Prevention by retinoids of azoxymethane-induced tumors and aberrant crypt foci and their modulation of cell proliferation in the colon of rats

Retinoids are proposed chemopreventive agents that inhibit cell proliferation and induce differentiation. Their ability to prevent azoxymethane (AOM)-induced aberrant crypt foci (ACF) and tumors and to modulate cell proliferation was investigated in the colon of male F344 rats. Thirteen retinoids were evaluated for prevention of ACF and two of them, 9-cis-retinoic acid (RA) and 4-(hydroxyphenyl)retinamide (4-HPR), were also evaluated for prevention of colon cancer. The retinoids were administered continuously in the diet starting 1 week prior to the first of two weekly 15 mg/kg i.p. injections of AOM and for a total of either 5 or 36 weeks in order to evaluate their effect on colonic ACF and tumors. At a concentration of 1 mmol/kg diet, 2-(carboxyphenyl)retinamide caused the greatest reduction (57.7%) in the yield of ACF. 9-cis-RA was toxic at 1 mmol/kg so that it was evaluated at 0.1 mmol/kg, resulting in a 41.6% reduction in ACF. The ability of the retinoids to reduce the proliferating cell nuclear antigen (PCNA) labeling index in ACF and in non-involved crypts correlated with their ability to prevent ACF. Both 9-cis-RA (0.1 and 0.2 mmol/kg diet) and 4-HPR (1 and 2 mmol/kg diet) were highly effective in decreasing the yield of AOM-induced colon tumors. In summary, retinoids were demonstrated to reduce cell proliferation and to prevent ACF and tumors in the colon, suggesting promise as preventive agents for colon cancer.     

Enhancement of experimental colon cancer by genistein

Several phytochemicals and micronutrients that are present in fruits and vegetables are known to exert cancer chemopreventive effects in several organs, including the colon. Among them, the soybean isoflavonoid genistein received much attention due to its potential anticarcinogenic, antiproliferative effects and its potential role in several signal transduction pathways. The present study was designed to investigate the effect of genistein on azoxymethane (AOM)-induced colon carcinogenesis and to study its modulatory role on the levels of activity of 8-isoprostane, cyclooxygenase (COX), and 15-hydroxyprostaglandin F2alpha dehydrogenase (15-PGDH) in the colonic mucosa and colon tumors of male F344 rats. At 5 weeks of age, groups of male F344 rats were fed control (AIN-76A) diet or a diet containing 250 ppm genistein. Beginning 2 weeks later, all animals except those in the vehicle-treated groups were given weekly s.c. injections of AOM (15 mg/kg body weight) for 2 successive weeks. All rats were continued on their respective dietary regimen for 52 weeks after AOM treatment and were then sacrificed. Colon tumors were evaluated histopathologically. Colonic mucosae and tumors were analyzed for COX, 15-PGDH, and 8-isoprostane levels. Administration of genistein significantly increased noninvasive and total adenocarcinoma multiplicity (P < 0.01) in the colon, compared to the control diet, but it had no effect on the colon adenocarcinoma incidence nor on the multiplicity of invasive adenocarcinoma (P > 0.05). Also, genistein significantly inhibited the 15-PGDH activity (>35%) and levels of 8-iosoprostane (50%) in colonic mucosa and in tumors. In contrast, genistein had no significant effect on the COX synthetic activity, as measured by the rate of formation of prostaglandins and thromboxane B2 from [14C]arachidonic acid. The results of this investigation emphasize that the biological effects of genistein may be organ specific, inhibiting cancer development in some sites yet showing no effect or an enhancing effect on the tumorigenesis at other sites, such as the colon. The inhibition of 8-isoprostane levels by genistein indicates its possible antioxidant potential, which is independent of the observed colon tumor enhancement, yet this agent may also possess several biological effects that overshadow its antioxidant potential. The exact mechanism(s) of colon tumor enhancement by genistein remain to be elucidated; it is likely that its colon tumor-enhancing effects may, at least in part, be related to inhibition of prostaglandin catabolic enzyme activities.     

