β-radiation reduces the reactivity of extracellular matrix proteins in intravascular brachytherapy (IVBT), resulting in decreased platelet adhesion

BACKGROUND

Intravascular Brachytherapy as a tool to reduce restenosis is thought to alter vascular wall biology and vessel wall protein function. Platelet accumulation is also indeed important in the genesis of restenosis. We examine the in vitro effects of beta-radiation on the certain vessel wall extra cellular matrix proteins. We hypothesized that vessel wall (proteins) had become less prone to thrombosis.

METHODS

We examined platelet adhesion to 20-Gy beta radiation treated extra cellular matrix proteins under flow conditions. Platelet flow adhesion was evaluated or quantified by image analysis, aggregation size analysis using the Watershed program and real-time fluorescence images of thrombus formation. The effect of beta radiation on vWF was further showing by measuring the binding of domain-specific antibodies to radiation treated vWF.

RESULTS

20-Gy beta radiation significantly decreased platelet adhesion to extra cellular matrix protein; vWF and collagen Type III and had no effect on the adhesion upon fibrinogen and fibronectin. The beta-radiation affected mostly the AI, A2 and A3 domains of the vWF molecule on the surface, whereas the D'-D3 and B-C1 domains on the surface remain unaffected and suggesting a significant decrease in vWF binding capacity to the GPIb, heparin and collagen ligands.

CONCLUSION

Beta radiation treatment can alter the reactivity of the certain vessel wall extra cellular matrix proteins, in particular vWF and collagen. The vessel wall may become less prone to platelet adhesion, which results in decrease thrombus formation. It might help to reduce the onset of acute coronary occlusion after the intervention.

Thrombotic molecule expression in cerebral vascular malformations

Thrombosis is an important end-point in the obliteration of vascular malformations after radiosurgery. The aim of this study was to investigate the expression of thrombotic molecules in arteriovenous malformations (AVMs) and cavernous malformations (CMs), and in AVMs after radiosurgery. Fresh-frozen surgical specimens from 18 AVMs (including three that had previously been treated with radiosurgery), seven CMs, and three control specimens were studied. The expression of tissue factor, thrombomodulin and von Willebrand factor (vWF) were examined using immunofluorescence. Thrombomodulin and vWF were expressed in the endothelium of all specimens, while tissue factor was predominately found in the perivascular region and vascular adventitia. Previous treatment of AVMs with either radiation or embolisation did not significantly alter the intensity of expression. In some irradiated lesions, vessels were found with absent endothelial vWF staining and exposed tissue factor. This study has demonstrated that loss of the endothelium and exposure of underlying tissue factor occurs in irradiated AVMs. There were no significant differences in the expression of these thrombotic molecules in vascular malformations when compared to control vessels. While no long-term alterations in antigen expression were observed after radiosurgery, further work may elucidate the nature of the immediate response to irradiation.

Effects of a new pathogen-reduction technology (Mirasol PRT) on functional aspects of platelet concentrates

BACKGROUND

Several strategies are being developed to reduce the risk of pathogen transmission associated with platelet (PLT) transfusion.

STUDY DESIGN AND METHODS

The impact of a new technology for pathogen reduction based on riboflavin plus illumination (Mirasol PRT, Navigant Biotechnologies, Inc.) at 6.2 and 12.3 J per mL on functional and biochemical characteristics of PLTs was evaluated. PLT concentrates (PCs) obtained by apheresis were treated with Mirasol PRT and stored at 22 degrees C. Modifications in major PLT glycoproteins (GPIbalpha, GPIV, and GPIIb-IIIa), adhesive ligands (von Willebrand factor [VWF], fibrinogen [Fg], and fibronectin), activation antigens (P-selectin and LIMP), and apoptotic markers (annexin V binding and factor [F]Va) were analyzed by flow cytometry. Adhesive and cohesive PLT functions were evaluated with well-established perfusion models. Studies were performed on the preparation day (Day 0) and during PCs storage (Days 3 and 5).

RESULTS

Levels of glycoproteins remained stable during storage in PCs treated with 6.2 J per mL pathogen reduction technology (PRT) and similar to those observed in nontreated PCs. When 12.3 J per mL PRT was applied, however, levels of GPIbalpha moderately decreased on Days 3 and 5. VWF, Fg, and FVa were not modified in their expression levels, either by treatment or by storage period. Fibronectin appeared more elevated in all PRT samples. A progressive increase in P-selectin and LIMP expression and in annexin V binding was observed during storage of PRT-treated PCs. Functional studies indicated that 6.2 J per mL Mirasol PRT-treated PLTs preserved adhesive and cohesive functions to levels compatible with those observed in the respective control PCs.

CONCLUSION

PLT function was well preserved in PCs treated with 6.2 J per mL Mirasol PRT and stored for 5 days.

