Vascular endothelial growth factor is increased following coronary artery occlusion in the dog heart

Is VEGF under-expressed in Indian children with Perthes disease?

BACKGROUND

The role of vascular endothelial growth factor (VEGF) after ischaemic necrosis of the femoral head in Legg-Calve-Perthes disease (LCPD) has not been adequately studied in humans, especially in Indian population. Therefore, we aimed to evaluate the serum levels of VEGF-A in Indian children with various stages of LCPD and compare them with those of an age- and sex-matched control group of healthy children.

METHODS

In this case-control study, we enrolled 42 children (below 14 years age) suffering from LCPD and 21 age- and sex-matched healthy controls. Patients were classified radiographically according to Waldenstrom's classification. Serum VEGF-A was estimated by sandwich enzyme-linked immunosorbent assay technique. The serum values were compared between the patient group and the control group, as well as between the Waldenstrom subgroups. Results were expressed as means with ranges or median with interquartile range.

RESULTS

The mean age in the patient as well as the control group was 9 years (range 4-13 years). The median value (interquartile range) of serum VEGF-A was 162.5 pg/ml (673.75 pg/ml) in the patient group and 652 pg/ml (190.5 pg/ml) in the control group (p = 0.013). When compared between lower Waldenstrom stages (initial stage + stage of fragmentation) and higher Waldenstrom stages (re-ossification stage + stage of healing), the mean values of serum VEGF-A were 464.7 pg/ml (range 0-2211 pg/ml) and 301.1 pg/ml (range 0-1910 pg/ml), respectively (p = 0.305).

CONCLUSIONS

VEGF is under-expressed in Indian children suffering from LCPD. As VEGF acts as a key regulator of endochondral ossification, our finding may open new therapeutic approaches to the disease. Also, serum VEGF may act as a valuable marker for the follow-up of the disease. Our study also provides baseline data about serum VEGF-A levels in Indian cohort of LCPD patients. Future multi-centre studies are warranted with a larger sample size to fully appreciate the patho-physiological changes in VEGF occurring in LCPD.

Cardiac tissue injury resistance during myocardial infarction at adulthood by developmental exposure to cadmium

It has been suggested that prenatal exposure to cadmium may alter the cardiovascular function during adulthood. Using the left coronary artery ligation model of acute myocardial infarction, we studied the cardiac function of female adult offspring rats exposed to cadmium (30 ppm) during gestation. The cardiac ischemic zone in the control and cadmium-exposed groups was measured 72 h post-ligation using the TPT staining technique. Offspring from cadmium-treated dams showed a significantly smaller infarcted area compared with the control group (7.1 ± 1.5 vs. 19.6 ± 2.8%, P ≤ 0.05). We also performed echocardiographic and biochemical studies, which positively correlated with the differences observed previously. To evaluate whether the effects were associated to pre-infarct tissue damage and/or angiogenic molecules, we performed histological studies and measured the expression of vascular endothelial growth factor (VEGF), and platelet endothelial cellular adhesion molecule-1 (PECAM-1). Results revealed a higher heart vascularization in the exposed offspring that was associated with an increase in PECAM and a decrease in VEGF expression. We conclude that prenatal exposure to cadmium induces fetal adaptive responses involving changes in the expression of some cardiac angiogenic molecules resulting in long-term resistance to infarction.

Regulatory systems for hypoxia-inducible gene expression in ischemic heart disease gene therapy

Ischemic heart diseases are caused by narrowed coronary arteries that decrease the blood supply to the myocardium. In the ischemic myocardium, hypoxia-responsive genes are up-regulated by hypoxia-inducible factor-1 (HIF-1). Gene therapy for ischemic heart diseases uses genes encoding angiogenic growth factors and anti-apoptotic proteins as therapeutic genes. These genes increase blood supply into the myocardium by angiogenesis and protect cardiomyocytes from cell death. However, non-specific expression of these genes in normal tissues may be harmful, since growth factors and anti-apoptotic proteins may induce tumor growth. Therefore, tight gene regulation is required to limit gene expression to ischemic tissues, to avoid unwanted side effects. For this purpose, various gene expression strategies have been developed for ischemic-specific gene expression. Transcriptional, post-transcriptional, and post-translational regulatory strategies have been developed and evaluated in ischemic heart disease animal models. The regulatory systems can limit therapeutic gene expression to ischemic tissues and increase the efficiency of gene therapy. In this review, recent progresses in ischemic-specific gene expression systems are presented, and their applications to ischemic heart diseases are discussed.

