Aminochrome as a preclinical experimental model to study degeneration of dopaminergic neurons in Parkinson’s disease

Four decades after L-dopa introduction to PD therapy, the cause of Parkinson's disease (PD) remains unknown despite the intensive research and the discovery of a number of gene mutations and deletions in the pathogenesis of familial PD. Different model neurotoxins have been used as preclinical experimental models to study the neurodegenerative process in PD, such as 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and rotenone. The lack of success in identifying the molecular mechanism for the degenerative process in PD opens the question whether the current preclinical experimental models are suitable to understand the degeneration of neuromelanin-containing dopaminergic neurons in PD. We propose aminochrome as a model neurotoxin to study the neurodegenerative processes occurring in neuromelanin-containing dopaminergic neurons in PD. Aminochrome is an endogenous compound formed during dopamine oxidation and it is the precursor of neuromelanin, a substance whose formation is a normal process in mesencephalic dopaminergic neurons. However, aminochrome itself can induce neurotoxicity under certain aberrant conditions such as (i) one-electron reduction of aminochrome catalyzed by flavoenzymes to leukoaminochrome o-semiquinone radical, which is a highly reactive neurotoxin; or (ii) the formation of aminochrome adducts with alpha-synuclein, enhancing and stabilizing the formation of neurotoxic protofibrils. These two neurotoxic pathways of aminochrome are prevented by DT-diaphorase, an enzyme that effectively reduces aminochrome with two-electrons preventing both aminochrome one-electron reduction or formation alpha synuclein protofibrils. We propose to use aminochrome as a preclinical experimental model to study the neurodegenerative process of neuromelanin containing dopaminergic neurons in PD.     

PFO and Migraine: Is There a Role for Closure?

Observational studies suggest that closure of a patent foramen ovale for other indications may reduce or even eliminate migraine attacks, particularly migraine with aura. The first randomized clinical trial of patent foramen ovale (PFO) closure for prevention of migraine, the MIST trial, showed negative results. The results of the other two completed studies in this area have recently been published in the last year. PRIMA and PREMIUM were also both negative for their primary endpoints. The PREMIUM trial did show a reduction in headache days in the migraine with aura subgroup but the final results of this subset analysis have not been published. There may be an as yet undetermined subgroup of patients with migraine who would benefit from closure, but slow recruitment has been a barrier to further study. Several potentially life-threatening procedure-related adverse events occurred in the clinical trials. At this time, we recommend against offering PFO closure as a preventive treatment for migraine. Based on available observational data, patients for whom PFO closure is indicated for other reasons may see some improvement in their migraines.     

Dopaminergic regulation of dopamine D3 and D3nf receptor mRNA expression

Dopamine D3 receptors have the highest dopamine affinity of all dopamine receptors, and may thereby regulate dopamine signaling mediated by volume transmission. Changes in D3 receptor isoform expression may alter D3 receptor function, however, little is known regarding coordination of D3 isoform expression in response to perturbations in dopaminergic stimulation. To determine the effects of dopamine receptor stimulation and blockade on D3 receptor alternative splicing, we determined D3 and D3nf isoform mRNA expression following treatment with the D3 receptor antagonist NGB 2904, and the indirect dopamine agonist amphetamine. Expression of tyrosine hydroxylase (TH) mRNA, the rate‐limiting enzyme in dopamine synthesis, was also determined. The D3/D3nf mRNA expression ratio was increased in ventral striatum, prefrontal cortex, and hippocampus 6 h following D3 antagonist NGB 2904 treatment, and remained persistently elevated at 24 h in hippocampus and substantia nigra/ventral tegmentum. D3 mRNA decreased 65% and D3nf mRNA expression decreased 71% in prefrontal cortex 24 h following amphetamine treatment, however, these changes did not reach statistical significance. TH mRNA expression was unaffected by D3 antagonist NGB 2904, but was elevated by amphetamine in ventral striatum, hippocampus, and prefrontal cortex. These findings provide evidence for an adaptive response to altered D3 receptor stimulation involving changes in D3 receptor alternative splicing. Additionally, these data suggest D3 autoreceptor regulation of dopamine synthesis does not involve regulation of TH mRNA expression. Finally, the observation of regulated TH mRNA expression in dopamine terminal fields provides experimental support for the model of local control of mRNA expression in adaptation to synaptic activity. Synapse, 2010. © 2010 Wiley‐Liss, Inc.     

False memories in patients with mild cognitive impairment and mild Alzheimer’s disease dementia: Can cognitive strategies help?

