Inverted U-Shaped Dose-Response Curve of the Anti-Atherosclerotic Effect of Protocatechuic Acid in Both Male and Female C57BL/6J Mice.

Dietary protocatechuic acid (PCA) inhibits atherosclerosis development in male ApoE-/- mice. However, its anti-atherosclerotic property in genetically unmodified (wild-type) male or female mice remains unknown.Five-week-old C57BL/6J mice (half males and females) were divided into negative (fed a chow diet), positive (fed an atherogenic diet), or 5, 25, 50, 100, or 200 mg/kg BW/d of PCA (fed an atherogenic diet) groups. Oral gavage with PCA between 25-100 mg/kg BW/d for 25 weeks significantly attenuated atherogenic diet-induced plaque formation in a dose-dependent manner, whereas the anti-atherosclerotic efficiency of 200 mg/kg BW/d of PCA was comparable with that of 50 mg/kg BW/d. PCA did not affect serum lipids (total triglyceride, total cholesterol, HDL cholesterol), pro-inflammatory cytokines (tumor necrosis factor alpha, IL-1b, IL-6), oxidized LDL, and total antioxidant capacity, and acetylcholine or sodium nitroprusside-induced aortic relaxation. Instead, PCA (≥25 mg/kg BW/d) reduced macrophage accumulation and content of tumor necrosis factor alpha, superoxide, and 4-hydroxynonenal within plaques, and inhibited monocyte adhesion to aortic endothelium in both male and female mice.PCA inhibits early atherosclerosis formation in both male and female C57BL/6J mice with a "U-shaped" dose-response relationship, possibly by reducing inflammation burden and oxidative stress within atherosclerotic plaques.