Rapid and irreversible inactivation of protein tyrosine phosphatases PTP1B, CD45, and LAR by peroxynitrite

Mechanism of CaM kinase IV activation during hypoxia in neuronal nuclei of the cerebral cortex of newborn piglets: the role of Src kinase

The present study aims to investigate the mechanism of CaM kinase IV activation during hypoxia and tests the hypothesis that hypoxia-induced increased activity of CaM kinase IV is due to Src kinase mediated increased tyrosine phosphorylation of calmodulin and CaM kinase IV in neuronal nuclei of the cerebral cortex of newborn piglets. Piglets were divided into normoxic (Nx, n = 5), hypoxic (Hx, F(i)O(2) of 0.07 for 1 h, n = 5) and hypoxic-pretreated with Src kinase inhibitor PP2 (Hx-Srci, n = 5) groups. Src inhibitor was administered (1.0 mg/kg, I.V.) 30 min prior to hypoxia. Neuronal nuclei were isolated and purified, and tyrosine phosphorylation of calmodulin (Tyr(99)) and CaM kinase IV determined by Western blot using anti-phospho-(pTyr(99))-calmodulin, anti-pTyrosine and anti-CaM kinase IV antibodies. The activity of CaM kinase IV and its consequence the phosphorylation of CREB protein at Ser(133) were determined. Hypoxia resulted in increased tyrosine phosphorylation of calmodulin at Tyr(99), tyrosine phosphorylation of CaM kinase IV, activity of CaM kinase IV and phosphorylation of CREB protein at Ser(133). The data show that administration of Src kinase inhibitor PP2 prevented the hypoxia-induced increased tyrosine phosphorylation of calmodulin (Tyr(99)) and tyrosine phosphorylation of CaM.kinase IV as well as the activity of CaM kinase IV and CREB phosphorylation at Ser(133). We conclude that the mechanism of hypoxia-induced increased activation of CaM kinase IV is mediated by Src kinase-dependent tyrosine phosphorylation of the enzyme and its activator calmodulin. We propose that Tyr(99) phosphorylated calmodulin, as compared to non-phosphorylated, binds with a higher affinity at the calmodulin binding site (rich in basic amino acids) of CaM kinase IV leading to increased activation of CaM kinase IV. Similarly, tyrosine phosphorylated CaM kinase IV binds its substrate with a higher affinity and thus increased tyrosine phosphorylation leads to increased activation of CaM kinase IV resulting in increased CREB phosphorylation that triggers increased transcription of proapoptotic proteins that initiate hypoxic neuronal death.

Brain tissue energy dependence of CaM kinase IV cascade activation during hypoxia in the cerebral cortex of newborn piglets

The present study aims to investigate the dependence of CaM kinase IV cascade activation during hypoxia and tests the hypothesis that hypoxia-induced tyrosine phosphorylation of CaM and CaM kinase IV, activation of CaM kinase IV and phosphorylation of CREB protein during hypoxia increases as a function of increase in cerebral tissue hypoxia as measured by decrease in tissue ATP and phosphocreatine (PCr). 3-5 days old newborn piglets were divided into normoxic (Nx, FiO₂ of 0.21 for 1h) and hypoxic (Hx, FiO₂ of 0.07 for 1h) groups. Cerebral tissue hypoxia was documented by determining the levels of high energy phosphates ATP and phosphocreatine (PCr). Cerebral cortical neuronal nuclei were isolated and purified, and tyrosine phosphorylation of calmodulin (Tyr⁹⁹), the activator of CaM kinase IV, and CaM kinase IV determined by Western blot using anti-phospho-(pTyr⁹⁹)-calmodulin, anti-pTyrosine and anti-CaM kinase IV antibodies. The activity of CaM kinase IV and its consequence the phosphorylation of CREB protein at Ser¹³³ were determined. The levels of ATP (μmole/g brain) ranged from 3.48 to 5.28 in Nx, and 0.41 to 2.26 in Hx. The levels of PCr (μmole/g brain) ranged from 2.46 to 3.91 in Nx and 0.72 to 1.20 in Hx. The pTyr⁹⁹ calmodulin (OD x mm²) ranged from 20.35 to 54.47.60 in Nx, and 84.52 to 181.42 in Hx (r²=0.5309 vs ATP and r²=0.6899 vs PCr). Expression of tyrosine phosphorylated CaM kinase IV ranged from 32.86 to 82.46 in Nx and 96.70 to 131.62 in Hx (r²=0.5132 vs ATP and r²=0.4335 vs PCr). The activity of CaM kinase IV (pmole/mg protein/min) ranged from 1263 to 3448 in Nx and 3767 to 6633 in Hx (r²=0.7113 vs ATP and r²=0.6182 vs PCr). The expression of p-CREB at Ser¹³³ ranged from 44.26 to 70.28 in Nx and 82.70 to 182.86 in Hx (r²=0.6621 vs ATP and r²=0.5485 vs PCr). The data show that hypoxia results in increased tyrosine phosphorylation of calmodulin (Tyr⁹⁹), increased tyrosine phosphorylation of CaM kinase IV, increased activity of CaM kinase IV and increased phosphorylation of CREB at Ser¹³³ as an inverse function of cerebral concentration of high energy phosphates, ATP and PCr. We conclude that the hypoxia-induced increased activation of CaM kinase IV cascade increases with the increase in the degree of cerebral tissue hypoxia as measured by cerebral tissue high energy phosphates in a curvilinear manner. The tyrosine kinases (Src kinase and EGFR kinase) mediated activation of CaM kinase IV cascade potentially results in increased CREB phosphorylation that triggers transcription of proapoptotic proteins during hypoxia.

Inhibition of aldehyde dehydrogenase 2 by oxidative stress is associated with cardiac dysfunction in diabetic rats

Left ventricular (LV) dysfunction is a common comorbidity in diabetic patients, although the molecular mechanisms underlying this cardiomyopathic feature are not completely understood. Aldehyde dehydrogenase 2 (ALDH2) has been considered a key cardioprotective enzyme susceptible to oxidative inactivation. We hypothesized that hyperglycemia-induced oxidative stress would influence ALDH2 activity, and ALDH2 inhibition would lead to cardiac functional alterations in diabetic rats. Diabetes was induced by intraperitoneal (i.p.) injection of 60 mg/kg streptozotocin. Rats were divided randomly into four groups: control, untreated diabetic, diabetic treated with N-acetylcysteine (NAC) and diabetic treated with α-lipoic acid (α-LA). Cardiac contractile function, oxidative stress markers and reactive oxygen species (ROS) levels were assessed. ALDH2 activity and expression also were determined. The role of ALDH2 activity in change in hyperglycemia-induced mitochondrial membrane potential (Δψ) was tested in cultured neonatal cardiomyocytes. Myocardial MDA content and ROS were significantly higher in diabetic rats than in controls, whereas GSH content and Mn-SOD activity were decreased in diabetic rats. Compared with controls, diabetic rats exhibited significant reduction in LV ejection fraction and fractional shortening, accompanied by decreases in ALDH2 activity and expression. NAC and α-LA attenuated these changes. Mitochondrial Δψ was decreased greatly with hyperglycemia treatment, and high glucose combined with ALDH2 inhibition with daidzin further decreased Δψ. The ALDH2 activity can be regulated by oxidative stress in the diabetic rat heart. ALDH2 inhibition may be associated with LV reduced contractility, and mitochondrial impairment aggravated by ALDH2 inhibition might reflect an underlying mechanism which causes cardiac dysfunction in diabetic rats.

