Osteoporose : uma análise ultraestrutural do tecido ósseo em camundongos C57 e apoeko ovariotectomizados
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Data
2014-09-26
Autores
Siqueira, Daniel de
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Universidade Federal do Espírito Santo
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It is currently observed an increase in the incidence of osteometabolic diseases, particularly osteoporosis. This disease is caused by an imbalance between bone formation and bone resorption, closely linked to aging. In osteoporosis, it is observed that the predominance of bone resorption leads to a lower bone mineral density (BMD). It is believed that decrease in BMD is the main risk factor for bone breaking observed in these patients. Although low BMD represents the main risk factor for osteoporosis, this disease is multifactorial. Another remarkable feature in osteoporosis is its prevalence in postmenopausal women. It is now known that estrogen is one of the major factors responsible for the formation of bone tissue and its mineralization. Therefore, its deficiency at menopause results in a higher incidence of the disease in this population. Nevertheless studies in humans have contributed immensely to the understanding of the disease, the limitations imposed by the techniques to be used prevents the investigation of some mechanisms associated with osteoporosis. To determine some intrinsic mechanisms of the disease, therefore, animal models that mimic the postmenopausal osteoporosis are commonly used. In this study, we used ovariectomized female mice (OVX) as a model for postmenopausal osteoporosis, aiming to study phenomena associated with the bone tissue ultrastructure under conditions that can be of great importance for the treatment of the disease. For this purpose, were used a combination of histological and biochemical analyses as well as electronic microscopy, besides the gold standard in the diagnosis of osteoporosis: Dual X-ray Absorptiometry (DXA). The drop in circulating estrogen led to profound changes in different markers of bone formation and bone resorption, decreased BMD, and the presence of microfractures in bone tissue. From this characterization, were conducted two parallel studies, despite complementary, on the role of vitamin K - molecule believed to be essential for bone mineralization - and apolipoprotein E, a molecule that is also associated to increased risk of osteoporosis. Results obtained throughout this study demonstrated that supplementation with vitamin K in OVX animals led to profund changes in the ultrastructure of bone tissue (determined by analysis of scanning electronic microscopy). However, supplementation with vitamin K did not lead to such deep changes in biomarkers of the disease. In contrast, the loss of ApoE in genetically modified animals (APOEKO) significantly changed several serum biomarkers for the diagnosis of osteoporosis and the ultrastructure of tissue in OVX mice. Taken together, our results indicate - through a combination of ultrastructural analyses on bone tissue and measurement of biomarkers - that vitamin K affects mainly microfractures in OVX mice while the absence of the ApoE gene led to a decrease in BMD. Therefore, even if the axis estrogen-ApoE-vitamin K is well defined in the context of the pathogenesis of osteoporosis, our results pointed to different effects of these molecules on bone metabolism.
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Apolipoproteína E