Combined treatment with a nitrofuranic and a corticoid in experimental Chagas' disease in the dog

Dogs as a Model for Chemotherapy of Chagas Disease and Leishmaniasis

BACKGROUND

Dogs are natural reservoir of Chagas disease (CD) and leishmaniasis and have been used for studies of these infections as they develop different clinical forms of these diseases similar to humans.

OBJECTIVE

This article describes publications on the dog model relative to CD and leishmaniasis chemotherapy.

METHODS

The search of articles was based on PubMed, Scopus and MESH using the keywords: dog, Trypanosoma cruzi, treatment (T. cruzi chemotherapy analysis), Leishmania chagasi, Leishmania infantum, canine visceral leishmaniasis, treatment (Leishmania chemotherapy evaluation).

RESULTS

Benznidazole and nifurtimox were used as a reference in the treatment of CD and in combination with other compounds. Eleven out of the fifteen studies have authors from the same team, using similar protocols and post-treatment evaluations, which assured more reproducibility and credibility. Twenty leishmaniasis studies, especially on visceral leishmaniasis, presenting at least one parasitological analysis tested in distinct monochemotherapy and polychemotherapy approaches were accessed. Data demonstrated that polychemotherapy was more effective in improving the clinical signs and parasitism control.

CONCLUSION

The benefits of treatment in terms of reducing or eliminating lesions and/or cardiac dysfunctions were demonstrated at acute and/or chronic phases relative to parasite load and/or the T. cruzi strain resistance to treatment. BZ presented better therapeutic results than the two EBI compounds evaluated. Although treatment of the canine visceral leishmaniasis was not able to induce complete parasite clearance, it can improve clinical recovery. Thus, the dog is a good model for CD and leishmaniasis studies of chemotherapy and may be indicated for pre-clinical trials of new treatments.

Polypharmacology in the Treatment of Chagas Disease

The current treatment of Chagas disease is based on monopharmacology where the used drugs have limited efficacy and severe side effects. In order to overcome these limitations, some tools have been described including the development or isolation of new drugs, drug repositioning, and polypharmacology. Here, we review the polypharmacology strategy where compounds belonging to different structural chemotypes were combined in order to affect different biochemical pathways of T. cruzi parasite. Therefore ergosterol biosynthesis inhibitors, anti-inflammatory agents, cardiac dysfunction drugs, trypanothione reductase inhibitors, vitamins, between others, were combined looking for new anti-Chagas treatment. Natural products were also used in the application of this strategy.

Mechanisms of myocardial damage in Trypanosoma cruzi infection

A study of pathological lesions caused by Trypanosoma cruzi in human and experimental hosts indicated that the main mechanisms of myocardial damage in Chagas' disease are the following. (1) During acute infection inflammatory lesions are related to parasite-induced destruction of myocardial cells, with probable participation of immune-complex reactions. When parasitism decreases, inflammation subsides and may disappear completely. (2) After recovery from acute infection the hosts remain infected but asymptomatic for a prolonged period of time. Focal fibrotic areas may be present in the myocardium, conducting tissue and autonomic nervous system, representing sequelae from the acute phase. Such sequelae may have or may acquire functional significance in some special circumstances. (3) Some patients with latent T. cruzi infection may progress to show a diffuse, active and fibrosing myocarditis without an apparent change in parasitological and immunological status from the asymptomatic phase. The microscopic changes in the heart are compatible with the presence of a delayed-type hypersensitivity process. An abolition of the suppressive factors of delayed hypersensitivity which are present during latent infection may be involved.

[Treatment of chronic Chagas' disease with an association of nifurtimox and corticoid]

Ten patients with chronic Chagas' disease were treated with nifurtimox (8-9 mg/kg/day) associated with betamethasone (9 mg/day initially and then gradually reduced) during 60 days, with one exception. It was intended to combine the respective anti-parasitic and anti-inflammatory actions of these drugs. The expected stimulating effect of betamethasone on the infection could possibly enhance the anti-Trypanosoma cruzi action of nifurtimox. Long term persistence of negative xenodiagnosis, used to control the results, was observed in only one of the cases. Regaridng the other patients, post-treatment positivity of xenodiagnosis and serological testes attested the failure of this therapy. As this study has demonstrated, adequate and long term follow-up of treated cases is necessary to ensure correct conclusions.

