Peripheral artery disease. Part 2: medical and endovascular treatment

Therapeutic potential and molecular mechanisms of salidroside in ischemic diseases

Rhodiola is an ancient wild plant that grows in rock areas in high-altitude mountains with a widespread habitat in Asia, Europe, and America. From empirical belief to research studies, Rhodiola has undergone a long history of discovery, and has been used as traditional medicine in many countries and regions for treating high-altitude sickness, anoxia, resisting stress or fatigue, and for promoting longevity. Salidroside, a phenylpropanoid glycoside, is the main active component found in all species of Rhodiola. Salidroside could enhance cell survival and angiogenesis while suppressing oxidative stress and inflammation, and thereby has been considered a potential compound for treating ischemia and ischemic injury. In this article, we highlight the recent advances in salidroside in treating ischemic diseases, such as cerebral ischemia, ischemic heart disease, liver ischemia, ischemic acute kidney injury and lower limb ischemia. Furthermore, we also discuss the pharmacological functions and underlying molecular mechanisms. To our knowledge, this review is the first one that covers the protective effects of salidroside on different ischemia-related disease.

Vitamin D: Not Just Bone Metabolism but a Key Player in Cardiovascular Diseases

Vitamin D is the first item of drug expenditure for the treatment of osteoporosis. Its deficiency is a condition that affects not only older individuals but also young people. Recently, the scientific community has focused its attention on the possible role of vitamin D in the development of several chronic diseases such as cardiovascular and metabolic diseases. This review aims to highlight the possible role of vitamin D in cardiovascular and metabolic diseases. In particular, here we examine (1) the role of vitamin D in diabetes mellitus, metabolic syndrome, and obesity, and its influence on insulin secretion; (2) its role in atherosclerosis, in which chronic vitamin D deficiency, lower than 20 ng/mL (50 nmol/L), has emerged among the new risk factors; (3) the role of vitamin D in essential hypertension, in which low plasma levels of vitamin D have been associated with both an increase in the prevalence of hypertension and diastolic hypertension; (4) the role of vitamin D in peripheral arteriopathies and aneurysmal pathology, reporting that patients with peripheral artery diseases had lower vitamin D values than non-suffering PAD controls; (5) the genetic and epigenetic role of vitamin D, highlighting its transcriptional regulation capacity; and (6) the role of vitamin D in cardiac remodeling and disease. Despite the many observational studies and meta-analyses supporting the critical role of vitamin D in cardiovascular physiopathology, clinical trials designed to evaluate the specific role of vitamin D in cardiovascular disease are scarce. The characterization of the importance of vitamin D as a marker of pathology should represent a future research challenge.

Vitamin D as A Protector of Arterial Health: Potential Role in Peripheral Arterial Disease Formation

Atherosclerotic occlusive diseases and aneurysms that affect large and medium-sized arteries outside the cardiac and cerebral circulation are collectively known as peripheral arterial disease (PAD). With a rise in the rate of aging population worldwide, the number of people diagnosed with PAD is rapidly increasing. The micronutrient vitamin D is an important steroid hormone that acts on many crucial cellular mechanisms. Experimental studies suggest that optimal levels of vitamin D have beneficial effects on the heart and blood vessels; however, high vitamin D concentrations have been implicated in promoting vascular calcification and arterial stiffness. Observations from various clinical studies shows that deficiency of vitamin D has been associated with a greater risk of PAD. Epidemiological studies have often reported an inverse relation between circulating vitamin D status measured in terms of 25-hydroxivitamin D [25(OH)D] levels and increased cardiovascular disease risk; however, randomized controlled trials did not show a consistent positive effect of vitamin D supplementation on cardiovascular disease risk or events. Even though PAD shares all the major risk factors with cardiovascular diseases, the effect of vitamin D deficiency in PAD is not clear. Current evidence suggests a strong role of vitamin D in promoting genomic and epigenomic changes. This review summarises the current literature that supports the notion that vitamin D deficiency may promote PAD formation. A better understanding of underlying pathological mechanisms will open up new therapeutic possibilities which is the main unmet need in PAD management. Furthermore, epigenetic evidence shows that a more holistic approach towards PAD prevention that incorporates a healthy lifestyle, adequate exercise and optimal nutrition may be more effective in protecting the genome and maintaining a healthy vasculature.

