Jonas Sarlauskas | Vilnius university Institute of Biochemistry (original) (raw)
Papers by Jonas Sarlauskas
Acta Biochimica Polonica, Feb 1, 2004
With an aim to understand the toxicity mechanisms of the explosive 4,6-dinitro- benzofuroxan (DNB... more With an aim to understand the toxicity mechanisms of the explosive 4,6-dinitro- benzofuroxan (DNBF), we studied its single-electron reduction by NADPH:cytochrome P450 reductase and ferredoxin:NADP(+) reductase, and two- electron reduction by DT-diaphorase and Enterobacter cloacae nitroreductase. The enzymatic reactivities of DNBF and another explosive 2,4,6-trinitrotoluene (TNT) were similar, except for the much lower reactivity of DNBF towards nitroreductase. DNBF was less cytotoxic in FLK cells than TNT. However, their action shared the same mechanisms, oxidative stress and activation by DT-diaphorase. The lower cytotoxicity of DNBF may be explained by the negative electrostatic charge of its adduct with water which may impede cellular membrane penetration, and by the formation of its less reactive adducts with intracellular reduced glutathione.
Chemical Research in Toxicology, 2015
Aziridinylquinone RH-1 (2,5-diaziridinyl-3-hydroxymethyl-6-methyl-cyclohexa-2,5-diene-1,4-dione) ... more Aziridinylquinone RH-1 (2,5-diaziridinyl-3-hydroxymethyl-6-methyl-cyclohexa-2,5-diene-1,4-dione) is a potential anticancer agent. RH-1 action is associated with NAD(P)H:quinone oxidoreductase (NQO1) which reduces this diaziridinylbenzoquinone into DNA-alkylating hydroquinone and is overexpressed in many tumors. Another suggested mechanism of RH-1 toxicity is the formation of reactive oxygen species (ROS) arising from its redox cycling. In order to improve anticancer action of this and similar antitumor quinones, we investigated the involvement of different signaling molecules in cytotoxicity induced by RH-1 by using wild-type tumor suppressor p53 bearing nonsmall cell lung carcinoma A549 cells as a model. Gradual and prolonged increase of mitogen-activated protein kinases (MAPK) ERK, P38, and JNK phosphorylation was observed during 24-h RH-1 treatment. In parallel, activation of DNA damage-sensing ATM kinase, upregulation, and phosphorylation of TP53 (human p53) took place. Inhibition studies revealed that RH-1-induced A549 apoptosis involved the NQO1-ATM-p53 signaling pathway and ROS generation. TP53 participated in ROS- and DNA damage-induced cell death differently. Moreover, MAP kinase JNK was another TP53 activator and death inducer in A549 cells. At the same time, rapid and prolonged activation of AKT kinase during RH-1 treatment was found, and it proved to be antiapoptotic kinase in our model system. Therefore, we identified that different and opposite cell death regulating signaling pathways, which may counteract one another, are induced in cancer cells during chemotherapeutic RH-1 treatment.
Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics, 2015
Acquired resistance of tumor cells to the therapeutic treatment is a major challenge in virtually... more Acquired resistance of tumor cells to the therapeutic treatment is a major challenge in virtually any chemotherapy. A novel anticancer agent 2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone (RH1) is designed to be activated by quinone oxidoreductase, an enzyme expressed at high levels in many types of tumors. Here we investigated the potential mechanisms of acquired RH1 drug resistance in cancer cells by applying high-throughput differential quantitative proteomic analysis of the newly established RH1-resistant hepatoma cell lines. Over 400 proteins display significantly altered levels between drug-sensitive and drug-resistant cell lines. Differentially expressed proteins were clustered into more than 14 groups according to their functional annotation and protein-protein interactions. Bioinformatic analysis highlights the biological processes that might be responsible for acquired resistance to RH1. The level of several xenobiotic metabolism enzymes (total n=17) involved in RH1 activation and detoxification is decreased (Nqo1, catalase, Gst, Gsr), corresponding with the decrease in their catalytic activity. The altered biological processes also include the decrease of cell cycle positive regulators (n=15) and the increase of DNA repair proteins (n=5) as well as annexin family members (n=5) in the RH1-resistant cells. Drug-resistant hepatoma cell proteomes are also distinguished by the altered level of proteins involved in energy production and metabolism (n=55). Our data provide the basis for in-depth study of molecular mechanisms of tumor cell resistance to the promising anticancer drug RH1 enabling the further validation of protein biomarkers for the drug insusceptibility and of potential secondary pharmacological targets of RH1 resistant cells.
Chemija
Among NAD(P)H-dependent disulfide-reducing flavoenzymes, mammalian lipoamide dehydrogenase (LipDH... more Among NAD(P)H-dependent disulfide-reducing flavoenzymes, mammalian lipoamide dehydrogenase (LipDH, EC1.8.1.4) possesses the highest quinone reductase activity. The mixed single-and two-electron reduction of quinones is performed via the FAD cofactor, with the participation of both 4e – -and 2e – -reduced forms of LipDH. We found that Lip-DH reduced the anticancer aziridinyl-substituted quinones AZQ, DZQ, MeDZQ, RH1, and BZQ, whose reactivity (k cat /K m) increased with an increase in their single-electron reduc-tion potential (E 1 7). At [NAD + ]/[NADH]=4.7 which corresponds to the LipDH turnover under the physiological conditions, i.e. its cycling between the oxidized and 2e – -reduced forms, the k cat /K m values for quinones were decreased by 8–20 times. We also found that the physiological substrate of LipDH, lipoamide, accelerated the reduction of aziridinyl-benzo-quinones because of their parallel reduction by the reduction product, dihydrolipoamide (Lip(SH) 2). These reaction...
Acta biochimica Polonica, 2004
With an aim to understand the toxicity mechanisms of the explosive 4,6-dinitro- benzofuroxan (DNB... more With an aim to understand the toxicity mechanisms of the explosive 4,6-dinitro- benzofuroxan (DNBF), we studied its single-electron reduction by NADPH:cytochrome P450 reductase and ferredoxin:NADP(+) reductase, and two- electron reduction by DT-diaphorase and Enterobacter cloacae nitroreductase. The enzymatic reactivities of DNBF and another explosive 2,4,6-trinitrotoluene (TNT) were similar, except for the much lower reactivity of DNBF towards nitroreductase. DNBF was less cytotoxic in FLK cells than TNT. However, their action shared the same mechanisms, oxidative stress and activation by DT-diaphorase. The lower cytotoxicity of DNBF may be explained by the negative electrostatic charge of its adduct with water which may impede cellular membrane penetration, and by the formation of its less reactive adducts with intracellular reduced glutathione.
