Experimental Colorectal Carcinogenesis Research Articles

Euterpe edulis pulp products and your effect on liver and kidney of in vivo model of colorectal cancer: Histopathological analysis / Produtos da polpa de Euterpe edulis e seus efeitos no fígado e nos rins em modelo in vivo de câncer colorretal: Análise histopatológica

The objective was to report the injuries on liver and kidney promoted by experimental colorectal carcinogenesis induction in rats and evaluate the effect of supplementation with Euterpe edulis M. pulp products on resolution of this injuries. Colorectal carcinogenesis with 1,2-dimethylhydrazine was induced in young male rats, allocated into: C - induced to carcinogenesis; CJ - induced to carcinogenesis and supplemented with juçara fruit pulp; and CE - induced to carcinogenesis and supplemented with juçara fruit lyophilized extract. Nine animals were a negative control. Supplementation occurred three times a week, totaling 54 days of administration with 1 mg of cyanidin-3-glycoside per kilogram live weight. The hepatic and renal histopathological injuries were assessed at 10 and 23 weeks. In liver, at 10-week biliary hyperplasia was more evident in colorectal cancer induced groups compared to N group (p = 0.0230), as well as megalocytosis (p = 0.0269), and juçara fruit-based product do not promote cytoprotection. At 23-week biliary hyperplasia continued present, and liver necrosis was evident in C group and CJ group. Hepatic degeneration was greater in C group, and megalocytosis was evident in the cancer-induced groups, without cytoprotection by juçara fruit-based product. In kidney, at 23-week, renal congestion was more evident in CJ group, and tubular degeneration in C and CE groups. Important hepatic and renal injuries were observed in rats induced to colorectal cancer and the supplementation with juçara fruit-based product, in the dose used, did not interfere in the prevention and resolution of these injuries, mainly with the chronic use.

Administration of Metabiotics Extracted From Probiotic Lactobacillus rhamnosus MD 14 Inhibit Experimental Colorectal Carcinogenesis by Targeting Wnt/β-Catenin Pathway.

Background and Objective: The cellular microenvironment, diet, and lifestyle play a key role in the occurrence of colorectal cancer. Due to its rising trend, attempts are being made to devise novel biointerventions as adjunct to conventional therapies to prevent this deadly disease. “Metabiotics,” the beneficial metabolic signatures of probiotics are emerging as potential anticancer agent due to their ability to alter metabolic processes in the gut lumen and reduce the severity of colon carcinogenesis. Although beneficial attributes of metabiotics have been elucidated in vitro, yet their anticancer mechanism in vivo needs to be explored. Thus, the present study was performed to envisage anticancer potential of metabiotic extract obtained from indigenous probiotic, Lactobacillus rhamnosus MD 14, in early experimental colon carcinogenesis.Materials and Methods: Sprague–Dawley rats were daily administered with low, medium, and high dose of metabiotic extract orally along with a single dose of weekly intraperitoneal injection of 1,2-dimethylhydrazine up to 6 weeks and monitored for the markers of early colon carcinogenesis.Results: It was observed that the medium dose of metabiotic extract attenuated early colon carcinogenesis by reducing fecal procarcinogenic enzymes, oxidants, aberrant crypt foci, vis-à-vis downregulating oncogenes [K-ras, β-catenin, Cox-2, nuclear factor kappa B (NF-κB)] and upregulating tumor suppressor p53 gene leading to almost normal colon histology.Conclusions: It can be suggested that metabiotics modulate experimental colorectal cancer and could be used as a promising alternative of probiotics, particularly in immunocompromised individuals.

Isolation, characterization and identification of antigenotoxic and anticancerous indigenous probiotics and their prophylactic potential in experimental colon carcinogenesis

