Normalization of arterial inflammation inhibits atherosclerosis. The preventive role for protocatechuic acid (PCA) in early-stage atherosclerosis is well recognized; however, its therapeutic role in late-stage atherosclerosis remains unexplored.We investigated whether PCA inhibits vulnerable atherosclerosis progression by normalizing arterial inflammation.Thirty-wk-old male apolipoprotein E-deficient (Apoe-/-) mice with vulnerable atherosclerotic lesions in the brachiocephalic artery were fed the AIN-93G diet alone (control) or supplemented with 0.003% PCA (wt:wt) for 20 wk. Lesion size and composition, IL-1β, and NF-κB in the brachiocephalic arteries, and serum lipid profiles, oxidative status, and proinflammatory cytokines (e.g., IL-1β, monocyte chemoattractant protein-1, and serum amyloid A) were measured. Moreover, the effect of PCA on the inflammation response was evaluated in efferocytic macrophages from C57BL/6J mice.Compared with the control treatment, dietary PCA supplementation significantly reduced lesion size (27.5%; P < 0.05) and also improved lesion stability (P < 0.05) as evidenced by increased thin fibrous cap thickness (31.7%) and collagen accumulation (58.3%), reduced necrotic core size (37.6%) and cellular apoptosis (73.9%), reduced macrophage accumulation (45.1%), and increased vascular smooth muscle cell accumulation (51.5%). Moreover, PCA supplementation inhibited IL-1β expression (53.7%) and NF-κB activation (64.4%) in lesions. However, PCA supplementation did not change serum lipid profiles, total antioxidant capacity, and inflammatory cytokines. In efferocytic macrophages, PCA at 0.5 and 1 μmol/L inhibited Il1b/IL-1β mRNA (27.2-46.5%) and protein (29.2-49.6%) expression and NF-κB activation (67.0-80.3%) by upregulation of MER proto-oncogene tyrosine kinase (MERTK) and inhibition of mitogen-activated protein kinase 3/1 (MAPK3/1). Strikingly, the similar pattern of the MERTK and MAPK3/1 changes in lesional macrophages of mice after PCA intervention in vivo was recapitulated.PCA inhibits vulnerable lesion progression in mice, which might partially be caused by normalization of arterial inflammation by upregulation of MERTK and inhibition of MAPK3/1 in lesional macrophages.
