Differential effects of doses and forms of dietary selenium on immune cell numbers in the skin of ultraviolet-irradiated and unirradiated mice.

The effect of three different doses of dietary L-selenomethionine (SM) and sodium selenite (SS) on skin selenium (Se) content, glutathione peroxidase (GPx) activity, Langerhans cell (LC) and mast cell numbers in ultraviolet radiation-B (UVB)-irradiated and unirradiated C3H/HeN mice was determined. After weaning, groups of mice were given Se-deficient, Se-adequate, or Se-high diets. Six weeks later, some animals in each group were exposed to a single UVB dose (acute), while others were exposed three times weekly for the following 40 weeks (chronic). The skin Se content and GPx activity increased in all the Se-supplemented groups, and the latter was not altered by UVB exposure. Generally, the Se-containing diets caused an increase in LC numbers at 6 weeks and a further rise at 40 weeks, but did not prevent the loss induced by acute or chronic UVB radiation. Skin mast cell numbers were highest in animals fed the Se-deficient diet after 6 and 40 weeks. Acute and chronic UVB radiation decreased the mast cell number and dietary Se did not prevent the reduction. While the present study shows that Se plays an important role in governing the number of LCs and mast cells in the skin, no protective effect against the immunomodulating properties of UVB radiation on these cell types was observed. However, this conclusion may only apply to the experimental conditions chosen, and additional studies at different Se dosages and reduced intensities of chronic UVB exposure are required to confirm the results.

Sulforaphane, erucin, and iberin up-regulate thioredoxin reductase 1 expression in human MCF-7 cells.

Isothiocyanates (ITCs) found in cruciferous vegetables are potentially important anticarcinogenic phytochemicals for many types of cancers including breast cancer. In this study, we have shown that three isothiocyanates, sulforaphane, erucin, and iberin, are potent inducers of thioredoxin reductase 1 (TrxR1) in human breast cancer MCF-7 cells. Sulforaphane, erucin, and iberin at 1 microM induce TrxR1 mRNA 2-3-fold within 8 h of treatment, and induce mRNA 5-7-fold with 12 microM ITC treatments. Selenium did not affect sulforaphane-induced TrxR1 mRNA levels, but significantly enhanced both TrxR1 protein expression (up to 9-fold in erucin treatment) and corresponding activities. These results suggest that dietary ITCs are important factors in the regulation of redox status through the induction of the selenoprotein thioredoxin reductase.

Comparison of bioenergetic activity of primary porcine hepatocytes cultured in four different media.

Primary hepatocytes have extensively been used in biochemical, pharmacological, and physiological research. Recently, primary porcine hepatocytes have been regarded as the cells of choice for bioartificial liver support systems. The optimum culture medium for hepatocytes to be used in such devices has yet to be defined. In this study we investigated the effectiveness of four culture media in driving energy metabolism of primary porcine hepatocytes. The media selected were William's E medium, medium 1640, medium 199, and hepatocyte medium. Cells (3 x 10(10); viability 87 +/- 6%) were isolated from weanling piglets and seeded on 90-mm plates in the above media supplemented with antibiotics and hormones at a density of 8 x 10(6) viable cells per plate. Using 1H NMR spectroscopy we looked at indices of glycolysis, gluconeogenesis. ketogenesis, and ureagenesis on days 2, 4, and 6 of the experiments (n = 9). We also studied urea and albumin synthesis and total P450 content. The examined metabolic pathways of the hepatocytes were maintained by all media, although there were statistically significant differences between them. All media performed well in glycolysis, ureagenesis, and albumin synthesis. William's E medium and medium 199 outperformed the rest in gluconeogenesis. Medium 199 was best in ketogenesis. Overall, medium 199 was the best at driving energy metabolism from its constituent substrates and we think that it preferentially should be used in the culture of primary porcine hepatocytes.

Synergy between sulforaphane and selenium in the induction of thioredoxin reductase 1 requires both transcriptional and translational modulation.

Thioredoxin reductases (TrxRs) catalyse the NADPH-dependent reduction of thioredoxin and play an important role in multiple cellular events related to carcinogenesis including cell proliferation, apoptosis and cell signaling. We have used human hepatoma HepG2 cells to examine the regulation of TrxRs by isothiocyanate (sulforaphane) and selenium (Se). We show that TrxR1 mRNA, but not TrxR2 mRNA, is induced up to 4-fold by sulforaphane, and this increase was abolished by actinomycin D, a transcription inhibitor. Se, in the form of sodium selenite, induced TrxR1 at the translational level, as shown by an increase in protein (2.1-fold) and activity (4.8-fold), but not mRNA. In combination, sulforaphane and Se synergistically induced TrxR1 protein (5.5-fold), activity (13-fold) and mRNA (6.5-fold). Although Se does not induce TrxR1 mRNA, Se can delay the degradation of sulforaphane-induced TrxR1 mRNA. Modulation of TrxR1 mRNA by sulforaphane was glutathione and protein kinase C-dependent, as L-buthionine-S,R-sulfoximine (a specific inhibitor of glutathione synthesis), and the protein kinase C inhibitor 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine, significantly reduced the induction. The combination of sulforaphane and Se also efficiently protected HepG2 cells from paraquat-induced cell death, whereas sulforaphane-only and Se-only treatments showed very little if any protective effect. These results demonstrate that synergy can result from a combination of induction at the levels of transcription and translation.