Growth hormone and adult bone remodelling

New therapeutics in promoting and modulating mandibular growth in cases with mandibular hypoplasia

Children with mandibular growth deficiency may develop airway obstruction. The standard treatment of severe airway obstruction involves invasive procedures such as tracheostomy. Mandibular distraction osteogenesis has been proposed in neonates with mandibular deficiency as a treatment option to avoid tracheostomy procedure later in life. Both tracheostomy and distraction osteogenesis procedures suffer from substantial shortcomings including scarring, unpredictability, and surgical complications. Forward jaw positioning appliances have been also used to enhance mandible growth. However, the effectiveness of these appliances is limited and lacks predictability. Current and future approaches to enhance mandibular growth, both experimental and clinical trials, and their effectiveness are presented and discussed.

Adynamic bone in patients with chronic kidney disease

Adynamic bone in patients with chronic kidney disease (CKD) is a clinical concern because of its potential increased risk for fracture and cardiovascular disease (CVD). Prevalence rates for adynamic bone are reportedly increased, although the variance for its prevalence and incidence is large. Differences in its prevalence are largely attributed to classification and population differences, the latter of which constitutes divergent groups of elderly patients having diabetes and other comorbidities that are prone to low bone formation. Most patients have vitamin D deficiency and the active form, 1,25-dihydroxyvitamin D, invariably decreases to very low levels during CKD progression. Fortunately, therapy with vitamin D receptor activators (VDRAs) appears to be useful in preventing bone loss, in part, by its effect to stimulate bone formation and in decreasing CVD morbidity, and should be considered as essential therapy regardless of bone turnover status. Future studies will depend on assessing cardiovascular outcomes to determine whether the risk/reward profile for complications related to VDRA and CKD is tolerable.

Growth hormone is permissive for skeletal adaptation to mechanical loading

The Lewis dwarf (DW) rat was used as a model to test the hypothesis that growth hormone (GH) is permissive for new bone formation induced by mechanical loading in vivo. Adult female Lewis DW rats aged 6.2 +/- 0.1 months (187 +/- 18 g) were allocated to four vehicle groups (DW), four GH treatment groups at 32.5 microg/100 g body mass (DWGH1), and four GH treatment groups at 65 microg/100 g (DWGH2). Saline vehicle or GH was injected intraperitoneally (ip) at 6:30 p.m. and 6:30 a.m. before mechanical loading of tibias at 7:30 a.m. A single period of 300 cycles of four-point bending was applied to right tibias at 2.0 Hz, and magnitudes of 24, 29, 38, or 48N were applied. Separate strain gauge analyses in 5 DW rats validated the selection of loading magnitudes. After loading, double-label histomorphometry was used to assess bone formation at the periosteal surface (Ps.S) and endocortical surface (Ec.S) of tibias. Comparing left (unloaded) tibias among groups, GH treatment had no effect on bone formation. Bone formation in tibias in DW rats was insensitive to mechanical loading. At the Ec.S, mechanically induced lamellar bone formation increased in the DWGH2 group loaded at 48N (p < 0.05), and no significant increases in bone formation were observed among other groups. The percentage of tibias expressing woven bone formation (Wo.B) at the Ps.S was significantly greater in the DWGH groups compared with controls (p < 0.05). We concluded that GH influences loading-related bone formation in a permissive manner and modulates the responsiveness of bone tissue to mechanical stimuli by changing thresholds for bone formation.

Bone metabolism and body composition in Japanese patients with active acromegaly

OBJECTIVE

Skeletal involvement is a common clinical feature in acromegalic patients. Although several recent reports are available concerning bone mineral density (BMD) in acromegaly, the controversy still exists as to whether BMD of acromegalic patients is increased or not. The present study was performed to examine biochemical bone metabolic indices and BMD as well as body composition in 26 Japanese patients with active acromegaly and 26 control subjects matched for age, sex, race and height in a cross-sectional study.

MEASUREMENTS

BMD of the lumbar spine and femoral neck, as well as body composition, was measured by dual-energy X-ray absorptiometry. Mid-radial BMD was measured by single-photon absorptiometry. We also determined serum levels of IGF-I, IGFBP-3 and osteocalcin (OC) as well as urinary levels of deoxy-pyridinoline (D-Pyr) and CrossLaps.

RESULTS

Percent lean body mass was increased and percent fat mass was decreased in the acromegalic patients compared to control subjects. Serum levels of OC, as well as urinary levels of D-Pyr and CrossLaps, were significantly higher in acromegalic patients compared to control subjects (9.8 +/- 1.2 vs. 5.7 +/- 0.77 for OC; 11.8 +/- 1.66 vs. 5.0 +/- 0.49 for D-Pyr; 437.6 +/- 68.4 vs. 156.5 +/- 39.6 for CrossLaps). Z scores of BMD at mid-radius as well as lumbar spine and femoral neck were significantly higher in acromegalic patients compared to control subjects (1.086 +/- 0.311 vs. -0.060 +/- 0.274 for mid-radius; 1.022 +/- 0.280 vs. 0.319 +/- 0.165 for lumbar spine; 1.292 +/- 0.347 vs. 0.232 +/- 0.264 for femoral neck).

CONCLUSIONS

The present study revealed that a decrease in percent fat mass and an increase in percent lean body mass were observed in Japanese patients with active acromegaly. Bone mineral density at all sites and bone metabolic markers were also increased in acromegaly. The present findings provide additional evidence that the GH/IGF-I axis might play an important role in the maintenance of bone mass as well as the regulation of body composition in Japanese adults.

