Deciphering the contribution of microbial biomass to the properties of dissolved and particulate organic matter in anaerobic digestates

The recalcitrant structures either from substrate or microbial biomass contained in digestates after anaerobic digestion (AD) highly influence digestate valorization. To properly assess the microbial biomass contribution to the digested organic matter (OM), a combination of characterization methods and the use of various substrate types in anaerobic continuous reactors was required. The use of totally biodegradable substrates allowed detecting soluble microbial products via fluorescence spectroscopy at emission wavelengths of 420 and 460 nm while the protein-like signature was enhanced by the whey protein. During reactors' operation, a transfer of complex compounds to the dissolved OM from the particulate OM was observed through fluorescence applied on biochemical fractionation. Consequently, the fluorescence complexity index of the dissolved OM increased from 0.59-0.60 to 1.06-1.07, whereas it decreased inversely for the extractable soluble from the particulate OM from 1.16-1.19 to 0.42-0.54. Accordingly, fluorescence regional integration showed differences among reactors based on visual inspection and orthogonal partial latent structures (OPLS) analysis. Similarly, the impact of the substrate type and operation time on the particulate OM was revealed by ¹³C nuclear magnetic resonance using OPLS, providing a good model (R²X = 0.93 and Q² = 0.8) with a clear time-trend. A high signal resonated at ∼30 ppm attributed to CH₂-groups in the aliphatic chain of lipid-like structure besides carbohydrates intensities at 60-110 ppm distinguished the reactor fed with whey protein from the other, which was mostly biomass related. Indeed, this latter displayed a higher presence of peptidoglycan (δH/C: 1.6-2.0/20-25 ppm) derived from microbial biomass by ¹H-¹³C heteronuclear single-quantum coherence (HSQC) nuclear magnetic resonance. Interestingly, the sample distribution obtained by non-metric multidimensional scaling of bacterial communities resembled the attained using ¹³C NMR properties, opening new research perspectives. Overall, this study discloses the microbial biomass contribution to digestates composition to improve the OM transformation mechanism knowledge.

Quantification of succinic acid levels, linked to succinate dehydrogenase (SDH) dysfunctions, by an automated and fully validated liquid chromatography tandem mass spectrometry method suitable for multi-matrix applications

The hallmarks of cancer include metabolism with deregulating cellular energetics. Dysfunctions in succinate dehydrogenase (SDH) metabolic enzyme activity, leading to an abnormal accumulation of succinic acid has been described in solid tumors but also in inflammation and ischemia reperfusion injury. Succinic acid is a potential biomarker of SDH related pathologies for diagnostic, evaluation of treatment response and follow-up of the disease. We developed a liquid chromatography tandem mass spectrometry (LC-MS/MS) method allowing a rapid, accurate and precise quantification of succinic acid levels in clinical (serum, urine) and preclinical (cellular pellets, supernatants) samples. ¹³C₄ succinic acid disodium salt was used as internal standard and added to samples before a solid phase extraction (SPE) on Phenomenex STRATA^TM XL-A (200 mg - 3 mL) 33 µm cartridges. This method is automated by a Freedom EVO® platform from TECAN and succinic acid is separated on a C18 column combined to a Xevo® TQ-S micro Waters mass spectrometer with electrospray ionization (ESI) source. This biomedical analysis allows standard curves to be linear over the range 1.0-135.5 µM with r² values > 0.999 and low matrix effects (<9.1 %). This method, which is validated according updated European Medicine Agency (EMA) guidelines, is accurate between-run (<11.0 %) and within-run (<7.8 %), precise between-run (<14.4 CV %) and within-run (<3.7 CV %), and is suitable for clinical and preclinical applications.

Development of a HILIC-MS/MS method for the quantification of histamine and its main metabolites in human urine samples

An LC-MS/MS method was developed enabling the separation and quantification of histamine and its main metabolites (imidazole acetaldehyde, imidazole acetic acid, methyl imidazole acetic acid, methyl histamine, acetyl histamine) in urine samples. A fast separation was achieved in 10 min on two HILIC columns connected in series by adopting a linear gradient followed by an isocratic hold. The sample preparation consisted of a simple dilution step wherein 10 μL of urine was diluted with acetonitrile (ACN) to a final volume comprising 95% ACN. For methyl imidazole acetic acid, an additional dilution step was incorporated due to its high natural levels. Hereafter, the samples were stored at -20 °C and centrifuged prior to injection. Matrix matched calibrators were unavailable due to the endogenous occurrence of the compounds of interest. The occurrence of matrix effects and the lack of labeled internal standards prompted the use of the standard addition method as a viable alternative to solvent calibration. The validation of the method entailed matrix effects, accuracy and precision and was performed in compliance with the recent guidelines on endogenous compounds issued by the International Conference of Harmonization (ICH). The method was then adopted for the quantification of histamine and its metabolites in human urine samples collected from healthy volunteers and patients suffering from gastrointestinal discomfort.