Gene expression profile of vascular endothelial growth factor (VEGF) and its receptors in various cell types of the canine lymph node using laser capture microdissection (LCM)

The role of VEGF and its receptors has extensively been studied in tumours. In contrast, the presence and function of VEGF in normal tissues like the lymph node has not been given much attention until now. To study the expression of VEGF, VEGFR-1, VEGFR-2 and VEGFR-3 in the heterogenous cell population of the canine lymph node, laser capture microdissection was used to isolate pure cell fractions of macrophages, lymphocytes, endothelial cells, and capsule cells of the canine lymph node. To clarify if macrophages take up VEGF from the environment or express VEGF, VEGFR-1, VEGFR-2 or VEGFR-3 themselves, the mRNA expression was studied by real-time RT-PCR. After RNA isolation and subsequent analysis with the Agilent 2100 Bioanalyzer only RNA samples with appropriate RNA integrity were used for real-time PCR. For the accurate relative quantification of mRNA expression levels several reference genes were evaluated. It was shown that the reference genes HPRT1 and B2M serve as reliable reference genes for gene expression studies in the canine lymph node. Expression data analysis revealed no significant difference in VEGF expression levels between endothelial cells and the other investigated cells. VEGFR-1 expression was significantly lower in lymphocytes. Also macrophages showed a highly significant lower expression of VEGFR-1 compared to endothelial cells. In addition, the VEGFR-2 expression in lymphocytes and macrophages was significantly lower in comparison to endothelial cells. We were not able to detect VEGFR-3 mRNA in the lymphocyte cell population, in macrophages and cells of the lymph node capsule VEGFR-3 was expressed at very low levels. It was shown that laser capture microdissection in combination with quantitative real-time PCR is a valuable tool for studying the expression patterns of specific cells in their microenvironment. Our results support the hypothesis that VEGF and its receptors have other biological roles besides stimulating angiogenesis in the normal lymph node. These biological functions need to be clarified in further studies.

Hypoxia-specific gene expression for ischemic disease gene therapy

Gene therapy for ischemic diseases has been developed with various growth factors and anti-apoptotic genes. However, non-specific expression of therapeutic genes may induce deleterious side effects such as tumor formation. Hypoxia-specific regulatory systems can be used to regulate transgene expression in hypoxic tissues, in which gene expression is induced in ischemic tissues, but reduced in normal tissues by transcriptional, translational or post-translational regulation. Since hypoxia-inducible factor 1 (HIF-1) activates transcription of genes in hypoxic tissues, it can play an important role in the prevention of myocardial and cerebral ischemia. Hypoxia-specific promoters including HIF-1 binding sites have been used for transcriptional regulation of therapeutic genes. Also, hypoxia-specific untranslated regions (UTRs) and oxygen dependent degradation (ODD) domains have been investigated for translational and post-translational regulations, respectively. Hypoxia-specific gene expression systems have been applied to various ischemic disease models, including ischemic myocardium, stroke, and injured spinal cord. This review examines the current status and future challenges of hypoxia-specific systems for safe and effective gene therapy of ischemic diseases.

The relationship between severity of coronary artery disease and plasma level of vascular endothelial growth factor

OBJECTIVE

It has been known that ischemia or occlusion of coronary arteries in animal models increases the production of vascular endothelial growth factor (VEGF); however, little is known about the relationship between coronary artery disease and VEGF in humans. In this study, our aim was to evaluate the relationships between the degree of coronary occlusion and plasma VEGF level as well as other risk factors, including age, weight, arterial blood pressure, cholesterol, triglyceride, blood glucose, and high-sensitive C-reactive protein (hsCRP) in patients with established coronary artery disease.

MATERIALS AND METHODS

Our study group consisted of 77 patients. Of these, 38 patients had normal coronary angiography (control group; group C) and 39 had abnormal angiography (17 critical lesion; group CL, 22 noncritical lesion; non-CL group).

RESULTS

Plasma VEGF level was 116.95+/-30.12 pg/ml in the control group, 212.47+/-75.28 pg/ml in group CL, and 138.89+/-45.18 pg/ml in the non-CL group. Plasma VEGF level of group C was found to be lower than that of group CL (P<.05), but the difference between groups C and non-CL was insignificant (P>.05). However, logistic regression analysis showed that VEGF level of group CL was significantly higher (P<.001). There was a negative correlation between VEGF and haemoglobin (r=-0.58, P<.01), and positive correlation between VEGF and age (r=0.29, P<.04). There was no relationship between plasma VEGF level and other cardiac risk parameters. Group CL had a higher level of total and LDL-cholesterol levels.

CONCLUSION

Increased plasma VEGF levels in patients with coronary artery disease may point that the coronary lesion is critical, and VEGF increase in patients with established coronary artery disease may be used as an indicator of the need for revascularization.

