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Sifat AE, Vaidya B, Villalba H, Albekairi TH, Abbruscato TJ. Neurovascular unit transport responses to ischemia and common coexisting conditions: smoking and diabetes. Am J Physiol Cell Physiol 2018; 316:C2-C15. [PMID: 30207783 DOI: 10.1152/ajpcell.00187.2018] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Transporters at the neurovascular unit (NVU) are vital for the regulation of normal brain physiology via ion, water, and nutrients movement. In ischemic stroke, the reduction of cerebral blood flow causes several complex pathophysiological changes in the brain, one of which includes alterations of the NVU transporters, which can exacerbate stroke outcome by increased brain edema (by altering ion, water, and glutamate transporters), altered energy metabolism (by altering glucose transporters), and enhanced drug toxicity (by altering efflux transporters). Smoking and diabetes are common risk factors as well as coexisting conditions in ischemic stroke that are also reported to change the expression and function of NVU transporters. Coexistence of these conditions could cause an additive effect in terms of the alterations of brain transporters that might lead to worsened ischemic stroke prognosis and recovery. In this review, we have discussed the effects of ischemic stroke, smoking, and diabetes on some essential NVU transporters and how the simultaneous presence of these conditions can affect the clinical outcome after an ischemic episode. Further scientific investigations are required to elucidate changes in NVU transport in cerebral ischemia, which can lead to better, personalized therapeutic interventions tailor-made for these comorbid conditions.
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Affiliation(s)
- Ali E Sifat
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center , Amarillo, Texas
| | - Bhuvaneshwar Vaidya
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center , Amarillo, Texas
| | - Heidi Villalba
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center , Amarillo, Texas
| | - Thamer H Albekairi
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center , Amarillo, Texas
| | - Thomas J Abbruscato
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center , Amarillo, Texas
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2
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Villalba H, Shah K, Albekairi TH, Sifat AE, Vaidya B, Abbruscato TJ. Potential role of myo-inositol to improve ischemic stroke outcome in diabetic mouse. Brain Res 2018; 1699:166-176. [PMID: 30165043 DOI: 10.1016/j.brainres.2018.08.028] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2018] [Revised: 08/17/2018] [Accepted: 08/26/2018] [Indexed: 12/17/2022]
Abstract
Brain edema is one of the critical factors causing hightened disability and mortality in stroke patients, which is exaggerated further in diabetic patients. Organic osmolytes could play a critical role in the maintenance of cytotoxic edema. The present study was aimed to assess the role of myo-inositol, an organic osmolyte, on stroke outcome in diabetic and non-diabetic animals. In situ brain perfusion and acute brain slice methods were used to assess transport of myo-inositol across the blood-brain barrier and uptake by brain cells using non-diabetic (C57BL/6) and diabetic (streptozotocin-induced) mice, respectively. In vitro studies were conducted to assess the role of myo-inositol during and after ischemia utilizing oxygen glucose deprivation (OGD) and reperfusion. Further, the expression of transporters, such as SGLT6, SMIT1 and AQP4 were measured using immunofluorescence. Therapeutic efficacy of myo-inositol was evaluated in a transient middle cerebral artery occlusion (tMCAO) mouse model using non-diabetic (C57BL/6) and diabetic (db/db) mice. Myo-inositol release from and uptake in astrocytes and altered expression of myo-inositol transporters at different OGD timepoints revealed the role of myo-inositol and myo-inositol transporters during ischemia reperfusion. Further, hyperglycemic conditions reduced myo-inositol uptake in astrocytes. Interestingly, in in-vivo tMCAO, infarct and edema ratios following 24 h reperfusion decreased in myo-inositol treated mice. These results were supported by improvement in behavioral outcomes in open-field test, corner test and neurological score in both non-diabetic and db/db animals. Our data suggest that myo-inositol and myo-inositol transporters may provide neuroprotection during/following stroke both in non-diabetic and diabetic conditions.
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Affiliation(s)
- Heidi Villalba
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, TX 79106, USA
| | - Kaushik Shah
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, TX 79106, USA
| | - Thamer H Albekairi
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, TX 79106, USA
| | - Ali E Sifat
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, TX 79106, USA
| | - Bhuvaneshwar Vaidya
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, TX 79106, USA
| | - Thomas J Abbruscato
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, TX 79106, USA.
