Scientists have found that the body’s natural endocannabinoid system plays a role in bone metabolism. The endocannabinoid system also plays a well-recognized role in regulating many other physiologic processes, including neurotransmission, pain perception, energy balance, appetite control, motor function, and the immune response.
Bone is a type of specialized connective tissue, it is full of cells, and it is very metabolically active. Bone is continually undergoing a process of renewal and repair known as “bone remodeling.” Bone forming cells are known as osteoblasts, and bone resorbing cells are known as osteoclasts.
Through early adulthood, the activity of osteoblasts and osteoclasts is balanced. As a result, a healthy bone mass is maintained.
Osteoporosis is a metabolic disorder characterized by osteoclast activity (bone resorption) exceeding osteoblast activity (bone formation). This leads to gradual deterioration of bone mass, increased bone fragility, and increased fracture risk. Osteoporotic fractures are one of the main causes of morbidity among elderly patients.
The medical literature shows that cannabinoids and cannabinoid receptors may play important roles in the development of treatments for bone diseases such as osteoporosis. Here are some highlights:
- CB1 cannabinoid receptors are present primarily in skeletal sympathetic nerve terminals that regulate bone formation. How CB1 receptors control bone turnover remains to be determined; a neuronal mechanism is speculated.
- CB2 cannabinoid receptors are located in osteoblasts and osteoclasts. CB2 receptors have been found to stimulate bone formation and inhibit bone resorption (thus a “bone building effect”).
- In the aging skeleton, CB1 and CB2 receptors have been found to have a protective effect against age-dependent bone loss in male and female mice.
- CB1 receptor deficiency in aged mice results in accelerated age-dependent osteoporosis due to increased bone resorption and decreased bone formation.
- CB2 receptor deficient mice had accelerated bone loss due to enhanced bone turnover.
- In humans, abnormalities of the CB2 receptor gene are strongly associated with postmenopausal osteoporosis.
References:
Bab I, Zimmer A. Cannabinoid receptors and the regulation of bone mass. British Journal of Pharmacology. 2008;153:182-188. (Review Article)
Bab I, Zimmer A, Melamed E. Cannabinoids and the skeleton: from marijuana to reversal of bone loss. Annals of Medicine. 2009;41(8):560-567.
Idris AI. Cannabinoid Receptors as Target for Treatment of Osteoporosis: A Tale of Two Therapies. Current Neuropharmacology. 2010;8:243-253. (Review Article)
Idris AI, Ralston SH. Cannabinoids and bone: friend or foe? Calcified Tissue International. 2010;87(4):285-297.
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Mark L. Rabe, MD, ABIHM
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