Therapeutic ketosis with ketone ester delays central nervous system oxygen toxicity seizures in rats

Abstract

Central nervous system oxygen toxicity (CNS-OT) seizures occur with little or no warning, and no effective mitigation strategy has been identified. Ketogenic diets (KD) elevate blood ketones and have successfully treated drug-resistant epilepsy. We hypothesized that a ketone ester given orally as R,S-1,3-butanediol acetoacetate diester (BD-AcAc(2)) would delay CNS-OT seizures in rats breathing hyperbaric oxygen (HBO(2)). Adult male rats (n = 60) were implanted with radiotelemetry units to measure electroencephalogram (EEG). One week postsurgery, rats were administered a single oral dose of BD-AcAc(2), 1,3-butanediol (BD), or water 30 min before being placed into a hyperbaric chamber and pressurized to 5 atmospheres absolute (ATA) O2. Latency to seizure (LS) was measured from the time maximum pressure was reached until the onset of increased EEG activity and tonic-clonic contractions. Blood was drawn at room pressure from an arterial catheter in an additional 18 animals that were administered the same compounds, and levels of glucose, pH, Po(2), Pco(2), β-hydroxybutyrate (BHB), acetoacetate (AcAc), and acetone were analyzed. BD-AcAc(2) caused a rapid (30 min) and sustained (>4 h) elevation of BHB (>3 mM) and AcAc (>3 mM), which exceeded values reported with a KD or starvation. BD-AcAc(2) increased LS by 574 ± 116% compared with control (water) and was due to the effect of AcAc and acetone but not BHB. BD produced ketosis in rats by elevating BHB (>5 mM), but AcAc and acetone remained low or undetectable. BD did not increase LS. In conclusion, acute oral administration of BD-AcAc(2) produced sustained ketosis and significantly delayed CNS-OT seizures by elevating AcAc and acetone.

Ketosis as a treatment for multiple metabolic and neurodegenerative pathologies

“…Oral administration of BHB and AcAc in their free acid form is expensive and ineffective at producing sustained ketosis. The sodium salt of BHB has been shown to elevate blood ketone levels in animal models [13], while esters of BHB or AcAc also promise great therapeutic potential [8,9,36]. These ketone esters of BHB are demonstrated to be safe and well tolerated in rats [84] and humans [85], while they produce fasting-level ketosis without dietary restriction.…”

“…Moreover, Bough and Eagles demonstrated how efficient a KD can be in PTZ-induced seizures in a rat model [23]. Viggiano and colleagues assessed the blood ketones increase following the oral administration of BD-AcAc2 in rats, in parallel with the CNS-OT seizure model reported previously [9]. The main preliminary finding from Viggiano's study was that oral administration of BDAcAc2 manifested a significant increase of BHB and an even more consistent resistance against the epileptic seizure onset, compared to the control group [24].…”

“…The group was interested in esters of AcAc because precursors to BHB do not prevent CNS-OT [12], and animal studies suggest that AcAc and acetone have the greatest anticonvulsant potential [13][14][15][16]. Authors demonstrated that a single oral administration of the ketone ester BD-AcAc2 caused rapid and sustained elevations of BHB (>3 mM), AcAc (>3 mM), and acetone (~0.7 mM) and increased resistance to seizures (LS = 574 ±115%, P < 0.001), compared with control (water) or BD, even though BD caused a significant increase in BHB (Figure 2) [9]. Ketone ester administration produces "fasting ketosis", which effect is well documented in humans and animal models and correlates with a rise in blood ketones [13,16].…”

“…BD-AcAc2 has little or no effect on blood glucose [9], and thus makes it an attractive option for mitigating CNS-OT and may represent a sought-after strategy for epilepsy to circumvent issues with compliance associated with KD [17]. In addition, D'Agostino and collaborators [9] demonstrated that the anticonvulsant benefits of fasting ketosis are conferred with BD-AcAc2, even during a standard diet ad libitum, reaching higher blood ketones levels than those typically reported in rats fasted 24-36 h [12] or rats eating a KD [18,19]. In fact, measurements of BHB, AcAc, and acetone together showed values of ~6 mM, usually achieved in a week of fasting for humans [20].…”

“…For example, fasting for 24 to 36 hours delays the latency time to CNS-OT seizure up to 300%, which is comparable to high doses of anti-epileptic drugs (AEDs) [4,5] and experimental excitatory glutamatergic neurotransmission blockers [6]. Esters of betaxydroxybutyrate (BHB) or acetoacetate (AcAc) can effectively induce a rapid and sustained ketosis [7,8], therefore D'Agostino and colleagues [9] synthesized and tested a ketone ester [R,S-1,3-butanediol acetoacetate diester (BD-AcAc2)], which has been shown to induce therapeutic ketosis in dogs [10,11] and pigs [8] and was proposed as a metabolic therapy for parenteral and enteral nutrition [7]. The group was interested in esters of AcAc because precursors to BHB do not prevent CNS-OT [12], and animal studies suggest that AcAc and acetone have the greatest anticonvulsant potential [13][14][15][16].…”