Acta biochimica Polonica, 2005
We aimed to characterize the role of NAD(P)H:quinone oxidoreductase (NQO1) in apoptosis induction... more We aimed to characterize the role of NAD(P)H:quinone oxidoreductase (NQO1) in apoptosis induction by antitumour quinones RH1 (2,5-diaziridinyl-3-hydroxymethyl-6-methyl-1,4-benzoquinone) and MeDZQ (2,5-dimethyl-3,6-diaziridinyl-1,4-benzoquinone). Digitonin-permeabilized FLK cells catalyzed NADPH-dependent single- and two-electron reduction of RH1 and MeDZQ. At equitoxic concentrations, RH1 and MeDZQ induced apoptosis more efficiently than the nonalkylating duroquinone or H(2)O(2). The antioxidant N,N'-diphenyl-p-phenylene diamine, desferrioxamine, and the inhibitor of NQO1 dicumarol, protected against apoptosis induction by all compounds investigated, but to a different extent. The results of multiparameter regression analysis indicate that RH1 and MeDZQ most likely induce apoptosis via NQO1-linked formation of alkylating species but not via NQO1-linked redox cycling.
Acta biochimica Polonica, 2006
We aimed to elucidate the role of electronic and structural parameters of nitroaromatic compounds... more We aimed to elucidate the role of electronic and structural parameters of nitroaromatic compounds in their two-electron reduction by NAD(P)H:quinone oxidoreductase (NQO1, DT-diaphorase, EC 1.6.99.2). The multiparameter regression analysis shows that the reactivity of nitroaromatic compounds (n=38) increases with an increase in their single-electron reduction potential and the torsion angle between nitrogroup(s) and the aromatic ring. The binding efficiency of nitroaromatics in the active center of NQO1 exerted a less evident role in their reactivity. The reduction of nitroaromatics is characterized by more positive entropies of activation than the reduction of quinones. This points to a less efficient electronic coupling of nitroaromatics with the reduced isoalloxazine ring of FAD, and may explain their lower reactivity as compared to quinones. Another important but poorly understood factor enhancing the reactivity of nitroaromatics is their ability to bind at the dicumarol/quinone ...
Acta biochimica Polonica, 2013
We examined the kinetics of single-electron reduction of a large number of structurally diverse q... more We examined the kinetics of single-electron reduction of a large number of structurally diverse quinones and nitroaromatic compounds, including a number of antitumour and antiparasitic drugs, and nitroaromatic explosives by recombinant rat neuronal nitric oxide synthase (nNOS, EC 1.14.13.39), aiming to characterize the role of nNOS in the oxidative stress-type cytotoxicity of the above compounds. The steady-state second-order rate constants (kcat/Km) of reduction of the quinones and nitroaromatics varied from 10² M⁻¹s⁻¹ to 10⁶ M⁻¹s⁻¹, and increased with an increase in their single-electron reduction potentials (E¹₇). The presence of Ca²⁺/calmodulin enhanced the reactivity of nNOS. These reactions were consistent with an 'outer sphere' electron-transfer mechanism, considering the FMNH∙/FMNH₂ couple of nNOS as the most reactive reduced enzyme form. An analysis of the reactions of nNOS within the 'outer sphere' electron-transfer mechanism gave the approximate values of ...
A single-electron oxidation of ascorbate by a series of low-potential quinones was investigated. ... more A single-electron oxidation of ascorbate by a series of low-potential quinones was investigated. It was determined that bimolecular rate constants correlate with the single-electron reduction potential (£7) of quinones. The results were interpreted in the framework of the "outer-sphere" electrontransfer theory given by Marcus. The consistency of Marcus model for these reactions was verified by comparison of the experimentally determined data with the predicted ones. Energetic considerations suggest that the single-electron transfer between ascorbate and quinone proceeds with a concomitant transfer of proton rather than via an electron transfer and a subsequent transfer of proton. This position to some extent was supported by the fact that over pH range, wjiere no protonation/deprotonation of reagents occurs, the coefficient of proportionality (Alog{/u e x P }ApH) for most active quinones in the ascorbate oxidation reaction was close to 0.5.
Ecotoxicology of Explosives, 2009
Zeitschrift für Naturforschung C, 2008
In spite of extensive studies, the structure-activity relationships in the action of polyphenols ... more In spite of extensive studies, the structure-activity relationships in the action of polyphenols against the malaria parasite Plasmodium falciparum are poorly understood so far. As the mammalian cell cytotoxicity of polyphenols shows a negative dependence on the potential of the phenoxyl radical/phenol redox couple (E(2)(7)), due to the involvement of prooxidant events, and a positive dependence on the octanol/water distribution coefficient at pH 7.0 (log D), we examined the role of these parameters in their antiplasmodial in vitro activity. We found that the concentrations of hydroxybenzenes causing 50% inhibition of the growth of P falciparum strain FcB1 (IC50) are described by the regression log IC50 (microM) = 0.36 + 1.81 E(2)(7) (V) - 0.10 log D [n = 11, r2 = 0.760, F(2.8) = 12.03]. The IC50 values of flavonoids (n = 5), comprising a separate less active series, did not depend on their E(2)(7) values, 0.33 V-0.75 V. These findings were similar to the mammalian cell cytotoxicity data. However, the mammalian cell cytotoxicity of hydroxybenzenes showed more pronounced dependence on their E(2)(7) values [delta log CL50/delta E(2)(7) = (6.9 - 5.1) V(-1), where CL50 is the compound concentration for 50% cell survival] than on their antiplasmodial activity. Although it is unclear whether the prooxidant action is the main factor in the antiplasmodial action of polyphenols or not, our data showed that the ease of their oxidation (decrease in E(2)(7)) may enhance their activity. On the other hand, the different sensitivity of the mammalian cell cytotoxicity and the antiplasmodial activity of the hydroxybenzenes to their E(2)(7) values implied that compounds with high oxidation potential may be used as relatively efficient antiplasmodial agents with low mammalian cell cytotoxicity.
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](International journal of molecular sciences, 2014
The enzymatic reactivity of a series of benzo[1,2-c]1,2,5-oxadiazole N-oxides (benzofuroxans; BFX... more The enzymatic reactivity of a series of benzo[1,2-c]1,2,5-oxadiazole N-oxides (benzofuroxans; BFXs) towards mammalian single-electron transferring NADPH:cytochrome P-450 reductase (P-450R) and two-electron (hydride) transferring quinone oxidoreductase (NQO1) was examined in this work. Since the =N+ (→O)O- moiety of furoxan fragments of BFXs bears some similarity to the aromatic nitro-group, the reactivity of BFXs was compared to that of nitro-aromatic compounds (NACs) whose reduction mechanisms by these and other related flavoenzymes have been extensively investigated. The reduction of BFXs by both P-450R and NQO1 was accompanied by O2 uptake, which was much lower than the NADPH oxidation rate; except for annelated BFXs, whose reduction was followed by the production of peroxide. In order to analyze the possible quantitative structure-activity relationships (QSARs) of the enzymatic reactivity of the compounds, their electron-accepting potency and other reactivity indices were assess...
