ROS and Trypanosoma cruzi: Fuel to infection, poison to the heart

Abstract

The activation of macrophage respiratory burst in response to infection with Trypanosoma cruzi inflicts oxidative damage to the host's tissues. For decades, the role of reactive oxygen species (ROS) in the elimination of T. cruzi was taken for granted, but recent evidence suggests parasite growth is stimulated in oxidative environments. It is still a matter of debate whether indeed oxidative environments provide ideal conditions (e.g., iron availability in macrophages) for T. cruzi growth and whether indeed ROS signals directly to stimulate growth. Nitric oxide (NO) and ROS combine to form peroxynitrite, participating in the killing of phagocytosed parasites by activated macrophages. In response to infection, mitochondrial ROS are produced by cardiomyocytes. They contribute to oxidative damage that persists at the chronic stage of infection and is involved in functional impairment of the heart. In this review, we discuss how oxidative stress helps parasite growth during the acute stage and how it participates in the development of cardiomyopathy at the chronic stage.

Fig 1. Oxidative stress fuels T. cruzi infection in macrophages, fibroblasts, and cardiomyocytes.

(a) Parasite burden of nonactivated C57BL/6 macrophages infected with CL-Brener (type VI) or Y strain (type II) trypomastigotes and cultivated in medium for 48 h. (b) Infected macrophages incubated with H₂O₂, PMA, or pro-oxidants have increased parasite burden [17, 27]. A similar result is obtained if parasites are treated with H₂O₂ before infection [17]. (c) Infected macrophages incubated with antioxidants have decreased parasite burden. (d) THP-1 human macrophage lineage transfected with an Nrf2- or HO-1-containing plasmid before infection presents smaller parasite burden than cells transfected with an empty expression plasmid [27]. (e) Infected gp91^phox-/- macrophages have smaller parasite burden than wild-type macrophages [17, 27]. (f) Trypomastigotes treated with H₂O₂ before infecting gp91^phox-/- macrophages give rise to parasite burden similar to that of nontreated trypomastigotes growing in wild-type macrophages, as in (a) [17]. (g) Trypomastigotes treated with H₂O₂ before infecting fibroblasts also give rise to increased parasite burden [50]. (h) Cardiomyocytes infected with the JG strain (type II) respond to CAT-PEG with decreased burden compared to nontreated cells, while cardiomyocytes infected with Col1.7G2 (type I) are unresponsive to CAT-PEG [57]. CAT-PEG, catalase conjugated to polyethylene glycol to permeate the cells; HO-1, heme oxygenase; JG, type II T. cruzi strain; Nrf2, nuclear erythroid factor-2; PMA, phorbol 12-myristate 13-acetate.

Fig 2. LIP is associated with oxidative conditions and parasite growth in macrophages.

Treatment of infected macrophages (Y strain) with antioxidants (NAC, apocynin, CoPP) reduces ROS content, LIP, and parasite burden, while reducing the expression of H-Ft and increasing the expression of the iron channel Fpn-1 [27]. CoPP, cobalt protoporphyrin; Fpn-1, ferroportin-1; H-Ft, H-ferritin; LIP, labile iron pool; NAC, N-acetyl-L-cysteine; ROS, reactive oxygen species.

Fig 3. In macrophages activated before infection, ROS is detrimental to T. cruzi infection.

Macrophages activated with LPS and IFNγ before infection eliminate phagocytosed T. cruzi CL-Brener by producing peroxynitrite. When the production of peroxynitrite is impaired by inhibiting NOX2-derived ROS with apocynin (right before the infection or after) or when T. cruzi expresses TcCPX, an enzyme that degrades peroxynitrite, the resulting parasite burden is increased [52]. IFNγ, interferon gamma; LPS, lipopolysaccharide; ROS, reactive oxygen species; TcCPX, triparedoxin peroxidase.

Fig 4. Antioxidants improve cardiac mechanical function in Sylvio X10/4 clone chronically infected animals.

Sprague-Dawley rats were infected with Sylvio X10/4 clone and treated with ROS-scavenger PBN from the beginning and throughout infection, improving heart mechanical function [61]. Infected C57BL/6 mice were treated with the antioxidants SRT1720 and resveratrol, resulting in improved heart mechanical function [62]. Infected C57BL/6-MnSOD overexpressing transgenic mice presented healthier mechanical heart function than wild-type mice at the chronic stage of infection [77, 79]. The effects of the antioxidant treatment or genetic modification on ROS, oxidative damage, parasitism, inflammatory infiltrates, and fibrosis are shown for each condition, together with the exact timing of infection and treatment. CO, cardiac output; EF, left ventricle ejection fraction; PBN, phenyl-α-tert-butyl; ROS, reactive oxygen species; Mn-SOD, manganese superoxide dismutase.

Fig 5. Antioxidants improve cardiac mechanical and electrical function in Colombian strain chronically infected mice.

BALB/c mice were infected with T. cruzi Colombian strain; their heart function was analyzed individually by electro and echocardiography [56]. The mice were treated with antioxidant resveratrol for a month after cardiac disease detection, and the reversal of heart systolic and electrical dysfunction, including arrhythmias, was verified. The treatment with resveratrol or control vehicle was prolonged for an additional month, or performed late after infection, with successful results. The treatment with antioxidant tempol for a month after heart disease detection also improved heart function. The effects of the antioxidant treatment on ROS, oxidative damage, parasitism, inflammatory infiltrates, and fibrosis are shown for each condition, together with the exact timing of infection and treatment. CO, cardiac output; EF, left ventricle ejection fraction; ROS, reactive oxygen species.