Chemoprevention of azoxymethane-induced intestinal carcinogenesis by a novel synthesized retinoidal butenolide, 5-hydroxy-4-(2-phenyl-(E)-ethenyl)-2(5H)-furanone, in rats

The present study was designed to investigate the modifying effects of dietary 5-hydroxy-4-(2-phenyl-(E)-ethenyl)-2(5H)-furanone (KYN-54), a new synthetic retinoidal butenolide, during the post-initiation phase on azoxymethane (AOM)-induced rat intestinal carcinogenesis. The number of aberrant crypt foci (ACF) in rat colon, colonic ornithine decarboxylase (ODC) activity and bromodeoxy-uridine (BrdUrd) labeling index in rat colonic epithelium were also assessed. At 7 weeks of age, male F344 rats (except the KYN-54 alone and control groups) were given weekly s.c. injections of AOM at 15 mg/kg body wt for 3 weeks. Starting 1 week after the last injection of AOM, rats (except the control group) were fed a diet containing KYN-54 at concentrations of 100 or 200 p.p.m. throughout the experiment. All animals were necropsied at 32 weeks after the start of the experiment. Compared with the AOM alone group, KYN-54 at both doses reduced the incidence and multiplicity of tumors in entire intestine (small and large intestines). In the 200 p.p.m. KYN-54 fed group especially, tumor incidence and multiplicity in the entire intestine were lower compared with the AOM alone group (P < 0.005 and P < 0.05 respectively). Also, the number of ACF/cm2 colon in the groups of rats treated with AOM and KYN-54 at both doses were significantly lower than that of rats treated with AOM alone (P < 0.05). Colonic ODC activity and BrdUrd labeling index in the groups of rats treated with AOM and KYN-54 at both doses were slightly lower than those treated with AOM alone. KYN-54 at 200 p.p.m. significantly lowered BrdUrd labeling index induced by AOM (P < 0.005). These results suggest that KYN-54 might be a promising chemopreventive agent for intestinal neoplasia.     

Inhibitory effects of lemon grass (Cymbopogon citratus Stapf) on formation of azoxymethane-induced DNA adducts and aberrant crypt foci in the rat colon

The 80%-ethanol extract of lemon grass (Cymbopogon citratus Stapf), a medicinal plant in Thailand, has been reported to be antimutagenic against various known mutagens in the Salmonella mutation assay. To investigate chemoprevention in an animal carcinogenesis model, we examined inhibitory effects of the lemon grass extract on the formation of azoxymethane (AOM)-induced DNA adducts and aberrant crypt foci (ACF) in the rat colon. One week after the start of the treatment with lemon grass extract at doses of 0.5 or 5 g/kg body wt by gavage, F344 rats received two s.c. injections of 15 mg of AOM per kg body weight at 1 week apart. For DNA adduct analysis of the colon and liver, the rats were killed 12 h after the second AOM injection. The DNA from the liver and colon were used for O6-methylguanine and N7-methylguanine analysis. For ACF analysis in the initiation stage, AOM-injected rats were continuously treated with lemon grass extract and were killed 3 weeks after the second AOM injection. For analysis in the promotion stage the treatment with the lemon grass extract (0.5 g/kg) started 2 weeks after the second AOM injection and continued for 12 weeks until the animals were killed. Lemon grass treatment significantly inhibited DNA adduct formation in both the colonic mucosa and the muscular layer but not in the liver. In addition, lemon grass extract treatment significantly inhibited ACF formation in both the initiation stage and the promotion stage. Especially in the promotion stage, lemon grass treatment inhibited the formation of larger ACF (with four or more crypts per focus), which was predictive of tumor incidence. Furthermore, lemon grass extract inhibited fecal beta-glucuronidase competitively and had antioxidant activity. These results suggest that the lemon grass extract inhibits the release of activated aglycon, methylazoxymethanol, from a glucuronide conjugate in the colon, and decreases the DNA adducts and ACF formation in the rat colon.     

