Interleukin-1 beta (IL-1 beta) induces thrombocytosis in mice: possible implication of IL-6

We administered recombinant human interleukin-1 beta (IL-1 beta), the common mediator of inflammation process, to C57B1/6 male mice (0.5 microgram, every 12 hours over five times) intraperitoneally and consequently induced a remarkable thrombocytosis. Day 1 was designated as the following day of the last injection in the morning. A significant thrombocytosis was observed on days 1 through 5 with a peak on day 2 (162 +/- 9 x 10(4)/mm3) compared with the control mice injected with heated IL-1 beta (101 +/- 11 x 10(4)/mm3). A striking increase in mean size of marrow megakaryocytes was noted on days 1 and 2. The incorporation of 75Se-selenomethionine into circulating platelets as a measure of platelet production was about 2.3 times higher in IL-1 beta-treated mice than in control mice. To determine which factor(s) is responsible for elicited thrombocytosis, the in vitro studies and bioassays for several hematopoietic factors were performed. IL-1 beta by itself did not stimulate megakaryocytopoiesis in vitro, suggesting that the thrombocytosis is attributed to other factor(s) via IL-1 beta stimulation. Serum colony-stimulating factor (CSF) activity after a single IL-1 beta (0.5 microgram) injection, monitored by colony assay with 10% tested serum, peaked at 3 hours. Formed colonies were mostly granulocyte (G) and granulocyte-macrophage (GM)-types, and studies using rabbit anti-mouse GM-CSF serum or using human marrow as target cells showed that the CSF activity of the tested serum consisted of, at least, GM-CSF and G-CSF. Addition of IL-3 concomitantly with the tested serum gave rise to a greater number of megakaryocytic colonies. Serum IL-3, monitored by IL-3-dependent cell line 32D clone 5, and erythropoietin activities were not detected at serum level in IL-1 beta-treated mice. Serum IL-6 assay by IL-6-dependent mouse hybridoma cell line MH-60.BSF2 showed high levels of the tested serum with a peak at 2.5 hours with no detection at 10 hours after the injection. Heated IL-1 beta caused an increase of neither IL-6 nor CSF activities. Our data suggest that the thrombocytosis induced by IL-1 beta is mediated by IL-6 or a combination of IL-6 and other cytokine(s), and that IL-6 may play a regulatory role in platelet production in vivo.

The effect of verapamil on the anti-tumour action of mitozantrone and doxorubicin against renal carcinoma cells in vitro

Ten renal carcinomas were established in culture and their sensitivity to mitozantrone +/- verapamil, as measured by (75Se) selenomethionine incorporation, was studied. The 5 tumours with spread beyond the kidney were those in which sensitivity to mitozantrone was enhanced by verapamil. With 4 of the 10 tumours and 1 further carcinoma, similar experiments were performed using doxorubicin. This drug was more active, its anti-tumour action being related to concentration. Verapamil was more effective in potentiation of doxorubicin and this action increased in proportion to the concentration of verapamil added.

Expression, purification, and crystallization of natural and selenomethionyl recombinant ribonuclease H from Escherichia coli

