[CANCER RESEARCH 53. 3914-3418. September
`
`I. 1
`
`Inhibitory Effect of Bifidobacterium longum on Colon, Mammary,
`Carcinogenesis
`Induced by 2-Amino-3-methylimidazo[4,5-/]quinoline,
`Mutagen1
`
`and Liver
`a Food
`
`Bandaru S. Reddy2 and Abraham Rivenson
`
`Division* of Nutritional Curcitm^t'tit'si.\ ¡ti.S. R.¡anil lixperiftu-nlal
`
`I'atliology ami Toxicology ¡A.R.j. Ameritan Health l-'oitfulanon. Valhalla, New York
`
`ABSTRACT
`
`The inhibitory effect of lyophili/ed cultures of Bifidobacterium longum
`on 2-amino-3-methylimidazo[4,5-/]quinoline
`(IQ)-induced
`carcinogenesis
`was investigated in male and female F344 rats. Beginning at 5 weeks of
`age, male and female rats were divided into various experimental
`groups
`and fed one of the high-fat,
`semipurified
`diets containing
`0 and 0.5%
`lyophilized cultures of li.
`longum with or without 125 ppm IQ in the diet.
`All animals were continued on this regimen until
`the termination of the
`study. All animals were necropsied
`during the 58th week. The results
`indicated that dietary I!, longum significantly
`inhibited the IQ-induced
`incidence
`(percentage of animals with tumors) of colon (100% inhibition)
`and liver (80% inhibition)
`tumors and multiplicity
`(tumors/animal)
`of
`colon,
`liver, and small
`intestinal
`tumors
`in male rats.
`In female
`rats,
`dietary supplementation
`of Bifldohacterium cultures also suppressed the
`IQ-induced mammary carcinogenesis
`to 50% and liver carcinogenesis
`to
`27% of those observed in animals
`fed the control diet, but the differences
`did not reach a statistical
`significance at P < 0.05; however,
`the mammary
`tumor multiplicity (tumors/animal) was significantly
`(/* < 0.05) inhibited
`in female
`rats fed the diet containing Bifidobacterium cultures. These
`findings
`suggest
`that Kifidobacterium supplements
`in the diet inhibit
`IQ-
`induced colon and liver tumors and to a lesser extent mammary tumors in
`K344 rats.
`
`INTRODUCTION
`
`There is a growing consensus on the beneficial aspects of fermented
`dairy products
`such as fermented milk and yogurt and of bacterial
`cultures that ferment
`the dairy products in human and animal nutrition
`(1-4). Epidemiological
`and experimental
`studies provide evidence
`that fermented milk and bacterial cultures that are routinely used to
`ferment
`the milk reduce the risk of certain types of cancer and inhibit
`the growth of certain tumors and tumor cells (1,2, 5-9). An inverse
`relationship
`has been demonstrated
`between the frequency of con
`sumption of yogurt and other
`fermented milk products and breast
`cancer in women (5. 6). There are also indications that fermentation of
`milk may result
`in the production of inhibitors of carcinogenesis
`(10).
`Several
`investigations
`revealed that dietary intake of
`fermented
`milk containing lactic bacteria altered the intestinal microecology of
`the host. Consumption
`of fermented milk containing Lactobacillus
`acidophilus
`has been shown to reduce significantly
`the counts of
`fecal putrefactive bacteria such as coliforms and increased the levels
`of lactobacilli
`in the intestine (2, 11) suggesting that supplemental
`L. acidophilus
`has a beneficial
`effect on the intestinal microeclogy
`by suppressing
`the putrefactive
`organisms
`that are presumably
`in
`volved in the production
`of tumor promoters
`and putative precar-
`cinogens. Goldin et al. (12) demonstrated
`that supplemental L. aci-
`dopliiltis
`cultures
`to healthy
`subjects
`consuming
`a western
`diet
`significantly decreased the metabolic activity of certain classes of in-
`
`Received 3/19/93; accepted 6/21/93.
`The costs of publication of this article were defrayed in part by the payment of page
`charges. This article must
`therefore be hereby marked athvriisemeni
`in accordance with
`18 U.S.C. Section 1734 solely to indicate this fact.
