Therapeutic angiogenesis induced by human hepatocyte growth factor gene in rat diabetic hind limb ischemia model: molecular mechanisms of delayed angiogenesis in diabetes

Local gene transfer and expression following intramuscular administration of FGF-1 plasmid DNA in patients with critical limb ischemia

NV1FGF is an expression plasmid encoding sp.FGF-1(21-154) currently under investigation for therapeutic angiogenesis in clinical trials. NV1FGF plasmid distribution and transgene expression following intramuscular (IM) injection in patients is unknown. The study involved six patients with chronic critical limb ischemia (CLI) planned to undergo amputation. A total dose of 0.5, 2, or 4 mg NV1FGF was administered as eight IM injections (0.006, 0.25, or 0.5 mg per injection) 3-5 days before amputation. Injected sites (30 cm(3)) were divided into equally sized smaller pieces to assess spatial distribution of NV1FGF sequences (PCR), NV1FGF mRNA (reverse transcriptase-PCR), and fibroblast growth factor-1 (FGF-1)-expressing cells (immunohistochemistry). Data indicated gene expression at all doses. The distribution area was within 5-12 cm for NV1FGF sequences containing the expression cassette, up to 5 cm for NV1FGF mRNA, and up to 3 cm for FGF-1-expressing myofibers. All FGF receptors were detected indicating robust potential for bioactivity after NV1FGF gene transfer. Circulating levels of NV1FGF sequences were shown to decrease within days after injection. Data support demonstration of plasmid-mediated gene transfer and expression in muscles from patients with CLI. FGF-1 expression was shown to be limited to injection sites, which supports the concept of multiple-site injection for therapeutic use.

Percutaneous nonviral delivery of hepatocyte growth factor in an osteotomy gap promotes bone repair in rabbits: a preliminary study

Hepatocyte growth factor (HGF) was initially identified in cultured hepatocytes and subsequently reported to induce angiogenic, morphogenic, and antiapoptotic activity in various tissues. These properties suggest a potential influence of HGF on bone healing. We asked if gene transfer of human HGF (hHGF) into an osteotomy gap with a hemagglutinating virus of Japan-envelope (HVJ-E) vector promotes bone healing in rabbits. HVJ-E that contained either hHGF or control plasmid was percutaneously injected into the osteotomy gap of rabbit tibias on Day 14. The osteotomy gap was evaluated by radiography, pQCT, mechanical tests, and histology at Week 8. The expression of hHGF was evaluated by reverse transcriptase-polymerase chain reaction and immunohistochemistry at Week 3. Radiography, pQCT, and histology suggested the hHGF group had faster fracture healing. Mechanical tests demonstrated the hHGF group had greater mechanical strength. The injected tissues at 3 weeks expressed hHGF mRNA by reverse transcriptase-polymerase chain reaction. hHGF-positive immunohistochemical staining was observed in various cells at the osteotomy gap at Week 3. The data suggest delivery of hHGF plasmid into the osteotomy gap promotes fracture repair, and HGF could become a novel agent for fracture treatment.

Polydeoxyribonucleotide (PDRN) restores blood flow in an experimental model of peripheral artery occlusive disease

OBJECTIVE

This study investigated whether polydeoxyribonucleotide (PDRN) may be efficacious in the treatment of peripheral artery occlusive diseases, which are a major cause of morbidity in Western countries and still lack standardized treatment.

METHODS

We investigated the effects of PDRN, a mixture of deoxyribonucleotides, in an experimental model of hind limb ischemia (HLI) in rats to stimulate vascular endothelial growth factor (VEGF)-A production and to avoid critical ischemia. The femoral artery was excised to induce HLI. Sham-operated on rats (sham HLI) were used as controls. Animals were treated daily with intraperitoneal PDRN (8 mg/kg) or its vehicle. Animals were euthanized at day 7, 14, and 21 after the evaluation of blood flow by laser Doppler. Dissected muscles were used to measure VEGF-A messenger RNA (mRNA) and protein expression, to evaluate edema, and to assess histologic damage.

RESULTS

Administration of PDRN dramatically increased VEGF mRNA throughout the study (day 14: HLI, 7 +/- 2.2 n-fold/beta-actin; HLI + PDRN, 13.3 +/- 3.8 n-fold/beta-actin; P < .0001) and protein expression (HLI, 11 +/- 3.4 integrated intensity; HLI + PDRN, 16 +/- 3.8 integrated intensity; P < .0001). The compound stimulated revascularization, as confirmed by blood flow restoration (P < .005 vs HLI + vehicle), and blunted the histologic damage and the degree of edema. PDRN did not modify VEGF-A expression and blood flow in sham HLI animals. Furthermore, the concomitant administration of 3,7-dimethyl-1-propargilxanthine (DMPX), a selective adenosine A(2A) receptor antagonist, abolished the positive effects of PDRN, confirming that PDRN acts through this receptor.

CONCLUSION

These results led us to hypothesize a role for PDRN in treating peripheral artery occlusive diseases.

Differences in the temporal expression of regulatory growth factors during choroidal neovascular development

Although the roles of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and hepatocyte growth factor (HGF) in pathologic neovascularization have been well characterized in certain tissues, their particular functions and expression patterns in choroidal neovascularization (CNV) have not been clearly established. After localized laser trauma to Bruch's membrane to induce CNV development, the temporal changes in mRNA and protein expression of these 3 cytokines were documented and compared histologically to areas of immunofluorescence, the proliferation of endothelial cells, neovascular development, and temporal changes in vascular permeability. Changes in mRNA and protein levels of bFGF and HGF occurred quickly and reached peak expression within hours. This activity corresponded in time to intense and localized immunofluorescence for these cytokines within the choriocapillaris within laser lesion sites. During this same initial time period, mRNA upregulation of VEGF occurred, primarily within the neural retina and this expression corresponded to intense immunolabeling of Müller cells immediately adjacent to the lesion sites. By 3 days after lasering, increased VEGF(164) protein expression was measurable, whereas early neovascular development histologically corresponded to HGF and bFGF mRNA expansion into the developing choroidal neovascular membrane (CNVM). At 7 days, CNV expansion, maturation, and increased vascular permeability corresponded to peak VEGF mRNA and protein expression and to immunofluorescence of the CNVM. Differences also occurred in the expression of precursor and activated isoforms of these cytokines in the retinal pigment epithelium/choroid as compared to those in the retina. These molecular and immunocytochemical results suggest that bFGF and HGF may be important as initial regulators neovascularization in this CNV model; whereas VEGF may be important during later phases of angiogenesis and neovascular hyperpermeability.

Cardiac malformations are associated with altered expression of vascular endothelial growth factor and endothelial nitric oxide synthase genes in embryos of diabetic mice

The aim of this study was to investigate the role of nitric oxide (NO), and the expression of endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) genes in developing hearts at embryonic day 13.5 of embryos from diabetic mice. The protein and mRNA expression levels of eNOS and VEGF were significantly altered in the developing hearts of embryos from diabetic mice. The NO level was significantly decreased, whereas the VEGF concentration was significantly increased in the developing hearts of the embryos from diabetic mice. In vitro study showed a significant reduction in eNOS expression and cell proliferation in cardiac myoblast cells exposed to high glucose concentrations. Further, high glucose induced apoptosis in myoblast cells. Ultrastructural changes characteristics of apoptosis, including cell blebbing, aggregation of ribosomes and vacuoles in the cytoplasm were also evident in myoblast cells exposed to high glucose. It is suggested that hyperglycemia alters the expression of eNOS and VEGF genes that are involved in the regulation of cell growth and vasculogenesis, thereby contributing to the cardiac malformations seen in embryos from diabetic mice.

