Antidotal treatment of GF-agent intoxication in mice with bispyridinium oximes.

It was shown that intoxications with GF-agent are rather resistant to convential oxime therapy; therefore, the development of new oximes in an effort to improve this unsatisfactory situation continues. Upon screening in vitro reactivation test for oximes, that were either newly synthesized at our department, or those that have never been tested for reactivation of GF-inhibited acetylcholinesterase (AChE), three oximes {(1,4-bis(4-hydroxyiminomethylpyridinium)butane dibromide) (K033); (1-(2-hydroxyiminomethylpyridinium)-3-(3-carbamoylpyridinium)-2-oxa-propane dichloride) (HS-6); and (1-(2-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium)-but-2-ene dibromide) (BI-6)} with the highest reactivation potency were chosen for in vivo testing in our study. 1,3-Bis(4-hydroxyiminomethylpyridinium)-2-oxa-propane dibromide) (obidoxime); (1-(2-hydroxyiminomethylpyridinium)-3-(4-carbamoylpyridinium)-2-oxa-propane dichloride) (HI-6); and (1,1-bis(4-hydroxyiminomethylpyridinium)-methane dibromide) (methoxime) were chosen for comparison as a standard antidotal treatment. All the oximes were applied at the same proportion of their LD50 value (5%), and because of the different acute toxicity of the oximes, the molar concentrations of their solutions for intramuscular (i.m.) administration were considerably different. The highest therapeutic ratio was achieved for therapeutic regimen consisting of HI-6 and atropine. The significantly (P < 0.05) lowest effectivity in treatment of supralethal GF-agent poisoning in comparison with all the other therapeutic regimens, was surprisingly observed for methoxime. HS-6, K033 and BI-6 as well as obidoxime were comparably effective antidotes against GF-agent intoxication and their therapeutic ratios were similar.

Biochemical and behavioral effects of soman vapors in low concentrations.

Soman belongs to the most dangerous nerve agents because of the low effectiveness of the presently available antidotes. Soman acts by inhibiting acetylcholinesterase (AChE) both peripherally and centrally, with a subsequent accumulation of neuromediator acetylcholine and other metabolic changes. From the data published in literature it can be concluded that exposure to nerve agents leading to acute effects or chronic exposure to nerve agents may lead to delayed and persistent adverse effects. The aim of this study was to demonstrate changes in AChE and butyrylcholinesterase (BuChE) activities, stressogenic markers (i.e., tyrosine aminotransferase [TAT] activity, and plasma corticosterone level), and neuroexcitability and behavior 24 h and 4 wk following a single soman inhalation exposure at low level. AChE activity in erythrocytes and BuChE activity in plasma was decreased (dependent on the dose of soman) 24 h and 4 wk after the exposure. A similar decrease in AChE activity in different brain parts was observed. One of the stressogenic parameters, TAT, was changed 24 h after exposure only. Behavior of experimental animals was changed 24 h after the exposure, and 4 behavioral parameters persisted 4 wk after the exposure. Neuroexcitability was increased at 24 h after the exposure and had become about normal 4 wk after the exposure. Summarizing, long-term effects (4 wk) were observed after inhalation exposure of guinea pigs to sublethal concentrations of soman.

The alteration of immune reactions in inbred BALB/c mice following low-level sarin inhalation exposure.

To study the influence of low-level sarin inhalation exposure on immune functions, inbred BALB/c mice were exposed to low concentrations of sarin for 60 min in the inhalation chamber. The evaluation of immune functions was carried out using phenotyping of CD3 (T lymphocytes), CD4 (helper T lymphocytes), CD8 (cytotoxic T lymphocytes), and CD19 cells (B lymphocytes) in the lungs, blood, and spleen, lymphoproliferation of spleen cells stimulated in vitro by various mitogens (concanavalin A, lipopolysaccharides), phagocyte activity of peritoneal and alveolar macrophages, production of N-oxides by peritoneal macrophages, and the measurement of the natural killer cell activity at 1 wk following sarin exposure. The results were compared to the values obtained from control mice exposed to pure air instead of sarin. The results indicate that low doses of sarin are able to alter the reaction of immune system at one week following exposure to sarin. While the numbers of CD3 cells in the lungs, blood, and spleen were slightly decreased, an increase in CD19 cells was observed, especially in the lungs and blood. The reduced proportion of T lymphocytes is caused by decay of CD4-positive T cells. Lymphoproliferation was significantly decreased regardless of the mitogen and sarin concentration used. The production of N-oxides by peritoneal macrophages was stimulated after exposure to the highest dose of sarin, whereas their ability to phagocytize the microbes was increased after exposure to the lowest dose of sarin. The natural killer cell activity was significantly higher in the case of inhalation exposure of mice to the highest level of sarin. Thus, not only organophosphorus insecticides but also nerve agents such as sarin are able to alter immune functions even at a dose that does not cause clinically manifested disruption of cholinergic nervous system in the case of inhalation exposure. Nevertheless, the alteration of immune functions following the inhalation exposure to a symptomatic concentration of sarin seems to be more pronounced.

