Chemically Modified Hydroxyethyl Cellulose

Synthetic, man-made polymers are produced from petroleum, however this activity may well decrease as a function of time because of the non-renewability of the oil. This will result in the decreased production of synthetic polymers with consequent problems to our everyday life because of their ubiquity (food, furniture, containers, electronics…). An alternative could be the use of biopolymers such as cellulose, starch, proteins, amylose and chitin which are extracted from renewable sources. Cellulose is the most abundant biopolymer on earth and is principally found in the cell walls of plants. Cellulose presents interesting properties such as a high thermal stability and high strength, however the principal drawback is its insolubility in both organic and aqueous solvents limiting considerably its use in industry. Chemical modification of the hydroxyl groups of cellulose overcomes some of this problem. In fact, hydroxyethyl cellulose (HEC), where the hydroxyl groups have been modified with ethylene oxide, shows good solubility in aqueous solvents (dimethyl sulfoxide, water) due to the interruption of the cellulose H-bonding networks. Although the chemical modification of cellulose has improved considerably the physical properties of cellulose, the derivatives are usually not competitive against synthetic polymers. Due to its solubility and the presence of the three hydroxyl groups, HEC was chosen as a substrate for chemical modification, with the aim of mimicking the properties of synthetic polymers. The synthetic polymer of reference in our work was poly(N-vinylpyrrolidone) (PVP) because of its solubility in organic and aqueous solvents and sorption properties. The introduction of lactam groups onto HEC could produce a material with properties similar to PVP and this was the goal of our work. Three methods for modifying HEC with lactam groups are reported. The first was the functionalization of HEC with 1-(hydroxymethyl)-2-pyrrolidone (HMP) with degrees of functionalization up to ~0.9 on the primary alcohol functionality of HEC. The functionalized HECs showed markedly different properties to unfunctionalized HEC, such as increased the thermal stability and reduced viscosity. The two others methods led to the preparation of well-defined HEC-g-PVPs using a “grafting from” strategy combined with Atom Transfer Radical Polymerisation (ATRP) and “grafting to” combined with Reversible Addition-Fragmentation Chain-Transfer (RAFT) polymerisation. The ATRP of N-vinylpyrrolidone (NVP) from a prior-synthesised macro-initiator, Br-HEC, did not work efficiently; however, RAFT polymerisation of NVP using an alkyne-terminated xanthate as transfer agent produced an 80% monomer conversion with a 1.4 ƉM. The alkyne-terminated PVP was coupled successfully to partially 15N-labelled N3-HEC and the copper-catalyzed azide-alkyne cycloaddition (CuAAC) was confirmed by 15N NMR spectroscopy. The versatility of the method was demonstrated using poly(N-isopropyl acrylamide) (PNIPAAM) which was synthesised using an alkyne-terminated trithiocarbonate as transfer agent with a 90% monomer conversion and a 1.2 ƉM. Subsequently, this straightforward method was used to prepare anti-microbial graft-copolymers of HEC from an ionic liquid (IL) monomer, 1-(11-acryloyloxyundecyl)-3-methylimidazolium bromide which was polymerised in high monomer conversion (70-80%) with some evidence of control over molecular weight distribution (ƉM =1.5). The influence of the chain length of the grafts on the antibacterial effects was minor with a 20 and 39 µg/mL minimum inhibition concentration (MIC) for E. coli and for S. aureus respectively. The MICs were comparable to those measured for ampicillin, which is known as an antibiotic, indicating the strong effect of our HEC-g-P(IL) on bacteria

Development of a gemcitabine-polymer conjugate with prolonged cytotoxicity against a pancreatic cancer cell line

