Neural correlates of stress-reactive rumination in depression - The role of childhood trauma and social anxiety.

Recent work showed an association of prefrontal dysfunctions in patients with Major Depressive Disorder (MDD) and social stress induced rumination. However, up to date it is unclear which etiological features of MDD might cause prefrontal dysfunctions. In the study at hand, we aimed to replicate recent findings, that showed prefrontal activation alterations during the Trier Social Stress Test (TSST) and subsequently increased stress-reactive rumination in MDD compared to healthy controls. Moreover, we aimed to explore the role of adverse childhood experiences and other clinical variables in this relationship. N = 55 patients currently suffering from MDD and n = 42 healthy controls (HC) underwent the TSST, while cortical activity in areas of the Cognitive Control Network (CCN) was measured via functional near-infrared spectroscopy (fNIRS). The TSST successfully induced a stress reaction (physiologically, as well as indicated by subjective stress ratings) and state rumination in all subjects with moderate to large effect sizes. In comparison to HC, MDD patients showed elevated levels of state rumination with large effect sizes, as well as a typical pattern of reduced cortical oxygenation during stress in the CCN with moderate effect sizes. Self-reported emotional abuse and social anxiety were moderately positively associated with increased stress-reactive rumination. Within the MDD sample, emotional abuse was negatively and social anxiety positively associated with cortical oxygenation within the CCN with moderate to large effect sizes. In conclusion, our results replicate previous findings on MDD-associated prefrontal hypoactivity during stress and extends the research toward specific subtypes of depression.

In situ fNIRS measurements during cognitive behavioral emotion regulation training in rumination-focused therapy: A randomized-controlled trial.

Repetitive negative thinking (RNT), including rumination, plays a key role in various psychopathologies. Although several psychotherapeutic treatments have been developed to reduce RNT, the neural correlates of those specific treatments and of psychotherapy in general are largely unknown. Functional near-infrared spectroscopy (fNIRS) offers the potential to investigate the neural correlates of psychotherapeutic techniques in situ. Therefore, in this study we investigated the efficacy and neural correlates of a fNIRS adapted Mindfulness-based Emotion Regulation Training (MBERT) for the treatment of depressive rumination in 42 subjects with major depressive disorder (MDD) in a cross-over designed randomized controlled trial. Using psychometric measures, subjective ratings and fNIRS, we analyzed in situ changes in depressive symptom severity, ruminative thoughts and cortical activity in the Cognitive Control Network (CCN). Our results show that MBERT is effective in treating depressive symptoms and rumination. On a neural level, we found consistently higher cortical activation during emotion regulation training compared to control trials in the bilateral inferior frontal gyrus (IFG) and dorsolateral prefrontal cortex (DLPFC). Furthermore, cortical oxygenation decreased from session to session in the bilateral DLPFC. The relevance of the results for the psychotherapeutic treatment of MDD as well as further necessary investigations are discussed.

Crystal structure of VnfH, the iron protein component of vanadium nitrogenase.

Nitrogenases catalyze the biological fixation of inert N2 into bioavailable ammonium. They are bipartite systems consisting of the catalytic dinitrogenase and a complementary reductase, the Fe protein that is also the site where ATP is hydrolyzed to drive the reaction forward. Three different subclasses of dinitrogenases are known, employing either molybdenum, vanadium or only iron at their active site cofactor. Although in all these classes the mode and mechanism of interaction with Fe protein is conserved, each one encodes its own orthologue of the reductase in the corresponding gene cluster. Here we present the 2.2 Å resolution structure of VnfH from Azotobacter vinelandii, the Fe protein of the alternative, vanadium-dependent nitrogenase system, in its ADP-bound state. VnfH adopts the same conformation that was observed for NifH, the Fe protein of molybdenum nitrogenase, in complex with ADP, representing a state of the functional cycle that is ready for reduction and subsequent nucleotide exchange. The overall similarity of NifH and VnfH confirms the experimentally determined cross-reactivity of both ATP-hydrolyzing reductases.

The Critical E4 State of Nitrogenase Catalysis.

