Effects of the Putative Antipsychotic Alstonine on Glutamate Uptake in Acute Hippocampal Slices ⇑ Ana P

Neurochemistry International 61 (2012) 1144–1150 Contents lists available at SciVerse ScienceDirect Neurochemistry International journal homepage: www.elsevier.com/locate/nci Effects of the putative antipsychotic alstonine on glutamate uptake in acute hippocampal slices ⇑ Ana P. Herrmann a,b, , Paula Lunardi b, Luísa Klaus Pilz a, Ana C. Tramontina b, Viviane M. Linck a,b, Christopher O. Okunji c, Carlos A. Gonçalves b, Elaine Elisabetsky a,b a Laboratório de Etnofarmacologia, Departamento de Farmacologia, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Sarmento Leite, 500, 90050-170 Porto Alegre, RS, Brazil b Programa de Pós-graduação em Ciências Biológicas: Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos, 2600, 90035-000 Porto Alegre, RS, Brazil c International Centre for Ethnomedicine and Drug Development (InterCEDD), Nsukka, Enugu State, Nigeria article info abstract Article history: A dysfunctional glutamatergic system is thought to be central to the negative symptoms and cognitive Received 8 March 2012 deficits recognized as determinant to the poor quality of life of people with schizophrenia. Modulating Received in revised form 13 August 2012 glutamate uptake has, thus, been suggested as a novel target for antipsychotics. Alstonine is an indole Accepted 15 August 2012 alkaloid sharing with atypical antipsychotics the profile in animal models relevant to schizophrenia, Available online 25 August 2012 though divergent in its mechanism of action. The aim of this study was to evaluate the effects of alstonine on glutamate uptake. Additionally, the effects on glutathione content and extracellular S100B levels were Keywords: assessed. Acute hippocampal slices were incubated with haloperidol (10 lM), clozapine (10 and 100 lM) Alstonine or alstonine (1–100 M), alone or in combination with apomorphine (100 M), and 5-HT receptor antag- Antipsychotics l l 2 Schizophrenia onists (0.01 lM altanserin and 0.1 lM SB 242084). A reduction in glutamate uptake was observed with Astrocytes alstonine and clozapine, but not haloperidol. Apomorphine abolished the effect of clozapine, whereas 5- Glutamate uptake HT2A and 5-HT2C antagonists abolished the effects of alstonine. Increased levels of glutathione were S100B observed only with alstonine, also the only compound that failed to decrease the release of S100B. This study shows that alstonine decreases glutamate uptake, which may be beneficial to the glutamatergic deficit observed in schizophrenia. Noteworthily, the decrease in glutamate uptake is compatible with the reversal of MK-801-induced social interaction and working memory deficits. An additional potential benefit of alstonine as an antipsychotic is its ability to increase glutathione, a key cellular antioxidant reported to be decreased in the brain of patients with schizophrenia. Adding to the characterization of the novel mechanism of action of alstonine, the lack of effect of apomorphine in alstonine-induced changes in glutamate uptake reinforces that D2 receptors are not primarily implicated. Though clearly mediated by 5-HT2A and 5-HT2C serotonin receptors, the precise mechanisms that result in the effects of alstonine on glutamate uptake warrant elucidation. Ó 2012 Elsevier Ltd. Open access under the Elsevier OA license. 1. Introduction prompted the idea of a glutamatergic dysfunction in the pathophysiology of schizophrenia. PCP, as well as the related drugs With lifetime prevalence commonly estimated in 1% of the pop- ketamine and MK-801, induce in normal volunteers psychosis-like ulation, schizophrenia is a severe psychiatric disorder marked by and neurocognitive disturbances similar to those of schizophrenia; profound retreat from reality and incapacitating cognitive deficits. unlike dopaminergic agonists, these drugs mimic all the symptoms It belongs to a group of complex multifactorial disorders, for which dimensions of the disease (Javitt, 2010). It is now widely accepted the etiology is understood as the intricate interaction between ge- that the dopaminergic alterations classically associated to schizo- netic and environmental factors (Gogos and Gerber, 2006; van Os phrenia may, in fact, be secondary to an underlying deficit in gluta- et al., 2010). matergic transmission (Carlsson, 2006; Marek et al., 2010). Of note, The observations of the behavioral effects induced by phencyc- Stone et al. (2010) reported in prodromic subjects with mild psy- lidine (PCP), an antagonist of glutamate NMDA receptors, chotic symptoms a negative relationship between hippocampal glutamate levels and striatal [18F]-DOPA uptake, reinforcing the idea of a coupling between glutamatergic transmission and striatal ⇑ Corresponding author