Ribonuclease H (RNase H) from Escherichia coli is an endonuclease that specifically degrades the RNAs of RNA:DNA hybrids. The enzyme is a single polypeptide chain of 155 amino acid residues, of which 4 are methionines. To solve the crystallographic three-dimensional structure of E. coli RNase H by the multi-wavelength anomalous diffraction technique, we have constructed methionine auxotrophic strains of E. coli that overexpress selenomethionyl RNase H. MIC88 yields about 10 mg of selenomethionyl RNase H per liter of culture, which is comparable to the overexpression of the natural recombinant protein. We have purified both proteins to homogeneity and crystallized them isomorphously in the presence of sulfate. These are Type I crystals of space group P2(1)2(1)2(1) with the cell parameters a = 41.8 A, b = 86.4 A, c = 36.4 A, one monomer per asymmetric unit, and approximately 36% (v/v) solvent. Crystals of both proteins diffract to beyond 2-A Bragg spacings and are relatively durable in an x-ray beam. On replacement of sulfate with NaCl, crystals of natural RNase H grow as Type I' (very similar to Type I) at pH between 7.0 and 8.0; at pH 8.8, crystals of Type II are obtained in space group P2(1)2(1)2(1) with a = 44.3 A, b = 87.3 A, and c = 35.7 A. Type II crystals can be converted to Type I by soaking in phosphate buffer. RNase H crystals of Type II have also been reported by Kanaya et al. (Kanaya, S., Kohara, A., Miyakawa, M., Matsuzaki, T., Morikawa, K., and Ikehara, M. (1989) J. Biol. Chem. 264, 11546-11549).

Biosynthesis of selenium-modified tRNAs in Methanococcus vannielii

Selenium-containing nucleosides are natural components of several tRNA species in Methanococcus vannielii. In the present study, the incorporation of selenium from 75SeO3(2-) into these macromolecules was investigated in sonic extracts of M. vannielii. Nucleoside analysis of the 75Se-labeled tRNAs from these in vitro reaction mixtures demonstrated that the selenium was present in 75Se-labeled nucleosides identical to the two naturally occurring 2-selenouridines produced in vivo. Incorporation of selenium into these nucleosides was ATP-dependent and was maximal after 20 min. Addition of O-acetylserine enhanced the activity 2- to 3-fold, implicating a role for selenocysteine in the reaction. Added L-selenocysteine could function as a selenium donor, but the D isomer and DL-selenomethionine were inactive. RPC-5 chromatography of bulk tRNA isolated from M. vannielii grown on 75SeO3(2-) separated five major species of seleno-tRNAs. The amino acid-accepting activity of these tRNAs was investigated.

Selenium utilization in humans--a long-term, self-labeling experiment with stable isotopes

A stable (nonradioactive) isotope of selenium in a chemical form common in foods (selenomethionine) or inorganic selenite was taken orally (200 micrograms/d) for 3 wk to label deep body pools. By deep body pools we mean selenium compartments that are large and/or have a slow turnover (exchange) rate. Blood plasma was removed, stored for 11 mo, and later reinfused as a labeled tracer dose with the selenium label in all of the biologically significant chemical forms. Accessible tissues such as red blood cells were highly labeled (20-25%) in the subjects receiving selenomethionine. Selenium from deep body pools is excreted primarily via the urine (80%). Reexcretion of previously absorbed selenium back into the gastrointestinal tract can be measured, avoiding a major source of error in conventional balance studies used to estimate nutrient absorption.

Metabolism of selenite and selenomethionine in the rhesus monkey

Female rhesus monkeys were fed a commercial monkey diet and given selenium (Se) as either selenite or selenomethionine (SeMet) in the drinking water for 11 mo. Muscle and liver biopsies were taken initially and at the end of the experiment for determination of Se levels and glutathione peroxidase (GPX) activity. Blood was collected at monthly to bimonthly intervals, and the plasma and erythrocytes were subjected to gel filtration to determine the distribution of Se among proteins of various molecular weights. At the end of the experiment, there was significantly more Se in liver, muscle and hair from the monkeys given SeMet than in tissues from those given selenite, but there were no differences in liver or muscle GPX activity between the two treatment groups. The erythrocyte and plasma Se levels were significantly higher in the monkeys given SeMet than in those receiving selenite, but there were no differences in the GPX levels between these groups. About 68% of erythrocyte Se was associated with GPX in monkeys given selenite whereas only 34% was associated with GPX in those administered SeMet. The correlation coefficient for blood Se level and erythrocyte GPX activity was 0.92 in monkeys given selenite but only 0.37 in those given SeMet. Gel filtration of plasma revealed only one Se peak for plasma from the monkeys given selenite but at least two major Se peaks for plasma from monkeys receiving SeMet. The possible implications of these results for humans are discussed, including the reasons for poor correlations of GPX activity and blood Se levels.

