Dana Yumani



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VRIJE UNIVERSITEIT NUTRITION IN RELATION TO THE ENDOCRINE REGULATION OF PRETERM GROWTH AND BODY COMPOSITION ACADEMISCH PROEFSCHRIFT ter verkrijging van de graad Doctor aan de Vrije Universiteit Amsterdam, op gezag van de rector magnificus prof.dr. J.J.G. Geurts, in het openbaar te verdedigen ten overstaan van de promotiecommissie van de Faculteit der Geneeskunde op woensdag 12 oktober 2022 om 13.45 uur in een bijeenkomst van de universiteit, De Boelelaan 1105 door Dana Foekina Johanna Yumani geboren te Enschede

Promotoren: prof.dr. M.M. van Weissenbruch prof.dr. H.N. Lafeber † promotiecommissie: prof.dr. J.B. van Goudoever prof.dr. R.M. van Elburg prof.dr. A.C. Heijboer prof.dr. A.C.S. Hokken-Koelega dr. W. Onland dr. J. Rotteveel

Voor papa

TABLE OF CONTENTS INTRODUCTION 11 CHAPTER 1: General introduction 13 Background 14 The regulation of fetal and postnatal growth and body composition 14 Aims and objectives 16 Study design 17 Thesis outline 20 References 21 PART I. THE ROLE OF NUTRITION AND IGF-I ON GROWTH, BODY COMPOSITION AND HEALTH OUTCOMES IN PRETERM INFANTS IN INFANCY 25 CHAPTER 2: Dietary proteins and IGF I levels in preterm infants: determinants of growth, body composition and neurodevelopment 27 Abstract 28 Introduction 29 IGF I regulation 30 The role of IGF I in growth and body composition 30 The role of IGF I in neurodevelopment 34 The role of dietary proteins in growth and body composition 35 The role of dietary proteins in neurodevelopment 37 IGF I and dietary proteins 38 Conclusions 39 References 40 CHAPTER 3: Associations between bronchopulmonary dysplasia, Insulin-like growth factor I and nutrition 47 Abstract 48 Introduction 49 Methods 49 Results 51 Discussion 56 Conclusions 58 References 59 Supplemental material 61

CHAPTER 4: The course of IGF-1 levels and nutrient intake in extremely and very preterm infants during hospitalisation 69 Abstract 70 Introduction 71 Methods 72 Results 75 Discussion 83 Conclusions 85 References 86 PART II. THE DETERMINANTS OF BODY COMPOSITION AND METHODS TO ASSESS BODY COMPOSITION IN PRETERM INFANTS 89 CHAPTER 5: IGF-I, growth and body composition in preterm infants up to term equivalent age 91 Abstract 92 Introduction 93 Methods 93 Results 96 Discussion 108 Conclusions 111 References 112 CHAPTER 6: A comparative study using Dual-energy X-ray absorptiometry, air displacement plethysmography and skinfolds to assess fat mass in preterms at term-equivalent age 115 Abstract 116 Introduction 117 Methods 118 Results 120 Discussion 126 References 128

CHAPTER 7: Body composition in preterm infants: a systematic review on measurement methods 131 Abstract 132 Introduction 133 Methods 133 Results 137 Discussion 156 Conclusions 161 References 163 DISCUSSION & SUMMARY 169 CHAPTER 8: General discussion 171 Nutrition in relation to the endocrine regulation of preterm growth and body composition 172 The developing endocrine axis in relation to comorbidities in preterm infants 174 Determinants and assessment of body composition in preterm infants 175 Future research directions 176 References 178 CHAPTER 9: Summary 183 Part I. IGF-I and nutrition in relation to growth, body composition and health outcomes in preterm infants 184 Part II. Determinants and assessment of body composition in preterm infants 184 APPENDIX 187 CHAPTER 10: PhD portfolio 189 CHAPTER 11: Acknowledgements 195


14 Chapter 1 Background Embryonic and fetal development are an exceptional phase of human life: a onecelled zygote develops into an infant with roughly 200 different cell types, weighing on average 3.5 kg at birth. This exponential growth and differentiation rate will never be equaled in later life. Preterm delivery, however, abruptly interrupts this process and results in a very precarious situation. The now premature infant finds itself in an alien extra-uterine environment while it is yet to go through a major part of its’ development. As premature infants can no longer rely on the regulatory function of the placenta for nutrient supply, immunity andendocrine control, their growthanddevelopment depend on immature organ systems. The developing gastro-intestinal tract still has an impaired digestive and absorptive capacity.(1) Furthermore, the intestines have an inadequate mucosal barrier function andmaternal antibodies, which are largely transferred across the placenta in the last trimester, are lacking.(1, 2) Combined with an overall immature immune response and a general pro-inflammatory state, premature infants are left prone to infections. Moreover, the regulation of growth is disrupted by insufficient levels of growth factors.(3) Altogether, preterm infants are faced with the preposterous task of thriving in the face of comorbidities and insufficient nutrient and hormone supplies. Obviously, this is a process prone to error, making postnatal growth failure a common problem in preterm infants. (4, 5) After an initial phase of impaired growth, preterm infants are likely to show accelerated growth up to 2-3 years of age.(6) Growth patterns in infancy and early childhood have been linked to health outcomes. Notably, postnatal growth restriction is associated with an increased incidence of co-morbidities during hospitalization (7) and may lead to impaired neurodevelopment in later life (8). Furthermore, there are concerns that impaired growth triggers a thrifty phenotype with increased adipose tissue and adverse cardiometabolic outcomes in later life. (9, 10) Therefore, it would be of interest to gain more insight in factors determining growth and body composition in early life, as a means to enhance health outcomes in infants born preterm. The regulation of fetal and postnatal growth and body composition The regulation of fetal growth and body composition is an intricate process. There is an interplay between oxygen, nutrients, and hormones of fetal, placental and maternal origin. In addition, genetic factors determine a part of the growth potential. After preterm birth, however, a new balance needs to be found between substrates, endocrine and genetic factors.

