B. Joy Snider

Safety and biomarker effects of solanezumab in patients with Alzheimer’s disease

To assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of 12 weekly infusions of solanezumab, an anti‐β‐amyloid (Aβ) antibody, in patients with mild‐to‐moderate Alzheimers disease. Cognitive measures were also obtained.

Apoptosis and Necrosis in Cerebrovascular Disease

ABSTRACT: Neuronal death following ischemic insults has been thought to reflect necrosis. However, recent evidence from several labs suggests that programmed cell death, leading to apoptosis, might additionally contribute to this death. We have used both in vitro and in vivo models to study the role of apoptosis in ischemic cell death. Some features of apoptosis (TUNEL staining, internucleosomal DNA fragmentation, sensitivity to cycloheximide) were observed following transient focal ischemia in rats. Brief transient focal ischemia was followed by delayed infarction more than 3 days later; this delayed infarction was sensitive to cycloheximide. A cycloheximide‐sensitive component of neuronal cell death was also observed in cultured murine neocortical neurons deprived of oxygen‐glucose in the presence of glutamate receptor antagonists. This presumed ischemic apoptosis was attenuated by caspase inhibitors, or by homozygous deletion of the bax gene. Neurons may undergo both apoptosis and necrosis after ischemic insults, and thus it may be therapeutically desirable to block both processes.

Transplantation of Embryonic Stem Cells Improves Nerve Repair and Functional Recovery After Severe Sciatic Nerve Axotomy in Rats

Extensive research has focused on transplantation of pluripotent stem cells for the treatment of central nervous system disorders, the therapeutic potential of stem cell therapy for injured peripheral nerves is largely unknown. We used a rat sciatic nerve transection model to test the ability of implanted embryonic stem (ES) cell‐derived neural progenitor cells (ES‐NPCs) in promoting repair of a severely injured peripheral nerve. Mouse ES cells were neurally induced in vitro; enhanced expression and/or secretion of growth factors were detected in differentiating ES cells. One hour after removal of a 1‐cm segment of the left sciatic nerve, ES‐NPCs were implanted into the gap between the nerve stumps with the surrounding epineurium as a natural conduit. The transplantation resulted in substantial axonal regrowth and nerve repair, which were not seen in culture medium controls. One to 3 months after axotomy, co‐immunostaining with the mouse neural cell membrane specific antibody M2/M6 and the Schwann cell marker S100 suggested that transplanted ES‐NPCs had survived and differentiated into myelinating cells. Regenerated axons were myelinated and showed a uniform connection between proximal and distal stumps. Nerve stumps had near normal diameter with longitudinally oriented, densely packed Schwann cell‐like phenotype. Fluoro‐Gold retrogradely labeled neurons were found in the spinal cord (T12–13) and DRG (L4‐L6), suggesting reconnection of axons across the transection. Electrophysiological recordings showed functional activity recovered across the injury gap. These data suggest that transplanted neurally induced ES cells differentiate into myelin‐forming cells and provide a potential therapy for severely injured peripheral nerves.

Potassium channel blockers attenuate hypoxia- and ischemia-induced neuronal death in vitro and in vivo.

Background and Purpose— In light of recent evidence suggesting that an upregulation of K+ efflux mediated by outward delayed rectifier (IK) channels promotes central neuronal apoptosis, we sought to test the possibility that blockers of IK channels might be neuroprotective against hypoxia/ischemia-induced neuronal death. Methods— Membrane currents were recorded with the use of patch clamp recordings in cultured murine cortical neurons. Protective effects of K+ channel blockers were examined in rats subjected to transient middle cerebral artery occlusion followed by 14-day reperfusion. Results— The K+ channel blocker tetraethylammonium (TEA) (5 mmol/L) selectively blocked IK without affecting N-methyl-d-aspartate receptor–mediated current or voltage-gated Ca2+ currents. Both TEA and a lipophilic K+ channel blocker, clofilium, attenuated neuronal apoptosis induced by hypoxia in vitro and infarct volume induced by ischemia in vivo. Conclusions— These data are consistent with the idea that K+ channel–mediated K+ efflux may contribute to ischemia-triggered apoptosis and suggest that preventing excessive K+ efflux through K+ channels may constitute a therapeutic approach for the treatment of stroke.

Extracellular apparent diffusion in rat brain.

The apparent diffusion coefficients (ADCs) of a series of markers concentrated in the extracellular space of normal rat brain were measured to evaluate, by inference, the ADC of water in the extracellular space. The markers (mannitol, phenylphosphonate, and polyethylene glycols) are defined as “compartment selective” because tissue culture experiments demonstrate some leakage into the intracellular space, making them less “compartment specific” than commonly believed. These primarily extracellular markers have ADCs similar to those of intracellular metabolites of comparable hydrodynamic radius, suggesting that water ADC values in the intra‐ and extracellular spaces are similar. If this is the case, then it is unlikely that a net shift of water from the extra‐ to the intracellular space contributes significantly to the reduction in water ADC detected following brain injury. Rather, this reduction is more likely due primarily to a reduction of the ADC of intracellular water associated with injury. Magn Reson Med 45:801–810, 2001.