Selenomethionyl proteins produced for analysis by multiwavelength anomalous diffraction (MAD): a vehicle for direct determination of three-dimensional structure

An expression system has been established for the incorporation of selenomethionine into recombinant proteins produced from plasmids in Escherichia coli. Replacement of methionine by selenomethionine is demonstrated at the level of 100% for both T4 and E. coli thioredoxins. The natural recombinant proteins and the selenomethionyl variants of both thioredoxins crystallize isomorphously. Anomalous scattering factors were deduced from synchrotron X-ray absorption measurements of crystals of the selenomethionyl proteins. Taken with reference to experience in the structural analysis of selenobiotinyl streptavidin by the method of multiwavelength anomalous diffraction (MAD), these data indicate that recombinant selenomethionyl proteins analyzed by MAD phasing offer a rather general means for the elucidation of atomic structures.

Contribution of hepatic fibronectin synthesis to regulation of plasma fibronectin

Intravenous injection of gelatinized particles, which are phagocytized by the reticuloendothelial system, elicits an acute depletion of plasma fibronectin followed by restoration to normal concentrations in 6-8 h and a rebound elevation at 24 h. We determined the contribution of hepatic fibronectin synthesis to the restoration of plasma fibronectin in rats after particle infusion by measuring the net incorporation of 75selenomethionine into plasma fibronectin during the recovery period. Rats injected intravenously with gelatinized particles had a greater (P less than 0.01) incorporation of labeled 75selenomethionine into fibronectin but less (P less than 0.05) incorporation of 75selenomethionine into total plasma protein than control rats. Inhibition (86%) of hepatic fibronectin synthesis by pretreatment with cycloheximide limited the recovery of fibronectin levels by only 60%, suggesting a source(s) other than hepatic synthesis may contribute to the restoration of plasma fibronectin. Using purified human plasma fibronectin as a tracer in the plasma pool, we found that 26% of the soluble fibronectin consumed from the plasma during particle clearance was subsequently released back into the plasma over a 4-h interval. Tissue analysis indicated that 125I-labeled fibronectin, which was previously incorporated into the tissues, was not released from the tissue pool after the injection of gelatinized particles. Thus the normalization and regulation of plasma fibronectin levels after its acute depletion due to blood-borne particles is a result of 1) an increase in hepatic synthesis of fibronectin, 2) the release of fibronectin previously consumed as an opsonin during particle clearance, and 3) the release of soluble intact fibronectin from a preformed storage pool.

Radiolabeling of infective third-stage larvae of Strongyloides stercoralis by feeding [75 Se]selenomethionine-labeled Escherichia coli to first- and second-stage larvae

A technique is described for radiolabeling Strongyloides stercoralis larvae with [75Se]selenomethionine. Cultures of an auxotrophic methionine-dependent stain of Escherichia coli were grown in a medium containing Dulbecco's modified Eagle's medium supplemented with 5% nutrient broth, amino acids, and [75Se]selenomethionine. When the 75Se-labeled bacterial populations were in the stationary phase of growth, cultures were harvested and the bacteria dispersed on agar plates to serve as food for S. stercoralis larvae. Use of nondividing bacteria is important for successful labeling because the isotope is not diluted by cell division and death of larvae attributable to overgrowth by bacteria is prevented. First-stage S. stercoralis larvae were recovered from feces of infected dogs and reared in humid air at 30 C on agar plates seeded with bacteria. After 7 days, infective third-stage larvae were harvested. The mean specific activity of 6 different batches of larvae ranged from 75 to 330 counts per min/larva with 91.8 +/- 9.5% of the population labeled sufficiently to produce an autoradiographic focus during a practicable, 6-wk period of exposure. Labeled infective larvae penetrated the skin of 10-day-old puppies and migrated to the small intestine, where the developed to adulthood.

