Polydatin protects against atherosclerosis by activating autophagy and inhibiting pyroptosis mediated by the NLRP3 inflammasome

Abstract

Ethnopharmacological relevance: Polydatin is a bioactive ingredient extracted from the roots of the Reynoutria japonica Houtt, and it is a natural precursor of resveratrol. Polydatin is a useful inhibitor of inflammation and acts as a regulator of lipid metabolism. However, the specific mechanisms of action of polydatin in atherosclerosis (AS) remains poorly explained.

Aim of the study: The aim of this study was to assess the efficacy of polydatin on inflammation induced by the inflammatory cell death and autophagy in AS.

Materials and methods: Apolipoprotein E knockout (ApoE^-/-) mice were fed with a high-fat diet (HFD) for 12 weeks to induce the formation of atherosclerotic lesions. The ApoE^-/- mice were then randomly divided into the following six groups: (1) model group, (2) simvastatin group, (3) MCC950 group, (4) low dose polydatin group (Polydatin-L), (5) medium dose polydatin group (Polydatin-M), (6) and high dose polydatin group (Polydatin-H). The C57BL/6J mice were treated as controls and administered a standard chow diet. All mice were gavaged once daily for 8 weeks. The distribution of aortic plaques was observed by En Oil-red-O staining and hematoxylin and eosin staining (H&E). Oil-red-O staining was used to observe lipid content in the aortic sinus plaque; Masson trichrome staining was used to gauge collagen content in the plaque; and immunohistochemistry was used to evaluate smooth muscle actin (α-SMA) and CD68 macrophages marker expression levels in the plaque, which were used to assess the vulnerability index of the plaque. The lipid levels were measured using an enzymatic assay with an automatic biochemical analyzer. The level of inflammation was detected by enzyme-linked-immunosorbent assay (ELISA). Autophagosomes were detected by transmission electron microscopy (TEM). Pyroptosis was detected by terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL)/caspase-1 and other proteins related to the expression levels of autophagy and pyroptosis were detected by Western blot analysis.

Results: Nucleotide oligomerization (NOD)-like receptor (NLR) family pyrin domain-containing protein 3 (NLRP3) inflammasome activation leads to pyroptosis, including the cleavage of caspase-1, interleukin (IL)-1β and IL-18 production, and the co-expression of TUNEL/caspase-1-all of these are inhibited by polydatin, whose inhibitory effect is similar to that of MCC950, a specific inhibitor of NLRP3. Further, polydatin decreased the protein expression of NLRP3 and the phosphorylated mammalian target of rapamycin (p-mTOR), and increased the number of autophagosomes as well as the increased the cytoplasmic microtubule-associated protein light chain 3 (LC3)/autophagosome membrane-type LC3 ratio. Moreover, the protein expression levels of p62 decreased, suggesting that polydatin can increase autophagy.

Conclusions: Polydatin can inhibit the activation of the NLRP3 inflammasome and cleavage of caspase-1, thereby inhibiting pyroptosis and secretion of inflammatory cytokines, and promoting autophagy through NLRP3/mTOR pathway in AS.

Keywords: Atherosclerosis; Autophagy; Inflammation; Polydatin; Pyroptosis.