at: Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Sarmento Leite, 500, sala 202, 90050-170 Porto dopaminergic activity. Alegre, RS, Brazil. Tel./fax: +55 51 33083121. Glutamate is released into the synapse and rapidly removed by E-mail address: [email protected] (A.P. Herrmann). a family of excitatory amino acid transporters (EAATs) localized in 0197-0186 Ó 2012 Elsevier Ltd. Open access under the Elsevier OA license. http://dx.doi.org/10.1016/j.neuint.2012.08.006 A.P. Herrmann et al. / Neurochemistry International 61 (2012) 1144–1150 1145 neurons and glial cells. Five members of EAATs have been identi- controlled environmental conditions (12-h light/dark cycle at a fied and termed EAAT1–5 to human homologs, or GLAST, GLT-1 constant temperature of 22 ± 1 °C) with free access to food and and EAAC-1 representing the rodent homologs of EAATs1–3, water. The study was approved by the University Ethics Committee respectively (Kanai and Hediger, 1992; Pines et al., 1992; Storck (approval #18237), and followed institutional policies on experi- et al., 1992; Fairman et al., 1995; Arriza et al., 1997). EAAT2/ mental animal handling. All efforts were made to minimize animal GLT-1 is predominantly expressed in astrocytes and provides more suffering, to reduce the number of animals used, and to utilize than 90% of total glutamate uptake in the central nervous system alternatives to in vivo techniques. (Tanaka et al., 1997). Given that astrocytes are fundamental in the control of gluta- 2.2. Drugs and reagents mate homeostasis, a significant role has recently been assigned to glial–neuronal interactions in the pathophysiology of schizo- Alstonine hydrochloride was isolated from Picralima nitida Th. & phrenia. There is increasing evidence that structural and functional H. Dur. (Apocynaceae) by Christopher O. Okunji, as earlier de- alterations in glial cells are present in the brain of people with scribed (Okunji et al., 2005). Clozapine, altanserin and SB 242084 schizophrenia (Cotter et al., 2001; Kondziella et al., 2006; Bernstein were purchased from Sigma Chemical Co. (St. Louis, MO, USA), et al., 2009; Katsel et al., 2011). Additionally, a DNA array study apomorphine was purchased from Research Biochemicals Interna- showed that the genes most frequently altered in the disorder tional (Natick, MA, USA), DL-threo-b-benzyloxyaspartic acid are related to glial function (Sugai et al., 2004). Signaling mole- (DL-TBOA) was acquired from Tocris Bioscience (Bristol, UK) and cules, such as S100B and GFAP, have also been examined as mark- haloperidol was used as commercial HaldolÒ from Janssen-Cilag ers of astrocytic function. Several studies reported increased S100B Farmacêutica Ltd. (São Paulo, SP, Brazil). Monoclonal anti-S100B levels in the serum or cerebrospinal fluid (CSF) of patients with antibody (SHB1), 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic schizophrenia (Wiesmann et al., 1999; Lara et al., 2001; Rother- acid (Hepes), o-phenylenediamine (OPD), 3-(4,5-dimethylthiazol- mundt et al., 2001, 2004a,b, 2007; Schroeter et al., 2003; Schmitt yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and L-glutamate et al., 2005); however, the effects of antipsychotic drugs in this were purchased from Sigma (St. Louis, MO, USA), polyclonal rabbit parameter remain unclear (Steiner et al., 2010). anti-S100 from Dako (Glostrup, Denmark), and horseradish perox- It is undisputable that over the past decades major advances 3 idase-conjugated anti-rabbit IgG and L-[2,3- H]-glutamate from have been accomplished in the understanding of the neurobiologi- Amersham International (Buckinghamshire, UK). All other chemical processes involved in schizophrenia. The acquired knowledge, cals were purchased from local commercial suppliers. however, has not translated into better treatment options, since all currently available antipsychotics share their mechanism of action with drugs discovered almost 60 years ago. Moreover, the 2.3. Hippocampal slices modest and controversial benefits of antipsychotics on cognitive deficits and negative symptoms, combined with the unwanted side Rats were killed by decapitation. Hippocampi were removed effects, result in high rates of treatment discontinuation (Lieber- and sliced in transverse sections of 0.3 mm using a McIlwain tissue man et al., 2005). The development of drugs with innovative mech- chopper. Slices were transferred to 24-well plates containing anisms of action is, thus, required (Gründer et al., 2009). 0.3 mL of Hepes-buffered saline solution (120 mM NaCl, 2 mM We have previously reported the properties of alstonine, a puta- KCl, 1 mM CaCl2, 1 mM MgSO4, 1 mM KH2PO4, 10 mM glucose tive antipsychotic which has consistently shown anxiolytic and and 25 mM Hepes, pH

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