Regressive Effects of Various Chemopreventive Agents on Azoxymethane-induced Aberrant Crypt Foci in the Rat Colon

Regressive effects of four chemopreventive agents [5-hydroxy-4-(2-phenyl-( E )-ethenyl)-2(5 H fura-none (KYN-54), S-methyl metbanethiosulfonate (MMTS), chlorogenic acid (CA), and piroxicam] on azoxymethane (AOM)-induced aberrant crypt foci (ACF) in the colon of male F344 rats were examined by dietary exposure. At six weeks of age, 60 rats of groups 1 through 5 received subcutaneous injections of AOM (15 mg/kg body weight) once a week for three weeks. Twelve weeks after the first carcinogen injection, wben the occurrence of ACF was maximal, the rats in groups 2 through 5 were started on diet containing the test chemicals as follows: group 2, KYN-54 (0.02%); group 3, MMTS (0.01%); group 4, CA (0.025%); and group 5, piroxicam (0.0125%). Group 1 (20 rats) was kept on the basal diet alone, and group 6 (12 rate) served as an untreated control. Rats in each group were killed at 6, 12, 18, or 24 weeks after the start of the experiment, and the yield of ACF in the colon of each group at 18 or 24 weeks was compared with that at 12 weeks. The number of ACF per rat colon of each group at 18 or 24 weeks was smaller than that at 12 weeks. The reduction rates at 18 weeks were 7% in group 1 (AOM alone), 11% in group 2 (AOM+KYN-54), 10% in group 3 (AOM+MMTS), 51% in group 4 (AOM + CA) ( P 0.01), and 33% in group 5 (AOM+piroxicam) ( P <0.02), while at 24 weeks they were 12%, 26%, 51% ( P <0.002), 43% ( P <0.05), and 70% ( P <0.001), respectively. These results indicate that chemopreventive agents for large bowel carcinogenesis, i.e., KYN-54, MMTS, CA, and piroxicam, are not only able to prevent the development of ACF, but also can regress ACF, which are regarded as precursor lesions of colorectal cancer.     

Dietary Conjugated Linolenic Acid Inhibits Azoxymethane-induced Colonic Aberrant Crypt Foci in Rats

The modifying effects of dietary feeding of conjugated linolenic acid (CLN) isolated from the seeds of bitter gourd ( Momordica charantia ) on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were investigated in male F344 rats to predict its possible cancer chemopreventive efficacy. The effect of CLN on the proliferating cell nuclear antigen (PCNA) index in colonic ACF was also examined. Rats were given subcutaneous injections of AOM (20 mg/ kg body weight) once a week for 2 weeks to induce ACF. They also received the experimental diet containing 0.01%, 0.1% or 1% CLN for 5 weeks, starting one week before the first dosing of AOM. AOM exposure produced a substantial number of ACF (108±21/rat) at the end of the study (week 4). Dietary administration of CLN caused a significant reduction in the frequency of ACF: 87±14 (19.4% reduction, P <0.05) at a dose of 0.01%, 69±28 (36.1% reduction, P <0.01) at a dose of 0.1% and 40±d6 (63.0% reduction, P <0.001) at a dose of 1%. Also, CLN administration lowered the PCNA index and induced apoptosis in ACF. These findings might suggest possible chemopreventive activity of CLN in the early phase of colon tumorigenesis through modulation of cryptal cell proliferation activity and/or apoptosis.     

