Characterization and Normalization of Rat Salivary Cholinesterase

Abstract

Cholinesterase (ChE) is an enzyme which allows neurons to return to a resting state by hydrolyzing the neurotransmitter acetylcholine. Organophosphate pesticides, which are commonly used in agriculture, inhibit the activity of ChE. The inhibition of ChE activity in plasma and red blood cells is used as a biomarker for human pesticide exposure. Currently, salivary ChE activity is being examined as a non-invasive biomarker; however little is known about baseline ChE activity in saliva. In order to characterize baseline salivary ChE, saliva was collected from 5 adult male SpragueDawley rats, salivary ChE was measured using the Ellman assay, and total salivary protein was measured using the bicinchoninic acid (BCA) protein assay. Comparison oftotal ChE activity indicated that rat salivary ChE is variable amongst individuals at a given time point (coefficient of variation=30% to 67%) and over the 2 hour collection time (coefficient of variation=66.8% or 71.6%). Variation of total protein was also seen with coefficients of variation of 36% to 57% between individuals at each collection time and 66.2% over collection. The correlation coefficient between total protein and total ChE activity was determined to be 0.731. Normalization of ChE activity by total protein resulted in a coefficient ofvariation of 37% over the collection time. These results demonstrate the variability of salivary ChE activity and suggest that total protein may be used as a normalization measure in saliva biomonitoring.