Nox4 promotes endothelial differentiation through chromatin remodeling

RATIONALE

Nox4 is a constitutively active NADPH oxidase that constantly produces low levels of H2O2. Thereby, Nox4 contributes to cell homeostasis and long-term processes, such as differentiation. The high expression of Nox4 seen in endothelial cells contrasts with the low abundance of Nox4 in stem cells, which are accordingly characterized by low levels of H2O2. We hypothesize that Nox4 is a major contributor to endothelial differentiation, is induced during the process of differentiation, and facilitates homeostasis of the resulting endothelial cells.

OBJECTIVE

To determine the role of No×4 in differentiation of murine inducible pluripotent stem cells (miPSC) into endothelial cells (ECs).

METHODS AND RESULTS

miPSC, generated from mouse embryonic wildtype (WT) and Nox4-/- fibroblasts, were differentiated into endothelial cells (miPSC-EC) by stimulation with BMP4 and VEGF. During this process, Nox4 expression increased and knockout of Nox4 prolonged the abundance of pluripotency markers, while expression of endothelial markers was delayed in differentiating Nox4-depleted iPSCs. Eventually, angiogenic capacity of iPSC-ECs is reduced in Nox4 deficient cells, indicating that an absence of Nox4 diminishes stability of the reached phenotype. As an underlying mechanism, we identified JmjD3 as a redox target of Nox4. iPSC-ECs lacking Nox4 display a lower nuclear abundance of the histone demethylase JmjD3, resulting in an increased triple methylation of histone 3 (H3K27me3), which serves as a repressive mark for several genes involved in differentiation.

CONCLUSIONS

Nox4 promotes differentiation of miPSCs into ECs by oxidation of JmjD3 and subsequent demethylation of H3K27me3, which forced endothelial differentiation and stability.

PAFAH1B1 and the lncRNA NONHSAT073641 maintain an angiogenic phenotype in human endothelial cells

AIM

Platelet-activating factor acetyl hydrolase 1B1 (PAFAH1B1, also known as Lis1) is a protein essentially involved in neurogenesis and mostly studied in the nervous system. As we observed a significant expression of PAFAH1B1 in the vascular system, we hypothesized that PAFAH1B1 is important during angiogenesis of endothelial cells as well as in human vascular diseases.

METHOD

The functional relevance of the protein in endothelial cell angiogenic function, its downstream targets and the influence of NONHSAT073641, a long non-coding RNA (lncRNA) with 92% similarity to PAFAH1B1, were studied by knockdown and overexpression in human umbilical vein endothelial cells (HUVEC).

RESULTS

Knockdown of PAFAH1B1 led to impaired tube formation of HUVEC and decreased sprouting in the spheroid assay. Accordingly, the overexpression of PAFAH1B1 increased tube number, sprout length and sprout number. LncRNA NONHSAT073641 behaved similarly. Microarray analysis after PAFAH1B1 knockdown and its overexpression indicated that the protein maintains Matrix Gla Protein (MGP) expression. Chromatin immunoprecipitation experiments revealed that PAFAH1B1 is required for active histone marks and proper binding of RNA Polymerase II to the transcriptional start site of MGP. MGP itself was required for endothelial angiogenic capacity and knockdown of both, PAFAH1B1 and MGP, reduced migration. In vascular samples of patients with chronic thromboembolic pulmonary hypertension (CTEPH), PAFAH1B1 and MGP were upregulated. The function of PAFAH1B1 required the presence of the intact protein as overexpression of NONHSAT073641, which was highly upregulated during CTEPH, did not affect PAFAH1B1 target genes.

CONCLUSION

PAFAH1B1 and NONHSAT073641 are important for endothelial angiogenic function.

A pirinixic acid derivative (LP105) inhibits murine 5-lipoxygenase activity and attenuates vascular remodelling in a murine model of aortic aneurysm

BACKGROUND AND PURPOSE Arachidonic acid derivatives play a central role in inflammation processes. Arachidonic acid is metabolized by several enzymes, particularly cyclooxygenases (COX), 5-lipoxygenase (5-LOX) and microsomal prostaglandin E-synthase-1 (mPGES-1) to pro-inflammatory mediators. EXPERIMENTAL APPROACH We determined the effect of LP105, a pirinixic acid derivative which acts as inhibitor of 5-LOX, COX and mPGES-1, on aortic aneurysm development in mice and on 5-LOX activity in murine monocytes. KEY RESULTS In a monocyte cell line (RAW264.7), LP105 inhibited 5-LOX in whole cells (IC(50) : 1-3 µM) and in supernatants (IC(50) : ∼10 µM). Oral administration of LP105 to mice resulted in therapeutic tissue and plasma levels. Aortic aneurysms were induced in ApoE(-/-) mice by angiotensin II (AngII) and LP105 (5 mg·day(-1) per animal) was co-administered to a subgroup. Compared with animals receiving AngII alone, the LP105+AngII group showed a lower heart rate, a trend towards reduced heart to body weight ratio but similar hypertensive responses. AngII alone significantly increased aortic weight and diameter but co-treatment with LP105+AngII prevented these changes. LC/MS-MS studies revealed increased 15-hydroxytetraenoic acid (15-HETE) and 14,15-epoxyeicosatrienoic acid (14,15-EET) plasma levels in LP105-treated animals. In the murine kidney, mRNAs of EET-generating or metabolizing enzymes and of 5-LOX and 15-LOX were unaffected by LP105. LP105 also did not inhibit the EET-metabolizing soluble epoxide hydrolase. CONCLUSIONS AND IMPLICATIONS LP105 was a potent inhibitor of monocyte 5-LOX and reduced AngII-induced vascular remodelling in mice. A shift of arachidonic acid metabolism to the protective EET pathway may contribute to the beneficial effects of LP105.

The fatter the better? Perivascular adipose tissue attenuates vascular contraction through different mechanisms

Adipose tissue releases several hormones and autacoids and expansion of the adipose tissue and excessive obesity is a risk factor for hypertension. Perivascular adipose tissue, on the other hand, has been reported to lower the vascular tone through the release of a transferable, thermosensitive, non-lipid factor. In this issue of the British Journal of Pharmacology, Gao et al. (2007) report that a factor generated by the adipose tissue also stimulates the generation of NO by endothelium and that NO is the predominant mediator of adipose tissue-induced relaxation in endothelium-intact vessels.

Pivotal role of xanthine oxidase in the initiation of tubulointerstitial renal injury in rats with hyperlipidemia

Hyperlipidemia can induce or aggravate renal tubulointerstitial injury. Experiments in a complex rat model with chronic glomerulonephritis and long-standing, coexisting hyperlipidemia suggested that induction of xanthine oxidase (XO), with increased oxygen radical generation, is involved in aggravation of tubulointerstitial injury. To separate the role of XO in the initial events of lipid-mediated tubulointerstitial injury, short-term experiments with diet-induced hyperlipidemia over 21 and 35 days were performed in otherwise healthy rats. XO expression in relation to the antioxidant enzymes was examined in the cortical tubulointerstitium (TIS) and proximal tubules (PT). Subsequent experiments with XO inhibition were performed, examining tubulointerstitial infiltration with ED1-positive cells and expression of adhesion molecules and monocyte chemoattractant protein-1 (MCP-1) as indicators of early injurious events. Hyperlipidemia increased XO activity in TIS by 40 and 86%, and in PT by 28 and 90% at days 21 and 35, compared with controls on regular diet. This increased activity was associated with increased reactive oxygen species. Among the antioxidant enzymes, glutathione peroxidase activity increased in TIS by 40% and in PT by 90%. Histological evaluation showed a three-fold increase in ED1-positive cells and increased MCP-1 and vascular cell adhesion molecule-1 (VCAM-1) expression at day 35 in the TIS. Inhibition of XO prevented tubulointerstitial ED1 cell infiltration, together with a decreased expression of MCP-1 and VCAM-1. These results point to an important role for XO in the early stage of hyperlipidemia-associated renal injury, mediating macrophage infiltration by a putatively redox-dependent upregulation of MCP-1 and VCAM-1.

gp91phox-Containing NADPH Oxidase Mediates Endothelial Dysfunction in Renovascular Hypertension

Background— Isoforms of the NADPH oxidase contribute to vascular superoxide anion ( · O 2 − ) formation and limit NO bioavailability. We hypothesized that the endothelial gp91phox-containing NADPH oxidase is predominant in generating the O 2 − to scavenge endothelial NO and thus is responsible for the development of endothelial dysfunction.

