Collagen formation and degradation increase during growth hormone therapy in children

Bone Turnover Markers in Children: From Laboratory Challenges to Clinical Interpretation

Bone turnover markers (BTMs) have been developed many years ago to study, in combination with imaging techniques, bone remodeling in adults. In children and adolescents, bone metabolism differs from adults since it implies both growth and bone remodeling, suggesting an age- and gender-dependent BTM concentration. Therefore, specific studies have evaluated BTMs in not only physiological but also pathological conditions. However, in pediatrics, the use of BTMs in clinical practice is still limited due to these many children-related specificities. This review will discuss about physiological levels of BTMs as well as their modifications under pathological conditions in children and adolescents. A focus is also given on analytical and clinical challenges that restrain BTM usefulness in pediatrics.

Idiopathic short stature and growth hormone sensitivity in prepubertal children

OBJECTIVE

We compared growth hormone sensitivity to an insulin-like growth factor I (IGF-I) generation test in children with idiopathic short stature (ISS) and of normal stature (NS) across the birthweight range.

METHODS

Forty-six prepubertal children (~7.1 years) born at term were studied: ISS (n = 23; 74% boys) and NS (n = 23; 57% boys). Children underwent a modified IGF-I generation test with recombinant human growth hormone (rhGH; 0.05 mg/kg/d) over four consecutive days. Hormonal concentrations were measured at baseline and day 5.

RESULTS

Children with idiopathic short stature were 1.90 SDS lighter (P < 0.0001) but had 4.5% more body fat (P = 0.0007) than NS children. Overall, decreasing birthweight SDS across the normal range (-1.9 to +1.5 SDS) was associated with lower percentage IGF-I response to rhGH stimulation in univariable (r = 0.45; P = 0.002) and multivariable models (β = 24.6; P = 0.006). Plasma IGF-I concentrations rose in both groups with rhGH stimulation (P < 0.0001). GHBP levels (P = 0.002) were suppressed in ISS children (-19%; P = 0.029) but increased among NS children (+18%; P = 0.028), with contrasting responses also observed for leptin and IGFBP-1. Further, the increase in insulin concentrations in response to rhGH stimulation was ~3-fold greater in NS children (142% vs 50%; P = 0.006).

CONCLUSIONS

A progressive decrease in birthweight SDS was associated with a reduction in GH sensitivity in both NS and ISS children. Thus, the lower IGF-I response to rhGH stimulation in association with decreasing birthweight indicates that the ISS children at the lower end of the birthweight spectrum may have partial GH resistance, which may contribute to their poorer growth.

Association Between Vitamin D and Carboxy-Terminal Cross-Linked Telopeptide of Type I Collagen in Children During Growth Hormone Replacement Therapy

Growth hormone and insulin-like growth factor-1 (IGF-1) play a crucial role in the regulation of bone turnover. Adequate vitamin D status supports proper bone remodeling, leading to normal longitudinal bone growth and normal peak bone mass. The aim of this study was to evaluate the association between serum 25-hydroxyvitamin D [25(OH)D] and carboxy-terminal cross-linked telopeptide of type I collagen (ICTP) in children and adolescents with growth hormone deficiency at baseline and during recombinant human growth hormone (rhGH) replacement therapy. The study was prospective and included 30 children and adolescents aged 5 to 17 years. Concentrations of 25(OH)D, ICTP, and IGF-1 were measured at baseline and during the first year of rhGH therapy. Baseline serum 25(OH)D concentration correlated with ICTP concentrations during the first trimester of rhGH therapy (r = 0.38, p < 0.050); the correlation was stronger in the second trimester of therapy (r = 0.6, p = 0.002). We conclude that proper vitamin D status is important in reaching the adequate dynamics of bone remodeling during growth, which is essential to achieve a catch-up growth during rhGH therapy.

Maturity assessment and curve progression in girls with idiopathic scoliosis

BACKGROUND

Scoliosis progression during adolescence is closely related to patient maturity. Maturity has various indicators, including chronological age, height and weight changes, and skeletal and sexual maturation. It is not certain which of these indicators correlates most strongly with scoliosis progression. The purpose of the present study was to evaluate various maturity measurements and how they relate to scoliosis progression.

METHODS

Physically immature girls with idiopathic scoliosis were evaluated every six months through their growth spurt with serial spinal radiographs; hand skeletal ages; Oxford pelvic scores; Risser sign determinations; height; weight; sexual staging; and serologic studies of the levels of selected growth factors, estradiol, bone-specific alkaline phosphatase, and osteocalcin. These measurements were then correlated with the curve-acceleration phase.

