A comparison of the neuroprotective efficacy of individual oxime (HI-6) and combinations of oximes (HI-6+trimedoxime, HI-6+K203) in soman-poisoned rats

The ability of two combinations of oximes (HI-6+trimedoxime, HI-6+K203) to reduce soman-induced acute neurotoxic signs and symptoms was compared with the neuroprotective efficacy of the oxime HI-6 alone, using a functional observational battery. Soman-induced neurotoxicity and the neuroprotective effects of HI-6 alone and HI-6 combined with trimedoxime or K203 in rats poisoned with soman at a sublethal dose (90 μg/kg intramuscularly, i.m.; 80% of LD?? value) were monitored by the functional observational battery at 24 hours following soman administration. The results indicate that both tested oxime mixtures combined with atropine were able to allow soman-poisoned rats to survive 24 hours following soman challenge, while 4 nontreated soman-poisoned rats and 1 soman-poisoned rat treated with oxime HI-6 alone combined with atropine died within 24 hours following soman poisoning. While the oxime HI-6 alone combined with atropine treatment was able to eliminate a few soman-induced neurotoxic signs and symptoms, both oxime mixtures showed higher neuroprotective efficacy in soman-poisoned rats. Especially, the combination of HI-6 with trimedoxime was able to eliminate most soman-induced neurotoxic signs and symptoms and markedly reduce acute neurotoxicity of soman in rats. Thus, both tested mixtures of oximes combined with atropine were able to increase the neuroprotective effectiveness of antidotal treatment of acute soman poisonings, compared to the individual oxime.     

HI-6 in man: efficacy of the oxime in poisoning by organophosphorus insecticides.

The efficacy of the oxime HI-6 was studied as a treatment for organophosphorus poisoning. HI-6 was given four times daily as a single intramuscular injection of 500 mg accompanied by atropine and diazepam therapy. Oxime treatment was started on admission and continued for a minimum of 48 h and a maximum of 7 d. HI-6 rapidly reactivated human blood acetylcholinesterase inhibited by dimethoxy organophosphorus compounds, while the dimethoxy-inhibited enzyme was mainly resistant to the treatment by HI-6. Although both HI-6 and pralidoxime chloride reactivated the red blood cell cholinesterase in quinalphos-poisoned subjects, the return of enzyme activities was more rapid following the use of HI-6. The general improvement of poisoned patients, which was sometimes more rapid than the rise of acetylcholinesterase activity, pointed to direct pharmacological effects of HI-6. No undesirable side-effects were noted in patients when HI-6 plasma concentrations were maintained at levels far above the 'therapeutic' concentration for up to 7 d.     

HI-6 modulates immunization efficacy in a BALB/c mouse model

HI-6 is used as an antidote to nerve agents. It can also act as an antagonist to acetylcholine receptors (AChRs) including the nicotinic receptor, α 7 nAChR which is involved in regulating the immune response through macrophages. This experiment investigated the efficacy of HI-6 to regulate the immune response. Laboratory BALB/c mice received HI-6 and/or keyhole limpet hemocyanin (KLH) as an antigen. Antibody production was investigated after either 21 or 65 days when either single or repeated dose of antigen was applied. We confirmed that HI-6 significantly improved vaccination efficacy when KLH was given in a dose of 1 mg/kg. The effect was dose dependent. A combination of HI-6 and KLH produced a vaccination of almost the same efficacy as that for Freund's complete adjuvant. The findings point at the suitability of HI-6 for improving vaccination efficacy at the level of immunity regulation by the nervous system.     

Behavioral effects of modafinil in marmoset monkeys

Rationale Modafinil is increasingly used in sleep disturbances in general and in neurodegenerative diseases and is recently being used in healthy people for attention control. However, the application of modafinil is possibly not only restricted to alertness enhancing effects. More insight in this compound may lead to new applications. Not all behavioral aspects have been studied sufficiently; therefore, more detailed investigations on modafinil’s positive and aversive behavioral effects are addressed in this paper.Objectives Determination of effects of modafinil in marmoset monkeys with observational methods and with behavioral tests measuring locomotor activity, hand–eye coordination, response to a threat situation and startle response.Materials and methods Two hours after oral administration of modafinil in doses of 50, 100, 150, and 225 mg/kg, animals were observed and tested in the behavioral test systems.Results Locomotor activity was increased after 100 mg/kg modafinil in the Bungalow test and after 100, 150, and 225 mg/kg, as found in the movement parameters of the human threat test. Moreover, modafinil showed anxiolytic-like effects in the human threat test. No other side effects were observed, nor were the hand–eye coordination and startle response affected.Conclusions Besides psychostimulation, modafinil has no aversive effects in the doses used in the domains measured. The potential anxiolytic-like effects of modafinil may create new possibilities for the therapeutic use of modafinil.     

