Chinifur, a Selective Inhibitor and "Subversive Substrate" for Trypanosoma congolense Trypanothione Reductase

Čėnas, Narimantas; Bironaitė, Daiva; Dičkancaitè, Egle; Anusevičius, Žilvinas; Šarlauskas, Jonas; Blanchard, John S.

doi:10.1006/bbrc.1994.2448

Cited by 47 publications

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“…K m values for substrates and k t ) observed are similar to those previously reported for other reductases, and the inhibition constant for rhein of 2 þ 0.24 WM compares to a K ii = 3 WM observed for yeast glutathione reductase [18]. This suggests a similarity in enzyme structure of the E. faecalis glutathione reductase with other known glutathione reductases, since it has been suggested that the site of inhibition of the anionic inhibitor, rhein, is the positively charged glutathione binding site [18]. The initial velocity, product, and dead-end inhibition patterns support a ping-pong kinetic mechanism for the E. faecalis glutathione reductase.…”

Section: Discussionsupporting

confidence: 73%

Enterococcus faecalis glutathione reductase: purification, characterization and expression under normal and hyperbaric O2 conditions

Patel¹

1998

FEMS Microbiology Letters

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Glutathione reductase is found ubiquitously in eukaryotes and Gram-negative bacteria, and plays a significant role in bacterial defense against oxidative stress. Glutathione reductase from the Gram-positive bacterium Enterococcus faecalis was purified to homogeneity using anion exchange, hydrophobic interaction, and affinity chromatography. The homogeneous 49-kDa enzyme contained 1 mol bound FAD per subunit. The determined N-terminal amino acid sequence of the E. faecalis enzyme displays significant identity with glutathione reductases from other Gram-negative and Gram-positive bacteria, as well as yeast and human erythrocyte reductases. The kinetic mechanism is ping-pong, and the determined kinetic parameters exhibited by the E. faecalis glutathione reductase are similar to those found for glutathione reductases from yeast, Escherichia coli, and human erythrocyte. A two-fold increased expression of glutathione reductase activity and a three-fold induction of glutathione peroxidase activity were observed under hyperbaric O P growth conditions without a corresponding change in the total glutathione and soluble thiol content. The difference in the expression of the enzyme, and its cognate substrate's intracellular concentration, under these conditions suggest that the gene encoding glutathione reductase is responsive to oxygen concentration, but that the genes encoding the glutathione synthesizing enzymes are not linked to an oxygen-sensitive promoter. z

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Section: Discussionsupporting

confidence: 73%

Enterococcus faecalis glutathione reductase: purification, characterization and expression under normal and hyperbaric O2 conditions

Patel¹

1998

FEMS Microbiology Letters

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“…; [111] nitrofurans are reduced by the enzyme to the nitroanion radical, which reacts with molecular oxygen to give superoxide anion radical, the nitrofuran being recycled [111][112][113][114] IC 50 …”

Section: Inhibitor Types Examplesmentioning

confidence: 99%

“…[111][112][113][114][115] Typical subversive substrates (X) are reduced in single-electron steps to the respective radicals [Eq. The dashed line marks the redox-active dithiol/disulfide.…”

Section: Subversive Substratesmentioning

confidence: 99%

Dithiol Proteins as Guardians of the Intracellular Redox Milieu in Parasites: Old and New Drug Targets in Trypanosomes and Malaria‐Causing Plasmodia

2005

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Parasitic diseases such as sleeping sickness, Chagas' heart disease, and malaria are major health problems in poverty-stricken areas. Antiparasitic drugs that are not only active but also affordable and readily available are urgently required. One approach to finding new drugs and rediscovering old ones is based on enzyme inhibitors that paralyze antioxidant systems in the pathogens. These antioxidant ensembles are essential to the parasites as they are attacked in the human host by strong oxidants such as peroxynitrite, hypochlorite, and H2O2. The pathogen-protecting system consists of some 20 thiol and dithiol proteins, which buffer the intraparasitic redox milieu at a potential of -250 mV. In trypanosomes and leishmania the network is centered around the unique dithiol trypanothione (N1,N8-bis(glutathionyl)spermidine). In contrast, malaria parasites have a more conservative dual antioxidative system based on glutathione and thioredoxin. Inhibitors of antioxidant enzymes such as trypanothione reductase are, indeed, parasiticidal but they can also delay or prevent resistance against a number of other antiparasitic drugs.

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“…The cytotoxic, antitumor, and antiparasitic activities of nitroaromatics are generally believed to stem mainly from the redox cycling of their free radicals formed after single-electron reduction by different flavoenzymes or from the alkylation of DNA and/or other cellular nucleophiles by the products of their two (or four)-electron reduction, the arylhydroxylamines (27)(28)(29)(30). It has been shown previously that enzymes analogous to TrxR, such as the pyridine nucleotidedisulfide reductases trypanothione reductase and glutathione reductase, may reduce nitroaromatics and produce redox cycling radicals, although at quite low rates (31)(32)(33)(34)(35)(36)(37)(38). Besides, nitroaromatic compounds may reversibly bind to these enzymes inhibiting the reduction of their natural disulfide substrates, glutathione and trypanothione, thus significantly impeding their natural antioxidant functions (31)(32)(33)(34)(35).…”

mentioning

confidence: 99%

“…It has been shown previously that enzymes analogous to TrxR, such as the pyridine nucleotidedisulfide reductases trypanothione reductase and glutathione reductase, may reduce nitroaromatics and produce redox cycling radicals, although at quite low rates (31)(32)(33)(34)(35)(36)(37)(38). Besides, nitroaromatic compounds may reversibly bind to these enzymes inhibiting the reduction of their natural disulfide substrates, glutathione and trypanothione, thus significantly impeding their natural antioxidant functions (31)(32)(33)(34)(35). The possible interaction of mammalian TrxR with nitroaromatics, except for the targeting of the Sec residue by dinitrohalobenzenes (2), has not been studied to date.…”

mentioning

confidence: 99%

Interactions of Nitroaromatic Compounds with the Mammalian Selenoprotein Thioredoxin Reductase and the Relation to Induction of Apoptosis in Human Cancer Cells

Čėnas¹,

Prast

Nivinskas³

et al. 2006

Journal of Biological Chemistry

107

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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°C using 50 M NADPH. As a nitroreductase, TrxR cycled between four-and twoelectron-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-Nmethylnitramine, 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.

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Chinifur, a Selective Inhibitor and "Subversive Substrate" for Trypanosoma congolense Trypanothione Reductase

Cited by 47 publications

References 0 publications

Enterococcus faecalis glutathione reductase: purification, characterization and expression under normal and hyperbaric O2 conditions

Enterococcus faecalis glutathione reductase: purification, characterization and expression under normal and hyperbaric O2 conditions

Dithiol Proteins as Guardians of the Intracellular Redox Milieu in Parasites: Old and New Drug Targets in Trypanosomes and Malaria‐Causing Plasmodia

Interactions of Nitroaromatic Compounds with the Mammalian Selenoprotein Thioredoxin Reductase and the Relation to Induction of Apoptosis in Human Cancer Cells

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