Progress 11/15/03 to 11/14/06
Outputs
Broccoli, Mung bean and onion sprouts were enriched in Se using hydroponic medium supplemented with up to 0.127 mM sodium selenite with no compromise in weight gain over a 5 to 7-day germination period. Sprouts were enriched more than 100-fold (12-58 ppm compared to 0.1 ppm dry wt basis for controls). Onion tolerated 1.27 mM Se and was enriched 1000-fold in Se. When Se-enriched sprouts were cultivated into mature plants, absolute levels of Se declined presumably by Se-volatilization through normal plant metabolism. Analysis of assimilated Se revealed that about 60% Se was extractable into aqueous-alcohol for broccoli and Mung bean sprouts, whereas only 20% Se was extractable in Se-enriched onion sprouts. Dialysis of the residue yielded from extraction revealed that less than 10% Se was associated with polymeric material (protein and polysaccharides). Thus, most Se accumulated in sprouts as low molecular weight material. Se enrichment of broccoli sprouts for 5 days led
to the accumulation of Se in fractions containing MeSeCys and Glu-MeSeCys. While Se enrichment did not lead to a net enhancement of quinone reductase (NQO1, a biomarker for phase II enzyme induction) inducing activity of sprout extracts, a shift in potencies among the isolated fractions, especially to those containing Glu-MeSeCys was observed. Thus, Se enrichment modulated the source of this bioactivity among metabolites. Little evidence was obtained for Se becoming enriched in glucosinolates and related metabolites. For onion sprouts, enrichment in 1.27 mM Se for 7 days prompted Se accumulation in the amino acid and peptide pools. Extracts from Se-sprouts did not enhance NQO1 inducing capacity over extracts from control onion sprouts. However, fractions containing Glu-MeSeCys in Se-sprouts exhibited elevated NQO1 inducing capacities. It was concluded that much of the accumulated Se in onion sprouts may exist as inorganic forms; longer germination periods may be required to assimilate
Se into the organo-Se pool. Mung bean sprouts germinated for 5 days in 0.127 mM Se was not accompanied by a net enhancement of NQO1 inducing capacity, even though Se accumulated in peptide pools containing Glu-MeSeCys or MeSeCys. Mung bean retained the greatest abundance of Se upon cultivation into mature plants relative to broccoli and onion sprouts. Although Se mostly accumulated as low molecular weight components in all sprouts, much of Se may be comprised of inorganic (salt) forms in Se-sprouts. A longer propagation period may allow greater assimilation into the organo-Se pool. Based on the maximum degrees of Se enrichment for broccoli and onion sprouts, daily consumption of 70-250 g fresh sprouts could provide 200-400 micrograms of dietary Se. Future work should place focus on the temporal patterns of Se uptake, changes in bioactivity and Se speciation in sprouts over an extended period of germination. Sprouts pose advantages over mature plants as vehicles for delivering luxus
levels of dietary Se for cancer chemoprevention, as sprouts tolerated greater Se levels in cultivation than mature plants have been reported to tolerate.
Impacts
Luxus Se in the diet is believed to enhance human health by immune system modulation and reducing risk of cancer. In this study, broccoli, Mung bean and onion sprouts were shown to be subject to Se-biofortification by 100-fold over non-selenized sprouts. These three vegetables represent the respective families of Brassicaceae, Fabaceae and Alliaceae plants. The feature they have in common is that they accumulate MeCys and Glu-MeCys, which comprise non-protein amino acid/peptide pools where Se can accumulate; Se assimilates into these species as MeSeCys and Glu-MeSeCys, the preferable organo-Se forms for promotion of human health. Although these three vegetable sprouts were specifically studied, it is reasonable to expect that other members of these families that also accumulate MeCys and Glu-MeCys will be amenable to Se-biofortification. Assimilated Se in sprouts was diminished during propagation into mature plants. This, plus the observation that sprouts can tolerate
greater Se levels in growth/germination media, favors the use of Se-sprouts over mature vegetables for Se-biofortification. Furthermore, propagation of Se-sprouts can be easily achieved in contained environments, avoiding the risk (toxicity) of cultivating Se-enriched plants in the soil or environment. While Se-enrichment did not lead to a net increase in phase II enzyme inducing activity in vitro, it is reasonable to expect that other health-promoting effects that were not examined in this study were elevated by Se-biofortification.
Publications
- Xiao, H. and Parkin, K.L. (2006). Phase II enzyme induction by various selenium and sulfur compounds. Nutrition and Cancer 55(2):210-223.
- Arscott, S. (2006). Novel strategies for the selenium-biofortification of vegetables as dietary vehicles for chemopreventive compounds. M.S. thesis, University of Wisconsin-Madison.
- Wijaya, D. (2006). Selenium-enriched vegetable sprouts as dietary vehicles for delivering cancer chemopreventive benefits. M.S. thesis, University of Wisconsin-Madison.
- Xiao, H. (2004). Identification of bioactive agents from green onion (Allium spp.) and organoselenium compounds with cancer chemopreventive potential. Ph.D. dissertation, University of Wisconsin-Madison.
