The Levels of Soluble Adhesion Molecules in Diabetic and Nondiabetic Patients with Combined Hyperlipoproteinemia and the Effect of Ciprofibrate Therapy

Selectins and Associated Adhesion Proteins in Inflammatory disorders

Inflammation is defined as the normal response of living tissue to injury or infection. It is important to emphasize two components of this definition. First, that inflammation is a normal response and, as such, is expected to occur when tissue is damaged. Infact, if injured tissue does not exhibit signs of inflammation this would be considered abnormal and wounds and infections would never heal without inflammation. Secondly, inflammation occurs in living tissue, hence there is need for an adequate blood supply to the tissues in order to exhibit an inflammatory response. The inflammatory response may be triggered by mechanical injury, chemical toxins, and invasion by microorganisms, and hypersensitivity reactions. Three major events occur during the inflammatory response: the blood supply to the affected area is increased substantially, capillary permeability is increased, and leucocytes migrate from the capillary vessels into the surrounding interstitial spaces to the site of inflammation or injury. The inflammatory response represents a complex biological and biochemical process involving cells of the immune system and a plethora of biological mediators. Cell-to-cell communication molecules such as cytokines play an extremely important role in mediating the process of inflammation. Inflammation and platelet activation are critical phenomena in the setting of acute coronary syndromes. An extensive exposition of this complex phenomenon is beyond the scope of this article (Rankin 2004).

The peroxisome proliferator-activated receptor-gamma agonist pioglitazone represses inflammation in a peroxisome proliferator-activated receptor-alpha-dependent manner in vitro and in vivo in mice

OBJECTIVES

Our aim was to investigate if the peroxisome proliferator-activated receptor (PPAR)-gamma agonist pioglitazone modulates inflammation through PPARalpha mechanisms.

BACKGROUND

The thiazolidinediones (TZDs) pioglitazone and rosiglitazone are insulin-sensitizing PPARgamma agonists used to treat type 2 diabetes (T2DM). Despite evidence for TZDs limiting inflammation and atherosclerosis, questions exist regarding differential responses to TZDs. In a double-blinded, placebo-controlled 16-week trial among recently diagnosed T2DM subjects (n = 34), pioglitazone-treated subjects manifested lower triglycerides and lacked the increase in soluble vascular cell adhesion molecules (sVCAM)-1 evident in the placebo group. Previously we reported PPARalpha but not PPARgamma agonists could repress VCAM-1 expression. Since both triglyceride-lowering and VCAM-1 repression characterize PPARalpha activation, we studied pioglitazone's effects via PPARalpha.

METHODS

Pioglitazone effects on known PPARalpha responses--ligand binding domain activation and PPARalpha target gene expression--were tested in vitro and in vivo, including in wild-type and PPARalpha-deficient cells and mice, and compared with the effects of other PPARgamma (rosiglitazone) and PPARalpha (WY14643) agonists.

RESULTS

Pioglitazone repressed endothelial TNFalpha-induced VCAM-1 messenger ribonucleic acid expression and promoter activity, and induced hepatic IkappaBalpha in a manner dependent on both pioglitazone exposure and PPARalpha expression. Pioglitazone also activated the PPARalpha ligand binding domain and induced PPARalpha target gene expression, with in vitro effects that were most pronounced in endothelial cells. In vivo, pioglitazone administration modulated sVCAM-1 levels and IkappaBalpha expression in wild-type but not PPARalpha-deficient mice.

CONCLUSIONS

Pioglitazone regulates inflammatory target genes in hepatic (IkappaBalpha) and endothelial (VCAM-1) settings in a PPARalpha-dependent manner. These data offer novel mechanisms that may underlie distinct TZD responses.

Measuring biomarkers to assess the therapeutic effects of PPAR agonists?

The metabolic syndrome is defined as a clustering of cardiovascular risk factors with insulin resistance, including dyslipidemia, coagulation disturbances and hypertension. Activators of the peroxisome proliferator-activated receptors (PPARs) modulate several of the metabolic risk factors predisposing to atherosclerosis. Fibrates are hypolipidemic drugs acting through activation of PPARα, whereas glitazones are insulin sensitizers activating PPARγ. In addition, these drugs exert pleiotropic anti-inflammatory actions. In this review, we will focus on the effects of fibrates and glitazones on biomarker modulation and their usefulness in the treatment of cardiovascular disease.

Gemfibrozil decreases atherosclerosis in experimental diabetes in association with a reduction in oxidative stress and inflammation

AIMS/HYPOTHESIS

It is postulated that peroxisome proliferator-activated receptor alpha agonists confer cardiovascular benefits in diabetes, independently of their effects on lipid metabolism. We investigated putative mechanisms responsible for these anti-atherogenic effects in an in vivo model of diabetes-associated atherosclerosis.

MATERIALS AND METHODS

Control and streptozotocin-induced diabetic apolipoprotein-deficient mice received gemfibrozil (100 mg kg(-1) day(-1)) or no treatment for 20 weeks. Aortic plaque deposition was assessed by Sudan IV staining and subsequent en face quantification. Superoxide production was measured using lucigenin-enhanced chemiluminescence. Markers of pathways including inflammation and oxidative stress were measured using real-time RT-PCR.

