GPBAR1 and Alzheimer disease: 2019). Additionally, in disease states and at high concentrations, bile acids can cause breakdown of the BBB (Quinn et al. 2014; Greenwood et al. 1991) Interestingly, TGR5 activation protects the BBB, indicating a potential for bile acids to attenuate their own effect on the BBB in healthy rodents (Liang et al. 2020). As noted in Figure 4, bile acid concentrations were higher in the rat model of AD.