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Jupin M.,Radboud University Nijmegen | Michiels P.J.,Spinnovation Analytical | Girard F.C.,Spinnovation Analytical | Spraul M.,Bruker Biospin Gmbh | Wijmenga S.S.,Radboud University Nijmegen
Journal of Magnetic Resonance | Year: 2014

Metabolite profiling by NMR of body fluids is increasingly used to successfully differentiate patients from healthy individuals. Metabolites and their concentrations are direct reporters of body biochemistry. However, in blood plasma the NMR-detected free-metabolite concentrations are also strongly affected by interactions with the abundant plasma proteins, which have as of yet not been considered much in metabolic profiling. We previously reported that many of the common NMR-detected metabolites in blood plasma bind to human serum albumin (HSA) and many are released by fatty acids present in fatted HSA. HSA is the most abundant plasma protein and main transporter of endogenous and exogenous metabolites. Here, we show by NMR how the two most common fatty acids (FAs) in blood plasma - the long-chain FA, stearate (C18:0) and medium-chain FA, myristate (C14:0) - affect metabolite-HSA interaction. Of the set of 18 common NMR-detected metabolites, many are released by stearate and/or myristate, lactate appearing the most strongly affected. Myristate, but not stearate, reduces HSA-binding of phenylalanine and pyruvate. Citrate signals were NMR invisible in the presence of HSA. Only at high myristate-HSA mole ratios 11:1, is citrate sufficiently released to be detected. Finally, we find that limited dilution of blood-plasma mimics releases HSA-bound metabolites, a finding confirmed in real blood plasma samples. Based on these findings, we provide recommendations for NMR experiments for quantitative metabolite profiling. © 2013 Elsevier Ltd. All rights reserved.

Jupin M.,Radboud University Nijmegen | Michiels P.J.,Spinnovation Analytical | Girard F.C.,Spinnovation Analytical | Wijmenga S.S.,Radboud University Nijmegen
Magnetic Resonance in Medicine | Year: 2015

Purpose: Accurate metabolite and protein quantification in blood plasma and other body fluids from one single NMR measurement, allowing for improved quantitative metabolic profiling and better assessment of metabolite-protein interactions. Theory and Methods: The total protein concentration is derived from the common chemical-shift changes - caused by protein-induced bulk magnetic susceptibility (BMS) - measured on well-accessible and exchange-free metabolite resonances. These BMS shifts are simply obtained by external referencing with respect to 3-(trimethylsilyl)propionic-2,2,3,3-d4 acid, sodium salt in a coaxial insert. Results: Based on blood-plasma data from five volunteers, the estimated accuracy of the BMS method is ≤ 5% with respect and comparable to the 3.8% error of the standard colorimetric, Biuret, method. Valine, alanine, glucose, leucine, and lactate display no exchange-induced shift changes. Their well-accessible signals act as reliable probes for pure protein-induced BMS. The slopes and intercepts of their chemical-shift change versus protein concentration were derived from metabolite mixtures with (fatted) human and bovine albumin acting as blood-plasma mimics. Conclusion: The BMS method, demonstrated on blood plasma, can also be used on other samples containing sufficient protein (> 10 g/L). Also, it allows measurement of the presence and sign of exchange-induced chemical-shift changes. © 2014 Wiley Periodicals, Inc.

Jupin M.,Radboud University Nijmegen | Michiels P.J.,Spinnovation Analytical | Girard F.C.,Spinnovation Analytical | Spraul M.,Bruker | Wijmenga S.S.,Radboud University Nijmegen
Journal of Magnetic Resonance | Year: 2013

