This investigation was performed to verify the effect of specific chemotherapy (Benznidazole or MK-346) on the inflammatory and fibrotic cardiac alterations in mice chronically infected with the strains 21 SF (Type II) and Colombian (Type III) of Trypanosoma cruzi. To obtain chronically infected mice, two groups of 100 Swiss mice each, were infected with either the 21 SF or the Colombian strain (2x 10 [raised to the power of] 4 and 5x 10 [raised to the power of] 4 blood forms respectively). The rate of morality in the acute phase was of 80% for both groups. Twenty surviving mice chronically infected with the 21 SF strain and 20 with the Colombian strain were then divided in treated and untreated groups. Excluding those that died during the course of treatment, 14 mice chronically infected with the 21 SF strain and 15 with the Colombian strain were evaluated in the present study. Chemotherapy was performed with Benznidazole (N-benzil-2-nitro-1-imidazolacetamide) in the dose of 100mg/k.b.w/day, for 60 days, or with the MK-436(3(1-methyl-5 nitroimidazol-2-yl) in two daily doses of 250 mg/k.b.w, for 20 days. Parasitological cure tests were performed (xenodiagnosis, haemoculture, subinovulation of the blood into newborn mice), and serological indirect immunofluorescence test. The treated and untreated mice as well as intact controls were killed at different periods after treatment and the heart were submitted to histopathological study with hematoxilineosin and picrosirius staining; ultrastructural study; collagen immunotyping, fibronectin and laminin identification by immunofluorescence tests. Results: the untreated controls either infected with 21 SF or Colombian strain, showed inflammatory and fibrotic alterations that were mild to moderate with the 21 SF strain and intense with the Colombian strain. Redpicrosirius staining showed bundles of collagen in the interstitial space and around cardiac fibers. Increased deposits of mitritial components and collagen fibers, macrophages and fibroblasts appeared at the ultra structural examination. Deposits of fibronectin, laminin, pro-III and IV collagens were seen, most intense in those infected with the Colombian strain. Treated nice, parasitologically cured, presented clear-cut regression of the inflammatory lesions and of the interstitial matrix thickening. Mice infected with the Colombian strain and treated with MK-436, was parasitologically cured in 5/6 cases and showed mild inflammatory infiltration and fibrosis. The mice treated with Benznidazole (Colombian strain) did not cure and showed moderate fibrosis and inflammation. Treatment of the nice infected with the 21 SF with Benznidazole determined parasitological cure of all animals, that showed mild inflammation and fibrosis of the myocardium. The cured mice of all groups and treated but uncured showed collagen degradation at electronmicroscopy and decrease of immunofluorescence pattern of the matrix.

In recent years, one of the most significant progress in the understanding of liver diseases was the demonstration that liver fibrosis is a dynamic process resulting from a balance between synthesis and degradation of several matrix components, collagen in particular. Thus, fibrosis has been found to be a very early event during liver diseases, be it of toxic, viral or parasitic origin, and to be spontaneously reversible, either partially or totally. In liver fibrosis cell matrix interactions are dependent on the existence of the many factors (sometimes acting in combination) which produce the same events at the cellular and molecular levels. These events are: (i) the recruitment of fiber-producing cells, (ii) their proliferation, (iii) the secretion of matrix constituents of the extracellular matrix, and (iv) the remodeling and degradation of the newly formed matrix. All these events represent, at least in principle, a target for a therapeutic intervention aimed at influencing the experimentally induced hepatic fibrosis. In this context, hepatosplenic schistosomiasis is of particular interest, being an immune cell-mediated granulomatous disease and a model of liver fibrosis allowing extensive studies in human and animals as well as providing original in vitro models.

Utilizando o modelo experimental do camundongo, foi realizado um estudo sorológico, histopatológico e ultraestrutural bem como a imunotipagem do colágeno na matriz conjuntiva do miocárdio em camundongos suiços cronicamente infectados com as cepas 21 SF e Mambaí (Tipo II) PMN e Bolívia (Tipo III) por períodos de 154 a 468 dias. Os testes sorológicos e de imunofluorescência indireta mostraram altos títulos de anticorpos específicos. O estudo estrutural definiu melhor a constituição celular do infiltrado inflamatório, mostrando a predominância de monócitos e de macrófagos com intensa atividade fagocítica, fibroblastos em atividade de síntese e miofibroblastos bem como abundante matriz colagênica sugerindo uma associação entre o processo inflamatório e fibrogênese na cardiomiopatia chagásica crônica. A imunotipagem do colágeno mostrou a predominância dos tipos III e IV. Alterações dos capilares sangüíneos e de arteríolas e sua dissociação das miocélulas, pelo infiltrado inflamatório, se relacionam com alterações ultraestruturais em miocélulas cardíacas não parasitadas. Havia intensificação do processo inflamatório em áreas focais correspondentes à rotura de fibras cardíacas parasitadas. Os achados do presente trabalho sugerem que o modelo do camundongo é adequado para o estudo dos mecanismos patogênicos na doença de Chagas, pela utilização de cepas do T. cruzi com baixa virulência e alta patogenicidade.

