Cu,Zn-superoxide dismutase increases toxicity of mutant and zinc-deficient superoxide dismutase by enhancing protein stability

Mass spectrometry imaging of SOD1 protein-metal complexes in SOD1G93A transgenic mice implicates demetalation with pathology

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of motor neurons in the central nervous system (CNS). Mutations in the metalloenzyme SOD1 are associated with inherited forms of ALS and cause a toxic gain of function thought to be mediated by dimer destabilization and misfolding. SOD1 binds two Cu and two Zn ions in its homodimeric form. We have applied native ambient mass spectrometry imaging to visualize the spatial distributions of intact metal-bound SOD1G93A complexes in SOD1G93A transgenic mouse spinal cord and brain sections and evaluated them against disease pathology. The molecular specificity of our approach reveals that metal-deficient SOD1G93A species are abundant in CNS structures correlating with ALS pathology whereas fully metalated SOD1G93A species are homogenously distributed. Monomer abundance did not correlate with pathology. We also show that the dimer-destabilizing post-translational modification, glutathionylation, has limited influence on the spatial distribution of SOD1 dimers.

An Overview of Reactive Oxygen Species Damage Occurring during In Vitro Bovine Oocyte and Embryo Development and the Efficacy of Antioxidant Use to Limit These Adverse Effects

The in vitro production (IVP) of bovine embryos has gained popularity worldwide and in recent years and its use for producing embryos from genetically elite heifers and cows has surpassed the use of conventional superovulation-based embryo production schemes. There are, however, several issues with the IVP of embryos that remain unresolved. One limitation of special concern is the low efficiency of the IVP of embryos. Exposure to reactive oxygen species (ROS) is one reason why the production of embryos with IVP is diminished. These highly reactive molecules are generated in small amounts through normal cellular metabolism, but their abundances increase in embryo culture because of oocyte and embryo exposure to temperature fluctuations, light exposure, pH changes, atmospheric oxygen tension, suboptimal culture media formulations, and cryopreservation. When uncontrolled, ROS produce detrimental effects on the structure and function of genomic and mitochondrial DNA, alter DNA methylation, increase lipid membrane damage, and modify protein activity. Several intrinsic enzymatic pathways control ROS abundance and damage, and antioxidants react with and reduce the reactive potential of ROS. This review will focus on exploring the efficiency of supplementing several of these antioxidant molecules on oocyte maturation, sperm viability, fertilization, and embryo culture.

Native Mass Spectrometry Coupled to Spectroscopic Methods to Investigate the Effect of Soybean Isoflavones on Structural Stability and Aggregation of Zinc Deficient and Metal-Free Superoxide Dismutase

The deficiency or wrong combination of metal ions in Cu, Zn-superoxide dismutase (SOD1), is regarded as one of the main factors causing the aggregation of SOD1 and then inducing amyotrophic lateral sclerosis (ALS). A ligands-targets screening process based on native electrospray ionization ion mobility mass spectrometry (ESI-IMS-MS) was established in this study. Four glycosides including daidzin, sophoricoside, glycitin, and genistin were screened out from seven soybean isoflavone compounds and were found to interact with zinc-deficient or metal-free SOD1. The structure and conformation stability of metal-free and zinc-deficient SOD1 and their complexes with the four glycosides was investigated by collision-induced dissociation (CID) and collision-induced unfolding (CIU). The four glycosides could strongly bind to the metal-free and copper recombined SOD1 and enhance the folding stability of these proteins. Additionally, the ThT fluorescence assay showed that these glycosides could inhibit the toxic aggregation of the zinc-deficient or metal-free SOD1. The competitive interaction experiments together with molecular docking indicate that glycitin, which showed the best stabilizing effects, binds with SOD1 between β-sheet 6 and loop IV. In short, this study provides good insight into the relationship between inhibitors and different SOD1s.

Metal migration and subunit swapping in ALS-linked SOD1: Zn2+ transfer between mutant and wild-type occurs faster than the rate of heterodimerization

The heterodimerization of WT Cu, Zn superoxide dismutase-1 (SOD1), and mutant SOD1 might be a critical step in the pathogenesis of SOD1-linked amyotrophic lateral sclerosis (ALS). Rates and free energies of heterodimerization (ΔG_Het) between WT and ALS-mutant SOD1 in mismatched metalation states-where one subunit is metalated and the other is not-have been difficult to obtain. Consequently, the hypothesis that under-metalated SOD1 might trigger misfolding of metalated SOD1 by "stealing" metal ions remains untested. This study used capillary zone electrophoresis and mass spectrometry to track heterodimerization and metal transfer between WT SOD1, ALS-variant SOD1 (E100K, E100G, D90A), and triply deamidated SOD1 (modeled with N26D/N131D/N139D substitutions). We determined that rates of subunit exchange between apo dimers and metalated dimers-expressed as time to reach 30% heterodimer-ranged from t_30% = 67.75 ± 9.08 to 338.53 ± 26.95 min; free energies of heterodimerization ranged from ΔG_Het = -1.21 ± 0.31 to -3.06 ± 0.12 kJ/mol. Rates and ΔG_Het values of partially metalated heterodimers were more similar to those of fully metalated heterodimers than apo heterodimers, and largely independent of which subunit (mutant or WT) was metal-replete or metal-free. Mass spectrometry and capillary electrophoresis demonstrated that mutant or WT 4Zn-SOD1 could transfer up to two equivalents of Zn²⁺ to mutant or WT apo-SOD1 (at rates faster than the rate of heterodimerization). This result suggests that zinc-replete SOD1 can function as a chaperone to deliver Zn²⁺ to apo-SOD1, and that WT apo-SOD1 might increase the toxicity of mutant SOD1 by stealing its Zn²⁺.

