1. Introduction
Infectious diseases caused by parasites are a major threat for entire mankind, especially in the tropics. These infections are not only restricted to humans, they are also predominant in animal health. Just a few years ago infectious diseases caused by parasites were classified as an issue of the past. Due to the elevating level of drug resistance of these pathogens against the current chemotherapeutics, the need for new drugs became even more important. In particular parasitic diseases such as malaria, leishmaniasis, trypanosomiasis, amoebiasis, trichomoniasis, soil-transmitted helminthiasis, filariasis and schistosomiasis are major health problems, especially in “developing” areas (Renslo and McKerrow, 2006; Pal and Bandyopadhyay, 2012). A variety of these parasitic diseases, which comprises the so called neglected diseases Chagas disease, leishmaniasis, sleeping sickness, schistosomiasis, lymphatic filariasis, onchocerciasis and of course malaria (Chatelain and Ioset, 2011), are transmitted by vectors and therefore attempts to combat transmission became prominent. In contrast to the treatment of bacterial infections with antibiotics there are no “general” antiparasitic drugs. The use of a specific drug is dependent on the parasitic organism and therefore has to be individually chosen (Khaw et al., 1995).
Reactive oxygen species (ROS) and oxidative stress are the inevitable consequences of aerobic metabolism, with partially reduced and highly reactive metabolites of O2 being formed in the mitochondria (Andreyev et al., 2005) or as by-products of other cellular sources such as the cytoplasm, the endoplasmatic reticulum, the plasma membrane and peroxisomes. Furthermore, environmental agents such as ionizing and UV radiation or xenobiotic exposure can generate intracellular ROS. O2 metabolites include superoxide anion (O2-) and hydrogen peroxide (H2O2), formed by one- and two electron reductions of O2 or the highly reactive hydroxyl radical (‧OH) which is formed in the presence of metal ions via Fenton and/or Haber-Weiss reactions (Massimine et al., 2006). At physiologically low levels, ROS can function as second messenger in redox signaling, with H2O2 best providing the specificity in its interaction with effectors in signaling processes (Forman et al., 2010). Balancing the generation and elimination of ROS maintains the proper function of redox-sensitive signalling proteins. However, severe increases of ROS induce oxidative modifications in the cellular macromolecules DNA, proteins and lipids, this leading to a disruption of redox homeostasis and irreversible oxidative damage (Trachootham et al., 2008). Depending on the cellular context, the levels of ROS and the redox state of the cells, alterations of the delicate redox balance can promote cell proliferation and survival or induce cell death.
To maintain redox homeostasis and eliminate ROS, aerobes are equipped with enzymatic/nonenzymatic antioxidants and metal sequestering proteins to either prevent or intercept the formation of pro-oxidants. Furthermore, protective mechanisms are put in place to repair and replace damaged macromolecules. Two central thiol/disulfide couples are involved in controlling the redox state of the cell: glutathione/glutathione disulfide (GSH/GSSG) is the major redox couple that determines the antioxidative capacity of cells, other redox couples include the active site dithiol/disulfide of thioredoxins (Trxred/Trxox) interacting with a different subset of proteins and thus forming a distinct but complementary redox system (Jones and Go, 2010).
Enzymatic antioxidants can be categorized into primary or secondary antioxidants, the first reacting directly with pro-oxidants (e.g. catalase, superoxide dismutase), the latter are involved in the regeneration of low molecular weight antioxidant species (Halliwell, 1999). Here, the reduced state of GSSG and Trx-enzymes is restored by the glutathione reductase (GSR) and the Trx reductase using electrons obtained from NADPH. Additionally glutaredoxins (Glrx) utilize GSH for the reduction of intracellular disulfides (Fernandes and Holmgren, 2004). While Trx, Trx reductase and Trx peroxidase (peroxiredoxin, Prx) constitute the Trx-system, the versatile GSH-system includes enzymes required for GSH synthesis and recycling, for its use in metabolism, in defense against ROS-induced damage and in a multitude of detoxification processes. Furthermore, for normal GSH turnover and disposition of GSH-conjugated metabolites and xenobiotics, export from the cell is required that is carried out by GSH efflux transporters and pumps (Sies, 1999) (Fig. 1).
In spite of the diversity of parasites, all are faced with similar biological problems that are related to their lifestyle. Besides coping with ROS levels generated from intrinsic sources, all have to deal with the oxidative stress imposed by the host´s immune response. Furthermore, parasites are faced with ROS that are produced during the epithelial innate immune response of their vector, by vector-resident gut bacteria (Cirimotich et al., 2011) or during melanotic encapsulation processes (Kumar et al., 2003).
Since the redox system plays such a fundamental and indispensable role for parasite survival within their host (Massimine et al., 2006), drugs that either promote ROS generation or inhibit cellular antioxidant systems will lead to redox imbalance by pushing ROS levels above a certain threshold level that will ultimately lead to parasite death (Müller et al., 2003). In general, drugs that target vital redox reactions or promote oxidative stress are named redox-active antiparasitic drugs (Seeber et al., 2005) on which we will mainly focus within this chapter.
2. The role of the antioxidant system in Leishmania
Leishmaniasis is caused by the protozoan flagellate
3. Antimonials
Despite the fact that antimonials were already identified in 1921, they still remain the first-line treatment, although the precise mode of action is not known. But it is generally accepted that pentavalent antimonials (SbV) represent a pro-drug which is converted to trivalent antimonials (SbIII) for antileishmanial activity. Recently it has been indicated that thiols act as reducing agents in this conversion. Furthermore, the participation of a unique parasite-specific trimeric glutathione transferase TDR1 in the activation of antimonial prodrugs has been suggested (Fyfe et al., 2012).
