Clin Osteol 2007; 12(4): 148-150
Effect of vitamin A on bone metabolismCase reports
Vitamin A is a generic term for a large group of chemically related substances exhibiting retinoid activity. In the human organism, they participate in the regulation of many essential functions. The most important retinoid is apparently retinoic acid synthesized from vitamin A in essentially all cell types including osteoblasts, osteoclasts and chondrocytes. Through retinoic acid receptors, retinoids play a major role in regulating gene expression, inhibition of cell proliferation, differentiation and apoptosis. Lack of vitamin A leads to congenital malformations of the eye, heart, gonads and lungs. The short communication deals with the effects of vitamin A and its metabolites on bone metabolism and development of osteoporosis. The results of clinical studies concerning these issues are not always explicit. However, most of them suggest that administration of vitamin A contributes to osteoporosis, which is consistent with our fin dings. At present, the results of experimental studies designed to clarify the molecular basis for the effect of retinoic acid on the bone do not allow to provide comprehensive information about the involved mechanisms. In this respect, of particular interest is the recent finding mentioned in the text suggesting that retinoic acid may affect the cell metabolism in two completely different ways, either through the retinoic acid receptor or through the PPAR p/8 nuclear receptor. Activation of the RAR produces the arrest of cellular growth, apoptosis and signs of antitumour activity, whereas activation of the PPAR p/8 potentiates cell survival, proliferation and pro motes tumour growth.
Keywords: vitamin A, retinoids, nuclear receptors RAR a PPAR p/8, bone metabolism, osteoporosis
Published: December 11, 2007 Show citation
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