Systematic Review The Repeated Antiphychotic Treatment Schizophrenla Model And The Application Of Model In Drug Development

Schizophrenia is an etiology unknown mental disorder. Onset of symptomstypically occurs in young adulthood, characterized by abnormalities in the thought,emotion and behavior. The symptoms of schizophrenia include positive and negativesymptoms, the positive symptoms most commonly manifests as hallucinations,disorganized thinking, and the negative symptoms most commonly manifests associal withdrawal and anhedonia. In addition, patients with schizophrenia also showcognitive impairment such as working memory and attention impairment.Antipsychotic drugs (APDs) are the main medications used to treatschizophrenia. The first-generation APDs (typical APDs, e.g., haloperidol) areprimarily dopamine D2 receptor antagonists. They are most effective in the control ofpsychotic symptoms but have a high propensity for producing severe side effects,such as extrapyramidal symptoms (EPS), sexual dysfunction, orthostatic hypotension,neuroendocrine disturbances, and sedation, which limit the therapeutic usefulness ofAPDs and reduce the patient's quality of life. The second-generation APDs (atypicalAPDs, clozapine, olanzapine) display a lower affinity for dopamine D2 receptors andhigher affinities for other receptors, such as 5-HT2A, 5-HT1A andα1- adrenergic and α2 - adrenergic receptors. In comparison to typicals, atypical APDs are equallyeffective against psychotic symptoms but have a reduced risk of EPS. However,atypicals can cause other unwanted side effects, such as weight gain, type II diabetes,hyperglycemia, and dyslipidemia. In addition, more than 30% of patients respondpoorly to any drug treatment and remain actively psychotic. Thus, it is it safe to saythat the current psychopharmacological treatments for schizophrenia areunsatisfactory because of their limited effectiveness on non-psychotic symptoms andthe disturbing side effects that they can cause. Consequently, there is a pressing needto develop better drugs that offer hope for the alleviation of negative symptoms andcognitive deficits in schizophrenia, to improve the quality of life of schizophrenicpatients.Animal behavior models are extremely useful tools in researching pathogenesisand treatment of human disease. Creating adequate animal models of complexneuropsychiatric disorders such as schizophrenia represents a particularly difficultchallenge. In the case of schizophrenia, little is certain regarding the etiology orpathophysiology of the human disease. In addition, many symptoms of the disorderare difficult to measure directly in rodents.Predictive validity for current and future therapies is one of the more desirablefeatures of an ideal animal model of schizophrenia. However, some current"predictive models"of schizophrenia treatment measure only a single dimension ofantipsychotic drug effects, often testing the effects of acute antipsychotic drugadministration on dopamine or glutamate receptor-mediated behaviors. Improvedmodels of schizophrenia will likely lead to unique advances in schizophreniatreatment.ATP-sensitive potassium channel (K-ATP channel) is a special class ofpotassium channel, which links cell metabolic state to excitability. K-ATP channelsconsist of discrete pore-forming and regulatory subunits and are activated by adecrease in ATP/ADP ratio. Recently, it is demonstrated that K-ATP channelespecially mitochondrial K-ATP (mitoK-ATP) channel is the importantneuroprotective target, and may be the endogenous protective mechanism after ischemic, hypoxia or oxidative stress-induced injury. Moreover. K-ATP channelparticipates in the initiation and progress of Parkinson s disease (PD), Alzherimer'sdisease (AD')Iptakalim was originally developed for the treatment of hypertension. It is anovel adenosine tnphosphate (ATP)-sensitive potassium channel activator that opensthe cardiovascular K-ATP channels and exerts an antihypertensive effect. Becauseiptakalim was later found to be able to easily pass through the blood-brain-barrier andto act on the neuronal plasma membrane and/or mitochondrial K-ATP channels, itspotential therapeutic