Treatment with antimonials requires parenteral administration and is accompanied by toxic side effects such as cardiac arrhythmia and acute pancreatitis (Sundar and Rai, 2002). Some studies have been carried out to investigate the activity mechanism of antimonials which correlates with an interference with the antioxidant defence system of the parasite: Trivalent antimonials decrease the thiol-reducing capacity of
4. Amphotericin B
Amphotericin B (Fig. 2), a polyene macrolide, has been employed in the treatment of
5. Miltefosine
Miltefosine (hexadecylphosphocholine) is the first and currently the only, orally administered antileishmanial drug (Fig. 2). However, despite cure rates of up to 98% (Roberts, 2006), the drug reveals serious side effects such as vomiting, diarrhea and can cause abnormal physiological development of the foetus. Furthermore, the drug has a relatively long half-life of about 150 hours (Seifert et al., 2007; Maltezou, 2010) which could lead to the development of rapid resistance. Related to its structure, the drug possibly interferes with membranes and membrane-linked enzymes. Currently no verified implications of the drug within the redox biology of the parasite have been found (Rakotomanga et al., 2004; Saint-Pierre-Chazalet et al., 2009).
6. Oxidative chemotherapeutic intervention of Trypanosoma infections
7. Approaches to increase oxidative stress within the malaria parasite
Malaria is a devastating and quite often a deadly parasitic disease, which causes important public health problems in the tropics. The population in more than 90 countries, with more than 2000 million citizens, is exposed to the infection. Malaria infection is responsible for an estimated 500 million clinical cases per annum, causing more than one million deaths; most of these are children in Africa. The malaria parasite
In general,
8. Molecules which inhibit the activities of redox balancing enzymes
The GSH-system plays an important role in the maintenance of the redox status in
The GST is one of the most abundant proteins expressed in
Another promising antimalarial drug target is the
For many years it was thought that the malaria parasite had no need for an endogenous SOD and simply adopted the host´s enzyme for its purpose. However, in 2002, an iron-dependent SOD was described in
9. Drugs inhibiting hemozoin formation and thereby inducing oxidative stress
Besides the attacks of the immune systems of the respective host, where ROS are deployed to kill invading pathogens, the parasite faces another even bigger challenge:
A number of drugs have been identified that act as inhibitors of the hemozoin formation by binding to heme. This leads to an accumulation of free heme, causes high levels of oxidative stress and ends in the death of the parasite (Meunier et al., 2010). Quinoline-containing derivatives such as amopyroquine, amodiaquine, tebuquine, halofantrine, pyronaridine, quinine, mepacrine, epiquinine, quinidine, bisquinoline chloroquine (see figure 2) are highly potent antimalarials that inhibit hemozoin formation at EC50-values in the low nano-molar range (Egan et al., 2000; Kotecka et al., 1997; O’Neill et al., 2003; Vennerstrom et al., 1992). Azole derivatives are also inhibitors of the hemozoin formation and reveal efficacy against chloroquine sensitive as well as resistant plasmodial strains (Banerjee et al., 2009; Rodrigues et al., 2011). Another novel class, which has been identified to interact with heme and thereby prevent the hemozoin formation, are xanthones (Docampo et al., 1990; Ignatushchenko et al., 1997; Xu Kelly et al., 2001). Moreover, a variety of isonitrile derivatives gain their antimalarial activity from inhibition of the hemozoin synthesis (Kumar et al., 2007; Wright et al., 2001) resulting in EC50-values in the low nano-molar range (Badyopadhyay et al., 2001; Singh et al., 2002; Kumar et al., 2007). Benzylmenadione derivatives do not show any cytotoxicity against two human cell lines while they are effective against the chloroquine resistant
10. Druggability of oxidative stress systems in helminths
Helminths are parasitic worms that encompass nematodes (roundworms), cestodes and trematodes (flatworms) and affect humans in all areas of the world, with more than one-third of humans harbouring these parasites that cause chronic, debilitating morbidity. Furthermore, co-endemicity and polyparasitism increase the burden of millions (Hotez et al., 2008). In the absence of vaccines, control relies on pharmacotherapy and pharmacoprophylaxis to easy symptoms and reduce transmission. Helminthosis are treated with a limited number of anthelmintics by chemotherapy of symptomatic individuals or, more general, by control programmes that rely on mass drug administration (MDA) and require annual or biannual treatment of at-risk populations over prolonged period of time (Prichard et al., 2012). A major problem, however, is the development of resistance or tolerance by the parasites to these common antiparasitic drugs (Vercruysse et al., 2011). It is therefore essential to understand the underlying mechanisms of drug resistance and find new drugs to circumvent it.
Praziquantel has been used for over 20 years to treat a variety of human trematode infections. Its precise mechanism of action has not been fully elucidated, however, there is experimental evidence that praziquantel acts by increasing the permeability of cell membranes towards calcium ions and/or by interfering with adenosine uptake (Jeziorski and Greenberg, 2006; Angelucci et al., 2007). Furthermore, it has been suggested that praziquantel reduces GSH concentrations, making the parasite more susceptible to the host immune response (Ribeiro et al., 1998). Interestingly, exposure to sub-lethal concentrations of praziquantel shows that schistosomes undergo a transcriptomic response similar to that observed during oxidative stress (Aragon et al., 2009).
Reliance on a single drug for mass treatment is risky. Therefore, anti-schistosomiasis drug development is on the way to identify new compounds with different modes of action. Recently it was demonstrated that artemisinin-based compounds (e.g. artemether, figure 2) are active against immature stages of schistosomes. Although a number of potential drug targets have been proposed, the mode of action remains ambiguous (O´Neill et al., 2010). It is thought that the primary activator of the drug is an iron source. Therefore, interaction with heme in the worm gut has been suggested, leading to the formation of an unstable species that generates ROS and thus kills the worm (Utzinger et al., 2001). Since artemisinins are critically important for malaria chemotherapy, they are not available for MDA.
Schistosomes seem to be poorly adapted to cope with oxidative stress. This is surprising, since they have to deal with host-immune and self-generated ROS and, furthermore, with ROS generated during the consumption of host haemoglobin (Huang et al., 2012).The highly restricted antioxidant network has been widely accepted as an excellent drug target for schistosomes and other platyhelminths, since it is unique and differs significantly from the human host. Interestingly, the parasites have merged the Trx- and GSH-system using a hybrid enzyme, the thioredoxin-glutathione reductase (TGR) (Salinas et al., 2004, Huang et al., 2012). Using RNA interference, the TGR was found to be essential for parasite survival (Kuntz et al., 2007). TGR was indicated to be the main target of schistosomicidal drugs used in the past (antimonyl potassium tartrate and oltipraz) and of the anti-arthritic drug auranofin (Fig. 2), with a significant worm reduction observed in infected mice (Kuntz et al., 2007; Angelucci et al., 2009). A quantitative high-throughput screen identified highly potent lead compounds against the Schistosoma TGR (Simeonov et al., 2008), with low inhibitory constants being found with derivatives of phosphinic amides, isoxazolones and the oxadiazole-2-oxide chemotype (Furoxan) (Fig. 2) (Huang et al., 2012).
