Fatty Acids and NLRP3 Inflammasome-Mediated Inflammation in Metabolic Tissues.

Worldwide obesity rates have reached epidemic proportions and significantly contribute to the growing prevalence of metabolic diseases. Chronic low-grade inflammation, a hallmark of obesity, involves immune cell infiltration into expanding adipose tissue. In turn, obesity-associated inflammation can lead to complications in other metabolic tissues (e.g., liver, skeletal muscle, pancreas) through lipotoxicity and inflammatory signaling networks. Importantly, although numerous signaling pathways are known to integrate metabolic and inflammatory processes, the nucleotide-binding and oligomerization domain-like receptor, leucine-rich repeat and pyrin domain-containing 3 (NLRP3) inflammasome is now noted to be a key regulator of metabolic inflammation. The NLRP3 inflammasome can be influenced by various metabolites, including fatty acids. Specifically, although saturated fatty acids may promote NLRP3 inflammasome activation, monounsaturated fatty acids and polyunsaturated fatty acids have recently been shown to impede NLRP3 activity. Therefore, the NLRP3 inflammasome and associated metabolic inflammation have key roles in the relationships among fatty acids, metabolites, and metabolic disease. This review focuses on the ability of fatty acids to influence inflammation and the NLRP3 inflammasome across numerous metabolic tissues in the body. In addition, we explore some perspectives for the future, wherein recent work in the immunology field clearly demonstrates that metabolic reprogramming defines immune cell functionality. Although there is a paucity of information about how diet and fatty acids modulate this process, it is possible that this will open up a new avenue of research relating to nutrient-sensitive metabolic inflammation.

Nutritional modulation of metabolic inflammation.

Metabolic inflammation is a very topical area of research, wherein aberrations in metabolic and inflammatory pathways probably contribute to atherosclerosis, insulin resistance (IR) and type 2 diabetes. Metabolic insults arising from obesity promote inflammation, which in turn impedes insulin signalling and reverse cholesterol transport (RCT). Key cells in the process are metabolically activated macrophages, which up-regulate both pro- and anti-inflammatory pathways in response to lipid spillover from adipocytes. Peroxisome proliferator-activated receptors and AMP-activated protein kinase (AMPK) are regulators of cellular homeostasis that influence both inflammatory and metabolic pathways. Dietary fats, such as saturated fatty acids (SFAs), can differentially modulate metabolic inflammation. Palmitic acid, in particular, is a well-characterized nutrient that promotes metabolic inflammation via the NLRP3 (the nod-like receptor containing a pyrin domain) inflammasome, which is partly attributable to AMPK inhibition. Conversely, some unsaturated fatty acids are less potent agonists of metabolic inflammation. For example, monounsaturated fatty acid does not reduce AMPK as potently as SFA and n-3 polyunsaturated fatty acids actively resolve inflammation via resolvins and protectins. Nevertheless, the full extent to which nutritional state modulates metabolic inflammation requires greater clarification.

A casein hydrolysate protects mice against high fat diet induced hyperglycemia by attenuating NLRP3 inflammasome-mediated inflammation and improving insulin signaling.

SCOPE: Activation of the nod-like receptor protein 3 (NLRP3) inflammasome is required for IL-1ß release and is a key component of obesity-induced inflammation and insulin resistance. This study hypothesized that supplementation with a casein hydrolysate (CH) would attenuate NLRP3 inflammasome mediated IL-1ß secretion in adipose tissue (AT) and improve obesity-induced insulin resistance. METHODS AND RESULTS: J774.2 macrophages were LPS primed (10 ng/mL) and stimulated with adenosine triphosphate (5 mM) to assess NLRP3 inflammasome activity. Pretreatment with CH (1 mg/mL; 48 h) reduced caspase-1 activity and decreased IL-1ß secretion from J774.2 macrophages in vitro. 3T3-L1 adipocytes cultured with conditioned media from CH-pretreated J774.2 macrophages demonstrated increased phosphorylated (p)AKT expression and improved insulin sensitivity. C57BL/6JOLaHsd mice were fed chow or high fat diet (HFD) for 12 wk ± CH resuspended in water (0.5% w/v). CH supplementation improved glucose tolerance in HFD-fed mice as determined by glucose tolerance test. CH supplementation increased insulin-stimulated pAKT protein levels in AT, liver, and muscle after HFD. Cytokine secretion was measured from AT and isolated bone marrow macrophages cultured ex vivo. CH supplementation attenuated IL-1ß, tumor necrosis factor alpha (TNF-α) and IL-6 secretion from AT and IL-1ß, IL-18, and TNF-α from bone marrow macrophages following adenosine triphosphate stimulation ex vivo. CONCLUSION: This novel CH partially protects mice against obesity-induced hyperglycemia coincident with attenuated IL-1ß secretion and improved insulin signaling.