MMP2 and Alzheimer disease: Preclinical studies have shown that tanshinone can improve the impaired learning and memory induced by Aβ1-40 in rat models of AD [5], inhibiting AD-induced expression levels of inducible nitric oxide synthase (iNOS) and matrix metalloproteinase II (MMP-2), reducing toxic free radicals, and suppressing oxidative injury in AD rats [6].