Effect of simvastatin on endothelium-dependent vaso-relaxation and endogenous nitric oxide synthase inhibitor

AIM: To investigate the effect of simvastatin on endothelium-dependent vasorelaxation and endogenous nitric oxide synthesis inhibitor asymmetric dimethylarginine (ADMA) in rats and cultured ECV304 cells. METHODS: Endothe-lial injury was induced by a single injection of low density lipoprotein (LDL) (4 mg/kg, 48 h) in rats or incubation with LDL (300 mg/L) or oxidative-modified LDL (100 mg/L) in cultured ECV304 cells, and vasodilator responses to acetylcholine (ACh) in the aortic rings and the level of ADMA, nitrite/nitrate (NO) and tumor necrosis factor-alpha (TNF-α) in the serum or cultured medium were determined. And the adhesion of the monocytes to endothe-lial cells and the activity of dimethylarginine dimethylaminohydrolase (DDAH) in the cultured ECV304 cells were measured. RESULTS: A single injection of LDL decreased endothelium-dependent relaxation to ACh, markedly increased the serum level of endogenous ADMA and TNF-α, and reduced serum level of NO. Pretreatment with simvastatin (30 or 60 mg/kg) markedly attenuated inhibition of vasodilator responses to ACh, the increased level of TNF-α and the decreased level of NO by LDL, but no effect on serum concentration of endogenous ADMA. In cultured ECV304 cells, LDL or ox-LDL markedly increased the level of ADMA and TNF-α and potentiated the adhesion of monocytes to endothelial cells, concomitantly with a significantly decrease in the activity of DDAH and serum level of NO. Pretreatment with simvastatin (0.1, 0.5, or 2.5 μmol/L) markedly decreased the level of TNF-α and the adhesion of monocytes to endothelial cells, but did not affect the concentration of endogenous ADMA and the activity of DDAH. CONCLUSION: Simvastatin protect the vascular endothelium against the damages induced by LDL or ox-LDL in rats or cultured ECV304 cells, and the beneficial effects of simvastatin may be related to the reduction of inflammatory cytokine TNF-α level.     

Taurine protects against low-density lipoprotein-induced endothelial dysfunction by the DDAH/ADMA pathway

Asymmetric dimethylarginine (ADMA), a major endogenous nitric oxide (NO) synthase inhibitor, is thought to be a key contributor for endothelial dysfunction. Decrease in activity of dimethylarginine dimethylaminohydrolase (DDAH), a major hydrolase of ADMA, causes accumulation of ADMA in some risk factors of atherosclerosis, including hypercholesterolemia. Taurine is a semi-essential amino acid that has previously been shown to have endothelial protective effects. The present study was to test whether the protective effect of taurine on endothelial function is related to modulation of the DDAH/ADMA pathway. A single injection of native LDL (4 mg/kg, i.v.) markedly reduced endothelium-dependent vasorelaxation and the plasma level of NO, and increased plasma concentrations of ADMA, malondialdehyde (MDA) and tumor necrosis factor-alpha (TNF-alpha). Treatment with taurine in vivo (60 or 180 mg/kg) significantly attenuated the inhibition of endothelium-dependent vasorelaxation and the reduced level of NO, and decreased the elevated levels of ADMA, MDA, and TNF-alpha. Incubation human umbilical vein endothelial cells (HUVECs) with ox-LDL (100 microg/ml) for 24 h markedly increased the medium levels of lactate dehydrogenase (LDH), ADMA, TNF-alpha and MDA, and decreased the level of NO in the medium and the intracellular activity of DDAH. Taurine (1 or 5 microg/ml) significantly attenuated the increases in the levels of LDH, ADMA, TNF-alpha and MDA, and the decrease in the level of NO and the activity of DDAH induced by ox-LDL in HUVECs. The present results suggested that taurine protected against endothelial dysfunction induced by native LDL in vivo or by ox-LDL in endothelial cells, and the protective effect of taurine on the endothelium is related to decrease in ADMA level by increasing of DDAH activity.     

