Inhibitory effect of aqueous extract of Scrophularia ningpoensis on β-cell pyroptosis in diabetic mice

Scrophularia ningpoensis Hemsl. (SN) is an herbal medicine used as a functional food in China. SN has traditionally been used to treat diabetes mellitus (DM), but its mechanism of action is not well understood. Our previous study indicated that the aqueous extract of SN can reduce hepatic insulin resistance and correct the irregular shape of pancreatic islets in diabetic mice. This study aims to investigate whether the aqueous extract of SN can regulate pyroptosis in pancreatic beta-cells and explore its underlying mechanisms. Db/db mice were orally given an aqueous extract of SN for eight weeks. Subsequently, their pancreatic tissues were collected for histopathological analysis and immunoblotting. Rat insulinoma (INS-1) cells were cultured either alone or with the aqueous extract of SN and evaluated for cell viability, pyroptotic body formation, AMP-activated protein kinase (AMPK) activity, the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome and gasdermin D (GSDMD) activation, and reactive oxygen species (ROS) production under high glucose (HG) exposure conditions. The aqueous extract of SN reduced insulitis and pancreatic beta-cell death in db/db mice. Increased AMPK phosphorylation and decreased NLRP3 inflammasome and GSDMD activation were observed in pancreatic tissues after administration of the aqueous extract of SN. In vitro, the aqueous extract of SN increased cell viability and AMPK phosphorylation in a concentration-dependent manner. Additionally, the aqueous extract of SN corrected excessive ROS generation, NLRP3 inflammasome and GSDMD activation, and pyroptotic body formation. Inhibition of AMPK negated these beneficial effects of the aqueous extract of SN on INS-1 cells. The study concluded that the aqueous extract of SN alleviates beta-cell pyroptosis by inhibiting NLRP3/GSDMD activation in an AMPK-dependent manner.