Kai Tuovinen

Success of pyridostigmine, physostigmine, eptastigmine and phosphotriesterase treatments in acute sarin intoxication

The acute toxicity of organophosphorus (OP) compounds in mammals is due to their irreversible inhibition of acetylcholinesterase (AChE) in the nervous system, which leads to increased synaptic acetylcholine levels. The protective actions of intravenously (i.v.) administered pyridostigmine, physostigmine, eptastigmine, and an organophosphate hydrolase, phosphotriesterase, in acute sarin intoxication were studied in mice. The acute intragastric (i.g.) toxicity (LD50) of sarin with and without the pretreatments was tested by the up-and-down method. The mice received pyridostigmine (0.06 mg/kg body weight), physostigmine (0.09 mg/kg body weight), the physostigmine derivative eptastigmine (0.90 mg/kg body weight) or phosphotriesterase (104 U/g, 10.7 microg/g body weight) 10 min prior to the i.g. administration of sarin. Physostigmine was also administered with phosphotriesterase. Phosphotriesterase was the most effective antidote in sarin intoxication. The LD50 value for sarin increased 3.4-fold in mice receiving phosphotriesterase. Physostigmine was the most effective carbamate in sarin exposure. The protective ratios of physostigmine and pyridostigmine were 1.5- and 1.2-1.3-fold, respectively. Eptastigmine did not give any protection against sarin toxicity. Both the phosphotriesterase and physostigmine treatments protected the brain AChE activities measured 24 h after sarin exposure. In phosphotriesterase and physostigmine-treated mice, a 4- and 2-fold higher sarin dose, respectively, was needed to cause a 50% inhibition of brain AChE activity. Moreover, the combination of phosphotriesterase-physostigmine increased the LD50 value for sarin 4.3-fold. The animals pretreated with phosphotriesterase-ephysostigmine tolerated four times the lethal dose in control animals, furthermore their survival time was 2-3 h in comparison to 20 min in controls. In conclusion, phosphotriesterase and physostigmine were the most effective treatments against sarin intoxication. However, eptastigmine did not provide any protection against sarin toxicity.

Phosphotriesterase - a promising candidate for use in detoxification of organophosphates

The effect of phosphotriesterase (PTE) on cholinesterase (ChE) activities was studied with exposures to different organophosphates in mice. Paraoxon (PO) (1.0 mg/kg, ip) almost totally inhibited serum ChE activity. This activity, however, recovered to the normal level within 24 hr. The PTE pretreatment (16.8 U/animal, 2.5 micrograms/10 g body wt, iv 10 min before the organophosphate) accelerated this reactivation. The same phenomenon was also seen in vitro. In vitro with human serum, there was only minimal reactivation of the inhibited ChE. PTE, however, reactivated it significantly. The PTE-pretreated mice (168 U/animal, 30 micrograms/10 g body wt, iv) tolerated even 50 mg/kg of PO without showing any remarkable signs of intoxication. In PTE-untreated animals, however, PO doses as low as 1.0 and 1.5 mg/kg caused severe signs of poisoning. PTE (16.8 U/animal, 4 micrograms/10 g body wt, iv) reduced the inhibition of brain and serum ChE activities after PO and diisopropyl fluorophosphate exposure. In sarin and soman intoxications, PTE decreased only slightly the inhibition of ChE activities. The results indicate that PTE pretreatment given iv prevents the inhibition of ChE activities after certain organophosphates and it also hastens the recovery of activities after PO poisoning.

The developmental toxicity of 2-ethylhexanoic acid in Wistar rats

Abstract The developmental toxicity of 2-ethylhexanoic acid (2-EHA), a wood preservative and a mammalian metabolite of di-(2-ethylhexyl) phthalate was examined in Wistar rats (20–21 pregnant females/dose). Mated animals were exposed to 2-EHA in their drinking water at doses of 100, 300, or 600 mg/kg/day on Days 6–19 of gestation. Control animals received vehicle water. The fetuses were examined (on Gestational Day 20) for external, visceral, and skeletal malformations and variations. 2-EHA was marginally toxic to the dams at 600 mg/kg, but not at lower doses, since the mean near term body weight was reduced by 11%. This dose level was also slightly fetotoxic as indicated by a 5 to 8% decrease in the mean fetal body weight both in males and females. No treatment-related effects were observed in the number of implantations or live fetuses. At doses of 100 mg/kg and above, 2-EHA caused skeletal malformations (clubfoot, absence of fibula, polydactyly), while the development of visceral tissues was less affected. The number of affected fetuses increased in a dose-dependent way (4.9, 8.9, and 15.3% of treated offspring at 100, 300, and 600 mg/kg/day, respectively, vs 2.4% control). These results indicate that 2-EHA is teratogenic in rats already at doses which are not yet maternally toxic. The skeleton appears to be the main target of 2-EHA in developing rats.

