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

Dimethylarginine dimethylaminohydrolase (DDAH) overexpression enhances wound repair in airway epithelial cells exposed to agricultural organic dust

OBJECTIVE

Workers exposed to dusts from concentrated animal feeding operations have a high prevalence of pulmonary diseases. These exposures lead to chronic inflammation and aberrant airway remodeling. Previous work shows that activating cAMP-dependent protein kinase (PKA) enhances airway epithelial wound repair while activating protein kinase C (PKC) inhibits wound repair. Hog barn dust extracts slow cell migration and wound repair via a PKC-dependent mechanism. Further, blocking nitric oxide (NO) production in bronchial epithelial cells prevents PKA activation. We hypothesized that blocking an endogenous NO inhibitor, asymmetric dimethylarginine, by overexpressing dimethylarginine dimethylaminohydrolase mitigates the effects of hog dust extract on airway epithelial would repair.

MATERIALS/METHODS

We cultured primary tracheal epithelial cells in monolayers from both wild-type (WT) and dimethylarginine dimethylaminohydrolase overexpressing C57Bl/6 (DDAH₁ transgenic) mice and measured wound repair using the electric cell impedance sensing system.

RESULTS

Wound closure in epithelial cells from WT mice occurred within 24 h in vitro. In contrast, treatment of the WT cell monolayers with 5% hog dust extract prevented significant NO-stimulated wound closure. In cells from DDAH₁ transgenic mice, control wounds were repaired up to 8 h earlier than seen in WT mice. A significant enhancement of wound repair was observed in DDAH cells compared to WT cells treated with hog dust extract for 24 h. Likewise, cells from DDAH₁ transgenic mice demonstrated increased NO and PKA activity and decreased hog dust extract-stimulated PKC.

DISCUSSION/CONCLUSION

Preserving the NO signal through endogenous inhibition of asymmetric dimethylarginine enhances wound repair even in the presence of dust exposure.

Pyrrolidine dithiocarbamate ameliorates endothelial dysfunction in thoracic aorta of diabetic rats by preserving vascular DDAH activity

Objective

Endothelial dysfunction plays a pivotal role in the development of diabetic cardiovascular complications. Accumulation of endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA) and inhibition of dimethylarginine dimethylaminohydrolase (DDAH) activity have been involved in diabetic endothelial dysfunction. This study was to investigate the effect of pyrrolidine dithiocarbamate (PDTC) on impairment of endothelium-dependent vasodilatation in diabetic rats and its potential mechanism.

Methods

Diabetic rats were induced by a single intraperitoneal injection of streptozotocin (60mg/kg), and PDTC (10mg/kg) was given in drinking water for 8 weeks. Blood glucose and serum ADMA concentrations were measured in experimental rats. Recombinant adenovirus encoding human DDAH2 gene were constructed and ex vivo transferred to isolated rat aortas. The maximal relaxation (E_max) and half maximal effective concentration (EC₅₀) of aortic rings response to accumulative concentrations of acetylcholine and vascular DDAH activity were examined before and after gene transfection.

Results

Diabetic rats displayed significant elevations of blood glucose and serum ADMA levels compared to control group (P<0.01). Vascular DDAH activity and endothelium-dependent relaxation of aortas were inhibited, as expressed by the decreased E_max and increased EC₅₀ in diabetic rats compared to control rats (P<0.01). Treatment with PDTC not only decreased blood glucose and serum ADMA concentration (P<0.01) but also restored vascular DDAH activity and endothelium-dependent relaxation, evidenced by the higher E_max and lower EC₅₀ in PDTC-treated diabetic rats compared to untreated diabetic rats (P<0.01). Similar restoration of E_max, EC₅₀ and DDAH activity were observed in diabetic aortas after DDAH2-gene transfection.

