Valproic acid induces extracellular signal-regulated kinase 1/2 activation and inhibits apoptosis in endothelial cells

The histone deacetylase (HDAC) inhibitor valproic acid (VPA) was recently shown to inhibit angiogenesis, but displays no toxicity in endothelial cells. Here, we demonstrate that VPA increases extracellular signal-regulated kinase 1/2 (ERK 1/2) phosphorylation in human umbilical vein endothelial cells (HUVEC). The investigation of structurally modified VPA derivatives revealed that the induction of ERK 1/2 phosphorylation is not correlated to HDAC inhibition. PD98059, a pharmacological inhibitor of the mitogen-activated protein kinase kinase 1/2, prevented the VPA-induced ERK 1/2 phosphorylation. In endothelial cells, ERK 1/2 phosphorylation is known to promote cell survival and angiogenesis. Our results showed that VPA-induced ERK 1/2 phosphorylation in turn causes phosphorylation of the antiapoptotic protein Bcl-2 and inhibits serum starvation-induced HUVEC apoptosis and cytochrome c release from the mitochondria. Moreover, the combination of VPA with PD98059 synergistically inhibited angiogenesis in vitro and in vivo.

Cytochrome P450 2C expression and EDHF-mediated relaxation in porcine coronary arteries is increased by cortisol

OBJECTIVES/METHODS

In addition to nitric oxide (NO) and prostacyclin, endothelium-dependent dilation is mediated by the endothelium-derived hyperpolarizing factor (EDHF) which, in the coronary circulation, has been characterised as a metabolite of arachidonic acid synthesised by an cytochrome P450 (CYP) epoxygenase homologous to CYP 2C8/9. As the promotor regions of CYP 2C8 and 2C9 contain consensus sequences for glucocorticoid response elements, we determined the effect of cortisol on EDHF-mediated relaxations as well as on the expression of CYP 2C in isolated segments of porcine coronary artery.

RESULTS

Bradykinin-induced NO-mediated relaxation of KCl-constricted arterial rings was slightly attenuated following exposure to cortisol. However, EDHF-mediated relaxations of U46619-constricted arterial rings assessed in the presence of the cyclo-oxygenase inhibitor diclofenac and the NO synthase inhibitor N(omega)nitro-L-arginine (0.3 mM), were significantly enhanced (maximum relaxation: 66+/-7%, P<0.05 vs. control rings: 36+/-8%). Cortisol treatment (0.1 microM, 24 h) did not affect the endothelium-independent relaxation elicited by sodium nitroprusside and acute incubation with cortisol (0.1 microM, 30 min) did not alter either NO- or EDHF-mediated responses. The expression of CYP 2C (quantified by RT-PCR, Western blot analysis and confocal microscopy) was enhanced in porcine coronary endothelial cells following incubation with cortisol for 18-24 h.

CONCLUSIONS

These results demonstrate the concomitant upregulation of EDHF-mediated relaxations and CYP 2C expression by long-term treatment with cortisol. These observations support the concept that an epoxygenase homologous to CYP 2C8/9 plays a crucial role in the generation of EDHF-mediated responses in the coronary endothelium.

Cyclic stretch enhances the expression and activity of coronary endothelium-derived hyperpolarizing factor synthase

Endothelium-derived hyperpolarizing factor (EDHF) mediates NO/prostacyclin-independent relaxation in the coronary circulation. Because hemodynamic stimuli modulate endothelial gene expression and because coronary arteries are subjected to pronounced variations in vessel distension, we determined the effects of cyclic stretch on the expression and activity of the coronary EDHF synthase/cytochrome P450 (CYP) 2C8/9. In cultured porcine coronary and human umbilical vein endothelial cells, acute application of cyclic stretch (6%, 1 Hz, 10 minutes) elicited the generation of 8,9-epoxyeicosatrienoic acid (EET), 11,12-EET, and 14,15-EET. Prolonged stretch (4 to 36 hours) increased the expression of CYP 2C mRNA and protein 5- to 10-fold and was accompanied by a 4- to 8-fold increase in EET generation. A corresponding increase in CYP 2C mRNA and protein was also observed in pressurized segments of porcine coronary artery perfused under pulsatile conditions (8%, 1 Hz) for 6 hours. Although in cultured endothelial cells, cyclic stretch elicited the rapid activation of tyrosine kinases as well as Akt and the p38 mitogen-activated protein kinase, the mechanism by which cyclic stretch induces the expression of CYP 2C could not be elucidated, because inhibitors of these pathways induced CYP 2C expression in cells maintained under static conditions. These results have identified coronary EDHF synthase/CYP 2C as a novel mechanosensitive gene product in native and cultured endothelial cells. Because this enzyme generates both EETs and superoxide anions, this finding has wide-reaching implications for vascular homeostasis in conditions of manifest endothelial dysfunction.

