A thiol-mediated active membrane transport of selenium by erythroid anion exchanger 1 protein

In this paper, we describe a thiol-mediated and energy-dependent membrane transport of selenium by erythroid anion exchanger 1 (AE1, also known as band 3 protein). The AE1 is the most abundant integral protein of red cell membranes and plays a critical role in the carbon dioxide transport system in which carbon dioxide is carried as bicarbonate in the plasma. This protein mediates the membrane transport of selenium, an essential antioxidant micronutrient, from red cells to the plasma in a manner that is distinct from the already known anion exchange mechanism. In this pathway, selenium bound to the cysteine 93 of the hemoglobin β chain (Hb-Cysβ93) is transported by the relay mechanism to the Cys317 of the amino-terminal cytoplasmic domain of the AE1 on the basis of the intrinsic interaction between the two proteins and is subsequently exported to the plasma via the Cys843 of the membrane-spanning domain. The selenium export did not occur in plain isotonic buffer solutions and required thiols, such as albumin, in the outer medium. Such a membrane transport mechanism would also participate in the export pathways of the nitric oxide vasodilator activity and other thiol-reactive substances bound to the Hb-Cysβ93 from red cells to the plasma and/or peripherals

Elevated amyloid-β plaque deposition in dietary selenium-deficient Tg2576 transgenic mice

Selenium-containing proteins (e.g., glutathione peroxidases) are important antioxidants in neuronal defense against oxidative stress. In this study, the production of amyloid-β (Aβ) plaques in the brain of the Tg2576 transgenic mice was investigated under dietary selenium-deficient conditions. The 16-week-old mice were fed a selenium-deficient diet (0.004 μg-selenium g-1-diet) or a selenium-adequate diet (0.386 μg-selenium g -1 diet) for 76 weeks. The selenium concentrations of the organs/tissues in the selenium-deficient diet-fed mice were significantly decreased in comparison to those in the selenium-adequate diet-fed mice; 1.7% of that in the selenium-adequate diet-fed mice in the liver and 43% of that in the selenium-adequate diet-fed mice in the brain. The Aβ plaques formed in the brain were fluorescently stained with thioflavin T, and then the obtained images of the brain slices were qualitatively analyzed. The feeding of the selenium-deficient diet to the Tg2576 transgenic mice resulted in more than a two-fold increase in the total area of the Aβ plaques in comparison to that of the selenium-adequate diet. The elevated Aβ plaque deposition in the selenium-deficient mice can be explained as a consequence of decrease in the selenium concentration, which suggests that the selenium status is associated with the production and/or the clearance of the Aβ peptide. The selenium-deficiency could possibly promote the onset and/or progression of Alzheimer\u27s disease (AD) dementia, if the Aβ peptides initiate a sequence of events that lead to AD dementia. Consequently, the results shown here suggest that AD has an important relation with the selenium status in vivo

Synthesis and evaluation of ethyleneoxylated and allyloxylated chalcone derivatives for imaging of amyloid β plaques by SPECT

We report radioiodinated chalcone derivatives as new SPECT imaging probes for amyloid β (Aβ) plaques. The monoethyleneoxy derivative 2 and allyloxy derivative 8 showed a high affinity for Aβ(1-42) aggregates with Ki values of 24 and 4.5 nM, respectively. Fluorescent imaging demonstrated that 2 and 8 clearly stained thioflavin-S positive Aβ plaques in the brain sections of Tg2576 transgenic mice. In vitro autoradiography revealed that [125I]2 displayed no clear accumulation toward Aβ plaques in the brain sections of Tg2576 mice, whereas the accumulation pattern of [125I]8 matched with the presence of Aβ plaques both in the brain sections of Tg2576 mice and an AD patient. In biodistribution studies using normal mice, [125I]2 showed preferable in vivo pharmacokinetics (4.82%ID/g at 2 min and 0.45%ID/g at 60 min), while [125I]8 showed only a modest brain uptake (1.62%ID/g at 2 min) with slow clearance (0.56%ID/g at 60 min). [125I]8 showed prospective binding properties for Aβ plaques, although further structural modifications are needed to improve the blood brain barrier permeability and washout from brain

99mTc/Re complexes based on flavone and aurone as SPECT probes for imaging cerebral β-amyloid plaques.

Two (99m)Tc/Re complexes based on flavone and aurone were tested as potential probes for imaging β-amyloid plaques using single photon emission computed tomography. Both (99m)Tc-labeled derivatives showed higher affinity for Aβ(1-42) aggregates than did (99m)Tc-BAT. In sections of brain tissue from an animal model of AD, the Re-flavone derivative 9 and Re-aurone derivative 19 intensely stained β-amyloid plaques. In biodistribution experiments using normal mice, (99m)Tc-labeled flavone and aurone displayed similar radioactivity pharmacokinetics. With additional modifications to improve their brain uptake, (99m)Tc complexes based on the flavone or aurone scaffold may serve as probes for imaging cerebral β-amyloid plaques

Development of alkoxy styrylchromone derivatives for imaging of cerebral amyloid-β plaques with SPECT

