Sennoside A Ameliorates Diabetic Atherosclerosis by Inhibiting OSCP1/ERK1/2 Pathway to Regulate Endothelial Dysfunction.

Abstract

Objective: To investigate the effect of sennoside A (SA) on atherosclerosis (AS) in type 2 diabetes mellitus (T2DM) mice and its underlying mechanisms.

Methods: Sixty-one 9-week-old AopE^-/- mice were randomly divided into 6 groups using the random number table: control, model (fed a high-fat diet for 4 weeks, followed by intraperitoneal injection of streptozotocin), SA low-, medium-, high-doses (15, 30, and 45 mg/kg per day, respectively for 8 weeks), and positive control groups (100 mg/kg metformin per day, for 8 weeks, 10 or 11 per group). The body weight and blood glucose levels of the mice were monitored regularly. Serum lipid content was measured using biochemical kits, and fasting insulin levels were qualified using ELISA kits. Aortic tissue was examined using Oil Red O, HE, Masson, and Picrosirius red stainings to observe the pathological changes. The mRNA expressions of CD31, VE-cadherin, α-smooth muscle actin (α-SMA) and vimentin were detected by RT-qPCR. The relative protein expressions of organic solute carrier partner (OSCP1), matrix metalloproteinase 9 (MMP9), vascular endothelial growth factor A (VEGFA) and p-ERK1/2 proteins were analyzed using Western blot. In vitro, endothelial cell dysfunction was induced using high glucose combined with oxidized low-density lipoprotein (ox-LDL). These cell groups included the blank control, model, different concentrations of SA (1, 30, 100 µ mol/L), metformin (Met), OSCP1 knockdown, SA combined with OSCP1 knockdown, and OSCP1 overexpressing combined with SA groups. Cell morphology was observed under a microscope. Cell proliferation was assessed utilizing cell count kit (CCK)-8 assay, migration was evaluated with scratch test, and invasion ability was determined using transwell assay. The methods for mRNA and protein detection were the same as in vivo.

Results: Animal experiments demonstrated that SA and Met improved blood glucose, lipid levels, and insulin sensitivity in T2DM mice, delayed AS progression, and reduced plaque area (P<0.05 or P<0.01). Compared with the model group, SA and Met treatment increased the expressions of CD31 and VE-cadherin, decreased the mRNA expressions of α-SMA and vimentin, and reduced the relative protein levels of OSCP1, MMP9, VEGFA and p-ERK1/2 (P<0.05 or P<0.01). Cell experiments showed that SA and Met can inhibit the morphological changes, excessive proliferation, migration, and invasion of endothelial cells induced by high glucose and ox-LDL (P<0.05 or P<0.01). The trends of mRNA and protein expression were consistent with the results of the animal experiments. In the si-OSCP1 and si-OSCP1+SA groups, mRNA levels of CD31 and VE-cadherin were increased, while α-SMA and vimentin mRNA levels were reduced (P<0.05 or P<0.01). Additionally, the relative expression levels of these proteins were downregulated (P<0.05 or P<0.01), and cellular morphological changes and excessive proliferation were reversed (P<0.01). However, OSCP1 overexpression resulted in the opposite effects (P<0.05 or P<0.01).

Conclusions: SA reduces plaque area and stabilizes plaque in T2DM mice. Its anti-AS effects may be mediated through the downregulation of OSCP1/ERK1/2 signaling pathway, which helps reverse endothelial-to-mesenchymal transition.