Infantile spasms: hypothesis-driven therapy and pilot human infant experiments using corticotropin-releasing hormone receptor antagonists

Biochemical mechanisms in pathogenesis of infantile epileptic spasm syndrome

The molecular mechanisms leading to infantile epileptic spasm syndrome (IESS) remain obscure. The only common factor seems to be that the spasms are restricted to a limited period of infancy, during a certain maturational state. Here the current literature regarding the biochemical mechanisms of brain maturation in IESS is reviewed, and various hypotheses of the pathophysiology are put together. They include: (1) imbalance of inhibitory (NGF, IGF-1, ACTH, GABA) and excitatory factors (glutamate, nitrites) which distinguishes the different etiological subgroups, (2) abnormality of the hypothalamic pituitary adrenal (HPA) axis linking insults and early life stress, (3) inflammation (4) yet poorly known genetic and epigenetic factors, and (5) glucocorticoid and vigabatrin action on brain development, pinpointing at molecular targets of the pathophysiology from another angle. An altered maturational process may explain why so many, seemingly independent etiological factors lead to the same clinical syndrome and frequently to developmental delay. Understanding these factors can provide ideas for novel therapies.

Pathogenesis and new candidate treatments for infantile spasms and early life epileptic encephalopathies: A view from preclinical studies

Early onset and infantile epileptic encephalopathies (EIEEs) are usually associated with medically intractable or difficult to treat epileptic seizures and prominent cognitive, neurodevelopmental and behavioral consequences. EIEEs have numerous etiologies that contribute to the inter- and intra-syndromic phenotypic variability. Etiologies include structural and metabolic or genetic etiologies although a significant percentage is of unknown cause. The need to better understand their pathogenic mechanisms and identify better therapies has driven the development of animal models of EIEEs. Several rodent models of infantile spasms have emerged that recapitulate various aspects of the disease. The acute models manifest epileptic spasms after induction and include the NMDA rat model, the NMDA model with prior prenatal betamethasone or perinatal stress exposure, and the γ-butyrolactone induced spasms in a mouse model of Down syndrome. The chronic models include the tetrodotoxin rat model, the aristaless related homeobox X-linked (Arx) mouse models and the multiple-hit rat model of infantile spasms. We will discuss the main features and findings from these models on target mechanisms and emerging therapies. Genetic models have also provided interesting data on the pathogenesis of Dravet syndrome and proposed new therapies for testing. The genetic associations of many of the EIEEs have also been tested in rodent models as to their pathogenicity. Finally, several models have tested the impact of subclinical epileptiform discharges on brain function. The impact of these advances in animal modeling for therapy development will be discussed.

17q21.31 microdeletion associated with infantile spasms

Patients with 17q21.31 microdeletions frequently have neurologic abnormalities, especially seizures. This report is of a child with a deletion in this location who developed infantile spasms, a seizure type not specifically described in this syndrome. FISH analysis of parental blood metaphases demonstrated that the deletions occurred de novo. The deleted region encompasses the previously defined critical region for the 17q21.31 microdeletion syndrome, and includes the gene encoding for corticotropin-releasing hormone receptor 1, a protein implicated in hyperexcitability, and potentially in infantile spasms. Treatment with ACTH led to spasm cessation, consistent with its expected repression of CRH levels, which should be augmented by CRHR1 deletion, although this response was transient.

Corticosteroids for the treatment of infantile spasms: a systematic review

Adrenocorticotropic hormone (ACTH) and corticosteroids are the usual first-line treatment options for infantile spasms. Despite significant differences, these agents are often lumped together in this context. There is a need to systematically explore the efficacy of corticosteroids in the treatment of infantile spasms, especially in comparison to ACTH. This review identified and analyzed corticosteroid clinical trials and summarized their short-term efficacy and tolerability. Primary outcome was cessation of spasms and abolition of hypsarrhythmia on prolonged video electroencephalographic monitoring. Eight corticosteroid clinical trials were found with only 2 fulfilling the criteria for adequate design. The weighted-mean efficacy of corticosteroids to achieve primary outcome was 31% for these 2 methodologically adequate studies. Including reanalyzed data from 3 other studies, the corticosteroid efficacy was found to be 42%. On the basis of the available evidence, the efficacy of high-dose corticosteroids is similar to low-dose ACTH and inferior to high-dose ACTH, the current standard treatment.

