Amphiphilic peroxynitrite decomposition catalysts in liposomal assemblies

The oxidative reactivity of three manganese(III) porphyrin complexes with hydrogen peroxide and nitrite toward catalytic nitration of protein tyrosine

Understanding the toxicological properties of MnIII-porphyrins (MnTPPS, MnTMPyP, or MnTBAP) can provide important biochemical rationales in developing them as the therapeutic drugs against protein tyrosine nitration-induced inflammation diseases. Here, we present a comprehensive understanding of the pH-dependent redox behaviors of these MnIII-porphyrins and their structural effects on catalyzing bovine serum albumin (BSA) nitration in the presence of H2O2 and NO2-. It was found that both MnTPPS and MnTBAP stand out in catalyzing BSA nitration at physiologically close condition (pH 8), yet they are less effective at pH 6 and 10. MnTMPyP was shown to have no ability to catalyze BSA nitration under all tested pHs (pH 6, 8, and 10). The kinetics and active intermediate determination through electrochemistry method revealed that both the pH-dependent redox behavior of the central metal cation and the antioxidant capability of porphin derivative contribute to the catalytic activities of three MnIII-porphyrins in BSA nitration in the presence of H2O2/NO2-. These comprehensive studies on the oxidative reactivity of MnIII-porphyrins toward BSA nitration may provide new clues for searching the manganese-based therapeutic drugs against the inflammation-related diseases.

Peroxynitrite decomposition catalyst enhances respiratory function in isolated brain mitochondria

Peroxynitrite (PN), generated from the reaction of nitric oxide (NO) and superoxide, is implicated in the pathogenesis of ischemic and neurodegenerative brain injuries. Mitochondria produce NO from mitochondrial NO synthases and superoxide by the electron transport chain. Our objective was to detect the generation of PN of mitochondrial origin and characterize its effects on mitochondrial respiratory function. Freshly isolated brain nonsynaptosomal mitochondria from C57Bl/6 (wild type, WT) and endothelial NO synthase knockout (eNOS-KO) mice were treated with exogenous PN (0.1, 1, 5 µmol/L) or a PN donor (SIN-1; 50 µmol/L) or a PN scavenger (FeTMPyP; 2.5 µmol/L). Oxygen consumption rate (OCR) was measured using Agilent Seahorse XFe24 analyzer and mitochondrial respiratory parameters were calculated. Mitochondrial membrane potential, superoxide, and PN were determined from rhodamine 123, dihydroethidium, and DAX-J2 PON green fluorescence measurements, respectively. Mitochondrial protein nitrotyrosination was determined by Western blots. Both exogenous PN and SIN-1 decreased respiratory function in WT isolated brain mitochondria. FeTMPyP enhanced state III and state IVo mitochondrial respiration in both WT and eNOS-KO mitochondria. FeTMPyP also elevated state IIIu respiration in eNOS-KO mitochondria. Unlike PN, neither SIN-1 nor FeTMPyP depolarized the mitochondria. Although mitochondrial protein nitrotyrosination was unaffected by SIN-1 or FeTMPyP, FeTMPyP reduced mitochondrial PN levels. Mitochondrial superoxide levels were increased by FeTMPyP but were unaffected by PN or SIN-1. Thus, we present the evidence of functionally significant PN generation in isolated brain mitochondria. Mitochondrial PN activity was physiologically relevant in WT mice and pathologically significant under conditions with eNOS deficiency.NEW & NOTEWORTHY Mitochondria generate superoxide and nitric oxide that could potentially react with each other to produce PN. We observed eNOS and nNOS immunoreactivity in isolated brain and heart mitochondria with pharmacological inhibition of nNOS found to modulate the mitochondrial respiratory function. This study provides evidence of generation of functionally significant PN in isolated brain mitochondria that affects respiratory function under physiological conditions. Importantly, the mitochondrial PN levels and activity were exaggerated in the eNOS-deficient mice, suggesting its pathological significance.

Antioxidants in Translational Medicine

SIGNIFICANCE

It is generally accepted that reactive oxygen species (ROS) scavenging molecules or antioxidants exert health-promoting effects and thus their consumption as food additives and nutraceuticals has been greatly encouraged. Antioxidants may be beneficial in situations of subclinical deficiency and increased demand or acutely upon high-dose infusion. However, to date, there is little clinical evidence for the long-term benefit of most antioxidants. Alarmingly, recent evidence points even to health risks, in particular for supplements of lipophilic antioxidants.

RECENT ADVANCES

The biological impact of ROS depends not only on their quantities but also on their chemical nature, (sub)cellular and tissue location, and the rates of their formation and degradation. Moreover, ROS serve important physiological functions; thus, inappropriate removal of ROS may cause paradoxical reductive stress and thereby induce or promote disease.

CRITICAL ISSUES

Any recommendation on antioxidants must be based on solid clinical evidence and patient-relevant outcomes rather than surrogate parameters.

