Phytate prevents tissue calcifications in female rats

The AIN-76 A, a purified rodent diet, has a propensity to cause kidney calcifications in female rats which is not observed with non-purified rodent diets, suggesting a nutritional factor that avoids these calcifications. One candidate is phytate, which inhibits crystallisation of calcium salts and is practically absent in purified diets. Therefore, the effects on calcification of kidney tissue of phytate addition to the AIN-76 A diet using female Wistar rats were studied. The rats were assigned to three groups: AIN-76 A, AIN-76 A + 1% phytate and standard nonpurified chow. Urinary phytate of the AIN-76 A fed group was undetectable. Urinary phytate of AIN-76 A + 1% phytate and standard fed groups did not differ and was significantly higher than in the AIN-76 A group. The concentrations of calcium and phosphorus in kidneys were greater in the AIN-76 A group than in AIN-76 A + 1% phytate and standard groups. Only rats of the AIN-76 A group displayed mineral deposits at the corticomedullary junction. These findings demonstrated that the absence of phytate in the AIN-76 A diet is one of the causes of renal calcification in female rats.     

Effect of phytate on element bioavailability in the second generation of rats

In this paper the relation between long term consumption of a high dose of sodium phytate and the mineral status of the organism is evaluated in rats. For this purpose, element concentrations (Ca, Mg, Fe, Zn, Mn) were determined in liver, heart, testicle, bone and urine of a second generation of Wistar rats, treated with a phytate free diet (AIN-76A) and with the same diet plus 1% phytate as sodium salt. The most significant differences were observed between bone zinc contents of male and female rats. The zinc content of rats fed a 1% phytate as sodium salt diet resulted clearly lower than that found in no-phytate treated rats. Hence, it is concluded that when up to 1% of phytate as sodium salt is consumed together with an equilibrated purified diet (free of phytate), no decrease in mineral bioavailability is observed in second generation rats, except for an indication of lower zinc availability by lower zinc concentrations in some organs, mainly bone. However, using this purified diet, the zinc concentration in bone resulted around 10 times higher than found in rats fed with a common non purified rat chow.     

The mouse bioassay for the detection of estrogenic activity in rodent diets: III. Stimulation of uterine weight by dextrose, sucrose and corn starch

We have shown previously that mice fed the American Institute of Nutrition (AIN-76A) purified diet experience a significant increase in uterine:body weight (U:BW) ratios when compared to the U:BW ratios of mice fed a closed formula natural ingredient diet (Certified Rodent Chow #5002) for 7 days. The AIN-76A purified diet contains 5% corn oil and 65% carbohydrates with 50% of the carbohydrates coming from sucrose or dextrose and 15% from corn starch. The objective of this study was to determine whether the fat and carbohydrate content contributed to the unexpected uterine growth promoting activity observed in mice fed the AIN-76A diet. Estrogen bioassays were performed using CD-1 mice weaned at 15 days of age and assigned randomly to the negative control diet (Certified Rodent Chow #5002) or to the positive control diet (#5002) containing 4 or 6 ppb DES for comparison or to the test diets. The test diets were prepared by adding sucrose, dextrose, corn starch, corn oil or soybean oil to the #5002 negative control diet at 10% w/w concentration. Uterine:BW ratios were determined at 7 days post-feeding. The uterine weights and the U:BW ratios of mice fed the test diets containing dextrose, corn starch, or corn oil, were increased significantly (P less than 0.05) over those of mice fed the negative control diet. The uterine weights and U:BW ratios of mice fed the test diets containing sucrose or soybean oil also were increased over those of mice fed the negative control diet. These increases in uterine weights and U:BW ratios were similar to the increases in uterine weights and U:BW ratios of mice fed the positive control diet containing 4 ppb DES. It was concluded that the fats and carbohydrates caused preferential increases in uterine weights and in U:BW ratios and may account for the estrogen-like uterine growth promoting activity observed in mice fed the AIN-76A purified diet.     

Vitamin K deficiency of germfree mice caused by feeding standard purified diet sterilized by gamma-irradiation.

