Abstract 13651: Angiotensin-Converting Enzyme Inhibitors Preserve Limb Function and Decrease Myofibrosis and Oxidative Damage in the Calf Muscle of Patients With Peripheral Artery Disease

Introduction: A six-month treatment with the Angiotensin-Converting Enzyme Inhibitor (ACEI) Ramipril improved the walking ability of Peripheral Artery Disease (PAD) patients, but the mechanism remains unknown. ACEI have been shown to reduce fibrosis in heart and kidney and improve arterial compliance. We have identified a myopathy in calf muscles of PAD patients, characterized by fibrosis and increased TGF-β1 produced exclusively in smooth muscle cells (SMC) of microvessels. These events were linked to myofiber oxidative damage and reduced myofiber cross-sectional area. Hypothesis: The myopathy of PAD patients taking ACEI is improved compared to patients who are not taking ACEI and this improvement is associated with improved walking ability. Methods: Calf muscle biopsies, from PAD patients (Fontaine Stage II) taking ACEI (ACEI+) and those who were not (ACEI-), were fixed, embedded in paraffin, sectioned at 4 microns and slide mounted. Oxidative damage (carbonyl groups) (N=13 for ACEI- and 22 for ACEI+) and TGF-β1 (N=13 for ACEI- and 20 for ACEI+) were analyzed by quantitative fluorescence microscopy and expressed as grey scale units (gsu). Myofiber cross-sectional area was determined from fluorescence-labeled sarcolemma. Fibrosis was determined as collagen density (gsu) by multi-spectral analysis of slide specimens (N=13 for ACEI- and 20 for ACEI+) stained with Mason Trichrome. Limb function was assessed by the six-minute walking distance (N=28 for ACEI- and 20 for ACEI+). Results: Compared to ACEI- patients, ACEI+ patients had reduced TGF-β1 (4.25 gsu +/- 0.69 vs. 1.51 gsu +/- 0.23; p = 0.001) and decreased collagen density (2067 gsu +/- 88 vs. 1671 gsu +/- 51; p < 0.001). Carbonyl adducts were reduced in myofibers of ACEI+ compared to ACEI- patients (1584 gsu +/- 55 vs. 1779 gsu +/- 58; p = 0.019) and myofiber cross sectional area was increased (4629 μm2 +/- 285 vs. 3816 μm2 +/- 267; p = 0.023). Six-minute walking distance was greater in ACEI+ compared to ACEI- patients (333 m +/- 20 vs. 266 m +/- 16; p = 0.011). Conclusions: Improved walking distance of PAD patients taking ACEI is associated with improved calf muscle myopathy, determined as reduced TGF-β1 production, collagen density, and myofiber oxidative damage, and increased myofiber cross-sectional area.