Increases in [IP3]i aggravates diastolic [Ca2+] and contractile dysfunction in Chagas' human cardiomyocytes

Abstract

Chagas cardiomyopathy is the most severe manifestation of human Chagas disease and represents the major cause of morbidity and mortality in Latin America. We previously demonstrated diastolic Ca2+ alterations in cardiomyocytes isolated from Chagas' patients to different degrees of cardiac dysfunction. In addition, we have found a significant elevation of diastolic [Na+](d) in Chagas' cardiomyocytes (FCII>FCI) that was greater than control. Exposure of cardiomyocytes to agents that enhance inositol 1,4,5 trisphosphate (IP3) generation or concentration like endothelin (ET-1) or bradykinin (BK), or membrane-permeant myoinositol 1,4,5-trisphosphate hexakis(butyryloxy-methyl) esters (IP3BM) caused an elevation in diastolic [Ca2+] ([Ca2+](d)) that was always greater in cardiomyocytes from Chagas' than non-Chagas' subjects, and the magnitude of the [Ca2+] d elevation in Chagas' cardiomyocytes was related to the degree of cardiac dysfunction. Incubation with xestospongin-C (Xest-C), a membrane-permeable selective blocker of the IP3 receptors (IP(3)Rs), significantly reduced [Ca2+](d) in Chagas' cardiomyocytes but did not have a significant effect on non-Chagas' cells. The effects of ET-1, BK, and IP3BM on [Ca2+] d were not modified by the removal of extracellular [Ca2+](e). Furthermore, cardiomyocytes from Chagas' patients had a significant decrease in the sarcoplasmic reticulum (SR) Ca(2+)content compared to control (Control>F-CI>FCII), a higher intracellular IP3 concentration ([IP3](i)) and markedly depressed contractile properties compared to control cardiomyocytes. These results provide additional and convincing support about the implications of IP3 in the pathogenesis of Chagas cardiomyopathy in patients at different stages of chronic infection. Additionally, these findings open the door for novel therapeutic strategies oriented to improve cardiac function and quality of life of individuals suffering from chronic Chagas cardiomyopathy (CC). Author summary Chagas disease, caused by the parasite Trypanosoma cruzi, is an endemic disease of Latin-American countries, affecting 10 million people are estimated to be infected with T. cruzi, and more than 120 million inhabitants are at risk of infection. The parasite is transmitted to humans in a vectorial way by infected triatomines and through other non-vector mechanisms such as the oral route, congenital transmission, organ transplants or blood transfusions. Due to immigration towards non-endemic regions, the disease can spread and affect people around the world via blood transfusions. The pathogenesis of this disease is still unwell understood; we previously demonstrated that cardiomyocytes isolated from Chagas patients have an intracellular Ca2+ overload, which appears to be associated with changes in the inositol 1,4,5 trisphosphate (IP3) signaling pathway. This study corroborates that human cardiomyocytes isolated from Chagas' patients have an increase in [Ca2+](d) and a partial membrane potential depolarization, which corresponds with the degree of cardiac dysfunction determined by the NYHA classification (23). In this report, we showed, for the first time, that IP3R activators, e.g., IP3BM, ET-1, and BK-induced a more significant elevation of [Ca2+] d in Chagas' compared to non-Chagas' human cardiomyocytes, which was not modified by the removal of [Ca2+](e). Additionally, these findings open the door for novel therapeutic strategies oriented to improve cardiac function and quality of life of individuals suffering from chronic Chagas cardiomyopathy (CC).