The enzymes of the oxidative phase of the pentose phosphate pathway as targets of reactive species: consequences for NADPH production.

The pentose phosphate pathway (PPP) is a key metabolic pathway. The oxidative phase of this process involves three reactions catalyzed by glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconolactonase (6PGL) and 6-phosphogluconate dehydrogenase (6PGDH) enzymes. The first and third steps (catalyzed by G6PDH and 6PGDH, respectively) are responsible for generating reduced nicotinamide adenine dinucleotide phosphate (NAPDH), a key cofactor for maintaining the reducing power of cells and detoxification of both endogenous and exogenous oxidants and electrophiles. Despite the importance of these enzymes, little attention has been paid to the fact that these proteins are targets of oxidants. In response to oxidative stimuli metabolic pathways are modulated, with the PPP often up-regulated in order to enhance or maintain the reductive capacity of cells. Under such circumstances, oxidation and inactivation of the PPP enzymes could be detrimental. Damage to the PPP enzymes may result in a downward spiral, as depending on the extent and sites of modification, these alterations may result in a loss of enzymatic activity and therefore increased oxidative damage due to NADPH depletion. In recent years, it has become evident that the three enzymes of the oxidative phase of the PPP have different susceptibilities to inactivation on exposure to different oxidants. In this review, we discuss existing knowledge on the role that these enzymes play in the metabolism of cells, and their susceptibility to oxidation and inactivation with special emphasis on NADPH production. Perspectives on achieving a better understanding of the molecular basis of the oxidation these enzymes within cellular environments are given.

Peroxyl radicals modify 6-phosphogluconolactonase from Escherichia coli via oxidation of specific amino acids and aggregation which inhibits enzyme activity.

6-phosphogluconolactonase (6PGL) catalyzes the second reaction of the pentose phosphate pathway (PPP) converting 6-phosphogluconolactone to 6-phosphogluconate. The PPP is critical to the generation of NADPH and metabolic intermediates, but some of its components are susceptible to oxidative inactivation. Previous studies have characterized damage to the first (glucose-6-phosphate dehydrogenase) and third (6-phosphogluconate dehydrogenase) enzymes of the pathway, but no data are available for 6PGL. This knowledge gap is addressed here. Oxidation of Escherichia coli 6PGL by peroxyl radicals (ROO•, from AAPH (2,2'-azobis(2-methylpropionamidine) dihydrochloride) was examined using SDS-PAGE, amino acid consumption, liquid chromatography with mass detection (LC-MS), protein carbonyl formation and computational methods. NADPH generation was assessed using mixtures all three enzymes of the oxidative phase of the PPP. Incubation of 6PGL with 10 or 100 mM AAPH resulted in protein aggregation mostly due to reducible (disulfide) bonds. High fluxes of ROO• induced consumption of Cys, Met and Trp, with the Cys oxidation rationalizing the aggregate formation. Low levels of carbonyls were detected, while LC-MS analyses provided evidence for oxidation of selected Trp and Met residues (Met1, Trp18, Met41, Trp203, Met220 and Met221). ROO• elicited little loss of enzymatic activity of monomeric 6PGL, but the aggregates showed diminished NADPH generation. This is consistent with in silico analyses that indicate that the modified Trp and Met are far from the 6-phosphogluconolactone binding site and the catalytic dyad (His130 and Arg179). Together these data indicate that monomeric 6PGL is a robust enzyme towards oxidative inactivation by ROO• and when compared to other PPP enzymes.

Implications of differential peroxyl radical-induced inactivation of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase for the pentose phosphate pathway.

