Abstract
BackgroundTeriparatide (TPTD) is a drug for osteoporosis that promotes bone formation and improves bone quality. However, the effects of TPTD on cortical bone are not well understood. Sweep imaging with Fourier transform (SWIFT) has been reported as a useful tool for evaluating bound water of cortical bone, but it has yet to be used to investigate the effects of TPTD on cortical bone. This study aimed to evaluate the consequences of the effect of TPTD on cortical bone formation using SWIFT.MethodsTwelve-week-old female Sprague-Dawley rats (n = 36) were reared after ovariectomy to create a postmenopausal osteoporosis model. They were divided into two groups: the TPTD and non-TPTD groups. Rats were euthanized at 4, 12, and 24 weeks after initiating TPTD treatment. Tibial bones were evaluated using magnetic resonance imaging (MRI) and bone histomorphometry. In MRI, proton density-weighted imaging (PDWI) and SWIFT imaging were performed. The signal-to-noise ratio (SNR) was calculated for each method. The same area evaluated by MRI was then used to calculate the bone formation rate by bone histomorphometry. Measurements were compared using the Mann-Whitney U-test, and a P-value of < 0.05 was considered significant.ResultsPDWI-SNR was not significantly different between the two groups at any time point (P = 0.589, 0.394, and 0.394 at 4, 12, and 24 weeks, respectively). Contrarily, SWIFT-SNR was significantly higher in the TPTD group than in the non-TPTD group at 4 weeks after initiating treatment, but it was not significantly different at 12 and 24 weeks (P = 0.009, 0.937, and 0.818 at 4, 12, and 24 weeks, respectively). The bone formation rate assessed by histomorphometry was significantly higher in the TPTD group than in the non-TPTD group at all timepoints (P < 0.05, all weeks). In particular, at 4 weeks, the bone formation rate was markedly higher in the TPTD group than in the non-TPTD group (P = 0.028, 1.98 ± 0.33 vs. 0.09 ± 0.05 μm3/μm2/day).ConclusionsSWIFT could detect increased signals of bound water, reflecting the effect of TPTD on the cortical bone. The signal detected by SWIFT reflects a marked increase in the cortical bone formation rate.
Highlights
Teriparatide (TPTD) is a drug for osteoporosis that promotes bone formation and improves bone qual‐ ity
Sweep imaging with Fourier transform (SWIFT) is a novel imaging method in magnetic resonance imaging (MRI) that can depict proton signals of bound water with very short T 2 relaxation times that cannot be measured by conventional MRI [10]
The results of this study showed that the volumetric BMD (vBMD) of the cortical bone did not differ at all weeks, the cortical bone width was higher in the TPTD group at all weeks, similar to previous reports [20]
Summary
Teriparatide (TPTD) is a drug for osteoporosis that promotes bone formation and improves bone qual‐ ity. This study aimed to evaluate the consequences of the effect of TPTD on cortical bone formation using SWIFT. Osteoporosis is defined as “a skeletal disorder characterized by compromised bone strength predisposing to an increased risk of fracture” [1]. Postmenopausal osteoporosis is the most common type of osteoporosis [3], and an increase of bone turnover, bone resorption exceeding bone formation, is associated with decreased BMD and bone quality, as well as an increased risk of fracture [4]. It is necessary to improve bone turnover to treat postmenopausal osteoporosis, and to this end, various therapeutic drugs have been developed. Teriparatide (TPTD) is a drug for the treatment of osteoporosis that promotes bone formation with intermittent administration [5]. The site and time at which osteogenesis occurs in the bone remain unclear
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