Increased Cell Proliferation of Azoxymethane-induced Aberrant Crypt Foci of Rat Colon

Aberrant crypt foci (ACF) were induced in the colon of F344 rats by s.c. injection of azoxymethane (AOM) twice in a three day-interval and examined after 4 and 12 weeks. The number and crypt multiplicity of ACF in each section of rat colon increased during this period. Histologically, aberrant crypts consisted of proliferating atypical epithelial cells. Cell proliferation of ACF consisting of 4 aberrant crypts [ACF(4)] and 2 aberrant crypts [ACF(2)], and normal crypts in the colon of rats treated with AOM [normal crypts/AOM(+)] or saline [normal crypts/AOM(-)] was investigated by measurement of the mitotic index, proliferating cell nuclear antigen-labeling index (PCNA-LI), and 5-bromo-2'-deoxyuridine-labeling index (BrdU-LI). All three parameters of the cell proliferative activity of ACF(4) were higher than those of normal crypts/AOM(+) and normal crypts/AOM(-). The PCNA-LI and BrdU-LI in ACF(2) were the same as those in ACF(4). These findings suggest that ACF have increased cell proliferative activity. The correlation of these three parameters confirmed that the PCNA-LI is also a useful parameter for evaluating cell proliferative activity in ACF. The presence of many cells stained by PCNA in the upper portion of ACF suggested that ACF have more G₁ phase cells, which readily respond to mitogenic stimulation, than G₀ phase cells, which are predominant in normal crypts.     

Suppressing Effects of 6-(2,5-Dichlorophenyl)-2,4-diamino-1,3,5-triazine and Related Synthetic Compounds on Azoxymethane-induced Aberrant Crypt Foci in Rat Colon

The modifying effects of dietary administration of 6-(2,5-dichlorophenyl)-2,4-diamino-1,3,5-triazine and 5 related compounds on the occurrence of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were investigated in rats. Male F344 rats were given s.c. injections of AOM (15 mg/kg body weight) once a week for 3 weeks to induce ACF. They also received the diet containing 200 ppm test compound for 5 weeks, starting one week before the first dosing of AOM. At the termination of experiment, all of the compounds had caused a significant reduction in ACF frequency, which might be associated with suppression of the expression of proliferation biomarkers. The apoptotic index in the colonic mucosal epithelium of rats killed at 6 h after the first AOM exposure revealed no blocking activity of the compounds.     

Relationship between the Nature of Mucus and Crypt Multiplicity in Aberrant Crypt Foci in the Rat Colon

Aberrant crypt foci (ACF)induced in the distal colon of F344 male rats, 4, 8, 12 and 35 weeks after the first administration of 1, 2-dimethylhydrazine-2HCl (DMH) were examined to determine whether a correlation exists between the nature of goblet cell mucin and the number of crypts (crypt multiplicity) comprising the ACF. According to the ACF score calculated from the results of the qualitative observation of sulfomucins (SuMs) and sialomucins (SiMs), the ACF in the 4th week showed a weak correlation between the nature of the mucus and crypt multiplicity, and the ACF of each class showed similar mucous profiles. From the 8th week, a significant difference ( P <0.01) was recognized between the ACF consisting of 3 crypts or less and those consisting of 4 crypts or more. The proportion of crypts with SiM predominance showed a decrease in the 8th.week in the ACF consisting of 1 crypt and in the 12th week in the ACF consisting of 2 or 3 crypts, implying a recovery tendency. The ACF consisting of more than 4 crypts showed little change over time, retaining the tendency of SiM predominance. Ulex europaeus agglutinin-I (UEA-I) lectin-positive crypts appeared in the ACF. This finding was significantly more prominent ( P < 0.001) in the ACF with SiM predominance than in the ACF with SuM predominance at each experimental period, and in the 12th week after the first administration of DMH, the incidence of ACF with UEA-I-reactive mucin was decreased in the ACF groups consisting of 3 crypts or less, compared with the ACF groups consisting of 4 or more crypts.These results suggest that the biological quality of mucus in ACF consisting of 4 or more crypts is different from that in ACF consisting of 3 crypts or less. This difference should be considered when ACF are used as an intermediate biomarker of colon cancer.     

