Interaction of aluminum with PHFτ in Alzheimer's disease neurofibrillary degeneration evidenced by desferrioxamine-assisted chelating autoclave method

To demonstrate that aluminum III (Al) interacts with PHFτ in neurofibrillary degeneration (NFD) of Alzheimer's disease (AD) brain, we developed a 'chelating autoclave method' that allows Al chelation by using trivalent-cationic chelator desferrioxamine. Its application to AD brain sections before Morin histochemistry for Al attenuated the positive fluorescence of neurofibrillary tangles, indicating Al removal from them. This method, applied for immunostaining with phosphorylation-dependent anti- τ antibodies, significantly enhanced the PHFτ immunoreactivity of the NFD. These results suggest that each of the phosphorylated epitopes in PHFτ are partially masked by Al binding. Incubation of AD sections with AlCl₃ before Morin staining revealed Al accumulation with association to neurofibrillary tangles. Such incubation before immunostaining with the phosphorylation- dependent anti-τ antibodies abolished the immunolabeling of the NFD and this abolition was reversed by the Al chelation. These findings indicate cumulative Al binding to and thereby antigenic masking of the phosphorylated epitopes of PHFτ. Al binding was further documented for electrophoretically- resolved PHFτ on immunoblots, indicating direct Al binding to PHFτ. In vitro aggregation by AlCl₃ was observed for PHFτ but was lost on dephosphorylation of PHFτ. Taken together, phosphorylation-dependent and direct PHFτ-Al interaction occurs in the NFD of the AD brain.