Methods and Results— Endothelial dysfunction was studied in aortic rings from wild-type (WT) and gp91phox-knockout (gp91phox −/− ) mice with and without renovascular hypertension induced by renal artery clipping (2K1C). Hypertension induced by 2K1C was more severe in WT than in gp91phox −/− mice (158±2 versus 149±2 mm Hg; P <0.05). Endothelium-dependent relaxation to acetylcholine (ACh) was attenuated in rings from clipped WT but not from clipped gp91phox −/− mice. The reactive oxygen species (ROS) scavenger Tiron, PEG-superoxide dismutase, and the NADPH oxidase inhibitory peptide gp91ds-tat enhanced ACh-induced relaxation in aortae of clipped WT mice. Inhibition of protein kinase C, Rac, and the epidermal growth factor receptor kinase, elements involved in the activation of the NADPH oxidase, restored normal endothelium-dependent relaxation in vessels from clipped WT mice but had no effect on relaxations in those from gp91phox −/− mice. Relaxations to exogenous NO were attenuated in vessels from clipped WT but not clipped gp91phox −/− mice. After removal of the endothelium or treatment with PEG-superoxide dismutase, NO-induced relaxations were identical in vessels from clipped and sham-operated WT and gp91phox mice.

Conclusions— These data indicate that the formation of O 2 − by the endothelial gp91phox-containing NADPH oxidase accounts for the reduced NO bioavailability in the 2K1C model and contributes to the development of renovascular hypertension and endothelial dysfunction.

Withdrawal of cerivastatin induces monocyte chemoattractant protein 1 and tissue factor expression in cultured vascular smooth muscle cells

OBJECTIVE

The withdrawal of 3-hydroxy-3-methylglutaryl-coenzyme A-reductase inhibitors (statins) deteriorates endothelial function. We determined in vascular smooth muscle cells whether statin withdrawal leads to the expression of proinflammatory genes involved in the development and progression of arteriosclerosis.

METHODS AND RESULTS

The withdrawal of cerivastatin from pretreated vascular smooth muscle cells induced an increase in monocyte chemoattractant protein 1 (MCP-1) and tissue factor (TF) mRNA expression and enhanced MCP-1 secretion as well as cell surface TF activity. In the presence of cerivastatin, this effect was mimicked by geranylgeranyl pyrophosphate or mevalonate. Withdrawal-induced MCP-1 expression was sensitive to PD98059, SB203580, and diphenylene iodonium, suggesting an involvement of extracellular signal-regulated kinase 1/2, p38 mitogen-activated protein kinase, and the NADPH oxidase. Withdrawal increased the activity of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase and enhanced radical generation. Because the latter effect may result from an Rac-mediated activation of the NADPH oxidase, the effect of withdrawal on Rac translocation was studied. Statin treatment induced an increase in Rac-1 content in the cytoplasm. On withdrawal, however, an "overshoot" translocation of Rac to the plasma membrane occurred.

CONCLUSIONS

These observations suggest that statin withdrawal results in the activation of Rac and enhanced oxidative stress. The subsequent activation of redox-activated signal-transduction cascades results in the expression of MCP-1 and TF.

Hyperthyroidism enhances endothelium-dependent relaxation in the rat renal artery

OBJECTIVE

Hyperthyroidism has pronounced effects on vascular function and endothelium-dependent relaxation. The aim of the present study was to identify mechanisms underlying hyperthyroidism-induced alterations in endothelial function in rats.

METHODS

Animals were subjected to either a single injection (36 h) or 8 weeks treatment with the thyroid hormone triiodothyronine (T3, i.p.). Vascular reactivity and agonist-induced hyperpolarization were studied in isolated renal arteries. Endothelial nitric oxide (NO) synthase expression and cyclic AMP accumulation were determined in aortic segments.

RESULTS

Endothelium-dependent relaxations to acetylcholine (ACh) were enhanced by T3 36 h after injection and after treatment for 8 weeks. Thirty-six hours after T3 application, relaxation mediated by the endothelium-derived hyperpolarizing factor (EDHF) and by endothelium-derived NO were significantly enhanced. After 8 weeks treatment with T3, however, EDHF-mediated relaxation was impaired, whereas NO-mediated relaxation remained enhanced. KCl- and ACh-induced hyperpolarizations were more pronounced in arteries from rats treated with T3 for 36 h compared to control, whereas in arteries from rats treated with T3 for 8 weeks both responses were attenuated. In rats treated for 36 h, vascular cyclic AMP levels were enhanced in the aorta and inhibition of protein kinase A attenuated EDHF-mediated relaxations of the renal artery without affecting responses in arteries from the control group. In the aorta from rats treated with T3 for 8 weeks, the expression of the endothelial NO synthase was markedly up-regulated (463+/-68%).

CONCLUSIONS

These data indicate that short-term treatment with T3 increases endothelium-dependent relaxation, most probably by increasing vascular cyclic AMP content. Following treatment with T3 for 8 weeks, expression of the endothelial NO synthase was enhanced. During this phase, NO appears to be the predominant endothelium-derived vasodilator.

Platelet-derived growth factor activates production of reactive oxygen species by NAD(P)H oxidase in smooth muscle cells through Gi1,2

Recent findings indicate that platelet-derived growth factor (PDGF) plays a role in the generation of reactive oxygen species (ROS) as second messengers in smooth muscle cells (SMC). To identify the source and signal transduction pathway of ROS formation in SMC, we investigated PDGF-induced ROS formation. Stimulation of SMC with PDGF resulted in a rapid increase of ROS production. Using an inactivating antibody, we identified the increase to be dependent on p22phox, a NAD(P)H-oxidase subunit. ROS release was completely inhibited by the Gi protein inhibitor PTX as well as an antibody against Galphai1,2, however, not by antibodies against Galphai3/0, Gas, and Gbeta1beta2. The effect of PDGF on ROS production in SMC membranes could likewise be mimicked by the use of a recombinant Galphai2 subunit but not by Galphai3, Galphai0, Gas, and Gbetagamma subunits. Immunoaffinity chromatography demonstrated coupling of Galphai1,2 to the PDGF a-receptor, which, after preincubation of the SMC membranes with PDGF, was increased in the absence of GTPgammaS but decreased in the presence of GTPgammaS and prevented by PTX treatment. These data define a novel G protein-dependent mechanism by which PDGF signaling is transduced through direct coupling of the Gai1,2 subunit of the trimeric G proteins to the PDGF tyrosine kinase receptor.

Mepivacaine for Spinal Anesthesia in Parturients Undergoing Elective Cesarean Delivery: Maternal and Neonatal Plasma Concentrations and Neonatal Outcome

OBJECTIVE

Worldwide, long-acting bupivacaine is most commonly used for spinal anesthesia in parturients undergoing elective Cesarean delivery. However, advances in surgical technique and shorter duration of surgery make short-acting local anesthetic like mepivacaine appropriate, particularly if combined with opioids to enhance postoperative maternal pain relief.

MATERIAL AND METHODS

We assessed the effect of 4% hyperbaric mepivacaine (60 mg) plus 10 microg fentanyl for spinal anesthesia in 11 parturients undergoing elective Cesarean delivery. Sensory, motor and analgesic block characteristics, neonatal outcome (Apgar scores, umbilical cord blood analysis, neurologic and adaptive capacity score) as well as fetal and maternal mepivacaine plasma concentrations at delivery were determined (HPLC/UV).