Effect of recombinant human growth hormone in elderly osteoporotic women

OBJECTIVE

Bone mineral density and growth hormone (GH) secretion rate both decline during normal human ageing. We evaluated the effects of recombinant human GH on markers of body composition and bone turnover in an open study in 8 elderly osteoporotic women aged 68-75 years (mean age 71 years).

DESIGN

Subjects were treated with GH as a single daily subcutaneous injection (0.125 IU/kg/week for the first 4 weeks and subsequently 0.25 IU/kg/week) for 48 weeks.

RESULTS

GH treatment caused a rapid (within 2 weeks) increase in serum levels of IGF-I and IGF-binding protein-3 (IGFBP-3) which was sustained throughout the study. Markers of bone formation and resorption were both gradually increased up to 24 weeks of GH treatment. The bone formation markers, osteocalcin (OC) and bone alkaline phosphatase, remained high during GH treatment, while the bone resorption marker, deoxypyridinoline (D-Pyr), tended to return to baseline levels after 24 weeks of GH therapy. GH treatment for 48 weeks caused a significant increase in hand grip and a decrease in waist/hip ratio. The mean percentage changes in bone mineral density (BMD) of mid-radius and lumbar spine were + 2.1% and + 1.2%, respectively, although they were not statistically significant. GH treatment was well tolerated and no major side-effects except mild oedema and joint pain were found. Since GH treatment produced durable increases in bone formation markers, BMD continued to be monitored after discontinuation of GH treatment for another 48 weeks, during which significant increases in radial and lumbar BMD (8.1 +/- 2.1 and 3.8 +/- 1.4% above pre- treatment values, respectively) were recorded.

CONCLUSION

These results indicate that GH attenuates the decrease in muscle strength and bone mass as well as the gain of abdominal fat with ageing in elderly women. The present data provide useful information about the application of GH treatment in elderly women.

Growth hormone stimulates tyrosine phosphorylation of focal adhesion kinase (p125(FAK)) and actin stress fiber formation in human osteoblast-like cells, Saos2

Bone is one of the essential target tissues of growth hormone (GH). In bone remodeling, cell-matrix attachment is important where focal adhesion kinase (FAK) is involved. FAK plays a central role in determining the shape and motility of cells in response to the extracellular matrix stimuli. In the present study, we have demonstrated that GH stimulated tyrosine phosphorylation of FAK in human osteoblast-like cells, Saos2. Moreover, GH rapidly enhanced the formation of actin stress fibers. In Saos2, Jak2 was tyrosine phosphorylated by GH stimulation, and AG490, a Jak2 specific inhibitor, inhibited GH-induced tyrosine phosphorylation of FAK and actin stress fiber reorganization. These results suggest that GH activates FAK via Jak2, and stimulates the formation of actin stress fibers in Saos2. Activation of FAK and actin stress fiber formation induced by GH seem to be important for the physiological role of osteoblast.

Hexarelin, a growth hormone - releasing peptide, counteracts bone loss in gonadectomized male rats

The age-related decline in growth hormone (GH) secretion has been implicated in the pathogenesis of involutional bone loss. Whether restoration of GH secretion might be helpful in maintaining and/or improving bone mass during aging is still unsettled. The aim of the present study was to examine the effects of 30-day treatment with hexarelin (HEXA, 50 microg/kg subcutaneously b.i.d.), a highly effective GH-releasing compound, on bone metabolism and bone mineral density (BMD) in intact and osteopenic gonadectomized (GDX) mature male rats. Serum total alkaline phosphatase (ALP, bone formation marker) and bone resorption markers (lysylpyridinoline, LP and hydroxylysylpyridinoline, HP) were measured before and 7, 14 and 30 days after treatment. BMD was measured by dual-energy X-ray absorptiometry at lumbar vertebrae, femoral metaphysis and diaphysis before and at the end of the experiment. In intact rats, HEXA significantly (P<0.05) decreased LP (-36.3%) and HP (-22.8%) excretion at day 7, whereas it did not change serum ALP activity and BMDs. In GDX rats, HEXA completely prevented the significant (P<0. 01) increase in urinary excretion of both LP (+143.8%) and HP (+119. 4%), the early decrease in ALP activity (-26.5%) and the significant (P<0.05) decrease in BMDs in the femoral metaphysis (-7.9%) and lumbar vertebrae (-6.8%) caused by androgen deficiency. The bone-protective effects of HEXA could be attributed, at least in part, to its GH-releasing activity since chronic-treated rats maintained the GH response to an acute challenge with HEXA. The evidence that HEXA, unlike GH, inhibits bone resorption indicates that other mechanisms contribute to the bone sparing effect of HEXA.

Bone mineral density and circulating cytokines in patients with acromegaly

Acromegalic patients present an increase of osteoblastic and osteoclastic activity, showing a different effect on the axial and appendicular skeletal structures. At this regard controversial data about bone mineral density (BMD) have been published in literature. In fact an increase of BMD levels in femoral neck and Ward's triangle without any difference in lumbar spine has been described. On the other hand normal BMD levels at forearm and reduced BMD levels at lumbar spine were found. These patients seem to have a reduction of trabecular BMD similar to postmenopausal osteoporotic patients despite normal or slightly elevated cortical BMD. Recently, it has been described that cytokines, in particular tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1), are implicated in the pathogenetic mechanism of postmenopausal osteoporosis. Taking into account that growth hormone (GH) can increase TNF-alpha and IL-1 secretion by mononuclear blood cells, the evaluation of possible relationship between the reduced BMD at lumbar spine and circulating cytokines levels was carried out in acromegalic patients. In addition we evaluated the effect of acute octreotide administration on serum TNF-alpha and IL-I concentrations. Eleven patients with active acromegaly and eleven healthy age-, sex-, weight- and heightmatched subjects were enrolled in this study. BMD was significantly reduced at lumbar spine (0.80 +/- 0.29 g/cm2 vs 1.02 +/- 0.11 g/cm2; p < 0.01), but not at femoral neck level or at Ward's triangle level (0.92 + 0.15 g/cm2 vs 0.97 + 0.11 g/cm2, p = NS; and 0.74 +/- 0.16 g/cm2 vs 0.85 +/- 0.1 g/cm2, p = NS) when compared to controls. Baseline serum levels of TNF-alpha and IL-1 were in the normal range both in patients and controls. After acute octreotide administration, no differences in circulating TNF-alpha and IL-1 levels were found. In conclusion, acromegalic patients present a reduced BMD at lumbar spine but not at femoral neck level and Ward's triangle. Circulating cytokines such as TNF-alpha and IL-1 are in the normal range. These data suggest that cytokines are not involved in the pathogenesis of GH-excess induced osteoporosis. The possibility that the GH excess might affect bone turnover inducing an increase of cytokines acting by a paracrine/autocrine mechanism cannot be ruled out.

