Dose-related gene expression changes in forebrain following acute, low-level chlorpyrifos exposure in neonatal rats

Abstract

Chlorpyrifos (CPF) is a widely used organophosphorus insecticide (OP) and putative developmental neurotoxicant in humans. The acute toxicity of CPF is elicited by acetylcholinesterase (AChE) inhibition. We characterized dose-related (0.1, 0.5, 1 and 2 mg/kg) gene expression profiles and changes in cell signaling pathways 24 hr following acute CPF exposure in seven day-old rats. Microarray experiments indicated that approximately 9% of the 44,000 genes were differentially expressed following either one of the four CPF dosages studied (546, 505, 522, and 3,066 genes with 0.1, 0.5, 1.0 and 2.0 mg/kg CPF). Genes were grouped according to dose-related expression patterns using K-means clustering while gene networks and canonical pathways were evaluated using Ingenuity Pathway Analysis®. Twenty clusters were identified and differential expression of selected genes was verified by RT-PCR. The four largest clusters (each containing from 276–905 genes) constituted over 50% of all differentially expressed genes and exhibited up-regulation following exposure to the highest dosage (2 mg/kg CPF). The total number of gene networks affected by CPF also rose sharply with the highest dosage of CPF (18, 16, 18 and 50 with 0.1, 0.5, 1 and 2 mg/kg CPF). Forebrain cholinesterase (ChE) activity was significantly reduced (26%) only in the highest dosage group. Based on magnitude of dose-related changes in differentially expressed genes, relative numbers of gene clusters and signaling networks affected, and forebrain ChE inhibition only at 2 mg/kg CPF, we focused subsequent analyses on this treatment group. Six canonical pathways were identified that were significantly affected by 2 mg/kg CPF (MAPK, oxidative stress, NFKB, mitochondrial dysfunction, arylhydrocarbon receptor and adrenergic receptor signaling). Evaluation of different cellular functions of the differentially expressed genes suggested changes related to olfactory receptors, cell adhesion/migration, synapse/synaptic transmission and transcription/translation. Nine genes were differentially affected in all four CPF dosing groups. We conclude that the most robust, consistent changes in differential gene expression in neonatal forebrain across a range of acute CPF dosages occurred at an exposure level associated with the classical marker of OP toxicity, AChE inhibition. Disruption of multiple cellular pathways, in particular cell adhesion, may contribute to the developmental neurotoxicity potential of this pesticide.

A review of experimental evidence linking neurotoxic organophosphorus compounds and inflammation

“…The authors postulate that gestational GFAP elevation is due to astrogliosis, whereas postnatal GFAP deficits are caused by a depression of cell differentiation during periods of glial proliferation. A similar decrease in GFAP expression is observed upon a single exposure of developing rat pups on postnatal day 7 to chlorpyrifos at 2 mg/kg (Ray et al, 2010). This suggests that developing glia are susceptible to the toxic effects of chlorpyrifos, but that the effect of chlorpyrifos on GFAP expression varies not only quantitatively but also qualitatively as a function of the developmental stage at the time of exposure.…”

PROTEOMIC ANALYSIS OF UBIQUITINATED PROTEINS FROM DELTAMETHRIN‐RESISTANT AND SUSCEPTIBLE STRAINS OF THE DIAMONDBACK MOTH, Plutella Xylostella L.

“…Thus, we inferred that the ubiquitin proteasome system acts in DM resistance. Many effects of organophosphorus pesticides are related to interactions between cellular proteins (Ray et al., ). Calore et al.…”

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.…”