Regulation of nitric oxide synthesis by proinflammatory cytokines in human umbilical vein endothelial cells. Elevations in tetrahydrobiopterin levels enhance endothelial nitric oxide synthase specific activity

Bacterial translocation up-regulates GTP-cyclohydrolase I in mesenteric vasculature of cirrhotic rats

In cirrhosis, arterial vasodilation and the associated hemodynamic disturbances are most prominent in the mesenteric circulation, and its severity has been linked to bacterial translocation (BT) and endotoxemia. Synthesis of nitric oxide (NO), the main vasodilator implicated, is dependent on the essential cofactor tetrahydrobiopterin (BH(4)). The key enzyme involved in BH(4) synthesis is GTP-cyclohydrolase I (GTPCH-I), which is stimulated by endotoxin. Therefore, we investigated GTPCH-I activity and BH(4) biosynthesis in the mesenteric vasculature of cirrhotic rats with ascites, as well as their relationship with BT and endotoxemia, serum NO, and mean arterial pressure (MAP). GTPCH-I activity and BH(4) content in mesenteric vasculature was determined by high-performance liquid chromatography. BT was assessed by standard bacteriologic culture of mesenteric lymph nodes (MLNs). Serum endotoxin was measured by a kinetic turbidimetric limulus amebocyte lysate assay, and serum NO metabolite (NOx) concentrations were assessed by chemiluminescence. BT was associated with local lymphatic and systemic appearance of endotoxin and was accompanied by increases in serum NOx levels. GTPCH-I activity and BH(4) content in mesenteric vasculature were both increased in animals with BT and correlated significantly (r = 0.69, P <.01). Both GTPCH-I activity and BH(4) levels significantly correlated with serum endotoxin and NOx levels (r = 0.69 and 0.54, 0.81 and 0.53, P <.05). MAP (a marker of systemic vasodilatation) correlated with endotoxemia (r = 0.58, P <.03) and with GTPCH-I activity (r = 0.69, P <.01). In conclusion, in cirrhotic animals BT appears to lead to endotoxemia, stimulation of GTPCH-I, increased BH(4) synthesis, and further enhancement of vascular NO production that leads to aggravation of vasodilatation.

cGMP inhibits GTP cyclohydrolase I activity and biosynthesis of tetrahydrobiopterin in human umbilical vein endothelial cells

Tetrahydrobiopterin (BH4) acts as an essential cofactor for the enzymatic activity of nitric oxide (NO) synthases. Biosynthesis of the cofactor BH4 starts from GTP and requires 3 enzymatic steps, which include GTP cyclohydrolase I (GCH I) catalysis of the first and rate-limiting step. In this study we examined the effects of cGMP on GCH I activity in human umbilical vein endothelial cells under inflammatory conditions. Exogenous application of the cGMP analogue 8-bromo-cGMP markedly inhibited GCH I activity in the short term, whereas an cAMP analogue had no effect on GCH I activity under the same condition. NO donors, NOR3 and sodium nitroprusside, elevated the intracellular cGMP level and reduced GCH I activity in the short term. This inhibition of GCH I activity was obliterated in the presence of an NO trapper carboxy-PTIO. NO donors had no effect on GCH I mRNA expression in the short term. Moreover, cycloheximide did not alter the inhibition by NO donors of GCH I activity. These findings suggest that stimulation of the cGMP signaling cascade down-regulates GCH I activity through post translational modification of the GCH I enzyme.

Alpha-naphthoflavone induces vasorelaxation through the induction of extracellular calcium influx and NO formation in endothelium

The effect of alpha-naphthoflavone (alpha-NF) on vascular function was studied in isolated ring segments of the rat thoracic aorta and in primary cultures of human umbilical vein endothelial cells (HUVECs). alpha-NF induced concentration-dependent relaxation of the phenylephrine-precontracted aorta endothelium-dependently and -independently at lower and higher concentrations, respectively. The cGMP, but not cAMP, content was increased significantly in alpha-NF-treated aorta. Pretreatment with N(omega)-nitro- l-arginine methyl ester (L-NAME) or methylene blue attenuated both alpha-NF induced vasorelaxation and the increase of cGMP content significantly. The increase of cGMP content induced by alpha-NF was also inhibited by chelating extracellular Ca(2+) with EGTA. These results suggest that the endothelium-dependent vasorelaxation induced by alpha-NF is mediated most probably through Ca(2+)-dependent activation of NO synthase and guanylyl cyclase. In HUVECs, alpha-NF induced concentration-dependent formation of NO and Ca(2+) influx. alpha-NF-induced NO formation was abolished by removal of extracellular Ca(2+) and by pretreatment with the Ca(2+) channel blockers SKF 96365 and Ni(2+), but not by the L-type Ca(2+) channel blocker verapamil. The Ca(2+) influx, as measured by (45)Ca(2+) uptake, induced by alpha-NF was also inhibited by SKF 96365 and Ni(2+). Our data imply that alpha-NF, at lower concentrations, induces endothelium-dependent vasorelaxation by promoting extracellular Ca(2+) influx in endothelium and the activation of the NO-cGMP pathway.

The effects of nitric oxide on prostanoid production and release by human umbilical vein endothelial cells

Human umbilical vein endothelial cells (HUVEC) express and synthesize both constitutive and inducible nitric oxide synthase (NOS) and cyclo-oxygenase (COX) enzymes, and have been extensively used as an in vitro model to investigate the role of these enzymes in the patho-physiology of placenta-fetal circulation. In this study we investigated the role of NO in regulating prostanoid production and release from HUVEC. Both untreated and IL-1beta-treated HUVEC were exposed to various NOS inhibitors and NO donors in short-term (1 or 3 hours) experiments, and the effects on prostanoid production were evaluated through the measurement of prostaglandins (PG) I2, E2 and F2alpha released in the incubation medium. We found that the inhibition of inducible NOS but not endothelial NOS antagonizes the IL-1beta-induced increase in PGI2 release. However, NOS inhibitors do not modify baseline PGI2 production. Pharmacological levels of NO, obtained with various NO donors, inhibit basal and IL-1beta-stimulated PG release.

Interleukin-10 induction of nitric-oxide synthase expression attenuates CD40-mediated interleukin-12 synthesis in human endothelial cells

Interleukin-10 (IL-10) is a potent anti-inflammatory cytokine in Th1 cell-mediated chronic inflammatory diseases such as, e.g. Crohn's disease. Moreover, IL-10 has been shown to limit the progression of atherosclerosis, presumably by influencing endothelial cell function. Here we demonstrate that under pro-inflammatory conditions expression of the human IL-10 receptor gene is enhanced in endothelial cells in vitro and in vivo. Subsequent exposure to IL-10 results in an up-regulation of both endothelial nitric-oxide synthase (NOS-3) expression and activity. Gel mobility shift analyses and decoy oligonucleotide experiments suggest that this effect of IL-10 is mediated through activation of the transcription factor STAT-3 (signal transducer and activator of transcription-3). One functional consequence of IL-10 up-regulation of NOS-3 abundance in cultured endothelial cells is the attenuation of CD154-induced IL-12 p40 expression. Moreover, CD154-induced IL-12 p40 expression is enhanced after blockade of NOS-3 activity but attenuated in the presence of exogenous nitric oxide. Increased NOS-3 expression may, thus, be one mechanism by which IL-10 exerts its anti-inflammatory effects in Th1 cell-mediated chronic inflammatory diseases.

The autoxidation of tetrahydrobiopterin revisited. Proof of superoxide formation from reaction of tetrahydrobiopterin with molecular oxygen

It has been known for quite some time that tetrahydrobiopterin (H4B) is prone to autoxidation in the presence of molecular oxygen. Evidence has been presented that in this process superoxide radicals may be released, although their intermediacy never has been directly proven. In the present study, the autoxidation of H4B was reinvestigated with the aim to find direct evidence for superoxide formation. By means of two specific assays, namely elicitation of luminescence from lucigenin and ESR-spectrometric detection of the DEPMPO-OOH radical adduct, the release of free superoxide radicals was unequivocally demonstrated. The production of superoxide radicals was further corroborated by interaction with nitric oxide. The kinetics of the autoxidation process was established. Our data fully confirm earlier conclusions that the direct reaction between H4B and oxygen serves as an initiation reaction for the further, rapid reaction of the thus formed superoxide with H4B, thereby very likely establishing a chain reaction process involving reduction of molecular oxygen by the intermediary tetrahydrobiopterin radical. Conclusively, because H4B can per se induce oxidative stress, an in vivo overproduction of this pterin, as is evident in various diseases, may be responsible for the observed acceleration of pathophysiological pathways.