The myeloperoxidase-derived oxidant HOSCN inhibits protein tyrosine phosphatases and modulates cell signalling via the mitogen-activated protein kinase (MAPK) pathway in macrophages

MPO (myeloperoxidase) catalyses the oxidation of chloride, bromide and thiocyanate by hydrogen peroxide to HOCl (hypochlorous acid), HOBr (hypobromous acid) and HOSCN (hypothiocyanous acid) respectively. Specificity constants indicate that SCN⁻ is a major substrate for MPO. HOSCN is also a major oxidant generated by other peroxidases including salivary, gastric and eosinophil peroxidases. While HOCl and HOBr are powerful oxidizing agents, HOSCN is a less reactive, but more specific, oxidant which targets thiols and especially low pK_a species. In the present study we show that HOSCN targets cysteine residues present in PTPs (protein tyrosine phosphatases) with this resulting in a loss of PTP activity for the isolated enzyme, in cell lysates and intact J774A.1 macrophage-like cells. Inhibition also occurs with MPO-generated HOCl and HOBr, but is more marked with MPO-generated HOSCN, particularly at longer incubation times. This inhibition is reversed by dithiothreitol, particularly at early time points, consistent with the reversible oxidation of the active site cysteine residue to give either a cysteine–SCN adduct or a sulfenic acid. Inhibition of PTP activity is associated with increased phosphorylation of p38a and ERK2 (extracellular-signal-regulated kinase 2) as detected by Western blot analysis and phosphoprotein arrays, and results in altered MAPK (mitogen-activated protein kinase) signalling. These data indicate that the highly selective targeting of some protein thiols by HOSCN can result in perturbation of cellular phosphorylation and altered cell signalling. These changes occur with (patho)physiological concentrations of SCN⁻ ions, and implicate HOSCN as an important mediator of inflammation-induced oxidative damage, particularly in smokers who have elevated plasma levels of SCN⁻.

Nasal delivery of antisense oligonucleotides: in vitro evaluation of a thiomer/glutathione microparticulate delivery system

PURPOSE

The aim of this study was to develop a nasal mucoadhesive microparticulate delivery system for phosphorothioate antisense oligonucleotides (PTO-ODNs) utilizing the thiomer technology.

METHODS

PTO-ODN microparticles, coated with either the mucoadhesive polymer polycarbophil-cysteine (PCP-Cys) or unmodified PCP and reduced glutathione (GSH) were prepared by the emulsification solvent evaporation technique. Particle size, drug load, decrease in thiol groups on microparticles, swelling properties, release of incorporated PTO-ODN, and mucoadhesive properties were examined. Permeation enhancing effect of the deployed thiomer conjugate was investigated on excised porcine respiratory mucosa of the nasal cavity.

RESULTS

Results demonstrated that microparticles were almost of spherical structure displaying particle diameter up to 30 microm. In addition, a controlled drug release of the incorporated PTO-ODN was achieved from these particles. Mucoadhesion studies revealed that thiolated PCP-Cys microparticles display 3-fold higher mucoadhesive properties than the corresponding unthiolated polycarbophil microparticles. The uptake of PTO-ODN, incubated in thiolated polycarbophil and glutathione microparticles, from the nasal mucosa was 2.2-fold improved.

CONCLUSIONS

According to these results, the thiolated polycarbophil/reduced GSH microparticles might be a promising formulation for systemic delivery of PTO-ODNs via the nasal route.

The nonphagocytic NADPH oxidase Duox1 mediates a positive feedback loop during T cell receptor signaling

Production of reactive oxygen species, often by NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidases, plays a role in the signaling responses of cells to many receptor stimuli. Here, we describe the function of the calcium-dependent, nonphagocytic NADPH oxidase Duox1 in primary human CD4(+) T cells and cultured T cell lines. Duox1 bound to inositol 1,4,5-trisphosphate receptor 1 and was required for early T cell receptor (TCR)-stimulated production of hydrogen peroxide (H(2)O(2)) through a pathway that was dependent on TCR-proximal kinases. Transient or stable knockdown of Duox1 inhibited TCR signaling, especially phosphorylation of tyrosine-319 of zeta chain-associated protein kinase of 70 kilodaltons (ZAP-70), store-operated entry of calcium ions (Ca(2+)), and activation of extracellular signal-regulated kinase. The production of cytokines was also inhibited by knockdown of Duox1. Duox1-mediated inactivation of Src homology 2 domain-containing protein tyrosine phosphatase 2 promoted the phosphorylation of ZAP-70 and its association with the Src family tyrosine kinase Lck and the CD3zeta chain of the TCR complex. Thus, we suggest that activation of Duox1, downstream of proximal TCR signals, generates H(2)O(2) that acts in a positive feedback loop to enhance and sustain further TCR signaling.

Peroxynitrite-An ugly biofactor?

Cellular damage occurring under oxidative conditions has been ascribed mainly to the formation of peroxynitrite (ONOOH/ONOO(-)) that originates from the reaction of NO(*) with O(2) (*-). The detrimental effects of peroxynitrite are exacerbated by the reaction with CO(2) that leads to ONOOC(O)O(-), which further decays to the strong oxidant radicals NO(2) (*) and CO(3) (*-). The reaction with CO(2), however, may redirect peroxynitrite specificity. An excessive formation of peroxynitrite represents an important mechanism contributing to the DNA damage, the inactivation of metabolic enzymes, ionic pumps, and structural proteins, and the disruption of cell membranes. Because of its ability to oxidize biomolecules, peroxynitrite is implicated in an increasing list of diseases, including neurodegenerative and cardiovascular disorders, inflammation, pain, autoimmunity, cancer, and aging. However, peroxynitrite displays also protective activities: (i) at high concentrations, it shows anti-viral, anti-microbial, and anti-parasitic actions; and (ii) at low concentrations, it stimulates protective mechanisms in the cardiovascular, nervous, and respiratory systems. The detrimental effects of peroxynitrite and related reactive species are impaired by (pseudo-) enzymatic systems, mainly represented by heme-proteins (e.g., hemoglobin and myoglobin). Here, we report biochemical aspects of peroxynitrite actions being at the root of its biomedical effects.

Analysis of the redox regulation of protein tyrosine phosphatase superfamily members utilizing a cysteinyl-labeling assay

The catalytic activity of protein tyrosine phosphatase (PTP) superfamily members is regulated by the reversible oxidation of their invariant catalytic Cys residue in vivo. Transient and specific regulation of PTP activity by reactive oxygen species (ROS) attenuates dephosphorylation and, thereby, promotes phosphorylation, hence facilitating signal transduction. We have recently developed a modified cysteinyl-labeling assay [Boivin, B., Zhang, S., Arbiser, J. L., Zhang, Z. Y., and Tonks, N. K. (2008). Proc. Natl. Acad. Sci. USA105, 9959-9964.] that showed broad selectivity in detecting reversible oxidation of members from different PTP subclasses in platelet-derived growth factor (PDGF)-BB overexpressing cells. Herein, we applied this assay, which utilizes the unique chemistry of the invariant catalytic Cys residue to enrich and identify PTPs that are reversibly oxidized upon acute growth factor stimulation. Performing the cysteinyl-labeling assay with Rat-1 fibroblasts enabled us to capture both PTEN and SHP-2 as a consequence to acute PDGF-BB stimulation. Given the ability of this assay to detect reversible oxidation of a broad array of members of the PTP family, we anticipate that it should permit profiling of the entire ROS-regulated PTPome in a wide array of signaling paradigms.