Conclusions

These results indicate that PDTC could ameliorate impairment of endothelium-dependent relaxation in diabetic rats. The underlying mechanisms might be related to preservation of vascular DDAH activity and consequent reduction of endogenous ADMA in endothelium via its antioxidant action. This study highlights the therapeutic potential of PDTC in impaired vasodilation and provides a new strategy for treatment of diabetic cardiovascular complications.

Inhibitors of the Hydrolytic Enzyme Dimethylarginine Dimethylaminohydrolase (DDAH): Discovery, Synthesis and Development

Dimethylarginine dimethylaminohydrolase (DDAH) is a highly conserved hydrolytic enzyme found in numerous species, including bacteria, rodents, and humans. In humans, the DDAH-1 isoform is known to metabolize endogenous asymmetric dimethylarginine (ADMA) and monomethyl arginine (l-NMMA), with ADMA proposed to be a putative marker of cardiovascular disease. Current literature reports identify the DDAH family of enzymes as a potential therapeutic target in the regulation of nitric oxide (NO) production, mediated via its biochemical interaction with the nitric oxide synthase (NOS) family of enzymes. Increased DDAH expression and NO production have been linked to multiple pathological conditions, specifically, cancer, neurodegenerative disorders, and septic shock. As such, the discovery, chemical synthesis, and development of DDAH inhibitors as potential drug candidates represent a growing field of interest. This review article summarizes the current knowledge on DDAH inhibition and the derived pharmacokinetic parameters of the main DDAH inhibitors reported in the literature. Furthermore, current methods of development and chemical synthetic pathways are discussed.

Evaluation of ADMA-DDAH-NOS axis in specific brain areas following nitroglycerin administration: study in an animal model of migraine

BACKGROUND

Nitric oxide (NO) is known to play a key role in migraine pathogenesis, but modulation of NO synthesis has failed so far to show efficacy in migraine treatment. Asymmetric dimethylarginine (ADMA) is a NO synthase (NOS) inhibitor, whose levels are regulated by dimethylarginine dimethylaminohydrolase (DDAH). Systemic administration of nitroglycerin (or glyceryl trinitrate, GTN) is a NO donor that consistently induces spontaneous-like headache attacks in migraneurs. GTN administration induces an increase in neuronal NOS (nNOS) that is simultaneous with a hyperalgesic condition. GTN administration has been used for years as an experimental animal model of migraine. In order to gain further insights in the precise mechanisms involved in the relationships between NO synthesis and migraine, we analyzed changes induced by GTN administration in ADMA levels, DDHA-1 mRNA expression and the expression of neuronal and endothelial NOS (nNOS and eNOS) in the brain. We also evaluated ADMA levels in the serum.

METHODS

Male Sprague-Dawley rats were injected with GTN (10 mg/kg, i.p.) or vehicle and sacrificed 4 h later. Brain areas known to be activated by GTN administration were dissected out and utilized for the evaluation of nNOS and eNOS expression by means of western blotting. Cerebral and serum ADMA levels were measured by means of ELISA immunoassay. Cerebral DDAH-1 mRNA expression was measured by means of RT-PCR. Comparisons between experimental groups were performed using the Mann Whitney test.

RESULTS

ADMA levels and nNOS expression increased in the hypothalamus and medulla following GTN administration. Conversely, a significant decrease in DDAH-1 mRNA expression was observed in the same areas. By contrast, no significant change was reported in eNOS expression. GTN administration did not induce any significant change in serum levels of ADMA.

CONCLUSION

The present data suggest that ADMA accumulates in the brain after GTN administration via the inhibition of DDAH-1. This latter may represent a compensatory response to the excessive local availability of NO, released directly by GTN or synthetized by nNOS. These findings prompt an additional mediator (ADMA) in the modulation of NO axis following GTN administration and offer new insights in the pathophysiology of migraine.