Serum nitric oxide metabolites and E-selectin in preterm premature rupture of membranes

BACKGROUND

Diseases with low-grade inflammation perturb endothelial function. We investigated whether preterm premature rupture of membranes (PPROM) is associated with endothelial dysfunction, as assessed by the levels of endothelium-derived nitric oxide metabolites (NOx) and E-selectin in maternal serum.

METHODS

The concentrations of NOx and E-selectin were measured in 32 pregnant women with PPROM and in 27 healthy gestational age-matched control women. The grade of inflammation was estimated by measuring serum C-reactive protein (CRP) and interleukin-6 (IL-6) concentrations.

RESULTS

NOx and E-selectin concentrations were not different in PPROM patients as compared to controls. In 17 patients with PPROM, CRP rose above 12 mg/L. In this group, IL-6 concentration was significantly higher than among controls, but concentrations of NOx and E-selectin remained unaltered. There was a negative correlation between the levels of NOx, CRP and IL-6 and the interval from PPROM to delivery. The levels of NOx correlated positively with those of IL-6.

CONCLUSIONS

PPROM, with or without CRP and IL-6 surges, does not affect endothelial function markedly, as judged from the unaltered concentrations of NOx and E-selectin in maternal serum.

Potential mechanisms of impaired endothelial function in arterial hypertension and hypercholesterolemia

This review focuses on the role of impaired endothelial function for the development of atherosclerosis in human arterial hypertension and hypercholesterolemia in vivo. Potential mechanisms underlying impaired endothelial function and decreased bioavailability of nitric oxide under these clinical conditions are discussed. It further addresses therapeutic strategies aimed at improving the bioavailability of nitric oxide in these patients. The overall conclusion is that the bioavailability of nitric oxide is probably impaired, not by a single defect, but by various mechanisms affecting nitric oxide synthesis as well as nitric oxide breakdown. In both diseases increased superoxide anion production and oxidative stress represent a major mechanism. Decreased bioavailability of nitric oxide not only impairs endothelium-dependent vasodilation, but also activates other mechanisms that play an important role in the pathogenesis of atherosclerosis. Thus, therapeutic strategies should aim to restore bioavailability of nitric oxide, which has been demonstrated for lipid-lowering therapy in hypercholesterolemia and blood pressure control in hypertension. In addition, antioxidative strategies will represent a major therapeutic tool against atherosclerotic diseases in the future. Statins and blockers of the renin-angiotensin system seem to have such antioxidative effects independent from their effects on lipid profiles or blood pressure control.

Induction of vasorelaxation through activation of nitric oxide synthase in endothelial cells by brazilin

The vasorelaxant activity of Caesalpinia sappan L., a traditional Chinese medicine, and its major component brazilin were investigated in isolated rat aorta and human umbilical vein endothelial cells. In isolated rat aorta, C. sappan L. extract and brazilin relaxed phenylephrine-induced vasocontraction and increased cyclic guanosine 3',5'-monophosphate (cGMP) content. Induction of vasorelaxation of brazilin was endothelium-dependent and could be markedly blocked by pretreatment with nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME); N(G)-monomethyl-L-arginine acetate (L-NMMA) and guanylyl cyclase inhibitor, methylene blue; 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and nitric oxide (NO) scavenger, hemoglobin. The increasing cGMP content induced by brazilin was also blocked by pretreatment with L-NAME, methylene blue, and the removal of extracellular Ca(2+). In human umbilical vein endothelial cells, brazilin dose-dependently induced an increase in NO formation and NOS activity, which were greatly attenuated by either the removal of extracellular Ca(2+) or the chelating of intracellular Ca(2+) chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM). Moreover, brazilin dose-dependently induced the influx of extracellular Ca(2+) in human umbilical vein endothelial cells. Collectively, these results suggest that brazilin induces vasorelaxation by the increasing intracellular Ca(2+) concentration in endothelial cells of blood vessels and hence activating Ca(2+)/calmodulin-dependent NO synthesis. The NO is released and then transferred into smooth muscle cells to activate guanylyl cyclase and increase cGMP content, resulting in vasorelaxation.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) sequentially upregulates nitric oxide and prostanoid production in primary human endothelial cells

Endothelial cells express tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors, but the function of TRAIL in endothelial cells is not completely understood. We explored the role of TRAIL in regulation of key intracellular signal pathways in endothelial cells. The addition of TRAIL to primary human endothelial cells increased phosphorylation of endothelial nitric oxide synthase (eNOS), NOS activity, and NO synthesis. Moreover, TRAIL induced cell migration and cytoskeleton reorganization in an NO-dependent manner. TRAIL did not activate the NF-kappaB or COX-2 pathways in endothelial cells. Instead, TRAIL increased prostanoid production (PGE2=PGI2>TXA2), which was preferentially inhibited by the COX-1 inhibitor SC-560. Because NO and prostanoids play a crucial role in the state of blood vessel vasodilatation and angiogenesis, our data suggest that TRAIL might play an important role in endothelial cell function.

Nitric oxide production by decidual endothelial cells is not reduced in preeclampsia

OBJECTIVE

To investigate whether decidual endothelial cells (DEC) contribute to the pathogenesis of preeclampsia through abnormal nitric oxide production. Decidual endothelial cells from normal (NDEC) and preeclamptic (PEDEC) pregnancies, and also human umbilical vein endothelial cells (HUVEC), were examined.

METHODS

HUVEC, NDEC, and PEDEC were incubated for 45 min in serum-free media with the addition of potential stimulators [calcium ionophore (A23187), sepiapterin, and a combination of cytokines (TNF-alpha, gamma-IFN and LPS)], and the competitive inhibitor, NG-monomethyl-L-arginine (L-NMMA). These were added alone or in combination. Supernatants were measured for nitrate/nitrite (NOx) levels and the cells acid-extracted for measurement of cyclic guanosine monophosphate (cGMP). The effect of 30 min of shear stress (approximately 20 dynes/cm2) on NO and cGMP production by NDEC and PEDEC and on production of prostacyclin and thromboxane A2, was assessed.

RESULTS

PEDEC and HUVEC both produced more NO than NDEC under all conditions examined. Cell-associated cGMP levels, however, were not different among the cell groups but were increased by A23187 and inhibited by L-NMMA. In control conditions, shear stress stimulated cGMP levels 5-fold (p<0.01) in both NDEC and PEDEC, and PGI2 production 2-fold (p<0.05).

CONCLUSIONS

DEC from preeclamptic women do not have reduced NO production and respond normally to shear stress by increasing cGMP and PGI2 production. Our results are consistent with other reports of equal or higher NO levels in preeclampsia and indicate that reduced NO production by endothelial cells is not the explanation for the vasoconstriction of uterine vessels.

The platelet-endothelium interaction mediated by lectin-like oxidized low-density lipoprotein receptor-1 reduces the intracellular concentration of nitric oxide in endothelial cells

OBJECTIVES

To address the potential role of the endothelial lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) in the thrombotic system, in this study we first examined whether platelet interaction with LOX-1 generated reactive oxygen species (ROS) and superoxide (O2.-) and then investigated the relationship between the intracellular production of O2.- and the availability of nitric oxide (NO).

BACKGROUND

Oxidative inactivation of NO is regarded as an important cause of its decreased biologic activity which may favor platelet-dependent arterial thrombosis.

METHODS

Bovine aortic endothelial cells (BAECs) and Chinese hamster ovary-K1 cells stably expressing bovine LOX-1 (BLOX-1-CHO) were incubated at different times with human platelets. The ROS, O2.-, and NO were measured in cells by flow cytometry.

RESULTS

The incubation of BAECs and BLOX-1-CHO cells with human platelets induced a sharp and dose-dependent increase in intracellular concentration of ROS and O2.- (p from <0.01 to <0.001). The increase in intracellular concentration of O2.- was followed by a dose-dependent reduction in basal and bradykinin-induced intracellular NO concentration (p from <0.01 to <0.001). The increase in O2.- and the reduction of NO were inhibited by the presence of vitamin C and anti-LOX-1 monoclonal antibody (p < 0.001).

CONCLUSIONS

The results of this study show that one of the pathophysiologic consequences of platelet binding to LOX-1 may be the inactivation of NO through an increased cellular production of O2.-.

HMG-CoA reductase inhibitor increases GTP cyclohydrolase I mRNA and tetrahydrobiopterin in vascular endothelial cells

OBJECTIVE

Endothelial nitric oxide synthase (eNOS) activity is supported by tetrahydrobiopterin (BH4), which appears to be important for generating protective NO but decreases uncoupling formation of superoxide. We investigated the effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, in terms of BH4 metabolism in human umbilical vein endothelial cells (HUVECs).

