The LargPAD Trial: Phase IIA evaluation of l -arginine infusion in patients with peripheral arterial disease

Abstract Objective Endothelial function is improved by l- arginine ( l- arg) supplementation in preclinical and clinical studies of mildly diseased vasculature; however, endothelial function and responsiveness to l- arg in severely diseased arteries is not known. Our objective was to evaluate the acute effects of catheter-directed l- arg delivery in patients with chronic lower extremity ischemia secondary to peripheral arterial disease. Methods The study enrolled 22 patients (45% male) with peripheral arterial disease (mean age, 62 years) requiring lower extremity angiography. Endothelium-dependent relaxation of patent but atherosclerotic superficial femoral arteries was measured using a combination of intravascular ultrasound (IVUS) imaging and a Doppler FloWire (Volcano Corporation, Rancho Cordova, Calif) during the infusion of incremental acetylcholine (10−6 to 10−4 molar concentration) doses. Patients received 50 mg (n = 3), 100 mg (n = 10), or 500 mg (n = 9) l- arg intra-arterially, followed by repeat endothelium-dependent relaxation measurement (limb volumetric flow). IVUS-derived virtual histology of the culprit vessel was also obtained. Endothelium-independent relaxation was measured using a nitroglycerin infusion. Levels of nitrogen oxides and arginine metabolites were measured by chemiluminescence and mass spectrometry, respectively. Results Patients tolerated limb l- arg infusion well. Serum arginine and ornithine levels increased by 43.6% ± 13.0% and 23.2% ± 10.3%, respectively ( P < .005), and serum nitrogen oxides increased by 85% ( P < .0001) after l- arg infusion. Average vessel area increased by 6.8% ± 1.3% with l- arg infusion (acetylcholine 10−4 ; P < .0001). Limb volumetric flow increased in all patients and was greater with l- arg supplementation by 130.9 ± 17.6, 136.9 ± 18.6, and 172.1 ± 24.8 mL/min, respectively, for each cohort. Maximal effects were seen with l- arg at 100 mg (32.8%). Arterial smooth muscle responsiveness to nitroglycerin was intact in all vessels (endothelium-independent relaxation, 137% ± 28% volume flow increase). IVUS-derived virtual histology indicated plaque volume was 14 ± 1.3 mm3 /cm, and plaque stratification revealed a predominantly fibrous morphology (46.4%; necrotic core, 28.4%; calcium, 17.4%; fibrolipid, 6.6%). Plaque morphology did not correlate with l- arg responsiveness. Conclusions Despite extensive atherosclerosis, endothelial function in diseased lower extremity human arteries can be enhanced