Indirect mechanisms of DNA strand scission by peroxynitrite.

Peroxynitrite is a highly reactive nitrogen species directly damaging diverse biomolecules in target cells. This is not the case for genomic DNA, as its cleavage is mediated by secondary reactive species produced at the mitochondrial level in a Ca(2+)-dependent reaction in which ubisemiquinone serves as an electron donor. Under these conditions, superoxide is produced in a time-dependent manner for up to 30 min and dismutates readily to H(2)O(2), which can now reach the nucleus and generate DNA strand scission in a reaction of the Fenton type. This chapter provides evidence for this mechanism using the alkaline halo assay, a simple technique for the assessment of DNA strand scission at the single cell level.