Melatonin - novel regulator of bone?

Hormone ofthe darkness - melatonin regulates a number ofphysiological processes including biorhytms, sleep, reproduction, neuroendocrine and car­ diovascular functions, respiration, immunity and oncogenesis. Melatonin is produced in pineal gland and in bone marrow cells as well. Thus melato­ nin can modulate bone metabolism in a paracrine way. The recent investigations have suggested that melatonin positively influenced bone remodeling most probably directly at the level of specific receptors localized at the bone cells. Melatonin stimulates bone formation and synthesis of procollagen type I and inhibits bone resorption via the TRANCE axis (RANK and osteoprotegerin). Moreover, activation of the superoxide-scavenging enzyme may be of bone protective importance. Melatonin affects the skeleton also indirectly, by increasing the release of somatotropin. Through the above mentio­ ned mechanisms, melatonin potentiates the osteoprotective effect of sexual steroids. The synthesis of melatonin declines progressively in the course of aging and most markedly after the menopause, which accelerates bone loss in these periods of life. The possible utility of melatonin in the treatment of osteoporosis needs to be extensively investigated.

Keywords: melatonin, bone remodeling, bone density, osteoporosis.