Breath Acetaldehyde: Evidence of Acetaldehyde Production by Oropharynx Microflora and by Lung Microsomes

Abstract

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.

Ethanol in expired air is commonly used as an indicator of blood ethanol concentration. Acetaldehyde--a product of ethanol oxidation--is also found in expired air. Breath acetaldehyde has been assumed to reflect blood acetaldehyde (Freund and O’Hollaren, 1965; Fukui, 1969) and it has also been used to monitor changes in blood concentrations (Zeiner et al., 1979). However, it is possible that there is a local production of acetaldehyde in the airways. Ethanol is continuously excreted in saliva when present in blood. Moreover, some bacteria and all yeasts, which are common inhabitants of the mouth and airways could oxidize ethanol to acetaldehyde by alcohol dehydrogenase or by alcohol oxidase systems (Davis et al., 1973). Moreover, though lung does not contain significant alcohol dehydrogenase activity, generation of acetaldehyde by microsomal ethanol oxidation, particularly after chronic alcohol consumption, has not been assessed. This study was conducted to determine whether breath acetaldehyde is derived exclusively from the blood or whether there are alternative sources.