PSEN1 and Alzheimer disease: Furthermore, studies have revealed that intraperitoneal injection with tirptolide improved spatial memory deficits in APP/PS1 models of AD, involving inhibition of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) (Wang et al., 2014), and inhibition of inflammatory responses and mitogen-activated protein kinase (MAPK)s activity (Cui et al., 2016).