RESULTS

Motor block (Induction-Bromage 0) duration lasted 113 +/- 20 min. Effective analgesia (VAS < or = 40) was 128 +/- 35 min. Maternal and fetal mepivacaine free plasma concentration were 0.18 +/- 0.05 microg/ml and 0.10 +/- 0.03 microg/ml, respectively. The fetal to maternal (UV/MV)-ratio for mepivacaine free plasma concentration was 0.56. Apgar scores, NACScores and the umbilical blood analysis showed no evidence of neonatal depression.

CONCLUSIONS

Particularly with short duration of surgery (21 +/- 5 min) intrathecal mepivacaine combined with fentanyl offers a favorable clinical alternative in parturients undergoing elective Cesarean delivery.

The extracellular regulated kinases (ERK) 1/2 mediate cannabinoid-induced inhibition of gap junctional communication in endothelial cells

1. Cannabinoids are potent inhibitors of endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxations. We set out to study the mechanism underlying this effect and the possible role of cannabinoid-induced changes in intercellular gap junction communication. 2. In cultured endothelial cells, Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and the cannabinoid receptor agonist HU210, increased the phosphorylation of extracellular regulated kinases 1/2 (ERK1/2) and inhibited gap junctional communication, as determined by Lucifer Yellow dye transfer and electrical capacity measurements. 3. Delta(9)-THC elicited a pronounced increase in the phosphorylation of connexin 43, which was sensitive to PD98059 and U0126, two inhibitors of ERK1/2 activation. Inhibition of ERK1/2 also prevented the Delta(9)-THC-induced inhibition of gap junctional communication. 4. Delta(9)-THC prevented both the bradykinin-induced hyperpolarization and the nitric oxide and prostacyclin-independent relaxation of pre-contracted rings of porcine coronary artery. These effects were prevented by PD98059 as well as U0126. 5. In the absence of Delta(9)-THC, neither PD98059 nor U0126 affected the NO-mediated relaxation of coronary artery rings but both substances induced a leftward shift in the concentration - relaxation curve to bradykinin when diclofenac and N(omega)nitro-L-arginine were present. Moreover, PD98059 and U0126 prolonged the bradykinin-induced hyperpolarization of porcine coronary arteries, without affecting the magnitude of the response. 6. These results indicate that the cannabinoid-induced activation of ERK1/2, which leads to the phosphorylation of connexin 43 and inhibition of gap junctional communication, may partially account for the Delta(9)-THC-induced inhibition of EDHF-mediated relaxation. Moreover, the activation of ERK1/2 by endothelial cell agonists such as bradykinin, appears to exert a negative feedback inhibition on EDHF-mediated responses.

Thrombin activates the hypoxia-inducible factor-1 signaling pathway in vascular smooth muscle cells: Role of the p22(phox)-containing NADPH oxidase

The heterodimeric transcription factor hypoxia-inducible factor-1 (HIF-1) is activated under hypoxic conditions, resulting in the upregulation of its target genes plasminogen activator inhibitor-1 (PAI-1) and vascular endothelial growth factor (VEGF). PAI-1 and VEGF are also induced in response to vascular injury, which is characterized by the activation of platelets and the coagulation cascade as well as the generation of reactive oxygen species (ROS). However, it is not known whether HIF-1 is also stimulated by thrombotic factors. We investigated the role of thrombin, platelet-associated growth factors, and ROS derived from the p22(phox)-containing NADPH oxidase in the activation of HIF-1 and the induction of its target genes PAI-1 and VEGF in human vascular smooth muscle cells (VSMCs). Thrombin, platelet-derived growth factor-AB (PDGF-AB), and transforming growth factor-beta(1) (TGF-beta(1)) upregulated HIF-1alpha protein in cultured and native VSMCs. This response was accompanied by nuclear accumulation of HIF-1alpha as well as by increased HIF-1 DNA-binding and reporter gene activity. The thrombin-induced expression of HIF-1alpha, PAI-1, and VEGF was attenuated by antioxidant treatment as well as by transfection of p22(phox) antisense oligonucleotides. Inhibition of p38 mitogen-activated protein kinase and phosphatidylinositol-3-kinase significantly decreased thrombin-induced HIF-1alpha, PAI-1, and VEGF expression. These findings demonstrate that the HIF-1 signaling pathway can be stimulated by thrombin and platelet-associated growth factors and that a redox-sensitive cascade activated by ROS derived from the p22(phox)-containing NADPH oxidase is crucially involved in this response.

Thrombin-induced MCP-1 expression involves activation of the p22phox-containing NADPH oxidase in human vascular smooth muscle cells

Activation of vascular smooth muscle cells (VMSC) by thrombin induces the expression of the chemokine, monocyte chemoattractant protein-1 (MCP-1). We investigated in cultured human and rat VSMC whether reactive oxygen species (ROS) derived from the vascular NADPH oxidase contribute to this effect. Exposure of cultured VSMC to thrombin rapidly increased ROS formation, phosphorylation of p38 MAP kinase as well as the expression of MCP-1. Specific inhibition of the p22phox subunit of the vascular NADPH oxidase using either p22phox neutralizing antibody or p22phox antisense oligonucleotides attenuated thrombin-induced ROS generation. Furthermore, thrombin-induced p38 MAP kinase activation as well as MCP-1 expression were impaired by antioxidants as well as by p22phox antisense oligonucleotides. Inhibition of p38 MAP kinase diminished the thrombin-induced expression of MCP-1.

CONCLUSION

Thrombin, by activating a p22phox-containing NADPH oxidase, elicits ROS generation and activation of p38 MAP kinase in VSMC. The subsequent induction of MCP-1 expression highligts the crucial role of the p22phox-containing NADPH oxidase in thrombin-induced signal transduction in VSMC.

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.

The terminal complement complex C5b-9 stimulates interleukin-6 production in human smooth muscle cells through activation of transcription factors NF-kappa B and AP-1

Activation of the complement system plays an important role in the pathogenesis of atherosclerosis. The proinflammatory cytokine interleukin (IL)-6 is potentially involved in the progression of the disease. We therefore investigated whether the terminal complement complex C5b-9 affects IL-6 production from vascular smooth-muscle cells (VSMC) and set out to determine the underlying signal transduction pathway. Stimulation of human VSMC with C5b-9 resulted in an increase of IL-6 transcript and production of IL-6 protein. Pretreatment with pertussis toxin or pyrrolidine dithiocarbamate inhibited complement-dependent IL-6 mRNA expression and IL-6 release, suggesting the involvement of Gi-proteins and nuclear factor-kB (NF-kB). C5b-9 also induced formation of reactive oxygen species, which, along with IL-6 release, was inhibited by the antioxidant N-acetylcysteine. C5b-9 activated the redox-sensitive transcription factors NF-kB and activator protein-1 (AP-1), which were both involved in the induction of IL-6 by C5b-9, as demonstrated by cis element double-stranded (decoy) oligonucleotides (ODN). The results demonstrate that activation of the complement system induces IL-6 release from human VSMC by a Gi-dependent pathway involving the generation of oxidative stressand the activation of the redox sensitive transcription factors NF-kB and AP-1. Our data support a new mechanism for the proatherogenic effect of the terminal complement complex.

