High-fat diet blocks the inhibition of skin carcinogenesis and reductions in protein kinase C by moderate energy restriction

The aim of this investigation was to determine the impact of dietary energy restriction (ER) with control (C) and high-fat (HF) diets on two-stage skin carcinogenesis and on the expression of specific isoforms of protein kinase C (PKC). Skin carcinogenesis was initiated on SENCAR mice with 10 nmol of 7,12-dimethylbenz[a]anthracene (DMBA) in 0.2 mL of acetone and then promoted with twice weekly treatments of 3.2 nmol of 12-O-tetradecanoylphorbol-13-acetate (TPA) in 0.2 mL of acetone for 18 wk. The experimental diets fed during TPA treatment and for 10 wk after the last TPA treatment were formulated with C (10% calories from fat) and HF (42% calories from fat) levels for freely fed groups. These diets were restricted by 20% (20% ER/C and 20% ER/HF) and by 40% (40% ER/C and 40% ER/HF). Papilloma incidence was reduced in the mice fed the 20% ER/C, 40% ER/C, and 40% ER/HF diets in comparison with the C, HF, and 20% ER/HF groups. Carcinoma incidence was also reduced in these groups. PKC α and ζ were assessed by western blot analysis in the epidermises of mice pre-fed the six diets for 8–10 wk (without DMBA or TPA treatment). PKC α was reduced in the particulate fraction by 32–44% in the 20% ER/C, 40% ER/C, and 40% ER/HF groups (P < 0.005). PKC ζ was reduced by 24–31% in the cytosol of mice fed the 20% ER/C diet and in the particulate fraction of mice fed the 40% ER/C diet (P < 0.05). The HF diet was able to block the inhibition of skin carcinogenesis and the reduction in the expression of PKC in the epidermis by 20% ER but not by 40% ER. © 1996 Wiley-Liss, Inc.     

Dietary energy restriction does not inhibit pancreatic carcinogenesis by N-nitrosobis-2-(oxopropyl)amine in the Syrian hamster

Dietary energy restriction was previously shown to be effective in preventing a wide range of experimentally induced cancers. Studies were conducted to assess the influence on pancreatic carcinogenesis of dietary energy restrictions (reduced fat and carbohydrate) of 10%, 20% or 40% in comparison with control in Syrian hamsters treated with N- nitrosobis(2-oxopropyl)amine (BOP). Two carcinogenesis studies were conducted. One used a single treatment with 20 mg BOP/kg body weight and followed hamsters for 102 weeks following treatment, and the other used three weekly treatments of 20 mg BOP/kg body weight and followed hamsters for 45 weeks after treatment. Hamsters were fed control or energy restricted diet beginning the week following the last BOP treatment. Pancreatic carcinomas were induced in 9-18% of the hamsters in the first experiment and in 59-66% of the animals in the second. Dietary energy restriction did not influence carcinoma incidence in either study, and in the second experiment the multiplicity of tumors was higher in the 40% energy restriction (ER) group than in control hamsters. Plasma corticosterone was suppressed by BOP treatment, particularly in the 20% and 40% ER hamsters in the second experiment, and diet or BOP treatment did not significantly alter plasma cortisol. Pancreatic protein kinase Czeta measured by Western blot was highest in the cytosol and particulate fractions of the 40% ER hamsters in the first experiment. These results indicate that dietary energy restriction is not effective in the prevention of BOP induced pancreatic carcinogenesis in the Syrian hamster.      

Identification of protein kinase C ζ isozyme in hamster pancreas and pancreatic carcinoma cell lines