Determining Copper and Zinc Content in Superoxide Dismutase Using Electron Capture Dissociation Under Native Spray Conditions

Localizing metal binding to specific sites in proteins remains a challenging analytical problem in vitro and in vivo. Although metal binding can be maintained by "native" electrospray ionization with intact proteins for quantitation by mass spectrometry, subsequent fragmentation of proteins with slow-heating methods like collision-induced dissociation (CID) can scramble and detach metals. In contrast, electron capture dissociation (ECD) fragmentation produces highly localized bond cleavage that is well known to preserve posttranslational modifications. We show how a newly available ECD tool that can be retrofitted on standard QTOF mass spectrometers allows the sites of copper and zinc binding to be localized in the antioxidant enzyme Cu, Zn superoxide dismutase (SOD1). The loss of zinc from Cu, Zn SOD1 has been shown to induce motor neuron death and could have a causal role in the fatal neurodegenerative disease, amyotrophic lateral sclerosis (ALS). The methods described enable copper loss to be distinguished from zinc using distinct ECD fragments of SOD1 and are broadly applicable to other metalloproteins.

Copper Toxicity Is Not Just Oxidative Damage: Zinc Systems and Insight from Wilson Disease

Essential metals such as copper (Cu) and zinc (Zn) are important cofactors in diverse cellular processes, while metal imbalance may impact or be altered by disease state. Cu is essential for aerobic life with significant functions in oxidation-reduction catalysis. This redox reactivity requires precise intracellular handling and molecular-to-organismal levels of homeostatic control. As the central organ of Cu homeostasis in vertebrates, the liver has long been associated with Cu storage disorders including Wilson Disease (WD) (heritable human Cu toxicosis), Idiopathic Copper Toxicosis and Endemic Tyrolean Infantile Cirrhosis. Cu imbalance is also associated with chronic liver diseases that arise from hepatitis viral infection or other liver injury. The labile redox characteristic of Cu is often discussed as a primary mechanism of Cu toxicity. However, work emerging largely from the study of WD models suggests that Cu toxicity may have specific biochemical consequences that are not directly attributable to redox activity. This work reviews Cu toxicity with a focus on the liver and proposes that Cu accumulation specifically impacts Zn-dependent processes. The prospect that Cu toxicity has specific biochemical impacts that are not entirely attributable to redox may promote further inquiry into Cu toxicity in WD and other Cu-associated disorders.

Utilizing Ion Mobility-Mass Spectrometry to Investigate the Unfolding Pathway of Cu/Zn Superoxide Dismutase

Native mass spectrometry has emerged as a powerful tool for structural biology as it enables the evaluation of molecules as they occur in their physiological conditions. Ion mobility spectrometry-mass spectrometry (IMS-MS) has shown essential in these analyses as it allows the measurement of the shape of a molecule, denoted as its collision cross section (CCS), and mass. The structural information garnered from native IMS-MS provides insight into the tertiary and quaternary structure of proteins and can be used to validate NMR or crystallographic X-ray structures. Additionally, due to the rapid nature (millisecond measurements) and ability of IMS-MS to analyze heterogeneous solutions, it can be used to address structural questions not possible with traditional structural approaches. Herein, we applied multiple solution conditions to systematically denature bovine Cu/Zn-superoxide dismutase (SOD1) and assess its unfolding pathway from the holo-dimer to the holo-monomer, single-metal monomer, and apo-monomer. Additionally, we compared and noted 1–2% agreement between CCS values from both drift tube IMS and trapped IMS for the SOD1 holo-monomer and holo-dimer. The observed CCS values were in excellent agreement with computational CCS values predicted from the homo-dimer crystal structure, showcasing the ability to use both IMS-MS platforms to provide valuable structural information for molecular modeling of protein interactions and structural assessments.

Choice of mobile phase: Implications for size exclusion chromatography-inductively coupled plasma-mass spectrometry analyses of copper, zinc and iron metalloproteins

The correct identification of the metalloproteins present in human tissues and fluids is essential to our understanding of the cellular mechanisms underpinning a host of health disorders. Separation and analysis of biological samples are typically done via size exclusion chromatography hyphenated with inductively coupled plasma-mass spectrometry (SEC-ICP-MS). Although this technique can be extremely effective in identification of potential metalloproteins, the choice of mobile phase may have a marked effect on results, results by adversely affecting metal-protein bonds of the metalloproteins of interest. To assess the choice of mobile phase on SEC-ICP-MS resolution and the resulting metalloproteome pattern, we analysed several different sample types (brain homogenate; Cu/Zn-superoxide dismutase (SOD1); a molecular weight standard mix containing ferritin (Ft), ceruloplasmin (Cp), cytochrome c (CytC), vitamin B12 (B12) and thyroglobulin (Tg) using six different mobile phase conditions (200 mM, pH 7.5 solutions of ammonium salts nitrate, acetate, and sulfate; HEPES, MOPS and Tris-HCl). Our findings suggest that ammonium nitrate, ammonium acetate and Tris-HCl are optimal choices for the mobile phase, with the specific choice being dependent on both the number of samples and method of detection that is hyphenated with separation. Furthermore, we found that MOPS, HEPES and ammonium sulfate mobile phases all caused significant changes to peak resolution, retention time and overall profile shape. MOPS and HEPES, in particular, produced additional Fe peaks that were not detected with any of the other mobile phases that were investigated. As well as this, MOPS and HEPES both caused significant concentration dependent matrix suppression of the internal standard.

