Individual propensity for thrombosis: comparison of venous and arterial circulations

Effects of arterial blood on the venous blood vessel wall and differences in percentages of lymphocytes and neutrophils between arterial and venous blood

Vascular sclerosis mostly occurs in arteries and is mainly related to anatomic structure and hemodynamics of artery. This study aimed to investigate effects of arterial blood on vein wall and explore differences of composition between arterial and venous blood.Ultrasound was used to examine the distal venous structure of arteriovenous fistula in uremia patients. Immunohistochemistry was used to study the pathology of the distal vein. Twelve patients were divided into control group and trial group. Patients received an arteriovenous fistula within 1 month in control group. Patients had undergone this surgery ≥2 years before in the trial group. Blood samples were collected from the aortic, arterial, and venous vessels of 51 patients who had taken coronary angiography and analyzed with blood routine rest, biochemical, and immunological measures to compare the differences of blood composition between artery and vein. This study was registered with the China Clinical Trial Center website under registration number ChiCTR-OOC-16008085.In the trial group, the vascular wall of distal veins of fistula were thickened and hardened. No significant differences of blood composition were found between the aortic and radial arterial blood. However, the differences in the percentages of lymphocytes and neutrophils between arterial and venous blood were significant (Pa = .0095, Pb = .01).Under smooth hemodynamic conditions, arterial blood caused hardening of the venous wall. Arterial and venous blood differed in the percentage of lymphocyte and neutrophils. This may contribute to the vascular sclerosis that is observed in arteries more often than veins.

MARCKS Signaling Differentially Regulates Vascular Smooth Muscle and Endothelial Cell Proliferation through a KIS-, p27kip1- Dependent Mechanism

Background

Overexpression of the myristolated alanine-rich C kinase substrate (MARCKS) occurs in vascular proliferative diseases such as restenosis after bypass surgery. MARCKS knockdown results in arrest of vascular smooth muscle cell (VSMC) proliferation with little effect on endothelial cell (EC) proliferation. We sought to identify the mechanism of differential regulation by MARCKS of VSMC and EC proliferation in vitro and in vivo.

Methods and Results

siRNA-mediated MARCKS knockdown in VSMCs inhibited proliferation and prevented progression from phase G₀/G₁ to S. Protein expression of the cyclin-dependent kinase inhibitor p27^kip1, but not p21^cip1 was increased by MARCKS knockdown. MARCKS knockdown did not affect proliferation in VSMCs derived from p27^kip1-/- mice indicating that the effect of MARCKS is p27^kip1-dependent. MARCKS knockdown resulted in decreased phosphorylation of p27^kip1 at threonine 187 and serine 10 as well as, kinase interacting with stathmin (KIS), cyclin D1, and Skp2 expression. Phosphorylation of p27^kip1 at serine 10 by KIS is required for nuclear export and degradation of p27^kip1. MARCKS knockdown caused nuclear trapping of p27^kip1. Both p27^kip1 nuclear trapping and cell cycle arrest were released by overexpression of KIS, but not catalytically inactive KIS. In ECs, MARCKS knockdown paradoxically increased KIS expression and cell proliferation. MARCKS knockdown in a murine aortic injury model resulted in decreased VSMC proliferation determined by bromodeoxyuridine (BrdU) integration assay, and inhibition of vascular wall thickening. MARCKS knockdown increased the rate of re-endothelialization.

Conclusions

MARCKS knockdown arrested VSMC cell cycle by decreasing KIS expression. Decreased KIS expression resulted in nuclear trapping of p27^kip1 in VSMCs. MARCKS knockdown paradoxically increased KIS expression in ECs resulting in increased EC proliferation. MARCKS knockdown significantly attenuated the VSMC proliferative response to vascular injury, but accelerated reestablishment of an intact endothelium. MARCKS is a novel translational target with beneficial cell type-specific effects on both ECs and VSMCs.

