Anna G. Johansson

Decreased Estradiol Levels and Free Androgen Index and Elevated Sex Hormone-Binding Globulin Levels in Male Idiopathic Osteoporosis

Abstract. Estrogen deficiency is an important pathogenetic factor in female osteoporosis, and androgens are known to have anabolic effects on bone. In this study we have compared 12 men with idiopathic osteoporosis, age 27–55 years, with 12 age-matched men, with respect to serum levels of sex steroids, biochemical markers of bone turnover, bone density, and body composition. All subjects showed values within the normal range for all hormonal parameters. The patient group compared with the controls had significantly lower serum levels of estradiol (71 ± 13 versus 85 ± 14 pmol/liter, P < 0.03); estradiol/sex hormone-binding globulin (SHBG) ratio (22.4 ± 12.1 versus 39.5 ± 18.6 pmol/mg, P < 0.02); free androgen index (51.0 ± 19.4 versus 74.1 ± 33.1%, P < 0.05); and higher SHBG (3.7 ± 1.6 versus 2.5 ± 1.0 mg/liter; P < 0.04). The men with idiopathic osteoporosis had significantly lower body mass index (23.2 ± 2.8 versus 25.9 ± 3.3 kg/m2, P < 0.05); and a tendency to lower percentage of total body fat (14.2 ± 5.5 versus 18.6 ± 6.0%; P < 0.10) than the controls. Regression analyses revealed that bone mineral density in femoral neck correlated significantly and positively with the ratio estradiol/SHBG (r = 0.67; P < 0.04) and negatively with SHBG concentrations (r =−0.63; P < 0.04) in the group of patients. These findings could represent a pathogenetic mechanism in male idiopathic osteoporosis.

Hormonal regulation of serum lipoprotein(a) levels. Contrasting effects of growth hormone and insulin-like growth factor-I

Hormonal regulation of serum lipoprotein(a) levels. Contrasting effects of growth hormone and insulin-like growth factor-I

Circulating levels of insulin-like growth factor-I and -II, and IGF-binding protein-3 in inflammation and after parathyroid hormone infusion

In order to assess if the anabolic action of PTH is related to changes in circulating levels of insulin-like growth factor-I and -II (IGF-I and -II), and IGF binding protein 3 (IGFBP-3), 24 h of PTH infusion was performed in healthy women and in patients with rheumatoid arthritis (RA), a state where both bone metabolism and PTH secretion is influenced by the inflammatory activity. The patients with RA had lower basal levels of both IGF-I and -II than the healthy controls (P < 0.05). In neither group did the IGFs change after 24 h of PTH administration, while IGFBP-3 was significantly increased in the healthy controls (4600 +/- 1200 to 5750 +/- 2200 micrograms/l, P < 0.05). IGFBP-3 was not affected by PTH infusion in patients with RA when the disease had high activity, but when inflammation had subsided they responded with a similar increase in IGFBP-3 as the control group and basal IGF-I and -II levels were normalised. Since IGFBP-3 can enhance the anabolic action of IGF-I, increased IGFBP-3 levels after PTH infusion may reflect a mechanism by which PTH is anabolic for bone. Inflammation may inhibit bone formation via decreased serum levels of IGFs and blocked IGFBP-3 response to PTH.

Regulation of Interleukin‐6 Secretion from Mononuclear Blood Cells by Extracellular Calcium

Interleukin‐6 (IL‐6) is known to enhance osteoclast recruitment, and thereby bone resorption. Thus, IL‐6 has been proposed to mediate hypercalcemia in multiple myeloma and the enhanced osteoclastic activity seen in postmenopausal osteoporosis. We recently reported that the calcium concentration in plasma affects IL‐6 secretion from mononuclear blood cells. To investigate the underlying mechanism, we have studied the effect of calcium on IL‐6 formation in mononuclear blood cells ex vivo and in vitro. Thirteen healthy volunteers were given 1 g of calcium orally after overnight fasting. Plasma levels of ionized calcium (pCa2+) and serum levels of parathyroid hormone (sPTH) were measured after 2 and 4 h, with all subjects still fasting. After 2 h, pCa2+ was increased and sPTH decreased in all 13 persons. IL‐6 secretion ex vivo from mononuclear blood cells drawn 4 h after calcium intake was increased 185% as compared with IL‐6 secretion from cells drawn just before calcium intake. In control experiments without calcium intake, there was no alteration in pCa2+ and no effect on IL‐6 secretion from mononuclear blood cells. In vitro studies revealed that stimulation of isolated mononuclear blood cells with physiological concentrations of calcium dose‐dependently increased IL‐6 secretion with an estimated EC50 at 1.2 mM Ca2+. No effect on the IL‐6 secretion was seen following treatment of the isolated mononuclear blood cells with PTH or calcitonin. These observations demonstrate that the plasma calcium concentration affects IL‐6 secretion from mononuclear blood cells. The in vitro data indicate the involvement of a direct calcium sensing mechanism. These findings might have implications in hypercalcemia and should also be borne in mind when considering the role of cytokines in osteoporosis.

