Hemostatic effects of polymerized albumin particles bearing rGPIa/IIa in thrombocytopenic mice

Intravenous Hemostats: Foundation, Targeting, and Controlled-Release

Uncontrollable blood loss is the greatest cause of mortality in prehospital patients and the main source of disability and death in hospital care. Compared with external hemostats, intravenous hemostats are more appropriate for preventing and treating uncontrolled bleeding in vivo and large bleeding on the body surface. This Review initially establishes intravenous hemostats' response basis, including the coagulation mechanism, fibrinolytic pathway, and protein corona. Second, the study of advancement of intravenous hemostat targeting was expanded from two perspectives, cellular hemostatic agents and synthetic hemostatic agents. Meanwhile, after discussing the progress of controlled-release intravenous hemostats with platelets as the stimuli, this Review offers insight into the possibility of controlled-release intravenous hemostats with microenvironment as the stimuli, combining the studies of controlled-release targeted thrombolysis.

Synthetic Strategies for Engineering Intravenous Hemostats

While there are currently many well-established topical hemostatic agents for field administration, there are still limited tools to staunch bleeding at less accessible injury sites. Current clinical methods to restore hemostasis after large volume blood loss include platelet and clotting factor transfusion, which have respective drawbacks of short shelf life and risk of viral transmission. Therefore, synthetic hemostatic agents that can be delivered intravenously and encourage stable clot formation after localizing to sites of vascular injury are particularly appealing. In the past three decades, platelet substitutes have been prepared using drug delivery vehicles such as liposomes and PLGA nanoparticles that have been modified to mimic platelet properties. Additionally, structural considerations such as particle size, shape, and flexibility have been addressed in a number of reports. Since platelets are the first responders after vascular injury, platelet substitutes represent an important class of intravenous hemostats under development. More recently, materials affecting fibrin formation have been introduced to induce faster or more stable blood clot formation through fibrin cross-linking. Fibrin represents a major structural component in the final blood clot, and a fibrin-based hemostatic mechanism acting downstream of initial platelet plug formation may be a safer alternative to platelets to avoid undesired thrombotic activity. This Review explores intravenous hemostats under development and strategies to optimize their clotting activity.

Surgical Materials: Current Challenges and Nano-enabled Solutions

Surgical adhesive biomaterials have emerged as substitutes to sutures and staples in many clinical applications. Nano-enabled materials containing nanoparticles or having a distinct nanotopography have been utilized for generation of a new class of surgical materials with enhanced functionality. In this review, the state of the art in the development of conventional surgical adhesive biomaterials is critically reviewed and their shortcomings are outlined. Recent advancements in generation of nano-enabled surgical materials with their potential future applications are discussed. This review will open new avenues for the innovative development of the next generation of tissue adhesives, hemostats, and sealants with enhanced functionality for various surgical applications.

Mimicking adhesive functionalities of blood platelets using ligand-decorated liposomes

Platelet transfusion is used for treating a variety of bleeding complications. Natural platelet-based transfusion products have very short storage life (3-7 days) and high risks of biological contamination and side effects. Consequently, there is significant clinical interest in synthetic platelet-mimetic constructs that can promote hemostasis, while allowing convenient large-scale production, easy portability, long storage life, and minimal biological risks. To this end, research efforts are being directed toward particles that can amplify aggregation of activated platelets or can mimic platelet's ability to undergo adhesion to various vascular matrix proteins. Here, we report on a synthetic construct design that combines the mimicry of platelet's shear-dependent adhesion to vWF and shear-independent adhesion to collagen under flow, on a single particle. For this, we have used 150-nm-diameter liposomes as model particles and have decorated their surface simultaneously with vWF-binding and collagen-binding recombinant protein fragments or synthetic peptide motifs. We demonstrate in vitro that these surface-modified liposomes are able to adhere onto vWF surfaces in a shear-dependent fashion and onto collagen surfaces in a shear-independent fashion under flow. Moreover, when the vWF-binding and the collagen-binding were integrated on a single liposomal platform, the resultant heteromultivalent liposomes showed significantly enhanced adhesion to a vWF/collagen mixed surface compared to liposomes bearing vWF-binding or collagen-binding ligands only, as long as the ligand motifs did not spatially interfere with each other. Altogether, our results establish the feasibility of efficiently mimicking platelet's dual adhesion mechanisms on synthetic particles.