Asymmetric dimethylarginine induces TNF-alpha production via ROS/NF-kappaB dependent pathway in human monocytic cells and the inhibitory effect of reinioside C

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, has been implicated in vascular inflammation through induction of reactive oxygen species (ROS) and proinflammatory genes in endothelial cells. However, relatively few attentions have been paid to the effect of ADMA on monocytes, one of the important cells throughout all stages of atherosclerosis. In the present study, we found that reinioside C, the main component extracted from Polygala fallax Hemsl., dose-dependently inhibited tumor necrosis factor-alpha (TNF-alpha) production induced by ADMA in monocytes, Furthermore, reinioside C attenuated ADMA-induced generation of reactive oxygen species and activation of nuclear factor-kappaB (NF-kappaB) activity in monocytes in a dose-dependent manner, this effect was inhibited by l-arginine (NOS substrate) and PDTC (inhibitor of NF-kappaB). These data suggest that reinioside C could attenuate the increase of TNF-alpha induced by exogenous ADMA through inhibition ROS/NF-kappaB pathway in monocytes.     

Lysophosphatidylcholine-induced elevation of asymmetric dimethylarginine level by the NADPH oxidase pathway in endothelial cells

Recent studies suggested that endothelium is a main source of reactive oxygen species (ROS) and the major source was via NADPH oxidase pathway. Various stimuli including lysophosphatidylcholine (LPC), a major component of oxidized low-density lipoprotein (ox-LDL), can enhance the activity of NADPH oxidase and lead to a marked ROS generation. Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide (NO) synthase (NOS) inhibitor, which is synthesized by protein arginine methyltransferase I (PRMT I) and degraded by dimethylarginine dimethylaminohydrolase (DDAH) in endothelial cells. Much evidence showed that ADMA was closely related to endothelial dysfunction. Our previous study showed that LPC elevated ADMA level in endothelial cells via increasing oxidative stress, but the precise cellular mechanism is not defined yet. The present study was to explore the mechanism of NADPH oxidase in LPC-induced elevation of ADMA. In LPC-treated endothelial cells, the ROS production, cell viability, ADMA and NO levels, the activity of DDAH and expression of PRMT I were detected. Treatment with LPC (10 microg/ml) for 24 h markedly increased intracellular ROS production, the expression of PRMT I, level of ADMA, decreased the concentration of NO and the activity of DDAH. These effects were attenuated by diphenyliodonium, the NADPH oxidase inhibitor. In summary, the present results suggested that LPC-induced elevation of ADMA was due to reduction of DDAH activity and the up-regulation of PRMT expression by stimulation of ROS production via NADPH oxidase pathway.     

Aspirin protected against endothelial damage induced by LDL： role of endogenous NO synthase inhibitors in rats

AIM: To study the protective effect of aspirin on damages of the endothelium induced by low-density lipoprotein (LDL), and whether the protective effect of aspirin is related to reduction of nitric oxide synthase inhibitor level.METHODS: Vascular endothelial injury was induced by a single injection of native LDL (4 mg/kg) in rats. Vasodilator responses to acetylcholine (ACh) in the isolated aortic rings were determined, and serum concentrations ofasymmetric dimethylarginine (ADMA), malondialdehyde (MDA), tumour necrosis factor-α (TNF-α), and the activity of dimethylaminohydrolase (DDAH) were measured. RESULTS: A single injection of LDL (4 mg/kg)significantly decreased vasodilator responses to ACh, increased the serum level of ADMA, MDA, and TNF-α, anddecreased DDAH activity. Aspirin (30 or 100 mg/kg) markedly reduced the inhibition of vasodilator responses toACh by LDL, and the protective effect of aspirin at the lower dose was greater compared with high-dose aspiringroup. Aspirin inhibited the increased level of MDA and TNF-α induced by LDL. Aspirin at the dose of 30 mg/kg,but not at higher dose (100 mg/kg), significantly reduced the concentration of ADMA and increased the activity ofDDAH. CONCLUSION: Aspirin at the lower dose (30 mg/kg) protects the endothelium against damages elicitedby LDL in vivo, and the protective effect of aspirin on endothelium is related to reduction of ADMA concentrationby increasing DDAH activity.     