Colorectal cancer, the third most commonly diagnosed cancer, is a lifestyle disease where diet and gut microbiome contribute intricately in its initiation and progression. Prophylactic bio-interventions mainly probiotics offer an alternate approach towards reducing or delaying its progression. Therefore, the present study was designed wherein a robust protocol for the isolation, characterization, and identification of indigenous probiotics having antigenotoxic and anticancerous activity was followed along with their prophylactic potential assessment in early experimental colorectal carcinogenesis. Among forty-six isolated lactic acid bacterial strains, only three were selected on the basis of antigenotoxicity against N,N-Dimethyl dihydrazine dihydrochloride and 4-Nitroquinoline 1-oxide and probiotic attributes. All three selected probiotic strains exhibited anticancerous potential as is evident by the reduced Aberrant Crypt Foci, reduced fecal pH, enhanced fecal lactic acid bacteria and altered fecal enzymes (β-glucuronidase, nitroreductase, β-glucosidase) that modulated gut microbiota and microenvironment resulting into restored histoarchitecture of the colon. The results are a clear indicator of the prophylactic potential of selected indigenous probiotics which may be used as an alternative prophylactic biological therapy against colon carcinogenesis particularly in highly susceptible individuals.

Triticum aestivum Sprouts Extract Inhibits Azoymethane (AOM)/Dextran Sodium Sulfate (DSS)-Induced Colon Carcinogenesis in Mice

Chronic intestinal inflammation is critical risk factor of colorectal cancer. Triticum aestivum sprouts have been reported to provide a number of health benefits and used as a dietary supplement. In this study, the authors investigated the regulatory effects of T. aestivum sprouts ethanol extract (TAEE) on experimental colorectal carcinogenesis in an azoxymethane (AOM)/dextran sulfate sodium (DSS)-induced mouse model. Oral administration of TAEE significantly attenuated crypt destruction and tumor formation in AOM/DSS-treated mice. Levels of inflammatory mediators involved in colorectal carcinogenesis, that is, tumor necrosis factor-α, interkeukin (IL)-1β, IL-6, cyclooxygenase-2, and inducible nitric oxide synthase, were lower in the colons of 200 mg/kg TAEE-treated mice than in AOM/DSS controls (p < 0.05). Immunohistochemical staining showed that levels of nuclear factor-kappa B p65 and β-catenin were attenuated by TAEE in the colon tissues of AOM/DSS-treated mice. Furthermore, levels of β-catenin-related genes (cyclin D1 and c-Myc), which are known to contribute to cell cycle regulation, were decreased in the colon tissues of TAEE-treated mice versus AOM/DSS controls (p < 0.01). These results showed TAEE inhibited colon inflammation and neoplasm formation caused by AOM/DSS treatment, suggesting that TAEE could be useful for the prevention and treatment of colitis-associated colon cancer.

Depletion of enteroendocrine and mucus-secreting cells is associated with colorectal carcinogenesis severity and impaired intestinal motility in rats.

This study investigated the relationship between enteroendocrine and mucus-secreting cells distribution, the severity of colonic mucosal injury and intestinal motility in experimental colorectal carcinogenesis. Using a standardized murine model of colorectal carcinogenesis, eight-weeks-old female Wistar rats weighting 147.30 ± 29.15g were randomized into two groups receiving a subcutaneous injection of 0.9% saline (control) or the chemical carcinogen 1,2-dimethylhydrazine (DMH) at 20 mg/kg per week during 10 weeks. Aberrant crypt foci (ACF) were more frequent in DMH group compared to control group (P < 0.001). The number of enteroendocrine and mucus-secreting cells, and intestinal motility was reduced in DMH animals (P < 0.05). The distribution of enteric neurons was similar in both groups. In DMH animals there was a direct correlation between colonic motility and distribution of enteroendocrine (R(2) = 0.68, P < 0.05) and mucus-secreting cells (R(2) = 0.77, P < 0.05). Inverse correlation between the number of ACF, mucus-secreting cells (R(2) = -0.57, P < 0.05), and enteroendocrine cells (R(2) = -0.74, P < 0.05) was also observed. There was inverse correlation between the severity of the mucosal lesion, the number of mucus-secreting cells (R(2) = -0.83, P < 0.05) and enteroendocrine cells (R(2) = -0.96, P < 0.05). There was a direct correlation between nucleolar organizer regions (AgNOR) and ACF number (R(2) = 0.62; P < 0.01). Inverse correlation was also found between AgNOR, the number of mucus-secreting cells (R(2) = -0.76; P < 0.001), and enteroendocrine cells (R(2) = -0.86; P < 0.001). Taken together, the results indicated that colonic malignant transformation is related to depletion of mucus-secreting and enteroendocrine cells, which was a useful indicator of the evolutionary status of intestinal neoplasm, partially explaining the intestinal motility disorders in the early stages of colorectal carcinogenesis.

