Significant outcomes
• Olanzapine and aripriprazole increased the activities of respiratory chain complexes I, II and II–III.
• Complex IV activity was inhibited by clozapine, olanzapine and aripriprazole.
• Creatine kinase (CK) activity was increased by clozapine in prefrontal cortex, cerebellum, striatum, hippocampus and posterior cortex of rats.
• Olanzapine and aripiprazole did not affect CK activity.
Limitations
• It is necessary to investigate other important steps of energy metabolism.
Introduction
Neuropsychiatric disorders such as schizophrenia, depression and bipolar disorder have been related to dysfunction in the brain metabolism Reference Albert, Hemmings and Adamo1, Reference Konradi, Eaton, MacDonald, Walsh, Benes and Heckers2, Reference Prince, Yassin and Oreland3, and on neurotrophic factor expression Reference Angelucci, Mathe and Aloe4, Reference Angelucci, Oliviero and Pilato5, Reference Duman6, Reference Duman7, alterations in the neuronal function and survival Reference Schlattner and Wallimann8, Reference Velligan, Newcomer and Pultz9, as well as abnormal synaptogenesis and neurotransmission Reference Albert, Hemmings and Adamo1, Reference Duman6, Reference Duman7. The metabolism dysfunction includes mitochondrial impairment Reference Konradi, Eaton, MacDonald, Walsh, Benes and Heckers2, Reference Kato and Kato10, increase in reactive oxygen species (ROS) production and expression of biochemical markers of cellular degeneration Reference Schlattner and Wallimann8, Reference Fatemi, Laurence and Araghi-Niknam11, Reference Machado-Vieira, Lara and Portela12, Reference Rothermundt, Missler and Arolt13, Reference Schroeter, Abdul-Khaliq and Fruhauf14.
Atypical antipsychotics such as clozapine and olanzapine exhibit serotonin/dopamine antagonistic properties associated with fewer extrapyramidal symptoms than conventional antipsychotics Reference Velligan, Newcomer and Pultz9, Reference Carlson, Cavazzoni, Berg, We, Beasley and Kane15. Aripiprazole is an atypical neuroleptic that exhibits a high binding affinity for D2 and D3 receptors, a moderate affinity for D4 receptors and a low affinity for D1 receptors. Preclinical studies have also indicated that aripiprazole has a relatively high affinity for serotonin 5-HT2A and 5-HT1A receptors. It displays partial agonist activity at the 5-HT1A receptor and antagonistic activity at the 5-HT2A receptor Reference Burris, Molski and Xu16. In humans, recent evidence suggests that schizophrenic patients treated with atypical antipsychotics may present a better performance in cognitive tasks when compared to patients treated with typical antipsychotics Reference Velligan, Newcomer and Pultz9, Reference Jordan, Koprivica, Chen, Tottori, Kikuchi and Altar17.
Mitochondria are intracellular organelles which play a crucial role in adenosine triphosphate (ATP) production Reference Beuzen, Taylor, Wesnes and Wood18. Mitochondrial oxidative phosphorylation is the major ATP-producing pathway Reference Calabrese, Scapagnini, Giuffrida-Stella, Bates and Clark19. Energy, in the form of ATP, is obtained in the mitochondria through a series of reactions in which electrons liberated from reducing substrates NADH and FADH2 are delivered to O2 via the electron transport chain, which consists of four multimeric complexes (I, II, III and IV) plus two small electron carriers, coenzyme Q (or ubiquinone) and cytochrome c. The energy obtained by the reactions of the electron transport chain is used to pump protons from the mitochondrial matrix into the intermembrane space located between the inner and outer mitochondrial membranes. This process creates an electrochemical proton gradient, which is utilised by complex V (or ATP synthase) to catalyse the formation of ATP by the adenosine diphosphate (ADP) Reference Madrigal, Olivenza and Moro20, Reference Fattal, Budur, Vaughan and Franco21. Another way to produce ATP is through CK (EC 2.7.3.2) which is a crucial enzyme for high energy-consuming tissues like brain, skeletal muscle and heart. This enzyme works as a buffering system of cellular ATP levels, playing a central role in energy metabolism. CK catalyses the reversible transfer of the phosphoryl group from phosphocreatine to ADP, regenerating ATP Reference Wallimann, Wyss, Brdiczka, Nicolay and Eppenberger22, Reference Bessman and Carpenter23. In addition, CK may be considered as a marker of creatine/phosphocreatine system functioning in brain Reference Tsuji, Nakamura, Ogata, Shibata and Kataoka24. In this context, it has been widely shown diminution of CK activity may potentially impair energy homeostasis, contributing to cell death Reference Tomimoto, Yamamoto, Homburger and Yanagihara25, Reference Aksenov, Aksenova, Butterfield and Markesbery26, Reference David, Shoemaker and Haley27, Reference Gross, Bak and Ingwall28, Reference Streck, Amboni and Scaini29.
