Metabolism-based drug discovery in zebrafish: An emerging strategy to uncover new anti-seizure therapies.

As one of the most common neurological disorders, epilepsy can occur throughout the lifespan and from a multiplicity of causes, including genetic mutations, inflammation, neurotrauma, or brain malformations. Although pharmacological agents are the mainstay of treatment for seizure control, an unyielding 30-40% of patients remain refractory to these medications and continue to experience spontaneous recurrent seizures with attendant life-long cognitive, behavioural, and mental health issues, as well as an increased risk for sudden unexpected death. Despite over eight decades of antiseizure drug (ASD) discovery and the approval of dozens of new medications, the percentage of this refractory population remains virtually unchanged, suggesting that drugs with new and unexpected mechanisms of action are needed. In this brief review, we discuss the need for new animal models of epilepsy, with a particular focus on the advantages and disadvantages of zebrafish. We also outline the evidence that epilepsy is characterized by derangements in mitochondrial function and introduce the rationale and promise of bioenergetics as a functional readout assay to uncover novel ASDs. We also consider limitations of a zebrafish metabolism-based drug screening approach. Our goal is to discuss the opportunities and challenges of further development of mitochondrial screening strategies for the development of novel ASDs. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

A novel metabolism-based phenotypic drug discovery platform in zebrafish uncovers HDACs 1 and 3 as a potential combined anti-seizure drug target.

Despite the development of newer anti-seizure medications over the past 50 years, 30-40% of patients with epilepsy remain refractory to treatment. One explanation for this lack of progress is that the current screening process is largely biased towards transmembrane channels and receptors, and ignores intracellular proteins and enzymes that might serve as efficacious molecular targets. Here, we report the development of a novel drug screening platform that harnesses the power of zebrafish genetics and combines it with in vivo bioenergetics screening assays to uncover therapeutic agents that improve mitochondrial health in diseased animals. By screening commercially available chemical libraries of approved drugs, for which the molecular targets and pathways are well characterized, we were able to reverse-identify the proteins targeted by efficacious compounds and confirm the physiological roles that they play by utilizing other pharmacological ligands. Indeed, using an 870-compound screen in kcna1-morpholino epileptic zebrafish larvae, we uncovered vorinostat (Zolinza™; suberanilohydroxamic acid, SAHA) as a potent anti-seizure agent. We further demonstrated that vorinostat decreased average daily seizures by ∼60% in epileptic Kcna1-null mice using video-EEG recordings. Given that vorinostat is a broad histone deacetylase (HDAC) inhibitor, we then delineated a specific subset of HDACs, namely HDACs 1 and 3, as potential drug targets for future screening. In summary, we have developed a novel phenotypic, metabolism-based experimental therapeutics platform that can be used to identify new molecular targets for future drug discovery in epilepsy.

Low-dose exposure to bisphenol A and replacement bisphenol S induces precocious hypothalamic neurogenesis in embryonic zebrafish.

Bisphenol A (BPA), a ubiquitous endocrine disruptor that is present in many household products, has been linked to obesity, cancer, and, most relevant here, childhood neurological disorders such as anxiety and hyperactivity. However, how BPA exposure translates into these neurodevelopmental disorders remains poorly understood. Here, we used zebrafish to link BPA mechanistically to disease etiology. Strikingly, treatment of embryonic zebrafish with very low-dose BPA (0.0068 µM, 1,000-fold lower than the accepted human daily exposure) and bisphenol S (BPS), a common analog used in BPA-free products, resulted in 180% and 240% increases, respectively, in neuronal birth (neurogenesis) within the hypothalamus, a highly conserved brain region involved in hyperactivity. Furthermore, restricted BPA/BPS exposure specifically during the neurogenic window caused later hyperactive behaviors in zebrafish larvae. Unexpectedly, we show that BPA-mediated precocious neurogenesis and the concomitant behavioral phenotype were not dependent on predicted estrogen receptors but relied on androgen receptor-mediated up-regulation of aromatase. Although human epidemiological results are still emerging, an association between high maternal urinary BPA during gestation and hyperactivity and other behavioral disturbances in the child has been suggested. Our studies here provide mechanistic support that the neurogenic period indeed may be a window of vulnerability and uncovers previously unexplored avenues of research into how endocrine disruptors might perturb early brain development. Furthermore, our results show that BPA-free products are not necessarily safer and support the removal of all bisphenols from consumer merchandise.