Comparative response in growth and bone status to three dexamethasone treatment regimens in infant piglets

Influence of benzoic acid and phytase in low-phosphorus diets on bone characteristics in growing-finishing pigs

In 2 simultaneous experiments (Exp. 1 and Exp. 2), the effects of benzoic acid (BA) and phytase (Phy) in low-P diets on bone metabolism, bone composition, and bone stability in growing and growing-finishing pigs were examined. Experiment 1 was conducted with 16 crossbred gilts in the BW range of 25 to 66 kg of BW, whereas in Exp. 2, 32 crossbred gilts (25 to 108 kg of BW) were used. All pigs were individually housed in pens and restrictively fed 1 of 4 diets throughout the experiment. Total P content of the wheat-soybean diets was 4 g/kg (all values on an as-fed basis). The experimental diets were 1) unsupplemented control diet; 2) control diet with 0.5% BA; 3) Phy diet with 750 Phy units (FTU) of Phy/kg and no BA; and 4) PhyBA, control diet with 750 FTU of Phy/kg and 0.5% BA. Blood samples were taken at the beginning of the experiment, wk 3 (only for pigs in Exp. 1), wk 6, and before slaughter to determine P and Ca in serum and concentrations of total alkaline phosphatase, serum crosslaps (marker for bone resorption), and osteocalcin (marker for bone formation). Ash, P, and Ca contents of bones and bone stability were examined using the left metatarsal bones and tibia of the pigs after slaughter. Benzoic acid did not influence any of the blood variables (P > 0.09). The addition of Phy increased (P < or =0.03) P concentration in serum from 2.71 +/- 0.08 to 3.03 +/- 0.07 mmol/L at wk 3 and content of serum crosslaps from 0.39 +/- 0.02 to 0.45 +/- 0.02 ng/mL at wk 6 and decreased (P < 0.05) osteocalcin at wk 6 by 160 ng/mL. No long-term effect of diets on serum mineral concentrations, alkaline phosphatase, and bone markers in serum could be detected. Benzoic acid negatively affected (P < or = 0.03) Ca content in bones and distal bone mineral density, especially in the younger pigs. In the control diet with 0.5% BA and the control diet with 750 FTU of Phy/kg and 0.5% BA, the CA content in bones and distal bone mineral density were reduced by 6 and 11%, respectively. Throughout the whole growing and finishing period, Phy increased (P < or =0.02) ash, P, and Ca contents in bones by 29.4, 4.8, and 11.6 g/kg of DM, respectively. Bone mineral density and bone mineral content were greater in diets with Phy (P < or = 0.03), as well as breaking strength of tibia (+22%) and metatarsal bones (+27%; P < 0.01). The results of this study indicate that for a healthy skeleton, BA should not be used in low-P diets without the addition of Phy.

Bone resorption varies as a function of time of day and quantity of dietary long chain polyunsaturated fatty acids

It is unclear whether dietary arachidonic acid (AA) and docosahexaenoic acid (DHA) alter the circadian rhythms of bone turnover markers, plasma osteocalcin (OC) and urinary N-telopeptide (NTx). We hypothesize that dietary AA and DHA will influence the circadian rhythm of NTx and OC. Piglets were randomized to receive one of four formulas for 15 days: control or control with AA:DHA (0.5:0.1, 1.0:0.2 or 2.0:0.4 g/100 g of fat). Measurements included polyunsaturated fatty acids (PUFA) and plasma OC (sampled at 0900, 1500 and 2100 h on day 15) and urinary NTx:creatinine (collected from 2100 h on day 14-0900 h, 0900-1500 h and 1500-2100 h on day 15). Main effects (litter, diet, time) were identified by mixed model repeated measures ANOVA. In those fed AA and DHA, regression identified relationships among plasma PUFA and NTx. There was a diet (P=.0467) and time (P<.0001) effect on urinary NTx:creatinine, whereby those receiving 1.0:0.2 g/100 g of fat as AA:DHA had the lowest values and values were lowest at 2100 h. Likewise, diet (P=.0001) and time (P< .0001) affected plasma AA and DHA; higher dietary AA and DHA elevated values and time reduced values. There was a diet by time interaction on eicosapentaenoic acid and DHA proportions, suggesting dietary AA and DHA altered their circadian rhythm. In regression, plasma AA and DHA were not associated with urinary NTx:creatinine. Dietary AA and DHA at amounts similar to that found in breast milk reduce bone resorption, but do not alter its circadian rhythm.

Early life factors predict abnormal growth and bone accretion at prepuberty in former premature infants with/without neonatal dexamethasone exposure

Growth, bone, and body composition were studied at prepuberty in former very low birth weight (VLBW) infants who received dexamethasone (DEX) for bronchopulmonary dysplasia (BPD) compared with VLBW infants without DEX and term-born infants (TERM) to identify early life risk factors for later low bone mass. Children (56 girls/63 boys, 5-10 y) previously studied in neonatal life were recruited into three groups: VLBW + DEX, VLBW - DEX, and TERM children. Anthropometry and whole body bone, fat, and lean mass were measured. At prepuberty, the average height and weight for VLBW + DEX group were significantly lower than that for VLBW - DEX and TERM. Both VLBW groups had lower bone mass even adjusted for height and lean mass than TERM children and lower lean mass both total and adjusted for height. Z-scores for whole body bone mineral content below -1.5 occurred in 27.9% of VLBW + DEX children. The key factors for low bone mass were earlier gestational age and having BPD with DEX in neonatal life. In former VLBW infants, growth and bone mass attainment before puberty can be predicted from early life variables. VLBW + DEX children may be protected from overweight, but are at risk for short stature and low bone mass.

