Neonatal erythrocyte glutathione peroxidase deficiency as a consequence of selenium imbalance during pregnancy

Environmental Exposures in the Etiology of Abortion: Placental Toxic and Trace Element Levels

PURPOSE

Intensive research has been conducted on the effects of toxic and trace elements on pregnancy. Previous studies indicated a possible relationship between placental levels of these elements and first-trimester abortion; however, their effects on the further gestational weeks are not clear. This study aimed to investigate the effect of changes in the levels of placental trace and toxic elements on second-trimester abortion.

METHODS

The patient group consisted of 30 women with missed abortion. The control group comprised 60 healthy term and singleton pregnant women who gave birth. Placental samples were obtained from the patients and the healthy controls, and the concentrations of placental elements were measured using inductively coupled plasma mass spectrometry.

RESULTS

In the abortion group, placental arsenic, cadmium, mercury, lead, antimony, tin, cobalt, manganese, and selenium levels were significantly higher than those of the control group (p<0.05). Antimony was determined as an independent predictor with an odds ratio of 6.1 in toxic elements (p=0.025), and selenium was determined as an independent predictor with an odds ratio of 2.3 in trace elements (p=0.015).

CONCLUSION

The changes in trace element and toxic element levels, especially an increase in antimony and selenium, in placental tissue due to environmental exposure may play an important role in second-trimester abortion.

Genetic Disorders Associated with Metal Metabolism

Genetic disorders associated with metal metabolism form a large group of disorders and mostly result from defects in the proteins/enzymes involved in nutrient metabolism and energy production. These defects can affect different metabolic pathways and cause mild to severe disorders related to metal metabolism. Some disorders have moderate to severe clinical consequences. In severe cases, these elements accumulate in different tissues and organs, particularly the brain. As they are toxic and interfere with normal biological functions, the severity of the disorder increases. However, the human body requires a very small amount of these elements, and a deficiency of or increase in these elements can cause different genetic disorders to occur. Some of the metals discussed in the present review are copper, iron, manganese, zinc, and selenium. These elements may play a key role in the pathology and physiology of the nervous system.

Selenium in Complicated Pregnancy. A Review

Selenium (Se) is an essential trace element of significant importance in human health. Diet is the major source of Se, and intake of this element depends on its concentration in food sources as well as the amount of those sources consumed. Unfortunately, daily dietary intake of Se in most European countries is generally low, ∼30-40μg/day, compared with the recommended dietary allowance, ∼55 and 70μg/day for adult females and males, respectively. The importance of Se as an essential trace element is linked to its role as selenocysteine in a number of selenoproteins including antioxidant enzymes glutathione peroxidases (GSH-Pxs), thioredoxin reductases (TrxRs), and selenoprotein P (SePP). These enzymes protect tissues against the damaging effect of reactive oxygen species (ROS) and other endogenous products of cellular metabolism implicated in DNA damage and potentially leading to mutagenesis, cell death, and carcinogenesis. Reduced body Se and antioxidant enzyme activity during pregnancy results in oxidative stress within tissues contributing to premature birth, miscarriage, preeclampsia, and intrauterine growth retardation. Because placenta development is highly dependent on oxygen status, uncontrolled ROS formation is likely detrimental. Despite these findings, the role of Se and Se-dependent enzymes in pregnancy remains controversial. The objective of this review is to explore Se status in pregnancy with respect to adverse outcomes. Effects related to decreased antioxidant activity and increased oxidative stress will be highlighted.

The possible role of selenium status in adverse pregnancy outcomes

The present study reviews the possible role of Se status during pregnancy regarding adverse pregnancy outcomes, with emphasis on those related to diminished antioxidant activity and increased oxidative stress. Studies have reported that Se could play an important role in adverse outcomes such as miscarriages, neural tube defects, diaphragmatic hernia, premature birth, low birth weight, pre-eclampsia, glucose intolerance and gestational diabetes. Also, low Se status has been associated with adverse outcomes among HIV-infected pregnant women and their offspring. Nevertheless, the function of Se in the aetiology of pregnancy complications is yet to be elucidated. Available evidence presents the following limitations: most study designs do not allow conclusions about causal relationships; study populations, selection of subjects, research setting, procedures for defining sample size and analytical methods are often poorly described; many studies fail to adjust for important confounding variables. In addition, population studies assessing the relationship between Se intake during pregnancy and health outcomes are scarce. Further research is still needed to clarify the role of Se status in adverse pregnancy outcomes, especially those related to augmented oxidative stress.

