Effects of recombinant growth hormone (GH) treatment on bone mineral density and body composition in adults with childhood onset growth hormone deficiency

Effects of recombinant human growth hormone therapy on bone mineral density in adults with growth hormone deficiency: a meta-analysis

OBJECTIVE

GH deficiency is associated with decreased bone mineral density (BMD) and increased fracture risk. Because the effects of recombinant human GH (rhGH) therapy on BMD and bone mineral content have not been systematically investigated, we conducted a meta-analysis of pertinent studies.

DESIGN

A thorough search of the literature (MEDLINE, EMBASE, and the Cochrane Register) was performed. Relevant studies were divided and analyzed according to their design (randomized/controlled or prospective/retrospective) and duration of rhGH therapy (≤12 months and > 12 months).

RESULTS

Administration of rhGH led to a significant increase in lumbar spine (LS) and femoral neck (FN) BMD in randomized/controlled studies of more than 1 year [weighted mean difference (95% confidence interval)] of 0.038 g/cm(2) (0.011-0.065) and 0.021 g/cm(2) (0.006-0.037) at the LS and FN, respectively, and a nonsignificant drop at the same sites in studies of shorter duration. In prospective studies, a significant increase in the LS and FN BMD was obtained. On meta-regression, a negative association was observed between the change in LS and FN BMD and subjects' age and a positive association between the BMD change and treatment duration. In a subgroup analysis, the increase in LS and FN BMD was significant in men [0.048 g/cm(2) (0.033-0.064) and 0.051 g/cm(2) (0.003-0.098), respectively] but not in women.

CONCLUSION

This meta-analysis suggests a beneficial effect of rhGH replacement on BMD in adults with GH deficiency. This effect is affected by gender, age, and treatment duration. Larger studies are needed to evaluate the effect of rhGH on fracture risk.

Growth hormone deficiency in the transition period: body composition and gonad function

Recombinant GH therapy is normally administered to GH-deficient children in order to achieve a satisfactory height - the main target during childhood and adolescence. However, the role of GH does not end once final height has been reached, but continues during the so-called transition period. In this phase of life, the body undergoes several changes, both physical and psychological, that culminate in adulthood. During this period, GH has a part in numerous metabolic functions. These include the lipid profile, where it increases HDL and reduces LDL, with the global effect of cardiovascular protection. It also has important effects on body composition (improved muscle strength and lean body mass and reduced body fat), the achievement of proper peak bone density, and gonad maturation. Retesting during the transition period, involving measurement of IGF-I plus a provocative test (insulin tolerance test or GHRH + arginine test), is thus necessary to establish any persistent GH deficiency requiring additional replacement therapy. The close cooperation of the medical professionals involved in the patient's transition from a pediatric to an adult endocrinologist is essential. The aim of this review is to point out the main aspects of GH treatment on body composition, metabolic and gonad functions in the transition period.

Effects of growth hormone on bone modeling and remodeling in hypophysectomized young female rats: a bone histomorphometric study

Growth hormone (GH) deficiency causes decreased bone mineral density and osteoporosis, predisposing to fractures. We investigated the mechanism of action of GH on bone modeling and remodeling in hypophysectomized (HX) female rats. Thirty female Sprague-Dawley rats at age 2 months were divided into three groups with 10 rats each: control (CON) group, HX group, and HX + GH (3 mg/kg daily s.c.) group, for a 4-week study. Hypophysectomy resulted in cessation of bone growth and decrease in cancellous bone mass. Periosteal bone formation decreased and bone turnover rate of endocortical and trabecular surfaces increased as compared to the CON group. GH administration for 4 weeks restored weight gain and bone growth and mitigated decrease in bone density after hypophysectomy. However, trabecular bone mass in the proximal tibial metaphysis remained lower in group HX + GH than in group CON. Dynamic histomorphometric analysis showed that bone modeling of periosteal bone formation and growth plate elongation was significantly higher in group HX + GH than in group HX. New bone formed beneath the growth plate was predominately woven bone in group CON and group HX + GH. Bone remodeling and modeling-remodeling mixed modes in the endocortical and PTM sites were enhanced by GH administration; both bone formation and resorption activities were significantly higher than in group HX. In conclusion, GH administration to HX rats reactivated modeling activities in modeling predominant sites and increased new bone formation. GH administration also increases remodeling activities in remodeling predominant sites, giving limited net gain in the bone mass.