Journal of Biological Chemistry, 2003
Mammalian thioredoxin reductases (TrxR) are important selenium-dependent antioxidant enzymes. Qui... more Mammalian thioredoxin reductases (TrxR) are important selenium-dependent antioxidant enzymes. Quinones, a wide group of natural substances, human drugs, and environmental pollutants may act either as TrxR substrates or inhibitors. Here we systematically analyzed the interactions of TrxR with different classes of quinone compounds. We found that TrxR catalyzed mixed single-and two-electron reduction of quinones, involving both the selenium-containing motif and a second redox center, presumably FAD. Compared with other related pyridine nucleotide-disulfide oxidoreductases such as glutathione reductase or trypanothione reductase, the k cat /K m value for quinone reduction by TrxR was about 1 order of magnitude higher, and it was not directly related to the one-electron reduction potential of the quinones. A number of quinones were reduced about as efficiently as the natural substrate thioredoxin. We show that TrxR mainly cycles between the four-electron reduced (EH 4 ) and two-electron reduced (EH 2 ) states in quinone reduction. The redox potential of the EH 2 /EH 4 couple of TrxR calculated according to the Haldane relationship with NADPH/NADP ؉ was ؊0.294 V at pH 7.0. Antitumor aziridinylbenzoquinones and daunorubicin were poor substrates and almost inactive as reversible TrxR inhibitors. However, phenanthrene quinone was a potent inhibitor (approximate K i ؍ 6.3 ؎ 1 M). As with other flavoenzymes, quinones could confer superoxide-producing NADPH oxidase activity to mammalian TrxR. A unique feature of this enzyme was, however, the fact that upon selenocysteine-targeted covalent modification, which inactivates its normal activity, reduction of some quinones was not affected, whereas that of others was severely impaired. We conclude that interactions with TrxR may play a considerable role in the complex mechanisms underlying the diverse biological effects of quinones.
Journal of Biological Chemistry, 2005
Here we described novel interactions of the mammalian selenoprotein thioredoxin reductase (TrxR) ... more Here we described novel interactions of the mammalian selenoprotein thioredoxin reductase (TrxR) with nitroaromatic environmental pollutants and drugs. We found that TrxR could catalyze nitroreductase reactions with either one- or two-electron reduction, using its selenocysteine-containing active site and another redox active center, presumably the FAD. Tetryl and p-dinitrobenzene were the most efficient nitroaromatic substrates with a k(cat) of 1.8 and 2.8 s(-1), respectively, at pH 7.0 and 25 degrees C using 50 muM NADPH. As a nitroreductase, TrxR cycled between four- and two-electron-reduced states. The one-electron reactions led to superoxide formation as detected by cytochrome c reduction and, interestingly, reductive N-denitration of tetryl or 2,4-dinitrophenyl-N-methylnitramine, resulting in the release of nitrite. Most nitroaromatics were uncompetitive and noncompetitive inhibitors with regard to NADPH and the disulfide substrate 5,5'-dithiobis(2-nitrobenzoic acid), respectively. Tetryl and 4,6-dinitrobenzofuroxan were, however, competitive inhibitors with respect to 5,5'-dithiobis(2-nitrobenzoic acid) and were clearly substrates for the selenolthiol motif of the enzyme. Furthermore, tetryl and 4,6-dinitrobenzofuroxan efficiently inactivated TrxR, likely by alkylation of the selenolthiol motif as in the inhibition of TrxR by 1-chloro-2,4-dinitrobenzene/dinitrochlorobenzene (DNCB) or juglone. The latter compounds were the most efficient inhibitors of TrxR activity in a cellular context. DNCB, juglone, and tetryl were highly cytotoxic and induced caspase-3/7 activation in HeLa cells. Furthermore, DNCB and juglone were potent inducers of apoptosis also in Bcl2 overexpressing HeLa cells or in A549 cells. Based on these findings, we suggested that targeting of intracellular TrxR by alkylating nitroaromatic or quinone compounds may contribute to the induction of apoptosis in exposed human cancer cells.
chemija, 2009
The reduction reactions of a series of pyridine-and nitropyridine-N-oxide compounds by single-ele... more The reduction reactions of a series of pyridine-and nitropyridine-N-oxide compounds by single-electron transferring flavoenzyme Anabaena PCC 7119 ferredo xin-NADP + oxidoreductase (FNR, EC 1.18.1.2) were examined. The steady-state bimolecular rate constants (k cat / K m ) of the reduction of pyridine N-oxides were determined to range between 1.3 × 10 1 and 2.0 × 10 4 M -1 s -1 . The quantitative structure activity relationships (QSARs) were defined between the logarithm of the k cat / K m parameter of the compounds' reduction and the energies of their lowest unoccupied molecular orbitals (E LUMO ) obtained by quantum-mechanical methods. QSARs studies showed that the reactivity of pyridine Noxide derivatives was generally higher than that of nitroaromatic model compounds. The pyridine N-oxide as well as nitropyridine N-oxide derivatives proved to be more efficient substrates for the single-electron flavin-dependent enzyme than the model nitroaromatics and thus can be attributed to a new series of closely related compounds. This preliminary study may serve as a useful tool for predicting the enzymatic reactivity of structurally related compounds and may be used for analysis of their cytotoxicity with respect to the possible involvement of their redox cycling.
Biochemical and Biophysical Research Communications, 1994
Nitrofurans with aromatic and heterocyclic substituents inhibit Trypanosoma congolense trypanothi... more Nitrofurans with aromatic and heterocyclic substituents inhibit Trypanosoma congolense trypanothione reductase (TR) and yeast glutathione reductase (GR), acting as uncompetitive inhibitors vs. NADPH and noncompetitive or uncompetitive inhibitors vs. disulfide substrate. Many of these compounds inhibited trypanothione reductase more efficiently than glutathione reductase. Chinifur (2-[5'-nitro(furo-2'-yl)-ethene-1-yl]-4(N,N-diethylamino)-1-methyl-but-1 -yl - aminocarbonyl-4-quinoline) was the most selective inhibitor of, and free radical-generating substrate for, trypanothione reductase (Ki = 4.5 microns, TN = 3 s-1, TN/Km = 3.2 x 10(4) M-1 s-1), only weakly inhibiting glutathione reductase (Ki = 100 microns). These findings point to the importance of hydrophobic interactions in the design of redox active heteroaromatic compounds acting as selective inhibitors of, and "subversive substrates" for, trypanothione reductase.
