Bioavailability of and interactions between zinc and selenium in rats fed wheat grain intrinsically labeled with 65Zn and 75Se

A whole-body radioassay procedure was used to assess the absorption by male rats of zinc (Zn) and selenium (Se) in wholewheat grain labeled either intrinsically or extrinsically with 65Zn and 75Se. Test meals fed to zinc-depleted and to zinc-adequate rats contained grain harvested from plants grown in nutrient solutions with varying amounts of zinc and selenium. Absorption of intrinsic 65Zn by zinc-depleted rats ranged from about 46 to 57% of the dose, and 65Zn absorption decreased as the selenium content of the grain increased. Absorption of intrinsic 65Zn by zinc-adequate rats ranged from about 21 to 26% of the dose, and 65Zn absorption was not affected by the amount of either zinc or selenium in the meal. Absorption of intrinsic 75Se ranged from about 43 to 52% of the dose in zinc-depleted rats and from about 35 to 48% of the dose in zinc-adequate rats. Absorption of intrinsic 75Se by zinc-adequate rats decreased as the zinc content of the grain increased. Relative to the absorption and retention by rats of intrinsic zinc and selenium in wholewheat grain, interactions occurred between natural forms of zinc and selenium at concentrations potentially encountered in wheat. Selenium had an antagonistic effect on zinc absorption by zinc-depleted rats, and zinc had an antagonistic effect on selenium absorption by zinc-adequate rats.     

The effect of various thermal processes on the glycemic response to whole grain wheat products in humans and rats

The effects of different thermal processes used to produce ready-to-eat cereals on the glycemic response to whole grain wheat were investigated in rats. The metabolic response to drum dried flour, which constitutes the major component in instant gruel and porridge, was also studied in healthy human subjects. Boiled flour was used for comparison. The degree of starch gelatinization and rate of starch hydrolysis in vitro were also measured. Incompletely gelatinized steam flaked and dry autoclaved products were digested more slowly in vitro and elicited lower glucose responses in rats compared with completely gelatinized drum dried, extrusion cooked or boiled samples. The initial glycemic response in rats was closely related to the rate of starch hydrolysis in the pepsin/alpha-amylase assay (r = 0.91, P less than 0.04). When pepsin was omitted, no significant correlation was obtained. The peak glucose, insulin and C-peptide responses in humans after breakfast meals of porridge prepared from drum dried flour and from boiled flour were similar, whereas the rate of depression of the glucose curve was more rapid after consuming drum dried porridge. It is concluded that the glycemic response to wheat products is affected by the processing conditions used. The more severe the processing conditions, the more rapid the digestion of starch.     

Bioavailability for rats of thiamin in whole wheat and thiamin-restored white bread

The relative biological value of thiamin in leavened bread (whole wheat and thiamin-restored white) and thiamin mononitrate was examined by using thiamin-deficient rats as the test model. Erythrocyte transketolase (ETK) activities and liver thiamin content responded positively to graded but suboptimal levels of dietary thiamin in these rats. Biological values were calculated (slope ratio assay) by using these response parameters, which may depict the body's thiamin status, at least in the deficient rats. Compared to thiamin in thiamin mononitrate (100%), the biological value of thiamin in breads measured 88% (white bread) and 91% (whole wheat bread) based on ETK activity and 68% (white bread) and 75% (whole wheat bread) based on liver thiamin response. Thus, diets high in fermented cereal foods (thiamin enriched or not) may require a generous allowance of thiamin to compensate for reduced biological value.     

Bioavailability of selenium from foods

Selenium (Se), an essential nutrient, is needed for activity of several important proteins. Additionally, the consumption of Se in amounts that exceed the Recommended Dietary Allowance (RDA) may protect against prostate and colorectal cancer. Supplemental Se may be acquired through the diet, but Se bioavailability depends on the source. Therefore, dietary advice concerning improvement of Se intake depends on characterization of Se bioavailability from Se-containing food sources.     

