Cocoa flavanols, Nrf2 activation, and oxidative stress in peripheral artery disease: mechanistic findings in muscle based on outcomes from a randomized trial.

The pathophysiology of muscle damage in peripheral artery disease (PAD) includes increased oxidant production and impaired antioxidant defenses. Epicatechin (EPI), a naturally occurring flavanol, has antioxidant properties that may mediate the beneficial effects of natural products such as cocoa. In a phase II randomized trial, a cocoa-flavanol-rich beverage significantly improved walking performance compared with a placebo in people with PAD. In the present work, the molecular mechanisms underlying the therapeutic effect of cocoa flavanols were investigated by analyzing baseline and follow-up muscle biopsies from participants. Increases in nuclear factor erythroid 2-related factor 2 (Nrf2) target antioxidants heme oxygenase-1 (HO-1) and NAD(P)H dehydrogenase [quinone] 1 (NQO1) in the cocoa group were significantly associated with reduced accumulation of central nuclei, a myopathy indicator, in type II muscle fibers (P = 0.017 and P = 0.023, respectively). Protein levels of the mitochondrial respiratory complex III subunit, cytochrome b-c1 complex subunit 2 (UQCRC2), were significantly higher in the cocoa group than in the placebo group (P = 0.032), and increases in UQCRC2 were significantly associated with increased levels of Nrf2 target antioxidants HO-1 and NQO1 (P = 0.001 and P = 0.035, respectively). Exposure of non-PAD human myotubes to ex vivo serum from patients with PAD reduced Nrf2 phosphorylation, an indicator of activation, increased hydrogen peroxide production and oxidative stress, and reduced mitochondrial respiration. Treatment of myotubes with EPI in the presence of serum from patients with PAD increased Nrf2 phosphorylation and protected against PAD serum-induced oxidative stress and mitochondrial dysfunction. Overall, these findings suggest that cocoa flavanols may enhance antioxidant capacity in PAD via Nrf2 activation.NEW & NOTEWORTHY The current study supports the hypothesis that in people with PAD, cocoa flavanols activate Nrf2, thereby increasing antioxidant protein levels, protecting against skeletal muscle damage, and increasing mitochondrial protein abundance. These results suggest that Nrf2 activation may be an important therapeutic target for improving walking performance in people with PAD.

Discordance of patient-reported outcome measures with objectively assessed walking decline in peripheral artery disease.

OBJECTIVE: Among people with peripheral artery disease (PAD), perceived change in walking difficulty over time, compared with people without PAD, is unclear. Among people reporting no change in walking difficulty over time, differences in objectively measured change in walking performance between people with and without PAD are unknown. METHODS: A total of 1289 participants were included. Eight hundred seventy-four participants with PAD (aged 71.1 ± 9.1 years) were identified from noninvasive vascular laboratories and 415 without PAD (aged 69.9 ± 7.6 years) were identified from people with normal vascular laboratory testing or general medical practices in Chicago. The Walking Impairment Questionnaire and 6-minute walk were completed at baseline and 1-year follow-up. The Walking Impairment Questionnaire assessed perceived difficulty walking due to symptoms in the calves or buttocks on a Likert scale (range, 0-4). Symptom change was determined by comparing difficulty reported at 1-year follow-up to difficulty reported at baseline. RESULTS: At 1-year follow-up, 31.9% of participants with and 20.6% of participants without PAD reported walking difficulty that was improved (P < .01), whereas 41.2% vs 55%, respectively, reported walking difficulty that was unchanged (P < .01). Among all reporting no change in walking difficulty, participants with PAD declined in 6-minute walk, whereas participants without PAD improved (-10 vs +15 meters; mean difference, -25; 95% confidence interval, -38 to -13; P < .01). CONCLUSIONS: Most people with PAD reported improvement or no change in walking difficulty from calf or buttock symptoms at one-year follow-up. Among all participants who perceived stable walking ability, those with PAD had significant greater declines in objectively measured walking performance, compared with people without PAD.

Study Design, Rationale, and Methodology for Promote Weight Loss in Patients With Peripheral Artery Disease Who Also Have Obesity: The PROVE Trial.