Vascular endothelial growth factor mRNA expression and peritumoral edema in canine primary central nervous system tumors

Vascular endothelial growth factor (VEGF) is an important regulator of tumor angiogenesis and vascular permeability, and has been implicated both in progression of central nervous system (CNS) tumors and development of vasogenic peritumoral edema. A retrospective study was done to characterize the levels of expression of the 3 major canine VEGF isoforms (VEGF(120), VEGF(164), VEGF(188)) in a variety of spontaneous canine CNS tumors using quantitative TaqMan reverse transcription real-time polymerase chain reaction. Presence and degree of peritumoral edema also were determined in sampled tumors using magnetic resonance imaging (MRI). Increased expression of VEGF relative to normal cerebral cortex tissue was seen predominantly in high grade astrocytic (grade IV) and oligodendroglial (grade III) tumors, with lower expression in low grade astrocytomas (grade II) and meningiomas (grade I). All 3 major VEGF isoforms were present; VEGF(164) was the predominant isoform, particularly in the tumors with the highest VEGF expression. Peritumoral edema was present in all tumor types; however, a significant association between the extent of peritumoral edema and the level of VEGF expression was not apparent.

Local tolerance and systemic safety of pegaptanib sodium in the dog and rabbit

PURPOSE

To evaluate the local tolerance, systemic toxicity, and toxicokinetics in dogs and rabbits of pegaptanib sodium, an aptamer that targets vascular endothelial growth factor (VEGF(165)).

METHODS

Dogs received biweekly, bilateral, intravitreous (IVT) injections of pegaptanib sodium for 9 months at doses of 0.3 (n = 10), 1 (n = 10), or 3 mg (n = 14); 14 control dogs received phosphate-buffered saline (PBS). In rabbits, pegaptanib sodium was administered by IVT injection biweekly for 6 months at doses of 0.2 (n = 14), 0.67 (n = 14), or 2 mg (n = 18); 18 rabbits received PBS. The systemic and ocular safety of pegaptanib sodium was assessed. Assessments in both dogs and rabbits included complete ophthalmologic examinations, serum chemistry, hematology, urinalysis, and coagulation assessments, as well as gross and microscopic pathologic examination. In addition, dogs were assessed by electroretinography and electrocardiography. In a cardiovascular safety study, loading intravenous boluses and maintenance infusions of pegaptanib sodium or PBS were administered to dogs (n = 4) in an ascending dose design, with each dose level separated by 2-3 days. The pegaptanib dosing regimens were designed to achieve pegaptanib plasma concentrations of approximately 90, 270, or 900 ng/mL.

RESULTS

There were no pegaptanib sodium-associated clinical, ophthalmologic, pathologic, or cardiovascular abnormalities at doses of pegaptanib that achieved systemic and ocular exposure levels in excess of those associated with the recommended pegaptanib IVT dosing regimen of 0.3 mg per study eye in patients with age-related macular degeneration.

CONCLUSION

These studies, together with data from clinical trials, provide strong evidence that inhibition of VEGF(165) by pegaptanib in the eye is a safe therapy for the treatment of ocular neovascular disease.

Imaging of angiogenesis in cardiology

In the past decade, there have been major improvements in our understanding of angiogenesis at the genetic, molecular and cellular levels. Concentrated efforts in this area have led to new therapeutic approaches to ischaemic heart disease using angiogenic factors, gene therapy and progenitor cells. Despite very promising experimental results in animal studies, large clinical trials have failed to confirm the results in patients with coronary artery disease. Important questions such as selection of growth factors and donor cells, as well as the timing, dose and route of administration, have been raised and need to be answered. Molecular imaging approaches which may provide specific markers of the angiogenic process (e.g. integrin expression in endothelial cells) have been introduced and are expected to address some of these questions. Although few clinical imaging results are currently available, animal studies suggest the potential role of molecular imaging for characterisation of the angiogenetic process in vivo and for the monitoring of therapeutic effects.

