Amino acid content in astroglial primary cultures from different brain regions during cultivation

Taurine reduces inflammatory responses after spinal cord injury

Taurine has multiple functions in the central nervous system (CNS), serving as an osmoregulator, antioxidant, inhibitory neuromodulator, and regulator of intracellular Ca(2+) flux. Since the role of taurine in traumatic spinal cord injury (SCI) is not fully understood, the present study was conducted with C57 black/6 mice (18-20 g) who underwent severe SCI at the Th-8 level using a weight compression device. Taurine was injected intraperitoneally at doses of 25, 80, 250, and 800 mg/kg within 30 min after SCI. Controls were injected with saline. The contusional cord segments were removed 6 h after SCI, and concentrations of interleukin-6 (IL-6) and myeloperoxidase (MPO) were measured using ELISA kits. Phosphorylation of STAT3, which is activated by IL-6, and expression of inducible cyclooxygenase-2 (COX-2) were also compared between the taurine treatment group (250 mg/kg) and the control group by Western blot analysis. Morphological changes were evaluated with H&E-stained sections. Taurine significantly decreased IL-6 and MPO levels in a dose-dependent manner, significantly reducing the phosphorylation of STAT3 and expression of COX-2 after SCI compared to controls. A reduced accumulation of neutrophils, especially in the subarachnoid spaces, and secondary degenerative changes in gray matter were also noted, and motor disturbances were significantly attenuated with taurine treatment (250 mg/kg). These findings indicate that taurine has anti-inflammatory effects against SCI, and may play a neuroprotective role against secondary damage, and thus it may have therapeutic potential.

Spinal taurine levels are increased 7 and 30 days following methylprednisolone treatment of spinal cord injury in rats

The amino acid taurine serves many functions in the nervous system serving as inhibitory neurotransmitter/neuromodulator, neurotrophin, antioxidant, and osmolyte. Taurine levels are increased following brain injury and glucocorticoid administration. Thus, the purpose of this study was to examine spinal taurine concentrations following spinal cord injury (SCI) and methylprednisolone (MP) treatment of SCI. A total of 44 adult male Sprague-Dawley rats were divided into control and lesion groups. Control rats received a T6 vertebral laminectomy while lesioned rats received a laminectomy followed by complete spinal transection. Half of the animals in each group received MP intravenously following sham-operation or SCI. Rats survived for 7 or 30 days and concentrations of taurine in spinal gray and white matter, in spinal segments both near and distant from the injury epicenter, were resolved by HPLC analysis. Taurine levels were increased 7 and 30 days following transection in spinal segments immediately adjacent to the lesion and were further elevated by MP treatment. No increases were seen in far rostral/caudal segments, and MP treatment alone had no effect on spinal taurine levels. These findings demonstrate that spinal injury results in increased taurine concentrations in spinal segments undergoing the greatest degree of cellular reactivity and tissue reorganization and that MP therapy potentiates these increases. These findings are significant in that they further characterize the effects of acute MP therapy in spinal tissue. Since taurine is thought to be involved in neuroprotection and/or regeneration following injury, the potentiation of taurine levels by MP treatment may relate to its therapeutic properties.

Metabolic differences between primary cultures of astrocytes and neurons from cerebellum and cerebral cortex. Effects of fluorocitrate

Astrocytes and neurons cultured from mouse cerebellum and cerebral cortex were analyzed with respect to content and synthesis of amino acids as well as export of metabolites to the culture medium and the response to fluorocitrate, an inhibitor of aconitase. The intracellular levels of amino acids were similar in the two astrocytic populations. The release of citrate, lactate and glutamine, however, was markedly higher from cerebellar than from cortical astrocytes. Neurons contained higher levels of glutamate, aspartate and GABA than astrocytic cultures. Cortical neurons were especially high in GABA and aspartate, and the level of aspartate increased specifically when the extracellular level of glutamine was elevated. Fluorocitrate inhibited the TCA cycle in the astrocytes, but was less effective in cerebellar neurons. Whereas neurons responded to fluorocitrate with an increase in the formation of lactate, reflecting glycolysis, astrocytes decreased the formation of lactate in the presence of fluorocitrate, indicating that astrocytes to a high degree synthesize pyruvate and hence lactate from TCA cycle intermediates.