Background Overweight and obesity are associated with adverse functional outcomes in people with peripheral artery disease (PAD). The effects of weight loss in people with overweight/obesity and PAD are unknown. Methods The PROVE (Promote Weight Loss in Obese PAD Patients to Prevent Mobility Loss) Trial is a multicentered randomized clinical trial with the primary aim of testing whether a behavioral intervention designed to help participants with PAD lose weight and walk for exercise improves 6-minute walk distance at 12-month follow-up, compared with walking exercise alone. A total of 212 participants with PAD and body mass index ≥25 kg/m2 will be randomized. Interventions are delivered using a Group Mediated Cognitive Behavioral intervention model, a smartphone application, and individual telephone coaching. The primary outcome is 12-month change in 6-minute walk distance. Secondary outcomes include total minutes of walking exercise/wk at 12-month follow-up and 12-month change in accelerometer-measured physical activity, the Walking Impairment Questionnaire distance score, and the Patient-Reported Outcomes Measurement Information System mobility questionnaire. Tertiary outcomes include 12-month changes in perceived exertional effort at the end of the 6-minute walk, diet quality, and the Short Physical Performance Battery. Exploratory outcomes include changes in gastrocnemius muscle biopsy measures of mitochondrial cytochrome C oxidase activity, mitochondrial biogenesis, capillary density, and inflammatory markers. Conclusions The PROVE randomized clinical trial will evaluate the effects of exercise with an intervention of coaching and a smartphone application designed to achieve weight loss, compared with exercise alone, on walking performance in people with PAD and overweight/obesity. Results will inform optimal treatment for the growing number of patients with PAD who have overweight/obesity. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT04228978.

Cigarette smoking and mitochondrial dysfunction in peripheral artery disease.

BACKGROUND: This study evaluated the association of smoking with mitochondrial function in gastrocnemius muscle of people with peripheral artery disease (PAD). METHODS: Participants were enrolled from Chicago, Illinois and consented to gastrocnemius biopsy. Mitochondrial oxidative capacity was measured in muscle with respirometry. Abundance of voltage-dependent anion channel (VDAC) (mitochondrial membrane abundance), peroxisome proliferator-activated receptor-γ coactivator (PGC-1α) (mitochondrial biogenesis), and electron transport chain complexes I-V were measured with Western blot. RESULTS: Fourteen of 31 people with PAD (age 72.1 years, ABI 0.64) smoked cigarettes currently. Overall, there were no significant differences in mitochondrial oxidative capacity between PAD participants who currently smoked and those not currently smoking (complex I+II-mediated oxidative phosphorylation: 86.6 vs 78.3 pmolO2/s/mg, respectively [p = 0.39]). Among participants with PAD, those who currently smoked had a higher abundance of PGC-1α (p < 0.01), VDAC (p = 0.022), complex I (p = 0.021), and complex III (p = 0.021) proteins compared to those not currently smoking. People with PAD who currently smoked had lower oxidative capacity per VDAC unit (complex I+II-mediated oxidative phosphorylation [137.4 vs 231.8 arbitrary units, p = 0.030]) compared to people with PAD not currently smoking. Among people without PAD, there were no significant differences in any mitochondrial measures between currently smoking (n = 5) and those not currently smoking (n = 63). CONCLUSIONS: Among people with PAD, cigarette smoking may stimulate mitochondrial biogenesis to compensate for reduced oxidative capacity per unit of mitochondrial membrane, resulting in no difference in overall mitochondrial oxidative capacity according to current smoking status among people with PAD. However, these results were cross-sectional and a longitudinal study is needed.

Barriers to participation in supervised exercise therapy reported by people with peripheral artery disease.

OBJECTIVE: This study identified barriers to participation in supervised exercise therapy covered by the Centers for Medicare and Medicaid Services (CMS), reported by people with lower extremity peripheral artery disease (PAD). METHODS: People with PAD participating in research studies of walking impairment due to PAD in the Chicagoland area were asked to complete a questionnaire between March 15, 2019, and July 12, 2022, assessing their experience and attitudes about supervised exercise therapy. Participants were identified using mailed postcards to people aged 50 and older in Chicagoland, from medical centers in Chicago, and using bus and train advertisements. The questionnaire was developed based on focus group feedback from people with PAD. RESULTS: Of 516 participants with PAD approached, 489 (94.8%) completed the questionnaire (mean age: 71.0 years [standard deviation: 8.7], mean ankle-brachial index: 0.71 [standard deviation: 0.25]; 204 [41.7%] women and 261 [53.4%] Black). Of the 489 participants, 416 (85.1%) reported that their physician had never prescribed or recommended supervised exercise therapy. Overall, 357 (73.2%) reported willingness to travel three times weekly to the medical center for supervised exercise participation. However, of these, 214 (59.9%) reported that they were unwilling or unable to pay the $11 per exercise session copay required for supervised exercise covered by CMS. Of 51 people with PAD who reported prior participation in supervised exercise, only 5 (9.8%) completed the 12 weeks of supervised exercise therapy covered by CMS and 29 (56.9%) completed 6 or fewer weeks. Of 131 (26.8%) unwilling to travel three times weekly to a center for supervised exercise, the most common reasons for unwillingness to participate were "too time-consuming" (55.0%), "too inconvenient" (45.8%), and "lack of interest in treadmill exercise" (28.2%). CONCLUSIONS: Approximately 2 to 4 years after CMS began covering supervised exercise for PAD, most people with PAD in this study from a large urban area had not participated in supervised exercise therapy. Of those who participated, most completed fewer than half of the sessions covered by CMS. The required CMS copayment was a common barrier to supervised exercise participation by people with PAD.