effects ou neurological and neuropsychiatric disorders havegenerated much interest Current research focuses on the neuronal protective effectsof lptakalim on ischenic stroke. Parkinson s disease (PD) and its potential therapeuticeffect on nicotine addictionSeveral lines of indirect evidence suggest lhat lptafcalim may be potentiallyuseful for schizophrenia and may offer needed efficacies on negative and cognitivesymptoms First, in vitro and in vivo experiments demonstrate that iptakalim has aninhibitory function on excess dopamine release. Iptakalim is found to significantlyreduce dopamine release induced by rotenone or GBR-I2909 in rat dopaminergicPC 12 cells and to attenuate dopamine release induced by1-methy1-4-phenylpyridinium ion (MPP(+)) or nicotine m freely moving ratsInterestingly, in the unilateral 6-hydroxydopamine (6-OHDA) lesioned rats (a modelof PD). iptakalim is shown to significantly decrease extracellular dopamine levels inthe intact side of the sratum. while increasing dopamine levels in the lesioned sideThis unique property in some ways resembles lhat of a dopamine partial agonist, suchas aripiprazole, and suggests that iptakalim may be capable of adjusting the level ofdopamine in different parts of the brain Second, iptakalim is demonstrated to possessan intrinsic neuroprotective effect against necrosis and apoptosis due to its ability tolimit glutamate release and receptor functions. Third, in animal behavioral studies.iptakalim is shown to reverse haloperidol-induced catalepsy and hypolocomotionPretreatment with iptakalim or diazoxide (a selective mitochondrial ATP-sensitivepotassium channel opener) can even prevent rotenone-induced catalepsy and the reduction of striatum dopamine contents. These fomdomgs, together with evidencereviewed above showing that lptakalim can inhibit excess dopamine release, stronglysuggest that iptakalim may function as a ""dopamine stabilizer to modulate theappropriate level of dopamine in different parts of the brain. It may increasedopamine release at the site where tbe dopamine level is low, while decreasingdopamine release at the site where the dopamine level is high. Fourth, iptakalim isshown to possess a unique antihypertensive effect via the opening of the K-AXPchannels in several animal models. This antihypertensive effect of iptakalim is anattractive feature because hypertension is common in patients with psychiatric illness.Interestingly, most antipsychotic drugs also have a similar hypotensive effect.although via quite different physiological mechanisms. Nevertheless, this similarityadds to the support for the proposition that iptakalim may possess an antipsychoticproperty. Fifth the target site of iptakalim -the K-ATP channel- is found in the neuralcircuits that are implicated in the pathophysiology of scluzophrenia. such as thesubstantia nigra, ventral tegmental area, the prefrontal cortex and hippocampus, andplays an important role in the regulation of release of neurotransmitters, such asglutamate. dopamine and GABA Finally, it has been hypothesized that the K-ATPchannel activators may be beneficial in schizophrenia based on the evidence thatdopamine receptors can modulate the K-ATP channel opening. Diazoxide theATP-sensitive potassium channel opener has been tried m the clinic as an adjunctivetreatment together with haloperidol. It potentiated the effects of haloperidol on thepositive and general psychopathological symptoms of schizophrenia as measured byPANSS.In the present study, we first evaluated several rat behavioral models forantipsychotic activity. Then we used these newly developed models and exploredthe behavioral and receptor mechanisms underlying acute and repeated effects ofantipsychotic treatment Finally, we investigated the potential antipsychotic effect ofK-ATP channel opener EPT on preclinical scluzophrenia behavior model. Part I Significance of the repeated antiphychotic treatmentschizophrenia modelAIM: To investigated whether repeated antipsychotic treatment could producean early-onset and progressively increased antagonistic effect on amphetamine orphencyclidineinduced hyperlocomotion and on conditioned avoidance