Effect of dietary fat on the initiation of hepatocarcinogenesis by diethylnitrosamine or 2-acetylaminofluorene in rats.

The purpose of this study was to determine if increasing dietary fat, either as saturated fat or polyunsaturated fat, would alter initiation of hepatocarcinogenesis by diethylnitrosamine (DEN) or 2-acetylaminofluorene (AAF). Rats were fed one of three purified diets: a low-fat (LF) diet (containing 5% of calories as safflower oil), a high saturated fat (HSF) diet (containing 48% of calories as palm oil) and a high polyunsaturated fat (HPUF) diet (containing 48% of calories as safflower oil). Four weeks later, all rats were subjected to partial hepatectomy (PH). Rats were then divided into four groups and received no carcinogen, DEN (10 mg/kg, p.o., 24 h after PH) or AAF (25 or 100 mg/kg, p.o., 12 h after PH). Five days later, all rats were fed an unrefined diet, and 9 weeks later, all rats were fed phenobarbital in the diet for 26 weeks as a tumor promoter. In rats initiated with DEN, the number of gamma-glutamyl transpeptidase-positive and ATPase-negative foci was higher in the rats fed the HPUF diet, but not the HSF diet, as compared to rats fed the LF diet. The incidence of neoplastic nodules, the mean focal volume and the volume fraction, however, were not significantly altered by dietary fat in DEN-injected rats. The dietary fat content of the diet did not affect the induction of altered hepatic foci or neoplastic nodules in rats initiated with AAF or receiving no initiation. This study shows that initiation of hepatocarcinogenesis can be influenced by dietary fat, but that the effect may be carcinogen-specific.     

The combined effects of dietary fat, protein, and energy intake on azoxymethane-induced intestinal and renal carcinogenesis.

Two 3 x 3 factorial experiments were conducted to examine the effects of dietary protein (8, 16, and 32% of energy from casein) and dietary fat (12, 24, and 48% of energy from corn oil) on the initiation and promotion of azoxymethane-induced carcinogenesis in rats. For the initiation study, 33 weanling male Sprague-Dawley rats were randomized to each of nine diets fed ad libitum. Azoxymethane was administered s.c. between the fourth to sixth weeks of feeding, providing a total dose of 6 mg/100 g body weight. All rats were subsequently fed a common diet containing 16% energy from protein and 24% energy from fat for an additional 30 to 38 weeks. For the promotion study, all rats were fed a common diet containing 16% of energy from protein and 12% of energy from fat until the completion of azoxymethane administration, when 33 rats were randomized to each of nine diets varying in fat and protein content and fed these diets until sacrifice. Low-protein diets during the initiation phase were associated with increased risk of renal adenocarcinomas (P less than 0.001) and mesenchymal (P = 0.005) malignancies. No other statistically significant relationships were found between the levels of dietary fat or protein and the prevalence of malignant lesions of the small intestine, colon, or kidney in either the initiation or promotion study (although polypoid adenocarcinoma of the colon increased suggestively from 13 to 19 to 26% of rats with increasing dietary protein during initiation). Results of a multiple logistic regression analysis, combining both studies, showed that ad libitum energy intake was significantly associated with intestinal carcinogenesis. The odds of finding an intestinal adenocarcinoma increased by 6.2 +/- 2.6% (SE) for each additional kilocalorie of mean daily ad libitum intake (P = 0.014). The quintile of rats which consumed the least averaged 60 kcal/day, while the most voracious quintile averaged 74 kcal/day. This 14 kcal/day difference in mean ad libitum intake corresponded to more than a doubling (146% increase) of the odds of developing an intestinal adenocarcinoma. These studies suggest that ad libitum energy intake is a critical factor modulating experimental colon carcinogenesis.     

