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Does the clock make the poison? Circadian variation in response to pesticides.

Hooven LA, Sherman KA, Butcher S, Giebultowicz JM - PLoS ONE (2009)

Bottom Line: Circadian clocks govern daily physiological and molecular rhythms, and putative rhythms in expression of xenobiotic metabolizing (XM) genes have been described in both insects and mammals.Peak expression of several XM genes cluster in late afternoon.Expression and activities of specific XM enzymes fluctuate during the day, and for specific insecticides, the concentration resulting in 50% mortality varies significantly during the day.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, Oregon State University, Corvallis, Oregon, United States of America. hoovenl@onid.orst.edu

ABSTRACT

Background: Circadian clocks govern daily physiological and molecular rhythms, and putative rhythms in expression of xenobiotic metabolizing (XM) genes have been described in both insects and mammals. Such rhythms could have important consequences for outcomes of chemical exposures at different times of day. To determine whether reported XM gene expression rhythms result in functional rhythms, we examined daily profiles of enzyme activity and dose responses to the pesticides propoxur, deltamethrin, fipronil, and malathion.

Methodology/principal findings: Published microarray expression data were examined for temporal patterns. Male Drosophila were collected for ethoxycoumarin-O-deethylase (ECOD), esterase, glutathione-S-transferase (GST), and, and uridine 5'-diphosphoglucosyltransferase (UGT) enzyme activity assays, or subjected to dose-response tests at four hour intervals throughout the day in both light/dark and constant light conditions. Peak expression of several XM genes cluster in late afternoon. Significant diurnal variation was observed in ECOD and UGT enzyme activity, however, no significant daily variation was observed in esterase or GST activity. Daily profiles of susceptibility to lethality after acute exposure to propoxur and fipronil showed significantly increased resistance in midday, while susceptibility to deltamethrin and malathion varied little. In constant light, which interferes with clock function, the daily variation in susceptibility to propoxur and in ECOD and UGT enzyme activity was depressed.

Conclusions/significance: Expression and activities of specific XM enzymes fluctuate during the day, and for specific insecticides, the concentration resulting in 50% mortality varies significantly during the day. Time of day of chemical exposure should be an important consideration in experimental design, use of pesticides, and human risk assessment.

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Related in: MedlinePlus

Diurnal variation in enzyme activity in LD conditions.(A) The diurnal profile of ECOD activity showed a significant difference (p = 0.013) in mean activity between the peak at ZT4 and the minimum at ZT12, a difference of 75 pmol 7HC/min/abdomen. (B) The diurnal profile of UGT activity showed a significant difference in means (p = 0.03). A peak in this activity was observed at ZT20 which was significantly different that at ZT16 (p = 0.05), a nearly two-fold difference of 366 nM 4MU/min/mg/ml. (C) The diurnal profile of esterase activity did not show any significant difference between means. (D) The diurnal profile of GST activity did not reveal any significant differences between means. All data are means of 3 biological replicates, with error bars representing SEM.
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pone-0006469-g002: Diurnal variation in enzyme activity in LD conditions.(A) The diurnal profile of ECOD activity showed a significant difference (p = 0.013) in mean activity between the peak at ZT4 and the minimum at ZT12, a difference of 75 pmol 7HC/min/abdomen. (B) The diurnal profile of UGT activity showed a significant difference in means (p = 0.03). A peak in this activity was observed at ZT20 which was significantly different that at ZT16 (p = 0.05), a nearly two-fold difference of 366 nM 4MU/min/mg/ml. (C) The diurnal profile of esterase activity did not show any significant difference between means. (D) The diurnal profile of GST activity did not reveal any significant differences between means. All data are means of 3 biological replicates, with error bars representing SEM.

Mentions: To examine whether reported expression rhythms in xenobiotic metabolizing genes lead to functional rhythms in enzyme activity, cytochrome P450, esterase, GST, and UGT enzyme activity were assayed (Figure 2). This experiment revealed a significant daily rhythm in P450 activity in unchallenged males. ECOD activity was significantly higher in mid-day than during early night: the mean value at ZT4 was 160% of the value observed at ZT12 (Figure 2A). UGT activity was also significantly rhythmic with nearly two-fold difference between peak enzyme activity at ZT20, and minimum activity at ZT16 (Figure 2B). No significant daily rhythm was observed in the daily profile of esterase activity (Figure 2C) or GST activity (Figure 2D).


