Albumin and fibrinogen adsorption on cibacron blue F3G-A immobilised onto PU-PHEMA (polyurethane-poly(hydroxyethylmethacrylate)) surfaces

Identification of unexplored substrates of the serine protease, thrombin, using N-terminomics strategy

The function and regulation of thrombin is a complex as well as an intriguing aspect of evolution and has captured the interest of many investigators over the years. The reported substrates of thrombin are coagulation factors V, VIII, XI, XIII, protein C and fibrinogen. However, these may not be all the substrate of thrombin and therefore its functional role(s), may not have been completely comprehended. The purpose of our study was to identify hitherto unreported substrates of thrombin from human plasma using a N-terminomics protease substrate identification method. We identified 54 putative substrates of thrombin of which 12 are already known and 42 are being reported for the first time. Amongst the proteins identified, recombinant siglec-6 and purified serum alpha-1-acid glycoprotein were validated by cleavage with thrombin. We have discussed the probable relevance of siglec-6 cleavage by thrombin in human placenta mostly because an upregulation in the expression of siglec-6 and thrombin has been reported in the placenta of preeclampsia patients. We also speculate the role of alpha-1-acid glycoprotein cleavage by thrombin in the acute phase as alpha-1-acid glycoprotein is known to be an inhibitor of platelet aggregation whereas thrombin is known to trigger platelet aggregation.

Infection of orthopedic implants with emphasis on bacterial adhesion process and techniques used in studying bacterial-material interactions

Staphylococcus comprises up to two-thirds of all pathogens in orthopedic implant infections and they are the principal causative agents of two major types of infection affecting bone: septic arthritis and osteomyelitis, which involve the inflammatory destruction of joint and bone. Bacterial adhesion is the first and most important step in implant infection. It is a complex process influenced by environmental factors, bacterial properties, material surface properties and by the presence of serum or tissue proteins. Properties of the substrate, such as chemical composition of the material, surface charge, hydrophobicity, surface roughness and the presence of specific proteins at the surface, are all thought to be important in the initial cell attachment process. The biofilm mode of growth of infecting bacteria on an implant surface protects the organisms from the host immune system and antibiotic therapy. The research for novel therapeutic strategies is incited by the emergence of antibiotic-resistant bacteria. This work will provide an overview of the mechanisms and factors involved in bacterial adhesion, the techniques that are currently being used studying bacterial-material interactions as well as provide insight into future directions in the field.

Platelet and leukocyte adhesion to albumin binding self-assembled monolayers

This study reports the use of tetraethylene glycol-terminated self-assembled monolayers (EG(4) SAMs) as a background non-fouling surface to study the effect of an 18 carbon ligand (C18) on albumin selective and reversible adsorption and subsequent platelet and leukocyte adhesion. Surface characterization techniques revealed an efficient immobilization of different levels of C18 ligand on EG(4) SAMs and an increase of surface thickness and hydrophobicity with the increase of C18 ligands. Albumin adsorption increased as the percentage of C18 ligands on the surface increased, but only 2.5%C18 SAMs adsorbed albumin in a selective and reversible way. Adherent platelets also increased with the amount of immobilized C18. Pre-immersion of samples in albumin before contact with platelets demonstrated an 80% decrease in platelet adhesion. Pre-immersion in plasma was only relevant for 2.5%C18 SAMs since this was the only surface to have less platelet adhesion compared to buffer pre-immersion. EG(4) SAMs adhered negligible amounts of leukocytes, but surfaces with C18 ligands have some adherent leukocytes. Except for 10%C18 SAMs, which increased leukocyte adhesion after albumin pre-adhesion, protein pre-immersion did not influence leukocyte adhesion. It has been shown that a surface with a specific surface concentration of albumin-binding ligands (2.5%C18 SAMs) can recruit albumin selectively and reversibly and minimize the adhesion of platelets, despite still adhering some leukocytes.

Covalent immobilization of antimicrobial peptides (AMPs) onto biomaterial surfaces

Bacterial adhesion to biomaterials remains a major problem in the medical devices field. Antimicrobial peptides (AMPs) are well-known components of the innate immune system that can be applied to overcome biofilm-associated infections. Their relevance has been increasing as a practical alternative to conventional antibiotics, which are declining in effectiveness. The recent interest focused on these peptides can be explained by a group of special features, including a wide spectrum of activity, high efficacy at very low concentrations, target specificity, anti-endotoxin activity, synergistic action with classical antibiotics, and low propensity for developing resistance. Therefore, the development of an antimicrobial coating with such properties would be worthwhile. The immobilization of AMPs onto a biomaterial surface has further advantages as it also helps to circumvent AMPs' potential limitations, such as short half-life and cytotoxicity associated with higher concentrations of soluble peptides. The studies discussed in the current review report on the impact of covalent immobilization of AMPs onto surfaces through different chemical coupling strategies, length of spacers, and peptide orientation and concentration. The overall results suggest that immobilized AMPs may be effective in the prevention of biofilm formation by reduction of microorganism survival post-contact with the coated biomaterial. Minimal cytotoxicity and long-term stability profiles were obtained by optimizing immobilization parameters, indicating a promising potential for the use of immobilized AMPs in clinical applications. On the other hand, the effects of tethering on mechanisms of action of AMPs have not yet been fully elucidated. Therefore, further studies are recommended to explore the real potential of immobilized AMPs in health applications as antimicrobial coatings of medical devices.