Effects of dexamethasone application in growing pigs on hormones, N-retention and other metabolic parameters

Many single effects of glucocorticoids are known but complex metabolic reactions in pigs in response to a glucocorticoid challenge were not reported. Seven pigs (mean weight 69 kg) with indwelling catheters were kept in metabolic crates. After a 7-day control period they were fed for 9 days with 0.4 mg dexamethasone (dex) per kg body weight daily, followed by another 9-day post-treatment period. Hormones and metabolic parameters were continuously determined in urine or blood plasma. Treatment significantly changed all parameters except non-esterified fatty acids. Cortisol decreased from 84.5 to 4.9 nmol/l, insulin-like growth factor I (IGF-I) from 17.5 to 10.8 nmol/l and aldosterone from 0.36 to 0.13 nmol/l. The N-retention decreased from 1.07 to 0.53 g/kg(0.75) and hydroxyproline from 2.97 to 1.05 mmol/day. An increase was found for urine volume (5.2 versus 13.6 l/day), urea-N (0.90 versus 1.43 g/kg(0.75)), allantoin (6.40 versus 8.75 mmol/day), glucose (3.9 versus 4.34 mmol/l) and insulin (6.21 versus 11.16 mU/l). In the post-treatment period IGF-I revealed a compensatory pattern (control period versus post-treatment period: 17.5 versus 22.9 nmol/l) whereas the other parameters were not significantly elevated. Data suggest that dex increased N-excretion both by inhibiting mitosis and resynthesis of proteins partly via a reduced collagen synthesis. Increased allantoin concentrations additionally pointed to increased apoptosis.

Short-term glucocorticoid treatment of piglets causes changes in growth plate morphology and angiogenesis

OBJECTIVE

Glucocorticoid treatment of children often leads to growth retardation, and the precise target(s) in the growth plate responsible for this effect are unknown. Angiogenesis is an important part of the endochondral ossification process, and VEGF expressed in the growth plate is essential for proper angiogenesis to occur. Since glucocorticoid treatment down-regulates VEGF expression in cultured chondrocytes, we hypothesized that in vivo glucocorticoid treatment could result in VEGF down-regulation in the growth plate and disturbed angiogenesis, thus contributing to the growth retardation.

DESIGN

We treated 6-week-old prepubertal piglets (10 kg) for 5 days with prednisolone (50 mg/day). Tibial growth plate sections were studied for apoptosis and the expression of VEGF protein and mRNA and MMP-9 protein. Capillaries in the metaphysis were visualized by CD31 immunostaining. Growth plate morphology (width of various zones) was determined by interactive measurements on hematoxylin/eosin stained sections and apoptotic cells were detected by TUNEL assay.

RESULTS

In the prednisolone-treated animals, the total width of the growth plate decreased to 81% of controls (P<0.02), which was explained by a decrease of the width of the proliferative zone to 73% (P<0.05). The treatment had no effect on the orderly organization of the chondrocyte columns. In the growth plates of control animals, apoptosis was shown in 5.8% of the hypertrophic chondrocytes and was limited to the terminal hypertrophic chondrocytes. In prednisolone-treated animals, 40.5% of the hypertrophic chondrocytes was apoptotic (P<0.02), with apoptotic chondrocytes also appearing higher in the hypertrophic zone. We observed fewer capillaries and loss of their parallel organization in the metaphysis in the prednisolone-treated animals. The capillaries were shorter and chaotic in appearance. In contrast to controls, in prednisolone-treated animals VEGF mRNA and protein could not be detected in the hypertrophic zone of the growth plate. Trabecular bone length in the primary spongiosa was also diminished by the treatment. No changes were observed in the expression pattern of MMP-9, a matrix metalloproteinase, which is also important for angiogenesis and bone formation.

CONCLUSIONS

These results indicate that short-term glucocorticoid treatment of growing piglets severely disturbs the width of the growth plate, apoptosis of chondrocytes, VEGF expression by hypertrophic chondrocytes, the normal invasion of blood vessels from the metaphysis to the growth plate and bone formation at the chondro-osseous junction. These effects could alter the dynamics of endochondral ossification and thus contribute to glucocorticoid-induced growth retardation.

