Recently, a new derivative of angiotensin (Ang) II, called "Ang A," has been discovered to be present in plasma of healthy humans and, in increased concentrations, in end-stage renal failure ...patients. The objectives of the study were to investigate the blood pressure and renal hemodynamic responses to Ang A in normotensive and hypertensive rats and in genetically modified mice and the binding properties of Ang A to Ang II type 1 (AT(1)) or Ang II type 2 (AT(2)) receptors. Intravenous and intrarenal administration of Ang A induced dose-dependent pressor and renal vasoconstrictor responses in normotensive rats, which were blocked by the AT(1) receptor antagonist candesartan but were not altered by the AT(2) receptor ligands PD123319, CGP42112A, or compound 21. Similar responses were observed after intravenous administration in spontaneously hypertensive rats. Deletion of AT(1a) receptors in mice almost completely abolished the pressor and renal vasoconstrictor responses to Ang A, indicating that its effects are mediated via AT(1a) receptors. Ang A was less potent than Ang II in vivo. The in vitro study demonstrated that Ang A is a full agonist for AT(1) receptors, with similar affinity for AT(1) and AT(2) receptors as Ang II. Overall, the responses to Ang A and Ang II were similar. Ang A has no physiological role to modulate the pressor and renal hemodynamic effects of Ang II.
A microbore LC–MS/MS method is developed and validated for the quantification of the anti-epileptic drug oxcarbazepine (OXC) and its active metabolite 10,11-dihydro-10-hydroxycarbamazepine (MHD) in ...rat brain microdialysates, together with the internal standard for microdialysis probe calibration, 2-methyl-5H-dibenz(b,f)azepine-5-carboxamide (
m-CBZ). The benefits of gradient versus isocratic separation are shown, next to the improved sensitivity resulting from the addition of 0.1% formic acid to the mobile phase. The coupling of microdialysis with ESI-MS requires sample desalting for which column switching was applied. Using weighed regression to calculate the calibration curves (1–1000
ng/mL), the assay was validated in terms of linearity, accuracy and precision, yielding a sensitive (limit of quantification is 1
ng/mL) and selective method for quantification of OXC, MHD and
m-CBZ. By applying this method, we were able to determine the extracellular concentrations of OXC and MHD during at least 4
h after intraperitoneal (i.p.) administration of 10
mg/kg OXC.
Neuromedin U (NmU) and neuromedin S (NmS) are two closely related neuropeptides belonging to the neuromedin family. NmU usually occurs either as a truncated eight amino acid long peptide (NmU-8) or ...as an 25 amino acid long peptide, although other molecular forms exist depending on the species considered. NmS, on the other hand, is a 36 amino acid long peptide, sharing the same amidated C-terminal heptapeptide with NmU. Nowadays, liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is the preferred analytical technique for peptide quantification, because of its excellent sensitivity and selectivity. However, reaching the required quantification limits for these compounds in biological samples remains an extremely challenging task, especially because of their nonspecific binding (NSB). This study highlights the difficulties that are faced when quantifying larger neuropeptides (23–36 amino acids) compared to smaller ones (< 15 amino acids). The first part of this work aims to solve the adsorption problem for NmU-8 and NmS, by investigating the different steps involved in the sample preparation, i.e. the different solvents applied and the pipetting protocol. The addition of 0.05% plasma as an adsorption competitor was found to be primordial to avoid peptide loss due to NSB. The second part of this work focusses on further improving the sensitivity of the LC-MS/MS method for NmU-8 and NmS, by evaluating some UHPLC-parameters, including the stationary phase, the column temperature and the trapping conditions. For both peptides of interest, the best results were achieved when combining a C18 trap column with a C18 iKey separation device containing a positively charged surface. Column temperatures of 35 and 45 °C for NmU-8 and NmS respectively, resulted in the highest peak areas and S/N ratios, while applying higher column temperatures substantially decreased sensitivity. Moreover, a gradient starting at 20% organic modifier instead of 5% significantly improved the peak shape of both peptides. Finally, some compound-specific MS parameters, i.e. the capillary and the cone voltages, were evaluated. The peak areas increased with a factor 2 and 7 for NmU-8 and NmS respectively and peptide detection in the low picomolar range is now feasible.
●Quantification of peptides remains challenging due to nonspecific binding.●Addition of an adsorption competitor is critical for analysis of larger peptides.●Miniaturized LC-MS/MS for the analysis of low-concentrated peptides.●Sample preparation, UHPLC and ESI-MS parameters are optimized.●Sensitivity clearly improved throughout the different optimization steps.
