VEGF165b Modulates Endothelial VEGFR1-STAT3 Signaling Pathway and Angiogenesis in Human and Experimental Peripheral Arterial Disease

RATIONALE

Atherosclerotic-arterial occlusions decrease tissue perfusion causing ischemia to lower limbs in patients with peripheral arterial disease (PAD). Ischemia in muscle induces an angiogenic response, but the magnitude of this response is frequently inadequate to meet tissue perfusion requirements. Alternate splicing in the exon-8 of vascular endothelial growth factor (VEGF)-A results in production of proangiogenic VEGF_xxxa isoforms (VEGF₁₆₅a, 165 for the 165 amino acid product) and antiangiogenic VEGF_xxxb (VEGF₁₆₅b) isoforms.

OBJECTIVE

The antiangiogenic VEGF_xxxb isoforms are thought to antagonize VEGF_xxxa isoforms and decrease activation of VEGF receptor-2 (VEGFR2), hereunto considered the dominant receptor in postnatal angiogenesis in PAD. Our data will show that VEGF₁₆₅b inhibits VEGFR1 signal transducer and activator of transcription (STAT)-3 signaling to decrease angiogenesis in human and experimental PAD.

METHODS AND RESULTS

In human PAD versus control muscle biopsies, VEGF₁₆₅b: (1) is elevated, (2) is bound higher (versus VEGF₁₆₅a) to VEGFR1 not VEGFR2, and (3) levels correlated with decreased VEGFR1, not VEGFR2, activation. In experimental PAD, delivery of an isoform-specific monoclonal antibody to VEGF₁₆₅b versus control antibody enhanced perfusion in animal model of severe PAD (Balb/c strain) without activating VEGFR2 signaling but with increased VEGFR1 activation. Receptor pull-down experiments demonstrate that VEGF₁₆₅b inhibition versus control increased VEGFR1-STAT3 binding and STAT3 activation, independent of Janus-activated kinase-1)/Janus-activated kinase-2. Using VEGFR1^+/- mice that could not increase VEGFR1 after ischemia, we confirm that VEGF₁₆₅b decreases VEGFR1-STAT3 signaling to decrease perfusion.

CONCLUSIONS

Our results indicate that VEGF₁₆₅b prevents activation of VEGFR1-STAT3 signaling by VEGF₁₆₅a and hence inhibits angiogenesis and perfusion recovery in PAD muscle.

Biomarkers and Genetics in Peripheral Artery Disease

BACKGROUND

Peripheral artery disease (PAD) is highly prevalent and there is considerable diversity in the initial clinical manifestation and disease progression among individuals. Currently, there is no ideal biomarker to screen for PAD, to risk stratify patients with PAD, or to monitor therapeutic response to revascularization procedures. Advances in human genetics have markedly enhanced the ability to develop novel diagnostic and therapeutic approaches across a host of human diseases, but such developments in the field of PAD are lagging.

CONTENT

In this article, we will discuss the epidemiology, traditional risk factors for, and clinical presentations of PAD. We will discuss the possible role of genetic factors and gene-environment interactions in the development and/or progression of PAD. We will further explore future avenues through which genetic advances can be used to better our understanding of the pathophysiology of PAD and potentially find newer therapeutic targets. We will discuss the potential role of biomarkers in identifying patients at risk for PAD and for risk stratifying patients with PAD, and novel approaches to identification of reliable biomarkers in PAD.

SUMMARY

The exponential growth of genetic tools and newer technologies provides opportunities to investigate and identify newer pathways in the development and progression of PAD, and thereby in the identification of newer biomarkers and therapies.

A multiscale computational model predicts distribution of anti-angiogenic isoform VEGF165b in peripheral arterial disease in human and mouse

Angiogenesis is the growth of new blood vessels from pre-existing microvessels. Peripheral arterial disease (PAD) is caused by atherosclerosis that results in ischemia mostly in the lower extremities. Clinical trials including VEGF-A administration for therapeutic angiogenesis have not been successful. The existence of anti-angiogenic isoform (VEGF_165b) in PAD muscle tissues is a potential cause for the failure of therapeutic angiogenesis. Experimental measurements show that in PAD human muscle biopsies the VEGF_165b isoform is at least as abundant if not greater than the VEGF_165a isoform. We constructed three-compartment models describing VEGF isoforms and receptors, in human and mouse, to make predictions on the secretion rate of VEGF_165b and the distribution of various isoforms throughout the body based on the experimental data. The computational results are consistent with the data showing that in PAD calf muscles secrete mostly VEGF_165b over total VEGF. In the PAD calf compartment of human and mouse models, most VEGF_165a and VEGF_165b are bound to the extracellular matrix. VEGF receptors VEGFR1, VEGFR2 and Neuropilin-1 (NRP1) are mostly in ‘Free State’. This study provides a computational model of VEGF_165b in PAD supported by experimental measurements of VEGF_165b in human and mouse, which gives insight of VEGF_165b in therapeutic angiogenesis and VEGF distribution in human and mouse PAD model.

Cardiovascular magnetic resonance detects the progression of impaired myocardial perfusion reserve and increased left-ventricular mass in mice fed a high-fat diet

BACKGROUND

Impaired myocardial perfusion reserve (MPR) is prevalent in obesity and diabetes, even in the absence of obstructive coronary artery disease (CAD), and is prognostic of adverse events. We sought to establish the time course of reduced MPR and to investigate associated vascular and tissue properties in mice fed a high-fat diet (HFD), as they are an emerging model of human obesity, diabetes, and reduced MPR without obstructive CAD.

METHODS

C57Bl/6 mice fed a HFD or a low-fat diet (control) were imaged at 6, 12, 18 and 24 weeks post-diet. The cardiovascular magnetic resonance (CMR) protocol included multi-slice cine imaging to assess ejection fraction (EF), left-ventricular (LV) mass, LV wall thickness (LVWT), and LV volumes, and first-pass perfusion CMR to quantify MPR. Coronary vascular reactivity, aortic atherosclerosis, myocardial capillary density and tissue fibrosis were also assessed.

RESULTS

Body weight was increased in HFD mice at 6-24 weeks post-diet (p < 0.05 vs. control). MPR in HFD mice was reduced and LV mass and LVWT were increased in HFD mice at 18 and 24 weeks post-diet (p < 0.05 vs. control). Coronary arteriolar vascular reactivity to adenosine and acetylcholine were reduced in HFD mice (p < 0.05 vs. control). There were no significant differences in cardiac volumes, EF, or capillary density measurements between the two groups. Histology showed interstitial fibrosis in HFD and no aortic atherosclerosis in either group.

CONCLUSIONS

C57Bl/6 mice fed a HFD for 18-24 weeks have progressively increased LV mass and impaired MPR with fibrosis, normal capillary density and no aortic plaque. These results establish C57Bl/6 mice fed a HFD for 18-24 weeks as a model of impaired MPR without obstructive CAD due to obesity and diabetes.

Neovascularization in intimal hyperplasia is associated with vein graft failure after coronary artery bypass surgery

Vein graft atherosclerosis is the major limitation of arterial bypass surgery. This study was carried out to determine if the number of microvessels per area of intimal hyperplasia correlated with vein graft disease. Vein grafts (n=24, graft age range 2-19 years) were taken from 22 patients undergoing redo-coronary artery bypass surgery. Mean age of the patients was 68 6 9 years; 92% were males. Samples were divided into three groups (n=8 per group): in group I segments were from grafts without angiographic or histologic disease, in groups II and III segments were from grafts with significant angiographic stenosis, without (group II) and with (group III) atheroma. Intimal hyperplasia was identified by Masson staining, morphometric analysis was performed with NIH image analysis software. Microvessels in the intimal hyper-plasia were identified using immunohistochemical techniques. significance was determined by single-factor ANOVA p, 0.05.

