Martin Broadstock

Association of Plasma Clusterin Concentration With Severity, Pathology, and Progression in Alzheimer Disease

CONTEXT Blood-based analytes may be indicators of pathological processes in Alzheimer disease (AD). OBJECTIVE To identify plasma proteins associated with AD pathology using a combined proteomic and neuroimaging approach. DESIGN Discovery-phase proteomics to identify plasma proteins associated with correlates of AD pathology. Confirmation and validation using immunodetection in a replication set and an animal model. SETTING A multicenter European study (AddNeuroMed) and the Baltimore Longitudinal Study of Aging. PARTICIPANTS Patients with AD, subjects with mild cognitive impairment, and healthy controls with standardized clinical assessments and structural neuroimaging. MAIN OUTCOME MEASURES Association of plasma proteins with brain atrophy, disease severity, and rate of clinical progression. Extension studies in humans and transgenic mice tested the association between plasma proteins and brain amyloid. RESULTS Clusterin/apolipoprotein J was associated with atrophy of the entorhinal cortex, baseline disease severity, and rapid clinical progression in AD. Increased plasma concentration of clusterin was predictive of greater fibrillar amyloid-beta burden in the medial temporal lobe. Subjects with AD had increased clusterin messenger RNA in blood, but there was no effect of single-nucleotide polymorphisms in the gene encoding clusterin with gene or protein expression. APP/PS1 transgenic mice showed increased plasma clusterin, age-dependent increase in brain clusterin, as well as amyloid and clusterin colocalization in plaques. CONCLUSIONS These results demonstrate an important role of clusterin in the pathogenesis of AD and suggest that alterations in amyloid chaperone proteins may be a biologically relevant peripheral signature of AD.

Clinical Trials of Dementia With Lewy Bodies and Parkinson’s Disease Dementia

Despite the frequency and importance of dementia associated with Parkinson’s disease (PDD) and dementia with Lewy bodies (DLB), there is relatively little evidence on which to base treatment. Evidence from meta-analysis suggests that rivastigmine can improve cognition and functioning in PDD and also reduce risk of falling. There is also evidence supporting its use in DLB. Recent evidence suggests that memantine may also be effective, particularly for PDD, although evidence is more conflicting. Memantine may also improve parkinsonism and dyskinesias. Few clinical trials of cognition in PD without dementia exist, but there is preliminary evidence for atomoxetine, memantine, and piribedil. There is a lack of systematic evidence for the treatment of visual hallucinations and depression in PDD and DLB. In addition, there is a need for studies of whether potentially disease-modifying agents can prevent or delay the progression to dementia in PD.

Latest treatment options for Alzheimer’s disease, Parkinson’s disease dementia and dementia with Lewy bodies

Introduction: Alzheimer’s disease (AD), Parkinson’s disease dementia (PDD) and dementia with Lewy bodies (DLB) together account for the vast majority of individuals with dementia. Approximately 35 million people worldwide are affected with this condition, and despite decades of research, effective therapies that slow or reverse disease progression have not yet been developed. The recent failure of several large-scale clinical trials is beginning to challenge the magnitude of focus on amyloid-related therapies for AD, and newer drug targets that have shown promise in the laboratory are being investigated in clinical trials. Areas covered: This review summarises the current understanding of the underlying biology of AD, PDD and DLB and outlines the most recent drug candidates in advanced clinical trials. Expert opinion: The lack of success in drug discovery for disease-modifying therapies for AD, PDD and DLB can be attributed to limitations in the design of clinical trials and the narrow focus of molecular targets for treatment. New avenues for drug discovery including repositioning and novel target identification may now provide opportunities for success, provided a critical mass of clinical trials is achieved through increased investment.

Transgenic expression of human glial cell line-derived neurotrophic factor from integration-deficient lentiviral vectors is neuroprotective in a rodent model of Parkinson's disease.

