A monoclonal antibody recognizing the activation domain of protein C in its calcium-free conformation

Synthesis and In vivo Studies of Protein C-loaded Nanoparticles with PEO Modified Surfaces

Protein C-loaded nanoparticles coated with monomethoxypoly (ethylene oxide) (MPEO) were prepared by double emulsion/solvent evaporation using water-soluble biocompatible copolymers of MPEO and polylactide, as surfactants of the secondary emulsion. The nanoparticle preparation was optimized to obtain the best yield of encapsulated protein C and provide the greatest retention of its biological activity. The nanoparticles were characterized in terms of size, zeta potential, and thickness of the MPEO external layer. Protein C-loaded nanoparticles were injected into the bloodstream of guinea pigs and the protein concentration in plasma is measured as a function of time. After a rapid release corresponding to 20% of the injected protein, the protein plasma concentration progressively decreased and reached a value close to zero after 5 h. Consequently, the in vivo fate of the fluorescent nanoparticles coated with or without MPEO is studied. The uncoated nanoparticles were rapidly captured by the circulating granulocytes while the coated ones were not. The histological analysis of the spleen, 1 hour after injection, showed that the MPEO-coated particles were retained in this organ, while the uncoated ones were not captured.

Regulation of blood coagulation

The protein C anticoagulant pathway converts the coagulation signal generated by thrombin into an anticoagulant response through the activation of protein C by the thrombin-thrombomodulin (TM) complex. The activated protein C (APC) thus formed interacts with protein S to inactivate two critical coagulation cofactors, factors Va and VIIIa, thereby dampening further thrombin generation. The proposed mechanisms by which TM switches the specificity of thrombin include conformational changes in thrombin, blocking access of normal substrates to thrombin and providing a binding site for protein C. The function of protein S appears to be to alter the cleavage site preferences of APC in factor Va, probably by changing the distance of the active site of APC relative to the membrane surface. The clinical relevance of this pathway is now established through the identification of deficient individuals with severe thrombotic complications and through the analysis of families with partial deficiencies in these components and an increased thrombotic tendency. One possible reason that even partial deficiencies are a thrombotic risk is that the function of the pathway can be down-regulated by inflammatory mediators. For instance, clinical studies have shown that the extent to which protein C levels decrease in patients with septic shock is predictive of a negative outcome. Initial clinical studies suggest that supplementation with protein C may be useful in the treatment of acute inflammatory diseases such as sepsis.

Identification of protein C epitopes altered during its nanoencapsulation

Protein C is a plasmatic inhibitor which regulates the blood coagulation mechanism by modulating the anticoagulant response. The improvement of its bioavailability would be beneficial for the treatment of the disorders caused by its homozygous deficiency or by an other plasmatic inhibitor deficiency. In this context, the protein C encapsulation into biodegradable nanoparticles could be used to approach the problem. However, the method used to prepare the nanoparticles requires the use of ultrasonication and of an organic solvent such as methylene chloride which interferes with protein activity. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that neither ultrasonication nor methylene chloride, singly or in combination, led to protein C aggregation or cleavage. Thus, a binding study using an ELISA assay with four characterized monoclonal antibodies was carried out to identify the epitopes damaged by these experimental constraints. The correlation between the immunological assay and a functional one i.e. by the means of the assay of its anticoagulant activity (activated partial thromboplastin time) made it possible to show that protein C amino acids 166-169 of the activation peptide were probably altered after ultrasonication and methylene chloride treatment. Indeed, it is likely that these residues were no longer surface-exposed but had moved inside the protein core.