Catalytic scavenging of peroxynitrite by isomeric Mn(III) N-methylpyridylporphyrins in the presence of reductants

Three isomers of manganese(III) 5,10,15, 20-tetrakis(N-methylpyridyl)porphyrin (MnTMPyP) were evaluated for their reaction with peroxynitrite. The Mn(III) complexes reacted with peroxynitrite anion with rate constants of 1.85 x 10(7), 3.82 x 10(6), and 4.33 x 10(6) M(-1) s(-1) at 37 degrees C for MnTM-2-PyP, MnTM-3-PyP, and MnTM-4-PyP, respectively, to yield the corresponding oxo-Mn(IV) complexes. Throughout the pH range from 5 to 8.5, MnTM-2-PyP reacted 5-fold faster than the other two isomers. The oxo-Mn(IV) complexes could in turn be reduced by glutathione, ascorbate, urate, or oxidize tyrosine. The rate constants for the reduction of the oxo-Mn(IV) complexes ranged from >10(7) M(-1) s(-1) for ascorbate to 10(3)-10(4) M(-1) s(-1) for tyrosine and glutathione. Cyclic voltammetry experiments show that there is no significant difference in the E1/2 of the Mn(IV)/Mn(III) couple; thus, the differential reactivity of the three isomeric complexes is interpreted in terms of electrostatic and steric effects. Micromolar concentrations of MnTM-2-PyP compete well with millimolar CO2 at reacting with ONOO-, and it can even scavenge a fraction of the ONOOCO2- that is formed. By being rapidly oxidized by ONOO- and ONOOCO2- and reduced by antioxidants such as ascorbate, urate, and glutathione, these manganese porphyrins, and especially MnTM-2-PyP, can redirect the oxidative potential of peroxynitrite toward natural antioxidants, thus protecting more critical targets such as proteins and nucleic acids.     

A combination of two antioxidants (an SOD mimic and ascorbate) produces a pro-oxidative effect forcing Escherichia coli to adapt via induction of oxyR regulon

Cationic Mn(III) N-alkylpyridyl (MnTalkyl-2(or 3)-PyP(5+)) and N, N'-dialkylimidazolylporphyrins (MnTDalkyl-2-ImP(5+)) have been regarded as the most powerful SOD mimics/peroxynitrite scavengers - i. e. antioxidants. The ethyl-, MnTE-2-PyP(5+) (AEOL10113), and hexylpyridyl-, MnTnHex-2-PyP(5+) and diethylimidazolylporphyrin, MnTDE-2-ImP(5+) (AEOL10150) have been mostly studied in vitro and in vivo. Given the in vivo abundance of cellular reductants, MnPs can couple with them in removing superoxide. Thus, they could be readily reduced from Mn(III)P to Mn(II)P with ascorbate and glutathione, and in a subsequent step reduce either O(2)(.-) (while acting as superoxide reductase) or oxygen (while exerting pro-oxidative action). Moreover, MnPs can catalyze ascorbate oxidation and in turn hydrogen peroxide production. The in vivo type of MnP action (anti- or pro-oxidative) will depend upon the cellular levels of reactive species, endogenous antioxidants, availability of oxygen, ratio of O(2)(.-)- to peroxide-removing systems, redox ability of MnPs and their cellular localization/bioavailibility. To exemplify the switch from an anti- to pro-oxidative action we have explored a very simple and straightforward system - the superoxide-specific aerobic growth of SOD-deficient E. coli. In such a system, cationic MnPs, ortho and meta MnTE-2-(or 3)-PyP(5+) act as powerful SOD mimics. Yet, in the presence of exogenous ascorbate, the SOD mimics catalyze the H(2)O(2) production, causing oxidative damage to both wild and SOD-deficient strains and inhibiting their growth. Catalase added to the medium reversed the effect indicating that H(2)O(2) is a major damaging/signaling species involved in cell growth suppression. The experiments with oxyR- and soxRS-deficient E. coli were conducted to show that E. coli responds to increased oxidative stress exerted by MnP/ascorbate system by induction of oxyR regulon and thus upregulation of antioxidative defenses such as catalases and peroxidases. As anticipated, when catalase was added into medium to remove H(2)O(2), E. coli did not respond with upregulation of its own antioxidant systems.     