Systemic over-secretion of growth hormone in transgenic mice results in a specific pattern of skeletal modeling and adaptation

The effects of growth hormone (GH) over-secretion on bone modeling and remodeling in transgenic mice were investigated using systematic and hierarchical methods. The results showed that continual systemic stimulation of GH over-secretion in mice resulted in an initial increase in bone mass, but its bone quality was not comparable with that of the littermate controls. Further continual over-stimulation of GH resulted in an increase in bone resorption leading to thinner cortices with inferior tissue mechanical properties. Three biological mechanisms following GH over-production are formulated to explain the observed results: GH over-secretion stimulated the production of inferior bone matrices, i.e., woven bone and cartilage, in addition to the production of normal lamellar bone; the increased bone formation stimulated by GH was followed by an exaggerated bone resorption process, resulting in cortical tissue with inferior mechanical properties; and a cortical shift occurred following GH over-stimulation that appeared to be caused by the combined effects of GH over-secretion and a variation in mechanical stimuli in the metallothionein-1 growth hormone regulating hormone transgenic mice. An "Optimal Strain Environment" model is proposed to help explain the observed results. From the results of the present and previous studies, we believe that the primary goal of bone adaptation to a biological perturbation, at least in mice, is to ensure proper mechanical function by maintaining structural integrity. In the process of maintaining a targeted whole bone structural integrity, the mechanical integrity of tissue may be sacrificed.

Benefits of growth hormone treatment on bone metabolism, bone density and bone strength in growth hormone deficiency and osteoporosis

Bone mass is reduced in patients with GH deficiency (GHD) leading to an increased vertebral fracture rate and clinically significant osteoporosis. Patients with GHD of juvenile onset have reduced skeletal mineralization. When substituting GH in patients with GHD, bone turnover is increased and bone mineral density initially decreases during the first year due to the increase in remodelling space. From the experience in patients with acromegaly, cortical bone mass is increased and trabecular bone mass is normal in eugonadal or decreased in the hypogonadal patients. However, bone mineral content and bone area are increased leading to a higher biomechanical competence of bone as shown in rats. In patients with GHD of juvenile onset, mineralization and bone maturation are achieved during treatment with GH in adult life after having reached final body height leading to an increase in bone mass. The GH/ IGF-I system is dysregulated in patients with post-menopausal osteoporosis. This is shown by reduced systemic IGF and IGFBP-3-levels in osteoporosis suggesting a decrease of endogenous GH-secretion or a dysregulation of the GH receptor system which is beyond the normal ageing process of the GH/IGF system, the "somatopause". A premature somatopause may be responsible for the dysregulation in some patients with osteoporosis. However, 24-h GH profiles do not differ between patients suffering from osteoporosis or osteoarthritis. Treatment of osteoporosis with GH might be beneficial due to the increased bone metabolism and improved bone geometry which occurs with GH. The substantial increase of bone remodelling achieved with GH may be helpful during late post-menopause with decreased bone turnover and impaired osteoblastic function. Using GH to prevent physiological bone loss that occurs with age seems possible, but has to be discussed on an ethical and economic basis.

Effects of short-term insulin-like growth factor-I (IGF-I) or growth hormone (GH) treatment on bone metabolism and on production of 1,25-dihydroxycholecalciferol in GH-deficient adults

Administration of insulin-like growth factor-I (IGF-I) or growth hormone (GH) is known to stimulate bone turnover and kidney function. To investigate the effects of IGF-I and GH on markers of bone turnover, eight adult GH-deficient patients (48 +/- 14 yr of age) were treated with IGF-I (5 micrograms/kg/h in a continuous s.c. infusion) and GH (0.03 IU/kg/daily s.c. injection at 2000 h) in a randomized cross-over study. We monitored baseline values for three consecutive days before initiating the five-day treatment period, as well as the wash-out period of ten weeks. Serum osteocalcin, carboxyterminal and aminoterminal propeptide of type I procollagen (PICP and PINP, respectively) increased significantly within 2-3 days of both treatments (P < 0.02) and returned to baseline levels within one week after the treatment end. The changes in resorption markers were less marked as compared with formation markers. Total 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) rose significantly, whereas PTH and calcium levels remained unchanged during either treatment.

CONCLUSIONS

Because the rapid increase in markers of bone formation was not preceded by an increase in resorption markers, IGF-I is likely to stimulate bone formation by a direct effect on osteoblasts. Moreover, because PTH, calcium, and phosphate remained unchanged, IGF-I appears to stimulate renal 1 alpha-hydroxylase activity in vivo.