Development of Aberrant Crypt Foci Involves a Fission Mechanism as Revealed by Isolation of Aberrant Crypts

Morphological analysis of isolated colonic crypts in rats, postnatally, indicated that the crypts reproduce themselves by a fission mechanism, the division beginning at the crypt base and proceeding upwards until there are two separate crypts. Occasionally, before the separation is complete, a second fission process starts on one or both sides of a bifurcating crypt and a triple-branched or quadruple-branched crypt results. Analysis of isolated aberrant crypt foci (ACF) in rats treated with 1,2-dimethylhydrazine revealed that the development of ACF consisting of multiple crypts is also due to a fission mechanism. Initially, an indentation appears at the base of a single ACF crypt, with subsequent formation of a bifurcation and eventual crypt division.     

Suppressive Effect of Pioglitazone,a PPAR Gamma Ligand,on Azoxymethane-induced Colon Aberrant Crypt Foci in KK-Ay Mice

Obesity is an established risk factor for colorectal cancer. Pioglitazone is a peroxisome proliferatoractivatedreceptorγ (PPARγ) agonist that induces differentiation in adipocytes and induces growth arrestand/or apoptosis in vitro in several cancer cell lines. In the present study, we investigated the effect ofpioglitazone on the development of azoxymethane-induced colon aberrant crypt foci (ACF) in KK-Ayobesity and diabetes model mice, and tried to clarify mechanisms by which the PPARγ ligand inhibitsACF development. Administration of 800 ppm pioglitazone reduced the number of colon ACF / mouseto 30% of those in untreated mice and improved hypertrophic changes of adipocytes in KK-Ay mice withsignificant reduction of serum triglyceride and insulin levels. Moreover, mRNA levels of adipocytokines,such as leptin, monocyte chemoattractant protein-1 and plasminogen activator inhibitor-1, in the visceralfat were decreased. PCNA immunohistochemistry revealed that pioglitazone treatment suppressed cellproliferation in the colorectal epithelium with elevation of p27 and p53 gene expression. These results suggestthat pioglitazone prevented obesity-associated colon carcinogenesis through improvement of dysregulatedadipocytokine levels and high serum levels of triglyceride and insulin, and increase of p27 and p53 mRNAlevels in the colorectal mucosa. These data indicate that pioglitazone warrants attention as a potentialchemopreventive agent against obesity-associated colorectal cancer.     

Chemoprevention of Azoxymethane-induced Rat Colon Carcinogenesis by a Xanthine Oxidase Inhibitor, 1'-Acetoxychavicol Acetate

In our studies to find natural compounds with chemopreventive efficacy in foods, using azoxymethane (AOM)-induced colonic aberrant crypt foci and colonic mucosal cell proliferation as biomarkers, a x an thine oxidase inhibitor, 1′-acetoxychavicol acetate (ACA), present in the edible plant Languas galanga from Thailand was found to be effective. This study was conducted to test the ability of ACA to inhibit AOM-induced colon tumorigenesis when it was fed to rats during the initiation or post-initiation phase. Male F344 rats were given three weekly s.c. injections of AOM (15mg/kg body weight) to induce colonic neoplasms. They were fed diet containing 100 or 500 ppm ACA for 4 weeks, starting one week before the first dosing of AOM (the initiation feeding). The other groups were fed the ACA diet for 34 weeks, starting one week after the last AOM injection (the post-initiation feeding). At the termination of the study (week 38), AOM had induced 71% incidence of colonic adenocarcinoma (12/17 rats). The initiation feeding with ACA caused significant reduction in the incidence of colon carcinoma (54% inhibition by 100 ppm ACA feeding and 77% inhibition by 500 ppm ACA feeding, P=0.03 and P=0.001, respectively). The post-initiation feeding with ACA also suppressed the incidence of colonic carcinoma (45% inhibition by 100 ppm ACA feeding and 93% inhibition by 500 ppm ACA feeding, P=0.06 and P=0.00003, respectively). Such inhibition was dose-dependent and was associated with suppression of proliferation biomarkers, such as ornithine decarboxylase activity in the colonic mucosa, and blood and colonic mucosal polyamine contents. ACA also elevated the activities of phase II enzymes, glutathione S-transferase (GST) and quinone reductase (QR), in the liver and colon. These results indicate that ACA could inhibit the development of AOM-induced colon tumorigenesis through its suppression of cell proliferation in the colonic mucosa and its induction of GST and QR. The results confirm our previous finding that ACA feeding effectively suppressed the development of colonic aberrant crypt foci. These findings suggest possible chemopreventive ability of ACA against colon tumorigenesis.     