Cellular differentiation and proliferation are dependent upon phosphorylation by endogenous protein kinase C (a) isozymes in many cell types. Western blotting with a C-terminally directed rabbit polyclonal anti-PKC ζ antibody detected a doublet of approximately 81 kDa in normal hamster pancreatic tissue and hamster pancreatic carcinoma (PC-1) and human pancreatic carcinoma (PANC-1) cells, Preabsorption of the antibody with the specific peptide blocked the appearance of the 81–kDa band, indicating that the band was specifically recognized by the PKC ζ antibody. In contrast, antibodies for PKC α, β, γ, δ, and ? failed to show specific immunoreactivity for normal pancreatic tissue or PANC-1 or PC-1 cells. Immunocytochemical analysis identified PKC ζ in the cytoplasm of ductules and large ducts, to a lesser extent in the islets of the hamster pancreas, and in the normal cultured pancreatic duct epithelial cells and pancreatic carcinoma (PANC-1 and PC-1) cell lines. Specific reactivity was seen by electron microscopy in the ductal cells of the normal pancreatic tissue. In normal pancreatic ductal tissue and primary pancreatic ductal hyperplasia and carcinoma, the proportional labeling of PKC ζ in nuclei and cytoplasm was similar. Our results demonstrating the presence of PKC ζ isozyme in the normal pancreas, cultured normal pancreatic duct epithelial cells, and pancreatic carcinoma cells or carcinoma tissue suggests a role for this isozyme in the normal physiology of the pancreas and perhaps in pancreatic carcinoma. © 1995 Wiley- Liss, Inc.     

Dietary energy restriction and fat modulation of protein kinase C isoenzymes and phorbol ester binding in Sencar mouse epidermis

The purpose of our research is to understand the biochemicalbasis for dietary enhancement of phorbol ester induced tumorpromotion in mice fed high-fat (HF) diet, and the inhibitionof promotion in mice fed diets restricted in energy from fatand carbohydrate (ER). The present study assessed the presenceof protein kinase C (PKC) isoenzymes in the Sencar mouse epidermisby Western blot and determined the influence of diet on theisoenzymes found. Mice were fed control, HF (24.5% corn oil)or ER (60 of control energy) diets for 6–29 weeks. Ourinitial studies assessed the immunoreactive levels of PKC     

Comparison of the effects of dietary beef tallow and corn oil on pancreatic carcinogenesis in the hamster model

We previously reported an enhancement of pancreatic carcinogenesis induced by N-nitrosobis(2-oxopropyl)amine (BOP) in hamsters fed diets containing high levels of corn oil. The research presented here compared diets high in corn oil with those high in beef tallow in the enhancement of pancreatic carcinogenesis. Pancreatic cancer was induced with 20 mg BOP/kg body wt, s.c. administered at 8 weeks of age. One week later, hamsters were assigned to one of five diet treatments: (i) 4.3% corn oil (control); (ii) 20.5% corn oil (high corn oil); (iii) 0.5% corn oil + 3.8% beef tallow (low beef tallow); (iv) 0.6% corn oil + 19.9% beef tallow (high beef tallow); and (v) 5.1% corn oil + 15.4% beef tallow (high fat mixture). These diets were fed until the study ended 84 weeks after BOP treatment. Hamsters were trained through pair feeding to consume the same calorie allotment as the control corn oil group. By the end of the experiment, BOP-treated hamsters that were fed diets containing beef tallow were consistently heavier than those fed corn oil. Survival was longer in hamsters fed the high-beef tallow and high-fat mixture compared with the other diet groups. Tumor data were age adjusted to correct for survival differences. Pancreatic adenoma incidence and multiplicity (no./effective animal) were higher in hamsters fed beef tallow than those fed corn oil diets. Carcinoma in situ multiplicity was elevated in hamsters fed high-fat diets irrespective of the nature of fat fed. Pancreatic adenocarcinoma multiplicity was elevated in hamsters fed the low- or high-beef tallow diets compared with the low- or high-corn oil diets. The mixture of fat resulted in an intermediate yield.     

