A potent activator of PPARα and γ reduces the vascular cell recruitment and inhibits the intimal thickning in hypercholesterolemic rabbits

Molecular mechanisms and therapeutic perspectives of peroxisome proliferator-activated receptor α agonists in cardiovascular health and disease

The prevalence of cardiovascular disease (CVD) has been rising due to sedentary lifestyles and unhealthy dietary patterns. Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor regulating multiple biological processes, such as lipid metabolism and inflammatory response critical to cardiovascular homeostasis. Healthy endothelial cells (ECs) lining the lumen of blood vessels maintains vascular homeostasis, where endothelial dysfunction associated with increased oxidative stress and inflammation triggers the pathogenesis of CVD. PPARα activation decreases endothelial inflammation and senescence, contributing to improved vascular function and reduced risk of atherosclerosis. Phenotypic switch and inflammation of vascular smooth muscle cells (VSMCs) exacerbate vascular dysfunction and atherogenesis, in which PPARα activation improves VSMC homeostasis. Different immune cells participate in the progression of vascular inflammation and atherosclerosis. PPARα in immune cells plays a critical role in immunological events, such as monocyte/macrophage adhesion and infiltration, macrophage polarization, dendritic cell (DC) embedment, T cell activation, and B cell differentiation. Cardiomyocyte dysfunction, a major risk factor for heart failure, can also be alleviated by PPARα activation through maintaining cardiac mitochondrial stability and inhibiting cardiac lipid accumulation, oxidative stress, inflammation, and fibrosis. This review discusses the current understanding and future perspectives on the role of PPARα in the regulation of the cardiovascular system as well as the clinical application of PPARα ligands.

PPARγ in Atherosclerotic Endothelial Dysfunction: Regulatory Compounds and PTMs

The formation of atherosclerotic plaques is one of the main sources of cardiovascular disease. In addition to known risk factors such as dyslipidemia, diabetes, obesity, and hypertension, endothelial dysfunction has been shown to play a key role in the formation and progression of atherosclerosis. Peroxisome proliferator-activated receptor-gamma (PPARγ), a transcription factor belonging to the steroid superfamily, is expressed in the aorta and plays a critical role in protecting endothelial function. It thereby serves as a target for treating both diabetes and atherosclerosis. Although many studies have examined endothelial cell disorders in atherosclerosis, the role of PPARγ in endothelial dysfunction is still not well understood. In this review, we summarize the possible mechanisms of action behind PPARγ regulatory compounds and post-translational modifications (PTMs) of PPARγ in the control of endothelial function. We also explore the potential use of endothelial PPARγ-targeted agents in the prevention and treatment of atherosclerosis.

Effects of fenofibrate on lipid profiles, cholesterol ester transfer activity, and in-stent intimal hyperplasia in patients after elective coronary stenting

Background

The association between modulation of detailed lipoprotein profiles and cholesterol ester transfer (CET) activity by peroxisome proliferator-activated receptor (PPAR)-a agonists in patients with coronary artery disease remains unclear. We assessed lipid profiles, plasma CET activity, and in-stent intimal hyperplasia after fenofibrate treatment in patients who underwent elective coronary stenting.

Methods

Forty-three consecutive patients who underwent elective coronary stenting were randomized to the fenofibrate group (300 mg/day for 25 weeks, n = 22) or the control group (n = 21). At baseline and follow up, CET activity and lipoprotein profiles were measured, and quantitative coronary angiography was performed.

Results

In the fenofibrate group, the levels of large very low-density lipoprotein cholesterol, and small low-density lipoprotein (LDL) cholesterol decreased and those of small high-density lipoprotein (HDL) cholesterol increased. Besides, CET activity decreased independent of the effect of fenofibrate on total and LDL cholesterol. The reduction of CET activity significantly correlated with the increase in LDL particle size (r = 0.47, P = 0.03) and the decrease of triglycerides in large HDL subclasses (r = 0.48, P = 0.03). Although there were no significant differences in restenosis parameters between the two groups, low CET activity significantly correlated with the inhibition of neointimal hyperplasia (r = 0.56, P = 0.01).

Conclusions

Fenofibrate inhibited CET activity and thereby improved atherogenic lipoprotein profiles, and reduced intimal hyperplasia after coronary stenting.

