Fluorescence determination of N-acetylaspartic acid in the rat cerebrum homogenate using high-performance liquid chromatography with pre-column fluorescence derivatization

An enzymatic fluorimetric assay for determination of N-acetylaspartate

N-acetylaspartate (NAA) is an abundant metabolite in the mammalian brain and a precursor of the neuropeptide N-acetylaspartylglutamate (NAAG). The physiological role of NAA is not fully understood and requires further studies. We here describe the development of a coupled enzymatic fluorimetric assay for the determination of NAA in biological samples. Deproteinized tissue extracts are first passed through a strong cation exchange column to remove aspartate. NAA in the sample is hydrolysed by aspartoacylase and released aspartate oxidized using l-aspartate oxidase. Generated H₂O₂ is measured with peroxidase in a fluorimetric assay using Ampliflu Red. The limit of detection and the lower limit of quantification are 1.0 μM (10 pmol/well) and 3.3 μM (33 pmol/well), respectively, with a linear range to 100 μM. Specificity of the assay was confirmed using samples from mice deficient in NAA synthase Nat8l that were spiked with NAA. Analysis of samples from aspartoacylase-deficient mice showed a 2 to 3-fold increase in brain NAA concentration, in line with previous reports. Mice lacking NAAG synthetases had a slightly reduced (-10%) brain NAA level. Thus, the new fluorimetric enzymatic assay is useful to perform sensitive and large scale quantification of NAA in biological samples without the need for expensive equipment.

Proteomics-driven Antigen Discovery for Development of Vaccines Against Gonorrhea

Expanding efforts to develop preventive gonorrhea vaccines is critical because of the dire possibility of untreatable gonococcal infections. Reverse vaccinology, which includes genome and proteome mining, has proven very successful in the discovery of vaccine candidates against many pathogenic bacteria. However, progress with this approach for a gonorrhea vaccine remains in its infancy. Accordingly, we applied a comprehensive proteomic platform-isobaric tagging for absolute quantification coupled with two-dimensional liquid chromatography and mass spectrometry-to identify potential gonococcal vaccine antigens. Our previous analyses focused on cell envelopes and naturally released membrane vesicles derived from four different Neisseria gonorrhoeae strains. Here, we extended these studies to identify cell envelope proteins of N. gonorrhoeae that are ubiquitously expressed and specifically induced by physiologically relevant environmental stimuli: oxygen availability, iron deprivation, and the presence of human serum. Together, these studies enabled the identification of numerous potential gonorrhea vaccine targets. Initial characterization of five novel vaccine candidate antigens that were ubiquitously expressed under these different growth conditions demonstrated that homologs of BamA (NGO1801), LptD (NGO1715), and TamA (NGO1956), and two uncharacterized proteins, NGO2054 and NGO2139, were surface exposed, secreted via naturally released membrane vesicles, and elicited bactericidal antibodies that cross-reacted with a panel of temporally and geographically diverse isolates. In addition, analysis of polymorphisms at the nucleotide and amino acid levels showed that these vaccine candidates are highly conserved among N. gonorrhoeae strains. Finally, depletion of BamA caused a loss of N. gonorrhoeae viability, suggesting it may be an essential target. Together, our data strongly support the use of proteomics-driven discovery of potential vaccine targets as a sound approach for identifying promising gonococcal antigens.

Deletion of SHATI/NAT8L decreases the N-acetylaspartate content in the brain and induces behavioral deficits, which can be ameliorated by administering N-acetylaspartate

We previously identified a novel molecule "SHATI/NAT8L" that exerts an inhibitory effect on methamphetamine (METH)-induced behavioral deficits. Recently, it has been reported that SHATI might function as an aspartate N-acetyltransferase, which synthesizes N-acetylaspartate (NAA) in vitro. However, whether SHATI actually synthesizes NAA in vivo in the brain is still unclear. In this study, we found that both Shati-deleted mice showed significantly lower NAA levels in all brain areas than wild-type (Shati(+/+)) mice using HPLC and fluorescence detection, suggesting that SHATI regulates NAA content in the brain. Next, we measured the levels of monoamines and their metabolites in the adult mouse brain and found that the activities of monoaminergic systems were altered in Shati(-/-) mice. In particular, dopaminergic turnover increased in the nucleus accumbens (NAc) in Shati(-/-) mice, suggesting activation of the dopaminergic system. In fact, basal level of extracellular dopamine, and METH-induced dopamine release in the NAc of Shati(-/-) mice was significantly higher than that of Shati(+/+) and Shati(+/-) mice, which is consistent with findings that Shati(-/-) mice showed enhanced hyperlocomotion induced by METH. Moreover, in the forced swimming test, Shati-deleted mice showed a shortened immobility time, which was improved by intracerebroventricular (i.c.v.) administration of NAA prior to the test in Shati(+/-) but not in Shati(-/-) mice. The i.c.v. preinjection of NAA inhibited dopamine release after high K(+) stimulation in the NAc of Shati(+/+) and Shati(+/-) mice, but not Shati(-/-) mice. These results suggested that the behavioral deficits in Shati-deleted mice were caused by dopaminergic abnormality via deprivation of NAA.