Treatment for 24 months with recombinant human GH has a beneficial effect on bone mineral density in young adults with childhood-onset GH deficiency

OBJECTIVE

Discontinuation of growth hormone (GH) therapy on completion of linear growth may adversely affect bone mineral density (BMD) in young adults with childhood-onset GH-deficiency (GHD). In the present study, we analyzed the impact of GH treatment on bone in young adults with GHD.

METHODS

BMD at the lumbar spine (L2-L4), total hip, and total body was measured at baseline and after 24 months in a cohort of young adults (18-25 years; n=160) with severe GHD treated with GH during childhood who were randomized to GH (n=109) or no treatment (n=51) in a multicenter, multinational, open-label study. GH starting doses (0.2 mg/day (males), 0.4 mg/day (females)) were increased after 1 month to 0.6 mg/day (males) and 0.9 mg/day (females) and then to 1.0 mg/day (males) and 1.4 mg/day (females) at 3 months for the remainder of the study.

RESULTS

After 24 months, lumbar spine BMD had increased significantly more in GH-treated patients than in controls (6 vs 2%; estimated treatment difference; 3.5% (95% confidence interval, 1.52-5.51) P<0.001). GH also had a significant positive effect on total hip BMD (P=0.015). Total body BMD was unchanged from baseline (P=0.315).

CONCLUSIONS

In young adults treated for childhood-onset GHD, there is a beneficial effect of continued GH treatment on BMD in adult life. Twenty-four months of GH treatment in these young adults was associated with an estimated 3.5% greater increase in BMD of the lumbar spine compared with controls.

Abnormalities in bone mineral density distribution and bone scintigraphy in patients with childhood onset hypopituitarism

The aim of our study was to evaluate the effects of long-life severe growth hormone deficiency on bone mineral density (BMD) and bone scintigraphy in adult patients with childhood onset (CO) hypopituitarism never treated with growth hormone. Our studies included 22 adult patients with CO hypopituitarism never treated with growth hormone (13 males and 9 females, aged 25-66 yr). The patients received replacement therapy with thyroxine, sex steroid hormones, and patients with secondary adrenocortical deficiency, hydrocortisone, but none of the patients had ever received GH treatment. In 22 patients, the total body with regional distribution of BMD, the lumbar spine L2-L4, and radial (33% site) BMD were determined by dual energy X-ray absorptiometry (DXA). In addition, 12 patients had the femoral neck BMD examined. In 10 cases, bone scintigraphy using 99-technetium labeled methylene diphosphonate was performed. Our studies revealed abnormalities, not yet described, in the regional distribution of BMD and bone scintigraphy in adults with CO hypopituitarism never treated with GH. In all patients, the results obtained from the total body showed definite disproportion in the regional distribution of BMD with a significantly advanced bone mineral deficit in the legs and a moderate deficit in the arms and total body. Local BMD measured at the radial (33% site) and lumbar spine L2-L4 revealed also a more pronounced bone mineral deficit in the cortical bone (33% distal radius) than in the trabecular bone (spine L2-L4). Bone scintigraphy showed a decrease in tracer accumulation in the shafts of the long bones but normal uptake in the spine, ribs, sternum, skull, and periarticular areas, indicating suppressed skeletal metabolism of cortical bone. Our studies indicate that long-life growth hormone deficiency leads to deficient and abnormal distribution of bone mineralization, a more pronounced deficit of BMD at the cortical bone, mainly expressed in the shafts of the long bones of the legs and arms, and moderately reduced BMD at the trabecular bone. Bone scans displaying low diphosphonates uptake in the shafts of the long bones point to greatly suppressed skeletal metabolism of the cortical bone in the patients with CO hypopituitarism never treated with GH.