Germfree mice died when they were fed a purified diet of AIN-76 formula sterilized by gamma-irradiation. Vitamin K deficiency was suspected and this study was performed to confirm the cause of the death. Germfree mice were fed purified diets of AIN-76 or AIN-93M formula, which were pelleted and sterilized by gamma-irradiation at a dose of 50 kGy. One half of the mice fed the AIN-76 diet died within two weeks and the surviving animals were also in poor health, while 91% of mice fed the AIN-93M diet survived. No hemorrhage was observed grossly in any organs of the surviving animals. Histologically, degeneration with inflammatory cell infiltration was observed as well as hemorrhage and fibrosis in the heart muscles of mice fed the AIN-76 diet. No microscopic lesions were observed in the other organs. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were extremely prolonged when mice were fed the AIN-76 diet. The animals totally recovered when they were intragastrically administered 1 microg/day of vitamin K(3) from the third day of feeding of the AIN-76 diet, except for PT and APTT which were still slightly longer than in mice fed the AIN-93M diet. The concentration of vitamin K(3) supplied in the AIN-76 diet decreased to an undetectable level after gamma-irradiation, while the AIN-93M diet contained 240 microg/kg of vitamin K(1). These results indicate that the deaths of the germfree mice fed the gamma-irradiated AIN-76 diet were caused by vitamin K deficiency. Vitamin K deficiency may cause fatal degeneration of cardiac muscle cells.     

The effect of purified compared with nonpurified diet on bone changes induced by hindlimb suspension of female rats

The purpose of this study was to compare the bone changes induced by unloading in rats fed different diets, because space flight studies use a semipurified diet, whereas space flight simulation studies typically use nonpurified diets. Female Sprague-Dawley rats were fed a purified American Institute of Nutrition (AIN) 93G diet or a standard nonpurified diet and kept ambulatory or subjected to unloading by hindlimb suspension (HLS) for 38 days. Bone mineral content (BMC), mechanical strength, and factors related to the diet that affect bone (i.e., urinary calcium excretion, estradiol, and corticosterone) were measured. Average food intakes (grams per day) differed for diets, but caloric intake (kilocalories per day) and the final body masses of treatment groups were similar. The HLS-induced decrease in femoral BMC was not statistically different for rats fed a nonpurified diet (-8.6%) compared with a purified AIN-93G diet (-11.4%). The HLS-induced decrease in femoral mechanical strength was not statistically different for rats fed a nonpurified diet (-24%) compared with a purified AIN-93G diet (-31%). However, bone lengths were decreased (P < 0.05) in rats fed a nonpurified diet compared with a purified diet. Plasma estradiol levels were lower (P < 0.05) in the HLS/AIN-93G group but similar in the HLS and ambulatory rats fed a nonpurified diet. Plasma estradiol was related to femoral BMC (r = 0.85, P < 0.01). Urinary calcium excretion was higher (P < 0.05) in rats fed a nonpurified diet than those fed a purified AIN-93G diet, which is consistent with the higher level of calcium in the nonpurified diet. Urinary corticosterone levels were higher (P < 0.05) in rats fed a nonpurified diet than rats fed the AIN-93G diet. Although the osteopenia induced by unloading was similar in both diet groups, there were differences in longitudinal bone growth, calcium excretion, plasma estradiol levels, and urinary corticosterone levels. Results indicate that the type of standard diet used is an important factor to consider when measuring bone end points.     

Effect of phytate in soy protein on the serum and liver cholesterol levels and liver fatty acid profile in rats

Dietary soy protein, in comparison with casein, generally lowers the serum cholesterol concentration in rats fed on a cholesterol-enriched diet, while mixed results were observed in rats fed on a diet free of cholesterol. Soy protein also suppresses the conversion of linoleic acid to arachidonic acid in the rat liver. The present study examines whether phytate, a minor component of a soy protein isolate, is responsible for these beneficial effects of soy protein. Weanling male rats were fed for 4 weeks on a purified diet containing a 20% level of protein (either casein (CAS), soy protein (SOY), phytate-depleted SOY (PDSOY) or phytate-replenished PDSOY (PRSOY)) and cholesterol (0 or 0.5%). The dietary protein source and phytate level only affected the serum and liver cholesterol concentrations when the animals were fed on the cholesterol-enriched diet, being significantly lower in those rats fed on the SOY and PRSOY diets than in those fed on the CAS diet, while the concentrations in the rats fed on the PDSOY diet were intermediate. When the animals were fed on the cholesterol-free diet, the ratio of (20:3n-6 + 20:4n-6)/18:2n-6 in liver phosphatidylcholine, a delta6 desaturation index, was significantly lower in the SOY diet group than in the CAS, PDSOY and PRSOY diet groups. Dietary cholesterol significantly depressed the ratio, but neither depletion nor replenishment of phytate affected the ratio. These results suggest that phytate in soy protein played a limited role in the cholesterol-lowering effect of soy protein and was not involved in the metabolism of linoleic acid.     

