A protective role of 1,25-dihydroxyvitamin D3 in chemically induced rat colon carcinogenesis.

The intriguing observation has been made that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] receptors are present in tissues not involved in calcium homeostasis and that 1,25(OH)2D3 exerts an antiproliferative, differentiation-promoting action in a variety of cancer cell lines, including cells of the large intestine. It was therefore deemed of interest to study 1,25(OH)2D3 expression and biological activity in a murine model of colon carcinogenesis. Colon carcinogenesis was induced in male rats by the sequential administration of 1,2-dimethylhydrazine dihydrochloride (DMH). Levels and binding characteristics of 1,25(OH)2D3 receptors were assessed in control and DMH-treated rat colonic mucosal high-speed supernatants. In concurrent studies, 1,25(OH)2D3 was administered (s.c., 400 ng/rat) prior to, together with and after DMH challenge and the activity of ornithine decarboxylase (ODC), a growth-related DMH-induced enzyme, was determined in colonic cytosols. Serum Ca2+ levels were measured concurrently. Rats submitted to identical treatment schedules were killed 10 weeks after termination of DMH administration and the whole colon was opened and examined for tumors. The results show that (i) rat colonic mucosa possesses a single class of high-affinity 1,25(OH)2D3 receptors; (ii) DMH administration provokes a marked reduction (50%) in 1,25(OH)2D3 binding sites without affecting Kd values; (iii) DMH administered concurrently with 1,25(OH)2D3 suppressed the vitamin D-induced hypercalcemia and restored serum Ca2+ concentrations to basal levels; and (iv) 1,25(OH)2D3 delivered prior to DMH challenge obliterated the typical DMH-induced early colonic ODC activity peak and markedly reduced (50%) the number of colon adenocarcinomas. The present findings indicate that a colon-specific potent carcinogen interferes with the biological expression of 1,25(OH)2D3 and that vitamin D administered prior to a carcinogenic insult is able to reduce significantly the incidence of colon tumors, presumably acting as an antiproliferative or differentiation-promoting agent.     

Dietary calcium and vitamin D modulate 1,2-dimethylhydrazine-induced colonic carcinogenesis in the rat

To determine whether supplemental dietary calcium and/or vitamin D deficiency are involved in modulating colon cancer induced by 1,2-dimethylhydrazine (DMH), Sprague-Dawley rats were fed diets containing either: (a) a normal content of calcium (0.87%) and phosphorus (0.60%) with 2.2 IU of vitamin D3 per g of feed (group A); (b) the same diet as group A, but with calcium and phosphorus increased to 1.80 and 0.80%, respectively (group B); or (c) a vitamin D-deficient diet with supplemental calcium (1.80%) and phosphorus (0.80%) (group C). After 6 weeks on their respective diets, one-half the animals in each group were given s.c. injections of either vehicle or DMH (20 mg/kg body weight/week) for 26 weeks. Animals were then sacrificed and the incidence of tumors as well as the number of tumors per tumor-bearing rat were determined. Colonic mucosal polyamine levels were measured after 15 weeks of exposure to vehicle or DMH, before development of histologically recognizable neoplasms. The results of these experiments demonstrated that neither calcium supplementation alone nor supplemental calcium in conjunction with vitamin D deficiency altered the incidence of colonic cancer induced by this carcinogen. Supplemental calcium, however, significantly decreased the number of rats with multiple tumors and reduced tumor size. Moreover, vitamin D deficiency abolished these protective effects of calcium on colon cancer in this experimental model. DMH treatment increased polyamine levels in the premalignant colonic mucosa in group A rats. This carcinogen-induced effect was blunted by high dietary calcium. Vitamin D-deficient, calcium-supplemented rats (group C) showed an increase in N1-acetylspermidine, but not the other polyamines, with DMH treatment.     

