Molecular actions of a Mn(III)Porphyrin superoxide dismutase mimetic and peroxynitrite scavenger: reaction with nitric oxide and direct inhibition of NO synthase and soluble guanylyl cyclase

The bacterial pigment pyocyanin inhibits the NLRP3 inflammasome through intracellular reactive oxygen and nitrogen species

Inflammasomes are cytosolic complexes that mature and secrete the inflammatory cytokines interleukin 1β (IL-1β) and IL-18 and induce pyroptosis. The NLRP3 (NACHT, LRR, and PYD domains–containing protein 3) inflammasome detects many pathogen- and danger-associated molecular patterns, and reactive oxygen species (ROS)/reactive nitrogen species (RNS) have been implicated in its activation. The phenazine pyocyanin (PCN) is a virulence factor of Pseudomonas aeruginosa and generates superoxide in cells. Here we report that PCN inhibits IL-1β and IL-18 release and pyroptosis upon NLRP3 inflammasome activation in macrophages by preventing speck formation and Caspase-1 maturation. Of note, PCN did not regulate the AIM2 (absent in melanoma 2) or NLRC4 inflammasomes or tumor necrosis factor (TNF) secretion. Imaging of the fluorescent glutathione redox potential sensor Grx1-roGFP2 indicated that PCN provokes cytosolic and nuclear but not mitochondrial redox changes. PCN-induced intracellular ROS/RNS inhibited the NLRP3 inflammasome posttranslationally, and hydrogen peroxide or peroxynitrite alone were sufficient to block its activation. We propose that cytosolic ROS/RNS inhibit the NLRP3 inflammasome and that PCN's anti-inflammatory activity may help P. aeruginosa evade immune recognition.

Heme Oxygenase-1 Mediates Up-Regulation of Adhesion Molecule Expression Induced by Peroxynitrite in Endothelial Cells

OBJECTIVE

Endothelial cell (EC) activation with up-regulation of cellular adhesion molecule (CAM) expression is a pathophysiologic feature in preeclampsia (PE). Enhanced peroxynitrite formation in the vasculature of women with PE was also reported. This study was to test whether EC oxidative stress induced by peroxynitrite could up-regulate EC CAM expression, and whether heme oxygenase-1 (HO-1) has protective effects on this peroxynitrite-induced cellular response.

METHODS

Confluent ECs were stimulated with 3-morpholinosydnonimine-HCl (SIN-1, a peroxynitrite generator) alone or combined with Mn(III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride (MnTMPyP, a peroxynitrite scavenger) up to 4 hours. EC surface protein expressions for ICAM, VCAM, P-selectin, and E-selectin were measured by colorimetric assay. ECs were also treated with Sn(IV) mesophorphyrin IX dichloride (SnMP, a HO-1 inhibitor) to determine if HO-1 was involved in the increased CAM expression in stressed cells. Protein and mRNA expressions for HO-1 were determined by Western blot analysis and reverse-transcriptase polymerase chain reaction (RT-PCR). Data are presented as the mean +/- SE and analyzed by analysis of variance (ANOVA).

RESULTS

Endothelial CAM expressions for VCAM, P-selectin, and E-selectin, but not ICAM, were significantly increased in SIN-1-treated ECs. Protein and mRNA expressions for HO-1 were also up-regulated in cells treated with SIN-1. MnTMPyP blocked both mRNA and protein expressions for HO-1, whereas SnMP only blocked HO-1 protein expression. Both MnTMPyP and SnMP abolished SIN-1-induced up-regulation of VCAM, P-selectin, and E-selectin expression in ECs.

CONCLUSIONS

Peroxynitrite-induced EC oxidative stress produces differential effects on CAM expression, which may be mediated by HO-1 regulation. Our results suggest that increased peroxynitrite formation in the maternal vasculature may contribute to the increased CAM expression and enhanced neutrophil-endothelial interaction associated with PE.

Impact of Superoxide Dismutase Mimetic AEOL 10150 on the Endothelin System of Fischer 344 Rats

Endothelin-1 is a potent vasoconstrictor and mitogenic peptide involved in the regulation of vasomotor tone and maintenance of blood pressure. Oxidative stress activates the endothelin system, and is implicated in pulmonary and cardiovascular diseases including hypertension, congestive heart failure, and atherosclerosis. Superoxide dismutase mimetics designed with the aim of treating diseases that involve reactive oxygen species in their pathophysiology may exert a hypotensive effect, but effects on the endothelin system are unknown. Our objective was to determine the effect of the superoxide dismutase mimetic AEOL 10150 on the basal endothelin system in vivo. Male Fischer-344 rats were injected subcutaneously with 0, 2 or 5 mg/kg body weight of AEOL 10150 in saline. Plasma oxidative stress markers and endothelins (bigET-1, ET-1, ET-2, ET-3) as well as lung and heart endothelin/nitric oxide system gene expressions were measured using HPLC-Coularray, HPLC-Fluorescence and RT-PCR respectively. AEOL 10150 reduced (p<0.05) the circulating levels of isoprostane (-25%) and 3-nitrotyrosine (-50%) measured in plasma 2h and 24h after treatment, confirming delivery of a physiologically-relevant dose and the potent antioxidant activity of the drug. The reduction in markers of oxidative stress coincided with sustained 24h decrease (p<0.05) of plasma levels of ET-1 (-50%) and ET-3 (-10%). Expression of preproET-1 and endothelin converting enzyme-1 mRNA were not altered significantly in the lungs. However preproET-1 (not significant) and ECE-1 mRNA (p<0.05) were increased (10-25%) in the heart. Changes in the lungs included decrease (p<0.05) of mRNA for the ET-1 clearance receptor ETB and the vasoconstriction-signaling ETA receptor (-30%), and an early surge of inducible nitric oxide synthase expression followed by sustained decrease (-40% after 24 hours). The results indicate that interception of the endogenous physiological flux of reactive nitrogen species and reactive oxygen species in rats impacts the endothelin/nitric oxide system, supporting a homeostatic relationship between those systems.

An educational overview of the chemistry, biochemistry and therapeutic aspects of Mn porphyrins--From superoxide dismutation to H2O2-driven pathways

Most of the SOD mimics thus far developed belong to the classes of Mn-(MnPs) and Fe porphyrins(FePs), Mn(III) salens, Mn(II) cyclic polyamines and metal salts. Due to their remarkable stability we have predominantly explored Mn porphyrins, aiming initially at mimicking kinetics and thermodynamics of the catalysis of O2(-) dismutation by SOD enzymes. Several MnPs are of potency similar to SOD enzymes. The in vivo bioavailability and toxicity of MnPs have been addressed also. Numerous in vitro and in vivo studies indicate their impressive therapeutic efficacy. Increasing insight into complex cellular redox biology has been accompanied by increasing awareness of complex redox chemistry of MnPs. During O2(-) dismutation process, the most powerful Mn porphyrin-based SOD mimics reduce and oxidize O2(-) with close to identical rate constants. MnPs reduce and oxidize other reactive species also (none of them specific to MnPs), acting as reductants (antioxidant) and pro-oxidants. Distinction must be made between the type of reactions of MnPs and the favorable therapeutic effects we observe; the latter may be of either anti- or pro-oxidative nature. H2O2/MnP mediated oxidation of protein thiols and its impact on cellular transcription seems to dominate redox biology of MnPs. It has been thus far demonstrated that the ability of MnPs to catalyze O2(-) dismutation parallels all other reactivities (such as ONOO(-) reduction) and in turn their therapeutic efficacies. Assuming that all diseases have in common the perturbation of cellular redox environment, developing SOD mimics still seems to be the appropriate strategy for the design of potent redox-active therapeutics.