Modulation of DNA modification (I-compound) levels in rat liver and kidney by dietary carbohydrate, protein, fat, vitamin, and mineral content.

I-compounds are DNA modifications detected by 32P-postlabeling that increase with age in rodents without known carcinogen exposure. Diet type (natural ingredient versus purified) greatly influences patterns and levels of I-compounds. To test the hypothesis that I-compound formation is affected, also, by dietary macro- and micronutrients, effects of carbohydrate, protein, fat, vitamin, and mineral content on rat liver and kidney I-compounds were determined. Female Sprague-Dawley rats were fed basic or modified AIN-76A purified diets for 3-6 months. High protein (HP) diet (50%, w/w) increased I-compound levels in liver but not kidney. High carbohydrate (HC) diet (78%) produced a significant increase in the polar as well as total I-compound levels in both tissues. High fat diets (20%) elicited significantly lower levels of liver I-compounds than HC, HP, and basic diets. There were few significant differences between high polyunsaturated (safflower oil) and saturated fat (lard) diet groups. No qualitative differences in I-compound profiles were observed in either tissue. In rats fed basic diet supplemented with vitamins and/or minerals, increased vitamin content reduced the levels of polar I-compounds in liver. No extra diet-induced adducts were observed; all effects were of a quantitative nature. These data provide direct evidence that nutrients significantly influence I-compound levels and support the hypothesis that normal metabolism of nutrients leads to the production of small amounts of DNA-reactive electrophiles. These observations suggest a novel mechanism where nutrient composition of the diet may play a role in development of neoplasia and other adverse health effects.     

Phytase supplementation increases bone mineral density,lean body mass and voluntary physical activity in rats fed a low-zinc diet

Phytic acid forms insoluble complexes with nutritionally essential minerals, including zinc (Zn). Animal studies show that addition of microbial phytase (P) to low-Zn diets improves Zn status and bone strength. The present study determined the effects of phytase supplementation on bone mineral density (BMD), body composition and voluntary running activity of male rats fed a high phytic acid, low-Zn diet. In a factorial design, rats were assigned to ZnLO (5 mg/kg diet), ZnLO+P (ZnLO diet with 1500 U phytase/kg) or ZnAD (30 mg/kg diet) groups and were divided into voluntary exercise (EX) or sedentary (SED) groups, for 9 weeks. SED rats were significantly heavier from the second week, and no catch-up growth occurred in EX rats. Feed intakes were not different between groups throughout the study. ZnLO animals had decreased food efficiency ratios compared to both phytase-supplemented (ZnLO+P) and Zn-adequate (ZnAD) animals (P<.01 compared to ZnLO). The ZnLO+P and ZnAD rats ran 56–75 km more total distance than ZnLO rats (P<.05), with the ZnLO+P rats running more kilometers per week than the ZnLO rats by Week 6. In vivo DEXA analyses indicate that rats fed phytase-supplemented diets had higher lean body mass (LBM) than those fed ZnLO diets; and that rats fed the Zn-adequate diets had the highest LBM. Body fat (%) was significantly lower in EX rats and was both Zn- and phytase insensitive. Rats fed phytase-supplemented diets had higher bone mineral content (BMC), bone area (BA) and BMD than rats fed ZnLO diets; and in rats fed ZnAD diets these indices were the highest. The dietary effects on BMC, BA and BMD were independent of activity level.We conclude that consuming supplemental dietary phytase or dietary Zn additively enhances Zn status to increase BMD, LBM and voluntary physical activity in rats fed a low-Zn diet. While the findings confirm that bone health is vulnerable to disruption by moderate Zn deficiency in rats, this new data suggests that if dietary Zn is limiting, supplemental phytase may have beneficial effects on LBM and performance activity.     