Reduction and binding of arsenate in marmoset monkeys

The metabolism of ⁷⁴As-arsenate (As V, 0.4 mg As/kg body weight, IV) in marmoset monkeys (two males and two females) was studied. Unlike all other animal species studied so far, the marmoset was found to be unable to metabolize the arsenate to dimethylarsinic acid. Most of the absorbed arsenate was reduced to arsenite (As III) in vivo. Only 20% was excreted in the urine as unchanged As V. A further 20% of the dose was excreted as As III. The rest of the As III produced was bound to the tissues, giving a distribution picture very similar to that reported earlier for marmoset monkeys given arsenite. The tissues with longest retention of arsenic were the liver, upper gastrointestinal tract (oral cavity and esophagus), skin, kidneys and gall bladder. The pronounced accumulation in the liver resulted from specific binding of arsenic to the rough microsomal membranes, unique to this animal species.At the time of this study, visiting researcher at the National Institute of Environmental Medicine and the Department of Environmental Hygiene, the Karolinska Institute, Stockholm, Sweden     

The pharmacokinetics of HI-6 in beagle dogs

The pharmacokinetics of HI-6 were studied following intravenous administration to beagle dogs (n = 7). The bioavailability of two different strength intramuscularly administered doses was also determined in the same animals. After a 20 mg kg-1 intravenous dose, the mean (+/- S.D.) initial HI-6 plasma concentration was 93.1 +/- 10.8 micrograms ml-1. The mean half-life was 48.2 +/- 17.7 min, the mean total body clearance was 5.16 +/- 0.81 ml min-1 kg-1, the mean apparent volume of distribution was 0.37 +/- 0.20 l kg-1 and 61.2 +/- 14.6 per cent of the dose was excreted as unchanged drug. The pharmacokinetic constants calculated following the 20 mg kg-1 intramuscular doses of 250 and 25 mg ml-1 solutions were not significantly different from those obtained following the intravenous dose. Also, the areas under the plasma concentration versus time curves were not significantly different indicating 100 per cent bioavailability from the intramuscular route of administration.     

HI-6 pharmacokinetics in rabbits after intravenous and intramuscular administration.

The pharmacokinetics of HI-6 ((4-carboxamidopyridinium (1) methyl)-(2'-hydroxyiminomethyl-pyridinium (1') methyl) ether dichloride) have been studied in rabbits receiving an intramuscular (50 micrograms kg-1) or intravenous (12.5 micrograms kg-1) dose. The plasma concentration-time profile for the intramuscular dose (n = 8) fits a one-compartment open model with first-order absorption and elimination. The absorption half-life was 2 min and maximum concentration (51 micrograms mL-1) was reached in 9 min. The pharmacokinetics for the intravenous dose (n = 8) was described by a two-compartment open model with first-order distribution and elimination. The apparent volume of distribution was 0.1 L kg-1. Half-lives of distribution and elimination were 5 and 38 min, respectively. The results indicate HI-6 is rapidly absorbed, distributed and eliminated in rabbits receiving an intramuscular dose.     

Treatment efficacy in a soman-poisoned guinea pig model: added value of physostigmine?