Induction of Aberrant Crypt Foci and Flat-type Adenocarcinoma in the Colons of Dogs by N-Ethyl-N'-nitro-N-nitrosoguanidine and Their Sequential Changes

Sequential endoscopic observation of dog colons was performed during colon carcinogenesis. Two beagle dogs were given suppositories containing N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) every day for five months. In month 3, aberrant crypt foci (ACF), a putative preneoplastic lesion, were found in the colons of both dogs, but not in an untreated dog. The frequency of ACF increased until month 10, and then decreased. In month 9, very small lesions, less than 1 mm in diameter, which were similar to human early flat tumors, were first noticed. One of these lesions grew to about 7 mm in size without a change in its shape for 10 months. There were more than ten flat-type tumors in the two dogs, but such lesions were not found in the untreated dog. By biopsy, two of the lesions were proved to be well-differentiated adenocarcinomas histologically. Four polypoid lesions were found in one of the carcinogen-treated dogs. Thus, flat-type adenocarcinomas were induced in the dog colon by ENNG, and their development was followed by magnifying endoscopy.     

Development and Distribution of 2-Amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP)-induced Aberrant Crypt Foci in the Rat Large Intestine

Aberrant crypt foci (ACF) are generally considered to be preneoplastic lesions for colon cancer. To assess their induction by 2-amino-1-methyl-6-phenylimidazo[4,5- b ]pyridine (PhIP), a colon carcinogen, we performed a sequential study of ACF morphology and localization. F344 male rats were given PhIP, and methylene blue-stained colon epithelium and isolated crypts were analyzed at weeks 12, 25, 50, and 75. Each crypt was classified into 2 groups, "single" with round bottoms and "bifurcating" displaying V-shaped clefts (indicating proliferation). In combination with the number of crypts in an ACF, this classification was a good indicator for the generation of ACF in line with the fission mechanism of growth. Increasing numbers of crypts in ACF through weeks 12 to 75 and decreased percentages of ACF with bifurcating crypts at the late time points indicated that proliferation of crypts occurs predominantly during the early stages. The distribution pattern showed a significant shift ( P < 0.000005) from the distal to the proximal part of the large intestine between weeks 25 and 50. Adenocarcinomas were first found to develop at week 50 in the ascending colon and cecum where bifurcating crypts were generally lacking at weeks 12 and 25. These data suggest the existence of (1) proliferating ACF which contains bifurcating crypt(s) and (2) quiescent or senescent ACF which consists of only single crypts.     

Induction of Aberrant Crypt Foci in the Large Intestine of F344 Rats by Oral Administration of 2-Amino-l-methyl-6-phenylimidazo[4,5-b]pyridine

Carcinogenicity of 2-amino-l-methyl-6-phenylimidazo[4,5- b ]pyridine (PhIP) to rat colon was investigated using the appearance of colonic aberrant crypt (AC), a preneoplastic lesion, as a marker. The number of AC foci per colon at experimental week 4 was 1.3 ± 0.8; almost half the level of AC foci induced by 2-amino-6-methyIdipyrido[l,2- a :3',2'- d ]imidazole (Glu-P-1), which is a known colon carcinogen. No ACs were observed in rats of the control group. A repeat experiment showed that induction of AC foci by PhIP administration was reproducible and a significant increase in the number of AC foci, 3.0 ±0.0, was observed after 12 weeks of PhIP administration. The majority of ACs induced by PhIP were localized in the distal part of the colon. The distribution was similar to those induced by Glu-P-1 and 1,2-dimethylhydrazine. Those data suggested that PhIP is possibly carcinogenic to rat colon.     