Adolescents with Childhood-Onset GHD: How Do We Get Them to Peak Bone Mass?

The development of osteoporosis, with its attendant risk of fragility fracture, is in part related to the peak bone mass (PBM) achieved in early adulthood. Adolescence is a critical time for the acquisition of bone mass, with around 40% of skeletal mass being accrued during pubertal maturation. Growth hormone (GH) plays an integral role in the achievement of PBM after completion of linear growth, and several recent studies have suggested that GH replacement should continue in individuals with childhood-onset GHD until PBM has been attained - irrespective of the height achieved. In those with severe GHD after growth and pubertal development are complete, a seamless transition of GH therapy into adult life may be preferable to allowing a gap in GH treatment. The 'window of opportunity' concept for achieving PBM will, nevertheless, continue to be challenged by GHD teenagers who may resent the seamless continuation of GH replacement beyond adolescence. Preparation for this possibility should therefore begin during childhood, with all GHD teenagers being encouraged to remain on GH therapy until at least their mid-20s.

Growth hormone replacement therapy (GHRT) in children and adolescents: skeletal impact

In addition to its well-established effects on linear growth in childhood and adolescence, growth hormone has both direct and indirect actions on bone remodelling and homeostasis. In this review the limitations of methods of assessment of bone mineral density are highlighted. The influence of growth hormone deficiency of childhood-onset, on bone mineral accretion and, the specific skeletal implications of GHD in long-term survivors of childhood cancers, are discussed. Specific influential factors, which affect peak bone mass achievement and therefore skeletal health in later life, are evaluated.

Skeletal requirements for optimal growth hormone replacement in the transitional years

In addition to its well-established effects on linear growth in childhood and adolescence, growth hormone (GH) has both direct and indirect actions on bone remodelling and homeostasis. In this review, the discussion begins with the influence of childhood-onset growth hormone deficiency (CO-GHD) on bone mineral accretion. The limitations of methods of assessing bone mineral density (BMD) are highlighted and specific influential factors, which affect peak bone mass achievement and therefore skeletal health in later life, are evaluated.

Currently used growth-promoting treatment of children results in normal bone mass and density. A prospective trial of discontinuing growth hormone treatment in adolescents

BACKGROUND AND AIMS

The need for continued GH replacement in patients with childhood-onset GH deficiency (GHD) into adulthood has been recognized. The consequences of discontinuing GH treatment on bone mineralization in adolescent patients with GHD and short stature were examined over a period of 2 years.

PATIENTS

Forty adolescents (aged 16-21 years) treated with GH for more than 3 years and 16 closely matched healthy controls were studied. After a baseline visit, GH treatment was discontinued. The patients were then re-examined with the same protocol after 1 and 2 years. Twenty-one patients had continuing severe GHD into adulthood, while 19 patients were regarded as having sufficient endogenous GH secretion (GHS).

RESULTS

At baseline, there were no differences between the groups in total bone mineral content (BMC) or bone mineral density (BMD). After 2 years without GH treatment, BMC increased similarly in the GHD and GHS groups. BMC of the lumbar spine (L2-L4) increased only in the GHD group. Lumbar spine BMD increased in the GHD and the GHS groups. No changes were observed in the femoral neck region. Biochemical measurements showed that carboxy-terminal cross-linked telopeptide of type I collagen (ICTP) and bone specific alkaline phosphates (ALP) were higher in the GHD and GHS groups at baseline compared with controls. Osteocalcin, carboxy-terminal propeptide of type I procollagen (PICP), ICTP and ALP decreased during the 2 years off treatment in both the GHD and GHS groups. PICP was also lower after 2 years in the GHD group compared with both the GHS group and controls.

