**3. Oxidative stress in Chagas disease**

Oxidative stress is a central phenomenon involved in aging, cancer, transmissible or infectious diseases, including COVID-19 [72], nontransmissible chronic conditions, such as metabolic diseases, autoimmune and degenerative disorders, inflammation, metal poisoning, etc. [73–75], produced by the imbalance on the production/ uptake of oxidant/antioxidant species [76].

A plethora of antioxidant defenses evolved in order to balance the redox homeostasis [76, 77]. Oxidant species such as superoxide (O2 •− ) and hydrogen peroxide (H2O2) are detoxified by SOD and catalase, respectively. Most cells rely also on the peptide glutathione (GSH), able to chelate reactive oxidant species (ROS) via cysteine sulfhydryl (SH) group and function as substrate for enzymes including GSH reductase and GSH peroxidase [78].

Although most of these processes are evolutionary conserved, some of the antioxidant defenses pathways differ between mammals and pathogens, therefore comprise potential chemotherapy targets. Contrary to mammals, GSH in trypanosomatid parasites mostly takes part in the adduct with the polyamine spermidine, forming *N*1,*N*8-bis(glutathionyl)spermidine (trypanothione, TSH), and therefore its expression depends on the GSH, TSH [79], and polyamine [80] metabolism pathways.

Metabolomics and gene expression studies [81] reveal the participation of both GSH and the spermidine synthesis pathway, indicating the participation

## *Translational Research on Chagas Disease: Focusing on Drug Combination and Repositioning DOI: http://dx.doi.org/10.5772/intechopen.104231*

of trypanothione, in the regulation of redox metabolism in trypanosomatids. GSH is very relevant not only in oxi-reductive homeostasis, as this molecule is also related to detoxification and resistance to different drugs/xenobiotics in tumor cells [82, 83] binding to drugs that are extruded via multidrug resistance transporters [84]. TSH binding to NFX and BZ is involved in the detoxication of these trypanocides [85, 86]. Therefore, glutathione/trypanothione can promote the action/reverse resistance to different drugs. *T. cruzi* parasites overexpressing trypanothione synthetase tolerated higher doses of BZ and NFX [87]. Conversely, the GSH biosynthesis inhibition using buthionine sulfoximine increases the efficacy of NFX and BZ upon *T. cruzi in vitro* [88] and NFX *in vivo* [89] as well as of stibogluconate on *Leishmania* (*L.*) *donovani* [90].

Interestingly, polyamine play pivotal roles in parasite cells [91, 92], including *T. cruzi* antioxidant defense [93], and its synthesis and transport pathways provide valuable chemotherapy targets [94, 95], including repositioned drugs [96].

Parasitic diseases such as CD are correlated to oxidative stress [97, 98], associated to triggered chronic inflammatory reactions [99, 100]. Endogenous oxidative stress may be produced by cell organelles, mainly mitochondria [101, 102]. The CD myocarditis is characterized by intense oxidative stress due both to inflammatory response associated to neutrophils and macrophages NADPH oxidase (Nox) activity and the macrophage superoxide produced by Nox2 is required for parasite control in early infection [103]. The mitochondrial ROS produced by cardiomyocytes plays a relevant role in intracellular oxidative stress and inflammation, causing myocardium tissue damage [104–106]. These events are not independent since mitochondrial ROS may trigger proinflammatory cytokines via NFkB and PARP/PAR pathways [107], and the mitochondrial MnSOD activity may revert much of the inflammatory foci and necrosis [105], and ineffective antioxidant defense is associated to oxidative stress [108]. Exosome or extracellular vesicles liberation may also contribute to inflammation and oxidative stress [107, 109]. The oxidative stress is also involved in neurodegeneration in both cardiac and gastrointestinal tissues [110]. The chronic oxidative stress in the nervous tissue is associated to cognitive deficit, which can be reversed by BZ treatment [111].

Thus, the use of adjuvant antioxidant agents may ameliorate the cardiac pathogenesis [107, 112, 113]. Interestingly, vitamin C, widely considered antioxidant, can at high concentrations also function as a prooxidant, undergoing pH-dependent autoxidation, leading to H2O2 formation [114, 115]. In CD models, ascorbic acid can also reduce parasitemia, promote BZ action, and enhance animal survival in murine infection [116, 117].

ROS production comprises a well-known microbicidal immune effector mechanism [118]; therefore parasite borne antioxidant systems are not only virulence factors [119]. Besides the parasiticidal activity, ROS may function as signaling molecules promoting parasite proliferation. As in the Paracelsus adage, "The dose makes the poison" (Latin: *sola dosis facit venenum*), ROS in mammalian cells may trigger different responses depending on concentration. Low ROS levels may have signal transduction roles, inducing responses such as activation, proliferation, and differentiation, whereas at higher levels such molecules are generally cytotoxic, leading to cell death [120]. Similarly, in *T. cruzi*, low ROS levels may signal for parasite invasion of host macrophages [121] and proliferation mainly in the acute phase [122], but high ROS levels culminate in programmed cell death, which may be inhibited by enhanced SOD expression [87]. Interestingly *T. cruzi* amastigotes undergo stressinduced proliferation [123].