Effect of type and amount of dietary fat on the enhancement of rat mammary tumorigenesis by exercise

The effect(s) of treadmill exercise and type and amount of dietary fat on the process of mammary tumorigenesis was investigated. Female Sprague-Dawley rats were fed a purified 5% fat diet (AIN-76A) from 21 to 64 days of age. At 50 days of age each rat was intubated p.o. with 5 mg 7,12-dimethylbenz(a)anthracene (DMBA). Fourteen days after DMBA, the rats were randomized into one of three diet groups: 5% fat as corn oil, 24.6% fat as corn oil, or 24.6% fat as a mixture of palm (21.8%) and corn oil (2.8%). The combination of palm and corn oil provided the same amount of linoleic acid per g as the 5% corn oil diet. Half the animals receiving each diet were exercised on a treadmill at a speed of 20 m/min, 1 degree incline, 15 min/day, 5 days/week, and were designated as the moderate intensity treadmill exercise group (MITE). The remaining animals were exercised at a speed of 2 m/min, 1 degree incline, 15 min/day, 5 days/week, and were designated as the low intensity treadmill exercise group (LITE). The experiment was terminated 154 days after DMBA was administered. The median tumor-free time was significantly shortened in MITE rats receiving the 24.6% fat, corn oil-formulated diet in comparison to LITE rats receiving the same diet (43 day vs. 62 day, P = 0.028). Similarly, tumor appearance was more rapid in MITE rats consuming the low fat corn oil diet in comparison to the low fat diet-fed LITE group (57 day vs. 67 day, P = 0.046). Exercise exerted no effect on the rate of tumor appearance in rats that received the 24.6% palm and corn oil mixture, (58 day, MITE, vs. 62 day, LITE, P = 0.502). Mean body weight gains were similar among groups, although MITE rats consistently weighed more than LITE rats consuming the same diet. Gross carcass composition was unaffected by either the level of exercise or the amount of dietary fat consumed. The data indicate that moderate intensity treadmill exercise for a short duration, that is without effect on carcass fat content, can stimulate mammary tumorigenesis in rats fed low or high fat diets. This effect can be influenced by the type of dietary fat ingested.     

Relative contribution of dietary protein level and aflatoxin B1 dose in generation of presumptive preneoplastic foci in rat liver

Male weanling F344 rats were orally gavaged with aflatoxin B1 (AFB1) in daily doses of 200, 235, 270, 300, and 350 micrograms/kg/day for a total of 10 doses over a 12-day period, and then 1 week after the last dose they were fed diets of varying protein (casein) content to compare the contribution of AFB1 dose and dietary protein level on the development of presumptive preneoplastic gamma-glutamyltransferase-positive (GGT+) foci in rat liver. All animals were fed the same 20% dietary casein level during the dosing period. One week after the end of the dosing period, one-half of the animals in each dose group were then continued on the 20% casein diet for the entire 12-week foci-development period; the remaining half in each dose group were fed lower levels of dietary casein during the foci-development period for the increasing AFB1 dose groups (20, 16, 12, 8, and 4% casein for the 235-, 250-, 270-, 300-, and 350-micrograms/kg/day groups, respectively). The AFB1 dose groups used were determined in a preliminary experiment. In this previous experiment, a clearly discernible threshold dose at about 100-150 micrograms AFB1/kg/day (below which no GGT+ foci were observed) and a steep slope between 150 and 400 micrograms/kg/day were produced. In the second experiment, while the expected positive slope of (AFB1) dose versus (GGT+ foci) response relationship was found for animals fed the 20% casein diet, the dose response for the animals fed the lower levels of casein was eliminated, providing evidence that nutrient intake during the postdosing foci development is more rate limiting toward the development of these preneoplastic lesions than is the carcinogen dose.     

Protective effect of dietary brussels sprouts against mammary carcinogenesis in Sprague-Dawley rats

The effect of dietary brussels sprouts (Brassica oleracea, L.) on mammary carcinogenesis induced by 7,12-dimethylbenz[a]anthracene (DMBA) was studied in Sprague-Dawley female rats. Rats fed a 20% brussels sprouts diet only during the initiation period of carcinogenesis had a palpable mammary tumor incidence of 13%, while those fed a casein-cornstarch semi-purified diet during this initiation period had a tumor incidence of 77% after 15 weeks post DMBA dose. When the rats were switched from the semi-purified diet to the 20% brussels sprouts diet at this time, there appeared to be a regression of small mammary tumors after 6 weeks on this dietary treatment. This regression was transitory since during the final 10 weeks of this 1 year study, 100% of this group of rats developed tumors. The rats fed the 20% brussels sprouts diet during tumor initiation exhibited a 67% incidence of fibroadenomas. The rats fed the semi-purified diet during initiation, but switched later to the brussels sprouts diet, showed over a 90% incidence of adenocarcinomas.     