The mean area of intimal hyperplasia was similar in groups I and II at 1.06 6 0.25mm2 and 0.97 6 0.37mm2, respectively. The extent of intimal hyperplasia was significantly greater in group III, 1.70 6 0.62mm2 (p < 0.01). In group I, the microvessel count in the intimal hyperplasia was 5.62 6 3.89 vessels/mm2, while in group III it was 15.26 6 3.66/mm2 (p < 0.01 versus group I). Interestingly the number of microvessels per area of intimal hyperplasia in group II was similar to that in group III).

In this study, the extent of neovascularization in intimal hyperplasia correlated with stenoses in human vein grafts. Strategies designed to limit neovascularization in intimal hyperplasia may lead to novel therapies to prevent vein graft failure.

Therapeutic angiogenesis for critical limb ischemia: design of the hepatocyte growth factor therapeutic angiogenesis clinical trial

The objective of the HGF-STAT clinical trial is to determine whether perfusion can be improved by gene transfer with a plasmid DNA containing hepatocyte growth factor (HGF) in the affected limb of patients with unreconstructable critical limb ischemia (CLI). CLI results in a high rate of limb loss and impaired quality of life. The current therapeutic strategies, including bypass surgery and percutaneous interventions, are only successful in treating a subset of patients. Therapeutic angiogenesis is an investigational method that seeks to favorably impact tissue per-fusion in CLI. HGF-STAT is a double-blind, parallel-group, placebo-controlled, dose response study in 100 patients with unreconstructable CLI. Eligible subjects will be randomized 1:1:1:1 to receive saline placebo or one of three dose/regimens of HGF plasmid DNA. The selection of outcome measures, including the primary endpoint, and changes in transcutaneous oxygen pressure (TcPO2) from baseline to 3 months will be discussed. In conclusion, this study will help to determine whether therapeutic angiogenesis with HGF is a viable option in the treatment of patients with CLI.

Computational Network Model Prediction of Hemodynamic Alterations Due to Arteriolar Rarefaction and Estimation of Skeletal Muscle Perfusion in Peripheral Arterial Disease

OBJECTIVE

To estimate the relative influence of input pressure and arteriole rarefaction on gastrocnemius muscle perfusion in patients with PAD after exercise and/or percutaneous interventions.

METHODS

A computational network model of the gastrocnemius muscle microcirculation was adapted to reflect rarefaction based on arteriolar density measurements from PAD patients, with and without exercise. A normalized input pressure was applied at the feeder artery to simulate both reduced and restored ABI in the PAD condition.

RESULTS

In simulations of arteriolar rarefaction, resistance increased non-linearly with rarefaction, leading to a disproportionally large drop in perfusion. In addition, perfusion was less sensitive to changes in input pressure as the degree of rarefaction increased. Reduced arteriolar density was observed in PAD patients and improved 33.8% after three months of exercise. In model simulations of PAD, ABI restoration yielded perfusion recovery to only 66% of baseline. When exercise training was simulated by reducing rarefaction, ABI restoration increased perfusion to 80% of baseline.

CONCLUSION

Microvascular resistance increases non-linearly with increasing arteriole rarefaction. Therefore, muscle perfusion becomes disproportionally less sensitive to ABI restoration as arteriole rarefaction increases. These results highlight the importance of restoring both microvascular structure and upstream input pressure in PAD therapy.

Abstract 510: Perivascular-Cell Derived Oct4 is Essential for Angiogenesis Following Hindlimb Ischemia

Ischemic vascular diseases such as coronary, carotid, and peripheral artery disease (PAD) require vascular growth and remodeling in order to restore blood flow to ischemic tissue. Human therapeutic studies aimed at promoting neovascularization have been largely unsuccessful in part because these approaches have focused on stimulating endothelial cell (EC) growth without coordinate investment of smooth muscle cells and pericytes (SMC-P) needed for functional blood vessels that are stable and able to regulate perfusion. Thus, there is a critical need to identify mechanisms that mediate perivascular cell coverage during vascular network remodeling, a process that requires perivascular cell detachment, migration, and investment of endothelial tubes. Previous work from the Owens lab demonstrated that the stem cell pluripotency gene Oct4, previously thought to be permanently epigenetically silenced in all somatic cells, is reactivated in SMC within atherosclerotic lesions. SMC specific KO of Oct4 results in marked reductions in the number of SMC within lesions due to failure of cells to migrate out of the media. That is, Oct4 reactivation appears to be critical for SMC migration, at least in the context of atherosclerosis. Therefore, the present study tested the hypothesis that SMC-P reactivation of Oct4 is essential for neovascularization following hindlimb ischemia (HLI), a mouse model of PAD. To test this hypothesis, we used a unique mouse line enabling SMC-P specific tamoxifen-inducible lineage tracing (termed Myh11 eYFP), allowing their tracking following phenotypic switching and loss of identifying genes, combined with SMC-P specific knockout of Oct4. We subjected both Oct4WT and Oct4KO Myh11 eYFP mice to HLI and monitored perfusion recovery via Laser Doppler at days 0, 3, 7, 14, and 21 post-HLI. We found that SMC-P specific KO of Oct4 results in significantly impaired perfusion recovery at days 14 and 21 post-HLI. We harvested hindlimb muscle at day 21 post-HLI and observed that Oct4 KO mice have significantly impaired angiogenesis, but intact arteriogenesis, compared to WT controls. Future studies will investigate Oct4 downstream targets necessary for angiogenesis following HLI.

Endothelial interleukin-21 receptor up-regulation in peripheral artery disease

In most patients with symptomatic peripheral artery disease (PAD), severe stenosis in or occlusion of the major blood vessels that supply the legs make the amount of distal blood flow dependent on the capacity to induce angiogenesis and collateral vessel formation. Currently, there are no medications that improve perfusion to the ischemic limb, and thus directly treat the primary problem of PAD. A recent report from our group in a pre-clinical mouse PAD model showed that interleukin-21 receptor (IL-21R) is up-regulated in the endothelial cells from ischemic hindlimb muscle. We further showed that loss of IL-21R resulted in impaired perfusion recovery in this model. In our study, we sought to determine whether IL-21R is present in the endothelium from ischemic muscle of patients with PAD. Using human gastrocnemius muscle biopsies, we found increased levels of IL-21R in the skeletal muscle endothelial cells of patients with PAD compared to control individuals. Interestingly, PAD patients had approximately 1.7-fold higher levels of circulating IL-21. These data provide direct evidence that the IL-21R pathway is indeed up-regulated in patients with PAD. This pathway may serve as a therapeutic target for modulation.

Computational drug repositioning for peripheral arterial disease: prediction of anti-inflammatory and pro-angiogenic therapeutics

Peripheral arterial disease (PAD) results from atherosclerosis that leads to blocked arteries and reduced blood flow, most commonly in the arteries of the legs. PAD clinical trials to induce angiogenesis to improve blood flow conducted in the last decade have not succeeded. We have recently constructed PADPIN, protein-protein interaction network (PIN) of PAD, and here we combine it with the drug-target relations to identify potential drug targets for PAD. Specifically, the proteins in the PADPIN were classified as belonging to the angiome, immunome, and arteriome, characterizing the processes of angiogenesis, immune response/inflammation, and arteriogenesis, respectively. Using the network-based approach we predict the candidate drugs for repositioning that have potential applications to PAD. By compiling the drug information in two drug databases DrugBank and PharmGKB, we predict FDA-approved drugs whose targets are the proteins annotated as anti-angiogenic and pro-inflammatory, respectively. Examples of pro-angiogenic drugs are carvedilol and urokinase. Examples of anti-inflammatory drugs are ACE inhibitors and maraviroc. This is the first computational drug repositioning study for PAD.