`Institute.
`1 Supported by USPHS Grant CA 17613 from Ihe National Cancer
`2 To whom requests
`for reprints should be addressed,
`at the Division of Nutritional
`Carcinogcnesis. American Health Foundation.
`1 Dana Road. Valhalla. NY 10595.
`
`as indicated by fecal bacterial ß-glucuronidase
`testinal microflora
`activities.
`and nitroreductase
`that fermented milk and certain bac
`Several
`recent studies suggest
`terial cultures
`that are used to ferment
`the dairy products possess
`antimutagenic
`and anticarcinogenic
`properties (10). Bodana and Rao
`(13) demonstrated
`antimutagenic
`properties of milk fermented with
`Lactobacillus
`bulgaricus and Streptococcus
`thermophilus
`using Sal
`monella l\pliimiiriuin strains TA 100 and TA 98 suggesting the pro
`duction of antimutagenic
`compounds during the fermentation of milk.
`A recent study by Zhang and Ohta (14) indicated that the cells of lactic
`acid bacteria including L. acidophilus
`and Bifidobacterium bifitliun
`bind various fried-food mutagens thereby suppressing the mutagenic-
`ity of these compounds by removing them from the intestine.
`It has
`also been demonstrated
`that certain lactobacilli degrade the carcino
`gens such as dimethylnitrosanine
`and diphenylnitrosamine
`(15). With
`regard to anticancer properties of Lactobacillus
`sp., several
`studies
`demonstrate
`that
`feeding of fermented milk or cultures containing
`L. acidophilus
`and Lactobacillus
`bulgaricus
`and/or Lactobacillus
`casei
`inhibited Ehrlich ascites tumor cell growth or suppressed the
`growth of Sarcoma 180 in mice (7, 16, 17). Goldin and Gorbach (9)
`showed that dietary supplements
`of L. acidophilus
`not only sup
`pressed the incidence of 1,2-dimethylhydrazine-induced
`colon car
`cinogenesis but
`increased the latency period. Shackelford et al. (8)
`demonstrated
`that
`the survival
`rate of rats fed fermented milk was
`higher than that of the animals fed the nonfermented milk. There are
`studies to suggest
`that cultures (tÃ(cid:173)Kifidobacterium longum increase the
`host's
`immune
`response
`(18). These studies
`indicate that cultured
`
`by
`tumorigenesis
`dairy products or cultures of lactic bacteria inhibit
`enhancing the host's
`immune response,
`suppressing
`the growth of
`
`intestinal microflora incriminated in generating putative carcinogen(s)
`and promoters, binding potential carcinogens,
`and/or producing anti-
`tumorigenic or antimutagenic
`compounds
`in the colon.
`The formation of mutagens upon broiling fish and meat was first
`discovered by Sugimura et al. ( 19). IO, a heterocyclic aromatic amine
`produced from food pyrolysis, was first
`isolated from broiled fish
`(20). Subsequently,
`it was isolated from a variety of broiled or cooked
`fish and meat (21, 22). IQ is a strong mutagen in S. tvphimurium and
`also induces mutations
`in Chinese hamster
`lung cells and hepatocel-
`lular carcinomas
`in rodents and nonhuman primates
`(23, 24). Other
`cooked food mutagens, which are heterocyclic
`aromatic
`amines,
`include IQ,1 2-amino-3,8-dimethylimidazo[4,5-/]quinoxaline.
`2-ami-
`no-3,4-dimethylimidazo[4,5-/]quinoline.
`and
`2-amino-l-methyl-6-
`phenylimidazo[4.5-i>]pyridine.
