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

The link between impaired oxygen supply and cognitive decline in peripheral artery disease

Although peripheral artery disease (PAD) primarily affects large arteries outside the brain, PAD is also associated with elevated cerebral vulnerabilities, including greater risks for brain injury (such as stroke), cognitive decline and dementia. In the present review, we aim to evaluate recent literature and extract information on potential mechanisms linking PAD and consequences on the brain. Furthermore, we suggest novel therapeutic avenues to mitigate cognitive decline and reduce risk of brain injury in patients with PAD. Various interventions, notably exercise, directly or indirectly improve systemic blood flow and oxygen supply and are effective strategies in patients with PAD or cognitive decline. Moreover, triggering protective cellular and systemic mechanisms by modulating inspired oxygen concentrations are emerging as potential novel treatment strategies. While several genetic and pharmacological approaches to modulate adaptations to hypoxia showed promising results in preclinical models of PAD, no clear benefits have yet been clinically demonstrated. We argue that genetic/pharmacological regulation of the involved adaptive systems remains challenging but that therapeutic variation of inspired oxygen levels (e.g., hypoxia conditioning) are promising future interventions to mitigate associated cognitive decline in patients with PAD.

An Overview of Clinical Examinations in the Evaluation and Assessment of Arterial and Venous Insufficiency Wounds

Arterial and venous insufficiency are two major causes of chronic wounds with different etiology, pathophysiology, and clinical manifestations. With recent advancements in clinical examination, clinicians are able to obtain an accurate diagnosis of the underlying disease, which plays an important role in the treatment planning and management of patients. Arterial ulcers are mainly caused by peripheral artery diseases (PADs), which are traditionally examined by physical examination and non-invasive arterial Doppler studies. However, advanced imaging modalities, such as computed tomography angiography (CTA) and indocyanine green (ICG) angiography, have become important studies as part of a comprehensive diagnostic process. On the other hand, chronic wounds caused by venous insufficiency are mainly evaluated by duplex ultrasonography and venography. Several scoring systems, including Clinical-Etiology-Anatomy-Pathophysiology (CEAP) classification, the Venous Clinical Severity Score (VCSS), the Venous Disability Score, and the Venous Segmental Disease Score (VSDS) are useful in defining disease progression. In this review, we provide a comprehensive overlook of the most widely used and available clinical examinations for arterial and venous insufficiency wounds.

Apolipoprotein E in Cardiometabolic and Neurological Health and Diseases

A preponderance of evidence obtained from genetically modified mice and human population studies reveals the association of apolipoprotein E (apoE) deficiency and polymorphisms with pathogenesis of numerous chronic diseases, including atherosclerosis, obesity/diabetes, and Alzheimer’s disease. The human APOE gene is polymorphic with three major alleles, ε2, ε3 and ε4, encoding apoE2, apoE3, and apoE4, respectively. The APOE gene is expressed in many cell types, including hepatocytes, adipocytes, immune cells of the myeloid lineage, vascular smooth muscle cells, and in the brain. ApoE is present in subclasses of plasma lipoproteins, and it mediates the clearance of atherogenic lipoproteins from plasma circulation via its interaction with LDL receptor family proteins and heparan sulfate proteoglycans. Extracellular apoE also interacts with cell surface receptors and confers signaling events for cell regulation, while apoE expressed endogenously in various cell types regulates cell functions via autocrine and paracrine mechanisms. This review article focuses on lipoprotein transport-dependent and -independent mechanisms by which apoE deficiency or polymorphisms contribute to cardiovascular disease, metabolic disease, and neurological disorders.

Identifying peripheral arterial disease in the elderly patients using machine-learning algorithms

BACKGROUND

Peripheral artery disease (PAD) is a common syndrome in elderly people. Recently, artificial intelligence (AI) algorithms, in particular machine-learning algorithms, have been increasingly used in disease diagnosis.

AIM

In this study, we designed an effective diagnostic model of PAD in the elderly patients using artificial intelligence.

METHODS

The study was performed with 539 participants, all over 80 years in age, who underwent the measurements of Doppler ultrasonography and ankle-brachial pressure index (ABI). Blood samples were collected. ABI and two machine-learning algorithms (MLAs)-logistic regression and a random forest (RF) model-were established to diagnose PAD. The sensitivity and specificity of the models were analyzed. An additional RF model was designed based on the most significant features of the original RF model and a prospective study was conducted to demonstrate its external validity.

RESULTS

Thirteen of the 28 features introduced to the MLAs differed significantly between PAD and non-PAD participants. The respective sensitivities and specificities of logistic regression, RF, and ABI were as follows: logistic regression (81.5%, 83.8%), RF (89.3%, 91.6%) and ABI (85.1%, 84.5%). In the prospective study, the newly designed RF model based on the most significant seven features exhibited an acceptable performance rate for the diagnosis of PAD with 100.0% sensitivity and 90.3% specificity.

CONCLUSIONS

An RF model was a more effective method than the logistic regression and ABI for the diagnosis of PAD in an elderly cohort.

Metabolomics of peripheral artery disease

The science of metabolomics has emerged as a novel tool for studying changes in metabolism that accompany different disease states. Several studies have applied this evolving field to the study of various cardiovascular disease states, which has led to improved understanding of metabolic changes that underlie heart failure and ischemic heart disease. A significant amount of progress has also been made in the identification of novel biomarkers of cardiovascular disease. Another common atherosclerotic disease, peripheral artery disease (PAD) affects arteries of the lower extremities. Although certain aspects of the disease pathophysiology overlap with other cardiovascular diseases in general, PAD patients suffer unique manifestations that lead to significant morbidity and mortality as well as severe functional limitations. Furthermore, because over half of PAD patients are asymptomatic, there is a need for improved diagnostic and screening methods. Identification of metabolites associated with the disease may thus be a promising approach for PAD. However, PAD remains highly understudied. In this chapter, we discuss the application of metabolomics to the study of PAD.