Cell death and cell proliferation contribute to the enhanced growth of foci by fasting in rat medial colon

We have recently shown that fasting before initiation markedly stimulated the growth of aberrant crypt foci (ACF) induced by azoxymethane (AOM) in the rat medial colon. Here we investigated the mechanisms by which fasting enhanced the growth of ACF. Rats were exposed to 4 day-starvation, then they were given AOM (20 mg/kg) on the first day of refeeding. 4 day-fasting depressed cell proliferation as shown by the decreased mitotic index and enhanced cell death by apoptosis. On the first day of refeeding, apoptotic index remained higher than control values, while mitotic index markedly increased in the colonic epithelium of fasted/ refed rats. The administration of AOM induced an apoptotic wave, that was higher in controls, and a transient drop in the mitotic index that recovered quickly in the fasted/refed group. These data suggest that starvation-induced apoptosis represents the mitogenic stimulus to increase the rates of cell proliferation responsible for the enhanced growth of ACF in fasted/refed rats.     

Cytolysis and piecemeal degranulation as distinct modes of activation of airway mucosal eosinophils

In contrast to the protective effect of chronic caloric restriction on tumor development, we have shown that fasting sustained tumor initiation in rat liver by a noninitiating dose of diethylnitrosamine. Here we investigated whether fasting had a similar favorable effect on initiation in the colorectal mucosa in 80 male F344 rats. Animals fasted for 4 days were given a single s.c. dose of azoxymethane (AOM) (20 mg/kg) on the first day of re-feeding, and rates of kinetic proliferative parameters, and development of the pre-neoplastic lesions such as aberrant crypt foci (ACF), were evaluated. Starvation before AOM treatment enhanced the growth of ACF, as shown by the significantly higher crypt multiplicity of fasted/re-fed rats as compared with fully fed rats (3.97 +/- 0.50 vs. 2.64 +/- 0.20, p < or = 0.025). This difference was associated with perturbations in cell death and cell proliferation. Fasting induced apoptosis and depressed cell division, while re-feeding had opposite effects, resulting in a higher percentage of S-phase cells at the time of AOM injection and 2 days thereafter. Starvation-induced apoptosis may represent the mitogenic stimulus to an increase in the number of cells susceptible to AOM damage, and may favor its fixation, leading to enhanced growth of ACF. Our data therefore suggest that fasting/re-feeding enhances colon cancer.     

A xanthine oxidase inhibitor 1'-acetoxychavicol acetate inhibits azoxymethane-induced colonic aberrant crypt foci in rats

The modifying effect of dietary administration of a xanthine oxidase inhibitor 1'-acetoxychavicol acetate (ACA) present in an edible plant Languas galanga in Thailand on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) was investigated in rats. Male F344 rats were given s.c. injections of AOM (15 mg/kg body wt) once a week for 3 weeks to induce colonic ACF. They were fed the diets containing 100 or 200 ppm ACA for 5 weeks, starting 1 week before the first dosing of AOM. At the termination of the study (week 5), AOM induced 118 +/- 28 ACF/colon. Dietary administration of ACA caused significant reduction in the frequency of ACF (41% inhibition by 100 ppm ACA feeding and 37% inhibition by 200 ppm ACA feeding, P<0.01). Such inhibition might be associated with suppression of the proliferation biomarkers' expression such as ornithine decarboxylase activity in the colonic mucosa, number of silver-stained nucleolar organizer regions' protein in the colonic mucosal cell nuclei and blood polyamine content. These results indicate that ACA could inhibit the development of AOM-induced ACF through its suppression of cell proliferation in the colonic mucosa and ACA might be a possible chemopreventive agent against colon tumourigenesis.     

The nonfermentable dietary fiber lignin alters putative colon cancer risk factors but does not protect against DMH-induced colon cancer in rats