Insulin-Like Growth Factor I Enhances the Formation of Type I Collagen in Hydrocortisone-Treated Human Osteoblasts

We have studied the effect of insulin-like growth factor I (IGF-I) on the formation of osteocalcin and type I collagen in isolated human osteoblasts. IGF-I at and above 0.1 nM stimulated the formation of type I collagen as measured by the type I procollagen carboxyterminal peptide (PICP), in human osteoblasts, incubated for 72 hrs in serumfree conditions. The secretion of osteocalcin was not affected by IGF-I while 1,25(OH)2 vitamin D3 significantly enhanced the formation of osteocalcin. When human osteoblast-like cells were incubated with hydrocortisone (1 μM), a significant decrease in the release of both PICP and osteocalcin was seen. Addition of IGF-I to human osteoblasts also treated with hydrocortisone normalized the PICP-formation but did not affect the suppressed osteocalcin-formation. These data indicate that IGF-I reverses selective effects of hydrocortisone on bone.

Growth hormone secretion and sensitivity in men with idiopathic osteoporosis

Previous studies have suggested that insulin-like growth factor-I (IGF-I) and its binding proteins (IGFBPs) have a pathogenetic role in idiopathic osteoporosis. To investigate this question further we compared 20 men with idiopathic osteoporosis with 12 healthy, age-matched men regarding growth hormone (GH) secretion and sensitivity. GH samples were drawn every 30 minutes for 24 hours from 12 of the patients and all controls, and cumulated GH secretion (24hGH) was derived. Peak GH secretion (peakGH) was provoked by an insulin tolerance test. There were no differences between the groups in serum IGF-I (162 ± 30 vs 163 ± 47 µg/liter, mean ± SD), IGFBP-3 (2474 ± 263 vs 2568 ± 197 µg/liter), 24hGH (1.34 ± 1.26 vs 0.79 ± 0.43 U), or peakGH (53.0 ± 21.5 vs 44.1 ± 19.8 mU/liter). Patients and controls were given GH (2.4 U/day) for 1 week. Serum levels of markers for bone turnover increased significantly in both groups, with no difference in response to GH between the groups. The increase in urinary bone resorption markers was only significant in the controls. In the patients, but not in the controls, there were significant positive correlations between indices for GH secretion and markers for bone turnover at baseline and significant negative correlations with relative changes in bone markers during GH treatment. In this study no difference in GH secretion was found between men with idiopathic osteoporosis and controls, but the findings suggest that the GH/IGF-I axis could play a regulatory role in bone metabolism in men with this condition.

Cellular retinoic acid-binding protein type II is expressed in adult human osteoblasts and in adult liver

In this study we have used a reverse transcription polymerase chain reaction (RT-PCR) to demonstrate that adult primary human osteoblasts and SaOS-2, a human osteosarcoma-derived cell line with osteoblastic properties, express cellular retinol-binding protein I (CRBP I), cellular retinoic acid-binding protein II (CRABP II), and very low levels of CRABP I. We also show that CRABP II is expressed in the adult liver, which does not express CRABP I. The results suggest that CRABP II is the important isoform in the adult bone as well as in the adult liver. Since the 9-cis retinoic acid receptor (RXR) alpha previously has been shown to be expressed predominantly in the liver, CRABP II might be involved in the transport of 9-cis retinoic acid to its nuclear receptor.

Interleukin-1β induces cyclic AMP formation in isolated human osteoblasts: a signalling mechanism that is not related to enhanced prostaglandin formation

Interleukin-1 (IL-1) is a potent stimulator of bone resorption. Induction of osteoclastic bone resorption by various endocrine or paracrine factors is mediated via the osteoblasts. We have therefore investigated the effects of IL-1 beta on cell signalling in isolated human osteoblasts. Special interest was focused on prostaglandin synthesis, since indomethacin, an inhibitor of prostaglandin synthesis, partly inhibits IL-1-induced bone resorption. IL-1 beta, at and above 0.3 pM, dose dependently stimulated PGE2 formation in isolated human osteoblasts, with half maximal stimulation, EC50, at 3 pM. Treatment with the calcium ionophore A23187 (1 microM), or with forskolin (30 microM), also stimulated PGE2 formation in human osteoblasts. The time-course for IL-1 beta-induced PGE2 formation was similar to that of forskolin, with a significant increase in the formation of PGE2 seen after 1 h. In contrast, A23187-induced PGE2 formation was seen within minutes. IL-1 beta stimulated the accumulation of cyclic AMP in isolated human osteoblasts incubated for 15 min. This increase in cyclic AMP formation was not secondary to PGE2 formation since it was not blocked by the addition of indomethacin (1 microM). Pretreatment with the phosphodiesterase inhibitor IBMX did not augment IL-1 beta-induced PGE2 formation, nor did the protein kinase A inhibitor Rp-cAMPs inhibit IL-1 beta-induced PGE2 formation, suggesting that cyclic AMP does not mediate the stimulatory effect of IL-1 on PGE2 formation. We conclude that IL-1 beta enhances the formation of cyclic AMP as well as PGE2 in primary cultures of isolated human osteoblasts. The IL-1 beta-induced cyclic AMP formation is, however, not related to the enhanced prostaglandin formation. The findings implicate that both cyclic AMP- and PGE2-formation in osteoblasts might be involved as independent mediators of IL-1 beta-induced bone resorption.