Do antipsychotics inflame the brain?

Psychological and neurological brain disorders including schizophrenia, affect approximately 38.2% of the total European Union (EU) population per year, corresponding to 164.7 million persons. The total cost of such disorders in Europe in 2010 was estimated to be 798 billion euros. Multiple hypotheses have been proposed to explain how schizophrenia develops. One hypothesis suggests the immune system of schizophrenia patients is over-active, a process known as inflammation. This process includes activation of microglia, a specific type of immune cell in the brain. Microglia are specialist cells, which can take on many functions, allowing them to shape the immune response. Whilst this is important to maintain the normal state of the brain, if unchecked, microglial activation may ultimately become detrimental, leading to damage and worsening of disease symptoms. Microglia also play a key role in shaping the development of the brain, by regulating the connections between nerve cells and thus the efficient flow of information from one part of the brain to another. Multiple studies have now provided evidence that inflammation and microglial activation are present in the brain of schizophrenia patients, either as a result of genetic mutation or environmental risk factors such as infections during pregnancy, or exposure to stress.

Antipsychotics used to treat schizophrenia and increasingly other psychiatric disoders, are often ineffective, fail to treat social and cognitive symptoms and are associated with adverse side effects. Blocking, or limiting inflammation, using "anti-inflammatory" drugs may therefore represent a novel and effective treatment for some schizophrenia patients. However, many studies have found only modest clinical benefits of such drugs. There is accumulating evidence that antipsychotics themselves are anti-inflammatory; however, this is based on unrepresentative cellular models that don't reflect what happens in the living brain. Furthermore, existing studies in animals have only used single, or non-clinical, doses of antipsychotics. Ethically, we cannot withhold antipsychotic treatment from schizophrenia patients, nor can we prescribe them to healthy individuals to study the effects in humans. It is therefore imperative to develop the evidence in realistic animal models.

Our previous studies, in which we closely match the way antipsychotics are given to patients, have shown that these drugs cause activation of microglial cells in the rat brain. Using the same imaging technology that is used in patients, we have also shown that the areas of the brain where the microglial cells are activated are also shrinking following antipsychotic drug treatment. This is similar to reports that antipsychotics may decrease the volume of the brain in schizophrenia patients (Nature; doi: 10.1038/news.2011.75). However, we do not know if these antipsychotic-induced brain volume changes are "good" or "bad" and if the microglial cells are trying to repair the brain, or are in fact causing the damage. In this proposal, we will answer these very questions using experimental animals, which mimic to some extent the inflammation seen in the brains of schizophrenia patients. We will treat these animals with antipsychotics or a placebo and scan the brains of these animals using the same methods that are used in patients. We will then dissect out the brain tissue to assess the effects of antipsychotics on brain microglia at the cellular and molecular level post-mortem. The results of these experiments will tell us whether antipsychotics are "pro" or "anti" inflammatory and how this relates to brain effects of these drugs, including changes in volume and behaviour. Answering these questions is essential to optimise anti-inflammatory treatment strategies for schizophrenia and clarify concerns over the effects of these drugs on brain volume.

Antipsychotic drugs have both pro- and anti-inflammatory effects. I have shown that clinically comparable, chronic, antipsychotic drug treatment increases microglial activation in the rat brain. Furthermore, this pattern of microglial activation overlaps topographically with brain regions that decrease in volume in antipsychotic-treated rats. The precise impact of antipsychotics on microglial function and how this relates to drug-induced brain volume changes is however, unknown. Furthermore, we do not have a detailed understanding of how antipsychotics affect the expression of the translocator protein (TSPO), a clinical imaging marker for microglial activation, but also a regulator of microglial activation state.

To address these questions I will expose rats to an immune stimulus (poly(I:C) in gestation, which recapitulates pathological and behavioural deficits relevant to schizophrenia. I will then treat these animals as adults with clinically comparable doses of typical or atypical antipsychotics, or a vehicle control and pursue the following specific aims:

1) I will use a combination of in vivo and ex vivo magnetic resonance imaging, coupled with post-mortem cellular (immunohistochemistry and stereology) and molecular (gene expression from isolated brain microglia) analysis to determine the effects of antipsychotics on microglial activation state and how this relates to brain volume.

2) I will elucidate the effects of antipsychotics on TSPO ligand binding using use post-mortem autoradiography and dissect the cellular origin of this signal and consequences on microglial activation using immunohistochemistry and gene expression analysis in isolated brain microglia.

3) I will measure peripheral inflammation in the blood using multiplex cytokine and correlate these to central microglia activation, MRI and TSPO signals. This will characterise the relationship between peripheral inflammation, central markers of inflammation and brain volume (MRI).

Antipsychotic drugs, have both pro- and anti-inflammatory effects, but their specific actions on brain microglia are unclear. Parsing this relationship is critical, to guide effective use of these medications, but also appropriate use of adjunct anti-inflammatory treatments. Furthermore, we do not have a detailed understanding of how antipsychotics affect the expression of the translocator protein (TSPO), a clinical imaging marker of microglial activation, but also a critical regulator of microglial activation state. Given the challenges in carrying out studies of these issues in patients, it is critical to develop the initial evidence in animal models, which offer the advantages of differentiating the effects of disease from drug, linking in-vivo whole-brain findings to ex-vivo histopathology. This work will directly and indirectly benefit a number of groups:

1) Clinical and basic researchers: The results will provide clarity on the effects of antipsychotics on neuroimaging signals, particularly for TSPO. Furthermore, our model offers a well-characterized 'preparation' to test and compare antipsychotic effects on inflammation. As newer non-D2 antipsychotics are developed, it will be critical to examine if they are similar or different to the present ones in terms of their effects on microglia. The model can then be used in the future to identify potential add-on strategies, which may avoid potential adverse effects. Clearly our findings in this model can only be used as a basis for a further clinical trial - but, because our approach uses clinic-like doses, drug exposure and clinically comparable measurements, the likelihood of translation is higher.

2) Patient groups and the general public: Schizophrenia is a devastating disorder affecting 1% of population; in the UK alone there in excess of 250,000 diagnosed patients. Schizophrenia is commonly treated with antipsychotic drugs but many patients show insufficient responses to current treatments. In addition, we still have an incomplete understanding on how antipsychotic drugs exert their beneficial or adverse effects. It is therefore critical to conduct detailed explorations of molecular and cellular changes in brains exposed to these medications to address this knowledge gap. Completion of this work will therefore facilitate a thoughtful revaluation of the effects of antipsychotics. This will ensure the optimised used of these medications for the ultimate benefit of patients and their families.

3) Government Agencies: The treatment of schizophrenia in the UK costs an estimated £6.7 billion per annum. To reduce this burden of cost for care, novel and more effective treatments for schizophrenia are required. It is equally essential however, to optimize the use of antipsychotic medications currently used clinically. Both approaches require detailed examinations of the effects of these drugs in the brain at the cellular and molecular level in controlled experimental settings. Therefore, the results of the current study, by providing this information will not only guide future studies aimed at developing novel treatments, but also have the potential to reconfigure how we currently view and use these medicines.

4) Pharmaceutical companies: We still lack a complete understanding of how antipsychotic drugs exert their beneficial or adverse effects, particularly with respect to the immune system. It is therefore critical to conduct detailed explorations of molecular and cellular changes in brains exposed to these medications to address this. The results of the proposed project will address this by pointing to brain effects of established medications on microglia and inflammatory pathways that are not well understood, but which may hold clues to new treatment approaches that may be exploited by pharmaceutical companies.