Propentofylline attenuates tau hyperphosphorylation in Alzheimer's Swedish mutant model Tg2576

Key pathological hallmarks of Alzheimer's disease (AD) are the deposition of amyloid plaques containing Abeta-peptides and the formation of neurofibrillary tangles containing hyperphosphorylated tau. Propentofylline (PPF) is a synthetic xanthine derivative that inhibits phosphodiesterase and adenosine uptake. These effects of PPF influence many cellular functions including stimulating synthesis/release of nerve growth factor. We tested the effects of PPF on disease progression in transgenic mice overexpressing the Swedish mutant human APP (Tg2576). The untreated Tg mice show, together with increased amyloidogenesis, increased levels of tau hyperphosphorylation and increased ratios of the activated to inactivated GSK-3beta, one of the key kinases that can phosphorylate tau. One month of PPF feeding (40 mg/kg per day) reduced the burden of amyloid plaques and the levels of hyperphosphorylated tau and immunoreactive IL-1beta. In parallel with these changes, PPF reduced the activated form of GSK-3beta and increased the inactivated form of GSK-3beta, restoring their ratio almost to normal values. These results demonstrate that PPF can exert multiple protective effects on both amyloidogenesis and tau hyperphosphorylation in an animal model of AD. Our earlier report [Neurochem. Int. 43(3) (2003) 225] demonstrated that Tg2576 animals show decreased levels of mRNA for NGF with increased amyloid burden while feeding of PPF results in a major shift from beta-amyloidogenic to alpha-secretory processing of APP together with increased expression of NGF mRNA. The current new data enlarge our understanding of PPF effects in brain and of tau hyperphosphorylation in Tg animals and are consistent with the hypothesis that GSK-3beta is a nodal point linking amyloid and tau pathology. Therapeutic interventions directed toward multiple pathological processes may be more protective than treatments directed toward a single process. The new results reported here indicate that further testing of PPF as a potential therapy in AD is warranted.