Metabolites and their concentrations are direct reporters on body biochemistry. Thanks to technical developments metabolic profiling of body fluids, such as blood plasma, by for instance NMR has in the past decade become increasingly accurate enabling successful clinical diagnostics. Human Serum Albumin (HSA) is the main plasma protein (∼60% of all plasma protein) and responsible for the transport of endogenous (e.g. fatty acids) and exogenous metabolites, which it achieves thanks to its multiple binding sites and its flexibility. HSA has been extensively studied with regard to its binding of drugs (exogenous metabolites), but only to a lesser extent with regard to its binding of endogenous (non-fatty acid) metabolites. To obtain correct NMR measured metabolic profiles of blood plasma and/or potentially extract information on HSA and fatty acids content, it is necessary to characterize these endogenous metabolite/plasma protein interactions. Here, we investigate these metabolite-HSA interactions in blood plasma and blood plasma mimics. The latter contain the roughly twenty metabolites routinely detected by NMR (also most abundant) in normal relative concentrations with fatted or non-fatted HSA added or not. First, we find that chemical shift changes are small and seen only for a few of the metabolites. In contrast, a significant number of the metabolites display reduced resonance integrals and reduced free concentrations in the presence of HSA or fatted HSA. For slow-exchange (or strong) interactions, NMR resonance integrals report the free metabolite concentration, while for fast exchange (weak binding) the chemical shift reports on the binding. Hence, these metabolites bind strongly to HSA and/or fatted HSA, but to a limited degree because for most metabolites their concentration is smaller than the HSA concentration. Most interestingly, fatty acids decrease the metabolite-HSA binding quite significantly for most of the interacting metabolites. We further find that competition between the metabolites for binding is absent for most of these metabolites. These mappings in plasma mimics may thus open new opportunities for improved metabolic profiling of blood plasma. For instance, correct metabolite concentrations can be determined for the non-interacting metabolites and/or concentration corrections made for interacting metabolites. Secondly, the interacting metabolites could be used to act as reporters on HSA and fatty acid concentration in plasma, and thus potentially act as biomarker in diagnostic studies of trauma or cardiovascular diseases. Finally, we find in the blood plasma mimics that after ultrafiltration, commonly used to remove the protein from plasma, the measured concentration equals the total metabolite concentration, except for the strongest binding metabolite citrate. © 2013 Elsevier Inc. All rights reserved.

Kellenbach E.,Quality Unit API Biotech NL Analytical Science Chemicals | Sanders K.,Quality Unit API Biotech NL Analytical Science Chemicals | Michiels P.J.A.,Spinnovation Analytical | Girard F.C.,Spinnovation Analytical
Analytical and Bioanalytical Chemistry | Year: 2011

The recently revised European Pharmacopeia and US Pharmacopeia heparin sodium monographs include nuclear magnetic resonance (NMR) tests on both identity and purity. In KMnO4-bleached heparin, an unidentified NMR signal is present at 2.10 ppm at a level of 15-20% of the mean of signal height of the major glucosamine (GlcNAc/GlcNS,6S) anomeric proton signal at 5.42 ppm and of the major iduronic acid (IdoA2S) anomeric proton signal at 5.21 ppm. According to the new monographs, no unidentified signals greater than 4% should be detected at that position. Thus, the material did not meet the acceptance criterion. The signal at 2.10 ppm has been present at the same level in all released MSD KMnO4-bleached heparin sodium batches analyzed over the past 10 years. The signal is a result of the KMnO4 bleaching. No (oversulfated) chondroitin sulfate or dermatan sulfate was detected in this material. A comprehensive NMR study using long-range heteronuclear 2D techniques identifies this signal at 2.10 ppm as originating from the acetyl methyl group of (6-sulfated) 2-N-acetyl-2-deoxy-glucono-1,5-lactone. This modified monosaccharide is formed by the KMnO4 oxidation of the reducing end of a terminal N-acetylglucosamine. © 2010 Springer-Verlag.

Smolinska A.,Radboud University Nijmegen | Posma J.M.,Radboud University Nijmegen | Blanchet L.,Radboud University Nijmegen | Ampt K.A.M.,Radboud University Nijmegen | And 8 more authors.
Analytical and Bioanalytical Chemistry | Year: 2012

Because cerebrospinal fluid (CSF) is the biofluid which interacts most closely with the central nervous system, it holds promise as a reporter of neurological disease, for example multiple sclerosis (MScl). To characterize the metabolomics profile of neuroinflammatory aspects of this disease we studied an animal model of MScl-experimental autoimmune/allergic encephalomyelitis (EAE). Because CSF also exchanges metabolites with blood via the blood-brain barrier, malfunctions occurring in the CNS may be reflected in the biochemical composition of blood plasma. The combination of blood plasma and CSF provides more complete information about the disease. Both biofluids can be studied by use of NMR spectroscopy. It is then necessary to perform combined analysis of the two different datasets. Mid-level data fusion was therefore applied to blood plasma and CSF datasets. First, relevant information was extracted from each biofluid dataset by use of linear support vector machine recursive feature elimination. The selected variables from each dataset were concatenated for joint analysis by partial least squares discriminant analysis (PLS-DA). The combined metabolomics information from plasma and CSF enables more efficient and reliable discrimination of the onset of EAE. Second, we introduced hierarchical models fusion, in which previously developed PLS-DA models are hierarchically combined. We show that this approach enables neuroinflamed rats (even on the day of onset) to be distinguished from either healthy or peripherally inflamed rats. Moreover, progression of EAE can be investigated because the model separates the onset and peak of the disease. © Springer-Verlag 2012.

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