Plain language summary
Intermittent fasting and caloric restriction have been shown to have beneficial effects on a particular inflammatory pathway, called NLRP3 inflammasome, which is associated with insulin resistance and asthma. In this highly technical paper the authors report a study which was conducted to confirm whether the beneficial effect of fasting on the NLRP3 inflammatory pathway is mediated via a particular protein called sirtuin and its effects on mitochondria (the energy producing parts of every cell). 19 healthy subjects fasted for 24 hours followed by a set meal. Bloods were drawn after the fast and 1 hour and 3 hours after the meal and evaluated for a number of inflammatory parameters. The NLRP3 inflammasome was less active in the fasted than in the fed state. The investigators established the involvement of sirtuin and mitochondria, as well as other inflammatory pathways in this fasting induced immune modulation.
Abstract
BACKGROUND Activation of the NLRP3 inflammasome is associated with metabolic dysfunction, and intermittent fasting has been shown to improve clinical presentation of NLRP3 inflammasome-linked diseases. As mitochondrial perturbations, which function as a damage-associated molecular pattern, exacerbate NLRP3 inflammasome activation, we investigated whether fasting blunts inflammasome activation via sirtuin-mediated augmentation of mitochondrial integrity. METHODS We performed a clinical study of 19 healthy volunteers. Each subject underwent a 24-hour fast and then was fed a fixed-calorie meal. Blood was drawn during the fasted and fed states and analyzed for NRLP3 inflammasome activation. We enrolled an additional group of 8 healthy volunteers to assess the effects of the sirtuin activator, nicotinamide riboside, on NLRP3 inflammasome activation. RESULTS In the fasting/refeeding study, individuals showed less NLRP3 inflammasome activation in the fasted state compared with that in refed conditions. In a human macrophage line, depletion of the mitochondrial-enriched sirtuin deacetylase SIRT3 increased NLRP3 inflammasome activation in association with excessive mitochondrial ROS production. Furthermore, genetic and pharmacologic SIRT3 activation blunted NLRP3 activity in parallel with enhanced mitochondrial function in cultured cells and in leukocytes extracted from healthy volunteers and from refed individuals but not in those collected during fasting. CONCLUSIONS Together, our data indicate that nutrient levels regulate the NLRP3 inflammasome, in part through SIRT3-mediated mitochondrial homeostatic control. Moreover, these results suggest that deacetylase-dependent inflammasome attenuation may be amenable to targeting in human disease. TRIAL REGISTRATION ClinicalTrials.gov NCT02122575 and NCT00442195. FUNDING Division of Intramural Research, NHLBI of the NIH.
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