Antibacterial Peptide-Based Gel for Prevention of Medical Implanted-Device Infection

Implanted medical devices are prone to infection. Designing new strategies to reduce infection and implant rejection are an important challenge for modern medicine. To this end, in the last few years many hydrogels have been designed as matrices for antimicrobial molecules destined to fight frequent infection found in moist environments like the oral cavity. In this study, two types of original hydrogels containing the antimicrobial peptide Cateslytin have been designed. The first hydrogel is based on alginate modified with catechol moieties (AC gel). The choice of these catechol functional groups which derive from mussel’s catechol originates from their strong adhesion properties on various surfaces. The second type of gel we tested is a mixture of alginate catechol and thiol-terminated Pluronic (AC/PlubisSH), a polymer derived from Pluronic, a well-known biocompatible polymer. This PlubisSH polymer has been chosen for its capacity to enhance the cohesion of the composition. These two gels offer new clinical uses, as they can be injected and jellify in a few minutes. Moreover, we show these gels strongly adhere to implant surfaces and gingiva. Once gelled, they demonstrate a high level of rheological properties and stability. In particular, the dissipative energy of the (AC/PlubisSH) gel detachment reaches a high value on gingiva (10 J.m^-2) and on titanium alloys (4 J.m^-2), conferring a strong mechanical barrier. Moreover, the Cateslytin peptide in hydrogels exhibited potent antimicrobial activities against P. gingivalis, where a strong inhibition of bacterial metabolic activity and viability was observed, indicating reduced virulence. Gel biocompatibility tests indicate no signs of toxicity. In conclusion, these new hydrogels could be ideal candidates in the prevention and/or management of periimplant diseases.     

F2-Isoprostanes in HDL are bound to neutral lipids and phospholipids

Low HDL cholesterol (HDL-C) is a risk factor for coronary artery disease (CAD). However, interventions that raise HDL-C have failed to reduce cardiovascular events. We previously reported that HDL is the main carrier of plasma F₂-isoprostanes (F₂-IsoPs) that are markers of oxidative stress formed upon oxidation of arachidonic acid. F₂-IsoPs are predominantly associated with phospholipids. However, there is evidence that F₂-IsoPs in the liver of rats treated with carbon tetrachloride associate with the neutral lipids. To date it is not known whether F₂-IsoPs are found in the neutral lipids in HDL in humans. Possible candidate neutral lipids include cholesteryl esters, triglycerides, diglycerides, and monoglycerides. This study aimed to identify the lipid classes within native and oxidized HDL that contain F₂-IsoPs. We showed that F₂-IsoPs in HDL are bound to neutral lipids as well as phospholipids. HDL-3 contained the highest concentration of F₂-IsoPs in all lipid classes before and after in vitro oxidation. Using targeted LC/MS and high resolution MS, we were unable to provide conclusive evidence for the presence of the synthesized standards 15(R)-15-F_2t-isoP cholesterol and 1-ent-15(RS)-15-F_2t-isoprostanoyl-sn-glycerol in the neutral lipids of HDL. Our findings show that oxidized lipids such as F₂-IsoPs are found in the core and surface of HDL. However, the exact molecular species remain to be definitively characterized. Future studies are required to determine whether the presence of F₂-IsoPs in neutral lipids alters HDL function.     

Using High Spatial Resolution to Improve BOLD fMRI Detection at 3T

For different functional magnetic resonance imaging experiments using blood oxygenation level-dependent (BOLD) contrast, the acquisition of T ₂*-weighted scans at a high spatial resolution may be advantageous in terms of time-course signal-to-noise ratio and of BOLD sensitivity when the regions are prone to susceptibility artifacts. In this study, we explore this solution by examining how spatial resolution influences activations elicited when appetizing food pictures are viewed. Twenty subjects were imaged at 3 T with two different voxel volumes, 3.4 μl and 27 μl. Despite the diminution of brain coverage, we found that high-resolution acquisition led to a better detection of activations. Though known to suffer to different degrees from susceptibility artifacts, the activations detected by high spatial resolution were notably consistent with those reported in published activation likelihood estimation meta-analyses, corresponding to taste-responsive regions. Furthermore, these regions were found activated bilaterally, in contrast with previous findings. Both the reduction of partial volume effect, which improves BOLD contrast, and the mitigation of susceptibility artifact, which boosts the signal to noise ratio in certain regions, explained the better detection noted with high resolution. The present study provides further evidences that high spatial resolution is a valuable solution for human BOLD fMRI, especially for studying food-related stimuli.     

