Immobilized enzymes for thrombolytic therapy

Conjugation of hyaluronan to proteins

Polymer conjugation has been widely exploited to prolong half-life and reduce immunogenicity of therapeutic proteins. Here, the potentials of hyaluronic acid (HA) have been investigated by studying the conjugates with two model enzymes, trypsin and RNase A, and with insulin. As the direct coupling of proteins to the HA's carboxylic groups can cause cross-linking problems, a hyaluronan-aldehyde derivative has been synthesized for N-terminal site-selective conjugation. HA conjugation, termed HAylation, preserved the activities of enzymes and their thermal stabilities. Insulin HAylation was studied by preparing two conjugates with different peptide loadings (32% and 17%, w/w). Noticeably, the conjugate with the lower loading showed the greater effect on blood glucose level. The 17% HA-insulin conjugate showed a lowering effect on blood glucose level for up to 6h, while free insulin exhausted its action after 1h. This study highlights the potentials of hyaluronan-aldehyde for protein delivery.

Liposomes for targeted delivery of antithrombotic drugs

BACKGROUND

Targeted delivery of antithrombotic (thrombolytic) drugs is expected to increase their efficacy and decrease side effects, especially in the case of thrombolytic enzymes. Liposomes, phospholipid nanosized bubbles with a bilayered membrane structure, have drawn a lot of interest as pharmaceutical carriers for drugs and genes. In particular, several attempts have been made to use liposomes as vehicles for antithrombotic agents.

OBJECTIVE

This review analyzes the available data on the application of liposomes, including liposomes targeted by specific ligands, for the delivery of antithrombotic/thrombolytic agents in order to increase their efficacy and decrease side effects.

METHODS

The papers published on the subject of liposomes loaded with antithrombotic agents, mainly over the last 10 - 15 years, will be discussed.

CONCLUSION

Liposomes loaded with various antithrombotic drugs, though they have been the subject of a significant number of experimental papers, can hardly be considered as real candidates for clinical application in the near future.

Chemical modification of hyaluronidase regulates its inhibition by heparin

Chemical modification of surface amino groups of bovine testicular hyaluronidase with aldehyde dextran was conducted. It was found that with the increase of modification degree of hyaluronidase amino groups the value of residual enzymatic catalytic activity is decreased rather monotonously. It turned out that the value of inhibition of enzyme activity by heparin considerably depends on modification degree of enzyme. This dependence is of a threshold character. Sharp conformational changes in the enzyme occurring at 70-90% degree of its modification considerably lowers heparin inhibition. The higher the degree of hyaluronidase modification, the weaker its inhibition by heparin. More completely/deeply modified derivatives of hyaluronidase (modification degree 96-100%) are practically not inhibited by heparin. Thus, chemical conjugation of hyaluronidase with aldehyde dextran regulates the value of enzyme inhibition by heparin. Hyaluronidase modification becomes an informative tool to study the mechanism of inhibition of its enzyme activity and an efficient means for the development of new therapeutic preparations improving tissue permeability during cardiovascular injuries.

Biochemical surface modification of Co-Cr-Mo

Because of the limited mechanical properties of tissue substitutes formed by culturing cells on polymeric scaffolds, other approaches to tissue engineering must be explored for applications that require complete and immediate ability to bear weight, e.g. total joint replacements. Biochemical surface modification offers a way to partially regulate events at the bone-implant interface to obtain preferred tissue responses. Tresyl chloride, gamma-aminopropyltriethoxysilane (APS) and p-nitrophenyl chloroformate (p-NPC) immobilization schemes were used to couple a model enzyme, trypsin, on bulk samples of Co-Cr-Mo. For comparison, samples were simply adsorbed with protein. The three derivatization schemes resulted in different patterns and levels of activity. Tresyl chloride was not effective in immobilizing active enzyme on Co-Cr-Mo. Aqueous silanization with 12.5% APS resulted in optimal immobilized activity. Activity on samples derivatized with 0.65 mg p-NPC cm-2 was four to five times greater than that on samples simple adsorbed with enzyme or optimally derivatized with APS and was about eight times that on tresylated samples. This work demonstrates that, although different methods have different effectiveness, chemical derivatization can be used to alter the amount and/or stability of biomolecules immobilized on the surface of Co-Cr-Mo.

Activity of enzyme immobilized on silanized Co-Cr-Mo

The surface of an orthopedic biomaterial was modified by the covalent immobilization of biomolecules. Derivatization of Co-Cr-Mo samples with organic and aqueous solutions of gamma-aminopropyltriethoxysilane (APS) resulted in a concentration-dependent number of reactive NH2 groups on the surface available for coupling to protein. The enzyme trypsin was used as a model biomolecule to investigate the effect of immobilization on proteolytic activity. Trypsin was coupled to the silanized samples by formation of Schiff's base linkages via glutaraldehyde. The nature of the interaction between trypsin and biomaterial was then probed by treatment with concentrated guanidine hydrochloride (GuHCl) and urea. Residual activity (following treatment with chaotropic agents) of trypsin immobilized on silanized Co-Cr-Mo was dependent both on the nature of the silane solution and on the type of chaotropic agent. Organic silanization with APS required a minimum density of approximately 49 NH2 per nm2 of nominal surface area (> 0.021 M APS) for residual activity of immobilized trypsin. For aqueous silanization, approximately 5.4 NH2/nm2 (0.51 M APS) resulted in maximal residual trypsin activity. Treatment with GuHCl removed more trypsin activity from Co-Cr-Mo samples silanized with organic solutions of APS than did treatment with urea. On the contrary, with aqueous silanization the samples possessed greater residual activity following treatment with GuHCl than following urea. Compared to simple adsorption with protein onto Co-Cr-Mo, both methods of silanization with APS resulted in superior residual immobilized enzyme activity.