Selenium homeostasis in human brain cells: Effects of copper (II) and Se species

BackgroundBoth essential trace elements selenium (Se) and copper (Cu) play an important role in maintaining brain function. Homeostasis of Cu, which is tightly regulated under physiological conditions, seems to be disturbed in Alzheimer´s (AD) and Parkinson´s disease (PD) patients. Excess Cu promotes the formation of oxidative stress, which is thought to be a major cause for development and progression of neurological diseases (NDs). Most selenoproteins exhibit antioxidative properties and may counteract oxidative stress. However, expression of selenoproteins is altered under conditions of Se deficiency. Serum Se levels are decreased in AD and PD patients suggesting Se as an important factor in the development and progression of NDs. The aim of this study was to elucidate the interactions between Cu and Se in human brain cells particularly with respect to Se homeostasis.MethodsFirstly, modulation of Se status by selenite or SeMet were assessed in human astrocytes and human differentiated neurons. Therefore, cellular total Se content, intra- and extracellular selenoprotein P (SELENOP) content, and glutathione peroxidase (GPX) activity were quantified. Secondly, to investigate the impact of Cu on these markers, cells were exposed to copper(II)sulphate (CuSO₄) for 48 h. In addition, putative protective effects of Se on Cu-induced toxicity, as measured by cell viability, DNA damage, and neurodegeneration were investigated.ResultsModulation of cellular Se status was strongly dependent on Se species. In detail, SeMet increased total cellular Se and SELENOP content, whereas selenite led to increased GPX activity and SELENOP excretion. Cu treatment resulted in 133-fold higher cellular Cu concentration with a concomitant decrease in Se content. Additionally, SELENOP excretion was suppressed in both cell lines, while GPX activity was diminished only in astrocytes. These effects of Cu could be partially prevented by the addition of Se depending on the cell line and Se species used. While Cu-induced oxidative DNA damage could not be prevented by addition of Se regardless of chemical species, SeMet protected against neurite network degeneration triggered by Cu.ConclusionCu appears to negatively affect Se status in astrocytes and neurons. Especially with regard to an altered homeostasis of those trace elements during aging, this interaction is of high physiological relevance. Increasing Cu concentrations associated with decreased selenoprotein expression or functionality might be a promoting factor for the development of NDs.     

Effects of selenium supplementation on diet-induced obesity in mice with a disruption of the selenocysteine lyase gene

BACKGROUNDThe amino acid selenocysteine (Sec) is an integral part of selenoproteins, a class of proteins mostly involved in strong redox reactions. The enzyme Sec lyase (SCLY) decomposes Sec into selenide allowing for the recycling of the selenium (Se) atom via the selenoprotein synthesis machinery. We previously demonstrated that disruption of the Scly gene (Scly KO) in mice leads to the development of obesity and metabolic syndrome, with effects on glucose homeostasis, worsened by Se deficiency or a high-fat diet, and exacerbated in male mice. Our objective was to determine whether Se supplementation could ameliorate obesity and restore glucose homeostasis in the Scly KO mice.METHODSThree-weeks old male and female Scly KO mice were fed in separate experiments a diet containing 45 % kcal fat and either sodium selenite or a mixture of sodium selenite and selenomethionine (selenite/SeMet) at moderate (0.25 ppm) or high (0.5–1 ppm) levels for 9 weeks, and assessed for metabolic parameters, oxidative stress and expression of selenoproteins.RESULTSSe supplementation was unable to prevent obesity and elevated epididymal white adipose tissue weights in male Scly KO mice. Serum glutathione peroxidase activity in Scly KO mice was unchanged regardless of sex or dietary Se intake; however, supplementation with a mixture of selenite/SeMet improved oxidative stress biomarkers in the male Scly KO mice.CONCLUSIONThese results unveil sex- and selenocompound-specific regulation of energy metabolism after the loss of Scly, pointing to a role of this enzyme in the control of whole-body energy metabolism regardless of Se levels.     

