Hydroxylation Increases the Neurotoxic Potential of BDE-47 to Affect Exocytosis and Calcium Homeostasis in PC12 Cells

BACKGROUND: Oxidative metabolism, resulting in the formation of hydroxylated polybrominated diphenyl ether (PBDE) metabolites, may enhance the neurotoxic potential of brominated flame retardants. OBJECTIVE: Our objective was to investigate the effects of a hydroxylated metabolite of 2,2',4,4'-tetra-bromodiphenyl ether (BDE-47; 6-OH-BDE-47) on changes in the intracellular Ca2+ concentration ([Ca2+]i) and vesicular catecholamine release in PC12 cells. METHODS: We measured vesicular catecholamine release and [Ca2+]i using amperometry and imaging of the fluorescent Ca2+-sensitive dye Fura-2, respectively. RESULTS: Acute exposure of PC12 cells to 6-OH-BDE-47 (5 microM) induced vesicular catecholamine release. Catecholamine release coincided with a transient increase in [Ca2+]i, which was observed shortly after the onset of exposure to 6-OH-BDE-47 (120 microM). An additional late increase in [Ca2+]i was often observed at > or =1 microM 6-OH-BDE-47. The initial transient increase was absent in cells exposed to the parent compound BDE-47, whereas the late increase was observed only at 20 microM. Using the mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) and thapsigargin to empty intracellular Ca2+ stores, we found that the initial increase originates from emptying of the endoplasmic reticulum and consequent influx of extracellular Ca2+, whereas the late increase originates primarily from mitochondria. CONCLUSION: The hydroxylated metabolite 6-OH-BDE-47 is more potent in disturbing Ca2+ homeostasis and neurotransmitter release than the parent compound BDE-47. The present findings indicate that bioactivation by oxidative metabolism adds considerably to the neurotoxic potential of PBDEs. Additionally, based on the observed mechanism of action, a cumulative neurotoxic effect of PBDEs and ortho-substituted polychlorinated biphenyls on [Ca2+]i cannot be ruled out

Subjective experience and D-2 receptor occupancy in patients with recent-onset schizophrenia treated with low-dose olanzapine or haloperidol: A randomized, double-blind study

objective: The authors tested the hypothesis that a dopamine D-2 receptor Occupancy level between 60% and 70% in patients with recent-onset schizophrenia would result in optimal subjective experience. in addition, they sought preliminary evidence on whether subjective experience is better with low-dose olanzapine than with low-dose haloperidol. Method: Subjects (N=24) who met DSM-IV criteria for schizophrenia were randomly assigned to 6 weeks of double-blind treatment with either olanzapine, 7.5 mg/day, or haloperidol, 2.5 mg/day. Subjective experience, psychopathology, and extrapyramidal symptoms were assessed at baseline and at endpoint. After 6 weeks, D-2 receptor occupancy was assessed with [I-123]iodobenzamide single photon emission computed tomography. Results: The two study groups were similar at baseline. After 6 weeks, patients receiving olanzapine had a significantly lower mean dopamine D-2 receptor occupancy (51.0%, range=36%-67%) than those given halopericlol (65.5%, range=45%-75%). Receptor occupancy between 60% and 70% was associated with optimal subjective experience, and subjective experience improved significantly in the haloperidol group. Conclusions: A level of D-2 receptor occupancy between 60% and 70% is optimal for subjective experience of patients with recent-onset schizophrenia. Substantial interindividual variation in D-2 receptor occupancy was seen at fixed low-dose levels of olanzapine and halopericlol. Olanzapine, 7.5 mg/day, showed no superior subjective response over halopericlol, 2.5 mg/day. Olanzapine may need to be dosed higher than 7.5 mg/day for most patients with recent-onset schizophrenia, and halopericlol needs to be individually titrated in the very low dose range to reach optimal occupanc