CONCLUSIONS

After discontinuation of GH therapy in adolescents at or near final height, there was a continued increase in BMC and BMD both for adolescents with growth hormone deficiency and for those classified as growth hormone sufficient. These groups did not differ from controls at baseline or after 2 years. In the growth hormone deficiency group, biochemical markers for bone formation decreased to levels below those in the growth hormone sufficient and healthy control groups. Although the number of patients and controls in this study were small, the results indicate that the present treatment of Swedish GH-deficient children to final height results in normal BMD.

Effects of 12-month GH treatment on bone metabolism and bone mineral density in adults with adult-onset GH deficiency

Serum bone-Gla protein (BGP), bone alkaline phosphatase (B-AP), and C-terminal cross-linked telopeptide of type I collagen (ICTP) levels were evaluated in 18 adults with acquired GH deficiency (GHD, 14 males and 4 females, age range: 25-59 yr) before, at 3, 6, 9 and 12 months of rec-GH treatment (0.125 IU/kg/week for the first month, followed by 0.25 IU/kg/week for 11 months) and 6 months after the withdrawal of therapy. Total body bone mineral density (BMD, g/cm2) was measured with dual energy X-ray absorptiometry (Hologic QDR 1000/W) before, at 12 months of GH treatment and 6 months after its withdrawal. Before treatment, BGP (mean+/-SE: 5.1+/-0.4 ng/ml), B-AP (59.4+/-6.5 IU/l), ICTP (3.1+/-0.3 ng/ml) levels of patients were similar to in healthy controls (BGP: 5.4+/-0.1 ng/ml; B-AP: 58.2+/-2.0 IU/l; ICTP: 4.1+/-0.3 ng/ml). GH treatment caused a significant increase of BGP, B-AP, ICTP levels, the maximal stimulation of bone resorption, occurring after 3 months of GH treatment, while the maximal effect on bone formation being evident later (at 6th month). A slight decline in BGP, B-AP, T-AP and ICTP levels occurred at 9-12 months of therapy, although the values remained significantly higher than in basal conditions and with respect to healthy controls. Before treatment, mean total body BMD of patients (1.110+/-0.027 g/cm2, range: 0.944-1.350 g/cm2) was not significantly different (z-score: +0.47+/-0.31, NS) from that observed in healthy controls (1.065+/-0.008 g/cm2, range: 1.008-1.121 g/cm2). GH therapy was associated with a significant reduction of mean total body BMD values (6th month: -1.8+/-0.5%, p<0.01; 12th month: -2.1+/-1.0%, p<0.05 vs baseline), particularly evident in the first six months of treatment. Six months after the withdrawal of GH therapy, BGP (5.9+/-0.5 ng/ml), B-AP (57.3+/-7.0 IU/l) and ICTP (3.2+/-0.1 ng/ml) levels returned similar to those recorded before treatment, while total BMD increased (+1.5+/-0.7, p<0.05), remaining however slightly lower than in basal conditions (-0.6+/-1.2, NS). In conclusion, our study shows that: a) acquired GHD in adulthood is associated with both normal bone formation/resorption indexes and normal total body BMD; b) GH therapy causes a significant rise of bone formation/resorption markers (earlier and greater for bone resorption); c) one-year GH therapy is associated with a reduction of total body BMD values, particularly evident in the first 6 months of treatment; d) the effects of GH therapy on bone turnover are transient, being completely reverted six months after the withdrawal of GH therapy; e) the increase of total body BMD (up to baseline values) after GH withdrawal might be explained as consequence of persisting effects of previous GH stimulation on bone remodeling.