Vitamin E supplementation in chemical colorectal carcinogenesis: a two-edged knife.

This work investigated the effects of Vitamin E (VE) on aberrant crypt foci (ACF) incidence, oxidative stress parameters (serum and hepatic VE concentration, and homocysteine, glutathione (GSH), and malondialdehyde (MDA) levels), and expression of both cyclooxygenase-2 (COX2) and proliferating cellular nuclear antigen (PCNA) in experimental colorectal carcinogenesis. Male Wistar rats received subcutaneous injections of 1,2-dimethylhydrazine (DMH) twice a week, for two weeks (40 mg/kg), except for the Control group. Animals were separated into groups that received different amounts of VE in the diet: 0 IU (0×), 75 IU (recommended daily intake, RDI), 225 IU (3× RDI), or 1500 IU (20× RDI), during (dDMH) or after (aDMH) administration of carcinogen. The 0×dDMH and 3×dDMH groups showed decreased serum VE levels. Hepatic VE concentration was higher in 3×aDMH as compared with the other groups. All the groups, except the Control and the 0×aDMH groups, had reduced GSH levels. The 0×dDMH, 0×aDMH, and 20×aDMH groups exhibited increased MDA levels. The aDMH groups had higher ACF incidence and PCNA expression. The 0×aDMH group presented higher ACF rate, followed by 20×aDMH. Moreover, the 3×aDMH group displayed reduced ACF incidence and COX2 expression. Multivariate analysis revealed that GSH modulated homocysteine levels and COX2. These results suggested that 1500 IU of VE is hazardous, whereas 225 IU of VE has beneficial effects on chemical colorectal carcinogenesis.

Wild-typeK-rashas a tumour suppressor effect on carcinogen-induced murine colorectal adenoma formation

K-ras mutations are found in ~40% of human colorectal adenomas and carcinomas and contribute to colorectal tumour formation at an early stage. Wild-type K-ras has been reported to be deleted in some tumours, but the consequences of changes in wild-type K-ras copy number for experimental colorectal carcinogenesis have not been investigated. To characterize the effects of K-ras copy number changes on formation of carcinogen-induced colorectal neoplasms in mice, wild-type (K-ras(+/+) ) and heterozygous K-ras exon 1 knockout (K-ras(+/-) ) mice were given 10 weekly treatments of 1, 2-dimethylhydrazine (DMH) to induce colorectal tumours. Colorectal expression levels of K-ras 4A and 4B transcripts in K-ras(+/-) mice were ~50% decreased compared with K-ras(+/+) mice. One year after DMH treatment, survival of K-ras(+/-) mice decreased from 88 to 82% compared with wild-type mice. Colorectal adenomas significantly increased from 0.52±0.15 in K-ras(+/+) mice to 0.87±0.14 in K-ras(+/-) mice (mean±SEM per mouse, P<0.01); total tumour volume increased 2.13-fold (P<0.05). Comparing K-ras(+/+) with K-ras(+/-) murine adenomas, Ki-67-positive proliferating tumour cells significantly increased from 7.77±0.64% to 9.15±0.92% and cleaved caspase-3-positive apoptotic tumour cells decreased from 1.40±0.37% to 0.80±0.22% (mean±SEM, P<0.05 for both). No K-ras or B-raf mutations were detected in the adenomas. Immunohistochemical studies showed no significant changes in extracellular signal regulating kinase/mitogen-activated protein kinase (Erk/MapK) or PI3K/Akt pathway activation in the adenomas. In conclusion, the data collectively show that a 50% reduction in K-ras gene dosage and RNA expression promoted experimental colorectal tumourigenesis, consistent with wild-type K-ras having a tumour suppressor effect on carcinogen-induced murine colorectal adenoma formation.