Nebivolol reduces asymmetric dimethylarginine in endothelial cells by increasing dimethylarginine dimethylaminohydrolase 2 (DDAH2) expression and activity

Asymmetric dimethylarginine (ADMA) has been reported to affect the synthesis of nitric oxide (NO) in endothelial cells by inhibiting endothelial NO synthase (eNOS) activity and to cause endothelial dysfunction in humans. This study was conducted in human umbilical vein endothelial cells (HUVECs) to evaluate the effect of nebivolol, a selective beta1-adrenergic receptor antagonist, on ADMA concentration and on dimethylarginine dimethylaminohydrolase (DDAH2), the enzyme that regulates ADMA catabolism. Nebivolol dose-dependently decreased ADMA/symmetric dimethylarginine (SDMA) ratio (p from <0.01 to <0.001). This was parallelled by a dose-dependent increase in DDAH2 mRNA (p from <0.01 to <0.001) and protein expression (p from <0.01 to <0.001) and activity (p from <0.01 to <0.001). The small interference RNA (siRNA)-mediated knockdown of DDAH2 abolished the modification of DDAH2 expression (p<0.001) and ADMA/SDMA ratio (p<0.001) induced by nebivolol. In conclusion, the results of this study demonstrate that nebivolol reduces ADMA concentration by increasing DDAH2 expression and activity. Our in vitro findings describe a novel vascular effect of nebivolol and clearly identify this compound as the first antihypertensive agent that modulates DDAH2 in endothelial cells.     

Probucol preserves endothelial function by reduction of the endogenous nitric oxide synthase inhibitor level

1. Oxide low-density lipoprotein (ox-LDL) is believed to play an important role in early events of atherogenesis, and asymmetric dimethylarginine (ADMA) is associated with the development of endothelial dysfunction. The present study examined the effect of a single injection of native low-density lipoprotein (LDL) on endothelium function and the serum level of ADMA and the effect of probucol on endothelium function and ADMA level in rats. 2. Endothelial injury was induced by intravenous injection of LDL at the dose of 2, 4, or 6 mg kg(-1) for 24, 48, or 72 h, and vasodilator responses to acetylcholine in the aortic rings and serum levels of ADMA, nitrite/nitrate (NO) and malondialdehyde (MDA) were determined. 3. Pretreatment with LDL markedly reduced endothelium-dependent relaxation in a concentration-dependent manner. Inhibition of vasodilator responses to acetylcholine by LDL was abolished in the presence of L-arginine (3 x 10(-4) M). Serum levels of ADMA and MDA were significantly elevated in the rats pretreated with LDL, while serum level of nitrite/nitrate was markedly decreased. 4. Pretreatment with probucol significantly improved endothelium-dependent relaxation, decreased concentrations of ADMA and MDA and increased nitrite/nitrate level in the rats treated with LDL. A similar effect was seen in the rats pretreated with an antioxidant vitamin E. 5. These results suggest that a single injection of native LDL causes endothelial dysfunction by elevation of ADMA levels and that the protective effect of probucol on endothelial cells is related to reduction of ADMA concentration.     

Inhibitory effect of reinioside C on monocyte–endothelial cell adhesion induced by oxidized low-density lipoprotein via inhibiting NADPH oxidase/ROS/NF-κB pathway

Monocyte adhesion to activated vascular endothelial cells is the critical event in the initiation of atherosclerosis. Adhesion molecules are inflammatory markers, which are upregulated by oxidized low-density lipoprotein (ox-LDL) and play a pivotal role in atherogenesis. In present study, the effect of reinioside C, a major compound of Polygala fallax Hemsl., on adhesion of monocytes to endothelial cells induced by ox-LDL was investigated. The results showed that incubation of endothelial cells with ox-LDL (100?µg/mL) for 24 h markedly increased the expression of ICAM-1 and P-selectin and enhanced the adhesion of monocytes to endothelial cells. Pretreatment with reinioside C (1, 3, or 10?µM) dose-dependently decreased ox-LDL-induced upregulation of expression of ICAM-1 and P-selectin and the enhanced adhesion of monocytes to endothelial cells. To determine the role of NADPH oxidase/reactive oxygen species (ROS)/nuclear factor-κB (NF-κB) pathway, endothelial cells were treated with ox-LDL (100?µg/mL) for 2 h, and NADPH oxidase subunit (Nox 2 and p22^phox) mRNA expression, intracellular ROS level, and NF-κB activity were measured. The results showed that reinioside C attenuated ox-LDL-induced NADPH oxidase subunit (Nox 2 and p22^phox) mRNA expression, generation of ROS, and activation of NF-κB in endothelial cells in a dose-dependent manner; the two latter effects were inhibited by pyrollidine dithiocarbamate, the inhibitor of NF-κB. These findings suggest that reinioside C attenuates ox-LDL-induced expression of adhesion molecules (P-selectin and ICAM-1) and the adhesion of monocytes to endothelial cells by inhibiting NADPH oxidase/ROS/NF-κB pathway.     