Single cell enzyme activity and proliferation in the growth plate: effects of growth hormone

Longitudinal growth is a result of proliferation and differentiation of chondrocytes in the growth plate. Growth hormone (GH) stimulates longitudinal growth, and GH receptors have been shown on growth plate chondrocytes, but the effects of GH on chondrocytes of different cell layers are not clear. To study the effect of GH on chondrocyte activity, in situ biochemical techniques were used to measure enzyme activities, which are associated with cell differentiation (alkaline phosphatase [ALP]) and osteoclast activity (tartrate-resistant acid phosphatase [TRAP]), within single cells of the growth plate. Uptake of bromodeoxyuridine (BrdU) was used as a parameter for proliferative activity. In addition, glucose-6-phosphate dehydrogenase (G6PD) was measured since increased proliferation has been associated with increased G6PD activity. The role of GH was studied in a model of isolated GH deficiency (dwarf rat) and complete pituitary deficiency (hypophysectomized rat). Groups of GH-deficient dwarf rats were infused with recombinant human GH in either a continuous or a pulsatile manner, since the pattern of GH secretion is an important regulator of growth in the rat. After 7 days, G6PD activity in proliferative chondrocytes and TRAP activity in osteoclasts was increased, while ALP activity in hypertrophic chondrocytes was decreased. GH not only increased the number of chondrocytes that incorporated BrdU but also the total number of chondrocytes in the proliferative zone; therefore, its ratio, the labeling index (an indicator of proliferative rate), was not increased. The widths of the proliferative and hypertrophic zones were increased by both patterns of GH administration. The width of the resting zone was unaffected by continuous GH but decreased by pulsatile GH. ALP and TRAP activities were, respectively, higher and lower in hypophysectomized rats compared with the GH-deficient animals. Hypophysectomized rats had smaller growth plates than dwarf rats with a disproportionally wide resting zone, which, like BrdU uptake, was not affected by GH. GH treatment resulted in increased TRAP and decreased ALP activity. These results indicate that GH stimulates the commitment of chondrocytes within the resting/germinal layer to a proliferative phenotype (as opposed to stimulating the rate of chondrocyte proliferation) but only in the presence of other pituitary hormones. Furthermore, this study shows that enzyme activities within single chondrocytes and osteoclasts are GH-sensitive. The extent to which these effects are direct or mediated by systemic or local growth factors remains to be clarified.

Cortical bone growth and maturational changes in dwarf rats induced by recombinant human growth hormone

The growth hormone (GH)-deficient dwarf rat was used to investigate recombinant human (rh) GH-induced bone formation and to determine whether rhGH facilitates simultaneous increases in bone formation and bone maturation during rapid growth. Twenty dwarf rats, 37 days of age, were randomly assigned to dwarf plus rhGH (GH; n = 10) and dwarf plus vehicle (n = 10) groups. The GH group received 1.25 mg rhGH/kg body wt two times daily for 14 days. Biochemical, morphological, and X-ray diffraction measurements were performed on the femur middiaphysis. rhGH stimulated new bone growth in the GH group, as demonstrated by significant increases (P < 0.05) in longitudinal bone length (6%), middiaphyseal cross-sectional area (20%), and the amount of newly accreted bone collagen (28%) in the total pool of middiaphyseal bone collagen. Cortical bone density, mean hydroxyapatite crystal size, and the calcium and collagen contents (microgram/mm3) were significantly smaller in the GH group (P < 0.05). Our findings suggest that the processes regulating new collagen accretion, bone collagen maturation, and mean hydroxyapatite crystal size may be independently regulated during rapid growth.

Effects of hormone replacement therapy on growth hormone secretion patterns in correlation to somatometric parameters in healthy postmenopausal women

OBJECTIVES

The aim of the present study was to investigate the influence of a continuous estrogen, cyclic progesterone replacement therapy on the secretion of growth hormone (GH) and IGF I as well as of somatometric-GH correlation patterns.

METHODS

The study included 23 healthy postmenopausal women. Of the proband group 13 randomly selected women were treated with orally applicated 2 mg estradiol-valerat (E2V) and 10 mg dydrogesterone for 10 months. Ten women did not receive any hormonal treatment during this time. After 10 months all probands were reexamined and their GH and IGF I secretion, as well as their somatometric-hormonal correlation patterns, compared with those of a fertile control group.

RESULTS

It could be shown, that in postmenopausal women a 10-month oral hormone replacement therapy led to a significant increase of GH- and IGF I levels, however, the treated postmenopausal women did not reach the levels of the fertile controls. Those women who did not receive any hormonal treatment and the postmenopausal women before HRT showed nearly identical GH- and IGF I levels as well as somatometric-GH correlation patterns.

CONCLUSIONS

The results of the present paper indicate a marked influence of estrogens on GH and IGF I secretion. Furthermore, hormonal replacement therapy (HRT) may influence somatometric GH correlation patterns too.

Urinary pyridinoline and deoxypyridinoline excretion in children

OBJECTIVE

There are few data on urinary markers of collagen breakdown in children. We have determined a normal range for urinary pyridinoline and deoxypyridinoline in children, assessed the variability in excretion in individual children and examined the effect of GH treatment on the excretion of these collagen cross-links.

DESIGN

A cross-sectional study of a group of healthy children and sequential samples from children receiving GH treatment.

PATIENTS

One hundred and nine healthy children aged 2-15 years, 8 healthy children aged 4-11 years and 4 children receiving GH treatment.

MEASUREMENTS

Total pyridinoline and deoxypyridinoline excretion were measured by high performance liquid chromatography after initial acid hydrolysis and cellulose extraction steps. Serum parathyroid hormone was measured using a two-site immunoradiometric assay and urinary hydroxyproline by Ehrlich's reaction using a colorimetric assay. Pyridinoline and deoxypyridinoline excretion were expressed as a ratio against urine creatinine.