Troglitazone, a Ligand for Peroxisome Proliferator-activated Receptor γ Inhibits Chemically-induced Aberrant Crypt Foci in Rats

The biological roles of peroxisome proliferator-activated receptors (PPARs) in various diseases, including inflammation and cancer, have been highlighted recently. Although PPARγ ligand is suspected to play an important role in carcinogenesis, its effects on colon tumorigenesis remain undetermined. The present tune-course study was conducted to investigate possible modifying effects of a PPARγ ligand, troglitazone, on the development and growth of aberrant crypt foci (ACF), putative precursor lesions for colon carcinoma, induced by azoxymethane (AOM) or dextran sodium sulfate (DSS) in male F344 rats. Oral troglitazone (10 or 30 mg/kg body weight (b.w.)) significantly reduced AOM (two weekly subcutaneous injections, 20 mg/kg b.w.)-induced ACF. Treatment with troglitazone increased apoptosis and decreased polyamine content and ornithine decarboxylase (ODC) activity in the colonic mucosa of rats treated with AOM. Gastric gavage of troglitazone also inhibited colitis and ACF induced by DSS (1% in drinking water), in conjunction with increased apoptosis and reduced colonic mucosal polyamine level and ODC activity. Our results suggest that troglitazone, a synthetic PPARγ ligand, can inhibit the early stage of colon tumorigenesis with or without colitis.     

Dietary Cardamom Inhibits the Formation of Azoxymethaneinduced Aberrant Crypt Foci in Mice and Reduces COX-2 and iNOS Expression in the Colon

Recently, considerable attention has been focused on identifying naturally occurring chemopreventive compounds ‍capable of inhibiting, retarding, or reversing the multi-step carcinogenesis. The primary aim of the present study ‍was to identify the effects of a commonly consumed spice, viz., cardamom against azoxymethane (AOM) induced ‍colonic aberrant crypt foci (ACF) in Swiss Albino mice. The secondary aim, was to explore the ability of cardamom ‍to modulate the status of proliferation and apoptosis, and to understand its role in altering cyclooxygenase-2 (COX- ‍2) and inducible nitric oxide synthase (iNOS) expression. Male Swiss albino mice were injected with AOM (dose: ‍5mg/Kg body weight) or saline (Group 1) weekly once for two weeks. The AOM-injected mice were randomly assigned ‍to two groups (Groups 2 and 3). While all the groups were on standard lab chow, Group 3 received oral doses of ‍0.5% cardamom, in aqueous suspension, daily for 8 weeks. Following treatment, significant reduction in the incidences ‍of aberrant crypt foci (p<0.05) was observed. This reduction in ACF was accompanied by suppression of cell ‍proliferation (mean Brdu LI in carcinogen control=13.91+3.31, and 0.5%cardamom=2.723+0.830) and induction of ‍apoptosis (mean AI in carcinogen control=1.547+0.42 and 0.5% cardamom= 6.61+0.55). Moreover, reduction of ‍both COX-2 and iNOS expression was also observed. These results suggest that aqueous suspensions of cardamom ‍have protective effects on experimentally induced colon carcinogenesis. Cardamom as a whole and its active ‍components require further attention if the use of this spice is to be recommended for cancer prevention.     

Suppression of Azoxymethane-induced Colonic Premalignant Lesion Formation by Coenzyme Q10 in Rats

Reactive oxygen species cause damage to proteins, lipids and DNA. Coenzyme Q10 (CoQ10) is a compound withmitochondrial bioenergetic functions. The reduced form of CoQ10 shows antioxidant activity. In the present study,effects of CoQ10 on development of azoxymethane (AOM)-induced aberrant crypt foci (ACF) and mucin-depletedfoci (MDF) in F344 male rats were investigated. To induce ACF and MDF, 6-week old rats were given two weeklysubcutaneous injections of AOM (15 mg/kg body weight) and also received a control diet or experimental dietscontaining CoQ10 (200 or 500 ppm) for 4 weeks, starting one day before the first dose of AOM. At 10 weeks of age,all animals were sacrificed and their colons were evaluated for numbers and sizes of ACF and MDF. Administrationof 200 and 500 ppm CoQ10 resulted in reduction of ACF numbers, to 77% and 68% of the carcinogen control value,respectively. The percentages of ACF consisting of more than 4 crypts in these groups were also significantly lowerthan in the controls. Treatment with 500 ppm CoQ10 furthermore decreased the number of sialomucin-producingACF and MDF per colon to 42% and 38% of the carcinogen control value without CoQ10, respectively. Theseresults suggest that CoQ10 may be an effective chemopreventive agent against colon carcinogenesis.     