Effects of a manganese (III) porphyrin catalytic antioxidant in a mouse closed head injury model

Closed head injury induces cerebral oxidative stress. The efficacy of a Mn (III) porphyrin catalytic antioxidant was assessed in a mouse closed head injury model. Mice were subjected to closed head injury and treated 15 min later with an i.v. bolus of vehicle or 3 mg/kg MnTE-2-PyP5+. Aconitase activity, Fluoro-Jade staining, glial fibrillary acidic protein immunoreactivity, and rotarod falling latencies were measured. Closed head injury altered all variables. MnTE-2-PyP5+ had no effect on any variable with the exception of attenuation of aconitase inactivation at 2 h post-closed head injury. In a second experiment, mice received 3 mg/kg or 6 mg/kg MnTE-2-PyP5+ or vehicle i.v. 15 min post-closed head injury. Rotarod and Morris water maze latencies were measured. Closed head injury altered performance in both tests. No statistically significant effect of MnTE-2-PyP5+ was observed. We conclude that single dose MnTE-2-PyP5+ does not alter outcome in this mouse closed head injury model.     

Protective effects of Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), a superoxide dismutase mimetic, in paw oedema induced by carrageenan in the rat.

In the present study we investigated the therapeutic efficacy of Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), a superoxide dismutase mimetic which possesses peroxynitrite scavenging effects, in rats subjected to carrageenan-induced paw oedema. Local administration of MnTBAP (5, 25, and 50 microg/paw) significantly and dose dependently reduced carrageenan-induced paw oedema at all time points. MnTBAP also caused a significant dose-dependent reduction in paw myeloperoxidase activity and lipid peroxidation, as well as preventing histological injury. Immunohistochemical analysis for nitrotyrosine revealed a positive staining in paw from carrageenan-treated rats. No positive nitrotyrosine staining was found in the paws of the carrageenan-treated rats that received MnTBAP. Our study demonstrates that MnTBAP exerts protective effects in carrageenan-induced paw oedema. Part of these anti-inflammatory effects may be related to: 1) reduction of superoxide formation due to the superoxide dismutase-like activity of the compound; and 2) scavenging of peroxynitrite.     

Beneficial effects of Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), a superoxide dismutase mimetic, in zymosan-induced shock

1 The therapeutic efficacy of Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), a novel superoxide dismutase mimetic which scavenges peroxynitrite, was investigated in rats subjected to shock induced by peritoneal injection of zymosan. 2 Our data show that MnTBAP (given at 1, 3 and 10 mg kg-1 intraperitoneally, 1 and 6 h after zymosan injection) significantly reduce in dose dependent manner the development of peritonitis (peritoneal exudation, high nitrate/nitrite and peroxynitrite plasma levels, leukocyte infiltration and histological examination). 3 Furthermore, our data suggest that there is a reduction in the lung, small intestine and liver myeloperoxidase (MPO) activity and lipid peroxidation activity from MnTBAP-treated rats. 4 MnTBAP also reduced the appearance of nitrotyrosine immunoreactivity in the inflamed tissues. 5 Furthermore, a significant reduction of suppression of mitochondrial respiration, DNA strand breakage and reduction of cellular levels of NAD+ was observed in ex vivo macrophages harvested from the peritoneal cavity of zymosan-treated rat. 6 In vivo treatment with MnTBAP significantly reduced in a dose-dependent manner peroxynitrite formation and prevented the appearance of DNA damage, the decrease in mitochondrial respiration and the loss of cellular levels of NAD+. 7 In conclusion our results showed that MnTBAP was effective in preventing the development of zymosan-induced shock.     