Parenteral Zinc Supplementation Increases Pregnancy Rates in Beef Cows

Zinc (Zn) is required for normal reproductive performance in cattle. The aim of this study was to evaluate the effect of subcutaneous injection of 400 mg Zn at the beginning of fixed-time artificial insemination (FTAI) on preovulatory follicle and corpus luteum (CL) size, plasma estradiol (E2) and progesterone (P4) concentrations, and pregnancy rates in beef cows. Copper (Cu) concentration and alkaline phosphatase (ALP) activity in plasma were also evaluated. Zinc supplementation at the beginning of the FTAI protocol (day 0) increased the area of preovulatory follicle (APF, day 9; P = 0.042) and plasma P4 concentration (day 16; P = 0.01), whereas plasma E2 concentration (day 9) and area of CL (ACL; day 16) were not modified by Zn supplementation in cows with adequate plasma Zn concentration. Zinc supplementation in Zn-deficient cows increased ACL with respect to controls (P = 0.048) but did not modify plasma E2 concentration. Pregnancy rate on day 41 after FTAI was higher in cows supplemented with Zn compared with controls (80.95% and 51.61%, respectively; P = 0.042). Plasma Zn and Cu concentrations on days 7, 9, and 16 were not affected by Zn supplementation. In conclusion, the results obtained in the present study determined that parenteral Zn supplementation at the beginning of the FTAI protocol increased preovulatory follicle size, plasma P4 concentration, and pregnancy rates in beef cows.

Ligand-independent activation of the P2X7 receptor by Hsp90 inhibition stimulates motor neuron apoptosis

Activation of the extracellular ATP ionotropic receptor P2X7 stimulates motor neuron apoptosis, whereas its inhibition in cell and animal models of amyotrophic lateral sclerosis can be protective. These observations suggest that P2X7 receptor activation is relevant to motor neuron disease and that it could be targeted for therapeutic development. Heat shock protein 90 (Hsp90) is an integral regulatory component of the P2X7 receptor complex, antagonizing ligand-induced receptor activation. Here, we show that the repressive activity of Hsp90 on P2X7 receptor activation in primary motor neurons is highly sensitive to inhibition. Primary motor neurons in culture are 100-fold more sensitive to Hsp90 inhibition by geldanamycin than other neuronal populations. Pharmacological inhibition and down-regulation of the P2X7 receptor prevented motor neuron apoptosis triggered by Hsp90 inhibition, which occurred in the absence of extracellular ATP. These observations suggest that inhibition of a seemingly motor neuron specific pool of Hsp90 leads to ligand independent activation of P2X7 receptor and motor neuron death. Downstream of Hsp90 inhibition, P2X7 receptor activated the phosphatase and tensin homolog (TPEN), which in turn suppressed the pro-survival phosphatidyl inositol 3 kinase (PI3K)/Akt pathway, leading to Fas-dependent motor neuron apoptosis. Conditions altering the interaction between P2X7 receptor and Hsp90, such as recruitment of Hsp90 to other subcellular compartments under stress conditions, or nitration following oxidative stress can induce motor neuron death. These findings may have broad implications in neurodegenerative disorders, including amyotrophic lateral sclerosis, in which activation of P2X7 receptor may be involved in both autonomous and non-autonomous motor neurons death.

Equilibrium study of dried orange peel for its efficiency in removal of cupric ions from water

Excess of copper ion (>2 mg/L) in water is toxic to human beings and the ecosystem. Various water treatment technologies for copper remediation have been investigated in the past. Along with industrial effluents, Bordeaux mixture is also a noteworthy copper contamination source in the agricultural ecosystem. In our study, the biosorbent efficiency of dried orange peel was investigated through an environment-friendly process for the removal of cupric ions. Effects of pH, adsorbate concentration, adsorbent dosage, and temperature for the removal of Cu (II) were studied. Slightly acidic environment (pH = 6) was found to be optimum for removal of copper. The equilibrium data were well fitted with the Langmuir and Freundlich isotherms. The surface morphology of the adsorbent was studied using scanning electron microscope. Crystalline nonhomogenous surface was observed after copper adsorption. Desorption study indicated that 0.1N H₂SO₄ is the best eluent for the removal of adsorbed copper from the powdered dried orange peel.

Targeting Extracellular Cyclophilin A Reduces Neuroinflammation and Extends Survival in a Mouse Model of Amyotrophic Lateral Sclerosis

