High preoperative blood oxaloacetate and 2-aminoadipic acid levels are associated with postoperative delayed neurocognitive recovery

Introduction

This study aimed to identify preoperative blood biomarkers related to development of delayed neurocognitive recovery (dNCR) following surgery.

Methods

A total of 67 patients (≥65 years old) who underwent head and neck tumor resection under general anesthesia were assessed using the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA). Preoperative serum metabolomics were determined using widely targeted metabolomics technology.

Results

Of the 67 patients, 25 developed dNCR and were matched to 25 randomly selected patients from the remaining 42 without dNCR. Differential metabolites were selected using the criteria of variable importance in projection > 1.0 in orthogonal partial least squares discrimination analysis, false discovery rate <0.05, and fold-change >1.2 or <0.83 to minimize false positives. Preoperative serum levels of oxaloacetate (OR: 1.054, 95% CI: 1.027-1.095, P = 0.001) and 2-aminoadipic acid (2-AAA) (OR: 1.181, 95% CI: 1.087-1.334, P = 0.001) were associated with postoperative dNCR after adjusting for anesthesia duration, education, and age. Areas under the curve for oxaloacetate and 2-AAA were 0.86 (sensitivity: 0.84, specificity: 0.88) and 0.86 (sensitivity: 0.84, specificity: 0.84), respectively. High levels of preoperative oxaloacetate and 2-AAA also were associated with postoperative decreased MoCA (β: 0.022, 95% CI: 0.005-0.04, P = 0.013 for oxaloacetate; β: 0.077, 95%CI: 0.016-0.137, P = 0.014 for 2-AAA) and MMSE (β: 0.024, 95% CI: 0.009-0.039, P = 0.002 for oxaloacetate; β: 0.083, 95% CI: 0.032-0.135, P = 0.002 for 2-AAA) scores after adjusting for age, education level, and operation time.

Conclusion

High preoperative blood levels of oxaloacetate and 2-AAA were associated with increased risk of postoperative dNCR.

Clinical trial registration

https://classic.clinicaltrials.gov/ct2/show/NCT05105451, identifier NCT05105451.

Mitochondrial aconitase suppresses immunity by modulating oxaloacetate and the mitochondrial unfolded protein response

Accumulating evidence indicates that mitochondria play crucial roles in immunity. However, the role of the mitochondrial Krebs cycle in immunity remains largely unknown, in particular at the organism level. Here we show that mitochondrial aconitase, ACO-2, a Krebs cycle enzyme that catalyzes the conversion of citrate to isocitrate, inhibits immunity against pathogenic bacteria in C. elegans. We find that the genetic inhibition of aco-2 decreases the level of oxaloacetate. This increases the mitochondrial unfolded protein response, subsequently upregulating the transcription factor ATFS-1, which contributes to enhanced immunity against pathogenic bacteria. We show that the genetic inhibition of mammalian ACO2 increases immunity against pathogenic bacteria by modulating the mitochondrial unfolded protein response and oxaloacetate levels in cultured cells. Because mitochondrial aconitase is highly conserved across phyla, a therapeutic strategy targeting ACO2 may eventually help properly control immunity in humans.

Citrate synthase from Cyanidioschyzon merolae exhibits high oxaloacetate and acetyl-CoA catalytic efficiency