RESULTS

The period and pattern of curve acceleration began during Risser stage 0 for all patients. Skeletal maturation scores derived with the use of the Tanner-Whitehouse-III RUS method, particularly those for the metacarpals and phalanges, were superior to all other indicators of maturity. Regression of the scores provided good estimates of maturity relative to the period of curve progression (Pearson r = 0.93). The initiation of this period occurred simultaneously with digital changes from Tanner-Whitehouse-III stage F to G. At this stage, curves also separated into rapid, moderate, and low-acceleration patterns, with specific curve types in the rapid and moderate-acceleration groups. The low-acceleration group was not confined to a specific curve type.

CONCLUSIONS

The curve-acceleration phase separates curves into various types of curve progression. The Tanner-Whitehouse-III RUS scores are highly correlated with timing relative to the curve-acceleration phase and provide better maturity determination and prognosis determination during adolescence than the other parameters tested. Accurate skeletal maturity determination should be used as the primary maturity measurement in girls with idiopathic scoliosis.

Correlates of the peak height velocity in girls with idiopathic scoliosis

STUDY DESIGN

Prospective longitudinal.

OBJECTIVE

Determine correlates of the peak height velocity (PHV) in girls with idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Only identifiable retrospectively, the PHV is the most useful known maturity marker in idiopathic scoliosis. Clinically useful correlates are needed to make PHV timing helpful.

METHODS

A total of 24 immature girls with idiopathic scoliosis were followed with serial heights, sexual staging, skeletal ages, spinal radiographs, insulin-like growth factor (IGF)-1, IGF binding protein-3, dehydroepiandrosterone sulfate, estradiol, bone-specific alkaline phosphatase, and osteocalcin levels. These markers were correlated to PHV timing.

RESULTS

There were 14 girls who had identifiable growth peaks that averaged 10.5 +/- 1.8 cm/y at age 11.7 +/- 1 years. At the PHV, all girls were Risser 0 with open triradiate cartilages. On a skeletal age radiograph, digital uncapped phalangeal epiphyses were indicative of pre-PHV and fused epiphyses of post-PHV. Capped but unfused epiphyses were indeterminate. Tanner stage 1 for breast strongly indicates pre-PHV. Stage 3 for breast and pubic hair occurred at or after the PHV, and stage 4 always occurred after PHV. Higher IGF-1 and estradiol levels after PHV are potentially discriminatory.

CONCLUSIONS

The PHV occurs during Risser 0 with open triradiate cartilages. If triradiate cartilages are open, then Tanner stages, IGF-1, estradiol levels, and the appearance of the epiphyses on a skeletal age radiograph are useful in determining status before or after PHV.

Effect of growth hormone therapy and puberty on bone and body composition in children with idiopathic short stature and growth hormone deficiency

The state of bone health and the effect of growth hormone (GH) therapy on bone and body composition in children with idiopathic short stature (ISS) are largely unknown. A direct role of GH deficiency (GHD) on bone density is controversial. Using dual-energy X-ray absorptiometry, this study measured total body bone mineral content (TB BMC), body composition, and volumetric bone mineral density (vBMD) at the lumbar spine (LS) and femoral neck (FN) in 77 children (aged 3-17 years) with ISS (n = 57) and GHD (n = 20). Fifty-five children (GHD = 13) receiving GH were followed over 24 months including measurement of bone turnover. At diagnosis, size-corrected TB BMC SDS was greater (P <or= 0.002) and LSvBMD SDS lower (P < 0.03) than zero in both prepubertal ISS and GHD subjects, but FNvBMD SDS was reduced only in the GHD group (P < 0.05). The muscle-bone relation, as assessed by the BMC/lean mass (LTM) ratio SDS was not different between groups. During GH therapy, prepubertal GHD children gained more height (1.58 [0.9] SDS) and LTM (0.87 [0.63] SDS) compared to prepubertal ISS children (0.75 [0.27] and 0.17 [0.25] SDS, respectively). Percent body fat decreased in GHD (-5.94% [4.29]) but not in ISS children. Total body BMC accrual was less than predicted in all groups accompanied by an increase in bone turnover. Puberty led to the greatest absolute, but not relative, increments in weight, LTM, BMI, bone mass, and LSvBMD. Our results show that children with ISS and GHD differ in their response to GH therapy in anthropometry, body composition, and bone measures. Despite low vBMD values at diagnosis in both prepubertal groups, size-corrected regional or TB bone data were generally within the normal range and did not increase during GH therapy in GHD or ISS children. Growth hormone had great effects on the growth plate and body composition with subsequent gains in height, LTM, bone turnover, and bone mass accrual, but no benefit for volumetric bone density over 2 years.