Bioavailability to rats of iron in six varieties of wheat grain intrinsically labeled with radioiron

Bioavailability to anemic rats of iron in six varieties of wheat grain was assessed by a whole-body radioassay procedure. Intrinsically labeled kernels were harvested from plants grown in 59Fe-labeled nutrient solutions. The varieties used were selected from 18 varieties of field-grown wheat grain that were analyzed for iron, protein and phytate content. Concentrations of iron, phytate and protein in grain of field-grown varieties ranged from 34 to 55 ppm, 0.7 to 1.2% dry wt and 11.3 to 15.4% dry wt, respectively. In grain from varieties grown in nutrient solutions, iron, phytate and protein concentrations ranged from 35 to 50 ppm, 1 to 1.2% dry wt, and 13.8 to 16.8% dry wt, respectively. Depending on the variety of intrinsically labeled grain fed in test meals to anemic rats (hemoglobin averaged 5.8 g/dL), absorption of 59Fe ranged from about 62 to 74% of the dose; differences among varieties were not significant (P greater than 0.05). Rats fed 59Fe-labeled FeCl3 absorbed about 71% of the dose, which was similar to the average amount (69% of dose) absorbed by rats fed wheat. We concluded that selection of wheat varieties for increased yield or protein content has not adversely affected the bioavailability of iron in the grain.     

不同硒水平的饲料对大鼠的毒性

本实验的目的是研究不同硒含量的饲料对大鼠的毒性,以期为确定安全补硒剂量及制订食品中硒的卫生标准提供科学依据。实验分为对照组、不同水平亚硒酸钠、不同水平湖北高硒玉米组,共8组。饲养16～18周。结果发现饲料硒水平近似的条件下(4μg/g,2μg/g),吃高硒玉米的动物血硒远远高于吃亚硒酸钠的动物。血硒量前者均分别为后者的2倍(雌性)和4倍(雄性),肝和肾硒前者也高于后者。但动物出现肝脏病变的剂量(4μg/g)相似。因此,认为2.0μg/g硒还是安全的,而4.0μg/g以上就有引起肝脏病变的可能。     

Bioavailability of selenium from raw and cooked ground beef assessed in selenium-deficient Fischer rats.

The literature on the bioavailability of selenium (Se) from meats, especially beef, is meager, and that which existed when this research began suggested that Se was not highly bioavailable. In addition, much of the analytical values for Se in beef predated the Food and Drug Administration's 1973 approval of Se as an additive to feeds and mineral premixes of livestock.

One hundred and thirty-six weanling female Fischer 344 rats were divided into two dietary groups: the selenium deficient group in which animals were fed a torula yeast (TY) basal diet which contained 0.008 mg/kg Se and the control group in which animals were fed the TY diet to which was added 0.10 mg/kg Se as sodium selenite.

After 6 weeks of dietary treatment liver glutathione peroxidase (GSHPx) activity had fallen in the Se-deficient rats to 2.4% of that of control rats. At this time (week 6) rats from the Se-deficient TY diet were refed diets containing 0.10 mg/kg Se as selenite, selenate, raw or cooked ground beef that had been freeze-dried. During the Se-repletion period rats were sacrificed at weeks 1, 3, 5 and 8. Liver GSHPx activity and total Se levels in liver and muscle tissue were the criteria of Se bioavailability. After 8 weeks of Se resupplementation the recovery of liver GSHPx activity compared to the control animals (set at 100%) were selenite (98%, p > 0.05), selenate (117%, p < 0.05), raw beef (127%, p < 0.05) and cooked ground beef (139%, p < 0.05). Total Se in both liver and muscle tissue reflected the liver GSHPx activity with the total Se concentration in tissues being highest for cooked beef.

The data suggest that bioavailability of Se from ground beef is greater than that from either selenite or selenate.     