response as away of assessing the validity of such models in capturing time course of antipsychoticaction.METHODS: For the hyperlocomotion test, on each of the five consecutive testdays, different groups of rats (n=6–7/group) received an initial injection of eitherhaloperidol (0.01–0.10 mg/kg, sc), clozapine (5–20.0 mg/kg, sc), olanzapine (1.0mg/kg, sc), chlordiazepoxide (10.0 mg/kg, ip) or vehicle (sterile water, sc) 30 minprior to a second injection of either amphetamine (1.5 mg/kg, sc) or phencyclidine(3.2 mg/kg, sc). Motor activity was subsequently monitored for 60 min afteramphetamine or phencyclidine treatment. For the CAR test, on each of the fiveconsecutive test days, different groups of rats (n=6–7/group) received an injection ofeither haloperidol (0.05 mg/kg, sc), clozapine (10.0 mg/kg, sc), or vehicle (sterilewater, sc). Conditioned avoidance response monitored 60 min after HAL,CLZ orVEH treatment.RESULTS: 1) Repeated treatment of haloperidol, clozapine, or olanzapineprogressively potentiated inhibition on repeated phencyclidine-inducedhyperlocomotion and prolonged this action over the five consecutive days；2) Incontrast, antipsychotic inhibition on repeated amphetamine-induced hyperlocomotionwas gradually attenuated and shortened；3) Repeated treatment of chlordiazepoxide, abenzodiazepine anxiolytic, retained its inhibition on amphetamine-inducedhyperlocomotion, but had no effect on phencyclidine-induced one；4) Repeatedtreatment of haloperidol progressively potentiated inhibition on conditionedavoidance response; 5) In contrast, repeated treatment of clozapine progressivelyattenuated inhibition on conditioned avoidance response.CONCLUSION: R e p eated phencyclidine-induced hyperlocomotion model repeated antipsychotic treatment regimen is capable of capturing theprogressive increase pattern of antipsychotic treatment seen in the clinic anddifferentiating antipsychotics from anxiolytics; thus it may serve as a better modelfor the investigation of the neurobiological mechanisms of action of antipsychoticdrugs and delineating the pathophysiology of schizophrenia.Part II Mechanisms underlying repeated antiphychotictreatment schizophrenia modelAIM: To investigate the behavioral and receptor mechanisms underlying acuteand repeated effects of antipsychotic treatment.METHODS: For different antipsychotic treatment history test: First, differentgroups of rats (n=6–7/group) received an injection of either haloperidol (0.05 mg/kg,sc), clozapine (5 mg/kg, sc), olanzapine (2.0 mg/kg, sc), or vehicle (sterile water, sc)in the homecages for daily for five consecutive days, then, on the next five test days,they were injected with either haloperidol (0.05 mg/kg, sc), clozapine (5 mg/kg, sc),olanzapine (2.0 mg/kg, sc), or vehicle (sterile water, sc) 30 min prior to a secondinjection of phencyclidine (3.2 mg/kg, sc) before being placed in the motor activitytesting boxes. Motor activity was monitored for 60 min after phencyclidine treatment.Some rats that received vehicle in the first five days received either haloperidol (0.05mg/kg, sc), clozapine (5 mg/kg, sc), olanzapine (2.0 mg/kg, sc) in the second test days.For different testing room exposure test: on each of 7 consecutive test days, differentgroups of rats (n=8/group) received an initial injection of either haloperidol (0.03mg/kg, sc), clozapine (5 mg/kg, sc), olanzapine (1.0 mg/kg, sc), or vehicle (sterilewater, sc) 30 min prior to a second injection of phencyclidine (1.6 mg/kg, sc) in theirhomecages or testing boxes. Motor activity was subsequently monitored for 60 minafter phencyclidine treatment.For the CAR test: well-trained rats were administered with haloperidol (0.05 mg/kg,sc), clozapine (10.0 mg/kg, sc), or olanzapine (1.0 mg/kg, sc) together with eithersterile water, quinpirole (a selective dopamine D2/D3 agonist, 1.0 mg/kg, sc), and/or 2,5-dimethoxy-4-iodo-amphetamine (DOI, a selective 5-HT2A/2C agonist, 2.5 mg/kg,sc), and their avoidance behavior were tested over three consecutive days. After twodays drug-free retraining, the repeated treatment effect (i.e. drug memory) wasassessed in a challenge test.RESULTSRESULTS: 1) Preexposure to the