Interaction of dietary fat and protein on pancreatic carcinogenesis in Syrian golden hamsters

The role of interactions between dietary fat and protein in experimental pancreatic cancer was determined in Syrian golden hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Two levels of corn oil [4.5 and 18 g/385 kilocalorie (kcal)] were fed with each of two levels of casein (9 g/385 kcal and 36 g/385 kcal), either before or after a single sc injection of BOP (10 mg/kg body wt) at 8 weeks of age. Control diet was fed at other times (9 g corn oil and 18 g casein/385 kcal). The pancreatic ductular carcinoma incidence and multiplicity (average No. of tumors/tumor-bearing animals) increased as dietary fat and protein levels rose in hamsters fed the four diets after carcinogen treatment. Enhanced carcinogenesis by high-fat (HF) diets occurred only in hamsters fed the high-protein (HP) level, and protein effects were seen only with the HF diets. The low-fat-low-protein (LF-LP) diet inhibited pancreatic carcinogenesis among the hamsters given the four diets before BOP treatment. Pancreatic adenoma yields were elevated in hamsters given either HF or HP diets following BOP treatment, by comparison with the low levels. However, when diets were fed before BOP treatment, an increased yield occurred with the rise in protein, but the yield was reduced in males with the increase in fat. Acinar cell nodules were observed primarily in hamsters fed LP levels after BOP, and their multiplicity was highest in those given the HF diet. The interaction between dietary fat and protein demonstrated the interdependence of the effects of these two nutrients on pancreatic carcinogenesis in hamsters.     

Sex differences in the dietary modulation of pancreatic cancer in Syrian hamsters treated continuously with N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine

The effect of continuous week-long administration of N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP) by s.c. implanted osmotic pumps was examined in male and female Syrian hamsters given access to three isocaloric synthetic diets containing 10 (LP), 20 (MP) and 30% (HP) casein respectively. At a total dose of 210 mg/kg, toxicity of HPOP, expressed as acute liver injury, was greater in male than in female hamsters. Such toxicity increased with protein intake in male, but not in female animals. Twenty-five weeks after initiation, female and male hamsters developed pancreatic ductal adenocarcinomas and to a lesser degree liver cholangiocellular and hepatocellular carcinomas. The highest incidence of pancreatic cancer was observed under HP diet regimens and was 75 and 67% in female and male hamsters respectively. Decrease of protein intake resulted in the reduction of the incidence of pancreatic cancer, which was more striking in males than in females. In males fed the MP and LP diets respectively, such an incidence declined to 33 and 6%. Although significant differences in the incidence of pancreatic cancer were not observed among female groups fed the above three diets, the multiplicity and the number of such tumors were significantly greater at the HP than the LP level. Differences in the incidence of pancreatic tumors between males and females were statistically significant only at the LP level. However, such differences were also significant at the MP level when comparisons were based on tumor number and multiplicity. Since the incidence, tumor multiplicity and size were generally greater in female than male hamsters, estrogenic hormones may play a role in the development of pancreatic ductal adenocarcinomas in this species.     

Inhibition of dietary fat promoted development of (pre)neoplastic lesions in exocrine pancreas of rats and hamsters by supplemental selenium and beta-carotene

The modulating effects of selenium and beta-carotene on the development of putative preneoplastic foci in exocrine pancreas were investigated in rats and hamsters, treated with azaserine and N-nitrosobis(2-oxopropyl)amine (BOP), respectively. The animals were fed a semipurified diet high in saturated fat (20% lard) either supplemented or not with beta-carotene or selenium. A separate group maintained on a diet low in saturated fat (5% lard) was incorporated as an extra control group. The animals were given their diets 12 days after the last treatment with carcinogen. Four months postinitiation, the pancreata were quantitatively examined for the number and size of putative (pre)neoplastic lesions. Rats as well as hamsters maintained on a low-fat diet had significantly less putative preneoplastic pancreatic lesions as compared to animals fed a diet containing 20% lard. Selenium and beta-carotene both inhibited the growth of basophilic foci in rat pancreas. In hamster pancreas, beta-carotene and selenium caused a significant decrease in the number of early ductal complexes. The number of carcinomas was decreased in the beta-carotene group and increased in the group fed a diet high in selenium.     

