scispace - formally typeset
Search or ask a question
Author

Peter C. Uden

Bio: Peter C. Uden is an academic researcher from University of Massachusetts Amherst. The author has contributed to research in topics: Gas chromatography & High-performance liquid chromatography. The author has an hindex of 41, co-authored 162 publications receiving 5706 citations.


Papers
More filters
Journal ArticleDOI
TL;DR: Comparison of biological activities of Se-garlic and Se-yeast was compared to elucidate how their disposition in tissues might account for the differences in cancer chemopreventive activity and the metabolism of these two compounds is discussed.
Abstract: A recent human intervention trial showed that daily supplementation with selenized yeast (Se-yeast) led to a decrease in the overall cancer morbidity and mortality by nearly 50%; past research has also demonstrated that selenized garlic (Se-garlic) is very effective in mammary cancer chemoprevention in the rat model. The goal of this study was to compare certain biological activities of Se-garlic and Se-yeast and to elucidate the differences based on the chemical forms of selenium found in these two natural products. Characterization of organic selenium compounds in yeast (1922 microg/g Se) and garlic (296 microg/g Se) was carried out by high-performance liquid chromatography with inductively coupled plasma mass spectrometry or with electrospray mass spectrometry. Analytical speciation studies showed that the bulk of the selenium in Se-garlic and Se-yeast is in the form of gamma-glutamyl-Se-methylselenocysteine (73%) and selenomethionine (85%), respectively. The above methodology has the sensitivity and capability to account for >90% of total selenium. In the rat feeding studies, supplementation of Se-garlic in the diet at different levels consistently caused a lower total tissue selenium accumulation when compared to Se-yeast. On the other hand, Se-garlic was significantly more effective in suppressing the development of premalignant lesions and the formation of adenocarcinomas in the mammary gland of carcinogen-treated rats. Given the present finding on the identity of selenomethionine and gamma-glutamyl-Se-methylselenocysteine as the major form of selenium in Se-yeast and Se-garlic, respectively, the metabolism of these two compounds is discussed in an attempt to elucidate how their disposition in tissues might account for the differences in cancer chemopreventive activity.

302 citations

Journal ArticleDOI
01 Jan 2000-Analyst
TL;DR: Selenium-enriched plants, such as hyperaccumulative phytoremediation plants, and reference samples with natural selenium levels, including onion and garlic controls, cooking garlic powder, baking yeast powder and a commercial garlic supplement were analyzed by HPLC-ICP-MS for theirSelenium content and speciation after hot water and enzymatic extractions.
Abstract: Selenium-enriched plants, such as hyperaccumulative phytoremediation plants (Astragalus praleongus, 517 μg g−1 Se, and Brassica juncea, 138 μg g−1 Se in dry sample), yeast (1200, 1922 and 2100, μg g−1 Se in dry sample), ramp (Allium tricoccum, 48, 77, 230, 252, 405 and 524 μg g−1 Se in dry sample), onion (Allium cepa, 96 and 140 μg g−1 Se in dry sample) and garlic (Allium sativum, 68, 112, 135, 296, 1355 μg g−1 Se in dry sample) were analyzed by HPLC-ICP-MS for their selenium content and speciation after hot water and enzymatic extractions. Reference samples with natural selenium levels, such as onion and garlic controls, cooking garlic powder, baking yeast powder and a commercial garlic supplement were also analyzed. Selected samples were also examined by HPLC-electrospray ionization (ESI)-MS. HPLC was mostly carried out with 0.1% heptafluorobutanoic acid (HFBA) as ion-pairing agent in 1 + 99 v/v methanol–water solution, but 0.1% trifluoroacetic acid (TFA) in 1 + 99 v/v methanol–water solution was also utilized to permit chromatography for compounds that did not elute with HFBA. More than 75% of the total eluting selenium compounds, based upon element specific detection, were identified from retention time data and standard spiking experiments, and between 60 and 85% of compounds were identified by MS, with up to 25% of the total eluting molecular selenium species being unidentified as yet. Limits of quantification (LOQ, defined as the concentration giving an S/N of 10) for HPLC-ICP-MS were in the range 2–50 ng mL−1 Se in the injected extracts for the selenium-enriched samples and 2–10 ng mL−1 Se for the natural selenium level samples. LOQ values for HPLC-ESI-MS were ca. 100 times higher than those measured by HPLC-ICP-MS.