FUTURE DIRECTIONS

Such evidence-based use may include site-directed application, time-limited high dosing, (functional) pharmacological repair of oxidized biomolecules, and triggers of endogenous antioxidant response systems. Ideally, these approaches need guidance by patient stratification through predictive biomarkers and possibly imaging modalities.

Surface-promoted aggregation of amphiphilic quadruplex ligands drives their selectivity for alternative DNA structures

The surface-promoted aggregation of a structurally fine-tuned TMPyP4 derivative allows for the straightforward visualization of the quadruplex/ligand interactionsviahigh-speed AFM.

Polymer nanoreactors with dual functionality: simultaneous detoxification of peroxynitrite and oxygen transport

The design of multifunctional systems is in focus today as a key strategy for coping with complex challenges in various domains that include chemistry, medicine, environmental sciences, and technology. Herein, we introduce protein-containing polymer nanoreactors with dual functionality: peroxynitrite degradation and oxygen transport. Vesicles made of poly-(2-methyloxazoline)-poly(dimethylsiloxane)-poly(2-methyloxazoline) successfully encapsulated hemoglobin (Hb), which serves as a model protein because of its dual function in oxygen transport and peroxynitrite degradation. By inserting channel proteins, the polymer membranes of vesicles permitted passage of various compounds that served for the assessment of in situ Hb activity. The requisite conformational changes in the protein structure and the change in oxidation states that took place within the confined space of the vesicle cavity demonstrated that Hb preserved its dual functionality: peroxynitrite degradation and oxygen transport. The functionality of our nanoreactor, combined with its simple procedure of production and extensive stability over several months, supports it as a promising system for further medical applications.

Targeting the overproduction of peroxynitrite for the prevention and reversal of paclitaxel-induced neuropathic pain

Chemotherapy-induced peripheral neuropathy (CIPN) accompanied by chronic neuropathic pain is a major dose-limiting side effect of a large number of antitumoral agents including paclitaxel (Taxol). Thus, CIPN is one of most common causes of dose reduction and discontinuation of what is otherwise a life-saving therapy. Neuropathological changes in spinal cord are linked to CIPN, but the causative mediators and mechanisms remain poorly understood. We report that formation of peroxynitrite (PN) in response to activation of nitric oxide synthases and NADPH oxidase in spinal cord contributes to neuropathological changes through two mechanisms. The first involves modulation of neuroexcitatory and proinflammatory (TNF-α and IL-1β) and anti-inflammatory (IL-10 and IL-4) cytokines in favor of the former. The second involves post-translational nitration and modification of glia-derived proteins known to be involved in glutamatergic neurotransmission (astrocyte-restricted glutamate transporters and glutamine synthetase). Targeting PN with PN decomposition catalysts (PNDCs) not only blocked the development of paclitaxel-induced neuropathic pain without interfering with antitumor effects, but also reversed it once established. Herein, we describe our mechanistic study on the role(s) of PN and the prevention of neuropathic pain in rats using known PNDCs (FeTMPyP(5+) and MnTE-2-PyP(5+)). We also demonstrate the prevention of CIPN with our two new orally active PNDCs, SRI6 and SRI110. The improved chemical design of SRI6 and SRI110 also affords selectivity for PN over other reactive oxygen species (such as superoxide). Our findings identify PN as a critical determinant of CIPN, while providing the rationale toward development of superoxide-sparing and "PN-targeted" therapeutics.

Responsive porphyrinoid nanoparticles: development and applications

The economy of space and materials and the continuously increasing demand for advanced functionalities for diverse technologies requires the development of new synthetic methods. Many nanomaterials have enhanced photophysical and photochemical properties in solutions and/or on surfaces, while others have enhanced chemical properties, compared to the atomic, molecular, or bulk phases. Nanomaterials have a wide range of applications in catalysis, sensors, photonic devices, drug delivery, and as therapeutics for treatment of a variety of diseases. Inorganic nanoparticles are widely studied, but the formation of organic nanomaterials via supramolecular chemistry is more recent, and porphyrinoids are at the forefront of this research because of their optical, chemical, and structural properties. The formation of nanoscaled materials via self-assembly and/or self-organization of molecular subunits is an attractive approach because of reduced energy requirements, simpler molecular subunits, and the material can be adaptive to environmental changes. The presence of biocompatible groups such as peptides, carbohydrates, polyglycols and mixtures of these on the periphery of the porphyrin macrocycle may make nanoparticles suitable for therapeutics. This perspective focuses on responsive, non-crystalline porphyrinoid nanomaterials that are less than about 100 nm in all dimensions and used for catalytic or therapeutic applications.

