SET overexpression decreases cell detoxification efficiency: ALDH2 and GSTP1 are downregulated, DDR is impaired and DNA damage accumulates

Alcohol and tobacco consumption are risk factors for head and neck squamous cell carcinoma (HNSCC). Aldehyde dehydrogenase 2 (ALDH2) and glutathione S-transferase pi 1 (GSTP1) are important enzymes for cellular detoxification and low efficiencies are implicated in cancer. We assessed the potential role of SET protein overexpression, a histone acetylation modulator accumulated in HNSCC, in gene regulation and protein activity of ALDH2 and GSTP1. SET was knocked down in HN13, HN12 and Cal27, and overexpressed in HEK293 cells; ethanol and cisplatin were the chemical agents. Cells with SET overexpression (HEK293/SET, HN13 and HN12) showed lower ALDH2 and GSTP1 mRNA levels and trichostatin A increased them (real-time PCR). Ethanol upregulated GSTP1 and ALDH2 mRNAs, whereas cisplatin upregulated GSTP1 in HEK293 cells. SET-chromatin binding revealed SET interaction with ALDH2 and GSTP1 promoters, specifically via SET NAP domain; ethanol and cisplatin abolished SET binding. ALDH2 and GSTP1 efficiency was assessed by enzymatic and comet assay. A lower ALDH2 activity was associated with greater DNA damage (tail intensity) in HEK293/SET compared with HEK293 cells, whereas HN13/siSET showed ALDH2 activity higher than HN13 cells. HN13/siSET cells showed increased tail intensity. Cisplatin-induced DNA damage response showed negative relationship between SET overexpression and BRCA2 recruitment. SET downregulated repair genes ATM, BRCA1 and CHEK2 and upregulated TP53. Cisplatin-induced cell-cycle arrest occurred in G(0) /G(1) and S in HEK293 cells, whereas HEK293/SET showed G(2) /M stalling. Overall, cisplatin was more cytotoxic for HN13 than HN13/siSET cells. Our data suggest a role for SET in cellular detoxification, DNA damage response and genome integrity.

SET protein accumulates in HNSCC and contributes to cell survival: antioxidant defense, Akt phosphorylation and AVOs acidification

OBJECTIVES

Determination of the SET protein levels in head and neck squamous cell carcinoma (HNSCC) tissue samples and the SET role in cell survival and response to oxidative stress in HNSCC cell lineages.

MATERIALS AND METHODS

SET protein was analyzed in 372 HNSCC tissue samples by immunohistochemistry using tissue microarray and HNSCC cell lineages. Oxidative stress was induced with the pro-oxidant tert-butylhydroperoxide (50 and 250μM) in the HNSCC HN13 cell lineage either with (siSET) or without (siNC) SET knockdown. Cell viability was evaluated by trypan blue exclusion and annexin V/propidium iodide assays. It was assessed caspase-3 and -9, PARP-1, DNA fragmentation, NM23-H1, SET, Akt and phosphorylated Akt (p-Akt) status. Acidic vesicular organelles (AVOs) were assessed by the acridine orange assay. Glutathione levels and transcripts of antioxidant genes were assayed by fluorometry and real time PCR, respectively.

RESULTS

SET levels were up-regulated in 97% tumor tissue samples and in HNSCC cell lineages. SiSET in HN13 cells (i) promoted cell death but did not induced caspases, PARP-1 cleavage or DNA fragmentation, and (ii) decreased resistance to death induced by oxidative stress, indicating SET involvement through caspase-independent mechanism. The red fluorescence induced by siSET in HN13 cells in the acridine orange assay suggests SET-dependent prevention of AVOs acidification. NM23-H1 protein was restricted to the cytoplasm of siSET/siNC HN13 cells under oxidative stress, in association with decrease of cleaved SET levels. In the presence of oxidative stress, siNC HN13 cells showed lower GSH antioxidant defense (GSH/GSSG ratio) but higher expression of the antioxidant genes PRDX6, SOD2 and TXN compared to siSET HN13 cells. Still under oxidative stress, p-Akt levels were increased in siNC HN13 cells but not in siSET HN13, indicating its involvement in HN13 cell survival. Similar results for the main SET effects were observed in HN12 and CAL 27 cell lineages, except that HN13 cells were more resistant to death.

CONCLUSION

SET is potential (i) marker for HNSCC associated with cancer cell resistance and (ii) new target in cancer therapy.

Release of NO from a nitrosyl ruthenium complex through oxidation of mitochondrial NADH and effects on mitochondria

Nitrosyl ruthenium complexes are promising NO donor agents with numerous advantages for the biologic applications of NO. We have characterized the NO release from the nitrosyl ruthenium complex [Ru(NO(2))(bpy)(2)(4-pic)](+) (I) and the reactive oxygen/nitrogen species (ROS/RNS)-mediated NO actions on isolated rat liver mitochondria. The results indicated that oxidation of mitochondrial NADH promotes NO release from (I) in a manner mediated by NO(2) formation (at neutral pH) as in mammalian cells, followed by an oxygen atom transfer mechanism (OAT). The NO released from (I) uncoupled mitochondria at low concentrations/incubation times and inhibited the respiratory chain at high concentrations/incubation times. In the presence of ROS generated by mitochondria NO gave rise to peroxynitrite, which, in turn, inhibited the respiratory chain and oxidized membrane protein-thiols to elicit a Ca(2+)-independent mitochondrial permeability transition; this process was only partially inhibited by cyclosporine-A, almost fully inhibited by the thiol reagent N-ethylmaleimide (NEM) and fully inhibited by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). These actions correlated with the release of cytochrome c from isolated mitochondria as detected by Western blotting analysis. These events, typically involved in cell necrosis and/or apoptosis denote a potential specific action of (I) and analogs against tumor cells via mitochondria-mediated processes.

Accumulation of the SET protein in HEK293T cells and mild oxidative stress: cell survival or death signaling

SET protein (I2PP2A) is an inhibitor of PP2A, which regulates the phosphorylated Akt (protein kinase B) levels. We assessed the effects of SET overexpression in HEK293T cells, both in the presence and the absence of mild oxidative stress induced by 50 μM tert-butyl hydroperoxide. Immunoblotting assays demonstrated that SET accumulated in HEK293T cells and increased the levels of phosphorylated Akt and PTEN; in addition, SET decreased glutathione antioxidant defense of cell and increased expression of genes encoding antioxidant defense proteins. Immunofluorescence analysis demonstrated that accumulated SET was equally distributed in cytoplasm and nucleus; however, in cells that had been exposed to oxidative stress, SET was found in large aggregates in the cytoplasm. SET accumulation in HEK293T cells correlated with inhibition of basal apoptosis as evidenced by a decrease in annexin V staining and activity of caspases; under mild oxidative stress, SET accumulation correlated with caspase-independent cell death, as evidenced by increased PI and annexin V/PI double staining. The results suggest that accumulated SET could act via Akt/PTEN either as cell survival signal or as oxidative stress sensor for cell death.

Characterization of the stimulus for reactive oxygen species generation in calcium-overloaded mitochondria

We have used two different probes with distinct detection properties, dichlorodihydrofluorescein diacetate and Amplex Red/horseradish peroxidase, as well as different respiratory substrates and electron transport chain inhibitors, to characterize the reactive oxygen species (ROS) generation by the respiratory chain in calcium-overloaded mitochondria. Regardless of the respiratory substrate, calcium stimulated the mitochondrial generation of ROS, which were released at both the mitochondrial-matrix side and the extra-mitochondrial space, in a way insensitive to the mitochondrial permeability transition pores inhibitor cyclosporine A. In glutamate/malate-energized mitochondria, inhibition at complex I or complex III (ubiquinone cycle) similarly modulated ROS generation at either mitochondrial-matrix side or extra-mitochondrial space; this also occurred when the backflow of electrons to complex I in succinate-energized mitochondria was inhibited. On the other hand, in succinate-energized mitochondria the modulation of ROS generation at mitochondrial-matrix side or extra-mitochondrial space depends on the site of complex III which was inhibited. These results allow a straight comparison between the effects of different respiratory substrates and electron transport chain inhibitors on ROS generation at either mitochondrial-matrix side or extra-mitochondrial space in calcium-overloaded mitochondria.

