Valproic acid selectively increases vascular endothelial tissue-type plasminogen activator production and reduces thrombus formation in the mouse.

Essentials Stimulating endogenous fibrinolysis could be a novel antithrombotic strategy. The effect of valproic acid on endothelial tissue plasminogen activator in mice was investigated. Valproic acid increased tissue plasminogen activator expression in vascular endothelium. Valproic acid reduced fibrin deposition and thrombus formation after vascular injury. SUMMARY: Background The endogenous fibrinolytic system has rarely been considered as a target to prevent thrombotic disease. Tissue-type plasminogen activator (t-PA) production is potently increased by histone deacetylase (HDAC) inhibitors in endothelial cells in vitro, but whether this translates into increased vascular t-PA production and an enhanced fibrinolytic capacity in vivo is unknown. Objectives To determine whether the HDAC inhibitor valproic acid (VPA) stimulates production of t-PA in the vasculature of mice, and whether VPA pretreatment affects fibrin deposition and clot formation after mechanical vessel injury. Methods Mice were injected with VPA twice daily for up to 5 days. t-PA mRNA, and antigen expression in the mouse aorta and the circulating levels of t-PA were determined. Fibrin and thrombus dynamics after mechanical vessel injury were monitored with intravital confocal microscopy. Potential effects of VPA on platelets and coagulation were investigated. Results and Conclusions We found that VPA treatment increased vascular t-PA production in vivo and, importantly, that VPA administration was associated with reduced fibrin accumulation and smaller thrombi in response to vascular injury, but still was not associated with an increased risk of bleeding. Furthermore, we observed that higher concentrations of VPA were required to stimulate t-PA production in the brain than in the vasculature. Thus, this study shows that VPA can be dosed to selectively manipulate the fibrinolytic system in the vascular compartment and reduce thrombus formation in vivo.

Introduction of embryonic stem cells into vein grafts reduces intimal hyperplasia in mice.

AIM: Atherosclerosis with its cardiovascular events including cardiac and peripheral ischemia represents the main cause of death in the developed countries. Although interventional treatments like percutaneous transluminal angioplasty or stents are increasingly applied for the treatment of peripheral arterial disease, they are not always technically applicable or durable and bypass surgery is needed. Compared to synthetic grafts, vein grafts show a better patency especially when used for the lower leg as well as a lower risk for infection compared to synthetic grafts. Still the long-term patency rates are unsatisfactory due to accelerated intimal hyperplasia, a thickening of the vessel wall. The aim of this study was to elucidate, if the implantation of embryonic stem cells into vein grafts can reduce the development of intimal hyperplasia in a mouse in vivo model. METHODS: In this study we implanted LacZ-tagged (ROSA26) murine embryonic stem cells into decellularized vein grafts. Control groups were: 1) untreated veins; 2) decellularized veins; 3) decellularized veins with gel and plastic film; and 4) decellularized veins with smooth muscle cells in gel surrounded by plastic film. Six weeks after insertion into the carotid artery of mice, the grafts were excised and analyzed immunohistochemically, morphologically, and by x-gal staining and compared to the control groups. The Mann-Whitney U test was used to compare groups. Statistical significance was indicated by a value of P<0.05. RESULTS: Decellularized veins with implanted stem cells showed significantly less intimal thickening compared to all control groups (intimal hyperplasia vs. luminal circumference mean±SD 7.3±3.5 µm, median 8 µm). The control groups: 1) untreated veins (60.3±25.5 µm, median 58.5 µm); 2) decellularized veins (53.9±22.4 µm, median 48.4 µm); 3) decellularized veins with gel and plastic film (70.6±22.4 µm, median 72.6 µm); and 4) decellularized veins with smooth muscle cells in gel surrounded by plastic film (73.5±18.1 µm, median 73.6 µm) all showed the same high degree of intimal hyperplasia. CONCLUSION: This study demonstrates that embryonic stem cells have a therapeutic competence to favourably modulate intimal hyperplasia in vivo.