Comparison of selenium level and glutathione peroxidase activity in tissues of vitamin B6-deficient rats fed sodium selenite or DL-selenomethionine

The effect of vitamin B₆ on the levels of tissue selenium (Se) and glutathione peroxidase (GSH-Px) was studied. Male Wistar 4-week-old rats were fed a vitamin B₆-Se-deficient basal diet for 2 weeks, then divided into 10 groups of five or six rats and fed their respective diets for 4 weeks. The experimental design was a 2×2×2 factorial with two levels of vitamin B₆, two forms of Se, and two levels of Se, plus two extra groups (vitamin B₆-supplemented and deficient without Se). Vitamin B₆ was 0 and 250 μg pyridoxine-HCl/100 g of diet; Se forms were Na₂SeO₃ and DL-selenomethionine; Se levels were 0.5 and 5.0 mg Se/kg of diet. Regardless of form or level of Se, vitamin B₆-deficient rats had lower body weights and organ weights than vitamin B₆-supplemented rats. At 5.0 mg Se/kg of diet, Na₂SeO₃ caused a further depression. Vitamin B₆ deficiency resulted in a higher Se level and GSH-Px activity in plasma of rats fed selenomethionine. However, Se content an GSH-Px activity in erythrocytes were significantly elevated in vitamin B₆-supplemented rats compared with vitamin B₆-deficient rats. Se levels in muscle and heart were significantly lower in vitamin B₆-deficient groups fed Na₂SeO₃ than in vitamin B₆-supplemented groups. Vitamin B₆-deficient rats fed selenomethionine had higher Se levels in muscle, heart, spleen, liver, and kidneys than vitamin B₆-supplemented rats. Activity of GSH-Px in muscle, heart, and spleen was significantly lower in vitamin B₆-deficient groups than in vitamin B₆-supplemented groups, regardless of form of Se. A significant decrease of GSH-Px in liver was observed in vitamin B₆-deficient rats fed selenomethionine compared with vitamin B₆-supplemented rats, whereas no significant decrease was observed in those fed Na₂SeO₃. These results suggest that vitamin B₆ is involved in the distribution and transportation of Se in body and the metabolism of selenomethionine in liver.     

Laboratory diet profoundly alters gene expression and confounds genomic analysis in mouse liver and lung

Nutritional studies in laboratory animals have long shown that various dietary components can contribute to altered gene expression and metabolism, but diet alone has not been considered in whole animal genomic studies. In this study, global gene expression changes in mice fed either a non-purified chow or a purified diet were investigated and background metal levels in the two diets were measured by ICP-MS. C57BL/6J mice were raised for 5 weeks on either the cereal-based, non-purified LRD-5001 diet or the purified, casein-based AIN-76A diet, as part of a larger study examining the effects of low dose arsenic (As) in the diet or drinking water. Affymetrix Mouse Whole Genome 430 2.0 microarrays were used to assess gene expression changes in the liver and lung. Microarray analysis revealed that animals fed the LRD-5001 diet displayed a significantly higher hepatic expression of Phase I and II metabolism genes as well as other metabolic genes. The LRD-5001 diet masked the As-induced gene expression changes that were clearly seen in the animals fed the AIN-76A diet when each dietary group was exposed to 100 ppb As in drinking water. Trace metal analysis revealed that the LRD-5001 diet contained a mixture of inorganic and organic As at a total concentration of 390 ppb, while the AIN-76A diet contained approximately 20 ppb. These findings indicate that the use of non-purified diets may profoundly alter observable patterns of change induced by arsenic and, likely, by other experimental treatments, particularly, altering gene and protein expression.     