Retooling manganese(III) porphyrin-based peroxynitrite decomposition catalysts for selectivity and oral activity: a potential new strategy for treating chronic pain

Redox-active metalloporphyrins represent the most well-characterized class of catalysts capable of attenuating oxidative stress in vivo through the direct interception and decomposition of superoxide and peroxynitrite. While many interesting pharmacological probes have emerged from these studies, few catalysts have been developed with pharmaceutical properties in mind. Herein, we describe our efforts to identify new Mn(III)-porphyrin systems with enhanced membrane solubilizing properties. To this end, seven new Mn(III)-tetracyclohexenylporphyin (TCHP) analogues, 7, 10, 12, 15, and 16a-c, have been prepared in which the beta-fused cyclohexenyl rings provide a means to shield the charged metal center from the membrane during passive transport. Compounds 7, 15, and 16a-c have been shown to be orally active and potent analgesics in a model of carrageenan-induced thermal hyperalgesia. In addition, oral administration of compound 7 (10-100 mg/kg, n=5) has been shown to dose dependently reverse mechano-allodynia in the CCI model of chronic neuropathic pain.

Manganese(III) complexes of bis(hydroxyphenyl)dipyrromethenes are potent orally active peroxynitrite scavengers

We report a new series of biscyclohexano-fused Mn(III) complexes of bis(hydroxyphenyl)dipyrromethenes, 4a-c, as potent and orally active peroxynitrite scavengers. Complexes 4a-c are shown to reduce peroxynitrite through a two-electron mechanism, thereby forming the corresponding Mn(V)O species, which were characterized by UV, NMR, and LC-MS methods. Mn(III) complex 4b and its strained BODIPY analogue 9b were analyzed by X-ray crystallography. Finally, complex 4a is shown to be an orally active and potent analgesic in a model carrageenan-induced hyperalgesia known to be driven by the overproduction of peroxynitrite.

Blockade of peroxynitrite-induced neural stem cell death in the acutely injured spinal cord by drug-releasing polymer

Therapeutic impact of neural stem cells (NSCs) for acute spinal cord injury (SCI) has been limited by the rapid loss of donor cells. Neuroinflammation is likely the cause. As there are close temporal-spatial correlations between the inducible nitric oxide (NO) synthase expression and the donor NSC death after neurotrauma, we reasoned that NO-associated radical species might be the inflammatory effectors which eliminate NSC grafts and kill host neurons. To test this hypothesis, human NSCs (hNSCs: 5 x 10(4) to 2 x 10(6) per milliliter) were treated in vitro with "plain" medium, 20 microM glutamate, or donors of NO and peroxynitrite (ONOO(-); 100 and 400 microM of spermine or DETA NONOate, and SIN-1, respectively). hNSC apoptosis primarily resulted from SIN-1 treatment, showing ONOO(-)-triggered protein nitration and the activation of p38 MAPK, cytochrome c release, and caspases. Therefore, cell death following post-SCI (p.i.) NO surge may be mediated through conversion of NO into ONOO(-). We subsequently examined such causal relationship in a rat model of dual penetrating SCI using a retrievable design of poly-lactic-co-glycolic acid (PLGA) scaffold seeded with hNSCs that was shielded by drug-releasing polymer. Besides confirming the ONOO(-)-induced cell death signaling, we demonstrated that cotransplantation of PLGA film embedded with ONOO(-) scavenger, manganese (III) tetrakis (4-benzoic acid) porphyrin, or uric acid (1 micromol per film), markedly protected hNSCs 24 hours p.i. (total: n = 10). Our findings may provide a bioengineering approach for investigating mechanisms underlying the host microenvironment and donor NSC interaction and help formulate strategies for enhancing graft and host cell survival after SCI.

Peroxynitrite: a strategic linchpin of opioid analgesic tolerance

Severe pain syndromes reduce quality of life in patients with inflammatory and neoplastic diseases, partly because the reduced analgesic effectiveness accompanying chronic opiate therapy (i.e. tolerance) leads to escalating doses and distressing side effects. Accordingly, there is major interest in new approaches to maintain opiate efficacy during repetitive dosing without engendering tolerance or causing unacceptable side effects. Recent mounting evidence implicates nitroxidative stress caused by the presence of superoxide (O(2*)(-)), nitric oxide (*NO) and subsequently peroxynitrite (ONOO(-)) in opiate analgesic tolerance. Here, we provide a pharmacological basis for developing inhibitors of ONOO(-) biosynthesis and/or ONOO(-) scavengers as potent adjuncts to opiates in the management of chronic pain, addressing an issue of major clinical and socio-economic importance while laying the basis for interventions with strong therapeutic potential.