Archives of Biochemistry and Biophysics, 2012
Thermotoga maritima peroxiredoxin-nitroreductase hybrid enzyme (Prx-NR) consists of a FMN-contain... more Thermotoga maritima peroxiredoxin-nitroreductase hybrid enzyme (Prx-NR) consists of a FMN-containing nitroreductase (NR) domain fused to a peroxiredoxin (Prx) domain. These domains seem to function independently as no electron transfer occurs between them. The reduction of quinones and nitroaromatics by NR proceeded in a two-electron manner, and follows a 'ping-pong' scheme with sometimes pronounced inhibition by quinone substrate. The comparison of steady-and presteady-state kinetic data shows that in most cases, the oxidative half-reaction may be rate-limiting in the catalytic cycle of NR. The enzyme was inhibited by dicumarol, a classical inhibitor of oxygen-insensitive nitroreductases. The reduction of quinones and nitroaromatic compounds by Prx-NR was characterized by the linear dependence of their reactivity (log k cat /K m ) on their single-electron reduction potentials E 1 7 , while the reactivity of quinones markedly exceeded the one with nitroaromatics. It shows that NR lacks the specificity for the particular structure of these oxidants, except their single-electron accepting potency and the rate of electron self-exchange. It points to the possibility of a single-electron transfer step in a net two-electron reduction of quinones and nitroaromatics by T. maritima Prx-NR, and to a significant diversity of the structures of flavoenzymes which may perform the two-electron reduction of quinones and nitroaromatics.
Acta biochimica Polonica, 2013
In order to characterize the possible mechanism(s) of cytotoxicity of a neuroleptic agent 6,7-din... more In order to characterize the possible mechanism(s) of cytotoxicity of a neuroleptic agent 6,7-dinitrodihydroquinoxaline-2,3-dione (DNQX) we examined the redox properties of DNQX, and its mononitro- (NQX) and denitro- (QX) derivatives. The irreversible electrochemical reduction of the nitro groups of DNQX was characterized by the reduction peak potentials (Ep,7) of -0.43 V and -0.72 V vs. Ag/AgCl at pH 7.0, whereas NQX was reduced at Ep,7 = -0.67 V. The reactivities of DNQX and NQX towards the single-electron transferring enzymes NADPH:cytochrome P-450 reductase and NADPH:adrenodoxin reductase/adrenodoxin complex were similar to those of model nitrobenzenes with the single-electron reduction potential (E¹₇) values of -0.29 V - -0.42 V. DNQX and NQX also acted as substrates for two-electron transferring mammalian NAD(P)H:quinone oxidoreductase (DT-diaphorase). The cytotoxicity of DNQX in bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK) was prevented by antioxidants...
Zeitschrift für Naturforschung C, 2004
The toxicity of conventional nitroaromatic explosives like 2,4,6-trinitrotoluene (TNT) is caused ... more The toxicity of conventional nitroaromatic explosives like 2,4,6-trinitrotoluene (TNT) is caused by their enzymatic free radical formation with the subsequent oxidative stress, the formation of alkylating nitroso and/or hydroxylamino metabolites, and oxyhemoglobin oxidation into methemoglobin. In order to get an insight into the mechanisms of toxicity of the novel explosives NTO (5-nitro-1,2,4-triazol-3-one) and ANTA (5-nitro-1,2,4-triazol-3-amine), we examined their reactions with the single-electron transferring flavoenzymes NADPH: cytochrome P-450 reductase and ferredoxin:NADP + reductase, two-electron transferring flavoenzymes mammalian NAD(P)H:quinone oxidoreductase (DT-diaphorase), and Enterobacter cloacae NAD(P)H:nitroreductase, and their reactions with oxyhemoglobin. The reactivity of NTO and ANTA in the above reactions was markedly lower than that of TNT. The toxicity of NTO and ANTA in bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK) was partly prevented by desferrioxamine and the antioxidant N,NЈ-diphenyl-pphenylene diamine, and potentiated by 1,3-bis-(2-chloroethyl)-1-nitrosourea. This points to the involvement of oxidative stress in their cytotoxicity, presumably to the redox cycling of free radicals. The FLK cell line cytotoxicity and the methemoglobin formation in isolated human erythrocytes of NTO and ANTA were also markedly lower than those of TNT, and similar to those of nitrobenzene. Taken together, our data demonstrate that the low toxicity of nitrotriazole explosives may be attributed to their low electron-accepting properties.
Biochimica Et Biophysica Acta-bioenergetics, 1998
Arabidopsis thaliana NADPH:thioredoxin reductase (TR, EC 1.6.4.5) catalyzed redox cycling of arom... more Arabidopsis thaliana NADPH:thioredoxin reductase (TR, EC 1.6.4.5) catalyzed redox cycling of aromatic nitrocompounds, including the explosives 2,4,6-trinitrotoluene and tetryl, and the herbicide 3,5-dinitro-o-cresol. The yield of nitro anion radicals was equal to 70^90%. Redox cycling of tetryl was accompanied by formation of N-methylpicramide. Bimolecular rate constants of nitroaromatic reduction (k cat /K m ) and reaction catalytic constants (k cat ) increased upon an increase in oxidant single-electron reduction potential (E 1 7 ). Using compounds with an unknown E 1 7 value, the reactivity of TR increased parallelly to the increase in reactivity of ferredoxin :NADP reductase of Anabaena PCC 7119 (EC 1.18.1.2). This indicated that the main factor determining reactivity of nitroaromatics towards TR was their energetics of singleelectron reduction. Incubation of reduced TR in the presence of tetryl or 2,4-dinitrochlorobenzene resulted in a loss of thioredoxin reductase activity, most probably due to modification of reduced catalytic disulfide, whereas nitroreductase reaction rates were unchanged. This means that on the analogy of quinone reduction by TR (D. Bironaite ç, Z í . Anusevic ius, J.-P. Jacquot, N. C í e çnas, Biochim. Biophys. Acta 1383 (1998) 82^92), FAD and not catalytic disulfide of TR was responsible for the reduction of nitroaromatics. Tetryl, 2,4,6-trinitrotoluene and thioredoxin increased the FAD fluorescence intensity of TR. This finding suggests that nitroaromatics may bind close to the thioredoxin-binding site at the catalytic disulfide domain of TR, and induce a conformational change of enzymes (S.B. Mulrooney, C.H. Williams Jr., Protein Sci. 6 (1997) 21882 195). Our data indicate that certain nitroaromatic herbicides, explosives and other classes of xenobiotics may interfere with the reduction of thioredoxin by plant TR, and confer prooxidant properties to this antioxidant enzyme. ß 0005-2728 / 98 / $^see front matter ß 1998 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 5 -2 7 2 8 ( 9 8 ) 0 0 1 2 8 -5
Acta Biochimica Polonica, Feb 1, 2004
With an aim to understand the toxicity mechanisms of the explosive 4,6-dinitro- benzofuroxan (DNB... more With an aim to understand the toxicity mechanisms of the explosive 4,6-dinitro- benzofuroxan (DNBF), we studied its single-electron reduction by NADPH:cytochrome P450 reductase and ferredoxin:NADP(+) reductase, and two- electron reduction by DT-diaphorase and Enterobacter cloacae nitroreductase. The enzymatic reactivities of DNBF and another explosive 2,4,6-trinitrotoluene (TNT) were similar, except for the much lower reactivity of DNBF towards nitroreductase. DNBF was less cytotoxic in FLK cells than TNT. However, their action shared the same mechanisms, oxidative stress and activation by DT-diaphorase. The lower cytotoxicity of DNBF may be explained by the negative electrostatic charge of its adduct with water which may impede cellular membrane penetration, and by the formation of its less reactive adducts with intracellular reduced glutathione.