The reaction catalyzed by the nitrogenase enzyme involves breaking the stable triple bond of the dinitrogen molecule and is consequently considered among the most challenging reactions in biology. While many aspects regarding its atomic mechanism remain to be elucidated, a kinetic scheme established by David Lowe and Roger Thorneley has remained a gold standard for functional studies of the enzyme for more than 30 years. Recent three-dimensional structures of ligand-bound states of molybdenum- and vanadium-dependent nitrogenases have revealed the actual site of substrate binding on the large active site cofactors of this class of enzymes. The binding mode of an inhibitor and a reaction intermediate further substantiate a hypothesis by Seefeldt, Hoffman, and Dean that the activation of N2 is made possible by a reductive elimination of H2 that leaves the cofactor in a super-reduced state that can bind and reduce the inert N2 molecule. Here we discuss the immediate implications of the structurally observed mode of binding of small molecules to the enzyme with respect to the early stages of the Thorneley-Lowe mechanism of nitrogenase. Four consecutive single-electron reductions give rise to two bridging hydrides at the cluster surface that can recombine to eliminate H2 and enable the reduced cluster to bind its substrate in a bridging mode.

A bound reaction intermediate sheds light on the mechanism of nitrogenase.

Reduction of N2 by nitrogenases occurs at an organometallic iron cofactor that commonly also contains either molybdenum or vanadium. The well-characterized resting state of the cofactor does not bind substrate, so its mode of action remains enigmatic. Carbon monoxide was recently found to replace a bridging sulfide, but the mechanistic relevance was unclear. Here we report the structural analysis of vanadium nitrogenase with a bound intermediate, interpreted as a µ2-bridging, protonated nitrogen that implies the site and mode of substrate binding to the cofactor. Binding results in a flip of amino acid glutamine 176, which hydrogen-bonds the ligand and creates a holding position for the displaced sulfide. The intermediate likely represents state E6 or E7 of the Thorneley-Lowe model and provides clues to the remainder of the catalytic cycle.

The structure of vanadium nitrogenase reveals an unusual bridging ligand.

Nitrogenases catalyze the reduction of dinitrogen (N2) gas to ammonium at a complex heterometallic cofactor. This most commonly occurs at the FeMo cofactor (FeMoco), a [Mo-7Fe-9S-C] cluster whose exact reactivity and substrate-binding mode remain unknown. Alternative nitrogenases replace molybdenum with either vanadium or iron and differ in reactivity, most prominently in the ability of vanadium nitrogenase to reduce CO to hydrocarbons. Here we report the 1.35-Å structure of vanadium nitrogenase from Azotobacter vinelandii. The 240-kDa protein contains an additional α-helical subunit that is not present in molybdenum nitrogenase. The FeV cofactor (FeVco) is a [V-7Fe-8S-C] cluster with a homocitrate ligand to vanadium. Unexpectedly, it lacks one sulfide ion compared to FeMoco, which is replaced by a bridging ligand, likely a µ-1,3-carbonate. The anion fits into a pocket within the protein that is obstructed in molybdenum nitrogenase, and its different chemical character helps to rationalize the altered chemical properties of this unique N2- and CO-fixing enzyme.

Comparative electronic structures of nitrogenase FeMoco and FeVco.

An investigation of the active site cofactors of the molybdenum and vanadium nitrogenases (FeMoco and FeVco) was performed using high-resolution X-ray spectroscopy. Synthetic heterometallic iron-sulfur cluster models and density functional theory calculations complement the study of the MoFe and VFe holoproteins using both non-resonant and resonant X-ray emission spectroscopy. Spectroscopic data show the presence of direct iron-heterometal bonds, which are found to be weaker in FeVco. Furthermore, the interstitial carbide is found to perturb the electronic structures of the cofactors through highly covalent Fe-C bonding. The implications of these conclusions are discussed in light of the differential reactivity of the molybdenum and vanadium nitrogenases towards various substrates. Possible functional roles for both the heterometal and the interstitial carbide are detailed.

Timing and Kinetics of Nonmotor Fluctuations in Advanced Parkinson's Disease.

