Role of IL-18 in adipose tissue remodeling and metabolic dysfunction.

BACKGROUND/OBJECTIVES: Proinflammatory cytokines are increased in obese adipose tissue, including inflammasome key masters. Conversely, IL-18 protects against obesity and metabolic dysfunction. We focused on the IL-18 effect in controlling adipose tissue remodeling and metabolism. MATERIALS/SUBJECTS AND METHODS: We used C57BL/6 wild-type (WT) and interleukine-18 deficient (IL-18-/-) male mice fed a chow diet and samples from bariatric surgery patients. RESULTS: IL-18-/- mice showed increased adiposity and proinflammatory cytokine levels in adipose tissue, leading to glucose intolerance. IL-18 was widely secreted by stromal vascular fraction but not adipocytes from mice's fatty tissue. Chimeric model experiments indicated that IL-18 controls adipose tissue expansion through its presence in tissues other than bone marrow. However, IL-18 maintains glucose homeostasis when present in bone marrow cells. In humans with obesity, IL-18 expression in omental tissue was not correlated with BMI or body fat mass but negatively correlated with IRS1, GLUT-4, adiponectin, and PPARy expression. Also, the IL-18RAP receptor was negatively correlated with IL-18 expression. CONCLUSIONS: IL-18 signaling may control adipose tissue expansion and glucose metabolism, as its absence leads to spontaneous obesity and glucose intolerance in mice. We suggest that resistance to IL-18 signaling may be linked with worse glucose metabolism in humans with obesity.

Obesity enhances the recruitment of mesenchymal stem cells to visceral adipose tissue.

In obesity, high levels of TNF-α in the bone marrow microenvironment induce the bone marrow-mesenchymal stem cells (BM-MSCs) towards a pro-adipogenic phenotype. Here, we investigated the effect of obesity on the migratory potential of BM-MSCs and their fate towards the adipose tissues. BM-MSCs were isolated from male C57Bl/06 mice with high-fat diet-induced obesity. The migratory potential of the BM-MSCs, their presence in the subcutaneous (SAT) and the visceral adipose tissues (VAT), and the possible mechanisms involved were investigated. Obesity did not affect MSC content in the bone marrow but increased the frequency of MSCs in blood, SAT, and VAT. In these animals, the SAT adipocytes presented a larger area, without any changes in adipokine production or the Sdf-1α gene expression. In contrast, in VAT, obesity increased leptin and IL-10 levels but did not modify the size of the adipocytes. The BM-MSCs from obese animals presented increased spontaneous migratory activity. Despite the augmented expression of Cxcr4, these cells exhibited decreased migratory response towards SDF-1α, compared to that of BM-MSCs from lean mice. The PI3K-AKT pathway activation seems to mediate the migration of BM-MSCs from lean mice, but not from obese mice. Additionally, we observed an increase in the spontaneous migration of BM-MSCs from lean mice when they were co-cultured with BM-HCs from obese animals, suggesting a paracrine effect. We concluded that obesity increased the migratory potential of the BM-MSCs and induced their accumulation in VAT, which may represent an adaptive mechanism in response to chronic nutrient overload.

Effect of obesity on biodistribution of nanoparticles.

Nanoparticles have specific features (lipophilicity, surface charge, composition and size). Studies regarding the biological behavior of nanoparticles in diseases such diabetics and obesity are scarce. Here, we evaluated two nanoparticles: magnetic core mesoporous silica (MSN) (58 nm) and polycaprolactone (PCL) nanoparticle (280 nm) in obese mice. Changes in the biodistribution were observed, especially considering the mononuclear phagocyte system (MPS), and the visceral fat tissue. Nonetheless, our data corroborates the influence of size in the biodistribution in obese animals, supporting that smaller nanoparticles, may show a higher tissue deposition at spleen, due the associated splenomegaly and the complications arising from this state. Finally, our study demonstrated that, in obesity, probably due the low-grade inflammatory state associated with metabolic syndrome a difference in accumulation of nanoparticles was found, with profound impact in the tissue deposition of nanoparticles.