Nitric oxide donor prevents hydrogen peroxide-mediated endothelial cell injury

6-Gingerol alleviates placental injury in preeclampsia by inhibiting oxidative stress via BNIP3/LC3 signaling-mediated trophoblast mitophagy

Background and aims: Preeclampsia (PE) is the leading cause of maternal and fetal morbidity and mortality worldwide. Apoptosis of trophoblast cells induced by oxidative stress is a principal reason of placental injury in PE. 6-Gingerol, an antioxidant from ginger, plays an important role in many disease models, but its effect on obstetric diseases has not been elucidated. In this study, we investigated the protective effect of 6-gingerol against placental injury. Methods: In vitro hypoxia/reoxygenation (H/R) model of HTR8/Svneo cells and preeclamptic mice model were established to simulate PE. The effects of 6-Gingerol on PE were evaluated by morphological detection, biochemical analysis, and Western blot. Results: We found that H/R treatment induced cell apoptosis, increased the production of reactive oxygen species, malondialdehyde and lactate dehydrogenase, and decreased superoxide dismutase in trophoblast. In addition, the polarization of mitochondrial membrane potential and the cellular calcium flux were also destroyed under H/R condition, which also activated BCL2-interacting protein 3 (BNIP3) and provoked excessive mitophagy. Importantly, 6-Gingerol reversed these corrosive effects. Furthermore, the placenta damage in PE-like mouse caused by the cell apoptosis, oxidative stress and mitophagy was mitigated by 6-Gingerol. Conclusion: These findings suggest that 6-Gingerol exerts a protective effect against placental injury in PE by reducing oxidative stress and inhibiting excessive mitophagy caused by mitochondrial dysfunction.

Anti-hypoxia Activity of the Novel NO Donor Acetyl Ferulic Isosorbide Mononitrate in Acute High-Altitude Hypoxia Mice

Nitric oxide (NO) may act as either a pro-oxidant or an antioxidant in biological systems. Previous work has found inhalation of NO improved survival in a high altitude rat model. NO donor isosorbide mononitrate derivants might have a protective effect against hypoxia. We synthesized a series of isosorbide mononitrate derivant compounds to test their anti-hypoxia activities. Normobaric hypoxia and hypobaric hypoxia models were used to study the protective role of NO donor in mice. The results showed isosorbide mononitrate derivants had protective effects in hypoxia mice. Among those compounds, acetyl ferulic isosorbide mononitrate (AFIM) was the most effective. It prolonged the survival time during the normobaric hypoxia test. It decreased malondialdehyde (MDA) and H2O2 in hypobaric hypoxia mice. The antioxidase activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) remained in normal ranges in the AFIM group. As a sign of mitochondrial dysfunction, the activities of ATPase were down regulated in mice under hypobaric hypoxia conditions. AFIM also protected ATPase activities. The protective effects of AFIM might come from a sustained NO supply and the release of acetyl ferulic acid with anti-oxidant activity.

Aspirin induces Nrf2-mediated transcriptional activation of haem oxygenase-1 in protection of human melanocytes from H2 O2 -induced oxidative stress

The removal of hydrogen peroxide (H2 O2 ) by antioxidants has been proven to be beneficial to patients with vitiligo. Aspirin (acetylsalicylic acid, ASA) has antioxidant activity and has great preventive and therapeutical effect in many oxidative stress-relevant diseases. Whether ASA can protect human melanocytes against oxidative stress needs to be further studied. Here, we investigated the potential protective effect and mechanisms of ASA against H2 O2 -induced oxidative injury in human melanocytes. Human melanocytes were pre-treated with different concentrations of ASA, followed by exposure to 1.0 mM H2 O2 . Cell apoptosis, intracellular reactive oxygen species (ROS) levels were evaluated by flow cytometry, and cell viability was determined by an Cell Counting Kit-8 assay. Total and phosphorylated NRF2 expression, NRF2 nuclear translocation and antioxidant response element (ARE) transcriptional activity were assayed with or without Nrf2-siRNA transfection to investigate the possible molecular mechanisms. Concomitant with an increase in viability, pre-treatment of 10-90 μmol/l ASA resulted in decreased rate of apoptotic cells, lactate dehydrogenase release and intracellular ROS levels in primary human melanocytes. Furthermore, we found ASA dramatically induced NRF2 nuclear translocation, enhanced ARE-luciferase activity, increased both p- NRF2 and total NRF2 levels, and induced the expression of haem oxygenase-1 (HO-1) in human melanocytes. In addition, knockdown of Nrf2 expression or pharmacological inhibition of HO-1 abrogated the protective action of ASA on melanocytes against H2 O2 -induced cytotoxicity and apoptosis. These results suggest that ASA protects human melanocytes against H2 O2 -induced oxidative stress via Nrf2-driven transcriptional activation of HO-1.