Ipsilateral Antegrade Angioplasty for Flush Superficial Femoral Artery Occlusion versus Open Bypass Surgery

BACKGROUND

Management of superficial femoral artery flush occlusion using the ipsilateral antegrade approach is challenging. The study aimed to assess technical feasibility, patency, and limb salvage of ipsilateral antegrade angioplasty versus surgery for this lesion in patients with lifestyle-limiting claudications and critical limb ischemia.

METHODS

Between June 2015 and March 2018, 53 patients were randomized to either ipsilateral antegrade angioplasty (n = 28) or surgical bypass (n = 25). We included patients with Trans-Atlantic Inter-Society Consensus IIB, C, or D lesions, having a patent popliteal artery. Technical success, patency, limb salvage, and major adverse events were assessed during the 12-month follow-up.

RESULTS

The technical success was 100% and 89.3% in the surgical and endovascular groups, respectively (P = 0.238). At 12 months, the primary, assisted, and secondary patency rates were 72% vs. 64.5%, 78.2% vs. 74.7%, and 81.6% vs. 74.2% in the surgical versus the endovascular groups, respectively, without significant differences between both groups. Limb salvage was 88% vs. 92% in the surgical versus the endovascular group, respectively (P = 0.564). The length of hospital stay was longer in the surgical versus the endovascular group (6.24 ± 0.37 vs. 1.84 ± 0.19 days, respectively, P = 0.001). Local complications were higher in the surgical group (P = 0.046).

CONCLUSIONS

Technical success, patency, and limb salvage of endovascular approach were comparable to surgical bypass. The endovascular approach had the advantages of reduced local complications and hospitalization.

In Vivo Photoacoustic Tracking of Mesenchymal Stem Cell Viability

Adult stem cell therapy has demonstrated improved outcomes for treating cardiovascular diseases in preclinical trials. The development of imaging tools may increase our understanding of the mechanisms of stem cell therapy, and a variety of imaging tools have been developed to image transplanted stem cells in vivo; however, they lack the ability to interrogate stem cell function longitudinally. Here, we report the use of a nanoparticle-based contrast agent that can track stem cell viability using photoacoustic imaging. The contrast agent consists of inert gold nanorods coated with IR775c, a reactive oxygen species (ROS) sensitive near-infrared dye. Upon cell death, stem cells produce ROS to degrade the cell. Using this feature of stem cells, the viability can be measured by comparing the IR775c signal to the ROS insensitive gold nanorod signal, which can also be used to track stem cell location. The nanoprobe was successfully loaded into mesenchymal stem cells (MSCs), and then, MSCs were transplanted into the lower limb of a mouse and imaged using combined ultrasound and photoacoustic imaging. MSC viability was assessed using the nanoprobe and displayed significant cell death within 24 h and an estimated 5% viability after 10 days. This nanoparticle system allows for longitudinal tracking of MSC viability in vivo with high spatial and temporal resolution which other imaging modalities currently cannot achieve.

Impact of calcification and infrapopliteal outflow on the outcome of endovascular treatment of femoropopliteal occlusive disease

Objectives

In this paper, we report the long-term outcomes of the endovascular treatment of femoropopliteal occlusive disease, focusing on the importance of calcification and runoff outflow on limb salvage and patency, and the factors associated with these outcomes at a single center.

Methods

This retrospective cohort study included consecutive patients with femoropopliteal occlusive who underwent femoropopliteal angioplasty at the Division of Vascular and Endovascular Surgery, Hospital do Servidor Público Estadual, São Paulo, Brazil, between January 2015 and July 2017.

