Insulin exposure mitigates the increase of arterial stiffness in patients with type 2 diabetes and albuminuria: an exploratory analysis.

AIMS: Insulin possesses both vasodilatory and sympathomimetic activities. The aim was to examine the relationship between changes in insulin exposure and arterial stiffness in type 2 diabetes (T2D). METHODS: Patients with T2D with (n = 22) or without (n = 24) albuminuria, and non-diabetic controls (n = 25) were randomized to a crossover study having a breakfast with or without pre-meal rapid-acting insulin. Pulse wave velocity (PWV) was measured at 30 min before and at 60-min intervals up to 240 min after the breakfast. RESULTS: At baseline, both postprandial aortic (p = 0.022) and brachial (p = 0.011) PWV were higher in individuals with T2D than in healthy controls irrespective of the presence of albuminuria. In patients with albuminuria, weight-adjusted insulin dose correlated inversely with the excursion of the aortic (r = - 0.412, p = 0.006) and brachial (r = - 0.372; p = 0.014) PWV. Similarly, circulating endogenous insulin concentrations correlated inversely with the aortic (r = - 0.347, p = 0.026) and brachial (r = - 0.622, p = <0.001) PWV. No correlations between insulin and PWV were observed in patients without albuminuria or in healthy controls. CONCLUSIONS: The inverse correlation between insulin and PWV in T2D with albuminuria may reflect a vasorelaxing effect of insulin. CLINICAL TRIAL REGISTRATION NUMBER: The study was registered (clinicaltrials.gov) with the identifier of NCT01159938.

Influence of Postprandial Hyperglycemic Conditions on Arterial Stiffness in Patients With Type 2 Diabetes.

CONTEXT: Patients with type 2 diabetes (T2D) are at an increased risk of cardiovascular disease. OBJECTIVE: The objective of the study was to determine whether postprandial hyperglycemia affects arterial function in T2D. DESIGN: A single-center, open-label study of three groups of men were studied: 1) T2D patients with albuminuria (n = 22), 2) T2D patients without albuminuria (n = 24), and 3) nondiabetic controls (n = 25). Patients were randomized to a two-period crossover study schedule, ingesting breakfast, with or without insulin lispro (to induce low or high postprandial glycemia). MAIN OUTCOME MEASURES: Arterial stiffness was assessed by calculating pulse wave velocity (PWV) and augmentation index using applanation tonometry, and endothelial dysfunction was assessed using peripheral arterial tonometry, 30 minutes before breakfast and up to 240 minutes after breakfast. RESULTS: At baseline, arterial stiffness was increased in patients. When adjusted for age and body mass index, in a combined group of patients with and without albuminuria, brachial PWV was higher during low (P = .032) and high (P = .038) postprandial glycemia vs controls. These differences were driven by the albuminuria group vs controls during low (P = .014) and high (P = .018) postprandial glycemia. No differences were observed in aortic PWV, augmentation index, or peripheral arterial tonometry ratio between patients and controls. Endothelin-1 and IL-6 were higher, and superoxide dismutase was lower, during postprandial hyperglycemia in T2D patients vs controls. CONCLUSIONS: In patients with T2D and albuminuria, brachial PWV was higher under postprandial hyperglycemic conditions, relative to controls. These data suggest that hyperglycemia induces an increase in stiffness of intermediate-sized arteries. We found no changes in other parts of the arterial bed.

The propeptides of VEGF-D determine heparin binding, receptor heterodimerization, and effects on tumor biology.

VEGF-D is an angiogenic and lymphangiogenic glycoprotein that can be proteolytically processed generating various forms differing in subunit composition due to the presence or absence of N- and C-terminal propeptides. These propeptides flank the central VEGF homology domain, that contains the binding sites for VEGF receptors (VEGFRs), but their biological functions were unclear. Characterization of propeptide function will be important to clarify which forms of VEGF-D are biologically active and therefore clinically relevant. Here we use VEGF-D mutants deficient in either propeptide, and in the capacity to process the remaining propeptide, to monitor the functions of these domains. We report for the first time that VEGF-D binds heparin, and that the C-terminal propeptide significantly enhances this interaction (removal of this propeptide from full-length VEGF-D completely prevents heparin binding). We also show that removal of either the N- or C-terminal propeptide is required for VEGF-D to drive formation of VEGFR-2/VEGFR-3 heterodimers which have recently been shown to positively regulate angiogenic sprouting. The mature form of VEGF-D, lacking both propeptides, can also promote formation of these receptor heterodimers. In a mouse tumor model, removal of only the C-terminal propeptide from full-length VEGF-D was sufficient to enhance angiogenesis and tumor growth. In contrast, removal of both propeptides is required for high rates of lymph node metastasis. The findings reported here show that the propeptides profoundly influence molecular interactions of VEGF-D with VEGF receptors, co-receptors, and heparin, and its effects on tumor biology.