Pubertal changes in biochemical markers of growth

Puberty is a crucial period of life during which dramatic hormonal changes induce notable modifications in linear growth, bone mass and body composition. These changes are associated with variations in some biochemical parameters such as markers of bone turnover and leptin, which may reflect changes in bone growth and fat mass, respectively. Children with growth hormone (GH) deficiency have reduced concentrations of bone markers, which increase during GH administration, while the levels of leptin decrease. There have been few studies analysing the behaviour of bone markers during puberty in GH-treated GH-deficient patients and no studies analysing the behaviour of leptin. Results from a longitudinal study showed that there was no change in serum osteocalcin, carboxy-terminal propeptide of type I procollagen, and cross-linked carboxy-terminal telopeptide of type I collagen levels during puberty in GH-treated GH-deficient children. Some studies have shown that changes in markers of bone turnover and leptin after short-term GH treatment may predict the growth response (at 6-12 months) to GH administration in GH-deficient children. At present, insufficient data are available for the clinical use of these parameters as markers of growth response during pubertal development and as predictors of long-term growth response to GH treatment in children with GH deficiency. Nevertheless, the use of more and possibly new markers might improve the accuracy of growth prediction models in the future.

Biochemical markers of growth hormone (GH) sensitivity in children with idiopathic short stature: individual capacity of IGF-I generation after high-dose GH treatment determines the growth response to GH

OBJECTIVE AND PATIENTS

To assess multiple dose-response relationships between three GH doses (1.5, 3.0 and 6.0 IU/m2) and nine different biochemical markers of GH sensitivity in a well-defined group of 17 children with idiopathic short stature (ISS).

DESIGN AND MEASUREMENTS

Serum levels of IGF-I, IGF-II and IGFBP-3, and peripheral markers leptin, C-terminal propeptide of type I collagen (PICP) and N-terminal propeptide of type III collagen (PIIINP), alkaline phosphatase (AP) and osteocalcin (OC) were measured at the start and after 2 and 12 weeks of periods of no treatment, GH 1.5 IU/m2 and GH 3.0 IU/m2. Twelve-week washout periods were applied between the 12-week GH-treatment periods. High-dose GH treatment was given during the second year of study and all serum markers were measured at start, after 2 and 12 weeks and 1 year of GH 6.0 IU/m2. In 18 non-GH-treated children with ISS the same parameters were measured yearly. The bone resorption marker urinary deoxypyridinoline (DPD) was measured during 12-h day and night periods at start and after 2 weeks GH 1.5, 3.0 and 6.0 IU/m2.

RESULTS

All markers were GH dependent, but the timing of maximal response varied among different markers. Height SDS at start, age at start and IGF-II at baseline were inversely related to the first-year growth response (r = -0.73, P = 0.001; r = -0.53, P = 0.03; and r = -0.53, P = 0.03, respectively). Some statistically significant correlations between biochemical responses on low GH doses (1.5 or 3.0 IU/m2) and second-year growth response were found, but these showed no consistent pattern. However, all changes in IGF-I SDS after GH 6.0 IU/m2 measured either after 2 or 12 weeks or 1 year correlated significantly with the second-year growth response (r = 0.55, P = 0.02; r = 0.81, P = 0.001; and r = 0.86, P < 0.001, respectively). Baseline or GH-stimulated levels of peripheral markers did not correlate with the growth response.

CONCLUSION

The individual capacity of IGF-I generation after high-dose GH treatment (6.0 IU/m2) determines the growth response on high-dose GH treatment. Peripheral markers do not seem to play a role in growth prediction of children with ISS.

Markers of collagen metabolism and insulin-like growth factor binding protein-1 in term infants

AIM

To study the relation between fetal growth and markers of collagen metabolism and insulin-like growth factor binding protein-1 (IGFBP-1) in term infants.

METHODS

Cord vein plasma was obtained from 67 term infants of gestational age 37.1-41.7 weeks (39 appropriate for gestational age (AGA), 11 large for gestational age (LGA; relative birth weight >/= 2.0 SD), and 17 small for gestational age (SGA; relative birth weight </= -2.0 SD)) for analysis of markers of metabolism of collagen type I (PICP and ICTP) and III (PIIINP) and of IGFBP-1.

RESULTS

Negative correlations existed between gestational age and PICP (r = -0.294, p = 0.0158), ICTP (r = -0.338, p = 0.0052), and PIIINP (r = -0.432, p = 0.0003). These correlations were also found in SGA infants (all p < 0.05). IGFBP-1 showed negative correlations with birth weight and relative birth weight (r = -0.644, p = 0.0001, and r = -0.693, p = 0.0001 respectively) but not with gestational age (p>0.05).

