Measuring Cholinesterase Activity in Human Saliva

Abstract

To assess the potential for using saliva in pesticide biomonitoring, the consistency of cholinesterase activity in human saliva collected over time was examined. In this pilot study, saliva was collected from 20 healthy adults once per week for 5 consecutive weeks using 2 different collection methods: a disposable plastic pipette, and a cotton-wool roll. A brief questionnaire was conducted each week to document changes in exposure to cholinesterase inhibitors for the duration of the sampling. To measure cholinesterase activity, an existing radiometric method was modified to make it suitable for human saliva. Using this method, cholinesterase activity was measurable in saliva, and duplicate samples showed reliable repeatability. Activity in both collection methods ranged from 3 to 265 nmol/h/ml saliva (mean = 52 ± 37 [SD] nmol/h/ml saliva). For some individuals, enzyme activity was consistent over the five sampling weeks; for others, activity was highly variable. Coefficients of variation (CVs) were calculated to assess variability, and mean CVs were the same for both collection methods (about 35%). Adjusting for protein concentration in the pipette-collected samples did not change results. Both collection methods worked well for collecting between 1 and 3 ml saliva, but at the majority of visits (86%), participants preferred the cotton-wool roll. Results from this study suggest that saliva may be a useful indicator of potential neurotoxic effects from exposure to organophosphorus and carbamate pesticides, but that factors affecting variability should be explored further.

This work was supported in part by U.S. EPA grant CX3830850. Birgit Claus Henn obtained support through the ASPH/EPA Environmental Health Research Fellowship program. We thank our participants for their time and saliva; Westat for recruiting and scheduling; and the U.S. EPA Human Studies Facility medical station staff for sharing their space. We also thank Pauline Mendola and Steve Brimijoin for reviewing this article. This research has been reviewed by the National Health and Environmental Effects Research Laboratory, U.S. EPA, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.