Melatonin and colon carcinogenesis: I. Inhibitory effect of melatonin on development of intestinal tumors induced by 1,2-dimethylhydrazine in rats

The effect of pineal indole hormone melatonin on colon carcinogenesis was firstly studied in rats. Two-month-old outbred female LIO rats were weekly exposed to 15 (experiment 1, groups 1 and 2) or to five (experiment 2, groups 1 and 2) s.c. injections of 1,2-dimethylhydrazine (DMH) at a single dose of 21 mg/kg of body weight. From the day of the first injection of the carcinogen DMH, the rats from groups 2 (experiments 1 and 2) were given melatonin five days a week during the night-time (from 18:00 h to 8:00 h), dissolved in tap water at 20 mg/l. The experiment was finalized in 6 months after the first injection of DMH. In both experiments the majority of tumors were localized in the descending colon. Tumors of the small intestines developed only in rats from experiment 1. Total incidence of colon tumors as well as tumors in different parts of the colon and the mean number of tumors per rat were much higher in rats from both groups in experiment 1 than that in rats from experiment 2. In experiment 1 melatonin failed to influence the total incidence of colon tumors. However, incidence of carcinomas in the ascending colon was significantly reduced (P < 0.01). The multiplicity of total colon tumors per rat, as well as the mean number of tumors, ascending and descending colon per rat, was also decreased under the influence of melatonin (group 2 vs group 1, P < 0.01). In the same experiment, melatonin slightly decreased the depth of tumor invasion and increased number of highly differentiated colon carcinomas induced by DMH. The percentage of small tumours in the descending colon among rats from group 2 was higher than that of group 1. Treatment with melatonin was also followed by a decrease in the multiplicity of DMH-induced tumors of the duodenum (group 2 vs group 1, P < 0.05) and by a decrease in the incidence of jejunum and ileum tumors (group 2 vs group 1, P < 0.05). In experiment 2, the inhibitory effect of melatonin on DMH-induced colon carcinogenesis was much more expressed than that in experiment 1. Thus, in group 1 the incidence of total colon tumors, ascending and descending colon tumors, was significantly decreased in comparison with group 2; also melatonin reduced the number of tumors per rat in the ascending and descending colon. The number of colon tumors that invaded only mucosa was significantly higher in group 2 than in group 1, P < 0.05. The ratio of highly differentiated tumors was increased (P < 0.05) and the ratio of low-differentiated tumors was decreased (P < 0.05) in rats exposed to melatonin (group 4) as compared with group 3. The number of large size tumors in the ascending and descending colon was decreased whereas the number of small size tumors (<10 mm2) was increased in those parts of the colon that were under the influence of melatonin in experiment 2. Thus, our results demonstrate the inhibitory effect of melatonin on intestinal carcinogenesis induced by DMH in rats.     

Malignant degeneration of experimental ulcerative colitis of the rat following s.c. injection of 1,2-dimethylhydrazine (author's transl)

Animal experiments were performed to answer the question whether ulcerative colitis is predisposed to malignant degeneration. Male Wistar rats were given aqueous solutions of degraded Carrageenan (4%; w/v). After induction of ulcerative colitis, 1,2-Dimethylhydrazine (DMH; 132 mg/kg body weight) was applicated during a period of 7 weeks. 17 of 18 rats developed multiple adenocarcinomas in the distal colon 15 weeks after the last injection of DMH. The Carrageenan induced colitis was localized predominantly in the distal part of the large bowel. Only 3 rats of a control group of 18 animals exposed to DMH only showed carcinomas of the colon. The difference is proven significant (P less than 0.01). Carrageenan for itself caused no malignancy. The results of the experiments demonstrate that, during ulcerative colitis, the colon of the rat is more susceptible to induction of cancer than the intact one.     

