Effects of repeated low-dose exposure of the nerve agent VX on monoamine levels in different brain structures in mice.

In a previous report, alterations of the serotonin metabolism were previously reported in mice intoxicated with repeated low doses of soman. In order to better understand the effects induced by repeated low-dose exposure to organophosphorus compounds on physiological and behavioural functions, the levels of endogenous monoamines (serotonin and dopamine) in different brain areas in mice intoxicated with sublethal dose of (O-ethyl-S-[2(di-isopropylamino) ethyl] methyl phosphonothioate) (VX) were analysed by HPLC method with electrochemical detection. Animals were injected once a day for three consecutive days with 0.10 LD50 of VX (5 µg/kg, i.p). Neither severe signs of cholinergic toxicity nor pathological changes in brain tissue of exposed animals were observed. Cholinesterase (ChE) activity was only inhibited in plasma (a maximum of 30% inhibition 24 h after the last injection of VX), but remained unchanged in the brain. Serotonin and dopamine (DA) metabolism appeared significantly modified. During the entire period of investigation, at least one of the three parameters investigated (i.e. DA and DOPAC levels and DOPAC/DA ratio) was modified. During the toxic challenge, an increase of the serotonin metabolism was noted in hippocampus (HPC), hypothalamus/thalamus, pons medulla and cerebellum (CER). This increase was maintained 4 weeks after exposure in HPC, pons medulla and CER whereas a decrease in cortex 3 weeks after the toxic challenge was observed. The lack of correlation between brain ChE activity and neurochemical outcomes points out to independent mechanisms. The involvement in possibly long-lasting behavioural disorders is discussed.

Skin decontamination of mustards and organophosphates: comparative efficiency of RSDL and Fuller's earth in domestic swine.

Research in skin decontamination and therapy of chemical warfare agents has been a difficult problem due to the simultaneous requirement of rapid action and non-aggressive behaviour. The aim of this study was to compare the performance of two decontaminating systems: the Canadian Reactive Skin Decontaminant Lotion (RSDL) and the Fuller's Earth (FE). The experiment was conducted with domestic swine, as a good model for extrapolation to human skin. RSDL and FE were tested against sulphur mustard (SM), a powerful vesicant, and VX, a potent and persistent cholinesterase inhibitor. When used 5 min after contamination, the results clearly showed that both systems were active against SM (10.1 mg/cm(2)) and VX (0.06 mg/cm(2)). The potency of the RSDL/sponge was statistically better than FE against skin injury induced by SM, observed 3 days post-exposure. RSDL was rather more efficient than FE in reducing the formation of perinuclear vacuoles and inflammation processes in the epidermis and dermis. Against a severe inhibition (67%) of plasmatic cholinesterases induced by VX poisoning, the potencies of the RSDL/sponge and FE were similar. Both systems completely prevented cholinesterase inhibition, which indirectly indicates a prevention of toxic absorption through the skin.

Protection against soman-induced neuropathology and respiratory failure: a comparison of the efficacy of diazepam and avizafone in guinea pig.

The purpose of this study was to compare the efficacy of diazepam and the pro-diazepam avizafone in preventing the severity of soman-induced pathology in guinea pig. Survival, respiration and seizures of experimental animals were investigated with on-line monitoring of respiratory and EEG parameters. Guinea pigs were pretreated with pyridostigmine (0.1mg/kg i.m.) and 30 min later challenged with 1 or 2 LD50 soman. One minute after intoxication they were treated with atropine (3 or 33.8 mg/kg), pralidoxime chloride (32 mg/kg) and either diazepam (2 mg/kg), avizafone (3.5 mg/kg) or saline solution. The highest dose of atropine (33.8 mg/kg) gave a protective effect in groups treated without anticonvulsants by reducing the severity of clinical signs and death within 24 h but also by decreasing seizure occurrence and brain injuries. When injected at the similar molar dose of 7 micromoles/kg, the protection of anticonvulsants against soman neurotoxicity was higher with the atropine/pralidoxime/avizafone combination than with atropine/pralidoxime/diazepam. Indeed, when atropine was used at the lowest dose, avizafone was found to prevent early mortality and seizures occurrence with better efficacy than diazepam. On the other hand, when added to the therapy, the both anticonvulsants did not prevent the moderate EEG depression (reduction of amplitude by 30-52%) observed under 2 LD50 soman. Moreover, the number of animals suffering from respiratory distress (defined as a decrease of minute ventilation of more than 20% from the baseline value) was enhanced when diazepam or avizafone were used in the therapy. This effect was dependent on the atropine dose and the nature of the anticonvulsant. The beneficial effects of the different therapeutics tested were assessed and compared to the previous data obtained with the same therapies against sarin and from the pharmacokinetics properties of the atropine/diazepam mixture.