Standard integration-proficient lentiviral vectors (IPLVs) are effective at much lower doses than other vector systems and have shown promise for gene therapy of Parkinsons disease (PD). Their main drawback is the risk of insertional mutagenesis. The novel biosafety-enhanced integration-deficient lentiviral vectors (IDLVs) may offer a significant enhancement in biosafety, but have not been previously tested in a model of a major disease. We have assessed biosafety and transduction efficiency of IDLVs in a rat model of PD, using IPLVs as a reference. Genomic insertion of lentivectors injected into the lesioned striatum was studied by linear amplification-mediated polymerase chain reaction (PCR), followed by deep sequencing and insertion site analysis, demonstrating lack of significant IDLV integration. Reporter gene expression studies showed efficient, long-lived, and transcriptionally targeted expression from IDLVs injected ahead of lesioning in the rat striatum, although at somewhat lower expression levels than from IPLVs. Transgenic human glial cell line-derived neurotrophic factor (hGDNF) expression from IDLVs was used for a long-term investigation of lentivector-mediated, transcriptionally targeted neuroprotection in this PD rat model. Vectors were injected before striatal lesioning, and the results showed improvements in nigral dopaminergic neuron survival and behavioral tests regardless of lentiviral integration proficiency, although they confirmed lower expression levels of hGDNF from IDLVs. These data demonstrate the effectiveness of IDLVs in a model of a major disease and indicate that these vectors could provide long-term PD treatment at low dose, combining efficacy and biosafety for targeted central nervous system applications.

Challenges for Gene Therapy of CNS Disorders and Implications for Parkinson's Disease Therapies

The CNS poses significant challenges for effective gene therapy, including the presence of the blood–brain barrier, which prevents the entry of large molecules. Adenoassociated viral (AAV) vectors have been developed that demonstrate efficient and stable transgene expression in the CNS and are the most advanced vector class in clinical application, but limitations still manifest. One of them is the difficulty to achieve extensive transduction volumes. Bearing this in mind, anti-parkinsonian therapies with relatively restricted targets are particularly suited for initial clinical attempts. In this issue of Human Gene Therapy a long-term follow-up of one such AAV Parkinson’s disease (PD) clinical trial is presented (Mittermeyer et al., 2012, this issue). Several important implications of this work are discussed, including the need for more widespread transduction to achieve a clinical benefit. Results obtained with AAV9 demonstrating blood–brain barrier crossing and extensive CNS transduction have raised hopes for noninvasive delivery of viral vectors to wide CNS targets. A second study in this issue of Human Gene Therapy explores AAV9 efficiency in nonhuman primates and underscores the importance of delivery route, preexisting antibody response, and vector tropism (Samaranch et al., 2012, this issue). Taken together, these two studies showcase progress and current challenges in clinical and nonhuman primate CNS gene therapy. Degeneration of the substantia nigra pars compacta and subsequent loss of striatal dopamine content is believed to underpin the cardinal motor symptoms of PD, namely tremor, rigidity, and bradykinesia. Although current pharmacotherapies are initially effective, they are associated with a decline in efficacy as the disease progresses and have a number of side effects, including hallucinations and uncontrollable motor movements (dyskinesias), that may effectively limit the dose of l-DOPA patients can tolerate (Obeso et al., 2000). Hence the search for alternative treatment, which needs to be safe and ideally requires a single administration, provides effective symptomatic relief, and even potentially halts or reverses the disease process. One way in which this may be achieved is through the use of gene therapy. The majority of current gene therapy approaches for the treatment of CNS disorders have focused on the use of AAV vectors, as they offer stable, long-term gene expression (McCown, 2011). Such vectors have been administered directly into the target sites of the CNS through stereotaxic surgery (Christine et al., 2009; Marks et al., 2010). However, this invasive approach requires specialist surgical facilities and accounts for some of the undesirable side effects of gene therapy reported in the literature (e.g., intracranial hemorrhage and edema; Christine et al., 2009). Nevertheless, localized infusions of vector can efficiently target specific brain regions, with the associated reduced risk of adverse events not directly related to vector delivery. The results of several phase I/II gene therapy trials for Parkinson’s have thus far been encouraging, with vectors showing good safety profiles and being well tolerated in patients. Current trials can be subdivided into three main strategies: increasing striatal dopamine content, using aromatic l-amino acid decarboxylase (rAAV2-hAADC; Genzyme, Cambridge, MA) alone or a combination of hAADC, tyrosine hydroxylase, and guanosine 5¢-triphosphate cyclohydrolase I (carried by equine infectious anemia virus-derived lentiviral vector ProSavin; Oxford BioMedica, Oxford, UK); changing basal ganglia circuitry by inhibiting the subthalamic nucleus, using the gene for glutamic acid decarboxylase (AAV-GAD; Neurologix, Fort Lee, NJ); or a trophic factor (neurturin) approach aiming to improve the nigrostriatal pathway (AAV2-NTN, CERE-120; Ceregene, San Diego, CA) (Witt and Marks, 2011). In this issue of Human Gene Therapy, Mittermeyer and colleagues report a long-term evaluation of a phase I study of AADC gene therapy for PD (Mittermeyer et al., 2012, this issue). AADC is the rate-limiting enzyme for the conversion of l-DOPA to dopamine, and loss of AADC may be associated with the wearing off of l-DOPA responsiveness in patients (Ichinose et al., 1994). Thus, restoration of AADC capacity within the putamen should result in elevated dopamine levels in response to exogenous l-DOPA. This study is a continuation of previous work by this group, who initially reported findings based on a 6-month follow-up of 10 patients who received either a low dose (9 · 10 vector genome copies [VG]) or a high dose (3 · 10 VG) of AADC

