Insecticide inhibition of 5alpha-dihydrotestosterone binding in the rat ventral prostate.

The chlorinated hydrocarbon insecticides dieldrin and o,p'-DDT inhibit binding of 5alpha-dihydrotestosterone to specific receptor proteins in rat prostate cytosol. Dieldrin is less inhibitory than o,p'-DDT.

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.

Nitrogen-stimulated orotic acid synthesis and nucleotide imbalance.

Orotic acid, first discovered in ruminant milk, is an intermediate in the pyrimidine biosynthesis pathway of animal cells. Its synthesis is initiated by the formation of carbamoyl phosphate (CP) in the cytoplasm, with ammonia derived from glutamine. Ureotelic species also form CP in the first step of urea synthesis in liver mitochondria. For that, ammonia is derived from tissue fluid. When there is insufficient capacity for detoxifying the load of ammonia presented for urea synthesis, CP leaves the mitochondria and enters the pyrimidine pathway, where orotic acid biosynthesis is stimulated, orotic acid excretion in urine then increases. Orotic acid synthesis is abnormally high with hereditary deficiencies of urea-cycle enzymes or uridine monophosphate synthase. It is also elevated by ammonia intoxication and during feeding of diets high in protein, high in lysine with respect to arginine, or deficient in arginine, ornithine, and citrulline. Rats fed 1% orotic acid or diets deficient in urea-cycle amino acids develop fatty livers, which has not been demonstrated in other species. Humans consuming 6 g of orotic acid daily have not shown adverse effects. Rats fed 1% orotic acid or arginine-deficient diets also showed more and larger foci positive for gamma-glutamyl transpeptidase and more liver tumors after administration of carcinogens and partial hepatectomy. Orotic acid feeding was also associated with the tendency for development of larger mammary tumors induced by chemical carcinogens in rats and with development of urinary bladder calculi containing high concentrations of orotic acid in mice. Conditions that raise tissue orotic acid change purine-pyrimidine ratios. It is unknown whether tissue orotate concentrations play a role in the recently observed enhanced proliferation of cells in the colon of rats fed high-protein, high-fat diets or in the promotion of chemically induced colon cancer by intrarectal administration of ammonium acetate.

Effect of dietary protein concentration on yield of mutagenic metabolites from 1,2-dimethylhydrazine in mice.

The effects of varying dietary protein concentrations on the metabolism of 1,2-dimethylhydrazine (DMH) to mutagenic products by male C57BL/6 X C3H F mice were assayed by in vivo and in vitro methods. DMH and its metabolite, azoxymethane (AOM), did not increase the mutation frequency of Salmonella typhimurium (strain G-46) in vitro alone or in the presence of mouse liver homogenates capable of activating the promutagen dimethylnitrosamine. Methylazoxymethanol (MAM), another metabolite of DMH, was mutagenic in vitro without activation. S.c. administration of DMH, AOM, or MAM at dosages ranging from 0.2 to 0.8 mmol/kg of body weight caused dose-dependent increases in mutations of S. typhimurium in the host-mediated assay, and molar potencies increased progressively from DMH to AOM to MAM. S.c. or i.p. injections of AOM increased host-mediated mutagenesis within 20 min, while increases in mutagenesis by DMH required at least 1 hr. When [14C]DMH was administered, [14C]azomethane was expired immediately, while 14CO2 began to appear 1 hr after DMH administration. The percentage of administered [14C]DMH expired as azomethane varied inversely with dietary protein concentration, while AOM-induced host-mediated mutagenesis was directly proportional to dietary protein (p less than 0.01). The percentage of DMH converted to mutagenic end products was limited by losses of the volatile metabolite azomethane, especially in protein-deficient mice. Greater expiration of azomethane and decreased conversion of AOM to MAM, both seen with restriction of dietary protein, were associated with a smaller body burden of DMH metabolites.

Effects of ammonium acetate and sodium cholate on N-methyl-N'-nitro-N-nitrosoguanidine-induced colon carcinogenesis of rats.

This study was conducted to determine the effects of ammonium acetate alone or in combination with sodium cholate upon N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced colon carcinogenesis in rats. Ammonia, acetate, and deconjugated bile acids are produced by microbial enzymes in the gastrointestinal lumen. One hundred twenty male Sprague-Dawley rats, weighing 196 +/- 2 g at 8 wk of age, were given four intrarectal doses of MNNG (2 mg/dose) over 2 wk. They were then randomly assigned among four treatment groups, each containing 30 rats. The groups were arranged in a 2 x 2 factorial design and given intrarectal infusions of the agents under study in 0.3 ml of double-distilled water 3 times weekly for 52 wk beginning 4 wk after the initial MNNG treatment. The experimental treatments were: double-distilled water as control; ammonium acetate (24.8 mg of ammonia); sodium cholate (2 mg of cholic acid); and a combination of ammonium acetate and sodium cholate. Ammonium acetate treatment increased the number of rats with fecal blood 4-fold after 56 wk, and this was associated with a higher incidence of adenocarcinomas with a polypoid morphology. The incidence and total number of carcinomas in situ (high grade dysplasia) increased with ammonium acetate treatment. Ammonium acetate increased the total number of adenocarcinomas. Sodium cholate had no significant main effects on the incidence or morphology of colon lesions. The data support the conclusion that ammonium acetate treatment acted as a promoting agent in MNNG-induced colon carcinogenesis.