ADAM12: a genetic modifier of preclinical peripheral arterial disease

In prior studies from multiple groups, outcomes following experimental peripheral arterial disease (PAD) differed considerably across inbred mouse strains. Similarly, in humans with PAD, disease outcomes differ, even when there are similarities in risk factors, disease anatomy, arteriosclerotic burden, and hemodynamic measures. Previously, we identified a locus on mouse chromosome 7, limb salvage-associated quantitative trait locus 1 (LSq-1), which was sufficient to modify outcomes following experimental PAD. We compared expression of genes within LSq-1 in Balb/c mice, which normally show poor outcomes following experimental PAD, with that in C57Bl/6 mice, which normally show favorable outcomes, and found that a disintegrin and metalloproteinase gene 12 (ADAM12) had the most differential expression. Augmentation of ADAM12 expression in vivo improved outcomes following experimental PAD in Balb/c mice, whereas knockdown of ADAM12 made outcomes worse in C57Bl/6 mice. In vitro, ADAM12 expression modulates endothelial cell proliferation, survival, and angiogenesis in ischemia, and this appeared to be dependent on tyrosine kinase with Ig-like and EGF-like domain 2 (Tie2) activation. ADAM12 is sufficient to modify PAD severity in mice, and this likely occurs through regulation of Tie2.

PADPIN: protein-protein interaction networks of angiogenesis, arteriogenesis, and inflammation in peripheral arterial disease

Peripheral arterial disease (PAD) results from an obstruction of blood flow in the arteries other than the heart, most commonly the arteries that supply the legs. The complexity of the known signaling pathways involved in PAD, including various growth factor pathways and their cross talks, suggests that analyses of high-throughput experimental data could lead to a new level of understanding of the disease as well as novel and heretofore unanticipated potential targets. Such bioinformatic analyses have not been systematically performed for PAD. We constructed global protein-protein interaction networks of angiogenesis (Angiome), immune response (Immunome), and arteriogenesis (Arteriome) using our previously developed algorithm GeneHits. The term "PADPIN" refers to the angiome, immunome, and arteriome in PAD. Here we analyze four microarray gene expression datasets from ischemic and nonischemic gastrocnemius muscles at day 3 posthindlimb ischemia (HLI) in two genetically different C57BL/6 and BALB/c mouse strains that display differential susceptibility to HLI to identify potential targets and signaling pathways in angiogenesis, immune, and arteriogenesis networks. We hypothesize that identification of the differentially expressed genes in ischemic and nonischemic muscles between the strains that recovers better (C57BL/6) vs. the strain that recovers more poorly (BALB/c) will help for the prediction of target genes in PAD. Our bioinformatics analysis identified several genes that are differentially expressed between the two mouse strains with known functions in PAD including TLR4, THBS1, and PRKAA2 and several genes with unknown functions in PAD including EphA4, TSPAN7, SLC22A4, and EIF2a.

Loss of interleukin-21 receptor activation in hypoxic endothelial cells impairs perfusion recovery after hindlimb ischemia

OBJECTIVE

Surgical hindlimb ischemia (HLI) in mice has become a valuable preclinical model to study peripheral arterial disease. We previously identified that the different phenotypic outcomes after HLI across inbred mouse strains is related to a region on the short arm of mouse chromosome 7. The gene coding the interleukin-21 receptor (IL-21R) lies at the peak of association in this region.

APPROACH AND RESULTS

With quantitative real-time polymerase chain reaction, we found that a mouse strain with a greater ability to upregulate IL-21R after HLI had better perfusion recovery than a strain with no upregulation after HLI. Immunofluorescent staining of ischemic hindlimb tissue showed IL-21R expression on endothelial cells (ECs) from C57BL/6 mice. An EC-enriched fraction isolated from ischemic hindlimb muscle showed higher Il-21R levels than an EC-enriched fraction from nonischemic limbs. In vitro, human umbilical vein ECs showed elevated IL-21R expression after hypoxia and serum starvation. Under these conditions, IL-21 treatment increased cell viability, decreased cell apoptosis, and augmented tube formation. In vivo, either knockout Il21r or blocking IL-21 signaling by treating with IL-21R-Fc (fusion protein that blocks IL-21 binding to its receptor) in C57BL/6 mice resulted in less perfusion recovery after HLI. Both in vitro and in vivo modulation of the IL-21/IL-21R axis under hypoxic conditions resulted in increased signal transducer and activator of transcription 3 phosphorylation and a subsequent increase in the B-cell lymphoma leukemia-2/BCL-2-associated X protein ratio.

CONCLUSION

Our data indicate that IL-21R upregulation and ligand activation in hypoxic ECs may help perfusion recovery by limiting/preventing apoptosis and favoring cell survival and angiogenesis through the signal transducer and activator of transcription 3 pathway.

Recombinant PAI-1 therapy restores myoendothelial junctions and erectile function in PAI-1-deficient mice

Myoendothelial junctions are specialised projections of cell : cell contact through the internal elastic lamina between endothelial cells and vascular smooth muscle cells. These junctions allow for endothelial cells and vascular smooth muscle cells to make direct membrane apposition and are involved in cell : cell communication. In this study, we evaluated for the presence of myoendothelial junctions in murine corporal tissue and used plasminogen activator inhibitor (PAI)-1-deficient mice, which lack myoendothelial junctions, to determine whether myoendothelial junctions affect erectile function. Transmission electron microscopy demonstrated the presence of myoendothelial junctions in the corporal tissue of wild-type mice and confirmed the decreased junction numbers in the tissue of PAI-1(-/-) mice. A potential role for myoendothelial junctions in tumescence was established; in that, PAI-1(-/-) mice demonstrated a significantly longer time to achieve maximal intracavernous pressure. Treatment of PAI-1(-/-) mice with recombinant PAI-1 restored the number of myoendothelial junctions in the corporal tissue and also induced a significant decrease in time to maximal corporal pressures. Myoendothelial junctions were similarly identified in the human corporal tissue. These results suggest a critical role for myoendothelial junctions in erectile pathophysiology and therapies aimed at restoring myoendothelial junction numbers in the corporal tissue may provide a novel therapy for erectile dysfunction.

Accelerated dual-contrast first-pass perfusion MRI of the mouse heart: development and application to diet-induced obese mice

PURPOSE

Gene-modified mice may be used to elucidate molecular mechanisms underlying abnormal myocardial blow flow (MBF). We sought to develop a quantitative myocardial perfusion imaging technique for mice and to test the hypothesis that myocardial perfusion reserve (MPR) is reduced in a mouse model of diet-induced obesity (DIO).

METHODS

A dual-contrast saturation-recovery sequence with ky -t undersampling and a motion-compensated compressed sensing reconstruction algorithm was developed for first-pass MRI on a small-bore 7 Tesla system. Control mice were imaged at rest and with the vasodilators ATL313 and Regadenoson (n = 6 each). In addition, we imaged mice fed a high-fat diet (HFD) for 24 weeks.

RESULTS

In control mice, MBF was 5.7 ± 0.8 mL/g/min at rest and it increased to 11.8 ± 0.6 mL/g/min with ATL313 and to 10.4 ± 0.3 mL/g/min with Regadenoson. In HFD mice, we detected normal resting MBF (5.6 ± 0.4 versus 5.0 ± 0.3 on control diet), low MBF at stress (7.7 ± 0.4 versus 10.4 ± 0.3 on control diet, P < 0.05), and reduced MPR (1.4 ± 0.2 versus 2.0 ± 0.3 on control diet, P < 0.05).

CONCLUSION

Accelerated dual-contrast first-pass MRI with motion-compensated compressed sensing provides spatiotemporal resolution suitable for measuring MBF in free-breathing mice, and detected reduced MPR in DIO mice. These techniques may be used to study molecular mechanisms that underlie abnormal myocardial perfusion.

