Leptin induces vascular permeability and synergistically stimulates angiogenesis with FGF-2 and VEGF

Macrophage infiltration into adipose tissue may promote angiogenesis for adipose tissue remodeling in obesity

The biological role of macrophage infiltration into adipose tissue in obesity remains to be fully understood. We hypothesize that macrophages may act to stimulate angiogenesis in the adipose tissue. This possibility was examined by determining macrophage expression of angiogenic factor PDGF (platelet-derived growth factor) and regulation of tube formation of endothelial cells by PDGF. The data suggest that endothelial cell density was reduced in the adipose tissue of ob/ob mice. Expression of endothelial marker CD31 was decreased in protein and mRNA. The reduction was associated with an increase in macrophage infiltration. In the obese mice, PDGF concentration was elevated in the plasma, and its mRNA expression was increased in adipose tissue. Macrophages were found to be a major source of PDGF in adipose tissue, as deletion of macrophages led to a significant reduction in PDGF mRNA. In cell culture, PDGF expression was induced by hypoxia, and tube formation of endothelial cells was induced by PDGF. The PDGF activity was dependent on S6K, as inhibition of S6K in endothelial cells led to inhibition of the PDGF activity. We conclude that, in response to the reduced vascular density, macrophages may express PDGF in adipose tissue to facilitate capillary formation in obesity. Although the PDGF level is elevated in adipose tissue, its activity in angiogenesis is dependent on the availability of sufficient endothelial cells. The study suggests a new function of macrophages in the adipose tissue in obesity.

Peritoneal fluid and serum leptin concentrations in women with primary infertility

AIM

Leptin is proposed to participate in the reproductive system of women by acting on either ovaries or hypothalamic-pituitary axis. The objective of the present study is to investigate the leptin concentrations in peritoneal fluid and serum samples of women diagnosed with primary infertility.

METHODS

A prospective study was carried out in women who underwent laparoscopy within the diagnostic process of primary infertility between January 2005 and January 2007. Leptin concentrations were determined in blood samples obtained before surgery and in peritoneal fluid samples collected during laparoscopy.

RESULTS

Peritoneal fluid was obtained from 112 subjects; 21 with unexplained infertility 28 with polycystic ovary syndrome (PCOS), 30 with bilateral tubal occlusion, and 33 with endometriosis. Subjects with PCOS have significantly higher body weights, BMI values and plasma leptin levels when compared to other study groups. Peritoneal fluid levels of leptin were significantly higher in the endometriosis group compared to other three study groups. A positive correlation was found between peritoneal fluid leptin levels and the endometriosis stage (r=0.51, P=0.01). However, plasma leptin levels were unrelated to the disease extent.

DISCUSSION

It might be hypothesized that leptin may be an active factor in the pathogenesis of PCOS and endometriosis, which are two major causes of primary infertility. A mild leptin deficiency in peritoneal environment may interrupt follicular development and ultimately lead to PCOS. Leptin has angiogenic and mitogenic properties, which trigger inflammatory cytokines and eventually result in the development of endometriosis implants. Significantly, higher levels of leptin in peritoneal environments of endometriosis subjects strongly imply the important role of this common pathology.

Serum leptin levels, skin leptin and leptin receptor expression in psoriasis

BACKGROUND

Recent studies support the relation of psoriasis with obesity and cardiovascular disease. Leptin, a peptide hormone secreted predominantly from adipose tissue, is involved in the regulation of energy intake and expenditure. Recently, it has been shown to have several immunological effects including induction of proinflammatory cytokine production.

OBJECTIVES

To investigate the possible role of leptin in psoriasis pathogenesis.

METHODS

Forty-three patients with psoriasis, 10 diseased and 10 healthy controls with normal body mass index were included. Serum fasting leptin levels of the study group were examined by enzyme-linked immunosorbent assay. Tissue leptin and leptin receptor expression of both patients and controls were investigated by immunohistochemistry.

RESULTS

Serum leptin levels, tissue leptin and leptin receptor expression were significantly higher in patients with severe psoriasis than patients with mild-moderate psoriasis and controls (P < 0.05). Serum leptin levels showed a positive correlation with Psoriasis Area and Severity Index and involved body surface area in patients with psoriasis. In addition, serum leptin levels, tissue leptin and leptin receptor expression showed a positive correlation with disease duration in patients with psoriasis (P < 0.01, r = 0.979; P < 0.01, r = 0.691; P < 0.01, r = 0.428, respectively).

CONCLUSIONS

We assume that leptin might serve as a marker of severity in psoriasis and also may be a pathogenetic cofactor contributing to chronicity of the disease. Consequently, its role in obesity and cardiovascular disease in patients with psoriasis deserves to be studied. In addition, drugs targeting the proinflammatory effects of leptin may be a new adjuvant therapeutic approach in psoriasis.

FOXC2 controls Ang-2 expression and modulates angiogenesis, vascular patterning, remodeling, and functions in adipose tissue

Adipogenesis is spatiotemporally coupled to angiogenesis throughout adult life, and the interplay between these two processes is communicated by multiple factors. Here we show that in a transgenic mouse model, increased expression of forkhead box C2 (FOXC2) in the adipose tissue affects angiogenesis, vascular patterning, and functions. White and brown adipose tissues contain a considerably high density of microvessels appearing as vascular plexuses, which show redistribution of vascular smooth muscle cells and pericytes. Dysfunction of these primitive vessels is reflected by impairment of skin wound healing. We further provide a mechanistic insight of the vascular phenotype by showing that FOXC2 controls Ang-2 expression by direct activation of its promoter in adipocytes. Remarkably, an Ang-2-specific antagonist almost completely reverses this vascular phenotype. Thus, the FOXC2-Ang-2 signaling system is crucial for controlling adipose vascular function, which is part of an adaptation to increased adipose tissue metabolism.

What is the mechanism of microalbuminuria in diabetes: a role for the glomerular endothelium?

Microalbuminuria is an important risk factor for cardiovascular disease and progressive renal impairment. This holds true in the general population and particularly in those with diabetes, in whom it is common and marks out those likely to develop macrovascular disease and progressive renal impairment. Understanding the pathophysiological mechanisms through which microalbuminuria occurs holds the key to designing therapies to arrest its development and prevent these later manifestations. Microalbuminuria arises from the increased passage of albumin through the glomerular filtration barrier. This requires ultrastructural changes rather than alterations in glomerular pressure or filtration rate alone. Compromise of selective glomerular permeability can be confirmed in early diabetic nephropathy but does not correlate well with reported glomerular structural changes. The loss of systemic endothelial glycocalyx--a protein-rich surface layer on the endothelium--in diabetes suggests that damage to this layer represents this missing link. The epidemiology of microalbuminuria reveals a close association with systemic endothelial dysfunction and with vascular disease, also implicating glomerular endothelial dysfunction in microalbuminuria. Our understanding of the metabolic and hormonal sequelae of hyperglycaemia is increasing, and we consider these in the context of damage to the glomerular filtration barrier. Reactive oxygen species, inflammatory cytokines and growth factors are key players in this respect. Taken together with the above observations and the presence of generalised endothelial dysfunction, these considerations lead to the conclusion that glomerular endothelial dysfunction, and in particular damage to its glycocalyx, represents the most likely initiating step in diabetic microalbuminuria.

Human leptin induces angiogenesis in vivo

Leptin is an adipocyte-produced peptide, which plays a crucial role in the regulation of body weight. There is also evidence that leptin stimulates endothelial cell proliferation and the formation of capillary-like tubes in vitro. The disc angiogenesis system was used to measure the angiogenic effect of leptin in vivo. Discs containing 25, 50, 100 and 250ng/ml of leptin were implanted subcutaneously in Wistar rats, removed after a growth period of 7 and 14 days, and compared with spontaneous growth controls and with positive controls containing equivalent doses of vascular endothelial growth factor (VEGF). Discs were examined morphologically for stroma and vessel development and by immunohistochemistry for quantitative evaluation of angiogenesis. The specificity of the angiogenic effect of leptin was tested by blocking leptin with a polyclonal anti-leptin antibody. Leptin induced a significant level of angiogenesis in a dose-dependent manner both at 7 and 14 days, with a peak at the dose of 100ng/ml. The angiogenic activity of leptin was completely abolished by the anti-leptin neutralizing antibody. VEGF also induced significant dose-dependent angiogenesis at the same time points with a peak observed at a concentration of 100ng/ml. The angiogenic response to leptin was significantly higher at 7 days compared with VEGF but not at the 14-day time point. In conclusion, leptin has a specific angiogenic effect in vivo, which is dose- and time-dependent in a concentration range of 25-250ng/ml. This effect is equivalent to the angiogenic effect of VEGF but is evident earlier compared with VEGF.