Analyses of serum and urinary metabolites in individuals with peripheral artery disease (PAD) consuming a bean-rich diet: Relationships with drug metabolites

Peripheral artery disease (PAD) has high morbidity and mortality rates. A metabolomics approach was employed to determine whether consumption of bean-rich diets for 8 weeks would impact the metabolomic profile of PAD individuals. Serum and urine, collected from 54 participants with clinical PAD at baseline and after 8 weeks on 0.3 cups beans/d (n=19), 0.6 cups beans/d (n= 20), or control (n=23) diet, and the beans were extracted and analyzed using LC-QTOF-MS. As a result, PGE2 p-acetamidophenyl ester, PGF2α diethyl amide and 5-L-glutamyl-L-alanine were significantly changed in the serum or urine of bean groups compared to control. Significant changes (P<0.05) in the profile and/or levels of 22 flavonoids present in bean extracts showed the potential importance of the mixture of beans used in this study. In a subset of participants taking metoprolol, after 8 weeks the bean-rich diets significantly elevated metoprolol in the serum while reducing it in urine compared to baseline. In addition, the diets significantly enhanced the urinary excretion of metformin. In conclusion, several biochemical pathways including prostaglandins and glutathione were affected by bean consumption. Significant changes in the metabolism of metoprolol and metformin with bean consumption suggested the presence of diet-drug interactions that may require adjustment of the prescribed dose. ClinicalTrials.gov Identifier: NCT01382056 Novelty: • Bean consumption by people with PAD alters the levels of certain metabolites in serum and urine • Different bean types (black, red kidney, pinto, navy) have unique flavonoid profiles • Metabolomics revealed potential diet-dug interactions as serum and/or urinary levels of metoprolol and metformin are modified by bean consumption.

Use of a Pre-Trained Neural Network for Automatic Classification of Arterial Doppler Flow Waveforms: A Proof of Concept

BACKGROUND

Arterial Doppler flow waveform analysis is a tool recommended for the management of lower extremity peripheral arterial disease (PAD). To standardize the waveform analysis, classifications have been proposed. Neural networks have shown a great ability to categorize data. The aim of the present study was to use an existing neural network to evaluate the potential for categorization of arterial Doppler flow waveforms according to a commonly used classification.

METHODS

The Pareto efficient ResNet-101 (ResNet-101) neural network was chosen to categorize 424 images of arterial Doppler flow waveforms according to the Simplified Saint-Bonnet classification. As a reference, the inter-operator variability between two trained vascular medicine physicians was also assessed. Accuracy was expressed in percentage, and agreement was assessed using Cohen's Kappa coefficient.

RESULTS

After retraining, ResNet-101 was able to categorize waveforms with 83.7 ± 4.6% accuracy resulting in a kappa coefficient of 0.79 (0.75-0.83) (CI 95%), compared with a kappa coefficient of 0.83 (0.79-0.87) (CI 95%) between the two physicians.

CONCLUSION

This study suggests that the use of transfer learning on a pre-trained neural network is feasible for the automatic classification of images of arterial Doppler flow waveforms.

Quantifying tissue perfusion after peripheral endovascular procedures: Novel tissue perfusion endpoints to improve outcomes

Peripheral artery disease (PAD) is a flow-limiting condition caused by narrowing of the peripheral arteries typically due to atherosclerosis. It affects almost 200 million people globally with patients either being asymptomatic or presenting with claudication or critical or acute limb ischemia. PAD-affected patients display increased mortality rates, rendering their management critical. Endovascular interventions have proven crucial in PAD treatment and decreasing mortality and have significantly increased over the past years. However, for the functional assessment of the outcomes of revascularization procedures for the treatment of PAD, the same tests that have been used over the past decades are still being employed. Those only allow an indirect evaluation, while an objective quantification of limb perfusion is not feasible. Standard intraarterial angiography only demonstrates post-intervention vessel patency, hence is unable to accurately estimate actual limb perfusion and is incapable of quantifying treatment outcome. Therefore, there is a significant necessity for real-time objectively measurable procedural outcomes of limb perfusion that will allow vascular experts to intraoperatively quantify and assess outcomes, thus optimizing treatment, obviating misinterpretation, and providing significantly improved clinical results. The purpose of this review is to familiarize readers with the currently available perfusion-assessment methods and to evaluate possible prospects.

Trends in Use of Cardioprotective Medication in Peripheral Artery Disease: A Nationwide Study

Background

Guideline‐based cardioprotective medical therapy is intended to reduce the burden of adverse cardiovascular and limb outcomes in patients with peripheral artery disease (PAD). However, contemporary data describing trends in use of medication remains limited. The present study, therefore, aims to investigate changes in use of cardioprotective medication in PAD.

Methods and Results

By using Danish national healthcare registries, we identified all patients with first‐time diagnosis of PAD (1997–2016) and classified them into two groups: (1) PAD+ that includes all patients with PAD with a history of cardiovascular disease, ie, myocardial infarction, atrial fibrillation, and stroke (n=162 627); and (2) PAD (n=87 935) that comprise patients without a history of cardiovascular disease. We determined the use of medication in the first 12 months after the incident diagnosis of PAD and estimated age standardized 1‐year mortality rates. Our results showed increase in use of cardioprotective medication throughout the study period in both groups. However, PAD+ had a higher use of medication (acetylsalicylic acid, 3.5%–48.4%; Clopidogrel, 0%–17.6%; vitamin K antagonists, 0.9%–7.8%; new oral anticoagulants, 0.0%–10.1%; Statins, 1.9%–58.1%; angiotensin‐converting enzyme inhibitors, 1.2%–20.6%), compared with PAD (acetylsalicylic acid, 2.9%–54.4%; Clopidogrel, 0%–11.9%; vitamin K antagonists, 0.9%–2.4%; new oral anticoagulants, 0.0%–3.4%; Statins, 1.5%–56.9%; angiotensin‐converting enzyme, 0.9%–17.2%), respectively. Furthermore, 1‐year mortality rates in PAD declined with increased use of medications during study.

Conclusions

In this nationwide study, use of cardioprotective medication increased considerably with time, but compared to patients with other atherosclerotic diseases, there remains an underuse of guideline‐based medical therapy in patients with PAD.

Peripheral Vascular Disease and Kidney Transplant Outcomes: Rethinking an Important Ongoing Complication

Peripheral vascular disease (PVD) is highly prevalent in patients on the waiting list for kidney transplantation (KT) and after transplantation and is associated with impaired transplant outcomes. Multiple traditional and nontraditional risk factors, as well as uremia- and transplant-related factors, affect 2 processes that can coexist, atherosclerosis and arteriosclerosis, leading to PVD. Some pathogenic mechanisms, such as inflammation-related endothelial dysfunction, mineral metabolism disorders, lipid alterations, or diabetic status, may contribute to the development and progression of PVD. Early detection of PVD before and after KT, better understanding of the mechanisms of vascular damage, and application of suitable therapeutic approaches could all minimize the impact of PVD on transplant outcomes. This review focuses on the following issues: (1) definition, epidemiological data, diagnosis, risk factors, and pathogenic mechanisms in KT candidates and recipients; (2) adverse clinical consequences and outcomes; and (3) classical and new therapeutic approaches.