Citrate synthase (CS) catalyzes the reaction that produces citrate and CoA from oxaloacetate and acetyl-CoA in the tricarboxylic acid (TCA) cycle. All TCA cycle enzymes are localized to the mitochondria in the model organism, the red alga Cyanidioschyzon merolae. The biochemical properties of CS have been studied in some eukaryotes, but the biochemical properties of CS in algae, including C. merolae, have not been studied. We then performed the biochemical analysis of CS from C. merolae mitochondria (CmCS4). The results showed that the k_cat/K_m of CmCS4 for oxaloacetate and acetyl-CoA were higher than those of the cyanobacteria, such as Synechocystis sp. PCC 6803, Microcystis aeruginosa PCC 7806 and Anabaena sp. PCC 7120. Monovalent and divalent cations inhibited CmCS4, and in the presence of KCl, the K_m of CmCS4 for oxaloacetate and acetyl-CoA was higher in the presence of MgCl₂, the K_m of CmCS4 for oxaloacetate and acetyl-CoA was higher and k_cat lower. However, in the presence of KCl and MgCl₂, the k_cat/K_m of CmCS4 was higher than those of the three cyanobacteria species. The high catalytic efficiency of CmCS4 for oxaloacetate and acetyl-CoA may be a factor in the increased carbon flow into the TCA cycle in C. merolae.

Enhancement of astaxanthin accumulation in Haematococcus pluvialis by exogenous oxaloacetate combined with nitrogen deficiency

Effective inducers and stress conditions play an essential role in the regulation of astaxanthin biosynthesis. This study reports a strategy developed by combining exogenous addition of oxaloacetate (OA) with nitrogen deficiency to facilitate astaxanthin production in Haematococcus pluvialis. Significantly, addition of 10 mM-OA enhanced the cellular astaxanthin content about 7.18-fold under nitrogen deficiency on day 7, with the content of astaxanthin esters increased concomitantly. To further elucidate the role and mechanism of OA on astaxanthin synthesis, the physiological and metabolic analyses of H. pluvialis treated with exogenous OA were performed. The results showed that exogenous OA promoted respiration over photosynthesis. Concurrently, the metabolite levels in the Embden-Meyerhof-Parnas pathway, pentose phosphate pathway and tricarboxylic acid cycle obviously increased. The enhancement of respiratory metabolic pathways led to elevated levels of substrates, thus directly promoted astaxanthin synthesis. The present findings provide a new and effective approach for optimizing astaxanthin production.

Light-enhanced dark respiration in leaves, isolated cells and protoplasts of various types of C4 plants

The rate of respiratory CO2 evolution from the leaves of Zea mays, Panicum miliaceum, and Panicum maximum, representing NADP-ME, NAD-ME, and PEP-CK types of C4 plants, respectively, was increased by approximately two to four times after a period of photosynthesis. This light-enhanced dark respiration (LEDR) was a function of net photosynthetic rate specific to plant species, and was depressed by 1% O2. When malate, aspartate, oxaloacetate or glycine solution at 50 mM concentration was introduced into the leaves instead of water, the rate of LEDR was enhanced, far less in Z. mays (by 10-25%) than in P. miliaceum (by 25-35%) or P. maximum (by 40-75%). The enhancement of LEDR under glycine was relatively stable over a period of 1 h, whereas the remaining metabolites caused its decrease following a transient increase. The metabolites reduced the net photosynthesis rate in the two Panicum species, but not in Z. mays, where this process was stimulated by glycine. The bundle sheath cells from P. miliaceum exhibited a higher rate of LEDR than those of Z. mays and P. maximum. Glycine had no effect on the respiration rate of the cells, but malate increased in cells of Z. mays and P. miliaceum by about 50% and 30%, respectively. With the exception of aspartate, which stimulated both the O2 evolution and O2 uptake in P. maximum, the remaining metabolites reduced photosynthetic O2 evolution from bundle sheath cells in Panicun species. The net O2 exchange in illuminated cells of Z. mays did not respond to CO2 or metabolites. Leaf mesophyll protoplasts of Z. mays and P. miliaceum, and bundle sheath protoplasts of Z. mays, which are unable to fix CO2 photosynthetically, also produced LEDR, but the mesophyll protoplasts, compared with bundle sheath protoplasts, required twice the time of illumination to obtain the maximal rate. The results suggest that the substrates for LEDR in C4 plants are generated during a period of illumination not only via the Calvin cycle reactions, but also by the conversion of endogenous compounds present in leaf cells. The stimulation of LEDR under glycine is discussed in relation to its direct or indirect effect on mitochondrial respiration.

