In-vitro and in-vivo evaluation of the modulatory effects of the multitarget compound ASS234 on the monoaminergic system.

OBJECTIVES: To evaluate the in-vitro and in-vivo effects on monoaminergic neurotransmission of ASS234, a promising multitarget-directed ligand (MTDL), for Alzheimer's disease (AD) therapy. METHODS: In vitro was explored the effect of ASS234 on the monoaminergic metabolism in SH-SY5Y and PC12 cell lines, and remaining activity of both monoamine oxidase (MAO) isoforms was assessed. The corresponding dopamine (DA), homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) and noradrenaline (NA) levels were determined by HPLC-ED. In-vivo experiments were carried out Wistar rats and intracerebral guide cannulas were implanted in the hippocampus and in the prefrontal cortex by sterotaxic coordinates. The day after microdialysis samples were collected and levels of 5-HT, DA and NA were determined by (UHPLC) with electrochemical detector. KEY FINDINGS: ASS234 induced a significant increase in serotonin (5-HT) levels in SH-SY5Y cells. In PC12 cells, ASS234 increased significantly the ratio of dopamine (DA)/(HVA + DOPAC), although no apparent differences in (NA) were observed. By in-vivo microdialysis, ASS234 showed a significant increase in the extracellular levels of 5-HT and NA in hippocampus whereas in the prefrontal cortex, DA and NA also increased significantly. CONCLUSIONS: This study reveals the ability of ASS234 a MTDL compound, to enhance the monoaminergic neurotransmission supporting its potential use in AD therapy.

An improved microbore UHPLC method with electrochemical detection for the simultaneous determination of low monoamine levels in in vivo brain microdialysis samples.

The simultaneous determination of the monoamines dopamine (DA), noradrenaline (NA) and serotonin (5-HT) in in vivo microdialysis samples remains challenging because of the low extracellular neurotransmitter levels in different brain regions, specific sample characteristics, and the quest for high temporal resolution and a multi-target strategy in neuropharmacological research. A fast and sensitive microbore (1.0mm i.d. column) UHPLC method coupled to electrochemical detection (ECD) is developed by means of design of experiments with the emphasis on sufficient retention of NA within an acceptable total analysis time. Indeed, NA is the earliest eluting compound and often interferes with the broad solvent front originating from the sample matrix. The sensitive UHPLC-ECD assay (LLOQ of 100pM for NA and 150pM for DA and 5-HT) with an analysis time of 8min for standard solutions and 20min for in vivo microdialysis samples originating from rat hippocampus, prefrontal cortex and striatum, is validated applying accuracy profiles. The combination of in vivo microdialysis and microbore UHPLC-ECD has shown to be particularly suitable for future contributions to neuropharmacological research on the monoaminergic system.

Miniaturized ultra-high performance liquid chromatography coupled to electrochemical detection: Investigation of system performance for neurochemical analysis.

The interest in implementation of miniaturized ultra-high performance liquid chromatography (UHPLC) in neurochemical research is growing because of the need for faster, more selective and more sensitive neurotransmitter analyses. The instrument performance of a tailor designed microbore UHPLC system coupled to electrochemical detection (ECD) is investigated, focusing on the quantitative monoamine determination in in vivo microdialysis samples. The use of a microbore column (1.0mm I.D.) requires miniaturization of the entire instrument, though a balance between extra-column band broadening and injection volume must be considered. This is accomplished through the user defined Performance Optimizing Injection Sequence, whereby 5 µL sample is injected on the column with a measured extra-column variance of 4.5-9.0 µL(2) and only 7 µL sample uptake. Different sub-2 µm and superficially porous particle stationary phases are compared by means of the kinetic plot approach. Peak efficiencies of about 16000-35000 theoretical plates are obtained for the Acquity UPLC BEH C18 column within 13 min analysis time. Furthermore, the coupling to ECD is shown suitable for microbore UHPLC analysis thanks to the miniaturized flow cell design, sufficiently fast data acquisition and mathematical data filtering. Ultimately, injection of in vivo samples demonstrates the applicability of the system for microdialysis analysis.

Reassessment of the antioxidative mixture for the challenging electrochemical determination of dopamine, noradrenaline and serotonin in microdialysis samples.

In recent years, the simultaneous monitoring of the monoamine neurotransmitters dopamine, noradrenaline and serotonin in vivo is advancing due to innovations in miniaturized and fast chromatographic techniques. However, the determination of the most hydrophilic compound, noradrenaline, in microdialysis samples by (ultra-)high performance liquid chromatography ((U)HPLC) with electrochemical detection (ECD) is impeded by a broad solvent front, caused by the addition of antioxidative agents. Hence, an elaborate reassessment of currently used antioxidative mixtures is necessary for further analytical improvements. The proposed mixture, containing 100mM acetic acid, 0.27mM Na2EDTA and 12.5µM ascorbic acid (pH 3.2), is less complex than previously described mixtures and shows minimal ECD interference. It stabilizes the three monoamines in standard solutions and in microdialysis samples, considering both autosampler stability at 4°C for 48h and long term stability at -20°C for a duration of six months. An in vivo microdialysis experiment demonstrates the possibility to monitor changes in extracellular levels of the three monoamines simultaneously in the rat hippocampus with UHPLC-ECD using the optimized antioxidative mixture.

