Gregory R. Stewart

Intracerebroventricular amyloid-β antibodies reduce cerebral amyloid angiopathy and associated micro-hemorrhages in aged Tg2576 mice

Although immunization against amyloid-β (Aβ) holds promise as a disease-modifying therapy for Alzheimer disease (AD), it is associated with an undesirable accumulation of amyloid in the cerebrovasculature [i.e., cerebral amyloid angiopathy (CAA)] and a heightened risk of micro-hemorrhages. The central and peripheral mechanisms postulated to modulate amyloid with anti-Aβ immunotherapy remain largely elusive. Here, we compared the effects of prolonged intracerebroventricular (icv) versus systemic delivery of anti-Aβ antibodies on the behavioral and pathological changes in an aged Tg2576 mouse model of AD. Prolonged icv infusions of anti-Aβ antibodies dose-dependently reduced the parenchymal plaque burden, astrogliosis, and dystrophic neurites at doses 10- to 50-fold lower than used with systemic delivery of the same antibody. Both icv and systemic anti-Aβ antibodies reversed the behavioral impairment in contextual fear conditioning. More importantly, unlike systemically delivered anti-Aβ antibodies that aggravated vascular pathology, icv-infused antibodies globally reduced CAA and associated micro-hemorrhages. We present data suggesting that the divergent effects of icv-delivered anti-Aβ antibodies result from gradually engaging the local (i.e., central) mechanisms for amyloid clearance, distinct from the mechanisms engaged by high doses of anti-Aβ antibodies that circulate in the vasculature following systemic delivery. With robust efficacy in reversing AD-related pathology and an unexpected benefit in reducing CAA and associated micro-hemorrhages, icv-targeted passive immunotherapy offers a promising therapeutic approach for the long-term management of AD.

Cholinergic denervation-induced increase of chelatable zinc in mossy-fiber region of the hippocampal formation

Chelatable zinc has repeatedly been associated with hippocampal mossy fibers, but the neurobiological functions of the zinc have remained unclear. Zinc is a constituent of the 7S Nerve Growth Factor (NGF) molecule. The hippocampal area is rich in neurotrophic factors and cholinergic deafferentation of the hippocampus appears to activate these neurotrophic factors. In this paper we report that cholinergic deafferentation of the hippocampus causes a transient rise in mossy-fiber zinc, as measured by zinc-dithizonate histochemistry. The changes are not significant until 10 days after the septal lesion, and the zinc returns to control levels by 21-28 days. Dithizonate has an association constant of 10(-15) with zinc, while NGF has an association constant of 10(-11). Thus densitometric measurement of zinc dithizone within the hippocampus may be a quantitative histochemical marker of a zinc-associated nerve growth-like substance. The data support recent findings that nerve growth-like factors increase in the hippocampal area following deafferentation, and in addition suggest that zinc is a critical factor in the regulation of trophic phenomena in the hippocampal formation.

Widespread suppression of huntingtin with convection-enhanced delivery of siRNA

Huntingtons disease is an autosomal dominant neurodegenerative disease caused by a toxic gain of function mutation in the huntingtin gene (Htt). Silencing of Htt with RNA interference using direct CNS delivery in rodent models of Huntingtons disease has been shown to reduce pathology and promote neuronal recovery. A key translational step for this approach is extension to the larger non-human primate brain, achieving sufficient distribution of small interfering RNA targeting Htt (siHtt) and levels of Htt suppression that may have therapeutic benefit. We evaluated the potential for convection enhanced delivery (CED) of siHtt to provide widespread and robust suppression of Htt in nonhuman primates. siHtt was infused continuously for 7 or 28 days into the nonhuman primate putamen to analyze effects of infusion rate and drug concentration on the volume of effective suppression. Distribution of radiolabeled siHtt and Htt suppression were quantified by autoradiography and PCR, respectively, in tissue punches. Histopathology was evaluated and Htt suppression was also visualized in animals treated for 28 days. Seven days of CED led to widespread distribution of siHtt and significant Htt silencing throughout the nonhuman primate striatum in an infusion rate and dose dependent manner. Htt suppression at therapeutic dose levels was well tolerated by the brain. A model developed from these results predicts that continuous CED of siHtt can achieve significant coverage of the striatum of Huntingtons disease patients. These findings suggest that this approach may provide an important therapeutic strategy for treating Huntingtons disease.

