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G E Kisby

Publications and source records attributed to G E Kisby.

At least 19 recordsLinked to original sources
PubMed2006

Proteomic analysis of the genotoxicant methylazoxymethanol (MAM)-induced changes in the developing cerebellum.

The genotoxicant methylazoxymethanol (MAM) is a widely used developmental neurotoxin, and its glucoside is an etiological factor for western Pacific amyotrophic lateral sclerosis-parkinsonism-dementia complex (ALS/PDC). Identification of global protein expression changes that occur in response to MAM in the developing cerebellum could provide valuable insight into the potential mechanisms involved in the neurodegeneration process. We have utilized fluorescence 2-dimensional differential gel electrophoresis (2D-DIGE), to determine the protein expression changes that occur during normal cerebellar development and in response to MAM. Three day-old postnatal C57BL/6 mice (PND3) received a single injection of MAM, and the cerebella of postnatal day 4 (PND4) and day 22 (PND22) were analyzed. Approximately, 1400 unique spots were matched and quantified in all samples. Comparison of PND4 and PND22 developing cerebellum showed that a significant fraction of the proteome (approximately 68%) changes at this stage. The immediate response of the developing cerebellum to MAM was minimal (approximately 10%). However, significant differences (27%) were noted 14 days after MAM exposure. In contrast, the transcriptome changes were more pronounced at 24 h compared to 14 days. MAM targeted several proteins networks including transport (e.g., alpha-synuclein), cytoskeletal (e.g., beta-tubulin, vimentin), and mitochondrial (e.g., Atp5b) proteins. Immunochemistry confirmed several of the changes in protein expression (alpha-synuclein). Comparison with gene expression changes revealed that the temporal changes observed in the transcriptome and proteome are not correlative. These studies demonstrate for the first time the potential networks involved during neuronal development and neurodegenerative processes that are perturbed by MAM.

Animals↗
PubMed2004

Role of nucleotide- and base-excision repair in genotoxin-induced neuronal cell death.

Base-excision (BER) and nucleotide-excision (NER) repair play pivotal roles in protecting the genomes of dividing cells from damage by endogenous and exogenous agents (i.e. environmental genotoxins). However, their role in protecting the genome of post-mitotic neuronal cells from genotoxin-induced damage is less clear. The present study examines the role of the BER enzyme 3-alkyladenine DNA glycosylase (AAG) and the NER protein xeroderma pigmentosum group A (XPA) in protecting cerebellar neurons and astrocytes from chloroacetaldehyde (CAA) or the alkylating agent 3-methyllexitropsin (Me-Lex), which produce ethenobases or 3-methyladenine (3-MeA), respectively. Neuronal and astrocyte cell cultures prepared from the cerebellum of wild type (C57BL/6) mice or Aag(-/-) or Xpa(-/-) mice were treated with 0.1-50 microM CAA for 24h to 7 days and examined for cell viability, DNA fragmentation (TUNEL labeling), nuclear changes, and glutathione levels. Aag(-/-) neurons were more sensitive to the acute (>20 microM) and long-term (>5 microM) effects of CAA than comparably treated wild type neurons and this sensitivity correlated with the extent of DNA fragmentation and nuclear changes. Aag(-/-) neurons were also sensitive to Me-Lex at comparable concentrations of CAA. In contrast, Xpa(-/-) neurons were more sensitive than either wild type or Aag(-/-) neurons to CAA (>10 microM), but less sensitive than Aag(-/-) neurons to Me-Lex. Astrocytes from the cerebellum of wild type, Aag(-/-) or Xpa(-/-) mice were essentially insensitive to CAA at the concentrations tested. These studies demonstrate that BER and NER are required to protect neurons from genotoxin-induced cell death.

Acetaldehyde↗
PubMed2001

Heterozygosity for the mouse Apex gene results in phenotypes associated with oxidative stress.

Apurinic/apyrimidinic endonuclease is a key enzyme in the process of base excision repair, required for the repair of spontaneous base damage that arises as a result of oxidative damage to DNA. In mice, this endonuclease is coded by the Apex gene, disruption of which is incompatible with embryonic life. Here we confirm the embryonic lethality of Apex-null mice and report the phenotypic characterization of mice that are heterozygous mutants for the Apex gene (Apex+/-). We show that Apex heterozygous mutant cells and animals are abnormally sensitive to increased oxidative stress. Additionally, such animals manifest elevated levels of oxidative stress markers in serum, and we show that dietary supplementation with antioxidants restores these to normal levels. Apex+/- embryos and pups manifest reduced survival that can also be partially rescued by dietary supplementation with antioxidants. These results are consistent with a proposed role for this enzyme in protection against the deleterious effects of oxidative stress and raise the possibility that humans with heterozygous mutations in the homologous HAP1 gene may be at increased risk for the phenotypic consequences of oxidative stress in cells.

