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Transcriptional response of rat frontal cortex following acute in vivo exposure to the pyrethroid insecticides permethrin and deltamethrin.

Harrill JA, Li Z, Wright FA, Radio NM, Mundy WR, Tornero-Velez R, Crofton KM - BMC Genomics (2008)

Bottom Line: In the present study, pyrethroids induced changes in gene expression in the frontal cortex near the threshold for decreases in ambulatory motor activity in vivo.Finally, SAFE analysis of gene expression data identified branching morphogenesis as a biological process sensitive to pyrethroids and subsequent in vitro experiments confirmed this predicted effect.The novel findings regarding pyrethroid effects on branching morphogenesis indicate these compounds may act as developmental neurotoxicants that affect normal neuronal morphology.

View Article: PubMed Central - HTML - PubMed

Affiliation: Curriculum in Toxicology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA. harrill.josh@epa.gov

ABSTRACT

Background: Pyrethroids are neurotoxic pesticides that interact with membrane bound ion channels in neurons and disrupt nerve function. The purpose of this study was to characterize and explore changes in gene expression that occur in the rat frontal cortex, an area of CNS affected by pyrethroids, following an acute low-dose exposure.

Results: Rats were acutely exposed to either deltamethrin (0.3 - 3 mg/kg) or permethrin (1 - 100 mg/kg) followed by collection of cortical tissue at 6 hours. The doses used range from those that cause minimal signs of intoxication at the behavioral level to doses well below apparent no effect levels in the whole animal. A statistical framework based on parallel linear (SAM) and isotonic regression (PIR) methods identified 95 and 53 probe sets as dose-responsive. The PIR analysis was most sensitive for detecting transcripts with changes in expression at the NOAEL dose. A sub-set of genes (Camk1g, Ddc, Gpd3, c-fos and Egr1) was then confirmed by qRT-PCR and examined in a time course study. Changes in mRNA levels were typically less than 3-fold in magnitude across all components of the study. The responses observed are consistent with pyrethroids producing increased neuronal excitation in the cortex following a low-dose in vivo exposure. In addition, Significance Analysis of Function and Expression (SAFE) identified significantly enriched gene categories common for both pyrethroids, including some relating to branching morphogenesis. Exposure of primary cortical cell cultures to both compounds resulted in an increase (approximately 25%) in the number of neurite branch points, supporting the results of the SAFE analysis.

Conclusion: In the present study, pyrethroids induced changes in gene expression in the frontal cortex near the threshold for decreases in ambulatory motor activity in vivo. The penalized regression methods performed similarly in detecting dose-dependent changes in gene transcription. Finally, SAFE analysis of gene expression data identified branching morphogenesis as a biological process sensitive to pyrethroids and subsequent in vitro experiments confirmed this predicted effect. The novel findings regarding pyrethroid effects on branching morphogenesis indicate these compounds may act as developmental neurotoxicants that affect normal neuronal morphology.

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Dose-response functions identified by PIR and SAM regression methods. Panels A-F plot dose-response functions for probe sets identified by PIR (B & E), SAM (C & F) or both regression methods (A & D) for deltamethrin (A-C) and permethrin (D-F). Only probe sets that had a Benjamini-Hochberg adjusted p-value < 0.05 for a main effect of dose in a one-way ANOVA are shown. For each probe set expression summaries for each treatment group were normalized to vehicle control and plotted as fold-change from control. The color scheme corresponds to that used in Figure 1, with green curves being detected by both PIR and SAM regression methods (A, D), blue curves being detected exclusively with the PIR method (B, E) and orange curves being detected exclusively with the SAM method (C, F). Insets on each panel are the summated results of a Dunnett's many-to-one mean contrast test performed within each probe set comparing the means of the lowest (C-L), middle (C-M) and highest (C-H) doses to the mean of vehicle treated control. y-axis is number of probe sets identified under each comparison at a significance level of p < 0.05. Note the green portion of the stacked bars in the insets are the same values in inset panels A-C and D-E, respectively.
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Figure 2: Dose-response functions identified by PIR and SAM regression methods. Panels A-F plot dose-response functions for probe sets identified by PIR (B & E), SAM (C & F) or both regression methods (A & D) for deltamethrin (A-C) and permethrin (D-F). Only probe sets that had a Benjamini-Hochberg adjusted p-value < 0.05 for a main effect of dose in a one-way ANOVA are shown. For each probe set expression summaries for each treatment group were normalized to vehicle control and plotted as fold-change from control. The color scheme corresponds to that used in Figure 1, with green curves being detected by both PIR and SAM regression methods (A, D), blue curves being detected exclusively with the PIR method (B, E) and orange curves being detected exclusively with the SAM method (C, F). Insets on each panel are the summated results of a Dunnett's many-to-one mean contrast test performed within each probe set comparing the means of the lowest (C-L), middle (C-M) and highest (C-H) doses to the mean of vehicle treated control. y-axis is number of probe sets identified under each comparison at a significance level of p < 0.05. Note the green portion of the stacked bars in the insets are the same values in inset panels A-C and D-E, respectively.