Structure-activity relationship of phenolic compounds (phenol, pyrocatechol and hydroquinone) on natural lymphocytotoxicity of carp (Cyprinus carpio).

We have tested the effects of phenol and two diphenols (pyrocatechol and hydroquinone) on a non-specific immune response, i.e. the natural cytotoxic activity, of the carp. After a 12-day exposure of fish, at a concentration of 0.1 mg/l, hydroquinone appeared to exert the most immunotoxic effect in vivo. In vitro, after a preincubation of 1 h, phenol (10(-2) M), pyrocatechol (4.25 x 10(-4) M) and hydroquinone (4.25 x 10(-5) M) decreased the natural cytotoxic activity of lymphoid cell suspension. In vivo and in vitro experiments show that hydroquinone is the most toxic compound, whereas diphenols are more toxic than phenol. These results demonstrate that the study of immune systems can reveal the presence of toxic substances with varying degrees of toxicity. Also, the position of a second hydroxic group on the benzonic nucleus seems to influence the compound toxicity.

Comparative efficacy of diazepam and avizafone against sarin-induced neuropathology and respiratory failure in guinea pigs: influence of atropine dose.

This investigation compared the efficacy of diazepam and the water-soluble prodiazepam-avizafone-in sarin poisoning therapy. Guinea pigs, pretreated with pyridostigmine 0.1 mg/kg, were intoxicated with 4LD(50) of sarin (s.c. route) and 1 min after intoxication treated by intramuscular injection of atropine (3 or 33.8 mg/kg), pralidoxime (32 mg/kg) and either diazepam (2 mg/kg) or avizafone (3.5 mg/kg). EEG and pneumo-physiological parameters were simultaneously recorded. When atropine was administered at a dose of 3 mg/kg, seizures were observed in 87.5% of the cases; if an anticonvulsant was added (diazepam (2 mg/kg) or avizafone (3.5 mg/kg)), seizure was prevented but respiratory disorders were observed. At 33.8 mg/kg, atropine markedly increased the seizure threshold and prevented early respiratory distress induced by sarin. When diazepam was administered together with atropine, seizures were not observed but 62.5% of the animals displayed respiratory difficulties. These symptoms were not observed when using avizafone. The pharmacokinetic data showed marked variation of the plasma levels of atropine and diazepam in different antidote combination groups, where groups receiving diazepam exhibited the lowest concentration of atropine in plasma. Taken together, the results indicate that avizafone is suitable in therapy against sarin when an anticonvulsant is judged necessary.

Xenobiotic-metabolizing enzymes in carp (Cyprinus carpio) liver, spleen, and head kidney following experimental Listeria monocytogenes infection.

