Pitavastatin alters the expression of thrombotic and fibrinolytic proteins in human vascular cells

In addition to lowering blood lipids, clinical benefits of 3-hydroxy-3-methylglutaryl coenzyme A (HMG Co-A; EC 1.1.1.34) reductase inhibitors may derive from altered vascular function favoring fibrinolysis over thrombosis. We examined effects of pitavastatin (NK-104), a relatively novel and long acting statin, on expression of tissue factor (TF) in human monocytes (U-937), plasminogen activator inhibitor-1 (PAI-1), and tissue-type plasminogen activator (t-PA) in human aortic smooth muscle cells (SMC) and human umbilical vein endothelial cells (HUVEC). In monocytes, pitavastatin reduced expression of TF protein induced by lipopolysaccharide (LPS) and oxidized low-density lipoprotein (OxLDL). Similarly, pitavastatin also reduced expression of TF mRNA induced by LPS. Pitavastatin reduced PAI-1 antigen released from HUVEC under basal, OxLDL-, or tumor necrosis factor-alpha (TNF-alpha)-stimulated conditions. Reductions of PAI-1 mRNA expression correlated with decreased PAI-1 antigen secretion and PAI-1 activity as assessed by fibrin-agarose zymography. In addition, pitavastatin decreased PAI-1 antigen released from OxLDL-treated and untreated SMC. Conversely, pitavastatin enhanced t-PA mRNA expression and t-PA antigen secretion in untreated OxLDL-, and TNF-alpha-treated HUVEC and untreated SMC. Finally, pitavastatin increased t-PA activity as assessed by fibrin-agarose zymography. Our findings demonstrate that pitavastatin may alter arterial homeostasis favoring fibrinolysis over thrombosis, thereby reducing risk for thrombi at sites of unstable plaques.     

Daunorubicin attenuates tumor necrosis factor-alpha-induced biosynthesis of plasminogen activator inhibitor-1 in human umbilical vein endothelial cells

The anthracycline antibiotic daunorubicin is reported to induce apoptosis in cells by triggering ceramide generation through de novo synthesis or sphingomyelin hydrolysis. Treatment of human umbilical vein endothelial cells (HUVEC) with daunorubicin markedly decreased the mRNA expression and protein release of plasminogen activator inhibitor-1 (PAI-1). This cellular event was accompanied by a significant increase in the total ceramide content in HUVEC. On the other hand, tumor necrosis factor (TNF)-alpha treatment of HUVEC led to an increase in both PAI-1 mRNA expression and protein release, and an enhancement of total ceramide content was also observed. The stimulating effect of TNF-alpha on PAI-1 synthesis was attenuated by the pretreatment of HUVEC with daunorubicin. Interestingly, the daunorubicin-induced increase in ceramide content was blocked by addition of the potent ceramide synthase inhibitor fumonisin B(1), while the TNF-alpha-induced ceramide increase was not affected by this drug. Fumonisin B(1) treatment restored the daunorubicin-induced decrease in PAI-1 release to approximately 70% of the control, but did not affect the TNF-alpha-induced increase in PAI-1 release. Thus, these data imply the possibility that the subcellular topology of ceramide production determines its lipid mediator function in the regulation of PAI-1 synthesis in HUVEC, because both TNF-alpha and daunorubicin could increase the ceramide levels.     

Synthesis and secretion of plasminogen activator inhibitor 1 by human endothelial cells in vitro. Effect of active site mutagenized tissue-type plasminogen activator

