The adipocyte as an important target cell for Trypanosoma cruzi infection

Adipose tissue plays an active role in normal metabolic homeostasis as well as in the development of human disease. Beyond its obvious role as a depot for triglycerides, adipose tissue controls energy expenditure through secretion of several factors. Little attention has been given to the role of adipocytes in the pathogenesis of Chagas disease and the associated metabolic alterations. Our previous studies have indicated that hyperglycemia significantly increases parasitemia and mortality in mice infected with Trypanosoma cruzi. We determined the consequences of adipocyte infection in vitro and in vivo. Cultured 3T3-L1 adipocytes can be infected with high efficiency. Electron micrographs of infected cells revealed a large number of intracellular parasites that cluster around lipid droplets. Furthermore, infected adipocytes exhibited changes in expression levels of a number of different adipocyte-specific or adipocyte-enriched proteins. The adipocyte is therefore an important target cell during acute Chagas disease. Infection of adipocytes by T. cruzi profoundly influences the pattern of adipokines. During chronic infection, adipocytes may represent an important long-term reservoir for parasites from which relapse of infection can occur. We have demonstrated that acute infection has a unique metabolic profile with a high degree of local inflammation in adipose tissue, hypoadiponectinemia, hypoglycemia, and hypoinsulinemia but with relatively normal glucose disposal during an oral glucose tolerance test.     

Energy transfer in “parasitic” cancer metabolism: Mitochondria are the powerhouse and Achilles' heel of tumor cells

It is now widely recognized that the tumor microenvironment promotes cancer cell growth and metastasis via changes in cytokine secretion and extra-cellular matrix remodeling. However, the role of tumor stromal cells in providing energy for epithelial cancer cell growth is a newly emerging paradigm. For example, we and others have recently proposed that tumor growth and metastasis is related to an energy imbalance. Host cells produce energy-rich nutrients via catabolism (through autophagy, mitophagy and aerobic glycolysis), which are then transferred to cancer cells, to fuel anabolic tumor growth. Stromal cell derived L-lactate is taken up by cancer cells and is used for mitochondrial oxidative phosphorylation (OXPHOS), to produce ATP efficiently. However, “parasitic” energy transfer may be a more generalized mechanism in cancer biology than previously appreciated. Two recent papers in Science and Nature Medicine now show that lipolysis in host tissues also fuels tumor growth. These studies demonstrate that free fatty acids produced by host cell lipolysis are re-used via β-oxidation (β-OX) in cancer cell mitochondria. Thus, stromal catabolites (such as lactate, ketones, glutamine and free fatty acids) promote tumor growth by acting as high-energy onco-metabolites. As such, host catabolism via autophagy, mitophagy and lipolysis may explain the pathogenesis of cancer-associated cachexia and provides exciting new druggable targets for novel therapeutic interventions. Taken together, these findings also suggest that tumor cells promote their own growth and survival by behaving as a “parasitic organism.” Hence, we propose the term “parasitic cancer metabolism” to describe this type of metabolic-coupling in tumors. Targeting tumor cell mitochondria (OXPHOS and β-OX) would effectively uncouple tumor cells from their hosts, leading to their acute starvation. In this context, we discuss new evidence that high-energy onco-metabolites (produced by the stroma) can confer drug resistance. Importantly, this metabolic chemo-resistance is reversed by blocking OXPHOS in cancer cell mitochondria, with drugs like Metformin, a mitochondrial “poison.” In summary, parasitic cancer metabolism is achieved architecturally by dividing tumor tissue into at least two well-defined opposing “metabolic compartments:” catabolic and anabolic.Key words: mitochondria, cancer metabolism, autophagy, mitophagy, aerobic glycolysis, lipolysis, oxidative phosphorylation, beta-oxidation, Metformin, drug discovery, drug resistance, chemo-resistance, Warburg effect, oncometabolite, parasite, metabolic compartments     

High fat diet aggravates cardiomyopathy in murine chronic Chagas disease

Infection with Trypanosoma cruzi, the etiologic agent in Chagas disease, may result in heart disease. Over the last decades, Chagas disease endemic areas in Latin America have seen a dietary transition from the traditional regional diet to a Western style, fat rich diet. Previously, we demonstrated that during acute infection high fat diet (HFD) protects mice from the consequences of infection-induced myocardial damage through effects on adipogenesis in adipose tissue and reduced cardiac lipidopathy. However, the effect of HFD on the subsequent stages of infection – the indeterminate and chronic stages – has not been investigated. To address this gap in knowledge, we studied the effect of HFD during indeterminate and chronic stages of Chagas disease in the mouse model. We report, for the first time, the effect of HFD on myocardial inflammation, vasculopathy, and other types of dysfunction observed during chronic T. cruzi infection. Our results show that HFD perturbs lipid metabolism and induces oxidative stress to exacerbate late chronic Chagas disease cardiac pathology.     

Alterations in myocardial gene expression associated with experimental Trypanosoma cruzi infection

Chagas disease, characterized by acute myocarditis and chronic cardiomyopathy, is caused by infection with the protozoan parasite Trypanosoma cruzi. We sought to identify genes altered during the development of parasite-induced cardiomyopathy. Microarrays containing 27,400 sequence-verified mouse cDNAs were used to analyze global gene expression changes in the myocardium of a murine model of chagasic cardiomyopathy. Changes in gene expression were determined as the acute stage of infection developed into the chronic stage. This analysis was performed on the hearts of male CD-1 mice infected with trypomastigotes of T. cruzi (Brazil strain). At each interval we compared infected and uninfected mice and confirmed the microarray data with dye reversal. We identified eight distinct categories of mRNAs that were differentially regulated during infection and identified dysregulation of several key genes. These data may provide insight into the pathogenesis of chagasic cardiomyopathy and provide new targets for intervention.     

