Emily A. Davis

Biomarkers of low-level exposure to soman vapor: comparison of fluoride regeneration to acetylcholinesterase inhibition.

The nerve agent O-pinacolyl methylphosphonofluoridate, also known as soman or by its military designation GD, is a highly toxic organophosphorous compound that exerts its effects through inhibition of the enzyme acetylcholinesterase (AChE). In the present study, a fluoride ion based regeneration assay was developed to quantify the level of soman present in the blood of rats following a low-level whole-body inhalation exposure. It was hypothesized that the amount of regenerated nerve agent in the blood would be dose dependent in rats subjected to a whole-body inhalation exposure to a low-level dose of soman vapor, and that the fluoride ion-based regeneration method would be more sensitive for the detection of a low-level exposure to soman vapor than the measurement of whole blood AChE activity. Regenerated soman was dose-dependently detected in both the red blood cells (RBCs) and plasma of exposed rats at all concentrations tested (0.033–0.280 mg/m3 for a 240-min exposure). Significant inhibition of whole blood AChE activity did not occur below a concentration of 0.101 mg/m3, and was only depressed by approximately 10–25% at concentrations ranging from 0.101 mg/m3 to 0.280 mg/m3. This study is the first to utilize a fluoride ion-based regeneration assay to demonstrate the dose-dependent increases in soman in the blood following whole-body inhalation exposure to low levels of vapor. Additionally, the results of the present study demonstrate that the fluoride ion based regeneration assay was approximately threefold more sensitive than the measurement of AChE activity in the blood for the detection of exposure to soman, and also that miosis is a more sensitive marker of soman exposure than inhibition of AChE activity.

Acute Toxic Effects of Inhaled Dichlorvos Vapor on Respiratory Mechanics and Blood Cholinesterase Activity in Guinea Pigs

Using a modified noninvasive volume-displacement plethysmography system, we investigated the effects of inhaled dichlorvos (2,2-dimethyl dichlorovinyl phosphate, or DDVP) vapor on the respiratory mechanics and blood cholinesterase activity of guinea pigs. Data revealed significant dose-dependent changes in several pulmonary parameters. Animals exposed to a DDVP concentration of 35 mg/m3 did not show any significant changes in frequency, tidal volume, or minute ventilation. However, animals exposed to 55 mg/m3 DDVP showed significantly decreased respiratory frequency and significantly increased tidal volume with no significant changes in minute ventilation. Similarly, animals exposed to 75 mg/m3 DDVP showed significantly decreased respiratory frequency along with significantly increased tidal volume. The decreased respiratory frequency was large enough in the high exposure group to offset the increased tidal volume. This effect resulted in significantly decreased minute ventilation by the end of exposure, which remained attenuated 10 min after exposure. An analysis of whole-blood cholinesterase activity revealed significantly decreased activity for both acetylcholinesterase (AChE) and butylcholinesterase (BChE). Peak inhibition occurred for both enzymes at the end of exposure for all three concentrations and rapidly recovered within several minutes of exposure. Analysis of blood samples using gas chromatography–mass spectroscopy (GC-MS) revealed that minute ventilation may only play a minimal role in the dosimetry of inhaled DDVP vapor.

Alterations in Autonomic Function in the Guinea Pig Eye Following Exposure to Dichlorvos Vapor

The present study investigated the effect of the organophosphate, dichlorvos (DDVP), on ocular function and cholinesterase activity in guinea pigs, using a single-animal-head-only vapor exposure system. All animals exhibited signs of mild organophosphate poisoning (e.g., salivation, chewing, lacrimation, urination, defecation, and rhinorrhea) after the 20-min exposure, regardless of the DDVP exposure concentration (e.g., 35 mg/m(3), 55 mg/m(3), and 75 mg/m(3)). Pupil constriction or miosis was the most pronounced effect seen after vapor exposure. The postexposure pupil size for the 35 mg/m(3) group was 45.8 +/- 3.68% of the preexposure baseline measurement. Postexposure pupil size in the 55- (38 +/- 1.36%) and 75 mg/m(3) (38.1 +/- 1.72%) groups was significantly less than both the preexposure baseline level and the 35 mg/m(3) group. All groups exhibited enhanced an pupillary response to light after DDVP exposure. The enhanced light response remained even after recovery from miosis (approximately 1 h after exposure). Measurement of cholinesterase activity revealed that even though pupil size had recovered, acetyl- and butyrylcholinesterase remained significantly inhibited in the blood.