The Effects of Zinc Treatment on the Blood–Brain Barrier Permeability and Brain Element Levels During Convulsions

We evaluated the effect of zinc treatment on the blood–brain barrier (BBB) permeability and the levels of zinc (Zn), natrium (Na), magnesium (Mg), and copper (Cu) in the brain tissue during epileptic seizures. The Wistar albino rats were divided into four groups, each as follows: (1) control group, (2) pentylenetetrazole (PTZ) group: rats treated with PTZ to induce seizures, (3) Zn group: rats treated with ZnCl₂ added to drinking water for 2 months, and (4) Zn?+?PTZ group. The brains were divided into left, right hemispheres, and cerebellum?+?brain stem regions. Evans blue was used as BBB tracer. Element concentrations were analyzed by inductively coupled plasma optical emission spectroscopy. The BBB permeability has been found to be increased in all experimental groups (p?<?0.05). Zn concentrations in all brain regions in Zn-supplemented groups (p?<?0.05) showed an increase. BBB permeability and Zn level in cerebellum?+?brain stem region were significantly high compared to cerebral hemispheres (p?<?0.05). In all experimental groups, Cu concentration decreased, whereas Na concentrations showed an increase (p?<?0.05). Mg content in all the brain regions decreased in the Zn group and Zn?+?PTZ groups compared to other groups (p?<?0.001). We also found that all elements’ levels showed hemispheric differences in all groups. During convulsions, Zn treatment did not show any protective effect on BBB permeability. Chronic Zn treatment decreased Mg and Cu concentration and increased Na levels in the brain tissue. Our results indicated that Zn treatment showed proconvulsant activity and increased BBB permeability, possibly changing prooxidant/antioxidant balance and neuronal excitability during seizures.     

Effects of Supplementary Selenium Source on the Blood Parameters in Beef Cows and Their Nursing Calves

Over 2 years, 32 beef cows nursing calves in southwest Arkansas were randomly selected from a herd of 120 that were managed in six groups and were assigned to six 5.1-ha bermudagrass (Cynodon dactylon [L.] Pers.) pastures. Treatments were assigned to pastures (two pastures/treatment) and cows had ad libitum access to one of three free-choice minerals: (1) no supplemental selenium (Se), (2) 26 mg of supplemental Se from sodium selenite per kilogram, and (3) 26 mg of supplemental Se from seleno-yeast per kilogram (designed mineral intake?=?113 g/cow daily). Data were analyzed using a mixed model; year and pasture were the random effects and treatment was the fixed effect. At the beginning of the calving and breeding seasons, cows supplemented with Se had greater (P?<?0.01) whole blood Se concentration (WBSe) and glutathione peroxidase activities (GSH-Px) than cows receiving no supplemental Se; cows fed seleno-yeast had greater (P?≤?0.05) WBSe than cows fed sodium selenite, but GSH-Px did not differ (P?≥?0.25) between the two sources. At birth and near peak lactation (late May), calves from cows supplemented with Se had greater (P?<?0.01) WBSe than calves from cows fed no Se and calves from cows fed seleno-yeast had greater (P?≤?0.01) WBSe and GSH-Px than calves from cows fed sodium selenite. Thyroxine (T₄), triiodothyronine (T₃), and the T₄:T₃ ratio in calves did not differ among treatments (P?≥?0.35). At birth, insulin-like growth factor 1 (IGF-1) was greater (P?=?0.02) in calves nursing cows with no supplemental Se than in ones with supplemental Se; in calves nursing cows with supplemental sodium selenite, IGF-1 did not differ (P?=?0.96) from ones offered supplemental seleno-yeast. Selenium supplementation of gestating beef cows benefited cows and calves by increasing WBSe and GSH-Px. The use of seleno-yeast as a Se supplement compared to sodium selenite increased the WBSe of both cows and their calves without affecting the T₄ to T₃ conversion or IGF-1 concentrations.     

