| Objective:In recent years, with the improvement of people's life quality and extended average life span, the rate of type 2 diabetes increased rapidly, which lead to increased osteoporosis. Postmenpausal women have high risk of osteoporosis. In china, 90.48% of over than 60 years old women have postmenopausal osteoporosis. Osteoporosis is characterized by low bone mass, increased fragility, decreased bone quality, and an increased fracture risk. Fracture is a serious complication of osteoporosis. Therefore, prevent the occurrence of osteoporotic fracture is the main purpose for osteoporosis treatment. Bone mineral density measured by Dual-energy X-ray absorptiometry(DEXA) is the gold standard for osteoporosis diagnose. However, bone mineral density only can reflect the amount of bone mineral concent, bone tissue and ultra-structure is more correlated with bone strength(bone quality) and racture. Both Osteopenia and bone structure alteration may affect bone biomechanics, which leads to decreased bone strength. Therefore, determination of the bone biomechanics marker is important for osteoporosis and bone strength. However, since it is difficult to determine the bone biomechanics index in vivo, bone mineral density measured by dual-energy X-ray absorptiometry is still considered to be an important method for clinical diagnosis and observation. The relationship between bone mineral density and bone biomechanics index still remains inconclusive. Reduced, unchanged or even increased bone density induced by type 2 diabetes have all been reported recently. In this study, we established the type 2 diabetic osteoporosis model in rats mimicking bone loss in postmenopausal and in type 2 diabetes, bone mineral density and biomechanics index at different times and different conditions will be discussed. The alteration of bone mineral density in type 2 diabetes will be investigated. Further, the value of bone mineral density in evaluation of bone fragility and prediction of fracture risk will also be clarified.Methods: 100 Wistar rats were randomly divided into four groups after fed normal feedstuff for 1 week: normal contorl(NC,N=24) group, normal ovariectomy(NOVX,N=26) group, diabetes contorl(DC,N=24) group, diabetes and ovariectomy(DOVX,N=26) group. Rats in NC group and NOVX group were fed with normal diet while DC group and DOVX group were fed with high-sugar-fat diet(mixed with 20% sugar, 2.5% cholesterin, 15% cooked lard) for 8 weeks, injectde T2DM were made by intraperitoneal injection of STZ(0.1mmol/L, prepared by citrate sodium, pH4.2, and 30mg/Kg) after 12 hours fasting. At the end of 9th weeks, rats with fasting blood glucose(FBG)≥7.8mmol/L and with insulin resistance were considered T2DM. Rats choosed for NOVX and DOVX group were ovariectomied under anesthesia 1 week later after T2DM model were done. This study takes 22 weeks. And all rats were allowed free access to food and water. At 0, 2, 4, 6, 8, 10, and 12 weeks after ovariectomy, body weight and fasting blood glucose were measured. my, bone mineral density of lumbar spine(3-6) and double femur were also measured by dual-energy X-ray absorptiometry by using small animals software at the same time points. At 0, 4, 8 and also 12 weeks, 3 rats chosen from each groups were killed and L3 and right femur were taken for biomechanical measurment. For the bone mineral density measurement: rats were anesthesised by intraperitoneal injection with 10% chloral hydrate and then lying under DEXA detector, limbs were fixed and make lumbar spine straight. Double femur maintained the plane state. Bone mineral density of lumbar spine(3-6) and double femur were measured. Biomechanics sample preparation: When rats were killed, right femur and lumbar spine (L3-L6 vertebral-continuous) were taken completely and muscles were removed. Samples were fixed with dental base acrylic resin powder and maximum stress and maximum compression strength were determined by the biomechanical testing machine, data were presented as mean±standard deviation and variance analysis or nonparametric test were used to test differences between groups by SPSS 11.5. p<0.05 was considered statistically significant.Results:1 Body weight and blood glucose at different times1.1 Body weightThe body weight of NOVX and NC group were increased, the NOVX group increased more due to ovariectomy. No change in body weight in DOVX group. The body weight of DC group was reduced because of high glucose.0 week: There are no difference found in body weight among NC, DC and DOVX groups(p>0.05). There no difference found in body weight between NC and NOVX groups(p>0.05). There were statistical differences found in body weight among NOVX group, DC group and DOVX group(p<0.05). 