`They demonstrate
`a multitarget orga-
`nospecificity with specific cancer
`induction in Zymbal gland, skin,
`colon, oral cavity, and mammary gland of rodents (23). The precursors
`of IQ-type heterocyclic amines are creatinine, amino acids, and sugars
`in meat and fish (25). It has been shown that IQ requires metabolic
`activation by liver microsomes
`for conversion to its ultimate carcin
`ogen (26) and forms high levels of DNA adducts
`in a number of
`organs (27). Although it is not clear whether these heterocyclic amines
`
`1The abbreviations
`
`used are: 10. 2-amino-3-methylimida/o(4.5-/|quinoline;
`
`3914
`
`
`
`Genome Ex. 1040
`Page 1 of 5
`
`

`

`CANCER INHIBITION BY DIETARY B. LONGUM CULTURES
`
`it is certain that these
`may contribute to human cancer development,
`compounds
`are present
`in cooked foods and pose a credible risk to
`humans.
`Because IQ induces colon and mammary tumors in male and female
`rats,
`respectively,
`and bacterial
`cultures
`that
`ferment milk possess
`anticarcinogenic
`properties,
`the possibility exists that these bacterial
`cultures may prevent
`IQ-induced
`carcinogenesis. Accordingly,
`the
`present study was designed to investigate the efficacy of cultures of B.
`languiti, a lactic bacteria indigenous
`to human intestine, on IQ-in
`duced carcinogenesis
`in male and female F344 rats fed the high-fat
`diet. The rationale for the high-fat content of the experimental diet was
`to simulate a western-style diet. It is hoped that the results generated
`from this study provide a rationale for additional studies to elucidate
`the mechanism(s) of action of Bifidobacterium cultures in inhibiting
`carcinogenesis.
`
`MATERIALS AND METHODS
`
`Animals, Diets, and Carcinogen. A total of 156 weanling male and female
`F344 rats obtained from Charles River Breeding Laboratories
`(Kingston, NY)
`were quarantined for 10 days and then housed in plastic cages with wood chip
`bedding and filter tops in an animal holding room under controlled environ
`mental conditions of a 12-h light-dark cycle, 50% humidity, and 22°Ctem
`perature. This study was conducted within (he guidelines
`of our
`Institute's
`
`Animal Care and Use Committee. They were all randomly assigned by weight
`into 2 treatment groups (male.
`IQ-fed, 60; female,
`IQ-fed. 60; male, without
`IO. 18; female, without
`IQ, 18). Lyophilized B. longitm (BB-536) cultures were
`kindly provided by Morinaga Milk Industry Co., Ltd. (Zama City, Japan). B.
`longum was cultured in a medium containing glucose, peptone, yeast extract,
`and salts. The cells were harvested by centrifugation
`and washed using a saline
`solution. After being mixed with a cryoprotectant
`solution containing sodium
`glutamate
`and sucrose,
`the cells were lyophilized. Each g of lyophilized ma
`terial contained about 2 X 10"'
`live bacterial cells. IQ (CAS 76180-96-6) was
`
`(Downsview, Ontario, Canada).
`purchased from Toronto Research Chemicals
`A high-fat semipurified
`diet was used throughout
`the study (28). All
`ingredi
`ents of semipurified
`diet were obtained from Dyets,
`Inc. (Bethlehem, PA). A
`high-fat control
`(modified AIN-76A) diet with or without
`IQ and the experi
`mental diets with or without
`IQ but containing
`0.5% lyophilized B. longum
`cultures were prepared in our laboratory once weekly and stored in a cold room
`in air-tight plastic containers
`filled with N2 (Table 1). The amount of IQ added
`to the diets was 125 ppm.
`Experimental Procedure. At 5 weeks of age, male and female animals
`were divided at random into various experimental
`groups and fed one of the
`high-fat diets containing 0 and 0.5% B. longum with or without
`IQ in the diet
`(Table 1). All animals were fed the control and experimental
`diets until
`the
`termination
`of the experiment. Animals were weighed weekly until
`they at
`tained 16 weeks of age and then every 4-6 weeks until
`the termination of the
`study. Female animals were palpated for mammary
`tumors every 2 weeks,
`beginning 8 weeks on experimental
`diets. As scheduled,
`the experiment was
`terminated 58 weeks after the start of experimental
`diets.
`including the
`All animals were sacrificed by CO;, euthanasia. All organs
`intestine,
`liver, and mammary glands were examined grossly under the dissec-
`
`in
`embedded
`tion microscope. They were fixed in 10% buffered formalin,
`paraffin blocks, and processed by routine histológica! methods with the use of
`hematoxylin
`and eosin stains. The histological
`criteria used for
`tumors of
`intestine,
`liver, and mammary gland were as described previously (28, 29).
