Influence of cellulose nanocrystals concentration and ionic strength on the elaboration of cellulose nanocrystals-xyloglucan multilayered thin films.

The effect of the variation of CNC concentration on the growth pattern of CNC-XG films is investigated. We found that a transition in the growth slope occurs at a CNC concentration of roughly 3-4gL(-1). A close effect can be obtained by the increase of the ionic strength of the CNC suspensions, suggesting that electrostatic interactions are involved. Static light scattering investigation of CNC dispersions at increasing concentrations demonstrated that the particle-particle interactions change as the CNC concentration increases. Neutron Reflectivity (NR) was used to probe the internal structure of the films. The increase of the CNC concentration as well as the increase of the ionic strength in the CNC suspension were found to induce a densification of the adsorbed CNC layers, even though the mechanisms are not strictly identical in both cases. Small changes in these parameters provide a straightforward way of controlling the architecture of CNC-based multilayered thin films and, as a result, their functional properties.

Kinetic aspects of the adsorption of xyloglucan onto cellulose nanocrystals.

In this work, the adsorption of a neutral flexible polysaccharide, xyloglucan (XG), onto thin cellulose nanocrystal (CNC) surfaces has been investigated to get more insight into the CNC-XG association. Gold-coated quartz crystals were spin-coated with one layer of CNC, and XG adsorption was monitored in situ using a quartz crystal microbalance with dissipation (QCM-D). The adsorption of XG under flow at different concentrations did not result in the same surface concentration, which evidenced a kinetically controlled process. In an attempt to describe the binding of XG to CNCs, adsorption data were fitted to a kinetic model comprising a contribution from XG adsorption onto uncovered CNC surfaces and a contribution from XG adsorption after rearrangement. Kinetic studies evidenced the presence of two adsorption regimes as a function of XG concentration. For low XG concentrations, the kinetic constant for chain rearrangement is comparable to the kinetic constant for adsorption. This fact implies a rearrangement and alignment of XG molecules on CNCs. Differently, for higher XG concentrations, the kinetic constant related to the conformational rearrangement decreases, indicating that XG molecules have no time to laterally rearrange before new XG molecules adsorb.

Exploring architecture of xyloglucan cellulose nanocrystal complexes through enzyme susceptibility at different adsorption regimes.

Xyloglucan (XG) is believed to act as a cementing material that contributes to the cross-linking and mechanical properties of the cellulose framework in plant cell walls. XG can adsorb to the cellulose nanocrystal (CNC) surface in vitro in order to simulate this in vivo relationship. The target of our work was to investigate the sorption behavior of tamarind seed XG on CNC extracted from cotton linters at different XG/CNC concentration ratios, that is, different adsorption regimes regarding the XG-CNC complex organization and the enzymatic susceptibility of XG. First, we determined the adsorption isotherm. Second, XG-CNC complexes were enzymatically hydrolyzed using a xyloglucan-specific endoglucanase in order to quantify the different XG fractions involved in binding to CNC and to determine adsorption regimes, that is, presence of loops, tails, and trains. Finally, the architecture of the XG-CNC complex was investigated by transmission electron microscopy imaging of negatively stained XG-CNC suspensions and XG immunolabeled suspensions at different XG/CNC concentration ratios, both before and after xyloglucanase hydrolysis process. This study revealed that an increasing XG/CNC concentration ratio led to a change in the XG binding organization to CNC. At low XG/CNC concentration ratios, almost all XG chains were bound as trains to the CNC surface. In contrast, at increasing XG/CNC concentration ratios, the proportion of loops and tails increases. The organization change induces CNC aggregation to form a cellulose/XG network at low XG/CNC regimes, whereas CNC remains in the form of individual particles at higher XG/CNC regimes. Results are discussed both regarding the biological role of XG in plant cell walls and in the perspective of designing new biobased materials.

Exploiting mitochondrial dysfunction for effective elimination of imatinib-resistant leukemic cells.

Challenges today concern chronic myeloid leukemia (CML) patients resistant to imatinib. There is growing evidence that imatinib-resistant leukemic cells present abnormal glucose metabolism but the impact on mitochondria has been neglected. Our work aimed to better understand and exploit the metabolic alterations of imatinib-resistant leukemic cells. Imatinib-resistant cells presented high glycolysis as compared to sensitive cells. Consistently, expression of key glycolytic enzymes, at least partly mediated by HIF-1α, was modified in imatinib-resistant cells suggesting that imatinib-resistant cells uncouple glycolytic flux from pyruvate oxidation. Interestingly, mitochondria of imatinib-resistant cells exhibited accumulation of TCA cycle intermediates, increased NADH and low oxygen consumption. These mitochondrial alterations due to the partial failure of ETC were further confirmed in leukemic cells isolated from some imatinib-resistant CML patients. As a consequence, mitochondria generated more ROS than those of imatinib-sensitive cells. This, in turn, resulted in increased death of imatinib-resistant leukemic cells following in vitro or in vivo treatment with the pro-oxidants, PEITC and Trisenox, in a syngeneic mouse tumor model. Conversely, inhibition of glycolysis caused derepression of respiration leading to lower cellular ROS. In conclusion, these findings indicate that imatinib-resistant leukemic cells have an unexpected mitochondrial dysfunction that could be exploited for selective therapeutic intervention.