Natalia Ferreira

Potential Mechanisms Supporting the Value of Motor Cortex Stimulation to Treat Chronic Pain Syndromes.

Throughout the first years of the twenty-first century, neurotechnologies such as motor cortex stimulation (MCS), transcranial magnetic stimulation (TMS), and transcranial direct current stimulation (tDCS) have attracted scientific attention and been considered as potential tools to centrally modulate chronic pain, especially for those conditions more difficult to manage and refractory to all types of available pharmacological therapies. Interestingly, although the role of the motor cortex in pain has not been fully clarified, it is one of the cortical areas most commonly targeted by invasive and non-invasive neuromodulation technologies. Recent studies have provided significant advances concerning the establishment of the clinical effectiveness of primary MCS to treat different chronic pain syndromes. Concurrently, the neuromechanisms related to each method of primary motor cortex (M1) modulation have been unveiled. In this respect, the most consistent scientific evidence originates from MCS studies, which indicate the activation of top-down controls driven by M1 stimulation. This concept has also been applied to explain M1-TMS mechanisms. Nevertheless, activation of remote areas in the brain, including cortical and subcortical structures, has been reported with both invasive and non-invasive methods and the participation of major neurotransmitters (e.g., glutamate, GABA, and serotonin) as well as the release of endogenous opioids has been demonstrated. In this critical review, the putative mechanisms underlying the use of MCS to provide relief from chronic migraine and other types of chronic pain are discussed. Emphasis is placed on the most recent scientific evidence obtained from chronic pain research studies involving MCS and non-invasive neuromodulation methods (e.g., tDCS and TMS), which are analyzed comparatively.

Anti-prion activity of a panel of aromatic chemical compounds: in vitro and in silico approaches.

The prion protein (PrP) is implicated in the Transmissible Spongiform Encephalopathies (TSEs), which comprise a group of fatal neurodegenerative diseases affecting humans and other mammals. Conversion of cellular PrP (PrPC) into the scrapie form (PrPSc) is the hallmark of TSEs. Once formed, PrPSc aggregates and catalyzes PrPC misfolding into new PrPSc molecules. Although many compounds have been shown to inhibit the conversion process, so far there is no effective therapy for TSEs. Besides, most of the previously evaluated compounds failed in vivo due to poor pharmacokinetic profiles. In this work we propose a combined in vitro/in silico approach to screen for active anti-prion compounds presenting acceptable drugability and pharmacokinetic parameters. A diverse panel of aromatic compounds was screened in neuroblastoma cells persistently infected with PrPSc (ScN2a) for their ability to inhibit PK-resistant PrP (PrPRes) accumulation. From ∼200 compounds, 47 were effective in decreasing the accumulation of PrPRes in ScN2a cells. Pharmacokinetic and physicochemical properties were predicted in silico, allowing us to obtain estimates of relative blood brain barrier permeation and mutagenicity. MTT reduction assays showed that most of the active compounds were non cytotoxic. Compounds that cleared PrPRes from ScN2a cells, were non-toxic in the MTT assay, and presented a good pharmacokinetic profile were investigated for their ability to inhibit aggregation of an amyloidogenic PrP peptide fragment (PrP109–149). Molecular docking results provided structural models and binding affinities for the interaction between PrP and the most promising compounds. In summary, using this combined in vitro/in silico approach we have identified new small organic anti-scrapie compounds that decrease the accumulation of PrPRes in ScN2a cells, inhibit the aggregation of a PrP peptide, and possess pharmacokinetic characteristics that support their drugability. These compounds are attractive candidates for prion disease therapy.

Cross-section measurements for the fragmentation of CHClF2 by electron impact

CFC compounds present in the upper atmosphere have a significant effect on the environment, strongly contributing to the increase of the hole in the ozone layer. Recent studies show that low-energy electron impact is an important process in the dissociation of these molecules, creating atomic chlorine, which breaks down ozone molecules. In this work, the CHClF2 fragmentation by electron impact in the 40–400 eV energy range is measured. Total and partial cross sections have been obtained, showing the predominance of the release of neutral chlorine, which amounts to around 60% of the total yield. There is a strong indication that this chlorine is being released as a result of the ionization of electrons from both chlorine and fluorine orbitals.

New Approaches for the Selection and Evaluation of Anti-Prion Organic Compounds

Transmissible spongiform encephalopathies (TSEs) are infectious neurodegenerative disorders for which symptomatic, curative, or prophylactic treatments are not available. TSEs arise as a consequence of the conversion of soluble cellular prion protein (PrP(C)) into the scrapie isoform (PrP(Sc)), which aggregates and accumulates in the central nervous system. Proposed drugs against TSEs range from small organic compounds to antibodies; various therapeutic strategies have been proposed, including blocking the conversion of PrP(C) to PrP(Sc), increasing PrP(Sc) clearance, and/or stabilizing PrP(C). While several compounds have been effective in vitro and in animal models, none have proven effective in clinical studies to date. Such lack of in vivo efficacy is attributable to high compound toxicity and the lack of permeability of the selected compounds across the blood-brain barrier. In this review, we discuss recent advances in the screening and evaluation of organic compounds for anti-prion activity using multiple approaches, including initial screening in prion-infected cell cultures, in silico prediction of pharmacokinetic and physicochemical properties, ex vivo evaluation of cellular toxicity, and in vitro assays using purified recombinant prion proteins. The main challenges for effective discrimination of candidate lead compounds as therapeutic agents for TSEs, and the disadvantages of each screening strategy are discussed. We propose that a combination of in vitro, ex vivo, and in silico approaches would be useful for the rapid identification of novel anti-prion drug candidates with suitable pharmacokinetic and pharmacodynamic properties that would support their use as drugs.