The effect of supplementation of the diet with autohydrolyzed lignin on 1,2-dimethylhydrazine (DMH)-induced colon carcinogenesis was studied using 112 male Sprague-Dawley rats. Rats received eight weekly injections of DMH (9.5 mg/kg s.c.) or the saline vehicle solution and then were maintained on a basal AIN-76 fiber-free diet or the basal fiber-free diet plus 5% or 10% (wt/wt) lignin for 24 weeks. Rats were killed 32 weeks after the start of the experiment. Colon tumor incidence, location, and multiplicity were determined. Body weight, caloric intake, fecal dry weight, gut transit time, pH of cecal contents, and total fecal bile acid excretion were measured. Supplementation of the diet with 5% or 10% lignin resulted in increased fecal dry weight and total fecal bile acid excretion and in decreased gut transit time, colon pH, and fecal bile acid concentration. Dietary lignin did not significantly affect colon tumor incidence or multiplicity compared with the fiber-free diet. Thus dietary supplementation with autohydrolyzed lignin, a food fiber with good bulking characteristics, had a significant effect on several factors that have previously been linked to reduction of colon cancer risk, but the consumption of high levels of lignin did not decrease the risk for colon cancer.     

Prevention of colon cancer by pre- and probiotics: evidence from laboratory studies

Oligofructose and inulin, selective fermentable chicory fructans, have been shown to stimulate the growth of bifidobacteria which are regarded as beneficial strains in the colon. Studies were designed to evaluate inulin (Raftiline) and oligofructose (Raftilose), for their potential inhibitory properties against aberrant crypt foci (ACF) formation in the colon of rats. ACF are putative preneoplastic lesions from which adenomas and carcinomas may develop. The results of this study demonstrate that dietary administration of oligofructose and inulin inhibits the formation of preneoplastic lesions in the colon suggesting the potential colon tumour inhibitory properties of chicory fructans. Since these prebiotics selectively stimulate the growth of bifidobacteria, tumour inhibitory activity of lyophilized cultures of Bifidobacterium longum (BL) against azoxymethane (AOM)-induced colon carcinogenesis in rats and modulating effect of these cultures on colonic tumour cell proliferation, ornithine decarboxylase (ODC) activity, and ras-p21 oncoprotein expression were investigated. Dietary administration of lyophilized cultures of BL strongly suppressed AOM-induced colon tumour development. Inhibition of colon carcinogenesis was associated with a decrease in colonic mucosal cell proliferation and colonic mucosal and tumour ODC and ras-p21 activities.     

Phenobarbital and 3-methylcholanthrene treatment alters phase I and II enzymes and the sensitivity of the rat colon to the carcinogenic activity of azoxymethane

It has been hypothesized that cancer risk may be influenced by phase I and II drug-metabolizing enzyme systems. This study attempted to determine the relationship between colon phase I and II enzyme activity and the subsequent induction of aberrant crypt foci (ACF), preneoplastic lesions by azoxymethane (AOM), a colon-specific carcinogen. Phenobarbital (PB) and 3-methylcholanthrene (MC) treatment (prototype hepatic inducers of phase I and II enzymes) provided the framework to study the induction of phase I and II enzymes in the rat colonic mucosa. Following induction for five consecutive days, the animals were given a single injection of AOM. Phase I and II enzymes were determined fluorometrically and spectrophotometrically and ACF were identified microscopically. Phase I and II xenobiotic metabolizing enzymes were induced in the rat colonic mucosa by prototype hepatic inducers. A lower number of ACF and crypt multiplicity was observed in animals induced with MC than in those in the non-induced and PB groups. Altered levels of phase I and II enzymes in the colon during preinitiation stages were associated with modulation in the growth of ACF, putative preneoplastic lesions.     

Inhibition of murine bladder tumorigenesis by soy isoflavones via alterations in the cell cycle, apoptosis, and angiogenesis

