Biomedical subjects

Christopher A Shaw

Publications and source records attributed to Christopher A Shaw.

3 recordsLinked to original sources

PubMed2003

Decrease in glial glutamate transporter variants and excitatory amino acid receptor down-regulation in a murine model of ALS-PDC.

Glutamate transporter proteins appear crucial to controlling levels of glutamate in the central nervous system (CNS). Abnormal and/or decreased levels of various transporters have been observed in amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD) and in other neurological disorders. We have assessed glutamate transporter (GLT-1/EAAT2) levels in mice fed washed cycad flour containing a suspected neurotoxin that induces features resembling the Guamanian disorder, ALS-PDC. Down-regulation of glutamate transporter subtypes was detected by immunohistology using antibodies specific for two glial glutamate transporter splice variants (GLT-1alpha and GLT-1B). Immunohistology showed a "patchy" loss of antibody label with the patches centered on blood vessels. Computer densitometry showed significantly decreased GLT-1alpha levels in the spinal cord and primary somatosensory cortex of cycad-fed mice. GLT-1B levels were significantly decreased in the spinal cord, in the motor, somatosensory, and piriform cortices, and in the striatum. Western blots showed a 40% decrease in frontal motor cortex and lumbar spinal cord of cycad-fed mice that appeared to be phosphorylation-dependent. Receptor-binding assays showed decreased NMDA and AMPA receptor levels and increased GABAA receptor levels in cycad-fed mice cortex. These receptor data are consistent with an increased level of extracellular glutamate. The generalized decrease in GLT-1, decreased excitatory amino acid receptor levels, and increased GABAA receptor levels may reflect an early glutamate-mediated excitotoxicity following cycad exposure. Deciphering the series of events leading to neurodegeneration in cycad-fed animals may provide clues leading to therapeutic approaches to halt the early stages of disease progression.

Amyotrophic Lateral Sclerosis↗

PubMed2002

Behavioral and neurological correlates of ALS-parkinsonism dementia complex in adult mice fed washed cycad flour.

Consumption of cycad seed products (Cycas circinalis) is one of the strongest epidemiological links to the Guamian neurological disorder amyotrophic lateral sclerosis-parkinsonism-dementia complex (ALS-PDC), however, the putative toxin which causes neurodegeneration has never been identified definitively. To reexamine this issue, 6-7-mo-old, male CD-1 mice were assessed for motor and cognitive behaviours during and following feeding with pellets made from washed cycad flour. Cycad-fed animals showed early evidence of progressive motor and cognitive dysfunctions. Neurodegeneration measured using TUNEL and caspase-3 labeling was found in neocortex, various hippocampal fields, substantia nigra, olfactory bulb, and spinal cord. In vitro studies using rat neocortex have identified toxic compounds in washed cycad flour that induce depolarizing field potentials and lead to release of lactate dehydrogenase (LDH), both blocked by AP5. High-performance liquid chromatography (HPLC)/mass spectrometry of cycad flour samples failed to show appreciable amounts of other known cycad toxins, cycasin, MAM, or BMAA; only trace amounts of BOAA were present. Isolation procedures employing these techniques identified the most toxic component as beta-sitosterol beta-D-glucoside (BSSG). The present data suggest that a neurotoxin, or a toxic metabolite, not previously identified in cycad, is able to gain access to central nervous system (CNS) resulting in neurodegeneration of specific neural populations and in motor and cognitive dysfunctions. These data are consistent with a number of major features of ALS-PDC in humans.

Amyotrophic Lateral Sclerosis↗

PubMed2002

Synergistic versus antagonistic actions of glutamate and glutathione: the role of excitotoxicity and oxidative stress in neuronal disease.

The etiology of various age-related neurological diseases remains unknown. Sporadic forms ofAlzheimer's, Parkinson's and Lou Gehrig's disease have been linked to environmental factors that cause neuronal cell death either by excitotoxicity or by inducing oxidative stress. Our recent studies have demonstrated that various compounds not previously associated with these diseases, i.e. methionine sulfoximine (MSO), originally isolated from 'agenized' flour, and sitosterol glucoside (BSSG), isolated from the seed of the cycad, appear to be neurotoxins, likely acting by excitotoxic mechanisms. For these compounds, the primary excitotoxic effect appears to involve glutamate release followed by NMDA receptor activation. Lactate dehydrogenase assays demonstrate that both compounds cause rapid cell death in vitro. In addition, both compounds appear to alter antioxidant defense mechanisms, acting particularly on levels of reduced glutathione (GSH). In vivo application of MSO has historically been linked to behavioral abnormalities, including seizures, in various species. Our recent experiments have demonstrated that mice fed cycad flour containing sitosterol glucoside have severe behavioral abnormalities of motor and cognitive function, as well as significant levels of neurodegeneration in cortex, hippocampus, spinal cord and other CNS regions measured post mortem. The combined weight of excitotoxic action, in concert to a decline in antioxidant defenses, induced by molecules such as methionine sulfoximine and sitosterol glucoside is hypothesized to be causal to neuronal degeneration in various neurological diseases. Understanding the mechanisms of action of these and functionally related molecules may serve to focus attention on potential neurotoxins present in the human environment. Only once such molecules have been identified, can we begin to design appropriate pharmaceutical strategies to prevent or halt the progression of the age-related neurological diseases.

Animals↗