Effect of oyster mushroom (Pleurotus ostreatus) on pathological changes in dimethylhydrazine-induced rat colon cancer

The effect of 5% of dried oyster mushroom (Pleurotus ostreatus) in the diet on the dimethylhydrazine (DMH)-induced colon carcinogenesis was studied in male Wistar rats. DMH in a dose of 20 mg/kg of body weight was applied to animals once a week during a period of 12 weeks. Mushroom diet was applied either after treatment with DMH for another 21 weeks or during the whole experiment. Mushroom diet reduced significantly the incidence of lymphoid hyperplasia foci when mushroom was supplemented during the whole experiment. Tumour lesions could be characterized either as carcinoma in situ, or as infiltrating adenocarcinoma. Mushroom diet did not affect significantly the incidence of tumours. Nevertheless, a reduction in total number of tumours was observed in both groups of animals fed mushroom diet. A significant reduction of the number of tumour foci of the type carcinoma in situ was observed in animals fed the oyster mushroom during the whole experiment. Also these animals had the significantly lower number of aberrant crypt foci. Mushroom diet reduced the ornithine decarboxylase activity in the colon and in the liver when oyster mushroom diet was administered during the whole experiment.     

Inhibition of development of N,N'-dimethylhydrazine-induced rat colonic aberrant crypt foci by pre, post and simultaneous treatments with 24R,25-dihydroxyvitamin D3

It has recently been reported that new vitamin D3 derivatives can exert inhibitory effects on colon carcinogenesis in rats. In the present study the chemopreventive potential of 24R,25-dihydroxyvitamin D3 (24R,25(OH)2vitamin D3) was assessed in a murine model of colon carcinogenesis. In experiment 1, male 6-week-old F344 rats were administered N,N'-dimethylhydrazine (DMH) 20 mg/kg s.c. once a week 4 times. The rats were fed 24R,25(OH)2vitamin D3 at 10 ppm in the diet prior to (pre), together with (simultaneous) or after (post) DMH treatment. Modifying effects were assessed using aberrant crypt foci (ACF), putative preneoplastic lesions, as the end point markers in this model of colon carcinogenesis. After 8 weeks, pre and more markedly simultaneous administration of 24R,25(OH)2vitamin D3 was found to have reduced the total numbers of ACF and significantly inhibited the development of foci. After 16 weeks, numbers of foci with > or = 4 crypts, which are more likely to progress to tumors, were significantly reduced. The most pronounced inhibition of ACF development was noted in rats fed the 24R,25(OH)2vitamin D3 after DMH administration. The reduction was particularly marked in the proximal colon. Blood levels of calcium were not significantly increased over the control levels in groups administered DMH and the vitamin. Immunohistochemical staining showed numbers of proliferating cell nuclear antigen-positive cells to be lower in the colonic epithelia of rats fed the vitamin D3 metabolite than in the controls. In experiment 2, the effect of 24R,25(OH)2vitamin D3 on the alterations in c-fos, c-myc and c-jun oncogene expression in response to DMH administration was examined by northern blot analysis. The early increase in expression of ornithine decarboxylase (ODC) activity was not altered by 24R,25(OH)2vitamin D3. The results suggest that 24R,25(OH)2vitamin D3 is a cancer chemopreventive agent which may suppresses DMH induction of lesions and their subsequent development via an antiproliferative action.     

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.     

Gas chromatographic-mass spectrometric identification and quantitation of benzyl alcohol in serum after derivatization with perfluorooctanoyl chloride: a new derivative

In the present study, the effect of melatonin on oxidative DNA damage induced by kainic acid (KA) treatment was investigated. 8-hydroxy-deoxyguanosine (8-OH-dG) is a main product of oxidatively damaged DNA and was used as the endpoint in these studies. The levels of 8-OH-dG were found to be elevated in the hippocampus and frontal cortex of rats treated with KA. These elevated levels were significantly reduced in animals that were co-treated with melatonin. Thus, there was no difference in 8-OH-dG levels in the brain of control rats compared to those treated with KA (10 mg/kg) plus melatonin (10 mg/kg). The levels of 8-OH-dG also increased in the liver of rats treated with KA. This rise in oxidatively damaged DNA was also prevented by melatonin administration. Melatonin's ability to reduce KA-induced increases in neural and hepatic 8-OH-dG levels presumably relates to its direct free radical scavenging ability and possibly to other antioxidative actions of melatonin.     