Quantitative stereological studies of a 'selection' protocol of hepatocarcinogenesis following initiation in neonatal male and female rats

A modified initiation-selection procedure for neonatal male and female rat hepatocarcinogenesis were examined utilizing the methods of quantitative stereology. In this study, diethylnitrosamine (10 mg DEN/kg) was given a few days after birth. At weaning, the rats were fed 0.02% 2-acetylaminofluorene (AAF) for 2 weeks with a mitotic stimulus [70% partial hepatectomy (PH)] after 1 week on the diet. Quantitative stereological analyses in conjunction with the use of several enzyme markers were used to determine the number and volume of altered hepatic foci (AHF) detected at 1 week, 3 months and 7 months after the selection procedure. This format resulted in an equivalent number of AHF in male and female rats. The AHF were three times larger in males than in females 1 week after discontinuation of AAF administration. Three months after the selection procedure, the number of AHF had decreased by at least a third and their volume percentage was the same in male and female rats. After 7 months, the number and volume fraction of detectable AHF in females were comparable to those which had been observed at 1 week after selection. In the male, the number but not the volume fraction were similar at 7 months compared with 1 week after selection. Both initiation with DEN and selection with AAF/PH contribute independently to the total population of AHF in male and female rats. At least half of the AHF detected 7 months after the selection protocol were due to DEN administration alone. Rats receiving only the AAF/PH selection exhibited one third of the number of AHF observed with the complete protocol. Administration of a non-necrogenic dose of DEN to neonatal rats when coupled with the AAF/PH selection procedure resulted in a significant promotion of the growth of initiated hepatocytes at 1 week, 3 months or 7 months after the selection procedure. These studies demonstrated that (i) the number of AHF detected after a non-necrogenic dose of DEN during the first week of life with subsequent AAF/PH selection after weaning decreases within the first 3 months after the selection procedure, but can re-develop with a promotion stimulus; (ii) the AAF/PH selection procedure itself may initiate hepatocytes in the absence of DEN administration; (iii) the AAF/PH selection procedure is equally effective with respect to the number of AHF observed after phenobarbital promotion in weaning male and female rats initiated near birth.      

Promotion of colonic microadenoma growth in mice and rats fed cooked sugar or cooked casein and fat

We studied the effect of cooked food components on the promotion of microadenoma growth in the colons of mice and rats. CF1 mice and Fisher 344 rats were initiated with azoxymethane, with 152 mice receiving four weekly i.p. injections of 5 mg/kg, 59 rats receiving a single injection of 20 mg/kg, and 24 rats receiving 30 mg/kg. A week after the last injection, the animals were randomly assigned to one of eight diets with identical ingredients, but the three components, sucrose, casein, and beef tallow, either uncooked or cooked. Control animals were given diets with uncooked ingredients. Experimental animals were fed diets in which one, two, or three of the components were cooked in an oven at 180 degrees C until golden brown before they were added to the diet. After 100 days on the diets, the colons were fixed, stained with methylene blue, and scored for microadenomas. The mice and the rats fed cooked sucrose, or casein and beef tallow cooked together, had three to five times more large microadenomas than did the controls (P ranging from 0.02 to 0.0001). No significant increase was observed with the five other cooked diets. Two rats fed the casein and beef tallow cooked together had adenocarcinomas. Thus, a diet containing 20% of cooked sucrose, or 40% of casein and beef tallow cooked together, promotes the growth of colonic microadenomas in initiated mice and rats, and would appear to contain promoters for colon cancer.     