Infection of carp with Listeria monocytogenes 4b resulted in decreased liver, spleen, and head kidney enzyme activities, involved in the metabolism of xenobiotics. After infection, cytochrome P-450 levels and ethoxyresorufin O-deethylase (EROD) activity were decreased while conjugation enzymes remained unaffected. The maximum decrease for phase I enzymes occurred on d 3. This loss of monooxygenase levels and activity could not be directly correlated with an increase in the number of organisms, as consistently high bacterial counts were observed in all three organs during infection. The effect of L. monocytogenes infection was also measured in carp exposed to 3-methylcholanthrene (MCA). Cytochrome P-450 levels and EROD activity were significantly reduced, especially on d 3. A significant decreased activity of conjugation enzymes such as glutathione S-transferase (GST) and UDP-glucuronosyltransferase (UDPGT) was also observed for all days studied. Listeria infection inhibited MCA-induced increases in xenobiotic-metabolizing enzyme activities. These results indicate that infection may have deleterious effects on basal cytochrome P-450 monooxygenase levels. Furthermore, MCA treatment aggravates the insult to xenobiotic biotransformation enzymes by L. monocytogenes infection, by impairing a number of detoxification enzymes. These findings could result in significant changes in the susceptibility of fish to pollutants.

3-Methylcholanthrene-induced EROD activity and cytochrome P-450 in immune organs of carp (Cyprinus carpio).

In this study, at first, we determined the optimal assay conditions for Ethoxyresorufin-O-deethylase activity and cytochrome P450 contents in the liver and two immune organs (spleen and head kidney) of carp. The Km values of cytochrome P450 1A activity were identical in the three organs, demonstrating that the enzyme belongs to the same isoform. In a second step, we showed that carp contained endogenous cytochrome P450 and EROD activity in two immune organs like in liver. These enzyme activities can be induced in a dose dependent manner by 3-methylcholanthrene, a specific inducer of cytochrome P450 1A, in the three organs. These results suggest that spleen and head kidney, the important immune organs in teleost fish, may be implicated in biotransformation for a class of contaminants like polycyclic aromatic hydrocarbons. In future, we can study the interaction between immune system and biotransformation system in fish.

Cutaneous challenge with chemical warfare agents in the SKH-1 hairless mouse (II): effects of some currently used skin decontaminants (RSDL and Fuller's earth) against liquid sulphur mustard and VX exposure.

Using the hairless mouse screening model presented in the companion paper(1) the aim of this study was to assess two skin decontaminating systems: Fuller's earth (FE) and Reactive Skin Decontamination Lotion (RSDL) against two extremely toxic chemical warfare agents that represent a special percutaneous hazard, sulphur mustard (SM) and O-ethyl-S-(2[di-isopropylamino]ethyl)methyl-phosphonothioate (VX). Five minutes after being exposed on the back to either 2 µL of neat sulphur mustard or 50 µg.kg(-1) of diluted VX, mice were decontaminated. Both systems were able to reduce blisters 3 days after SM exposure. However, RSDL was found to be more efficient than FE in reducing the necrosis of the epidermis and erosion. In the case of VX exposure, RSDL, whatever the ratio of decontaminant to toxicant used (RSDL 10, 20, 50), was not able to sufficiently prevent the inhibition of plasma cholinesterases taken as a surrogate marker of exposure and toxicity. Only FE reduced significantly the ChE inhibition. Some of these observations are different from our previous results obtained in domestic swine and these changes are thus discussed in the perspective of using SKH-1 hairless mice for the initial in vivo screening of decontaminants.

Cutaneous challenge with chemical warfare agents in the SKH-1 hairless mouse. (I) Development of a model for screening studies in skin decontamination and protection.

Exposure to lethal chemical warfare agents (CWAs) is no longer only a military issue due to the terrorist threat. Among the CWAs of concern are the organophosphorus nerve agent O-ethyl-S-(2[di-isopropylamino]ethyl)methyl-phosphonothioate (VX) and the vesicant sulfur mustard (SM). Although efficient means of decontamination are available, most of them lose their efficacy when decontamination is delayed after exposure of the bare skin. Alternatively, CWA skin penetration can be prevented by topical skin protectants. Active research in skin protection and decontamination is thus paramount. In vivo screening of decontaminants or skin protectants is usually time consuming and may be expensive depending on the animal species used. We were thus looking for a suitable, scientifically sound and cost-effective model, which is easy to handle. The euthymic hairless mouse Crl: SKH-1 (hr/hr) BR is widely used in some skin studies and has previously been described to be suitable for some experiments involving SM or SM analogs. To evaluate the response of this species, we studied the consequences of exposing male anaesthetized SKH-1 mice to either liquid VX or to SM, the latter being used in liquid form or as saturated vapours. Long-term effects of SM burn were also evaluated. The model was then used in the companion paper (Taysse et al.(1)).

