where Alda-1 treatment of SNU-182 cells expressing ALDH2*2 can reduce basal levels of mitochondrial FA. ALDH2 is responsible for the clearance of several toxic, endogenous produced aldehydes, including acetaldehyde, a product of the metabolism of consumed and internally generated ethanol. Alda-1 activates ALDH2*2 activity towards smaller substrates, like acetaldehyde and propionaldehyde, and this present study suggests that clearance of excess formaldehyde could be a benefit of Alda-1 treatment. This situation is particularly important given our recent findings that FA is a 1C epigenetic regulator by modulating cellular levels of the major 1C methyl carrier SAM. Finally, we used MitoRFAP-2 to comparatively profile basal levels of mitochondrial FA across a panel of breast cancer cell lines using flow cytometry. Increases in endogenous mitochondrial FA pools detected by MitoRFAP-2 correlate with high expression levels of the mitochondrial FA-generating enzyme SHMT2 and low expression levels of the mitochondrial FAscavenging enzyme ALDH2. Given that FA is a carcinogen and genotoxin, an emerging signal that regulates epigenetics and 1-C metabolic cycles, and acts as a 1C stock, these data provide a starting point for the use of this reagent to decipher complex contributions of mitochondrial FA to cancer, metabolism and a range of other diseases, and underscore the broader importance of developing chemical tools with improved spatial resolution to unveil new biology.