Antioxidant therapeutic targets in COPD

Oxidative stress and chronic inflammation are important features in the pathogenesis of chronic obstructive pulmonary disease (COPD). Oxidative stress has important consequences for several elements of lung physiology and for the pathogenesis of COPD, including oxidative inactivation of antiproteases and surfactants, mucus hypersecretion, membrane lipid peroxidation, alveolar epithelial injury, remodeling of extracellular matrix, and apoptosis. Therefore, targeting oxidative stress with antioxidants or boosting the endogenous levels of antioxidants is likely to be beneficial in the treatment of COPD. Antioxidant and/or anti-inflammatory agents such as thiol molecules (glutathione and mucolytic drugs, such as N-acetyl-L-cysteine and N-acystelyn), dietary polyphenol (curcumin-diferuloylmethane, a principal component of turmeric), resveratrol (a flavanoid found in red wine), green tea (theophylline and epigallocatechin-3- gallate), ergothioneine (xanthine and peroxynitrite inhibitor), quercetin, erdosteine and carbocysteine lysine salt, have been reported to control NF-kappaB activation, regulation of glutathione biosynthesis genes, chromatin remodeling and hence inflammatory gene expression. Specific spin traps such as alpha-phenyl-N-tert-butyl nitrone, a catalytic antioxidant (ECSOD mimetic), manganese (III) meso-tetrakis (N,N'-diethyl-1,3-imidazolium-2-yl) porphyrin (AEOL 10150 and AEOL 10113), and a SOD mimetic M40419 have also been reported to inhibit cigarette smoke-induced inflammatory responses in vivo. Since a variety of oxidants, free radicals and aldehydes are implicated in the pathogenesis of COPD it is possible that therapeutic administration of multiple antioxidants will be effective in the treatment of COPD. Various approaches to enhance lung antioxidant capacity and clinical trials of antioxidant compounds in COPD are discussed.     

Determination of residual manganese in Mn porphyrin-based superoxide dismutase (SOD) and peroxynitrite reductase mimics

The awareness of the beneficial effects of Mn porphyrin-based superoxide dismutase (SOD) mimics and peroxynitrite scavengers on decreasing oxidative stress injuries has increased the use of these compounds as mechanistic probes and potential therapeutics. Simple Mn²⁺ salts, however, have SOD-like activity in their own right both in vitro and in vivo. Thus, quantification/removal of residual Mn²⁺ species in Mn-based therapeutics is critical to an unambiguous interpretation of biological data. Herein we report a simple, sensitive, and specific method to determine residual Mn²⁺ in Mn porphyrin preparations that combines a hydrometallurgical approach for separation/speciation of metal compounds with a spectrophotometric strategy for Mn determination. The method requires only common chemicals and a spectrophotometer and is based on the extraction of residual Mn²⁺ by bis(2-ethylhexyl)hydrogenphosphate (D2EHPA) into kerosene, re-extraction into acid, and neutralization followed by UV–vis determination of the Mn²⁺ levels via a Cd²⁺-catalyzed metallation of the H₂TCPP⁴⁻ porphyrin indicator. The overall procedure is simple, sensitive, specific, and amenable to adaptation. This quantification method has been routinely used by us for a large variety of water-soluble porphyrins.     

Pneumococcal meningitis in the rat: evaluation of peroxynitrite scavengers for adjunctive therapy

We evaluated the effect of different peroxynitrite scavengers for adjunctive therapy of experimental bacterial meningitis. Twenty hours after intracisternal injection of Streptococcus pneumoniae, rats were treated with ceftriaxone [100 mg/kg intraperitoneal (i.p.)] and either urate (300 mg/kg i.p.), Mn(III)tetrakis(4-benzoic acid)porphyrin (MnTBAP, 15 mg/kg i.p.), ascorbate (100 mg/kg i.p.), or urate (300 mg/kg i.p.) + ascorbate (100 mg/kg i.p.). Six hours after initiation of treatment, the cerebrospinal fluid (CSF) pleocytosis was significantly (p<0.05) reduced by urate (8697 +/- 1526 cells/microl) and MnTBAP (8542 +/- 4059 cells/microl) vs. ceftriaxone alone (15,793 +/- 3202 cells/microl). Brain concentrations of proinflammatory cytokines [interleukin-1beta (IL-beta), interleukin-6 (IL-6), and macrophage inflammatory protein-2 (MIP-2)] were also reduced by urate and MnTBAP. The intracranial hypertension was significantly reduced by MnTBAP (14.0 +/- 5.4 mm Hg), but not by urate (25.5 +/- 7.1 mm Hg) vs. ceftriaxone alone (22.5 +/- 5.9 mm Hg). Ascorbate alone had no effect on CSF pleocytosis (15,775 +/- 7058 cells/microl), intracranial pressure (25.6 +/- 8.8 mm Hg), and brain cytokine concentrations. However, the combination of urate and ascorbate was as effective as MnTBAP (CSF pleocytosis: 5392 +/- 4232 cells/microl, intracranial pressure: 13.3 +/- 6.9 mm Hg).     

