Anti-inflammatory effect of β2 adrenergic stimulation on circulating monocytes with a pro-inflammatory state in high-fat diet-induced obesity

Obesity is a chronic condition associated with low-grade inflammation, and it also involves alterations of the function of the hypothalamic-pituitaryadrenal axis and the sympathetic nervous system. Adrenergic agonists such as catecholamines are important immunoregulatory molecules that are involved in modulating both metabolism and most of the mechanisms of the immune response. The first objective of this study was to determine whether the systemic inflammatory state associated with obesity is also manifested in the inflammatory profile and phenotype of circulating monocytes; and the second objective was to evaluate the effects of beta 2 adrenergic stimulation on the inflammatory profile and phenotype of monocytes in obesity, and whether this response could be different from that in lean individuals. C57BL/6J mice were randomly allocated to one of two diets for 18 weeks: high-fat diet in order to obtain an experimental model of obesity, and standard diet in the control lean group. Circulating monocyte expression of inflammatory cytokines (MCP-1, TNF-alpha, IL-8, IL-6, IL-10, and TGF-beta), surface membrane marker Ly6C, inducible nitric oxide synthase and arginase-1, and Toll-like receptor 4 were evaluated through flow cytometry in the presence or absence of selective beta 2 adrenergic receptor agonist terbutaline. Monocytes from high-fat diet-induced obese animals presented higher expression levels of all pro inflammatory cytokines and a higher percentage of monocytes with a pro-inflammatory phenotype than those from lean animals beta 2 adrenergic stimulation induced a shift towards an anti-inflammatory activity profile and phenotype in obese mice, whereas it induced a shift towards a pro-inflammatory activity profile and phenotype in lean mice. In conclusion, beta 2 adrenergic stimulation in monocytes was anti-inflammatory only in obese animals, which presented a pro-inflammatory state at baseline.