Aluminum access to the brain: a role for transferrin and its receptor

The toxicity of aluminum in plant and animal cell biology is well established, although poorly understood. Several recent studies have identified aluminum as a potential, although highly controversial, contributory factor in the pathology of Alzheimer disease, amyotrophic lateral sclerosis, and dialysis dementia. For example, aluminum has been found in high concentrations in senile plaques and neurofibrillary tangles, which occur in the brains of subjects with Alzheimer disease. However, a mechanism for the entry of aluminum (Al3+) into the cells of the central nervous system (CNS) has yet to be found. Here we describe a possible route of entry for aluminum into the cells of the CNS via the same high-affinity receptor-ligand system that has been postulated for iron (Fe3+) delivery to neurons and glial cells. These results suggest that aluminum is able to gain access to the central nervous system under normal physiological conditions. Furthermore, these data suggest that the interaction between transferrin and its receptor may function as a general metal ion regulatory system in the CNS, extending beyond its postulated role in iron regulation.