Ankle-Brachial Index and Energy Production in People Without Peripheral Artery Disease: The BLSA.

Background Lower ankle-brachial index (ABI) values within the 0.90 to 1.40 range are associated with poorer mitochondrial oxidative capacity of thigh muscles in cross-sectional analyses. Whether ABI decline is associated with greater declines in thigh muscle oxidative capacity with aging is unknown. Method and Results We analyzed data from 228 participants (100 men) of the BLSA (Baltimore Longitudinal Study of Aging), aged 39 to 97 years, with an ABI between 0.9 and 1.40 at baseline and at follow-up (mean follow-up period of 2.8 years). We examined mitochondrial oxidative capacity of the left thigh muscle, by measuring the postexercise phosphocreatine recovery rate constant (kPCr) from phosphorus-31 magnetic resonance spectroscopy. Greater kPCr indicated higher mitochondrial oxidative capacity. Although kPCr was available on the left leg only, ABI was measured in both legs. Longitudinal rates of change (Change) of left and right ABI and kPCr of the left thigh muscle were estimated using linear mixed effects models, and their association was analyzed by standardized multiple linear regressions. In multivariate analysis including sex, age, baseline kPCr, both left and right baseline ABI, and ABI change in both legs, (kPCr)Change was directly associated with ipsilateral (left) (ABI)Change (standardized [STD]-ß=0.14; P=0.0168) but not with contralateral (right) (ABI)Change (P=0.22). Adjusting for traditional cardiovascular risk factors, this association remained significant (STD-ß=0.18; P=0.0051). (kPCr)Change was steeper in White race participants (STD-ß=0.16; P=0.0122) and body mass index (STD-ß=0.13; P=0.0479). There was no significant association with current smoking status (P=0.63), fasting glucose (P=0.28), heart rate (P=0.67), mean blood pressure (P=0.78), and low-density lipoprotein (P=0.75), high-density lipoprotein (P=0.82), or triglycerides (P=0.15). Conclusions In people without peripheral arterial disease, greater decline in ABI over time, but not baseline ABI, was associated with faster decline in thigh mitochondrial oxidative capacity in the ipsilateral leg. Further studies are needed to examine whether early interventions that improve lower extremity muscle perfusion can improve and prevent the decline of muscle energetics.

Identifying gaps in disease knowledge among patients with peripheral artery disease.

OBJECTIVE: An individual's understanding of disease risk factors and outcomes is important for the ability to make healthy lifestyle choices and decisions about disease treatment. Peripheral artery disease (PAD) is a condition with increasing global prevalence and high risk of adverse patient outcomes. This study seeks to understand the adequacy of disease understanding in patients with PAD. METHODS: This was an observational study of patients with PAD recruited from vascular surgery outpatient clinic and PAD clinical studies at a single academic medical center over an 8-month period. A 44-item paper survey assessed demographic and socioeconomic information, knowledge of personal medical history, PAD risk factors, consequences of PAD, and health education preferences. Patients with documented presence of PAD were offered the survey. Patients unable to complete the survey or provide informed consent were not considered eligible. Disease "awareness" was defined as correct acknowledgement of the presence or absence of a disease, including PAD, in the personal medical history. "PAD knowledge score" was the percentage of correct responses to questions on general PAD risk factors and consequences. Of 126 eligible patients, 109 participated. Bivariate analysis was used to study factors associated with awareness of PAD diagnosis. Factors associated with the PAD knowledge score were studied using the Pearson correlation coefficient, two-sample t test, or one-way analysis of variance. P value < .05 was considered statistically significant. RESULTS: The mean participant age was 69.4 ± 11.0 years, and 39.4% (n = 43) were female. Most participants (78.9%; n = 86) had critical limb-threatening ischemia. Only 65.4% (n = 70) of participants were aware of a diagnosis of PAD, which was less than their awareness of related comorbidities. Factors positively associated with PAD diagnosis awareness were female sex (81.4% vs 54.7%; P = .004) and history of percutaneous leg revascularization (78.6% vs 47.9%; P = .001). Among 17 patients who had undergone major leg amputation, 35% (n = 6) were unaware of a diagnosis of PAD. PAD knowledge scores correlated positively with an awareness of PAD diagnosis (59.1% vs 48.7%; P = .02) and negatively with a history of hypertension (53.4% vs 68.1%; P = .001). Most participants (86.5%; n = 90) expressed a desire to be further educated on PAD. The most popular education topics were dietary recommendations, causes, and treatment for PAD. CONCLUSIONS: Patients with PAD have deficits in their awareness of this diagnosis and general knowledge about PAD. Future research priorities should further define these deficits and their causes in order to inform new strategies that foster information-seeking behavior and effective educational programs for PAD.