RESULTS

High excretion of pyridinoline (Pyr) and deoxypyridinoline (DPyr) was seen at all ages with no apparent relation to age (mean Pyr/Cr 115 nmol/mmol and DPyr/Cr 31 nmol/mmol). No correlation was found with serum parathyroid hormone or urinary hydroxyproline excretion. Marked day to day variation was seen in individual children. A progressive rise in excretion was seen in children receiving GH treatment with no significant correlation to height velocity.

CONCLUSIONS

There is a high excretion of the pyridinium cross-linking amino acids in children of all ages compared to adults. However, a high variability exists in single morning urine samples which will limit the usefulness of these markers in growing children.

The effects of prolonged growth hormone replacement on bone metabolism and bone mineral density in hypopituitary adults

OBJECTIVE

Short-term GH replacement in hypopituitary adults increases bone turnover; data on the consequences of longer-term GH treatment are limited. We report on the effects of 12-18 months of GH replacement treatment with biosynthetic human GH on bone metabolism and bone mass in hypopituitary adults.

DESIGN

Patients were studied before and after GH treatment for 12 months (n = 11) and 18 months (n = 27) respectively in an open trial. GH dose was 0.04 +/- 0.01 IU/kg daily.

MEASUREMENTS

Plasma calcium, phosphate and intact PTH concentrations, 24-hour urinary calcium excretion, 3 markers of bone formation (total alkaline phosphatase, osteocalcin and procollagen 1 carboxy terminal peptide (P1CP)) and serum concentration of carboxyterminal cross-linked telopeptide of type 1 collagen (ICTP), as a marker of bone resorption, were measured at 6-month intervals. Lumbar spine and total body bone mineral mass was measured by dual-energy X-ray absorptiometry.

RESULTS

Small increases were observed in plasma calcium and phosphate concentrations at 12 months of GH therapy but the differences at 18 months were not statistically significant. Serum intact PTH concentration did not change. Plasma total alkaline phosphatase increased significantly on GH from 75 +/- 26 to 92 +/- 30 (P < 0.01) and 85 +/- 31 U/I (NS) at 12 and 18 months respectively. Serum osteocalcin increased from 6.5 +/- 3.7 to 15.7 +/- 6.2 (P < 0.0001) and 16.6 +/- 5.7 micrograms/I (P < 0.001) at 12 and 18 months respectively and P1CP increased significantly from 106.0 +/- 47.3 micrograms/I to 165.5 +/- 95.3 (P < 0.0001) and 177.2 +/- 72.2 micrograms/I (P < 0.01) at 12 and 18 months respectively. Plasma ICTP concentration increased also from 3.4 +/- 1.8 to 7.3 +/- 3.4 (P < 0.0001) and 7.0 +/- 2.7 micrograms/I (P < 0.003) at 12 and 18 months of GH therapy respectively. No significant change was observed in total body or lumbar spine bone mass, over the 18 months of GH treatment

CONCLUSIONS

Replacement therapy with GH in hypopituitary adults for 6-18 months produced a sustained increase in bone turnover (both formation and resorption). Bone mass was maintained but did not increase over the study period.

Anthropometric characteristics and pulsatile growth hormone secretion patterns in premenopausal and postmenopausal women from Austria

The intercorrelations between 18 anthropometric variables, describing amount and distribution of subcutaneous fat tissue, and 12 growth hormone (GH) levels which had been obtained at intervals of 2 hours over a period of 24 hours, were tested in 25 premenopausal and 23 postmenopausal women from Austria. The 12 GH levels were included in the analyses because the GH shows typical pulsatile secretion patterns with peak values about midnight. Initially, premenopausal and postmenopausal women showed significantly different secretion patterns of GH; furthermore it became evident that the GH constantly correlated positively, however insignificantly, with stature height, but significantly negatively with all those measures describing amount and distribution of subcutaneous fat tissue. Beyond that the present paper indicates that age and menopausal status have a marked influence on GH secretion patterns. It became evident that, independent of menopausal status, typical association patterns between frequency of GH pulses per 24 hours, as well as the amplitude of the individual bursts and the amount of subcutaneous fat tissue, occur.

Interactions of growth hormone and parathyroid hormone in renal phosphate, calcium, and calcitriol metabolism and bone remodeling in postmenopausal women

The mechanisms underlying the effects of recombinant human growth hormone (rhGH) on vitamin D, mineral, and bone metabolism are not known. We examined whether these effects are mediated by parathyroid hormone (PTH) by measuring renal phosphorus (P) and calcium (Ca) handling, serum calcitriol, and markers of bone turnover for 24 h before and 72 h after an infusion of hPTH(1-34) in eight healthy postmenopausal women at baseline and following short-term (1 week) and sustained (5 weeks) rhGH treatment. On short-term rhGH, serum phosphorus and basal TmP/GFR were unaffected, but the fall in TmP/GFR after hPTH infusion was exaggerated (integrated response: -99.2 +/- 22.3 versus -144.1 +/- 15.0 minute-mg/dl, P = 0.0021). Basal calcitriol levels rose from 115 +/- 17 to 163 +/- 16 pM (P = 0.0002), but the increase in calcitriol following hPTH infusion was unaffected by short-term rhGH. The basal Ca excretion index (CEI) rose from 0.054 +/- 0.005 to 0.073 +/- 0.007 mM (P = 0.0095), but markers of bone turnover were unaffected. With sustained rhGH treatment, serum P (1.47 +/- 0.05 mM), basal TmP/GFR (4.29 +/- 0.24 mg/dl), and basal CEI (0.067 +/- 0.005 mM) were elevated compared with control values, and the PTH-induced lowering of TmP/GFR was again enhanced (-158.7 +/- 22.8 minute-mg/dl, P = 0.0021). Basal calcitriol concentrations returned to control levels (108 +/- 10 pM), but the calcitriol response to hPTH remained unchanged. Markers of bone remodeling were elevated with sustained rhGH treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of growth hormone replacement therapy in hypopituitary adults on calcium and bone metabolism

OBJECTIVE

The importance of growth hormone (GH) for normal skeletal growth in childhood and adolescence is well established but much less is known about its action on the adult skeleton. We therefore wished to investigate the effects of replacement treatment with biosynthetic human GH in hypopituitary adults on aspects of calcium homeostasis, bone metabolism and bone mineral mass.