Mentions: The dose-dependent changes in mRNA expression identified with the above analyses are relatively small in magnitude, < 2-fold change from control, and have varying patterns of expression across dose (Figure 2). Post-hoc analysis (Dunnett's mean contrast test) of these dose-response functions indicate that significant alterations in mRNA expression occur at doses below those needed to produce acute behavioral effects (Figure 2, insets). A majority of the probe sets identified as dose-responsive had mean expression values in the 3 mg/kg deltamethrin and 100 mg/kg permethrin dose groups different from those in the vehicle treated control group (78.9% and 77.3%, respectively). Of those probe sets, 25.3% and 19.5% also had mean expression values in the 1 mg/kg deltamethrin and 10 mg/kg permethrin dose groups different from controls. These latter doses are below those needed to produce acute neurotoxic effects on behavior. In addition, these data demonstrate that the PIR analyses detected a greater number of probe sets with mean expression values in the behavioral "NOAEL" dose groups (see Table 1) as being different from control as compared to the SAM analyses (compare Figure 2B &2E, insets to Figure 2C &2F, insets).


Transcriptional response of rat frontal cortex following acute in vivo exposure to the pyrethroid insecticides permethrin and deltamethrin.

Harrill JA, Li Z, Wright FA, Radio NM, Mundy WR, Tornero-Velez R, Crofton KM - BMC Genomics (2008)

Dose-response functions identified by PIR and SAM regression methods. Panels A-F plot dose-response functions for probe sets identified by PIR (B & E), SAM (C & F) or both regression methods (A & D) for deltamethrin (A-C) and permethrin (D-F). Only probe sets that had a Benjamini-Hochberg adjusted p-value < 0.05 for a main effect of dose in a one-way ANOVA are shown. For each probe set expression summaries for each treatment group were normalized to vehicle control and plotted as fold-change from control. The color scheme corresponds to that used in Figure 1, with green curves being detected by both PIR and SAM regression methods (A, D), blue curves being detected exclusively with the PIR method (B, E) and orange curves being detected exclusively with the SAM method (C, F). Insets on each panel are the summated results of a Dunnett's many-to-one mean contrast test performed within each probe set comparing the means of the lowest (C-L), middle (C-M) and highest (C-H) doses to the mean of vehicle treated control. y-axis is number of probe sets identified under each comparison at a significance level of p < 0.05. Note the green portion of the stacked bars in the insets are the same values in inset panels A-C and D-E, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2626604&req=5

