Jiří Bajgar

Toxic effects of sarin in rats at three months following single or repeated low-level inhalation exposure

Male albino Wistar rats were once or repeatedly exposed to three various low concentrations of sarin for 60 min. in the inhalation chamber. The clinical status of control as well as sarin-poisoned rats was tested 3 months after exposure to sarin using biochemical, haematological, neurophysiological, behavioural and immunotoxicological methods. While biochemical and haematological parameters, including the activities of cholinesterases in erythrocytes, plasma and various organs (brain, diaphragm), did not differ from the control values regardless of the sarin concentration used, few signs of sarin-induced neurotoxicity and immunotoxicity in sarin-poisoned rats were demonstrated. This was especially true when the single exposure of rats to non-convulsive symptomatic concentration and repeated exposure of rats to clinically asymptomatic concentration of sarin was used. In rats repeatedly poisoned with clinically asymptomatic concentrations of sarin, the alteration of the gait characterized by ataxia, the increase in the stereotyped behaviour, the increase in the excitability of the central nervous system following the administration of the convulsive drug pentamethylenetetrazol were observed. In rats poisoned with non-convulsive symptomatic concentration of sarin, the subtle supression of spontaneous, as well as lipopolysaccharides-stimulated, proliferation of spleen lymphocytes and the bactericidal activity of peritoneal macrophages was primarily observed besides the signs of neurotoxicity. Our findings confirm that both non-convulsive symptomatic and clinically asymptomatic concentrations of sarin can only cause very few, subtle long-term signs of neurotoxicity and immunotoxicity in sarin-poisoned rats when the rats were exposed to asymptomatic sarin concentrations repeatedly.

Comparison of the efficacy of HI-6 and obidoxime against cyclohexyl methyl phosphonofluoridate (GF) in rats

1 The efficacy of HI-6 and obidoxime in combination with atropine on cyclohexyl methylphosphonofluoridate (GF)- induced cholinergic and stressogenic effects in rats was studied. 2 HI-6 sufficiently reactivated cholinesterase activity in blood as well as acetylcholinesterase activity in brain and diaphragm following GF intoxication, and practically eliminated stressogenic effects of GF (an increase in plas ma corticosterone level and liver tyrosine aminotrans ferase activity). 3 Obidoxime had practically no effect on enzyme activity or stressogenic effects of GF agent. 4 These findings confirm that HI-6 has definite advan tages over obidoxime in the treatment of intoxication with GF.

The influence of pharmacological pretreatment on efficacy of HI-6 oxime in combination with benactyzine in soman poisoning in rats

1 The influence of pharmacological pretreatment (pyr idostigmine, benactyzine and trihexyphenidyle), de signated PANPAL, on soman-induced cholinergic and stressogenic effects as well as on the efficacy of antidotal treatment (HI-6 plus obidoxime) in rats was studied. 2 PANPAL prophylaxis significantly decreased soman- induced cholinesterase inhibition in blood, brain and diaphragm as well as stressogenic effects of soman (an increase in plasma corticosterone level and liver tyrosine aminotransferase activity). 3 PANPAL pretreatment did not improve the efficacy of HI-6 in combination with benactyzine on soman- induced anticholinesterase and stressogenic effects. 4 These findings confirm that PANPAL prophylaxis can improve prognosis of soman poisoning especially by protection of cholinesterases.

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 overtimulation of cholinergic nervous system because of long-term manifestation of alteration of neurophysiological and neurobehavioral functions in sarin-exposed rats.

Changes of acetylcholinesterase activity in various parts of brain following nontreated and treated soman poisoning in rats

Changes of acetylcholinesterase (AChE) activity in various parts of the brain (frontal cortex, medulla oblongata, pons Varoli, cerebellum, hypothalamus, and hippocampus), following im sublethal non-treated and treated soman poisoning were studied. As a treatment, two antidotal mixtures containing atropine and either obidoxime or oxime HI-6 were used. This antidotal treatment was administered im for 30 s following soman intoxication. The AChE activities in the various brain tissues were evaluated at 1 and 3 h following soman administration. As expected, the highly toxic organophosphorus compound, soman, markedly inhibited AChE activity in all the brain sections at both time intervals. Both oximes had little influence on soman-induced AChE inhibition, but only the HI-6 mixture was able to reactivate soman-inhibited AChE significantly in some of the brain parts (frontal cortex, pons Varoli, hypothalamus). In the brain, the effect of HI-6 against soman-induced AChE inhibition is higher in comparison with obidoxime, but not quite satisfactory. Despite its limited effectiveness in the brain, HI-6 seems to be the most effective oxime yet found against soman poisoning because of its high reactivating effect in the peripheral compartment and other beneficial effects.

