Whole blood aggregation, coagulation, and markers of platelet activation in diet-induced diabetic C57BL/6J mice

Effects of Salvia hispanica L. (chia) seed on blood coagulation, endothelial dysfunction and liver fibrosis in an experimental model of Metabolic Syndrome

The aim of this study was to analyze blood coagulation, endothelial dysfunction and liver fibrosis in an experimental model of Metabolic Syndrome (MS) induced by chronic administration of a sucrose-rich diet (SRD) and to evaluate the effects of chia seed as a therapeutic strategy. Male Wistar rats were fed with a reference diet (RD) - 6 months - or a SRD - 3 months. Then, the last group was randomly divided into two subgroups. One subgroup continued receiving the SRD for up to 6 months and the other was fed with a SRD where whole chia seed was incorporated as the source of dietary fat for the next 3 months (SRD + CHIA). Results showed that rats fed a SRD for a long period of time develop dyslipidemia, visceral adiposity, insulin resistance, and a hypercoagulable and hypofibrinolytic basal state. Hepatic VCAM-1 (main adhesion molecules involved in endothelial dysfunction) expression was significantly increased. In addition, the SRD group presented hepatic steatosis, a significant increase in interstitial collagen deposition and hydroxyproline content. Liver TGF-β1 (a key cytokine involved in fibrogenesis) levels increased and a negative correlation with PPARα protein mass levels was found. The administration of chia seed for 3 months reversed dyslipidemia, visceral adiposity and insulin resistance. Platelet count, coagulation parameters and plasma fibrinogen levels were normalized. In the liver tissue, VCAM-1 expression, steatosis, interstitial collagen deposition and the hydroxyproline content decreased. TGF-β1 expression was decreased and this was associated with an increase in the PPARα protein levels. The present study showed new aspects in the progression from liver steatosis to fibrosis in dyslipidemic insulin-resistant rats chronically fed a sucrose-rich diet. Chia seed supplementation could be used as a functional food and a potential dietary strategy to prevent or ameliorate disorders related to atherothrombotic cardiovascular events and NASH.

Constitutive activation of AMPK α1 in vascular endothelium promotes high-fat diet-induced fatty liver injury: role of COX-2 induction

BACKGROUND AND PURPOSE

AMP-activated protein kinase (AMPK), an important regulator of energy metabolism, comprises three (α, β and γ) subunits, each with a unique tissue distribution. As AMPK has a wide range of protein and gene targets, defining its role has been difficult. Here, we have studied a transgenic mouse model overexpressing the constitutively active α1 subunit of AMPK in endothelial cells (EC-AMPK) to elucidate its role in energy homeostasis.

EXPERIMENTAL APPROACH

Wild-type and EC-AMPK mice were fed with a high fat diet for 16 weeks. Drugs (or vehicles) were given daily by oral gavage. Body weight, fat mass composition, glucose and lipid levels were monitored regularly. Tissues including aortae and liver were collected for quantitative RT-PCR, Western blotting, elisa, histological and biochemical evaluations.

KEY RESULTS

Compared with wild-type animals, high fat diet caused more severe metabolic defects in EC-AMPK mice, which exhibited increased body weight and fat mass, elevated blood pressure, augmented glucose and lipid levels, impaired glucose tolerance, hepatomegaly and steatohepatitis. Constitutive activation of AMPK α1 in endothelial cells induced COX-2 expression and arterial inflammation. Genes involved in lipid metabolism were down-regulated in aortae and livers of EC-AMPK mice. Chronic treatment with selective COX-2 inhibitors, celecoxib or nimesulide, significantly ameliorated arterial inflammation, steatohepatitis and hyperlipidaemia in EC-AMPK mice, without altering their blood pressure or clotting.

CONCLUSIONS AND IMPLICATIONS

Constitutive activation of endothelial AMPK α1 promotes vascular inflammation and the development of obesity-induced fatty livers largely via induction of COX-2.