The effects of recombinant tissue-type plasminogen activator (rt-PA) and of an inactive mutant of rt-PA, obtained by mutagenesis of the active site Ser478 to Ala (rt-PA-Ala478), on the synthesis and secretion of plasminogen activator inhibitor-1 (PAI-1) by human umbilical vein endothelial cells (HUVEC) in culture were studied. Under base-line conditions, PAI-1 antigen secretion was 4.3 +/- 1.0 micrograms (mean +/- S.D., n = 8) per 10(6) cells in 24 h. This PAI-1 had a low specific activity (6,000 +/- 1,600 units/mg) and Mr of 50,000, which was not altered by addition of rt-PA. In HUVEC cultured with 2 micrograms/ml rt-PA-Ala478, PAI-1 antigen secretion was 2.1 +/- 0.8 micrograms (n = 5) per 10(6) cells in 24 h with a specific activity of 120,000 +/- 42,000 units/mg and Mr of 50,000. Addition of rt-PA to this conditioned medium resulted in generation of three main components: 16% migrated as an Mr 106,000 rt-PA.PAI-1 complex, 16% as an Mr 81,000 degraded rt-PA.PAI-1 complex and the remainder as an Mr 45,000 degradation product of PAI-1. HUVEC cultured with 2 micrograms/ml rt-PA secreted 3.9 +/- 0.6 micrograms (n = 8) PAI-1 antigen per 10(6) cells within 24 h, of which 20-50% occurred as intact or degraded complexes with t-PA (Mr 106,000 and 81,000) and the rest as an inactive Mr 45,000 degradation product of PAI-1. PAI-1 mRNA levels, determined by Northern blot analysis and expressed relative to beta-actin mRNA levels, were very similar for HUVEC cultured in the absence or the presence of rt-PA or rt-PA-Ala478. It is concluded that PAI-1 is secreted by HUVEC in culture in fully active form which spontaneously inactivates. PAI-1 can be stabilized by addition of rt-PA-Ala478 to the culture medium, resulting in a 20-fold increase in specific activity. Interaction of rt-PA with active PAI-1 produces both t-PA.PAI-1 complex and an inactive degradation product of PAI-1.     

Peroxisome proliferator-activated receptor-gamma agonists increase vascular endothelial growth factor expression in human vascular smooth muscle cells

Vascular endothelial growth factor (VEGF), expressed in a variety of mesenchymal cells including vascular smooth muscle cells (VSMC), is a potent mitogen for endothelial cells, and is used clinically applied for ischemic disease of peripheral vessels. To determine whether peroxisome proliferator-activated receptor gamma (PPARgamma) regulates VEGF production in VSMC, we examined VEGF secretion from VSMC treated with PPAR agonists. Troglitazone increased VEGF secretion in a time- and dose-dependent manner (261 +/- 35% with 25 mM of troglitazone for 24 h), and also increased levels of VEGF mRNA. VEGF secretion was also increased by other PPARgamma agonists, pioglitazone, LY171883, and 15d-PGJ2 (224 +/- 17.1%, 247 +/- 36.8% and 171 +/- 7.8%, respectively), but not the PPARgamma agonists bezafibrate and Wy14643 (85.2 +/- 1.5%, 94.6 +/- 3.2, respectively). Our findings suggest that thiazolidinediones might be useful for the therapeutic angiogenesis for ischemic artery disease.     

Effect of retinoic acid on the synthesis of tissue-type plasminogen activator and plasminogen activator inhibitor-1 in human endothelial cells

The synthesis of plasminogen activators and inhibitors in endothelial cells is highly regulated by hormones, drugs and growth factors. The present study evaluates the effect of retinoic acid on the synthesis of tissue-type plasminogen activator (t-PA) and of plasminogen activator inhibitor-1 (PAI-1) by cultured human umbilical vein endothelial cells (HUVEC). Retinoic acid produced a time- and concentration-dependent increase in the secretion of t-PA-related antigen but not of PAI-1 related antigen into the culture medium. A maximal sevenfold increase of t-PA antigen after 24 h was observed with 10 microM and a half-maximal increase with 0.1 microM retinoic acid. Retinoic acid induced a time-dependent increase of the t-PA mRNA, with a maximum at 8 h and returning to normal at 24 h. The protein kinase inhibitor H7 decreased the t-PA antigen induced by both retinoic acid and phorbol 12-myristate 13-acetate. These results suggest that treatment of HUVEC with retinoic acid increases t-PA production by a pathway which, at some level, involves protein kinases. Thus, retinoic acid induces t-PA synthesis in the absence of altered PAI-1 synthesis, which may enhance the fibrinolytic potential of the endothelium.     

