Study on construction of nano tPA plasmid to prevent thrombosis after mechanical valve replacement in dogs

Retrovirus-Mediated Transfection of the Tissue-type Plasminogen Activator Gene Results in Increased Thrombolysis of Blood Clots

Tissue-type plasminogen activator (tPA) is involved in the lysis of blood clots. In this study, we attempted to target thrombolysis and enhance blood clot lysis by generating a construct (pLEGFP-N1-tPA) to integrate tPA gene into the genome of different cell lines. pLEGFP-N1-tPA construct was generated and used to target the tPA gene in different cell lines. The thrombolytic effects mediated by the supernatant from transfected HeLa cells and Linx cells were assessed using plasma thrombus plates. Furthermore, enhanced green fluorescent protein (EGFP), which was fused to the tPA gene in the pLEGFP-N1-tPA construct, was analyzed under the fluorescent microscope to assess tPA localization. We also monitored tPA activity and expression in the transfected cell lines. As part of the study, we successfully generated the pLEGFP-N1-tPA construct. The sequence of this construct was verified and the construct was subsequently used to generate the PT67/pLEGFP-N1-tPA cell line. The pLEGFP-N1-tPA construct was also used to transfect HeLa cells and Linx cells. We observed that supernatants from transfected cells were capable of lysing thrombi. In addition, tPA activity and tPA concentration were elevated in the latter supernatants and tPA was rapidly and stably expressed in the transfected cell lines. These results reveal a potentially important thrombolytic role for tPA-targeted gene therapy following cardiac valve replacement.

Thrombosis: Novel nanomedical concepts of diagnosis and treatment

Intravascular thrombosis, a critical pathophysiological feature of many cardiovascular disorders, leads to the formation of life-threatening obstructive blood clots within the vessels. Rapid recanalization of occluded vessels is essential for the patients’ outcome, but the currently available systemic fibrinolytic therapy is associated with low efficacy and tremendous side effects. Additionally, many patients are ineligible for systemic thrombolytic therapy, either due to delayed admission to the hospital after symptom onset, or because of recent surgery, or bleeding. In order to improve the treatment efficacy and to limit the risk of hemorrhagic complications, both precise imaging of the affected vascular regions, and the localized application of fibrinolytic agents, are required. Recent years have brought about considerable advances in nanomedical approaches to thrombosis. Although these thrombus-targeting imaging agents and nanotherapies are not yet implemented in humans, substantial amount of successful in vivo applications have been reported, including animal models of stroke, acute arterial thrombosis, and pulmonary embolism. It is evident that the future progress in diagnosis and treatment of thrombosis will be closely bound with the development of novel nanotechnology-based strategies. This Editorial focuses on the recently reported approaches, which hold a great promise for personalized, disease-targeted treatment and reduced side effects in the patients suffering from this life-threatening condition.

Cardiac-targeting transfection of tissue-type plasminogen activator gene to prevent the graft thrombosis and vascular anastomotic restenosis after coronary bypass

AIM

To observe the tissue-type plasminogen activator gene (t-PA) plasmid packaged with albumin nanoparticles crosslinked to albumin ultrasound microbubbles for targeting transfection to myocardium to prevent the graft thrombosis and vascular anastomotic restenosis after coronary bypass.

METHODS

A dog model of coronary bypass using the autoallergic saphenous vein as the graft was made. A highly expressive t-PA gene plasmid packaged with albumin nanoparticles crosslinked to albumin ultrasound microbubbles was constructed. Targeting myocardial transfection was performed with this gene vector under the aid of therapeutic ultrasound(1MHz, 1.5 w/cm2, 6minutes, intravenously) after the bypass. The expression of t-PA in myocardium was detected with a multiclonal antibody to t-PA by the indirect immunohistochemical method. Venous blood t-PA and D-dimer contents were tested before and 1, 2 and 4weeks after the operation. The effects of this gene vector on thrombosis of the grafts and the coronary intimal hyperplasia around the anastomotic stoma were observed using a routine pathological examination, a morphometry for intimal thickness and area and the immuno-histochemical stain with a monoclonal antibody to PCNA for estimating the intimal SMC proliferation.