Changes in cholinesterase activities after daunorubicin administration to rabbits

1 Acetyl- and butyrylcholinesterase (AChE, BuChE) activities were studied in rabbits with experimentally induced daunorubicin cardiomyopathy. 2 A significant decrease of the plasma BuChE in the daunorubicin group was observed. 3 In the daunorubicin group, AChE activity in the heart was significantly decreased only in the interventricu lar septum. 4 BuChE activity was significantly decreased in the cardiac septum and ventricles and in the liver following daunorubicin treatment. 5 Changes in cholinesterase activities are probably caused by an effect of daunorubicin oon protein synthesis during the development of certain types of cardiomyopathy.

The present approaches to the development of prophylactic and therapeutic antidotes against nerve agents

The present approaches to the development of prophylactic and therapeutic antidotes against nerve agents Nerve agents belong to highly toxic organophosphorus compounds misused as chemical warfare agents for military as well as terroristic purposes. Basic mechanism of action of nerve agents is based on acetylcholinesterase (AChE, EC 3.1.1.7) inhibition and subsequent accumulation of neuromediator acetylcholine at the cholinergic synapses, either peripheral or central leading to cholinergic hyperstimulation and development of symptoms of poisoning, followed by metabolic dysbalance and death without effective prophylaxis/treatment. The antidotal treatment of acute poisonings with nerve agents still represents a serious problem and, therefore, we are searching how to satisfactorily protect people against acute toxicity of nerve agents. There are two approaches how to improve the medical protection against nerve agents: to increase the resistance of nerve agent-exposed organism and the efficacy of post-exposure antidotal treatment by pharmacological prophylaxis the development of new, more effective antidotes, expecially AChE reactivators, to achieve the satisfactorily effective antidotal treatment of acute poisonings with nerve agents.

Cyclosporine A inhibits acetylcholinesterase activity in selected parts of the rat brain

Cyclosporine A (CsA) is the major immunosuppressive drug used for organ and neural transplantation and the therapy of selected autoimmune diseases. We investigated the effect of CsA on the activity of acetylcholinesterase (AChE) in the frontal cortex, hippocampus, septum, and basal ganglia. AChE was determined spectrophotometrically with acetylthiocholine as substrate and 5,5-bis-2-nitrobenzoic acid as chromogen. CsA was administered in single doses of 20 or 45 mg/kg perorally; in the case of the higher dose we also performed a repeated administration of CsA in three consecutive doses separated by 24 h intervals. Both lower and higher doses of CsA decreased AChE activity in the frontal cortex and hippocampus to practically the same extent. On the contrary, AChE activity was more diminished in the case of the higher dose of CsA used in the septum and basal ganglia. Repeated administration of the higher dose of CsA did not lead, with the exception of the hippocampus, to a further decrease in AChE activity in the brain structures observed. These findings contribute to rare evidence concerning the interaction of CsA and the cholinergic system in the brain.

Myocardial elements content and cardiac function after repeated i.v. administration of DMPS in rabbits

1 A dithiol chelating agent-2,3-dimercapto-1-propane-sulphonate (DMPS)- may be administered in acute or chronic intoxication with certain heavy metals (e.g. cadmium, cobalt, lead) that may cause cardiotoxicity. 2 DMPS can act as a depleter of physiologically important elements (e.g. potassium, magnesium, calcium) in various tissues including cardiac one. The possibility of subsequent alteration in cardiac function cannot be excluded. 3 Changes in the myocardial concentration of the abovementioned elements at the end of the experiment and cardiac function were studied during repeated I.V. administration of DMPS as single doses of 50 mg/kg/ week for 10 weeks in rabbits. Biochemical, haemato-logical and histological examinations were also performed. 4 Most of the measured parameters were not affected by the repeated administration of DMPS. A significant decrease in magnesium and a near significant decrease in calcium in cardiac muscle was not accompanied by functional or morphological changes. It is still suggested, however, that care should be taken in using DMPS for treating patients with cardiotoxicity as a result of poisoning with heavy metals.