Strongyloides stercoralis: is there a canonical migratory route through the host?

It is generally accepted that the skin-penetrating larvae of Strongyloides stercoralis travel from the skin to the intestinal habitat of the adult stage by an obligatory migratory route that includes the blood, lungs, trachea, and upper gastrointestinal tract in sequence (the pulmonary route). It is assumed, furthermore, that following autoinfective invasion of the bowel wall, S. stercoralis larvae follow this same route to return to the small intestine where they mature. We reexamined the parasite's migratory behavior using a canine isolate of S. stercoralis, specific-pathogen-free pups, radiolabeled larvae, and compressed tissue autoradiography. Compartmental analysis of the number of larvae found in the organ sets examined revealed no reason to reject the simple idea that the pulmonary route was just one of several possible pathways to the duodenum. This was true whether the larvae began their journey in the subcutaneous tissue of the inguinal area or in the distal part of the ileum. Direct sampling of the larvae traversing the trachea indicated that the number of larvae reaching the duodenum by way of the presumptive pulmonary route was insufficient to account for the estimated absolute number actually found there.

Influence of dietary methionine on the metabolism of selenomethionine in rats

To determine the influence of methionine on selenomethionine (SeMet) metabolism, weanling male rats were fed for 8 wk a basal diet marginally deficient in sulfur amino acids, containing 2.0 micrograms selenium (Se)/g as DL-SeMet and supplemented with 0, 0.3, 0.6 or 1.2% DL-methionine. Increased dietary methionine caused decreased selenium deposition in all tissues examined but increased glutathione peroxidase (GSHPx, EC 1.11.1.9) activity in testes, liver and lungs. A positive correlation was found between dietary methionine and the calculated percentage of selenium associated with GSHPx. In a second experiment, 75SeMet was injected into weanling male rats which had been fed the basal diet containing 2.0 micrograms selenium as DL-SeMet with or without the addition of 1.0% methionine. The selenoamino acid content of tissues and the distribution of 75Se in erythrocyte proteins were determined. In comparison to the rats fed the basal diet without added methionine, significantly more 75Se-selenocysteine was found in liver and muscle, more 75Se was found in erythrocyte GSHPx and less 75Se was found in erythrocyte hemoglobin of rats fed 1.0% methionine. These data suggest that methionine diverts SeMet from incorporation into general proteins and enhances its conversion to selenocysteine for specific selenium-requiring proteins, such as GSHPx.

Testing the chemosensitivity of renal carcinoma in vitro

Tumour cells from 23 renal carcinomas were exposed in vitro to increasing concentrations of medroxyprogesterone acetate (MPA) or one of several cytotoxic agents. Thereafter the uptake of 75Selenomethionine (75SeM) was compared to that of tumour cells not exposed to the drug. Using drug concentrations similar to those seen following in vivo administration in patients, MPA produced greater than or equal to 50% inhibition of 75SeM uptake in 5 of 23 cases. The comparable proportion for doxorubicin was 4 of 5 and for mitozantrone 7 of 12. Methotrexate and Vinblastine were much less effective. In all cases where greater than or equal to 50% inhibition was obtained with doxorubicin and mitozantrone the carcinoma had spread beyond the kidney. Thus drug sensitivity may be associated with a high mitotic rate.

Transport of selenoamino acids and their sulfur analogues across the intestinal brush border membrane of pigs

Transport of selenomethionine (Se-Met) and its sulfur analogue, methionine (Met), across the pig jejunal brush border membrane (BBM) was investigated using isolated BBM vesicles. Experiments were also performed to gain insight into the transport mechanism(s) for selenocystine. Se-Met as well as Met were transported by a single, Na+-dependent, carrier-mediated process common for both amino acids. Evaluation of the kinetic parameters revealed no differences between Se-Met and Met in the maximal transport velocity (Vmax) or in the Michaelis constant (Km). Furthermore, transport of Se-Met and Met showed similar characteristics with respect to electrogenicity and substrate specificity. In addition, evidence was obtained for a competitive inhibition of cystine transport across the BBM by selenocystine and basic amino acids.