Diabetes status differentiates endothelial function and plasma nitrite response to exercise stress in peripheral arterial disease following supervised training

AIMS

To determine if type 2 diabetes mellitus (T2D) differentiates endothelial function and plasma nitrite response (a marker of nitric oxide bioavailability) during exercise in peripheral arterial disease (PAD) subjects prior to and following 3 months supervised exercise training (SET).

METHODS

In subjects with T2D+PAD (n = 13) and PAD-only (n = 14), endothelial function was measured using brachial artery flow-mediated dilation. On a separate day, venous blood draws were performed at rest and 10 min following a symptom-limited graded treadmill test (SL-GXT). Plasma samples were snap-frozen for analysis of nitrite by reductive chemiluminescence. All testing was repeated following 3 months of SET.

RESULTS

Prior to training both groups demonstrated endothelial dysfunction, which was correlated with a net decrease in plasma nitrite following a SL-GXT (p ≤ 0.05). Following SET, the PAD-only group demonstrated an improvement in endothelial function (p ≤ 0.05) and COT (p ≤ 0.05), which was related to a net increase in plasma nitrite following the SL-GXT (both p ≤ 0.05). The T2D+PAD group had none of these increases.

CONCLUSIONS

T2D in the presence of PAD attenuated improvements in endothelial function, net plasma nitrite, and COT following SET. This suggests that T2D maybe associated with an inability to endogenously increase vascular NO bioavailability to SET.

Despite normal arteriogenic and angiogenic responses, hind limb perfusion recovery and necrotic and fibroadipose tissue clearance are impaired in matrix metalloproteinase 9-deficient mice

OBJECTIVE

The relative contributions of arteriogenesis, angiogenesis, and ischemic muscle tissue composition toward reperfusion after arterial occlusion are largely unknown. Differential loss of bone marrow-derived cell (BMC) matrix metalloproteinase 9 (MMP9), which has been implicated in all of these processes, was used to assess the relative contributions of these processes during limb reperfusion.

METHODS

We compared collateral growth (arteriogenesis), capillary growth (angiogenesis), and ischemic muscle tissue composition after femoral artery ligation in FVB/NJ mice that had been reconstituted with bone marrow from wild-type or MMP9(-/-) mice.

RESULTS

Laser Doppler perfusion imaging confirmed decreased reperfusion capacity in mice with BMC-specific loss of MMP9; however, collateral arteriogenesis was not affected. Furthermore, when accounting for the fact that muscle tissue composition changes markedly with ischemia (ie, necrotic, fibroadipose, and regenerating tissue regions are present), angiogenesis was also unaffected. Instead, BMC-specific loss of MMP9 caused an increase in the proportion of necrotic and fibroadipose tissue, which showed the strongest correlation with poor perfusion recovery. Similarly, the reciprocal loss of MMP9 from non-BMCs showed similar deficits in perfusion and tissue composition without affecting arteriogenesis.

CONCLUSIONS

By concurrently analyzing arteriogenesis, angiogenesis, and ischemic tissue composition, we determined that the loss of BMC-derived or non-BMC-derived MMP9 impairs necrotic and fibroadipose tissue clearance after femoral artery ligation, despite normal arteriogenic and angiogenic vascular growth. These findings imply that therapeutic revascularization strategies for treating peripheral arterial disease may benefit from additionally targeting necrotic tissue clearance or skeletal muscle regeneration, or both.

Extracellular superoxide dismutase ameliorates skeletal muscle abnormalities, cachexia, and exercise intolerance in mice with congestive heart failure

BACKGROUND

Congestive heart failure (CHF) is a leading cause of morbidity and mortality, and oxidative stress has been implicated in the pathogenesis of cachexia (muscle wasting) and the hallmark symptom, exercise intolerance. We have previously shown that a nitric oxide-dependent antioxidant defense renders oxidative skeletal muscle resistant to catabolic wasting. Here, we aimed to identify and determine the functional role of nitric oxide-inducible antioxidant enzyme(s) in protection against cardiac cachexia and exercise intolerance in CHF.

METHODS AND RESULTS

We demonstrated that systemic administration of endogenous nitric oxide donor S-nitrosoglutathione in mice blocked the reduction of extracellular superoxide dismutase (EcSOD) protein expression, as well as the induction of MAFbx/Atrogin-1 mRNA expression and muscle atrophy induced by glucocorticoid. We further showed that endogenous EcSOD, expressed primarily by type IId/x and IIa myofibers and enriched at endothelial cells, is induced by exercise training. Muscle-specific overexpression of EcSOD by somatic gene transfer or transgenesis (muscle creatine kinase [MCK]-EcSOD) in mice significantly attenuated muscle atrophy. Importantly, when crossbred into a mouse genetic model of CHF (α-myosin heavy chain-calsequestrin), MCK-EcSOD transgenic mice had significant attenuation of cachexia with preserved whole body muscle strength and endurance capacity in the absence of reduced HF. Enhanced EcSOD expression significantly ameliorated CHF-induced oxidative stress, MAFbx/Atrogin-1 mRNA expression, loss of mitochondria, and vascular rarefaction in skeletal muscle.

CONCLUSIONS

EcSOD plays an important antioxidant defense function in skeletal muscle against cardiac cachexia and exercise intolerance in CHF.

Glycaemic control improves perfusion recovery and VEGFR2 protein expression in diabetic mice following experimental PAD

AIMS

Diabetes mellitus (DM) is associated with poor clinical outcomes in humans with peripheral arterial disease (PAD) and in pre-clinical models of PAD, but the effects of glycaemic control are poorly understood. We investigated the effect of glycaemic control on experimental PAD in mice with Type 1 DM and explored the effects of hyperglycaemia on vascular endothelial growth factor receptor 2 (VEGFR2) expression in ischaemia.

METHODS AND RESULTS

Hind limb ischaemia was induced in non-diabetic, untreated Type 1 DM, and treated Type 1 DM mice. We assessed perfusion recovery, capillary density, VEGFR2 levels, and VEGFR2 ubiquitination in ischaemic hind limbs. We found that untreated Type 1 DM mice showed impaired perfusion recovery, lower hind limb capillary density 5 weeks post-ischaemia, and lower VEGFR2 protein in Day 3 post-ischaemic hind limbs when compared with non-DM controls. Treated Type 1 DM mice had perfusion recovery, capillary density, and VEGFR2 protein levels comparable with that of non-diabetic mice at the same time points. Treatment with anti-VEGFR2 antibody negated that the improved perfusion recovery displayed by treated Type 1 DM mice. In ischaemic Type 1 DM hind limbs and endothelial cells exposed to simulated ischaemia, high glucose impaired VEGFR2 expression and was associated with increased VEGFR2 ubiquitination. Inhibition of the ubiquitin-proteasome complex restored normal endothelial VEGFR2 expression in simulated ischaemia.

CONCLUSION

Hyperglycaemia in Type 1 DM impairs VEGFR2 protein expression in ischaemic hind limbs, likely due to increased ubiquitination and degradation by the proteasome complex. Glycaemic control allows normal levels of VEGFR2 in ischaemia and improved perfusion recovery.

Sodium nitrite in patients with peripheral artery disease and diabetes mellitus: safety, walking distance and endothelial function

Nitrite stores decrease after exercise in patients with peripheral artery disease (PAD) and diabetes represents decreased nitric oxide (NO) bioavailability that may contribute to endothelial dysfunction and limit exercise duration. The primary objective of this placebo-controlled study was the safety and tolerability of multiple doses of oral sodium nitrite in patients with PAD, predominantly with diabetes, over a period of 10 weeks. The primary efficacy endpoint was endothelial flow-mediated dilatation (FMD) and secondary efficacy endpoints included a 6-minute walk test and quality of life assessment. Of the 55 subjects, the most common side effects attributed to sodium nitrite were a composite of headache and dizziness occurring in 21% with the 40 mg dose and 44% with the 80 mg dose. There was no clinically significant elevation of methemoglobin. FMD non-significantly worsened in the placebo and 40 mg groups, but was stable in the 80 mg group. Diabetic patients receiving 80 mg had significantly higher FMD compared with the placebo and 40 mg groups. There was no significant change in 6-minute walk test or quality of life parameters over time compared to placebo. In conclusion, sodium nitrite therapy is well tolerated in patients with PAD. The possible clinical benefit of sodium nitrite should be studied in a larger and fully powered trial.