15 General introduction 1 The endocrine regulation of growth and body composition Insulin like growth factors (IGFs), insulin and growth hormone (GH) have been established to play an important role in regulating growth in the fetal as well as the postnatal phase. IGF-II mainly stimulates growth in the embryonic and early fetal period. IGF-I, on the other hand, is the major growth stimulating factor in late gestation and the postnatal period. (11) Hence, IGF-I is a key factor in the endocrine regulation of growth in preterm infants. IGF-I is a small polypeptide with a wide range of function. It is mainly synthesized in the liver and stimulates cell division, growth, and motility, as well as glucose uptake, and protein synthesis. In addition, IGF I inhibits apoptosis and has an antiinflammatory and anti-oxidative effect. (12-15) In utero, IGF-I is secreted into the blood under control of insulin. After birth, GH gradually takes over this role. Insulin like growth factor binding proteins (IGFBPs) are also important factors which regulate the bioavailability of IGF-I. (11) In addition, thyroid hormones in general stimulate cell differentiation and support tissue accretion by regulating the IGF-I receptor and oxidative metabolism. Glucocorticoids also stimulate cell differentiation and negatively modulate growth in late gestation. Other factors implicated in fetal and postnatal growth are leptin and ghrelin. Both hormones have a possible growth promoting effect, yet their precise roles remain to be elucidated. (16) IGF-I has also been associated with the regulation of body composition. (12) Interestingly, the relationship between IGF-I and body composition has been reported to vary depending on the timing of IGF-I and body composition measurement. For example, in preterm infants higher IGF-I in the first month of life has been associated with an increased fat free mass. Meanwhile, higher IGF-I levels at and after term equivalent age have been associated with a decreased fat free mass.(17) Nevertheless, studies on this are rare in the preterm population and definitive conclusions on the relationship between IGF-I and body composition are yet to be drawn. Nutrition in relation to growth and body composition Nutrients are a substrate for growth and are crucial for the development of the endocrine axes. In particular protein availability has significant impact on hormone levels and hormone sensitivity in fetal as well as neonatal life.(18-20) Protein malnutrition in infants depresses hepatic IGF-I, IGFBP-3 and IGFBP-4 synthesis and enhances hepatic IGFBP-1 and IGFBP-2 synthesis, leading to reduced IGF-I bioavailability and impaired growth. Preterm infants require 3 to 4 grams of protein per kg per day depending on their gestational age and co-morbidities. To optimize nitrogen accretion, the protein

16 Chapter 1 intake needs to be combined with sufficient fatty acids and carbohydrates, resulting in a high energy diet of 95-140 kcal per kg per day. In an attempt to prevent complications from the high energy and high protein diet, nutritional intake has to be build up in the first week of life causing relative malnutrition in this period. Moreover, parenteral nutrition is required until the preterm infant is able to tolerate full enteral feeds and studies have shown that parenteral nutrition, in contrast to enteral feeding, is associated with lower IGF-I levels. (21, 22) In addition, the type of enteral nutrition, i.e. own mother’s milk, donor human milk or formula, influences IGF-I levels. (23) Furthermore, macronutrient intake has been linked to body composition. A high protein intake has been associated with decreased fat mass and increased fat free mass in infancy. (24, 25) Therefore, the route of administration and the type of nutrition play a vital role in optimizing postnatal growth and body composition. Aims and objectives The research outlined in this thesis aims to explore the postnatal modulation of growth and body composition in very preterm and extremely preterm infants (gestational age at birth 24 – 32 weeks). Furthermore, the influence of the developing endocrine axis on health outcomes in infancy is investigated. It is hypothesized that: • IGF-I has to reach a threshold concentration before it can effectively influence growth. Once IGF-I passes this threshold concentration, themaximumgrowth rate is expected to be potentiated by IGF-I; • In states with low IGF I levels to ensure an easily accessible energy store, but resulting in an increased fat mass percentage at term age; • Before IGF-I reaches the threshold con, such as critical illness, nutrient restriction and extreme prematurity, the IGF system would stimulate mesenchymal stemcell differentiation towards adipogenesis as amechanism centration, a high-energy and high-nutrient diet is required to potentiate growth; • Once IGF-I reaches the threshold concentration, a continued high-energy and high-nutrient diet could potentially lead to increased fat deposition; • The protective effect on inflammation and the anti-oxidative effects of IGF-I may be important in decreasing the risk of developing comorbidities. To investigate these hypotheses a longitudinal cohort study was designed and literature reviews were conducted. In this thesis all papers, except the literature reviews, are based on the results of the Nutrition in relation to the endocrine regulation of preterm growth study (NUTRIE study).

