Synthesis and secretion of plasminogen activator inhibitor-1 by human preadipocytes

Adipose Tissue Development Relies on Coordinated Extracellular Matrix Remodeling, Angiogenesis, and Adipogenesis

Despite developing prenatally, the adipose tissue is unique in its ability to undergo drastic growth even after reaching its mature size. This development and subsequent maintenance rely on the proper coordination between the vascular niche and the adipose compartment. In this review, the process of adipose tissue development is broken down to explain (1) the ultrastructural matrix remodeling that is undertaken during simultaneous adipogenesis and angiogenesis, (2) the paracrine crosstalk involved during adipose development, (3) the mechanical regulators involved in adipose growth, and (4) the proteolytic and paracrine oversight for matrix remodeling during adipose development. It is crucial to gain a better understanding of the complex relationships that exist between adipose tissue and the vasculature during tissue development to provide insights into the pathological tissue expansion of obesity and to develop improved soft-tissue reconstruction techniques.

PAI-1: A Major Player in the Vascular Dysfunction in Obstructive Sleep Apnea?

Obstructive sleep apnea is a chronic and prevalent condition that is associated with endothelial dysfunction, atherosclerosis, and imposes excess overall cardiovascular risk and mortality. Despite its high prevalence and the susceptibility of CVD patients to OSA-mediated stressors, OSA is still under-recognized and untreated in cardiovascular practice. Moreover, conventional OSA treatments have yielded either controversial or disappointing results in terms of protection against CVD, prompting the need for the identification of additional mechanisms and associated adjuvant therapies. Plasminogen activator inhibitor-1 (PAI-1), the primary inhibitor of tissue-type plasminogen activator (tPA) and urinary-type plasminogen activator (uPA), is a key regulator of fibrinolysis and cell migration. Indeed, elevated PAI-1 expression is associated with major cardiovascular adverse events that have been attributed to its antifibrinolytic activity. However, extensive evidence indicates that PAI-1 can induce endothelial dysfunction and atherosclerosis through complex interactions within the vasculature in an antifibrinolytic-independent matter. Elevated PAI-1 levels have been reported in OSA patients. However, the impact of PAI-1 on OSA-induced CVD has not been addressed to date. Here, we provide a comprehensive review on the mechanisms by which OSA and its most detrimental perturbation, intermittent hypoxia (IH), can enhance the transcription of PAI-1. We also propose causal pathways by which PAI-1 can promote atherosclerosis in OSA, thereby identifying PAI-1 as a potential therapeutic target in OSA-induced CVD.

Adipokines, Hepatokines and Myokines: Focus on Their Role and Molecular Mechanisms in Adipose Tissue Inflammation

Chronic low-grade inflammation in adipose tissue (AT) is a hallmark of obesity and contributes to various metabolic disorders, such as type 2 diabetes and cardiovascular diseases. Inflammation in ATs is characterized by macrophage infiltration and the activation of inflammatory pathways mediated by NF-κB, JNK, and NLRP3 inflammasomes. Adipokines, hepatokines and myokines - proteins secreted from AT, the liver and skeletal muscle play regulatory roles in AT inflammation via endocrine, paracrine, and autocrine pathways. For example, obesity is associated with elevated levels of pro-inflammatory adipokines (e.g., leptin, resistin, chemerin, progranulin, RBP4, WISP1, FABP4, PAI-1, Follistatin-like1, MCP-1, SPARC, SPARCL1, and SAA) and reduced levels of anti-inflammatory adipokines such as adiponectin, omentin, ZAG, SFRP5, CTRP3, vaspin, and IL-10. Moreover, some hepatokines (Fetuin A, DPP4, FGF21, GDF15, and MANF) and myokines (irisin, IL-6, and DEL-1) also play pro- or anti-inflammatory roles in AT inflammation. This review aims to provide an updated understanding of these organokines and their role in AT inflammation and related metabolic abnormalities. It serves to highlight the molecular mechanisms underlying the effects of these organokines and their clinical significance. Insights into the roles and mechanisms of these organokines could provide novel and potential therapeutic targets for obesity-induced inflammation.

A Serpin With a Finger in Many PAIs: PAI-1's Central Function in Thromboinflammation and Cardiovascular Disease

Plasminogen activator inhibitor 1 (PAI-1) is a member of the serine protease inhibitor (serpin) superfamily. PAI-1 is the principal inhibitor of the plasminogen activators, tissue plasminogen activator (tPA), and urokinase-type plasminogen activator (uPA). Turbulence in the levels of PAI-1 tilts the balance of the hemostatic system resulting in bleeding or thrombotic complications. Not surprisingly, there is strong evidence that documents the role of PAI-1 in cardiovascular disease. The more recent uncovering of the coalition between the hemostatic and inflammatory pathways has exposed a distinct role for PAI-1. The storm of proinflammatory cytokines liberated during inflammation, including IL-6 and TNF-α, directly influence PAI-1 synthesis and increase circulating levels of this serpin. Consequently, elevated levels of PAI-1 are commonplace during infection and are frequently associated with a hypofibrinolytic state and thrombotic complications. Elevated PAI-1 levels are also a feature of metabolic syndrome, which is defined by a cluster of abnormalities including obesity, type 2 diabetes, hypertension, and elevated triglyceride. Metabolic syndrome is in itself defined as a proinflammatory state associated with elevated levels of cytokines. In addition, insulin has a direct impact on PAI-1 synthesis bridging these pathways. This review describes the key physiological functions of PAI-1 and how these become perturbed during disease processes. We focus on the direct relationship between PAI-1 and inflammation and the repercussion in terms of an ensuing hypofibrinolytic state and thromboembolic complications. Collectively, these observations strengthen the utility of PAI-1 as a viable drug target for the treatment of various diseases.

A Narrative Review on Plasminogen Activator Inhibitor-1 and Its (Patho)Physiological Role: To Target or Not to Target?

Plasminogen activator inhibitor-1 (PAI-1) is the main physiological inhibitor of plasminogen activators (PAs) and is therefore an important inhibitor of the plasminogen/plasmin system. Being the fast-acting inhibitor of tissue-type PA (tPA), PAI-1 primarily attenuates fibrinolysis. Through inhibition of urokinase-type PA (uPA) and interaction with biological ligands such as vitronectin and cell-surface receptors, the function of PAI-1 extends to pericellular proteolysis, tissue remodeling and other processes including cell migration. This review aims at providing a general overview of the properties of PAI-1 and the role it plays in many biological processes and touches upon the possible use of PAI-1 inhibitors as therapeutics.

