDL has reduced their assessment in large clinical end-points trials. However, on the basis of available data, the therapeutic modulation of small, dense LDL is significantly associated with reduced cardiovascular risk, even after adjustment for confounding factors. In conclusion, the routine measurement of oxidised and small, dense LDL in patients with type-2 diabetes cannot be recommended in daily clinical practice so far; yet, their measurement is strongly encouraged to better understand their role on the cardiovascular risk of patients with type-2 diabetes.

Dyslipidaemia in the metabolic syndrome and type 2 diabetes: pathogenesis, priorities, pharmacotherapies

IMPORTANCE OF THE FIELD

Dyslipoproteinaemia is a cardinal feature of the metabolic syndrome that accelerates atherosclerosis. It is usually characterized by high plasma concentrations of triglyceride-rich and apolipoprotein B (apoB)-containing lipoproteins, with depressed concentrations of high-density lipoprotein (HDL). Drug interventions are essential for normalizing metabolic dyslipidaemia.

AREAS COVERED IN THIS REVIEW

This review discusses the mechanisms and treatment for dyslipidaemia in the metabolic syndrome and type 2 diabetes.

WHAT THE READER WILL GAIN

A comprehensive understanding of the pathophysiology and pharmacotherapy of dyslipidaemia in the metabolic syndrome and diabetes.

TAKE HOME MESSAGE

Dysregulation of lipoprotein metabolism may be due to a combination of overproduction of triglyceride-rich lipoproteins, decreased catabolism of apoB-containing particles, and increased catabolism of HDL particles. These abnormalities may be consequent on a global metabolic effect of insulin resistance and an excess of both visceral and hepatic fat. Lifestyle modifications may favourably alter lipoprotein transport in the metabolic syndrome. Patients with dyslipidaemia and established cardiovascular disease should receive a statin as first-line therapy. Combination with other lipid-regulating agents, such as ezetimibe, fibrates, niacins and fish oils may optimize the benefit of statin on atherogenic dyslipidaemia.

Circadian change of serum concentration of small dense LDL-cholesterol in type 2 diabetic patients

BACKGROUND

Type 2 diabetic patients have a higher risk of atherosclerosis than non-diabetic subjects. This difference may be attributable to increased levels of small dense low-density lipoprotein-cholesterol (sLDL-C) in diabetic patients. As the sLDL-C concentration is elevated in hypertriglyceridemia, which is exaggerated postprandially, we examined whether the sLDL-C level increases postprandially in type 2 diabetes.

METHODS

We obtained 7 blood samples (30min before and 2h after each meal, and at midnight) from 15 patients with diabetes and ten normal controls. Following the precipitation of very low-density lipoprotein and large buoyant LDL (bLDL) with heparin-Mg(2+), the sLDL-C concentration was determined as the cholesterol concentration by a homogeneous assay.

RESULTS

The fasting sLDL-C concentration was 60.3% higher in the diabetic patients than in the controls (1.01+/-0.21 vs. 0.63+/-0.21mmol/l, p<0.001). The sLDL-C concentrations in both groups were highest in the fasting state, decreased after breakfast, and remained low until midnight. The maximal reduction in the absolute sLDL-C concentration was 56.5% greater in the diabetic patients than in the controls (0.36+/-0.13 vs. 0.23+/-0.16mmol/l, p<0.05). Thus, the sLDL-C/bLDL-cholesterol (bLDL-C) ratio was reduced with increases in bLDL-C.

CONCLUSIONS

The sLDL-C concentration decreases postprandially in diabetes. This absolute reduction in sLDL-C may contribute to an acceleration of atherosclerosis in diabetic patients.

Atherogenic dyslipidemia and oxidative stress: a new look

Although results from in vitro studies and clinical trials demonstrate strong associations between oxidative stress and cardiovascular risk, to date still no convincing data are available to suggest that treatment with antioxidants might reduce vascular events. Oxidative modifications of low-density lipoproteins (LDL) represent an early stage of atherosclerosis, and small, dense LDL are more susceptible to oxidation than larger, more buoyant particles. Oxidized LDL are independent predictors of subclinical and clinical atherosclerosis. Recent studies suggested that novel therapeutic strategies may take into account the removal of such particles from circulation. Future research is required to explore the potential synergistic impact of markers of oxidative stress and atherogenic dyslipidemia, particularly small dense LDL, on cardiovascular risk.

Quantitative and qualitative effects of rosuvastatin on LDL-cholesterol: what is the clinical significance?

