Baseline assessment and comparison of arterial anatomy, hyperemic flow, and skeletal muscle perfusion in peripheral artery disease: The Cardiovascular Cell Therapy Research Network "Patients with Intermittent Claudication Injected with ALDH Bright Cells" (CCTRN PACE) study

Update on the pathophysiology and medical treatment of peripheral artery disease

Approximately 6% of adults worldwide have atherosclerosis and thrombosis of the lower limb arteries (peripheral artery disease (PAD)) and the prevalence is rising. PAD causes leg pain, impaired health-related quality of life, immobility, tissue loss and a high risk of major adverse events, including myocardial infarction, stroke, revascularization, amputation and death. In this Review, I describe the pathophysiology, presentation, outcome, preclinical research and medical management of PAD. Established treatments for PAD include antithrombotic drugs, such as aspirin and clopidogrel, and medications to treat dyslipidaemia, hypertension and diabetes mellitus. Randomized controlled trials have demonstrated that these treatments reduce the risk of major adverse events. The drug cilostazol, exercise therapy and revascularization are the current treatment options for the limb symptoms of PAD, but each has limitations. Novel therapies to promote collateral and new capillary growth and treat PAD-related myopathy are under investigation. Methods to improve the implementation of evidence-based medical management, novel drug therapies and rehabilitation programmes for PAD-related pain, functional impairment and ischaemic foot disease are important areas for future research.

Regenerative effect of platelet-rich plasma in the murine ischemic limbs

AIMS

The purpose of this study was to investigate the effect of PPRP (pure PRP) and LPRP (PRP with leukocytes) on recovery from limb ischemia and on expression of growth factors involved in angiogenesis, myogenesis and fibrogenesis.

MATERIAL AND METHODS

PPRP and LPRP prepared by centrifugation were added to cultures of C2C12 and NIH3T3 cells (1 or 10% PRPs) to evaluate alterations in cell metabolism and expression of growth factors by MTT, ELISA and RT-qPCR, respectively. To evaluate in vivo regenerative effects, PRPs were injected into the ischemic limbs of BALB/c mice and muscle mass/strength and histomorphometry were evaluated after 30 days.

KEY FINDINGS

Mice treated with PRPs after limb ischemia showed an increase in the size of myofibers and muscle strength, reduced fibrosis and adipocytes, and decreased capillary density and necrosis scores compared to untreated mice. In cell culture, serum deprivation reduced the viability of C2C12 and NIH3T3 cells to about 50%, but the addition of 1% PRPs completely recovered this loss. Both PRPs, downregulated most of the tested genes; however, angiogenic gene Vegfa in C2C12 and the fibrogenic genes Col1a1 and Col3a1 in NIH3T3 cells were upregulated by LPRP.

SIGNIFICANCE

PPRP and LPRP had similar effects in regulation of genes involved in angiogenesis, myogenesis and fibrogenesis. However, the presence of leucocytes did not significantly affect regenerative activities of PRP in the ischemic limb.

Association between calf girth and peripheral artery disease in the Atherosclerosis Risk in Communities Study

BACKGROUND

The pathogenesis of peripheral artery disease (PAD) is associated with impaired calf muscle. We sought to investigate the association between gender-specific calf girth and the prevalence of PAD among participants from a community-based cohort study.

METHODS

A total 13,808 participants in the Atherosclerosis Risk in Communities (ARIC) study without prior PAD were included in the final analysis. Calf girth was measured at baseline (1985-1987). A hospital diagnosis with an ICD-9 code defined incident PAD during follow up. Cox regression analysis adjusted for demographic variables and other covariates was used to estimate hazard ratios (HR) and 95% confidence interval (CI) for the association between calf girth and PAD.

RESULTS

After a medium follow-up of 25.2 years, the overall prevalence of PAD in our study was 5.2% (721/13,808), 335 patients were women and 386 were men. The adjusted HR for PAD with calf girth as continuous variables was 0.99 (95% CI 0.95-1.04) in females and 0.93 (95% CI 0.88-0.99) in males, respectively. Moreover, interaction for gender was statistically significant between calf girth and PAD in overall population (p=0.001).

CONCLUSIONS

Our findings revealed a linear association of calf girth with the prevalence of PAD among male participants in ARIC.

