Von Willebrand Pigs Research Articles

Absence of incorporation of plasma von Willebrand factor into porcine platelet alpha-granules.

In order to study the relationship between plasma and platelet von Willebrand factor (vWF), we used an experimental model of crossed bone marrow transplantation (BMT) between SLA immunocompatible normal and homozygous von Willebrand (vWD) pigs. A normal pig received bone marrow from a vWD pig and a second pig with vWD was engrafted with marrow from a normal pig. Each recipient, after total irradiation of 10 Grays, received by a central catheter 10(10) monocellular bone marrow cells without immunosuppression. The animals were followed for 50 d and no graft rejection or graft-versus-host disease was observed. After aplasia occurring 3 weeks after BMT, white blood cells and platelets returned to normal. Before transplantation, in the vWD pig, vWFAg and vWF activity were not detected in plasma and in platelet and megakaryocyte alpha-granules. After transplantation with normal marrow, platelet vWFAg and platelet vWF activity wer normal and high molecular weight multimers and numerous tubular structures were present in alpha-granules. Before transplantation, the normal pig had normal plasma and platelet vWFAg-vWF activity, normal multimeric pattern, and the platelet and megakaryocyte alpha-granules displayed many tubular structures, eccentrically located in one of their poles, coinciding with immunogold staining vWFAg. After transplantation with homozygous vWD marrow, platelet and megakaryocyte alpha-granules lacked tubular structures. Alpha-granule immunogold staining for vWF was consistently negative, although plasma vWF was at a normal level. In conclusion, this study shows that, unlike other plasma proteins such as fibrinogen. vWF endocytosis does not occur from plasma to the platelet alpha-granules. Platelet and megakaryocyte vWF solely originates from megakaryocyte endogenous synthesis and is independent of plasma vWF.

Bone marrow transplantation between normal and von Willebrand pigs: An interesting model when studying the roles of the von Willebrand factor

Bone marrow transplantation between normal and von Willebrand pigs: An interesting model when studying the roles of the von Willebrand factor

Hemostatic Plug Formation in Normal and von Willebrand Pigs: The Effect of the Administration of Cryoprecipitate and a Monoclonal Antibody to Willebrand Factor

Hemostatic plug (HP) formation was investigated in the ear bleeding time incision in normal and von Willebrand pigs. HP volume was calculated by integrating the areas of serial sections. In normal pigs (n = 11), platelets immediately formed a layer on the surface of the cut channel. Platelet aggregates formed at the ends of transected vessels and gradually enlarged. Finally, all transected vessels were occluded by HP and bleeding stopped. In contrast, large HPs were formed in the incision in von Willebrand's disease (vWD) pigs (n = 4); these HPs did not cover the ends of the transected vessels, which continued to bleed, allowing the formation of large hemostatically ineffective platelet aggregates in the incision. Canals traversed these HPs, and bleeding from the open vessels may have continued through them. After infusion of cryoprecipitate into a vWD pig, the bleeding time shortened, and the morphological findings of the HPs were similar to those of normal pigs. In normal pigs (n = 3) infused with an anti-Willebrand factor monoclonal antibody, which prolonged the bleeding time, a large HP formed in the incision, similar to that observed in the vWD pig. The volume of the normal and vWD HPs increased with time. These in vivo findings suggest that Willebrand factor is involved in the localization of the HP to the damaged vessel and may also play a role in platelet-platelet interaction. A computerized morphometric technique was used for measuring the volume of the hemostatic plugs and the distance of sequential points on the perimeter of the HP from the center of selected bleeding vessels.

Hemostatic plug formation in normal and von Willebrand pigs: the effect of the administration of cryoprecipitate and a monoclonal antibody to Willebrand factor

Hemostatic plug (HP) formation was investigated in the ear bleeding time incision in normal and von Willebrand pigs. HP volume was calculated by integrating the areas of serial sections. In normal pigs (n = 11), platelets immediately formed a layer on the surface of the cut channel. Platelet aggregates formed at the ends of transected vessels and gradually enlarged. Finally, all transected vessels were occluded by HP and bleeding stopped. In contrast, large HPs were formed in the incision in von Willebrand's disease (vWD) pigs (n = 4); these HPs did not cover the ends of the transected vessels, which continued to bleed, allowing the formation of large hemostatically ineffective platelet aggregates in the incision. Canals traversed these HPs, and bleeding from the open vessels may have continued through them. After infusion of cryoprecipitate into a vWD pig, the bleeding time shortened, and the morphological findings of the HPs were similar to those of normal pigs. In normal pigs (n = 3) infused with an anti- Willebrand factor monoclonal antibody, which prolonged the bleeding time, a large HP formed in the incision, similar to that observed in the vWD pig. The volume of the normal and vWD HPs increased with time. These in vivo findings suggest that Willebrand factor is involved in the localization of the HP to the damaged vessel and may also play a role in platelet-platelet interaction. A computerized morphometric technique was used for measuring the volume of the hemostatic plugs and the distance of sequential points on the perimeter of the HP from the center of selected bleeding vessels.

