Epilepsia^® Prize 2021 Basic Science

Shruthi Iyer was awarded the 2021 Epilepsia Prize for Basic Science Research for her article, Progressive cardiorespiratory dysfunction in Kv1.1 knockout mice may provide temporal biomarkers of pending sudden unexpected death in epilepsy (SUDEP): The contribution of orexin. Shruthi H. Iyer, Ankita Aggarwal, Ted J. Warren, Jodi Hallgren, Peter W. Abel, Timothy A. Simeone, Kristina A. Simeone. Epilepsia. Vol 61(3) DOI: 10.1111/epi.16434 .

An interview with Shruthi Iyer, 2021 Epilepsia Prize Winner for Basic Science Research

Astrid Nehlig and Michael R. Sperling. Version of record online: 07 July 2021

Who are you?

My fascination for pharmaceutical research during the second year of my Pharmacy degree, when I worked as a research assistant in the Department of Pharmacology. I received my Pharmacy degree in 2014 from Bombay College of Pharmacy, Mumbai, India. In 2014, I joined the Masters’ program in the department of Pharmacology and Neuroscience in Creighton University and started my epilepsy research in Dr. Kristina Simeone’s lab. After my graduation in 2016, I continued to work in the same lab as a research technician.

What got you interested in epilepsy research? 

As a teenager, I remember that one of my friends from high school was diagnosed with epilepsy, or rather ‘fits’ as they called it there, and she was prescribed a diet with ‘no cakes, pastries, no sugar’. It really helped with her fits episodes, but at the time I often wondered about the connection between brain disorder and this so called diabetic diet.

Years later a lot of my questions were answered, when I joined Dr. Simeone’s lab, incidentally a lab which worked in the field of temporal lobe epilepsy, role of sleep and ketogenic diet in alleviating refractory epilepsy. I was immediately interested in correlation between sleep and epilepsy, and how sleep dysregulation and seizures form a vicious cycle in both epileptic patients and animal models alike.

During this time, Dr.Simeone was starting the branch out in the field of sudden unexpected death in epilepsy (SUDEP) and she designed my Master’s project to study the sleep and cardiac dysfunction leading to sudden death in the Kv1.1 knockout (KO) model of epilepsy. Eventually, we expanded our research to study the effects of orexin receptor blockers in slowing down the progression to sudden death in epilepsy.

Explain for our general readership what question your study addressed and how did you go about designing you study?

Clinical studies in SUDEP, have found that immediately prior to death, patients experienced a final generalized tonic-clonic (GTC) seizure, and a sequence of cardiovascular events ending in terminal asystole. One of our key questions was whether this pathophysiology progressively develops, and overtime increases the probability of SUDEP.

Our lab has previously reported that in the Kv1.1 (KO) mice, a model of TLE and SUDEP, there is a temporal development of respiratory dysfunction and sleep dysregulation that start with the onset of epilepsy and progressively worsen in the proximity of sudden death in these mice.

Since respiratory dysfunction is closely connected to bradycardia, as seen in SUDEP patients, our first hypothesis tested whether intermittent bradycardia would be apparent in KO mice with higher probability of death. We tested the mice at three different age points, when ~20%, ~35% and ~55% of KO mice have succumbed to sudden death (called SD20, SD35, SD55 respectively).

ECG was recorded non-invasively using the ECGenie recording platform. Arterial blood saturation was recorded using pulse oximetry. Respiratory parameters were measured using the non-invasive airway mechanics chamber where mice were exposed to aerosolized saline followed by increased doses of parasympathomimetic methacholine (MCh). Seizures were monitored throughout the course of the challenge. We also looked at the contribution of increased parasympathetic drive to the bradycardia and sudden death, where the heart rate was recorded in SD55 mice before and after administration of parasympathetic blocked atropine sulfate.

We have previously reported a temporal increase in the number of cells expressing the cardiorespiratory neuromodulator orexin. The second hypothesis focused on the possibility of orexin being upstream of the cardiorespiratory dysfunction and resultant SUDEP. We determined the heart rate, apnea, breathing frequency and seizures in these mice at SD20, SD35, SD55 during vehicle treatment, then again 48-hrs later following administration of a dual orexin receptor antagonist (DORA). We also looked at the possible synergistic action of DORA on the atropine mediated changes in heart rate in SD55 KO mice.

Finally, we tested the third hypothesis that a daily intervention with DORA on SD50, a point where the cardiorespiratory pathophysiology is well progressed, would postpone SUDEP in the KO mice.

What were the results and how do you interpret your findings? 

Overall, this study found that KO mice experience a temporal cardiorespiratory pathophysiology characterized by changes in five interdependent endpoints: severe seizures, chronic intermittent hypoxia, apnea, rapid breathing-induced apnea, and bradycardia. This is strikingly similar to the pathophysiology experienced by people with epilepsy immediately prior to succumbing to SUDEP.

The intermittent bradycardia is more prevalent in the older high risk KO mice, and is partially mediated by the parasympathetic drive. These cardiorespiratory parameters may be possible biomarkers for SUDEP proximity to death and may provide us with a temporal window for intervention and possibly prevention of sudden death in this preclinical model.

Our results also suggest that there is a concurrent increase of the orexinergic system which might contribute to the SUDEP probability in KO mice. Antagonizing orexin receptors increased heart rate, and decreased the heart rate variability, breathing frequency, hypopnea-apnea, improved the oxygen saturation and attenuated MCh-induced seizures. Daily DORA treatment also increased the longevity in the high risk KO mice and enabled the atropine-induced changes in heart rate.

What are the next steps that you plan to take, and what are your career goals? 

One of my current manuscript in preparation is long term intervention with ketogenic diet and its possible role in alleviating the progressive cardiorespiratory dysfunction and sudden death in the KO mice. Additionally, we are also working with various SUDEP foundations to collect information from caretakers of patients with SUDEP to get possible information about sleep and cardio-respiratory profiles of the patients in the days and months leading to their death. My long-term goal is to further the SUDEP research and hope to identify concrete temporal biomarkers for prevention of sudden death in epilepsy.

What does the Epilepsia Prize mean for you, your laboratory, research institute, and your future? 

Receiving the 2021 Epilepsia Prize has been a great honor to me and my entire lab. I am extremely thankful to my PI, Dr. Kristina Simeone for her amazing insights in the field of SUDEP and her constant intellectual support and encouragement. I am also grateful for the support of my co-authors, Dr. Ankita Aggarwal, Dr. Tim Simeone, Dr. Peter Abel, Jodi Hallgren and Dr.Ted Warren, without whom this research would not have been possible.

This award is a huge validation and encouragement of our path in furthering SUDEP research, and we hope that this acknowledgement would open new avenues for the entire epilepsy research community in the near future.