Fenofibrate effects on arterial endothelial function in adults with type 2 diabetes mellitus: A FIELD substudy

OBJECTIVE

Dislipidaemia in type 2 diabetes mellitus contributes to arterial endothelial dysfunction and an increased risk of cardiovascular disease. Fenofibrate, a lipid-regulating peroxisome proliferator-activated receptor-α (PPARα) agonist, has been shown to reduce vascular complications in adults with type 2 diabetes. However, the mechanisms for such benefit are not well understood. We examined the effects of fenofibrate on brachial artery endothelial function in adults with type 2 diabetes.

METHODS

In a prospectively designed substudy of the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study, we assessed arterial flow-mediated dilatation (FMD; endothelium-dependent dilatation) and dilator responses to glyceryl trinitrate (GTN, an endothelium-independent dilator) in a subset of 193 representative adults. Traditional risk factors were assessed at baseline, 4 months and 2 years after randomised treatment allocation to fenofibrate (200 mg daily) or placebo. The prespecified primary study endpoint was the difference in FMD between treatment groups at 4 months.

RESULTS

Fenofibrate was associated with a significant improvement at 4 months compared with placebo (+1.05% (absolute); P=0.03); GTN-dilator responses were unchanged (P=0.77). After 2 years, FMD was similar in both groups (P=0.46). In multivariable models, none of the fenofibrate-related changes in lipoproteins and lipids were significantly associated with improved FMD on fenofibrate at 4 months.

CONCLUSION

Treatment with fenofibrate significantly improved arterial endothelial function after 4 months. However, the effect was no longer apparent after 2 years. The long-term beneficial vascular effects of fenofibrate in type 2 diabetes are likely to be mediated via mechanisms other than improvement in endothelium-dependent dilatation of conduit arteries, and may differ for the microcirculation.

Fenofibrate in cancer: mechanisms involved in anticancer activity

Objective: To review the mechanisms of anti-cancer activity of fenofibrate (FF) and other Peroxisome Proliferator Activator Receptor α (PPARα) agonists based on evidences reported in the published literature.Methods: We extensively reviewed the literature concerning FF as an off target anti-cancer drug. Controversies regarding conflicting findings were also addressed.Results: The main mechanism involved in anti-cancer activity is anti-angiogenesis through down-regulation of  Vascular Endothelial Growth Factor (VEGF), Vascular Endothelial Growth Factor Receptor (VEGFR) and Hypoxia Inducible factor-1 α (HIF-1α), inhibition of endothelial cell migration, up-regulation of endostatin and thrombospondin-1, but there are many other contributing mechanisms like apoptosis and cell cycle arrest, down-regulation of Nuclear Factor Kappa B (NF-kB) and Protein kinase B (Akt) and decrease of cellular energy by impairing mitochondrial function. Growth impairment is related to down-regulation of Phospho-Inositol 3 Kinase (PI3K)/Akt axis and down-regulation of the p38 map kinase (MAPK) cascade. A possible role should be assigned to FF stimulated over-expression of Tribbles Homolog-3 (TRIB3) which inhibits Akt phosphorylation. Important anti-cancer and anti-metastatic activities are due to down-regulation of MCP-1 (monocyte chemotactic protein-1), decreased Metalloprotease-9 (MMP-9) production, weak down-regulation of adhesion molecules like E selectin, intercellular adhesion molecules (ICAM) and Vascular Endothelial Adhesion Molecules (VCAM), and decreased secretion of chemokines like Interleukin-6 (IL-6), and down-regulation of cyclin D-1. There is no direct link between FF activity in lipid metabolism and anticancer activity, except for the fact that many anticancer actions are dependent from PPARα agonism. FF exhibits also PPARα independent anti-cancer activities.Conclusions: There are strong evidences indicating that FF can disrupt growth-related activities in many different cancers, due to anti-angiogenesis and anti-inflammatory effects. Therefore FF may be useful as a complementary adjunct treatment of cancer, particularly included in anti-angiogenic protocols like those currently increasingly used in glioblastoma. There are sound reasons to initiate well planned phase II clinical trials for FF as a complementary adjunct treatment of cancer.