Effects of 12 months rec-GH therapy on bone and collagen turnover and bone mineral density in GH deficient children with thalassaemia major

Children suffering from thalassaemia major are reported to have growth delay and bone alterations even when well transfused and chelated. In the present study we evaluated bone and collagen turnover (bone Gla-protein, BGP; carboxyterminal telopeptide of type I collagen, ICTP; aminoterminal propeptide of type III procollagen, PIIINP, respectively) and bone mineral density (BMD) in 5 pre-pubertal GH deficient thalassaemic children before and during rec-GH treatment (0.6 IU/kg/week). Data were compared with those recorded in an age- and sex-matched control group. Before treatment, serum BGP and ICTP levels were significantly lower (p<0.0001) in children with thalassaemia (9.3+/-0.7 ng/ml and 5.3+/-0.5 ng/ml, respectively) than in healthy controls (18.9+/-0.9 ng/ml and 14.4+/-0.6 ng/ml, respectively), while serum PIIINP levels did not significantly differ in the two groups (6.7+/-0.7 ng/ml vs 6.7+/-0.7 ng/ml). Mean lumbar BMD values of patients (0.62+/-0.05 g/cm2) were significantly lower (p<0.05) than those recorded in healthy controls (0.78+/-0.01 g/cm2), while femoral BMD values were similar in the two groups (patients: 0.70+/-0.08 g/cm2 vs controls: 0.74+/-0.01 g/cm2). One-year GH therapy significantly increased height velocity (from 2.3+/-0.2 cm/year to 6.1+/-0.4 cm/yr, p<0.0001) and IGF-I levels (from 61.6+/-15.4 to 342+/-38.5 ng/ml, p<0.005). Serum BGP (basal: 9.3+/-0.7 ng/ml, 6th month: 10.8+/-0.6 ng/ml, 12th month: 14.9+/-1.4 ng/ml), ICTP (basal: 5.3+/-0.5 ng/ml, 6th month: 7.9+/-0.8 ng/ml, 12th month: 10.9+/-1.7 ng/ml) and PIIINP levels (basal: 6.7+/-0.7 ng/ml, 6th month: 9.9+/-1.0 ng/ml, 12th month: 9.6+/-1.4 ng/ml) significantly increased (p<0.05), while no significant effects were observed on lumbar and femoral BMD values. Although the GH-induced stimulation of bone turnover markedly increased BGP (+60%) and ICTP (+105%) levels, one-year GH therapy was not sufficient to completely normalize these parameters, which remained significantly lower than in healthy controls. In conclusion, our study shows that pre-pubertal GH deficient children with thalassaemia major have reduced bone turnover (both bone formation and resorption) and lumbar BMD values, thus indicating that bone metabolism should be monitored and improved even in well-transfused patients. One-year GH treatment is able to increase, but not normalize, bone turnover, this effect being insufficient to improve BMD values. More prolonged periods of GH therapy are probably requested to positively affect both bone turnover and BMD values in GH deficient thalassaemic patients, as occurs in children and adults with GH deficiency.

Continuation of growth hormone (GH) replacement in GH-deficient patients during transition from childhood to adulthood: a two-year placebo-controlled study

