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Extreme variability in the formation of chlorpyrifos oxon (CPO) in patients poisoned by chlorpyrifos (CPF).

Eyer F, Roberts DM, Buckley NA, Eddleston M, Thiermann H, Worek F, Eyer P - Biochem. Pharmacol. (2009)

Bottom Line: There was a hundred-fold variation in the ratio between samples and the interquartile range (between individuals) indicated over half the samples had a 5-fold or greater variation from the mean.The effectiveness of pralidoxime in reactivating the inhibited acetylcholinesterase is strongly dependent on the CPO concentration.Differences in clinical outcomes and the response to antidotes in patients with acute poisoning may occur due to inter-individual variability in metabolism.

View Article: PubMed Central - PubMed

Affiliation: Toxicological Department of the 2nd Medical Clinic, Technische Universität München, Ismaninger Str. 22, D-81664 Munich, Germany.

ABSTRACT
Chlorpyrifos (CPF) is a pesticide that causes tens of thousands of deaths per year worldwide. Chlorpyrifos oxon (CPO) is the active metabolite of CPF that inhibits acetylcholinesterase. However, this presumed metabolite has escaped detection in human samples by conventional methods (HPLC, GC-MS, LC-MS) until now. A recently developed enzyme-based assay allowed the determination of CPO in the nanomolar range and was successfully employed to detect this metabolite. CPO and CPF were analysed in consecutive plasma samples of 74 patients with intentional CPF poisoning. A wide concentration range of CPO and CPF was observed and the ratio of CPO/CPF varied considerably between individuals and over time. The ratio increased during the course of poisoning from a mean of 0.005 in the first few hours after ingestion up to an apparent steady-state mean of 0.03 between 30 and 72h. There was a hundred-fold variation in the ratio between samples and the interquartile range (between individuals) indicated over half the samples had a 5-fold or greater variation from the mean. The ratio was independent of the CPF concentration and the pralidoxime regimen. CPO was present in sufficient quantities to explain any observed acetylcholinesterase inhibitory activity. The effectiveness of pralidoxime in reactivating the inhibited acetylcholinesterase is strongly dependent on the CPO concentration. Differences in clinical outcomes and the response to antidotes in patients with acute poisoning may occur due to inter-individual variability in metabolism.

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Ratio of found and expected CPO concentrations in 20 patients who were treated with pralidoxime. CPO was calculated from the ratio of active and inhibited, but reactivatable AChE, the measured pralidoxime concentration and the known kinetic constants as indicated in the Section 2. Data are given as median values (n ≥ 3; IQR) of 20 eligible patients during the expected steady-state of AChE inhibition and reactivation. Note the semilogarithmic scale. The dotted line intersecting the Y-axis at 6 corresponds to 85% reversible albumin binding of CPO in plasma, which is pharmacodynamically inactive, but was determined by solvent extraction.
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fig7: Ratio of found and expected CPO concentrations in 20 patients who were treated with pralidoxime. CPO was calculated from the ratio of active and inhibited, but reactivatable AChE, the measured pralidoxime concentration and the known kinetic constants as indicated in the Section 2. Data are given as median values (n ≥ 3; IQR) of 20 eligible patients during the expected steady-state of AChE inhibition and reactivation. Note the semilogarithmic scale. The dotted line intersecting the Y-axis at 6 corresponds to 85% reversible albumin binding of CPO in plasma, which is pharmacodynamically inactive, but was determined by solvent extraction.

Mentions: The mutual dependence of the RBC–AChE activity on the pralidoxime and the CPO concentration was analysed according to the equation given in the Section 2. Forty-four patients who received pralidoxime, were eligible for the analysis contrasting the CPO concentration predicted from the RBC–AChE activity with the measured CPO. We excluded all data where CPO was below 0.5 nM (LOQ), pralidoxime given less than 1 h before sampling and where the pralidoxime concentration was below 13 μM. At this concentration the half-life for reactivation is approximately 1 h [19] and steady-state conditions could not be expected at lower concentrations. The expected free CPO concentration could be calculated from the ratio of inhibited, but reactivatable enzyme and the active enzyme, i.e. [EP + EPOx]/[E]. In doing so, we observed a large scattering of the ratio of CPO found/CPO predicted. Fig. 7 shows a plot of data (from 20 subjects with at least 3 samples that met the above criteria). The ratio of CPO found vs. CPO predicted is given in a logarithmic scale (median, IQR). The predicted CPO concentration is the free (active) fraction. Thus we expected a mean ratio of about 6 (dashed line), corresponding to 85% reversible albumin binding [7] as CPO from plasma was extracted by an organic solvent determining both the bound and free fractions of CPO.


