The Application of the Fluoride Reactivation Process to the Detection of Sarin and Soman Nerve Agent Exposures in Biological Samples

The fluoride reactivation process was evaluated for measuring the level of sarin or soman nerve agents reactivated from substrates in plasma and tissue from in vivo exposed guinea pigs (Cava porcellus), in blood from in vivo exposed rhesus monkeys (Macaca mulatta), and in spiked human plasma and purified human albumin. Guinea pig exposures ranged from 0.05 to 44 LD50, and reactivated nerve agent levels ranged from 1.0 ng/mL in plasma obtained from 0.05 LD50 sarin-exposed guinea pigs to an average of 147 ng/g in kidney tissue obtained from two 2.0 LD50 soman-exposed guinea pigs. Positive dose-response relationships were observed in all low-level, 0.05 to 0.4 LD50, exposure studies. An average value of 2.4 ng/mL for reactivated soman was determined in plasma obtained from two rhesus monkeys three days after a 2 LD50 exposure. Of the five types of guinea pig tissue studied, plasma, heart, liver, kidney and lung, the lung and kidney tissue yielded the highest amounts of reactivated agent. In similar tissue and with similar exposure procedures, reactivated soman levels were greater than reactivated sarin levels. Levels of reactivated agents decreased rapidly with time while the guinea pig was alive, but decreased much more slowly after death. This latter chemical stability should facilitate forensic retrospective identification. The high level of reactivated agents in guinea pig samples led to the hypothesis that the principal source of reactivated agent came from the agent-carboxylesterase adduct. However, there could be contributions from adducts of the cholinesterases, albumin and fibrous tissue, as well. Quantitative analysis was performed with a GC-MS system using selected ion monitoring of the 99 and 125 ions for sarin and the 99 and 126 ions for soman. Detection levels were as low as 0.5 ng/mL. The assay was precise and easy to perform, and has potential for exposure analysis from organophosphate nerve agents and pesticides in other animal species.

Intramuscular diazepam pharmacokinetics in soman-exposed guinea pigs

Intramuscular (i.m.) diazepam is included by the US military as an anticonvulsant in the standard therapeutic regimen for organophosphorus nerve agent intoxication. In this study we investigated the pharmacokinetics of diazepam after i.m. administration while monitoring pharmacodynamic (electroencephalogram, EEG) data in soman-exposed guinea pigs. Prior to experiments the animals were surgically implanted with EEG leads to monitor seizure activity. For the study, animals were administered pyridostigmine (0.026 mg x kg(-1) i.m.) 30 min prior to soman (56 microg x kg(-1), 2 x LD50; subcutaneously, s.c.), which was followed in 1 min by atropine sulfate (2 mg x kg(-1) i.m.) and pralidoxime chloride (25 mg x kg(-1) i.m.). All animals receiving this regimen developed seizure activity. Diazepam (10 mg x kg(-1) i.m.) was administered 5 min after onset of seizure activity. Based on EEG data, animals were categorized as either seizure terminated or not terminated at 30 min after diazepam. Serial blood samples were obtained from each animal. Diazepam (10 mg x kg(-1) i.m.) terminated seizure activity in 52% of the animals within 30 min. The pharmacokinetics were characterized by a one-compartment model with first-order absorption and elimination. The maximum plasma concentrations (Cmax) were 991 and 839 ng x ml(-1) for seizure terminated and not terminated, respectively. Mean plasma concentrations of diazepam were significantly different (P < 0.05) for seizure terminated vs not terminated groups at 30 min. The plasma Cmax in seizure-terminated animals in this study is similar to the minimum range of plasma diazepam (200-800 ng x ml(-1)) reported to suppress seizure activity in humans. It has been reported in an earlier study that the minimum effective i.m. dose (0.1 mg x kg(-1)) required to prevent soman-induced convulsions in Rhesus monkeys produces a mean Cmax of 50 ng x ml(-1) for diazepam. The data from our current study suggest that a higher dose (and corresponding Cmax) is necessary to terminate ongoing seizure activity.