Peptide-decorated liposomes promote arrest and aggregation of activated platelets under flow on vascular injury relevant protein surfaces in vitro

Platelet-mimetic synthetic hemostats are highly attractive in transfusion medicine. To this end, past research reports have described particles that either amplify platelet aggregation or mimic platelet adhesion. However, a construct design that effectively combines both functionalities has not been reported. Here we describe the design of a liposomal construct simultaneously surface-decorated with three peptides (a vWF-binding peptide (VBP), a collagen-binding peptide (CBP), and an active platelet clustering cyclic-RGD (cRGD) peptide), that can integrate platelet-mimetic dual hemostatic activities of adhesion and aggregation. We first demonstrate that surface-immobilized cRGD-liposomes are capable of aggregating activated platelets onto themselves. Subsequently, we demonstrate that hetero-multivalent liposomes bearing VBP, CBP, and cRGD, when introduced in flow with ≈ 20,000 activated platelets per microliter, are capable of adhering to vWF/collagen surfaces and promoting the recruitment/aggregation of platelets onto themselves. We envision that optimizing this construct can lead to a highly refined synthetic hemostat design for potential application in transfusion medicine.

Ultrastructural analysis of thrombin-induced interaction between human platelets and liposomes carrying fibrinogen γ-chain dodecapeptide as a synthetic platelet substitute

BACKGROUND

The dodecapeptide HHLGGAKQAGDV (H12) in the carboxy-terminus of the fibrinogen γ-chain is a specific binding site of the ligand for platelet GPIIb/IIIa complex. We have evaluated liposomes carrying fibrinogen γ-chain dodecapeptide as a synthetic platelet substitute.

OBJECTIVES

We examined the interaction between human platelets and H12-liposomes during thrombin-induced activation using flow cytometry and electron microscopy (EM).

METHODS AND RESULTS

After thrombin-activation, a remarkable time-dependent increase in binding of the H12-liposomes to platelets was found by flow cytometry. A large-sized swollen open canalicular system (OCS) was observed in the spheroidal platelets from 60 sec to 5 min after thrombin-activation, but intact H12-liposomes were not evident by conventional EM. Cryoultramicrotomy and immunogold staining with anti-H12 antibody were successful in identifying the liposomes; they appeared as small particles with a unit membrane around 0.2 to 0.4 μm in diameter, and gold labels representing H12 were distributed homogeneously on the surface. Abundant H12-liposomes were localized not only on the surface membrane but also in the lumen of the large-sized swollen OCS in the platelets at 60 sec after thrombin-activation. The formation of the large-sized swollen OCS was inhibited by pre-incubation with unbound H12, EDTA or anti-GPIIb/IIIa antibody. In thrombin-induced platelet aggregates we observed electron-transparent areas between adherent platelets, in which abundant H12-liposomes were distributed.

CONCLUSIONS

We demonstrate morphologically that H12-liposomes bind to thrombin-activated platelets and accumulate between adherent platelets like fibrinogen, leading to large-scale aggregation.

Novel platelet substitutes: disk-shaped biodegradable nanosheets and their enhanced effects on platelet aggregation

We have studied biocompatible spherical carriers carrying a dodecapeptide, HHLGGAKQAGDV (H12), on their surface as platelet substitutes. This peptide is a fibrinogen γ-chain carboxy-terminal sequence (γ400-411) and specifically recognizes the active form of glycoprotein IIb/IIIa on activated platelets. Our purpose is to assess the possibility of making a novel platelet substitute consisting of disk-shaped nanosheets having a large contact area for the targeting site, rather than conventional small contact area spherical carriers. The H12 peptide was conjugated to the surface of the free-standing nanosheets made of biodegradable poly(d,l-lactide-co-glycolide) (PLGA). These H12-PLGA nanosheets were fabricated onto 3 μm disk-shaped patterned hydrophobic octadecyl regions on a SiO(2) substrate. By way of comparison, spherical H12-PLGA microparticles with the same surface area and conjugation number of H12 were also prepared. The resulting H12-PLGA nanosheets specifically interacted with the activated platelets adhered on the collagen surface at twice the rate of the H12-PLGA microparticles under flow conditions, and showed platelet thrombus formation in a two-dimensional spreading manner. Thus, H12-PLGA nanosheets might be a suitable candidate novel platelet alternative substitute for infused human platelet concentrates for the treatment of bleeding in patients with severe thrombocytopenia.