`The data were analyzed statistically
`by the \2 test and Fisher's
`exact
`test
`(tumor
`incidence)
`and by Student's
`; test (body weights and tumor multiplic
`
`ity). Analyses were carried out on a VAX 11/750 computer
`package.
`
`using the SAS
`
`RESULTS
`
`The body weights of male and female animals fed the control and
`Bifidobacterium diets containing IQ were comparable throughout
`the
`study (Table 2). In groups that were not given IQ, body weights of
`male and female animals fed the control diet were similar to those fed
`the Bifidobacterium diet
`in their respective gender. As expected,
`IQ-
`fed animals weighed less than those that were not fed IQ in all dietary
`groups during the course of the study.
`small
`colon,
`IQ-induced
`Table 3 summarizes
`the incidences of
`intestine,
`liver, and mammary gland tumors. There was no evidence of
`tumors in animals that were not fed IQ. In the present
`investigation,
`IQ-induced
`tumors of colon,
`small
`intestine,
`and mammary gland
`were all adenocarcinomas. The tumors of the small intestine and colon
`were well-differentiated
`adenocarcinomas
`that
`invaded the submu-
`cosal and muscular
`layers. Liver tumors were hepatocellular
`carcino
`mas. Dietary supplementation
`of B. longum resulted in a significant
`inhibition of colon, small intestine, and liver tumor incidences in male
`rats (P < 0.05). In female rats, dietary supplementation
`of B. longum
`also decreased the mammary carcinogenesis
`to 50% and liver car
`cinogenesis
`to 27% of those observed in animals fed the control diet,
`but the differences did not reach a statistical significance (P > 0.05).
`It is noteworthy that the incidence of liver tumors was lower in female
`rats as compared to their male counterparts
`irrespective of dietary
`treatment. Also, none of the female rats developed IQ-induced colon
`and small
`intestinal
`tumors.
`The data summarized in Table 4 show that colon tumor multiplicity
`(tumors/animal
`and tumors/tumor-bearing
`animal) followed the same
`pattern as tumor
`incidence
`summarized
`in Table 3. Although
`the
`effects of dietary Bifidobacterium on small
`intestinal
`tumor incidence
`in male rats and on mammary tumor incidence in female rats did not
`reach a statistical significance (Table 3), it significantly suppressed the
`multiplicity (tumors/animal)
`of small
`intestinal and mammary gland
`tumors in their respective gender
`(Table 4); dietary Bifidobacterium,
`however, had no significant
`effect when small
`intestinal and mam
`mary tumor data were expressed as tumors/tumor-bearing
`animal.
`
`DISCUSSION
`
`composition of expérimentaidiets
`
`the results of the present study indicated sex
`It is interesting that
`differences
`in the susceptibility of liver and intestines
`to IQ-induced
`carcinogenesis
`in F344 rats. IQ-induced liver tumors were lower
`in
`female rats compared to male animals in both dietary groups;
`inter
`estingly, none of the female animals developed colon and small
`in
`diet'723.500.3523.5232.408.305.904.111.180.240.5
`diet"23.500.3523.5232.908.305.904.111.180.24IIHigh-fatexperimental
`testinal
`tumors. Our previous
`studies also demonstrated
`lower
`inci
`dence of 3,2'-dimethyl-4-aminobiphenyl-induced
`colon and small
`
`Table 1 Percentage
`
`
`
`DietingredientsCaseinm.-MethionineCorn
`
`oilCorn
`starchDextroseAlphacelMineral
`
`Mix,AINVitamin
`
`
`Mix. AINrevisedCholine
`hitartrateB.
`longum (lyophilized)High-fatcontrol
`" This high-fat diet was formulated on the basis of the American Institute of Nutrition
`(AIN) standard reference diet with the modification of varying sources of carbohydrate
`(28).
`1 b
`
`Lyophilized B. longum was added at the expense of starch.
