RANK Ligand and Bone Loss

RANK Ligand and Bone Loss

While it has long been known that excessive osteoclast activity is the primary driver of bone loss associated with postmenopausal osteoporosis, only recently have the underlying mechanisms of bone loss been identified.[1]

In postmenopausal osteoporosis, increased osteoclast activity leads to increased bone loss and fracture risk [1][2]
Normal bone

Before menopause, osteoclast activity is regulated by normal estrogen levels[3][4]

Image reproduced with permission from David W. Dempster, PhD.

Osteoclast-mediated
bone resorption

After menopause, decreased estrogen can lead to an increase in osteoclast activity[3][4]

Adapted from www.brsoc.org.uk/gallery
/arnett_osteoclast.jpg Electron micrograph photo reproduced with permission, ©Tim Arnett, The Bone Research Society.

Osteoporotic bone

Increased osteoclast activity can lead to increased bone loss and greater fracture risk throughout the skeleton[5][6]

Image reproduced with permission from David W. Dempster, PhD.

The RANK Ligand Pathway

An important discovery in bone biology has led to a new understanding of the mechanism underlying bone loss.[1]

The role of RANK Ligand in Postmenopausal Osteoporosis [1]

After menopause, decreased estrogen leads to increased production of RANK Ligand (RANKL)—an essential mediator of osteoclast-induced bone loss.[1][4][5] The resulting increased osteoclast activity leads to increased resorption and decreased bone mass. Over time, this process leads to compromised bone strength and increased risk of fracture throughout the skeleton.[5][6]

The RANKL pathway mediates osteoclast activity:[5]

Rank Ligand IconRANKL is a protein that is expressed by various bone-forming cells and bone-resorbing
cells—including osteoblasts and bone lining cells.[1][5]

Receptor IconRANK is a receptor found on osteoclasts and osteoclast precursors.[5]

Binding of RANKL to RANK promotes osteoclast formation, function, and survival.[1][5] Several factors, including cytokines and hormones, stimulate the expression of RANKL.[1]

Synopsis

Estrogen regulates bone resorption by limiting the release of RANKL from osteoblasts (among other cells).[1][4] However, in postmenopausal osteoporosis, loss of estrogen leads to significantly increased RANKL expression. Increased levels of RANKL expression result in excess formation and activity of osteoclasts, leading to bone loss.[1][4]

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Indications

Prolia® (denosumab) is indicated for the treatment of postmenopausal women with osteoporosis at high risk for fracture, defined as a history of osteoporotic fracture, or multiple risk factors for fracture; or patients who have failed or are intolerant to other available osteoporosis therapy. In postmenopausal women with osteoporosis, Prolia® reduces the incidence of vertebral, nonvertebral, and hip fractures.

Prolia® is indicated for treatment to increase bone mass in men with osteoporosis at high risk for fracture, defined as a history of osteoporotic fracture, or multiple risk factors for fracture; or patients who have failed or are intolerant to other available osteoporosis therapy.

Important Safety Information

Contraindications:
Prolia® is contraindicated in patients with hypocalcemia. Pre-existing hypocalcemia must be corrected prior to initiating Prolia®. Prolia is contraindicated in women who are pregnant and may cause fetal harm. Prolia is contraindicated in patients with a history of systemic hypersensitivity to any component of the product. Reactions have included facial swelling and urticaria.

Same Active Ingredient:
Prolia® contains the same active ingredient (denosumab) found in XGEVA®. Patients receiving Prolia® should not receive XGEVA®.

Hypocalcemia:
Hypocalcemia may worsen with the use of Prolia®, especially in patients with severe renal impairment. In patients predisposed to hypocalcemia and disturbances of mineral metabolism, clinical monitoring of calcium and mineral levels is highly recommended. Adequately supplement all patients with calcium and vitamin D.

Serious Infections:
In a clinical trial (N = 7808) in women with postmenopausal osteoporosis, serious infections leading to hospitalization were reported more frequently in the Prolia® group than in the placebo group. Serious skin infections, as well as infections of the abdomen, urinary tract and ear, were more frequent in patients treated with Prolia®. Endocarditis was also reported more frequently in Prolia®-treated patients. The incidence of opportunistic infections and the overall incidence of infections were similar between the treatment groups. Advise patients to seek prompt medical attention if they develop signs or symptoms of severe infection, including cellulitis.

