Jun-ichi Sagara

Ibaraki Prefectural University of Health Sciences, Ibaragi, Ōsaka, Japan

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Publications (10)29.14 Total impact

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    ABSTRACT: Glutathione (GSH) plays an important neuroprotective role, and its synthesis depends on the amount of available cysteine (CSH) in the cells. Various kinds of evidence suggest that astrocytes can provide CSH or GSH to neurons, but the delivery mechanism of the thiol-compounds has not been elucidated. In this study, the dynamics of CSH, GSH and their disulphides in astrocyte culture medium were investigated by following the time-course of concentration changes and by computer simulation and curve fitting to experimental data using a mathematical model. The model consists of seven reactions and three transports, which are grouped into four categories: autoxidation of thiols into disulphides, thiol-disulphide exchange and reactions of thiols with medium components, as well as the cellular influx and efflux of thiols and disulphides. The obtained results are interpreted that cystine (CSSC) after entering astrocyte is reduced to CSH, most of which is released to medium and autoxidized to CSSC. The efflux of GSH was estimated to be considerably slower than that of CSH, and most of the excreted GSH is converted to cysteine-glutathione disulphide principally through the thiol-disulphide exchange. The results seem to indicate that astrocytes provide neurons mainly with CSH, rather than GSH, as the antioxidant material for neuroprotection.
    Journal of Biochemistry 03/2011; 150(1):95-102. · 3.07 Impact Factor
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    ABSTRACT: High expression of the system L amino acid transporter has been observed in clinically important tissues including tumors and the blood-brain barrier. We examined amino acid transport system L selectivity of (14)C(U)-L-tyrosine ((14)C-Tyr), (125)I-4-iodo-L-meta-tyrosine (4-(125)I-mTyr), (125)I-6-iodo-L-meta-tyrosine (6-(125)I-mTyr), (125)I-3-iodo-α-methyl-L-tyrosine ((125)I-IMT) and (125)I-3-iodo-L-tyrosine (3-(125)I-Tyr) using Chinese hamster ovary cells (CHO-K1). Cells in the exponential growth phase were incubated with 18.5 kBq of labeled amino acid in 2 mL of phosphate-buffered saline-based uptake solution and an uptake solution with/without Na(+) at 37°C or 4°C. We examined the effects of the following compounds (1.0 mM) on transport: 2-(methylamino)isobutyric acid (a specific inhibitor of system A, in Na(+)-containing uptake solution); 2-amino-bicyclo[2,2,1]heptane-2-carboxylic acid (a specific inhibitor of system L, in Na(+)-free uptake solution); sodium azide and 2,4-dinitrophenol (NaN(3) and DNP, inhibitors of the generation of adenosine triphosphate); p-aminohippurate and tetraethylammonium (PAH and TEA, inhibitors of organic anion and cation transporters); and L- and D-isomers of natural amino acids. (14)C-Tyr exhibited affinity for systems L, A and ASC. 4-(125)I-mTyr and 3-(125)I-Tyr exhibited high specificity for system L, whereas 6-(125)I-mTyr and (125)I-IMT exhibited affinity for both systems L and ASC. Uptake of 4-(125)I-mTyr was markedly reduced by incubation at 4 °C, and was not significantly inhibited by NaN(3), DNP, PAH or TEA. The inhibition profiles of the L- and D-isomers of natural amino acids indicated that system L mediates the transport of 4-(125)I-mTyr. 4-(125)I-mTyr exhibited the greatest system L specificity (93.46 ± 0.13%) of all of the tested amino acids.
    Nuclear Medicine and Biology 11/2010; 37(8):903-10. · 2.52 Impact Factor
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    ABSTRACT: We examined the protective effects of N-acetylcysteine (NAC) on the death of glia-free neurons in culture. Under normoxic conditions, the protection by NAC was observed only in cystine-free but not complete medium. When the cells were cultured under hypoxic conditions, NAC much elongated their survival even in the presence of cystine. H2O2 was found to be generated to considerable concentration in the presence of both NAC and cystine, and the administration of catalase prevented the cell death. These results suggest that the harmful effect of NAC is because of H2O2 generated by autoxidation of cysteine, which derives from the reaction between NAC and cystine. The present results raise the possibility that NAC can act as either antioxidant or prooxidant depending on the milieu.