Enhancement by homocysteine of plasminogen activator inhibitor-1 gene expression and secretion from vascular endothelial and smooth muscle cells

In order to elucidate the relationship between homocysteine and the fibrinolytic system, we examined the effect of homocysteine on plasminogen activator inhibitor-1 (PAI-1) and tissue-type plasminogen activator (tPA) gene expression and protein secretion in cultured human vascular endothelial and smooth muscle cells in vitro. PAI-1 mRNA and secreted protein levels were both enhanced by homocysteine in a dose dependent manner, with significant stimulation of PAI-1 secretion observed at concentrations greater than 0.5 mM homocysteine. In contrast, secretion and mRNA expression of tPA were not significantly altered by homocysteine stimulation. Secretion of TGFbeta (transforming growth factor beta) and TNFalpha (tumor necrosis factor alpha), possible regulators of PAI-1 expression and secretion, were not stimulated by treatment with 1.0 mM homocysteine. These results suggests that hyperhomocysteinemia-induced atherosclerosis and/or thrombosis may be caused by homocysteine-induced stimulation of PAI-1 gene expression and secretion in the vasculatures by a mechanism independent from paracrine-autocrine activity of TGFbeta and TNFalpha.     

Transmembrane signaling pathway mediates oxidized low-density lipoprotein-induced expression of plasminogen activator inhibitor-1 in vascular endothelial cells

Atherosclerotic cardiovascular disease is the number one cause of death for adults in Western society. Plasminogen activator inhibitor-1 (PAI-1), the major physiological inhibitor of plasminogen activators, has been implicated in both thrombogenesis and atherogenesis. Previous studies demonstrated that copper-oxidized low-density lipoprotein (C-oLDL) stimulated production of PAI-1 in vascular endothelial cells (EC). The present study examined the involvement of lectin-like oxidized LDL receptor-1 (LOX-1) and Ras/Raf-1/ERK1/2 pathway in the upregulation of PAI-1 in cultured EC induced by oxidized LDLs. The results demonstrated that C-oLDL or FeSO(4)-oxidized LDL (F-oLDL) increased the expression of PAI-1 or LOX-1 in human umbilical vein EC (HUVEC) or coronary artery EC (HCAEC). Treatment with C-oLDL significantly increased the levels of H-Ras mRNA, protein, and the translocation of H-Ras to membrane fraction in EC. LOX-1 blocking antibody, Ras farnesylation inhibitor (FTI-277), or small interference RNA against H-Ras significantly reduced C-oLDL or LDL-induced expression of H-Ras and PAI-1 in EC. Incubation with C-oLDL or F-oLDL increased the phosphorylation of Raf-1 and ERK1/2 in EC compared with LDL or vehicle. Treatment with Raf-1 inhibitor blocked Raf-1 phosphorylation and the elevation of PAI-1 mRNA level in EC induced by C-oLDL or LDL. Treatment with PD-98059, an ERK1/2 inhibitor, blocked C-oLDL or LDL-induced ERK1/2 phosphorylation or PAI-1 expression in EC. The results suggest that LOX-1, H-Ras, and Raf-1/ERK1/2 are implicated in PAI-1 expression induced by oxidized LDLs or LDL in cultured EC.     

