Nickel (II) complexes of histidyl-peptides as Fenton-reaction catalysts

Role of endolysosome function in iron metabolism and brain carcinogenesis

Iron, the most abundant metal in human brain, is an essential microelement that regulates numerous cellular mechanisms. Some key physiological roles of iron include oxidative phosphorylation and ATP production, embryonic neuronal development, formation of iron-sulfur clusters, and the regulation of enzymes involved in DNA synthesis and repair. Because of its physiological and pathological importance, iron homeostasis must be tightly regulated by balancing its uptake, transport, and storage. Endosomes and lysosomes (endolysosomes) are acidic organelles known to contain readily releasable stores of various cations including iron and other metals. Increased levels of ferrous (Fe2+) iron can generate reactive oxygen species (ROS) via Fenton chemistry reactions and these increases can damage mitochondria and genomic DNA as well as promote carcinogenesis. Accumulation of iron in the brain has been linked with aging, diet, disease, and cerebral hemorrhage. Further, deregulation of brain iron metabolism has been implicated in carcinogenesis and may be a contributing factor to the increased incidence of brain tumors around the world. Here, we provide insight into mechanisms by which iron accumulation in endolysosomes is altered by pH and lysosome membrane permeabilization. Such events generate excess ROS resulting in mitochondrial DNA damage, fission, and dysfunction, as well as DNA oxidative damage in the nucleus; all of which promote carcinogenesis. A better understanding of the roles that endolysosome iron plays in carcinogenesis may help better inform the development of strategic therapeutic options for cancer treatment and prevention.

Risk Assessment of Oxidative Stress Induced by Metal Ions Released from Fixed Orthodontic Appliances during Treatment and Indications for Supportive Antioxidant Therapy: A Narrative Review

The treatment with fixed orthodontic appliances could have an important role in the induction of oxidative stress and associated negative consequences. Because of the simultaneous effects of corrosion, deformation, friction, and mechanical stress on fixed orthodontic appliances during treatment, degradation of orthodontic brackets and archwires occurs, causing higher concentrations of metal ions in the oral cavity. Corroded appliances cause the release of metal ions, which may lead to the increased values of reactive oxygen species (ROS) due to metal-catalyzed free radical reactions. Chromium, iron, nickel, cobalt, titanium, and molybdenum all belong to the group of transition metals that can be subjected to redox reactions to form ROS. The estimation of health risk due to the amount of heavy metals released and the level of selected parameters of oxidative stress generated for the time of treatment with fixed orthodontic appliances is presented. Approaches to avoid oxidative stress and recommendations for the preventive use of topical or systemic antioxidants during orthodontic treatment are discussed.

Investigation of inflammation inducing substances in PM2.5 particles by an elimination method using thermal decomposition

The substances associated with PM2.5-induced inflammatory response were investigated using an elimination method. PM2.5 were heated at temperatures of 120, 250, and 360°C. The results demonstrated microbial substances such as LPS and b-glucan, and chemicals including BaP, 1,2-NQ, and 9,10-PQ were reduced drastically in PM2.5 heated at 120°C. On the other hand, DBA, 7,12-BAQ, and BaP-1,6-Q were not noticeably reduced. Most of these substances had disappeared in PM2.5 heated at 250°C and 360°C. Metals (eg, Fe, Cu, Cr, Ni) in PM2.5 exhibited a slight thermo-dependent increase. RAW264.7 macrophages with or without NAC were exposed to unheated PM2.5, oxidative stress-related and unrelated inflammatory responses were induced. PM2.5-induced lung inflammation in mice is caused mainly by thermo-sensitive substances (LPS, b-glucan, BaP, 1,2-NQ, 9,10-PQ, etc.). Also, a slight involvement of thermo-resistant substances (DBA, 7,12-BAQ, BaP-1,6-Q, etc.) and transition metals was observed. The thermal decomposition method could assist to evaluate the PM2.5-induded lung inflammation.