Imbalance of peroxisome proliferator-activated receptor gamma and adiponectin predisposes Kawasaki disease patients to developing atherosclerosis

BACKGROUND

It remains controversial whether Kawasaki disease (KD) is a risk factor for the onset of atherosclerosis. An imbalance of peroxisome proliferator-activated receptor γ (PPARγ) and adiponectin appears to play a role in the onset of atherosclerosis in adults, and we therefore examined PPARγ mRNA expression and adiponectin profiles in the peripheral white blood cells obtained from KD patients.

METHODS

A total of 50 subjects were studied: nine patients with acute KD, 20 patients with convalescent KD, and 21 age-matched controls. The gene expression of PPARγ, monocyte chemoattractant protein-1, and CC chemokine receptor 2 present in the blood were quantified. The relative gene expression, adiponectin levels, and the three adiponectin isoforms were compared among the subjects.

RESULTS

The abundance of PPARγ and CC chemokine receptor 2 mRNA was significantly increased in convalescent KD patients. The monocyte chemoattractant protein-1 level was also increased in convalescent KD patients. The level of high-molecular-weight adiponectin was significantly lower in convalescent patients compared to controls. The PPARγ transcription levels negatively correlated with apolipoprotein A-I levels in acute KD patients.

CONCLUSIONS

The transcript abundance of PPARγ and low levels of high-molecular-weight adiponectin in KD patients may have important clinical implications on the development of premature atherosclerosis. Because the potential risk for developing atherosclerosis has not yet been verified, long-term observation is important, even in convalescent KD patients without coronary artery lesions.

Sclerochorioretinal abnormalities in hypercholesterolemic rabbits treated with rosiglitazone

BACKGROUND AND OBJECTIVE

To evaluate early retinal, choroidal, and scleral abnormalities induced by a hypercholesterolemic diet and the prevention of these abnormalities after oral administration of rosiglitazone in rabbits.

MATERIALS AND METHODS

Fifty-four New Zealand rabbits were divided into four study groups: control group, normal diet; group 1, hypercholesterolemic diet; group 2, hypercholesterolemic diet associated with daily administration of 3 mg of rosiglitazone from day 14 after beginning the diet; and group 3, hypercholesterolemic diet associated with daily administration of 3 mg of rosiglitazone since the beginning of the experiment. Sclera and choroid underwent histologic and histomorphometric analyses. Retina underwent immunohistochemical analysis with anti-calretinin and anti-glial fibrillary acidic protein (GFAP) antibodies.

RESULTS

No abnormalities were observed in the control group. Group 1 had significant increases in scleral and choroidal thicknesses compared with the control group (P < .01) and group 3 (P < .05). Group 1 presented significant increases in immunoreactivity (P < .001) to the anti-calretinin antibody compared with the other groups. Groups 2 and 3 had significant (P < .002) increases in calretinin immunoreactivity compared with the control group. GFAP was negative in all groups.

CONCLUSION

The hypercholesterolemic diet induced early retinal, choroidal, and scleral abnormalities. Rosiglitazone preserved the structural anatomy.

Peroxisome proliferator-activated receptor-gamma(PPARgamma) agonist improves coronary artery endothelial function in diabetic patients with coronary artery disease

The aim of this study was to assess the effect of rosiglitazone on endothelial function of the coronary arteries and on plasma levels of inflammatory markers in diabetic patients with coronary artery disease (CAD). Fifty-six patients with type 2 diabetes and CAD were randomized to receive either rosiglitazone (4 mg/day) or a control for 12 weeks. The coronary flow velocity reserve (CFVR) was assessed using transthoracic Doppler echocardiography at baseline and after 12 weeks. After 12 weeks of rosiglitazone treatment, plasma levels of C-reactive protein were significantly decreased and the median CFVR was significantly increased compared with baseline levels and compared with the control group. These results suggest that, in addition to its beneficial metabolic effects, rosiglitazone, via its anti-inflammatory effects, may improve endothelial function of the coronary arteries in patients with diabetes and CAD.

Regulation of arterial remodeling and angiogenesis by urokinase-type plasminogen activatorThis article is one of a selection of papers from the NATO Advanced Research Workshop on Translational Knowledge for Heart Health (published in part 2 of a 2-part Special Issue)

A wide variety of disorders are associated with an imbalance in the plasminogen activator system, including inflammatory diseases, atherosclerosis, intimal hyperplasia, the response mechanism to vascular injury, and restenosis. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that in addition to its fibrinolytic and matrix degradation capabilities also affects growth factor bioavailability, cytokine modulation, receptor shedding, cell migration and proliferation, phenotypic modulation, protein expression, and cascade activation of proteases, inhibitors, receptors, and modulators. uPA is the crucial protein for neointimal growth and vascular remodeling. Moreover, it was recently shown to be implicated in the stimulation of angiogenesis, which makes it a promising multipurpose therapeutic target. This review is focused on the mechanisms by which uPA can regulate arterial remodeling, angiogenesis, and cell migration and proliferation after arterial injury and the means by which it modulates gene expression in vascular cells. The role of domain specificity of urokinase in these processes is also discussed.