17 General introduction 1 Study design The NUTRIE study, a longitudinal cohort study, was conducted between August 2015 andAugust 2018. The primary objective of this studywas to study the endocrine regulation of preterm growth and body composition. Secondary objectives were to study the influence of the endocrine regulation and early nutritional intake on neurodevelopmental outcome, bonemineralization, lipidprofileandbloodpressure in preterm infants. To detect a medium size effect (r = 0.35) of IGF-I concentration on fat mass percentage a sample size of at least 62 infants was required (power 80%, significance 5%). With an expected dropout rate of 10% drop out rate, the aim was to include 70 patients. Infants admitted to the neonatal intensive care unit (NICU) of the AmsterdamUMC - location VU University Medical Center were assessed for eligibility if they were born at a gestational age of 24 weeks + 0/7 days up to and including 31 weeks + 6/7 days. Infants who had substantial congenital abnormalities were excluded. Informed consent was obtained within the first week of life. Ninety patients were enrolled in the study. (Figure 1) Study participants were followed-up until 2 years corrected age. Anthropometric measures and endocrine parameters were registered during hospital stay as well as at follow-up. Body composition and bone mineral density were assessed at term age and 3, 6, 12, and 24 months corrected age, using air displacement plethysmography (PEA POD®/BOD POD®) and Dual Energy X-ray Absorptiometry (DXA). (Figure 2 and Figure 3) In addition cord blood analysis of infants with a gestational age of 24 to 42 weeks born at the VU University Medical Center in the study period took place to establish neonatal reference ranges for IGF I, IGF BP 3, Insulin, C-peptide, glucose, cortisol, cortisone and lipid profiles. (Figure 2 and Figure 3)

18 Chapter 1 Figure 1. NUTRIE study recruitment and inclusion

19 General introduction 1 Figure 2. NUTRIE Study: procedures during hospitalization Figure 3. NUTRIE Study: procedures during follow-up

20 Chapter 1 Thesis outline Part I of this thesis focuses on the role of nutrition and IGF-I on growth, body composition and health outcomes in preterm infants in infancy. Chapter 2 elaborates on the role of dietary proteins and IGF-I on growth, body composition and neurodevelopment. Chapter 3 aims to explore how the developing IGF-I axis, in relation to nutrition, is associated with the occurrence of bronchopulmonary dysplasia. Chapter 4 investigates the influence of the route of administration and the type of nutrition on IGF-I levels and growth in preterm infants during hospitalisation. Part II of this thesis focuses on the determinants of body composition and methods to assess body composition in preterm infants. Chapter 5 describes the role of IGF-I and weight gain in determining body composition of preterm infants at term equivalent age. Chapter 6 compares body composition, generated by air displacement plethysmography and dual-energy X-ray absorptiometry. Furthermore, it evaluates the potential predictive value of the sum of skinfolds for body composition measured in preterm infants at term equivalent age. In Chapter 7 a systematic review is reported, comparing different methods to assess body composition in preterm infants up to 6 months corrected age. Chapter 8 discusses the conclusions of this thesis and the implications for future research.

21 General introduction 1 References 1. Neu J. Gastrointestinal development and meeting the nutritional needs of premature infants. Am J Clin Nutr. 2007;85(2):629s-34s. 2. Sharma AA, Jen R, Butler A, Lavoie PM. The developing human preterm neonatal immune system: a case for more research in this area. Clin Immunol. 2012;145(1):61-8. 3. HellstromA, Ley D, Hansen-Pupp I, Hallberg B, Ramenghi LA, Lofqvist C, et al. Role of Insulinlike Growth Factor 1 in Fetal Development and in the Early Postnatal Life of Premature Infants. American journal of perinatology. 2016;33(11):1067-71. 4. Horbar JD, Ehrenkranz RA, Badger GJ, Edwards EM, Morrow KA, Soll RF, et al. Weight Growth Velocity and Postnatal Growth Failure in Infants 501 to 1500 Grams: 2000-2013. Pediatrics. 2015;136(1):e84-92. 5. Lee SM, Kim N, Namgung R, Park M, Park K, Jeon J. Prediction of Postnatal Growth Failure among Very Low Birth Weight Infants. Scientific reports. 2018;8(1):3729. 6. Euser AM, de Wit CC, Finken MJ, Rijken M, Wit JM. Growth of preterm born children. Horm Res. 2008;70(6):319-28. 7. Griffin IJ, Tancredi DJ, Bertino E, Lee HC, Profit J. Postnatal growth failure in very low birthweight infants born between 2005 and 2012. Archives of disease in childhood Fetal and neonatal edition. 2016;101(1):F50-5. 8. Cormack BE, Harding JE, Miller SP, Bloomfield FH. The Influence of Early Nutrition on Brain Growth and Neurodevelopment in Extremely Preterm Babies: A Narrative Review. Nutrients. 2019;11(9). 9. Nakano Y. Adult-Onset Diseases in Low Birth Weight Infants: Association with Adipose Tissue Maldevelopment. J Atheroscler Thromb. 2020;27(5):397-405. 10. Euser AM, Finken MJ, Keijzer-Veen MG, Hille ET, Wit JM, Dekker FW, et al. Associations between prenatal and infancy weight gain and BMI, fat mass, and fat distribution in young adulthood: a prospective cohort study in males and females born very preterm. Am J Clin Nutr. 2005;81(2):480-7. 11. Gicquel C, Le Bouc Y. Hormonal regulation of fetal growth. Horm Res. 2006;65 Suppl 3:28-33. 12. Yumani DF, Lafeber HN, van Weissenbruch MM. Dietary proteins and IGF I levels in preterm infants: determinants of growth, body composition, and neurodevelopment. Pediatr Res. 2015;77(1-2):156-63. 13. Rowland KJ, Choi PM, Warner BW. The role of growth factors in intestinal regeneration and repair in necrotizing enterocolitis. Semin Pediatr Surg. 2013;22(2):101-11. 14. Xu L, Zhang W, Sun R, Liu J, Hong J, Li Q, et al. IGF-1 may predict the severity and outcome of patients with sepsis and be associated with microRNA-1 level changes. Experimental and therapeutic medicine. 2017;14(1):797-804. 15. Tanner SM, Berryhill TF, Ellenburg JL, Jilling T, Cleveland DS, Lorenz RG, et al. Pathogenesis of necrotizing enterocolitis: modeling the innate immune response. Am J Pathol. 2015;185(1):4-16. 16. Ohkawa N, Shoji H, Kitamura T, Suganuma H, Yoshikawa N, Suzuki M, et al. IGF-I, leptin and active ghrelin levels in very low birth weight infants during the first 8 weeks of life. Acta Paediatr. 2010;99(1):37-41. 17. Hernandez MI, Rossel K, Pena V, Cavada G, Avila A, Iniguez G, et al. Leptin and IGF-I/II during the first weeks of life determine body composition at 2 years in infants born with very low birth weight. J Pediatr Endocrinol Metab. 2012;25(9-10):951-5. 18. DJP B. Programming the baby. Mothers, Babies and Health in Later Life: Churchill Livingstone; 1998. p. 13-41. 19. Yeung MY, Smyth JP. Nutritionally regulated hormonal factors in prolonged postnatal growth retardation and its associated adverse neurodevelopmental outcome in extreme prematurity. Biol Neonate. 2003;84(1):1-23.