Neurochemical changes in a double transgenic mouse model of Alzheimer's disease fed a pro-oxidant diet.

Oxidative stress is implicated in the pathogenesis of Alzheimers disease (AD) causing neurodegeneration and decreased monoamine neurotransmitters. We investigated the effect of administration of a pro-oxidant diet on the levels of monoamines and metabolites in the brains of wildtype and transgenic mice expressing mutant APP and PS-1 (TASTPM mice). Three-month-old TASTPM and wildtype (C57BL6/J) mice were fed either normal or pro-oxidant diet for 3 months. The neocortex, cerebellum, hippocampus and striatum were assayed for their monoamine and monoamine metabolite content using HPLC with electrochemical detection. Striatal tyrosine hydroxylase (TOH) levels were analysed by Western blotting. In the striatum, female TASTPM mice had higher levels of DOPAC and male TASTPM mice had higher levels of 5-HIAA compared to wildtype mice. Administration of pro-oxidant diet increased striatal MHPG, turnover of NA and 5-HT levels in female TASTPM mice compared to TASTPM mice fed control diet. The pro-oxidant diet also decreased DOPAC levels in female TASTPM mice compared to those fed control diet. Striatal TOH did not depend on diet, gender or genotype. In the neocortex, the TASTPM genotype increased levels of 5-HIAA in male mice fed control diet compared to wildtype mice. In the cerebellum, the TASTPM genotype led to decreased levels of HVA (male mice only) and also decreased turnover of DA (female mice only) compared to wildtype mice. These data suggest a sparing of monoaminergic neurones in the cortex, striatum and hippocampus of TASTPM mice fed pro-oxidant diet and could be indicative of increased activity in corticostriatal circuits. The decreased cerebellar levels of HVA and turnover of DA in TASTPM mice hint at possible axonal degeneration within this subregion.

Reduction of RPT6/S8 (a Proteasome Component) and Proteasome Activity in the Cortex is Associated with Cognitive Impairment in Lewy Body Dementia

Lewy body dementia is the second most common neurodegenerative dementia and is pathologically characterized by α-synuclein positive cytoplasmic inclusions, with varying amounts of amyloid-β (Aβ) and hyperphosphorylated tau (tau) aggregates in addition to synaptic loss. A dysfunctional ubiquitin proteasome system (UPS), the major proteolytic pathway responsible for the clearance of short lived proteins, may be a mediating factor of disease progression and of the development of α-synuclein aggregates. In the present study, protein expression of a key component of the UPS, the RPT6 subunit of the 19S regulatory complex was determined. Furthermore, the main proteolytic-like (chymotrypsin- and PGPH-) activities have also been analyzed. The middle frontal (Brodmann, BA9), inferior parietal (BA40), and anterior cingulate (BA24) gyrus’ cortex were selected as regions of interest from Parkinson’s disease dementia (PDD, n = 31), dementia with Lewy bodies (DLB, n = 44), Alzheimer’s disease (AD, n = 16), and control (n = 24) brains. Clinical and pathological data available included the MMSE score. DLB, PDD, and AD were characterized by significant reductions of RPT6 (one-way ANOVA, p < 0.001; Bonferroni post hoc test) in prefrontal cortex and parietal cortex compared with controls. Strong associations were observed between RPT6 levels in prefrontal, parietal cortex, and anterior cingulate gyrus and cognitive impairment (p = 0.001, p = 0.001, and p = 0.008, respectively). These findings highlight the involvement of the UPS in Lewy body dementia and indicate that targeting the UPS may have the potential to slow down or reduce the progression of cognitive impairment in DLB and PDD.