Role of Shear Stress and tPA Concentration in the Fibrinolytic Potential of Thrombi

The resolution of arterial thrombi is critically dependent on the endogenous fibrinolytic system. Using well-established and complementary whole blood models, we investigated the endogenous fibrinolytic potential of the tissue-type plasminogen activator (tPA) and the intra-thrombus distribution of fibrinolytic proteins, formed ex vivo under shear. tPA was present at physiologically relevant concentrations and fibrinolysis was monitored using an FITC-labelled fibrinogen tracer. Thrombi were formed from anticoagulated blood using a Chandler Loop and from non-anticoagulated blood perfused over specially-prepared porcine aorta strips under low (212 s⁻¹) and high shear (1690 s⁻¹) conditions in a Badimon Chamber. Plasminogen, tPA and plasminogen activator inhibitor-1 (PAI-1) concentrations were measured by ELISA. The tPA–PAI-1 complex was abundant in Chandler model thrombi serum. In contrast, free tPA was evident in the head of thrombi and correlated with fibrinolytic activity. Badimon thrombi formed under high shear conditions were more resistant to fibrinolysis than those formed at low shear. Plasminogen and tPA concentrations were elevated in thrombi formed at low shear, while PAI-1 concentrations were augmented at high shear rates. In conclusion, tPA primarily localises to the thrombus head in a free and active form. Thrombi formed at high shear incorporate less tPA and plasminogen and increased PAI-1, thereby enhancing resistance to degradation.

Targeting PAI-1 in Cardiovascular Disease: Structural Insights Into PAI-1 Functionality and Inhibition

Plasminogen activator inhibitor-1 (PAI-1), a member of the serine protease inhibitor (serpin) superfamily with antiprotease activity, is the main physiological inhibitor of tissue-type (tPA) and urokinase-type (uPA) plasminogen activators (PAs). Apart from being crucially involved in fibrinolysis and wound healing, PAI-1 plays a pivotal role in various acute and chronic pathophysiological processes, including cardiovascular disease, tissue fibrosis, cancer, and age-related diseases. In the prospect of treating the broad range of PAI-1-related pathologies, many efforts have been devoted to developing PAI-1 inhibitors. The use of these inhibitors, including low molecular weight molecules, peptides, antibodies, and antibody fragments, in various animal disease models has provided ample evidence of their beneficial effect in vivo and moved forward some of these inhibitors in clinical trials. However, none of these inhibitors is currently approved for therapeutic use in humans, mainly due to selectivity and toxicity issues. Furthermore, the conformational plasticity of PAI-1, which is unique among serpins, poses a real challenge in the identification and development of PAI-1 inhibitors. This review will provide an overview of the structural insights into PAI-1 functionality and modulation thereof and will highlight diverse approaches to inhibit PAI-1 activity.

Plasminogen activator inhibitor-1 gene polymorphism as a risk factor for vascular complications in type 2 diabetes mellitus

Background

Diabetes mellitus (DM) can lead to microvascular and macrovascular damages through hyperglycemia that is the main cause of diabetic complications. Other factors such as hypertension, obesity, and hyperlipidemia may worsen or accelerate the others. Several studies have revealed definitive genetic predispositions to the development of type 2 diabetes mellitus (T2DM) and development of vascular complications. This study aimed to address the association between plasminogen activator inhibitor-1 (PAI-1) gene polymorphism and T2DM, and if this gene polymorphism may have a possible role in the development of vascular complications in T2DM. This study is a case control; it included 200 patients with T2DM, 117 patients had no vascular complications, and 83 had previous vascular complications (VCs). One hundred eighty volunteer blood donors were selected as a healthy control group. All patients and controls were subjected to clinical examination, and laboratory investigations included lipid profile, fasting and 2 h blood glucose, complete blood cell count, d-dimer, PAI-1, thrombin activatable fibrinolysis inhibitor (TAFI), and detection of PAI-1 gene polymorphism by real-time polymerase chain reaction (PCR).

Results

The most prevalent genotype of PAI-1 gene polymorphism in all studied groups, including controls, was 4G/5G with the highest allele frequency as 4G. The 4G/5G and 4G/4G genotypes were associated with increased risk of DM development as compared to 5G/5G genotype. The 4G/5G and 4G/4G genotypes also had a highly significant increased risk of VCs among diabetic patients, as compared to 5G/5G. The 4G allele also was highly associated with DM with VCs. The d-dimer TAFI, PAI-1 showed the highest levels in 4G/5G genotype followed by 4G/4G genotype. The lowest level was expressed in 5G/5G genotype in diabetic patients with and without VCs. The univariable analysis showed that genotypes 4G/5G and 4G/4G were potentially risk factors for development of VCs with T2DM patients.

Conclusion

This study concludes that the PAI-1 4G/5G polymorphism may be associated with T2DM and may be considered as a risk factor for development of thrombotic events. It may also help in selection and dosing of patients being treated with anticoagulant and fibrinolytic agents. Further large-scale studies are recommended to assess the possible role of environmental factors and gene interactions in the development of T2DM vascular risks.

Neurogenic obesity and systemic inflammation following spinal cord injury: A review

CONTENT

Spinal Cord Injury (SCI) results in physiological changes that markedly reduces whole-body metabolism, resulting in neurogenic obesity via adipose tissue accumulation. Adipose tissue has been implicated in the release of proinflammatory adipokines that lead to chronic, systemic inflammation, and evidence suggests these adipokines contribute to the pathogeneses of metabolic diseases that often accompany obesity. In this review, we propose the concept of neurogenic obesity through paralysis-induced adiposity as the primary source of systemic inflammation and metabolic dysfunction reported in chronic SCI. We also briefly discuss how exercise in SCI can attenuate the negative consequences of obesity-induced inflammation and its comorbidities.