Peripheral arterial disease screening and diagnostic practice: A scoping review

Early reliable, valid screening, diagnosis, and treatment improve peripheral arterial disease outcomes, yet screening and diagnostic practices vary across settings and specialties. A scoping literature review described reliability and validity of peripheral ischaemia diagnosis or screening tools. Clinical studies in the PUBMED database January 1, 1970, to August 13, 2018, were reviewed summarising ranges of reliability and validity of peripheral ischaemia diagnostic and screening tools for patients with non-neuropathic lower leg ischaemia. Peripheral ischaemia screening and diagnostic practices varied in parameters measured such as timing, frequency, setting, ordering clinicians, degree of invasiveness, costs, definitions, and cut-off points informing clinical and referral decisions. Traditional ankle/brachial systolic blood pressure index <0.9 was a reliable, valid lower leg ischaemia screening test to trigger specialist referral for detailed diagnosis. For patients with advanced peripheral ischaemia or calcified arteries, toe-brachial index, claudication, or invasive angiographic imaging techniques that can have complications were reliable, valid screening, and diagnostic tools to inform management decisions. Ankle/brachial index testing is sufficiently reliable and valid for use during routine examinations to improve timing and consistency of peripheral ischaemia screening, triggering prompt specialist referral for more reliable, accurate Doppler, or other diagnosis to inform treatment decisions.

Sampling arterial input function (AIF) from peripheral arteries: Comparison of a temporospatial-feature based method against conventional manual method

It is often difficult to accurately localize small arteries in images of peripheral organs, and even more so with vascular abnormality vasculatures, including collateral arteries, in peripheral artery disease (PAD). This poses a challenge for manually sampling arterial input function (AIF) in quantifying dynamic contrast-enhanced (DCE) MRI data of peripheral organs. In this study, we designed a multi-step screening approach that utilizes both the temporal and spatial information of the dynamic images, and is presumably suitable for localizing small and unpredictable peripheral arteries. In 41 DCE MRI datasets acquired from human calf muscles, the proposed method took <5 s on average for sampling AIF for each case, much more efficient than the manual sampling method; AIFs by the two methods were comparable, with Pearson's correlation coefficient of 0.983 ± 0.004 (p-value < 0.01) and relative difference of 2.4% ± 2.6%. In conclusion, the proposed temporospatial-feature based method enables efficient and accurate sampling of AIF from peripheral arteries, and would improve measurement precision and inter-observer consistency for quantitative DCE MRI of peripheral tissues.

Dynamic contrast-enhanced MRI perfusion of normal muscle in adult hips: Variation of permeability and semi-quantitative parameters

The purpose of this prospective study was to ascertain the degree of variation of semi-quantitative and permeability parameters on DCE-MRI of normally appearing striated muscles. Dynamic contrast-enhanced MRI of the right hip was performed in 20 women and 24 men. Mean age was 39.1 ± 12.4 years. Two regions of interest (ROI) were drawn in twelve muscles of anterior, medial and gluteal compartments: a free-form ROI covering the largest muscle section and a smaller elliptical ROI. Semi-quantitative and permeability parameters were calculated using the extended Tofts model. Statistical analysis was performed with a linear mixed model to assess perfusion parameters variation. Intra- and inter-observer agreements were assessed. The intra-observer agreement was considered to be good for free-form ROI (minimum Intra-Class Coefficient (ICC) = 0.72) and moderate for elliptical ROI (minimum ICC = 0.51), while the inter-observer agreement was considered to be bad in both cases (minimum ICC = 0.11). There was a high inter-individual variation in most of the perfusion parameters evaluated. The average coefficients of variation were: Time To Peak = 9%, Area Under the Curve = 44%, V_e = 61%, K_ep = 90%, Initial Slope = 99%, and K^trans = 128%. A considerable variation in resting muscle perfusion parameters was seen. This could lead to errors in the analysis of muscle DCE-MRI studies or oncologic/non oncologic studies using muscle as a referential. Further studies targeted on acquisition protocols and post-processing software are necessary to improve the performance of muscle MR perfusion.

Leg blood flow and skeletal muscle microvascular perfusion responses to submaximal exercise in peripheral arterial disease

Peripheral arterial disease (PAD) is characterized by stenosis and occlusion of the lower limb arteries. Although leg blood flow is limited in PAD, it remains unclear whether skeletal muscle microvascular perfusion is affected. We compared whole leg blood flow and calf muscle microvascular perfusion after cuff occlusion and submaximal leg exercise between patients with PAD ( n = 12, 69 ± 9 yr) and healthy age-matched control participants ( n = 12, 68 ± 7 yr). Microvascular blood flow (microvascular volume × flow velocity) of the medial gastrocnemius muscle was measured before and immediately after the following: 1) 5 min of thigh-cuff occlusion, and 2) a 5-min bout of intermittent isometric plantar-flexion exercise (400 N) using real-time contrast-enhanced ultrasound. Whole leg blood flow was measured after thigh-cuff occlusion and during submaximal plantar-flexion exercise using strain-gauge plethysmography. Postocclusion whole leg blood flow and calf muscle microvascular perfusion were lower in patients with PAD than control participants, and these parameters were strongly correlated ( r = 0.84, P < 0.01). During submaximal exercise, total whole leg blood flow and vascular conductance were not different between groups. There were also no group differences in postexercise calf muscle microvascular perfusion, although microvascular blood volume was higher in patients with PAD than control participants (12.41 ± 6.98 vs. 6.34 ± 4.98 arbitrary units, P = 0.03). This study demonstrates that the impaired muscle perfusion of patients with PAD during postocclusion hyperemia is strongly correlated with disease severity and is likely mainly determined by the limited conduit artery flow. In response to submaximal leg exercise, microvascular flow volume was elevated in patients with PAD, which may reflect a compensatory mechanism to maintain muscle perfusion and oxygen delivery during recovery from exercise.