The brain contains a large number of mitochondria, being more susceptible to fluctuations on aerobic metabolism. Neurons have a high metabolic rate, limited stores of glucose or glycogen, low anaerobe capacity and a near exclusive dependence on glucose as an energy substrate Reference Lee, Grabb, Zipfel and Choi30. It is well described that impairment of energy production caused by mitochondrial dysfunction has been implicated in the pathogenesis of a number of diseases, including neurological conditions such as dementia, cerebral ischaemia, Alzheimer's disease and Parkinson's disease Reference Machado-Vieira, Lara and Portela12, Reference Streck, Amboni and Scaini29, Reference Lee, Grabb, Zipfel and Choi30, Reference Blass31, Reference Brennan, Bird and Aprille32, Reference Gruno, Peet and Tein33, Reference Schurr34. Neuropsychiatry disorders such as schizophrenia, depression and bipolar disorder have also been related to dysfunction on neurotrophic factor expression Reference Angelucci, Mathe and Aloe4, Reference Angelucci, Oliviero and Pilato5, Reference Duman6, Reference Duman7, dysfunction in the brain metabolism Reference Albert, Hemmings and Adamo1, Reference Prabakaran, Swatton and Ryan35 alterations in the neuronal function and survival Reference Rothermundt, Ponath and Arolt36, Reference Weis and Llenos37 as well as abnormal synaptogenesis and neurotransmission Reference Albert, Hemmings and Adamo1, Reference Duman6, Reference Duman7. In addition, Assis and colleagues Reference Assis, Scaini and Di-Pietro38 have recently shown that brain CK activity is altered by antipsychotics. Moreover, succinate dehydrogenase activity was inhibited in cerebellum and striatum after olanzapine and clozapine administration, respectively, whereas aripiprazole increased the enzyme in prefrontal cortex Reference Streck, Rezin, Barbosa, Assis, Grandi and Quevedo39. Some studies also reported that chronic exposure to clozapine resulted in significant changes in the activities of antioxidant enzymes and oxidative damage in rat brain, but no change was observed with olanzapine administration Reference Polydoro, Schröder and Lima40.
Considering that reduction of brain energy metabolism is related to neurological dysfunction and that some neuroleptics alter oxidative stress parameters and cognitive function, in this study we evaluated the effects in vitro of some antipsychotics, named clozapine, olanzapine and aripiprazole on mitochondrial respiratory chain and CK activities in brain (hippocampus, striatum, cerebellum, posterior cortex and prefrontal cortex) of rats.
Materials and methods
Animals
Adult male Wistar rats (250–300 g) were obtained from the Central Animal House of University of Extremo Sul Catarinense, Criciúma, SC, Brazil. They were caged in groups of five with free access to food and water and were maintained on a 12-h light:dark cycle (lights on 07:00 h), at a temperature of 22 ± 1°C. All experimental procedures were carried out in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the Brazilian Society for Neuroscience and Behavior recommendations for animal care, with the approval of UNESC Ethics Committee.
Drugs
Clozapine was purchased from Novartis Biociências AS, São Paulo, Brazil (Leponex®). Olanzapine was provided from Eli Lilly do Brasil Ltda, São Paulo, Brazil (Zyprexa®). Aripiprazole was purchased from Bristol-Myers Squibb, São Paulo, Brazil (Abilify®).
