Dataset DOI: 10.5061/dryad.xksn02vtj

Description of the data and file structure

Participants with and without PAD were enrolled from the Chicago, Illinois area. The study was approved by a university Institutional Review Board. All participants provided written informed consent.

Participants with and without PAD were identified using lists of patients and by advertisements placed on Chicago Transit Authority buses and trains, and by mailed recruitment postcards, using a purchased mailing list. Enrollment occurred between 7/23/2018 and 8/26/2021.

PAD was defined as an ABI < 0.90 in either leg (914). Absence of PAD was defined as an ABI of 1.00-1.40. Potential participants with ABI of 0.90 to 0.99 were excluded, because they may have mild lower extremity atherosclerosis. To attain similar ages between people with vs. without PAD, only older people were included among those without PAD.

Individuals taking part in a randomized clinical trial or who completed a randomized clinical trial in the past three months were not eligible. Potential participants with diabetes were initially excluded. Due to challenges with recruitment, diabetes mellitus was not an exclusion criterion beginning 9/20/2019.

ABI Measurement: A hand-held Doppler probe (Pocket Dop II; Nicolet Biomedical Inc) was used to measure systolic pressures twice in the right and left brachial, dorsalis pedis, and posterior tibial arteries while the participant was supine. The ABI was measured by staff, following study protocol. Staff were certified by co-investigator MMM prior to beginning data collection and approximately every six months. The ABI was calculated by dividing the mean of the dorsalis pedis and posterior tibial pressures in each leg by the mean of the four brachial pressures.

Six-minute Walk: The 6-minute walk test was used to assess functional performance, because the 6-minute walk is a well validated measure of walking endurance that reflects walking ability in daily life better than treadmill walking performance. For example, the 6-minute walk was more closely correlated with physical activity in daily life than treadmill walking performance. Participants walked up and down a 100-foot hallway after receiving scripted instructions from a trained and certified research coordinator. Participants were advised that the goal of the test was to cover as much distance as possible in six minutes. The distance completed after six minutes was recorded. Distance to first report of leg symptoms during the walk and whether the participant reported leg symptoms at the end of the walk was recorded. The intra-class correlation coefficient for the test-retest reliability of the 6-minute walk among 155 participants who performed the 6-minute walk test twice, 1-2 weeks apart, was 0.90 (p<0.001).

Physical Activity: Physical activity was measured over seven days with the ActiGraph accelerometer. Low, medium, and high intensity activity were combined into a single “activity count” outcome as previously described.

Gastrocnemius biopsy: An open muscle biopsy was performed in the medial head of the gastrocnemius muscle of the leg with the lower ABI. If the left and right legs had identical ABI values, the leg for biopsy was selected randomly. All muscle biopsies were performed by two co-investigators (RS and KJH). Anesthesia was achieved with subcutaneous lidocaine. Subcutaneous tissue was dissected until muscle was identified. After muscle tissue was removed, 10-20 mg was transported in cold biopsy media for immediate respirometry testing. Remaining muscle was immediately prepared for freezing at -80 degree Celsius.

Mitochondrial respiratory function: High-resolution respirometry was performed using an Oroboros O2k (Oroboros Instruments, Innsbruck, Austria) per established protocols. Respirometry was performed on muscle immediately after the biopsy was obtained. Muscle fiber bundles were separated in ice-cold preservation media (BIOPS) under a dissecting microscope to obtain four replicates per participant (approximately 2-3mg each), which were permeabilized with saponin for 20 min followed by a 10 min wash in mitochondrial respiration media (MiR05). All data were collected at 37°C in hyperoxygenated (200–450µM O2) conditions in MiR05 to avoid limitations to oxygen diffusion. Two substrate-uncoupler-inhibitor titrations (SUIT) respiration protocols (carbohydrate and fatty acid) assessed maximal phosphorylation (OXPHOS) and electron transport chain (ETC) capacity of complex-I and complex-II mediated respiration. Malate, pyruvate (carbohydrate) or octanoylcarnitine (fatty acid), ADP, glutamate, cytochrome c, and succinate were sequentially added, followed by titrations of carbonyl cyanide m-chlorophenyl hydrazine (CCCP), rotenone, and antimycin A. The state of respiration in the presence of malate, pyruvate, glutamate and ADP was defined as carbohydrate complex-I mediated maximal OXPHOS capacity (PCI). Respiration after subsequent succinate addition was defined as carbohydrate complex-I+II mediated maximal OXPHOS capacity(PCI+II). The state of respiration after adding CCCP (uncoupler) was considered maximal ETC capacity (ECI+II). Fatty acid-supported respiration in the presence of malate, octanoylcarnitine, and ADP was measured using complex-I and electron-transferring flavoprotein complex mediated maximal OXPHOS (PCI/FA). Results from replicates that increased by more than 15% after adding cytochrome c were considered over-permeabilized and not included in analyses.