Endothelial progenitor cells in neovascularization of infarcted myocardium

Historically, revascularization of ischemic tissue was believed to occur through the migration and proliferation of endothelial cells in nearby tissues; however, evidence accumulated in recent years indicates that a subpopulation of adult, peripheral-blood cells, collectively referred to as endothelial progenitor cells (EPCs), can differentiate into mature endothelial cells. After ischemic insult, EPCs are believed to home to sites of neovascularization, where they contribute to vascular regeneration by forming a structural component of capillaries and by secreting angiogenic factors; new evidence indicates that EPCs can also differentiate into cardiomyocytes and smooth-muscle cells. These insights into the molecular and cellular processes of tissue formation suggest that cardiac function may be preserved after myocardial infarction by transplanting EPCs into ischemic heart tissue, thereby enhancing vascular and myocardial recovery. This therapeutic strategy has been effective in animal models of ischemic disorders, and results from randomized clinical trials suggest that cell-based strategies may be safe and feasible for treatment of myocardial infarction in humans and have provided early evidence of efficacy. However, the scarcity of EPCs in the peripheral blood and evidence that several disease states reduce EPC number and/or function have prompted the development of several strategies to overcome these limitations, such as the administration of genetically modified EPCs that overexpress angiogenic growth factors. To optimize therapeutic outcomes, researchers must continue to refine methods of EPC purification, expansion, and administration, and to develop techniques that overcome the intrinsic scarcity and phenotypic deficiencies of EPCs.

Enhanced cell cycle entry and mitogen-activated protein kinase-signaling and downregulation of matrix metalloproteinase-1 and -3 in human diabetic arterial vasculature

Diabetic patients have a strong predilection for atherosclerosis and postangioplasty restenosis. Accelerated cell proliferation and excessive extracellular matrix deposition are believed to contribute to the development of atherosclerotic plaques and neointima. We investigated the effect of diabetes on cell cycle, proliferation signaling, and the activation of matrix metalloproteinases (MMPs). Segments of internal mammary arteries from 26 type 2 diabetic and 26 non-diabetic patients undergoing coronary artery bypass grafting surgery were compared. Increased levels of cyclin D1 mRNA (by 135+/-14%) and protein expression (by 93.8+/-7.0%), retinoblastoma protein phosphorylation (by 45.9+/-4.8%), and beta-catenin nuclear localization (by 176+/-16%) indicated the enhanced cell cycle entry in the diabetic arteries. Diabetes increased phosphorylation of extracellular signal-regulated kinase-1/2 and p-38-mitogen-activated protein kinase (MAPK) by 76.0+/-6.8 and 62.3+/-4.3%. Increased collagen deposition was evidenced in the diabetic arteries. mRNA levels of MMP-1 and MMP-3 were decreased in the diabetic tissue to 55 and 82%, respectively, compared to the non-diabetic group; protein levels were also decreased accompanied with decreased enzymatic activities by 21 and 50%, respectively. In conclusion, enhanced cell cycle entry, increased MAPK signaling, and downregulated MMP-1 and MMP-3 were characteristic of diabetic arterial vasculature, and could contribute to the progressive atherosclerosis and postangioplasty restenosis in diabetic patients.

Cardiovascular gene therapy: current status and therapeutic potential

Gene therapy is emerging as a potential treatment option in patients suffering from a wide spectrum of cardiovascular diseases including coronary artery disease, peripheral vascular disease, vein graft failure and in-stent restenosis. Thus far preclinical studies have shown promise for a wide variety of genes, in particular the delivery of genes encoding growth factors such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) to treat ischaemic vascular disease both peripherally and in coronary artery disease. VEGF as well as other genes such as TIMPs have been used to target the development of neointimal hyperplasia to successfully prevent vein graft failure and in-stent restenosis in animal models. Subsequent phase I trials to examine safety of these therapies have been successful with low levels of serious adverse effects, and albeit in the absence of a placebo group some suggestion of efficacy. Phase 2 studies, which have incorporated a placebo group, have not confirmed this early promise of efficacy. In the next generation of clinical gene therapy trials for cardiovascular disease, many parameters will need to be adjusted in the search for an effective therapy, including the identification of a suitable vector, appropriate gene or genes and an effective vector delivery system for a specific disease target. Here we review the current status of cardiovascular gene therapy and the potential for this approach to become a viable treatment option.

Therapeutic angiogenesis induced by controlled release of fibroblast growth factor-2 from injectable chitosan/non-anticoagulant heparin hydrogel in a rat hindlimb ischemia model

The addition of non-anticoagulant heparin [periodate-oxidized (IO4) heparin] and fibroblast growth factor (FGF)-2 to a viscous water-soluble chitosan (CH-LA) aqueous solution produces an injectable FGF-2/CH-LA/IO4-heparin hydrogel. The purpose of this study was to examine the ability of the injected FGF-2/CH-LA/IO4-heparin hydrogel to induce vascularization and fibrous tissue formation. FGF-2/CH-LA/IO4-heparin hydrogels (100 microL of hydrogel consisting of 20 mg/mL of CH-LA, 2 mg/mL of IO4-heparin, and 50 microg/mL of FGF-2) were subcutaneously injected into the backs of wound healing-impaired diabetic (db/db) mice. Furthermore, the effect of percutaneous injection of FGF-2/CH-LA/IO4-heparin hydrogel at eight sites (25 microL/site) into ischemic left lower limbs of rats was examined from day 4 to at least day 28 postinjection. The injection of FGF-2/CH-LA/IO4-heparin hydrogels into the backs of db/db mice resulted in significant increases in blood vessel formation, significant vascularization, and fibrous tissue formation near the injection site. Injection of FGF-2/CH-LA/IO4-heparin hydrogel into ischemic left lower limbs of rats also significantly recovered and increased blood flow and blood oxygen in the calf and thigh. These results indicate that the controlled release of biologically active FGF-2 molecules from FGF-2/CH-LA/IO4-heparin induces angiogenesis and possibly collateral circulation in db/db mice and the ischemic limbs of rats.

Hind Limb Ischemia-Reperfusion in the Leptin Receptor Deficient (db/db) Mouse

BACKGROUND

Diabetic patients have high incidence of peripheral vascular disease and limb loss after acute extremity injury. Experiments were designed to test the hypothesis that acute tissue injury in leptin receptor deficient (Db) diabetic (type2) mice would be more severe than in non-diabetic mice.

METHODS

Db and wild type (Wt) mice were subjected to 3 h of ischemia followed by either 4 or 24 h of reperfusion (3/4 IR, 3/24 IR). Muscle analyzed for tissue viability (mitochondrial activity), cytokines (KC-murine equivalent of human IL-8, TNFalpha, IL-6), growth factor, and histological evaluation (neutrophils/uninjured muscle fibers). Tissue perfusion was detected during basal and reperfusion conditions using laser Doppler imaging.

RESULTS

Mitochondrial activity and histological evaluation for tissue injury did not differ in the Db versus Wt mice at the time intervals studied. When compared with their respective sham animals, both Db and Wt mice had similarly increased levels of KC, IL-6, and VEGF after 3/24 IR. TNFalpha levels increased in Db but not Wt mice after IR. Although absolute increases in TNFalpha and KC were higher in Db mice, VEGF levels were actually lower in the Db mice.

CONCLUSION

The patterns of tissue perfusion, cytokines, and growth factors were different in Db versus Wt mice. At the acute time intervals studied, these differences did not correlate with an expected greater degree of acute muscle injury in Db mice.

