The present study was performed to investigate the role of insulin-like growth factor I (IGF-I), IGF-binding protein-2 (IGFBP-2), and IGFBP-3 in age-dependent bone loss in postmenopausal Japanese women. One hundred and sixty-five Japanese women aged 43-88 years (mean age, 62) were enrolled in the cross-sectional study. Bone mineral density (BMD) was measured at the lumbar spine, femoral neck, and midradius by dual-energy X-ray absorptiometry or single-photon absorptiometry. Serum levels of IGF-I, IGFBP-2, and IGFBP-3 were measured by radioimmunoassay. BMD at all sites as well as serum levels of IGF-I and IGFBP-3 declined with age, while the serum IGFBP-2 level increased with age. Serum IGFBP-3 and -2 levels were positively and negatively correlated with the serum IGF-I level, respectively. Serum IGF-I and IGFBP-3 levels showed positive correlationship with BMD at any site, particularly at the midradius, while the serum IGFBP-2 level showed negative correlation with BMD. Multiple regression analyses showed age-independent positive correlation between the serum IGF-I level and BMD at all sites as well as age-independent positive correlation between the serum IGFBP-3 level and midradius BMD. The relationship between susceptibility to osteoporotic spinal fracture and serum IGF-I, IGFBP-3, or -2 levels was examined by decade to exclude the influence of aging. Serum levels of IGF-I and IGFBP-3 were significantly lower in subjects with spinal fractures than those without fractures at any decade. No significant difference of serum IGFBP-2 level was observed between subjects with and without fractures. The present findings suggest that IGF-I and IGFBP-3 are important to maintaining bone mass quantitatively as well as qualitatively, and that the determination of serum IGF-I and IGFBP-3 levels could be clinically useful to predict the severity of osteoporosis, particularly the risk of bone fracture associated with

Although the action of bone morphogenetic protein (BMP) on osteoblast differentiation has been extensively investigated, its effect on osteoclast differentiation remains unknown. In the present study, in vitro effects of BMP-2 on osteoclast-like cell formation and bone resorption were examined. BMP-2 (1-100 ng/ml) significantly stimulated bone resorption by preexistent osteoclast-like cells in mouse bone cell cultures containing stromal cells, whereas it did not affect the bone-resorbing activity of isolated rabbit osteoclast-like cells. When BMP-2 was added to unfractionated bone cells after degeneration of preexistent osteoclast-like cells, BMP-2 dose-dependently stimulated osteoclast-like formation at a minimal effective concentration of 10 pg/ml. BMP-2 also enhanced the osteoclast-like cell formation induced by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Moreover, osteoclast-like cells newly formed by BMP-2 from unfractionated bone cells possessed the ability to form pits on dentine slices. Because these results indicated that BMP-2 directly or indirectly stimulated osteoclast differentiation and activity, we next examined the direct effect of BMP-2 on osteoclast precursors in the absence of stromal cells using hemopoietic blast cells derived from spleen cells. The mRNA for BMP-2/4 receptor was detected in hemopoietic blast cells supported by granulocyte-macrophage colony-stimulating factor (GM-CSF) as well as osteoblastic MC3T3-E1 cells and MC3T3-G2/PA6 stromal cells by RNase protection assay. BMP-2 dose-dependently stimulated osteoclast-like cell formation from hemopoietic blast cells supported by GM-CSF at a minimal effective concentration of 10 pg/ml. BMP-2 also enhanced 1,25(OH)2D3-induced osteoclast-like formation from hemopoietic blast cells. The present data are the first to indicate that BMP-2 stimulates bone resorption through both direct stimulation of osteoclast formation and activation of mature osteoclasts, possibly via stomal cells, in vitro.