Myoglobin overexpression inhibits reperfusion in the ischemic mouse hindlimb through impaired angiogenesis but not arteriogenesis

Adaptive vascular remodeling in response to arterial occlusion takes the form of capillary growth (angiogenesis) and outward remodeling of pre-existing collateral arteries (arteriogenesis). However, the relative contributions of angiogenesis and arteriogenesis toward the overall reperfusion response are both highly debated and poorly understood. Here, we tested the hypothesis that myoglobin overexpressing transgenic mice (MbTg(+)) exhibit impaired angiogenesis in the setting of normal arteriogenesis in response to femoral artery ligation, and thereby serve as a model for disconnecting these two vascular growth processes. After femoral artery ligation, MbTg(+) mice were characterized by delayed distal limb reperfusion (by laser Doppler perfusion imaging), decreased foot use, and impaired distal limb muscle angiogenesis in both glycolytic and oxidative muscle fiber regions at day 7. Substantial arteriogenesis occurred in the primary collaterals supplying the ischemic limb in both wild-type and MbTg(+) mice; however, there were no significant differences between groups, indicating that myoglobin overexpression does not affect arteriogenesis. Together, these results uniquely demonstrate that functional collateral arteriogenesis alone is not necessarily sufficient for adequate reperfusion after arterial occlusion. Angiogenesis is a key component of an effective reperfusion response, and clinical strategies that target both angiogenesis and arteriogenesis could yield the most efficacious treatments for peripheral arterial disease.

Adeno-associated virus serotype 9 administered systemically after reperfusion preferentially targets cardiomyocytes in the infarct border zone with pharmacodynamics suitable for the attenuation of left ventricular remodeling

BACKGROUND

Adeno-associated virus serotype 9 (AAV9) vectors provide efficient and uniform gene expression to normal myocardium following systemic administration, with kinetics that approach steady-state within 2-3 weeks. However, as a result of the delayed onset of gene expression, AAV vectors have not previously been administered intravenously after reperfusion for post-infarct gene therapy applications. The present study evaluated the therapeutic potential of post-myocardial infarction gene delivery using intravenous AAV9.

METHODS

AAV9 vectors expressing firefly luciferase, enhanced green fluorescent protein (eGFP) or extracellular superoxide dismutase genes from the cardiac troponin-T (cTnT) promoter (AcTnTLuc, AcTnTeGFP, AcTnTEcSOD) were employed. AcTnTLuc was administered intravenously at 10 min and at 1, 2 and 3 days post-ischemia/reperfusion (IR), and the kinetics of luciferase expression were assessed with bioluminescence imaging. AcTnTeGFP was used to evaluate the distribution of eGFP expression. High-resolution echocardiography was used to evaluate the effects of AcTnTEcSOD on left ventricular (LV) remodeling when injected 10 min post-IR.

RESULTS

Compared to sham animals, luciferase expression at 2 days after vector administration was elevated by four-, 24-, 210- and 213-fold in groups injected at 10 min, 1 day, 2 days and 3 days post-IR, respectively. The expression of cTnT-driven eGFP was strongest in cardiomyocytes bordering the infarct zone. In the efficacy study of EcSOD, post-infarct LV end-systolic and end-diastolic volumes at days 14 and 28 were significantly smaller in the EcSOD group compared to the control.

CONCLUSIONS

Systemic administration of AAV9 vectors after IR both elevates and accelerates gene expression that preferentially targets cardiomyocytes in the border zone with pharmacodynamics suitable for the attenuation of LV remodeling.

MicroRNA-93 controls perfusion recovery after hindlimb ischemia by modulating expression of multiple genes in the cell cycle pathway

BACKGROUND

MicroRNAs are key regulators of gene expression in response to injury, but there is limited knowledge of their role in ischemia-induced angiogenesis, such as in peripheral arterial disease. Here, we used an unbiased strategy and took advantage of different phenotypic outcomes that follow surgically induced hindlimb ischemia between inbred mouse strains to identify key microRNAs involved in perfusion recovery from hindlimb ischemia.

METHODS AND RESULTS

From comparative microRNA profiling between inbred mouse strains that display profound differences in their extent of perfusion recovery after hindlimb ischemia, we found that the mouse strain with higher levels of microRNA-93 (miR-93) in hindlimb muscle before ischemia and the greater ability to upregulate miR-93 in response to ischemia had better perfusion recovery. In vitro, overexpression of miR-93 attenuated hypoxia-induced apoptosis in both endothelial and skeletal muscle cells and enhanced proliferation in both cell types. In addition, miR-93 overexpression enhanced endothelial cell tube formation. In vivo, miR-93 overexpression enhanced capillary density and perfusion recovery from hindlimb ischemia, and antagomirs to miR-93 attenuated perfusion recovery. Both in vitro and in vivo modulation of miR-93 resulted in alterations in the expression of >1 cell cycle pathway gene in 2 different cell types.

CONCLUSIONS

Our data indicate that miR-93 enhances perfusion recovery from hindlimb ischemia by modulation of multiple genes that coordinate the functional pathways of cell proliferation and apoptosis. Thus, miR-93 is a strong potential target for pharmacological modulation to promote angiogenesis in ischemic tissue.

Adeno-associated virus serotype 9 efficiently targets ischemic skeletal muscle following systemic delivery

Targeting therapeutic gene expression to the skeletal muscle following intravenous (IV) administration is an attractive strategy for treating peripheral arterial disease (PAD), except that vector access to the ischemic limb could be a limiting factor. As adeno-associated virus serotype 9 (AAV-9) transduces skeletal muscle at high efficiency following systemic delivery, we employed AAV-9 vectors bearing luciferase or enhanced green fluorescent protein (eGFP) reporter genes to test the hypothesis that increased desialylation of cell-surface glycans secondary to hindlimb ischemia (HLI) might help offset the reduction in tissue perfusion that occurs in mouse models of PAD. The utility of the creatine kinase-based (CK6) promoter for restricting gene expression to the skeletal muscle was also examined by comparing it with the cytomegalovirus (CMV) promoter after systemic administration following surgically induced HLI. Despite reduced blood flow to the ischemic limbs, CK6 promoter-driven luciferase activities in the ischemic gastrocnemius (GA) muscles were ∼34-, ∼28- and ∼150-fold higher than in the fully perfused contralateral GA, heart and liver, respectively, 10 days after IV administration. Furthermore, luciferase activity from the CK6 promoter in the ischemic GA muscles was ∼twofold higher than with CMV, while in the liver CK6-driven activity was ∼42-fold lower than with CMV, demonstrating that the specificity of ischemic skeletal muscle transduction can be further improved with the muscle-specific promoters. Studies with Evans blue dye and fluorescently labeled lectins revealed that vascular permeability and desialylation of the cell-surface glycans were increased in the ischemic hindlimbs. Furthermore, AAV9/CK6/Luc vector genome copy numbers were ∼sixfold higher in the ischemic muscle compared with the non-ischemic muscle in the HLI model, whereas this trend was reversed when the same genome was packaged in the AAV-1 capsid (which binds sialylated, as opposed to desialylated glycans), further underscoring the importance of desialylation in the ischemic enhancement of transduction displayed by AAV-9. Taken together, these findings suggest two complementary mechanisms contributing to the preferential transduction of ischemic muscle by AAV-9: increased vascular permeability and desialylation. In conclusion, ischemic muscle is preferentially targeted following systemic administration of AAV-9 in a mouse model of HLI. Unmasking of the primary AAV-9 receptor as a result of ischemia may contribute importantly to this effect.

