PPIF and Alzheimer disease: The main aim of the present study was (i) to determine the kinetic parameters of the interaction between 17β-HSD10 and cypD in vitro using the SPR biosensor method and (ii) to estimate the levels of 17β-HSD10–cypD complexes formed in vivo either in brain mitochondria isolated from Tg rat model of AD or in CSF samples of AD patients in order to clarify changes occurring in brain mitochondria of individuals with AD in more detail and to evaluate CSF levels of 17β-HSD10–cypD complexes as a promising diagnostic biomarker of AD.