Role of nitric oxide in downregulation of cytochrome P450 1a1 and NADPH: Quinone oxidoreductase 1 by tumor necrosis factor-alpha and lipopolysaccharide

We previously demonstrated that tumor necrosis factor alpha (TNF-alpha) and lipopolysaccharide (LPS) downregulate aryl hydrocarbon receptor (AhR)-regulated genes, such as cytochrome P450 1a1 (Cyp1a1) and NADPH: quinone oxidoreductase 1 (Nqo1) gene expression, yet the mechanisms involved remain unknown. The correlation between the inflammation-mediated suppression of AhR-regulated genes and the TNF-alpha or LPS-induced nitric oxide (NO) production especially in murine hepatoma Hepa 1c1c7 cells has been questioned; therefore we investigated whether NO is involved in the modulation of Cyp1a1 and Nqo1 by TNF-alpha or LPS in Hepa 1c1c7 cells. A significant dose-dependent increase in the inducible nitric oxide synthase (NOS2) expression and NO production were observed by various concentrations of TNF-alpha (1, 5, and 10 ng/mL) and LPS (1 and 5 microg/mL) which was completely inhibited by a NOS2 inhibitor, L-N6-(1-iminoethyl) lysine (L-NIL) (1 mM). Furthermore, TNF-alpha and LPS significantly induced NOS2 expression. Both TNF-alpha and LPS repressed the beta-naphthoflavone (betaNF)-mediated induction of Cyp1a1 and Nqo1 at mRNA and activity levels. The downregulation of Cyp1a1, but not Nqo1, was significantly prevented by L-NIL. However, proxynitrite decomposer, iron tetrakis (N-methyl-4'-pyridyl) porphyrinato (FeTMPyP) (5 microM) did not affect TNF-alpha- and LPS-mediated downregulation of Cyp1a1 and Nqo1 at mRNA and activity levels. These results show that NO, but not peroxynitrite, may be involved in TNF-alpha- and LPS-mediated downregulation of Cyp1a1 without affecting the downregulation of Nqo1.

meso-Tetra(pentafluorophenyl)porphyrin as an efficient platform for combinatorial synthesis and the selection of new photodynamic therapeutics using a cancer cell line

The four para fluoro groups on 5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin (TPPF20) are known to react with a variety of nucleophiles, but the reaction conditions for this substitution reaction depend on the nature of the nucleophiles, e.g. primary amines versus thiols. Glycosylated derivatives of this core porphyrin have been shown to be effective photodynamic agents in the induction of necrosis or apoptosis in several cancer cell lines. The present report demonstrates that TPPF20 can be used as a core platform to efficiently generate a variety of solution-phase combinatorial libraries. The focused combinatorial libraries have substituents that are chosen from a set of motifs known to bind biopolymers such as DNA, be taken up by cancer cells, or to render the compounds amphipathic. Incubation of a breast cancer cell line with these solution-phase libraries, followed by cell lyses and extraction, affords a selection assay. Matrix-assisted laser desorption ionization (MALDI) mass spectrometry of the extracts allows identification of the molecules taken up by the cells. Cell binding assays of the winning compounds synthesized directly indicate that both glycosylation and amphipathicity are key properties since neither tetraglycosylated porphyrins nor those with four polar groups are selected to the same extent. In addition, photodynamic efficacy was evaluated.

Catalytic antioxidants to treat amyotropic lateral sclerosis

Catalytic antioxidants are comprised of specialised classes of organometallic complexes that can catalyse the decomposition of injurious biological oxidants. These complexes have been shown to prevent the formation of several oxidative markers in spinal cord of G93A amyotropic lateral sclerosis mice and markedly extend survival, even when administered at symptom onset; however, it is now clear that some complexes lacking in antioxidant activity are also protective. New proteomics data suggest that these complexes also induce a broad spectrum of endogenous cellular defense mechanisms. The combination of antioxidant and adaptive resistance effects may explain the remarkable potency of these compounds and may also suggest wide applicability for them in a number of neurodegenerative diseases.

High-valent iron in chemical and biological oxidations

Various aspects of the reactivity of iron(IV) in chemical and biological systems are reviewed. Accumulated evidence shows that the ferryl species [Fe(IV)O](2+) can be formed under a variety of conditions including those related to the ferrous ion-hydrogen peroxide system known as Fenton's reagent. Early evidence that such a species could hydroxylate typical aliphatic C-H bonds included regioselectivities and stereospecificities for cyclohexanol hydroxylation that could not be accounted for by a freely diffusing hydroxyl radical. Iron(IV) porphyrin complexes are also found in the catalytic cycles of cytochrome P450 and chloroperoxidase. Model oxo-iron(IV) porphyrin complexes have shown reactivity similar to the proposed enzymatic intermediates. Mechanistic studies using mechanistically diagnostic substrates have implicated a radical rebound scenario for aliphatic hydroxylation by cytochrome P450. Likewise, several non-heme diiron hydroxylases, AlkB (Omega-hydroxylase), sMMO (soluble methane monooxygenase), XylM (xylene monooxygenase) and T4moH (toluene monooxygenase) all show clear indications of radical rearranged products indicating that the oxygen rebound pathway is a ubiquitous mechanism for hydrocarbon oxygenation by both heme and non-heme iron enzymes.

