Torula Yeast Diet Research Articles

Nutritional value of torula yeast as an alternative protein feedstuff for hybrid Striped Bass (White Bass × Striped Bass)

AbstractObjectiveTwo separate trials were conducted to evaluate the digestibility of a novel alternative ingredient, enhanced torula yeast (TY) Cyberlindnera jadinii, in diets for hybrid Striped Bass (HSB; White Bass Morone chrysops × Striped Bass M. saxatilis) and to evaluate graded inclusion levels of this product when replacing soybean products.MethodsIn trial 1, the digestibility of TY was determined by testing a reference diet and a TY diet (reference and TY ingredient at an 80:20 ratio). A total of 90 fish were fed the experimental digestibility diets for 21 days, and fecal samples were collected using the stripping technique. In trial 2, a comparative feeding trial evaluated the replacement of soybean meal by TY on a crude protein basis at 50, 100, 200, and 300 g of TY/kg of experimental diet. A total of 150 HSB (18.6 ± 0.21 g/fish [mean + SE]) were distributed among fifteen 110‐L glass aquaria. Each diet was fed to triplicate groups of fish for 9 weeks.ResultIn trial 1, apparent digestibility coefficients for protein, lipid, organic matter, and energy of TY were 0.97, 0.98, 0.75, and 0.75, respectively. The availability of essential amino acids also was generally high, ranging from 0.74 to 0.99. For trial 2, a second‐order polynomial regression indicated that the optimal inclusion levels of TY in diets were 102, 112, and 109 g/kg for weight gain, feed efficiency, and protein conversion efficiency, respectively. However, the muscle yield linearly decreased with the graded inclusion levels of TY. Linear increases in intraperitoneal fat, hepatosomatic index, and whole‐body lipid were observed as the inclusion of TY increased in the diet.ConclusionIn conclusion, nutrients from TY were well utilized by HSB, and it can replace soybean products without affecting growth performance, with the optimal TY inclusion level being 102–112 g/kg of diet.

PSIII-4 Effect of Two Torula Yeast Sources on Growth Performance, Intestinal Health, and Immune Function of Weanling Pigs

Abstract An experiment was conducted to test the hypothesis that dietary inclusion of either a conventional or a novel source of torula yeast in diets for weanling pigs improves growth performance and intestinal health. The novel torula yeast was produced using forestry byproducts (i.e., wood hydrolysate) as the carbon source, whereas the conventional torula yeast was produced using wheat dextrose as the carbon source. A total of 120 weanling pigs (6.53 ± 0.78 kg) were allotted to three treatments with four pigs per pen and ten replicate pens per diet. Pigs were fed one of three diets from d 1 to 14 post-weaning (phase 1), whereas all pigs were fed a common diet in phase 2 (d 15 to 28). The three dietary treatments included a control diet that contained 5% fishmeal, 3.5% plasma protein, and no torula yeast. The second diet contained 1.5% fishmeal, 14% of the novel torula yeast, and no plasma protein, whereas the third diet contained 1.5% fishmeal, 14% of the conventional torula yeast, and no plasma protein. Pig weights were recorded on d 1, d 14, and d 28. Feed allotments were recorded daily, and feed left in the feeders was recorded on d 14 and 28 to calculate average daily gain, average daily feed intake, and average gain to feed ratio. Fecal scores were visually assessed every other day. On d 7, one pig per pen was euthanized to collect ileal tissue for assessment of morphology. At the end of phases 1 and 2, blood samples were collected, and cytokines, plasma urea nitrogen, peptide YY, immunoglobulin G, total protein, and albumin were analyzed. Data were analyzed using an ANOVA in the Mixed Procedure of SAS with pen as the experimental unit. Diet was the fixed effect, whereas weaning weight was the random effect. Results indicated that both sources of torula yeast could replace fish meal and plasma protein without negatively affecting overall growth performance, intestinal morphology, or blood characteristics of pigs (Table 1). Pigs fed one of the diets containing torula yeast had reduced (P < 0.05) fecal scores during phase 1 compared with pigs fed the control diet. On d 14, pigs fed the conventional torula yeast diet had greater (P < 0.05) concentration of interleukin-2 in plasma compared with pigs fed the control diet. Greater (P < 0.05) concentrations of interleukin-4 and interleukin-10 were observed in plasma from pigs fed one of the diets containing torula yeast compared with pigs fed the control diet on d 14. In conclusion, inclusion of either a conventional or a novel source of torula yeast at the expense of animal proteins in diets for weanling pigs may improve intestinal health without influencing growth performance of weanling pigs.