METHODS AND RESULTS

We measured the mRNA levels of GTP cyclohydrolase I (GTPCH), the rate-limiting enzyme in the first step of de novo BH4 synthesis, by real-time polymerase chain reaction. The mRNA of GTPCH, as well as of eNOS, was upregulated in HUVECs treated with cerivastatin. This increase was time and dose dependent. Fluvastatin was also observed to enhance GTPCH and eNOS mRNA levels. In parallel with this observation, cerivastatin increased intracellular BH4. Incubating HUVECs with tumor necrosis factor (TNF-alpha) was observed to increase GTPCH mRNA while decreasing eNOS mRNA. In the presence of cerivastatin, the TNF-alpha-mediated increase in GTPCH mRNA was enhanced, and the TNF-alpha-mediated decrease in eNOS mRNA was attenuated. Cerivastatin increased the stability of eNOS mRNA. However, it did not alter the stability of GTPCH mRNA but increased GTPCH gene transcription, as shown by nuclear run-on assays. Preteatment of HUVECs with the selective GTPCH inhibitor, 2,4-diamino-6-hydroxypyrimidine, caused a decrease in intracellular BH4 and decreased citrulline formation after stimulation with ionomycin. Furthermore, the potentiating effect of cerivastatin was decreased by limiting the cellular availability of BH4.

CONCLUSIONS

Our data demonstrate that statins elevate GTPCH mRNA, thereby increasing BH4 levels in vascular endothelial cells. In addition to augmenting eNOS expression, statins potentiate GTPCH gene expression and BH4 synthesis, thereby increasing NO production and preventing relative shortages of BH4.

Long-term vitamin C treatment increases vascular tetrahydrobiopterin levels and nitric oxide synthase activity

In cultured endothelial cells, the antioxidant, L-ascorbic acid (vitamin C), increases nitric oxide synthase (NOS) enzyme activity via chemical stabilization of tetrahydrobiopterin. Our objective was to determine the effect of vitamin C on NOS function and tetrahydrobiopterin metabolism in vivo. Twenty-six to twenty-eight weeks of diet supplementation with vitamin C (1%/kg chow) significantly increased circulating levels of vitamin C in wild-type (C57BL/6J) and apolipoprotein E (apoE)--deficient mice. Measurements of NOS enzymatic activity in aortas of apoE-deficient mice indicated a significant increase in total NOS activity. However, this increase was mainly due to high activity of inducible NOS, whereas eNOS activity was reduced. Significantly higher tetrahydrobiopterin levels were detected in aortas of apoE-deficient mice. Long-term treatment with vitamin C restored endothelial NOS activity in aortas of apoE-deficient mice, but did not affect activity of inducible NOS. In addition, 7,8-dihydrobiopterin levels, an oxidized form of tetrahydrobiopterin, were decreased and vascular endothelial function of aortas was significantly improved in apoE-deficient mice. Interestingly, vitamin C also increased tetrahydrobiopterin and NOS activity in aortas of C57BL/6J mice. In contrast, long-term treatment with vitamin E (2000 U/kg chow) did not affect vascular NOS activity or metabolism of tetrahydrobiopterin. In vivo, beneficial effect of vitamin C on vascular endothelial function appears to be mediated in part by protection of tetrahydrobiopterin and restoration of eNOS enzymatic activity.

Peroxisome proliferator-activated receptor gamma ligands increase release of nitric oxide from endothelial cells

OBJECTIVE

Peroxisome proliferator-activated receptor gamma (PPARgamma) ligands reduce lesion formation in animal models of atherosclerosis by mechanisms that have not been defined completely. We hypothesized that PPARgamma ligands stimulate endothelial-derived nitric oxide release (*NO) to protect the vascular wall.

METHODS AND RESULTS

The PPARgamma ligands, 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) or ciglitazone, stimulated a PPAR response element-luciferase reporter construct in transfected porcine pulmonary artery endothelial cells (PAECs), demonstrating that PPARgamma was transcriptionally functional. Treatment with 15d-PGJ2 or ciglitazone significantly increased release of *NO from PAECs or human aortic endothelial cells and augmented calcium ionophore-induced *NO release from human umbilical vein endothelial cells measured by chemiluminescence analysis of culture media. Increases in *NO release caused by treatment with 15d-PGJ2 occurred at 24 hours, but not after 1 to 16 hours, and were abrogated by treatment with the transcriptional inhibitor alpha-amanitin. Overexpression of PPARgamma or treatment with 9-cis retinoic acid also enhanced PAEC *NO release. Neither 15d-PGJ2 nor ciglitazone altered eNOS mRNA, whereas 15d-PGJ2, but not ciglitazone, decreased eNOS protein.

CONCLUSIONS

Taken together, these findings demonstrate that PPARgamma ligands stimulate *NO release from endothelial cells derived from multiple vascular sites, through a transcriptional mechanism unrelated to eNOS expression.

Regulation of amino acid and glucose transporters in endothelial and smooth muscle cells

While transport processes for amino acids and glucose have long been known to be expressed in the luminal and abluminal membranes of the endothelium comprising the blood-brain and blood-retinal barriers, it is only within the last decades that endothelial and smooth muscle cells derived from peripheral vascular beds have been recognized to rapidly transport and metabolize these nutrients. This review focuses principally on the mechanisms regulating amino acid and glucose transporters in vascular endothelial cells, although we also summarize recent advances in the understanding of the mechanisms controlling membrane transport activity and expression in vascular smooth muscle cells. We compare the specificity, ionic dependence, and kinetic properties of amino acid and glucose transport systems identified in endothelial cells derived from cerebral, retinal, and peripheral vascular beds and review the regulation of transport by vasoactive agonists, nitric oxide (NO), substrate deprivation, hypoxia, hyperglycemia, diabetes, insulin, steroid hormones, and development. In view of the importance of NO as a modulator of vascular tone under basal conditions and in disease and chronic inflammation, we critically review the evidence that transport of L-arginine and glucose in endothelial and smooth muscle cells is modulated by bacterial endotoxin, proinflammatory cytokines, and atherogenic lipids. The recent colocalization of the cationic amino acid transporter CAT-1 (system y(+)), nitric oxide synthase (eNOS), and caveolin-1 in endothelial plasmalemmal caveolae provides a novel mechanism for the regulation of NO production by L-arginine delivery and circulating hormones such insulin and 17beta-estradiol.

Increased lipopolysaccharide binding protein in cirrhotic patients with marked immune and hemodynamic derangement

Intestinal bacterial overgrowth and translocation, both common in cirrhosis with ascites, may lead to the activation of monocytes and lymphocytes, increased levels of proinflammatory cytokines, and enhanced synthesis of nitric oxide present in cirrhosis. Bacterial endotoxin promotes the synthesis of lipopolysaccharide (LPS)-binding protein (LBP), and forms a LPS-LBP complex that binds to CD14. This study was designed to evaluate LBP levels and their correlation to the immune response and the hemodynamic status in cirrhotic patients. Plasma LBP, endotoxin, soluble CD14 (sCD14), cytokines, renin, nitrites, and systemic vascular resistance were determined before and 4 weeks after norfloxacin or placebo in 102 cirrhotic patients and 30 controls. LBP was elevated in 42% of ascitic cirrhotic patients (15.7 +/- 0.7 versus 6.06 +/- 0.5 microg/mL, P <.01). In 60% of high LBP patients, endotoxin was within normal range. Among ascitic patients, those with high LBP showed greater (P <.05) levels of sCD14, tumor necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), nitrites + nitrates (NOx)/creatinine, and renin, and lower vascular resistance. In the cirrhotic patients with high LBP, norfloxacin normalized (P <.01) LBP (from 16.6 +/- 0.5 to 5.82 +/- 0.8 microg/mL) and sCD14; reduced the level of cytokines, NOx/creatinine, and renin; and increased vascular resistance; but lacked effect in patients with normal LBP. Portal pressure was unchanged after norfloxacin in another group of 18 cirrhotic patients with high and 19 with normal LBP. In conclusion, the subset of ascitic cirrhotic patients with marked immune and hemodynamic derangement is identified by increased LBP levels. Amelioration of these abnormalities by norfloxacin suggests the involvement of enteric bacteria or their products in the triggering of the process.