Emotional stress and blood melatonin levels

Blood serum melatonin concentrations were measured in male Wistar rats exposed to acute water-immersion emotional stress (ES) during intraperitoneal injections of physiological saline or different doses of melatonin. ES increased blood melatonin levels in rats receiving physiological saline 1 hour before or just after ES. When physiological saline was administered just ES, blood melatonin concentrations remained unchanged. The blood levels of melatonin both in control and stressed animals injected with exogenous melatonin were higher than those in rats given physiological saline alone. Immersion ES decreased blood melatonin concentrations in rats receiving different exogenous melatonin doses just before ES. However, in rats given melatonin, 1.0 mg/kg, after ES, its blood levels after ES was higher than those in the animals unexposed to stress. The findings suggest that it is just exogenous rather than endogenous melatonin that is consumed in rats injected with its different doses just prior to immersion ES.     

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.     

An automatic infusion system for the measurement and control of uterine activity

23-day-old male rats were left intact, rendered blind and anosmic, pinealectomized together with blinding and anosmia, or subcutaneously implanted with graded doses of melatonin in beeswax immediately following surgical blinding and anosmia. 5 weeks later, blind, anosmic animals were found to have significantly depressed anterior pituitary, testicular, and accessory sex organ weights. Both pituitary and plasma prolactin and luteinizing hormone (LH) concentrations were also significantly suppressed. Pinealectomy of blind, anosmic animals completely restored testicular and accessory organ weights. Likewise, pituitary LH and prolactin and plasma LH levels were also restored to intact control levels by pineal removal. Only the highest dose of melatonin (1 mg) restored the testicular and accessory sex organ weights to those of the intact controls. As little as 1 microgram melatonin restored plasma and pituitary LH concentrations to the levels of the intact controls. However, none of the dosages of melatonin reversed plasma prolactin concentrations to those of the untreated animals. The decrease in pituitary prolactin induced by blinding and anosmia was reversed by pinealectomy or by the lower doses (1, 50 or 100 micrograms) of melatonin. These results indicate that melatonin can reverse the antigonadotrophic effects of blinding and anosmia in male rats. The minimal dose of melatonin required to restore testicular and accessory sex organ weights in blind, anosmic rats is 1 mg implanted subcutaneously in beeswax.     

Sulindac enhances cell proliferation in DMH-treated mouse colonic mucosa

In a previous study we reported that the NSAID sulindac had a marked inhibitory effect on the development of colonic tumours in mice treated with the carcinogen 1,2-dimethylhydrazine (DMH). In this study we examined the effects of sulindac in respect of cell-kinetic changes in mouse colonic mucosa as determined by flash labelling with the thymidine analogue bromodeoxyuridine (BrdUrd) at varying intervals during the process of colonic carcinogenesis. We also investigated the possibility that these changes may be modulated by misoprostol a prostaglandin E1 analogue. Four groups of 36 mice each were treated for 18 weeks with the following drug/s respectively: (1) DMH; (2) DMH and sulindac; (3) DMH, sulindac and misoprostol; and (4) DMH and misoprostol. Three animals from each group were killed each week between the sixth week and the eighteenth week after the start of the experiment. A 1-h flash label technique was employed and paraffin sections of colonic mucosa were examined. For each animal a total of 50 perfect axially cut crypts were chosen and the following parameters determined: crypt length, labelling index and labelling index distribution: the data were analysed using the computer program GLIM. For each of the four groups, crypt lengths increased significantly with the duration of treatment with no significant difference between the groups. In sulindac-treated animals the labelling index for all positions increased with duration of treatment whereas for animals not treated with sulindac there was no significant difference in labelling index with respect to duration of treatment. The administration of misoprostol did not appear to significantly alter the effects of sulindac. It is postulated that the observed increase in cell proliferation could be a compensatory phenomenon occurring secondary to loss of crypt epithelial cells by apoptosis induced by sulindac. Also the finding of an increase in labelling index mediated by a chemopreventive agent indirectly questions the rationale behind the therapeutic manipulation of crypt cell proliferation in order to reduce the risk of colon cancer.     