Preventive chemotherapy is the mainstay in the control of human soil-transmitted helminthiasis (STH). STH is primarily caused by the nematodes
Filarial parasites are classified according to the habitat of the adult worms in the vertebral host, with the cutaneous (
Diethylcarbamazine (DEC) is still the mainstay for the treatment of lymphatic filariasis and first choice of therapy of loiasis. Surprisingly, its molecular mechanism of action is still not completely understood. Since pharmacologically relevant concentrations of DEC do not have an effect on microfilariae in culture, its mode of action must involve both the worm and its host. A possible involvement of host arachidonate- and NO-dependent pathways was observed (McGarry et al., 2005). Currently no verification of an influence on the redox biology of helminths is available.
It has been postulated that antioxidant enzymes, that defend against host-generated ROS, are of particular importance for long-lived tissue-dwelling parasites that are involved in chronic infections. Here, surface or secreted antioxidant enzymes are of great importance since they can directly neutralize ROS that pose real danger, thereby protecting surface membranes against peroxides. Secreted filarial antioxidant enzymes include SOD, GPx and Prx (Henkle-Dührsen and Kampkötter, 2001). Additionally to their antioxidant role, the Prx have recently been shown to contribute to the development of Th2-responses by altering the function of macrophages (Donnelly et al., 2008). Interestingly, GSH-dependent proteins have been observed that are capable of modifying the local environment via modulation of the immune response. Here the secretory GSTs from
As outlined above, GSH-dependent detoxification pathways defend against current drugs and also play a role in mediating resistance to anthelmintics. The antioxidant pathways also provide the parasite with a means to protect against ROS-attack by its host and/or vector. In the model nematode
11. Conclusion
The current bottle-neck for the treatment of parasitic diseases with chemotherapeutics is the increasing drug resistance which forces the continuous discovery and development of new antiparasitic drugs. There is an urgent need for novel chemotherapeutic targets. New drugs should be generated to specifically target the parasite with minimal (or no) toxicity to the human host. Therefore, good drug targets should be distinctly different from processes in the host, or ideally be absent in the latter. Targeting the peculiarities - which are absent in the host - is proposed as such a strategy. In this sense, the parasite-specific biosyntheses represent ideal drug targets; similar to the already exploited antifolate interference with the parasite’s dihydrofolate (vitamin B9) biosynthesis. There are a variety of reports about reactive compounds that have antiparasitic activity; however, not all of these are therapeutically viable drug-like molecules due to various limitations such as toxicity, low bioavailability, rapid inactivation under
In this chapter we have tried to give an outline of the present situation of redox-active antiparasitic molecules that target human infectious diseases. In future the mechanisms, evolutionarily developed by the parasite to circumvent the crucial presence of ROS, will open new avenues for the development of novel antiparasitic drugs that combat resistant human pathogens effectively.
Acknowledgement
The authors would like to thank FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) for financial support (Project No. 2009/54325-2 to CW). The support of the DFG (Deutsche Forschungsgemeinschaft, grant LI 793/5-0 to EL) is acknowledged.
References
- 1.
Ahmad R, Srivastava AK, Tripathi RP, Batra S, Walter RD. (2007) Synthesis and biological evaluation of potential modulators of malarial glutathione-S-transferase(s). J Enzym Inhib Med Chem. 22:327-342 - 2.
Akoachere M, Buchholz K, Fischer E, Burhenne J, Haefeli WE, Schirmer RH, Becker K. (2005) In vitro assessment of methylene blue on chloroquine-sensitive and -resistant Plasmodium falciparum strains reveals synergistic action with artemisinins. Antimicrob Agents Chemother. 49:4592-4597 - 3.
Amato VS, Tuon FF, Bacha HA, Neto VA, Nicodemo AC. (2008) Mucosal leishmaniasis: current scenario and prospects for treatment. Acta Trop. 105:1-9 - 4.
An JH, Blackwell TK. (2003) SKN-1 links C. elegans mesendodermal specification to a conserved oxidative stress response. Genes Dev. 17:1882-93 - 5.
Angelucci F, Basso A, Bellelli A, Brunori M, Pica Mattoccia L, Valle C. (2007) The anti-schistosomal drug praziquantel is an adenosine antagonist. Parasitology 134:1215-1221 - 6.
Angelucci F, Sayed AA, Williams DL, Boumis G, Brunori M, Dimastrogiovanni D, Miele AE, Pauly F, Bellelli A. (2009) Inhibition of Schistosoma mansoni thioredoxin-glutathione reductase by auranofin: structural and kinetic aspects. J Biol Chem. 284:28977-28985 - 7.
Andreyev AY, Kushnareva YE, Starkov AA. (2005) Mitochondrial metabolism of reactive oxygen species. Biochemistry (Moscow) 70:200-214 - 8.
Aragon AD, Imani RA, Blackburn VR, Cupit PM, Melman SD, Goronga T, Webb T, Loker ES, Cunningham C. (2009) Towards an understanding of the mechanism of action of praziquantel. Mol Biochem Parasitol. 164:57-65 - 9.
Atamna H, Ginsburg H. (1995) Heme degradation in the presence of glutathione. A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells. J Biol Chem. 270:24876-24883 - 10.
Balana-Fouce R, Reguera RM, Cubria JC, Ordonez D. (1998) The pharmacology of leishmaniasis. Gen Pharmacol. 30:435-443 - 11.
Bandyopadhyay U, Dey S. (2011) Antimalarial drugs and molecules inhibiting hemozoin formation. In: Apicomplexan Parasites: Molecular Approaches Toward Targeted Drug Development, edited by Becker K. Weinheim, Germany: Wiley-VCH Verlag & Co. KGaA, 205-234. - 12.