Current treatment of organophosphate poisoning is insufficient, and survivors may suffer from long-lasting adverse effects, such as cognitive deficits and sleep-wake disturbances. In the present study, we aimed at developing a guinea pig model to investigate the benefits of immediate and delayed stand-alone therapy on the development of clinical signs, EEG, heart rate, respiration and AChE activity in blood and brain after soman poisoning. The model allowed the determination of the therapeutic effects at the short-term of obidoxime, atropine and physostigmine. Obidoxime exerted the highest therapeutic efficacy at administration of the lowest dose (3.1 mg/kg i.m.), whereas two higher doses (9 and 18 mg/kg) were less effective on most parameters. Addition of atropine at 0.03 and 3 mg/kg (i.m.) to the treatment did not improve the therapeutic effects of obidoxime alone. Physostigmine (0.8 mg/kg im) at 1 min after poisoning increased mortality. Two lower doses (0.1 and 0.3 mg/kg i.m.) showed improvements on all parameters but respiration. The middle dose was most effective in preventing seizure development and therefore assessed as the most efficacious dose. Combined treatment of obidoxime and physostigmine shortened the duration of seizures, if present, from up to 80 min to ~10–15 min. In practice, treatment will be employed when toxic signs appear, with the presence of high levels of AChE inhibition in both blood and brain. Administration of physostigmine at that moment showed to be redundant or even harmful. Therefore, treatment of OP poisoning with a carbamate, such as physostigmine, should be carefully re-evaluated.     

Cardiopulmonary effects of HI-6 treatment in soman intoxication

The cardiopulmonary effects of HI-6, together with atropine and soman, were studied in the rat. HI-6 is an effective antidote in acute poisoning with the nerve agent soman. The therapeutic efficiency of HI-6 is still unclear and cannot be explained entirely by the HI-6 reactivating ability of acetylcholinesterase (AChE). Other non-cholinergic factors must be involved. One possible detoxifying process might be an effect of HI-6 on the blood flow to sensitive organs. The purpose of the present study was to investigate 1) whether soman per se induces changes in regional blood flow and 2) whether the blood flow to different organs is affected when HI-6 (50 mg x kg(-1) i.m.) and atropine (10 mg x kg(-1) i.m.) are given either before or immediately after soman intoxication (90 microg x kg(-1) s.c.). For regional blood flow determinations the microsphere method was used with male Wistar rats weighing 300-400 g. The rats were anaesthetised and breathed spontaneously during the experiment. Three different blood flow measurements were made in the same animal and concomitant physiological parameters such as mean arterial blood pressure and respiratory rate were recorded. The blood AChE activity was followed throughout the experiment. Our results show that when HI-6 is given after intoxication with soman, dramatic changes in blood flow occur with a significant decrease in both respiratory rate and blood AChE activity. If HI-6 is given prior to the intoxication, however, all rats are unaffected and none of the parameters measured are changed.     

Non-reactivating effects of HI-6 on hippocampal neurotransmission

 Effects of the oxime HI-6, unrelated to reactivation of acetylcholinesterase (AChE), on field potentials in the dentate gyrus of the rat hippocampus following AChE inhibition, were investigated both in vitro and in vivo. In hippocampal slices, AChE inhibition decreased the perforant path evoked population spike amplitude (PSA). This effect could be prevented by pre-incubation of the slices with atropine (0.1–1 μM) or with the M₁ muscarinic receptor antagonist pirenzepine (1 μM). A similar preventive effect was found after pre-incubation with the GABA_A antagonist picrotoxin (20 μM), suggesting that the effects of AChE inhibition in vitro may be due to an enhancement of GABAergic inhibitory activity via activation of M₁-muscarinic receptors. The effects of AChE inhibition in vivo were variable; both increases and decreases of the PSA were found. Following AChE inhibition, HI-6 increased the PSA dose-dependently, both in the in vivo and in the in vitro hippocampus. At higher oxime doses the perforant path stimulation elicited multiple population spikes. The effects of the oxime were presumably not mediated by an antagonism of cholinergic receptors, since they could not be mimicked with cholinergic antagonists like atropine, mecamylamine or gallamine. Further testing of the nature of the HI-6 effect in hippocampal slices in vitro, using a paired antidromic-orthodromic stimulation protocol, showed that HI-6 may interfere with GABAergic inhibition. Received: 21 March 1994 / Accepted: 13 June 1994     

Therapeutic effects of Delta9-THC and modafinil in a marmoset Parkinson model.