Effect of Phenobarbital and β-Naphthoflavone on Activities of Different Rat Esterases After Paraoxon Exposure

1. The effects of two model inducers of the cytochrome P450 system, phenobarbital (PB) and beta-naphthoflavone (NF), on the toxicity of paraoxon were studied in rats. 2. Paraoxon toxicity was measured by inhibition of brain acetylcholinesterase (AChE) activity. 3. PB treatment did not affect the toxicity of paraoxon, whereas NF increased the inhibition of brain AChE. PB administration slightly increased the activities of some peripheral cholinesterases and carboxylesterases, as well as liver microsomal paraoxonase (Pxase). 4. NF administration, in contrast, decreased the activities of peripheral esterases. Serum Pxase activity was reduced by both inducers. 5. Hepatic CYP2B and CYP1A were markedly induced by PB and NF, respectively. 6. Cytochrome P450 isoenzymes induced by PB or NF seemed not to be critical in the detoxification of paraoxon in vivo. NF caused a general reduction of peripheral esterases, which led to an increase in paraoxon toxicity. 7. The results indicated the great importance of peripheral cholinesterases and carboxylesterases as a detoxifying mechanism of paraoxon. The role of serum paraoxonase was not critical.

Protection of mice against soman by pretreatment with eptastigmine and physostigmine

Organophosphate (OP) compounds such as the nerve agents sarin, soman and VX are powerful inhibitors of acetylcholinesterases (AChEs), butyrylcholinesterases (BChEs), and carboxylesterases (CaEs) The acute toxicity of OPs is the result of their irreversible binding with AChEs in the nervous system, which elevates the acetylcholine (ACh) levels. In this study the protective actions of intravenously (i.v.), administered eptastigmine and physostigmine in acute soman intoxication were studied in mice. The mice received eptastigmine (0.9 mg/kg body weight) or physostigmine (0.1 mg/kg body weight) 10 min prior to the intraperitoneal (i.p.) administration of soman. To avoid possible signs of poisoning, the animals received atropine 37.5 mg/kg body weight subcutaneously (s.c.) in saline immediately after soman injection. Eptastigmine was the most effective carbamate against soman intoxication. The LD50 value of soman was 0.44 mg/kg, and the protective ratios of eptastigmine and physostigmine were 2.1- and 1.3-fold, respectively. Both eptastigmine and physostigmine had protected AChEs when measured 24 h after soman exposure. In this study, there was no inhibition of microsomal CaEs in soman treated mice. Nonetheless, the role of microsomal CaEs might be more important with prophylaxis at multiple LD50s of soman. In conclusion, these results indicate that eptastigmine treatment given i.v. protects better than physostigmine against soman exposure.

Gender differences in activities of mouse esterase and sensitivities to DFP and sarin toxicity

1. Gender differences in the toxicity of diisopropylfluorophosphate (DFP; 4.0 mg/kg) and isopropyl methylphosphonofluoridate (sarin; 0.3 mg/kg) were studied in mice. 2. The animals were killed 3 hr after intraperitoneal (IP) injection of the organophosphates (OPs). 3. Although the activity of plasma butyrylcholinesterase (BChE) was two-fold higher and carboxylesterase (CaE) 1.3-fold higher in females than in males, the elevated BChE and CaE activities did not prevent inhibition of the enzyme by OPs in brain. 4. The differences in plasma BChE and CaE activities do not seem to be critical for the detoxification of OPs used in this study.

Ion mobility spectrometric monitoring of phosdrin® from foliage in greenhouse

The monitoring of Phosdrin (mevinphos; insecticide) from foliage and foliage extracts was achieved by an aspiration-type ion mobility spectrometer. This technique is based on ion mobility, which is proportional to the molecular weight, shape, and charge. The operation principle of the ion mobility spectrometer is to measure mobility distribution changes of product and reactant ions. This technique can measure positive and negative ion clusters at the same time in six different measuring electrodes. Each measuring electrode detects a different portion of the ion mobility distribution formed within the cells radioactive source. The pattern recognition used is based on differences in the gas profiles for different compounds. This study shows that an ion mobility spectrometer can be used to monitor Phosdrin from foliage without the need for any time-consuming extraction procedure. The responses for Phosdrin-containing and background (control) samples were easily separated from each other. The responses declined as a function of time in the positive and sum response channels. In addition, the sum of the absolute values of signals at six measuring channels (sum response) were linearly proportional to the concentration of Phosdrin. Just before application (i.e., in background), this value was 41 bits, whereas these values were 10-fold, 11-fold, 8-fold, 6-fold, 5-fold, and 3.5-fold at the time points 4, 8, 11, 24, 50, and 72 hours after the spraying of Phosdrin.