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.

Role of nitric oxide, reactive oxygen species, and p38 MAP kinase in the regulation of human chondrocyte apoptosis

This study addresses mechanisms by which interleukin-1beta (IL-1beta) regulates human chondrocyte apoptosis induced by a combination of the anti-CD95 antibody CH-11 and the proteasome inhibitor (PSI). The effect of IL-1beta on apoptosis varied among tissue samples. IL-1beta either enhanced (16/22 samples) or inhibited (6/22 samples) DNA fragmentation and caspase-3 processing. The protective effect of IL-1beta was abrogated by the nitric oxide (NO) synthesis inhibitor N-monomethyl-l-arginine (L-NMMA) while apoptosis stimulation was not affected. The NO-donors sodium nitroprusside (SNP) and S-nitroso-N-acetyl penicillamine (SNAP) blocked DNA fragmentation, and this was associated with partial inhibition of caspase-3 processing. Pyrrolidine dithiocarbamate (PDTC), a scavenger of reactive oxygen species (ROS) blocked apoptosis induction by CH-11/PSI as well as the enhancement by IL-1beta. The pro-apoptotic effects of IL-1beta were also abrogated by the p38 inhibitor SB 202190. In conclusion, IL-1beta augments CH-11/PSI induced apoptosis in the majority of chondrocyte samples. The pro-apoptotic effect of IL-1beta is not dependent on NO. In contrast, the anti-apoptotic effect of IL-1beta observed in a minority of samples is partially NO-dependent.

Can the ebselen derivatives catalyze the isomerization of peroxynitrite to nitrate?

The reaction of ebselen and its derivatives (1-7) with peroxynitrite anion (ONOO(-); PN) has been studied in gas phase and in aqueous, dichloromethane, benzene, and cyclohexane solutions using B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p) and PCM-B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p) approaches, respectively. It was shown that the reaction of 2 (R=H) with PN proceeds via 2 + PN --> 2-PN --> 2-TS1 (O-O activation) --> 2-O(NO(2)(-)()) --> 2-SeO + NO(2)(-) pathway with a rate-determining barrier of 25.3 (14.8) kcal/mol at the NO(2)(-) dissociation step (numbers presented without parentheses are enthalpies, and those in parentheses are Gibbs free energies). The NO(3)(-) formation process, starting from the complex 2-O(NO(2)(-)()), requires by (7.9) kcal/mol more energy than the NO(2)(-) dissociation process and is unlikely to compete with the latter. Thus, in the gas phase, the peroxynitrite --> nitrate isomerization catalyzed by complex 2 is unlikely to occur. It is shown that the NO(3)(-) formation process is slightly more favorably than the NO(2)(-) dissociation process for complex 4, with a strongest electron-withdrawing ligand R=CF(3). Therefore, complex 4 (as well as complex 6 with R=OH) is predicted to be a good catalyst for peroxynitrite <--> nitrite isomerization in the gas phase. Solvent effects (a) change the rate-determining step of the reaction 2 + PN from NO(2)(-) dissociation in the gas phase to O-O activation, which occurs with barriers of (13.9), (8.4), (8.4), and (8.2) kcal/mol in water, dichloromethane, benzene, and cyclohexane, respectively, and (b) significantly reduce the NO(2)(-) dissociation energy, while only slightly destabilizing the NO(3)(-) formation barrier, and make the peroxynitrite <--> nitrate isomerization process practically impossible, even for complex 4.

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.

Methamphetamine-induced dopaminergic neurotoxicity: role of peroxynitrite and neuroprotective role of antioxidants and peroxynitrite decomposition catalysts

Oxidative stress, reactive oxygen (ROS), and nitrogen (RNS) species have been known to be involved in a multitude of neurodegenerative disorders such as Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). Both ROS and RNS have very short half-lives, thereby making their identification very difficult as a specific cause of neurodegeneration. Recently, we have developed a high performance liquid chromatography/electrochemical detection (HPLC/EC) method to identify 3-nitrotyrosine (3-NT), an in vitro and in vivo biomarker of peroxynitrite production, in cell cultures and brain to evaluate if an agent-driven neurotoxicity is produced by the generation of peroxynitrite. We show that a single or multiple injections of methamphetamine (METH) produced a significant increase in the formation of 3-NT in the striatum. This formation of 3-NT correlated with the striatal dopamine depletion caused by METH administration. We also show that PC12 cells treated with METH has significantly increased formation of 3-NT and dopamine depletion. Furthermore, we report that pretreatment with antioxidants such as selenium and melatonin can completely protect against the formation of 3-NT and depletion of striatal dopamine. We also report that pretreatment with peroxynitrite decomposition catalysts such as 5, 10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and 5, 10, 15, 20-tetrakis (2,4,6-trimethyl-3,5-sulfonatophenyl) porphinato iron III (FETPPS) significantly protect against METH-induced 3-NT formation and striatal dopamine depletion. We used two different approaches, pharmacological manipulation and transgenic animal models, in order to further investigate the role of peroxynitrite. We show that a selective neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole (7-NI), significantly protect against the formation of 3-NT as well as striatal dopamine depletion. Similar results were observed with nNOS knockout and copper zinc superoxide dismutase (CuZnSOD)-overexpressed transgenic mice models. Finally, using the protein data bank crystal structure of tyrosine hydroxylase, we postulate the possible nitration of specific tyrosine moiety in the enzyme that can be responsible for dopaminergic neurotoxicity. Together, these data clearly support the hypothesis that the reactive nitrogen species, peroxynitrite, plays a major role in METH-induced dopaminergic neurotoxicity and that selective antioxidants and peroxynitrite decomposition catalysts can protect against METH-induced neurotoxicity. These antioxidants and decomposition catalysts may have therapeutic potential in the treatment of psychostimulant addictions.