Current therapies for Parkinson's disease (PD) like l-dopa and dopamine (DA) agonists have declined efficacy after long term use. Therefore, research towards supplementary or alternative medication is needed. The implementation in PD can be expedited by application of compounds already used in the clinic. In this study the therapeutic effects of the psychoactive compounds Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and modafinil were tested in the 1-methyl-1,2,3,6-tetrahydropyridine (MPTP)-marmoset model for PD. The anti-parkinson effects of Delta(9)-THC (4 mg/kg) and modafinil (100 mg/kg) in parkinsonian marmosets were assessed with two behavioral rating scales covering parkinsonian symptoms and involuntary movements and two test systems assessing the locomotor activity and hand-eye coordination. Delta(9)-THC improved activity and hand-eye coordination, but induced compound-related side-effects. Modafinil improved activity and observed parkinsonian symptoms but not hand-eye coordination. It can be concluded that both compounds have therapeutic values and could supplement existing therapies for PD.     

Bioavailability and disposition kinetics of HI-6 in Beagle dogs

The absorption and disposition kinetics of HI-6 were determined in Beagle dogs given single doses (25 mg kg^?1) of the drug by the intravenous, intramuscular, and oral routes. Concentrations of the oxime in plasma and urine were measured by HPLC. A twocompartment open model was used to describe the disposition curve following intravenous drug administration while a one-compartment open model with first-order absorption adequately described the data following intramuscular or oral administration of the dose. Extravascular distribution of HI-6 was limited (V_ss 203 ml kg^?1) and the drug was eliminated rapidly after intravenous administration (t_1/2 46.5 min, MAT 55.4 min). Systemic clearance was 3.68 ml min^?1 × kg. A major fraction of the dose (63.7 per cent) was excreted in urine over a 24-h collection period. Following intramuscular drug administration, the absorption half-life (t_1/2(a), 5.3 min), MAT (17.1 min), C_max (70.37 μg ml^?1) and t_max (15.9 min) indicate that the drug was rapidly absorbed. Systemic availability was 83.43 per cent after oral drug administration, absorption was preceded by a lag time (23.2 min). The t_1/2(a) (41.5 min), MAT (81.6 min), C_max (4.30 μg ml^?1) and T_max (90.6 min) indicate somewhat delayed absorption. Systemic availability (11.38 per cent) and the fraction of dose excreted unchanged in the urine (9.3 per cent) show that the drug was poorly absorbed. The apparent half-life (58.0 min) and MRT (137.6 min) following oral administration were significantly longer (p <0.05) than following intravenous or intramuscular administration suggesting that the rate of absorption from the gastrointestinal tract decreases the elimination rate of the drug. In conclusion, HI-6 has limited distribution within the body, is rapidly eliminated mainly by renal excretion unchanged in the urine, and the bioavailability (i.e. rate and extent of absorption) of the drug varies with the route of administration.     

The pharmacokinetics and pharmacodynamics of two HI-6 salts in swine and efficacy in the treatment of GF and soman poisoning

Anesthetized pigs were injected i.m. with 500 mg HI-6 dichloride (HI-6 2Cl) (1-[[[4-(aminocarbonyl)-pyridinio]methoxy]methyl]-2[(hydroxyimino)methyl]pyridinium dichloride; CAS 34433-31-3)) or the molar equivalent of HI-6 dimethanesulphonate (HI-6 DMS) 633 mg. Plasma HI-6 concentrations were measured by HPLC (1, 3, 5, 10, 15, 30, 60 min and every 30 min until 4h or 6h following the i.v. or i.m. dose respectively) while a variety of physiological responses were continuously examined. HI-6 (500 mg 2Cl or 633 mg DMS) resulted in an identical pharmacokinetic profile unaffected by atropine co-administration. Neither HI-6 salt resulted in clinically significant changes in cardiovascular or respiratory function. HI-6 DMS (1899 mg i.v.) resulted in plasma HI-6 concentrations about 10 times higher than measured following i.m. 500 mg 2Cl or 633 mg DMS and resulted in small transitory effect on mean arterial pressure. Atropine plus HI-6 DMS (1-9 mg/kg or 127-172 mg/kg i.m.) protected up to 100% of guinea pigs exposed to 5 x LD50 of GF (cyclohexyl methyl phosphonoflouridate) or soman (pinacolyl methylphosphonofluoridate) (GD) respectively. The results suggest that the two HI-6 salts have a similar pharmacokinetic profile while HI-6 DMS appears extremely safe and effective against nerve agents and may be as suitable for human use.     