antipshchotic did not afftect the inhibition ofantipsychotic treatment on acute PCP-induced hyperlocomotion.; 2) Differentexposure times affect the inhibition effect of HAL, but not CLZ, OLZ, onPCP-induced hyperlocomotion；3) Pretreatment of quinpirole, but not DOI,attenuated the acute haloperidol-induced disruption of avoidance responding and to alesser extent, olanzapine-induced disruption；4) In contrast, pretreatment of DOI, butnot quinpirole, attenuated that of clozapine；5) On the repeated effect, pretreatmentof DOI attenuated the haloperidol drug memory, whereas pretreatment of quinpiroleattenuated olanzapine drug memory and potentiated that of clozapine.CONCLUSION: The progressively potentiated inhibition of repeated treatmentof haloperidol, clozapine, or olanzapine on repeated phencyclidine inducedhyperlocomotion depends on the drug-drug interaction and drug-environmentinteraction. Acute haloperidol and olanzapine disrupt avoidance responding primarilyby immediately blocking dopamine D2 receptors, whereas acute clozapine exerts itsdisruptive effect primarily by blocking the 5-HT2A/2C receptors. The repeatedhaloperidol and clozapine effect may be mediated by brain changes initiated by5-HT2A/2C blockade, whereas the repeated olanzapine effect may be mediated by brainchanges initiated by D2 blockade.Part III Effect of iptakalim in schizophrenia modelsAIM: To examine the potential antipsychotic activity of iptakalim (IPT) inseveral schizophrenia animal behavioral modelsMETHODS: We used some preclinical animal behavioral model to investigatethe potential antipsychotic activity of IPT:1) amphetamine- andphencyclidine-induced hyperlocomotion；2) conditioned avoidance responding model; 3) amphetamine- and phencyclidine-induced prepulse inhibition deficit model; 4)Immunohistochemistry was taken for analyses of IPT induced C-fos expression inthe nucleus accumbens, medial prefrontal cortex, lateral septal nucleus, anddorsolateral striatum.RESULTSRESULTS: 1) IPT is effective in reducing amphetamine- andphencyclidine-induced hyperlocomotion and shows a preferential effect in reducingthe PCP-induced hyperlocomotion over the amphetamine-induced one；2) acuteiptakalim treatment selectively and dose-dependently disrupts conditioned avoidanceresponding. Repeated iptakalim treatment gradually loses its inhibition on avoidanceresponding, an effect shared only by clozapine, but not by other antipsychotics tested,such as haloperidol, olanzapine and risperidone; 3) iptakalim itself does not disruptprepulse inhibition (PPI) of acoustic startle reflex or cause catalepsy. It potentiates theamphetamine-induced reduction of PPI but is ineffective in reversing thephencyclidine-induced disruption; 4) iptakalim and clozapine, but not haloperidol,preferentially induces Fos-like immunoreactivity (FLI) in the nucleus accumbens,medial prefrontal cortex and lateral septal nucleus, but not in the dorsolateralstriatum..CONCLUSION: These findings indicate that iptakalim is a drug that maypossess an atypical clozapine-like antipsychotic property with a distinct mechanismof action.The major contributions of the present study lie in:1. For the first time, we validated several preclinical animal models forantipsychotic activity based on repeated treatment regimen. We show that repeatedphencyclidine-induced hyperlocomotion model based on repeated antipsychotictreatment regimen is capable of capturing the progressive increase pattern ofantipsychotic treatment seen in the clinic and differentiating antipsychotics fromanxiolytics; which serve as a better model for the investigation of the neurobiologicalmechanisms of action of antipsychotic drugs and delineating the pathophysiology ofschizophrenia 2. For the first time, we explored the behavior and receptor mechanismsunderlying acute and repeated effects of antipsychotic.3. For the first time, we determined that iptakalim is a drug that may possess anatypical clozapine-like antipsychotic property with a distinct mechanism of action,and points out that neuronal and astrocytic plasma membrane and/or mitochondrialK-ATP channels may be a target that deserves attention for antipsychotic drugdevelopment.