In vitro and in vivo protection against kainate-induced excitotoxicity by melatonin

In this study, the protective effect of melatonin against kainate (KA)-induced neurotoxicity was evaluated in vitro and in vivo. In rat brain synaptosomes, KA-induced oxidative stress was measured as shown by significant increases in both the basal generation of reactive oxygen species (ROS), assessed by a fluorescent method, and lipid peroxidation, evaluated as malondialdehyde (MDA) levels. Melatonin decreased, in a concentration-dependent manner, KA-induced lipid peroxidation. The intrinsic fluorescence of melatonin molecule hindered the evaluation of its protective effect against KA-induced ROS generation. However, melatonin was able to reduce FeSO4/ascorbate-induced ROS generation. The melatonin protective effect was confirmed by in vivo experiments: 73% of rats injected with KA (10 mg/kg i.p.) died within 5 days; melatonin administration i.p. significantly reduced mortality of the animals. The present results suggest that melatonin might be considered a pharmacological agent for the treatment of neurodegenerative pathologies.     

Lack of melatonin effects on insulin action in normal rats

Despite a large number of studies, the role of melatonin on glucose metabolism is still controversial. The aim of the present work was to further characterize the effect of melatonin on insulin action during: i) intravenous insulin tolerance test performed at different times of the day using melatonin, a melatonin agonist (S-20304), a melatonin antagonist (S-20928) or in pinealectomized rats. ii) euglycemic-hyperinsulinemic clamp performed in melatonin agonist-treated as well as in pinealectomized rats. The fall in glycemia after the insulin injection was not significantly affected by melatonin and melatonin agonist (S-20304) at ZT6, nor by the melatonin antagonist (S-20928) at ZT13 nor in pinealectomized animals at ZT6 in comparison to their respective control. Acute treatment with S-20304 or chronic suppression of melatonin by pinealectomy did not significantly alter basal plasma glucose and insulin levels or hepatic glucose production and whole body or individual tissue glucose utilization. These data do not give support to a crucial role of melatonin on insulin action in normal rats.     

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.     

Melatonin decreases bone marrow and lymphatic toxicity of adriamycin in mice bearing TLX5 lymphoma

When CBA male mice bearing TLX5 lymphoma were treated in the evening with a single i.v. dose of adriamycin (20-40 mg/Kg), the administration of a single pharmacological dose of melatonin (10 mg/kg s.c.) 1 hr earlier reduced the acute mortality from 10/24 to 2/24. The increase in survival time caused by adriamycin over drug untreated controls was not reduced by melatonin. The administration of melatonin alone did not cause any antitumor or evident toxic effect. Melatonin also attenuated the reduction caused by adriamycin in the number of bone marrow GM-CFU, and of CD3+, CD4+ and CD8+ splenic T-lymphocyte subsets. Reduced and total glutathione levels were decreased in the bone marrow and in the liver cells of the animals treated with adriamycin, and were significantly restored by melatonin. Moreover, lipid peroxidation by adriamycin was reduced by melatonin, as indicated by malondialdehyde measurement in the liver of the treated animals. These data indicate that the protective effects of melatonin against the host toxicity of the prooxidant antitumor drug, adriamycin, might be attributed at least partially to its antioxidant properties. These findings appear of interest in relation to the physiological rhythmic levels of endogenous melatonin and to the chronotoxicology of anthracyclines.     