RESULTS

The effective expression of t-PA protein by myocardium was obtained, followed by the persistent raises of blood t-PA and D-dimer 1, 2 and 4weeks after the transfection. Thrombosis of the grafts was successfully restrained. The expression of PCNA by coronary intimal vSMCs and intimal hyperplasia were remarkablely reduced.

CONCLUSION

This t-PA gene targeting vector could be used to prevent the dog thrombosis, which provided the experimental identification for prevention on human thrombotic diseases.

Gene therapy for cardiovascular disease mediated by ultrasound and microbubbles

Gene therapy provides an efficient approach for treatment of cardiovascular disease. To realize the therapeutic effect, both efficient delivery to the target cells and sustained expression of transgenes are required. Ultrasound targeted microbubble destruction (UTMD) technique has become a potential strategy for target-specific gene and drug delivery. When gene-loaded microbubble is injected, the ultrasound-mediated microbubble destruction may spew the transported gene to the targeted cells or organ. Meanwhile, high amplitude oscillations of microbubbles increase the permeability of capillary and cell membrane, facilitating uptake of the released gene into tissue and cell. Therefore, efficiency of gene therapy can be significantly improved. To date, UTMD has been successfully investigated in many diseases, and it has achieved outstanding progress in the last two decades. Herein, we discuss the current status of gene therapy of cardiovascular diseases, and reviewed the progress of the delivery of genes to cardiovascular system by UTMD.

Ultrasound-targeted transfection of tissue-type plasminogen activator gene carried by albumin nanoparticles to dog myocardium to prevent thrombosis after heart mechanical valve replacement

Background

There are more than 300,000 prosthetic heart valve replacements each year worldwide. These patients are faced with a higher risk of thromboembolic events after heart valve surgery and long-term or even life-long anticoagulative and antiplatelet therapies are necessary. Some severe complications such as hemorrhaging or rebound thrombosis can occur when the therapy ceases. Tissue-type plasminogen activator (t-PA) is a thrombolytic agent. One of the best strategies is gene therapy, which offers a local high expression of t-PA over a prolonged time period to avoid both systemic hemorrhaging and local rebound thrombosis. There are some issues with t-PA that need to be addressed: currently, there is no up-to-date report on how the t-PA gene targets the heart in vivo and the gene vector for t-PA needs to be determined.

Aims

To fabricate an albumin nano-t-PA gene ultrasound-targeted agent and investigate its targeting effect on prevention of thrombosis after heart mechanic valve replacement under therapeutic ultrasound.

Methods

A dog model of mechanical tricuspid valve replacement was constructed. A highly expressive t-PA gene plasmid was constructed and packaged by nanoparticles prepared with bovine serum albumin. This nanopackaged t-PA gene plasmid was further cross-linked to ultrasonic microbubbles prepared with sucrose and bovine serum albumin to form the ultrasonic-targeted agent for t-PA gene transfection. The agent was given intravenously followed by a therapeutic ultrasound treatment (1 MHz, 1.5 w/cm², 10 minutes) of the heart soon after valve replacement had been performed. The expression of t-PA in myocardium was detected with multiclonal antibodies to t-PA by the indirect immunohistochemical method. Venous blood t-PA and D-dimer contents were tested before and 1, 2, 4, and 8 weeks after the operation.

Results

The high expression of t-PA could be seen in myocardium with increases in blood t-PA and D-dimer contents and thrombosis was prevented 8 weeks after operation.

Conclusion

We successfully fabricated an albumin nano-t-PA gene ultrasound-targeted agent that could prevent dog thrombosis after mechanical heart valve replacement. Our study provides an experimental basis for prevention of human thrombosis-related diseases.