Angiogenesis in adipose tissue

Angiogenesis is required for the growth and expansion of both healthy and pathological tissues. The plasticity of the adipose tissue is reflected by its remarkable ability to expand or to reduce in size throughout the adult lifespan. We, and others, have recently shown that expansion of fat mass is dependent on angiogenesis, and suppression of angiogenesis might provide a novel therapeutic approach for prevention and treatment of obesity. Here, we outline two technical procedures for assessment of angiogenesis in adipose tissues.

Mammary alveolar development during lactation is inhibited by the endogenous antiangiogenic growth factor isoform, VEGF165b

Extensive tissue remodeling occurs in breast tissue during pregnancy, resulting in growth and development of the mammary gland associated with extensive vascular remodeling, which is thought to be dependent on vascular endothelial growth factor (VEGF). We show here that the endogenous antiangiogenic splice isoform of VEGF, VEGF(165)b, is normally expressed in nonlactating human and mouse breast, and is down-regulated in WT mice during lactation. To demonstrate the physiological role of VEGF(165)b in mammary tissue, we generated transgenic (TG) mice expressing VEGF(165)b, under the control of the mouse mammary tumor virus (MMTV) enhancer/promoter. These mice increase expression of VEGF(165)b in mammary tissue during mammary development. The offspring of TG mothers, but not TG fathers, die shortly after birth. The female TG mice have fewer blood vessels, less blood in the mammary tissue, and impaired alveolar coverage of the fat pad, and do not produce sufficient milk for nourishment of their pups. These findings demonstrate that endogenous overexpression of VEGF(165)b in the mammary gland inhibits physiological angiogenesis and that the regulation of the balance of VEGF isoforms is a requirement for mammary alveolar development and milk production. This study provides the first evidence for the role of endogenous antiangiogenic VEGF isoforms in normal physiology--their down-regulation is required for effective milk production.

Vascular endothelial growth factor gene-transferred bone marrow stromal cells engineered with a herpes simplex virus type 1 vector can improve neurological deficits and reduce infarction volume in rat brain ischemia

OBJECTIVE

Several reports recently suggested that vascular endothelial growth factor (VEGF) may have a therapeutic benefit against experimental cerebral infarction animal models. In addition, bone marrow stromal cells (BMSCs) are known to have therapeutic potency in improving neurological deficits after occlusive cerebrovascular diseases. In the present study, we evaluated the hypothesis that intracerebral transplantation of VEGF gene-transferred BMSCs could provide a greater therapeutic effect than intracerebral transplantation of native (non-gene-transformed) BMSCs by using a transient middle cerebral artery occlusion (MCAO) rat model.

METHODS

Adult Wistar rats (Japan SLC, Inc., Hamamatsu, Japan) were anesthetized. VEGF gene-transferred BMSCs engineered with a replication-deficient herpes simplex virus type 1 1764/4-/pR19-hVEGF165 vector, native BMSCs, or phosphate-buffered saline were administered intracerebrally 24 hours after transient MCAO. All animals underwent behavioral testing for 28 days, and the infarction volume was determined 14 days after MCAO. The brain water contents in the ipsilateral and contralateral hemispheres of the MCAO were measured 2 and 7 days after the MCAO. Fourteen days after MCAO, immunohistochemical staining for VEGF was performed.

RESULTS

The group receiving VEGF-modified BMSCs demonstrated significant functional recovery compared with those receiving native BMSCs. Fourteen days after the MCAO, there was a significantly lower infarct volume without aggravating cerebral edema in the group treated with VEGF gene-modified BMSCs compared with the control groups. The transplanted VEGF gene-modified BMSCs strongly expressed VEGF protein for at least 14 days.

CONCLUSION

Our data suggest that the intracerebral transplantation of VEGF gene-transferred BMSCs may provide a more potent autologous cell transplantation therapy for stroke than the transplantation of native BMSCs alone.

Endothelial stomatal and fenestral diaphragms in normal vessels and angiogenesis

Vascular endothelium lines the entire cardiovascular system where performs a series of vital functions including the control of microvascular permeability, coagulation inflammation, vascular tone as well as the formation of new vessels via vasculogenesis and angiogenesis in normal and disease states. Normal endothelium consists of heterogeneous populations of cells differentiated according to the vascular bed and segment of the vascular tree where they occur. One of the cardinal features is the expression of specific subcellular structures such as plas-malemmal vesicles or caveolae, transendothelial channels, vesiculo-vacuolar organelles, endothelial pockets and fenestrae, whose presence define several endothelial morphological types. A less explored observation is the differential expression of such structures in diverse settings of angiogenesis. This review will focus on the latest developments on the components, structure and function of these specific endothelial structures in normal endothelium as well as in diverse settings of angiogenesis.

Melanoma risk in association with serum leptin levels and lifestyle parameters: a case-control study

BACKGROUND

Solar radiation has been identified as a principal factor for the causation of melanoma, whereas changing lifestyle patterns associated with obesity and diabetes might also contribute to the increasing incidence of the malignancy. No study has investigated the role of leptin, a hormone whose levels increase in obesity and which has also been related to cancer.

PATIENTS AND METHODS

Fifty-five patients with incident melanomas and 165 age- and gender-matched healthy controls were interviewed on the basis of a questionnaire that covers phenotypic features, sociodemographic and medical history variables, lifestyle habits and frequency of consumption of major food groups. Anthropometrical measures were also recorded and blood samples were obtained for determination of serum leptin levels. Adjusted odds ratios (ORs) for melanoma risk were derived through multiple logistic regression analyses.

RESULTS

An excess melanoma risk was observed for sun sensitive individuals and those with high circulating levels of leptin (OR: 1.56, 95% confidence interval 1.07-2.28, P = 0.02), after controlling for obesity indices, diabetes mellitus and education. Increased physical exercise, lower alcohol consumption and plant food consumption seem to play a protective role against melanoma development.

CONCLUSIONS

Melanoma risk was found to be positively associated with serum leptin levels and inversely with healthy lifestyle factors. The findings need to be confirmed in prospective studies.

The role of endothelial cells in inflamed adipose tissue

In recent years, the general concept has emerged that chronic low-grade inflammation can be the condition linking excessive development of adipose tissue (AT) and obesity-associated pathologies such as type II diabetes and atherosclerosis. Moreover, the evidence that the growth of the fat mass was associated with an accumulation of adipose tissue macrophages (ATM) has raised the hypothesis that the development of an inflammatory process within the growing fat mass is a primary event involved in the genesis of systemic metabolic and vascular alterations. As ATM originate from the bone marrow/blood compartment, enhanced macrophage recruitment to growing AT is suspected. However, the mechanisms responsible for attracting the blood cells and their entry into the fat mass remain to be clearly defined. The present review highlights the key role of endothelial cells in the control of the inflammatory process and describes the potential involvement of AT-endothelial cells as well as the factors involved in the regulation of their phenotype in the 'inflamed fat tissue'.

Angiogenesis modulates adipogenesis and obesity

Substantial evidence shows that neoplastic and nonneoplastic tissue growth is dependent on angiogenesis. Neovascularization and adipogenesis are temporally and spatially coupled processes during prenatal life and they continue to reciprocally interact via paracrine signaling systems throughout adult life. Activated adipocytes produce multiple angiogenic factors including leptin, angiopoietins, HGF, GM-CSF, VEGF, FGF-2, and TGF-beta, which either alone or collectively stimulate neovascularization during fat mass expansion. Thus antiangiogenic agents provide a novel therapeutic option for prevention and treatment of human obesity and its related disorders.

