Marion F. Robinson

Long-term supplementation with selenate and selenomethionine: selenium and glutathione peroxidase (EC 1.11.1.9) in blood components of New Zealand women.

Thirty-three New Zealand women aged 18-23 years received daily for 32 weeks, 200 micrograms Se as Se-enriched yeast (selenomethionine), or brewers yeast mixed with selenate, or no added Se (placebo) in a double-blind trial. Se supplementation raised (P = 0.001) platelet glutathione peroxidase (EC 1.11.1.9; GSHPx) activity, and also Se and GSHPx in whole blood, erythrocytes and plasma. Selenomethionine was more effective in raising blood Se concentrations than selenate, but both were equally effective in raising GSHPx activities in whole blood, erythrocytes and plasma, indicating a similar bioavailability for the two forms. These observations and those of gel filtration studies of erythrocytes and plasma proteins reported elsewhere (Butler et al. 1991) are consistent with the incorporation of Se from selenomethionine into a general tissue protein pool while selenate is directly available for GSHPx synthesis, and explain the poorer correlation between Se and GSHPx in individuals with higher Se status. However, selenate raised platelet GSHPx activities to a greater extent than did selenomethionine suggesting some other effect of selenate on platelets which needs further investigation. A response of GSHPx activity in these New Zealand subjects indicates that their dietary Se intake is insufficient to meet recommended intakes based on the criterion of saturation of GSHPx activity, and could reflect a marginal Se status. The level of blood Se necessary for saturation of GSHPx of about 100 ng Se/ml whole blood confirms observations in earlier studies.

Quantitative selenium metabolism in normal New Zealand women.

1. Quantitative selenium metabolism has been studied in normal young New Zealand women by measuring total Se intake and urinary and faecal Se output, and by using values for absorption, excretion and turnover of 75Se determined after administration of[75Se]selenomethionine or [75Se]selenite. 2. In a period of 14 d when a normal ad lib. diet was being consumed, mean dietary Se for four women was 24.2 microgram/d, mean urinary Se was 13.1 microgram/d and mean faecal Se was 10.8 microgram/d; mean Se balance during this time was + 0.3 microgram/d. 3. Intestinal absorption of food Se was 0.76--0.83 of intake (mean 0.79). 4. Whole-body Se was calculated in three different ways; (a) using the specific activity of urinary Se and retained whole-body 75Se; (b) using plasma Se and the occupancy of 75Se in whole-body and plasma; (c) using absorbed food Se and the occupancy of absorbed 75Se in whole-body. 5. Whole-body Se calculated from measurements obtained following the administration of [75Se]selenomethionine was 4.7--10.0 mg (mean 6.9) using method (a), 4.1--7.2 mg (mean 5.2) using method (b) and 4.3--8.9 mg (mean 6.2) using method (c). 6. Whole-body Se calculated from results obtained after giving [75Se]selenite was 2.7--3.4 mg (mean 2.9) using method (a), 2.3--5.0 mg (mean 3.5) using method (b) and 2.1--3.0 mg (mean 2.6) using method (c). 7. The results of this study indicate that the minimum dietary requirement of Se for the maintenance of normal human health is probably not more than 20 microgram/d.

Selenium concentrations and glutathione peroxidase activities in whole blood of New Zealand residents.

1. A relationship was found between selenium concentrations and glutathione peroxidase (EC 1.11.1.9) activities in whole blood of 264 New Zealand residents (r 0-71, P less than 0-001). 2. New Zealand residents returning from visits overseas of 7 months to 3 years had elevated blood Se, but normal GSH-Px activities, whereas for some new settlers in New Zealand both Se and GSH-Px activities were high.

