GPBAR1 and Parkinson disease: For PD, alteration of secondary BAs is a key finding in patients with Parkinsonism compared with controls.167–169 In addition, TGR5 agonism alleviates the inflammatory neurodegeneration in a mouse model of PD170 and TUDCA, a TGR5 agonist, improves motor symptoms in a mouse model of PD.171 Better methods to more mechanistically study the relationship between bacterial BA modifications and neuroinflammation and neuropathological diseases are necessary to move this field forward.