Effect of vitamin C on the availability of tetrahydrobiopterin in human endothelial cells

Vitamin C has long been known for its beneficial vascular effects, but its mechanism of action remains unclear. Recent reports suggest that vitamin C may prevent endothelial dysfunction by scavenging free radicals and increasing the bioavailability of nitric oxide. To investigate this area further, we studied the effect of vitamin C (10(-4) M) and Mn(III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP; 10(-5) M), a scavenger of superoxide, hydrogen peroxide, and peroxynitrite, on endothelial nitric oxide synthase (eNOS) enzymatic activity in cultured human umbilical vein endothelial cells. L-Citrulline formation (a measure of eNOS enzymatic activity) was significantly increased in cells treated for 24 h with vitamin C. No effect was observed after MnTBAP treatment. Chronic administration of vitamin C also had no effect on eNOS protein expression. Treatment with vitamin C for 24 h significantly increased levels of the eNOS co-factor tetrahydrobiopterin (BH4), whereas MnTBAP did not affect its levels. Sepiapterin (10(-4) M), a precursor of BH4, significantly increased eNOS activity, whereas addition of vitamin C to cells treated with sepiapterin did not cause any further increase in eNOS activity. Our results suggest that the beneficial effect of vitamin C on endothelial function is best explained by increased intracellular BH4 content and subsequent enhancement of eNOS activity. This effect appears to be independent of the ability of vitamin C to scavenge superoxide anions.     

Stability, disposition, and penetration of catalytic antioxidants Mn-porphyrin and Mn-salen and of methylprednisolone in spinal cord injury

This study measured the time courses of concentration changes following administration of the catalytic antioxidants Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP) and Mn (III) 3-methoxy N, N' bis (salicyclidene) ethylenediamine chloride (EUK-134) in blood and cerebrospinal fluid (CSF) of rats with a spinal cord injury (SCI) and sham controls. Parallel measurements were made for methylprednisolone, the only drug presently used clinically for treating SCI. The time courses kinetically characterized the agents in their stability, disposition, and ability to penetrate the blood-spinal cord barrier (BSB). In both the SCI and control groups, MnTBAP was stable in CSF and in blood across the collection periods (10 h and 24 h, respectively) following administration. In the blood, [EUK-134] and [methylprednisolone] rapidly declined to near basal concentrations at 4 h and 2 h, respectively, post-administration. Therefore the order of stability in CSF and blood was MnTBAP > EUK-134 > methylprednisolone. The maximum CSF/blood concentration ratios for EUK-134, methylprednisolone and MnTBAP post-administration were: 32 ± 3.1%, 19.2 ± 6.4%, and 4.42 ± 0.73% in the injured rats, and 22 ± 6.5%, 17.8 ± 2.9%, and 1.0 ± 0.5% in the sham control animals. This suggests an order of BSB penetration of EUK-134 > methylprednisolone > MnTBAP. Despite much lower penetration by MnTBAP compared with EUK-134 and methylprednisolone, a lower dose of MnTBAP because of its stability provided a higher concentration in CSF than did the other agents given at higher doses. This finding supports further exploration of MnTBAP as a potential treatment for SCI.     

Model systems for metabolism studies. Biomimetic oxidation of acetaminophen and ellipticine derivatives with water-soluble metalloporphyrins associated to potassium monopersulfate.

Some original water-soluble metalloporphyrins/KHSO5 systems were developed to mimic the metabolic biooxidation of drugs. Oxidation of acetaminophen and various ellipticine derivatives were used as model reactions. Oxidative products (mainly quinone-imine structures) were obtained in good yield after 2 min of reaction, for a catalyst/substrate ratio of 0.04. Iron(III) derivative of tetrasodium meso-tetrakis(p-sulfonatophenyl)porphyrin and manganese(III) derivative of tetraacetate meso-tetrakis(4-N-methyl-pyridiniumyl)-porphyrin were the best catalysts for the oxidation of acetaminophen and ellipticine compounds, respectively. At low catalyst concentration, initial turnover rates could rise up to 8 catalytic cycles/sec. In some conditions, these catalytic systems are nearly as efficient as horseradish peroxidase/H2O2. They might have a real future as oxidation catalysts, in complement to the use of purified monooxygenase and peroxidases, to predict the possible in vivo oxidative metabolite pathways.     

