eNOS-Nitric Oxide System Contributes to a Novel Antiatherogenic Effect of Leonurine via Inflammation Inhibition and Plaque Stabilization

Leonurine (LEO) is a bioactive small molecular compound that has protective effects on the cardiovascular system and prevents the early progression of atherosclerosis; however, it is not clear whether LEO is effective for plaque stability. A novel mouse atherosclerosis model involving tandem stenosis (TS) of the right carotid artery combined with western diet (WD) feeding was used. Apolipoprotein E gene-deficient mice were fed with a WD and received LEO administration daily for 13 weeks. TS was introduced 6 weeks after the onset of experiments. We found that LEO enhanced plaque stability by increasing fibrous cap thickness and collagen content while decreasing the population of CD68-positive cells. Enhanced plaque stability by LEO was associated with the nitric oxide synthase (NOS)-nitric oxide (NO) system. LEO restored the balance between endothelial NOS(E)- and inducible NOS(iNOS)-derived NO production; suppressed the NF-κB signaling pathway; reduced the level of the inflammatory infiltration in plaque, including cytokine interleukin 6; and downregulated the expression of adhesion molecules. These findings support the distinct role of LEO in plaque stabilization. In vitro studies with oxidized low-density lipoprotein-challenged human umbilical vein endothelial cells revealed that LEO balanced NO production and inhibited NF-κB/P65 nuclear translocation, thus mitigating inflammation. In conclusion, the restored balance of the NOS-NO system and mitigated inflammation contribute to the plaque-stabilizing effect of LEO. SIGNIFICANCE STATEMENT: LEO restored the balance between endothelial NOS and inducible NOS in NO production and inhibited excessive inflammation in atherosclerotic "unstable" and rupture-prone plaques in apolipoprotein E gene-deficient mice. The protective effect of LEO for stabilizing atherosclerotic plaques was due to improved collagen content, increased fibrous cap thickness, and decreased accumulation of macrophages/foam cells. So far, LEO has passed the safety and feasibility test of phase I clinical trial.

Vitamin K2-MK-7 improves nitric oxide-dependent endothelial function in ApoE/LDLR-/- mice

Although, vitamin K₂ displays vasoprotective effects, it is still not known whether K₂ treatment improves endothelial function. In ApoE/LDLR^-/- mice at the stage prior to atherosclerosis development, four-week treatment with K₂-MK-7, given at a low dose (0.05 mg/kg), improved acetylcholine- and flow-induced, endothelium-dependent vasodilation in aorta or in femoral artery, as assessed by MRI in vivo. This effect was associated with an increased NO production, as evidenced by EPR measurements in ex vivo aorta. Treatment with higher doses of K₂-MK-7 (0.5; 5 mg/kg) resulted in a dose-dependent increase in plasma K₂-MK-7 and K₂-MK-4 concentration, without further improvement in endothelial function. In ApoE/LDLR^-/- mice with developed atherosclerotic plaques, treatment with a low (0.03 mg/kg) or high (10 mg/kg) dose of K₂-MK-7 resulted in a similar degree of endothelium-dependent vasodilation improvement and increase in plasma nitrate concentration, what was not associated with changes in thrombin generation as measured by CAT. Both doses of K₂-MK-7 also reduced media thickness in the brachiocephalic artery, but did not modify atherosclerotic plaque size. In conclusion, K₂-MK-7 improves NO-dependent endothelial function in ApoE/LDLR^-/- mice. This study, identifies the endothelial profile of the pharmacological activity of vitamin K₂, which has not been previously described.

Hydrogen sulfide stabilizes atherosclerotic plaques in apolipoprotein E knockout mice

Hydrogen sulfide gas (H₂S) has protective effects in the cardiovascular system that includes preventing the development of atherosclerosis when tested in several in vivo models. Plaque instability is a major risk factor for thromboembolism, myocardial infarction, and stroke, so we examined if H₂S can promote plaque stability and the potential underlying mechanisms. Apolipoprotein E knockout mice fed an atherogenic diet were administered the exogenous H₂S donor sodium hydrosulfide (NaHS) or pravastatin as a positive control daily for 14 weeks. NaHS significantly enhanced plaque stability by increasing fibrous cap thickness and collagen content compared to vehicle-treated controls. NaHS treatment also reduced blood lipid levels and plaque formation. Preservation of plaque stability by NaHS was associated with reductions in vascular smooth muscle cells (VSMCs) apoptosis and expression of the collagen-degrading enzyme matrix metallopeptidase-9 (MMP-9) in plaque. While pravastatin also increased fibrous cap thickness and reduced VSMC apoptosis, but did not enhance plaque collagen or reduce MMP-9 significantly, suggesting distinct mechanisms of plaque stabilization. in vitro, NaHS also decreased MMP-9 expression in macrophages stimulated with tumor necrosis factor-α by inhibiting ERK/JNK phosphorylation and activator protein 1 nuclear translocation. Moreover, H₂S reduced caspase-3/9 activity, Bax/Bcl-2 ratio, and LOX-1 mRNA expression in VSMCs stimulated with oxidized low-density lipoprotein. These results suggest that H₂S enhances plaque stability and protects against atherogenesis by increasing plaque collagen content and VSMC count. In conclusion, H₂S exerts protective effects against atherogenesis at least partly by stabilizing atherosclerotic plaque.

Effects of serum lipid smoothness on the progression and vulnerability of atherosclerotic plaques in rabbits

Objective

We aimed to explore the effects of lipid smoothness on the progression and vulnerability of atherosclerotic plaques.

Approach

24 rabbits were divided into three groups randomly. Group 1 was given standard chow diet; group 2 was fed with cholesterol-rich diet; for group 3, subjects were planned to take cholesterol-rich diet at the first phase for 12 weeks and during the second phase, low-fat and cholesterol-rich diet was then applied alternately every three weeks till the end of the experiment. Lipid profiles, inflammatory factors, endothelium functions, pathological and histological changes were examined. Expressions of matrix metalloproteinase-9 and lectin-like oxidized LDL receptor-1 were measured by immunohistochemical staining.

Results

According to data collected during the whole experiment, lipid smoothness index of group 3 was the lowest. Compared with group 2, statistics of the group 3 indicated that: the development of plaques progressed faster; the plaque area and plaque thickness (53.53[22.6]% vs 33.90[24.91]% , 800.38[98.25]µm vs 675.00[109.67]µm) were higher while the fibrous cap thickness (103.50[45.66]µm vs 295.83[97.90]µm) was lower; hs-CRP (0.53[0.07]mg/dL vs 0.45[0.06]mg/dL), interleukin-18 (186.01[8.41]ng/L vs 158.08[2.37]ng/L), OX-LDL (177.15[5.93]µg/L vs 139.57[2.35] µg/L) and endothelin-1 (164.66[9.54]ng/L vs 131.52[4.39]ng/L) were higher while nitric-oxide (22.41[1.69]µmol/L vs 27.23[1.36]µmol/L) was lower; expressions of matrix metalloproteinase-9 (IOD: 37375.87[5634.52] vs 20956.57[4616.93]) and lectin-like oxidized LDL receptor-1 (IOD: 45213.04[16653.81] vs 21921.68[6142.32]) were higher.

Conclusions

Lipids fluctuation could accelerate the progression and vulnerability of atherosclerotic plaques through worsening arterial endothelium dysfunction and inflammatory reactions.