(+)α-Tocopheryl succinate inhibits the mitochondrial respiratory chain complex I and is as effective as arsenic trioxide or ATRA against acute promyelocytic leukemia in vivo

The vitamin E derivative (+)α-tocopheryl succinate (α-TOS) exerts pro-apoptotic effects in a wide range of tumors and is well tolerated by normal tissues. Previous studies point to a mitochondrial involvement in the action mechanism; however, the early steps have not been fully elucidated. In a model of acute promyelocytic leukemia (APL) derived from hCG-PML-RARα transgenic mice, we demonstrated that α-TOS is as effective as arsenic trioxide or all-trans retinoic acid, the current gold standards of therapy. We also demonstrated that α-TOS induces an early dissipation of the mitochondrial membrane potential in APL cells and studies with isolated mitochondria revealed that this action may result from the inhibition of mitochondrial respiratory chain complex I. Moreover, α-TOS promoted accumulation of reactive oxygen species hours before mitochondrial cytochrome c release and caspases activation. Therefore, an in vivo antileukemic action and a novel mitochondrial target were revealed for α-TOS, as well as mitochondrial respiratory complex I was highlighted as potential target for anticancer therapy.

The anti-cancer agent guttiferone-A permeabilizes mitochondrial membrane: ensuing energetic and oxidative stress implications

Guttiferone-A (GA) is a natural occurring polyisoprenylated benzophenone with cytotoxic action in vitro and anti-tumor action in rodent models. We addressed a potential involvement of mitochondria in GA toxicity (1-25 μM) toward cancer cells by employing both hepatic carcinoma (HepG2) cells and succinate-energized mitochondria, isolated from rat liver. In HepG2 cells GA decreased viability, dissipated mitochondrial membrane potential, depleted ATP and increased reactive oxygen species (ROS) levels. In isolated rat-liver mitochondria GA promoted membrane fluidity increase, cyclosporine A/EGTA-insensitive membrane permeabilization, uncoupling (membrane potential dissipation/state 4 respiration rate increase), Ca²⁺ efflux, ATP depletion, NAD(P)H depletion/oxidation and ROS levels increase. All effects in cells, except mitochondrial membrane potential dissipation, as well as NADPH depletion/oxidation and permeabilization in isolated mitochondria, were partly prevented by the a NAD(P)H regenerating substrate isocitrate. The results suggest the following sequence of events: 1) GA interaction with mitochondrial membrane promoting its permeabilization; 2) mitochondrial membrane potential dissipation; 3) NAD(P)H oxidation/depletion due to inability of membrane potential-sensitive NADP+ transhydrogenase of sustaining its reduced state; 4) ROS accumulation inside mitochondria and cells; 5) additional mitochondrial membrane permeabilization due to ROS; and 6) ATP depletion. These GA actions are potentially implicated in the well-documented anti-cancer property of GA/structure related compounds.

Involvement of an alternative oxidase in oxidative stress and mycelium-to-yeast differentiation in Paracoccidioides brasiliensis

Paracoccidioides brasiliensis is a thermodimorphic human pathogenic fungus that causes paracoccidioidomycosis (PCM), which is the most prevalent systemic mycosis in Latin America. Differentiation from the mycelial to the yeast form (M-to-Y) is an essential step for the establishment of PCM. We evaluated the involvement of mitochondria and intracellular oxidative stress in M-to-Y differentiation. M-to-Y transition was delayed by the inhibition of mitochondrial complexes III and IV or alternative oxidase (AOX) and was blocked by the association of AOX with complex III or IV inhibitors. The expression of P. brasiliensis aox (Pbaox) was developmentally regulated through M-to-Y differentiation, wherein the highest levels were achieved in the first 24 h and during the yeast exponential growth phase; Pbaox was upregulated by oxidative stress. Pbaox was cloned, and its heterologous expression conferred cyanide-resistant respiration in Saccharomyces cerevisiae and Escherichia coli and reduced oxidative stress in S. cerevisiae cells. These results reinforce the role of PbAOX in intracellular redox balancing and demonstrate its involvement, as well as that of other components of the mitochondrial respiratory chain complexes, in the early stages of the M-to-Y differentiation of P. brasiliensis.

Impact of adenosine nucleotide translocase (ANT) proline isomerization on Ca2+-induced cysteine relative mobility/mitochondrial permeability transition pore

Mitochondrial membrane carriers containing proline and cysteine, such as adenine nucleotide translocase (ANT), are potential targets of cyclophilin D (CyP-D) and potential Ca(2+)-induced permeability transition pore (PTP) components or regulators; CyP-D, a mitochondrial peptidyl-prolyl cis-trans isomerase, is the probable target of the PTP inhibitor cyclosporine A (CsA). In the present study, the impact of proline isomerization (from trans to cis) on the mitochondrial membrane carriers containing proline and cysteine was addressed using ANT as model. For this purpose, two different approaches were used: (i) Molecular dynamic (MD) analysis of ANT-Cys(56) relative mobility and (ii) light scattering techniques employing rat liver isolated mitochondria to assess both Ca(2+)-induced ANT conformational change and mitochondrial swelling. ANT-Pro(61) isomerization increased ANT-Cys(56) relative mobility and, moreover, desensitized ANT to the prevention of this effect by ADP. In addition, Ca(2+) induced ANT "c" conformation and opened PTP; while the first effect was fully inhibited, the second was only attenuated by CsA or ADP. Atractyloside (ATR), in turn, stabilized Ca(2+)-induced ANT "c" conformation, rendering the ANT conformational change and PTP opening less sensitive to the inhibition by CsA or ADP. These results suggest that Ca(2+) induces the ANT "c" conformation, apparently associated with PTP opening, but requires the CyP-D peptidyl-prolyl cis-trans isomerase activity for sustaining both effects.

Assessment of the potential genotoxic risk of medicinal Tamarindus indica fruit pulp extract using in vivo assays

Tamarindus indica has been used in folk medicine as an antidiabetic, a digestive aid, and a carminative, among other uses. Currently, there is no information in the toxicology literature concerning the safety of T. indica extract. We evaluated the clastogenic and/or genotoxic potential of fruit pulp extract of this plant in vivo in peripheral blood and liver cells of Wistar rats, using the comet assay, and in bone marrow cells of Swiss mice, using the micronucleus test. The extract was administered by gavage at doses of 1000, 1500 and 2000 mg/kg body weight. Peripheral blood and liver cells from Wistar rats were collected 24 h after treatment, for the comet assay. The micronucleus test was carried out in bone marrow cells from Swiss mice collected 24 h after treatment. The extract made with T. indica was devoid of clastogenic and genotoxic activities in the cells of the rodents, when administered orally at these three acute doses.

Modulatory effects of rutin on biochemical and hematological parameters in hypercholesterolemic Golden Syrian hamsters

Flavonoids have been reported to exhibit several pharmacological properties, mainly in cardiovascular and inflammatory diseases. In the present study, we observed that rutin, a known glycosylated flavonoid isolated from Dimorphandra mollis, had a lowering effect on plasma triglyceride levels of diet-induced hypercholesterolemic Golden Syrian hamsters, but did not change total cholesterol and high-density lipoprotein cholesterol levels. Moreover, high-fat or rutin supplemented diets showed no immunotoxic effects, since no significant changes were observed on total white blood cells, granulocytes and mononuclear cells, as well as on the neutrophil apoptosis degree, when compared to untreated animals. Therefore, rutin seems to be a selective and non-toxic modulator of hypercholesterolemia, which can be promising for the development of new drugs.

Mitochondrial function in the yeast form of the pathogenic fungus Paracoccidioides brasiliensis

Differences between the respiratory chain of the fungus Paracoccidioides brasiliensis and its mammalian host are reported. Respiration, membrane potential, and oxidative phosphorylation in mitochondria from P. brasiliensis spheroplasts were evaluated in situ, and the presence of a complete (Complex I-V) functional respiratory chain was demonstrated. In succinate-energized mitochondria, ADP induced a transition from resting to phosphorylating respiration. The presence of an alternative NADH-ubiquinone oxidoreductase was indicated by: (i) the ability to oxidize exogenous NADH and (ii) the lack of sensitivity to rotenone and presence of sensitivity to flavone. Malate/NAD(+)-supported respiration suggested the presence of either a mitochondrial pyridine transporter or a glyoxylate pathway contributing to NADH and/or succinate production. Partial sensitivity of NADH/succinate-supported respiration to antimycin A and cyanide, as well as sensitivity to benzohydroxamic acids, suggested the presence of an alternative oxidase in the yeast form of the fungus. An increase in activity and gene expression of the alternative NADH dehydrogenase throughout the yeast's exponential growth phase was observed. This increase was coupled with a decrease in Complex I activity and gene expression of its subunit 6. These results support the existence of alternative respiratory chain pathways in addition to Complex I, as well as the utilization of NADH-linked substrates by P. brasiliensis. These specific components of the respiratory chain could be useful for further research and development of pharmacological agents against the fungus.