Results

In total, 86 femoropopliteal occlusive angioplasties were performed in 86 patients, with an initial technical success rate of 95.34%. The mean ± standard deviation follow-up time was 880 ± 68.84 days. The analysis was performed at 720 days. Technical failure occurred in four patients, who were excluded from the analysis, leaving 82 patients and 82 femoropopliteal occlusive angioplasties. The estimated primary patency, secondary patency, limb salvage, and overall survival rates at 720 days were 60%, 96%, 90%, and 82.5%, respectively. In univariate and multivariate analyses, Cox regression showed worse primary patency rates in patients with one tibial vessel or isolated popliteal artery runoff (p = 0.005), calcification grade 4 (p = 0.019), calcification grade > 2 (p = 0.017), small vessel diameter < 4 mm (p = 0.03) or primary angioplasty without stenting (p = 0.021). A univariate analysis showed worse limb salvage in patients with one tibial vessel or isolated popliteal artery runoff (p = 0.039).

Conclusions

In this study, the main factors associated with worse outcomes in the endovascular treatment of femoropopliteal occlusive in terms of loss of primary patency were one tibial vessel or isolated popliteal artery runoff, calcification grade 4, or calcification grade > 2, small vessel diameter < 4 mm, and no stents use. One tibial vessel or isolated popliteal artery runoff was also associated with limb loss in a univariate Cox regression analysis.

Stent revascularization versus bypass surgery for peripheral artery disease in type 2 diabetic patients - an instrumental variable analysis

The objective of this study was to use instrumental variable (IV) analyses to evaluate the clinical effectiveness of percutaneous stent revascularization versus bypass surgery in the treatment of peripheral artery disease (PAD) among type 2 diabetic patients. Type 2 diabetic patients who received peripheral artery bypass surgery (n = 5,652) or stent revascularization (n = 659) for lower extremity arterial stenosis between 2000 and 2007 were identified from the Taiwan National Health Insurance claims database. Patients were followed from the date of index hospitalization for 2 years for lower-extremity amputation, revascularization, and hospitalization for medical treatment. Analysis using treatment year, patients’ monthly income level, and regional difference as IVs were conducted to reduce unobserved treatment selection bias. The crude analysis showed a statistically significant risk reduction in favor of stent placement in lower extremity amputation and in the composite endpoint of amputation, revascularization, or hospitalization for medical treatment. However, peripheral artery stent revascularization and bypass surgery had similar risk of lower limb amputation and composite endpoints in the analyses using calendar year or patients’ monthly income level as IVs. These two treatment modalities had similar risk of lower limb amputation among DM patients with PAD.

Peripheral Artery Disease: Evolving Role of Exercise, Medical Therapy, and Endovascular Options

The prevalence of peripheral artery disease (PAD) continues to increase worldwide. It is important to identify patients with PAD because of the increased risk of myocardial infarction, stroke, and cardiovascular death and impaired quality of life because of a profound limitation in exercise performance and the potential to develop critical limb ischemia. Despite effective therapies to lower the cardiovascular risk and prevent progression to critical limb ischemia, patients with PAD continue to be under-recognized and undertreated. The management of PAD patients should include an exercise program, guideline-based medical therapy to lower the cardiovascular risk, and, when revascularization is indicated, an "endovascular first" approach. The indications and strategic choices for endovascular revascularization will vary depending on the clinical severity of the PAD and the anatomic distribution of the disease. In this review, we discuss an evidence-based approach to the management of patients with PAD.

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.

Syndecan-4 Enhances Therapeutic Angiogenesis after Hind Limb Ischemia in Mice with Type 2 Diabetes

Delivering syndecan-4 with FGF-2 improves the effectiveness of FGF-2 therapy for ischemia in the diabetic disease state. The syndecan-4 proteoliposomes significantly enhance in vitro tubule formation as well as blood perfusion and vessel density in the ischemic hind limbs of diseased ob/ob mice. Syndecan-4 therapy also induces a marked immunomodulation in the tissues, increasing the polarization of macrophages toward the M2 phenotype.