The NFY transcription factor mediates induction of the von Willebrand factor promoter by irradiation

Ionizing irradiation in patients is proposed to cause thrombus formation. An increase in von Willebrand factor secretion in response to irradiation is a major contributing factor to thrombus formation. We have previously reported that the increased VWF secretion in response to irradiation is mediated at the transcriptional level. The VWF core promoter fragment (sequences -90 to +22) was shown to contain the necessary cis-acting element(s) to mediate the irradiation response of the VWF gene. Here we report that a CCAAT element in the VWF promoter is the cis-acting element necessary for irradiation induction and that the NFY transcription factor interacts with this element. These analyses demonstrate that inhibition of NFY's interaction with the CCAAT element abolishes the irradiation induction of the VWF promoter. These results provide a novel role for NFY and add this factor to the small list of irradiation-responsive transcription factors. Coimmunoprecipitation experiments demonstrated that NFY is associated with the histone acetylase P/CAF in vivo and that irradiation resulted in an increased association of NFY with coactivator P/CAF. We propose that irradiation induction of the VWF promoter involves a mechanism resulting in increased recruitment of the coactivator P/CAF to the promoter via the NFY transcription factor.

Glycoproteins Ib and IIb/IIIa in the quality assessment of platelet concentrates during storage

We have previously shown that levels of soluble glycocalicin (GC) in plasma supernatants derived from units of platelet concentrates (PC) increase progressively during storage. We now report further studies which show that the levels of both microparticle-bound and soluble GC in PC during storage are influenced by exposure of PC samples to EDTA and treatment of PC packs with ultraviolet B (UVB) irradiation. EDTA leads to a significant increase in the release of microvesicle-bound and soluble GC, while UVB irradiation leads to a dose- and rate-dependent increase in GC release. Paradoxically, UVB leads to an unexpected decrease in supernatant levels of von Willebrand factor (vWf) during storage which contrasts with its increase in untreated, stored PC. Moreover, an increase in GC release during storage is associated with a corresponding decrease in platelet size as determined by measurement of mean platelet volume (MPV) in citrated PC. The GC release is significantly correlated with standard platelet functional tests and other new generation tests such as dMPV and supernatant levels of vWf. In addition, preliminary results show the presence of microparticle-bound and soluble glycoprotein (Gp) IIb/IIIa in the supernatant plasma of stored PC. Our results suggest that supernatant levels of GpIb, GpIIb/IIIa, and vWf, together with alteration in MPV, provide essential new informative parameters for quality assessment of PC.

The effect of radiation therapy on von Willebrand factor in patients with angiosarcoma

Radiation damages endothelial cells (EC) of malignant and normal tissues. Shortly after radiation injury platelet thrombi cause small vessel obstruction. Radiation doses of 20 Gy or higher release von Willebrand factor (VWF) from cultured human umbilical vein EC. Angiosarcoma (AS) is a vascular tumor with abnormal appearing EC which have detectable cytoplasmic VWF. We examined the effect of radiation therapy on VWF in three patients with AS. Each patient's malignant tissue was demonstrated to have cytoplasmic VWF present. Venous blood samples were drawn immediately before and at weekly intervals during treatment. Patient 1 received 80 Gy over 6 weeks and had no alterations in the VWF. Patient 2 received 64 Gy over 6 weeks and was noted to have loss of the high molecular weight multimers of VWF without loss of FVIII:C, VW: RIST, or von Willebrand antigen activity (VW:Ag). Patient 3 was treated with 64.4 Gy over 9 weeks and had a disproportionate increase of the VW: Ag and VW: RIST to FVIII: C. This returned to normal after completion of therapy. These changes were minimal and might be explained by either limited local release or no increased release of VWF from the irradiated tissue. The minimally abnormal multimeric pattern in patient 2 may be due to the release of an abnormal VWF in normal amounts or small amounts of proteolysis. The alteration in the VW: RIST and VW: Ag to FVIII: C ratio can be explained by activated coagulation secondary to radiation injury.

Irradiation induces release of von Willebrand protein from endothelial cells in culture

Human umbilical vein endothelial cells in tissue culture were irradiated with doses between 0 and 40 Gy, and the released von Willebrand (vW) protein and that which remained associated with the cells was quantitated. Doses of 20 Gy and higher produced a statistically significant increase in amount of vW protein secreted. This release was present whether the cells were labeled continuously throughout the experiment or just prelabeled before irradiation. An increase in fibronectin secretion was not observed. The release response to radiation was slow, reaching significance close to 24 hours after irradiation. The release of vW protein was not due to cell lysis, because the secreted vW protein contained very little of the large 260-kilodalton vW precursor subunit present in cell lysates and the cells appeared intact by immunofluorescence staining.