Subregion analysis of the rat femur: a sensitive indicator of changes in bone density following treatment with thyroid hormone or bisphosphonates

The preventive effects of pulsed electromagnetic fields on diabetic bone loss in streptozotocin-treated rats

The present study was the first report demonstrating that pulsed electromagnetic field (PEMF) could partially prevent bone strength and architecture deterioration and improve the impaired bone formation in streptozotocin-induced diabetic rats. The findings indicated that PEMF might become a potential additive method for inhibiting diabetic osteopenia or osteoporosis.

INTRODUCTION

Diabetes mellitus (DM) can cause various musculoskeletal abnormalities. Optimal therapeutic methods for diabetic bone complication are still lacking. It is essential to develop more effective and safe therapeutic methods for diabetic bone disorders. Pulsed electromagnetic field (PEMF) as an alternative noninvasive method has proven to be effective for treating fracture healing and osteoporosis in non-diabetic conditions. However, the issue about the therapeutic effects of PEMF on diabetic bone complication has not been previously investigated.

METHODS

We herein systematically evaluated the preventive effects of PEMF on diabetic bone loss in streptozotocin-treated rats. Two similar experiments were conducted. In each experiment, 16 diabetic and eight non-diabetic rats were equally assigned to the control, DM, and DM + PEMF group. DM + PEMF group was subjected to daily 8-h PEMF exposure for 8 weeks.

RESULTS

In experiment 1, three-point bending test suggested that PEMF improved the biomechanical quality of diabetic bone tissues, evidenced by increased maximum load, stiffness, and energy absorption. Microcomputed tomography analysis demonstrated that DM-induced bone architecture deterioration was partially reversed by PEMF, evidenced by increased Tb.N, Tb.Th, BV/TV, and Conn.D and reduced Tb.Sp and SMI. Serum OC analysis indicated that PEMF partially prevented DM-induced decrease in bone formation. In experiment 2, no significant difference in the bone resorption marker TRACP5b was observed. These biochemical findings were further supported by the dynamic bone histomorphometric parameters BFR/BS and Oc.N/BS.

CONCLUSIONS

The results demonstrated that PEMF could partially prevent DM-induced bone strength and architecture deterioration and improve the impaired bone formation. PEMF might become a potential additive method for inhibiting diabetic osteoporosis.

Validation of peripheral dual-energy X-ray absorptiometry for the measurement of bone mineral in intact and excised long bones of rats

We evaluated the precision and accuracy of peripheral dual-energy X-ray absorptiometry (DXA) for the measurement of bone mineral density (BMD) and bone mineral content (BMC) in intact and excised femurs and tibias from rats. Thirty-one Sprague-Dawley rats (18F/13M; 114-360 g) were used in the study. Precision and accuracy were determined in 23 rats and prediction equations were evaluated in an independent sample of 8 animals. Precision was determined by measuring the right hindquarter three times with repositioning between scans. The femur and tibia were then excised, cleaned, and scanned in triplicate, with repositioning. CVs ranged from 0.66 to 2.24%. Accuracy of BMC was determined by comparison to bone ash values. BMC values for the intact and excised femur significantly overestimated bone ash (p < 0.001) by 33% and 5.5%, respectively. BMC for the intact tibia overestimated ash by 37% (p < 0.001), whereas BMC for the excised tibia underestimated ash by 1% (p < 0.05). However, BMC and bone ash were highly related for both bones, whether BMC was measured in the intact animal or after excision (r2 > 0.99). Cross-validation of prediction equations in an independent sample showed that there were no significant differences between predicted ash (based on BMC from DXA) and measured bone ash. These results suggest the peripheral DXA is a useful tool for measuring intact and excised rat leg bones.

No adverse effects of clodronate on fracture healing in rats

Clodronate was administered daily 28 days before and after an experimental tibial fracture in 35 male rats, and the effect on fracture healing and posttraumatic bone loss was studied. 5 groups were tested. The clodronate/clodronate group received clodronate in daily doses of 10 mg/kg body weight for 28 days before being subjected to a standardized fracture of the right tibia, and during the fracture healing period of 28 days. The clodronate/saline group received clodronate before fracture and saline during the healing period. The saline/clodronate group received saline before and clodronate after fracture. The saline/saline group received saline only, while the control group served as unfractured, untreated controls. After 28 days of fracture healing, the tibias were evaluated with dual energy x-ray absorptiometry, and tested mechanically in a 3-point ventral bending test. Bone mineral content and bone mineral density were approximately 30% higher in the groups receiving clodronate during the experiment, compared to the untreated groups. The weight and cross-sectional area of the fracture callus were equal in all groups. Whether clodronate was administered before the fracture, after the fracture or both, did not affect the bone mineral. Ultimate bending moment, energy absorption, stiffness and deflection were not significantly different between the groups. Our findings suggest that clodronate increases bone mineral both when given before and after a tibial shaft fracture, without affecting fracture healing at 28 days.