Mineral supplementation of white wheat flour is necessary to maintain adequate mineral status and bone characteristics in rats

This experiment was designed to compare the effect of ingestion of a wheat flours on mineral status and bone characteristics in rats. White flour was tested either without further mineral supplementation or with Mg, Fe, Zn and Cu supplementation. The flour diets were compared to a control purified diet. Four groups of 10 male Wistar rats each were fed one of the experimental diets for 6 wk and mineral status and tissue retention as well as bone characteristics were determined. As expected, mineral intake, except for calcium, was significantly lesser in rats fed the white flour diet than in the other groups. The rats fed the white flour diet had the lowest food intake, weight gain, fecal excretion and intestinal fermentation. The most important result was that Mg and Fe status were drastically lower in rats fed the white flour diet than in those fed whole flour or control diets. The status of these both elements were significantly improved by the mineral supplementation of white flour. There were no major significant differences between mineral-supplemented white flour and whole flour groups in mineral status. Furthermore, bone mineral densities (total, metaphyseal and diphyseal) were significantly lower in rats fed white flour diet compared to the other diet groups, while no significant difference was observed between the mineral-supplemented white flour, whole flour or control diet groups. In conclusion, the present work shows clearly the importance of mineral-supplementation of white wheat flour to sustain an adequate intake of minerals. Our results indicate also that the whole wheat flour did not negatively alter mineral bioavailability, in comparison to mineral supplemented white flour. Clinical studies are still needed to confirm these rat results in human.     

The effect of sucrose or starch-based diet on short-chain fatty acids and faecal microflora in rats

An investigation was carried out to determine whether variations of dietary carbohydrates could modify the colonic flora in rats. Sprague-Dawley rats were fed with two equicaloric diets based on the AIN-76 diet (American Institute of Nutrition 1977) but differing from that diet in content of carbohydrates, i.e. high sucrose (64%) of high corn starch (64%). Feeding was continued for 9 months ad libitum and no variation in weight gain was recorded among the different diets. A prevalence of aerobes, and a significant reduction in the ratio anaerobes/aerobes in the faeces of rats on the high starch diet compared with the high sucrose diet, was observed. The anaerobe genera identified included Actinomyces, Bacteroides, Bifidobacterium, Clostridium, Eubacterium, Lactobacillus and Propionibacterium. Bacteroides was the most prevalent genus in both dietary groups (51.2 and 29.5% in the faeces of rats fed the sucrose and starch diets, respectively). In contrast, clostridia were prevalent in the starch-fed group (23.8%) and less so in the sucrose diet (11.5%), as propionibacteria were prevalent in faeces of rats fed the starch diet (15.5%), and low in the sucrose diet (3.9%). The remaining genera were scarce in faeces from rats on either diet. Total short-chain fatty acids (SCFA) were significantly higher in the faeces of animals fed the starch diet compared with those fed the sucrose diet. The relative concentrations of acetic, propionic and butyric acids were not significantly different between the two dietary groups. In conclusion, high starch diet can markedly modify the composition of faecal flora and alter considerably the faecal concentration of SCFAs, compound which might have a health-promoting effect.     

Chromium is not an essential trace element for mammals: effects of a “low-chromium�?diet

Chromium was proposed to be an essential trace element over 50?years ago and has been accepted as an essential element for over 30?years. However, the studies on which chromium’s status are based are methodologically flawed. Whether chromium is an essential element has been examined for the first time in carefully controlled metal-free conditions using a series of purified diets containing various chromium contents. Male Zucker lean rats were housed in specially designed metal-free cages for 6?months and fed the AIN-93G diet with no added chromium in the mineral mix component of the diet, the standard AIN-93G diet, the standard AIN-93G diet supplemented with 200?μg?Cr/kg, or the standard AIN-93G diet supplemented with 1,000?μg?Cr/kg. The chromium content of the diet had no effect on body mass or food intake. Similarly, the chromium content of the diet had no effect on glucose levels in glucose tolerance or insulin tolerance tests. However, a distinct trend toward lower insulin levels under the curve after a glucose challenge was observed with increasing chromium content in the diet; rats on the supplemented AIN-93G diets had significantly lower areas (P?<?0.05) than rats on the low-chromium diet. The studies reveal that a diet with as little chromium as reasonably possible had no effect on body composition, glucose metabolism, or insulin sensitivity compared with a chromium-“sufficient??diet. Together with the results of other recent studies, these results clearly indicate that chromium can no longer be considered an essential element.     