22 Chapter 1 20. Bloomfield F, Spiroski A, Harding J. Fetal growth factors and fetal nutrition. Semin Fetal Neonatal Med. 2013. 21. Wojnar MM, Fan J, Li YH, Lang CH. Endotoxin-induced changes in IGF-I differ in rats provided enteral vs. parenteral nutrition. The American journal of physiology. 1999;276(3):E455-64. 22. Yumani DFJ, Calor AK, van Weissenbruch MM. The Course Of IGF-1 Levels and Nutrient Intake in Extremely and Very Preterm Infants During Hospitalisation. Nutrients. 2020;12(3). 23. Larnkjaer A, Molgaard C, Michaelsen KF. Early nutrition impact on the insulin-like growth factor axis and later health consequences. Current opinion in clinical nutrition and metabolic care. 2012;15(3):285-92. 24. Embleton ND, Cooke RJ. Protein requirements in preterm infants: effect of different levels of protein intake on growth and body composition. Pediatr Res. 2005;58(5):855-60. 25. Roggero P, Gianni ML, Amato O, Liotto N, Morlacchi L, Orsi A, et al. Growth and fat-free mass gain in preterm infants after discharge: A randomized controlled trial. Pediatrics. 2012;130(5):e1215-e21.

23 General introduction 1


28 Chapter 2 Abstract It has been demonstrated that a high protein diet in preterm born infants during the first weeks of life may enable a growth rate equal to that seen in utero and may also result in a better long term neurodevelopmental outcome. This diet may limit immediate postnatal growth retardation andmay hence lower the risk of increased fat deposition after birth leading to the metabolic syndrome in later life. Insulin like growth factor I (IGF I) has proven to play an important role in early postnatal growth of preterm infants, but also seems to have a persisting influence on body composition in childhood. Furthermore increased IGF I concentrations in preterm infants have been associated with improved neurodevelopmental outcome. This review will elaborate on the role of dietary proteins and IGF I on growth, body composition and neurodevelopment of preterm infants. Possible causal pathways will be explored and areas for future research will be proposed.

29 Dietary proteins and IGF I levels in preterm infants 2 Introduction Postnatal growth restriction is a major problem faced in the care for preterm infants. At 36 weeks postmenstrual age 91% of all preterm infants show postnatal growth restriction (weight < -1.3 SD) (1). At term age approximately 30% of infants are reported to still be growth restricted (2). As survival rates of preterm infants with an increasingly younger gestational age rise, we are subsequently confronted with the long term sequelae of pretermbirth. At 11 years of age 40% of children born before 26 weeks of gestation have been reported to have serious neurocognitive impairment andmoderate to severe impairment of neuromotor function, vision and hearing was reported in respectively 10%, 9% and 2% of cases (3). Preterm birth and postnatal growth restriction have both been associated with impaired neurodevelopmental outcome (4). However Franz and colleagues found that only a small percentage of the variability, roughly 3%, of the mental processing composite score was explained by growth (5). There might be a common factor leading to both poor growth and poor neurodevelopment, e.g. a poor nutritional status or major neonatal morbidities. Nonetheless several studies suggest that there might be independent pathways (5, 6). Either way these poor ourcomes warrant an intervention. Furthermore preterm infants are prone to develop risk factors for the onset of the metabolic syndrome. They are reported to have lower insulin sensitivity, increased blood pressure and increased fat mass in childhood and young adulthood (79). Nutritional interventions in these infants have been found to influence the development of risk factors for the metabolic syndrome (10). Hence neonatologists are challenged to compose and administer a diet which limits postnatal growth restriction; yet with caution to also limit the development of risk factors for the onset of the metabolic syndrome. Dietary factors, endocrine function and the simple immaturity of organ systems are entangled in the endeavour to optimize postnatal growth and metabolic programming. Dietary proteins are essential in enabling a growth rate similar to intrauterine growth (11). Nevertheless the balance between proteins and other nutrients are essential to understand how growth and body composition in preterm infants can be optimized. Insulin-like growth factors (IGF) are a key in the endocrine regulation of growth. Notably IGF I has an anabolic and mitogenic effect which is crucial for symmetric growth due to the presence of the IGF I receptor in multiple cell types and tissues. Moreover IGF I synthesis in multiple peripheral tissues causes it to function as an auto- and paracrine factor which does not merely influence growth, but also organ functioning. IGF I’s possible influence on neurodevelopmental outcome may be potentiated through its trophic effect or through altering the functioning of the central nervous system. In this review we aim to explore the possible pathways relating neonatal dietary proteinintakeandIGFI levels togrowth, bodycompositionandneurodevelopmental outcome in infancy, childhood and young adulthood.