Gemcitabine (GEM) is a nucleoside analogue of deoxycytidine with limited therapeutic efficacy due to enzymatic hydrolysis by cytidine deaminase (CDA) resulting in compromised half-life in the bloodstream and poor pharmacokinetics. To overcome these limitations, we have developed a methacrylate-based GEM-monomer conjugate, which was polymerized by reversible addition–fragmentation chain transfer (RAFT) polymerization with high monomer conversion (∼90%) and low dispersity (<1.4). The resulting GEM-polymer conjugates were found to form well-defined sub-90 nm nanoparticles (NPs) in aqueous suspension. Subsequently, the GEM release was studied at different pH (∼7 and ∼5) with and without the presence of an enzyme, Cathepsin B. The GEM release profiles followed a pseudo zero-order rate and the GEM-polymer conjugate NPs were prone to acidic and enzymatic degradation, following a two-step hydrolysis mechanism. Furthermore, the NPs exhibited significant cytotoxicity in vitro against a model pancreatic cell line. Although, the half-maximal inhibitory concentration (IC50) of the GEM-monomer and -polymer conjugate NPs was higher than free GEM, the conjugates showed superiorly prolonged activity compared to the parent drug

Graft copolymers of hydroxyethyl cellulose by a ‘grafting to’ method: 15N labelling as a powerful characterisation tool in ‘click’ polymer chemistry

We demonstrate how 15N labelling can be used to probe the success of ‘grafting to’ processes, through the preparation of well-defined graft copolymers of hydroxyethyl cellulose by combining RAFT polymerisation and copper-catalysed azide-alkyne cycloaddition (CuAAC). Using synthesised alkyne-functionalised chain transfer agents, short-chain (DP=10) poly(N-vinylpyrrolidone) (PVP) and poly(N-isopropyl acrylamide) (PNIPAAM) were prepared in high conversion in a controlled manner (ƉM of ~1.4 and 1.2 respectively). Separately, partially 15N-labelled N3-HEC was synthesised and characterised using solid state 13C, 15N CP-MAS NMR and FTIR spectroscopies. Alkyne-terminated PVP and PNIPAAM were grafted at different graft densities onto partially 15N-labelled N3-HEC using the click reaction. The hybrid HEC-g-polymer materials were fully characterised using solid state 13C and 15N CP-MAS NMR and FTIR spectroscopies. While 13C and FTIR spectroscopies gave indirect or weak evidence of CuAAC coupling, the cycloaddition of the alkyne-terminated polymers with N3-HEC was proven unambiguously by 15N solid state NMR spectroscopy. This indicates the utility of 15N labelling for probing the coupling efficiency of CuAAC reactions when employed in ‘grafting to’ processes with cellulosic substrates

Nanoparticle forming polyelectrolyte complexes derived from well-defined block copolymers

Polymers can be used in nanoparticle associated formulations to encapsulate cytotoxic drugs (e.g., paclitaxel). Polyelectrolyte complexes (PECs) that form drug associated colloids also have potential to form particulate associated formulations. We used RAFT polymerisation to prepare small families of narrow molecular weight distributed (i) methacrylate block co-polymers comprised of oligomeric ethylene glycol, poly(ethylene glycol) methyl ether methacrylate (PEGMA), and dimethyl amino pendent chains, 2-(dimethylamino) ethyl methacrylate (DMAEMA), and (ii) poly(methacrylic acid), PMAA. These polymers were examined for their ability to form PECs capable of drug encapsulation. Optimal control in RAFT polymerisation was confirmed by the linear increase of molecular weight and the narrow dispersity of the polymers (<1.2) as determined by 1H nuclear magnetic resonance and gel permeation chromatography. Dynamic light scattering and transmission electron microscopy showed formation of well-defined monodispersed nanoparticles with a hydrodynamic diameter of 25 ± 3 nm upon self-assembly of poly(PEGMA0.23-b-DMAEMA0.77)99 and PMAA75. These PECs are highly haemocompatible. Thin film hydration was used to encapsulate two hydrophobic drugs, paclitaxel and carmofur, into spherical nanoparticles. The results show that carmofur was encapsulated markedly more effectively than paclitaxel (72 vs 1.5%)

