Growth factors, inflammatory cytokines and postnatal bone strength in preterm infants.
OBJECTIVE
To assess the relationships between growth factors, inflammatory cytokines and postnatal bone development in preterm infants.


METHODS
Fifty premature infants (24-32 weeks gestational age, mean birth weight: 1,024 +/- 50 g) participated in the study. Bone strength was determined weekly by quantitative ultrasound measurements of bone speed of sound (SOS). Blood serum measurements of growth factors included circulating IGF-I and GH binding protein. Measurements of circulating cytokines included the pro-inflammatory mediator interleukin (IL)-6, and the anti-inflammatory mediator IL-1 receptor antagonist. Samples were collected when the preterm infants were stabilized and prior to discharge.


RESULTS
Despite a significant increase in body weight (from 1,024 +/- 50 to 2,420 +/- 59 g, p < 0.001) and body length (from 35.4 +/- 0.6 to 44.6 +/- 0.4 cm, p < 0.001) there was a significant decrease in bone SOS during the follow-up period. There was a significant increase in growth factors and a decrease in inflammatory cytokines during the follow-up. Participants were divided into preterm infants who increased bone SOS (bone gainers, n = 16, from 2,867 +/- 38 to 2,910 +/- 41 m/sec), or decreased bone SOS (bone losers, n = 34, from 2,967 +/- 33 to 2,818 +/- 28 m/sec) during follow-up. Baseline bone SOS was significantly lower in the bone gainers. Baseline circulating growth factors were higher and inflammatory cytokines lower in the bone gainers; however, only the difference in IL-6 reached statistical significance (6.4 +/- 1.6 versus 10.5 +/- 1.2 pg/ml, in bone gainers and losers, respectively; p < 0.05).


CONCLUSIONS
Preterm infants with lower bone SOS at birth tend to 'catch-up' during early postnatal weeks. Increases in bone strength in preterm infants were associated with reduced inflammatory state as suggested by lower levels of circulating IL-6.
Eliakim
Alon
A
Child Health and Sports Center, Pediatric Department, Meir Medical Center, Kfar Saba, Israel. eliakim.alon@clalit.org.il
Nemet
Dan
D
Ahmad
Irfan
I
Zaldivar
Frank
F
Koppel
Robin
R
Grochow
Donna
D
Waffarn
Feizal
F
Cooper
Dan M
DM
D015415:Biomarkers / Q000097:blood; D001827:Body Height; D001835:Body Weight; D015519:Bone Density; D001846:Bone Development / Q000502:physiology; D002352:Carrier Proteins / Q000097:blood*; D005260:Female; D005865:Gestational Age; D006257:Head / Q000254:growth & development; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature / Q000097:blood* / Q000254:growth & development; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D053590:Interleukin 1 Receptor Antagonist Protein / Q000097:blood*; D015850:Interleukin-6 / Q000097:blood*; D008297:Male; D013977:Tibia / Q000000981:diagnostic imaging; D014463:Ultrasonography
D015415:Biomarkers; D002352:Carrier Proteins; C508600:IL6 protein, human; D053590:Interleukin 1 Receptor Antagonist Protein; D015850:Interleukin-6; D007334:Insulin-Like Growth Factor I; C051815:somatotropin-binding protein