Increased mucosal ornithine decarboxylase activity in human gastric cancer

The induction of ornithine decarboxylase (ODC), a key enzyme of polyamine biosynthesis, is an early and obligatory event in the tumor-promoting step in animal models. The enzyme activity is also elevated in some human premalignant lesions. We determined the ODC activity in human gastric cancer tissue and in the mucosa of cancer-bearing stomach. We concluded that gastric cancer tissue had significantly elevated ODC levels over those of mucosa (157.8 versus 45.7, respectively; P less than 0.05). Among mucosa of the stomach, that of the pyloric gland had higher ODC activity than that of the fundic gland (42.8 versus 21.6, respectively; P less than 0.05). Moreover, mucosa from the cancer-bearing stomach had high ODC activity compared with gastric mucosa without cancer. ODC activity in cancer tissue and mucosa from cancer-bearing stomach was activated by GTP. In rat experiments, the properties of ODC induced by gastric carcinogen were analyzed. Transiently induced ODC by a single gastric intubation of N-methyl-N'-nitro-N-nitrosoguanidine was not activated by GTP whereas constitutively expressed ODC of N-methyl-N'-nitro-N-nitrosoguanidine-induced cancer-bearing stomach was activated by GTP. These results suggest that some tumor-promoting stimuli may be concerned in human gastric carcinogenesis and that mucosal ODC activity may be a useful marker for assessing the risk of gastric malignancy.     

Selenium and difluoromethylornithine additively inhibit DMH-induced distal colon tumor formation in rats fed a fiber-free diet

We investigated the effects of difluoromethylornithine, an inhibitorof ornithine decarboxylase (ODC) and selenium supplementationon tumor formation induced by the carcinogen 1, 2-dimethylhydrazine(DMH) in Sprague-Dawley rats. A biochemical link between polyaminebiosynthesis and selenium metabolism to its cancer preventativeform has been suggested by the common requirement of S-adenosylmethio-nine.One-hundred and twenty male Sprague-Dawley rats were dividedinto experimental (n = 80) and control (n = 40) groups. Experimentalanimals received DMH 20 mg/kg s.c. for 20 weeks. Animals werefed either a regular diet (selenium content 0.2 p.p.m.) or ahigh selenium diet (5 p.p.m.) with or without 0.2% DFMO in thedrinking water. At death, week 30, animal weights within experimentalor control groups were not different between the four diet treatmentgroups. Tumor number and incidence in the proximal colon wasnot affected by DFMO treatment, selenium supplementation orthe combined treatment. In contrast, in the distal colon, 19tumors developed in the DFMO treated group, 22 tumors in thehigh selenium group and only 12 tumors in the combined highselenium/DFMO treatment group compared to 32 tumors in the regulardiet group. Similarly, tumor incidence was decreased by DFMOand selenium supplementation and their effects were additive.In control animals, ODC activity was decreased by DFMO treatmentand selenium supplementation in the distal colon and liver,but not the proximal colon. ODC activity of tumor tissue wasgreater than normal colon tissue from diet paired animals forproximal and distal colon, except for distal colonic tumorsin the high selenium/DFMO treatment group. Polyamine content,however, did not correlate with ODC activity in normal or neoplastictissue. In general, S-adenosylmethionine levels from normalcolon and liver tissue were unaffected by diet treatment. Seleniumsupplementation in combination with DFMO treatment selectivelyinhibited distal colon tumor formation in rats fed a fiber-freediet.     

Effect of diallyl sulfide on MNNG-induced nuclear aberrations and ornithine decarboxylase activity in the glandular stomach mucosa of the Wistar rat

In previous investigations using models for gastrointestinal cancer, the anticarcinogenic effects of diallyl sulfide (DAS), an organosulfur compound present in garlic, was established. In this study, we conducted experiments to determine whether DAS modulates two biomarkers, nuclear aberrations (NA) and ornithine decarboxylase (ODC) activity, in the glandular stomach mucosa of the Wistar rat. N-methyl-N'-nitro-N-nitrosoguanidine (MN-NG) induced dose-related NA and ODC activity in the glandular stomach 24 h and 6 h, respectively, after oral intubation with the carcinogen. Either oral or parenteral pretreatment with DAS significantly reduced the MNNG induction of NA or ODC. Furthermore, the suppressions were observed to be dose dependent. These data suggest that DAS may potentially inhibit MNNG-induced gastric cancer. In view of recent epidemiologic evidence linking reduced risk for gastric cancer with increased consumption of allium vegetables, it is clear that DAS has pluripotent effects as an anticarcinogen, although studies addressing a mechanism of action have yet to be reported.     