Effects of repeated low-dose soman exposure on monoamine levels in different brain structures in mice.

In order to better understand the effects of repeated low-dose exposure to organophosphorus (OPs) on physiological and behavioural functions, we analysed the levels of endogenous monoamines (serotonin and dopamine) in different brain areas after repeated exposure of mice to sublethal dose of soman. Animals were injected once a day for 3 days with 0.12 LD50 of soman (47 microg/kg, i.p.). They did not show either severe signs of cholinergic toxicity or pathological changes in brain tissue. 24 h after the last injection of soman, inhibition of cholinesterase was similar in plasma and brain (32% and 37% of inhibition respectively). Afterwards, recovery of cholinesterase activity was faster in the plasma than in the brain. Dopamine levels were not significantly modified. On the other hand, we observed a significant modification of the serotoninergic system. An increase of the 5-HIAA/5-HT ratio was maintained for 2 and 4 weeks after exposure in the hippocampus and the striatum respectively. This study provides the first evidence of a modification of the 5-HT turnover in the hippocampus and the striatum after repeated low-dose intoxication with a nerve agent. Further experiments are necessary to evaluate the relationship between these modifications and the unexpected neuropsychological disorders usually reported after chronic exposure of organophosphorus.

Interleukin-1alpha and tumor necrosis factor alpha modulate cytochrome P450 activities in carp (Cyprinus carpio).

In mammals, it has been shown that the activation of host defense mechanisms down-regulates microsomal cytochrome P450 by the liberation of cytokines. We investigated the effect of interleukin-1alpha (IL1alpha) and tumor necrosis factoralpha (TNFalpha) on constitutive and 3-methylcholanthrene (3-MC)-induced biotransformation activities in carp. We have first measured the time course response of ethoxyresorufine O-decthylase (EROD) activity in liver, head kidney, and spleen 1, 2, 3, 5, and 7 days after intraperitoneal injection of a prototypical Cyp 1A inducer (3-MC). This activity was compared to the rate of 3-MC accumulation in all organs tested. A correlation between a diminution of EROD activity and an increase in 3-MC concentration in each organ was observed. We have also tested the effects of two inflammatory cytokines (IL1alpha and TNFalpha) on biotransformation activities. Intravenous injection of these compounds resulted in a marked depression of 3-MC-induced glutathione S-transferase activity in all organs tested and in 3-MC-increased cytochrome P450 content in the liver and head kidney. TNFalpha produced an increase in basal EROD activity in the liver and head kidney. Taken together, these results suggested that, as in mammals, the activation of host defense mechanisms regulates microsomal cytochrome P450 and related enzymes in fish.

Peripheral ChE inhibition modulates brain monoamines levels and c-fos oncogene in mice subjected to a stress situation.

The present study examined, in mice, whether regional patterns of brain monoamines concentrations (DA, 5-HT and their metabolites) and expression of c-Fos protein, that may represent a prolonged functional change in neurons, could be changed after a combined exposure to stress and the peripheral cholinesterase reversible inhibitor pyridostigmine (PYR). Animals were subjected every day to a random combination of mild unescapable electric footshocks and immobilization over a 12-day period, resulting in a significant increase of glucocorticoids levels and an activation of c-fos in hippocampus, thalamus and piriform cortex. This stress protocol induced a significant increase of 5-HT levels in striatum, hippocampus and ponto mesencephalic area (PMA) but failed to induce any DA activation. When PYR (0.2 mg/kg s.c. inducing 19-35% inhibition of the plasmatic ChE activity) was administered twice a day during the last 5 days of the stress session, 5-HIAA levels and expression of c-fos oncogene were significantly increased in the most of the brain areas studied. DA levels were also enhanced in striatum/hippocampus as a result of a possible activation of mesolimbic and nigrostriatal dopamine systems. Taken together, these results suggest that a combined exposure to certain stress conditions and PYR leads, in mice, to functional changes in neurons and may affect centrally controlled functions. The mechanisms underlying these modifications and their behavioral implications remain to be further investigated.