Banerjee AK, Arora N, Murty US. (2009) Structural model of the Plasmodium falciparum thioredoxin reductase: a novel target for antimalarial drugs. J Vector Borne Dis. 46:171-183 - 13.
Becker K, Kanzok SM, Iozef R, Fischer M, Schirmer RH, Rahlfs S. (2003) Plasmoredoxin, a novel redox-active protein unique for malarial parasites. Eur J Biochem. 270:1057-1064 - 14.
Beech RN, Skuce P, Bartley DJ, Martin RJ, Prichard RK, Gilleard JS (2011) Anthelmintic resistance: markers for resistance, or susceptibility? Parasitology. 138:160–174 - 15.
Bennett JL, Williams JF, Dave V (1993) Pharmacology of ivermectin. Parasitol Today 4:226-228 - 16.
Biot C, Bauer H, Schirmer RH, Davioud-Charvet E. (2004) 5-substituted tetrazoles as bioisosteres of carboxylic acids. Bioisosterism and mechanistic studies on glutathione reductase inhibitors as antimalarials. J Med Chem. 47:5972-5983 - 17.
Boucher IW, Brzozowski AM, Brannigan JA, Schnick C, Smith DJ, Kyes SA, Wilkinson AJ. (2006) The crystal structure of superoxide dismutase from Plasmodium falciparum . BMC Struct Biol. 6:20 - 18.
Buchholz K, Schirmer RH, Eubel JK, Akoachere MB, Dandekar T, Becker K, Gromer S. (2008) Interactions of methylene blue with human disulfide reductases and their orthologues from Plasmodium falciparum . Antimicrob Agents Chemother. 52:183-191 - 19.
Butzloff S, Groves MR, Wrenger C, Müller IB. (2012) Cytometric quantification of singlet oxygen in the human malaria parasite Plasmodium falciparum . Cytometry A. 81:698-703 - 20.
Chatelain E, Ioset JR. (2011) Drug discovery and development for neglected diseases: the DNDi model. Drug Des Devel Ther. 5:175-181. - 21.
Chibale K, Haupt H, Kendrick H, Yardley V, Saravanamuthu A, Fairlamb AH, Croft SL. (2001) Antiprotozoal and cytotoxicity evaluation of sulfonamide and urea analogues of quinacrine. Bioorg Med Chem Lett 11: 2655-2657 - 22.
Choe KP, Leung CK, Miyamoto MM. (2012) Unique structure and regulation of the nematode detoxification gene regulator, SKN-1: implications to understanding and controlling drug resistance. Drug Metab Rev. 44:209-23 - 23.
Cirimotich CM, Dong Y, Clayton AM, Sandiford SL, Souza-Neto JA, Mulenga M, Dimopoulos G (2011) Natural microbe-mediated refractoriness to Plasmodium infection in Anopheles gambiae . Science, 332:855-858 - 24.
Croft SL, Sundar S, Fairlamb AH. (2006) Drug resistance in leishmaniasis. Clin. Microbiol. Rev. 19:111-126 - 25.
Davioud-Charvet E, McLeish MJ, Veine DM, Giegel D, Arscott LD, Andricopulo AD, Becker K, Müller S, Schirmer RH, Williams CH, Jr., Kenyon GL. (2003) Mechanism-based inactivation of thioredoxin reductase from Plasmodium falciparum by Mannich bases. Implication for cytotoxicity. Biochemistry 42:13319-13330 - 26.
Dedet JP, Pratlong F. (2009) Protozoa infection in G. Cook, A. Zumla (Eds.), Manson's Tropical Diseases, Saunders, Philadelphia 1341-1367 - 27.
Díaz de Toranzo EG, Castro JA, Franke de Cazzulo BM, Cazzulo JJ. (1988) Interaction of benznidazole reactive metabolites with nuclear and kinetoplastic DNA, proteins and lipids from Trypanosoma cruzi. Experientia, 44:880-881 - 28.
Docampo R. (1990) Sensitivity of parasites to free radical damage by antiparasitic drugs. Chem Biol Interact. 73:1-27 - 29.
Donnelly S, Stack CM, O’Neill SM, Sayed AA, Williams DL, Dalton JP. (2008) Helminth 2-Cys peroxiredoxin drives Th2 responses through a mechanism involving alternatively activated macrophages. FASEB J 22:4022–4032 - 30.
Ehrenshaft M, Chung KR, Jenns AE, Daub ME. (1999) Functional characterization of SOR1, a gene required for resistance to photosensitizing toxins in the fungus Cercospora nicotianae . Curr Genet. 34:478-485 - 31.
Egan TJ, Hunter R, Kaschula CH, Marques HM, Misplon A, Walden J. (2000) Structure-function relationships in aminoquinolines: effect of amino and chloro groups on quinoline-hematin complex formation, inhibition of beta-hematin formation, and antiplasmodial activity. J Med Chem. 43:283-291 - 32.
Fairlamb AH, Blackburn P, Ulrich P, Chait BT, Cerami A. (1985) Trypanothione: a novel bis(glutathionyl)spermidine cofactor for glutathione reductase in trypanosomatids. Science 227:1485-1487 - 33.
Fernandes AP, Holmgren A (2004) Glutaredoxins: Glutathione-dependent redox enzymes with functions far beyond a simple thioredoxin backup system. Antioxid Redox Signal. 6:63-74 - 34.
Filardi LS, Brener Z. (1987) Susceptibility and natural resistance of Trypanosoma cruzi strains to drugs used clinically in Chagas disease. Trans R Soc Trop Med. Hyg. 81:755-759 - 35.
Forman HJ, Maiorino M, Ursini F (2010) Signaling functions of reactive oxygen species. Biochemistry 49:835-842 - 36.
Frey PA. (1997) Radicals in enzymatic reactions. Curr Opin Chem Biol. 1:347-356 - 37.
Freinbichler W, Colivicchi MA, Stefanini C, Bianchi L, Ballini C, Misini B, Weinberger P, Linert W, Varešlija D, Tipton KF, Della Corte L. (2011). Highly reactive oxygen species: detection, formation, and possible functions. Cell Mol Life Sci. 68:2067-2079 - 38.