Endothelial cell-by-cell profiling reveals the temporal dynamics of VEGFR1 and VEGFR2 membrane localization after murine hindlimb ischemia

VEGF receptor (VEGFR) cell surface localization plays a critical role in transducing VEGF signaling toward angiogenic outcomes, and quantitative characterization of these parameters is critical to advancing computational models for predictive medicine. However, studies to this point have largely examined intact muscle; thus, essential data on the cellular localization of the receptors within the tissue are currently unknown. Therefore, our aims were to quantitatively analyze VEGFR localization on endothelial cells (ECs) from mouse hindlimb skeletal muscles after the induction of hindlimb ischemia, an established model for human peripheral artery disease. Flow cytometry was used to measure and compare the ex vivo surface localization of VEGFR1 and VEGFR2 on CD31(+)/CD34(+) ECs 3 and 10 days after unilateral ligation of the femoral artery. We determined that 3 days after hindlimb ischemia, VEGFR2 surface levels were decreased by 80% compared with ECs from the nonischemic limb; 10 days after ischemia, we observed a twofold increase in surface levels of the modulatory receptor, VEGFR1, along with increased proliferating cell nuclear antigen, urokinase plasminogen activator, and urokinase plasminogen activator receptor mRNA expression compared with the nonischemic limb. The significant upregulation of VEGFR1 surface levels indicates that VEGFR1 indeed plays a critical role in the ischemia-induced perfusion recovery process, a process that includes both angiogenesis and arteriogenesis. The quantification of these dissimilarities, for the first time ex vivo, provides insights into the balance of modulatory (VEGFR1) and proangiogenic (VEGFR2) receptors in ischemia and lays the foundation for systems biology approaches toward therapeutic angiogenesis.

Increased phosphodiesterase type 5 levels in a mouse model of type 2 diabetes mellitus

INTRODUCTION

Diabetes mellitus (DM) is a major risk factor for developing erectile dysfunction (ED) and men with DM are often less responsive to phosphodiesterase type 5 (PDE5) inhibitors than ED due to other causes.

AIMS

The aim of this study was to explore potential mechanisms whereby PDE5 inhibitors may have reduced efficacy in type 2 DM.

METHODS

At 4 weeks of age, mice were either fed a high-fat diet (HFD) for 22-36 weeks or fed regular chow (control). An additional group of mice in the same genetic background had a genetic form of type 1 DM.

MAIN OUTCOME MEASURES

Glucose tolerance testing, intracorporal pressures (ICPs), oxidative stress (OS), apoptotic cell death (active caspase-3 and apostain), PDE5, p53, and cyclic guanosine monophosphate (cGMP) levels, and histological examination of inflow arteries were performed in mice fed a HFD and control mice. A group of mice with type 1 DM were studied for PDE5 expression levels.

RESULTS

All mice fed a HFD had impaired glucose tolerance compared with the age-matched mice fed on standard chow diet (control). HFD fed mice had reduced maximum ICPs following in vivo cavernous nerve electrical stimulation and increased apoptotic cell death, OS, and p53 levels in the corporal tissue. Interestingly, PDE5 levels were increased and cGMP levels were decreased. In contrast, mice with type 1 DM did not have increases in PDE5.

CONCLUSIONS

Taken together, our results suggest that type 2 DM-induced ED is associated with findings that could lead to reduced cGMP and may account for reduced efficacy of PDE5 inhibitors.

Percutaneous intervention in peripheral artery disease improves calf muscle phosphocreatine recovery kinetics: a pilot study

We hypothesized that percutaneous intervention in the affected lower extremity artery would improve calf muscle perfusion and cellular metabolism in patients with claudication and peripheral artery disease (PAD) as measured by magnetic resonance imaging (MRI) and spectroscopy (MRS). Ten patients with symptomatic PAD (mean ± SD: age 57 ± 9 years; ankle-brachial index (ABI) 0.62 ± 0.17; seven males) were studied 2 months before and 10 months after lower extremity percutaneous intervention. Calf muscle phosphocreatine recovery time constant (PCr) in the revascularized leg was measured by (31)P MRS immediately after symptom-limited exercise on a 1.5-T scanner. Calf muscle perfusion was measured using first-pass gadolinium-enhanced MRI at peak exercise. A 6-minute walk and treadmill test were performed. The PCr recovery time constant improved significantly following intervention (91 ± 33 s to 52 ± 34 s, p < 0.003). Rest ABI also improved (0.62 ± 0.17 to 0.93 ± 0.25, p < 0.003). There was no difference in MRI-measured tissue perfusion or exercise parameters, although the study was underpowered for these endpoints. In conclusion, in this pilot study, successful large vessel percutaneous intervention in patients with symptomatic claudication, results in improved ABI and calf muscle phosphocreatine recovery kinetics.

Skeletal muscle-specific genetic determinants contribute to the differential strain-dependent effects of hindlimb ischemia in mice

Genetics plays an important role in determining peripheral arterial disease (PAD) pathology, which causes a spectrum of clinical disorders that range from clinically silent reductions in blood flow to limb-threatening ischemia. The cell-type specificity of PAD pathology, however, has received little attention. To determine whether strain-dependent differences in skeletal muscle cells might account for the differential responses to ischemia observed in C57BL/6 and BALB/c mice, endothelial and skeletal muscle cells were subjected to hypoxia and nutrient deprivation (HND) in vitro, to mimic ischemia. Muscle cells were more susceptible to HND than were endothelial cells. In vivo, C57BL/6 and BALB/c mice displayed strain-specific differences in myofiber responses after hindlimb ischemia, with significantly greater myofiber atrophy, greater apoptosis, and attenuated myogenic regulatory gene expression and stress-responsive signaling in BALB/c mice. Strain-specific deficits were recapitulated in vitro in primary muscle cells from both strains after HND. Muscle cells from BALB/c mice congenic for the C57BL/6 Lsq-1 quantitative trait locus were protected from HND-induced atrophy, and gene expression of vascular growth factors and their receptors was significantly greater in C57BL/6 primary muscle cells. Our results indicate that the previously identified specific genetic locus regulating strain-dependent collateral vessel density has a nonvascular or muscle cell-autonomous role involving both the myogenic program and traditional vascular growth factor receptor expression.

Alteration in angiogenic and anti-angiogenic forms of vascular endothelial growth factor-A in skeletal muscle of patients with intermittent claudication following exercise training

The aims of this study were twofold: (1) to identify whether peripheral artery disease (PAD) patients had increased muscle concentration of angiogenic VEGF-A, anti-angiogenic VEGF₁₆₅b or VEGF receptor 1 (VEGF-R1) when compared with control subjects, and (2) to evaluate whether exercise training in PAD patients was associated with changes in muscle concentration of VEGF-A, VEGF₁₆₅b or VEGF-R1. At baseline, 22 PAD and 30 control subjects underwent gastrocnemius muscle biopsy. Twelve PAD patients were treated with supervised exercise training (SET) and underwent muscle biopsy after 3 weeks and 12 weeks of training and had sufficient tissue to measure VEGF-A, VEGF₁₆₅b and VEGF-R1 concentrations in skeletal muscle lysates by ELISA. Muscle concentrations of VEGF-A and VEGF₁₆₅b were similar in PAD patients versus controls at baseline. At both time points after the start of SET, VEGF-A levels decreased and there was a trend towards increased VEGF₁₆₅b concentrations. At baseline, VEGF-R1 concentrations were lower in PAD patients when compared with controls but did not change after SET. Skeletal muscle concentrations of VEGF-A are not different in PAD patients when compared with controls at baseline. SET is associated with a significant reduction in VEGF-A levels and a trend towards increased VEGF₁₆₅b levels. These somewhat unexpected findings suggest that further investigation into the mechanism of vascular responses to exercise training in PAD patients is warranted.