An endothelium-derived hyperpolarizing factor distinct from NO and prostacyclin is a major endothelium-dependent vasodilator in resistance vessels of wild-type and endothelial NO synthase knockout mice

In addition to nitric oxide (NO) and prostacyclin (PGI(2)), the endothelium generates the endothelium-derived hyperpolarizing factor (EDHF). We set out to determine whether an EDHF-like response can be detected in wild-type (WT) and endothelial NO synthase knockout mice (eNOS -/-) mice. Vasodilator responses to endothelium-dependent agonists were determined in vivo and in vitro. In vivo, bradykinin induced a pronounced, dose-dependent decrease in mean arterial pressure (MAP) which did not differ between WT and eNOS -/- mice and was unaffected by treatment with N(omega)-nitro-l-arginine methyl ester and diclofenac. In the saline-perfused hindlimb of WT and eNOS -/- mice, marked N(omega)-nitro-l-arginine (l-NA, 300 micromol/liter)- and diclofenac-insensitive vasodilations in response to both bradykinin and acetylcholine (ACh) were observed, which were more pronounced than the agonist-induced vasodilation in the hindlimb of WT in the absence of l-NA. This endothelium-dependent, NO/PGI(2)-independent vasodilatation was sensitive to KCl (40 mM) and to the combination of apamin and charybdotoxin. Gap junction inhibitors (18alpha-glycyrrhetinic acid, octanol, heptanol) and CB-1 cannabinoid-receptor agonists (Delta(9)-tetrahydrocannabinol, HU210) impaired EDHF-mediated vasodilation, whereas inhibition of cytochrome P450 enzymes, soluble guanylyl cyclase, or adenosine receptors had no effect on EDHF-mediated responses. These results demonstrate that in murine resistance vessels the predominant agonist-induced endothelium-dependent vasodilation in vivo and in vitro is not mediated by NO, PGI(2), or a cytochrome P450 metabolite, but by an EDHF-like principle that requires functional gap junctions.

Oxidative stress and expression of p22phox are involved in the up-regulation of tissue factor in vascular smooth muscle cells in response to activated platelets

Vascular injury after balloon angioplasty results in the rapid activation of platelets leading to the release of growth factors and vasoactive substances. In addition, up-regulation of tissue factor (TF) and an increased production of reactive oxygen species (ROS) have been detected at sites of vascular injury. We investigated whether platelet-derived products (PDP) released from activated human platelets increase ROS production, resulting in the induction of TF expression in vascular smooth muscle cells (SMC). PDP induced a time- and concentration-dependent increase in ROS generation in cultured SMC that was mediated mainly by PDGF-AB and TGF-beta1 and impaired by the flavin inhibitor diphenylene iodonium. Increased ROS formation was associated with enhanced mRNA levels of the small NAD(P)H oxidase subunit p22phox or its smooth muscle isoform. Transient transfection with a p22phox antisense vector decreased PDP-induced ROS generation. PDP up-regulated TF mRNA expression, which was redox sensitive and reduced by transfection of the p22phox antisense vector. In addition, PDP-stimulated reporter gene activity of two TF promoter constructs was decreased by coexpression of the p22phox antisense vector. These results indicate that activated platelets up-regulate TF expression and that this response involves ROS generation and a p22phox-containing NAD(P)H oxidase in SMC.

A gp91phox containing NADPH oxidase selectively expressed in endothelial cells is a major source of oxygen radical generation in the arterial wall

Reactive oxygen species (ROS) play an important role in regulating vascular tone and intracellular signaling; the enzymes producing ROS in the vascular wall are, however, poorly characterized. We investigated whether a functionally active NADPH oxidase similar to the leukocyte enzyme, ie, containing the subunits p22phox and gp91phox, is expressed in endothelial cells (ECs) and smooth muscle cells (SMCs). Phorbol 12-myristate 13-acetate (PMA), a stimulus for leukocyte NADPH oxidase, increased ROS generation in cultured ECs and endothelium-intact rat aortic segments, but not in SMCs or endothelium-denuded arteries. NADPH enhanced chemiluminescence in all preparations. p22phox mRNA and protein was detected in ECs and SMCs, whereas the expression of gp91phox was confined to ECs. Endothelial gp91phox was identical to the leukocyte form as determined by sequence analysis. In contrast, mitogenic oxidase-1 (mox1) was expressed in SMCs, but not in ECs. To determine the functional relevance of gp91phox expression, experiments were performed in aortic segments from wild-type, gp91phox(-/-), and endothelial NO synthase (eNOS)(-/-) mice. PMA-induced ROS generation was comparable in aortae from wild-type and eNOS(-/-) mice, but was attenuated in segments from gp91phox(-/-) mice. Endothelium-dependent relaxation was greater in aortae from gp91phox(-/-) than from wild-type mice. The ROS scavenger tiron increased endothelium-dependent relaxation in segments from wild-type, but not from gp91phox(-/-) mice. These data demonstrate that ECs, in contrast to SMCs, express a gp91phox-containing leukocyte-type NADPH oxidase. This enzyme is a major source for arterial ROS generation and affects the bioavailability of endothelium-derived NO.

L-arginine supplementation in hypercholesterolemic rabbits normalizes leukocyte adhesion to non-endothelial matrix

L-arginine slows the development of atheromatous lesions, improves endothelium-dependent relaxation, and reduces the vascular superoxide anion production in hypercholesterolemic rabbits. These beneficial effects have been attributed to L-arginine-dependent formation of nitric oxide within the endothelial layer; a direct effect of L-arginine on other cells, however, has not been investigated. We hypothesised that in hypercholesterolemia L-arginine also specifically acts via a direct inhibitory effect on leukocytes, without affecting endothelial cells. The action of L-arginine was compared to vitamin E and the HMG CoA reductase inhibitor lovastatin which are known to attenuate progression of atherosclerosis. Rabbits were fed cholesterol enriched diet and from week five on lovastatin (10 mg/day), vitamin E (300 mg/d) or L-arginine (2% in drinking water) were given. After 16 weeks, blood cholesterol concentration was determined and leukocyte adhesion to cotton wool was measured. In order to exclude any endothelium-mediated effects an adhesion assay to endothelial cells was avoided. Cholesterol-enriched diet increased plasma cholesterol concentration (19+/-3 vs. 1427+/-117 mg/dl). Cholesterol levels were not affected by L-arginine (1344+/-163 mg/dl) or vitamine E (1312+/-243 mg/dl). Lovastatin treatment reduced cholesterol concentration by 35% as compared to the cholesterol group (899+/-51, p<0.05 vs. cholesterol). Cholesterol diet significantly increased leukocyte adhesion to cotton wool (16+/-3% vs 27+/-4%, p<0.05). Lovastatin or vitamine E had no effect on leukocyte adhesion (31+/-4%, 39+/-5), whereas L-arginine completely normalized adhesion (8.8+/-3%).

CONCLUSION

Rabbits fed high cholesterol diet have increased leukocyte adhesion, which is not affected by lovastatin or vitamine E treatment, but prevented by L-arginine supplementation. A direct inhibitory effect of L-arginine on leukocyte adhesion may contribute to the beneficial effects observed with this substance.

Oxidant stress in hyperlipidemia-induced renal damage

Hyperlipoproteinemia can aggravate glomerulosclerosis and chronic tubulointerstitial (ti) damage in kidneys without primary immunologic disease. We evaluated whether the effect of hyperlipidemia on progression of renal damage differed between kidneys without preexisting glomerular disease and kidneys with mesangioproliferative glomerulonephritis and whether the renal actions of hyperlipidemia were dependent on oxidant-antioxidant balance. Hyperlipidemia was induced by high-fat and high-cholesterol diet in uninephrectomized rats. In rats without glomerulonephritis, hyperlipidemia led to a rise in glomerular and ti generation of reactive oxygen species (ROS). Oxygen radicals were mainly generated by enhanced xanthine oxidoreductase (XO), which rose with protein concentration and activity during hyperlipidemia; concurrently, glomerulosclerosis and chronic ti injury were noticed during hyperlipidemia [ti damage (% of total tubulointerstitium (TI) after 150 days): normolipidemia 0.1 +/- 0% vs. hyperlipidemia 3.4 +/- 0. 9%; P < 0.05]. In mesangioproliferative Thy-1 nephritis, ti injury was significantly accelerated by hyperlipidemia (ti damage after 150 days: normolipidemic Thy-1 nephritis 2.5 +/- 0.6% vs. hyperlipidemic Thy-1 nephritis 12.5 +/- 3.1%; P < 0.05). Antioxidant enzyme activities decreased and XO activity rose markedly in the TI (XO activity in TI after 150 days: normolipidemic Thy-1 nephritis 2.2 +/- 0.5 vs. hyperlipidemic Thy-1 nephritis 4.5 +/- 0.7 cpm/microg protein; P < 0.05). In hyperlipidemic Thy-1 nephritis rats, which had a higher urinary protein excretion than normolipidemic rats, hypochlorite-modified proteins, an indirect measure for enhanced myeloperoxidase activity, were detected in renal tissue and in urine, respectively. During hyperlipidemia, chronic damage increased in renal TI. Enhanced generation of ROS, rise in oxidant enzyme activity, and generation of hypochlorite-modified proteins in renal tissue and urine were noticed. These data suggest that oxidant stress contributed to the deleterious effects of hyperlipidemia on the renal TI.