Retention of atherogenic lipoproteins in the artery wall and its role in atherogenesis.

AIMS: In this review, we discuss the mechanisms behind the binding of low-density lipoproteins (LDL) to the arterial wall and how this interaction might be targeted to prevent atherosclerosis. DATA SYNTHESIS: An increasing body of evidence shows that accumulation of LDL in the vessel wall is a critical step in the development of atherosclerosis. The retained lipoproteins subsequently provoke an inflammatory response that ultimately leads to atherosclerosis. In the arterial wall, LDL binds ionically to proteoglycans in the extracellular matrix. In particular, proteoglycans with elongated glycosaminoglycan (GAG) chains seem to play a crucial role in this process. CONCLUSIONS: The LDL-proteoglycan interaction is a highly regulated process that might provide new therapeutic targets against cardiovascular disease.

Photodynamic therapy reduces intimal hyperplasia in prosthetic vascular bypass grafts in a pig model.

BACKGROUND: Bypass surgery has a failing frequency of 30% during the first year, mainly due to intimal hyperplasia (IH). This negative effect is most pronounced in artificial grafts. Photodynamic therapy (PDT) is a technique in which light activates photosensitizer dyes to produce free-radicals resulting in an eradication of cells in the vascular wall. The aim of this study was to determine the effectiveness of PDT to reduce IH in a preclinical porcine PTFE bypass model. MATERIAL AND METHODS: Ten pigs were used. After a pilot PDT dosimetry study (n=3) PTFE grafts were bilaterally placed into the circulation as bypasses from the common to the external iliac arteries (n=7). The right sides served as controls (C). Before implantation of the left grafts, the arterial connecting sites of the left distal anastomoses were PDT-treated. The arteries were pressurized at 180 mmHg for 5 minutes with the photosensitizer Methylene Blue (330 microg/ml), and thereafter endoluminally irradiated with laser light (lambda = 660 nm, 100 mW/cm(2), 150 J/cm(2)). After 4 weeks the specimens were retrieved and formalin fixed. Cross sections through the midportions of the distal anastomoses and the grafts were used for histology, immunohistochemistry to identify inflammatory cells and morphometric evaluation (n=7). RESULTS: No systemic side effects and no graft occlusions were noted. PDT-treated anastomoses showed reduced IH in the mid-portions of the anastomoses (Area of IH: microm(2)/microm graft: C: 6970+/-1536, PDT: 2734+/-2560; P<0.005) as well as in the grafts (C: 5391+/-4031, PDT: 777+/-1331; P<0.02). The number of inflammatory cells per microscopic field was increased after PDT (C: 24+/-16, PDT: 37+/-15; P<0.009). CONCLUSIONS: Adjuvant PDT, performed in an endovascular fashion, was a safe method to reduce prosthetic graftstenosis in a preclinical setting. This study underscores the clinical potential of PDT to inhibit the development of clinical bypass graftstenosis.

Healing of PTFE grafts in a pig model recruit neointimal cells from different sources and do not endothelialize.

OBJECTIVES: The aim of this study was to analyze the cellular sources for the neointima and the cell type that is lining the lumen in artificial grafts implanted in pigs. MATERIALS AND METHODS: We used polytetrafluoroethylene grafts as bypasses from the common to the external iliac arteries. The animals were sacrificed after 1, 4, 7, 14, 21, 30, 60 and 90 days. Morphological, immunohistochemical and electron microscope assessments were made. RESULTS: After 7 days a circumferential neoadventitia was formed. At day 14 isolated cellular islets of proliferating cells were observed on the luminal side of the graft without connection to the neoadventitia or the adjacent arteries. In the anastomotic regions at day 14 we observed an isolated neointima in contact with the adjacent artery. The cells lining the lumen had characteristics of both smooth muscle cells and endothelial cells. CONCLUSIONS: Our study suggests that in artificial porcine grafts, the perivascular tissue, the blood and the adjacent artery contribute to the formation of the neointima. The luminal surface is covered by a hybrid cell with both smooth muscle cell and endothelial cell properties.