BACKGROUND

Statins have emerged as the global leader in pharmacologic therapy for dyslipidaemia, and rosuvastatin has demonstrated clinical efficacy as well as safety in several clinical trials and postmarketing analyses.

AIM

The present article reviewed the effects of rosuvastatin on the quantity and the quality of low-density lipoproteins (LDL).

METHODS

We searched for and reviewed all the available evidence in a systematic way. A literature search (by Medline and Scopus) was performed using the following headings: 'LDL-cholesterol', 'LDL size', 'LDL subclasses', 'small dense LDL', 'apolipoprotein B, apo B' and 'rosuvastatin' up to 11 November 2008. The authors also manually reviewed the references of selected articles for any pertinent material.

RESULTS

Rosuvastatin reduces LDL-cholesterol levels to a greater extent than other statins and is able to modulate significantly LDL size and subclasses towards less atherogenic particles as well as the LDL particle number, as indirectly measured by the levels of apo B.

DISCUSSION AND CONCLUSIONS

The recent Justification for the Use of statins in Primary prevention: an Intervention Trial Evaluating Rosuvastatin study provides more evidence about the effectiveness of rosuvastatin therapy in reducing cardiovascular risk, even among persons who would not currently be considered for pharmacotherapy. Further insights on cardiovascular outcomes will be available by the on-going trials included in the GALAXY program that includes subjects with type-2 diabetes, haemodialysis recipients, patients with congestive heart failure and specific ethnic groups, such as African American, Hispanic and South Asian populations.

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.

Does simultaneous determination of LDL and HDL particle size improve prediction of coronary artery disease risk?

BACKGROUND

Alterations in plasma lipoprotein subclass distribution affect the risk for coronary artery disease (CAD). However, it is unclear whether the determination of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) phenotypes may or may not improve the ability to predict CAD development.

METHODS

Polyacrylamide gradient (3-31%) gel electrophoresis was used to simultaneously determine size and distribution of lipoprotein subclasses in 181 CAD patients and 178 controls.

RESULTS

Mean LDL and HDL subclass sizes were significantly smaller in patients than in controls (p < 0.001). Multivariate logistic regression analysis showed that small dense LDL particles were independent CAD risk predictors (OR = 2.867, p < 0.01), even when adjusted for other traditional risk factors, while small HDL particles lost their significance after adjustment (OR = 2.071, p = 0.054). The area under the ROC curve for LDL (0.671) and HDL (0.643) particle size measurement demonstrated low clinical accuracy when compared to the combination of traditional lipid risk factor measurements.

CONCLUSIONS

CAD is associated with the predominance of smaller LDL and HDL particles. However, simultaneous determination of these two lipoprotein phenotypes provides no additional power in discriminating CAD and non-CAD subjects, beyond that obtained by the traditional risk factors.

Hypothyroidism results in small dense LDL independent of IRS traits and hypertriglyceridemia

There is evidence of an association between hypothyroidism and coronary heart disease. We decided to look at the relationship between hypothyroidism and LDL subclasses' pattern including small, dense LDL to define a biochemical basis for better management of the CHD risk of these patients. We utilized a case-control design to evaluate differences in lipid parameters between cases and controls. Univariate analysis revealed that many factors were associated with LDL particle size. Binary logistic regression however revealed that only thyroid status and serum triglyceride (TG) levels were independently associated with LDL particle size. Results from this study support an independent association between LDL particle size phenotype and both plasma TG concentrations and thyroid status. After adjusting for TG levels, other insulin resistance syndrome (IRS) traits were not associated with LDL size phenotype, suggesting that the IRS related sdLDL is linked most strongly to alterations in TG levels.

Metabolic syndrome and dyslipidemia in youth

Obesity is a well-known risk factor for metabolic syndrome. Although the cause or causes of metabolic syndrome are debated, insulin resistance, dyslipidemia, and hypertension are increasingly recognized in children and adolescents, especially those who are overweight or obese. Although adoption of a healthy lifestyle early in life offers the best long-term solution, many children and adolescents are currently at risk for future cardiovascular disease. Although long-term outcome data are lacking, the dyslipidemic triad commonly seen in youth with metabolic syndrome (elevated triglycerides, low high-density lipoprotein, and small dense low-density lipoprotein) is likely to significantly contribute to future vascular disease. Surrogate markers (carotid intima-media thickness and flow-mediated vasodilatation) for the precursors of cardiovascular disease are increased in obese youth, consistent with early vascular damage. In this work, we review the features of metabolic syndrome in children and adolescents, including age- and gender-specific norms for lipid values. Diagnostic criteria and modifications of screening guidelines unique to youth are discussed. Although recommendations for lifestyle modification are suggested for all, many youth at high risk of future cardiovascular risk may need more aggressive medical interventions to improve insulin sensitivity, achieve a less atherogenic lipid profile, and lower blood pressure.