Thiolated polycarbophil as an adjuvant for permeation enhancement in nasal delivery of antisense oligonucleotides

The purpose of this study was to investigate the effect of thiolated polycarbophil as an adjuvant to enhance the permeation and improve the stability of a phosphorothioate antisense oligonucleotide (PTO-ODN) on the nasal mucosa. Polycarbophil-cysteine (PCP-Cys) was synthesized by the covalent attachment of L-cysteine to the polymeric backbone. Cytotoxicity tests were examined on human nasal epithelial cells from surgery of nasal polyps confirmed by histological studies. Deoxyribonuclease I activity in respiratory region of the porcine nasal cavity was analyzed by an enzymatic assay. The enzymatic degradation of PTO-ODNs on freshly excised porcine nasal mucosa was analyzed and protection of PCP-cysteine toward DNase I degradation was evaluated. Permeation studies were performed in Ussing-type diffusion chambers. PCP-Cys/GSH did not arise a remarkable mortal effect. Porcine respiratory mucosa was shown to possess nuclease activity corresponding to 0.69 Kunitz units/mL. PTO-ODNs were degraded by incubation with nasal mucosa. In the presence of 0.45% thiolated polycarbophil and 0.5% glutathione (GSH), this degradation process could be lowered. In the presence of thiolated polycarbophil and GSH the uptake of PTO-ODNs from the nasal mucosa was 1.7-fold improved. According to these results thiolated polycarbophil/GSH might be a promising excipient for nasal administration of PTO-ODNs.

Redox modulation of global phosphatase activity and protein phosphorylation in intact skeletal muscle

Skeletal muscles produce transient reactive oxygen species (ROS) in response to intense stimulation, disuse atrophy, heat stress, hypoxia, osmotic stress, stretch and cell receptor activation. The physiological significance is not well understood. Protein phosphatases (PPases) are known to be highly sensitive to oxidants and could contribute to many different signalling responses in muscle. We tested whether broad categories of PPases are inhibited by levels of acute oxidant exposure that do not result in loss of contractile function or gross oxidative stress. We also tested if this exposure results in elevated levels of global protein phosphorylation. Rat diaphragm muscles were treated with either 2,3-dimethoxy-1-naphthoquinone (DMNQ; 1, 10, 100 microm; a mitochondrial O(2)(.-)/H2O2 generator) or exogenous H2O2 (5, 50, 500 microm) for 30 min. Supernatants were assayed for serine/threonine PPase (Ser/Thr-PPase) or protein tyrosine PPase (PTP) activities. With the exception of 500 microm H2O2, no other oxidant exposures significantly elevated protein carbonyl formation, nor did they alter the magnitude of twitch force. DMNQ significantly decreased all categories of PPase activity at 10 and 100 microm and reduced PTP at 1 microm. Similar reductions in Ser/Thr-PPase activity were seen in response to 50 and 500 microm H2O2 and PTP at 500 microm H2O2. ROS treatments resulted a dose-dependent increase in the phosphorylation states of many proteins. The data are consistent with the concept that PPases, within intact skeletal muscles, are highly sensitive to acute changes in ROS activity and that localized ROS play a critical role in lowering the barriers for effective phosphorylation events to occur in muscle cells, thus increasing the probability for cell signalling responses to proceed.

The two faces of PTP1B in cancer

PTP1B is a classical non-transmembrane protein tyrosine phosphatase that plays a key role in metabolic signaling and is a promising drug target for type 2 diabetes and obesity. Accumulating evidence also indicates that PTP1B is involved in cancer, but contrasting findings suggest that it can exert both tumor suppressing and tumor promoting effects depending on the substrate involved and the cellular context. In this review, we will discuss the diverse mechanisms by which PTP1B may influence tumorigenesis as well as recent in vivo data on the impact of PTP1B deficiency in murine cancer models. Together, these results highlight not only the great potential of PTP1B inhibitors in cancer therapy but also the need for a better understanding of PTP1B function prior to use of these compounds in human patients.

Peroxynitrite mediates muscle insulin resistance in mice via nitration of IRbeta/IRS-1 and Akt

Accumulating evidence suggests that peroxynitrite (ONOO(-)) is involved in the pathogenesis of insulin resistance. In the current study, we investigated whether insulin resistance in vivo could be mediated by nitration of proteins involved in the early steps of the insulin signal transduction pathway. Exogenous peroxynitrite donated by 3-morpholinosydnonimine hydrochloride (SIN-1) induced in vivo nitration of the insulin receptor beta subunit (IRbeta), insulin receptor substrate (IRS)-1, and protein kinase B/Akt (Akt) in skeletal muscle of mice and dramatically reduced whole-body insulin sensitivity and muscle insulin signaling. Moreover, in high-fat diet (HFD)-fed insulin-resistant mice, we observed enhanced nitration of IRbeta and IRS-1 in skeletal muscle, in parallel with impaired whole-body insulin sensitivity and muscle insulin signaling. Reversal of nitration of these proteins by treatment with the peroxynitrite decomposition catalyst FeTPPS yielded an improvement in whole-body insulin sensitivity and muscle insulin signaling in HFD-fed mice. Taken together, these findings provide new mechanistic insights for the involvement of peroxynitrite in the development of insulin resistance and suggest that nitration of proteins involved in the early steps of insulin signal transduction is a novel molecular mechanism of HFD-induced muscle insulin resistance.

Mechanism of increased tyrosine (Tyr(99)) phosphorylation of calmodulin during hypoxia in the cerebral cortex of newborn piglets: the role of nNOS-derived nitric oxide

The present study aims to investigate the mechanism of calmodulin modification during hypoxia and tests the hypothesis that hypoxia-induced increase in Tyr(99) phosphorylation of calmodulin in the cerebral cortex of newborn piglets is mediated by NO derived from nNOS. Fifteen piglets were divided into normoxic (Nx, n = 5), hypoxic (Hx, F(i)O(2) of 0.07 for 1 h, n = 5) and hypoxic-pretreated with nNOSi (Hx-nNOSi, n = 5) groups. nNOS inhibitor I (selectivity >2,500 vs. eNOS and >500 vs. iNOS) was administered (0.4 mg/kg, I.V.) 30 min prior to hypoxia. Cortical membranes were isolated and tyrosine phosphorylation (Tyr(99) and total) of calmodulin determined by Western blot using anti-phospho-(pTyr(99))-calmodulin and anti-pTyr antibodies. Protein bands were detected by enhanced chemiluminescence, analyzed by densitometry and expressed as absorbance. The pTyr(99) calmodulin (ODxmm(2)) was 78.55 +/- 10.76 in Nx, 165.05 +/- 12.26 in Hx (P < 0.05 vs. Nx) and 96.97 +/- 13.18 in Hx-nNOSi (P < 0.05 vs. Hx, P = NS vs. Nx). Expression of total tyrosine phosphorylated calmodulin was 69.24 +/- 13.69 in Nx, 156.17 +/- 16.34 in Hx (P < 0.05 vs. Nx) and 74.18 +/- 3.9 in Hx-nNOSi (P < 0.05 vs. Hx, P = NS vs. Nx). The data show that administration of nNOS inhibitor prevented the hypoxia-induced increased Tyr(99) phosphorylation of calmodulin. Total tyrosine phosphorylation of calmodulin was similar to Tyr(99) phosphorylation. We conclude that the mechanism of hypoxia-induced modification (Tyr(99) phosphorylation) of calmodulin is mediated by NO derived from nNOS. We speculate that Tyr(99) phosphorylated calmodulin, as compared to non-phosphorylated, binds with a higher affinity at the calmodulin binding site of nNOS leading to increased activation of nNOS and increased generation of NO.