Toward 21st Century Blood Component Replacement Therapeutics: Artificial Oxygen Carriers, Platelet Substitutes, Recombinant Clotting Factors, and Others

In this brief overview, recent progress and current status of blood substitute research and development is summarized. Current blood substitute development efforts are focused on red blood cell substitutes but substitutes for platelets and other blood components are also in progress. Red cell substitutes currently in various stages of development are semi-synthetic or synthetic oxygen carriers that include "stealth" or "masked" red cells, hemoglobin-based oxygen carriers and perfluorocarbon-based oxygen carriers. Artificial platelets (or platelet substitutes) are in early stages of development and include human platelet fragments or particles of synthetic/semi-synthetic materials or recombinant human serum albumin coupled with platelet surface receptor fragments. Of note, some recombinant clotting factors (Factors VII, VIII, IX) have already been successfully developed and licensed for treatment of hemophilia. In addition, some future approaches and prospects of blood component replacement therapeutics are discussed.

Development of biodegradable nanosheets as nanoadhesive plaster

Sheet-shaped carriers having both obverse and reverse surfaces (thus, a large contact area for targeting a site and adhesive properties without any chemical cross-linker onto tissue surface) have several advantages as surgical dressings. These advantages include active targeting over spherically shaped carriers, which thus have an extremely small contact area for targeting sites. Here, we propose a novel methodology for preparation of a free-standing, ultra-thin, and biocompatible polymer nanosheet having heterosurfaces, fabricated through macromolecular assembly. In the context of biomedical applications, the targeted properties include injectable sheet-shaped drug carriers having precisely controlled size by exploiting micropatterned substrate, and giant polymer nanosheets composed of biocompatible polysaccharides. A huge aspect ratio, in excess of 106, is particularly applicable for novel surgical dressings. These biocompatible polymer nanosheets having heterosurfaces can thus be regarded as new biomaterials for minimally invasive treatment.

Prolonged hemostatic ability of polyethylene glycol?modified polymerized albumin particles carrying fibrinogen ?-chain dodecapeptide

BACKGROUND

Second-generation platelet (PLT) substitutes for treatment of bleeding were studied and the focus was on a dodecapeptide, HHLGGAKQAGDV (H12), which is a fibrinogen gamma-chain carboxy-terminal sequence (gamma 400-411) and exists only in a fibrinogen domain.

STUDY DESIGN AND METHODS

H12 was conjugated to the surface of polymerized albumin particles (polyAlb) modified with polyethylene glycol (PEG) chains to produce biocompatible particles (H12-PEG-polyAlb) that had prolonged blood circulation t((1/2)) and were more stable in vitro and in vivo compared with H12-polyAlb (not modified with PEG). H12-PEG-polyAlb was administered intravenously into thrombocytopenic rats and the t((1/2)) of the particles and the tail bleeding time were measured to evaluate the prolongation in the hemostatic effect.

RESULTS

H12-PEG-polyAlb particles modified with PEG prolonged the t((1/2)) and maintained specific binding ability to activated PLTs. The particles dose dependently shortened the tail bleeding time of thrombocytopenic rats 6 hours after injection.

CONCLUSION

H12-PEG-polyAlb may be a suitable candidate for treatment of bleeding into thrombocytopenic patients as an alternative to PLT concentrate transfusion.

Engineering blood cells and proteins as blood substitutes: A short review

In this brief review, basic principles and recent progresses on the development of therapeutic substitutes for major blood components are briefly discussed with primary focus on the red cell substitutes.

