Thrombotic phenotype of mice with a combined deficiency in plasminogen activator inhibitor 1 and vitronectin

OBJECTIVE

The role of vitronectin (VN) in thrombosis is not fully understood, primarily because this adhesive glycoprotein not only stabilizes plasminogen activator inhibitor 1 (PAI-1) and thus protects fibrin from premature lysis, but also because it binds to platelet integrins and may influence platelet aggregation. The absence of quantitative approaches to characterize the thrombi formed in animal models under different conditions further complicates this analysis.

METHODS

In this report, we describe a more comprehensive approach to assess the stability of thrombi formed in mice deficient in PAI-1 (PAI-1(-/-)), VN (VN(-/-)) or both (PAI-1(-/-)/VN(-/-)).

RESULTS

We observed that all deficient mice developed unstable thrombi compared with wild type (WT) mice. Thus, only 31% of the thrombi formed in WT mice were unstable compared with 74% of PAI-1(-/-), 80% of VN(-/-), and 87% of PAI-1(-/-)/VN(-/-) mice. In this regard, the average number of emboli per WT mouse was significantly lower (0.55) compared with VN(-/-) (2.66), PAI-1(-/-) (2.1), and VN(-/-)/PAI-1(-/-) (2.35) mice. Finally, the total duration of complete vascular occlusion was higher and the rate of vascular patency was lower in the WT mice compared with the deficient mice.

CONCLUSIONS

Taken together, these observations indicate that the thrombotic phenotype of mice with a combined deficiency in PAI-1 and VN does not differ significantly from the phenotype of mice with deficiencies in only PAI-1 or VN. This observation suggests that PAI-1 and VN may influence thrombus stability by regulating a common pathway.

The leptin receptor system of human platelets

Obesity is associated with elevated levels of leptin in the blood. Elevated leptin is a risk factor for thrombosis in humans, and leptin administration promotes platelet activation and thrombosis in the mouse. The current study examines the effect of leptin on human platelets, and provides initial insights into the nature of the leptin receptor on these platelets. Leptin potentiated the aggregation of human platelets induced by low concentrations of ADP, collagen and epinephrine. However, the response varied significantly between donors, with platelets from some donors (approximately 40%) consistently responding to leptin (responders) and those from other donors (approximately 60%) never responding (non-responders). Western blotting and reverse transcriptase-polymerase chain reaction (RT-PCR) experiments showed that platelets from both groups only express the signaling form of the leptin receptor, and that responder platelets express higher levels of this receptor than non-responders. Ligand-binding assays demonstrate specific, saturable binding of leptin to platelets from both groups with apparent K(d) values of 76 +/- 20 nM for responders and 158 +/- 46 nM for non-responders. Thus, the decreased sensitivity of non-responder platelets to leptin does not result from the absence of the signaling form of this receptor, but may reflect differences in its level of expression and/or affinity for leptin. These preliminary studies demonstrate that platelets are a major source of leptin receptor in the circulation, and suggest that leptin-responsive individuals may have a higher risk for obesity-associated thrombosis than non-responsive individuals.

Leptin-dependent platelet aggregation and arterial thrombosis suggests a mechanism for atherothrombotic disease in obesity

Obesity is associated with increased cardiovascular morbidity and mortality and with elevated circulating levels of the satiety factor leptin. This study provides evidence for a direct link between leptin and the risk for thrombotic complications in obese individuals. For example, although arterial injury provokes thrombosis in both lean and obese (ob/ob) mice, the time to complete thrombotic occlusion is significantly delayed in the ob/ob mice, and the thrombi formed are unstable and frequently embolize. The ob/ob mice lack leptin, and intraperitoneal administration of leptin to these mice before injury restores the phenotype of lean mice by shortening the time to occlusion, stabilizing the thrombi, and decreasing the patency rate. The thrombi that form when leptin receptor-deficient obese (db/db) mice are injured also are unstable. However, in this instance, leptin has no effect. Platelets express the leptin receptor, and leptin potentiates the aggregation of platelets from ob/ob but not db/db mice in response to known agonists. These results reveal a novel receptor-dependent effect of leptin on platelet function and hemostasis and provide new insights into the molecular basis of cardiovascular complications in obese individuals. The results suggest that these prothrombotic properties should be considered when developing therapeutic strategies based on leptin.

A murine tumor progression model for pancreatic cancer recapitulating the genetic alterations of the human disease

This study describes a tumor progression model for ductal pancreatic cancer in mice overexpressing TGF-alpha. Activation of Ras and Erk causes induction of cyclin D1-Cdk4 without increase of cyclin E or PCNA in ductal lesions. Thus, TGF-alpha is able to promote progression throughout G1, but not S phase. Crossbreeding with p53 null mice accelerates tumor development in TGF-alpha transgenic mice dramatically. In tumors developing in these mice, biallelic deletion of Ink4a/Arf or LOH of the Smad4 locus is found suggesting that loci in addition to p53 are involved in antitumor activities. We conclude that these genetic events are critical for pancreatic tumor formation in mice. This model recapitulates pathomorphological features and genetic alterations of the human disease.