`
`tumors in female F344 rats compared to their male coun
`intestinal
`terparts (30). Although the precise mechanism of sex differences in the
`susceptibility
`of
`liver and intestine
`to IQ and other heterocyclic
`amines remains to be elucidated,
`it is possible that male and female
`rats metabolize IQ differently that might explain the organospecificity
`of IQ in male and female animals.
`The purpose of the current study was to investigate the efficacy of
`dietary B. longum cultures on IQ-induced tumorigenesis
`in male and
`female F344 rats. The results of this study are of considerable interest
`3915
`
`
`
`Genome Ex. 1040
`Page 2 of 5
`
`

`

`wk"Dietary
`
`regimenMale
`
`ratsControl
`
`diet + 10(30)''0.5%
`
`BL diet + 10(30)Control
`diet
`(9)0.5%
`
`BL diet(9)Female
`
`
`
`bodywt(wkO)113
`
`±f>c-d114
`
`±6115
`
`±7''116
`
`
`
`±1291
`
`CANCER INHIBITION BY DIETARY S. LONGUM CULTURES
`
`Table 2 Body weights of male and female F344 rats
`Body wl (g) on experimental diets at
`
`±14rf253
`
`
`±12261
`
`±12''256
`
`
`
`±15161
`
`±28d380
`
`±21396
`±21
`'394
`
`±27203
`
`±37rf459
`
`
`±30482
`±2<)c482
`±36234
`
`
`±44d460
`
`
`±50495
`±39
`'520
`
`±48250
`
`±33''466
`
`±40519
`±44'524
`
`±38272
`
`±5*91
`±
`590
`
`±9«-94
`
`ratsControl
`±Sd159
`
`±13d197
`
`diet + 10
`(30)0.5%
`±9161
`
`BL diet + 10(30)Control
`
`±12206
`±9'164
`±10"210
`
`diet(9)0.5%BL
`±916380
`±84252
`diet (9)Initial
`±1732461
`" At 5 weeks of age, groups of male and female rats were fed the control diets with or without 10 and with or without
`as week 0.
`in parentheses, number of animals.
`h Numbers
`* Mean ±SD.
`</.c Differences among the dietary subgroups
`
`in IQ-fed and in non-IQ-fed animals are not significant, P > 0.05.
`
`±16''228
`±16242
`
`
`±17''237
`
`±23d278
`
`±25286
`
`±22'292
`±2048464
`±2456468
`±24
`lyophilized B. longum cultures (BL). This period is denoted
`
`±22rf254
`
`±24261
`
`±19''278
`
`Table 3 Effect of dietary B. longum on IQ-induced intestinal,
`
`liver, and mammary carcinogenesis
`
`in F344 rats
`
`incidence
`Tumor
`(% of animals with tumors)
`
`intestine20(6)
`
`50(15)rf37(11)
`
`3(1)00Intestine"40(12)3m"00Mammary
`
`DietaryregimenMale
`
`rats (30)*
`Control diet
`0.5%BLdiel'Female
`
`rats (30)
`Control diet
`27(8)Colon23(7)(1
`0.5% BL dietLiver80(24)*
`intestine.
`a Intestine represents colon and small
`'' Numbers
`in parentheses, number of animals.
`'' BL diet, control diet containing 0.5% lyophilized B. languiti cultures.
`'' Significantly different
`from its respective control diet group in the same gender, P < 0.05.
`
`0Small
`
`gland027(8)
`
`13(4)
`
`long
`this is the first report showing that
`because to our knowledge,
`term administration
`of cultures of B. longum, a human lactic bacte
`rium, can effectively reduce the tumorigenesis
`induced by IQ, a het-
`erocyclic
`amine produced from broiling or frying of meat or fish.