Chronic ethanol intake modulates vascular levels of endothelin-1 receptor and enhances the pressor response to endothelin-1 in anaesthetized rats

BACKGROUND AND PURPOSE

The contribution of endothelin-1 (ET-1) to vascular hyper-reactivity associated with chronic ethanol intake, a major risk factor in several cardiovascular diseases, remains to be investigated.

EXPERIMENTAL APPROACH

The biphasic haemodynamic responses to ET-1 (0.01-0.1 nmol kg(-1), i.v.) or to the selective ETB agonist, IRL1620 (0.001-1.0 nmol kg(-1), i.v.), with or without ETA or ETB antagonists (BQ123 (c(DTrp-Dasp-Pro-Dval-Leu)) at 1 and 2.5 mg kg(-1) and BQ788 (N-cis-2,6-dimethyl-piperidinocarbonyl-L-gamma-methylleucyl1-D-1methoxycarbonyltryptophanyl-D-norleucine) at 0.25 mg kg(-1), respectively) were tested in anaesthetized rats, after 2 weeks' chronic ethanol treatment. Hepatic parameters and ET receptor protein levels were also determined.

KEY RESULTS

The initial hypotensive responses to ET-1 or IRL1620 were unaffected by chronic ethanol intake, whereas the subsequent pressor effects induced by ET-1, but not by IRL1620, were potentiated. BQ123 at 2.5 but not 1 mg kg(-1) reduced the pressor responses to ET-1 in ethanol-treated rats. Conversely, BQ788 (0.25 mg kg(-1)) potentiated ET-1-induced increases in mean arterial blood pressure in control as well as in ethanol-treated rats. Interestingly, in the latter group, increases in heart rate, induced by ET-1 at a dose of 0.025 mg kg(-1) were enhanced following ETB receptor blockade. Finally, we observed higher levels of ETA receptor in the heart and mesenteric artery and a reduction of ETB receptor protein levels in the aorta and kidney from rats chronically treated with ethanol.

CONCLUSIONS AND IMPLICATIONS

Increased vascular reactivity to ET-1 and altered protein levels of ETA and ETB receptors could play a role in the pathogenesis of cardiovascular complications associated with chronic ethanol consumption.

Dehydromonocrotaline inhibits mitochondrial complex I. A potential mechanism accounting for hepatotoxicity of monocrotaline

Monocrotaline is a pyrrolizidine alkaloid present in plants of the Crotalaria species, which causes cytotoxicity and genotoxicity, including hepatotoxicity in animals and humans. It is metabolized by cytochrome P-450 in the liver to the alkylating agent dehydromonocrotaline. We evaluated the effects of monocrotaline and its metabolite on respiration, membrane potential and ATP levels in isolated rat liver mitochondria, and on respiratory chain complex I NADH oxidase activity in submitochondrial particles. Dehydromonocrotaline, but not the parent compound, showed a concentration-dependent inhibition of glutamate/malate-supported state 3 respiration (respiratory chain complex I), but did not affect succinate-supported respiration (complex II). Only dehydromonocrotaline dissipated mitochondrial membrane potential, depleted ATP, and inhibited complex I NADH oxidase activity (IC50=62.06 microM) through a non-competitive type of inhibition (K(I)=8.1 microM). Therefore, dehydromonocrotaline is an inhibitor of the activity of respiratory chain complex I NADH oxidase, an action potentially accounting for the well-documented monocrotaline's hepatotoxicity to animals and humans. The mechanism probably involves change of the complex I conformation resulting from modification of cysteine thiol groups by the metabolite.

Cloning and functional expression of the mitochondrial alternative oxidase ofAspergillus fumigatusand its induction by oxidative stress

Aspergillus fumigatus possesses a branched mitochondrial electron transport chain, with both cyanide-sensitive and -insensitive oxygen-consumption activities. Mitochondrial reactive oxygen species mediate signaling for alternative oxidase (AOX) expression. A 1173 bp-long Afaox gene encoding a 40 kDa protein has been cloned and identified. Recombinant constructs containing the Afaox ORF were transformed into Escherichia coli and Saccharomyces cerevisiae for heterologous expression. In A. fumigatus, AOX activity and mRNA expression were both induced with menadione or paraquat, suggesting an important role of AOX under oxidative stress. Therefore, positive transformants showed a cyanide-resistant and salicylhydroxamic acid-sensitive respiration, whereas in control cells the oxygen uptake was completely inhibited after KCN addition.

Effect of rutin on polymorphonuclear leukocytes oxidative metabolism in hypercholesterolemic Golden Syrian hamsters: evaluation by chemiluminescence and flow cytometry

Atherosclerosis has been described as an inflammatory disease in which polymorphonuclear leukocytes (PMNLs) seem to be involved. These cells may induce atherosclerotic lesions by releasing reactive oxygen species (ROS) and a sort of pro-inflammatory mediators. In this study, the PMNL oxidative metabolic status of Golden Syrian hamsters fed a normal diet (ND), or a high-fat diet (10% coconut oil plus 0.2% cholesterol) supplemented (R-HCD) or not (HCD) with 0.1% (w/w) rutin was evaluated after 120 days of treatment. PMNL oxidative metabolism was assessed by whole blood luminol-enhanced chemiluminescence and 2',7'-dichlorofluorescein diacetate-dependent flow cytometry. The results obtained by both methods were similar and showed no significant changes in ROS generation by PMNLs in blood samples from HCD or R-HCD animals when compared to ND. Furthermore it was shown that rutin supplementation did not significantly affect plasma lipid and lipoprotein levels in the hypercholesterolemic animals characterized by significantly increased total plasma cholesterol, triglycerides and low- and high-density lipoprotein cholesterol levels. The results suggest that in this model atherosclerosis development is not related to circulating PMNL activation and rutin supplementation has no immunomodulatory or hypocholesterolemic effects.

Antioxidant activity of isocoumarins isolated from Paepalanthus bromelioides on mitochondria

The isocoumarins (1-50 microM) paepalantine (9,10-dihydroxy-5,7-dimethoxy-1H-naptho(2,3c)pyran-1-one), 8,8'-paepalantine dimer, and vioxanthin isolated from Paepalanthus bromelioides, were assessed for antioxidant activity using isolated rat liver mitochondria and non-mitochondrial systems, and compared with the flavonoid quercetin. The paepalantine and paepalantine dimers, but not vioxanthin, were effective at scavenging both 1,1-diphenyl-2-picrylhydrazyl (DPPH(*)) and superoxide (O(2)(-)) radicals in non-mitochondrial systems, and protected mitochondria from tert-butylhydroperoxide-induced H(2)O(2) accumulation and Fe(2+)-citrate-mediated mitochondrial membrane lipid peroxidation, with almost the same potency as quercetin. These results point towards paepalantine, followed by paepalantine dimer, as being a powerful agent affording protection, apparently via O(2)(-) scavenging, from oxidative stress conditions imposed on mitochondria, the main intracellular source and target of those reactive oxygen species. This strong antioxidant action of paepalantine was reproduced in HepG2 cells exposed to oxidative stress condition induced by H(2)O(2).

4-hydroxy nimesulide effects on mitochondria and HepG2 cells. A comparison with nimesulide

We previously reported that the nonsteroidal anti-inflammatory drug, nimesulide (N-[4-nitro-2-phenoxyphenyl]-methanesulfonamide), is an uncoupler and oxidizes NAD(P)H in isolated rat liver mitochondria, triggering mitochondrial Ca2+ efflux or, if this effect is inhibited, eliciting mitochondrial permeability transition (Mingatto et al., Br. J. Pharmacol. 131:1154-1160, 2000). We presently demonstrated that nimesulide's hydroxylated metabolite (4-hydroxy nimesulide) lacks the uncoupling property of the parent drug, while keeping its ability to oxidize mitochondrial NADPH. In the presence of 10 microM Ca2+, low (5-50 microM) concentrations of 4-hydroxy nimesulide elicited mitochondrial permeability transition, as assessed by cyclosporin A-sensitive mitochondrial swelling, associated with mitochondrial Ca2+ efflux/membrane potential dissipation (Deltapsi), apparently occurring on account of the oxidation of mitochondrial protein thiols; no involvement of reactive oxygen species was observed. While nimesulide (0.5 or 1 mM, 30 h incubation) did not lead to significant HepG2 cell death, 4-hydroxy nimesulide caused a low extent (approximately 15%) of cell necrosis, partly prevented by cyclosporine A, suggesting the involvement of mitochondrial permeability transition. Both nimesulide and 4-hydroxy nimesulide caused NADPH oxidation and Deltapsi dissipation in HepG2 cells. Because such Deltapsi dissipation induced by the metabolite was almost completely inhibited by cyclosporine A, it probably results from the mitochondrial permeability transition. Therefore, mitochondrial permeability transition, in apparent association with NADPH oxidation, constitutes the most probable cause of HepG2 cell death elicited by 4-hydroxy nimesulide.