Pathways for the release of atomic chlorine from CHClF2 fragmentation by electron impact

Chlorine atoms released in the upper atmosphere from CFC and HCFC compounds when impacted by energetic particles are recognized as the main mechanism for the enlargement of the hole in the ozone layer. A recent study showed a strong indication that the chlorine atom could be released from CHClF2 due to the ionization of either chlorine or fluorine present in the molecule. Investigation of the possible pathways for the dissociation of chlorine from CHClF2 by electron impact has been performed by scanning its relative contribution to Cl production along the 2p fluorine threshold and by measuring the energy distributions of the fragments produced by this collision for energies below and above the 2p fluorine threshold using the new delayed extraction time-of-flight technique. The data presented here provide the kinetic energy distribution of the fragments emerging from the collision and show direct experimental evidence that the release of chlorine can be triggered by the removal either of a chlorine electron or of a non-bonding fluorine electron, a result that should also apply to photoionization.

Diversity of plasmids and transmission of high‐level mupirocin mupA resistance gene in Staphylococcus haemolyticus

The coagulase-negative staphylococci are known for their ability to acquire resistance genes, which limits the choice of therapeutic options for the treatment of infections caused by these microorganisms. In this study, the diversity of high-level mupirocin resistance plasmids (Mup(R) ) was investigated in four strains of Staphylococcus haemolyticus belonging to different pulsed-field gel electrophoresis (PFGE) types or subtypes, isolated in a Brazilian hospital. These strains harbor the mupA gene in large plasmids. In addition, the presence of IS257 sequences flanking the mupA gene was also shown. Two isolates belonging to two different PFGE types exhibited a similar polymorphism for a fragment of the mupA gene and the closest proximal flanking copies of the IS257, suggesting horizontal transmission of S. haemolyticus mupirocin resistance plasmids in the environment and a role of this species as a reservoir of the mupA gene.

Transfer of mupirocin resistance from Staphylococcus haemolyticus clinical strains to Staphylococcus aureus through conjugative and mobilizable plasmids.

Coagulase-negative staphylococci are thought to act as reservoirs of antibiotic resistance genes that can be transferred to Staphylococcus aureus, thus hindering the combat of this bacterium. In this work, we analyzed the presence of plasmids conferring resistance to the antibiotic mupirocin-widely used to treat and prevent S. aureus infections in hospital environments-in nosocomial S. haemolyticus strains. About 12% of the 75 strains tested were resistant to mupirocin, and this phenotype was correlated with the presence of plasmids. These plasmids were shown to be diverse, being either conjugative or mobilizable, and capable of transferring mupirocin resistance to S. aureus Our findings reinforce that S. haemolyticus, historically and mistakenly considered as a less important pathogen, is a reservoir of resistance genes which can be transferred to other bacteria, such as S. aureus, emphasizing the necessity of more effective strategies to detect and combat this emergent opportunistic pathogen.

Toxicological Evaluation of Anti-Scrapie Trimethoxychalcones and Oxadiazoles

An altered form of the cellular prion protein, the PrPScor PrPRes, is implicated in the occurrence of the still untreatable transmissible spongiform encephalopathies. We have previously synthesized and characterized aromatic compounds that inhibit protease-resistant prion protein (PrPRes) accumulation in scrapie-infected cells. These compounds belong to different chemical classes, including acylhydrazones, chalcones and oxadiazoles. Some of the active compounds were non-toxic to neuroblastoma cells in culture and seem to possess drugable properties, since they are in agreement with the Lipinski´s rule of 5 and present desirable pharmacokinetic profiles as predicted in silico. Before the evaluation of the in vivo efficacy of the aromatic compounds in scrapie-infected mice, safety assessment in healthy mice is needed. Here we used Swiss mice to evaluate the acute toxicity profile of the six most promising anti-prionic compounds, the 2,4,5-trimethoxychalcones (J1, J8, J20 and J35) and the 1,3,4-oxadiazoles (Y13 and Y17). One single oral administration (300 mg/kg) of J1, J8, J20, J35, Y13 and Y17 or repeated intraperitoneal administration (10 mg/kg, 3 times a week, for 4 weeks) of J1, J8 and J35, did not elicit toxicity in mice. We strongly believe that the investigated trimethoxychalcones and oxadiazoles are interesting compounds to be further analyzed in vivo against prion diseases.

Measurements of Energy Distribution of Molecular Ions and their Fragments Produced by Electron Impact with a New Spectroscopic Technique

The energy distribution function of molecules and molecular fragments produced by electron impact is measured using a Delayed Extraction Time-Of- Flight (DETOF) spectroscopy. This new technique is able to measure energy distribution of ions from thermal energies up to a few electron volts.

Identification of the CHClF2 molecule fragmentation paths by electron impact

CFC compounds in the atmosphere play a crucial role to the environment, being the main responsible for the enlargement of the ozone hole. Recent studies show that electron impact can be a significant process for the fragmentation of these molecules; for this reason, the collisional processes of CHClF2 by electron impact were studied. Total and partial cross sections have been obtained, showing the predominance of the release of neutral chlorine, which is the main responsible for the breaking down of ozone molecules. There is a strong indication that this chlorine is being released as a result of the ionization of electrons from both chlorine and fluorine orbitals.