Interaction between secretin and a cholecystokinin-like peptide on pancreatic protein secretion and synthesis in the rat

The effects of secretin and a cholecystokinin-like peptide alone and in combination on pancreatic protein secretion and synthesis were examined in anesthetized rats. L-[75Se]selenomethionine was given as an i.v. shot (5 microCi) followed by a continuous infusion (1 microCi/h). Pancreatic juice was collected basally for 1 h and then during a 4-h i.v. infusion of 0.5, 2.5, and 12.5 micrograms/kg/h of Thr28Nle31CCK25-33 (CCK-LP) alone or combined with 5 micrograms/kg/h of secretin, as well as during an infusion of secretin alone. The protein-bound radioactivity in pancreatic juice was taken to indicate secretion of newly synthesized proteins. The free and protein-bound radioactivity remaining in the gland after 2 h of stimulation was also investigated. Secretin alone slightly increased both protein secretion and secretion of newly synthesized proteins. Considerably greater effects were found with CCK-LP. The two lowest doses behaved similarly, whereas the volume and protein responses to 12.5 micrograms/kg/h were significantly lower and associated with large amounts of free radioactivity in pancreatic juice, suggesting leakage and cell damage. The addition of secretin transiently potentiated protein discharge and secretion of newly synthesized proteins and permanently increased the amount of protein-bound radioactivity per milligram of protein in response to all doses of CCK-LP. Secretin markedly increased volume and reduced the amount of free radioactivity in pancreatic juice with the largest dose of CCK-LP. The peptides were not found to influence amino acid uptake or incorporation of radioactivity into tissue proteins. This study demonstrates an interaction between the effects of secretin and those of CCK-LP on pancreatic protein secretion and synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of recombinant human erythropoietin on megakaryocytes and on platelet production in the rat

The contention that erythropoietin (Epo) affects platelet production was investigated in the rat with recombinant human Epo (rHuEpo). In normal rats, Epo caused a dose-dependent increase in both reticulocyte and platelet numbers, the reticulocyte response preceding that of platelets. Withdrawal of Epo resulted in reticulocytes and platelets returning to control levels. [75Se]-selenomethionine incorporation into platelets was also enhanced in response to Epo. Chronic daily administration of rHuEpo resulted in steady state erythrocyte levels after 12 to 14 days, which were elevated 20% above controls. Attainment of this steady state was associated with both reticulocytes and platelets returning to control levels despite continued administration of Epo, an effect not associated with a change in the half-life of circulating Epo. In polycythemic rats a platelet response was observed before an effect on reticulocytes. Erythropoietin caused a 2.4-fold increase in the frequency of small acetylcholinesterase-positive cells within 24 hours, and increased the mean megakaryocyte diameter within 48 hours. Furthermore, the [3H]-thymidine labeling index of megakaryocytes from rats treated for 24 hours with rHuEpo was increased for all stages of megakaryocyte maturation. These results support the proposal of an effect of Epo on rat megakaryocytes causing increased platelet production.

Effects of various dietary levels of selenium as selenite or selenomethionine on tissue selenium levels and glutathione peroxidase activity in rats

Weanling rats were fed a basal diet or this diet plus 0.2, 1.0, 2.0 or 4.0 mg/kg selenium (Se) as either selenite or selenomethionine (SeM). Except at the 0.2 mg/kg Se level, Se accumulated in all tissues at higher levels when SeM was fed than when selenite was given, and the magnitude of difference became more pronounced with increasing levels of dietary Se. This was particularly true for muscle and brain. Se levels in whole blood, testes, kidney and lungs were not significantly different between rats fed 0.2 mg/kg Se as selenite or as SeM, but the Se levels in liver, muscle and brain were higher in rats fed SeM. Although the tissue Se concentrations differed markedly, there were no differences in the glutathione peroxidase (GPX) activity in tissues of rats fed SeM rather than selenite. The percentage of Se associated with GPX was lower in all tissues from rats fed SeM than in those from rats fed selenite. These results indicate that the chemical forms of dietary Se can have a marked influence on biological responses, including bioavailability of dietary Se.

