EVALUATION OF NOVEL EPILEPSY TREATMENT APPROACHES

该项目的总体目标是通过动物模型的药理学研究和人类受试者的临床研究来研究癫痫的药物治疗策略。研究继续评估神经活性类固醇在癫痫中的作用及其在癫痫治疗中的可能用途。神经活性类固醇是内源性类固醇激素（及其合成类似物），通过直接作用于膜离子通道（包括GABA-A和NMDA受体）迅速改变神经元的兴奋性。在之前的报告期内，在小鼠戊四氮（PTZ）癫痫发作试验中证明了几种结构相关的神经活性类固醇（包括内源性孕酮代谢物别孕烯醇酮）是强效抗惊厥药，这种作用与其增强GABA-A受体介导的氯电流反应的能力相关。此外，还显示GABA-A受体增强神经活性类固醇在癫痫持续状态模型中具有高度保护作用。长期治疗研究表明，与其他GABA增强药物不同，耐受性不会发展到神经活性类固醇的抗惊厥活性，支持其在癫痫治疗中的潜在效用。在进一步的研究中，发现孕酮具有强大的抗惊厥活性，并证明这是由于其通过5 α-羟基化转化为神经类固醇别孕烯醇酮。在本报告期内，我们试图探索月经期月经癫痫的潜在机制，并探讨神经活性类固醇作为治疗这种疾病的方法的潜在用途。月经性癫痫，在月经周期的特定时间癫痫发作加剧，影响10%至72%的癫痫妇女。目前，月经性癫痫尚无特效治疗方法。在最常见的月经性癫痫中，当血清Progresterone水平较低时，在围月经期癫痫发作增加。这种形式的月经性癫痫发作加重可能是由于孕激素戒断。神经甾体替代是一种潜在的治疗方法，但天然神经甾体生物利用度差，可能会代谢转化为具有不希望的促孕活性的类似物。合成的别孕烯醇酮（加奈索酮）的3 β-甲基类似物是一种口服有效的神经类固醇，不会转化为具有生殖活性的3-酮形式。我们建立了一种月经期癫痫动物模型，以评估加奈索酮治疗月经期癫痫发作的潜力。用5 α-还原酶抑制剂非那肽诱导神经类固醇戒断，所述非那肽阻断Progresterone向别孕烯醇酮的转化。在假性癫痫发作期间，芬必得诱导的神经类固醇戒断与PTZ癫痫发作易感性增强相关。停药后，加奈索酮的抗惊厥效力意外增加了三倍。相比之下，诱导毒性（运动障碍）的效力没有显著变化，因此在神经类固醇停药后的时间段内，治疗活性和毒性之间的分离显著更大。与加奈索酮的增强效力相反，神经类固醇戒断与地西泮和丙戊酸盐的抗惊厥效力显著降低相关。这些结果支持神经活性类固醇，如加奈索酮在治疗月经期月经癫痫的月经发作加重的潜在用途，并可能解释为什么月经癫痫妇女往往是耐药的治疗与传统的抗惊厥药物。- 癫痫，月经性癫痫，癫痫发作，神经活性类固醇，gaba受体，加奈索酮

The overall goal of this project is to investigate strategies for the drug treatment of epilepsy through pharmacological studies in animal models and clinical investigation in human subjects. Research was continued evaluating the role of neuroactive steroids in epilepsy and their possible uses in epilepsy therapy. Neuroactive steroids are endogenous steroid hormones (and their synthetic analogs) that rapidly alter the excitability of neurons by direct actions on membrane ion channels, including GABA-A and NMDA receptors. In prior reporting periods, several structurally-related neuroactive steroids, including the endogenous progesterone metabolite allopregnanolone, were demonstrated to be potent anticonvulsants in the mouse pentylenetetrazol (PTZ) seizure test, an effect that was associated with their ability to potentiate GABA-A receptor-mediated chloride current responses. In addition, it was shown that GABA-A receptor- potentiating neuroactive steroids are highly protective in models of status epilepticus. Chronic treatment studies indicated that unlike other GABA potentiating drugs tolerance does not develop to the anticonvulsant activity of neuroactive steroids, supporting their potential utility in seizure therapy. In a further study, it was found that progesterone has powerful anticonvulsant activity and demonstrated that this is due to its conversion via 5alpha-hydroxylation to the neurosteroid allopregnanolone. In the present reporting period, we sought to explore the mechanism underlying perimenstrual catamenial epilepsy and to explore the potential use of neuroactive steroids as a treatment approach in this disorder. Catamenial epilepsy, the exacerbation of seizures at specific times during the menstrual cycle, affects from 10 to 72 percent of women with epilepsy. At present, there is no specific therapy for catamenial epilepsy. In the most common form of catamenial epilepsy, there is an increase in seizures during the perimenstrual period, when serum progresterone levels are low. Seizure exacerbations in this form of catamenial epilepsy could be due to progesterone withdrawal. Neurosteroid replacement is a potential approach to therapy, but natural neurosteroids have poor bioavailability and may undergo metabolic conversion to analogs with undesired progestational activity. The synthetic 3beta-methyl analog of allopregnanolone (ganaxolone) is an orally effective neurosteroid that is not converted to the hormonally active 3-keto form. We developed an animal model of catamenial epilepsy to evalate the potential of ganaxolone in treating perimenstrual catamenial seizure exacerbations.A state of persistently high serum progesterone (pseudopregnancy) was produced in female rats by treatment with gonadotropins. Neurosteroid withdrawal was induced with the 5alpha-reductase inhibitor finasteride that blocks the conversion of progresterone to allopregnanolone. Finasteride-induced neurosteroid withdrawal during pseudopregnancy is associated with enhanced susceptibility to PTZ seizures. Following withdrawal, there was an unexpected three-fold increase in the anticonvulsant potency of ganaxolone. In contrast, there was no significant change in the potency for induction of toxicity (motor impairment), so that the separation between therapeutic activity and toxicity was substantially larger in the period following neurosteroid withdrawal. In contrast to the enhanced potency of ganaxolone, neurosteroid withdrawal was associated with a marked decrease in the anticonvulsant potency of diazepam and valproate. These results support the potential use of neuroactive steroids such as ganaxolone in the treatment of catamenial seizure exacerbations in perimenstrual catamenial epilepsy, and may explain why women with catamenial epilepsy are often resistant to treatment with conventional anticonvulsant agents. - epilepsy, catamenial epilepsy, seizure, neuroactive steroid, gaba receptor, ganaxolone