Regulation of endothelial-type NO synthase expression in pathophysiology and in response to drugs

In many types of cardiovascular pathophysiology such as hypercholesterolemia and atherosclerosis, diabetes, cigarette smoking, or hypertension (with its sequelae stroke and heart failure) the expression of endothelial NO synthase (eNOS) is altered. Both up- and downregulation of eNOS have been observed, depending on the underlying disease. When eNOS is upregulated, the upregulation is often futile and goes along with a reduction in bioactive NO. This is due to an increased production of superoxide generated by NAD(P)H oxidase and by an uncoupled eNOS. A number of drugs with favorable effects on cardiovascular disease upregulate eNOS expression. The resulting increase in vascular NO production may contribute to their beneficial effects. These compounds include statins, angiotensin-converting enzyme inhibitors, AT1 receptor antagonists, calcium channel blockers, and some antioxidants. Other drugs such as glucocorticoids, whose administration is associated with cardiovascular side effects, downregulate eNOS expression. Stills others such as the immunosuppressants cyclosporine A and FK506/tacrolimus or erythropoietin have inconsistent effects on eNOS. Thus regulation of eNOS expression and activity contributes to the overall action of several classes of drugs, and the development of compounds that specifically upregulate this protective enzyme appears as a desirable target for drug development.

Altered tetrahydrobiopterin metabolism in atherosclerosis: implications for use of oxidized tetrahydrobiopterin analogues and thiol antioxidants

OBJECTIVE

Tetrahydrobiopterin (BH4) is of fundamental importance for the normal function of endothelial NO synthase. The purpose of this study was to investigate the effects of hyperlipidemia on vascular BH4 levels and the effect of supplementation with sepiapterin in the presence and absence of N-acetylcysteine (NAC).

METHODS AND RESULTS

New Zealand White rabbits were fed normal chow (normocholesterolemic [NC] group) or hyperlipidemic chow (hyperlipidemic [HL] group) for 8 to 10 weeks. Mean cholesterol levels were 1465+/-333 and 53+/-17 mg/dL in the HL and NC group, respectively. Markedly diminished BH4 levels were found in the HL group compared with the NC group, but these levels could be restored after 6 hours of incubation with sepiapterin. Peak relaxations to acetylcholine and A23187 were impaired in the HL group. Supplementation with sepiapterin resulted in a further diminution of relaxation in the HL but not NC group. Incubation with NAC for 6 hours failed to raise BH4 levels, whereas NAC in conjunction with sepiapterin raised BH4 levels approximately 221-fold. However, this increase did not improve relaxations to A23187 and acetylcholine.

CONCLUSIONS

Prolonged exposure to sepiapterin impairs vasorelaxation in hyperlipidemia despite repletion of endogenous BH4. Antioxidant thiols do not correct this impairment. These studies have implications for the use of sepiapterin in the correction of vasomotor tone in atherosclerosis.

Functionally novel tumor necrosis factor-alpha-modulated CHR-binding protein mediates cyclin A transcriptional repression in vascular endothelial cells

Local expression of tumor necrosis factor-alpha (TNF-alpha) at the sites of arterial injury after balloon angioplasty, suppresses endothelial cell (EC) proliferation and negatively affects reendothelialization of the injured vessel. We have previously reported that in vitro exposure of ECs to TNF-alpha induced EC growth arrest and apoptosis. These effects were mediated, at least in part, by downregulation of cell cycle regulatory proteins. In the present study, we report potential mechanism(s) for TNF-alpha-mediated suppression of cyclin A in ECs. TNF-alpha exposure to ECs completely abrogated cyclin A mRNA expression via mechanisms involving both transcriptional and posttranscriptional modifications. TNF-alpha inhibited de novo cyclin A mRNA synthesis and suppressed cyclin A promoter activity. Utilizing deletion mutants of human cyclin A promoter, we have identified CDE-CHR (Cell cycle-Dependent Elements-Cell cycle genes Homology Region) region of cyclin A promoter as a target for TNF-alpha suppressive action. Experiments to investigate CDE-CHR binding proteins/factors revealed a TNF-alpha-mediated increase in specific DNA binding activity to the CHR elements. This increase in binding activity by TNF-alpha was mediated via the induction of a functionally novel 84-kDa protein that binds specifically to CHR in Southwestern assays. UV cross-linking and SDS-PAGE analysis of proteins eluted from specific complex confirmed the presence of this 84-kDa protein. Moreover, induction of this protein by TNF-alpha was protein synthesis dependent. Additionally, exposure of ECs to TNF-alpha markedly reduced cyclin A mRNA stability. Targeted disruption of this protein could potentially be a therapeutic strategy to rescue EC proliferation in vivo.

Interaction between reactive oxygen metabolites and nitric oxide in oxidant tolerance

The excessive generation of reactive oxygen metabolites (ROM) leads to an oxidative stress in the microvasculature of a variety of tissues and has been implicated as a causative event in a number of pathologies. There are numerous reviews on this topic that have been published recently. Herein, we will focus on a beneficial effect of ROM generation that leads to the development of an adaptive response that protects tissue from a subsequent oxidative stress (oxidant tolerance). We will focus on reductionist approaches (studies in isolated cells) used by our laboratory and those of others to define the mechanisms involved in this adaptational response and potential interactions between different cells within the tissue. As our prototype organ system, we target the heart, which has received the greatest amount of attention in this area. We will summarize evidence from isolated endothelial cells and cardiac myocytes that supports (i) the role of ROM in the development of oxidant tolerance, (ii) the possibility of an interaction between cardiac myocytes and endothelial cells in this phenomenon, and (iii) the potential interactions between ROMs and nitric oxide.

Differential antibacterial activity of nitric oxide from the immunological isozyme of nitric oxide synthase transduced into endothelial cells

Primary cultures of endothelial cells, grown on the three-dimensional matrix Gelfoam where they take on the morphology of these cells in vivo, were found to phagocytose Staphylococcus aureus and two strains of Escherichia coli. The phagocytosis was independent of opsonization, although once opsonized, these bacteria were phagocytosed by endothelial cells. As cytochalsin D inhibited the internationalization of S. aureus and E. coli, the phagocytosis by endothelial cells appears to be actin-dependent. Transducing the gene for nitric oxide synthase (NOS) II into endothelial cells allowed us to determine the importance of NO(*) in host immunity against these bacteria. While the growth of S. aureus was impeded by NOS II endothelial cells, two strains of E. coli were killed by an NO(*)-dependent pathway. We conclude that endothelial cells have microbicidal mechanisms that are selective for the type of pathogen encountered.

Inhibition of major histocompatibility complex class II gene transcription by nitric oxide and antioxidants

Interferon (IFN)-gamma facilitates cellular immune response, in part, by inducing the expression of major histocompatibility complex class II (MHC-II) molecules. We demonstrate that IFN-gamma induces the expression of HLA-DRA in vascular endothelial cells via mechanisms involving reactive oxygen species. IFN-gamma-induced HLA-DRA expression was inhibited by nitric oxide (NO) and antioxidants such as superoxide dismutase, catalase, pyrrolidine dithiocarbamate, and N-acetylcysteine. Nuclear run-on assays demonstrated that NO and antioxidants inhibited IFN-gamma-induced HLA-DRA gene transcription. Transient transfection studies using a fully functional HLA-DRA promoter construct ([-300]DR alpha.CAT) showed that inhibition of endogenous NO synthase activity by N(omega)-monomethyl-l-arginine or addition of exogenous hydrogen peroxide (H(2)O(2)) augmented basal and IFN-gamma-stimulated [-300]DR alpha.CAT activity. However, H(2)O(2) and N(omega)-monomethyl-l-arginine could induce HLA-DRA expression suggesting that H(2)O(2) is a necessary but not a sufficient mediator of IFN-gamma-induced HLA-DRA expression. Electrophoretic mobility shift assay and Western blotting demonstrated that NO and antioxidants had little or no effect on IFN-gamma-induced IRF-1 activation or MHC-II transactivator (CIITA) expression but did inhibit IFN-gamma-induced activation of STAT1 alpha (p91) and Y box transcription factors, NF-Y(A) and NF-Y(B). These results indicate that NO and antioxidants may attenuate vascular inflammation by antagonizing the effects of intracellular reactive oxygen species generation by IFN-gamma, which is necessary for MHC-II gene transcription.

Native low-density lipoprotein induces endothelial nitric oxide synthase dysfunction: role of heat shock protein 90 and caveolin-1

Although native LDL (n-LDL) is well recognized for inducing endothelial cell (EC) dysfunction, the mechanisms remain unclear. One hypothesis is n-LDL increases caveolin-1 (Cav-1), which decreases nitric oxide (*NO) production by binding endothelial nitric oxide synthase (eNOS) in an inactive state. Another is n-LDL increases superoxide anion (O(2)(*-)), which inactivates *NO. To test these hypotheses, EC were incubated with n-LDL and then analyzed for *NO, O(2)(*-), phospho-eNOS (S1179), eNOS, Cav-1, calmodulin (CaM), and heat shock protein 90 (hsp90). n-LDL increased NOx by more than 4-fold while having little effect on A23187-stimulated nitrite production. In contrast, n-LDL decreased cGMP under basal and A23187-stimulated conditions and increased O(2)(*-) by a mechanism that could be inhibited by L-nitroargininemethylester (L-NAME) and BAPTA/AM. n-LDL increased phospho-eNOS by 149%, eNOS by approximately 34%, and Cav-1 by 28%, and decreased the association of hsp90 with eNOS by 49%. n-LDL did not appear to alter eNOS distribution between membrane fractions (approximately 85%) and cytosol (approximately 15%). Only 3-6% of eNOS in membrane fractions was associated with Cav-1. These data support the hypothesis that n-LDL increases O(2)(*-), which scavenges *NO, and suggest that n-LDL uncouples eNOS activity by decreasing the association of hsp90 as an initial step in signaling eNOS to generate O(2)(*-).