Catalytic antioxidant AEOL 10150 treatment ameliorates sulfur mustard analog 2-chloroethyl ethyl sulfide-associated cutaneous toxic effects

Our previous studies and other published reports on the chemical warfare agent sulfur mustard (SM) and its analog 2-chloroethyl ethyl sulfide (CEES) have indicated a role of oxidative stress in skin injuries caused by these vesicating agents. We examined the effects of the catalytic antioxidant AEOL 10150 in the attenuation of CEES-induced toxicity using our established skin injury models (skin epidermal cells and SKH-1 hairless mice) to validate the role of oxidative stress in the pathophysiology of mustard vesicating agents. Treatment of mouse epidermal JB6 and human HaCaT cells with AEOL 10150 (50μM) 1h post-CEES exposure resulted in significant (p < 0.05) reversal of CEES-induced decreases in both cell viability and DNA synthesis. Similarly, AEOL 10150 treatment 1h after CEES exposure attenuated CEES-induced DNA damage in these cells. Similar AEOL 10150 treatments also caused significant (p < 0.05) reversal of CEES-induced decreases in cell viability in normal human epidermal keratinocytes. Cytoplasmic and mitochondrial reactive oxygen species measurements showed that AEOL 10150 treatment drastically ameliorated the CEES-induced oxidative stress in both JB6 and HaCaT cells. Based on AEOL 10150 pharmacokinetic studies in SKH-1 mouse skin, mice were treated with a topical formulation plus subcutaneous injection (5mg/kg) of AEOL 10150 1h after CEES (4mg/mouse) exposure and every 4h thereafter for 12h. This AEOL 10150 treatment regimen resulted in over 50% (p < 0.05) reversal of CEES-induced skin bi-fold and epidermal thickness, myeloperoxidase activity, and DNA oxidation in mouse skin. Results from this study demonstrate the potential therapeutic efficacy of AEOL 10150 against CEES-mediated cutaneous lesions, supporting AEOL 10150 as a medical countermeasure against SM-induced skin injuries.

Redox modulation of HMGB1-related signaling

SIGNIFICANCE

In the cells' nuclei, high-mobility group box protein 1 (HMGB1) is a nonhistone chromatin-binding protein involved in the regulation of transcription. Extracellularly, HMGB1 acts as a danger molecule with properties of a proinflammatory cytokine. It can be actively secreted from myeloid cells or passively leak from any type of injured, necrotic cell. Increased serum levels of active HMGB1 are often found in pathogenic inflammatory conditions and correlate with worse prognoses in cancer, sepsis, and autoimmunity. By damaging cells, superoxide and peroxynitrite promote leakage of HMGB1.

RECENT ADVANCES

The activity of HMGB1 strongly depends on its redox state: Inflammatory-active HMGB1 requires an intramolecular disulfide bond (Cys23 and Cys45) and a reduced Cys106. Oxidation of the latter blocks its stimulatory activity and promotes immune tolerance.

CRITICAL ISSUES

Reactive oxygen and nitrogen species create an oxidative environment and can be detoxified by superoxide dismutase (SOD), catalase, and peroxidases. Modifications of the oxidative environment influence HMGB1 activity.

FUTURE DIRECTIONS

In this review, we hypothesize that manipulations of an oxidative environment by SOD mimics or by hydrogen sulfide are prone to decrease tissue damage. Both the concomitant decreased HMGB1 release and its redox chemical modifications ameliorate inflammation and tissue damage.

Plant polyphenols regulate chemokine expression and tissue repair in human keratinocytes through interaction with cytoplasmic and nuclear components of epidermal growth factor receptor system

AIMS

To evaluate mechanisms underlying modulation of inflammatory chemokines in primary human keratinocytes (normal human epidermal keratinocytes) and repair-related processes in wound models by plant polyphenols (PPs) with antioxidant and superoxide scavenging properties (verbascoside [Vb], resveratrol [Rv], polydatin [Pd], quercetin [Qr], and rutin).

RESULTS

Epidermal growth factor receptor (EGFR)-controlled chemokines CXCL8/interleukin 8 (IL-8), CCL2/monocyte chemotactic protein-1 (MCP-1), and CXCL10/interferon gamma-produced protein of 10 kDa (IP-10) were modulated by transforming growth factor alpha (TGF-α) and by the tumor necrosis factor alpha/interferon gamma combination (T/I). EGFR phosphorylation, nuclear translocation, and downstream cytoplasmic signaling pathways (extracellular regulation kinase [ERK]1/2, p38, STAT3, and PI-3K) were studied. All PPs did not affect TGF-α-induced STAT3 phosphorylation, whereas they suppressed T/I-activated NFkappaB and constitutive and T/I-induced but not TGF-α-induced ERK1/2 phosphorylation. Vb and Qr suppressed total EGFR phosphorylation, but they synergized with TGF-α to enhance nuclear accumulation of phosphorylated EGFR. Vb strongly inhibited TGF-α-induced p38 phosphorylation and T/I-induced NFkappaB and activator protein-1 (AP-1) binding to DNA. Vb was an effective inhibitor of T/I-stimulated chemokine synthesis, and it accelerated scratch wound healing in vitro. Anti-inflammatory and wound healing activities of Vb were confirmed in vivo in the full-thickness excision wound. Although Pd and Rv did not affect EGFR activation/translocation, they and Qr synergized with TGF-α and T/I in the induction of IL-8 transcription/synthesis while opposing enhanced MCP-1 and IP-10 transcription/synthesis connected with pharmacologically impaired EGFR functioning.

INNOVATION

PPs perturb the EGFR system in human keratinocytes, and this effect may be implicated in the regulation of inflammatory and repair-related processes in the skin.

CONCLUSION

Anti-inflammatory and wound healing effects of PPs depend on their interaction with EGFR-controlled cytoplasmic and nuclear pathways rather than on their direct redox properties.

Role of reactive oxygen and nitrogen species in olfactory epithelial injury by the sulfur mustard analogue 2-chloroethyl ethyl sulfide

The inhalation of sulfur mustard (SM) causes substantial deposition in the nasal region. However, specific injury has not been characterized. 2-chloroethyl ethyl sulfide (CEES) is an SM analogue used to model injury and screen potential therapeutics. After the inhalation of CEES, damage to the olfactory epithelium (OE) was extensive. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells were present by 4 hours, and maximal at 18-72 hours. Cleaved caspase 3 immunohistochemistry (IHC) was maximal at 18 hours after the inhalation of 5% CEES. Olfactory marker protein (OMP)-positive olfactory neurons were markedly decreased at 18 hours. IHC-positive cells for 3-nitrotyrosine (3-NT) within epithelium were elevated by 8 hours, waning by 18 hours, and absent by 72 hours. AEOL 10150, a catalytic manganoporphyrin antioxidant, administered both subcutaneously (5 mg/kg) and intranasally (50 μM, "combined treatment"), decreased OE injury. CEES-induced increases in markers of cell death were decreased by combined treatment involving AEOL 10150. CEES-induced changes in OMP and 3-NT immunostaining were markedly improved by combined treatment involving AEOL 10150. The selective inducible nitric oxide synthase inhibitor 1400W (5 mg/kg, subcutaneous), administered 1 hour after inhalation and thereafter every 4 hours (five doses), also reduced OE damage with improved OMP and 3-NT staining. Taken together, these data indicate that reactive oxygen and nitrogen species are important mediators in CEES-induced nasal injury.

Design of Mn porphyrins for treating oxidative stress injuries and their redox-based regulation of cellular transcriptional activities

The most efficacious Mn(III) porphyrinic (MnPs) scavengers of reactive species have positive charges close to the Mn site, whereby they afford thermodynamic and electrostatic facilitation for the reaction with negatively charged species such as O (2) (•-) and ONOO(-). Those are Mn(III) meso tetrakis(N-alkylpyridinium-2-yl)porphyrins, more specifically MnTE-2-PyP(5+) (AEOL10113) and MnTnHex-2-PyP(5+) (where alkyls are ethyl and n-hexyl, respectively), and their imidazolium analog, MnTDE-2-ImP(5+) (AEOL10150, Mn(III) meso tetrakis(N,N'-diethylimidazolium-2-yl) porphyrin). The efficacy of MnPs in vivo is determined not only by the compound antioxidant potency, but also by its bioavailability. The former is greatly affected by the lipophilicity, size, structure, and overall shape of the compound. These porphyrins have the ability to both eliminate reactive oxygen species and impact the progression of oxidative stress-dependent signaling events. This will effectively lead to the regulation of redox-dependent transcription factors and the suppression of secondary inflammatory- and oxidative stress-mediated immune responses. We have reported on the inhibition of major transcription factors HIF-1α, AP-1, SP-1, and NF-κB by Mn porphyrins. While the prevailing mechanistic view of the suppression of transcription factors activation is via antioxidative action (presumably in cytosol), the pro-oxidative action of MnPs in suppressing NF-κB activation in nucleus has been substantiated. The magnitude of the effect is dependent upon the electrostatic (porphyrin charges) and thermodynamic factors (porphyrin redox ability). The pro-oxidative action of MnPs has been suggested to contribute at least in part to the in vitro anticancer action of MnTE-2-PyP(5+) in the presence of ascorbate, and in vivo when combined with chemotherapy of lymphoma. Given the remarkable therapeutic potential of metalloporphyrins, future studies are warranted to further our understanding of in vivo action/s of Mn porphyrins, particularly with respect to their subcellular distribution.

