Intramuscular gene transfer of fibroblast growth factor-1 using improved pCOR plasmid design stimulates collateral formation in a rabbit ischemic hindlimb model.

Fibroblast growth factor 1 (FGF1) is an angiogenic factor known to play a role in the growth of arteries. The purpose of this study was to evaluate the usefulness of direct intramuscular injection of an optimized expression plasmid encoding FGF1 to augment collateral formation and tissue perfusion in a rabbit ischemic hindlimb model. Truncated FGF1 fused to the human fibroblast interferon (FIN) signal peptide was expressed from a newly designed plasmid backbone with an improved safety profile for gene therapy applications. In vitro, optimization of plasmid design yielded in a dramatic increase in expression efficiency for FGF1, independent of the presence of a signal peptide, as analyzed by Western Blotting. In vivo, successful transgene expression could be demonstrated by FGF1 immunostaining after gene application. FGF1 plasmid containing FIN signal peptide (100, 500, and 1,000 mug), when injected into ischemic muscle areas of rabbits 10 days after ligation of the external iliac artery, exhibited a pronounced therapeutic effect on collateral formation to the ischemic hindlimb in a dose-depending manner, as assessed by physiological (blood pressure ratio, maximal intra-arterial Doppler flow) and anatomical (angiographic score, histologic evaluation of capillary density) measurements 30 days after therapy, compared to saline or lacZ control plasmid. FGF1 plasmid without a signal peptide sequence resulted in a comparable therapeutic effect on collateral formation at comparable doses (500 and 1,000 mug). Our results indicate that intramuscular FGF1 gene application could be useful to stimulate collateral formation in a situation of chronic peripheral ischemia. The presence of a signal peptide does not seem to be obligatory to achieve bioactivity of intramuscular transfected FGF1. An optimized vector design improved both biosafety of gene transfer and expression efficiency of the transgene, rendering this vector highly suitable for human gene therapy. Therefore, this new generation vector encoding FGF1 might be useful as an alternative treatment for patients with chronic ischemic disorders not amenable to conventional therapy.

Human FGF-1 gene transfer promotes the formation of collateral vessels and arterioles in ischemic muscles of hypercholesterolemic hamsters.

BACKGROUND: Acidic fibroblast growth factor (FGF-1) has been identified as a potent mitogen for vascular cells, inducing formation of mature blood vessels in vitro and in vivo and represents one of the most promising approaches for the treatment of ischemic cardiovascular diseases by gene therapy. Nevertheless, and most probably due to the few experimental models able to address the issue, no study has described the therapeutic effects of FGF-1 gene transfer in subjects with peripheral arterial disease (PAD) exhibiting a clinically relevant cardiovascular pathology. METHODS: In order to assess the potency of FGF-1 gene transfer for therapeutic angiogenesis in ischemic skeletal muscles displaying decreased gene expression levels and sustained impaired formation of collateral vessels and arterioles, we developed a model of PAD in hamsters with a background of hypercholesterolemia. Hamsters fed a cholesterol-rich diet and subjected to hindlimb ischemia exhibit a sustained impaired angiogenic response, as evidenced by decreased angiographic score and histological quantification of arterioles in the ischemic muscles. RESULTS: In this model, we demonstrate that NV1FGF (a human FGF-1 expression plasmid), given intramuscularly 14 days after induction of hindlimb ischemia, promoted the formation of both collateral vessels and arterioles 14 days after treatment (i.e. 28 days post-ischemia). CONCLUSIONS: Our data provide evidence that NV1FGF can reverse the cholesterol-induced impairment of revascularization in a hamster model of hindlimb ischemia by promoting the growth of both collateral vessels and arterioles in ischemic muscles exhibiting significantly decreased levels of gene expression compared with control muscles. Therefore, this study underscores the relevance of NV1FGF gene therapy to overcome perfusion defects in patients with PAD.

Adenovirus-mediated fibroblast growth factor 1 expression in the lung induces epithelial cell proliferation: consequences to hyperoxic lung injury in rats.

High concentrations of oxygen can induce pulmonary toxicity and cause injury to alveolar epithelial and endothelial cells. The present study was performed to determine whether the potent epithelial and endothelial fibroblast growth factor 1 (FGF-1) protected against hyperoxia-induced lung injury. Recombinant adenovirus carrying the gene encoding human secreted FGF-1 (Ad. FGF1) increased the proliferation of lung epithelial cells in vitro. Ad.FGF1 or control vector with an empty expression cassette (Ad.V152) was administered intratracheally to Wistar rats. With Ad.FGF1 (10(9), 5 x 10(9), 10(10), or 5 x 10(10) viral particles [VP]), FGF-1 protein was found in bronchoalveolar lavage fluid 4 days postinfection at levels proportional to the viral dose and was detected in plasma after doses of 10(10) VP or more were administered. Histological examination of the lungs showed intense proliferation and apoptosis of alveolar and bronchial epithelial cells, with few inflammatory cells. The alveolar architecture returned to normal within 17 days. Rats pretreated with Ad.FGF1 (10(9) or 5 x 10(9) VP) 2 days before exposure to hyperoxia (95% O2) survived, whereas rats pretreated with Ad.V152 died within 3 days. In conclusion, adenovirus-mediated FGF-1 overexpression in the lungs causes epithelial cell proliferation and has beneficial effects in hyperoxic lung injury.