Molecular characterization of zebrafish Gstr1, the only member of teleost-specific glutathione S- transferase class

Glutathione S-transferases (GSTs) are multifunctional phase II detoxification enzymes with primary function of glutathione conjugation of various endogenous and exogenous compounds. Teleost-specific Gstr1 in zebrafish (Danio rerio) was previously shown to have high expression in toxicologically relevant tissues and high activity towards model substrates. The aim of this study was a detailed functional characterization of zebrafish Gstr1. Molecular docking analyses were used to get novel insight into structural characteristics of Gstr1 and elucidation of the mechanistic interactions with both GSH and various Gstr1 substrates or inhibitors. An initial screening inhibition assay performed using model fluorescence substrate monochlorobimane (MCB) revealed interactions of different endogenous compounds and environmentally relevant xenobiotics with zebrafish Gstr1. All interacting compounds were further analyzed to determine their inhibition type and K_i values. Our data revealed that pregnenolone, progesterone, testosterone, DHEAS and corticosterone competitively inhibited transformation of MCB by Gstr1 with the calculated K_i values in the range 14-26 μM, implying that these hormones are physiological substrates of zebrafish Gstr1. Estrogens had no effect on Gstr1 activity. Taurochenodeoxycholate (TCDC) expressed lower inhibition potency toward Gstr1 with the K_i value of 33 μM. Among tested xenobiotics tributyltin chloride and rifampicin non-enzymatically bound Gstr1 enzyme (the calculated K_i values are 0.26 μM and 65 μM, respectively) and inhibited its activity, showing that these compounds are reversible noncompetitive inhibitors of zebrafish Gstr1. Insecticide diazinon competitively inhibited Gstr1 activity with calculated K_i value of 27 μM, while other Gstr1-interacting insecticides, chlorpyrifos-methyl (CPF-methyl) and malathion, showed allosteric activation-like effect. Among tested pharmaceuticals, tetracycline, erythromycin and methotrexate demonstrated competitive type of inhibition with the calculated K_i values of 17.5, 36.5 and 29 μM, respectively. In summary, we suggest that zebrafish Gstr1 has an important role in steroidogenesis, metabolism and/or physiological actions of androgens, but not estrogens in fish. Finally, our results imply the role of Gstr1 in metabolism of xenobiotics and protection of fish against deleterious environmental contaminants such as organophosphate insecticides and pharmaceuticals.

A fit-for-purpose LC-MS/MS method for the simultaneous quantitation of ATP and 2,3-DPG in human K2EDTA whole blood

Many hemolytic anemias results in major metabolic abnormalities: two common metabolite abnormalities include increased levels of 2,3-diphosphoglycerate (2,3-DPG) and decreased levels of adenosine triphosphate (ATP). To better monitor the concentration changes of these metabolites, the development of a reliable LC-MS/MS method to quantitatively profile the concentrations of 2, 3-DPG and ATP in whole blood is essential to understand the effects of investigational therapeutics. Accurate quantification of both compounds imposes great challenges to bioanalytical scientists due to their polar, ionic and endogenous nature. Here we present an LC-MS/MS method for the reliable quantification of 2,3-DPG and ATP from K₂EDTA human whole blood (WB) simultaneously. Whole blood samples were spiked with stable isotope labeled internal standards, processed by protein precipitation extraction, and analyzed using zwitterionic ion chromatography-hydrophilic interaction chromatography (ZIC-HILIC) coupled with tandem mass spectrometry. The linear analytical range of the assay was 50-3000μg/mL. The fit-for-purpose method demonstrated excellent accuracy and precision. The overall accuracy was within ±10.5% (%RE) for both analytes and the intra- and inter-assay precision (%CV) were less than 6.7% and 6.2% for both analytes, respectively. ATP and 2,3-DPG were found to be stable in human K₂EDTA blood for at least 8h at 4°C, 96days when stored at -70°C and after three freeze/thaw cycles. The assay has been successfully applied to K₂EDTA human whole blood samples to support clinical studies.