Differential effect of dietary methionine on the biopotency of selenomethionine and selenite in cancer chemoprevention

The influence of a low methionine intake on the chemopreventive efficacy of selenomethionine versus selenite was compared in the 7,12-dimethylbenz[a]anthracene-induced mammary tumor model in rats. Animals were fed from weaning a purified 20% casein diet with or without 0.3% methionine supplementation. Selenomethionine or selenite, at a final concentration of 3 ppm of selenium (Se), was added to the diet starting 5 days after DMBA administration. Control rats continued to receive the basal diets which contained 0.1 ppm of Se. Results of the carcinogenesis experiment indicated that suboptimal dietary methionine significantly reduced the protective effect of selenomethionine in cancer prevention. In contrast, the efficacy of selenite was not affected. In rats given 3 ppm of selenomethionine, tissue Se was actually higher in those fed a diet with a suboptimal amount of methionine than in those with an adequate intake of methionine. On the other hand, dietary methionine did not influence the level of tissue Se in animals given selenite. An increase of dietary methionine to 0.6% did not enhance the efficacy of selenomethionine in cancer protection but would allow the use of a higher level of selenite without the accompanying adverse effects. The biological significance of Se utilization under suboptimal or adequate methionine intake was also assessed using the glutathione peroxidase assay in the liver of Se-deficient rats given graded levels of Se as either selenite or selenomethionine. The enzyme study demonstrated that low dietary methionine decreased the nutritional biopotency of selenomethionine in restoring glutathione peroxidase activity but not that of selenite. These experiments suggest that adequate methionine intake is required for the utilization of selenomethionine for nutritional and anticarcinogenic purposes.

Effect of dietary methionine on utilization of tissue selenium from dietary selenomethionine for glutathione peroxidase in the rat

To study the effect of dietary methionine on the bioavailability of Se from selenomethionine ([Se]Met), weanling rats were first loaded with Se by feeding 0.5 mg Se as [Se]Met per kg diet of a low methionine (0.17% by analysis) torula yeast-based diet for 21 d, and then were fed an Se-deficient diet (less than 0.02 mg Se/kg) supplemented with 0, 0.4 or 0.9% methionine for 28 d. Plasma, liver and muscle Se increased 2.6-, 2.5- and 2.2-fold, respectively, during [Se]Met supplementation, and then the tissue Se declined exponentially during the Se-deficient diet period. Plasma, liver and muscle glutathione peroxidase (GSH-Px) activities decreased 43-50% during the [Se]Met supplementation period in spite of the increase in tissue Se. When these [Se]Met-loaded rats were fed the Se-deficient diet and supplemented with methionine, tissue GSH-Px activities increased significantly within 3 to 7 d, but then decreased for the remainder of the experiment. Calculation of the percentage of tissue Se present as Se in GSH-Px indicated that substantial Se from dietary [Se]Met was stored in tissues in a form different from GSH-Px when a low methionine diet was fed. These results indicate that the dietary methionine level can modulate the availability of Se from dietary [Se]Met and from stored tissue [Se]Met; the inability of stored [Se]Met to provide Se for GSH-Px synthesis over a prolonged period of time suggests that [Se]Met may not be an optimum form for Se supplementation.

