Red Raspberry Polyphenols Reduce the High Fat Diet-driven Adipocyte Hypertrophy by Suppressing NLRP3 Inflammasome Activation (P08-028-19)

Abstract

ObjectivesNLRP3 inflammasome is an innate immune machinery for caspase-1 cleavage and IL-1β secretion. Activation of the NLRP3 inflammasome is a metabolic culprit linking adipose inflammation to systemic metabolic dysfunction. Red raspberry (RR) is rich in polyphenols shown to exert protective role against obesity and metabolic syndrome. This study aimed to investigate the impact of RR polyphenols on activation of NLRP3 inflammasome and its metabolic benefits. MethodsThe whole, seed, and pulp RR polyphenols were fractionated and lyophilized. C57BL/6 male mice were assigned 1 of 5 diets of LF (10% total calorie from fat), HF (45% calorie from fat), or HF diet containing RR polyphenols from whole (0.4%), pulp (0.3%) and seed (0.1%) fraction for 12 weeks. Macrophage infiltration and NLRP3 inflammasome activation were determined by macrophage signature gene/protein expression and caspase-1 cleavage in the epididymal fat and stromal vascular fraction. Adipogenic potential was evaluated by epigenetic marks of H3K27Ac in the stromal vascular fraction. IL-1β reporter assay was used to validate the NLRP3 inflammasome activation in vitro. To explore the paracrine effects of IL-1β in regulating adipogenesis, we designed the conditioned medium experiments between macrophages and C3H10T1/2 murine pluripotent stem cells. ResultsThe whole and pulp, but not seed, RR polyphenols significantly reduced the HF-driven weight gain, dyslipidemia, and insulin resistance. Whole or pulp RR polyphenols decreased inflammation, macrophage recruitment, and adipocyte size in epididymal fat compared to HF alone or seed polyphenols. Reduced adipocyte size by whole and pulp polyphenols was linked with 1) reduced NLRP3 inflammasome in the stromal vascular fraction, evidenced by reduced IκBα degradation and caspase-1 cleavage, and 2) augmented new fat cell formation via epigenetic modifications for adipogenesis (i.e., H3K27Ac, H3K9Ac, and H3K4m2). Supporting these in vivo results, RR polyphenol treatment in macrophages not only attenuated IL-1β reporter assay but also reversed the paracrine action of IL-1β in blocking adipogenesis in vitro. ConclusionsBlocking NLRP3 by RR polyphenols is a promising dietary intervention strategy to promote healthy adipose remodeling, preventing adipocyte hypertrophy, fatty acid spillover, and further metabolic complications. Funding SourcesUSDA NIFA.