Orally available Mn porphyrins with superoxide dismutase and catalase activities

Superoxide dismutase/catalase mimetics, such as salen Mn complexes and certain metalloporphyrins, catalytically neutralize reactive oxygen and nitrogen species, which have been implicated in the pathogenesis of many serious diseases. Both classes of mimetic are protective in animal models of oxidative stress. However, only AEOL11207 and EUK-418, two uncharged Mn porphyrins, have been shown to be orally bioavailable. In this study, EUK-418 and several new analogs (the EUK-400 series) were synthesized and shown to exhibit superoxide dismutase, catalase, and peroxidase activities in vitro. Some also protected PC12 cells against staurosporine-induced cell death. All EUK-400 compounds were stable in simulated gastric fluid, and most were substantially more lipophilic than the salen Mn complexes EUK-189 and EUK-207, which lack oral activity. Pharmacokinetics studies demonstrate the presence of all EUK-400 series compounds in the plasma of rats after oral administration. These EUK-400 series compounds are potential oral therapeutic agents for cellular damage caused by oxidative stress.

Oxidative inactivation of key mitochondrial proteins leads to dysfunction and injury in hepatic ischemia reperfusion

BACKGROUND & AIMS

Ischemia-reperfusion (I/R) is a major mechanism of liver injury following hepatic surgery or transplantation. Despite numerous reports on the role of oxidative/nitrosative stress and mitochondrial dysfunction in hepatic I/R injury, the proteins that are oxidatively modified during I/R damage are poorly characterized. This study was aimed at investigating the oxidatively modified proteins underlying the mechanism for mitochondrial dysfunction in hepatic I/R injury. We also studied the effects of a superoxide dismutase mimetic/peroxynitrite scavenger metalloporphyrin (MnTMPyP) on oxidatively modified proteins and their functions.

METHODS

The oxidized and/or S-nitrosylated mitochondrial proteins from I/R-injured mouse livers with or without MnTMPyP pretreatment were labeled with biotin-N-maleimide, purified with streptavidin-agarose, and resolved by 2-dimensional gel electrophoresis. The identities of the oxidatively modified proteins were determined using mass spectrometric analysis. Liver histopathology, serum transaminase levels, nitrosative stress markers, and activities of oxidatively modified mitochondrial proteins were measured.

RESULTS

Comparative 2-dimensional gel analysis revealed markedly increased numbers of oxidized and S-nitrosylated mitochondrial proteins following hepatic I/R injury. Many key mitochondrial enzymes involved in cellular defense, fat metabolism, energy supply, and chaperones were identified as being oxidatively modified proteins. Pretreatment with MnTMPyP attenuated the I/R-induced increased serum transaminase levels, histologic damage, increased inducible nitric oxide synthase expression, and S-nitrosylation and/or nitration of various key mitochondrial proteins. MnTMPyP pretreatment also restored I/R-induced suppressed activities of mitochondrial aldehyde dehydrogenase, 3-ketoacyl-CoA thiolases, and adenosine triphosphate synthase.

CONCLUSIONS

These results suggest that increased nitrosative stress is critically important in promoting S-nitrosylation and nitration of various mitochondrial proteins, leading to mitochondrial dysfunction with decreased energy supply and increased hepatic injury.

MnTMPyP, a metalloporphyrin-based superoxide dismutase/catalase mimetic, protects INS-1 cells and human pancreatic islets from an in vitro oxidative challenge

AIMS

Pancreatic islets can be lost early following allotransplantation from oxidative stress. Antioxidant enzyme overexpression could confer a beneficial effect on islets exposed to reactive oxygen species (ROS) and nitrogen species. Here, we tested the effect of MnTMPyP, a superoxide dismutase/catalase mimetic.

METHODS

INS-1 insulin-secreting cells or human islets were cultured with MnTMPyP and exposed to a superoxide donor (the hypoxanthine/xanthine oxidase (HX/XO) system), a nitric oxide donor [3-morpholinosydnonimine (SIN-1)] or menadione. Viability of INS-1 cells was assessed by WST-1 colorimetric assay and FACS analysis (Live/Dead test). ROS production was determined using fluorescent probes. Islet viability was estimated by WST-1 assay and endocrine function by static incubation.

RESULTS

Following MnTMPyP treatment, ROS production in INS-1 cells was reduced by 4- to 20-fold upon HX/XO challenge and up to 2-fold upon SIN-1 stress. This phenomenon correlated with higher viability measured by WST-1 or Live/Dead test. MnTMPyP preserved islet viability upon exposure to SIN-1 or menadione but not upon an HX/XO challenge. Similarly, decrease in insulin secretion tended to be less pronounced in MnTMPyP-treated islets than in control islet when exposed to SIN-1, but no changes were noticed during an HX/XO stress.

CONCLUSIONS

MnTMPyP was able to improve the viability of INS-1 cells and human islets exposed to oxidative challenges in vitro. Protection of INS-1 cells could be as high as 90%. This agent is therefore potentially attractive in situations involving the overproduction of ROS, such as islet transplantation.

Unconventional neuroprotection against Ca2+ -dependent insults by metalloporphyrin catalytic antioxidants

We evaluated whether both inert and catalytically active metalloporphyrin antioxidants, meso-substituted with either phenyl-based or N-alkylpyridinium-based groups, suppress Ca(2+)-dependent neurotoxicity in cell culture models of relevance to cerebral ischemia. Representatives from both metalloporphyrin classes, regardless of antioxidant strength, protected cultured cortical neurons or PC-12 cultures against the Ca(2+) ionophores ionomycin or A23187, by suppressing neurotoxic Ca(2+) influx. Some metalloporphyrins suppressed excitotoxic Ca(2+) influx indirectly induced by the Ca(2+) ionophores in cortical neurons. Metalloporphyrins did not quench intracellular fluorescence, suggesting localization to the plasma membrane interface and/or interference with Ca(2+) ionophores. Metalloporphyrins suppressed ionomycin-induced Mn(2+) influx, but did not protect cortical neurons against pyrithione, a Zn(2+) ionophore. In other Ca(2+)-dependent paradigms, Ca(2+) influx via plasma membrane depolarization, but not through reversal of plasmalemmal Na(+)/Ca(2+) exchangers, was modestly suppressed by Mn(III)meso-tetrakis(4-benzoic acid)porphyrin (Mn(III)TBAP) or by an inert analog, Zn(II)TBAP. Mn(III)TBAP and Zn(II)TBAP potently protected cortical neurons against long-duration oxygen-glucose deprivation (OGD), performed in the presence of antagonists of NMDA, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and L-type voltage-gated Ca(2+) channels, raising the possibility of an unconventional mode of blockade of transient receptor protein melastatin 7 channels by a metalloTBAP family of metalloporphyrins. The present study extends the range of Ca(2+)-dependent insults for which metalloporphyrins demonstrate unconventional neuroprotection. MetalloTBAPs appear capable of targeting an OGD temporal continuum.

