Protection against soman or VX poisoning by human butyrylcholinesterase in guinea pigs and cynomolgus monkeys.

Human butyrylcholinesterase (HuBuChE), purified from outdated human plasma, is being evaluated for efficacy against nerve agents in guinea pigs and cynomolgus monkeys. Previous studies in rodents and nonhuman primates demonstrated that pretreatment of animals with enzymes that can scavenge nerve agents could provide significant protection against behavioral and lethal effects of nerve agent intoxication. In preparation for evaluation of efficacy of HuBuChE prior to initiating an investigational new drug (IND) application, the pharmacokinetics of HuBuChE were evaluated in guinea pigs and in cynomolgus monkeys. HuBuChE was injected intramuscularly (i.m.) at two doses, and blood samples were taken to follow the time-course of HuBuChE in blood for up to 168 h after administration. In guinea pigs, the two doses of HuBuChE, 19.9 and 32.5 mg/kg, produced similar times of maximal blood concentration (T(max) of 26.0 and 26.8 h, respectively) and similar elimination half-times (t(1/2) of 64.6 and 75.5 h, respectively). Enzyme levels were still 10-fold over baseline at 72 h. Based on these data, guinea pigs were administered 150 mg/kg of enzyme i.m. and challenged at T(max). Soman or VX doses were approximately 1.5, 2.0 and 2.0 x LD50 administered subcutaneously (s.c.) in sequence at 90-120 min apart. None of the animals displayed signs of organophosphorus (OP) anticholinesterase intoxication at any of the challenge levels, and all survived for the 14-day duration of the experiment. Similar experiments were carried out with cynomolgus monkeys to determine the pharmacokinetics of HuBuChE and its efficacy against soman. The complete survival of nearly all animals tested to date, coupled with the maximal blood concentration and half-life elimination profile obtained for HuBuChE after i.m. injection, provides strong support for the continued development of HuBuChE as a product to protect against nerve agents.

Field verification of Test-mate ChE.

The objective was to evaluate the ability of the Test-mate ChE to determine acetylcholinesterase (AChE) activity under field conditions. To mimic nerve agent exposure, the U.S. Army Medical Research Institute of Chemical Defense spiked blood samples with variable amounts of soman. Blinded to the identity of the samples, the 520th Theater Army Medical Laboratory tested the samples during a field training exercise inside their environmentally controlled mobile facility. The technicians repeated measurements for 6 consecutive days, and on 1 of the days repeated the measurements six times. The technicians accurately identified all of the samples and quantified the AChE activity. The major trend was that the Test-mate ChE is more precise and reproducible for smaller doses of soman. The results were reliable over all temperatures during the field exercise. In conclusion, the Test-mate ChE is a reliable field instrument to determine blood AChE activity.

Response of rats to low levels of sarin.

The purpose of this study was to determine whether exposure to levels of sarin causing no overt clinical signs would cause more subtle, adverse health effects that persisted after the exposure ended. Inhalation exposures of male Fischer 344 rats to 0, 0.2, or 0.4 mg/m(3) of sarin for 1 h/day for 1, 5, or 10 days under normal (25 degrees C) and heat-stressed (32 degrees C) conditions were completed and observations were made at 1 day and 1 month after the exposures. The sarin exposures had no observed effects on body weight, respiration rate, and minute volume during exposure nor in body temperature and activity during the 30-day recovery period. There was no evidence of cellular changes in brain determined by routine histopathology nor of any increase in apoptosis. Brain mRNA for interleukin (IL)-1beta, tumor necrosis factor-alpha, and IL-6 was increased in a dose-dependent manner. Autoradiographic studies demonstrated that M1 cholinergic receptor site densities were unchanged at 1 day after repeated exposures with or without heat stress. At 30 days, there was a decrease in M1 receptors in the olfactory tubercle (with and without heat), and, with heat stress, M1 sites also decreased in a dose-dependent manner in the frontal cortex, anterior olfactory nucleus, and hippocampus. M3 receptor sites were not affected by sarin exposure alone. In the presence of heat stress, there was an upregulation in binding site densities in the frontal cortex, olfactory tubercle, anterior nucleus, and striatum immediately after exposure, and these effects persisted at 30 days. Although red blood cell acetylcholinesterase (AChE) was not greatly inhibited by the 1-day exposure, there were 30 and 60% inhibitions after repeated exposures at the low and high doses, respectively. Histochemical staining for AChE demonstrated that sarin exposure alone reduced AChE in the cerebral cortex, striatum, and olfactory bulb. Sarin exposure under heat stress reduced AChE staining in the hippocampus, an area important for memory function. Thus, repeated exposures under heat-stress conditions, to levels of sarin that would not be noticed clinically, resulted in delayed development of brain alterations in cholinergic receptor subtypes that may be associated with memory loss and cognitive dysfunction.