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.

Diet and cell growth modulation by ammonia.

Fiber is not digested by endogenous enzymes but is fermented by microbes principally in the large intestine. With fermentable energy available, microbes synthesize protein by using ammonia released by their enzymes from urea and other nitrogenous substances in ingesta and intestinal secretions. Fibber fermentation also yields fatty acids that lower the concentration of free ammonia by lowering pH. Fiber increases bulk and water of intestinal contents, shortens transit time, and decreases the concentration of toxic substances in contact with the intestinal mucosa. These processes decrease duration and intensity of exposure of the intestinal mucosa to free ammonia, the form of nitrogen that is most toxic and most readily absorbed by cells. At concentrations found in the lower bowel on usual Western diets, ammonia destroys cells, alters nucleic acid synthesis, increases intestinal mucosal cell mass, increases virus infections, favors growth of cancerous cells over noncancerous cells in tissue culture, and increases virus infections. Ammonia in the bowel increases as protein intake increases. The attributes of ammonia and the epidemiological evidence comparing populations that maintain low intakes of unrefined carbohydrate with those that consume high intakes of protein, fat, and refined carbohydrates implicate ammonia in carcinogenesis and other disease processes.

Priorities for nutrition content in a medical school curriculum: a national consensus of medical educators.

The ASCN Committee on Medical/Dental School and Residency Nutrition Education conducted a series of activities to establish guidelines for nutrition core content in a medical school curriculum. These activities included mail surveys of medical-nutrition educators and a representative group of medical school curriculum administrators and a national consensus workshop of nutrition educators. Results indicated close agreement between the nutrition educators and curriculum administrators (r = 0.89, p less than 0.0001) on the importance ratings of 41 nutrition topics and on the number of hours of nutrition course work that medical schools should provide (44 vs 37 h, respectively, p = 0.14). There was consensus among the nutrition educators that 26 topics should be given priority ratings as essential for inclusion in medical course work. Further prioritization of these topics resulted in a listing of core content topics and subtopics to serve as a guide to administrators and educators for planning nutrition course work in a medical school curriculum.

Issues and current applications of interspecies extrapolation of carcinogenic potency as a component of risk assessment.

The Life Sciences Research Office (LSRO) of the Federation of American Societies for Experimental Biology (FASEB) is conducting this symposium under contract with the Center for Food Safety and Applied Nutrition (CFSAN) of the Food and Drug Administration (FDA). The FDA has requested information on the strengths and weaknesses of current interspecies extrapolation methods using metabolic and pharmacokinetic data, identity of data for these methods, bases for choice of extrapolation method and selection of data base, validity and uniformity of interspecies extrapolation from target organ data, and nature and completeness of supporting data. Definitions and basic concepts of dose scaling are addressed and questions regarding appropriate units of measurement (e.g., mg/kg body weight, mg/m3 respired air, mg/m2 surface area) are raised. The use of DNA damage as a marker or end point upon which to scale carcinogenic potency is considered. Genotoxic mechanisms of carcinogenesis are emphasized because the roles of DNA adducts and DNA repair processes in initiation and promotion are much better defined than the mechanism for nongenotoxic carcinogenesis. The problems encountered in evaluating the human carcinogenicity of trichloroethylene are reviewed. The broad objectives of the symposium are discussed and the development of a structured format for the presentation of invited papers is presented.

Urinary metabolites characteristic of urea-cycle amino acid deficiency.

Experiments with 45-75-g male rats gave conclusive evidence that the simultaneous absence from the diet of arginine, ornithine, or citrulline caused an immediate and persistent elevation of orotic and citric acids in the urine. The experiments also demonstrated that a deficiency of no other individual amino acid increased urinary citrate and orotate. Elevated urinary excretion of orotic and citric acid occurred independently of the form of nonessential nitrogen. Replacement of arginine isonitrogenously with ornithine or citrulline prevented the rise in urinary orotic acid, but had different effects on growth, urinary citrate, and urinary urea. These differences were probably due to differential uptake of arginine, ornithine, and citrulline by tissues; In the reported experiments employing L-amino acids as sources of dietary nitrogen, a deficiency of any amino acid indispensable for growth and nitrogen balance or a deficiency of arginine, ornithine, or citrulline retarded growth, increased urinary urea, and decreased urinary ammonia. It is concluded that the severe loss of orotic acid during urea-cycle amino acid deficiency arises from a decreased capacity of the urea cycle to detoxify ammonia, thereby causing increased shunting of intramitochondrial carbamyl phosphate into pyrimidine synthesis. The similarities in metabolism during arginine deficiency and ammonia intoxication are discussed. The evidence shows that urinary orotic acid may be a valuable measure of arginine nutrition in mammals.

