Progress in Neuro-Psychopharmacology and Biological Psychiatry
Short communicationEffects of clozapine, olanzapine and haloperidol on nitric oxide production by lipopolysaccharide-activated N9 cells
Introduction
Schizophrenia is a severe illness that affects approximately 1% of the world's population. The etiology of schizophrenia is only partially understood and, consequently, the basis for its treatment rests in the symptomatic response to antipsychotics. Although classic antipsychotic drugs, such as haloperidol, produce a marked reduction in positive symptoms of schizophrenia, they do not improve the negative symptoms such as apathy, confusion, and social withdrawal, nor do they alter the progressive deterioration in the mental abilities of the patients. In recent years, several new drugs, such as clozapine and olanzapine, have been shown to improve both positive and negative symptoms of schizophrenia, and seem to prevent further worsening of psychotic symptoms (Buckley, 1997, Blin, 1999, Bhana et al., 2001). The atypical antipsychotic drugs are potent 5-HT2A and weak D2 antagonist, which distinguishes them from typical antipsychotic drugs (Altar et al., 1986, Meltzer et al., 1989, Meltzer, 1999, Rasmussen and Aghajanian, 1988). They also have many other pharmacologic properties that may contribute to their superior therapeutic actions in schizophrenia and that could be the basis for their usefulness in controlling psychotic symptoms in other disorders as well (Tran et al., 1997, Stoppe and Staedt, 1999, Wolfgang, 1999).
Microglial cells are ubiquitously distributed in the central nervous system (CNS) and comprise up to 20% of the total glial cell population in the brain (Lawson et al., 1991). As a kind of cells of the macrophage lineage in the CNS, microglial cells are quiescent in the normal brain. However, these cells can be activated by cytokines produced by infiltrating immune effector cells after CNS injury or by LPS during bacterial infection (Gonzalez-Scarano and Baltuch, 1999, Stoll and Jander, 1999). Activation of microglial cells is associated with increased phagocytosis and release of NO, oxygen radicals, proteases as well as pro-inflammatory cytokines (Stoll and Jander, 1999, Lee et al., 2002). In recent years, microglial cells have been shown to be involved in many CNS illnesses. For example, prolonged and excessive stimulation of microglial cells initiates an inflammatory cascade in the CNS that contributes to the pathogenesis of Alzheimer's disease, Parkinson's disease (Stoll and Jander, 1999, Mcgeer et al., 1993), multiple sclerosis (Boyle and McGeer, 1990) and HIV-associated dementia (Kaul et al., 2001). Recently, Munn (2000) has proposed microglia dysfunction in schizophrenia as an integrated theory. The study of Bayer et al. (1999) showed that some of the patients with schizophrenia elicited microglia activation, suggesting microglia activation might be involved in the pathophysiological process of schizophrenia. Taken together, the present study used LPS-activated mouse microglial cell line N9 as an in vitro model to mimic microglia activation seen in the patients with schizophrenia. The effects of clozapine, olanzapine and haloperidol on the release of NO by LPS-stimulated N9 cells were investigated.
Section snippets
Materials
Clozapine and haloperidol were purchased from Sigma (St. Louis, MO, USA). Olanzapine was purified from the tablets (Eli Lilly and Co. Ltd.) by the Department of Pharmaceutical Engineering, Shenyang Pharmaceutical University (Shenyang, China). The drug concentrations were determined according to the results of our preliminary study. In our preliminary study, the highest concentrations tested for haloperidol, olanzapine and clozapine were all up to 100 μM. It was found that haloperidol and
The effect of clozapine on N9 cell viability and LPS-induced NO release
Treatment with clozapine (1–10 μM) alone or with 1 μg/ml of LPS for 24 h did not cause any change in MTT absorbance in N9 cells, indicating that clozapine did not affect the viability of N9 cells at the doses used (Fig. 1).
Next, the release of NO by LPS-stimulated N9 cells was examined. In unstimulated N9 cells, only small amounts of NO2− (4.23 ± 2.18 μM) occurred in the medium. Pretreatment of unstimulated cells with clozapine (1–10 μM) for 24 h did not result in any change of NO2−. The
Discussion
This is the first report showing that olanzapine suppressed LPS-induced NO release, reflecting the activation of microglial cells, suggesting that it might be beneficial for the treatment of neurodegenerative diseases. In fact, olanzapine has been shown to be safe and effective in the treatment of schizophrenia (Beasley et al., 1996a, Beasley et al., 1996b, Beasley et al., 1997, Tollefson et al., 1997, Bhana et al., 2001).
Olanzapine showed neuroproliferative effect above 60 μM in the study of
Conclusions
In conclusion, the present study demonstrated for the first time that olanzapine suppressed LPS-induced microglial cell activation. Clozapine and haloperidol showed no effect on this model. However, the mechanisms underlying the effect of olanzapine on the release of NO by LPS-stimulated microglial cells merits further investigation.
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