Effect of vitamin A nutriture on experimental esophageal carcinogenesis.

The effect of mild vitamin A deficiency or vitamin A supplementation on methylbenzylnitrosamine (MBN; CAS: 937-40-6)-induced esophageal carcinogenesis was examined in Sprague-Dawley rats. The animals were fed semipurified diets containing levels of retinyl acetate, which were adequate (2.2 mg/kg diet), deficient (0.30 mg/kg diet), or supplemented (29.9 mg/kg diet) with respect to vitamin A content. Carcinogen-treated rats received 2.5 mg MBN/kg (body wt) twice a week for 5 weeks; they were then sacrificed for evaluation of esophageal tumorigenesis 15 weeks later. Liver levels of retinol reflected vitamin A nutriture, but there were no clinical signs of deficiency or toxicity. There were no significant differences in the frequency or incidence of esophageal tumors (either carcinomas or papillomas) among the dietary groups. There was also no indication that either vitamin A deficiency or vitamin A supplementation influenced the formation of preneoplastic lesions. Although the time was short for the neoplastic development, tumors were observed. These data suggest that vitamin A is selective in tissues it may protect from cancer induction and that the esophagus is less involved than other tissues.

Morphology and distribution of 1,2-dimethylhydrazine dihydrochloride-induced colon tumors and their relationship to gut-associated lymphoid tissue in the rat.

The histopathology and relationship of sym-dimethylhydrazine dihydrochloride [(DMH) CAS: 306-37-6; 1,2-dimethylhydrazine dihydrochloride]-induced colon tumors to colonic lymphoid aggregates were examined in outbred male Sprague-Dawley rats treated with saline or DMH and sacrificed at three intervals after treatment. The ratio of polypoid:sessile tumors was 71:29 four months after DMH treatment and 62:38 when tumors were fully developed. Colonic lymphoid aggregates were found 3-5 cm from the cecal-colonic junction, near the flexure of the ascending and transverse colon, and 3-5 cm from the rectum. There were no significant differences between saline-treated and DMH-treated rats regarding the size, cellularity, and number of lymphoid aggregates per rat. A significant association (P less than .001) was seen between tumor development and the presence of a lymphoid aggregate in a given segment of the colon. Sessile adenocarcinomas, but not polypoid tumors, were significantly associated (P less than .001) with lymphoid aggregates and usually presented as mucinous tumors adjacent to or intermixed with the lymphoid tissue.

Effect of alterations in the quality and quantity of dietary fat on 1,2-dimethylhydrazine-induced colon tumorigenesis in rats.

The effect of alterations in the quality and quantity of dietary fat on 1,2-dimethylhydrazine-induced colon cancer in rats was studied. Weanling Sprague-Dawley rats were fed semipurified diets containing 24% beef fat, 24% corn oil, 24% Crisco, or the three fats in equal parts to make a total of 5% fat with other macronutrients and micronutrients adjusted to balance the ratios of nutrient to calorie. After 4 weeks of dietary treatment, all rats, except vehicle-treated animals, received 1,2-dimethylhydrazine (15 mg/kg) by gavage, once a week for 5 weeks. The animals were fed the experimental diets until intestinal tumors developed, and surviving animals were sacrificed at 60 weeks. There was no effect of any of the high-fat diets tested on intestinal tumor incidence, latency, size, or frequency. All groups contained the same proportion of adenomas (less than 3%) as well as adenocarcinomas classified as mucinous. In the group fed 24% Crisco, tumors occurred with greater frequency in the proximal section of the colon than in lower segments, but the distribution was approximately uniform in the other groups. Cumulative probability of death with colon carcinoma was lowest in the 24% Crisco group, but the other high-fat groups did not differ significantly from the 5% mixed fat group nor from one another.

Lipotropes, immunocompetence, and cancer.

Lipotropes (choline, methionine, folic acid, and vitamin B12) are required for normal metabolic function at the cellular and subcellular levels. Deficiencies of any or all of them to a point of influence on methyl group metabolism has a profound effect on synthesis of cellular macromolecules and on cell proliferation. Lipotrope deficiency results in a diminished immunocompetence and an increased susceptibility to a number of types of cancer in experimental animals. A challenge now being addressed is to identify the linkage between lipotropes, the immune system, and cancer and to determine mechanisms which can be useful in cancer prevention.

Impairment of blastogenic response of splenic lymphocytes from iron-deficient mice: in vivo repletion.

