Facile surface PEGylation via tyrosinase-catalyzed oxidative reaction for the preparation of non-fouling surfaces

Highly efficient site-specific protein modification using tyrosinase from Streptomyces avermitilis: Structural insight

Tyrosinase-mediated protein conjugation has recently drawn attention as a site-specific protein modification tool under mild conditions. However, the tyrosinases reported to date act only on extremely exposed tyrosine residues, which limits where the target tyrosine can be located. Herein, we report a tyrosinase from Streptomyces avermitilis (SaTYR), that exhibits a much higher activity against tyrosine residues on the protein surface than other tyrosinases. We determined the crystal structure of SaTYR and revealed that the enzyme has a relatively flat and shallow substrate-binding pocket to accommodate a protein substrate. We demonstrated SaTYR-mediated fluorescence dye tagging and PEGylation of a surface tyrosine residue that was unreacted by other tyrosinases with an approximately 95.2 % conjugation yield in 1 h. We also present a structural rationale that considers the steric hindrance from adjacent residues and surrounding structures along with the extent of solvent exposure of residues, as necessary when determining the optimal positions for introducing target tyrosine residues in SaTYR-mediated protein modification. The study demonstrated that the novel tyrosinase, SaTYR, extends the scope of tyrosinase-mediated protein modification, and we propose that site-specific tyrosine conjugation using SaTYR is a promising strategy for protein bioconjugation in various applications.

Multifunctional surfaces through synergistic effects of heparin and nitric oxide release for a highly efficient treatment of blood-contacting devices

Thrombosis and inflammation after implantation remain unsolved problems associated with various medical devices with blood-contacting applications. In this study, we develop a multifunctional biomaterial with enhanced hemocompatibility and anti-inflammatory effects by combining the anticoagulant activity of heparin with the vasodilatory and anti-inflammatory properties of nitric oxide (NO). The co-immobilization of these two key molecules with distinct therapeutic effects is achieved by simultaneous conjugation of heparin (HT) and copper nanoparticles (Cu NPs), an NO-generating catalyst, via a simple tyrosinase (Tyr)-mediated reaction. The resulting immobilized surface showed long-term, stable and adjustable NO release for 14 days. Importantly, the makeup of the material endows the surface with the ability to promote endothelialization and to inhibit coagulation, platelet activation and smooth muscle cell proliferation. In addition, the HT/Cu NP co-immobilized surface enhanced macrophage polarization towards the M2 phenotype in vitro, which can reduce the inflammatory response and improve the adaptation of implants in vivo. This study demonstrated a simple but efficient method of developing a multifunctional surface for blood-contacting devices.

Graphene oxide immobilized surfaces facilitate the sustained release of doxycycline for the prevention of implant related infection

Preventing implant-associated infection, which can lead to implant failure and increased medical costs, is one of the biggest challenges in the orthopaedic surgeons. Therefore, the development of stable and highly effective surface modifications to increase the antimicrobial properties of implants is required. In this study, graphene oxide (GO-)-immobilized titanium dioxide (TiO₂) was developed to efficiently carry and release antimicrobial drugs. Firstly, tyramine-conjugated GO (GOTA) was synthesized and immobilized onto the surfaces of TiO₂ through tyrosinase (Tyr)-catalyzed oxidative reaction (GOTA/TiO₂). Doxycycline hyclate (Dox) was then loaded onto GOTA/TiO₂ via non-covalent interactions between GO and Dox (Dox/GOTA/TiO₂), including electrostatic interaction, π-π stacking, hydrophobic interaction, and hydrogen bonds. The amount of loaded drug was able to be controlled, reaching a maximum of 36 μg/cm². in vitro experiments revealed that the sustained release of Dox from the TiO₂ surfaces continued for over 30 days. Compared with bare TiO₂ and GOTA/TiO₂, Dox/GOTA/TiO₂ exhibited superior antibacterial activity against both gram-negative Escherichia coli and gram-positive Staphylococcus aureus bacteria, without affecting the viability of human dermal fibroblasts. The obtained results indicated that GO-immobilized TiO₂ is an effective carrier for antimicrobial drug delivery to reduce implant-associated infection through the synergistic antimicrobial effect of GO and the prescribed drugs.

Heparin-functionalized polymer graft surface eluting MK2 inhibitory peptide to improve hemocompatibility and anti-neointimal activity

The leading cause of synthetic graft failure includes thrombotic occlusion and intimal hyperplasia at the site of vascular anastomosis. Herein, we report a co-immobilization strategy of heparin and potent anti-neointimal drug (Mitogen Activated Protein Kinase II inhibitory peptide; MK2i) by using a tyrosinase-catalyzed oxidative reaction for preventing thrombotic occlusion and neointimal formation of synthetic vascular grafts. The binding of heparin-tyramine polymer (HT) onto the polycarprolactone (PCL) surface enhanced blood compatibility with significantly reduced protein absorption (64.7% decrease) and platelet adhesion (85.6% decrease) compared to bare PCL surface. When loading MK2i, 1) the HT depot surface gained high MK2i-loading efficiency through charge-charge interaction, and 2) this depot platform enabled long-term, controlled release over 4weeks (92-272μg/mL of MK2i). The released MK2i showed significant inhibitory effects on VSMC migration through down-regulated phosphorylation of target proteins (HSP27 and CREB) associated with intimal hyperplasia. In addition, it was found that the released MK2i infiltrated into the tissue with a cumulative manner in ex vivo human saphenous vein (HSV) model. This present study demonstrates that enzymatically HT-coated surface modification is an effective strategy to induce long-term MK2i release as well as hemocompatibility, thereby improving anti-neointimal activity of synthetic vascular grafts.