Synergistic activity of acetohydroxamic acid on prokaryotes under oxidative stress: the role of reactive nitrogen species

One-electron oxidation of acetohydroxamic acid (aceto-HX) initially gives rise to nitroxyl (HNO), which can be further oxidized to nitric oxide (NO) or react with potential biological targets such as thiols and metallo-proteins. The distinction between the effects of NO and HNO in vivo is masked by the reversible redox exchange between the two congeners and by the Janus-faced behavior of NO and HNO. The present study examines the ability of aceto-HX to serve as an HNO donor or an NO donor when added to Escherichia coli and Bacillus subtilis subjected to oxidative stress by comparing its effects to those of NO and commonly used NO and HNO donors. The results demonstrate that: (i) the effects of NO and HNO on the viability of prokaryotes exposed to H2O2 depend on the type of the bacterial cell; (ii) NO synergistically enhances H2O2-induced killing of E. coli, but protects B. subtilis depending on the extent of cell killing by H2O2; (iii) the HNO donor Angeli׳s salt alone has no effect on the viability of the cells; (iv) Angeli׳s salt synergistically enhances H2O2-induced killing of B. subtilis, but not of E. coli; (v) aceto-HX alone (1-4 mM) has no effect on the viability of the cells; (vi) aceto-HX enhances the killing of both cells induced by H2O2 and metmyoglobin, which may be attributed in the case of B. subtilis to the formation of HNO and to further oxidation of HNO to NO in the case of E. coli; (vii) the synergistic activity of aceto-HX on the killing of both cells induced by H2O2 alone does not involve reactive nitrogen species. The effect of aceto-HX on prokaryotes under oxidative stress is opposite to that of other hydroxamic acids on mammalian cells.

Pro-oxidative synergic bactericidal effect of NO: kinetics and inhibition by nitroxides

NO plays diverse roles in physiological and pathological processes, occasionally resulting in opposing effects, particularly in cells subjected to oxidative stress. NO mostly protects eukaryotes against oxidative injury, but was demonstrated to kill prokaryotes synergistically with H2O2. This could be a promising therapeutic avenue. However, recent conflicting findings were reported describing dramatic protective activity of NO. The previous studies of NO effects on prokaryotes applied a transient oxidative stress while arbitrarily checking the residual bacterial viability after 30 or 60min and ignoring the process kinetics. If NO-induced synergy and the oxidative stress are time-dependent, the elucidation of the cell killing kinetics is essential, particularly for survival curves exhibiting a "shoulder" sometimes reflecting sublethal damage as in the linear-quadratic survival models. We studied the kinetics of NO synergic effects on H2O2-induced killing of microbial pathogens. A synergic pro-oxidative activity toward gram-negative and gram-positive cells is demonstrated even at sub-μM/min flux of NO. For certain strains, the synergic effect progressively increased with the duration of cell exposure, and the linear-quadratic survival model best fit the observed survival data. In contrast to the failure of SOD to affect the bactericidal process, nitroxide SOD mimics abrogated the pro-oxidative synergy of NO/H2O2. These cell-permeative antioxidants, which hardly react with diamagnetic species and react neither with NO nor with H2O2, can detoxify redox-active transition metals and catalytically remove intracellular superoxide and nitrogen-derived reactive species such as (•)NO2 or peroxynitrite. The possible mechanism underlying the bactericidal NO synergy under oxidative stress and the potential therapeutic gain are discussed.

cGMP increases antioxidant function and attenuates oxidant cell death in mouse lung microvascular endothelial cells by a protein kinase G-dependent mechanism