Survival pathways triggered by peroxynitrite in cells belonging to the monocyte/macrophage lineage

Peroxynitrite, a highly reactive nitrogen species, promotes in U937 cells (a promonocytic cell line) a mitochondrial permeability transition (MPT)-dependent necrosis. An initial event triggered by peroxynitrite (i.e., inhibition of complex III of the mitochondrial respiratory chain) is responsible for the time-dependent formation of H(2)O(2), essential for the occurrence of cell death. Otherwise non-toxic concentrations of peroxynitrite nevertheless commit cells to MPT-dependent necrosis, which is however prevented by a cytoprotective signaling driven by arachidonic acid (AA) released by the cytosolic PLA(2) isoform. Interestingly, the mechanism whereby delayed formation of H(2)O(2) promotes toxicity in cells exposed to intrinsically toxic concentrations of peroxynitrite is independent of the accumulation of additional damage. Cell death is in fact mediated by inhibition of the AA-dependent cytoprotective signaling. Exogenous AA, however, prevented toxicity also under these conditions. An additional point to be made is that the major findings obtained using U937 cells were reproduced in different cell types belonging to the monocyte/macrophage lineage. Hence, within the context of the inflammatory response, monocytes and macrophages may cope with peroxynitrite by using AA, a signaling molecule largely available at the inflammatory sites.

An alternative Ca2+‐dependent mechanism of neuroprotection by the metalloporphyrin class of superoxide dismutase mimetics

This study challenges the conventional view that metalloporphyrins protect cultured cortical neurons in models of cerebral ischemia by acting as intracellular catalytic antioxidants [superoxide dismutase (SOD) mimetics]. High SOD-active Mn(III)porphyrins meso-substituted with N,N'-dimethylimidazolium or N-alkylpyridinium groups did not protect neurons against oxygen-glucose deprivation (OGD), although lower SOD-active and -inactive para isomers protected against N-methyl-D-aspartate (NMDA) exposure. Mn(III)meso-tetrakis(4-benzoic acid)porphyrin (Mn(III)TBAP), as well as SOD-inactive metalloTBAPs and other phenyl ring- or beta-substituted metalloporphyrins that contained redox-insensitive metals, protected cultures against OGD and NMDA neurotoxicity. Crucially, neuroprotective metalloporphyrins suppressed OGD- or NMDA-induced rises in intracellular Ca2+ concentration in the same general rank order as observed for neuroprotection. Results from paraquat toxicity, intracellular fluorescence quenching, electrophysiology, mitochondrial Ca2+, and spontaneous synaptic activity experiments suggest a model in which metalloporphyrins, acting at the plasma membrane, protect neurons against OGD by suppressing postsynaptic NMDA receptor-mediated Ca2+ rises, thereby indirectly preventing accumulation of neurotoxic mitochondrial Ca2+ levels. Though neuroprotective in a manner not originally intended, SOD-inactive metalloporphyrins may represent promising therapeutic agents in diseases such as cerebral ischemia, in which Ca2+ toxicity is implicated. Conventional syntheses aimed at improving the catalytic antioxidant capability and/or intracellular access of metalloporphyrins may not yield improved efficacy in some disease models.

A novel class of cytochrome P450 reductase redox cyclers: cationic manganoporphyrins

Manganese porphyrins are a potent class of catalytic antioxidants whose activity was recently shown to be partially dependent upon flavin-containing enzymes (R. Kachadourian et al., 2004, Biochem. Pharmacol. 67, 77-85). We tested whether manganese porphyrins could redox cycle with the flavin-containing enzyme, cytochrome P450 reductase, and whether this results in the inhibition of xenobiotic metabolism. The effect of manganese porphyrins on xenobiotic metabolism in rat and human liver microsomes was assessed spectrofluorometrically by following the O-dealkylation of benzyloxy- (BROD) and methoxyresorufin (MROD). Redox cycling of manganese porphyrins with human cytochrome P450 reductase was assessed both spectrophotometrically and polarographically by following the consumption of NADPH and oxygen, respectively. The tetrakis(N-pyridinium-2-yl) meso-substituted manganoporphyrin, MnTEPyP5+, and the tetrakis(1,3-dimethyl imidazolium-2-yl) meso-substituted manganoporphyrin, MnTDMIP5+, were 40 to 100 times more potent inhibitors of rat and human liver microsomal BROD metabolism than the tetrakis(1,3-diethyl imidazolium-2-yl) meso-substituted manganoporphyrin, MnTDEIP5+, or the tetrakis(4-benzoic acid) meso-substituted manganoporphyrin, MnTBAP. A similar pattern of inhibition was also seen in beta-naphthoflavone-induced rat liver microsomal MROD metabolism. This pattern of xenobiotic metabolism inhibition correlated with the compound's ability to redox cycle with cytochrome P450 reductase where MnTEPyP5+ was more potent than MnTDEIP5+. Furthermore, redox cycling of MnTEPyP5+ with cytochrome P450 reductase was inhibited by the flavin domain inhibitor diphenyleneiodonium. Small changes to the carbon chain length on the imidazolium side groups had a large effect on this activity. It is possible that interactions between manganoporphyrins and flavin-dependent oxidoreductases can account for both adverse and beneficial effects of the compounds.

Tetrahydrobiopterin rapidly reduces the SOD mimic Mn(III) ortho-tetrakis(N-ethylpyridinium-2-yl)porphyrin

Mn(III) ortho-tetrakis(N-ethylpyridinium-2-yl)porphyrin (Mn(III)TE-2-PyP(5+)) effectively scavenges reactive oxygen and nitrogen species in vitro, and protects in vivo, in different rodent models of oxidative stress injuries. Further, Mn(III)TE-2-PyP(5+) was shown to be readily reduced by cellular reductants such as ascorbic acid and glutathione. We now show that tetrahydrobiopterin (BH(4)) is also able to reduce the metal center. Under anaerobic conditions, in phosphate-buffered saline (pH 7.4) at 25 +/- 0.1 degrees C, reduction of Mn(III)TE-2-PyP(5+) occurs through two reaction steps with rate constants k(1) = 1.0 x 10(4) M(-1) s(-1) and k(2) = 1.5 x 10(3) M(-1) s(-1). We ascribe these steps to the formation of tetrahydrobiopterin radical (BH(4)(.+)) (k(1)) that then undergoes oxidation to 6,7-dihydro-8H-biopterin (k(2)), which upon rearrangement gives rise to 7,8-dihydrobiopterin (7,8-BH(2)). Under aerobic conditions, Mn(III)TE-2-PyP(5+) catalytically oxidizes BH(4). This is also true for its longer chain alkyl analog, Mn(III) ortho-tetrakis(N-n-octylpyridinium-2-yl)porphyrin. The reduced Mn(II) porphyrin cannot be oxidized by 7,8-BH(2) or by l-sepiapterin. The data are discussed with regard to the possible impact of the interaction of Mn(III)TE-2-PyP(5+) with BH(4) on endothelial cell proliferation and hence on tumor antiangiogenesis via inhibition of nitric oxide synthase.

Tetrahydrobiopterin improves endothelial dysfunction and vascular oxidative stress in microvessels of intrauterine undernourished rats

In the present study, we investigated the effects of the exogenous application of tetrahydrobiopterin on the endothelium-dependent vasorelaxation and superoxide anion generation in the mesenteric microvessels of intrauterine undernourished rats. In addition, we investigated the presence of peroxynitrite in these rats by evaluation of nitrotyrosine-containing proteins, a stable end-product of peroxynitrite oxidation. For this, female pregnant Wistar rats were fed either normal or 50% of the normal intake diets during the whole gestational period. Male offspring (16 weeks of age) were studied to assess microvascular reactivity, superoxide production using a hydroethidine staining assay, nitric oxide synthase (NOS) activity and nitric oxide (NO) production. Western blot analysis was used to quantify nitrotyrosine-containing proteins and relative multiplex RT-PCR analysis for endothelial NOS (eNOS) mRNA expression. Superfusion with tetrahydrobiopterin significantly decreased superoxide generation and improved vascular function. Intrauterine malnutrition induced a decrement of NOS activity and NO production without affecting the gene expression of eNOS. However, incubation with tetrahydrobiopterin significantly improved NO production after stimulation with acetylcholine or bradykinin in intrauterine undernourished rats. The fact that the nitrotyrosine-containing proteins were increased could, at first sight, suggest that the peroxynitrite is the mediator responsible for the excessive oxidation and depletion of tetrahydrobiopterin. Our study shows that exogenous application of tetrahydrobiopterin leads to a significant improvement of endothelium-dependent vasodilatation, enhanced NO production and decreased superoxide generation in microvessels of intrauterine undernourished rats. Since we found a decrease in NOS activity without an alteration in the gene expression of eNOS, we suggest that impaired NOS-dependent responses of mesenteric arterioles are related to the impairment of tetrahydrobiopterin pathways.