Effect of chronic ethanol consumption on endothelin-1 generation and conversion of exogenous big-endothelin-1 by the rat carotid artery

The purpose of the present work was to investigate whether conversion of exogenous applied big-endothelin-1 (Big-ET-1) as well as the basal release and mRNA levels of endothelin-1 (ET-1) is altered by ethanol consumption in the rat carotid. The measurement of the contraction induced by Big-ET-1 served as an indicative of functional endothelin (ET)-converting enzyme (ECE) activity. Cumulative application of exogenous Big-ET-1 elicited a concentration-related contraction with the concentration-response curve shifted to the right when compared to ET-1. In endothelium-intact rings, phosphoramidon (1 mmol/l), a nonselective ECE/neutral endopeptidase (NEP) inhibitor, produced a rightward displacement of the concentration-response curves and reduced the maximal contractile response to Big-ET-1. However, in endothelium-denuded rings phosphoramidon reduced the maximum contraction for Big-ET-1 but did not alter the potency when compared to the curves obtained in the absence of the inhibitor. Ethanol consumption for 2, 6, or 10 weeks reduced the contractile effect elicited by Big-ET-1 in carotid rings with intact endothelium when compared to control or isocaloric rings. However, no differences on Big-ET-1-induced contraction were observed after endothelial denudation. On the other hand, ethanol consumption increased ET-1-induced contraction. Finally, chronic ethanol consumption did not alter either the mRNA levels for pre-pro-ET-1 nor the basal release of ET-1. The present findings show that chronic ethanol consumption does not alter the mRNA levels for ET-1 or its basal release in the rat carotid. Moreover, ethanol intake reduces the contraction induced by exogenously applied Big-ET-1 in carotid rings with intact endothelium, a fact that might be the result of a reduced conversion of this peptide by ECE on its mature active peptide ET-1.

Potential toxicity of toluene and xylene evoked by mitochondrial uncoupling

Toluene and xylene are chemicals present in various laboratory and other industrial products. Their toxicity to the nervous system and to the liver has been well documented. In the present work, we have studied in vitro effects of toluene and xylene on the respiration of succinate-energized isolated rat liver mitochondria, membrane potential, Ca2+ release, reactive oxygen species (ROS), and ATP levels. Also Ca2+-dependent, cyclosporine A-sensitive mitochondrial swelling, an indicator of mitochondrial permeability transition (MPT), was studied. At 0.5-2.5 and 0.25-1mM concentrations respectively, toluene and xylene stimulated state 4 respiration in apparent association with mitochondrial membrane potential dissipation and Ca2+ release; these actions of both solvents are consistent with mitochondrial uncoupling. At higher concentrations (2.5 and 5mM, respectively) toluene and xylene also inhibited state 3 respiration. At 0.1-1mM concentrations, xylene elicited significant increase of ROS generation and partly Ca2+-dependent cyclosporine A-sensitive mitochondrial swelling. At 1 mM concentration, toluene or xylene caused depletions of mitochondrial ATP, amounting to 66.3% and 40.3%, respectively; depletions were only slightly dependent on Ca2+. It was concluded that mitochondrial uncoupling via ATP depletion might be responsible for the cell toxicity of toluene described earlier and in particular, of xylene. In the case of xylene, mitochondrial ROS generation and MPT also appear to be involved.

Effects of isocoumarins isolated from Paepalanthus bromelioides on mitochondria: Uncoupling, and induction/inhibition of mitochondrial permeability transition

Isolated mitochondria may undergo uncoupling, and in presence of Ca(2+) at different conditions, a mitochondrial permeability transition (MPT) linked to protein thiol oxidation, and demonstrated by CsA-sensitive mitochondrial swelling; these processes may cause cell death either by necrosis or by apoptosis. Isocoumarins isolated from the Brazilian plant Paepalanthus bromelioides (Eriocaulaceae) paepalantine (9,10-dihydroxy-5,7-dimethoxy-1H-naptho(2,3c)pyran-1-one), 8,8'-paepalantine dimer, and vioxanthin were assayed at 1-50 microM on isolated rat liver mitochondria, for respiration, MPT, protein thiol oxidation, and interaction with the mitochondrial membrane using 1,6-diphenyl-1,3,5-hexatriene (DPH). The isocoumarins did not significantly affect state 3 respiration of succinate-energized mitochondria; they did however, stimulate 4 respiration, indicating mitochondrial uncoupling. Induction of MPT and protein thiol oxidation were assessed in succinate-energized mitochondria exposed to 10 microM Ca(2+); inhibition of these processes was assessed in non-energized organelles in the presence of 300 microM t-butyl hydroperoxide plus 500 microM Ca(2+). Only paepalantine was an effective MPT/protein thiol oxidation inducer, also releasing cytochrome c from mitochondria; the protein thiol oxidation, unlike mitochondrial swelling, was neither inhibited by CsA nor dependent on the presence of Ca(2+). Vioxanthin was an effective inhibitor of MPT/protein thiol oxidation. All isocoumarins inserted deeply into the mitochondrial membrane, but only paepalantine dimer and vioxantin decreased the membrane's fluidity. A direct reaction with mitochondrial membrane protein thiols, involving an oxidation of these groups, is proposed to account for MPT induction by paepalantine, while a restriction of oxidation of these same thiol groups imposed by the decrease of membrane fluidity, is proposed to account for MPT inhibition by vioxanthin.

Ethanol consumption enhances endothelin-1-induced contraction in the isolated rat carotid

We investigated the mechanisms involved in the enhancement of endothelin (ET)-1 vascular reactivity induced by ethanol consumption. Ethanol intake for 2, 6, and 10 weeks enhanced the ET-1-induced contractile response of endothelium-intact but not endothelium-denuded rat carotid rings independently of the treatment duration. Conversely, phenylephrine-induced contraction was not affected by ethanol intake. The contraction induced by IRL1620 [succinyl-(Glu(9),Ala(11,15))-ET-1-(8-21)], a selective ET(B) agonist, was increased after treatment with ethanol in endothelium-intact but not in endothelium-denuded carotid rings. Moreover, ET-1- and IRL1620-induced relaxation was reduced in endothelium-intact phenylephrine-precontracted rings from ethanol-treated rats. Acetylcholine-induced relaxation was not affected by ethanol treatment. N(G)-Nitro-l-arginine methyl ester, 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one, indomethacin, and tetraethylammonium reduced the relaxation induced by IRL1620 in carotid glands from control but not ethanol-treated rats. The mRNA levels for ET(A) and ET(B) receptors were not altered by ethanol consumption. However, ethanol treatment reduced the protein expression of ET(B) receptors. Furthermore, immunohistochemical assays showed reduced immunostaining for endothelial ET(B) receptors after treatment with ethanol. We conclude that ethanol consumption enhances ET-1-induced contraction in the rat carotid and that this response is not different among the three periods of treatment used in this study. Finally, the potentiation of ET-1-induced vascular reactivity is probably caused by reduced expression of relaxing endothelial ET(B) receptors.

Hypolipemic and antioxidant activities from Tamarindus indica L. pulp fruit extract in hypercholesterolemic hamsters

Dietary modifications may significantly reduce cardiovascular disease (CVD) risk factors, including cholesterol and atherosclerosis. The present study addressed the effects of the crude extract from the pulp fruit of Tamarindus indica L. on lipid serum levels and early atherosclerotic lesions in hypercholesterolemic hamsters in vivo, and the extract's antioxidant action, in vitro. Animals were fed on either chow or atherogenic diet during 10 weeks and concomitantly received either water or T. indica L. extract for drinking. Treatment of hypercholesterolemic hamsters with the T. indica pulp fruit extract (5%) led to a decrease in the levels of serum total cholesterol (50%), non-HDL cholesterol (73%) and triglyceride (60%), and to an increase of high-density lipoprotein (HDL) cholesterol levels (61%). In vitro, the extract presented radical scavenging ability, as assessed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide radicals assays, and led to decreased lipid peroxidation in serum, as assessed by the thiobarbituric acid reactive substances (TBARS) assay. In vivo, the extract improved the efficiency of the antioxidant defense system, as assessed by the superoxide dismutase, catalase and glutathione peroxidase activities. Together these results indicate the potential of tamarind extracts in diminishing the risk of atherosclerosis development in humans.