Arteriosclerosis in normal and von Willebrand pigs: long-term prospective study and aortic transplantation study.

In a long-term prospective study, five normal control pigs and five pigs with homozygous von Willebrand's disease received a nonfatty diet from age 3 months to 4 years; then the aortas were analyzed. The fibrous arteriosclerotic plaques in the distal abdominal aortic region involved an average of 28% of the surface area in control pigs and only 7% of the surface area in pigs with von Willebrand's disease (P less than 0.01). In a subsequent study of 3-month-old pigs, the distal abdominal aortic segments from nine normal pigs were cross-transplanted with segments from nine other normal pigs (control study), and aortic segments from four normal pigs were transplanted into four host pigs with von Willebrand's disease (exchange study). All pigs received a 2% cholesterol diet for up to 6 months; then the transplanted aortic segments were analyzed. The donor normal aortic segments in the host normal pigs developed arteriosclerosis that involved an average of 20% of the surface; the endothelial fluorescent pattern of von Willebrand factor was identified. In contrast, the donor normal aortic segments in the host pigs with von Willebrand's disease had arteriosclerosis that involved an average of only 4% of the surface (P less than 0.01); the endothelial cell von Willebrand factor was not identified. The long-term prospective study indicates that pigs with von Willebrand's disease are resistant to the development of spontaneous arteriosclerosis. The aortic transplantation data are compatible with the hypothesis that the absence of von Willebrand factor in pigs with von Willebrand's disease may cause impairment of platelet-arterial wall interaction and resistance to arteriosclerosis.

Correction of Various Abnormalities in Cultured Porcine von Willebrand Endothelial Cells by Inhibition of Plasminogen-Dependent Protease Activity

AbstractCultured aortic endothelial cells (EC) from severe homozygous von Willebrand (vWd) pigs were compared to cultured normal pig EC at the same passage (passage 3, 5, 7, and 9). In vWd EC cultures, the quantity of immunologically identifiable (immunofluorescence staining), fibronectin-containing microfilaments was considerably decreased. The distribution and composition of the vWd subendothelial (SE) components was altered as indicated by quantitative polyacrylamide slab gel/autofluorography; total protein synthesis (incorporation of 14C-proline) and collagen synthesis (hydroxy 14C-proline-containing protein) was decreased and total protein and collagen turnover increased (two-fold). The interaction of washed pig platelets with vWd SE was decreased (1.27 × 103 ± 100 platelets/sq cm of SE for vWd versus 1.58 × 105 ± 1.32 × 104 platelets/sq cm of SE for normal) with no spread platelets associated with the vWd SE; and finally, plasminogen (Pmg) dependent protease activity was 2–3-fold higher (after 48 hr) than in normal EC cultures when assayed by growing cells directly in 12BI-labeled fibrin-coated chambers in the presence of added human Pmg. Short-term inhibition (3 passages) of this increased Pmg-dependent protease activity in vWd EC cultures with either 20% heat-deactivated Pmg-free fetal calf serum (FCS) or 20% heat-deactivated FCS plus 2 × 10–5M Trasylol resulted in the partial or complete correction of the structural and functional abnormalities in cultured vWd porcine ECs, described above. These inhibition data suggest that increased Pmg-dependent protease activity in cultured vWd porcine aortic ECs may be responsible, in part, for the expression of one or more of the SE-associated defects in porcine vWd ECs, as studied in a culture system, and may also play a role in the expression of the molecular defect(s) in porcine vWd in vivo.

The role of Willebrand factor in platelet - blood vessel interaction, including a discussion of resistance to atherosclerosis in pigs with von Willebrand's disease.