Neuroinflammation is a major hallmark of amyotrophic lateral sclerosis (ALS), which is currently untreatable. Several anti-inflammatory compounds have been evaluated in patients and in animal models of ALS, but have been proven disappointing in part because effective targets have not yet been identified. Cyclophilin A, also known as peptidylprolyl cis-/trans-isomerase A (PPIA), as a foldase is beneficial intracellularly, but extracellularly has detrimental functions. We found that extracellular PPIA is a mediator of neuroinflammation in ALS. It is a major inducer of matrix metalloproteinase 9 and is selectively toxic for motor neurons. High levels of PPIA were found in the CSF of SOD1^G93A mice and rats and sporadic ALS patients, suggesting that our findings may be relevant for familial and sporadic cases. A specific inhibitor of extracellular PPIA, MM218, given at symptom onset, rescued motor neurons and extended survival in the SOD1^G93A mouse model of familial ALS by 11 d. The treatment resulted in the polarization of glia toward a prohealing phenotype associated with reduced NF-κB activation, proinflammatory markers, endoplasmic reticulum stress, and insoluble phosphorylated TDP-43. Our results indicates that extracellular PPIA is a promising druggable target for ALS and support further studies to develop a therapy to arrest or slow the progression of the disease in patients.SIGNIFICANCE STATEMENT We provide evidence that extracellular cyclophilin A, also known as peptidylprolyl cis-/trans-isomerase A (PPIA), is a mediator of the neuroinflammatory reaction in amyotrophic lateral sclerosis (ALS) and is toxic for motor neurons. Supporting this, a specific extracellular PPIA inhibitor reduced neuroinflammation, rescued motor neurons, and extended survival in the SOD1^G93A mouse model of familial ALS. Our findings suggest selective pharmacological inhibition of extracellular PPIA as a novel therapeutic strategy, not only for SOD1-linked ALS, but possibly also for sporadic ALS. This approach aims to address the neuroinflammatory reaction that is a major hallmark of ALS. However, given the complexity of the disease, a combination of therapeutic approaches may be necessary.

Effect of metal accumulation-associated oxidative stress on the combined toxicity of quantum dots with Cu(2+) to Bacillus subtilis

Quantum dot (QD) nanoparticles can coexist with Cu(2+) in soil and can adsorb Cu(2+) entering into bacterial cells, thereby promoting cellular copper accumulation and enhancing the combined toxicity of these two chemicals. Toxicity test results on Bacillus subtilis showed that the addition of safe concentrations of MPA-CdTe QDs to Cu(2+) culture (levels under IC50 value) resulted in higher toxicity with about twofold reduction in cell viability and increased intracellular Cu content. ROS levels also increased by about 500%, and SOD activity was altered after QD addition. Treatment with Cu(2+) alone decreased the α-amylase activity of B. subtilis by 8%-35%. This finding was not affected by QD addition. Moreover, increased cellular copper concentration as a result of QD addition enhanced toxicity primarily by producing superoxide anions. However, this phenomenon did not interrupt the physical-biological responses of soil microbes.

Nitration of Hsp90 on Tyrosine 33 Regulates Mitochondrial Metabolism

Peroxynitrite production and tyrosine nitration are present in several pathological conditions, including neurodegeneration, stroke, aging, and cancer. Nitration of the pro-survival chaperone heat shock protein 90 (Hsp90) in position 33 and 56 induces motor neuron death through a toxic gain-of-function. Here we show that nitrated Hsp90 regulates mitochondrial metabolism independently of the induction of cell death. In PC12 cells, a small fraction of nitrated Hsp90 was located on the mitochondrial outer membrane and down-regulated mitochondrial membrane potential, oxygen consumption, and ATP production. Neither endogenous Hsp90 present in the homogenate nor unmodified and fully active recombinant Hsp90 was able to compete with the nitrated protein for the binding to mitochondria. Moreover, endogenous or recombinant Hsp90 did not prevent the decrease in mitochondrial activity but supported nitrated Hsp90 mitochondrial gain-of-function. Nitrotyrosine in position 33, but not in any of the other four tyrosine residues prone to nitration in Hsp90, was sufficient to down-regulate mitochondrial activity. Thus, in addition to induction of cell death, nitrated Hsp90 can also regulate mitochondrial metabolism, suggesting that depending on the cell type, distinct Hsp90 nitration states regulate different aspects of cellular metabolism. This regulation of mitochondrial homeostasis by nitrated Hsp90 could be of particular relevance in cancer cells.

Metal-deficient SOD1 in amyotrophic lateral sclerosis

Mutations to the ubiquitous antioxidant enzyme Cu/Zn superoxide dismutase (SOD1) were the first established genetic cause of the fatal, adult-onset neurodegenerative disease amyotrophic lateral sclerosis (ALS). It is widely accepted that these mutations do not cause ALS via a loss of antioxidant function, but elucidating the alternate toxic gain of function has proven to be elusive. Under physiological conditions, SOD1 binds one copper ion and one zinc ion per monomer to form a highly stable and functional homodimer, but there is now ample evidence to indicate aberrant persistence of SOD1 in an intermediate metal-deficient state may contribute to the protein’s involvement in ALS. This review briefly discusses some of the data to support a role for metal-deficient SOD1 in the development of ALS and some of the outcomes from drug development studies that have aimed to modify the symptoms of ALS by targeting the metal state of SOD1. The implications for the metal state of SOD1 in cases of sporadic ALS that do not involve mutant SOD1 are also discussed.