Friebolin W, Jannack B, Wenzel N, Furrer J, Oeser T, Sanchez CP, Lanzer M, Yardley V, Becker K, Davioud-Charvet E. (2008) Antimalarial dual drugs based on potent inhibitors of glutathione reductase from Plasmodium falciparum . J Med Chem. 51:1260-1277 - 39.
Francis SE, Sullivan DJ, Daniel E. (1997) Hemoglobin metabolism in the malaria parasite Plasmodium falciparum . Annu. Rev. Microbiol. 51:97-123 - 40.
Fyfe PK, Westrop GD, Silva AM, Coombs GH, Hunter WN. (2012) Leishmania TDR1 structure, a unique trimeric glutathione transferase capable of deglutathionylation and antimonial prodrug activation. Proc Natl Acad Sci U S A. 109:11693-11698 - 41.
Geary TG, Woo K, McCarthy JS, Mackenzie CD, Horton J, Prichard RK, de Silva NR, Olliaro PL, Lazdins-Helds JK, Engels DA, Bundy DA. (2010) Unresolved issues in anthelmintic pharmacology for helminthiases of humans. Int J Parasitol. 40:1-13 - 42.
Gallo V, Schwarzer E, Rahlfs S, Schirmer RH, van Zwieten R, Roos D, Arese P, Becker K. (2009) Inherited glutathione reductase deficiency and Plasmodium falciparum malaria—a case study. PLoS One 4:e7303 - 43.
Garavito G, Bertani S, Rincon J, Maurel S, Monje MC, Landau I, Valentin A, Deharo E. (2007) Blood schizontocidal activity of methylene blue in combination with antimalarials against Plasmodium falciparum . Parasite. 14:135-140 - 44.
Gradoni L, Soteriadou K, Louzir H, Dakkak A, Toz SO, Jaffe C et al. (2008) Drug regimens for visceral leishmaniasis in Mediterranean countries. Trop Med Int Health 13:1272-1276 - 45.
Gratepanche S, Menage S, Touati D, Wintjens R, Delplace P, Fontecave M, Masset A, Camus D, Dive D. (2002) Biochemical and electron paramagnetic resonance study of the iron superoxide dismutase from Plasmodium falciparum . Mol Biochem Parasitol. 120:237-246 - 46.
Grellier P, Maroziene A, Nivinskas H, Sarlauskas J, Aliverti A, Cenas N. (2010) Antiplasmodial activity of quinones: roles of aziridinyl substituents and the inhibition of Plasmodium falciparum glutathione reductase. Arch Biochem Biophys. 494:32-39 - 47.
Halliwell B (1999) Antioxidant defense mechanisms: from the beginning to the end (of the beginning) Free Radic Res. 31:261-272. - 48.
Henkle-Dührsen K, Kampkötter A (2001) Antioxidant enzyme families in parasitic nematodes. Mol Biochem Parasitol. 114:129-142. - 49.
Herwaldt, BL (1999). "Leishmaniasis." Lancet 354 (9185): 1191-1199 - 50.
Holzmuller P, Sereno D, Lemesre JL. (2005) Lower nitric oxide susceptibility of trivalent antimony-resistant amastigotes of Leishmania infantum . Antimicrob Agents Chemother. 49:4406-4409 - 51.
Hotez PJ, Brindley PJ, Bethony JM, King CH, Pearce EJ, Jacobson J (2008) Helminth infections: the great neglected tropical diseases. J Clin Invest. 118:1311-1321 - 52.
Huang HH, Rigouin C, Willams DL (2012) The redox biology of schistosome parasites and application for drug development. Curr Pharm Des. 18:3595-3611 - 53.
Ignatushchenko MV, Winter RW, Bachinger HP, Hinrichs DJ, Riscoe MK. (1997) Xanthones as antimalarial agents; studies of a possible mode of action. FEBS Lett. 409:67-73 - 54.
James CE, Davey MW. (2009) Increased expression of ABC transport proteins is associated with ivermectin resistance in the model nematode Caenorhabditis elegans . Int J Parasitol. 39:213-20 - 55.
Jeziorski MC, Greenberg RM. (2006) Voltage-gated calcium channel subunits from platyhelminths: potential role in praziquantel action. Int J Parasitol 36:625–632 - 56.
Jones DP, Go YM. (2010) Redox compartmentalization and cellular stress. Diabetes, Obes. Metab. 12:116–125. - 57.
Kanzok SM, Rahlfs S, Becker K, and Schirmer RH. (2002) Thioredoxin, thioredoxin reductase, and thioredoxin peroxidase of malaria parasite Plasmodium falciparum . Methods Enzymol. 347:370-381 - 58.
Kanzok SM, Schirmer RH, Turbachova I, Iozef R, Becker K. (2000) The thioredoxin system of the malaria parasite Plasmodium falciparum . Glutathione reduction revisited. J Biol Chem. 275:40180-40186 - 59.
Kawazu S, Komaki K, Tsuji N, Kawai S, Ikenoue N, Hatabu T, Ishikawa H, Matsumoto Y, Himeno K, Kano S. (2001) Molecular characterization of a 2-Cys peroxiredoxin from the human malaria parasite Plasmodium falciparu m. Mol Biochem Parasitol. 116:73-79 - 60.
Kehr S, Jortzik E, Delahunty C, Yates JR, Rahlfs S, Becker K. (2011) Protein s-glutathionylation in malaria parasites. Antioxid Redox Signal. 15:2855-2865 - 61.
Khan AU, Kasha M. (1994) Singlet molecular oxygen in the Haber-Weiss reaction. Proc Natl Acad Sci USA. 91:12365-12367 - 62.
Khaw M, Panosian CB. (1995) Human antiprotozoal therapy: past, present, and future. Clin Microbiol Rev. 8:427-439. - 63.
Kirchhoff LV. (2000) American trypanosomiasis (Chagas' disease) in R.E. Rakel (Ed.), Conn's Current Therapy, W. B. Saunders, New York: 101-102 - 64.
