The Effect of the GH/IGF-1 Axis During Trypanosoma Cruzi Infection

Abstract

Trypanosoma cruzi is the parasite responsible for Chagas disease (CD), that affects 6-8 million people worldwide. CD treatment is limited to two drugs (benznidazole and nifurtimox). Treatment is mostly effective during the acute phase of the disease (initial two months post-infection), while their efficacy during the chronic phase is controversial. In the absence of treatment, 30% of infected individuals suffer irreversible chronic cardiac and digestive damages, which lead to inability and, in some instances, death. Patients with Laron Syndrome (LS, a form of congenital GH insensitivity) are short in stature with low levels of IGF-1, elevated levels of GH and, surprisingly, are resistant to cancer and diabetes. A cohort of LS patients living in southern Ecuador, where CD is endemic, has been studied by Dr. Jaime Guevara for over 25 years (1). Few, if any, cases of CD have been reported among these patients (Dr. Guevara, personal communications). T. cruzi infection has been shown to directly modulate pituitary hormones such as GH, PRL and glucocorticoids (stress related hormones), leading to immunosuppression and thymic atrophy by depletion of CD4+ CD8+ cells. Previously, rats infected with T. cruzi and treated with GH showed reduced parasitism and less tissue damage compared to controls (2). The purpose of this research is to investigate the in vitro effect of GH during T. cruzi infection, simulating conditions of GH insensitivity. First, we separately treated T. cruzi and the host cells [human cervical cancer cell line (HeLa) and male mouse fibroblast (L-cells)] with relatively low or high levels of GH, IGF-1, PRL, and EGF. Next, we treated the parasite and host cells simultaneously with these hormones. When the parasites were treated alone, T. cruzi responded to exogenous GH (5ng/ml-50ng/ml) by significantly increasing the percentage of amastigotes (less infective form of the parasite). Also, when GH (50ng/ml) were administered to the host cells, T. cruzi infectivity was significantly reduced by 12% (percentage of infection) compared to 20% from untreated conditions. Similarly, both parasite and host cells treated with GH significantly reduced T. cruzi infectivity (10%) compared to untreated conditions (18%). We further treated both cell lines with a combination of GH/IGF-1. Conditions used were as follows: control (no-treatment), moderate levels (5ng/ml GH+150 ng/ml IGF-1), relatively high levels (50ng/ml GH+600ng/ml IGF-1), or levels that would simulate those found in patients with LS(50ng/ml GH+20 ng/ml IGF-1). Of these, the LS concentrations significantly reduced infection in both cell lines (11%) compared to control (16%). Together these results indicate that GH can influence T. cruzi infectivity and that GH, not IGF-1, is mediating the decreased infectivity. Finally, the results suggest that high concentrations of GH, as seen in LS patients, could be protective during T. cruzi infection.1)Guevara-Aguirre et al., 2011 2) Frare et al., 2010