Cardiac and skeletal muscle mitochondrial disorders provoked by Trypanosoma cruzi infection

BÁEZ A; GUZMÁN G; LO PRESTI MS; RIVAROLA H; FRETES R; PAGLINI P

Río de Janeiro. Brasil

Simposio; International Symposium The Centenary of Chagas disease discovery.; 2009

The role of the energy supply, specially ATP levels, is critical for myocardial contractility and electrophysiology, making mitochondria very abundant in the heart, where they constitute 20-40% of the cell volume. Fatty acids are the primary energy substrate for the heart muscle. ATP generation by mitochondrial oxidative phosphorylation and the respiratory chain, the most important energetic pathway, provides over 90% of the cardiac energy. ATP supply from other sources, such as pyruvate oxidation, Krebs cycle and fatty acid â-oxidation, is limited in normal cardiac tissues. An important number of observations have shown that mitochondria are involved in the pathophysiology of many cardiac diseases and it has been proposed that in failing hearts mitochondria dysfunction is related to similar mitochondrial abnormalities in the skeletal muscle. Trypanosoma cruzi infection induces the production of inflammatory cytokines that play an important role in modulating the resistance to the parasite; it has been demonstrated that mitochondria are targets of these inflammatory mediators, as well as of many other noxa of exogenous or endogenous origin. Having these in mind, the aim of the present paper was to study the mitochondria structure and function, in cardiac and skeletal muscle samples from mice infected with T. cruzi, Tulahuen strain, in the acute stage of infection to establish if there is a correlation between the abnormalities from both muscle samples. Albino Swiss female and male mice weighing 30 ± 1 g (n = 40) were used as follows: 20 mice were inoculated, by intraperitoneal injection, with 50 trypomastigote forms of T. cruzi,Tulahuen strain. A non infected group (n = 20) was also studied. The study was carried out in the acute stage of the infection (30 days post-infection –dpi); mitochondria were isolated by ultracentrifugation; the ultrastructure was studied by electron microscopy and the activities of the respiratory complex III (CIII) and the citrate synthase (Krebs cycle enzyme) were monitored by spectrophotometric methods. The histopathology of cardiac and skeletal muscle were also studied. Parasites were not detected in the cardiac sections, however profuse mononuclear infiltrates were observed. Ultrastructural studies showed 71% of cardiac mitochondria with cristae disruption, vacuolization and an increase in their matrix. Skeletal muscle samples presented amastigotes nests, inflammatory infiltrates consisting of mononuclear cells and areas of fiber disorganization. Mitochondria showed changes in their shape with a diminished number of cristae and increase in their matrix. The citrate synthase enzymatic activity (umol / min.mg of proteins) in cardiac mitochondria from infected mice was significantly higher than in the non infected ones (0.45 ± 0.01 and 0.23 ± 0.01 respectively, p<0.05); on the other hand its activity in skeletal muscle mitochondria was significantly diminished in the infected group (0.02 ± 2.8 x 10 -3 ) when compared with the non infected ones (0.03 ± 2.1 x 10-3, p< 0.05). CIII complex activity (umol / min.mg of proteins) decreased in cardiac mitochondria of infected mice (0.04 ± 0.01) when compared to the non infected one (0.21 ± 0.03, p< 0.05); whereas those obtained from the skeletal muscle samples presented similar activities than the observed in the non infected group (0.01 ± 0.01 and 4.5 x 10-3  respectively). These results indicate that T. cruzi infection have a direct effect upon the structure and function of cardiac and skeletal muscle mitochondria, but, even though the skeletal muscle presented higher inflammatory activity and amastigotes nests, cardiac mitochondria were more seriously damaged, demonstrating that they are related with the pathological mechanisms of chagasic cardiopathy.