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Application of a mathematical model to describe the effects of chlorpyrifos on Caenorhabditis elegans development.

Boyd WA, Smith MV, Kissling GE, Rice JR, Snyder DW, Portier CJ, Freedman JH - PLoS ONE (2009)

Bottom Line: Concentration response curves with respect to several model-estimated quantities (numbers of measured nematodes, mean log(TOF) and log(EXT), growth rates, and time to reach change points) showed a significant decrease in C. elegans growth with increasing chlorpyrifos concentration.Statistical tests confirmed a significant concentration effect on several model endpoints.The most noticeable effect on growth occurred during early larval stages: L2 and L3.

View Article: PubMed Central - PubMed

Affiliation: Biomoleclular Screening Branch, National Toxicology Program, Research Triangle Park, North Carolina, USA.

ABSTRACT

Background: The nematode Caenorhabditis elegans is being assessed as an alternative model organism as part of an interagency effort to develop better means to test potentially toxic substances. As part of this effort, assays that use the COPAS Biosort flow sorting technology to record optical measurements (time of flight (TOF) and extinction (EXT)) of individual nematodes under various chemical exposure conditions are being developed. A mathematical model has been created that uses Biosort data to quantitatively and qualitatively describe C. elegans growth, and link changes in growth rates to biological events. Chlorpyrifos, an organophosphate pesticide known to cause developmental delays and malformations in mammals, was used as a model toxicant to test the applicability of the growth model for in vivo toxicological testing.

Methodology/principal findings: L1 larval nematodes were exposed to a range of sub-lethal chlorpyrifos concentrations (0-75 microM) and measured every 12 h. In the absence of toxicant, C. elegans matured from L1s to gravid adults by 60 h. A mathematical model was used to estimate nematode size distributions at various times. Mathematical modeling of the distributions allowed the number of measured nematodes and log(EXT) and log(TOF) growth rates to be estimated. The model revealed three distinct growth phases. The points at which estimated growth rates changed (change points) were constant across the ten chlorpyrifos concentrations. Concentration response curves with respect to several model-estimated quantities (numbers of measured nematodes, mean log(TOF) and log(EXT), growth rates, and time to reach change points) showed a significant decrease in C. elegans growth with increasing chlorpyrifos concentration.

Conclusions: Effects of chlorpyrifos on C. elegans growth and development were mathematically modeled. Statistical tests confirmed a significant concentration effect on several model endpoints. This confirmed that chlorpyrifos affects C. elegans development in a concentration dependent manner. The most noticeable effect on growth occurred during early larval stages: L2 and L3. This study supports the utility of the C. elegans growth assay and mathematical modeling in determining the effects of potentially toxic substances in an alternative model organism using high-throughput technologies.

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Effect of chlorpyrifos on the estimated times to change points.Regression lines correspond to the time required for the C. elegans cohort to develop to the first (dotted line) or the second (solid line) change point for log(EXT) (red) and log(TOF) (blue) values. For the first change point, log(EXT) and log(TOF) times at lower chlorpyrifos concentrations (0.5 and 0.75 µM) are indistinguishable from control nematodes while, at higher concentrations, log(EXT) was more affected than log(TOF). In contrast, the difference in time to reach the second change point between log(TOF) and log(EXT) is 17 h, regardless of chlorpyrifos concentration.
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pone-0007024-g006: Effect of chlorpyrifos on the estimated times to change points.Regression lines correspond to the time required for the C. elegans cohort to develop to the first (dotted line) or the second (solid line) change point for log(EXT) (red) and log(TOF) (blue) values. For the first change point, log(EXT) and log(TOF) times at lower chlorpyrifos concentrations (0.5 and 0.75 µM) are indistinguishable from control nematodes while, at higher concentrations, log(EXT) was more affected than log(TOF). In contrast, the difference in time to reach the second change point between log(TOF) and log(EXT) is 17 h, regardless of chlorpyrifos concentration.

Mentions: The expected length of time needed for a nematode to reach each change point was computed from the estimated growth rates (Fig. 6), and then straight lines were fit as functions of concentration. The final models for both change points were chosen using the Akaike information criterion [22]. The expected time for L1s to develop and reach the first change point was similar in the controls for both log(EXT) and log(TOF), approximately 10 h, and increased significantly with chlorpyrifos concentration. Expected length of time to reach the first change point, based on optical density (log(EXT)), was somewhat more affected by increasing chlorpyrifos concentration than that based on nematode length (log(TOF)), as indicated by the steeper slope (Fig. 6). These results are consistent with the visual observations that chlorpyrifos-exposed nematodes appeared to be starved and thinner than controls, but not shorter in length (Table 3). The expected length of time for L1s to develop to the second change point also showed a concentration-dependent increase for both log(EXT) and log(TOF). These observations further demonstrate the inhibitory effects of chlorpyrifos on growth. In contrast to the time to reach the first change point, for the second change point there was a consistent 17 h difference between log(TOF) and log(EXT), regardless of chlorpyrifos concentration.