Pharmacokinetics of the oxime HI-6 from a mixture with atropine sulphate in dogs.

The pharmacokinetics of the oxime HI-6 from an aqueous solution and from a mixture containing HI-6 and atropine (in doses similar as proposed for their combination in an automatic injector) was studied in German shepherd dogs. A standard manual injection of mixed drugs was followed by enhanced resorption of HI-6 while the elimination curves were quite similar. A comparison of the parameters describing relative bioavailability at the 80% probability level did not reveal any significant differences between the formulations of HI-6. The increase in HI-6 level in blood of animals receiving a mixture is more likely to be attributed to the local vasodilatation than to the systemic cardiovascular effects of atropine.     

The influence of anticholinergic drug selection on the efficacy of antidotal treatment of soman-poisoned rats

The influence of some anticholinergic drugs (atropine, benactyzine, biperiden, scopolamine) on the efficacy of antidotal treatment to eliminate soman (O-pinacolyl methylphosphonofluoridate)-induced disturbance of respiration and circulation and to protect experimental animals poisoned with supralethal dose of soman (1.5 x LD(50)) was investigated in a rat model with on-line monitoring of respiratory and circulatory parameters. While the oxime HI-6 in combination with atropine prevented soman-induced changes in monitored physiological parameters insufficiently and very shortly, the combination of HI-6 with benactyzine or biperiden is able to prevent soman-induced alteration of respiration and circulation much more longer. Nevertheless, only rats treated with HI-6 in combination with scopolamine were fully protected against the lethal toxic effects of soman within 2 h following soman challenge. Our findings confirm that anticholinergic drugs with the strong central antimuscarinic activity, such as benactyzine, biperiden and especially scopolamine, seem to be more effective adjuncts to HI-6 treatment of severe acute soman-induced poisoning than atropine.     

Diazepam-induced decrease in anxiety-like behaviors of marmoset monkeys exposed to a novel open-field

Unfamiliar environments can be a source of stress, fear and anxiety for marmoset monkeys. In spite of existing data, the influence of putative anxiolytics on the effects of novel environments has yet to be tested in primates. Therefore, the behavior of adult black tufted-ear marmosets to a single brief (15 min) exposure to a novel environment was analyzed in the presence and absence of diazepam (DZP). Marmosets were pre-treated with vehicle (n = 5) or diazepam (0.5 mg/kg, ip; n = 5) and submitted to a 15 min free exploration trial within a rectangular open-field arena. DZP-treated subjects, compared to vehicle controls, demonstrated significantly lower rates of (phee) contact calls and exploration, while a higher scan duration. Sojourn time in the arena's central zone was also significantly higher in the former group and sedation was not observed. Thus, pre-treatment with the benzodiazepine DZP decreased several anxiety-related behaviors induced by subjecting the marmosets to a new environment. The results also indicate that, as with rodent subjects, the open-field may provide a useful simple paradigm for assessing anxiety-like behaviors in this primate and, as such, constitutes a unique opportunity for direct comparative studies between rodents and marmoset monkeys in terms of anxiety and/or sedation.     

Neuroprotective effects of currently used antidotes in soman-poisoned rats

The neuroprotective effects of antidotes (atropine, obidoxime, obidoxime/atropine mixture) on rats poisoned with soman at a sublethal dose (54 microg/kg, im, 80% of LD(50) value) were studied. The soman-induced neurotoxicity was monitored using a functional observational battery (FOB) and an automatic measurement of motor activity. The neurotoxicity of soman was monitored at 24 h and 7 days following soman challenge. The results indicate that obidoxime alone is not able to protect the rats from the lethal effects of soman. Three soman-poisoned rats treated with obidoxime alone died within 24 h. On the other hand, atropine alone or combined with obidoxime allows all soman-poisoned rats to survive within 7 days following soman challenge. Atropine alone and combined with obidoxime seems to be relatively effective antidotal treatment for the elimination of soman-induced neurotoxicity in the case of sublethal poisonings, although the antidotal mixture is significantly less effective than atropine alone because obidoxime can counteract the beneficial effects of atropine. Obidoxime appears to be practically ineffective to diminish soman-induced neurotoxicity. The neuroprotective effects of antidotal mixture consisting of atropine and obidoxime depend on the antimuscarinic effects of atropine only. Thus, the replacement of obidoxime by more effective acetylcholinesterase (AChE) reactivators is necessary to increase the neuroprotective efficacy of antidotal treatment in the case of soman poisonings.     