Chemical Research in Toxicology, 2015
Aziridinylquinone RH-1 (2,5-diaziridinyl-3-hydroxymethyl-6-methyl-cyclohexa-2,5-diene-1,4-dione) ... more Aziridinylquinone RH-1 (2,5-diaziridinyl-3-hydroxymethyl-6-methyl-cyclohexa-2,5-diene-1,4-dione) is a potential anticancer agent. RH-1 action is associated with NAD(P)H:quinone oxidoreductase (NQO1) which reduces this diaziridinylbenzoquinone into DNA-alkylating hydroquinone and is overexpressed in many tumors. Another suggested mechanism of RH-1 toxicity is the formation of reactive oxygen species (ROS) arising from its redox cycling. In order to improve anticancer action of this and similar antitumor quinones, we investigated the involvement of different signaling molecules in cytotoxicity induced by RH-1 by using wild-type tumor suppressor p53 bearing nonsmall cell lung carcinoma A549 cells as a model. Gradual and prolonged increase of mitogen-activated protein kinases (MAPK) ERK, P38, and JNK phosphorylation was observed during 24-h RH-1 treatment. In parallel, activation of DNA damage-sensing ATM kinase, upregulation, and phosphorylation of TP53 (human p53) took place. Inhibition studies revealed that RH-1-induced A549 apoptosis involved the NQO1-ATM-p53 signaling pathway and ROS generation. TP53 participated in ROS- and DNA damage-induced cell death differently. Moreover, MAP kinase JNK was another TP53 activator and death inducer in A549 cells. At the same time, rapid and prolonged activation of AKT kinase during RH-1 treatment was found, and it proved to be antiapoptotic kinase in our model system. Therefore, we identified that different and opposite cell death regulating signaling pathways, which may counteract one another, are induced in cancer cells during chemotherapeutic RH-1 treatment.
Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics, 2015
Acquired resistance of tumor cells to the therapeutic treatment is a major challenge in virtually... more Acquired resistance of tumor cells to the therapeutic treatment is a major challenge in virtually any chemotherapy. A novel anticancer agent 2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone (RH1) is designed to be activated by quinone oxidoreductase, an enzyme expressed at high levels in many types of tumors. Here we investigated the potential mechanisms of acquired RH1 drug resistance in cancer cells by applying high-throughput differential quantitative proteomic analysis of the newly established RH1-resistant hepatoma cell lines. Over 400 proteins display significantly altered levels between drug-sensitive and drug-resistant cell lines. Differentially expressed proteins were clustered into more than 14 groups according to their functional annotation and protein-protein interactions. Bioinformatic analysis highlights the biological processes that might be responsible for acquired resistance to RH1. The level of several xenobiotic metabolism enzymes (total n=17) involved in RH1 activation and detoxification is decreased (Nqo1, catalase, Gst, Gsr), corresponding with the decrease in their catalytic activity. The altered biological processes also include the decrease of cell cycle positive regulators (n=15) and the increase of DNA repair proteins (n=5) as well as annexin family members (n=5) in the RH1-resistant cells. Drug-resistant hepatoma cell proteomes are also distinguished by the altered level of proteins involved in energy production and metabolism (n=55). Our data provide the basis for in-depth study of molecular mechanisms of tumor cell resistance to the promising anticancer drug RH1 enabling the further validation of protein biomarkers for the drug insusceptibility and of potential secondary pharmacological targets of RH1 resistant cells.
Chemija
Among NAD(P)H-dependent disulfide-reducing flavoenzymes, mammalian lipoamide dehydrogenase (LipDH... more Among NAD(P)H-dependent disulfide-reducing flavoenzymes, mammalian lipoamide dehydrogenase (LipDH, EC1.8.1.4) possesses the highest quinone reductase activity. The mixed single-and two-electron reduction of quinones is performed via the FAD cofactor, with the participation of both 4e – -and 2e – -reduced forms of LipDH. We found that Lip-DH reduced the anticancer aziridinyl-substituted quinones AZQ, DZQ, MeDZQ, RH1, and BZQ, whose reactivity (k cat /K m) increased with an increase in their single-electron reduc-tion potential (E 1 7). At [NAD + ]/[NADH]=4.7 which corresponds to the LipDH turnover under the physiological conditions, i.e. its cycling between the oxidized and 2e – -reduced forms, the k cat /K m values for quinones were decreased by 8–20 times. We also found that the physiological substrate of LipDH, lipoamide, accelerated the reduction of aziridinyl-benzo-quinones because of their parallel reduction by the reduction product, dihydrolipoamide (Lip(SH) 2). These reaction...
Acta biochimica Polonica, 2004
With an aim to understand the toxicity mechanisms of the explosive 4,6-dinitro- benzofuroxan (DNB... more With an aim to understand the toxicity mechanisms of the explosive 4,6-dinitro- benzofuroxan (DNBF), we studied its single-electron reduction by NADPH:cytochrome P450 reductase and ferredoxin:NADP(+) reductase, and two- electron reduction by DT-diaphorase and Enterobacter cloacae nitroreductase. The enzymatic reactivities of DNBF and another explosive 2,4,6-trinitrotoluene (TNT) were similar, except for the much lower reactivity of DNBF towards nitroreductase. DNBF was less cytotoxic in FLK cells than TNT. However, their action shared the same mechanisms, oxidative stress and activation by DT-diaphorase. The lower cytotoxicity of DNBF may be explained by the negative electrostatic charge of its adduct with water which may impede cellular membrane penetration, and by the formation of its less reactive adducts with intracellular reduced glutathione.