The influence of sarin on various physiological functions in rats following single or repeated low-level inhalation exposure.

Long-term effects of low doses of highly toxic organophosphorus agent sarin on various hematological and biochemical markers and physiological functions were studied in rats exposed to sarin by inhalation. The results indicate that low-level sarin-exposed rats show long-term increase in studied markers of stress and decrease in synthesis of DNA de novo without the disturbance of the functions of cholinergic nervous system. Moreover, sarin at low doses is able to induce some neurotoxic effects including an increase in the excitability of central nervous system in rats at 3 mo following inhalation exposure. Relatively long-term spatial discrimination impairments in rats exposed to low-level sarin was demonstrated too. Therefore, nerve agents such as sarin seem to be harmful not only at high, clinically symptomatic doses but also at low doses without acute clinical manifestation of overstimulation of cholinergic nervous system because of long-term manifestation of alteration of neurophysiological and neurobehavioral functions in sarin-exposed rats.

Protective effect of equine butyrylcholinesterase in inhalation intoxication of rats with sarin: determination of blood and brain cholinesterase activities.

The effect of pretreatment with equine butyrylcholinesterase (EqBuChE) on cholinesterase inhibition in the blood and brain of rats following inhalation intoxication with low concentrations (1.25 microg/L for 60 min) of sarin were studied. Animals pretreated with different doses of equine butyrylcholinesterase showed significant increases in plasma butyrylcholinesterase activity. However, erythrocyte acetylcholinesterase activity was unchanged. The decrease in acetylcholinesterase and butyrylcholinesterase activity after inhalation intoxication was dependent on the dose of equine butyrylcholinesterase used for pretreatment and was always greater for erythrocyte acetylcholinesterase. Acetylcholinesterase activity in different brain regions was unchanged following pretreatment with equine butyrylcholinesterase. After inhalation exposure to sarin, acetylcholinesterase activity was diminished markedly in the pontomedullar area (51.5% of normal activity) and frontal cortex (72.0% of normal activity), and slightly in basal ganglia (91.4% of normal activity). Plasma levels of sarin were determined using fluoride-induced reactivation of inhibited enzyme. As expected, the amounts of sarin in plasma were almost identical in rats pretreated with EqBuChE as well as in untreated rats. In pretreated animals, the plasma amount of sarin did not depend on the dose of equine butyrylcholinesterase used for pretreatment. Our results demonstrate that equine butyrylcholinesterase pretreatment can be considered as an effective prophylaxis against nerve agents (at least with sarin) and seems to be an alternative or superior to prophylaxis provided by reversible cholinesterase inhibitors.

Effect of methoxime combined with anticholinergic, anticonvulsant or anti-HCN drugs in tabun-poisoned mice.

The effect of methoxime combined with a) atropine, b) benactyzine, c) atropine and natrium thiosulphate, d) atropine and diazepam on antidotal treatment effectiveness was studied in tabun-poisoned mice. In addition, the influence of pretreatment consisiting of pyridostigmine, benactyzine and trihexyphenidyle (PANPAL) administered 2 hours before tabun intoxication on the treatment effectivity of methoxime combined with e) atropine or f) benactyzine was tested. The most efficacious therapeutic mixture in non-pretreated mice was methoxime, atropine and diazepam. Natrium thiosulphate did not significantly increase neither decrease the antidotal treatment efficacy in comparison with methoxime and atropine alone. Pretreatment with PANPAL significantly decreased tabun toxicity (nearly 4 times in methoxime and benactyzine combination and more than 4 times in atropine and methoxime mixture). The present study demonstrates that the tabun toxicity in mice is more effectively reduced when PANPAL prophylactically is administered than in case of treatment with methoxime and cholinergic drug alone. We established that anticholinergic drug option in the therapeutic mixture of methoxime and anticholinergic drug did not cause the difference in the antidotal treatment effectivities.

Inhalation apparatus for generating sarin and soman toxic vapors.

The developed inhalation system is a dynamic and whole-body exposure model designated for generating sarin or soman vapors. It consists of an evaporating apparatus, an inhalation chamber and a carbon filter. The inhalation chamber is made of stainless steel and its total volume is 36 l. The concentration of organophosphorus compound depends on airflow through the chamber, syringe volume of the dosing pump and dosing speed. For determination of organophosphorus compound (OPC) concentration, a modification of Ellman method is used. At generating of vapors in the inhalation chamber the means of the yield were 61.4 +/- 6.6% for sarin and 35.8 +/- 3.5% for soman. The better yield for sarin than for soman, because of the higher volatility of sarin in comparison with soman was achieved. The stable concentration of the OPC for several hours could be maintained in the inhalation chamber when only relatively small amount of the OPC is used. Using the developed inhalation system LCt50 for sarin and for soman in rats was determined. At 1 h exposure the LCt50 values were 4.72 mg x h(-1) x m(-3) for sarin and 4.81 mg x h(-1) x m(-3) for soman. The results presented show that the inhalation chamber successfully fulfils the role of instrument for inhalation intoxication of small laboratory animals with highly toxic OPC.