Peripheral arterial disease (PAD) is caused by atherosclerotic occlusion of the lower extremities that reduces blood flow and leads to intermittent claudication and critical limb ischemia. PAD is diagnosed by calculating the ratio of blood pressure at the ankle to that of the arm (the ankle-brachial index \[ABI\]). An ABI of \<0.90 is indicative of atherosclerosis in the leg. Recent data from developed and developing countries have estimated that \>200 million people worldwide and approximately 12 million people in United States have PAD3. Both symptomatic and asymptomatic PAD patients have an increased risk of mortality, morbidity, and a lower quality of life. With the increasing incidence of type 2 diabetes (T2D) and a rising aging population, the number of PAD patients is likely to increase. Because PAD is an under-recognized disease, currently few medications are available to improve the functional performance of these patients. Although surgical revascularization is an available treatment, grafts can fail and the stenosis can reoccur in these patients. To adequately compensate the loss of tissue due to occlusion, the current emphasis is to increase the therapeutic angiogenesis and arteriogenesis in the ischemic limb that could improve the walking ability and the quality of life in PAD patients. In a recent pre-clinical study it was shown that supplementation of carnosine(β-alanine-histidine) (500 mg/day) in heart failure patients for 6 months improves their performance on the 6-minute walking test (6MWT) compared with placebo-treated patients. Carnosine is a histidyl dipeptide present in high concentration in the skeletal muscle, brain, and heart. It is a food constituent that is present in red meat, chicken, and turkey. This dipeptide is synthesized by the ATP grasp enzyme carnosine synthetase and hydrolyzed to β-alanine and histidine by the serum and kidney carnosinase. Carnosine has the abilities to quench reactive aldehydes, bind metals, and buffer intracellular pH7. Numerous studies have shown that the supplementation of beta-alanine or carnosine increases the levels of carnosine in the skeletal muscle and improves the exercise performance in humans. Our preliminary studies with the mice model of hind limb ischemia (HLI) showed that both the pretreatment and supplementation of carnosine after femoral artery ligation increased blood flow in the ischemic limb compared with the non-treated mice. Mechanistic studies showed that the metal quenching ability of carnosine increased the expression of angiogenic factor VEGF and endothelial progenitor cells mobilization in the carnosine treated HLI mice. Similarly, the stabilization of HIF-1α, the master regulator of angiogenesis and angiogenic factor VEGF, was increased in the hypoxic C2C12 cells (murine myoblasts). Based on these pre-clinical studies, in this study PAD subjects will be recruited and supplemented with carnosine (2 g/day) for 3 months to examine if its supplementation improves walking performance compared with the baseline. Further, we will examine whether the supplementation of carnosine increases the capacity of pain-free treadmill walking time, extrusion of oxidative stress markers and mobilizes the endothelial progenitor cells in the blood.