Escherichia coli glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) are key enzymes of the pentose phosphate pathway, responsible for the NADPH production in cells. We investigated modification of both enzymes mediated by peroxyl radicals (ROO·) to determine their respective susceptibilities to and mechanisms of oxidation. G6PDH and 6PGDH were incubated with AAPH (2,2'-azobis(2-methylpropionamidine)dihydrochloride), which was employed as ROO· source. The enzymatic activities of both enzymes were determined by NADPH release, with oxidative modifications examined by electrophoresis and liquid chromatography (LC) with fluorescence and mass (MS) detection. The activity of G6PDH decreased up to 62.0 ± 15.0% after 180 min incubation with 100 mM AAPH, whilst almost total inactivation of 6PGDH was determined under the same conditions. Although both proteins contain abundant Tyr (particularly 6PGDH), these residues were minimally affected by ROO·, with Trp and Met being major targets. LC-MS and in silico analysis showed that the modification sites of G6PDH are distant to the active site, consistent with a dispersed distribution of modifications, and inactivation resulting from oxidation of multiple Trp and Met residues. In contrast, the sites of oxidation detected on 6PGDH are located close to its catalytic site indicating a more localized oxidation, and a consequent high susceptibility to ROO·-mediated inactivation.

Role of amino acid oxidation and protein unfolding in peroxyl radical and peroxynitrite-induced inactivation of glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides.

The mechanisms underlying the inactivation of Leuconostoc mesenteroides glucose 6-phosphate dehydrogenase (G6PDH) induced by peroxyl radicals (ROO●) and peroxynitrite (ONOO-), were explored. G6PDH was incubated with AAPH (2,2' -azobis(2-methylpropionamidine)dihydrochloride), used as ROO● source, and ONOO-. Enzymatic activity was assessed by NADPH generation, while oxidative modifications were analyzed by gel electrophoresis and liquid chromatography (LC) with fluorescence and mass detection. Changes in protein conformation were studied by circular dichroism (CD) and binding of the fluorescent dye ANS (1-anilinonaphthalene-8-sulfonic acid). Incubation of G6PDH (54.4 µM) with 60 mM AAPH showed an initial phase without significant changes in enzymatic activity, followed by a secondary time-dependent continuous decrease in activity to ∼59% of the initial level after 90 min. ONOO- induced a significant and concentration-dependent loss of G6PDH activity with ∼46% of the initial activity lost on treatment with 1.5 mM ONOO-. CD and ANS fluorescence indicated changes in G6PDH secondary structure with exposure of hydrophobic sites on exposure to ROO●, but not ONOO-. LC-MS analysis provided evidence for ONOO--mediated oxidation of Tyr, Met and Trp residues, with damage to critical Met and Tyr residues underlying enzyme inactivation, but without effects on the native (dimeric) state of the protein. In contrast, studies using chloramine T, a specific oxidant of Met, provided evidence that oxidation of specific Met and Trp residues and concomitant protein unfolding, loss of dimer structure and protein aggregation are involved in G6PDH inactivation by ROO●. These two oxidant systems therefore have markedly different effects on G6PDH structure and activity.

Effect of macromolecular crowding on protein oxidation: Consequences on the rate, extent and oxidation pathways.

Biological systems are heterogeneous and crowded environments. Such packed milieus are expected to modulate reactions both inside and outside the cell, including protein oxidation. In this work, we explored the effect of macromolecular crowding on the rate and extent of oxidation of Trp and Tyr, in free amino acids, peptides and proteins. These species were chosen as they are readily oxidized and contribute to damage propagation. Dextran was employed as an inert crowding agent, as this polymer decreases the fraction of volume available to other (macro)molecules. Kinetic analysis demonstrated that dextran enhanced the rate of oxidation of free Trp, and peptide Trp, elicited by AAPH-derived peroxyl radicals. For free Trp, the rates of oxidation were 15.0 ± 2.1 and 30.5 ± 3.4 µM min-1 without and with dextran (60 mg mL-1) respectively. Significant increases were also detected for peptide-incorporated Trp. Dextran increased the extent of Trp consumption (up to 2-fold) and induced short chain reactions. In contrast, Tyr oxidation was not affected by the presence of dextran. Studies on proteins, using SDS-PAGE and LC-MS, indicated that oxidation was also affected by crowding, with enhanced amino acid loss (45% for casein), chain reactions and altered extents of oligomer formation. The overall effects of dextran-mediated crowding were however dependent on the protein structure. Overall, these data indicate that molecular crowding, as commonly encountered in biological systems affect the rates, and extents of oxidation, and particularly of Trp residues, illustrating the importance of appropriate choice of in vitro systems to study biological oxidations.