Modifying effect of dietary fat on benzo[a]pyrene-induced respiratory tract tumours in hamsters

Groups of 40 Syrian golden hamsters of both sexes were fed dietscontaining either 5% fat (control), 20% saturated fat (beeftallow) or 20% unsaturated fat (sunflower seed oil) from weaningand during the whole experimental period (up to 656 days). Respiratorytract tumours were induced by intratracheal instillation ofbenzo[a]pyrene attached to ferric oxide and suspended in saline.Mortality was slightly, but not statistically significantlyhigher in the high fat groups than in the low fat control group.Microscopic examination of the respiratory tract revealed anincreased number of tumour bearing animals, an increased multiplicityof respiratory tract tumours and an increased total number ofrespiratory tract tumours in animals fed high fat diets. Thetumour enhancing effect of fat was most pronounced in the highunsaturated fat group. Especially epidermoid papillomas, epidermoidcarcinomas and combined epidermoid and adenocardnomas contributedto the observed differences in tumour response amongst groups.It was concluded that dietary fat enhances benzo[a]pyrene-inducedrespiratory tract carcinogenesis in hamsters.     

Effects of high fat diet and cholecystokinin receptor blockade on pancreatic growth and tumor initiation in the hamster

The mechanism by which high-fat diet potentiates pancreaticcancer is not known, but trophic hormones may be involved. Inpreliminary growth studies, hamsters fed a high fat diet (17.5%lard, 17.5% corn oil) for 14 days showed a 16.3% increase (P< 0.01) in pancreatic weight compared to controls on lowfat diet (2.5% lard, 2.5% corn oil). A significant increasewas also seen at 28 days. Similar increases were seen in pancreaticDNA (29%, P < 0.01) and pancreatic RNA (22%, P < 0.05)at 14 days. Plasma cholecystokinin (CCK) levels at 14 days were2.5 fold higher in the animals fed high fat (P < 0.01). Infusionof the CCK antagonist MK329 (25 nmol/kg/h) completely abolishedthe increase in pancreatic weight, pancreatic DNA and pancreaticRNA. The effect of CCK receptor blockade during the initiationperiod of carcinogenesis was investigated in hamsters fed thesame diets used in the growth studies. One hundred animals receiveda single injection of N-nitrosobis(2-oxopropyl)amine, (BOP,20 mg/kg). Half of the hamsters in each diet group receiveda 2 week infusion of MK329 (25 nmol/kg/h), beginning 8 daysbefore carcinogen administration. At the time of death, 55 weeksafter carcinogen administration, non-fasting plasma CCK levelswere 31% higher in the high fat fed hamsters than in the lowfat fed animals (P < 0.01). The high-fat diet group had a3-fold increase in total cancer incidence and a 5-fold increasein advanced lesions (adenocarcinomas). Tumor incidence and yieldwere not changed in either diet group by CCK-receptor blockadeduring the initiation period. Cholecystokinin appears to mediatethe short-term trophic effect that high-fat feeding has on thepancreas. However, potentiation of pancreatic cancer by high-fatdiet in the hamster cancer model does not appear to be influencedby endogenous cholecystokinin at the time of tumor induction.     

Enhancement of experimental pancreatic cancer in Syrian golden hamsters by dietary fat

The effects of dietary fat on the induction and development of pancreatic ductular adenocarcinoma were studied in randombred Syrian golden hamsters. Diets containing low-fat (LF) or high-fat (HF) levels of corn oil [4.5 or 18.0 g/385 kilocalorie (kcal)], contributing 10 or 41% of the calories, respectively, were fed either before or after a single injection of N-nitrosobis(2-oxopropyl)amine (BOP) (10 mg/kg body wt). Control hamsters were fed corn oil at a medium-fat (MD) level (9 g/385 kcal) for life. The incidence of ductular adenocarcinomas increased in both males and females (LF diet, 16%; HF diet, 34%) when the HF diet was fed after BOP treatment. The average number of carcinomas per carcinoma-bearing animal also increased (LF diet, 1.3; HF diet, 3.0), but the carcinoma incidence was not influenced by these diets being fed before carcinogen treatment. The incidence of ductular adenomas was high with all treatments and was not influenced by diet. However, the number of adenomas was increased in animals fed HF diets. In addition, the incidence of acinar cell nodules was elevated in animals fed the MF and HF diets after BOP administration. These results showed that dietary fat modified the development of experimental ductular adenocarcinoma of the pancreas.     

