Myofiber Type Sensitivity of Gastrocnemius Muscle to Oxidative Stress in Peripheral Arterial Disease Patients

Abstract

Peripheral arterial disease (PAD) affects approximately 8.5 million Americans and is characterized by the formation of atherosclerotic plaques in the arteries limiting the blood supply in the legs. Previous studies have demonstrated that oxidative damage (carbonyl and 4-hydroxyl-2-nonenal adducts) in PAD muscle fibers is higher than control gastrocnemius and correlates with disease progression. In this study, we investigated the effect of oxidative damage in myofiber type (slow and fast twitch) of gastrocnemius muscle while the disease is progressing. Muscle biopsies were collected with a Bergstrom needle from PAD-claudication patients (PAD-C; n = 28), PAD-critical limb ischemia patients (PAD-CLI; n = 25), and control subjects (n = 25). Quantitative fluorescence microscopy was used to label the myofiber sarcolemmas, carbonyl adducts, and the slow/fast/hybrid twitch fibers. Differences between and within the groups of carbonyl adducts and myofiber cross-sectional area of each myofiber type were measured. A discriminant model was used to categorize muscle specimens on the basis of the disease progression. Carbonyl adducts in gastrocnemius fibers were higher in PAD-C and PAD-CLI patients when compared with control fibers for all myofiber types. Cross-sectional area of fast twitch and hybrid fibers was significantly decreased when compared with control fibers (P < .05). Fast twitch and hybrid fibers demonstrated a significant increase of oxidative damage (P < .01) when compared with slow twitch fibers for both the PAD-C and PAD-CLI groups. Fast twitch fibers frequency was decreased while the disease was progressing, while slow and hybrid twitch fibers frequency was increased. The discriminant model demonstrated that ankle-branchial index, oxidative damage, and cross-sectional area of fast twitch fibers can accurately identify controls (100% accuracy), PAD-C (78.6% accuracy), and PAD-CLI (84% accuracy) with an overall classification accuracy of 87.2%. Oxidative damage is myofiber-type-sensitive towards fast twitch and hybrid fibers. The discriminant model establishes that fast twitch fibers are more susceptible to degeneration in association with increased oxidative damage.