The importance of having zinc during in vitro maturation of cattle cumulus-oocyte complex: role of cumulus cells

The aim of this study was to investigate the influence of zinc (Zn) on the health of cumulus-oocyte complex (COC) during in vitro maturation (IVM). Experiments were designed to evaluate the effect of Zn added to IVM medium on: DNA integrity, apoptosis, cumulus expansion and superoxide dismutase (SOD) activity of cumulus cells (CC). Also, role of CC on Zn transport during IVM was evaluated on oocyte developmental capacity. DNA damage and early apoptosis were higher in CC matured with 0 μg/ml Zn compared with 0.7, 1.1 and 1.5 μg/ml Zn (p < 0.05). Cumulus expansion did not show differences in COC matured with or without Zn supplementation (p > 0.05). Superoxide dismutase activity was higher in COC matured with 1.5 μg/ml Zn than with 0 μg/ml Zn (p < 0.05). Cleavage and blastocyst rates were recorded after IVM in three maturation systems: intact COCs, denuded oocytes with cumulus cells monolayer (DO + CC) and denuded oocytes (DO). Cleavage rates were similar when COC, DO + CC or DO were matured with 1.5 μg/ml Zn compared with control group (p > 0.05). Blastocyst rates were significantly higher in COC than in DO + CC and DO with the addition of 1.5 μg/ml Zn during IVM (p < 0.01). Blastocyst quality was enhanced in COC and DO + CC compared with DO when Zn was added to IVM medium (p < 0.001). The results of this study indicate that Zn supplementation to IVM medium (i) decreased DNA damage and apoptosis in CC; (ii) increased SOD activity in CC; (iii) did not modify cumulus expansion and cleavage rates after in vitro fertilization; (iv) improved subsequent embryo development up to blastocyst stage; and (v) enhanced blastocyst quality when CC were present either in intact COC or in coculture during IVM.

Oral treatment with Cu(II)(atsm) increases mutant SOD1 in vivo but protects motor neurons and improves the phenotype of a transgenic mouse model of amyotrophic lateral sclerosis

Mutations in the metallo-protein Cu/Zn-superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS) in humans and an expression level-dependent phenotype in transgenic rodents. We show that oral treatment with the therapeutic agent diacetyl-bis(4-methylthiosemicarbazonato)copper(II) [Cu(II)(atsm)] increased the concentration of mutant SOD1 (SOD1G37R) in ALS model mice, but paradoxically improved locomotor function and survival of the mice. To determine why the mice with increased levels of mutant SOD1 had an improved phenotype, we analyzed tissues by mass spectrometry. These analyses revealed most SOD1 in the spinal cord tissue of the SOD1G37R mice was Cu deficient. Treating with Cu(II)(atsm) decreased the pool of Cu-deficient SOD1 and increased the pool of fully metallated (holo) SOD1. Tracking isotopically enriched (65)Cu(II)(atsm) confirmed the increase in holo-SOD1 involved transfer of Cu from Cu(II)(atsm) to SOD1, suggesting the improved locomotor function and survival of the Cu(II)(atsm)-treated SOD1G37R mice involved, at least in part, the ability of the compound to improve the Cu content of the mutant SOD1. This was supported by improved survival of SOD1G37R mice that expressed the human gene for the Cu uptake protein CTR1. Improving the metal content of mutant SOD1 in vivo with Cu(II)(atsm) did not decrease levels of misfolded SOD1. These outcomes indicate the metal content of SOD1 may be a greater determinant of the toxicity of the protein in mutant SOD1-associated forms of ALS than the mutations themselves. Improving the metal content of SOD1 therefore represents a valid therapeutic strategy for treating ALS caused by SOD1.

Metalloporphyrins as therapeutic catalytic oxidoreductants in central nervous system disorders

SIGNIFICANCE

Metalloporphyrins, characterized by a redox-active transitional metal (Mn or Fe) coordinated to a cyclic porphyrin core ligand, mitigate oxidative/nitrosative stress in biological systems. Side-chain substitutions tune redox properties of metalloporphyrins to act as potent superoxide dismutase mimics, peroxynitrite decomposition catalysts, and redox regulators of transcription factor function. With oxidative/nitrosative stress central to pathogenesis of CNS injury, metalloporphyrins offer unique pharmacologic activity to improve the course of disease.

RECENT ADVANCES

Metalloporphyrins are efficacious in models of amyotrophic lateral sclerosis, Alzheimer's disease, epilepsy, neuropathic pain, opioid tolerance, Parkinson's disease, spinal cord injury, and stroke and have proved to be useful tools in defining roles of superoxide, nitric oxide, and peroxynitrite in disease progression. The most substantive recent advance has been the synthesis of lipophilic metalloporphyrins offering improved blood-brain barrier penetration to allow intravenous, subcutaneous, or oral treatment.

CRITICAL ISSUES

Insufficient preclinical data have accumulated to enable clinical development of metalloporphyrins for any single indication. An improved definition of mechanisms of action will facilitate preclinical modeling to define and validate optimal dosing strategies to enable appropriate clinical trial design. Due to previous failures of "antioxidants" in clinical trials, with most having markedly less biologic activity and bioavailability than current-generation metalloporphyrins, a stigma against antioxidants has discouraged the development of metalloporphyrins as CNS therapeutics, despite the consistent definition of efficacy in a wide array of CNS disorders.

FUTURE DIRECTIONS

Further definition of the metalloporphyrin mechanism of action, side-by-side comparison with "failed" antioxidants, and intense effort to optimize therapeutic dosing strategies are required to inform and encourage clinical trial design.