Acta biochimica Polonica, 2005
We aimed to characterize the role of NAD(P)H:quinone oxidoreductase (NQO1) in apoptosis induction... more We aimed to characterize the role of NAD(P)H:quinone oxidoreductase (NQO1) in apoptosis induction by antitumour quinones RH1 (2,5-diaziridinyl-3-hydroxymethyl-6-methyl-1,4-benzoquinone) and MeDZQ (2,5-dimethyl-3,6-diaziridinyl-1,4-benzoquinone). Digitonin-permeabilized FLK cells catalyzed NADPH-dependent single- and two-electron reduction of RH1 and MeDZQ. At equitoxic concentrations, RH1 and MeDZQ induced apoptosis more efficiently than the nonalkylating duroquinone or H(2)O(2). The antioxidant N,N'-diphenyl-p-phenylene diamine, desferrioxamine, and the inhibitor of NQO1 dicumarol, protected against apoptosis induction by all compounds investigated, but to a different extent. The results of multiparameter regression analysis indicate that RH1 and MeDZQ most likely induce apoptosis via NQO1-linked formation of alkylating species but not via NQO1-linked redox cycling.
Acta biochimica Polonica, 2006
We aimed to elucidate the role of electronic and structural parameters of nitroaromatic compounds... more We aimed to elucidate the role of electronic and structural parameters of nitroaromatic compounds in their two-electron reduction by NAD(P)H:quinone oxidoreductase (NQO1, DT-diaphorase, EC 1.6.99.2). The multiparameter regression analysis shows that the reactivity of nitroaromatic compounds (n=38) increases with an increase in their single-electron reduction potential and the torsion angle between nitrogroup(s) and the aromatic ring. The binding efficiency of nitroaromatics in the active center of NQO1 exerted a less evident role in their reactivity. The reduction of nitroaromatics is characterized by more positive entropies of activation than the reduction of quinones. This points to a less efficient electronic coupling of nitroaromatics with the reduced isoalloxazine ring of FAD, and may explain their lower reactivity as compared to quinones. Another important but poorly understood factor enhancing the reactivity of nitroaromatics is their ability to bind at the dicumarol/quinone ...
Acta biochimica Polonica, 2013
We examined the kinetics of single-electron reduction of a large number of structurally diverse q... more We examined the kinetics of single-electron reduction of a large number of structurally diverse quinones and nitroaromatic compounds, including a number of antitumour and antiparasitic drugs, and nitroaromatic explosives by recombinant rat neuronal nitric oxide synthase (nNOS, EC 1.14.13.39), aiming to characterize the role of nNOS in the oxidative stress-type cytotoxicity of the above compounds. The steady-state second-order rate constants (kcat/Km) of reduction of the quinones and nitroaromatics varied from 10² M⁻¹s⁻¹ to 10⁶ M⁻¹s⁻¹, and increased with an increase in their single-electron reduction potentials (E¹₇). The presence of Ca²⁺/calmodulin enhanced the reactivity of nNOS. These reactions were consistent with an 'outer sphere' electron-transfer mechanism, considering the FMNH∙/FMNH₂ couple of nNOS as the most reactive reduced enzyme form. An analysis of the reactions of nNOS within the 'outer sphere' electron-transfer mechanism gave the approximate values of ...
A single-electron oxidation of ascorbate by a series of low-potential quinones was investigated. ... more A single-electron oxidation of ascorbate by a series of low-potential quinones was investigated. It was determined that bimolecular rate constants correlate with the single-electron reduction potential (£7) of quinones. The results were interpreted in the framework of the "outer-sphere" electrontransfer theory given by Marcus. The consistency of Marcus model for these reactions was verified by comparison of the experimentally determined data with the predicted ones. Energetic considerations suggest that the single-electron transfer between ascorbate and quinone proceeds with a concomitant transfer of proton rather than via an electron transfer and a subsequent transfer of proton. This position to some extent was supported by the fact that over pH range, wjiere no protonation/deprotonation of reagents occurs, the coefficient of proportionality (Alog{/u e x P }ApH) for most active quinones in the ascorbate oxidation reaction was close to 0.5.
Ecotoxicology of Explosives, 2009
Zeitschrift für Naturforschung C, 2008
In spite of extensive studies, the structure-activity relationships in the action of polyphenols ... more In spite of extensive studies, the structure-activity relationships in the action of polyphenols against the malaria parasite Plasmodium falciparum are poorly understood so far. As the mammalian cell cytotoxicity of polyphenols shows a negative dependence on the potential of the phenoxyl radical/phenol redox couple (E(2)(7)), due to the involvement of prooxidant events, and a positive dependence on the octanol/water distribution coefficient at pH 7.0 (log D), we examined the role of these parameters in their antiplasmodial in vitro activity. We found that the concentrations of hydroxybenzenes causing 50% inhibition of the growth of P falciparum strain FcB1 (IC50) are described by the regression log IC50 (microM) = 0.36 + 1.81 E(2)(7) (V) - 0.10 log D [n = 11, r2 = 0.760, F(2.8) = 12.03]. The IC50 values of flavonoids (n = 5), comprising a separate less active series, did not depend on their E(2)(7) values, 0.33 V-0.75 V. These findings were similar to the mammalian cell cytotoxicity data. However, the mammalian cell cytotoxicity of hydroxybenzenes showed more pronounced dependence on their E(2)(7) values [delta log CL50/delta E(2)(7) = (6.9 - 5.1) V(-1), where CL50 is the compound concentration for 50% cell survival] than on their antiplasmodial activity. Although it is unclear whether the prooxidant action is the main factor in the antiplasmodial action of polyphenols or not, our data showed that the ease of their oxidation (decrease in E(2)(7)) may enhance their activity. On the other hand, the different sensitivity of the mammalian cell cytotoxicity and the antiplasmodial activity of the hydroxybenzenes to their E(2)(7) values implied that compounds with high oxidation potential may be used as relatively efficient antiplasmodial agents with low mammalian cell cytotoxicity.
International journal of molecular sciences, 2014
The enzymatic reactivity of a series of benzo[1,2-c]1,2,5-oxadiazole N-oxides (benzofuroxans; BFX... more The enzymatic reactivity of a series of benzo[1,2-c]1,2,5-oxadiazole N-oxides (benzofuroxans; BFXs) towards mammalian single-electron transferring NADPH:cytochrome P-450 reductase (P-450R) and two-electron (hydride) transferring quinone oxidoreductase (NQO1) was examined in this work. Since the =N+ (→O)O- moiety of furoxan fragments of BFXs bears some similarity to the aromatic nitro-group, the reactivity of BFXs was compared to that of nitro-aromatic compounds (NACs) whose reduction mechanisms by these and other related flavoenzymes have been extensively investigated. The reduction of BFXs by both P-450R and NQO1 was accompanied by O2 uptake, which was much lower than the NADPH oxidation rate; except for annelated BFXs, whose reduction was followed by the production of peroxide. In order to analyze the possible quantitative structure-activity relationships (QSARs) of the enzymatic reactivity of the compounds, their electron-accepting potency and other reactivity indices were assess...