Tumor location and nature of lymphatic vessels are key determinants of cancer metastasis.

Tumor metastasis to lymph nodes is a key indicator of patient survival, and is enhanced by the neo-lymphatics induced by tumor-secreted VEGF-C or VEGF-D, acting via VEGFR-3 signalling. These targets constitute important avenues for anti-metastatic treatment. Despite this new understanding, clinical observations linking metastasis with tumor depth or location suggest that lymphangiogenic growth factors are not the sole determinants of metastasis. Here we explored the influence of tumor proximity to lymphatics capable of responding to growth factors on nodal metastasis in a murine VEGF-D over-expression tumor model. We found that primary tumor location profoundly influenced VEGF-D-mediated lymph node metastasis: 89 % of tumors associated with the flank skin metastasised, in contrast with only 19 % of tumors located more deeply on the body wall (p < 0.01). Lymphatics in metastatic tumors arose from small lymphatics, and displayed distinct molecular and morphological profiles compared with those found in normal lymphatics. Smaller lymphatic subtypes were more abundant in skin (2.5-fold, p < 0.01) than in body wall, providing a richer source of lymphatics for VEGF-D(+) skin tumors, a phenomenon also confirmed in human samples. This study shows that the proximity of a VEGF-D(+) primary tumor to small lymphatics is an important determinant of metastasis. These observations may explain why tumor location relative to the lymphatic network is prognostically important for some human cancers.

Proteolytic processing of vascular endothelial growth factor-D is essential for its capacity to promote the growth and spread of cancer.

VEGF-D is a mitogen for endothelial cells that promotes tumor growth and metastatic spread in animal models, and expression of which correlates with lymph node metastasis in some human cancers. It is secreted from the cell as a full-length form with propeptides flanking a central region containing binding sites for VEGFR-2 and VEGFR-3, receptors that signal for angiogenesis and lymphangiogenesis. The propeptides can be cleaved from VEGF-D, enhancing affinity for VEGFR-2 and VEGFR-3 in vitro; however, the importance of this processing in cancer is unclear. To explore the necessity of processing for the effects of VEGF-D in cancer, we use a mutant full-length form that cannot be processed, and show that, in contrast to full-length VEGF-D that is processed, this mutant does not promote tumor growth and lymph node metastasis in a mouse tumor model. Processing of VEGF-D is required for tumor angiogenesis, lymphangiogenesis, and recruitment of tumor-associated macrophages. These observations may be explained by the requirement of processing for VEGF-D to bind neuropilin receptors and activate VEGFR-2. Our results indicate that proteolytic processing is necessary for VEGF-D to promote the growth and spread of cancer, and suggest that enzymes catalyzing this processing could be targets for antimetastatic therapeutics.

Advanced glycation end-products induce vascular dysfunction via resistance to nitric oxide and suppression of endothelial nitric oxide synthase.