Mechanisms of Peroxynitrite Decomposition Catalyzed by FeTMPS, a Bioactive Sulfonated Iron Porphyrin

Peroxynitrite is a known cytotoxic agent that plays a role in many pathological conditions. Various peroxynitrite decomposition catalysts and pathways are being explored to develop efficient therapeutic agents that can safely remove peroxynitrite from cells and tissues. Water-soluble porphyrins, such as iron(III) meso-tetra(2,4,6-trimethyl-3,5-disulfonato)porphine chloride (FeTMPS) and iron(III) meso-tetra(N-methyl4-pyridyl)porphine chloride (FeTMPyP), have been shown to react catalytically with peroxynitrite (ONOO-). However, their mechanisms are yet to be fully understood. In this study, we have explored the reactivity of FeTMPS in the catalytic decomposition of peroxynitrite. The mechanism of this complex process has been determined. According to this mechanism, Fe(III)TMPS is oxidized by peroxynitrite to produce oxoFe(lV)TMPS and NO2 (k1 = 1.3 x 10(5) M(-1)(s(-1). The porphyrin is then reduced back to Fe(III)TMPS by nitrite, but this rate (k2 = 1.4 x 10(4) M(-1)s(-1)) is not sufficient to maintain the catalytic process at the observed rate. The overall rate of peroxynitrite decomposition catalysis, kcat, was determined to be 6 x 10(4) M(-1)s(-1), under typical conditions. We have postulated that an additional reduction pathway must exist. Kinetic simulations showed that a reaction of oxoFe(IV)TMPS with NO2 (k3 = 1.7 x 10(7) M((-1)s(-1)) could explain the behavior of this system and account for the fast reduction of oxoFe(IV)TMPS to Fe(III). Using the kinetic simulation analysis, we have also shown that two other rearrangement reactions, involving FeTMPS and peroxynitrite, are plausible pathways for peroxynitrite decay. A "cage-return" reaction between the generated oxoFe(IV)TMPS and NO2 (k8 = 5.4 x 10(4) M(-1)s(-1)), affording Fe(III)TMPS and nitrate, and a reaction between oxoFe(IV)TMPS and peroxynitrite (k7 = 2.4 x 10(4) M(-1)s(-1)) that affords oxoFe(IV)TMPS and nitrate are presented. The mechanism of FeTMPS-catalyzed peroxynitrite decay differs markedly from that of FeTMPyP, providing some insight into the reactivity of metal centers with peroxynitrite and biologically important radicals such as NO2.

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.

Manganese and iron porphyrins catalyze peroxynitrite decomposition and simultaneously increase nitration and oxidant yield: implications for their use as peroxynitrite scavengers in vivo

Twelve substituted metalloporphyrins (MPs), some of which have been previously characterized with respect to superoxide dismutase and peroxynitrite decomposing activities, were evaluated for their ability to scavenge peroxynitrite in vitro at 37 degrees C. Because the overall effectiveness of MPs as catalytic peroxynitrite scavengers is a function of (1) how fast they react with peroxynitrite, (2) how fast they cycle back to the starting compound, and (3) how well they contain or quench the reactive intermediates generated, all of these properties were evaluated and compared directly under the same conditions. Of the various MPs tested, only the iron and manganese porphyrins showed significant reactivity with peroxynitrite. The Mn(IV) intermediates resulting from oxidation by peroxynitrite were relatively stable and rereduction to the Mn(III) forms was rate-limiting to catalytic decomposition of peroxynitrite. However, in the presence of oxidizeable substrates like phenolics, rereduction of Mn(IV) forms occurred very rapidly and both the Mn- and Fe-porphyrins catalyzed nitration and oxidation by peroxynitrite. Mn- and Fe-porphyrins enhanced the yield of nitrated phenolics by peroxynitrite as much as 5-fold at pH 7.4 and up to 12-fold at pH 9. 1, while total oxidative yield was more than doubled. Nitration enhancement by MPs was effectively inhibited by ascorbate, glutathione, or serum, although much higher concentrations of ascorbate were required to inhibit nitration catalyzed by either Mn or Fe tetramethylpyridyl porphyrin. Catalysis of peroxynitrite nitration by MPs appears to proceed via a radical-mediated reaction mechanism whereby the phenolic substrate rapidly reduces Mn(IV) = O or Fe[IV] = O to the +3 state to yield phenoxyl radical which then combines with the other primary product, nitrogen dioxide. Based on the rate constants and the proposed reaction mechanism, it is reasonable to suggest that Mn and Fe porphyrins could detoxify peroxynitrite in vivo by efficiently trapping the relatively unreactive peroxynitrite anion and, in effect, channeling it into a single reaction pathway which could then be more effectively scavenged by cellular reductants like ascorbate.

