Reversed-phase HPLC with UV detection for the determination of N-acetylaspartate and creatine

Deletion of the creatine transporter gene in neonatal, but not adult, mice leads to cognitive deficits

Creatine (Cr) is a guanidino compound that provides readily available phosphate pools for the regeneration of spent adenosine triphosphate (ATP). The lack of brain Cr causes moderate to severe intellectual disability, language impairment, and epilepsy. The most prevalent cause of Cr deficiency are mutations in the X-linked SLC6A8 (Creatine transporter; CrT) gene, known as CrT deficiency (CTD). One of the most critical areas that need to be addressed is whether Cr is necessary for brain development. To address this concern, the Slc6a8 gene was knocked out in either neonatal (postnatal day (P)5) or adult (P60) mice using a tamoxifen-inducible Cre recombinase driven by the human ubiquitin C (UBC) promoter. Mice were tested in the Morris water maze, novel, object recognition, and conditioned fear 60 days after Slc6a8 deletion. In addition, overnight locomotor activity was analyzed. Mice that had the gene deleted on P5 showed deficits in the Morris water maze and novel object recognition, while there were no deficits in P60 knockout mice. Interestingly, the P5 knockout mice showed hyperactivity during the dark phase; however, when examining control mice, the effect was due to the administration of tamoxifen from P5 to 10. Taken together, the results of this study show that Cr is necessary during periods of brain development involved in spatial and object learning. This study also highlights the continued importance of using proper control groups for behavioral testing.

N-acetylglutamate and N-acetylaspartate in soybeans (Glycine max L.), maize (Zea mays L.), [corrected] and other foodstuffs

N-Acetylglutamate (NAG) and N-acetylaspartate (NAA) are amino acid derivatives with reported activities in a number of biological processes. However, there is no published information on the presence of either substance in foodstuffs. We developed a method for extracting and quantifying NAG and NAA from soybean seeds and maize grain using ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS). The lower limit of quantification for both NAG and NAA was 1 ng/mL. The method was then utilized to quantify NAG and NAA in other foodstuffs (fruits, vegetables, meats, grains, milk, coffee, tea, cocoa, and others). Both NAG and NAA were present in all of the materials analyzed. The highest concentration of NAG was found in cocoa powder. The highest concentration of NAA was found in roasted coffee beans. Both NAG and NAA were found at quantifiable concentrations in all foods tested indicating that these two acetylated amino acids are common components of the human diet.

Stimulated efflux of amino acids and glutathione from cultured hippocampal slices by omission of extracellular calcium: likely involvement of connexin hemichannels

Omission of extracellular Ca(2+) for 15 min from the incubation medium of cultured hippocampal slices stimulated the efflux of glutathione, phosphoethanolamine, hypotaurine, and taurine. The efflux was reduced by several blockers of gap junctions, i.e. carbenoxolone, flufenamic acid, and endothelin-1, and by the connexin43 hemichannel blocking peptide Gap26 but was unchanged by the P2X(7) receptor inhibitor oxidized ATP, a pannexin1 hemichannel blocking peptide and an inactive analogue of carbenoxolone. Pretreatment of the slices with the neurotoxin N-methyl-d -aspartate left the efflux by Ca(2+) omission unchanged, indicating that the stimulated efflux primarily originated from glia. Elevated glutamate efflux was detected when Ca(2+) omission was combined with the glutamate uptake blocker l-trans-pyrrolidine-2,4-dicarboxylate and when both Ca(2+) and Mg(2+) were omitted from the medium. Omission of Ca(2+) for 15 min alone did not induce delayed toxicity, but in combination with blocked glutamate uptake, significant cell death was observed 24 h later. Our results indicate that omission of extracellular Ca(2+) stimulates efflux of glutathione and specific amino acids including glutamate via opening of glial hemichannels. This type of efflux may have protective functions via glutathione efflux but can aggravate toxicity in situations when glutamate reuptake is impaired, such as following a stroke.

Hydrophilic chromatographic determination of carnosine, anserine, balenine, creatine, and creatinine

A new HPLC procedure based on hydrophilic interaction chromatography (HILIC) has been developed for the simultaneous determination of carnosine, anserine, balenine, creatine, and creatinine in meat. This is the first time that HILIC has been directly applied to the study of meat components, having the advantage of not requiring complex cleanup and/or sample derivatization procedures. The chromatographic separation has been developed using a silica column (4.6 x 150 mm, 3 microm), and the proposed methodology is simple, reliable, and fast (<13 min per sample). The method has been validated in terms of linearity, repeatability, reproducibility, and recovery and represents an interesting alternative to methods currently in use for determining the mentioned compounds and other polar substances. The detection limits are 5.64, 8.23, 3.66, 3.99, and 0.06 microg/mL for carnosine, anserine, balenine, creatine, and creatinine, respectively.

In Vitro Studies on the Putative Function of N-acetylaspartate as an Osmoregulator

Efflux and tissue content of N-acetylaspartate (NAA) and amino acids were evaluated from cultured and acutely prepared hippocampal slices in response to changes in osmolarity. The osmoregulator taurine, but not NAA, was lost from both types of slices after moderate reductions in extracellular osmolarity (-60 mOsm) for 10-48 h. Hypoosmotic shock (-166 mOsm) for 5 min resulted in unselective efflux of several amino acids from acutely prepared slices. Notably, the efflux of taurine, but not NAA, was prominent also after the shock. Efflux of NAA was markedly enhanced by NMDA and high K(+), in particular after the stimulation period. The high K(+)-mediated efflux was decreased by high extracellular osmolarity and a NMDA-receptor antagonist. The results indicate that NAA efflux can be induced by a sudden non-physiological decrease in extracellular osmolarity but not by prolonged more moderate changes in osmolarity. The mechanisms behind the efflux of NAA by high K(+) are complex and may involve both swelling and activation of NMDA-receptors.

N-acetylaspartate monomethyl ester increases N-acetylaspartate concentration in cultured rat hippocampal slices: effects on excitotoxicity and levels of amino acids and chloride

N-acetylaspartate (NAA) was discovered in mammalian brain 50 years ago but its functions remain debated. One reason for the relatively slow progress of NAA research is the paucity of tools to specifically modify NAA concentrations. In this work we evaluated the use of the monomethyl ester of NAA (NAA MME) to increase the relatively low level of NAA in cultured hippocampal slices. When slices were treated with 30 mM NAA MME for 3 days the NAA concentration increased from 31.6 to 185.3 nmol/mg protein. Incubation with NAA alone increased the NAA concentration non-significantly to 65.6 nmol/mg protein. NAA MME treatment increased NAA in neurons and the increase was non-toxic as determined by the low uptake of propidium iodide, a dye that only enters damaged cells. NMDA-mediated excitotoxicity which is initiated by influx of Ca(2+) was unaltered by increased NAA levels indicating poor intracellular Ca(2+)-chelation by NAA.