Nonclassic Endogenous Novel Regulators of Angiogenesis

Angiogenesis, the process through which new blood vessels arise from preexisting ones, is regulated by several "classic" factors, among which the most studied are vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2). In recent years, investigations showed that, in addition to the classic factors, numerous endogenous peptides play a relevant regulatory role in angiogenesis. Such regulatory peptides, each of which exerts well-known specific biological activities, are present, along with their receptors, in the blood vessels and may take part in the control of the "angiogenic switch." An in vivo and in vitro proangiogenic effect has been demonstrated for erythropoietin, angiotensin II (ANG-II), endothelins (ETs), adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide (PAMP), urotensin-II, leptin, adiponectin, resistin, neuropeptide-Y, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and substance P. There is evidence that the angiogenic action of some of these peptides is at least partly mediated by their stimulating effect on VEGF (ANG-II, ETs, PAMP, resistin, VIP and PACAP) and/or FGF-2 systems (PAMP and leptin). AM raises the expression of VEGF in endothelial cells, but VEGF blockade does not affect the proangiogenic action of AM. Other endogenous peptides have been reported to exert an in vivo and in vitro antiangiogenic action. These include somatostatin and natriuretic peptides, which suppress the VEGF system, and ghrelin, that antagonizes FGF-2 effects. Investigations on "nonclassic" regulators of angiogenesis could open new perspectives in the therapy of diseases coupled to dysregulation of angiogenesis.

Association of plasma leptin levels and complexity of the culprit lesion in patients with unstable angina

BACKGROUND

Angiographically visible complex lesions which are associated with plaque vulnerability have been shown to correlate strongly with clinical severity of unstable angina (UA). By activating different immune/inflammatory cells or directly acting on the vessel wall leptin has been shown to play a potential role in the development of acute coronary syndrome. However, the relationship between leptin and simple or complex lesion morphology in UA has not been investigated. Therefore, we designed this study to determine the association between plasma leptin level and simple or complex lesions in patients with UA and to see any correlation between leptin and other inflammatory markers in these patients.

METHODS

Plasma concentrations of leptin, interleukin (IL)-6, IL-10 and high-sensitivity C-Reactive Protein (hsCRP) were analyzed in 47 patients with UA. These patients were also angiographically studied and divided into two groups: simple lesion (n=18) and complex lesion (n=29) based on the coronary plaque morphology. We further compared them with 20 control subjects having no evidence of coronary artery diseases.

RESULTS

Plasma leptin concentrations were higher in patients having complex lesions compared to those having simple lesions as well as normal controls. Similarly IL-6 and hsCRP were also higher in complex lesion group compared to simple lesion group and controls, and leptin was positively correlated with IL-6 and hsCRP. Concentrations of IL-10 were lower in simple and complex lesion groups compared to the controls and leptin was negatively correlated with IL-10, but no significant difference between simple and complex lesions was found. Furthermore, leptin was found to be an independent predictor for the complex lesion morphology in UA patients.

CONCLUSION

These findings suggested that angiographically visible complex lesions are associated with increased concentrations of leptin, and thus leptin can be a useful biomarker for risk stratification in UA.

Roles for VEGF in the adult

The role of VEGF during development and in pathology is well known, but its function in normal adult tissues is poorly understood. Adverse effects associated with the use of anti-angiogenic therapies targeting VEGF in human pathologies have begun to reveal potential functions of VEGF in quiescent vasculature. Further clues from expression studies of VEGF and its receptors in the adult, from the disease preeclampsia, and from experimental neutralization studies, have suggested that VEGF is involved in endothelial cell survival and fenestration, as well as in the signaling and maintenance of non-endothelial cells. The various biochemical properties of VEGF, and its interaction with other growth factors, may be an important point in determining whether VEGF functions as a maintenance factor versus an angiogenic factor. A thorough understanding of the function of VEGF in the adult may lead to more efficacious pro- and anti-angiogenic therapies.

Embryonic adhesion is not affected by endometrial leptin receptor gene silencing

OBJECTIVE

In rodents, evidence suggests that the leptin system is mandatory for embryonic implantation. We aimed to investigate the functional relevance of the endometrial leptin receptor (OB-R) in the adhesion phase of human implantation.

DESIGN

We used an in vitro model for embryonic adhesion, composed of a human endometrial cell line (HEC1-A) and B6C3F1 mouse embryos. The OB-R gene was silenced in a stable manner by RNA interference, and embryonic adhesion rates were analyzed.

SETTING

Research laboratory at a university-affiliated center.

INTERVENTION(S)

RNA interference.

MAIN OUTCOME MEASURE(S)

Embryonic adhesion in cells treated with OB-R RNAi.

RESULT(S)

The OB-R shRNA-transfected cells exhibited up to 80% lower OB-R mRNA levels than those of cells nontransfected or transfected with scrambled shRNA. The OB-R protein was also highly diminished in the stable OB-R shRNA-transfected HEC1A cells, whereas OAS1 expression was similar in both nontransfected and transfected cells. Embryonic adhesion rate was similar in nontransfected (94%) and HEC1-A transfected cells with a scrambled sequence (94%) or with OB-R silencing sequence (92%).

CONCLUSION(S)

Knocking down the OB-R gene in a human endometrial cell line has no effect on the embryonic adhesion rate. Nevertheless, the functional relevance of this system can not be excluded in other phases of embryonic implantation, such as the invasion phase. Moreover, we describe a new approach to the functional analysis of candidate molecules implicated in blastocyst adhesion.

On the role of placental growth factor in murine adipogenesis

The potential role of placental growth factor (PlGF) in early stages of adipogenesis was investigated in vivo using a murine model of obesity, as well as in vitro using cultured preadipocytes. PlGF-deficient (PlGF-/-) and wild-type (WT) mice, kept on high fat diet (HFD) for 3 weeks, had comparable body weight and weight of subcutaneous (SC) and gonadal (GON) adipose tissues. Blood vessel size and blood vessel density, normalized to adipocyte number, were not significantly different in SC and GON adipose tissues of both genotypes. Differentiation of embryonic fibroblasts derived from WT or PlGF-/- mice into mature adipocytes was comparable. Furthermore, addition of recombinant PlGF, of the PlGF neutralizing MAb PL5D11D4 or of the anti-Flk-1 MAb DC101 to cultured 3T3-F442A preadipocytes did not significantly affect their differentiation into mature adipocytes. Ex vivo blood vessel outgrowth following seeding of adipose tissue-derived microvessel fragments in 3D-collagen gels was not affected by PlGF deficiency. Thus, in murine model systems, PlGF does not seem to play an important role in early adipogenesis.

Leptin-mediated neovascularization is a prerequisite for progression of nonalcoholic steatohepatitis in rats

Nonalcoholic steatohepatitis (NASH) may cause fibrosis, cirrhosis, and hepatocellular carcinoma (HCC); however, the exact mechanism of disease progression is not fully understood. Angiogenesis has been shown to play an important role in the progression of chronic liver disease. The aim of this study was to elucidate the role of angiogenesis in the development of liver fibrosis and hepatocarcinogenesis in NASH. Zucker rats, which naturally develop leptin receptor mutations, and their lean littermate rats were fed a choline-deficient, amino acid-defined diet. Both Zucker and littermate rats showed marked steatohepatitis and elevation of oxidative stress markers (e.g., thiobarbital acid reactive substances and 8-hydroxydeoxyguanosine). In sharp contrast, liver fibrosis, glutathione-S-transferase placental form (GST-P)-positive preneoplastic lesions, and HCC developed in littermate rats but not in Zucker rats. Hepatic neovascularization and the expression of vascular endothelial growth factor (VEGF), a potent angiogenic factor, only increased in littermate rats, almost in parallel with fibrogenesis and carcinogenesis. The CD31-immunopositive neovessels were mainly localized either along the fibrotic septa or in the GST-P-positive lesions. Our in vitro study revealed that leptin exerted a proangiogenic activity in the presence of VEGF. In conclusion, these results suggest that leptin-mediated neovascularization coordinated with VEGF plays an important role in the development of liver fibrosis and hepatocarcinogenesis in NASH.

