Bacteria Used for the Production of Yogurt Inactivate Carcinogens and Prevent DNA Damage in the Colon of Rats

Abstract

Lactic acid-producing bacteria prevent carcinogen-induced preneoplastic lesions and tumors in rat colon. Because the mechanisms responsible for these protective effects are unknown, two strains of lactic acid bacteria, Lactobacillus delbrueckii ssp. bulgaricus 191R and Streptococcus salivarius ssp. thermophilus CH3, that are used to produce yogurt, were investigated in vitro and in vivo to elucidate their potential to deactivate carcinogens. Using the "Comet assay" to detect genetic damage, we found that L. bulgaricus 191R applied orally to rats could prevent 1, 2-dimethylhydrazine-induced DNA breaks in the colon in vivo, whereas St. thermophilus CH3 were not effective. However, in vitro, both strains prevented DNA damage induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in isolated primary rat colon cells. Extracts prepared from milk fermented with St. thermophilus CH3 were as efficient in deactivating MNNG as was L-cysteine. Isolated metabolites arising from bacteria during fermentation in the colon or in milk [L(+) lactate, D(-) lactate, palmitic acid and isopalmitic acid] were not effective. We postulate that thiol-containing breakdown products of proteins, via catalysis by bacterial proteases, could be one mechanism by which MNNG or other carcinogens are deactivated in the gut lumen resulting in reduced damage to colonic mucosal cells.

Modulatory activity of a Lactobacillus casei strain on 1,2‐dimethylhydrazine‐induced genotoxicity in rats

“…Cells were isolated from the colon with proteinase K as described by Wollowski et al [1999]. The colons were flushed with prewarmed RPMI 1640 medium, filled with the digestion solution (50 U/ml proteinase K in RPMI 1640), and incubated at 378C for 30 min.…”

Inhibitory Effect of Yogurt on Aberrant Crypt Foci Formation in the Rat Colon and Colorectal Tumorigenesis in RasH2 Mice

“…Beneficial bacterial strains include Lactobacillus acidophilus [11], L. casei [15], Bifidobacterium longum [37], B. infantis [16] and some other lactic acid bacteria. Two bacterial species, L. bulgaricus and Streptococcus thermophilus, are used as a starter culture for the fermentation of milk to make yogurt, and various reports regarding the antitumor effects of these two lactic acid bacteria have been published: the anti-mutagenic activity of yogurt [4], the protective effect of L. bulgaricus against DNA damage [12,42,44], and the preventive role of yogurt against colon cancer [7,36]. Of note, Shackeford et al reported that drinking milk fermented by L. bulgaricus and S. thermophilus altered the metabolism of DMH and shifted the colon tumor distribution toward the anus [36].…”

“…There are abundant reports on the beneficial effects of yogurt on human health [1], and many investigators have suggested that the consumption of fermented dairy products, including yogurt, elicits anti-tumor effects [12,42,44]. However, the reported anti-tumor effects of yogurt are inconsistent, and these inconsistencies may have arisen from the different bacterial strains and culture conditions and different experimental protocols used in the studies -Original- [36,42].…”

Analysis of DNA Damage Using the Comet Assay in Infants Fed Cow’s Milk

“…It is reported that tea decreases mammary and colon tumor induction, and milk potentiates these inhibiting effects [20]. Dairy products and milk were also reported to inhibit tumor growth [21] and particularly yoghurt inactivates carcinogens and prevents DNA damage [22]. Cow's milk was also suggested in older infants for its anticarcinogenic effects [23].…”