Surgical management of retinal detachments related to coloboma of the choroid

We examined the influence of extruded chickpeas and wheat relative to casein and wheat in a dimethylhydrazine (DMH)-induced colon tumor study in male Sprague-Dawley rats. The three diets, based on a modified AIN76 rodent diet with fat present at 10 g/100 g dry matter (DM), were as follows: casein with wheat starch (Cas/S) as control, casein with wheat (Cas/W) and chickpeas with wheat (CP/W). All diets were fed from 5 wk of age throughout the 28-wk study. At 28 wk, there was a significantly lower incidence of large intestinal tumors in rats fed Cas/W relative to those fed CP/W ( 11 vs. 56%, chi-square test, P = 0.018). The colonic tumor burden (tumors/tumor-bearing animal) was not different in Cas/W-fed and CP/W-fed rats (1 vs. 1.7), but the tumor mass index was significantly lower in the former group (0.22 vs. 1.21, P = 0.026). Rats fed the CP/W diet had significantly lower plasma cholesterol concentration (P < 0.01) than rats fed the other two diets. The cecal contents of rats fed the CP/W diet had significantly greater relative weights (46%, P < 0.05) than those of the Cas/W-fed rats; this was associated with higher concentrations of all short-chain fatty acids. Fecal analyses showed significantly (P < 0.05) higher concentrations of total fat (54%), total steroids (83%) and secondary bile acids (179%) in the CP/W-fed rats relative those fed Cas/W. There were higher concentrations of nitrogen in the feces of CP/W rats relative to the Cas/W-fed rats (84%, P < 0.05), associated with greater fecal weights (67%, P < 0.05). Although wheat and its fibers have been shown to be protective against DMH-induced cancers in rats, this was not the case in this study in which chickpeas (45 g/100 g diet) provided the protein and were an important source of soluble fiber. Elevated fat, secondary bile acid concentrations and/or nitrogenous compounds could be responsible for the increased colon tumorigenesis seen and may reflect a legume effect.     

Daily melatonin administration at middle age suppresses male rat visceral fat, plasma leptin, and plasma insulin to youthful levels

Human and rat pineal melatonin secretion decline with aging, whereas visceral fat and plasma insulin levels increase. Melatonin modulates fat metabolism in some mammalian species, so these aging-associated melatonin, fat and insulin changes could be functionally related. Accordingly, we investigated the effects of daily melatonin supplementation to male Sprague-Dawley rats, starting at middle age (10 months) and continuing into old age (22 months). Melatonin was added to the drinking water (92% of which was consumed at night) at a dosage (4 microg/ml) previously reported to attenuate the aging-associated decrease in survival rate in male rats, as well as at a 10-fold lower dosage. The higher dosage produced nocturnal plasma melatonin levels in middle-aged rats which were 15-fold higher than in young (4 months) rats; nocturnal plasma melatonin levels in middle-aged rats receiving the lower dosage were not significantly different from young or middle-aged controls. Relative (% of body wt) retroperitoneal and epididymal fat, as well as plasma insulin and leptin levels, were all significantly increased at middle age when compared to young rats. All were restored within 10 weeks to youthful (4 month) levels in response to both dosages of melatonin. Continued treatment until old age maintained suppression of visceral (retroperitoneal + epididymal) fat levels. Plasma corticosterone and total thyroxine (T4) levels were not significantly altered by aging or melatonin treatment. Plasma testosterone, insulin-like growth factor I (IGF-I) and total triiodothyronine (T3) decreased by middle age; these aging-associated decreases were not significantly altered by melatonin treatment. Thus, visceral fat, insulin and leptin responses to melatonin administration may be independent of marked changes in gonadal, thyroid, adrenal or somatotropin regulation. Since increased visceral fat is associated with increased insulin resistance, diabetes, and cardiovascular disease, these results suggest that appropriate melatonin supplementation may potentially provide prophylaxis or therapy for some prominent pathologies associated with aging.     