Adenocarcinoma, Papillary↗
PubMed2000

In vitro neurotoxic and DNA-damaging properties of nitrogen mustard.

Sulfur mustard and nitrogen mustard (HN2) are reported to produce neurobehavioral and neuropathological changes in animals and humans, but the mechanisms are unknown. We examined the cytotoxic properties of HN2 in cultures of dividing and post-mitotic neurons and astrocytes, which comprise the majority of cells in the central nervous system. Cultures of rat cerebellar astrocytes, post-mitotic granule cell neurons or dividing and terminally differentiated human SY5Y neuroblastoma cell cultures were treated with various concentrations of HN2 for 24 h. After treatment, culture medium was removed, the cell monolayer was incubated for 30 min with calcein-AM (green, live cells) and propidium iodide (red, dead cells) in control medium, the fluorochrome-containing medium was removed and replaced with control medium and cell density and viability were examined by fluorescence and light microscopy. Extensive cell loss (>90%) was observed in rat neuronal and SY5Y neuroblastoma cell cultures treated with 10 microM HN2, whereas cell loss was similar to controls in comparably treated astrocyte cultures. The DNA from HN2-treated cultures of rat neurons and SY5Y neuroblastoma cells was examined by high-performance liquid chromatography with electrochemical detection for the major HN2 DNA adduct N-(2-hydroxyethyl)-N[2-(7-guaninyl)ethyl]methylamine (GMOH). GMOH was detected in rat neuronal (85 fmol microg(-1) DNA) and SY5Y neuroblastoma cell cultures (46 fmol microg(-1) DNA) treated with 10 microM HN2 for 24 h, but was not detected in comparably treated astrocyte cell cultures. These findings are consistent with HN2 preferentially targeting neurons in vivo, possibly through a mechanism involving DNA damage.

Animals↗
PubMed1999

Damage and repair of nerve cell DNA in toxic stress.

It is generally agreed that ALS/PDC is triggered by a disappearing environmental factor peculiar to the lifestyle of people of the western Pacific (i.e., Guam, Irian Jaya, Indonesia, and the Kii Peninsula of Japan). A strong candidate is the cycad plant genotoxin cycasin, the beta-D-glucoside of methylazoxymethanol (MAM). We propose that prenatal or postnatal exposure to low levels of cycasin/MAM may damage neuronal DNA, compromise DNA repair, perturb neuronal gene expression, and irreversibly alter cell function to precipitate a slowly evolving disease ("slow-toxin" hypothesis). In support of our hypothesis, we have demonstrated the following: 1. DNA from postmitotic rodent central nervous system neurons is particularly sensitive to damage by MAM. 2. MAM reduces DNA repair in human and rodent neurons, whereas DNA-repair inhibitors potentiate MAM-induced DNA damage and toxicity in mature rodent nervous tissue. 3. Human neurons (SY5Y neuroblastoma) that are deficient in DNA repair are susceptible to MAM-induced cytotoxicity and DNA damage, whereas overexpression of DNA repair in similar cells is protective. 4. MAM alters gene expression in SY5Y human neuroblastoma cells and, in the presence of DNA damage and reduced DNA repair, enhances glutamate-modulated expression of tau mRNA in rat primary neurons; the corresponding protein (TAU) is elevated in ALS/PDC and Alzheimer's disease. These findings support a direct relationship between MAM-induced DNA damage and neurotoxicity and suggest the genotoxin may operate in a similar manner in vivo. More broadly, a combination of genotoxin-induced DNA damage (via exogenous and/or endogenous agents) and disturbed DNA repair may be important contributing factors in the slow and progressive degeneration of neurons that is characteristic of sporadic neurodegenerative disease. Preliminary studies demonstrate that DNA repair is reduced in the brain of subjects with western Pacific ALS/PDC, ALS, and Alzheimer's disease, which would increase the susceptibility of brain tissue to DNA damage by endogenous/exogenous genotoxins. Interindividual differences in the extent of prior exposure to DNA-damaging agents and/or the efficiency of its repair might produce population variety in the rate of damage accumulation and explain the susceptibility of certain individuals to sporadic neurodegenerative disease. Studies are underway using DNA-repair proficient and deficient neuronal cell cultures and mutant mice to explore gene-environment interplay with respect to MAM treatment, DNA damage, and DNA repair, and the age-related appearance of neurobehavioral and neuropathological compromise.

