Cardiovascular-Kidney-Metabolic Syndrome: Association with Adverse Events After Major Noncardiac Surgery.

BACKGROUND: The American Heart Association (AHA) recently defined the cardiovascular-kidney-metabolic syndrome (CKM) as a new entity to address the complex interactions between heart, kidneys, and metabolism. The aim of this study was to assess the outcome impact of CKM syndrome in patients undergoing noncardiac surgery. METHODS: This is a secondary analysis of a prospective international cohort study including patients aged ≥45 years with increased cardiovascular risk undergoing noncardiac surgery. Main exposure was CKM syndrome according to the AHA definition. The primary end point was a composite of major adverse cardiovascular events (MACE) 30 days after surgery. Secondary end points included all-cause mortality and non-MACE complications (Clavien-Dindo class ≥3). RESULTS: This analysis included 14,634 patients (60.8% male, mean age = 72±8 years). MACE occurred in 308 patients (2.1%), and 335 patients (2.3%) died. MACE incidence by CKM stage was as follows: CKM 0: 5/367 = 1.4% (95% confidence interval [CI], 0.4%-3.2%); CKM 1: 3/367 = 0.8% (95% CI, 0.2%-2.4%); CKM 2: 102/7440 = 1.4% (95% CI, 1.1%-1.7%); CKM 3: 27/953 = 2.8% (95% CI, 1.9%-4.1%); CKM 4a: 164/5357 = 3.1% (95% CI, 2.6%-3.6%); CKM 4b: 7/150 = 4.7% (95% CI, 1.9%-9.4%). In multivariate logistic regression, CKM stage ≥3 was independently associated with MACE, mortality, and non-MACE complications, respectively (MACE: OR 2.26 [95% CI, 1.78-2.87]; mortality: OR 1.42 [95% CI: 1.13 -1.78]; non-MACE complications: OR 1.11 [95% CI: 1.03-1.20]). CONCLUSION: The newly defined CKM syndrome is associated with increased morbidity and mortality after non-cardiac surgery. Thus, cardiovascular, renal, and metabolic disorders should be regarded in mutual context in this setting.

Possible effect of the early administration of tranexamic acid on myocardial injury in patients with severe trauma.

Hemodynamic stabilization plays a crucial role in the treatment of patients suffering from severe trauma. Current guidelines recommend the early administration of tranexamic acid (TXA) for bleeding control. While less blood loss can result in less end-organ damage, including myocardial injury, TXA also exhibits prothrombotic effects with potentially adverse myocardial effects. The aim of this study was to investigate the association between the administration of TXA and myocardial injury in patients with severe trauma. We conducted a monocentric cohort study including severely injured patients ≥ 18 years [defined by Injury severity score (ISS) ≥ 16], who were admitted to a tertiary care hospital between 2016 and 2019. Primary outcome measure was myocardial injury according to the fourth Universal Definition (= high sensitive troponin T ≥ 14 ng/l). Secondary endpoints were in-hospital major adverse cardiovascular events (MACE) and mortality. Main exposure was defined as administration of TXA during prehospital period. We conducted multivariate logistic regression models including predefined covariables. A total of 368 patients were screened. Among the 297 included patients (72% male, age. 55?21 years), 119 (40%) presented myocardial injury at hospital arrival. TXA was administered to 20/297 (7%) patients in the prehospital setting, and in 96/297 (32%) patients during pre-or in-hospital period. MACE incidence was 9% (26/297) and in-hospital mortality was 26% (76/297). The adjusted odds ratios (OR) for prehospital TXA and myocardial injury, MACE and mortality were 0.75 [95% confidence interval (CI): 0.25-2.23], 0.51 [95%CI: 0.06-4.30] and 0.84 [0.21-3.33], respectively. In the present cohort of patients suffering from severe trauma, prehospital TXA did not affect the incidence of myocardial injury.

Perioperative copeptin: predictive value and risk stratification in patients undergoing major noncardiac surgery-a prospective observational cohort study.

