Cerebrovascular Reserve Capacity as a Predictor of Postoperative Delirium: A Pilot Study.

Introduction: Postoperative delirium is a common complication after cardiac surgery with cardiopulmonary bypass (CPB). Compromised regulation of the cerebral circulation may be a predisposing factor for delirium. However, the potential relationship between cerebrovascular reserve capacity and delirium is unknown. The aim of this study was to investigate if impaired cerebrovascular reserve capacity was associated with postoperative delirium. Methods: Forty-two patients scheduled for cardiac surgery with CPB were recruited consecutively. All patients underwent preoperative transcranial Doppler (TCD) ultrasound with calculation of breath-hold index (BHI). BHI < 0.69 indicated impaired cerebrovascular reserve capacity. In addition, patients were examined with preoperative neuropsychological tests such as MMSE (Mini Mental State Examination) and AQT (A Quick Test of cognitive speed). Postoperative delirium was assessed using Nursing Delirium Screening Scale (Nu-DESC) in which a score of ≥2 was considered as delirium. Results: Six patients (14%) scored high for postoperative delirium and all demonstrated impaired preoperative cerebrovascular reserve capacity. Median (25th-75th percentile) BHI in patients with postoperative delirium was significantly lower compared to the non-delirium group [0.26 (-0.08-0.44) vs. 0.83 (0.57-1.08), p = 0.002]. Preoperative MMSE score was lower in patients who developed postoperative delirium (median, 25th-75th percentile; 26.5, 24-28 vs. 28.5, 27-29, p = 0.024). Similarly, patients with postoperative delirium also displayed a slower performance during the preoperative cognitive speed test AQT color and form (mean ± SD; 85.8 s ± 19.3 vs. 69.6 s ± 15.8, p = 0.043). Conclusion: The present findings suggest that an extended preoperative ultrasound protocol with TCD evaluation of cerebrovascular reserve capacity and neuropsychological tests may be valuable in identifying patients with increased risk of developing delirium after cardiac surgery.

Iron-induced oligomerization of human FXN81-210 and bacterial CyaY frataxin and the effect of iron chelators.

Patients suffering from the progressive neurodegenerative disease Friedreich's ataxia have reduced expression levels of the protein frataxin. Three major isoforms of human frataxin have been identified, FXN42-210, FXN56-210 and FXN81-210, of which FXN81-210 is considered to be the mature form. Both long forms, FXN42-210 and FXN56-210, have been shown to spontaneously form oligomeric particles stabilized by the extended N-terminal sequence. The short variant FXN81-210, on other hand, has only been observed in the monomeric state. However, a highly homologous E. coli frataxin CyaY, which also lacks an N-terminal extension, has been shown to oligomerize in the presence of iron. To explore the mechanisms of stabilization of short variant frataxin oligomers we compare here the effect of iron on the oligomerization of CyaY and FXN81-210. Using dynamic light scattering, small-angle X-ray scattering, electron microscopy (EM) and cross linking mass spectrometry (MS), we show that at aerobic conditions in the presence of iron both FXN81-210 and CyaY form oligomers. However, while CyaY oligomers are stable over time, FXN81-210 oligomers are unstable and dissociate into monomers after about 24 h. EM and MS studies suggest that within the oligomers FXN81-210 and CyaY monomers are packed in a head-to-tail fashion in ring-shaped structures with potential iron-binding sites located at the interface between monomers. The higher stability of CyaY oligomers can be explained by a higher number of acidic residues at the interface between monomers, which may result in a more stable iron binding. We also show that CyaY oligomers may be dissociated by ferric iron chelators deferiprone and DFO, as well as by the ferrous iron chelator BIPY. Surprisingly, deferiprone and DFO stimulate FXN81-210 oligomerization, while BIPY does not show any effect on oligomerization in this case. The results suggest that FXN81-210 oligomerization is primarily driven by ferric iron, while both ferric and ferrous iron participate in CyaY oligomer stabilization. Analysis of the amino acid sequences of bacterial and eukaryotic frataxins suggests that variations in the position of the acidic residues in helix 1, ß-strand 1 and the loop between them may control the mode of frataxin oligomerization.

SAXS and stability studies of iron-induced oligomers of bacterial frataxin CyaY.