METHODS

A MEDLINE, PubMed, Google Scholar, and ClinicalKey search was performed using the following search terms: obesity, adiposity, adipose tissue, proinflammatory adipokines, proinflammatory cytokines, metabolic dysfunction, exercise, physical activity, and spinal cord injury. All papers identified were full-text, English language papers. The reference list of identified papers was also searched for additional papers.

RESULTS

Research suggests that obesity in SCI results in a state of chronic, systemic inflammation primarily through proinflammatory adipokines secreted from excess adipose tissue. The reduction of adipose tissue through the use of diet and exercise demonstrates promise to combat neurogenic obesity, inflammation, and cardiometabolic dysfunction in SCI.

CONCLUSION

Proinflammatory adipokines may serve as biomarkers for the development of obesity-related complication in SCI. Mechanistic and interventional studies on neurogenic obesity-induced inflammation in chronic SCI are warranted.

Plasminogen Activator Inhibitor-1 is Regulated Through Dietary Fat Intake and Heritability: Studies in Twins

In different pathophysiological conditions plasminogen activator inhibitor-1 (PAI-1) plasma concentrations are elevated. As dietary patterns are considered to influence PAI-1 concentration, we aimed to determine active PAI-1 plasma concentrations and mRNA expression in adipose tissue before and after consumption of a high-fat diet (HFD) and the impact of additive genetic effects herein in humans. For 6 weeks, 46 healthy, non-obese pairs of twins (aged 18–70) received a normal nutritionally balanced diet (ND) followed by an isocaloric HFD for 6 weeks. Active PAI-1 plasma levels and PAI-1 mRNA expression in subcutaneous adipose tissue were assessed after the ND and after 1 and 6 weeks of HFD. Active PAI-1 plasma concentrations and PAI-1 mRNA expression in adipose tissue were significantly increased after both 1 and 6 weeks of HFD when compared to concentrations determined after ND (p< .05), with increases of active PAI-1 being independent of gender, age, or changes of BMI and intrahepatic fat content, respectively. However, analysis of covariance suggests that serum insulin concentration significantly affected the increase of active PAI-1 plasma concentrations. Furthermore, the increase of active PAI-1 plasma concentrations after 6 weeks of HFD was highly heritable (47%). In contrast, changes in PAI-1 mRNA expression in fatty tissue in response to HFD showed no heritability and were independent of all tested covariates. In summary, our data suggest that even an isocaloric exchange of macronutrients — for example, a switch to a fat-rich diet — affects PAI-1 concentrations in humans and that this is highly heritable.

Glucose starvation and hypoxia, but not the saturated fatty acid palmitic acid or cholesterol, activate the unfolded protein response in 3T3-F442A and 3T3-L1 adipocytes

Obesity is associated with endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) in adipose tissue. In this study we identify physiological triggers of ER stress and of the UPR in adipocytes in vitro. We show that two markers of adipose tissue remodelling in obesity, glucose starvation and hypoxia, cause ER stress in 3T3-F442A and 3T3-L1 adipocytes. Both conditions induced molecular markers of the IRE1α and PERK branches of the UPR, such as splicing of XBP1 mRNA and CHOP, as well as transcription of the ER stress responsive gene BiP. Hypoxia also induced an increase in phosphorylation of the PERK substrate eIF2α. By contrast, physiological triggers of ER stress in many other cell types, such as the saturated fatty acid palmitic acid, cholesterol, or several inflammatory cytokines including TNF-α, IL-1β, and IL-6, do not cause ER stress in 3T3-F442A and 3T3-L1 adipocytes. Our data suggest that physiological changes associated with remodelling of adipose tissue in obesity, such as hypoxia and glucose starvation, are more likely physiological ER stressors of adipocytes than the lipid overload or hyperinsulinemia associated with obesity.

D-dimer: An Overview of Hemostasis and Fibrinolysis, Assays, and Clinical Applications

D-dimer is the smallest fibrinolysis-specific degradation product found in the circulation. The origins, assays, and clinical use of D-dimer will be addressed. Hemostasis (platelet and vascular function, coagulation, fibrinolysis, hemostasis) is briefly reviewed. D-dimer assays are reviewed. The D-dimer is very sensitive to intravascular thrombus and may be markedly elevated in disseminated intravascular coagulation, acute aortic dissection, and pulmonary embolus. Because of its exquisite sensitivity, negative tests are useful in the exclusion venous thromboembolism. Elevations occur in normal pregnancy, rising two- to fourfold by delivery. D-dimer also rises with age, limiting its use in those >80 years old. There is a variable rise in D-dimer in active malignancy and indicates increased thrombosis risk in active disease. Elevated D-dimer following anticoagulation for a thrombotic event indicates increased risk of recurrent thrombosis. These and other issues are addressed.

Adipose tissue engineering with cells in engineered matrices

Tissue engineering has shown promise for the development of constructs to facilitate large volume soft tissue augmentation in reconstructive and cosmetic plastic surgery. This article reviews the key progress to date in the field of adipose tissue engineering. In order to effectively design a soft tissue substitute, it is critical to understand the native tissue environment and function. As such, the basic physiology of adipose tissue is described and the process of adipogenesis is discussed. In this article, we have focused on tissue engineering using a cell-seeded scaffold approach, where engineered extracellular matrix substitutes are seeded with exogenous cells that may contribute to the regenerative response. The strengths and limitations of each of the possible cell sources for adipose tissue engineering, including adipose-derived stem cells, are detailed. We briefly highlight some of the results from the major studies to date, involving a range of synthetic and naturally derived scaffolds. While these studies have shown that adipose tissue regeneration is possible, more research is required to develop optimized constructs that will facilitate safe, predictable and long-term augmentation in clinical applications.

Does body weight influence the response to intravenous tissue plasminogen activator in stroke patients?

BACKGROUND

The recommended dose of IV tissue plasminogen activator (t-PA) for ischemic stroke patients weighing >100 kg (ISPW >100 kg) is fixed at 90 mg. Elevated levels of plasminogen activator inhibitor-1 (PAI-1) and impaired fibrinolysis have been reported in heavy patients, suggesting that ISPW >100 kg may require higher doses of t-PA. We hypothesized that ISPW >100 kg are less likely to benefit from IV t-PA compared to patients who weigh <or=100 kg and receive a weight-based dose.

