High-turnover osteopenia in preterm infants: determination of urinary pyridinium cross-links of collagen

Caffeine is a risk factor for osteopenia of prematurity in preterm infants: a cohort study

Background

Caffeine, the most commonly used medication in Neonatal Intensive Care Units, has calciuric and osteoclastogenic effects.

Methods

To examine the association between the cumulative dose and duration of therapy of caffeine and osteopenia of prematurity, a retrospective cohort study was conducted including premature infants less than 31 weeks and birth weight less than 1500 g. Osteopenia of prematurity was evaluated using chest X-rays on a biweekly basis over 12 weeks of hospitalization.

Results

The cohort included 109 infants. 51% had osteopenia of prematurity and 8% had spontaneous rib fractures. Using the generalized linear mixed model, caffeine dose and duration of caffeine therapy showed a strong association with osteopenia of prematurity. Steroids and vitamin D were also significantly correlated with osteopenia of prematurity while diuretic use did not show a statistically significant effect.

Conclusion

The cumulative dose and duration of therapy of caffeine, as well as steroid are associated with osteopenia of prematurity in this cohort. Future studies are needed to confirm these findings and determine the lowest dose of caffeine needed to treat effectively apnea of prematurity.

The Clinical and Biochemical Predictors of Bone Mass in Preterm Infants

BACKGROUND

Metabolic bone disease of prematurity still occurs in preterm infants, although a significant improvement in neonatal care has been observed in recent decades. Dual-energy X-ray absorptiometry (DXA) is the precise technique for assessing bone mineral content (BMC) in preterm infants, but is not widely available.

AIM

To investigate the clinical and biochemical parameters, including bone metabolism markers as potential predictors of BMC, in preterm infants up to 3 months corrected age (CA).

MATERIALS AND METHODS

Ca-P homeostasis, iPTH, 25-hydroxyvitamin D, osteocalcin, N-terminal propeptide, cross-linked C-telopeptide and amino-terminal pro C-type natriuretic peptide and the DXA scans were prospectively performed in 184 preterm infants (≤ 34 weeks' gestation) between term age and 3 mo CA. Lower bone mass was defined as BMC below or equal to respective median value for the whole study group, rounded to the nearest whole number.

RESULTS

The appropriate quality DXA scans were available for 160 infants (87%) examined at term and for 130 (71%) tested at 3 mo CA. Higher iPTH level was the only independent predictor of lower BMC at term, whereas lower BMC at 3 mo CA was associated both with lower urinary phosphate excretion and higher serum osteocalcin level. ROC analysis showed that iPTH >43.6 pg/mL provided 40% sensitivity and 88% specificity in identification of preterm infants with lower BMC at term. In turn, urinary phosphate excretion (TRP>97% or UP/Cr ≤0.74 mg/mg) and serum osteocalcin >172 ng/mL provided 40% sensitivity and 93% specificity in identification of infants with decreased BMC at 3 mo CA.

CONCLUSION

Serum iPTH might to be a simple predictor of reduced BMC in preterm infants at term age, but urinary phosphate excretion and serum osteocalcin might predict reduced BMC at 3 mo CA. These results represent a promising diagnostic tool based on simple, widely available biochemical measurements for bone mass assessment in preterm infants.

Quantitative ultrasound and biochemical parameters for the assessment of osteopenia in preterm infants

OBJECTIVE

Our study aimed to evaluate the feasibility of quantitative ultrasound (QUS) evaluation in osteopenia of prematurity and to compare the results to biochemical parameters.

METHODS

QUS assessment of bone was performed at the end of the first postnatal week and at term-corrected age (CA) in premature infants (N = 30) and within the first week in full-term infants (N = 25). On the same day of measurement of QUS, the serum calcium, phosphorus (inorganic), and alkaline phosphatase (ALP) activity were measured in the preterm infants.

