Center for Free Radical and Biomedical Research

Montevideo, Uruguay

Center for Free Radical and Biomedical Research

Montevideo, Uruguay
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Carballal S.,Center for Free Radical and Biomedical Research | Ghazaryan R.,Yerevan State Medical University | Melikyan L.,Yerevan State Medical University | Maia C.G.C.,Federal University of Paraiba | And 4 more authors.
Inorganic Chemistry | Year: 2014

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). © 2014 American Chemical Society.

Silva V.,University of the Republic of Uruguay | Silva V.,Center for Free Radical and Biomedical Research | Genta G.,University of the Republic of Uruguay | Genta G.,Center for Free Radical and Biomedical Research | And 14 more authors.
Journal of Agricultural and Food Chemistry | Year: 2011

The antioxidant capacity of propolis from the southern region of Uruguay was evaluated using in vitro as well as cellular assays. Free radical scavenging capacity was assessed by ORAC, obtaining values significantly higher than those of other natural products (8000 μmol Trolox equiv/g propolis). ORAC values correlated well with total polyphenol content (determined by Folin-Ciocalteu method) and UV absorption. Total polyphenol content (150 mg gallic acid equiv/g propolis) and flavonoids (45 mg quercetin equiv/g propolis) were similar to values reported for southern Brazilian (group 3) and Argentinean propolis. Flavonoid composition determined by RP-HPLC indicates a strong poplar-tree origin. Samples high in polyphenols efficiently inhibit low-density lipoprotein lipoperoxidation and tyrosine nitration. In addition, Uruguayan propolis was found to induce the expression of endothelial nitric oxide synthase and inhibit endothelial NADPH oxidase, suggesting a potential cardiovascular benefit by increasing nitric oxide bioavailability in the endothelium. © 2011 American Chemical Society.

Botti H.,Instituto Pasteur Of Montevideo | Botti H.,Center for Free Radical and Biomedical Research | Moller M.N.,Center for Free Radical and Biomedical Research | Moller M.N.,University of the Republic of Uruguay | And 9 more authors.
Journal of Physical Chemistry B | Year: 2010

The fast reaction of •NO and O2 •- to give ONOO- has been extensively studied at irreversible conditions, but the reasons for the wide variations in observed forward rate constants (3.8 ≥ kf ≥ 20 × 109 M-1 s-1) remain unexplained. We characterized the diffusion-dependent aqueous (pH > 12) chemical equilibrium of the form •NO + O2 •- = ONOO- with respect to its dependence on temperature, viscosity, and [ONOO-] eq by determining [ONOO-]eq and [ •NO]eq. The equilibrium forward reaction rate constant (kf eq) has negative activation energy, in contrast to that found under irreversible conditions. In contradiction to the law of mass action, we demonstrate that the equilibrium constant depends on ONOO- concentration. Therefore, a wide range of kf eq values could be derived (7.5-21 × 109 M -1 s-1). Of general interest, the variations in k f can thus be explained by its dependence on the distance between ONOO- particles (sites of generation of •NO and O2 •-). © 2010 American Chemical Society.

Trostchansky A.,Center for Free Radical and Biomedical Research | Bonilla L.,Center for Free Radical and Biomedical Research | Thomas C.P.,University of Cardiff | O'Donnell V.B.,University of Cardiff | And 3 more authors.
Journal of Biological Chemistry | Year: 2011

Prostaglandin endoperoxide H synthase (PGHS) catalyzes the oxidation of arachidonate to prostaglandin H 2. We have previously synthesized and chemically characterized nitroarachidonic acid (AANO 2), a novel anti-inflammatory signaling mediator. Herein, the interaction of AANO 2 with PGHS was analyzed. AANO 2 inhibited oxygenase activity of PGHS-1 but not PGHS-2. AANO 2 exhibited time- and concentration-dependent inhibition of peroxidase activity in both PGHS-1 and -2. The plot of k obs versus AANO 2 concentrations showed a hyperbolic function with k inact = 0.045 s -1 and K i *app = 0.019 μM for PGHS-1 and k inact = 0.057 s -1 and K i *app = 0.020 μM for PGHS-2. Kinetic analysis suggests that inactivation of PGHS by AANO 2 involves two sequential steps: an initial reversible binding event (described by Ki) followed by a practically irreversible event (K i *app) leading to an inactivated enzyme. Inactivation was associated with irreversible disruption of heme binding to the protein. The inhibitory effects of AANO 2 were selective because other nitrofatty acids tested, such as nitrooleic acid and nitrolinoleic acid, were unable to inhibit enzyme activity. In activated human platelets, AANO 2 significantly decreased PGHS-1-dependent thromboxane B 2 formation in parallel with a decrease in platelet aggregation, thus confirming the biological relevance of this novel inhibitory pathway. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.

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