Lipid peroxidation of liver microsome membranes induced by choline-deficient diets and its relationship to the diet-induced promotion of the induction of gamma-glutamyltranspeptidase-positive foci

The effects of varying the type of dietary fat in the choline-deficient (CD) diet on the development of gamma-glutamyltranspeptidase (GGT)-positive foci in the liver of carcinogen-treated rats were investigated, and the results were correlated with the extent of membrane lipid peroxidation induced by the diets. Male Sprague Dawley rats were initiated with a single dose of diethylnitrosamine. Thereafter, groups of rats were fed choline-supplemented or CD diets in which the amount of saturated fat was varied by using hydrogenated vegetable oil (Primex) and corn oil (CO), either alone or in combination. The number and size of GGT-positive foci induced by the CD diet with CO as the sole source of fat were larger than those induced by the diet containing mixtures of Primex and CO. The CD diet with Primex alone was the least effective in inducing GGT-positive foci. Peroxidation of liver microsomal membrane lipids in rats fed regular CD or CD:CO diets was examined by determining the formation of conjugated dienes. The generation of diene conjugate in rats fed a CD:CO diet was evident after 2 days of the diet feeding, and the levels increased at 1 and 2 weeks. No significant diene conjugate was demonstrated in rats fed a regular CD diet for 2 days. However, after 1 and 2 weeks, there was generation of diene conjugate, the levels of which were lower in rats fed the CD diet than those on a CD:CO diet. Addition of an antioxidant, 0.25% butylated hydroxytoluene, to both CD and CD:CO diets abolished the generation of diene conjugate in rat liver microsomal membranes and markedly inhibited the promotion of GGT-positive foci in the liver of diethylnitrosamine-initiated rats. The results suggest that membrane lipid peroxidation in the liver may be related to the promotion of the induction of GGT-positive foci by a CD diet. The enhanced promotion by the inclusion of a higher level of polyunsaturated fat in the diet may be, in part, due to its greater susceptibility to peroxidation.     

Resistant starch prevents colonic DNA damage induced by high dietary cooked red meat or casein in rats

In a previous study we have shown that high levels of dietary protein (as casein) result in increased levels of colonic DNA damage, measured by the comet assay, and thinning of the colonic mucus layer in rats when dietary resistant starch (RS) is negligible. Feeding RS abolishes these effects. This study aimed to establish whether a diet high in protein as cooked red meat would have similar effects and whether RS was protective. Rats were fed a diet containing 15% or 25% casein or 25% cooked lean red beef, each with or without the addition of 48% high amylose maize starch (a rich source of RS) for four weeks. As expected, high dietary casein caused a 2-fold increase in colonic DNA damage compared with a low casein diet and reduced the thickness of the colonic mucus layer by 41%. High levels of cooked meat caused 26% greater DNA damage than the high casein diet but reduced mucus thickness to a similar degree to casein. Addition of RS to the diet abolished the increase in DNA damage and the loss of colonic mucus thickness induced by either high protein diet. Cecal and fecal short chain fatty acid pools were also increased by inclusion of RS in the diet. Because DNA damage is an early step in the initiation of cancer, these findings suggest that increased DNA damage due to high dietary protein as cooked red meat or casein could increase colorectal cancer risk but inclusion of resistant starch in the diet could significantly reduce that risk.     

Chemoprevention of colon carcinogenesis by the synthetic organoselenium compound 1,4-phenylenebis(methylene)selenocyanate.

The chemopreventive effect of 40% and 80% maximum tolerated dose (MTD) levels of 1,4-phenylenebis(methylene)selenocyanate (p-XSC) administered in the diet during the initiation phase (2 weeks before, during, and up to 3 days after carcinogen administration) and the post-initiation phase (3 days after carcinogen treatment until termination) of azoxymethane (AOM)-induced colon carcinogenesis was studied in male F344 rats. The MTD of p-XSC was determined in male F344 rats and found to be 50 ppm. Beginning at 5 weeks of age, all animals were divided into various experimental groups (42 rats/group) and fed the high-fat semipurified diet or diets containing 20 (40% MTD) and 40 (80% MTD) ppm p-XSC. At 7 weeks of age, all animals (30 rats/group) except the vehicle-treated groups (12 rats/group) were administered s.c. injections of AOM (15 mg/kg body weight/week for 2 weeks). Three days after the second injection of AOM or vehicle (normal saline), groups of animals fed the p-XSC diets and control diet were transferred, respectively, to control diet and p-XSC diets and continued on these diets until the termination of the study. All animals were necropsied during the 36th week after AOM treatment. Colonic mucosal prostaglandin E2 and selenium-dependent glutathione peroxidase were measured in animals fed the control and p-XSC diets at the termination of the study. The results indicate that 40 ppm p-XSC administered during the initiation phase significantly inhibited the colon tumor incidence (percentage of animals with tumors). Dietary p-XSC administered at 20 and 40 ppm levels during the initiation phase significantly inhibited colon tumor multiplicity (tumors/animal and tumors/tumor-bearing animal). Colon tumor incidence and multiplicity were significantly reduced in groups fed 20 and 40 ppm p-XSC diets at the postinitiation phase of carcinogenesis. Colonic mucosal selenium-dependent glutathione peroxidase activity was increased, and prostaglandin E2 was reduced in animals fed the p-XSC diet compared to animals fed the control diet. Whereas the precise mechanisms of p-XSC-induced inhibition of colon carcinogenesis remain to be elucidated, it is likely that the effect during the initiation and postinitiation phases may be due to alteration in carcinogen metabolism and to modulation of prostaglandin synthesis and selenium-dependent glutathione peroxidase activity.     

