Simple Quantitative HPLC Method for Measuring Physiologic Amino Acids in Cerebrospinal Fluid without Pretreatment

A chemical genetic approach using genetically encoded reporters to detect and assess the toxicity of plant secondary metabolites against bacterial pathogens

Plant secondary metabolites are emerging as attractive alternatives in the development of therapeutics against infectious and chronic diseases. Due to the present pandemic, therapeutics showing toxicity against bacterial pathogens and viruses are gaining interest. Plant metabolites of terpenoid and phenylpropanoid categories have known antibacterial and antiviral properties. These metabolites have also been associated with toxicity to eukaryotic cells in terms of carcinogenicity, hepatotoxicity, and neurotoxicity. Sensing methods that can report the exact antibacterial dosage, formation, and accumulation of these antibacterial compounds are needed. The whole-cell reporters for such antibacterial metabolites are cost-effective and easy to maintain. In the present study, battery of toxicity sensors containing fluorescent transcriptional bioreporters was constructed, followed by fine-tuning the response using gene-debilitated E. coli mutants. This study shows that by combining regulatory switches with chemical genetics strategy, it may be possible to detect and elucidate the mode of action of effective antibacterial plant secondary metabolites - thymol, cinnamaldehyde, eugenol, and carvacrol in both pure and complex formats. Apart from the detection of adulteration of pure compounds present in complex mixture of essential oils, this approach will be useful to detect authenticity of essential oils and thus reduce unintended harmful effects on human and animal health.

Spread spectrum SERS allows label-free detection of attomolar neurotransmitters

The quantitative label-free detection of neurotransmitters provides critical clues in understanding neurological functions or disorders. However, the identification of neurotransmitters remains challenging for surface-enhanced Raman spectroscopy (SERS) due to the presence of noise. Here, we report spread spectrum SERS (ss-SERS) detection for the rapid quantification of neurotransmitters at the attomolar level by encoding excited light and decoding SERS signals with peak autocorrelation and near-zero cross-correlation. Compared to conventional SERS measurements, the experimental result of ss-SERS shows an exceptional improvement in the signal-to-noise ratio of more than three orders of magnitude, thus achieving a high temporal resolution of over one hundred times. The ss-SERS measurement further allows the attomolar SERS detection of dopamine, serotonin, acetylcholine, γ-aminobutyric acid, and glutamate without Raman reporters. This approach opens up opportunities not only for investigating the early diagnostics of neurological disorders or highly sensitive biomedical SERS applications but also for developing low-cost spectroscopic biosensing applications.

Identification of neurotransmitters remains challenging for surface enhanced Raman spectroscopy (SERS) due to presence of noise. Here, the authors present spread spectrum SERS, which by encoding excited light and decoding SERS signals enables detection of unlabelled neurotransmitters at attomolar concentrations.

Cerebrospinal fluid of chronic osteoarthritic patients induced interleukin-6 release in human glial cell-line T98G

BACKGROUND

Chronic osteoarthritic pain is not well understood in terms of its pathophysiological mechanism. Activated glial cells are thought to play a role in the maintenance of chronic pain. T98G glioblastoma cell line was previously observed to release higher amounts of interleukin-6 (IL-6) when treated with cerebrospinal fluid (CSF) from patients with another chronic pain condition, post-herpetic neuralgia. In this study, we investigated the ability of CSF from patients diagnosed with knee osteoarthritis suffering from chronic pain, to trigger the release of pro-inflammatory cytokines, IL-6, IL-1beta and tumour necrosis factor alpha (TNF-α) from T98G. Characterization of upstream signalling was also explored.