Inhibition of Azoxymethane-induced Colon Carcinogenesis in Rat by Green Tea Polyphenol Fraction

The effect of green tea polyphenol fraction (GTP) on azoxymethane(AOM)-induced colon carcino-genesis was investigated in male Fischer rate. The rats were given AOM (7.4 mg/kg body weight) s.c. once a week for 10 weeks. A week after the treatment, they were divided into three groups: AOM-control (26 rats), AOM-GTP1 (26 rats) and AOM-GTP2 (25 rats). AOM-GTPl and AOM-GTP2 groups respectively received 0.01 and 0.1% GTP in drinking water from week 11 to 26. AOM-control group received tap water throughout this experiment. Autopsy on week 26 showed that tumor incidence and average numbers of tumors per rat in the AOM-GTPl and AOM-GTP2 groups were significantly lower than those of the AOM-control group: 38.1% and 47.6% versus 77.3%; 0.6 and 0.7 versus 1.5. Thus, it was concluded that GTP inhibited the development of AOM-indnced colon carcinogenesis. The inhibition by GTP did not show significant dose dependence.     

Inhibition of Azoxymethane-induced Colorectal Aberrant Crypt Foci in Mice Fed a High-fat Diet by Pleurotus eryngii (Eringi) and Hypsizygus marmoreus (Bunashimeji)

Obesity markedly increases the risk of colorectal cancer. Recently, the preventive effects of edible mushroomson triglyceride elevation and visceral fat accumulation have been reported. Here, the effects of Pleurotus eryngii(Eringi) and Hypsizygus marmoreus (Bunashimeji) on azoxymethane (AOM)-induced aberrant crypt foci (ACF;precancerous lesions) in the colorectums of mice fed a high-fat diet were examined. Eringi (ER) and Bunashimeji(BU) mushroom powder samples were used. Six-week-old male C57BL/6J mice received an intraperitonealinjection of AOM (10 mg/kg) once a week for two weeks, and were sacrificed and dissected at 6 weeks after thestart of the experiment. After the initiation of the experiment, they received a normal diet (ND), high-fat diet(HFD), HFD + ER (1 or 5% of diet), or HFD + BU (1 or 5% of diet). As a result, body and fat weights weresignificantly lower in the 5% ER and BU groups than in the HFD group. Liver triglyceride levels were alsosignificantly lower in the 5% ER and BU groups. Total liver cholesterol levels were significantly lower in the5% ER group. The numbers of ACF (especially large ACF) showed strong inhibitory effects in both ER and BUgroups. Measurement of the cell proliferation marker Ki-67 labeling index in the colonic mucosa demonstratedmore significant suppression in both ER and BU groups than in the HFD group. These results suggest that thesimultaneous intake of ER and BU may inhibit colorectal tumorigenesis in HFD-fed mice.     