BACKGROUND: Nonmotor symptoms (NMS) are known to fluctuate together with motor oscillations in advanced PD, but their timing and kinetics remains enigmatic. OBJECTIVE: To evaluate timing and kinetics of NMS fluctuations. METHODS: Analysis of diary data from 17 fluctuating PD patients. Diaries were completed by rating NMS as absent (defined herein as NMS On state) or present (NMS Off state) and motor function for every hour for 5 consecutive days. Timing and kinetics were analyzed by synchronizing motor Off periods and subsequent cross-classification of NMS Off periods for each motor Off hour into 2×2 contingency tables. RESULTS: We found clear temporal connections of NMS Off periods with motor Off periods only for anxiety/depression, concentration/attention deficiency and bladder urgency. Psychiatric NMS Off periods had a longer duration (median: 3-4 hours) compared to motor Off periods (2 hours; P < 0.05, Mann-Whitney U-test). CONCLUSIONS: Our data on timing and kinetics of NMS fluctuations show close temporal connection with motor Off periods only for mood and cognitive symptoms. Variances in both timing and/or kinetics of NMS fluctuations might explain both the weak/absent correlations of NMS and motor symptom severity in fluctuating patients and the rather low rates of simultaneous switches between On and Off states for NMS and motor function.

Production and isolation of vanadium nitrogenase from Azotobacter vinelandii by molybdenum depletion.

The alternative, vanadium-dependent nitrogenase is employed by Azotobacter vinelandii for the fixation of atmospheric N2 under conditions of molybdenum starvation. While overall similar in architecture and functionality to the common Mo-nitrogenase, the V-dependent enzyme exhibits a series of unique features that on one hand are of high interest for biotechnological applications. As its catalytic properties differ from Mo-nitrogenase, it may on the other hand also provide invaluable clues regarding the molecular mechanism of biological nitrogen fixation that remains scarcely understood to date. Earlier studies on vanadium nitrogenase were almost exclusively based on a ΔnifHDK strain of A. vinelandii, later also in a version with a hexahistidine affinity tag on the enzyme. As structural analyses remained unsuccessful with such preparations we have developed protocols to isolate unmodified vanadium nitrogenase from molybdenum-depleted, actively nitrogen-fixing A. vinelandii wild-type cells. The procedure provides pure protein at high yields whose spectroscopic properties strongly resemble data presented earlier. Analytical size-exclusion chromatography shows this preparation to be a VnfD2K2G2 heterohexamer.

Assessment of Nonmotor Fluctuations Using a Diary in Advanced Parkinson's disease.

BACKGROUND: Since previous studies aimed to study nonmotor symptom (NMS) fluctuations in direct conjunction with motor oscillations, there are no data available on the temporal context of NMS fluctuations and motor oscillations in advanced Parkinson's disease (PD). OBJECTIVE: To evaluate circadian patterns and temporal connections of NMS and motor fluctuations in PD. METHODS: 15 controls, 17 non-fluctuating and 15 fluctuating PD patients completed two diaries by rating 4 key psychiatric (anxiety, depressive mood, inner restlessness, concentration/attention deficits), fatigue and 4 autonomic NMS (excessive sweating, sialorrhea, bladder urgency, dizziness) absent or present and motor function (Off, On with/without dyskinesia, and asleep) for every hour for 5 consecutive days. RESULTS: NMS Off state hours (hours with NMS rated as present) were less frequent compared to motor Off state hours and NMS On-Off-switches were less prevalent compared to those of the motor state. Off time and number of On-Off-switches of psychiatric NMS were moderately correlated with motor Off time and number of motor On-Off switches on the individual patient level. Changes in NMS state occurred largely independent of changes in motor states with concordance rates of only 26-43% of all NMS changes for psychiatric and 7-17% for autonomic NMS. In controls and non-fluctuating PD patients, there were no NMS state switches in concordance to motor state switches. CONCLUSION: We provide first data on the temporal context of NMS fluctuations showing similar frequencies of psychiatric NMS Off, fatigue Off and motor Off times as well as their On-Off-fluctuations, but low concordance rates of NMS with motor On-Off-state switches. We found no evidence for NMS fluctuations in non-fluctuating PD patients. Our data implicate similar fluctuation patterns of mood NMS and motor function without close timing and/or different kinetics.

Nitrogenase FeMoco investigated by spatially resolved anomalous dispersion refinement.