Functional inhibition of constitutive nitric oxide synthase in a rat model of sepsis

Induction of inducible nitric oxide synthase (iNOS) expression is likely important in the pathogenesis of sepsis. However, the sepsis-mediated induction of iNOS is associated with a decrease in constitutive NO synthase (cNOS) activity (which is reversible following acute but not chronic sepsis). Whether this decreased cNOS activity is due to functional inhibition of cNOS by the high concentrations of NO produced by iNOS or to downregulation of cNOS expression is not clear. Thus, we tested the hypothesis that sepsis produces a reversible iNOS/NO-mediated inhibition of cNOS activity. Using a rat cecal ligation and perforation (CLP) model of sepsis, we examined the time course of the changes in iNOS and cNOS activities in lung and thoracic aortae. Reversibility of the sepsis-induced decrease in cNOS activity was assessed in vitro by enzyme activity determination following selective inhibition of iNOS. iNOS and endothelial cNOS protein concentrations were determined by Western blotting. In all septic tissues, cNOS activity was depressed at 6, 12, 24, and 48 hours post-CLP. Inhibition of the increased iNOS activity with aminoguanidine, in vitro, partially restored cNOS activity following acute (6-12 hours) but not chronic sepsis (24-48 hours post-CLP). Consistent with the irreversible depression of cNOS activities in tissues following chronic sepsis, endothelial NOS protein concentrations declined progressively during the time course of sepsis. We have demonstrated the restoration of cNOS activity following in vitro inhibition of iNOS, early, and the downregulation of endothelial NOS, later, in a rat CLP model of sepsis. This suggests that further study is required before iNOS-selective inhibition can be considered in human sepsis.

Regulation of endothelial nitric oxide synthase activity and gene expression

Endothelial nitric oxide synthase (eNOS) is constitutively expressed in endothelial cells lining the blood vessel and the heart. It plays a major role in vascular and tissue protection. Its activity is tightly controlled by an intramolecular autoinhibitory element that hinders calmodulin binding. This molecular hindrance is removed by elevated intracellular calcium levels. The catalytic activity of eNOS is augmented by phosphorylation of a C-terminal serine residue (Ser-1177 of human eNOS) through the phosphatidyl-3 kinase (PI-3K)/Akt pathway. Its activity is also enhanced by binding to heat shock protein-90. These two processes are calcium independent. The two biochemical events appear to facilitate calmodulin access to its binding site. eNOS is upregulated at the transcriptional level. Its upregulation is mediated by an increased Sp1 binding to its cognate site on eNOS promoter/enhancer region via the action of protein phosphatase 2A (PP2A). PP2A is activated by a signaling pathway including PI-3gamma --> Janus activated kinase 2 (Jak2) --> MEK-1 --> ERK1 and 2. The transcriptional and posttranslational enhancement of eNOS activity is two- to threefold above the basal level. A higher magnitude of augmentation of eNOS gene expression can be achieved by gene transfer, which confers protection against vascular diseases and ischemia-induced tissue injury in experimental animals. These findings provide new insight into the protective role of eNOS and the therapeutic potential of eNOS gene therapy.

cAMP inhibits cytokine-induced biosynthesis of tetrahydrobiopterin in human umbilical vein endothelial cells

We studied the effects of cAMP on cytokine (interferon-gamma plus tumor necrosis factor-alpha)-induced stimulation of tetrahydrobiopterin (BH4) synthesis in human umbilical vein endothelial cells (HUVEC). The cytokine mixture caused a marked increase in the biosynthesis and release of BH4 by HUVEC. Dibutyryl-cAMP produced a dose-dependent inhibition of this cytokine-induced stimulation of synthesis and release of BH4 by these cells. 8-Bromo-cAMP also caused a significant inhibition, although the effects were less marked than those of dibutyryl-cAMP. Both forskolin and the stable analog of prostacyclin, iloprost, caused cAMP accumulation and a concomitant diminution of the cytokine-induced BH4 synthesis in HUVEC. Dibutyryl-cAMP and iloprost also significantly inhibited the cytokine-induced stimulation of GTP cyclohydrolase I (GCHI) activity and mRNA production. We concluded that the suppression by the cAMP messenger system of cytokine-induced stimulation of synthesis and release of BH4 by HUVEC can be attributed to the inhibition of the activity of GCHI, the rate-limiting enzyme in BH4 biosynthetic pathway, in HUVEC. The data also suggest that the cAMP-mediated reduction in the GCHI mRNA level may at least partially explain the decline in GCHI activity. It is reasoned that under inflammatory conditions, cAMP-elevating agents such as prostacyclin exert regulatory effects on circulation by inhibiting cytokine-induced synthesis and release of BH4 by HUVEC.

Activation of eNOS in rat portal hypertensive gastric mucosa is mediated by TNF-alpha via the PI 3-kinase-Akt signaling pathway

Activation of endothelial nitric oxide synthase (eNOS) in portal hypertensive (PHT) gastric mucosa leads to hyperdynamic circulation and increased susceptibility to injury. However, the signaling mechanisms for eNOS activation in PHT gastric mucosa and the role of TNF-alpha in this signaling remain unknown. In PHT gastric mucosa we studied (1) eNOS phosphorylation (at serine 1177) required for its activation; (2) association of the phosphatidylinositol 3-kinase (PI 3-kinase), and its downstream effector Akt, with eNOS; and, (3) whether TNF-alpha neutralization affects eNOS phosphorylation and PI 3-kinase-Akt activation. To determine human relevance, we used human microvascular endothelial cells to examine directly whether TNF-alpha stimulates eNOS phosphorylation via PI 3-kinase. PHT gastric mucosa has significantly increased (1) eNOS phosphorylation at serine 1177 by 90% (P <.01); (2) membrane translocation (P <.05) and phosphorylation (P <.05) of p85 (regulatory subunit of PI 3-kinase) by 61% and 85%, respectively; (3) phosphorylation (P <.01) and activity (P <.01) of Akt by 40% and 52%, respectively; and (4) binding of Akt to eNOS by as much as 410% (P <.001). Neutralizing anti-TNF-alpha antibody significantly reduced p85 phosphorylation, phosphorylation and activity of Akt, and eNOS phosphorylation in PHT gastric mucosa to normal levels. Furthermore, TNF-alpha stimulated eNOS phosphorylation in human microvascular endothelial cells. In conclusion, these findings show that in PHT gastric mucosa, TNF-alpha stimulates eNOS phosphorylation at serine 1177 (required for its activation) via the PI 3-kinase-Akt signal transduction pathway.

Intraplatelet tetrahydrobiopterin plays an important role in regulating canine coronary arterial thrombosis by modulating intraplatelet nitric oxide and superoxide generation

BACKGROUND

Platelet-derived nitric oxide inhibits platelet aggregation via constitutive NO synthase (NOS). Tetrahydrobiopterin (BH(4)), a cofactor of NOS, augments NO formation, whereas its deficiency decreases NO bioactivity and increases superoxide generation by NOS. The roles of intraplatelet BH(4) in platelet aggregation and thrombus formation, however, are unknown. Accordingly, we investigated whether intraplatelet BH(4) is involved in regulating cyclic flow variations (CFVs) and platelet aggregation in a canine model with stenosed and endothelium-injured coronary arteries that mimics acute coronary syndromes in humans.

METHODS AND RESULTS

After developing CFVs, dogs received saline or BH(4) (10 or 30 mg/kg) intravenously. Intraplatelet BH(4) and cGMP levels were decreased and intraplatelet nitrotyrosine production was increased during CFVs. ADP- and U46619-induced ex vivo platelet aggregation and platelet P-selectin expression were augmented during CFVs. BH(4) administration restored intraplatelet BH(4) and cGMP levels and decreased intraplatelet nitrotyrosine production, resulting in reduced CFVs and inhibited ex vivo platelet aggregation and platelet P-selectin expression. CFVs again developed after N(G)-monomethyl-L-arginine, an inhibitor of NOS, in BH(4)-treated dogs. Ex vivo platelet NOS activity at baseline, during CFVs, and after BH(4) administration did not differ.