Effect of dietary cellulose on cell proliferation and progression of 1,2-dimethylhydrazine-induced colon carcinogenesis in rats

The effects of different levels of dietary cellulose on colonic crypt mitotic activity and colon carcinogenesis were studied in 190 male Sprague-Dawley rats. Rats were divided into groups and fed a basal fiber-free diet supplemented with either 0, 5, or 15% pure cellulose (w/w), for periods of 10 weeks (initiation stage) or 32 weeks (promotional stage). Half of the rats in each group were given weekly s.c. injections of 9.5 mg 1,2-dimethylhydrazine (the base) (DMH) for 8 weeks. Some of the rats were killed at 10 weeks while most were killed 22 weeks later. In some groups the dietary cellulose level was changed to a different level at 10 weeks. Food intake and body weight data showed that the rats within each experiment were isocalorically fed. There was a direct correlation between crypt height and the percentage of cellulose in the diet. Addition of 5 or 15% dietary cellulose during the initiation stage of carcinogenesis resulted in a significant increase in crypt height. Increasing dietary cellulose after the initiation stage (0 to 5% and 5 to 15%) or maintaining a high dietary cellulose level throughout both the initiation and promotional stages (15%) resulted in a significant increase in crypt height. A DMH-induced increase in mitotic activity that was observed during the initiation stage was no longer evident after the 22-week promotional stage. The significant DMH-induced increases in proliferative zone height and crypt height that were initially observed during the initiation stage were also observed after the 22-week promotional stage. These data indicate that the initial DMH-induced increases observed in proliferative zone height and crypt height are irreversible. Addition of 5 or 15% cellulose was found to suppress DMH-enhanced mitotic activity in the crypts of the descending colon during the initiation stage of carcinogenesis. This finding was correlated with a significantly lower incidence of adenocarcinomas in rats maintained on 5 or 15% cellulose throughout both the initiation and promotional stages.     

Effects of dietary fats and soybean protein on azaserine-induced pancreatic carcinogenesis and plasma cholecystokinin in the rat

Both dietary unsaturated fat and raw soybean products are known to enhance pancreatic carcinogenesis when fed during the postinitiation phase. A comparison of these two dietary components was made to evaluate the relative potency of each ingredient for enhancing pancreatic carcinogenesis and to determine if this enhancement was correlated with an increase in plasma cholecystokinin (CCK) levels. Male Wistar rats were initiated with a single dose of azaserine (30 mg/kg body weight) at 14 days of age. The rats were weaned to test diets formulated from purified ingredients. Dietary protein at 20% by weight was either casein or soy protein isolate (heat treated or raw). Corn oil was the unsaturated fat of major interest and it was fed at either 5 or 20% by weight. Pancreases were quantitatively evaluated for carcinogen-induced lesions at 2- and 4-month postinitiation. In a second experiment designed to closely mimic the above experiment, rats were implanted with cannulae which allowed plasma to be repetitively sampled over a 2.5-week period during which the test diets were fed. Plasma was collected both prior to introduction of the test diets and afterwards. Plasma CCK was measured by a specific radioimmunoassay. Both the 20% corn oil diet and the raw soy protein isolate diet enhanced pancreatic carcinogenesis. The effects of the raw soy protein isolate on the growth of the carcinogen-induced lesions were significantly greater than the effects of the 20% corn oil diet. Plasma CCK values were not elevated in the rats fed the 20% corn oil diet, but they were significantly elevated in the rats fed the raw soy protein isolate. Heat-treated soy protein isolate neither enhanced carcinogenesis nor elevated the plasma CCK level. This study demonstrates that certain plant proteins enhance the growth of carcinogen-induced pancreatic foci and that this effect is considerably greater than the enhancement by high levels of dietary unsaturated fat. Furthermore, the enhancement by the raw soy protein isolate may be mediated by CCK; but this does not appear to be the mechanism by which the unsaturated fat, corn oil, enhances pancreatic carcinogenesis.     