Application of a mathematical model to describe the effects of chlorpyrifos on Caenorhabditis elegans development.

Boyd WA, Smith MV, Kissling GE, Rice JR, Snyder DW, Portier CJ, Freedman JH - PLoS ONE (2009)

Effect of chlorpyrifos on the estimated times to change points.Regression lines correspond to the time required for the C. elegans cohort to develop to the first (dotted line) or the second (solid line) change point for log(EXT) (red) and log(TOF) (blue) values. For the first change point, log(EXT) and log(TOF) times at lower chlorpyrifos concentrations (0.5 and 0.75 µM) are indistinguishable from control nematodes while, at higher concentrations, log(EXT) was more affected than log(TOF). In contrast, the difference in time to reach the second change point between log(TOF) and log(EXT) is 17 h, regardless of chlorpyrifos concentration.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2737145&req=5

pone-0007024-g006: Effect of chlorpyrifos on the estimated times to change points.Regression lines correspond to the time required for the C. elegans cohort to develop to the first (dotted line) or the second (solid line) change point for log(EXT) (red) and log(TOF) (blue) values. For the first change point, log(EXT) and log(TOF) times at lower chlorpyrifos concentrations (0.5 and 0.75 µM) are indistinguishable from control nematodes while, at higher concentrations, log(EXT) was more affected than log(TOF). In contrast, the difference in time to reach the second change point between log(TOF) and log(EXT) is 17 h, regardless of chlorpyrifos concentration.
Mentions: The expected length of time needed for a nematode to reach each change point was computed from the estimated growth rates (Fig. 6), and then straight lines were fit as functions of concentration. The final models for both change points were chosen using the Akaike information criterion [22]. The expected time for L1s to develop and reach the first change point was similar in the controls for both log(EXT) and log(TOF), approximately 10 h, and increased significantly with chlorpyrifos concentration. Expected length of time to reach the first change point, based on optical density (log(EXT)), was somewhat more affected by increasing chlorpyrifos concentration than that based on nematode length (log(TOF)), as indicated by the steeper slope (Fig. 6). These results are consistent with the visual observations that chlorpyrifos-exposed nematodes appeared to be starved and thinner than controls, but not shorter in length (Table 3). The expected length of time for L1s to develop to the second change point also showed a concentration-dependent increase for both log(EXT) and log(TOF). These observations further demonstrate the inhibitory effects of chlorpyrifos on growth. In contrast to the time to reach the first change point, for the second change point there was a consistent 17 h difference between log(TOF) and log(EXT), regardless of chlorpyrifos concentration.

Bottom Line: Concentration response curves with respect to several model-estimated quantities (numbers of measured nematodes, mean log(TOF) and log(EXT), growth rates, and time to reach change points) showed a significant decrease in C. elegans growth with increasing chlorpyrifos concentration.Statistical tests confirmed a significant concentration effect on several model endpoints.The most noticeable effect on growth occurred during early larval stages: L2 and L3.

View Article: PubMed Central - PubMed

Affiliation: Biomoleclular Screening Branch, National Toxicology Program, Research Triangle Park, North Carolina, USA.

ABSTRACT

Background: The nematode Caenorhabditis elegans is being assessed as an alternative model organism as part of an interagency effort to develop better means to test potentially toxic substances. As part of this effort, assays that use the COPAS Biosort flow sorting technology to record optical measurements (time of flight (TOF) and extinction (EXT)) of individual nematodes under various chemical exposure conditions are being developed. A mathematical model has been created that uses Biosort data to quantitatively and qualitatively describe C. elegans growth, and link changes in growth rates to biological events. Chlorpyrifos, an organophosphate pesticide known to cause developmental delays and malformations in mammals, was used as a model toxicant to test the applicability of the growth model for in vivo toxicological testing.

Methodology/principal findings: L1 larval nematodes were exposed to a range of sub-lethal chlorpyrifos concentrations (0-75 microM) and measured every 12 h. In the absence of toxicant, C. elegans matured from L1s to gravid adults by 60 h. A mathematical model was used to estimate nematode size distributions at various times. Mathematical modeling of the distributions allowed the number of measured nematodes and log(EXT) and log(TOF) growth rates to be estimated. The model revealed three distinct growth phases. The points at which estimated growth rates changed (change points) were constant across the ten chlorpyrifos concentrations. Concentration response curves with respect to several model-estimated quantities (numbers of measured nematodes, mean log(TOF) and log(EXT), growth rates, and time to reach change points) showed a significant decrease in C. elegans growth with increasing chlorpyrifos concentration.

Conclusions: Effects of chlorpyrifos on C. elegans growth and development were mathematically modeled. Statistical tests confirmed a significant concentration effect on several model endpoints. This confirmed that chlorpyrifos affects C. elegans development in a concentration dependent manner. The most noticeable effect on growth occurred during early larval stages: L2 and L3. This study supports the utility of the C. elegans growth assay and mathematical modeling in determining the effects of potentially toxic substances in an alternative model organism using high-throughput technologies.

Show MeSH
Related in: MedlinePlus