THE EQUILIBRIUM OF THE REACTION CATALYSED BY CITRATE OXALOACETATE-LYASE

1. A method of preparation and purification of citrate oxaloacetate-lyase (EC 4.1.3.6) from Aerobacter aerogenes is described. 2. The equilibrium of this reaction has been determined at pH 8.4 and 25 degrees . It has been shown that K, i.e. [citrate(3-)]/[oxaloacetate(keto) (2-)][acetate (-)], is 3.08+/-0.72, but that K(app.), i.e. [total citrate]/[total oxaloacetate][total acetate], is markedly affected by the initial concentrations of the reactants and magnesium. 3. The free-energy change during the cleavage of citrate has been calculated and compared with data from other sources. 4. The free energy of hydrolysis of acetyl-CoA has been evaluated from the present data. 5. A detailed knowledge of the interactions of the reactants with metal ions has been shown to be important in the calculation of the equilibrium constant and related thermodynamic functions.

OXALOACETATE DECARBOXYLATION AND OXALOACETATE-CARBON DIOXIDE EXCHANGE IN ACETOBACTER XYLINUM

Benziman, Moshe (The Hebrew University of Jerusalem, Jerusalem, Israel), and N. Heller . Oxaloacetate decarboxylation and oxaloacetate-carbon dioxide exchange in Acetobacter xylinum . J. Bacteriol. 88: 1678–1687. 1964.—Extracts of Acetobacter xylinum , prepared by sonic treatment, were shown to catalyze the decarboxylation of oxaloacetate (OAA) to pyruvate and CO 2 , and the exchange of C 14 -carbon dioxide into the β-carboxyl of OAA. Fractionation of the extracts with ammonium sulfate resulted in a 10-fold increase of the specific activity of the enzyme system catalyzing the CO 2 exchange and OAA decarboxylation reactions. The purified preparation catalyzed the exchange of pyruvate- 3-C 14 into OAA. Similar pH curves with a pH optimum of 5.6 were obtained for the CO 2 exchange and OAA decarboxylation reactions. Both reactions require the presence of Mn 2+ or Mg 2+ ions. OAA decarboxylation was more strongly inhibited than the exchange of CO 2 by dialysis or metal-chelating agents. Avidin did not inhibit either reaction. Adenosine triphosphate (ATP), adenosine diphosphate (ADP), guanosine triphosphate (GTP), guanosine diphosphate (GDP), pyrophosphate, or inorganic phosphate did not promote OAA decarboxylation and the CO 2 -exchange reaction catalyzed by the purified preparation. The purified preparation failed to catalyze the carboxylation of phosphoenolpyruvate in the presence of GDP, ADP, or inorganic phosphate, and that of pyruvate in the presence of ATP or GTP, even when supplemented with an OAA-trapping system. A scheme for OAA decarboxylation which could account for the observed exchange reactions and for the failure to obtain net fixation of CO 2 is proposed. The relation between the exchange reaction and the synthesis of cellulose from pyruvate by A. xylinum is discussed.

CHANGES IN GLUTAMIC ACID – OXALOACETIC ACID – TRANSAMINASE ACTIVITY IN THE LIVER AND KIDNEYS ON THE EFFECT OF HIGH DOSES OF PYRAMIDON (AMINOPYRINE)

On each of 5 days, rabbits were given subcutaneously 75% of the single lethal dose of Pyramidon (aminopyrine), divided into three daily doses. The animals were killed on the 6th day and the degree of glutamic acid – oxaloacetic acid – transaminase activity of the liver and kidneys was examined. It could be established that activity in the liver increased by 41% and that of the kidneys by 87%. These values are correlated with the lesions which were previously noted in these organs. The increased seral activity as well as the ratio of activity of the organs of the treated and untreated animals is attributed to increased permeability and necrosis in hepatic and renal cells.