Les cytochromes P450 astrocytaires, une famille d’enzymes clés dans le métabolisme cérébral et la neuroprotection

Clozapine treatment and astrocyte activity in treatment resistant schizophrenia: A proton magnetic resonance spectroscopy study

Clozapine is the only antipsychotic approved for treating treatment-resistant schizophrenia (TRS), characterized by persistent positive symptoms despite adequate antipsychotic treatment. Unfortunately, clozapine demonstrates clinical efficacy in only ~30-60 % of patients with TRS (clozapine-responders; ClzR+), while the remaining ~40-70 % are left with no pharmacological recourse for improvement (clozapine-resistant; ClzR-). Mechanism(s) underlying clozapine's superior efficacy remain unclear. However, in vitro evidence suggests clozapine may mitigate glutamatergic dysregulations observed in TRS, by modulating astrocyte activity in ClzR+, but not ClzR-. A factor that if proven correct, may help the assessment of treatment response and development of more effective antipsychotics. To explore the presence of clozapine-astrocyte interaction and clinical improvement, we used 3 T proton-magnetic resonance spectroscopy to quantify levels of myo-Inositol, surrogate biomarker of astrocyte activity, in regions related to schizophrenia neurobiology: Dorsal-anterior-cingulate-cortex (dACC), left-dorsolateral-prefrontal-cortex (left-DLPFC), and left-striatum (left-striatum) of 157 participants (ClzR- = 30; ClzR+ = 37; responders = 38; controls = 52). Clozapine treatment was assessed using clozapine to norclozapine plasma levels, 11-12 h after last clozapine dose. Measures for symptom severity (i.e., Positive and Negative Symptoms Scale) and cognition (i.e., Mini-Mental State Examination) were also recorded. Higher levels of myo-Inositol were observed in TRS groups versus responders and controls (dACC (p < 0.001); left-striatum (p = 0.036); left-DLPFC (p = 0.023)). In ClzR+, but not ClzR-, clozapine to norclozapine ratios were positively associated with myo-Inositol levels (dACC (p = 0.004); left-DLPFC (p < 0.001)), and lower positive symptom severity (p < 0.001). Our results support growing in vitro evidence of clozapine-astrocyte interaction in clozapine-responders. Further research may determine the viability of clozapine-astrocyte interactions as an early marker of clozapine response.

Cytotoxicity of the Diterpene 14-O-Methyl-ryanodanol from Erythroxylum passerinum in an Astrocytic Cells Model

Plant secondary metabolites, such as, specifically, alkaloids and terpenes, may present psychoactive properties that modify the function of the central nervous system (CNS) and induce neurotoxicity. Neurotoxicity involves the response of glial cells, mainly astrocytes, which play a fundamental role in the control of homeostasis of the CNS. Some Erythroxylum species are indigenous to the state of Bahia in Brazil. This study investigated the cytotoxic activity of the diterpene AEP-1, extracted from the fruit of E. passerinum in a GL-15 cell line, astrocytic, glial cells model. The effects on cell viability, analyzed by the MTT assay, demonstrated a dose-dependent cytotoxic effect, with maximum effect at 500 μg/mL of AEP-1, and with a reduction of about 40 and 47% on cellular viability after 24 h and 72 h treatment, respectively. Evidence for induction of apoptosis by AEP-1 was first obtained when GL-15 glial cells were incubated with 250 μg/mL AEP-1 causing reniform and/or pyknotic nuclei and apoptotic bodies revealed by chromatin staining with Hoechst 33258. Increase in DNA fragmentation was also observed by comet assays in cells incubated with 500 μg/mL of AEP-1. Moreover, cells exposed to a sub toxic dose of AEP-1 (250 μg/mL) showed significant changes in morphology – contraction of the cytoplasm and expansion of cellular projections – signifying the presence of astrocytic cytoskeletal protein and glial fibrillary acidic protein (GFAP). These findings indicated astrocytic cells as the target for terpene AEP-1 and suggest the involvement of glial cells with psychoactive symptoms observed in humans and animals after consumption of fruits of plants of the genus Erythroxylum.

Monocrotophos induces the expression and activity of xenobiotic metabolizing enzymes in pre-sensitized cultured human brain cells

The expression and metabolic profile of cytochrome P450s (CYPs) is largely missing in human brain due to non-availability of brain tissue. We attempted to address the issue by using human brain neuronal (SH-SY5Y) and glial (U373-MG) cells. The expression and activity of CYP1A1, 2B6 and 2E1 were carried out in the cells exposed to CYP inducers viz., 3-methylcholanthrene (3-MC), cyclophosphamide (CPA), ethanol and known neurotoxicant- monocrotophos (MCP), a widely used organophosphorous pesticide. Both the cells show significant induction in the expression and CYP-specific activity against classical inducers and MCP. The induction level of CYPs was comparatively lower in MCP exposed cells than cells exposed to classical inducers. Pre-exposure (12 h) of cells to classical inducers significantly added the MCP induced CYPs expression and activity. The findings were concurrent with protein ligand docking studies, which show a significant modulatory capacity of MCP by strong interaction with CYP regulators-CAR, PXR and AHR. Similarly, the known CYP inducers- 3-MC, CPA and ethanol have also shown significantly high docking scores with all the three studied CYP regulators. The expression of CYPs in neuronal and glial cells has suggested their possible association with the endogenous physiology of the brain. The findings also suggest the xenobiotic metabolizing capabilities of these cells against MCP, if received a pre-sensitization to trigger the xenobiotic metabolizing machinery. MCP induced CYP-specific activity in neuronal cells could help in explaining its effect on neurotransmission, as these CYPs are known to involve in the synthesis/transport of the neurotransmitters. The induction of CYPs in glial cells is also of significance as these cells are thought to be involved in protecting the neurons from environmental insults and safeguard them from toxicity. The data provide better understanding of the metabolizing capability of the human brain cells against xenobiotics.