Corticosterone supplementation reduced selective protein kinase C isoform expression in the epidermis of adrenalectomized mice.

Previous research in this laboratory demonstrated elevated plasma corticosterone and reduced protein kinase C (PKC) activity and selective isoform expression in the epidermis of dietary energy-restricted mice. Because PKC is implicated in skin carcinogenesis and because both energy restriction and glucocorticoid hormone inhibit skin carcinogenesis, the purpose of the present research was to determine whether the elevated glucocorticoid hormone in the energy-restricted mouse contributed to the changes in PKC protein expression. Two strategies were used to control corticosterone in adrenalectomized mice: (a) corticosterone-containing pellets were implanted in mice, and a dose response increase in corticosterone was observed with 5-, 10-, and 35-mg corticosterone implants with average peak values of 68 +/- 22 ng/ml (P < 0.01); and (b) corticosterone was administered in the drinking water, and plasma corticosterone was elevated in a dose-dependent manner in mice killed at 6:00-6:30 p.m. (P < 0.01; peak values of 300-400 ng/ml). The expression of PKCalpha, PKCdelta, and PKCepsilon protein were not consistently altered by corticosterone with the two strategies. PKCeta protein expression was elevated in the adrenalectomized mice administered 3 or 60 microg of corticosterone/ml in drinking water (P < 0.01). PKCzeta protein expression was reduced by all doses of corticosterone in the implant or drinking water (P < 0.05), and a reduction of 41% was achieved with the mice administered 60 microg of corticosterone/ml in drinking water. In mice fed control or energy-restricted diet, with or without adrenalectomy, PKCzeta protein was reduced in sham-operated, energy-restricted mice in comparison with control diet, sham-operated mice (P < 0.02), whereas PKCzeta protein was not significantly different between adrenalectomized control and adrenalectomized, energy-restricted mice. These data indicate that administration of corticosterone in drinking water most closely mimicked the circulating corticosterone and epidermal PKC changes observed in dietary energy restriction. Elevated plasma glucocorticoid levels in the dietary energy-restricted mouse may contribute to the alteration of PKC protein levels in the epidermis.     

Estrogen-induced pituitary tumor development in the ACI rat not inhibited by dietary energy restriction

We have demonstrated that a 40% restriction of dietary energy consumption virtually abolishes the development of prolactin (PRL)-producing pituitary tumors in Fischer 344 (F344) rats treated chronically with estrogen, apparently by inhibiting the ability of estrogen to enhance survival within a rapidly proliferating lactotroph population. The purpose of the study reported here was to determine whether energy restriction exerts a similar antitumorigenic action in another rat strain, August x Copenhagen-Irish (ACI), in which PRL-producing pituitary tumors develop in response to estrogen treatment. Ovariectomized female ACI rats were either allowed to consume a control diet ad libitum or were fed a modified diet that restricted energy consumption by 40% relative to the amount of energy consumed by animals fed the control diet. We also examined the ability of 17beta-estradiol (E2) administered for 20 wk via subcutaneous Silastic implants to induce development of PRL-producing pituitary tumors. Treatment with E2 increased pituitary weight as well as the pituitary weight-to-body weight ratio and induced gross hyperprolactinemia to the same extent in ACI rats fed either the control or the energy-restricted diet. Moreover, dietary energy restriction did not affect the ability of E2 to induce pituitary cell proliferation or inhibit apoptosis, as evidenced by quantification of two surrogate markers. These data provide compelling evidence that a 40% restriction of energy consumption does not inhibit the ability of E2 to induce pituitary tumor development in the ACI rat. In conjunction with our published studies of the F344 rat strain, the data presented herein indicate that the inhibitory effects of dietary energy restriction on estrogen-induced pituitary tumor development are rat-strain specific and suggest that sensitivity to specific antitumorigenic actions of energy restriction is strongly affected by genetic background.     