Chronic ethanol consumption alters cardiovascular functions in conscious rats

Chronic ethanol intake and hypertension are related. In the present work, we investigated the effect of chronic ethanol (20% v/v) intake for 2, 6 and 10 weeks on basal arterial blood pressure, baroreflex and heart rate levels, as well as on the cardiovascular responses to the infusion of vasoactive agents in unanesthetized rats. Mild hypertension was observed after 2 weeks, 6 weeks or 10 weeks of treatment. On the other hand, no changes were observed in heart rate after long-term ethanol intake. Similar baroreflex changes were observed in 2- or 6-week ethanol-treated rats, and affected all parameters of baroreflex sigmoid curves, when compared to the control group. These changes were characterized by an enhanced baroreflex sympathetic component and a reduction in the baroreflex parasympathetic component. No differences in baroreflex parameters were observed in 10-week ethanol-treated animals. The pressor effects of i.v. phenylephrine were enhanced in 2-week ethanol-treated rats; not affected in 6-week treated animals and reduced in 10-week ethanol-treated rats, when compared to respective control and isocaloric groups. The hypotensive response to i.v. sodium nitroprusside (SNP) was enhanced at all different times of treatment, when compared to respective control and isocaloric groups. In conclusion, the present findings showed increased arterial pressure in the early phase of chronic ethanol consumption, which was consequent of rise in both systolic and diastolic pressures. Ethanol intake affected both the sympathetic and the parasympathetic components of the baroreflex. Vascular responsiveness to the pressor agent phenylephrine was initially enhanced and later on decreased during chronic ethanol intake. Vascular responsiveness to the depressor agent SNP was enhanced during chronic ethanol intake.

The interaction of flavonoids with mitochondria: effects on energetic processes

The study addressed aspects of energetics of isolated rat liver mitochondria exposed to the flavonoids quercetin, taxifolin, catechin and galangin, taking into account influences of the 2,3 double bond/3-OH group and 4-oxo function on the C-ring, and o-di-OH on the B-ring of their structures, as well as mitochondrial mechanisms potentially involved in cell necrosis and apoptosis. The major findings/hypothesis, were: The 2,3 double bond/3-OH group in conjugation with the 4-oxo function on the C-ring in the flavonoid structure seems favour the interaction of these compounds with the mitochondrial membrane, decreasing its fluidity either inhibiting the respiratory chain of mitochondria or causing uncoupling; while the o-di-OH on the B-ring seems favour the respiratory chain inhibition, the absence of this structure seems favour the uncoupling activity. The flavonoids not affecting the respiration of mitochondria, induced MPT. The ability of flavonoids to induce the release of mitochondria-accumulated Ca(2+) correlated well with their ability to affect mitochondrial respiration on the one hand, and their inability to induce MPT, on the other. The flavonoids causing substantial respiratory chain inhibition or mitochondrial uncoupling, quercetin and galangin, respectively, also decreased the mitochondrial ATP levels, thus suggesting an apparent higher potential for necrosis induction in relation to the flavonoids inducing MPT, taxifolin and cathechin, which did not decrease significantly the ATP levels, rather suggesting an apparent higher potential for apoptosis induction.

A PMR1-like calcium ATPase ofAspergillus fumigatus: cloning, identification and functional expression inS. cerevisiae

The understanding of the controlling factors of calcium homeostasis in Aspergillus fumigatus is very poor, although this ion is involved in several important events of these particular cells. We have cloned, identified and expressed for functional complementation a PMR1-like Ca(2+)-ATPase gene from A. fumigatus. The Afpmr1 gene encodes a protein of 1061 deduced amino acids, containing all the conserved subdomains found in other P-type ATPases: the phosphatase region, phosphorylation site, FITC labelling site, ATP binding domain; E(386), N871, D875 amino acid residues for calcium ion interaction and Q880, a residue that alters ion selectivity in PMR1. The expressed AfPMR1 in S. cerevisiae K616 strain functionally complemented the deficient growth in EGTA (5-20 mM)- and MnCl2 (4 mM)-containing medium. These results demonstrate the first evidence of a Ca(2+)-ATPase in A. fumigatus and strongly suggest a role for this enzyme in calcium and manganese homeostasis.

A proposed sequence of events for cadmium-induced mitochondrial impairment

Cadmium is a very important environmental toxicant, the cytotoxicity mechanism of which is likely to involve mitochondria as a target. In the present study we addressed the cause/effect relationship between the multiple cadmium-induced responses involving the mitochondrial energetic and oxidative status. Assays were performed with succinate-energized rat liver mitochondria incubated with 5 microM CdCl(2) for 0-25 min, in the absence or presence, respectively, of N-ethylmaleimide (NEM), butylhydroxytoluene (BHT), ruthenium red (RR), and cyclosporine A+ADP. A sequence of events accounting for cadmium-induced mitochondrial impairment is proposed, beginning with an apparent interaction of Cd(2+) with specific protein thiols in the mitochondrial membrane, which stimulates the cation's uptake via the Ca(2+) uniporter, and is followed by the onset of mitochondrial permeability transition (MPT); both effects dissipate the transmembrane electrical potential (Deltapsi), causing uncoupling, followed by an early depression of mitochondrial ATP levels. The respiratory chain subsequently undergoes inhibition, generating reactive oxygen species which together with iron mobilized by the cation, cause late, gradual mitochondrial membrane lipid peroxidation.

The critical role of mitochondrial energetic impairment in the toxicity of nimesulide to hepatocytes

We described the effects of nimesulide (N-[4-nitro-2-phenoxyphenyl]-methanesulfonamide) and its reduced metabolite in isolated rat hepatocytes. Nimesulide stimulated the succinate-supported state 4 respiration of mitochondria, indicating an uncoupling effect of the drug. Incubation of hepatocytes with nimesulide (0.1-1 mM) elicited a concentration- and time-dependent decrease in cell viability as assessed by lactate dehydrogenase leakage, a decrease of mitochondrial membrane potential as assessed by rhodamine 123 retention, and cell ATP depression. Nimesulide also decreased the levels of NAD(P)H and glutathione in hepatocytes, but the extent of the effects was less pronounced in relation to the energetic parameters; in addition, these effects did not imply the peroxidation of membrane lipids. The decrease in the viability of hepatocytes was prevented by fructose and, to a larger extent, by fructose plus oligomycin; it was stimulated by proadifen, a cytochrome P450 inhibitor. In contrast, the reduced metabolite of nimesulide did not present any of the effects observed for the parent drug. These results indicate that: 1) nimesulide causes injury to the isolated rat liver cells, 2) this effect is mainly mediated by impairment of ATP production by mitochondria due to uncoupling, and 3) on account of the activity of its nitro group, the parent drug by itself is the main factor responsible for its toxicity to the hepatocytes.

Thioridazine interacts with the membrane of mitochondria acquiring antioxidant activity toward apoptosis--potentially implicated mechanisms

We evaluated the effects of the phenothiazine derivative thioridazine on mechanisms of mitochondria potentially implicated in apoptosis, such as those involving reactive oxygen species (ROS) and cytochrome c release, as well as the involvement of drug interaction with mitochondrial membrane in these effects. Within the 0 - 100 microM range thioridazine did not reduce the free radical 1,1-diphenyl-2-picryl-hydrazyl (DPPH) nor did it chelate iron. However, at 10 microM thioridazine showed important antioxidant activity on mitochondria, characterized by inhibition of accumulation of mitochondria-generated O2*-, assayed as lucigenin-derived chemiluminescence, inhibition of Fe2+/citrate-mediated lipid peroxidation of the mitochondrial membrane (LPO), assayed as malondialdehyde generation, and inhibition of Ca2+/t-butyl hydroperoxide (t-BOOH)-induced mitochondrial permeability transition (MPT)/protein-thiol oxidation, assayed as mitochondrial swelling. Thioridazine respectively increased and decreased the fluorescence responses of mitochondria labelled with 1-aniline-8-naphthalene sulfonate (ANS) and 1-(4-trimethylammonium phenyl)-6 phenyl 1,3,5-hexatriene (TMA-DPH). The inhibition of LPO and MPT onset correlated well with the inhibition of cytochrome c release from mitochondria. We conclude that thioridazine interacts with the inner membrane of mitochondria, more likely close to its surface, acquiring antioxidant activity toward processes with potential implications in apoptosis such as O2*- accumulation, as well as LPO, MPT and associated release of cytochrome c.

