Hemostatic/fibrinolytic predictors of allograft coronary artery disease after cardiac transplantation

The role of fibrinolytic genes and proteins in the development of allograft vascular disease

BACKGROUND

We have previously shown that lack of plasminogen activator inhibitor-1 (PAI-1) expression in donor tissue greatly increases intimal proliferation (IP) after allogeneic transplantation. We sought to determine the relative role of PAI-1 and other fibrinolytic proteins in the development of IP.

METHODS

We used an abdominal aortic transplant model in mice to investigate IP in 3 groups of 6 recipients. In the isograft group, CBA/J strain mice were donors and recipients, donors for allograft group were C57BL/6J mice, and for the allograft/knockout group, C57BL/6J PAI-1 knockout mice. All groups received weekly injections of anti-CD8/CD4 monoclonal antibodies. IP was calculated at 50 days, and sections were analyzed for fibrinolytic proteins, messenger RNA (mRNA) and PAI-1 activity using immunohistochemistry (IHC), in situ hybridization (ISH), reverse transcription-polymerase chain reaction (RT-PCR), and Western blot analysis.

RESULTS

Significantly more IP developed in the allograft/knockout group vs the isograft (p < 0.001) and the allograft groups (p = 0.003). There was marked intimal expression of tissue plasminogen activator (tPA), urokinase PA (uPA), and uPA receptor (uPAR) proteins and mRNA in the allograft and allograft/knockout groups vs the isograft group. Allografts also showed significant intimal staining for PAI-1 protein and mRNA. RT-PCR demonstrated a stepwise increase in profibrinolytic protein mRNA from isograft to allograft to allograft/knockout groups, particularly uPA (p = 0.02) and uPAR (p = 0.016). Western blot data showed complementary findings. PAI-1 activity was persistently present in isograft and allograft animals, only. Intimas in allograft and allograft/knockout groups were primarily smooth muscle cells.

CONCLUSIONS

PAI-1 reduces IP by limiting smooth muscle cell activity, with little change in matrix composition likely by modulating profibrinolytic protein expression.

Endothelial replacement and angiogenesis in arteriosclerotic lesions of allografts are contributed by circulating progenitor cells

BACKGROUND

Endothelial regeneration and angiogenesis in the intima of the arterial wall are key events in the pathogenesis of transplantation arteriosclerosis. The traditional hypothesis that damaged endothelial cells are replaced by remaining cells of the donor vessel has been challenged by recent observations, but the cell origins of large arteries and microvessels are still not well established.

METHODS AND RESULTS

Aortic segments were allografted between Balb/c and TIE2-LacZ (C57BL/6) mice expressing beta-galactosidase (gal) in endothelial cells. beta-gal+ cells in TIE2-LacZ vessels grafted to Balb/c mice completely disappeared, whereas the positive cells found in Balb/c aorta allografted into TIE2-LacZ mice 4 weeks after surgery indicated a host origin. En face analysis of allograft vessels displayed a unique distribution of beta-gal+ cells on the surface at 3 days, 1 week, and 4 weeks. Interestingly, 35+/-19% beta-gal+ cells were found in arterial segments allografted into chimeric mice with TIE2-LacZ bone marrows. Furthermore, endothelial cells of microvessels within allografts had a beta-gal+ staining in the media at 1 week and in the neointimal lesions and adventitia at 4 weeks. Allograft studies in chimeric mice demonstrated that beta-gal+ cells of microvessels in transplant arteriosclerosis were derived from bone marrow progenitors.

CONCLUSIONS

We provide strong evidence that endothelial cells of neointimal lesions in allografts are derived from circulating progenitor cells and that bone marrow-derived progenitors are responsible for angiogenesis of the allograft, that is, the formation of microvessels in transplant arteriosclerosis.

Cardiomyopathy and heart transplantation in children

Cardiac transplantation has become a standard therapeutic option for certain disorders in which poor cardiac output without other surgical options exists in the face of maximized medical therapy. The most common disorder requiring transplantation is dilated cardiomyopathy, although other forms of cardiomyopathy (ie, restrictive cardiomyopathy, arrhythmogenic right ventricular dysplasia/cardiomyopathy, and hypertrophic cardiomyopathy with poor ventricular function) may require transplantation as well. In this review, the current indications and outcomes of heart transplantation in patients with cardiomyopathy are discussed.