Losartan inhibits monocytic adhesion induced by ADMA via downregulation of chemokine receptors in monocytes

Objective  Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, can induce the adhesiveness of monocytes to vascular endothelium, and chemokines play an important role in this process. The present study was carried out to test whether the inhibitory effect of losartan on ADMA-induced monocytic adhesion is mediated by chemokine receptors. Methods  Human monocytoid cells (THP-1) were incubated with exogenous ADMA (30 μM) for 4 or 24 h in the absence or presence of losartan. The monocytic adhesion, the levels of chemokines, and the expression of chemokine receptors were determined. The possible signal pathway was also explored. Results  In cultured monocytes, ADMA (30 μM) markedly increased monocytic adhesion to endothelial cells, elevated the levels of monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8), and upregulated the mRNA expression of chemokine receptors CCR₂ and CXCR₂. Exposure to ADMA (30 μM) significantly induced the generation of intracellular reactive oxygen species (ROS) and activation of nuclear factor (NF)-κB. Pretreatment with AT₁ receptor blocker (ARB) losartan (1, 3, 10 μM) attenuated monocytic adhesiveness elicited by ADMA and downregulated the expression of CCR₂ and CXCR₂ mRNA, accompanied by a significant decrease in ROS generation and NF-κB activity and expression. Conclusion  The present study suggests that the inhibitory effect of losartan on ADMA-induced monocytic adhesion may be related to downregulation of chemokine receptors by inhibiting the ROS/NF-κB pathway.     

Protective effects of daviditin A against endothelial damage induced by lysophosphatidylcholine

Previous investigations have indicated that endogenous inhibitors of nitric oxide synthase (NOS) such as asymmetric dimethylarginine (ADMA) may play an important role in endothelium dysfunction, and some antioxidant drugs improve endothelium function via reduction of ADMA level. The present study examined the antioxidation and endothelial protection of daviditin A, a xanthone compound. Daviditin A significantly inhibited Cu(2+)-induced low-density lipoprotein (LDL) oxidation (EC50: 38.7 microM) and scavenged 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals (EC50: 57.5 microM). Vasodilator responses to acetylcholine in rings of the isolated thoracic aorta were impaired in the presence of lysophosphatidylcholine (LPC)(5 mg/l). Daviditin A (10 or 30 microM) significantly attenuated inhibition by LPC of endothelium-dependent relaxation. Incubation of ECV304 cells with LPC (5 mg/l) for 24 h markedly elevated lactate dehydrogenase (LDH) activity and the levels of malondialdehyde (MDA) and ADMA, and decreased the content of nitric oxide (NO) and the activity of dimethylarginine dimethylaminohydrolase (DDAH). Daviditin A (1, 3 or 10 microM) significantly attenuated the increased release of LDH, increased content of MDA, and decreased level of NO induced by LPC. Daviditin A (3 or 10 microM) significantly inhibited the increased concentration of ADMA. Daviditin A (10 microM) significantly attenuated the decreased activity of DDAH. The present results suggest that daviditin A preserves endothelial dysfunction elicited by LPC, and the protective effect of daviditin A on the endothelium is related to reduction of ADMA concentration.     

Suppression of endothelial cell adhesion by XJP-1, a new phenolic compound derived from banana peel

The adhesion of monocytes to activated vascular endothelial cells is a critical event in the initiation of atherosclerosis. Adhesion is mediated by oxidized low-density lipoprotein (ox-LDL) which up-regulates inflammatory markers on endothelial cells. Here we report that (±) 7, 8-dihydroxy-3-methyl-isochromanone-4 (XJP-1), an inhibitor of ox-LDL-induced adhesion of monocytes to endothelial cells blocks cellular functions which are associated with adhesion. We show that XJP-1 down-regulates ox-LDL-induced over-expression of adhesion molecules (ICAM-1 and VCAM-1) in a dose-dependent manner in human umbilical vein endothelial cells (HUVECs), attenuates ox-LDL-induced up-regulation of low-density lipoprotein receptor (LOX)-1, decreases generation of reactive oxygen species (ROS), blocks translocation of nuclear factor-kappa B (NF-κB) activity, and prevents activation of c-Jun N-terminal kinase (JNK)/p38 pathways in endothelial cells. These findings suggest that XJP-1 may attenuate ox-LDL-induced endothelial adhesion of monocytes by blocking expression of adhesion molecules through suppressing ROS/NF-κB, JNK and p38 pathways.     