Increased nitrovasodilator sensitivity in endothelial nitric oxide synthase knockout mice: role of soluble guanylyl cyclase

Endogenously produced nitric oxide (NO) modulates nitrovasodilator-induced relaxation. We investigated the underlying mechanism in wild-type (WT) mice and endothelial NO synthase knockout (eNOS(-/-)) mice to determine whether a chronic lack of endothelial NO alters the soluble guanylyl cyclase (sGC) pathway. In aortic segments from eNOS(-/-) mice, the vasodilator sensitivity to sodium nitroprusside (SNP) was significantly greater than that in WT mice. There was no difference in sensitivity to the G-kinase I activator 8-para-chlorophenylthio-cGMP or to cromakalim. N(omega)-Nitro-L-arginine had no effect on the SNP-induced relaxation in eNOS(-/-) but increased the sensitivity in WT mice so it was no longer different than that of eNOS(-/-). Basal cGMP levels in aortic rings were significantly lower in eNOS(-/-) mice than in WT mice. SNP (300 nmol/L) induced a significantly greater cGMP accumulation in eNOS(-/-) mice than in WT mice. The maximal SNP-induced (10 micromol/L) increase in cGMP was similar in both strains. SNP-stimulated sGC activity was significantly greater in eNOS(-/-) mice than in WT mice. Incubation of aortic segments from WT mice with N(omega)-nitro-L-arginine increased sGC activity, an effect prevented by coincubation with SNP (10 micromol/L). The aortic expressions of the sGC alpha1 and beta1 subunits in WT and eNOS(-/-) mice were identical as determined with Western blot analysis. These data suggest that chronic exposure to endothelium-derived NO, as well as acute exposure to nitrovasodilator-derived NO, desensitizes sGC to activation by NO but does not alter sGC expression. Both the acute cessation of endothelial NO formation in WT mice and the chronic deficiency of NO in eNOS(-/-) mice restore the NO sensitivity of sGC and enhance vascular smooth muscle relaxation in response to nitrovasodilator agents.

Role of increased production of superoxide anions by NAD(P)H oxidase and xanthine oxidase in prolonged endotoxemia

Superoxide anions (O2-) are supposedly involved in the pathogenesis of endothelial dysfunction. We investigated whether the enhanced formation of O2- is involved in the attenuation of endothelium-dependent relaxation induced by lipopolysaccharide (LPS). Rats were injected with LPS (10 mg/kg IP), the aorta was removed after 12 or 30 hours, and generation of O2-, H2O2, and ONOO- was measured using chemiluminescence assays. Protein tyrosine nitration and expression of xanthine oxidase (XO), NAD(P)H oxidase, and manganese superoxide dismutase were determined by Western or Northern blotting, and endothelium-dependent relaxation in aortic rings was studied. LPS treatment increased vascular O2- (from 35+/-2 cpm/ring at baseline to 166+/-21 cpm/ring at 12 hours and 225+/-16 cpm/ring at 30 hours) and H2O2 formation, which was partially sensitive to the NAD(P)H oxidase inhibitor diphenylene iodonium at both time points studied and to the XO inhibitor oxypurinol only 30 hours after LPS treatment. Expression of XO and NAD(P)H oxidase (p22phox, p67phox, and gp91phox) were increased by LPS in a time-dependent manner, as were protein tyrosine nitration and ONOO- formation. LPS also induced expression of the oxidative stress-sensitive protein manganese superoxide dismutase. Endothelium-dependent relaxation was impaired after LPS treatment and could not be restored by inhibition of inducible NO synthase. Inhibition of O2- with superoxide dismutase, oxypurinol, tiron, or the superoxide dismutase mimetic Mn(III)tetrakis(4-benzoic acid)porphyrin chloride did not restore but further deteriorated the relaxation of LPS-treated rings. In summary, treatment of rats with LPS enhances vascular expression of XO and NAD(P)H oxidase and increases formation of O2- and ONOO-. Because removal of O2- compromised rather than restored endothelium-dependent relaxation, a direct role of O2- in the induction of endothelial dysfunction is unlikely. Other mechanisms, such as prolonged protein tyrosine nitration by peroxynitrite (which is formed from NO and O2-) or downregulation of the NO effector pathway, are more likely to be involved.

Role of xanthine oxidase in passive Heymann nephritis in rats

Passive Heymann nephritis (PHN) in rats is a model of human membranous nephropathy characterized by formation of subepithelial immune deposits in the glomerular capillary wall and complement activation. Oxygen radicals have been implicated in the subsequent glomerular damage which leads to proteinuria. This study examines the involvement of xanthine oxidase in this process. Xanthine oxidase activity was increased nearly twofold in glomeruli isolated 1 and 12 d after induction of PHN, and this was associated with increased glomerular superoxide anion generation. Analysis of glomerular samples by Northern and Western blotting revealed no quantitative changes in xanthine oxidoreductase expression in PHN, suggesting conversion of xanthine dehydrogenase to the oxidase form as the cause of increased activity. Treatment of rats with tungsten, an inhibitor of xanthine oxidase, before induction of PHN resulted in a marked decrease in glomerular xanthine oxidase activity and superoxide anion generation, and decreased proteinuria by 80% (day 12: 423+/-245 mg/d in PHN versus 78+/-53 mg/d in tungsten-treated PHN animals, P < 0.01). These findings point to a pivotal role of xanthine oxidase in the pathophysiology of PHN and could be of importance in the therapy of human membranous nephropathy.

Lovastatin maintains nitric oxide--but not EDHF-mediated endothelium-dependent relaxation in the hypercholesterolemic rabbit carotid artery

The endothelium contributes to the regulation of vascular tone by producing nitric oxide (NO) and the endothelium-derived hyperpolarising factor (EDHF). In hypercholesterolemia, endothelium-dependent relaxation is impaired but can be restored by treatment with lovastatin (LOVAS). We investigated the effects of LOVAS on NO and EDHF-mediated relaxation. Rabbits were fed 1% cholesterol diet for 4 weeks and 0.5%) cholesterol for the following 12 weeks (CHOL-group). The LOVAS group additionally received 10 mg of lovastatin over the last 12-week period. Experiments were performed in carotid artery rings. Relaxant responses to acetylcholine (ACh) were recorded in the presence of indomethacin. Nitro-L-arginine (NOARG, 100 microM) and potassium chloride (KCl, 35 mM) were used to differentiate between NO- and EDHF-mediated relaxations. Cholesterol impaired ACh-induced relaxations and this effect was prevented by LOVAS (control 100+/-1%, CHOL 81+/-6%, LOVAS 98+/-1%). In the presence of NOARG, relaxations to ACh were not different between the LOVAS and CHOL groups (control 78+/-4%, CHOL 64+/-6%, LOVAS 64+/-5%). When KCl was used, ACh-induced relaxations were similar in the LOVAS and control group (control 75+/-5%, CHOL 49+/-6%, LOVAS 76+/-2%). In arteries treated with NOARG and KCl together, no relaxations were observed. Relaxations of arteries from the control group were not affected by 18 h preincubation with lovastatin (10 microM). Lovastatin selectively maintains nitric oxide-mediated endothelium-dependent relaxation in hypercholesterolemic rabbit carotid arteries.