Fucoidan Stimulates Monocyte Migration via ERK/p38 Signaling Pathways and MMP9 Secretion

Critical limb ischemia (CLI) induces the secretion of paracrine signals, leading to monocyte recruitment and thereby contributing to the initiation of angiogenesis and tissue healing. We have previously demonstrated that fucoidan, an antithrombotic polysaccharide, promotes the formation of new blood vessels in a mouse model of hindlimb ischemia. We examined the effect of fucoidan on the capacity of peripheral blood monocytes to adhere and migrate. Monocytes negatively isolated with magnetic beads from peripheral blood of healthy donors were treated with fucoidan. Fucoidan induced a 1.5-fold increase in monocyte adhesion to gelatin (p < 0.05) and a five-fold increase in chemotaxis in Boyden chambers (p < 0.05). Fucoidan also enhanced migration 2.5-fold in a transmigration assay (p < 0.05). MMP9 activity in monocyte supernatants was significantly enhanced by fucoidan (p < 0.05). Finally, Western blot analysis of fucoidan-treated monocytes showed upregulation of ERK/p38 phosphorylation. Inhibition of ERK/p38 phosphorylation abrogated fucoidan enhancement of migration (p < 0.01). Fucoidan displays striking biological effects, notably promoting monocyte adhesion and migration. These effects involve the ERK and p38 pathways, and increased MMP9 activity. Fucoidan could improve critical limb ischemia by promoting monocyte recruitment.

Bioresorbable Electronic Stent Integrated with Therapeutic Nanoparticles for Endovascular Diseases

Implantable endovascular devices such as bare metal, drug eluting, and bioresorbable stents have transformed interventional care by providing continuous structural and mechanical support to many peripheral, neural, and coronary arteries affected by blockage. Although effective in achieving immediate restoration of blood flow, the long-term re-endothelialization and inflammation induced by mechanical stents are difficult to diagnose or treat. Here we present nanomaterial designs and integration strategies for the bioresorbable electronic stent with drug-infused functionalized nanoparticles to enable flow sensing, temperature monitoring, data storage, wireless power/data transmission, inflammation suppression, localized drug delivery, and hyperthermia therapy. In vivo and ex vivo animal experiments as well as in vitro cell studies demonstrate the previously unrecognized potential for bioresorbable electronic implants coupled with bioinert therapeutic nanoparticles in the endovascular system.

Outcomes of endovascular treatment for patients with TASC II D femoropopliteal occlusive disease: a single center study

BACKGROUND

Advances in endovascular technology led to an alternative treatment option for TASC II D (TransAtlantic Inter-Society Consensus II class D) lesions. This study was aimed to evaluate the outcomes of endovascular treatment for TASC II D femoropopliteal lesions.

METHODS

Endovascular intervention with bare nitinol stent implantation was performed on 58 limbs (53 patients) with TASC II D femoropopliteal lesions from January 2011 to March 2013. Kaplan-Meier curves of primary patency, assisted patency and second patency were performed. Predictive factors of re-stenosis/occlusion were evaluated by univariate methods.

RESULTS

Total 53 patients with mean age of 74.2 ± 8.2 (range, 58.0-91.0 years) and mean lesion length of 314.8 ± 64.3 mm (188.2-400.4 mm) were enrolled. The mean follow-up time was 12.2 ± 6.1 months (5-38 months). Revascularization was successfully on 95% lesions by bare nitinol stent implantation. Primary patency rates at 1, 2 and 3 years were 63%, 12% and 12%, respectively. Assisted primary patency rates at 1, 2 and 3 years were 77%, 31% and 31%, respectively. Secondary patency rates at 1, 2 and 3 years were 96%, 63% and 63%. During one-year follow-up, no major amputation was occurred. Univariate analysis revealed that number of run-off vessels was a potential predictor of re-stenosis/occlusion.

CONCLUSION

Endovascular treatment of TASC II D femoropopliteal artery occlusion has a high technical success rate with acceptable one-year patency rate. The long-term outcomes are poor, but endovascular intervention could be a good alternative for patients unsuitable for surgical bypass.