METHODS

Fifteen osteoarthritis patients undergoing total knee replacement due to chronic knee pain and 15 patients without pain undergoing other surgeries with spinal anaesthesia were prospectively recruited. CSF was collected during anaesthesia. CSF were added to cultured T98G cells in the presence of lipopolysaccharide. IL-6, IL-1β and TNF-α release from T98G cells were measured using enzyme immunoassay. Antibody array and western blotting were performed using CSF-triggered T98G cell lysates to identify possible signalling targets. Age, gender and pain scores were recorded. Mann-Whitney U test was used to compare IL-6 release and protein expression between groups. Association between IL-6 and pain score was analysed using linear regression.

RESULTS

Significant higher levels of IL-6 were released by T98G cells when induced by osteoarthritis patients' CSF in the presence of LPS. The IL-6 levels showed positive association with pain score (adjusted B estimate = 10.1 (95% Confidence Interval 4.3-15.9); p = 0.001). Antibody array conducted with 6 pooled T98G cell lysate induced with osteoarthritis pain patient CSF identified greater than 2-fold proteins including STE20-related kinase adaptor protein and spleen tyrosine kinase. Further validation done using western blotting of individual CSF-triggered T98G cell lysate showed non-significant increase.

CONCLUSION

Higher IL-6 release from T98G when triggered by OA-CSF, in the presence of LPS, suggest the presence of "unknown molecule" in CSF that may be crucial in the maintenance phase of chronic pain in our osteoarthritis population. Further studies on the signalling pathways involved in pain and relevance of IL-6 release from T98G cells in other pain models are needed.

Baseline separation of amino acid biomarkers of hepatocellular carcinoma by polyvinylpyrrolidone-filled capillary electrophoresis with light-emitting diode-induced fluorescence in the presence of mixed micelles

Separation of amino acid biomarkers could be performed by polyvinylpyrrolidone-filled capillary electrophoresis in the presence of mixed micelles.

Homoserine and quorum-sensing acyl homoserine lactones as alternative sources of threonine: a potential role for homoserine kinase in insect-stage Trypanosoma brucei

De novo synthesis of threonine from aspartate occurs via the β-aspartyl phosphate pathway in plants, bacteria and fungi. However, the Trypanosoma brucei genome encodes only the last two steps in this pathway: homoserine kinase (HSK) and threonine synthase. Here, we investigated the possible roles for this incomplete pathway through biochemical, genetic and nutritional studies. Purified recombinant TbHSK specifically phosphorylates L-homoserine and displays kinetic properties similar to other HSKs. HSK null mutants generated in bloodstream forms displayed no growth phenotype in vitro or loss of virulence in vivo. However, following transformation into procyclic forms, homoserine, homoserine lactone and certain acyl homoserine lactones (AHLs) were found to substitute for threonine in growth media for wild-type procyclics, but not HSK null mutants. The tsetse fly is considered to be an unlikely source of these nutrients as it feeds exclusively on mammalian blood. Bioinformatic studies predict that tsetse endosymbionts possess part (up to homoserine in Wigglesworthia glossinidia) or all of the β-aspartyl phosphate pathway (Sodalis glossinidius). In addition S. glossinidius is known to produce 3-oxohexanoylhomoserine lactone which also supports trypanosome growth. We propose that T. brucei has retained HSK and threonine synthase in order to salvage these nutrients when threonine availability is limiting.

Cell-based method utilizing fluorescent Escherichia coli auxotrophs for quantification of multiple amino acids

A cell-based assay system for simultaneous quantification of the three amino acids, phenylalanine (Phe), methionine (Met), and leucine (Leu) in a single biological sample, was developed and applied in the multiplex diagnosis of three key metabolic diseases of newborn babies. The assay utilizes three Escherichia coli auxotrophs, which grow only in the presence of the corresponding target amino acids and which contain three different fluorescent reporter plasmids that produce distinguishable fluorescence signals (red, green, and cyan) in concert with cell growth. To mixtures of the three auxotrophs, immobilized on agarose gels arrayed on a well plate, is added a test sample. Following incubation, the concentrations of the three amino acids in the sample are simultaneously determined by measuring the intensities of three fluorescence signals that correspond to the reporter plasmids. The clinical utility of this assay system was demonstrated by employing it to identify metabolic diseases of newborn babies through the quantification of Phe, Met, and Leu in clinically derived dried blood spot specimens. The general strategy developed in this effort should be applicable to the design of new assay systems for the quantification of multiple amino acids derived from complex biological samples and, as such, to expand the utilization of cell-based analytical systems that replace conventional, yet laborious methods currently in use.