Homocysteine and glutathione peroxidase-1

Mildly elevated homocysteine levels (Hcy) increase the risk for atherothrombotic vascular disease in the coronary, cerebrovascular, and peripheral arterial circulations. The molecular mechanisms responsible for decreased bioavailability of endothelium-derived nitric oxide (NO) by Hcy involve an increase of vascular oxidant stress and inhibition of important antioxidant capacity. Glutathione peroxidase-1 (GPx-1), a selenocysteine-containing antioxidant enzyme, may be a key target of Hcy's deleterious actions, and several experimental and clinical studies have demonstrated a complex relationship between plasma total homocysteine (tHcy), GPx-1, and endothelial dysfunction. Hcy may promote endothelial dysfunction, in part by decreasing GPx-1 expression; however, there is evidence to suggest that overexpression of GPx-1 can compensate for these effects. This review summarizes the current knowledge of the metabolism of Hcy, the effects of hyperhomocysteinemia observed in in vitro and in vivo models that lead to endothelial dysfunction and the possible mechanisms for these actions, and the role of GPx-1 in the pathogenesis of Hcy-induced cardiovascular disease (CVD).

Selenium in global food systems

Food systems need to produce enough of the essential trace element Se to provide regular adult intakes of at least 40 μg/d to support the maximal expression of the Se enzymes, and perhaps as much as 300 μg/d to reduce risks of cancer. Deprivation of Se is associated with impairments in antioxidant protection, redox regulation and energy production as consequences of suboptimal expression of one or more of the Se-containing enzymes. These impairments may not cause deficiency signs in the classical sense, but instead contribute to health problems caused by physiological and environmental oxidative stresses and infections. At the same time, supranutritional intakes of Se, i.e. intakes greater than those required for selenocysteine enzyme expression, appear to reduce cancer risk. The lower, nutritional, level is greater than the typical intakes of many people in several parts of the world, and few populations have intakes approaching the latter, supranutritional, level. Accordingly, low Se status is likely to contribute to morbidity and mortality due to infectious as well as chronic diseases, and increasing Se intakes in all parts of the world can be expected to reduce cancer rates.

Selenium status in Saudi Arabia

Selenium (Se) is a naturally occurring trace element that is essential for animal and human nutrition, but the range between dietary requirements and toxic levels is relatively narrow. In this review, we are interested in the beneficial effects of selenium and we report on a number of studies of the selenium status of different populations in Saudi Arabia. The Status reflects the geographical area inhabited by the populations. Apart from the few available studies reviewed here, no data on the human status of Se in Saudi Arabia has been obtained. A further objective of this paper is throw some the light on the direction of future studies.

Indicators of selenium status in Australian infants

OBJECTIVE

To provide the first Australian data for the commonly used indicators of selenium (Se) status including plasma and erythrocyte Se and erythrocyte glutathione peroxidase (GSHPx) activity in newborn term and preterm infants from Adelaide, South Australia. Plasma Se levels from adults from Adelaide and Tasmania are also reported.

METHODOLOGY

Descriptive, cross-sectional study of the indicators of Se status of newborn Australian preterm and term infants.

RESULTS

Mean (+/- SD) plasma Se concentrations in the first 5 days of life for term (n = 48) and preterm (n = 90) infants were similar at 33 +/- 11 and 29 +/- 14 microg/L, respectively. Glutathione peroxidase activity was lower in preterm than term infants (P < 0.001). Erythrocyte Se was lower in male (n = 74) compared with female (n = 57) infants (491 +/- 98 vs 561 +/- 134 ng/g Hb; P < 0.001). Adelaide adult plasma Se levels were 88 +/- 20 microg/L and higher than those of adult Tasmanian blood donors (77 +/- 13 microg/l, P < 0.05).