Animals↗
PubMed1998

Na+-dependent and phlorizin-inhibitable transport of glucose and cycasin in brain endothelial cells.

Although cycasin (methylazoxymethanol beta-D-glucoside) is proposed to be a significant etiological factor for the prototypical neurodegenerative disorder Western Pacific amyotrophic lateral sclerosis and parkinsonism-dementia complex, the mechanism underlying transport of cycasin across the blood-brain barrier (BBB) is unknown. We examined cycasin transport in cultured bovine brain endothelial cells, a major element of the BBB. Cycasin was taken up into endothelial cells in a dose-dependent manner with maximal uptake observed at a concentration of 10 microM. Cycasin uptake was significantly inhibited by alpha-methyl-D-glucoside, a specific analogue for the Na+-dependent glucose transporter (SGLT), by the SGLT inhibitor phlorizin, by replacement of extracellular NaCl with LiCl, and by dinitrophenol (DNP), an inhibitor of energy metabolism. In addition, cycasin produced inward currents in a whole-cell voltage clamp configuration. Peak currents were observed at 10 microM with a trend toward reduction at higher concentrations, and currents were clearly blocked by alpha-methyl-D-glucoside, phlorizin, and DNP. In addition, cycasin never evoked currents in Na+-free extracellular solution. These results suggest that cycasin is selectively transported across brain endothelial cells, possibly across the BBB by a Na+/energy-dependent glucose transporter.

Animals↗
PubMed1997

Evidence of reduced DNA repair in amyotrophic lateral sclerosis brain tissue.

Oxidative stress is proposed to play a central role in the pathogenesis of amyotrophic lateral sclerosis (ALS). Anti-oxidant enzymes and DNA repair proteins are two major mechanisms by which cells counteract the deleterious effects of reactive oxygen species (ROS). Neurons may be particularly vulnerable to ROS-induced oxidative DNA damage; this is repaired by the base-excision repair (BER) pathway. Frontal cortical levels and activity of the pivotal BER protein apurinic/apyrimidinic endonuclease (APE) were determined in 11 patients with sporadic ALS and six age-matched control subjects. APE levels (p < 0.003) and activity (p < 0.000007) were significantly lower in ALS subjects than in controls. These findings suggest that ALS brain tissue is inefficient in repairing oxidative DNA damage.

Aged↗
PubMed1996

Potential role of environmental genotoxic agents in diabetes mellitus and neurodegenerative diseases.

Epidemiological data suggest that environmental genotoxins are risk factors for some forms of diabetes mellitus and neurodegenerative diseases. The present commentary focuses on mechanisms involved in genotoxin-induced pancreatic beta-cell and neuronal damage. These two cell types seem to share a similar vulnerability to different forms of DNA damage, and the long-term consequences of repeated genotoxic insults to post-mitotic neurons or slowly proliferating beta-cells remain to be clarified. One intriguing possibility is that genotoxins could act as "slow" toxins in these cells, triggering a cascade of cellular events, which culminates in progressive cell dysfunction and loss. Indeed, exposure to mutagenic nitroso agents such as streptozotocin and cycasin induces long-lasting damage to both beta -cells and neurons. These data on cycasin, a toxin obtained from the cycad plant (Cycas spp.), are of special interest, since this agent may be implicated in both amyotrophic lateral sclerosis/Parkinson dementia complex and diabetes mellitus in the western Pacific area. Future studies are required to sort out the interactions between different genotoxic agents, viral infections, and cellular repair mechanisms on cellular survival and function. Moreover, further epidemiological studies are needed to clarify the role of N-nitrosoureas in diabetes mellitus and neurodegenerative diseases in populations with different genetic backgrounds. Answers to these questions may provide useful information on the pathogenesis of these devastating diseases, and open the possibility for their primary prevention.

Diabetes Mellitus↗
PubMed1995

Cycad toxin-induced damage of rodent and human pancreatic beta-cells.

