The effect of fenofibrate treatment on endothelium-dependent relaxation induced by oxidative modified low density lipoprotein from hyperlipidemic patients

The Effect of Hyperlipidemia on the Course of Diabetic Retinopathy—Literature Review

Diabetes mellitus is a very important social issue, and its retinal complications continue to be one of the major causes of blindness worldwide. The effect of glucose level on the development of retinal retinopathy has been the subject of numerous studies and is well understood. Hypertension and hyperlipidemia have been known to be important risk factors in the development of diabetes complications. However, the mechanisms of this effect have not been fully explained and raise a good deal of controversy. The latest research results suggest that some lipoproteins are closely correlated with the incidence of diabetic retinopathy and that by exerting an impact on their level the disease course can be modulated. Moreover, pharmacotherapy which reduces the level of lipids, particularly by means of statins and fibrate, has been shown to alleviate diabetic retinopathy. Therefore, we have decided to review the latest literature on diabetic retinopathy with respect to the impact of hyperlipidemia and possible preventive measures

Effects of Modified Low-Density Lipoproteins and Fenofibrate on an Outer Blood-Retina Barrier Model: Implications for Diabetic Retinopathy

Purpose: There is a lack of treatment for early diabetic retinopathy (DR), including blood-retina barrier (BRB) breakdown. The robust clinical benefit of fenofibrate in DR provides an opportunity to explore disease mechanisms and therapeutic targets. We have previously found that modified lipoproteins contribute to DR and that fenofibrate protects the inner BRB. We now investigate (1) whether modified lipoproteins elicit outer BRB injury and (2) whether fenofibrate may alleviate such damage.

Methods: Human retinal pigment epithelium ARPE-19 cells were cultured in semipermeable transwells to establish a monolayer barrier and then exposed to heavily oxidized, glycated low-density lipoprotein (HOG-LDL, 25–300 mg/L, up to 24 h) versus native (N)-LDL. Transepithelial electric resistance (TEER) and FITC-dextran permeability were measured. The effects of fenofibrate, its active metabolite fenofibric acid, and other peroxisome proliferator-activated receptor (PPARα) agonists (gemfibrozil, bezafibrate, and WY14643) were evaluated, with and without the PPARα antagonist GW6471 or the adenosine monophosphate-activated protein kinase (AMPK) inhibitor Compound C.

Results: HOG-LDL induced concentration- and time-dependent barrier impairment, decreasing TEER and increasing dextran leakage, effects that were amplified by high glucose. Fenofibric acid, but not fenofibrate, gemfibrozil, bezafibrate, or WY14643, attenuated barrier impairment. This effect was reversed significantly by Compound C, but not by GW6471.

Conclusions: Modified lipoproteins elicited outer BRB injury in an experimental model, which was reduced by fenofibric acid through a PPARα-independent, AMPK-mediated mechanism. These findings suggest a protective role of fenofibric acid on the outer BRB in diabetic retina.

Oxidized Low-Density Lipoprotein and the Incidence of Proliferative Diabetic Retinopathy and Clinically Significant Macular Edema Determined From Fundus Photographs

IMPORTANCE

Studies have shown oxidized low-density lipoprotein to be associated with the incidence of proliferative retinopathy and other complications of type 1 diabetes mellitus. Because low-risk interventions are available to modify oxidized low-density lipoprotein, it is important to examine the relationships between this factor and the incidence of proliferative retinopathy and of macular edema, 2 important causes of visual impairment in people with type 1 diabetes.

OBJECTIVE

To determine the association of oxidized low-density lipoprotein with the worsening of diabetic retinopathy and the incidence of proliferative retinopathy and of macular edema.

DESIGN, SETTING, AND PARTICIPANTS

Of 996 participants with type 1 diabetes in the Wisconsin Epidemiologic Study of Diabetic Retinopathy, 730 were examined up to 4 times (1990-1992, 1994-1996, 2005-2007, and 2012-2014) over 24 years and had assays of oxidized low-density lipoprotein and fundus photographs gradable for diabetic retinopathy and macular edema. Analyses started July 2014 and ended February 2015.

MAIN OUTCOMES AND MEASURES

Worsening of diabetic retinopathy, incidence of proliferative diabetic retinopathy, and incidence of macular edema as assessed via grading of color stereo film fundus photographs. The levels of oxidized low-density lipoprotein collected from serum samples at the time of each examination were measured in 2013 and 2014 from frozen serum.