大蒜天然提取物二烯丙基硫醚对亚硝基胍诱发的大鼠腺胃粘损害...

In order to predict the chemopreventive activity of garlic on gastric cancer, the effect of diallyl sulfide (DAS), a natural extract of the garlic, on MNNG-induced nuclear aberration (NA) and ornithine decarboxylase (ODC) activity in Wistar rat glandular stomach mucosa was studied. The results showed that NA and ODC activity were positively correlated to MNNG dose given 24 and 6 hr after oral intubation with MNNG. Oral or parenteral pretreatment with DAS significantly and dose-dependently inhibited MNNG-induced NA and ODC. These data suggest that DAS has the potential to inhibit MNNG-induced gastric cancer, supporting the epidemiological evidence of the chemopreventive effect of garlic on gastric cancer.     

Risk analysis of carcinogenesis in the remnant stomach with measurement of ornithine decarboxylase activity

Gastric ornithine decarboxylase (ODC) activity was measured as a biomarker of tumor-promoting activity in the remnant stomach of rats and humans. Gastrectomy of Wistar rats utilizing the Billroth I method caused a significantly high induction of ODC, and use of the Billroth II method caused a significantly higher induction of ODC than the Billroth I method. In humans, ODC activity of remnant gastric cancer tissue, normal-appearing mucosa of remnant gastric cancer patient, and remnant gastric mucosa without cancer after the Billroth II method were significantly higher than that of normal gastric mucosa without gastrectomy. ODC activity of remnant gastric mucosa without cancer after the Billroth II method was significantly higher than that after the Billroth I method. Risk of carcinogenesis was high in the remnant stomach, especially after the Billroth II method. © 1994 Wiley-Liss, Inc.     

In vivo exposure of rats to a weak alternating magnetic field increases ornithine decarboxylase activity in the mammary gland by a similar extent as the carcinogen DMBA

Magnetic field (MF) exposure has been discussed in the process of tumor promotion as indicated by epidemiologic data as well as laboratory studies. However, the precise mechanisms of tumor promoting effects of MFs are unknown. Tumor promotion is often accompanied by an increase in the activity of the enzyme ornithine decarboxylase (ODC), i.e. a key enzyme in the biosynthesis of polyamines, which have roles in cell proliferation and control of gene expression. In the present work, we studied if exposure of female rats to a 50-Hz MF with a flux density of 50 μT influences ODC activity in different tissues, including the mamma. Rats were exposed for a period of 6 weeks either with or without oral administration of the chemical carcinogen DMBA and all data were compared with those from shamexposed controls. Magnetic field exposure resulted in an approximate doubling of ODC in mammary tissue. A significant ODC increase was also seen in the spleen, but not in the liver, small intestine, bone marrow, and ear skin. The ODC increase produced by MF exposure in the mammae was of similar magnitude as that observed after treatment with DMBA. Combined treatment with MF and DMBA was not more effective in increasing ODC than treatment with DMBA alone, except for liver tissue. The present results on in vivo increases of ODC by MF exposure strengthen the hypothesis that weak 50-Hz MFs affect ODC activity and may thus function as a tumor-promoting or copromoting agent.     