Evaluation of tumor suppressor gene expressions and aberrant methylation in the colon of cancer-induced rats: a pilot study

Altered expression and methylation pattern of tumor suppressor and DNA repair genes, in particular involved in mismatch repair (MMR) pathway, frequently occur in primary colorectal (CRC) tumors. However, little is known about (epi)genetic changes of these genes in precancerous and early stages of CRC. The aim of this pilot study was to analyze expression profile and promoter methylation status of important tumor suppressor and DNA repair genes in the early stages of experimentally induced colorectal carcinogenesis. Rats were treated with azoxymethane (AOM), dextran sodium sulphate (DSS) or with their combination, and sacrificed 1 or 4 months post-treatment period. The down-regulation of Apc expression in left colon, detectable in animals treated with DSS-AOM and sacrificed 1 month after the end of treatment, represents most early marker of the experimental colorectal carcinogenesis. Significantly reduced gene expressions were also found in 5 out of 7 studied MMR genes (Mlh1, Mlh3, Msh3 Pms1, Pms2), regarding the sequential administration of DSS-AOM at 4 months since the treatment. Strong down-regulation was also discovered for Apc, Apex1, Mgmt and TP53. Tumors developed in rectum-sigmoid region displayed significantly lower Apc and Pms2 expressions. The decreased expression of studied genes was not in any case associated with aberrant methylation of promoter region. Present data suggest that down-regulation of Apc and MMR genes are prerequisite for the development of CRC. In this study we addressed for the first time early functional alterations of tumor suppressor genes with underlying epigenetic mechanisms in experimentally induced CRC in rats.

Metabolic profiling, a noninvasive approach for the detection of experimental colorectal neoplasia.

Colorectal cancer is the second leading cause of cancer-related deaths in the United States. Although noninvasive stool-based screening tests are used for the early detection of colorectal neoplasia, concerns have been raised about their sensitivity and specificity. A metabolomics-based approach provides a potential noninvasive strategy to identify biomarkers of colorectal carcinogenesis including premalignant adenomas. Our primary objective was to determine whether a distinct metabolic profile could be found in both feces and plasma during experimental colorectal carcinogenesis. Feces, plasma as well as tumor tissue and normal colorectal mucosa were obtained from A/J mice at several time points following administration of azoxymethane or saline. Ultra-performance liquid chromatography tandem mass spectroscopy and gas chromatography mass spectroscopy were used to quantify metabolites in each of these matrices. Here, we show that colorectal carcinogenesis was associated with significant metabolic alterations in both the feces and plasma, some of which overlap with metabolic changes in the tumor tissue. These consisted of 33 shared changes between feces and tumor, 14 shared changes between plasma and tumor, and 3 shared changes across all 3 matrices. For example, elevated levels of sarcosine were found in both tumor and feces whereas increased levels of 2-hydroxyglutarate were found in both tumor and plasma. Collectively, these results provide evidence that metabolomics can be used to detect changes in feces and plasma during azoxymethane-induced colorectal carcinogenesis and thus provide a strong rationale for future studies in humans.

Adaptation to jejunoileal bypass promotes experimental colorectal carcinogenesis.

The co-carcinogenic potential of 85 per cent jejunoileal bypass (JIB) was tested in male Sprague-Dawley rats (n = 81) given 6 preliminary injections of the selective intestinal carcinogen azoxymethane (total dose 90 mg/kg). Controls had sham JIB. Colorectal adaptation was studied 30 weeks postoperatively in rats given injections of vehicle alone. JIB caused 17-33 per cent increments in colonic length, weight and crypt depth; crypt cell production rate was more than doubled (P less than 0.01). Despite lowering body weight by 27 per cent, JIB increased the median number of colorectal tumours per rat from 3 to 8 (P less than 0.01). The findings suggest that evidence of hyperplasia and dysplasia should be sought in patients receiving subtotal jejunoileal bypass for obesity.

Relative effects of ileal resection and bypass on intestinal adaptation and carcinogenesis.