Improvement of survival of skin flaps by combined gene transfer of hepatocyte growth factor and prostacyclin synthase

BACKGROUND

Increasing the local blood flow is a critical factor for long-term survival of skin flaps. Thus, a molecular therapy to increase the blood flow by means of an angiogenic factor is considered to be a useful strategy to improve skin flap survival. We focused on a combined strategy to stimulate not only angiogenesis, but also vasodilation of local microvessels, using co-transfection of the hepatocyte growth factor (HGF) and prostacyclin synthase (PGIS) genes to enhance the survival of random-pattern skin flaps.

METHODS AND RESULTS

A 2 x 8 cm full thickness cranial pedicled random-pattern flap was made on the back of each 12-week-old male rat. At 3 days before operation, 400 microg of human HGF and PGIS naked plasmid DNA or control plasmid was transfected into the flaps by needle-less injection using a Shima Jet, resulting in successful expression of human HGF and PGIS in the skin flaps. Transfection of both genes into the distal half of skin flaps at 3 days prior to operation significantly increased the survival rate of skin flaps, while transfection all over the flaps did not. In addition, transfection prior to operation was more effective than simultaneous treatment. Moreover, co-transfection of these genes improved the survival area of skin flaps, accompanied by an increase in blood flow of skin flaps, even in a diabetic model.

CONCLUSIONS

Overall, these results indicate that combination treatment with HGF and PGIS genes by Shima Jet could be an effective strategy to improve skin flap survival.

Non-ionic amphiphilic biodegradable PEG-PLGA-PEG copolymer enhances gene delivery efficiency in rat skeletal muscle

Naked plasmid DNA (pDNA)-based gene therapy has low delivery efficiency, and consequently, low therapeutic effect. We present a biodegradable nonionic triblock copolymer, PEG(13)-PLGA(10)-PEG(13), to enhance gene delivery efficiency in skeletal muscle. Effects of PEG(13)-PLGA(10)-PEG(13) on physicochemical properties of pDNA were evaluated by atomic force microscopy (AFM) imaging, gel electrophoresis and zeta-potential analysis. AFM imaging suggested a slightly compacted structure of pDNA when it was mixed with the polymer, while zeta-potential measurement indicated an increased surface potential of negatively charged pDNA. PEG(13)-PLGA(10)-PEG(13) showed a relatively lower toxicity compared to Pluronic P85 in a skeletal muscle cell line. The luciferase expression of pDNA delivered in 0.25% polymer solution was up to three orders of magnitude more than branched polyethylenimine (bPEI(25 k))/pDNA and three times more than that of naked pDNA five days after intramuscular administration. This in vivo gene delivery enhancement was also observed displaying a two-fold higher expression of human vascular endothelial growth factor (VEGF). Based on fluorescence labeled pDNA distribution, it is speculated that the greater diffusivity of PEG(13)-PLGA(10)-PEG(13)/pDNA compared to bPEI(25 k)/pDNA accounts for better transfection efficiency in vivo. To summarize, combining PEG(13)-PLGA(10)-PEG(13) with pDNA possesses the potential to improve gene delivery efficiency in skeletal muscle.

c-jun amino-terminal kinase and mitogen activated protein kinase 1/2 mediate hepatocyte growth factor-induced migration of brain endothelial cells

Hepatocyte growth factor (HGF) influences several components of the angiogenic response, including endothelial cell migration. While recent studies indicate a crucial role of HGF in brain angiogenesis, the signaling pathways that regulate brain endothelial cell migration by HGF remain uncharacterized. Herein, we report that HGF stimulated human brain microvascular endothelial cell (HBMEC) migration in a dose- and time-dependent manner. Challenge of HBMECs with HGF activated the c-jun amino-terminal kinase (JNK), increased phosphorylation of the proline-rich tyrosine kinase 2 (Pyk-2) at Tyr(402) and activated c-Src. Inhibition of JNK by SP600125 or expression of a dominant negative JNK1 construct abrogated the migratory response of HBMECs to HGF. Treatment of HBMECs with the Src inhibitor PP2 markedly decreased HGF-stimulated JNK activation and migration to HGF. Moreover, expression of a mutant Pyk-2 construct prevented HGF-induced Pyk-2 phosphorylation at Tyr(402) and stimulation of HBMEC migration. Next, we examined activation of the extracellular signal regulated kinase (ERK) pathway. Stimulation of HBMECs by HGF led to rapid activation of ERK1/2, phosphorylation of Raf-1 at Ser(338) and Tyr(340/341) and MEK1/2 at Ser(222). Moreover, inhibition of ERK activation by UO126 and PD98059 markedly decreased HGF-stimulated HBMEC migration. HGF also activated AKT, while inhibition of AKT by LY294002 induced a modest decrease of HGF-induced HBMEC migration. These results highlight a model whereby JNK and ERK play a critical role in regulation of brain endothelial cell migration by HGF.

Angiogenesis in Tissue Engineering: Breathing Life into Constructed Tissue Substitutes

Long-term function of three-dimensional (3D) tissue constructs depends on adequate vascularization after implantation. Accordingly, research in tissue engineering has focused on the analysis of angiogenesis. For this purpose, 2 sophisticated in vivo models (the chorioallantoic membrane and the dorsal skinfold chamber) have recently been introduced in tissue engineering research, allowing a more detailed analysis of angiogenic dysfunction and engraftment failure. To achieve vascularization of tissue constructs, several approaches are currently under investigation. These include the modification of biomaterial properties of scaffolds and the stimulation of blood vessel development and maturation by different growth factors using slow-release devices through pre-encapsulated microspheres. Moreover, new microvascular networks in tissue substitutes can be engineered by using endothelial cells and stem cells or by creating arteriovenous shunt loops. Nonetheless, the currently used techniques are not sufficient to induce the rapid vascularization necessary for an adequate cellular oxygen supply. Thus, future directions of research should focus on the creation of microvascular networks within 3D tissue constructs in vitro before implantation or by co-stimulation of angiogenesis and parenchymal cell proliferation to engineer the vascularized tissue substitute in situ.

Angiogenic and antifibrotic actions of hepatocyte growth factor improve cardiac dysfunction in porcine ischemic cardiomyopathy

Impairment of cardiac function in ischemic cardiomyopathy has been postulated to be due to the decrease in blood flow and increase in collagen synthesis. Therefore, an approach to alter them directly by means of a growth factor may open up a new therapeutic concept in ischemic cardiomyopathy. From this viewpoint, hepatocyte growth factor (HGF) is a unique growth factor with angiogenic and antifibrotic effects. Thus, we examined the feasibility of gene therapy using HGF plasmid DNA for ischemic cardiomyopathy. Human HGF plasmid DNA at a dose of 0.4 or 4 mg was injected into ischemic myocardium of pigs induced by ameroid constrictor with the NOGA system. At 1 month after injection, the ischemic area was significantly reduced in the HGF group, accompanied by a significant increase in capillary density and regional myocardial perfusion in the ischemic area (P<0.01). In contrast, a significant decrease in fibrotic area was observed in the HGF group, associated with a significant decrease in collagen I, III and TGF-beta synthesis as compared to the control group (P<0.01). Consistently, cardiac function was significantly improved in the 4 mg HGF group as compared to the control group (P<0.05). Overall, the present in vivo experiments demonstrated that intramyocardial injection of human HGF plasmid DNA in ischemic cardiomyopathy resulted in a significant improvement in cardiac function through an increase in blood flow and decrease in fibrosis. These favorable outcomes suggest potential utility to treat patients with ischemic heart disease using HGF gene transfer. Currently, a phase I study using human HGF plasmid DNA is ongoing to test the validity of this concept.