Patients on concomitant immunosuppressant agents or with impaired immune systems may be at increased risk for serious infections. In patients who develop serious infections while on Prolia®, prescribers should assess the need for continued Prolia® therapy.

Dermatologic Adverse Reactions:
In the same clinical trial in women with postmenopausal osteoporosis, epidermal and dermal adverse events such as dermatitis, eczema and rashes occurred at a significantly higher rate with Prolia® compared to placebo. Most of these events were not specific to the injection site. Consider discontinuing Prolia® if severe symptoms develop.

Osteonecrosis of the Jaw (ONJ):
ONJ, which can occur spontaneously, is generally associated with tooth extraction and/or local infection with delayed healing, and has been reported in patients receiving Prolia®. An oral exam should be performed by the prescriber prior to initiation of Prolia®. A dental examination with appropriate preventive dentistry should be considered prior to treatment in patients with risk factors for ONJ. Good oral hygiene practices should be maintained during treatment with Prolia®.

For patients requiring invasive dental procedures, clinical judgment should guide the management plan of each patient. Patients who are suspected of having or who develop ONJ should receive care by a dentist or an oral surgeon. Extensive dental surgery to treat ONJ may exacerbate the condition. Discontinuation of Prolia® should be considered based on individual benefit-risk assessment.

Atypical Femoral Fractures:
Atypical low-energy, or low trauma fractures of the shaft have been reported in patients receiving Prolia® (denosumab). Causality has not been established as these fractures also occur in osteoporotic patients who have not been treated with anti-resorptive agents.

During Prolia® treatment, patients should be advised to report new or unusual thigh, hip, or groin pain. Any patient who presents with thigh or groin pain should be evaluated to rule out an incomplete femur fracture. Interruption of Prolia® therapy should be considered, pending a risk/benefit assessment, on an individual basis.

Suppression of Bone Turnover:
In clinical trials in women with postmenopausal osteoporosis, Prolia® resulted in significant suppression of bone remodeling as evidenced by markers of bone turnover and bone histomorphometry. The significance of these findings and the effect of long-term treatment are unknown. Monitor patients for consequences, including ONJ, atypical fractures, and delayed fracture healing.

Adverse Reactions:
The most common adverse reactions (> 5% and more common than placebo) in women with postmenopausal osteoporosis are back pain, pain in extremity, musculoskeletal pain, hypercholesterolemia, and cystitis. The most common adverse reactions (> 5% and more common than placebo) in men with osteoporosis are back pain, arthralgia, and nasopharyngitis. Pancreatitis has been reported with Prolia®.

In women with postmenopausal osteoporosis, the overall incidence of new malignancies was 4.3% in the placebo group and 4.8% in the Prolia® groups. In men with osteoporosis, new malignancies were reported in no patients in the placebo group and 4 (3.3%) patients in the Prolia® group. A causal relationship to drug exposure has not been established. Denosumab is a human monoclonal antibody. As with all therapeutic proteins, there is potential for immunogenicity.

Prolia® Postmarketing Active Safety Surveillance Program:
The surveillance program is available to collect information from prescribers on specific adverse events. Please see www.proliasafety.com or call 1-800-772-6436 for more information.

References
  1. Boyle WJ, Simonet WS, Lacey DL. Osteoclast differentiation and activation. Nature. 2003;423:337-342.

  2. National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis. Washington, DC: National Osteoporosis Foundation; 2010.

  3. US Department of Health and Human Services. Bone Health and Osteoporosis: A Report of the Surgeon General. Rockville, MD: US Department of Health and Human Services, Office of the Surgeon General, 2004.

  4. Sambrook P, Cooper C. Osteoporosis. Lancet. 2006;367:2010-2018.

  5. Kostenuik PJ. Osteoprotegerin and RANKL regulate bone resorption, density, geometry and strength. Curr Opin Pharmacol. 2005;5:618-625.

  6. Chavassieux P, Seeman E, Delmas PD. Insights into material and structural basis of bone fragility from diseases associated with fractures: how determinants of the biomechanical properties of bone are compromised by disease. Endocr Rev. 2007;28:151-164.