Maternal perinatal transfer of vitamins and trace elements to piglets

Nursing piglets are entirely dependent, for their micronutrient provisions, upon in utero, colostrum and milk transfers from the dam. An adequate maternal transfer of micronutrients is all the more important during these periods which, in fact, lasts for approximately half the life cycle (conception to slaughter) of modern pigs. The present study aimed to set up a simple approach to assess the maternal perinatal transfer of vitamins and trace elements in sows. Prenatal transfer (R-u) was estimated as limited, passive or active using the ratio between pre-colostral serum concentrations of a given micronutrient in newborn piglets and corresponding pre-farrowing values in sows. Efficiency of the postnatal transfer (R-c) was estimated from the ratio between serum concentrations of post- and pre-colostral micronutrients in piglets. Data from literature (12 studies) were used for vitamins A, D, E, C, folic acid and B₁₂, whereas vitamins B₂, B₃, B₆ and B₈ as well as Zn, Fe, Cu and Se were generated from a trial where blood sera from 20 sows, and their litter were collected during the perinatal period. In sow trial, statistical t tests were used to determine if ratios differed from 1. Prenatal transfer was active and in favour of piglets (R-u > 1, P < 0.03) for Zn and vitamins B₆ and B₈ (sow trial) as well as for vitamins C and B₁₂ (literature data). This transfer was limited (R-u < 1, P < 0.01) for vitamin B₂, Fe, Cu and Se (sow trial) and for vitamins A, E, D and folic acid (literature data) whereas it was passive for vitamin B₃ (R-u = 1, P > 0.37). After birth, the early postnatal transfer through colostrum was active towards piglets for most micronutrients but vitamins B₆ and B₈ (R-c < 1, P < 0.01). Globally, the perinatal transfer (combination of R-u and R-c) was favourable to the neonatal piglets for most micronutrients except for vitamins A and D as well as Fe, Cu and Se whereas there is apparently a barrier for prenatal transfer which is not compensated by the colostrum provision to neonatal piglets. Then, post-colostral concentrations of these micronutrients in piglets remain below prenatal levels of their dam. Neonatal strategies of micronutrient provision are known for Fe (intramuscular injection) and Se (sow milk enrichment). Further studies are needed to assess the importance of the unfavourable perinatal transfer for Cu and vitamins A and D for piglet robustness later in life.     

Deletion of Thioredoxin Reductase and Effects of Selenite and Selenate Toxicity in Caenorhabditis elegans

Thioredoxin reductase-1 (TRXR-1) is the sole selenoprotein in C. elegans, and selenite is a substrate for thioredoxin reductase, so TRXR-1 may play a role in metabolism of selenium (Se) to toxic forms. To study the role of TRXR in Se toxicity, we cultured C. elegans with deletions of trxr-1, trxr-2, and both in axenic media with increasing concentrations of inorganic Se. Wild-type C. elegans cultured for 12 days in Se-deficient axenic media grow and reproduce equivalent to Se-supplemented media. Supplementation with 0–2 mM Se as selenite results in inverse, sigmoidal response curves with an LC₅₀ of 0.20 mM Se, due to impaired growth rather than reproduction. Deletion of trxr-1, trxr-2 or both does not modulate growth or Se toxicity in C. elegans grown axenically, and ⁷⁵Se labeling showed that TRXR-1 arises from the trxr-1 gene and not from bacterial genes. Se response curves for selenide (LC₅₀ 0.23 mM Se) were identical to selenite, but selenate was 1/4^th as toxic (LC₅₀ 0.95 mM Se) as selenite and not modulated by TRXR deletion. These nutritional and genetic studies in axenic media show that Se and TRXR are not essential for C. elegans, and that TRXR alone is not essential for metabolism of inorganic Se to toxic species.     

Treatment with outgrowth endothelial cells protects cerebral barrier against ischemic injury

Background and aimsWe have previously reported that outgrowth endothelial cells (OECs) restore cerebral endothelial cell integrity through effective homing to the injury site. This study further investigates whether treatment with OECs can restore blood–brain barrier (BBB) function in settings of ischemia-reperfusion injury both in vitro and in vivo.MethodsAn in vitro model of human BBB was established by co-culture of astrocytes, pericytes, and human brain microvascular endothelial cells (HBMECs) before exposure to oxygen-glucose deprivation alone or followed by reperfusion (OGD±R) in the absence or presence of exogenous OECs. Using a rodent model of middle cerebral artery occlusion (MCAO), we further assessed the therapeutic potential of OECs in vivo.ResultsOwing to their prominent antioxidant, proliferative, and migratory properties, alongside their inherent capacity to incorporate into brain vasculature, treatments with OECs attenuated the extent of OGD±R injury on BBB integrity and function, as ascertained by increases in transendothelial electrical resistance and decreases in paracellular flux across the barrier. Similarly, intravenous delivery of OECs also led to better barrier protection in MCAO rats as evidenced by significant decreases in ipsilateral brain edema volumes on day 3 after treatment. Mechanistic studies subsequently showed that treatment with OECs substantially reduced oxidative stress and apoptosis in HBMECs subjected to ischemic damages.ConclusionThis experimental study shows that OEC-based cell therapy restores BBB integrity in an effective manner by integrating into resident cerebral microvascular network, suppressing oxidative stress and cellular apoptosis.     