CONCLUSIONS

In the term fetus, collagen metabolism is primarily dependent on maturity and not on intrauterine growth status, whereas IGFBP-1 reflects intrauterine growth independently of maturity.

In vivo expression of human growth hormone by genetically modified murine bone marrow stromal cells and its effect on the cells in vitro

Human growth hormone (hGH) is frequently used clinically for growth abnormalities in children and also in adults with growth hormone deficiency. The hormone is usually administered to the individuals by frequent injections. In the present study we investigated the potential of bone marrow stromal cells as vehicles to deliver the GH in vivo by infusion of cells transduced with hGH cDNA into mice femurs. The effect of the hormone on the transduced cells in vitro was also assessed. Bone marrow stromal cells established from a mouse model of human osteogenesis imperfecta mice (oim) were transduced with a retrovirus containing hGH and neomycin resistance genes. The hGH-expressing cells were selected in a medium containing G418 and were then assessed for the hGH expression in vitro. The selected cells synthesized 15 ng/10(6) cells of hGH per 24 h in vitro and exhibited alkaline phosphatase activity when they were treated with the human recombinant bone morphogenetic protein 2 (rhBMP-2). The transduced cells also proliferated faster than the LacZ transduced cells but they did not exhibit a higher rate of matrix synthesis. When 2 x 10(6) hGH+ cells were injected into the femurs of mice, hGH was detected in the serum of the recipient mice up to 10 days after injection. The highest level of growth hormone expression, 750 pg/ml, was detected in the serum of the recipient mice I day after injection of the transduced cells. hGH was also detected in the medium conditioned by cells that were flushed from the femurs of the recipient mice at 1, 3, and 6 days after cell injection. These data indicate that bone marrow stromal cells could potentially be used therapeutically for the delivery of GH or any other therapeutic proteins targeted for bone. The data also suggest that GH may exert its effects on bone marrow stromal cells by increasing their rate of proliferation.

Long-term monitoring of rec-GH treatment by serial determination of serum aminoterminal propeptide of type III procollagen in children and adults with GH deficiency

Serum aminoterminal propeptide of type III procollagen (PIIINP) levels, a reliable marker of collagen formation, were evaluated in children (C=7) and adults with childhood-onset (CO=10) and acquired (A=18) GH deficiency (GHD) before, during and after withdrawal of rec-GH therapy (C=0.6 IU/kg/week, CO=0.5 IU/kg/week, A=0.25 IU/kg/week). The duration of treatment was 12 months for C and A and 6 months for CO; investigations were carried out before and at 3, 6, 9 and 12 months (for C and A) and at 3 and 6 months (for CO) of GH treatment and 6 months after the withdrawal of therapy (for A and CO). Data obtained from patients were compared with those recorded in two age- and sex-matched control groups. Before treatment, serum PIIINP levels were significantly lower (p<0.001) in C with GHD (mean+/-SE: 2.9+/-0.4 ng/ml) than in controls (6.1+/-0.4 ng/ml), while no significant differences were recorded between adults with CO/A-GHD (3.7+/-0.5 ng/ml and 3.4+/-0.2 ng/ml) and controls (3.2+/-0.2 ng/ml). GH treatment caused a significant increase (p<0.0001) of PIIINP levels both in C (3rd month: 4.4+/-0.2 ng/ml, 6th month: 5.1+/-0.4 ng/ml, 12th month: 5.1+/-0.5 ng/ml), CO-GHD (3rd month: 12.7+/-1.2 ng/ml; 6th month: 10.2+/-0.6 ng/ml) and A-GHD (3rd month: 10.0+/-1.0 ng/ml; 6th month: 8.4+/-0.6 ng/ml; 12th month: 7.0+/-0.7 ng/ml), the increase being dose-dependent (more marked and sustained in adults with CO-GHD). The maximal stimulation of collagen synthesis occurred after 3 months of GH treatment in adults with GHD, while a more gradual and less relevant increase was observed in C with GHD. Six months after the withdrawal of GH therapy, serum PIIINP levels of adults with CO-GHD (3.6+/-0.3 ng/ml) were similar to those recorded before treatment, while in adults with A-GHD serum PIIINP levels (2.6+/-0.2 ng/ml) were significantly lower (p<0.01) than in basal condition. In conclusion, our study shows that: a) GHD is associated with a reduction of soft tissue formation in children, while it seems to exert no relevant effects in adults with GHD; b) GH therapy causes a rapid stimulation of collagen turnover, which shows a different pattern in children and adults; c) the GH-induced stimulation of collagen synthesis is rapidly removed after the withdrawal of GH treatment. For these reasons, the determination of peripheral markers of GH effects appears useful for the monitoring of GH therapy and can contribute to assess the "tailored" substitutive dose for the individual patient.