The coronary endothelium-derived hyperpolarizing factor (EDHF) stimulates multiple signalling pathways and proliferation in vascular cells

In the present study we determined whether the endothelium-derived hyperpolarizing factor (EDHF), in addition to its acute effects on vascular tone, activates intracellular signalling pathways other than those associated with Ca2+-dependent K+ channels. EDHF was generated by rhythmic distension of porcine coronary arteries under conditions of combined nitric oxide (NO) synthase/cyclo-oxygenase blockade, and the EDHF-containing luminal incubate was applied to cultured human coronary endothelial or smooth muscle cells. In both cell types, the luminal incubate activated tyrosine kinases, the mitogen-activated protein (MAP) kinases, extracellular signal regulated kinases 1 and 2 (Erk1/2) and p38, as well as protein kinase B/Akt. The constituent responsible for Erk1/2 phosphorylation was identified as a cytochrome P450 (CYP) metabolite, as Erk1/2 activation was attenuated by pretreating the EDHF donor with the CYP 2C inhibitor sulfaphenazole as well as by CYP 2C antisense oligonucleotides. Erk1/2 phosphorylation in detector cells was also observed following the transfer of supernatant from cultured endothelial cells treated with the CYP inducer beta-naphthoflavone. The CYP 2C product 11,12-epoxyeicosatrienoic acid (11,12-EET) also activated tyrosine kinases, Erk1/2 and p38 MAP kinase. Overexpression of CYP 2C8 in native porcine coronary artery endothelial cells resulted in an increase in endothelial 11,12-EET production and Erk1/2 phosphorylation compared to that detected in untreated cells or cells transfected with an antisense CYP 2C8. Endothelial cell number was unaffected by transfection with LacZ or CYP 2C8 antisense but was significantly enhanced in cells overexpressing CYP 2C8. These observations indicate that EDHF/11,12-EET is not simply a vasodilator and that its continuous release under pulsatile conditions in vivo may affect vascular cell signalling and proliferation.

Endothelium-derived hyperpolarizing factor synthase (Cytochrome P450 2C9) is a functionally significant source of reactive oxygen species in coronary arteries

In the porcine coronary artery, a cytochrome P450 (CYP) isozyme homologous to CYP 2C8/9 has been identified as an endothelium-derived hyperpolarizing factor (EDHF) synthase. As some CYP enzymes are reported to generate reactive oxygen species (ROS), we hypothesized that the coronary EDHF synthase may modulate vascular homeostasis by the simultaneous production of ROS and epoxyeicosatrienoic acids. In bradykinin-stimulated coronary arteries, antisense oligonucleotides against CYP 2C almost abolished EDHF-mediated responses but potentiated nitric oxide (NO)-mediated relaxation. The selective CYP 2C9 inhibitor sulfaphenazole and the superoxide anion (O(2-)) scavengers Tiron and nordihydroguaretic acid also induced a leftward shift in the NO-mediated concentration-relaxation curve to bradykinin. CYP activity and O(2-) production, determined in microsomes prepared from cells overexpressing CYP 2C9, were almost completely inhibited by sulfaphenazole. Sulfaphenazole did not alter the activity of either CYP 2C8, the leukocyte NADPH oxidase, or xanthine oxidase. ROS generation in coronary artery rings, visualized using either ethidium or dichlorofluorescein fluorescence, was detected under basal conditions. The endothelial signal was attenuated by CYP 2C antisense treatment as well as by sulfaphenazole. In isolated coronary endothelial cells, bradykinin elicited a sulfaphenazole-sensitive increase in ROS production. Although 11,12 epoxyeicosatrienoic acid attenuated the activity of nuclear factor-kappaB in cultured human endothelial cells, nuclear factor-kappaB activity was enhanced after the induction or overexpression of CYP 2C9, as was the expression of vascular cell adhesion molecule-1. These results suggest that a CYP isozyme homologous to CYP 2C9 is a physiologically relevant generator of ROS in coronary endothelial cells and modulates both vascular tone and homeostasis.