Asaronic Acid Attenuates Macrophage Activation toward M1 Phenotype through Inhibition of NF-κB Pathway and JAK-STAT Signaling in Glucose-Loaded Murine Macrophages

Macrophage polarization has been implicated in the pathogenesis of obesity and type 2 diabetes, which are recognized as chronic proinflammatory diseases. This study investigated that high level of glucose, similar to lipopolysaccharide (LPS), activated macrophages toward M1 phenotypes and 1-20 μM asaronic acid (AA) counteracted diabetic macrophage activation. AA reduced the LPS-promoted secretion of proinflammatory interleukin (IL)-6 and monocyte chemoattractant protein-1. The LPS markedly elevated the macrophage induction of the M1 markers of Toll-like receptor 4 (TLR4), CD36, and CD68, which was attenuated by AA. Also, the LPS significantly enhanced the nuclear factor (NF)-κB transactivation, signal transducers, and activators of transcription 1 (STAT1)/STAT3 activation and suppressor of cytokine signaling 3 (SOCS3) induction in macrophages. However, AA highly suppressed the aforementioned effects of LPS. Glucose-stimulated macrophages expressed advanced glycation end products (AGEs) and receptor for AGE (RAGE). Administration of 20 μM AA to macrophages partly but significantly attenuated such effects (1.65 ± 0.12 vs 0.95 ± 0.25 times glucose control for AGE; 2.33 ± 0.31 vs 1.40 ± 0.22 times glucose control for RAGE). Furthermore, glucose enhanced the macrophage induction of TLR4 and inducible nitric oxide synthase and IL-6 production, while it demoted the production of anti-inflammatory arginase-1 and IL-10. In contrast, AA reversed the induction of these markers in glucose-loaded macrophages. AA dose-dependently and significantly encumbered NF-κB transactivation, Janus kinase 2 (JAK2) and STAT1/STAT3 activation, and SOCS3 induction upregulated in glucose-supplemented macrophages. These results demonstrated for the first time that AA may limit diabetic macrophage activation toward the M1 phenotype through the inhibition of TLR4-/IL-6-mediated NF-κB/JAK2-STAT signaling entailing AGE-RAGE interaction.