Meta-analysis of selenium accumulation and expression of antioxidant enzymes in chicken tissues

A meta-analysis integrating results of 40 selenium (Se) supplementation experiments that originated from 35 different controlled randomized trials was carried out in an attempt to identify significant factors that affect tissue Se accumulation in chicken. Examined factors included: Se source (12 different sources examined), type of chicken (laying hens or broilers), age of birds at the beginning of supplementation, duration of supplementation, year during which the study was conducted, sex of birds, number of chickens per treatment, method of analysis, tissue type, concentration of Se determined and Se added to feed. A correlation analysis was also carried out between tissue Se concentration and glutathione peroxidase activity. Data analysis showed that the factors significantly affecting tissue Se concentration include type of chicken (P=0.006), type of tissue (P<0.001) and the analytical method used (P=0.014). Although Se source was not found to affect tissue Se concentration (overall P>0.05), certain inorganic (sodium selenite), calcium selenite, sodium selenate and organic sources (B-Traxim Se), Se-yeast, Se-malt, Se-enriched cabbage and Se-enriched garlic as well as background Se level from feed ingredients were found to significantly affect tissue Se concentration. The Se accumulation rate (estimated as linear regression coefficient of Se concentrations to Se added to feed) discriminated between the various tissues with highest values estimated in the leg muscle and lowest in blood plasma. Correlation analysis has also shown that tissue Se concentration (pooled data) was correlated to Se added to feed (r=0.529, P<0.01, log values) and to glutathione peroxidase activity (r=0.332, P=0.0478), with the latter not being correlated with Se added to feed. Although significant factors affecting Se concentration were reported in the present study, they do not necessarily indicate the in vivo function of the antioxidant system or the level of accumulated Se as other factors, not examined in the present study, may interact at the level of trace element absorption, distribution and retention.     

Selenium Supplementation Decreases Hepatic Fibrosis in Mice After Chronic Carbon Tetrachloride Administration

Oxidative stress stimulates fibrogenesis, and selenium (Se) has antioxidant properties. This study determined whether Se supplementation affects CCl₄-induced liver injury and fibrosis. Mice were administered CCl₄ over 4 weeks, while controls received olive oil. Se was provided as sodium selenite in the drinking water. Se increased liver Se-dependent glutathione peroxidase activity and decreased liver malondialdehyde after CCl₄. Se decreased liver inflammation but not necrosis caused by CCl₄. Se increased hepatocyte apoptosis after CCl₄ and the pro-apoptotic BAX and Bcl Xs/l proteins. Stellate cell apoptosis occurred only after CCl₄ in Se-supplemented mice. Se decreased stellate cell number and fibrosis after CCl₄. Liver matrix metalloproteinase-9 increased after CCl₄ with Se supplementation. In conclusion, Se supplementation decreased hepatic fibrosis after CCl₄ in the setting of decreased inflammation but increased apoptosis. The principal mechanisms for the decreased fibrosis are a lower number of collagen-producing stellate cells and increased collagen degradation.     

