Resumo

Introduction: Disruption in dam-pup interaction constitutes a potent stressor event in early life, since animals submitted to prolonged periods of maternal separation become usually hyperresponsive to stress in the adult life, exhibiting high levels of mRNA for corticotropin-releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus (PVN), adrenocorticotropic hormone (ACTH) and corticosterone (CORT), and increased anxiety behavior. In this model, pups are separated from the mother during critical periods of development and the effects of this manipulation are assessed in the adult animal. Studies have shown that activation of the hypothalamus-ptuitary-adrenal (HPA) axis is an important regulatory mechanism during inflammatory responses in several pathologies. Evidence from animal models and human studies suggest that stress induced impaired immune response, promoting the initiation and progression of some types of cancer. With the activation of the HPA axis, the mediators released during stress suppress specific and non-specific immune responses, including the NK cell activity, phagocytosis, production of inflammatory cytokines (IL-2, IFN, and TNF by Th1 cells), and the activity of cytotoxic T cells, compromising the immune effector response against tumors. Aim: In the present study, we evaluated the effects of long maternal separation (LMS) on the onset of melanoma metastatization, looking at the specific T cell proliferation and cytotoxic response to tumor cells, in vitro. Material and Methods: C57BL/6 male mice were submitted to LMS – consisting of removing the litter from the home-cage for 3 h/day, from 2 to 14 days of age – and challenged as adults with acute (2 h before tumor cell injection) or chronic restraint stress (2 h daily for one week before tumor cell injection) protocols. Lung metastasis and in vitro cytotoxic and lymphoproliferative responses towards cancer cells were analyzed by flow citometry. Data were expressed as average ± SEM. Results of citotoxicity assay were expressed as percentage of dead cells and in the lymphoproliferative assay results were expressed as average of fluorescence intensity. Results: The results showed that LMS favored the increase of lung metastasis, with more dramatic results seen when acute stress preceded inoculation of B16F10 tumor cells (unstressed CTRL= 30 ± 20; acute stress CTRL= 15,5 ± 12,2; chronic stress CTRL= 23 ± 4,2; unstressed LMS=47,2 ± 15,9; acute LMS= 30,67 ± 17,83; chronic LMS = 30,66 ± 17,34), leading to a three-fold increase in metastatic colonies. There was also a decrease in cytotoxic (unstressed CTRL= 20,21 ± 0,99; acute stress CTRL= 21,73 ± 2,18; chronic stress CTRL= 18,82 ± 1,08; unstressed LMS = 22,3 ± 1,7; acute LMS= 17,65 ± 2,8; chronic LMS = 22,95 ± 3,15) and lymphoproliferative responses (unstressed CTRL= 2351,93 ± 195,07; acute stress CTRL= 2414,2 ±144,8; chronic stress CTRL= 2370,18 ± 188,85; unstressed LMS= 2101,75 ± 111,25; acute LMS= 1805,53 ±276,47; chronic LMS = 2040,74 ± 255,26) to B16F10 cells in vitro. On the other hand, chronically stressed mice displayed similar responses to non-stressed control animals. Conclusion: Taken together, these findings show that LMS associated to acute, but not chronic stress in adult life, impairs anti-cancer immunologic responses, promoting the progression of melanoma in this mouse model.