Lipid peroxidation and decomposition--conflicting roles in plaque vulnerability and stability

The low density lipoprotein (LDL) oxidation hypothesis has generated considerable interest in oxidative stress and how it might affect atherosclerosis. However, the failure of antioxidants, particularly vitamin E, to affect the progression of the disease in humans has convinced even staunch supporters of the hypothesis to take a step backwards and reconsider alternatives. Preponderant evidence for the hypothesis came from animal antioxidant intervention studies. In this review we point out basic differences between animal and human atherosclerosis development and suggest that human disease starts where animal studies end. While initial oxidative steps in the generation of early fatty streak lesions might be common, the differences might be in the steps involved in the decomposition of peroxidized lipids into aldehydes and their further oxidation into carboxylic acids. We suggest that these steps may not be amenable to attenuation by antioxidants and antioxidants might actually counter the stabilization of plaque by preventing the formation of carboxylic acids which are anti-inflammatory in nature. The formation of such dicarboxylic acids may also be conducive to plaque stabilization by trapping calcium. We suggest that agents that would prevent the decomposition of lipid peroxides and promote the formation and removal of lipid hydroxides, such as paraoxonase (PON 1) or apo A1/high density lipoprotein (HDL) might be more conducive to plaque regression.

Gilbert syndrome, UGT1A1*28 allele, and cardiovascular disease risk: possible protective effects and therapeutic applications of bilirubin

Serum bilirubin has been shown to be inversely related to cardiovascular disease (CVD) in both retrospective and prospective studies. Meta-analysis of existing studies has also confirmed that serum bilirubin concentrations are inversely related to CVD. Less information is known about the protective effects of slightly elevated serum bilirubin concentrations. In this review, we will focus primarily on the association of serum bilirubin and CVD and the possible protective roles of bilirubin, heme oxygenase (HO), and bilirubin UDP-glucuronosyltransferase (UGT1A1). HO and biliverdin reductase control the formation of bilirubin, whereas UGT1A1 controls bilirubin conjugation and clearance. Because of the health and therapeutic implications of slightly elevated serum bilirubin concentrations, we will discuss the recent prospective studies on cardiovascular risk in individuals with Gilbert syndrome (GS) as well as those with the UGT1A1*28 allele. Such individuals have decreased hepatic bilirubin UDP-glucuronosyltransferase activity, decreased bilirubin clearance, and increased serum bilirubin concentrations. Lastly, we will discuss some of the therapeutic approaches that could be used to increase serum bilirubin concentrations to prevent CVD and other oxidative and inflammatory diseases.

PAI-1 activity, but not fibrinogen or von Willebrand factor, is inversely related to LDL particle size in type 2 diabetes

BACKGROUND

Levels of fibrinogen, von Willebrand factor (vWF) and plasminogen activator inhibitor-1 (PAI-1) have been associated with small low-density lipoprotein (LDL) particles. However, it is not clear whether these associations are independent of visceral adiposity or other components of the metabolic syndrome such as triglycerides or insulin resistance.

METHODS

Visceral adipose tissue (VAT; CT-scan), fibrinogen, von Willebrand factor antigen (vWF:Ag), PAI-1 activity and different metabolic parameters such as total cholesterol (chol), HDL-chol, triglycerides, insulin resistance (homeostasis model assessment; HOMA-IR) were determined in 41 women and 78 men with type 2 diabetes. LDL particle size was assessed by polyacrylamide gradient gel electrophoresis.

RESULTS

PAI-1 activity was inversely related to LDL particle size after adjustment for age and body mass index (BMI) (r=-0.28; p=0.006) or age and VAT (r=-0.26; p=0.01), but not after adjustment for age and HOMA-IR (r=-0.15; p=0.148) or age and triglycerides (r=-0.04; p=0.679). In multiple regression analysis, LDL particle size did not independently determine PAI-1 activity levels. Fibrinogen and vWF:Ag did not seem to be related to LDL size.

CONCLUSIONS

PAI-1 activity levels, in contrast to fibrinogen and vWF:Ag, seem to be related to the small LDL phenotype in patients with type 2 diabetes. However, this relationship was not independent of insulin resistance or triglycerides.