Alteration of cellular phenotype and responses to oxidative stress by manganese superoxide dismutase and a superoxide dismutase mimic in RWPE-2 human prostate adenocarcinoma cells

To study biologic effects of increased manganese superoxide dismutase (MnSOD) on cell behavior, we overexpressed MnSOD in a human prostate cancer cell line RWPE-2 by cDNA transfection. Stable transfectants of MnSOD showed a two- to threefold increase in MnSOD protein and enzymatic activity and a decrease in growth rate with prolonged cell population doubling times. Western blot analysis showed a 1.5- to twofold increase in the cyclin-dependent kinase inhibitor p21(Waf1) in MnSOD transfectants. Overexpression of MnSOD resulted in a seven- to eightfold increase in reduced glutathione (GSH), 18- to 26-fold increase in oxidized glutathione (GSSG), and a two- to threefold decrease in the ratio of GSH to GSSG. MnSOD-overexpressing cells showed an increase in sensitivity to the cytotoxicity of buthionine sulfoximine, a glutathione-depleting agent, and vitamin C, but a decrease in sensitivity to sodium selenite. Treatment with a superoxide dismutase (SOD) mimic MnTMPyP resulted in similar effects of MnSOD overexpression on cell responses to vitamin C and selenium. These data demonstrate that overexpression of MnSOD or treatment with SOD mimics can result in antioxidant or prooxidant effects in cells, depending on the presence of other antioxidants and prooxidants. MnSOD also has redox regulatory effects on cell growth and gene expression. These findings suggest that MnSOD and SOD mimics have the potential for cancer prevention or treatment.

Interference of the polyphenol epicatechin with the biological chemistry of nitric oxide- and peroxynitrite-mediated reactions

The formation of reactive nitrogen species in mammalians has both beneficial and undesirable effects. Nitric oxide (NO) production in endothelial cells leads to vascular smooth muscle relaxation, but if reactive nitrogen species are generated in high amounts by cells under inflammatory conditions they are toxic. Flavonoids like (-)-epicatechin show an inverse association of their intake with diseases thought to be associated with overproduction of reactive nitrogen species. We found that the formation of cyclic GMP in cultured porcine aortic endothelial cells was not affected by up to 1 mM (-)-epicatechin. Half maximal inhibition of interferon-gamma/lipopolysaccharide induced nitrite accumulation in murine macrophages required about 0.5 mM of the flavonoid. In contrast, nitration of free tyrosine triggered by 0.1 and 1 mM authentic peroxynitrite was inhibited by (-)-epicatechin with IC(50) values of 6.6 and 28.0 microM, respectively. The presence of 15 mM sodium bicarbonate had no significant effect. Nitration of protein-bound tyrosine in phorbol 12-myristate 13-acetate treated HL-60 cells in the presence of nitrite was inhibited by (-)-epicatechin at a similar concentration range (IC(50)=10-100 microM). Myeloperoxidase activity of phorbol 12-myristate 13-acetate stimulated HL-60 cells was inhibited by (-)-epicatechin with an IC(50) value of 77.4 microM. Epicatechin inhibited dihydrorhodamine oxidation by 50 microM authentic peroxynitrite and 1 mM 3-morpholino-sydnonimine with IC(50) values of 11.8 and 0.63 microM, respectively. Our data suggest that at up to 0.1 mM (-)-epicatechin preferentially inhibits NO-related nitration and oxidation reactions without affecting NO synthesis and cyclic GMP signaling.

Flavin-dependent antioxidant properties of a new series of meso-N,N′-dialkyl-imidazolium substituted manganese(III) porphyrins

A number of synthetic manganese complexes exhibit both in vitro and in vivo catalytic antioxidant activities. This study reports that the antioxidant potencies of a new series of meso-N,N'-dialkyl-imidazolium substituted manganese(III) porphyrins are dependent, in part, on their ability to redox cycle with endogenous flavin-dependent oxidoreductases. Inhibition of lipid peroxidation activities of these novel cationic porphyrins was compared using rat brain homogenate as a source of lipids and endogenous oxidoreductases. Iron and ascorbate was used as initiators of lipid peroxidation, and two indices of lipid peroxidation (thiobarbituric acid reactive species (TBARS) and F(2)-isoprostanes) were determined. All meso-N,N'-dialkyl-imidazolium substituted porphyrins tested were potent inhibitors of lipid peroxidation with IC(50) ranging from 0.1 to 34 microM with a metal-dependent potency of Mn(III)>>Co(III)>Zn(II). A flavin-dependent oxidoreductase antioxidant process was supported by the ability of the diphenyleneiodonium chloride (DPI, a flavoenzyme inhibitor) to decrease the potency of Mn-porphyrins in the lipid peroxidation model and that Mn-porphyrins stimulate NADPH oxidation in rat brain homogenates. These data suggest that metalloporphyrins may have differential antioxidant effects in tissues due to the presence or absence of flavin-dependent oxidoreductases.

Peroxynitrite decomposition activity of iron porphyrin complexes

Peroxynitrite (ONOO(-)/ONOOH), a putative cytotoxin formed by combination of nitric oxide (NO.) and superoxide (HO(2)(.)) radicals, is decomposed catalytically by micromolar concentrations of water-soluble Fe(III) porphyrin complexes, including 5,10,15,20-tetrakis(2',4',6'-trimethyl-3,5-disulfonatophenyl)porphyrinatoferrate(7-), Fe(TMPS); 5,10,15,20-tetrakis(4'-sulfonatophenyl)porphyrinatoiron(3-), Fe(TPPS); and 5,10,15,20-tetrakis(N-methyl-4'-pyridyl) porphyrinatoiron(5+), Fe(TMPyP). Spectroscopic (UV-visible), kinetic (stopped-flow), and product (ion chromatography) studies reveal that the catalyzed reaction is a net isomerization of peroxynitrite to nitrate (NO(3)(-)). One-electron catalyst oxidation forms an oxoFe(IV) intermediate and nitrogen dioxide, and recombination of these species is proposed to regenerate peroxynitrite or to yield nitrate. Michaelis-Menten kinetics are maintained accordingly over an initial peroxynitrite concentration range of 40-610 microM at 5.0 microM catalyst concentrations, with K(m) in the range 370-620 microM and limiting turnover rates in the range of 200-600 s(-1). Control experiments indicate that nitrite is not a kinetically competent reductant toward the oxidized intermediates, thus ruling out a significant role for NO(2)(.) hydrolysis in catalyst turnover. However, ascorbic acid can intercept the catalytic intermediates, thus directing product distributions toward nitrite and accelerating catalysis to the oxidation limit. Additional mechanistic details are proposed on the basis of these and various other kinetic observations, specifically including rate effects of catalyst and peroxynitrite concentrations, solution pH, and isotopic composition.

Pivotal role of superoxides generated in the mitochondrial respiratory chain in peroxynitrite-dependent activation of phospholipase A2

Exposure of PC12 cells to reagent peroxynitrite promotes the release of arachidonic acid (AA) mediated by activation of phospholipase A(2) [Guidarelli, Palomba and Cantoni (2000) Br. J. Pharmacol. 129, 1539-1542]. We now present experimental evidence consistent with the notion that this response is not directly triggered by peroxynitrite but, rather, by reactive oxygen species generated at the level of complex III of the mitochondrial respiratory chain. In particular, superoxide (and not hydrogen peroxide) has a pivotal role in peroxynitrite-dependent activation of phospholipase A(2). This observation was confirmed by results showing that superoxide, or peroxynitrite, promotes release of AA in isolated mitochondria. Consistently, the release of AA elicited by either peroxynitrite or A23187 in intact cells was shown to be calcium-dependent and differentially affected by phospholipase A(2) inhibitors with different levels of specificity. In particular, the effects of peroxynitrite, unlike those of A23187, were both sensitive to low concentrations of two general phospholipase A(2) inhibitors and insensitive to arachidonyltrifluoromethyl ketone, which shows some selectivity towards cytosolic phospholipase A(2). In addition, peroxynitrite and A23187 synergistically enhanced the release of AA. Collectively, the above results demonstrate that peroxynitrite causes inhibition of complex III, followed by enforced formation of superoxides that stimulate the activity of a calcium-dependent PLA(2) isoform, probably localized in the mitochondria.

