Drug connectivity mapping and functional analysis reveal therapeutic small molecules that differentially modulate myelination.

Disruption or loss of oligodendrocytes (OLs) and myelin has devastating effects on CNS function and integrity, which occur in diverse neurological disorders, including Multiple Sclerosis (MS), Alzheimer's disease and neuropsychiatric disorders. Hence, there is a need to develop new therapies that promote oligodendrocyte regeneration and myelin repair. A promising approach is drug repurposing, but most agents have potentially contrasting biological actions depending on the cellular context and their dose-dependent effects on intracellular pathways. Here, we have used a combined systems biology and neurobiological approach to identify compounds that exert positive and negative effects on oligodendroglia, depending on concentration. Notably, next generation pharmacogenomic analysis identified the PI3K/Akt modulator LY294002 as the most highly ranked small molecule with both pro- and anti-oligodendroglial concentration-dependent effects. We validated these in silico findings using multidisciplinary approaches to reveal a profoundly bipartite effect of LY294002 on the generation of OPCs and their differentiation into myelinating oligodendrocytes in both postnatal and adult contexts. Finally, we employed transcriptional profiling and signalling pathway activity assays to determine cell-specific mechanisms of action of LY294002 on oligodendrocytes and resolve optimal in vivo conditions required to promote myelin repair. These results demonstrate the power of multidisciplinary strategies in determining the therapeutic potential of small molecules in neurodegenerative disorders.

The Buffalo study: Outcome and associated predictors in endodontic microsurgery- a cohort study.

AIM: To (i) evaluate and compare the outcome of endodontic microsurgery (EMS) using periapical radiographs (PAs) and cone-beam computed tomography (CBCT) scans; (ii) identify prognostic factors affecting the outcome; and (iii) correlate the effect of guided tissue regeneration (GTR) on the pattern of apical bone remodelling. METHODOLOGY: Eighty-two patients (101 teeth) who received EMS were included and followed-up using clinical and radiographic examinations (PAs and CBCT scans). Two calibrated endodontists evaluated the radiographic healing (favourable or unfavourable) by assessing PAs and CBCT. The success (favourable radiographic outcome with no clinical symptoms) and survival rates (tooth retention without clinical symptoms) were calculated, and the cause of failure (diseased or fractured) was identified. Pre-treatment (age, sex, tooth type, position, sequence of treatment, quality of root canal before surgery, presence/absence of through-and-through lesion, presence/absence apico-marginal defect) and treatment (presence/absence of errors during surgery, type of error (major or minor), retro-preparation depth, presence/absence of an isthmus, retro-filling material used, presence/absence bone graft material and/or resorbable membrane) factors were recorded. Data were analysed statistically to determine the inter-observer, intra-observer and inter-radiographic agreements. Univariate, bivariate and logistic regression analysis were used to determine prognostic factors affecting the outcome and the effect of GTR on the pattern of apical bone remodelling. The significance level was set at 5%. RESULTS: Sixty-eight patients (83 teeth) presented for outcome evaluation (recall rate: 84%). The survival rate was 93%. The success rate was 88% using PA and 86% using CBCT when vertical root fracture (VRF) cases were included and 94% using PAs, and 91% using CBCT when VRF cases were excluded. The intra- and inter-observer agreements were substantial using CBCT, slight to a fair agreement using PA (P < 0.001), and slight to moderate for inter-radiographic agreement. The occurence of a major procedural error during surgery was the only negative predictor for the outcome of EMS (P = 0.013). GTR did not affect the success rate or the type of healing when assessed using PA but it affected the type of healing on CBCT scans (complete vs incomplete healing) and the pattern of cortical plate remodelling (P < 0.001). CONCLUSION: The success and survival rate of endodontic microsurgery was very high, and the occurrence of a major procedural error during surgery was the only factor affecting the outcome. GTR did not improve the outcome, but did affect the quality of apical bone remodelling following EMS.

Substitution reactions of iron(ii) carbamoyl-thioether complexes related to mono-iron hydrogenase.

