Applying metabolic flux analysis to hydrogen fermentation using a metabolic network constructed for anaerobic mixed cultures

In this study, a mixed-cultural metabolic network for anaerobic digestion that included the concept of a "universal bacterium" was constructed, and metabolic flux analysis (MFA) applying this network was conducted to evaluate the flow of electrons and materials during H2 fermentation under various conditions. The MFA results from two H2 fermenters feeding glucose with (GP) or without (GA) the addition of peptone suggest that hydraulic retention time (HRT) presents a significant impact on hydrogen production, and the reversed trends could be observed at HRTs below and above 4 h. From the MFA results of lactate/acetate-fed H2 fermenter, the highest flux of H2 production is associated with more significant acetate consumption and the following pathways toward the anaplerotic reactions cycle that produces NADH. The occurrence of acetogenesis in the H2 fermenters using various types of bioethanol-fermented residues (BEFRs) was also identified according to the MFA results. By analyzing the MFA results of all 49 sets of data from H2 fermenters via Pearson's correlation, it was revealed that the flux of H2 production positively correlates to the reduction of ferredoxin with pyruvate oxidation, acetate formation, and acetate emission when lactate was produced in the system. On the contrary, negative relationships were found between the flux of H2 production and these three fluxes. The extended application of MFA provides additional information, including the fluxes between intracellular metabolites, and the information has the potential to be used in decision-making systems during the future operation of anaerobic processes by connecting operational parameters.

Comprehensive characterization of in vitro and in vivo metabolites of 2',3',5'‑tri‑O‑acetyl‑N6‑(3‑hydroxyphenyl) adenosine and study of the metabolites distribution in rats by combined methods of HPLC-DAD, off-line cryoNMR, and HPLC-QTOFMS

The compound 2',3',5'‑tri‑O‑acetyl‑N₆‑(3‑hydroxyphenyl) adenosine (also known as IMM-H007) is a new adenosine analogue that displays anti-hyperlipidaemic activity in many preliminary studies. To clarify its biotransformation process, in vitro and in vivo metabolic patterns of IMM-H007 in rat liver microsomes (RLMs), urine, feces, serum, and various tissues were investigated using high-performance liquid chromatography coupled to a diode array detector (HPLC-DAD), off-line cryogenically cooled probe nuclear magnetic resonance (cryoNMR), and high-performance liquid chromatography quadrupole TOF MS (HPLC-QTOFMS) measurements. A total of 21 metabolites were detected and identified based on accurate mass measurements, diagnostic product ions, and 1D and 2D NMR data. All of the 21 metabolites were detected in vivo besides the 7 ones (LM1-3, LM4a-b, LM5, LM6 (M8)) in vitro. Among them, eight metabolites were phase I metabolites composed of the hydrolysis products LM1-3, LM4a, LM4b, LM5 and M7-8, and hydrolysis and hydroxylation products M6. Others were phase II metabolites including glucuronidation products M2, M4, M9, M11a-c, and M12a-c; and sulfation products M3, M5, and M10. Notably, 14 metabolites (LM1-3, LM4a-b, LM5, M9-10, M11a-c, M12a-c) were unreported before and the distribution of IMM-H007 and its all metabolites was reported for the first time. The results revealed IMM-H007 was metabolized mainly in the small intestine and serum, kidney, stomach, small and large intestines were important samples for metabolites presence. This work improves understanding of the metabolism, distribution, and excretion of IMM-H007, and demonstrates the HPLC/HPLC-MS/off-line cryoNMR approach can be applied for detection and identification of metabolites in complex biological matrices.

In vivo metabolism of organophosphate flame retardants and distribution of their main metabolites in adult zebrafish

Understanding the metabolism of chemicals as well as the distribution and depuration of their main metabolites in tissues are essential for evaluating their fate and potential toxicity in vivo. Herein, we investigated the metabolism of six typical organophosphate (OP) flame retardants (tripropyl phosphate (TPRP), tri-n-butyl phosphate (TNBP), tris(2-butoxyethyl) phosphate (TBOEP), tris(2-chloroethyl) phosphate (TCEP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and tri-p-cresyl phosphate (p-TCP)) in adult zebrafish in laboratory at three levels (0, 1/150 LC₅₀ (environmentally relevant level), and 1/30 LC₅₀ per OP analog). Twenty main metabolites were detected in the liver of OPs-exposed zebrafish using high resolution mass spectrometry (Q-TOF). The reaction pathways involving scission of the ester bond (hydrolysis), cleavage of the ether bond, oxidative hydroxylation, dechlorination, and coupling with glucuronic acid were proposed, and were further confirmed by the frontier electron density and point charge calculations. Tissue distribution of the twenty metabolites revealed that liver and intestine with the highest levels of metabolites were the most active organs for OPs biotransformation among the studied tissues of intestine, liver, roe, brain, muscle, and gill, which showed the importance of hepatobiliary system (liver-bile-intestine) in the metabolism and excretion of OPs in zebrafish. Fast depuration of metabolites from tissues indicated that the formed metabolites might be not persistent in fish, and easily released into water. This study provides comprehensive information on the metabolism of OPs in the tissue of zebrafish, which might give some hints for the exploration of their toxic mechanism in aquatic life.