METHODS

We queried the National Institute of Neurological Disorders and Stroke t-PA study database, and performed multivariate logistic regression analyses to analyze the effects of weight (>100 vs. <or=100 kg) and t-PA dose on functional outcomes at 3 months.

RESULTS

Six percent of the t-PA and 10% of the placebo cohorts had an actual body weight >100 kg. Weight >100 kg emerged as a predictor of worse outcome (OR = 5.76; p = 0.017) and neurological deterioration (OR = 3.4; p = 0.07) after t-PA. This negative impact of body weight on outcome was not seen among placebo-treated patients. We also found a trend for an association between lower doses of t-PA and unfavorable 3-month outcomes in t-PA-treated patients (OR = 1.9; p = 0.05).

CONCLUSIONS

ISPW >100 kg seem to derive less benefit from IV t-PA than their lighter counterparts. This may be partly attributed to the use of fixed non-weight-adjusted dosing in heavier patients. The mechanism(s) underlying this observation and its potential therapeutic implications require further investigations.

Secreted proteins and genes in fetal and neonatal pig adipose tissue and stromal-vascular cells

Although microarray and proteomic studies have indicated the expression of unique and unexpected genes and their products in human and rodent adipose tissue, similar studies of meat animal adipose tissue have not been reported. Thus, total RNA was isolated from stromal-vascular (S-V) cell cultures (n = 4; 2 arrays; 2 cultures/array) from 90-d (79% of gestation) fetuses and adipose tissue from 105-d (92% of gestation) fetuses (n = 2) and neonatal (5-d-old) pigs (n = 2). Duplicate adipose tissue microarrays (n = 4) represented RNA samples from a pig and a fetus. Dye-labeled cDNA probes were hybridized to custom microarrays (70-mer oligonucleotides) representing more than 600 pig genes involved in growth and reproduction. Microarray studies showed significant expression of 40 genes encoding for known adipose tissue secreted proteins in fetal S-V cell cultures and adipose tissue. Expression of 10 genes encoding secreted proteins not known to be expressed by adipose tissue was also observed in neonatal adipose tissue and fetal S-V cell cultures. Additionally, the agouti gene was detected by reverse transcription-PCR in pig S-V cultures and adipose tissue. Proteomic analysis of adipose tissue and fetal and young pig S-V cell culture-conditioned media identified multiple secreted proteins including heparin-like epidermal growth factor-like growth factor and several apolipoproteins. Another adipose tissue secreted protein, plasminogen activator inhibitor-1, was identified by ELISA in S-V cell culture media. A group of 20 adipose tissue secreted proteins were detected or identified using the gene microarray and the proteomic and protein assay approaches including apolipoprotein-A1, apolipoprotein-E, relaxin, brain-derived neurotrophic factor, and IGF binding protein-5. These studies demonstrate, for the first time, the expression of several major secreted proteins in pig adipose tissue that may influence local and central metabolism and growth.

Secretome of primary cultures of human adipose-derived stem cells: modulation of serpins by adipogenesis

Studies of adipogenic protein induction have led to a new appreciation of the role of adipose tissue as an endocrine organ. Adipocyte-derived "adipokines" such as adiponectin, leptin, and visceral adipose tissue-derived serine protease inhibitor (vaspin) exert hormone-like activities at the systemic level. In this study, we examined the secretome of primary cultures of human subcutaneous adipose-derived stem cells as an in vitro model of adipogenesis. Conditioned media obtained from four individual female donors after culture in uninduced or adipogenic induced conditions were compared by two-dimensional gel electrophoresis and tandem mass spectrometry. Over 80 individual protein features showing > or =2-fold relative differences were examined. Approximately 50% of the identified proteins have been described previously in the secretome of murine 3T3-L1 preadipocytes or in the interstitial fluid derived from human mammary gland adipose tissue. As reported by others, we found that the secretome included proteins such as actin and lactate dehydrogenase that do not display a leader sequence or transmembrane domain and are classified as "cytoplasmic" in origin. Moreover we detected a number of established adipokines such as adiponectin and plasminogen activator inhibitor 1. Of particular interest was the presence of multiple serine protease inhibitors (serpins). In addition to plasminogen activator inhibitor 1, these included pigment epithelium-derived factor (confirmed by Western immunoblot), placental thrombin inhibitor, pregnancy zone protein, and protease C1 inhibitor. These findings, together with the recent identification of vaspin, suggest that the serpin protein family warrants further proteomics investigation with respect to the etiology of obesity and type 2 diabetes.

Bone Marrow Plasminogen Activator Inhibitor-1 Influences the Development of Obesity

Plasma levels of plasminogen activator inhibitor-1 (PAI-1) are elevated in obesity and correlate with body mass index. The increase in PAI-1 associated with obesity likely contributes to increased cardiovascular risk and may predict the development of type 2 diabetes mellitus. Although adipocytes are capable of synthesizing PAI-1, the bulk of evidence indicates that cells residing in the stromal fraction of visceral fat are the primary source of PAI-1. We hypothesized that bone marrow-derived PAI-1, e.g. derived from macrophages located in visceral fat, contributes to the development of diet-induced obesity. To test this hypothesis, male C57BL/6 wild-type mice and C57BL/6 PAI-1 deficient mice were transplanted with either PAI-1(-/-), PAI-1(+/-), or PAI-1(+/+) bone marrow. The transplanted animals were subsequently fed a high fat diet for 24 weeks. Our findings show that only the complete absence of PAI-1 protects from the development of diet-induced obesity, whereas the absence of bone marrow-derived PAI-1 protects against expansion of the visceral fat mass. Remarkably, there is a link between the PAI-1 levels, the degree of inflammation in adipose tissue, and the development of obesity. Based on these findings we suggest that bone marrow-derived PAI-1 has an effect on the development of obesity through its effect on inflammation.

PAI-1 and the Metabolic Syndrome

The link between plasminogen activator inhibitor (PAI)-1 and the metabolic syndrome with obesity was established many years ago. Increased PAI-1 level can be now considered a true component of the syndrome. The metabolic syndrome is associated with an increased risk of developing cardiovascular disease, and PAI-1 overexpression may participate in this process. The mechanisms of PAI-1 overexpression during obesity are complex, and it is conceivable that several inducers are involved at the same time at several sites of synthesis. Interestingly, recent in vitro and in vivo studies showed that besides its role in atherothrombosis, PAI-1 is also implicated in adipose tissue development and in the control of insulin signaling in adipocytes. These findings suggest PAI-1 inhibitors serve in the control of atherothrombosis and insulin resistance.