Exercise dose response in muscle

Exercise increases peak VO2 partially through muscle adaptations. However, understanding muscle adaptations related to exercise dose is incomplete. This study investigated exercise training dose on capillaries per fiber and capillaries per area; and citrate synthase from vastus lateralis and related both to changes in peak VO2. This randomized trial compared 3 exercise doses: low amount-moderate intensity (n=40), low amount-high intensity (n=47), high amount-high intensity (n=41), and a control group (n=35). Both measures of capillary supply increased in all exercise groups (p<0.05). Low amount-high intensity and high amount-high intensity improved citrate synthase (p<0.05) and the low amount-moderate intensity citrate synthase approached significance (p=0.059). Muscle improvements were only related to improvements in peak VO2 in high amount-high intensity (citrate synthase, r=0.304; capillaries:fiber, r= - 0.318; p<0.05 and capillaries/mm2 r= - 0.310, p<0.05). These data suggest muscle adaptations occur following both low and high exercise doses, but are only related to improved peak VO2 following high amount-high intensity training.

Abstract 3542: Novel Differences in a Mouse Model of Hyperglycemia after Cerebral Ischemia

Background: Stroke is a leading cause of serious long-term adult disability in the United States. Hyperglycemia has consistently been associated with worse clinical outcomes from ischemic stroke. Animal studies utilizing genetic models of type II diabetes have shown greater ischemic injury in the setting of hyperglycemia. However, these models may not well represent all physiological aspects of human type II diabetes and post-stroke hyperglycemia. Diet induced diabetes may prove more analogous to human disease. The high fat diet mouse model of type II diabetes reliably creates a subacute hyperglycemic state. We evaluated normal and high fat diet (HFD) fed mice following middle cerebral artery occlusion (MCAO) to determine if post-ischemic functional status is influenced by hyperglycemia in this model.

Methods: C57BL/6 male mice (12-18 weeks) fed either normal diet or HFD (60%kCal fat) were subjected to 60 minutes of transient MCAO via 6-0 monofilament. Triphenyltetrazolium chloride staining confirmed infarction in a subset of mice. A glucose tolerance test was performed, and fasting blood sugar was tested prior to surgery to verify hyperglycemia. Neurologic deficit score (NDS) was measured before and after surgery, and 24 hours post MCAO.

Results: HFD fed mice demonstrated worse NDS following ischemia compared to normal fed mice. This was significant at 24 hours post MCAO (p<0.0001). Normal fed mice showed improvement in functional score 24 hours post MCAO (p<0.05), but HFD fed mice demonstrated no improvement.

Conclusion: Our data show that HFD fed mice have worse outcomes post-MCAO and without the recovery in functional scores seen in normal fed mice. This mirrors the human condition, where worse clinical outcomes are seen in hyperglycemic patients with ischemic stroke. This model provides an opportunity to investigate mechanisms underlying differential recovery in the setting of hyperglycemia and to test if insulin treatment can prevent the adverse recovery in HFD animals as has been postulated in humans. We are conducting gene expression experiments to test candidates that may mediate ischemic damage and recovery and to identify novel therapeutic targets.

Angiogenesis in skeletal muscle precede improvements in peak oxygen uptake in peripheral artery disease patients

OBJECTIVE

Peripheral artery disease (PAD) is characterized by impaired blood flow to the lower extremities, causing claudication and exercise intolerance. The mechanism(s) by which exercise training improves functional capacity is not understood. This study tested the hypothesis that in PAD patients who undergo supervised exercise training, increases in capillary density (CD) in calf muscle take place before improvements in peak oxygen uptake (VO(2)).

METHODS AND RESULTS

Thirty-five PAD patients were randomly assigned to 12 weeks of directly supervised or home-based exercise training. Peak VO(2) testing and gastrocnemius muscle biopsies were performed at baseline and after training. CD (endothelial cells/mm(2)) was measured using immunofluorescence staining. After 3 weeks of directly supervised training, patients had an increase in CD (216±66 versus 284±77, P<0.01) but no increase in peak VO(2). However, after 12 weeks, peak VO(2) increased (15.3±2.8 versus 16.8±3.8, P<0.01), whereas in muscle, CD remained increased over baseline, but there were no changes in markers of oxidative capacity. Within subjects, CD was related to peak VO(2) before and after directly supervised training.

CONCLUSION

Changes in CD in ischemic muscle with training may modulate the response to training, and those changes precede the increase in VO(2).

Effect of hypoxia-inducible factor-1alpha gene therapy on walking performance in patients with intermittent claudication

BACKGROUND

Hypoxia-inducible factor-1α (HIF-1α) is a transcriptional regulatory factor that orchestrates cellular responses to hypoxia. It increases collateral vessel growth and blood flow in models of hind-limb ischemia. This study tested whether intramuscular administration of Ad2/HIF-1α/VP16, an engineered recombinant type 2 adenovirus vector encoding constitutively active HIF-1α, improves walking time in patients with peripheral artery disease and intermittent claudication.

METHODS AND RESULTS

Two hundred eighty-nine patients with claudication were randomized in a double-blind manner to 1 of 3 doses of Ad2/HIF-1α/VP16 (2×10(9), 2×10(10), or 2×10(11) viral particles) or placebo, administered by 20 intramuscular injections to each leg. Graded treadmill tests were performed at baseline and then 3, 6, and 12 months after treatment. The primary end point was the change in peak walking time from baseline to 6 months. The secondary end point was change in claudication onset time, and tertiary end points included changes in ankle-brachial index and quality-of-life assessments. Median peak walking time increased by 0.82 minutes (interquartile range, -0.05-1.93 minutes) in the placebo group and by 0.82 minutes (interquartile range, -0.07-2.12 minutes), 0.28 minutes (interquartile range, -0.37-1.70 minutes), and 0.78 minutes (interquartile range, -0.02-2.10 minutes) in the HIF-1α 2×10(9), 2×10(10), and 2×10(11) viral particle groups, respectively (P=NS between placebo and each HIF-1α treatment group). There were no significant differences in claudication onset time, ankle-brachial index, or quality-of-life measurements between the placebo and each HIF-1α group.

CONCLUSIONS

Gene therapy with intramuscular administration of Ad2/HIF-1α/VP16 is not an effective treatment for patients with intermittent claudication. Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT00117650.

Adeno-associated virus serotype 9-mediated overexpression of extracellular superoxide dismutase improves recovery from surgical hind-limb ischemia in BALB/c mice

OBJECTIVE

Neovascularization is a physiologic repair process that partly depends on nitric oxide. Extracellular superoxide dismutase (EcSOD) is the major scavenger of superoxide. It is an important regulator of nitric oxide bioavailability and thus protects against vascular dysfunction. We hypothesized that overexpression of EcSOD in skeletal muscle would improve recovery from hind-limb ischemia.

METHODS

Adeno-associated virus serotype 9 (AAV9) vectors expressing EcSOD or luciferase (control) from the cytomegalovirus promoter were cross-packaged into AAV9 capsids and injected intramuscularly into the hind-limb muscles (1 × 10(11) viral genomes/limb) of 12-week-old mice. Ischemia was induced after intramuscular injections. Laser Doppler was used to measure limb perfusion on days 0, 7, and 14 after injection. Values were expressed as a ratio relative to the nonischemic limb. EcSOD expression was measured by Western blotting. Capillary density was documented by immunohistochemical staining for platelet endothelial cell adhesion molecule. Apoptosis was assessed by terminal deoxynucleotide transferase-mediated biotin-deoxy uridine triphosphate nick-end labeling and necrosis was visually evaluated daily.