Fat tissue regulates the pathogenesis and severity of cardiomyopathy in murine chagas disease

Chronic Chagas cardiomyopathy (CCC) caused by a parasite Trypanosoma cruzi is a life-threatening disease in Latin America, for which there is no effective drug or vaccine. The pathogenesis of CCC is complex and multifactorial. Previously, we demonstrated T. cruzi infected mice lose a significant amount of fat tissue which correlates with progression of CCC. Based on this an investigation was undertaken during both acute and chronic T. cruzi infection utilizing the FAT-ATTAC murine model (that allows modulation of fat mass) to understand the consequences of the loss of adipocytes in the regulation of cardiac parasite load, parasite persistence, inflammation, mitochondrial stress, ER stress, survival, CCC progression and CCC severity. Mice were infected intraperitoneally with 5x10⁴ and 10³ trypomastigotes to generate acute and chronic Chagas models, respectively. Ablation of adipocytes was carried out in uninfected and infected mice by treatment with AP21087 for 10 days starting at 15DPI (acute infection) and at 65DPI (indeterminate infection). During acute infection, cardiac ultrasound imaging, histological, and biochemical analyses demonstrated that fat ablation increased cardiac parasite load, cardiac pathology and right ventricular dilation and decreased survival. During chronic indeterminate infection ablation of fat cells increased cardiac pathology and caused bi-ventricular dilation. These data demonstrate that dysfunctional adipose tissue not only affects cardiac metabolism but also the inflammatory status, morphology and physiology of the myocardium and increases the risk of progression and severity of CCC in murine Chagas disease.     

High Fat Diet Modulates Trypanosoma cruzi Infection Associated Myocarditis

Background

Trypanosoma cruzi, the causative agent of Chagas disease, has high affinity for lipoproteins and adipose tissue. Infection results in myocarditis, fat loss and alterations in lipid homeostasis. This study was aimed at analyzing the effect of high fat diet (HFD) on regulating acute T. cruzi infection-induced myocarditis and to evaluate the effect of HFD on lipid metabolism in adipose tissue and heart during acute T. cruzi infection.

Methodology/Principal Findings

CD1 mice were infected with T. cruzi (Brazil strain) and fed either a regular control diet (RD) or HFD for 35 days following infection. Serum lipid profile, tissue cholesterol levels, blood parasitemia, and tissue parasite load were analyzed to evaluate the effect of diet on infection. MicroPET and MRI analysis were performed to examine the morphological and functional status of the heart during acute infection. qPCR and immunoblot analysis were carried out to analyze the effect of diet on the genes involved in the host lipid metabolism during infection. Oil red O staining of the adipose tissue demonstrated reduced lipolysis in HFD compared to RD fed mice. HFD reduced mortality, parasitemia and cardiac parasite load, but increased parasite load in adipocytes. HFD decreased lipolysis during acute infection. Both qPCR and protein analysis demonstrated alterations in lipid metabolic pathways in adipose tissue and heart in RD fed mice, which were further modulated by HFD. Both microPET and MRI analyses demonstrated changes in infected RD murine hearts which were ameliorated by HFD.

Conclusion/Significance

These studies indicate that Chagasic cardiomyopathy is associated with a cardiac lipidpathy and that both cardiac lipotoxicity and adipose tissue play a role in the pathogenesis of Chagas disease. HFD protected mice from T. cruzi infection-induced myocardial damage most likely due to the effects of HFD on both adipogenesis and T. cruzi infection-induced cardiac lipidopathy.     

Mechanisms of Trypanosoma cruzi persistence in Chagas disease

Trypanosoma cruzi infection leads to development of chronic Chagas disease. In this article, we provide an update on the current knowledge of the mechanisms employed by the parasite to gain entry into the host cells and establish persistent infection despite activation of a potent immune response by the host. Recent studies point to a number of T. cruzi molecules that interact with host cell receptors to promote parasite invasion of the diverse host cells. T. cruzi expresses an antioxidant system and thromboxane A(2) to evade phagosomal oxidative assault and suppress the host's ability to clear parasites. Additional studies suggest that besides cardiac and smooth muscle cells that are the major target of T. cruzi infection, adipocytes and adipose tissue serve as reservoirs from where T. cruzi can recrudesce and cause disease decades later. Further, T. cruzi employs at least four strategies to maintain a symbiotic-like relationship with the host, and ensure consistent supply of nutrients for its own survival and long-term persistence. Ongoing and future research will continue to help refining the models of T. cruzi invasion and persistence in diverse tissues and organs in the host.     

Synthesis and antibacterial activity of novel oxazolidinones with methylene oxygen- and methylene sulfur-linked substituents at C5-position

Novel oxazolidinone derivatives of the lead compound RBx 8700, containing methylene oxygen- and methylene sulfur-linked substituents at the C5-position, were synthesized. Antibacterial screening of these compounds against a panel of resistant and susceptible Gram-positive and fastidious Gram-negative bacteria gave compounds 2 and 4 as new antibacterial agents.