Once-weekly teriparatide reduces serum sclerostin levels in postmenopausal women with osteoprosis

Journal of Orthopaedic Science 24 (2019) 532e538

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Original Article

Once-weekly teriparatide reduces serum sclerostin levels in postmenopausal women with osteoprosis Terumasa Ikeda a, *, Hiroshi Kaji b, Yukinori Tamura b, Masao Akagi a a b

Division of Orthopedic Surgery, Kindai University Faculty of Medicine, Ohnohigashi, Osakasayama 589-8511, Japan Department of Physiology and Regenerative Medicine, Kindai University Faculty of Medicine

a r t i c l e i n f o

a b s t r a c t

Article history: Received 5 March 2018 Received in revised form 24 October 2018 Accepted 28 October 2018 Available online 17 December 2018

Once-weekly teriparatide treatment is widely used in the treatment of osteoporosis in Japan but the mechanisms causing the increase in bone mineral density (BMD) of the lumbar spine remain unknown. Methods: This prospective study examined the effects of once-weekly teriparatide treatment on the serum levels of sclerostin, osteocalcin, and bone formation markers as well as BMD of the lumbar spine and femoral neck in 32 postmenopausal women with osteoporosis. Results: The mean age of subjects was 76.3 ± 7.0 years old. Teriparatide significantly reduced serum sclerostin levels at 12 and 18 months in postmenopausal women with osteoporosis, and significantly increased serum osteocalcin levels at 3,12 and 18 months and PINP levels at 1 and 3 months, respectively. Teriparatide treatment significantly increased BMD of the lumbar spine at 6, 12, and 18 months, but did not affect BMD of the femoral neck. Examination of the relationships between percent changes in bone metabolic indices and BMD of the lumbar spine during the teriparatide treatment showed serum sclerostin changes at 3 months were negatively correlated with BMD changes of the lumbar spine at 6, 12, and 18 months. Serum osteocalcin changes were not correlated with BMD changes in the lumbar spine at 12 months. Conclusions: The present study showed that once-weekly teriparatide treatment reduced serum sclerostin levels in postmenopausal women with osteoporosis. The effects of teriparatide on sclerostin may be associated with the response of the BMD of the lumbar spine. © 2018 Published by Elsevier B.V. on behalf of The Japanese Orthopaedic Association.

1. Introduction Osteoporosis is a skeletal disease that is characterized by compromised bone strength and, as a consequence, susceptibility to fractures. The significance of osteoporosis has been increasing due to rapid elevations in the number of elderly individuals. Bone remodeling is maintained by osteoclastic bone resorption followed by osteoblastic bone formation. Recent evidence has suggested that osteocytes abundantly embedded in the bone matrix participate in bone formation and resorption [1]. In postmenopausal women with osteoporosis, a reduced bone mass and structure have been attributed to an imbalance in the bone remodeling process due to insufficient bone formation after bone resorption. Although numerous bone resorption inhibitors, such as bisphosphonates, selective estrogen receptor modulators, and anti-receptor activator

* Corresponding author. Division of Orthopedic Surgery, Kinki University Faculty of Medicine, 377-2 Ohnohigashi, Osakasayama 589-8511, Japan. Fax: þ72 366-0206. E-mail address: [email protected] (T. Ikeda).

nuclear factor kB ligand (RANKL) monoclonal antibodies, have been effectively used in the treatment of postmenopausal osteoporosis, and bone formation-stimulating agents such as teriparatide have been employed in the treatment of patients with severe osteoporosis or low turnover osteoporosis. Intermittent parathyroid hormone (PTH) treatment has been shown to strongly enhance osteoblastic bone formation, resulting in increased bone mineral density (BMD) and reduction in the risk of fractures in humans and animals; however, continuous administration or excessive endogenous secretion of PTH, such as primary hyperparathyroidism, causes osteopenia [2]. Teriparatide, PTH(1e34), exerts osteoblastic bone anabolic actions both dependently and independently of bone resorption, and the daily intermittent administration of teriparatide at a dose of 20 mg is effective in the treatment of patients with osteoporosis [2]. Daily teriparatide treatment induces increased BMD and reduction in the risk of fractures in patients with osteoporosis [2]. On the other hand, onceweekly teriparatide was shown to be effective for BMD of the lumbar spine and vertebral fractures in patients with postmenopausal osteoporosis [3,4]. A recent study suggested that once-

https://doi.org/10.1016/j.jos.2018.10.028 0949-2658/© 2018 Published by Elsevier B.V. on behalf of The Japanese Orthopaedic Association.

