NOS3 and Hypertension: For example, 4-hydroxy-3,5-dimethoxybenzoic acid (syringic acid) has increased endothelial nitric oxide synthase expression and NO levels in cultured human endothelial cells (54, 55), whereas 3,4-dihydroxyphenylpropionic acid (dihydrocaffeic acid) and 4-hydroxy-3-methoxybenzoic acid (vanillic acid) levels were associated with improved cardiometabolic health in animal models of hypercholesterolemia (56) and hypertension (57).