Effects of thyroid hormone administration and estrogen deficiency on bone mass of female rats

To investigate the effects of thyroxine (T4) administration on bone mass, five 81-day-old female rats were treated with T4 (25 microg of T4/100 g of body weight [bw]/day), and bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DXA) 28 days later. The BMD values for the total skeleton, femoral, and tibial subsegments were lower than in controls (p < or = 0.05). The lumbar spine (L2-L5) was not significantly affected by T4 treatment. Next, thirty-seven 211 +/- 1.5 (mean +/- SEM)-day-old female rats were divided into six groups as follows: (1) control; (2) ovariectomized (OVX); (3) 1xT4 (approximately 1.0 microg of T4/100 g of bw/day; approximately physiological replacement dose); (4) OVX + 1xT4; (5) 2xT4 (approximately 2.0 microg of T4/100 g of bw/day); (6) OVX + 2xT4. DXA scans were performed at days 0 and 85. Control rats showed a generalized BMD increase, as opposed to a decrease in OVX rats. The trabecular bone volume of the fifth lumbar vertebra was also lower in OVX rats than in controls (p < 0.05). The 1xT4 treatment had no effect on BMD of intact rats, while treatment with 2xT4 impaired the expected BMD increase. Unexpectedly, the OVX + 1xT4 group presented a generalized BMD increase that was significant for the total skeleton, L2-L5, and femoral subsegments (p < 0.05), comparable to controls. Treating OVX animals with 2xT4 did not potentiate the osteopenic effects of estrogen deficiency, nor did it reverse the osteopenic effects of OVX. In conclusion, treatment with high doses of T4 caused BMD to decrease substantially, particularly at the femur, whereas near physiological doses of T4 prevented bone loss associated with OVX, and regardless of bone type (trabecular or cortical), the skeleton site seems to be a more important determinant of the effects of thyroid hormone on bone mass.

Increase in femoral bone mass by ipriflavone alone and in combination with 1 alpha-hydroxyvitamin D3 in growing rats with skeletal unloading

We assessed the possibility that ipriflavone treatment might result in bone restoration in immobilized rats. We also investigated the effect of combined treatment with ipriflavone and vitamin D3 on the bone. Male Sprague-Dawley rats, 6 weeks of age, were subjected to unilateral sciatic neurectomy. Three weeks after the operation, ipriflavone (100 mg/kg), 1 alpha-hydroxyvitamin D3 [1 alpha (OH)D3, 25 ng/kg], or both ipriflavone and 1 alpha (OH)D3 were orally administered every day for 12 or 24 weeks. After 12 weeks of treatment, only the group receiving combined treatment with ipriflavone and 1 alpha (OH)D3 showed increases in total femur calcium content (+16.4%, compared with the control). After 24 weeks, both animals treated with ipriflavone alone and those that had received the combination of ipriflavone and 1 alpha (OH)D3 showed significant increases in femur calcium content (+18.0% and +23.8%, respectively). In these treatment groups, X-ray analysis revealed an increase in bone mineral density over the entire length of the femur, and an increase in cortical diameter at the midshaft without affecting medullary width. Administration of 1 alpha (OH)D3 (25 ng/kg) alone had no effect. Body weight, femur length, and serum markers of calcium and bone metabolism were not affected in any group. We evaluated the relationship between ipriflavone and vitamin D3 in bone cells in a culture system using rat bone marrow stromal cells in which the cells subsequently form mineralized bone-like tissue. Continuous treatment with ipriflavone (10(-5) M) for 21 days resulted in an increase in osteocalcin secretion, and enhanced its response to 1 alpha, 25-dihydroxyvitamin D3 (10(-11) M-10(-8 M)). These findings indicate that ipriflavone treatment increases the femoral bone mass in immobilized rats. In addition, a low dose of 1 alpha (OH)D3, which did not induce hypercalcemia, in combination with ipriflavone, augmented the stimulatory effect of ipriflavone alone on the bone mass, possibly due to a direct effect of each agent on osteoblastic cells.