Modifying factors in pancreatic carcinogenesis in the hamster model. IV. Effects of dietary protein

The possible effects of dietary protein on pancreatic cancer induced in outbred Syrian golden hamsters by N-nitrosobis(2-oxopropyl)amine (BOP) were studied. Three levels of casein as protein at low [LP = 9 g/385 kilocalories (kcal)], medium (MP = 18 g/385 kcal), or high levels (HP = 36 g/385 kcal) were fed in two sequences to 4 groups of hamsters. The effects of protein level on the initiation phase of BOP carcinogenesis were examined in hamsters fed LP or HP from 3 through 7 weeks of age, followed by MP for the remainder of their lives. The role of protein level on the promotional (developmental) phase of carcinogenesis was evaluated in hamsters fed (from 3 through 7 wk of age) MP, followed by LP or HP for the rest of their lives. One-half of the hamsters from each of the 4 groups received a single sc BOP injection (10 mg/kg body wt) at 8 weeks of age. Changes in diet from one type to the other occurred 2 days after BOP treatment. An MP diet fed before and after BOP served as the experimental control diet. The results demonstrated that the LP diet inhibited the developmental phase of carcinogenesis only in females, whereas the MP and HP diets did not affect initiation or promotion of cancer in either sex. The inhibitory effect of the LP diet in pancreatic carcinogenicity only in females calls for further studies.     

Consumption of reduced-energy/low-fat diet or constant-energy/high-fat diet during mezerein treatment inhibited mouse skin tumor promotion

Previous studies in our laboratory have shown that promotionof two-stage skin carcinogenesis in the SENCAR mouse model wasinhibited in mice fed energy-restricted/low-fat diets, and elevatedin mice fed high-fat diets. Studies reported here describe theinfluence of dietary energy restriction from fat and carbohydrate(ER) or high-fat (HF) diet on early promotion by 12-O-tetradecanoylphorbol-13-acetate(TPA) and on late promotion by mezerein (MEZ). Female SENCARmice were initiated topically with 10 nmol 7,12-dimethylbenz[a]anthracene(DMBA) in 0.2 ml acetone at 9 weeks of age. For the following2 weeks they received 3.2 nmol TPA in 0.2 ml acetone twice weekly,and for the next 16 weeks they received 10 nmol MEZ in 0.2 mlacetone twice weekly. All mice were fed control diet beforeTPA began and following the final MEZ treatment. Control micereceived the control diet (c) throughout TPA and MEZ (C/C).The six experimental groups received: (1) ER diet throughoutTPA and MEZ treatment (ER/ER); (2) HF diet throughout TPA andMEZ treatment (HF/HF); (3) ER during TPA (ER/C); (4) ER duringMEZ (C/ER); (5) HF diet during TPA (HF/C); or (6) HF diet duringMEZ (C/HF). Papilloma incidence and multiplicity, and carcinomaincidence were similarly reduced in the mice fed ER diet duringMEZ (ER/ER and C/ER groups). In comparing the HF groups, papillomamultiplicity was highest in the HF/C group, intermediate inthe C/C and lowest in the C/HF groups, but papilloma and carcinomaincidences were not modified by the HF diet protocols. Papillomaregression was greater in the C/HF group (27%, 4 regressions/15tumor-bearing mice) than in the controls (0/18) during weeks21–23, immediately following the end of MEZ treatment(P < 0.05).     

Energy intake and prostate tumor growth, angiogenesis, and vascular endothelial growth factor expression