Torula yeast may improve intestinal health and immune function of weanling pigs.

An experiment was conducted to test the hypothesis that inclusion of a conventional torula yeast or a torula yeast produced from forestry byproducts (i.e., woody torula yeast) in diets for weanling pigs instead of fish meal and plasma protein improves growth performance and intestinal health of pigs. A total of 120 weanling pigs (6.53 ± 0.78 kg) were allotted to three treatments with ten replicate pens per diet. Pigs were fed one of three diets from days 1 to 14 post-weaning (phase 1), whereas all pigs were fed a common diet in phase 2 (days 15 to 28). The three treatments in phase 1 included a control diet with 5% fish meal, 3.5% plasma protein, and no torula yeast. The second diet contained 1.5% fish meal, 14% woody torula yeast, and no plasma protein, whereas the third diet contained 1.5% fish meal, 14% conventional torula yeast, and no plasma protein. Fecal scores were assessed every other day. On day 7, one pig per pen was euthanized to collect ileal tissue and mucosa for determination of morphology and for ribonucleic acid (RNA) sequencing analysis. At the end of phases 1 and 2, blood samples were collected and concentrations of cytokines, plasma urea nitrogen (PUN), peptide YY, immunoglobulin G, total protein, and albumin were analyzed. Results indicated that both torula yeast sources could replace fish meal and plasma protein without affecting growth performance, intestinal morphology, or blood characteristics of pigs. Pigs fed a diet containing torula yeast had improved (P < 0.05) fecal scores during phase 1. Pigs fed the conventional torula yeast diet had greater (P < 0.05) concentration of interleukin-2 compared with pigs fed the control diet. On day 14, greater (P < 0.05) concentrations of interleukin-4 and interleukin-10 were observed in pigs fed the diet containing the woody torula yeast or conventional torula yeast compared with pigs fed the control diet. Results from the RNA sequencing indicated that 19 of 24 analyzed genes involved in digestion and absorption of protein and vitamins were downregulated in pigs fed the diet containing woody torula yeast compared with pigs fed the control diet. However, only two genes (i.e., ANKS4B and FAM54A) were downregulated in pigs fed the woody torula yeast diet compared with the conventional torula yeast diet. In conclusion, using woody or conventional torula yeast instead of fish meal and plasma protein in the phase 1 diet for weanling pigs may improve intestinal health without influencing growth performance of pigs.

Selenium Requirements in Rats, Mice, Lambs, Chicks and Turkeys Based on Selenoprotein Enzyme Activity and Transcript Level

Over the past several years, my lab has conducted a series of studies to evaluate selenium (Se) status and requirements in rats, mice and lambs, all using virtually the same diets. These studies progressed from using glutathione peroxidase (GPX) activity as the primary biomarker, to use of GPX protein and GPX mRNA levels as biomarkers, and recently we expanded to include additional selenoenzyme activities as well as transcript levels for the full selenoproteome. Literature reports of Se requirements of turkeys have consistently indicated that turkeys have a markedly higher Se requirement than mammals (NRC: 0.2 μg Se/g). Thus we evaluated the Se requirements of turkey poults, and in parallel, of chicks. The objective here is to compare resulting requirements and to identify clues to better understand the underlying differences in Se requirements and in Se‐deficiency target tissues. For all studies, animals were fed a basal torula yeast diet (0.005–0.007 μg Se/g) with graded levels of Se supplemented as selenite for 4 weeks (lambs 8 wk). Se response curves result in well‐defined Se‐adequate plateaus for all biomarkers except RBC GPX1 activity. Based on plasma GPX3, liver GPX1, and RBC GPX1 activities, the mammalian minimal dietary Se requirement is uniformly 0.1 μg Se/g, whereas the turkey requirement is clearly 3‐times higher at 0.3 μg Se/g; the chick minimum Se requirement is 0.15 μg Se/g based on plasma GPX3 and GPX1 activities. Liver GPX4 activity is only modestly affected by Se deficiency in rats, but falls to ~10% of plateau levels in mice, chicks and poults. In contrast to selenoenzyme activity biomarkers, requirements based on liver GPX1 mRNA are uniformly 0.04–0.11 μg Se/g for rodents and avians, with GPX1 mRNA in Se deficiency falling more dramatically in rodents vs. avians. GPX4 mRNA is little affected by Se deficiency in rodents but falls to 30% in avians. Other unique species differences include high expression of GPX3 mRNA in avian liver; plasma GPX3 activity in Se deficiency falls to 1–3% of plateau levels in rats, chicks, poults and lambs and but only to 35% in mice. Sigmoidal Se response curves are observed for liver GPX1 activity in rats, chicks, turkeys and lambs, and for plasma GPX3 activity in mice, indicating that Se is preferentially directed to other selenoenzymes and/or tissues under Se‐deficient conditions. No mRNA response curves are markedly sigmoidal. Notably, there are no selenoprotein mRNAs that can be used as biomarkers for supernutritional Se status. These studies demonstrate that the minimum dietary Se requirement of young mammals falls over a narrow range, while the requirement of chicks is slightly higher, and turkey requirements are 3‐times that of mammals. Differences in these biomarker Se response curves may help to understand Se metabolism and targeting of tissues in Se deficiency, and thus help to better characterize Se requirements.Support or Funding InformationUSDA Hatch 233618 and 1004389, Northeast Agricultural Univ NECT‐1207‐02 and 1252‐ NCET‐009, and UW Selenium Nutrition Research Fund