Tissue and homogenate preparation
On the day of the experiments the animals were killed by decapitation (n = 6), the brain was removed and cerebellum, hippocampus, striatum, prefrontal cortex and posterior cortex were homogenised (1:10, w/v) in SETH buffer, pH 7.4 (250 mM sucrose, 2 mM ethylenediaminetetraacetic acid, 10 mM Trizma base, 50 IU/ml heparin). The homogenates were centrifuged at 800 × g for 10 min and the supernatants kept at −70 °C until used for enzymes activity determination. The maximal period between homogenate preparation and enzyme analysis was always less than 5 days. Protein content was determined by the method described by Lowry and colleagues Reference Lowry, Rosebrough, Farr and Randall41 using bovine serum albumin as standard. Clozapine (0.1, 0.5 and 1.0 mg/ml), olanzapine (0.1, 0.5 and 1.0 mg/ml) and aripiprazole (0.05, 0.15 and 0.3 mg/ml) were dissolved on the day of the experiments in the incubation medium (buffer) used for each technique.
Activities of mitochondrial respiratory chain enzymes
In the day of the assays, the samples were frozen and thawed in hypotonic assay buffer three times to fully expose the enzymes to substrates and achieve maximal activities. NADH dehydrogenase (complex I) was evaluated according to the method described by Cassina and Radi Reference Cassina and Radi42 by the rate of NADH-dependent ferricyanide reduction at 420 nm. The activities of succinate: 2,6-dichlorophenolindophenol (DCIP) oxidoreductase (complex II) and succinate: cytochrome c oxidoreductase (complexes II–III) were determined according to the method of Fischer and colleagues Reference Fischer, Ruitenbeek and Berden43. Complex II activity was measured by following the decrease in absorbance due to the reduction of 2,6-DCIP at 600 nm. The activity of complexes II–III was measured by cytochrome c reduction from succinate. The activity of cytochrome c oxidase (complex IV) was assayed according to the method described by Rustin and colleagues Reference Rustin, Chretien and Bourgeron44, measured by following the decrease in absorbance due to the oxidation of previously reduced cytochrome c at 550 nm. The activities of the mitochondrial respiratory chain complexes were expressed as nmol/min/mg protein.
CK activity
CK activity was measured in brain homogenates pre-treated with 0.625 mM lauryl maltoside. Briefly, the reaction mixture consisted of 60 mM Tris–HCl, pH 7.5, containing 7.0 mM phosphocreatine, 9.0 mM MgSO4 and approximately 0.4–1.2 mg protein in a final volume of 100 ml. After 15 min of preincubation at 37°C, the reaction was then started by the addition of 4.0 mM of ADP and stopped after 10 min by the addition of 20 ml of 50 mM phydroxy-mercuribenzoic acid. The creatine formed was estimated according to the colorimetric method of Hughes Reference Hughes45. The colour was developed by the addition of 100 ml 2% α-naphtol and 100 ml 0.05% diacetyl in a final volume of 1.0 ml and read spectrophotometrically after 20 min at λ = 540 nm. Results were expressed as units/min × mg protein.
Statistical analysis
Data were analysed by one-way analysis of variance followed by the Tukey test when F was significant and are expressed as mean ± SD. All analyses were performed using the Statistical Package for the Social Science (SPSS) software (IBM Corporation, NY, USA).
Results
In this study, we evaluated the effects of clozapine, olanzapine and aripiprazole on activities of mitochondrial respiratory chain enzymes and CK activity in some brain areas (hippocampus, striatum, cerebellum, prefrontal cortex and posterior cortex) of rats. It can be seen in Fig. 1 that complex I activity was increased in prefrontal cortex and striatum by olanzapine at 0.5 mg/ml and higher concentrations (prefrontal cortex p = 0.005 and p = 0.001; striatum p = 0.004 and p = 0.000). As shown in Fig. 1, olanzapine at 0.5 and 1.0 mg/ml increased complex II activity in cerebellum, striatum and posterior cortex (cerebellum p = 0.003 and p = 0.000; striatum p = 0.002 and p = 0.000; posterior cortex p = 0.002 and p = 0.000), whereas prefrontal cortex and hippocampus were not affected. Furthermore, olanzapine at 0.5 mg/ml and higher concentrations increased the activity of complexes II–III in prefrontal cortex, striatum and posterior cortex (prefrontal cortex p = 0.012 and p = 0.002; striatum p = 0.000 and p = 0.000; posterior cortex p = 0.000 and p = 0.000). In cerebellum and hippocampus, olanzapine increased the activity of complexes II–III only in the higher dose (cerebellum p = 0.000; hippocampus p = 0.000) (Fig.1). On the other hand, olanzapine inhibited complex IV activity in cerebellum only in the higher dose (cerebellum p = 0.001), without affecting prefrontal cortex, striatum, hippocampus and posterior cortex (Fig.1).