Leptin and cancer

The prevalence of obesity has markedly increased over the past two decades, especially in the industrialized countries. While the impact of excess body weight on the development of cardiac disease and diabetes has been well documented, the link between obesity and carcinogenesis is just being recognized. This review will focus on the link between leptin, a cytokine that is elevated in obese individuals, and cancer development. First, we briefly discuss the biological functions of leptin and its signaling pathways. Then, we summarize the effects of leptin on different cancer types in experimental cellular and animal models. Next, we analyze epidemiological data on the relationship between obesity and the presence of cancer or cancer risk in patients. Finally, leptin as a target for cancer treatment and prevention will be discussed.

Anti-angiogenic effects of liposomal prednisolone phosphate on B16 melanoma in mice

Prednisolone phosphate (PLP) encapsulated in long-circulating liposomes can inhibit tumor growth after intravenous administration (i.v.). These antitumor effects of liposomal PLP are the result of the tumor-targeting property of the liposome formulation. The mechanism by which liposomal PLP inhibits tumor growth is unclear. We investigated the effects of liposome-encapsulated PLP versus free PLP on angiogenic protein production in tumor tissue in vivo and on viability and proliferation of tumor and endothelial cells in vitro. In vivo, liposomal PLP had a stronger reducing effect on pro-angiogenic protein levels than free PLP, whereas levels of anti-angiogenic proteins were hardly affected. Cell viability was only slightly affected with either treatment. Liposomal PLP had strong anti-proliferative effects on human umbilical vein endothelial cells, whereas free PLP had hardly any effect. Taken together, the present study points to a strong inhibitory effect of liposomal PLP on tumor angiogenesis by reduction of the intratumoral production of the majority of pro-angiogenic factors studied and direct inhibition of endothelial cell proliferation, which is the result of high prolonged levels of prednisolone in the tumor by liposomal delivery.

Adiponectin suppression of high-glucose-induced reactive oxygen species in vascular endothelial cells: evidence for involvement of a cAMP signaling pathway

Adiponectin is an abundant adipocyte-derived plasma protein with antiatherosclerotic effects. Vascular signal transduction by adiponectin is poorly understood and may involve 5'-AMP-activated protein kinase (AMPK), cAMP signaling, and other pathways. Hyperglycemia sharply increases the production of reactive oxygen species (ROS), which play a key role in endothelial dysfunction in diabetes. Because the recombinant globular domain of human adiponectin (gAd) reduces the generation of endothelial ROS induced by oxidized LDL, we sought to determine whether adiponectin could also suppress ROS production induced by high glucose in cultured human umbilical vein endothelial cells. Incubation in 25 mmol/l glucose for 16 h increased ROS production 3.8-fold (P<0.05), using a luminol assay. Treatment with gAd for 16 h suppressed glucose-induced ROS in a dose-dependent manner up to 81% at 300 nmol/l (P<0.05). The AMPK activator 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR; 1 mmol/l, 16 h) only partially decreased glucose-induced ROS by 22% (P<0.05). Cell pretreatment with AMPK inhibitors, however, failed to block the effect of gAd to suppress glucose-induced ROS, suggesting that the action of gAd was independent of AMPK. Interestingly, activation of cAMP signaling by treatment with forskolin (2 micromol/l) or dibutyryl-cAMP (0.5 mmol/l) reduced glucose-induced ROS generation by 43 and 67%, respectively (both P<0.05). Incubation with the cAMP-dependent protein kinase (PKA) inhibitor H-89 (1 micromol/l) fully abrogated the effect of gAd, but not that of AICAR, on ROS induced by glucose. gAd also increased cellular cAMP content by 70% in an AMPK-independent manner. Full-length adiponectin purified from a eukaryotic expression system also suppressed ROS induced by high glucose or by treatment of endothelial cells with oxidized LDL. Thus, adiponectin suppresses excess ROS production under high-glucose conditions via a cAMP/PKA-dependent pathway, an effect that has implications for vascular protection in diabetes.

PLASMA OBTAINED DURING HUMAN ENDOTOXEMIA INCREASES ENDOTHELIAL ALBUMIN PERMEABILITY IN VITRO

To gain insight in the pathogenesis of increased vascular permeability during sepsis, we studied the effect of plasma obtained during human experimental endotoxemia on the permeability of cultured endothelial monolayers. Eight healthy subjects received an i.v. dose of 2 ng/kg Escherichia coli O:113 lipopolysaccharide (LPS). The concentration of various plasma mediators that supposedly induce vascular permeability was measured over time. Plasmas that were obtained before, and 2 and 4 h after the administration of LPS were added to human umbilical venular endothelial cells that were cultured on semipermeable membranes.The permeability of the endothelial monolayers to fluorescein isothiocyanate-labeled bovine serum albumin was determined and expressed as the relative concentration of fluorescein isothiocyanate-bovine serum albumin when compared with that measured across empty Transwell-COL (Corning Life Sciences B.V., Schiphol-Rijk, The Netherlands) membranes (i.e., without endothelial monolayers). The permeability levels were correlated with the concentrations of various mediators.Experimental endotoxemia resulted in elevated levels of tumor necrosis factor alpha, interleukin (IL) 1beta, IL-6, IL-8, IL-10, and vascular endothelial growth factor and a moderate increase of IL-12 and IFN-gamma (all P values < 0.01). Incubation of human umbilical venular endothelial cells with plasma obtained 2 and 4 h after the administration of LPS increased the relative permeability from a baseline level (median) of 17% (range, 14% - 31%) to 23% (range, 12% - 39%; P = not significant) and 28% (range, 11% - 40%; P < 0.05), respectively. Plasma levels of vascular endothelial growth factor and IL-10, but not TNF-alpha or any other mediators, significantly correlated with the increase in endothelial permeability (r = 0.47, P = 0.038; r = 0.43, P = 0.038, respectively). The data presented here demonstrate that plasmas obtained from experimental human endotoxemia increase endothelial albumin permeability in vitro. Thus, cultured human endothelial monolayers provide a model to study sepsis-associated vascular changes.

Role of leptin in atherogenesis

The pathogenesis of atherosclerosis involves multiple cellular events, including endothelial cell dysfunction, inflammation, proliferation of vascular smooth muscle cells and matrix alteration that is subsequently characterized by hardening, thickening, loss of elasticity and, finally, a reduction in the vessel's lumen. Leptin, a peptide hormone, is produced by adipocytes, and the majority of obese individuals have high plasma leptin concentrations. Leptin regulates food intake as well as metabolic function. Originally thought to be a satiety factor, leptin is a pleiotropic molecule. In addition to its metabolic effects, leptin regulates the production of several pro- and anti-inflammatory cytokines by activating immune cells. It is associated with increased plasma C-reactive protein concentrations, vascular proliferation, calcification and decreased arterial distensibility. Leptin also increases oxidative stress. Moreover, leptin contributes to increases in blood pressure, and thus, probably plays an important role in the initiation and progression of atherosclerosis. 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) lower lipid concentrations and also decrease endothelial apoptosis, inhibit smooth muscle cell proliferation, and lower concentrations of C-reactive protein and proinflammatory cytokines; moreover, it is now known that statins can inhibit leptin release by adipocytes. Therefore, statins have been shown to be beneficial in atherosclerosis. The present review mainly focuses on the various evidence that suggest a potential atherogenic mechanism of leptin, and also briefly addresses the beneficial role of statins in atherosclerosis.

Effects of intraperitoneal vitamin E, melatonin and aprotinin on leptin expression in the guinea pig eye during experimental uveitis

PURPOSE

To observe ultrastructural changes and leptin expression in the guinea pig eye during experimental uveitis (EU) and the effects of vitamin E, melatonin and aprotinin on leptin expression.