PURPOSE: Biomarkers can aid in perioperative risk stratification. While preoperative copeptin has been associated with adverse events, intraoperative information is lacking and this association may rather reflect a baseline risk. Knowledge about correlations between postoperative copeptin measurements and clinically relevant outcomes is scarce. We examined the association of perioperative copeptin concentrations with postoperative all-cause mortality and/or major adverse cardiac and cerebrovascular events (MACCE) at 12 months and 30 days as well as with perioperative myocardial injury (PMI). METHODS: We conducted a prospective observational cohort study of adults undergoing noncardiac surgery with intermediate to high surgical risk in Basel, Switzerland, and Düsseldorf, Germany from February 2016 to December 2020. We measured copeptin and cardiac troponin before surgery, immediately after surgery (0 hr) and once between the second and fourth postoperative day (POD 2-4). RESULTS: A primary outcome event of a composite of all-cause mortality and/or MACCE at 12 months occurred in 48/502 patients (9.6%). Elevated preoperative copeptin (> 14 pmol·L-1), immediate postoperative copeptin (> 90 pmol·L-1), and copeptin on POD 2-4 (> 14 pmol·L-1) were associated with lower one-year MACCE-free and/or mortality-free survival (hazard ratio [HR], 2.89; 95% confidence interval [CI], 1.62 to 5.2; HR, 2.07; 95% CI, 1.17 to 3.66; and HR, 2.47; 95% CI, 1.36 to 4.46, respectively). Multivariable analysis continued to show an association for preoperative and postoperative copeptin on POD 2-4. Furthermore, elevated copeptin on POD 2-4 showed an association with 30-day MACCE-free survival (HR, 2.15; 95% CI, 1.18 to 3.91). A total of 64 of 489 patients showed PMI (13.1%). Elevated preoperative copeptin was not associated with PMI, while immediate postoperative copeptin was modestly associated with PMI. CONCLUSION: The results of the present prospective observational cohort study suggest that perioperative copeptin concentrations can help identify patients at risk for all-cause mortality and/or MACCE. Other identified risk factors were revised cardiac risk index, body mass index, surgical risk, and preoperative hemoglobin. TRIAL REGISTRATION: ClinicalTrials.gov (NCT02687776); first submitted 9 February 2016.

RéSUMé: OBJECTIF: Les biomarqueurs peuvent aider à la stratification du risque périopératoire. Bien que la copeptine préopératoire ait été associée à des événements indésirables, les informations peropératoires font défaut; plutôt, cette association pourrait refléter un risque de base. Les connaissances sur les corrélations entre les mesures postopératoires de la copeptine et les résultats cliniquement pertinents sont rares. Nous avons examiné l'association entre les concentrations de copeptine périopératoires et la mortalité postopératoire toutes causes confondues et/ou les événements indésirables cardiaques et cérébrovasculaires majeurs (EICCM/MACCE) à 12 mois et 30 jours ainsi qu'en cas de lésion myocardique périopératoire (LMP/PMI). MéTHODE: Nous avons réalisé une étude de cohorte observationnelle prospective d'adultes bénéficiant d'une chirurgie non cardiaque à risque chirurgical intermédiaire à élevé à Bâle, en Suisse, et à Düsseldorf, en Allemagne, de février 2016 à décembre 2020. Nous avons mesuré la copeptine et la troponine cardiaque avant la chirurgie, immédiatement après la chirurgie (0 h) et une fois entre le deuxième et le quatrième jour postopératoire (JPO 2-4). RéSULTATS: Un événement constituant un critère d'évaluation principal d'un composite de mortalité toutes causes confondues et/ou de MACCE à 12 mois est survenu chez 48/502 patient·es (9,6 %). Une élévation de la copeptine préopératoire (> 14 pmol·L−1), de la copeptine postopératoire immédiate (> 90 pmol·L−1) et de la copeptine aux JPO 2 à 4 (> 14 pmol·L−1) était associée à une survie sans MACCE et/ou sans mortalité à un an plus faible (rapport de risque [RR], 2,89; intervalle de confiance [IC] à 95 %, 1,62 à 5,2; RR, 2,07; IC 95 %, 1,17 à 3,66; et RR, 2,47; IC 95 %, 1,36 à 4,46, respectivement). L'analyse multivariée a aussi montré une association entre la copeptine préopératoire et postopératoire aux JPO 2 à 4. De plus, un taux élevé de copeptine aux JPO 2 à 4 a montré une association avec la survie sans MACCE à 30 jours (RR, 2,15; IC 95 %, 1,18 à 3,91). Au total, 64 des 489 patient·es présentaient une LMP (13,1 %). Un taux élevé de copeptine préopératoire n'a pas été associé à la LMP, tandis que la copeptine postopératoire immédiate était modestement associée à la LMP. CONCLUSION: Les résultats de la présente étude de cohorte observationnelle prospective suggèrent que les concentrations périopératoires de copeptine peuvent aider à identifier les personnes à risque de mortalité toutes causes confondues et/ou de MACCE. Les autres facteurs de risque identifiés étaient l'indice de risque cardiaque révisé, l'indice de masse corporelle, le risque chirurgical et l'hémoglobine préopératoire. ENREGISTREMENT DE L'éTUDE: ClinicalTrials.gov (NCT02687776); première soumission le 9 février 2016.