Microvascular prothrombogenicity and transplant coronary artery disease

A major impediment for the long-term success of heart transplantation is the development of transplant coronary artery disease (CAD). Several risk factors for the development of transplant CAD are associated with the transformation of a normal thromboresistant microvasculature into a prothrombogenic microvasculature. Prothrombogenicity is characterized by loss of anticoagulation (i.e. loss of antithrombin), loss of fibrinolytic activity (i.e., loss of tissue plasminogen activator) and presence of endothelial activation (i.e. upregulation of endothelial intercellular adhesion molecule-1 and major histocompatibility class II antigen human leukocyte antigen-DR) in the arterial allograft microvasculature. Microvascular prothrombogenicity during the first trimester after transplantation is directly associated with subsequent development of transplant CAD. Although the mechanisms responsible for the loss of thromboresistant endothelium are unclear, the fact that changes in the anticoagulant, fibrinolytic, and activational status of endothelial cells may occur early after transplantation suggests a peritransplant phenomenon as an initiating event. Reducing prothrombogenicity of the cardiac microvasculature early after transplantation could slow the development of transplant CAD and significantly improve allograft survival.

Pathologic markers of allograft arteriopathy: insight into the pathophysiology of cardiac allograft chronic rejection

Transplant-associated coronary artery disease (CAD) is the principal limiting factor for the long-term survival of heart transplant patients. This review discusses early risk factors for the subsequent development of transplant-associated CAD. Early risk factors associated with a prothrombogenic microvasculature, such as deposition of microvascular fibrin, depletion of vascular tissue plasminogen activator, presence of endothelial activation of the allograft arterial tree, and loss of vascular antithrombin, as well as changes in circulation (ie, detectable serum cardiac troponin I and elevated serum soluble intercellular adhesion molecule-1 levels) are presented and discussed. New therapies that could improve the status of the allograft microvasculature and may prevent or mitigate the development of transplant-associated CAD are considered.

Immunohistochemical characterization of coronary thrombi in allograft vascular disease

BACKGROUND

Coronary thrombosis is a frequent complication of allograft vascular disease (AVD) in cardiac transplant recipients. No data are available on thrombus composition in these hearts.

METHODS

The present study aimed at characterizing thrombus components in coronary arteries from transplanted hearts with AVD, using single and double immunostain with anti-gpIIb-IIIa, anti-fibrin, and anti-endothelial antibodies. The pathologic series consists of 55 grafts survived longer than 2 months, and obtained from 55 patients deceased (n=44) or undergone repeat transplantation (n=11).

RESULTS

Mural thrombi were found in multiple segments of 75 of 440 total coronary vessels (17%) (recent in 33, organizing in 28, and organized in 14), whereas occlusive thrombi were found in 19 vessels (8 recent and 11 with multichannel pattern of organization). Recent and thin mural thrombi were mostly constituted of CD41a- and CD61-positive platelets; the amount of fibrin progressively increased with the increase of thrombus size. In organizing mural thrombi, gpIIb-IIIa immunostain was still present. Fibrin was the only identifiable thrombus component in old mural thrombi embedded within the intimal lesions. Recent occlusive thrombi immunoreacted both with anti-CD41a and anti-CD61 and with anti-fibrin antibodies, whereas organized occlusive thrombi with multichannel pattern exclusively immunoreacted with anti-fibrin antibodies. Double immunostain showed that mural thrombi were stratified on de-endothelized arterial segments.

CONCLUSIONS

Thrombus composition is related to both type and "age" of thrombus, with platelets as the early and major components of mural microthrombi at one end of the spectrum, and fibrin as the dominant component of occlusive thrombi at the other end.

Relationship of fibrin deposition in microvasculature to outcomes in cardiac transplantation

The development of transplant coronary artery disease (CAD) is directly associated with outcome in cardiac transplantation. The relationship between microvascular fibrin deposition early after transplantation and subsequent development of transplant CAD is discussed in this article. In this article the presence of microvascular fibrin and its association with other prothrombogenic changes within the cardiac microvasculature, such as loss of vascular antithrombin, depletion of arteriolar tissue plasminogen activator, and presence of arterial and arteriolar endothelium activation, as well as changes in circulation associated with prothrombogenic changes that have predictive value for subsequent transplant outcome are presented and discussed. Novel therapeutic approaches that may prevent the development of transplant CAD and consequently affect outcome are considered.