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。研究仍在继续，评估神经活性类固醇在癫痫中的作用以及它们在癫痫治疗中的可能用途。神经活性类固醇是一种内源性类固醇激素(及其合成类似物)，通过直接作用于包括GABA-A和NMDA受体在内的膜离子通道，迅速改变神经元的兴奋性。在以前的报道中，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酮，在小鼠戊四氮(PTZ)惊厥试验中被证明是有效的抗惊厥药物，这种作用与它们增强GABA-A受体介导的氯电流反应的能力有关。此外，研究还表明，GABA-A受体增强型神经活性类固醇在癫痫持续状态模型中具有高度的保护作用。慢性治疗研究表明，与其他GABA增强药物不同，耐受性不会发展为神经活性类固醇的抗惊厥活性，支持它们在癫痫治疗中的潜在效用。在进一步的研究中，人们发现孕酮具有强大的抗惊厥活性，并证明这是由于它通过5α-羟化作用转化为神经类固醇别孕酮。在本报告期间，我们试图探索月经期周围癫痫的发病机制，并探索神经活性类固醇作为这一疾病的一种治疗方法的可能性。月经性癫痫是指在月经周期的特定时间癫痫发作加剧，在10%到72%的癫痫妇女中受到影响。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，在血清孕酮水平较低的围绝经期癫痫发作增加。这种形式的月经性癫痫的发作加剧可能是由于黄体酮停用。神经类固醇替代是一种潜在的治疗方法，但天然神经类固醇的生物利用度较低，可能会代谢转化为具有不希望看到的孕激素活性的类似物。合成的别孕酮的3β-甲基类似物(加纳索龙)是一种口服有效的神经类固醇，不会转化为具有激素活性的3-酮形式。我们建立了一种月经性癫痫的动物模型，以评价加纳索龙治疗围绝经期癫痫发作的潜力。用促性腺激素治疗雌性大鼠，造成持续高孕酮(假孕)的状态。5α-还原酶抑制剂非那雄胺可阻断孕激素向别孕酮的转化，从而诱导神经类固醇的停用。假孕期间非那雄胺诱导的神经类固醇撤药与PTZ惊厥的易感性增加有关。停药后，加纳索龙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，因此在停用神经类固醇后的一段时间内，治疗活性和毒性之间的分离明显更大。与Ganaxolone的增强效力相反，停用神经类固醇与安定和丙戊酸盐的抗惊厥效力显著降低有关。这些结果支持神经活性类固醇如加纳索龙在治疗经期周围癫痫的月经发作加重方面的潜在应用，并可能解释为什么月经性癫痫的女性通常对传统的抗惊厥药物治疗有抵抗力。-癫痫、月经性癫痫、癫痫、神经活性类固醇、GABA受体、加纳松龙

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