Atherogenic lipoprotein parameters in patients with aggressive periodontitis

BACKGROUND AND OBJECTIVE

Certain types of chronic infection increase the plasma level of very-low-density lipoprotein, leading to formation of the particularly atherogenic low-density lipoprotein subclass, small dense low-density lipoprotein. In the present study, we examined whether aggressive forms of periodontitis are associated with these atherogenic lipoprotein parameters.

MATERIAL AND METHODS

Twelve healthy control subjects without periodontitis, 12 subjects with localized aggressive periodontitis and 12 subjects with generalized aggressive periodontitis were studied. Lipoprotein subclass levels were determined using nuclear magnetic resonance methodology.

RESULTS

Healthy control subjects, localized aggressive periodontitis subjects and generalized aggressive periodontitis subjects had progressively higher plasma levels of very-low-density lipoprotein and progressively smaller average low-density lipoprotein size (p < 0.05, one-way analysis of variance). In pairwise comparisons, differences were only significant between healthy controls and generalized aggressive periodontitis subjects (p < 0.05, Tukey's post test). After adjustment for body mass index, the mean periodontal pocket depth correlated positively with plasma very-low-density lipoprotein levels (p = 0.047). Very-low-density lipoprotein concentrations correlated positively with small dense low-density lipoprotein levels and negatively with average low-density lipoprotein size. Prevalence of the atherogenic lipoprotein pattern-B in healthy controls, localized aggressive periodontitis subjects and generalized aggressive periodontitis subjects was 8.3%, 33.3% and 66.6%, respectively.

CONCLUSION

These results indicate that periodontal infection is associated with elevated plasma levels of atherogenic lipoprotein species. This association may account for the increased risk of periodontitis patients for cardiovascular disease.

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.

Association of oxidative stress and PON1 with LDL and HDL particle size in middle-aged subjects

BACKGROUND

Alterations in plasma lipoprotein subclass distributions affect atherosclerosis risk. Smaller, denser low-density lipoprotein (LDL) particles (sdLDL) are more susceptible to oxidation. In contrast, most of the protective effects of high-density lipoproteins (HDL) are attributable to larger particles. This study investigates the connection between LDL and HDL particle heterogeneity and oxidative stress, antioxidative defence (AOD) and paraoxonase (PON1) status in a healthy middle-aged Serbian population.

MATERIALS AND METHODS

LDL and HDL particle sizes and subclass distributions were measured by gradient gel electrophoresis in 104 men and 103 women, aged 53 +/- 9.4 years. PON1 activities and PON1(Q192R) phenotypes were determined with paraoxon and diazoxon as substrates. The oxidative stress/AOD status was estimated by measuring malondialdehyde (MDA) and superoxide-anion (O2*(-)) levels and superoxide-dismutase (SOD) activity.

RESULTS

Subjects with sdLDL had significantly higher MDA (P < 0.001) and O2*(-)(P < 0.05) levels and greater diazoxonase (DZOase) activity (P < 0.05) compared to subjects with larger LDL particles. A high MDA concentration was a significant predictor of the sdLDL phenotype (P < 0.005). Increased levels of and MDA were associated with smaller HDL(3) subclass abundance. Reduced HDL particle size was associated with lower DZOase activity (P < 0.01).

CONCLUSIONS

Even in the absence of symptoms of atherosclerosis, sdLDL particles are associated with increased oxidative stress, which may stimulate a compensatory rise in PON1 DZOase activity. Elevated oxidative stress may significantly affect HDL subclass distribution, resulting in the accumulation of smaller, denser HDL particles with diminished antioxidative capacity.

LDL particle subclasses, LDL particle size, and carotid atherosclerosis in the Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND

Previous studies showing that smaller low-density lipoprotein (LDL) size is associated with greater atherosclerotic risk did not adequately control for small and large LDL particle correlation.

METHODS AND RESULTS

We studied the association of lipoproteins measured by proton nuclear magnetic resonance spectroscopy with carotid intima-media thickness (IMT) in apparently healthy individuals (N = 5538, 38% White, 28% African American, 22% Hispanic, 12% Chinese). Small and large LDL particle concentrations (LDL-p) were inversely correlated (r = /-0.63, P < 0.0001). Controlling for risk factors but not for LDL subclass correlation, LDL size and small LDL-p separately were associated with IMT (-20.9 and 31.7 microm change in IMT per 1-S.D., respectively, both P < 0.001), but large LDL-p was not (4.9 microm, P = 0.27). When LDL subclasses were included in the same model, large and small LDL-p were both associated with IMT (36.6 and 52.2 microm higher IMT per 1-S.D., respectively, both P < 0.001; 17.7 and 11.6 microm per 100 nmol/L, respectively). LDL size was not significant after accounting for LDL subclasses and risk factors (P = 0.10).