Gemfibrozil attenuates the inflammatory response and protects rats from abdominal sepsis

Sepsis is a serious condition characterized by an infectious process that induces a severe systemic inflammatory response. In this study, the effects of gemfibrozil (GFZ) on the inflammatory response associated with abdominal sepsis were investigated using a rat model of cecal-ligation and puncture (CLP). Male Wistar rats were randomly divided into three groups: Sham-operated group (sham), where laparotomy was performed, the intestines were manipulated, and the cecum was ligated but not punctured; control group, subjected to CLP; and GFZ group, which received GFZ prior to undergoing CLP. The groups were then subdivided into three different time-points: 2, 4 and 24 h, indicating the time at which blood samples were obtained for analysis. Serum concentrations of tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), malondialdehyde (MDA), aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) were determined. The LDH, AST and ALT values were significantly elevated following CLP compared with those in the sham group, and GFZ treatment was able to reduce these elevations. GFZ also reduced the sepsis-induced elevations of TNF-α and IL-1. In conclusion, GFZ treatment was able to attenuate the inflammatory response associated with CLP-induced sepsis, by diminishing the release of inflammatory cytokines, thereby reducing tissue injury and oxidative stress.

The protective effect of fenofibrate against TNF-α-induced CD40 expression through SIRT1-mediated deacetylation of NF-κB in endothelial cells

Fenofibrate, as a lipid-lowering drug in clinic, participates in the regulation of inflammatory response. Recently, increasing studies have indicated that sirtuin1 (SIRT1), a NAD+-dependent deacetylase, has potential anti-inflammatory effect in endothelial cells. However, whether the regulatory effect of fenofibrate on inflammation response is mediated by SIRT1 remains unclear. The aim of this study was to investigate the effect of fenofibrate on the expressions of SIRT1 and pro-inflammatory cytokine CD40 in endothelial cells and explore the underlying mechanisms. The results showed that fenofibrate upregulated SIRT1 expression and inhibited CD40 expression in TNF-α-stimulated endothelial cells, but these effects were reversed by peroxisome proliferator-activated receptor-α (PPARα) antagonist GW6471. Furthermore, SIRT1 inhibitors sirtinol/nicotinamide (NAM) or SIRT1 knockdown could attenuate the effect of fenofibrate on CD40 expression in endothelial cells. Importantly, NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) augmented the effect of fenofibrate on CD40 expression. Further study found that fenofibrate decreased the expression of acetylated-NF-κB p65 (Ac-NF-κB p65) in TNF-α-stimulated endothelial cells, which was abolished by SIRT1 knockdown. These results indicate that fenofibrate has protective effect against TNF-α-induced CD40 expression through SIRT1-mediated deacetylation of the p65 subunit of NF-κB.

Vaspin increases nitric oxide bioavailability through the reduction of asymmetric dimethylarginine in vascular endothelial cells

Vaspin is an adipocytokine recently identified in the visceral adipose tissue of diabetic rats and having anti-diabetic effects. We have recently shown that vaspin has anti-atherogenic effect through Akt-mediated inhibition of endothelial cell apoptosis. Decreased activity of endothelial nitric oxide synthase (eNOS) plays an important role in the pathogenesis of atherosclerosis. Asymmetric dimethylarginine (ADMA) is a well-known endogenous competitive inhibitor of eNOS and risk factor of cardiovascular diseases. The aim of this study was to examine whether vaspin might protect against atherosclerosis through its beneficial effects on the ADMA-eNOS system. Treatment of vaspin significantly increased NO secretion from endothelial cells and isolated aorta from Sprague-Dawley (SD) rats. Furthermore, treatment of vaspin prevented fatty acid-induced decrease in endothelium-dependent vasorelaxation in isolated aorta of SD rat. For the mechanism of vaspin-induced NO biosynthesis, vaspin activated the STAT3 signaling pathway and stimulated eNOS phosphorylation (Ser 1177), a marker of eNOS activation, through STAT3-dependent mechanism. Furthermore, vaspin treatment increased the expression of dimethylarginine dimethylaminohydrolase (DDAH) II, the responsible enzyme for the degradation of ADMA, leading to a reduction in ADMA levels. Vaspin-induced increase in DDAH II gene expression was through STAT3-mediated stimulation of DDAH II promoter activity. These results suggest that vaspin increases eNOS activity by reducing ADMA level through STAT3-mediated regulation of DDAH II expression. Our findings provide a novel molecular mechanism of antiatherogenic actions of vaspin.