Cardiovascular Rehabilitation Increases Walking Distance in Patients With Intermittent Claudication. Results of the CIPIC Rehab Study: A Randomised Controlled Trial

OBJECTIVE

To examine whether a cardiac rehabilitation programme in a community based setting for patients with intermittent claudication (IC) affects walking ability, quality of life, and changes in health behaviour. The trial investigated a cross sector cardiovascular rehabilitation programme compared with usual care for patients having non-operative management.

METHODS

The trial allocated 118 patients, with 1:1 individual randomisation to either an intervention or control group. Data were collected at a department of vascular surgery and at a healthcare centre in Denmark. The rehabilitation intervention consisted of usual care plus 12 weeks of exercise training, pedometer, health education, and text messages. The primary outcome was maximum walking distance at six months measured by treadmill walking test. The secondary outcomes were maximum walking distance at 12 months and pain free walking distance measured by treadmill walking test, healthy diet, level of physical activity, and quality of life (QoL) at six and 12 months.

RESULTS

In the intervention group, 46 participants were analysed, with 47 in the control group. Following three months of rehabilitation, a 37% difference (95% CI 1.10 - 1.70; p = .005) was found between groups in maximum walking distance at six and 12 months, in favour of the intervention group. The same positive effect was found in physical activity, QoL, and healthy diet, but was not statistically significant in pain free walking distance and smoking.

CONCLUSION

A specialised community based cardiac rehabilitation programme for patients with IC showed statistically and clinically significant effects on maximum walking distance, physical activity, quality of life, and healthy diet, but not on pain free walking distance and smoking, compared with usual care without rehabilitation.

Vascular imaging of atherosclerosis: Strengths and weaknesses

Atherosclerosis is an inflammatory disease that can lead to several complications such as ischemic heart disease, stroke, and peripheral vascular disease. Therefore, researchers and clinicians rely heavily on the use of imaging modalities to identify, and more recently, quantify the burden of atherosclerosis in the aorta, carotid arteries, coronary arteries, and peripheral vasculature. These imaging techniques vary in invasiveness, cost, resolution, radiation exposure, and presence of artifacts. Consequently, a detailed understanding of the risks and benefits of each technique is crucial prior to their introduction into routine cardiovascular screening. Additionally, recent research in the field of microvascular imaging has proven to be important in the field of atherosclerosis. Using techniques such as contrast-enhanced ultrasound and superb microvascular imaging, researchers have been able to detect blood vessels within a plaque lesion that may contribute to vulnerability and rupture. This paper will review the strengths and weaknesses of the various imaging techniques used to measure atherosclerotic burden. Furthermore, it will discuss the future of advanced imaging modalities as potential biomarkers for atherosclerosis.

Time trends in the risk of atrial fibrillation and ischaemic stroke in patients with peripheral artery disease between 1997 and 2015

Objective

The risk of atrial fibrillation (AF) and stroke in patients with peripheral artery disease (PAD) is an important issue that has not been investigated adequately. Our aim with the present study was to explore trends in the incidence of AF and stroke in patients with PAD.

Methods

We employed Danish nationwide registers to identify all patients with first-time diagnosis of PAD (aged ≥18 years) between 1997 and 2015. Age-standardised incidence rates per 1 000 person-years were calculated to estimate trends of AF and stroke. Risk of AF and stroke was estimated by 1 year cumulative incidence.

Results

A total of 121.241 patients with first-time diagnosis of PAD were identified. The 1-year cumulative incidence of AF in patients with PAD were 1.97% for year 1997–2000, 2.63% for year 2001–2005, 2.66% for year 2006–2010 and 2.78% for year 2011–2015, respectively. The 1-year cumulative incidence of stroke in patients with PAD were 2.71%, 2.71%, 1.95% and 1.81%, for the 1997–2000, 2001–2005, 2006–2010 and 2011–2015 year groups, respectively. Likewise, the age-standardised incidence rates showed increasing trends of AF during the study period, whereas trends of stroke demonstrated a decline. During study, the initiation of cholesterol-lowering agents and clopidogrel increased markedly from 7.0% to 51.3% and 0.1% to 5.9%, whereas use of warfarin slightly dropped from 4.29% to 3.21%.

Conclusions

The incidence of AF in patients with PAD has significantly increased over time, whereas a marked decline has occurred in the incidence of stroke. This may suggest that the secondary prevention strategies aimed at reducing risk of stroke are broadly effective.

Assessment of carotid artery stenosis and lower limb peripheral ischemia before coronary artery bypass grafting operations: a non-randomized clinical trial

BACKGROUND

Atherosclerosis is a systemic disease affecting the coronary, carotid, and lower limb arteries. Cerebrovascular accidents and lower limb ischemia are devastating postoperative complications. We aimed to evaluate the role of non-selective routine arterial duplex scanning in patients undergoing coronary artery bypass grafting (CABG).

METHODS

This non-randomized clinical trial included 360 patients scheduled for elective isolated CABG who were divided into two groups: low-risk (n = 180) and high-risk (n = 180). Both groups underwent preoperative carotid and lower limb ultrasound screening for associated arteriopathy.

RESULTS

16 (8.9%) patients and 22 (12.2%) patients showed ≥70% carotid artery stenosis while 11 patients (6.1%) and 20 patients (11.1%) showed ≥50% lower limb arterial stenosis in the low-risk group and the high-risk group, respectively; though the difference was not statistically significant in both the cases (p > 0.1).

CONCLUSION

Routine preoperative peripheral arterial screening by sonography is a feasible and effective strategy to avoid unnecessary post CABG complications.

TRIAL REGISTRATION

NCT03516929 , Registered in 24 th of April 2018.

Acute Lower Limb Ischemia-Etiology, Pathology, and Management

Acute limb ischemia (ALI) is a vascular emergency associated with a high risk for limb loss and death. Most cases result from in situ thrombosis in patients with preexisting peripheral arterial disease or those who have undergone vascular procedures including stenting and bypass grafts. The other common source is cardioembolic. The incidence has decreased in recent times due to better anticoagulation strategies. Patients with suspected ALI should be evaluated promptly by a vascular specialist and consideration should be given for transfer to a higher level of care if such expertise is not available locally. Initial assessment should focus on staging severity of ischemic injury and potential for limb salvage. Neurological deficits can occur early and are an important poor prognostic sign. Duplex ultrasound and computed tomography angiography help plan intervention in patients with a still-viable limb and prompt catheter-based angiography is mandated in patients with an immediately threatened limb. Further investigations need to be pursued to differentiate embolic from thrombotic cause for acute occlusion as this can change management. Options include intravascular interventions, surgical bypass, or a hybrid approach. In this article, the authors discuss the common etiologies, clinical evaluation, and management of patients presenting with acute limb ischemia.