In an attempt to define the mouse-model for chronic Chagas' disease, a serological, histopathological and ultrastructural study as well as immunotyping of myocardium collagenic matrix were performed on Swiss mice, chronically infected with Trypanosoma cruzi strains: 21 SF and mambaí (Type II); PMN and Bolivia (Type III), spontaneously surviving after 154 to 468 days of infection. Haemagglutination and indirect immunofluorescence tests showed high titres of specific antibodies. The ultrastructural study disclosed the cellular constitution of the inflammatory infiltrate showing the predominance of monocytes, macrophages with intense phagocytic activity, fibroblasts, myofibroblasts and abundant collagen matrix suggesting the association of the inflammatory process with fibrogenesis in chronic chagasic cardiomyopathy. Artertolar and blood capillary alterations together with dissociation of cardiac cells from the capillary wall by edema and inflammation were related to ultrastructural lesions of myocardial cells. Rupture of parasitized cardiac myocells contribute to intensify the inflammatory process in focal areas. Collagen immunotyping showed the predominance of Types III and IV collagen. Collagen degradation and phagocytosis were present suggesting a reversibility of the fibrous process. The mouse model seems to be valuable in the study of the pathogenetic mechanisms in Chagas cardiomyopathy, providing that T. cruzi strains of low virulence and high pathogenecity are used.

Foram utilizados no presente estudo, quinze ratos albinos (Sprague Dawley) portadores de fibronas transplantados no tecido subcutâneo da parede abdominal. O tumor era constituído por fibroblastos típicos, em uma densa matriz colagênica e eram provenientes de um fibroma que apareceu espontaneamente em um rato albino da mesma linhagem. Ultraestruturalmente o colágeno mostrava periodicidade normal e os fibroblastos mostravam núcleo irregularmente denteado, com cromatina irregularmente distribuída, sugerindo aspectos transicionais para um fibrossarcoma. Os quinze animais, de diferentes grupos de passagem do tumor, foram divididos em: oito animais submetidos a tratamento com a droga CY-168F (Plastenan) e sete animais controles não tratados. Três dos animais tratados mostraram uma transformação malígna para um fibrossarcoma. Em um dos animais emque foram feitas biópsias sucessivas, foram observados aspectos histológicos transicionais de um fibroma típico até um fibrossarcoma altamente indiferenciado. O estudo ultraestrutural demonstrou alterações nucleares, ergastoplasma hiperativo e inclusções contendo colágeno, no citoplasma dos fibroblastos. No grupo dos sete animais não tratados, não foi verificada transformação malígna do tumor. Dois aspectos merecem atenção neste estudo; o potencial malígno de um fibroma típico e o aparente efeito de um antifibrosante na indução da malignização deste tumor.

Fifteen albino (Sprague Dawley) rats with subcutaneous transplanted fibromas was used in the present study. The tumour was formed by typical fibroblasts in a dense collagen matrix and was provenient from a fibroma that appeared spontaneously in an albino rat of the same strain. Ultrastructurally collagen disclosed normal periodicity and the fibroblasts showed irregular notched nuclei with irregular distribution of chromatin, that suggests transitional aspects to fibrosarcoma. The 15 animals, from different passage groups, were divided into: 8 animals submitted to treatment with the drug acexamic acid (CY-168F) - N acetyl-amino-6-hexanoic acid (plastenan) and 7 untreated control animals. Three of the treated animals showed a malignant transformation to fibrosarcoma. transitional histological features from typical fibroma to highly indifferentiated fibrosarcoma could be detected in come animal subjected to repeated biopsies. Ultrastructural study disclosed nuclear alterations and hyperactive ergastoplasm and collagen containing inclusions into the cytoplasm of fibroblasts. In the group of 7 untreated naimals, no malignant transformation could be detected histologically. Two aspects deserve attention: the malignant potential of a typical fibroma and the apparent effect of an antifibrosing drug in inducing malignization of this tumour.