GSK3B and Alzheimer disease: There is no report for an in vitro IC50 of the synthetic xanthine propentofylline (PPF, compound 138, Table 15(a)), but studies in the Tg mouse model of AD indicated that PPF exerts a dual effect: reduction of both pathological amyloidogenesis and tau phosphorylation while reducing the ratio of activated versus inactivated GSK-3β [136].