Tumorigenesis, metabolism, speciation, bioavailability, and tissue deposition of selenium in selenium-enriched ramps (Allium tricoccum).

Ramps (Allium tricoccum) were grown either in a mixture of vermiculite and peat moss or hydroponically with various concentrations of selenium as sodium selenate. The concentrations used were from 30 to 300 mg of selenium/kg of vermiculite-peat moss or from 10 to 120 mg/L in the hydroponic solutions. Levels as high as 784 mg of selenium/kg were obtained in the ramp bulbs when grown with high levels of selenium in the vermiculite-peat moss, and up to 600 mg of selenium/kg was obtained hydroponically. The predominant form of selenium in the ramp bulbs at all concentrations of selenium was Se-methylselenocysteine, with lower amounts of selenate, Se-cystathionine, and glutamyl-Se-methylselenocysteine. There was a approximately 43% reduction in chemically induced mammary tumors when rats were fed a diet with Se-enriched ramps. Dietary Se-enriched ramps for rats did not result in excessive tissue selenium accumulation or undesirable side effects. Bioavailability studies with rats indicated that selenium in ramps was 15-28% more available for regeneration of glutathione peroxidase activity than inorganic selenium as selenite. Therefore, Se-enriched ramps appear to have potential for the reduction of cancer in humans.

Chemical speciation influences comparative activity of selenium-enriched garlic and yeast in mammary cancer prevention.

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.

Optimization and evaluation of atomic emission gas chromatographic detection for nitrogen using the 388 nm molecular emission spectral band.

Nitrogen determination by gas chromatography with atomic emission (microwave-induced plasma) detection (GC-AED) has been accomplished using the 174 nm atomic emission line, but with very limited selectivity and sensitivity. Nitrogen can also be detected using the cyanogen (CN) molecular band at 388 nm. A commercial GC-AED system was modified to allow the use of the 388 nm line for nitrogen detection, giving an improvement of 100-fold in sensitivity and selectivity, when compared with the 174 nm mode. Limits of detection of 10 pg/s were common, representing a 10-fold improvement. Compound-independent behavior was found for the system, working with optimum operating conditions, while instrumental problems were clearly reflected by a drastic compound dependent behavior. Response factors showed an important dependency upon the concentration of the element present. This dependency affected the accuracy of the determination of empirical formulae using GC-AED.

High-performance liquid chromatography of selenoamino acids and organo selenium compounds. Speciation by inductively coupled plasma mass spectrometry.

As part of an ongoing study to identify selenium compounds with cancer chemopreventive activity, extracts of selenium-enriched samples were analyzed by HPLC-inductively coupled plasma (ICP)-MS. Ion-exchange, ion pair and derivatization methods for reversed-phase HPLC were considered and advantages and disadvantages for each compared. Anion exchange allows separation of selenite and selenate, but otherwise provides poor separation. Pre-column derivatization and reversed-phase chromatography provides separation of compounds with terminal amine functionalities, but many other species elute in the void volume. The ion pair method gave optimal separation and was compatible with standard ICP-MS operating conditions.

Development, validation, and application of a method for quantification of methylmercury in biological marine materials using gas chromatography atomic emission detection.

A gas chromatographic method was developed for the quantification of alkylmercury species using microwave-induced plasma atomic emission detection (GC-AED). The column conditioning and analyte derivatization required for previous methods were found to be unnecessary for stable, accurate, and sensitive element-specific detection using GC-AED. Chromatographic and detection parameters such as stationary phase type, stationary phase film thickness, GC column dimensions, helium mobile phase column head pressure, detector makeup gas flow rate, and detector reagent gas type and flow rate were found to significantly affect analyte response. The detection limit for the optimized GC-AED conditions was 0.8 pg (0.1 pg/s) of methylmercury chloride (as mercury). A solid-liquid extraction procedure with preparative gel permeation chromatography cleanup and GC-AED analysis was used to quantify methylmercury in a variety of complex matrix marine materials. The methylmercury quantification method was validated with four marine certified reference materials (CRMs). The method was then applied to 13 standard reference materials, CRMs, and control materials for which no certified reference values for methylmercury have been determined. Four National Institute of Standards and Technology Standard Reference Materials and one control material, which were analyzed using the GC-AED method, were also analyzed by two other laboratories using independent methods to further validate the method.

Preparative gas chromatography of volatile metal compounds-I Separation of aluminium, chromium and iron beta-diketonates.

The analytical gas chromatography of a range of fluorinated and unfluorinated beta-diketonates of aluminium, chromium and iron has been studied m detail and conditions have been established for their complete separation; the complexes of trifluoroacetylpivaloylmethane show the best characteristics for this purpose. A range of liquid phases and column conditions have been considered and Apiezon substrates have been shown to give optimal resolution. The technique has been extended to a preparative scale with up to 0.1-g chelate samples, and the efficiency of the process demonstrated by the removal of 2% proportions of two metal complexes from a sample of the third. Implications of the technique for the purification of metals are discussed.

Adsorption and displacement effects in the gas-chromatography of metal beta-diketonates.

A detailed study of the gas chromatography of the aluminium(III), chromium(III) and iron(III) beta-diketonates has shown that their elution and separation characteristics arise from a number of adsorptive effects. Conditions of optimal peak shape for individual compounds are established by varying Chromatographie parameters, and the adsorption of one metal chelate on a column and its subsequent displacement by another chelate are investigated. The chromatography of iron(III) beta-diketonates is seen to be further complicated by gradual elution of a portion of the chelate before the rest of the sample.