BACKGROUND: A sedentary lifestyle coupled with excessive energy intake is speculated to be a factor associated with increased incidence of prostate cancer. We have investigated the effects of energy intake on prostate tumor growth in experimental animals. METHODS: Two transplantable prostate tumor models, i.e., the androgen-dependent Dunning R3327-H adenocarcinoma in rats and the androgen-sensitive LNCaP human carcinoma in severe combined immunodeficient mice, were studied. R3327-H tumor growth and relevant tumor biomarkers (proliferation index, apoptosis [programmed cell death], microvessel density, and vascular endothelial growth factor [VEGF] expression) were compared in ad libitum fed control rats, ad libitum fed castrated rats, and groups restricted in energy intake by 20% or 40%. A second set of experiments involving both tumor models examined tumor growth in ad libitum fed rats or in animals whose energy intake was restricted by 30% using three different methods, i.e., total diet restriction, carbohydrate restriction, or lipid restriction. All P values are two-sided. RESULTS: R3327-H tumors were smaller in energy-restricted or castrated rats than in control rats (P<.001). Tumors from energy-restricted rats exhibited changes in tumor architecture characterized by increased stroma and more homogeneous and smaller glands. In castrated rats, the tumor proliferation index was reduced (P<.0001), whereas apoptosis was increased in both energy-restricted (P<.001) and castrated (P<.001) rats. Tumor microvessel density and VEGF expression were reduced by energy restriction and castration (P<.003 versus control). Restriction of energy intake by reduction of carbohydrate intake, lipid intake, or total diet produced a similar inhibition of growth of R3327-H or LNCaP tumors. These effects were associated with reduced circulating insulin-like growth factor-I. CONCLUSIONS: Our observations are consistent with the hypothesis that energy restriction reduces prostate tumor growth by inhibiting tumor angiogenesis. Furthermore, dietary fat concentration does not influence prostate tumor growth when energy intake is reduced.     

Dietary energy restriction in the SENCAR mouse: Elevation of glucocorticoid hormone levels but no change in distribution of glucocorticoid receptor in epidermal cells

The purpose of this study was to demonstrate that dietary energy restriction elevates plasma glucocorticoid hormone (GCH) levels while maintaining a circadian profile. Furthermore, we indirectly measured the effect of energy restriction on receptor activation in epidermis by determining the cellular localization of receptor protein in control-fed and energy-restricted (ER) mice. SENCAR mice were maintained on an ad libitum control diet or an ER diet that provided 60% of the total energy consumed by control-fed mice. Plasma corticosterone levels were determined by radioimmunoassay. Glucocorticoid receptor (GR) protein levels in epidermal lysates were measured by western blotting. Electron microscopy was used to identify gold-conjugated immunoreactive GR in epidermal cells of the skin in control and ER mice. Plasma corticosterone levels in ER mice were significantly increased 10 times over the levels in control mice at 0700 h, significantly increased two times over control levels at 1600 h, and not different from controls at 2300 h in the circadian cycle. The total amount of epidermal GR protein in ER mice was 140% (95% confidence interval, 104–169%) of that in controls at the early time point, not different at the midpoint, and 60% (95% confidence interval, 48–79%) of that in controls at the late time point. The distribution of gold-conjugated GR in the cytoplasmic and nuclear compartments of epidermal cells was similar in control and ER mice. Thus, we showed that dietary ER increased the level of plasma GCH without abolishing diurnal variation. However, an increase in ligand activation in epidermal cells, as indicated by nuclear localization of GR protein, was not supported by the results of this study. Mol. Carcinog. 21:62–69, 1998. © 1998 Wiley-Liss, Inc.     

Dose-related inhibition of colon carcinogenesis by dietary piroxicam, a nonsteroidal antiinflammatory drug, during different stages of rat colon tumor development