CONCLUSIONS

These data indicate that values for indicators of Se status of Australian infants and adults are at the lower end of the international range. This article highlights the paucity of Australian data on the Se content in the food supply and the Se status of the Australian population. Given the increasing range and complexity of the biological roles of Se and the emerging evidence that Se may have important roles in prevention of cancer and other disorders, further data are required to clarify the Se status of Australians.

Reference values for selected trace elements in serum of term newborns from the urban area of Rome

Reference values for Al, Cd, Co, Cu, Li, Mn, Mo, Ni, Rb, Se and Zn, and indicative intervals for Sb are proposed in serum from cord blood of 143 term newborns of the urban area of Rome. On the basis of the eligibility criteria adopted, only babies with gestational age > 37 weeks and body weight at the delivery > 2500 g, i.e., "normal" term infants, were included in this study. With the exception of Cd, Li, Ni and Sb, experimental data for each of the other analytes were found to approach a normal distribution. The estimated references values (in ng/ml) were the following: Al, 1. 12-6.79; Cd, 0.10-0.52; Co, 0.20-0.43; Cu, 140-691; Li, 0.31-2.23; Mn, 0.79-3.26; Mo, 0.36-1.56; Ni, 0.20-3.15; Rb, 196-1302; Sb, 0. 10-1.48 (indicative range); Se, 20.2-69.7; and Zn, 318-1405. For several elements, the information available in the relevant literature does not allow adequate comparisons to be performed. This was actually possible only for Cu, Se and Zn. The correlations between the weights at birth (BW), gestational ages (GA) and elemental concentrations were elucidated. As expected, significant positive correlations were found for Cu and Se with GA and BW, respectively. Strong mutual associations were observed for several other elements, but their interpretation is still debatable.

Theoretical mechanistic basis of oxidants of methaemoglobin formation

The mechanism of oxidation or reduction using the electron method was investigated for (I) aniline; (II) nitrobenzene; (III) nitrate; (IV) sulphanilamide; (V) hydrogen peroxide; (VI) hydroxyl free radical; (VII) ferricyanide; (VIII) acetylphenylhydrazine; (IX) nitrite; (X) chlorate and (XI) hydroxylamine respectively. Substances (II), (III), (V), (VI), (VII), (IX), (X) and (XI) evolved as oxidants, with (II), nitrobenzene and (X), chlorate as the most powerful oxidants (number of moles of HbFe(2+)(haemoglobin) of 6 reacting with 1.0 mole of the substance). Substances (I), (IV) and (VII) evolved as reductants of equal reducing power (number of moles of HbFe(3+)(methaemoglobin) of 4 reacting with 1.0 mole of the substance). Using the following equations, the impact of oxidants and reductants on glutathione (GSH) peroxidase, glutathione (GSSC) reductase and NADHmetHb reductase respectively on methaemoglobinaemia generation was investigated. [Equation in text]. Redox potential change (DeltaE' (o)) of 1.77, -1.77 and 1.86 volt and free energy change (DeltaG(o)') of -81, 81 and -85.8 kcal/mol were calculated for GSH peroxidase, GSSG reductase and NADHmetHb reductase systems respectively. In sustained methaemoglobinaemia, these mechanisms predict low levels of NADHmetHb reductase and glutathione peroxidase respectively, but high levels of glutathione reductase in red blood cells on exposure to oxidants. The significance of these mechanisms was investigated in cord blood, neonatal, adult red blood cells and other biological systems. It was concluded that any reaction with a positive DeltaE(o)' and negative DeltaG(o)' with the Fe(3+): Fe(2+)couple will indicate methaemoglobin oxidizing power. The effects on red blood cells and white blood cells were manifested in the biochemical toxicology of nitroso (PhN = 0), arylamine glucuronide (PhNHG) and arene imine respectively.