A comparison of cholinergic effects of HI-6 and pralidoxime-2-chloride (2-PAM) in soman poisoning

The effects of HI-6 and pralidoxime chloride (2-PAM) on soman-induced lethality, time to death and several cholinergic parameters in rats were compared to understand the beneficial action of HI-6. Treatment with atropine sulfate (ATS) or HI-6 alone protected against 1.2 and 2.5 LD50s of soman respectively, whereas 2-PAM or methylated atropine (AMN) alone afforded no protection. Addition of ATS, but not AMN, to HI-6-treated rats enhanced the protection from 2.5 to 5.5 LD50s. HI-6 increased the time-to-death, while 2-PAM had no effect; a combination of HI-6 and ATS provided the most significant increase in time-to-death. Cholinesterase (ChE) activity was not altered in any tissue by ATS, HI-6 or 2-PAM treatment individually, but was markedly inhibited in all tissues by 100 micrograms/kg of soman. In soman-poisoned rats, the HI-6, but not the 2-PAM, group had significantly higher levels of ChE in blood and other peripheral tissues than did the group given soman alone. Neither HI-6 nor 2-PAM affected soman-inhibited ChE in the brain. Additional ATS treatment had no effect on ChE activity. HI-6 and 2-PAM neither modified baseline brain acetylcholine (ACh) or choline (Ch) levels nor protected against soman-induced ACh or Ch elevation. 2-PAM exhibited a 4-fold more potent in vitro inhibition of 3H-quinuclidinyl benzilate (3H-QNB) binding and sodium-dependent high-affinity Ch uptake (HACU) than did HI-6 in brain tissues. The findings that 2-PAM is a more potent in vitro inhibitor of muscarinic receptor binding and HACU than HI-6, and yet neither elevates ChE activity in the periphery nor protects rats against soman poisoning, indicate the importance of higher ChE activity in the periphery of HI-6-treated rats. Maintenance by HI-6 of a certain amount of active ChE in the periphery appears to be important for survival after soman exposure.

Effects of soman and sarin on high affinity choline uptake by rat brain synaptosomes

Synaptosomes were incubated at various time intervals following injection of 120 micrograms/kg SC of soman or sarin or with various concentrations (10(-8) to 10(-2) M) of soman or sarin in vitro. Total cholinesterase (ChE) activities in each brain region were also measured. Following soman injection, sodium-dependent, high affinity choline uptake (SDHACU) was decreased from 1 to 4 hr in the cortex and from 1 to 2 hr in the hippocampus, but increased from 2 to 24 hr in the striatum. Similarly, following sarin injection SDHACU was decreased at 0.5 hr in the cortex and from 1 to 4 hr in the hippocampus, but increased at 1 hr in the striatum. Injection of soman severely inhibited (83-99%) total ChE activity in the cortex, hippocampus and striatum from 1 to 24 hr. In contrast, sarin did not severely inhibit ChE activity in these regions and maximal inhibition (40-60%) did not occur until 24 hr after injection. With both compounds, by 168 hr ChE activity in all regions had partially recovered. Incubation of synaptosomes with soman or sarin in vitro at concentrations below 10(-4) M did not affect SDHACU in any of the brain regions. These data demonstrated that acute soman and sarin injection produced similar effects upon SDHACU in different brain regions, although the time-course of these effects was different for the two compounds. These effects were probably neither due to a direct action of these compounds on the uptake process nor dependent on ChE inhibition.

Peptides readily penetrate the blood-brain barrier: uptake of peptides by synaptosomes is passive

The intracarotid artery quick injection technique of Oldendorf was utilized to determine the Brain Uptake Index (BUI) of radio-labeled peptides in comparison with 3H2O or 14C-antipyrine as counterlabels. The normalized BUI values for 3H-MIF-I, 3H-alpha-MSH and 14C-AVP were 13.7, 9.6 and 13.0 respectively at 15 sec after injection consistent with their having readily penetrated the blood-brain barrier. The BUI values were similar, though somewhat increased, at 10 min postinjection consistent with their ready exit across the blood-brain barrier. At 15 sec after injection 0.5+/-0.1%/g brain of the originally injected peptide label was recovered; and 0.1+/-0.2%/g brain was recovered after 10 min. The label was distributed uniformly in the major brain regions at both times. However, the percentage of the originally injected label/g of pineal and pituitary gland tissue was 10-20 X increased as compared with the major brain regions as would be expected by their location outside the blood-brain barrier. The in vitro uptake of the radio-labeled peptides by synaptosomes prepared from the whole brain and the major brain regions was passive; it was not temperature dependent, nor was it Na+ dependent. However, the binding of the three peptides by the synaptosomes varied considerably: AVP greater than MSH greater MIF: 50 greater than 5 greater 1. The penetratin of the blood-brain barrier by the three peptides is consistent with their having CNS effects.