A novel liquid chromatography/tandem mass spectrometry method for the quantification of glycine as biomarker in brain microdialysis and cerebrospinal fluid samples within 5min

Glycine is an important amino acid neurotransmitter in the central nervous system (CNS) and a useful biomarker to indicate biological activity of drugs such as glycine reuptake inhibitors (GRI) in the brain. Here, we report how a liquid chromatography/tandem mass spectrometry (LC-MS/MS) method for the fast and reliable analysis of glycine in brain microdialysates and cerebrospinal fluid (CSF) samples has been established. Additionally, we compare this method with the conventional approach of high performance liquid chromatography (HPLC) coupled to fluorescence detection (FD). The present LC-MS/MS method did not require any derivatisation step. Fifteen microliters of sample were injected for analysis. Glycine was detected by a triple quadrupole mass spectrometer in the positive electrospray ionisation (ESI) mode. The total running time was 5min. The limit of quantitation (LOQ) was determined as 100nM, while linearity was given in the range from 100nM to 100μM. In order to demonstrate the feasibility of the LC-MS/MS method, we measured glycine levels in striatal in vivo microdialysates and CSF of rats after administration of the commercially available glycine transporter 1 (GlyT1) inhibitor LY 2365109 (10mg/kg, p.o.). LY 2365109 produced 2-fold and 3-fold elevated glycine concentrations from 1.52μM to 3.6μM in striatal microdialysates and from 10.38μM to 36μM in CSF, respectively. In conclusion, we established a fast and reliable LC-MS/MS method, which can be used for the quantification of glycine in brain microdialysis and CSF samples in biomarker studies.

Simultaneous determination of l-citrulline and l-arginine in plasma by high performance liquid chromatography

OBJECTIVE

To develop a method for simultaneously determining l-citrulline and L-arginine levels in plasma using RP-HPLC with ultraviolet detection.

DESIGN AND METHODS

Plasma samples were deproteinized by trichloroacetic acid and heat. Phenyl-isothiocyanate (PITC) solution was used as derivatization reagent and a gradient elution was carried out.

RESULTS

The linearity for L-citrulline and L-arginine ranged from 0 to at least 1000 micromol/L. R(2) values were above 0.9999 for both. LODs for L-citrulline and L-arginine were 0.0201 micromol/L and 0.0476 micromol/L, respectively, while LOQs were 0.240 micromol/L and 0.448 micromol/L, respectively. Intra- and inter-day CVs were less than 3.40% and 7.2%, respectively. The average recovery was from 86.22% to 118.9%. L-citrulline and L-arginine concentrations in healthy controls were 60.77+/-9.18 micromol/L and 58.19+/-16.43 micromol/L, respectively.

CONCLUSION

This approach offers a reliable, efficient analytical platform for the simultaneous determination of citrulline and arginine levels in plasma.

Simultaneous Analysis of d- and l-Serine in Cerebrospinal Fluid by Use of HPLC

Background: d-Serine is a coagonist for the glycine-binding site of the N-methyl-d-aspartate receptors and has been implicated in various neuropsychiatric functions such as learning, memory, and nociception, as well as schizophrenia and Alzheimer disease. We developed an HPLC method for d- and l-serine in cerebrospinal fluid (CSF).

Methods: The dabsylated racemic serine peak, automatically collected using a previously reported HPLC separation process for CSF amino acids, was desalted and subjected to a chiral resolution HPLC step with a Sumichiral column using an ultraviolet-visible detector.