The effect of the hydrolytic state of dietary protein on post-irradiation morbidity and mucosal cell regeneration

Diets containing hydrolyzed casein have been observed to enhance post-irradiation intestinal mucosal recovery. The intake and the composition of such diets were not carefully controlled. This study attempted to do so. Male specific pathogen-free Sprague-Dawley rats were randomized to receive either an enzymatically hydrolyzed casein semi-purified diet (EHC), a whole casein semi-purified diet (WC), or powdered lab chow (C). All diets were isonitrogenous, and the WC and C rats were pair-fed to the ad libitum fed EHC rats. Seven days after initiation of feeding, the rats were abdominally irradiated with a single 9.0 Gy dose of 137Cs gamma rays. The rats were continued on the diets for another 5 days. Intestinal mucosa from transverse segments at the duodenum, jejunum, proximal ileum, and distal ileum were measured for incorporation of (3H methyl) Thymidine 1 hour after interperitoneal injection. Incorporation reached a maximum by day 4 post-irradiation regardless of diet or segment. Incorporation in the duodenum was enhanced by the EHC diet compared to the C diet, while the incorporation in the jejunum was initially suppressed by the EHC diet compared to the WC diet. In the jejunum, the number of mitoses per crypt of 25 anti-mesenteric crypts post-irradiation was increased by the EHC diet. Prior to irradiation, all groups gained similar amounts of weight. After irradiation, the C rats lost weight, while the EHC and WC rats remained the same or gained weight. Guaiac tests for occult blood were negative prior to irradiation, but positive for all rats on days 1-5 postirradiation. When calorie and protein intakes were controlled, different areas of the small intestine responded differently to EHC.     

Effects of varying fat content of a high tryptophan diet on the induction of gamma-glutamyltranspeptidase positive foci in the livers of rats treated with hepatocarcinogen

The influence of varying the dietary fat content on the emergence of gamma-glutamyltranspeptidase (GGT)-positive foci in the livers of male rats fed elevated (2%) L-tryptophan (TRP) and exposed to a hepatocarcinogen was investigated. Subtotal hepatectomies were performed, and 18 h later the rats were treated with diethylnitrosamine (DEN) (30 mg/kg). Ten days later 4 dietary groups were followed for 10 weeks: (1) control diet containing 15% fat (C-HF); (2) control diet containing 5% fat (C-LF); (3) C-HF + TRP; (4) C-LF + TRP. Rats fed elevated TRP diets (C-HF + TRP and C-LF + TRP) similarly developed more and larger GGT+ foci than did rats fed the regular TRP diets (C-HF and C-LF), indicating that the promotional effect of elevated dietary TRP was not affected by the fat level (15% vs. 5%).     

Ectopic pituitary grafts modify the response of male rats to sex differentiated promotion of diethylnitrosamine-initiated hepatic lesions with a choline-deficient diet