Chronobiology of epilepsy: diagnostic and therapeutic implications of chrono-epileptology

The combination of chronobiology and epilepsy offers novel diagnostic and therapeutic management options. Knowledge of the interactions between circadian periodicity, entrainment, sleep patterns, and epilepsy may provide additional diagnostic options beyond sleep deprivation and extended release medication formulations. It may also provide novel insights into the physiologic, biochemical, and genetic regulation processes of epilepsy and the circadian clock, rendering new treatment options. Temporal fluctuations of seizure susceptibility based on sleep homeostasis and circadian phase in selected epilepsies may provide predictability based on mathematical models. Chrono-epileptology offers opportunities for individualized patient-oriented treatment paradigms based on chrono-pharmacology, differential medication dosing, chrono-drug delivery systems, and utilization of "zeitgebers" such as chronobiotics or light-therapy and desynchronization strategies among others.

Neurobehavioral consequences of stressor exposure in rodent models of epilepsy

Both normal, non-epileptic as well as seizure-prone rodents exhibit a spectrum of anxiogenic-like behaviors in response to stressor exposure. Comparative analysis reveals that the same set of emotionality dependent measures is sensitive to both stress reactivity in normal rodents as well as stress hyperreactivity typically seen in seizure-prone rodents. A variety of unconditioned, exploratory tasks reflect global sensitivity to stressor exposure in the form of behavioral inhibition of locomotor output. Moreover, well chosen stressors can trigger de novo seizures with or without a history of seizure incidence. Seizures may be elicited in response to stressful environmental stimuli such as noxious noises, tail suspension handling, or home cage disturbance. Stress reactivity studies in rodents with a genetic predisposition to seizures have yielded important clues regarding brain substrates that mediate seizure ontogeny and modulate ictogenesis. Brains of seizure susceptible rodents reflect elevated content of the stress-related neuropeptide, corticotropin-releasing factor (CRF) in several nuclei relative to non-susceptible controls and neutralization of brain CRF attenuates seizure sensitivity. Findings outlined in this review support a diathesis-stress hypothesis in which behavioral- and neuro-pathologies of genetically seizure susceptible rodents arise in part due to multifaceted hyperreactivity to noxious environmental stimuli.

Depression and epilepsy: do glucocorticoids and glutamate explain their relationship?

Depression is the most common psychiatric comorbidity in people with epilepsy, but it remains underrecognized and undertreated. In addition to its negative impact on quality of life, depressive disorders are predictive of a worse response to pharmacologic and surgical treatment of seizure disorders. This phenomenon is probably an expression of a bidirectional relationship between epilepsy and depression, which in turn is indicative of common pathogenic mechanisms that are operant in the two conditions. The abnormal role of the hypothalamic-pituitary-adrenal axis is one of the common pathogenic mechanisms that explains why patients with depression are at greater risk for developing epilepsy and vice versa.

Olfactory Neophobia and Seizure Susceptibility Phenotypes in an Animal Model of Epilepsy Are Normalized by Impairment of Brain Corticotropin Releasing Factor

PURPOSE

The present study explored the causal relationship between stressor exposure/stress neuropeptide activation and avoidant exploratory phenotype/enhanced seizure susceptibility in an animal model of epilepsy.

METHODS

The olfactory detection and investigation phenotype of seizure susceptible El (epilepsy) strain and nonsusceptible ddY control mice was first evaluated in untreated mice. In a second series of experiments, the olfactory exploration phenotype, food intake/body weight regulation, circadian locomotor activity, and seizure susceptibility were assessed over a 14-day period following central administration of the neurotoxin saporin alone or a conjugate of the stress neuropeptide, corticotropin releasing factor (CRF), and saporin (CRF-SAP) which impairs CRF system function following central administration.

RESULTS

In support of the main experimental hypothesis, administration of CRF-SAP in El mice reduced handling-induced seizure susceptibility by 75% for up to 2 weeks following treatment. Similarly, El mice were slow to detect a cache of buried food pellets relative to ddY controls and this exploratory deficit was reversed 3 days following administration of CRF-SAP. Efficacy of CRF-SAP treatment was confirmed using CRF immunohistochemistry, which revealed suppression of brain CRF content in El mice treated with CRF-SAP relative to El controls. Other functional and persistent effects of CRF-SAP included increased locomotor activity and hyperphagia.