2 week: There were no statistical differences found in body weight among NC, DC and DOVX groups(p<0.05). Rats in NOVX group had significantly higher body weight than the other groups(p<0.05). 4 week: Rats in DC group had significantly lower body weight than those in NC and NOVX groups(p<0.05), while NOVX group had significantly higher body weights than other groups(p<0.05). 6 and 8 weeks: Our results had shown that there are differences between any two groups(p<0.05). The body weight of DC group was lowest while NOVX was highest. 10 week: The body weight in DC group was significantly lower than other groups(p<0.05), while NOVX group had significantly higher body weight than other groups(p<0.05). 12 week: It was found that rats in NOVX group had significantly higher body weight than other groups(p<0.05). There were significant differences between DC and NC groups(p<0.05).1.2 Fasting blood glucose0 week: The FBG of diabetic rats(DC,DOVX) was significantly higher than non-diabetic rats(NC,NOVX)(p<0.05). 2 week: The FBG of DC and DOVX groups was decreased. The FBG of rats in DC group was significantly higher than NC and NOVX groups(p<0.05). There were significant differences found in FBG levels between DOVX and NOVX groups(p<0.05). Rats in DC group had significantly higher FBG than DOVX group(p<0.05). There were no differences found in FBG between NC and NOVX groups(p>0.05). The FBG of DOVX seems higher than NC, but there were no statistical differences(p>0.05). 4 week: There no differences in FBG found in all groups(p>0.05). 6 week: The FBG of diabetic rats was significantly higher than non-diabetic rats(p<0.05). There were no differences found in FBG between NC and NOVX groups(P>0.05). Neither between DC and DOVX groups(p>0.05). 8 week: The FBG of DC and DOVX groups was significantly higher than that of NC and NOVX groups(p<0.05). There were no differences found in FBG between NC and NOVX(p>0.05), neither between rats in DC and DOVX groups(p>0.05). 10 week and 12 week: There were no differences found in FBG in all groups(p>0.05).1.3 Plasms insulin level0 week: Plasma insulin level was higher than in DOVX rat scompared with that in NC group(p<0.05). No differences found in insulin level in other groups(p>0.05). 2 week: It was found that DC group had significantly higher insulin level than NC, NOVX and DOVX groups(p<0.05). NOVX group animals had significantly lower insulin level than other groups(p<0.05). There were no differences found in insulin between NC and DOVX group(p>0.05). 4 week: Rats in DC group had significantly higher insulin than NC, NOVX and DOVX groups(p<0.05). No differences found between other two groups(p>0.05). 6 week: There were on differences found in insulin among all groups(p>0.05). 8 week: It was found that DC and DOVX group had significantly higher insulin levels than NC and NOVX groups(p<0.05). 10 week and 12 week: There were on differences found in insulin among all groups(p>0.05).2 Bone mineral density and biomechanics index2.1 Bone mineral density2.1.1 The BMD of the lumbar spine0 week and 2 week: There are no significantly difference found in the BMD of the lumbar spine among NC, NOVX, DC and DOVX groups(p>0.05). 4 week: BMD in NOVX group and DOVX group were significantly deceased than NC group and DC group(p<0.01), but there are no significantly difference found in NOVX group and DOVX group, NC group and DC group(p>0.05). 6 week: BMD in NOVX,DOVX and DC group were significantly lower than that of NC group(p<0.01), there are no significantly difference found in NOVX group, DOVX group and DC group(p>0.05). 