Biogenic Fenton-like Reaction Involvement in Cometabolic Degradation of Tetrabromobisphenol A by Pseudomonas sp. fz

Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant (BFR) that has frequently been detected in various environmental compartments. Although TBBPA biotransformation has been observed under both aerobic and anaerobic conditions, knowledge of the detailed mechanism of direct aerobic TBBPA biodegradation still remains limited. In this study, the underlying mechanism of cometabolic degradation of TBBPA by Pseudomonas sp. fz under aerobic conditions was investigated. Two key degradation pathways (beta scission and debromination) were proposed based on triple quadrupole liquid chromatography-mass spectrometry (LC-MS) analysis. TBBPA degradation by strain fz was demonstrated to be an extracellular process associated with the low-molecular-mass component (LMMC). Moreover, LMMC was preliminarily identified as oligopeptides, mainly consisting of glycine, proline, and alanine in a 2:1:1 molar ratio. Quenching studies suggested the involvement of hydroxyl radicals ((•)OH) in extracellular TBBPA degradation. To the best of our knowledge, we provide the first evidence that TBBPA was degraded by a biogenic Fenton-like reaction mediated via extracellular H2O2 and Fe(II)-oligopeptide complexes by the genus Pseudomonas. This study provides a new insight into the fate and biodegradation of TBBPA and other organic pollutants in natural and artificial bioremediation environments.

The neuroprotective effects of taurine against nickel by reducing oxidative stress and maintaining mitochondrial function in cortical neurons

Previous studies have indicated that oxidative stress and mitochondrial dysfunction are involved in the toxicity of nickel. Taurine is recognized as an efficient antioxidant and is essential for mitochondrial function. To investigate whether taurine could protect against the neurotoxicity of nickel, we exposed primary cultured cortical neurons to various concentrations of nickel chloride (NiCl2; 0.5mM, 1mM and 2mM) for 24h or to 1mM NiCl2 for various periods (0 h, 12h, 24h and 48 h). Our results showed that taurine efficiently reduced lactate dehydrogenase (LDH) release induced by NiCl2. Along with this protective effect, taurine pretreatment not only significantly reversed the increase of ROS production and mitochondrial superoxide concentration, but also attenuated the decrease of superoxide dismutase (SOD) activity and glutathione (GSH) concentration in neurons exposed to NiCl2 for 24h. Moreover, nickel exposure reduced ATP production, disrupted the mitochondrial membrane potential and decreased mtDNA content. These types of oxidative damage in the mitochondria were efficiently ameliorated by taurine pretreatment. Taken together, our results indicate that the neuroprotective effects of taurine against the toxicity of nickel might largely depend on its roles in reducing oxidative stress and improving mitochondrial function. Taurine may have great pharmacological potential in treating the adverse effects of nickel in the nervous system.

Melatonin protects against Nickel-induced neurotoxicity in vitro by reducing oxidative stress and maintaining mitochondrial function

Nickel is a potential neurotoxic pollutant. Oxidative stress is supposed to be involved in the mechanism underlying nickel-induced neurotoxicity. Melatonin has efficient protective effects against various oxidative damages in nervous system. The purpose of this study was to investigate whether melatonin could efficiently protect against neurotoxicity induced by nickel. Here, we exposed primary cultured cortical neurons and mouse neuroblastoma cell lines (neuro2a) to different concentrations of nickel chloride (NiCl(2)) (0.125, 0.25, 0.5, and 1 mm) for 12 hr or 0.5 mm NiCl(2) for various periods (0, 3, 6, 12, and 24 hr). We found that nickel significantly increased reactive oxygen species production and caused the loss of cell viability both in cortical neurons and neuro2a cells. In addition, nickel exposure obviously inhibited the mitochondrial function, disrupted the mitochondrial membrane potential (DeltaPsim), reduced ATP production, and decreased mitochondrial DNA (mtDNA) content. However, each of these oxidative damages was efficiently attenuated by melatonin pretreatment. These protective effects of melatonin may be attributable to its roles in reducing oxidative stress and improving mitochondrial function in nickel-treated nerve cells. Our results suggested that melatonin may have great pharmacological potential in protecting against the adverse effects of nickel in the nervous system.

Compositional complementarity and prebiotic ecology in the origin of life

We hypothesize that life began not with the first self-reproducing molecule or metabolic network, but as a prebiotic ecology of co-evolving populations of macromolecular aggregates (composomes). Each composome species had a particular molecular composition resulting from molecular complementarity among environmentally available prebiotic compounds. Natural selection acted on composomal species that varied in properties and functions such as stability, catalysis, fission, fusion and selective accumulation of molecules from solution. Fission permitted molecular replication based on composition rather than linear structure, while fusion created composomal variability. Catalytic functions provided additional chemical novelty resulting eventually in autocatalytic and mutually catalytic networks within composomal species. Composomal autocatalysis and interdependence allowed the Darwinian co-evolution of content and control (metabolism). The existence of chemical interfaces within complex composomes created linear templates upon which self-reproducing molecules (such as RNA) could be synthesized, permitting the evolution of informational replication by molecular templating. Mathematical and experimental tests are proposed.