T. Ikeda et al. / Journal of Orthopaedic Science 24 (2019) 532e538

weekly teriparatide reduces renal phosphate reabsorption and serum phosphate levels, which may be associated with increased BMD of the lumbar spine [5]. Although a once-weekly teriparatide treatment is widely used in the treatment of osteoporotic patients in Japan for its efficacy in reducing the risk of vertebral fractures, previous studies suggested that its effects on bone formation are weaker than those of daily teriparatide [3,4]. The mechanisms by which a once-weekly teriparatide treatment increases BMD of the lumbar spine and reduces the risk of vertebral fractures are unknown. The bone anabolic action of PTH may be partly mediated by local growth factors such as insulin-like growth factor-1 and fibroblast growth factor-2, transcriptional regulators including Runx2 and CREB, an enhancement in early stage osteoblastic differentiation, and the anti-apoptotic effects of osteoblasts [6]. Recent evidence indicated the involvement of canonical Wnt-b-catenin signaling in the enhancement of PTH in osteoblastic bone formation [7]. Guo et al. reported that the inhibition of canonical Wnt-b-catenin signaling blunted PTH-induced bone formation in mice [8]. Moreover, a low-density lipoprotein-related protein (LRP) 6 deficiency in osteoblasts blunted bone formation enhanced by PTH in mice [9]. However, the mechanisms by which PTH stimulates bone formation are unclear. Recent studies indicated that osteocytes are the target of PTH actions in bone cells [10,11]. Osteocytes are an important type of cells that produce sclerostin and osteocalcin [1]. Sclerostin is encoded by the Sost gene, and Sost-deficient genetic diseases such as sclerosteosis and Van Buchem disease as well as inhibition of sclerostin by monoclonal antibodies exhibit enhanced bone formation and subsequent BMD increases [1]. Sclerostin suppresses bone formation by antagonizing canonical Wnt-b-catenin signaling through the binding inhibition of LRP5 and 6 in osteoblasts [1]. Numerous studies have suggested that PTH signaling suppresses the expression and serum levels of sclerostin [10,11]. Although the long-term effects of a daily intermittent teriparatide treatment on serum sclerostin were negligible in postmenopausal women [12,13], the long-term effects of once-weekly teriparatide on serum sclerostin levels have not yet been reported. The present study, we prospectively investigated the effects of once-weekly teriparatide on serum levels of sclerostin and osteocalcin as well as bone formation markers and BMD of the lumbar spine and femoral neck in postmenopausal women with osteoporosis for 18 months.

533

2. Methods 2.1. Patients Subjects were 43 Japanese postmenopausal women with osteoporosis who visited Kindai University Hospital for the assessment of osteoporosis and provided informed consent for once-weekly teriparatide treatment and (Fig. 1). Eleven subjects dropped out because of adverse events (nausea, headache, general malaise, abdominal discomfort and vomiting) or patient circumstances (moving) within 1 month, so that 32 subjects completed the study for 1 year. Background data of the 32 subjects are shown in Table 1. Finally, 31 subjects completed the study for 18 months after the treatment was discontinued in one subject after 1 year. Eighteen subjects had previously suffered vertebral fragility fractures. No patients had been pretreated with any drugs for osteoporosis. No patients had systemic complications or any systemic disease that may affect serum sclerostin levels. The mean age of patients was 76.3 years. Subjects were treated with weekly subcutaneous injections of 56.5 mg teriparatide (Asahi Kasei Pharma Corporation, Tokyo, Japan) for 18 months. No untreated control group was included in this study for ethical considerations. Patients with diabetes, rheumatoid arthritis, respiratory, endocrinological, and other diseases, and drug use that may affect bone metabolism were excluded. No subjects were treated with bisphosphonates before the study, or calcium and/or vitamin D supplements during the study. Subjects with diminishing activities of daily living were also excluded based on medical reviews and physical examinations. Osteoporosis is diagnosed as BMD in less than 70% of the young adult mean (YAM) Japanese population and the presence of fragility fractures and BMD in less than 80% of the YAM population. The BMD of 10 subjects was greater than -2.5 SD in the lumbar spine and femoral neck. The study protocol was approved by the Institutional Review Board of Kindai University Faculty of Medicine. This study was registered with UMIN Clinical Research Registration (UMIN 000032090). 2.2. Measurement of BMD BMD values of the lumbar spine at L1-4 and femoral neck were measured at baseline and at 6, 12, and 18 months with dual-energy X-ray absorptiometry (DXA; DERPYH, Hologic Inc.; Waltham, MA, USA). BMD was automatically calculated from the bone area (cm2)

