Treatment of status epilepticus with ketamine, are we there yet?

Status epilepticus (SE), a neurological emergency both in adults and in children, could lead to brain damage and even death if untreated. Generalized convulsive SE (GCSE) is the most common and severe form, an example of which is that induced by organophosphorus nerve agents. First- and second-line pharmacotherapies are relatively consensual, but if seizures are still not controlled, there is currently no definitive data to guide the optimal choice of therapy. The medical community seems largely reluctant to use ketamine, a noncompetitive antagonist of the N-methyl-d-aspartate glutamate receptor. However, a review of the literature clearly shows that ketamine possesses, in preclinical studies, antiepileptic properties and provides neuroprotection. Clinical evidences are scarcer and more difficult to analyze, owing to a use in situations of polytherapy. In absence of existing or planned randomized clinical trials, the medical community should make up its mind from well-conducted preclinical studies performed on appropriate models. Although potentially active, ketamine has no real place for the treatment of isolated seizures, better accepted drugs being used. Its best usage should be during GCSE, but not waiting for SE to become totally refractory. Concerns about possible developmental neurotoxicity might limit its pediatric use for refractory SE.

Ketamine combinations for the field treatment of soman-induced self-sustaining status epilepticus. Review of current data and perspectives.

Organophosphorus nerve agents (NA), potent irreversible cholinesterase inhibitors, could induce severe seizures, status epilepticus (SE), seizure-related brain damage (SRBD) and lethality. Despite the lack of data in the case of NA, clinical evidences suggest that SE survivors could suffer from neurological/cognitive deficits and impairments such as spontaneous recurrent seizures (epilepsy) after a latent period of epileptogenesis. It is beyond doubt that an effective and quick management of the initial seizures and prevention of SRBD are critical to prevent these long-term consequences, explaining why most experimental data are focusing on the 5-40min post-exposure time frame. However, in field conditions, treatment may be delayed and with the exception of NMDA receptor antagonists, currently no drug provides protection (against lethality, seizures, SRBD and neurological consequences) when seizures are left unabated for one hour or more. Ketamine (KET) is the only NMDA antagonist licensed as an injectable drug in different countries and remains an anesthetic of choice in some difficult field conditions. In this short review paper, after a presentation of some of the key points of the pathophysiology of NA-induced SE and a quick survey of the potential therapeutic avenues in the context of delayed treatment of NA-induced SE, we will review the recent data we obtained showing that KET, in combination with atropine sulfate (AS), with or without a benzodiazepine, considerably reduces soman-induced neuroinflammation, provides neuroprotection, histologically and functionally, and also positively modify soman-induced changes in brain metabolism. Finally, we will also mention some results from safety studies including those bringing evidence that, at difference with MK-801, KET does not impair thermoregulation and even seems to reduce AS-induced heat stress. All in all, KET, in combination, appears a good candidate for the out-of-hospital treatment of severe NA-induced SE.

Prediction of neuroprotective treatment efficiency using a HRMAS NMR-based statistical model of refractory status epilepticus on mouse: a metabolomic approach supported by histology.

This work presents a model combining quantitative proton HRMAS NMR data and PLS-DA for neuropathology and neuroprotection evaluation. Metabolic data were also confronted to histopathological results obtained using the same experimental conditions. Soman, when not lethal, can induce status epilepticus (SE), brain damage, histological lesions, and profound cerebral metabolic disorders as revealed using (1)H HRMAS NMR. Our challenge was to evaluate delayed treatments, which could control refractory SE and avoid brain lesions. For this aim, we have built a statistical model of soman intoxication describing brain metabolite evolution during 7 days. We have then used this model to evaluate the efficiency of a combination of ketamine/atropine (KET/AS) administrated 1 and 2 h after SE induction, compared to the immediate anticonvulsant therapy midazolam/atropine sulfate (MDZ/AS). Furthermore, quantitation of HRMAS NMR data allowed us to follow individual evolution of 17 metabolites. N-Acetylaspartate, lactate, or taurine presented a long lasting disruption, while glutamine, alanine, glycerophosphocholine and myo-inositol showed disruptions for 3 days with a reversion at day 7. These changes were completely normalized by the administration of MDZ/AS. Interestingly, they were also almost completely reversed by KET/AS 1 h postsoman. This work suggests further the predictive interest of HRMAS and PLS-DA for neuropathology/neuroprotection studies and also confirms, on the metabolic aspects, the neuroprotective potentials of KET/AS combinations for the delayed treatment of soman-induced SE.

Combinations of ketamine and atropine are neuroprotective and reduce neuroinflammation after a toxic status epilepticus in mice.