Abstract We report here the development of radioiodinated styrylchromone derivatives with alkoxy groups as single photon emission computed tomography (SPECT) imaging probes for cerebral amyloid-β (Aβ) plaques. Among the derivatives, the methoxy derivative 14 and the dimethoxy derivative 15 displayed relatively high affinity for the Aβ(1-42) aggregates with Ki values of 22 and 46 nM, respectively. Fluorescent imaging demonstrated that 14 and 15 clearly labeled thioflavin-S positive Aβ plaques in the brain sections of Tg2576 transgenic mice. In the in vivo studies, [125I]14 and [125I]15 showed high initial brain uptake expressed as the percentage of the injected dose per gram (2.25% and 2.49% ID/g at 2 min, respectively) with favorable clearance (0.12% and 0.20% ID/g at 180 min, respectively) from the brain tissue of normal mice. Furthermore, in vitro autoradiography confirmed that [125I]15 binds thioflavin-S positive regions in Tg2576 mouse brain sections. The derivative 15 may be a potential scaffold for the development of in vivo imaging probes targeting Aβ plaques in the brain. In particular, further structural modifications are required to improve the compounds binding affinity for Aβ

Thiol-targeted introduction of selenocysteine to polypeptides for synthesis of glutathione peroxidase mimics.

Because the seleno-l-cysteine (SeCys or Sec) insertion into selenoproteins occurs by a specific translational control process, it is quite difficult to express the SeCys-containing polypeptides even by the state-of-the-art genetic engineering techniques. In this paper, we describe a convenient synthetic method for the selective introduction of a SeCys derivative to polypeptides under physiological conditions. One SeCys residue in the seleno-l-cystine (SeCys-Se-Se-SeCys) methyl ester was first substituted with the Boc-protected penicillamine (Pen) methyl ester to form selenenylsulfide (SeCys-Se-S-Pen), an intermediate in the cellular glutathione peroxidase (GPx) catalytic cycle. Subsequently, the SeCys-Pen was coupled with the thiol-specific N-carboxymethylmaleimide through the α-amino group of the SeCys {[2-(N-maleimidyl)-1-oxo-ethyl-SeCys-methyl-Se-yl]-S-Pen methyl ester, MOE-SeCys-Pen}. The use of the MOE-SeCys-Pen allowed the selective introduction of the SeCys moiety to human serum albumin by alkylation of the thiol at its cysteine34, which generated the GPx-like activity responsible for the selenium atom in the MOE-SeCys-Pen. Consequently, this synthetic method will allow generating SeCys-containing artificial polypeptides with a GPx-like activity

Hemoglobin-mediated selenium export from red blood cells.

On the basis of the fact that selenium from selenite binds to hemoglobin (Hb), we investigated the missing process in the selenium export from red blood cells (RBCs), i.e., the transfer of selenium bound to Hb to RBC membrane proteins. To elucidate the molecular events of the Hb-associated selenium export from RBC, a Hb-Se complex was synthesized from thiol-exchange of Cys-beta93 in Hb with penicillamine-substituted glutathione selenotrisulfide, as a model of major metabolic intermediates, and then interactions between the Hb-Se complex and RBC inside-out vesicles (IOVs) were examined. Selenium bound to Hb was transferred to the IOV membrane on the basis of the intrinsic interactions between Hb and the cytoplasmic domains of band 3 protein (CDB3). The observed selenium transfer was inhibited by the pretreatments of IOVs with iodoacetamide and the alpha-chymotrypsin digestion, indicating that the Hb mediates the selenium transfer to the thiol groups of CDB3. In addition, it was found that deoxygenated Hb, with a high binding affinity for CDB3, more favorably transferred selenium to the IOV membranes than oxygenated Hb, with a low affinity. When selenium export from RBC to the plasma was examined by continuously introducing nitrogen gas, the selenium export rate was promoted with an increase in the rate of deoxygenated Hb. Overall, these data suggested that Hb could possibly play a role in the selenium export from RBC treated with selenite in an oxygen-linked fashion

Synthesis and biological evaluation of radio-iodinated benzimidazoles as SPECT imaging agents for NR2B subtype of NMDA receptor.

In this study, the benzimidazole derivatives were synthesized and evaluated as imaging agents for the NR2B subtype of NMDA receptor. Among these ligands, 2-{[4-(4-iodobenzyl)piperidin-1-yl]methyl}benzimidazol-5-ol (8) and N-{2-[4-(4-iodobenzyl)-piperidin-1-ylmethyl]benzoimidazol-5-yl}-methanesulfonamide (9) exhibited high affinity for the NR2B subunit (K(i) values; 7.28 nM for 8 and 5.75 nM for 9). In vitro autoradiography experiments demonstrated high accumulation in the forebrain regions but low in the cerebellum for both [(125)I]8 and [(125)I]9. These regional distributions of the radioligands correlated with the expression of the NR2B subunit. The in vitro binding of these ligands was inhibited by NR2B antagonist but not by other site ligands, which suggested the high selectivity of [(125)I]8 and [(125)I]9 for the NR2B subunit. In mice, the regional brain uptakes of [(125)I]8 and [(125)I]9 at 5-180 min after administration were 0.42-0.56% and 0.44-0.67% dose/g, respectively. The brain-to-blood ratio of [(125)I]8 at 180 min was reduced by 34% in the presence of non-radioactive ligands and by 59% in the presence of the NR2B ligand Ro-25,6981. These results indicated that [(125)I]8 could be partially bound to the NR2B subunit in vivo. Although the brain uptake of these benzimidazole derivatives was too low to allow for in vivo SPECT imaging, these compounds might be useful scaffolds for the development of imaging probes specific for the NMDA receptors