RESULTS

The median of tibia z score at term-CA in premature infants was significantly lower compared to that of first postnatal week (-1 and 0.4, respectively; p < 0.0001) and it was also lower than that of term-matched controls (0.0; p = 0.001). Preterm infants at term-CA had lower weights and lengths in comparison to term infants. The median ALP value was 585 IU/L at the first postnatal week and 703 IU/L at term-CA in preterm infants (p = 0.003). The median tibia z score of infants with ALP >or=900 IU/L was significantly lower than that of the infants with ALP <900 IU/L (-1.4 vs. 0.1; p = 0.001). An inverse correlation was found between ALP levels and tibia z score at term-CA in preterm infants (rho = -0.61, p = 0.01).

CONCLUSIONS

Bone density of preterm infants at term-CA was lower than that at first postnatal week. Serum ALP levels increased during the first postnatal weeks. The tibia z scores were correlated to serum ALP levels. QUS is a good screening tool for the detection of osteopenia.

High bone turnover of type I collagen depends on fetal growth

The bone metabolic processes of proliferation and differentiation in preterm and term newborns have yet to be fully elucidated. Seventy-four umbilical cord blood samples were collected from preterm and term newborns delivered at 27 to 42 gestational weeks (GWs). Carboxy-terminal propeptide of type I procollagen (PICP), pyridinoline cross-linked telopeptide domain of type I collagen (ICTP), alkaline phosphatase (ALP), and bone-specific alkaline phosphatase (BAP) were measured. Calcitonin (CT), estrogen (E2), intact parathyroid hormone, and insulin-like growth factor-I (IGF-I) were also examined in 20 or 23 randomly selected samples. We conducted cross-sectional regression analyses for bone metabolic markers, fetal growth markers including GWs, birth weight (BW), height (BH) and head circumference (HC), and bone related hormones. PICP and ICTP activities were very high, but decreased significantly with fetal growth based on GWs, BW, BH, and HC changes (GWs, BW, and BH to both PICP and ICTP, P < 0.0001; HC to ICTP, P < 0.0001; HC to PICP, P < 0.05), while BAP and ALP did not change significantly. E2 and CT both showed a significant positive correlation with Ca (P < 0.05), but neither hormone had any apparent correlation with PICP, ALP, BAP, or ICTP. These results suggest very active bone formation and resorption of type I collagen to be dependent on fetal growth and that fetal osteoblasts dominate the proliferation phase of development rather than the maturation phase. However, factors contributing to high bone turnover in the fetus remain to be elucidated.

Dose response of bone mass to dietary arachidonic acid in piglets fed cow milk-based formula

BACKGROUND

The addition of arachidonic acid (AA) and docosahexaenoic acid (DHA) to infant formula was recently approved in North America. In piglets, dietary AA is linked to elevations in bone mass.

OBJECTIVE

The objective was to investigate the effects of varied amounts of dietary AA on bone modeling and bone mass with the use of the piglet model for infant nutrition.

DESIGN

Male piglets (n = 32) were randomly assigned to receive 1 of 4 formulas supplemented with AA (0.30%, 0.45%, 0.60%, or 0.75% of fat) plus DHA (0.1% of fat) from days 5 to 20 of life. Measurements included biomarkers of bone modeling, fatty acid status, and whole-body and femur bone mineral content; bone area was measured by dual-energy X-ray absorptiometry. Differences among groups were detected with two-factor analysis of variance. Regression analyses were used to determine factors responsible for bone mineral content after dietary AA was accounted for.

RESULTS

Proportions of AA in plasma, liver, and adipose were modified by the dietary treatments, but bone modeling was not affected. Liver AA was positively related to plasma insulin-like growth factor 1 and calcitriol and urinary N-telopeptide. Whole-body bone mineral content was elevated in the piglets fed 0.60% and 0.75% AA and was best predicted by dietary AA and bone resorption.

CONCLUSIONS

This study confirms that dietary AA alters bone mass and clarifies the best amount of AA to add to the diet of pigs born at term. Because the amount of dietary DHA was held constant, whether other amounts of DHA are related to bone mass requires investigation.