Soy isoflavones exhibit a number of biological effects, suggesting that they may have a role in cancer prevention. Our objectives are to determine whether components of soy products or purified soy isoflavones can inhibit the progression of bladder cancer. We compared the in vitro effects of pure soy isoflavones and soy phytochemical concentrate on growth curves, cell cycle progression, and apoptosis in murine and human bladder cancer cell lines. Pure soy isoflavones (genistein, genistin, daidzein, and biochanin A) and soy phytochemical concentrate exhibit dose-dependent growth inhibition of murine (MB49 and MBT-2) and human (HT-1376, UM-UC-3, RT-4, J82, and TCCSUP) bladder cancer cell lines, although the degree of inhibition varies among lines. Soy isoflavones induce a G2-M cell cycle arrest in all human and murine lines evaluated by flow cytometry. In addition, some bladder cancer lines show DNA fragmentation consistent with apoptosis. We next evaluated the ability of genistein, soy phytochemical concentrate, and soy protein isolate, respectively, to inhibit the growth of transplantable murine bladder cancer in vivo. C57BL/6 mice were randomly assigned to treatment groups (n = 12/group): (a) AIN-76A diet; (b) AIN-76A diet plus genistein, i.p., 50 mg/kg body weight/day; (c) AIN-76 diet with soy phytochemical concentrate at 0.2% of the diet; (d) AIN-76 diet with soy phytochemical concentrate at 1.0% of the diet; and (e) AIN-76A diet with soy protein isolate, 20% by weight. Mice were inoculated s.c. with 5 x 10(4) syngeneic MB49 bladder carcinoma cells, and tumor growth was quantitated. Neither genistein nor soy products reduced body weight gain. Tumor volumes from mice treated with genistein, dietary soy phytochemical concentrate at 1%, or dietary soy protein isolate were reduced by 40% (P < 0.007), 48% (P < 0.001), or 37% (P < 0.01), respectively, compared with controls. We characterized the effects of treatment on several biomarkers in tumor tissue: proliferation index by proliferating cell nuclear antigen staining, apoptotic index by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling staining, and angiogenesis by microvessel quantitation. Soy products reduced angiogenesis, increased apoptosis, and slightly reduced proliferation while showing no histopathological effects on the normal bladder mucosa. Our data suggest that soy isoflavones can inhibit bladder tumor growth through a combination of direct effects on tumor cells and indirect effects on the tumor neovasculature. Soy products warrant further investigation in bladder cancer prevention and treatment programs or as antiangiogenic agents.     

Lateral preference in post-traumatic stress disorder

Two sets of experiments on the role of tea in azoxymethane (AOM) induced colon cancer were performed. The first test involved male F344 rats given 1.25% solutions of black tea beginning at 5 weeks of age and ending at 51 days of age. At 6 and 7 weeks of age, they received 15 mg/kg AOM and were held for 50 weeks. Another group received the AOM dosage at 6 and 7 weeks and were placed on the tea solutions 2 days after the last AOM dosage, at 51 days of age, and held for the 50-week period. The end point was the occurrence and multiplicity of colon cancer, classified as in situ, exophytic, invasive and Peyer's patch carcinomas. Tea failed to affect the incidence and multiplicity of colon cancers when given during or after the AOM administration, but tea after AOM increased the multiplicity of exophytic carcinomas. In a second series of tests, solutions of 0.6, 1.25, 1.75 or 2.5% tea were given, beginning 1 week prior to the two AOM doses and extending for 42 weeks. Also, one group received 1.25% tea and 1.85% whole milk. The incidence of exophytic or invasive colon cancer and tumor multiplicity were similar in all treatment groups, although the incidence of exophytic neoplasms was higher with 2.5% tea. Thus, chronic administration failed to significantly change the incidence and multiplicity of the AOM-induced colon cancers. These findings are accounted for by the underlying mechanism, namely the fact that tea solutions do not alter the amount of cytochrome P-4502E1 required for the metabolic activation of AOM.     

Influence of diets containing high and low risk factors for colon cancer on early stages of carcinogenesis in human flora-associated (HFA) rats

Germ-free rats colonised with a human intestinal flora were fed diets containing high risk (HR) or low risk (LR) factors for colorectal cancer, and putative biomarkers were evaluated in the colonic mucosa; (i) proliferation, (ii) 1,2-dimethylhydrazine (DMH)-induced aberrant crypt foci and (iii) DMH-induced DNA damage. The HR diet was high in fat (45% of calories) and low in calcium and fibre, reflecting levels characteristic of typical western diets. The LR diet was low in fat (<5% of calories), and high in calcium and fibre. The nutrient/energy ratio of the two diets were similar. Mucosal crypt cell proliferation, assessed after microdissection, was higher on the LR diet (mean number of mitoses per crypt was 2.65 on the LR diet, and 1.62 on the HR diet; P < 0.05). Aberrant crypt foci (ACF) were assessed in the mucosa 12 weeks after DMH treatment. On the HR diet there were significantly more small ACF with 1 and 2 crypts per focus, but fewer ACF with 3, 5 and 7 or more crypts per focus. There was no significant difference in total ACF or the total number of crypts. The effect of diet on DNA damage in the colon was assessed in vivo by the comet assay. Animals were fed a HR or LR diet for 12 weeks before treatment with DMH or saline. For carcinogen-treated animals, DNA damage was significantly higher in colon cells from animals on the HR diet. On the LR diet both DNA damage and the induction of small ACF were reduced despite an increase in cell proliferation. The increase in large ACF on the LR diet may be attributable to elevated crypt cell proliferation possibly increasing crypt fission rates.     