Selenium bioavailability from soybeans in rats fed a modified Torula yeast diet

Selenium (Se) is an essential nutrient, and soy is a major plant source of dietary protein to humans. The United States produces one third of world's soybeans, and the Se‐rich Northern Plains states produce a large share of the Nation's soybeans. The present study examined the bioavailability of Se from a high‐protein cultivar we developed for Nebraska producers. Selenium fertilization was used during the seed development to produce high‐Se seeds to mimic those naturally produced. Male Sprague‐Dawley rats were depleted for Se after 56 days on a 30% Torula yeast diet (4.05 µg Se/kg) and repleted after 50 days on the same diet supplemented with 20, 30 and 40 µg Se/kg from the protein isolate or tofu (bean curd) prepared from that cultivar. The Se bioavailability was determined on the ability of Se from the test items to restore Se dependent enzyme glutathione peroxidase activity and tissue Se content in Se‐deficient rats compared with the standard responses in rats fed selenomethionine‐supplemented diets. Dietary supplementation with the protein isolate or tofu with 20, 30, and 40 µg Se/kg resulted in a dose‐dependent increase in glutathione peroxidase activity compared to rats fed the Se‐deficient diet. Similar increases were observed in the restoration of tissue Se. These dose‐dependent increases were comparable to that of selenomethionine. These results suggest that Se is bioavailable from this high‐protein cultivar and high‐Se soybeans may be a good source of dietary Se.

Knockouts of Se‐glutathione peroxidase‐1 and Cu,Zn superoxide dismutase exert different impacts on femoral mechanical performance of growing mice

The objective of this study was to determine the impact of knockout of Cu,Zn-superoxide dismutase (SOD1) and Se-glutathione peroxidase-1 (GPX1) on murine bone biomechanical properties. Femora samples were collected from wild-type (WT), SOD1-knockout [SOD1(-/-)] and GPX1-knockout [GPX1(-/-)] female mice (9-wk old, n = 7-8 per genotype) to assay for bone enzyme activities and mechanical properties in three point bending. Prior to testing, all mice were fed a torula yeast diet supplemented with 0.4 mg Se/kg as sodium selenite. Compared with the WT mice, SOD1(-/-) mice displayed a series of reductions (p < 0.05): 24% in body mass, 8% in femoral length, 43% in femoral structural strength, and 32% in bending stiffness. When differences in body size were accounted for, femoral failure moment in SOD1(-/-) mice remained lower (p < 0.05) than that of WT. Femoral tartrate resistant acid phosphatase activity in SOD1(-/-) was 47% greater (p < 0.05) than the WT. In contrast, GPX1(-/-) mice showed no significant differences in femoral mechanical properties from those of WT mice. In conclusion, knockout of SOD1 exerted a greater impact on femoral mechanical characteristics than that of GPX1 in growing mice.