Urinary excretion of cross-linked N-telopeptides of type 1 collagen to assess bone resorption in infants from birth to 1 year of age

OBJECTIVES

To evaluate noninvasively bone resorption in infants and more specifically, to assess the accuracy of urinary collagen type 1 cross-linked N-telopeptide (NTX) excretion normalized to creatinine (NTX/Cr) in a spot urine sample as a reflection of daily NTX production in infants and to compute normative values for NTX excretion from birth to 1 year of age.

METHODS

NTX/Cr values obtained from a single spot urine sample were compared with daily urinary NTX excretion and NTX/Cr obtained in 24-hour urine collected from 8 hospitalized infants. Normative values for NTX excretion were collated with a cross-sectional study in 70 healthy French infants (42 boys, 28 girls) aged 0 to 374 days (weight: 2700-11 340 g; length: 46-76.5 cm) and free of diseases or treatments that could influence growth, bone mineralization, or renal function.

RESULTS

NTX/Cr values from single spot urine sample were significantly and linearly correlated with both daily NTX excretion (r = 0.783) and daily NTX/Cr (r = 0.952). In healthy infants, NTX excretion is low at birth, increases dramatically and significantly during the first 10 days of life, remains significantly elevated for approximately 3 months, and then decreases progressively to return to values similar to that observed at birth by 1 year of age.

CONCLUSIONS

These data provide new insights regarding the use of spot urine analysis for assessing NTX excretion during the first year of life. The normative data demonstrate significant age-related variations in this marker, which probably reflect adaptation to extrauterine life and accelerated bone turnover in infancy and which should be considered for the interpretation of this noninvasive bone resorption marker in the clinical setting.

Changes in markers of bone metabolism during dexamethasone treatment for chronic lung disease in preterm infants

AIM

To characterise the change in serum and urinary bone markers in the early postnatal period, and to assess the effect of systemic corticosteroid on bone metabolism in preterm infants.

METHODS

Bone formation was quantified by measurement of serum concentrations of bone specific alkaline phosphatase (BALP) and osteocalcin. Bone resorption was measured by monitoring creatinine adjusted urinary deoxypyridinoline (Dpd) concentration. Blood and urinary samples were collected from corticosteroid treated infants (n = 19) immediately before the start (T(d-pre)), three weeks after the start (T(d-end)), and two (T(d-post2)) and four weeks (T(d-post4)) after the end of the dexamethasone course. Untreated patients (n = 30) had specimens taken at week 3 (T(wk-3)), 6 (T(wk-6)), 8 (T(wk-8)), and 10 (T(wk-10)) of postnatal age.

RESULTS

Serum concentrations of BALP and osteocalcin at T(d-end) were significantly lower than pretreatment levels and the levels at the corresponding time point (T(wk-6)) of the non-treatment group. In contrast, urinary Dpd concentration at T(d-end) was not significantly decreased compared with the pretreatment level. However, it was significantly lower than the urinary Dpd concentration at T(wk-6) of the non-treatment group. The rate of increase in lower leg length was significantly higher in the non-treatment group between weeks 3 and 6 than in the corresponding period during dexamethasone treatment in the corticosteroid group.

CONCLUSION

Systemic corticosteroid causes appreciable suppression of serum BALP and osteocalcin and, to a lesser extent, urinary Dpd. The results suggest that corticosteroid inhibits bone growth mainly by decreasing bone formation.

Zinc and perinatal growth

AIM

To study the relationship between zinc, insulin-like growth factor (IGF-I), osteocalcin and perinatal growth.

MATERIALS AND METHODS

Anthropometric variables, serum levels of IGF-I, osteocalcin and zinc were measured in preterm (PT) appropriate for gestational age (AGA), full term (FT) small for gestational age (SGA) and FT AGA newborns at birth (n=52), at first week (n=38) and at third week (n=38) of postnatal age.

RESULTS

At birth, the FT SGA had lower levels of IGF-I. At the first week after birth, both FT SGA and PT AGA infants had less deposits of subcutaneous fat; FT SGA infants also showed significantly lower osteocalcin and zinc levels. At 3 weeks of postnatal life, FT SGA infants continued to show significantly lower zinc levels. They had increased their fat deposits so that differences between groups in skinfold measurements failed to be significant. The highest levels of osteocalcin were found in PT AGA infants at the third week after birth.