CONCLUSIONS

Taken together, these results support strongly the possibility that activated brain stress neuropeptide systems are necessary for the expression of motivational and neurological perturbations in seizure susceptible El mice.

Antisocial and seizure susceptibility phenotypes in an animal model of epilepsy are normalized by impairment of brain corticotropin-releasing factor

Social interaction phenotyping is an unexplored niche in animal modeling of epilepsy despite the sensitivity of affiliative behaviors to emotionality and stress, which are known seizure triggers. Thus, the present studies examined the social phenotype of seizure-susceptible El and nonsusceptible ddY strains both in untreated animals and following preexposure to a handling stressor. The second aim of the present studies was to evaluate the dependence of sociability in El mice on the proconvulsive, stress neuropeptide corticotropin-releasing factor (CRF) using CRF-SAP, a conjugate of CRF and the toxin saporin, which selectively reduced CRF peptide levels in the basolateral amygdala of El mice. El mice exhibited lower social investigation times than ddY counterparts, whereas central administration of CRF-SAP normalized social investigation times relative to ddY controls. Moreover, handling-induced seizures in El mice were reduced by 50% following treatment with CRF-SAP relative to saporin alone-injected El controls. The results of this study suggest that tonically activated CRF systems in the El mouse brain suppress affiliative behavior and facilitate evoked seizures.

Neural, endocrine and electroencephalographic hyperreactivity to human contact: a diathesis-stress model of seizure susceptibility in El mice

The El mouse strain provides a non-induced model of idiopathic, multifactorial epilepsy in which seizures are elicited in response to stressful environmental stimuli such as tail suspension handling. In the present studies, genetically seizure susceptible El and non-susceptible ddY control mice were exposed to tail suspension, foot-shock and social stressors in order to test the hypothesis that neural and physiological responses to such stimuli would be exaggerated in the El strain. The first experiment assessed neural cell density, stress neuropeptide (corticotropin releasing factor--CRF) levels, and plasma corticosterone activation in El and ddY mice in an unhandled control condition or following exposure to tail suspension or foot-shock stressors. The second experiment assessed brain electroencephalographic activity using telemetrically monitored skull surface electrodes in El and ddY mice exposed to tail suspension or social interaction stressors. Assessment of El mouse brains revealed higher cell counts in amygdala and elevated CRF peptide content in the paraventricular thalamic nucleus relative to ddY controls. El mice exhibited significantly elevated plasma corticosterone levels 60 min following exposure to tail suspension and foot-shock stressors relative to ddY controls. Finally, El mice exhibited significantly elevated brain electroencephalographic (1-4 Hz) activity in response to tail suspension, but not social interaction, relative to ddY controls. These results indicate that potentiated neural, endocrine and physiological activation arises in the El strain following exposure to a known seizure trigger stimulus, involuntary tail suspension handling. The findings support a diathesis-stress hypothesis in which genetically seizure susceptible El mice exhibit a multifaceted hyperreactivity to noxious environmental stimuli.

Behavioral seizure correlates in animal models of epilepsy: a road map for assay selection, data interpretation, and the search for causal mechanisms

A broad spectrum of learning/memory, social interaction, and affective behavioral measures serve as functional correlates for neurobiological changes in seizure-prone animals as well as in epileptic clinical populations. The utility of such measures is demonstrated by their ability to distinguish anomalous characteristics in developing organisms predisposed to seizure onset, as well as to discriminate prior seizure history in organisms with established pathology. For instance, typical findings that generalize across species suggest that seizure-experienced organisms exhibit a variety of deficits in cognitive function as well as inappropriate social neglect and aggression. Behavioral testing batteries have also proven useful in assessing neural mechanisms for seizure induction, subcortical neural circuits, and neuropeptide modulators, for example, as well as in identifying neural pathology resulting from prior seizure activity. However, the wanton application of behavioral tests can also produce false positives in the identification of seizure-related disorders unless alternative performance and motivational hypotheses are discounted effectively. Accordingly, the present review attempts to provide the reader interested in behavioral phenotyping and characterization of seizure-prone rats and mice with a roadmap for rational selection, implementation, and interpretation of data from behavior assays while highlighting potential successes and pitfalls inherent in employing functional correlates of brain activity using animal models of epilepsy.