Environmental toxins may be risk factors for some forms of diabetes mellitus and neurodegenerative diseases. The medicinal and food use of seed from the cycad plant (Cycas spp.), which contains the genotoxin cycasin, is a proposed etiological factor for amyotrophic lateral sclerosis/Parkinsonism-dementia complex (ALS/PDC), a prototypical neurodegenerative disease found in the western Pacific. Patients with ALS/PDC have a very high prevalence of glucose intolerance and diabetes mellitus (in the range of 50-80%). We investigated whether the cycad plant toxin cycasin (methylazoxymethanol (MAM) beta-D-glucoside) or the aglycone MAM are toxic in vitro to mouse or human pancreatic islets of Langerhans. Mouse pancreatic islets treated for 6 days with cycasin impaired the beta-cell insulin response to glucose, but this effect was reversible after a further 4 days in culture without the toxin. When mouse islets were exposed for 24 hr to MAM/MAM acetate (MAMOAc; 0.1-1.0 mM), there was a dose-dependent impairment in insulin release and glucose metabolism, and a significant decrease in islet insulin and DNA content. At higher MAM/MAMOAc concentrations (1.0 mM), widespread islet cell destruction was observed. Glucose-induced insulin release remained impaired even after removal of MAM and a further culturing for 4 days without the toxin. MAM damages islets by two possible mechanisms: (a) nitric oxide generation, as judged by increased medium nitrite accumulation; and (b) DNA alkylation, as judged by increased levels of O6-methyldeoxyguanosine in cellular DNA. Incubation of mouse islets with hemin (10 or 100 microM), a nitric oxide scavenger, or nicotinamide (5-20 mM) protected beta-cells from a decrease in glucose oxidation by MAM. In separate studies, a 24 hr treatment of human beta-islet cells with MAMOAc (1.0 mM) produced a significant decrease in both insulin content and release in response to glucose. In conclusion, the present data indicate that cycasin and its aglycone MAM impair both rodent and human beta-cell function which may lead to the death of pancreatic islet cells. These data suggest that a "slow toxin" may be a common aetiological factor for both diabetes mellitus and neurodegenerative disease.

Alkylating Agents↗
PubMed1994

Transport of cycasin by the intestinal Na+/glucose cotransporter.

The medicinal and food use of seed from the cycad plant (Cycas spp.), which contains the neurotoxin cycasin, is a proposed etiological factor for amyotrophic lateral sclerosis/Parkinsonism dementia complex (ALS/PDC), a prototypical neurodegenerative disease found in the western Pacific. Cycasin, the beta-D-glucoside of methylazoxymethanol might enter neurons and other cells via a glucose transporter. Since the intestinal brush-border Na+/glucose cotransporter plays a major role in the absorption of monosaccharides, the following studies were conducted to determine if cycasin, the beta-D-glucoside of methylazoxymethanol, is a substrate for the transporter. We measured the ability of cycasin to (i) inhibit Na+/glucose uptake into rabbit intestinal brush-border membrane vesicles, and (ii) to generate current by the cloned Na+/glucose cotransporter (SGLT1) expressed in Xenopus laevis oocytes. The results show that cycasin inhibits Na(+)-dependent sugar transport in the vesicles, and cycasin generates phlorizin-sensitive currents in oocytes. We conclude that cycasin is a substrate for the intestinal brush-border Na+/glucose cotransporter, albeit with a lower affinity than D-glucose. This suggests that cycasin may be absorbed from the gut lumen by the cotransporter, and as a result either cycasin or the aglycone is presented to the blood-brain barrier for uptake into the brain.

Animals↗
PubMed1993

Neurologic diseases associated with use of plant components with toxic potential.

Epidemics of neurotoxic disease in developing regions of the world are often associated with dietary dependence on plant components with inherent toxic potential or which have spoiled and become contaminated with mycotoxins. Diseases triggered by plant toxins include lathyrism and cassavism, types of irreversible spastic parapareses associated with staple diets of grass pea and bitter cassava root, respectively. Mildewed sugarcane poisoning, an encephalopathy and tardive dystonia, illustrates the neurotoxic effects of a widely distributed plant and fungal toxin. Food and medicinal use of the neurotoxic cycad plant is thought to have a role in the etiology of western Pacific amyotrophic lateral sclerosis and parkinsonism-dementia. Plant-associated neurotoxicity is a significant and preventable cause of morbidity in certain regions of Africa, Asia, and Oceania.

Humans↗
PubMed1992

Are human neurodegenerative disorders linked to environmental chemicals with excitotoxic properties?