A C,N,S pincer complex has been synthesized for structural modeling of the organometallic active site of mono-[Fe] hydrogenase (HMD). The C,N,S chelate allows for systematic investigation of the substitution reactions of CO and other exogenous X/L-type ligands, as well as examination of the exact roles of the Fe-carbamoyl and {Fe(CO)2}2+ units in stabilizing the low-spin Fe(ii) center. Reaction of the 'apo-ligand' 6-(2-(methylthio)phenyl)pyridin-2-amine (H2NNpySMe) with [Fe(CO)4(Br)2] affords the organometallic complex [(O[double bond, length as m-dash]CNHNpySMe)Fe(CO)2(Br)] (1). Facile substitutions of the halide with L-type ligands such as MeCN, PR3 (R = C6H5, OEt, Me), pyridine and tBuNC afford diamagnetic cations of the type [(O[double bond, length as m-dash]CNHNpySMe)Fe(CO)2(L)]+ (2a-f). Treatment of 1 with Na[S(2,6-Me2C6H3)] affords the neutral complex [(O[double bond, length as m-dash]CNHNpySMe)Fe(CO)2(S(2,6-Me2C6H3))] (2g). Substitution for CO ligand(s) was achieved with trimethylamine-N-oxide (TMAO), and in the presence of PPh3 or pyridine it afforded the six-coordinate monocarbonyl complexes [(O[double bond, length as m-dash]CNHNpySMe)Fe(CO)(Br)(PPh3)] (3a), [(O[double bond, length as m-dash]CNHNpySMe)Fe(CO)(PPh3)2](BArF4) (3b), and [(O[double bond, length as m-dash]CNHNpySMe)Fe(CO)(py)2](BArF4) (3c). Interestingly the stable low-spin Fe(ii), 5-coordinate complex of the formula [(O[double bond, length as m-dash]CNHNpySMe)Fe(CO)2](BArF4) (4) was accessed by treating 1 with TlBArF4 in non-coordinating solvents (DCE, FPh); notably, 4 does not react with H2 in the presence (or absence) of a base. To elucidate the electronic structure differences between the five-coordinate versus six-coordinate complexes, DFT calculations for 4 and 1 were performed. Geometry optimization indicates that 4+ maintains a square-pyramidal geometry, and the Hessian calculation accurately simulates the ν(C[triple bond, length as m-dash]O) in 4+. The electronic structure of 4+ predicts that the HOMO (comprised of Fe|Ncarb) and LUMO (Fe only) orbitals in 4+ are properly oriented to interact with an incoming ligand. However, we postulate that codirectional orientation of the HOMO and LUMO orbitals explains the lack of H2 reactivity with this equatorial CNS donor set, despite many other structural similarities to the endogenous active site. Based on a related work from our lab, we conclude that a facial C,N,S coordination mode is necessary to promote H2 activation and cleavage.

Structures, Interconversions, and Spectroscopy of Iron Carbonyl Clusters with an Interstitial Carbide: Localized Metal Center Reduction by Overall Cluster Oxidation.

The syntheses, interconversions, and spectroscopic properties of a set of iron carbonyl clusters containing an interstitial carbide are reported. This includes the low temperature X-ray structures of the six-iron clusters (Y)2[Fe6(µ6-C)(µ2-CO)4(CO)12] (1a-c; where Y = NMe4, NEt4, PPh4); the five-iron cluster [Fe5(µ5-C)(CO)15] (3); and the novel formulation of the five-iron cluster (NMe4)2[Fe5(µ5-C)(µ2-CO)(CO)13] (4). Also included in this set is the novel charge-neutral cluster, [Fe6(µ6-C)(CO)18] (2), for which we were unable to obtain a crystallographic structure. As synthetic proof for the identity of 2, we performed a closed loop of interconversions within a family of crystallographically defined species (1, 3, and 4): [Fe6]2- → [Fe6]0 → [Fe5]0 → [Fe5]2- → [Fe6]2-. The structural, spectroscopic, and electronic properties of this "missing link" cluster 2 were investigated by IR, Raman, XPS, and Mössbauer spectroscopies-as well as by DFT calculations. A single νCO feature (1965 cm-1) in the IR spectrum of 2, as well as a prominent Raman feature (νsymm = 1550 cm-1), are consistent with the presence of terminal carbonyls and a {(µ6-C)Fe6} arrangement of iron centers around the central carbide. The XPS of 2 exhibits a higher energy Fe 2p3/2 feature (707.4 eV) as compared to that of 1 (705.5 eV), consistent with the two-electron oxidation induced by treatment of 1 with two equivalents of [Fc](PF6) under CO atmosphere (for the two added CO ligands). DFT calculations indicate two axial and four equatorial Fe sites in 1, all of which have the same or similar oxidation states, for example, two Fe(0) and four Fe(+0.5). These assignments are supported by Mössbauer spectra for 1, which exhibit two closely spaced quadrupole doublets with δ = 0.076 and 0.064 mm s-1. The high-field Mössbauer spectrum of 2 (4.2 K) exhibits three prominent quadrupole doublets with δ = -0.18, -0.11, and +0.41 mm s-1. This indicates three pairs of chemically equivalent Fe sites. The first two pairs arise from irons of a similar oxidation state, while the last pair arises from irons in a different oxidation state, indicating a mixed-valent cluster. Variable field Mössbauer spectra for 2 were simulated assuming these two groups and a diamagnetic ground state. Taken together, the Mössbauer results and DFT calculations for 2 indicate two axial Fe(II) sites and four equatorial sites of lower valence, probably Fe(0). In the DFT optimized pentagonal bipyramidal structure for 2, the Fe(II)-Ccarbide distances are compressed (∼1.84 Å), while the Fe(0)-Ccarbide distances are elongated (∼2.05 Å). Analysis of the formulations for 1 (closo-square bipyramid) and 2 (nido-pentagonal bipyramid) is considered in the context of the textbook electron-counting rules of 14n+2 and 14n+4 for closo and nido clusters, respectively. This redox-dependent intracluster disproportionation of Fe oxidation states is concluded to arise from changes in bonding to the central carbide. A similar phenomenon may be promoted by the central carbide of the FeMoco cluster of nitrogenase, which may in turn stimulate N2 reduction.