Comparative analysis of hydrogen peroxide and peroxynitrite reactivity with thiols

Peroxides are chemical compounds in which two oxygen atoms are linked together by a single covalent bond. Hydrogen peroxide (H2O2), the simplest peroxide, is formed through different routes in biological systems: superoxide radical (O2•-) dismutation, which can be spontaneous, or, depending on the organism and cellular compartment, catalyzed by different superoxide dismutases (SODs); one-electron O2•- reduction, such as during aconitase oxidation; or direct two-electron reduction of oxygen, which can be catalyzed by the divalent activity of several oxidases, including xanthine oxidase, Ero1, aldehyde oxidase, and monoamine oxidase. Depending on the cell type, those sites could be mitochondria, phagosomes of inflammatory cells, as well as the extracellular space. In biological systems, thiol functional groups can be found as part of low-molecular-weight (LMW) compounds and in protein Cys residues. Most living organisms contain millimolar concentrations of LMW thiols that play biological functions, such as to keep an intracellular reducing environment, to provide electrons for redox enzymes, and to react with electrophilic compounds.Fil: Trujillo, Madia. Universidad de la República de Uruguay; UruguayFil: Carballal, Sebastian. Universidad de la República de Uruguay; UruguayFil: Zeida Camacho, Ari Fernando. Universidad de la República de Uruguay; Uruguay. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Radi, Rafael. Universidad de la República de Uruguay; Urugua

Mechanism of the Reaction of Peroxynitrite with Mn-Superoxide Dismutase: Nitration of Critical Tyrosine-34

Manganese superoxide dismutase (MnSOD) is an antioxidantenzyme that acts as a superoxide detoxifier. Superoxide can reactwith nitric oxide to lead peroxynitrite and this reaction, that takesplace at near diffusion limited rates, can compete with MnSOD forsuperoxide. One of the most important bio-markers forperoxynitrite formation in vivo is tyrosine nitration, a posttranslationalmodification that can alter both the structure andfunction of a protein.Fil: Demicheli, Veronica. Centro de Investigaciones Biomédicas; UruguayFil: Moreno, Diego Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Jara, Gabriel Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Carballal, Sebastian. Centro de Investigaciones Biomédicas; UruguayFil: Quijano, Celia. Centro de Investigaciones Biomédicas; UruguayFil: Ferrer Sueta, Gerardo. Centro de Investigaciones Biomédicas; UruguayFil: Rios, Natalia. Centro de Investigaciones Biomédicas; UruguayFil: Estrin, Dario Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Marti, Marcelo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Radi, Rafael. Centro de Investigaciones Biomédicas; Urugua

Rational design of superoxide dismutase (sod) mimics: The evaluation of the therapeutic potential of new cationic Mn porphyrins with linear and cyclic substituents

Our goal herein has been to gain further insight into the parameters which control porphyrin therapeutic potential. Mn porphyrins (MnTnOct-2-PyP5+, MnTnHexOE-2-PyP5+, MnTE-2-PyPhP5+, and MnTPhE-2-PyP5+) that bear the same positive charge and same number of carbon atoms at meso positions of porphyrin core were explored. The carbon atoms of their meso substituents are organized to form either linear or cyclic structures of vastly different redox properties, bulkiness, and lipophilicities. These Mn porphyrins were compared to frequently studied compounds, MnTE-2-PyP5+, MnTE-3-PyP5+, and MnTBAP3-. All Mn(III) porphyrins (MnPs) have metal-centered reduction potential, E1/2 for MnIIIP/MnIIP redox couple, ranging from 194 to +340 mV versus NHE, log kcat(O2¢-) from 3.16 to 7.92, and log kred(ONOO-) from 5.02 to 7.53. The lipophilicity, expressed as partition between n-octanol and water, log POW, was in the range 1.67 to 7.67. The therapeutic potential of MnPs was assessed via: (i) in vitro ability to prevent spontaneous lipid peroxidation in rat brain homogenate as assessed by malondialdehyde levels; (ii) in vivo O2¢- specific assay to measure the efficacy in protecting the aerobic growth of SOD-deficient Saccharomyces cerevisiae; and (iii) aqueous solution chemistry to measure the reactivity toward major in vivo endogenous antioxidant, ascorbate. Under the conditions of lipid peroxidation assay, the transport across the cellular membranes, and in turn shape and size of molecule, played no significant role. Those MnPs of E1/2∼+300 mV were the most efficacious, significantly inhibiting lipid peroxidation in 0.5-10 M range. At up to 200 M, MnTBAP3- (E1/2 = 194 mV vs NHE) failed to inhibit lipid peroxidation, while MnTE-2-PyPhP5+ with 129 mV more positive E1/2 (65 mV vs NHE) was fully efficacious at 50 M. The E1/2 of MnIIIP/MnIIP redox couple is proportional to the log kcat(O2¢-), i.e., the SOD-like activity of MnPs. It is further proportional to kred(ONOO-) and the ability of MnPs to prevent lipid peroxidation. In turn, the inhibition of lipid peroxidation by MnPs is also proportional to their SOD-like activity. In an in vivo S. cerevisiae assay, however, while E1/2 predominates, lipophilicity significantly affects the efficacy of MnPs. MnPs of similar log POW and E1/2, that have linear alkyl or alkoxyalkyl pyridyl substituents, distribute more easily within a cell and in turn provide higher protection to S. cerevisiae in comparison to MnP with bulky cyclic substituents. The bell-shape curve, with MnTE-2-PyP5+ exhibiting the highest ability to catalyze ascorbate oxidation, has been established and discussed. Our data support the notion that the SOD-like activity of MnPs parallels their therapeutic potential, though species other than O2¢-, such as peroxynitrite, H2O2, lipid reactive species, and cellular reductants, may be involved in their mode(s) of action(s)