Quantitation of isocitrate dehydrogenase (IDH)-induced D and L enantiomers of 2-hydroxyglutaric acid in biological fluids by a fully validated liquid tandem mass spectrometry method, suitable for clinical applications

A recent update of the hallmarks of cancer includes metabolism with deregulating cellular energetics. Activating mutations in isocitrate dehydrogenase (IDH) metabolic enzymes leading to the abnormal accumulation of 2-hydroxyglutaric acid (2-HGA) have been described in hematologic malignancies and solid tumours. The diagnostic value of 2-HGA levels in blood to identify IDH mutations and its prognostic significance have been reported. We developed a liquid chromatography tandem mass spectrometry method allowing a rapid, accurate and precise simultaneous quantification of both L and D enantiomers of 2-HGA in blood samples from acute myeloid leukaemia (AML) patients, suitable for clinical applications. The method was also develop for preclinical applications from cellular and tissues samples. Deuterated (R,S)-2-hydroxyglutaric acid, disodium salt was used as internal standard and added to samples before a solid phase extraction on Phenomenex STRATA™-XL-A (200mg-3mL) 33μm cartridges. A derivatization step with (+)- o,o'-diacetyl-l-tartaric anhydride permitted to separate the two resulting diastereoisomers without chiral stationary phase, on a C18 column combined to a Xevo TQ-MS Waters mass spectrometer with an electrospray ionization (ESI) source. This method allows standard curves to be linear over the range 0.34-135.04μM with r(2) values>0.999 and low matrix effects (<11.7%). This method, which was validated according to current EMA guidelines, is accurate between-run (<3.1%) and within-run (<7.9%) and precise between-run (<5.3CV%) and within-run (<6.2CV%), and is suitable for clinical and preclinical applications.

A novel fully validated LC-MS/MS method for quantification of pyridoxal-5'-phosphate concentrations in samples of human whole blood

Quantification of pyridoxal-5'-phosphate (PLP) in biological samples is challenging due to the presence of endogenous PLP in matrices used for preparation of calibrators and quality control samples (QCs). Hence, we have developed an LC-MS/MS method for accurate and precise measurement of the concentrations of PLP in samples (20μL) of human whole blood that addresses this issue by using a surrogate matrix and minimizing the matrix effect. We used a surrogate matrix comprising 2% bovine serum albumin (BSA) in phosphate buffer saline (PBS) for making calibrators, QCs and the concentrations were adjusted to include the endogenous PLP concentrations in the surrogate matrix according to the method of standard addition. PLP was separated from the other components of the sample matrix using protein precipitation with trichloroacetic acid 10% w/v. After centrifugation, supernatant were injected directly into the LC-MS/MS system. Calibration curves were linear and recovery was >92%. QCs were accurate, precise, stable for four freeze-thaw cycles, and following storage at room temperature for 17h or at -80°C for 3 months. There was no significant matrix effect using 9 different individual human blood samples. Our novel LC-MS/MS method has satisfied all of the criteria specified in the 2012 EMEA guideline on bioanalytical method validation.

Fully validated LC-MS/MS method for quantification of homocysteine concentrations in samples of human serum: a new approach

Reported homocysteine (HCY) concentrations in human serum show poor concordance amongst laboratories due to endogenous HCY in the matrices used for assay calibrators and QCs. Hence, we have developed a fully validated LC-MS/MS method for measurement of HCY concentrations in human serum samples that addresses this issue by minimising matrix effects. We used small volumes (20μL) of 2% Bovine Serum Albumin (BSA) as surrogate matrix for making calibrators and QCs with concentrations adjusted for the endogenous HCY concentration in the surrogate matrix using the method of standard additions. To aliquots (20μL) of human serum samples, calibrators or QCs, were added HCY-d4 (internal standard) and tris-(2-carboxyethyl) phosphine hydrochloride (TCEP) as reducing agent. After protein precipitation, diluted supernatants were injected into the LC-MS/MS. Calibration curves were linear; QCs were accurate (5.6% deviation from nominal), precise (CV%≤9.6%), stable for four freeze-thaw cycles, and when stored at room temperature for 5h or at -80°C (27 days). Recoveries from QCs in surrogate matrix or pooled human serum were 91.9 and 95.9%, respectively. There was no matrix effect using 6 different individual serum samples including one that was haemolysed. Our LC-MS/MS method has satisfied all of the validation criteria of the 2012 EMA guideline.