223 citations

Journal ArticleDOI
TL;DR: Etude de la teneur en chloroforme, en hydrate de chloral et en acides dichloro-and trichloroacetique d'une eau potable municipale traitee par chloration as discussed by the authors.
Abstract: Etude de la teneur en chloroforme, en hydrate de chloral et en acides dichloro- et trichloroacetique d'une eau potable municipale traitee par chloration

204 citations

Journal ArticleDOI
TL;DR: The formation of nonvolatile chloroorganics produced during the aqueous chlorination of humic substances was followed qualitatively and quantitatively and chlorine-selective fingerprint studies were undertaken to follow the formation of 17 major chlorinated products.
Abstract: The formation of nonvolatile chloroorganics produced during the aqueous chlorination of humic substances was followed qualitatively and quantitatively. The effects of reaction time, NaOCl to C ratio, pH, and source of humic material were studied with respect to the quantitative formation of chloroform, dichloroacetic acid, trichloroacetic acid, and chloral hydrate. Other gas-chromatographable chloroorganics formed from the chlorination of fulvic acid were produced at levels below these four compounds. Chlorine-selective fingerprint studies were also undertaken to follow the formation of 17 major chlorinated products.

204 citations

Journal ArticleDOI
TL;DR: In this article, an interface between fused silica gas chromatographic capillary columns and a microwave-excited atmospheric pressure helium plasma (MED) was investigated. Butler et al. used a TM/sub 010/ resonant cavity for axial viewing of plasma emission.
Abstract: Interfacing of fused silica gas chromatographic capillary columns to a microwave-excited atmospheric pressure helium plasma (MED) is investigated. The system for glass and fused silica capillary operation incorporates an interface where excess solvent can be vented by a chemically deactivated fluidic-logic gas switching system. A TM/sub 010/ resonant cavity allows axial viewing of plasma emission. A quartz refractor plate background corrector improves selectivity ratios for elements whose emission occurs in the high-carbon (cyanogen) background region. Background emission characteristics of the helium plasma under various conditions are established from 200 to 500 nm. Calibration curves, selectivity ratios, and detection limits are established for the elements vanadium, niobium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, osmium, cobalt, nickel, mercury, boron, aluminum, carbon, silicon, germanium, tin, lead, phosphorus, arsenic, sulfur, selenium, fluorine, chlorine, bromine, iodine, hydrogen, and deuterium.

177 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: This Review Article is focused on the action of the reactive oxygenated species in inducing oxidative injury of the lipid membrane components, as well as on the ability of antioxidants (of different structures and sources, and following different mechanisms of action) in fighting against oxidative stress.

1,667 citations

Journal ArticleDOI
TL;DR: Comparison of chlorine to ozone reactivity towards aromatic compounds (electrophilic attack) shows a good correlation, with chlorine rate constants being about four orders of magnitude smaller than those for ozone.

1,579 citations

Journal ArticleDOI
TL;DR: In this paper, a proton transfer reaction mass spectrometer (PTR-MS) was developed which allows for on-line measurements of trace components with concentrations as low as a few pptv.

1,542 citations

Journal ArticleDOI
TL;DR: The relationships between selenium intake/status and health, or risk of disease, are complex but require elucidation to inform clinical practice, to refine dietary recommendations, and to develop effective public health policies.
Abstract: This review covers current knowledge of selenium in the environment, dietary intakes, metabolism and status, functions in the body, thyroid hormone metabolism, antioxidant defense systems and oxidative metabolism, and the immune system. Selenium toxicity and links between deficiency and Keshan disease and Kashin-Beck disease are described. The relationships between selenium intake/status and various health outcomes, in particular gastrointestinal and prostate cancer, cardiovascular disease, diabetes, and male fertility, are reviewed, and recent developments in genetics of selenoproteins are outlined. The rationale behind current dietary reference intakes of selenium is explained, and examples of differences between countries and/or expert bodies are given. Throughout the review, gaps in knowledge and research requirements are identified. More research is needed to improve our understanding of selenium metabolism and requirements for optimal health. Functions of the majority of the selenoproteins await characterization, the mechanism of absorption has yet to be identified, measures of status need to be developed, and effects of genotype on metabolism require further investigation. The relationships between selenium intake/status and health, or risk of disease, are complex but require elucidation to inform clinical practice, to refine dietary recommendations, and to develop effective public health policies.

1,034 citations

Journal ArticleDOI
TL;DR: Low Se status is likely to contribute to morbidity and mortality due to infectious as well as chronic diseases, and increasing Se intakes in all parts of the world can be expected to reduce cancer rates.
Abstract: Food systems need to produce enough of the essential trace element Se to provide regular adult intakes of at least 40 microg/d to support the maximal expression of the Se enzymes, and perhaps as much as 300 microg/d to reduce risks of cancer. Deprivation of Se is associated with impairments in antioxidant protection, redox regulation and energy production as consequences of suboptimal expression of one or more of the Se-containing enzymes. These impairments may not cause deficiency signs in the classical sense, but instead contribute to health problems caused by physiological and environmental oxidative stresses and infections. At the same time, supranutritional intakes of Se, i.e. intakes greater than those required for selenocysteine enzyme expression, appear to reduce cancer risk. The lower, nutritional, level is greater than the typical intakes of many people in several parts of the world, and few populations have intakes approaching the latter, supranutritional, level. Accordingly, low Se status is likely to contribute to morbidity and mortality due to infectious as well as chronic diseases, and increasing Se intakes in all parts of the world can be expected to reduce cancer rates.

977 citations