3,4,5,6-Tetrahydroxyxanthone preserves intercellular communication by reduction of the endogenous nitric oxide synthase inhibitor level

To observe the direct effects of 3,4,5,6-tetrahydroxyxanthone on connexin43 (Cx43) expression in cultured endothelial cells, cells were treated with lysophosphatidylcholine (LPC, 10?mg/l) for 24?h in the presence or absence of different concentrations of 3,4,5,6-tetrahydroxyxanthone (1, 3, or 10?μmol?l(-?1)). The reactive oxygen species (ROS) production, cell viability, asymmetric dimethylarginine (ADMA) levels, and Cx43 expression were detected. 3,4,5,6-Tetrahydroxyxanthone significantly inhibited the increase in ROS production and ADMA level, increased cell viability and up-regulated Cx43 mRNA and protein expression induced by LPC. 3,4,5,6-Tetrahydroxyxanthone has protective effect in LPC-induced atherosclerotic lesions, which is at least partly related to the reduction of ADMA level and downregulation of Cx43 expression.     

Azelnidipine, a new calcium channel blocker, inhibits endothelial inflammatory response by reducing intracellular levels of reactive oxygen species

Oxidized low-density lipoprotein (ox-LDL) plays an important in the development of atherosclerosis by stimulating the production of reactive oxygen species in endothelial cells, and thereby up-regulating vascular cell adhesion molecule-1 (VCAM-1). The objectives of the present study were to determine the effects of azelnidipine, a new calcium channel blocker, on the expression of VCAM-1 induced by 7-ketocholesterol, components of ox-LDL, and tumor necrosis factor-alpha (TNF-alpha). The scavenging activities of azelnidipine against superoxide, hydroxyl, and carbon-centered radicals were determined by electron spin resonance assay. The levels of intracellular reactive oxygen species were determined fluorometrically with the use of dichlorodihydrofluorescein diacetate (H(2)DCF-DA). Human aortic endothelial cells and U937 were used as endothelial cells and monocytic cells, respectively. The surface expression and mRNA levels of VCAM-1 were determined by enzyme immunoassay and RT-PCR performed on endothelial cell monolayers stimulated with 7-ketocholesterol or TNF-alpha. The numbers of monocytic cells adhering on the stimulated endothelial cells were counted in the microscopic fields. Translocation of p65 protein to the nucleus was estimated by fluorescence microscopy. Azelnidipine, but not nifedipine, reduced the signal intensity of 1,1-diphenyl-2-picrylhydrazyl radicals. Azelnidipine scavenged hydroxyl radicals, but not superoxide radicals. Intracellular levels of reactive oxygen species and RelA (p65) nuclear translocation in stimulated endothelial cells were reduced by azelnidipine. Azelnidipine significantly inhibited the expression of protein and mRNA of VCAM-1, and prevented the U937 cell adhesion to endothelial cells treated with 7-ketocholesterol or TNF-alpha. These results suggest that azelnidipine works as an anti-atherogenic agent by inhibiting the reactive oxygen species-dependent expression of VCAM-1 induced by 7-ketocholesterol and TNF-alpha.     

Involvement of asymmetric dimethylarginine and Rho kinase in the vascular remodeling in monocrotaline-induced pulmonary hypertension

Recent studies have shown that the plasma level of asymmetric dimethylarginine (ADMA) was increased accompanied by the decreased dimethylarginine dimethylaminohydrolase (DDAH) activity in pulmonary hypertension (PH) and ADMA was able to regulate pulmonary endothelial cells mobility through increasing the activity of Rho kinase (ROCK). This work was conducted to explore the role of ADMA/DDAH pathway in vascular remodeling in PH and the underlying mechanisms. The rat model of PH was established by a single injection of monocrotaline (60 mg/kg, s.c.). The pulmonary arterial pressure, the remodeling of pulmonary artery, the hypertrophy of right ventricle, the plasma levels of ADMA and NO, the expression of DDAH2, ROCK1 or ROCK2 and the ROCK activity were determined. In vitro studies, the pulmonary artery smooth muscle cells (PASMCs) were isolated and cultured. The effect of ADMA on PASMCs proliferation and ROCK activation was investigated. The results showed that the injection of monocrotaline successfully induced PH characterized by the increased pulmonary arterial pressure, vascular remodeling and right ventricle hypertrophy. The plasma level of ADMA was elevated concomitantly with the increased ROCK activity and ROCK1 expression as well as the decreased DDAH2 expression in pulmonary arteries. In the cultured PASMCs, ADMA promoted cellular proliferation accompanied by the increased ROCK1 expression and ROCK activity, which was attenuated by the ROCK inhibitor or by the intracellular antioxidant. These results suggest that ADMA could promote the proliferation of PASMCs through activating ROCK pathway, which may account for, at least partially, the vascular remodeling in monocrotaline-induced PH.     