Polyamine levels in sarcoma-bearing rats in relation to growth and necrosis of the tumour cells

Putrescine (PU), spermidine (SPD) and spermine (SPM) levels in blood serum of MC Sa 1828 P-bearing rats have been studied in relation to tumour weight and the histological picture. A statistically significant increase of PU and SPD was found in the course of tumour development. Decrease in the level of polyamines in the necrosis stage was also found. Only increased SPD level appeared in the period of intensified necrosis, accompanied by lymphocyte infiltration.     

Effect of retinoids on the induction of colon cancer in F344 rats by N-methyl-N-nitrosourea or by 1,2-dimethyihydrazine

The possible modifying effect of synthetic and natural retinoidson the incidence of colon cancer in rats induced by 2 intrarectaldoses of 2.5 mg of N-methyl-N-nitrosourea (MNU) given once aweek for 2 successive weeks or a single 150 mg/kg body weightdose of 1,2-dime-thylhydrazine (DMH), s.c. was investigated.Emphasis was on the effect of the development of early tumorsas visualized by endoscopy. With the retinoids N-ethyl-retinamide,N-2-hydroxyethylretinamide, N-(4-hydro- xyphenyl)-all-trans-retinamide(RAHA), and retinyl acetate (RA) administered orally after thecarcinogens, significant differences in early developing tumorswere not found. At histopathological examination of the tumorsthe RAHA + DMH group had significantly fewer adenomas per animal.The percentage of adenoma bearing rats was significantly lowerin groups receiving RAHA + DMH or RA + DMH. However, food consumptionwas lower in rats consuming either RAHA or RA. Retinyl palmitate(RP) and RAHA was administered intrarectally to MNU-inducedrats either before or after the carcinogen. When administeredbefore MNU, RP caused a significant increase in the percentageof tumor bearing animals and the average number of tumors peranimal as visualized endos copically. At histopathological examination,all retinoid groups except RAHA given after the carcinogen,produced significantly more adenomas per animal and a significantlygreater adenoma incidence than did the control groups. Thus,in two systems, the oral administration of retinoids did notclearly inhibit the early or later stages of colon tumor development.Inirarectal infusion of two retinoids had no effect on colonicmor phology but at histopathological examination of later stagetumors there was an enhanced adenoma response.     

The role of polyamines in interferon and retinoic acid mediated synergistic antiproliferative action

Retinoic acid alone has no effect on the human breast cancer cell line BT-20 but can amplify the antiproliferative action of interferon-gamma (IFN-gamma). In our system ornithine decarboxylase (ODC) activity correlates well with growth rate; it was investigated whether the antiproliferative effects of IFN-gamma and IFN-gamma plus retinoic acid could be attributed to suppression of ODC activity. The ODC inhibitor difluoromethylornithine (DFMO), which is active as a single agent did not enhance growth inhibition induced by the biological response modifiers. The substitution of the BT-20 cells with putrescine, the product of the enzymatic reaction mediated by ODC, reversed DFMO induced antiproliferative action. On the other hand putrescine did not affect the proliferation of BT-20 cells treated with interferon alone or in combination with retinoic acid.     

Spermidine/spermine N-1-acetyltransferase as a marker of dimethylhydrazine-induced colonic carcinogenesis in the rat

We investigated whether spermidine/spermine N-1-acetyltransferase (SSAT) might be a useful marker of 1,2-dimethylhydrazine (DMH)-induced colorectal tumors in rats. Male Wistar rats were given DMH weekly for 5 weeks (150 mg/kg/dose), and then sacrificed 5, 10, 15 or 20 weeks after the first dose. Tumors were detected in 2 of 6 rats sacrificed at 10 weeks. Colorectal mucosal SSAT activity was 25.8+/-2.4 pmoles/mg/min before dosing, and only slightly higher at 5 weeks (36.8+/-10.0). From week 5 onward, activity rose sharply and significantly, reaching 87.2+/-29.0 by week 20. These results indicate that SSAT is an excellent marker of DMH-induced colonic carcinogenesis.     