METHODS

Thirty male guinea pigs were randomly classified into five groups. Group 1 was the control group. Groups 2, 3, 4 and 5 received intravitreal injections of bovine serum albumin (BSA) to induce EU. At the same time on the third day, groups 3 (EU + vitamin E), 4 (EU + melatonin) and 5 (EU + aprotinin) received intraperitoneal vitamin E (150 mg/kg), melatonin (10 mg/kg) and aprotinin (20,000 IU/kg), respectively. On the sixth day, histopathological and clinical scoring of inflammation were performed, and leptin expression was investigated in the retina, choroid, sclera, episclera and cornea, and compared.

RESULTS

There was a remarkable increase in leptin expression in the retina, choroid, sclera and episclera in the EU group. Leptin expression in the treatment groups was similar to that in the control group. At light and electron microscopic levels, ganglion cells were oedematous and inner plexiform layer thickness had increased in the EU group retinas. Oedema was decreased in the treatment groups. Comparison of the EU and treatment groups revealed significant differences histopathologically and clinically.

CONCLUSION

Experimental uveitis causes an increase in leptin expression in the retina, choroid, sclera and episclera of guinea pigs. Vitamin E, melatonin and aprotinin inhibit this increase. Leptin seems to be closely related to ocular inflammation.

Leptin in corneas from keratoconus and infectious keratitis patients

PURPOSE

Leptin is produced primarily by adipose tissue. More recent studies have shown extra sites of leptin production in physiologic and ill human tissues. However, whether leptin originates from human corneas in infectious keratitis and keratoconus is not known. The aim of this study was to demonstrate and quantitate leptin expression in corneas with infectious keratitis and keratoconus and make comparisons to control corneas.

METHODS

We examined the immunohistochemical staining of leptin in nine corneas surgically excised from patients with infectious keratitis (3 patients), keratoconus (3 patients), and donor corneas (3 patients).

RESULTS

The results were analyzed using a semiquantitative scoring system of mild, moderate, and strong. Cells of the infectious keratitis group had the strongest leptin staining intensity, the control group had moderate, and the keratoconus group had mild staining intensity. The more vascular corneas in the infectious keratitis group were also associated with the greatest leptin staining.

CONCLUSIONS

Our findings indicate that leptin expression was present in all three sources of corneas (infectious keratitis, keratoconus, and normal control). Quantitative scoring would imply it may play a role in infectious keratitis, although further experiments are necessary to establish any causal relationship.

Protective effect of leptin against ischemia-reperfusion injury in the rat small intestine

BACKGROUND

The small intestine is extremely sensitive to ischemia-reperfusion (I/R) injury and a range of microcirculatory disturbances which contribute to tissue damage. Previous studies have shown that leptin plays an important physiological role in the microvasculature. The aim of this study was to evaluate the protective effects of leptin in I/R--induced mucosal injury in the small intestine.

METHODS

Forty rats were divided into 5 groups (n = 8). Group I was subjected to a sham operation. Following mesenteric ischemia in group II (control); physiologic saline 1 cm3, in group III; leptin 100 microg/kg, and physiologic saline 1 cm3, in group IV; NG-L-arginine methyl ester (L-NAME) 20 mg/kg, and physiologic saline 1 cm3, in group V; leptin 100 microg/kg, L-NAME 20 mg/kg, and physiologic saline 1 cm3 were given intra-peritoneally. In these groups, an I/R procedure was performed by occlusion of the superior mesenteric artery for 45 min followed by 120 min reperfusion. After reperfusion, the small intestines were resected for malondialdehyde (MDA) and nitric oxide (NO) concentration and histopathologic properties. Mucosal lesions were scored between 0 and 5. Tissue MDA and NO concentration and histopathologic grades were compared statistically.

RESULTS

Tissue MDA level significantly increased (P < 0.05), tissue NO level significantly decreased in group V animals, compared to group III animals respectively (P < 0.001). Histopathologically, intestinal injury significantly decreased in the leptin treated ischemic group.

CONCLUSION

Leptin can be used safely in mesenteric occlusive diseases, since it induces NO formation and release in mesenteric vessels.

Directional secretion and transport of leptin and expression of leptin receptor isoforms in human placental BeWo cells

Placental leptin secretion has important implications for maternal adaptation to pregnancy, fetal growth and development, and local autocrine/paracrine actions within trophoblast. In this study we used a cell culture insert model to examine directional secretion of leptin from the basal and apical surfaces of human choriocarcinoma BeWo cells, and to assess the effects of dexamethasone and syncytialization. Additionally, the effects of dexamethasone on transcellular passage of leptin across BeWo monolayers, and on expression of the leptin receptor isoforms Ob-Rs and Ob-RL were examined. Leptin was secreted into both the basal and apical chambers and was stimulated by dexamethasone. Treatment of BeWo cells with forskolin induced syncytialization and loss of monolayer integrity, but resulted in a marked increase in total leptin secretion, an effect further enhanced by co-treatment with dexamethasone. Bidirectional transfer of 125I-leptin between the apical and basal chambers of BeWo cell cultures was low but indicative of specific transcellular passage of leptin; transfer was unaffected by dexamethasone. Treatment of BeWo cells with forskolin increased Ob-Rs mRNA expression, whilst Ob-RL mRNA expression increased in response to forskolin only in the presence of dexamethasone. In conclusion, our data show that leptin is secreted from both the apical and basal surfaces of BeWo placental cells and is increased by both syncytialization and glucocorticoids. Moreover, transport of exogenous leptin occurred in both the apical to basal and reverse directions, suggesting the potential for maternal-fetal exchange of leptin across the human placenta.

Microvascular growth, development, and remodeling in the embryonic avian kidney: the interplay between sprouting and intussusceptive angiogenic mechanisms

Embryonic development is associated with extensive vascular growth and remodeling. We used immunohistochemical, light and electron microscopical techniques, as well as vascular casting methods to study the developing chick embryo kidney with special attention to the interplay between sprouting and intussusceptive vascular growth modes. During inauguration at embryonic day 5 (E5), the early mesonephros was characterised by extensive microvascular sprouting. By E7, the vascular growth mode switched to intussusception, which contributed to rapid kidney vasculature growth up to E11, when the first obvious signs of vascular degeneration were evident. The metanephros underwent similar phases of vascular development inaugurating at E8 with numerous capillary sprouts and changing at E13 to intussusceptive growth, which was responsible for vascular amplification and remodeling. A phenomenal finding was that future renal lobules arose as large glomerular tufts, supplied by large vessels, which were split into smaller intralobular feeding and draining vessels with subsequent formation of solitary glomeruli. This glomerular duplication was achieved by intussusception, i.e., by formation of pillars in rows and their successive merging to delineate the vascular entities. Ultimately, the maturation of the vasculature was achieved by intussusceptive pruning and branching remodeling. An interesting finding was that strong VEGF expression was associated with the sprouting phase of angiogenesis while bFGF was upregulated during the phase of intussusceptive microvascular growth. We conclude that microvascular growth and remodeling in avian kidney follows an adroitly crafted pattern, which entails a precise spaciotemporal interplay between sprouting and intussusceptive angiogenic growth modes supported partly by VEGF and bFGF.

VEGF-dependent plasticity of fenestrated capillaries in the normal adult microvasculature

Unlike during development, blood vessels in the adult are generally thought not to require VEGF for normal function. However, VEGF is a survival factor for many tumor vessels, and there are clues that some normal blood vessels may also depend on VEGF. In this study, we sought to identify which, if any, vascular beds in adult mice depend on VEGF for survival. Mice were treated with a small-molecule VEGF receptor (VEGFR) tyrosine kinase inhibitor or soluble VEGFRs for 1-3 wk. Blood vessels were assessed using immunohistochemistry or scanning or transmission electron microscopy. In a study of 17 normal organs after VEGF inhibition, we found significant capillary regression in pancreatic islets, thyroid, adrenal cortex, pituitary, choroid plexus, small-intestinal villi, and epididymal adipose tissue. The amount of regression was dose dependent and varied from organ to organ, with a maximum of 68% in thyroid, but was less in normal organs than in tumors in RIP-Tag2-transgenic mice or in Lewis lung carcinoma. VEGF-dependent capillaries were fenestrated, expressed high levels of both VEGFR-2 and VEGFR-3, and had normal pericyte coverage. Surviving capillaries in affected organs had fewer fenestrations and less VEGFR expression. All mice appeared healthy, but distinct physiological changes, including more efficient blood glucose handling, accompanied some regimens of VEGF inhibition. Strikingly, most capillaries in the thyroid grew back within 2 wk after cessation of treatment for 1 wk. Our findings of VEGF dependency of normal fenestrated capillaries and rapid regrowth after regression demonstrate the plasticity of the adult microvasculature.

