Rationale:
Sudden Unexpected Death in Epilepsy (SUDEP) is one of the most common causes of death in individuals with epilepsy. Cardiac arrhythmias are implicated as a mechanism contributing to SUDEP. This study investigated if cardiac mitochondrial energetics are altered in the pilocarpine-induced mouse model of temporal lobe epilepsy (TLE). Both epileptic patients and rodent models of TLE exhibit persistent electrocardiogram changes and an increased susceptibility to potentially fatal arrhythmias. We hypothesized that mitochondrial respiration and ROS production are compromised in TLE mouse hearts, leading to cardiac arrhythmias.
Methods:
To generate the pilocarpine model of TLE, a single injection of pilocarpine (200 mg/kg; i.p) was used to induce status epilepticus in adult (10-12 weeks old) C57BL/6J mice. Control mice were given equivalent volumes of saline. To assess mitochondrial function at the acute, latent, and chronically epileptic periods, we collected hearts from TLE and saline treated mice at 24 hours, one week, and four weeks post pilocarpine administration and isolated mitochondria from ventricular samples. Using high-resolution respirometry (O2k-Oroboros), we concurrently measured mitochondrial oxygen and H2O2 flux under different electron transport pathway states in our mitochondrial preparations.
Results:
At the 24 hour timepoint, we found that mitochondrial respiration was significantly decreased in TLE hearts after the addition of substrates supporting Complex II-linked respiration (succinate, 1.40-fold; ADP, 1.41-fold), and Complex I-linked respiration (pyruvate, 1.46-fold). In addition, at the four week timepoint, we found that mitochondrial respiration was decreased in TLE hearts after the addition of succinate (1.31-fold), ADP (1.52-fold), and pyruvate (1.47-fold). No differences in respiration were detected in the TLE model at one week post pilocarpine treatment compared to the one week saline cohort. Furthermore, in isolated mitochondria from TLE hearts, mitochondrial H2O2 production was not significantly at any timepoint (24-hour, one week, or four weeks) compared to matched saline mice.
Conclusions:
Our results suggest that TLE mice display depressed mitochondrial function at both the acute and chronically epileptic periods, suggesting that changes occur during the epileptogenic process. This imbalance sets up the potential for increased arrhythmia susceptibility that may underlie SUDEP. Considering the prevalence of TLE, and the ongoing challenges with therapeutic intervention by
anti-epileptic drugs, it is imperative that new therapeutic targets are identified. A better understanding of alterations to mitochondrial mechanisms that underlie epileptogenesis and lead to TLE may be crucial to the development of new pharmaceutical interventions to treat TLE and reduce SUDEP incidence.
Funding:
This work was supported by a grant from the Research Development Committee at East Tennessee State University and NIH grant R21NS116647 to C.R.F.