Iron-deficiency anemia impaired the blastogenic response of splenic lymphocytes and partially purified T cells to Concanavalin A and phytohemagglutinin. The response of splenic lymphocytes and partially B cells to bacterial lipopolysaccharide was also significantly impaired. Caloric restriction in pair-fed mice did not have any significant effect. Blastogenic response to the three mitogens was restored to normal after anemic mice were fed the regular diet containing 25 to 30 mg Fe/kg (FeSO4) for approximately 10 days. We also found that in the anemic mice the mean wet weights per 100 g of body of spleen, heart, brain, and kidney increased, while those of the thymus and liver decreased. In the pair-fed mice only the mean wet weight of the liver significantly decreased. There was a small but significant decrease in the white blood count and peripheral lymphocyte count in the anemic but not the pair-fed mice. The mechanism by which iron deficiency impairs the cell-mediated immune response is discussed.

Impairment of blastogenic response of splenic lymphocytes from iron-deficient mice. In vitro repletion by hemin, transferrin, and ferric chloride.

Splenic lymphocytes from iron deficient C57BL/6 mice gave smaller proliferative responses to T and B cell mitogens than those from either the control of pair-fed mice. The addition of hemin to the culture medium partially restored the responses to Con A and phytohemagglutinin but not to bacterial lipopolysaccharide in unfractionated spleen cells and enriched T cell fractions. The responses of lymphocytes from the control and pair-fed mice were either unchanged or decreased. Hemin restored the blastogenic response to Con A more efficiently than to phytohemagglutinin. The blastogenic responses were increased linearly with increasing doses of hemin. Ferric chloride and iron saturated mouse transferrin did not restore the response to either Con A or lipopolysaccharide. However, both transferrin and ferric chloride partially restored the response to phytohemagglutinin. The possible mechanism of selective restoration of blastogenesis by hemin, transferrin, and ferric chloride in iron-deficient T lymphocytes is discussed.

Comparison of immune status and 1,2-dimethylhydrazine induced tumorigenesis in brown--Norway and Fischer rats. Emphasis on splenic and colonic lymphocyte function.

Sym 1,2-dimethylhydrazine (DMH)-induced colon tumorigenesis was studied in immunologically different strains of rat: the Brown--Norway which is known to be immunologically a low-responder and the Fischer a high-responder. Brown--Norway rats received a total dose of 75, 150 or 225 mg DMH/kg or vehicle and Fischer rats received 150 mg DMH/kg or vehicle over a 3-week period. Rats were killed 5 months after the final treatment. Lymphocytes were isolated from the spleen and colon from rats treated with 150 mg DMH/kg or vehicle. Natural killer (NK) cell activity and the autologous mixed lymphocyte response (AMLR) as well as colon tumor incidence were compared between the two strains. Splenic and colonic intraperithelial lymphocytes (IEL) from the Brown--Norway strain demonstrated low NK activity and reduced splenic T lymphocyte proliferation in response to autologous non-T lymphocytes. As well, colonic lamina propria lymphocyte (LPL) proliferation was low and Brown--Norway rats had a low incidence of DMH-induced colon neoplasms (7%). In comparison, the Fischer rats had more effective splenic and IEL NK killing, enhanced splenic AMLR, enhanced LPL proliferation and a higher incidence of colon tumors (20%).

Effect of dietary selenium levels on methylbenzylnitrosamine-induced esophageal cancer in rats.

Male Sprague-Dawley rats fed selenium deficient diets received either 0 ppm, 0.15 ppm or 4.0 ppm selenium in the drinking water. Animals were treated with methylbenzylnitrosamine (MBN). Dietary selenium deficiency had no effect on MBN-induced esophageal carcinogenesis. Animals treated with 4 ppm selenium in the drinking water during the initiation and post-initiation period had the same number of tumors as the group which received 0.15 ppm selenium for the entire experimental period. The incidence and frequency of carcinomas was lowest in the group which was supplemented with extra selenium (4.0 ppm) during the period of carcinogen administration and highest in the group which received 4.0 ppm selenium during the post-initiation period.

The toxicity of inhaled methanol vapors.

Methanol could become a major automotive fuel in the U.S., and its use may result in increased exposure of the public to methanol vapor. Nearly all of the available information on methanol toxicity in humans relates to the consequences of acute, rather than chronic, exposures. Acute methanol toxicity evolves in a well-understood pattern and consists of an uncompensated metabolic acidosis with superimposed toxicity to the visual system. The toxic properties of methanol are rooted in the factors that govern both the conversion of methanol to formic acid and the subsequent metabolism of formate to carbon dioxide in the folate pathway. In short, the toxic syndrome sets in if formate generation continues at a rate that exceeds its rate of metabolism. Current evidence indicates that formate accumulation will not challenge the metabolic capacity of the folate pathway at the anticipated levels of exposure to automotive methanol vapor.

