Stéphane Bach

Raman spectra of birnessite manganese dioxides

Structural features of layered manganese dioxides of the birnessite family are studied using Raman scattering spectroscopy. This local probe is capable of analysing directly the near-neighbour environment of oxygen coordination around manganese and lithium cations. Four types of sol–gel birnessite (SGB) are considered: lithium birnessite (Li-Bir), sodium birnessite (Na-Bir), sol–gel birnessite (SG-Bir), and sol–gel Co-doped birnessite (SGCo-Bir). Thus, in a first approach, we consider the overall spectral features of birnessites such as the superposition of the spectra of local structures, while the lattice modes are discussed in the spectroscopic symmetry. Results show the specific spectroscopic fingerprints of SG-Bir single phases, the site occupancy of Co ions in the substituted SGCo-Bir compound, and vibrations due to lithium ions with their oxygen neighbours in Li-Bir, Li0.32MnO2·0.6H2O. A correlation between the interlayer d-spacing and the stretching mode frequencies of birnessite oxides has been established.

The BRET technology and its application to screening assays

The bioluminescence resonance energy transfer (BRET) method is based on resonance energy transfer between a light‐emitting enzyme and a fluorescent acceptor. Since its first description in 1999, several versions of BRET have been described using different substrates and energy donor/acceptor couples. Today, BRET is considered as one of the most versatile techniques for studying the dynamics of protein‐protein interactions in living cells. Various studies have applied BRET‐based assays to screen new receptor ligands and inhibitors of disease‐related‐proteases. Inhibitors of protein‐protein interactions are likely to become a new major class of therapeutic drugs, and BRET technology is expected to play an important role in the identification of such compounds. This review describes the original BRET‐based methodology, more recent variants, and potential applications to drug screening.

Degradation of Hof1 by SCFGrr1 is important for actomyosin contraction during cytokinesis in yeast

SCF‐type (SCF: Skp1–Cullin–F‐box protein complex) E3 ligases regulate ubiquitin‐dependent degradation of many cell cycle regulators, mainly at the G1/S transition. Here, we show that SCFGrr1 functions during cytokinesis by degrading the PCH protein Hof1. While Hof1 is required early in mitosis to assemble a functional actomyosin ring, it is specifically degraded late in mitosis and remains unstable during the entire G1 phase of the cell cycle. Degradation of Hof1 depends on its PEST motif and a functional 26S proteasome. Interestingly, degradation of Hof1 is independent of APCCdh1, but instead requires the SCFGrr1 E3 ligase. Grr1 is recruited to the mother–bud neck region after activation of the mitotic‐exit network, and interacts with Hof1 in a PEST motif‐dependent manner. Our results also show that downregulation of Hof1 at the end of mitosis is necessary to allow efficient contraction of the actomyosin ring and cell separation during cytokinesis. SCFGrr1‐mediated degradation of Hof1 may thus represent a novel mechanism to couple exit from mitosis with initiation of cytokinesis.

Independent actions on cyclin-dependent kinases and aryl hydrocarbon receptor mediate the antiproliferative effects of indirubins

Indirubin, a bis-indole obtained from various natural sources, is responsible for the reported antileukemia activity of a Chinese Medicinal recipe, Danggui Longhui Wan. However, its molecular mechanism of action is still not well understood. In addition to inhibition of cyclin-dependent kinases and glycogen synthase kinase-3, indirubins have been reported to activate the aryl hydrocarbon receptor (AhR), a cotranscriptional factor. Here, we confirm the interaction of AhR and indirubin using a series of indirubin derivatives and show that their binding modes to AhR and to protein kinases are unrelated. As reported for other AhR ligands, binding of indirubins to AhR leads to its nuclear translocation. Furthermore, the apparent survival of AhR−/− and +/+ cells, as measured by the MTT assay, is equally sensitive to the kinase-inhibiting indirubins. Thus, the cytotoxic effects of indirubins are AhR-independent and more likely to be linked to protein kinase inhibition. In contrast, a dramatic cytostatic effect, as measured by actual cell counts and associated with a sharp G1 phase arrest, is induced by 1-methyl-indirubins, a subfamily of AhR-active but kinase-inactive indirubins. As shown for TCDD (dioxin), this effect appears to be mediated through the AhR-dependent expression of p27KIP1. Altogether these results suggest that AhR activation, rather than kinase inhibition, is responsible for the cytostatic effects of some indirubins. In contrast, kinase inhibition, rather than AhR activation, represents the main mechanism underlying the cytotoxic properties of this class of promising antitumor molecules.

Birnessite manganese dioxide synthesized via a sol—gel process: a new rechargeable cathodic material for lithium batteries

In comparison with the classical birnessite compound synthesized by a conventional reaction, sol—gel lamellar birnessite having the formula MnO1.84,0.6H2O exhibits an important preferred orientation. Electrochemical Li insertion in this compound occurs in two reduction processes in both galvanostatic and voltammetric curves: the first (0 < x < 0.4) occurs between 4.25 and 2.85 V with a high kinetic transport and a strong decrease of the interlayer spacing, the second (0.4 < x < 0.9) occurs at 2.8 V with slower kinetics and no variation of the c parameter. Cycling capacity studies show that the sol—gel birnessite is the most promising rechargeable manganese dioxide with a high d.o.d. of 75% of the initial capacity (200 A h kg−1) reached after the fiftieth cycle.

Antihypertensive drug guanabenz is active in vivo against both yeast and mammalian prions.