NEW & NOTEWORTHY This study suggests that peripheral arterial disease (PAD) has different effects on the microvascular perfusion responses to cuff occlusion and submaximal leg exercise. Patients with PAD have impaired microvascular perfusion after cuff occlusion, similar to that previously reported after maximal exercise. In response to submaximal exercise, however, the microvascular flow volume response was elevated in patients with PAD compared with control. This finding may reflect a compensatory mechanism to maintain perfusion and oxygen delivery during recovery from exercise.

The potential of aldehyde dehydrogenase 2 as a therapeutic target in cardiovascular disease

INTRODUCTION

Mitochondrial aldehyde dehydrogenase (ALDH-2) plays a major role in the ethanol detoxification pathway by removing acetaldehyde. Therefore, ALDH-2 inhibitors such as disulfiram represent the first therapeutic targeting of ALDH-2 for alcoholism therapy. Areas covered: Recently, ALDH-2 was identified as an essential bioactivating enzyme of the anti-ischemic organic nitrate nitroglycerin, bringing ALDH-2 again into the focus of clinical interest. Mechanistic studies on the nitroglycerin bioactivation process revealed that during bioconversion of nitroglycerin and in the presence of reactive oxygen and nitrogen species the active site thiols of ALDH-2 are oxidized and the enzyme activity is lost. Thus, ALDH-2 activity represents a useful marker for cardiovascular oxidative stress, a concept, which has been meanwhile supported by a number of animal disease models. Mechanistic studies on the protective role of ALDH-2 in different disease processes identified the detoxification of 4-hydroxynonenal by ALDH-2 as a fundamental process of cardiovascular, cerebral and antioxidant protection. Expert opinion: The most recent therapeutic exploitation of ALDH-2 includes activators of the enzyme such as Alda-1 but also cell-based therapies (ALDH-bright cells) that deserve further clinical characterization in the future.

Evaluation of Cell Therapy on Exercise Performance and Limb Perfusion in Peripheral Artery Disease: The CCTRN PACE Trial (Patients With Intermittent Claudication Injected With ALDH Bright Cells)

BACKGROUND

Atherosclerotic peripheral artery disease affects 8% to 12% of Americans >65 years of age and is associated with a major decline in functional status, increased myocardial infarction and stroke rates, and increased risk of ischemic amputation. Current treatment strategies for claudication have limitations. PACE (Patients With Intermittent Claudication Injected With ALDH Bright Cells) is a National Heart, Lung, and Blood Institute-sponsored, randomized, double-blind, placebo-controlled, phase 2 exploratory clinical trial designed to assess the safety and efficacy of autologous bone marrow-derived aldehyde dehydrogenase bright (ALDHbr) cells in patients with peripheral artery disease and to explore associated claudication physiological mechanisms.

METHODS

All participants, randomized 1:1 to receive ALDHbr cells or placebo, underwent bone marrow aspiration and isolation of ALDHbr cells, followed by 10 injections into the thigh and calf of the index leg. The coprimary end points were change from baseline to 6 months in peak walking time (PWT), collateral count, peak hyperemic popliteal flow, and capillary perfusion measured by magnetic resonance imaging, as well as safety.

RESULTS

A total of 82 patients with claudication and infrainguinal peripheral artery disease were randomized at 9 sites, of whom 78 had analyzable data (57 male, 21 female patients; mean age, 66±9 years). The mean±SEM differences in the change over 6 months between study groups for PWT (0.9±0.8 minutes; 95% confidence interval [CI] -0.6 to 2.5; P=0.238), collateral count (0.9±0.6 arteries; 95% CI, -0.2 to 2.1; P=0.116), peak hyperemic popliteal flow (0.0±0.4 mL/s; 95% CI, -0.8 to 0.8; P=0.978), and capillary perfusion (-0.2±0.6%; 95% CI, -1.3 to 0.9; P=0.752) were not significant. In addition, there were no significant differences for the secondary end points, including quality-of-life measures. There were no adverse safety outcomes. Correlative relationships between magnetic resonance imaging measures and PWT were not significant. A post hoc exploratory analysis suggested that ALDHbr cell administration might be associated with an increase in the number of collateral arteries (1.5±0.7; 95% CI, 0.1-2.9; P=0.047) in participants with completely occluded femoral arteries.

CONCLUSIONS

ALDHbr cell administration did not improve PWT or magnetic resonance outcomes, and the changes in PWT were not associated with the anatomic or physiological magnetic resonance imaging end points. Future peripheral artery disease cell therapy investigational trial design may be informed by new anatomic and perfusion insights.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01774097.