Increased plasma and erythrocyte selenium concentrations but decreased erythrocyte glutathione peroxidase activity after selenium supplementation in children with Down syndrome

Reactive oxygen species, toxicity, oxidative stress, and antioxidants: chronic diseases and aging

A physiological level of oxygen/nitrogen free radicals and non-radical reactive species (collectively known as ROS/RNS) is termed oxidative eustress or "good stress" and is characterized by low to mild levels of oxidants involved in the regulation of various biochemical transformations such as carboxylation, hydroxylation, peroxidation, or modulation of signal transduction pathways such as Nuclear factor-κB (NF-κB), Mitogen-activated protein kinase (MAPK) cascade, phosphoinositide-3-kinase, nuclear factor erythroid 2-related factor 2 (Nrf2) and other processes. Increased levels of ROS/RNS, generated from both endogenous (mitochondria, NADPH oxidases) and/or exogenous sources (radiation, certain drugs, foods, cigarette smoking, pollution) result in a harmful condition termed oxidative stress ("bad stress"). Although it is widely accepted, that many chronic diseases are multifactorial in origin, they share oxidative stress as a common denominator. Here we review the importance of oxidative stress and the mechanisms through which oxidative stress contributes to the pathological states of an organism. Attention is focused on the chemistry of ROS and RNS (e.g. superoxide radical, hydrogen peroxide, hydroxyl radicals, peroxyl radicals, nitric oxide, peroxynitrite), and their role in oxidative damage of DNA, proteins, and membrane lipids. Quantitative and qualitative assessment of oxidative stress biomarkers is also discussed. Oxidative stress contributes to the pathology of cancer, cardiovascular diseases, diabetes, neurological disorders (Alzheimer's and Parkinson's diseases, Down syndrome), psychiatric diseases (depression, schizophrenia, bipolar disorder), renal disease, lung disease (chronic pulmonary obstruction, lung cancer), and aging. The concerted action of antioxidants to ameliorate the harmful effect of oxidative stress is achieved by antioxidant enzymes (Superoxide dismutases-SODs, catalase, glutathione peroxidase-GPx), and small molecular weight antioxidants (vitamins C and E, flavonoids, carotenoids, melatonin, ergothioneine, and others). Perhaps one of the most effective low molecular weight antioxidants is vitamin E, the first line of defense against the peroxidation of lipids. A promising approach appears to be the use of certain antioxidants (e.g. flavonoids), showing weak prooxidant properties that may boost cellular antioxidant systems and thus act as preventive anticancer agents. Redox metal-based enzyme mimetic compounds as potential pharmaceutical interventions and sirtuins as promising therapeutic targets for age-related diseases and anti-aging strategies are discussed.

Antioxidants in Down Syndrome: From Preclinical Studies to Clinical Trials

There is currently no effective pharmacological therapy to improve the cognitive dysfunction of individuals with Down syndrome (DS). Due to the overexpression of several chromosome 21 genes, cellular and systemic oxidative stress (OS) is one of the most important neuropathological processes that contributes to the cognitive deficits and multiple neuronal alterations in DS. In this condition, OS is an early event that negatively affects brain development, which is also aggravated in later life stages, contributing to neurodegeneration, accelerated aging, and the development of Alzheimer's disease neuropathology. Thus, therapeutic interventions that reduce OS have been proposed as a promising strategy to avoid neurodegeneration and to improve cognition in DS patients. Several antioxidant molecules have been proven to be effective in preclinical studies; however, clinical trials have failed to show evidence of the efficacy of different antioxidants to improve cognitive deficits in individuals with DS. In this review we summarize preclinical studies of cell cultures and mouse models, as well as clinical studies in which the effect of therapies which reduce oxidative stress and mitochondrial alterations on the cognitive dysfunction associated with DS have been assessed.

Systematic review and meta-analysis shows a specific micronutrient profile in people with Down Syndrome: Lower blood calcium, selenium and zinc, higher red blood cell copper and zinc, and higher salivary calcium and sodium