Redox Out of the Box: Catalytic Versatility Across NAD(P)H-Dependent Oxidoreductases.

The asymmetric reduction of double bonds using NAD(P)H-dependent oxidoreductases has proven to be an efficient tool for the synthesis of important chiral molecules in research and on industrial scale. These enzymes are commercially available in screening kits for the reduction of C=O (ketones), C=C (activated alkenes), or C=N bonds (imines). Recent reports, however, indicate that the ability to accommodate multiple reductase activities on distinct C=X bonds occurs in different enzyme classes, either natively or after mutagenesis. This challenges the common perception of highly selective oxidoreductases for one type of electrophilic substrate. Consideration of this underexplored potential in enzyme screenings and protein engineering campaigns may contribute to the identification of complementary biocatalytic processes for the synthesis of chiral compounds. This review will contribute to a global understanding of the promiscuous behavior of NAD(P)H-dependent oxidoreductases on C=X bond reduction and inspire future discoveries with respect to unconventional biocatalytic routes in asymmetric synthesis.

ESAIC focused guideline for the use of cardiac biomarkers in perioperative risk evaluation.

BACKGROUND: In recent years, there has been increasing focus on the use of cardiac biomarkers in patients undergoing noncardiac surgery. AIMS: The aim of this focused guideline was to provide updated guidance regarding the pre-, post- and combined pre-and postoperative use of cardiac troponin and B-type natriuretic peptides in adult patients undergoing noncardiac surgery. METHODS: The guidelines were prepared using Grading of Recommendations Assessment Development and Evaluation (GRADE) methodology. This included the definition of critical outcomes, a systematic literature search, appraisal of certainty of evidence, evaluation of biomarker measurement in terms of the balance of desirable and undesirable effects including clinical outcomes, resource use, health inequality, stakeholder acceptance, and implementation. The panel differentiated between three different scopes of applications: cardiac biomarkers as prognostic factors, as tools for risk prediction, and for biomarker-enhanced management strategies. RESULTS: In a modified Delphi process, the task force defined 12 critical outcomes. The systematic literature search resulted in over 25,000 hits, of which 115 full-text articles formed the body of evidence for recommendations. The evidence appraisal indicated heterogeneity in the certainty of evidence across critical outcomes. Further, there was relevant gradient in the certainty of evidence across the three scopes of application. Recommendations were issued and if this was not possible due to limited evidence, clinical practice statements were produced. CONCLUSION: The ESAIC focused guidelines provide guidance on the perioperative use of cardiac troponin and B-type natriuretic peptides in patients undergoing noncardiac surgery, for three different scopes of application.