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3
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Rae CD. A Guide to the Metabolic Pathways and Function of Metabolites Observed in Human Brain 1H Magnetic Resonance Spectra. Neurochem Res 2013; 39:1-36. [PMID: 24258018 DOI: 10.1007/s11064-013-1199-5] [Citation(s) in RCA: 327] [Impact Index Per Article: 29.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2013] [Revised: 11/08/2013] [Accepted: 11/11/2013] [Indexed: 12/20/2022]
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4
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Nitz M, Fenili D, Darabie AA, Wu L, Cousins JE, McLaurin J. Modulation of amyloid-β aggregation and toxicity by inosose stereoisomers. FEBS J 2008; 275:1663-74. [DOI: 10.1111/j.1742-4658.2008.06321.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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5
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Fenili D, Brown M, Rappaport R, McLaurin J. Properties of scyllo–inositol as a therapeutic treatment of AD-like pathology. J Mol Med (Berl) 2007; 85:603-11. [PMID: 17279347 DOI: 10.1007/s00109-007-0156-7] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2006] [Revised: 12/21/2006] [Accepted: 12/27/2006] [Indexed: 12/24/2022]
Abstract
Inositol is a simple polyol with eight naturally occurring stereoisomers. myo-Inositol, D-chiro- and epi-inositol have been examined as potential therapeutic agents for various diseases, with favorable results, but treatment with scyllo-inositol has not been previously investigated. Our laboratory has shown that scyllo-inositol inhibits cognitive deficits in TgCRND8 mice and significantly ameliorates disease pathology, suggesting it might be effective in treating Alzheimer's disease (AD). In this paper, we show that scyllo-inositol has a sustained ability to treat animals at advanced stages of AD-like pathology. Significant decreases in insoluble Abeta40, Abeta42, and plaque accumulation were observed in the brains of treated versus untreated TgCRND8 mice. The growth of plaques of all sizes was inhibited by scyllo-inositol administration. To demonstrate that the scyllo-inositol effects were within the CNS, gas chromatography/mass spectrometry was used to examine myo- and scyllo-inositol concentrations after oral administration. Further, we examined how closely scyllo- and myo-inositol are inter-regulated in the CNS and whether scyllo-inositol, if elevated within the CNS, would incorporate into phosphatidylinositol lipids. Cerebral spinal fluid levels of scyllo-inositol increased after scyllo-inositol treatment but not myo-inositol treatment. scyllo-Inositol treatment also caused increased levels of scyllo-inositol in the brain. We further show that scyllo-inositol, even at elevated levels, does not incorporate into the phosphatidylinositol family of lipids. These combined results demonstrate that scyllo-inositol accumulates within the CNS up to tenfold endogenous levels and does not interfere with phosphatidylinositol lipid production.
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Affiliation(s)
- Daniela Fenili
- Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, M5S 3H2, Canada
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6
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Shared effects of all three conventionalanti-bipolar drugs on the phosphoinositide system in astrocytes. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s1569-2558(03)31046-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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7
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Fisher SK, Novak JE, Agranoff BW. Inositol and higher inositol phosphates in neural tissues: homeostasis, metabolism and functional significance. J Neurochem 2002; 82:736-54. [PMID: 12358779 DOI: 10.1046/j.1471-4159.2002.01041.x] [Citation(s) in RCA: 465] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Inositol phospholipids and inositol phosphates mediate well-established functions in signal transduction and in Ca2+ homeostasis in the CNS and non-neural tissues. More recently, there has been renewed interest in other roles that both myo-inositol and its highly phosphorylated forms may play in neural function. We review evidence that myo-inositol serves as a clinically relevant osmolyte in the CNS, and that its hexakisphosphate and pyrophosphorylated derivatives may play roles in such diverse cellular functions as DNA repair, nuclear RNA export and synaptic membrane trafficking.
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Affiliation(s)
- Stephen K Fisher
- Mental Health Research Institute, and Department of Pharmacology, University of Michigan, Ann Arbor, Michigan 48109, USA.