Epileptic seizures and status epilepticus (SE) induced by the poisoning with organophosphorus nerve agents (OP), like soman, are accompanied by neuroinflammation whose role in seizure-related brain damage (SRBD) is not clear. Antagonists of the NMDA glutamate ionotropic receptors are currently among the few compounds able to arrest seizures and provide neuroprotection even during refractory status epilepticus (RSE). Racemic ketamine (KET), in combination with atropine sulfate (AS), was previously shown to counteract seizures and SRBD in soman-poisoned guinea-pigs. In a mouse model of severe soman-induced SE, we assessed the potentials of KET/AS combinations as a treatment for SE/RSE-induced SRBD and neuroinflammation. When starting 30min after soman challenge, a protocol involving six injections of a sub-anesthetic dose of KET (25mg/kg) was evaluated on body weight loss, brain damage, and neuroinflammation whereas during RSE, anesthetic protocols were considered (KET 100mg/kg). After confirming that during RSE, KET injection was to be repeated despite some iatrogenic deaths, we used these proof-of-concept protocols to study the changes in mRNA and related protein contents of some inflammatory cytokines, chemokines and adhesion molecules in cortex and hippocampus 48h post-challenge. In both cases, the KET/AS combinations showed important neuroprotective effects, suppressed neutrophil granulocyte infiltration and partially suppressed glial activation. KET/AS could also reduce the increase in mRNA and related pro-inflammatory proteins provoked by the poisoning. In conclusion, the present study confirms that KET/AS treatment has a strong potential for SE/RSE management following OP poisoning. The mechanisms involved in the reduction of central neuroinflammation remain to be studied.

Hyperosmolar treatment of soman-induced brain lesions in mice: evaluation of the effects through diffusion-weighted magnetic resonance imaging and through histology.

PURPOSE: A convulsive dose of soman induces seizure-related brain damage (SRBD), including cerebral edema (CE) and neuronal loss. In the present study on soman-intoxicated mice, we applied diffusion-weighted magnetic resonance imaging (DW-MRI) and quantitative histology, and we measured brain water content to investigate the antiedematous and neuroprotective efficacies of two hyperosmolar treatments: mannitol (Mann) and hypertonic saline (HTS). METHODS: Mice intoxicated with soman (172 microg/kg after a protective pretreatment) were administered 1 min and 5-h post-challenge an i.v. bolus of saline, of Mann or of HTS. 1 day later, mice were examined with DW-MRI and then sacrificed for brain histology. Additional animals were intoxicated and treated similarly for the measurement of the brain water content (dry/wet weight method). RESULTS: In intoxicated controls, a significant decrease of the apparent diffusion coefficient (ADC), numerous damaged (eosinophilic) cells, high edema scores, and a significant increase in brain water content were detected 24-h post-challenge in sensitive brain structures. These soman-induced changes were not significantly modified by treatment with Mann or HTS. CONCLUSIONS: Treatment with hyperosmolar solutions did not reduce the effects of soman on ADC, on cell damage and on CE. Therefore, despite similar treatment protocols, the prominent protection by Mann that was previously demonstrated by others in poisoned rats, was not reproduced in our murine model.

Protective effects of S+ ketamine and atropine against lethality and brain damage during soman-induced status epilepticus in guinea-pigs.

Soman poisoning is known to induce full-blown tonic-clonic seizures, status epilepticus (SE), seizure-related brain damage (SRBD) and lethality. Previous studies in guinea-pigs have shown that racemic ketamine (KET), with atropine sulfate (AS), is very effective in preventing death, stopping seizures and protecting sensitive brain areas when given up to 1h after a supra-lethal challenge of soman. The active ketamine isomer, S(+) ketamine (S-KET), is more potent than the racemic mixture and it also induces less side-effects. To confirm the efficacy of KET and to evaluate the potential of S-KET for delayed medical treatment of soman-induced SE, we studied different S-KET dose regimens using the same paradigm used with KET. Guinea-pigs received pyridostigmine (26 microg/kg, IM) 30min before soman (62 microg/kg, 2 LD(50), IM), followed by therapy consisting of atropine methyl nitrate (AMN) (4 mg/kg, IM) 1min following soman exposure. S-KET, with AS (10mg/kg), was then administered IM at different times after the onset of seizures, starting at 1h post-soman exposure. The protective efficacy of S-KET proved to be comparable to KET against lethality and SRBD, but at doses two to three times lower. As with KET, delaying treatment by 2h post-poisoning greatly reduced efficacy. Conditions that may have led to an increased S-KET brain concentration (increased doses or number of injections, adjunct treatment with the oxime HI-6) did not prove to be beneficial. In summary, these observations confirm that ketamine, either racemic or S-KET, in association with AS and possibly other drugs, could be highly effective in the delayed treatment of severe soman intoxication.

Cerebral edema induced in mice by a convulsive dose of soman. Evaluation through diffusion-weighted magnetic resonance imaging and histology.