Increasing evidence suggests that endothelial cytotoxicity from reactive oxygen species (ROS) contributes to the pathogenesis of acute lung injury. Treatments designed to increase intracellular cGMP attenuate ROS-mediated apoptosis and necrosis in several cell types, but the mechanisms are not understood, and the effect of cGMP on pulmonary endothelial cell death remains controversial. In the current study, increasing intracellular cGMP by either 8pCPT-cGMP (50 microM) or atrial natriuretic peptide (10 nM) significantly attenuated cell death in H(2)O(2)-challenged mouse lung microvascular (MLMVEC) monolayers. 8pCPT-cGMP also decreased perfusate LDH release in isolated mouse lungs exposed to H(2)O(2) or ischemia-reperfusion. The protective effect of increasing cGMP in MLMVECs was accompanied by enhanced endothelial H(2)O(2) scavenging (measured by H(2)O(2) electrode) and decreased intracellular ROS concentration (measured by 2',7'-dichlorofluorescin fluorescence) as well as decreased phosphorylation of p38 MAPK and Akt. The cGMP-mediated cytoprotection and increased H(2)O(2) scavenging required >2 h of 8pCPT-cGMP incubation in wild-type MLMVEC and were absent in MLMVEC from protein kinase G (PKG(I))-/- mice suggesting a PKG(I)-mediated effect on gene regulation. Catalase and glutathione peroxidase 1 (Gpx-1) protein were increased by cGMP in wild-type but not PKG(I)-/- MLMVEC monolayers. Both the cGMP-mediated increases in antioxidant proteins and H(2)O(2) scavenging were prevented by inhibition of translation with cycloheximide. 8pCPT-cGMP had minimal effects on catalase and Gpx-1 mRNA. We conclude that cGMP, through PKG(I), attenuated H(2)O(2)-induced cytotoxicity in MLMVEC by increasing catalase and Gpx-1 expression through an unknown posttranscriptional effect.

Netrin-1 prevents ischemia/reperfusion-induced myocardial infarction via a DCC/ERK1/2/eNOS s1177/NO/DCC feed-forward mechanism

We have recently shown that a novel endothelial mitogen netrin-1 potently stimulates nitric oxide (NO()) production via a DCC-ERK1/2 dependent mechanism. In view of the well-established cardioprotective role of NO(), the present study investigated whether netrin-1 is cardioprotective via NO(*) signaling in the heart. Netrin-1 receptor DCC was abundantly expressed in the C57BL/6J mouse hearts. Perfusion of heart with netrin-1 (100 ng/mL) using a Langendorff system significantly increased NO(*) production. Under ischemia/reperfusion (I/R), netrin-1 induced a substantial reduction in infarct size (21.8+/-4.9% from 42.5+/-3.6% in the controls), which was accompanied by an augmented production of NO(*). Pre-perfusion with DCC-antibody, U0126 (MEK1/2 inhibitor), L-NAME or PTIO (NO(*) scavenger) attenuated protective effects of netrin-1 on infarct size and NO(*) production, indicating upstream roles of DCC and ERK1/2 in NO(*) production, as well as an essential role of NO(*) in cardioprotection. Netrin-1 induced reduction in infarct size was significantly attenuated in DCC+/- mice, confirming an intermediate role of DCC. In additional experiments we found netrin-1 increased ERK1/2 and eNOS(s1177) phosphorylation, and DCC protein expression, which was diminished by I/R. Furthermore, netrin-1-induced DCC upregulation was NO(*) and ERK1/2-dependent, implicating a feed-forward mechanism. DAF-AM staining revealed enhanced NO(*) production in both cardiac endothelial cells (ECs) and myocytes. In primarily isolated cardiomyocytes, netrin-1 also increased NO(*) production, DCC abundance and ERK1/2 phosphorylation. Of note, cardiac apoptosis was significantly attenuated by netrin-1, which was reversed by DCC-antibody, U0126, L-NAME or PTIO. In summary, our data clearly demonstrate that netrin-1 potently protects the heart from I/R injury by stimulating NO(*) production from cardiac ECs and myocytes. This potent effect is mediated by a DCC/ERK1/2/eNOS(s1177)/NO(*)/DCC feed-forward mechanism in both cell types.