Progressive Structural Defects in Canine Centronuclear Myopathy Indicate a Role for HACD1 in Maintaining Skeletal Muscle Membrane Systems

Mutations in HACD1/PTPLA cause recessive congenital myopathies in humans and dogs. Hydroxyacyl-coA dehydratases are required for elongation of very long chain fatty acids, and HACD1 has a role in early myogenesis, but the functions of this striated muscle-specific enzyme in more differentiated skeletal muscle remain unknown. Canine HACD1 deficiency is histopathologically classified as a centronuclear myopathy (CNM). We investigated the hypothesis that muscle from HACD1-deficient dogs has membrane abnormalities in common with CNMs with different genetic causes. We found progressive changes in tubuloreticular and sarcolemmal membranes and mislocalized triads and mitochondria in skeletal muscle from animals deficient in HACD1. Furthermore, comparable membranous abnormalities in cultured HACD1-deficient myotubes provide additional evidence that these defects are a primary consequence of altered HACD1 expression. Our novel findings, including T-tubule dilatation and disorganization, associated with defects in this additional CNM-associated gene provide a definitive pathophysiologic link with these disorders, confirm that dogs deficient in HACD1 are relevant models, and strengthen the evidence for a unifying pathogenesis in CNMs via defective membrane trafficking and excitation-contraction coupling in muscle. These results build on previous work by determining further functional roles of HACD1 in muscle and provide new insight into the pathology and pathogenetic mechanisms of HACD1 CNM. Consequently, alterations in membrane properties associated with HACD1 mutations should be investigated in humans with related phenotypes

The preparation of graft copolymers of cellulose and cellulose derivatives using ATRP under homogeneous reaction conditions

In this comprehensive review, we report on the preparation of graft-copolymers of cellulose and cellulose derivatives using atom transfer radical polymerization (ATRP) under homogeneous conditions. The review is divided into four sections according to the cellulosic material that is graft-copolymerised; (i) cellulose, (ii) ethyl cellulose, (iii) hydroxypropyl cellulose and (iv) other cellulose derivatives. In each section, the grafted synthetic polymers are described as well as the methods used for ATRP macro-initiator formation and graft-copolymerisation. The physical properties of the graft-copolymers including their self-assembly in solution into nanostructures and their stimuli responsive behaviour are described. Potential applications of the self-assembled graft copolymers in areas such as nanocontainers for drug delivery are outline

Mise en œuvre opérationnelle d’un projet de compensation carbone de foyers améliorés au Niger

L’utilisation de foyers « ouverts » traditionnels utilisés au Niger a de lourdes conséquences au niveau environnemental, sanitaire et économique. Le projet de compensation carbone de foyers améliorés présenté ici consiste à remplacer ces foyers traditionnels par des foyers améliorés plus performants (appelés Kiva-Hybride) permettant de réduire la consommation de bois d'origine non renouvelable. La mise en œuvre d’un tel projet nécessite un travail préalable conséquent afin d’assurer sa pérennité sur le terrain : études statistiques, élaboration de différents prototypes de foyers avec tests de performance énergétique, réunions de consultations publiques avec les parties prenantes. Répondant à la méthodologie Gold Standard, ce projet permet non seulement de réduire les émissions de gaz à effet de serre à l’échelle mondiale, mais aussi d’améliorer les conditions de vie des populations locales (lutte contre la déforestation, amélioration de la qualité de l’air intérieur, économies des dépenses et de temps liés à la collecte du bois). En effet, le Kiva-Hybride permet de réduire les besoins en bois d’environ 1,5 tonne/foyer/an en moyenne conduisant à 2,79 teqCO2 d’émissions évitées par an et à l’économie de 47 500 FCFA/an par ménage.The use of traditional cookstove in Niger has serious consequences for the environmental, health and economic development. The carbon offset improved cookstoves project presented here aims to replace these traditional cookstoves with more efficient cookstoves (called Kiva-Hybrid) in order to reduce wood consumption. The implementation of such a project requires a substantial preliminary work to ensure its sustainability: statistical studies, development and performance tests of several cookstoves prototypes, local stakeholder consultation meetings. Following the Gold Standard methodology, this project will not only reduce worldwide greenhouse gases emissions but also improve the local populations’ livelihoods (fight against deforestation, improvement of indoor air quality, savings of money and time collecting woods). Indeed, wood savings are assessed at 1.5 tons/stove/year on average, which leads to 2.79 tCO2e emissions avoided per year and savings of 47 500 FCFA/year/household

