Targeting of neurotrophic factors, their receptors, and signaling pathways in the developmental neurotoxicity of organophosphates in vivo and in vitro

Abstract

Neurotrophic factors control neural cell differentiation and assembly of neural circuits. We previously showed that organophosphate pesticides differentially regulate members of the fibroblast growth factor (fgf) gene family. We administered chlorpyrifos and diazinon to neonatal rats on postnatal days 1-4 at doses devoid of systemic toxicity or growth impairment, and spanning the threshold for barely-detectable cholinesterase inhibition. We evaluated the impact on gene families for different classes of neurotrophic factors. Using microarrays, we examined the regional expression of mRNAs encoding the neurotrophins (ntfs), brain-derived neurotrophic factor (bdnf), nerve growth factor (ngf), the wnt and fzd gene families and the corresponding receptors. Chlorpyrifos and diazinon both had widespread effects on the fgf, ntf, wnt and fzd families but much less on the bdnf and ngf groups. However, the two organophosphates showed disparate effects on a number of key neurotrophic factors. To determine if the actions were mediated directly on differentiating neurons, we tested chlorpyrifos in PC12 cells, an in vitro model of neural cell development. Effects in PC12 cells mirrored many of those for members of the fgf, ntf and wnt families, as well as the receptors for the ntfs, especially during early differentiation, the stage known to be most susceptible to disruption by organophosphates. Our results suggest that actions on neurotrophic factors provide a mechanism for the developmental neurotoxicity of low doses of organophosphates, and, since effects on expression of the affected genes differed with test agent, may help explain regional disparities in effects and critical periods of vulnerability.

Chlorpyrifos Induced Region Specific Vulnerability in Rat CNS and Modulation by Age and Cold Stress: An Interactive Study

“…Increased oxidative stress has also been directly linked to oxidation of cellular macromolecules which may cause injury to the CNS or induce a variety of adverse cellular responses. Interference of CPF with normal neurite development through a variety of mechanisms has been reported in the previous studies [17][18][19][20]. Examination of CNS vulnerability under the exposure conditions of cold stress and CPF toxicity and their interaction in different age groups (neonatal, juvenile and young adult rats) exhibited more pronounced alterations in the antioxidant levels along with MDA in neonatal rats followed by juveniles when compared to young adults.…”

Developmental neurotoxicity of succeeding generations of insecticides

“…As for early-postnatal exposure, defined here as the 1 st week of postnatal development in rats, several studies focused on gene transcription related to neuronal differentiation and survival. CPF affects a plethora of neurochemical targets evoking immediate transcriptional changes in genes involved in pathways for brain cell development (neural cell growth, development of glia and myelin, cell adhesion/migration, neural cell differentiation, neurothrophic factors, their receptors and signaling), cytotocicity (apoptosis, oxidative stress, excitotoxicity, mitochondrial dysfunction), cAMP-related cell signaling and development of neurotransmitter synthesis, storage and receptors for ACh, serotonin, norepinephrine and dopamine (Betancourt and others 2006; Ray and others 2010; Slotkin and Seidler 2007; Slotkin and others 2007b; 2008a). The effects are not restricted to the transcription level, as indicated by altered function of a wide variety of neural systems.…”

Developmental exposure to organophosphates triggers transcriptional changes in genes associated with Parkinson's disease in vitro and in vivo

“…Along with the nerve growth factor, we added 30 μM of each of the test agents: chlorpyrifos (Chem Service, West Chester, PA), diazinon (Chem Service), dieldrin (Chem Service) or NiCl 2 (Sigma). The concentration was chosen from earlier studies that demonstrated adverse effects on differentiation of PC12 cells without outright cytotoxicity [17,26,39,46]. Because of the limited water solubility of the three insecticides, these agents were dissolved in dimethylsulfoxide (final concentration 0.1%), which was also added to the control cultures and to cultures containing NiCl 2 ; this concentration of dimethylsulfoxide has no effect on PC12 cell growth or differentiation [26,28,51].…”

“…Despite their similarities as cholinesterase inhibitors, chlorpyrifos and diazinon differ in their propensity to elicit oxidative stress [31,40,41] and therefore could have different effects on PD-related endpoints. For our evaluations, we used PC12 cells, a classical in vitro model for neuronal development [52] that has already been validated to reproduce the mechanisms and outcomes found after in vivo organophosphate exposures [26,27,38,39,41,42,46,47,51]. We evaluated gene expression patterns with cDNA microarrays, using a planned comparisons approach that focused on the relevant PD-related genes, rather than performing a blanket evaluation of the entire transcriptome [40,43,45–47].…”