Methylmercury (MeHg) is a potent neurotoxin capable of crossing the blood-brain barrier causing a profound negative impact on the central nervous system. After its release, Hg may be transported worldwide and eventually deposited in colder Arctic regions. Exposure of Aboriginal communities to MeHg occurs primarily through the consumption of traditional food. Dietary exposure studies are conducted using the total concentration of mercury in the food multiplied by the food consumption rate. This method does not take into account the oral bioavailability of Hg. Therefore, this study determines the bioavailability of Hg in four key traditional foods to provide a better estimation of Hg exposure and to improve the characterization of overall Hg risk to human health. We found that Hg concentrations significantly decreased for all foods after undergoing an in-vitro digestion process. Hg bioaccessibility percentage of ringed seal liver was 32.3%, ringed seal muscle was 69.0%, lake trout muscle was 28.8%, and lastly air-dried beluga muscle was 34.0%. Furthermore, no relationship was observed between bioaccessible Hg concentrations and original Hg concentrations in the raw food. The concentration of MeHg in the bioaccessible fraction was also examined and found to be significantly higher in muscle tissues than in the liver. Bioavailability of the foods was determined using Caco-2 cells. Hg bioavailability percentages were found to be 0.42% for RSL 5.24% for RSM, 7.30% for ADB, and finally, 12.70% for LT. Correlations were found between increased Hg uptake and higher percentages of bioaccessible MeHg as well as lower concentrations of bioaccessible selenium. Lastly, a significant decrease in MeHg uptake after 24 hours was observed when co-incubating with selenium. These results suggest that risk assessments should incorporate bioaccessibility and bioavailability when estimating mercury exposure. Additionally, nutrients such as selenium in traditional food may play a role in reducing mercury uptake in the gut.

Laboratory and field experiments measured urea uptake and assimilation with ¹⁴C⁻ and ¹⁵N-urea and by disappearance of dissolved urea. A modified diacetyl monoxime method was developed, which accurately and precisely determined dissolved urea concentrations in seawater. In the Strait of Georgia, chlorophyll α (chl α) specific uptake rates of ammonium (NH₄⁺) and urea were greatest in stratified water; whereas, chl α specific uptake rates of nitrate (NO₃⁻) were greatest in frontal water. Ammonium and urea regeneration rates were calculated by a mass balance method and the rates were similar. Differences between measurements of particulate nitrogen, dissolved NH₄⁺, NO₃⁻ and urea, and ¹⁵N uptake were used to explain the dominant N transformations in frontal and stratified seawater. Uptake rates measured by ¹⁴C-urea were ca. 1.4 times faster than those determined by ¹⁵N-urea in the Sargasso Sea. Turnover times of urea in the surface-mixed layer were ca. 12 h. Within some seawater samples, phytoplankton utilized urea at rates which approximated the maximum rates of utilization. In a nitrate-sufficient culture of Thaiassiosira pseudonana (clone 3H) (Hustedt) Hasle and Heimdal, urea uptake rates measured by three methods disagreed; whereas, no discrepancies occurred in a nitrate-starved culture. NH₄⁺ was released from cells after urea was taken up and was later reabsorbed. A model of urea uptake and assimilation by T. pseudonana is proposed. An obligate selenium (Se) requirement for growth of T. pseudonana was demonstrated in axenic culture in artificial seawater. The addition of 10⁻⁹ M SeO₃²⁻ to culture medium was sufficient for good growth of this alga; SeO₄²⁻ was only effective at concentrations greater than 10⁻⁷ M. To elucidate the biochemical role of Se in T. pseudonana, cells were cultured in medium containing 10⁻⁹ M Na₂ ⁷⁵SeO₃. Two soluble polypeptides of 21 and 29 kD contained ⁷⁵Se. Glutathione peroxidase was detected on non-denaturing polyacrylamide gels and ⁷⁵Se co-migrated with the enzyme. It was concluded that Se is an essential element for growth of T. pseudonana due, in part, to the presence of the selenoenzyme glutathione peroxidase. / Science, Faculty of / Botany, Department of / Graduate

Selenium, the essential trace element, is well known as its antioxidant function, antiviral properties, and its anti-inflammatory function to human health. The relationships between selenium status and diabetes mellitus have been widely studied, but the consistency of results is lacking. This study used diagnosed diabetes incidence from year 2004 to 2012 and soil selenium content by counties within 48 contiguous states in the U.S. with Generalized Linear Mixed Model- R-Side as the major statistical method to determine whether there is a significant correlation or not. Results showed that the diagnosed diabetes population had been increased from 2004 to 2012 for all 48 states. The South region showed the highest increased rate whereas the Northeast region showed the least. Also, Kentucky, Louisiana, Maryland, and Massachusetts are the four states showed the significant correlation between soil selenium content and diabetes incidence. However, improved analytical methods and data are needed for further research.