Does the clock make the poison? Circadian variation in response to pesticides.

Hooven LA, Sherman KA, Butcher S, Giebultowicz JM - PLoS ONE (2009)

Diurnal variation in enzyme activity in LD conditions.(A) The diurnal profile of ECOD activity showed a significant difference (p = 0.013) in mean activity between the peak at ZT4 and the minimum at ZT12, a difference of 75 pmol 7HC/min/abdomen. (B) The diurnal profile of UGT activity showed a significant difference in means (p = 0.03). A peak in this activity was observed at ZT20 which was significantly different that at ZT16 (p = 0.05), a nearly two-fold difference of 366 nM 4MU/min/mg/ml. (C) The diurnal profile of esterase activity did not show any significant difference between means. (D) The diurnal profile of GST activity did not reveal any significant differences between means. All data are means of 3 biological replicates, with error bars representing SEM.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2714471&req=5

pone-0006469-g002: Diurnal variation in enzyme activity in LD conditions.(A) The diurnal profile of ECOD activity showed a significant difference (p = 0.013) in mean activity between the peak at ZT4 and the minimum at ZT12, a difference of 75 pmol 7HC/min/abdomen. (B) The diurnal profile of UGT activity showed a significant difference in means (p = 0.03). A peak in this activity was observed at ZT20 which was significantly different that at ZT16 (p = 0.05), a nearly two-fold difference of 366 nM 4MU/min/mg/ml. (C) The diurnal profile of esterase activity did not show any significant difference between means. (D) The diurnal profile of GST activity did not reveal any significant differences between means. All data are means of 3 biological replicates, with error bars representing SEM.
Mentions: To examine whether reported expression rhythms in xenobiotic metabolizing genes lead to functional rhythms in enzyme activity, cytochrome P450, esterase, GST, and UGT enzyme activity were assayed (Figure 2). This experiment revealed a significant daily rhythm in P450 activity in unchallenged males. ECOD activity was significantly higher in mid-day than during early night: the mean value at ZT4 was 160% of the value observed at ZT12 (Figure 2A). UGT activity was also significantly rhythmic with nearly two-fold difference between peak enzyme activity at ZT20, and minimum activity at ZT16 (Figure 2B). No significant daily rhythm was observed in the daily profile of esterase activity (Figure 2C) or GST activity (Figure 2D).

Bottom Line: Circadian clocks govern daily physiological and molecular rhythms, and putative rhythms in expression of xenobiotic metabolizing (XM) genes have been described in both insects and mammals.Peak expression of several XM genes cluster in late afternoon.Expression and activities of specific XM enzymes fluctuate during the day, and for specific insecticides, the concentration resulting in 50% mortality varies significantly during the day.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, Oregon State University, Corvallis, Oregon, United States of America. hoovenl@onid.orst.edu

ABSTRACT

Background: Circadian clocks govern daily physiological and molecular rhythms, and putative rhythms in expression of xenobiotic metabolizing (XM) genes have been described in both insects and mammals. Such rhythms could have important consequences for outcomes of chemical exposures at different times of day. To determine whether reported XM gene expression rhythms result in functional rhythms, we examined daily profiles of enzyme activity and dose responses to the pesticides propoxur, deltamethrin, fipronil, and malathion.

Methodology/principal findings: Published microarray expression data were examined for temporal patterns. Male Drosophila were collected for ethoxycoumarin-O-deethylase (ECOD), esterase, glutathione-S-transferase (GST), and, and uridine 5'-diphosphoglucosyltransferase (UGT) enzyme activity assays, or subjected to dose-response tests at four hour intervals throughout the day in both light/dark and constant light conditions. Peak expression of several XM genes cluster in late afternoon. Significant diurnal variation was observed in ECOD and UGT enzyme activity, however, no significant daily variation was observed in esterase or GST activity. Daily profiles of susceptibility to lethality after acute exposure to propoxur and fipronil showed significantly increased resistance in midday, while susceptibility to deltamethrin and malathion varied little. In constant light, which interferes with clock function, the daily variation in susceptibility to propoxur and in ECOD and UGT enzyme activity was depressed.

Conclusions/significance: Expression and activities of specific XM enzymes fluctuate during the day, and for specific insecticides, the concentration resulting in 50% mortality varies significantly during the day. Time of day of chemical exposure should be an important consideration in experimental design, use of pesticides, and human risk assessment.

Show MeSH
Related in: MedlinePlus