Knöckel J, Müller IB, Butzloff S, Bergmann B, Walter RD, Wrenger C. (2012) The antioxidative effect of de novo generated vitamin B6 inPlasmodium falciparum validated by protein interference. Biochem J. 443:397-405 - 65.
Koenderink JB, Kavishe RA, Rijpma SR, Russel FG. (2010) The ABCs of multidrug resistance in malaria. Trends Parasitol. 26:440-446 - 66.
Kotecka BM, Barlin GB, Edstein MD, Rieckmann KH. (1997) New quinoline di-Mannich base compounds with greater antimalarial activity than chloroquine, amodiaquine, or pyronaridine. Antimicrob Agents Chemother. 41:1369-1374 - 67.
Krauth-Siegel RL, Bauer H, Schirmer RH. (2005) Dithiol proteins as guardians of the intracellular redox milieu in parasites: old and new drug targets in trypanosomes and malaria-causing plasmodia. Angew Chem Int Ed Engl. 44:690-715 - 68.
Krauth-Siegel RL, Comini MA. (2008) Redox control in trypanosomatids, parasitic protozoa with trypanothione-based thiol metabolism. Biochim. Biophys. Acta 1780:1236-1248 - 69.
Krnajski Z, Gilberger TW, Walter RD, Cowman AF, Müller S. (2002) Thioredoxin reductase is essential for the survival of Plasmodium falciparum erythrocytic stages. J Biol Chem. 277:25970-25975 - 70.
Krnajski Z, Walter RD, Müller S. (2001) Isolation and functional analysis of two thioredoxin peroxidases (peroxiredoxins) from Plasmodium falciparum . Mol Biochem Parasitol. 113:303-308 - 71.
Kumar S, Christophides GK, Cantera R, Charles B, Han YS, Meister S, Dimopoulos G, Kafatos FC, Barillas-Mury C. (2003) The role of reactive oxygen species on Plasmodium melanotic encapsulation in Anopheles gambiae. Proc Natl Acad Sci USA. 100:14139-14144 - 72.
Kumar S, Das SK, Dey S, Maity P, Guha M, Choubey V, Panda G, Bandyopadhyay U. (2008) Antiplasmodial activity of [(aryl)arylsulfanylmethyl]Pyridine. Antimicrob Agents Chemother. 52:705-715 - 73.
Kuntz AN, Davioud-Charvet E, Sayed AA, Califf LL, Dessolin J, Arnér ES, Williams DL. (2007) Thioredoxin glutathione reductase from Schistosoma mansoni: an essential parasite enzyme and a key drug target. PLoS Med. 4:e206 - 74.
Lewis JA, Wu CH, Berg H, Levine JH (1980) The genetics of levamisole resistance in the nematode Caenorhabditis elegans . Genetics 95:905–928 - 75.
Li R, Kenyon GL, Cohen FE, Chen X, Gong B, Dominguez JN, Davidson E, Kurzban G, Miller RE, Nuzum EO, et al. (1995) In vitro antimalarial activity of chalcones and their derivatives. J Med Chem. 38:5031–5037 - 76.
Liebau E, Bergmann B, Campbell AM, Teesdale-Spittle P, Brophy PM, Luersen K, Walter RD. (2002) The glutathione S-transferase from Plasmodium falciparum . Mol Biochem Parasitol. 124:85-90 - 77.
Liebau E, De Maria F, Burmeister C, Perbandt M, Turella P, Antonini G, Federici G, Giansanti F, Stella L, Lo Bello M, Caccuri AM, Ricci G. (2005) Cooperativity and pseudo-cooperativity in the glutathione S-transferase from Plasmodium falciparum . J Biol Chem. 280:26121-26128. - 78.
Liebau E, Höppner J, Mühlmeister M, Burmeister C, Lüersen K, Perbandt M, Schmetz C, Büttner D, Brattig N. (2008) The secretory omega-class glutathione transferase OvGST3 from the human pathogenic parasite Onchocerca volvulus . FEBS J. 275:3438-3453. - 79.
Liebau E, Dawood KF, Fabrini R, Fischer-Riepe L, Perbandt M, Stella L, Pedersen JZ, Bocedi A, Petrarca P, Federici G, Ricci G.(2009) Tetramerization and cooperativity in Plasmodium falciparum glutathione S-transferase are mediated by atypic loop 113-119. J Biol Chem. 284:22133-22139. - 80.
Maltezou HC. (2010) Drug resistance in visceral leishmaniasis. J. Biomed. Biotechnol. 617521 - 81.
Martin RJ, Robertson AP, Bjorn H (1997) Target sites of anthelmintics. Parasitology 114:111–124 - 82.
Massimine KM, McIntosh MT, Doan LT, Atreya CE, Gromer S, Sirawaraporn W, Elliott DA, Joiner KA, Schirmer RH, Anderson KS. (2006) Eosin B as a novel antimalarial agent for drug-resistant Plasmodium falciparum . Antimicrob Agents Chemother. 50:3132-3141 - 83.
Mason RP, Holtzman JL. (1975) The role of catalytic superoxide formation in the O2 inhibition of nitroreductase. Biochem Biophys Res Commun. 67:1267-1274 - 84.
Maya JD, Rodríguez A, Pino L, Pabon A, Ferreira J, Pavani M, Repetto Y, Morello A. (2004) Effects of buthionine sulfoximine nifurtimox and benznidazole upon trypanothione and metallothionein proteins in Trypanosoma cruzi . Biol Res. 37:61-69 - 85.
Maya JD, Cassels BK, Iturriaga-Vásquez P, Ferreira J, Faúndez M, Galanti N, Ferreira A, Morello A. (2007) Mode of action of natural and synthetic drugs against Trypanosoma cruzi and their interaction with the mammalian host. Comp Biochem Physiol A Mol Integr Physiol. 146:601-620 - 86.
McGarry HF, Plant LD, Taylor MJ (2005) Diethylcarbamazine activity against Brugia malayi microfilariae is dependent on inducible nitric-oxide synthase and the cyclooxygenase pathway. Filaria J. 4:4 - 87.