Background Prion-based diseases are incurable transmissible neurodegenerative disorders affecting animals and humans. Methodology/Principal Findings Here we report the discovery of the in vivo antiprion activity of Guanabenz (GA), an agonist of α2-adrenergic receptors routinely used in human medicine as an antihypertensive drug. We isolated GA in a screen for drugs active in vivo against two different yeast prions using a previously described yeast-based two steps assay. GA was then shown to promote ovine PrPSc clearance in a cell-based assay. These effects are very specific as evidenced by the lack of activity of some GA analogues that we generated. GA antiprion activity does not involve its agonist activity on α2-adrenergic receptors as other chemically close anti-hypertensive agents possessing related mechanism of action were found inactive against prions. Finally, GA showed activity in a transgenic mouse-based in vivo assay for ovine prion propagation, prolonging slightly but significantly the survival of treated animals. Conclusion/Significance GA thus adds to the short list of compounds active in vivo in animal models for the treatment of prion-based diseases. Because it has been administrated for many years to treat hypertension on a daily basis, without major side-effects, our results suggest that it could be evaluated in human as a potential treatment for prion-based diseases.

Structural and Electrochemical Properties of ω ­ Li x V 2 O 5 ( 0.4 ⩽ x ⩽ 3 ) as Rechargeable Cathodic Material for Lithium Batteries

The ω-Li x V 2 O 5 phase (0.4 ≤ x ≤ 3) has been investigated as rechargeable cathodic material for lithium batteries. The interest in using the w phase as rechargeable electrode consists in the stability of its tetragonal structure (ΔV/V < 1%) as the Li insertion-extraction proceeds. Lithium ions are found to be responsible for the ordering of the structure. AC impedance measurements have shown important kinetic limitations appear in the Li composition range 2.2 ≤ x ≤ 3, hindering the use of high current densities. However, at C/20 rate a remarkable and stable specific capacity of 310 mAh g - 1 is obtained over 30 cycles. Its cycling behavior in the 3.8/1.5 V voltage window has been shown to strongly depend on the C rate and temperature. At a higher rate (C/5), the capacity decline observed as galvanostatic cycling proceeds has been found to originate from a significant dissolution process of the vanadium oxide, leading to the presence of V I V and Vm species in electrolyte.

Delayed Treatment with Systemic (S)-Roscovitine Provides Neuroprotection and Inhibits In Vivo CDK5 Activity Increase in Animal Stroke Models

Background Although quite challenging, neuroprotective therapies in ischemic stroke remain an interesting strategy to counter mechanisms of ischemic injury and reduce brain tissue damage. Among potential neuroprotective drug, cyclin-dependent kinases (CDK) inhibitors represent interesting therapeutic candidates. Increasing evidence indisputably links cell cycle CDKs and CDK5 to the pathogenesis of stroke. Although recent studies have demonstrated promising neuroprotective efficacies of pharmacological CDK inhibitors in related animal models, none of them were however clinically relevant to human treatment. Methodology/Principal Findings In the present study, we report that systemic delivery of (S)-roscovitine, a well known inhibitor of mitotic CDKs and CDK5, was neuroprotective in a dose-dependent manner in two models of focal ischemia, as recommended by STAIR guidelines. We show that (S)-roscovitine was able to cross the blood brain barrier. (S)-roscovitine significant in vivo positive effect remained when the compound was systemically administered 2 hrs after the insult. Moreover, we validate one of (S)-roscovitine in vivo target after ischemia. Cerebral increase of CDK5/p25 activity was observed 3 hrs after the insult and prevented by systemic (S)-roscovitine administration. Our results show therefore that roscovitine protects in vivo neurons possibly through CDK5 dependent mechanisms. Conclusions/Significance Altogether, our data bring new evidences for the further development of pharmacological CDK inhibitors in stroke therapy.

Protein Folding Activity of Ribosomal RNA Is a Selective Target of Two Unrelated Antiprion Drugs

Background 6-Aminophenanthridine (6AP) and Guanabenz (GA, a drug currently in use for the treatment of hypertension) were isolated as antiprion drugs using a yeast-based assay. These structurally unrelated molecules are also active against mammalian prion in several cell-based assays and in vivo in a mouse model for prion-based diseases. Methodology/Principal Findings Here we report the identification of cellular targets of these drugs. Using affinity chromatography matrices for both drugs, we demonstrate an RNA-dependent interaction of 6AP and GA with the ribosome. These specific interactions have no effect on the peptidyl transferase activity of the ribosome or on global translation. In contrast, 6AP and GA specifically inhibit the ribosomal RNA-mediated protein folding activity of the ribosome. Conclusion/Significance 6AP and GA are therefore the first compounds to selectively inhibit the protein folding activity of the ribosome. They thus constitute precious tools to study the yet largely unexplored biological role of this protein folding activity.

Rechargeable 3 V Li Cells Using Hydrated Lamellar Manganese Oxide

The synthesis and the electrochemical features of hydrated lamellar manganese oxides are reported. The authors use the reduction of aqueous permanganate solution by fumaric acid and the oxidation of manganese hydroxide by an aqueous permanganate solution to obtain sol-gel birnessite and classical X-exchanged birnessites (X = Li, Al, Na), respectively. The high oxidation state of Mn associated with the 2D character of the hot lattice allows high specific capacities (150 to 200 Ah/kg) available in the potential range of 4 to 2 V. Interlayer water provides the structural stability of the host lattice required for long cycling. Rechargeable two-electrode Li cells using starved or flooded electrolytes were built with the cathodic materials. The batteries exhibit a satisfactory behavior with a specific capacity of 160 Ah/kg recovered after 30 cycles at the C/20 discharge-charge rate for the sol-gel birnessite. This paper demonstrates an interest in cathodic materials based on oxides containing structural water for use in secondary Li batteries.