The [Mo:7Fe:9S:C] iron-molybdenum cofactor (FeMoco) of nitrogenase is the largest known metal cluster and catalyses the 6-electron reduction of dinitrogen to ammonium in biological nitrogen fixation. Only recently its atomic structure was clarified, while its reactivity and electronic structure remain under debate. Here we show that for its resting S=3/2 state the common iron oxidation state assignments must be reconsidered. By a spatially resolved refinement of the anomalous scattering contributions of the 7 Fe atoms of FeMoco, we conclude that three irons (Fe1/3/7) are more reduced than the other four (Fe2/4/5/6). Our data are in agreement with the recently revised oxidation state assignment for the molybdenum ion, providing the first spatially resolved picture of the resting-state electron distribution within FeMoco. This might provide the long-sought experimental basis for a generally accepted theoretical description of the cluster that is in line with available spectroscopic and functional data.

The Fe-V Cofactor of Vanadium Nitrogenase Contains an Interstitial Carbon Atom.

The first direct evidence is provided for the presence of an interstitial carbide in the Fe-V cofactor of Azotobacter vinelandii vanadium nitrogenase. As for our identification of the central carbide in the Fe-Mo cofactor, we employed Fe Kß valence-to-core X-ray emission spectroscopy and density functional theory calculations, and herein report the highly similar spectra of both variants of the cofactor-containing protein. The identification of an analogous carbide, and thus an atomically homologous active site in vanadium nitrogenase, highlights the importance and influence of both the interstitial carbide and the identity of the heteroatom on the electronic structure and catalytic activity of the enzyme.

Molybdenum L-Edge XAS Spectra of MoFe Nitrogenase.

A molybdenum L-edge X-ray absorption spectroscopy (XAS) study is presented for native and oxidized MoFe protein of nitrogenase as well as Mo-Fe model compounds. Recently collected data on MoFe protein (in oxidized and reduced forms) is compared to previously published Mo XAS data on the isolated FeMo cofactor in NMF solution and put in context of the recent Mo K-edge XAS study, which showed a MoIII assignment for the molybdenum atom in FeMoco. The L3-edge data are interpreted within a simple ligand-field model, from which a time-dependent density functional theory (TDDFT) approach is proposed as a way to provide further insights into the analysis of the molybdenum L3-edges. The calculated results reproduce well the relative spectral trends that are observed experimentally. Ultimately, these results give further support for the MoIII assignment in protein-bound FeMoco, as well as isolated FeMoco.

Clinical Ethics in Gabon: The Spectrum of Clinical Ethical Issues Based on Findings from In-Depth Interviews at Three Public Hospitals.

INTRODUCTION: Unlike issues in biomedical research ethics, ethical challenges arising in daily clinical care in Sub-Saharan African countries have not yet been studied in a systematic manner. However this has to be seen as a distinct entity as we argue in this paper. Our aim was to give an overview of the spectrum of clinical ethical issues and to understand what influences clinical ethics in the Sub-Saharan country of Gabon. MATERIALS AND METHODS: In-depth interviews with 18 health care professionals were conducted at three hospital sites in Gabon. Interview transcripts were analyzed using a grounded theory approach (open and axial coding), giving a qualitative spectrum of categories for clinical ethical issues. Validity was checked at a meeting with study participants and other health care experts in Gabon after analysis of the data. RESULTS: Twelve main categories (with 28 further-specified subcategories) for clinical ethical issues were identified and grouped under three core categories: A) micro level: "confidentiality and information", "interpersonal, relational and behavioral issues", "psychological strain of individuals", and "scarce resources"; B) meso level: "structural issues of medical institutions", "issues with private clinics", "challenges connected to the family", and "issues of education, training and competence"; and C) macro level: "influence of society, culture, religion and superstition", "applicability of western medicine", "structural issues on the political level", and "legal issues". DISCUSSION: Interviewees reported a broad spectrum of clinical ethical issues that go beyond challenges related to scarce financial and human resources. Specific socio-cultural, historical and educational backgrounds also played an important role. In fact these influences are central to an understanding of clinical ethics in the studied local context. Further research in the region is necessary to put our study into perspective. As many participants reported a lack of awareness of ethical issues amongst other health care professionals in daily clinical practice, we suggest that international organizations and national medical schools should consider infrastructure and tools to improve context-sensitive capacity building in clinical ethics for Sub-Saharan African countries like Gabon.