CONCLUSIONS

Intraplatelet BH(4) may play an important role in regulating thrombus formation by modulating platelet-derived nitric oxide and superoxide generation by platelet NOS.

Cytokine treatment increases arginine metabolism and uptake in bovine pulmonary arterial endothelial cells

L-Arginine (L-Arg) is metabolized to nitric oxide (NO) by NO synthase (NOS) or to urea by arginase (AR). L-Arg is transported into bovine pulmonary arterial endothelial cells (BPAECs) by cationic amino acid transporter-2 (CAT-2). We hypothesized that cytokine treatment would increase L-Arg metabolism and increase CAT-2 mRNA expression. BPAECs were incubated for 24 h in medium (control) or medium with lipopolysaccharide and tumor necrosis factor-alpha (L-T). L-T increased nitrite production (3.1 +/- 0.4 nmol/24 h vs. 1.8 +/- 0.1 nmol/24 h for control; P < 0.01) and urea production (83.5 +/- 29.5 nmol/24 h vs. 17.8 +/- 8.6 nmol/24 h for control; P < 0.05). L-T-treated BPAECs had greater endothelial and inducible NOS mRNA expression compared with control cells. Increasing the medium L-Arg concentration resulted in increased nitrite and urea production in both the control and the L-T-treated BPAECs. L-T treatment resulted in measurable CAT-2 mRNA. L-T increased L-[(3)H]Arg uptake (5.78 +/- 0.41 pmol vs. 4.45 +/- 0.10 pmol for control; P < 0.05). In summary, L-T treatment increased L-Arg metabolism to both NO and urea in BPAECs and resulted in increased levels of CAT-2 mRNA. This suggests that induction of NOS and/or AR is linked to induction of CAT-2 in BPAECs and may represent a mechanism for maintaining L-Arg availability to NOS and/or AR.

Vascular endothelial dysfunction: does tetrahydrobiopterin play a role?

Tetrahydrobiopterin is one of the most potent naturally occurring reducing agents and an essential cofactor required for enzymatic activity of nitric oxide synthase (NOS). The exact role of tetrahydrobiopterin in the control of NOS catalytic activity is not completely understood. Existing evidence suggests that it can act as allosteric and redox cofactors. Suboptimal concentration of tetrahydrobiopterin reduces formation of nitric oxide and favors "uncoupling" of NOS leading to NOS-mediated reduction of oxygen and formation of superoxide anions and hydrogen peroxide. Recent findings suggest that accelerated catabolism of tetrahydrobiopterin in arteries exposed to oxidative stress may contribute to pathogenesis of endothelial dysfunction present in arteries exposed to hypertension, hypercholesterolemia, diabetes, smoking, and ischemia-reperfusion. Beneficial effects of acute and chronic tetrahydrobiopterin supplementation on endothelial function have been reported in experimental animals and humans. Furthermore, it appears that beneficial effects of some antioxidants (e.g., vitamin C) on vascular function could be mediated via increased intracellular concentration of tetrahydrobiopterin. In this review, the potential role of tetrahydrobiopterin in the pathogenesis of vascular endothelial dysfunction and mechanisms underlying beneficial vascular effects of tetrahydrobiopterin will be discussed.

Lipopolysaccharide reduces intercellular coupling in vitro and arteriolar conducted response in vivo

Our recent in vitro study (Lidington et al. J Cell Physiol 185: 117-125, 2000) suggested that lipopolysaccharide (LPS) reduces communication along blood vessels. The present investigation extended this study to determine whether any effect of LPS and/or inflammatory cytokines [tumor necrosis factor-alpha, interleukin (IL)-1beta, and IL-6] on endothelial cell coupling in vitro could also be demonstrated for an arteriolar conducted response in vivo. Using an electrophysiological approach in monolayers of microvascular endothelial cells, we found that LPS (10 microg/ml) but not these cytokines reduced intercellular conductance (c(i)) (an index of cell communication) and that LPS together with these cytokines did not further reduce c(i). Also, c(i) was restored after LPS washout, and the LPS-induced reduction was prevented by protein tyrosine kinase (PTK) inhibitors (1.5 microM Tyr A9 and 10 nM PP-2). In our in vivo experiments in arterioles of the mouse cremaster muscle, local electrical stimulation evoked vasoconstriction that conducted along arterioles. LPS in the muscle superfusate did not alter local vasoconstriction but reduced the conducted response. Washout of LPS restored the conducted response, whereas PTK inhibitors prevented the effect of LPS. On the basis of a newly developed mathematical model, the LPS-induced reduction in conducted response was predicted to reduce the arteriolar ability to increase resistance to blood flow. We conclude that LPS can reduce communication in in vitro and in vivo systems comparably in a reversible and tyrosine kinase-dependent manner. Based on literature and present results, we suggest that LPS may compromise microvascular hemodynamics at both the arteriolar responsiveness and the conduction levels.

Mast cells and nitric oxide: control of production, mechanisms of response

Mast cells are involved in numerous activities ranging from control of the vasculature, to tissue injury and repair, allergic inflammation and host defences. They synthesize and secrete a variety of mediators, activating and modulating the functions of nearby cells and initiating complex physiological changes. Interestingly, NO produced by mast cells and/or other cells in the microenvironment appears to regulate these diverse roles. This review outlines some of the pathways central to the production of NO by mast cells and identifies many of the tightly controlled regulatory mechanisms involved. Several cofactors and regulatory elements are involved in NO production, and these act at transcriptional and post-translational sites. Their involvement in NO production will be outlined and the possibility that these pathways are critically important in mast cell functions will be discussed. The effects of NO on mast cell functions such as adhesion, activation and mediator secretion will be examined with a focus on molecular mechanisms by which NO modifies intracellular signalling pathways dependent or independent of cGMP and soluble guanylate cyclase. The possibility that NO regulates mast cell function through effects on selected ion channels will be discussed. Metabolic products of NO including peroxynitrite and other reactive species may be the critical elements that affect the actions of NO on mast cell functions. Further understanding of the actions of NO on mast cell activities may uncover novel strategies to modulate inflammatory conditions.

Cellular and molecular basis of portal hypertension

The molecular basis of the vascular wall abnormalities that contribute to development of portal hypertension are an area of active investigation. Studies to date suggest that diminution in eNOS-derived NO production in liver contributes to this process by causing increased intrahepatic resistance. This process seems to be mediated through inhibitory posttranslational regulatory mechanisms of eNOS. Endothelin-1 signaling is also increased in the intrahepatic vasculature. The mechanisms responsible for increased ET-1 signaling include increased ET-1 production and increased ET-A receptor expression, particularly within hepatic stellate cells, although the stimulus responsible for activation of the ET-1 system remains uncertain. In the splanchnic circulation, increases in eNOS-derived NO contribute to increased portal venous inflow through transcriptional and posttranslational regulation of eNOS. Development of the porto-systemic collateral circulation characteristic of portal hypertension occurs through a combination of NO-dependent dilation of preexisting vessels and through growth factor-mediated angiogenesis and neovascularization (Fig. 3). Further studies in vascular wall biology are continuing to elucidate more clearly the molecular mechanisms of portal hypertension. The [figure: see text] mechanism by which eNOS-derived NO production is increased in the splanchnic arteriolar endothelial cell but decreased in the liver endothelial cell and the role of specific ET receptor subtypes in the mechanism of activation of the ET-1 system and its effect on contractile cells in liver cirrhosis are areas that require further investigation. Further studies are needed to determine the intrahepatic site of pressure and perfusion regulation, be it the hepatic sinusoid and its unique, specialized cell types or the endothelial and smooth muscle cells in the hepatic and portal venules. The role of more recently delineated vasoactive pathways such as urotensin-II/GPR 14 and anandamide/CB1 receptor in portal hypertension must be examined. Most importantly, future studies must focus on novel experimental therapies, using pharmacologic and genetic approaches to modulate these vascular biologic systems and thereby to ameliorate complications and symptoms relating to portal hypertension in patients with cirrhosis.