Cross-sectoral rehabilitation intervention for patients with intermittent claudication versus usual care for patients in non-operative management - the CIPIC Rehab Study: study protocol for a randomised controlled trial

INTRODUCTION

Intermittent claudication (IC) caused by peripheral artery disease (PAD) is a common cardiovascular disease. Patients with IC have reduced walking capacity, restricted activity levels and mobility, and reduced health-related quality of life. The disease leads to social isolation, the risk of cardiovascular morbidity, and mortality. Non-operative management of IC requires exercise therapy and studies show that supervised exercise training is more effective than unsupervised training, yet many patients with IC lack motivation for changes in health behaviour. No studies investigating the effects of existing cardiac rehabilitation targeted patients with IC have been published. The aim of this article is to present the rationale and design of the CIPIC Rehab Study, which examines the effect of a cross-sectoral rehabilitation programme versus usual care for patients in non-operative management for IC.

METHODS AND ANALYSIS

A randomised clinical trial aims to investigate whether cardiac rehabilitation for patients with IC in non-operative management versus usual care is superior to treatment as usual. The trial will allocate 118 patients, with a 1:1 individual randomisation to either the intervention or control group. The primary outcome is maximal walking distance measured by the standardised treadmill walking test. The secondary outcome is pain-free walking distance measured by the standardised treadmill walking test, healthy diet measured by a fat-fish-fruit-green score, and level of physical activity measured by an activity score within official recommendations. Statistical analyses will be blinded. Several exploratory analyses will be performed. A mixed-method design is used to evaluate qualitative and quantitative findings. A qualitative and a survey-based complementary study will be undertaken to investigate patients' post-discharge experiences. A qualitative post-intervention study will explore experiences of participation in rehabilitation.

DISCUSSION

The study is the first to assess the effect of a cardiac rehabilitation programme designed for patients with IC. The study will describe how to monitor and improve rehabilitation programmes for patients with IC in a real-world setting. Mixed-method strategies can allow for both exploration and generalisation in the same study, but the research design is a complex intervention and any effects found cannot be awarded a specific component.

TRIAL REGISTRATION

Retrospectively registered in Clinicaltrials.gov identifier: NCT03730623.

Changes of circulating neuregulin 4 and its relationship with 25-hydroxy vitamin D and other diabetic vascular complications in patients with diabetic peripheral neuropathy

BACKGROUND

Neuregulin 4 (Nrg4) is a novel neurotrophic adipokine associated with the development of diabetic peripheral neuropathy (DPN), however, the pathological mechanism remains poorly understood. The purpose of our study was to investigate the association of circulating Nrg4 with DPN and 25-hydroxy vitamin D [25(OH)D], a multifunctional secosteroid hormone that regulates other neurotrophic factors and adipokines gene expression, and other diabetic vascular complications.

METHODS

Circulating Nrg4 levels were measured with an ELISA kit in 164 newly diagnosed type 2 diabetes mellitus (nT2DM) patients. The relationship between circulating Nrg4 and DPN and other parameters was analyzed.

RESULTS

Circulating Nrg4 levels were significantly lower in nT2DM patients with DPN than those without, and subjects in the highest quartile of circulating Nrg4 had significantly lower vibration perception threshold (VPT), the prevalence of DPN, the proportion of persons with VPT > 25 V, and significantly higher circulating 25(OH)D (all P < 0.01). Moreover, circulating Nrg4 was positively and independently associated with 25(OH)D, and was negatively with VPT (P < 0.01 or P < 0.05), but showed no associations with the prevalence of peripheral arterial disease, diabetic nephropathy, and diabetic retinopathy (all P > 0.05). Additionally,the prevalence of DPN and risk of DPN development were progressively decreased with increasing circulating Nrg4 quartiles, independently of potential confounding factors.

CONCLUSIONS

These data demonstrate that decreased levels of circulating Nrg4 might lead to the development of DPN through its close interaction with circulating 25(OH)D not with other diabetic vascular complications. Further prospective studies are needed to identify our findings in these populations.

Recent advances in magnetic resonance imaging for peripheral artery disease

The global burden of peripheral artery disease (PAD) is significant. This has led to numerous recent advances in magnetic resonance imaging (MRI) techniques in PAD. Older techniques such as time of flight MRI or phase contrast MRI are burdened by long acquisition times and significant issues with artifacts. In addition, the most used MRI modality, contrast-enhanced MR angiography (CE-MRA) is limited by the use of gadolinium contrast and its potential toxicity. Novel MRI techniques such as arterial spin labeling (ASL), blood-oxygen-level dependent imaging (BOLD), and first-pass perfusion gadolinium enhancement are advancing the field by providing skeletal muscle perfusion/oxygenation data while maintaining excellent spatial and temporal resolution. Perfusion data can be critical to providing objective clinical data of a visualized stenosis. In addition, there are a number of new MRI sequences assessing plaque composition and lesion severity in the absence of contrast. These approaches used in combination can provide useful clinical and prognostic data and provide critical endpoints in PAD research.

Exposure of Endothelium to Biomimetic Flow Waveforms Yields Identification of miR-199a-5p as a Potent Regulator of Arteriogenesis

Arteriogenesis, the growth of endogenous collateral arteries bypassing arterial occlusion(s), is a fundamental shear stress-induced adaptation with implications for treating peripheral arterial disease (PAD). Nonetheless, endothelial mechano-signaling during arteriogenesis is incompletely understood. Here we tested the hypothesis that a mechanosensitive microRNA, miR-199a-5p, regulates perfusion recovery and collateral arteriogenesis following femoral arterial ligation (FAL) via control of monocyte recruitment and pro-arteriogenic gene expression. We have previously shown that collateral artery segments exhibit distinctly amplified arteriogenesis if they are exposed to reversed flow following FAL in the mouse. We performed a genome-wide analysis of endothelial cells exposed to a biomimetic reversed flow waveform. From this analysis, we identified mechanosensitive miR-199a-5p as a novel candidate regulator of collateral arteriogenesis. In vitro, miR-199a-5p inhibited pro-arteriogenic gene expression (IKKβ, Cav1) and monocyte adhesion to endothelium. In vivo, following FAL in mice, miR-199a-5p overexpression impaired foot perfusion and arteriogenesis. In contrast, a single intramuscular anti-miR-199a-5p injection elicited a robust therapeutic response, including complete foot perfusion recovery, markedly augmented arteriogenesis (>3.4-fold increase in segment conductance), and improved gastrocnemius tissue composition. Finally, we found plasma miR-199a-5p to be elevated in human PAD patients with intermittent claudication compared to a risk factor control population. Through our transformative analysis of endothelial mechano-signaling in response to a biomimetic amplified arteriogenesis flow waveform, we have identified miR-199a-5p as both a potent regulator of arteriogenesis and a putative target for treating PAD.