RESULTS

The cohort at baseline had a mean (SD) level of oxidized low-density lipoprotein of 30.0 (8.5) U/L. While adjusting for duration of diabetes, glycated hemoglobin A1c level, and other factors, we found that neither the level of oxidized low-density lipoprotein at the beginning of a period nor the change in it over a certain period was associated with the incidence of proliferative diabetic retinopathy (hazard ratio [HR], 1.11 [95% CI, 0.91-1.35], P = .30; odds ratio [OR], 1.77 [95% CI, 0.99-3.17], P = .06), the incidence of macular edema (HR, 1.04 [95% CI, 0.83-1.29], P = .74; OR, 1.08 [95% CI, 0.44-2.61], P = .87), or the worsening of diabetic retinopathy (HR, 0.94 [95% CI, 0.83-1.07], P = .34; OR, 1.32 [95% CI, 0.83-2.09], P = .24).

CONCLUSIONS AND RELEVANCE

Our findings do not provide evidence for a relationship between increasing levels of serum oxidized low-density lipoprotein and the incidence of macular edema or the worsening of diabetic retinopathy in persons with type 1 diabetes. The potential increase in the HR for incident proliferative retinopathy, with an increase in oxidized low-density lipoprotein level over the preceding period, warrants further investigation of this relationship.

Modified Lipoproteins in Diabetic Retinopathy: A Local Action in the Retina

Clinical epidemiological studies have revealed relatively weak, yet statistically significant, associations between dyslipidemia/dyslipoproteinemia and diabetic retinopathy (DR). Recent large interventional studies, however, demonstrated an unexpectedly robust efficacy of fenofibrate on the development of DR, possibly independent of plasma lipids. To unify the apparent discrepancies, we hypothesize that plasma lipoproteins play an indirect but important role in DR, contingent on the integrity of the blood-retina-barrier (BRB). In retinas with an intact BRB, plasma lipoproteins may be largely irrelevant; however, important effects become operative after the BRB is impaired in diabetes, leading to lipoprotein extravasation and subsequent modification, hence toxicity to the neighbouring retinal cells. In this hypothesis, BRB leakage is the key, plasma lipoprotein concentrations mainly modulate its consequences, and fenofibrate has intra-retinal actions. This review summarizes our current knowledge of the direct effects and mechanisms of modified lipoproteins on retinal cells and their potential contribution to the pathogenesis of DR.

Fenofibrate attenuates tubulointerstitial fibrosis and inflammation through suppression of nuclear factor-κB and transforming growth factor-β1/Smad3 in diabetic nephropathy

Fibrates, the ligands of peroxisome proliferator-activated receptor-alpha, have been shown to have a renal protective action in diabetic models of renal disease, but the mechanisms underlying this effect are unknown. In the present study, we sought to investigate in greater detail the effect of fenofibrate and its mechanism of action on renal inflammation and tubulointerstitial fibrosis in an animal model of type 2 diabetes mellitus. Twelve-week-old non-diabetic Zucker lean (ZL) and Zucker diabetic fatty (ZD) rats were treated with vehicle or fenofibrate for 10 weeks. mRNA and protein analyses were performed by real-time polymerase chain reaction, Western blot and immunostaining. The diabetic condition of ZD rats was associated with an increase in collagen and alpha-smooth muscle actin accumulation in the kidney, which was significantly reduced by fenofibrate. Chronic treatment of ZD rats with fenofibrate attenuated renal inflammation and tubular injury as evidenced by a decrease in mRNA and protein expression of secreted phosphoprotein-1, monocyte chemotactic protein-1 and kidney injury molecule-1 in the kidneys. Renal interstitial macrophage infiltration was also significantly reduced in the kidneys of fenofibrate-treated diabetic animals. Moreover, renal nuclear factor (NF)-kappaB DNA-binding activity, transforming growth factor (TGF)-beta1 and phospho-Smad3 proteins were significantly higher in ZD animals compared with ZL ones. This increase in NF-kappaB activity, TGF-beta1 expression and Smad3 phosphorylation was greatly attenuated by fenofibrate in the diabetic kidneys. Taken together, fenofibrate suppressed NF-kappaB and TGF-beta1/Smad3 signaling pathways and reduced renal inflammation and tubulointerstitial fibrosis in diabetic ZD animals.