Leptin induces vascular smooth muscle cell hypertrophy through angiotensin II- and endothelin-1-dependent mechanisms and mediates stretch-induced hypertrophy

Various cardiovascular pathologies are associated with vascular smooth muscle cell (VSMC) hypertrophy and elevated plasma leptin levels. We used the rat portal vein (RPV) cultured for three days to investigate the effect of mechanical stretch on autocrine secretion of leptin and the effect of exogenous leptin (3.1 nM) on VSMC. Stretching the RPV significantly up-regulated leptin production by greater than 100-fold and leptin receptor expression by up to 10-fold. In addition, stretch increased tissue weight by 23 +/- 1.3 and 30 +/- 1% (P < 0.05), respectively, in the absence or presence of leptin, although this was significantly attenuated by an antileptin antibody (166 ng/ml). Unstretched RPV weight decreased by 7.5 +/- 1.8% in the absence of leptin, whereas in the presence of leptin, weight increased by 6.5 +/- 1.8% (P < 0.05). VSMC size and [3H]leucine incorporation rates were significantly increased by leptin in stretched and unstretched tissues. Leptin-induced hypertrophy was associated with significant extracellular signal-regulated kinase (ERK1/2) activation as well as increased expression of angiotensinogen, the angiotensin type 1 receptor as well as preproendothelin-1, and the endothelin type A receptor, whereas ERK inhibition or inhibition of either the angiotensin II or endothelin-1 systems at both the synthesis and receptor levels blocked the hypertrophic response. The effects of leptin were also completely blocked by the cholesterol-chelating agent methyl-beta-cyclodextrin. Therefore, our study demonstrates stretch-dependent leptin release and a direct hypertrophic effect of leptin on RPV, the latter likely dependent on intact cholesterol-rich membrane microdomains and locally produced paracrine factors.

Endothelial effects of leptin: implications in health and diseases

Leptin is an adipocyte-derived hormone that plays a major role in the regulation of energy homeostasis through its action in the central nervous system. Leptin also acts on several peripheral tissues, including the vascular endothelium. The leptin receptor has been identified in endothelial cells. Leptin action on the endothelium modulates several physiologic processes, with potential implications in pathophysiologic diseases associated with obesity. Leptin stimulation of angiogenesis has attracted attention because of its potential involvement in retinopathy and atherosclerosis. Leptin activation of endothelial oxidative stress also has implications in atherosclerosis and inflammation. However, data on the impact of the endothelial effect of leptin on arterial pressure are contrasting. Although some investigators have shown that leptin action on the endothelial nitric oxide system tends to decrease arterial pressure, others have shown no contribution from the endothelial effect of leptin to the control of arterial pressure. Further characterization of the endothelial effects of leptin will, it is hoped, help in the understanding of the different pathophysiologic diseases associated with obesity.

Impaired revascularization in a mouse model of type 2 diabetes is associated with dysregulation of a complex angiogenic-regulatory network

OBJECTIVE

Diabetes is a risk factor for the development of cardiovascular diseases associated with impaired angiogenesis or increased endothelial cell apoptosis.

METHODS AND RESULTS

Here it is shown that angiogenic repair of ischemic hindlimbs was impaired in Lepr(db/db) mice, a leptin receptor-deficient model of diabetes, compared with wild-type (WT) C57BL/6 mice, as evaluated by laser Doppler flow and capillary density analyses. To identify molecular targets associated with this disease process, hindlimb cDNA expression profiles were created from adductor muscle of Lepr(db/db) and WT mice before and after hindlimb ischemia using Affymetrix GeneChip Mouse Expression Set microarrays. The expression patterns of numerous angiogenesis-related proteins were altered in Lepr(db/db) versus WT mice after ischemic injury. These transcripts included neuropilin-1, vascular endothelial growth factor-A, placental growth factor, elastin, and matrix metalloproteinases implicated in blood vessel growth and maintenance of vessel wall integrity.

CONCLUSIONS

These data illustrate that impaired ischemia-induced neovascularization in type 2 diabetes is associated with the dysregulation of a complex angiogenesis-regulatory network.

Adrenomedullin and Leptin Levels in Diabetic Retinopathy and Retinal Diseases

PURPOSE

Proliferative and vascular retinal diseases are important cause of irreversible blindness. Consistent features of these diseases are endothelial dysfunction and angiogenesis. Adrenomedullin (ADM) is a multifunctional vasorelaxant peptide. Leptin is a recently discovered metabolic peptide that regulates energy metabolism in human. In the present study, we aimed to investigate the possible roles of adrenomedullin and leptin in the pathophysiology of diabetic and proliferative diseases.

METHODS

Ten patients with proliferative diabetic retinopathy (57.1 years, 5 female and 5 male) and 8 patients (51 years, 5 female and 3 male) with other retinal diseases including macular hole and epiretinal membrane were included in this study. All the patients had undergone pars plana vitrectomy for complications of the diseases. Vitreous samples were collected by vitreous tap during the vitrectomy. Adrenomedullin analysis was made by using reverse-phase high-performance liquid chromatography (HPLC). Leptin was measured by enzyme-linked immunosorbent assay (ELISA). Body mass index (BMI) [weight (kg)/height (m2)] was calculated for each group. The Mann-Whitney U test was used for statistics.

RESULTS

The age, gender ratio and BMI were not substantially different between the two groups. The mean vitreous adrenomedullin levels (63.9+/-7.1 pmol/l) were significantly higher (p<0.05) in group I than in group II (34.25+/-3.0 pmol/l). Leptin levels in vitreous (4.54+/-1.6 ng/ml) were also significantly higher (p<0.05) in patients with diabetic retinopathy than in those without diabetes (1.83+/-0.5 ng/ml).

CONCLUSION

Increased adrenomedullin and leptin levels in vitreous humor might be a possible newly associated factor in the course of vascular and proliferative retinal diseases.

Leptin and prostate: implications for cancer prevention--overview of genetics and molecular interactions

Leptin's relation with obesity has been clearly demonstrated while its role in oncobiology is still largely unknown. Epidemiological studies on serum leptin provide valuable though controversial data, while in vitro studies consistently show leptin's angiogenic and proliferative potential in cancer. Leptin's activity is mediated by tissue-specific receptors, differentially expressed in organs such as the prostate. The molecular cascades triggered by leptin result in prostatic cell proliferation and angiogenic activity, thus linking the hormone mainly to prostate cancer prognosis. This review also addresses leptin's metabolic interactions with cytokines, growth factors or hormones, establishing perceptive pathways leading to carcinogenesis or prostate cancer progression and metastasis. Better understanding of these mechanisms may help in the development of new and more effective treatments for prostate cancer. The consolidation of leptin molecular genetics profile in prostate cancer patients may help to create susceptibility groups in normal individuals, facilitating a preventive dietary intervention or strategies for chemoprevention. We hypothesize that the balance between androgen and leptin levels may facilitate the increase in the ratio of androgen-independent prostate cancer cells to androgen-dependent cells in the tumour.

Leptin system in embryo development and implantation: a protein in search of a function

Implantation is a crucial moment in the reproduction process that requires perfect synchronization between the embryo and the maternal endometrium. The embryo must reach the blastocyst stage and the endometrium must be prepared to receive it. An appropriate and specific molecular dialogue must also take place between them. There is ample evidence to show that the leptin system is implicated in this cross-talk. Examples are described. Although there is some controversy surrounding the data, they are supported by the presence of leptin receptor mRNA in mouse and human oocytes and embryos throughout preimplantation development. Otherwise, the leptin mRNA is only detected at the blastocyst stage in both human and mouse. Furthermore, leptin is found at higher concentrations in the conditioned media from competent human blastocysts than in those from arrested embryos, suggesting that this molecule is a marker for blastocyst viability. Given that expression of the leptin receptor increases in the human endometrium during the luteal phase, the secreted leptin could trigger its activation. Finally, leptin and the leptin receptor have been detected in implantation sites. All these findings point to the involvement of the leptin system in the molecular mechanism of the implantation process and embryo development.

