Determination of DFPase in rabbit and rat tissues using DF32P

Relationship between the pharmacological effects and the biodisposition of [3H]diisopropylfluorophosphate in mice after inhalation

The biodisposition of [3H]diisopropylfluorophosphate (DFP) and its metabolites was studied in mice after inhalation administration. In addition, the time course of DFP-induced cholinesterase inhibition in selected tissues, hypothermia, and motor coordination were studied to determine a possible correlation with [3H]DFP, or its metabolites. The time course of tissue concentrations of [3H]DFP showed that [3H]DFP rapidly penetrated all tissues and was quickly hydrolyzed to [3H]diisopropylphosphoric acid (free [3H]DIP) or was covalently bound to tissue (bound [3H]DIP). By 1 hr, the greater portion of the radioactivity was in the form of bound [3H]DIP. Cholinesterase inhibition in brain, lung, diaphragm, and plasma was temporally related to concentrations of bound [3H]DIP between 5 min and 1 day, except at early time points for the lung. Motor incoordination (rotarod test) produced by DFP exposure had a rapid onset, with complete recovery by 10 hr. DFP-induced hypothermia (rectal temperature) had a very similar time-course profile to that of motor incoordination. The time course of hypothermia and motor incoordination was correlated with neither free [3H]DFP nor bound [3H]DIP concentrations in the brain, nor with cholinesterase inhibition in brain. These findings suggest that non-cholinesterase bound [3H]DIP may contribute to the depression of these centrally mediated effects.

Biodisposition of [3H]diisopropylfluorophosphate in mice

The disposition of [3H]diisopropylfluorophosphate (DFP) and its metabolites was studied in mice after iv treatment. In addition, disposition of [3H]DFP in selected tissues was correlated with cholinesterase activity and spontaneous activity following DFP treatment. Within 1 min of administration [3H]DFP had penetrated tissues and was already irreversibly bound. The tissue concentrations of [3H]DFP declined in a rapid fashion so that after 2 hr all concentrations were below 50 pg/mg tissue. The major portion of radioactivity was bound to tissue in the form of [3H]diisopropylphosphoric acid (DIP). There was a decline in [3H]DIP with time in all tissues except liver, kidneys, and fat, which reached a maximum at 30 min before declining. The only appreciable quantities of [3H]DIP remaining after 3 days were in liver and kidneys. There was also evidence that [3H]DFP was rapidly hydrolyzed to free [3H]DIP which was found in all tissues within 1 min of [3H]DFP administration. [3H]DIP concentrations were equivalent to or exceeded those of [3H]DFP in all tissues, except brain. Cholinesterase inhibition in plasma, diaphragm, and brain following DFP treatment (1 mg/kg, iv) was temporarily correlated with the concentrations of bound [3H]DIP in these same tissues between 1 hr and 3 days. Cholinesterase inhibition in brain and diaphragm did not correlate well with bound [3H]DIP at earlier time points which suggested the presence of noncholinesterase binding. DFP treatment (1 mg/kg) also induced motor hypoactivity which lasted up to 6 hr after iv injection. The time course of motor hypoactivity was not correlated with free [3H]DFP, bound [3H]DIP concentrations in the brain, or with cholinesterase inhibition in the brain, which suggested that noncholinesterase bound [3H]DIP was responsible for this CNS depression.

Importance of aliesterase as a detoxification mechanism for soman (Pinacolyl methylphosphonofluoridate) in mice

CBDP (2-/O-cresyl/4H:1:2-benzodioxaphosphorin-2-oxide) pretreatment produced a dramatic increase in the toxicity of soman in mice following the subcutaneous (s.c.) or intraperitoneal (i.p.) route of administration. This increase in soman toxicity was very highly correlated with inhibition of plasma aliesterase activity. Other enzymes (e.g. liver aliesterase and plasma cholinesterase) were inhibited by CBDP pretreatment; however, they did not appear to play a significant role in the potentiation of soman toxicity by CBDP. Liver aliesterase was not inhibited by doses of CBDP which produced significant increases in soman toxicity. Similarly, doses of Iso-OMPA, a selective inhibitor of pseudocholinesterase, which completely inhibited plasma cholinesterase, had no effect on soman toxicity. Pyridostigmine pretreatment which inhibited brain, diaphragm and plasma acetylcholinesterase 27, 57 and 60%, respectively, while not inhibiting plasma aliesterase, did not affect soman toxicity. The results of this study demonstrate that, in mice, plasma aliesterase is an extremely important detoxification route for soman.