|
Progress 01/01/05 to 12/31/05
Outputs
Seeds of onion, broccoli and Mung bean were each germinated in water and compared to individual treatments of water supplemented with 127 uM Se and 1270 uM Se. Relative to respective controls, weight gain (growth) in the Mung bean and broccoli sprouts (in order of sensitivity) were compromised by the 1270 uM Se treatments, whereas onion sprouts could tolerate this level of Se in the sprouting medium with no compromise in weight gain. Se analysis by ICP-MS revealed about 100-fold and 1000-fold enrichments in Se (dry matter basis) when sprouting occurred in the 127 uM Se and 1270 uM Se supplemented medium, respectively, for all plant species. Thus, as sprouts, onion appears to have greater capacity for supplementation with Se than Mung bean and broccoli. However, all species can be efficiently supplemented by 100-fold Se. Solvent fractionation of dry matter into an isoluble residue (containing protein), glucosinolate pool (GP) and non-protein amino acid pool (PP) was
conducted to determine the fate of Se assimilation and affects on quinone reducatase (QR)-inducing bioactivity in Hepa 1c1c7 cells. Both GP and PP were separated into 4 sub-fractions. For broccoli sprouts water-imbibed controls contained 0.2 ppm Se (dry wt. basis) and only GP1 had detectable Se while GP4 (glucosinolate sub-fraction) had no detectable Se. For the PP only PP1 (containing S-alkyl-cysteine sulfoxides, ACSO) contained detectable Se. In 127 mM Se-supplemented sprouts, Se in the dry matter was enriched to 17 ppm (85-fold over controls). Se was observed in GP2>GP1>GP4 with none in GP3, with a total enrichment over controls in the GP fractions of 40-fold. Se was only observed in the PP in PP1 (about 12-fold that of control PP1 sub-fraction). The insoluble residue (protein) was also enriched in Se by about 40-fold over controls. Thus, Se supplementation enhanced Se enrichment in all metabolic pools assessed by a similar order of magnitude. QR inducing potency was quantified on
the basis of what level of isolate was capable of doubling QR specific activity, estimated as a CD value, with lower CD values meaning proportionally greater potency. The most potent isolates obtained from the control broccoli sprouts were GP3 (CD value of 24 ppm) and PP2 and PP3 (with CD values of <0.2-0.3 ppm). For isolates prepared from Se-supplemented broccoli, a shift in potency to the GP2 fraction (CD value of 21 ppm) was observed, at the expense of some inducing power of GP3 (CD value of 62 ppm). For the PP sub-fractions, a shift in greatest potency to PP3 and PP4 (<0.2-0.3 ppm) at the expense of >10-fold less QR inducing power in PP2 (CD value of 28 ppm) was observed. Thus, while it is clear that Se enrichment occurred in the GP and PP pools, a correlation between the association of Se enrichment and bioactivity in the sub-fractions of these pools did not exist. These results show that Se supplementation is elevating both Se content and bioactivity by altering the metabolite
pools, in a way that bioactivity is becoming enriched in some pools while being diminished in others.
Impacts
This project is examining the means to enrich specific plant foods in selenium, an essential micronutrient for humans. Consumption of selenium-enriched plant foods, especially where selenium occurs in certain forms, has potential to improve public health in terms of reduction of cancer risk and enhancement of the immune system.
Publications
- No publications reported this period
|
Progress 01/01/04 to 12/31/04
Outputs
Attempts to supplement plants with selenium were initiated by preparing 5-8 day old sprouts germinated in an aqueous medium containing up to 127 mM selenium. Sprouts were prepared from seeds of onion, broccoli and mung bean, representing one member from each of the three plant families to be examined in this project. All sprouts could tolerate growth media containing 1.27 mM selenium, as indicated by similar rates of biomass increase and high degrees of germination as controls grown in the absence of selenium. At 12.7 mM and greater selenium levels, sprout viability was progressively compromised, both in terms of biomass and germination rate. Onion sprouts appeared to be somewhat more tolerant to high selenium levels than the mung bean and broccoli sprouts. Sprout germination protocols have been modified to afford scale-up to produce sufficient material to analyze and also to be reflective of commercial practice. At the 12.7 mM selenium level of supplementation of the
growth medium, tissue selenium contents reached 14-26 microgram Se/gdw, compared with 0.36 microgram Se/gdw for water-germinated (control) samples, representing almost two orders of magnitude enrichment. The fluorometric and ICP-MS methods for selenium analysis were generally corroborative in this regard, with the fluorometric analysis giving greater estimates. The fluorometric method is being modified to reduce interferences that are believed to yield overestimates of selenium content. Methods have been adopted for isolating glucosinolate pools (recovery >95% using sinigrin as a standard) from tissue using solid-phase extraction (SPE) and analyzing total glucosinolate content by a colorimetric method. An HPLC protocol has also been adopted for the purposes of profiling glucosinolates in tissue extracts if it is judged necessary in future studies. Protocols are currently being adopted for isolating the non-protein amino acids pools that are expected to be potential sinks for selenium
enrichment, using previously published methods. Once these methods are adopted into routine use, larger scale studies will commence on scaling-up selenium supplementation in sprouts, determine the fate of assimilated selenium, and determine what impact modulation of metabolic pools in selenium content has on in vitro cancer chemopreventive activities. A study was completed on the evaluation of over 40 organoselenium and related organosulfur compounds for the ability to induce quinone reductase (QR) activity in vitro as a marker for phase II enzyme induction. Seventeen organoselenium compounds could double QR specific activity in the bioassay. Of the eleven most potent QR inducers, nine were putative selenol-generating compounds with the ability to double QR activity at levels ranging from 0.2 to 150 microM. Comparatively, the Se-methylselenocysteine derivative which is expected to become enriched in selenium-supplemented sprouts/plants was capable of doubling QR activity in the
bioassay at 350 microM.
Impacts
Identifying which edible plant species are subject to enrichment in selenium, in a manner that improves health-promoting effects, will afford new dietary interventions for reducing disease risk. Depending on how selenium is assimilated into the various metabolic pools/sinks that exist in sprouts and/or mature plants, food processing interventions may be of further utility in enhancing health-promoting activities in selenium-supplemented vegetables.
Publications
- Xiao, H.. (2004). Identification of bioactive agents from green onion (Allium spp.) and organoselenium compounds with cancer chemopreventive potential. Ph.D. dissertation, University of Wisconsin-Madison, 338 p.
|
|