Obtained informed consent N= 43

Adverse events

N=8

ConƟnuaƟon judged as impossible due to paƟent circumstances (moving)

N=3

Completed study N=32 (1 year) DisconƟnued N=1 (1 year) Completed study N=31 (18 months) Fig. 1. Trial profile.

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T. Ikeda et al. / Journal of Orthopaedic Science 24 (2019) 532e538

2.4. Statistical analysis

Table 1 Baseline characteristics of teriparatide-treated patients. Patients (n) Age (years) BMD （L1-4) (g/cm2) T-score (L1-4) BMD (FN) (g/cm2) T-score (FN) Osteocalcin (ng/ml) Sclerostin(pmol/l) P1NP (mg/l) TRAP (ml/dl) Serum calcium (mg/dl) Serum phosphorus (mg/dl)

32 76.3 ± 7.0 0.715 ± 0.170 2.7 ± 1.4 0.509 ± 0.11 2.7 ± 0.8 11.2 ± 10.0 51.0 ± 24.4 77.3 ± 46.6 576.5 ± 226.1 9.3 ± 0.6 3.9 ± 1.4

Data are presented as means ± SD. L1-4: Lumbar spine, FN: Femoral neck.

Statistical analyses of data were performed with Stat Flex Ver.6 (Artech Co., Ltd., Osaka, Japan). Friedman's test was used to compare differences between each point. Then, each point value was compared with the value before the treatment in Figs. 2e4 using Dunnett's test. Results are presented as the mean ± SE, and p < 0.05 was considered to indicate a significant difference. BMD, PINP, sclerostin, and osteocalcin levels were expressed as percent changes from baseline values. Simple or multiple regression analyses were used to assess the relationships between study parameters, and then Spearman's correlation coefficient was calculated. 3. Results 3.1. Baseline characteristics

and bone mineral content (BMC) (g), and expressed absolutely in g/cm2. The coefficients of variation of measurements of the lumbar spine and femoral neck were 0.9 and 1.7%, respectively, as calculated using the healthy volunteers.

All subjects were diagnosed with osteoporosis based on the criteria described in the Methods. The mean age of the subjects was 76.3 ± 7.0 years old (Table 1). Neither fractures nor hypercalcemia were observed in the subjects during the teriparatide treatment for 18 months.

2.3. Biochemical measurement

3.2. Effects of once-weekly teriparatide on bone metabolic indices

Blood samples were collected in the morning after overnight fasting before each teriparatide administration at 0, 3, 6, 12, and 18 months. Serum samples were promptly separated and stored at -80  C until the time of assays. Measurements of serum procollagen type I N-terminal propeptide (PINP) were performed using bone radioimmunoassays (SRL, Tokyo, Japan). Serum sclerostin concentrations were measured using a human sclerostin ELISA kit (Biomedica Medinzinprodukte GmbH & Co KG, Vienna, Austria) [14]. The mean reference value and 95% confidence interval of serum sclerostin levels were 61.95 and 69.98e63.91 pmol/l), respectively, in healthy postmenopausal women (aged 70e79 years), as previously reported [15]. The detection limit of the ELISA kit was 3.2 pmol/l (0.073 ng/ml), and intra-assay and inter-assay variabilities were 7% and 8%, respectively. The measurement of serum osteocalcin concentrations was performed using a BGP immunoradiometric assay (IRMA) LSI M kit (LSI Medience Corporation, Tokyo, Japan) [16]. The detection limit of this kit was 1.0 ng/ml, and intra-assay and inter-assay variabilities were 10% and 13.5%, respectively.