OBJECTIVE: A number of factors contribute to diabetes-associated vascular dysfunction. In the present study, we tested whether exposure to advanced glycation end-products (AGEs) impairs vascular reactivity independently of hyperglycemia and examined the potential mechanisms responsible for diabetes and AGE-associated vascular dysfunction. METHODS: Vasodilator function was studied using infusion of exogenous AGEs into Sprague-Dawley rats as compared with control and streptozotocin-induced diabetic rats all followed for 16 weeks (n = 10 per group). The level of arginine metabolites and expression of endothelial nitric oxide synthase (eNOS) and downstream mediators of nitric oxide-dependent signaling were examined. To further explore these mechanisms, cultured bovine aortic endothelial cells (BAECs) were exposed to AGEs. RESULTS: Both diabetic and animals infused with AGE-modified rat serum albumin (AGE-RSA) had significantly impaired vasodilatory response to acetylcholine. Unlike diabetes-associated endothelial dysfunction, AGE infusion was not associated with changes in plasma arginine metabolites, asymmetric dimethyl-L-arginine levels or eNOS expression. However, expression of the downstream mediator cGMP-dependent protein kinase 1 (PKG-1) was significantly reduced by both AGE exposure and diabetes. AGEs also augmented hyperglycemia-associated depletion in endothelial nitric oxide production and eNOS protein expression in vitro, and the novel AGE inhibitor, alagebrium chloride, partly restored these parameters. CONCLUSION: We demonstrate that AGEs represent a potentially important cause of vascular dysfunction, linked to the induction of nitric oxide resistance. These findings also emphasize the deleterious and potentially additive effects of AGEs and hyperglycemia in diabetic vasculature.

Sox18 induces development of the lymphatic vasculature in mice.

The lymphatic system plays a key role in tissue fluid regulation and tumour metastasis, and lymphatic defects underlie many pathological states including lymphoedema, lymphangiectasia, lymphangioma and lymphatic dysplasia. However, the origins of the lymphatic system in the embryo, and the mechanisms that direct growth of the network of lymphatic vessels, remain unclear. Lymphatic vessels are thought to arise from endothelial precursor cells budding from the cardinal vein under the influence of the lymphatic hallmark gene Prox1 (prospero homeobox 1; ref. 4). Defects in the transcription factor gene SOX18 (SRY (sex determining region Y) box 18) cause lymphatic dysfunction in the human syndrome hypotrichosis-lymphoedema-telangiectasia, suggesting that Sox18 may also play a role in lymphatic development or function. Here we use molecular, cellular and genetic assays in mice to show that Sox18 acts as a molecular switch to induce differentiation of lymphatic endothelial cells. Sox18 is expressed in a subset of cardinal vein cells that later co-express Prox1 and migrate to form lymphatic vessels. Sox18 directly activates Prox1 transcription by binding to its proximal promoter. Overexpression of Sox18 in blood vascular endothelial cells induces them to express Prox1 and other lymphatic endothelial markers, while Sox18-null embryos show a complete blockade of lymphatic endothelial cell differentiation from the cardinal vein. Our findings demonstrate a critical role for Sox18 in developmental lymphangiogenesis, and suggest new avenues to investigate for therapeutic management of human lymphangiopathies.

Overexpression of vascular endothelial growth factor-B in mouse heart alters cardiac lipid metabolism and induces myocardial hypertrophy.

Vascular endothelial growth factor (VEGF)-B is poorly angiogenic but prominently expressed in metabolically highly active tissues, including the heart. We produced mice expressing a cardiac-specific VEGF-B transgene via the alpha-myosin heavy chain promoter. Surprisingly, the hearts of the VEGF-B transgenic mice showed concentric cardiac hypertrophy without significant changes in heart function. The cardiac hypertrophy was attributable to an increased size of the cardiomyocytes. Blood capillary size was increased, whereas the number of blood vessels per cell nucleus remained unchanged. Despite the cardiac hypertrophy, the transgenic mice had lower heart rate and blood pressure than their littermates, and they responded similarly to angiotensin II-induced hypertension, confirming that the hypertrophy does not compromise heart function. Interestingly, the isolated transgenic hearts had less cardiomyocyte damage after ischemia. Significantly increased ceramide and decreased triglyceride levels were found in the transgenic hearts. This was associated with structural changes and eventual lysis of mitochondria, resulting in accumulation of intracellular vacuoles in cardiomyocytes and increased death of the transgenic mice, apparently because of mitochondrial lipotoxicity in the heart. These results suggest that VEGF-B regulates lipid metabolism, an unexpected function for an angiogenic growth factor.

Reevaluation of the role of VEGF-B suggests a restricted role in the revascularization of the ischemic myocardium.