In vivo detection of free radicals using molecular MRI and immuno-spin trapping in a mouse model for amyotrophic lateral sclerosis

Free radicals associated with oxidative stress play a major role in amyotrophic lateral sclerosis (ALS). By combining immuno-spin trapping and molecular magnetic resonance imaging, in vivo trapped radical adducts were detected in the spinal cords of SOD1(G93A)-transgenic (Tg) mice, a model for ALS. For this study, the nitrone spin trap DMPO (5,5-dimethyl-1-pyrroline N-oxide) was administered (ip) over 5 days before administration (iv) of an anti-DMPO probe (anti-DMPO antibody covalently bound to an albumin-gadolinium-diethylenetriamine pentaacetic acid-biotin MRI contrast agent) to trap free radicals. MRI was used to detect the presence of the anti-DMPO radical adducts by a significant sustained increase in MR signal intensities (p < 0.05) or anti-DMPO probe concentrations measured from T₁ relaxations (p < 0.01). The biotin moiety of the anti-DMPO probe was targeted with fluorescence-labeled streptavidin to locate the probe in excised tissues. Negative controls included either Tg ALS mice initially administered saline rather than DMPO followed by the anti-DMPO probe or non-Tg mice initially administered DMPO and then the anti-DMPO probe. The anti-DMPO probe was found to bind to neurons via colocalization fluorescence microscopy. DMPO adducts were also confirmed in diseased/nondiseased tissues from animals administered DMPO. Apparent diffusion coefficients from diffusion-weighted images of spinal cords from Tg mice were significantly elevated (p < 0.001) compared to wild-type controls. This is the first report regarding the detection of in vivo trapped radical adducts in an ALS model. This novel, noninvasive, in vivo diagnostic method can be applied to investigate the involvement of free radical mechanisms in ALS rodent models.

Mitochondria in lung diseases

Mitochondria are autonomous cellular organelles that oversee a variety of functions such as metabolism, energy production, calcium buffering and cell fate determination. Regulation of their morphology and diverse activities beyond energy production are being recognized as playing major roles in cellular health and dysfunction. This review is aimed at summarizing what is known regarding mitochondrial contributions to pathogenesis of lung diseases. Emphasis is given to understanding the importance of structural and functional aspects of mitochondria in both normal cellular function (based on knowledge from other cell types) and in development and modulation of lung diseases such as asthma, chronic obstructive pulmonary disease, cystic fibrosis and cancer. Emerging techniques that allow examination of mitochondria, and potential strategies to target mitochondria in the treatment of lung diseases are also discussed.

P2X7 receptor-induced death of motor neurons by a peroxynitrite/FAS-dependent pathway

The P2X7 receptor/channel responds to extracellular ATP and is associated with neuronal death and neuroinflammation in spinal cord injury and amyotrophic lateral sclerosis. Whether activation of P2X7 directly causes motor neuron death is unknown. We found that cultured motor neurons isolated from embryonic rat spinal cord express P2X7 and underwent caspase-dependent apoptosis when exposed to exceptionally low concentrations of the P2X7 agonist 2'(3')-O-(4-Benzoylbenzoyl)-ATP. The P2X7 inhibitors BBG, oATP, and KN-62 prevented 2'(3')-O-(4-Benzoylbenzoyl)-ATP-induced motor neuron death. The endogenous P2X7 agonist ATP induced motor neuron death at low concentrations (1-100 μM). High concentrations of ATP (1 mM) paradoxically became protective due to degradation in the culture media to produce adenosine and activate adenosine receptors. P2X7-induced motor neuron death was dependent on neuronal nitric oxide synthase-mediated production of peroxynitrite, p38 activation, and autocrine FAS signaling. Taken together, our results indicate that motor neurons are highly sensitive to P2X7 activation, which triggers apoptosis by activation of the well-established peroxynitrite/FAS death pathway in motor neurons.

Nitration of Hsp90 induces cell death

Oxidative stress is a widely recognized cause of cell death associated with neurodegeneration, inflammation, and aging. Tyrosine nitration in these conditions has been reported extensively, but whether tyrosine nitration is a marker or plays a role in the cell-death processes was unknown. Here, we show that nitration of a single tyrosine residue on a small proportion of 90-kDa heat-shock protein (Hsp90), is sufficient to induce motor neuron death by the P2X7 receptor-dependent activation of the Fas pathway. Nitrotyrosine at position 33 or 56 stimulates a toxic gain of function that turns Hsp90 into a toxic protein. Using an antibody that recognizes the nitrated Hsp90, we found immunoreactivity in motor neurons of patients with amyotrophic lateral sclerosis, in an animal model of amyotrophic lateral sclerosis, and after experimental spinal cord injury. Our findings reveal that cell death can be triggered by nitration of a single protein and highlight nitrated Hsp90 as a potential target for the development of effective therapies for a large number of pathologies.

Molecular signatures of amyotrophic lateral sclerosis disease progression in hind and forelimb muscles of an SOD1(G93A) mouse model

AIMS

This study utilized proteomics, biochemical and enzymatic assays, and bioinformatics tools that characterize protein alterations in hindlimb (gastrocnemius) and forelimb (triceps) muscles in an amyotrophic lateral sclerosis (ALS) (SOD1(G93A)) mouse model. The aim of this study was to identify the key molecular signatures involved in disease progression.

RESULTS

Both muscle types have in common an early down-regulation of complex I. In the hindlimb, early increases in oxidative metabolism are associated with uncoupling of the respiratory chain, an imbalance of NADH/NAD(+), and an increase in reactive oxygen species (ROS) production. The NADH overflow due to complex I inactivation induces TCA flux perturbations, leading to citrate production, triggering fatty acid synthase (FAS), and lipid peroxidation. These early metabolic changes in the hindlimb followed by sustained and comparatively higher metabolic and cytoskeletal derangements over time precede and may catalyze the progressive muscle wasting in this muscle at the late stage. By contrast, in the forelimb, there is an early down-regulation of complexes I and II that is associated with the reduction of oxidative metabolism, which promotes metabolic homeostasis that is accompanied by a greater cytoskeletal stabilization response. However, these early compensatory systems diminish by a later time point.

