β-hydroxybutyrate (β-HB)’s antiseizure action is mediated by Neuronal Hydroxycarboxylic acid receptor 2 (HCAR2)
Abstract number :
2.001
Submission category :
10. Dietary Therapies (Ketogenic, Atkins, etc.)
Year :
2025
Submission ID :
865
Source :
www.aesnet.org
Presentation date :
12/7/2025 12:00:00 AM
Published date :
Authors :
Presenting Author: Soudabeh Naderi, PhD, MSc – University of Virginia
John M Williamson, BS – University of Virginia
Huayu sun, PhD – University of Virginia
Rachel Jane Spera, BS – University of Virginia
Chengsan Sun, PhD – University of Virginia
Ifrah Zawar, MD – University of Virginia
Jaideep Kapur, MD, PhD – University of Virginia
Rationale: The ketogenic diet, a high-fat, low-carbohydrate regimen, is commonly used to treat drug-resistant seizures. β-HB, a main circulating ketone body, has emerged as a key mediator of KD’s antiseizure properties. However, the mechanism of β-HB’s action is unknown. HCAR2 is a Gi-coupled receptor, also known as a niacin receptor, that binds to β-HB. We tested whether HCAR2 mediates the anti-seizure effects of β-HB.
Methods: We used 4-8-week-old C57BL/6, HCAR2 knockout (HCAR2⁻/⁻), wild-type (HCAR2⁺/⁺), and microglia-deficient mice (FIRE⁻/⁻). We generated HCAR2⁻/⁻ mice using CRISPR-Cas technology on an S129 background. Two complementary in vivo mouse models evaluated the β-HB anti-seizure effects. We used continuous hippocampal stimulation (CHS) to induce status epilepticus (SE) and the hippocampal kindling paradigm. β-HB (1 g/kg, i.p.) or saline was administered after the onset of SE or in fully kindled mice. Seizure duration and behavioral seizure score (BSS) were measured via video-EEG monitoring. Whole-cell current-clamp recordings from dentate granule cells (DGCs) in acute hippocampal slices were performed to measure the passive and active neuronal membrane properties. The voltage-clamp technique was used to record synaptic currents. Calcium imaging was conducted using stereotaxic viral delivery to inject a genetically encoded calcium indicator (GCaMP7) into the hippocampus. HCAR2 expression was localized using RNA in situ hybridization. Immunohistochemistry was used to identify different cell types. Real-time quantitative PCR (RT-qPCR) evaluated HCAR2 expression in mouse brains.
Results: Systemic β-HB administration rapidly reduced SE duration by ~81 minutes and suppressed high-frequency discharge in C57BL/6 mice. In HCAR2⁻/⁻ mice, β-HB had no impact on SE. However, it shortened SE duration by ~ 67.38 minutes and attenuated BSS (grade 3-4) in HCAR2⁺/⁺ mice. In fully kindled mice, β-HB transiently reduced ADD and seizure severity (from grade 5 to 4) in HCAR2⁺/⁺ mice, but not in HCAR2⁻/⁻ mice (grade 5). Similarly, niacin reduced ADD and BSS in HCAR2⁺/⁺ mice but had no impact on HCAR2⁻/⁻ mice. β-HB decreased calcium dynamics and neuronal activity of CA1 neurons. RT-qPCR validated the dense mRNA HCAR2 in the mouse brain and was absent in HCAR2⁻/⁻. RNAscope demonstrated robust HCAR2 mRNA expression in hippocampal DGCs and microglia. β-HB hyperpolarized the resting membrane potential, raised action potential thresholds, and reduced firing frequency in response to depolarizing currents in C57BL/6 and HCAR2⁺/⁺ mice. Also, it reduced the frequency of sEPSC in those mice. These effects were nullified in HCAR2⁻/⁻ mice. This suppressive effect was maintained in mice lacking microglia.
Conclusions: β-HB reduced the duration and severity of SE and suppressed kindling seizures. It decreased neuronal excitability and excitatory synaptic transmission of DGCs. HCAR2 mediates these effects. β-HB’s effect was abolished in HCAR2⁻/⁻
Dietary Therapies (Ketogenic, Atkins, etc.)