[Diabetes and peripheral arterial occlusive disease: therapeutic potential and pro-angiogenic strategies]

Cardiovascular complications are the leading cause of morbidity and mortality in patients with diabetes mellitus; up to 80% of deaths in patients with diabetes are closely associated with vascular disease. The ability of the organism to form a collateral network of blood vessels constitutes an important response to vascular occlusive disease and determines to a large part the clinical consequences and severity of tissue ischemia. The development of new vessels is significantly reduced in diabetic patients with coronary or peripheral artery disease. This probably contributes to the severe course of limb ischemia in diabetic patients, in which peripheral artery disease often results in foot ulceration and lower extremity amputation. Diabetic retinopathy remains one of the major causes of acquired blindness in developed nations. This is true despite the development of laser treatment, which can prevent blindness in the majority of those who develop macular edema or proliferative diabetic retinopathy. The hallmark of diabetic retinopathy is the lack of microvessels in the macula, leading to hypoxia, associated with peripheral retinal neovascularization that may ultimately cause severe vitreous cavity bleeding and/or retinal detachment. The factors that stimulate retinal blood vessel growth have not been fully defined, but there is accumulating evidence that the renin-angiotensin-bradykinin system may be involved in a number of retinal vascular disorders, including retinopathy of prematurity and proliferative diabetic retinopathy. Only a few studies have specifically evaluated the effect of diabetes on angiogenesis in ischemic vascular disease and in the retina. Moreover, the mechanisms by which diabetes could both limit the formation of new blood vessels in most organs and simultaneously induce proliferative diabetic retinopathy remain largely undefined. In the present review, we aimed to briefly describe the main molecular mechanisms involved in the ischemia-induced angiogenesis, and their alterations in diabetes. Possible therapeutic strategies to restore angiogenesis in diabetic patients are also listed.

Hepatocyte growth factor secreted by cultured adipocytes promotes tube formation of vascular endothelial cells in vitro

OBJECTIVE

Adipose tissue is closely associated with angiogenesis, but the mechanisms are not fully understood. Some of the adipocyte-derived cytokines are hypothesized to play an important role in angiogenesis. We evaluated tube formation of human umbilical vascular endothelial cells (HUVECs) cultured in type I collagen gel when overlaid with the supernatant of 3T3-L1 cell culture, and expression of tube-forming factor(s) in 3T3-L1 cells with or without pioglitazone. We also studied plasma growth factor levels in patients with type 2 diabetes mellitus treated with pioglitazone.

RESULTS AND METHODS

The supernatant of 3T3-L1 cells increased tube formation of HUVECs by 9.03-fold of control. Reverse transcription-polymerase chain reaction showed that hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF) mRNA were expressed in 3T3-L1 cells. Western blot analysis also demonstrated HGF and VEGF protein expression. When 3T3-L1 cells were treated with 100 nM small interfering RNAs (siRNAs) for HGF, the HGF mRNA and protein were suppressed. The VEGF mRNA and protein in the cells were also suppressed by siRNA for VEGF. The supernatant of 3T3-L1 cells treated with HGF siRNA suppressed tube formation of HUVECs by 61% compared with the supernatant of cells treated with control siRNA. Addition of VEGF siRNA resulted in no significant changes. The supernatant conditioned with pioglitazone further promoted the tube formation. Pioglitazone enhanced HGF mRNA expression in 3T3-L1 cells. After 12 weeks of pioglitazone treatment, the changes of plasma HGF levels in patients treated with pioglitazone were significantly higher than those in control.

CONCLUSION

These results suggest that HGF secreted from 3T3-L1 cells may be the major factor regulating the tube formation, and agents that enhance the differentiation of adipocytes may promote tube formation of HUVECs mediated by HGF secreted by adipocytes.

Benfotiamine accelerates the healing of ischaemic diabetic limbs in mice through protein kinase B/Akt-mediated potentiation of angiogenesis and inhibition of apoptosis

AIMS/HYPOTHESIS

Benfotiamine, a vitamin B1 analogue, reportedly prevents diabetic microangiopathy. The aim of this study was to evaluate whether benfotiamine is of benefit in reparative neovascularisation using a type I diabetes model of hindlimb ischaemia. We also investigated the involvement of protein kinase B (PKB)/Akt in the therapeutic effects of benfotiamine.

METHODS

Streptozotocin-induced diabetic mice, given oral benfotiamine or vehicle, were subjected to unilateral limb ischaemia. Reparative neovascularisation was analysed by histology. The expression of Nos3 and Casp3 was evaluated by real-time PCR, and the activation state of PKB/Akt was assessed by western blot analysis and immunohistochemistry. The functional importance of PKB/Akt in benfotiamine-induced effects was investigated using a dominant-negative construct.

RESULTS

Diabetic muscles showed reduced transketolase activity, which was corrected by benfotiamine. Importantly, benfotiamine prevented ischaemia-induced toe necrosis, improved hindlimb perfusion and oxygenation, and restored endothelium-dependent vasodilation. Histological studies revealed the improvement of reparative neovascularisation and the inhibition of endothelial and skeletal muscle cell apoptosis. In addition, benfotiamine prevented the vascular accumulation of advanced glycation end products and the induction of pro-apoptotic caspase-3, while restoring proper expression of Nos3 and Akt in ischaemic muscles. The benefits of benfotiamine were nullified by dominant-negative PKB/Akt. In vitro, benfotiamine stimulated the proliferation of human EPCs, while inhibiting apoptosis induced by high glucose. In diabetic mice, the number of circulating EPCs was reduced, with the deficit being corrected by benfotiamine.

CONCLUSIONS/INTERPRETATION

We have demonstrated, for the first time, that benfotiamine aids the post-ischaemic healing of diabetic animals via PKB/Akt-mediated potentiation of angiogenesis and inhibition of apoptosis. In addition, benfotiamine combats the diabetes-induced deficit in endothelial progenitor cells.

Intravitreous hepatocyte growth factor in patients with proliferative diabetic retinopathy: a case-control study

The aim of the present study was to evaluate the vitreous levels of hepatocyte growth factor (HGF) in patients with proliferative diabetic retinopathy (PDR) and to investigate its relationship with vascular endothelial growth factor (VEGF) and retinopathy activity. In addition, the relationship between intravitreous HGF levels and the presence of epiretinal membranes (ERM), as well as the expression of c-Met in ERM were also investigated. In this case-control study, serum and vitreous samples as well as ERM specimens were obtained during vitrectomy from 28 diabetic patients with PDR and 30 non-diabetic control subjects. HGF and VEGF were determined by ELISA and c-Met expression by immunohistochemistry. Vitreal levels of both VEGF and HGF were higher in patients with PDR in comparison with the control group (p<0.0001). However, after correcting for total vitreous protein concentration, HGF (ng/mg of proteins) was lower in diabetic patients than in non-diabetic control subjects (p=0.02). No correlation was detected between the vitreal levels of HGF and VEGF. In addition, intravitreous VEGF but not HGF was found to be related to PDR activity. Both diabetic patients and non-diabetic patients in whom ERM had been excised presented higher HGF intravitreous levels. Finally, a significant expression of c-Met in ERM membranes were observed in both diabetic patients with PDR and in non-diabetic subjects. In conclusion, both HGF and VEGF increased, but were not related, in the vitreous fluid of diabetic patients with PDR. Our findings suggest that HGF is related to pathological conditions in which fibroproliferative processes or wound healing are involved rather than with angiogenesis itself.