Do Ants Need to Estimate the Geometrical Properties of Trail Bifurcations to Find an Efficient Route? A Swarm Robotics Test Bed

Interactions between individuals and the structure of their environment play a crucial role in shaping self-organized collective behaviors. Recent studies have shown that ants crossing asymmetrical bifurcations in a network of galleries tend to follow the branch that deviates the least from their incoming direction. At the collective level, the combination of this tendency and the pheromone-based recruitment results in a greater likelihood of selecting the shortest path between the colony''s nest and a food source in a network containing asymmetrical bifurcations. It was not clear however what the origin of this behavioral bias is. Here we propose that it results from a simple interaction between the behavior of the ants and the geometry of the network, and that it does not require the ability to measure the angle of the bifurcation. We tested this hypothesis using groups of ant-like robots whose perceptual and cognitive abilities can be fully specified. We programmed them only to lay down and follow light trails, avoid obstacles and move according to a correlated random walk, but not to use more sophisticated orientation methods. We recorded the behavior of the robots in networks of galleries presenting either only symmetrical bifurcations or a combination of symmetrical and asymmetrical bifurcations. Individual robots displayed the same pattern of branch choice as individual ants when crossing a bifurcation, suggesting that ants do not actually measure the geometry of the bifurcations when travelling along a pheromone trail. Finally at the collective level, the group of robots was more likely to select one of the possible shorter paths between two designated areas when moving in an asymmetrical network, as observed in ants. This study reveals the importance of the shape of trail networks for foraging in ants and emphasizes the underestimated role of the geometrical properties of transportation networks in general.     

Biochemical and genetic studies of four patients with pyruvate dehydrogenase E1α deficiency

We report studies of four patients with pyruvate dehydrogenase complex (PDH) deficiency caused by mutations in the E1α subunit. Two unrelated male patients presented with Leigh syndrome and a R263G missense mutation in exon 8. This mutation has previously been described in males with the same phenotype. The two other patients had different novel mutations: (1) an 8-bp deletion at the C-terminus (exon 11) was found in one allele of a young girl suffering from microcephaly and (2) a C88S missense mutation (exon 3) in a boy who only presented with motor neuropathy. These mutations were not found in the mothers of any of the four cases. Immunoblot analysis revealed decreased immunoreactivity for the E1α and E1β subunits in three out of the four patients. These findings confirm that: (1) PDH deficiencies are genetically heterogeneous, (2) the R263G mutation is more frequent in male cases than are other mutations and this amino acid is a hot spot for gene mutations, (3) the last eight amino acids may be important for the conformation of the tetrameric E1-PDH enzyme, and (4) the amino acids at positions 88, 263 and 382–387 are essential for the linking of the α subunit with the β subunit and for the activity of the holoenzyme. Received: 28 October 1996 / Revised: 13 January 1997     

Maleated thermoplastic starch by reactive extrusion

Novel maleated thermoplastic starch (MTPS) with both improved processing and reactivity useful in the melt-blending with biodegradable polyester was prepared through in situ reactive modification of thermoplastic starch (TPS) with maleic anhydride (MA) as esterification agent. Glycerol was used as plasticizer. Physico-chemical parameters of MTPS were determined at different MA contents, while keeping both the content in glycerol (20 wt% by starch), and the processing temperature constant (150 °C). Soxhlet extraction attested for the complete incorporation of glycerol into the starch backbone during the maleation process at low content in MA. In addition, two-dimensional liquid-phase NMR measurements attested for the preferential esterification of starch backbone at C6, together with the occurrence of some hydrolysis and glucosidation reactions. Such reactions promoted by MA moieties reduced the intrinsic viscosity of the MTPS, expecting an improvement in its processability. WAXS diffraction analyses confirmed the complete disruption of the granular structure of native starch in MTPS during the reactive extrusion processing.     