Dietary composition can impact colonization and composition of gut microbiota. The first aim of this dissertation was to evaluate the effect of dietary Se deprivation, sex and, aging on taxonomic composition of gut microbiota in mice. We have previously shown that long-term dietary Se deprivation promotes health span deteriorate including type-2 diabetes like symptoms in later state Terc-/- mice carrying humanized telomeres. In the present study, the data suggested that the dietary Se deprivation and aging significantly and comparably altered the gut microflora composition. The ratio of Firmicutes/Bacteroidetes was decreased by dietary Se deprivation or aging in both sexes. Abundance of selective gut bacteria genus was associated with dietary Se status and aging as evidenced by heat map and principal coordinate analyses. Moreover, the abundance of Akkermensia muciniphila, a bacterium in association with obesity, differed by Se-deprivation, aging and sex. Taken together, changes in gut microbiota composition by dietary Se deprivation may accelerate mouse aging in a sex-specific manner. The second aim of this dissertation was to investigate the effects and underlying mechanism of fecal fermentation of non-digestible fibers isolated from common beans on adipocyte differentiation and fat accumulation to elucidate the cellular mechanisms. Treatment of 3T3-L1 murine preadipocytes with fermented product resulted in a reduction of triglyceride accumulation in a dose- and time-dependent manner. The fermentation product exhibited antiipogenic effects through suppression of the adipogenesis-associated key transcription factors or activators peroxisome proliferator-activated receptor gamma (Ppar gamma), CCAAT enhancer-bind protein alpha (C/ebp alpha) and fatty acid binding protein 4 (Fabp4). Moreover, the mRNA expression lipolytic genes including peroxisome proliferator-activated receptor delta (Ppar delta) and mitochondrial uncoupling protein 2 (Ucp2) were induced by the fermentation products of non-digestible fiber isolated from common beans counteract adipogenesis through regulation of key targets.Altogether, optimizing gut microbiota by nutritionally adequate level of dietary Se and non-digestible fiber appears to represent a promising strategy to control or prevent early onset of aging and age-related metabolic diseases.

The methods available for the calculation of ratios of partition functions for isotopic molecules were examined critically and compared. A number of calculations were made for carbon as well as for selenium systems using the exact method rather than an approximate one. Improvements were made to the sample handling system of the mass spectrometer to prevent sample cross-contamination and to reduce the time needed for sample changeover. Four sets of experiments were performed. The kinetic isotope effects in the reductions to Se° of Se^V1 and Se^1V were studied as were the isotope exchange reactions between Se° and Se^1V and between Se^1V and Se^V1. Estimates were made of the ratios of rate constants and isotope exchange equilibrium constants for 82Se and 76Se in these systems and these were compared with the theoretical values. / Thesis / Doctor of Philosophy (PhD)

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No description available.