    Neuroreport 04/2010; 21(6):416-21. · 1.40 Impact Factor
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    ABSTRACT: Transport of the amino acid analog (123)I-3-iodo-alpha-methyl-L-tyrosine, which is used in clinical SPECT imaging, occurs mainly via L-type amino acid transporter type 1 (LAT1; an amino acid exchanger). As LAT1 is highly expressed in actively proliferating tumors, we made a preliminary investigation of the effects of amino acid esters on enhancement of (125)I-3-iodo-alpha-methyl-L-tyrosine (IMT) uptake via LAT1 in Chinese hamster ovary (CHO-K1) cells. Because the sequence of the CHO-K1 LAT1 gene is not available, we confirmed LAT1 expression through IMT (18.5 kBq) uptake mechanisms using specific inhibitors. L-Gly, L-Ser, L-Leu, L-Phe, L-Met, L-Tyr, D-Tyr, L-Val and L-Lys ethyl/methyl esters were tested in combination with IMT. Time-course studies over a 3-h period were conducted, and the concentration dependence of L-Tyr ethyl and methyl esters (0.001 to 10 mM) in combination with IMT was also examined. For a proof of de-esterification of L- and D-Tyr ethyl and methyl esters in the cells (by enzymatic attack or other cause), the concentration of L- and D-Tyr was analyzed by high-performance liquid chromatography of the esters in phosphate buffer (pH 7.4) and cell homogenates at 37 degrees C or under ice-cold conditions. Inhibition tests suggested that LAT1 is involved in IMT uptake by CHO-K1 cells. Co-administration of 1 mM of l-Tyr ethyl or methyl ester with IMT produced the greatest enhancement. The de-esterification reaction was stereo selective and temperature dependent in the homogenate. De-esterification kinetics were very fast in the homogenate and very slow in the phosphate buffer. The L-Tyr ethyl or methyl esters were the most effective enhancers of IMT uptake into CHO-K1 cells and acted by trans-stimulation of the amino acid exchange function of LAT1. This result suggests that de-esterification in the cells may be caused by enzymatic attack. We will use IMT and L-Tyr ethyl or methyl esters to examine LAT1 function in tumor cells or tissues in vivo.
    Nuclear Medicine and Biology 02/2010; 37(2):189-96. · 2.52 Impact Factor
  • Nobuo Makino, Takeshi Mise, Jun-Ichi Sagara
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    ABSTRACT: Oxidative stress is implicated in a variety of disorders including neurodegenerative diseases, and H(2)O(2) is important in the generation of reactive oxygen and oxidative stress. In this study, we have examined the rate of extracellular H(2)O(2) elimination and relevant enzyme activities in cultured astrocytes and C6 glioma cells and have analyzed the results based on a mathematical model. As compared with other types of cultured cells, astrocytes showed higher activity of glutathione peroxidase (GPx) but lower activities for GSH recycling. C6 cells showed relatively low GPx activity, and treatment of C6 cells with dibutyryl-cAMP, which induces astrocytic differentiation, increased catalase activity and H(2)O(2) permeation rate but exerted little effect on other enzyme activities. A mathematical model [N. Makino, K. Sasaki, N. Hashida, Y. Sakakura, A metabolic model describing the H(2)O(2) elimination by mammalian cells including H(2)O(2) permeation through cytoplasmic and peroxisomal membranes: comparison with experimental data, Biochim. Biophys. Acta 1673 (2004) 149-159.], which includes relevant enzymes and H(2)O(2) permeation through membranes, was found to be fitted well to the H(2)O(2) concentration dependences of removal reaction with the permeation rate constants as variable parameters. As compared with PC12 cells as a culture model for neuron, H(2)O(2) removal activity of astrocytes was considerably higher at physiological H(2)O(2) concentrations. The details of the mathematical model are presented in Appendix.