Regulators of angiogenesis and strategies for their therapeutic manipulation

Angiogenesis provides a mechanism by which delivery of oxygen and nutrients is adapted to compliment changes in tissue mass or metabolic activity. However, maladaptive angiogenesis is integral to the process of several diseases common in Western countries, including tumor growth, vascular insufficiency, diabetic retinopathy and rheumatoid arthritis. Understanding the process of capillary growth, including the identification and functional analyses of key pro- and anti-angiogenic factors, provides knowledge that can be applied to improve/reverse these pathological states. Initially, angiogenesis research focused predominantly on vascular endothelial growth factor (VEGF) as a main player in the angiogenesis cascade. It is apparent now that participation of multiple angiogenic factors and signal pathways is critical to enable effective growth and maturation of nascent capillaries. The purpose of this review is to focus on recent progress in identifying angiogenesis signaling pathways that show promise as targets for successful induction or inhibition of capillary growth. The strategies applied to achieve these contradictory tasks are discussed within the framework of our existing fundamental knowledge of angiogenesis signaling cascades, with an emphasis on comparing the employment of distinctive tactics in modulation of these pathways. Innovative developments that are presented include: (1) inducing a pleiotropic response via activation or inhibition of angiogenic transcription factors; (2) modulation of nitric oxide tissue concentration; (3) manipulating the kallikrein-kinin system; (4) use of endothelial progenitor cells as a means to either directly contribute to capillary growth or to be used as a vehicle to deliver "suicide genes" to tumor tissue.

Endothelial progenitor cell dysfunction in type 1 diabetes: another consequence of oxidative stress?

Endothelial progenitor cells (EPC) have been shown to contribute to neovascularization and vascular maintenance and repair in adults. Recently, the concept has evolved that EPC dysfunction, in patients at risk for cardiovascular disease, may contribute to the development of atherosclerosis and ischemic vascular disease. Particularly, patients with diabetes mellitus are likely to be affected by EPC dysfunction as several studies have shown a reduced number and function of EPC in patients, as well as in preclinical models for type 1 diabetes. Here, we review our current understanding of EPC (dys)function in diabetes and discuss some potential mechanisms underlying their altered properties. Moreover, we provide circumstantial evidence indicating that increased oxidative stress could play a role in the development of EPC dysfunction in type 1 diabetes. Finally, we discuss the potential implication of our findings for EPC-based therapies and the potential impact of pharmacological interventions on the vascular regenerative capacity of EPC.

Oxidized LDL inhibit hepatocyte growth factor synthesis in coronary smooth muscle cells

Hepatocyte growth factor (HGF) is a potent regeneration factor for endothelial and epithelial cells, and has also been shown to modulate extracellular matrix synthesis and matrix metalloproteinase activity in renal epithelial cells and tumor cells. Controversial results have been published concerning the possible role of HGF in the pathogenesis of coronary atherosclerosis. In this study, we have investigated the effect of oxidized low density lipoproteins (LDL) and elevated glucose concentrations on HGF synthesis in cultured human coronary artery smooth muscle cells. In addition, we have studied whether HGF modulates the release of extracellular matrix, extracellular matrix metalloproteinase inducer (EMMPRIN) and matrix metalloproteinases (MMP) by coronary artery smooth muscle cells. Oxidized LDL (1-10 microg/ml) induced a significant dose-dependent decrease of HGF release and a concomitant decrease of HGF mRNA expression, whereas native LDL and elevated glucose concentrations induced no significant changes of HGF synthesis. Incubation of cultured human coronary smooth muscle cells with human HGF (1-100 ng/ml) did not significantly alter cell migration and collagen I, fibronectin, EMMPRIN, MMP-1, MMP-2 and MMP-9 release. In summary, our results provide evidence that HGF does not promote coronary plaque growth or plaque destabilization. Regarding the fact that HGF is a potent endothelial cell regeneration factor, the observed downregulation of HGF synthesis by oxidized LDL supports the concept that HGF might be a protective factor in coronary atherosclerosis and that a decrease rather than an increase of HGF synthesis might promote coronary atherosclerosis.

Efficacy of Photocrosslinkable Chitosan Hydrogel Containing Fibroblast Growth Factor-2 in a Rabbit Model of Chronic Myocardial Infarction

BACKGROUND

Therapeutic angiogenesis in ischemic myocardium has been shown to be an effective strategy to improve regional blood flow and myocardial function. However, no effective delivery system for growth factor administration is yet known to induce important therapeutic angiogenic responses in ischemic myocardium.

MATERIALS AND METHODS

FGF-2-incorporated chitosan (FGF-2/chitosan) hydrogels were immobilized on the surface of ischemic myocardium of rabbit models of chronic myocardial infarction by UV-irradiation. After 4 weeks, cardiac functional analyses by noradrenalin challenge and histopathological analyses were performed to evaluate the efficacy of a controlled release of FGF-2 from FGF-2/chitosan hydrogel immobilized on the surface of ischemic myocardium.

RESULTS

Significant improvement by application of FGF-2/chitosan hydrogels was found in systolic pressure at the left ventricle, +dp/dt maximum, and -dp/dt maximum during noradrenalin challenge at a dose of 1 microg/kg/min. Histological observations showed that a significantly larger amount of viable myocardium and CD 31 immunostained blood vessels were found in the FGF-2/chitosan hydrogel-applied group than only the chitosan-applied and control groups.

CONCLUSIONS

These preliminary results indicate that the controlled release of biologically active FGF-2 molecules from FGF-2/chitosan hydrogel induces angiogenesis and possibly collateral circulation in ischemic myocardium, thereby protecting the myocardium.

Matrix metalloproteinases and diabetic vascular complications

Diabetes mellitus (DM) is associated with an increased incidence of cardiovascular events and microvascular complications. These complications contribute to the morbidity and mortality associated with DM. There is increasing evidence supporting a role for matrix metalloproteinases (MMPs) and their inhibitors (tissue inhibitors of matrix metalloproteinases - TIMPs) in the atherosclerotic process. However, the relationship between MMPs/TIMPs and diabetic angiopathy is less well defined. Hyperglycemia directly or indirectly (eg, via oxidative stress or advanced glycation products) increases MMP expression and activity. These changes are associated with histologic alterations in large vessels. On the other hand, low proteolytic activity of MMPs contributes to diabetic nephropathy. Within atherosclerotic plaques an imbalance between MMPs and TIMPs may induce matrix degradation, resulting in an increased risk of plaque rupture. Furthermore, because MMPs enhance blood coagulability, MMPs and TIMPs may play a role in acute thrombotic occlusion of vessels and consequent cardiovascular events. Some drugs can inhibit MMP activity. However, the precise mechanisms involved are still not defined. Further research is required to demonstrate the causative relationship between MMPs/TIMPs and diabetic atherosclerosis. It also remains to be established if the long-term administration of MMP inhibitors can prevent acute cardiovascular events.

Does gene therapy become pharmacotherapy?

Recent progress in molecular and cellular biology has led to the development of numerous effective cardiovascular drugs. However, there are still a number of diseases for which no known effective therapy exists, such as peripheral arterial disease, ischaemic heart disease, restenosis after angioplasty, and vascular bypass graft occlusion. Currently, gene therapy is emerging as a potential strategy for the treatment of cardiovascular disease despite its limitations. The first human trial in gene therapy for cardiovascular disease was started at 1994 to treat peripheral vascular disease using vascular endothelial growth factor (VEGF). Then, many different potent angiogenic growth factors were tested in clinical trials to treat peripheral arterial disease and ischaemic heart disease. Improvement of clinical symptoms in peripheral arterial disease and ischaemic heart disease has been reported. This review focuses on the future potential of gene therapy for the treatment of cardiovascular disease. In the future, gene therapy might become a real pharmacotherapy to treat cardiovascular disease.