Dietary Aloe Vera Gel Powder and Extract Inhibit AzoxymethaneinducedColorectal Aberrant Crypt Foci in Mice Fed a Highfat Diet

Aloe vera gel exhibits protective effects against insulin resistance as well as lipid-lowering and anti-diabeticeffects. The anti-diabetic compounds in this gel were identified as Aloe-sterols. Aloe vera gel extract (AVGE)containing Aloe-sterols has recently been produced using a new procedure. We previously reported that AVGEreduced large-sized intestinal polyps in Apc-deficient Min mice fed a high fat diet (HFD), suggesting that Aloevera gel may protect against colorectal cancer. In the present study, we examined the effects of Aloe vera gelpowder (AVGP) and AVGE on azoxymethane-induced colorectal preneoplastic aberrant crypt foci (ACF) in micefed a HFD. Male C57BL/6J mice were given a normal diet (ND), HFD, HFD containing 0.5% carboxymethylcellulose solution, which was used as a solvent for AVGE (HFDC), HFD containing 3% or 1% AVGP, and HFDCcontaining 0.0125% (H-) or 0.00375% (L-) AVGE. The number of ACF was significantly lower in mice given3% AVGP and H-AVGE than in those given HFD or HFDC alone. Moreover, 3% AVGP, H-AVGE and L-AVGEsignificantly decreased the mean Ki-67 labeling index, assessed as a measure of cell proliferation in the colonicmucosa. In addition, hepatic phase II enzyme glutathione S-transferase mRNA levels were higher in the H-AVGEgroup than in the HFDC group. These results suggest that both AVGP and AVGE may have chemopreventiveeffects on colorectal carcinogenesis under the HFD condition. Furthermore, the concentration of Aloe-sterolswas similar between 3% AVGP and H-AVGE, suggesting that Aloe-sterols were the main active ingredients inthis experiment.     

Effects of Apple Pectin on Fecal Bacterial Enzymes in Azoxymethane-induced Rat Colon Carcinogenesis

Because of the potential significance of colonic bacteria in colon carcinogenesis, we investigated the effect of pectin of different types on fecal bacterial enzymes (β-glucuronidase, β-glucosidase and tryptophanase) at various periods of time after feeding rats with pectin-containing diets during azoxymethane-induced colon carcinogenesis. The diet supplemented with 20% apple pectin or 20% citrus pectin decreased the multiplicity of colon tumors, and the number of tumors was significantly decreased in the group fed apple pectin. The incidence of colon tumors in the apple pectin group was lower than that in the control group. The mean tumor size was similar among the three groups. Apple pectin feeding decreased fecal β-glucosidase and tryptophanase levels. Furthermore, a significant decrease in the activity of β-glucuronidase was observed in the apple pectin group during the initiation phase. These findings suggest that the protective effect of pectin on colon carcinogenesis may be dependent on the type of pectin and be related to the decrease of β-glucuronidase activity in the initiation stage of carcinogenesis.     

Inhibition by Dietary Benzylselenocyanate of Hepatocarcinogenesis Induced by Azoxymethane in Fischer 344 Rats1

The effect of dietary benzylselenocyanate (BSC), a novel organoselenium compound and its sulfur analog, benzylthiocyanate (BTC), on hepatocarcinogenesis induced by azoxymethane (AOM) was investigated in male F344 rats. Eighty-one weanling rats were divided into 3 groups and were raised on a semipurificd diet (control diet). Starting from 5 weeks of age, groups of animals consuming the control diet were fed one of the experimental diets containing 25 ppm BSC or BTC. An additional group was continued on the control diet. At 7 weeks of age, animals were given weekly sc injections of AOM (15 mg/kg body weight once weekly for 2 weeks). One week after the second AOM injection, those groups receiving BSC and BTC diets were transferred to the control diet and continued on this diet until termination of the experiment at 34 weeks after the last AOM injection. For quantitative analysis of enzyme-altered liver cell foci, glutathione S-transferase placental form was stained by an immunohistochemical technique. The results indicate that the incidence and the density of the enzyme-altered foci were significantly lower in AOM-treated rats fed the diet containing 25 ppm BSC (foci incidence 56%, foci density 2.43/cm²) than in AOM-treated animals fed the control diet (foci incidence 92%, foci density 4.79/cm²). The incidence of small altered foci was significantly inhibited in rats fed the BTC diet (35%) as compared to those fed the control diet (68%), but the degree of inhibition was more pronounced in animals fed the BSC diet than in those fed the BTC diet.