Nitric oxide manipulation: a therapeutic target for peripheral arterial disease?

Peripheral Arterial Disease (PAD) is a cause of significant morbidity and mortality in the Western world. Risk factor modification and endovascular and surgical revascularisation are the main treatment options at present. However, a significant number of patients still require major amputation. There is evidence that nitric oxide (NO) and its endogenous inhibitor asymmetric dimethylarginine (ADMA) play significant roles in the pathophysiology of PAD. This paper reviews experimental work implicating the ADMA-DDAH-NO pathway in PAD, focussing on both the vascular dysfunction and effects within the ischaemic muscle, and examines the potential of manipulating this pathway as a novel adjunct therapy in PAD.

Fenofibrate improves endothelial function in the brachial artery and forearm resistance arterioles of statin-treated Type 2 diabetic patients

Dyslipidaemia contributes to endothelial dysfunction and CVD (cardiovascular disease) in Type 2 diabetes mellitus. While statin therapy reduces CVD in these patients, residual risk remains high. Fenofibrate corrects atherogenic dyslipidaemia, but it is unclear whether adding fenofibrate to statin therapy lowers CVD risk. We investigated whether fenofibrate improves endothelial dysfunction in statin-treated Type 2 diabetic patients. In a cross-over study, 15 statin-treated Type 2 diabetic patients, with LDL (low-density lipoprotein)-cholesterol <2.6 mmol/l and endothelial dysfunction [brachial artery FMD (flow-mediated dilatation) <6.0%] were randomized, double-blind, to fenofibrate 145 mg/day or matching placebo for 12 weeks, with 4 weeks washout between treatment periods. Brachial artery FMD and endothelium-independent NMD (nitrate-mediated dilatation) were measured by ultrasonography at the start and end of each treatment period. PIFBF (post-ischaemic forearm blood flow), a measure of microcirculatory endothelial function, and serum lipids, lipoproteins and apo (apolipoprotein) concentrations were also measured. Compared with placebo, fenofibrate increased FMD (mean absolute 2.1+/-0.6 compared with -0.3+/-0.6%, P=0.04), but did not alter NMD (P=0.75). Fenofibrate also increased maximal PIFBF {median 3.5 [IQR (interquartile range) 5.8] compared with 0.3 (2.1) ml/100 ml/min, P=0.001} and flow debt repayment [median 1.0 (IQR 3.5) compared with -1.5 (3.0) ml/100 ml, P=0.01]. Fenofibrate lowered serum cholesterol, triacylgycerols (triglycerides), LDL-cholesterol, apoB-100 and apoC-III (P < or = 0.03), but did not alter HDL (high-density lipoprotein)-cholesterol or apoA-I. Improvement in FMD was inversely associated with on-treatment LDL-cholesterol (r=-0.61, P=0.02) and apoB-100 (r=-0.54, P=0.04) concentrations. Fenofibrate improves endothelial dysfunction in statin-treated Type 2 diabetic patients. This may relate partly to enhanced reduction in LDL-cholesterol and apoB-100 concentrations.