The two faces of selenium

The nutritionally important trace elements share a high biological activity, implemented through association with enzymes, hormones or vitamins. The same activity responsible for physiological responses at extremely low dietary levels implies the potential for metabolic upset when the elements are ingested at elevated, although still relatively low levels. Selenium provides a classic example of this dichotomy of effects and has generated concerns at both ends of its supply spectrum. Experiences in the Dakotas, mid-19th century, led to identification of toxicity symptoms for which selenium was later shown to be responsible, while separate studies showed that excess selenium was teratogenic in the developing avian fetus. These toxic reactions suggested that selenium might be useful in restricting abnormal cell growth, and recent studies have proved it to be anticarcinogenic in certain specific circumstances. Investigation of selenium's nutrient function has been equally interesting, and when Schwarz showed it to be an essential nutrient in 1957, he began an era of intense research activity. Dietary levels of selenium below 0.02 ppm were found to cause deficiency symptoms affecting muscles, liver and pancreas and glutathione peroxidase was shown to be an active form through which selenium acted to prevent such aberrations. Research continues to seek other active organic combinations for selenium to identify interfering compounds that restrict its bioactivity and to explore biochemical mechanisms involved in its toxicity.

Selenium-mercury interaction during intestinal absorption of 75Se compounds in chicks

The effects of inorganic (HgCl2) and organic (CH3HgCl) mercury on the intestinal absorption of Se compounds [Na2(75)SeO3, Na2(75)SeO4, L-[75Se]methionine ([75Se]Met)] were determined in 3-wk-old White Leghorn cockerels by the in vivo ligated duodenal loop procedure. The intraduodenal dose contained 0.05 microCi 75Se, 0.01 mM Se, 150 mM NaCl and 0-1.0 mM Hg. In the presence of 1 mM inorganic Hg in the intraduodenal dose, the absorption of the inorganic 75Se compounds was only about 65% of that in the control group, whereas only a slight inhibitory effect on [75Se]Met absorption was observed. Methylmercury had no effect on [75Se]selenite absorption. Precipitation of the 75Se-selenite in the intestinal lumen partly explained the direct interaction between inorganic Hg and Se compounds. Absorption of [75Se]Met and [75Se]selenite was also determined in chicks fed after hatching a purified diet supplemented with varying amounts of Hg (0-500 mg/kg) and Se (0-4 mg/kg). Dietary Hg significantly reduced the transfer of [75Se]selenite to body by enhancing the accumulation of the isotope in the intestinal tissue. Dietary Hg did not affect the absorption of [75Se]Met, but altered the whole-body distribution of this Se compound. Because interaction between Se and Hg was observed mainly between the inorganic compounds and with use of a manyfold excess of Hg over Se, the data suggest that intestinal interaction between these metals is not of great nutritional importance.

Metabolism of selenomethionine and effects of interacting compounds by mammalian cells in culture

Since differences have been found in animals, the efficacies of selenomethionine (SeMet), selenite, and selenocystine (SeCys) for glutathione peroxidase (GPx) induction and cellular incorporation were compared and some effects of interacting nutrients on SeMet utilization were examined in tissue cultures. In three cell lines, Chang liver cells, mouse myoblasts and human fibroblasts, selenite was more effective than SeMet for GPx induction. However, radiotracer studies showed that SeMet was more rapidly incorporated into all cells than either selenite or SeCys. Chromatography of acid hydrolysates of Chang liver cells grown with 75Se-labeled SeMet indicated that approximately 90% of incorporated 75Se remained as SeMet, and less than 10% was as SeCys, the form of Se in GPx. Selenite supplementation slightly reduced both the incorporation of 75SeMet and the proportion of cellular 75Se recoverable as SeCys in Chang liver cells. Supplementation with L-methionine, however, significantly reduced 75SeMet incorporation, but significantly increased the proportion of cellular 75Se recovered as SeCys. L-cystine supplementation had no effect on either the cellular incorporation of 75SeMet or the proportion of cellular 75Se recovered as SeCys. These studies of SeMet utilization and effects of interacting nutrients are reflective of observations on SeMet metabolism in whole animals and humans.