Insulin-like growth factor-I is an autocrine regulator of chromogranin A secretion and growth in human neuroendocrine tumor cells

Carcinoid tumors are predominantly found in the gastrointestinal tract and are characterized by hypersecretion of various substances, including bioamines and neuropeptides, leading to functional tumor disease. Here, we demonstrate that human BON carcinoid tumor cells express functionally active insulin-like growth factor-I (IGF-I) receptors and secrete IGF-I, suggesting an autocrine action of this growth factor. The IGF-I receptor was functionally active. IGF-I stimulated phosphatidylinositol 3-kinase (PI3-kinase), p70 S6 kinase (p70s6k), and extracellular signal-regulated kinase 2 activity in BON cells. Furthermore, immunoneutralization of endogenously released IGF-I markedly reduced the high basal activity of p70s6k and extracellular signal-regulated kinase 2 in serum-starved BON cells. Exogenously added IGF-I induced a marked increase in chromogranin A secretion, a marker protein for neuroendocrine secretion, by a process that was largely dependent on PI3-kinase activity. In addition, immunoneutralization of endogenously released IGF-I markedly reduced basal chromogranin A release by BON cells. Thus, the autocrine IGF-I loop regulates basal neuroendocrine secretion in BON cells. Next, we investigated the role of IGF-I as a growth promoting agent for BON cells. Our data demonstrate that IGF-I stimulates anchorage-dependent and anchorage-independent growth of BON cells by a pathway that involves PI3-kinase, mammalian target of rapamycin/p70s6k, and mitogen-activated protein kinase kinase 1 activity. Interestingly, mitogen-activated protein kinase kinase 1 activity was less important for anchorage-independent growth of BON cells. Endogenously released IGF-I was found to be largely responsible for autonomous growth of BON cells in serum-free medium and for the constitutive expression of cyclin D1 in these cells. In conclusion, IGF-I is a major autocrine regulator of neuroendocrine secretion and growth of human BON neuroendocrine tumor cells. Because our data also demonstrate that a significant proportion of neuroendocrine tumors express the IGF-I receptor and its ligand, interference with this pathway could be useful in the treatment of hypersecretion syndromes and growth of human neuroendocrine tumors.

High-dose diltiazem prevents migration and proliferation of vascular smooth muscle cells in various in-vitro models of human coronary restenosis

BACKGROUND

Restenosis after coronary angioplasty is considered to be caused mainly by increased migration and proliferation of smooth muscle cells (SMC). The concept of local, site-specific delivery of pharmacologic therapies has opened the door for new, high-dose drug regimes.

METHODS AND RESULTS

SMC were isolated by enzymatic disaggregation with collagenase/elastase from human coronary plaque tissue of 29 patients (pSMC) and post mortem from the coronary media of 33 corpses (mSMC). Endothelial cells were isolated from human umbilical veins by enzymatic disaggregation with collagenase/dispase. By positive reaction with antibodies against smooth muscle alpha-actin and von Willebrand factor cells were identified as SMC or endothelial cells. In proliferation studies 5-150 micrograms/ml diltiazem was added to the culture media of pSMC, mSMC and endothelial cells. After 5 days there was a significant dose-dependent inhibition of cell proliferation (for pSMC with > 50 micrograms/ml, for mSMC with > 25 micrograms/ml, and for endothelial cells with > 5 micrograms/ml). In migration studies the effect of 5-150 micrograms/ml diltiazem on the velocity of migration of pSMC was investigated over a period of 48 h. Administration of diltiazem at concentrations of 100 and 150 micrograms/ml caused a significant inhibition of the migration of pSMC. The cytoskeletal components smooth muscle alpha-actin, vimentin, and alpha-tubulin of pSMC and the expression of von Willebrand factor of endothelial cells were investigated after an incubation period of 5 days with 50 and 150 micrograms/ml diltiazem. In the transfilter coculture model the effect of 50 micrograms/ml diltiazem on mSMC was investigated after mechanical injury of cocultured endothelial cells. Administration of diltiazem at a concentration of 50 micrograms/ml inhibited the development of a neointimal proliferate in the transfilter coculture model significantly (P < 0.001).

CONCLUSIONS

A high dose of diltiazem inhibited the migratory and proliferative activities of coronary SMC significantly. In further experimental studies the effect of locally applied high doses of diltiazem on postangioplasty restenosis should be elucidated.