Novel pharmaceuticals in the treatment of psychosis in Parkinson’s disease

Parkinson’s disease (PD) affects 10 million people worldwide. Half will develop psychosis, the majority experiencing hallucinations rather than delusions. Emergence of psychosis increases the likelihood of institutionalization and mortality. Where pharmacological treatment is warranted, options are limited. Most currently licensed atypical antipsychotics are ineffective or worsen motor symptoms in people with PD. This review of provides an overview of the current landscape of treatments and the opportunities in emerging research. Clozapine is the only licensed antipsychotic with proven efficacy, although the associated side effects limit its use. With recent advances in understanding the role of serotonin, rational drug design approaches have delivered a novel pharmacological treatment with recently proven efficacy in clinical trials of people with PD and psychosis. Pimavanserin represents an important addition to treatment.

A genetically immortalized human stem cell line: a promising new tool for Alzheimer's disease therapy.

Amyloid-β peptides and hyper-phosphorylated tau are the main pathological hallmarks of Alzheimers disease (AD). Given the recent failure of several large-scale clinical trials and the lack of disease-modifying pharmacological treatments, there is an urgent need to develop alternative therapies. A clinical grade human CTX0E03 neural stem cell line has recently passed phase I trials in people with stroke. However, this cell line has not been investigated in other neurodegenerative disorders. This study investigates the survival of CTX0E03 cells under conditions based on the underlying AD pathology. Cell viability assays showed a concentration dependence of this cell line to the toxic effects of Aβ1-42, but not Aβ1-40, and okadaic acid, a phosphatase 2A inhibitor. Notably, CTX0E03 cell line displayed toxicity at concentrations significantly higher than both rat neural stem cells and those previously reported for primary cultures. These results suggest CTX0E03 cells could be developed for clinical trials in AD patients.

A role for APP in Wnt signalling links synapse loss with β-amyloid production

In Alzheimer’s disease (AD), the canonical Wnt inhibitor Dickkopf-1 (Dkk1) is induced by β-amyloid (Aβ) and shifts the balance from canonical towards non-canonical Wnt signalling. Canonical (Wnt-β-catenin) signalling promotes synapse stability, while non-canonical (Wnt-PCP) signalling favours synapse retraction; thus Aβ-driven synapse loss is mediated by Dkk1. Here we show that the Amyloid Precursor Protein (APP) co-activates both arms of Wnt signalling through physical interactions with Wnt co-receptors LRP6 and Vangl2, to bi-directionally modulate synapse stability. Furthermore, activation of non-canonical Wnt signalling enhances Aβ production, while activation of canonical signalling suppresses Aβ production. Together, these findings identify a pathogenic-positive feedback loop in which Aβ induces Dkk1 expression, thereby activating non-canonical Wnt signalling to promote synapse loss and drive further Aβ production. The Swedish familial AD variant of APP (APPSwe) more readily co-activates non-canonical, at the expense of canonical Wnt activity, indicating that its pathogenicity likely involves direct effects on synapses, in addition to increased Aβ production. Finally, we report that pharmacological inhibition of the Aβ-Dkk1-Aβ positive feedback loop with the drug fasudil can restore the balance between Wnt pathways, prevent dendritic spine withdrawal in vitro, and reduce Aβ load in vivo in mice with advanced amyloid pathology. These results clarify a relationship between Aβ accumulation and synapse loss and provide direction for the development of potential disease-modifying treatments.