[Protective effect of benznidazole against parasite reactivation in patients chronically infected with Trypanosoma cruzi and treated with corticoids for associated diseases]

Patients in the chronic phase of Chagas' disease and receiving corticoid because of concommitant diseases were treated with benznidazole, which was initiated at the same time of the use of corticoid in a group of 12 patients or 15 days afterwards in 6 patients. It has been proved in another paper that in the chronic phase of Chagas' disease corticoid use is associated with increased parasitemia, as evaluated by xenodiagnosis. In this study benznidazole use prevented this increase, and we suggest that in immunocompromised patients with chronic Chagas' disease the use of this drug could be useful.

[Nifurtimox as a prophylactic drug to prevent reactivation in chronic chagasic patients treated with corticoid for associated diseases]

Patients in the chronic phase of Chagas' disease and receiving corticoid because of concommitant diseases were treated with nifurtimox. We proved in another paper that in the chronic phase of Chagas' disease corticoid use is associated with increased parasitemia, as evaluated by xenodiagnosis. In this study nifurtimox use prevented this increase, and we suggest that in immunocompromised patients with chronic Chagas' disease the use of this drug could be useful.

[The influence of corticoids, in Chronic Chagas disease, administered in virtue of associated disorders]

Patients with chronic Chagas' disease and simultaneous medical problems treated with corticosteroid were studied in order to evaluate steroid influence on chronic Trypanosoma cruzi infection. Parasitological assessment, radiological and electrocardiographic studies as well as non specific tests were performed in patients and in a control group that included chronic infected patients not treated with steroid. Xenodiagnosis showed a clear increase in T. cruzi parasitemia, related to the corticosteroid dosage, without clinical manifestations during the study follow-up period.

Effects of betamethasone on the course of experimental infection with Trypanosoma cruzi

In this experiment, the effect of betamethasone administered in the early post- acute infection of mice by Trypanosoma cruzi was studied. This drug was administered during 30 days after the 42nd day of infection in a dose of 0.15 mg/day. The betamethasone treatment did not cause fresh outbreaks of parasitemia and the histopathological findings in the chronic phase were not different from those in the control group. The higher cumulative mortality after treatment in the experimental group was due to superimposed bacterial infections. Outbred albino mice infected with low numbers ofY strain Trypanosoma cruzi trypomastigotes were not suitable models for Chagas' disease, since after 7 months of observation only mild histological lesions developed in all the animais. Prolonged betamethasone treatment of mice infected with low numbers o/Trypanosoma cruzi of the Y strain, during the post-acute phase did not aggravate the course of infection.

Damage and healing in the conducting tissue of the heart (an experimental study in dogs infected with Trypanosoma cruzi)

The consequences of acute inflammatory damage and chronic repair in the conducting system of the canine heart were observed after experimental Trypanosoma cruzi infection of young dogs. Acute infection lasted for 18-25 days and caused hyaline and lytic necrosis of the atrio-ventricular conducting fibres, the sinus node and the neurons in the cardiac para-sympathetic ganglia. Dogs that survived acute disease were examined after periods from 8 months to 3 years. Three main types of healing were found in the conducting system: fibrosis (diffuse and/or focal), sclero-atrophy and fatty infiltration. No signs of active chronic inflammation were present, although small focal residual accumulations of mononuclear cells were present in some animals. No evident electrocardiographic alterations were elicited by the presence of such cicatricial lesions. The animal model appears worthwhile for the study of the healing process in conducting tissue of the heart and for the better understanding of the asymptomatic phase of T. cruzi infection in man.