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that presents predominantly with impairments in learning and memory. Patients with AD are also susceptible to false memories, a clinically relevant memory distortion where a patient remembers an incorrect memory that they believe to be true. The use of cognitive strategies to improve memory performance among patients with AD by reducing false memories has taken on added importance given the lack of disease-modifying agents for AD. However, existing evidence suggests that cognitive strategies to reduce false memories in patients with AD are of limited effectiveness, although these strategies may be useful at earlier stages of the disease. The purpose of this review is to examine experimental findings of false memories and associated memory processes in patients with mild cognitive impairment due to AD and mild AD dementia. Cognitive strategies to reduce false memories in these patient populations are also reviewed. Approaches to clinically relevant future research are suggested and discussed.     

Autophagy in neurodegenerative disorders: pathogenic roles and therapeutic implications

Autophagy is a highly conserved intracellular pathway involved in the elimination of proteins and organelles by lysosomes. Known originally as an adaptive response to nutrient deprivation in mitotic cells, autophagy is now recognized as an arbiter of neuronal survival and death decisions in neurodegenerative diseases. Studies using postmortem human tissue, genetic and toxin-induced animal and cellular models indicate that many of the etiological factors associated with neurodegenerative disorders can perturb the autophagy process. Emerging data support the view that dysregulation of autophagy might play a critical role in the pathogenesis of neurodegenerative disorders. In this review, we highlight the pathophysiological roles of autophagy and its potential therapeutic implications in debilitating neurodegenerative disorders, including amyotrophic lateral sclerosis and Alzheimer's, Parkinson's and Huntington's diseases.     

Increased seizure severity and seizure‐related death in mice lacking HCN1 channels

Persistent down‐regulation in the expression of the hyperpolarization‐activated HCN1 cation channel, a key determinant of intrinsic neuronal excitability, has been observed in febrile seizure, temporal lobe epilepsy, and generalized epilepsy animal models, as well as in patients with epilepsy. However, the role and importance of HCN1 down‐regulation for seizure activity is unclear. To address this question we determined the susceptibility of mice with either a general or forebrain‐restricted deletion of HCN1 to limbic seizure induction by amygdala kindling or pilocarpine administration. Loss of HCN1 expression in both mouse lines is associated with higher seizure severity and higher seizure‐related mortality, independent of the seizure‐induction method used. Therefore, down‐regulation of HCN1 associated with human epilepsy and rodent models may be a contributing factor in seizure behavior.     

Early cognitive development in children born to women with epilepsy: A prospective report

Purpose: In this prospective study the early cognitive development of children born to women with epilepsy (n = 198) was assessed and compared to a group of children representative of the general population (n = 230). Methods: The children were assessed when younger than the age of 2 years using the Griffiths Mental Development Scales, either in their local participating hospital or in their home. The assessments were completed by an assessor who was blinded to whether the child’s mother had epilepsy and to antiepileptic drug type. Results: Children exposed to sodium valproate had a statistically significant increased risk of delayed early development in comparison to the control children. Linear regression analysis showed a statistically significant effect of sodium valproate exposure on the child’s overall developmental level that was not accounted for by confounding variables. Delayed early development is also noted for children within an ad hoc group of less commonly utilized antiepileptic drugs, although conclusions cannot be drawn due to the size of this group (n = 13). Children exposed to either carbamazepine or lamotrigine in utero did not differ significantly in their overall developmental ability. Differences noted in specific developmental areas for these two groups were not statistically significant after the control for confounders such as socioeconomic status and maternal IQ. Discussion: Women with epilepsy should be informed of the risks posed to their potential offspring prior to pregnancy to allow for informed decisions regarding treatment. Children exposed in utero to antiepileptic drugs should be monitored throughout childhood to allow for early intervention when necessary.     

Automation of the ELISpot assay for high-throughput detection of antigen-specific T-cell responses

The enzyme linked immunospot (ELISpot) assay is a fundamental tool in cellular immunology, providing both quantitative and qualitative information on cellular cytokine responses to defined antigens. It enables the comprehensive screening of patient derived peripheral blood mononuclear cells to reveal the antigenic restriction of T-cell responses and is an emerging technique in clinical laboratory investigation of certain infectious diseases. As with all cellular-based assays, the final results of the assay are dependent on a number of technical variables that may impact precision if not highly standardised between operators. When studies that are large scale or using multiple antigens are set up manually, these assays may be labour intensive, have many manual handling steps, are subject to data and sample integrity failure and may show large inter-operator variability. Here we describe the successful automated performance of the interferon (IFN)-γ ELISpot assay from cell counting through to electronic capture of cytokine quantitation and present the results of a comparison between automated and manual performance of the ELISpot assay. The mean number of spot forming units enumerated by both methods for limiting dilutions of CMV, EBV and influenza (CEF)-derived peptides in six healthy individuals were highly correlated (r > 0.83, p < 0.05). The precision results from the automated system compared favourably with the manual ELISpot and further ensured electronic tracking, increased through-put and reduced turnaround time.