CONCLUSIONS

Perinatal nutrition influences the IGF-I levels. The low concentration of osteocalcin found in SGA infants at first week of life probably reflects decreased bone turnover. During the first weeks of life, there is a progressive decrease in the serum levels of zinc, accentuated in the FT SGA group.

Bone mineral metabolism in the micropremie

Environmental factors, nutritional supplies, hormonal status, diseases, and treatments appear to affect postnatal skeletal growth and mineralization in VLBW infants. Compared with their term counterparts, ELBW infants are at risk of postnatal growth deficiency and osteopenia at the time of hospital discharge. From recent data, DXA is becoming one of the reference techniques to evaluate mineral status, whole-body composition, and effects of dietary manipulations on weight gain composition and mineral accretion in preterm infants. Weight gain and length increases need to be evaluated carefully during the first weeks of life, in the intensive care unit and out of it, in the step down unit. Nutritional survey is required to improve the nutritional supply and to maximize linear growth. As the critical epoch of growth extends, during the first weeks or months after discharge, follow-up and nutritional support need to be provided during the first years to promote early catch-up growth and mineralization. Further studies need to determine precisely the most optimal feeding regimen during this period but also need to evaluate the long-term implications of such a policy on stature, peak bone mass, and general health at adulthood.

Bone and collagen markers in preterm infants: relationship with growth and bone mineral content over the first 10 weeks of life

In a longitudinal study of 25 preterm infants, we have examined the relationship of bone-specific alkaline phosphatase (ALP), C-terminal propeptide of type I collagen (PICP), N-terminal propeptide of type III procollagen (P3NP), C-terminal telopeptide of type I collagen, urinary pyridinoline (Pyd) and deoxypyridinoline (Dpd), with rates of gain in weight, length, and lower leg length and with bone mineral content (BMC), all measured at weekly intervals over the first 10 wk of life. Concentrations of all collagen markers were 10-fold higher than in older children. Each marker showed a distinctive pattern of postnatal change, with early increases in PICP and P3NP and decreases in ICTP reflecting postnatal growth. Once markers had reached a plateau during weeks 4-10, P3NP was positively correlated, whereas Pyd and Dpd were negatively correlated with rate of weight gain (r = +0.44, -0.46, and -0.40, respectively, p < 0.05). P3NP was also positively correlated with overall linear growth (r = +0.44, p < 0.05). PICP was strongly correlated with mean BMC (r = +0.63,p < 0.01) and with total BMC attained by the end of the study period (r = +0.81, p < 0.001). Bone ALP was positively correlated with the rate of bone mineral accretion (r = +0.55, p = 0.01). We conclude that the marker of soft-tissue collagen formation, P3NP, is a good marker for overall ponderal and linear growth in preterm infants, whereas the markers of collagen breakdown, Pyd and Dpd, have inverse relationships with weight gain. The osteoblast markers, PICP and bone ALP, seem to be good surrogate markers for bone mineralization in preterm infants. Markers may provide information on whole-body turnover of bone and collagen that is complementary to traditional physical measures of growth and bone mineralization.

Assessment of bone turnover in term and preterm newborns at birth: measurement of urinary collagen crosslink excretion

We measured urinary excretion of collagen crosslinks, pyridinoline and deoxypyridinoline, in term and preterm newborns at birth and evaluated the developmental changes in bone turnover. Collagen crosslink excretion in newborns was more than 10 times higher than reported adult values and several times higher than those of older children. The values were significantly higher in preterm newborns than in term newborns. In addition, a significant and inverse correlation was found between urinary collagen crosslinks and gestational age in preterm newborns. Excretion of crosslinks during this period did not correlate with beta2-microglobulin, suggesting that the excretion was not directly influenced by renal function in newborns. We conclude that bone turnover assessed by measurement of collagen crosslink excretion is high at birth and that preterm newborns have higher bone turnover than term newborns.