Local and regional immune function of vitamin A-deficient rats with ocular herpes simplex virus (HSV) infections.

Experimental ocular herpes virus (HSV) infections are more severe in vitamin A-deficient rats (-A) compared with normal pair-fed controls (+A). In an effort to determine whether alterations in specific or nonspecific immune responses were responsible for the increased susceptibility of -A rats, cell-mediated responses and natural killer cell (NK) activity were monitored during the course of ocular herpetic infections in -A and +A rats. Prior to infection the concanavalin A (Con A)-induced response of splenic lymphocytes from -A rats was significantly less than that of +A animals. Three days following topical application of HSV to abraded corneas, the Con A-induced splenic response decreased in both -A and +A animals and remained at low levels for 10 d following infection. The cervical lymph node (CLN) response to Con A was depressed 7 d following infection but was higher in the -A group than in the +A group at all time points. In vitro response to inactivated HSV antigen appeared on d 7 in the spleen and d 10 in the CLN. The responses were higher in -A animals compared with +A pair-fed controls and were related to the severity of the disease rather than to dietary treatment. Splenic NK cytotoxic responses were higher in +A than -A animals and decreased in both groups during the 10-d post-infection period. Cervical lymph node NK responses were unaffected by diet or ocular HSV infection.

Effect of beef fat on DMH-induced colon tumorigenesis: influence of rat strain and nutrient composition.

The modulating effect of high levels of dietary fat on chemically induced colon tumorigenesis has been studied in animal models, with conflicting results. The present study was designed to examine the influence of rat strain, stage of tumor development and micronutrient composition of the diet on 1,2-dimethylhydrazine (DMH)-induced intestinal tumorigenesis. Two strains of rats [Sprague-Dawley (SD) and Fischer-344 (F-344)] were fed one of three experimental diets. The diets contained 5 or 20% dietary fat but differed in nutrient composition and nutrient-energy ratio. After receiving the experimental diets for 4 wk, animals were treated with DMH X 2HCl (10 mg/kg body wt) once a week for 20 wk and killed 10 wk after receiving the last dose of carcinogen. Long-term administration of DMH was more toxic to F-344 rats than to SD animals, and the toxicity was potentiated by reductions in the micronutrient composition of the diet. High levels of dietary fat (20%) resulted in a barely significantly higher incidence in colon tumor (but not frequency or size) in SD rats that received the diet promoting optimal growth than did low levels of dietary fat. No effect of 20% beef fat was seen in SD animals fed a diet that produced a slower growth rate or in F-344 animals.

The effect of vitamin A deficiency on the in vitro cellular immune response of rats.

The effect of vitamin A deficiency on the response of splenic lymphocytes to mitogenic stimulation was determined in an experimental rat model. Male Lewis rats were divided into three groups. The ad libitum group (AL) was fed unlimited amounts of a vitamin A-supplemented diet. The vitamin A-deficient group (DEF) received a commercial vitamin A-free diet. The pair-fed group (PF) received a vitamin A-containing diet equivalent in amount to that consumed by the DEP group. During the early stages of vitamin A deficiency (determined by cessation of weight gain), the rats were killed and the isolated splenic lymphocytes subjected to mitogenic stimulation. Lymphocytes from DEF rats had one-third the transformation response to the mitogens Concanavalin A, Phytohemagglutinin and E. coli Lipopolysaccharide S of the AL and PF groups. When the DEF rats were supplemented with vitamin A, the transformation response returned to control values within 3 days. In addition to the alterations in the immune response, the DEF rats showed a marked leukopenia, a decrease in the number of circulating lymphocytes and an increase in the number of circulating neutrophils.

Alterations in immune function in rats caused by dietary lipotrope deficiency: effect of culture medium, 2-mercaptoethanol and mitogen dose on the in vitro lymphocyte transformation response.

The effect of variations in culture media, mitogen dose, harvest time, 2-mercaptoethanol (2-ME) addition and length of [3H]thymidine pulse on the concanavalin A (Con A)-stimulated splenic lymphocyte transformation response of male, weanling Sprague-Dawley rats maintained on a control (C), folacin-deficient (F) or marginal methionine-choline (M/C) diet was examined. Splenocytes cultured in minimal essential medium reached an optimal response on day 4. The response of F rats was significantly lower than C rats on day 3 and day 4. The response of M/C rats were lower on day 3. The addition of 2-ME to the culture medium shifted the cell cycle kinetics toward and earlier peak response time (day 2), and significant differences among groups were seen only under suboptimal conditions. Cells cultured in Medium 199 had a low transformation response, which reached peak stimulation on day 5. The response of F and M/C rats was significantly lower than C animals on days 3 and 4. In contrast, splenocytes cultured in medium 199 + 2-ME reached optimal stimulation on day 2, with no significantly differences between groups. No effect on cell viability was seen from 2-ME, but it did accelerate cell cycle kinetics and reversed the normal age-induced immunosuppression seen in C animals.