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 xanthine 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 (15 mg/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.     

Computerized thermistor technique for indirect studies of esophageal blood flow

1. Intestinal atrophy contributes to the clinical difficulties of patients on parenteral nutrition. Systemic administration of epidermal growth factor reverses this effect, but there is concern over the clinical safety of intravenous administration of growth factors. We therefore investigated whether administration of luminal epidermal growth factor could reverse the atrophy induced in a rat model of parenteral nutrition when epidermal growth factor was given alone or in combination with soya bean trypsin inhibitor to reduce proteolytic digestion of the epidermal growth factor. 2. Infusion of soya bean trypsin inhibitor alone decreased intraluminal tryptic activity by about 90% but did not result in increased proliferation. Intragastric infusion of epidermal growth factor (72 micrograms/day per rat) caused a 26% increase in proliferation (determined by 2-h metaphase arrest) in the duodenum (P < 0.01) when compared with animals receiving 'control' intragastric infusion. However, intragastric epidermal growth factor had no effect on more distal regions of the bowel, probably reflecting rapid proteolysis of the epidermal growth factor by luminal proteases. In contrast, a trophic effect of luminal epidermal growth factor was seen in the duodenum (28% increase, P < 0.01) and jejunum (24% increase, P < 0.05) of animals which had received epidermal growth factor with soya bean trypsin inhibitor. This was probably due to the soya bean trypsin inhibitor decreasing the rate of degradation of epidermal growth factor by intestinal proteases, allowing biologically active epidermal growth factor to reach more distal portions of the bowel.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhancement by the tricyclic antidepressant, desipramine, of experimental carcinogenesis in rat colon induced by azoxymethane

The effects of the tricyclic antidepressant drug desipramine on the incidence, number and histology of colon tumors induced by azoxymethane (AOM), and on the serum norepinephrine (NE) concentration and the labeling index of colon mucosa were investigated in Wistar rats. Rats were treated s.c. with 7.4 mg AOM/kg body wt once a week for 10 weeks, and also s.c. with 10 mg desipramine hydrochloride (desipramine)/kg body weight until the end of the experiment. Treatment with desipramine significantly increased the incidence, but not the number, of colon tumors in week 35. However, it did not influence the location and the histological appearance of the colon tumors or the histological types of colon adenocarcinomas. Furthermore, it significantly increased the serum NE level and the labeling index of colon mucosa during and after AOM treatment. These findings indicate that desipramine enhanced the development of colon tumors and that its effect may be related to its effect in increasing proliferation of colon epithelial cells.     

Recent bacterial and viral infection is a risk factor for cerebrovascular ischemia: clinical and biochemical studies