Although the actions of GH on osteoblasts have been extensively investigated, its effects on osteoclasts remain unknown. In the present study, the effects of GH on bone resorption and osteoclast differentiation were examined in vitro. Bovine GH (bGH; 1-100 ng/ml) significantly stimulated bone resorption by preexistent osteoclasts in stromal cell-containing mouse bone cell cultures, whereas it did not affect the bone-resorbing activity of isolated rabbit osteoclasts. When bGH was added to unfractionated bone cells after degeneration of preexistent osteoclasts, it concentration dependently stimulated osteoclast-like cell formation. GH also enhanced 1,25-dihydroxyvitamin D3-induced osteoclast-like cell formation. Moreover, osteoclast-like cells newly formed from unfractionated bone cells in the presence of bGH possessed the ability to form pits on dentine slices. The conditioned medium from osteoblastic MC3T3-E1 cells or MC3T3-G2/PA-6 stromal cells pretreated with bGH stimulated osteoclast-like cell formation from mouse hemopoietic blast cells supported by granulocyte-macrophage colony-stimulating factor. On the other hand, the PCR products corresponding in size to the mouse GH receptor were detected in mouse hemopoietic blast cells as well as liver. GH concentration dependently stimulated osteoclast-like cell formation from these hemopoietic blast cells in the absence of stromal cells, and these osteoclast-like cells formed pits on dentine slices in the presence of MC3T3-G2/PA-6 stromal cells. The present study indicated for the first time that GH stimulates osteoclastic bone resorption through both its direct and indirect actions on osteoclast differentiation and through its indirect activation of mature osteoclasts, possibly via stromal cells, including osteoblasts.

Although an excess of glucocorticoid induces secondary osteoporosis, the mechanism still remains unclear, particularly in regard to glucocorticoid-stimulated bone resorption. We examined the effects of dexamethasone

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Metformin is an important antidiabetic drug and often used as a probe for drug–drug interactions ( DDIs ) mediated by renal transporters. Despite evidence supporting the inhibition of multidrug and toxin extrusion proteins as the likely DDI mechanism, the previously reported physiologically‐based pharmacokinetic ( PBPK ) model required the substantial lowering of the inhibition constant values of cimetidine for multidrug and toxin extrusion proteins from those obtained in vitro to capture the clinical DDI data between metformin and cimetidine. 1 We constructed new PBPK models in which the transporter‐mediated uptake of metformin is driven by a constant membrane potential. Our models successfully captured the clinical DDI data using in vitro inhibition constant values and supported the inhibition of multidrug and toxin extrusion proteins by cimetidine as the DDI mechanism upon sensitivity analysis and data fitting. Our refined PBPK models may facilitate prediction approaches for DDI involving metformin using in vitro inhibition constant values.

The activity of serum angiotensin-converting enzyme (S-ACE) was determined spectrophotometrically in 45 patients with hyperthyroidism (30 untreated and 15 treated and euthyroid patients), 14 patients with hypothyroidism, and 135 normotensive healthy subjects. S-ACE was significantly higher in the patients with untreated hyperthyroidism (51.6 +/- 1.9 less than SE greater than nmol.min/ml) than in the healthy controls (28.6 +/- 0.6 nmol.min/ml; P less than 0.001). On the other hand, S-ACE was found to be within the normal range in patients with hypothyroidism (23.2 +/- 1.3 nmol.min/ml). In patients with hyperthyroidism, S-ACE gradually fell into the normal range as the thyroid function became normalized, and there were significant positive correlations between S-ACE and the plasma T3 or T4 concentration (r = 0.60 and P less than 0.001; r = 0.61 and P less than 0.001, respectively ). S-ACE had no definite relation to blood pressure, serum glutamic oxaloacetic acid transaminase, or glutamic pyruvic acid transaminase. When the physicochemical characteristics of the enzyme in the sera of hyperthyroidism patients were compared with those in sarcoidosis patients, similar peak activities of S-ACE on gel chromatography and identical Michaelis constants were obtained; the effects of ethyldiaminetetraacetic acid, SQ14225, and pH on the enzymatic reaction were also similar in both diseases. Thus, hyperthyroidism is considered to be one of the diseases in which S-ACE is elevated. The elevation of S-ACE might be directly or indirectly related to the hyperthyroid state. In addition, it is suggested that the enzyme characteristics are identical in hyperthyroidism and sarcoidosis.

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