PATIENTS

Forty hypopituitary adults (21 females and 19 males; aged 19-67 years).

DESIGN

A prospective randomized double-blind placebo-controlled trial lasting for 6 months.

PROTOCOL

Following baseline assessments, GH was given in a daily dose of 0.02-0.05 IU/kg body weight subcutaneously (or a placebo (P)) at bedtime. Patients were reviewed at 1, 3 and 6 months.

MEASUREMENTS

Plasma calcium, phosphate and total plasma alkaline phosphatase were measured at 0, 1, 3 and 6 months. Serum insulin like growth factor I (IGF-I), osteocalcin, procollagen 1 carboxyterminal peptide (P1CP) and intact parathyroid hormone (PTH) level, 24-hour urinary calcium and creatinine excretion were all measured at 0 and 6 months. Bone mineral density of total body and lumbar spine was also measured by dual energy X-ray absorptiometry at 0 and 6 months in 12 patients on GH and 14 on placebo.

RESULTS

Thirty-eight patients completed the study (18 on GH, 20 on placebo). Serum IGF-I increased significantly on GH treatment (mean +/- SD) (GH: 276 +/- 197 vs P: 88 +/- 50 micrograms/l, P < 0.0001 at 6 months). Plasma calcium increased slightly but significantly in the GH-treated group (2.23 +/- 0.11-2.29 +/- 0.11 mmol/l, P < 0.05). At the end of the study, plasma calcium was however similar on GH and placebo (GH, 2.29 +/- 0.11; P, 2.26 +/- 0.09 mmol/l). Plasma phosphate increased on GH (GH: 1.02 +/- 0.23-1.32 +/- 0.19; P: 0.99 +/- 0.16-0.96 +/- 0.12 mmol/l over the 6 months of treatment, P < 0.001). There was no significant change in the urinary calcium excretion on GH therapy. Plasma total alkaline phosphatase, osteocalcin and P1CP were significantly higher on GH than P at 6 months (alkaline phosphatase: GH: 104 +/- 32 vs P: 69 +/- 32 U/l, P < 0.01, osteocalcin: GH: 17.2 +/- 8.0 vs P: 5.3 +/- 3.2 micrograms/l, P < 0.001 and P1CP: GH: 207 +/- 152 vs P: 93 +/- 31 micrograms/l, P < 0.01). There was no difference in the intact parathyroid hormone level (GH: 31 +/- 14 vs P: 31 +/- 15 ng/l, NS). No significant change was observed in bone mass after 6 months of GH treatment, either in total body bone mineral content or in the lumbar spine.

CONCLUSION

In this large study, GH replacement in hypopituitary adults for 6 months increased bone turnover but did not affect bone mineral content. Longer-term studies are required to assess further any effect on bone mass.

Ultrastructural localization of endogenous hormones and receptors in bone tissue: an immunocytological approach in frozen samples

In addition to their well-known mechanical role, bones are essential for the regulation of calcium phosphate metabolism. Most of the peptide and steroid hormones acting on bone tissue exert their cellular effects directly on bone cells after binding to cell receptors. A combined method using immunocytology on ultrathin frozen sections has been applied to bone tissue and made possible the ultrastructural localization of endogenous hormones and hormone receptors. There is immunocytological evidence, at the osteoblast level, for: (1) the presence of calcitonin, parathyroid hormone, growth hormone, 1,25 dihydroxyvitamin D3, aldosterone, corticosterone and progesterone; (2) the existence of 1,25 dihydroxyvitamin D3 and progesterone receptors; (3) the absence of estradiol and receptors, testosterone and gonadoliberin. Ultimate goals of future studies are to extend the ultrastructural localization of hormones at the osteoclast level, to assess the distribution of adhesive proteins and of their receptors in bone cells and matrix, and to use well-calcified human bone samples in order to evaluate better the role of therapeutic agents.

Growth hormone treatment in adults with GH deficiency: effects on new biochemical markers of bone and collagen turnover

Serum bone Gla protein (BGP) and bone alkaline phosphatase (B-AP), markers of bone formation, carboxyterminal cross-linked telopeptide of type I collagen (ICTP), marker of bone resorption, and aminoterminal propeptide of type III procollagen (PIIINP) levels, index of collagen synthesis, were determined in 8 adults (mean age +/- SE: 29.6 +/- 1.2 yr) with childhood onset GHD before and after 3 and 6 months of recombinant GH treatment (0.5 IU/kg/week). Before treatment, mean BGP (3.8 +/- .5 ng/ml) and B-AP (44.9 +/- 6.9 IU/L) were significantly (P < 0.001 and p < 0.05, respectively) lower than those recorded in normals (5.4 +/- 0.1 ng/ml and 61.8 +/- 1.9 IU/L, respectively), while serum ICTP and PIIINP levels were similar to those found in controls (ICTP: 4.7 +/- 0.8 vs 4.1 +/- 0.3 ng/ml; PIIINP: 3.7 +/- 0.6 vs 3.2 +/- 0.2 ng/ml). BGP and ICTP levels significantly (p < 0.005) increased after 3 (28.4 +/- 5.3 ng/ml and 17.5 +/- 2.8 ng/ml, respectively) and 6 months (25.1 +/- 5.0 ng/ml and 15.0 +/- 1.9 ng/ml, respectively) of recombinant GH treatment. B-AP levels significantly (p < 0.01) increased during the treatment (basal: 44.9 +/- 6.9 IU/L, 3rd month: 173.6 +/- 40 IU/L, 6th month: 194.4 +/- 40 IU/L), while non B-AP levels remained similar to those recorded in basal condition. Serum PIIINP levels significantly (p < 0.0001) rose up after 3 (12.5 +/- 1.4 ng/ml) and 6 months (10.2 +/- 0.8 ng/ml). Serum BGP and ICTP levels were directly (r = 0.85, p < 0.001; r = 0.53, p < 0.01) correlated with serum IGF-I levels.(ABSTRACT TRUNCATED AT 250 WORDS)