New strategy of platelet substitutes for enhancing platelet aggregation at high shear rates: cooperative effects of a mixed system of fibrinogen γ-chain dodecapeptide- or glycoprotein Ibα-conjugated latex beads under flow conditions

To construct platelet substitutes that have hemostatic properties over a wide range of shear rates, we used fibrinogen gamma-chain carboxy-terminal sequence HHLGGAKQAGDV (H12), which recognizes activated platelets at low shear rates, and a recombinant water-soluble moiety of the platelet glycoprotein (rGPIbalpha), which recognizes von Willebrand factor at high shear rates. Three kinds of samples were prepared for this purpose: H12-conjugated latex beads (H12-latex beads), rGPIbalpha-latex beads, and H12/rGPIbalpha-latex beads. These samples were evaluated in thrombocytopenia-imitation blood at various flow conditions. Based on ADP-induced platelet aggregation studies, the H12-latex beads significantly enhanced platelet aggregation via H12 binding with GPIIb/IIIa activated on the surface of activated platelets, whereas the rGPIbalpha-latex beads did not support platelet aggregation. In the case of the H12/rGPIbalpha-latex beads, the function of H12 was suppressed by steric hindrance from the larger rGPIbalpha bound to the latex bead. A mixture of the H12-latex beads and the rGPIbalpha-latex beads adhered to a collagen surface over a wide range of shear rates. In particular, at high shear rates, a cooperative effect was observed in the enhancement of platelet thrombus formation compared with H12-latex beads or rGPIbalpha-latex beads alone. We propose that a mixed system of H12- and rGPIbalpha-conjugated nanoparticles is a more effective platelet substitute than each of the beads used alone and has enhanced platelet aggregation properties.

Hemostatic effects of fibrinogen gamma-chain dodecapeptide-conjugated polymerized albumin particles in vitro and in vivo

BACKGROUND

Prototypes of platelet (PLT) substitutes have been studied and the focus was on a dodecapeptide, HHLGGAKQAGDV (H12), which is a fibrinogen gamma-chain carboxy-terminal sequence (gamma 400-411) and exists only in the fibrinogen domain.

STUDY DESIGN AND METHODS

H12 was conjugated to the surface of polymerized albumin particles (polyAlb) as biocompatible and biodegradable particles with a mean diameter of 260 +/- 60 nm, and the hemostatic ability of H12-conjugated polyAlb (H12-polyAlb) under flow conditions and thrombocytopenic rats have been studied.

RESULTS

H12-polyAlb enhanced the in vitro thrombus formation of activated PLTs on a collagen-immobilized plate when exposed to the flowing thrombocytopenic imitation blood. Furthermore, the analysis of the tail bleeding time of rats that were made thrombocytopenic by busulfan injection showed that H12-polyAlb had a hemostatic effect. Based on the bleeding time and the amount injected, the hemostatic capacity of 20 H12-polyAlb was estimated to correspond to that of one PLT.

CONCLUSION

These results were important first steps toward the development of PLT substitutes and indicated that H12-polyAlb may be a suitable candidate for an alternative to human PLT concentrates transfused into thrombocytopenic patients in the future.

Function of fibrinogen γ-chain dodecapeptide-conjugated latex beads under flow

In order to perform a fundamental study of platelet substitutes, novel particles that bound to activated platelets were prepared using two oligopeptides conjugated to latex beads. The oligopeptides were CHHLGGAKQAGDV (H12), which is a fibrinogen gamma-chain carboxy-terminal sequence (gamma 400-411), and CGGRGDF (RGD), which contains a fibrinogen alpha-chain sequence (alpha 95-98 RGDF). Both peptides contained an additional amino-terminal cysteine to enable conjugation. Human serum albumin was adsorbed onto the surface of latex beads (average diameter 1microm) and pyridyldisulfide groups were chemically introduced into the adsorbed protein. H12 or RGD peptides were then chemically linked to the modified surface protein via disulfide linkages. H12- or RGD-conjugated latex beads prepared in this way enhanced the in vitro thrombus formation of activated platelets on collagen-immobilized plates under flowing thrombocytopenic-imitation blood. Based on the result of flow cytometric analyses of agglutination, PAC-1 binding, antiP-selectin antibody binding, and annexin V binding, the H12-conjugated latex beads showed minimal interaction with non-activated platelets. These results indicate the excellent potential of H12-conjugated particles as a candidate for a platelet substitute.