Study of the influence of progestin of gonane family on the respiratory drive determination of the implicated central mechanisms

Ce travail doctoral est consacré aux interactions entre la commande respiratoire et le désogestrel et son métabolite actif, l’étonogestrel. Le syndrome d’hypoventilation alvéolaire centrale congénitale (CCHS) est une pathologie neuro-respiratoire caractérisée par une absence de sensibilité à l’hypercapnie. Au sein du laboratoire, une observation a montré, chez deux patientes CCHS, une récupération de la chémosensibilité au CO2/H+ après exposition au désogestrel (Straus et al. 2010). Cependant, cette récupération n’étant pas systématique, il est important de caractériser les mécanismes d’action de ces molécules. Nous avons d’abord analysé rétrospectivement les variables respiratoires de base de ces deux patientes puis, chez le rongeur, utilisé différentes approches pharmacologiques et d’histologie fonctionnelle. Nous avons observé, chez les deux patientes CCHS, une augmentation de la fréquence respiratoire induite par le désogestrel. Chez l’animal, nous avons montré que l’étonogestrel exerçait un effet facilitateur bulbaire sur la fréquence respiratoire avec implication des systèmes sérotoninergiques. In vivo, l’étonogestrel exerce un effet dose-dépendant avec un effet facilitateur pour de faibles concentrations et un effet modérateur pour de plus fortes concentrations. D’autre part, nous avons montré que l’étonogestrel induit une potentialisation de la réponse à l’hypercapnie qui impliquerait des structures supra-bulbaires. Les résultats obtenus caractérisent les interactions de ce progestatif avec la commande respiratoire permettant d’ouvrir des perspectives quant aux conditions dans lesquelles des patients souffrant de ce syndrome pourraient recevoir ce progestatif dans le cadre d’un traitement.The present doctoral work was investigated after clinical observations in patients suffering of congenital central alveolar hypoventilation syndrome (CCHS). This pathology is characterized by a decrease in the sensitivity to hypercapnia. In our laboratory, an observation shown, in such patients, a recovery of the chemosensibility to CO2/H+ after exposure to a gonane progestin, the desogestrel (Straus et al. 2010). However, this recovery was not systematic. So, it is important to characterize action mechanisms of etonogestrel, the active metabolite of the desogestrel. We retrospectively analyzed basal respiratory variables in the two CCHS patients include in the previous study (Straus et al. 2010) and used pharmacological and functional histological approaches on in vivo and ex vivo rodents. In both CCHS patients, we observed an increase in basal respiratory frequency induced by desogestrel. Results obtained in ex vivo central nervous system preparations highlighted, in normocapnia, a facilitatory effect of etonogestrel on the respiratory frequency involving medullary serotoninergic mechanisms. In vivo, this facilitatory effect is observed at 10-4/10-3mg/kg of etonogestrel but not at 1mg/kg, suggesting the activation of 1moderator mechanisms depending on supramedullary or peripheral systems. Furthermore, a potentiation of the respiratory response to hypercapnia was observed after exposure to etonogestrel. Data coming from ex vivo experiments pointed out the involvement of supramedullary areas. To conclude, whole of results reveal or characterize interactions of gonane progestin with the respiratory driveleading to perspectives for determining the conditions in which CCHS patients may receive this progestin for their treatment