Peroxynitrite scavenging activity of herb extracts

Peroxynitrite (ONOO(-)) is a cytotoxicant with strong oxidizing properties toward various cellular constituents, including sulphydryls, lipids, amino acids and nucleotides and can cause cell death, lipid peroxidation, carcinogenesis and aging. The aim of this study was to characterize ONOO(-) scavenging constituents from herbs. Twenty-eight herbs were screened for their ONOO(-) scavenging activities with the use of a fluorometric method. The potency of scavenging activity following the addition of authentic ONOO(-) was in the following order: witch hazel bark > rosemary > jasmine tea > sage > slippery elm > black walnut leaf > Queen Anne's lace > Linden flower. The extracts exhibited dose-dependent ONOO(-) scavenging activities. We found that witch hazel (Hamamelis virginiana L.) bark showed the strongest effect for scavenging ONOO(-) of the 28 herbs. Hamamelitannin, the major active component of witch hazel bark, was shown to have a strong ability to scavenge ONOO(-). It is suggested that hamamelitannin might be developed as an effective peroxynitrite scavenger for the prevention of ONOO(-) involved diseases.

Delayed formation of hydrogen peroxide mediates the lethal response evoked by peroxynitrite in U937 cells

The toxicity paradigm used in the present study involves exposure of U937 cells to a concentration of authentic peroxynitrite, leading to a rapid necrotic response mediated by mitochondrial permeability transition. We found that addition of catalase after treatment with peroxynitrite specifically prevents the loss of mitochondrial membrane potential and the ensuing lethal response. The protective effects of catalase were mimicked by the cocktail glutathione peroxidase/reduced glutathione. A defensive role of intracellular catalase was implied by experiments showing that catalase-depleted cells are hypersensitive to peroxynitrite and that cells with an increased catalase content, selected for their resistance to H(2)O(2), are cross-resistant to peroxynitrite. Further experiments demonstrated that H(2)O(2) formation takes place after peroxynitrite exposure. Various approaches using inhibitors of the mitochondrial respiratory chain as well as respiration-deficient cells revealed that the oxidant is produced upon dismutation of superoxides generated at the level of complex III. Interestingly, respiration-deficient cells were found to be resistant to peroxynitrite toxicity, and all those treatments increasing formation of H(2)O(2) produced a parallel increase in toxicity. In conclusion, the results presented in this study indicate that peroxynitrite-induced impairment of electron transport from cytochrome b to cytochrome c1 leads to delayed formation of hydrogen peroxide, which plays a pivotal role in the ensuing necrotic response.

Protein tyrosine nitration in cytokine-activated murine macrophages. Involvement of a peroxidase/nitrite pathway rather than peroxynitrite

Peroxynitrite, formed in a rapid reaction of nitric oxide (NO) and superoxide anion radical (O(2)), is thought to mediate protein tyrosine nitration in various inflammatory and infectious diseases. However, a recent in vitro study indicated that peroxynitrite exhibits poor nitrating efficiency at biologically relevant steady-state concentrations (Pfeiffer, S., Schmidt, K., and Mayer, B. (2000) J. Biol. Chem. 275, 6346-6352). To investigate the molecular mechanism of protein tyrosine nitration in intact cells, murine RAW 264.7 macrophages were activated with immunological stimuli, causing inducible NO synthase expression (interferon-gamma in combination with either lipopolysaccharide or zymosan A), followed by the determination of protein-bound 3-nitrotyrosine levels and release of potential triggers of nitration (NO, O(2)*, H(2)O(2), peroxynitrite, and nitrite). Levels of 3-nitrotyrosine started to increase at 16-18 h and exhibited a maximum at 20-24 h post-stimulation. Formation of O(2) was maximal at 1-5 h and decreased to base line 5 h after stimulation. Release of NO peaked at approximately 6 and approximately 9 h after stimulation with interferon-gamma/lipopolysaccharide and interferon-gamma/zymosan A, respectively, followed by a rapid decline to base line within the next 4 h. NO formation resulted in accumulation of nitrite, which leveled off at about 50 microm 15 h post-stimulation. Significant release of peroxynitrite was detectable only upon treatment of cytokine-activated cells with phorbol 12-myristate-13-acetate, which led to a 2.2-fold increase in dihydrorhodamine oxidation without significantly increasing the levels of 3-nitrotyrosine. Tyrosine nitration was inhibited by azide and catalase and mimicked by incubation of unstimulated cells with nitrite. Together with the striking discrepancy in the time course of NO/O(2) release versus 3-nitrotyrosine formation, these results suggest that protein tyrosine nitration in activated macrophages is caused by a nitrite-dependent peroxidase reaction rather than peroxynitrite.

Peroxynitrite scavenging and cytoprotective activity of 2,3,6-tribromo-4,5-dihydroxybenzyl methyl ether from the marine alga Symphyocladia latiuscula

Peroxynitrite (ONOO(-)), formed from the reaction of superoxide (O(2)*(-)) and nitric oxide (*NO), is a cytotoxic species that can oxidize several cellular components such as proteins, lipids, and DNA. It has been implicated in diseases such as Alzheimer's disease, rheumatoid arthritis, cancer, and atherosclerosis. Due to the lack of endogenous enzymes responsible for ONOO(-) inactivation, developing a specific ONOO(-) scavenger is of considerable importance. The aim of this study was to evaluate the ability of marine natural products to scavenge ONOO(-) and to protect cells against ONOO(-). Methanolic extracts of 17 marine alga were tested for their ONOO(-) scavenging activity. Among them, Symphyocladia latiuscula showed the potent scavenging activity. CH(2)CH(2) fraction was partitioned with CH(2)CH(2) following n-hexanal extraction from the methanol extract of S. latiuscula. It was highly effective for ONOO(-) scavenging activity. Further analysis of the active fractionated extract identified 2,3,6-tribromo-4,5-dihydroxybenzyl methyl ether (TDB) as a potent ONOO(-) scavenger. The data demonstrated that TDB led to decreased ONOO(-)-mediated nitration of tyrosine through electron donation. TDB showed significant inhibition on nitration of bovine serum albumin and low-density lipoprotein by ONOO(-) in a dose-dependent manner. It also provided cytoprotection from cell damage induced by ONOO(-). TDB can be developed as an effective peroxynitrite scavenger for the prevention of the involved diseases.

Unraveling peroxynitrite formation in biological systems

Peroxynitrite promotes oxidative damage and is implicated in the pathophysiology of various diseases that involve accelerated rates of nitric oxide and superoxide formation. The unambiguous detection of peroxynitrite in biological systems is, however, difficult due to the combination of a short biological half-life, limited diffusion, multiple target molecule reactions, and participation of alternative oxidation/nitration pathways. In this review, we provide the conceptual framework and a comprehensive analysis of the current experimental strategies that can serve to unequivocally define the existence and quantitation of peroxynitrite in biological systems of different levels of organization and complexity.

