Lethal and sublethal toxicity of ammonia to native, invasive, and parasitised freshwater amphipods

In lethal and sublethal ammonia toxicity tests, we examined differences in tolerance of three species of freshwater amphipods, one native and two invasive in Ireland. The native Gammarus duebeni celticus was slightly less tolerant to ammonia than the invasive G. pulex (96 h LC50= 1.155 and 1.544 mg l(-1), respectively), while another invader, Crangonyx pseudogracilis, had the lowest tolerance (LC50= 0.36 mg l(-1)). Parasitism of G. pulex by the acanthocephalan Echinorhynchus truttae greatly reduced the tolerance of the invader to ammonia (LC50= 0.381 mg l(-1)). Further, precopula pair disruption tests indicated that G. d. celticus was more sensitive to ammonia than G. pulex at sublethal levels. We discuss these results in the context of the ecological replacements of native by invader amphipods.     

Antimicrobial activity of novel biocompatible wound dressings based on triblock copolymer hydrogels

Wound infection is a common complication often resulting in delayed healing with adverse clinical and financial consequences. Current antimicrobial treatments are far from ideal, side effects can include both bacterial resistance and toxicity. As a result, a great deal of effort over the last 20 years has been spent on investigating new forms of antimicrobial dressings. Here, we report the unexpected antimicrobial activity of a relatively new biocompatible thermo-responsive PHPMA–PMPC–PHPMA triblock copolymer gelator [where PHPMA denotes poly(2-hydroxypropyl methacrylate) and PMPC denotes poly(2-(methacryloyloxy)ethyl phosphorylcholine)]. In a radial diffusion assay, a 20% w/v copolymer gel produced an inhibitory zone up to six times greater than the corresponding control against Staphylococcus aureus. Similarly, in a broth inhibition assay the same copolymer reduced bacterial growth by 45% compared with control experiments conducted in the absence of any copolymer. Moreover, addition of the copolymer to a 3D-infected skin model reduced bacterial recovery by 38% compared to that of controls over 24–48 h. This is particularly relevant since these antimicrobial triblock copolymers were recently shown to be non-toxic when exposed to a tissue-engineered skin model. This antimicrobial activity was also successfully immobilised by grafting PMPC–PHPMA diblock copolymer brushes onto silicon wafers. Our results indicate that both PMPC–PHPMA diblock and PHPMA homopolymer brushes exhibit antimicrobial activity. Our hypothesis for the mode of action is that the moderately hydrophobic PHPMA chains penetrate the bacterial membrane, causing leakage of the cell contents. In summary, these gels and surfaces offer a promising new approach to antimicrobial dressings.     

Lump localisation through a deformation-based tactile feedback system using a biologically inspired finger sensor

The ability to localise harder areas in soft tissues is often desired during robot-assisted surgical operations. A deformation-based tactile feedback system was tested for the detection of objects within soft tissues, after being chosen over common pressure-based designs. This system uses a biologically inspired sensor that offers a new finger-like approach to tactile sensing. A tactile shape display developed from previous successful designs was used to output the sensed tactile information. Using the tactile feedback system on a mechanical teleoperated device, test subjects palpated a number of artificial tissue models to locate objects of varying stiffness. The addition of the tactile feedback system improved the detection of the objects from 64% to 98%, reduced the localisation error from 18 to 11 mm, and also decreased the time the users spent palpating the tissue from 55 to 37 s. This demonstrates that a deformation-based tactile feedback system can be used to successfully locate hard embedded objects within soft tissue, with a significant improvement over force and visual feedback alone. During testing, it was found that the users were able to more accurately locate the softest embedded objects compared to stiffer ones. Reasons for this observation are discussed.     

Guided tissue regeneration. Absorbable barriers

Over the past 15 years, techniques aimed at regeneration of lost periodontal tissue have become widely used and accepted in clinical practice. Among these techniques are those which use the principles of guided tissue regeneration (GTR), wherein barriers (i.e., membranes) are used to control cell and tissue repopulation of the periodontal wound. A variety of non-absorbable and absorbable barriers have been developed and used for this purpose, with a trend in recent years toward increased use of absorbable GTR materials. This article describes the evolution of absorbable barrier materials and overview materials available for clinical use today. In addition, advantages and disadvantages of these materials are discussed, as well as possible new developments in barrier-based GTR therapy.     