Asymmetric dimethylarginine association with antioxidants intake in healthy young adults: a role as an indicator of metabolic syndrome features

The purpose of this study was to evaluate the potential associations between serum asymmetric dimethylarginine (ADMA) and several anthropometric, biochemical, and lifestyle features in healthy young adults, emphasizing on the putative effects of the antioxidant intake on ADMA concentrations. Anthropometric and blood pressure measurements as well as lifestyle features and antioxidant intake were analyzed in 93 healthy young adults aged 18 to 34 years. Fasting blood samples were collected for the measurement of glucose, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triacylglycerols, and ADMA concentrations, as well as erythrocyte glutathione peroxidase activity. Nail samples were collected for the analysis of selenium and zinc concentrations. Values of body mass index (P = .004), waist circumference (P = .008), waist-to-height ratio (P = .046), systolic blood pressure (P < .001), serum glucose (P < .001), and nail selenium (P = .004) and zinc (P = .018) were significantly different between subjects with serum ADMA higher and lower than the median (cutoff, 458 nmol/L). Furthermore, ADMA showed a positive association with several adiposity markers such as body weight (P < .001), body mass index (P < .001), waist circumference (P = .006), waist-to-height ratio (P = .020), body fat mass (P = .001), systolic blood pressure (P = .001), and serum glucose (P < .001), whereas erythrocyte glutathione peroxidase activity (P = .021) and nail selenium (P = .040) and zinc values (P = .013) were statistically significant negative predictors of ADMA concentrations. In conclusion, ADMA seems to be related with selenium and zinc status and several anthropometric and biochemical measurements linked to metabolic syndrome in apparently healthy young adults. These findings support a role for antioxidant/trace element intake in the modulation of ADMA, whose assessment may be a marker of metabolic syndrome manifestations.

Regulation of myometrial contractivity during pregnancy in the rat: potential role for DDAH

There has been little information demonstrating the roles of dimethylarginine dimethylaminohydrolase (DDAH), which is the hydrolyzing enzyme of endogenous nitric oxide synthase (NOS) inhibitors and, in turn, modulates the intracellular concentrations of NOS inhibitors, in the myometrium during the course of pregnancy. Therefore, the present experiments were designed to investigate whether or not DDAH activity, protein and mRNA expression levels are altered during gestation of the rat and, if altered, those changes reflect on the levels of endogenous inhibitors and endothelin-1 (ET-1), and NO-dependent cyclic GMP generation in the myometrium. The up-regulated changes in DDAH activity, DDAH-2 protein and DDAH-2 mRNA expression at mid-gestation were accompanied by the reduced monomethylarginine and asymmetric dimethylarginine as NOS inhibitors, and ET-1 levels, and by the enhanced NO-dependent cyclic GMP production. At term gestation, on the other hand, down-regulated changes in DDAH activity, DDAH-2 protein and DDAH-2 mRNA expression were accompanied by the increased NOS inhibitors and ET-1 levels, and decreased NO-dependent cyclic GMP generation. These results suggest that alterations in DDAH/NOS inhibitors/NO-dependent cyclic GMP/ET-1 pathway are possibly involved in maintaining myometrial quiescence during gestation and controlling delivery at term.

Dimethylarginine dimethylaminohydrolase regulation: a novel therapeutic target in cardiovascular disease

Asymmetric dimethylarginine (ADMA), an endogenous methylated form of the amino acid L-arginine, inhibits the activity of the enzyme endothelial nitric oxide synthase, with consequent reduced synthesis of nitric oxide. ADMA is metabolised to L-citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). The modulation of DDAH activity and expression plays a pivotal role in regulating intracellular ADMA concentrations, with important effects on vascular homeostasis. For example, impairment in DDAH activity, resulting in elevated ADMA concentrations and reduced nitric oxide synthesis, can promote the onset and progression of atherosclerosis in experimental models. This review discusses the current role of ADMA and DDAH in vascular health and disease, the techniques used to assess DDAH activity and expression, and the results of recent studies on pharmacological and biological agents modulating DDAH activity and expression. Suggestions for future basic and clinical research directions are also discussed.

