Authors :
Presenting Author: Anamika Choudhary, MSc – Cumming School of Medicine, University of Calgary
Quentin Pittman, PhD – University of Calgary; Karlene Ricketts, PhD – University of Calgary; Morris Scantlebury, MD – Cumming School of Medicine, University of Calgary; Cezar Gavrilovici, PhD – Cumming School of Medicine, University of Calgary
Rationale:
Infantile Spasms (IS), a profound developmental encephalopathy of infancy, often present refractory to first-line antiepileptic interventions. The Ketogenic Diet (KD) has emerged as an alternative therapy. Using the triple-hit model of symptomatic IS, we previously elucidated that the KD’s anti-seizure effects are linked to intracerebral acidosis (PMID: 34734183). Acid-Sensing Ion Channels (ASICs) play a pivotal role in acid-evoked currents, and given ASIC1a's crucial role in modulating pH fluctuations relevant to our model (pH 6.8), we hypothesize that acidosis-induced activation of ASIC1a underlies the KD’s mechanism of action in IS.
Methods:
We employed the triple-hit IS model to evaluate spasm frequency in CRISPR ASIC1a knockout (KO) rat pups (SD, males and females) from postnatal days (P) 4-12. Pups were artificially reared using the pup-in-cup setup and fed either the KD (4:1 fats:carbs+protein) or a control-milk diet (CMD; 1.7:1). We used the zero-magnesium(0-Mg) acute slice seizure model to record extracellular field potentials in the somatosensory cortex in brain slices from CMD or KD-fed P7 pups to assess the effect of intracerebral acidosis on epileptiform brain activity. Brain slices were exposed to low pH (6.8) to activate ASIC1a, and the resulting epileptiform activity analyzed across the experimental groups.
Results:
We found that spasm frequency was profoundly exacerbated in ASIC1a KO pups (n=8) compared to their wild-type (WT) counterparts between P4 to P12, with the highest frequency at P8 (CMD: 12.94±0.08 spasms/hr; KD: 13.21±0.09 spasms/hr) compared to P5 on WT controls (CMD: 9.68±0.19 spasms/hr; KD: 6.59±0.11 spasms/hr). At baseline (P4), we observed an 83% increase spasm frequency in ASIC1a-KO pups compared to WT pups. Whereas WT animals were spasm free by P12, spasms were still evident in ASIC1a KO pups at this age (CMD: 2.64±0.06 spasms/hr; KD: 2.77±0.04 spasms/hr). In addition, the anti-convulsant effects of the KD were completely abolished in ASIC1a KO pups, with no significant difference in spasm frequency between ASIC1a pups fed the KD or CMD (p >0.438). Using the 0-Mg acute slice seizure model, we show that acidosis-induced ASIC1a activation (pH=6.8), significantly attenuated epileptiform activity in WT pups ( >72.6%). This attenuation was more pronounced in IS pups fed the KD (n=7) with a spiking event frequency (SF) reduction of 96.8%±1.7 and a peak spiking amplitude (PA) reduction of 97.2%±1.13. Ictal-like activity was observed in WT pups fed the CMD (n=7) but not in those on the KD, and this pattern was abolished with low pH. In ASIC1a KO animals, low pH (6.8) had no significant effect on epileptiform activity in pups fed either the CMD (n=6, SF=0.02%±0.01; PA=0.001%±0.03) or KD (n=6, SF=0.03%±0.02; PA=0.07%±0.01).
Conclusions:
Our results provide strong evidence for the interaction between ASIC1a and acidosis (pH=6.8) to gatekeep the antiseizure effects in the model. These findings collectively underscore the pivotal role of ASIC1a in mediating the efficacy of KD in IS, offering insights into potential therapeutic interventions for this debilitating disease.
Funding: CIHR, University Calgary, Albert Children’s Hospital Research Institute