Neonatal maternal separation causes colonic dysfunction in rat pups including impaired host resistance

Previous studies have shown that early life stress in the form of intermittent maternal separation (MS) predisposes adult rats to develop stress-induced intestinal mucosal dysfunction and visceral hypersensitivity. However, the mechanism involved in the functional abnormalities is unclear. Our aim was to study immature animals during or shortly after exposure to MS to determine whether there are early pathophysiological changes in the gut. Sprague-Dawley rat pups were individually separated from the dam for 3 h/d from 4 to 21 d of age; nonseparated (NS) control pups remained in the home cage with the dam. On d 19-20, d 24-25, and d 29-30, blood was collected for corticosterone measurement, and colonic tissues were removed for functional and morphologic assessment. Corticosteroid levels were elevated in MS pups compared with NS, indicating that MS was indeed stressful. The distal colon demonstrated significantly enhanced ion secretion and macromolecular permeability at d 19-20 and d 24-25, returning to normal by d 29-30. Electron microscopy and bacterial culture studies indicated bacteria adhering to and penetrating into the colonic epithelium of the MS pups at all time points, while such events were rare in NS pups. The pathophysiological changes were inhibited by injecting pups sc with a corticotropin-releasing hormone (CRH) receptor antagonist daily during MS. Our studies indicate that early psychological trauma predisposes neonatal rats to develop persistent mucosal barrier dysfunction, including impaired host defense to luminal bacteria, by a mechanism involving peripheral CRH receptors.

Pathogenesis of infantile spasms: a model based on developmental desynchronization

Infantile spasms is a severe epileptic encephalopathy of infancy. The fundamental cause is unknown, although a number of predisposing conditions are recognized. In this article, the authors critically review current knowledge concerning the pathophysiologic basis of infantile spasms and propose a new model based on developmental desynchronization. It is suggested that infantile spasms may result from a particular temporal desynchronization of two or more central nervous system developmental processes, resulting in a specific disturbance of brain function. The disturbance of function is postulated to be crucially dependent on an unbalanced maturational pattern, in which certain brain systems become dysfunctional owing to divergent developmental status. An important aspect of this model is the idea that disturbed function of a specific kind can result from multiple causative factors, and so can be associated with a variety of different anatomic and/or biochemical abnormalities. Thus, this concept is compatible with the observed diversity of pathologic findings and multiplicity of etiological associations observed in infantile spasms patients.

Shared mechanisms of antidepressant and antiepileptic treatments: drugs and devices

Many treatments for the epilepsies and affective disorder share the properties of seizure suppression and mood stabilization. Moreover, affective disorders and the epilepsies appear to share partially similar pathogenic mechanisms. A component of the shared predisposition appears to arise from noradrenergic and serotonergic deficits. Increasing evidence supports the hypothesis that noradrenergic and/or serotonergic elevation is a mechanism of therapeutic benefit shared by most antidepressants and many antiepileptic medications. Medication induced alterations in GABAergic, glutamatergic, and CRH (corticotropin releasing hormone) containing neurons may also contribute to the shared therapeutic properties of antidepressant and antiepileptic medications.

Electroconvulsive therapy in complex regional pain syndromes

Three cases are presented in which electroconvulsive therapy (ECT) for depression led to the relief of comorbid complex regional pain syndrome as well as depression. In one of the cases, concomitant fibromyalgia was not relieved during 2 separate series of ECT. The literature regarding the role of ECT in the management of chronic pain is reviewed and discussed in light of recent findings about ECT and changes in neurotransmission associated with seizures.

Neuropeptides: general characteristics and neuropharmaceutical potential in treating CNS disorders

The general characteristics of neuropeptides are discussed as a background for the understanding of their role in regulation of physiological systems. The extent of those systems that are crucially affected by neuropeptides is vast and the complexity of their interactions makes the clinical focus on a specific neuropeptide unsatisfactory. The clinical potential of neuropeptides affecting eating disorders, CNS behavioral disorders and the neuroregenerative and neuroprotective action of neuropeptides is discussed. It is probable that successful neuropeptide therapeutics will depend upon the application of translational and combinational research using various ingenious combinations of neuropeptides, their agonists and antagonists, neuropeptide receptor agonists and antagonists, improved methods of delivery and the development of peptides targeted to the genetic profile of individual patients.

