Deleterious effects of social isolation on neuroendocrine-immune status, and cancer progression in rats

Accumulating evidence indicates that social isolation (SI) in humans and rodents is associated with increased cancer incidence and mortality, yet mediating mechanisms remain elusive. Here, we examine the neuroendocrine and immunological consequences of SI and its short- and long-term physiological impacts in naïve and cancer-bearing rats. Findings indicate that isolated animals experienced a significant decrease in weight compared to controls. Specifically, females showed a marked weight decrease during the first week of isolation. Isolated rats had significantly higher numbers of MADB106 experimental pulmonary metastases. Although mortality rates were higher in isolated tumor-bearing rats, unexpectedly, they exhibited a reduced growth rate of orthotopically implanted MADB106 tumors. Transcriptomic analyses of these excised tumors indicated a major downregulation in the expression of various genes, including those associated with pro-metastatic processes (e.g., EMT). In naïve rats (no cancer), levels of IL-6 increased, and total IgG levels decreased under SI conditions. A mixed effect was found for TNFα, which increased in females and decreased in males. In the central nervous system, isolated rats showed altered gene expression in key brain regions associated with stress responses and social behavior. The paraventricular nucleus of the thalamus emerged as a significantly affected region, along with the bed nucleus of the stria terminalis. Changes were observed in the expression of oxytocin, serotonin, and dopamine receptors. Isolated rats also exhibited greater alterations in hypothalamic–pituitary–adrenal (HPA) axis-related regulation and an increase in plasma CORT levels. Our study highlights the profound impact of SI on metastatic processes. Additionally, the potential detrimental effects of SI on thermoregulation were discussed, emphasizing the importance of social thermoregulation in maintaining physiological stability and highlighting the need to avoid single-caging practices in research. We report neuro-immune interactions and changes in brain gene expression, highlighting the need for further research into these underlying processes to improve outcomes in animal models and potential interventions for cancer patients through increased social support.