The ketone metabolite β-hydroxybutyrate blocks NLRP 3 inflammasome – mediated inflammatory disease

nature medicine advance online publication The ketone bodies b-hydroxybutyrate (BHB) and acetoacetate (AcAc) support mammalian survival during states of energy deficit by serving as alternative sources of ATP1. BHB levels are elevated by starvation, caloric restriction, high-intensity exercise, or the low-carbohydrate ketogenic diet2. Prolonged fasting reduces inflammation; however, the impact that ketones and other alternative metabolic fuels produced during energy deficits have on the innate immune response is unknown2–6. We report that BHB, but neither AcAc nor the structurally related shortchain fatty acids butyrate and acetate, suppresses activation of the NLRP3 inflammasome in response to urate crystals, ATP and lipotoxic fatty acids. BHB did not inhibit caspase-1 activation in response to pathogens that activate the NLR family, CARD domain containing 4 (NLRC4) or absent in melanoma 2 (AIM2) inflammasome and did not affect non-canonical caspase-11, inflammasome activation. Mechanistically, BHB inhibits the NLRP3 inflammasome by preventing K+ efflux and reducing ASC oligomerization and speck formation. The inhibitory effects of BHB on NLRP3 are not dependent on chirality or starvationregulated mechanisms like AMP-activated protein kinase (AMPK), reactive oxygen species (ROS), autophagy or glycolytic inhibition. BHB blocks the NLRP3 inflammasome without undergoing oxidation in the TCA cycle, and independently of uncoupling protein-2 (UCP2), sirtuin-2 (SIRT2), the G protein–coupled receptor GPR109A or hydrocaboxylic acid receptor 2 (HCAR2). BHB reduces NLRP3 inflammasome– mediated interleukin (IL)-1b and IL-18 production in human monocytes. In vivo, BHB or a ketogenic diet attenuates caspase-1 activation and IL-1b secretion in mouse models of NLRP3mediated diseases such as Muckle–Wells syndrome, familial cold autoinflammatory syndrome and urate crystal–induced peritonitis. Our findings suggest that the anti-inflammatory effects of caloric restriction or ketogenic diets may be linked to BHB-mediated inhibition of the NLRP3 inflammasome. The NLRP3 inflammasome controls the activation of caspase-1 and the release of the pro-inflammatory cytokines IL-1β and IL-18 in macrophages7–11. It is an important innate immune sensor that is activated in response to structurally diverse damage-associated molecular patterns (DAMPs) such as toxins8, ATP8, excess glucose7, ceramides12, amyloids13,14, urate15 and cholesterol crystals16. Ablation of NLRP3 attenuates type 2 diabetes12,14,17, atherosclerosis16, multiple sclerosis18, Alzheimer disease14, age-related functional decline19, bone loss19 and gout15. Thus, identification of endogenous mechanisms that control NLRP3 inflammasome deactivation may provide insights into the control of several chronic diseases. Although it is known that immune-metabolic interactions dampen pro-inflammatory responses via glycolysis inhibition6, it is not known whether the alternative metabolic fuels that are produced during energy deficits, such as ketones, impact the innate immune response. The ketone bodies β-hydroxybutyrate (BHB) and acetoacetate (AcAc) are produced in the liver of mammals and serve as alternative energy sources for the brain, heart, and skeletal muscles during nutrient deprivation and adherence to low carbohydrate diets1,2. With prolonged fasting, circulating concentrations of BHB can increase to as much as 6–8 mM as liver glycogen stores get used1,2. These nutritional states are associated with altered immune cell function, but it is unknown whether ketone bodies serve as immune effectors. To test whether BHB affects inflammasome activation, we treated lipopolysaccharide (LPS)-primed mouse bone marrow–derived macrophages (BMDMs) with the NLRP3 activator ATP along with BHB for 60 min and measured caspase-1 activation using a western blot that detects the enzymatically active p20 subunit of caspase-1. BHB dose-dependently inhibited both the ATP-induced cleavage of caspase-1 into p20 and the processing of the biologically active p17 form of IL-1β. This inhibition occurred at BHB concentrations similar to the BHB elevations induced by strenuous exercise or 2 d of fasting1,2 (Fig. 1a and Supplementary Fig. 1a). AcAc and the microbiota-derived short-chain fatty acids butyrate and acetate, which The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome–mediated inflammatory disease