Hyperplastic Changes within the Leptomeninges of the Rat and Monkey in Response to Chronic Intracerebroventricular Infusion of Nerve Growth Factor

Recombinant human nerve growth factor (rhNGF) was delivered for up to 6 months by continuous intracerebroventricular (i.c.v.) infusion to CD (Sprague-Dawley derived) rats and cynomolgus monkeys. Rats (n = 15/sex/group) received doses of 0 (vehicle), 6, 60, or 300 ng/day; monkeys (n = 5/sex/group) received 0, 0.6, 6, or 60 microg/day of rhNGF. Animals tolerated i.c.v. infusion with no behavioral signs attributable to rhNGF. Body weight was transiently decreased in female rats at the highest dose. At the completion of dosing, histological examination in both species revealed an increase in the thickness of the leptomeninges along the ventral and lateral surfaces of the hindbrain and extending over the dorsal aspect of the spinal cord. The change was present to varying degrees at all doses of rhNGF and tended to be more severe at higher doses. At the light microscopic level, the leptomeninges contained layers of well-differentiated, spindle-shaped cells and a plexus of axonal fibers. Cells were immunoreactive for S-100 protein and were associated with an accumulation of Type IV collagen, suggesting Schwann cell origin. Electron microscopy revealed numerous fine caliber axons ensheathed by the presumptive Schwann cells, with myelination of individual axonal segments. These findings suggest that chronic i.c.v. delivery of rhNGF has stimulated axonal sprouting and secondary hyperplasia of Schwann or Schwann-like support cells within the pia-arachnoid.

Distribution of Radioiodinated Recombinant Human Nerve Growth Factor in Primate Brain Following Intracerebroventricular Infusion

The distribution of radioiodinated recombinant human nerve growth factor ([125I]rhNGF) was evaluated in adult cynomolgus monkeys following unilateral intracerebroventricular (icv) administration. Animals were cannulated into the right ventricle and recovered for 7 days. Monkeys were infused with 1.2 micrograms of [125I]rhNGF or [125I]rhNGF with a 140-fold excess of rhNGF. Twenty-four hours after infusion, animals were anesthetized and transcardially perfused with an aldehyde fixative. Coronal brain sections were processed for quantitative film autoradiography or for choline-acetyltransferase immunohistochemistry and then emulsion dipped. Specific radiolabel was distributed bilaterally and, with equal density, throughout the basal forebrain and was colocalized with choline acetyltransferase-positive neurons. Specific labeling was also present in the superficial ventral cortex. Nonspecific binding was observed surrounding the ventricles and lining blood vessels. These results demonstrate that unilateral icv infusion is an effective approach for delivering NGF to basal forebrain cholinergic neurons in primates and represents a viable drug delivery strategy for the therapeutic use of NGF in Alzheimers Disease.

Dose-response comparison of recombinant human nerve growth factor and recombinant human basic fibroblast growth factor in the fimbria fornix model of acute cholinergic degeneration

Both nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) have been proposed for the treatment of Alzheimers disease. This study describes a comparative, dose-response analysis of recombinant human (rh)NGF and rhbFGF in a rat unilateral fimbria-fornix model of acute cholinergic neuronal degeneration. Doses for rhNGF were 0.6, 6, 60, 600 and 1,800 ng/rat/day and for rhbFGF were 600, 1,800, 3,000 and 6,000 ng/rat/day, delivered for 4 weeks. The number of surviving septal cholinergic neurons was evaluated using ChAT immunohistochemistry. In control animals, the number of ChAT-positive neurons remaining on the lesioned side was between 22 and 18% compared to the non-lesioned side. Infusion with either neurotrophic factor increased the number of ChAT-positive neurons on the lesioned side in a dose-dependent manner. The maximal response to rhbFGF peaked at 3,000 ng/rat/day with a cell savings of 47%. However, there was evidence of neuropathological changes associated with rhbFGF. In contrast, rhNGF produced a maximal response with an infusion of 600 ng rhNGF/rat/day and a cell savings of 70% and no evidence of neuropathology, indicating that rhNGF was better tolerated and more efficacious than rhbFGF.

Onset Time and Durability of Huntingtin Suppression in Rhesus Putamen After Direct Infusion of Antihuntingtin siRNA

One possible treatment for Huntingtons disease involves direct infusion of a small, interfering RNA (siRNA) designed to reduce huntingtin expression into brain tissue from a chronically implanted programmable pump. Here, we studied the suppression of huntingtin mRNA achievable with short infusion times, and investigated how long suppression may persist after infusion ceases. Rhesus monkeys received 3 days of infusion of Magnevist into the putamen to confirm catheter patency and fluid distribution. After a 1-week washout period, monkeys received radiolabeled siRNA targeting huntingtin. After 1 or 3 days of siRNA delivery, monkeys were either terminated, or their pumps were shut off and they were terminated 10 or 24 days later. Results indicate that the onset of huntingtin mRNA suppression in the rhesus putamen occurs rapidly, achieving a plateau throughout the putamen within 4 days. Conversely, loss of huntingtin suppression progresses slowly, persisting an estimated 27–39 days in the putamen and surrounding white matter. These findings indicate the rapid onset and durability of siRNA-mediated target gene suppression observed in other organs also occurs in the brain, and support the use of episodic delivery of siRNA into the brain for treatment of Huntingtons disease and possibly other neurodegenerative diseases.