Nitric oxide-mediated protection of endothelial cells from hydrogen peroxide is mediated by intracellular zinc and glutathione

Oxidative stress may cause endothelial dysfunction and vascular disease. It has been shown that NO protects endothelial cells (EC) against H(2)O(2)-induced toxicity. In addition, it is known that NO within cells induces a zinc release from proteins containing zinc-sulfur complexes. The aim of this study was to investigate whether zinc released intracellularly by NO plays a signaling role in the NO-mediated protection against H(2)O(2) in rat aortic EC. Our results show that the NO-mediated protection toward H(2)O(2) depends on the activities of glutathione peroxidase and glutamate cysteine ligase (GCL), the rate-limiting enzyme of glutathione (GSH) de novo biosynthesis. Moreover, NO increases the synthesis of the antioxidant GSH by inducing the expression of the catalytic subunit of GCL (GCLC). Chelating intracellular "free" zinc abrogates the NO-mediated increase of GCLC and of cellular GSH levels. As a consequence, the NO-mediated protection against H(2)O(2)-induced toxicity is impaired. We also show that under proinflammatory conditions, both cellular NO synthesis and intracellular "free" zinc are required to maintain the cellular GSH levels. Using RNA interference and laser scanning microscopy, we found that the NO-induced expression of GCLC depends on the activation of the transcription factor Nrf2 but not on the activity of the "zinc-sensing" transcription factor MTF-1. These findings show that intracellular "free" zinc plays a signaling role in the protective activity of NO and could explain why maintenance of an adequate zinc status in the endothelium is important to protect from oxidative stress and the development of vascular disease.

Reactive oxygen species production in energized cardiac mitochondria during hypoxia/reoxygenation: modulation by nitric oxide

Mitochondria are an important source of reactive oxygen species (ROS), implicated in ischemia/reperfusion injury. When isolated from ischemic myocardium, mitochondria demonstrate increased ROS production as a result of damage to electron transport complexes. To investigate the mechanisms, we studied effects of hypoxia/reoxygenation on ROS production by isolated energized heart mitochondria. ROS production, tracked using Fe(2+)-catalyzed, H(2)O(2)-dependent H(2)DCF oxidation or Amplex Red, was similar during normoxia and hypoxia but markedly increased during reoxygenation, in proportion to the duration of hypoxia. In contrast, if mitochondria were rapidly converted from normoxia to near-anoxia ([O(2)], <1 micromol/L), the increase in H(2)DCF oxidation rate during reoxygenation was markedly blunted. To elicit the robust increase in H(2)DCF oxidation rate during reoxygenation, hypoxia had to be severe enough to cause partial, but not complete, respiratory chain inhibition (as shown by partial dissipation of membrane potential and increased NADH autofluorescence). Consistent with its cardioprotective actions, nitric oxide ( O) abrogated increased H(2)DCF oxidation under these conditions, as well as attenuating ROS-induced increases in matrix [Fe(2+)] and aconitase inhibition caused by antimycin. Collectively, these results suggest that (1) hypoxia that is sufficient to cause partial respiratory inhibition is more damaging to mitochondria than near-anoxia; and (2) O suppresses ROS-induced damage to electron transport complexes, probably by forming O-Fe(2+) complexes in the presence of glutathione, which inhibit hydroxyl radical formation.

Pollutant particles enhanced H2O2 production from NAD(P)H oxidase and mitochondria in human pulmonary artery endothelial cells

Particulate matter (PM) induces oxidative stress and cardiovascular adverse health effects, but the mechanistic link between the two is unclear. We hypothesized that PM enhanced oxidative stress in vascular endothelial cells and investigated the enzymatic sources of reactive oxygen species and their effects on mitogen-activated protein kinase (MAPK) activation and vasoconstriction. We measured the production of extracellular H2O2, activation of extracellular signal-regulated kinases1/2 (ERK1/2) and p38 MAPKs in human pulmonary artery endothelial cells (HPAEC) treated with urban particles (UP; SRM1648), and assessed the effects of H2O2 on vasoconstriction in pulmonary artery ring and isolated perfused lung. Within minutes after UP treatment, HPAEC increased H2O2 production that could be inhibited by diphenyleneiodonium (DPI), apocynin (APO), and sodium azide (NaN3). The water-soluble fraction of UP as well as its two transition metal components, Cu and V, also stimulated H2O2 production. NaN3 inhibited H2O2 production stimulated by Cu and V, whereas DPI and APO inhibited only Cu-stimulated H2O2 production. Inhibitors of other H2O2-producing enzymes, including Nomega-methyl-L-argnine, indomethacin, allopurinol, cimetidine, rotenone, and antimycin, had no effects. DPI but not NaN3 attenuated UP-induced pulmonary vasoconstriction and phosphorylation of ERK1/2 and p38 MAPKs. Knockdown of p47phox gene expression by small interfering RNA attenuated UP-induced H2O2 production and phosphorylation of ERK1/2 and p38 MAPKs. Intravascular administration of H2O2 generated by glucose oxidase increased pulmonary artery pressure. We conclude that UP induce oxidative stress in vascular endothelial cells by activating NAD(P)H oxidase and the mitochondria. The endothelial oxidative stress may be an important mechanism for PM-induced acute cardiovascular health effects.