The effects of the once-weekly teriparatide treatment for 18 months on serum sclerostin levels were examined in postmenopausal women with osteoporosis. Once-weekly teriparatide treatment significantly reduced the serum levels of sclerostin at 12 and 18 months as shown in Fig. 2. Longitudinal changes in the serum levels of osteocalcin and PINP for 18 months were then examined in postmenopausal women with osteoporosis treated with teriparatide. As shown in Fig. 3A, teriparatide increased the serum levels of osteocalcin over 18 months, and elevations in osteocalcin levels appeared to be greater as the duration of the teriparatide treatment increased. Moreover, the teriparatide treatment significantly increased the serum levels of PINP, a bone formation marker, at 1 and 3 months, but not at 6, 12, or 18 months (Fig. 3B).

15 Change from baseline (%)

10 5

3.3. Effects of once-weekly teriparatide on BMD of the lumbar spine and femoral neck We examined the effects of the once-weekly teriparatide treatment on BMD of the lumbar spine and femoral neck in postmenopausal women with osteoporosis for 18 months. As shown in Fig. 4, the once-weekly teriparatide treatment significantly increased BMD of the lumbar spine at 6, 12, and 18 months, but did not affect BMD of the femoral neck. 3.4. Relationships between bone metabolic indices and BMD at the lumbar spine during the teriparatide treatment

0 -5

*

-10 -15 -20

*

-25 -30 -35 0M

1M

3M

6M

12M

18M

Fig. 2. Effects of teriparatide on serum sclerostin levels in postmenopausal women with osteoporosis. Sclerostin values (% of baseline) were followed for the indicated times in patients treated with teriparatide. Data are presented as means ± SE. *p < 0.05.

The relationship between percent changes in bone metabolic indices and BMD of the lumbar spine during the teriparatide treatment was analyzed using a simple regression analysis. As shown in Table 2, serum sclerostin changes at 3 months were negatively correlated with BMD changes in the lumbar spine at 6, 12, and 18 months, whereas serum PINP changes were not correlated with BMD changes in the lumbar spine at 6, 12, or 18 months. Moreover, serum sclerostin changes at 3 months were negatively correlated with BMD changes in the lumbar spine at 6 and 18 months, when age, BMD of the lumbar spine before treatment, and previous vertebral fragility fractures were adjusted in multiple regression analysis (Table 3). Serum sclerostin levels before

T. Ikeda et al. / Journal of Orthopaedic Science 24 (2019) 532e538

Osteocalcin 200 180 160 140 120 100 80 60 40 20 0

P1NP

B * *

*

90

Change from baseline (%)

Change from baseline (%)

A

535

*

80 70

*

60 50 40 30

20 10 0

0M

1M

3M

6M

12M

18M

0M

1M

3M

6M

12M

18M

Fig. 3. Effects of teriparatide on serum osteocalcin and PINP levels in postmenopausal women with osteoporosis. Osteocalcin values (a) and PINP values (b) (% of baseline) were followed for the indicated times in patients treated with teriparatide. Data are presented as means ± SE. *p < 0.05.

B

9

Change from baseline (%)

8

*

Lumbar spine

7

*

6 5 4 *

3 2 1 0

9 8

Change from baseline (%)

A

Femora neck

7 6

5 4 3 2 1 0

0M

6M

12M

18M

0M

6m

12M

18M

Fig. 4. Effects of teriparatide on BMD of the lumbar spine and femoral neck in postmenopausal women with osteoporosis. BMD values of the lumbar spine (a) and femoral neck (b) (% of baseline) were followed for the indicated times in patients treated with teriparatide. Data are presented as means ± SE. *p < 0.05.

treatment were not significantly related to BMD or BMD changes in the lumbar spine at 6, 12 and 18 months (correlation coefficient, r; sclerostin vs BMD of the lumbar spine: 0 month r ¼ 0.109, p ¼ 0.55, 6 month r ¼ 0.162, p ¼ 0.47, 12 month r ¼ 0.038, p ¼ 0.98, 18 month r ¼ 0.348, p ¼ 0.26; sclerostin vs BMD changes in the lumbar spine: 6 month r ¼ 0.167, p ¼ 0.76, 12 month r ¼ 0.195, p ¼ 0.71, 18 month r ¼ 0.294, p ¼ 0.53). However, serum sclerostin levels before treatment were significantly related to BMD changes in the femoral neck at 12 and 18 months (sclerostin vs BMD at the femoral neck: 0 month r ¼ 0.068, p ¼ 0.68, 6 month r ¼ 0.067, p ¼ 0.83, 12 month r ¼ 0.013, p ¼ 0.66, 18 month r ¼ 0.241 p ¼ 0.65; sclerostin vs BMD changes in the femoral neck: 6 month r ¼ 0.209, p ¼ 0.57, 12 month r ¼ 0.563, p ¼ 0.01 18 month r ¼ 0.570 p ¼ 0.03). Serum osteocalcin changes was not correlated with BMD changes in the lumbar spine at 6, 12, or 18 months. The relationships between the percent changes in serum sclerostin and PINP or osteocalcin levels the teriparatide treatment in postmenopausal women with osteoporosis were then examined. As shown in Table 4, serum sclerostin changes were not correlated with serum PINP or osteocalcin changes. 4. Discussion The significance of the measurement of serum sclerostin levels has been demonstrated for various bone metabolic disorders.