Since ileal resection and ileal bypass are commonly performed in man and might stimulate colonic hyperplasia, their co-carcinogenic potential was explored in male Sprague-Dawley rats (n = 135). One week after 33 per cent distal small-bowel resection, 33 per cent distal small-bowel bypass or distal ileal transection (control), animals started a 6-week course of azoxymethane injections (total dose 90 mg/kg ip). Findings in rats killed at 20 and 25 weeks were similar: bypass produced a higher yield of colorectal tumours (4.0 +/- 0.6 per rat: mean +/- s.e.) than controls (2.4 +/- 0.4; P less than 0.05), but resection caused maximal enhancement (5.2 +/- 0.5: P less than 0.01). In rats killed at 30 weeks, however, tumour yields were almost identical. Overall, resection increased colonic tumour yield by 55 per cent (P less than 0.02) and bypass by 32 per cent. Stathmokinetic measurements of crypt cell production rate (CCPR) at 20 weeks showed similar increases after resection and bypass both in residual functioning small bowel (109-200 per cent: P less than 0.01) and in colorectum (63-100 per cent: P less than 0.05). At 30 weeks these adaptive effects persisted, despite an overall increase in CCPR with age. Loss of functioning ileum enhances experimental colorectal carcinogenesis principally by reducing the latent period for tumour development. Resection has a greater effect than bypass probably by producing earlier hyperplasia, though later adaptive effects are similar.

Dietary polyunsaturated fatty acids and colorectal neoplasia

Epidemiology has implicated dietary fat in mortality associated with some of the most common forms of cancer, including those affecting the intestinal tract, breast and prostate. Polyunsaturated fatty acids, and arachidonate in particular, have been unequivocally linked to experimental colorectal carcinogenesis. Dietary, pharmacologic and genetic manipulation of tissue arachidonic acid and its conversion to bioactive lipids has provided insights into pathogenic mechanisms as well as compelling evidence to support rational preventative and therapeutic methods of disease intervention. While it is clear that conversion of arachidonate to prostaglandins and other bioactive lipids contributes significantly to tumorigenesis in the intestinal tract and other organs, it is also clear that no single metabolic pathway or lipid in this complex biochemical network is solely responsible for dietary or pharmacologic benefits evident in epidemiologic studies. We will review some of these data and provide a summary of our own work showing that conversion of arachidonate to prostaglandin E 2 contributes significantly to tumor growth through the modulation of apoptosis and cellular proliferation.

The inhibitory effect of octreotide on experimental colorectal carcinogenesis.

This study was conducted to investigate the effect of octreotide on colorectal carcinogenesis by administering octreotide either alone or combined with polyglactin, which is a well-known suture material, on chemically induced colorectal cancer development in rats. A total of 72 rats were divided into six groups. Two groups were subjected to a colotomy and repair using polyglactin. Another two groups underwent a sham procedure. The fifth group received octreotide alone and the sixth group served as a control. Both groups of rats in the polyglactin and sham groups received octreotide additionally. Methylnitrosourea was administered rectally to all the animals at a dose of 4 mg/kg per week for 20 weeks to induce carcinogenesis. Octreotide was injected twice a day at a total daily dose of 100 microg/kg. The thymidine labeling index was used to assess the synthesis phase fraction in order to measure the cell proliferation rate. The mean number of tumors per rat was significantly higher in the polyglactin group than in both the sham and control groups. It was significantly lower in the octreotide and polyglactin + octreotide groups than in the control and polyglactin groups, respectively. All the animals in the octreotide group had one tumor, while 66.6% of the control group had multiple tumors. The number of multiple tumors was significantly lower in the polyglactin + octreotide and sham + octreotide groups than in the polyglactin and sham groups, respectively. The mean tumor size in the octreotide group was significantly smaller than in the control group, whereas it was larger in the polyglactin group in comparison with the sham and control groups. It was also reduced in the polyglactin + octreotide group in comparison with the polyglactin group. The thymidine labeling index was significantly higher in the polyglactin group compared with both the sham and control groups, whereas it was lower in the octreotide group in comparison with the control group. The addition of octreotide administration to the polyglactin usage and the sham procedure significantly decreased the thymidine labeling indexes. These results indicate that octreotide reduces the frequency of tumor occurrence and has an inhibitory effect on its development in chemically induced experimental colorectal cancer. Octreotide can also reduce the enhancing effect of polyglactin on colorectal carcinogenesis when it is combined with polyglactin.

The proto-oncogene AKT is overexpressed in human and experimental colorectal carcinogenesis

The proto-oncogene AKT is overexpressed in human and experimental colorectal carcinogenesis

Omeprazole may inhibit initiation of experimental colorectal carcinogenesis

Omeprazole may inhibit initiation of experimental colorectal carcinogenesis

Mutations of the Apc gene in experimental colorectal carcinogenesis induced by azoxymethane in F344 rats.