Modulation of adipose tissue development by pharmacological inhibition of PAI-1

OBJECTIVE

The effect of a novel small molecule plasminogen activator inhibitor (PAI-1) inhibitor on adipose tissue physiology was investigated.

METHODS AND RESULTS

In human preadipocyte cultures, PAI-039 inhibited both basal and glucose-stimulated increases in active PAI-1 antigen, yet had no effect on PAI-1 mRNA, suggesting a direct inactivation of PAI-1. Differentiation of human preadipocytes to adipocytes was associated with leptin synthesis, which was significantly reduced in the presence of PAI-039, together with an atypical adipocyte morphology characterized by a reduction in the size and number of lipid containing vesicles. In a model of diet-induced obesity, pair-fed C57 Bl/6 mice administered PAI-039 in a high-fat diet exhibited a dose-dependent reduction in body weight, epididymal adipose tissue weight, adipocyte volume, and circulating plasma active PAI-1. Plasma glucose, triglycerides, and leptin were also significantly reduced in drug-treated mice, and concentrations of PAI-039 associated with these physiological effects were near the in vitro IC50 for the inhibition of PAI-1.

CONCLUSIONS

Our results indicate that a small molecule inactivator of PAI-1 can neutralize glucose-stimulated increases in PAI-1 in human preadipocyte cultures, reduce adipocyte differentiation, and prevent the development of diet-induced obesity. These data suggest the pharmacological inhibition of PAI-1 could be beneficial in diseases associated with expansion of adipose tissue mass.

Evaluation of low PAI-1 activity as a risk factor for hemorrhagic diathesis

BACKGROUND

Prospective studies of the epidemiology and clinical significance of low plasminogen activator inhibitor type 1 (PAI-1) activity are lacking.

OBJECTIVE

To evaluate the prevalence of low PAI-1 activity in patients with a bleeding tendency in comparison with a normal population.

METHODS

In 586 consecutive patients, referred because of bleeding symptoms, we added analyses of PAI-1 activity and tissue plasminogen activator complex with PAI-1 (t-PA-PAI-1) to the routine investigation, consisting of platelet count, bleeding time, prothrombin time, activated partial thromboplastin time, fibrinogen, factor VIII, von Willebrand factor activity, and antigen. Controls were 100 blood donors and 100 age- and sex-matched healthy individuals. The latter were also evaluated regarding the previous bleeding episodes. The bleeding history was classified as clinically significant or not, and the criteria were fulfilled in 75% of the patients and 18% of the healthy controls.

RESULTS

The routine laboratory investigation of the patients was negative in 57%. Low PAI-1 activity, defined as <1.0 U mL(-1), was found in 23% of the patients and in 13% and 10% of the blood donors and healthy controls, respectively (odds ratio and 95% CI, 2.04; 1.11-3.77 and 2.75; 1.39-5.42, respectively). The difference remained statistically significant after the adjustment for body mass index, use of estrogens, sex and age (odds ratio for patients vs. healthy controls 3.23; 95% CI, 1.22-8.56, P = 0.019). The distribution of the 4G/5G genotypes in the patients was not different from that of two control populations. No specific symptom predicted for low PAI-1, which did not aggravate the clinical picture in association with the other hemostatic defects. Low tPA-PAI-1 was not associated with the increased bleeding tendency.

CONCLUSION

Low PAI-1 activity is common in patients with a bleeding diathesis, but it is a risk factor of minor clinical importance and not associated with specific bleeding manifestations.

Inflammatory Cytokines Interleukin-6 and Oncostatin M Induce Plasminogen Activator Inhibitor-1 in Human Adipose Tissue

Background— Adipose tissue is a prominent source of plasminogen activator inhibitor-1 (PAI-1), the primary physiological inhibitor of plasminogen activation. Increased PAI-1 expression acts as a cardiovascular risk factor, and plasma levels of PAI-1 strongly correlate with body mass index (BMI). Elevated serum levels of interleukin-6 (IL-6), an inflammatory cytokine and a member of the glycoprotein 130 (gp130) ligand family, are found in obese patients and might indicate low-grade systemic inflammation. Another gp130 ligand, oncostatin M (OSM), upregulates PAI-1 in cardiac myocytes, astrocytes, and endothelial cells. We used tissue explants and primary cultures of preadipocytes and adipocytes from human subcutaneous and visceral adipose tissue to investigate whether IL-6 and OSM affect PAI-1 expression in fat.

Methods and Results— Human subcutaneous and visceral adipose tissue responded to treatment with IL-6 and OSM with a significant increase in PAI-1 production. Human preadipocytes were isolated from subcutaneous and visceral adipose tissue. Adipocyte differentiation was induced by hormone supplementation. All cell types expressed receptors for IL-6 and OSM and produced up to 12-fold increased levels of PAI-1 protein and up to 9-fold increased levels of PAI-1 mRNA on stimulation with IL-6 and OSM. AG-490, a janus kinase/signal transducer and activator of transcription inhibitor, abolished the OSM-dependent PAI-1 induction almost completely.

Conclusions— We have for the first time established a link between the gp130 ligands, the proinflammatory mediators IL-6 and OSM, and the expression of PAI-1 in human adipose tissue. Thus, we speculate that IL-6 and OSM, by upregulating PAI-1 in adipose tissue, can contribute to the increased cardiovascular risk of obese patients.