Endothelium-dependent vasodilatation in Sprague-Dawley rats with postinfarction hypertrophy: lack of endothelial dysfunction in vitro

The hypothesis was tested whether postinfarction hypertrophy/congestive heart failure in rats is associated with endothelial dysfunction and increased vascular generation of reduced oxygen species. Myocardial infarction was induced in Sprague-Dawley rats by ligation of the left coronary artery. After 16 weeks, endothelium-dependent (with acetylcholine) and -independent (with sodium nitro-prusside) relaxations were studied in isolated aortic rings, and isolated rings from the femoral and mesenteric arteries. The generation of superoxide, hydrogenperoxide, and peroxynitrite was measured in arteries using lucigenin- and luminol-enhanced chemiluminescence techniques. Systolic blood pressure decreased over the 16 week study period as compared to shamoperated control rats; organ weights (lungs, right and left ventricles) significantly increased in coronary artery ligated rats indicating development of congestive heart failure. Surprisingly, concentration response curves with acetylcholine and sodium nitroprusside were almost identical in myocardial infarction rats as compared to control animals, irrespective of which type of vessel was studied (aorta, femoral or mesenteric arteries). In addition, no differences in the production of reduced radical species were found in aortic tissue from heart failure rats as compared to control rats.

Glucocorticoids inhibit superoxide anion production and p22 phox mRNA expression in human aortic smooth muscle cells

-Recent reports suggest that the increased production of reactive oxygen species (ROS) in the vascular wall may contribute to the functional and structural changes associated with hypertension and atherosclerosis. Although glucocorticoid therapy can promote atherosclerosis, protective effects of these compounds on vascular lesion formation have been reported. In the present study, we investigated whether ROS production in cultured human aortic smooth muscle cells (HSMCs) can be modulated by glucocorticoids. Pretreatment of HSMCs with dexamethasone for 24 hours attenuated the basal and platelet-derived growth factor (PDGF)-AB- and angiotensin II-induced superoxide anion (O2. -) production. PDGF-AB-stimulated O2. - production was also inhibited by prednisolone and hydrocortisone but not by other steroids, such as testosterone and norgestrel. Incubation of HSMCs with glucocorticoids for 24 hours decreased 2',7'-dichlorodihydrofluorescein (DCHF) oxidation, an indicator of intracellular ROS levels. Dexamethasone decreased the mRNA expression of p22 phox, one of the components of NADPH oxidase, but had no effect on the activity of superoxide dismutase. The effects of dexamethasone on DCHF oxidation, and p22 phox mRNA expression and PDGF-AB-stimulated O2. - production were inhibited by the glucocorticoid receptor antagonist RU486. These results indicate that glucocorticoids decrease O2. - production by HSMCs via a receptor-dependent pathway. This effect is likely to be mediated by a decrease in the generating system, such as downregulation of p22 phox mRNA, rather than an increased inactivation of O2. -. The inhibition of ROS production might contribute to the local protective effects that glucocorticoids have on vascular lesion formation.

Dietary L-arginine and alpha-tocopherol reduce vascular oxidative stress and preserve endothelial function in hypercholesterolemic rabbits via different mechanisms

Vascular oxidative stress brought about by superoxide radicals and oxidized low-density lipoproteins (oxLDL) is a major factor contributing to decreased NO-dependent vasodilator function in hypercholesterolemia and atherosclerosis. We investigated whether chronic administration of L-arginine (2% in drinking water) or of alpha-tocopherol (300 mg/day) improves endothelium-dependent vasodilator function and systemic NO production, reduces vascular oxidative stress, and reduces the progression of atherosclerosis in cholesterol-fed rabbits with pre-existing hypercholesterolemia. Systemic NO production was assessed as urinary nitrate excretion; oxidative stress was measured by urinary 8-iso-PGF2alpha excretion in vivo, by lucigenin-enhanced chemiluminescence of isolated aortic rings ex vivo, and by copper-mediated LDL oxidation in vitro. Endothelium-dependent relaxation was almost completely abrogated in cholesterol-fed rabbits. Urinary nitrate excretion was reduced by 46+/-10%, and 8-iso-PGF2alpha excretion was increased by 61+/-18% as compared to controls (each P <0.05). Vascular superoxide radical release stimulated by PMA ex vivo was increased by 273+/-93% in this group, and the lag time of LDL oxidation was reduced by 35+/-6% (each P <0.05). Treatment with L-arginine and alpha-tocopherol reduced intimal lesion formation (by 68+/-6 and 4+/-11%, respectively; P <0.05) and improved endothelium-dependent relaxation. Both treatments also normalized urinary 8-iso-PGF2alpha excretion. L-Arginine increased urinary nitrate excretion by 43+/-13% (P <0.05) and reduced superoxide radical release by isolated aortic rings to control levels, which was unaffected by vitamin E treatment. By contrast, vitamin E dramatically increased the resistance of isolated LDL to copper-mediated oxidation in vitro by 178+/-7% (P <0.05), which was only marginally prolonged by L-arginine. Intimal thickening was reduced by both treatments. We conclude that both L-arginine and alpha-tocopherol reduce the progression of atherosclerotic plaques in cholesterol-fed rabbits. However, while L-arginine increases NO formation and reduces superoxide release, alpha-tocopherol antagonizes mainly oxLDL-related events in atherogenesis. Thus, both treatments reduce urinary isoprostane excretion and improve endothelium-dependent vasodilation via different mechanisms.

Dietary L-arginine normalizes endothelin-induced vascular contractions in cholesterol-fed rabbits

The endothelium regulates vascular function by releasing the vasodilator autacoid nitric oxide (NO) and the vasoconstrictor peptide endothelin-1 (ET-1). Impaired activity of NO as well as excessive activity of ET-1 have been demonstrated in hypercholesterolemia and atherosclerosis. Because dietary L-arginine can restore NO function and improve abnormal endothelium-dependent relaxation in hypercholesterolemic rabbits, we examined the effects of dietary supplementation with L-arginine in cholesterol-fed rabbits on endothelium-dependent vascular relaxation and ET-1-induced vascular contraction, as well as the systemic synthesis of ET-1. Rabbits were initially fed a diet enriched with 1% cholesterol for 4 weeks, followed by 0.5% cholesterol alone or supplemented with 2% L-arginine in drinking water during the next 12 weeks. Cholesterol feeding impaired endothelium-dependent relaxation of rabbit aortic rings ex vivo and increased urinary immunoreactive ET-1 excretion, along with decreased urinary nitrate excretion, an index of NO production. L-Arginine partially restored endothelium-dependent relaxation in parallel to increased urinary nitrate excretion and decreased urinary immunoreactive ET-1 excretion. Selective inhibition of ET-A receptors with BQ123 partially restored endothelium-dependent relaxation in hypercholesterolemic rabbits but had no effect on arterial rings from rabbits supplemented with L-arginine or from control animals. The contractile vascular response of aortic rings to exogenous ET-1 was increased in rabbits fed a high-cholesterol diet; this enhanced contractility to ET-1 was completely reversed by L-arginine. These data suggest that L-arginine restores endothelial function and normalizes the synthesis and vasoconstrictor response to ET-1 in hypercholesterolemia.

Antioxidant-oxidant balance in the glomerulus and proximal tubule of the rat kidney

1. Antioxidant and oxidative enzymes were examined in renal glomeruli and proximal tubules of healthy young rats (10-12 weeks old), and results were related to the superoxide anion generation of these tissues. 2. Activities of superoxide dismutases, catalase, and glutathione peroxidase were 3- to 6-fold higher in proximal tubules than in glomeruli. Similarly, enzyme levels and mRNA levels of superoxide dismutases and catalase were significantly higher in proximal tubules. 3. NADH- and NADPH-dependent oxidase activity and xanthine oxidase activity were not different in glomeruli and proximal tubules. 4. Measurements with lucigenin-enhanced chemiluminescence in vital tissues indicated 10-fold higher rates of superoxide anion in glomeruli than in tubules. 5. Compared with the young rats, tubules of 8-month-old rats had significantly higher superoxide anion rates and lower superoxide dismutase activity, whereas NADH- and NADPH-dependent oxidase activities were unchanged. 6. We conclude that considerable differences in the antioxidant-oxidant balance exist between the glomerulus and proximal tubule. Results from experiments using chemiluminescence in vital tissues suggest that changes in the antioxidant-oxidant balance have an effect on oxygen radical levels. The relevance of the observed differences to glomerular and tubulo-interstitial disease remains to be determined, but a greater susceptibility of the glomerulus to oxidant stress might be anticipated.