Vascular endothelial cell cyclic nucleotide phosphodiesterases and regulated cell migration: implications in angiogenesis

Angiogenesis is necessary during embryonic development and wound healing but can be detrimental in pathologies, including cancer. Because initiation of angiogenesis involves migration and proliferation of vascular endothelial cells (VECs) and cAMP-elevating agents inhibit these events, such agents may represent a novel therapeutic avenue to controlling angiogenesis. Intracellular cAMP levels are regulated by their synthesis by adenylyl cyclases and hydrolysis by cyclic nucleotide phosphodiesterases (PDEs). In this report, we show that human VECs express variants of PDE2, PDE3, PDE4, and PDE5 families and demonstrate that the levels of these enzymes differ in VECs derived from aorta, umbilical vein, and microvascular structures. Selective inhibition of PDE2 did not increase cAMP in any VECs, whether in the absence or presence of forskolin, but it did inhibit migration of all VECs studied. Inhibition of PDE4 activity decreased migration, and in conjunction with forskolin, increased cAMP in all VECs studied. PDE3 inhibition potentiated forskolin-induced increases in cAMP and inhibited migration in VECs derived from aorta and umbilical vein but not in microvascular VECs. In experiments with combinations of PDE2, PDE3, and PDE4 inhibitors, a complex interaction between the abilities of these agents to limit human VEC migration was observed. Overall, our data are consistent with the hypothesis that PDE subtype inhibition allows different effects in distinct VEC populations and indicate that these agents may represent novel therapeutic agents to limit angiogenesis in complex human diseases.

Leptin stimulates ischemia-induced retinal neovascularization: possible role of vascular endothelial growth factor expressed in retinal endothelial cells

Diabetic retinopathy is the leading cause of new blindness in adults in developed countries. Leptin, an adipocyte-derived hormone, stimulates endothelial proliferation and angiogenesis. This study was designed to elucidate the pathophysiologic role of leptin in the progression of retinal neovascularization. Using the retinopathy of prematurity model, a mouse model of ischemia-induced retinal neovascularization, we have demonstrated more pronounced retinal neovascularization in 17-day-old transgenic mice overexpressing leptin than in age-matched wild-type littermates. Ischemia-induced retinal neovascularization was markedly suppressed in 17-day-old leptin-deficient ob/ob mice. Western blot analysis revealed that a biologically active leptin receptor isoform is expressed in mouse retinal endothelial cells. Leptin receptor expression was also detected in primary cultures of porcine retinal endothelial cells, where it upregulated vascular endothelial growth factor (VEGF) mRNA expression. This effect was thought to be mediated at least partly through the activation of signal transducers and activators of transcription (STAT)3, because adenoviral transfection of the dominant-negative form of STAT3 abolished the leptin-induced upregulation of VEGF mRNA expression in retinal endothelial cells. This study provides evidence that leptin stimulates the ischemia-induced retinal neovasucularization possibly through the upregulation of endothelial VEGF, thereby suggesting that leptin antagonism may offer a novel therapeutic strategy to prevent or treat diabetic retinopathy.

Maternal serum, amniotic fluid and cord leptin levels at term: their correlations with fetal weight

AIMS

To investigate the relationship between fetal weight and leptin levels in maternal serum, amniotic fluid and umbilical cord.

METHODS

Forty pregnant women presenting for antenatal care at early weeks of gestation were enrolled for the study. Maternal and cord blood samples for leptin measurement were obtained at birth. Amniotic fluid samples were recovered by amniotomy performed during labor. Maternal body mass index and placental weight were also recorded. Leptin measurement was carried out using the ELISA method. Spearman's correlation test was used for comparison of non-parametric data.

RESULTS

Leptin concentration in venous cord blood correlated significantly with birth weight and placental weight whereas maternal serum and amniotic fluid leptin levels did not show correlation with birth weight. There were no significant correlations between leptin levels in maternal serum, cord blood and amniotic fluid.

CONCLUSION

We conclude that lack of correlation between leptin levels in mother, cord and amniotic fluid suggest that these compartments may be non-communicating separate units or have different mechanisms regulating leptin synthesis or degradation, and that leptin in maternal blood and amniotic fluid may not have a direct effect on fetal growth but rather a different role in pregnancy.

Adipose tissue angiogenesis

A review of adipose tissue angiogenesis includes the morphological and cytochemical development of adipose tissue vasculature and the concept of primitive fat organs. Spatial and temporal relationships between fetal vascular and fat cell development are discussed, including depot- and genetic-dependent arteriolar differentiation. The relationship between connective tissue deposition and elaboration of adipose tissue vasculature is discussed with respect to regulating adipocyte development in a depot-dependent manner. In vitro studies indicated that depot-dependent vascular traits may be attributable to intrinsic growth characteristics of adipose tissue endothelial cells. These studies indicate that adipogenesis may be regulated by factors that drive angiogenesis. Fundamental aspects of angiogenesis, including basement membrane breakdown, vasculogenesis, angiogenic remodeling, vessel stabilization, and vascular permeability were reviewed. Critical angiogenic factors include vascular endothelial growth factor (VEGF), VEGF receptors, angiopoietins (Ang), ephrins, matrix metalloproteinases, and the plasminogen enzymatic system. Vascular endothelial growth factor is the most critical factor because it initiates the formation of immature vessels and disruption of a single VEGF allele leads to embryonic lethality in mice. Expression of VEGF is influenced by hypoxia, insulin, growth factors, and several cytokines. Angiogenic factors secreted and/or produced by adipocytes or preadipocytes are discussed. Vascular endothelial growth factor expression and secretion by adipocytes is regulated by insulin and hypoxia, and is associated with adipose tissue accretion. Vascular endothelial growth factor accounts for most of the angiogenic activity of adipose tissue. The proposed role of leptin as an adipogenic factor is reviewed with respect to efficacy on various aspects of angiogenesis relative to other angiogenic factors. The VEGF and leptin genes are both hypoxia inducible, but potential links between VEGF and leptin gene expression have not been examined. Finally, several studies including a study of mice treated with antiangiogenic factors indicate that adipose tissue accretion can be controlled through the vasculature per se.

Leptin-induced increase in leukemia inhibitory factor and its receptor by human endometrium is partially mediated by interleukin 1 receptor signaling

Leptin and leukemia inhibitory factor (LIF) have been implicated as important mediators of implantation. The present study was designed to investigate whether leptin can directly regulate the expression of LIF and its receptor (LIF-R) in human endometrial cells and/or whether leptin-induced effects are linked to, or regulated in part by IL-1 signaling. Primary endometrial cells and endometrial epithelial cell lines (HES and Ishikawa cells) were cultured for 24-48 h in a medium containing insulin (5 microg/ml) and leptin (3, 10, and 62 nm) or IL-1beta (0.6, 3, and 10 nm) in the presence or absence of cytokines and/or receptor antagonists. The endpoints included phosphorylation of signal transducer and activator of transcription 3 (STAT3) and the relative levels of LIF, LIF-R, IL-1beta, IL-1 receptor antagonist (IL-1Ra) and IL-1 receptor type I (IL-1R tI) as determined by ELISA or Western blotting techniques. Leptin treatment increases the level of phosphorylated STAT3, LIF-R, and LIF. Leptin also increases the levels of IL-1 ligand, receptor, and antagonist as was previously reported. Blockade of OB-R with antibodies or with a specific OB-R inhibitor (leptin peptide antagonist-2) abrogated leptin-induced effects, suggesting that leptin binding to its receptor activates Janus kinase 2/STAT3 signaling. Treatment of endometrial cells with IL-1beta also results in elevated levels of LIF-R. Interestingly, the inhibition of IL-1R tI with a specific antibody or with IL-1Ra negatively affects both leptin-induced and IL-1-induced effects on LIF-R levels. Abnormal endometrial LIF expression has been associated with human infertility and leptin has profound effects on the levels of LIF, IL-1, and their cognate receptors in vitro. Thus, it is tempting to speculate that leptin's role in vivo could include the regulation of other key cytokines to be fundamental to endometrial receptivity during implantation (i.e. LIF and IL-1).