Zucker Diabetic Fatty rats exhibit hypercoagulability and accelerated thrombus formation in the Arterio-Venous shunt model of thrombosis

INTRODUCTION

Diabetes is a significant risk factor for thrombosis. The present study aimed at assessing coagulability, platelet reactivity, and thrombogenicity of the diabetic female Zucker Diabetic Fatty (ZDF) rat model and its relevance in studying antithrombotic mechanisms.

MATERIALS AND METHODS

The basal coagulant state in ZDF rats was evaluated by clotting times, thromboelastography, and thrombin generation assay. A 14-day treatment with dapagliflozin in ZDF rats was pursued to investigate if glycemic control can improve coagulability. Thrombus formation in the Arterio-Venous (A-V) shunt model and the FeCl3-induced arterial thrombosis model was studied, with the antithrombotic effect of apixaban in the former model further investigated.

RESULTS

ZDF rats exhibited significantly shortened clotting times, enhanced thrombin generation, and decreased fibrinolysis at baseline. Effective glycemic control achieved with dapagliflozin did not improve any of these parameters. ZDF rats displayed accelerated thrombus formation and were amenable to apixaban treatment in the A-V shunt model albeit with less sensitivity than normal rats. ZDF rats exhibited less platelet aggregation in response to ADP, collagen and PAR-4, and attenuated thrombotic response in the FeCl3 model.

CONCLUSIONS

ZDF rats are at a chronic hypercoagulable and hypofibrinolytic state yet with compromised platelet reactivity. They display accelerated and attenuated thrombosis in the A-V shunt and FeCl3 model of thrombosis, respectively. Results shed new light on the pathophysiology of the ZDF rat model and illustrate its potential value in translational research on anticoagulant agents in diabetics. Caution needs to be exerted in utilizing this model in assessing antiplatelet mechanisms in diabetes-associated atherothrombosis.

Ectonucleotide triphosphate diphosphohydrolase-1 (CD39) mediates resistance to occlusive arterial thrombus formation after vascular injury in mice

Modulation of purinergic signaling, which is critical for vascular homeostasis and the response to vascular injury, is regulated by hydrolysis of proinflammatory ATP and/or ADP by ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD-1; CD39) to AMP, which then is hydrolyzed by ecto-5'-nucleotidase (CD73) to adenosine. We report here that compared with littermate controls (wild type), transgenic mice expressing human ENTPDase-1 were resistant to the formation of an occlusive thrombus after FeCl(3)-induced carotid artery injury. Treatment of mice with the nonhydrolyzable ADP analog, adenosine-5'-0-(2-thiodiphosphate) trilithium salt, Ado-5'-PP[S], negated the protection from thrombosis, consistent with a role for ADP in platelet recruitment and thrombus formation. ENTPD-1 expression decreased whole-blood aggregation after stimulation by ADP, an effect negated by adenosine-5'-0-(2-thiodiphosphate) trilithium salt, Ado-5'-PP[S] stimulation, and limited the ability to maintain the platelet fibrinogen receptor, glycoprotein α(IIb)/β(3), in a fully activated state, which is critical for thrombus formation. In vivo treatment with a CD73 antagonist, a nonselective adenosine-receptor antagonist, or a selective A(2A) or A(2B) adenosine-receptor antagonist, negated the resistance to thrombosis in transgenic mice expressing human ENTPD-1, suggesting a role for adenosine generation and engagement of adenosine receptors in conferring in vivo resistance to occlusive thrombosis in this model. In summary, our findings identify ENTPDase-1 modulation of purinergic signaling as a key determinant of the formation of an occlusive thrombus after vascular injury.

