Summary. Background: The dodecapeptide HHLGGAK-QAGDV (H12), corresponding to the fibrinogen c-chain carboxy-terminal sequence (c400-411), is a specific binding site of the ligand for platelet GPIIb/IIIa complex. We have evaluated H12-coated nanoparticles (polymerized albumin or liposome) as platelet function-supporting synthetic products. Objectives: To strengthen the hemostatic ability of H12-coated particles as a platelet substitute, we exploited installation of a drug delivery function by encapsulating adenosine diphosphate (ADP) into liposomes [H12-(ADP)-liposomes]. Methods and results: Via selective interaction with activated platelets through GPIIb/IIIa, H12-(ADP)-liposomes were capable of augmenting agonist-induced platelet aggregation by releasing ADP in an aggregation-dependent manner. When intravenously injected into rats, liposomes were readily targeted to sites of vascular injury as analyzed on computed tomography. In fact, comparable to fresh platelets, liposomes exhibited considerable hemostatic ability for correcting prolonged bleeding time in a busulphan-induced thrombocytopenic rabbit model. In addition, the liposomes showed no activating or aggregating effects on circulating platelets in normal rabbits. Conclusion: H12-(ADP)-liposome may thus offer a promising platelet substitute, being made with only synthetic materials and exerting hemostatic functions in vivo via reinforcement of primary thrombus formation by residual platelets in thrombocytopenia at sites of vascular injury, but not in circulation.

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We studied prototypes of platelet substitutes that bear on their surface a dodecapeptide, HHLGGAKQAGDV (H12). The peptide is a fibrinogen gamma chain carboxy-terminal sequence (gamma400-411) and recognizes specifically the active form of glycoprotein (GP) IIb/IIIa on the surface of activated platelets. We conjugated H12 to the end of poly(ethylene glycol) chains on the surface of a phospholipid vesicle with an average diameter of 220 nm to prepare H12-PEG-vesicles. The half-life of the H12-PEG-vesicles was significantly prolonged by PEG modification, and the ability of H12 on the surface of the vesicle to recognize GPIIb/IIIa was maintained even though the surface was modified with PEG chains. The H12-PEG-veiscles enhanced the in vitro thrombus formation of platelets that were adhering to a collagen-immobilized plate, when thrombocytopenia-imitation blood was passed over the plate. Based on the flow cytometric analyses of PAC-1 binding and P-selectin expression, the H12-PEG-vesicles were shown not to cause platelet activation. Furthermore, the H12-PEG-vesicles dose-dependently shortened the tail bleeding time of thrombocytopenic rats. It was confirmed that the H12-PEG-vesicles had a hemostatic effect and may be a suitable candidate for an alternative to human platelet concentrates transfused into thrombocytopenic patients.

Ytterbium-doped solid-core photonic bandgap fiber amplifiers operating at the long-wavelength edge of the ytterbium gain band are reported. The low-loss bandgap transmission window is formed in the very low gain region, whilst outside the bandgap, large attenuation inhibits the exponential growth of amplified spontaneous emission in the huge-gain 1030-1100 nm region. Hence parasitic-lasing-free, high-power amplification with a marked efficiency is enabled. A 32 W output at 1156 nm with a 66% slope efficiency and 30 W output at 1178 nm with a 58% slope efficiency were successfully obtained. To our knowledge, these are the highest output powers generating from active photonic bandgap fibers, as well as from ytterbium-doped fiber lasers at these wavelengths.

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.

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Our purpose was to produce a platelet substitute that could enhance haemostatic ability using rabbits with severe thrombocytopenia. We have developed polymerized albumin particles (polyAlb) for treatment of bleeding and focused on a dodecapeptide, HHLGGAKQAGDV (H12), as a useful ligand for activated platelet. This sequence occurs only at the carboxy-terminus of the fibrinogen gamma-chain (gamma 400-411). H12 was conjugated to the surface of polyAlb modified with poly(ethylene glycol) (PEG) chains to produce blood-compatible particles (H12-PEG-polyAlb) that had prolonged blood residence time and enhanced stability in vitro and in vivo. The H12-PEG-polyAlb was administered intravenously to rabbits with severe thrombocytopenia, and the ear bleeding time was measured in order to evaluate the haemostatic effect. The H12-PEG-polyAlb significantly shortened the ear bleeding time of severely thrombocytopenic rabbits and showed no effect on the inhibition or promotion of endogenous and exogenous coagulation activities. Furthermore, we could assess the haemostatic capacity of the H12-PEG-polyAlb, based on the relationship between transfused platelet count and the bleeding time. The H12-PEG-polyAlb may be a suitable candidate for an alternative to human platelet concentrates infused to treat bleeding in patients with severe thrombocytopenia.

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