NO-mediated activation of Src kinase during hypoxia in the cerebral cortex of newborn piglets

The present study aims to investigate the mechanism of Src kinase activation during hypoxia and tests the hypothesis that the hypoxia-induced activation of Src kinase, as determined by Src kinase phosphorylation, in the cerebral cortical membranes of newborn piglets is mediated by NO derived from neuronal nitric oxide synthase (nNOS). Fifteen piglets were divided into normoxic (Nx, n=5), hypoxic (Hx, n=5) and hypoxic-treated with nNOS inhibitor I (Hx-nNOSi) groups. Hypoxia was induced by decreasing FiO(2) to 0.06 for 1h. nNOS inhibitor I (selectivity >2500 vs eNOS and >500 vs iNOS) was administered (0.4 mg/kg, i.v.) 30 min prior to hypoxia. Cortical membranes were isolated and phosphorylation of Src kinase was determined by Western blot analysis. Src kinase activity was determined by radioactive assay using immunopurified enzyme. Membrane proteins were separated by 12% SDS-PAGE and probed with anti-phospho (pTyr(418))-Src kinase antibody. Protein bands were detected, analyzed by densitometry and expressed as absorbance (ODxmm(2)). Density (ODxmm(2)) of phosphorylated Src kinase was 111.7+/-21.1 in Nx, 234.5+/-23.8 in Hx (p<0.05 vs Nx) and 104.7+/-18.1 in Hx-nNOSi (p<0.05 vs Hx, p=NS vs Nx). Src kinase activity (pmol/mgprotein/ h) was 2472+/-75 in Nx, 4556+/-358 in Hx (p<0.05 vs Nx) and 2259+/-207 in Hx-nNOSi (p<0.05 vs Hx, p=NS vs Nx). The data show that pretreatment with nNOS inhibitor prevents the hypoxia-induced increase in tyrosine phosphorylation and the activity of Src kinase. We conclude that the mechanism of hypoxia-induced increased activation of Src kinase is mediated by nNOS derived NO. We propose that NO mediated inhibition of protein tyrosine phosphatases SH-PTP-1 and SH-PTP-2 leads to increased tyrosine phosphorylation and activation of Src kinase in the cerebral cortex of newborn piglets.

Zinc fingers as biologic redox switches?

Despite zinc ions being redox inert in biologic systems, zinc-finger structures act as redox-sensitive molecular switches controlling several crucial cellular processes. Oxidative or nitrosative stress, via modification of zinc finger cysteine thiols, leads to a release of Zn(2+) from these structures, causing not only a loss of zinc-finger function but also an increase of cytoplasmic or nuclear free Zn(2+) that may, in turn, stimulate and interfere with cellular signaling cascades. A signaling cascade stimulated by exposure of cells to zinc ions or to stressful stimuli that are reported to cause an intracellular release of zinc ions involves phosphoinositide 3'-kinases and the Ser/Thr protein kinase Akt, resulting in an inactivation of transcriptional regulators of the FoxO family. Possible modes of action of zinc ions to stimulate this signaling cascade and consequences of stimulation are discussed. Moreover, we present an overview on human diseases or disorders characterized by an intracellular Zn(2+) dyshomeostasis.

Cellular senescence: molecular mechanisms, in vivo significance, and redox considerations

Cellular senescence is recognized as a critical cellular response to prolonged rounds of replication and environmental stresses. Its defining characteristics are arrested cell-cycle progression and the development of aberrant gene expression with proinflammatory behavior. Whereas the mechanistic events associated with senescence are generally well understood at the molecular level, the impact of senescence in vivo remains to be fully determined. In addition to the role of senescence as an antitumor mechanism, this review examines cellular senescence as a factor in organismal aging and age-related diseases, with particular emphasis on aberrant gene expression and abnormal paracrine signaling. Senescence as an emerging factor in tissue remodeling, wound repair, and infection is considered. In addition, the role of oxidative stress as a major mediator of senescence and the role of NAD(P)H oxidases and changes to intracellular GSH/GSSG status are reviewed. Recent findings indicate that senescence and the behavior of senescent cells are amenable to therapeutic intervention. As the in vivo significance of senescence becomes clearer, the challenge will be to modulate the adverse effects of senescence without increasing the risks of other diseases, such as cancer. The uncoupled relation between cell-cycle arrest and the senescent phenotype suggests that this is an achievable outcome.

Proteomic analysis of protein tyrosine nitration after ischemia reperfusion injury: mitochondria as the major target

Endothelial nitric oxide synthase-derived NO and its derivative, peroxynitrite (ONOO(-)), suppresses oxygen consumption by nitration of mitochondrial proteins after reperfusion. However, very few nitrated proteins are identified to date. In this paper, ischemia/reperfusion (I/R) injury was induced in mouse heart by ligation and release of the left anterior descending coronary artery. Western blotting showed that tyrosine nitration was higher in I/R hearts. Nitrated proteins were identified by capillary-liquid chromatography-nanospray tandem mass spectrometry. A total of 23 proteins were identified as being nitrated after I/R and 10 of them were from mitochondria. The nitrated mitochondrial proteins included 4 subunits from the oxidative phosphorylation system (the 24 and the 30 kDa subunits of complex I, the Rieske ISP of complex III, and the alpha subunit of ATP synthase), five enzymes in the matrix, and voltage-dependent anion channel. In purified complex I treated with ONOO(-), 3-NT was identified locating at the residue of Y247 of the 30 kDa subunit and the residues of Y47, Y53 of the 49 kDa subunit. In conclusion, I/R induced protein nitration and mitochondrial proteins were the major targets. Selective nitration of proteins from the oxidative phosphorylation system at the beginning of reperfusion may contribute to the suppression of oxygen consumption.

Epidermal growth factor receptor activation by diesel particles is mediated by tyrosine phosphatase inhibition

Exposure to particulate matter (PM) is associated with increased cardiopulmonary morbidity and mortality. Diesel exhaust particles (DEP) are a major component of ambient PM and may contribute to PM-induced pulmonary inflammation. Proinflammatory signaling is mediated by phosphorylation-dependent signaling pathways whose activation is opposed by the activity of protein tyrosine phosphatases (PTPases) which thereby function to maintain signaling quiescence. PTPases contain an invariant catalytic cysteine that is susceptible to electrophilic attack. DEP contain electrophilic oxy-organic compounds that may contribute to the oxidant effects of PM. Therefore, we hypothesized that exposure to DEP impairs PTPase activity allowing for unopposed basal kinase activity. Here we report that exposure to 30 microg/cm(2) DEP for 4 h induces differential activation of signaling in primary cultures of human airway epithelial cells (HAEC), a primary target cell in PM inhalation. In-gel kinase activity assay of HAEC exposed to DEPs of low (L-DEP), intermediate (I-DEP) or high (H-DEP) organic content showed differential activation of intracellular kinases. Exposure to these DEP also induced varying levels of phosphorylation of the receptor tyrosine kinase EGFR in a manner that requires EGFR kinase activity but does not involve receptor dimerization. We demonstrate that treatment with DEP results in an impairment of total and EGFR-directed PTPase activity in HAEC with a potency that is independent of the organic content of these particles. These data show that DEP-induced EGFR phosphorylation in HAEC is the result of a loss of PTPase activities which normally function to dephosphorylate EGFR in opposition to baseline EGFR kinase activity.

