Efficient clearance of Aß protofibrils in AßPP-transgenic mice treated with a brain-penetrating bifunctional antibody.

BACKGROUND: Amyloid-ß (Aß) immunotherapy is one of the most promising disease-modifying strategies for Alzheimer's disease (AD). Despite recent progress targeting aggregated forms of Aß, low antibody brain penetrance remains a challenge. In the present study, we used transferrin receptor (TfR)-mediated transcytosis to facilitate brain uptake of our previously developed Aß protofibril-selective mAb158, with the aim of increasing the efficacy of immunotherapy directed toward soluble Aß protofibrils. METHODS: Aß protein precursor (AßPP)-transgenic mice (tg-ArcSwe) were given a single dose of mAb158, modified for TfR-mediated transcytosis (RmAb158-scFv8D3), in comparison with an equimolar dose or a tenfold higher dose of unmodified recombinant mAb158 (RmAb158). Soluble Aß protofibrils and total Aß in the brain were measured by enzyme-linked immunosorbent assay (ELISA). Brain distribution of radiolabeled antibodies was visualized by positron emission tomography (PET) and ex vivo autoradiography. RESULTS: ELISA analysis of Tris-buffered saline brain extracts demonstrated a 40% reduction of soluble Aß protofibrils in both RmAb158-scFv8D3- and high-dose RmAb158-treated mice, whereas there was no Aß protofibril reduction in mice treated with a low dose of RmAb158. Further, ex vivo autoradiography and PET imaging revealed different brain distribution patterns of RmAb158-scFv8D3 and RmAb158, suggesting that these antibodies may affect Aß levels by different mechanisms. CONCLUSIONS: With a combination of biochemical and imaging analyses, this study demonstrates that antibodies engineered to be transported across the blood-brain barrier can be used to increase the efficacy of Aß immunotherapy. This strategy may allow for decreased antibody doses and thereby reduced side effects and treatment costs.

Experimental evaluation of radioiodinated sennoside B as a necrosis-avid tracer agent.

Necrosis-avid agents are a class of compounds that selectively accumulate in the necrotic tissues after systemic administration, which can be used for in vivo necrosis imaging and targeted therapies. In order to search for a necrosis-avid tracer agent with improved drugability, we labelled iodine-131 on sennoside B (SB) as a naturally occurring median dianthrone compound. The necrosis targetability and clearance properties of (131)I-SB were evaluated in model rats with liver and muscle necrosis. On SPECT/CT images, a "hot spot" in the infarcted liver lobe and necrotic muscle was persistently observed at 24 h and 72 h post-injection (p.i.). Gamma counting of the tissues of interest revealed a radioactivity ratio of necrotic to viable liver at 4.6 and 3.4 and of necrotic to viable muscle at 7.0 and 8.8 at 24 h and 72 h p.i., respectively. The good match of autoradiographs and fluoromicroscopic images with corresponding histochemical staining suggested preferential uptake of (131)I-SB in necrotic tissue. Pharmacokinetic study revealed that (131)I-SB has an elimination half-life of 8.6 h. This study indicates that (131)I-SB shows not only prominent necrosis avidity but also favourable pharmacokinetics, which may serve as a potential necrosis-avid diagnostic agent for assessment of tissue viability.

Frontal dopamine D(2/3) receptor binding in drug-naive first-episode schizophrenic patients correlates with positive psychotic symptoms and gender.

BACKGROUND: The aim of the study was to examine extrastriatal dopamine D(2/3) receptor binding and psychopathology in schizophrenic patients, and to relate binding potential (BP) values to psychopathology. METHODS: Twenty-five drug-naive schizophrenic patients and 20 healthy controls were examined with single-photon emission computerized tomography (SPECT) using the D(2/3)-receptor ligand [123I]epidepride. RESULTS: In the hitherto largest study on extrastriatal D(2/3) receptors we detected a significant correlation between frontal D(2/3) BP values and positive schizophrenic symptoms in the larger group of male schizophrenic patients, higher frontal BP values in male (n = 17) compared to female (n = 8) patients, and - in accordance with this - significantly fewer positive schizophrenic symptoms in the female patients. No significant differences in BP values were observed between patients and controls; the patients, however, had significantly higher BP in the right compared to the left thalamus, whereas no significant hemispheric imbalances were observed in the healthy subjects. CONCLUSIONS: The present data are the first to confirm a significant correlation between frontal D(2/3) receptor BP values and positive symptoms in male schizophrenic patients. They are in agreement with the hypothesis that frontal D(2/3) receptor activity is significant for positive psychotic symptoms. Additionally, the data support a thalamic hemispheric imbalance in schizophrenia.

Dental pulp cells provide neurotrophic support for dopaminergic neurons and differentiate into neurons in vitro; implications for tissue engineering and repair in the nervous system.

Glial cell line-derived neurotrophic factor (GDNF) mRNA is highly expressed by dental pulp cells (DPCs) prior to the initiation of dental pulp innervation. We show that radioactively labelled exogenous GDNF is retrogradely transported from neonatal teeth and vibrissae to the trigeminal neurons, indicating that GDNF acts as a classical neurotrophic factor in the trigeminal system. We also show that DPCs from both rats and humans produce nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and GDNF mRNAs in vitro, promote the survival and phenotypic characteristics of embryonic dopaminergic (DA) neurons and protect DA neurons against the neurotoxin 6-hydroxy-dopamine (6-OHDA) in vitro. By using inhibitory antibodies to NGF, BDNF and GDNF, we show that the promotion of DA neuron survival relates to the production and release of neurotrophic proteins by DPCs in vitro. We suggest that in vivo production of neurotrophic factors by DPCs play roles in tooth innervation. However, continued production of neurotrophic factors by the DPCs might have wider implications. We propose that the dental pulp is a viable source of easily attainable cells with possible potential for development of autologous cell transplantation therapies. We also show that a population of neural crest-derived dental pulp cells acquire clear neuronal morphology and protein expression profile in vitro, indicating the presence of a cell population in the dental pulp with neuronal differentiation capacity that might provide additional benefits when grafted into the CNS.

Distribution of dopamine D2-like receptors in the human thalamus: autoradiographic and PET studies.

The distribution of dopamine (DA) D(2)-like receptors in the human thalamus was studied using in vitro autoradiographic techniques and in vivo positron emission tomography in normal control subjects. [(125)I]Epidepride, which binds with high affinity to DA D(2) and D(3) receptors, was used in autoradiographic studies to determine the distribution and density of D(2)-like receptors, and the epidepride analogue [(18)F]fallypride positron was used for positron emission tomography studies to delineate D(2)-like receptors in vivo. Both approaches revealed a heterogeneous distribution of thalamic D(2/3) receptors, with relatively high densities in the intralaminar and midline thalamic nuclei, including the paraventricular, parataenial, paracentral, centrolateral, and centromedian/parafascicular nuclei. Moderate densities of D(2/3) sites were seen in the mediodorsal and anterior nuclei, while other thalamic nuclei expressed lower levels of D(2)-like receptors. Most thalamic nuclei that express high densities of D(2)-like receptors project to forebrain DA terminal fields, suggesting that both the thalamic neurons expressing D(2)-like receptors and the projection targets of these neurons are regulated by DA. Because the midline/intralaminar nuclei receive prominent projections from both the ascending reticular activating core and the hypothalamus, these thalamic nuclei may integrate activity conveying both interoceptive and exteroceptive information to telencephalic DA systems involved in reward and cognition.