Frataxin is a highly conserved protein found in both prokaryotes and eukaryotes. It is involved in several central functions in cells, which include iron delivery to biochemical processes, such as heme synthesis, assembly of iron-sulfur clusters (ISC), storage of surplus iron in conditions of iron overload, and repair of ISC in aconitase. Frataxin from different organisms has been shown to undergo iron-dependent oligomerization. At least two different classes of oligomers, with different modes of oligomer packing and stabilization, have been identified. Here, we continue our efforts to explore the factors that control the oligomerization of frataxin from different organisms, and focus on E. coli frataxin CyaY. Using small-angle X-ray scattering (SAXS), we show that higher iron-to-protein ratios lead to larger oligomeric species, and that oligomerization proceeds in a linear fashion as a results of iron oxidation. Native mass spectrometry and online size-exclusion chromatography combined with SAXS show that a dimer is the most common form of CyaY in the presence of iron at atmospheric conditions. Modeling of the dimer using the SAXS data confirms the earlier proposed head-to-tail packing arrangement of monomers. This packing mode brings several conserved acidic residues into close proximity to each other, creating an environment for metal ion binding and possibly even mineralization. Together with negative-stain electron microscopy, the experiments also show that trimers, tetramers, pentamers, and presumably higher-order oligomers may exist in solution. Nano-differential scanning fluorimetry shows that the oligomers have limited stability and may easily dissociate at elevated temperatures. The factors affecting the possible oligomerization mode are discussed.

Architecture of the Human Mitochondrial Iron-Sulfur Cluster Assembly Machinery.

Fe-S clusters, essential cofactors needed for the activity of many different enzymes, are assembled by conserved protein machineries inside bacteria and mitochondria. As the architecture of the human machinery remains undefined, we co-expressed in Escherichia coli the following four proteins involved in the initial step of Fe-S cluster synthesis: FXN42-210 (iron donor); [NFS1]·[ISD11] (sulfur donor); and ISCU (scaffold upon which new clusters are assembled). We purified a stable, active complex consisting of all four proteins with 1:1:1:1 stoichiometry. Using negative staining transmission EM and single particle analysis, we obtained a three-dimensional model of the complex with ∼14 Å resolution. Molecular dynamics flexible fitting of protein structures docked into the EM map of the model revealed a [FXN42-210]24·[NFS1]24·[ISD11]24·[ISCU]24 complex, consistent with the measured 1:1:1:1 stoichiometry of its four components. The complex structure fulfills distance constraints obtained from chemical cross-linking of the complex at multiple recurring interfaces, involving hydrogen bonds, salt bridges, or hydrophobic interactions between conserved residues. The complex consists of a central roughly cubic [FXN42-210]24·[ISCU]24 sub-complex with one symmetric ISCU trimer bound on top of one symmetric FXN42-210 trimer at each of its eight vertices. Binding of 12 [NFS1]2·[ISD11]2 sub-complexes to the surface results in a globular macromolecule with a diameter of ∼15 nm and creates 24 Fe-S cluster assembly centers. The organization of each center recapitulates a previously proposed conserved mechanism for sulfur donation from NFS1 to ISCU and reveals, for the first time, a path for iron donation from FXN42-210 to ISCU.

The Structure of the Complex between Yeast Frataxin and Ferrochelatase: CHARACTERIZATION AND PRE-STEADY STATE REACTION OF FERROUS IRON DELIVERY AND HEME SYNTHESIS.

Frataxin is a mitochondrial iron-binding protein involved in iron storage, detoxification, and delivery for iron sulfur-cluster assembly and heme biosynthesis. The ability of frataxin from different organisms to populate multiple oligomeric states in the presence of metal ions, e.g. Fe(2+) and Co(2+), led to the suggestion that different oligomers contribute to the functions of frataxin. Here we report on the complex between yeast frataxin and ferrochelatase, the terminal enzyme of heme biosynthesis. Protein-protein docking and cross-linking in combination with mass spectroscopic analysis and single-particle reconstruction from negatively stained electron microscopic images were used to verify the Yfh1-ferrochelatase interactions. The model of the complex indicates that at the 2:1 Fe(2+)-to-protein ratio, when Yfh1 populates a trimeric state, there are two interaction interfaces between frataxin and the ferrochelatase dimer. Each interaction site involves one ferrochelatase monomer and one frataxin trimer, with conserved polar and charged amino acids of the two proteins positioned at hydrogen-bonding distances from each other. One of the subunits of the Yfh1 trimer interacts extensively with one subunit of the ferrochelatase dimer, contributing to the stability of the complex, whereas another trimer subunit is positioned for Fe(2+) delivery. Single-turnover stopped-flow kinetics experiments demonstrate that increased rates of heme production result from monomers, dimers, and trimers, indicating that these forms are most efficient in delivering Fe(2+) to ferrochelatase and sustaining porphyrin metalation. Furthermore, they support the proposal that frataxin-mediated delivery of this potentially toxic substrate overcomes formation of reactive oxygen species.

Collagenase treatment of Dupuytren's contracture using a modified injection method: a prospective cohort study of skin tears in 164 hands, including short-term outcome.