Protein nitration in placenta - functional significance

Crucial roles of the placenta are disrupted in early and mid-trimester pregnancy loss, preeclampsia, eclampsia and intrauterine growth restriction. The pathophysiology of these disorders includes a relative hypoxia of the placenta, ischemia/reperfusion injury, an inflammatory response and oxidative stress. Reactive oxygen species including nitric oxide (NO), carbon monoxide and superoxide have been shown to participate in trophoblast invasion, regulation of placental vascular reactivity and other events. Superoxide, which regulates expression of redox sensitive genes, has been implicated in up-regulation of transcription factors, antioxidant production, angiogenesis, proliferation and matrix remodeling. When superoxide and nitric oxide are present in abundance, their interaction yields peroxynitrite a potent pro-oxidant, but also alters levels of nitric oxide, which in turn affect physiological functions. The peroxynitrite anion is extremely unstable thus evidence of its formation in vivo has been indirect via the occurrence of nitrated moieties including nitrated lipids and nitrotyrosine residues in proteins. Formation of 3-nitrotyrosine (protein nitration) is a "molecular fingerprint" of peroxynitrite formation. Protein nitration has been widely reported in a number of pathological states associated with inflammation but is reported to occur in normal physiology and is thought of as a prevalent, functionally relevant post-translational modification of proteins. Nitration of proteins can give either no effect, a gain or a loss of function. Nitration of a range of placental proteins is found in normal pregnancy but increased in pathologic pregnancies. Evidence is presented for nitration of placental signal transduction enzymes and transporters. The targets and extent of nitration of enzymes, receptors, transporters and structural proteins may markedly influence placental cellular function in both physiologic and pathologic settings.

Effect of nitric oxide donor and gamma irradiation on modifications of ERK and JNK in murine peritoneal macrophages

Mitogen activated protein kinases (MAPKs) play an important role in activation, differentiation and proliferation of macrophages. Macrophages, upon activation, produce large amounts of nitric oxide that inhibit the growth of variety of microorganisms and tumor cells. This nitric oxide which is known to interfere with tyrosine phosphorylation may result in changes in the pattern of activation of MAPKs. In a previous study we have found that tyrosine phosphorylation of MAPKs was completely abolished in the presence of nitric oxide donor and radiation but this did not affect the function of macrophages. In this study the other post translational modifications namely nitration and ubiquitination of JNK and ERK have been looked at. Both ERK and JNK were found to be nitrated. However, there was no increase in ubiquitination of ERK and JNK, indicating that ubiquitination, in this case was not a natural consequence of nitration and may serve in signaling. Additionally, when the nitration was extensive, phosphorylation was also inhibited. The activation of substrates of ERK and JNK were looked at to determine the consequences of such modifications. Inhibition of phosphorylation and extensive nitration of JNK did not prevent activation of its substrate, c-jun. This study indicates that ERK and JNK may be under regulation by different type of modifications in macrophages.

Effect of nitric oxide donor and gamma irradiation on MAPK signaling in murine peritoneal macrophages

Irradiation (IR) of cells is known to activate enzymes of mitogen activated protein kinase (MAPK) family. These are known to be involved in cellular response to stress and are determinants of cell death or survival. When radiotherapy is delivered to malignant cells, macrophages, being radioresistant, survive, get activated, and produce large amounts of nitric oxide. As a result of activation they recognize and phagocytose tumor and normal cell apoptotic bodies leading to tumor regression. In this study, the MAPK signaling in peritoneal macrophages was investigated which plays an important role in its various functions, in an environment which is predominantly nitric oxide, as is after IR. The behavior of macrophages in such an environment was also looked at. The three MAPK (ERK1/2, p38, and JNK) respond differently to Sodium nitroprusside (SNP) alone or IR alone. All the three were activated following IR but only JNK was activated following SNP treatment. Surprisingly, when both the stresses were given simultaneously or one after the other, this differential response was lost and there was a complete inhibition of phosphorylation of all the three MAPKs, irrespective of the order of the two insults (IR and SNP). The noteworthy observation was that despite the complete inhibition of MAPK signaling there was no effect on either the viability or the phagocytic efficiency of peritoneal macrophages.

Protein tyrosine phosphorylation and protein tyrosine nitration in redox signaling

Reversible phosphorylation of protein tyrosine residues by polypeptide growth factor-receptor protein tyrosine kinases is implicated in the control of fundamental cellular processes including the cell cycle, cell adhesion, and cell survival, as well as cell proliferation and differentiation. During the last decade, it has become apparent that receptor protein tyrosine kinases and the signaling pathways they activate belong to a large signaling network. Such a network can be regulated by various extracellular cues, which include cell adhesion, agonists of G protein-coupled receptors, and oxidants. It is well documented that signaling initiated by receptor protein tyrosine kinases is directly dependent on the intracellular production of oxidants, including reactive oxygen and nitrogen species. Accumulated evidence indicates that the intracellular redox environment plays a major role in the mechanisms underlying the actions of growth factors. Oxidation of cysteine thiols and nitration of tyrosine residues on signaling proteins are described as posttranslational modifications that regulate, positively or negatively, protein tyrosine phosphorylation (PTP). Early observations described the inhibition of PTP activities by oxidants, resulting in increased levels of proteins phosphorylated on tyrosine. Therefore, a redox circuitry involving the increasing production of intracellular oxidants associated with growth-factor stimulation/cell adhesion, oxidative reversible inhibition of protein tyrosine phosphatases, and the activation of protein tyrosine kinases can be delineated.

Metabolic regulation and function of glutathione peroxidase-1

Glutathione peroxidase-1 (GPX1) represents the first identified mammalian selenoprotein, and our understanding in the metabolic regulation and function of this abundant selenoenzyme has greatly advanced during the past decade. Selenocysteine insertion sequence-associating factors, adenosine, and Abl and Arg tyrosine kinases are potent, Se-independent regulators of GPX1 gene, protein, and activity. Overwhelming evidences have been generated using the GPX1 knockout and transgenic mice for the in vivo protective role of GPX1 in coping with oxidative injury and death mediated by reactive oxygen species. However, GPX1 exerts an intriguing dual role in reactive nitrogen species (RNS)-related oxidative stress. Strikingly, knockout of GPX1 rendered mice resistant to toxicities of drugs including acetaminophen and kainic acid, known as RNS inducers. Intracellular and tissue levels of GPX1 activity affect apoptotic signaling pathway, protein kinase phosphorylation, and oxidant-mediated activation of NFkappaB. Data are accumulating to link alteration or abnormality of GPX1 expression to etiology of cancer, cardiovascular disease, neurodegeneration, autoimmune disease, and diabetes. Future research should focus on the mechanism of GPX1 in the pathogeneses and potential applications of GPX1 manipulation in the treatment of these disorders.