30 Chapter 2 IGF I regulation IGF I is a small polypeptide which is mainly synthesized in the liver. It stimulates cell division, cell growth, cell motility, glucose uptake and protein synthesis. Furthermore IGF I inhibits apoptosis. Prenatally it is secreted into the blood under control of insulin. Postnatally growth hormone (GH) gradually takes over this role. In addition malnutrition and hypothyroidismnegatively influence IGF I plasma levels. IGF I is also synthesized in multiple peripheral tissues, e.g. kidney, bone and muscle, where it is released under control of GH and local factors. 99% of IGF I in plasma is bound to high affinity IGF binding proteins which control IGF I transportation and distribution. (12) The role of IGF I in growth and body composition Fetal IGF I levels gradually increase during pregnancy to reach approximately 46 to 90 ng/ml at term age (13). After preterm birth IGF I levels slowly increase (14). Meanwhile infants born at term show a quick surge in IGF-I levels (15). Figure 1 illustrates postnatal IGF I levels in preterm and term infants. In preterm infants IGF I levels at birth are positively correlated with birth weight (16). Until term age these infants IGF I levels’ are also positively correlated with their preceding as well as their subsequent weight gain, indicating higher previous as well as higher subsequent growth rate in those infants with higher IGF I levels (14). Figure 1. Postnatal Insulin-like growth factor I (IGF I) levels in preterm and term infants. Preterm infants: Hansen-Pupp (○) (14), Ohkawa (□) (17), Van de Lagemaat (△) (18), Giapros (◊) (19), Wang (▽) (20). Term infants: Iniguez (▲) (21), Kurtoglu (●) (15), Wang (◆) (20), Larnkjaer (■) (22), Hyun (▼) (23), Ong (+) (24)

31 Dietary proteins and IGF I levels in preterm infants 2 However after term age contradictory findings have been reported. Several studies observed IGF I levels to positively correlate with current growth parameters and preceding growth velocity in pretermas well as healthy term infants (18, 19, 25, 26). In contrast findings concerning the correlation between IGF I levels and subsequent growth velocity are inconclusive (Table 1). Table 1. Associations between IGF I and growth Van de Lagemaat (18) Van de Lagemaat (18) Giapros (19) Chellakooty (25) Ong (24) Socha (26) Study population Very preterm infants Very preterm infants Late preterm infants Healthy term infants Healthy term infants Healthy term infants Timing IGF I blood draw Term age 3 months 6 weeks, 3 & 6 monthsb 3 months 3 months 6 months IGF I & previous growth velocity ↗Δ weight SDS (birth - term age) ↗Δ length SDS (birth - term age) ↗Δ weight SDS (birth - 3 monthsa) ↗Δ length SDS (birth - 3 monthsa) ↗ weightc ↗ lengthc ↗Δ weight SDS (birth - 3 months) ↗Δ length SDS (birth - 3 months) Not reported ↗ΔWFL SDS (birth - 6 months) IGF I & current growth ↗ weight and length SDS ↗ weight and length SDS ↗ weight and length SDS ↗ weight; → length ↗ weight; →length ↗ WFL SDS IGF I & subsequent growth velocity ↘Δ weight SDS (term age - 6 monthsa) ↘Δ length SDS (term age - 6 monthsa ) →Δ weight SDS (3 - 6 monthsa ) →Δ length SDS (3 - 6 monthsa) → (growth parameters not specified) ↘Δ weight SDS (3 - 18 months) →Δ length SDS (3 - 18 months) →Δ weight (3 - 12 months) ↗Δ length (3 - 12 months) →Δ WFL SDS (6 – 12 months) ↗ = positive correlation; ↘ = negative correlation; → = no correlation; Δ = gain; a = correctedage; b = chronological age; c = higher IGF I levels in infants with accelerated previous weight and length gain (a difference of more than 0.67 SDS between two study points); IGF I = Insulin-like growth factor I; SDS = standard deviation score; WFL = weight-for-length Hypothesizing these findings might reflect that after term age a turning point occurs. At this point infants with the lowest IGF I levels and thus the poorest previous growth may tend to show accelerated growth. This hypothesis would be in line with the negative correlation between IGF I and subsequent growth velocity found in the above stated studies: infants with the lowest IGF I levels had the highest subsequent growth velocity. Less comorbidity in preterm infants after term age might create a less stressful environment in which catch-up growth could occur, i.e. an increased growth rate compared to the infant’s previous growth