Development of pro-angiogenic engineered transcription factors for the treatment of cardiovascular disease

Gene therapies that use engineered transcription factors to regulate a patient's own endogenous genetic loci offer several advantages over cDNA-based approaches, including the capacity to upregulate all splice variants of a therapeutic gene. Currently, two engineered transcription factors are being developed for use in gene-mediated revascularisation therapies of cardiovascular disease. Both proteins target a powerful, constitutive transcriptional activation module to a defined sequence in the promoter region of vascular endothelial growth factor-A via linkage to an appropriately specific DNA-binding domain, either the basic helix-loop-helix motif of hypoxia-inducible factor-1alpha (HIF-1alpha) or a designed zinc finger protein. Both factors activate the expression of vascular endothelial growth factor-A in cellular studies and induce angiogenesis in animal models of cardiovascular disease. Phase I studies are underway for the HIF-1alpha-based factor and are expected to commence for the zinc finger protein-based factor by the second half of 2004.

A New Technique With Calcium Phosphate Precipitate Enhances Efficiency of In Vivo Plasmid DNA Gene Transfer

In vivo gene transfer with plasmid vector has been applied experimentally and clinically; however, the low level of gene transfer efficiency with plasmid vector is a problem. We speculated that the combination of calcium phosphate precipitate (CaP) and plasmid vector could solve this problem because CaP stabilizes plasmid DNA. In the present study, we used a plasmid exression vector encoding enhanced green fluorescent protein and combined the vector with CaP. Then, this combination was mixed with bovine type I atelocollagen. After incubating this mixture in phosphate-buffered saline, the amount of the plasmid DNA in the supernatant was low when the plasmid DNA was combined with CaP. Furthermore, the plasmid DNA, which was combined with CaP, was stable in DNase digestion in vitro. The plasmid vector with or without CaP, together with the atelocollagen, was transplanted subcutaneously or injected in the bone marrow of the femurs of rats. Then, the fluorescence was observed under a confocal laser scanning microscope and the fluorescence intensity in the tissue homogenates was measured. In these animal experiments, the fluorescence was extensive when the plasmid DNA was combined with CaP. These results indicate that our formula, collagen/CaP/DNA, appeared efficient for in vivo gene transfer.

Intravitreous levels of hepatocyte growth factor/scatter factor and vascular cell adhesion molecule-1 in the vitreous fluid of diabetic patients with proliferative retinopathy

OBJECTIVE

Hepatocyte growth factor, also know as the scatter factor (HGF/SF) has been involved in the etiopathogenesis of proliferative diabetic retinopathy (PDR). To further explore this issue we have determine the intravitreous levels of HGF/SF taking into account the problems that could lead to misinterpretation of the results when the vitreous fluid is used to indirectly explore the events that are taking place in the retina. In addition, the relationship between HGF/SF and vascular cell adhesion molecule 1 (VCAM-1) was also investigated.

PATIENTS AND METHODS

Serum and vitreous samples were obtained during vitrectomy from 22 diabetic patients with PDR and 25 non-diabetic control subjects. Patients in whom intravitreous hemoglobin was detectable were excluded. A correction for plasma levels of either HGF/SF and VCAM-1 and intravitreal proteins was performed.

RESULTS

Vitreal levels of both HGF/SF and VCAM-1 were higher in patients with PDR in comparison with the control group (p<0.001 and p=0.003, respectively). However, after correcting for total vitreal proteins both HGF/SF and VCAM-1 (ng/mg of proteins) were lower in diabetic patients than in non-diabetic control subjects (p=0.03 and p<0.0001, respectively). No relationship between the vitreous levels of either HGF/SF or VCAM-1 with PDR activity was detected. Finally, a correlation between the vitreal levels of HGF/SF and VCAM-1 was observed in diabetic patients (r=0.61, p=0.005) but not in the control group.

CONCLUSION

Our results suggest that intraocular production of HGF/SF might be more important in mediating inflammatory and fibroproliferative processes rather than in angiogenesis itself.

A novel ex vivo angiogenesis assay based on electroporation-mediated delivery of naked plasmid DNA to skeletal muscle

An angiogenesis assay based on gene transfer would be extremely useful for angiogenic gene therapy. A simple, reproducible, and quantitative assay to test angiogenic genes would provide more accurate predictions than conventional peptide-based assays. Here, we have developed a semiquantitative angiogenesis assay utilizing gene transfer into skeletal muscle, which is a target tissue for ischemic limb diseases. To facilitate quick and clean analysis, a naked plasmid DNA vector combined with an electroporation procedure was used for gene transfer. When the plasmid vector encoding vascular endothelial growth factor cDNA (pJDK-VEGF165) was injected into the tibialis anterior muscle of BALB/c mice, followed by in vivo electroporation and explant culture in growth factor-reduced Matrigel, the outward migration of sprouting cells was observed as early as day 2. The cells soon formed capillary networks, which peaked at day 7 and persisted until day 14. The capillary-like structures were positive for von Willebrand factor, platelet endothelial cell adhesion molecule, and vimentin, suggesting they were endothelial cells. There was little, if any, sprouting or formation of capillaries from the control vector (pJDK)-injected group. Consistent with the region of sprouting and network formation, the amount of secreted VEGF increased in the conditioned medium of explant cultures. The angiogenic potential of connective tissue growth factor (CTGF) was examined using the new assay. Whereas the CTGF gene alone induced weak sprouting activity, it appeared to inhibit the angiogenic activity of the VEGF165 gene during cotreatment. This attenuating activity of CTGF on VEGF was reproduced in vivo in a murine model of hindlimb ischemia. In a group of mice treated with both pJDK-CTGF and pJDK-VEGF165, the blood flow measured by laser Doppler imaging was significantly lower than that of the pJDK-VEGF165-treated group 10 days after femoral artery excision. These results are consistent with recent reports that suggest that CTGF inhibits VEGF. This confirms the usefulness of this novel ex vivo assay in assessing the angiogenic capacity of genes of interest. In summary, this new gene-based angiogenesis assay should be widely applicable in the study of angiogenic or antiangiogenic genes because it can readily predict the angiogenic potential of specific genes and their combinations.

Gene therapy for chronic myocardial ischemia using platelet-derived endothelial cell growth factor in dogs

Platelet-derived endothelial cell growth factor (PD-ECGF), also known as thymidine phosphorylase (TP), has been reported to possess angiogenic activity and to inhibit apoptosis. This study was performed to determine whether PD-ECGF/TP can be used to ameliorate chronic myocardial ischemia. Myocardial ischemia was created in 40 mongrel dogs by placement of an ameroid constrictor on the proximal left anterior descending coronary artery (LAD). Plasmid vector encoding human PD-ECGF/TP cDNA (pCIhTP group; n = 12), empty vector pCI (pCI group; n = 12), or saline (Saline group; n = 12) was directly injected into the LAD territory 3 wk after ameroid constrictor implantation. Myocardial blood flow was detected using PET at baseline, 3 wk after ameroid constrictor implantation, and 2 wk after therapeutic treatment. At the end of the experiment, the hearts were isolated for biological and histological analysis. In the pCIhTP group, the transfected heart strongly expressed PD-ECGF/TP. The size of the infarct was smaller in the pCIhTP group than in the pCI or Saline group. The number of apoptotic myocardial cells was decreased in the pCIhTP group compared with the control groups based on triple immunohistochemical staining for von Willebrand factor, alpha-actin smooth muscle cells, and single-strand DNA. The level of proapoptotic protein Bax markedly decreased in the pCIhTP group compared with the other groups. Double immunohistochemical staining for von Willebrand factor and alpha-actin smooth muscle cells demonstrated that angiogenesis and arteriogenesis occurred, and paralleled the changes in myocardial blood flow and myocardial function in the pCIhTP group. We conclude that genetic approaches using PD-ECGF/TP to target the myocardium are effective for alleviating chronic myocardial ischemia.