Activated protein C induces endothelial cell proliferation by mitogen-activated protein kinase activation in vitro and angiogenesis in vivo

Activated protein C (APC), a natural anticoagulant, has recently been demonstrated to activate the mitogen-activated protein kinase (MAPK) pathway in endothelial cells in vitro. Because the MAPK pathway is implicated in endothelial cell proliferation, it is possible that APC induces endothelial cell proliferation, thereby causing angiogenesis. We examined this possibility in the present study. APC activated the MAPK pathway, increased DNA synthesis, and induced proliferation in cultured human umbilical vein endothelial cells dependent on its serine protease activity. Antibody against the endothelial protein C receptor (EPCR) inhibited these events. Early activation of the MAPK pathway was inhibited by an antibody against protease-activated receptor-1, whereas neither late and complete activation of the MAPK pathway nor endothelial cell proliferation were inhibited by this antibody. APC activated endothelial nitric oxide synthase (eNOS) via phosphatidylinositol 3-kinase-dependent phosphorylation, followed by activation of protein kinase G, suggesting that APC bound to EPCR might activate the endothelial MAPK pathway by a mechanism similar to that of VEGF. APC induced morphogenetic changes resembling tube-like structures of endothelial cells, whereas DIP-APC did not. When applied topically to the mouse cornea, APC clearly induced angiogenesis in wild-type mice, but not in eNOS knockout mice. These in vitro events induced by APC might at least partly explain the angiogenic activity in vivo. This angiogenic activity of APC might contribute to maintain proper microcirculation in addition to its antithrombotic activity.

Angiogenesis inhibitor, TNP-470, prevents diet-induced and genetic obesity in mice

Adipose tissue growth has been proposed to involve recruitment of new blood vessels. Here, we test the hypothesis that delivery of an angiogenesis inhibitor in mice may prevent diet-induced obesity, the most common type of obesity in humans. We show that systemic administration of a selective angiogenesis inhibitor, TNP-470 (AGM-1470), prevents obesity in high caloric diet-fed wt mice as well as in genetically leptin-deficient ob/ob mice. Inhibition of obesity in mice by TNP-470 involves a reduction of vascularity in the adipose tissue. This therapeutic strategy appears to selectively affect the growth of adipose tissue as measured by the ratio between total fat and lean body mass. Interestingly, the treatment with TNP-470 results in decreased serum levels of low-density lipoprotein cholesterol. Furthermore, insulin levels are reduced, which indicates increased insulin sensitivity, suggesting that angiogenesis inhibitors may prevent the development of type II diabetes. Our findings suggest that similarly to growth and organogenesis in other tissues, adipose tissue growth is dependent on angiogenesis. Our observations may have conceptual implications for the prevention of obesity and related disorders.

Boar seminal immunosuppressive fraction attenuates the leptin concentration and restores the thymus mass during pregnancy in mice

The immunosuppressive fraction (ISF) of boar seminal vesicle fluid was recently demonstrated to inhibit production of T helper (Th)1 cytokines and enhance production of Th2 cytokines. The present study shows the effect of the ISF on leptin concentrations in blood plasma and adipose tissue in mice during pregnancy. The ISF effect on thymus weight during pregnancy is also demonstrated. The leptin concentration in blood plasma and adipose tissue increased and remained high in the latter half of pregnancy. ISF treatment at the beginning of pregnancy significantly lowered the leptin concentration both in blood plasma and adipose tissue of pregnant mice. Thymus involution has been described previously in pregnant mice. ISF treatment compensated for the loss of thymus mass during the whole pregnancy in the ISF-treated mice. The treatment of pregnant mice with ISF did not affect pregnancy and litter size.

Intravitreous leptin concentrations in patients with proliferative diabetic retinopathy

BACKGROUND

Previous studies have demonstrated that leptin is an angiogenic factor, and an increase in intravitreous leptin concentrations in diabetic patients with proliferative diabetic retinopathy (PDR) has also been described. The aim of the present study was to investigate the source of intravitreal leptin and to determine whether it is related to PDR activity.

METHODS

Serum and vitreous fluid samples were obtained simultaneously at the time of vitreoretinal surgery from 25 patients with PDR and 32 nondiabetic patients with nonproliferative ocular diseases (controls). Both groups were matched by age, sex, and body mass index. Leptin levels were determined by ELISA.

RESULTS

We did not observe any significant differences in vitreal levels of leptin between diabetic patients with PDR and controls (4.22 [2.6-9.7] versus 3.49 [1.9-9.7] ng/mL; P = not significant). Leptin concentrations were lower in vitreous fluid than in serum samples from diabetic patients with PDR (P < 0.001) and controls (P < 0.001). A direct correlation between serum and vitreous leptin concentrations was detected in diabetic patients with PDR (r = 0.60; P = 0.01) and controls (r = 0.51; P = 0.01). Finally, we did not observe any relationship between intravitreous leptin levels and PDR activity.

CONCLUSIONS

The intraocular production of leptin is not critically involved in the etiopathogenesis of PDR. In addition, our results suggest that serum diffusion is a relevant source of leptin in vitreous fluid.

Angiogenesis in an in vivo model of adipose tissue development

Obesity is associated with an increased risk for cardiovascular disease and cancer. Angiogenesis is a critical component of these pathological processes, and expanding adipose tissue represents one of the few sites of active angiogenesis in the adult. Despite the potential importance of angiogenesis in obesity, little is known about underlying mechanisms. This problem is magnified by the absence of useful quantitative model systems. In this report, we examine the angiogenic process using the 3T3-F442A model of adipose tissue development. In this model, 3T3-F442A preadipocytes are implanted subcutaneously into athymic Balb/c nude mice. We show that these cells develop into highly vascularized fat pads over the next 14-21 days, and that these fat pads are morphologically similar to normal subcutaneous adipose tissue. Histological studies demonstrate that a new microvasculature is evident as early as 5 days after cell implantation, and real-time quantitative RT-PCR analyses show that the expression of endothelial cell markers and adipogenesis markers increase in parallel during fat pad development. Finally, these preliminary studies suggest that the neovasculature originates by sprouting from larger, host-derived blood vessels that run parallel to peripheral nerves and that endothelial progenitor cells play little, if any, role in this process.

Adiponectin-induced antiangiogenesis and antitumor activity involve caspase-mediated endothelial cell apoptosis

Obesity is a risk factor for the development of many severe human diseases such as cardiovascular disorders, diabetes, and cancer, which are tightly linked to angiogenesis. The adipose tissue produces several growth factors/hormones including leptin, tumor necrosis factor alpha, and adiponectin. It has been found that adiponectin levels are reduced in obesity. Here, we report a unique function of adiponectin as a negative regulator of angiogenesis. In vitro, adiponectin potently inhibits endothelial cell proliferation and migration. In the chick chorioallantoic membrane and the mouse corneal angiogenesis assays, adiponectin remarkably prevents new blood vessel growth. Further, we demonstrate that the antiendothelial mechanisms involve activation of caspase-mediated endothelial cell apoptosis. Adiponectin induces a cascade activation of caspases-8, -9, and -3, which leads to cell death. In a mouse tumor model, adiponectin significantly inhibits primary tumor growth. Impaired tumor growth is associated with decreased neovascularization, leading to significantly increased tumor cell apoptosis. These data demonstrate induction of endothelial apoptosis as an unique mechanism of adiponectin-induced antiangiogenesis. Adiponectin, as a direct endogenous angiogenesis inhibitor, may have therapeutic implications in the treatment of angiogenesis-dependent diseases.