Solubilization of meso-tetraphenylporphyrin photosensitizers by substitution with fluorine and with 2,3-dihydroxy-1-propyloxy groups

The tetra(hydroxyphenyl)porphyrins (5,10,15,20-tetrakis(2-hydroxyphenyl)porphyrin (3), 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (4), and 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (5) and the tetrahydroporphyrins (5,10,15,20-tetrakis(2-fluoro-3-hydroxyphenyl)porphyrin (6), 5,10,15,20-tetrakis(2,4-difluoro-3-hydroxyphenyl)porphyrin (7), and 5,10,15,20-tetrakis(3,5-difluoro-4-hydroxyphenyl)porphyrin (8)) have been reported as potential photosensitizers for photodynamic therapy. In particular, the tetrahydroporphyrin 7, which has been in Phase III clinical trials for three years in the USA and Canada, has shown great promise for primary and recurrent head and neck cancer. It is expected to be on the market soon. A potentially limiting property of compounds 3-8 is their hydrophobicity, which renders them insoluble in aqueous media. We therefore set out to develop an approach for their solubilization in aqueous media. The first attempt was to prepare analogues with fluorine substituents at the positions ortho to each of the four hydroxy groups on the meso-phenyl rings. This was expected to increase the acidity of the ortho hydroxy groups, and therefore the solubility of the compounds in hydroxylic media. This structural alteration resulted in a slight but significant decrease in the partition coefficients. The second attempt was substitution of each of the hydroxy groups on the phenyl rings with 2,3-dihydroxy-1-propyloxy groups. This structural alteration resulted in a substantial decrease in the partition coefficients. To harness the combined effect of these two structural variations porphyrins were prepared containing both 2,3-dihydroxy-1-propyloxy and ortho fluorine groups on the meso-phenyl rings. The partition coefficients decreased by more than two orders of magnitude. The most significant decrease was due to the substitution with 2,3-dihydroxy-1-propyloxy groups, rather than the substitution with fluorine, although fluorination alone contributed significantly. The effect of this method was demonstrated most clearly by comparison of the partition coefficients of meta and para isomers of these porphyrins.     

In-vitro activity and tissue distribution of new fluorinated meso-tetrahydroxyphenylporphyrin photosensitizers.

Tetra(hydroxyphenyl)porphyrins started to attract interest as potential photosensitizers for photodynamic therapy in the early eighties. Subsequently, a number of derivatives of these compounds have been studied. In 1997 we reported the synthesis of the fluorinated derivatives 5,10,15,20-tetrakis(2-fluoro-3-hydroxyphenyl)porphyrin (8), 5,10,15,20-tetrakis(2,4-difluoro-3-hydroxyphenyl)porphyrin (9), and 5,10,15,20-tetrakis(3,5-difluoro-4-hydroxyphenyl)porphyrin (10). We have measured their biological activity, using the MTT test, against cancer cell cultures in-vitro. The test showed that these compounds were as potent as 5,10,15,20-tetrakis(3-hydroxyphenyl)chlorin (5), one of the leading photosensitizers in photodynamic therapy. The highest photoactivity was shown by the meta-hydroxy compounds 8 and 9. The para-compound showed high toxicity in the dark. Distribution of these compounds between normal and cancer tissue was studied using 19F NMR spectroscopy. The highest cancer tissue localization was also shown by the meta-hydroxy compounds 8 and 9. The para compound showed poor localization in tumour tissue. This study has shown that 19F NMR spectroscopy can be used to estimate the tissue distribution of fluorinated tetrahydroxyphenylporphyrins in-vivo.     

