Measurements of bone turnover markers in premature infants

Screening of Serum Alkaline Phosphatase and Phosphate Helps Early Detection of Metabolic Bone Disease in Extremely Low Birth Weight Infants

Background: Extremely low birth weight (ELBW, <1,000 g) infants have a high risk of metabolic bone disease (MBD). Because of the late appearance of radiological signs, diagnosis of MBD in ELBW infants might be delayed, and its prevalence underestimated in this group of patients. This study adopted serial screening of serum alkaline phosphatase (ALP) and phosphate (P) of ELBW infants to determine whether such screening is helpful for the early detection of MBD. Materials and Methods: We performed a retrospective study of preterm infants with a gestational age ≤ 31 weeks and birth weight <1,000 g. MBD was absent (ALP ≤500 IU/L), mild (ALP >500 IU/L, P ≥4.5 mg/dL), and severe (ALP >500 IU/L, P <4.5 mg/dL); MBD was divided into early MBD (≤4 weeks after birth) and late MBD (>4 weeks after birth) according to the time of onset. Results: A total of 142 ELBW infants were included, with a median gestational age of 28.1 (26.5-29.7) weeks and a median birth weight of 875 (818-950) g. Seventy-three cases of MBD were diagnosed, and the total prevalence was 51.4% (mild MBD, 10.6%; and severe MBD, 40.8%). Male sex, breastfeeding, and sepsis would increase the risk of severe MBD. Most MBD in ELBW infants occurred at 3-4 weeks after birth. Sixty-two percent (45/73) of infants were diagnosed as having early MBD, which are diagnosed earlier than late MBD [24 (21-26) vs. 39 (36-41), t = -7.161; P < 0.001]. Male sex [odds ratio (OR), 2.86; 95% confidence interval (CI), 1.07-7.64; P = 0.036], initial high ALP levels (OR, 1.02; 95% CI, 1.01-1.03; P < 0.001), and breastfeeding (OR, 5.97; 95% CI, 1.01-25.12; P = 0.049) are independent risk factors for the development of early MBD. Conclusion: The risk of MBD among ELBW infants is very high. Most cases occurred early and were severe. Male sex, initial high ALP levels, and breastfeeding are closely related to the increased risk of early MBD. Serial screening of serum ALP and P helps early detection of MBD; it is recommended to start biochemical screening for ELBW infants 2 weeks after birth and monitor their biochemical markers weekly.

The Role of Exercise in Prevention and Treatment of Osteopenia of Prematurity: An Update

Premature infants have an increased risk of osteopenia due to limited bone mass accretion in utero and a greater need for bone nutrients. Until recently, most efforts to prevent osteopenia of prematurity focused on nutritional changes. Recent studies indicate that passive range-of-motion exercise of the extremities may lead to beneficial effects on body weight, increased bone mineralization, increased bone formation markers and leptin levels, and attenuation of the natural postnatal decline in bone speed of sound. These results suggest that exercise may play an important role in the prevention and treatment of osteopenia of prematurity. This review summarizes our current knowledge on the role of exercise in the prevention and treatment of osteopenia of prematurity.

Procollagen type I N-terminal peptide in preterm infants is associated with growth during the first six months post-term

OBJECTIVE

To identify growth-related collagen and bone parameters in small-for-gestational-age (SGA) and appropriate-for-gestational-age (AGA) preterm infants during the first six months post-term. In SGA preterm infants, increased growth and decreased bone acquisition, which we demonstrated previously, may be reflected by these markers.

DESIGN

Observational study within a randomized controlled trial.

PATIENTS

Thirty-three SGA (weight, length or both at birth <-2 SDS) and 98 AGA preterm infants (gestational age [median (IQR)]: 31·1 (1·6) vs 30·3 (2·0) weeks; 72·7% vs 42·9% boys).

MEASUREMENTS

Weight (g), length (cm), procollagen type I N-terminal peptide (PINP; μg/l), urinary helical peptide (UHP; μg/mmol creatinine) and alkaline phosphatase (ALP; U/l) expressed as standard deviation scores (SDS) at term age, three and six months post-term.

RESULTS

Weight and length gain during the first six months post-term and PINP SDS at term age, three months and six months post-term were higher in SGA compared with AGA infants. UHP SDS and ALP SDS were similar in SGA and AGA infants. PINP SDS and UHP SDS at term age and PINP SDS at three months were associated with subsequent weight and length gain until six months post-term.