INNOVATION

The identification of potential early- and late-stage disease molecular signatures in an ALS model: muscle albumin, complex I, complex II, citrate synthase, FAS, and phosphoinositide 3-kinase functions as diagnostic markers and peroxisome proliferator-activated receptor γ co-activator 1α (PGC1α), Sema-3A, and Rho-associated protein kinase 1 (ROCK1) play the role of disease progression markers.

CONCLUSION

The differing pattern of cellular metabolism and cytoskeletal derangements in the hind and forelimb identifies the potential dysmetabolism/hypermetabolism molecular signatures associated with disease progression, which may serve as diagnostic/disease progression markers in ALS patients.

Mutant SOD1G93A triggers mitochondrial fragmentation in spinal cord motor neurons: neuroprotection by SIRT3 and PGC-1α

Mutations in the Cu/Zn Superoxide Dismutase (SOD1) gene cause an inherited form of ALS with upper and lower motor neuron loss. The mechanism underlying mutant SOD1-mediated motor neuron degeneration remains unclear. While defects in mitochondrial dynamics contribute to neurodegeneration, including ALS, previous reports remain conflicted. Here, we report an improved technique to isolate, transfect, and culture rat spinal cord motor neurons. Using this improved system, we demonstrate that mutant SOD1(G93A) triggers a significant decrease in mitochondrial length and an accumulation of round fragmented mitochondria. The increase of fragmented mitochondria coincides with an arrest in both anterograde and retrograde axonal transport and increased cell death. In addition, mutant SOD1(G93A) induces a reduction in neurite length and branching that is accompanied with an abnormal accumulation of round mitochondria in growth cones. Furthermore, restoration of the mitochondrial fission and fusion balance by dominant-negative dynamin-related protein 1 (DRP1) expression rescues the mutant SOD1(G93A)-induced defects in mitochondrial morphology, dynamics, and cell viability. Interestingly, both SIRT3 and PGC-1α protect against mitochondrial fragmentation and neuronal cell death by mutant SOD1(G93A). This data suggests that impairment in mitochondrial dynamics participates in ALS and restoring this defect might provide protection against mutant SOD1(G93A)-induced neuronal injury.

Nitric oxide-mediated oxidative damage and the progressive demise of motor neurons in ALS

Oxidative damage is a common and early feature of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS), and other neurodegenerative disorders. Dr. Mark Smith and his colleagues have built the case for oxidative stress being a primary progenitor rather than a secondary end-stage epiphenomenon of neurodegeneration. They proposed that reactive oxygen species contribute to the "age-related cascade of neurodegeneration," whereby accumulative oxidative damage with age promotes other characteristic pathological changes in afflicted brain regions, including protein aggregation, metabolic deficiencies, and inflammation. Nitric oxide (NO) likely plays a critical role in this age-related cascade. NO is a major signaling molecule produced in the central nervous system to modulate neurological activity through stimulating cyclic GMP synthesis. However, the same physiological concentrations of NO, relevant in cellular signaling, may also initiate and amplify oxidative damage by diffusion-limited reactions with superoxide (O(2)(•-)) to produce peroxynitrite (ONOO(-)). This is perhaps best illustrated in ALS where physiological levels of NO promote survival of motor neurons, but the same concentrations can stimulate motor neuron apoptosis and glial cell activation under pathological conditions. While these changes represent a complex mechanism involving multiple cell types in the pathogenesis of ALS, they also reveal general processes underlying neurodegeneration.

Structural analysis and molecular modelling of the Cu/Zn-SOD from fungal strain Humicola lutea 103

The native form of Cu/Zn-superoxide dismutase, isolated from fungal strain Humicola lutea 103 is a homodimer that coordinates one Cu(2+) and one Zn(2+) per monomer. Cu(2+) and Zn(2+) ions play crucial roles in enzyme activity and structural stability, respectively. It was established that HLSOD shows high pH and temperature stability. Thermostability of the glycosylated enzyme Cu/Zn-SOD, isolated from fungal strain H. lutea 103, was determined by CD spectroscopy. Determination of reversibility toward thermal denaturation for HLSOD allowed several thermodynamic parameters to be calculated. In this communication we report the conditions under which reversible denaturation of HLSOD exists. The narrow range over which the system is reversible has been determined using the strongest test of two important thermodynamic independent variables (T and pH). Combining both these variables, the "phase diagram" was determined, as a result of which the real thermodynamic parameters (ΔC(p), ΔH(exp)°, and ΔG(exp)°) was established. Because very narrow pH-interval of transitions we assume they are as result of overlapping of two simple transitions. It was found that ΔH(o) is independent from pH with a value of 1.3 kcal/mol and 2.8 kcal/mol for the first and the second transition, respectively. ΔG(o) was pH-dependent in all studied pH-interval. This means that the transitions are entropically driven, these. Based on this, these processes can be described as hydrophobic rearrangement of the quaternary structure. It was also found that glycosylation does not influence the stability of the enzyme because the carbohydrate chain is exposed on the surface of the molecule.

