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

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.

Alterations in cell adhesion molecules and other biomarkers of cardiovascular disease in patients with metabolic syndrome

Metabolic syndrome is considered a hyperinsulinemic and inflammatory state closely associated to endothelial dysfunction causing an increased incidence of ischemic cardiovascular events and high mortality. The main objective of the present study was to determine whether leukocitary and soluble cell adhesion molecules were altered in patients with metabolic syndrome in comparison with control subjects. Cell adhesion molecules, mainly of leukocitary location, have been not previously evaluated in specifically designed cross-sectional studies involving male patients with metabolic syndrome. Moreover, other circulating markers of different candidate atherogenic risk parameters were also studied and the potential existence of a progressive relation between the number of metabolic syndrome components and the above mentioned biomarkers was analyzed. Thirty one male patients with metabolic syndrome (ATPIII definition) and 56 male control subjects were studied. We evaluated different markers of insulin resistance, inflammation and atherosclerosis, as well as protective factors. Patients with metabolic syndrome showed (a) hypoadiponectinemia (4551 +/- 2302 ng/ml vs. 5865 +/- 2548 ng/ml, respectively; p<0.05), (b) an atherogenic lipid and lipoprotein profile, (c) altered HDL chemical composition accompanied by higher cholesteryl ester-triglyceride interchange carried out by CETP, (d) diminished Lp-PLA(2) activity (6.5 +/- 1.9 vs. 7.3 +/- 2.2, p<0.05, respectively), antioxidant enzyme related with LDL oxidation, which was positively associated with QUICKI and negatively with VCAM-1 and lymphocyte CD18, and (e) high soluble (VCAM-1: 17 +/-5 vs. 13 +/- 4 ng/ml, respectively; p<0.0005) and leukocyte adhesion molecule expression (monocyte CD54: 52 +/- 15 vs. 45 +/-12 arbitrary units, respectively; p<0.0005; and lymphocyte CD49d: 312 +/- 56 vs. 284 +/- 64 arbitrary units, respectively; p < 0.05). The increment in leukocyte and soluble cell adhesion molecules, crucial for leukocyte interaction with the endothelium and migration into the artery wall, in combination with the other disorders described above reinforce the presence of a clinical status with high propensity to type 2 diabetes and atherosclerotic cardiovascular disease.

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.

Update on the role of the atherogenic lipoprotein phenotype in cardiovascular prevention

Higher plasma triglyceride levels and decreased HDL-cholesterol concentrations are usually accompanied by the presence of small, dense LDL in the so-called lipid triad or ‘atherogenic lipoprotein phenotype’. This phenotype is highly atherogenic and its prevalence may suggest an even higher overall burden of atherosclerotic disease as compared with that associated with hypercholesterolemia. As stated by the National Cholesterol Education Program Adult Treatment Panel III, there is evidence suggesting each component of this lipid triad is individually atherogenic. However, the relative contribution of each component cannot be easily determined. Therefore, it has been suggested to consider the atherogenic lipoprotein phenotype as a whole as a risk factor. This is supported by data from epidemiological studies considering high-risk populations, which showed that the contribution to cardiovascular risk of each individual component cannot be dissected from the sum of all factors. We recently investigated the prevalence of the atherogenic lipoprotein phenotype in different categories of patients at higher cardiovascular risk: with coronary and noncoronary forms of atherosclerosis or metabolic diseases, including Type 2 diabetes, polycystic ovary syndrome and growth hormone deficiency. Subjects with higher triglyceride levels, decreased HDL-cholesterol concentrations and increased levels of small, dense LDL (i.e., subjects with the atherogenic lipoprotein phenotype) are common in coronary and noncoronary forms of atherosclerosis. In the future, it may be possible to measure the presence of small, dense LDL to identify subgroups at higher cardiovascular risk.

Innate immune system regulation of nuclear hormone receptors in metabolic diseases

The immune system modulates a number of biological processes to properly defend against pathogens. Here, we review how crosstalk between nuclear hormone receptors and the innate immune system may influence multiple biological functions during an immune response. Although nuclear hormone receptor repression of innate immune responses and inflammation has been well studied, a number of new studies have identified repression of nuclear hormone receptor signaling by various innate immune responses. IFN regulatory factor 3, a key transcription factor involved in the induction of antiviral genes, may play a role in mediating such crosstalk between the innate immune response and nuclear receptor-regulated metabolism. This crosstalk mechanism is now implicated in the pathogenesis of atherosclerosis and Reye's syndrome and could provide an explanation for other pathogen-associated metabolic and developmental disorders.