The effect of four dose levels of piroxicam administered during different stages of colon tumor development was studied in male F344 rats to obtain a data base on the efficacy of piroxicam as an inhibitor of colon carcinogenesis. Piroxicam was added at levels of 25, 50, 75, and 150 ppm to the NIH-07 open-formula diet and fed to male F344 rats starting 1, 13, and 23 wk after the carcinogen administration. At 7 wk of age, while the animals were consuming the control diet, all animals except the vehicle-treated controls were given s.c. injection of azoxymethane (CAS:25843-45-2; 29.6 mg/kg body weight, once) to induce intestinal tumors. Forty wk after AOM injection, all animals were necropsied, and tumor incidences were compared among the various dietary groups. Colon tumor incidence (percentage of animals with tumors) was inhibited in a dose-dependent manner in rats fed the diets containing 25, 50, 75, and 150 ppm piroxicam starting 1 and 13 wk after carcinogen treatment. The colon tumor incidences in animals fed the diets containing 0, 25, 50, 75, and 150 ppm of piroxicam starting at 1 wk after carcinogen treatment were 89, 61, 58, 50, and 39%, respectively. When the diets containing 0, 25, 50, 75, and 150 ppm were fed 13 wk after carcinogen treatment, the colon tumor incidences were 89, 69, 69, 44, and 33%, respectively. Colon tumor multiplicity (tumors/animal; tumors/tumor-bearing animal) was also significantly inhibited in animals fed the diets containing 25 to 150 ppm piroxicam starting 1 and 13 wk after carcinogen administration. The number of colon tumors/animal was inhibited by about 80 to 84% in animals fed the 150 ppm piroxicam diet. When the diets containing different levels of piroxicam were fed 23 wk after carcinogen treatment, the colon tumor incidence was significantly inhibited in animals fed the 75 and 150 ppm piroxicam diets. The colon tumor incidences in animals fed the diets containing 0, 25, 50, 75, and 150 ppm were 89, 78, 67, 64, and 64%, respectively. The colon tumor multiplicity (colon tumors/animal) was slightly but significantly inhibited in animals fed the diets containing 25 to 150 ppm piroxicam. The results of this study demonstrate that increasing levels of piroxicam in the diet, when fed 1 or 13 wk after carcinogen insult, inhibit colon tumor incidence in a dose-dependent manner.     

Chemoprevention of colon carcinogenesis by dietary organoselenium, benzylselenocyanate, in F344 rats

The effect of feeding benzylselenocyanate (BSC) and its sulfur analogue, benzylthiocyanate (BTC), 2 wk before, during, and until 1 wk after carcinogen administration (initiation phase) on intestinal carcinogenesis induced by azoxymethane (CAS:25843-45-2) was studied in male F344 rats. Weanling rats were raised on a semipurified diet (AIN-76A diet; control diet). Beginning at 5 wk of age, groups of animals consuming the control diet were fed one of the diets containing 25 ppm BSC or BTC. An additional group was continued on the control diet. At 7 wk of age, all animals in 3 groups, except the vehicle-treated controls, were administered s.c. injections of azoxymethane (15 mg/kg body weight, once weekly for 2 wk). Animals were continued on the control diet and BSC and BTC diets until 1 wk after carcinogen treatment, when those groups receiving BSC and BTC diets were fed the control diet until termination of the experiment. Tissue and blood plasma glutathione peroxidase activity was measured in vehicle-treated animals fed the control diet and BSC and BTC diets for 5 wk. The results indicate that body weights were comparable among the various dietary groups. BSC in the diet significantly inhibited the incidence (percentage of animals with tumors) and multiplicity (tumors/animal) of adenocarcinomas in the colon and multiplicity of adenocarcinomas in the small intestine compared to those fed the control diet. BTC in the diet had no effect on colon and small intestinal tumors. Selenium-dependent glutathione peroxidase activity was significantly increased in kidneys and colon and small intestinal mucosae of animals fed the BSC diet compared to animals fed the BTC and control diets.     

Inhibition by methionine of pancreatic carcinogenesis in hamsters after initiation with N-nitrosobis(2-oxopropyl) amine

The modifying effects of dietary L-methionine in the post-initiation phase of pancreatic carcinogenesis were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Groups consisting of 20 and 30 animals, respectively, were given BOP subcutaneously, once a week five times at a dose of 10 mg/kg body wt. and then continuously fed diet supplemented with 2% (group 1) or 0% (group 2) methionine (weeks 5-32). After five subcutaneous injections of saline, group 3 animals were similarly fed diet supplemented with 2% methionine for the same period. The incidence of pancreatic ductal adenocarcinomas was significantly lower in group 1 (36.8%, P<0.05) than in group 2 (71.4%). Multiplicity of adenocarcinomas was also significantly lowered (0.52 and 1.28/hamster, P<0.05). Similarly, total numbers of combined adenocarcinomas and dysplastic lesions were significantly decreased in group 1 (2.05, P<0.05) as compared with group 2 (3.67). Methionine enhanced atrophic change of pancreatic acinar cells in hamsters given BOP, indicating that the inhibitory effects on the post-initiation stage of BOP-induced pancreatic carcinogenesis in hamsters could be generally linked to suppression of growth.