Mineralization of the globus pallidus following excitotoxic lesions of the basal forebrain

The excitotoxin N-methyl aspartic acid was injected into the rat nucleus basalis to destroy basal forebrain cholinergic (BFC) neurons. In long-term survival experiments (up to 11 months post-lesion), conspicuous mineralized deposits were found in the globus pallidus and to a lesser extent in the thalamus. Deposits stained in a manner consistent with a composition of calcium and iron. Typically, deposits were absent from the center of the injection site, where BFC cell loss was most severe, but were present within the ventral and lateral globus pallidus where there was substantial sparing of BFC neurons. The similarity of this pathology to basal ganglia calcification and its relationship to Alzheimers Disease and Downs syndrome is discussed.

Recombinant human ciliary neurotrophic factor stimulates the metabolic activity of SH-SY5Y cells as measured by a cytosensor microphysiometer

Information on the transmembrane signaling events and subsequent biochemical processes initiated by ciliary neurotrophic factor (CNTF) receptor activation in neurons is lacking. SH-SY5Y cells, a human neuroblastoma cell line expressing CNTF receptors, were used to study metabolic changes associated with functional ligand-receptor interactions. Real-time measurements quantifying the rate of extracellular acidification by SH-SY5Y cells (a measure of metabolic activity) were made using a silicon-based cytosensor. Application of recombinant human CNTF (rhCNTF) to resting SH-SY5Y cells increased their acidification rate in a concentration and time-dependent manner with an apparent EC50 of 60 ng/ml. Pretreatment of cells with phosphatidylinositol-specific phospholipase C (PI-PLC) prevented the CNTF, but not an NGF-stimulated increase in acidification rate. Collectively, these results demonstrate that: (1) SH-SY5Y cells express functional CNTF receptors; and (2) the initial signal transduction mechanism activated by the CNTF receptor in SH-SY5Y cells is distinct from that activated by the NGF receptor; however, both may ultimately stimulate the same downstream biochemical messengers to increase cellular metabolism.

502. Optimization of Intrathecal Delivery of AAV for Targeting the Spinal Compartment

Adeno-associated viral (AAV) vectors are a platform of great potential for therapeutic gene delivery. One of the major challenges regarding AAV gene therapy is to deliver the transgene of interest to target cells at levels that result in expression that is both safe and effective. For diseases of the central nervous system (CNS) such as amyotrophic lateral sclerosis (ALS) and Friedreichs ataxia, it is important to identify a dosing paradigm that provides a relatively homogenous distribution of gene transfer along the rostral-caudal axis of the spinal column in the CNS and is translatable. Intrathecal (IT) administration is a delivery approach that has shown promise for providing such distribution. AAV dosing via the IT route has been reported in large mammals to provide greater CNS distribution, less exposure to peripheral organs and tissues, and reduced impact of immune responses than systemic dosing. However, to-date, IT dosing of AAV in large mammals has been investigated primarily by lumbar bolus administration, with a few studies assessing administration at more rostral sites either alone or in combination with a lumbar site. Parameters that are likely to have a major impact on CNS distribution such as volume, rate and duration of infusion have not been reported previously for IT dosing of AAV. Here, we studied the effects of these parameters as well as site of infusion on distribution of transgene expression in the non-human primate CNS, using AAVrh10 to package a vector genome (vg) containing the human frataxin gene driven by the chicken β-actin promoter. Four weeks after dosing, frataxin (FXN) expression was assessed in spinal cord and dorsal root ganglia (DRG) at multiple rostral-caudal levels, as well as in brain, cerebellum, and peripheral organs such as liver, spleen and heart. Quantitative assessments included measurements of vector genome copy number and mRNA and protein expression levels. Our results showed that the distribution of transgene expression in the spinal cord, DRG, cerebellum and brain were significantly impacted by the site(s) of IT delivery (i.e. cervical vs lumbar), and volume, rate and duration of infusion. As expected, there was transduction of peripheral organs, indicating systemic exposure of the AAV vector following IT delivery. In addition, FXN expression across different cell types is being studied by histological methods. These results will not only guide the optimization of IT delivery of AAV gene therapy for diseases such as ALS and Friedreichs ataxia, but also provide useful information for IT dosing for other CNS disorders.