CONCLUSIONS

Increased growth in SGA compared with AGA preterm infants is reflected by increased collagen type I synthesis during the first six months post-term, suggesting that PINP and UHP correspond with growth in preterm infants. An explanation for decreased bone acquisition of SGA preterm infants may be that increased collagen type I synthesis is not directly followed by increased bone mineralization.

Higher vitamin D intake in preterm infants fed an isocaloric, protein- and mineral-enriched postdischarge formula is associated with increased bone accretion

During the first half of infancy, bone accretion in preterm infants fed an isocaloric, protein- and mineral-enriched postdischarge formula (PDF) is higher compared with those fed term formula (TF) or human milk (HM). This may be related to higher protein, calcium, phosphorus, and vitamin D intakes. This study investigated serum calcium, phosphate, and 25-hydroxyvitamin D [25(OH)D] in relation to bone mineral content (BMC) in PDF-, TF-, and HM-fed preterm infants between term age (40 wk postmenstrual age) and 6 mo corrected age (CA). Between term age and 6 mo CA, 52 preterm infants were fed PDF (per 100 mL: 67 kcal, 1.7 g protein, 65 mg calcium, 38 mg phosphorus, 56 IU vitamin D), 41 were fed TF (per 100 mL: 67 kcal, 1.47 g protein, 50 mg calcium, 30 mg phosphorus, 48 IU vitamin D), and 46 were fed HM. Serum calcium, phosphorus, and 25(OH)D were measured at term age and at 3 and 6 mo CA. BMC (g) was measured by whole-body dual-energy X-ray absorptiometry at term age and at 6 mo CA. Between term age and 6 mo CA, intakes of calcium, phosphorus, and vitamin D were significantly higher in PDF- compared with TF-fed infants, and PDF-fed infants reached significantly higher serum 25(OH)D concentrations at 6 mo CA (103 ± 24.3 vs. 92.8 ± 15.5 nmol/L, P = 0.003). Between term age and 6 mo CA, increases in serum 25(OH)D were associated with an increase in BMC (β = 0.001; 95% CI: 0.00, 0.003; P = 0.046). In conclusion, during the first 6 mo postterm, higher vitamin D intake and greater increase in serum 25(OH)D concentration in PDF-fed preterm infants were associated with increased bone accretion.

Prematurity and related biochemical outcomes: study of bone mineralization and renal function parameters in preterm infants

Preterm is defined as a baby with a gestation of less than 37 completed weeks. In this study, serum calcium, phosphorus, ALP, creatinine, and electrolytes were measured in preterm babies. The present study comprised of 75 preterm babies of which 25 were of 28-30 weeks, 25 were of 30-32 weeks, and remaining 25 were of 34-36 weeks (controls) of gestational age. Serum calcium and phosphorus levels were found to be significantly decreased, and serum ALP, creatinine, and electrolytes were found to be significantly increased (P < 0.001) at 28-30 weeks as compared to controls, but serum calcium and phosphorous levels were found to be insignificantly decreased, whereas serum ALP activities were found to be insignificantly increased at 28-30 weeks as compared to 30-32 weeks of gestational age in preterm babies. It can be concluded that high serum ALP activity and low serum calcium and phosphorus levels are associated with preterm babies. A significant difference in the mean values of these renal function parameters was also obtained, except for serum sodium and potassium.

Domain-based assays of individual antibody concentrations in an oligoclonal combination targeting a single protein

Quantitation of individual monoclonal antibodies (mAbs) within a combined antibody drug product is required for preclinical and clinical drug development, including pharmacokinetic (PK), toxicology, stability, and biochemical characterization studies of such drugs. We have developed an antitoxin, XOMA 3AB, consisting of three recombinant mAbs that potently neutralize the known subtypes of type A botulinum neurotoxin (BoNT/A). The three mAbs bind nonoverlapping BoNT/A epitopes with high affinity. XOMA 3AB is being developed as a treatment for botulism resulting from BoNT/A. To develop antibody-specific assays, we cloned, expressed, and purified BoNT/A domains from Escherichia coli. Each mAb bound only to its specific domain with affinity comparable to the binding to holotoxin. mAb-specific domains were used to develop an enzyme-linked immunosorbent assay (ELISA) for characterization of the integrity and binding activity of the three mAbs in the drug product. An electrochemiluminescence bridging assay that is robust to interference from components in serum was also developed, and we demonstrate that it can be used for PK assays. This type of antigen engineering to generate mAb-specific domains is a general method allowing quantitation and characterization of individual mAbs in a mAb cocktail that binds the same protein and is superior to anti-idiotype approaches.