Products of the phospholipase A(2) pathway mediate the dihydrorhodamine fluorescence response evoked by endogenous and exogenous peroxynitrite in PC12 cells

A short-term exposure of PC12 cells to tert-butylhydroperoxide promotes a rapid oxidation of dihydrorhodamine sensitive to nitric oxide synthase inhibitors and peroxynitrite scavengers. This response was not directly caused by peroxynitrite, but rather appeared to be mediated by peroxynitrite-dependent activation of phospholipase A(2). The following lines of evidence support this inference: (i) the peroxynitrite-dependent dihydrorhodamine fluorescence response was blunted by low concentrations of two structurally unrelated phospholipase A(2) inhibitors; (ii) under similar conditions, the phospholipase A(2) inhibitors prevented release of arachidonic acid; (iii) low levels of arachidonic acid restored the dihydrorhodamine fluorescence response in nitric oxide synthase- as well as phospholipase A(2)-inhibited cells; (iv) the dihydrorhodamine fluorescence response induced by authentic peroxynitrite was also blunted by phospholipase A(2) inhibitors and restored upon addition of reagent arachidonic acid. We conclude that endogenous, or exogenous, peroxynitrite does not directly oxidize dihydrorhodamine in intact cells. Rather, peroxynitrite appears to act as a signalling molecule promoting release of arachidonic acid, which in turn leads to formation of species causing the dihydrorhodamine fluorescence response.

Nitrosylation of manganese(II) tetrakis(N-ethylpyridinium-2-yl)porphyrin: a simple and sensitive spectrophotometric assay for nitric oxide

Reaction between NO(*) and manganese tetrakis(N-ethylpyridinium-2-yl)porphyrin (Mn(III)TE-2-PyP(5+)) was investigated at 25 degrees C. At high excess of NO(*) (1.5 mM) the reaction with the oxidized, air-stable form Mn(III)TE-2-PyP(5+) (5 microM), proceeds very slowly (t(1/2) congruent with 60 min). The presence of excess ascorbate (1 mM) produces the reduced form, Mn(II)TE-2-PyP(4+), which reacts with NO(*) stoichiometrically and in the time of mixing (k congruent with 1 x 10(6) M(-1) s(-1)). The high rate of formation and the stability of the product, Mn(II)TE-2-PyP(NO)(4+) (¿Mn(NO)¿(6)), make the reaction outcompete the reaction of NO(*) with O(2). Our in vitro measurements show a linear absorbance response upon addition of NO to a PBS, pH 7.4, solution containing an excess of ascorbate over Mn(III)TE-2-PyP(5+). Thus, the observed interactions can be the basis of a convenient and sensitive spectrophotometric assay for NO(*). Also, it may have important implications for the in vivo behavior of Mn(III)TE-2-PyP(5+) which is currently exploited as a possible therapeutic agent for various oxygen-radical related disorders.

Adaptive responses to peroxynitrite: increased glutathione levels and cystine uptake in vascular cells

We and others recently demonstrated increased glutathione levels, stimulated cystine uptake, and induced gamma-glutamylcysteinyl synthase (gamma-GCS) in vascular cells exposed to nitric oxide donors. Here we report the effects of peroxynitrite on glutathione levels and cystine uptake. Treatment of bovine aortic endothelial and smooth muscle cells with 3-morpholinosydnonimine (SIN-1), a peroxynitrite donor, resulted in transient depletion of glutathione followed by a prolonged increase beginning at 8-9 h. Concentration-dependent increases in glutathione of up to sixfold occurred 16-18 h after 0.05-2.5 mM SIN-1. Responses to SIN-1 were inhibited by copper-zinc superoxide dismutases and manganese(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride, providing evidence for peroxynitrite involvement. Because glutathione synthesis is regulated by amino acid availability, we also studied cystine uptake. SIN-1 treatment resulted in a prolonged increase in cystine uptake beginning at 6-9 h. Increases in cystine uptake after SIN-1 were blocked by inhibitors of protein and RNA synthesis, by extracellular glutamate but not by extracellular sodium. These studies suggest induction of the x(c)(-) pathway of amino acid uptake. A close correlation over time was observed for increases in cystine uptake and glutathione levels. In summary, vascular cells respond to chronic peroxynitrite exposure with adaptive increases in cellular glutathione and cystine transport.

Inducible nitric oxide synthase-derived superoxide contributes to hypereactivity in small mesenteric arteries from a rat model of chronic heart failure

The aims of this study were to (a) determine whether inducible nitric oxide synthase (iNOS) is expressed in small mesenteric arteries from rats with chronic heart failure (CHF), (b) investigate the functional significance of this potential source of nitric oxide (NO) on vascular responsiveness and (c) investigate the role that superoxide plays in modulating vascular function in these arteries. CHF was induced in male Wistar rats by coronary artery ligation (CAL). In sham-operated rats the ligature was not tied but pulled under the artery. Six weeks after surgery CAL rats had left ventricular (LV) infarctions and elevated LV end-diastolic pressures. Immunoreactive iNOS was found in endothelial cells, vascular smooth muscle cells and in the adventitia of small mesenteric arteries from CAL rats but not those from sham-operated rats. Third order mesenteric arteries (300-350 microm) were mounted in a small vessel pressure myograph. Endothelium-intact arteries from CAL rats were more responsive to phenylephrine (PE) than arteries from sham-operated rats (pD(2) value, CAL, 6.2+/-0.1; sham-operated, 5.9+/-0.1, P<0.05). Both the selective iNOS inhibitor, N-(3-(Aminomethyl) benzyl) acetamidine dihydrochloride (1400W; 10(-6) M) and the superoxide dismutase mimetic, Mn [III] tetrakis [1-methyl-4-pyridyl] porphyrin, (MnTMPyP; 10(-4) M) reversed the hyperesponsiveness (pD(2) values, 1400W, 5.9+/-0.1; MnTMPyP, 5.81+/-0.1, P<0.05). The NOS substrate, L-arginine (10(-3) M), reduced responsiveness of endothelium-denuded small mesenteric arteries from CAL rats (P<0.01). None of these drugs altered responses to PE in arteries from sham-operated rats. In summary, this study demonstrates that iNOS is expressed in mesenteric arteries from rats with CHF. However, instead of generating large quantities of NO, iNOS appears to be generating superoxide, perhaps because of a deficiency in its substrate, L-arginine. Increased superoxide generation from iNOS contributes to the hyperesponsive nature of endothelium-intact small mesenteric arteries from rats with CHF.

Protection by a manganese porphyrin of endogenous peroxynitrite-induced death of glial cells via inhibition of mitochondrial transmembrane potential decrease

In the cerebral ischemic penumbra, progressive metabolic deterioration eventually leads to death of glial cells. The exact mechanism for the death of glial cells is unclear. Here we report that under glucose-deprived conditions immunostimulated glial cells rapidly underwent death via production of large amounts of peroxynitrite. The cell-permeable Mn(III)tetrakis(N-methyl-4'-pyridyl)porphyrin (MnTMPyP) caused a concentration-dependent attenuation of the increased death in glucose-deprived immunostimulated glial cells. The structurally related compound H(2)TMPyP, which lacks metals, did not attenuate this augmented cell death. MnTMPyP prevented the elevation in nitrotyrosine immunoreactivity (a marker of ONOO(-)) in glucose-deprived immunostimulated glial cells. In glucose-deprived glial cells, MnTMPyP also completely blocked the augmented death and nitrotyrosine immunoreactivity induced by the ONOO(-)-producing reagent 3-morpholinosydnonimine (SIN-1). The mitochondrial transmembrane potential (MTP), as measured using the dye JC-1, was rapidly decreased in immunostimulated or SIN-1-treated glial cells deprived of glucose. MnTMPyP, but not H(2)TMPyP, blocked the depolarization of MTP in those glial cells. The present data, at least in part, provide evidence for how glial cells die in the postischemic and/or recurrent ischemic brain.