Endothelin-1 and nitric oxide synthase in short rebound reaction to short exposure to inhaled nitric oxide

On withdrawal of inhalation of nitric oxide (INO) administered after lung injury, pulmonary artery pressure (PAP) and arterial oxygen tension (Pa(O(2))) may deteriorate more than before INO (rebound response). In this study, we investigated the possible roles of endothelin (ET)-1 and nitric oxide (NO) synthase (NOS) activity in the short rebound reaction to short-term inhalation of NO. Twenty-six anesthetized mechanically ventilated piglets were given endotoxin infusion. Twelve animals then received INO (30 parts per million) for two 30-min periods. Nine controls were not given NO. Measurements were made of blood gases and hemodynamic parameters, lung tissue ET-1 expression and NOS activity, and plasma ET-1 concentration. INO decreased PAP and increased Pa(O(2)), but INO withdrawal caused a short rebound reaction with an increase in PAP. Lung tissue expression and plasma concentration of ET-1 increased during INO, and plasma ET-1 increased further after its withdrawal. Activity of constitutive NOS decreased during INO, whereas that of inducible NOS was unchanged. Upregulation of ET-1 and downregulation of NOS activity may have influenced the short rebound reaction to short-term INO.

Increased serum nitrate levels in infants with atopic dermatitis

BACKGROUND

The pathogenesis of atopic dermatitis (AD) is still unknown. A recent study has shown that inducible nitric oxide synthase (iNOS) is expressed in the atopic skin lesion, suggesting the involvement of nitric oxide in the skin inflammation of AD. The purpose of the study was to examine serum nitrate (NO3) levels in relation to the disease severity in children with AD.

METHODS

Serum nitrate levels were assessed in relation to the skin scores in 88 patients with atopic dermatitis (AD) (aged 0.4-8 years: mean+/-SD, 2.2+/-1.9, 41 boys and 47 girls) and 12 nonatopic children (aged 0.8-4 years: mean+/-SD, 1.8+/-0.9, seven boys and five girls).

RESULTS

Serum nitrate levels of patients with AD were significantly increased as compared to nonatopic controls and were also correlated with the disease severity. The skin scores were significantly correlated with serum nitrate levels as well as peripheral eosinophil counts.

CONCLUSION

Our results indicate that nitric oxide may be involved in the pathogenesis of vasodilation and erythema in AD skin.

Profile of eicosanoids produced by human saphenous vein endothelial cells and the effect of dietary fatty acids

Human saphenous vein endothelial cells (HSVECs) derived from primary cultures of adult human veins constitute an excellent in vitro model for studying human endothelial metabolism. In this study we report the (14)C-labelled prostanoid profile of HSVECs under resting and stimulated conditions and the effect of the n-3 polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid on them. Results indicate that HSVECs while under resting conditions produce mainly prostaglandin F(2alpha)(PGF(2alpha)). After stimulation with calcium ionophore A23187, the cells were found to synthesise PGI(2), PGE(2)and PGF(2alpha) as major products and thromboxane B(2)and PGD(2)as minor products. Production of (14)C-labelled hydroxyeicosatetraenoic acids was not detected. Eicosapentaenoic acid was found to inhibit basal and stimulated prostanoid production whereas docosahexaenoic acid inhibited basal but strongly increased stimulated prostanoid production. These results may offer the basis for further studies aiming to investigate targets for pharmacological intervention in inflammatory conditions.

Nitric oxide and the liver

In recent years, the role of nitric oxide (NO) in the pathogenesis of liver disease and its complications has been extensively studied. There remain, however, many areas of controversy. In particular, the effect of NO on vascular function in the systemic circulation and the hepatic microcirculation has received the greatest attention. It has been proposed on the one hand that increased NO synthesis is responsible for the development of the hyperdynamic circulation in cirrhosis, while decreased production of NO within the hepatic microcirculation may be important in the development of parenchymal tissue damage and the onset of portal hypertension. The purpose of this review is to examine the available data concerning the role of NO in liver disease and to discuss some of the controversies and contradictions that surround it.

The binding of oxidized low density lipoprotein (ox-LDL) to ox-LDL receptor-1 reduces the intracellular concentration of nitric oxide in endothelial cells through an increased production of superoxide

Oxidized low density lipoprotein (ox-LDL) has been suggested to affect endothelium-dependent vascular tone through a decreased biological activity of endothelium-derived nitric oxide (NO). Oxidative inactivation of NO is regarded as an important cause of its decreased biological activity, and in this context superoxide (O(2)) is known to inactivate NO in a chemical reaction during which peroxynitrite is formed. In this study we examined the effect of ox-LDL on the intracellular NO concentration in bovine aortic endothelial cells and whether this effect is influenced by ox-LDL binding to the endothelial receptor lectin-like ox-LDL receptor-1 (LOX-1) through the formation of reactive oxygen species and in particular of O(2). ox-LDL induced a significant dose-dependent decrease in intracellular NO concentration both in basal and stimulated conditions after less than 1 min of incubation with bovine aortic endothelial cells (p < 0.01). In the same experimental conditions ox-LDL also induced O(2) generation (p < 0.001). In the presence of radical scavengers and anti-LOX-1 monoclonal antibody, O(2) formation induced by ox-LDL was reduced (p < 0.001) with a contemporary rise in intracellular NO concentration (p < 0.001). ox-LDL did not significantly modify the ability of endothelial nitric oxide synthase to metabolize l-arginine to l-citrulline. The results of this study show that one of the pathophysiological consequences of ox-LDL binding to LOX-1 may be the inactivation of NO through an increased cellular production of O(2).

Reactive oxygen species mediate endothelium-dependent relaxations in tetrahydrobiopterin-deficient mice

(6R)-5,6,7,8-Tetrahydro-biopterin (H(4)B) is essential for the catalytic activity of all NO synthases. The hyperphenylalaninemic mouse mutant (hph-1) displays 90% deficiency of the GTP cyclohydrolase I, the rate-limiting enzyme in H(4)B synthesis. A relative shortage of H(4)B may shift the balance between endothelial NO synthase (eNOS)-catalyzed generation of NO and reactive oxygen species. Therefore, the hph-1 mouse represents a unique model to assess the effect of chronic H(4)B deficiency on endothelial function. Aortas from 8-week-old hph-1 and wild-type mice (C57BLxCBA) were compared. H(4)B levels were determined by high-performance liquid chromatography and NO synthase activity by [(3)H]citrulline assay in homogenized tissue. Superoxide production by the chemiluminescence method was measured. Isometric tension was continuously recorded. The intracellular levels of H(4)B as well as constitutive NO synthase activity were significantly lower in hph-1 compared with wild-type mice. Systolic blood pressure was increased in hph-1 mice. However, endothelium-dependent relaxations to acetylcholine were present in both groups and abolished by inhibition of NO synthase with N(G)-nitro-L-arginine methyl ester as well. Only in hph-1 mice were the relaxations inhibited by catalase and enhanced by superoxide dismutase. After incubation with exogenous H(4)B, the differences between the 2 groups disappeared. Our findings demonstrate that H(4)B deficiency leads to eNOS dysfunction with the formation of reactive oxygen species, which become mediators of endothelium-dependent relaxations. A decreased availability of H(4)B may favor an impaired activity of eNOS and thus contribute to the development of vascular diseases.

Repression of proinflammatory cytokine and inducible nitric oxide synthase (NOS2) gene expression in activated microglia by N-acetyl-O-methyldopamine: protein kinase A-dependent mechanism

Excessive proinflammatory cytokine and NO production by activated microglia play a role in neurodegenerative disorders. To investigate whether the neuroprotectant N-acetyl-O-methyldopamine (NAMDA) downregulates genes associated with microglial activation, we measured gene expression of TNF-alpha, IL-1beta, inducible nitric oxide synthase (NOS2), and an associated cofactor synthesis gene, GTP cyclohydrolase I (GTPCH) in LPS-stimulated microglia cells in the presence or absence of NAMDA. The temporal pattern of cytokine gene expression showed that LPS (0.2 microg/ml) increased TNF-alpha and IL-1beta gene expression at 1 and 3 h, which was repressed by cotreatment of NAMDA. Similarly, LPS also induced GTPCH and NOS2 gene expression at 3 and 6 h, and cotreatment of NAMDA repressed the induction with parallel reduction of nitrite, an oxidative metabolite of nitric oxide. Since transcription factor NF-kappaB is involved in regulating expression of these genes, the effects of NAMDA on NF-kappaB nuclear translocation and DNA binding in immunostimulated microglia were investigated. We found that neither LPS-induced NF-kappaB translocation nor DNA binding activity was affected by cotreatment with NAMDA in BV-2 microglia. On the other hand, NAMDA increased intracellular cAMP levels and potentiated LPS-induced phosphorylated cAMP-responsive element binding protein (pCREB) expression. Treatment with adenosine 3'5'-cyclic monophosphothioate, a specific inhibitor of cAMP-dependent protein kinase (PKA), reversed not only NAMDA-induced pCREB upregulation but also NAMDA-induced repression of TNF-alpha and IL-1beta gene transcription. The data demonstrate that NAMDA represses LPS-induced proinflammatory cytokines gene expression via a cAMP-dependent protein kinase pathway. Thus, repressing proinflammatory cytokines and NOS2 gene expression in activated microglia by NAMDA may provide new therapeutic strategies for ischemic cerebral disease as well as other neurodegenerative diseases.