The sterol composition of Trypanosoma cruzi changes after growth in different culture media and results in different sensitivity to digitonin-permeabilization

Respiration, oxidative phosphorylation. and the corresponding changes in membrane potential (deltapsi) of Trypanosoma cruzi epimastigotes grown either in liver infusion-tryptose (LIT) or brain heart infusion (BHI) culture medium were assayed in situ using digitonin to render their plasma membrane permeable to succinate, ADP, safranine O, and other small molecules. When the cells were permeabilized with 64 microM digitonin, a concentration previously used with epimastigotes, the ability of the cells grown in LIT medium to sustain oxidative phosphorylation was demonstrated by the detection of an oligomycin-sensitive decrease in mitochondrial membrane potential induced by ADP. In contrast, the cells grown in BHI medium were not able to sustain a stable membrane potential and did not respond to ADP addition. Analyses of oxygen consumption by these permeabilized cells indicated that the rate of basal respiration, which was similar in both cell types, was significantly decreased by 64 microM digitonin. Addition of ADP to the permeabilized cells grown in LIT medium promoted an oligomycin-sensitive transition from resting to phosphorylating respiration in contrast to the cells grown in BHI medium, whose respiration decreased steadily and did not respond either to ADP or CCCP. Titration of the cells grown in BHI medium with different digitonin concentrations indicated that their mitochondria have higher sensitivity to digitonin than those grown in LIT medium. Analysis of the sterol composition of epimastigotes grown in the two different media showed a higher percentage of cholesterol in total and mitochondrial extracts of epimastigotes grown in BHI medium as compared to those grown in LIT medium, suggesting the involvement of this sterol in their increased sensitivity to digitonin-permeabilization.

Flufenamic acid as an inducer of mitochondrial permeability transition

To assess the mechanism by which mitochondrial permeability transition (MPT) is induced by the nonpolar carboxylic acids, we investigated the effects of flufenamic acid (3'-trifluoromethyl diphenylamine-2-carboxylic acid, FA) on mitochondrial respiration, electrical transmembrane potential difference (delta psi), osmotic swelling, Ca2+ efflux, NAD(P)H oxidation and reactive oxygen species (ROS) generation. Succinate-energized isolated rat liver mitochondria incubated in the absence or presence of 10 microM Ca2+, 5 microM ruthenium red (RR) or 1 microM cyclosporin A (CsA) were used. The dose response-curves for both respiration release and delta psi dissipation were nearly linear, presenting an IC50 of approximately 10 microM and reaching saturation within 25-50 microM, indicating that FA causes mitochondrial uncoupling by a protonophoric mechanism. Within this same concentration range FA showed the ability to induce MPT in energized mitochondria incubated with 10 microM Ca2+, followed by delta psi dissipation and Ca2+ efflux, and even in deenergized mitochondria incubated with 0.5 mM Ca2+. ADP, Mg2+, trifluoperazine (TFP) and N-ethylmaleimide (NEM) reduced the extent of FA-promoted swelling in energized mitochondria by approximately one half, whereas dithiothreitol (DTT) slightly enhanced it. NAD(P)H oxidation and ROS generation (H2O2 production) by mitochondria were markedly stimulated by FA; these responses were partly prevented by CsA, suggesting that they may be implicated as both a cause and effect of FA-induced MPT. FA incubated with mitochondria under swelling assay conditions caused a decrease of approximately 40% in the content of protein thiol groups reacting with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). The present results are consistent with a ROS-intermediated sensitization of MPT by a direct or indirect FA interaction with inner mitochondrial membrane at a site which is in equilibrium with the NAD(P)H pool, namely thiol groups of integral membrane proteins.

Oxidative phosphorylation, Ca(2+) transport, and fatty acid-induced uncoupling in malaria parasites mitochondria

Respiration, oxidative phosphorylation, calcium uptake, and the mitochondrial membrane potential of trophozoites of the malaria parasite Plasmodium berghei were assayed in situ after permeabilization with digitonin. ADP promoted an oligomycin-sensitive transition from resting to phosphorylating respiration. Respiration was sensitive to antimycin A and cyanide. The capacity of trophozoites to sustain oxidative phosphorylation was additionally supported by the detection of an oligomycin-sensitive decrease in mitochondrial membrane potential induced by ADP. Phosphorylation of ADP could be obtained in permeabilized trophozoites in the presence of succinate, citrate, alpha-ketoglutarate, glutamate, malate, dihydroorotate, alpha-glycerophosphate, and N,N,N',N'-tetramethyl-p-phenylenediamine. Ca(2+) uptake caused membrane depolarization compatible with the existence of an electrogenically mediated Ca(2+) transport system in these mitochondria. An uncoupling effect of fatty acids was partly reversed by bovine serum albumin, ATP, or GTP and not affected by atractyloside, ADP, glutamate, or malonate. Evidence for the presence of a mitochondrial uncoupling protein in P. berghei was also obtained by using antibodies raised against plant uncoupling mitochondrial protein. Together these results provide the first direct biochemical evidence of mitochondrial function in ATP synthesis and Ca(2+) transport in a malaria parasite and suggest the presence of an H(+) conductance in trophozoites similar to that produced by a mitochondrial uncoupling protein.

Calcium mobilization by arachidonic acid in trypanosomatids

A recent report (Eintracht J, Maathai R, Mellors A, Ruben L. Calcium entry in Trypanosoma brucei is regulated by phospholipase A, and arachidonic acid, Biochem J 1998:336:659-66) provided evidence that calcium entry in Trypanosoma brucei bloodstream trypomastigotes is regulated via a signaling pathway involving phospholipase A2-mediated generation of arachidonic acid and stimulation of a plasma membrane-located calcium channel. Here we show that Ca2+ influx in T. brucei procyclic trypomastigotes, Leishmania donovani promastigotes and T. cruzi amastigotes was also stimulated in a dose-dependent manner (50-400 nM) by the amphiphilic peptide melittin. This effect was blocked by the phospholipase A, inhibitor 3-(4-octadecyl)-benzoylacrylic acid. The unsaturated fatty acid arachidonic acid, in the range of 10-75 microM, induced Ca2+ entry by a mechanism sensitive to LaCl3. However, both melittin and arachidonic acid induced an increase in [Ca2+]i in T. brucei procyclic trypomastigotes incubated in Ca2+-free medium implying Ca2+ mobilization from intracellular stores. This hypothesis was supported by experiments showing that arachidonic acid promoted Ca2+ release from the acidocalcisomes of these cells. The results showing changes in mitochondrial membrane potential, release of acridine orange and Ca2+ from the acidocalcisomes and Ca2+ transport across the plasma membrane suggest that in addition to the possible stimulation of a Ca2+ channel-mediated process, arachidonic acid, in the range of concentrations used here, have other nonspecific effects on the trypanosomatids membranes.

Fluoxetine interacts with the lipid bilayer of the inner membrane in isolated rat brain mitochondria, inhibiting electron transport and F1F0-ATPase activity

The effects of fluoxetine on the oxidative phosphorylation of mitochondria isolated from rat brain and on the kinetic properties of submitochondrial particle F1F0-ATPase were evaluated. The state 3 respiration rate supported by pyruvate + malate, succinate, or ascorbate + tetramethyl-p-phenylenediamine (TMPD) was substantially decreased by fluoxetine. The IC50 for pyruvate + malate oxidation was approximately 0.15 mM and the pattern of inhibition was the typical one of the electron-transport inhibitors, in that the drug inhibited both ADP- and carbonyl cyanide m-chlorophenylhydrazone (CCCP)-stimulated respirations and the former inhibition was not released by the uncoupler. Fluoxetine also decreased the activity of submitochondrial particle F1F0-ATPase (IC50 approximately 0.08 mM) even though K0.5 and activity of Triton X-100 solubilized enzyme were not changed substantially. As a consequence of these effects, fluoxetine decreased the rate of ATP synthesis and depressed the phosphorylation potential of mitochondria. Incubation of mitochondria or submitochondrial particles with fluoxetine under the conditions of respiration or F1F0-ATPase assays, respectively, caused a dose-dependent enhancement of 1-anilino-8-naphthalene sulfonate (ANS) fluorescence. These results show that fluoxetine indirectly and nonspecifically affects electron transport and F1F0)-ATPase activity inhibiting oxidative phosphorylation in isolated rat brain mitochondria. They suggest, in addition, that these effects are mediated by the drug interference with the physical state of lipid bilayer of inner mitochondrial membrane.