Influence of cortisol, gonadal steroids and an energy deficit on biochemical indicators of bone turnover in Swine

In the pig a high growth potential seems to favour a disposition for skeletal problems. Hormones of growth hormone (GH)/insulin-like growth factor (IGF)-I axis as well as cortisol and gonadal steroids are endocrine determinants of the anabolic potential but their effects on bone turnover in pigs have not been described. Thus, key hormones were either infused for 7 days (cortisol, 5alpha-dihydrotestosterone (DHT), oestradiol) or influenced by Metyrapone (inhibition of cortisol synthesis) or energy deficit (increasing GH). Each treatment was carried out in six growing barrows/treatment. Bone turnover was characterized by daily measurements indirect parameter of osteoblastic and osteoclastic activity, osteocalcin (OC) and tartrate-resistant acid phosphatase (TRAP) respectively. All treatments except cortisol infusion seemed to favour bone formation, as they led either to a pronounced increase in OC (Metyrapone: +14%) or to significantly reduced TRAP (DHT: -9%, E2: -17%, energy deficit: -25%) followed by significantly higher OC (DHT: +9%, E2: +6%, energy deficit: +18%). Cortisol infusion affected bone loss mainly by a severe inhibition of osteoblastic activity (OC: -61%). Some reactions are explained by direct effects of the infused gonadal steroids on bone cells (inhibition of osteoclasts) or of the experimentally modified cortisol levels (inhibition of osteoblasts by cortisol). Other effects seem to be mediated by concomitant changes of IGF-I (inhibition of osteoclasts after energy deficit or cortisol) and GH-secretion (increased osteoblastic activity during energy deficit), respectively. Consequences for co-ordinated bone turnover are discussed.

Special nutritional needs of infants for prevention of and recovery from bronchopulmonary dysplasia

Extremely low birth weight infants who develop severe respiratory disease may have special nutrient requirements imposed by a combination of enhanced utilization of nutrients or the need for epithelial cell repair resulting from the disease process, as well as to support catch-up growth. Inositol, free fatty acids, vitamin E and vitamin A are proposed as nutrients for which infants at risk of chronic pulmonary insufficiency may have special requirements. Of these nutrients, only for vitamin A does suggestive evidence exist that high doses when given intramuscularly may reduce the incidence of death or chronic lung disease. Exogenous steroid therapy (dexamethasone), which is often used to improve pulmonary compliance in ventilated premature infants, may compromise vitamin A status and induce restricted somatic and bone mineral growth. Supplemental nutrition by means of enriched infant formulas has provided benefits in growth and bone mass accretion to infants recovering from bronchopulmonary dysplasia up to 3-mo corrected age. This growth advantage was not sustained over the subsequent 9 mo, suggesting that prolonged nutritional support is required until catch-up growth is complete. Further studies are required to delineate the needs for specific nutrients such as antioxidant vitamins and minerals or vitamin A that may play a role in preventing severe chronic lung disease in premature infants. As well, the role of supplemental nutrition (beyond the requirements of term infants) to support catch-up growth and maintenance during the critical stages of early development requires further investigation before evidence-based nutrient recommendations can be developed for this special population of infants.

Growth restriction in dexamethasone-treated preterm infants may be mediated by reduced IGF-I and IGFBP-3 plasma concentrations

OBJECTIVE

Preterm infants receiving dexamethasone for respiratory morbidity frequently suffer restricted growth. The aim of this study was to investigate the interactions between dexamethasone treatment regimen and circulating IGFBP-3 and IGF-I levels, and the associations between these variables and linear growth rate in preterm babies receiving dexamethasone for chronic lung disease of prematurity.

DESIGN

A randomised, unblinded, clinical trial of two different courses of dexamethasone: a 42-day tapering course (the long course) and a repeatable 3 day pulse course.

PATIENTS

Forty preterm infants (19 in the pulse group, 21 in the long group) with a birthweight < or = 1250 g who were ventilated at 7 days of age.

MEASUREMENTS

Lower leg length was measured thrice weekly by knemometry, and IGFBP-3 and IGF-I levels were measured prior to commencing treatment, at 14 and 42 days of treatment and at 36 weeks postmenstrual age (PMA). Interactions between variables were analysed by stepwise regression analysis and analysis of covariance (ANCOVA). Associations between variables were assessed by correlation coefficients.

RESULTS

In an ANCOVA, mean daily dose of dexamethasone/kg (MDDD) and treatment group both significantly influenced IGFBP-3 levels (P = 0.0009 and P = 0.017, respectively), and tended to influence IGF-I levels similarly (P = 0.098 and P = 0.07). MDDD also significantly influenced mean daily increase in lower leg length (MDILL; P < 0.01). IGFBP-3 and IGF-I levels were significantly related to MDILL (ANCOVA: P < 0.01). The correlation coefficients for IGFBP-3 and IGF-I levels and MDILL were 0.2 and 0.3 (both P < 0.0001), respectively. IGFBP-3 and IGF-I levels were highly correlated (r(2) = 0.52, P < 0.0001) and both increased significantly with increasing PMA (P < 0.0001). IGF-I levels were higher in females (P = 0.036).

CONCLUSION

This study provides evidence that the growth-restricting effects of dexamethasone may be mediated, at least in part, via suppression of the IGF axis. Both dexamethasone dose and treatment regimen influence circulating IGF-I and IGFBP-3 levels, and both are important in inducing growth restriction.