Paeonol inhibits oxidized low density lipoprotein-induced monocyte adhesion to vascular endothelial cells by inhibiting the mitogen activated protein kinase pathway

Atherosclerosis is a chronic inflammatory disease characterized by increased expression of adhesion molecules, which contribute to monocytes adhesion to vascular endothelial cells (VECs). Paeonol, an active compound isolated from cortex Moutan, has been shown to have therapeutic effects on atherosclerotic animals. The present study aims to investigate whether paeonol can inhibit monocyte adhesion to vascular endothelial cells induced by oxidized Low-Density Lipoprotein (ox-LDL) and its possible therapeutic molecular mechanism. Exposure to ox-LDL (50, 100 μg/mL) induced damaged to VECs leading to decreased survival rates (p<0.01). Paeonol (7.2-18.0 μM) partially restored survival and reduced lactate dehydrogenase (LDH) release in VECs in a concentration-dependent manner (p<0.01). Adhesion of monocytes to VECs was dramatically prevented by paeonol at 21.6 and 25.2 μM (p<0.01). In addition, paeonol (14.4-21.6 μM) repressed the expression of vascular cell adhesion molecule-1 (VCAM-1) and lowered the levels of phosphor-c-Jun N-terminal kinase (P-JNK)1/2, phosphor-extracellular signal-regulated kinase (P-ERK)1/2 and P-p38 in a dose-dependent manner. The molecular effects of paeonol were more pronouced when companied with mitogen activated protein kinases (MAPKs) inhibitors. These data suggest that paeonol (10.8-25.2 μM), at certain concentrations, prevents monocyte adhesion to VEC induced by ox-LDL, probably by means of blocking one or more target proteins on MAPKs signaling pathway. These results indicate that paeonol has potential protective effects on the development of atherosclerosis.     

3,4,5,6-Tetrahydroxyxanthone preserves intercellular communication by reduction of the endogenous nitric oxide synthase inhibitor level

To observe the direct effects of 3,4,5,6-tetrahydroxyxanthone on connexin43 (Cx43) expression in cultured endothelial cells, cells were treated with lysophosphatidylcholine (LPC, 10 mg/l) for 24 h in the presence or absence of different concentrations of 3,4,5,6-tetrahydroxyxanthone (1, 3, or 10 μmol l^? 1). The reactive oxygen species (ROS) production, cell viability, asymmetric dimethylarginine (ADMA) levels, and Cx43 expression were detected. 3,4,5,6-Tetrahydroxyxanthone significantly inhibited the increase in ROS production and ADMA level, increased cell viability and up-regulated Cx43 mRNA and protein expression induced by LPC. 3,4,5,6-Tetrahydroxyxanthone has protective effect in LPC-induced atherosclerotic lesions, which is at least partly related to the reduction of ADMA level and downregulation of Cx43 expression.     

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- (TNF-) in the conditioned medium were measured. Cell viability and the activity of dimethylarginine dimethylaminohydrolase (DDAH) and nuclear factor-B (NF-B) in the cultured HUVECs were also determined. Incubation of HUVECs with ox-LDL (100 g/ml) for 24 h markedly elevated ADMA, LDH and TNF- in the conditioned medium and significantly increased the activity of NF-B, concomitantly with a significant decrease in the activity of DDAH and the content of NO. Pretreatment with fenofibrate (3, 10 or 30 M) significantly inhibited the increases in ADMA, LDH and TNF-, attenuated the decreased levels of NO and the decreased activity of DDAH and prevented the activation of NF-B. Similar effects were observed in the presence of pyrrolidine dithiocarbamate (PDTC, 10 M), an antagonist of NF-B. The beneficial effects of fenofibrate on cultured endothelial cells were abolished by MK-886, a specific peroxisome proliferator-activated receptor- (PPAR) 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-B activity by activation of the PPAR receptor.     

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- (TNF-). 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-, 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.