Síncope y paro cardiorrespiratorio, formas graves de presentación de la embolia pulmonar central: reporte de tres casos clínicos / Syncope and cardiorespiratory arrest, severe forms of presentation of central pulmonary embolism: report of three clinical cases / Síncope e parada cardiorrespiratória, formas graves de apresentação de embolia pulmonar central: relato de três casos clínicos

El tromboembolismo pulmonar tiene una presentación clínica variada. Es fundamental tener un alto índice de sospecha para arribar al diagnóstico oportuno. El síncope se asocia a casos graves y tiene importancia pronóstica. El tratamiento trombolítico es la piedra angular en el subgrupo de pacientes de alto riesgo. Se presentan tres casos clínicos de tromboembolia pulmonar de alto riesgo con el fin de discutir el escenario clínico de presentación y el tratamiento instaurado.

Pulmonary thromboembolism has a varied clinical presentation. It is essential to have a high index of suspicion to arrive at a timely diagnosis. Syncope is associated with severe cases and is of prognostic significance. Thrombolytic treatment is the cornerstone in the subgroup of high-risk patients. Three clinical cases of high-risk pulmonary thromboembolism are presented in order to discuss the clinical presentation scenario and the established treatment.

O tromboembolismo pulmonar tem a presentação clínica variada. É essencial ter um alto índice de suspeita para chegar a um diagnóstico oportuno. A síncope está associada a casos graves e tem significado prognóstico. O tratamento trombolítico é a pedra angular no subgrupo de pacientes de alto risco. São apresentados três casos clínicos de tromboembolismo pulmonar de alto risco para discutir o quadro clínico e o tratamento instituído.

Novedades de las guías de la Sociedad Europea de Cardiología 2020 sobre manejo del síndrome coronario agudo sin elevación persistente del segmento ST / News from the European Society of Cardiology 2020 guidelines on the management of acute coronary syndrome without persistent ST-segment elevation / Novidades da Sociedade Europeia de Cardiologia 2020 diretrizes sobre o tratamento da síndrome coronariana aguda sem elevação persistente do segmento ST

Las enfermedades cardiovasculares representan la primera causa de muerte en el mundo. El manejo de los síndromes coronarios ha avanzado formidablemente en los últimos 50 años, reduciendo el riesgo isquémico, a expensas del consiguiente aumento del riesgo hemorrágico. La Sociedad Europea de Cardiología publicó en el año 2020 la guía sobre el manejo de síndrome coronario agudo sin elevación del segmento ST, donde se destacan cambios en los algoritmos de estratificación de riesgo y la terapia antiplaquetaria y anticoagulante como dos de los aspectos principales. En el presente editorial se resumen las principales novedades publicadas en este documento.

Cardiovascular disease is the leading cause of death worldwide. The management of coronary syndromes has advanced dramatically in the last 50 years, reducing ischemic risk, but observing an increase in bleeding risk. The European Society of Cardiology published in 2020 the guideline on the management of acute coronary syndrome without ST-segment elevation, where changes in risk stratification algorithms and antiplatelet and anticoagulant therapy are highlighted as two of the main aspects. This editorial summarizes the main developments published in this document.

A doença cardiovascular é a principal causa de morte em todo o mundo. O manejo das síndromes coronarianas avançou dramaticamente nos últimos 50 anos, reduzindo o risco isquêmico, mas observando um aumento no risco de sangramento. A Sociedade Europeia de Cardiologia publicou em 2020 a diretriz sobre o manejo da síndrome coronariana aguda sem supradesnivelamento do segmento ST, onde as alterações nos algoritmos de estratificação de risco e na terapia antiplaquetária e anticoagulante são destacadas como dois dos principais aspectos. Este editorial resume os principais desenvolvimentos publicados neste documento.

M. jannaschii FtsZ, a key protein in bacterial cell division, is inactivated by peroxyl radical-mediated methionine oxidation.