Previous studies have demonstrated beneficial effects of GH replacement, in adults with GH deficiency (GHD), on body composition, physical fitness, and quality of life. These studies, however, concern patients with adult-onset GHD or childhood-onset (CO) patients enrolled several years after withdrawal of initial therapy. So far, the effects of continuation of GH-administration in patients with CO-GHD have not been examined. We studied a group of nineteen young adults (13 males + 6 females; 16-26 yr old; mean age, 20.2 +/- 0.65 yr) with CO-GHD, in a randomized, parallel, double-blind, placebo-controlled trial for 1 yr, followed by an open phase with GH for 1 yr. All patients received GH therapy at the start of study, and trial medication (GH/placebo) was given in a similar dose. Patients randomized to continued GH treatment exhibited no significant changes in any parameters tested, but intra- and interindividual variations in insulin-like growth factor (IGF)-I levels could suggest compliance problems. Discontinuation of GH for 1 yr resulted in a decrease in serum IGF-I, from 422.0 +/- 56.8 to 147.8 +/- 33.4 microg/L, in the placebo group (P = 0.003). After discontinuation of GH for 1 yr, an increase in total body fat (TBF, kg), measured by dual-energy x-ray absorptiometry scan, was seen [placebo: 22.7 +/- 2.7 to 26.5 +/- 2.5 (P = 0.01); GH: 16.2 +/- 2.1 to 17.2 +/- 2.1 (not significant)]. Resumption of GH after placebo was followed by increments in serum IGF-I (microg/L) [from 147.8 +/- 33.4 to 452 +/- 76 (P = 0.001)] and IGF-binding protein 3, as well as in fasting glucose (mmol/L) [4.9 +/- 0.2 vs. 5.3 +/- 0.2 (P = 0.03)]. After resumption of GH lean body mass (kg) increased [52.4 +/- 4.9 vs. 60.7 +/- 5.6 (P = 0.006)]. Likewise, resumption of GH therapy increased thigh muscle volume and thigh muscle/fat ratio, as assessed by computed tomography [muscle volume (cm2/10 mm): 118.2 +/- 11.7 vs. 130.0 +/- 10.9 (P = 0.002); muscle/fat ratio: 1.33 +/- 0.24 vs. 1.69 +/- 0.36 (P = 0.02)]. In conclusion, discontinuation of GH treatment in GHD patients, during the transition from childhood to adulthood, induces significant and potentially unfavorable changes in IGF-I and body composition, both of which are reversed after resumption of GH treatment. By contrast, continuation of GH therapy results in unaltered IGF-I and body composition. We recommend continuation of GH therapy in these patients, to be undertaken in collaboration between pediatricians and adult endocrinologists.

Changes in bone mineral density after discontinuation and early reinstitution of growth hormone (GH) in patients with childhood-onset GH deficiency

We measured bone mass density (BMD) in 28 childhood-onset adult GHD patients (20 MPHD, 8 IGHD) treated with hGH until final height. Twelve were re-treated with hGH (0.06 U/kg/day three times per week) for 16-24 months and eight of them followed for up to 5 years. Age at start of the study was 23.6 +/- 5.7 years (mean +/- SD) and the interval since the first hGH treatment was 5.8 +/- 4.4 years Baseline BMD was 82% of young normal healthy subjects. Patients < 20 years had a lower BMD than those > 20 years (75 vs 87%;P = 0.004). In the 12 patients re-treated with GH, BMD was 5.3% above baseline at 6 months after treatment was stopped (P< 0.002), and remained so for 3.5 years in eight patients who completed follow-up. In conclusion, increases in BMD occur after cessation of growth, but continuation of hGH treatment after final height achievement may prevent the late osteopenia of patients with childhood-onset GHD.

Effects of two years of growth hormone (GH) replacement therapy on bone metabolism and mineral density in childhood and adulthood onset GH deficient patients