CONCLUSION

Both LDL subclasses were significantly associated with subclinical atherosclerosis, with small LDL confounding the association of large LDL with atherosclerosis. Future studies of LDL size should account for the strong inverse correlation of LDL subclasses.

Statins and Peripheral Arterial Disease: Effects on Claudication, Disease Progression, and Prevention of Cardiovascular Events

Peripheral arterial disease (PAD) of the lower limbs is the third most important site of atherosclerotic disease alongside coronary heart disease (CHD) and cerebrovascular disease (CVD). Best medical treatment is beneficial even in patients who eventually need invasive treatment, as the safety, immediate success, and durability of intervention is greatly improved in patients who adhere to best medical treatment. In recent years, a number of studies have suggested that the ACE-inhibitor ramipril and different statins, together with antiplatelet drugs, reduce cardiovascular morbidity and mortality in PAD. Patients with PAD are really a category of patients with a very high cardiovascular risk burden for fatal and nonfatal cerebrovascular and cardiovascular events; therefore, they need to be treated not only for local problems deriving from arteriopathy (intermittent claudication, rest pain and/or ulcers) but, above all, for preventing vascular events. Statins not only lower the risk of vascular events, but they also improve the symptoms associated with PAD. Statins exert beneficial pleiotropic effects on hemostasis, vasculature and inflammatory markers; there is also evidence that statins improve renal function considering that the plasma creatinine level is considered as an emerging vascular risk factor.

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

BACKGROUND

Beyond total low-density-lipoproteins (LDL) levels, increasing evidence suggests that the 'quality' of LDL exerts a great influence on the cardiovascular risk. Several studies have also shown that the therapeutic modulation of LDL size is of benefit in reducing the risk of cardiovascular events. Hypolipidaemic treatment is able to alter LDL subclass distribution but strong variations have been noticed among different agents. Fibrates have a major impact on triglyceride metabolism and in modulating LDL size and subclasses, but variations exist among the different molecules.

METHODOLOGY

A literature search (by Medline and Scopus) was performed using the following headings: 'small dense LDL', 'LDL size', 'LDL subfractions', 'LDL subclasses', 'LDL distribution' and 'fenofibrate', 'bezafibrate', 'ciprofibrate' and 'gemfibrozil' up to 20 January 2007. The authors also manually reviewed the references of selected articles for any pertinent material.

RESULTS

Analysis of all published studies revealed that treatment with fenofibrate, ciprofibrate, bezafibrate and gemfibrozil is usually beneficial, and fenofibrate may be more efficacious than the other molecules. This is supported by using all the available techniques in subjects with a very wide range of lipid alterations.

CONCLUSION

Among the different agents, fenofibrate has been found to be particularly effective in modulating LDL size and subclasses in patients at higher cardiovascular risk, such as those with type 2 diabetes or the metabolic syndrome.

Polyacrylamide gradient gel electrophoresis of lipoprotein subclasses

High-density (HDL), low-density (LDL), and very-low-density (VLDL) lipoproteins are heterogeneous cholesterol-containing particles that differ in their metabolism, environmental interactions, and association with disease. Several protocols use polyacrylamide gradient gel electrophoresis (GGE) to separate these major lipoproteins into known subclasses. This article provides a brief history of the discovery of lipoprotein heterogeneity and an overview of relevant lipoprotein metabolism, highlighting the importance of the subclasses in the context of their metabolic origins, fates, and clinical implications. Various techniques using polyacrylamide GGE to assess HDL and LDL heterogeneity are described, and how the genetic and environmental determinations of HDL and LDL affect lipoprotein size heterogeneity and the implications for cardiovascular disease are outlined.

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.

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.

Significance of small dense low-density lipoprotein as a risk factor for coronary artery disease and acute coronary syndrome

Small dense LDL (sd-LDL) has recently emerged as an important coronary artery disease (CAD) risk factor. This study was performed to investigate how LDL particle size is related to CAD and acute coronary syndrome (ACS). Blood samples were collected from 504 patients that underwent coronary angiography to evaluate chest pain. The LDL particle size of these samples was measured. The mean LDL particle size was smaller in patients with angiographically proven CAD than in the controls (26.41 +/- 0.95 vs 26.73 +/- 0.64 nm, p < 0.001), and was negatively correlated with the Framingham risk score (r=-0.121, p=0.007). Patients with more extensive CAD had smaller LDL particles. LDL particle size was also smaller in patients with acute coronary syndrome as compared to non-ACS patients (26.09 +/- 1.42 vs 26.54 +/- 0.63 nm, p=0.011). These results suggest that sd-LDL is independently associated with the incidence and extent of CAD, and can be a risk factor for the development of ACS in the Korean population.