Lower Extremity Peripheral Artery Disease: Contemporary Epidemiology, Management Gaps, and Future Directions: A Scientific Statement From the American Heart Association.

Lower extremity peripheral artery disease (PAD) affects >230 million adults worldwide and is associated with increased risk of various adverse clinical outcomes (other cardiovascular diseases such as coronary heart disease and stroke and leg outcomes such as amputation). Despite its prevalence and clinical importance, PAD has been historically underappreciated by health care professionals and patients. This underappreciation seems multifactorial (eg, limited availability of the first-line diagnostic test, the ankle-brachial index, in clinics; incorrect perceptions that a leg vascular disease is not fatal and that the diagnosis of PAD would not necessarily change clinical practice). In the past several years, a body of evidence has indicated that these perceptions are incorrect. Several studies have consistently demonstrated that many patients with PAD are not receiving evidence-based therapies. Thus, this scientific statement provides an update for health care professionals regarding contemporary epidemiology (eg, prevalence, temporal trends, risk factors, and complications) of PAD, the present status of diagnosis (physiological tests and imaging modalities), and the major gaps in the management of PAD (eg, medications, exercise therapy, and revascularization). The statement also lists key gaps in research, clinical practice, and implementation related to PAD. Orchestrated efforts among different parties (eg, health care providers, researchers, expert organizations, and health care organizations) will be needed to increase the awareness and understanding of PAD and improve the diagnostic approaches, management, and prognosis of PAD.

Effects of supervised exercise therapy on blood pressure and heart rate during exercise, and associations with improved walking performance in peripheral artery disease: Results of a randomized clinical trial.

OBJECTIVE: Supervised exercise therapy (SET) improves walking ability in people with peripheral artery disease (PAD). However, the effects of SET on cardiovascular health in PAD remain unclear. Using data from a randomized clinical trial, this post hoc analyses investigated the effects of a 6-month SET intervention, compared with a control group, on changes in blood pressure (BP) and heart rate (HR) during a graded treadmill exercise test in people with PAD. METHODS: We randomized 210 participants with PAD to either SET (3× weekly) or control (1× weekly health lectures) for 6 months. A graded treadmill exercise test, 6-minute walk test, and Walking Impairment Questionnaire were completed at baseline and the 6-month follow-up. BP and HR were measured at the end of each 2-minute stage of the graded treadmill exercise test. Mixed effects regression models compared the overall mean 6-month change in systolic BP, diastolic BP, pulse pressure (PP), and HR during the first 5 stages of the graded treadmill exercise test between groups. RESULTS: Of the 210 randomized participants with PAD, 176 (67 ± 9 years; 72 [41%] female, 115 [65%] Black) completed the graded treadmill exercise test at baseline and the 6-month follow-up. Compared with the control group at the 6-month follow-up, SET significantly decreased overall mean systolic BP (-12 mm Hg; P < .001), PP (-9 mm Hg; P < .001), and HR (-7 b/min; P < .01) during a graded treadmill exercise test but not diastolic BP. Among participants randomized to SET, a greater decrease in systolic BP, PP, and HR during a graded treadmill exercise test was significantly associated with a greater improvement in 6-minute walk distance (systolic BP, r = -0.19 [P = .03] and PP, r = -0.23 [P < .01]; and HR, r = -0.21 [P < .01]) and with maximal treadmill walking distance (systolic BP, r = -0.21 [P < .01] and PP, r = -0.17 [P = .03]) at the 6-month follow-up. A greater decrease in the HR during a graded treadmill exercise test was significantly associated with a better WIQ distance score (r = -0.27; P = .03) at the 6-month follow-up. CONCLUSIONS: In people with PAD, compared with a control group, SET improved cardiovascular health, measured by changes in BP and HR during exercise. The degree of improvement in cardiovascular health correlated with the degree of improvement in walking performance in people with PAD. NCT: 01408901.

Effect of Low-Intensity vs High-Intensity Home-Based Walking Exercise on Walk Distance in Patients With Peripheral Artery Disease: The LITE Randomized Clinical Trial.

