Hydroxyapatite (Bone mineral) (HAP)

Bone mineral at osteoclast resorption surfaces consists primarily of hydroxyapatite, a crystalline form of calcium phosphate that provides the structural framework of the skeleton (StatPearls, 2023). This mineralized matrix serves as the physical substrate for bone remodeling, where osteoclasts attach and create an acidic "resorption lacuna" to dissolve the mineral and digest the underlying collagen (NIH, 2022). In clinical pharmacology, this surface is the primary target for bisphosphonates, which possess a high affinity for the calcium ions within the hydroxyapatite lattice (PubMed: 16035944). Once these drugs bind to the mineral at active resorption sites, they are internalized by osteoclasts during the bone-eating process (Mayo Clinic Proceedings, 2008). Inside the osteoclast, bisphosphonates inhibit the mevalonate pathway, specifically the enzyme farnesyl pyrophosphate synthase, which leads to the disruption of protein prenylation and eventually triggers cell apoptosis (PubMed: 21664015). This targeted action effectively reduces the rate of bone turnover, making it a cornerstone therapy for metabolic bone diseases such as osteoporosis, Paget's disease, and skeletal complications of cancer (StatPearls, 2023).

Other names

Bone mineralCalcium hydroxyapatiteMineralized bone matrixBone resorption surface

Bisphosphonates bind to hydroxyapatite crystals at sites of active bone remodeling; they are internalized by osteoclasts during resorption, leading to inhibition of the mevalonate pathway and osteoclast apoptosis (PubMed: 16035944, 21664015).