Serial measurements of serum alkaline phosphatase for early prediction of osteopaenia in preterm infants

AIM

Osteopaenia commonly occurs in preterm infants; however, its diagnosis is often delayed when based on radiological findings. The aim of this study was to examine whether serial measurements of bone turnover markers are useful for early prediction of osteopaenia in preterm infants.

METHODS

Premature infants of ≤ 34 weeks gestation were enrolled. Serum alkaline phosphatase (ALP), bone form ALP (BALP), calcium and inorganic phosphate were concurrently measured biweekly from 3 weeks post-natal age until 40 weeks post-conceptional age. Radiographic examination of the forearm was performed at term age. Osteopaenia was defined as positive radiographic findings according to Koo's criteria.

RESULTS

Of the 46 premature infants completing the follow-up study at term age, 18 showed osteopaenia in radiographic examination. Serum ALP was highly correlated with BALP (R(2) = 0.93, P < 0.001). Infants who had osteopaenia showed a higher level of ALP and BALP after 3 weeks post-natal age than those who had no osteopaenia. ALP concentration exceeding 700 IU/L at 3 weeks post-natal age was predictive of osteopaenia at term age (sensitivity 73% and specificity 73%) and so did for the predictive value of BALP concentration exceeding 95 ug/L (sensitivity 73% and specificity 80%). BALP measures provided no greater benefit of diagnostic performance than ALP in early detection of osteopaenia. Furthermore, premature infants with osteopaenia showed similar levels of calcium and inorganic phosphatase concentration compared with those without.

CONCLUSION

Serum ALP concentration exceeding 700 IU/L at 3 weeks post-natal age can predict the risk of osteopaenia in preterm infants.

Effects of motor physical therapy on bone mineralization in premature infants: a randomized controlled study

OBJECTIVE

To study the effect of physical therapy on bone mineralization, weight gain and growth in preterm infants.

METHOD

After fulfilling the inclusion criteria, preterm infants were matched for gestational age and birth weight and then randomly assigned to the physiotherapy group (PG, n=15) and control group (CG, n=14). The PG received motor physical therapy for 15 min daily, 5 times per week until hospital discharge. Bone mineralization was measured by total body dual energy X-ray beam absorptiometry (DEXA) at the onset and end of the study. Statistical analysis was realized by ANCOVA and linear correlation tests.

RESULT

The physical therapy group (PG) presented greater body weight gain per day (27.4+/-2.4 vs 21.01+/-4.4 g, P<0.001) and length (1.3+/-0.3 vs 0.8+/-0.2 cm week(-1), P<0.001) than did the control group (CG). Body composition values verified by DEXA were greater for the PG. The mean gain in bone mineral content (BMC) (mg) was greater in the PG (434+/-247.5 vs -8.9+/-11.4, P<0.001), as was the mean bone mineral density (BMD) gain (mg cm(-2)) (8.4+/-5.6 vs -3.1+/-5.5, P<0.001). The gain in bone area (BA,cm(2)) was 10.3+/-5 in the PG vs 1.5 +/-2 in the CG (P<0.001). The gain in lean mass (LM) (g) in the PG was also greater than in the CG (271.1+/-21.4 vs 109.1+/-1.0, P<0.009). The fat mass (g) was similar between the groups (P=0.432).

CONCLUSION

These results showed that physiotherapy in preterm infants produced greater gains in growth, body weight, BMC, BMD, BA and LM.

