Progress toward Acetate Supplementation Therapy for Canavan Disease: Glyceryl Triacetate Administration Increases Acetate, but NotN-Acetylaspartate, Levels in Brain

Abstract

Canavan disease (CD) is a fatal genetic neurodegenerative disorder caused by mutations in the gene for aspartoacylase, an enzyme that hydrolyzes N-acetylaspartate (NAA) into L-aspartate and acetate. Because aspartoacylase is localized in oligodendrocytes, and NAA-derived acetate is incorporated into myelin lipids, we hypothesize that an acetate deficiency in oligodendrocytes is responsible for the pathology in CD, and we propose acetate supplementation as a possible therapy. In our preclinical efforts toward this goal, we studied the effectiveness of orally administered glyceryl triacetate (GTA) and calcium acetate for increasing acetate levels in the murine brain. The concentrations of brain acetate and NAA were determined simultaneously after intragastric administration of GTA. We found that the acetate levels in brain were increased in a dose-and time-dependent manner, with a 17-fold increase observed at 1 to 2 h in 20-to 21-day-old mice at a dose of 5.8 g/kg GTA. NAA levels in the brain were not significantly increased under these conditions. Studies using mice at varying stages of development showed that the dose of GTA required to maintain similarly elevated acetate levels in the brain increased with age. Also, GTA was significantly more effective as an acetate source than calcium acetate. Chronic administration of GTA up to 25 days of age did not result in any overt pathology in the mice. Based on these results and the current Food and Drug Administration-approved use of GTA as a food additive, we propose that it is a potential candidate for use in acetate supplementation therapy for CD.

N-Acetylaspartate in the CNS: From neurodiagnostics to neurobiology

“…Esterases present in most tissues of the body can cleave the acetate moieties, generating free acetate. Dosing experiments in mice demonstrated that GTA was 10 to 20 times more effective at delivering acetate to the brain than calcium acetate, and that it was well tolerated by developing mice (Mathew et al, 2005). If substantially elevated levels of acetate can be maintained in oligodendrocytes through dietary acetate supplementation during postnatal myelination, this should theoretically correct the acetate deficiency that occurs in Canavan disease.…”

“…Currently there is no effective treatment available for restoring proper myelination and motor function. The pathogenic mechanisms operative in Canavan disease currently remain a matter of debate, but it has been proposed that the etiology involves a lack of NAA-derived acetate, which is required for some portion of myelin lipid synthesis during postnatal axonal myelination (Hagenfeldt et al, 1987;Kirmani et al, 2002;Madhavarao et al, 2005;Mathew et al, 2005;Mehta and Namboodiri, 1995;Namboodiri et al, 2006b;Namboodiri et al, 2006a). Under this hypothesis, infants born with Canavan disease are normal at birth because ASPA activity is not critical until myelin synthesis is dramatically increased shortly after birth.…”

Non-genetic therapeutic approaches to Canavan disease

“…Intragastric administration of equivalent amounts of CA or GTA to 21-day-old C57BL/6 mice showed GTA to raise CNS Ac levels much more effectively 5 and to have fewer adverse effects than CA, although both were found to be reasonably safe (Mathew et al, 2005;Namboodiri et al, 2006).…”

“…Other studies have focused on the "Ac-myelin-lipid" hypothesis and attempted to restore myelination through Ac-supplementation (Arun et al, 2010;Madhavarao et al, 2009;Mathew et al, 2005;Namboodiri et al, 2006;Segel et al, 2011) (Table 2). To this end, calcium Ac (CA) and glyceryl triacetate (GTA) have both been tested in their ability to deliver Ac to the CNS (Mathew et al, 2005;Namboodiri et al, 2006).…”

“…To this end, calcium Ac (CA) and glyceryl triacetate (GTA) have both been tested in their ability to deliver Ac to the CNS (Mathew et al, 2005;Namboodiri et al, 2006).…”