Oxidation and inactivation of FtsZ is of interest due to the key role of this protein in bacterial cell division. In the present work, we studied peroxyl radical (from AAPH, 2,2'-azobis(2-methylpropionamidine)dihydrochloride) mediated oxidation of the highly stable FtsZ protein (MjFtsZ) from M. jannaschii, a thermophilic microorganism. MjFtsZ contains eleven Met, and single Tyr and Trp residues which would be expected to be susceptible to oxidation. We hypothesized that exposure of MjFtsZ to AAPH-derived radicals would induce Met oxidation, and cross-linking (via di-Tyr and di-Trp formation), with concomitant loss of its functional polymerization and depolymerization (GTPase) activities. Solutions containing MjFtsZ and AAPH (10 or 100 mM) were incubated at 37 °C for 3 h. Polymerization/depolymerization were assessed by light scattering, while changes in mass were analyzed by SDS-PAGE. Amino acid consumption was quantified by HPLC with fluorescence detection, or direct fluorescence (Trp). Oxidation products and modifications at individual Met residues were quantified by UPLC with mass detection. Oxidation inhibited polymerization-depolymerization activity, and yielded low levels of irreversible protein dimers. With 10 mM AAPH only Trp and Met were consumed giving di-alcohols, kynurenine and di-Trp (from Trp) and the sulfoxide (from Met). With 100 mM AAPH low levels of Tyr oxidation (but not di-Tyr formation) were also observed. Correlation with the functional analyses indicates that Met oxidation, and particularly Met164 is the key driver of MjFtsZ inactivation, probably as a result of the position of this residue at the protein-protein interface of longitudinal interactions and in close proximity to the GTP binding site.

Supradesnivel del segmento ST como forma de presentación atípica de un tumor cardíaco: rol diagnóstico de la multimodalidad de imagen / ST segment elevation as an atypical presentation of a cardiac tumor: diagnostic role of a multimodal imaging approach / Elevação do segmento ST como apresentação de tumor cardíaco: papel diagnóstico da multimodalidade de imagem

Los tumores cardíacos malignos son neoplasias poco frecuentes que pueden presentarse de diversas formas, lo que dificulta su diagnóstico. La ecocardiografía y la resonancia magnética cardíaca son técnicas fundamentales para el diagnóstico, la caracterización y la evaluación de su extensión tumoral. La identificación de la línea tumoral es esencial al iniciar un tratamiento oncológico dirigido. Si bien el "estándar de oro" para este fin es el estudio anatomopatológico (obtenido por biopsia o resección quirúrgica), en los casos en que esto no es posible, la resonancia magnética cardíaca es la técnica no invasiva que proporciona un mejor abordaje diagnóstico. El tratamiento de elección es la resección quirúrgica y el pronóstico, en general, es malo. Presentamos el caso de una paciente con un tumor cardíaco de presentación clínica atípica, en la que un abordaje imagenológico multimodal aporta información clave y complementaria para el diagnóstico y la caracterización tisular.

Malignant cardiac tumors are rare neoplasms that can present in various forms, making their diagnosis difficult. Echocardiography and cardiac magnetic resonance imaging are fundamental techniques for the diagnosis, characterization, and evaluation of tumor extension. Identification of the tumor line is essential when initiating targeted cancer therapy. Although the "gold standard" for this purpose is the pathological study (obtained by biopsy or surgical resection), in cases where this is not possible, cardiac resonance is the non-invasive technique that provides a better diagnostic approach. The treatment of choice is surgical resection and the prognosis is generally poor. We present the case of a patient with an atypical clinical presentation, in which a multimodal approach provides key and complementary information for tumor diagnosis and tissue characterization.

Os tumores cardíacos malignos são neoplasias raras que podem se apresentar de várias formas, dificultando seu diagnóstico. A ecocardiografia e a ressonância magnética cardíaca são técnicas fundamentais para o diagnóstico, caracterização e avaliação da extensão tumoral. A identificação da linha do tumor é essencial ao iniciar a terapia direcionada do câncer. Embora o "padrão ouro" para esse fim seja o estudo patológico (obtido por biópsia ou ressecção cirúrgica), nos casos em que isso não seja possível, a ressonância cardíaca é a técnica não invasiva que proporciona melhor abordagem diagnóstica. O tratamento de escolha é a ressecção cirúrgica e o pronóstico geralmente é ruim. Apresentamos o caso de uma paciente com apresentação clínica atípica, em que a abordagem multimodal fornece informações essenciais e complementares para o diagnóstico do tumor e caracterização do tecido.