Potential role of orexin and sleep modulation in the pathogenesis of Alzheimer’s disease

Modulation of orexin and its effects on sleep/wakefulness affect amyloid-β pathology in the brain of mouse models for Alzheimer’s disease.

Dominantly Inherited Alzheimer Network: facilitating research and clinical trials

The Dominantly Inherited Alzheimer Network (DIAN) is an international registry of individuals at risk for developing autosomal dominant Alzheimer’s disease (AD). Its primary aims are to investigate the temporal ordering of AD pathophysiological changes that occur in asymptomatic mutation carriers and to identify those markers that herald the transition from cognitive normality to symptomatic AD. DIAN participants undergo longitudinal evaluations, including clinical and cognitive assessments and measurements of molecular and imaging AD biomarkers. This review details the unique attributes of DIAN as a model AD biomarker study and how it provides the infrastructure for innovative research projects, including clinical trials. The recent design and launch of the first anti-amyloid-beta secondary prevention trial in AD, led by the related DIAN Trials Unit, also are discussed.

A proteasomal stress response: pre-treatment with proteasome inhibitors increases proteasome activity and reduces neuronal vulnerability to oxidative injury.

We report here that exposure to low concentrations of proteasome inhibitors (e.g. 10–100 nm MG‐132, 0.1–3 nm epoxomicin or 10–30 nmclasto‐lactacystin β‐lactone) resulted in an enhancement, rather than an inhibition, of proteasome activity in cultured neocortical neurons. Size‐fractionation chromatography confirmed that the enhanced peptide cleavage activity was associated with proteasome‐sized complexes. This sub toxic exposure reduced neuronal death caused by subsequent exposure to oxidative stress (100–200 µm H2O2 for 30 min, 24‐h exposure to 100 µm paraquat or 7.5 µm menadione), but did not alter vulnerability to excitotoxicity (5‐min exposure to 30–100 µm NMDA or 24 exposure to 12 µm NMDA). Sub toxic proteasome inhibitor exposure caused an increase in levels of proteasome core subunit proteins and mRNAs, but not in levels of potentially cytoprotective heat shock proteins (hsp70, hsp90 and hsp40). The neuroprotective effects of proteasome inhibitor pre‐treatment were blocked by coapplication of proteasome inhibitors during the oxidative insult. These findings support a model in which sublethal proteasome inhibition induces neurons to increase proteasome activity and promotes resistance to oxidative injury and suggests that enhancement of proteasome activity is a potential therapeutic target for diseases in which oxidative stress has been implicated.

Optimal promoter usage for lentiviral vector-mediated transduction of cultured central nervous system cells.

Lentiviral vectors transduce both dividing and non-dividing cells and can support sustained expression of transgenes. These properties make them attractive for the transduction of neurons and other neural cell types in vitro and in vivo. Lentiviral vectors can be targeted to specific cell types by using different promoters in the lentiviral shuttle vector. Even with identical constructs, however, levels of expression can vary significantly in different types of neurons and different culture preparations; expression levels in the same neuronal subtypes can be very different in primary cell culture and in vivo. We systematically assessed the ability of different promoters to direct expression of foreign transgenes in primary murine neocortical neurons, cerebellar granule cells and in undifferentiated and differentiated neuroblastoma cells. In primary cortical neurons, constructs using the ubiquitin C promoter directed the highest level of transgene expression; the phosphoglycerate kinase (PGK) promoter also directed robust transgene expression, while the cytomegalovirus (CMV) and MND (a synthetic promoter that contains the U3 region of a modified MoMuLV LTR with myeloproliferative sarcoma virus enhancer) promoters resulted in the expression of the transgenes in only limited number of neurons. In contrast, in cerebellar granule cells and in differentiated SH-SY5Y neuroblastoma cultures, the CMV promoter directed the most robust transgene expression. There was similar variability in transgene expression directed by these promoters in primary cultures of oligodendrocytes and astrocytes. These findings may prove useful in the design of lentiviral vectors for use in cell culture models of the nervous system.

TrkB mediates BDNF-induced potentiation of neuronal necrosis in cortical culture.

In the present study, the signaling mechanisms underlying the effect of brain-derived neurotrophic factor (BDNF) on neuronal necrosis were investigated. Exposure of mature mouse cortical cultures (more than 10 days in vitro (DIV)) to 50-100 ng/ml BDNF for 48 h induced widespread neuronal necrosis that was antioxidant-sensitive. This neuronal necrosis was blocked by the selective NMDA antagonist MK-801, suggesting that prolonged BDNF exposure caused endogenous levels of NMDA receptor activation to become excitotoxic. We examined whether the p75(NTR) played a role in BDNF-induced neuronal death. However, p75(NTR) expression was low in cultured cortical cells, and neutralizing antibodies to p75(NTR) did not attenuate BDNF-triggered neuronal death. In contrast, trkB antisense oligonucleotides and inhibitors of Trk tyrosine kinase blocked BDNF-triggered neuronal death as well as BDNF potentiation of iron-induced oxidative neuronal necrosis, suggesting a critical role for TrkB in this phenomenon. Furthermore, BDNF did not potentiate neuronal necrosis in cortical cultures prepared from embryonic TrkB-null mice. These results suggest that TrkB plays an important role in BDNF-mediated neuronal necrosis.