Importance: Supervised high-intensity walking exercise that induces ischemic leg symptoms is the first-line therapy for people with lower-extremity peripheral artery disease (PAD), but adherence is poor. Objective: To determine whether low-intensity home-based walking exercise at a comfortable pace significantly improves walking ability in people with PAD vs high-intensity home-based walking exercise that induces ischemic leg symptoms and vs a nonexercise control. Design, Setting, and Participants: Multicenter randomized clinical trial conducted at 4 US centers and including 305 participants. Enrollment occurred between September 25, 2015, and December 11, 2019; final follow-up was October 7, 2020. Interventions: Participants with PAD were randomized to low-intensity walking exercise (n = 116), high-intensity walking exercise (n = 124), or nonexercise control (n = 65) for 12 months. Both exercise groups were asked to walk for exercise in an unsupervised setting 5 times per week for up to 50 minutes per session wearing an accelerometer to document exercise intensity and time. The low-intensity group walked at a pace without ischemic leg symptoms. The high-intensity group walked at a pace eliciting moderate to severe ischemic leg symptoms. Accelerometer data were viewable to a coach who telephoned participants weekly for 12 months and helped them adhere to their prescribed exercise. The nonexercise control group received weekly educational telephone calls for 12 months. Main Outcomes and Measures: The primary outcome was mean change in 6-minute walk distance at 12 months (minimum clinically important difference, 8-20 m). Results: Among 305 randomized patients (mean age, 69.3 [SD, 9.5] years, 146 [47.9%] women, 181 [59.3%] Black patients), 250 (82%) completed 12-month follow-up. The 6-minute walk distance changed from 332.1 m at baseline to 327.5 m at 12-month follow-up in the low-intensity exercise group (within-group mean change, -6.4 m [95% CI, -21.5 to 8.8 m]; P = .34) and from 338.1 m to 371.2 m in the high-intensity exercise group (within-group mean change, 34.5 m [95% CI, 20.1 to 48.9 m]; P < .001) and the mean change for the between-group comparison was -40.9 m (97.5% CI, -61.7 to -20.0 m; P < .001). The 6-minute walk distance changed from 328.1 m at baseline to 317.5 m at 12-month follow-up in the nonexercise control group (within-group mean change, -15.1 m [95% CI, -35.8 to 5.7 m]; P = .10), which was not significantly different from the change in the low-intensity exercise group (between-group mean change, 8.7 m [97.5% CI, -17.0 to 34.4 m]; P = .44). Of 184 serious adverse events, the event rate per participant was 0.64 in the low-intensity group, 0.65 in the high-intensity group, and 0.46 in the nonexercise control group. One serious adverse event in each exercise group was related to study participation. Conclusions and Relevance: Among patients with PAD, low-intensity home-based exercise was significantly less effective than high-intensity home-based exercise and was not significantly different from the nonexercise control for improving 6-minute walk distance. These results do not support the use of low-intensity home-based walking exercise for improving objectively measured walking performance in patients with PAD. Trial Registration: ClinicalTrials.gov Identifier: NCT02538900.

Elevated IL-6 and CRP Levels Are Associated With Incident Self-Reported Major Mobility Disability: A Pooled Analysis of Older Adults With Slow Gait Speed.

BACKGROUND: Elevated interleukine-6 (IL-6) and C-reactive protein (CRP) are associated with aging-related reductions in physical function, but little is known about their independent and combined relationships with major mobility disability (MMD), defined as the self-reported inability to walk a quarter mile. METHODS: We estimated the absolute and relative effect of elevated baseline IL-6, CRP, and their combination on self-reported MMD risk among older adults (≥68 years; 59% female) with slow gait speed (<1.0 m/s). Participants were MMD-free at baseline. IL-6 and CRP were assessed using a central laboratory. The study combined a cohort of community-dwelling high-functioning older adults (Health ABC) with 2 trials of low-functioning adults at risk of MMD (LIFE-P, LIFE). Analyses utilized Poisson regression for absolute MMD incidence and proportional hazards models for relative risk. RESULTS: We found higher MMD risk per unit increase in log IL-6 (hazard ratio [HR] = 1.26; 95% confidence interval [95% CI] 1.13-1.41). IL-6 meeting predetermined threshold considered to be high (>2.5 pg/mL) was similarly associated with higher risk of MMD (HR = 1.31; 95% CI 1.12-1.54). Elevated CRP (CRP >3.0 mg/L) was also associated with increased MMD risk (HR = 1.38; 95% CI 1.10-1.74). The CRP effect was more pronounced among participants with elevated IL-6 (HR = 1.62; 95% CI 1.12-2.33) compared to lower IL-6 levels (HR = 1.19; 95% CI 0.85-1.66). CONCLUSIONS: High baseline IL-6 and CRP were associated with an increased risk of MMD among older adults with slow gait speed. A combined biomarker model suggests CRP was associated with MMD when IL-6 was elevated.

Clinical characteristics and response to supervised exercise therapy of people with lower extremity peripheral artery disease.