32 Chapter 2 rate enabling the infant to reach a body size comparable to that of healthy infants at a corresponding age. Also further maturation of the neuroendocrine axes and target organs may improve feedback mechanisms and thus optimize growth control. Hypothesizing more into detail eventually a point may be reached where growth velocity is fixed regardless of the previous growth pattern. This would then correspond with the absence of a correlation between IGF I levels and subsequent growth. At this point the neuroendocrine axes and target organsmay be completely programmed setting the growth rate at a fixed point. Concluding these diverse associations may possibly illustrate a regulatory effect to direct growth towards the mean. For IGF I to function optimally, i.e. to enable growth to the full potential of each individual, certain conditions are paramount. The neuroendocrine axes and target organs need to be matured to such an extent that feedback mechanisms can reliably control growth, i.e. correct too slow as well as too fast growth. Furthermore the environment needs to reinforce a steady growth rate; meaning that sufficient nourishment needs to be available and stressful factors, such as comorbidities, should be limited. Hypothesizing after term age there may be an optimal combination of these conditions, creating a window of opportunity to catch up in growth. In comparison, in children who are adopted from impoverished and stressful situations growth restriction occurs. When they are placed in a more nurturing environment through adoption catch-up growth is observed. In a study by Miller et al. adopted children with the lowest IGF I had 4.9 times higher odds (95%CI: 1.1 – 22.9) of showing catch up growth in height than children with the highest IGF I (mean age at adoption 20.1 months + 9.8) (27). Simplified, preterm infants show three growth patterns: small size at birth and persistent small size at term age (small for gestational age infants), appropriate size at birth but small size at term age (appropriate for gestational age infants with postnatal growth restriction) and appropriate size at birth and appropriate size at term age (appropriate for gestational age infants without postnatal growth restriction). In analogy with children following adoption it is hypothesized that infants small at term age come into a less stressful period after term age which enables them to catch up in growth. Indeed some infants, but not all, show ‘catchup’ growth. The majority of this ‘catch-up’ growth occurs in the first 6 to 12 months of life (28). However there is a concern that rapid growth leads to an unfavourable metabolic and cardiovascular outcome in later life. Indeed De Jong et al. found increased length gain between 6 and 12 months corrected age and weight gain between term and 2 years corrected age to be associated with increased systolic blood pressure at 2 years corrected age (29). In addition Singhal and colleagues found a poorer endothelial function in preterm born adolescents with the highest rate of weight gain in the first two weeks after birth (30). In comparison in term born young adults rapid weight gain in the first three months of life has also been associated with decreased insulin sensitivity, a higher percentage of body fat and more central adiposity (31). Moreover Hovi et al. demonstrated that a decrease in

33 Dietary proteins and IGF I levels in preterm infants 2 weight z-score from birth to term was associated with a higher blood pressure in adulthood. However, this association did not remain significant after adjusting for gestational age at birth (32). Nonetheless a recent review by Lapillonne and Griffin on the effect of postnatal growth on metabolic and cardiovascular outcomes in preterm born adults concluded that, in contrast to growth during late infancy and childhood, growth up to 1 year was not associated with adult blood pressure, glucose tolerance or lipid profile (33). However, the studies described in the review were heterogenic and did not all take a possible confounding effect of nutrition and small versus appropriate for gestational age into account. Therefore the concern of a possible negative impact of initial growth restriction and subsequent catch-up growth expressed through several studies cannot yet be disregarded. Currently there is no full understanding of which infants will and which ones will not completely ‘catch-up’. As in children following adoption onemight hypothesize that infants with the lowest IGF I level in the early post term period are the ones who will show catch up growth. However to our knowledge as of yet there is no evidence supporting this hypothesis in preterm infants. This hypothesis regarding catch-up growth might depend on the plasticity of the neuroendocrine axes and target organs. In certain infants intrauterine or early-life insults may completely program the neuroendocrine axes and target organs. However if there is some plasticity left, alteration of the growth rate may occur. This might further depend on environmental factors, e.g. lack of comorbidities and sufficient nourishment, in combination with the genetic make-up of the infant. Remarkably, in term infants several studies did not find a correlation between IGF I and subsequent weight gain, while they did find a positive correlation with subsequent length gain. Thus higher IGF I levels were associated with a subsequent lower BMI (24, 34). This might imply that high IGF I levels protect against adiposity. Growth restricted and preterm infants would then be at increased risk of developing obesity, because of their presumably low IGF I levels. Indeed, in small for gestational age very low birth weight infants IGF I levels up to 3 months corrected age have been positively associated with lean mass at 2 years (35). Moreover preterms were found to have increased fat mass and decreased lean mass in childhood (9). However a recent meta-analysis could not confirm that this trend persists into adulthood (36). Yet it remains to be clarified whether IGF I is primarily associated with change in height or is equally related to change in weight. Surely IGF I is involved in bone accretion, but it is also implied in adipogenesis (37, 38). Indeed Stigson et al. found that higher IGF I levels at a postmenstrual age of 30 to 32 weeks were associated with increased bone mass (9). Also, a trend of higher IGF I levels was found in preterm infants who increased in bone strength compared to preterm infants with a decrease in bone strength measured by bone speed of sound (39). In line with these findings preterm infants born small for gestational age had decreased bone accretion at 6 months corrected age. In addition 20 year olds who were born

34 Chapter 2 preterm, especially those small for gestational age, had decreased bone mineral density and were shorter compared to term controls (40, 41). Interestingly, however, others found normal bonemass in 4 year old childrenwhowere born preterm (9). As stated by Stigson and colleagues, osteoblasts as well as adipocytes are derived from the same progenitor cells and the IGF system could be important in directing the differentiation to either adipocytes or osteoblasts (9). It may well be that states with low IGF I levels, such as critical illness, nutrient restriction and extreme prematurity, stimulate differentiation towards adipogenesis as a mechanism to ensure an easily accessible energy store, in this relatively catabolic state, as compared to anabolic states with high IGF I levels where sustainable growth through bone formation might be obtained. Nevertheless the role of IGF I in growth, body composition and development of the metabolic syndrome remains complex. For instance lower IGF I levels in infancy have been associated with higher IGF I levels in later life (22). This suggests that events in early life can program IGF I and possibly metabolic outcomes in later life. However low as well as high IGF I levels in adulthood have been associated with the metabolic syndrome and cardiovascular disease (42). Therefore it is difficult to give a clear-cut view of the role of IGF I alone in growth, body composition and the development of the metabolic syndrome. The role of IGF I in neurodevelopment In clinical studies, brain and cranial growth have been associated with subsequent neurodevelopment (5, 43). A polymorphism in the IGF I promotor gene, which is known to regulate serum IGF I levels, has been related with slower cranial growth from birth until 5 years of age (44). Moreover Hansen-Pupp and colleagues found IGF I levels to correlate with brain volumes while there was no association with cerebral spinal fluid volume. The authors hypothesize that this could imply that IGF I does not limit atrophy secondary to brain damage, but rather stimulates brain growth (45). In premature infants a higher rate of increase of IGF I until 35 weeks postmenstrual age has directly been related to a better neurodevelopmental outcome at 2 years of age (43). In line with that, Okuma and colleagues found that IGF I levels were associated with white matter organization (46). Interestingly, mean IGF I concentration was positively correlated to neurodevelopmental outcome during a period, from 30 to 35 weeks postmenstrual age, when a surge in IGF I levels occurred and infants started growing after a phase of postnatal growth restriction (14, 43). Thismay suggest that IGF I has to reach a certain level before it can enhance neurodevelopmental outcome. Even so, the premature disruption of the maternalplacental-fetal unit alters more neuroendocrine factors than merely IGF I, which also influences the final neurodevelopmental outcome.