8 week: NOVX group, DOVX group and DC group had significantly deceased BMD than NC group(p<0.01), while BMD in NOVX and DOVX group were significantly lower than DC group(p<0.01), there are no significantly difference found in NOVX group and DOVX group(p>0.05). 10 week: Rats in NOVX group, DOVX group and DC group has significantly deceased BMD than NC group(p<0.01), NOVX group and DOVX group were significantly deceased than DC group(p<0.01), there are no significantly difference found between NOVX group and DOVX group(p>0.05). 12 week: NOVX group,DOVX group and DC group were significantly lower than NC group(p<0.01), DOVX group was significantly lower, there are no significantly difference found in NOVX group, DC group and DOVX group(p>0.05).2.1.2 The BMD of femurThere were no significant diference in femur BMD at any time point and between any groups(p>0.05).2.2 The biomechanics index2.2.1 Maximum compressive force of the lumbar spine4 week 8 week: NOVX group and DOVX group were significantly deceased than NC group(p<0.01), while there are no significantly difference found in NOVX group and DOVX group,DC group and NC group(p>0.05).12 week: NOVX group,DOVX group and DC group were significantly lower than NC group(p<0.01), DC group were significantly deceased than NC group(p<0.01), NOVX group and DOVX group were significantly deceased than DC group(p<0.01). There are no significantly difference found in NOVX group and DOVX group(p>0.05). 2.2.2 Maximum stress of right femurThere were no significant difference found in maximum stress of right femur at any time point and between any groups(p>0.05).3 Results of correlate analysis3.1 The correlation between BMD and biomechanics index.There were positive correlation between the BMD and maximum compressive force of the lumbar spine in four groups(p<0.01): NC group(r=0.737,p=0.002), NOVX group (r=0.784,p=0.001), DC group (r=0.691,p=0.004), DOVX group (r=0.653,p=0.008). No correlation was found between the BMD and maximum stress force of the right femur (p>0.05);NC group (r=0.05,p=0.86), NOVX group (r=0.273,p=0.477), DC group (r=-0.012,p=0.968), DOVX group (r=0.156,p=0.667).3.2 Correlation between fasting blood glucose,biomechanics index and bone mineral density.Fasting blood glucose was not correlated with bone mineral density of lumbar: NC group (r=0.115,p=0.293) (p>0.05), NOVX group (r=0.18,p=0.087) (p>0.05), DC group (r=0.204,p=0.073) (p>0.05), DOVX group (r=0.059,p=0.569) (p>0.05).Fasting blood glucose also had no correlation with bone mineral density of right femur:NC group (r=-0.115,p=0.314) (p>0.05),NOVX group (r=-0.062,p=0.561) (p>0.05), DC group(r=-0.103,p=0.374) (p>0.05), DOVX group(r=0.007,p=0.942) (p>0.05).There were no correlations between fasting blood glucose and bone mineral density of left femur: NC group(r=-0.037,p=0.752)(p>0.05), NOVX group (r=-0.035,p=0.752)(p>0.05), DC group (r=-0.065,p=0.598)(p>0.05), DOVX group (r=0.043,p=0.695)(p>0.05).There were no correlation between the maximum compressive force of the lumbar spine and glucose: NC group (r=-0.041,p=0.884)(p>0.05), NOVX group (r=-0.115,p=0.683)(p>0.05), DC group (r=-0.015,p=0.956)(p>0.05), DOVX group (r=0.374,p=0.208)(p>0.05). There were also no correlation between the maximum stress of the right femur and glucose: NC group (r=0.153,p=0.586)(p>0.05), NOVX group (r=0.177,p=0.648)(p>0.05), DC group (r=0.019,p=0.952)(p>0.05), DOVX group (r=0.445,p=0.198)(p>0.05).Conclusions:1 Type 2 diabetes and the loss of ovary function may induce bone loss, resulting in decreased bone density, mainly in vertebral.2 With the bone mineral density decreasing, biomechanics index was also decreased in type 2 diabetes osteoporosis process. A positive correlation was found between bone mineral density and maximum compressive force of the lumbar spine. Decreased bone mass is the part of the reason for bone strength reduction, and bone mineral density may reflect changes in bone strength.3 No correlation was found between fasting blood glucose and bone mineral density of lumbar spine, and even maximum compressive force of lumbar spine.4 No correlation was found between maximum stress and bone mineral density of right femur.5 Fasting blood glucose had no correlation with bone mineral density of dural femur and maximum stress of right femur.
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