Strong Cooperativity and Loose Geometry between CUB Domains Are the Basis for Procollagen C-Proteinase Enhancer Activity

Procollagen C-proteinase enhancers (PCPE-1 and -2) specifically activate bone morphogenetic protein-1 (BMP-1) and other members of the tolloid proteinase family during C-terminal processing of fibrillar collagen precursors. PCPEs consist of two CUB domains (CUB1 and CUB2) and one NTR domain separated by one short and one long linker. It was previously shown that PCPEs can strongly interact with procollagen molecules, but the exact mechanism by which they enhance BMP-1 activity remains largely unknown. Here, we used a series of deletion mutants of PCPE-1 and two chimeric constructs with repetitions of the same CUB domain to study the role of each domain and linker. Out of all the forms tested, only those containing both CUB1 and CUB2 were capable of enhancing BMP-1 activity and binding to a mini-procollagen substrate with nanomolar affinity. Both these properties were lost by individual CUB domains, which had dissociation constants at least three orders of magnitude higher. In addition, none of the constructs tested could inhibit PCPE activity, although CUB2CUB2NTR was found to modulate BMP-1 activity through direct complex formation with the enzyme, resulting in a decreased rate of substrate processing. Finally, increasing the length of the short linker between CUB1 and CUB2 was without detrimental effect on both activity and substrate binding. These data support the conclusion that CUB1 and CUB2 bind to the procollagen substrate in a cooperative manner, involving the short linker that provides a flexible tether linking the two binding regions.     

Cloning and nucleotide sequence of the gene encoding the γ-d-glutamyl-l-diamino acid endopeptidase II of Bacillus sphaericus

The gene encoding the Bacillus sphaericus gamma-D-glutamyl-L-diamino acid endopeptidase II, a cytoplasmic enzyme involved in cell sporulation [1], contains the information for a 271-amino acid protein devoid of a signal peptide. The endopeptidase lacks sequence relatedness with other proteins of known primary structure except that its C-terminal region has significant similarity with the C-terminal region of the 54-kDa P54 protein of Enterococcus faecium, of unknown function [2].     

Insertion Mutagenesis of the Ferric Pyoverdine Receptor FpvA of Pseudomonas aeruginosa: Identification of Permissive Sites and a Region Important for Ligand Binding

Insertion of an 18-amino-acid-encoding sequence within the fpvA gene identified permissive sites at residues Y350, A402, R451, R521, and R558, consistent with these residues occurring in extramembranous loop regions of the protein. Insertions at R451, R521, and R558 did not adversely affect receptor function, although insertions at Y350 and A402 compromised ferric pyoverdine binding and uptake. The latter region likely contributes to or interacts with the ligand-binding site.     

Human factor VIII procoagulant activity and phospholipid interaction

The interaction between purified human factor VIII and phospholipid vesicles was investigated. The binding of factor VIII to an equimolecular mixture of phosphatidylserine (PS) and phosphatidylcholine (PC) was studied by sucrose gradient ultracentrifugation (10–40% w/v saccharose in 0.01 M Tris-HCl/0.15 M NaCl buffer (pH 7). In the absence of phospholipids all factor VIII activities (VIII : C, VIII R : WF and VIII R : AG) were found in the zone of highest sucrose density including the factor VIII related protein subunit (200 000 molecular weight). In the presence of an equimolecular mixture of PS/PC VIII R : WF activity, VIII R : AG and a factor VIII related protein still migrated to the bottom of the tube, while VIII : C activity remained at the top where phospholipids were found. Thus a dissociation phenomenon between VIII : C and the other factor VIII relateda activities was apparent in the presence of phospholipids. These results also demonstrate the binding of factor VIII : C to certain active phospholipids.