High-resolution one- and two-dimensional 1H MRS of human brain tumor and normal glial cells

Astrocytoma (WHO grade II, III), glioblastoma, malignant melanoma, and normal glial cell cultures, established from biopsies, were investigated by 1H MRS. At a 1H resonance frequency of 500 MHz (11.75 T) a high spectral resolution was achieved in 1D 1H spectra; in conjunction with 2D shift-correlated (COSY) MRS, resonances of alanine, aspartate, choline, creatine, glutamate, glutamine, hypotaurine, myo-inositol, phosphocreatine, phosphoryl-ethanolamine, phosphoryl-choline, lactate, lysine, N-acetylaspartate, taurine, threonine and valine could be identified. T1 relaxation times for the most prominent compounds are presented. T1 values of lactate ranged between 450 ms and 850 ms. The intensity of the lactate signal revealed differences between individual spectra, but exhibited no correlation between different tumor specimens or degree of malignancy. It was shown that the lactate signal at 1.3 ppm is covered by peaks arising from threonine and fatty acids. The choline signal level varied among spectra of different tumors, among tumors with similar degree of malignancy, and within the same tumor. Further preliminary differences due to aspartate, inositol and glutamine/glutamate were found in 1D and 2D COSY spectra between normal glial cells as well as different tumors. These results indicate that some differences observed in in vivo spectra may be attributable to secondary macroscopic structural changes (hypoxia, necrosis) and not to tumor inherent characteristics. Further correlation between in vivo and in vitro spectroscopy is therefore required.

In vivo, ex vivo, and in vitro one- and two-dimensional nuclear magnetic resonance spectroscopy of an intracerebral glioma in rat brain: assignment of resonances

An in vivo study of intracerebral rat glioma using proton-localized NMR spectroscopy showed important modifications of the spectra in the tumor as compared with the contralateral brain. To carry out the assignment of the resonances of the glioma spectra, tumoral and normal rat brain tissues were studied in vivo, ex vivo, and in vitro by one-dimensional and two-dimensional proton spectroscopy. N-Acetylaspartate was found at an extremely low level in the glioma. The change of peak ratio total creatine/3.2 ppm peak was found to be due to a simultaneous decrease of the total creatine content and an increase of the 3.2 ppm peak. The 3.2 ppm resonance in the glioma spectra has been shown to originate from choline, phosphocholine, glycerophosphocholine, taurine, inositol, and phosphoethanolamine. The increase of the 3.2 ppm peak in the glioma was found to result from the increase of taurine and phosphoethanolamine contents. The peak in the 1.3 ppm region of the glioma spectra was due to both lactate and mobile fatty acids. Moreover, two-dimensional spectroscopy of excised tissues and extracts showed the presence of hypotaurine only in the tumor.

Contribution of organic and inorganic osmolytes to volume regulation in rat brain cells in culture

In this work we examined the time course and the amount released, by hyposmolarity, for the most abundant free amino acids (FAA) in rat brain cortex astrocytes and neurons in culture. The aim was to evaluate their contribution to the process of cell volume regulation. Taurine, glutamate, and D-aspartate in the two types of cells, beta-alanine in astrocytes and GABA in neurons were promptly released by hyposmolarity, reaching a maximum within 1-2 min. after an osmolarity change. A substantial amount of the intracellular pool of these amino acids was mobilized in response to hyposmolarity. The amount released in media with osmolarity reduced from 300 mOsm to 150 mOsm or 210 mOsm, represented 50%-65% and 13%-31%, respectively, of the total amino acid content in cells. In both astrocytes and neurons, the efflux of glutamine and alanine was higher under isosmotic conditions and increased only marginally during hyposmotic conditions. 86Rb+, used as tracer for K+, was released from astrocytes, 30% and 11%, respectively, in hyposmotic media of 150 mOsm or 210 mOsm but was not transported in neurons. From these results it was calculated that FAA contribute 54% and inorganic ions 46% to the process of volume regulation in astrocytes exposed to a 150 mOsm hyposmotic medium. This contribution was 55% for FAA and 45% for K+ and Cl- in cells exposed to 210 mOsm hyposmotic solutions. These results indicate that the contribution of FAA to the process of cell volume regulation is higher in astrocytes than in other cell types including renal and blood cells.