Platelet recruitment to venous stent thrombi

Thrombosis following venous stent placement is a morbid clinical outcome. Whether to target platelets or coagulation factors for venous stent thromboprophylaxis remains unclear. We sought to determine whether integrin α(IIb)β3 antagonism with lamifiban would inhibit platelet recruitment to venous stent thrombosis. Anti-thrombotic efficacy was compared between venous and arterial circulations. Pigs received either lamifiban (0.2 mg/kg bolus plus 0.2 mg/kg/h infusion; n = 6) or saline (n = 12). Carotid arteries were crush injured and then harvested 30 min later to provide an assessment of antithrombotic efficacy in the arterial circulation. Iliac venous stents were then deployed and thrombi allowed to propagate for 2 h before harvesting. Platelet deposition was measured by scintillation detection of autologous (111)In-platelets. Venous thrombi were quantified by weight and compared to platelet, Von Willebrand factor (VWF) and fibrinogen content. Arterial platelet deposition (×10(6)/cm(2)) was reduced >80% by lamifiban (398 ± 437) compared to controls (1,540 ± 883; p < 0.005). Lamifiban also reduced venous thrombus platelet deposition (139 ± 88 vs. 281 ± 167) however did not prevent thrombosis. In control animals, venous stent platelet deposition correlated with plasma fibrinogen content (R(2) = 0.29; p = 0.03). Fibrinogen content correlated directly with venous stent platelet deposition (p = 0.03) but not thrombus weight. Neither venous platelet deposition nor thrombus weights varied by VWF content. Platelet recruitment to venous stent thrombi occurs in part through the integrin α(IIb)β3 receptor. Unlike arterial thrombosis, inhibition of this receptor is insufficient to prevent venous stent thrombosis.

Inhibition of platelet-rich arterial thrombus in vivo: acute antithrombotic effect of intravenous HMG-CoA reductase therapy

OBJECTIVE

To test the hypothesis that statins will acutely inhibit platelet thrombus formation, intravenous lovastatin was assessed in our well-characterized porcine carotid injury model.

METHODS AND RESULTS

The first carotid artery was crush-injured and harvested after 30 minutes. Pigs then received intravenous lovastatin (100 microg/kg bolus+100 microg/kg/h infusion, n=6) or saline (n=11) before injury of the second carotid artery. Thrombus size was quantified by scintillation detection of autologous (111)In-platelets. Sequential carotid injury produced a thrombus more than 50% greater in volume in the second (3149+/-2053 x 10(6)/cm(2)) relative to the first injured artery (2081+/-1552 x 10(6)/cm(2); P=0.04) in control pigs. This augmentation was inhibited by intravenous lovastatin which acutely reduced platelet deposition (944+/-246 x 10(6)/cm(2)) relative to saline control (P=0.02). Flow chamber closure times increased on average by 2.45-fold in response to whole blood lovastatin incubation. Lovastatin (P<0.05) and simvastatin (P<0.05) reduced platelet dense granule secretion in vitro.

CONCLUSIONS

Sequential arterial injury augments the thrombotic response suggesting that the propensity for arterial thrombosis is at least partially acquired. This thrombotic augmentation can be acutely attenuated by intravenous lovastatin which may result from a pleiotropic impact on platelet function. These results appear to be a class effect of 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors.

Analysis of the spatial and temporal characteristics of platelet-delivered factor VIII-based clots

Normally factor (F) VIII is not expressed in megakaryocytes, but when human FVIII was transgenically expressed in murine megakaryocytes, it was stored in platelet alpha-granules and released at sites of injury. This platelet FVIII (pFVIII) is effective in correcting hemostasis, even in the presence of circulating inhibitors, so it offers a potential gene therapy strategy for hemophilia A. To understand clot development by pFVIII, we have examined clot response to laser injury in both cremaster arterioles and venules in FVIII(null) mice either infused with FVIII or transgenic for pFVIII. In both sets of vessels, pFVIII is at least as effective as infused FVIII. However, there are temporal and spatial differences in fibrin and platelet accumulation within clots depending on how FVIII is delivered. These differences may be related to the temporal and spatial distribution of the alpha-granular-released FVIII within the developing clot, and may explain the increased frequency and size of embolic events seen with pFVIII. These observations may not only have implications for the use of pFVIII in gene therapy for hemophilia A, but may also have physiologic consequences, explaining why many procoagulant factors are delivered both in the plasma and in platelet alpha-granules.