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8
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McLaurin J, Golomb R, Jurewicz A, Antel JP, Fraser PE. Inositol stereoisomers stabilize an oligomeric aggregate of Alzheimer amyloid beta peptide and inhibit abeta -induced toxicity. J Biol Chem 2000; 275:18495-502. [PMID: 10764800 DOI: 10.1074/jbc.m906994199] [Citation(s) in RCA: 216] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Inositol has 8 stereoisomers, four of which are physiologically active. myo-Inositol is the most abundant isomer in the brain and more recently shown that epi- and scyllo-inositol are also present. myo-Inositol complexes with Abeta42 in vitro to form a small stable micelle. The ability of inositol stereoisomers to interact with and stabilize small Abeta complexes was addressed. Circular dichroism spectroscopy demonstrated that epi- and scyllo- but not chiro-inositol were able to induce a structural transition from random to beta-structure in Abeta42. Alternatively, none of the stereoisomers were able to induce a structural transition in Abeta40. Electron microscopy demonstrated that inositol stabilizes small aggregates of Abeta42. We demonstrate that inositol-Abeta interactions result in a complex that is non-toxic to nerve growth factor-differentiated PC-12 cells and primary human neuronal cultures. The attenuation of toxicity is the result of Abeta-inositol interaction, as inositol uptake inhibitors had no effect on neuronal survival. The use of inositol stereoisomers allowed us to elucidate an important structure-activity relationship between Abeta and inositol. Inositol stereoisomers are naturally occurring molecules that readily cross the blood-brain barrier and may represent a viable treatment for AD through the complexation of Abeta and attenuation of Abeta neurotoxic effects.
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Affiliation(s)
- J McLaurin
- Centre for Research in Neurodegenerative Diseases, Department of Laboratory Medicine, University of Toronto, Toronto, Ontario, M5S 3H2, Canada.
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9
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van Calker D, Belmaker RH. The high affinity inositol transport system--implications for the pathophysiology and treatment of bipolar disorder. Bipolar Disord 2000; 2:102-7. [PMID: 11252649 DOI: 10.1034/j.1399-5618.2000.020203.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The 'inositol-depletion hypothesis' postulates that the therapeutic effects of lithium are due to inhibition of inositol monophosphatase, which leads to depletion of brain cells of myo-inositol and consequently to dampening of phosphoinositide (PI) signaling. This article examines the potential relevance of an alternative mechanism for inositol depletion: inhibition of myo-inositol uptake that proceeds via the sodium/myo-inositol cotransport (SMIT). We discuss recent in vitro experiments that show a pronounced downregulation of SMIT after chronic treatment with lithium, carbamazepine, and valproate at therapeutically relevant concentrations. It is concluded that downregulation of SMIT could represent a common mechanism of action of mood stabilizers.
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Affiliation(s)
- D van Calker
- Department of Psychiatry, University of Freiburg, Germany.
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10
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Wolfson M, Einat H, Bersudsky Y, Berkin V, Belmaker RH, Hertz L. Nordidemnin potently inhibits inositol uptake in cultured astrocytes and dose-dependently augments lithium's proconvulsant effect in vivo. J Neurosci Res 2000; 60:116-21. [PMID: 10723074 DOI: 10.1002/(sici)1097-4547(20000401)60:1<116::aid-jnr12>3.0.co;2-u] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
It has been suggested that inositol uptake across the cell membrane is of importance for maintenance of the inositol pool involved in lithium's therapeutic effect in bipolar disease and in the lithium-pilocarpine seizure test in freely moving rats (measuring the latency of a normally subconvulsive concentration of pilocarpine to seizure induction in the additional presence of lithium). We have tested this hypothesis by: 1) demonstrating an extremely high potency of nordidemnin as an inhibitor of myo-inositol uptake in primary cultures of mouse astrocytes; and 2) determining the dose-response correlation of a nordidemnin-induced decrease in the latency before appearance of seizures in the lithium-pilocarpine test after intracerebroventricular injection of minute samples (10 microl) of virtually isotonic saline solution.
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Affiliation(s)
- M Wolfson
- Department of Microbiology and Immunology and Mental Health Center, Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel.