Evidence for peroxynitrite as a signaling molecule in flow-dependent activation of c-Jun NH(2)-terminal kinase

The c-Jun NH(2)-terminal kinase (JNK), also known as stress-activated protein kinase, is a mitogen-activated protein kinase that determines cell survival in response to environmental stress. Activation of JNK involves redox-sensitive mechanisms and physiological stimuli such as shear stress, the dragging force generated by blood flow over the endothelium. Laminar shear stress has antiatherogenic properties and controls structure and function of endothelial cells by mechanisms including production of nitric oxide (NO) and superoxide (O(-)(2)). Here we show that both NO and O(-)(2) are required for activation of JNK by shear stress in endothelial cells. The present study also demonstrates that exposure of endothelial cells to shear stress increases tyrosine nitration, a marker of reactive nitrogen species formation. Furthermore, inhibitors or scavengers of NO, O(-)(2), or reactive nitrogen species prevented shear-dependent increase in tyrosine nitration and activation of JNK. Peroxynitrite alone, added to cells as a bolus or generated over 60 min by 3-morpholinosydnonimine, also activates JNK. These results suggest that reactive nitrogen species, in this case most likely peroxynitrite, act as signaling molecules in the mechanoactivation of JNK.

Methamphetamine generates peroxynitrite and produces dopaminergic neurotoxicity in mice: protective effects of peroxynitrite decomposition catalyst

Methamphetamine (METH)-induced dopaminergic neurotoxicity is believed to be produced by oxidative stress and free radical generation. The present study was undertaken to investigate if METH generates peroxynitrite and produces dopaminergic neurotoxicity. We also investigated if this generation of peroxynitrite can be blocked by a selective peroxynitrite decomposition catalyst, 5, 10,15, 20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and protect against METH-induced dopaminergic neurotoxicity. Administration of METH resulted in the significant formation of 3-nitrotyrosine (3-NT), an in vivo marker of peroxynitrite generation, in the striatum and also caused a significant increase in the body temperature. METH injection also caused a significant decrease in the concentration of dopamine (DA), 3, 4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) by 76%, 53% and 40%, respectively, in the striatum compared with the control group. Treatment with FeTMPyP blocked the formation of 3-NT by 66% when compared with the METH group. FeTMPyP treatment also provided significant protection against the METH-induced hyperthermia and depletion of DA, DOPAC and HVA. Administration of FeTMPyP alone neither resulted in 3-NT formation nor had any significant effect on DA or its metabolite concentrations. These findings indicate that peroxynitrite plays a role in METH-induced dopaminergic neurotoxicity and also suggests that peroxynitrite decomposition catalysts may be beneficial for the management of psychostimulant abuse.

Biological aspects of reactive nitrogen species

Nitric oxide (NO) plays an important role as a cell-signalling molecule, anti-infective agent and, as most recently recognised, an antioxidant. The metabolic fate of NO gives rise to a further series of compounds, collectively known as the reactive nitrogen species (RNS), which possess their own unique characteristics. In this review we discuss this emerging aspect of the NO field in the context of the formation of the RNS and what is known about their effects on biological systems. While much of the insight into the RNS has been gained from the extensive chemical characterisation of these species, to reveal biological consequences this approach must be complemented by direct measures of physiological function. Although we do not know the consequences of many of the dominant chemical reactions of RNS an intriguing aspect is now emerging. This review will illustrate how, when specificity and amplification through cell signalling mechanisms are taken into account, the less significant reactions, in terms of yield or rates, can explain many of the biological responses of exposure of cells or physiological systems to RNS.

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.

Mycobacterium tuberculosis KatG is a peroxynitritase

Mycobacterium tuberculosis resides within the highly oxidative environment of the human macrophage and previous reports have indicated that these mycobacteria are susceptible to reactive nitrogen intermediates including peroxynitrite. This work provides evidence that the Mycobacterium tuberculosis hemoprotein KatG acts as an efficient peroxynitritase exhibiting a kapp of 1.4 x 10(5) M-1s-1 for peroxynitrite decomposition at pH 7.4 and 37 degrees C. The ability of KatG to act as a peroxynitritase adds to its growing list of enzymatic activities and may in part explain the ability of Mycobacterium tuberculosis to persist in macrophages.