Aktuell gibt es für Selen (Se) keine Bedarfsempfehlungen für das Damwild (Dama dama) in Gehegehaltung. Diese Studie soll die typische Se-Aufnahme bei Gehegehaltung von Damwild ermitteln und klären, welche Parameter sich eignen, um die Se-Versorgung des Damwildes zu reflektieren. Dazu wurden 19 Damhirsche in zwei Gruppen unter identischen Bedingungen gehalten. Die Tiere ernährten sich von dem natürlichen Grasaufwuchs und Mischfutter (0,15 mg/kg TS bzw. 1,07 - 1,91 mg/kg TS). In Blut, Plasma und die Organen wurden der Se-Gehalt, die Aktivität der Se-abhängigen Glutathionperoxidase (GPx) sowie teilweise die Gesamt-GPx-Aktivität (gesGPx), die Aktivität der Glutathion-S-Transferase (GST) und die Expression verschiedener GPx analysiert. Durch die Se-Supplementierung wurden ein signifikanter Anstieg des Plasma-Se in der Versuchsgruppe und ein moderater Unterschied der Vollblut-Se-Konzentration sowie der Vollblut-GPx-Aktivität zwischen der Kontroll- und der Versuchsgruppe beobachtet (p = 0,08). Außerdem wurde in allen Organen der Versuchsgruppe ein höherer Se-Gehalt als in der Kontrollgruppe festgestellt. In der Hierarchie der untersuchten Organe ist die Niere am höchsten angeordnet, absteigend folgen der Herz- und Skelettmuskel, die Milz und die Leber. Eine Se-Aufnahme von 0,05 - 0,08 mg/kg TS führt beim Damwild nicht zur Ausprägung von Se-Mangelsymptomen und stellt daher eine ausreichende Se-Versorgung dar. Die Empfehlungen zur Se-Versorgung für Damwild sind somit nicht von Hauswiederkäuern zu übernehmen. Im Plasma und im Vollblut scheinen Se-Konzentrationen von 28 - 64 µg/l und 81 - 200 µg/l für eine ausreichende Se-Versorgung zu sprechen, in der Leber Se-Konzentrationen von 270 - 663 µg/kg TS.

Male weanling inbred, mice were inoculated with fibrosarcoma cells (hindquarter) originally produced by 2-methylcholanthrene. Before inoculation, mice were randomly divided into three groups of 24 and one of 12 (control). After a one week acclimation period, each group was fed a diet containing either suboptimal vitamin B-6, 0.5 mg/kg diet; adequate, 7.0 mg/kg diet; or excess, 100 mg/kg diet. Controls were fed the adequate vitamin. B-6 diet. Twenty-four hours after tumor cell inoculation, a series of sodium selenite injections (0.5 μg/.10 mL) were given to half of each treatment group and all controls. Mice were sacrificed two wk after tumor inoculation. Tumors were excised and weighed. Selenium-treated mice had significantly smaller tumors as compared to untreated mice regardless of vitamin B-6 treatment. The smallest tumors were found in the selenium-treated group maintained on adequate B-6, while the largest tumors were developed by mice on the excess B-6 diet without selenium treatments. All groups had similar blood selenium levels as measured by gas chromatography. Tumor selenium levels, analyzed by atomic absorption, were significantly higher for untreated groups than selenium-treated groups (larger tumor size). The excess and adequate vitamin B-6 selenium-treated groups had significantly lower tumor selenium levels than the adequate vitamin B-6 untreated group. Plasma pyridoxal phosphate (concentrations) determined radiometrically and tumor vitamin B-6 levels determined microbiologically, related directly to dietary treatments. Sodium selenite injections and adequate vitamin B-6 diets reduced the size of fibrosarcomas in BALB/c inbred mice. / Master of Science

Numerous dietary factors have been shown to influence the fatty acid profiles (FAP) in breast milk from lactating women. However, few studies have evaluated the effect of trace minerals on milk FAP. Consequently, the purpose of this study was to determine the effect of selenium status on the FAP in breast milk. Subjects were lactating women from three different regions in China; Xichang (n=21), an area where selenium intakes are among the lowest in the world, Beijing (n=20), where there are adequate selenium intakes, and Enshi (n=19), where selenium intakes are among the highest in the world. Plasma and milk samples were obtained from women at birth of their baby and within 10 months postpartum and analyzed for selenium content, glutathione peroxidase (Gpx) activity and FAP. Plasma and breast milk selenium levels were significantly lower in the Xichang women and significantly higher in the Enshi women when compared to Beijing women. Despite the fact that the highest level of plasma selenium was measured in the samples from Enshi, the Gpx activity was greatest in the samples from Beijing; there was no effect of time of sampling on these samples. In breast milk, on the other hand, all the samples obtained at birth had similar activity of Gpx. The samples taken later, however, followed the same trend as plasma with the samples obtained from the women in Beijing having the highest activity. FAP indicated a significant difference in the amount of unsaturated fatty acids in both the plasma and milk for the Beijing women, when compared to the women from Xichang and Enshi. In particular, there were higher levels of linoleic acid, 18:2(n-6), in the plasma and milk of the women whose selenium intake was adequate. / Graduation date: 1997