Therapeutic Angiogenesis in Peripheral Arterial Disease: Can Biotechnology Produce an Effective Collateral Circulation?

The physiological processes of angiogenesis, vasculogenesis and arteriogenesis contribute to the growth of collateral vessels in response to obstructive arterial disease causing lower limb or myocardial ischaemia, but in clinical practice the endogenous angiogenic response is often suboptimal or impaired, e.g. by factors such as ageing, diabetes or drug therapies. Therapeutic angiogenesis is an application of biotechnology to stimulate new vessel formation via local administration of pro-angiogenic growth factors in the form of recombinant protein or gene therapy, or by implantation of endothelial progenitor cells that will synthesize multiple angiogenic cytokines. Numerous experimental and clinical studies have sought to establish 'proof of concept' for therapeutic angiogenesis in PAD and myocardial ischaemia using different treatment modalities, but the results have been inconsistent. This review summarises the mechanisms of angiogenesis and the results of recent trials evaluating the efficacy and safety of different gene therapy, recombinant protein and cellular-based treatment approaches to enhance collateral vessel formation.

Tissue regeneration based on growth factor release

Tissue engineering is an emerging biomedical field intended to assist the regeneration of body tissue defects too large to self-repair as well as to substitute for the biological functions of damaged and injured organs by using cells with proliferative and differentiative potential. In addition to basic research on such cells, it is undoubtedly indispensable for successful tissue engineering to create an artificial environment enabling cells to induce tissue regeneration. Such an environment can be achieved by making use of a scaffold for cell proliferation and differentiation and for growth factors, as well as their combination. Growth factors are often required to promote tissue regeneration, as they can induce angiogenesis, which supplies oxygen and nutrients to cells transplanted for organ substitution to maintain their biological functions. However, the biological effects of growth factors cannot always be expected because of their poor in vivo stability, unless a drug delivery system is contrived. In this article, tissue regeneration based on the release of growth factors is reviewed to emphasize the significance of drug delivery systems in tissue engineering.

Prophylactic gene therapy with human tissue kallikrein ameliorates limb ischemia recovery in type 1 diabetic mice

Diabetes macro- and microvascular disease causes tissue hypoperfusion. This deficit, together with a failure to mount an adequate angiogenic response, might explain why vascular occlusion evolves more severely among diabetic patients. The present study investigated whether prophylactic gene therapy with human tissue kallikrein (hTK) may protect diabetic limbs from the consequences of supervening ischemia. Vehicle (saline) or an adenovirus carrying the gene for either hTK (Ad.hTK) or luciferase (Ad.Luc) was injected into left adductor muscles of streptozotocin-induced type 1 diabetic mice 2 weeks before operative occlusion of the ipsilateral femoral artery. Saline-injected nondiabetic mice served as controls. Hindlimb blood flow recovery was analyzed sequentially over the 2 weeks after ischemia induction. At necroscopy, microvessel density and endothelial cell proliferation and apoptosis were quantified in skeletal muscles. We found that limb perfusion recovery of saline-injected type 1 diabetic mice is delayed because of insufficient reparative neovascularization and excessive activation of endothelial cell apoptosis. By contrast, prophylactic Ad.hTK renewed the ability to mount an appropriate neovascularization response to ischemia, suppressed apoptosis, and upregulated endothelial nitric oxide synthase expression. Ultimately, correction of diabetic endotheliopathy by Ad.hTK allowed proper perfusion recovery as seen in nondiabetic mice. These discoveries disclose new therapeutic options for the treatment of diabetic complications.

Vascular endothelial growth factor (VEGF) fails to improve blood flow and to promote collateralization in a diabetic mouse ischemic hindlimb model

Background

Angiogenic therapy with vascular endothelial growth factor (VEGF) has been proposed as a treatment paradigm for patients suffering from an insufficiency of collateral vessels. Diabetes is associated with increase in the production of VEGF and therefore additional VEGF may not be beneficial. Accordingly, we sought to determine the efficacy of VEGF therapy to augment collateral formation and tissue perfusion in a diabetic mouse ischemic hindlimb model.

Methods

Diabetic and non-diabetic mice were studied in parallel for the efficacy of VEGF administration. Diabetes was induced with streptozotocin. Hindlimb ischemia was produced by severing the left iliac artery. An outlet tube from an osmotic infusion pump with placebo/ 500 micrograms of plasmid-DNA encoding VEGF was fenestrated and tunneled into the left quadriceps muscle.

Results

VEGF induced more rapid and complete restoration of blood flow in normal mice. However, in the setting of diabetes there was no difference between VEGF Vs. placebo in the rate or adequacy of flow restoration. There was a significant increase in smooth muscle actin and Factor-VIII antigen densities in diabetic animals and in animals which received VEGF.

Conclusions

Angiogenic therapy with VEGF in the setting of diabetes does not appear to have the beneficial effects seen in the absence of diabetes.

Miniaturization: an overview of biotechnologies for monitoring the physiology and pathophysiology of rodent animal models

Recent advances in bioengineering technologies have made it possible to collect high-quality reproducible data quantitatively in a wide range of laboratory animal species, including rodents. Several of these technologies are incorporated into a plan called Miniaturization, which aims to design, develop, and maintain rodent animal models to study the pathophysiology and therapy of human diseases. Laser Doppler flowmetry, digital sonomicrometry, bioelectrical impedance, and microdialysis are some of the most widely used methods under the plan because they cause minimal pain and distress, reduce the number of animals used in biomedical research, and allow chronic, nonterminal assessment of physiological parameters in rodents. An overview of each of these technologies and their major applications in rodents used for biomedical research is provided.

The N-terminal domain of hepatocyte growth factor inhibits the angiogenic behavior of endothelial cells independently from binding to the c-met receptor

Hepatocyte growth factor (HGF) is a pleiotropic factor that plays an important role in complex biological processes such as embryogenesis, tissue regeneration, cancerogenesis, and angiogenesis. HGF promotes cell proliferation, survival, motility, and morphogenesis through binding to its receptor, a transmembrane tyrosine kinase encoded by the MET proto-oncogene (c-met). Structurally speaking, HGF is a polypeptide related to the enzymes of the blood coagulation cascade. Thus, it comprises kringle domains that in some other proteins have been shown to be responsible for the anti-angiogenic activity. To check whether the isolated kringles of HGF were able to inhibit angiogenesis, we produced them as recombinant proteins and compared their biological activity with that of the recombinant HGF N-terminal domain (N). We showed that (i) none of the isolated HGF kringle exhibits an anti-angiogenic activity; (ii) N is a new anti-angiogenic polypeptide; (iii) the inhibitory action of N is not specific toward HGF, because it antagonized the angiogenic activity of other growth factors, such as fibroblast growth factor-2 and vascular endothelial growth factor; and (iv) in contrast with full-length HGF, N does not bind to the c-met receptor in vitro, but fully retains its heparin-binding capacity. Our results suggest that N inhibits angiogenesis not by disrupting the HGF/c-met interaction but rather by interfering with the endothelial glycosaminoglycans, which are the secondary binding sites of HGF.