PURPOSE: In the present study, diffusion-weighted magnetic resonance imaging (DW-MRI) and histology were used to assess cerebral edema and lesions in mice intoxicated by a convulsive dose of soman, an organophosphate compound acting as an irreversible cholinesterase inhibitor. METHODS: Three hours and 24 h after the intoxication with soman (172 microg/kg), the mice were anesthetized with an isoflurane/N(2)O mixture and their brain examined with DW-MRI. After the imaging sessions, the mice were sacrificed for histological analysis of their brain. RESULTS: A decrease in the apparent diffusion coefficient (ADC) was detected as soon as 3 h after the intoxication and was found strongly enhanced at 24 h. A correlation was obtained between the ADC change and the severity of the overall brain damage (edema and cellular degeneration): the more severe the damage, the stronger the ADC drop. Anesthesia was shown to interrupt soman-induced seizures and to attenuate edema and cell change in certain sensitive brain areas. Finally, brain water content was assessed using the traditional dry/wet weight method. A significant increase of brain water was observed following the intoxication. CONCLUSIONS: The ADC decrease observed in the present study suggests that brain edema in soman poisoning is mainly intracellular and cytotoxic. Since entry of water into the brain was also evidenced, this type of edema is certainly mixed with others (vasogenic, hydrostatic, osmotic). The present study confirms the potential of DW-MRI as a non-invasive tool for monitoring the acute neuropathological consequences (edema and neurodegeneration) of soman-induced seizures.

Acetylcholine release, EEG spectral analysis, sleep staging and body temperature studies: a multiparametric approach on freely moving rats.

We present a neurochemical, electrophysiological and physiological study on freely moving rats. During 3 days, we have simultaneously monitored acetylcholine (ACh) release in the hippocampus using the microdialysis technique, electroencephalogram (EEG), electromyogram (EMG) and subcutaneous temperature. A spectral analysis of EEG was performed and sleep stages were determined. Energy ratio in the delta (0-4 Hz), slow theta (4-6.5 Hz) and fast theta (6.5-9 Hz) band was calculated. Sleep stages were quantified using an automatic staging method. The circadian cycle of these parameters was observed. Waking, body temperature and ACh release presented synchronized cycles with close acrophases. The relationship between the central cholinergic system and the other parameters is discussed. The influence of handling on the measured parameters, as well as possible artifacts linked to the use of neostigmine in the microdialysis method are considered. Attention was focused on the cholinergic control of EEG theta rhythms.

Declarative memory impairments following a military combat course: parallel neuropsychological and biochemical investigations.

The aim of this study was to investigate the impact on several forms of memory and metabolism of a 5-day combat course including heavy and continuous physical activities and sleep deprivation. Mnemonic performance and biochemical parameters of 21 male soldiers were examined before and at the end of the course. Our results showed that short-term memory (memory span, visual memory, audiovisual association) and long-term memory were significantly impaired, whereas short-term spatial memory and planning tasks were spared. Parallel biochemical analysis showed an adaptation of energy metabolism. The observed decrease in glycaemia may be partly responsible for the long-term memory impairment, whereas the decreases in plasma cholinesterases and choline may be involved in the short-term memory deterioration. However, there are also many other reasons for the observed memory changes, one of them being chronic sleep deprivation.

Disruption of mice sleep stages induced by low doses of organophosphorus compound soman.

We have explored during 7 days, EEG spectral response and sleep pattern of mice after a mild intoxication with soman. Using an automatic staging method, we have quantified the sleep stage of the mice to identify disruptions of the sleep pattern. The 50 microg/kg dose of soman produced several effects during several time windows after intoxication. A first decrease followed by an increase of theta energy, a disturbance of slow wave sleep during 5 days and an increase of the REM sleep during the first and second day after intoxication. During the first 6h, we have observed some effects which were not consistent with a muscarinic activation and might have involved GABA-ergic system. After this early period, the observed effects were in accordance with a muscarinic activation. We observed an increase of energy in the EEG theta band during 3 days after soman injection and an increase of slow wave sleep during the second to the fifth day after soman injection.

Review of the value of huperzine as pretreatment of organophosphate poisoning.

Today, organophosphate (OP) nerve agents are still considered as potential threats in both military or terrorism situations. OP agents are potent irreversible inhibitors of central and peripheral acetylcholinesterases. Pretreatment of OP poisoning relies on the subchronic administration of the reversible acetylcholinesterase (AChE) inhibitor pyridostigmine (PYR). Since PYR does not penetrate into the brain, it does not afford protection against seizures and subsequent neuropathology induced by an OP agent such as soman. Comparatively, huperzine (HUP) is a reversible AChE inhibitor that crosses the blood-brain barrier. HUP is presently approved for human use or is in course of clinical trials for the treatment of Alzheimer's disease or myasthenia gravis. HUP is also used as supplementary drug in the USA for correction of memory impairment. Besides, HUP has also been successfully tested for pretreatment of OP poisoning. This review summarizes the therapeutical value of HUP in this field. Moreover, the modes of action of HUP underlying its efficacy against OP agents are described. Efficacy appears mainly related to both the selectivity of HUP for red cell AChE which preserves scavenger capacity of plasma butyrylcholinesterases for OP agents and to the protection conferred by HUP on cerebral AChE. Finally, recent data, showing that HUP seems to be devoid of deleterious effects in healthy subjects, are also presented. Globally, this review reinforces the therapeutical value of HUP for the optimal pretreatment of OP poisoning.