Hypergastrinemia in rats with azoxymethane-induced colon cancers

Gastrin has been suggested to be involved in the promotion and progression of colon cancer. Mice colon cancers and colon-carcinoma cell lines are stimulated to grow by gastrin, and gastrin receptors have been found in the majority of human colon-tumor specimens. High serum gastrin levels have been reported in patients with colon polyps and cancers, together with increased ornithine decarboxylase (ODC) activity. Since gastrin stimulates ornithine decarboxylase in colon cancer cells in vitro it has been suggested that increased synthesis of intracellular polyamines is one of the mechanisms activated by the hormone. In order to confirm the presence of hypergastrinemia in colon cancer and to investigate the relationship between plasma gastrin and tumor growth, we used an animal model of colon carcinogenesis that minimizes the possible bias of human studies, related to varying diet, age and environmental factors. We evaluated blood gastrin levels in 35 rats with colon cancer induced by the carcinogen azoxymethane (AOM), and we correlated gastrinemia with tumor proliferation, assessed by thymidine-labeling index (TLI) and ODC activity; 6 animals constituted the control group. Gastrin levels in rats with AOM-induced tumors were significantly higher than in controls. Significantly higher TLI and ODC activity were found in the tumors of hypergastrinemic rats than in neoplasms of animals with normal gastrin levels. Our data provide additional evidence of a role for gastrin as trophic hormone for colon neoplastic cells. © 1995 Wiley-Liss, Inc.     

Induction of hepatic ornithine decarboxylase by hypolipidemic drugs with hepatic peroxisome proliferative activity

The present investigation was conducted to determine (1) ifhepatomegalic and mitogenic effects of selected hypolipidemicperoxisome proliferators are associated with an elevation ofhepatic ornithine decarboxylase (ODC) levels and (2) if inductionof ODC is a specific event associated with the development ofpreneoplastic hepatocellular foci and the eventual formationof hepatomas. Following a single i.p. dose of Wy-14, 643 (Wy),the hepatic ODC activity in rats rose sharply, reaching a peakat 8 h, and returned to the normal level by 24 h. Other peroxisomeproliferators tested (methyl clofenapate, BR-931 and nafenopin)also increased the hepatic ODC activities significantly 8 hafter i.p. administration of a single dose. Continuous dietaryadministration of Wy, whether or not these animals were previouslyinitiated with the carcinogen diethylnitros-amine (DEN), resultedin a sustained elevation of hepatic ODC activity. Although Wyexerted an enhancing effect on DEN-initiated tumorigenesis,there was no additional increase of ODC activity. There wasno correlation between the level of ODC induction and the presenceor absence of altered liver cell foci. These results suggestthat induction of ODC by peroxisome proliferators is not a specificevent associated with the development of preneoplastic fociand hepatocarcino-genesis, but is an event associated with thesustained maintenance of hepatomegaly and increased liver cellproliferation.     

Growth-related enzyme activities in crypt compartments during rat colon carcinogenesis

The activities of the growth-related enzymes ornithine decarboxylase (ODC) and casein kinase II (CK-II) were assayed along the colon crypt axis in a precise temporal sequence following administration of 1,2-dimethylhydrazine (DMH) to male rats. The time course of events monitored in colonic cell populations sequentially harvested by a scraping procedure shows that the potent carcinogenic insult induces an early and late ODC activity peak: the distinct biphasic response of the decarboxylase was observed in all colonic crypt compartments. The activity gradient of CK-II was markedly altered in DMH-treated cell populations: brisk activity of the kinase was observed in the upper crypt zone, the preserve of the mature, non-dividing colonocyte. The enhanced responses of ODC and of CK-II to DMH proceeded the actual polyp and tumor formation. The polycations spermine and spermidine, bioactive molecules formed in the ODC-controlled polyamine pathway, were shown to markedly activate colonic CK-II. This observation suggests that ODC and CK-II, enzymes with different catalytic purposes, crosstalk within the colonic crypt continuum. The present findings indicate that the differentiation arrest of colonic cells and their misplacement in forbidden zones of the crypt axis during DMH-induced carcinogenesis is accompanied by early alterations in the activity and topology of disparate enzymes which are part of the orderly growth program of the normal colonic cell.     