OBJECTIVE: The endogenous role of the VEGF family member vascular endothelial growth factor-B (VEGF-B) in pathological angiogenesis remains unclear. METHODS AND RESULTS: We studied the role of VEGF-B in various models of pathological angiogenesis using mice lacking VEGF-B (VEGF-B(-/-)) or overexpressing VEGF-B(167). After occlusion of the left coronary artery, VEGF-B deficiency impaired vessel growth in the ischemic myocardium whereas, in wild-type mice, VEGF-B(167) overexpression enhanced revascularization of the infarct and ischemic border zone. By contrast, VEGF-B deficiency did not affect vessel growth in the wounded skin, hypoxic lung, ischemic retina, or ischemic limb. Moreover, VEGF-B(167) overexpression failed to enhance vascular growth in the skin or ischemic limb. CONCLUSIONS: VEGF-B appears to have a relatively restricted angiogenic activity in the ischemic heart. These insights might offer novel therapeutic opportunities.

Receptor for advanced glycation end products (RAGE) deficiency attenuates the development of atherosclerosis in diabetes.

OBJECTIVE: Activation of the receptor for advanced glycation end products (RAGE) in diabetic vasculature is considered to be a key mediator of atherogenesis. This study examines the effects of deletion of RAGE on the development of atherosclerosis in the diabetic apoE(-/-) model of accelerated atherosclerosis. RESEARCH DESIGN AND METHODS: ApoE(-/-) and RAGE(-/-)/apoE(-/-) double knockout mice were rendered diabetic with streptozotocin and followed for 20 weeks, at which time plaque accumulation was assessed by en face analysis. RESULTS: Although diabetic apoE(-/-) mice showed increased plaque accumulation (14.9 +/- 1.7%), diabetic RAGE(-/-)/apoE(-/-) mice had significantly reduced atherosclerotic plaque area (4.9 +/- 0.4%) to levels not significantly different from control apoE(-/-) mice (4.3 +/- 0.4%). These beneficial effects on the vasculature were associated with attenuation of leukocyte recruitment; decreased expression of proinflammatory mediators, including the nuclear factor-kappaB subunit p65, VCAM-1, and MCP-1; and reduced oxidative stress, as reflected by staining for nitrotyrosine and reduced expression of various NADPH oxidase subunits, gp91phox, p47phox, and rac-1. Both RAGE and RAGE ligands, including S100A8/A9, high mobility group box 1 (HMGB1), and the advanced glycation end product (AGE) carboxymethyllysine were increased in plaques from diabetic apoE(-/-) mice. Furthermore, the accumulation of AGEs and other ligands to RAGE was reduced in diabetic RAGE(-/-)/apoE(-/-) mice. CONCLUSIONS: This study provides evidence for RAGE playing a central role in the development of accelerated atherosclerosis associated with diabetes. These findings emphasize the potential utility of strategies targeting RAGE activation in the prevention and treatment of diabetic macrovascular complications.

Molecular pathways for lymphangiogenesis and their role in human disease.

The lymphatic network functions to return fluid, cells and macromolecules to the circulation. Recent characterization of growth factors that control the growth and development of the lymphatics, and markers which specify lymphatic endothelial cells have enhanced our understanding of this system. Members of the VEGF family of factors are key regulators of these vessels with VEGF-C/VEGF-D and VEGFR-3 being the best validated signalling pathways in lymphangiogenesis. The study of these molecules in various pathologies has shown that they are important in the processes of cancer metastasis and in the formation of lymphoedema. Knowledge of these molecular pathways allows for the generation of modulators of these pathways which could form the basis of novel therapeutic approaches.

Proprotein convertases promote processing of VEGF-D, a critical step for binding the angiogenic receptor VEGFR-2.

Vascular endothelial growth factor (VEGF)-D is a secreted glycoprotein that induces angiogenesis and lymphangiogenesis. It consists of a central domain, containing binding sites for VEGF receptor-2 (VEGFR-2) and VEGFR-3, and N- and C-terminal propeptides. It is secreted from the cell as homodimers of the full-length form that can be proteolytically processed to remove the propeptides. It was recently shown, using adenoviral gene delivery, that fully processed VEGF-D induces angiogenesis in vivo, whereas full-length VEGF-D does not. To better understand these observations, we monitored the effect of VEGF-D processing on receptor binding using a full-length VEGF-D mutant that cannot be processed. This mutant binds VEGFR-2, the receptor signaling for angiogenesis, with approximately 17,000-fold lower affinity than mature VEGF-D, indicating the importance of processing for interaction with this receptor. Further, we show that members of the proprotein convertase (PC) family of proteases promote VEGF-D processing, which facilitates the VEGF-D/VEGFR-2 interaction. The PCs furin and PC5 promote cleavage of both propeptides, whereas PC7 promotes cleavage of the C-terminal propeptide only. The finding that PCs promote activation of VEGF-D and other proteins with roles in cancer such as matrix metalloproteinases, emphasizes the importance of these enzymes as potential regulators of tumor progression and metastasis.