Extreme variability in the formation of chlorpyrifos oxon (CPO) in patients poisoned by chlorpyrifos (CPF).

Eyer F, Roberts DM, Buckley NA, Eddleston M, Thiermann H, Worek F, Eyer P - Biochem. Pharmacol. (2009)

Ratio of found and expected CPO concentrations in 20 patients who were treated with pralidoxime. CPO was calculated from the ratio of active and inhibited, but reactivatable AChE, the measured pralidoxime concentration and the known kinetic constants as indicated in the Section 2. Data are given as median values (n ≥ 3; IQR) of 20 eligible patients during the expected steady-state of AChE inhibition and reactivation. Note the semilogarithmic scale. The dotted line intersecting the Y-axis at 6 corresponds to 85% reversible albumin binding of CPO in plasma, which is pharmacodynamically inactive, but was determined by solvent extraction.
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fig7: Ratio of found and expected CPO concentrations in 20 patients who were treated with pralidoxime. CPO was calculated from the ratio of active and inhibited, but reactivatable AChE, the measured pralidoxime concentration and the known kinetic constants as indicated in the Section 2. Data are given as median values (n ≥ 3; IQR) of 20 eligible patients during the expected steady-state of AChE inhibition and reactivation. Note the semilogarithmic scale. The dotted line intersecting the Y-axis at 6 corresponds to 85% reversible albumin binding of CPO in plasma, which is pharmacodynamically inactive, but was determined by solvent extraction.
Mentions: The mutual dependence of the RBC–AChE activity on the pralidoxime and the CPO concentration was analysed according to the equation given in the Section 2. Forty-four patients who received pralidoxime, were eligible for the analysis contrasting the CPO concentration predicted from the RBC–AChE activity with the measured CPO. We excluded all data where CPO was below 0.5 nM (LOQ), pralidoxime given less than 1 h before sampling and where the pralidoxime concentration was below 13 μM. At this concentration the half-life for reactivation is approximately 1 h [19] and steady-state conditions could not be expected at lower concentrations. The expected free CPO concentration could be calculated from the ratio of inhibited, but reactivatable enzyme and the active enzyme, i.e. [EP + EPOx]/[E]. In doing so, we observed a large scattering of the ratio of CPO found/CPO predicted. Fig. 7 shows a plot of data (from 20 subjects with at least 3 samples that met the above criteria). The ratio of CPO found vs. CPO predicted is given in a logarithmic scale (median, IQR). The predicted CPO concentration is the free (active) fraction. Thus we expected a mean ratio of about 6 (dashed line), corresponding to 85% reversible albumin binding [7] as CPO from plasma was extracted by an organic solvent determining both the bound and free fractions of CPO.

Bottom Line: There was a hundred-fold variation in the ratio between samples and the interquartile range (between individuals) indicated over half the samples had a 5-fold or greater variation from the mean.The effectiveness of pralidoxime in reactivating the inhibited acetylcholinesterase is strongly dependent on the CPO concentration.Differences in clinical outcomes and the response to antidotes in patients with acute poisoning may occur due to inter-individual variability in metabolism.

View Article: PubMed Central - PubMed

Affiliation: Toxicological Department of the 2nd Medical Clinic, Technische Universität München, Ismaninger Str. 22, D-81664 Munich, Germany.

ABSTRACT
Chlorpyrifos (CPF) is a pesticide that causes tens of thousands of deaths per year worldwide. Chlorpyrifos oxon (CPO) is the active metabolite of CPF that inhibits acetylcholinesterase. However, this presumed metabolite has escaped detection in human samples by conventional methods (HPLC, GC-MS, LC-MS) until now. A recently developed enzyme-based assay allowed the determination of CPO in the nanomolar range and was successfully employed to detect this metabolite. CPO and CPF were analysed in consecutive plasma samples of 74 patients with intentional CPF poisoning. A wide concentration range of CPO and CPF was observed and the ratio of CPO/CPF varied considerably between individuals and over time. The ratio increased during the course of poisoning from a mean of 0.005 in the first few hours after ingestion up to an apparent steady-state mean of 0.03 between 30 and 72h. There was a hundred-fold variation in the ratio between samples and the interquartile range (between individuals) indicated over half the samples had a 5-fold or greater variation from the mean. The ratio was independent of the CPF concentration and the pralidoxime regimen. CPO was present in sufficient quantities to explain any observed acetylcholinesterase inhibitory activity. The effectiveness of pralidoxime in reactivating the inhibited acetylcholinesterase is strongly dependent on the CPO concentration. Differences in clinical outcomes and the response to antidotes in patients with acute poisoning may occur due to inter-individual variability in metabolism.

Show MeSH
Related in: MedlinePlus