Efficacy of the ketogenic diet for infantile spasms

OBJECTIVE

The objective of this study was to determine whether the ketogenic diet is safe, well-tolerated, and efficacious in the treatment of infantile spasms.

METHODS

During a 4-year period, 23 children with infantile spasms, aged 5 months to 2 years, were started on the ketogenic diet; 9 (39%) had symptomatic infantile spasms, and 16 (70%) had hypsarrhythmia. Children had an average prediet exposure to 3.3 anticonvulsants. Two children were enrolled before any medication had been tried. Seizure reduction was analyzed retrospectively, using parent reports and electroencephalograms (EEGs) when available.

RESULTS

At 3, 6, 9, and 12 months, 38%, 39%, 53%, and 46%, respectively, of all patients currently on the diet were >90% improved (3 were seizure-free at 12 months); 67%, 72%, 93%, and 100% were >50% improved. Fifty-six percent remained on the diet at 12 months, 46% of whom were >90% improved and 100% were >50%. Fifty percent of those with hypsarrhythmia and follow-up EEGs had EEG improvement. Fifty-seven percent had their medications reduced or discontinued by 12 months. Fifty-seven percent had improvement in development, which was correlated with seizure control. Independent factors that predicted improvement included age younger than 1 year and previous exposure to 3 or fewer anticonvulsants. No child has died, and 7 children had diet-related adverse reactions (nephrolithiasis, gastroesophageal reflux).

DISCUSSION

The ketogenic diet is a safe, well-tolerated, and possibly effective potential alternative to other therapies for infantile spasms.

ACTH treatment of infantile spasms: mechanisms of its effects in modulation of neuronal excitability

The efficacy of ACTH, particularly in high doses, for rapid and complete elimination of infantile spasms (IS) has been demonstrated in prospective controlled studies. However, the mechanisms for this efficacy remain unknown. ACTH promotes the release of adrenal steroids (glucocorticoids), and most ACTH effects on the central nervous system have been attributed to activation of glucocorticoid receptors. The manner in which activation of these receptors improves IS and the basis for the enhanced therapeutic effects of ACTH--compared with steroids--for this disorder are the focus of this chapter. First, a possible "common excitatory pathway," which is consistent with the many etiologies of IS and explains the confinement of this disorder to infancy, is proposed. This notion is based on the fact that all of the entities provoking IS activate the native "stress system" of the brain. This involves increased synthesis and release of the stress-activated neuropeptide, corticotropin-releasing hormone (CRH), in limbic, seizure-prone brain regions. CRH causes severe seizures in developing experimental animals, as well as limbic neuronal injury. Steroids, given as therapy or secreted from the adrenal gland upon treatment with ACTH, decrease the production and release of CRH in certain brain regions. Second, the hypothesis that ACTH directly influences limbic neurons via the recently characterized melanocortin receptors is considered, focusing on the effects of ACTH on the expression of CRH. Experimental data showing that ACTH potently reduces CRH expression in amygdala neurons is presented. This downregulation was not abolished by experimental elimination of steroids or by blocking their receptors and was reproduced by a centrally administered ACTH fragment that does not promote steroid release. Importantly, selective blocking of melanocortin receptors prevented ACTH-induced downregulation of CRH expression, providing direct evidence for the involvement of these receptors in the mechanisms by which ACTH exerts this effect. Thus, ACTH may reduce neuronal excitability in IS by two mechanisms of action: (1) by inducing steroid release and (2) by a direct, steroid-independent action on melanocortin receptors. These combined effects may explain the robust established clinical effects of ACTH in the therapy of IS.