Red blood cell enzymes and their clinical application

Red blood cell enzyme activities are measured mainly to diagnose hereditary nonspherocytic hemolytic anemia associated with enzyme anomalies. At least 15 enzyme anomalies associated with hereditary hemolytic anemia have been reported. Some nonhematologic disease can also be diagnosed by the measurement of red blood cell enzyme activities in the case in which enzymes of red blood cells and the other organs are under the same genetic control. Progress in molecular biology has provided a new perspective. Techniques such as the polymerase chain reaction and single-strand conformation polymorphism analysis have greatly facilitated the molecular analysis of erythroenzymopathies. These studies have clarified the correlation between the functional and structural abnormalities of the variant enzymes. In general, the mutations that induce an alteration of substrate binding site and/or enzyme instability might result in markedly altered enzyme properties and severe clinical symptoms.

Selenium in human lactation

The primary factor determining selenium concentration in human milk is the maternal selenium intake. A significant correlation between selenium in human milk and maternal selenium intake has been reviewed in papers from different regions of the world. Infants fed human milk have higher selenium intake than those fed commercially available formula milk or baby foods. Selenium compounds found in breast milk seem to be more biologically available for infant nutrition than those in formulas. Increased requirements of selenium have been observed in pregnant and lactating women. Supplementation of lactating and pregnant women with different selenium compounds has been assayed, and selenium supplementation of soil and cows has been used to increase the selenium status of children fed infant formula made from cow's milk.

Inter-individual variation of selenium in maternal plasma, cord plasma and placenta

Selenium (Se) in high doses has been known to cause injury to the fetus and newborn. The major difficulty in assessing the effects of selenium on human reproduction stems from the need for a suitable means of estimating maternal and fetal exposure. The present investigation, therefore, examines the respective reliability of maternal plasma, cord plasma and placenta as epidemiological indicators as well as inter-individual variation of this trace element. An unselected population of 128 pregnancies was studied. Obstetrical characteristics were noted. Selenium concentrations were determined for maternal plasma, cord plasma, and placental tissue by fluorometric analysis. Maternal plasma selenium concentrations (Se-Bm) were significantly greater than fetal concentrations (Se-Bc). Placental selenium (Se-Pl) levels were four times that of fetal levels. Variability of Se-Bc is best explained by placental concentrations. Maternal weight and ethnic origin are significantly correlated with Se-Bc. Female newborn have higher selenium levels than male newborn. The present study demonstrates the significance of the placenta as an indicator of fetal selenium exposure.

Human erythrocyte superoxide dismutase in adults, neonates, and normal, hypoxaemic, anaemic, and chromosomally abnormal fetuses

An enzyme-linked immunosorbent method is described for the assay of human erythrocyte superoxide dismutase (SOD). The method was specific and precise as well as simple, economical, and reliable. The mean levels of adult SOD with SD were 652 +/- 122 mg/kg hemoglobin (Hb) for males and 635 +/- 100 mg/kg Hb for females. In neonates the levels were 528 +/- 92 mg/kg Hb. Normal fetal levels at 20-36 weeks gestation were 421 +/- 90 mg/kg Hb. Mean SOD levels in hypoxemic growth-retarded fetuses and in anemic fetuses from red cell iso-immunised pregnancies (before their first intrauterine blood transfusion) were the same as those in normal fetuses. However, in a case of trisomy 21 the fetal level of SOD was significantly increased.

Selenium and glutathione peroxidase variations induced by polyunsaturated fatty acids oral supplementation in humans

