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Canadian Journal of Anesthesia 53:208-209 (2006)
© Canadian Anesthesiologists' Society, 2006

Correspondence

Temperature, the benzoylcholine substrate, and fluoride inhibition of pseudocholinesterase

Gunther Wiesner, MD*, Markus Hartwig{dagger} and Michael Gruber, PhD{dagger}

* Institute of Anesthesiology, German Heart Centre Munich, Munich;
{dagger} University of Regensburg, Regensburg, Germany, E-mail: wiesner{at}dhm.mhn.de

To the Editor:

The magnitude of sevoflurane’s (and enflurane’s) effect on fluoride inhibition of pseudocholinesterase (PCHE) deserves attention in modern anesthetic practice. Nearly all studies dealing with this topic1–3 refer to the study of Kambam et al.4 who reported an inhibition of PCHE between 16 to 73% with 10 to 100 µmol·L–1 fluoride, the concentrations usually obtained during sevoflurane (and enflurane) anesthesia. Since we could not confirm this inhibition with mivacurium and butyrylthiocholine as substrates and at temperatures between 28 to 37° C3,5 we investigated fluoride inhibition of PCHE with benzoylcholine at 25°C, the substrate and temperature Kambam et al. used in their study, and at 37°C, the temperature currently recommended for determination of enzymatic activity.

After approval by our Local Ethics Committee and with written informed consent, serum samples of eight healthy volunteers were obtained, spiked with fluoride (0, 10, 50 and 100 µmol·L–1) and adjusted to 25°C and 37°C, respectively. Thereafter, 50 µmol·L–1 benzoylcholine were added, and at timed interval aliquots were withdrawn to measure the concentrations of benzoylcholine by high-performance liquid chromatography. After calculating the half-lives with KINETICA 2000 (InnaPhase Corp. Philadelphia, PA, USA) a one-factor (fluoride concentration) analysis of variance with a post hoc Dunnett test was performed at each temperature, using the fluoride-free sample as the control category. The results are presented in the FigureGo. At 25°C there was an increase of the benzoyl-choline half-time of 9.3% with 10 µmol·L–1 fluoride, and a 36% increase with 50 µmol·L–1 fluoride. The 68% increase in benzoylcholine half-time was significant (P < 0.05) at a concentration of 100 µmol·L–1. In contrast, no change was observed over the same range of fluoride concentrations at 37°C.


Figure 1
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  		FIGURE Dependence of the benzoylcholine half-lives on the fluoride concentration (0, 10, 50, and 100 µmol·L–1) at 25°C and 37°C. Data are presented as mean ± standard deviation. *P < 0.05 vs 0 µmol·L–1 fluoride at the corresponding temperature.

 
We thus confirm one aspect of the study of Kambam et al.4 who measured PCHE activity at 25°C with a photometric assay. In contrast, when using a high-performance liquid chromatography assay at clinically relevant body temperature (37°C) and with fluoride concentrations up to 100 µmol·L–1, fluoride inhibition of PCHE is not apparent, whether using the substrates mivacurium and butyrylthiocholine3,5 or benzoylcholine, as reported here. In conclusion, the influence of substrate and temperature on fluoride inhibition of PCHE must be taken into consideration when interpreting the results of investigations with sevoflurane and enflurane.

Footnotes

Accepted for publication October 18, 2005.

References

1 Wiesner G, Drescher J, Schneider A, Gruber M, Hobbhahn J. Fluoride generated by sevoflurane-biotransformation does not inhibit pseudocholinesterase in vivo. Eur J Anaesth 2000; 17(Suppl 19): 129 (abstract).

2 Lejus C, Delaroche O, Le Roux C, et al. The effect of sevoflurane on serum cholinesterase in children. Anaesthesia 2002; 57: 44–8.[Medline]

3 Wiesner G, Gruber M, Keyl C, Schneider A, Drescher J, Hobbhahn J. In vitro effects of fluoride on pseudocholinesterase activity and the metabolism of the cis-trans and trans-trans isomers of mivacurium. Anesthesiology 2001; 95: 806–7.[Medline]

4 Kambam JR, Parris WC, Naukam RJ, Franks JJ, Rama Sastry BV. In vitro effects of fluoride and bromide on pseudocholinesterase and acetylcholinesterase activitites. Can J Anaesth 1990; 37: 916–9.[Abstract/Free Full Text]

5 Gruber M, Lindner R, Prasser C, Wiesner G. The effect of fluoride on the in vitro metabolism of mivacurium. Anesth Analg 2002; 95: 397–9.[Abstract/Free Full Text]





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