A novel molecularly imprinted monolithic (MIM) column was designed and fabricated using the epitope approach, and was used for the selective capillary microextraction (CME) of the neuropeptides ...neurotensin (NT) and neuromedin N (NmN). The MIMs were synthesized in a capillary by thermally initiated polymerization of the functional monomer (methacrylic acid (MAA)), in the presence of a dummy template (Pro-Tyr-Ile-Leu (PYIL)), a crosslinker and porogens. The resulting monoliths were characterized by scanning electron microscopy, pore size distribution measurement, and Fourier transform infrared spectroscopy. Different synthesis conditions of the MIM column were investigated. The parameters affecting the MIM-CME performance, including loading, washing and elution protocols, were optimized as well. The MIMs were used to enrich NT and NmN from human plasma prior to HPLC-UV analysis. The imprinted monolith showed an excellent maximum adsorption capacity of 245–711 mg mL−1 and selectivity (imprinting factor of 5.7–13.4) towards its target peptides. Low detection limits of 0.62 and 1.20 nM, and satisfactory recoveries (82.5–98.8%) were obtained for NT and NmN, respectively. The proposed MIM-CME/HPLC-UV method was found suitable to be used as an effective tool for the highly efficient and specific analysis of NT and NmN in human plasma samples.
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●Molecularly imprinted monolith (MIM) synthesized via epitope approach with dummy template.●Neurotensin (NT) and neuromedin N (NmN) are targeted.●A selective capillary microextraction (CME) technique for NT and NmN is developed.●The optimal synthesized monolithic column showed high affinity and selectivity for the neuropeptides.●A MIM-CME/HPLC-UV method for neuropeptides analysis in human plasma.
The use of biologics in the therapeutic landscape has increased exponentially since the last 3 decades. Nevertheless, patients with central nervous system (CNS) related disorders could not yet ...benefit from this revolution because the blood-brain barrier (BBB) severely hampers biologics from entering the brain. Considerable effort has been put into generating methods to modulate or circumvent the BBB for delivery of therapeutics to the CNS. A promising strategy is receptor-mediated transcytosis (RMT). Recently, Wouters et al. (2020) discovered a mouse anti-transferrin receptor nanobody that is able to deliver a biologically active peptide to the brain via RMT. The present study aims to sample a derivative of this brain-penetrating nanobody (Nb105) in the CNS. Therefore, we compared the applicability of cerebral open flow microperfusion (cOFM) and microdialysis as sampling techniques to directly obtain high molecular weight substances from the cerebral interstitial fluid. A custom AlphaScreen™ assay was validated to quantify nanobody concentrations in the samples. In vitro microdialysis probe (AtmosLM™, 1 MDa cut-off) recovery by gain and by loss for Nb105 was 18.3 ± 3.2% and 27.0 ± 2.5% respectively, whereas for cOFM it was 87.2 ± 4.0% and 97.3 ± 1.6%. Although a large difference in in vitro recovery is observed between cOFM and microdialysis, in vivo similar results were obtained. Immunohistochemical stainings showed an astrocytic and microglial reaction in the immediate vicinity along the implantation track for both probe types. Coronal sections showed higher fluorescein isothiocyanate-dextran and immunoglobulin G extravasation around the microdialysis probe track than after cOFM sampling experiments, however this leakage was clearly limited compared to a positive control where the BBB was disrupted. This is the first study that samples a bispecific nanobody in the brain's interstitial fluid in function of time, providing a pharmacokinetic profile of nanobodies in the CNS. Furthermore, this is the first time a cOFM study is performed in awake freely moving mice, providing data on inflammation and blood-brain barrier integrity in the mouse brain. Overall, this work demonstrates that, while taking into account the (bio)analytical considerations, both microdialysis and cOFM are suitable in vivo sampling techniques for quantification of nanobodies in the CNS.
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•Microdialysis and cerebral open flow microperfusion (cOFM) suitable to sample macromolecules.•Evaluating inflammation, blood-brain barrier integrity, in vitro recoveries and in vivo AUCs.•First study assessing the cOFM set-up in awake, freely moving mice.•An AlphaScreen™ assay is validated for nanobody quantification.•Quantification of a ±31 kDa brain-penetrating nanobody in the interstitial fluid of mice.
Brain metabolomics is gaining interest because of the aging of the population, resulting in more central nervous system disorders such as Alzheimer's and Parkinson's disease. Most often these ...diseases are studied in vivo, such as for example by analysing cerebrospinal fluid or brain extracellular fluid. These sample types are often considered in pre-clinical studies using animal models. However, the scarce availability of both matrices results in some challenges related to sampling, sample preparation and normalization. Much effort has been made towards the development of alternative, less invasive sampling techniques for collecting small sample volumes (pL till mid μL range) over the past years. Despite recent advances, the analysis of low volumes is still a tremendous challenge. Therefore, proper preconcentration and sample pretreatment strategies are necessary together with sensitive analysis and detection techniques suitable for low-volume samples. In this review, an overview is given of the state-of-the-art mass spectrometry-based analytical workflows for probing (endogenous) metabolites in volume-restricted in-vivo brain samples. In this context, special attention is devoted to challenges related to sampling, sample preparation and preconcentration strategies. Finally, some general conclusions and perspectives are provided.