Nitration of a critical tyrosine residue in the allosteric inhibitor site of muscle glycogen phosphorylase impairs its catalytic activity

Muscle glycogen phosphorylase (GP) is a key enzyme in glucose metabolism, and its impairment can lead to muscle dysfunction. Tyrosine nitration of glycogen phosphorylase occurs during aging and has been suggested to be involved in progressive loss of muscle performance. Here, we show that GP (in its T and R form) is irreversibly impaired by exposure to peroxynitrite, a biological nitrogen species known to nitrate reactive tyrosine residues, and to be involved in physiological and pathological processes. Kinetic and biochemical analysis indicated that irreversible inactivation of GP by peroxynitrite is due to the fast (k(inact)=3 x 10(4) M(-1) s(-1)) nitration of a unique tyrosine residue of the enzyme. Endogenous GP was tyrosine nitrated and irreversibly inactivated in skeletal muscle cells upon exposure to peroxynitrite, with concomitant impairment of glycogen mobilization. Ligand protection assays and mass spectrometry analysis using purified GP suggested that the peroxynitrite-dependent inactivation of the enzyme could be due to the nitration of Tyr613, a key amino acid of the allosteric inhibitor site of the enzyme. Our findings suggest that GP functions may be regulated by tyrosine nitration.

Inhibition of protein tyrosine phosphatases by amino acid, peptide, and protein hydroperoxides: potential modulation of cell signaling by protein oxidation products

Reaction of radicals in the presence of O2, or singlet oxygen, with some amino acids, peptides, and proteins yields hydroperoxides. These species are key intermediates in chain reactions and protein damage. They can be detected in cells and are poorly removed by enzymatic defenses. Previously we have shown that peptide and protein hydroperoxides react rapidly with thiols, with this resulting in inactivation of some thiol-dependent enzymes. In light of these data, we hypothesized that inactivation of protein tyrosine phosphatases (PTPs), by hydroperoxides present on oxidized proteins, may contribute to cellular and tissue dysfunction by modulation of phosphorylation-dependent cell signaling. We show here that PTPs in cell lysates, and purified PTP-1B, are inactivated by amino acid, peptide, and protein hydroperoxides in a concentration- and structure-dependent manner. Protein hydroperoxides are particularly effective, with inhibition occurring with greater efficacy than with H2O2. Inactivation involves reaction of the hydroperoxide with the conserved active-site Cys residue of the PTPs, as evidenced by hydroperoxide consumption measurements and a diminution of this effect on blocking the Cys residue. This inhibition of PTPs, by oxidized proteins containing hydroperoxide groups, may contribute to cellular dysfunction and altered redox signaling in systems subject to oxidative stress.

Stimulation of phosphoinositide 3-kinase/Akt signaling by copper and zinc ions: mechanisms and consequences

The phosphoinositide 3'-kinase (PI3K)/Akt signaling cascade controls cellular processes such as apoptosis and proliferation. Moreover, it is a mediator of insulin effects on target cells and as such is a major regulator of fuel metabolism. The PI3K/Akt cascade was demonstrated to be activated by stressful stimuli, including heat shock and reactive oxygen species (ROS). This minireview focuses on activation of the pathway by exposure of cells to heavy metal ions, Cu2+ and Zn2+. It is hypothesized that stimulation of PI3K/Akt is the molecular mechanism underlying the known insulin-mimetic effects of copper and zinc ions. Following a brief summary of PI3K/Akt signaling and of activation of the cascade by Cu2+ and Zn2+, mechanisms of metal-induced PI3K/Akt activation are discussed with a focus on the role of ROS and of cellular thiols (glutathione, thioredoxin) and protein tyrosine phosphatases in Cu2+ and Zn2+ signaling. Finally, consequences of metal-induced PI3K/Akt activation are discussed, focusing on the modulation of FoxO-family transcription factors by Cu2+ and Zn2+.

Nitric oxide generation is associated with an unbalance of protein tyrosine phosphatases during liver transplantation

Organ dysfunction secondary to ischemia-reperfusion (I/R) injury still represents a major problem in liver transplantation. Apoptosis has been observed in hepatocytes and sinusoidal endothelial cell, following I/R injury and it has been postulated as a contributing factor in ischemia-reperfusion graft dysfunction, involving a complex series of events, as changes of protein tyrosine-kinase phosphorylation. We evaluated hepatic purine metabolites, protein tyrosine phosphatases (PTPs), nitrate plus nitrite levels (NOx), caspase-3 (C-3) activity and DNA fragmentation in the time course of twelve pig orthotopic liver transplantation. Biopsies were taken before explantation (t0), after cold ischemic storage (t1) and 30 min from reperfusion (t2). During the ischemic period we observed a reduction of high energy phosphates and an increase of purine bases; PTP activity was largely increased. At t2 high energy phosphates showed a tendency to increase with respect to t1, with a partial restoration of phosphorylation potential, measured as ATP/ADT ratio. PTP activity was significantly reduced, with a concomitant increase of NOx production and C-3 activity; in a considerable number of cases we observed a sustained DNA fragmentation. We speculate that NOx production could be related to nitrosative stress, which in turn leads to dynamic alteration in PTP balance and cell signalling, regulating the activity of a number of proteins implicated in apoptotic cell death. These findings could be of interest in new potential strategy to prevent and treat I/R injury.

Prevention of peroxynitrite-induced apoptosis of motor neurons and PC12 cells by tyrosine-containing peptides

Although peroxynitrite stimulates apoptosis in many cell types, whether peroxynitrite acts directly as an oxidant or the induction of apoptosis is because of the radicals derived from peroxynitrite decomposition remains unknown. Before undergoing apoptosis because of trophic factor deprivation, primary motor neuron cultures become immunoreactive for nitrotyrosine. We show here using tyrosine-containing peptides that free radical processes mediated by peroxynitrite decomposition products were required for triggering apoptosis in primary motor neurons and in PC12 cells cultures. The same concentrations of tyrosine-containing peptides required to prevent the nitration and apoptosis of motor neurons induced by trophic factor deprivation and of PC12 cells induced by peroxynitrite also prevented peroxynitrite-mediated nitration of motor neurons, brain homogenates, and PC12 cells. The heat shock protein 90 chaperone was nitrated in both trophic factor-deprived motor neurons and PC12 cells incubated with peroxynitrite. Tyrosine-containing peptides did not affect the induction of PC12 cell death by hydrogen peroxide. Tyrosine-containing peptides should protect by scavenging peroxynitrite-derived radicals and not by direct reactions with peroxynitrite as they neither increase the rate of peroxynitrite decomposition nor decrease the bimolecular peroxynitrite-mediated oxidation of thiols. These results reveal an important role for free radical-mediated nitration of tyrosine residues, in apoptosis induced by endogenously produced and exogenously added peroxynitrite; moreover, tyrosine-containing peptides may offer a novel strategy to neutralize the toxic effects of peroxynitrite.