Reactive oxygen species and antioxidant defense in puromycin aminonucleoside glomerulopathy

Results from several radical scavenger studies indirectly suggested an involvement of reactive oxygen species in the pathogenesis of puromycin aminonucleoside glomerulopathy. In this study, generation of reactive oxygen species was examined directly in glomeruli isolated from rats in the acute phase of puromycin aminonucleoside nephrosis and related to the changes in the glomerular antioxidant defense. Five and nine days after puromycin aminonucleoside injection, gross proteinuria, reduced creatinine clearances, and typical changes of glomerular morphology were present. Levels of reactive oxygen species were increased eightfold in glomeruli isolated 15 min after puromycin aminonucleoside injection, returned to baseline levels on days 1 and 5 after injection, and rose again to 14-fold on day 9 after injection, as determined by chemiluminescence with luminol. Further analysis of increased glomerular radical generation, using the chemiluminescence enhancer lucigenin and different radical scavengers, suggested a predominant involvement of hydroxyl radical and hydrogen peroxide in the initial increase in reactive oxygen species 15 min after puromycin aminonucleoside. Nine days after induction of nephrosis, primarily superoxide anion and hydroxyl radical were found to contribute to increased reactive oxygen species. Despite oxidative stress, antioxidant enzymes were not induced in the course of nephrosis. On the contrary, catalase and glutathione peroxidase activities declined 9 d after puromycin aminonucleoside injection. The results indicate that a transient increase in glomerular reactive oxygen species is sufficient to induce the oxidative glomerular injury observed in this model and that the glomerulus may not necessarily respond to oxidative stress with an induction of antioxidant enzymes.

N(G)-nitro-L-arginine- and indomethacin-resistant endothelium-dependent relaxation in the rabbit renal artery: effect of hypercholesterolemia

Studies were designed to compare the N(G)-nitro-L-arginine- and indomethacin-resistant, endothelium-dependent relaxation to acetylcholine in isolated renal artery rings from normal and cholesterol-fed rabbits. It was assumed that the resistant part in response to acetylcholine is mediated by the endothelial-derived hyperpolarizing factor (EDHF). Rabbits were fed normal (n = 15) or cholesterol enriched chow (n = 13, 1% cholesterol for 4 weeks, 0.5% for 12 weeks). In organ chamber experiments, renal artery rings were precontracted with 0.1-1 microM phenylephrine or 35 mM KCl, and relaxed with acetylcholine (0.001-10 microM) in the presence of 10 microM indomethacin. Studies were performed in the presence or absence of: 100 microM N(G)-nitro-L-arginine (L-NOARG) to inhibit the nitric oxide pathway, 100 nM charybdotoxin (CTX) or 1 mM tetrabutylammonium (TBA) to inhibit Ca2+-activated K+ channels, and 100 microM SKF 525a to inhibit cytochrome P450 monoxygenase pathway. In normal arteries, L-NOARG partially inhibited acetylcholine-induced relaxation. The resistant part was almost abolished when the arteries were depolarized with KCl, or when L-NOARG was combined with either CTX, TBA or SKF 525a. In arteries from hypercholesterolemic animals, the relaxation to acetylcholine was only slightly impaired as compared to normal animals. However, in comparison to arteries from normal animals, the L-NOARG-resistant part of acetylcholine-induced endothelium-dependent relaxation was enhanced. It is speculated that differences in the balance between nitric oxide (NO)- and EDHF-mediated control of vascular tone may maintain acetylcholine-induced vasodilatation of the renal artery in hypercholesterolemia.

Anatomic heterogeneity of vascular aging: role of nitric oxide and endothelin

We investigated the effects of aging, a cardiovascular risk factor, on vascular function with regard to endothelial nitric oxide synthase (eNOS), superoxide dismutase (SOD), and endothelin (ET-1) in aorta and femoral artery of the rat. Concentration-response curves to acetylcholine, calcium ionophore A23187, norepinephrine, ET-1, big endothelin, sodium nitroprusside, and exogenous SOD were obtained. Expression of eNOS mRNA was analyzed by reverse-transcription polymerase chain reaction, SOD activity was assessed using a chemiluminescence-based cytochrome c assay, and ET-1 plasma concentrations were measured by radioimmunoassay. In aorta of old rats, relaxations to acetylcholine and calcium ionophore A23187, basal NO release, and expression of eNOS mRNA in aortic endothelial cells were reduced (P<.05). In femoral arteries, relaxations to acetylcholine were preserved, whereas basal release of NO was attenuated (P<.05). Aging selectively increased contractions to norepinephrine and functional endothelin converting enzyme activity and attenuated contractions to ET-1 in aortas but not femoral arteries. Vascular SOD activity was higher in the femoral artery (P<.05) and unaffected by aging. Plasma ET-1 levels increased and plasma SOD activity decreased with age (P<.05). Aging was associated with an anatomic heterogeneity of endothelial dysfunction, functional endothelin converting enzyme activity, and vascular SOD activity. Vascular function was impaired in the aorta but not the femoral artery, which may be related to lower eNOS mRNA expression and SOD activity. These data suggest differential regulation of the vascular aging process that may contribute to the anatomic heterogeneity of atherosclerosis.

Dietary L-arginine reduces the progression of atherosclerosis in cholesterol-fed rabbits: comparison with lovastatin

BACKGROUND

We investigated whether L-arginine induces regression of preexisting atheromatous lesions and reversal of endothelial dysfunction in hypercholesterolemic rabbits, whether similar effects can be obtained by cholesterol-lowering therapy with lovastatin, and which mechanism leads to these effects.

METHODS AND RESULTS

Rabbits were fed 1% cholesterol for 4 weeks and 0.5% cholesterol for an additional 12 weeks. Two groups of cholesterol-fed rabbits were treated with L-arginine (2.0% in drinking water) or lovastatin (10 mg/d) during weeks 5 through 16. Systemic nitric oxide (NO) formation was assessed as the urinary excretion rates of nitrate and cGMP in weekly intervals. Cholesterol feeding progressively reduced urinary nitrate excretion to approximately 40% of baseline (P<.05) and increased plasma concentrations of asymmetrical dimethylarginine (ADMA), an endogenous NO synthesis inhibitor. Dietary L-arginine reversed the reduction in plasma L-arginine/ADMA ratio and partly restored urinary excretion of nitrate and cGMP (each P<.05 vs cholesterol) but did not change plasma cholesterol levels. L-Arginine completely blocked the progression of carotid intimal plaques, reduced aortic intimal thickening, and preserved endothelium-dependent vasodilator function. Lovastatin treatment reduced plasma cholesterol by 32% but did not improve urinary nitrate or cGMP excretion or endothelium-dependent vasodilation. Lovastatin had a weaker inhibitory effect on carotid plaque formation and aortic intimal thickening than L-arginine. L-Arginine inhibited but lovastatin potentiated superoxide radical generation in the atherosclerotic vascular wall.

CONCLUSIONS

Dietary L-arginine improves NO-dependent vasodilator function in cholesterol-fed rabbits and completely blocks the progression of plaques via restoration of NO synthase substrate availability and reduction of vascular oxidative stress. Lovastatin treatment has a weaker inhibitory effect on the progression of atherosclerosis and no effect on vascular NO elaboration, which may be due to its stimulatory effect on vascular superoxide radical generation.