Journal of Biological Chemistry, 2003
Mammalian thioredoxin reductases (TrxR) are important selenium-dependent antioxidant enzymes. Qui... more Mammalian thioredoxin reductases (TrxR) are important selenium-dependent antioxidant enzymes. Quinones, a wide group of natural substances, human drugs, and environmental pollutants may act either as TrxR substrates or inhibitors. Here we systematically analyzed the interactions of TrxR with different classes of quinone compounds. We found that TrxR catalyzed mixed single-and two-electron reduction of quinones, involving both the selenium-containing motif and a second redox center, presumably FAD. Compared with other related pyridine nucleotide-disulfide oxidoreductases such as glutathione reductase or trypanothione reductase, the k cat /K m value for quinone reduction by TrxR was about 1 order of magnitude higher, and it was not directly related to the one-electron reduction potential of the quinones. A number of quinones were reduced about as efficiently as the natural substrate thioredoxin. We show that TrxR mainly cycles between the four-electron reduced (EH 4 ) and two-electron reduced (EH 2 ) states in quinone reduction. The redox potential of the EH 2 /EH 4 couple of TrxR calculated according to the Haldane relationship with NADPH/NADP ؉ was ؊0.294 V at pH 7.0. Antitumor aziridinylbenzoquinones and daunorubicin were poor substrates and almost inactive as reversible TrxR inhibitors. However, phenanthrene quinone was a potent inhibitor (approximate K i ؍ 6.3 ؎ 1 M). As with other flavoenzymes, quinones could confer superoxide-producing NADPH oxidase activity to mammalian TrxR. A unique feature of this enzyme was, however, the fact that upon selenocysteine-targeted covalent modification, which inactivates its normal activity, reduction of some quinones was not affected, whereas that of others was severely impaired. We conclude that interactions with TrxR may play a considerable role in the complex mechanisms underlying the diverse biological effects of quinones.
Journal of Biological Chemistry, 2005
Here we described novel interactions of the mammalian selenoprotein thioredoxin reductase (TrxR) ... more Here we described novel interactions of the mammalian selenoprotein thioredoxin reductase (TrxR) with nitroaromatic environmental pollutants and drugs. We found that TrxR could catalyze nitroreductase reactions with either one- or two-electron reduction, using its selenocysteine-containing active site and another redox active center, presumably the FAD. Tetryl and p-dinitrobenzene were the most efficient nitroaromatic substrates with a k(cat) of 1.8 and 2.8 s(-1), respectively, at pH 7.0 and 25 degrees C using 50 muM NADPH. As a nitroreductase, TrxR cycled between four- and two-electron-reduced states. The one-electron reactions led to superoxide formation as detected by cytochrome c reduction and, interestingly, reductive N-denitration of tetryl or 2,4-dinitrophenyl-N-methylnitramine, resulting in the release of nitrite. Most nitroaromatics were uncompetitive and noncompetitive inhibitors with regard to NADPH and the disulfide substrate 5,5'-dithiobis(2-nitrobenzoic acid), respectively. Tetryl and 4,6-dinitrobenzofuroxan were, however, competitive inhibitors with respect to 5,5'-dithiobis(2-nitrobenzoic acid) and were clearly substrates for the selenolthiol motif of the enzyme. Furthermore, tetryl and 4,6-dinitrobenzofuroxan efficiently inactivated TrxR, likely by alkylation of the selenolthiol motif as in the inhibition of TrxR by 1-chloro-2,4-dinitrobenzene/dinitrochlorobenzene (DNCB) or juglone. The latter compounds were the most efficient inhibitors of TrxR activity in a cellular context. DNCB, juglone, and tetryl were highly cytotoxic and induced caspase-3/7 activation in HeLa cells. Furthermore, DNCB and juglone were potent inducers of apoptosis also in Bcl2 overexpressing HeLa cells or in A549 cells. Based on these findings, we suggested that targeting of intracellular TrxR by alkylating nitroaromatic or quinone compounds may contribute to the induction of apoptosis in exposed human cancer cells.
chemija, 2009
The reduction reactions of a series of pyridine-and nitropyridine-N-oxide compounds by single-ele... more The reduction reactions of a series of pyridine-and nitropyridine-N-oxide compounds by single-electron transferring flavoenzyme Anabaena PCC 7119 ferredo xin-NADP + oxidoreductase (FNR, EC 1.18.1.2) were examined. The steady-state bimolecular rate constants (k cat / K m ) of the reduction of pyridine N-oxides were determined to range between 1.3 × 10 1 and 2.0 × 10 4 M -1 s -1 . The quantitative structure activity relationships (QSARs) were defined between the logarithm of the k cat / K m parameter of the compounds' reduction and the energies of their lowest unoccupied molecular orbitals (E LUMO ) obtained by quantum-mechanical methods. QSARs studies showed that the reactivity of pyridine Noxide derivatives was generally higher than that of nitroaromatic model compounds. The pyridine N-oxide as well as nitropyridine N-oxide derivatives proved to be more efficient substrates for the single-electron flavin-dependent enzyme than the model nitroaromatics and thus can be attributed to a new series of closely related compounds. This preliminary study may serve as a useful tool for predicting the enzymatic reactivity of structurally related compounds and may be used for analysis of their cytotoxicity with respect to the possible involvement of their redox cycling.
Biochemical and Biophysical Research Communications, 1994
Nitrofurans with aromatic and heterocyclic substituents inhibit Trypanosoma congolense trypanothi... more Nitrofurans with aromatic and heterocyclic substituents inhibit Trypanosoma congolense trypanothione reductase (TR) and yeast glutathione reductase (GR), acting as uncompetitive inhibitors vs. NADPH and noncompetitive or uncompetitive inhibitors vs. disulfide substrate. Many of these compounds inhibited trypanothione reductase more efficiently than glutathione reductase. Chinifur (2-[5'-nitro(furo-2'-yl)-ethene-1-yl]-4(N,N-diethylamino)-1-methyl-but-1 -yl - aminocarbonyl-4-quinoline) was the most selective inhibitor of, and free radical-generating substrate for, trypanothione reductase (Ki = 4.5 microns, TN = 3 s-1, TN/Km = 3.2 x 10(4) M-1 s-1), only weakly inhibiting glutathione reductase (Ki = 100 microns). These findings point to the importance of hydrophobic interactions in the design of redox active heteroaromatic compounds acting as selective inhibitors of, and "subversive substrates" for, trypanothione reductase.