Serum and erythrocyte selenium, erythrocyte and platelet glutathione-peroxidase (GSH-Px) activities, and erythrocyte reduced glutathione (GSH) content were measured in 25 healthy adult individuals before and after daily supplementation with 20 ml of fish oil for 10 weeks. Serum-Se decreased from 0.83 +/- 0.01 mumol/l to 0.75 +/- 0.02 mumol/l (mean +/- S.E.M.) (P less than 0.01); erythrocyte-Se decreased from 4.39 +/- 0.17 nmol/g hemoglobin (Hb) to 2.83 +/- 0.15 nmol/g (P less than 0.001). GSH-Px activities increased both in erythrocytes (6.93 +/- 0.24 iu/g vs 8.18 +/- 0.27 iu/g Hb, P less than 0.01) and in platelets (69.2 +/- 2.8 iu/g vs 90.9 +/- 3.6 iu/g protein, P less than 0.001). The concentration of GSH in erythrocytes fell from 9.56 +/- 0.29 mumol/g Hb to 5.90 +/- 0.30 mumol/g Hb (P less than 0.001). The effects on plasma lipids were evident only for triglycerides (before 1.96 +/- 0.16 mmol/l, after 1.75 +/- 0.14 mmol/l, P less than 0.001). We hypothesise the enrichment of erythrocyte and platelet membranes with polyunsaturated fatty acids (PUFAs), following fish oil intake, can generate increased amounts of lipid peroxides and thus allosterically activate GSH-Px: with time this is harmful for the integrity of the enzyme molecule and Se release may result. We suggest that the Se status of individuals given PUFAs is assessed before and during intake; Se supplements should only be given when serum and/or erythrocyte Se are reduced.

The physiological consequences of glutathione variations

The major low molecular weight thiol inside cells, the tripeptide glutathione (GSH), is of importance for protection of the cell against oxidative challenge, for thiol homeostasis required to guarantee basic functions, and for defence mechanisms against xenobiotics. Since the pathophysiological significance of a perturbed GSH status in human disease is less clear, this review evaluates the consequences of in vivo variations of GSH. Owing to intracellular GSH concentrations above 2 mM depletion of GSH as such has little metabolic consequences unless an additional stress is superimposed. The kinetic properties of GSH-dependent enzymes imply that loss of up to 90% of intracellular GSH may still be compatible with cellular integrity. Mitochondrial GSH, which accounts for about 10% of total cellular GSH, may define the threshold beyond that toxicity commences. Thus, in cases of severe GSH-depletion a substitution of GSH as a therapeutic measure seems justified. Such a severe depletion of GSH has been described for some diseases such as liver dysfunction, AIDS or pulmonary fibrosis.

Low selenium status and cot deaths

Selenium is a naturally occurring trace element essential to the health of many mammal and avian species. Low levels of selenium are evidenced by a variety of symptoms, mainly in the cardiac and musculo-skeletal systems. Tasmania and South Island, New Zealand, both have low soil levels of selenium and high rates of cot death. Evidence is presented to suggest that these may be related via a pathway involving maternal selenium status during gestation or low selenium content in mothers' milk.

Cod liver oil inhibits indomethacin induced gastropathy without affecting its bioavailability and pharmacological activity

The upper gastrointestinal toxicity is one of the most common side effects associated with the use of nonsteroidal anti-inflammatory drugs (NSAIDs). Many attempts to prepare potent NSAIDs free from gastrotoxicity have failed. Hence, development of formulations to mask the gastropathy of NSAIDs are warranted. The present study was undertaken to investigate the effect of concomitant use of cod liver oil (CLO) on pharmacological activity and gastropathy of indomethacin in rats. The animals were treated with CLO (5 and 10 ml/kg body weight) along with indomethacin (30 mg/kg, body weight). Blood samples were collected for analysis of indomethacin at 0.25, 0.5, 1.0, 1.5, 2.0, 4.0, 6.0 and 24 hours. The anti-inflammatory activity of indomethacin alone and in combination with CLO was studied using carrageenan-induced paw oedema. Our studies related to the effect of these drugs on gastrointestinal tract showed that concurrent use of CLO protects gastric mucosa against indomethacin induced depletion of gastric wall mucus, non protein sulfhydryl (NP-SH) levels and gastric lesions. The result of this study also showed that the concurrent use of the CLO does not affect the bioavailability and anti-inflammatory activity of indomethacin while it inhibits the ulcerogenic effect of indomethacin in a dose dependent manner. These findings suggest that NSAIDs formulations containing CLO may reduce gastrotoxicity without affecting their therapeutic efficacy.

Determination of selenium in blood components by X-ray emission spectrometry. Procedures, concentration levels, and health implications

Sampling, storing, sample pretreatment, and experimental conditions for selenium (Se) determination in human serum, plasma, and whole blood by X-ray emission spectrometric (XRS) methods are described. Concentration levels in these biological fluids, found by this technique, are discussed and compared to values found by other techniques for the same healthy population group in the same area. XRS analysis of blood from patients with various pathological conditions is reviewed, with special attention to the relation of Se with the concentration level of other essential or nonessential trace elements.