Importance of Molar Ratios in Selenium-Dependent Protection Against Methylmercury Toxicity

The influence of dietary selenium (Se) on mercury (Hg) toxicity was studied in weanling male Long Evans rats. Rats were fed AIN-93G-based low-Se torula yeast diets or diets augmented with sodium selenite to attain adequate- or rich-Se levels (0.1, 1.0 or 15 micromol/kg, respectively) These diets were prepared with no added methylmercury (MeHg) or with moderate- or high-MeHg (0.2, 10 or 60 micromol/kg, respectively). Health and weights were monitored weekly. By the end of the 9-week study, MeHg toxicity had impaired growth of rats fed high-MeHg, low-Se diets by approximately 24% (p < 0.05) compared to the controls. Growth of rats fed high-MeHg, adequate-Se diets was impaired by approximately 8% (p < 0.05) relative to their control group, but rats fed high-MeHg, rich-Se diets did not show any growth impairment. Low-MeHg exposure did not affect rat growth at any dietary Se level. Concentrations of Hg in hair and blood reflected dietary MeHg exposure, but Hg toxicity was more directly related to the Hg to Se ratios. Results support the hypothesis that Hg-dependent sequestration of Se is a primary mechanism of Hg toxicity. Therefore, Hg to Se molar ratios provide a more reliable and comprehensive criteria for evaluating risks associated with MeHg exposure.

Selenium Sources Affect Protein Concentration, Thioredoxin Reductase Activity and Selected Production Parameters in Reovirus Infected Broiler Chickens

Successful Avian Reovirus (ARV) infections ultimately result in decreased weight gains coupled with increased mortality. Selenium (Se) is a structural component of Thioredoxin Reductase (TRX), an enzyme capable of quenching intracellular free radicals and influencing redox balance. The aim of this study was to determine the various effects that Se-containing diets fed to ARV-infected broilers had on protein concentrations, TRX activity, body weights and mortality. Eggs were obtained from Cobb breeders that had been maintained on isocaloric Torula yeast diets containing either no supplemental Se, sodium selenite at 0.3 ppm, or organic Se (Sel-Plex®, Alltech, Inc., Nicholasville, KY) at 0.3 ppm. Chicks hatched from those eggs were placed on Torula yeast broiler diets containing 1) no supplemental Se, 2) 0.3 ppm sodium selenite, or 3) 0.3 ppm organic Se similar to their respective parents' diets. On day of hatch, 60 chicks per dietary Se treatment were placed into either Control or Virus-infected groups in heated-growing batteries in separate isolation rooms. Chicks in the Virus-infected groups were given each an oral gavage of 0.5 ml of ARV-CU98 (10 pfu/ml/chick), and Control chicks were given the medium only. At 14 and 21 days of age, the 4.2 birds were weighed, bled, killed by CO asphyxiation, and tissues collected for analyses. Data from this 2 2 X 3 factorially arranged, completely randomized experimental design were analyzed using the GLM procedure of SAS. ARV-infected birds had significantly lower average body weights (ABW) at 14 and 21 days (P<0.0001), three times higher mortality rates, and decreased tissue protein concentration (p<0.001) than controls. Se treatments did not affect ABW and mortality, but did significantly improve plasma protein concentration (p<0.05) and TRX activity in both, healthy and virus-challenged bird. Our findings suggest that ARV infection depresses growth, increases mortality and reduces protein concentration in various tissues, whereas Se is beneficial against ARV infection in broilers through an improved antioxidant status.

Hyperinsulinemia in GPX1 Overexpressing Mice is Independent of Obesity

Our laboratory has previously reported insulin resistance, along with hyperglycemia, hyperinsulinemia and obesity, in Se-dependent glutathione peroxidase-1 (GPX1) overexpressing (OE) mice. A subsequent experiment has shown that a caloric restriction of the obese OE mice (10 months of age) for three months eliminated all of the phenotypes except for hyperinsulinemia. The objective of the present study was to determine if hyperinsulinemia, along with insulin resistance, in OE mice could be completely prevented by caloric restriction at a younger age prior to the onset of those disorders. A total of 24 OE and the wild-type (WT) male mice (2-month old, n = 6 per treatment-genotype) were fed a Se-adequate (0.4 mg Se/kg), torula yeast diet at 5 (full feeding) or 3 g per day (caloric restricted) for four months. There was no significant difference in any measure between the two genotypes at initial, and the full feeding OE mice developed all of previously-reported signs. With the caloric restriction, the OE mice had body weight, fasting blood glucose level and insulin sensitivity similar to those of the WT mice at the end of study (6 months of age). The caloric restricted OE mice still had higher (P < 0.05) plasma insulin level after overnight fasting (702 vs. 406 pg/mL), and at 15 min after a glucose challenge (1782 vs. 602 pg/mL) than the WT mice, respectively. Both restricted and full feeding OE mice demonstrated improved (P < 0.05) glucose tolerance than the WT mice. In conclusion, hyperinsulinemia either at fasting or upon glucose stimulation in the OE mice was independent of obesity, and could not be removed by caloric restriction even at the early age. [NIH DK 53018 to XGL]