Postpneumonectomy lung expansion elicits hypoxia-inducible factor-1α signaling

We ( 42 ) previously reported differential regulation of hypoxia-inducible factors (HIF-1α, -2α, and -3α) mRNA in canine lungs during normal maturation and postpneumonectomy (PNX) compensatory growth in the absence of overt hypoxia. To test the hypothesis that lung expansion activates HIF signaling, we replaced the right lung of six adult foxhounds with inflated custom-shaped silicone prosthesis to keep the mediastinum in the midline and minimize lateral expansion of the remaining lung. After 3 wk of recovery and stabilization of perfusion, the prosthesis was acutely deflated in three animals, causing the remaining lung to expand by 114%. In three other animals, the prosthesis remained inflated. Three days following deflation, we observed significant elevation in the mRNA and nuclear protein levels of HIF-1α (∼60%) as well as activation of its transcriptional regulator, the serine/threonine protein kinase B (phospho-Akt-to-total Akt ratio, 124%), and the mRNA and protein levels of its downstream targets, erythropoietin receptor (71–183%) as well as VEGF (33–58%) compared with the pre-PNX control lung from the same animal. The mRNA of HIF-2α, HIF-3α, and VEGF receptors did not change with acute deflation. We conclude that in vivo lung expansion by post-PNX deflation of space-occupying prosthesis elicits coordinated activation of HIF-1α signaling in adult lungs. This pathway could play an important role in mediating lung growth and remodeling during maturation and post-PNX compensation.

Activation of ASK1 during reperfusion of ischemic spinal cord

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase (MAPKKK), which plays a pivotal role in cell apoptosis. To determine the mechanism of ASK1 induction during reperfusion of ischemic spinal tissue, we used a model of rabbit spinal cord ischemia and reperfusion. To assess the role of ASK1 in spinal cord ischemia-reperfusion injuries, we examined alterations in spinal tissue morphology, protein-protein interactions, and activation of key members of the ASK1-mediated signaling pathway. Changes in spinal cord morphology were observed with hematoxylin and eosin (H&E) staining and electron microscopy. The phosphorylation levels of ASK1, JNK, and p38 were assessed by immunoblotting proteins from animals that received 30 min of ischemia followed by 1 or 24h of reperfusion. We observed increased phosphorylation of ASK1, JNK, and p38 after reperfusing ischemic spinal cords. Immunohistochemical studies were performed to determine the cellular localization of phosphorylated ASK1 (pASK1) and 14-3-3. Following reperfusion for 24h, we observed increased cytoplasmic localization of pASK1 and decreased cytoplasmic localization of 14-3-3. Immunoprecipitation analyses suggested that 14-3-3 dissociates from ASK1 during reperfusion of ischemic spinal cords. These results indicate that activation of ASK1 may play an important role in the apoptotic signaling mechanisms that occur in reperfused spinal cord injuries.

High circulating vascular endothelial growth factor (VEGF) is related to a better systolic function in diabetic hypertensive patients

BACKGROUND

VEGF seems to have a protective role on cardiac microcirculation, but no data are available on its action on cardiac function and morphology in diabetic patients. We sought to test the hypothesis that circulating VEGF levels could influence the cardiac performance in type 2 diabetic hypertensive patients.

METHODS

We studied 30 patients with type 2 diabetes and hypertension, without severe cardiac, retinal, renal and peripheral vascular damage. Ten non-diabetic hypertensive patients represented the control group. VEGF plasma levels (ELISA) and echocardiographic parameters were evaluated.

RESULTS

Diabetic patients had VEGF plasma levels higher than hypertensive non-diabetic subjects [median 82 (IQR 12-190) vs 50.5 (IQR 28-77) pg/mL, p=0.05]. Simple linear regression analysis showed that VEGF levels are related to relative wall thickness (RWT) and both endocardial and midwall systolic parameters in the diabetic patients. Multiple linear regression analysis showed that RWT and ejection fraction (EF) were the only independent correlates of VEGF (r2=0.274, p=0.03, p=0.05; respectively).

CONCLUSIONS

Our data showed that high VEGF plasma levels are associated to a better systolic function in diabetic hypertensive patients with cardiac remodeling. VEGF may play a role in the improvement of cardiac performance in diabetes.

Increased VEGF expression in the epiphyseal cartilage after ischemic necrosis of the capital femoral epiphysis

Ischemic injury to the immature femoral head produces epiphyseal cartilage damage and cessation of endochondral ossification. This study suggests that VEGF facilitates the repair of the necrotic epiphyseal cartilage, which is essential for restoration of endochondral ossification and re-establishment of the growth of the immature femoral head after ischemic necrosis.

INTRODUCTION

Legg-Calve-Perthes disease (LCPD) is a childhood form of osteonecrosis that produces growth arrest of the secondary center of ossification. The cessation of growth is caused by ischemic damage to the hypertrophic zone of the epiphyseal cartilage where endochondral ossification normally occurs. The role of vascular endothelial growth factor (VEGF) in restoring endochondral ossification in the epiphyseal cartilage after ischemic necrosis was investigated in a piglet model of LCPD because the resumption of normal growth is important for maintaining the spherical shape of the femoral head.