Serum sclerostin levels are related to age and are higher in postmenopausal women than in premenopausal women [17]. Estrogen treatment was shown to reduce elevations in serum sclerostin levels in postmenopausal women [1]. Serum sclerostin levels are reduced by exercise and elevated by long-term immobilization of patients with cerebral infarction, respectively [1,17]. Regarding the relationship between PTH and sclerostin, several animal studies suggested a negative relationship between the expression of PTH and sclerostin in osteocytes. The activation of bone formation by continuous elevations in PTH is due to its direct effects on osteocytes through the inhibition of sclerostin in mice [18]. A study using PTH receptor transgenic mice showed that PTH receptor signaling in osteocytes is sufficient for the inhibition of sclerostin [19]. Regarding the relationship between PTH and sclerostin in humans, previous studies suggested that serum sclerostin levels were decreased in patients with primary hyperparathyroidism, and that serum sclerostin was negatively correlated with serum PTH levels in these patients [20]. The present study showed that a onceweekly teriparatide treatment significantly and continuously decreased serum sclerostin levels in patients with postmenopausal osteoporosis for 12 and 18 months (Fig. 2). In contrast, a daily teriparatide treatment for 6 months did not affect serum sclerostin levels in 13 postmenopausal women [21]. Yu et al. was reported that the administration of teriparatide caused acute decrease in serum sclerostin levels within 6 h in healthy men [12]. A long-term

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T. Ikeda et al. / Journal of Orthopaedic Science 24 (2019) 532e538

Table 2 Correlations between the percent changes in the lumbar spine BMD and bone metabolic indexes.

Lumbar spine BMD 6M Sclerostin

12M

18M

r

p

r

p

r

p

-0.25

0.33

-0.28

0.32

-0.24

0.41

-0.36

0.20

1M Osteocalcin

-0.23

0.38

-0.54

0.03 *

P1NP

0.16

0.52

0.35

0.18

0.34

0.22

Sclerostin

-0.59

0.01 *

-0.66

0.01 *

-0.61

0.03 *

3M Osteocalcin

-0.08

0.79

-0.41

0.14

-0.24

0.43

P1NP

0.21

0.77

0.10

0.33

0.01

0.98

Sclerostin

-0.41

0.09

-0.34

0.20

-0.48

0.07

6M Osteocalcin

-0.22

0.42

-0.32

0.24

-0.24

0.40

P1NP

0.09

0.73

0.04

0.90

-0.12

0.67

0.21

0.47

0.03

0.91

-0.49

0.07

-0.25

0.38

-0.16

0.58

-0.25

0.39

-0.19

0.51

-0.38

0.18

-0.20

0.50

Sclerostin

12M Osteocalcin P1NP Sclerostin

18M Osteocalcin P1NP

Table 3 Regression coefficient between the percent changes in the lumbar spine BMD and serum sclerostin levels (adjusted with age, BMD at the lumbar spine before treatment, and previous fragility fractures). Lumbar spine BMD

1M Sclerostin (95%CI) 3M Sclerostin 6M Sclerostin 12M Sclerostin 18M Sclerostin

6M

12M

r ¼ 0.001 p ¼ 0.97 (0.003e0.001) r ¼ 0.97 p ¼ 0.04 (2.871e0.931) r ¼ 0.051 p ¼ 0.22 (0.151e0.049)

r r r r

¼ ¼ ¼ ¼

18M

0.001 0.132 0.042 0.008

p p p p

¼ ¼ ¼ ¼

0.58 0.05 0.45 0.86

(0.091e0.03) (0.391e0.127) (0.124e0.04) (0.023e0.008)

r r r r r

¼ ¼ ¼ ¼ ¼

0.005 0.142 0.005 0.003 0.013

p p p p p

¼ ¼ ¼ ¼ ¼

0.94 0.42 0.45 0.60 0.85

(0.005e0.015) (0.42e0.136) (0.142e0.046) (-0.029e0.89) (-0.038e0.012)

Table 4 Correlations between percent changes in serum sclerostin levels and bone metabolic indices.