Effect of Physical Restraint on Oxidative Stress in Mice Fed a Selenium and Vitamin E Deficient Diet

Physical restraint has been associated with increased oxidative damage to lipid, protein, and DNA. The purpose of this experiment was to determine whether physical restraint would further exacerbate oxidative stress in mice fed a selenium (Se) and vitamin E (VE) deficient diet. Three-week- old mice were fed a Torula yeast diet containing adequate or deficient Se and VE. Menhaden oil was added to the deficient diet to impose an additional oxidative stress. After 4 wk feeding, half the mice in each group were restrained for 5 d in well-ventilated conical tubes for 8 h daily. Mice fed the Se and VE deficient diets had increased liver thiobarbituric acid-reactive substance (TBARS) levels and decreased liver glutathione peroxidase (GPX1) activity and alpha-tocopherol levels. Plasma corticosterone levels were elevated in restrained mice fed the deficient diet compared to unrestrained mice fed the adequate diet. Restraint had no effect on liver TBARS or alpha-tocopherol levels. Liver GPX1 activity, however, was lower in restrained mice fed the adequate diet. In addition, liver superoxide dismutase (SOD) activity was lower in the restrained mice fed the adequate or deficient diet. Thus, under our conditions, Se and VE deficient diet, but not restraint, increased lipid peroxidation in mice. Restraint, however, decreased antioxidant protection in mice due to decreased activities of GPX1 and SOD enzymes.

Effect of the chemical form of supranutritional selenium on selenium load and selenoprotein activities in virgin, pregnant, and lactating rats1

Virgin, pregnant, and lactating rats were used to assess the influence of selenomethionine and selenocystine, fed at four to seven times the daily Se requirement (supranutritional), on Se load and selenoprotein activities. Female Sprague Dawley rats (n = 48; age = 13 wk), reared on a low-Se torula yeast diet, were assigned to one of three reproductive states (n = 16 per reproductive state) to occur simultaneously: virgin, pregnant, and lactating. Once reproductive state was achieved, rats were fed (ad libitum) either l-selenomethionine (n = 24) or L-selenocystine (n = 24) diets providing 2.0 microg Se/g of diet (as-fed basis) for 18 d, and then killed. Lactating rats consuming selenomethionine had the greatest Se concentration in the brain, with pregnant rats being intermediate, and virgin rats having the least (P < 0.02). When selenocystine was fed, the concentration of Se in the brain was greater (P = 0.008) in lactating rats, but not different (P = 0.34) between pregnant and virgin rats. Selenium concentrations in the heart, liver, lung, muscle, spleen, plasma, placenta, uterus, and fetus were greatest (P < 0.001) in rats consuming selenomethionine. Brain, kidney, and liver thioredoxin reductase, and brain, erythrocyte, kidney, and liver glutathione peroxidase activities did not differ (P = 0.13 to P = 0.85) between Se treatments. Lactating rats exhibited the greatest (P < 0.006) Se concentration in the heart, lung, muscle, plasma, and spleen compared with pregnant and virgin rats. Thioredoxin reductase was greatest (P < 0.004) in the brain of pregnant rats, greatest (P < 0.004) in the liver of lactating rats, and greater (P < 0.03) in the kidney of lactating and pregnant vs. virgin rats. Regardless of reproductive state, supranutritional Se (2.0 microg/g of diet) fed as selenocystine resulted in less Se load, and when fed as selenomethionine, was equally available for thioredoxin reductase synthesis as the Se in selenocystine. Independent of dietary Se chemical form, thioredoxin reductase activity was responsive to reproductive state.