The biology of the Ets1 proto-oncogene

The Ets1 proto-oncoprotein is a member of the Ets family of transcription factors that share a unique DNA binding domain, the Ets domain. The DNA binding activity of Ets1 is controlled by kinases and transcription factors. Some transcription factors, such as AML-1, regulate Ets1 by targeting its autoinhibitory module. Others, such as Pax-5, alter Ets1 DNA binding properties. Ets1 harbors two phosphorylation sites, threonine-38 and an array of serines within the exon VII domain. Phosphorylation of threonine-38 by ERK1/2 activates Ets1, whereas phosphorylation of the exon VII domain by CaMKII or MLCK inhibits Ets1 DNA binding activity. Ets1 is expressed by numerous cell types. In haemotopoietic cells, it contributes to the regulation of cellular differentiation. In a variety of other cells, including endothelial cells, vascular smooth muscle cells and epithelial cancer cells, Ets1 promotes invasive behavior. Regulation of MMP1, MMP3, MMP9 and uPA as well as of VEGF and VEGF receptor gene expression has been ascribed to Ets1. In tumors, Ets1 expression is indicative of poorer prognosis.

Remodeling of the skeletal muscle microcirculation increases resistance to perfusion in obese Zucker rats

Whereas previous studies have demonstrated that the development of syndrome X in obese Zucker rats (OZR) is associated with impaired arteriolar reactivity to vasoactive stimuli, additional results from these studies indicate that the passive diameter of skeletal muscle arterioles is reduced in OZR versus lean Zucker rats (LZR). On the basis of these prior observations, the present study evaluated structural alterations to the skeletal muscle microcirculation as potential contributors to an elevated vascular resistance. Isolated skeletal muscle resistance arterioles exhibited a reduced passive diameter at all levels of intralumenal pressure and a left-shifted stress-strain curve in OZR versus LZR, indicative of structural remodeling of individual arterioles. Histological analyses using Griffonia simplicifolia I lectin-stained sections of skeletal muscle demonstrated reduced microvessel density (rarefaction) in OZR versus LZR, suggesting remodeling of entire microvascular networks. Finally, under maximally dilated conditions, constant flow-perfused skeletal muscle of OZR exhibited significant elevations in perfusion pressure versus LZR, indicative of an increased resistance to perfusion within the microcirculation. These data suggest that developing structural alterations to the skeletal muscle microcirculation in OZR result in elevated vascular resistance, which may, acting in concert with impaired arteriolar reactivity, contribute to blunted active hyperemic responses and compromised performance of in situ skeletal muscle with elevated metabolic demand.

HGF receptor up-regulation contributes to the angiogenic phenotype of human endothelial cells and promotes angiogenesis in vitro

Hepatocyte growth factor (HGF) is a mesenchyme-derived pleiotropic growth factor and a powerful stimulator of angiogenesis, which acts on cells by binding to the c-met receptor. The exact role of the endogenous HGF/c-met system in one or more steps of the angiogenic process is not completely understood. To contribute to this question we used immunocytochemical analysis, Western blotting, and reverse transcription-polymerase chain reaction to study the expression of c-met in endothelial cells cultured in different growth conditions. We found that c-met is not colocalized with vascular endothelial (VE)-cadherin in cell-cell junctions. c-met and VE-cadherin were shown to be inversely regulated by cell density, at both the protein and the mRNA levels. We established that c-met is up-regulated during the in vitro recapitulation of several steps of angiogenesis. The c-met expression was increased shortly after switching to angiogenic growth conditions and remained high during the very first steps of angiogenesis, including cell migration, and cell proliferation. The endothelial cells in which the expression of c-met was up-regulated were more responsive to HGF and exhibited a higher rate of morphogenesis. Moreover, the antibody directed against the extracellular domain of the c-met inhibited angiogenesis in vitro. Our results suggest that c-met is a marker of angiogenic phenotype for endothelial cells and represents an attractive target for the development of new antiangiogenic therapies.

Obesity is associated with increased levels of circulating hepatocyte growth factor

OBJECTIVES

This study evaluated whether obesity in humans was associated with an increase in circulating hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF) levels.

BACKGROUND

Obesity acts as a cardiovascular risk factor by mechanisms that are not fully understood. Adipose tissue is able to secrete multiple cytokines and growth factors ex vivo. We hypothesized that the increased presence of adipose tissue in obese subjects results in systemic elevations of the mitogenic factors HGF and VEGF.

METHODS

Blood samples were obtained from lean (n = 21) and obese (n = 44) volunteers. Serum HGF and VEGF levels were assessed by enzyme-linked immunoadsorbent assay. Insulin and fasting glucose levels were measured to evaluate insulin sensitivity. Conditioned medium of adipose cells was assayed for HGF secretion.

RESULTS

Serum HGF levels in obese subjects were more than three-fold higher than those of lean subjects (2,462 +/- 184 pg/ml vs. 765 +/- 48 pg/ml, p < 0.0001). The VEGF levels were not significantly elevated in obese subjects (135 +/- 31 pg/ml vs. 128 +/- 37 pg/ml). The HGF concentrations, but not VEGF concentrations, were significantly correlated with body mass index (BMI) (p < 0.0001, r = 0.74). The observed increases in HGF concentrations of obese subjects were not secondary to insulin resistance or hypertension. Freshly isolated human adipose cells secreted HGF.

CONCLUSIONS

Our results indicate that obesity is associated with a marked increase in circulating HGF levels, which correlate linearly with BMI. Because vascular growth factors have been associated with the pathogenesis of atherosclerosis, the possible role of such humoral factors as a link between obesity and cardiovascular disease is very intriguing.

Enhanced angiogenesis and improvement of neuropathy by cotransfection of human hepatocyte growth factor and prostacyclin synthase gene

The current therapeutic angiogenesis strategy to treat ischemic disease by using angiogenic growth factors has been limited to use of a single gene. However, as vasodilator substances such as prostacyclin are widely used for the treatment of peripheral arterial disease, it might be useful to combine angiogenesis with vasodilation of new vessels. In a mouse hind limb ischemia model, cotransfection of the hepatocyte growth factor (HGF) gene with the prostacyclin synthase gene demonstrated a further increase in blood flow and capillary density compared with a single gene. Even in the rabbit ischemia model, cotransfection of HGF plasmid with the prostacyclin synthase gene demonstrated a further increase in angiogenic activity compared with HGF alone. Because peripheral neuropathy due to diabetes is common for significant morbidity, we examined the hypothesis that experimental diabetic neuropathy can be reversed by HGF and prostacyclin synthase genes. Severe peripheral neuropathy, characterized by significant slowing of nerve conduction velocity compared with nondiabetic control animals, was ameliorated. Overall, cotransfection of the prostacyclin synthase and HGF genes is more effective than single-gene transfection to stimulate angiogenesis, and it significantly improved neuropathy. These data provide important information relating to the clinical application of therapeutic angiogenesis to treat peripheral arterial disease.

Hepatocyte growth factor: from diagnosis to clinical applications

Hepatocyte growth factor (HGF), initially identified and molecularly cloned as a potent mitogen of primary cultured hepatocytes, has multiple activities in a variety of tissues during the course of development and also in various disease states. HGF plays key roles in the attenuation of disease progression as an intrinsic repair factor. It is also evident that HGF levels are regulated under different conditions, for example, during the course of pregnancy, aging, and disease. This review focuses on the levels of HGF in normal and pathophysiological situations and examines the relationships between HGF levels and disease, disease stage, and disease prognosis. The clinical potential of HGF as a treatment for subjects with various diseases is also given attention.