Monostori P, Wittmann G, Karg E, Turi S. (2009) Determination of glutathione and glutathione disulfide in biological samples: an in-depth review. J. Chromatogr. B Analyt Technol Biomed Life Sci 877:3331-3346 - 88.
Moreno SN, Docampo R, Mason RP, León W, Stoppani AO. (1982) Different behaviors of benznidazole as free radical generator with mammalian and Trypanosoma cruzi microsomal preparations. Arch Biochem Biophys. 218:585-591 - 89.
Mukherjee AK, Gupta G, Bhattacharjee S, Guha SK, Majumder S, Adhikari A et al. (2010) Amphotericin B regulates the host immune response in visceral leishmaniasis: reciprocal regulation of protein kinase C isoforms. J Infect. 61:173–184 - 90.
Meunier B, Robert A. (2010) Heme as trigger and target for trioxane-containing antimalarial drugs. Acc Chem Res 43: 1444-1451 - 91.
Müller S, Liebau E, Walter RD, Krauth-Siegel RL. (2003) Thiol-based redox metabolism of protozoan parasites. Trends Parasitol. 19:320-328 - 92.
Müller S. (2003) Thioredoxin reductase and glutathione synthesis in Plasmodium falciparum . Redox Rep. 8:251-255 - 93.
Muller T, Johann L, Jannack B, Bruckner M, Lanfranchi DA, Bauer H, Sanchez C, Yardley V, Deregnaucourt C, Schrevel J, Lanzer M, Schirmer RH, Davioud-Charvet E. (2011) A glutathione reductase-catalyzed cascade of redox reactions to bioactivate potent antimalarial 1,4-naphthoquinones-a new strategy to combat malarial parasites. J Am Chem Soc. 133:11557-11571 - 94.
O'Neill PM, Mukhtar A, Stocks PA, Randle LE, Hindley S, Ward SA, Storr RC, Bickley JF, O'Neil IA, Maggs JL, Hughes RH, Winstanley PA, Bray PG, Park BK. (2003) Isoquine and related amodiaquine analogues: a new generation of improved 4-aminoquinoline antimalarials. J Med Chem. 46:4933-4945 - 95.
O'Neill PM, Barton VE, Ward SA. (2010) The molecular mechanism of action of artemisinin--the debate continues. Molecules. 15:1705-1721 - 96.
Olliaro P, Seiler J, Kuesel A, Horton J, Clark JN, Don R, Keiser J. (2011) Potential drug development candidates for human soil-transmitted helminthiases. PLoS Negl Trop Dis. 5:e1138 - 97.
Pal C, Bandyopadhyay U. (2012) Redox-active antiparasitic drugs. Antioxid Redox Signal. 17:555-582 - 98.
Perbandt M, Höppner J, Burmeister C, Lüersen K, Betzel C, Liebau E. (2008) Structure of the extracellular glutathione S-transferase OvGST1 from the human pathogenic parasite Onchocerca volvulus . J Mol Biol. 377:501-511. - 99.
Prata A. (2001) Clinical and epidemiological aspects of Chagas disease. Lancet, Infect. Dis. 1:92-100 - 100.
Prichard RK, Basáñez MG, Boatin BA, McCarthy JS, García HH, Yang GJ, Sripa B, Lustigman S. (2012) A research agenda for helminth diseases of humans: intervention for control and elimination. PLoS Negl Trop Dis. 6:e1549. - 101.
Rakotomanga M, Loiseau PM, Saint-Pierre-Chazalet M. (2004) Hexadecylphosphocholine interaction with lipid monolayers. Biochim Biophys Acta. 1661:212-218 - 102.
Renslo AR, McKerrow JH. (2006) Drug discovery and development for neglected parasitic diseases. Nat Chem Biol. 2:701-710 - 103.
Ribeiro F, Coelho PM, Vieira LQ, Watson DG, Kusel JR. (1998) The effect of praziquantel treatment on glutathione concentration in Schistosoma mansoni . Parasitology. 116:229-236 - 104.
Roberts, MT. (2006). Current understandings on the immunology of leishmaniasis and recent developments in prevention and treatment. Br Med Bull 75-76:115-130 - 105.
Rodriques Coura J, de Castro SL. (2002) A critical review on Chagas disease chemotherapy. Mem. Inst. Oswaldo Cruz. 97:3-24 - 106.
Saint-Pierre-Chazalet M, Ben BM, Le ML, Bories C, Rakotomanga M, Loiseau PM. (2009) Membrane sterol depletion impairs miltefosine action in wild-type and miltefosine-resistant Leishmania donovani promastigotes. J Antimicrob Chemother. 64:993-1001 - 107.
Salinas G, Selkirk ME, Chalar C, Maizels RM, Fernández C. (2004) Linked thioredoxin-glutathione systems in platyhelminths. Trends Parasitol. 20:340-346 - 108.
Sarma GN, Savvides SN, Becker K, Schirmer M, Schirmer RH, Karplus PA. (2003) Glutathione reductase of the malarial parasite Plasmodium falciparum : crystal structure and inhibitor development. J Mol Biol. 328:893-907 - 109.
Sau A, Pellizzari Tregno F, Valentino F, Federici G, Caccuri AM. (2010) Glutathione transferases and development of new principles to overcome drug resistance. Arch Biochem Biophys. 500:116-122. - 110.
Seeber F, Aliverti A, Zanetti G. (2005) The plant-type ferredoxin-NADP+reductase/ferredoxin redox system as a possible drug target against apicomplexan human parasites. Curr Pharm Des. 11:3159-3172 - 111.
Seifert K, Perez-Victoria FJ, Stettler M, Sanchez-Canete MP, Castanys S, Gamarro F et al. (2007) Inactivation of the miltefosine transporter, LdMT, causes miltefosine resistance that is conferred to the amastigote stage of Leishmania donovani and persistsin vivo . Int J Antimicrob Agents. 30:229-235 - 112.
Sharma U, Singh S. (2008) Insect vectors of Leishmania: distribution, physiology and their control. J Vector Borne Dis. 45:255-272 - 113.