    Biochimica et Biophysica Acta 07/2008; 1780(6):927-36. · 4.66 Impact Factor
  • Jun-ichi Sagara, Nobuo Makino
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    ABSTRACT: It has been reported that rat bone marrow stromal cells (BMSCs) are differentiated into neuronal cells by administration of 2-mercaptoethanol [Woodbury et al (2000) J Neurosci Res 61:364-370]. In this study, we examined the effects of various sulfhydryl (SH) compounds on the differentiation of BMSCs obtained from rat femurs. Neuronal differentiation was detected morphologically and immunocytochemically. It was found that the cells treated with reduced glutathione (GSH) apparently differentiated into neurons, showing extensive processes, and expressing neuron-specific enolase and microtubule-associated protein 2. Glutathione monoethyl ester (GEE), which increased the cellular GSH content, showed no effect on the expression of neuronal markers. It is concluded that the neural differentiation of BMSCs occurs by the administration of GSH. It was suggested that extracellular and not intracellular GSH have effects on the induction of the neuronal differentiation of BMSCs.
    Neurochemical Research 02/2008; 33(1):16-21. · 2.13 Impact Factor
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    ABSTRACT: The fact that d-amino acids have been found in various tissues and are involved in various functions is a clue to how to develop new imaging agents. We examined d-amino acid transport mechanisms in Chinese hamster ovary (CHO-K1) cells because CHO-K1 cells are widely used in biomedical studies and are thought to be useful for expression of genes involved in metabolism of D-amino acids. Uptake experiments were performed. CHO-K1 cells cultured in 60-mm plastic culture dishes under ordinary culture conditions were incubated with 18.5 kBq of radiolabeled amino acid in 2 ml of phosphate-buffered-saline-based uptake solution at 37 degrees C. The following radiolabeled amino acid tracers were used: D-[1-(14)C]-alanine, L-[1-(14)C]-alanine, D-[1-(14)C]-serine, L-[1-(14)C]-serine, D-[1-(14)C]-methionine, L-[1-(14)C]-methionine, D-[1-(14)C]-phenylalanine, L-[1-(14)C]-phenylalanine, D-[1-(14)C]-leucine, L-[1-(14)C]-leucine, D-[1-(14)C]-valine, L-[1-(14)C]-valine, D-[1-(14)C]-tyrosine, L-[1-(14)C]-tyrosine, D-[1-(14)C]-glutamic acid, L-[1-(14)C]-glutamic acid, D-[1-(14)C]-lysine, L-[1-(14)C]-lysine, D-[1-(14)C]-arginine and L-[L-(14)C]-arginine. We tested the inhibitory effects of the following compounds (1.0 mM) on transport: 2-(methylamino)isobutyric acid (a specific inhibitor of system A, in Na(+)-containing uptake solution) and 2-amino-bicyclo[2,2,1]heptane-2-carboxylic acid (a specific inhibitor of system L, in Na(+)-free uptake solution). D-[1-(14)C]-methionine, D-[1-(14)C]-phenylalanine and D-[1-(14)C]-tyrosine accumulated mainly via system L. D-[1-(14)C]-alanine and D-[1-(14)C]-serine accumulated primarily via system ASC. High uptake of D-[1-(14)C]-alanine, D-[1-(14)C]-methionine, D-[1-(14)C]-phenylalanine and D-[1-(14)C]-leucine was observed. The uptake of radiolabeled serine, valine, tyrosine, glutamic acid and arginine into CHO-K1 was highly stereoselective for l-isomers. We observed high uptake of D-[1-(14)C]-alanine via system ASC (most likely alanine-serine-cysteine-selective amino acid transporter-1) and high uptake of D-[1-(14)C]-methionine and D-[1-(14)C]-phenylalanine via system L (most likely L-type amino acid transporter-1).