How do the many etiologies of West syndrome lead to excitability and seizures? The corticotropin releasing hormone excess hypothesis

West syndrome (WS) is associated with diverse etiological factors. This fact has suggested that there must be a 'final common pathway' for these etiologies, which operates on the immature brain to result in WS only at the maturational state present during infancy. Any theory for the pathogenesis of WS has to account for the unique features of this disorder. For example, how can a single entity have so many etiologies? Why does WS arise only in infancy, even when a known insult had occurred prenatally, and why does it disappear? Why is WS associated with lasting cognitive dysfunction? And, importantly, why do these seizures--unlike most others--respond to treatment by a hormone, ACTH? The established hormonal role of ACTH in human physiology is to function in the neuroendocrine cascade of the responses to all stressful stimuli, including insults to the brain. As part of this function, ACTH is known to suppress the production of corticotropin releasing hormone (CRH), a peptide that is produced in response to diverse insults and stressors.The many etiologies of WS all lead to activation of the stress response, including increased production and secretion of the stress-neurohormone CRH. CRH has been shown, in infant animal models, to cause severe seizures and death of neurons in areas involved with learning and memory. These effects of CRH are restricted to the infancy period because the receptors for CRH, which mediate its action on neurons, are most abundant during this developmental period. ACTH administration is known to inhibit production and release of CRH via a negative feedback mechanism. Therefore, the efficacy of ACTH for WS may depend on its ability to decrease the levels of the seizure-promoting stress-neurohormone CRH.This CRH-excess theory for the pathophysiology of WS is consistent not only with the profile of ACTH effects, but also with the many different 'causes' of WS, with the abnormal ACTH levels in the cerebrospinal fluid of affected infants and with the spontaneous disappearance of the seizures. Furthermore, if CRH is responsible for the seizures, and CRH-mediated neuronal injury contributes to the worsened cognitive outcome of individuals with WS, then drugs which block the actions of CRH on its receptors may provide a better therapy for this disorder.

What is West syndrome?

The combination of axial spasms in clusters, hypsarrhythmia, and psychomotor delay beginning in the first year of life defines West syndrome. Variants of this classical triad comprise variations of age of onset ranging from the first month to 4 years, spasms that may be asymmetrical or combined with focal seizures, asymmetrical, synchronous or fragmented hypsarrhythmia, and psychomotor function which may be delayed, deteriorated or normal. These variations mainly seem to depend on etiology, and specific patterns have been identified for the various causes. Most causes relate to non-progressive uni- or multifocal cortical lesions, although some are due to inborn errors of metabolism. Ten to 20% exhibit no evidence of brain lesion and are considered idiopathic. This condition is intermediary between epilepsy in which the disorder is limited to paroxysmal events during which time the patient returns to his prior condition, and status epilepticus in which the paroxysmal activity is not interrupted. Here, there are both paroxysmal events and a continuous non-convulsive paroxysmal activity that contributes to the deterioration. In the present understanding of pathophysiology, spasms seem to involve subcortical structures, whereas hypsarrhythmia affects cortical areas, also causing psychomotor deterioration. Deafferentation of subcortical structures by the continuous spiking and slow wave activity could account for release of autonomic activity in the basal ganglia. Cortical paroxysmal activity could be caused by age-related hyperexcitability linked to the development of cortical neuronal networks throughout infancy. The mode of action of steroid and vigabatrin therapies, the two therapies with demonstrated efficacy, can be explained on this basis.

Corticotropin (ACTH) acts directly on amygdala neurons to down-regulate corticotropin-releasing hormone gene expression

The hormone corticotropin (ACTH) is employed as therapy for diverse neurological disorders, but the mechanisms for its efficacy remain unknown. ACTH promotes the release of adrenal steroids (glucocorticoids), and most ACTH effects on the central nervous system (CNS) have been attributed to activation of glucocorticoid receptors. However, in several human disorders, ACTH has therapeutic actions that differ qualitatively or quantitatively from those of steroids. This study tested the hypothesis that ACTH directly influences limbic neurons via the recently characterized melanocortin receptors and focused on the effects of ACTH on the expression of corticotropin-releasing hormone (CRH), a neuropeptide involved in neuroimmune functions and in certain developmental seizures. The results demonstrated that ACTH potently reduced CRH expression in amygdala neurons. This down-regulation was not abolished by experimental elimination of steroids or by blocking their receptors and was reproduced by a centrally administered ACTH fragment that does not promote steroid release. Importantly, selective blocking of melanocortin receptors prevented ACTH-induced down-regulation of CRH expression. Taken together, these data indicate that ACTH activates central melanocortin receptors to modulate CRH gene expression in amygdala, supporting the notion that direct, steroid-independent actions of ACTH may account for some of its established clinical effects on the CNS.