Von Willebrand pigs have all the manifestations of the severe human disease. The role of Willebrand antigen (VIII R:AG) and ristocetin cofactor (VIII: RWF) was assessed in these pigs by (1) transfusion and (2) "in vitro" bleeding time assay. The skin bleeding time became normal when the level of transfused Willebrand factor (VIII R:AG/RWF) was raised in the plasma above 30 U/dl. After single or repeated transfusions, skin capillary endothelium and platelets were still distinguished from normal by VIII R:AG deficiency. When incisions in excised porcine skin ("in vitro" bleeding time) were perfused with blood and plasma fractions, haemostasis occurred when plasmatic Willebrand factor exceeded 30 U/dl whether the skin or platelets came from normal or from von Willebrand pigs. The platelet plug occluding the skin incision contained VIII R:AG by immunofluorescence. Willebrand factor appears to coat surfaces and to serve as a platelet attachment protein. These bleeder pigs are resistant to atherosclerosis. If platelets are involved in early atherosclerotic lesions, the role of Willebrand factor in platelet - blood vessel interaction may be important.

Willebrand factor in hemostasis in the in vitro bleeding time

Heparinized porcine blood and plasma, at constant hydrostatic pressure, was allowed to flow through a 5-mm incision in a small piece of porcine skin. Changes in the exuded blood volume were measured, and the incision site was examined microscopically. When normal blood flowed through either normal or von Willebrand skin, the exuded blood volume decreased gradually and eventually stopped. Microscopic examination revealed a platelet plug in the incision site. This plug was positive for Willebrand factor when examined by immunofluorescence. In contrast, the blood from von Willebrand pigs continued to flow constantly, and a platelet plug was not seen. The delayed in vitro hemostasis in von Willebrand blood was corrected to the normal range by the addition of either normal plasma or partially purified Willebrand factor. Normal blood, in which the Willebrand factor was immunologically inhibited, showed delayed hemostasis. For this in vitro system, it appeared that plasmatic Willebrand factor played an essential role in hemostasis.

Willebrand Factor in Hemostasis in the In Vitro Bleeding Time

Heparinized porcine blood and plasma, at constant hydrostatic pressure, was allowed to flow through a 5-mm incision in a small piece of porcine skin. Changes in the exuded blood volume were measured, and the incision site was examined microscopically. When normal blood flowed through either normal or von Willebrand skin, the exuded blood volume decreased gradually and eventually stopped. Microscopic examination revealed a platelet plug in the incision site. This plug was positive for Willebrand factor when examined by immunofluorescence. In contrast, the blood from von Willebrand pigs continued to flow constantly, and a platelet plug was not seen. The delayed in vitro hemostasis in von Willebrand blood was corrected to the normal range by the addition of either normal plasma or partially purified Willebrand factor. Normal blood, in which the Willebrand factor was immunologically inhibited, showed delayed hemostasis. For this in vitro system, it appeared that plasmatic Willebrand factor played an essential role in hemostasis.

The von Willebrand Pig as a Model for Atherosclerosis Research

In order to evaluate a possible role played by platelets in the development of atherosclerosis, the aortas of 11 control pigs and 11 homozygous von Willebrand (vWd) pigs were examined for spontaneous atherosclerosis. Of the 11 normal pigs, 6 showed multiple atherosclerotic plaques with an intimal thickening of 63 to 130 micrometer. In contrast, none of the von Willebrand pigs had multiple plaques and only one showed a single lesion of more than 2 mm in diameter. In a prospective study 5 control pigs and 5 vWd pigs were given a high (2%) cholesterol diet from the age of 3 to 9 months. All of the controls developed atherosclerotic plaques. In 4 of the pigs the plaques exceeded 13% of the aortic surface with an intimal thickening of 50 to 390 micrometer. In contrast, only one of the vWd pigs developed atherosclerotic plaques which only involved 7% of the aortic surface. Most of the vWd pigs, however, developed non-atherosclerotic flat fatty lesions. These findings may be related to the impaired platelet arterial wall interaction in vWd. The vWd pigs seem to be an ideal model for atherosclerosis research.

Stability of porcine factor VIII

Citrated porcine plasmas, when incubated at 37°, lose their factor VIII activity as a function of time. This loss of activity is a first order process and the half-life of the factor VIII activity from von Willebrand (vWd) pigs (∼6 h) is shorter than the half-life of factor VIII from normals (∼ 14 h). After stimulation of a vWd pig by transfusion a factor VIII activity is found with an extremely short half-life (∼ 2.5 h). Carriers of porcine vWd disease have both a labile and stable fraction of factor VIII.