VEGF-C-induced lymphangiogenesis in sentinel lymph nodes promotes tumor metastasis to distant sites.

The mechanisms by which tumors metastasize to sentinel and distant lymph nodes, and beyond, are poorly understood. We developed transgenic mice that overexpress vascular endothelial growth factor-C (VEGF-C) and green fluorescent protein specifically in the skin and studied the effects of chemically-induced skin carcinogenesis in this model. We found that in contrast to VEGF-A, VEGF-C does not increase the growth of primary tumors, but instead induces expansion of lymphatic networks within sentinel lymph nodes, even before the onset of metastasis. Once the metastatic cells arrived at the sentinel lymph nodes, the extent of lymphangiogenesis at these sites increased. Of importance, in mice with metastasis-containing sentinel lymph nodes, tumors that expressed VEGF-C were more likely to metastasize to additional organs, such as distal lymph nodes and lungs. No metastases were observed in distant organs in the absence of lymph node metastases. These findings indicate an important role of VEGF-C-induced lymph node lymphangiogenesis in the promotion of cancer metastasis beyond the sentinel lymph nodes. VEGF-C is therefore a good target to slow or even prevent the onset of metastasis.

Pulmonary vascular endothelial growth factor-C in development and lung injury in preterm infants.

RATIONALE: In mice, vascular endothelial growth factor-C (VEGF-C) plays an important role in development of the lymphatic system and in pathogenesis of pulmonary inflammation. Its role in development of the lymphatic system in human lung and in lung injury in newborns remains unclear. OBJECTIVES: We studied the role of VEGF-C in developing human lung, and in acute and chronic lung injury in preterm infants. METHODS: Included in the immunohistochemistry study were 10 fetuses, 15 control neonates without primary lung disease, 15 preterm infants with respiratory distress syndrome, and 8 infants with bronchopulmonary dysplasia. Tracheal aspirate fluid samples of intubated very-low-birth-weight infants during Postnatal Weeks 1-5 were analyzed with ELISA. RESULTS: Bronchiolar staining for VEGF-C was observed in all 48 samples. Alveolar epithelial staining was seen in most fetuses (8/10). In addition, staining was observed in alveolar macrophages in bronchopulmonary dysplasia (4/8), and late respiratory distress syndrome (2/7). VEGF receptor-3 (VEGFR-3) staining was observed in lymphatic endothelium adjacent to vascular endothelium. VEGF-C was expressed consistently in tracheal aspirate fluid, being highest during the first 2 postnatal days. Antenatal administration of glucocorticoids was associated with higher VEGF-C in tracheal aspirate fluid. CONCLUSIONS: The pattern of pulmonary VEGF-C and VEGFR-3 protein expression and consistent VEGF-C protein appearance in tracheal aspirate fluid in human preterm infants indicate a role for VEGF-C in the physiologic development of the lymphatic system of the lung.

The biology of vascular endothelial growth factors.

The discovery of the vascular endothelial growth factor (VEGF) family members VEGF, VEGF-B, placental growth factor (PlGF), VEGF-C and VEGF-D and their receptors VEGFR-1, -2 and -3 has provided tools for studying the vascular system in development as well as in diseases ranging from ischemic heart disease to cancer. VEGF has been established as the prime angiogenic molecule during development, adult physiology and pathology. PlGF may primarily mediate arteriogenesis, the formation of collateral arteries from preexisting arterioles, with potential future therapeutic use in for example occlusive atherosclerotic disease. VEGF-C and VEGF-D are primarily lymphangiogenic factors, but they can also induce angiogenesis in some conditions. While many studies have addressed the role of angiogenesis and the blood vasculature in human physiology, the lymphatic vascular system has until recently attracted very little attention. In this review, we will discuss recent advances in angiogenesis research and provide an overview of the molecular players involved in lymphangiogenesis.

