Intestinal Dysbiosis Alters Seizure Burden and Antiseizure Medicine Activity Profile in the Theiler’s Virus Model of Acute Encephalitis

Abstract ID 96848 Poster Board 203 Rationale: Brain infection with Theiler's murine encephalomyelitis virus (TMEV) in C57BL/6J mice models infection-induced acute seizures and epileptogenesis. Diet manipulation can modify the presentation of acute seizures in TMEV-infected mice (Zierath et al, BioRxiV 2023); however, no study has yet assessed whether antibiotic-induced intestinal dysbiosis influences the activity of antiseizure medicines (ASM) in the TMEV model. Whether the gut microbiome influences the phenotype of symptomatic seizures after TMEV infection is also unclear. We thus sought to define the extent to which antibiotic administration influences acute seizure presentation, the activity of ASMs, and the pharmacokinetic profile of ASMs in this mouse seizure model. Methods: Male C57BL/6J mice (4-5 weeks-old) received a broad-spectrum antibiotic cocktail (ABX) containing ampicillin, metronidazole, neomycin sulfate, and vancomycin (n=55) or vehicle (n=60) by oral gavage once daily beginning at arrival (Day -2) to Day 7 post-TMEV infection. Mice were infected with either intracerebral TMEV or PBS on Day 0. Mice received carbamazepine (CBZ; 20 mg/kg, i.p.) or vehicle (0.5% MC) twice daily Days 3-7 p.i. and were assessed for handling-induced seizures 30 min after CBZ treatment. Plasma samples were collected on Day 7 p.i. at 15 and 60 min post-CBZ treatment to quantify the extent to which ABX-induced gut dysbiosis influences ASM pharmacokinetics. Results: TMEV infection induced acute symptomatic seizures, regardless of pretreatment and ASM history as 18/25 (72%) ABX-CBZ mice, 7/20 (35%) ABX-VEH mice, 7/20 (35%) SAL-CBZ mice, and 15/20 (75%) SAL-VEH mice presented with seizures during the 7-day monitoring period. Average seizure burden was: 12.5 in ABX-CBZ, 4.7 in ABX-VEH, 5.7 in SAL-CBZ, and 16.1 in SAL-VEH mice. There was a significant pretreatment x ASM interaction (F (1, 81) = 16.0, p=0.0001), with post-hoc tests revealing marked differences in seizure burden in SAL- versus ABX-pretreated mice (p=0.004). Further, the latency to Stage 5 seizure was substantially increased by CBZ during days 3-7 post-infection; an effect absent in ABX-treated mice similarly administered CBZ. In TMEV-infected mice, spleens were 0.32% of body weight in ABX-CBZ mice, 0.34% in ABX-VEH mice, 0.36% in SAL-CBZ mice, and 0.38% in SAL-VEH mice. In sham-infected mice, spleens were 0.45% of body weight in ABX-CBZ mice, 0.65% in SAL-CBZ mice, and 0.36% in SAL-VEH mice. Plasma CBZ concentrations in TMEV-infected mice receiving ABX were 9.8±2.0 mg/mL 15 min post-dosing and 4.0±0.5 at 60 min post-dose, consistent with published CBZ plasma concentrations in mice (Bialer et al, 2004) suggesting no pharmacokinetic differences because of ABX history. Conclusions: Gut dysbiosis markedly alters the presentation of symptomatic seizures and acute disease burden in the TMEV mouse model, reflecting a novel therapeutic target for seizure control. The gut-brain axis is an understudied target in epilepsy that may benefit from greater investigation. Acknowledgements: This work was supported by the University of Washington Department of Pharmacy and the University of Washington Plein Center for Geriatric Pharmacy.