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11
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Lubrich B, Spleiss O, Gebicke-Haerter PJ, van Calker D. Differential expression, activity and regulation of the sodium/myo-inositol cotransporter in astrocyte cultures from different regions of the rat brain. Neuropharmacology 2000; 39:680-90. [PMID: 10728889 DOI: 10.1016/s0028-3908(99)00162-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The high-affinity sodium/myo-inositol cotransporter (SMIT) is involved in osmoregulation in several cells and tissues. In the CNS the activity of SMIT also determines the individual susceptibility of neural cells to the inositol depleting effect of lithium, which is considered to be important in lithium's therapeutic effects in manic-depressive illness. Among neural cells SMIT is particularly active in astrocytes. In the present work we have cloned the cDNA of SMIT of the rat and assessed its activity, expression and regulation in primary astroglia cultures derived from five different rat brain regions: cerebellum, cortex, diencephalon, hippocampus and tegmentum. After an incubation period of 24 h in medium containing 3[H]labeled myo-inositol different steady-state concentrations were detected which were dependent on the brain region from which the astrocytes were cultured. In addition, myo-inositol uptake in astrocytes from different areas was characterized by two different Km values (27 microM for cerebellum and diencephalon, 50 microM for cortex, hippocampus and tegmentum) and by three different v(max) values (approx. 200 pmol/mg protein/min for astrocytes from cerebellum and tegmentum, 298 for hippocampus and 465 for cortex), indicating that the active myo-inositol uptake into astroglial cells is distinct in the various brain regions. The efficacy of uptake as determined by v(max) values of 3[H]myo-inositol uptake correlated with the level of mRNA of SMIT in the astrocyte cultures from the various brain regions as determined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Both 3[H]myo-inositol uptake and SMIT mRNA content was upregulated by incubation of astrocytes in medium of increased osmolarity. In astrocytes from cerebellum, cortex, hippocampus and tegmentum 3[H]myo-inositol uptake was downregulated by chronic incubation with 400 microM inositol. This effect was not observed in astrocytes from diencephalon. Furthermore, in astrocytes from cortex and hippocampus but not from cerebellum, diencephalon and tegmentum incubation with corticosterone for three days upregulated 3[H]myo-inositol uptake. It is concluded that SMIT is differentially expressed and regulated in astrocytes from distinct brain regions. These regional differences suggest particular consideration of localized effects in investigations of the role of myo-inositol in the mechanism of action of antibipolar drugs.
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Affiliation(s)
- B Lubrich
- Department of Psychiatry, University of Freiburg, Germany
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12
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Yamashita T, Yamauchi A, Miyai A, Taniguchi M, Yoshimine T, Tohyama M. Neuroprotective role of Na+/myo-inositol cotransporter against veratridine cytotoxicity. J Neurochem 1999; 72:1864-70. [PMID: 10217262 DOI: 10.1046/j.1471-4159.1999.0721864.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Na+/myo-inositol cotransporter has been shown to protect cells from the perturbing effects of hypertonic stress by the accumulation of myo-inositol. Here we report a regulatory mechanism for the cotransporter. Induction of myo-inositol cotransporter mRNA was observed after exposure to veratridine, a voltage-gated sodium channel opener. The veratridine-elicited induction was inhibited when Na+ was eliminated from the bath, although calcium chelation failed to modify the gene expression. Veratridine evoked an accumulation of Na+ in the cells, which paralleled the abundance of the mRNA. These results strongly suggested that an increase in Na+ influx due to sodium channel opening affected transcription of the cotransporter gene. Activity of the myo-inositol cotransporter was also up-regulated after veratridine exposure. To clarify the possible roles of myoinositol accumulation under veratridine exposure, we next examined the neurotoxic effects of veratridine when myo-inositol uptake was blocked. Neither 30 microM veratridine nor 500 microM 2-O,C-methylene myo-inositol, a competitive inhibitor of myo-inositol, elicited apparent cytotoxicity. However, a combination of these agents markedly increased cytotoxicity in culture, suggesting that an adequate amount of myo-inositol was necessary when the cells were stimulated with veratridine.
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Affiliation(s)
- T Yamashita
- Department of Anatomy and Neuroscience, Osaka University Medical School Suita, Japan
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13
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Novak JE, Turner RS, Agranoff BW, Fisher SK. Differentiated human NT2-N neurons possess a high intracellular content of myo-inositol. J Neurochem 1999; 72:1431-40. [PMID: 10098846 DOI: 10.1046/j.1471-4159.1999.721431.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
myo-Inositol plays a key role in signal transduction and osmotic regulation events in the CNS. Despite the known high concentrations of inositol in the human CNS, relatively little is known about its distribution within the different cell types. In this report, inositol homeostasis was studied in NT2-N cells, a unique cell culture model of human CNS neurons. Differentiation of precursor NT2 teratocarcinoma cells into NT2-N neurons by means of retinoic acid treatment resulted in an increase in inositol concentration from 24 to 195 nmol/mg of protein. After measurement of intracellular water spaces, inositol concentrations of 1.6 and 17.4 mM were calculated for NT2 and NT2-N cells, respectively. The high concentrations of inositol in NT2-N neurons could be explained by (1) an increased uptake of inositol (3.7 vs. 1.6 nmol/mg of protein/h, for NT2-N and NT2 cells, respectively) and (2) a decreased efflux of inositol (1.7%/h for NT2-N neurons vs. 9.0%/h for NT2 cells). Activity of inositol synthase, which mediates de novo synthesis of inositol, was not detected in either cell type. The observation that CNS neurons maintain a high intracellular concentration of inositol may be relevant to the regulation of both phosphoinositide signaling and osmotic stress events in the CNS.