Chemoprevention of colon cancer by organoselenium compounds and impact of high- or low-fat diets

BACKGROUND: Observational and experimental studies have suggested that dietary supplementation with selenium can inhibit the development of colon cancer. However, many forms of selenium are toxic. Consequently, the development of efficacious compounds with low toxicity has been pursued. PURPOSE: Two synthetic organoselenium compounds, p-methoxy-benzyl selenocyanate (p-methoxy-BSC) and 1,4-phenylenebis(methylene)selenocyanate (p-XSC), were tested for their ability to inhibit colon carcinogenesis in rats that were treated with the carcinogen azoxymethane and fed low- or high-fat diets. METHODS: Groups of 5-week-old male F344 rats (42 animals/ group) were fed either a high-fat diet or a low-fat diet with or without added p-methoxy-BSC (10 or 20 parts per million [ppm]) or p-XSC (20 ppm). Two weeks later, 30 animals in each group received a subcutaneous injection of azoxymethane (15 mg/kg body weight); 1 week later, they received a second injection. The remaining 12 rats in each group received two injections of saline. Three days after the second injection of carcinogen or saline, animals being fed diets with p-methoxy-BSC or p-XSC were switched to corresponding organoselenium-free low- or high-fat diets for the remainder of the study to determine the effects of the selenium compounds on the initiation phase of colon carcinogenesis. At that time, groups of animals that had been maintained on organoselenium-free low- or high-fat diets were switched to diets containing p-methoxy-BSC or p-XSC until the end of the study to determine the effects of these compounds on the postinitiation phase of colon carcinogenesis. All animals were killed during the 38th week after azoxymethane or saline treatment, and histopathologic analysis of the colon tumors was performed. Colon tumor incidence and multiplicity were analyzed statistically. RESULTS: No obvious toxic effects were observed following dietary administration of 10 or 20 ppmp-methoxy-BSC or 20 ppm p-XSC. Administration of 20 ppm p-methoxy-BSC in a high-fat diet during the initiation and postinitiation phases of colon carcinogenesis significantly (statistically) reduced colon tumor incidence; 10 ppmp-methoxy-BSC in a high-fat diet significantly reduced colon tumor incidence but only when it was given during the postinitiation phase. Colon tumor incidence was also significantly reduced when 20 ppm p-XSC was given in a high-fat diet during the initiation phase of colon carcinogenesis. When 20 ppm p-XSC was administered in either a high-fat diet or a low-fat diet during the postinitiation phase, both colon tumor incidence and multiplicity were significantly reduced; the greatest reductions were in animals fed a low-fat diet. CONCLUSIONS: In this model system, p-methoxy-BSC and p-XSC are effective agents for the chemoprevention of colon cancer. The effects of p-XSC were enhanced in animals fed a low-fat diet.     

Histopathological and lipid changes in experimental colon cancer: effect of coconut kernal (Cocos nucifera Linn.) and (Capsicum annum Linn.) red chilli powder

Influence of coconut kernal and red chilli on the metabolism of lipids was studied in animals given 1,2-dimethylhydrazine (DMH). The average weight gain by the animals in the coconut kernal group was more than DMH and chilli treated groups. The concentration of cholesterol showed a decrease and phospholipids an increase in most of the tissues studied, of the kernal groups. The cholesterol-phospholipid ratio was found to be increased in most of the tissues of all experimental groups, when compared to control animals. HMG CoA reductase activity decreased in the high fat and most of the tissues of the kernal + DMH, kernal + chilli and kernal + chilli + DMH groups, while it increased in the DMH, chilli and chilli + DMH groups. Histopathological studies showed that coconut kernal supplemented animals had fewer papillae, lesser infiltration into the submucosa and lesser changes in the cytoplasm with decreased mitotic figures. Coconut kernal, thus reduced the mutagenic and carcinogenic effect of chilli and DMH respectively.     