Biomarkers in critically ill patients with systemic inflammatory response syndrome or sepsis supplemented with high-dose selenium

ObjectiveLow levels of selenium (Se) and glutathione peroxidase (GSHPx), a key selenoenzyme, were documented in systemic inflammatory response syndrome (SIRS) and sepsis, both associated with high mortality. Se supplementation had mixed effects on outcome. We hypothesized that Se supplementation could have a different impact on biomarkers and 28-day mortality in patients with SIRS vs. sepsis.MethodsAdult patients with SIRS or sepsis were randomized to either high-dose (Se+, n = 75) or standard-dose (Se−, n = 75) Se supplementation. Plasma Se, whole blood GSHPx activity, C-reactive protein (CRP), procalcitonin (PCT), prealbumin, albumin and cholesterol levels were measured serially up to day 14.ResultsThere was no difference in mortality between Se− (24/75) vs. Se+ group (19/75; p = 0.367) or between SIRS and septic patients (8/26 vs. 35/124; p = 0.794). There was a trend to reduced mortality in SIRS patients in the Se+ vs. Se− group (p = 0.084). Plasma Se levels increased in the Se+ group only in patients with sepsis but not in patients with SIRS. Plasma Se levels correlated with GSHPx. In SIRS/Se+ group, Se correlated only with GSHPx. In SIRS/Se− group, Se correlated with cholesterol but not with other biomarkers. In sepsis patients, Se levels correlated with cholesterol, GSHPx and prealbumin. Cholesterol levels were higher in survivors in the Se− group.ConclusionsSe levels correlated with GSHPx activity and other nutritional biomarkers with significant differences between SIRS and sepsis groups. High-dose Se supplementation did not affect mortality but a strong trend to decreased mortality in SIRS patients warrants further studies in this population.     

Microencapsulated sodium selenite supplementation in dairy cows: effects on selenium status

The objective of this study was to compare the efficiency of transfer of selenium (Se) to plasma and milk from inorganic sodium selenite, either free or microencapsulated, and from selenized yeast in dairy cows. The study consisted of an in situ-nylon bags incubation, and in an in vivo experiment to compare the Se status of cows supplemented with either sodium selenite, microencapsulated sodium selenite, or Se yeast. Thirty dairy cows, divided in five groups, were fed the following diets: the control group (CTR) received a total mixed ration supplemented with sodium selenite in order to have 0.3 mg/kg DM of total Se; 0.3M and 0.5M groups received the same control diet supplemented with lipid microencapsulated sodium selenite to provide 0.3 and 0.5 mg/kg DM of total Se, respectively; 0.3Y and 0.5Y groups received selenized yeast to provide 0.3 and 0.5 mg/kg of total Se, respectively. Cows were fed the supplements for 56 days during which milk, blood, and fecal samples were collected weekly to conduct analysis of Se and glutathione peroxidase (GSH-px) activity. Se concentration in the nylon bags was assessed to 72%, 64%, and 40% of the initial value (time 0) after 4, 8, and 24 h of incubation, respectively. In vivo, cows supplemented with 0.3 mg/kg of microencapsulated Se had higher milk Se concentration compared to CTR. The increment was more pronounced at the highest inclusion rate (0.5 mg/kg, 0.5M group). GSH-px activity was not significantly affected by treatments. The results indicate that lipid microencapsulation has the potential to protect nutrients from complete rumen reduction and that Se from microencapsulated selenite is incorporated in milk more efficiently than the free form. Microencapsulated sodium selenite was shown to be comparable to Se-yeast in terms of availability and incorporation in milk when fed at 0.3 mg/kg DM, whereas the inclusion in the diet at 0.5 mg/kg DM resulted in higher plasma and milk concentrations than selenized yeast.     

Phospholipid Transfer Protein Is Expressed in Cerebrovascular Endothelial Cells and Involved in High Density Lipoprotein Biogenesis and Remodeling at the Blood-Brain Barrier