[Interaural stimulation timing mismatch in listeners provided with a cochlear implant and a hearing aid : A review focusing on quantification and compensation]. / Unterschiedliche Stimulationszeitpunkte bei bimodaler Versorgung mit Hörgerät und Cochleaimplantat : Übersichtsartikel zu Quantifizierung und Kompensation.

Bimodal provision of patients with asymmetric hearing loss with a hearing aid ipsilaterally and a cochlear implant (CI) contralaterally is probably the most complicated type of CI provision due to a variety of inherent variables. This review article presents all the systematic interaural mismatches between electric and acoustic stimulation that can occur in bimodal listeners. One of these mismatches is the interaural latency offset, i.e., the time difference of activation of the auditory nerve by acoustic and electric stimulation. Methods for quantifying this offset are presented by registering electrically and acoustically evoked potentials and measuring processing delays in the devices. Technical compensation of the interaural latency offset and its positive effect on sound localization ability in bimodal listeners is also described. Finally, most recent findings are discussed which may explain why compensation of the interaural latency offset does not improve speech understanding in noise in bimodal listeners.

Evaluation of clinical outcomes in patients treated with heparin or direct thrombin inhibitors during extracorporeal membrane oxygenation: a systematic review and meta-analysis.

BACKGROUND: The number of patients treated with extracorporeal membrane oxygenation (ECMO) devices is increasing. Anticoagulation therapy is crucial to prevent thrombosis during ECMO therapy. Predominantly, heparin has been used as primary anticoagulant but direct thrombin inhibitors (DTI) have been established as alternatives. The aim of this systematic review and meta-analysis was to evaluate clinical outcomes in patients treated with heparin compared to different DTI during ECMO. METHODS: A systematic search was conducted. Full scientific articles were sought for inclusion if heparin anticoagulation was compared to DTI (argatroban/bivalirudin) in ECMO patients. Risk of bias was assessed by Newcastle Ottawa scale. Primary endpoint was in-hospital mortality. Bleeding events, thrombotic events, hours of ECMO support, days of hospital stay, percentage of time within therapeutic range and time to therapeutic range were extracted from full texts as secondary endpoints. Results were presented as Forrest-plots. GRADE was used for confidence assessment in outcomes. RESULTS: Systematic search identified 4.385 records, thereof 18 retrospective studies for a total of 1942 patients, complied with the predefined eligibility criteria:15 studies investigated bivalirudin and 3 studies investigated argatroban versus heparin. Risk of bias was high for most studies. In-hospital mortality, major bleeding events and pump-related thrombosis were less frequent in DTI group as compared to heparin [mortality-OR 0.69, 95% CI 0.54-0.86; major bleeding-OR 0.48, 95% CI 0.29-0.81; pump thrombosis-OR 0.55, 95% CI 0.40-0.76]. Additionally, percentage of time within therapeutic range was higher for DTI [SMD 0.54, 95% CI 0.14-0.94]. GRADE approach revealed a very low level of certainty for each outcome. CONCLUSION: In this meta-analysis, DTI and especially bivalirudin showed beneficial effects on clinical outcomes in ECMO patients as compared to heparin. However, due to the lack of randomized trials, certainty of evidence is low. TRIAL REGISTRATION: This systematic review and meta-analysis was prospectively registered at PROSPERO data base (reference number CRD42021237252 ).

Influence of Short and Long Hyperglycemia on Cardioprotection by Remote Ischemic Preconditioning-A Translational Approach.