    Nuclear Medicine and Biology 09/2007; 34(6):659-65. · 2.52 Impact Factor
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    ABSTRACT: Reactive oxygen species (ROS) produced by neutrophils are essential in the host defense against infections but may be harmful to neutrophils themselves. Glutathione (GSH) plays a pivotal role in protecting cells against ROS-mediated oxidant injury. Cystine/glutamate transporter, designated as system xc- and consisting of two proteins, xCT and 4F2hc, is important to maintain GSH levels in mammalian-cultured cells. In the present paper, we have investigated system xc- in neutrophils. In human peripheral blood neutrophils, neither the activity of system xc- nor xCT mRNA was detected. The activity was induced, and xCT mRNA was expressed when they were cultured in vitro. The mRNA expression was much enhanced in the presence of opsonized zymosan or PMA. In contrast, mouse peritoneal exudate neutrophils, immediately after preparation, exhibited system xc- activity and expressed xCT mRNA. The activity and the expression were heightened further when they were cultured. Peritoneal exudate cells (mostly neutrophils) from xCT-deficient (xCT-/-) mice had lower cysteine content than those from the wild-type mice. GSH levels in the xCT-/-cells decreased rapidly when they were cultured, whereas those in the wild-type cells were maintained during the culture. Apoptosis induced in culture was enhanced in the xCT-/-cells compared with the wild-type cells. These results suggest that system xc- plays an important role in neutrophils when they are activated, and their GSH consumption is accelerated.
    Journal of Leukocyte Biology 05/2007; 81(4):974-82. · 4.57 Impact Factor
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    ABSTRACT: Brain cell suspensions obtained from cerebrum of fetal rats were cultured and after 5 days neurons were separated from the residual cells. These purified neurons, which were replated on the dish, started to die within 24 h in culture. Glutathione content of these neurons decreased rapidly to less than one-tenth of the initial level after 24 h. In the presence of alpha-tocopherol, a well-known antioxidant, the neurons survived for at least 3 days, though glutathione content remained very low. Butylated hydroxyanisol had similar effect, but ascorbic acid and uric acid had no or very little effect. Serotonin, which is assumed to have an antioxidant activity, kept the neurons alive for 3 days. These results suggest that neurons separated from the other types of cells cannot survive due to the oxidative stress, which may otherwise be neutralized by a mechanism involving glutathione, and that antioxidants including serotonin has a beneficial effect on these purified neurons.
    Brain Research 03/2007; 1131(1):11-6. · 2.88 Impact Factor
  • J Sagara, Y Sugita
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    ABSTRACT: To elucidate the contribution of glutathione S-transferase (GST) and glutathione peroxidase (GPx) to the protection against oxidative stress in rat brain, we prepared GST and GPx from newborn rat liver, brain and cultured astrocytes, and investigated the characteristics and kinetics of the enzymes. The activity of cytosolic GST of the cultured astrocytes toward 1-chloro-2,4-dinitrobenzene (CDNB) was much higher than that of GPx toward peroxides. The GST activity toward 4-hydroxy-2-nonenal (4HNE) was almost the same as the GPx activity. GST isozymes were purified from the cytosolic fraction of the liver and astrocytes. In the case of the astrocytes, a major GST isozyme with an isoelectric point (pI) of 9.02 accounted for approximately 40% of total GST activity toward CDNB, while hepatic GST isozymes showed seven peaks in the basic region. Each of astrocytes and liver showed a single GST peak with high activity toward 4HNE, namely AVIII and LVIII, respectively, and both of them had a similar pI value of about 6.7. The kinetic parameters of AVIII and LVIII were found to be similar to each other. These data suggest that the same types of GST isozymes are expressed in the astrocytes and liver, and take part mainly in the detoxification of 4HNE.
    Brain Research 07/2001; 902(2):190-7. · 2.88 Impact Factor