What is bone resorption?

From the Guidelines

Bone resorption is the process by which specialized cells called osteoclasts break down bone tissue and release minerals, resulting in the transfer of calcium from bone to blood, and it is a key factor in the development of osteoporosis, as stated in the American College of Physicians guideline update 1. This process is a normal physiological process that works in balance with bone formation to maintain bone health and calcium homeostasis in the body. During bone resorption, osteoclasts attach to the bone surface and secrete acids and enzymes that dissolve the bone matrix and release stored calcium and phosphate into the bloodstream. This process is essential for bone remodeling, fracture healing, and maintaining proper calcium levels in the body. However, when bone resorption exceeds bone formation, it can lead to decreased bone density and conditions like osteoporosis, which can be diagnosed by the occurrence of fragility fracture or low bone mineral density (BMD) measured by dual-energy x-ray absorptiometry (DXA) 1. Several factors can influence bone resorption, including hormones (particularly parathyroid hormone and estrogen), vitamin D levels, physical activity, and certain medications, such as glucocorticoids, anticoagulants, anticonvulsants, aromatase inhibitors, cancer chemotherapeutic drugs, and gonadotropin-releasing hormone agonists 1. Medications called antiresorptives, such as bisphosphonates (alendronate, risedronate), denosumab, and hormone replacement therapy, can be prescribed to slow excessive bone resorption in conditions like osteoporosis, as recommended by the American College of Physicians guideline update 1. Some of the key points to consider when evaluating bone resorption include:

• The role of osteoclasts in breaking down bone tissue and releasing minerals
• The importance of balance between bone resorption and bone formation in maintaining bone health
• The factors that can influence bone resorption, such as hormones, vitamin D levels, and certain medications
• The use of antiresorptive medications to slow excessive bone resorption in conditions like osteoporosis
• The diagnosis of osteoporosis by the occurrence of fragility fracture or low BMD measured by DXA 1.

From the FDA Drug Label

Osteoporosis occurs as a result of inhibited bone formation and increased bone resorption resulting in net bone loss Excessive osteoclastic bone resorption is followed by osteoblastic new bone formation, leading to the replacement of the normal bone architecture by disorganized, enlarged, and weakened bone structure. Alendronate reduces bone resorption with no direct effect on bone formation, although the latter process is ultimately reduced because bone resorption and formation are coupled during bone turnover

• Bone resorption is the process by which osteoclasts break down bone tissue, releasing minerals such as calcium and phosphate into the bloodstream.
• It is a natural process that occurs in the body, but when it exceeds bone formation, it can lead to net bone loss and conditions such as osteoporosis.
• Bone resorption is increased in certain conditions, such as osteoporosis, and can be reduced by medications such as alendronate 2, 2.

From the Research

Definition of Bone Resorption

• Bone resorption is a process where osteoclasts break down bone tissue, removing its mineral and organic components 3, 4.
• This process is essential for bone homeostasis and remodeling, allowing for the replacement of old or damaged bone with new tissue 5.

Role of Osteoclasts in Bone Resorption

• Osteoclasts are the only cells capable of efficiently resorbing bone, and they play a crucial role in bone development and remodeling 3, 4.
• Osteoclasts seal themselves to the bone surface and remove the mineral and organic components, allowing for the resorption of bone tissue 3.

Regulation of Bone Resorption

• The bone remodeling cycle is a highly regulated process that replaces old and damaged bone with new tissue, and it involves the coordinated actions of osteoclasts and osteoblasts 5.
• The regulation of bone resorption is controlled by various signaling pathways, including the RANK/RANKL/OPG pathway and the Wnt signaling pathway 5.
• Cytokines, growth factors, and hormones also play important roles in regulating bone resorption and formation 5.

Relationship between Bone Resorption and Disease

• Increased bone resorption is associated with various bone diseases, including osteoporosis, Paget's disease, and osteopetrosis 3, 4, 6.
• Bisphosphonates, a class of drugs that inhibit bone resorption, are commonly used to treat osteoporosis and other bone diseases 6, 7.
• The effect of bisphosphonates on osteoclast precursor cells and circulating cytokines has been studied, and it has been shown that these drugs can reduce the population of osteoclast precursor cells and decrease bone turnover 7.