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Affiliation(s)
- J E Novak
- Mental Health Research Institute, and Department of Pharmacology, University of Michigan, Ann Arbor 48104-1687, USA
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Yamashita T, Yamauchi A, Miyai A, Taniguchi M, Yoshimine T, Tohyama M. Differential regulation of adenine nucleotide translocators by hypertonicity in the brain. J Neurochem 1999; 72:1259-65. [PMID: 10037499 DOI: 10.1046/j.1471-4159.1999.0721259.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To determine the gene(s) induced by hypertonicity in the brain, we performed a differential display analysis using RNA isolated from isotonic and hypertonic rat astrocytes. One cDNA rapidly up-regulated by hypertonicity was isolated, and the DNA sequence revealed that it was identical to adenine nucleotide translocator (ANT)2. ANT2 protein exchanges intramitochondrial ATP for cytoplasmic ADP. Among three ANT isoforms, only ANT2 mRNA was up-regulated markedly from 1 to 4 h after exposure to hypertonicity. Induction of the mRNA did not require de novo protein synthesis. Furthermore, ADP translocase activity in mitochondria of astrocytes was increased significantly by hypertonicity. To see the localization and regulation of ANT2 mRNA in the brain, we performed in situ hybridization of rat brain after intraperitoneal injection of a high concentration of NaCl. Although there were only weak signals in the control, intense hybridization signals were seen in hypertonic rat whole brain. Microscopic examination showed that ANT2 signals were present in the neurons, as well as glial cells. These results suggest that ANT2 may play a role in brain cells to adapt to the hypertonic environment.
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Affiliation(s)
- T Yamashita
- Department of Anatomy and Neuroscience, Osaka University Medical School, Suita, Japan
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15
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Wolfson M, Hertz E, Belmaker RH, Hertz L. Chronic treatment with lithium and pretreatment with excess inositol reduce inositol pool size in astrocytes by different mechanisms. Brain Res 1998; 787:34-40. [PMID: 9518542 DOI: 10.1016/s0006-8993(97)00775-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Chronic treatment with a lithium salt is the classical treatment for manic-depressive disorder. It is hypothesized that the therapeutic action of lithium is caused by its inhibition of inositol phosphatases which leads to a relative deficiency of inositol and, therefore, an impairment of inositol recycling and production of precursor for the second messengers inositol triphosphate (IP3) and diacylglycerol (DAG). However, peculiarly enough, treatment with high doses of inositol also has an antidepressant effect. In the present work, we have studied the acute and chronic effects of lithium and of excess inositol, in separation or together, on accumulation of 50 microM [3H]inositol (a physiologically relevant concentration) into primary cultures of mouse astrocytes. Two parameters were investigated: (1) rate of unidirectional uptake across the cell membrane (measured during short-term exposure to the radioisotope), and (2) magnitude of the intracellular pool of inositol, equilibrating with extracellular inositol (measured during long-term exposure to the radioisotope). Inositol uptake was highly concentrative and occurred with a Km of approximately 500 microM and a Vmax of 1.5 nmol/min/mg protein. The uptake rate was not affected by either acute or chronic treatment with LiCl (or both), but it was substantially reduced ('down-regulated') after pretreatment with a high concentration of inositol. The inositol pool size was decreased to a similar extent as the uptake rate by previous exposure to excess inositol. In spite of the fact that inositol uptake rate was unaffected by lithium, the magnitude of the inositol pool was significantly decreased by chronic treatment with a pharmacologically relevant concentration of LiCl (1 mM), but not by treatment with lower concentrations. This decrease is likely to reflect a reduction in either inositol synthesis or replenishment of inositol from IP3, due to the inhibition of inositol phosphatases by the lithium ion. In agreement with the different mechanisms by which lithium and pretreatment with excess inositol appear to reduce the pool size of inositol, the effects of pretreatment with excess inositol and of LiCl were additive. It is noteworthy that both effects could be observed in astrocytes, suggesting that there might be a significant astrocytic target during clinical treatment.