Induction of acute lung injury after intranasal administration of toxin botulinum a complex.

The inhalation of aerozolized botulinum toxin may represent a potential significant hazard to both military and civilian personnel. Since the lung is the primary target organ for inhaled toxin, the investigation reported herein was conducted to examine lung function in mice exposed to botulinum toxin A complex by intranasal route. Data includes lethality, symptomatology, measurement of respiratory function (minute ventilation, respiratory frequency, and tidal volume), and histopathology of the lungs. The clinical signs of intoxication are similar to those observed in foodborne botulism. Plethysmography revealed severe impairment of all respiratory parameters tested from 7 hours postexposure. Severe lung lesions, possibly secondary to the intoxication, were observed in mice who survived 14 days after the toxin challenge. These included intra-alveolar hemorrhage and interstitial edema. Mice immunized by the pentavalent (ABCDE) toxoid were protected against the neurotoxin (4 LD50) as revealed by the decrease of lethality and severity of nervous signs of intoxication, but not against histopathological changes in the lungs. These effects are nonspecific and require further experiments in order to specify the relationships between the pathology and the inflammatory process in the lung due to mediators such as cytokines,and possibly permanent physiological sequelae.

Modulation of drug-metabolizing systems by bacterial endotoxin in carp liver and immune organs.

This report describes a study of the effects of bacterial endotoxin [lipopolysaccharide (LPS)] on cytochrome P450 levels and ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST) activities in liver and two main immune organs of carp: spleen and head kidney. Also studied was the paucity of the carp drug-metabolizing system in an environment subject to pollution by a polycyclic aromatic hydrocarbon, 3-methylcholanthrene (3MC), when fish respond to an immune activation by lipopolysaccharide (LPS). In the presence of bacterial endotoxin the basal cytochrome P450 levels were decreased in liver and spleen. EROD activity was increased in liver and basal GST activity was increased in spleen. When fish were treated concomitantly with 3MC and LPS, a suppression of cytochrome P450 induction in liver and head kidney was observed. EROD activity induced by 3MC was not modified by administration of LPS. GST activity was suppressed by treatment with LPS and inducing agent in liver and head kidney. In the present study it was found that endotoxin can have profound and differential effects on fish basal biotransformation of drugs in the liver and immune organs. Also, the induction of biotransformation enzymes by 3MC was modified when fish responded to an immune stimulation.

The effects of 3-methylcholanthrene on macrophage respiratory burst and biotransformation activities in the common carp (Cyprinus carpio L.).

The sensitivity of phagocytic cell function as a bioindicator of pollution stress by polycyclic aromatic hydrocarbons was evaluated in the common carp (Cyprinus carpio L). The time course response of the head-kidney macrophage respiratory burst was measured 1, 2, 3, 5 and 7 days after intraperitoneal injection of a prototypical Cyp 1A inducer (3-methylcholanthrene). This immune activity was compared to the rate of induction of total cytochrome P450, ethoxyresorufin O-deethylase activity (EROD) and glutathione S-transferase activity (GST) in the liver and head-kidney. 3-methylcholanthrene (40 mg kg(-1)) caused a rapid increase in the macrophage respiratory burst. This response was maximal at day 3 post exposure and coincided with maximum induction of cytochrome P450 and EROD activity in liver and head-kidney. Moreover, alpha-naphtoflavone, which functions as both an Ah receptor antagonist and an inhibitor of cytochrome P450 1A activity, reversed the 3-methylcholanthrene induction of immune and enzymatic parameters measured, suggesting metabolic processes. Taken together these results suggest that the induction of macrophage oxidative function may be an equally sensitive marker of exposure to polycyclic aromatic hydrocarbon as the induction of biotransformation activities and confirm that responses mediated by the Ah receptor are similar, if not identical, to those of mammals.