Allicin suppresses atherosclerosis by up-regulating protein S-nitrosylation

Objective: To investigate the effect of allicin on the development of atherosclerosis in apoE^-/- mice and explore its underlying mechanism from the perspective of protein S-nitrosylation. Methods: Thirty male apoE^-/- mice were randomly divided into 3 groups: control group (saline, ig), low-dose group (allicin, 9 mg/kg·d, ig) and high-dose group (allicin, 18 mg/kg·d, ig). They were fed with high cholesterol diet for 12 weeks. The levels of plasma lipids, oxidized-LDL (ox-LDL), malondialdehyde, tumor necrosis factor-alpha and nitric oxide (NO) were measured. The atherosclerotic lesions in aortic root were evaluated after hematoxylin and eosin staining and elastica van Gieson and immunohistochemical staining, respectively. Furthermore, in vitro experiments were performed using human umbilical vein endothelial cells (HUVECs). The HUVECs were treated with allicin (10 μmol/L or 20 μmol/L) for 24 hours in the presence of ox-LDL (50 μg/mL). The level of NO in supernatant was measured by a nitrate/nitrite assay. The protein S-nitrosylation of the HUVECs was detected through immunofluorescence. Results: The histological analysis revealed that allicin treatment not only significantly decreased the areas of the atherosclerotic lesion (all P<0.05) but also suppressed the macrophage accumulation and smooth muscle cell proliferation in the lesion. There was no significant difference in the levels of plasma lipids between control and treated groups. However, allicin exerted obvious anti-oxidative and anti-inflammatory effects. Interestingly, the allicin treatment led to marked increase of the plasma NO level (P<0.05) and aortic protein S-nitrosylation. The experiments in vitro further proved that the allicin up-regulated the levels of NO and protein S-nitrosylation in HUVECs treated with ox-LDL (P<0.01). Conclusion: Allicin can inhibit the development of atherosclerosis. The mechanism is associated with the up-regulation of protein S-nitrosylation in endothelial cells, which plays an important role in anti-oxidization and anti-inflammation.