IN-VITRO ACETALDEHYDE FORMATION BY HUMAN COLONIC BACTERIA

Incubation of human colonic contents with various ethanol concentratio ns (2.75-44 mM) in vitro at 37 degrees C resulted in significant accum ulation of acetaldehyde - a toxic and highly reactive compound, At pH 9.6, all samples produced notable acetaldehyde concentrations (58 (13) mu M; mean (SEM)) even from the lowest (2.75 mM) ethanol concentratio n, and the production of acetaldehyde increased linearly with rising e thanol concentration (r=0.97; p<0.005), reaching a peak concentration of 238 (37) mu M at 44 mM ethanol. The formation of acetaldehyde took place rapidly, as almost 50% of acetaldehyde formed during the total e ight hour incubation was detectable after one hour, and 75% of the tot al after four hours. Maximal acetaldehyde production from 22 mM ethano l occurred at pH 9.6 (160 (35) mu M) but appreciable concentrations we re also seen at pH 7.4 (110 (38) mu M) and pH 6.0 (63 (19) mu M). At p H 4.0, by contrast, acetaldehyde formation was negligible (17 (5) mu M ). 4-Methylpyrazole, a potent inhibitor of alcohol dehydrogenase, show ed a decreasing effect on acetaldehyde production in vitro but first a t a concentration of 100 mM. Considerable acetaldehyde production by h uman colonic bacteria - if it occurs also in vivo - could constitute a risk factor for rectal cancer in heavy drinkers and also provide a pa thogenetic mechanism for alcohol induced diarrhoea.