Vitamin E, Selenium, Trolox C, Ascorbic Acid Palmitate, Acetylcysteine, Coenzyme Q, β-Carotene, Canthaxanthin, and (+)-Catechin Protect Against Oxidative Damage to Kidney, Heart, Lung and Spleen

Male Sprague-Dawley rats were fed diets that varied qualitatively and quantitatively in antioxidants. Kidney, heart, lung, and spleen homogenates were incubated at 37°C with and without hydroperoxide or Fe⁺². Protection of antioxidants against oxidative damage to tissue was determined by measurement of oxidized heme proteins. Tissues from rats supplemented with dietary vitamin E and selenium showed protection compared to tissues from rats on the basal diet. Tissues from rats with diets containing larger quantities of antioxidants and both fat soluble antioxidants: vitamin E, β-carotene, coenzyme Q₁₀, ascorbic acid 6-palmitate and water soluble antioxidants: selenium, trolox C, acetylcysteine, coenzyme Q₀, (+)-catechin, showed the highest protection.     

Milk calcium taken with cheese increases bone mineral density and bone strength in growing rats

We investigated the calcium bioavailability of milk calcium, taken with or without cheese. Twenty-four 6-week-old male rats for a meal-feeding experiment were trained to consume an AIN-76 diet within 2 h (2 times per day) for 2 weeks. The rats were then divided into three experimental groups, each fed 2 types of experimental diets: Control group, Cheese group, and Ca-Cheese group. The rats were each alternately given 2 types of experimental diets at 2-h meal-feeding for 31 days. The breaking force and energy of the femur in the Ca-Cheese group were significantly higher than in the control group. The bone mineral density (BMD) of the lumbar spine and the femur in the Ca-Cheese group was also significantly higher than in the other two groups. These results indicate that milk calcium taken with cheese increases bone strength and BMD efficiently, results that may be useful for the prevention of osteoporosis.     

Chemically Defined Diet Alters the Protective Properties of Fructo-Oligosaccharides and Isomalto-Oligosaccharides in HLA-B27 Transgenic Rats

Non-digestible oligosaccharides (NDO) were shown to reduce inflammation in experimental colitis, but it remains unclear whether microbiota changes mediate their colitis-modulating effects. This study assessed intestinal microbiota and intestinal inflammation after feeding chemically defined AIN-76A or rat chow diets, with or without supplementation with 8 g/kg body weight of fructo-oligosaccharides (FOS) or isomalto-oligosaccharides (IMO). The study used HLA-B27 transgenic rats, a validated model of inflammatory bowel disease (IBD), in a factorial design with 6 treatment groups. Intestinal inflammation and intestinal microbiota were analysed after 12 weeks of treatment. FOS and IMO reduced colitis in animals fed rat chow, but exhibited no anti-inflammatory effect when added to AIN-76A diets. Both NDO induced specific but divergent microbiota changes. Bifidobacteria and Enterobacteriaceae were stimulated by FOS, whereas copy numbers of Clostridium cluster IV were decreased. In addition, higher concentrations of total short-chain fatty acids (SCFA) were observed in cecal contents of rats on rat chow compared to the chemically defined diet. AIN-76A increased the relative proportions of propionate, iso-butyrate, valerate and iso-valerate irrespective of the oligosaccharide treatment. The SCFA composition, particularly the relative concentration of iso-butyrate, valerate and iso-valerate, was associated (P≤0.004 and r≥0.4) with increased colitis and IL-1 β concentration of the cecal mucosa. This study demonstrated that the protective effects of fibres on colitis development depend on the diet. Although diets modified specific cecal microbiota, our study indicates that these changes were not associated with colitis reduction. Intestinal inflammation was positively correlated to protein fermentation and negatively correlated with carbohydrate fermentation in the large intestine.     

Effects of iron deficiency upon the antibody response to influenza virus in rats

The effects of severe and moderate iron deficiency upon the antibody response to influenza virus were investigated in rats. Three groups of weanling male Wistar rats were fed one of two iron-deficient diets (5 mg and 15 mg iron/kg diet) or a normal iron-containing diet (35 mg iron/kg diet). A group of individually pair-fed rats was introduced with the low iron-consuming rats. The effects of the diets upon various iron status parameters were followed during the 4th, 5th, 6th, and 7th week of diet. After 4 weeks of feeding different diets, an intraperitoneal injection of inactivated influenza virus A/New Jersey/76 was performed and a recall injection was done at 5 weeks. Primary and secondary antibody responses were assayed. Rats were sacrificed at 7 weeks of diet. After 4 weeks of feeding different diets, the rats fed the 5 mg iron/kg diet were severely anemic and rats fed 15 mg iron/kg diet were moderately iron-deficient, as shown by their iron status parameters. Growth was delayed in anemic and matched pair-fed rats. A primary antibody response was almost nonexistent in all groups. Secondary antibody titers were significantly weaker in anemic rats than in ad libitum controls, but were not different from those of pair-fed rats. This response was similar in moderately iron-deficient, ad libitum, and pair-fed rats. These results show that antibody synthesis in response to the influenza virus vaccine is preserved in moderate iron deficiency but is reduced in severe anemia. The reduction in energy consumption associated with severe iron deficiency in the rat could play a part in the altered humoral response.     