Selenium regulates expression in rat liver of genes for proteins involved in iron metabolism.

Suppression subtractive hybridization analysis in our laboratory recently revealed that transferrin mRNA may be elevated in Sedeficient rat liver. In this work, we compared expression in rat liver of genes for transferrin, transferrin receptor, ferritin light and heavy chains, and iron-regulatory proteins 1 and 2 in Se adequacy and deficiency. Weanling male Sprague-Dawley rats were fed Torula yeast diets supplemented with 0 or 0.15 microg Se/kg diet as sodium selenite for 15 wk. Activity of cellular glutathione peroxidase was virtually abolished in Se-deficient rat liver, whereas activity of glutathione S-transferase was 43% higher than in Se-adequate liver. There were no differences in hematocrit, hemoglobin, or liver iron content. To examine differential gene expression, we used a multiplex relative reverse transcriptase-polymerase chain reaction method. Three of the six genes examined showed modest but consistent upregulation in Se deficiency. Transferrin mRNA was 30% more abundant in Se-deficient than in Se-adequate liver. For the transferrin receptor, the difference was 32%, and for iron regulatory protein 1, it was 63%. No consistent differences were observed for iron regulatory protein 2 or for ferritin light or heavy chain. These findings suggest a possible role for dietary Se in moderating iron metabolism.

Knockout of cellular glutathione peroxidase affects selenium-dependent parameters similarly in mice fed adequate and excessive dietary selenium.

This study was to determine whether or not effects of the cellular glutathione peroxidase (GPX1) knockout on several Se-dependent parameters in mice were tissue, dietary Se concentration, and selenoprotein specific. A 2 x 3 factorial experiment was conducted with 18 GPX1 knockout mice [GPX1(-)] and 18 controls (3 weeks old, half males and females). These mice were fed a torula yeast diet supplemented with all-rac-alpha-tocopheryl acetate (50 mg/kg of feed) and Se (sodium selenite) at 0, 0.5, or 3.0 mg/kg of feed for 6 weeks. Both kidney GPX1 mRNA levels and liver, kidney, lung, and testis total GPX activities, assayed using hydrogen peroxide, were affected (p < 0.001) by the GPX1 knockout and dietary Se concentrations, whereas kidney extracellular or plasma GPX (GPX3) mRNA levels and phospholipid hydroperoxide GPX (GPX4) activities in the four tissues were affected (p < 0.001) by only dietary Se concentrations. Total GPX activity in testis was reduced approximately 90% (p < 0.01) by the GPX1 knockout. Neither the GPX1 knockout nor the dietary Se concentrations affected mRNA levels of GPX4 in testis or selenoprotein P in kidney. Total liver Se concentrations were not different between the GPX1(-) and control mice at 0 mg Se/kg of feed, but were reduced (p < 0.01) by 61 and 64% in the GPX1(-) mice at 0.5 and 3.0 mg Se/kg of feed, respectively. These results not only confirm the independent expression of GPX3, GPX4, and selenoprotein P from that of GPX1, but also show similar effects of the GPX1 knockout on Se-dependent parameters in mice between different dietary Se concentrations, tissues, and selenoproteins.

Dietary selenium regulation of glutathione peroxidase mRNA and other selenium-dependent parameters in male rats

Weanling male rats were fed a basal torula yeast diet (0.007 μg Se/g diet) supplemented with graded levels of Se (0 to 0.2 μg Se/g diet as Na 2SeO 3) (three rats/group) to evaluate classical glutathione peroxidase (GPXI, GSH:H 2O 2 oxidoreductase, EC 1.11.1.9) mRNA level as an indicator of intracellular Se status. Growth was followed throughout the dietary treatment and a number of Se-dependent parameters including liver GPX1 mRNA levels were determined after 33 days. Growth was not impaired at any level of dietary Se supplementation. In rats fed the Se-deficient basal diet, liver Se concentration was 5 ± 1%, liver GPX1 mRNA levels were 10 ± 2%, plasma GPX activity was 2 ± 1%, erythrocyte GPX activity was 37 ± 1%, and liver GPX activity was 0 ± 2% of the levels in rats fed 0.1 μg Se/g diet; these parameters increased sigmoidally with increasing dietary Se, showing a breakpoint near 0.1 μg Se/g diet. Graphical analysis indicated that the increase in liver GPX1 mRNA level with increasing dietary Se, preceded the increase in liver GPX activity. Se supplementation had no effect on polyadenylated mRNA levels or on β-actin mRNA levels, demonstrating that Se regulation of GPX1 mRNA is specific. Se-deficient liver selenoprotein P mRNA levels were 69 ± 2% of the levels in rats fed 0.1 μg Se/g diet. We hypothesize that GPX1 mRNA is a primary target of the Se regulatory mechanism, making GPX1 mRNA level a potentially useful indicator of the status of an important intracellular regulatory pool of Se.