Sulodexide as Adjunctive Therapy in Diabetic Foot Patients With Critical Limb Ischemia Treated With Percutaneous Transluminal Angioplasty

We evaluated the safety and efficacy of sulodexide, a biocompound of glycosamin-glicans, as adjunct medical therapy to percutaneous transluminal angioplasty (PTA) in diabetes mellitus (DM) patients with critical limb ischemia (CLI). We studied 27 consecutive DM patients with CLI successfully subjected to PTA who, on top of standard antiplatelet therapy, received sulodexide 25 mg bid, and were followed-up for 24 weeks, monitoring adverse events, transcutaneous oxygen tension (TcPO₂), ankle-brachial pressure index, pain, and ulcer dimension. At the end of follow-up, ulcer healing, amputation rates, and cardiovascular risk profile of patients were evaluated. Patients were compared with a historical superimposable control group that was treated for the same indications in the same way as the study group, except for sulodexide inception. No differences in ulcer healing and amputation rates were found at the end of follow-up between the groups. In the study group, TcPO₂ was significantly (P < .05) higher at the end of follow-up, and pain intensity was reduced more rapidly. Plasma fibrinogen and plasma creatinine concentration were significantly (P < .05) reduced in study group at the end of follow-up. No differences in adverse events were observed between the groups during follow-up. Our data suggest that sulodexide administration after PTA, on top of antiplatelet therapy, may improve the outcome of PTA in DM patients with CLI by improving microcirculatory function.

Combination of autologous transplantation of G-CSF-mobilized peripheral blood mononuclear cells and Panax notoginseng saponins in the treatment of unreconstructable critical limb ischemia

BACKGROUND

The aim of this study is to explore the efficacy and safety of the combination of autologous transplantation of granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood mononuclear cells (PBMNCs) and Panax notoginseng saponins (PNS) in the treatment of unreconstructable critical limb ischemia (CLI).

METHODS

We performed an open-label, parallel-group, single-center, randomized clinical trial in this study. A total of 52 patients were enrolled and randomly divided into 2 groups (the PBMNC + PNS group and the PBMNC group) in a 1:1 ratio. Evaluation variables, including changes in the ankle-brachial index (ABI) of ischemic limbs, ulcer area, severity of rest pain, transcutaneous oxygen pressure (T(C)PO2), and 6-min walk distance from baseline to week 8 and 16, as well as angiographic scores for new collateral vessel formation at week 16, were used to compare the benefits of these 2 treatment approaches.

RESULTS

After 16 weeks of treatment, improvement in ABI, T(C)PO2, and 6-min walk distance was significantly better in the PBMNC + PNS group. In addition, the combination of PBMNC transplantation and PNS administration yielded a greater reduction in ulcer area and severity of rest pain than did PBMNC transplantation alone. The proportion of patients experiencing any adverse event was similar between both treatment groups. Adverse events caused by PBMNC transplantation or PNS were generally mild and no serious adverse events occurred throughout the entire period of study.

CONCLUSIONS

A combination of PNS and PBMNC transplantation appears to be a safe and effective treatment for patients with unreconstructable CLI. This combination may have great potential advantages in comparison with PBMNC transplantation alone and might constitute a novel therapeutic option for unreconstructable CLI.

Clearance kinetics of biomaterials affects stem cell retention and therapeutic efficacy

The use of biomaterial carriers to improve the therapeutic efficacy of stem cells is known to augment cell delivery, retention, and viability. However, the way that carrier clearance kinetics boosts stem cell delivery and impacts stem cell function remains poorly characterized. In this study, we designed a platform to simultaneously quantify carrier clearance and stem cell retention to evaluate the impact of carrier clearance kinetics on stem cell retention. Additionally, a murine model of hindlimb ischemia was employed to investigate the effects of various cell retention profiles on mitigating peripheral arterial disease. To image the in vivo behaviors of material and cells, we used biotinylated hyaluronan with fluorescently labeled streptavidin and Discosoma sp. Red (Ds-Red)-expressing human mesenchymal stem cells. We found that the retention of transplanted stem cells was closely related to the remaining biomaterial. Furthermore, therapeutic effectiveness was also affected by stem cell retention. These results demonstrate that low-molecular-weight hyaluronan had a slow clearance and high cell retention profile, improving the therapeutic efficacy of human stem cells.