New markers of bone and collagen turnover in children and adults with growth hormone deficiency

Serum bone Gla protein (BGP), a marker of osteoblastic function, serum carboxyterminal cross-linked telopeptide of type I collagen (ICTP), a marker of bone resorption, and serum aminoterminal propeptide of type III procollagen (PIIINP) levels, an index of collagen synthesis, were determined in seven children and eight adults with congenital growth hormone deficiency (GHD). In children with GHD, serum BGP (mean +/- s.e.: 12.9 +/- 0.7 ng/ml), ICTP (8.3 +/- 1.3 ng/ml) and PIINP (3.5 +/- 0.5 ng/ml) levels were significantly lower (P < 0.001) than those recorded in normal children (BGP 18.9 +/- 0.8 ng/ml, ICTP 14.4 +/- 0.5 ng/ml and PIIINP 6.7 +/- 0.7 ng/ml). Total alkaline phosphatase (184.7 +/- 13.4 IU/l) and bone alkaline phosphatase (77.8 +/- 4.1 IU/l) levels were also significantly lower (P < 0.0001) than in controls (338.1 +/- 14.9 IU/l and 181.0 +/- 7.8 IU/l, respectively). Serum BGP, ICTP and PIIINP levels were not significantly correlated with height velocity values. In adults with GHD, mean BGP levels (3.8 +/- 0.3 ng/ml) were significantly lower (P < 0.0001) than those recorded in normals (5.4 +/- 0.1 ng/ml). On the contrary, serum ICTP levels were similar to those found in controls (patients: 4.7 +/- 0.8 ng/ml vs normals: 4.1 +/- 0.3 ng/ml), suggesting the presence of a normal resorption activity associated with a reduced osteoblastic function. This finding was also confirmed by the presence of reduced bone alkaline phosphatase levels (GHD: 44.9 +/- 6.9 IU/I vs controls: 58.3 +/- 2.0 IU/I; P<0.02), while the less specific total alkaline phosphatase levels (119.5 +/- 14.8 IU/I) were similar to those recorded in normal subjects (122.3 +/- 4.0 IU/I). Serum PIIINP levels (3.7 +/- 0.6 ng/ml) were similar to those recorded in normals (3.2 +/- 0.2 ng/ml), suggesting that in adulthood the collagen turnover is not negatively influenced by the chronic GHD. No significant correlations were found between BGP/ICTP/PIIINP and IGF-I levels. In conclusion, our data show that in children with GHD the lack of GH insulin-like growth factor-I (IGF-I) effects on bone and collagen turnover is associated with a significant reduction of bone turnover (low bone formation plus low bone resoRption) and collagen synthesis. On the contrary, adult GHD seems to exert less relevant effects on bone and collagen turnover, probably due to the fact that in adult life further hormones or local factors might partially counteract the negative consequences of chronic GH-IGF-I deficiency.

Short and long-term effects of growth hormone treatment on bone turnover and bone mineral content in adult growth hormone-deficient males

OBJECTIVE

In view of the fact that GH-deficient adults present with pronounced osteopaenia and can be considered at risk for osteoporotic fractures, we wanted to investigate the effects of biosynthetic GH replacement therapy (0.25 IU/kg/week) on biochemical indices of bone turnover and on bone mineral content (BMC) in a group of GH-deficient adult males.

DESIGN

We performed a 6-month randomized, double-blind, placebo-controlled study, followed by 12-24 months of GH treatment in all patients.

PATIENTS

Twenty adult males with GH deficiency of childhood onset were studied.

MEASUREMENTS

We measured serum IGF-I, serum phosphate, biochemical indices of bone turnover (serum alkaline phosphatase activity, serum osteocalcin, serum carboxyterminal propeptide of type-I procollagen, fasting urinary hydroxyproline/creatinine and calcium/creatinine ratios) and bone mineral content, measured at the forearm and the lumbar spine by single and dual-photon absorptiometry respectively.

RESULTS

After 3 and 6 months of GH administration, the serum levels of alkaline phosphatase, osteocalcin and carboxyterminal propeptide of type-I procollagen, and the fasting urinary hydroxyproline/creatinine ratio were significantly increased compared to placebo-treated patients (P < 0.01 to P < 0.001). During the open study phase, the values for these indices of bone turnover remained elevated above pretreatment levels (P < 0.01 to P < 0.001 at 12 months), a downward trend becoming apparent after about one year of GH treatment. BMC values showed an initial decline after 3 months of GH treatment (most likely due to an expansion of the remodelling space), followed by a significant and progressive increase above pretreatment values, reaching 7.8% for total BMC at the lumbar spine (L2-L4) and 9.9% for total BMC at the forearm, after 30 months of GH administration.

CONCLUSIONS

The data of our study show that administration of substitutive doses of growth hormone to GH-deficient adult males activates bone turnover for a period of at least one year and suggests that this may have a beneficial effect on bone mass in these patients.

