Dieldrin elicits a widespread DNA repair and antioxidative response in mouse brain.
ABSTRACT Dieldrin is an organochlorine pesticide that is toxic for monoaminergic neurons. This study was designed to test the hypothesis that a weak DNA repair response to dieldrin by nigrostriatal dopaminergic (DA) neurons results in depletion of striatal DA. The activity of the mammalian base excision repair enzyme oxyguanosine glycosylase was utilized as the index of DNA repair. Other measures of oxidative stress were also studied, including the regional distribution of lipid peroxidation and superoxide dismutase (SOD) activity. The effects of acute and slow infusion of dieldrin on striatal DA levels were biphasic with a transient initial depression followed by increases beyond normal steady-:state levels. Dieldrin administration caused a global oxidative stress evidenced by increased levels of lipid peroxidation in all brain regions, an effect consistent with its capacity to affect mitochondrial bioenergetics. Dieldrin also elicited strong antioxidative and DNA repair responses across the entire mouse brain. Although mitochondrial SOD was not as increased in midbrain as it was in other regions following a cumulative dose of 24 mg/kg, this response, along with the robust DNA repair response, appeared to be sufficient to protect potentially vulnerable DA neurons from cytotoxicity. However, the long-:term consequences of chronic low-:dose dieldrin exposure remain to be studied, especially in light of the concept of "slow excitotoxicity,'' which postulates that even a mild bioenergetic compromise can over time result in the demise of neurons.
- SourceAvailable from: Nancy Denslow
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- "To identify cell processes impacted by dieldrin in the hypothalamus, sexually mature male LMB were fed a diet that contained 2.95 mg dieldrin/kg feed (measured) during a 2-month subchronic feeding study. It has been acknowledged that long-term consequences of chronic low concentration dieldrin exposure are not well studied (Sava et al., 2007), and this study contributes to a better understanding of how environmental exposures may lead to neuronal damage. In this study, LMB were fed a contaminated diet that would result in dieldrin tissue burdens comparable with levels in LMB found in sites with significant sediment contamination. "
ABSTRACT: Dieldrin is a persistent organochlorine pesticide that induces neurotoxicity in the vertebrate central nervous system and impairs reproductive processes in fish. This study examined the molecular events produced by subchronic dietary exposures to 2.95 mg dieldrin/kg feed in the neuroendocrine brain of largemouth bass, an apex predator. Microarrays, proteomics, and pathway analysis were performed to identify genes, proteins, and cell processes altered in the male hypothalamus. Fifty-four genes were induced, and 220 genes were reduced in steady-state levels (p < 0.001; fold change greater than +/- 1.5). Functional enrichment analysis revealed that the biological gene ontology categories of stress response, nucleotide base excision repair, response to toxin, and metabolic processes were significantly impacted by dieldrin. Using isobaric tagging for relative and absolute quantitation, 90 proteins in the male hypothalamus were statistically evaluated for changes in protein abundance. Several proteins altered by dieldrin are known to be associated with human neurodegenerative diseases, including apolipoprotein E, microtubule-associated tau protein, enolase 1, stathmin 1a, myelin basic protein, and parvalbumin. Proteins altered by dieldrin were involved in oxidative phosphorylation, differentiation, proliferation, and cell survival. This study demonstrates that a subchronic exposure to dieldrin alters the abundance of messenger RNAs and proteins in the hypothalamus that are associated with cell metabolism, cell stability and integrity, stress, and DNA repair.Toxicological Sciences 09/2010; 117(1):190-9. DOI:10.1093/toxsci/kfq192 · 4.48 Impact Factor
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- "Dieldrin has been previously shown to induce DNA repair mechanisms in mammals. Male mice i.p. injected with either 6 or 30 mg/kg dieldrin and treated between 6–72 h showed significant increases in the activity of 8-oxoguanine DNA glycosylase, an enzyme that repairs oxidatively damaged guanosine nucleotides (Sava et al., 2007). In the LMB hypothalamus, there appears to be a dynamic genomic response that includes both processes of DNA damage and repair/regeneration mechanisms. "
ABSTRACT: Exposure to dieldrin induces neurotoxic effects in the vertebrate CNS and disrupts reproductive processes in teleost fish. Reproductive impairment observed in fish by dieldrin is likely the result of multiple effects along the hypothalamic-pituitary-gonadal axis, but the molecular signaling cascades are not well characterized. To better elucidate the mode of action of dieldrin in the hypothalamus, this study measured neurotransmitter levels and examined the transcriptomic response in female largemouth bass (LMB) to an acute treatment of dieldrin. Male and female LMB were injected with either vehicle or 10 mg dieldrin/kg and sacrificed after 7 days. There were no significant changes in dopamine or DOPAC concentrations in the neuroendocrine brain of males and females after treatment but GABA levels in females were moderately increased 20-30% in the hypothalamus and cerebellum. In the female hypothalamus, there were 227 transcripts (p<0.001) identified as being differentially regulated by dieldrin. Functional enrichment analysis revealed transcription, DNA repair, ubiquitin-proteasome pathway, and cell communication, as biological processes over-represented in the microarray analysis. Pathway analysis identified DNA damage, inflammation, regeneration, and Alzheimer's disease as major cell processes and diseases affected by dieldrin. Using multiple bioinformatics approaches, this study demonstrates that the teleostean hypothalamus is a target for dieldrin-induced neurotoxicity and provides mechanistic evidence that dieldrin activates similar cell pathways and biological processes that are also associated with the etiology of human neurological disorders.NeuroToxicology 08/2010; 31(4):356-66. DOI:10.1016/j.neuro.2010.04.008 · 3.05 Impact Factor
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ABSTRACT: Among age-related neurodegenerative diseases, Parkinson's disease (PD) represents the best example for which oxidative stress has been strongly implicated. The etiology of PD remains unknown, yet recent epidemiological studies have linked exposure to environmental agents, including pesticides, with an increased risk of developing the disease. As a result, the environmental hypothesis of PD has developed, which speculates that chemical agents in the environment are capable of producing selective dopaminergic cell death, thus contributing to disease development. The use of environmental agents such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, rotenone, paraquat, dieldrin, and maneb in toxicant-based models of PD has become increasingly popular and provided valuable insight into the neurodegenerative process. Understanding the unique and shared mechanisms by which these environmental agents act as selective dopaminergic toxicants is critical in identifying pathways involved in PD pathogenesis. In this review, we discuss the neurotoxic properties of these compounds with specific focus on the induction of oxidative stress. We highlight landmark studies along with recent advances that support the role of reactive oxygen and reactive nitrogen species from a variety of cellular sources as potent contributors to the neurotoxicity of these environmental agents. Finally, human risk and the implications of these studies in our understanding of PD-related neurodegeneration are discussed.Free Radical Biology and Medicine 07/2008; 44(11):1873-86. DOI:10.1016/j.freeradbiomed.2008.02.008 · 5.71 Impact Factor