Peroxynitrite scavenging by metalloporphyrins and thiolates

The rate constant for the reaction of nitric oxide with superoxide virtually assures that peroxynitrite will be formed to some extent in any cell or tissue where both radicals exist simultaneously. The precise biological targets for peroxynitrite and the nature of the modification of those targets vary dramatically depending on their relative concentrations and the rates and duration of peroxynitrite formation. Thus, peroxynitrite may have physiological functions in addition to pathological ones. Peroxynitrite scavenger compounds may prove to be therapeutic by effectively intercepting higher levels of peroxynitrite and thereby preventing injurious oxidative modifications of cellular components. Thiols and thiolates comprise a class of sacrificial scavengers that react with peroxynitrite anion with rate constants ranging from 2 x 10(3) M(-1) s(-1) to 2 x 10(8) M(-1) s(-1), depending on the microenvironment of the thiol. Several Mn and Fe porphyrins have been shown to react quite rapidly with peroxynitrite (10(6) to 10(7) M(-1) s(-1)) and decompose it in a catalytic manner; Mn porphyrins require exogenous reductants for complete cycling whereas Fe porphyrins do not. Sacrificial thiol/thiolate scavengers effectively quench the total oxidative yield of peroxynitrite, whereas the catalytic porphyrins redirect it and can, under some conditions, enhance total nitration and oxidative yield.

Synergistic depletion of astrocytic glutathione by glucose deprivation and peroxynitrite: correlation with mitochondrial dysfunction and subsequent cell death

Previously we reported that immunostimulated astrocytes were highly vulnerable to glucose deprivation. The augmented death was mimicked by the peroxynitrite (ONOO )-producing reagent 3-morpholinosydnonimine (SIN-1). Here we show that glucose deprivation and ONOO- synergistically deplete intracellular reduced glutathione (GSH) and augment the death of astrocytes via formation of cyclosporin A-sensitive mitochondrial permeability transition (MPT) pore. Astrocytic GSH levels were only slightly decreased by glucose deprivation or SIN-1 (200 microM) alone. In contrast, a rapid and large depletion of GSH was observed in glucose-deprived/ SIN-1-treated astrocytes. The depletion of GSH occurred before a significant release of lactate dehydrogenase (a marker of cell death). Superoxide dismutase and ONOO-scavengers completely blocked the augmented death, indicating that the reaction of nitric oxide with superoxide to form ONOO was implicated. Furthermore, nitrotyrosine immunoreactivity (a marker of ONOO-) was markedly enhanced in glucose-deprived/SIN-1 -treated astrocytes. Mitochondrial transmembrane potential (MTP) was synergistically decreased in glucose-deprived/SIN-1-treated astrocytes. The glutathione synthase inhibitor L-buthionine-(S,R)-sulfoximine markedly decreased the MTP and increased lactate dehydrogenase (LDH) releases in SIN-1-treated astrocytes. Cyclosporin A, an MPT pore blocker, completely prevented the MTP depolarization as well as the enhanced LDH releases in glucose-deprived/SIN-1-treated astrocytes.

Despite the internucleosomal cleavage of DNA, reactive oxygen species do not produce other markers of apoptosis in cultured neurons

The cell death induced by hydroxyl radicals generated by Cu-phenanthroline and peroxynitrite generated by 3-morpholinosydnonimine hydrochloride (SIN-1) in rat primary cortical neuronal cultures was compared with the apoptotic death induced by staurosporine and the necrotic death induced by glutamate. Both SIN-1 and Cu-phenanthroline were capable of generating internucleosomal cleavage of DNA-a hallmark of apoptosis. Other characteristics of this cell death, such as nuclear morphology by light microscopy; DNA breaks by single-cell gel electrophoresis; the effects of the apoptotic inhibitors cycloheximide, aurintricarboxylic acid, and tosyl-l-lysine chloromethyl ketone; the measurement of caspase activity; and the effects of antioxidants, were then analyzed. The conclusion from these hallmarks of apoptosis is that the cell death induced by these reactive oxygen species is not apoptosis.

Na(+)/Ca(2+) exchange facilitates Ca(2+)-dependent activation of endothelial nitric-oxide synthase

Recent evidence suggests the expression of a Na(+)/Ca(2+) exchanger (NCX) in vascular endothelial cells. To elucidate the functional role of endothelial NCX, we studied Ca(2+) signaling and Ca(2+)-dependent activation of endothelial nitric-oxide synthase (eNOS) at normal, physiological Na(+) gradients and after loading of endothelial cells with Na(+) ions using the ionophore monensin. Monensin-induced Na(+) loading markedly reduced Ca(2+) entry and, thus, steady-state levels of intracellular free Ca(2+) ([Ca(2+)](i)) in thapsigargin-stimulated endothelial cells due to membrane depolarization. Despite this reduction of overall [Ca(2+)](i), Ca(2+)-dependent activation of eNOS was facilitated as indicated by a pronounced leftward shift of the Ca(2+) concentration response curve in monensin-treated cells. This facilitation of Ca(2+)-dependent activation of eNOS was strictly dependent on the presence of Na(+) ions during treatment of the cells with monensin. Na(+)-induced facilitation of eNOS activation was not due to a direct effect of Na(+) ions on the Ca(2+) sensitivity of the enzyme. Moreover, the effect of Na(+) was not related to Na(+) entry-induced membrane depolarization or suppression of Ca(2+) entry, since neither elevation of extracellular K(+) nor the Ca(2+) entry blocker 1-(beta-[3-(4-methoxyphenyl)-propoxy]-4-methoxyphenethyl)-1H-imidazol e hydrochloride (SK&F 96365) mimicked the effects of Na(+) loading. The effects of monensin were completely blocked by 3', 4'-dichlorobenzamil, a potent and selective inhibitor of NCX, whereas the structural analog amiloride, which barely affects Na(+)/Ca(2+) exchange, was ineffective. Consistent with a pivotal role of Na(+)/Ca(2+) exchange in Ca(2+)-dependent activation of eNOS, an NCX protein was detected in caveolin-rich membrane fractions containing both eNOS and caveolin-1. These results demonstrate for the first time a crucial role of cellular Na(+) gradients in regulation of eNOS activity and suggest that a tight functional interaction between endothelial NCX and eNOS may take place in caveolae.

Evidence for a feedback inhibition of NO synthesis in enteric synaptosomes via a nitrosothiol intermediate

The exact mechanisms controlling nitric oxide synthase (NOS) activity within enteric neurons are largely unknown. In this study, the effect of exogenous nitric oxide (NO) on NOS activity was investigated in enteric synaptosomes of rat ileum. 3-Morpholinosydnonimine (SIN-1; 10(-4) M) and S-nitroso-N-acetylpenicillamine (SNAP; 10(-4) M) significantly inhibited NOS activity by 53% and 48%, respectively. However, superoxide dismutase (SOD; 160 U/ml) as well as the NO scavenger oxyhemoglobin (10(-3) M) did not influence NO donor-induced inhibition. In contrast, the inhibitory effect was antagonized by diethyldithiocarbamate (3 x 10(-4) M), an inhibitor of endogenous Cu/Zn SOD. Inhibition of NOS by exogenous NO was dependent on glutathione (GSH), since the inhibitory effect was augmented in the presence of GSH (5 x 10(-4) M) and antagonized by the GSH-depletor DL-buthionine-SR-sulfoximine (5 x 10(-4) M), suggesting that NO might be protected from extracellular breakdown by reaction with GSH. The reaction product of SIN-1/SNAP and GSH was identified as a nitrosothiol. In the presence of the Cu(+)-chelator neocuproine (10(-5) M), inhibition of NOS by SNAP/SIN-1 was reversed, suggesting that nitrosothiol formation is intermediary. These findings are indicative of a feedback inhibition of enteric NOS, presumably via formation of a nitrosothiol intermediate.

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

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

Peroxynitrite: reactive, invasive and enigmatic

The reactive oxygen and nitrogen species superoxide ion, nitric oxide, nitrogen dioxide and peroxynitrite ion all react with biological target molecules. Some of these interactions are carefully orchestrated segments of signal transduction cascades or part of the armamentarium of the immune system, others are pathological events and may lie at the root of many diseases. As a result of these small reactive molecules, proteins, particularly metalloproteins, can be altered with loss of function, DNA can be cleaved and lipid components can be oxidized to disrupt membranes. The interactions of these species with each other and their aftermath can be sensed by the cell, resulting in a variety of responses including gene regulation and transcription. Indeed, there is recent, tantalizing evidence that the currency of reactive oxygen and nitrogen species is central to the life and death cellular decisions in homeostasis or the initiation of apoptosis. New families of metallopharmaceuticals may serve both to probe the nature and mechanisms of these events and to effect the outcome.