MicroRNA-138 regulates hypoxia-induced endothelial cell dysfunction by targeting S100A1

The Ca²⁺ sensor S100A1 is essential for proper endothelial cell (EC) nitric oxide (NO) synthase (eNOS) activation. S100A1 levels are greatly reduced in primary human microvascular ECs subjected to hypoxia, rendering them dysfunctional. However mechanisms that regulate S100A1 levels in ECs are unknown. Here we show that ECs transfected with a S100A1–3′ untranslated region (UTR) luciferase reporter construct display significantly reduced gene expression when subjected to low oxygen levels or chemical hypoxia. Bioinformatic analysis suggested that microRNA -138 (MiR-138) could target the 3′UTR of S100A1. Patients with critical limb ischemia (CLI) or mice subjected to femoral artery resection (FAR) displayed increased MiR-138 levels and decreased S100A1 protein expression. Consistent with this finding, hypoxia greatly increased MiR-138 levels in ECs, but not in skeletal muscle C2C12 myoblasts or differentiated myotubes or primary human vascular smooth muscle cells. Transfection of a MiR-138 mimic into ECs reduced S100A1–3 ‘UTR reporter gene expression, while transfection of an anti MiR-138 prevented the hypoxia-induced downregulation of the reporter gene. Deletion of the 22 nucleotide putative MiR-138 target site abolished the hypoxia-induced loss of reporter gene expression. Knockdown of Hif1-α mediated by siRNA prevented loss of hypoxia-induced reporter gene expression. Conversely, specific activation of Hif1-α by a selective prolyl-hydroxylase inhibitor (IOX2) reduced reporter gene expression even in the absence of hypoxia. Finally, primary ECs transfected with a MiR-138 mimic displayed reduced tube formation when plated onto Matrigel matrix and expressed less NO when stimulated with VEGF. These effects were reversed by gene transfer of S100A1 using recombinant adenovirus. We conclude that hypoxia-induced MiR-138 is an essential mediator of EC dysfunction via its ability to target the 3′UTR of S100A1.

Multimodality imaging approach for serial assessment of regional changes in lower extremity arteriogenesis and tissue perfusion in a porcine model of peripheral arterial disease

BACKGROUND

A standard quantitative imaging approach to evaluate peripheral arterial disease does not exist. Quantitative tools for evaluating arteriogenesis in vivo are not readily available, and the feasibility of monitoring serial regional changes in lower extremity perfusion has not been examined.

METHODS AND RESULTS

Serial changes in lower extremity arteriogenesis and muscle perfusion were evaluated after femoral artery occlusion in a porcine model using single photon emission tomography (SPECT)/CT imaging with postmortem validation of in vivo findings using gamma counting, postmortem imaging, and histological analysis. Hybrid 201Tl SPECT/CT imaging was performed in pigs (n=8) at baseline, immediately postocclusion, and at 1 and 4 weeks postocclusion. CT imaging was used to identify muscle regions of interest in the ischemic and nonischemic hindlimbs for quantification of regional changes in CT-defined arteriogenesis and quantification of 201Tl perfusion. Four weeks postocclusion, postmortem tissue 201Tl activity was measured by gamma counting, and immunohistochemistry was performed to assess capillary density. Relative 201Tl retention (ischemic/nonischemic) was reduced immediately postocclusion in distal and proximal muscles and remained lower in calf and gluteus muscles 4 weeks later. Analysis of CT angiography revealed collateralization at 4 weeks within proximal muscles (P<0.05). SPECT perfusion correlated with tissue gamma counting at 4 weeks (P=0.01). Increased capillary density was seen within the ischemic calf at 4 weeks (P=0.004).

CONCLUSIONS

201Tl SPECT/CT imaging permits serial, regional quantification of arteriogenesis and resting tissue perfusion after limb ischemia. This approach may be effective for detection of disease and monitoring therapy in peripheral arterial disease.