Peripheral vascular disease assessment in the lower limb: a review of current and emerging non-invasive diagnostic methods

BACKGROUND

Worldwide, at least 200 million people are affected by peripheral vascular diseases (PVDs), including peripheral arterial disease (PAD), chronic venous insufficiency (CVI) and deep vein thrombosis (DVT). The high prevalence and serious consequences of PVDs have led to the development of several diagnostic tools and clinical guidelines to assist timely diagnosis and patient management. Given the increasing number of diagnostic methods available, a comprehensive review of available technologies is timely in order to understand their limitations and direct future development effort.

MAIN BODY

This paper reviews the available diagnostic methods for PAD, CVI, and DVT with a focus on non-invasive modalities. Each method is critically evaluated in terms of sensitivity, specificity, accuracy, ease of use, procedure time duration, and training requirements where applicable.

CONCLUSION

This review emphasizes the limitations of existing methods, highlighting a latent need for the development of new non-invasive, efficient diagnostic methods. Some newly emerging technologies are identified, in particular wearable sensors, which demonstrate considerable potential to address the need for simple, cost-effective, accurate and timely diagnosis of PVDs.

Myocardial injury after endovascular revascularization in critical limb ischemia predicts 1-year mortality: a prospective observational cohort study

BACKGROUND

Patients with critical limb ischemia (CLI) are at increased risk of cardiovascular complications and mortality. To determine (1) incidence of myocardial injury following endovascular revascularization, and (2) relationship between myocardial injury with 1-year mortality and major adverse cardiovascular events (MACE; i.e., composite of myocardial infarction, stroke, and death).

METHODS AND RESULTS

Single-center, prospective cohort study of CLI patients ≥ 45 years of age, who underwent endovascular revascularization with overnight hospitalization. High-sensitive troponins T (hsTnTs) were measured on admission, 3-6 h after endovascular revascularization and the subsequent morning. Myocardial injury after endovascular revascularization was defined as an hsTnT ≥ 14 ng/L with a relative increase ≥ 30% from the baseline value. We also evaluated other myocardial injury hsTnT thresholds (i.e., ≥ 30, ≥ 40, ≥ 60, and ≥ 80 ng/L). 239 consecutive patients (56% male, mean age 71.5 ± 10.1 years) were included; one patient was lost to follow-up. At 1 year, there were 34 deaths (14.2%), and 48 MACE (20.5%). Myocardial injury with the hsTnT threshold of 14 ng/L and relative increase by ≥ 30% from the baseline level occurred in 61 patients (25.5%). Myocardial injury was independently associated with 1-year mortality ([aHR], 2.44; 95% CI 1.18-5.06, for hsTnT ≥ 14 ng/L to aHR, 3.34; 95% CI 1.29-8.65 for hsTnT ≥ 80 ng/L). Myocardial injury was also independently associated with 1-year MACE ([AOR] 2.89; 95% CI 1.41-5.92 for hsTnT ≥ 14 ng/L to AOR, 6.69; 95% CI 2.17-20.68 for hsTnT ≥ 80 ng/L). 85.2% patients who had myocardial injury did not have ischemic clinical symptoms or electrocardiography changes. In sensitive analysis with exclusion of symptomatic patients that developed myocardial injury for the hsTnT ≥ 14 ng/L threshold, both the 1-year mortality (aHR: 2.19; CI 1.02-4.68; p = 0.04), and 1-year MACE (OR 2.25; CI 1.06-4.77; p = 0.036) remained significant.

CONCLUSIONS

Myocardial injury is common following endovascular revascularization for CLI and associated with the risk of 1-year mortality and MACE.

VEGF and IGF Delivered from Alginate Hydrogels Promote Stable Perfusion Recovery in Ischemic Hind Limbs of Aged Mice and Young Rabbits

Biomaterial-based delivery of angiogenic growth factors restores perfusion more effectively than bolus delivery methods in rodent models of peripheral vascular disease, but the same success has not yet been demonstrated in clinically relevant studies of aged or large animals. These studies explore, in clinically relevant models, a therapeutic angiogenesis strategy for the treatment of peripheral vascular disease that overcomes the challenges encountered in previous clinical trials. Alginate hydrogels providing sustained release of vascular endothelial growth factor (VEGF) and insulin-like growth factor-1 (IGF) were injected into ischemic hind limbs in middle-aged and old mice, and also in young rabbits, as a test of the scalability of this local growth factor treatment. Spontaneous perfusion recovery diminished with increasing age, and only the combination of VEGF and IGF delivery from gels significantly rescued perfusion in middle-aged (13 months) and old (20 months) mice. In rabbits, the delivery of VEGF alone or in combination with IGF from alginate hydrogels, at a dose 2 orders of magnitude lower than the typical doses used in past rabbit studies, enhanced perfusion recovery when given immediately after surgery, or as a treatment for chronic ischemia. Capillary density measurements and angiographic analysis demonstrated the benefit of gel delivery. These data together suggest that alginate hydrogels providing local delivery of low doses of VEGF and IGF constitute a safe and effective treatment for hind-limb ischemia in clinically relevant animal models, thereby supporting the potential clinical translation of this concept.

MicroRNA let-7g possesses a therapeutic potential for peripheral artery disease

Peripheral artery disease (PAD) is a manifestation of systemic atherosclerosis and conveys a significant health burden globally. Critical limb ischaemia encompasses the most severe consequence of PAD. Our previous studies indicate that microRNA let‐7g prevents atherosclerosis and improves endothelial functions. This study aimed to investigate whether and how let‐7g therapy may improve blood flow to ischaemic limbs. The present study shows that let‐7g has multiple pro‐angiogenic effects on mouse ischaemic limb model and could be a potential therapeutic agent for PAD. Mice receiving intramuscular injection of let‐7g had more neovascularization, better local perfusion and increased recruitment of endothelial progenitor cells after hindlimb ischaemia. The therapeutic effects of let‐7g's on angiogenesis are mediated by multiple regulatory machinery. First, let‐7g increased expression of vascular endothelial growth factor‐A (VEGF‐A) and VEGF receptor‐2 (VEGFR‐2) through targeting their upstream regulators HIF‐3α and TP53. In addition, let‐7g affected the splicing factor SC35 which subsequently enhanced the alternative splicing of VEGF‐A from the anti‐angiogenic isoform VEGF‐A_165b towards the pro‐angiogenic isoform VEGF‐A_164a. The pleiotropic effects of let‐7g on angiogenesis imply that let‐7g may possess a therapeutic potential in ischaemic diseases.