The adverse impact of common diseases like diabetes mellitus and acute hyperglycemia on morbidity and mortality from myocardial infarction (MI) has been well documented over the past years of research. In the clinical setting, the relationship between blood glucose and mortality appears linear, with amplifying risk associated with increasing blood glucose levels. Further, this seems to be independent of a diagnosis of diabetes. In the experimental setting, various comorbidities seem to impact ischemic and pharmacological conditioning strategies, protecting the heart against ischemia and reperfusion injury. In this translational experimental approach from bedside to bench, we set out to determine whether acute and/or prolonged hyperglycemia have an influence on the protective effect of transferred human RIPC-plasma and, therefore, might obstruct translation into the clinical setting. Control and RIPC plasma of young healthy men were transferred to isolated hearts of young male Wistar rats in vitro. Plasma was administered before global ischemia under either short hyperglycemic (HGs Con, HGs RIPC) conditions, prolonged hyperglycemia (HGl Con, HGl RIPC), or under normoglycemia (Con, RIPC). Infarct sizes were determined by TTC staining. Control hearts showed an infarct size of 55 ± 7%. Preconditioning with transferred RIPC plasma under normoglycemia significantly reduced infarct size to 25 ± 4% (p < 0.05 vs. Con). Under acute hyperglycemia, control hearts showed an infarct size of 63 ± 5%. Applying RIPC plasma under short hyperglycemic conditions led to a significant infarct size reduction of 41 ± 4% (p < 0.05 vs. HGs Con). However, the cardioprotective effect of RIPC plasma under normoglycemia was significantly stronger compared with acute hyperglycemic conditions (RIPC vs. HGs RIPC; p < 0.05). Prolonged hyperglycemia (HGl RIPC) completely abolished the cardioprotective effect of RIPC plasma (infarct size 60 ± 7%; p < 0.05 vs. HGl Con; HGl Con 59 ± 5%).

Pharmacological Conditioning of the Heart: An Update on Experimental Developments and Clinical Implications.

The aim of pharmacological conditioning is to protect the heart against myocardial ischemia-reperfusion (I/R) injury and its consequences. There is extensive literature that reports a multitude of different cardioprotective signaling molecules and mechanisms in diverse experimental protocols. Several pharmacological agents have been evaluated in terms of myocardial I/R injury. While results from experimental studies are immensely encouraging, translation into the clinical setting remains unsatisfactory. This narrative review wants to focus on two aspects: (1) give a comprehensive update on new developments of pharmacological conditioning in the experimental setting concentrating on recent literature of the last two years and (2) briefly summarize clinical evidence of these cardioprotective substances in the perioperative setting highlighting their clinical implications. By directly opposing each pharmacological agent regarding its recent experimental knowledge and most important available clinical data, a clear overview is given demonstrating the remaining gap between basic research and clinical practice. Finally, future perspectives are given on how we might overcome the limited translatability in the field of pharmacological conditioning.

[New cardiac biomarkers for early detection of myocardial infarction in cardiac surgery]. / Neue kardiale Biomarker zur frühen Detektion des Myokardinfarktes in der Herzchirurgie.

In-hospital mortality after cardiac surgery ranges from 2% to 8%. Many patients suffer from major adverse cardiovascular events, e.g. myocardial infarction, which in the long term can result in severe limitations in routine activities. Troponin plays the central role in identifying myocardial infarction; however, interpretation after cardiac surgery is difficult due to ischemia reperfusion injury and direct surgical trauma. Thus, the distinction between procedure-related myocardial injury and additional myocardial injury due to a new event is difficult. The fourth universal definition of type 5 myocardial infarction uses the 10â€¯× upper limit of normal (ULN) as cut-off and notably > 90% of patients after on-pump procedures exceed this cut-off. Clinical consequences are mostly unclear. The dynamics of copeptin and heart-type fatty acid binding protein (H-FABP) concentrations start very early, i.e. several hours before troponin. The characteristics of copeptin and H­FABP might help to overcome the limitations of troponin. This short narrative review gives a concise overview on this topic. Moreover, a brief view of future perspectives in this field is given.

[Perioperative cardioprotection - From bench to bedside : Current experimental evidence and possible reasons for the limited translation into the clinical setting]. / Perioperative Kardioprotektion ­ "From bench to bedside" : Aktuelle experimentelle Evidenz und mögliche Gründe für die limitierte Translation in die klinische Praxis.