Promotion of lipid oxidation by selenate and selenite and indicators of lipid peroxidation in the rat

The AIN-93 reformulation of the AIN-76A rodent diet includes a change in selenium supplement from sodium selenite to sodium selenate to reduce dietary lipid peroxidation. A change to selenate as the standard form of Se in rat diets would render results from previous work using selenite less relevant for comparison with studies using the AIN-93 formulation. To critically examine the rationale for the AIN-93 recommendation, we prepared Torula yeast basal diets patterned as closely as possible after the AIN-93 formulation and supplemented with 0, 0.15 (adequate), or 2.0 (high) mg selenium/kg diet as sodium selenite or sodium selenate. Livers isolated from male Sprague-Dawley rats fed these diets for 15 wk showed no differences in thiobarbituric acid-reactive substances or lipid hydroperoxides measured with the ferrous oxidation in xylenol orange method. Lipids isolated from samples of high-selenate and high-selenite diets showed no differences in conjugated dienes. The addition of selenate or selenite to soybean oil did not result in an altered Oil Stability Index. These results demonstrate that selenate is not less likely than selenite to cause oxidation of other dietary components. Benefits of selenate over selenite in the diets of rodents remain to be demonstrated. Results included in this paper were presented at the meeting of Experimental Biology 98, San Francisco, CA, April 18–22, 1998, and published in abstract form (Moak, M. A., Johnson, B. L., & Christensen, M. J. [1998] On the AIN-93G recommendation for selenium. FASEB J. 12, A824).     

Oral enzyme therapy and experimental rat mammary tumor metastasis

Although there has been much interest over the years in the medical use of orally administered proteolytic enzymes, there is considerable controversy about their efficacy against advanced stages of cancer. In light of this, the goal of the present study was to assess the inhibitory effects of different doses of an orally administered porcine pancreas preparation on the growth and metastasis of the R13762 transplantable rat mammary tumor. Five groups of 12 F-344 female retired breeders were inoculated orthotopically with a 2mm3 tumor implant and placed on the following diets: (1) AIN-76A diet + 20% porcine pancreas preparation (PPP); (2) AIN-76A + 20% PPP + 10 mg Mg citrate/rat/day; (3) AIN-76A + 2% PPP; (4) AIN-76A + 2% PPP + 10 mg Mg citrate and (5) AIN-76A only (control). Primary tumor development was monitored for 40 days and following sacrifice, lungs were excised, stained and metastatic foci quantitated. Metastatic foci were sorted into 3 groups based on their radii: small (<1mm), medium (1-3mm) and large (>3mm), and volumes calculated. The oral enzyme preparation had no effect on primary tumor growth or on body weight change over the duration of the study. The percent (incidence) of rats with pulmonary metastases among the five groups were not significantly different. However, among the three size categories of pulmonary foci, decreased incidence was found only in the large (>3mm) volume subset of the 2% PPP group supplemented with Mg++. When assessed in terms of mean number of pulmonary foci/rat, the 20% PPP group exhibited the highest and controls the lowest frequency with the important exception of the 2% PPP + Mg++ group (large volume) which exhibited the lowest frequency of all treatment groups. In general, the presence of Mg++ resulted in marked decreases in mean number of pulmonary foci/rat compared to groups fed PPP without the Mg++ supplement. Similar results were obtained when foci were quantitated in terms of metastatic volume rather than frequency. The results of this laboratory animal study suggest that to show effective inhibition of metastatic dissemination of the R13762 tumor by PPP, lower doses of PPP and larger numbers of animals, to account for the high variability in the model, will be required.