Obesity and impaired fibrinolysis: role of adipose production of plasminogen activator inhibitor-1

Obesity is the central promoter of the metabolic syndrome which also includes disturbed fibrinolysis in addition to hypertension, dyslipidaemia and impaired glucose tolerance/type 2 diabetes mellitus. Plasminogen activator inhibitor-1 (PAI-1) is the most important endogenous inhibitor of tissue plasminogen activator and uro-plasminogen activator, and is a main determinant of fibrinolytic activity. There is now compelling evidence that obesity and, in particular, an abdominal type of body fat distribution are associated with elevated PAI-1 antigen and activity levels. Recent studies established that PAI-1 is expressed in adipose tissue. The greater the fat cell size and the adipose tissue mass, the greater is the contribution of adipose production to circulating PAI-1. Experimental data show that visceral adipose tissue has a higher capacity to produce PAI-1 than subcutaneous adipose tissue. Studies in human adipocytes indicate that PAI-1 synthesis is upregulated by insulin, glucocorticoids, angiotensin II, some fatty acids and, most potently, by cytokines such as tumour necrosis factor-alpha and transforming growth factor-beta, whereas catecholamines reduce PAI-1 production. Interestingly, pharmacological agents such as thiazolidinediones, metformin and AT(1)-receptor antagonists were found to reduce adipose expression of PAI-1. In addition, weight loss by dietary restriction or comprehensive lifestyle modification is effective in lowering PAI-1 plasma levels. In conclusion, impaired fibrinolysis in obesity is probably also due to an increased expression of PAI-1 in adipose tissue. An altered function of the endocrine system and an impaired auto-/paracrine function at the fat cell levels may mediate this disturbance of the fibrinolytic system and thereby increase the risk for cardiovascular disease..

Effect of the angiotensin II receptor blocker candesartan on fibrinolysis in patients with mild hypertension

AIM

Impaired fibrinolysis is frequently observed in patients with the metabolic syndrome. Aim of the study was to examine the short-term effect of angiotensin II receptor blockade on the fibrinolytic system.

METHODS

Seventy-four patients with mild hypertension were randomly assigned to a 7-day treatment period with either 16 mg candesartan cilexetil or placebo. Several variables of the fibrinolytic system such as plasminogen activator inhibitor-1 (PAI-1) antigen and activity, tissue plasminogen activator (t-PA) antigen and activity as well as circulating t-PA/PAI-1 complexes were determined.

RESULTS

At baseline, the body mass index but not blood pressure was positively associated with PAI-1 antigen (r=0.314, p<0.01) and PAI-1 activity (r=0.425, p<0.01) but negatively with t-PA activity (r=-0.187, p < 0.05). A 7-day treatment with 16 mg candesartan cilexetil resulted in a significant greater reduction of diastolic blood pressure (-10.3 +/- 10.8 mmHg vs.-5.8 +/- 8.5 mmHg, p=0.03). However, there was no significant effect of candesartan on all parameters of the fibrinolytic system under investigation, i.e. circulating PAI-1 antigen, PAI-1 activity, t-PA antigen, t-PA activity and t-PA/PAI-1 complexes. Furthermore, candesartan did not affect the characteristic circadian pattern of the variables of the fibrinolytic system.

CONCLUSION

We conclude that short-term blockade of the angiotensin II receptor subtype 1 with candesartan does not have an impact on fibrinolysis in patients with mild hypertension.

Rosiglitazone inhibits the insulin-mediated increase in PAI-1 secretion in human abdominal subcutaneous adipocytes

OBJECTIVE

The aim of this study was to investigate the effect of insulin and an insulin-sensitizing agent, rosiglitazone (RSG), on the production of plasminogen-activator inhibitor-1 (PAI-1) in isolated subcutaneous abdominal adipocytes. Human tissue-type plasminogen activator (t-PA) was also measured to assess changes in overall thrombotic risk.

METHODS

The mean depot-specific expression of PAI-1 and t-PA mRNA (n = 42) in subcutaneous abdominal (n = 21), omental (n = 10) and thigh (n = 11) adipose tissue depots was examined. Furthermore, subcutaneous adipocytes were treated with insulin, RSG and insulin in combination with RSG (10-8 m) for 48 h. Conditioned media were collected and enzyme-linked immunosorbent assays performed for PAI-1 and t-PA (n = 12) antigen. PAI-1 and t-PA mRNA levels were also assessed.

RESULTS

PAI-1 mRNA levels were significantly higher in subcutaneous and omental abdominal tissue than in thigh fat (p = 0.037 and p = 0.014). No change in t-PA mRNA expression between the adipose tissue depots was observed. Insulin stimulated PAI-1 protein secretion in a concentration-dependent manner in adipocytes (control: 68.3 +/- 1.2 ng/ml (s.e.m.); 10 nm insulin: 73.7 +/- 3.8 ng/ml upward arrow; 100 nm insulin: 86.8 +/- 4.1 ng/ml upward arrow **; 1000 nm insulin: 102.0 +/- 4.8 ng/ml upward arrow ***; **p < 0.01, ***p < 0.001). In contrast, insulin + RSG (10-8 m) reduced PAI-1 production relative to insulin alone (***p < 0.001), whilst RSG alone reduced PAI-1 protein secretion in a concentration-dependent manner (RSG at 10-10 m: 50.4 +/- 2.87 ng/ml downward arrow ***; RSG at 10-5 m: 30.3 +/- 2.0 ng/ml downward arrow ***; p < 0.001). No difference was observed between control and treatments for t-PA secretion (range 7-11 ng/ml).

CONCLUSIONS

Insulin stimulated PAI-1 secretion, whilst RSG reduced both PAI-1 secretion alone and in combination with insulin. These data suggest that adipose tissue may contribute significantly to the elevated circulating PAI-1 in obesity. Therefore, RSG's effects on PAI-1 production in adipose tissue may contribute to the fall in circulating PAI-1 levels observed in patients receiving RSG therapy.

Macrophage inflammatory protein-related protein-2, a novel CC chemokine, can regulate preadipocyte migration and adipocyte differentiation

Adipocytes not only store energy, but also secrete biologically active molecules called adipocytokines, which play a pivotal role in adipocyte-related pathological processes such as diabetes and cardiovascular disease. Recent studies have shown that preadipocyte/adipocyte expresses chemokines (e.g. monocyte chemoattractant protein-1, macrophage inflammatory protein-1 alpha) which alter adipocyte function, indicating the involvement of chemokines in adipocyte-related pathologies. The current study investigated the potential of macrophage inflammatory protein-related protein-2 (MRP-2), a novel CC chemokine, to modulate preadipocyte trafficking and adipocyte differentiation. MRP-2 and its receptors were highly expressed in preadipocytes and differentiated adipocytes as well as in the mouse fat pad. Chemotaxis assays revealed that MRP-2 was a specific chemotactic regulator in preadipocyte migration. The levels of MRP-2 expression in adipose tissue were enhanced in obese mice compared to lean mice. MRP-2 secretion by preadipocytes was suppressed during differentiation. MRP-2 suppressed the expression of adipocyte differentiation markers such as adipocyte fatty acid-binding protein and glycerol-3 phosphate dehydrogenase. Taken together, our data suggest that MRP-2 plays a role in the regulation of preadipocyte migration and adipocyte differentiation during adipose tissue development. MRP-2 may be another adipocytokine, which can be involved in the adipocyte-related pathological process.