Respiration and oxidative phosphorylation in the apicomplexan parasite Toxoplasma gondii

Respiration, oxidative phosphorylation, and the mitochondrial membrane potential (DeltaPsi) of tachyzoites of the apicomplexan parasite Toxoplasma gondii were assayed in situ using very low concentrations of digitonin to render their plasma membrane permeable to succinate, ADP, safranin O, and other small molecules. The rate of basal respiration was slightly increased by digitonin when the cells were incubated in medium containing succinate. ADP promoted an oligomycin-sensitive transition from resting to phosphorylating respiration. Respiration was sensitive to antimycin A and cyanide, and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) was oxidized by antimycin A-poisoned mitochondria. The addition of ADP after TMPD/ascorbate also resulted in phosphorylating respiration. The antitoxoplasmosis drug atovaquone, at a very low concentration (0.03 microM), totally inhibited respiration and disrupted the mitochondrial membrane potential. Atovaquone was shown to inhibit the respiratory chain of T. gondii and mammalian mitochondria between cytochrome b and c1 as occurs with antimycin A1. Phosphorylation of ADP could not be obtained in permeabilized tachyzoites in the presence of either pyruvate, 3-oxo-glutarate, glutamate, isocitrate, dihydroorotate, alpha-glycerophosphate, or endogenous substrates. Although ADP phosphorylation was detected in the presence of malate, this activity was rotenone-insensitive and was probably due to the conversion of malate into succinate through a fumarate reductase activity that was detected in mitochondrial extracts. Together these results provide the first direct biochemical evidence that the respiratory chain and oxidative phosphorylation are functional in apicomplexan parasites, although the terminal respiratory pathway is different from that in the mammalian host.

Influence of nonsteroidal anti-inflammatory drugs on calcium efflux in isolated rat renal cortex mitochondria and aspects of the mechanisms involved

In the present study we investigated the influence of several nonsteroidal anti-inflammatory drugs on calcium efflux in isolated rat renal cortex mitochondria in order to assess their potential to disrupt cell calcium homeostasis, as well as aspects of the mechanisms associated with oxidation of mitochondrial pyridine nucleotides (NAD(P)H) and with inhibition of the process by cyclosporin A (CsA). Calcium efflux was estimated with arsenazo III as an indicator and the redox state of NAD(P)H was monitored fluorimetrically at the 366/450 nm excitation/emission wavelength pair. Dipyrone, paracetamol and ibuprofen did not induce calcium efflux even at 1 mM, piroxicam and salicylate were poor inducers, while diclofenac sodium and mefenamic acid were potent inducers releasing calcium even at 20 microM and 10 microM, respectively. In the presence of 10 microM calcium, CsA had no appreciable effect while in the presence of 30 microM calcium it delayed calcium efflux. Oxidation of mitochondrial NAD(P)H, concomitant with calcium efflux and inhibited by CsA, was observed only in the presence of 30 microM calcium. The results suggest that diclofenac sodium and mefenamic acid induce calcium efflux in mitochondria through both a mechanism intrinsic to the mitochondrial membrane permeability transition and a mechanism including the electroneutral Ca2+/nH+ porter.

Effect of naturally occurring flavonoids on lipid peroxidation and membrane permeability transition in mitochondria

The ability of eight structurally related naturally occurring flavonoids in inhibiting lipid peroxidation and mitochondrial membrane permeability transition (MMPT), as well as respiration and protein sulfhydryl oxidation in rat liver mitochondria, was evaluated. The flavonoids tested exhibited the following order of potency to inhibit ADP/ Fe(II)-induced lipid peroxidation, estimated with the thiobarbituric acid assay: 3'-O-methyl-quercetin > quercetin > 3,5,7,3',4'-penta-O-methyl-quercetin > 3,7,3',4'-tetra-O-methyl-quercetin > pinobanksin > 7-O-methyl-pinocembrin > pinocembrin > 3-O-acyl-pinobanksin. MMPT was estimated by the extent of mitochondrial swelling induced by 10 microM CaCl2 plus 1.5 mM inorganic phosphate or 30 microM mefenamic acid. The most potent inhibitors of MMPT were quercetin, 7-O-methyl-pinocembrin, pinocembrin, and 3,5,7,3',4'-penta-O-methyl-quercetin. The first two inhibited in parallel the oxidation of mitochondrial protein sulfhydryl involved in the MMPT mechanism. The most potent inhibitors of mitochondrial respiration were 7-O-methyl-pinocembrin, quercetin, and 3'-O-methyl-quercetin while the most potent uncouplers were pinocembrin and 3-O-acyl-pinobanksin. In contrast 3,7,3',4'-tetra-O-methyl-quercetin and 3,5,7,3',4'-penta-O-methyl-quercetin showed the lowest ability to affect mitochondrial respiration. We conclude that, in general, the flavonoids tested are able to inhibit lipid peroxidation on the mitochondrial membrane and/or MMPT. Multiple methylation of the hydroxyl substitutions, in addition to sustaining good anti-lipoperoxidant activity, reduces the effect of flavonoids on mitochondrial respiration, and therefore, increases the pharmacological potential of these compounds against pathological processes related to oxidative stress.

Hg(II)-induced renal cytotoxicity: in vitro and in vivo implications for the bioenergetic and oxidative status of mitochondria

The effects of Hg(II) on bioenergetic and oxidative status of rat renal cortex mitochondria were evaluated both in vitro, and in vivo 1 and 24 h after treatment of animals with 5 mg HgCl2/kg i.p. The parameters assessed were mitochondrial respiration, ATP synthesis and hydrolysis, glutathione content, lipid peroxidation, protein oxidation, and activity of antioxidant enzymes. At low concentration (5 microM) and during a short incubation time, Hg(II) uncoupled oxidative phosphorylation while at slightly higher concentration or longer incubation time the ion impaired the respiratory chain. The rate of ATP synthesis and the phosphorylation potential of mitochondria were depressed, although inhibition of ATP synthesis did not exceed 50%. In vivo, respiration and ATP synthesis were not affected 1 h post-treatment, but were markedly depressed 24 h later. ATP hydrolysis by submitochondrial particle FoF1-ATPase was inhibited (also by no more than 50%) both in vitro, and in vivo 1 and 24 h post-treatment. Hg(II) induced maximum ATPase inhibition at about 1 microM concentration but did not have a strong inhibitory effect in the presence of Triton X-100. Oxidative stress was not observed in mitochondria 1 h post-treatment. However, 24 h later Hg(II) reduced the GSH/GSSG ratio and increased mitochondrial lipid peroxidation and protein oxidation, as well as inhibited GSH-peroxidase and GSSG-reductase activities. These results suggest that the following sequence of events may be involved in Hg(II) toxicity in the kidney: (1) inhibition of FoF1-ATPase, (2) uncoupling of oxidative phosphorylation, (3) oxidative stress-associated impairment of the respiratory chain, and (4) inhibition of ATP synthesis.

Diclofenac sodium and mefenamic acid: potent inducers of the membrane permeability transition in renal cortex mitochondria

The ability of nonsteroidal anti-inflammatory drugs (NSAIDs) to induce Ca(2+)-mediated/cyclosporin A-sensitive mitochondrial membrane permeability transition (MMPT) was evaluated by monitoring swelling of isolated rat renal cortex mitochondria in the presence of 20 microM CaCl2. Dipyrone and paracetamol did not induce MMPT, while piroxicam and acetylsalicylic acid (and its metabolite salicylate) were poor inducers. In contrast, diclofenac sodium and mefenamic acid were potent triggering agents, inducing MMPT at 2 microM, a concentration below those previously shown to uncouple and/or inhibit oxidative phosphorylation. When compared to salicylate, a classical uncoupler and inducer of MMPT, the potency of diclofenac sodium and mefenamic acid was about 50-fold greater. Swelling was completely prevented by EGTA, cyclosporin A, or MgCl2, and only partially by ADP or dithiothreitol. Under the same experimental conditions as for the swelling assays, the drugs depressed the membrane potential of mitochondria, an effect prevented by cyclosporin A and restored by EGTA. Also, the drugs did not induce membrane lipid peroxidation or changes in GSSG levels, but led to a small decrease in protein thiol content, as well as to a substantial decrease in the NADPH levels of mitochondria. Hence, membrane depolarization and pyridine nucleotide oxidation seem to be involved in MMPT induction by these NSAIDs. The potency in eliciting the process, like the uncoupling activity, seems to be influenced by the lipophilic character of the molecules.