Hypoxia-induced angiogenesis: good and evil

The vascular network delivers oxygen (O(2)) and nutrients to all cells within the body. It is therefore not surprising that O(2) availability serves as a primary regulator of this complex organ. Most transcriptional responses to low O(2) are mediated by hypoxia-inducible factors (HIFs), highly conserved transcription factors that control the expression of numerous angiogenic, metabolic, and cell cycle genes. Accordingly, the HIF pathway is currently viewed as a master regulator of angiogenesis. HIF modulation could provide therapeutic benefit for a wide array of pathologies, including cancer, ischemic heart disease, peripheral artery disease, wound healing, and neovascular eye diseases. Hypoxia promotes vessel growth by upregulating multiple pro-angiogenic pathways that mediate key aspects of endothelial, stromal, and vascular support cell biology. Interestingly, recent studies show that hypoxia influences additional aspects of angiogenesis, including vessel patterning, maturation, and function. Through extensive research, the integral role of hypoxia and HIF signaling in human disease is becoming increasingly clear. Consequently, a thorough understanding of how hypoxia regulates angiogenesis through an ever-expanding number of pathways in multiple cell types will be essential for the identification of new therapeutic targets and modalities.

O(2) regulates skeletal muscle progenitor differentiation through phosphatidylinositol 3-kinase/AKT signaling

Skeletal muscle stem/progenitor cells, which give rise to terminally differentiated muscle, represent potential therapies for skeletal muscle diseases. Delineating the factors regulating these precursors will facilitate their reliable application in human muscle repair. During embryonic development and adult regeneration, skeletal muscle progenitors reside in low-O(2) environments before local blood vessels and differentiated muscle form. Prior studies established that low O(2) levels (hypoxia) maintained muscle progenitors in an undifferentiated state in vitro, although it remained unclear if progenitor differentiation was coordinated with O(2) availability in vivo. In addition, the molecular signals linking O(2) to progenitor differentiation are incompletely understood. Here we show that the muscle differentiation program is repressed by hypoxia in vitro and ischemia in vivo. Surprisingly, hypoxia can significantly impair differentiation in the absence of hypoxia-inducible factors (HIFs), the primary developmental effectors of O(2). In order to maintain the undifferentiated state, low O(2) levels block the phosphatidylinositol 3-kinase/AKT pathway in a predominantly HIF1α-independent fashion. O(2) deprivation affects AKT activity by reducing insulin-like growth factor I receptor sensitivity to growth factors. We conclude that AKT represents a key molecular link between O(2) and skeletal muscle differentiation.

Nanomedical Theranostics in Cardiovascular Disease

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide. New diagnostic and therapeutic strategies are needed to mitigate this public health issue. Advances in nanotechnology have generated innovative strategies for diagnosis and therapy in a variety of diseases, foremost in cancer. Based on these studies, a novel concept referred to as nanomedical theranostics, or the combinatory application of nanoparticulate agents to allow diagnostic therapy, is being explored to enable image-guided, personalized, or targeted treatment. Preclinically, theranostics have been gradually applied to CVD with several interesting and encouraging findings. This article summarizes studies and challenges of nanotheranostic strategies in CVD. It also evaluates nanotheranostic strategies that may potentially be utilized to benefit patients.

Peripheral artery disease. Part 1: clinical evaluation and noninvasive diagnosis

Peripheral artery disease (PAD) is a marker of systemic atherosclerosis. Most patients with PAD also have concomitant coronary artery disease (CAD), and a large burden of morbidity and mortality in patients with PAD is related to myocardial infarction, ischemic stroke, and cardiovascular death. PAD patients without clinical evidence of CAD have the same relative risk of death from cardiac or cerebrovascular causes as those diagnosed with prior CAD, consistent with the systemic nature of the disease. The same risk factors that contribute to CAD and cerebrovascular disease also lead to the development of PAD. Because of the high prevalence of asymptomatic disease and because only a small percentage of PAD patients present with classic claudication, PAD is frequently underdiagnosed and thus undertreated. Health care providers may have difficulty differentiating PAD from other diseases affecting the limb, such as arthritis, spinal stenosis or venous disease. In Part 1 of this Review, we explain the epidemiology of and risk factors for PAD, and discuss the clinical presentation and diagnostic evaluation of patients with this condition.