ACP5 and osteoporosis: Our recent cohort study, though, has found a positive association between circulating CCL15 and the risk of incident peripheral artery disease.21 TR-AP, also called ACP5 or TRACP-5b, is involved in bone homeostasis and is a known marker of osteoporosis, which has also been associated with the severity of coronary atherosclerosis in patients with CHD.6