At the present time, it seems unlikely that progressive neurodegenerative diseases, such as ALS, Parkinson's disease, and dementia of the Alzheimer type, are triggered by environmental agents with excitotoxic potential. These include excitotoxic agents that behave as glutamate agonists or disrupt energy metabolism: both types elicit permanent but self-limiting neuronal diseases with patterns of neuronal deficit that reflect selective chemical exposure (MPP+ and parkinsonism), differential susceptibility to energy dysmetabolism (NPA and dystonia), or the distribution of glutamate-receptors (domoic acid and memory loss). If environmental agents play an etiologic role in progressive neurodegenerative diseases, they are likely to target a critical, irreplaceable neuronal molecule that is required to maintain long-term neuronal integrity.

Alzheimer Disease↗
PubMed1992

Content of the neurotoxins cycasin (methylazoxymethanol beta-D-glucoside) and BMAA (beta-N-methylamino-L-alanine) in cycad flour prepared by Guam Chamorros.

Exposure to cycad seed kernel is an etiologic factor for the western Pacific amyotrophic lateral sclerosis (ALS) and parkinsonism-dementia complex (PDC). Traditionally processed cycad flours (n = 17) obtained from Chamorro residents of Guam and the adjacent island of Rota at risk for neurodegenerative disease were extracted and analyzed by high-performance liquid chromatography for content of beta-N-methylamino-L-alanine (BMAA) and methyl-azoxymethanol beta-D-glucoside (cycasin). Cycasin (detection limit: picomole) was present in concentrations of 0.004 to 75.93 micrograms/g (mean, 12.45 +/- 5.0 micrograms/g), and levels of BMAA (detection limit: subpicomole) ranged from 0.00 to 18.39 micrograms/g (mean, 5.44 +/- 1.56 micrograms/g). On average, cycasin content was approximately 10 times higher than that of BMAA. The largest concentrations of cycasin were found in samples from villages with a high reported prevalence of ALS/PDC. Ingestion of cycad-derived food would result in estimated human exposure to milligram amounts of cycasin per day. The cytotoxic properties of cycasin merit consideration in relation to the etiology of western Pacific ALS/PDC.

Amino Acids, Diamino↗
PubMed1991

Slow toxins, biologic markers, and long-latency neurodegenerative disease in the western Pacific region.

The western Pacific parkinsonism-dementia and amyotrophic lateral sclerosis complex is a prototypical neurodegenerative disorder found among inhabitants of Guam, New Guinea (Irian Jaya, Indonesia) and Japan (Kii Peninsula, Honshu). Nonviral environmental factors peculiar to the affected populations seem to play a prominent etiologic role. Although cause-effect relationships cannot be established by epidemiologic studies alone, we have shown in all three affected population groups that individuals develop the amyotrophic lateral sclerosis variant of this disorder after heavy exposure to the raw or incompletely detoxified seed of neurotoxic cycad plants. Since long periods may elapse between cycad exposure and the appearance of neurological disease in humans, cycads may harbor a "slow toxin" that causes the postmitotic neuron to undergo slow irreversible degeneration. Two cycad neurotoxins are recognized, one of which (cycasin) is known to have long-latency effects (tumorigenesis) on mitotic neurons and replicating cells in other tissues. This paper explores the possible relationship between tumorigenesis and long-latency neurotoxicity, and discusses possible biologic markers of cycad exposure and subclinical neurodegenerative disease.

Biomarkers↗
PubMed1991

Long-latency neurodegenerative disease in the western Pacific.

The western Pacific parkinsonism-dementia and amyotrophic lateral sclerosis complex is a prototypical neurodegenerative disorder found among inhabitants of Guam, New Guinea (Irian Jaya, Indonesia) and Japan (Kii Peninsula, Honshu). Nonviral environmental factors peculiar to the affected populations seem to play a prominent etiologic role. Although cause-effect relationships cannot be established by epidemiologic studies alone, we have shown in all three affected population groups that individuals develop the amyotrophic lateral sclerosis variant of this disorder after heavy exposure to the raw or incompletely detoxified seed of neurotoxic cycad plants. Since long periods may elapse between cycad exposure and the appearance of neurological disease in humans, cycads may harbor a "slow toxin" that causes the postmitotic neuron to undergo slow irreversible degeneration. Two cycad neurotoxins are recognized, one of which (cycasin) is known to have long-latency effects (tumorigenesis) on mitotic neurons and replicating cells in other tissues. This paper explores the possible relationship between tumorigenesis and long-latency neurotoxicity, and discusses possible biologic markers of cycad exposure and subclinical neurodegenerative disease.

Biomarkers↗