The influence of implantation of ectopic pituitary grafts (PGs)under the kidney capsule in male rats on the sex differencesin response to promotion with a choline-deficient (CD) dietwas studied in the livers of diethylnitrosamine (DEN)-initiatedWistar rats. Growth of enzyme-altered foci, liver regenerationin response to partial hepatectomy (PH) and hepatic c-myc expressionwere studied. The area per enzyme-altered focus was significantlylarger in initiated males fed a CD diet for 10 weeks when comparedwith the corresponding females. The sex difference was morepronounced 1 week after a PH performed following 10 weeks onthe diet. In males carrying PCs the area per focus was reducedto the same size as in females. Liver weight gain after PH wasreduced in males, but not in females, by the CD diet, and thelevel in PG-bearing males was intermediary, significantly differentfrom that of males without grafts. A significantly lower labelingindex in surrounding, but not in focal, hepatocytes was observedin initiated, CD-treated males than in the corresponding females1 week after PH. In initiated as well as in uninitiated maleson a CD diet the expression of the c-myc gene was 3- to 4-foldhigher when compared with males fed a choline-supplemented dietat the time of PH. The mRNA level in females fed a CD diet was{small tilde}2.5-fold lower than in males, but still significantlyabove the level in females without the dietary treatment. Asignificant decrease in male c-myc expression was observed asa result of implantation of ectopic pituitaries. In conclusion,sex-differentiated promotion of DEN-initiated lesions with aCD diet is regulated by a pituitary influence on rat liver,in analogy with results preciously obtained in the resistanthepatocyte model and with dietary deoxycholic acid promotion.This might suggest that pituitary factors are major determinantsof sex-differentiated promotion in rat liver.     

Dietary protein intervention during the postdosing phase of aflatoxin B1-induced hepatic preneoplastic lesion development

The effects of high and low dietary protein intervention on the growth and development of hepatic preneoplastic lesions were examined. Inbred male F344 rats fed a semipurified (AIN-76) 20% casein diet were given doses orally of aflatoxin B1 (10 doses, each 250 micrograms/kg). One week after the last dose, animals were fed diets containing either 5 or 20% casein. Animals fed a 5% casein diet throughout the 12-week postdosing period had a marked reduction in development of gamma-glutamyltransferase-positive foci. Animals fed a 20% casein diet throughout the same period had the highest response. Groups fed the 5% casein diet for half of the postdosing period and 20% for the other half had intermediate responses. The data show that the high response observed in animals fed a high-protein diet can be inhibited by the postinitiation intervention of a low-protein diet. Likewise, the low response observed in the animals fed a low-protein diet was increased by the introduction of a high-protein diet late in the experiment.     

Effects of short-term dietary restriction on survival of mammary ascites tumor-bearing rats

We studied the effects of short-term dietary restriction on the survival of 3-4-month-old tumor-free and tumor-bearing Fisher rats. The diet-restricted food regimen consisted of alternate day ad libitum feeding followed by alternate day fasting. Diet-unrestricted control rats were fed ad libitum daily. Six tumor-free rats on the diet-restricted regimen compensated for the dietary restriction by an increase in food consumption during the alternate feeding days, and lost an average of only 2-3% of their weight in 13 days. Six tumor-free rats on a daily ad libitum feeding regimen gained an average of 6.8% in 15 days. The above dietary-restricted regimen was initiated 1 week before 24 rats were inoculated intraperitoneally with 15 million Mat 13762 ascites tumor cells. Sixteen of 24 (66.7%) diet-restricted tumor-bearing hosts and 5/24 (20.8%) diet-unrestricted tumor-bearing hosts survived at 9 days after tumor inoculation (p less than 0.005). Twelve of 24 (50%) diet-restricted tumor-bearing hosts, and 3 of 24 (12.5%) diet-unrestricted tumor-bearing hosts, survived at 10 days after tumor inoculation (p less than 0.025). Thus, the survival of tumor-bearing rats was enhanced by short-term relatively mild dietary restrictions. We suggest that relatively mild dietary restrictions should be included in clinical trials designed to inhibit cancer growth and enhance the survival of human cancer patients.     