Inhibition of PTEN by peroxynitrite activates the phosphoinositide-3-kinase/Akt neuroprotective signaling pathway

Peroxynitrite is usually considered as a neurotoxic nitric oxide-derivative. However, an increasing body of evidence suggests that, at low concentrations, peroxynitrite affords transient cytoprotection, both in vitro and in vivo. Here, we addressed the signaling mechanism responsible for this effect, and found that rat cortical neurons in primary culture acutely exposed to peroxynitrite (0.1 mmol/L) rapidly elicited Akt-Ser(473) phosphorylation. Inhibition of phosphoinositide-3-kinase (PI3K)/Akt pathway with wortmannin or Akt small hairpin RNA (shRNA) abolished the ability of peroxynitrite to prevent etoposide-induced apoptotic death. Endogenous peroxynitrite formation by short-term incubation of neurons with glutamate stimulated Akt-Ser(473) phosphorylation, whereas Akt shRNA enhanced the vulnerability of neurons against glutamate. We further show that Akt-Ser(473) phosphorylation was consequence of the oxidizing, but not the nitrating properties of peroxynitrite. Peroxynitrite failed to nitrate or phosphorylate neurotrophin tyrosine kinase receptors (Trks), and it did not modify the ability of brain-derived neurotrophic factor (BDNF), to phosphorylate its cognate receptor, TrkB; however, peroxynitrite enhanced BDNF-mediated Akt-Ser(473) phosphorylation. Finally, we found that peroxynitrite-stimulated Akt-Ser(473) phosphorylation was associated with an increased proportion of oxidized phosphoinositide phosphatase, PTEN, in neurons. Moreover, peroxynitrite prevented the increase of apoptotic neuronal death caused by over-expression of PTEN. Thus, peroxynitrite exerts neuroprotection by inhibiting PTEN, hence activating the anti-apoptotic PI3K/Akt pathway in primary neurons.

Reprint of “Oxidative alterations of cyclooxygenase during atherogenesis” [Prostag. Oth. Lipid. M. 80 (2006) 1–14]

Nitric oxide (*NO) and eicosanoids are critical mediators of physiological and pathophysiological processes. They include inflammation and atherosclerosis. *NO production and eicosanoid synthesis become disrupted during atherosclerosis and thus, it is important to understand the mechanisms that may contribute to this outcome. We, and others, have shown that nitrogen oxide (NOx) species modulate cyclooxygenase (COX; also known as prostaglandin H2 synthase) activity and alter eicosanoid production. We have determined that peroxynitrite (ONOO-) has multiple effects on COX activity. ONOO- can provide the peroxide tone necessary for COX activation, such that simultaneous exposure of COX to its arachidonic acid substrate and ONOO- results in increased eicosanoid production. Alternatively, in the absence of arachidonic acid, ONOO- can modify COX through nitration of an essential tyrosine residue (Tyr385) such that it is incapable of catalysis. In this regard, we have shown that COX nitration occurs in human atherosclerotic tissue and in aortic lesions from ApoE-/- mice kept on a high fat diet. Additionally, we have demonstrated that Tyr nitration in ApoE-/- mice is dependent on the inducible form of NO synthase (iNOS). Under conditions where ONOO- persists and arachidonic acid is not immediately available, the cell may try to correct the situation by responding to ONOO- and releasing arachidonic acid via a signaling pathway to favor COX activation. Other post-translational modifications of COX by NOx species include S-nitrosation of cysteine (Cys) residues (which may have an activating effect) and Cys oxidation. The central focus of this review will include a discussion of how NOx species alter COX activity at the molecular level and how these modifications may contribute to altered eicosanoid output during atherosclerosis and lesion development.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Singlet oxygen inactivates protein tyrosine phosphatase-1B by oxidation of the active site cysteine

Singlet oxygen ((1)O(2)), an electronically excited form of molecular oxygen, is a mediator of biological effects of ultraviolet A radiation, stimulating signaling cascades in human cells. We demonstrate here that (1)O(2) generated by photosensitization or by thermodecomposition of 3,3'-(1,4-naphthylidene)dipropionate-1,4-endoperoxide inactivates isolated protein tyrosine phosphatases (PTPases). PTPase activities of PTP1B or CD45 were abolished by low concentrations of (1)O(2), but were largely restored by post-treatment with dithiothreitol. Electrospray ionization mass spectrometry analysis of tryptic digests of PTP1B exposed to (1)O(2) revealed oxidation of active-site Cys215 as the only cysteine residue oxidized. In summary, (1)O(2) may activate signaling cascades by interfering with phosphotyrosine dephosphorylation.

Peroxynitrite and myocardial contractility: in vivo versus in vitro effects

Generation of peroxynitrite (ONOO-) as a result of altered redox balance has been shown to affect cardiac function; however, inconsistencies in the data exist, particularly for myocardial contractility. The hypothesis that the cardiac impact of ONOO- formation depends on its site of generation, intravascular or intramyocardial, was examined. Cardiac contractility was assessed by pressure-volume analysis to delineate vascular versus cardiac changes on direct infusion of ONOO- into the right atria of conscious dogs both with normal cardiac function and in heart failure. Additionally, ONOO- was administered to isolated murine cardiomyocytes to mimic in situ cardiac generation. When infused in vivo, ONOO- had little impact on inotropy but led to systemic arterial dilation, likely as a result of rapid decomposition to NO2- and NO3-. In contrast, infused ONOO- was long lived enough to abolish beta-adrenergic (dobutamine)-stimulated contractility/relaxation, most likely through catecholamine oxidation to aminochrome. When administered to isolated murine cardiomyocytes, ONOO- induced a rapid reduction in sarcomere shortening and whole cell calcium transients, although neither decomposed ONOO- or NaNO2 had any effect. Thus, systemic generation of ONOO- is unlikely to have primary cardiac effects, but may modulate cardiac contractile reserve, via blunted beta-adrenergic stimulation, and vascular tone, as a result of generation of NO2- and NO3-. However, myocyte generation of ONOO- may impair contractile function by directly altering Ca2+ handling. These data demonstrate that the site of generation within the cardiovascular system largely dictates the ability of ONOO- to directly or indirectly modulate cardiac pump function.

Role of reduced lipoic acid in the redox regulation of mitochondrial aldehyde dehydrogenase (ALDH-2) activity. Implications for mitochondrial oxidative stress and nitrate tolerance

Chronic therapy with nitroglycerin results in a rapid development of nitrate tolerance, which is associated with an increased production of reactive oxygen species. We have recently shown that mitochondria are an important source of nitroglycerin-induced oxidants and that the nitroglycerin-bioactivating mitochondrial aldehyde dehydrogenase is oxidatively inactivated in the setting of tolerance. Here we investigated the effect of various oxidants on aldehyde dehydrogenase activity and its restoration by dihydrolipoic acid. In vivo tolerance in Wistar rats was induced by infusion of nitroglycerin (6.6 microg/kg/min, 4 days). Vascular reactivity was measured by isometric tension studies of isolated aortic rings in response to nitroglycerin. Chronic nitroglycerin infusion lead to impaired vascular responses to nitroglycerin and decreased dehydrogenase activity, which was corrected by dihydrolipoic acid co-incubation. Superoxide, peroxynitrite, and nitroglycerin itself were highly efficient in inhibiting mitochondrial and yeast aldehyde dehydrogenase activity, which was restored by dithiol compounds such as dihydrolipoic acid and dithiothreitol. Hydrogen peroxide and nitric oxide were rather insensitive inhibitors. Our observations indicate that mitochondrial oxidative stress (especially superoxide and peroxynitrite) in response to organic nitrate treatment may inactivate aldehyde dehydrogenase thereby leading to nitrate tolerance. Glutathionylation obviously amplifies oxidative inactivation of the enzyme providing another regulatory pathway. Furthermore, the present data demonstrate that the mitochondrial dithiol compound dihydrolipoic acid restores mitochondrial aldehyde dehydrogenase activity via reduction of a disulfide at the active site and thereby improves nitrate tolerance.

