Mechanism of Huanglian Wendan Decoction in improving impaired glucose tolerance based on skeletal muscle NLRP3/caspase-1/IL-1β, IL-18 pathway

Abstract

This study investigated the mechanism of improving impaired glucose tolerance(IGT) of rats by Huanglian Wendan Decoction from the perspective of the skeletal muscle Nod-like receptor protein 3(NLRP3)/cysteinyl aspartate specific proteinase-1(caspase-1)/interleukin-1β(IL-1β), interleukin-18(IL-18) pathway. Healthy male SD rats were fed with the diet containing 45% fat for 20 weeks, accompanied by a high-temperature and high-humidity environment and an inactive lifestyle, for the establishment of the IGT rat model. The rats were divided into the blank control group, model control group, metformin hydrochloride group(positive drug group, 0.05 g·kg~(-1)·d~(-1)) and Huanglian Wendan Decoction group(7.8 g·kg~(-1)·d~(-1)). After continuous intragastric administration for 4 weeks, the obesity and glycemic indexes of all the rats were measured. The fasting serum insulin(FINS) level was determined by ELISA, with the insulin sensitivity index(ISI) and insulin resistance index(IRI) calculated. The mRNA and protein expression le-vels of nuclear factor kappaB(NF-κB), NLRP3, caspase-1, IL-1β and IL-18 in skeletal muscle tissue were detected by real-time polymerase chain reaction(PCR), Western blot and immunofluorescence. Compared with the blank control group, the model control group witnessed significantly increased mRNA and protein expression of NF-κB, NLRP3, caspase-1, IL-1β and IL-18. As revealed by the comparison with the model control group, Huanglian Wendan Decoction could effectively regulate the obesity status, reduce body weight, correct the abnormal levels of 2-hour plasma glucose(2 hPG), insulin resistance index(IRI), insulin sensitivity index(ISI), and lower the mRNA and protein expression of NF-κB, NLRP3, caspase-1, IL-1β and IL-18 in the skeletal muscle tissue of IGT rats. Combined with previous studies, the above results showed that the occurrence and development of IGT was closely related to inflammatory response and the classic pyroptosis pathway in skeletal muscle, such as NLRP3/caspase-1/IL-1β, IL-18. It is inferred that the mechanism of Huanglian Wendan Decoction was to alleviate insulin resistance(IR) and then reverse the course of IGT lies in the regulation of the abnormal insulin receptor signaling pathway based on the NLRP3 inflammasome pathway.