Phospholipid transfer protein (PLTP) is a key protein involved in biogenesis and remodeling of plasma HDL. Several neuroprotective properties have been ascribed to HDL. We reported earlier that liver X receptor (LXR) activation promotes cellular cholesterol efflux and formation of HDL-like particles in an established in vitro model of the blood-brain barrier (BBB) consisting of primary porcine brain capillary endothelial cells (pBCEC). Here, we report PLTP synthesis, regulation, and its key role in HDL metabolism at the BBB. We demonstrate that PLTP is highly expressed and secreted by pBCEC. In a polarized in vitro model mimicking the BBB, pBCEC secreted phospholipid-transfer active PLTP preferentially to the basolateral (“brain parenchymal”) compartment. PLTP expression levels and phospholipid transfer activity were enhanced (up to 2.5-fold) by LXR activation using 24(S)-hydroxycholesterol (a cerebral cholesterol metabolite) or TO901317 (a synthetic LXR agonist). TO901317 administration elevated PLTP activity in BCEC from C57/BL6 mice. Preincubation of HDL₃ with human plasma-derived active PLTP resulted in the formation of smaller and larger HDL particles and enhanced the capacity of the generated HDL particles to remove cholesterol from pBCEC by up to 3-fold. Pre-β-HDL, detected by two-dimensional crossed immunoelectrophoresis, was generated from HDL₃ in pBCEC-derived supernatants, and their generation was markedly enhanced (1.9-fold) upon LXR activation. Furthermore, RNA interference-mediated PLTP silencing (up to 75%) reduced both apoA-I-dependent (67%) and HDL₃-dependent (30%) cholesterol efflux from pBCEC. Based on these findings, we propose that PLTP is actively involved in lipid transfer, cholesterol efflux, HDL genesis, and remodeling at the BBB.     

Blood-to-brain influx transport of nicotine at the rat blood–brain barrier: Involvement of a pyrilamine-sensitive organic cation transport process

Nicotine is the most potent neural pharmacological alkaloid in tobacco, and the modulation of nicotine concentration in the brain is important for smoking cessation therapy. The purpose of this study was to elucidate the net flux of nicotine transport across the blood–brain barrier (BBB) and the major contributor to nicotine transport in the BBB. The in vivo brain-to-blood clearance was determined by a combination of the rat brain efflux index method and a rat brain slice uptake study, and the blood-to-brain transport of nicotine was evaluated by in vivo vascular injection in rats and a conditionally immortalized rat brain capillary endothelial cell line (TR-BBB13 cells) as an in vitro model of the rat BBB. The blood-to-brain nicotine influx clearance was obtained by integration plot analysis as 272 μL/(min g brain), and this value was twofold greater than the brain-to-blood efflux clearance (137 μL/(min g brain)). Thus, it is suggested that the net flux of nicotine transport across the BBB is dominated by blood-to-brain influx transport. In vivo blood-to-brain nicotine transport was inhibited by pyrilamine. [³H]Nicotine uptake by TR-BBB13 cells exhibited time-, temperature-, and concentration-dependence with a K_m value of 92 μM. Pyrilamine competitively inhibited nicotine uptake by TR-BBB13 cells with a K_i value of 15 μM, whereas substrates and inhibitors of organic cation transporters had little effect. These results suggest that pyrilamine-sensitive organic cation transport process(es) mediate blood-to-brain influx transport of nicotine at the BBB, and this is expected to play an important role in regulating nicotine-induced neural responses.     

Copper/zinc and copper/selenium ratios,and oxidative stress as biochemical markers in recurrent aphthous stomatitis

ProjectRecurrent aphthous stomatitis (RAS) is a common oral mucosal disorder characterized by recurrent, painful oral aphthae, and oxidative stress presumably contributes to its pathogenesis. The aim of this study is to scrutinize the relationship between oxidative stress and serum trace elements (copper, Cu; zinc, Zn; selenium, Se), and to evaluate the ratios of Cu/Zn and Cu/Se in this disorder.ProcedurePatients with RAS (n = 33) and age- and sex-matched healthy control subjects (n = 30) were enrolled in this study. Malondialdehyde (MDA) concentrations in plasma and the activities of superoxide dismutase (SOD1; CuZnSOD), glutathione peroxidase (GPx) and catalase (CAT) in erythrocyte were determined as spectrophotometric. Also, the levels of Se, Zn and Cu in serum were determined on flame and furnace atomic absorption spectrophotometer using Zeeman background correction.Results and conclusionsOxidative stress was confirmed by the significant elevation in plasma MDA, and by the significant decrease in CAT, SOD1, and GPx (p < 0.05). When compared to controls, Zn and Se levels were significantly lower in patients, whereas Cu levels was higher in RAS patients than those in controls (p < 0.05). In addition, the correlation results of this study were firstly shown that there were significant and positive correlations between Se–CAT, Se–GPx, and Cu–MDA parameters, but negative correlations between Se–Cu, Se–MDA, Cu–CAT, Cu–SOD1 and Cu–GPx parameters in RAS patients. Furthermore, the ratios of Cu/Zn and Cu/Se were significantly higher in the patients than the control subjects (p < 0.05). Our results indicated that lipid peroxidation associated with the imbalance of the trace elements seems to play a crucial role in the pathogenesis of RAS. Furthermore, the serum Cu/Zn and Cu/Se ratios may be used as biochemical markers in these patients.     