•In vivo brain metabolomics is challenging because of low neuromodulator concentrations and volumes.•Novel trends in sampling, sample preparation and analysis of low volume samples are discussed.•Miniaturization of sampling probes largely reduces the invasiveness of brain fluid sampling.•Increased interest in solid-phase and liquid-phase microextraction.
•Brain metabolomics studies mediators of cell signaling and biochemical processes.•In vivo measurements are important to gain better understanding of the brain.•Microdialysis is a powerful sampling ...technique for measurement of brain mediators.•Several quantitative, targeted methods for brain metabolomics are described.•Analysis of brain mediators in microdialysis samples presents some challenges.
In vivo determination of brain mediators plays an important role in providing insight in how the brain functions. For this purpose, targeted metabolomics can be a very useful tool. Targeted metabolomics detects and measures certain known low-molecular-weight biomolecules involved in signaling pathways and biochemical processes in the central nervous system. Microdialysis is a powerful technique to sample brain mediators in the central nervous system. Several analytical techniques that can possibly be coupled to microdialysis are available. However, selection of an appropriate technique should be considered carefully, since sensitivity and specificity are critical when measuring these mediators in volume-restricted microdialysis samples. This review outlines some of the commonly applied sampling methods and analytical techniques and discusses some of the challenges encountered during the in vivo determination of central nervous system mediators.
Neuromedin U (NMU) is a highly conserved neuropeptide that has been implicated in the stress response. To better understand how it influences various aspects of the stress response, we studied the ...effects of intracerebroventricular NMU-8 administration on stress-related behavior and activity of the hypothalamus-pituitary-adrenal (HPA) axis in male C57BL/6J mice. We investigated these NMU-8 effects when mice remained in their home cage and when they were challenged by exposure to forced swim stress. NMU-8 administration resulted in increased grooming behavior in mice that remained in their home cage and in a significant increase in c-Fos immunoreactivity in the paraventricular hypothalamus (PVH) and arcuate nucleus (ARC). Surprisingly, NMU-8 administration significantly decreased plasma corticosterone concentrations. Furthermore, NMU-8 administration increased immobility in the forced swim test in both naïve mice and mice that were previously exposed to swim stress. The effect of NMU-8 on c-Fos immunoreactivity in the PVH was dependent on previous exposure to swim stress given that we observed no significant changes in mice exposed for the first time to swim stress. In contrast, in the ARC we observed a significant increase in c-Fos immunoreactivity regardless of previous stress exposure. Interestingly, NMU-8 administration also significantly decreased plasma corticosterone concentrations in mice that were exposed to single forced swim stress, while this effect was no longer observed when mice were exposed to forced swim stress for a second time. Taken together, our data indicate that NMU-8 regulates stress responsiveness and suggests that its effects depend on previous stress exposure.
•NMU-8 increases stress-related behavior in C57BL/6J mice.•Effects of NMU-8 on hypothalamic c-Fos expression depend on previous stress exposure.•Effects of NMU-8 on plasma corticosterone levels depend on previous stress exposure.
Liquid chromatography with amperometric detection remains the most widely used method for acetylcholine quantification in microdialysis samples. Separation of acetylcholine from choline and other ...matrix components on a microbore chromatographic column (1 mm internal diameter), conversion of acetylcholine in an immobilized enzyme reactor and detection of the produced hydrogen peroxide on a horseradish peroxidase redox polymer coated glassy carbon electrode, achieves sufficient sensitivity for acetylcholine quantification in rat brain microdialysates. However, a thourough validation within the concentration range required for this application has not been carried out before. Furthermore, a rapid degradation of the chromatographic columns and enzyme systems have been reported. In the present study an ion-pair liquid chromatography assay with amperometric detection was validated and its long-term stability evaluated. Working at pH 6.5 dramatically increased chromatographic stability without a loss in sensitivity compared to higher pH values. The lower limit of quantification of the method was 0.3 nM. At this concentration the repeatability was 15.7%, the inter-day precision 8.7% and the accuracy 103.6%. The chromatographic column was stable over 4 months, the immobilized enzyme reactor up to 2-3 months and the enzyme coating of the amperometric detector up to 1-2 months. The concentration of acetylcholine in 30 μl microdialysates obtained under basal conditions from the hippocampus of freely moving rats was 0.40 ± 0.12 nM (mean ± SD, n = 30). The present method is therefore suitable for acetylcholine determination in rat brain microdialysates.
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