Targeting the NLRP3 inflammasome to reduce diet-induced metabolic abnormalities in mice.

BACKGROUND AND PURPOSE: Although the molecular links underlying the causative relationship between chronic low-grade inflammation and insulin resistance are not completely understood, compelling evidence suggests a pivotal role of the NLRP3 inflammasome, a large multimeric danger-sensing platform that promotes autocatalytic activation of the cysteine protease caspase-1 and mediates the cleavage of inactive pro-IL-1β and IL-18 into their active forms(1). We and others have recently demonstrated that either a high fat diet or a high sugar diet evoke NLRP3 inflammasome formation and activation in target organs of metabolic inflammation (2, 3). Here we tested the hypothesis that either a selective pharmacological inhibition or a genetic ablation of the NLRP3 inflammasome results in reduction of the diet-induced metabolic alterations.

EXPERIMENTAL APPROACH: Male C57/BL6 wild-type (WT) mice and NLRP3-/- littermates were fed normal diet (ND) or high-fat high-fructose diet (HD) for 12 weeks. A sub-group of HD-fed wild-type mice was treated with the NLRP3 inflammasome inhibitor BAY 11-7082 (3 mg/kg, i.p.) (4). During the study period, in vivo (oGTT) and ex vivo (Western Blot, Histological analysis) were performed. Data were analysed by a one-way ANOVA and presented as mean ± SEM of n observations. *P<0.05

KEY RESULTS: WT mice fed the HD diet exhibited increased serum levels of glycemia (158±22 mg/dL), insulin (1.16±0.04 ng/mL) and triglycerides (0.60±0.06mmol/L) when compared to mice fed the control diet (81±9 mg/dL; 065±0.09 ng/mL and 0.39±0.04mmol/L, respectively). BAY 11-7082administration evoked a significant (p<0.05) improvement in the measured markers (99±8 mg/dL; 081±0.03 ng/mL and 0.40±0.03mmol/L, respectively). None of these metabolic abnormalities were detected in HD-fed NLRP3-/- mice. The improved glucose tolerance by NLRP3 pharmacological and genetic inhibition was at least partially mediated by enhancing the insulin-related signaling pathway in the liver of HD-fed mice. When compared with ND WT mice, WT mice subjected to dietary manipulation demonstrated a significant increase in the albumin-to-creatinine ratio (ACR) (98.06±13.16 vs. 401.23±33.16 μg/mg, P<0.05), which was significantly attenuated by BAY-11-7082 administration (271.36±5.63μg/mg, P<0.05). An impaired ACR was recorded also in the kidney of NLRP3-/- mice fed the experimental diet in comparison to control NLRP3-/- mice (263.95±48.18 vs. 114.03±41.94 μg/mg, P<0.05). However, the diet-induced increase in ACR in HD KO was significantly lower than that recorded in HD WT mice (P<0.05).BAY 11-7082 attenuated the diet-induced increase in NLRP3 inflammasome expression, resulting in inhibition of hepatic and renal caspase-1 activation and interleukin-(IL)-1β and IL-18 production. NF-kB Translocation was inhibited in BAY-11-7082 treated mice, but not in NLRP3-/- mice.

CONCLUSIONS: We demonstrate here that the selective pharmacological inhibition of the NLRP3 inflammasome attenuates the metabolic abnormalities and the related organ damage caused by chronic exposure to HD, with effects similar to those obtained by NLRP3 gene silencing. Overall, the use of small molecules as selective inhibitors of NLRP3 might present certain advantages over the use of biological agents targeted at IL-1β and its receptor, including fewer immunosuppressive effects and better pharmacokinetics and cost effectiveness. Further preclinical and clinical studies are needed to further explore this possibility and to investigate/ensure the safety of this innovative pharmacological approach.

1. Benetti E (2013). Mediators Inflamm. 2013: 1-12.

2. Collino M (2013). BiochemPharmacol. 85: 257-264.

3. Paternostro C (2014) Journal of Hepatology 60: S153

4. Juliana C (2010) J Biol Chem. 285: 9792-802