Effect of colon tumor development and dietary fat on the immune system of rats treated with DMH.

We examined the effect of dietary fat and colon tumorigenesis on the morphology and function of the rat mesenteric lymph node (MLN) and spleen at two stages of tumor development. Male Sprague-Dawley rats were fed semipurified diets of varying fat content (5% mixed fat, 24% beef fat, 24% corn oil, or 24% Crisco) and treated for five weeks with either the colon carcinogen 1,2-dimethylhydrazine (DMH) or the vehicle (saline). Animals consuming high-fat diets had an increased incidence of splenic follicular and germinal center hyperplasia. Carcinogen treatment had no significant effect on the histological morphology of the spleen. MLN morphology was not dramatically affected by either diet or DMH treatment. At this time period, the splenic lymphocyte transformation response induced by concanavalin A (Con A), phytohemagglutinin, or pokeweed mitogen was significantly depressed in the group fed 24% corn oil (vehicle-treated) and in the DMH-treated groups fed 5% fat compared with the vehicle-treated group fed 5% fat. In contrast, the MLN transformation response was elevated in the group fed 24% Crisco. DMH treatment did not significantly influence the MLN response. Four months after carcinogen or vehicle treatment, at the point of colon tumor development, no statistically significant differences were seen in the splenic or MLN blastogenic responses of DMH- or saline-treated animals. Splenic natural killer cell cytotoxic activity was also not significantly affected by dietary fat, carcinogen treatment, or tumor development.

Natural killer cell activity and autologous mixed lymphocyte response of splenic, mesenteric lymph node, and colonic lymphocytes during DMH-induced colon carcinogenesis in the rat.

Two in vitro models of immune surveillance were used to examine the immune status of the gut-associated lymphoid tissue, mesenteric lymph nodes, and spleen during the early stages of 1,2-dimethylhydrazine (DMN)-induced colon tumorigenesis. DMH- and vehicle-treated Fischer rats were sacrificed at one of three time points: one week, two months, or five months after cessation of treatment. Colonic, lymph node, and splenic natural killer cell cytolytic activity toward YAC-1 tumor targets and T-cell response to autologous Ia-induced blastogenesis were measured at each time point. We found little change in natural killer cell activity or T-cell proliferation induced by autologous Ia gene products at these time periods.

The effect of quality and quantity of dietary fat on the immune system.

The effect of the quality and quantity of dietary fats on the morphology and function of the immune system of Sprague-Dawley rats fed either 5% mixed fat, 24% saturated fat, 24% polyunsaturated fat, or 24% partially saturated fat was examined. After 2.5 months of dietary treatment high fat groups showed evidence of splenic hyperplasia, however, no consistent morphologic changes were seen in the mesenteric lymph nodes (MLN). Splenocytes from rats fed the 24% polyunsaturated fat diet were cultured in fetal bovine serum (FBS) and had a depressed lymphocyte transformation response, which persisted after 5 months of dietary treatment. Supplementing the culture medium with 10% rat serum altered the transformation response profile, but high fat serum did not have an immunosuppressive effect. MLN lymphocytes from rats fed the 24% partially saturated diet for 2.5 months had an enhanced response to concanavalin A; at five months the response was elevated in the groups fed saturated as well as partially saturated fat diets. These results suggest that the modulating effect of fat on the immune system depends on the duration of feeding, the type of fat consumed and the organ examined.

Lack of effect of dietary fat on N-nitrosomethyl urea (NMU)-induced colon tumorigenesis in rats.

The effect of alterations in the quality and quantity of dietary fat on N-nitrosomethyl urea (NMU)-induced colon cancer in rats was studied. Weanling Sprague-Dawley rats were fed semipurified diets containing 24% beef fat, 24% corn oil, 24% Crisco or the three fats in equal parts to make a total of 5% fat. Macronutrients and micronutrients were adjusted to balance the nutrient to calorie ratios. After 4 weeks of dietary treatment, all rats, except vehicle-treated animals received NMU (1.5 mg) via intrarectal instillation, twice a week for 2 weeks. The animals continued receiving the experimental diets until intestinal tumors developed and surviving animals were sacrificed at 43 weeks. There was no effect of any of the high fat diets tested on intestinal tumor incidence, latency, distribution or size. Cumulative probability of death with colon carcinoma did not differ significantly among the dietary groups.