Dimethylarginine dimethylaminohydrolase (DDAH): expression, regulation, and function in the cardiovascular and renal systems

Asymmetric (N(G),N(G))-dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS). ADMA is a risk factor for endothelial dysfunction, cardiovascular mortality, and progression of chronic kidney disease. Two isoforms of dimethylarginine dimethylaminohydrolase (DDAH) metabolize ADMA. DDAH-1 is the predominant isoform in the proximal tubules of the kidney and in the liver. These organs extract ADMA from the circulation. DDAH-2 is the predominant isoform in the vasculature, where it is found in endothelial cells adjacent to the cell membrane and in intracellular vesicles and in vascular smooth muscle cells among the myofibrils and the nuclear envelope. In vivo gene silencing of DDAH-1 in the rat and DDAH +/- mice both have increased circulating ADMA, whereas gene silencing of DDAH-2 reduces vascular NO generation and endothelium-derived relaxation factor responses. DDAH-2 also is expressed in the kidney in the macula densa and distal nephron. Angiotensin type 1 receptor activation in kidneys reduces the expression of DDAH-1 but increases the expression of DDAH-2. This rapidly evolving evidence of isoform-specific distribution and regulation of DDAH expression in the kidney and blood vessels provides potential mechanisms for nephron site-specific regulation of NO production. In this review, the recent advances in the regulation and function of DDAH enzymes, their roles in the regulation of NO generation, and their possible contribution to endothelial dysfunction in patients with cardiovascular and kidney diseases are discussed.

The inhibitory effect of simvastatin on the ADMA-induced inflammatory reaction is mediated by MAPK pathways in endothelial cells

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is emerging as a key contributor for endothelial dysfunction associated with inflammation. Statins can inhibit vascular inflammatory reaction and improve endothelial function. The aim of this study was to investigate in human endothelial cells the signaling pathways of ADMA-induced inflammatory reaction and potential inhibitory effects of simvastatin. Endothelial cells were cultured and used for all of the studies. Tumor necrosis factor-alpha(TNF-alpha) and soluble intercellular adhesion molecule-1 (sICAM-1) were determined by enzyme-linked immunosorbent assay. Nuclear factor-kappaB (NF-kappaB) was assayed by electrophoretic mobility shift assay. The activation of mitogen-activated protein kinases (MAPKs), including p38 MAPK and extracellular signal-related kinase (ERK(1/2)), were characterized by Western blot analysis. Treatment with ADMA (3-30 micromol/L) increased the concentration of sICAM-1 in a dose-dependent manner. ADMA (30 micromol/L) significantly enhanced the concentrations of TNF-alpha and sICAM-1, the activity of NF-kappaB and the phosphorylation of p38 MAPK and ERK(1/2). The increased secretion of TNF-alpha and sICAM-1 and the increased activity of NF-kappaB by ADMA were altered by SB203580 (5 micromol/L) or PD98059 (20 micromol/L), but not by LY294002 (20 micromol/L). Simvastatin (0.1, 0.5, or 2.5 micromol/L) markedly inhibited the elevated concentrations of TNF-alpha and sICAM-1, the activity of NF-kappaB, and the phosphorylation of p38 MAPK and ERK(1/2) induced by ADMA. Simvastatin inhibited ADMA-induced inflammatory reaction by p38 MAPK and ERK(1/2) pathways in cultured endothelial cells.

