Atherosclerosis is caused by various factors, and Glabridin may have protective effects on the cardiovascular system. The purpose of the present study was to evaluate the effects of Glabridin on atherosclerosis and evaluate whether Glabridin attenuates arteriosclerosis and endothelial permeability by suppressing the myosin light chain (MLC) kinase (MLCK)/phosphorylated (p)-MLC system via the mitogen activated protein kinase (MAPK) signaling pathway. Male New Zealand rabbits were randomly divided into 3 groups: The control group was administered an ordinary diet, whereas the high fat group and the Glabridin (2 mg/kg/d) intervention group were administered a high fat diet. Following 12 weeks, the blood lipid levels of rabbits, the morphological structure of the arterial wall, the arterial intimal permeability, the endothelial function and the mRNA levels of MLCK were measured. Western blot analysis was used to detect the levels of MLCK, p-c-Jun N-terminal kinase (JNK), p-extracellular signal regulated kinase (ERK), and p-p38. The high-fat diet group exhibited significantly increased total cholesterol and triglycerides, and endothelial dysfunction, which were attenuated by Glabridin treatment. Notably, the aortic endothelial permeability was increased in the high-fat diet group but was ameliorated in the Glabridin treatment group. Hyperlipidemia enhanced the expression of p-MLC and MLCK, which were associated with the increased phosphorylation of ERK, p38 and JNK. These changes were also ameliorated by Glabridin. In conclusion, the results of the present study suggested that atherosclerosis may be associated with upregulated MLCK expression and activity, which was downregulated by Glabridin. The mechanism of action of Glabridin was thought to proceed through modulating MAPK pathway signal transduction. However, further studies are required to adequately illuminate the exact regulatory mechanisms involved.

All-trans retinoic acid (ATRA) is a natural derivative of vitamin A that ameliorates atherosclerosis (AS) by regulating inflammatory factors. However, studies concerning the role of retinoic acid in artery endothelial function are rare. Therefore, the present study investigated its role in regulating the production of endothelin‑1 (ET‑1) and nitric oxide (NO) in rabbits with AS. The rabbits were randomly divided into 3 groups: The control group was administered an ordinary diet, while the high fat group and the ATRA drug intervention group were administered a high fat diet. After 12 weeks, the blood lipid levels of rabbits, the morphological structure of the arterial wall, the arterial intimal permeability, the activity of blood endothelial nitric oxide synthase (eNOS) and the level of plasma NO were investigated. Western blot analysis was used to detect the levels of ET‑1, eNOS and eNOS phosphorylation at Ser‑1177 (p‑eNOS), and a radioimmunoassay was performed to detect the level of ET‑1 in the plasma. It was identified that plaque formation was alleviated in the ATRA group compared with the high fat group, as revealed by hematoxylin and eosin and oil red O staining, and a similar trend was reflected in the immunofluorescence results for endothelial permeability. Western blotting demonstrated significantly decreased ET‑1 expression levels in the arterial tissue of rabbits in the ATRA group compared with the high fat group, together with increased p‑eNOS level (P<0.05), however, no difference was observed in the expression of eNOS (P>0.05). The trends observed for ET‑1 and the activity of eNOS in plasma were similar to those for arterial tissue. Therefore, the present study demonstrated that ATRA may regulate the grade of AS by the reduction of ET‑1 secretion and increased NO formation via increased phosphorylation of eNOS. ATRA provides a potential novel method for the treatment of atherosclerosis.