Assisted exercise and bone strength in preterm infants

Studies have previously demonstrated that brief (4 weeks) passive range-of-motion exercise is beneficial for bone development in very low birth weight (VLBW) preterm infants. However, the optimal duration of exercise for bone development in preterm infants is yet unknown. The aim of the present study was to examine the effect of 8 weeks of assisted exercise on bone strength and metabolism in VLBW premature infants. Sixteen infants (mean +/- standard error of the mean birth weight 1,009 +/- 55 g and gestational age 27.3 +/- 0.3 weeks) were randomly assigned into exercise (n = 8) and control (n = 8) groups. The intervention started at the first week of life and involved 8 weeks of daily passive extension and flexion range-of-motion exercise of the upper and lower extremities. Biochemical markers of bone turnover were measured at enrollment and after 8 weeks. Bone strength was measured weekly by quantitative ultrasound measurement of tibial bone speed of sound (SOS). Bone SOS decreased significantly in the control group (-108.1 +/- 33.7 m/second, P < 0.0001) during the study period, while remaining stable in the exercise group (11.3 +/- 22.8 m/second). The main beneficial effect of exercise occurred in the first 4 weeks of the intervention. There were no significant differences in the bone turnover marker changes between the groups. There is a significant postnatal decrease in bone SOS in VLBW preterm infants. Eight weeks of assisted range-of-motion exercise attenuates the decrease in bone strength and may decrease the risk of osteopenia in premature infants.

Influence of genetic polymorphisms on bone disease of preterm infants

Bone disease is an important complication among very low birth weight (VLBW, <1500 g) infants. In adults, osteoporosis is associated with polymorphisms of vitamin D receptor (VDR), estrogen receptor (ER), and collagen Ialpha1 (COLIA1) genes. However, limited information is available regarding the role of these polymorphisms in bone disease in premature infants. We have investigated the possible association between bone disease and the allelic polymorphisms of these three genes in 65 VLBW infants. Twenty infants (30.8%) were diagnosed with bone disease based on high activity of bone formation (serum alkaline phosphatase and osteocalcin), bone resorption (urinary excretion of calcium and pyridinium crosslink) markers, and positive radiologic signs. Statistically significant correlation between thymine-adenine repeat [(TA)(n)] allelic variant of ER gene and bone disease was observed. Infants without bone disorder more often carried a high number of repeats [(TA)(n) >18] [odds ratio (OR): 0.17, 95% confidence interval (CI): 0.05-0.55]. A low number of repeats [(TA)(n) <19] was found more frequently in infants suffering from bone disease (OR: 6.00, 95% CI: 1.77-20.31). Significant interaction (p = 0.009) between VDR and COLIA1 genotypes was observed. In a logistic regression model, bone disorder of preterms significantly correlated with male gender (p = 0.002), lower gestational age (p = 0.015), homozygous allelic variants of high number of (TA)(n) repeats (p = 0.006), and interaction between VDR and COLIA1 genotype (p = 0.009).

Gestational age, sex and maternal parity correlate with bone turnover in premature infants

Factors affecting bone turnover in premature infants are not entirely clear but certainly are different from those influencing bones of adults and children. To identify fetal and maternal factors that might influence bone turnover, we prospectively studied 50 infants (30 preterm and 20 full-term) born at Ain Shams University Obstetric Hospital in Cairo, Egypt. Maternal parity and medical history and infant's weight, gestational age, gender and anthropometrical measurements were recorded. Cord blood samples were collected and serum type I collagen C-terminal propeptide (PICP) was assessed as a marker for fetal bone formation. First morning urine samples were collected and pyridinoline cross-links of collagen (Pyd) were measured as an index for bone resorption. Serum PICP was higher in premature infants when compared with full-term infants (73.30 +/- 15.1 versus 64.3 +/- 14.7, p = 0.022) and was higher in male premature infants when compared with females (81.64 +/- 9.06 versus 66.0 +/- 15.7, p = 0.018). In a multiple regression model using PICP as the dependent variable and controlling for different infant and maternal conditions, PICP significantly correlated with infant gender (r = 8.26 +/- 4.1, p = 0.05) maternal parity (r = -2.106 +/- 0.99, p = 0.041) and diabetes (r = 22.488 +/- 8.73, p = 0.041). Urine Pyd tended to increase in premature infants (612 +/- 308 versus 434 +/- 146, p = 0.057) and correlated significantly with gestational age (r = -63.93 +/- 19.55, p = 0.002). Therefore, bone formation (PICP) is influenced by fetal age and gender, as well as maternal parity and diabetes. Bone resorption (Pyd) is mostly dependent on gestational age only. Further in-depth studies are needed to enrich management of this vulnerable population.

Early physical activity intervention prevents decrease of bone strength in very low birth weight infants

OBJECTIVE

To evaluate the effect of early range-of-motion intervention on bone strength and bone turnover in very low birth weight infants.

