Structural determinants of alpha4beta2 nicotinic acetylcholine receptor trafficking.

The structural determinants of nicotinic acetylcholine receptor (AChR) trafficking have yet to be fully elucidated. Hydrophobic residues occur within short motifs important for endoplasmic reticulum (ER) export or endocytotic trafficking. Hence, we tested whether highly conserved hydrophobic residues, primarily leucines, in the cytoplasmic domain of the alpha4beta2 AChR subunits were required for cell surface expression of alpha4beta2 AChRs. Mutation of F350, L351, L357, and L358 to alanine in the alpha4 AChR subunit attenuates cell surface expression of mutant alpha4beta2 AChRs. Mutation of F342, L343, L349, and L350 to alanine at homologous positions in the beta2 AChR subunit abolishes cell surface expression of mutant alpha4beta2 AChRs. The hydrophobic nature of the leucine residue is a primary determinant of its function because mutation of L343 to another hydrophobic amino acid, phenylalanine, in the beta2 AChR subunit only poorly inhibits trafficking of mutant alpha4beta2 AChR to the cell surface. All mutant alpha4beta2 AChRs exhibit high-affinity binding for [3H]epibatidine. In both tsA201 cells and differentiated SH-SY5Y neural cells, wild-type alpha4beta2 AChRs colocalize with the Golgi marker giantin, whereas mutant alpha4beta2 AChRs fail to do so. The striking difference between mutant alpha4 versus mutant beta2 AChR subunits on cell surface expression of mutant alpha4beta2 AChRs points to a cooperative or regulatory role for the alpha4 AChR subunit and an obligatory role for the beta2 AChR subunit in ER export. Collectively, our results identify, for the first time, residues within AChR subunits that are essential structural determinants of alpha4beta2 AChR ER export.

Inosine to increase serum and cerebrospinal fluid urate in Parkinson disease: a randomized clinical trial.

IMPORTANCE: Convergent biological, epidemiological, and clinical data identified urate elevation as a candidate strategy for slowing disability progression in Parkinson disease (PD). OBJECTIVE: To determine the safety, tolerability, and urate-elevating capability of the urate precursor inosine in early PD and to assess its suitability and potential design features for a disease-modification trial. DESIGN, SETTING, AND PARTICIPANTS: The Safety of Urate Elevation in PD (SURE-PD) study, a randomized, double-blind, placebo-controlled, dose-ranging trial of inosine, enrolled participants from 2009 to 2011 and followed them for up to 25 months at outpatient visits to 17 credentialed clinical study sites of the Parkinson Study Group across the United States. Seventy-five consenting adults (mean age, 62 years; 55% women) with early PD not yet requiring symptomatic treatment and a serum urate concentration less than 6 mg/dL (the approximate population median) were enrolled. INTERVENTIONS: Participants were randomized to 1 of 3 treatment arms: placebo or inosine titrated to produce mild (6.1-7.0 mg/dL) or moderate (7.1-8.0 mg/dL) serum urate elevation using 500-mg capsules taken orally up to 2 capsules 3 times per day. They were followed for up to 24 months (median, 18 months) while receiving the study drug plus 1 washout month. MAIN OUTCOMES AND MEASURES: The prespecified primary outcomes were absence of unacceptable serious adverse events (safety), continued treatment without adverse event requiring dose reduction (tolerability), and elevation of urate assessed serially in serum and once (at 3 months) in cerebrospinal fluid. RESULTS Serious adverse events (17), including infrequent cardiovascular events, occurred at the same or lower rates in the inosine groups relative to placebo. No participant developed gout and 3 receiving inosine developed symptomatic urolithiasis. Treatment was tolerated by 95% of participants at 6 months, and no participant withdrew because of an adverse event. Serum urate rose by 2.3 and 3.0 mg/dL in the 2 inosine groups (P < .001 for each) vs placebo, and cerebrospinal fluid urate level was greater in both inosine groups (P = .006 and <.001, respectively). Secondary analyses demonstrated nonfutility of inosine treatment for slowing disability. CONCLUSIONS AND RELEVANCE: Inosine was generally safe, tolerable, and effective in raising serum and cerebrospinal fluid urate levels in early PD. The findings support advancing to more definitive development of inosine as a potential disease-modifying therapy for PD. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00833690.

Rivastigmine in Parkinson's disease dementia.