RESULTS

No significant effect of gemfibrozil was observed on glycated haemoglobin, cholesterol or insulin in diabetic mice. Diabetes was associated with a three-fold increase in plaque area and a significant increase in NADPH-dependent superoxide compared with control mice. Gemfibrozil significantly attenuated plaque area and superoxide production in diabetic mice. In addition, gemfibrozil reduced the expression of the genes encoding the NADPH oxidase subunits p47phox, gp91phox and Rac-1. In addition, gemfibrozil reduced the expression of the genes encoding nuclear factor kappa B (NF-kappaB) subunit, p65, the NF-kappaB-dependent chemokine monocyte chemoattractant protein-1, and tissue factor.

CONCLUSIONS/INTERPRETATIONS

This study demonstrates that gemfibrozil exerts anti-atherogenic actions, independently of changes in cholesterol and glucose metabolism. Such findings emphasise the possible usefulness of fibrates such as gemfibrozil in a setting of atherosclerosis even in the absence of dyslipidaemia.

Suppression of vascular cell adhesion molecule-1 expression by crocetin contributes to attenuation of atherosclerosis in hypercholesterolemic rabbits

To elucidate the molecular mechanism by which antioxidants alleviate atherosclerosis, we investigated the effect of crocetin, a naturally occurred carotinoid with potent antioxidant power, on vascular cell adhesion molecule-1 (VCAM-1) expression in atherosclerotic rabbits. Twenty-four male New Zealand White rabbits were allocated to three groups fed on standard diet (control group), high lipid diet (HLD group) or high lipid diet supplemented with crocetin (crocetin group), respectively. After 8 weeks of treatment, rabbits in HLD group developed severe hypercholesterolemia and atherosclerosis in aortas, together with a significantly up-regulated expression of both protein and mRNA for VCAM-1. In contrast, supplementation with crocetin resulted in markedly ameliorated atherosclerosis, coupled with a significantly decreased VCAM-1 expression, though plasma lipids level remained comparable to that of HLD group. Regression analysis revealed a positive correlation between VCAM-1 expression and the extent of atherosclerosis (P < 0.01). In addition, immunohistochemical analysis showed an increased activation of nuclear factor kappa B (NF-kappaB), a redox sensitive transcription factor essential for VCAM-1 expression, in aortas from rabbits fed on high lipid diet, which was evidently suppressed by crocetin supplementation. These findings suggest that the antiatherosclerotic effect of crocetin might be attributed, at least in part, to the suppressed expression of VCAM-1, which might result from reduced NF-kappaB activation. This study provides a further insight into the molecular mechanism by which antioxidants attenuate atherosclerosis and suggests a potential target for the treatment of atherosclerosis with antioxidants.

Peroxisome proliferator-activated receptors and inflammation

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptors family. PPARs are a family of 3 ligand-activated transcription factors: PPARalpha (NR1C1), PPARbeta/delta (NUC1; NR1C2), and PPARgamma (NR1C3). PPARalpha, -beta/delta, and -gamma are encoded by different genes but show substantial amino acid similarity, especially within the DNA and ligand binding domains. All PPARs act as heterodimers with the 9-cis-retinoic acid receptors (retinoid X receptor; RXRs) and play important roles in the regulation of metabolic pathways, including those of lipid of biosynthesis and glucose metabolism, as well as in a variety of cell differentiation, proliferation, and apoptosis pathways. Recently, there has been a great deal of interest in the involvement of PPARs in inflammatory processes. PPAR ligands, in particular those of PPARalpha and PPARgamma, inhibit the activation of inflammatory gene expression and can negatively interfere with pro-inflammatory transcription factor signaling pathways in vascular and inflammatory cells. Furthermore, PPAR levels are differentially regulated in a variety of inflammatory disorders in man, where ligands appear to be promising new therapies.

Circulating adhesion molecules in apoE-deficient mouse strains with different atherosclerosis susceptibility

Recruitment of inflammatory cells in the arterial wall by vascular adhesion molecules plays a key role in development of atherosclerosis. Apolipoprotein E-deficient (apoE(-/-)) mice have spontaneous hyperlipidemia and develop all phases of atherosclerotic lesions. We sought to examine plasma levels of soluble vascular cell adhesion molecule-1 (sVCAM-1) and sP-selectin in two apoE(-/-) strains C57BL/6 (B6) and BALB/c with early or advanced lesions. Mice were fed chow or a Western diet containing 42% fat, 0.15% cholesterol, and 19.5% casein. On either diet, BALB/c.apoE(-/-) mice developed much smaller atherosclerotic lesions and displayed significantly lower levels of sVCAM-1 and sP-selectin than B6.apoE(-/-) mice. The Western diet significantly elevated sVCAM-1 levels in both strains and sP-selectin levels in B6.apoE(-/-) mice. BALB/c.apoE(-/-) mice exhibited 2-fold higher HDL cholesterol levels on the chow diet and 15-fold higher HDL levels on the Western diet than B6.apoE(-/-) mice, although the two strains had comparable levels of total cholesterol and triglyceride. Thus, increased atherosclerosis is accompanied by increases in circulating VCAM-1 and P-selectin levels in the two apoE(-/-) mouse strains, and the high HDL level may protect against atherosclerosis by inhibiting the expression of adhesion molecules in BALB/c.apoE(-/-) mice.