The aim of the current study was to evaluate bone metabolism and mass before and after 2 years of GH replacement therapy in adults with childhood or adulthood onset GH deficiency. Thirty-six adults with GH deficiency, 18 with childhood onset, 18 with adulthood onset GH deficiency and 28 sex-, age-, height- and weight-matched healthy subjects entered the study. Biochemical indexes of bone turnover such as serum osteocalcin, serum carboxyterminal telopeptide of type-I procollagen, urinary hydroxyproline/creatinine and deoxypyridinoline/creatinine, of soft tissue formation such as aminoterminal propeptide of type-III and bone mineral density were evaluated. Childhood onset GH deficient patients had significantly decreased bone (osteocalcin: 2.5+/-1.3 vs 6.6+/-4.8 mcg/l, p<0.001) and soft tissue formation (aminoterminal propeptide of type III: 273+/-49 vs 454+/-23 U/I, p<0.001) indexes and normal bone resorption indexes (serum carboxyterminal telopeptide of type-I procollagen: 105+/-48 vs 128+/-28 mcg/l p=NS; urinary hydroxyproline/creatinine: 0.19+/-0.16 vs 0.28+/-0.16 mmol/mol, p=NS; urinary deoxypyridinoline/creatinine: 21 +/-10 vs 25+/-8 mcmol/mol, p=NS) compared to healthy subjects. On the contrary, no significant difference in bone turnover indexes between adulthood onset GH deficient patients and healthy subjects was found. Moreover, significantly decreased bone mineral density at any skeletal site and at whole skeleton was found in GH deficient patients compared to healthy subjects (e.g. femoral neck: 0.74+/-0.13 vs 0.97+/-0.11 g/cm2, p<0.001). In addition, a significant reduction of bone mineral density was found in childhood compared to adulthood onset GH deficient patients at any skeletal site, except at femoral neck. After 3-6 months of treatment, both groups of patients had a significant increase in bone turnover and in soft tissue formation. In particular, in childhood onset GH deficient patients after 3 months osteocalcin increased from 2.5+/-1.3 to 7.9+/-2.1 mcg/l, p<0.001 aminoterminal propeptide of type-III from 273+/-49 to 359+/-15 U/I p<0.001; serum carboxyterminal telopeptide of type-I procollagen from 105+/-48 to 201+/-45 mcg/l, p<0.001; urinary hydroxyproline/creatinine from 0.19+/-0.16 to 0.81+/-0.17 mmol/mol, p<0.001; urinary deoxypyridinoline/creatinine from 21 +/-10 to 54+/-20 mcmol/mol, p<0.001; while in adulthood onset GH deficient patients after 6 months osteocalcin increased from 4.2+/-3.6 to 6.5+/-1.9 mcg/l, p<0.05; aminoterminal propeptide of type- III from 440+/-41 to 484+/-37 U/I, p<0.05; serum carboxyterminal telopeptide of type-I procollagen from 125+/-40 to 152+/-22 mcg/l, p<0.05; urinary hydroxyproline/creatinine from 0.24+/-0.12 to 0.54+/-0.06 mmol/mol, p<0.001; urinary deoxypyridinoline/creatinine from 23+/-8 to 42+/-5 mcmol/mol, p<0.001. No significant difference in bone turnover between pre- and post-treatment period was found after 18-24 months of GH therapy. Conversely, bone mineral density was slightly reduced after 3-6 months of GH therapy, while it was significantly increased after 18-24 months. In fact, femoral neck bone mineral density values significantly rose from 0.74+/-0.13 g/cm2 to 0.87+/-0.11 g/cm2 (pre-treatment vs 2 years of GH treatment values). In conclusion, patients with childhood or adulthood onset GH deficiency have osteopenia that can be improved by long-term treatment with GH.

Adult vs childhood onset GHD: is there a real clinical difference?

As growth hormone (GH) secretion and insulin-like growth factor I (IGF-I) levels decrease with age, it is important to have reliable age- and sex-specific control data for both GH stimulation tests and circulating IGF-I levels. This is particularly true for elderly patients with a history of pituitary disease but with normal production of the anterior pituitary hormones other than GH. The potential impact of these factors on GH deficiency (GHD) has led to a need for the development of reliable, sensitive and specific tests to assess GH reserve. Before starting treatment with recombinant human GH in adults with suspected GHD, it is important to differentiate between adults with childhood onset GHD (CO-GHD) and those with adult onset GHD (AO-GHD). Adults with untreated CO-GHD have significantly lower values for body weight, body mass index, lean body mass and height than those with AO-GHD, while patients with AO-GHD show a more pronounced deviation from normal in psychosocial distress. Following treatment with GH, 12.5 microg/kg/day s.c., patients with AO-GHD showed a decrease in waist/hip ratio and low-density lipoprotein. Quality of life, as measured using the Nottingham Health Profile, changed significantly in both patient groups after 18 months of therapy, though these results were only consistent in subjects with AO-GHD. Improvements were also reported in physical mobility and energy. Side-effects were mainly reported in patients with AO-GHD, and this may have been due to the GH dosage being too high for older patients. In conclusion, CO-GHD in adults appears to be a developmental disorder in patients who have not attained full somatic maturation. The hormonal/metabolic balance and lifestyle of these individuals have adapted to their condition. AO-GHD is a metabolic disorder characterized by a hormonal imbalance affecting the health status, physical condition and quality of life of previously normal adults.