`There are no previous
`reports on the tumor
`inhibitory properties of
`dietary B. longum in laboratory animal models. Our results demon
`strated that lyophilized cultures of B. longum administered in the diet
`not only inhibited completely the colon (100%) and small
`intestinal
`tumors (80%) but also suppressed the liver tumorigenesis
`(38%)
`in
`male F344 rats. Although the inhibitory effect of Bifidobacterium
`cultures on the incidence of IQ-induced mammary carcinogenesis
`in
`female rats was not found to be significant at P < 0.05,
`the tumor
`multiplicity, expressed as tumors/animal, was significantly suppressed
`in female rats fed the Bifidobacterium diet suggesting an inhibitory
`effect of these bacterial
`cultures
`in mammary carcinogenesis. The
`reason for the insignificant effect oÃ(cid:173)Bifidobacterium cultures on small
`intestinal
`tumor incidence in males and mammary tumor incidence in
`females may, in part, be due to low overall
`incidence of IQ-induced
`tumors in these organs.
`
`A number of animal model studies have already demonstrated that
`dietary L. acidopliilus,
`a lactic acid-producing
`bacterium;
`cultured
`dairy products; and milk fermented with L. acidopliiliis
`inhibit 1,2-
`dimethylhydrazine-induced
`colon carcinogenesis
`in rats and prolifer
`ation of Ehrlich ascites tumor cells in mice (1, 9, 16, 17). The results
`of present
`study, which indicate that
`the lyophilized cultures of B.
`longum, a lactic acid-producing bacterium indigenous to human colon,
`administered
`in the diet
`inhibit
`liver, colon, and mammary carcino
`genesis, provide further evidence for tumor-inhibitory
`properties of
`lactic cultures and fermented dairy products.
`While the mechanism of inhibition of colon and mammary carcino
`genesis by dietary B. longum has not been elucidated,
`it is likely that
`the effect of lactic bacteria can proceed through diverse mechanism
`including the alteration of physiological
`conditions
`in the colon af
`fecting the metabolic
`activity of intestinal microflora,
`the action of
`bile acids, and to quantitative and/or qualitative alterations
`in the bile
`acid-degrading
`bacteria. The species of lactobacilli
`and bifidobacte-
`rium, most often suggested as beneficial dietary supplements, have all
`been reported to exert antagonistic
`actions
`toward several entero-
`
`Tablc 4 Effect of tlictarv B. longum on IQ-induct'd intestinal and mammary tumor multiplicity in F'344 rats
`
`Intestine
`
`Mammary gland
`
`intestineTumors/animal0.23
`
`
`
`DietaryregimenMale
`
`tumors13
`
`rats
`Control diet
`
`0.5% BLdietFemale
`
`rats
`Control
`0.5% BL dietTotal
`" TBA,
`tumor-bearing
`* Mean ±SD.
`'' Significantly different
`
`±0.89*
`±0.89
`Oc00Totaltumors7 100Small
`Oc00TumorsATBA"1.86
`000ColonTumors/animal0.43
`
`±0.5
`0.03 ±0.18C0
`
`±0.4
`1.0 ±0(1
`
`0145Tumors/animal000.46
`
`01.75
`
`0Tumors/TBA1.16
`animals; BL diet, control diet containing 0.5% lyophilized B. longum cultures.
`
`0Tola!tumors0
`
`from its respective control diet
`
`in the same gender, P < 0.05.
`
`±0.80
`±0.46
`0.16 ±0.46 <'Tumorsn~BA0
`1.25 ±0.5
`
`3916
`
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`
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`Page 3 of 5
`
`

`

`CANCER INHIBITION BY DIETARY B. LONGUM CULTURES
`
`microflora should provide a stimulus
`investigate the mechanism of colon,
`bition by the cultures of B. longum.
`
`studies to
`to design additional
`liver, and mammary tumor inhi
`
`ACKNOWLEDGMENTS
`
`for
`We thank Donna Virgil for preparation of the manuscript, Aliga Cesar
`expert
`technical assistance and Morinaga Milk Industry Company Ltd., Japan,
`for providing lyophilized B. longum (BB-536).
`
`REFERENCES
`1.
`
`coli and
`in the intestine such as Escherichia
`pathogenic organisms
`Clostridium perfringens,
`to cite a few (31-34). C. perfringens
`and
`other enteropathogenic
`anaerobic bacteria contain high levels of 7a-
`dehydroxylase which is an important enzyme in the formation of the
`secondary bile acids from the primary bile acids in the colon (35, 36).