Astrocyte Heterogeneity: Endogenous Amino Acid Levels and Release Evoked by Non-N-Methyl-D-Aspartate Receptor Agonists and by Potassium-Induced Swelling in Type-1 and Type-2 Astrocytes

The aim of the present study was to determine whether endogenous amino acids are released from type-1 and type-2 astrocytes following non-N-methyl-D-aspartate (NMDA) receptor activation and whether such release is related to cell swelling. Amino acid levels and release were measured by HPLC in secondary cultures from neonatal rat cortex, highly enriched in type-1 or type-2 astrocytes. The following observations were made. (a) The endogenous level of several amino acids (glutamate, alanine, glutamine, asparagine, taurine, serine, and threonine) was substantially higher in type-1 than in type-2 astrocytes. (b) The spontaneous release of glutamine and taurine was higher in type-1 than in type-2 astrocytes; that of other amino acids was similar. (c) Exposure of type-2 astrocyte cultures to 50 microM kainate or quisqualate doubled the release of glutamate and caused a lower, but significant increase in that of aspartate, glycine, taurine, alanine, serine (only in the case of kainate), and glutamine (only in the case of quisqualate). These effects were reversed by the antagonist CNQX. (d) Exposure of type-1 astrocyte cultures to 50-200 microM kainate or 50 microM quisqualate did not affect endogenous amino acid release, even after treating the cultures with dibutyryl cyclic AMP. (e) Exposure of type-1 or type-2 astrocyte cultures to 50 mM KCl (replacing an equimolar concentration of NaCl) enhanced the release of taurine greater than glutamate greater than aspartate. The effect was somewhat more pronounced in type-2 than in type-1 astrocytes. Veratridine (50 microM) did not cause any increase in amino acid release. (f) The release of amino acids induced by high [K+] appeared to be related to cell swelling, in both type-1 and type-2 astrocytes. Swelling and K(+)-induced release were somewhat higher in type-2 than in type-1 astrocytes. In contrast, neither kainate nor quisqualate caused any appreciable increase in cell volume. It is concluded that non-NMDA receptor agonists stimulate the release of several endogenous amino acids (some of which are neuroactive) from type-2 but not from type-1 astrocytes. The effect does not seem to be related to cell swelling, which causes a different release profile in both type-1 and type-2 astrocytes. The absence of kainate- and quisqualate-evoked release in type-1 astrocytes suggests that the density of non-NMDA receptors in this cell type is very low.

Amino acids as volume-regulatory osmolytes in mammalian cells

1. This review summarizes current knowledge relating to the volume-regulatory and osmoprotective functions of amino acids in mammalian cells exposed to anisosmotic fluids. 2. Experiments in vivo and in vitro have established that they play a significant role in regulating brain cell volume under these conditions, and that taurine may be of particular importance in this respect. 3. Their possible role in renal medulla is discussed, and it is suggested that they may protect cells against acute (but not long-term) osmotic variation. 4. Evidence is briefly presented regarding adaptive changes in amino acid content of other cell types.

Beta-adrenergic receptor regulation, through cyclic AMP, of nerve growth factor expression in rat cortical and cerebellar astrocytes

1. Type 1 astrocytes prepared from 3-day rat cortex and cerebellum express the 1.3-kb nerve growth factor (NGF) mRNA and synthesize and release beta-NGF. 2. Isoproterenol (IP), a beta-adrenergic agonist, stimulates NGF mRNA content in cortical astrocytes; this increase is blocked by the beta-adrenergic antagonist propranolol but not the alpha-antagonist phenoxybenzamine. The EC50 for the effect of IP is 5 nM. 3. IP increases astrocyte cyclic AMP as does forskolin, which directly activates adenylate cyclase and also increases NGF mRNA content. Cerebellar astrocytes contain about one-third as much NGF mRNA, which can also be increased by forskolin and cyclic AMP. 4. These results suggest that CNS astrocytes can serve as a source of NGF and that the NGF gene is one of the class of cyclic AMP regulated genes.

Volume regulation in astrocytes: a role for taurine as an osmoeffector

Astrocytes in culture regulate their volume under anisosmotic conditions by as yet unclear mechanisms. In a number of other cells this process involves a loss of intracellular osmotically active solutes, including taurine. The possibility that taurine participates as an osmoeffector in astrocytes was examined in cultured astrocytes exposed to hyposmolar conditions. Astrocytes responded to decreases in osmolarity by rapid swelling followed by a volume regulatory phase. Hyposmotic conditions induced a dramatic increase of 3H-taurine efflux, with a time course corresponding to the cell volume regulatory phase. Decreasing osmolarity from 310 to 254, 198 or 150 m osmoles resulted in the release of 8.2%, 17%, and 54%, respectively, of 3H-taurine previously accumulated by astrocytes. Endogenous taurine concentration decreased 64%. The efflux of 3-H GABA, 3H-glycine, or 3H-D-aspartate was much less affected under similar conditions. These results suggest a role for taurine as an osmoeffector in astrocytes.