Insulin resistance but not visceral adipose tissue is associated with plasminogen activator inhibitor type 1 levels in overweight and obese premenopausal African-American women

OBJECTIVE

To compare plasma plasminogen activator inhibitor type 1 (PAI-1) levels and to examine the association of PAI-1 with visceral adiposity and other components of the metabolic syndrome in overweight and obese premenopausal African-American (AA) and Caucasian (CC) women.

DESIGN

Cross-sectional study.

SUBJECTS

33 CC and 23 AA healthy, overweight and obese, premenopausal women (age 19-53 y, body mass index 28.1-48.9 kg/m(2)).

MEASUREMENTS

Body mass index, sagittal diameter, waist circumference, percentage body fat, visceral and subcutaneous adipose tissue (by anthropometry, magnetic resonance imaging (MRI), and bioelectric impedance techniques), PAI-1, leptin, lipids, glucose, insulin, and insulin resistance (by HOMA IR).

RESULTS

AA women had lower triglyceride levels and less visceral adipose tissue (VAT) volume than CC despite similar BMI. PAI-1 levels were not significantly different in the two groups. Insulin resistance was associated with PAI-1 in both groups but only in CC women were VAT, triglyceride, HDL cholesterol and blood pressure related to plasma PAI-1 levels. Multiple regression analysis showed that VAT in CC and insulin resistance in AA were independent predictors of PAI-1.

CONCLUSION

VAT is significantly associated with circulating PAI-1 levels in overweight and obese CC but not AA premenopausal women.

Stromal cells are the main plasminogen activator inhibitor-1-producing cells in human fat: evidence of differences between visceral and subcutaneous deposits

Elevated plasma plasminogen activator inhibitor (PAI)-1 observed during insulin resistance has been connected with an excessive PAI-1 adipose tissue secretion mainly by visceral fat. Our aim was to compare the localization of PAI-1 in human visceral and subcutaneous fats. PAI-1 secretion was also investigated in vitro during human adipocyte differentiation. PAI-1 antigen and mRNA were localized in the stromal area of the tissue and were also present in a few CD14-positive monocytes, in direct contact with adipocytes. In addition, in subcutaneous tissue, PAI-1 mRNA contents, determined by using real-time polymerase chain reaction, were higher in the stromal fraction than in the adipocyte fraction. PAI-1 mRNA-positive cells were 5-fold more frequent in the visceral area than in the subcutaneous stromal area (P=0.004). Such a difference was also observed for PAI-1 mRNA content between both whole adipose tissues. In contrast to leptin, during adipocyte differentiation, PAI-1 secretion did not follow adipocyte maturation. In situ hybridization in culture did not reveal PAI-1 mRNA in lipid-filled cells. Our results demonstrate that PAI-1 production is mainly due to stromal cells, which were more numerous in the visceral than in the subcutaneous depot. These results could explain the strong relationship observed between circulating PAI-1 levels and the accumulation of visceral fat.

Reciprocal regulation of tissue-type and urokinase-type plasminogen activators in the differentiation of murine preadipocyte line 3T3-L1 and the hormonal regulation of fibrinolytic factors in the mature adipocytes

Adipose tissue expresses a variety of genes including tumor necrosis factor alpha and type-1 plasminogen activator inhibitor (PAI-1); and these factors, produced by adipocytes, may be associated with the risk of coronary events in obesity. In this study, we characterized the production of fibrinolytic factors including tissue-type plasminogen activator (tPA), urokinase-type PA (uPA), and PAI-1 in the differentiation of preadipocytes, and examined the hormonal regulation of these fibrinolytic factors in mature adipocytes. Mouse 3T3-L1 preadipocytes were employed as a model of adipocytes. Adipocyte differentiation was induced by insulin, dexamethasone, and 3-isobutyl-1-methyl xanthine (IBMX). alpha-Glycerophosphate dehydrogenase (GPDH) activity and glucose transporter 4 (GLUT4) mRNA, indices for adipocyte maturation, were induced on Day 4, and gradually increased. GPDH activity reached its maximum level on Day 14. The level of tPA, a major PA in preadipocytes, dramatically decreased with differentiation. On the other hand, that of uPA reciprocally increased. PAI-1 production was also dramatically induced concomitant with differentiation. In mature adipocytes, uPA production was dominant (25 microg/ml/24 h vs. 0.8 microg/ml/24 h for tPA). Total PA activity in the mature adipocytes was reduced by insulin or dexamethasone, but not by glucagon. Insulin, IBMX, and dexamethasone significantly decreased both uPA and tPA production, and increased PAI-1 production. Glucagon had no effect on the production of these fibrinolytic factors. Our results reveal that uPA is one of the markers for the differentiation of 3T3-L1 cells and that insulin, IBMX, and dexamethasone are potent regulators of the fibrinolytic activity in differentiated 3T3-L1 cells, reciprocally affecting PA and PAI-1 levels in them.