On supplementing the selenium intake of New Zealanders

1. The daily intake of selenium by three subjects was supplemented with 100 microgram Se as selenomethionine (Semet-Se) or sodium selenite (selenite-Se)/d for 10-11 weeks, or with 65 microgram Se as in mackerel (Scomber japonicus) (fish-Se)/d for 4 weeks. 2. Urinary and faecal excretion of Se was measured and also Se concentration in whole blood, plasma and erythrocytes. Measurements on blood were made at intervals after supplementation had ceased. 3. Selenite-Se was not as well absorbed (0.46 of the intake) during the first 4 weeks as Semet-Se (0.75 of the intake) and fish Se (0.66 of the intake). 4. Blood Se increased steadily with Semet-Se, from 0.08 to 0.18 microgram Se/ml, but more slowly with selenite-Se, reaching a plateau in 7-8 weeks at 0.11 microgram Se/ml. Plasma Se increased more rapidly with Semet-Se than with selenite-Se, so that initially with Semet-Se plasma Se was greater than erythrocyte Se. 5. Daily urinary excretion increased with all forms of supplement, with initially a greater proportion of absorbed selenite-Se being excreted than Semet-Se or fish-Se. A close relationship was found between plasma Se and 24 h urinary excretion. The findings suggested that there was a rapid initial excretion of presumably unbound Se then a slower excretion of residual unbound, loosely bound or bound Se. 6. Total retentions of 3.5 mg selenite-Se and 4.5 mg Semet-Se were large when compared with an estimate of body content of 6 mg Se, derived in another paper (Stewart, Griffiths, Thomson & Robinson, 1978). Retention of Semet-Se and fish-Se appeared to be reflected in blood Se, whereas for selenite-Se, blood Se reflected retention for only a short period after which Se appeared to be retained without altering the blood Se. This suggested that Semet-Se and selenite-Se were metabolized differently. 7. A double blind-dosing trail with 100 microgram Semet-Se was carried out for 12 weeks on twenty-four patients with muscular complaints in Tapanui, a low-Se-soil area. Blood Se increased in the experimental group (from 0.067 to 0.143 microgrm Se/ml); clinical findings were not conclusive and will be presented elsewhere. 8. Bood Se was measured in New Zealand residents before travelling to Europe or to North America. On return their blood Se was increased, and depending upon the period of time spent outside New Zealand some values reached concentrations found in visitors and new settlers to New Zealand. 9. The results from these studies and the earlier studies of single and multiple dosing have been used to look at the various criteria in use for assessing Se status of subjects. It is suggested that plasma Se be used in preference to 24 h urinary excretion, and in addition to whole blood Se and glutathione peroxidase (EC 1.11.1.9) activity.

The metabolism of [75Se]selenomethionine in four women.

1. The long-term fate of an oral dose [75Se]selenomethionine was studied in four women. 2. Urinary and faecal excretion, respiratory losses and whole-body retention of 75Se were measured, and also 75Se turnover in whole body, plasma and erythrocyte during a period of 33-34 weeks. 3. Intestinal absorption of [75Se]selenomethionine by the four subjects was 95.5-97.3% of the administered dose. 4. Urinary excretion accounted for 6-9% of absorbed 75Se in the first 2 weeks. No radioactivity was detected in expired air.

Metabolic balance of zinc, copper, cadmium, iron, molybdenum and selenium in young New Zealand women

1. Metabolic balance studies of zinc, copper, cadmium, iron, molybdenum and selenium were made on four young New Zealand women, using brilliant blue and chromic oxide as faecal markers. 2. Zn, Cu, Cd and Fe concentrations in foods, faeces and urine were measured by atomic absorption spectrophotometry, whereas Mo was determined spectrophotometrically with dithiol and Se fluorimetrically with diaminonaphthalene. 3. The dietary intakes of Zn, Cu and Fe were similar to those reported in the USA and the UK, whereas those of Cd, Mo and Se were less. The subjects ate a diet consisting of foods normally consumed by New Zealand women. 4. For each subject there was little variation in the urinary output of each element for three 6 d periods. Day-to-day variation was small for each subject. The individual variation in urinary output of each element among the subjects was smaller when expressed as a ratio of intake, except for Mo. Retentions were small for Zn, Cu and Fe, all elements which are poorly absorbed. Balances of Se, Mo and possibly Cd were in equilibrium.

Copper, manganese, zinc, nickel, cadmium and lead in human foetal tissues.