Differences in the expression and sensitivity of cultured rat brain neuronal and glial cells toward the monocrotophos

Inducible expressions cytochrome P450s (CYPs) against environmental chemicals in brain tissues of experimental animals is well-documented. However, the precise role of specific brain cell type in the metabolism of different class of xenobiotics has not been explored adequately. We study the expression of selected CYPs (1A1/1A2, 2B1/2B2, 2E1) in primary cultures of rat brain neuronal and glial cell exposed to an organophosphate pesticide-monocrotophos (MCP), a known neurotoxicant. The cultured neurons and glial cells express significant expression of CYP1A1, 2B2 and 2E1 isoenzymes, where the levels were comparatively higher in neuronal cells. Neuronal cells exhibited greater induction of CYP2E1 against MCP exposure, while glial cells were having more vulnerability for CYP1A and 2B isoenzymes. Similarly, cells were showing substrate specific responses against the specific inducers of CYPs, that is, ethanol (2E1), cyclophosphamide (2B1/2B2), 3-methylcholanthrene (1A1/1A2). The altered expression and activity of selected CYPs in cultured neuronal and glial cells could be helpful in explaining the association between MCP-induced neurotoxicity/metabolism and synthesis or transport of the neurotransmitters. The induction of CYPs in glial cells may also have significance as these cells are thought to be involved in protecting the neurons from environmental insults and safeguard them from toxicity. The differential expression pattern of CYPs in neuronal and glial cells exposed to MCP also indicate the selective sensitivity of these cells against the xenobiotics, hence suggested their suitability as tool to screen neurotoxicity potential of variety of xenobiotics.

Alcohol consumption effect on antiretroviral therapy and HIV-1 pathogenesis: role of cytochrome P450 isozymes

INTRODUCTION

Alcohol consumption, which is highly prevalent in HIV-infected individuals, poses serious concerns in terms of rate of acquisition of HIV-1 infection, HIV-1 replication, response to highly active antiretroviral therapy (HAART) and AIDS/neuroAIDS progression. However, little is known about the mechanistic pathways by which alcohol exerts these effects, especially with respect to HIV-1 replication and the patient's response to HAART.

AREAS COVERED

In this review, the authors discuss the effects of alcohol consumption on HIV-1 pathogenesis and its effect on HAART. They also describe the role of cytochrome P450 2E1 (CYP2E1) in alcohol-mediated oxidative stress and toxicity, and the role of CYP3A4 in the metabolism of drugs used in HAART (i.e., protease inhibitors (PI) and non-nucleoside reverse transcriptase inhibitors (NNRTI)). Based on the most recent findings the authors discuss the role of CYP2E1 in alcohol-mediated oxidative stress in monocytes/macrophages and astrocytes, as well as the role of CYP3A4 in alcohol-PI interactions leading to altered metabolism of PI in these cells.

EXPERT OPINION

The authors propose that alcohol and PI/NNRTI interact synergistically in monocytes/macrophages and astrocytes through the CYP pathway leading to an increase in oxidative stress and a decrease in response to HAART. Ultimately, this exacerbates HIV-1 pathogenesis and neuroAIDS.

The Role of Astrocytes in Metabolism and Neurotoxicity of the Pyrrolizidine Alkaloid Monocrotaline, the Main Toxin of Crotalaria retusa

The metabolic interactions and signaling between neurons and glial cells are necessary for the development and maintenance of brain functions and structures and for neuroprotection, which includes protection from chemical attack. Astrocytes are essential for cerebral detoxification and present an efficient and specific cytochrome P450 enzymatic system. Whilst Crotalaria (Fabaceae, Leguminosae) plants are used in popular medicine, they are considered toxic and can cause damage to livestock and human health problems. Studies in animals have shown cases of poisoning by plants from the genus Crotalaria, which induced damage to the central nervous system. This finding has been attributed to the toxic effects of the pyrrolizidine alkaloid (PA) monocrotaline (MCT). The involvement of P450 enzymatic systems in MCT hepatic and pulmonary metabolism and toxicity has been elucidated, but little is known about the pathways implicated in the bioactivation of these systems and the direct contribution of these systems to brain toxicity. This review will present the main toxicological aspects of the Crotalaria genus that are established in the literature and recent findings describing the mechanisms involved in the neurotoxic effects of MCT, which was extracted from Crotalaria retusa, and its interaction with neurons in isolated astrocytes.

Secretion of S100B, an astrocyte-derived neurotrophic protein, is stimulated by fluoxetine via a mechanism independent of serotonin

S100B is a calcium-binding protein, produced and secreted by astrocytes, which has a putative paracrine neurotrophic activity. Clinical studies have suggested that peripheral elevation of this protein is positively correlated with a therapeutic antidepressant response, particularly to selective serotonin reuptake inhibitors (SSRIs); however, the mechanism underlying this response remains unclear. Here, we measured S100B secretion directly in hippocampal astrocyte cultures and hippocampal slices exposed to fluoxetine and observed a significant increment of S100B release in the presence of this SSRI, apparently dependent on protein kinase A (PKA). Moreover, we found that serotonin (possibly via the 5HT1A receptor) reduces S100B secretion and antagonizes the effect of fluoxetine on S100B secretion. These data reinforce the effect of fluoxetine, independently of serotonin and serotonin receptors, suggesting a putative role for S100B in depressive disorders and suggesting that other molecular targets may be relevant for antidepressant activity.