1M P1NP r

3M Osteocalcin

p

r

p

P1NP

r

6M

Osteocalcin

p

r

p

Osteocalcin

P1NP

r

p

18M

12M

r

p

P1NP

r

Osteocalcin

p

r

p

P1NP

r

Osteocalcin

p

r

p

1M Sclerostin 0.07 0.69 0.14 0.46 0.13 0.55 0.17 0.45 -0.07 0.73 0.07 0.76 0.08 0.76 -0.10 0.70 0.19 0.47

0.08 0.76

3M Sclerostin

0.30 0.30 0.21 0.47

0.15 0.62

0.04 0.83 0.24 0.28 0.14 0.60 0.28 0.30 0.23 0.38

0.38 0.15

6M Sclerostin 12M Sclerostin 18M Sclerostin

0.07 0.74 0.32 0.13 -0.13 0.57 0.21 0.35 0.09 0.75

-0.01 0.96 -0.31 0.91 -0.09 0.72 -0.25 0.37 -0.09 0.72

0.36 0.17

T. Ikeda et al. / Journal of Orthopaedic Science 24 (2019) 532e538

daily teriparatide treatment did not significantly reduce serum sclerostin levels in a study on 10 women with osteoporosis pretreated with bisphosphonates for 18 months [13]. The changes induced in serum sclerostin levels by a daily intermittent teriparatide treatment were not continuously increased, compared to those of once-weekly teriparatide. Although the effects of onceweekly teriparatide on serum sclerostin levels have not yet been reported, the present study showed that a once-weekly teriparatide treatment continuously decreased serum sclerostin levels in patients with postmenopausal osteoporosis, in contrast to previous findings for daily intermittent teriparatide treatments in postmenopausal women [12,13,21]. Since previous studies speculated that a daily treatment and once-weekly treatment with teriparatide mainly affects the stimulation of bone formation and inhibition of bone resorption, respectively, based on data obtained using bone metabolic indices in Japan [2e4], once-weekly teriparatide may affect the production of sclerostin from osteocytes differently from a daily intermittent teriparatide treatment. The present results suggest that the decrease in osteocyte sclerostin production induced by once-weekly teriparatide treatment is related to the increase in BMD of the lumbar spine induced by once-weekly teriparatide treatment in postmenopausal women with osteoporosis. Osteocalcin is relatively exclusively expressed in welldifferentiated mature osteoblasts and osteocytes. Serum osteocalcin levels decrease in patients treated with glucocorticoids and diabetes, whereas PTH and active vitamin D promote the expression of osteocalcin with enhanced osteoblastic bone formation [22]. The present study revealed that once-weekly teriparatide treatment enhanced serum levels of osteocalcin in patients with postmenopausal osteoporosis for 18 months. As shown in Fig. 3A, serum level of osteocalcin significantly enhanced at 12 and 18 months. This result was consistent with the previous findings for onceweekly or daily teriparatide treatments in patients with osteoporosis [3,16]. However, a no relationship is generally observed between serum osteocalcin and BMD or the risk of fracture. The changes induced in serum osteocalcin levels by once-weekly teriparatide were not related to those in BMD of the lumbar spine over 12 months in the present study. These results suggest that osteocalcin is not related to the effectiveness of once-weekly teriparatide treatment for postmenopausal osteoporosis. Once-weekly teriparatide treatment enhanced serum PINP levels and BMD of the lumbar spine at 1 and 3 months, and 6, 12, and 18 months, respectively, in the present study. These results were consistent with previously reported changes in PINP and BMD at the lumbar spine induced by once-weekly teriparatide treatment [5,16,23]. PINP is the most reliable bone formation marker for the evaluation of teriparatide effects on bone formation [25]. Changes in PINP 3 months after a daily intermittent teriparatide treatment are strongly related to BMD increases at the lumbar spine in patients with postmenopausal osteoporosis [24]. Changes induced in serum sclerostin levels by once-weekly teriparatide for 3 months were negatively correlated with BMD changes at the lumbar spine at 6, 12 and 18 months in patients with postmenopausal osteoporosis in the present study but were not correlated with serum PINP changes. The reason for the absence of significant relationships between serum PINP and BMD changes might be due the lower effects of once-weekly teriparatide on serum PINP levels, compared to daily teriparatide. The serum PINP level considered to be the same changes at 1, 3 months. However, the administered dose is different between daily intermittent teriparatide and once-weekly teriparatide, as the result the accumulative effects of a once-weekly teriparatide 56.5 mg might lead to decrease in PINP at 6 months after treatment. Since PINP and sclerostin are mainly derived from osteoblasts and bone-embeded osteocytes, respectively, these results suggest that the reductions