Bioavailability of selenium to residents in a low-selenium area of China

For 8 wk 5 groups of 10 men each were given 0.5 g/day DL-methionine, 150 micrograms Se/day as sodium selenite with or without methionine or 150 micrograms Se/day as selenomethionine with or without methionine. Twenty subjects received placebo as controls. Initially plasma Se rose more rapidly than RBC Se. Increases in Se levels were significantly greater with selenomethionine than with the selenite supplement. In the placebo and methionine supplemented groups neither plasma nor RBC Se varied significantly over the course of the study. Supplementation with selenium resulted in marked increases in plasma and RBC GSH-Px within 2 and 4 wk, respectively. Plasma and RBC GSH-Px activity did not differ significantly between Se-supplemented groups. These studies suggest that selenomethionine-Se was more effective in raising plasma and RBC Se than was selenite-Se. Methionine supplements may increase the bioavailability of selenium in severely deficient subjects.     

Efficacy of selenium in tuna and selenite in modifying methylmercury intoxication

Efficacy of selenium naturally occurring in tuna was compared to that of selenium in selenite with respect to protection against the toxicity of methylmercury. Male weaning rats were fed diets for 70 days which contained 20 ppm methylmercury chloride (MMC) and graded concentrations of selenium originating from either tuna or sodium selenite. Regardless of its origin, selenium showed protective effect, generally corresponding to its added levels (0.5, 1.0, 1.5 ppm) in terms of survival rate, morbidity and growth rate. Efficacy of selenium in tuna, as compared to that of selenium in selenite, was roughly equivalent in growth rate but approximately half as effective in preventing neurological manifestations. Possible mechanisms were discussed as regards protection offered by selenium and the discrepancy of efficacy between tuna selenium and selenite selenium in preventing neurological signs. This study seems to warrant further investigations upon the protective activity of naturally occurring selenium against methylmercury toxicity, particularly in those fish known to contain high concentrations of both methylmercury and selenium.     

Bioavailability of selenium in mushrooms, Boletus edulis, to young women

The bioavailability of selenium (Se) in mushrooms, Boletus edulis, to young Finnish women was studied by giving them 150 micrograms Se as mushrooms for 4 weeks. The indicators of body selenium status were plasma and erythrocyte Se levels and plasma and platelet glutathione peroxidase (GSH-Px) activity. The Se level in erythrocytes increased significantly (26%), while only slight enhancement were found in plasma Se and plasma or platelet GSH-Px activity. The results indicate that the metabolism of mushroom-Se is different from that of wheat-Se or sodium selenate. However, by the criteria of plasma Se level or plasma and platelet GSH-Px activity the bioavailability of mushroom-Se is reasonably low.     

Bioavailability of iron from wheat bran in pigs

Iron anemia was induced in pigs immediately after birth by feeding an iron depletion diet containing only 17 mg iron/kg feed. (The requirement for iron in this period is 50 mg iron/kg feed). When Hb concentrations were 5 g/100 ml the pigs were given iron repletion diets. One group received 7% bran in the diet, about 60% of the iron derived from the bran and 40% from ferrous sulfate. The other group received no bran and 80% of the iron from ferrous sulfate. There were no differences, either in the increase of Hb or in the increase of serum iron, in the two groups. In a second experiment, one group received all their iron from cereals, and an addition of 20% bran in the diet. The other group received no bran and 80% of the iron from ferrous sulfate. There was no significant difference in the bioavailability of the iron present in the diets. In our experiments bran seemed to have no inhibitory effect on iron absorption, even when 20% bran was included in the diet.     

Effects of various dietary levels of selenium as selenite or selenomethionine on tissue selenium levels and glutathione peroxidase activity in rats

Weanling rats were fed a basal diet or this diet plus 0.2, 1.0, 2.0 or 4.0 mg/kg selenium (Se) as either selenite or selenomethionine (SeM). Except at the 0.2 mg/kg Se level, Se accumulated in all tissues at higher levels when SeM was fed than when selenite was given, and the magnitude of difference became more pronounced with increasing levels of dietary Se. This was particularly true for muscle and brain. Se levels in whole blood, testes, kidney and lungs were not significantly different between rats fed 0.2 mg/kg Se as selenite or as SeM, but the Se levels in liver, muscle and brain were higher in rats fed SeM. Although the tissue Se concentrations differed markedly, there were no differences in the glutathione peroxidase (GPX) activity in tissues of rats fed SeM rather than selenite. The percentage of Se associated with GPX was lower in all tissues from rats fed SeM than in those from rats fed selenite. These results indicate that the chemical forms of dietary Se can have a marked influence on biological responses, including bioavailability of dietary Se.     