Inbred mice vary in susceptibility to colon carcinogens such as 1,2-dimethylhydrazine (DMH). Differential susceptibility may depend, in part, on formation of promutagenic DNA methyl adducts within target colonic mucosa. The present study was undertaken to evaluate the extent of DNA adduct formation in susceptible (SWR) and resistant (AKR) mice acutely exposed to the colon carcinogen azoxymethane (AOM), a direct metabolite of DMH. In the first experiment, 8-week-old SWR and AKR mice were treated i.p. with 20 mg/kg AOM and sacrificed 6 h later. DNA was isolated from distal colon and liver, and O6-methylguanine (O6-MeGua) adduct levels were assessed by immunoslot blot (ISB) analysis, using a monospecific antibody raised against O6-methyldeoxyguanosine. HPLC-fluorescence detection was also used to quantitate 06-MeGua and 7-methylguanine (7-MeGua), and to generate standard curves. At 6 h, both O6-MeGua and 7-MeGua were significantly higher (2- to 3-fold, p < 0.05) in AKR colon, while an opposite pattern was found in liver. In Experiment 2, mice were injected with AOM (20 mg/kg) and euthanized 12 and 48 h later. At 12 h, O6-MeGua levels were higher in colons (1.4-fold) of SWR mice. Forty-eight hours after treatment, however, adduct levels in colon were markedly (5-fold) reduced in SWR but were unchanged from 12 h in AKR. To further compare activation of AOM in both strains, colon microsomes were incubated with AOM and calf thymus DNA. Comparable levels of O6-MeGua were detected by ISB, demonstrating equivalent metabolic capacity in both SWR and AKR mice. These studies suggest that differential susceptibility to AOM-induced colon carcinogenesis is not based on initial target tissue DNA alkylation and unlikely to depend on differential metabolic capacity.     

Effects of dietary magnesium deficiency in the rat: with special reference to ultrastructural examination

Epidemiologically, it has been suggested that dietary magnesium/calcium imbalance is associated with the risk of heart diseases. In the present study, the effects of magnesium deficiency and/or calcium over intake were investigated in rats. Male Sprague-Dawley rats were divided into 4 groups, and respectively fed basal diet (AIN-76) alone (Group 1), calcium-doubled AIN-76 diet (Group 2), magnesium-deficient AIN -76 diet (Group 3) and magnesium-deficient/calcium-doubled AIN-76 diet (Group 4) for 19 days. A biochemical assay using inductively coupled plasma showed that the magnesium concentrations of the femoral bone and serum were significantly (p < 0.001) lower in Groups 3 and 4 than in Group 1. The lipid peroxides of the heart in Group 4 and of the liver in Groups 3 and 4 were increased as compared to the Group 1 values although there was no statistical significance. Ultrastructurally, degenerative changes of organellas including mitochondria were observed in myocardial, liver and renal tubule cells of Groups 2-4. Severe degeneration such as disorganization, lysis and disarrangement of myofibrils was most evident in myocardial cells of Group 4. Our results thus suggest that dietary magnesium deficiency gives rise to retrogressive changes in some organs including the heart, and concurrent calcium overintake synergistically enhances the myocardial injury due to magnesium deficiency.     

Inhibition of N'-nitrosonornicotine-induced esophageal tumorigenesis by 3-phenylpropyl isothiocyanate

The ability of dietary isothiocyanates to inhibit the esophageal metabolism of N'-nitrosonornicotine (NNN) was examined in F344 rats. Following feeding of benzyl isothiocyanate (BITC), phenethyl isothiocyanate (PEITC), 3-phenylpropyl isothiocyanate (PPITC), 4-phenylbutyl isothiocyanate (PBITC) or 6-phenylhexyl isothiocyanate for 2 weeks, rats were killed and the esophagi were incubated in vitro with [5-3H]NNN. While dietary BITC, PEITC and PBITC all decreased NNN metabolism, dietary PPITC had the greatest effect, yielding inhibition ranging from 55 to 91% of the control production of various NNN metabolites. To determine the chemopreventive efficacy of PPITC on NNN-induced esophageal tumorigenesis, rats were fed AIN-76A diets containing 0, 1.0 or 2.5 micromol/g PPITC and were given untreated drinking water or drinking water containing 5 p.p.m. NNN. After 87 weeks, the experiment was terminated and the esophageal tumors were counted. Rats that were given untreated drinking water developed no tumors. Rats that were given 5 p.p.m. NNN and unadulterated AIN-76A diet had an esophageal tumor incidence of 71% and a multiplicity of 1.57 tumors/animal. The two dietary concentrations of PPITC reduced the incidence and multiplicity of NNN-induced esophageal tumors by >95%. These results demonstrate the remarkable chemopreventive efficacy of PPITC in the NNN-induced esophageal tumor model.