Aminoglutethimide first generation aromatase inhibitor has b
Aminoglutethimide, first generation aromatase inhibitor, has been tried as an antiepileptic drug in combination with other standard drugs (Aguilar et al., 1961). Letrozole is a third generation reversible non-steroidal aromatase inhibitor, approved by US-FDA, for the treatment of postmenopausal women with hormone receptor-positive or hormone receptor unknown locally advanced or metastatic breast cancer (NIH, 2013). A recent preclinical study in our laboratory demonstrated the protective effect of letrozole in the prevention of kindling induced by pentylenetetrazole (PTZ) in mice (Rashid et al., 2015). Also, letrozole was previously reported inhibiting the testosterone-induced increase in PTZ seizure activity in mice (Reddy, 2004b). Clinically, letrozole has been shown to improve seizure control in a 61-year-old man with temporal lobe epilepsy (Harden and MacLusky, 2004, Harden and MacLusky, 2005). It suggests that letrozole should be further investigated as a beneficial treatment for male patients with epilepsy. Therefore, in the present work, we examined the effect of letrozole against kainic acid-induced seizures and neurotoxicity in mice. Kainic CD 2665 (KA) is an excitotoxic analog of glutamate and an agonist of ionotropic KA receptors. KA-induced status epilepticus model is the most accepted model of temporal lobe epilepsy (TLE) (Levesque and Avoli, 2013; Loscher and Brandt, 2010). To explore the mechanisms involved, we utilized pharmacological tools including finasteride, a selective inhibitor of 5α-reductase and indomethacin, a selective inhibitor of the 3α-HSOR enzyme, to ascertain whether the effects are mediated by increased synthesis of 5α-DHT or 3α-Diol respectively. Further, since systemic administration of KA induces epileptic seizures, behavioral changes, and consequent neuropathological changes bilaterally in the CA1, CA3 and dentate gyrus (DG) regions of the hippocampus (Haas et al., 2001; Hellier et al., 1998), we evaluated the histopathological changes in the hippocampus and measured the levels of the hormones involved in the testosterone metabolic pathway. We hypothesize that aromatase inhibitors will reduce local estradiol levels by inhibiting the conversion of testosterone to 17β-estradiol, and will reduce brain excitability as estrogens are excitatory and potentiate seizures. 3α-Diol is a structural analog of allopregnanolone and plays a significant part in mediating the anticonvulsant effects. Thus, it is possible that aromatase inhibition could be a potential approach for reducing brain excitability.
Material and methods
Discussion KA-induced seizures and associated neurotoxicity in the hippocampal region is a well-established animal model of temporal lobe epilepsy. As per WHO, around 30% of estimated 50 million people with epilepsy, mostly suffering from TLE, remain refractory to therapy (WHO, 2015). Moreover, current antiepileptic drugs (AEDs) merely affect seizure expression without having disease-modifying properties. To address these unmet needs, considerable research is underway to explore novel targets for the disease. In the present work, we proposed aromatase as one such target. To the best of our knowledge, there are only three pre-clinical studies and two case reports available in this area. We have previously demonstrated the effect of letrozole in delaying PTZ-kindling in mice (Rashid et al., 2015). Our results are also supported by some case reports where aromatase inhibition reduced seizures in addition to standard antiepileptic drugs which suggests that aromatase inhibition might be the beneficial treatment for men suffering from both testosterone deficiency and epilepsy and also for post-menopausal women suffering from both breast cancer and epilepsy (Harden and MacLusky, 2004, Harden and MacLusky, 2005). The antiepileptic effects of aromatase inhibitors are also supported by the fact that many of the conventional AEDs inhibit aromatase enzyme (Jacobsen et al., 2008) and have structural and chemical similarities (Muftuoglu and Mustata, 2011). First generation aromatase inhibitors, aminoglutethimide, and testolactone had shown significant improvement in seizures when tried in combination with other standard antiepileptic drugs (Aguilar et al., 1961; Herzog et al., 1998). These reports suggested that aromatase inhibition may be helpful in reducing seizure frequency. Our results on KA-induced seizures are in agreement with a recent preclinical study by Sato and Wolley, where they showed that acute administration of aromatase inhibitors might be an effective treatment for status epilepticus. They demonstrated that systemic administration of an aromatase inhibitor, fadrozole in rats after seizure onset strongly suppresses both electrographic and behavioral seizures induced by KA (Sato and Woolley, 2016). However, their study neither demonstrated the mechanisms responsible for antiepileptic effects of letrozole nor evaluated the effects on KA mediated neurotoxicity.