BACKGROUND: Among people with lower extremity peripheral artery disease (PAD), little is known about variation in response to supervised exercise therapy (SET). Clinical characteristics associated with greater responsiveness to SET have not been identified. METHODS: Data from participants with PAD in two randomized clinical trials comparing SET vs nonexercising control were combined. The exercise intervention consisted of three times weekly supervised treadmill exercise. The control groups received lectures on health-related topics. RESULTS: Of 309 unique participants randomized (mean age, 67.9 years [standard deviation, 9.3 years]; 132 [42.7%] women; 185 [59.9%] black), 285 (92%) completed 6-month follow-up. Compared with control, those randomized to SET improved 6-minute walk distance by 35.6 meters (95% confidence interval, 21.4-49.8; P < .001). In the 95 (62.1%) participants who attended at least 70% of SET sessions, change in 6-minute walk distance varied from -149.4 to +356.0 meters. Thirty-four (35.8%) had no 6-minute walk distance improvement. Among all participants, age, sex, race, body mass index, prior lower extremity revascularization, and other clinical characteristics did not affect the degree of improvement in 6-minute walk distance after SET relative to the control group. Participants with 6-minute walk distance less than the median of 334 meters at baseline had greater percentage improvement in 6-minute walk distance compared with those with baseline 6-minute walk distance above the median (+20.5% vs +5.3%; P for interaction = .0107). CONCLUSIONS: Among people with PAD, substantial variability exists in walking improvement after SET. Shorter 6-minute walk distance at baseline was associated with greater improvement after SET, but other clinical characteristics, including age, sex, prior lower extremity revascularization, and disease severity, did not affect responsiveness to exercise therapy.

Meaningful change in 6-minute walk in people with peripheral artery disease.

OBJECTIVE: The 6-minute walk test is a common outcome measure in clinical trials of people with lower extremity peripheral artery disease (PAD). However, what constitutes a meaningful change in the 6-minute walk distance has not been well defined for people with PAD. The present study related the change in the 6-minute walk distance to the degree of participant-reported improvement or decline in the 6-minute walk distance to define a meaningful change in the 6-minute walk distance for those with PAD. METHODS: Participants with PAD from three observational longitudinal studies completed the walking impairment questionnaire (WIQ) distance score and 6-minute walk at baseline and 1 year later. The WIQ distance score measures participants' perceived difficulty walking seven different distances without stopping (ranging from walking around the home to walking 5 blocks) on a 0 to 4 Likert scale, with 0 representing an inability to walk the distance and 4 representing no difficulty. The mean changes in the 6-minute walk distance corresponding to the participants' report of no change, 1-unit change, or 2-unit change, respectively, in the Likert scale score between the baseline and 1-year follow-up measures were calculated for each WIQ distance. RESULTS: A total of 777 participants with PAD (mean age, 71.2 ± 8.8 years; mean baseline 6-minute walk distance, 350.1 ± 118.1 meters) completed 5439 questions about their difficulty walking each WIQ distance at baseline and follow-up. Participants with PAD who reported no change in their difficulty in walking each WIQ distance between baseline and follow-up had a decline of 7.2 meters (95% confidence interval [CI], -11.6 to -2.8 meters) in the 6-minute walk test. Relative to those reporting no change in difficulty walking, the participants reporting 1- and 2-point improvements in walking ability showed 6-minute walk distance improvements of 7.8 meters (95% CI, -0.3 to 15.9 meters) and 20.1 meters (95% CI, 1.1-39.2 meters), respectively. Relative to those reporting no change in walking difficulty, those reporting 1- and 2-point declines in perceived walking difficulty showed declines of -11.2 meters (95% CI, -19.0 to -3.4 meters) and -23.8 meters (95% CI, -37.4 to -10.3 meters) in the 6-minute walk distance. CONCLUSIONS: Among people with PAD, ∼8- and ∼20-meter improvements in the 6-minute walk distance represent small and large improvements in walking ability, respectively. People with PAD who reported no change in their ability to walk distances over 1 year simultaneously declined by a mean of 7 meters in the 6-minute walk test. These findings will be useful for interpreting the results from randomized trials of interventions to improve the walking performance of people with PAD.

Skeletal Muscle Pathology in Peripheral Artery Disease: A Brief Review.