Noninvasive Physiologic Vascular Studies: A Guide to Diagnosing Peripheral Arterial Disease

Noninvasive physiologic vascular studies play an important role in the diagnosis and characterization in peripheral arterial disease (PAD) of the lower extremity. These studies evaluate the physiologic parameters of blood flow through segmental arterial pressures, Doppler waveforms, and pulse volume recordings. Collectively, they comprise a powerful toolset for defining the functionality of the arterial system, localizing the site of disease, and providing prognostic data. This technology has been widely adopted by diverse medical specialty practitioners, including radiologists, surgeons, cardiologists, and primary care providers. The use of these studies increased substantially between 2000 and 2010. Although they do not employ imaging, they remain a critical component for a comprehensive radiologic vascular laboratory. A strong presence of radiology in the diagnosis of PAD adds value in that radiologists have shifted to noninvasive alternatives to diagnostic catheter angiography (DCA), such as computed tomography (CT) and magnetic resonance (MR) angiography, which provide a more efficient, less-expensive, and lower-risk alternative. Other specialties have increased the use of DCA during the same period. The authors provide a review of the relevant anatomy and physiology of PAD as well as the associated clinical implications. In addition, guidelines for interpreting the ankle-brachial index, segmental pressures, Doppler waveforms, and pulse volume recordings are reviewed as well as potential limitations of these studies. Noninvasive physiologic vascular studies are provided here for review with associated correlating angiographic, CT, and/or MR findings covering the segmental distribution of PAD as well as select nonatherosclerotic diagnoses. ^©RSNA, 2016.

Prasugrel, a Platelet P2Y12 Receptor Antagonist, Improves Abnormal Gait in a Novel Murine Model of Thrombotic Hindlimb Ischemia

Background

The efficacy of P2Y₁₂ inhibition for the prevention of cardiovascular events in patients with peripheral arterial disease (PAD) has been established. However, the therapeutic effects on ischemic limb complications are less clear. Accordingly, we aimed to develop a novel murine model of thrombotic hindlimb ischemia to reflect that found in patients with PAD exhibiting ischemic limb symptoms. We further investigated the effects of P2Y₁₂ deficiency and P2Y₁₂ inhibition by prasugrel in this model.

Methods and Results

Thrombus formation induced by application of ferric chloride to the femoral artery resulted in a significant reduction in blood flow in the injured limb. In gait analysis using the CatWalk system, moderate difficulties in grounding and weight bearing of the ischemic limb, including reduction of maximum contact area and stance phase duration and increasing in swing phase duration in the ischemic limb, were observed in this model. Blood flow reduction and gait abnormalities gradually recovered over 21 days to levels present before arterial injury. Compared to wild‐type (WT) mice, significant increases in blood flow and improvement in gait were observed in P2Y₁₂‐deficient mice. In addition, daily oral administration of prasugrel (3 mg/kg per day) to WT mice resulted in significant inhibition of blood flow reduction and gait abnormalities to levels found in P2Y₁₂ deficient mice.

Conclusions

Acute femoral artery thrombosis resulted in hindlimb ischemia and moderate gait abnormalities in mice. In addition, the present study suggests a possible role of P2Y₁₂ in the complications with thrombotic limb ischemia.

Assessment, Definition, and Classification of Lower Limb Ulcers in Systemic Sclerosis: A Challenge for the Rheumatologist

OBJECTIVE

To evaluate pathogenesis and clinical features of lower limb ulcers in systemic sclerosis (SSc) and to propose a classification that could be used in clinical practice.

METHODS

Charts of 60 patients with SSc who had lower limb cutaneous lesions were reviewed. All patients had videocapillaroscopy and arterial and venous lower limb color Doppler ultrasonography (US). Arteriography was performed if occlusive peripheral arterial disease was suspected.

RESULTS

The 554 lesions were classified as hyperkeratosis, ulcers, and gangrenes. There were 341 (61.6%) hyperkeratoses, 208 (37.5%) ulcers, and 5 (0.9%) gangrenes. Ulcers were divided into pure ulcers, ulcers associated with hyperkeratosis, and ulcers secondary to calcinosis. Involvement of arterial and venous macrocirculation as determined by color Doppler US was observed in 17 (18.3%) and 18 (30%) patients, respectively. Seventeen out of 37 patients with pure ulcers (45.9%) presented neither venous insufficiency nor hemodynamically significant macrovascular arterial disease. In these patients, pure ulcers were most likely caused by isolated SSc-related microvascular involvement (pure microvascular ulcers). The only significant risk factor for development of pure microvascular ulcers in the multivariate analysis was the history of lower limb ulcers (OR 26.67, 95% CI 2.75-259.28; p < 0.001).

CONCLUSION

Results of our study indicate that lower limb ulcers in SSc often have a multifactorial pathogenesis that may be difficult to manage. Further studies are needed to validate the proposed classification and to assess the most appropriate management of lower limb ulcers in SSc.

A shear gradient-activated microfluidic device for automated monitoring of whole blood haemostasis and platelet function

Accurate assessment of blood haemostasis is essential for the management of patients who use extracorporeal devices, receive anticoagulation therapy or experience coagulopathies. However, current monitoring devices do not measure effects of haemodynamic forces that contribute significantly to platelet function and thrombus formation. Here we describe a microfluidic device that mimics a network of stenosed arteriolar vessels, permitting evaluation of blood clotting within small sample volumes under pathophysiological flow. By applying a clotting time analysis based on a phenomenological mathematical model of thrombus formation, coagulation and platelet function can be accurately measured in vitro in patient blood samples. When the device is integrated into an extracorporeal circuit in pig endotoxemia or heparin therapy models, it produces real-time readouts of alterations in coagulation ex vivo that are more reliable than standard clotting assays. Thus, this disposable device may be useful for personalized diagnostics and for real-time surveillance of antithrombotic therapy in clinic.

The current hemostasis assays are unable to predict thrombotic or bleeding risk in clinics. Here, Jain et al. present a novel microfluidic device mimicking stenosed arterioles that determines clotting times in vitro and in extracorporeal circuits, offering a simple and reliable monitoring of blood homeostasis and platelet function.

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.