Thiazolidinediones inhibit TNFalpha induction of PAI-1 independent of PPARgamma activation

Increased plasminogen activator inhibitor type 1 (PAI-1) levels are observed in endothelial cells stimulated by tumour necrosis factor alpha (TNFalpha). Thiazolidinediones (TZDs) may inhibit elevated endothelial cell PAI-1 accounting, in part, for the putative atheroprotective effects of TZDs. In an endothelial cell line, Rosiglitazone (RG) and Pioglitazone (PG) inhibited induction of PAI-1 by TNFalpha. The specific peroxisome proliferator-activated receptor gamma (PPARgamma) inhibitor, SR-202, failed to modulate this effect. RG also inhibited the effect of TNFalpha on a reporter gene construct harbouring the proximal PAI-1 promoter and PAI-1 mRNA in cells co-transfected with a dominant-negative PPARgamma construct. RG and PG attenuated TNFalpha-mediated induction of trans-acting factor(s) Nur77/Nurr1 and binding of nuclear proteins (NP) to the cis-acting element (NBRE). SR-202 failed to modulate these effects. The observations suggest TZDs inhibit TNFalpha-mediated PAI-1 induction independent of inducible PPARgamma activation and this may involve in the modulation of Nur77/Nurr1 expression and NP binding to the PAI-1 NBRE.     

AMPK inhibits fatty acid-induced increases in NF-kappaB transactivation in cultured human umbilical vein endothelial cells

The fuel sensing enzyme AMP-activated protein kinase (AMPK) enhances processes that generate ATP when stresses such as exercise or glucose deprivation make cells energy deficient. We report here a novel role of AMPK, to prevent the activation of NF-kappaB in endothelial cells exposed to the fatty acid palmitate or the cytokine TNF-alpha. Incubation of cultured human umbilical vein endothelial cells (HUVEC) with elevated levels of palmitate (0.4mM) increased NF-kappaB reporter gene expression by 2- to 4-fold within 8h and caused a 7-fold increase in VCAM-1 mRNA expression at 24h. In contrast, no increase in reporter gene expression was detected for AP-1, glucocorticoid-, cyclic AMP-, or serum response elements. Similar increases in NF-kappaB activation and VCAM-1 expression were not observed in cells incubated with an elevated concentration of glucose (25mM). The increases in NF-kappaB activation and VCAM-1 expression caused by palmitate were markedly inhibited by co-incubation with the AMPK activator AICAR and, where studied, by expression of a constitutively active AMPK. Likewise, AMPK activation inhibited the increase in NF-kappaB reporter gene expression observed in HUVEC incubated with TNF-alpha. The results suggest that AMPK inhibits the activation of NF-kappaB caused by both palmitate and TNF-alpha. The mechanism responsible for this action, as well as its relevance to the reported anti-atherogenic actions of exercise, metformin, thiazolidinediones, and adiponectin, all of which have been shown to activate AMPK, remains to be determined.     

Tissue-type plasminogen activator binding to human endothelial cells. Evidence for two distinct binding sites

The endothelium may contribute to fibrinolysis through the binding of plasminogen activators or plasminogen activator inhibitors to the cell surface. Using a solid-phase radioimmunoassay, we observed that antibodies to recombinant tissue-type plasminogen activator (rt-PA) and plasminogen activator inhibitor type 1 (PAI-1) bound to the surface of cultured human umbilical vein endothelial cells (HUVEC). HUVEC also specifically bound added radiolabeled rt-PA with apparent steady-state binding being reached by 1 h at 4 degrees C. When added at low concentrations (less than 5 nM), rt-PA bound with high affinity mainly via the catalytic site, forming a sodium dodecyl sulfate-stable 105-kDa complex which dissociates from the cell surface over time and which could be immunoprecipitated by a monoclonal antibody to PAI-1. rt-PA bound to this high affinity site retained less than 5% of its expected plasminogen activator activity. At higher concentrations, binding did not require the catalytic site and was rapidly reversible. rt-PA initially bound to this site retained plasminogen activator activity. These studies suggest that tissue-type plasminogen activator and PAI-1 are expressed on the surface of cultured HUVEC. HUVEC also express unoccupied binding sites for exogenous tissue-type plasminogen activator. The balance between the expression of plasminogen activator inhibitors and these unoccupied binding sites for plasminogen activators on the endothelial surface may contribute to the regulation of fibrinolysis.     