The role of ABCG2 and ABCB6 in porphyrin metabolism and cell survival

The porphyrins (such as heme) are essential molecules within cells and have multiple roles in essential cellular processes such as: the mitochondrial electron transport chain, free-radical detoxification, and metabolism. The porphyrins need energy to traverse biological membranes. Our understanding of ABC transporters role in regulating intracellular porphyrin homeostasis is only now beginning to be understood. Two important contributors are members of the ABC transporter gene family: ABCB6 and ABCG2. ABCB6 is the first ABC transporter located in the outer mitochondrial membrane and oriented to facilitate porphyrin import. Consequently, ABCB6 can regulate and appropriately orchestrate porphyrin synthesis. This leads to an ability to regulate the amount of heme associated with heme requiring proteins. This ability can facilitate a cells protective response to an array of toxic insults. ABCG2 also binds and transports porphyrins, however its location at the plasma membrane provides a mechanism to remove excess porphyrins. Because ABCG2 is upregulated by hypoxia this provides a mechanism to export porphyrins, rebalance porphyrins and protect cells from porphyrin overaccumulation. Such a mechanism would be important to hypoxic cells which exhibit an increase in porphyrin synthesis under hypoxic conditions. Finally, we propose that these two transporters (ABCB6 and ABCG2) are coordinately regulated to modulate porphyrin concentrations under normal physiological and pathological conditions.     

Pulmonary inflammation by ambient air particles is mediated by superoxide anion

Lung inflammation is a key response to increased levels of particulate air pollution (PM); however, the cellular mechanisms leading to this response remain poorly understood. We have previously shown that oxidants are critical mediators of the inflammatory response elicited by inhalation of ambient air particles. Here we tested the possible role of a specific oxidant, superoxide anion, by using the membrane-permeable analog of superoxide dismutase, Mn(III) tetrakis(4-benzoic acid)porphyrin chloride (MnTBAP). Adult Sprague-Dawley rats were instilled with either urban air particles (UAP) or saline. MnTBAP-treated rats received 10 mg/kg (ip) MnTBAP 2 h prior to exposure to UAP. Recruitment of inflammatory cells into bronchoalveolar lavage was evaluated 4 h after instillation. Rats exposed to UAP showed significant increases in the total cell number (8.9 +/- 0.6 x 10(6); sham: 5.1 +/- 0.6 x 10(6), p < .02), the numbers of polymorphonuclear leukocytes (26 +/- 4%; sham: 6 +/- 1%, p < .0001), protein levels (1.2 +/- 0.5 mg/ml, sham: 0.4 +/- 0.1 mg/ml, p < .001), and a trend of increase in myeloperoxidase levels (5 +/- 1; sham: 2 +/- 1 mU/ml) in bronchoalveolar lavage (BAL). Pretreatment with MnTBAP at a dose that prevented UAP-induced increases in oxidants effectively prevented increase in BAL cells (2.7 +/- 0.6 x 10(6), p < .0001 vs. UAP), PMN influx into the lungs (4 +/- 3%, p < .0001 vs. UAP), and increase in myeloperoxidase (2 +/- 1 mU/ml) and protein levels in BAL (0.1 +/- 0.1 mg/ml). These data indicate that superoxide anion is a critical mediator of the inflammatory response elicited by PM deposition in the lung.     

Nitric oxide, peroxynitrite and lipoxygenase in atherogenesis: mechanistic insights

Nitric oxide (*NO) is a free radical species that diffuses and concentrates in the hydrophobic core of low-density lipoprotein (LDL) to serve as a potent antioxidant. Peroxynitrite, the product of the diffusion-limited reaction between *NO and superoxide anion, as well as lipoxygenase, represent relevant mediators of oxidative modifications in LDL. The focus of this review is the analysis of interactions between *NO, peroxynitrite and lipoxygenase during LDL oxidation, which are relevant in the development of the early steps as well as progression of atherosclerosis. The role of CO2 to redirect peroxynitrite reactivity in LDL, as well as the lipophilic antioxidant sparing actions of *NO, ascorbate and CO2 is also analyzed. In this context, the effects of novel potential pharmacological strategies against atherosclerosis such as Mn(III)porphyrins will be discussed.     

Quantitative evaluation of urinary porphyrins as a measure of kidney mercury content and mercury body burden during prolonged methylmercury exposure in rats.

