Léopold Molle

6 Selenium deficiency

Summary Selenium is undoubtedly an essential trace element: its involvement in GPx structure, the presence of deleterious effects of selenium deficiency in animals, and the recognition of deficiency states in man attest to its importance. However, if the consequences of selenium deficiency in man are now widely recognized, the mechanisms underlying these conditions are poorly understood. The definition of the exact role of selenium in human homeostasis has been hampered by the lack of a sensitive parameter, usable in routine investigation, to assess selenium status. Measurements of plasma and urinary levels, although useful in clinical practice, are inadequate indicators. The only true evidence of selenium deficiency lies in a positive response to selenium therapy. Deficiency states have been demonstrated for inhabitants of regions where selenium supply is limited, in protein-energy malnutrition, and in patients maintained on total parenteral nutrition without selenium supplementation. The benefit of selenium supplementation, together with other antioxidant drugs, in non-deficient subjects is still a matter of debate; its protective effect in neoplastic, cardiovascular and neurological degenerative diseases is not yet proven.

Study of some systematic errors during the determination of the total selenium and some of its ionic species in biological materials

A method using nitric acid alone for the digestion of biological materials for the determination of total selenium or of some of its ionic species leads to erroneous results because of incomplete mineralisation of some organic selenium compounds, including the selenonium derivatives, the main metabolites of the element in urine, and a selenoamino acid present in plant and animal tissues; such a method also suffers from many interferences owing to the presence of incompletely digested organic constituents of the sample. The use of perchloric acid under certain conditions and of sulphuric acid, in conjunction with nitric acid, leads to an excellent recovery of the selenium added to biological materials or included in organic selenium compounds. The nitric acid method, the only one which affords a selective determination of some selenium ionic species in aqueous solution, has been critically examined but its efficiency cannot be improved; all of the parameters investigated are helpful, however, in choosing an adequate digestion procedure for the determination of the total selenium content of a complex sample.

Plasma and erythrocyte zinc, copper and selenium in cystic fibrosis

ABSTRACT. Plasma and erythrocyte zinc, copper and selenium were measured in 20 cystic fibrosis children, aged 7 to 19 years. Mean plasma zinc and copper levels were not different from those in age‐matched controls but very low zinc levels occurred sporadically. Plasma zinc concentrations were significantly lower in patients with moderate‐to‐severe growth retardation and with severe pulmonary disease as compared to patients without growth failure and with moderate pulmonary disease. Mean erythrocyte zinc (40.8 μg/g Hb ±9.2) and copper levels (3.56 μg/g Hb ±0.50) were very significantly increased (30.4 μg/g Hb ±5.2 and 2.73 μg/g Hb ±0.30 respectively, for age‐matched controls). Mean plasma and erythrocyte selenium levels (63 ng/ml ±15 and 329 ng/g Hb ±86) were significantly lower than those in age‐matched controls (82 ng/ml ±13 and 404 ng/g Hb ±116). The trace element concentrations in erythrocytes are discussed in relation to the activities of the copper‐ and zinc‐containing enzyme superoxide dismutase and the seleno‐enzyme glutathione peroxidase. We consider that more data on trace element metabolism in CF should be collected before specific supplementation is considered.

Erythrocyte and plasma trace element levels in clinical assessments : Zinc, copper, and selenium in normals and patients with Down's syndrome and cystic fibrosis.

On the basis of original investigations on zinc, copper, and selenium levels in plasma and erythrocytes of Downs syndrome (DS), cystic fibrosis (CF), and control subjects, the possible importance of erythrocytic trace element concentrations in clinical analysis is emphasized. Red blood cell levels of copper and zinc were found significantly increased in both groups of diseased patients as compared to age-matched controls, although plasma levels did not statistically differ. Plasma selenium levels were significantly lower in both investigated groups, but red blood cell levels were only decreased in CF and were not different from controls in DS. Significant differences were also found between zinc, copper, and selenium levels in erythrocytes of two control groups originating from distinct geographic areas, although plasma levels were not statistically different. Some factors likely to modify trace element concentrations in erythrocytes are examined and a more systematic determination of these levels is suggested for use in clinical analysis.

Degradation study of catecholamines, indole amines and some of their metabolites in different extraction media by chromatography and electrochemical detection

Optimal conditions for the extraction from brain tissue and the simultaneous quantification of catechol and indole derivatives were determined after a systematic degradation study in water and perchloric acid. The roles of three parameters, namely temperature, presence of antioxidant agents, and time, were considered. Adrenaline, noradrenaline, dopamine, homovanillic acid, 5-hydroxytryptophan, 5-hydroxyindole acetic acid, serotonin, and epinephrine were separated by HPLC and detected electrochemically. The results indicated a great instability of the indole derivatives at an ambient temperature, in an acid medium, and in the absence of a protective agent. Therefore, when perchloric acid has to be used for deproteinization, the lowest concentration (0.1 M) is preferable. The samples have to be kept on ice, in darkness, and protected by ascorbic acid and sodium ethylenediamine tetracetate.