Parkinson's disease has now evolved beyond what was considered to be a traditional motor disorder. It is being increasingly recognized that non-motor symptoms such as cognitive impairment, frank dementia, psychosis, depression, autonomic dysfunction and sleep disturbances are just as integral to the disease spectrum. The cholinergic system has been proposed to play a pivotal role in cognitive dysfunction. Based on interpretation of clinical studies in patients with Alzheimer's, cholinesterase inhibitors have also been studied for dementia associated with Parkinson's disease. Most of these include large and small placebo-controlled studies and several pilot studies have indicated that cholinesterase inhibitors have a favorable effect on cognition, psychiatric symptoms and global function in Parkinson's disease dementia. A large randomized placebo-controlled clinical trial showed that rivastigmine had moderate improvement in dementia associated with Parkinson's disease. The magnitude of effects in terms of scores for the cognitive subscale of the Alzheimer's disease assessment scale and Alzheimer's disease cooperative study-clinicians global impression of change were similar to those observed among patients with Alzheimer's disease who were treated with cholinesterase inhibitors. A transdermal patch which gradually releases rivastigmine over the application period is now available for use in mild to moderate dementia associated with Parkinson's disease and Alzheimer's disease.

Presynaptic targeting of alpha4beta 2 nicotinic acetylcholine receptors is regulated by neurexin-1beta.

The mechanisms involved in the targeting of neuronal nicotinic acetylcholine receptors (AChRs), critical for their functional organization at neuronal synapses, are not well understood. We have identified a novel functional association between alpha4beta2 AChRs and the presynaptic cell adhesion molecule, neurexin-1beta. In non-neuronal tsA 201 cells, recombinant neurexin-1beta and mature alpha4beta2 AChRs form complexes. alpha4beta2 AChRs and neurexin-1beta also coimmunoprecipitate from rat brain lysates. When exogenous alpha4beta2 AChRs and neurexin-1beta are coexpressed in hippocampal neurons, they are robustly targeted to hemi-synapses formed between these neurons and cocultured tsA 201 cells expressing neuroligin-1, a postsynaptic binding partner of neurexin-1beta. The extent of synaptic targeting is significantly reduced in similar experiments using a mutant neurexin-1beta lacking the extracellular domain. Additionally, when alpha4beta2 AChRs, alpha7 AChRs, and neurexin-1beta are coexpressed in the same neuron, only the alpha4beta2 AChR colocalizes with neurexin-1beta at presynaptic terminals. Collectively, these data suggest that neurexin-1beta targets alpha4beta2 AChRs to presynaptic terminals, which mature by trans-synaptic interactions between neurexins and neuroligins. Interestingly, human neurexin-1 gene dysfunctions have been implicated in nicotine dependence and in autism spectrum disorders. Our results provide novel insights as to possible mechanisms by which dysfunctional neurexins, through downstream effects on alpha4beta2 AChRs, may contribute to the etiology of these neurological disorders.

Treatment of Levodopa-induced Dyskinesia.

Levodopa provides the most effective symptomatic treatment for Parkinson's disease (PD). Initiation of treatment of PD too early and/or very aggressive treatment with large doses of levodopa results in severe motor fluctuations and dyskinesias in 30% of patients with PD. Chronic levodopa treatment over a period of 9 years or more will invariably result in disabling motor fluctuations in 90% of PD patients. The motor fluctuations and associated dyskinesia are due to progressive dopamine denervation, an unregulated pattern of release of dopamine in the synapse, fluctuating levels of receptor sensitivity, and fluctuating levels of dopamine receptor stimulation. Once the dyskinesias are established, they are difficult to treat. The current medical therapy is a by-product of several explorative open-label trials, as well as a few blinded and double-label placebo-controlled clinical trials, of varying duration in a small number of patients. These studies suggest that amantadine, a glutamate antagonist, may be the most effective, easily available, and inexpensive medical treatment for levodopa-induced dyskinesia. Several other drugs, already approved for other medical ailments, also have been tried but not evaluated in large-scale clinical trials. None of these drugs is approved by the US Food and Drug Administration specifically for levodopa-induced dyskinesia. By far, the most effective treatment of levodopa-induced dyskinesia appears to be deep brain stimulation, with globus pallidus interna or the subthalamic nucleus as the two major targets of placement of electrodes.

Treatment of phenylketonuria-associated tremor with deep brain stimulation: case report.

OBJECTIVE AND IMPORTANCE: Phenylketonuria (PKU) is an inborn error of metabolism that causes severe neurological impairment, despite dietary treatment. We present a case of PKU-induced cerebellar tremor treated with deep brain stimulation. There have been no previously reported cases of a patient with a PKU tremor treated with deep brain stimulation. CLINICAL PRESENTATION: A 36-year-old male patient with PKU presented with signs of cerebellar disease including dysmetria, resting tremor, and intention tremor in the left upper extremity. INTERVENTION: A deep brain stimulation electrode was placed in the ventral intermediate nucleus of the right thalamus. CONCLUSION: Immediately after surgery, the patient had nearly complete resolution of intention tremor in the left arm. His resting tremor in the left hand was also greatly improved. The 30-month follow-up examination revealed maintenance of the immediate postoperative improvement.