The Selenium Requirement for Glutathione Peroxidase mRNA Level Is Half of the Selenium Requirement for Glutathione Peroxidase Activity in Female Rats

To determine critically the selenium (Se) requirement for weanling female rats, we used glutathione peroxidase (GSH: H2O2 oxidoreductase, EC 1.11.1.9) (GPX) mRNA and a number of other parameters to assess Se status. Rats were fed a basal torula-yeast diet (0.007 µg Se/g) supplemented with Se as Na2SeO3 in graded levels from 0 to 0.3 µg Se/g diet for 32 d (3 rats/group). Selenium supplementation had no effect on growth, showing that the Se requirement for growth is less than 0.007 µg Se/g diet, whereas other parameters showed significant increases with Se supplementation. In rats fed the Se-deficient basal diet, liver Se concentration was 4 ± 0%, plasma GPX activity was 8 ± 1%, erythrocyte GPX activity was 40 ± 3%, liver GPX activity was 2 ± 1%, and liver GPX mRNA levels were 11–17% of the levels in rats fed 0.1 µg Se/g diet. Liver Se concentration and GPX activity in plasma, erythrocytes and liver all reached a plateau breakpoint at or near 0.1 µg Se/g diet, indicating that the dietary Se requirement for maximal GPX activity in growing female rats is 0.1 µg Se/g diet. Liver GPX mRNA levels reached the plateau breakpoint at 0.05 µg Se/g diet, showing that the minimum dietary Se requirement for maximal GPX mRNA levels in female rats is half of the Se requirement for maximal GPX activity. This experiment demonstrates that GPX mRNA can be used to determine the dietary Se requirement; the gap between the dietary Se necessary for maximal GPX mRNA and that for maximal GPX activity may represent an evolutionarily derived biological margin of safety.

Selenium from beef is highly bioavailable as assessed by liver glutathione peroxidase (EC 1·11·1·9) activity and tissue selenium*

The bioavailability of Se from ground beef has been previously found in this laboratory to be greater than that of selenite or selenate when fed to female Fischer 344 rats. In the present study we examined the bioavailability of Se from various commercial portions of beef, the liver, striploin, round, shoulder and brisket. All beef was cooked, freeze-dried, finely powdered and mixed with the other dietary ingredients. The experimental diets were fed to the weanling Fischer 344 rats which had been subjected to dietary depletion of Se for 6 weeks. The bioavailability of Se from the beef diets was compared with that of Se as selenite or L-selenomethionine (SeMet) added to torula-yeast diets. Each experimental diet contained 0.10 mg Se/kg. After 8 weeks of dietary Se repletion, relative activity of liver glutathione peroxidase (EC 1.11.1.9; GSHPx) from the different dietary groups compared with that of control animals (100%) was (%): selenite 91, SeMet 122 (P < 0.05), liver 108, striploin 105, round 106, shoulder 106, brisket 103. Se recovery for liver GSHPx was generally highest from SeMet > beef muscle = beef liver > selenite. Muscle tissue deposition of Se was highest from SeMet > beef muscle > selenite = beef liver. In addition, the faecal excretion of Se was lowest from the SeMet dietary group and highest from the selenite dietary group. The experimental results suggest that all cuts of beef appear to be highly bioavailable sources of dietary Se when compared with selenite or L-SeMet.

