Acetate-based Energy Supplements Preserved Mitochondrial Bioenergetic Responses After Penetrating Traumatic Brain Injury

Abstract Text:

Background:
Mitochondria play a pivotal role in maintaining the brain energy homeostasis following traumatic brain injury (TBI). The time-course analysis of mitochondrial bioenergetics parameters in a preclinical model of penetrating TBI (PTBI) showed altered metabolic substrate utilization, and impaired energy homeostasis together with altered redox and calcium homeostasis between 30 minutes to 14 days post-injury. The higher energy demand and decreased energy supplementation could lead to mitochondrial bioenergetics failure in the acute phase of PTBI. While glucose serves as the primary metabolic substrate for the brain energy (i.e., adenosine triphosphate, ATP) metabolism, the other alternative energy supplements may replenish the higher energy demand during an acute injury phase of PTBI. Therefore, the alternative supplements are being evaluated in response to mitigate the metabolic disruption observed after PTBI. The current study tested acetyl-L-carnitine (ALC), glyceryl triacetate (GTA) and analog of resveratrol (RA) as acetate-based alternative energy supplements for PTBI. These drugs were selected based on their ability to bypass key metabolic enzymatic reactions of glucose oxidation and readily provide “acetate” metabolite for mitochondrial ATP synthesis.

Methods:
Anesthetized adult male rats were subjected to either 10% unilateral PTBI or uninjured sham craniectomy. The dose-response experiments of drugs were conducted to evaluate therapeutic efficacy based on improvement in bioenergetics measured at 7 days post-PTBI. The ALC (50-500 mg/kg or vehicle) was administered intraperitoneally (i.p.) at 15min and 6h post-injury, then once daily for 7 days. The GTA (1-7.5g/kg or vehicle) was administered intragastrically at 15min and 6h post-injury, then once daily for 7 days. The RA (100 mg/kg or vehicle) was administered i.p. at 15min, 6h, and 24h post-injury. Additionally, the therapeutic window of ALC and GTA drugs were evaluated by delaying the first dose of drug administration up to 24h, and then once daily for 7 days. Following the last dose administration of acetate therapy, animals were euthanized, and mitochondria were isolated from the injury core and perilesional area (i.e., frontal cortex + striatum) to evaluate mitochondrial bioenergetics in real-time ex-vivo condition using Seahorse Extracellular Flux Analyzer. The remaining samples from the RA study were further used to assess mitochondrial oxidative stress responses using Western blot following PTBI.

Results:
The ALC 50mg/kg group had significantly higher mitochondrial ATP synthesis rates (*p < 0.05 vs. vehicle) at 7 days post-PTBI. The RA 100mg/kg showed improved bioenergetics and redox homeostasis at 24h post-PTBI. Likewise, GTA displayed dose-dependent improvements in bioenergetics, particularly GTA (7.5mg/kg) group had a significantly higher ATP synthesis rate (*p < 0.05 vs. vehicle) at 7 days post-PTBI. Furthermore, therapeutic window experiments have indicated that ALC has a longer therapeutic window of opportunity up to 6h post-injury, whereas GTA has a shorter therapeutic window than ALC.

Conclusion:
Pharmacological evaluation based on the results of dose response and therapeutic window experiments indicates that “acetate” therapy may serve as an alternative energy biofuel for acute brain trauma. Mitochondria targeted acetate drugs may serve as innovative nutrition-based treatment strategies to alleviate symptoms or slow down the progression of TBI. In the future, this may aid in developing prolonged nutrition care using oral and/or intramuscular approaches to treat acute TBI, thereby may enhance and sustain warfighter’s performance in operational environments, extreme climates/weather, or resource-limited military settings.

Keywords: Mitochondria, Acetate Therapy, Energy Homeostasis, Oxidative Stress, Antioxidants, Time-course, Penetrating Traumatic Brain Injury (PTBI), Drug Interventions.