Biochemical markers of bone metabolism

In this article we review the biochemical basis for markers of bone metabolism and comment on their bone specificity and representativeness for bone tissue. Major developments have recently taken place particularly with respect to markers of bone collagen metabolism; accordingly, they are in the focus of this review. We also attempt to relate the various collagenous and non-collagenous markers to each other and to the phases of the osteoblast phenotype.

Androgens and aging in men

Androgen levels decrease with aging in men. Androgen deficiency in elderly men may lead to asthenia, decrease in muscle mass, osteoporosis, decrease in sexual activity, and, in some cases, changes in mood and cognitive function. Combination of these factors may result in impaired quality of life in the elderly male. Androgen replacement therapy may increase bone and muscle mass, enhance muscle and cardiovascular function, and improve sexual function and general well-being. These potential benefits of androgens have to be weighed against the possible adverse effects on prostate and cardiovascular diseases. Careful long-term studies will be required to assess the risk-to-reward ratios of androgen or other hormone replacement therapy before the development of treatment strategies similar to estrogen and progestagen substitution therapy for the postmenopausal female.

Effect of estrogen deficiency on IGF-I plasma levels: relationship with bone mineral density in perimenopausal women

Bone tissue is a source of growth factors; among them, insulinlike growth factor I (IGF-I) is probably an important local regulator of bone formation. This study has been carried out in order to assess the effects of natural menopause on plasma concentrations of IGF-I in the first 6 years after the cessation of gonadal function independent of age. We also examined the relationship between plasma IGF-I levels and bone mineral density (BMD) measured at the lumbar spine (LS), at the ultradistal radius (UDR), and at the junction of the distal and middle thirds of the radius (MR). Sixty-seven healthy nonobese women, aged 45-55, were studied (premenopausal n = 21; postmenopausal n = 46, from 1 to 6 years since menopause). Plasma IGF-I levels were measured by RIA, after acid-ethanol extraction. BMD of the forearm was measured by dual-photon densitometer and BMD of the LS was assessed by quantitative digital radiography. Mean values of IGF-I plasma levels were significantly reduced in postmenopausal women compared to the premenopausal group. Menopausal duration did not influence IGF-I plasma levels in postmenopausal women. We also found a positive correlation between IGF-I levels and BMD measured at MR both in pre- and postmenopausal women, while a correlation with LS and UDR-BMD was found only in fertile subjects. The results show that IGF-I plasma levels decrease immediately after menopause, since significantly lower levels are reached in the first years. The correlations found between plasma IGF-I levels and BMD suggest a possible role of reduced IGF-I in bone loss at particular skeletal sites.

Serum levels of bone Gla protein (osteocalcin, BGP) and carboxyterminal propeptide of type I procollagen (PICP) in acromegaly: effects of long-term octreotide treatment

We measured serum concentrations of bone Gla-protein (osteocalcin, BGP) and carboxyterminal propeptide of type I procollagen (PICP) in 14 patients with active acromegaly. Blood was collected at 0800 for measurement of bone Gla-protein (BGP), carboxyterminal propeptide of type I procollagen (PICP), and insulin-like growth factor I (IGF-I); growth hormone (GH) was then determined at 15-minute intervals for 3 hours and the integrated mean was calculated. The same protocol was repeated at regular intervals during treatment with the long-acting somatostatin analog, octreotide, 150-450 micrograms/day for 6-33 months (median 15). In a case-control analysis, serum BGP concentrations recorded in the acromegalic patients were significantly elevated (14.2 +/- 4.2 micrograms/liter versus 8.0 +/- 3.3 micrograms/liter, P < 0.001). Octreotide treatment induced a roughly parallel reduction in serum GH, IGF-I, and BGP. We found a significant positive correlation between BGP levels recorded before and during therapy and the logarithm of corresponding mean GH levels (r = 0.67, P < 0.001). Also IGF-I concentrations were positively correlated with BGP (r = 0.66, P < 0.001). On the other hand, PICP levels recorded in the acromegalics did not differ from control subjects (146 +/- 46 micrograms/liter versus 127 +/- 44 micrograms/liter, NS) and no correlation was found between either GH and PICP or IGF-I and PICP. To conclude, the present data are compatible with the view that GH and IGF-I play an important role in the control of BGP but not PICP production. It could be that BGP and PICP are submitted to different hormonal modulation.

The bone mineral density in acquired growth hormone deficiency correlates with circulating levels of insulin-like growth factor I

Insulin-like growth factor I (IGF-I) is an important anabolic factor for osteoblasts in vitro. Low plasma levels of IGF-I have been observed in young men with osteoporosis. In the present study, we have studied bone mineral density (BMD) and the circulating levels of IGF-I and growth hormone (GH) in adults with acquired GH deficiency. BMD was determined by dual-energy x-ray absorptiometry in 17 men and 12 women (age 27-54 years). Spinal BMD was positively correlated with the plasma levels of IGF-I (r = 0.43, P = 0.019), with the median of GH values obtained by repeated sampling at night (r = 0.43, P = 0.0019), and with the peak of GH values during GHRH provocation test (r = 0.49, P = 0.039). The total BMD was positively related to plasma IGF-I and median of GH values, but not to peak GH by GHRH provocation. In a multiple regression analysis model, IGF-I, peak GH by GHRH provocation test and duration of GH deficiency explained 49% of the variation in spinal BMD. As compared to healthy controls, total, but not spinal, bone mass was lower in men with GH deficiency, but no clinical symptoms of osteoporosis were observed. The positive relationships between BMD and circulating IGF-I and other indices of GH secretion suggest that IGF-I has an endocrine effect on bone mass.