Different metabolic profiles as well as comorbidities are common in people with Down Syndrome (DS). Therefore it is relevant to know whether micronutrient levels in people with DS are also different. This systematic review was designed to review the literature on micronutrient levels in people with DS compared to age and sex-matched controls without DS. We identified sixty nine studies from January 1967 to April 2016 through main electronic medical databases PubMed, Scopus, and Web of knowledge. We carried out meta-analysis of the data on four essential trace elements (Cu, Fe, Se, and Zn), six minerals (Ca, Cl, K, Mg, Na, and P), and five vitamins (vitamin A, B9, B12, D, and E). People with DS showed lower blood levels of Ca (standard mean difference (SMD) = -0.63; 95% confidence interval (CI): -1.16 to -0.09), Se (SMD = -0.99; 95% CI: -1.55 to -0.43), and Zn (SMD = -1.30; 95% CI: -1.75 to -0.84), while red cell levels of Zn (SMD = 1.88; 95% CI: 0.48 to 3.28) and Cu (SMD = 2.77; 95% CI: 1.96 to 3.57) were higher. They had also higher salivary levels of Ca (SMD = 0.85; 95% CI: 0.38 to 1.33) and Na (SMD = 1.04; 95% CI: 0.39 to 1.69). Our findings that micronutrient levels are different in people with DS raise the question whether these differences are related to the different metabolic profiles, the common comorbidities or merely reflect DS.

Oxidative stress: A bridge between Down's syndrome and Alzheimer's disease

Besides the genetic, biochemical and neuropathological analogies between Down's syndrome (DS) and Alzheimer's disease (AD), there is ample evidence of the involvement of oxidative stress (OS) in the pathogenesis of both disorders. The present paper reviews the publications on DS and AD in the past 10 years in light of the "gene dosage" and "two-hit" hypotheses, with regard to the alterations caused by OS in both the central nervous system and the periphery, and the main pipeline of antioxidant therapeutic strategies. OS occurs decades prior to the signature pathology and manifests as lipid, protein and DNA oxidation, and mitochondrial abnormalities. In clinical settings, the assessment of OS has traditionally been hampered by the use of assays that suffer from inherent problems related to specificity and/or sensitivity, which explains some of the conflicting results presented in this work. For DS, no scientifically proven diet or drug is yet available, and AD trials have not provided a satisfactory approach for the prevention of and therapy against OS, although most of them still need evidence-based confirmation. In the future, a balanced up-regulation of endogenous antioxidants, together with multiple exogenous antioxidant supplementation, may be expected to be one of the most promising treatment methods.

Selenium and the brain: a review

Similar to other tissues selenium from selenomethionine is deposited in the brain at higher concentrations than selenium in other forms. Vitamin E has a greater effect than selenium in reducing lipid peroxidation in various brain regions. Selenium does not have as great effect on glutathione peroxidase (GPX) activity in the brain as in most other organs. Prolonged selenium and iodine deficiencies will compromise thyroid hormone homeostatus in the brain and this is due to changes in deiodinases activities and lipid peroxidation. Even though selenium deficiency results in reduced GPX activity and selenium content in the brain, there is no reduction in thioredoxin reductase activity or selenoprotein W levels. Selenoprotein P is taken up in greater amounts by the brain but not by other organs in selenium deficient animals, suggesting a critical function of this selenoprotein in this organ. Selenium will influence compounds with hormonal activity (and neurotransmitters) in the brain, and this is postulated to be the reason selenium affects moods in humans and behavior in animals. Even though selenium counteracts the neurotoxicity of mercury, cadmium, lead and vanadium, it causes them to accumulate in the brain, presumably in a nontoxic complex.

Antioxidative metabolism in Down syndrome

Down syndrome is the most common cause of mental retardation, affecting 1 in 700-800 liveborn infants. Although numerous biochemical abnormalities accompanying the syndrome have not yet been completely clarified, the antioxidant defense system enzymes have shown to be altered due to increased gene dosage on chromosome 21 and overproduction of superoxide dismutase (SOD-1 or Cu/Zn SOD). The purpose of this study was to investigate the activities of SOD-1 and glutathione peroxidase (GSH-Px) enzymes and the levels of their cofactors zinc (Zn), copper (Cu) and selenium (Se) in plasma of 20 Down syndrome patients. In comparison with age and sex-matched controls (n = 15), plasma GSH-Px, SOD, and Cu levels were significantly decreased in the patient group, but Zn and Se concentrations remained unchanged.

Changed serum trace element profile in Down's syndrome

Being cofactors of important antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx), which are significantly modified in Down's syndrome (trisomy 21), serum levels of microtrace elements zinc, copper, and selenium and of macroelement magnesium are reported in 16 subjects with Down's syndrome (DS) and their respective well age- and sex-matched controls. Serum zinc and selenium levels were significantly lowered in DS subjects, whereas copper levels were elevated. Consequently, a marked increase (40%) of the copper/zinc ratio in DS persons was observed. There were no differences in serum levels of magnesium between DS and control subjects.