Selenium: clinical significance and analytical concepts

Selenium is an essential trace element in humans and animals. Its only established function in humans is the antioxidant activity of glutathione peroxidase, a selenoenzyme. Severe prolonged deficiency may cause a fatal cardiomyopathy. Iatrogenic causes of selenium deficiency include parenteral and enteral nutrition. Low plasma selenium is also found in malabsorption, cystic fibrosis, rheumatoid arthritis, neoplasia, and other varied clinical disorders. Death has resulted from a single massive ingestion of selenium, while chronic excessive intake causes skin, nail, and hair pathology. Extreme geographical variation in population blood and urine selenium levels and a marked age-specific variation in population reference intervals are important factors in understanding selenium nutrition. Nutritional requirements, biological availability, and metabolism are discussed in relation to geographical, age, and method variability. Sampling, processing procedures, and methods for selenium quantitation are reviewed. Selenium content in different biological matrices and reference values for pediatric, adult, and obstetric populations are provided.

Antioxidant system and serum trace elements in alpha-thalassaemia and Hb Lepore trait

Erythrocyte antioxidant enzymes, superoxide dismutase, catalase and glutathione peroxidase were found to be significantly high in subjects with alpha-thalassaemia and Hb Lepore trait, as a consequence of the increased oxidant stress which is known to exist in these conditions. Among the serum trace elements present in these enzymes, selenium was increased in subjects with Hb Lepore trait and significantly low in those with alpha-thalassaemia trait, while selenium erythrocyte content was significantly increased in alpha-thalassaemic subjects.

Nutritional management of pregnancy in patients on home parenteral nutrition

Three pregnancies are reported in two patients on home parenteral nutrition for intestinal failure. The nutritional regimen, 2300 kcal (9.63 MJ) (18% as lipid emulsion), 14 g amino acid nitrogen and electrolytes supplied daily in a 'big bag', was based on the measured resting energy expenditure and urinary nitrogen excretion during the third trimester in a 30-year-old woman on home parenteral nutrition. Commercial preparations of trace elements were added to the infusion as dictated by serum levels. Iron, iodine and fluoride were given orally, and vitamin B12 by monthly intramuscular injection. There were no serious deficiencies in trace elements and maternal weight-gain and fetal growth were satisfactory in all three pregnancies. The two pregnancies in one patient went to term and both infants had birthweights at the 50th centile for gestational age. The second patient who had had two spontaneous abortions went into premature labour at 30 weeks and gave birth to a baby with a minor facial deformity who subsequently developed the idiopathic respiratory distress syndrome. All three placentas were histologically normal. The growth and development of all three babies has been satisfactory. This nutritional regimen should be adequate for most pregnant patients who have attained a normal nutritional status on parenteral nutrition.

Glutathione peroxidase activity, selenium, and lipid peroxide concentrations in blood from a healthy Polish population : I. Maternal and cord blood

Selenium (Se) concentrations in whole blood and plasma of 19 nonpregnant women. 14 mothers at delivery, 14 neonates, and 13 infants, aged 2-12 mo, were evaluated. The activity of glutathione peroxidase (GSH-Px) in erythrocytes and plasma and the level of lipid peroxides in plasma were also analyzed. Selenium concentrations in whole blood and plasma in mothers at delivery were significantly lower compared to nonpregnant women. Selenium concentrations in cord blood components were lower compared to mothers, but the differences were not significant. The concentration of the element decreased in the first few months of life. Glutathione peroxidase activity in erythrocytes differed only slightly in the examined groups. In plasma, however, the enzyme activity was significantly lower in pregnant compared to nonpregnant women and in neonates compared to their mothers. Lipid peroxide concentrations in plasma differed only slightly in the examined groups. The results obtained are discussed in terms of the observations of other investigators.