Archives of Biochemistry and Biophysics, 2012
Thermotoga maritima peroxiredoxin-nitroreductase hybrid enzyme (Prx-NR) consists of a FMN-contain... more Thermotoga maritima peroxiredoxin-nitroreductase hybrid enzyme (Prx-NR) consists of a FMN-containing nitroreductase (NR) domain fused to a peroxiredoxin (Prx) domain. These domains seem to function independently as no electron transfer occurs between them. The reduction of quinones and nitroaromatics by NR proceeded in a two-electron manner, and follows a 'ping-pong' scheme with sometimes pronounced inhibition by quinone substrate. The comparison of steady-and presteady-state kinetic data shows that in most cases, the oxidative half-reaction may be rate-limiting in the catalytic cycle of NR. The enzyme was inhibited by dicumarol, a classical inhibitor of oxygen-insensitive nitroreductases. The reduction of quinones and nitroaromatic compounds by Prx-NR was characterized by the linear dependence of their reactivity (log k cat /K m ) on their single-electron reduction potentials E 1 7 , while the reactivity of quinones markedly exceeded the one with nitroaromatics. It shows that NR lacks the specificity for the particular structure of these oxidants, except their single-electron accepting potency and the rate of electron self-exchange. It points to the possibility of a single-electron transfer step in a net two-electron reduction of quinones and nitroaromatics by T. maritima Prx-NR, and to a significant diversity of the structures of flavoenzymes which may perform the two-electron reduction of quinones and nitroaromatics.
Acta biochimica Polonica, 2013
In order to characterize the possible mechanism(s) of cytotoxicity of a neuroleptic agent 6,7-din... more In order to characterize the possible mechanism(s) of cytotoxicity of a neuroleptic agent 6,7-dinitrodihydroquinoxaline-2,3-dione (DNQX) we examined the redox properties of DNQX, and its mononitro- (NQX) and denitro- (QX) derivatives. The irreversible electrochemical reduction of the nitro groups of DNQX was characterized by the reduction peak potentials (Ep,7) of -0.43 V and -0.72 V vs. Ag/AgCl at pH 7.0, whereas NQX was reduced at Ep,7 = -0.67 V. The reactivities of DNQX and NQX towards the single-electron transferring enzymes NADPH:cytochrome P-450 reductase and NADPH:adrenodoxin reductase/adrenodoxin complex were similar to those of model nitrobenzenes with the single-electron reduction potential (E¹₇) values of -0.29 V - -0.42 V. DNQX and NQX also acted as substrates for two-electron transferring mammalian NAD(P)H:quinone oxidoreductase (DT-diaphorase). The cytotoxicity of DNQX in bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK) was prevented by antioxidants...
Zeitschrift für Naturforschung C, 2004
The toxicity of conventional nitroaromatic explosives like 2,4,6-trinitrotoluene (TNT) is caused ... more The toxicity of conventional nitroaromatic explosives like 2,4,6-trinitrotoluene (TNT) is caused by their enzymatic free radical formation with the subsequent oxidative stress, the formation of alkylating nitroso and/or hydroxylamino metabolites, and oxyhemoglobin oxidation into methemoglobin. In order to get an insight into the mechanisms of toxicity of the novel explosives NTO (5-nitro-1,2,4-triazol-3-one) and ANTA (5-nitro-1,2,4-triazol-3-amine), we examined their reactions with the single-electron transferring flavoenzymes NADPH: cytochrome P-450 reductase and ferredoxin:NADP + reductase, two-electron transferring flavoenzymes mammalian NAD(P)H:quinone oxidoreductase (DT-diaphorase), and Enterobacter cloacae NAD(P)H:nitroreductase, and their reactions with oxyhemoglobin. The reactivity of NTO and ANTA in the above reactions was markedly lower than that of TNT. The toxicity of NTO and ANTA in bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK) was partly prevented by desferrioxamine and the antioxidant N,NЈ-diphenyl-pphenylene diamine, and potentiated by 1,3-bis-(2-chloroethyl)-1-nitrosourea. This points to the involvement of oxidative stress in their cytotoxicity, presumably to the redox cycling of free radicals. The FLK cell line cytotoxicity and the methemoglobin formation in isolated human erythrocytes of NTO and ANTA were also markedly lower than those of TNT, and similar to those of nitrobenzene. Taken together, our data demonstrate that the low toxicity of nitrotriazole explosives may be attributed to their low electron-accepting properties.
Biochimica Et Biophysica Acta-bioenergetics, 1998
Arabidopsis thaliana NADPH:thioredoxin reductase (TR, EC 1.6.4.5) catalyzed redox cycling of arom... more Arabidopsis thaliana NADPH:thioredoxin reductase (TR, EC 1.6.4.5) catalyzed redox cycling of aromatic nitrocompounds, including the explosives 2,4,6-trinitrotoluene and tetryl, and the herbicide 3,5-dinitro-o-cresol. The yield of nitro anion radicals was equal to 70^90%. Redox cycling of tetryl was accompanied by formation of N-methylpicramide. Bimolecular rate constants of nitroaromatic reduction (k cat /K m ) and reaction catalytic constants (k cat ) increased upon an increase in oxidant single-electron reduction potential (E 1 7 ). Using compounds with an unknown E 1 7 value, the reactivity of TR increased parallelly to the increase in reactivity of ferredoxin :NADP reductase of Anabaena PCC 7119 (EC 1.18.1.2). This indicated that the main factor determining reactivity of nitroaromatics towards TR was their energetics of singleelectron reduction. Incubation of reduced TR in the presence of tetryl or 2,4-dinitrochlorobenzene resulted in a loss of thioredoxin reductase activity, most probably due to modification of reduced catalytic disulfide, whereas nitroreductase reaction rates were unchanged. This means that on the analogy of quinone reduction by TR (D. Bironaite ç, Z í . Anusevic ius, J.-P. Jacquot, N. C í e çnas, Biochim. Biophys. Acta 1383 (1998) 82^92), FAD and not catalytic disulfide of TR was responsible for the reduction of nitroaromatics. Tetryl, 2,4,6-trinitrotoluene and thioredoxin increased the FAD fluorescence intensity of TR. This finding suggests that nitroaromatics may bind close to the thioredoxin-binding site at the catalytic disulfide domain of TR, and induce a conformational change of enzymes (S.B. Mulrooney, C.H. Williams Jr., Protein Sci. 6 (1997) 21882 195). Our data indicate that certain nitroaromatic herbicides, explosives and other classes of xenobiotics may interfere with the reduction of thioredoxin by plant TR, and confer prooxidant properties to this antioxidant enzyme. ß 0005-2728 / 98 / $^see front matter ß 1998 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 5 -2 7 2 8 ( 9 8 ) 0 0 1 2 8 -5