METHODS

Twenty-four infants (mean birth weight: 1135 +/- 247 g; mean gestational age: 28.5 +/- 2.3 weeks) were matched for gestational age and birth weight and then randomly assigned into exercise (n = 12) and control (n = 12) groups. Exercise protocol started at the first week of life and involved daily extension and flexion range of motion against passive resistance of the upper and lower extremities (5 minutes per day, 5 days per week, 4 weeks). Growth parameters, bone strength, and biochemical markers of bone homeostasis were measured at enrollment and after 4 weeks. Bone strength was determined using quantitative ultrasound measurement of bone speed of sound (SOS) at the middle left tibial shaft.

RESULTS

Bone SOS decreased significantly in the control group during the study period (from 2892 +/- 30 m/sec to 2799 +/- 26), whereas bone SOS of the exercise group remained stable (2825 +/- 32 m/sec and 2827 +/- 26 m/sec at baseline and 4 weeks, respectively). This significant difference in bone SOS was not expressed in the biochemical markers of bone homeostasis.

CONCLUSIONS

There is a significant postnatal decrease in the bone SOS of very low birth weight infants. A brief range-of-motion exercise attenuates the decrease in bone strength and may decrease the risk of osteopenia.

Perinatal bone turnover in term human neonates and the influence of maternal smoking

Bone turnover in neonates appears independently of the comparably low maternal bone turnover, but there is only sparse information on the effect of the in utero environment on fetal bone turnover. Postnatally, the resuming growth velocity and alterations in mineral homeostasis affect neonatal bone turnover. This study evaluated the relationship of bone marker concentrations to maternal and fetal auxological variables as well as maternal smoking and assessed the short-term change in bone markers during the first days of life. Serum markers of bone formation [osteocalcin and bone-specific alkaline phosphatase (BALP)] and bone resorption (C-terminal telopeptide of type I collagen) were measured in cord blood and at discharge (median d 3) in 69 healthy term neonates. Concentrations of BALP were significantly lower in neonates of smokers (n = 16) compared with nonsmokers (n = 53), both at birth (p = 0.013) and at discharge (p = 0.036). Both cord osteocalcin and BALP were negatively related to maternal weight and maternal body mass index. Maternal smoking and pregnancy weight gain were the predictors of cord BALP (r2 = 0.24; p < 0.001), whereas the mode of delivery best predicted cord C-terminal telopeptide of type I collagen levels (r2 = 0.19; p < 0.001). C-terminal telopeptide of type I collagen and osteocalcin increased significantly (p < 0.001) from birth to discharge, whereas BALP levels did not change significantly during the same period. Our results suggest that maternal smoking during pregnancy and maternal obesity may have a negative impact on fetal bone formation. The significant increase of osteocalcin and C-terminal telopeptide of type I collagen may result either from an increase in bone turnover or altered renal clearance.

The effect of neonatal sepsis on bone turnover in very-low birth weight premature infants

Neonatal sepsis is very common in preterm infants, and severe morbidity during the neonatal period is a major cause of osteopenia of prematurity. We examined the effect of neonatal sepsis on bone turnover markers in premature infants. Twenty-four premature infants participated in the study. Ten of the premature infants developed sepsis during their hospitalization in the neonatal intensive care unit (mean gestational age [GA] 27.3 +/- 0.4 weeks; mean birth weight [BW] 898 +/- 82 g). Fourteen infants who did not develop sepsis served as controls (GA: 26.8 +/- 0.8 weeks, BW: 892 +/- 66 g). Blood samples for bone turnover markers were collected during the initial sepsis workup, and at the end of the first week of treatment, and were compared to the corresponding weekly changes in bone markers in the controls. In addition, samples were collected at the end of the 10th week of life to determine long-term effects of sepsis on bone turnover. Bone osteoblastic activity was assessed by measurements of circulating osteocalcin, bone-specific alkaline phosphatase (BSAP) and the C-terminal procollagen peptide (PICP) levels. Bone resorption was assessed by measurements of circulating carboxy terminal cross-links telopeptide of type I collagen (ICTP). There were no significant differences in the weekly changes of all bone turnover markers in premature infants who developed or did not develop sepsis. No significant differences were found in bone turnover markers at the age of 10 weeks between the groups. Neonatal sepsis in premature infants was not associated with biochemical evidence of reduced bone turnover.