Heart FoF1-ATPase changes during the acute phase of Trypanosoma cruzi infection in rats

The kinetic properties of ATP hydrolysis and synthesis by FoF1-ATPase of heart mitochondria were evaluated during the acute phase of T. cruzi infection in rats. Mitochondria and submitochondrial particles were isolated 7 days (early stage) and 25 days (late stage) following infection of rats with 2 x 10(5) trypomastigote forms of the Y strain of T. cruzi. The kinetic properties for ATP hydrolysis were altered for the early but not the late stage, showing a changed pH profile, increased K0.5 values, and a decreased total Vmax. The Arrhenius' plot for membrane-associated enzyme showed a higher transition temperature with a lower value for the activation energy in body temperature. For the Triton X-100-solubilized enzyme, the plot was similar to the control. A decrease in the efficiency of ADP phosphorylation by mitochondria, measured by the firefly-luciferase luminescence, was observed only during the late stage and appeared to be correlated with a decrease in the affinity of the FoF1-ATPase for ADP. It is proposed that in the early stage, during the acute phase of T. cruzi infection in rats, heart FoF1-ATPase undergoes a membrane-dependent conformational change in order to maintain the phosphorylation potential of mitochondria, which would compensate for the uncoupling of mitochondrial function. Also, during both the early and late stages, the enzyme seems to be under the regulation of the endogenous inhibitor protein for the preservation of cellular ATP levels.

In vitro interaction of nonsteroidal anti-inflammatory drugs on oxidative phosphorylation of rat kidney mitochondria: respiration and ATP synthesis

The in vitro interference of some of most important nonsteroidal anti-inflammatory drugs (NSAIDs) with the respiration of rat kidney (renal cortex) mitochondria and ATP synthesis was evaluated. Acetylsalicylic acid, diclofenac sodium, mefenamic acid, and piroxicam both uncoupled and inhibited oxidative phosphorylation in mitochondria energized with glutamate plus malate or with succinate, while dipyrone only uncoupled and paracetamol only inhibited it. The drug concentrations affecting mitochondrial respiration were in the low to middle micromolar range for diclofenac, mefenamic acid, and piroxicam, and in the low millimolar range for acetylsalicylic acid, dipyrone, and paracetamol. The pattern of inhibition, except for the paracetamol, was similar to that expressed by the respiratory chain inhibitors. NSAIDs also inhibited the rate of ATP synthesis in mitochondria energized with glutamate plus malate, as well as the phosphorylation potential of mitochondria. The IC50 values for rate of ATP synthesis, using 2 mM ADP, were about 0.1 mM for diclofenac sodium and mefenamic acid, 0.7 mM for piroxicam, and in the range of 5-8 mM for acetylsalicylic acid, dipyrone, and paracetamol. The potential for renal energetic cytotoxicity of NSAIDs is discussed considering their ability to interact with the oxidative phosphorylation in rat renal cortex mitochondria. A comparison is made with the interference of salicylate, the main metabolite of acetylsalicylic acid, and a classical uncoupler of oxidative phosphorylation.

Energetics of heart mitochondria during acute phase of Trypanosoma cruzi infection in rats

The energetics of heart mitochondria was studied in the acute phase of Trypanosoma cruzi infection in rats. Wistar rats were infected with 2 x 10(5) trypomastigote forms of the Y strain of T. cruzi, and heart mitochondria and submitochondrial particles isolated after 7 and 25 days of infection. Ultrastructure of mitochondria seemed to be preserved, but cytochrome c levels were significantly depressed. Respiratory control ratios (RCR) were decreased for glutamate and succinate oxidations, as a consequence of inhibition of respiration in state 3 and/or of stimulation of respiration in state 4. Stimulation of hydrolytic activity of FoF1-ATPase by energization of mitochondria was approx. 2-fold higher in relation to controls. Mitochondrial ATP concentration remained constant. In conclusion, during the acute phase of T. cruzi infection in rats there is an energy impairment at the level of heart mitochondria, but their ultrastructure and ATP concentration seem to be preserved; the maintenance of ATP may be due to an adaptative mechanism of the cell which includes inhibition of the hydrolytic activity of FoF1-ATPase.

Effect of fluoxetine on rat liver mitochondria

The in vitro and in vivo effects of fluoxetine (and its active metabolite norfluoxetine) on mitochondrial respiration and F0F1-ATPase were studied, respectively, in mitochondria and submitochondrial particles isolated from rat liver. Fluoxetine in vitro inhibited state 3 mitochondrial respiration for alpha-ketoglutarate and succinate oxidations (50% of effect at 0.25 and 0.35 mM drug concentrations, respectively); stimulated state 4 for succinate; and induced a decrease in the respiratory control ratio (RCR) for both oxidizable substrates. The F0F1-ATPase activity was determined at various pH levels in the absence and presence of Triton X-100. The solubilized form was not affected markedly, but an inhibition, apparently non-competitive, was observed for the membrane-bound enzyme, with 50% of the effect at a 0.06 mM drug concentration in pH 7.4. These results suggest that fluoxetine in vitro acts on F0F1-ATPase through direct interaction with the membrane F0 component (similar to oligomycin), or first with mitochondrial membrane and then affecting F0. A very similar behavior concerning the respiratory parameters and F0F1-ATPase properties was observed with norfluoxetine. The in vivo studies with fluoxetine showed stimulation of mitochondrial respiration in state 4 for alpha-ketoglutarate or succinate oxidations in acute or prolonged treatments (1 hr after a single i.p. dose of 20 mg of drug/kg of body weight, and 22 hr after 12 days of treatment with a daily dose of 10 mg/kg of body weight, respectively), indicating uncoupling of oxidative phosphorylation. Pronounced changes were not observed in the K0.5 values of F0F1-ATPase catalytic sites, but the Vmax decreased during the prolonged treatment. The results show that fluoxetine (as well as norfluoxetine) has multiple effects on the energy metabolism of rat liver mitochondria, being potentially toxic in high doses. The drug effects seem to be a consequence of the drug and/or metabolite solubilization in the inner membrane of the mitochondria.

Steady-state kinetic properties of FoF1-ATPase: the pH effect

1. The kinetic properties of FoF1-ATPase from submitochondrial particles isolated from rat heart were studied, with emphasis to the pH effect. The velocity data were treated according to the Hill equation, and the results were discussed on the basis of the knowledge on the soluble F1-ATPase properties. 2. Three kinetic phases were observed in the range of pH 6.0-8.5, with apparent dissociation constant values (K0.5) of 0.001, 0.04 and 1.5 mM (respectively sites I, II and III) at pH 7.0. Their contribution to the total activity of the enzyme were pH-dependent on the range of 6.0-7.0, but not from 7.0 to 8.5, where the maximal velocity (V) for site III was some 4-fold larger than for site II, and the total V of sites II and III was some 40-fold larger than V assumed for site I. Therefore, two catalytic sites seem to participate significantly in the catalysis at steady-state condition. 3. Azide increased the sites II and III K0.5 values as well as decreased the site III V. In the presence of bicarbonate these two sites were not distinguishable, and the kinetic parameters at pH 7.0 were similar to those for sites II and III combined. Both azide and bicarbonate did not have a significant effect on site I, and this behavior was not pH-dependent. 4. The studies on the effect of pH on the kinetic parameters showed the following results: (1) the optimum pH for V was around 8.5; (2) decrease in the K0.5 values at pH below 7.0 for site II, and increase at pH over 7.0 for sites II and III; (3) in the pH range of 6.0-8.5 the Hill coefficient increased for site II, decreased for site III, and an intermediary effect was observed for the sites II and III combined, with a Michaelis-Menten behavior in the highest affinity pH, which was found in the physiological range.

Respiration and mitochondrial ATPase in energized mitochondria during isoproterenol-induced cell injury of myocardium

1. Respiration of mitochondria, membrane potential and mitochondrial ATPase under energized conditions were studied in rat myocardium during cell injury induced by treatment with isoproterenol. 2. Increase in the state 4 rate of respiration and ADP:O ratio, as well as decrease in the state 3 rate and Respiratory Control Ratio (RCR) were found. 3. The optimum pH for RCR and for maximum ATPase activity was shifted to lower values. 4. The state 3 respiration was more sensitive to oligomycin inhibition. 5. The mitochondria showed lower ability to generate membrane potential. 6. An increase in the K0.5 values for catalytic sites II and III of mitochondrial ATPase at pH 7.4 and 5.5 was found. 7. These results are consistent with alterations on the integrity of mitochondrial membrane, and corroborate with the hypothesis of changes on the mitochondrial ATPase during isoproterenol-induced cell injury of myocardium.

Kinetic properties of mitochondrial ATPase during isoproterenol-induced cardiomyopathy

1. The kinetic characteristics of the ATP hydrolysis by membrane-bound and Triton X-100 solubilized mitochondrial ATPase, during the isoproterenol-induced cardiomyopathy, were investigated. 2. An increase in the inhibitory action of the oligomycin, a decrease in the affinity of the ATP binding sites and an increase of both activation energy and rate of thermal inactivation were observed for mitochondrial ATPase. 3. The possibility that the changes described are related to the modifications of the active configuration of mitochondrial ATPase, during the isoproterenol-induced cardiomyopathy, is discussed.