Effect of chemopreventive agents on intermediate biomarkers during different stages of azoxymethane-induced colon carcinogenesis.

Chemoprevention of colon cancer is emerging as an alternative to therapy with a broad potential for reducing cancer incidence in defined high-risk groups and the general population. Besides several chemopreventive agents in use and under investigation, D,L-alpha-difluoromethylornithine (DFMO) and piroxicam have been shown to effectively inhibit colon carcinogenesis in rodents. A variety of proliferation-related parameters have been suggested as potential intermediate markers of cancer risk that could be used to monitor the progress of chemoprevention in clinical trials. We have investigated the effect of chemopreventive agents, DFMO, and piroxicam on mucosal ornithine decarboxylase (ODC) and tyrosine-specific protein kinase (TPK) activities during different stages of azoxymethane (AOM)-induced colonic carcinogenesis in male F344 rats in order to examine the plausibility of using these enzymes as intermediate biochemical markers of colon cancer. Groups of male F344 rats were fed modified AIN-76A diets containing 0 or 150 ppm piroxicam or 4000 ppm DFMO and given s.c. injections of AOM dissolved in normal saline at a dose of 15 mg/kg body weight/week, once weekly, for 4 weeks. Vehicle control groups received s.c. equal volumes of normal saline. Groups of animals were then sacrificed at 0, 4, 16, 24, and 32 weeks after AOM or saline treatment, and their colonic mucosa was analyzed for ODC and TPK activities. AOM treatment significantly increased mucosal ODC as well as TPK activities. AOM-induced ODC and TPK activities were significantly suppressed by dietary DFMO progressively at all stages of colon carcinogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic Trypanosoma cruzi infection associated with low incidence of 1,2-dimethylhydrazine-induced colon cancer in rats

Experimental data have demonstrated that chronic infection with intracellular parasites may enhance resistance against some types of tumour. This phenomenon has not yet been demonstrated for experimental Trypanosoma cruzi chronic infection. This study investigated the effect of a specific colon cancer inducing drug, 1,2-dimethylhydrazine (DMH), on chronically T.cruzi infected Wistar rats. Infection was obtained by inoculation of 10(5) tripomastigote forms by subcutaneous (s.c.) route. Acute phase of the infection was monitored every other day by examination of a blood smear from each animal until negativation. In the early chronic phase of the infection, colon adenocarcinoma was induced by weekly s.c. injections of DMH at a dose of 20 mg/kg body weight for 12 weeks. 102 animals were divided in four test groups: 39 infected rats received DMH (group 1); 32 non-infected rats received DMH (group 2); 16 infected rats and 15 non-infected animals were used as control groups. Animals were killed 6 months after the first dose of DMH. The whole colon was removed and prepared for light microscopic examination. Twelve animals from group 1 and 22 from group 2 had colon adenocarcinomas, the proportion of cancer being 30.7 and 68.7%, respectively (chi(2) = 10.16; P < 0.05). The relative risk of having a colon tumor in infected animals (group 1) was 0.45 (IC 95% 0.26-0.76), which is a protective risk compared with non-infected animals. These findings show that chronic infection with T.cruzi is associated with a lower incidence of DMH-induced colon cancer in rats.     