PPAR-alpha activator fenofibrate increases renal CYP-derived eicosanoid synthesis and improves endothelial dilator function in obese Zucker rats

Previous studies have shown that the synthesis of renal cytochrome P-450 (CYP)-derived eicosanoids is downregulated in genetic or high-fat diet-induced obese rats. Experiments were designed to determine whether fenofibrate, a peroxisome proliferator-activated receptor (PPAR)-alpha agonist, would induce renal eicosanoid synthesis and improve endothelial function in obese Zucker rats. Administration of fenofibrate (150 mg.kg(-1).day(-1) for 4 wk) significantly reduced plasma insulin, triglyceride, and total cholesterol levels in obese Zucker rats. CYP2C11 and CYP2C23 proteins were downregulated in renal vessels of obese Zucker rats. Consequently, renal vascular epoxygenase activity decreased by 15% in obese Zucker rats compared with lean controls. Chronic fenofibrate treatment significantly increased renal cortical and vascular CYP2C11 and CYP2C23 protein levels in obese Zucker rats, whereas it had no effect on epoxygenase protein and activity in lean Zucker rats. Renal cortical and vascular epoxygenase activities were consequently increased by 54% and 18%, respectively, in fenofibrate-treated obese rats. In addition, acetylcholine (1 microM)-induced vasodilation was significantly reduced in obese Zucker kidneys (37% +/- 11%) compared with lean controls (67% +/- 9%). Chronic fenofibrate administration increased afferent arteriolar responses to 1 microM of acetylcholine in obese Zucker rats (69% +/- 4%). Inhibition of the epoxygenase pathway with 6-(2-propargyloxyphenyl)hexanoic acid attenuated afferent arteriolar diameter responses to acetylcholine to a greater extent in lean compared with obese Zucker rats. These results demonstrate that the PPAR-alpha agonist fenofibrate increased renal CYP-derived eicosanoids and restored endothelial dilator function in obese Zucker rats.

Effect of fenofibrate on the level of asymmetric dimethylarginine in individuals with hypertriglyceridemia

OBJECTIVE

To test whether treatment with fenofibrate decreases asymmetric dimethylarginine (ADMA) level in hypertriglyceridemic individuals.

METHODS

In the present study, 45 subjects with hypertriglyceridemia were recruited to receive treatment with fenofibrate (200 mg/d). Serum concentrations of ADMA, malondialdehyde (MDA), nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) were measured. Endothelial function assessed by flow-mediated dilation (FMD) of the brachial artery was performed.

RESULTS

Compared with control, serum levels of ADMA (0.47+/-0.05 micromol/L in control and 0.62+/-0.28 micromol/L in hypertriglyceridemic patients, P<0.01), MDA and TNF-alpha were markedly elevated, and the level of NO was significantly reduced, concomitantly with impaired endothelium-dependent vasodilation in individuals with hypertriglyceridemia. 8-week treatment with fenofibrate significantly reduced the elevated levels of ADMA (0.53+/-0.12 micromol/L, P<0.01), MDA and TNF-alpha, attenuated the decreased level of NO and improved endothelial function.

CONCLUSIONS

These results suggest that the beneficial effect of fenofibrate on the endothelium in hypertriglyceridemic individuals may be related to reduction of ADMA level.

Fenofibrate: a novel formulation (Triglide) in the treatment of lipid disorders: a review

Cardiovascular disease is the major cause of mortality worldwide and accounts for approximately 40% of all deaths. Dyslipidemia is one of the primary causes of atherosclerosis and effective interventions to correct dyslipidemia should form an integral component of any strategy aimed at preventing cardiovascular disease. Fibrates have played a major role in the treatment of hyperlipidemia for more than two decades. Fenofibrate is one of the most commonly used fibrates worldwide. Since fenofibrate was first introduced in clinical practice, a major drawback has been its low bioavailability when taken under fasting conditions. Insoluble Drug Delivery-Microparticle fenofibrate is a new formulation that has an equivalent extent of absorption under fed or fasting conditions. In this review, we will discuss the clinical pharmacology of fenofibrate, with particular emphasis on this novel formulation, as well as its lipid-modulating and pleiotropic actions. We will also analyze the major trial that evaluated fibrates for primary and secondary prevention of cardiovascular disease, the safety and efficacy profile of fibrate-statin combination treatment, and the current recommendations regarding the use of fibrates in clinical practice.