Sesamol induces nitric oxide release from human umbilical vein endothelial cells

Sesamol, which is derived from sesame seed lignans, is reportedly an antioxidant. Nitric oxide (NO), the most important vascular relaxing factor, is regulated in the endothelium. In addition, NO is involved in protecting endothelium and has antiatherosclerotic and antithrombotic activities. The endothelium produces NO through the regulation of both endothelial NO synthase (eNOS) expression and activity in endothelial cells. This study sought to investigate the effect of sesamol on NO released from human umbilical vein endothelial cells (HUVEC) and to examine the expression and activity of eNOS. Sesamol induced NO release from endothelial cells in a dose-dependent manner (from 1 to 10 microM), as measured 24 h after treatment; the expression of the eNOS gene at both transcription and translation levels; and NOS activity in endothelial cells. The content of cGMP was also increased by sesamol through NO signaling. The transcription of eNOS induced by sesamol was confirmed through the activation of PI-3 kinase-Akt (protein kinase B) signaling. The results demonstrate that sesamol induces NOS signaling pathways in HUVEC and suggest a role for sesamol in cardiovascular reactivity in vivo.

Nitric oxide modulates murine yolk sac vasculogenesis and rescues glucose induced vasculopathy

Nitric oxide (NO) has been demonstrated to mediate events during ovulation,pregnancy, blastocyst invasion and preimplantation embryogenesis. However,less is known about the role of NO during postimplantation development. Therefore, in this study, we explored the effects of NO during vascular development of the murine yolk sac, which begins shortly after implantation. Establishment of the vitelline circulation is crucial for normal embryonic growth and development. Moreover, functional inactivation of the endodermal layer of the yolk sac by environmental insults or genetic manipulations during this period leads to embryonic defects/lethality, as this structure is vital for transport, metabolism and induction of vascular development. In this study, we describe the temporally/spatially regulated distribution of nitric oxide synthase (NOS) isoforms during the three stages of yolk sac vascular development (blood island formation, primary capillary plexus formation and vessel maturation/remodeling) and found NOS expression patterns were diametrically opposed. To pharmacologically manipulate vascular development,an established in vitro system of whole murine embryo culture was employed. During blood island formation, the endoderm produced NO and inhibition of NO(L-NMMA) at this stage resulted in developmental arrest at the primary plexus stage and vasculopathy. Furthermore, administration of a NO donor did not cause abnormal vascular development; however, exogenous NO correlated with increased eNOS and decreased iNOS protein levels. Additionally, a known environmental insult (high glucose) that produces reactive oxygen species(ROS) and induces vasculopathy also altered eNOS/iNOS distribution and induced NO production during yolk sac vascular development. However, administration of a NO donor rescued the high glucose induced vasculopathy, restored the eNOS/iNOS distribution and decreased ROS production. These data suggest that NO acts as an endoderm-derived factor that modulates normal yolk sac vascular development, and decreased NO bioavailability and NO-mediated sequela may underlie high glucose induced vasculopathy.