BACKGROUND: Perioperative cardioprotection aims to minimize the consequences of myocardial ischemia reperfusion injury. These strategies appear particularly relevant for anesthesia provision during on-pump cardiac surgery but they potentially affect any cause of perioperative myocardial ischemia. In recent years, several pharmacological and nonpharmacological strategies of cardioprotection have been explored. Results from studies in isolated tissue and animal experiments are promising; however, translation of myocardial conditioning strategies to the clinical setting has been disappointing: in large trials cardioprotective interventions failed to significantly improve outcome. OBJECTIVE: This review aims to provide an overview of the current experimental evidence regarding pharmacological and nonpharmacological cardioprotection. Moreover, it discusses reasons why translation from bench to bedside is hampered by potential confounders and suggests future approaches that might overcome these limitations. MATERIAL AND METHODS: Narrative review. RESULTS AND CONCLUSION: Results of experimental studies are convincing but translation into clinical practice remains challenging. Several confounders have been identified contributing to the mainly inconclusive results from clinical studies, such as comorbidities and comedications, choice of anesthetic regimen and also methodological issues. Carefully designed clinical trials in well-defined patient cohorts evaluating combinations of protective strategies targeting different pathways and cell types might support bench to bedside translation.

Systematic Evaluation of Imine-Reducing Enzymes: Common Principles in Imine Reductases, ß-Hydroxy Acid Dehydrogenases, and Short-Chain Dehydrogenases/ Reductases.

The enzymatic, asymmetric reduction of imines is catalyzed by imine reductases (IREDs), members of the short-chain dehydrogenase/reductase (SDR) family, and ß-hydroxy acid dehydrogenase (ßHAD) variants. Systematic evaluation of the structures and substrate-binding sites of the three enzyme families has revealed four common principles for imine reduction: structurally conserved cofactor-binding domains; tyrosine, aspartate, or glutamate as proton donor; at least four characteristic flanking residues that adapt the donor's pKa and polarize the substrate; and a negative electrostatic potential in the substrate-binding site to stabilize the transition state. As additional catalytically relevant positions, we propose alternative proton donors in IREDs and ßHADs as well as proton relays in IREDs, ßHADs, and SDRs. The functional role of flanking residues was experimentally confirmed by alanine scanning of the imine-reducing SDR from Zephyranthes treatiae. Mutating the "gatekeeping" phenylalanine at standard position 200 resulted in a tenfold increase in imine-reducing activity.

Crossing the Border: From Keto- to Imine Reduction in Short-Chain Dehydrogenases/Reductases.

The family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDRs) comprises numerous biocatalysts capable of C=O or C=C reduction. The highly homologous noroxomaritidine reductase (NR) from Narcissus sp. aff. pseudonarcissus and Zt_SDR from Zephyranthes treatiae, however, are SDRs with an extended imine substrate scope. Comparison with a similar SDR from Asparagus officinalis (Ao_SDR) exhibiting keto-reducing activity, yet negligible imine-reducing capability, and mining the Short-Chain Dehydrogenase/Reductase Engineering Database indicated that NR and Zt_SDR possess a unique active-site composition among SDRs. Adapting the active site of Ao_SDR accordingly improved its imine-reducing capability. By applying the same strategy, an unrelated SDR from Methylobacterium sp. 77 (M77_SDR) with distinct keto-reducing activity was engineered into a promiscuous enzyme with imine-reducing activity, thereby confirming that the ability to reduce imines can be rationally introduced into members of the "classical" SDR enzyme family. Thus, members of the SDR family could be a promising starting point for protein approaches to generate new imine-reducing enzymes.

Perioperative Cardioprotection: Clinical Implications.