The oxidative modification hypothesis of atherosclerosis: The comparison of atherogenic effects on oxidized LDL and remnant lipoproteins in plasma

A tremendous number of articles on oxidized LDL (Ox-LDL) and scavenger receptor in macrophage have been published since Steinberg proposed Ox-LDL hypothesis as the major cause of atherosclerosis. This hypothesis has provided strong support for the efficacy of LDL lowering drugs, indicating that lowering LDL means lowering Ox-LDL in vivo. This manuscript proposed a new oxidative modification hypothesis that remnant lipoproteins determined as remnant-like lipoprotein particles (RLP), not LDL are the major oxidized lipoproteins in plasma, resulting from the plasma concentration of these oxidized lipoproteins. Remnant lipoproteins may play a pivotal role for the initiation of atherosclerosis via lectin-like oxidized LDL receptor-1 (LOX-1) in endothelial cells. Isolated remnant lipoproteins were found to be oxidized or susceptible to be oxidized in plasma, not necessary to be further oxidized in vitro as Ox-LDL. High similarity of proatherogenic and proinflammatory properties of isolated Ox-LDL and remnant lipoporteins have been reported and predicted the presence of similar oxidized phospholipids in both lipoproteins as bioactive components. These results suggest the possibility that reducing plasma remnant lipoproteins rather than LDL should be the target for hyperlipidemic therapy especially in patients with metabolic syndrome for the prevention of endothelial dysfunction in the initiation of atherosclerosis.

Visceral adipose tissue accumulation, secretory phospholipase A2-IIA and atherogenecity of LDL

OBJECTIVE

The aim of the present study was to investigate the combined impact of visceral adipose tissue (VAT) and secretory group IIA phospholipase A(2) (sPLA(2)-IIA) concentrations on the atherogenicity of low-density lipoprotein (LDL) particles among men.

SUBJECTS

Analyses were conducted in 74 mid-obese healthy men (age: (mean+/-s.d.) 37.9+/-11.7 years).

METHODS

Plasma levels of sPLA(2)-IIA were measured with a commercial ELISA and VAT levels were assessed by computed tomography. Distinct subpopulations of LDL particles were characterized from whole plasma using nondenaturating 2-16% gradient gel electrophoresis.

RESULTS

Data indicated that plasma sPLA(2)-IIA levels were approximately 29% (P=0.007) higher among men characterized by a higher accumulation of VAT (>142 vs < or =142 cm(2)). Men having high plasma sPLA(2)-IIA levels (> or =127.2 ng/dl, the median value), were characterized by higher levels of plasma cholesterol (C) and apolipoprotein (apo) B, LDL-C, LDL-apoB, oxidized LDL (OxLDL) and by smaller LDL particles compared to men with sPLA(2)-IIA<127.2 ng/dl. Multiple regression analyses showed that plasma triglycerides and sPLA(2)-IIA levels explained 22.7 and 11.8% of the variance in LDL peak particle size, respectively. Levels of VAT and of sPLA(2)-IIA were the strongest correlates of OxLDL levels explaining, respectively, 15.0 and 5.5% of their variability.

CONCLUSION

Both VAT and sPLA(2)-IIA levels modulate the atherogenecity of LDL by accounting for the reduction in their size and their susceptibility to oxidation.

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.

Obesity and lipids

Obesity increases cardiovascular risk through multiple mechanisms. Abdominal (visceral) adiposity is metabolically active and is largely responsible for the atherogenic dyslipidemia, hyperinsulinemia, hypertension, chronic inflammatory state, and prothrombotic state that constitute the metabolic syndrome, and the subsequent increased risk for cardiovascular disease and acute coronary events. Cholesterol guidelines for assessing cardiovascular risk have traditionally focused on low-density lipoprotein (LDL) levels, and reduction of plasma LDL has been shown to reduce cardiovascular events and total mortality. However, the cardiovascular risks associated with the dyslipidemia of obesity--characterized by low levels of high-density lipoprotein; increased triglycerides; increased subfractions of small, dense LDL; and increased levels of apolipoprotein B-100--are also now well recognized.