Figure 2: Dose-response functions identified by PIR and SAM regression methods. Panels A-F plot dose-response functions for probe sets identified by PIR (B & E), SAM (C & F) or both regression methods (A & D) for deltamethrin (A-C) and permethrin (D-F). Only probe sets that had a Benjamini-Hochberg adjusted p-value < 0.05 for a main effect of dose in a one-way ANOVA are shown. For each probe set expression summaries for each treatment group were normalized to vehicle control and plotted as fold-change from control. The color scheme corresponds to that used in Figure 1, with green curves being detected by both PIR and SAM regression methods (A, D), blue curves being detected exclusively with the PIR method (B, E) and orange curves being detected exclusively with the SAM method (C, F). Insets on each panel are the summated results of a Dunnett's many-to-one mean contrast test performed within each probe set comparing the means of the lowest (C-L), middle (C-M) and highest (C-H) doses to the mean of vehicle treated control. y-axis is number of probe sets identified under each comparison at a significance level of p < 0.05. Note the green portion of the stacked bars in the insets are the same values in inset panels A-C and D-E, respectively.
Mentions: The dose-dependent changes in mRNA expression identified with the above analyses are relatively small in magnitude, < 2-fold change from control, and have varying patterns of expression across dose (Figure 2). Post-hoc analysis (Dunnett's mean contrast test) of these dose-response functions indicate that significant alterations in mRNA expression occur at doses below those needed to produce acute behavioral effects (Figure 2, insets). A majority of the probe sets identified as dose-responsive had mean expression values in the 3 mg/kg deltamethrin and 100 mg/kg permethrin dose groups different from those in the vehicle treated control group (78.9% and 77.3%, respectively). Of those probe sets, 25.3% and 19.5% also had mean expression values in the 1 mg/kg deltamethrin and 10 mg/kg permethrin dose groups different from controls. These latter doses are below those needed to produce acute neurotoxic effects on behavior. In addition, these data demonstrate that the PIR analyses detected a greater number of probe sets with mean expression values in the behavioral "NOAEL" dose groups (see Table 1) as being different from control as compared to the SAM analyses (compare Figure 2B &2E, insets to Figure 2C &2F, insets).

Bottom Line: In the present study, pyrethroids induced changes in gene expression in the frontal cortex near the threshold for decreases in ambulatory motor activity in vivo.Finally, SAFE analysis of gene expression data identified branching morphogenesis as a biological process sensitive to pyrethroids and subsequent in vitro experiments confirmed this predicted effect.The novel findings regarding pyrethroid effects on branching morphogenesis indicate these compounds may act as developmental neurotoxicants that affect normal neuronal morphology.

View Article: PubMed Central - HTML - PubMed

Affiliation: Curriculum in Toxicology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA. harrill.josh@epa.gov

ABSTRACT

Background: Pyrethroids are neurotoxic pesticides that interact with membrane bound ion channels in neurons and disrupt nerve function. The purpose of this study was to characterize and explore changes in gene expression that occur in the rat frontal cortex, an area of CNS affected by pyrethroids, following an acute low-dose exposure.

Results: Rats were acutely exposed to either deltamethrin (0.3 - 3 mg/kg) or permethrin (1 - 100 mg/kg) followed by collection of cortical tissue at 6 hours. The doses used range from those that cause minimal signs of intoxication at the behavioral level to doses well below apparent no effect levels in the whole animal. A statistical framework based on parallel linear (SAM) and isotonic regression (PIR) methods identified 95 and 53 probe sets as dose-responsive. The PIR analysis was most sensitive for detecting transcripts with changes in expression at the NOAEL dose. A sub-set of genes (Camk1g, Ddc, Gpd3, c-fos and Egr1) was then confirmed by qRT-PCR and examined in a time course study. Changes in mRNA levels were typically less than 3-fold in magnitude across all components of the study. The responses observed are consistent with pyrethroids producing increased neuronal excitation in the cortex following a low-dose in vivo exposure. In addition, Significance Analysis of Function and Expression (SAFE) identified significantly enriched gene categories common for both pyrethroids, including some relating to branching morphogenesis. Exposure of primary cortical cell cultures to both compounds resulted in an increase (approximately 25%) in the number of neurite branch points, supporting the results of the SAFE analysis.

Conclusion: In the present study, pyrethroids induced changes in gene expression in the frontal cortex near the threshold for decreases in ambulatory motor activity in vivo. The penalized regression methods performed similarly in detecting dose-dependent changes in gene transcription. Finally, SAFE analysis of gene expression data identified branching morphogenesis as a biological process sensitive to pyrethroids and subsequent in vitro experiments confirmed this predicted effect. The novel findings regarding pyrethroid effects on branching morphogenesis indicate these compounds may act as developmental neurotoxicants that affect normal neuronal morphology.

Show MeSH
Related in: MedlinePlus