Sharmeen S, Skrtic M, Sukhai MA, Hurren R, Gronda M, Wang X, Fonseca SB, Sun H, Wood TE, Ward R, Minden MD, Batey RA, Datti A, Wrana J, Kelley SO, Schimmer AD. (2010) The antiparasitic agent ivermectin induces chloride-dependent membrane hyperpolarization and cell death in leukemia cells. Blood 116:3593-603. - 114.
Sherman IW. (1977) Amino acid metabolism and protein synthesis in malarial parasites. Bull World Health Organ. 55:265-276 - 115.
Sies H (1999) Glutathione and its role in cellular functions. Free Radic Biol Med. 27:916-921. - 116.
Simeonov A, Jadhav A, Sayed AA, Wang Y, Nelson ME, Thomas CJ, Inglese J, Williams DL, Austin CP. (2008) Quantitative high-throughput screen identifies inhibitors of the Schistosoma mansoni redox cascade. PLoS Negl Trop Dis. 2:e127 - 117.
Singh C, Srivastav NC, Puri SK. (2002) In vivo active antimalarial isonitriles. Bioorg Med Chem Lett. 12:2277-2279 - 118.
Sommer A, Rickert R, Fischer P, Steinhart H, Walter RD, Liebau E. (2003) A dominant role for extracellular glutathione S-transferase from Onchocerca volvulus is the production of prostaglandin D2. Infect Immun. 71:3603-3606 - 119.
Soulere L, Delplace P, Davioud-Charvet E, Py S, Sergheraert C, Perie J, Ricard I, Hoffmann P, Dive D. (2003) Screening of Plasmodium falciparum iron superoxide dismutase inhibitors and accuracy of the SOD-assays. Bioorg Med Chem. 11:4941-4944 - 120.
Souza AS, Giudice A, Pereira JM, Guimaraes LH, de Jesus AR, de Moura TR et al. (2010) Resistance of Leishmania (Viannia) braziliensis to nitric oxide: correlation with antimony therapy and TNF-alpha production. BMC Infect Dis 10:209 - 121.
Sturm N, Hu Y, Zimmermann H, Fritz-Wolf K, Wittlin S, Rahlfs S, Becker K. (2009) Compounds structurally related to ellagic acid show improved antiplasmodial activity. Antimicrob Agents Chemother. 53:622-630 - 122.
Sundar S, Rai M. (2002) Advances in the treatment of leishmaniasis. Curr Opin Infect Dis 15:593–598 - 123.
Tambasco-Studart M, Titiz O, Raschle T, Forster G, Amrhein N, Fitzpatrick TB. (2005) Vitamin B6 biosynthesis in higher plants. Proc Natl Acad Sci USA. 102:13687-13692 - 124.
Temperton NJ, Wilkinson SR, Meyer DJ, Kelly JM. (1998) Overexpression of superoxide dismutase in Trypanosoma cruzi results in increased sensitivity to the trypanocidal agents gentian violet and benznidazole. Mol Biochem Parasitol. 96:167-176 - 125.
Trachootham D, Weiqin L, Ogasawara MA, Valle NRD, Huang P. (2008) Redox Regulation of Cell Survival. Antioxid Redox Signal. 10:1343-1374 - 126.
Turrens JF, Watts Jr BP, Zhong L, Docampo R. (1996) Inhibition of Trypanosoma cruzi andT. brucei NADH fumarate reductase by benznidazole and anthelmintic imidazole derivatives. Mol Biochem Parasitol. 82:125-129 - 127.
Utzinger J, Xiao S, N'Goran EK, Bergquist R, Tanner M. (2001) The potential of artemether for the control of schistosomiasis. Int J Parasitol 31:1549-1562. - 128.
Utzinger J, Keiser J. (2004) Schistosomiasis and soil-transmitted helmintiasis: common drugs for treatment and control. Expert Opin. Pharmacother. 5:263-285. - 129.
Vanaerschot M, Maes I, Ouakad M, Adaui V, Maes L, De DS et al. (2010) Linking in vitro and in vivo survival of clinical Leishmania donovani strains. PLoS One 5:e12211 - 130.
Van Assche T, Deschacht M, da Luz RA, Maes L, Cos P. (2007) Leishmania-macrophage interactions: insights into the redox biology. Free Radic Biol Med. 51:337-351 - 131.
Vennerstrom JL, Ellis WY, Ager AL, Jr., Andersen SL, Gerena L, Milhous WK. (1992) Bisquinolines. N,N-bis(7-chloroquinolin-4-yl)alkanediamines with potential against chloroquine-resistant malaria. J Med Chem. 35:2129-2134 - 132.
Vercruysse J, Albonico M, Behnke J, Kotze A, Prichard R, et al.(2011) Is anthelmintic resistance a concern for the control of human soil-transmitted helminths? Int J Parasitol: Drugs Drug Res. 1:14–27 - 133.
Wang X, Quinn PJ. (1999). Vitamin E and its function in membranes. Prog Lipid Res. 38:309-336 - 134.
Wangroongsarb P, Satimai W, Khamsiriwatchara A, Thwing J, Eliades JM, Kaewkungwal J, Delacollette C. (2011) Respondent-driven sampling on the Thailand-Cambodia border. II. Knowledge, perception, practice and treatment-seeking behaviour of migrants in malaria endemic zones. Malar J. 10:117 - 135.
Wrenger C, Eschbach ML, Müller IB, Warnecke D, Walter RD. (2005) Analysis of the vitamin B6 biosynthesis pathway in the human malaria parasite Plasmodium falciparum . J Biol Chem. 280:5242-5248 - 136.
Wright AD, Wang H, Gurrath M, Konig GM, Kocak G, Neumann G, Loria P, Foley M, Tilley L. (2001) Inhibition of heme detoxification processes underlies the antimalarial activity of terpene isonitrile compounds from marine sponges. J Med Chem. 44:873-885 - 137.
Xu Kelly J, Winter R, Riscoe M, Peyton DH. (2001) A spectroscopic investigation of the binding interactions between 4,5-dihydroxyxanthone and heme. J Inorg Biochem. 86:617-625 - 138.
Zahoor A, Lafleur MV, Knight RC, Loman H, Edwards DI. (1987) DNA damage induced by reduced nitroimidazole drugs. Biochem Pharmacol. 36:3299–3304