BACKGROUND AND PURPOSE: Treatment of Dupuytren's contracture (DC) with collagenase Clostridium histolyticum (CCH) consists of injection followed by finger manipulation. We used a modified method, injecting a higher dose than recommended on the label into several parts of the cord, which allows treatment of multiple joint contractures in 1 session and may increase efficacy. We studied the occurrence of skin tears and short-term outcome with this procedure. PATIENTS AND METHODS: We studied 164 consecutive hands with DC, palpable cord, and extension deficit of ≥ 20º in the metacarpophalangeal (MCP) and/or proximal interphalangeal (PIP) joint (mean patient age 70 years, 82% men). A hand surgeon injected all the content of 1 CCH vial (approximately 0.80 mg) into multiple spots in the cord and performed finger extension under local anesthesia after 1 or 2 days. A nurse recorded skin tears on a diagram and conducted a standard telephone follow-up within 4 weeks. A hand therapist measured joint contracture before injection and at a median of 23 (IQR: 7-34) days after finger extension. RESULTS: A skin tear occurred in 66 hands (40%). The largest diameter of the tear was ≤ 5 mm in 30 hands and > 10 mm in 14 hands. Hands with skin tear had greater mean pretreatment MCP extension deficit than those without tear: 59º (SD 26) as opposed to 32º (SD 23). Skin tear occurred in 21 of 24 hands with MCP contracture of ≥ 75º. All tears healed with open-wound treatment. No infections occurred. Mean improvement in total (MCP + PIP) extension deficit was 55º (SD 28). INTERPRETATION: Skin tears occurred in 40% of hands treated with collagenase injections, but only a fifth of them were larger than 1 cm. Tears were more likely in hands with severe MCP joint contracture. All tears healed without complications. Short-term contracture reduction was good.

Costs for collagenase injections compared with fasciectomy in the treatment of Dupuytren's contracture: a retrospective cohort study.

OBJECTIVES: To compare collagenase injections and surgery (fasciectomy) for Dupuytren's contracture (DC) regarding actual total direct treatment costs and short-term outcomes. DESIGN: Retrospective cohort study. SETTING: Orthopaedic department of a regional hospital in Sweden. PARTICIPANTS: Patients aged 65 years or older with previously untreated DC of 30° or greater in the metacarpophalangeal (MCP) and/or proximal interphalangeal (PIP) joints of the small, ring or middle finger. The collagenase group comprised 16 consecutive patients treated during the first 6 months following the introduction of collagenase as treatment for DC at the study centre. The controls were 16 patients randomly selected among those operated on with fasciectomy at the same centre during the preceding 3 years. INTERVENTIONS: Treatment with collagenase was given during two standard outpatient clinic visits (injection of 0.9 mg, distributed at multiple sites in a palpable cord, and next-day finger extension under local anaesthesia) followed by night-time splinting. Fasciectomy was carried out in the operating room (day surgery) under general or regional anaesthesia using standard technique, followed by therapy and splinting. PRIMARY AND SECONDARY OUTCOME MEASURES: Actual total direct costs (salaries of all medical personnel involved in care, medications, materials and other relevant costs), and total MCP and PIP extension deficit (degrees) measured by hand therapists at 6-12 weeks after the treatment. RESULTS: Collagenase injection required fewer hospital outpatient visits to a therapist and nurse than fasciectomy. Total treatment cost for collagenase injection was US$1418.04 and for fasciectomy US$2102.56. The post-treatment median (IQR) total extension deficit was 10 (0-30) for the collagenase group and 10 (0-34) for the fasciectomy group. CONCLUSIONS: Treatment of DC with one collagenase injection costs 33% less than fasciectomy with equivalent efficacy at 6 weeks regarding reduction in contracture.

The molecular basis of iron-induced oligomerization of frataxin and the role of the ferroxidation reaction in oligomerization.

The role of the mitochondrial protein frataxin in iron storage and detoxification, iron delivery to iron-sulfur cluster biosynthesis, heme biosynthesis, and aconitase repair has been extensively studied during the last decade. However, still no general consensus exists on the details of the mechanism of frataxin function and oligomerization. Here, using small-angle x-ray scattering and x-ray crystallography, we describe the solution structure of the oligomers formed during the iron-dependent assembly of yeast (Yfh1) and Escherichia coli (CyaY) frataxin. At an iron-to-protein ratio of 2, the initially monomeric Yfh1 is converted to a trimeric form in solution. The trimer in turn serves as the assembly unit for higher order oligomers induced at higher iron-to-protein ratios. The x-ray crystallographic structure obtained from iron-soaked crystals demonstrates that iron binds at the trimer-trimer interaction sites, presumably contributing to oligomer stabilization. For the ferroxidation-deficient D79A/D82A variant of Yfh1, iron-dependent oligomerization may still take place, although >50% of the protein is found in the monomeric state at the highest iron-to-protein ratio used. This demonstrates that the ferroxidation reaction controls frataxin assembly and presumably the iron chaperone function of frataxin and its interactions with target proteins. For E. coli CyaY, the assembly unit of higher order oligomers is a tetramer, which could be an effect of the much shorter N-terminal region of this protein. The results show that understanding of the mechanistic features of frataxin function requires detailed knowledge of the interplay between the ferroxidation reaction, iron-induced oligomerization, and the structure of oligomers formed during assembly.