Determination of de novo synthesized amino acids in cellular proteins revisited by 13C NMR spectroscopy

Supplemented Alkaline Phosphatase Supports the Immune Response in Patients Undergoing Cardiac Surgery: Clinical and Computational Evidence

Alkaline phosphatase (AP) is an enzyme that exhibits anti-inflammatory effects by dephosphorylating inflammation triggering moieties (ITMs) like bacterial lipopolysaccharides and extracellular nucleotides. AP administration aims to prevent and treat peri- and post-surgical ischemia reperfusion injury in cardiothoracic surgery patients. Recent studies reported that intravenous bolus administration and continuous infusion of AP in patients undergoing coronary artery bypass grafting with cardiac valve surgery induce an increased release of liver-type “tissue non-specific alkaline phosphatase” (TNAP) into the bloodstream. The release of liver-type TNAP into circulation could be the body's way of strengthening its defense against a massive ischemic insult. However, the underlying mechanism behind the induction of TNAP is still unclear. To obtain a deeper insight into the role of AP during surgery, we developed a mathematical model of systemic inflammation that clarifies the relation between supplemented AP and TNAP and describes a plausible induction mechanism of TNAP in patients undergoing cardiothoracic surgery. The model was validated against clinical data from patients treated with bovine Intestinal AP (bIAP treatment) or without AP (placebo treatment), in addition to standard care procedures. We performed additional in-silico experiments adding a secondary source of ITMs after surgery, as observed in some patients with complications, and predicted the response to different AP treatment regimens. Our results show a strong protective effect of supplemented AP for patients with complications. The model provides evidence of the existence of an induction mechanism of liver-type tissue non-specific alkaline phosphatase, triggered by the supplementation of AP in patients undergoing cardiac surgery. To the best of our knowledge this is the first time that a quantitative and validated numerical model of systemic inflammation under clinical treatment conditions is presented.

In vivo 2D mapping of impaired murine cardiac energetics in NO-induced heart failure

(31)P MRS studies in humans have shown that an impairment of cardiac energetics is characteristic of heart failure. Although numerous transgenic mouse models with a heart-failure phenotype have been generated, current methods to analyze murine high-energy phosphates (HEPs) in vivo are hampered by limited spatial resolution. Using acquisition-weighted 2D (31)P chemical shift imaging (CSI) at 9.4 Tesla, we were able to acquire (31)P MR spectra over the entire thorax of the mouse with high spatial resolution in defined regions of the heart (the anterior, lateral, posterior, and septal walls) within a reasonable acquisition time of about 75 min. Analysis of a transgenic cardiomyopathy model (double mutant: cardiospecific inducible nitric oxide synthase (iNOS) overexpression and lack of myoglobin (tg-iNOS(+)/myo(-/-)) revealed that cardiac dysfunction in the mutant was associated with an impaired energy state (phosphocreatine (PCr)/adenosine triphosphate (ATP) 1.54 +/- 0.18) over the entire left ventricle (LV; wild-type (WT): PCr/ATP 2.06 +/- 0.22, N = 5, P < 0.05), indicating that in the absence of efficient cytosolic NO scavenging, iNOS-derived NO critically interferes with the respiratory chain. In vivo data were validated against (31)P MR spectra of perchloric acid extracts (PCr/ATP: 1.87 +/- 0.21 (WT), 1.39 +/- 0.17 (tg-iNOS(+)/myo(-/-), N = 5, P < 0.05). Future applications will substantially benefit studies on the cause-and-effect relationship between cardiac energetics and function in other genetically well-defined models of heart failure.

Strategies for metabolic flux analysis in plants using isotope labelling

Flux measurements through metabolic pathways generate insights into the integration of metabolism, and there is increasing interest in using such measurements to quantify the metabolic effects of mutation and genetic manipulation. Isotope labelling provides a powerful approach for measuring metabolic fluxes, and it gives rise to several distinct methods based on either dynamic or steady-state experiments. We discuss the application of these methods to photosynthetic and non-photosynthetic plant tissues, and we illustrate the different approaches with an analysis of the pathways interconverting hexose phosphates and triose phosphates. The complicating effects of the pentose phosphate pathway and the problems arising from the extensive compartmentation of plant cell metabolism are considered. The non-trivial nature of the analysis is emphasised by reference to invalid deductions in earlier work. It is concluded that steady-state isotopic labelling experiments can provide important information on the fluxes through primary metabolism in plants, and that the combination of stable isotope labelling with detection by nuclear magnetic resonance is particularly informative.

Alterations in glial cell metabolism during recovery from chronic osmotic stress

NMR spectroscopy of F98 glioma cell extracts showed that chronic hypertonic conditions largely increased the intracellular content of small, osmotically active molecules. Moreover, hypertonic stress decreased the incorporation of 13C-labeled amino acids into the cellular proteins albeit their cytosolic concentrations were increased, which reflects an inhibition of protein synthesis under these conditions. Reincubation with isotonic medium restored almost completely the control values for the cytosolic metabolites but not for amino acid incorporation into the protein. An increased amount of 13C label was found in the phospholipids, which indicates stimulation of membrane synthesis processes due to the recovery-induced cell swelling. On the other hand, chronic hypotonic conditions largely decreased the steady state concentration and synthesis of small, cytosolic molecules, whereas the effect on the incorporation of 13C-labeled amino acids into the cellular proteins was variable. Reincubation with isotonic medium partially restored the depressed cytosolic metabolite content and also the incorporation of labeled amino acids into cellular protein, but induced an inhibition of phospholipid synthesis. The results verify that 'readaptation' of glial cell metabolism during recovery from chronic osmotic stress is impaired or at least seriously retarded.

Effects of sulfanilamide and methotrexate on 13C fluxes through the glycine decarboxylase/serine hydroxymethyltransferase enzyme system in arabidopsis

In C3 plants large amounts of photorespiratory glycine (Gly) are converted to serine by the tetrahydrofolate (THF)-dependent activities of the Gly decarboxylase complex (GDC) and serine hydroxymethyltransferase (SHMT). Using 13C nuclear magnetic resonance, we monitored the flux of carbon through the GDC/SHMT enzyme system in Arabidopsis thaliana (L.) Heynh. Columbia exposed to inhibitors of THF-synthesizing enzymes. Plants exposed for 96 h to sulfanilamide, a dihydropteroate synthase inhibitor, showed little reduction in flux through GDC/SHMT. Two other sulfonamide analogs were tested with similar results, although all three analogs competitively inhibited the partially purified enzyme. However, methotrexate or aminopterin, which are confirmed inhibitors of Arabidopsis dihydrofolate reductase, decreased the flux through the GDC/SHMT system by 60% after 48 h and by 100% in 96 h. The uptake of [alpha-13C]Gly was not inhibited by either drug class. The specificity of methotrexate action was shown by the ability of 5-formyl-THF to restore flux through the GDC/SHMT pathway in methotrexate-inhibited plants. The experiments with sulfonamides strongly suggest that the mitochondrial THF pool has a long half-life. The studies with methotrexate support the additional, critical role of dihydrofolate reductase in recycling THF oxidized in thymidylate synthesis.