Pathophysiology of nitric oxide and related species: free radical reactions and modification of biomolecules

Since its initial discovery as an endogenously produced bioactive mediator, nitric oxide (.NO) has been found to play a critical role in the cellular function of nearly all organ systems. Furthermore, aberrant production of .NO or reactive nitrogen species (RNS) derived from .NO, has been implicated in a number of pathological conditions, such as acute lung disease, atherosclerosis and septic shock. While .NO itself is fairly non-toxic, secondary RNS are oxidants and nitrating agents that can modify both the structure and function of numerous biomolecules both in vitro, and in vivo. The mechanisms by which RNS mediate toxicity are largely dictated by its unique reactivity. The study of how reactive nitrogen species (RNS) derived from .NO interact with biomolecules such as proteins, carbohydrates and lipids, to modify both their structure and function is an area of active research, which is lending major new insights into the mechanisms underlying their pathophysiological role in human disease. In the context of .NO-dependent pathophysiology, these biochemical reactions will play a major role since they: (i) lead to removal of .NO and decreased efficiency of .NO as an endothelial-derived relaxation factor (e.g. in hypertension, atherosclerosis) and (ii) lead to production of other intermediate species and covalently modified biomolecules that cause injury and cellular dysfunction during inflammation. Although the physical and chemical properties of .NO and .NO-derived RNS are well characterised, extrapolating this fundamental knowledge to a complicated biological environment is a current challenge for researchers in the field of .NO and free radical research. In this review, we describe the impact of .NO and .NO-derived RNS on biological processes primarily from a biochemical standpoint. In this way, it is our intention to outline the most pertinent and relevant reactions of RNS, as they apply to a diverse array of pathophysiological states. Since reactions of RNS in vivo are likely to be vast and complex, our aim in this review is threefold: (i) address the major sources and reactions of .NO-derived RNS in biological systems, (ii) describe current knowledge regarding the functional consequences underlying .NO-dependent covalent modification of specific biomolecules, and (iii) to summarise and critically evaluate the available evidence implicating these reactions in human pathology. To this end, three areas of special interest have been chosen for detailed description, namely, formation and role of S-nitrosothiols, modulation of lipid oxidation/nitration by RNS, and tyrosine nitration mechanisms and consequences.

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

Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP), described as a superoxide dismutase mimetic and peroxynitrite scavenger, has been used previously to investigate the cytotoxic potential of superoxide and peroxynitrite in several pathological models. Here we report on the interference of MnTMPyP with NO/cGMP signaling using cultured endothelial cells as well as purified soluble guanylyl cyclase (sGC) either activated by the NO donor 2,2-diethyl-1-nitroso-oxyhydrazine sodium salt (DEA/NO) or reconstituted with nitric oxide synthase (NOS). MnTMPyP inhibited endothelial cGMP accumulation induced by A23187 (0.3 microM) with an IC50 of 75.0 +/- 10.4 microM but had no significant effect on the potency of the Ca2+ ionophore. Purified NOS was inhibited by MnTMPyP (IC50 = 5.5 +/- 0.8 microM) because of an interference of the Mn-porphyrin with the reductase domain of the enzyme. The most pronounced actions of MnTMPyP were direct inhibition of sGC and scavenging of NO. Purified sGC stimulated with either Ca2+/calmodulin-activated NOS (in the presence of GSH) or DEA/NO (in the absence of GSH) was inhibited with IC50 values of 0.8 +/- 0.09 microM and 0.6 +/- 0.2 microM, respectively. In the presence of GSH, MnTMPyP was reduced to the Mn(II) complex, resulting in efficient scavenging of NO under these conditions. Our data demonstrate that MnTMPyP (i) interferes with the reductase domain of NOS, (ii) scavenges NO in the presence of GSH, and (iii) is a potent direct inhibitor of sGC. These results cast doubt on the usefulness of MnTMPyP and related Mn-porphyrin complexes as probes to study the involvement of peroxynitrite/superoxide in biological systems.

Peroxynitrite rapidly permeates phospholipid membranes

Peroxynitrite (ONOO-) is a potent oxidant implicated in a number of pathophysiological processes. The activity of ONOO- is related to its accessibility to biological targets before its spontaneous decomposition (t1/2 approximately 1 s at pH 7.4, 37 degrees C). Using model phospholipid vesicular systems and manganese porphyrins as reporter molecules, we demonstrated that ONOO- freely crosses phospholipid membranes. The calculated permeability coefficient for ONOO- is approximately 8.0 x 10(-4) cm.s-1, which compares well with that of water and is approximately 400 times greater than that of superoxide. We suggest that ONOO- is a significant biological effector molecule not only because of its reactivity but also because of its high diffusibility.