We investigated in the rat the role of the Apc gene, which is mutated in familial adenomatous polyposis and sporadic colon cancer in the process leading from normal colonic mucosa to aberrant crypt foci (ACF) and finally to adenomas and adenocarcinomas. We analysed mutations in exon 15 of the rat Apc gene using in vitro synthesized protein assay in 66 ACF and in 28 colon tumours induced by azoxymethane. No Apc mutations were found in ACF, whereas five mutations were found in the tumours. The data suggest that mutations of the Apc gene are associated with the transition from ACF to adenoma and adenocarcinoma and not from normal mucosa to ACF.

Modulation of colonocyte proliferation and apoptosis by dietary fish oil in experimental colorectal carcinogenesis.

Accumulating epidemiological and experimental evidence demonstrates an inverse relationship between consumption of marine fish oils rich in eicosapentaenoic acid (205, n-3, EPA) and development of colorectal cancer. Clinical studies on patients at high risk of developing colorectal cancer have shown that low level fish oil dietary supplementation can normalise aberrant proliferative patterns associated with the early stages of neoplasia[ 11. In chemically induced rodent models of colorectal neoplasia, diets rich in n-3 fatty acids such as EPA significantly reduce the incidence and multiplicity of colorectal adenocarcinomas relative to diets rich in n-6 fatty acids[2]. Further studies on a number of human tumour cell lines have clearly demonstrated a selective low dose tumoricidal capacity for EPA, proving cytotoxic or at least cytostatic to tumour cells but not to normal cells[3]. A number of mechanisms have been proposed to account for these anticarcinogenic effects including augmentation of free-radical generation leading to loss of cell viability in sensitive cell populations[4], inhibition of cyclooxygenase and lipoxygenase eicosanoid synthesising enzyme systems[ll, modulation of cell signalling pathway@] and gene expression[6]. Ultimately fish oil exerts its effects through control of cellular proliferation[7,8] and recent evidence suggests EPA may induce apoptosis both in vivo[9] and in vitro[lO]. The objectives of this study are firstly to determine the effects of short-term fish oil dietary supplementation on colonocyte proliferation and spontaneous apoptosis in the distal colon of normal healthy animals. Secondly, to provide insight into the influence of fish oil on crypt cell kinetics immediately following carcinogenic insult with 1,2 dimethylhydrazine (DMH), since modifications of the initiating stages of chemical carcinogenesis are likely to effect neoplastic outcome within the colon. Forty male Wistar rats fed a semi-synthetic diet containing starch (280g/kg), sucrose (380g/kg), casein (200g/kg), corn oil (CO) (80g/kg) and a balanced mineral and vitamin mix were divided randomly into four groups (Con-CO, Con-FO, DMHCO, and DMH-FO) prior to the start of the experiment. Accordingly, half the animals were injected subcutaneously with DMH (30mg/kg body weight), the remaining controls with an equal volume of saline. Immediately, the Con-FO and DMH-FO assigned groups were fed a freshly prepared diet where corn oil was substituted by fish oil ( EPA 18.7%:DHA 8.0%). The ConCO and DMH-CO groups remained on the standard corn oil diet. Five animals from each group were killed at 24 hours and at 48 hours and their colons removed and flushed with saline. Tissue samples were collected from the distal end of the colon, fixed in ethano1:acetic acid (75:25), and stained with Feulgen's reagent. Crypts were then micro-dissected from the tissue, lightly compressed under a cover-slip and morphologically identifiable mitosis and apoptosis counted in twenty crypts per animal (100 cryptdgroup) under a light microscope. Data was collated and significance determined by two-way analysis of variance. As expected, injection of DMH significantly reduced proliferation and increased apoptosis in the distal colon both 24 hours and 48 hours following administration. The effects of fish oil dietary supplementation were most marked after 48 hours (see Table 1). Proliferation was lower in the distal colon in FO compared to CO fed rats both in the presence and absence of DMH, though the effect was not statistically significant at 24 hours. Apoptosis was significantly raised by fish oil at both 24 and 48 hours in the presence and absence of DMH. Table 1. hffect of diet and DMH on proliferation and apoptosis in the distal colon after 48 hours. Each value represents the mean f S.E.M for 100 crypts. Mitosis Apoptosis DMH Corn oil Fish oil :::: :::; 2: O.O f b

Dietary manipulation during experimental colorectal carcinogenesis: a morphological study in the rat.