An in vitro study of the use of chelating agents in cleaning nickel-contaminated human skin: an alternative approach to preventing nickel allergic contact dermatitis

The purpose of this study was to investigate the efficacy of organic ligands in cleaning human skin contaminated with nickel. 4 ligands were investigated, 5-chloro-7-iodoquinolin-8-ol (either as HL(1) or NaL(1)), ethylenediaminetetraacetic acid (either as H4L(2) or Na2H2L(2)), sodium diethyldithiocarbamate (NaL(3)) and L-histidine (HL(4)). The cytotoxicity of these ligands was assessed using HaCaT cells (a transformed human keratinocyte cell line). The cytotoxicity order of the ligands was NaL(1) >Na2H2L(2)>NaL(3)>HL(4). An in vitro methodology for examining nickel removal from viable human skin was developed. This methodology was then used to compare the efficiency of the ligands in removing nickel from skin, both alone and in combination with soap solutions. HL(1) and NaL(3) were no more effective than control solutions in removing nickel over the pH range 2-11. In contrast, both H4L(2) and HL(4) removed between 74 and 87% (mean=82+/-3%) of nickel from human skin over the same pH range. Nickel removal from skin by sodium lauryl ethoxy sulfate (SLES, the active ingredient in most liquid skin cleansers) was independent of concentration and no more effective than phosphate-buffered saline (PBS). The amount of nickel removed by PBS solutions of Na2H2L(2) and HL(4) was significantly greater than the amount removed by SLES and was concentration dependent. An evaluation of nickel removal from skin by commercial solid soap, liquid soap and PBS, both alone and with added Na2H2L(2) or HL(4), was conducted. Commercial liquid soap with added HL(4) was more effective than the untreated soap. PBS with either added Na2H2L(2) or HL(4) was more effective than PBS alone.     

Perforin-deficient CD8+ T cells: in vivo priming and antigen-specific immunity against Listeria monocytogenes

CD8+ T cells require perforin to mediate immunity against some, but not all, intracellular pathogens. Previous studies with H-2b MHC perforin gene knockout (PO) mice revealed both perforin-dependent and perforin-independent pathways of CD8+ T cell-mediated immunity to Listeria monocytogenes (LM). In this study, we address two previously unresolved issues regarding the requirement for perforin in antilisterial immunity: 1) Is CD8+ T cell-mediated, perforin-independent immunity specific for a single Ag or generalizable to multiple Ags? 2) Is there a deficiency in the priming of the CD8+ T cell compartment of PO mice following an immunizing challenge with LM? We used H-2d MHC PO mice to generate CD8+ T cell lines individually specific for three known Ags expressed by a recombinant strain of virulent LM. Adoptive transfer experiments into BALB/c host mice revealed that immunity can be mediated by PO CD8+ T cells specific for all Ags examined, indicating that perforin-independent immunity is not limited to CD8+ T cells that recognize listeriolysin O. Analysis of epitope-specific CD8+ T cell expansion by MHC class I tetramer staining and ELISPOT revealed no deficiency in either the primary or secondary response to LM infection in PO mice. These results demonstrate that the perforin-independent pathway of antilisterial resistance mediated by CD8+ T cells is generalizable to multiple epitopes. Furthermore, the results show that reduced antilisterial resistance observed with polyclonal PO CD8+ T cells is a consequence of a deficiency in effector function and not a result of suboptimal CD8+ T cell priming.     

The agonist selectivity of a mouse B1 bradykinin receptor differs from human and rabbit B1 receptors

A genomic clone encoding the mouse B1 receptor was isolated by homology to the human B1 receptor cDNA. The deduced amino acid sequence of the mouse B1 receptor is 72% identical to the human B1 receptor and 73% identical to the rabbit B1 receptor. Ligand binding studies of the mouse B1 receptor expressed in COS cells indicate that it has the pharmacological properties associated with the B1 receptor subtype. However the pharmacology of the mouse receptor is unique in that it possesses a 2-3-fold selectivity for the 'classical' B1 agonist des-Arg9BK over the agonist des-Arg10 kallidin. In contrast, the human and rabbit B1 receptors exhibit an approx. 2000- and 150-fold selectivity, respectively, for des-Arg10kallidin over des-Arg9BK. Thus relative to the human and rabbit B1 receptors the mouse B1 receptor has the opposite selectivity for kinin agonists. The DNA sequence of the region encoding bradykinin was determined for two different mouse kininogen cDNA clones, both encode the sequence Arg-BK. Antipeptide antibodies directed against a C-terminal peptide of the human B1 receptor were produced. Initial characterization of this antibody indicates that it detects specific bands by Western blot analyses that are present in membranes prepared from COS cells transfected with the human B1 receptor cDNA but not from mock transfected COS cells.