Distribution of serum selenium, copper, and zinc in normal human pregnancy

The distribution of the serum levels of selenium, zinc, and copper in human pregnancy at various gestational ages were determined from two ethnically and geographically different populations (Rosebud Indian Reservation and southeastern South Dakota) of 410 normal subjects. As gestation age increased, there was a significant increase and a slight decrease in the mean levels of copper and zinc, respectively. No change in the levels of selenium was observed. Significantly higher levels of both pregnancy and non-pregnancy serum copper were observed in the Rosebud population compared to that in southeastern South Dakota, possibly due to the significantly higher level of copper in the Rosebud water. No differences were observed in the zinc or selenium levels between the two populations. Serial measurements of these trace metals during the third trimester of pregnancy were performed on 18 subjects, and supported the trends described for copper and selenium. No decrease in zinc was observed in the individual subjects.

Assessment of trace element status

Biochemical and clinical investigations involving trace elements are made for the diagnosis of inherited or acquired deficiencies of essential trace elements and their treatment, to monitor the efficacy of the therapeutic administration of non-essential trace elements in order to achieve maximum clinical response with minimum toxicity, and for the early detection of excessive ingestion of non-essential toxic trace elements. The wide range of tests used to assess trace element status in these three areas of clinical importance is discussed with examples of essential and of toxic trace elements since therapeutic use of trace elements is discussed elsewhere in this issue. Particular attention is given to zinc, copper, selenium, lead and cadmium because the various tests used to assess the status of these elements encompass the principles of all currently available tests. Although trace element analysis of body fluids and tissues is the most useful and most commonly used method of assessment of trace element status, this is of limited value and no single test may be considered as ideal for any element. The provision of more detailed information from elemental analysis of cellular and subcellular fractions and of protein fractions from plasma leads inexorably to measurements of element-dependent enzymes, metalloproteins and of low molecular weight element-binding ligands. Even at this level of discrimination the choice of body tissue or tissue fluid for investigation is determined by the trace element and its principal metabolic targets.

Methemoglobin formation and glutathione disappearance in cord blood red cells exposed to acetylphenylhydrazine

Methemoglobin formation in the presence of acetylphenyl hydrazine occurs faster in red cells from cord blood than in normal adult erythrocytes. Under the same conditions, the rate of disappearance of glutathione is slower in cord blood erythrocytes. The mean NADH-methemoglobin reductase activity of cord blood red cells is less than half of the adult value. The results point to a potential danger in the administration of oxidant drugs to expectant mothers or new-born infants.

Erythrocyte antioxidant enzymes and selenium serum levels in an Andean population

A preliminary study indicated that erythrocyte antioxidant enzyme activities were enhanced in chronic hypoxaemic patients, in whom an increased oxidant stress could be present as a consequence of augmented haemoglobin autoxidation. We have now evaluated the behaviour of erythrocyte antioxidant enzymes and of their related trace metal serum levels in conditions of chronic hypobaric hypoxia in an Andean population living at high altitude (3800 m above sea level), and in a similar ethnic group living at sea level. The results indicate a significant reduction in erythrocyte glutathione peroxidase activity and a low serum level of selenium in the Andean population. Thus, in contrast to what happens in chronic hypoxaemic patients, this group of Andean subjects seems to be poorly protected against oxidant stress, probably as a consequence of selenium deficiency in the diet.

Superoxide dismutase, catalase and glutathione peroxidase activities in maternal and cord blood erythrocytes

The "antioxidant" enzymes superoxide dismutase, catalase and glutathione peroxidase were assayed in a biological model with low oxygen tension (red cells from cord blood of newborn infants). Catalase and glutathione peroxidase activities in red cells of newborns were significantly lower when compared with their mothers and with normal controls. In contrast, superoxide dismutase activity was unchanged. Thus, normal activities of superoxide dismutase seem to be necessary in order to protect red blood cells from superoxide radicals during foetal life, while even low activities of catalase and glutathione peroxidase are sufficient to protect red blood cells from hydrogen peroxide. No correlation was found between the "antioxidant" enzyme activities present in cord blood erythrocytes and the bilirubin concentrations during the first days of life.