The effect of the dietary manipulation of fat and fibre on the gross pathological, histopathological and scanning electron microscopic appearances of colonic mucosa was studied before and during experimental carcinogenesis in 232 male Albino Swiss rats. Carcinogen treated animals were given 12 consecutive weekly injections of Azoxymethane in a dose of 10 mg/kg per week. The animals were divided between four dietary groups (1: high fat high fibre, 2: low fat high fibre, 3: high fat low fibre and 4: low fat low fibre). The colorectal morphology was assessed at autopsy using standard histopathological techniques. In addition, scanning electron microscopic studies on selected samples were performed. A scoring system was introduced to allow a more accurate comparison of the surface architectural appearances. The high fat low fibre diet was associated with the greatest risk for macroscopic tumour production and the low fat high fibre diet with the lowest risk. Statistically significant differences between each of the dietary groups were noted with the exception of the comparison for tumour induction between the high fat high fibre and low fat high fibre dietary groups. Histopathological analysis confirmed the inter dietary relationships with respect to the extent of neoplastic change. The scanning electron microscopic study revealed that both dietary manipulation and carcinogen treatment influenced the surface characteristics. Control animals fed diet 2 (low fat high fibre) but not treated with carcinogen, showed the greatest deviation from the normal appearances. Animals treated with carcinogen and fed diet 3 (high fat low fibre) consistently showed the greatest surface abnormalities.

The effect of dietary milk and calcium on experimental colorectal carcinogenesis.

This investigation was based on an epidemiologic association of milk consumption and decreased intestinal cancer risk. Furthermore, there is also some indirect evidence that calcium supplementation in humans and animals may decrease colon cancer risk and that calcium, by inference, may be the protective factor in milk. In order to investigate these associations in a controlled laboratory setting, dietary supplementation of low fat dried milk (37 g/kg diet; N = 18) and calcium carbonate (40 mg/kg rat/day; N = 17) were compared separately to regular diet controls in the rat-dimethylhydrazine colon carcinogenesis model. The results of this investigation showed that neither milk-supplemented rats nor calcium carbonate-supplemented rats had fewer DMH-induced colorectal (P = .374) or total gastrointestinal tumors (P = .291) than did regular diet controls (N = 10; by analysis of variance [ANOVA]). Milk supplementation did result in a significant decrease in tumor burden when measured by incidence of metastases (P = .035) and of intestinal obstruction (P = .011; by chi-square test), when compared with calcium-supplemented and control rats. Though this implies that milk supplementation provides protection against some aspects of carcinogenesis of the colon, in rats fed low fat diets, this does not appear to be mediated through the calcium content of milk.

The tropic effect of intrarectal deoxycholate on rat colorectum is unaffected by oral metronidazole.

Intrarectal administration of sodium deoxycholate (SDC) enhances experimental colorectal carcinogenesis, an effect that is partly vitiated by oral metronidazole. The effect of topical SDC with or without concurrent metronidazole on colorectal cell proliferation was explored in male Sprague-Dawley rats (n = 30) allocated to five groups. Two groups received thrice weekly intrarectal instillations of 1 ml N saline or 1 ml 0.12 M SDC. A third group received SDC plus metronidazole 22.5 mg/kg/day in the drinking water. Controls had no instillations or metronidazole alone. At time of killing (10 weeks), crypt cell production rate (CCPR) was determined by the stathmokinetic technique for four large-bowel segments. Saline had no significant effect on colorectal CCPR but SDC produced increases throughout, varying from 53% in the proximal colon to 222% in the rectum (P less than 0.01). Metronidazole did not reduce this effect, although given alone it reduced colonic CCPR by 40 to 50%. The direct tropic effect of bile acids could largely explain their cocarcinogenic properties. Since metronidazole does not prevent this increase in cell proliferation, its mildly protective role against cancer may reflect the presence of fewer anaerobes capable of degrading bile acids to carcinogenic metabolites.