Dynamic regulation of metabolism and respiration by endogenously produced nitric oxide protects against oxidative stress

One of the many biological functions of nitric oxide is the ability to protect cells from oxidative stress. To investigate the potential contribution of low steady state levels of nitric oxide generated by endothelial nitric oxide synthase (eNOS) and the mechanisms of protection against H(2)O(2), spontaneously transformed human ECV304 cells, which normally do not express eNOS, were stably transfected with a green fluorescent-tagged eNOS cDNA. The eNOS-transfected cells were found to be resistant to injury and delayed death following a 2-h exposure to H(2)O(2) (50-150 microM). Inhibition of nitric oxide synthesis abolished the protective effect against H(2)O(2) exposure. The ability of nitric oxide to protect cells depended on the presence of respiring mitochondria as ECV304+eNOS cells with diminished mitochondria respiration (rho(-)) are injured to the same extent as nontransfected ECV304 cells and recovery of mitochondrial respiration restores the ability of nitric oxide to protect against H(2)O(2)-induced death. Nitric oxide also found to have a profound effect in cell metabolism, because ECV304+eNOS cells had lower steady state levels of ATP and higher utilization of glucose via the glycolytic pathway than ECV304 cells. However, the protective effect of nitric oxide against H(2)O(2) exposure is not reproduced in ECV304 cells after treatment with azide and oligomycin suggesting that the dynamic regulation of respiration by nitric oxide represent a critical and unrecognized primary line of defense against oxidative stress.

Tetrahydrobiopterin levels regulate endothelial cell proliferation

Vascular abnormalities, including altered angiogenesis, are major factors contributing to the morbidity and mortality of diabetes. We hypothesized that impaired angiogenesis in diabetes results from decreased tetrahydrobiopterin (BH4)-dependent synthesis of nitric oxide (NO) by endothelial cells (EC). To test this hypothesis, we utilized EC from spontaneously diabetic BB (BBd) and nondiabetes-prone BB (BBn) rats to investigate the link between BH4 and EC proliferation. There were significant decreases in the proliferation rate and expression of proliferating cell nuclear antigen in BBd versus BBn EC, with no evidence of apoptosis in either group. Sepiapterin (a precursor of BH4 via the salvage pathway) increased BH4 synthesis and enhanced proliferation of BBd EC. The stimulating effect of sepiapterin on EC proliferation was attenuated by NG-monomethyl-L-arginine, a NO synthase inhibitor. Reducing BH4 concentrations in BBn EC caused a decrease in proliferation, which was attenuated by a long-acting NO donor. Our results suggest that BH4 levels regulate proliferation of normal EC and that a BH4 deficiency impairs NO-dependent proliferation of BBd EC.

Nitric oxide attenuates H(2)O(2)-induced endothelial barrier dysfunction: mechanisms of protection

Nitric oxide (.NO) attenuates hydrogen peroxide (H(2)O(2))-mediated injury in porcine pulmonary artery endothelial cells (PAECs) and modulates intracellular levels of cGMP and cAMP. We hypothesized that.NO attenuates H(2)O(2)-induced PAEC monolayer barrier dysfunction through cyclic nucleotide-dependent signaling mechanisms. To examine this hypothesis, cultured PAEC monolayers were treated with H(2)O(2), and barrier function was measured as transmonolayer albumin clearance. H(2)O(2) caused significant PAEC barrier dysfunction that was attenuated by intracellular as well as extracellular.NO generation.NO increased PAEC cGMP and cAMP levels, but treatment with inhibitors of soluble guanylate cyclase or protein kinase G did not abrogate.NO-mediated barrier protection. In contrast, H(2)O(2) decreased protein kinase A activity, and inhibiting protein kinase A abrogated the protective effect of.NO. H(2)O(2)-induced barrier dysfunction was not associated with decreased levels of cGMP or cAMP. 3-Isobutyl-1-methylxanthine and the cGMP analog 8-bromo-cGMP had little effect on H(2)O(2)-mediated endothelial barrier dysfunction, whereas 8-bromo-cAMP plus 3-isobutyl-1-methylxanthine was protective. These results indicate that.NO modulates vascular endothelial barrier function through cAMP-dependent signaling mechanisms.