Zwitterionic sulfobetaine polymer-immobilized surface by simple tyrosinase-mediated grafting for enhanced antifouling property

Introducing antifouling property to biomaterial surfaces has been considered an effective method for preventing the failure of implanted devices. In order to achieve this, the immobilization of zwitterions on biomaterial surfaces has been proven to be an excellent way of improving anti-adhesive potency. In this study, poly(sulfobetaine-co-tyramine), a tyramine-conjugated sulfobetaine polymer, was synthesized and simply grafted onto the surface of polyurethane via a tyrosinase-mediated reaction. Surface characterization by water contact angle measurements, X-ray photoelectron spectroscopy and atomic force microscopy demonstrated that the zwitterionic polymer was successfully introduced onto the surface of polyurethane and remained stable for 7days. In vitro studies revealed that poly(sulfobetaine-co-tyramine)-coated surfaces dramatically reduced the adhesion of fibrinogen, platelets, fibroblasts, and S. aureus by over 90% in comparison with bare surfaces. These results proved that polyurethane surfaces grafted with poly(sulfobetaine-co-tyramine) via a tyrosinase-catalyzed reaction could be promising candidates for an implantable medical device with excellent bioinert abilities.

STATEMENT OF SIGNIFICANCE

Antifouling surface modification is one of the key strategy to prevent the thrombus formation or infection which occurs on the surface of biomaterial after transplantation. Although there are many methods to modify the surface have been reported, necessity of simple modification technique still exists to apply for practical applications. The purpose of this study is to modify the biomaterial's surface by simply immobilizing antifouling zwitterion polymer via enzyme tyrosinase-mediated reaction which could modify versatile substrates in mild aqueous condition within fast time period. After modification, pSBTA grafted surface becomes resistant to various biological factors including proteins, cells, and bacterias. This approach appears to be a promising method to impart antifouling property on biomaterial surfaces.

Tyrosinase-Mediated Surface Coimmobilization of Heparin and Silver Nanoparticles for Antithrombotic and Antimicrobial Activities

Thrombus and infections are the most common causes for the failure of medical devices, leading to higher hospitalization costs and, in some cases, patient morbidity. It is, therefore, necessary to develop novel strategies to prevent thrombosis and infection caused by medical devices. Herein, we report a simple and a highly efficient strategy to impart antithrombotic and antimicrobial properties to substrates, by simultaneously immobilizing heparin and in situ-synthesized silver nanoparticles (Ag NPs) via a tyrosinase-catalyzed reaction. This consists of tyrosinase-oxidized phenolic groups of a heparin derivative (heparin-grafted tyramine, HT) to catechol groups, followed by immobilizing heparin and inducing the in situ Ag NP formation onto poly(urethane) (PU) substrates. The successful immobilization of both heparin and in situ Ag NPs on the substrates was confirmed by analyses of water contact angles, XPS, SEM, and AFM. The sustained silver release and the surface stability were observed for 30 days. Importantly, the antithrombotic potential of the immobilized surfaces was demonstrated by a reduction in fibrinogen absorption, platelet adhesion, and prolonged blood clotting time. Additionally, the modified PU substrates also exhibited remarkable antibacterial properties against both Gram-positive and Gram-negative bacteria. The results of this work suggest a useful, effective, and time-saving method to improve simultaneous antithrombotic and antibacterial performances of a variety of substrate materials for medical devices.

In situ forming gelatin hydrogels by dual-enzymatic cross-linking for enhanced tissue adhesiveness

In situ forming hydrogels show promise as therapeutic implants and carriers in a wide range of biomedical applications.

Characterization of hLF1-11 immobilization onto chitosan ultrathin films, and its effects on antimicrobial activity

hLF1-11 (GRRRRSVQWCA) is an antimicrobial peptide (AMP) with high activity against methicillin-resistant Staphylococcus aureus (MRSA), the most prevalent species in implant-associated infection. In this work, the effect of the surface immobilization on hLF1-11 antimicrobial activity was studied. Immobilization was performed onto chitosan thin films as a model for an implant coating due to its reported osteogenic and antibacterial properties. Chitosan thin films were produced by spin-coating on gold surfaces. hLF1-11 was immobilized onto these films by its C-terminal cysteine in an orientation that exposes the antimicrobial activity-related arginine-rich portion of the peptide. Two levels of exposure (with and without a polyethylene glycol (PEG) spacer) were analyzed. Covalent immobilization was further compared with the AMP physical adsorption onto chitosan films. Surfaces were characterized using ellipsometry, contact angle measurements, atomic force microscopy, infrared and X-ray photoelectron spectroscopies and using a fluorimetric assay for hLF1-11 quantification. Surface antimicrobial activity was assessed through surface adhesion and viability assays using an MRSA (S. aureus ATCC 33591). The incorporation of hLF1-11 increased significantly bacterial adhesion to chitosan films. However, the presence of hLF1-11, namely when immobilized through a PEG spacer, decreased the viability of adherent bacteria with regard to the control surface. These results demonstrated that hLF1-11 after covalent immobilization by its cysteine can maintain activity, particularly if a spacer is applied. However, further studies, exploring the opposite orientation or the same C-terminal orientation, but non-cysteine related, can help to clarify the potential of the hLF1-11 immobilization strategy.