In the “catecholaldehyde hypothesis” of Parkinson’s disease neurodegeneration, cytoplasmic dopamine (DA) is converted to 3,4-dihydroxyphenylacetaldehyde (DOPAL) by the enzyme monoamine oxidase-A (MAO-A). DOPAL is a toxic substance, generating free radicals and inhibiting mitochondrial function. Scientists at NIH wanted to compare the abilities of currently available MAO-A and MAO-B inhibiting drugs at decreasing endogenous DOPAL levels. Using PC12 cells, six drugs were tested for their effects on DOPAL: MAO-A inhibitor clorygyline, three reversible MAO-A inhibitors, and the MAO-B inhibitors selegiline and rasagiline. The Cellometer was used to count the cells throughout experimentation. Clorgyline, rasagiline, and selegiline decreased DOPAL levels in both [...]