Use of rosiglitazone before and after vascular injury in hypercholesterolemic rabbits: Assessment of neointimal formation

Objectives

To analyse the effects of rosiglitazone administered at different times on neointimal formation in hypercholesterolemic rabbits following vascular injury.

Methods

Thirty-nine rabbits on a hypercholesterolemic diet were included. The animals underwent balloon catheter injury to the right iliac artery on day 14. They were divided into three groups as follows: control group, 13 rabbits without rosiglitazone; group I, 13 rabbits treated with rosiglitazone (3 mg/Kg body weight/day) for 28 days after the vascular injury; and group II, 13 rabbits treated with rosiglitazone (3 mg/Kg body weight/day) during all the experiment (42 days). Histological analysis was done by an experienced pathologist who was unaware of the rosiglitazone treatment. Histomorphometric parameters were performed by calculation of the luminal and intimal layer area, and intima/media layer area ratio (the area of the intimal layer divided by the area of the medial layer).

Results

Intimal area was significantly lower in group II vs. CG (p = 0.024) and group I (p = 0.006). Luminal layer area was higher in group II vs. CG (p < 0.0001) and group I (p < 0.0001). Intima/media layer area ratio was equal between CG and group I. Intima/media layer ratio area was significantly lower in group II vs. control group (p < 0.021) and group I (p < 0.003). There was a significant reduction of 65% and 71% in intima/media layer area ratio in group II vs. control group and group I, respectively.

Conclusion

Pretreatment with rosiglitazone in hypercholesterolemic rabbits submitted to vascular injury significantly reduces neointimal formation.

Newly developed PPAR-alpha agonist (R)-K-13675 inhibits the secretion of inflammatory markers without affecting cell proliferation or tube formation

Peroxisome proliferator-activated receptor-alpha (PPAR-alpha) is a key regulator of lipid and glucose metabolism and has been implicated in inflammation. The vascular effects of activator for PPARs, particularly PPAR-alpha, on vascular cells remain to be fully elucidated. Therefore, we analyzed the hypothesis that newly developed (R)-K-13675 decreases the secretion of inflammatory markers without affecting cell proliferation or tube formation. Human coronary endothelial cells (HCECs) were maintained in different doses of (R)-K-13675 under serum starvation. After 20h, the levels of monocyte chemoattractant protein-1 (MCP-1), regulated on activation, normal T expressed and secreted (RANTES), interleukin-6 (IL-6) and interferon-gamma (INF-gamma) secreted in the medium and nuclear factor kappa B (NFkappaB) in cell lysate were analyzed using enzyme-linked immunosorbent assays (ELISA). Upon treatment with (R)-K-13675 at 0, 10, 20, 50 and 100nM, with the inflammatory markers at 0nM as 100 (arbitrary units), MCP-1 levels were significantly suppressed (94+/-9, 88+/-2, 80+/-5 and 74+/-11, respectively). RANTES, IL-6 and INF-gamma levels were also significantly suppressed (RANTES: 92+/-2, 74+/-9, 64+/-7 and 60+/-2, respectively, IL-6: 97+/-2, 89+/-10, 82+/-1 and 66+/-7, respectively, INF-gamma: 98+/-7, 94+/-3, 76+/-8 and 64+/-8, respectively). NFkappaB levels were also decreased to 91+/-5, 90+/-5, 84+/-7 and 82+/-8, respectively. In addition, (R)-K-13675 did not affect HCEC proliferation or tube formation at up to 100nM. Thus, (R)-K-13675 was associated with the inhibition of inflammatory responses without affecting cell proliferation or angiogenesis, and subsequently may induce an anti-atherosclerotic effect.

Effects of rosiglitazone on contralateral iliac artery after vascular injury in hypercholesterolemic rabbits

Background

The objective was to evaluate the effects of rosiglitazone on iliac arteries of hypercholesterolemic rabbits undergoing balloon catheter injury in the contralateral iliac arteries.