Metal resistance in yeast mediated by the expression of a maize 20S proteasome alpha subunit

Transformation of yeast cells with a maize cDNA ZmPAA, encoding a 20S proteasome alpha-subunit, conferred resistance to nickel, cadmium and cobalt. This resistance is not linked to a modification of the intracellular nickel content, as no accumulation of nickel was measured between yeast cells transformed with a void vector or the ZmPAA cDNA. The abundance of the ZmPAA mRNA was increased in the shoots of maize plants upon nickel treatment. These results suggest that the proteasome might be involved in nickel resistance by scavenging metal oxidized proteins both in plants and yeast.

Detection of tandem CC-->TT mutations induced by oxygen radicals using mutation-specific PCR

DNA lesions caused by reactive oxygen species (ROS) are considered to be one of the major contributors to DNA damage and mutagenesis. In this study, we developed a modification of allele-specific PCR to detect CC-->TT mutations caused by oxidative damage. These tandem mutations have been previously demonstrated to be indicative of oxygen damage in the absence of UV-irradiation. Using a CC target site in the rat DNA polymerase beta (pol beta) gene and a thermostable restriction enzyme that cuts the wild type sequence but not the TT mutation, we demonstrate that the TT mutation can be preferentially amplified from plasmid DNA damaged by oxygen radicals but not other DNA-damaging agents. We evaluated the potential utility of this assay in screening for mutations in cells and in analyzing those that arise during clonal proliferation in carcinogenesis.

Hydrogen Peroxide Bleaching of Amaranth Catalysed by Nickel(II) Nitrilotriacetic Acid

The complex of NiII with nitrilotriacetic acid (NTA) (but not other aminocarboxylate complexes) autocatalyses the hydrogen peroxide bleaching of amaranth, although the reaction is inhibited by the absence of light or presence of alcohol, suggesting a radical-based mechanism.

Nickel-catalyzed N-terminal oxidative deamination in peptides containing histidine at position 2 coupled with sulfite oxidation

Peptides containing histidine at position 2 were observed to undergo spontaneous N-terminal oxidative deamination in aqueous solution in the presence of Ni(II), sulfite, and ambient oxygen. The reaction resulted in the formation of a free carbonyl on the N-terminal alpha-carbon (alpha-ketoamide) and was catalytic with respect to nickel. This oxidative deamination was confirmed by 13C NMR, 1H NMR, mass spectrometry, and chemical tests. No evidence of modification of histidine was found. It was demonstrated that the nickel-dependent N-terminal oxidative deamination also occurred in His-2 peptides using potassium peroxymonosulfate (oxone) as an oxidant. When oxone was used, oxygen was not required for the deamination to proceed. The results suggest that both nickel-catalyzed reactions (sulfite and oxygen, and oxone) produce an imine intermediate that spontaneously hydrolyzes to form the free carbonyl. These findings may provide a physiologically relevant model for oxidative carbonyl formation in vivo, as well as a useful method for producing a site-specific carbonyl on peptides and proteins.

Identification of a nickel(II) binding site on hemoglobin which confers susceptibility to oxidative deamination and intramolecular cross-linking

Complexation of Ni(II) with native state recombinant hemoglobin is shown to produce NH2-terminal deamination and globin cross-linking in the presence of the oxidant potassium peroxymonosulfate (OxoneTM). Both the oxidative deamination and cross-linking are exclusive to the beta chains. Recombinant hemoglobin mutants have been created to identify protein sequence requirements for these reactions. It was found that His-2 of the beta globin is required for redox active Ni(II) complexation, oxidative deamination, and cross-linking. The oxidative deamination results in the formation of a free carbonyl in place of the NH2-terminal amine of the beta chain. Most cross-linking of the beta globin occurs intramolecularly, forming beta globin dimers. Structural characterization of the beta globin dimers indicates the presence of heterogeneous cross-links within the central hemoglobin cavity between the NH2 terminus of one beta chain and the COOH-terminal region of the other.