A Simple Method for Assessing Free Brain/Free Plasma Ratios Using an In Vitro Model of the Blood Brain Barrier

Historically, the focus has been to use in vitro BBB models to optimize rate of drug delivery to the CNS, whereas total in vivo brain/plasma ratios have been used for optimizing extent. However, these two parameters do not necessarily show good correlations with receptor occupancy data or other pharmacological readouts. In line with the free drug hypothesis, the use of unbound brain concentrations (Cu,br) has been shown to provide the best correlations with pharmacological data. However, typically the determination of this parameter requires microdialysis, a technique not ideally suited for screening in early drug development. Alternative, and less resource-demanding methodologies to determine Cu,br employ either equilibrium dialysis of brain homogenates or incubations of brain slices in buffer to determine fraction unbound brain (fu,br), which is subsequently multiplied by the total brain concentration to yield Cu,br. To determine Cu,br/Cu,pl ratios this way, still requires both in vitro and in vivo experiments that are quite time consuming. The main objective of this study was to explore the possibility to directly generate Cu,br/Cu,pl ratios in a single in vitro model of the BBB, using a co-culture of brain capillary endothelial and glial cells in an attempt to mimick the in vivo situation, thereby greatly simplifying existing experimental procedures. Comparison to microdialysis brain concentration profiles demonstrates the possibility to estimate brain exposure over time in the BBB model. A stronger correlation was found between in vitro Cu,br/Cu,pl ratios and in vivo Cu,br/Cu,pl obtained using fu,br from brain slice than with fu,br from brain homogenate for a set of 30 drugs. Overall, Cu,br/Cu,pl ratios were successfully predicted in vitro for 88% of the 92 studied compounds. This result supports the possibility to use this methodology for identifying compounds with a desirable in vivo response in the CNS early on in the drug discovery process.     

Neurological diseases at the blood-brain barrier: Stemming new scientific paradigms using patient-derived induced pluripotent cells

The blood-brain barrier (BBB) is a component of the neurovascular unit formed by specialized brain microvascular endothelial cells (BMECs) surrounded by a specific basement membrane interacting with astrocytes, neurons, and pericytes. The BBB plays an essential function in the maintenance of brain homeostasis, by providing a physical and chemical barrier against pathogens and xenobiotics. Although the disruption of the BBB occurs with several neurological disorders, the scarcity of patient material source and lack of reliability of current in vitro models hindered our ability to model the BBB during such neurological conditions. The development of novel in vitro models based on patient-derived stem cells opened new venues in modeling the human BBB in vitro, by being more accurate than existing in vitro models, but also bringing such models closer to the in vivo setting. In addition, patient-derived models of the BBB opens the avenue to address the contribution of genetic factors commonly associated with certain neurological diseases on the BBB pathophysiology. This review provides a comprehensive understanding of the BBB, the current development of stem cell-based models in the field, the current challenges and limitations of such models.     

Performance,carcass characteristics and meat quality of Nellore cattle supplemented with supranutritional doses of sodium selenite or selenium-enriched yeast