Study of the electrooxidative behaviour of 5-hydroxyindole-3-acetic acid, 5-hydroxytryptophan and serotonine in the presence of sodium ethylenediaminetetraacetic acid

Abstract The great instability of the indole derivatives 5-hydroxytryptophan (5-HTP), serotonine (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA) in strong acid medium and the protective role of sodium ethylenediaminetetracetate (EDTA H2Na2) could be explained by their electrooxidative behaviour on a carbon paste electrode. Voltamperometric curves obtained in a 1–8 pH range show that oxidation occurs in two irreversible steps; the mechanism is more complex than a simple electron transfer. For the three molecules, new redox couples have been detected on cyclic voltammograms at lower potentials than the parent compound, indicating that more easily oxidized derivatives are formed. On the other hand, the anodic oxidation of EDTA H2Na2 has been investigated and in the present case the molecule is not acting by complexing metal traces but should actually be considered a competitive agent preventing the second oxidation step of the indole derivatives.

Critical study of some wet digestion methods for decomposition of biological materials for the determination of total selenium and selenium(VI)

SummaryThree important techniques for decomposition of organic materials for differential determination of the selenium oxidation states present have been examined. After a study on aqueous samples, the methods were applied to vegetable and biological samples. The only method found suitable for the selective determination in aqueous samples gave unsatisfactory results for organic materials, the recovery of both native and added selenium being very low. The methods are critically discussed and a procedure is recommended for the accurate determination of total selenium in organic samples.ZusammenfassungDrei wichtige Verfahren zur Zerstörung organischen Materials zwecks Bestimmung der verschiedenen Wertigkeitsstufen von Selen wurden geprüft. Nach der Untersuchung wäßriger Proben wurden diese Verfahren auf pflanzliche und biologische Proben angewandt. Das einzige für die selektive Bestimmung in wäßrigen Proben geeignete Verfahren gab bei der Untersuchung organischen Materials unzureichende Ergebnisse, die Resultate für ursprüngliches und für zugesetztes Selen waren zu tief. Die Verfahren wurden diskutiert und eine Methode empfohlen, die sich für die genaue Bestimmung des Gesamtgehaltes an Selen in organischen Proben eignet.

Determination spectrophotometrique des constantes d'acidite de quelques 2,1,3-benzoselenadiazoles (piazselenoles)

The variation with increasing acidity of the ultraviolet/visible region absorption spectrum of 2,1,3-benzoselenadiazole and five of its derivatives has been studied and the ionization constants were determined by using a new computer method for the correction of the medium effect. An infrared spectroscopic study was also done on these derivatives and the corresponding substituted 1,2-diamino-benzenes. Positive correlations were found between some infrared frequencies and either the values of the ionization constants or the sum of the Hammett substitution constants sigma(m) + sigma(p).

Separation, identification and quantitative analysis of substituted benzamides in pharmaceutical dosage forms by high pressure liquid chromatography

Abstract Reverse phase high pressure liquid chromatography has been used to separate, identify and analyse five closely structurally related benzamides: procainamide, sultopride, tiapride, sulpiride and metoclopramide. The influence of various parameters on the separation (solvent composition, pH, type and concentration of the anion modifying the ionic strength of the buffer) has been examined. The results of this study suggest that the separation mode is similar to an ion pair partition chromatography in which the nature of the counter-ion is essential. The method has been applied successfully to the quantitative analysis of some of the above mentioned compounds in pharmaceutical dosage forms.

Etude critique de la determination par spectrometrie d'absorption atomique sans flamme du selenium dans les milieux complexes apres extraction a l'aide d'o-diamines aromatiques et ajout de nickel(II)

Critical study of the graphite-furnace atomic absorption determination of selenium in biological samples after extraction with aromatic o-diamines and addition of nickel(II) A new method for the determination of traces of selenium in natural samples is proposed. After digestion with nitric, sulfuric and perchloric acids, selenium is quantitatively converted to the tetravalent state with perhydrol. Reaction with an aromatic o-diamine gives the corresponding piazselenol which can be extracted into toluene and determined by atomic absorption spectrometry after addition of nickel(II). Calibration graphs are linear in the range 0–1.5 ppm Se. A critical study shows the advantages of the method.