Rational Design of Superoxide Dismutase (SOD) Mimics: The Evaluation of the Therapeutic Potential of New Cationic Mn Porphyrins with Linear and Cyclic Substituents

Our goal herein has been to gain further insight into the parameters which control porphyrin therapeutic potential. Mn porphyrins (MnTnOct-2-PyP⁵⁺, MnTnHexOE-2-PyP⁵⁺, MnTE-2-PyPhP⁵⁺, and MnTPhE-2-PyP⁵⁺) that bear the same positive charge and same number of carbon atoms at <i>meso</i> positions of porphyrin core were explored. The carbon atoms of their <i>meso</i> substituents are organized to form either linear or cyclic structures of vastly different redox properties, bulkiness, and lipophilicities. These Mn porphyrins were compared to frequently studied compounds, MnTE-2-PyP⁵⁺, MnTE-3-PyP⁵⁺, and MnTBAP^3–. All Mn­(III) porphyrins (MnPs) have metal-centered reduction potential, <i>E</i>_1/2 for Mn^IIIP/Mn^IIP redox couple, ranging from −194 to +340 mV versus NHE, log <i>k</i>_cat(O₂^•–) from 3.16 to 7.92, and log <i>k</i>_red(ONOO^–) from 5.02 to 7.53. The lipophilicity, expressed as partition between n-octanol and water, log <i>P</i>_OW, was in the range −1.67 to −7.67. The therapeutic potential of MnPs was assessed via: (i) <i>in vitro</i> ability to prevent spontaneous lipid peroxidation in rat brain homogenate as assessed by malondialdehyde levels; (ii) <i>in vivo</i> O₂^•– specific assay to measure the efficacy in protecting the aerobic growth of SOD-deficient <i>Saccharomyces cerevisiae</i>; and (iii) aqueous solution chemistry to measure the reactivity toward major <i>in vivo</i> endogenous antioxidant, ascorbate. Under the conditions of lipid peroxidation assay, the transport across the cellular membranes, and in turn shape and size of molecule, played no significant role. Those MnPs of <i>E</i>_1/2 ∼ +300 mV were the most efficacious, significantly inhibiting lipid peroxidation in 0.5–10 μM range. At up to 200 μM, MnTBAP^3– (<i>E</i>_1/2 = −194 mV vs NHE) failed to inhibit lipid peroxidation, while MnTE-2-PyPhP⁵⁺ with 129 mV more positive <i>E</i>_1/2 (−65 mV vs NHE) was fully efficacious at 50 μM. The <i>E</i>_1/2 of Mn^IIIP/Mn^IIP redox couple is proportional to the log <i>k</i>_cat(O₂^•–), <i>i.e</i>., the SOD-like activity of MnPs. It is further proportional to <i>k</i>_<i>r</i>ed(ONOO^–) and the ability of MnPs to prevent lipid peroxidation. In turn, the inhibition of lipid peroxidation by MnPs is also proportional to their SOD-like activity. In an <i>in vivo S. cerevisiae</i> assay, however, while <i>E</i>_1/2 predominates, lipophilicity significantly affects the efficacy of MnPs. MnPs of similar log <i>P</i>_OW and <i>E</i>_1/2, that have linear alkyl or alkoxyalkyl pyridyl substituents, distribute more easily within a cell and in turn provide higher protection to <i>S. cerevisiae</i> in comparison to MnP with bulky cyclic substituents. The bell-shape curve, with MnTE-2-PyP⁵⁺ exhibiting the highest ability to catalyze ascorbate oxidation, has been established and discussed. Our data support the notion that the SOD-like activity of MnPs parallels their therapeutic potential, though species other than O₂^•–, such as peroxynitrite, H₂O₂, lipid reactive species, and cellular reductants, may be involved in their mode(s) of action(s)