Inhibition of ornithine decarboxylase with 2-difluoromethylornithine: reduced incidence of dimethylhydrazine-induced colon tumors in mice

2-Difluoromethylornithine (DFMO) was administered to 1,2-dimethylhydrazine (DMH)-treated mice to reduce colonic polyamine levels and mucosal hyperplasia. Mice received 1% DFMO in drinking water throughout the experiment and were given injections of DMH (20 mg/kg) weekly for 28 weeks. DFMO inactivated 93% of colonic ornithine decarboxylase activity. Although DMH treatment did not induce colonic ornithine decarboxylase activity by Week 28, the putrescine content was increased 31% in DMH-treated mice (p less than 0.01). Concurrent treatment with DFMO depressed putrescine content (42 to 63%) and spermidine content (27 to 38%), but it increased spermine content (18 to 22%). At Week 28 of treatment with DMH alone, RNA content was increased 8.6% (p less than 0.01), DNA content 10% (p less than 0.01), DNA specific activity 24% (p less than 0.01), and crypt depth 20% (p less than 0.01), but not in mice receiving DMH and DFMO. At 28 weeks, 13 of 17 mice (76%) treated with DMH alone had histologically confirmed colon cancers; of mice treated with DMH and DFMO, two of 18 (11%) had colonic tumors. Throughout the experiment, 50 colon cancers developed in 16 DMH-treated mice (mean, 3.12 tumors/mouse); three mice treated with DMH and DFMO developed three colon cancers total (p less than 0.001). Reduction of colonic polyamine levels after DFMO treatment prevents proliferative changes induced by DMH and reduces the incidence of tumors.     

Effect of Ornithine in Parenteral Nutrition Regimens on Difluoromethylornithine-Induced Platelet Suppression and Changes in Tumor Polyamine Content

We have demonstrated that DFMO-induced thrombocytopenia can be ameliorated with concomitant ornithine (Orn) in chow-fed rats; a reversal in DFMO-associated tumor polyamine reduction and antitumor activity, however, was also evident. To determine the effect of Orn in total parenteral nutrition (TPN) regimens on DFMO-induced thrombocytopenia and changes in tumor polyamine concentrations, Ward-colon-tumor-bearing (WCT) rats were given TPN with arginine (ENA) or with ornithine substituted for arginine (ENO) alone or with DFMO (1.5 g/day) added directly to the infusate. After 4 days, the peripheral blood platelet counts for ENA (917 ± 151 × 10³/mm³) or ENO (908 ±67x 10³/mm³) were equivalent to those of chow-fed rats (901 ±42 × 10³/mm³). ENA/DFMO rats had significant thrombocytopenia (607 ± 185 × 10³/mm³), which was completely ameliorated for ENO/DFMO rats (939 ± 111 × 10³/mm³). Peripheral white blood count, hematocrit, and other hematological parameters were not affected. Tumor putrescine content for ENA rats (46.9 ±8.7 nmol/g) was equal to that for chow-fed rats (44.8 ± 6.2 nmol/g) and ENO rats (53.6± 8.3 nmol/g). The reduction in tumor putrescine content for ENO/DFMO rats (19.6 ±6.9 nmol/g) was equivalent to that of ENA/DFMO rats (14.7 ± 3.0 nmol/g). Tumor spermidine was reduced only for the ENA/DFMO rats while spermine was slightly elevated. Tumor spermine content for ENO/DFMO rats (57.2 ±12.0 nmol/g) was equal to that for ENO rats (65.6 ±8.7 nmol/g) but was significantly (p = 0.004)reduced when compared with rats receiving ENA/DFMO (89.4 ± 20.4 nmol/g). The results of this study show that TPN with Orn substituted for arginine can be used with a chemotherapeutic dose of DFMO to ameliorate the thrombocytopenia. The DFMO-induced reduction in tumor putrescine content, however, was not affected when Orn was substituted for arginine in a parenteral nutrition regimen. These results suggest that the antitumor activity of DFMO would not be adversely affected by coadministering DFMO with a TPN regimen with Orn substituted for arginine.     

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 (24ff,25(OH)₂vitainin D₃) was assessed in a murine model of colon carcinogenesis. In experiment 1, male 6-week-old F344 rats were administered N₂N-dimethylhydrazme (DMH) 20 mg/kg s.c. once a week 4 times. The rats were fed 24R,25(OH)₂vitaniin 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 ≥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)₂vitaniin 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.