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Affiliation(s)
- M Wolfson
- Department of Microbiology and Immunology and Mental Health Center, Faculty of Health Sciences, Ben Gurion University of the Negev, P.O. B. 653, Beer Sheva 84105, Israel.
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16
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Isaacks RE, Bender AS, Kim CY, Norenberg MD. Effect of osmolality and myo-inositol deprivation on the transport properties of myo-inositol in primary astrocyte cultures. Neurochem Res 1997; 22:1461-9. [PMID: 9357011 DOI: 10.1023/a:1021950311308] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
myo-Inositol uptake measured in primary astrocyte cultures was saturable in the presence of Na+ with a Km of 13-18 microM and a Vmax of 9.4 nmoles/mg protein/hour in myo-inositol-fed cells, indicating a high affinity transport system. In myo-inositol-deprived cells, Km was about 53 microM with a Vmax of 13.2 nmoles/mg protein/hour. Decreasing osmolality decreased the Vmax to about 1.9 nmoles/mg protein/hour whereas increasing osmolality increased Vmax about 5-fold, while Kms were essentially unchanged in myo-inositol fed cells. In cells deprived of myo-inositol, Vmax decreased in hypotonic medium and increased in hypertonic medium almost 10-fold, but with more than a doubling of the Km regardless of the osmolality. Glucose (25 mM) inhibited myo-inositol uptake 51% whereas the other hexoses used inhibited uptake much less. Our findings indicate that myo-inositol uptake in astrocytes occurs through an efficient carrier-mediated Na(+)-dependent co-transport system that is different from that of glucose and its kinetic properties are affected by myo-inositol availability and osmotic stress.
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Affiliation(s)
- R E Isaacks
- Research Laboratories, Veterans Affairs Medical Center, Miami, Florida 33125, USA
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17
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Isaacks RE, Bender AS, Kim CY, Prieto NM, Norenberg MD. Osmotic regulation of myo-inositol uptake in primary astrocyte cultures. Neurochem Res 1994; 19:331-8. [PMID: 8177373 DOI: 10.1007/bf00971582] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Uptake of myo-inositol by astrocytes in hypertonic medium (440 mosm/kg H2O) was increased near 3-fold after incubation for 24 hours, which continued for 72 hours, as compared with the uptake by cells cultured in isotonic medium (38 nmoles/mg protein). myo-Inositol uptake by astrocytes cultured in hypotonic medium (180 mosm/kg H2O) for periods up to 72 hours was reduced by 74% to 8 to 10 nmoles/mg protein. Astrocytes incubated in either hypotonic or hypertonic medium for 24 hours and then placed in isotonic medium reversed the initial down- or up-regulation of uptake. Activation of chronic RVD and RVI correlates with regulation of myo-inositol uptake. A 30 to 40 mosm/kg H2O deviation from physiological osmolality can influence myo-inositol homeostasis. The intracellular content of myo-inositol in astrocytes in isotonic medium was 25.6 +/- 1.3 micrograms/mg protein (28 mM). This level of myo-inositol is sufficient for this compound to function as an osmoregulator in primary astrocytes and it is likely to contribute to the maintenance of brain volume.
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Affiliation(s)
- R E Isaacks
- Research Laboratories, Veterans Affairs Medical Center, Miami, Florida 33125
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Pohjanvirta R, Hirvonen MR, Unkila M, Savolainen K, Tuomisto J. TCDD decreases brain inositol concentrations in the rat. Toxicol Lett 1994; 70:363-72. [PMID: 8284804 DOI: 10.1016/0378-4274(94)90131-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) reduced significantly brain regional inositol levels in both the most TCDD-susceptible (Long-Evans; LD50 9.8 micrograms/kg) and the most TCDD-resistant (Han/Wistar; LD50 > 7200 micrograms/kg) rat strain. The decrease emerged earlier in Long-Evans rats but was similar in magnitude at 8 days in both strains. There were some inconsistent and largely dose-independent changes in inositol-1- and inositol-4-monophosphate concentrations at 2 days. On day 8, a tendency towards reduced levels was seen especially in H/W rats. We conclude that TCDD reduces brain inositol levels presumably by inhibiting its synthesis by way of substrate deficit (hypoglycemia), but this effect does not appear to be causally related to the lethal action of TCDD.
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Affiliation(s)
- R Pohjanvirta
- National Public Health Institute, Department of Toxicology, Kuopio, Finland
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