35 Dietary proteins and IGF I levels in preterm infants 2 Inanalogywith thedevelopment of retinopathyof prematurity the suddendecrease in IGF I at birth could cause stagnation in vascular growth. It is hypothesized that the surge in IGF I might lead to neovascularisation with abnormal vessel formation, which could cause intracranial haemorrhage and consequently influence neurodevelopmental outcome. In experimental studies it has been suggested that IGF I may limit damage after hypoxic-ischemic brain injury and inflammation (47, 48). Moreover mice treated with IGF I seemed to have increased proliferation of immature oligodendrocytes, while the number of mature oligodendrocytes remained the same. This was hypothesized to possibly promote myelination at later stages when the immature oligodendrocytes mature and start myelinating (49). In addition lipopolysaccharide induced brain inflammation in a mouse model led to lower IGF I levels and impaired myelination in the subcortical white matter (50). However in a rat periventricular leukomalacia model it was demonstrated that exogenous IGF I limited lipopolysaccharide induced damage at a low dose, while it increased damage at higher doses (51). Recently IGF I administration has been investigated in a phase I study in preterm infants and showed to effectively increase IGF I levels without any adverse events (52). In the near future this might offer a therapeutic intervention potentially improving neurodevelopment as well as growth and body composition. The role of dietary proteins in growth and body composition In the first weeks of life preterm infants almost universally accumulate a protein deficit and show postnatal growth restriction. In an attempt to achieve an intrauterine-like growth rate neonatologists are challenged to administer the right composition of amino acids and the optimal amount of proteins, combined with sufficient fatty acids and carbohydrates, to optimize nitrogen accretion. Currently the recommended range of protein intake for preterm infants is 3.5 to 4.5 g/kg/day (53). Over the past few years increasing amounts of parenteral amino acids have been administered to preterm infants showing a consistent increase in protein balance. Recent nutritional studies have actually demonstrated that by administering high dose parenteral amino acids current recommendations for protein intake and intrauterine-like growth rates can be achieved, nutritional deficits can drastically be reduced and postnatal growth restriction can in part be prevented (Figure 2) (11). It is recognized that high and early introduction of proteins can limit the initial postnatal weight loss (54). By reducing initial weight loss the tendency for rapid ‘catch-up’ growth might be reduced, which may lead to more favourable metabolic programming. Indeed low protein levels are associated with low IGF I levels (55), which in turn is associated with fat mass accretion in childhood (35).

36 Chapter 2 Figure 2. Protein intake and change in weight z-sore. Protein intake (a) and change in weight z-score (b) in the first 6 weeks of life achieved by standard practice in our neonatal intensive care unit in Amsterdam, the Netherlands (■) (unpublished data) compared with that reported by Embleton (●) (56) before current ESPGHAN guidelines and Senterre (▲) (57) using current ESPGHAN guidelines. However after the initial period of weight loss, in which parenteral feeding is the primary source of nutrition, growth sets in. When growth occurs, protein requirements can be re-evaluated and slowly tapered off to reach 2-3 g/kg/day at term age (58). Caution is warranted to maintain an appropriate protein intake when transitioning from parenteral to enteral nutrition. However enteral and parenteral protein intake might not be similar. For instance, bypassing the enteral route is likely to lower the systemic availability of certain amino acids which are metabolised from other amino acids in the intestine and/or liver (54). In spite of several studies which did not find an increased growth after augmenting protein intake (59, 60), most studies demonstrate that increased protein intake in the neonatal period positively influences growth up to term age (61-65). These studies report improved absolute and standardized measures of weight, length and head circumference as well as an increased growth velocity. No intolerance of high protein diets has been reported (58, 66) and glycaemic control might actually be improved with a high protein intake (59, 60). However protein intake in the neonatal period will not necessarily have an impact on growth indices in childhood