The next set of experiments was performed in order to evaluate the in vitro effect of clozapine on the respiratory chain complex activities. Fig. 2 shows that clozapine did not affect the activities of complexes I, II and II–III in the cerebral regions evaluated in this study (Fig. 2, respectively). In contrast, clozapine at 0.1 mg/ml and higher concentrations inhibited complex IV activity in prefrontal cortex and hippocampus (prefrontal cortex p = 0.002, p = 0.000 and p = 0.004; hippocampus p = 0.000, p = 0.001 and p = 0.000), on the other hand, as clozapine at 0.5 and 1.0 mg/ml decreased complex IV activity in cerebellum (p = 0.001 and p = 0.006), but striatum and posterior cortex were not affected (Fig. 2).
Fig. 3 shows that aripiprazole 0.15 and 0.3 mg/ml increased complex I activity in striatum (p = 0.006 and p = 0.003), but not affect prefrontal cortex, cerebellum, hippocampus and posterior cortex (Fig. 3). On the other hand, aripriprazole at 0.15 and 0.3 mg/ml increased complex II activity in posterior cortex (p = 0.002 and p = 0.007). In cerebellum aripiprazole increased complex II activity only in the higher dose (p = 0.020). Moreover, prefrontal cortex, striatum and hippocampus were not affected (Fig. 3). In contrast, the activity of complexes II–III was increased by aripiprazole (0.3 mg/ml) in striatum and hippocampus (striatum p = 0.038; hippocampus p = 0.004) (Fig. 3). On the other hand, aripiprazole inhibited complex IV activity in prefrontal cortex only in the higher dose (prefrontal cortex p = 0.014), without affecting cerebellum, striatum, hippocampus and posterior cortex (Fig. 3).
Finally, we tested the influence of olanzapine, clozapine and aripiprazole on the CK activity. It can be seen in Fig. 4 that CK activity was increased by clozapine at 0.5 and 1.0 mg/ml in prefrontal cortex, cerebellum, striatum, hippocampus and posterior cortex of rats (prefrontal cortex p = 0.000 and p = 0.000; cerebellum p = 0.015 and p = 0.000; striatum p = 0.018 and p = 0.000; hippocampus p = 0.002 and p = 0.009; posterior cortex p = 0.001 and p = 0.000). Olanzapine and aripiprazole did not affect CK activity in either tested structure (Fig. 4, respectively).
Discussion
Dysfunction in brain metabolism is related to neuropsychiatric disorders, such as schizophrenia, depression and bipolar disorder Reference Albert, Hemmings and Adamo1, Reference Konradi, Eaton, MacDonald, Walsh, Benes and Heckers2, Reference Prince, Yassin and Oreland3, Reference Kato and Kato10. Some evidence also point to the possibility that drugs used in the treatment of such disorders modulate energy metabolism, especially by increasing it. In this context, we reported recently that mood stabilisers prevent and reverse inhibitory effect on cytrate synthase activity caused by amphetamine in an animal model of mania Reference Corrêa, Amboni and Assis46. Regarding antipsychotics, reports from literature show that the atypical antipsychotic olanzapine only inhibited succinate dehydrogenase (SDH) in cerebellum and aripiprazole increased the same enzyme in prefrontal cortex, whereas clozapine inhibited the enzyme only in striatum.
Volz and colleagues Reference Volz, Riehemann and Maurer47 observed decreased levels of ATP in the frontal lobes of antipsychotic-free patients. Furthermore, reports from literature show that ATP levels may inversely correlate with the degree of negative symptoms in schizophrenic patients Reference Volz, Rzanny and Rossger48. Additionally, two groups reported a lower ATP concentration in the basal ganglia of medicated schizophrenic patients, suggesting an imbalance between ATP production and ATP utilisation by oxidative phosphorylation in this disorder Reference Deicken, Calabrese, Merrin, Fein and Weiner49. Andreassen and colleagues Reference Andreassen, Ferrante, Beal and Jorgensen50 verified that mild mitochondrial impairment in combination with neuroleptics results in striatal excitotoxic neurodegeneration, which may underlie the development of persistent vacuous chewing movements in rats.