Mannose-binding lectin-associated serine protease-1 is a significant contributor to coagulation in a murine model of occlusive thrombosis

Bleeding disorders and thrombotic complications constitute a major cause of death and disability worldwide. Although it is known that the complement and coagulation systems interact, no studies have investigated the specific role or mechanisms of lectin-mediated coagulation in vivo. FeCl(3) treatment resulted in intra-arterial occlusive thrombogenesis within 10 min in wild-type (WT) and C2/factor B-null mice. In contrast, mannose-binding lectin (MBL)-null and MBL-associated serine protease (MASP)-1/-3 knockout (KO) mice had significantly decreased FeCl(3)-induced thrombogenesis. Reconstitution with recombinant human (rh) MBL restored FeCl(3)-induced thrombogenesis in MBL-null mice to levels comparable to WT mice, suggesting a significant role of the MBL/MASP complex for in vivo coagulation. Additionally, whole blood aggregation demonstrated increased MBL/MASP complex-dependent platelet aggregation. In vitro, MBL/MASP complexes were captured on mannan-coated plates, and cleavage of a chromogenic thrombin substrate (S2238) was measured. We observed no significant differences in S2238 cleavage between WT, C2/factor B-null, MBL-A(-/-), or MBL-C(-/-) sera; however, MBL-null or MASP-1/-3 KO mouse sera demonstrated significantly decreased S2238 cleavage. rhMBL alone failed to cleave S2238, but cleavage was restored when rMASP-1 was added to either MASP-1/-3 KO sera or rhMBL. Taken together, these findings indicate that MBL/MASP complexes, and specifically MASP-1, play a key role in thrombus formation in vitro and in vivo.

Microvascular responses to cardiovascular risk factors

Hypertension, hypercholesterolemia, diabetes, and obesity are among a growing list of conditions that have been designated as major risk factors for cardiovascular disease (CVD). While CVD risk factors are well known to enhance the development of atherosclerotic lesions in large arteries, there is also evidence that the structure and function of microscopic blood vessels can be profoundly altered by these conditions. The diverse responses of the microvasculature to CVD risk factors include oxidative stress, enhanced leukocyte- and platelet-endothelial cell adhesion, impaired endothelial barrier function, altered capillary proliferation, enhanced thrombosis, and vasomotor dysfunction. Emerging evidence indicates that a low-grade systemic inflammatory response that results from risk factor-induced cell activation and cell-cell interactions may underlie the phenotypic changes induced by risk factor exposure. A consequence of the altered microvascular phenotype and systemic inflammatory response is an enhanced vulnerability of tissues to the deleterious effects of secondary oxidative and inflammatory stresses, such as ischemia and reperfusion. Future efforts to develop therapies that prevent the harmful effects of risk factor-induced inflammation should focus on the microcirculation.

Enhanced platelet reactivity and thrombosis in Apoe-/- mice exposed to cigarette smoke is attenuated by P2Y12 antagonism

INTRODUCTION

Smoking increases the risk of acute arterial thrombosis, including myocardial infarction, likely due to multi-factorial effects on the vasculature. Heightened platelet reactivity may be among the adverse effects of smoke exposure.

METHODS

To examine the effects of smoke exposure on platelet function in an atherosclerotic environment, Apoe-deficient female mice, maintained on a Western diet, were exposed (4 hrs/d, 5 d/wk) to sidestream cigarette smoke in a whole-body exposure chamber for 12 weeks. A separate group of wild type C57BL/6J mice were also exposed to smoke in an identical fashion.

RESULTS

In comparison to control Apoe-/- mice exposed to filtered ambient air, smoke-exposed Apoe-/- mice displayed a 1.8±0.3 fold enhanced ADP-induced fibrinogen binding ex vivo (P<0.001) and had a shorter time to thrombotic occlusion following ferric chloride injury of the carotid artery (median time to thrombosis of 8 vs. 13 min; P=0.015). Administration of the direct-acting P2Y12 antagonist cangrelor blunted ex vivo fibrinogen binding and attenuated thrombosis (median time 20 min) in Apoe-/- mice exposed to sidestream smoke. The effects of smoke exposure required a proatherosclerotic background, as wild-type C57Bl/6J mice exposed to smoke displayed similar fibrinogen binding and thrombotic occlusion times as did control mice.

CONCLUSIONS

Our results demonstrate that exposure to smoke heightens platelet reactivity and thrombosis in Apoe-/- mice and implicate signaling through platelet P2Y12 receptor as a mediator of the adverse consequence of smoke exposure. These results may partially explain the recent observations that smokers derive greater clinical benefit from the P2Y12 antagonist clopidogrel than do non-smokers.