1. Concentrations of copper, manganese, zinc, nickel, cadmium and lead were measured in samples of liver, kidney, brain, heart, lung, skeletal muscle and vertebral bone from forty foetuses of 23-43 weeks gestation. 2. Cu concentrations in the liver were up to 100 times those in other tissues, but only those in the brain showed a significant increase with gestational age. 3. Mn concentrations were similar in all tissues; the over-all range was 0.35-9.27 microgram/g dry matter (DM). 4. Concentrations of Zn in the liver were much higher than in other tissues and decreased with gestational age, whereas levels in skeletal muscle increased. 5. In all tissues Ni concentrations were within the range 0.04-2.8 microgram/g DM and levels in kidney and muscle decreased significantly with age. 6. Cd was detected in most of the tissue samples and concentrations were within the range 0.01-0.58 microgram/g DM. 7. Concentrations of Pb, where it was detected, varied from 0.1 to 2.4 microgram/g DM in the soft tissues and from 0.4 to 4.3 microgram/g DM in the bone samples.

Daily intakes of manganese, copper, zinc and cadmium by New Zealand women.

1. A total of 179 duplicate diets were collected by twenty-three women consuming their habitual diet. Twelve of the subjects were living in a residential hall for students, the others were living in their own homes or in flats. Collection periods varied from 3 to 21 d. 2. Average daily intakes were: manganese 2-7 mg; copper 1-5 mg for diets not containing liver, 7-6 mg for fifteen diets containing liver; zinc 10-0 mg; cadmium 21 microgram for diets not containing liver, 27 microgram for fifteen diets containing liver. 3. The intakes were compared with values for adults from other countries and with current recommended dietary allowances or estimated minimum requirements. Mn intakes were typical for non-vegeratian Western diets. Cu and Zn intakes may have been marginally low. The intakes of Cd were low. 4. Daily intakes of protein (71 g), fat (83 g), fat (83 g), carbohydrate (224 g) and energy (8-1 MJ) from 129 of the diets were similar to recent values obtained for New Zealand women. 5. Subjects living in the residential hall had higher intakes of all nutrients than subjects living in their own homes or flats.

Selenium Supplementation in Total Parenteral Nutrition

Four adult patients with very low plasma selenium (Se) levels ( less than or equal to 1.5 microgram/100 ml) were given Se supplements while receiving total parenteral nutrition. A comparison was made using the compounds selenomethionine and sodium selenite given either intravenously or by mouth. Urinary excretion and Se plasma responses differed, and indicated that selenomethionine retention was greater. However, the incorporation of Se into the erythrocyte and its enzyme glutathione peroxidase was unpredictable and delayed and was not a good indicator of supplement response. No deleterious effects of supplements were observed. Se supplements are indicated especially in patients with a high risk of developing low Se levels and are best monitored by plasma Se levels.

Long-term supplementation with selenate and selenomethionine : urinary excretion by New Zealand women

Thirty-six New Zealand women aged between 18 and 23 years received daily for 32 weeks, 200 micrograms Se as Se-enriched yeast (selenomethionine, SeMet), or brewers yeast mixed with selenate, or no added Se (placebo) in a double-blind trial. Mean daily Se excretion increased with both supplements; the selenate group excreted more than the SeMet group, 123 v. 66 micrograms/d respectively at week 2, equivalent to 57 v. 27% of the dose. Thereafter Se output increased for the SeMet group reaching a plateau at about 100 micrograms/d at week 16, when plasma Se had also plateaued at 190 ng/ml. The selenate group had reached an earlier plateau of 110 ng Se/ml at week 7. There was a close relationship between 24 h urine and plasma Se for the SeMet group but not for the selenate group. Renal plasma clearances showed two distinctly different responses; the clearance of 0.4 ml/min reached by the SeMet group at week 2 plateaued as plasma Se increased almost 2-fold; whereas for the selenate group the clearance varied between 0.8 and 1.1 ml/min whilst plasma Se remained almost constant at 110 ng/ml. Previous studies, also of 200 micrograms Se/d as Se-rich bread, in New Zealand (NZ) and elsewhere showed similar responses to Se-yeast; the selenite response was intermediate between selenate and Se-yeast (SeMet). The full significance of these studies awaits identification of Se components in plasma, glomerular filtrate and urine; meanwhile renal clearances serve as a pointer to changes in the distribution of Se-containing fractions in the plasma. Trimethylselenonium was detected in basal urines, and was a minor component in urines of supplemented NZ subjects at about 1% of the total Se.