Methods

White male rabbits were fed a hypercholesterolemic diet for 6 weeks and divided into two groups as follows: rosiglitazone group, 14 rabbits treated with rosiglitazone (3 mg/Kg body weight/day) during 6 weeks; and control group, 18 rabbits without rosiglitazone treatment. All animals underwent balloon catheter injury of the right iliac artery on the fourteenth day of the experiment.

Results

There was no significant difference in intima/media layer area ratio between the control group and the rosiglitazone group. Rosiglitazone did not reduce the probability of lesions types I, II, or III (72.73% vs. 92.31%; p = 0.30) and types IV or V (27.27% vs. 7.69%; p = 0.30). There were no differences in the extent of collagen type I and III deposition or in the percentage of animals with macrophages in the intima layer. The percentage of rabbits with smooth muscle cells in the intima layer was higher in rosiglitazone group (p = 0.011).

Conclusion

These findings demonstrate that rosiglitazone given for 6 weeks did not prevent atherogenesis at a vessel distant from the injury site.

3-(4'-hydroxyl-3',5'-dimethoxyphenyl)propionic acid, an active principle of kimchi, inhibits development of atherosclerosis in rabbits

The effects of 3-(4'-hydroxyl-3',5'-dimethoxyphenyl)propionic acid (HDMPPA) originating from Korean cabbage kimchi were investigated, showing an antioxidant effect on the prevention of atherosclerosis in hypercholesterolemic rabbits. Twenty-one 3-month-old rabbits were fed an atherogenic diet containing 0.5% (w/w) cholesterol and 10% (w/w) coconut oil, whereas another two groups were given an atherogenic diet with intravenous injection of either HDMPPA or simvastatin (0.33 mg/kg/day) for 4 weeks. HDMPPA inhibited the oxidative modification of low-density lipoprotein (IC 50 = 1.4 microg/mL) and increased 2,2'-diphenyl-1-picrylhydrazyl radical scavenging activity (IC 50 = 0.78 microg/mL) in a dose-dependent manner. In hypercholesterolemic rabbits, the thickness of intima of aorta of the HDMPPA group was significantly reduced (control versus HDMPPA, 42%; simvastatin, 38%) without a plasma cholesterol-lowering effect. Thiobarbituric acid reactive substance formation in the plasma of the HDMPPA group was significantly decreased compared to that of the control group. Furthermore, the generation of vascular reactive oxygen species in HDMPPA group was suppressed as the cyclooxygenase-2 protein level decreased. These findings suggest that HDMPPA prevents the development of aortic atherosclerosis in high-cholesterol-fed rabbits. The antiatherosclerotic effect of HDMPPA may be due to an antioxidative effect at a low dose without cholesterol-lowering effects.

A novel peroxisome proliferator--activated receptor alpha/gamma dual agonist ameliorates dyslipidemia and insulin resistance in prediabetic rhesus monkeys

TAK-559, a newly developed non-thiazolidinedione, activates both peroxisome proliferator-activated receptors alpha and gamma. We investigated the effects of TAK-559 on dyslipidemia and insulin resistance in nonhuman primates. Five adult male obese prediabetic rhesus monkeys were studied on vehicle and after TAK-559 treatment (0.3, 1.0, 3.0 mg/kg per day) for a total of 12 weeks. No significant changes were observed in body weight and fasting plasma glucose, total plasma cholesterol, very low-density lipoprotein-triglyceride, and low-density lipoprotein cholesterol levels. TAK-559 treatment resulted in significant elevation of circulating high-density lipoprotein (HDL) cholesterol levels, consisting of an increase in large HDL particles and a decrease in small dense HDL particles. Nuclear magnetic resonance data exhibited a less atherogenic lipoprotein profile with treatment. Plasma triglyceride and apolipoprotein B-100 levels decreased, whereas apolipoprotein A-I increased during TAK-559 treatment. Hyperinsulinemia and insulin resistance (quantitative insulin sensitivity check index and homeostasis model assessment) were significantly corrected with the highest dose of 3.0 mg/kg per day in these prediabetic monkeys. In addition, no adverse effects on representative liver function parameters were observed during the study period. These results suggest that TAK-559 had beneficial effects on lipoprotein profiles and insulin sensitivity, without any side effect on body weight, which suggests that TAK-559 may provide a potentially safe approach for delaying the onset of type 2 diabetes mellitus and may reduce the risk of cardiovascular disease. The positive effects of TAK-559 in nonhuman primates have led to further clinical trials of TAK-559 in Europe and the United States.