A review of the pathophysiology and potential biomarkers for peripheral artery disease

Peripheral artery disease (PAD) is due to the blockage of the arteries supplying blood to the lower limbs usually secondary to atherosclerosis. The most severe clinical manifestation of PAD is critical limb ischemia (CLI), which is associated with a risk of limb loss and mortality due to cardiovascular events. Currently CLI is mainly treated by surgical or endovascular revascularization, with few other treatments in routine clinical practice. There are a number of problems with current PAD management strategies, such as the difficulty in selecting the appropriate treatments for individual patients. Many patients undergo repeated attempts at revascularization surgery, but ultimately require an amputation. There is great interest in developing new methods to identify patients who are unlikely to benefit from revascularization and to improve management of patients unsuitable for surgery. Circulating biomarkers that predict the progression of PAD and the response to therapies could assist in the management of patients. This review provides an overview of the pathophysiology of PAD and examines the association between circulating biomarkers and PAD presence, severity and prognosis. While some currently identified circulating markers show promise, further larger studies focused on the clinical value of the biomarkers over existing risk predictors are needed.

Therapeutic Efficacy of Stem Cell-based Therapy in Peripheral Arterial Disease: A Meta-Analysis

Several cell-based therapies for peripheral arterial disease (PAD) have been studied in multiple clinical trials; however, the outcome of this treatment remains controversial. The aim of this study was to perform a meta-analysis of the clinical trials on stem cell-based therapy after PAD. We searched for clinical trials that investigated the effect of stem cell-based therapy on patients with PAD and were published between January 2000 and October 2014. The outcomes of interest comprised all-cause mortality, amputation rate, ulcer healing, and ankle-brachial index (ABI). In addition, pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the safety and efficacy of the stem cell-based therapies for PAD. Thirteen studies were retrieved from 261 citations for the analysis, and in total, 527 patients (mean age: 64.2 years; median follow up: 6 months) were included in the analysis. After synthesizing data, the meta-analysis showed significant improvement in the amputation rate (OR=0.33, 95%CI=0.22-0.51; P<0.001), ulcer healing (OR=6.11, 95%CI=3.04-12.28; P<0.001), and ABI (SMD=0.65, 95%CI=0.33-0.97; P<0.001) for the stem cell-based therapy group compared with the controls. Moreover, significant improvement in the amputation rate, ulcer healing, and ABI were also found based on the time point and stem cell source. In addition, no significant difference was found in the all-cause mortality (OR=0.80, 95%CI=0.39-1.641; P=0.546) between the stem cell-based therapy and control groups. Therefore, according to the results of our meta-analysis, stem cell-based therapy is safe and shows a beneficial outcome for patients with PAD, especially in the short term.

High prevalence of lower extremity peripheral artery disease in type 2 diabetes patients with proliferative diabetic retinopathy

Little is known about the relationship between lower extremity peripheral arterial disease (PAD) and proliferative diabetic retinopathy (PDR) in type 2 diabetes (T2D). Here, we explored the relationship between sight-threatening PDR and PAD. We screened for diabetic retinopathy (DR) and PAD in hospitalized patients with T2D. Patients with a diabetic duration of more than 10 years, HbA1c ≥7.5%, eGFR ≥60mL/min/1.73m2 and with PDR or with no diabetic retinopathy (NDR) were eligible for this cross-sectional study. Severities of DR were graded by digital retinal photographs according to the Early Treatment Diabetic Retinopathy Study (ETDRS) scale. We assessed PAD by measuring Ankle Brachial Index (ABI), Toe Brachial Index (TBI) and Doppler ultrasound. Statistical analyses were performed using SPSS 17.0 software. Of the 1544 patients, 169 patients with extreme eye (57 PDR and 112 NDR) phenotypes met the inclusion criteria. Patients with PDR had a significantly higher proportion of low ABI (≤0.99) and high ABI (≥1.3) than patients with NDR (28.1% and 15.8% vs. 14.3% and 6.2% respectively, P<0.05). PDR patients also had lower TBI than NDR patients (0.56±0.09 vs. 0.61±0.08, P<0.01). The proportion of patients with abnormal duplex ultrasound was higher in PDR than in NDR (21.1% vs. 9.8%, P<0.001). This showed that PDR associated with PAD could be defined in multiple ways: abnormal ABI (≤0.9) (OR = 3.61, 95% CI: 1.15–11.26), abnormal TBI (OR = 2.84, 95% CI: 1.19–6.64), abnormal duplex (OR = 3.28, 95% CI: 1.00–10.71), and critical limb ischemia (OR = 5.52, 95% CI: 2.14–14.26). Moreover, PDR was a stronger independent correlation factor for PAD than a diabetic duration of 10 years. In conclusion, PAD is more common in PDR than in NDR. It implies that PDR and PAD are mostly concomitant in T2D. We should focus on screening PAD in patients with PDR in clinical practice.

Gene therapy in peripheral artery disease

INTRODUCTION

Despite the remarkable progress of medicine and endovascular procedures for revascularization, patients with critical limb ischemia (CLI) remain at high risk for amputation and often have a low quality of life due to pain and ulcers in the ischemic leg. Thus, a novel strategy for generating new blood vessels in CLI patients without treatment options is vital. Pre-clinical studies and Phase I clinical trials using VEGF and fibroblast growth factor (FGF) demonstrated promising results; however, more rigorous Phase II and III clinical trials failed to demonstrate benefits for CLI patients. Recently, two multicenter, double-blind, placebo-controlled clinical trials in Japan (Phase III) and the USA (Phase II) showed the benefits of hepatocyte growth factor (HGF) gene therapy for CLI patients. Although the number of patients included in these trials was relatively small, these results imply a distinct beneficial function for HGF over other angiogenic growth factors in a clinical setting.

AREAS COVERED

In this review, data from Phase I-III clinical trials of gene therapy for patients with peripheral artery disease (PAD) are examined. In addition, the potential mechanisms behind the success or failure of clinical trials are discussed.

EXPERT OPINION

Compared with VEGF and FGF, HGF has a unique molecular effect on inflammation, fibrosis and cell senescence under pathological conditions. These features may explain the clinical benefits of HGF in PAD patients.

Matrix metalloproteinase 10 is associated with disease severity and mortality in patients with peripheral arterial disease

OBJECTIVE

Peripheral arterial disease (PAD) is associated with poor prognosis in terms of cardiovascular (CV) morbidity and mortality. Matrix metalloproteinases (MMPs) contribute to vascular remodeling by degrading extracellular matrix components and play a role in atherosclerosis as demonstrated for MMP-10 (stromelysin-2). This study analyzed MMP-10 levels in PAD patients according to disease severity and CV risk factors and evaluated the prognostic value of MMP-10 for CV events and mortality in lower limb arterial disease after a follow-up period of 2 years.