Endothelial-derived superoxide anions in pig coronary arteries: evidence from lucigenin chemiluminescence and histochemical techniques

1. The generation of superoxide anions (O2-) by intact pig coronary artery rings was measured using a lucigenin-enhanced chemiluminescence technique and a histochemical technique with Nitroblue Tetrazolium (NBT) staining. 2. Isolated arteries with intact endothelium generated O2- at a rate of 9.0 +/- 0.8 pmol min-1 (mg dry weight)-1; this rate was diminished by about 24% when the endothelium was removed. The NBT staining of arterial ring preparations showed formazan precipitation mainly in the intima. Arterial rings were pretreated with diethylthiocarbamate in order to inhibit Cu-Zn superoxide dismutase (SOD) activity which increased the O2- generation by 184 +/- 55% (n = 10; P < 0.01). Stimulation of protein kinase C with phorbol 12-myristate 13-acetate (5 microM) enhanced endothelium-dependent O2- generation by 136 +/- 20% (n = 19; P < 0.01). Neither stimulation with bradykinin or substance P, nor inhibition with NG-nitro-L-arginine methyl ester of endothelial nitric oxide synthase had a significant effect on O2- generation. In contrast, the inhibition of flavoproteins with diphenyliodonium decreased concentration-dependent O2- generation (IC50, 1.85 +/- 5.33 microM). Inhibition of tetrahydrobiopterin synthesis with 2,4-diamino-6-hydroxy-pyrimidine resulted in a reduced generation of O2- by about 55%. 3. The addition of 100 microM NADH and 100 microM NADPH resulted in an excessive generation of O2- at a rate of 0.68 +/- 0.03 and 0.26 +/- 0.01 nmol O2- min-1 (mg protein)-1, respectively, in the membrane fraction, but not in the cytosolic fraction, of homogenates obtained from arteries. 4. The results suggest that intact coronary arteries do generate O2- under basal conditions and that the endothelial layer significantly contributes to this phenomenon. This generation of O2- is greatly influenced by intrinsic SOD activity. It is suggested that basal vascular O2- generation is mainly due to membrane-bound NAD(P)H oxidase activity and/or tetrahydrobiopterin-dependent processes.

Gender differences in the generation of superoxide anions in the rat aorta

Generation of superoxide anions was measured in the isolated aorta of female and male rats using a lucigenin chemiluminescence technique. Aortae from male rats produced significantly more O2- (about 34%) than the aortae from female animals. Removal of endothelium reduced generation of O2- in the aorta of male and female rats by 23.9 +/- 1.3 and 15.3 +/- 2.3 pmole O2- min-1 mg-1 dry weight (p < 0.05), respectively. The denuded aortae of both sexes showed no different O2- production. Generation of O2- could not be influenced by inhibition of cycloxygenase with indomethacin or xanthine oxidase with oxypurinol. In contrast to the generation of O2- under basal conditions, stimulated generation of O2- by either addition of phorbol 12-myristate 13-acetate (to stimulate protein kinase C) or diethylthiocarbamate (to inhibit vascular superoxide dismutase activity) showed no significant gender differences. It is concluded that the endothelium from male rats produces more O2- under basal conditions than the endothelium from female rats.

Endothelial dysfunction in heart transplanted patients with graft vasculopathy

The pathological mechanism of cardiac transplant vasculopathy (TVP) is uncertain. We tested the hypothesis that the endothelial function, in terms of the release of endothelium-derived relaxing factor, is impaired in patients with angiographic evidence of transplant vasculopathy. In a pilot study, the effects of the substances used (substance P, acetylcholine, nitroglycerin) were assessed as regards tone of pre-contracted human coronary arteries in vitro, obtained from recipient hearts during cardiac transplantation. The study shows that substance P is a "pure' endothelium-dependent dilator of epicardial human coronary arteries, whereas acetylcholine has a more complex effect on vascular tone involving both a direct effect on the endothelium and the smooth muscle cells. In a second pilot study, the effects of intracoronary infusions of substance P (5-100 pmol.min-1) and acetylcholine (2-50 nmol.min-1) on flow velocity were compared in 10 patients undergoing cardiac catherization after heart transplantation. Flow velocity was determined by a 3F Doppler catheter placed into the proximal segment of the left anterior descending artery (LAD). Both drugs increased concentration-dependent flow velocity; substance P and acetylcholine maximally increased flow velocity by about 85 +/- 24% and 143 +/- 15%, respectively (P < 0.05). In a third study, 23 patients undergoing diagnostic cardiac catheterization were included approximately 40 months after heart transplantation. Patients were classified into those with (n = 8) and those without (n = 15) angiographic evidence of TVP. Coronary flow velocity (by Doppler) and epicardial coronary diameter (by quantitative angiography) were determined after intracoronary injections of substance P (20 pmol), nitroglycerin (0.1 mg), and papaverine (8 mg). Substances were injected through the central lumen which was placed into the LAD. Increases in flow velocity in response to substance P were significantly less in patients with TVP than in patients without evidence of TVP. Moreover, flow-mediated vasodilation in response to papaverine was almost abolished in patients with TVP. Vasodilation in response to nitroglycerin and maximal increase in flow velocity in response to papaverine was similar in both groups. These results suggest that TVP is associated with endothelial dysfunction, which may contribute to the pathogenesis of TVP and its vascular complications.

Vascular release of superoxide radicals is enhanced in hypercholesterolemic rabbits

Production/release of superoxide anions from aortic rings was measured by a modified lucigenin-enhanced chemiluminescence (CL) technique. The aortic rings were obtained from control and cholesterol-fed (1% for 12 weeks) rabbits. The CL signal was significantly increased in aortic wall of cholesterol-fed rabbits. Pretreatment with oxypurinol, an inhibitor of xanthine oxidase, had a slight but insignificant effect on the CL response produced by aortic rings from control animals but significantly reduced CL response to aortic rings from cholesterol-fed rabbits. Pretreatment with diethyldithiocarbamate (DETC), an inhibitor of intrinsic superoxide dismutase (SOD), increased the CL signal for both animal groups, but this increase was greatly aggravated in aortic rings from hypercholesterolemic rabbits. Addition of phorbol 12-myristate 13 acetate (PMA) to stimulate the respiratory burst of wall-adherent and/or resident leukocytes had only slight effect on the CL response to aortic rings from control animals but extensively stimulated photon emission of aortic rings from cholesterol-fed rabbits. These findings are in agreement with the concept that the arterial wall in hypercholesterolemia and/or atherosclerosis is under increased "oxidative stress."

The basal and stimulated release of the endothelium-derived relaxing factor from isolated pig coronary arteries does not interfere with the vascular release of superoxide

Oxygen-derived free radicals, in particular superoxide anions, are known to inactivate the endogenous vasodilator endothelium-derived relaxing factor (EDRF) which is probably identical with the gaseous radical nitric oxide. It is possible that EDRF is not the target of superoxide anions but may also be an endogenous scavenger of this radical. Superoxide anions generated by the vessel wall were measured by a modified lucigenin-enhanced chemiluminescence technique in isolated pig coronary artery rings with intact endothelium. The addition of bovine superoxide dismutase, a scavenger of superoxide anions, decreased the chemiluminescence signal by 40 +/- 26% (mean +/- SD; P < 0.05; n = 21) indicating reduced generation/release of superoxide anions. In contrast, pretreatment of coronary artery rings with diethyldithiocarbamate, an inhibitor of the intrinsic copper-zinc superoxide dismutase, increased the chemiluminescence response by 136 +/- 128% (P < 0.05; n = 21). This increase in the chemiluminescence response induced by diethyldithiocarbamate-pretreatment was almost abolished in the presence of added bovine superoxide dismutase. Specific inhibition of the EDRF release with nitro-L-arginine (100 microM) did not affect the chemiluminescence response. On the other hand, stimulation of the EDRF release by substance P (10 nM) or addition of the endothelium-mediated relaxant bradykinin (0.1 microM) did not affect the chemiluminescence response. Stimulation of the EDRF release with serotonin (0.1 microM) significantly reduced the photon emission by 15 +/- 16% (n = 27).(ABSTRACT TRUNCATED AT 250 WORDS)