Abstract
It is well known that physical inactivity during space flight or prolonged bed rest causes rapid bone loss. Soy isoflavones (ISOs) and resveratrol (RES) have been reported to be useful to maintain a positive balance for bone turnover. Therefore, we examined the combined effects of ISO and RES on bone loss that was induced by hindlimb-unloading in mice. Female eight-week-old ddY mice were divided into the following six groups (n = 6–8 each): normally housed mice, loading mice, hindlimb-unloading (UL) mice fed a control diet, UL mice fed a 0.16% ISO conjugates, UL mice fed a 0.15% RES diet, and UL mice fed a 0.16% ISO and 0.15% RES diet. After three weeks, femoral bone mineral density was markedly decreased in unloading mice. The combination of ISO and RES prevented bone loss and especially maintained the trabecular bone mineral density more effectively compared with cortical bones. ISO and/or RES inhibited the increase in the RANKL/OPG expression ratio in bone marrow cells in UL mice. These results suggest that the combination of ISO and RES had a preventive effect against bone loss induced by hindlimb-unloading in mice. These osteoprotective effects of ISO and RES may result from the inhibition of bone resorption.
Highlights
Osteoporosis, a major health problem, is an age-related disease that is characterised by bone mineralisation and microstructural declension, which raises the risk for bone fracture
Our results showed that the decrease in bone mineral density (BMD) caused by unloading was significantly prevented by the decrease in total bone and trabecular bone BMDs caused by unloading was slightly the combination of 0.16% Isoflavone-supplemented diets (ISO) conjugates and 0.15% RES treatment (Figure 2A)
Several experimental studies demonstrated that ISO significantly inhibited a reduction of BMD, breaking strength, and bone quality in OVX rats [31,32]. These results suggest that the combination of ISO and RES prevent unloading-induced trabecular bone loss with consequent ameliorative effects on bone strength
Summary
Osteoporosis, a major health problem, is an age-related disease that is characterised by bone mineralisation and microstructural declension, which raises the risk for bone fracture. Bone mass is influenced by genetic and environmental factors, such as mechanical loading, lifestyle, and nutrition. Mechanical loading and nutrition appear to be critical for prevention of osteoporosis. It has been reported that the older people and patients without weight-bearing activity exhibit reduced mechanical loading because increased bed rest and decreased physical activity promote bone loss [3,4]. Spaceflight raises rapid bone loss, especially in astronauts who are exposed to long-duration spaceflight, who lose a presumed 1.0–1.6% of their bone mineral density (BMD) per month, which primarily arises in the cancellous compartments of the lower weight-bearing skeleton [5,6]
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