Increased plasma tetrahydrobiopterin in septic shock is a possible therapeutic target

Hemoperfusion with a column of polymyxin B immobilized on fibers (PMX) has been used to adsorb endotoxin in-patients with septic shock. PMX hemoperfusion (PMX-H) increases blood pressure (BP) too rapidly for the effect to be attributable to endotoxin removal. Since inducible NO synthase (iNOS) is known to be involved in the profound hypotension, we hypothesized that a decrease of tetrahydrobiopterin (BH(4)), an essential cofactor of iNOS, might account for the rapid effect of PMX-H on BP, if plasma BH(4) is increased concomitantly with NO in septic shock patients and if PMX can decrease BH(4). BH(4) was evaluated by measuring total biopterin, which can include derivatives of BH(4) by using high-performance liquid chromatography (HPLC). We confirmed that PMX fabric time dependently decreased total biopterin concentration in vitro. The plasma level of total biopterin in shock patients was indeed markedly elevated compared with that in volunteers (131.1+/-33.4 vs. 10.4+/-1.1 nM, n=5, P<0.01). Level of NO metabolites (NOx) were 173.9+/-104.7 versus 28.7+/-11.6 µM (P<0.01). In beagles, plasma total biopterin was 44.7+/-6.9 nM at baseline, reached 118+/-28.6 nM after lipopolysaccharide (LPS) injection, and fell to 70.2+/-15.8 nM after PMX-H. Plasma NOx concentration was increased from 15.2+/-4.2 to 41.0+/-7.5 µM by LPS treatment. BP was 130+/-11.3 mmHg at baseline, 82.2+/-8.3 mmHg at 14 h after LPS, and 115.2+/-16.0 mmHg after PMX-H. In rats, plasma total biopterin was 88.8+/-1.5 nM at baseline, 383.7+/-144.2 nM after LPS and 177.0+/-14.2 nM after PMX-H. Plasma NOx was also increased after LPS (from 34.6+/-4.4 to 1445.6+/-376.0 nM). The marked increase in total biopterin concomitantly with NOx in septic shock patients and its reduction by PMX-H in animal models of septic shock are consistent with our hypothesis, and appear to justify further research on BH(4) removal as a potential therapeutic target.

Antineutrophil cytoplasm antibody-induced neutrophil nitric oxide production is nitric oxide synthase independent

BACKGROUND

Antineutrophil cytoplasm antibodies (ANCAs) are implicated in the pathogenesis of systemic vasculitis. We asked whether ANCA could induce nitric oxide (NO) release from human neutrophils and, if so, whether this NO production was dependent on NO synthase (NOS) activity.

METHODS

Neutrophil NO production was measured using a chemiluminescence assay, and NOS activity was determined by the conversion of [(14)C] L-arginine to [(14)C] L-citrulline and NOS mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Human neutrophils isolated from healthy donors were incubated at 37 degrees C with human ANCA, normal human IgG, murine monoclonal myeloperoxidase ANCA, murine proteinase-3 ANCA, or their respective isotypic controls for 6 to 12 hours in RPMI. Both human and monoclonal ANCA led to a dose-dependent increase of NO compared with control IgG. Neutrophils, either freshly isolated or incubated for seven hours with murine monoclonal myeloperoxidase ANCA, proteinase-3 ANCA, or a mixture of interleukin-1 beta, tumor necrosis factor-alpha, interferon-gamma plus lipopolysaccharide showed no NOS activity with low conversion rates of [(14)C] L-arginine to [(14)C] L-citrulline, which could not be inhibited by N(G)-monomethyl-L-arginine (NOS inhibitor). To detect NOS mRNA expression, RT-PCR was performed using oligonucleotide primers derived from mRNA sequences of either human constitutive endothelial NOS (eNOS), constitutive neuroneal NOS (nNOS), or human hepatocyte inducible NOS (iNOS). There was no expression of either eNOS, nNOS, or iNOS in untreated, human and murine monoclonal ANCA-treated, or cytokine-treated neutrophils.

CONCLUSION

These data suggest that human neutrophils produce NO in response to ANCA but in a NOS-independent way. NO can be generated from a nonenzymatic interaction between hydrogen peroxide and arginine. We postulate that this is the predominant pathway of NO synthesis in neutrophils, since ANCAs are capable of inducing reactive oxygen species production from neutrophils.

L-ascorbic acid potentiates endothelial nitric oxide synthesis via a chemical stabilization of tetrahydrobiopterin

Ascorbic acid has been shown to stimulate endothelial nitric oxide (NO) synthesis in a time- and concentration-dependent fashion without affecting NO synthase (NOS) expression or l-arginine uptake. The present study investigates if the underlying mechanism is related to the NOS cofactor tetrahydrobiopterin. Pretreatment of human umbilical vein endothelial cells with ascorbate (1 microm to 1 mm, 24 h) led to an up to 3-fold increase of intracellular tetrahydrobiopterin levels that was concentration-dependent and saturable at 100 microm. Accordingly, the effect of ascorbic acid on Ca(2+)-dependent formation of citrulline (co-product of NO) and cGMP (product of the NO-activated soluble guanylate cyclase) was abolished when intracellular tetrahydrobiopterin levels were increased by coincubation of endothelial cells with sepiapterin (0.001-100 microm, 24 h). In contrast, ascorbic acid did not modify the pterin affinity of endothelial NOS, which was measured in assays with purified tetrahydrobiopterin-free enzyme. The ascorbate-induced increase of endothelial tetrahydrobiopterin was not due to an enhanced synthesis of the compound. Neither the mRNA expression of the rate-limiting enzyme in tetrahydrobiopterin biosynthesis, GTP cyclohydrolase I, nor the activities of either GTP cyclohydrolase I or 6-pyruvoyl-tetrahydropterin synthase, the second enzyme in the de novo synthesis pathway, were altered by ascorbate. Our data demonstrate that ascorbic acid leads to a chemical stabilization of tetrahydrobiopterin. This was evident as an increase in the half-life of tetrahydrobiopterin in aqueous solution. Furthermore, the increase of tetrahydrobiopterin levels in intact endothelial cells coincubated with cytokines and ascorbate was associated with a decrease of more oxidized biopterin derivatives (7,8-dihydrobiopterin and biopterin) in cells and cell supernatants. The present study suggests that saturated ascorbic acid levels in endothelial cells are necessary to protect tetrahydrobiopterin from oxidation and to provide optimal conditions for cellular NO synthesis.

Effects of tumor necrosis factor alpha on sin nombre virus infection in vitro

Previous data indicate that immune mechanisms may be involved in developing capillary leakage during Sin Nombre virus (SNV) infection. Therefore, we investigated production of tumor necrosis factor alpha (TNF-alpha) by human alveolar macrophages and human umbilical vein endothelial cells (HUVEC) after infection with SNV. In addition, we examined the effect of TNF-alpha on HUVEC monolayer leakage. Our results reveal that although TNF-alpha decreases accumulation of viral nucleoproteins, TNF-alpha levels do not change in SNV-infected cells. In addition, supernatants from SNV-infected human alveolar macrophages did not cause a significant increase in endothelial monolayer permeability.

Stable expression of varied levels of inducible nitric oxide synthase in primary cultures of endothelial cells

Nitric oxide (NO*), generated by nitric oxide synthase (NOS II) from immunostimulated cells during infection, plays an important role in host immune defense against microbial invasion. The impact of different rates of NO* production on host cell function has not been defined. Herein, we describe the development of a method to express varied levels of murine NOS II in bovine pulmonary artery endothelial cells. A retroviral vector (pMFGSNOS) encoding NOS II was used to transduce primary cultures of endothelial cells. Bovine endothelial cells were susceptible to this transduction and up to 18% of the cells expressed immunodetectable murine NOS II. The NOS II-transduced endothelial cells were cultured on the three-dimensional matrix, Gelfoam, for 8-10 days. Stable expression of NOS II was assessed by measuring nitrite accumulation in media every 2 days. By day 10, endothelial cells on Gelfoam were found to secrete NO* at a rate exceeding 1.0 microM/h/10(6) cells, concomitant with an enhanced level of NOS II activity. Argininosuccinate synthetase, a key enzyme in the metabolism of l-citrulline to l-arginine, increased as well, perhaps in response to dimunition of the intracellular arginine pool corresponding to the observed high output of NO*. In spite of the continuous flux of NO*, endothelial cell viability was not effected. This system provides the opportunity to assess the impact of different levels of sustained NO* production on endothelial cell physiology.