Selenium homeostasis in the central nervous system of the rat

These experiments have investigated selenium movement between blood and CNS in anaesthetised rats. Each animal was surgically anaesthetised and the left femoral blood vessels cannulated for blood withdrawal and solute infusion. Each rat received 75-selenium as sodium selenite infused in normal saline and experiments lasted between 5 minutes and 5 hours during which blood samples were periodically taken. At termination, the CNS was removed, regionally dissected and analysed with the plasma samples for 75-Se radioactivity by gamma-counting. Data were analysed by graphical analysis. Results showed unidirectional uptake of 75-Se into the CNS and regional differences were not found except for the hypothalamus. On average the CNS influx rate constant (Kin) was about 7 +/- 1 x 10(-5) ml/min/g. Data suggest that the 75-Se most likely entered the CNS as a free ionic form.

Uptake of 75-Selenium into the central nervous system of the rat

These experiments have investigated selenium movement between blood and the CNS in anaesthetized rats. Each animal was anaesthetized and the left femoral blood vessels cannulated for blood withdrawal and solute infusion. Each rat received 75-Se as sodium selenite infused in normal saline and experiments lasted between 5 minutes and 5 hours during which blood samples were periodically taken. At termination, the CNS was removed, dissected and analysed with the plasma samples for 75-Se radioactivity by gamma-counting. Data were analyzed by multiple-time uptake analysis. Results showed unidirectional uptake of 75-Se into the CNS and some regional differences were found. On average the CNS influx rate constant (Kin) was about 7 +/- 1 x 10(-5) ml/min/g. This indicates that the 75-Se most likely entered the CNS in a protein-bound form.

Modulation of procainamide toxicity by selenium-enriched yeast in rats

Free radical processes are proposed to play a crucial role in the development of procainamide adverse effects. Therefore, selenium, as a potent antioxidant, may modified procainamide toxicity. To test this hypothesis plasma and liver thiobarbituric acid-reacting substances (TBARS), plasma antioxidant activity (AOA), erythrocyte and liver superoxide dismutase (SOD), catalase, as well as selenium-dependent glutathione peroxidase (Se-GPX) were determined in the following four groups of rats: selenium-treated (Se), procainamide-treated (P), procainamide and selenium-treated (P + Se), and control (C). Morphological studies of leukocytes [tested for lupus erythematosus (LE) cells] and liver were also made. Atypical, i.e. enlarged and swollen, leukocytes resulting from procainamide and selenium treatment were observed. These changes were found in four out of five rats in the Se group, eight out of ten in the P group, and in seven out of ten in the P + Se group. LE-like cells were observed in two rats in the P + Se group. A statistically significant decrease in plasma and liver TBARS by 20% and 36%, respectively, increased activity of SOD by 20%, catalase by 48% and Se-GPX by 15% in erythrocytes, and decreased activity of liver SOD by 17% and catalase by 22% were found in the P + Se group as compared to the P group. These results indicated that selenium exerted antioxidant effects on the procainamide-treated rats. However, selenium did not prevent the development of disturbances in leukocyte morphology, on the contrary, it possibly promoted the conversion of leukocytes to LE cells.

Down's syndrome, dementia, and superoxide dismutase

Mental handicap includes specific behavioural phenotypes apparently caused by single enzyme errors or deletions, for example, compulsive self-mutilation and hypoxanthine-guanine phosphoribosyl transferase deficiency in the Lesch-Nyham syndrome. In Down's syndrome, the possession of additional genetic material is found to be linked to various physical abnormalities (premature cataract formation and hypothyroidism). These close associations between types of behaviour, illnesses, and known genetic abnormalities offer promising avenues for research. In this article we concentrate on the well known link between Down's syndrome and presenile dementia.

Increase in serum concentrations of IgG2 and IgG4 by selenium supplementation in children with Down's syndrome

In a previous study on children with Down's syndrome a reduced rate of infections was reported by their parents after the children had received six months' treatment with selenium supplements. In the present study the concentrations of the four IgG subclasses were measured in 29 of these children in samples of serum obtained before and immediately after the period of supplementation and one year after it had finished. Selenium had a significant augmentative effect on the serum concentrations of IgG2 and IgG4, but not of IgG1 and IgG3. This effect was not related to age, as among children over the age of 6 years the serum concentrations of IgG2 and IgG4 had decreased significantly one year after the treatment had been stopped. This study suggests that selenium has an immunoregulatory effect, which might be of importance in both basic research and clinical practice.