Results: The limits of quantification (signal-to-noise ratio = 10) for d- and l-serine were 0.8 and 1.3 μmol/L, respectively. The mean imprecision values (CVs) for within-day measurements of d- and l-serine were 2.1% and 1.8%, respectively, and for between-day were 6.2% and 6.6%. Mean recovery of CSF serine (sum of d-serine + l-serine) applied to the Sumichiral column was 87%. The mean (SD) d-serine concentrations in 45 CSF samples obtained from 16 patients with chronic pain due to degenerative osteoarthritis of the knees, 16 with postherpetic neuralgia, and 13 with no pain were, respectively, 3.97 (0.44), 1.85 (0.21), and 2.72 (0.32) μmol/L.

Conclusion: d- and l-serine can be quantified with ultraviolet-visible detection of dabsyl derivatives. The dabsyl derivatives are stable and allow duplicate analysis of CSF samples in multisample runs.

Changes in amino acids and nitric oxide concentration in cerebrospinal fluid during labor pain

This study analyzes the relationship between amino acids and pain perception during active labor. Cerebrospinal fluid (CSF) levels of the excitatory amino acids (EAAs)-glutamate, aspartate and their amide forms, inhibitory amino acids (IAAs)-glycine, gamma-amino butyric acid (GABA) and taurine and nitric oxide (NO) related compounds-arginine and citrulline (by-product of NO synthesis) were compared between pregnant women at term pregnancy with labor pain (n = 38) and without labor pain (Caesarian section; n = 30). The levels of aspartate, glycine, GABA and citrulline were significantly higher; whilst taurine was significantly lower in the labor pain group. These findings suggest that aspartate and NO are associated with labor pain. An inhibitory role for the IAA taurine and a pronociceptive role for glycine in labor pain are proposed.

Stacking, derivatization, and separation by capillary electrophoresis of amino acids from cerebrospinal fluids

This paper describes the in-column derivatization, stacking, and separation of amino acids by CE in conjunction with light-emitting diode-induced fluorescence using naphthalene-2,3-dicarboxaldehyde (NDA). According to the relative electrophoretic mobilities and the migration direction in tetraborate solution (pH 9.3), the injection order is cyanide, then amino acids, then NDA. Once poly(ethylene oxide) (PEO) migrates through the capillary under EOF, the amino acid.NDA derivatives, amino acids, and CN- ions migrating against the EOF enter the PEO zone. As a result of increases in viscosity and possible interactions with PEO molecules, the reagents/analytes slow down such that they become stacked at the boundary. In comparison with the off-column approach to the analysis of amino acids, our proposed method provides a lower degree of interference from polymeric NDA compounds and other side products. As a result, the plot of the peak height as a function of gamma-aminobutyric acid (GABA) concentration is linear over the range from 10(-5) to 10(-8) M, with the LOD being 4 nM. We demonstrate the diagnostic potential of this approach for the determination of amino acids, including GABA and glutamine, in biological samples through the analysis of large volumes of cerebral spinal fluids without the need for sample pretreatment.

Determination of amino acids associated with cerebral ischaemia in rat brain microdialysates using narrowbore liquid chromatography and fluorescence detection

Microdialysis coupled to liquid chromatography (LC) has proven to be a valuable in vivo sampling technique for studying neurotransmitter changes in normal and ischaemic brain. However, few analytical methods have described the simultaneous determination of amino acids, relevant in stroke research, together with the nitric-oxide-related compound citrulline. Therefore, we developed a gradient LC method for the quantitative simultaneous determination of aspartate, glutamate, serine, glutamine, arginine, taurine, alanine and citrulline in dialysates of rat brain using narrowbore LC with o-phthalaldehyde-2-mercaptoethanol pre-column derivatisation and fluorescence detection. The proposed method is a thoroughly validated, fully automated and robust LC method for the determination of amino acids in a wide concentration range. The method was applied for the determination of amino acids and the citrulline/arginine ratio in the Et-1 model for focal cerebral ischaemia.