It is well described that some side-effects of antipsychotics limited their long-term use and are probably associated to oxidative stress Reference Cadet and Lohr51, Reference Lohr, Cadet and Lohr52 and metabolism impairment Reference Arnaiz, Coronel and Boveris53. The biochemical and physiological characteristics of the brain, with high-unsaturated phospholipids content and energy requirement, make this organ particularly susceptible to free radical-mediated damage Reference Madrigal, Olivenza and Moro20, Reference Gross, Bak and Ingwall28. It is well known that mitochondrial oxidative phosphorylation system generates ROS and the electron transport chain, mainly complexes I and III, is vulnerable to damage by them Reference Adam-Vizi54, Reference Torres, Torres and Gamaro55. In this context, several studies show that antipsychotics cause oxidative stress Reference Jordan, Koprivica, Chen, Tottori, Kikuchi and Altar17, Reference Polydoro, Schröder and Lima40. Augmented ROS production causes defects in the mitochondrial genome, leading to impaired oxidative phosphorylation, which not only limits ATP generation but also further promotes ROS production Reference Gruno, Peet and Tein33. Moreover, oxidative damage can be cause or consequence of mitochondrial dysfunction Reference Madrigal, Olivenza and Moro20, Reference Torres, Torres and Gamaro55.
In this study, we observed that olanzapine and aripriprazole increased the activities of respiratory chain complexes. On the other hand, complex IV activity was inhibited by clozapine, olanzapine and aripriprazole. Prince and colleagues Reference Prince, Yassin and Oreland3 evaluated regional alterations in neuronal functional activity in rat brain using complex IV histochemistry following chronic treatment with haloperidol, fluphenazine and clozapine for 28 days. The authors verified that increases in complex IV activity were evident in the frontal cortex of all treated animals. Moreover, clozapine and fluphenazine, but not haloperidol, caused significant increases in complex IV activity in other areas. The authors also suggest that neuroleptics achieve their therapeutic effects primarily via an enhancement of brain function in the frontal cortex, but also point to other brain regions which may be involved in the actions of these drugs Reference Prince, Yassin and Oreland3. In contrast, ours result suggests that chronic treatment using clozapine increases complex IV activity by an indirect mechanism, probably mediated by signal transduction and/or gene expression pathways.
The creatine/phosphocreatine/CK system is important for normal energy homeostasis by exerting several integrated functions, such as temporary energy buffering, metabolic capacity, energy transfer and metabolic control Reference Schlattner and Wallimann8, Reference Khuchua, Qin and Boero56. The brain of adult rats, like other tissues with high and variable rates of ATP metabolism, presents high phosphocreatine concentration and CK activity. It has been widely shown that a decrease in CK activity is associated with a neurodegenerative pathway that results in neuronal loss following brain ischaemia Reference Tomimoto, Yamamoto, Homburger and Yanagihara25, neurodegenerative diseases Reference Aksenov, Aksenova, Butterfield and Markesbery26, Reference David, Shoemaker and Haley27 and other pathological states Reference Streck, Amboni and Scaini29, Reference Lee, Grabb, Zipfel and Choi30.
Considering that CK is sensitive to free radicals Reference Wolosker, Panizzutti and Englender57 and that we have recently shown that antipsychotics lead to oxidative stress, we speculate that the enzyme inhibition in vivo may occur by the oxidation of thiol groups of its structure. In this context, Assis and colleagues Reference Assis, Scaini and Di-Pietro38 observed that chronic administration of clozapine inhibited CK activity in cerebellum and prefrontal cortex. Moreover, the increase in vitro CK activity by clozapine differs from in vivo studies; thus we suggest that the increased activity occur by direct mechanisms, whereas inhibition in vivo may occur by the oxidation of thiol groups of its structure.
Acknowledgements
This research was supported by grants from Programa de Pós-graduação em Ciências da Saúde – Universidade do Extremo Sul Catarinense (UNESC), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Instituto Nacional de Ciência e Tecnologia Translacional em Medicina (INCT).