Obesity is a chronic inflammatory disease that affects millions of people worldwide. Most studies observe the effects of a high-fat diet (HFD) in 10-12 weeks. This work investigated the effects induced by a HFD administered for 6 weeks on the nutritional status of mice and some aspects of the inflammatory response in mouse peritoneal macrophages. Male Swiss Webster mice, 2-3 months of age, were fed a control diet or HFD for 6 weeks. After this period, the mice were euthanized, and peritoneal macrophages were collected for immunoassays and assessment of biochemical parameters. A HFD was associated with increased cholesterol, insulin resistance, C-reactive protein (CRP), leptin, and serum resistin levels. Lipopolysaccharide (LPS)- stimulated adipocyte cultures of animals subjected to a HFD showed increased production of proinflammatory cytokines such as tumor necrosis factor alpha (TNF-α), interleukin-1 (IL-1), and interleukin-6 (IL-6). However, peritoneal macrophages of the HFD group showed no changes in the levels of these cytokines. LPS-stimulated peritoneal macrophages from HFD-treated animals showed a reduction in mRNA expression of TNF-α and IL-6, as well as a decrease in expression of the transcription factor nuclear factor-kappa B (NF-kB). In conclusion, HFD treatment for 6 weeks induces similar signs to metabolic syndrome and decreases the capacity of peritoneal macrophages to develop an appropriate inflammatory response to a bacterial component.

ABSTRACT It is well established that protein malnutrition (PM) impairs immune defenses and increases susceptibility to infection. Macrophages are cells that play a central role in innate immunity, constituting one of the first barriers against infections. Macrophages produce several soluble factors, including cytokines and growth factors, important to the immune response. Among those growth factors, granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF). GM-CSF and M-CSF are important to monocyte and macrophage development and stimulation of the immune response process. Knowing the importance of GM-CSF and M-CSF, we sought to investigate the influence of PM on macrophage production of these growth factors. Two-month-old male BALB/c mice were subjected to PM with a low-protein diet (2%) and compared to a control diet (12%) mouse group. Nutritional status, hemogram and the number of peritoneal cells were evaluated. Additionally, peritoneal macrophages were cultured and the production of GM-CSF and M-CSF and mRNA expression were evaluated. To determine if PM altered macrophage production of GM-CSF and M-CSF, they were stimulated with TNF-α. The PM animals had anemia, leukopenia and a reduced number of peritoneal cells. The production of M-CSF was not different between groups; however, cells from PM animals, stimulated with or without TNF-α, presented reduced capability to produce GM-CSF. These data imply that PM interferes with the production of GM-CSF, and consequently would affect the production and maturation of hematopoietic cells and the immune response.