Biotransformation of monoterpenes, bile acids, and other isoprenoids in anaerobic ecosystems

RGH-2716 is a novel 1-oxa-3,8-diazaspiro[4.5] decan 2-one, which was published to have potent inhibitory effect on neuronal Na and Ca movement and stimulatory action on nerve growth factor (NGF)-production, as well as to show significant antiamnesic activity in experimental amnesia models. The aim of the present experiments was to study the effect of the compound on the learning process and on the different stages of memory using water-labyrinth in normal and memory impaired young animals, as well as to study cognitive effect of RGH-2716 on aged animals. At the doses of 0.5 mg/kg i.p. or 3 mg/kg p.o. given before daily swimming, this compound improved the learning process of young animals impaired by either diazepam (DIA) or scopolamine (SCOP). In retrograde amnesia model RGH-2716 (3 mg/kg p.o.) significantly ameliorated consolidation process and retrieval of information impaired by SCOP or DIA. Nimodipine and vinpocetine (10 mg/kg p.o.) showed moderate effect compared to RGH-2716. Aged rats pretreated with daily i.p. RGH-2716 performed the tasks with significantly fewer errors and shorter swimming time than untreated aged rats. When aged animals had to solve a new labyrinth problem, treated aged rats showed significantly better learning ability than aged controls. One month of oral treatment of aged rats with 3 mg/kg dose of RGH-2716 two times daily resulted in a "tendency-like" improvement in learning of aged Fischer 344 and spontaneously hypertensive (SH) rats. The present results make RGH-2716 an interesting compound for the treatment of cognitive disorders.     

Comparative anticancer effects of vaccination and dietary factors on experimentally-induced cancers

The role of two major factors were analyzed in the prevention of experimentally-induced cancers: a) vaccination of animals with polyclonal IgG generated against the soluble p53 antigen and b) feeding of animals with diets rich with dietary fibers or fat. a) In vaccination, a few attempts have been made to utilize p53 protein as a tumor suppressor. IgG generated against the cytoplasmic, soluble p53 antigen from tumor-bearing rats prevents the carcinogenic effect of 1,2-dimethylhydrazine (DMH) decreasing significantly the number of tumor-bearing rats in vaccinated group compared with non vaccinated controls and preventing benign tumors from becoming malignant. The antitumor effect of vaccination is accompanied by a significant increase in the serum-level of p53 antigen in vaccinated rats compared with non vaccinated controls. The immune response of a host to vaccination activates the lymph components of the spleen, and this activation is manifested by the multiplication of the number of lymphocytes which are generated against specific antigens. This multiplication is achieved by the higher division of the antigen-specific lymphoblasts with their subsequent transformation into plasma cells. These cells synthesize the specific protein (IgG). One such protein is the tumor-associated p53 protein, which is synthesized by rats against rabbit anti-p53 IgG. b) The role of dietary factors in the prevention of chemically induced cancer was reviewed on two models: the role of high fiber diets in prevention of colon cancer, and the role of high fat diets in the prevention of mammary gland cancer. Experiments in colon cancer showed that 20% cellulose decreased significantly tumor incidence caused by DMH. The tumor-preventive effect of a cellulose diet was accompanied by increased enzyme concentrations, such as ornithine decarboxylase, thymidine kinase and beta-glucuronidase. This effect was accompanied by activation of some cellular mechanisms, i.e. apoptosis, proliferating cell nuclear antigen (PCNA) and p53 protein synthesis. Experiments in mammary glands cancer showed that a 15% olive-oil diet reduced significantly the tumor incidence caused by 9,10-dimethyl-1,2-benzanthracene. The antitumor effect of the olive-oil diet was connected to its content of monounsaturated fatty acids, such as oleic and palmitic acids. The promotive tumorigenic effects of other high-fat diets (avocado, soybeans) were associated with high content of some polyunsaturated fatty acids (linoleic and alpha-linolenic). Different diets have different targets. The effect of the same diet depends on its anti-tumor substances content. CONCLUSIONS: Vaccination and some diets have similar mechanism in their tumor-preventive effects.