Laboratory Evaluation of Diets of Processed Corncob, Torula Yeast, and Wheat Germ on Four Developmental Stages of Mediterranean Fruit Fly (Diptera: Tephritidae)

Mediterranean fruit fly, Ceratitis capitata (Wiedemann), larvae were reared on five diets (wheat millfeed [standardl, processed corncob [PCC] + torula yeast, PCC + torula yeast + 1% wheat germ [WG], PCC + torula yeast + 3% WG, and PCC + torula yeast + 6% We) through five consecutive generations to obtain measurements of the following five life history traits: duration of larval development, pupal recovery, pupal weight, adult fecundity, and egg fertility. The PCC + torula yeast diets produced insects with shorter larval developmental times and higher pupal recovery than the standard millfeed diet. In contrast, the millfeed diet produced the highest pupal weight and adult fecundity. PCC diets fortified with wheat germ produced Mediterranean fruit flies with the highest egg fertility. These results suggest that PCC/wheat germ diets produce Mediterranean fruit flies of comparable quality to those commonly used in sterile insect programs.

Glucose tolerance factor potentiation of insulin action in adipocytes from rats raised on a torula yeast diet cannot be attributed to a deficiency of chromium or glucose tolerance factor activity in the diet.

The nature of the dietary component responsible for adipocytes having the ability to respond to Glucose Tolerance Factor (GTF) was investigated. Rats were raised on either a control diet or one of three diets differing only in the protein source (torula yeast, brewer's yeast, or casein). Only in adipocytes from rats fed the torula yeast diet did a GTF fraction prepared from brewer's yeast potentiate the action of suboptimal concentrations of insulin in the incorporation of label from D-[1-14C]-glucose and D-[U-14C]-glucose into CO2 and fatty acids. It was concluded that this potentiation was not the result of a deficiency of GTF activity in torula yeast, because a GTF fraction prepared from torula yeast had similar insulin potentiating activity. Differences in response among diets were not owing to differences in levels of amino acids or owing to concentrations of 22 (Al, As, B, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mo, Na, Ni, P, Pb S, Se, Si, Sn, Sr, Zn) of the 23 trace elements investigated. The level of Mn was low in all diets, but particularly low in the torula yeast diet. Mn deficiencies have previously been implicated in perturbations of glucose metabolism, so that it is possible that this deficiency may be responsible for the effects attributed to the torula yeast diet.

Effects of selenium deficiency on sperm morphology and spermatocyte chromosomes in mice

Sperm morphology and spermatocyte chromosomes were examined in mice maintained on a Torula yeast diet for 5 weeks. In the selenium-deficient group, the proportion of abnormal sperm was high, ranging from 6.8% to 49.6%, while in the control group it ranged from only 4.0% to 15.0%. The most frequently occurring abnormalities in sperm shape were in the sperm head. There was also a tendency for abnormalities in other regions (neck, midpiece and tail) to be increased. However, in metaphase-I spermatocytes, the frequencies of various types of abnormal chromosomes (univalent chromosomes, translocations and structural anomalies) did not differ between the selenium-deficient and control groups. These findings indicate that selenium may be an essential constituent for spermatogenesis in mice.

Comparison of the Magnitude of the Selenite-Exchangeable Metabolic Pool and Whole Body Endogenous Selenium in Adult Rats

The quantitative relationship between the size of the selenite-exchangeable metabolic pool (WSe-EMP) and whole body endogenous selenium (Seend) was investigated in adult male rats. Two experiments based on multiple labeling with stable isotopes were performed. One focused on short-term (7 d, Expt. 1) and the other on long-term (60 d, Expt. 2) relationships. Rats were fed a Torula yeast diet and water supplemented with [76Se]selenite at 0.1 micrograms Se/mL; the in vivo [74Se]selenite tracer was administered orally. Groups of three or four animals were killed at timed intervals and whole carcass or selected organs were analyzed for the stable isotopes 74Se, 77Se and 82Se with hydride generation/inductively coupled plasma mass spectrometry. The value of WSe-EMP was determined from plasma or urine isotope ratios. In Experiment 1, with plasma as the sampling compartment, WSe-EMP at 24 h was 36.5 +/- 1.2% of the baseline value of whole body endogenous selenium (Seend) and 36.3 +/- 1.8% at 7 d. When urine was the sampling compartment, the corresponding values were 3.9 +/- 0.3% and 43.1 +/- 2.8%, respectively. In Experiment 2, WSe-EMP (plasma) was 38.9 +/- 1.3% of Seend at 7 d, increasing to 45.5 +/- 1.6% at 60 d. The corresponding values for urine as the sampling compartment were 45.5 +/- 2.0% (7 d) and 61.5 +/- 1.7% (60 d), respectively.