ANTIGENOTOXIC PROPERTIES OF LACTIC-ACID BACTERIA IN-VIVO IN THE GASTROINTESTINAL-TRACT OF RATS

In view of the high incidence of dietary-related tumors, one important research goal is to identify the participating genotoxic carcinogens and the nutritional factors that may counteract their activities. We t herefore have further developed a method to assess DNA damage in tumor target tissues of the gastrointestinal tract. Subsequently the preven tion of this inducible DNA damage by lactic acid bacteria and by milk products fermented with probiotics was studied as well. The microgel e lectrophoresis technique was applied to cells of the esophageal, gastr ic, duodenal, and colonic mucosa. Cells were grouped according to thei r degree of DNA damage, the simplest measure of which is to discrimina te between those with damage (comets) and those without damage. When t hese cells were isolated from animals treated with a genotoxic carcino gen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and exposed to MNNG for 1-24 hours, it was possible to follow the course of genotoxicity t hroughout the gastrointestinal tract. After the animals were treated w ith the lactic acid bacteria under study, it was possible to detect an tigenotoxic properties as well. The gavage of 10(10) viable Lactobacil lus casei cells in 10 ml of 0.9% NaCl per kilogram body weight immedia tely before the oral administration of MNNG (5 mg/kg body wt) resulted in a reduction of induced DNA damage in gastric and colonic mucosa ce lls. A sequential treatment schedule was even more effective: when the animals were treated orally with lactic acid bacteria or yogurt (10 m l/kg body wt) in the morning followed by MNNG (7.5 mg/kg body wt) eigh t hours later and the colon cells were isolated 16 hours later, the pe rcentages of cells remaining intact were distinctly higher in the comb ination groups (68 +/- 10 and 68 +/- 19 for L. casei and a ''Bio '' yo gurt, respectively) than in the group receiving only MNNG (45 +/- 17). The effect of heating L. casei was studied and was found to yield les s clear-cut effects in preventing genotoxicity. The method is an effic ient tool to elucidate antigenotoxic properties of food components in vivo in those target tissues actually afflicted by dietary-related tum ors.