This brief review summarizes current evidence regarding lower extremity peripheral artery disease (PAD) and lower extremity skeletal muscle pathology. Lower extremity ischemia is associated with reduced calf skeletal muscle area and increased calf muscle fat infiltration and fibrosis on computed tomography or magnetic resonance imaging. Even within the same individual, the leg with more severe ischemia has more adverse calf muscle characteristics than the leg with less severe ischemia. More adverse computed tomography-measured calf muscle characteristics, such as reduced calf muscle density, are associated with higher rates of mobility loss in people with PAD. Calf muscle in people with PAD may also have reduced mitochondrial activity compared with those without PAD, although evidence is inconsistent. Muscle biopsy document increased oxidative stress in PAD. Reduced calf muscle perfusion, impaired mitochondrial activity, and smaller myofibers are associated with greater walking impairment in PAD. Preliminary evidence suggests that calf muscle pathology in PAD may be reversible. In a small uncontrolled trial, revascularization improved both the ankle-brachial index and mitochondrial activity, measured by calf muscle phosphocreatine recovery time. A pilot clinical trial showed that cocoa flavanols increased measures of myofiber health, mitochondrial activity, and capillary density while simultaneously improving 6-minute walk distance in PAD. Calf muscle pathological changes are associated with impaired walking performance in people with PAD, and interventions that both increase calf perfusion and improve calf muscle health are promising therapies to improve walking performance in PAD.

Associations of Poly (ADP-Ribose) Polymerase1 abundance in calf skeletal muscle with walking performance in peripheral artery disease.

OBJECTIVE: This study investigated associations of markers of oxidative stress and mitochondrial function in calf muscle biopsies with walking performance in people with and without lower extremity peripheral artery disease (PAD). METHODS: Participants with PAD (ankle-brachial index (ABI) <0.90) and without PAD (ABI: 0.90-1.50) underwent calf muscle biopsy and measurement of 6-min walk and four-meter walking velocity. PARP1 (Poly (ADP-Ribose) Polymerase 1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), silent information regulator 1 (SIRT1) and 4-hydroxynonenal (4HNE) expression were measured in calf muscle using western blot. RESULTS: Among 15 participants with PAD mean age: 66.8 years (standard deviation (SD): 6.4) and six without PAD (age: 64.4 years, SD: 5.9), mean PARP1-abundance in calf muscle was 1.16 ± 0.92 AU and 0.96 ± 0.38 AU, respectively (P = 0.61). Among participants with PAD after adjustment with ABI, a greater abundance of PARP1 was associated with poorer 6-min walking distance (r = -0.65, P = 0.01), usual-paced 4-m walking velocity (r = -0.73, P = 0.003) and slower fast-paced four-meter walking velocity (r = -0.51, P = 0.07). Among participants with PAD, ABI was not associated with PARP1 abundance in calf muscle (r = 0.02, P = 0.93). Among participants without PAD, skeletal muscle PARP1 abundance was not significantly associated with 6-min walk distance (r = -0.58; P = 0.22), usual-paced walking velocity (r = -0.26; P = 0.62), or fast-paced walking velocity (r = -0.21; P = 0.69), perhaps due to lack of statistical power. There were no associations of remaining calf muscle measures with walking performance. CONCLUSIONS: These findings are consistent with the hypothesis that calf skeletal muscle characteristics are related to walking performance, independently of severity of lower extremity arterial obstruction in people with PAD.

The relationship between interleukin-6 levels and physical performance in mobility-limited older adults with chronic low-grade inflammation: The ENRGISE Pilot study.

Previous studies have found an inverse relation between serum concentrations of interleukin (IL)-6 and physical performance in seniors, however this was limited to higher functioning older adults with low to moderate levels of inflammation. We explored the consistency of this association in a cohort of mobility limited older adults with chronic low-grade inflammation. This study included 289 participants (≥ 70 years old) with IL-6 level between 2.5 and 30 pg/mL and a walking speed < 1.0 m/sec from the ENRGISE Pilot study. Physical performance was assessed using the short physical performance battery (SPPB), usual gait speed over 400 m, grip strength, and knee extensor and flexor strength measured by isokinetic dynamometry at 60 and 180°/sec. There was a significant inverse correlation between log IL-6 and knee extensor strength at 60°/sec (r= -0.20, p = 0.002), at 180°/sec (r = -0.14, p = 0.037), and knee flexor strength at 60°/sec (r = -0.15, p = 0.021). After adjustment for potential confounders, the values of knee extensor strength at 60°/sec showed a trend toward a progressive reduction across IL-6 tertiles as IL-6 levels increased (p = 0.024). No significant association was found between IL-6 and other objectively measured physical performance. The findings were generally of smaller magnitude and less consistent than previously reported, which suggests that the associations are attenuated in those with both elevated inflammation and mobility limitations. These results have implications for planning and interpreting future intervention studies in older adults with low-grade inflammation and mobility limitations.

Correlations of Calf Muscle Macrophage Content With Muscle Properties and Walking Performance in Peripheral Artery Disease.