37 Dietary proteins and IGF I levels in preterm infants 2 (65). A high protein intake in the in-hospital as well as in the post discharge period seems to decrease fat mass and increase lean mass up to 6 months corrected age (67-69). Whether this trend persists into childhood is not known. Using bone transmission time Scattolin and colleagues found protein intake to positively correlate with bone mineral status at 36 weeks postmenstrual age (66). However Fewtrell was unable to correlate protein intake in infancy with peak bone mass or bone turnover in young adulthood (41). Thus a persisting beneficial effect of early protein intake on growth and body composition in later life has not yet been confirmed. Even though protein is vital to optimize growth, its relation to other nutrient components and the administration of specific amino acids are equally important. Indeed Mcleod and colleagues demonstrated that an increased protein/energy ratio reduced adipose tissue accretion as compared to muscle accretion. Surely energy from another source than protein itself is necessary for net protein gain. However when non-protein caloric intake surpasses 60 kcal/kg/day, protein intake itself is the primary determinant of protein gain. Nevertheless it should be questioned to which level the protein/energy ratio should be increased. The ESPGHAN committee on nutrition recommends a ratio of 3.2 to 4.1 g protein/100 kcal (53). Yet there is a need of supportive evidence as to which ratio should be maintained at specific points in time. Several studies found that when preterm infants were on complete enteral nutrition increasing the protein/energy ratio above 3 g protein/ 100 kcal did not improve fat free mass accretion compared to a ratio of 2.7-2.8 g protein/100 kcal (67, 70). To our knowledge studies conducted so far have not assessed the effects on body composition of various protein/energy ratios in the first two weeks of life. Because preterm infants have limited ability to synthesize certain non-essential amino acids those amino acids become conditionally essential. Some have proposed that the addition of these so called semi-essential amino acids to the diet of preterm infants will improve growth. Cysteine for example, has been implied to be one of the key factors which potentiate the trophic effect of high protein diets (71). The role of dietary proteins in neurodevelopment During hospitalisation increased protein intake improves head growth in preterm infants (72, 73). Even so total energy and lipid intake also have been positively correlated with head growth (73, 74). Nonetheless Hansen-Pupp and colleagues could not associate protein and caloric intake with brain volumes (43) and in several studies protein-enriched nutrition failed to improve neurodevelopmental outcome up to 18 months corrected age (59, 72, 75, 76). Macro- and microstructural brain analyses could not be correlated to intake of protein or other nutritional components either (46). Yet, two studies by Stephens et al. and Cormack et al.

38 Chapter 2 showed that protein intake in the first weeks of life was positively correlated with the cognitive and motor score on the Bayley Scales of Infant Development (77, 78). In addition Biasini and colleagues found that increased protein intake in extremely low birth weight infants improved performance and hearing/language scores on the Griffith Development Mental Score at 3 and 12 months corrected age (79). Moreover increased fat free mass, which is claimed to reflect protein accretion, was associated with faster neuronal processing at 4 months corrected age (80). Also, perinatal protein restriction in mice altered the intracerebral dopamine circuit whichcausedaltered reward-processingandhyperactivity (81). The authors suggest that this could possibly be translated to adverse neurodevelopmental outcome, such as ADHD, in growth restricted infants. Furthermore in preterm infants who were fed a high nutrient diet larger caudate volumes and higher verbal IQ were found in adolescence (82). So far pathways explaining the associationbetweenneurodevelopment andprotein intake are still speculative. Compared to other nutrient components the unique feature of protein might just lie in the alteration of neuronal processing. Perhaps that the underlying mechanism works through increased neurotransmitter- and receptor synthesis. Indeed increased lactalbumin intake in rats increased cortex tryptophan. Nevertheless casein had a negative effect on tryptophan (83). Also de Kieviet and colleagues found an increased oral glutamine intake to be associated with increased white matter-, hippocampus-, and brain stem volumes in very preterm children at school age (84). Since glutamine has been shown to reduce the number of serious infections in very preterm children, they hypothesized that increased glutamine intake indirectly influences neurodevelopment by reducing infections in the neonatal period. IGF I and dietary proteins As stated earlier IGF I levels are related to nutritional intake. Socha et al. demonstrated that infants fed high-protein follow-up formula had higher IGF I levels than those fed low-protein follow-up formula (26). Moreover a minimal caloric as well as a minimal protein intake has to be reached to maintain normal IGF I levels (12). Furthermore there is a strong negative effect of breast milk on IGF I levels. Next to the lower protein content other, yet to be determined, factors might play a role in establishing this effect (85). Given the reciprocal relation between IGF I and nutrition, nutritional interventions might be the key factor in improving growth, body composition and neurodevelopmental outcome of preterm infants. Interestingly, Hansen-Pupp and colleagues found that IGF I and nutritional intake only correlated after a postmenstrual age of 30 weeks (14). The timing of a nutritional intervention may therefore be crucial for the sustainability of its effect.

39 Dietary proteins and IGF I levels in preterm infants 2 Conclusions Altogether preterm and small for gestational age infants are at risk for impaired growth and a suboptimal body composition, making them prone to risk factors for the metabolic syndrome. Low early postnatal IGF I levels seem to be at the origin of this problem. Increased early dietary protein intake has shown to improve growth and body composition in infancy. However it is yet to be elucidated whether this trend persists in later life, thus calling for long-term follow-up studies. Higher IGF I levels and increased dietary protein intake have been found to also improve neurodevelopmental outcome of preterm infants. Evidence supports a trophic role of IGF I in the development of the central nervous system. So far signs of a direct mechanism which limits damage from hypoxic-ischemic and inflammatory insults have only been found in experimental studies. However it is plausible that improved neuronal processing due to higher IGF I levels and an increased dietary protein intake may play a role in preterm infants. Since IGF I levels are related to dietary protein intake it would be valuable to investigate whether a nutritional intervention could improve the long-term outcome of preterm infants by optimizing IGF I levels as well as optimally using the potential of IGF I. It may be argued whether initial IGF I levels are sufficient or should be further increased by increasing nutrient intake in the early postnatal period. On the other hand nutrient intake might have to be reduced once IGF I reaches the level where it’s trophic and neurodevelopment enhancing potential becomes effective, creating a more favourable setting for further development. Moreover, assessment of the optimal protein/energy ratio in this period may be a key to improve metabolic programming and studies on specific amino acids could ameliorate dietary advices. In addition it has to be questioned whether IGF I administration to preterm infants could offer a potential future therapeutic intervention. Altogether the above illustrates the important gap of knowledge in potential causal pathways between dietary protein intake, IGF I levels and longterm outcomes of preterm infants that needs to be explored in future research.