Monoamine oxidase (MAO) A and B are mitochondrial enzymes involved in the o
xidative deamination of endogenous and exogenous amines. At present, the pr
oduction of H2O2 by MAO in intact cells and its functional consequences in
cell function have not been extensively investigated. The aim of this study
was to define whether, in intact cells, the metabolism of small amounts of
MAO substrates was able to induce a detectable H2O2 production. Hydrogen p
eroxide production was measured using a luminol-amplified chemiluminescence
assay in three cell types, rat mesangial cells, rabbit proximal tubule cel
ls and Hep-G2 cells, containing different MAO A/MAO B ratios. Our results s
howed that cell incubation with tyramine (50 mu mol/l) led to a time-depend
ent H2O2 generation which was fully inhibited by MAO A (clorgyline and RO 4
1-1049) and MAO B (selegiline and RO 19-6327) inhibitors. The extent of inh
ibition of H2O2 production by selective inhibitors was in agreement with th
e amount of MAO isoforms expressed in each cell type, as determined by West
ern blot analysis and enzyme assay. Altogether, these findings show that, i
n a normal cell environment, MAO can be a source of reactive oxygen species
which could have a functional impact on cell functions. In addition, we pr
opose the luminol-amplified chemiluminescence assay as a rapid and sensitiv
e procedure to characterize the monoamine oxidase isoforms and their regula
tion in intact cells.