METHODS

MMP-10 was measured by enzyme-linked immunosorbent assay in 187 PAD patients and 200 sex-matched controls.

RESULTS

PAD patients presented with increased levels of MMP-10 (702 ± 326 pg/mL control vs 946 ± 473 pg/mL PAD; P < .001) and decreased levels of tissue inhibitor of matrix metalloproteinase 1 (312 ± 117 ng/mL control vs 235 ± 110 ng/mL PAD; P < .001) compared with controls. Among PAD patients, those with critical limb ischemia (n = 88) showed higher levels of MMP-10 (1086 ± 478 pg/mL vs 822 ± 436 pg/mL; P < .001) compared with those with intermittent claudication (n = 99), whereas the MMP-10/tissue inhibitor of matrix metalloproteinase 1 ratio remained similar. The univariate analysis showed an association between MMP-10, age (P = .015), hypertension (P = .021), and ankle-brachial index (P = .006) in PAD patients that remained significantly associated with PAD severity after adjustment for other CV risk factors. Patients with the highest MMP-10 tertile had an increased incidence of all-cause mortality and CV mortality (P < .03).

CONCLUSIONS

Our results suggest that MMP-10 is associated with severity and poor outcome in PAD.

A practical approach to interpreting lower extremity noninvasive physiologic studies

Peripheral arterial disease (PAD) is an important manifestation of atherosclerosis, with an estimated age-adjusted prevalence of approximately 13% in people older than 50 years. Noninvasive vascular laboratory physiologic studies are indispensable tools in the initial evaluation and workup and postintervention follow-up. In this review, we describe a practical approach to the technique, interpretation, pitfalls, and limitations of these physiologic studies. We also provide an algorithmic approach for using these studies in the initial workup of patients with suspected PAD. Noninvasive techniques that primarily provide anatomic information have not been included in this review.

Significance of an abnormal ankle-brachial index in patients with established coronary artery disease with and without associated diabetes mellitus

An abnormal ankle-brachial index (ABI) is associated with higher risk for future cardiovascular (CV) events; however, it is unknown whether this association is true in patients with established coronary artery disease (CAD) and associated diabetes mellitus (DM). We evaluated 679 patients with stable CAD enrolled in the Excellence in Peripheral Arterial Disease and Veterans Affairs North Texas Healthcare System peripheral arterial disease databases. ABI and 12-month major adverse CV events (MACEs, a composite of all-cause death, nonfatal myocardial infarction, need for repeat coronary revascularization, and ischemic stroke) were assessed. Cox proportional hazard models were used to assess the association of ABI and DM with subsequent CV events. An abnormal ABI (<0.9 or >1.4) was present in 72% of patients with stable CAD and 68% had DM. Using patients without DM and normal ABI as reference, the adjusted hazard ratio for 12-month MACE was 1.7 (95% confidence interval [CI] 0.71 to 4.06) for patients with DM and normal ABI; 2.03 (95% CI 0.83 to 4.9) for patients without DM with abnormal ABI; and 4.85 (95% CI 2.22 to 10.61) for patients with DM and abnormal ABI. In conclusion, in patients with stable CAD, an abnormal ABI confers an incremental risk of MACE in addition to DM and traditional CV risk factors.

Therapeutic Angiogenesis by Gene Therapy for Critical Limb Ischemia: Choice of Biological Agent

Peripheral artery disease (PAD) is caused by atherosclerosis, hardening and narrowing arteries over time due to buildup of fatty deposit in vascular bed called plaque. Severe blockage of an artery of the lower extremity markedly reduce blood flow, resulting in critical limb ischemia (CLI) manifested by a variety of clinical syndromes including rest pain in the feet or toes, ulcer and gangrene with infection. Despite significant advances in clinical care and interventions for revascularization, patients with CLI remain at high risk for amputation and cardiovascular death. To overcome this unmet need, therapeutic angiogenesis using angiogenic growth factors has evolved in an attempt to increase blood flow in ischemic limb. Initial animal studies and phase I clinical trials with vascular endothelial growth factor (VEGF) or fibroblast growth factor (FGF) demonstrated promising results, inspiring scientists to progress forward. However, more rigorous phase II and III clinical trials have failed to demonstrate beneficial effects of these angiogenic growth factors to date. Recently, two multicenter, double-blind, placebo-controlled clinical trials in Japan (phase III) and US (phase II) demonstrated that hepatocyte growth factor (HGF) gene therapy for CLI significant improved primary end points and tissue oxygenation up to two years in comparison to placebo. These clinical results implicate a distinct action of HGF on cellular processes involved in vascular remodeling under pathological condition. This review presents data from phase I-III clinical trials of therapeutic angiogenesis by gene therapy in patients with PAD. Further, we discuss the potential explanation for the success or failure of clinical trials in the context of the biological mechanisms underlying angiogenesis and vascular remodeling, including cellular senescence, inflammation, and tissue fibrosis.

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.

Plasma free H2S levels are elevated in patients with cardiovascular disease

BACKGROUND

Hydrogen sulfide (H2S) has been implicated in regulating cardiovascular pathophysiology in experimental models. However, there is a paucity of information regarding the levels of H2S in health and cardiovascular disease. In this study we examine the levels of H2S in patients with cardiovascular disease as well as bioavailability of nitric oxide and inflammatory indicators.

METHODS AND RESULTS

Patients over the age of 40 undergoing coronary or peripheral angiography were enrolled in the study. Ankle brachial index (ABI) measurement, measurement of plasma-free H2S and total nitric oxide (NO), thrombospondin-1 (TSP-1), Interleukin-6 (IL-6), and soluble intercellular adhesion molecule-1 (sICAM-1) levels were performed. Patients with either coronary artery disease alone (n = 66), peripheral arterial disease (PAD) alone (n = 13), or any vascular disease (n = 140) had higher plasma-free H2S levels compared to patients without vascular disease (n = 53). Plasma-free H2S did not distinguish between disease in different vascular beds; however, total NO levels were significantly reduced in PAD patients and the ratio of plasma free H2S to NO was significantly greater in patients with PAD. Lastly, plasma IL-6, ICAM-1, and TSP-1 levels did not correlate with H2S or NO bioavailability in either vascular disease condition.

CONCLUSIONS

Findings reported in this study reveal that plasma-free H2S levels are significantly elevated in vascular disease and identify a novel inverse relationship with NO bioavailability in patients with peripheral arterial disease.