Inflammation in diabetes mellitus: role of peroxisome proliferator-activated receptor-alpha and peroxisome proliferator-activated receptor-gamma agonists

Patients with type 2 diabetes mellitus and/or the metabolic syndrome have considerable cardiovascular risk. Treatment with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) and with antihypertensive and some antihyperglycemic agents reduces this risk, but residual macrovascular morbidity and mortality persist, even in patients assigned to intensive multifactorial intervention programs. Therapeutic strategies that target inflammation and lipid abnormalities not well addressed by statins may offer additional opportunities for improving the prognosis of these patients. Inflammation, a key mechanism of atherogenesis, appears to have particular relevance to diabetic vascular complications, as well as in the development of diabetes itself. Oxidative stress and hyperglycemia also figure among the pathogenic factors that promote cardiovascular complications in patients with the metabolic syndrome and/or diabetes and may augment the ongoing inflammation. Peroxisome proliferator-activated receptor (PPAR)-alpha and PPAR-gamma, members of the nuclear receptor family, form ligand-activated transcription factors that regulate key important metabolic pathways. PPARs have become therapeutic targets through the use of the fibrate class of antidyslipidemic drugs (PPAR-alpha) and the insulin-sensitizing thiazolidinediones (PPAR-gamma). The activation of these PPARs may also suppress inflammation and atherosclerosis. Recent clinical trials (Fenofibrate Intervention and Event Lowering in Diabetes [FIELD], Prospective Pioglitazone Clinical Trial in Macrovascular Events [PROactive]) have considered the impact of these PPAR agonists on cardiovascular disease, with mixed effects that require careful analysis, especially given ongoing trials and additional PPAR agonists in development.

Pioglitazone Inhibits In-Stent Restenosis in Atherosclerotic Rabbits by Targeting Transforming Growth Factor-β and MCP-1

Objective— Although emerging data from preclinical and clinical studies suggests a reduction of in-stent restenosis with peroxisome proliferator-activated receptor (PPAR)-γ agonists, the reduction of neointimal growth via anti-inflammatory mechanisms has not been explored.

Methods and Results— Hypercholesterolemic New Zealand White rabbits (n=45) received bilateral balloon-expandable stents implanted into atherosclerotic iliac arteries. Animals were randomized to oral pioglitazone 3 (low dose) or 10 mg/kg per day (high dose) started on the day of stent implantation; control rabbits received placebo. Tissue harvest was performed 28 days after stenting, and stented segments underwent histology, morphometry, immunostaining for macrophages, and scanning electron microscopy. In selected animals, stented arterial segments were placed in organoid culture for 48 hours, and the conditioned media was assayed for 23 different cytokines. There was a 21% reduction in neointimal area for high-dose pioglitazone treated versus placebo rabbits ( P <0.005), which was associated with a significant reduction of neointimal macrophages. Analysis of conditioned media revealed an 82% and 74% reduction in the release of monocyte chemoattractant protein-1 (MCP-1) ( P <0.007) and transforming growth factor (TGF)-β1 ( P <0.01), respectively, in stented segments from animals treated with 10 mg/kg per day pioglitazone versus placebo.

Conclusions— Oral pioglitazone suppresses in-stent neointimal growth by limiting local inflammatory pathways and may be useful as an adjunctive therapy in patients undergoing percutaneous interventions.

Selective PPAR modulators, dual and pan PPAR agonists: multimodal drugs for the treatment of Type 2 diabetes and atherosclerosis

More than 70% of patients with Type 2 diabetes mellitus (T2DM) die because of cardiovascular diseases. Current therapeutic strategies are based on separate treatment of insulin resistance and dyslipidaemia. Development of drugs with multimodal activities should improve management of the global cardiovascular risk of T2DM patients and result in better patient compliance. New therapeutic strategies are aimed at targeting the entire spectrum of dysfunctioning organs, cells and regulatory pathways implicated in the pathogenesis of T2DM, dyslipidaemia and atherosclerosis. PPAR family members play major roles in the regulation of lipid metabolism, glucose homeostasis and inflammatory processes, making these transcription factors ideal targets for therapeutic strategies against these diseases. This review discusses why PPARs and development of novel selective PPAR modulators, dual and pan PPAR agonists constitute promising approaches for the treatment of diabetes, dyslipidaemia and atherosclerosis.