PDGF-D induces macrophage recruitment, increased interstitial pressure, and blood vessel maturation during angiogenesis.

Platelet-derived growth factor-D (PDGF-D) is a recently characterized member of the PDGF family with unknown in vivo functions. We investigated the effects of PDGF-D in transgenic mice by expressing it in basal epidermal cells and then analyzed skin histology, interstitial fluid pressure, and wound healing. When compared with control mice, PDGF-D transgenic mice displayed increased numbers of macrophages and elevated interstitial fluid pressure in the dermis. Wound healing in the transgenic mice was characterized by increased cell density and enhanced recruitment of macrophages. Macrophage recruitment was also the characteristic response when PDGF-D was expressed in skeletal muscle or ear by an adeno-associated virus vector. Combined expression of PDGF-D with vascular endothelial growth factor-E (VEGF-E) led to increased pericyte/smooth muscle cell coating of the VEGF-E-induced vessels and inhibition of the vascular leakiness that accompanies VEGF-E-induced angiogenesis. These results show that full-length PDGF-D is activated in tissues and is capable of increasing interstitial fluid pressure and macrophage recruitment and the maturation of blood vessels in angiogenic processes.

Bmx tyrosine kinase transgene induces skin hyperplasia, inflammatory angiogenesis, and accelerated wound healing.

The Bmx gene, a member of the Tec family of nonreceptor protein tyrosine kinases, is expressed in arterial endothelium and in certain hematopoietic and epithelial cells. Previous in vitro studies have implicated Bmx signaling in cell migration and survival and suggested that it contributes to the progression of prostate carcinomas. However, the function of Bmx in normal tissues in vivo is unknown. We show here that Bmx expression is induced in skin keratinocytes during wound healing. To analyze the role of Bmx in epidermal keratinocytes in vivo, we generated transgenic mice overexpressing Bmx in the skin. We show that Bmx overexpression accelerates keratinocyte proliferation and wound reepithelialization. Bmx expression also induces chronic inflammation and angiogenesis in the skin, and gene expression profiling suggests that this occurs via cytokine-mediated recruitment of inflammatory cells. Our studies provide the first data on Bmx function in vivo and form the basis of evaluation of its role in epithelial neoplasia.

Vascular endothelial growth factors C and D and their VEGFR-2 and 3 receptors in blood and lymphatic vessels in healthy and arthritic synovium.

OBJECTIVE: To localize vascular endothelial growth factor C (VEGF-C) and VEGF-D in synovial specimens in relation to their VEGFR-2 and VEGFR-3 receptors in blood and lymphatic vessels. METHODS: Immunohistochemical staining and messenger RNA analysis from control and arthritic synovial membrane specimens. RESULTS: Quantitative RT-PCR disclosed that VEGF-C mRNA copy numbers were higher than VEGF-D mRNA copy numbers in the rheumatoid arthritis (RA), osteoarthritis, and control patient groups studied (p < 0.01). Immunohistochemical staining localized VEGF-C to synovial lining cell layer, pericytes, and smooth muscle cells of blood vessels. The number of VEGF-C positive cells was increased in the synovial lining of ankylosing spondylitis (AS) and RA compared to control synovium. However, in contrast to control synovial lining, little if any VEGF-D was detected in AS or RA synovial lining. VEGFR-2 expressing stromal blood vessels, also positive for the vascular endothelial marker PAL-E and the basement membrane marker laminin, were more abundant in RA and AS than in controls. Interestingly, the lymphatic endothelial receptor VEGFR-3 was also expressed in most synovial vessels, especially in the sublining capillaries and venules. CONCLUSION: VEGF-C is strongly expressed in the hypertrophic synovial lining of arthritic joints, whereas VEGF-D expression is very low in AS and RA. The expression of VEGF-C and VEGF-D in pericytes and smooth muscle cells suggests that these factors may have a role in maintaining vascular homeostasis. The VEGF receptors VEGFR-2 and VEGFR-3 are present in most of the sublining blood vessels. The expression of the lymphatic marker VEGFR-3 in the sublining blood vessels may relate to fluid filtration and/or fenestrations. The relatively few lymphatic vessels along with increased vascular permeability in RA may contribute to the development of tissue edema and joint stiffness.