Diapocynin and apocynin administration fails to significantly extend survival in G93A SOD1 ALS mice

NADPH oxidase has recently been identified as a promising new therapeutic target in ALS. Genetic deletion of NADPH oxidase (Nox2) in the transgenic SOD1(G93A) mutant mouse model of ALS was reported to increase survival remarkably by 97 days. Furthermore, apocynin, a widely used inhibitor of NADPH oxidase, was observed to dramatically extend the survival of the SOD1(G93A) ALS mice even longer to 113 days (Harraz et al. J Clin Invest 118: 474, 2008). Diapocynin, the covalent dimer of apocynin, has been reported to be a more potent inhibitor of NADPH oxidase. We compared the protection of diapocynin to apocynin in primary cultures of SOD1(G93A)-expressing motor neurons against nitric oxide-mediated death. Diapocynin, 10 μM, provided significantly greater protection compared to apocynin, 200 μM, at the lowest statistically significant concentrations. However, administration of diapocynin starting at 21 days of age in the SOD1(G93A)-ALS mouse model did not extend lifespan. Repeated parallel experiments with apocynin failed to yield protection greater than a 5-day life extension in multiple trials conducted at two separate institutions. The maximum protection observed was an 8-day extension in survival when diapocynin was administered at 100 days of age at disease onset. HPLC with selective ion monitoring by mass spectrometry revealed that both apocynin and diapocynin accumulated in the brain and spinal cord tissue to low micromolar concentrations. Diapocynin was also detected in the CNS of apocynin-treated mice. The failure to achieve significant protection with either apocynin or diapocynin raises questions about the utility for treating ALS patients.

Biochemical properties and in vivo effects of the SOD1 zinc-binding site mutant (H80G)

This study presents the initial characterization of transgenic mice with mutations in a primary zinc-binding residue (H80), either alone or with a G93A mutation. H80G;G93A superoxide dismutase 1 (SOD1) transgenic mice developed paralysis with motor neuron loss, and ubiquitin inclusion-type rather than mitochondrial vacuolar pathology. Unlike G93A SOD1-related disease, the course was not accelerated by over-expression of copper chaperone for SOD1. H80G SOD1 transgenic mice did not manifest disease at levels of SOD1 transgene expressed. The H80G mutation altered certain biochemical parameters of both human wild-type SOD1 and G93A SOD1. The H80G mutation does not substantially change the age-dependent accumulation of G93A SOD1 aggregates and hydrophobic species in spinal cord. However, both H80G;G93A SOD1 and H80G SOD1 lack dismutase activity, the ability to form homodimers, and co-operativity with copper chaperone for SOD1, indicating that their dimerization interface is abnormal. The H80G mutation also made SOD1 susceptible to protease digestion. The H80G mutation alters the redox properties of SOD1. G93A SOD1 exists in either reduced or oxidized form, whereas H80G;G93A SOD1 and H80G SOD1 exist only in a reduced state. The inability of SOD1 with an H80G mutation to take part in normal oxidation-reduction reactions has important ramifications for disease mechanisms and pathology in vivo.

Measuring copper and zinc superoxide dismutase from spinal cord tissue using electrospray mass spectrometry

Metals are key cofactors for many proteins, yet quantifying the metals bound to specific proteins is a persistent challenge in vivo. We have developed a rapid and sensitive method using electrospray ionization mass spectrometry to measure Cu,Zn superoxide dismutase (SOD1) directly from the spinal cord of SOD1-overexpressing transgenic rats. Metal dyshomeostasis has been implicated in motor neuron death in amyotrophic lateral sclerosis (ALS). Using the assay, SOD1 was directly measured from 100 μg of spinal cord, allowing for anatomical quantitation of apo, metal-deficient, and holo SOD1. SOD1 was bound on a C(4) Ziptip that served as a disposable column, removing interference by physiological salts and lipids. SOD1 was eluted with 30% acetonitrile plus 100 μM formic acid to provide sufficient hydrogen ions to ionize the protein without dislodging metals. SOD1 was quantified by including bovine SOD1 as an internal standard. SOD1 could be measured in subpicomole amounts and resolved to within 2 Da of the predicted parent mass. The methods can be adapted to quantify modifications to other proteins in vivo that can be resolved by mass spectrometry.

Copper and zinc metallation status of copper-zinc superoxide dismutase from amyotrophic lateral sclerosis transgenic mice

Mutations in the metalloenzyme copper-zinc superoxide dismutase (SOD1) cause one form of familial amyotrophic lateral sclerosis (ALS), and metals are suspected to play a pivotal role in ALS pathology. To learn more about metals in ALS, we determined the metallation states of human wild-type or mutant (G37R, G93A, and H46R/H48Q) SOD1 proteins from SOD1-ALS transgenic mice spinal cords. SOD1 was gently extracted from spinal cord and separated into insoluble (aggregated) and soluble (supernatant) fractions, and then metallation states were determined by HPLC inductively coupled plasma MS. Insoluble SOD1-rich fractions were not enriched in copper and zinc. However, the soluble mutant and WT SOD1s were highly metallated except for the metal-binding-region mutant H46R/H48Q, which did not bind any copper. Due to the stability conferred by high metallation of G37R and G93A, it is unlikely that these soluble SOD1s are prone to aggregation in vivo, supporting the hypothesis that immature nascent SOD1 is the substrate for aggregation. We also investigated the effect of SOD1 overexpression and disease on metal homeostasis in spinal cord cross-sections of SOD1-ALS mice using synchrotron-based x-ray fluorescence microscopy. In each mouse genotype, except for the H46R/H48Q mouse, we found a redistribution of copper between gray and white matters correlated to areas of high SOD1. Interestingly, a disease-specific increase of zinc was observed in the white matter for all mutant SOD1 mice. Together these data provide a picture of copper and zinc in the cell as well as highlight the importance of these metals in understanding SOD1-ALS pathology.