Inhibition of chemically induced mammary carcinogenesis in rats by short-term exposure to butylated hydroxytoluene (BHT): interrelationships among BHT concentration, carcinogen dose, and diet

Dietary butylated hydroxytoluene (BHT) fed 14 days before and 14 days after carcinogen administration resulted in a dose-dependent inhibition of 7, 12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumor incidence in outbred Sprague-Dawley rats. In addition, the inhibitory effects of BHT were strongly influenced by the dose of initiating carcinogen and the type of diet in which BHT was administered. In animals fed the NIH-07 diet and receiving a low dose of DMBA (5 mg/rat), the inhibitory effect of BHT was manifested at all four BHT concentrations (6,000 leads to 300 ppm). Maximal inhibition was approximately 50% in animals given 5 mg DMBA and receiving 6,000 ppm BHT. However, in the group administered a high dose of DMBA (15 mg/rat), the inhibitory effect of BHT was expressed only at 6,000 ppm, the highest concentration given. Lower concentrations (300 and 1,000 ppm) of BHT had no detectable effect on tumor incidence. In animals fed the defined, semipurified AIN-76A diet during the 4-week treatment period and initiated with 5 mg DMBA, BHT at 6,000 ppm inhibited tumor development. However, at 15 mg DMBA animals fed the AIN-76A diet differed markedly from those fed the NIH-07 diet. In the former group, BHT at 6,000 ppm was unable to elicit any inhibitory response; in the latter group, BHT inhibited tumor development by 40%. Dietary BHT also inhibited DMBA-induced adrenocortical hyperplastic nodules in a dose-dependent fashion. These results indicate that short-term exposure to dietary BHT can inhibit experimental mammary tumor development at environmentally relevant concentrations.     

Alternative methods of selecting rat hepatocellular nodules resistant to 2-acetylaminofluorene

Dietary 2-acetylaminofluorene (2-AAF) coupled with a stimulus for cell proliferation such as a 2/3 partial hepatectomy (PH) or a necrotizing dose of carbon tetrachloride is frequently employed to generate nodules of resistant ("initiated") rat hepatocytes. This regimen is a useful model for experimental analysis of alterations in hepatocytes during carcinogenesis, and also as an assay for initiation by various carcinogens. Because of the decreasing availability of carcinogen-containing diets from commercial sources, we have developed alternative methods of 2-AAF administration to generate nodules in rats initiated with N-nitrosodiethylamine. This study compared the nodule-selecting and cancer-promoting efficacy of 2-AAF administered by the Solt-Farber procedure (0.02% in diet for 2 weeks) with 2-AAF administered by gavage, as a suspension in 1% aqueous carboxymethyl-cellulose (CMC). Three or 4 daily administrations of 2-AAF by gavage (20 mg/kg/day) followed by PH on day 4 were equivalent to the dietary regimen in generating early resistant nodules, late persistent nodules and hepatocellular carcinomas. These regimens were similar to the dietary regimen of 2-AAF in inhibiting virtually all normal hepatocyte proliferation. These regimens permit control over the duration and level of 2-AAF exposure and the resulting size of selected nodules.     

Effect of a high-protein-low-carbohydrate diet on toxicity and antitumor activity of 5-fluorouracil in mice

The effect of different levels of dietary protein on 5-fluorouracil (FUra) toxicity and antitumor activity was assessed in female (BALB/c X DBA/2Ha)F1 (CDF1) and BALB/c mice bearing the P1798 lymphosarcoma. In the toxicity experiments, CDF1 mice were fed diets containing 5% [low protein (LP)], 20% [normal protein (NP)], or 60% [high protein (HP)] casein for 22 days and were then given a single ip injection of 275 mg FUra/kg. As determined by effects on the white blood cell count and by changes in body weight, FUra was least toxic in mice fed the HP diet. Moreover, mortality was 77.0, 42.9, and 11.4% for mice fed the LP, NP, and HP diets, respectively. In the antitumor studies, BALB/c mice bearing the P1798 lymphosarcoma were fed one of the 3 diets starting 5 days after transplant. Mice were given injections of 50 mg FUra/kg or the vehicle control on days 14 and 15 after transplant. As measured by tumor weights on day 16, FUra was least effective in mice fed the LP diet and most effective in mice fed the NP and HP diets. Survival time of mice given injections of FUra on days 14 and 15 was increased when compared to the survival time of control mice, but no difference in the percent increase in survival time was noted among the 3 dietary groups. If mice were given two cycles of FUra therapy (days 14 and 15 and days 20 and 21), mice fed the HP diet survived significantly longer than did mice fed the LP or NP diet. These data demonstrate that the feeding of an HP diet markedly decreases the toxicity of FUra while preserving or actually enhancing the antitumor effect.