Mitochondrial protein measures: Protein expression of mitochondrial ETC complexes I, II, III, IV and V (ATP synthase) subunits; voltage-dependent anion channels (VDAC); and peroxisome-proliferator activated receptor-γ coactivator (PGC-1α) were measured by Western blot.

Statistical analyses:  Characteristics of participants with and without PAD were summarized as means and standard deviations (SD) for continuous variables and as frequencies and percentages for categorical variables. Two sample t-tests were used to compare continuous characteristics. Chi-squared or Fisher’s exact tests were used to compare categorical characteristics of participants with vs. without PAD. Pearson correlation coefficients were used to evaluate associations of the ABI, six-minute walk distance, and physical activity, respectively, with mitochondrial respiratory function and with abundance of the mitochondrial proteins. Analyses were performed separately among people with and without PAD. We studied whether these associations were significantly different between people with and without PAD by testing the interaction between PAD status and ABI in a linear regression model with ABI as the independent variable of interest and mitochondrial respirometry as the dependent variable of interested. We also tested the interaction between PAD status with mitochondrial respirometry as the independent variable of interest and 6-minute walk and physical activity as separate dependent variables of interest. Statistical tests were two-sided and the criterion for statistical significance was P-value<0.05. Statistical analyses were conducted using SAS 9.4.

Files and variables

File: MDD_dataset.xlsx

Description: This file contains all variables from this research project, except for those that could be used to identify specific individuals.  Missing variables are gender and race. 

Each row in the dataset is one individual, and the ID_Index variable included in the submission has been anonymized

Variables

• PAD or no PAD
• Ankle-brachial index (ABI)
• Body Mass Index (BMI)
• Current Smoker - 0=no
• Diabetes - 0=no
• History of Myocardial Infarction - 0=no
• History of Heart Failure - 0=no
• History of stroke - 0=no
• History of angina - 0=no
• History of cancer - 0=no
• Baseline 6-minute walk distance in feet
• Actigraph activity counts per minute
• City blocks walked
• Flights of stairs climbed
• Report of regular walking
• Baseline CHO Phosphorylation, Complex I
• Baseline CHO Phosphorylation Complexes I & II
• Baseline CHO electron transport chain Complexes I& II
• Baseline Fatty acid phosphorylation, Complexes I
• Baseline Fatty acid phosphorylation, Complexes I & II
• Baseline Fatty acid electron transport chain, complexes I/II
• PGC1 alpha_Normalized Value (AU - Arbitrary Units)
• VDAC_Normalized Value (AU - Arbitrary Units)
• Complex I _Normalized Value (AU - Arbitrary Units)
• Complex II _Normalized Value (AU - Arbitrary Units)
• Complex III _Normalized Value (AU - Arbitrary Units)
• Complex IV _Normalized Value (AU - Arbitrary Units)
• Complex IV _Normalized Value (AU - Arbitrary Units)

Code/software

None

Access information

Other publicly accessible locations of the data:

• N/A

Data was derived from the following sources:

• N/A

Human subjects data

This file contains de-identified data from this study which looked at mitochondrial function in people with and without peripheral artery disease. Only de-identified data is available here.