537

induced in sclerostin levels by the once-weekly teriparatide treatment are related to the effects of the treatment on BMD increases through a mechanism other than the enhancement of osteoblastic bone formation. Osteocytes may be involved in the bone anabolic effects of once-weekly teriparatide. Garnero et al. reported that serum sclerostin levels were negatively correlated with serum PINP and PTH levels in a cross-sectional study on postmenopausal women [26]. Sagg et al. reported Romosozumab of antibody that binding to and inhibits sclerostin were decreased serum PINP level at 3 months after treatment [27]. Regarding the relationship between sclerostin and PINP, these results were consistent with the change of sclerostin and PINP in present study. A previous study revealed that serum sclerostin levels were not significantly affected over 36 months in postmenopausal women with osteoporosis [28]; however, denosumab treatment was significantly increased serum sclerostin levels [28]. These findings suggest that the decrease induced in serum sclerostin levels by the once-weekly teriparatide treatment in the present study was significant. Further studies are needed to clarify the relationship between serum sclerostin levels and bone formation during teriparatide treatments. In the present study, changes in serum sclerostin at 3 months after treatment, but not at 6 months were significantly related to BMD changes in the lumbar spine after 6 months. Moreover, serum sclerostin changes at 3 months after the treatment were significantly related to BMD changes in the lumbar spine after 18 months (Table 2). There are several limitations in our study. The first major limitation is that the number of subjects was very low. The second major limitation is the lack of a control group. Although the reason is not all clear in our study, we speculate that the accumulative effects of a once-weekly teriparatide treatment on sclerostin might lead to an increase in BMD at the lumbar spine at the later time. 5. Conclusions The present study revealed that a once-weekly teriparatide treatment reduced the serum levels of sclerostin in postmenopausal women with osteoporosis. Conflict of interest There are no conflicts of interest for this paper. Acknowledgements We acknowledge the staff at the Department of Orthopedics for their collaboration in this study and Dr. Yasutaka Chiba (Clinical Research Center, Kindai University Hospital) for his assistance with the statistical analysis. References [1] Ke HZ, Richards WG, Li X, Ominsky MS. Sclerostin and dickkopf-1 as therapeutic targets in bone diseases. Endocr Rev 2012 Oct 33;(5):747e83. [2] Neer RM, Arnaud CD, Zanchetta JR, Prince R, Gaich GA, Reginster JY, Hodsman AB, Eriksen EF, Ish-Shalom S, Genant HK, Wang O, Mitlak BH. Effect of parathyroid hormone (1-34) on fractures and bone mineral density in postmenopausal women with osteoporosis. N Engl J Med 2001 May 10;344(19):1434e41. [3] Nakamura T, Sugimoto T, Nakano T, Kishimoto H, Ito M, Fukunaga M, Hagino H, Soen S, Yoshikawa H, Nishizawa Y, Fujita t, Shiraki M. Randomized teriparatide [human parathyroid hormone (PTH) 1-34] once-weekly efficacy research (TOWER) trial for examining the reduction in new vertebral fractures in subjects with primary osteoporosis and high fracture risk. J Clin Endocrinol Metab 2012 Sep;97(9):3097e106. [4] Nakano T, Shiraki M, Sugimoto T, Kishimoto H, Ito M, Fukunaga M, Hagino H, Soen T, Kuroda T, Nakamura T. Once-weekly teriparatide reduces the risk of vertebral fracture in patients with various fracture risks: subgroup analysis of

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