An ultrasensitive nano UHPLC-ESI-MS/MS method for the quantification of three neuromedin-like peptides in microdialysates.

AIM: An ultrasensitive nano UHPLC-ESI-MS/MS method is developed to simultaneously monitor three low-concentration neuromedin-like peptides in microdialysates. RESULTS: Peptide preconcentration and sample desalting is performed online on a trap column. A shallow gradient slope at 300 nl/min on the analytical column maintained at 35°C, followed by two saw-tooth column wash cycles, results in the highest sensitivity and the lowest carryover. The validated method allows the accurate and precise quantification of 0.5 pM neurotensin and neuromedin N (2.5 amol on column), and of 3.0 pM neuromedin B (15.0 amol on column) in in vivo microdialysates without the use of internal standards. CONCLUSION: The assay is an important tool for elucidating the role of these neuromedin-like peptides in the pathophysiology of neurological disorders.

Impaired islet function in commonly used transgenic mouse lines due to human growth hormone minigene expression.

The human growth hormone (hGH) minigene is frequently used in the derivation of transgenic mouse lines to enhance transgene expression. Although this minigene is present in the transgenes as a secondcistron, and thus not thought to be expressed, we found that three commonly used lines, Pdx1-Cre(Late), RIP-Cre, and MIP-GFP, each expressed significant amounts of hGH in pancreatic islets. Locally secreted hGH binds to prolactin receptors on ß cells, activates STAT5 signaling, and induces pregnancy-like changes in gene expression, thereby augmenting pancreatic ß cell mass and insulin content. In addition, islets of Pdx1-Cre(Late) mice have lower GLUT2 expression and reduced glucose-induced insulin release and are protected against the ß cell toxin streptozotocin. These findings may be important when interpreting results obtained when these and other hGH minigene-containing transgenic mice are used.

Improved sensitivity of the nano ultra-high performance liquid chromatography-tandem mass spectrometric analysis of low-concentrated neuropeptides by reducing aspecific adsorption and optimizing the injection solvent.

Obtaining maximal sensitivity of nano UHPLC-MS/MS methods is primordial to quantify picomolar concentrations of neuropeptides in microdialysis samples. Since aspecific adsorption of peptides to Eppendorf tubes, pipette tips and UHPLC vials is detrimental for method sensitivity, a strategy is presented to reduce adsorption of these peptides during standard preparation. Within this respect, all procedural steps from dissolution of the lyophilized powder until the injection of the sample onto the system are investigated. Two peptides of the neuromedin family, i.e. neuromedin B and neuromedin N, and a neuromedin N-related neuropeptide, neurotensin, are evaluated. The first part of this study outlines a number of parameters which are known to affect peptide solubility. The main focus of the second part involves the optimization of the sample composition in the UHPLC vial by using design of experiments. Contradictory findings are observed concerning the influence of acetonitrile, salts and matrix components. They are found important for injection of the peptides into the system, but crucially need to be excluded from the dilution solvent. Furthermore, the type of surface material, temperature and the pipetting protocol considerably affect the adsorption phenomenon. Statistical analysis on the results of the central composite design reveals that the highest peptide responses are obtained with the injection solvent consisting of 13.1% V/V ACN and 4.4% V/V FA. This aspect of the optimization strategy can be identified as the main contributor to the gain in method sensitivity. Since the reduction of peptide adsorption and the optimization of the injection solvent resulted in a clear and quantifiable signal of the three peptides, optimization of both issues should be considered in the early stage of method development, in particular when the analysis of low-concentration peptide solutions is envisaged.

Ion-pair ultra-high performance liquid chromatographic analysis of monoamines: peak-splitting at high flow rates.

The use of ion-pair ultra-high performance liquid chromatography (UHPLC) coupled with electrochemical detection (ECD) is of great interest for the fast and sensitive determination of the monoamine neurotransmitters dopamine, noradrenaline and serotonin in microdialysis samples. However, when applying high flow rates in ion-pair UHPLC, other peaks than the initial compound peaks appear on the chromatogram. This peak-splitting phenomenon is caused by disturbed ion-pair retention mechanisms. The influence of several chromatographic parameters is investigated. Peak-splitting is delayed to higher flow rates when increasing the concentration of ion-pair reagent or buffering agent in the mobile phase, when decreasing the percentage of organic modifier in the mobile phase, when applying a stationary phase with a smaller amount of packing material or when increasing the separation temperature. One or a combination of these conditions can be applied to analyze the monoamine neurotransmitters using ion-pair UHPLC-ECD at high flow rates.