Background Peripheral artery disease (PAD) is a manifestation of atherosclerosis characterized by reduced blood flow to the lower extremities and mobility loss. Preliminary evidence suggests PAD damages skeletal muscle, resulting in muscle impairments that contribute to functional decline. We sought to determine whether PAD is associated with an altered macrophage profile in gastrocnemius muscles and whether muscle macrophage populations are associated with impaired muscle phenotype and walking performance in patients with PAD. Methods and Results Macrophages, satellite cells, and extracellular matrix in gastrocnemius muscles from 25 patients with PAD and 7 patients without PAD were quantified using immunohistochemistry. Among patients with PAD, both the absolute number and percentage of cluster of differentiation (CD) 11b+CD206+ M2-like macrophages positively correlated to satellite cell number (r=0.461 [P=0.023] and r=0.416 [P=0.042], respectively) but not capillary density or extracellular matrix. The number of CD11b+CD206- macrophages negatively correlated to 4-meter walk tests at normal (r=-0.447, P=0.036) and fast pace (r=-0.510, P=0.014). Extracellular matrix occupied more muscle area in PAD compared with non-PAD (8.72±2.19% versus 5.30±1.03%, P<0.001) and positively correlated with capillary density (r=0.656, P<0.001). Conclusions Among people with PAD, higher CD206+ M2-like macrophage abundance was associated with greater satellite cell numbers and muscle fiber size. Lower CD206- macrophage abundance was associated with better walking performance. Further study is needed to determine whether CD206+ macrophages are associated with ongoing reparative processes enabling skeletal muscle adaptation to damage with PAD. Registration URL: https://www.clini​caltr​ials.gov; Unique identifiers: NCT00693940, NCT01408901, NCT0224660.

Association of six-minute walk distance with subsequent lower extremity events in peripheral artery disease.

The prognostic significance of the six-minute walk distance for lower extremity events in people with peripheral artery disease (PAD) is unknown. This longitudinal study assessed whether a poorer six-minute walk distance at baseline was associated with higher rates of subsequent lower extremity atherosclerotic disease events in PAD. A total of 369 patients (mean age 69.4 ± 10.0 years; mean ankle-brachial index (ABI) 0.67 ± 0.17; 31% women; 30% black individuals) from Chicago-area medical centers with PAD were enrolled. Participants underwent baseline six-minute walk testing and returned for annual study visits. Lower extremity events consisted of one or more of the following: ABI decline greater than 15% or medical record adjudicated lower extremity revascularization, critical limb ischemia, or amputation. At a mean follow-up of 33.3 months, lower extremity events occurred in 66/123 (53.7%) people in the first (worst) tertile of six-minute walk performance, 55/124 (44.4%) in the second tertile, and 56/122 (45.9%) in the third (best) tertile. After adjusting for age, sex, race, ABI, comorbidities, and other confounders, participants in the first (worst) tertile of six-minute walk distance at baseline had higher rates of lower extremity events during follow-up, compared to those in the best tertile at baseline (HR = 1.74, 95% CI 1.17-2.60, p = 0.0067). Among people with PAD, a poorer six-minute walk distance was associated with higher rates of subsequent lower extremity PAD-related events after adjusting for confounders. Further study is needed to determine whether interventions that improve six-minute walk distance can reduce lower extremity adverse events in people with PAD.

Associations of Peripheral Artery Disease With Calf Skeletal Muscle Mitochondrial DNA Heteroplasmy.

Background Patients with peripheral artery disease (PAD) undergo frequent episodes of ischemia-reperfusion in lower extremity muscles that may negatively affect mitochondrial health and are associated with impaired mobility. We hypothesized that skeletal muscle from PAD patients will show high mitochondrial DNA heteroplasmy, especially in regions more susceptible to oxidative damage, such as the displacement loop, and that the degree of heteroplasmy will be correlated with the severity of ischemia and mobility impairment. Methods and Results Mitochondrial mutations and deletions and their relative abundance were identified by targeted mitochondrial DNA sequencing in biopsy specimens of gastrocnemius muscle from 33 PAD (ankle brachial index <0.9) and 9 non-PAD (ankle brachial index >0.9) subjects aged ≥60 years. The probability of heteroplasmy per DNA base was significantly higher for PAD subjects than non-PAD within each region. In adjusted models, PAD was associated with higher heteroplasmy than non-PAD (P=0.003), but the association was limited to microheteroplasmy, that is heteroplasmy found in 1% to 5% of all mitochondrial genomes (P=0.004). Heteroplasmy in the displacement loop and coding regions were significantly higher for PAD than non-PAD subjects after adjustment for age, sex, race, and diabetes mellitus (P=0.037 and 0.004, respectively). Low mitochondrial damage, defined by both low mitochondrial DNA copy number and low microheteroplasmy, was associated with better walking performance. Conclusions People with PAD have higher "low frequency" heteroplasmy in gastrocnemius muscle compared with people without PAD. Among people with PAD, those who had evidence of least mitochondrial damage, had better walking performance than those with more mitochondrial damage. Registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT02246660.