Changes in urinary porphyrin excretion patterns (porphyrin profiles) during prolonged mercury exposure are attributable to mercury accumulation in the kidney and to consequent effects of Hg2+ on renal porphyrin metabolism. In the present study, we evaluated the quantitative relationship of urinary porphyrin concentrations to mobilizable renal mercury content, using the metal chelator 2,3-dimercapto-1-propanesulfonic acid (DMPS) to modulate kidney mercury levels. Rats exposed to methylmercury hydroxide (MMH) at 10 ppm in drinking water for 6 weeks were treated with up to 3 consecutive doses of DMPS (100mg/kg, ip) at 72-h intervals. Consistent with previous findings, the concentrations of pentacarboxyl- (5-) and copro- (4-) porphyrins and of an atypical porphyrin specific to mercury exposure, precoproporphyrin, were significantly elevated in urine of MMH-exposed rats, compared with that of rats exposed to distilled water (dH2O) for the same period. Consecutive DMPS treatments of MMH-exposed rats significantly decreased kidney concentrations of total, as well as Hg2+ and CH3Hg+ species, and promoted increased urinary mercury excretion. Concomitantly, DMPS treatment decreased both kidney and urinary porphyrin concentrations, consistent with depletion of renal mercury levels. Regression analyses demonstrated a high correlation (r approximately 0.9) between prechelation urinary porphyrins and postchelation urinary mercury levels and also between prechelation urinary porphyrins and prechelation kidney mercury concentrations. These findings demonstrate that urinary porphyrin concentrations relate quantitatively to DMPS-mobilizable mercury in the kidney and, therefore, serve as a biochemical measure of renal mercury content.     

Ochratoxin A-induced cytotoxicity,genotoxicity and reactive oxygen species in kidney cells: An integrative approach of complementary endpoints

Ochratoxin A (OTA) is a well-known nephrotoxic and potential carcinogenic agent but no consensus about the molecular mechanisms underlying its deleterious effects has been reached yet. The aim of this study is to integrate several endpoints concerning OTA-induced toxicological effects in Vero kidney cells in order to obtain additional mechanistic data, especially regarding the influence of reactive oxygen species (ROS). One innovative aspect of this work is the use of the superoxide dismutase mimic (SODm) MnTnHex-2-PyP as a mechanistic tool to clarify the involvement of oxidative stress in OTA toxicity. The results showed concentration and time-dependent cytotoxic effects of OTA (crystal violet, neutral red and LDH leakage assays). While the SODm mildly increased cell viability, trolox and ascorbic acid had no effect with regards to this endpoint. OTA induced micronuclei formation. Using the FPG modified comet assay, OTA modestly increased the % of DNA in tail, revealing the presence of oxidative DNA lesions. This mycotoxin increased apoptosis, which was attenuated by SODm. In addition, the SODm decreased the ROS accumulation observed in DHE assay. Taken together, our data suggest that ROS partially contribute to the cytotoxicity and genotoxicity of OTA, although other mechanisms may be relevant in OTA-induced deleterious effects.     

Contribution of peroxynitrite to fatal cardiovascular depression induced by overproduction of nitric oxide in rostral ventrolateral medulla of the rat

We evaluated the contribution of peroxynitrite to the fatal cardiovascular depression induced by overproduction of nitric oxide (NO) after activation of inducible NO synthase (iNOS) in the rostral ventrolateral medulla (RVLM), the origin of sympathetic vasomotor tone. In Sprague-Dawley rats maintained under propofol anesthesia, microinjection of E. coli lipopolysaccharide (LPS) bilaterally into the RVLM elicited significant hypotension, bradycardia, reduction in sympathetic vasomotor tone and mortality. There was also a discernible elevation of iNOS expression in the ventrolateral medulla, followed by a massive production of nitrotyrosine, an experimental index for peroxynitrite. Co-administration bilaterally into the RVLM of the selective iNOS inhibitor, S-methylisothiourea (50, 100 or 250 pmol), an active peroxynitrite decomposition catalyst, 5,10,15,20-tetrakis- (N-methyl-4'-pyridyl)-porphyrinato iron (III) (10 or 50 pmol), a peroxynitrite scavenger, L-cysteine (5, 50 or 100 pmol), or a superoxide dismutase mimetic, Mn(III)-tetrakis-(4-benzoic acid) porphyrin (1 or 10 pmol), significantly prevented mortality, reduced nitrotyrosine production and reversed the NO-induced cardiovascular suppression after application of LPS into the RVLM. We conclude that the formation of peroxynitrite by a reaction between superoxide anion and NO is primarily responsible for the fatal cardiovascular depression induced by overproduction of NO after activation of iNOS at the RVLM.