MATERIALS AND METHODS

Piglet femoral heads were assessed 24 h to 8 weeks after the surgical induction of ischemia. Western blot analysis, ribonuclease protection assay (RPA), immunohistochemistry, and in situ hybridization were performed.

RESULTS

Western blot analysis and RPA showed increased VEGF protein and mRNA expression, respectively, in the epiphyseal cartilage of the infarcted heads compared with the contralateral normal heads. In the normal femoral heads, VEGF-immunoreactivity (VEGF-IR) and transcripts were observed in the hypertrophic zone of the epiphyseal cartilage. In the infarcted heads, VEGF-IR and transcripts were no longer observed in the hypertrophic zone because of diffuse cell death in that zone from ischemia. However, VEGF-IR and transcripts were observed in the proliferative zone above the necrotic hypertrophic zone. At 8 weeks, vascular granulation tissue invasion of the necrotic hypertrophic zone was observed with active resorption of the necrotic cartilage. In some areas where the necrotic cartilage was completely resorbed, restoration of endochondral ossification was observed. In these areas, VEGF transcripts were observed in the newly formed hypertrophic zone.

CONCLUSIONS

VEGF expression was increased, and its spatial expression was altered in the epiphyseal cartilage after ischemic necrosis of the immature femoral head. VEGF upregulation in the proliferative zone after ischemic damage may play a role in stimulating vascular invasion and granulation tissue formation in the necrotic hypertrophic zone of the epiphyseal cartilage. This may be an important step toward facilitating the resorption of the necrotic cartilage and restoration of endochondral ossification leading to further growth and development of the femoral head.

Exercise training enhances vasodilation responses to vascular endothelial growth factor in porcine coronary arterioles exposed to chronic coronary occlusion

BACKGROUND

Chronic coronary occlusion (CCO) impairs endothelial function of distal collateral-dependent microvasculature; however, long-term exercise training (EX) seems to improve endothelial dysfunction. We hypothesized that EX enhances vasodilation responses to vascular endothelial growth factor (VEGF165), mediated via nitric oxide (NO), in arterioles exposed to CCO.

METHODS AND RESULTS

The proximal left circumflex coronary artery (LCx) of female Yucatan miniswine was surgically instrumented with an ameroid occluder to induce CCO; 8 weeks after surgery, animals were randomized into 14-week sedentary (SED) or EX (treadmill; 5 d/wk) protocols. Coronary arterioles ( approximately 100 microm in diameter) were isolated from collateral-dependent (LCx) and nonoccluded (left anterior descending; LAD) perfused myocardium of SED and EX animals. Vasodilation was assessed by videomicroscopy and MacLab data acquisition. Responses to VEGF165 were unaffected by EX in nonoccluded LAD arterioles; in contrast, EX markedly enhanced VEGF165-induced vasodilation of collateral-dependent LCx arterioles (P<0.05; EX versus SED). Furthermore, VEGF165-induced vasodilation of EX LCx arterioles exceeded that of EX or SED LAD arterioles (P<0.05). Enhanced vasodilation of EX LCx arterioles was abolished by inhibition of NO synthase and tyrosine kinase activity. Combined inhibition of NO synthase and cyclooxygenase decreased VEGF165-induced vasodilation of all vessels.

CONCLUSIONS

EX enhances VEGF165-induced vasodilation in arterioles distal to CCO; EX effects seem to be mediated through increases in NO.

Reactive oxygen species are critical mediators of coronary collateral development in a canine model

Recent evidence suggests that reactive oxygen species (ROS) promote proliferation and migration of vascular smooth muscle (VSMC) and endothelial cells (EC). We tested the hypothesis that ROS serve as crucial messengers during coronary collateral development. Dogs were subjected to brief (2 min), repetitive coronary artery occlusions (1/h, 8/day, 21 day duration) in the absence (occlusion, n = 8) or presence of N-acetylcysteine (NAC) (occlusion + NAC, n = 8). A sham group (n = 8) was instrumented identically but received no occlusions. In separate experiments, ROS generation after a single 2-min coronary artery occlusion was assessed with dihydroethidium fluorescence. Coronary collateral blood flow (expressed as a percentage of normal zone flow) was significantly increased (71 +/- 7%) in occlusion dogs after 21 days but remained unchanged (13 +/- 3%) in sham dogs. Treatment with NAC attenuated increases in collateral blood flow (28 +/- 8%). Brief coronary artery occlusion and reperfusion caused ROS production (256 +/- 33% of baseline values), which was abolished with NAC (104 +/- 12%). Myocardial interstitial fluid produced tube formation and proliferation of VSMC and EC in occlusion but not in NAC-treated or sham dogs. The results indicate that ROS are critical for the development of the coronary collateral circulation.