Bioavailability to rats of iron and zinc in wheat bran: response to low-phytate bran and effect of the phytate/zinc molar ratio

Low-phytate wheat bran was produced by enzymatic hydrolysis and extraction. Rat bioassay methods were utilized to determine bioavailability of iron and zinc in the low-phytate brans and to study the effect of dietary phytate/zinc molar ratio on zinc bioavailability when the phytate source was bran. Endogenous phytase activity hydrolyzed 80-100% of the phytate when wheat bran was incubated in water overnight. The relative biological values of the iron in raw bran and phytate-free bran were 98 and 113, respectively, compared to 100 for ferrous ammonium sulfate in a hemoglobin repletion assay. Low-phytate brans with phytate/zinc molar ratios of 8 or less were equivalent to zinc sulfate as dietary sources of zinc for growth of rats. Rats fed diets that contained wheat bran with zinc sulfate added to reduce the dietary phytate/zinc molar ratio from 40 or 50 to 20 grew at the same rate as rats fed a phytate-free diet, but femur zinc values were lower than those in the reference group. Gel filtration chromatography of extracts of raw and low-phytate brans suggested that zinc might be associated with phytate in wheat bran.     

Organ and subcellular distribution of selenium in rats exposed to cadmium,mercury, and selenium

Three groups of rats were given sodium selenite (Se), sodium selenite and cadmium chloride (Se + Cd), or sodium selenite, cadmium chloride, and mercuric chloride (Se + Cd + Hg), respectively. All animals received subcutaneous doses of ¹¹⁵CdCl₂ (0.3 mg Cd/kg) every other day for a fortnight. Mercuric chloride was administered intravenously at doses of 0.5 mg Hg/kg every other day and Na₂⁷⁵SeO₃ intragastrically at doses of 0.1 mg Se/kg every other day for 2 weeks. The whole-body retention of selenium was slightly elevated by cadmium and increased threefold by cadmium with mercury (mainly blood, liver, and kidneys). Cadmium did not affect subcellular levels of selenium in the kidneys and slightly increased the selenium content in the soluble fraction of the liver. On the other hand, combined administration of mercury and cadmium induced a significant elevation of the selenium content in all subcellular fraction of the kidneys and in the nuclear and mitochondrial fractions of the liver. In all animal groups selenium was bound in the soluble fractions of both the liver and kidneys by high-molecular-weight proteins.     

Bioavailability to rats of iron and zinc in calcium-iron-phytate and calcium-zinc-phytate complexes

The bioavailability of iron in Fephytate and Ca₃Fephytate and of zinc in Zn₂phytate and Ca₄Zn₂phytate was assayed in rats. Hemoglobin response was the same to the iron of Fephytate as the reference iron compound, Fe(NH₄)₂(SO₄)₂.6H₂) but the response to iron of Ca₃Fephytate was significantly less than to both Fephytate and the reference. The zinc of Zn₂phytate and Ca₄Zn₂phytate promoted growth as effectively as did ZnSO₄. The femur bone zinc response to Ca₃Zn₂phytate and Zn₂phytate did not differ significantly but the femur zinc responses to both complexes were significantly less than to ZnSO₄. In contrast to iron, calcium in a preformed calcium-zinc-phytate complex appears to have no significant effect on the bioavailability to rats of the zinc in the complex.     