Fenofibrate decreases asymmetric dimethylarginine level in cultured endothelial cells by inhibiting NF-κB activity

Previous investigations have demonstrated that endogenous inhibitors of nitric oxide synthase (NOS), such as asymmetric dimethylarginine (ADMA), contribute importantly to endothelial dysfunction, and that fenofibrate has a protective effect on the endothelium in rats treated with low-density lipoprotein (LDL) by reducing ADMA levels. In the present study, we explored further the possible mechanism underlying inhibition of ADMA generation by fenofibrate in cultured human umbilical vein endothelial cells (HUVECs). Endothelial injury was induced in cultured HUVECs by incubation with oxidative LDL (ox-LDL) and the levels of ADMA, lactate dehydrogenase (LDH), NO and tumour necrosis factor-alpha (TNF-alpha) in the conditioned medium were measured. Cell viability and the activity of dimethylarginine dimethylaminohydrolase (DDAH) and nuclear factor-kappaB (NF-kappaB) in the cultured HUVECs were also determined. Incubation of HUVECs with ox-LDL (100 microg/ml) for 24 h markedly elevated ADMA, LDH and TNF-alpha in the conditioned medium and significantly increased the activity of NF-kappaB, concomitantly with a significant decrease in the activity of DDAH and the content of NO. Pretreatment with fenofibrate (3, 10 or 30 microM) significantly inhibited the increases in ADMA, LDH and TNF-alpha, attenuated the decreased levels of NO and the decreased activity of DDAH and prevented the activation of NF-kappaB. Similar effects were observed in the presence of pyrrolidine dithiocarbamate (PDTC, 10 microM), an antagonist of NF-kappaB. The beneficial effects of fenofibrate on cultured endothelial cells were abolished by MK-886, a specific peroxisome proliferator-activated receptor-alpha (PPARalpha) antagonist. The present results suggest that fenofibrate inhibits ox-LDL-induced endothelial cell damage by decreasing ADMA and increasing DDAH activity, and the protective effects of fenofibrate on endothelial cells may be related to reduction of NF-kappaB activity by activation of the PPARalpha receptor.

Fenofibrate lowers adiposity and corrects metabolic abnormalities, but only partially restores endothelial function in dietary obese rats

In humans, dietary-induced obesity markedly increases plasma lipid profile and impairs vascular function leading to increased incidence of cardiovascular events. We have recently reported that chronic withdrawal of obesity-inducing diet attenuates obesity and completely corrects endothelial function. The aim of this study was to investigate whether fenofibrate-induced decrease in adiposity would also correct vascular function in the presence of obesity-inducing diet. Wistar rats were fed with either standard laboratory chow (lean, n = 9) or given a highly palatable diet (diet-fed, n = 18) for 15 weeks. After 7 weeks, half of the diet-fed group was treated with fenofibrate (fenofibrate-treated, n = 9) for 8 weeks before being sacrificed. Untreated diet-fed (n = 9) rats had significantly higher body weight, total fat mass (by up to two-fold, p < 0.001 for both), and raised fasting plasma levels of insulin, leptin and triglycerides (up to 110%; p < 0.001), but not glucose or nonesterified fatty acids (NEFA) than both lean control and fenofibrate-treated groups. Resistance mesenteric arteries responses to KCl- and noradrenaline-induced vasoconstriction were similar in all three groups. However, compared with lean controls, endothelium-dependent vasorelaxation responses were shifted to the right in both untreated and fenofibrate-treated diet-fed groups. Fenofibrate treatment improved endothelium-dependent vasorelaxation at only high carbamycholine concentrations (10 microM). There were no differences in endothelium-independent vasorelaxation between the three groups. These results indicate that, in the presence of obesity-inducing diet, fenofibrate markedly reverses obesity and corrects insulin resistance and lipid profile, but it only has a limited beneficial effect on vascular function. Therefore, it seems that diet component rather than obesity per se plays a key role in the genesis of vascular abnormalities.

Effect of fenofibrate on LDL-induced endothelial dysfunction in rats

Previous investigations have demonstrated that asymmetric dimethylarginine (ADMA) is an important factor contributing to endothelial dysfunction, and that fenofibrate has a protective effect on the endothelium in hyperlipidaemic patients. In the present study in rats treated with native low-density lipoprotein (nLDL), we addressed the question of whether the beneficial effect of fenofibrate on endothelial cells is related to reduction of the ADMA concentration. A single injection of nLDL (4 mg/kg, 48 h) markedly reduced endothelium-dependent relaxation in response to acetylcholine and the plasma level of nitrite/nitrate and increased the plasma concentrations of ADMA, malonyldialdehyde (MDA) and tumour necrosis factor-alpha (TNF-alpha). Treatment with fenofibrate (30 or 100 mg/kg) significantly reduced the inhibition of vasodilator responses to acetylcholine, decreased the elevated levels of ADMA, MDA and TNF-alpha, and enhanced the decreased level of nitrite/nitrate in the rats treated with LDL. These results suggest that the protective effect of fenofibrate on endothelial cells in rats treated with LDL may be related to the reduction of ADMA concentration.