LACTOBACILLUS-MEDIATED AND BIFIDOBACTERIUM-MEDIATED ANTIGENOTOXICITY IN THE COLON OF RATS

Lactic acid bacteria (LAB) are proposed to have several beneficial eff ects, including the inactivation of carcinogens. We have studied the p otential of Lactobacillus acidophilus (from a commercially available y ogurt), Lactobacillus gasseri (P79), Lactobacillus confusus (DSM 20196 ), Streptococcus thermophilus (NCIM 50083), Bifidobacterium breve and Bifidobacterium longum (from human infant stool) to prevent the induct ion of DNA damage by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, 7.5 m g/kg body wt) in colon cells of the rat. Using the new technique of si ngle cell microgel electrophoresis, all investigated strains were anti genotoxic toward MNNG after a single dose of 10(10) viable cell/kg bod y wt p.o. eight hours before the carcinogen One-half and one-tenth of this initial close resulted in a loss of protective activity. High dos es of heat-treated L. acidophilus strains were also not antigenotoxic. One mechanism of the preventive effect could be that bacterial metabo lites or components me responsible. Accordingly, selected examples wer e investigated in vitro in colon cells of the rat. Metabolically activ e L. acidophilus cells, as well as an acetone extract of the culture p revented MNNG-induced DNA damage. Different cell fractions from L. aci dophilus (cytoplasm, cell wall skeleton, cell wall) were devoid of ant igenotoxic activity, whereas the peptidoglycan fraction and whole free ze-dried cells were antigenotoxic. As a second carcinogen, 1,2-dimethy lhydrazine (DMH) was used A dose- and time-response study was first pe rformed to assess the effects of DMH in several segments of the gastro intestinal (GI) tract. Exposure for 16 hours to 15 or 25 mg DMH/kg bod y wt p.o. induced DNA damage in cells of the distal colon of rats, whe reas no cytotoxicity was seen Pretreatment orally with LAB on four con secutive mornings before DMH gavage (8 hours after the last LAB applic ation) revealed that L. acidophilus, L. confusus, L. gasseri, B. longu m, and B., breve inhibited the genotoxic effect of DMH. One of four S. thermophilus and one of three Lactobacillus delbrueckeii ssp. bulgari cus strains were also protective. Heat-treated L. acidophilus did not inhibit DMH-induced genotoxicity. A few aliquots of the colon cells we re processed immunohistochemically for the presence of the ''prolifera tion cell nuclear antigen'' (PCNA). DMH treatment did not increase PCN A, nor was there my modulation by LAB. The effect of L. acidophilus on foreign compound-metabolizing enzymes (Phase I and Phase II) in liver and colon cells of rats revealed only one parameter to be modulated, namely, a two- to three-fold increase in the levels of NADPH-cytochrom e P-450 reductase. The meaning of this finding, in terms of possible c hemoprevention by LAB, remains unclear In conclusion, our studies show that most, but not all, LAB tested could strongly inhibit genotoxicit y in the GI tract of the rat and that viable LAB organisms are require d for the protective effect in vivo. The comet assay technique is a po werful tool to elucidate such in vivo antigenotoxic activities in tumo r target tissues.