Growth hormone and bone

It is well known that GH is important in the regulation of longitudinal bone growth. Its role in the regulation of bone metabolism in man has not been understood until recently. Several in vivo and in vitro studies have demonstrated that GH is important in the regulation of both bone formation and bone resorption. In Figure 9 a simplified model for the cellular effects of GH in the regulation of bone remodeling is presented (Fig. 9). GH increases bone formation in two ways: via a direct interaction with GHRs on osteoblasts and via an induction of endocrine and autocrine/paracrine IGF-I. It is difficult to say how much of the GH effect is mediated by IGFs and how much is IGF-independent. GH treatment also results in increased bone resorption. It is still unknown whether osteoclasts express functional GHRs, but recent in vitro studies indicate that GH regulates osteoclast formation in bone marrow cultures. Possible modulations of the GH/IGF axis by glucocorticoids and estrogens are also included in Fig. 9. GH deficiency results in a decreased bone mass in both man and experimental animals. Long-term treatment (> 18 months) of GHD patients with GH results in an increased bone mass. GH treatment also increases bone mass and the total mechanical strength of bones in rats with a normal GH secretion. Recent clinical studies demonstrate that GH treatment of patients with normal GH secretion increases biochemical markers for both bone formation and bone resorption. Because of the short duration of GH treatment in man with normal GH secretion, the effect on bone mass is still inconclusive. Interestingly, GH treatment to GHD adults initially results in increased bone resorption with an increased number of bone-remodeling units and more newly produced unmineralized bone, resulting in an apparent low or unchanged bone mass. However, GH treatment for more than 18 months gives increased bone formation and bone mineralization of newly produced bone and a concomitant increase in bone mass as determined with DEXA. Thus, the action of GH on bone metabolism in GHD adults is 2-fold: it stimulates both bone resorption and bone formation. We therefore propose "the biphasic model" of GH action in bone remodeling (Fig. 10). According to this model, GH initially increases bone resorption with a concomitant bone loss that is followed by a phase of increased bone formation. After the moment when bone formation is stimulated more than bone resorption (transition point), bone mass is increased. However, a net gain of bone mass caused by GH may take some time as the initial decrease in bone mass must first be replaced (Fig. 10). When all clinical studies of GH treatment of GHD adults are taken into account, it appears that the "transition point" occurs after approximately 6 months and that a net increase of bone mass will be seen after 12-18 months of GH treatment. It should be emphasized that the biphasic model of GH action in bone remodeling is based on findings in GHD adults. It remains to be clarified whether or not it is valid for subjects with normal GH secretion. A treatment intended to increase the effects of GH/IGF-I axis on bone metabolism might include: 1) GH, 2) IGF, 3) other hormones/factors increasing the local IGF-I production in bone, and 4) GH-releasing factors. Other hormones/growth factors increasing local IGF may be important but are not discussed in this article. IGF-I has been shown to increase bone mass in animal models and biochemical markers in humans. However, no effect on bone mass has yet been presented in humans. Because the financial cost for GH treatment is high it has been suggested that GH-releasing factors might be used to stimulate the GH/IGF-I axis. The advantage of GH-releasing factors over GH is that some of them can be administered orally and that they may induce a more physiological GH secretion. (ABSTRACT TRUNCATED)