Effect of NADPH oxidase inhibition on endothelial cell ELAM-1 mRNA expression.

Neutrophil adherence to endothelium is partially mediated by the expression of endothelial leukocyte adhesion molecule-1 (ELAM-1) on endothelial cells activated by agents such as lipopolysaccharide (LPS) and phorbol myristate acetate (PMA). To elucidate molecular mechanisms involved in the induction of ELAM-1 on endothelial cells, we investigated the effect of the NADPH oxidase inhibitor, apocynin (4-hydroxy-3-methoxyacetophenone), on ELAM-1 mRNA expression in human umbilical vein endothelial cells (HUVEC) by Northern blot analysis. Apocynin downregulated both LPS- and PMA-induced ELAM-1 mRNA expression in a dose-dependent manner. Our results suggest NADPH oxidase might play a key role in ELAM-1 mRNA expression in HUVEC.     

Kaposi's sarcoma-associated herpesvirus infection promotes invasion of primary human umbilical vein endothelial cells by inducing matrix metalloproteinases

Matrix metalloproteinases (MMPs) play important roles in cancer invasion, angiogenesis, and inflammatory infiltration. Kaposi's sarcoma is a highly disseminated angiogenic tumor of proliferative endothelial cells linked to infection by Kaposi's sarcoma-associated herpesvirus (KSHV). In this study, we showed that KSHV infection increased the invasiveness of primary human umbilical vein endothelial cells (HUVEC) in a Matrigel-based cell invasion assay. KSHV-induced cell invasion was abolished by an inhibitor of MMPs, BB-94, and occurred in both autocrine- and paracrine-dependent fashions. Analysis by zymography and Western blotting showed that KSHV-infected HUVEC cultures had increased secretion of MMP-1, -2, and -9. KSHV increased the secretion of MMP-2 within 1 h following infection without upregulating its mRNA expression level. In contrast, the secretion of MMP-1 and -9 was not increased until 6 h after KSHV infection and was correlated with the upregulation of their mRNA expression levels. Promoter analysis by reporter assays and electrophoretic mobility shift assays identified an AP-1 cis-element as the dominant KSHV-responsive site in the MMP-1 promoter. Together, these results suggest that KSHV infection modulates the production of multiple MMPs to increase cell invasiveness and thus contributes to the pathogenesis of KSHV-induced malignancies.     

Reactive oxygen species upregulate expression of PAI-1 in endothelial cells

Second messengers involved in the signal transduction pathway leading to induction of the plasminogen activator inhibitor (PAI-1) have not yet been well characterized. This study focuses on the mechanisms of regulation of PAI-1 expression by reactive oxygen species (ROS) in human endothelial cells. Inhibition of the tumor necrosis factor alpha (TNFalpha?-induced expression of PAI-1 by antioxidant N-acetyl-L-cysteine (NAC) indicated redox-sensitive mechanisms involved in the signaling pathway. Because TNFalpha induces PAI-1 production in endothelial cells, and NAC attenuated this response, we attempted to investigate the possible involvement of ROS in the activation of PAI-1 by TNFalpha. Upregulation of PAI-1 expression in endothelial cells by the stimulation with TNFalpha (50 ng/ml) or H2O2 (10-200 micro M), observed by measurement of the antigen and mRNA levels, was reversed in the presence of NAC (20mM). The stimulatory effect of ROS was detected also at the level of the PAI-1 promoter in endothelial cells transfected with plasmid p800 LUC containing a PAI-1 promoter fragment (+71 to -800). The PAI-1 promoter activity was increased in the presence of ROS, and was suppressed by up to 75% in the presence of antioxidants. On the basis of this study we can conclude that reactive oxygen species play an important role in a cytokine-induced activation of PAI-1 expression, and may act as a signal transduction messenger.