56 research outputs found

    The Cycad Genotoxin MAM Modulates Brain Cellular Pathways Involved in Neurodegenerative Disease and Cancer in a DNA Damage-Linked Manner

    Get PDF
    Methylazoxymethanol (MAM), the genotoxic metabolite of the cycad azoxyglucoside cycasin, induces genetic alterations in bacteria, yeast, plants, insects and mammalian cells, but adult nerve cells are thought to be unaffected. We show that the brains of adult C57BL6 wild-type mice treated with a single systemic dose of MAM acetate display DNA damage (O6-methyldeoxyguanosine lesions, O6-mG) that remains constant up to 7 days post-treatment. By contrast, MAM-treated mice lacking a functional gene encoding the DNA repair enzyme O6-mG DNA methyltransferase (MGMT) showed elevated O6-mG DNA damage starting at 48 hours post-treatment. The DNA damage was linked to changes in the expression of genes in cell-signaling pathways associated with cancer, human neurodegenerative disease, and neurodevelopmental disorders. These data are consistent with the established developmental neurotoxic and carcinogenic properties of MAM in rodents. They also support the hypothesis that early-life exposure to MAM-glucoside (cycasin) has an etiological association with a declining, prototypical neurodegenerative disease seen in Guam, Japan, and New Guinea populations that formerly used the neurotoxic cycad plant for food or medicine, or both. These findings suggest environmental genotoxins, specifically MAM, target common pathways involved in neurodegeneration and cancer, the outcome depending on whether the cell can divide (cancer) or not (neurodegeneration). Exposure to MAM-related environmental genotoxins may have relevance to the etiology of related tauopathies, notably, Alzheimer's disease

    Aag DNA Glycosylase Promotes Alkylation-Induced Tissue Damage Mediated by Parp1

    Get PDF
    Alkylating agents comprise a major class of front-line cancer chemotherapeutic compounds, and while these agents effectively kill tumor cells, they also damage healthy tissues. Although base excision repair (BER) is essential in repairing DNA alkylation damage, under certain conditions, initiation of BER can be detrimental. Here we illustrate that the alkyladenine DNA glycosylase (AAG) mediates alkylation-induced tissue damage and whole-animal lethality following exposure to alkylating agents. Aag-dependent tissue damage, as observed in cerebellar granule cells, splenocytes, thymocytes, bone marrow cells, pancreatic β-cells, and retinal photoreceptor cells, was detected in wild-type mice, exacerbated in Aag transgenic mice, and completely suppressed in Aag−/− mice. Additional genetic experiments dissected the effects of modulating both BER and Parp1 on alkylation sensitivity in mice and determined that Aag acts upstream of Parp1 in alkylation-induced tissue damage; in fact, cytotoxicity in WT and Aag transgenic mice was abrogated in the absence of Parp1. These results provide in vivo evidence that Aag-initiated BER may play a critical role in determining the side-effects of alkylating agent chemotherapies and that Parp1 plays a crucial role in Aag-mediated tissue damage.National Institutes of Health (U.S.) (NIH grant R01-CA075576)National Institutes of Health (U.S.) (NIH grant R01-CA055042)National Institutes of Health (U.S.) (NIH grant R01-CA149261)National Institutes of Health (U.S.) (NIH grant P30-ES00002)National Institutes of Health (U.S.) (NIH grant P30-ES02109)National Center for Research Resources (U.S.) (grant number M01RR-01066)National Center for Research Resources (U.S.) (grant number UL1 RR025758, Harvard Clinical and Translational Science Center

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

    No full text
    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.In VitroJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.info:eu-repo/semantics/publishe

    Creative Histories of Witchcraft:France, 1790-1940

    No full text

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

    No full text
    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.Journal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.Reviewinfo:eu-repo/semantics/publishe

    Assessing policy success and failure: targets, aims and processes

    No full text
    Assessing policy success and failure is a significant challenge. This article seeks to address this by utilizing two case studies of legislation from the United Kingdom Parliament, the National Minimum Wage Act 1998 and the Academies Act 2010, so as to develop a nuanced understanding of how and in what ways policies have been successful, or otherwise. Drawing on these two case studies, and the work of a variety of authors, the article illustrates the complex nature of the challenge, but suggests that by identifying “targets”, “aims” and “processes” it is possible to make reasonable judgements about the relative success of a policy. It concludes that this framework therefore has considerable potential utility

    Cigarette smoke induces DNA damage and alters base-excision repair and tau levels in the brain of neonatal mice.

    No full text
    The prenatal and perinatal periods of brain development are especially vulnerable to insults by environmental agents. Early life exposure to cigarette smoke (CS), which contains both genotoxicants and oxidants, is considered an important risk factor for both neurodevelopmental and neurodegenerative disorders. Yet, little is known regarding the underlying pathogenetic mechanisms. In the present study, neonatal Swiss ICR (CD-1) albino mice were exposed to various concentrations of CS for 4 weeks and the brain examined for lipid peroxides, DNA damage, base-excision repair (BER) enzymes, apoptosis, and levels of the microtubule protein tau. CS induced a dose-dependent increase in both malondialdehyde and various types of DNA damage, including single-strand breaks, double-strand breaks, and DNA-protein cross-links. However, the CS-induced DNA damage in the brain returned to basal levels 1 week after smoking cessation. CS also modulated the activity and distribution of the BER enzymes 8-oxoguanine-DNA-glycosylase (OGG1) and apyrimidinic/apurinic endonuclease (APE1) in several brain regions. Normal tau (i.e., three-repeat tau, 3R tau) and various pathological forms of tau were also measured in the brain of CS-exposed neonatal mice, but only 3R tau and tau phosphorylated at serine 199 were significantly elevated. The oxidative stress, genomic dysregulation, and alterations in tau metabolism caused by CS during a critical period of brain development could explain why CS is an important risk factor for both neurodevelopmental and neurodegenerative disorders appearing in later life
    corecore