Leptin induces mitochondrial superoxide production and monocyte chemoattractant protein-1 expression in aortic endothelial cells by increasing fatty acid oxidation via protein kinase A

Leptin, a circulating hormone secreted mainly from adipose tissues, is involved in the control of body weight. The plasma concentrations are correlated with body mass index, and are reported to be high in patients with insulin resistance, which is one of the major risk factors for cardiovascular disease. However, the direct effect of leptin on vascular wall cells is not fully understood. In this study, we investigated the effects of leptin on reactive oxygen species (ROS) generation and expression of monocyte chemoattractant protein-1 (MCP-1) in bovine aortic endothelial cells (BAEC). We found that leptin increases ROS generation in BAEC in a dose-dependent manner and that its effects are additive with those of glucose. Rotenone, thenoyltrifluoroacetone (TTFA), carbonyl cyanide m-chlorophenylhydrazone (CCCP), Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), uncoupling protein-1 (UCP1) HVJ-liposomes, or manganese superoxide dismutase (MnSOD) HVJ-liposomes completely prevented the effect of leptin, suggesting that ROS arise from mitochondrial electron transport. Leptin increased fatty acid oxidation by stimulating the activity of carnitine palmitoyltransferase-1 (CPT-1) and inhibiting that of acetyl-CoA carboxylase (ACC), pace-setting enzymes for fatty acid oxidation and synthesis, respectively. Leptin-induced ROS generation, CPT-1 activation, ACC inhibition, and MCP-1 overproduction were found to be completely prevented by either genistein, a tyrosine kinase inhibitor, H-89, a protein kinase A (PKA) inhibitor, or tetradecylglycidate, a CPT-1 inhibitor. Leptin activated PKA, and the effects of leptin were inhibited by the cAMP antagonist Rp-cAMPS. These results suggest that leptin induces ROS generation by increasing fatty acid oxidation via PKA activation, which may play an important role in the progression of atherosclerosis in insulin-resistant obese diabetic patients.

Angiotensin II and its metabolites stimulate PAI-1 protein release from human adipocytes in primary culture

Plasminogen activator inhibitor (PAI)-1 is the main inhibitor of the fibrinolytic system and was recently shown to be produced by adipose cells. Obesity is associated with an increased production and release of PAI-1 protein. The aim of this study was to investigate the role of angiotensin (Ang) II and its degradation products for PAI-1 release from human adipose cells. For this purpose, we used the model of in vitro differentiated human adipocytes in primary culture. Exposure of human adipocytes to Ang II resulted in a dose- and time-dependent stimulation of PAI-1 release into the culture medium. The maximum effect of Ang II was found at a concentration of 10(-5) mol/L for 48 hours, increasing PAI-1 release by 276+/-53% compared with control cultures (P<0.05). This stimulation was preceded by an increase in specific PAI-1 mRNA copies by 65+/-12% (P<0.05), with a maximum after 6 hours. Incubation of adipocytes with 10(-5) mol/L Ang III and Ang IV, respectively, also resulted in a stimulation of PAI-1 release into the medium by 195+/-60% (P<0.05) and 142+/-24% (P<0.05), respectively, compared with control cultures. Addition of the angiotensin-receptor subtype 1 (AT(1)) blocker candesartan abolished the stimulatory action of Ang II and its metabolites, indicating that this effect is mediated by AT(1). Addition of the AT(1) blocker alone to unstimulated cultures reduced PAI-1 release by 41%+/-25% (P<0.05), suggesting that endogenous Ang II synthesis contributes to PAI-1 secretion from adipose tissue in an autocrine/paracrine manner. In conclusion, Ang II and its metabolites promote PAI-1 production and release by human fat cells and may contribute to the impairment of the fibrinolytic system typical for obesity. AT(1) receptor blockade reduces basal and abolishes Ang II-stimulated PAI-1 release from human adipocytes.

Release of PAI-1 by human preadipocytes and adipocytes independent of insulin and IGF-1

The effect of insulin and insulin-like growth factor-1 (IGF-1) on plasminogen activator inhibitor-1 (PAI-1) release from primary cultures of human preadipocytes and adipocytes has been investigated. Initial experiments measuring basal PAI-1 release (ng/ml) indicated variability between individual cultures. Using a novel technique for adipocyte quantitation, additional experiments were performed to determine PAI-1 release per cell, indicating a significant reduction with differentiation. Insulin and IGF-1 over a range of concentrations had no effect on PAI-1 release, and RT-PCR of PAI-1 mRNA following treatment with insulin and IGF-1 also indicated similar expression between treatments. The cultures did exhibit insulin-stimulated glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression and leptin synthesis following differentiation to the adipocyte phenotype. This is the first report of PAI-1 secretion by primary cultures of human preadipocytes and adipocytes, indicating PAI-1 release independent of insulin and IGF-1 and implicating other factors in the elevated plasma PAI-1 observed with insulin resistance.

Metabolic complications of obesity

The rising prevalence of obesity is accompanied by an increasing number of patients with the metabolic complications of obesity. The major complications come under the heading of the metabolic syndrome. This syndrome is characterized by plasma lipid disorders (atherogenic dyslipidemia), raised blood pressure, elevated plasma glucose, and a prothrombotic state. The clinical consequences of the metabolic syndrome are coronary heart disease and stroke, type 2 diabetes and its complications, fatty liver, cholesterol gallstones, and possibly some forms of cancer. At the heart of the metabolic syndrome is insulin resistance, which represents a generalized derangement in metabolic processes. Obesity is the predominant factor leading to insulin resistance, although other factors play a role. The mechanistic link between insulin resistance and the metabolic syndrome is complex. The relationship is modulated by yet other factors, such as physical activity, body fat distribution, hormones, and a person's genetic polymorphic architecture. A better understanding of the molecular basis of this relationship is needed to suggest new targets for prevention and treatment of the complications of obesity. In addition, understanding at the clinical level will lead to improved management of these complications.

Relationship between plasma plasminogen activator inhibitor 1 and insulin resistance

High plasminogen activator inhibitor 1 (PAI-1) levels are associated with an increased cardiovascular risk of atherothrombosis. Furthermore, increased plasma PAI-1 levels are associated with dyslipidemia, hyperinsulinemia and hypertension. This association between PAI-1 and metabolic components of the Metabolic Syndrome could explain the predisposition of insulin resistant patients to atherothrombosis. Recent studies have suggested that visceral adipose tissue might be the link between elevated plasma PAI-1 and insulin resistance in the Metabolic Syndrome. Indeed, visceral adipose tissue was proposed as a potentially important source of PAI-1 in humans. However, in light of recent studies, visceral adipose tissue appears to be involved in the increase of plasma PAI-1 via the metabolic disorders usually associated with central obesity, rather than directly. High plasma PAI-1 levels are undoubtedly related to insulin resistance, and the mechanisms which could explain such an increase in the Metabolic Syndrome appear to be multi-factorial and remain to be elucidated. These mechanisms may involve several metabolic disorders such as hyperinsulinemia, dyslipidemia, impaired glucose tolerance and hypertension, which would favor PAI-1 synthesis and release from different cell types.