Comparison of reactivating and therapeutic efficacy of two salts of the oxime HI-6 against tabun, soman and cyclosarin in rats

The reactivating and therapeutic efficacy of two salts of the oxime HI-6 (dichloride and dimethanesulphonate) against chosen nerve agents (tabun, soman and cyclosarin) was compared in rats. The potency of both salts of HI-6 to decrease the acute toxicity of tabun, soman and cyclosarin was similar in nerve agent-poisoned rats. While the potency of HI-6 dichloride and HI-6 dimethanesulphonate to counteract acute toxic effects of tabun is rather low, both salts of HI-6 were able to decrease the acute toxicity of soman two times and acute toxicity of cyclosarin more than three times. The therapeutic efficacy of both salts of the oxime HI-6 corresponds to their reactivating potency. While the reactivating efficacy of HI-6 dichloride as well as HI-6 dimethanesulphonate against tabun was negligible, their potency to reactivate soman-inhibited acetylcholinesterase and cyclosarin-inhibited acetylcholinesterase in peripheral (blood) and central (brain) compartment was relatively high. HI-6 dichloride showed a somewhat higher potency to reactivate tabun-inhibited acetylcholinesterase in brain, and soman-inhibited acetylcholinesterase in blood and brain than HI-6 dimethanesulphonate but the differences were not significant. Thus, the replacement of dichloride anion by dimethanesulphonate anion in the oxime HI-6 does not influence the therapeutic and reactivating efficacy of the oxime HI-6 against nerve agents. In addition, the higher solubility and stability of HI-6 dimethanesulphonate in comparison with HI-6 dichloride makes it possible to increase the dose and thus, the effectiveness of the oxime HI-6 in the antidotal treatment of acute nerve agent poisonings.     

Four-week oral toxicity studies of the new quinolone antibacterial agent cetefloxacin tosylate in rats and marmoset monkeys.

Four-week oral toxicity studies with cetefloxacin tosylate ((-)-7[3-(R)-amino-2-(S)-methyl-1-azetidinyl]-1-(2,4- difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-3-quinolinecarboxylic acid tosylate, CAS 141725-88-4 (base), E-4868.Ts) a new quinolone antibacterial agent, were performed in Sprague-Dawley rats and marmoset monkeys at doses of 100, 450, 2000 mg/kg/d and 25, 50, 125, 300 mg/kg/d, respectively. In rats, due to its toxicity the high dose was decreased to 1000 mg/kg/d after 3 days of treatment. Mortality was recorded among high dose rats receiving 2000 or 1000 mg/kg/d. Rats receiving dosages of 450 or 2000/1000 mg/kg/d showed less activated mandibular lymph nodes, cortical lymphocyte depletion of mandibular and/or mesenteric lymph nodes, atrophy of the white pulp of the spleen, cortical atrophy of thymus and thymic apoptosis. Enlarged caeca, increased water consumption and variations in plasma electrolyte levels were observed in animals receiving these dosages and in male rats receiving 100 mg/kg/d. Low neutrophil counts were observed in rats receiving dosages of 100 or 450 mg/kg/d, and increased alkaline phosphatase and alanine transaminase plasma levels and slightly decreased plasma protein levels in females receiving 450 or 2000/1000 mg/kg/d. Marmosets receiving dosages of 50 mg/kg/d and above displayed several clinical signs which included emesis, diarrhoea, ptosis, occasional episodes of under- and overactivity, and excessive scratching activity. Skin reddening was observed during the first week of treatment in marmosets receiving 300 mg/kg/d. On the basis of the results obtained it can be concluded that the non-toxic doses of E-4868. Ts after 4-week oral administration in rats and marmoset monkeys were 100 and 25 mg/kg/d, respectively.