ACP5 and osteoporosis: In patients with osteoporosis, MMP-2 levels correlated negatively with BMD [106,107,108,109] and correlated positively with levels of osteocalcin (OC), serum cross-linked N-telopeptides of type I collagen (NTX), bone alkaline phosphatase (BALP) [106,107,108], tartrate-resistant acid phosphatase 5b (TRACP-5b) [117], or other factors, such as sB7-H3 protein [105].