Dyshomeostasis of transition metals
iron and
copper as well as accumulation of oxidative DNA damage have been implicated in multitude of human
neurodegenerative diseases, including
Alzheimer disease and
Parkinson disease. These metals oxidize
DNA bases by generating
reactive oxygen species. Most oxidized bases in mammalian genomes are repaired via the base excision repair pathway, initiated with one of four major
DNA glycosylases: NTH1 or OGG1 (of the Nth family) or NEIL1 or NEIL2 (of the Nei family). Here we show that Fe(II/III) and Cu(II) at physiological levels bind to NEIL1 and NEIL2 to alter their secondary structure and strongly inhibit repair of mutagenic
5-hydroxyuracil, a common
cytosine oxidation product, both in vitro and in
neuroblastoma (SH-SY5Y)
cell extract by affecting the base excision and
AP lyase activities of NEILs. The specificity of
iron/
copper inhibition of NEILs is indicated by a lack of similar inhibition of OGG1, which also indicated that the inhibition is due to
metal binding to the
enzymes and not
DNA. Fluorescence and surface plasmon resonance studies show submicromolar binding of
copper/
iron to NEILs but not OGG1. Furthermore, Fe(II) inhibits the interaction of NEIL1 with downstream base excision repair
proteins DNA polymerase beta and
flap endonuclease-1 by 4-6-fold. These results indicate that
iron/
copper overload in the
neurodegenerative diseases could act as a double-edged sword by both increasing oxidative genome damage and preventing their repair. Interestingly, specific
chelators, including the natural chemopreventive compound
curcumin, reverse the inhibition of NEILs both in vitro and in cells, suggesting their therapeutic potential.