Effect of time and vascular pressure on permeability and cyclic nucleotides in ischemic lungs

We previously found that increased intravascular pressure decreased ischemic lung injury by a nitric oxide (NO)-dependent mechanism (Becker PM, Buchanan W, and Sylvester JT. J Appl Physiol 84: 803-808, 1998). To determine the role of cyclic nucleotides in this response, we measured the reflection coefficient for albumin (sigma(alb)), fluid flux (), cGMP, and cAMP in ferret lungs subjected to either 45 min ("short"; n = 7) or 180 min ("long") of ventilated ischemia. Long ischemic lungs had "low" (1-2 mmHg, n = 8) or "high" (7-8 mmHg, n = 6) vascular pressure. Other long low lungs were treated with the NO donor (Z)-1-[N-(3-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium -1, 2-diolate (PAPA-NONOate; 5 x 10(-4) M, n = 6) or 8-bromo-cGMP (5 x 10(-4) M, n = 6). Compared with short ischemia, long low ischemia decreased sigma(alb) (0.23 +/- 0.04 vs. 0.73 +/- 0.08; P < 0.05) and increased (1.93 +/- 0.26 vs. 0.58 +/- 0.22 ml. min(-1). 100 g(-1); P < 0.05). High pressure prevented these changes. Lung cGMP decreased by 66% in long compared with short ischemia. Lung cAMP did not change. PAPA-NONOate and 8-bromo-cGMP increased lung cGMP, but only 8-bromo-cGMP decreased permeability. These results suggest that ischemic vascular injury was, in part, mediated by a decrease in cGMP. Increased vascular pressure prevented injury by a cGMP-independent mechanism that could not be mimicked by administration of exogenous NO.

Endogenous nitric oxide is implicated in the regulation of lipolysis through antioxidant-related effect

We studied the influence of nitric oxide (NO) endogenously produced by adipocytes in lipolysis regulation. Diphenyliodonium (DPI), a nitric oxide synthase (NOS) inhibitor, was found to completely suppress NO synthesis in intact adipocytes and was thus used in lipolysis experiments. DPI was found to decrease both basal and dibutyryl cAMP (DBcAMP)-stimulated lipolysis. Inhibition of DBcAMP-stimulated lipolysis by DPI was prevented by S-nitroso-N-acetyl-penicillamine (SNAP), a NO donor. This antilipolytic effect of DPI was also prevented by two antioxidants, ascorbate or diethyldithiocarbamic acid (DDC). Preincubation of isolated adipocytes with DPI (30 min) before exposure to DBcAMP almost completely abolished the stimulated lipolysis. Addition of SNAP or antioxidant during DPI preincubation restored the lipolytic response to DBcAMP, whereas no preventive effects were observed when these compounds were added simultaneously to DBcAMP. Exposure of isolated adipocytes to an extracellular generating system of oxygen species (xanthine/xanthine oxidase) or to H(2)O(2) also resulted in an inhibition of the lipolytic response to DBcAMP. H(2)O(2) or DPI decreased cAMP-dependent protein kinase (PKA) activation. The DPI effect on PKA activity was prevented by SNAP, ascorbate, or DDC. These results provide clear evidence that 1) the DPI antilipolytic effect is related to adipocyte NOS inhibition leading to PKA alterations, and 2) endogenous NO is required for the cAMP lipolytic process through antioxidant-related effect.

Dynamics of haem oxygenase-1 expression and bilirubin production in cellular protection against oxidative stress

The inducible isoform of haem oxygenase (HO-1) has been proposed as an effective system to counteract oxidant-induced cell injury. In several circumstances, this cytoprotective effect has been attributed to increased generation of the antioxidant bilirubin during haem degradation by HO-1. However, a direct implication for HO-1-derived bilirubin in protection against oxidative stress remains to be established. In the present study, we examined the dynamics of HO-1 expression and bilirubin production after stimulation of vascular smooth-muscle cells with hemin, a potent inducer of the HO-1 gene. We found that hemin-mediated increase in HO-1 protein expression and haem oxygenase activity is associated with augmented bilirubin levels. The majority of bilirubin production occurred early after exposure of cells to hemin. Hemin pre-treatment also resulted in high resistance to cell injury caused by an oxidant-generating system. Interestingly, this protective effect was manifest only when cells were actively producing bilirubin as a consequence of increased haem availability and utilization by HO-1. Tin protoporphyrin IX, an inhibitor of haem oxygenase activity, significantly reduced bilirubin generation and reversed cellular protection afforded by hemin treatment. Furthermore, addition of bilirubin to the culture medium markedly reduced the cytotoxicity produced by oxidants. Our findings provide direct evidence that bilirubin generated after up-regulation of the HO-1 pathway is cytoprotective against oxidative stress.