Role of asymmetric dimethylarginine in inflammatory reactions by angiotensin II

Previous investigations have demonstrated that angiotensin (Ang) II induces inflammatory reactions and asymmetric dimethylarginine (ADMA), an endogenous NOS inhibitor, might be a novel inflammatory factor. Endothelial cell activation was induced by incubation with Ang II or ADMA. Incubation with Ang II (10(-6) M) for 24 h elevated the levels of ADMA and decreased the levels of nitrite/nitrate concomitantly with a significant increase in the expression of protein arginine methyltransferase and a decrease in the activity of dimethylarginine dimethylaminohydrolase (DDAH). Exposure to Ang II (10(-6) M for 24 h) also enhanced intracellular ROS elaboration and the levels of tumor necrosis factor (TNF)-alpha and interleukin (IL)-8, upregulated chemokine receptor CXCR2 mRNA expression, increased adhesion of endothelial cells to monocytes and induced a significant increase in the activity of nuclear factor (NF)-kappaB, which was attenuated by pretreatment with the Ang II receptor blocker losartan (1, 3 and 10 muM). Exogenous ADMA (30 microM) also increased ROS generation and the levels of TNF-alpha and IL-8, decreased the levels of nitrite/nitrate, upregulated CXCR2 gene expression, increased endothelial cell binding with monocytes and activated the NF-kappaB pathway, which was inhibited by pretreatment with losartan or L-arginine. These data suggest that ADMA is a potential proinflammatory factor and may be involved in the inflammatory reaction induced by Ang II.

Effect of asymmetric dimethylarginine on atherogenesis and erythrocyte deformability in apolipoprotein E deficient mice

Previous investigations have shown that the level of asymmetric dimethylarginine (ADMA) was increased in hypercholesterolemic animal and humans, and the decreased erythrocyte deformability has been suggested to be a factor contributing to atherogenesis. In the present study, we investigated the effect of ADMA, endogenous or exogenous, on atherogenesis and erythrocyte deformability in apolipoprotein E deficient (ApoE-/-) mice. On a regular chow diet, ApoE-/- mice or C57BL/6 J mice at 12 weeks of age were treated with ADMA (5 mg/kg/day) for 4 weeks. Atherosclerotic lesion area, erythrocyte deformability, plasma lipids and asymmetric dimethylarginine (ADMA) level were determined. Plasma concentrations of triglyceride (TG), low-density lipoprotein-cholesterol (LDL-C), total cholesterol (TC), ADMA, and atherosclerotic lesion area were significantly increased, and the level of plasma high-density lipoprotein-cholesterol (HDL-C), erythrocyte deformability in ApoE-/- mice were markedly decreased compared with that of C57BL/6J mice (P<0.05 or P<0.01). Exogenous ADMA treatment increased the plasma TG level, produced atherosclerotic lesions, and decreased erythrocyte deformability in C57BL/6J mice (P<0.05 or P<0.01). Treatment with exogenous ADMA further increased the plasma TG level and lesion areas, and decreased erythrocyte deformability in ApoE-/- mice. In vitro, exogenous ADMA caused a decrease of erythrocyte deformability in a concentration-dependent manner, and the effect of ADMA was reversed by L-arginine. The present results suggest that endogenous ADMA is an important contributor to the development of atherosclerosis and that reduction of erythrocyte deformability and impaired endothelial function induced by ADMA may be an important factor facilitating atherosclerotic lesions.

Effects of rosiglitazone on native low-density-lipoprotein-induced respiratory burst in circulating monocytes and on the leukocyte-endothelial interaction in cholesterol-fed rats

Low-density lipoprotein (LDL) has been implicated in the initiation and progression of atherosclerotic vascular disease. But whether LDL can elicit similar effects in the microcirculation remain unexplored. To approach this issue, the hypothesis that LDL promotes oxidative stress in monocytes and results in microvascular inflammation was tested. Native LDL was capable of stimulating respiratory burst in rat monocytes, and this was blocked by BAPTA, cytochalasin B, apocynin, and diphenyliodonium. In monocytes from rats on a high-cholesterol (4%) diet, increased intracellular calcium, actin polymerization, respiratory burst, and surface CD18 expression were found. Concurrently, leukocyte-endothelial interaction was enhanced in the cremaster microcirculation. Rosiglitazone, an insulin-sensitizing agent with antiinflammatory properties, was found to suppress native-LDL-induced actin polymerization and respiratory burst in monocytes. It also improved leukocytes activation and leukocyte-endothelial interaction due to the high cholesterol intake. Hence, native LDL stimulation of monocytes contributed to hypercholesterolemia-associated microvascular inflammation, which could be treated by rosiglitazone.

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.