Growth, liver lipid and blood amino acids in rats fed ethanol with an adequate diet.

The weight, histology and RNA, DNA, protein and lipid content of the liver and arterial and portal plasma amino acid concentrations were determined in male Sprague-Dawley rats fed a liquid diet which met AIN-76A standards with 36% of the calories supplied by ethanol. The dietary components of the dry mixture in percentages by weight included 20% casein, 22% sucrose, 43% dextrin, 5% corn oil, vitamins, minerals and other dietary factors. For feeding these were suspended in distilled water containing 2.5% xanthan gum with or without ethanol to supply 1 kcal/ml. The feeding method employed perforated neoprene discs floated on top of the suspended diet to control evaporative losses. Animals were pair fed or ad libitum fed for 8-10 weeks. Gain/feed ratios were virtually identical for ethanol-fed rats and their pair-fed controls. Ethanol intake of ad libitum fed rats averaged 14.8, 10.3 and 7.4 g/kg BW/day after 1, 5 and 10 weeks, respectively. No chemical or histological evidence of liver fat accumulation or significant differences in arterial or portal amino acid concentrations were detected in animals fed ethanol. The lack of apparent ethanol toxicity is discussed in relation to the results of others and to our earlier report of increased orotic acid excretion by ethanol-fed rats.

Fatty liver of growing rats fed excess lysine and its prevention by adenine or allopurinol.

Weanling male Sprague-Dawley rats were fed ad libitum 15% casein diets with and without 5.0% lysine-HCI, 0.25% adenine sulfate or 0.1% allopurinol for 2 weeks. Addition of lysine alone depressed 2-week growth from 94 to 65 g increased average daily urinary orotic acid excretion from 0.39 to 1.77 mg and increased the percentage of total liver lipids from 3.6 to 11.2. Adenine or allopurinol did not change growth but markedly enhanced lysine-induced orotic aciduria and completely prevented lysine-induced fatty livers. Reports by other show that adenine and allopurinol also prevent fatty livers or rats fed arginine-free diets or excess orotic acid. The authors conclude that lysine-induced orotic aciduria results from arginine deficiency caused by antagonism of arginine function by lysine, and that lysine-induced fatty liver probably results from a lesion identical to that produced by feeding excess orotic acid.

Carcinogenesis studies with the lyophilized mushroom Agaricus bisporus in mice.

Continuous administration of 10, 5, and 2.5% lyophilized Agaricus bisporus (AB) mushroom in the diet of six-week-old, randomly bred Swiss mice for life induced tumors in the lungs, forestomach, glandular stomach, and ovaries in certain groups. Some of the tumor incidences were found to be statistically significant, although no dose-response relationship was established. Histopathologically, the neoplasms were classified as adenomas and adenocarcinomas of lungs, glandular stomach, and ovaries and squamous cell papillomas and carcinomas of the forestomach. AB given in both raw and baked forms induced tumors in the same species in earlier experiments. Since this fungus is consumed in lyophilized form to a certain degree in the United States, the results may carry practical significance.

Dietary protein and experimental carcinogenesis.

This review summarizes selected information about the influence of proteins, protein-fat interactions, and calorie intake on carcinogenesis. Most of the definitive studies concerning protein and cancer have utilized protein underfeeding and feed restriction. Optimal or less than optimal protein intakes have generally inhibited spontaneous and chemically induced tumor growth as well as the growth of transplantable tumors. Studies have focused on the quantity of protein and its amino acid supply rather than its source. Raising protein intake increases carcinogen metabolizing capacity, and the incidence of tumors depends upon the biologic activity of the metabolites that are formed. The few published studies dealing with the effects of protein on chemically induced colon, mammary, and liver cancers show that the incidence varied with the carcinogen and the level of protein fed at the time of carcinogen administration. With 1,2-dimethylhydrazine, a colon cancer-inducing agent, the toxic and tumorigenic responses have varied with the route of administration, the level of protein fed, and the level and duration of exposure to the carcinogen. In some instances, high protein diets may have led to a lower incidence of tumors because of depressed feed intake, a known confounding factor. The existing data about the relation of protein to cancer make generalizations about mechanisms hazardous because experimental models and protocols have varied widely. Some early studies undoubtedly used diets that lacked nutrients now known to be essential. Unfortunately, some recent studies have overlooked established nutritional principles and the known nutritional requirements appropriate for the age and species of animals used as models.