Bioavailability of elemental iron powder in white wheat bread

OBJECTIVE: Iron fortification of wheat flour is widely used. In most cases, elemental iron powders are utilized as fortificants due to their lower cost and few, if any, sensory problems. However, their bioavailability is unknown. We aimed to measure the bioavailability of H(2)-reduced elemental iron powder in white wheat bread made from 72% extraction flour. DESIGN: A stable isotope of H(2)-reduced iron powder (mean particle size 15 microm) was used as fortificant in bread prepared from unfortified wheat flour. In all, 12 5- to 7-y-old children were fed bread with 4 mg of H(2)-reduced (58)Fe /100 g of flour. The next day (57)Fe ascorbate was given as reference dose. After 14 days, erythrocytes were analyzed for isotopic enrichment using mass spectrometry. RESULTS: When normalized to 40% absorption of the reference dose, the geometric mean (+/-range of 1 s.d.) bioavailability of reduced (58)Fe in wheat bread rolls was 6.5% (3.7-11.8). CONCLUSIONS: When compared to previous radioiron studies of ferrous sulfate showing 10% absorption from an identical meal in adult women, the relative bioavailability can be estimated at about 65%. However, the bioavailability of this smaller particle size (58)Fe (15 microm) is likely to be higher than that of commercial iron powder (45 microm) although the precise difference cannot be ascertained with current methods. Thus, the bioavailability of commercial elemental iron powders currently used in fortification programs is likely to be substantially lower than that of ferrous sulfate. SPONSORSHIP: This work was funded in part by Grant No 910313 by Micronutrient Initiative, IDRC, Ottawa, Canada.     

不同饲料硒水平饲养大鼠的多组织内参基因筛选

目的筛选不同饲料硒(selenium,Se)水平饲喂大鼠时,不同组织中稳定表达的内参基因(reference genes,RGs)。方法 24只断乳雄性SD大鼠在缺Se饲养5周后,随机均分为4组,分别以Se含量0.01、0.25、3、5 mg/kg饲料饲喂4周后处死,取肝、睾丸、骨骼肌、脂肪组织等样品待检。以荧光定量PCR检测Actb、Atp5f1、B2m、Gapdh、Gusb、Hprt、Pgk1、Ppia、Rplp2、Rps18、Tbp、Ywhaz等12个候选内参基因的mRNA水平,以geNorm、NormFinder、BestKeeper、Delta CT和RefFinder等方法对其表达稳定性进行评价。结果各组织中稳定性排名前4的内参基因是:肝中PpiaAtp5f1Rplp2Hprt;睾丸中YwhazAtp5f1Rplp2Ppia;骨骼肌中TbpPpiaB2mRps18;脂肪组织中HprtTbpAtp5f1Pgk1;综合4种组织,则Rps18HprtRplp2Atp5f1。结论分析不同饲料Se水平饲养大鼠的目标基因表达水平时,应根据组织类型选择适宜的内参基因。     

Bioavailability of phloretin and phloridzin in rats.

Phloretin is a flavonoid found exclusively in apples and in apple-derived products where it is present as the glucosidic form, namely, phloridzin (phloretin 2'-O-glucose). In the present study, we compared the changes in plasma and urine concentrations of these two compounds in rats fed a single meal containing 0.25% phloridzin or 0.157% phloretin (corresponding to the ingestion of 22 mg of phloretin equivalents). In plasma, phloretin was recovered mainly as the conjugated forms (glucuronided and/or sulfated) but some unconjugated phloretin was also detected. By contrast, no trace of intact phloridzin was detected in plasma of rats fed a phloridzin meal. These compounds presented different kinetics of absorption; phloretin appeared more rapidly in plasma when rats were fed the aglycone than when fed the glucoside. However, whatever compound was administered, no significant difference in the plasma concentrations of total phloretin were observed 10 h after food intake. At 24 h after the beginning of the meal, the plasma concentrations of phloretin were almost back to the baseline, indicating that this compound was excreted rapidly in urine. The total urinary excretion rate of phloretin was not affected by the forms administered, and was estimated to be 8.5 micromol/24 h in rats fed phloretin or phloridzin. Thus, 10.4% of the ingested dose was recovered in urine after 24 h.