Sulfenic acid in human serum albumin

Sulfenic acid (RSOH) is a central intermediate in both the reversible and irreversible redox modulation by reactive species of an increasing number of proteins involved in signal transduction and enzymatic pathways. In this paper we focus on human serum albumin (HSA), the most abundant plasma protein, proposed to serve antioxidant functions in the vascular compartment. Sulfenic acid in HSA has been previously detected using different methods after oxidation of its single free thiol Cys34 through one- or two-electron mechanisms. Since recent evidence suggests that sulfenic acid in HSA is stabilized within the protein environment, this derivative represents an appropriate model to examine protein sulfenic acid biochemistry, structure and reactivity. Sulfenic acid in HSA could be involved in mixed disufide formation, supporting a role of HSA-Cys34 as an important redox regulator in extracellular compartments.

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.

Oxidative alterations of cyclooxygenase during atherogenesis

Nitric oxide (*NO) and eicosanoids are critical mediators of physiological and pathophysiological processes. They include inflammation and atherosclerosis. *NO production and eicosanoid synthesis become disrupted during atherosclerosis and thus, it is important to understand the mechanisms that may contribute to this outcome. We, and others, have shown that nitrogen oxide (NO(x)) species modulate cyclooxygenase (COX; also known as prostaglandin H(2) synthase) activity and alter eicosanoid production. We have determined that peroxynitrite (ONOO(-)) has multiple effects on COX activity. ONOO(-) can provide the peroxide tone necessary for COX activation, such that simultaneous exposure of COX to its arachidonic acid substrate and ONOO(-) results in increased eicosanoid production. Alternatively, in the absence of arachidonic acid, ONOO(-) can modify COX through nitration of an essential tyrosine residue (Tyr385) such that it is incapable of catalysis. In this regard, we have shown that COX nitration occurs in human atherosclerotic tissue and in aortic lesions from ApoE(-/-) mice kept on a high fat diet. Additionally, we have demonstrated that Tyr nitration in ApoE(-/-) mice is dependent on the inducible form of NO synthase (iNOS). Under conditions where ONOO(-) persists and arachidonic acid is not immediately available, the cell may try to correct the situation by responding to ONOO(-) and releasing arachidonic acid via a signaling pathway to favor COX activation. Other post-translational modifications of COX by NO(x) species include S-nitrosation of cysteine (Cys) residues (which may have an activating effect) and Cys oxidation. The central focus of this review will include a discussion of how NO(x) species alter COX activity at the molecular level and how these modifications may contribute to altered eicosanoid output during atherosclerosis and lesion development.

Hydrogen peroxide: a signaling messenger

Hydrogen peroxide (H2O2) is a well-documented component of living cells. It plays important roles in host defense and oxidative biosynthetic reactions. In addition there is growing evidence that at low levels, H2O2 also functions as a signaling agent, particularly in higher organisms. This review evaluates the evidence that H2O2 functions as a signaling agent in higher organisms in light of the known biology and biochemistry of H2O2. All aerobic organisms studied to date from prokaryotes to humans appear to tightly regulate their intracellular H2O2 concentrations at relatively similar levels. Multiple biochemical strategies for rapidly reacting with these low endogenous levels of H2O2 have been elucidated from the study of peroxidases and catalases. Well-defined biochemical pathways involved in the response to exogenous H2O2 have been described in both prokaryotes and yeast. In animals and plants, regulated enzymatic systems for generating H2O2 have been described. In addition oxidation-dependent steps in signal transduction pathways are being uncovered, and evidence is accumulating regarding the nature of the specific reactive oxygen species involved in each of these pathways. Application of physiologic levels of H2O2 to mammalian cells has been shown to stimulate biological responses and to activate specific biochemical pathways in these cells.

Nitration of tyrosine 92 mediates the activation of rat microsomal glutathione s-transferase by peroxynitrite

There is increasing evidence that protein function can be modified by nitration of tyrosine residue(s), a reaction catalyzed by proteins with peroxidase activity, or that occurs by interaction with peroxynitrite, a highly reactive oxidant formed by the reaction of nitric oxide with superoxide. Although there are numerous reports describing loss of function after treatment of proteins with peroxynitrite, we recently demonstrated that the microsomal glutathione S-transferase 1 is activated rather than inactivated by peroxynitrite and suggested that this could be attributed to nitration of tyrosine residues rather than to other effects of peroxynitrite. In this report, the nitrated tyrosine residues of peroxynitrite-treated microsomal glutathione S-transferase 1 were characterized by mass spectrometry and their functional significance determined. Of the seven tyrosine residues present in the protein, only those at positions 92 and 153 were nitrated after treatment with peroxynitrite. Three mutants (Y92F, Y153F, and Y92F, Y153F) were created using site-directed mutagenesis and expressed in LLC-PK1 cells. Treatment of the microsomal fractions of these cells with peroxynitrite resulted in an approximately 2-fold increase in enzyme activity in cells expressing the wild type microsomal glutathione S-transferase 1 or the Y153F mutant, whereas the enzyme activity of Y92F and double site mutant was unaffected. These results indicate that activation of microsomal glutathione S-transferase 1 by peroxynitrite is mediated by nitration of tyrosine residue 92 and represents one of the few examples in which a gain in function has been associated with nitration of a specific tyrosine residue.

Impairment of the activity of the xenobiotic-metabolizing enzymes arylamine N-acetyltransferases 1 and 2 (NAT1/NAT2) by peroxynitrite in mouse skeletal muscle cells

Reactive nitrogen species and their by-products, such as peroxynitrite, modulate many physiological functions of skeletal muscle. Peroxynitrite generation occuring under specific conditions, such as inflammation, may also lead to skeletal muscle dysfunction and pathologies. Arylamine N-acetyltransferases (NATs) are xenobiotic-metabolizing enzymes (XMEs) involved in the detoxification and/or metabolic activation of several drugs and chemicals. In addition to other XMEs, such as gluthatione S-transferases or cytochromes P450, NAT enzymes are expressed in skeletal muscle. We show here that functional NAT1 and NAT2 isoforms are expressed in mouse myotubes and that peroxynitrite may impair their activity in these cells. We show that this inactivation is likely due to the irreversible modification of NATs catalytic cysteine residue in vivo. Our results suggest that peroxynitrite-dependent inactivation of muscle XMEs such as NATs may contribute to muscle dysfunction by impairing the biotransformation activity of this key cellular defense enzyme system.

Phosphoinositide 3-kinase signaling in the cellular response to oxidative stress

Oxidative stress is linked to the pathogenesis and pathobiochemistry of various diseases, including cancer, diabetes and cardiovascular disorders. The non-specific damaging effect of reactive oxygen species (ROS) generated during oxidative stress is involved in the development of diseases, as well as the activation of specific signaling cascades in cells exposed to the higher oxidant load. A cellular signaling cascade that is activated by several types of reactive oxygen species is the phosphoinositide 3'-kinase (PI 3-kinase)/protein kinase B (PKB) pathway, which regulates cellular survival and fuel metabolism, thus establishing a link between oxidative stress and signaling in neoplastic, metabolic or degenerative diseases. Several links of PI 3-kinase/PKB signaling to ROS are discussed in this review, with particular focus on the molecular mechanisms involved in the regulation of PI 3-kinase signaling by oxidative stress and important players such as (i) the glutathione and glutaredoxin system, (ii) the thioredoxin system and (iii) Ser/Thr- and Tyr phosphatases.