Leptin contributes to arterial thrombosis following vascular injury in vivo and these prothrombotic effects appear to be mediated through the platelet leptin receptor.

Background-Tissue factor initiates blood coagulation after atherosclerotic plaque disruption. Tissue factor pathway inhibitor (TFPI) inhibits tissue factor activity and may reduce thrombus formation in this setting. We evaluated the effect of heterozygous TFPI deficiency on the development of atherosclerosis and thrombosis in atherosclerosis-prone mice. Methods and Results-Mice with a combined heterozygous TFPI deficiency and homozygous apolipoprotein E deficiency (TFPI

Objective-The direct role of leptin in vascular disease remains controversial. The objective of this study was to examine the effects of leptin treatment on atherosclerosis and thrombosis in atherosclerotic-prone mice. Methods and Results-Sixteen-week-old, male apolipoprotein E-deficient mice were treated with injections of recombinant leptin (125 g per day IP; nϭ10) or vehicle (nϭ10) 4 and platelets. 5 Plasma leptin levels have also been correlated with cardiovascular complications in humans, an effect independent of body mass index and traditional risk factors. 6 -8 Nevertheless, the direct role of leptin in vascular disease remains controversial. Atherosclerotic mouse models with complete deficiency of leptin suggest that the absence of leptin might promote atherosclerosis. 9,10 However, these studies have been confounded by the extreme obesity and dyslipidemia that result from the loss of leptin-mediated central effects. 9,10 As a result, the direct effect of leptin on atherosclerosis has not yet been addressed. Therefore, to examine the direct role of leptin in atherosclerosis, we analyzed the effect of exogenous recombinant murine leptin on atherosclerosis using apolipoprotein E (apoE)-deficient mice.In addition, we tested the effects of chronic leptin therapy on thrombosis in these atherosclerotic-prone mice to determine whether potential metabolic improvements achieved with leptin therapy would outweigh the acute prothrombotic effect of leptin described previously. 11,12 Methods MiceMale apoE-deficient mice were purchased from the Jackson Laboratory (stock No. 002052; Bar Harbor, Maine) and provided Western chow (TD88137; Harlan Teklad) from 14 to 20 weeks of age. All procedures complied with the principles of laboratory and animal care established by the National Society for Medical Research and were approved by the University of Michigan committee on use and care of animals. Leptin TreatmentBeginning at 16 weeks of age, mice received 200 L intraperitoneal injections daily of either 125 g of recombinant murine leptin (R & D Systems) or vehicle control (nϭ10 per group). The dose of leptin chosen was based on a protocol used to achieve weight loss and fertility in leptin-deficient mice. 13 We determined that a 4-week duration of injections at this dose would be adequate to test the hypothesis that leptin promotes atherosclerosis in this particular model of hyperlipidemia. 14 http://atvb.ahajournals.org/ Downloaded from esthesia (100 mg/kg). Mice were perfused with saline and fixed using formalin with a 25-gauge needle inserted into the left ventricle at a rate of 1 mL/min. After formalin fixation, the arterial tree was meticulously dissected from the carcass and placed in 70% ethanol for Ն72 hours. The surface area occupied by atherosclerosis was then quantitated at the thoracic aorta and major branches, including the brachiocephalic, carotid, and subclavian arteries, via Oil Red O staining and quantitative morphometry, as described previously. 15 The lesion area was calculated for the control and treat...

Background— Activated protein C resistance due to factor V Leiden (FVL) is a common genetic risk factor for venous thrombosis in humans. Although the impact of FVL on the development of venous thrombosis is well established, its effect on arterial thrombosis and atherosclerosis is controversial. Methods and Results— To determine the effect of the FVL mutation on arterial thrombosis in the mouse, wild-type ( Fv +/+ ), heterozygous FVL ( Fv Q /+ ), and homozygous FVL ( Fv Q/Q ) mice underwent photochemical carotid arterial injury to induce occlusive thrombosis. Fv Q/Q mice formed occlusive thromboses 27±3 minutes (n=7) after the onset of injury, which was significantly shorter than that observed for Fv +/+ mice (56±7 minutes, n=9, P <0.01), whereas Fv Q /+ mice (41±7 minutes, n=5) were intermediate ( P =0.5, compared with Fv +/+ ). To determine the source of FVL relevant to the enhanced vascular thrombosis, bone marrow transplantation experiments were performed between Fv +/+ and Fv Q/Q mice. Fv Q/Q mice transplanted with Fv +/+ bone marrow formed occlusive thromboses at 35±5 minutes (n=7, P <0.05 compared with Fv +/+ mice), whereas Fv +/+ mice transplanted with Fv Q/Q bone marrow occluded at 59±7 minutes (n=6, P <0.001 compared with Fv Q/Q mice). To assess the effect of the FVL mutation on the development of atherosclerosis, Fv Q/Q mice were crossed with the atherosclerosis-prone apolipoprotein E (ApoE)–deficient strain ( ApoE −/− ) to generate Fv Q/Q ,ApoE −/− mice. By 52 weeks of age, Fv Q/Q ,ApoE −/− mice (n=8) had developed more aortic atherosclerosis (40±6% lesion area) compared with Fv +/+ ,ApoE −/− mice (15±3% lesion area; n=12, P <0.02). Conclusions— In conclusion, homozygosity for the FVL mutation in mice leads to enhanced arterial thrombosis and atherosclerosis. The source of the FVL leading to accelerated thrombosis appears to be circulating, non–platelet-derived plasma FVL.