`These secondary bile acids have been shown to play a role as tumor
`promoters
`in the colon (36). Hill et al.
`(35) showed a correlation
`between the incidence of colon cancer and the number of bacteria per
`g of feces possessing 7a-dehydroxylase
`enzyme activity in the hu
`mans. In view of above results,
`it is possible that dietary lactic cultures
`modulate the metabolic
`activity of intestinal microflora and the ac
`tivity of 7a-dehydroxylase
`thereby producing lower levels of second
`ary bile acids in the colon. Goldin and Gorbach (37) observed that
`supplementation of normal diet of rats with L. acidophilus
`lowered the
`activity of fecal bacterial ß-glucuronidase, nitroreductase,
`and azore-
`ductase. The significance
`of these bacterial enzymes
`including the
`7a-dehydroxylase
`activity should be considered in the light of their
`importance in the etiology of certain types of cancer including cancer
`of the colon (38). It was also demonstrated
`that lactic acid, a major
`metabolite produced by lactic bacteria in yogurt and other fermented
`milk products, and fresh unfermented milk products had no inhibitory
`effect on Ehrlich ascites tumor cells in mice whereas
`the lactic fer
`mented milk had an effect (39). In this connection, Ayebo et al. (IO)
`reported that this antitumorgenic
`activity of fermented milk is located
`in the cell wall fraction of lactic bacteria. Thus, dietary B.
`longum
`cultures and associated physiological
`alterations in the intestine could
`act at one or more of these loci and cause inhibition of IQ-induced
`carcinogenesis.
`Another possible mechanism that should to be considered is the
`metabolic
`activation of
`IQ in the intestine. Heterocyclic
`aromatic
`amines such as IQ,
`like many carcinogens, must be metabolized in
`order to exert their carcinogenicity. The predominant pathway for the
`metabolic
`activation
`of most carcinogenic
`heterocyclic
`amines
`is
`through the initial activation step involving TV-oxidation and is cata
`lyzed predominantly by cytochrome P4501A2 in the liver (40). IQ is
`also converted to the N-glucuronide,
`a minor metabolite, but
`to a
`considerable extent
`to the 5-hydroxy derivative, excreted via bile into
`the intestinal
`tract as glucuronide
`conjugate (41, 42). The bacterial
`enzyme, ß-glucuronidase, has the ability to hydrolyze many glucu-
`ronides due to its wide substrate specificity and thus may liberate
`aglycones in the colon. It is possible that glucuronide conjugates of IQ
`metabolites
`are hydrolyzed
`in the intestine by bacterial
`enzyme,
`ß-glucuronidase, to active metabolites
`and that
`these active com
`pounds are absorbed and distributed to various target organs including
`the colon and mammary gland. In this connection, Goldin et a!. (9, 12)
`have demonstrated
`that
`the addition of viable lactic bacilli supple
`ments to the diets of humans and rats decreased the fecal bacterial
`ß-glucuronidase activity.
`It
`is therefore possible that a similar de
`crease in the ß-glucuronidase activity in the colon due to B. longum,
`a lactic bacillus, may result
`in the decreased production of active
`metabolites of IQ in the colon and delivery of these metabolites
`to the
`colon and to the mammary gland via the blood stream. Another
`possible mechanism of tumor
`inhibition by B.
`longum may be ex
`plained on the basis that the bacterial cultures bind IQ and other food
`mutagens in the intestine and eliminate them in the feces (14), thereby
`reducing the amount available for reabsorption.
`that dietary
`In conclusion,
`the results of this study demonstrate
`lyophilized cultures of B. longum, a lactic bacillus present
`in human
`colon,
`inhibit IQ-induced intestinal,
`liver, and mammary carcinogen
`esis in F344 rats. Although the exact mechanisms by which the cul
`tures of B.
`longum inhibit
`IQ-induced carcinogenesis
`in the target
`organs are not understood at present,
`the results of earlier studies on
`the metabolic
`activation of IQ and metabolic
`activity of intestinal
`
`in gastrointestinal
`
`and therapeutic
`
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