Bone mineral density in feline mucopolysaccharidosis VI measured using dual-energy X-ray absorptiometry

Dual-energy X-ray absorptiometry (DXA) was used to determine the in vivo bone mineral density (BMD) and bone mineral content (BMC) of lumbar vertebrae in six cats affected with the inherited lysosomal storage disease mucopolysaccharidosis VI (MPS VI). DXA was also performed on MPS cats that had a bone marrow transplant (BMT) and total body irradiation (TBI) (MPS + BMT; n = 7), normal cats that had a bone marrow transplant, and TBI (control + BMT; n = 8) and normal cats (control; n = 14). Following euthanasia, one of the lumbar vertebrae that had been scanned (L5) was harvested and bone volume (BV/TV%) was determined by histomorphometry. The in vivo BMD and BMD measurements were compared with the BV/TV%. There was a greater BMD and BMC in the MPS + BMT cats compared with the MPS cats but the difference was not statistically significant. However, there was a greater BV/TV% in the MPS + BMT cats compared with the MPS cats and the difference was significant (P = 0.0152). Correlation between the noninvasive in vivo DXA measurements of BMD and BMC and the BV/TV% was significant (r2 = 0.767, P < 0.0001; r2 = 0.504, P < 0.0001). Noninvasive in vivo DXA was a rapid and precise method for measuring the lumbar BMD and BMC in cats and it correlated well with histomorphometric determination of bone mass. Further, the response of inherited storage diseases such as MPS VI to therapy, such as BMT, could be monitored in a longitudinal fashion using DXA.

Treatment with growth hormone and IGF-I in growing rats increases bone mineral content but not bone mineral density

Human growth hormone (hGH) and insulin-like growth factor I (IGF-I) both stimulate bone formation and have been proposed as therapeutic agents for osteoporosis. We examined the effect of hGH and IGF-I alone and in combination on bone size, bone mineral content (BMC), and bone mineral density (BMD) in 10- to 12-week old growing female Sprague-Dawley rats. Sixty rats were assigned to treatment with either placebo, hGH, IGF-I, or both for 4 weeks. After 4 weeks, the right femurs and tibias were excised, and ex vivo BMC and the area of the tibia and femur were measured by dual-energy X-ray absorptiometry (DXA); volume of these bones was measured by Archimedes' principle. In addition, proximal tibial bone density was measured directly by peripheral quantitative computerized tomography (pQCT). Bone length, area, and volume in all treated groups was greater than controls. Areal bone density by DXA (BMC/area) was higher in IGF-treated rats and lower in GH-treated rats than in controls. Volumetric bone density (BMC/volume) was lower in treated groups than in controls. Measurements by pQCT confirmed that true bone density was lower in all treated groups than in controls. We conclude that treatment with hGH or IGF-I increased bone size and mineral content but decreased bone density in growing rats. Because areal correction of BMC did not adequately correct for the increased bone volume in IGF-treated rats, results of areal bone density by DXA should be interpreted with caution when treatment causes a disparity in bone size between groups.

Differentiating between orchiectomized rats and controls using measurements of trabecular bone density: a comparison among DXA, histomorphometry, and peripheral quantitative computerized tomography

In studies of rat bone metabolism, trabecular bone density should be measured. Three established methods of measuring trabecular bone include trabecular bone volume by histomorphometry (BV/TV%), trabecular bone density by peripheral quantitative computerized tomography (pQCT), and areal bone density of trabecular-rich regions by dual x-ray absorptiometry (DXA). We compared the ability of these three methods to discriminate between orchiectomized (orchidectomized) rats and controls. Sixteen male Sprague-Dawley rats (400-425 g) were orchiectomized, and 16 others were controls. In vivo spine bone mineral density (BMD) was measured at the beginning of the study and again after 11 weeks. Rats were sacrificed, and ex vivo BMDs of the right femur and tibia were measured by DXA, followed by trabecular bone density of the right proximal tibia by pQCT. BT/TV% of the left proximal tibia was measured by histomorphometry. Differences between groups were detected by all three methods, but both the magnitude of the difference between groups and the variance of the measurements was much greater for histomorphometry and pQCT than for DXA. Consequently, the statistical significance for the difference between groups was comparable for all three methods. Of the sites measured with DXA, the proximal tibia had the greatest statistical significance for the difference between groups. In summary, all three methods can demonstrate the effect of orchiectomy on trabecular bone. The large differences between groups seen by histomorphometry are also seen by pQCT but not by DXA. We conclude that trabecular bone density by pQCT may be a reasonable surrogate for measurements by histomorphometry.