Breath acetaldehyde: evidence of acetaldehyde production by oropharynx microflora and by lung microsomes

After alcohol ingestion, acetaldehyde is found in expired air and is thought to originate from blood. However, we found that the ratio of acetaldehyde to ethanol was higher in dead space than in alveolar (end-expiratory) air. This observation suggested production of acetaldehyde in the airways. To study this, we washed the mouth of normal subjects with 10 ml of either saline or 5 mM ethanol. Washings with ethanol produced 5.1 +/- 1.3 nmol/ml of acetaldehyde per minute (vs none with saline). Saline mouth washings incubated with ethanol produced acetaldehyde. This reaction could be prevented by boiling or by microfiltration of the washings suggesting that it was due to microbial enzymes of the oropharynx. We also studied the possibility of pulmonary production of acetaldehyde. Rat lung slices produced 1.32 +/- 0.19 mnol of acetaldehyde/g lung (wet weight)/minute; microsomal production of acetaldehyde was also detected and this was enhanced by chronic ethanol feeding.