The enrichment of meat with selenium is important to improve the intake of selenium by humans. The effects of supranutritional doses of sodium selenite or selenium-enriched yeast on performance, carcass characteristics and meat quality were evaluated using 63 Nellore cattle in a completely randomized design with two sources (sodium selenite and selenium-enriched yeast), three levels (0.3, 0.9 and 2.7 mg Se/kg DM) and control treatment (without addition of selenium). Final body weight (BW), average daily gain, dry matter intake and gain to feed ratio (G : F) at the end of 84 days of supplementation were not influenced by treatments (P>0.05). Values of pH, ribeye area, back fat thickness and marbling score were also not influenced by treatments (P>0.05). Dressing percentage was greater (P=0.02) in Nellore cattle supplemented with organic Se (58.70%) compared to animals supplemented with inorganic Se (57.94%). Hot carcass weight increased (P=0.05) with the increasing of Se levels in the diet. Colour, shear force (SF), cooking and drip loss remained unchanged (P>0.05); however thiobarbituric acid reactive substances was 15.51% higher with inorganic Se compared with organic Se. The selenium concentration in the meat of animals receiving organic selenium was higher (P<0.001) than that of animals receiving sodium selenite, at all levels (0.3; 0.9 and 2.7 mg/kg DM). The meat of animals receiving 2.7 mg of organic Se/kg of DM presented concentration of 372.7 μg Se/kg in the L.dorsi muscle, and the intake of 150 g of this meat by humans provides approximately 100% of the recommended Se intake (55 μg Se/day for adults). Therefore, the use of supranutritional doses of 2.7 mg Se/kg of DM, regardless of source, is a way of naturally producing selenium-enriched meat without compromising performance, carcass characteristics and quality of Nellore bovine meat.     

Selenium Improves Physiological Parameters and Alleviates Oxidative Stress in Shoots of Lead-Exposed <Emphasis Type="Italic">Vicia faba</Emphasis> L. <Emphasis Type="Italic">minor</Emphasis> Plants Grown Under Phosphorus-Deficient Conditions

The goal of the study was to investigate the effects of exogenous selenium (Se) on the tolerance of faba bean plants to lead (Pb) stress under P-deficient conditions. The bean plants were grown for 2 weeks on Hoagland solution supplied with Pb (0, 50 μM) and Se (0, 1.5, or 6 μM), separately or simultaneously. It was shown that Pb did not affect shoot growth but caused major damage in the leaves, which was accompanied by Pb accumulation in these tissues. The exposure of the shoots to Pb led to significant changes in the biochemical parameters: the MDA content, glutathione peroxidase (GSH-Px), guaiacol peroxidase (GPOX), and catalase (CAT) activity increased. Furthermore, Pb intensified O ₂ ^?? and H₂O₂ production. Both the Se concentrations used increased the chlorophyll b, chlorophyll a+b, and carotenoid content in the faba bean plants. Selenite also generally enhanced CAT, GPOX, and GSH-Px activities and the T-SH level. Our results imply that the degree of disturbances caused by Pb could be partially ameliorated by Se supplementation. Selenite at a lower dose alleviated Pb toxicity by decreased H₂O₂ and O ₂ ^?? production and decreased the GSH-Px, GPOX, and CAT activities. The beneficial effect of the higher selenite concentration could be related to reduction of lipid peroxidation in the shoots of the Pb-treated plants. However, the effect of Se on the Pb-stressed plants greatly depended on the selenite dose in the nutrient solution.     

Cellular and nephrotoxicity of selenium species

ProjectBeside its useful functions at very low concentrations, selenium including supplementary Se sources pose a potential toxicological risk. The toxicity of selenium species was tested in HaCaT cell culture and related nephrotoxicity in mice.ProcedureThe apoptotic shrinkage and necrotic expansion of cells were measured by time-lapse image microscopy. Acute nephrotoxicity was estimated upon administration of various selenium species to mice for two weeks. To confirm or to refute the accumulation of Se in the kidney and its potential chronic effect, Se concentration in kidney tissue and histopathlology were tested.ResultsThe comparison of selenium species showed that organic lactomicroSe did not affect cell growth at 5 ppm, but inorganic nanoSe severely hampered it at lower concentration (1 ppm). The in vivo Se treatment (0.5, 5, 50 ppm, corresponding to 4, 40 and 400 μg/kg) was misleading as it did neither affect the outward appearance nor the weight of the kidney. Se accumulation was observed after selenate, selenite, SelPlex, selenite and nanoSe administration, while lactomicroSe caused no traceable accumulation. In vivo, ex vivo and in vitro experiments reflected this order of selenium toxicity: selenate > selenite > SelPlex = nanoSe > lactomicroSe.ConclusionWithin the tested species lactomicroSe was the only non-nephrotoxic selenium source recommended for nutritional Se supplementation.