Perioperative cardioprotection aims to minimize the consequences of myocardial ischemia-reperfusion injury. In isolated tissue and animal experiments, several treatments have been identified providing cardioprotection. Some of these strategies have been confirmed in clinical proof-of-concept studies. However, the final translation of cardioprotective strategies to really improve clinical outcome has been disappointing: large randomized controlled clinical trials mostly revealed inconclusive, neutral, or negative results. This review provides an overview of the currently available evidence regarding clinical implications of perioperative cardioprotective therapies from an anesthesiological perspective, highlighting nonpharmacological as well as pharmacological strategies. We discuss reasons why translation of promising experimental results into clinical practice and outcome improvement is hampered by potential confounders and suggest future perspectives to overcome these limitations.

[Management of patients with MELAS syndrome : A case report and general characteristics from an anesthesiological perspective]. / Management von Patienten mit MELAS-Syndrom : Ein Fallbericht und allgemeine Besonderheiten aus anästhesiologischer Sicht.

BACKGROUND: Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome is a rare progressive disease with acute neurological episodes caused by a mitochondriopathy. Due to a defect of oxidative phosphorylation in the respiratory chain, there is impaired mitochondrial energy production with subsequent lactic acidosis, especially in situations with increased stress. Due to the high risk of metabolic derailment MELAS syndrome is a great challenge with respect to the perioperative management of anesthesia. OBJECTIVE: This article gives a general overview of the special features of anesthesia management in patients with MELAS syndrome. A case report is presented in order to demonstrate how intraoperative parenteral nutrition can possibly be used to counteract the formation of lactic acidosis. MATERIAL AND METHODS: A systematic review of the literature was performed. As only very few reports on MELAS syndrome are available, a case report was also integrated into this overview article for illustration purposes. RESULTS AND CONCLUSION: Patients with MELAS syndrome represent a challenging cohort with respect to management of anesthesia and an intensive monitoring of the metabolic status is crucial. In cases of increasing lactate values, the administration of intraoperative parenteral nutrition seems to be a suitable approach to avoid lactic acidosis and to improve the perioperative treatment of patients with MELAS syndrome in the future.

Exploiting the Catalytic Diversity of Short-Chain Dehydrogenases/Reductases: Versatile Enzymes from Plants with Extended Imine Substrate Scope.

Numerous short-chain dehydrogenases/reductases (SDRs) have found biocatalytic applications in C=O and C=C (enone) reduction. For NADPH-dependent C=N reduction, imine reductases (IREDs) have primarily been investigated for extension of the substrate range. Here, we show that SDRs are also suitable for a broad range of imine reductions. The SDR noroxomaritidine reductase (NR) is involved in Amaryllidaceae alkaloid biosynthesis, serving as an enone reductase. We have characterized NR by using a set of typical imine substrates and established that the enzyme is active with all four tested imine compounds (up to 99 % conversion, up to 92 % ee). Remarkably, NR reduced two keto compounds as well, thus highlighting this enzyme family's versatility. Using NR as a template, we have identified an as yet unexplored SDR from the Amaryllidacea Zephyranthes treatiae with imine-reducing activity (≤95 % ee). Our results encourage the future characterization of SDR family members as a means of discovering new imine-reducing enzymes.

Extended Catalytic Scope of a Well-Known Enzyme: Asymmetric Reduction of Iminium Substrates by Glucose Dehydrogenase.

NADP(H)-dependent imine reductases (IREDs) are of interest in biocatalytic research due to their ability to generate chiral amines from imine/iminium substrates. In reaction protocols involving IREDs, glucose dehydrogenase (GDH) is generally used to regenerate the expensive cofactor NADPH by oxidation of d-glucose to gluconolactone. We have characterized different IREDs with regard to reduction of a set of bicyclic iminium compounds and have utilized 1 H NMR and GC analyses to determine degree of substrate conversion and product enantiomeric excess (ee). All IREDs reduced the tested iminium compounds to the corresponding chiral amines. Blank experiments without IREDs also showed substrate conversion, however, thus suggesting an iminium reductase activity of GDH. This unexpected observation was confirmed by additional experiments with GDHs of different origin. The reduction of C=N bonds with good levels of conversion (>50 %) and excellent enantioselectivity (up to >99 % ee) by GDH represents a promiscuous catalytic activity of this enzyme.