Vascular endothelial growth factor-B promotes in vivo angiogenesis.

Vascular endothelial growth factors (VEGFs) and their receptors have emerged as central regulators of the angiogenic process. However, involvement of VEGF-B, one of these factors, in angiogenesis remains obscure. Mice received subcutaneous injection of Matrigel alone or Matrigel with human recombinant protein rhVEGF-B167 or with rhVEGF-A165. After 14 days, cell ingrowth in the Matrigel plug was increased by 2.0- and 2.5-fold in rhVEGF-B167-treated and rhVEGF-A165-treated mice, respectively (P<0.01), in association with a raise in phospho-Akt/Akt (1.8-fold, P<0.01) and endothelial NO synthase (eNOS) (1.80- and 1.60-fold, respectively; P<0.05) protein levels measured by Western blot. VEGF-B-induced cell ingrowth was impaired by treatment with NOS inhibitor (NG-nitro-l-arginine methyl ester; L-NAME, 10 mg/kg per day). Treatment with neutralizing antibody directed against the VEGF-B receptor VEGF-R1 (anti-VEGFR1, 10 microg) completely abrogated VEGF-B-related effects. Proangiogenic effect of VEGF-B was confirmed in a mouse model of surgically induced hindlimb ischemia. Plasmids containing human form of VEGF-A (phVEGF-A165) or VEGF-B (phVEGF-B167 or phVEGF-B186) were administered by in vivo electrotransfer. Angiographic score at day 28 showed significant improvement in ischemic/nonischemic leg ratio by 1.4- and 1.5-fold in mice treated with phVEGF-B167 and phVEGF-B186, respectively (P<0.05). Laser Doppler perfusion data also evidenced a 1.5-fold increase in phVEGF-B167-treated and phVEGF-B186-treated mice (P<0.05). Such an effect was associated with an upregulation of phospho-Akt/Akt and eNOS protein levels in the ischemic legs and was hampered by treatment with anti-VEGFR1. This study demonstrates for the first time that VEGF-B, in part through its receptor VEGF-R1, promotes angiogenesis in association with an activation of Akt and eNOS-related pathways.

Role of VEGF-B in the lung during development of chronic hypoxic pulmonary hypertension.

Angiogenic factors exert protective effects on the lung. To investigate the effect of VEGF-B, a factor coexpressed in the lung with VEGF-A, we assessed chronic hypoxic pulmonary hypertension in VEGF-B knockout mice (VEGF-B-/-) and in rats with lung overexpression of VEGF-B induced by adenovirus transfer. No significant difference in pulmonary hemodynamics, right ventricular hypertrophy, distal vessel muscularization, or vascular density was found between VEGF-B-/- and control mice after 3 wk of hypoxia. When overexpressed, VEGF-B(167) or VEGF-B(186) had protective effects similar to those of human VEGF-A(165). Lung endothelial nitric oxide synthase (eNOS) expression was increased by 5 days of hypoxia or VEGF-A adenovirus vector (Ad.VEGF-A) overexpression, whereas VEGF-B(167) or VEGF-B(186) had no effect. With hypoxia or normoxia, the wet-to-dry lung weight ratio was increased 5 days after Ad.VEGF-A administration compared with control (Ad.nul), Ad.VEGF-B(167), or Ad.VEGF-B(186). Endogenous VEGF-B does not counteract the development of hypoxic pulmonary hypertension. However, when overexpressed in the lung, VEGF-B can be as potent as VEGF-A in attenuating pulmonary hypertension, although it has no effect on eNOS expression or vascular permeability.

Myogenic Akt signaling regulates blood vessel recruitment during myofiber growth.

Blood vessel recruitment is an important feature of normal tissue growth. Here, we examined the role of Akt signaling in coordinating angiogenesis with skeletal muscle hypertrophy. Hypertrophy of C2C12 myotubes in response to insulin-like growth factor 1 or insulin and dexamethasone resulted in a marked increase in the secretion of vascular endothelial growth factor (VEGF). Myofiber hypertrophy and hypertrophy-associated VEGF synthesis were specifically inhibited by the transduction of a dominant-negative mutant of the Akt1 serine-threonine protein kinase. Conversely, transduction of constitutively active Akt1 increased myofiber size and led to a robust induction of VEGF protein production. Akt-mediated control of VEGF expression occurred at the level of transcription, and the hypoxia-inducible factor 1 regulatory element was dispensable for this regulation. The activation of Akt1 signaling in normal mouse gastrocnemius muscle was sufficient to promote myofiber hypertrophy, which was accompanied by an increase in circulating and tissue-resident VEGF levels and high capillary vessel densities at focal regions of high Akt transgene expression. In a rabbit hind limb model of vascular insufficiency, intramuscular activation of Akt1 signaling promoted collateral and capillary vessel formation and an accompanying increase in limb perfusion. These data suggest that myogenic Akt signaling controls both fiber hypertrophy and angiogenic growth factor synthesis, illustrating a mechanism through which blood vessel recruitment can be coupled to normal tissue growth.