RESULTS

EcSOD expression was twofold upregulated in EcSOD treated vs control ischemic muscles at day 14. Capillary density (capillaries/fiber) was 1.9-fold higher in treated (1.65 ± 0.02) vs control muscle (0.78 ± 0.17, P < .05). Recovery of perfusion ratio at day 14 after ischemia was 1.5-fold greater in EcSOD vs control mice (P < .05). The percentage of apoptotic nuclei was 1.3% ± 0.4% in EcSOD-treated mice compared with 4.2% ± 0.2% in controls (P < .001). Limb necrosis was also significantly lower in EcSOD vs control mice.

CONCLUSION

AAV9-mediated overexpression of EcSOD in skeletal muscle significantly improves recovery from hind-limb ischemia in mice, consistent with improved capillary density and perfusion ratios in treated mice.

A randomized, controlled study of autologous therapy with bone marrow-derived aldehyde dehydrogenase bright cells in patients with critical limb ischemia

OBJECTIVES

The safety and efficacy of direct intramuscular injections of aldehyde dehydrogenase bright (ALDH(br)) cells isolated from autologous bone marrow mononuclear cells (ABMMNCs) and ABMMNCs were studied in patients with critical limb ischemia (CLI) who were not eligible for percutaneous or surgical revascularization.

BACKGROUND

Many CLI patients are not candidates for current revascularization procedures, and amputation rates are high in these patients. Cell therapy may be a viable option for CLI patients.

METHODS

Safety was the primary objective and was evaluated by occurrence of adverse events. Efficacy, the secondary objective, was evaluated by assessment of Rutherford category, ankle-brachial index (ABI), transcutaneous partial pressure of oxygen (TcPO(2)), quality of life, and pain.

RESULTS

ALDH(br) cells and ABMMNCs were successfully administered to all patients. No therapy-related serious adverse events occurred. Patients treated with ALDH(br) cells (n = 11) showed significant improvements in Rutherford category from baseline to 12 weeks (mean, 4.09 ± 0.30 to 3.46 ± 1.04; P = 0.05) and in ABI at 6 (mean, 0.22 ± 0.19 to 0.30 ± 0.24; P = 0.02), and 12 weeks (mean, 0.36 ± 0.18; P = 0.03) compared with baseline. Patients in the ABMMNC group (n = 10) showed no significant improvements at 6 or 12 weeks in Rutherford category but did show improvement in ABI from baseline to 12 weeks (0.38 ± 0.06 to 0.52 ± 0.16; P = 0.03). No significant changes from baseline were noted in ischemic ulcer grade or TcPO(2) in either group.

CONCLUSIONS

Administration of autologous ALDH(br) cells appears to be safe and warrants further study in patients with CLI.

Relationship between leg muscle capillary density and peak hyperemic blood flow with endurance capacity in peripheral artery disease

The aim of this study was to determine if skeletal muscle capillary density is lower in patients with peripheral artery disease (PAD) and if capillary density relates to functional limitations. PAD patients with intermittent claudication (IC) have a decreased exercise tolerance due to exercise-induced muscle ischemia. Despite the apparent role diminished arterial flow has in this population, the degree of walking pain and functional limitation is not entirely explained by altered hemodynamics of the affected limbs. We hypothesized that skeletal muscle capillary density is lower in PAD and is related to the functional impairment observed in this population. Sixty-four patients with PAD and 56 controls underwent cardiopulmonary exercise testing and a gastrocnemius muscle biopsy. A subset of these patients (48 PAD and 47 controls) underwent peak hyperemic flow testing via plethysmography. Capillary density in PAD patients was lower compared with controls (P < 0.001). After adjustment for several baseline demographic imbalances the model relating capillary density to peak oxygen consumption (Vo(2)) remained significant (P < 0.001). In PAD subjects, capillary density correlated with peak Vo(2), peak walking time (PWT), and claudication onset time (COT). Peak hyperemic blood flow related to peak Vo(2) in both PAD and control subjects. PAD is associated with lower capillary density, and capillary density is related to the functional impairment as defined by a reduced peak Vo(2), PWT, and COT. These findings suggest that alterations in microcirculation may contribute to functional impairment capacity in PAD.

Safety and efficacy of patient specific intramuscular injection of HGF plasmid gene therapy on limb perfusion and wound healing in patients with ischemic lower extremity ulceration: results of the HGF-0205 trial

OBJECTIVES

We have previously reported the results of a dose-finding phase II trial showing that HGF angiogenic gene therapy can increase TcPO2 compared with placebo in patients with critical limb ischemia (CLI). The purpose of this randomized placebo controlled multi-center trial was to further assess the safety and clinical efficacy of a modified HGF gene delivery technique in patients with CLI and no revascularization options.

METHODS

Patients with lower extremity ischemic tissue loss (Rutherford 5 and 6) received three sets of eight intramuscular injections every 2 weeks of HGF plasmid under duplex ultrasound guidance. Injection locations were individualized for each patient based on arteriographically defined vascular anatomy. Primary safety end point was incidence of adverse events (AE) or serious adverse events (SAE). Clinical end points included change from baseline in toe brachial index (TBI), rest pain assessment by a 10 cm visual analogue scale (VAS) as well as wound healing, amputation, and survival at 3 and 6 months.

RESULTS

Randomization ratio was 3:1 HGF (n = 21) vs placebo (n = 6). Mean age was 76 ± 2 years, with 56% male and 59% diabetic. There was no difference in demographics between groups. There was no difference in AEs or SAEs, which consisted mostly of transient injection site discomfort, worsening of CLI, and intercurrent illnesses. Change in TBI significantly improved from baseline at 6 months in the HGF-treated group compared with placebo (0.05 ± 0.05 vs -0.17 ± 0.04; P = .047). Change in VAS from baseline at 6 months was also significantly improved in the HGF-treated group compared with placebo (-1.9 ± 1.3 vs +0.06 ± 0.2; P = .04). Complete ulcer healing at 12 months occurred in 31% of the HGF group and 0% of the placebo (P = .28) There was no difference in major amputation of the treated limb (HGF 29% vs placebo 33%) or mortality at 12 months (HGF 19% vs placebo 17%) between groups.

CONCLUSION

HGF gene therapy using a patient vascular anatomy specific delivery technique appears safe, maintained limb perfusion, and decreased rest pain in patients with CLI compared with placebo. A larger study to assess the efficacy of this therapy on more clinically relevant end points is warranted.

Systems biology of pro-angiogenic therapies targeting the VEGF system

Vascular endothelial growth factor (VEGF) is a family of cytokines for which the dysregulation of expression is involved in many diseases; for some, excess VEGF causes pathological hypervascularization, while for others VEGF-induced vascular remodeling may alleviate ischemia and/or hypoxia. Anti-angiogenic therapies attacking the VEGF pathway have begun to live up to their promise for treatment of certain cancers and of age-related macular degeneration. However, the corollary is not yet true: in coronary artery disease and peripheral artery disease, clinical trials of pro-angiogenic VEGF delivery have not, so far, proven successful. The VEGF and VEGF-receptor system is complex, with at least five ligand genes, some encoding multiple protein isoforms and five receptor genes. A systems biology approach for designing pro-angiogenic therapies, using a combination of quantitative experimental approaches and detailed computational models, is essential to deal with this complexity and to understand the effects of drugs targeting the system. This approach allows us to learn from unsuccessful clinical trials and to design and test novel single therapeutics or combinations of therapeutics. Among the parameters that can be varied in order to determine optimal strategy are dosage, timing of multiple doses, route of administration, and the molecular target.