Serum insulin-like growth factors (IGFs) and IGF binding proteins 1, 2, and 3 in children with chronic renal failure: relationship to height and glomerular filtration rate. The European Study Group for Nutritional Treatment of Chronic Renal Failure in Childhood

Chronic Kidney Disease and Dietary Measures to Improve Outcomes

Chronic kidney disease is an ongoing deterioration of renal function that often progresses to end-stage renal disease. Management goals in children include slowing disease progression, prevention and treatment of complications, and optimizing growth, development, and quality of life. Nutritional management is critically important to achieve these goals. Control of blood pressure, proteinuria, and metabolic acidosis with dietary and pharmacologic measures may slow progression of chronic kidney disease. Although significant progress in management has been made, further research is required to resolve many outstanding controversies. We review recent developments in pediatric chronic kidney disease, focusing on dietary measures to improve outcomes.

Growth and Nutrition in Pediatric Chronic Kidney Disease

Children with chronic kidney disease (CKD) feature significant challenges to the maintenance of adequate nutrition and linear growth. Moreover, the impaired nutritional state contributes directly to poor growth. Therefore, it is necessary to consider nutritional status in the assessment of etiology and treatment of sub-optimal linear growth. The major causes of poor linear growth including dysregulation of the growth hormone/insulin-like growth factor-I (IGF-I) axis, nutritional deficiency, metabolic acidosis, anemia, renal osteodystrophy/bone mineral disease, and inflammation. This review summarizes the causes and assessment tools of growth and nutrition while providing a summary of state of the art therapies for these co-morbidities of pediatric CKD.

Impaired phosphorylation of JAK2-STAT5b signaling in fibroblasts from uremic children

BACKGROUND

Chronic kidney disease (CKD) in children is characterized by severe growth failure. The growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis in uremic animals shows a post-receptor impaired phosphorylation of Janus kinase 2/signal transducer and activator of transcription (JAK-STAT) proteins. The objective of our study was to characterize the intracellular phosphorylation of JAK-STAT signaling in fibroblasts from children with CKD on chronic peritoneal dialysis (PD).

METHODS

Serum GH-binding protein (GHBP), IGF-1 and IGFBP3 were measured in 15 prepubertal CKD stage-5 children on PD. Cytoplasmic JAK2, cytoplasmic/nuclear STAT5b and nuclear IGFBP3, acid-labile subunit (ALS) and IGF-1 mRNA expression were quantified in fibroblasts obtained from skin biopsies before and after stimulation with 200 ng/ml recombinant human growth hormone (rhGH). Phosphorylation activity at both the cytoplasmic and nuclear level was expressed as the ratio phosphorylated (p)/total (t) abundance of the product (p/t) at 30 and 60 min. Fifteen healthy children were recruited as the control group. Values were expressed in arbitrary units (AU) and normalized for comparison. Significance was defined as p < 0.05.

RESULTS

Thirty minutes after rhGH stimulus, the cytoplasmic (p/t) JAK2 ratio was significantly lower in patients than in controls [median and interquartile range (IQR): 7.4 (4.56) vs. 20.5 (50.06) AU]. At 60 min after rhGH stimulation, median JAK2 phosphorylation activity was still significantly lower in the patients [7.14 (IQR 3.8) vs. 10.2 (IQR 29.8) AU; p < 0.05]. The increase in the cytoplasmic (p/t) STAT5b/β-actin ratio was lower at both measurement points in the patients compared to the controls, without reaching statistical significance between groups. Median IGFBP3 mRNA abundance was significantly decreased in fibroblasts from uremic patients 24 h after rhGH stimulation compared to the healthy controls [1.27 (IQR 0.83) vs. 2.37 (IQR 0.80) AU]. Median ALS and IGF-1 mRNA expression changed in response to rhGH stimuli at 24 and 48 h.

CONCLUSION

In this study, children with CKD undergoing PD therapy showed an impaired phosphorylation of JAK2/STAT5b signaling in fibroblasts after GH stimulation, as well as impaired IGFBP3 mRNA abundance. Both impairments may be partially responsible for the observed resistance to the growth-promoting actions of GH in chronic kidney failure.

Growth in children on renal replacement therapy: a shrinking problem?

Growth failure has been almost inextricably linked with chronic kidney disease (CKD) and end-stage renal disease (ESRD) since initial reports of renal dwarfism dating back to the turn of the twentieth century. Growth failure in CKD has been associated with both increased morbidity and mortality. Growth failure in the setting of kidney disease is multifactorial and is related to poor nutritional status as well as comorbidities, such as anemia, bone and mineral disorders, and alterations in hormonal responses, as well as to aspects of treatment such as steroid exposure. In this issue of Pediatric Nephrology, Franke et al. report on the gains made in growth and maturation in pediatric patients with ESRD in recent decades, particularly in Germany. Through advances in the care of CKD and ESRD over recent decades, the prevalence of growth failure appears to be decreasing. These findings, along with a recent report demonstrating decreases in mortality in childhood ESRD in the United States Renal Data System (USRDS), suggest overall improvements in the outcomes of care, perhaps reflecting improvements in the quality of care for children with kidney disease worldwide.

The insulin-like growth factor system in chronic kidney disease: Pathophysiology and therapeutic opportunities

The growth hormone-insulin-like growth factor-insulin-like growth factor binding protein (GH-IGF-IGFBP) axis plays a critical role in the maintenance of normal renal function and the pathogenesis and progression of chronic kidney disease (CKD). Serum IGF-I and IGFBPs are altered with different stages of CKD, the speed of onset, the amount of proteinuria, and the potential of remission. Recent studies demonstrate that growth failure in children with CKD is due to a relative GH insensitivity and functional IGF deficiency. The functional IGF deficiency in CKD results from either IGF resistance due to increased circulating levels of IGFBPs or IGF deficiency due to increased urinary excretion of serum IGF-IGFBP complexes. In addition, not only GH and IGFs in circulation, but locally produced IGFs, the high-affinity IGFBPs, and low-affinity insulin-like growth factor binding protein-related proteins (IGFBP-rPs) may also affect the kidney. With respect to diabetic kidney disease, there is growing evidence suggesting that GH, IGF-I, and IGFBPs are involved in the pathogenesis of diabetic nephropathy (DN). Thus, prevention of GH action by blockade either at the receptor level or along its signal transduction pathway offers the potential for effective therapeutic opportunities. Similarly, interrupting IGF-I and IGFBP actions also may offer a way to inhibit the development or progression of DN. Furthermore, it is well accepted that the systemic inflammatory response is a key player for progression of CKD, and how to prevent and treat this response is currently of great interest. Recent studies demonstrate existence of IGF-independent actions of high-affinity and low-affinity-IGFBPs, in particular, antiinflammatory action of IGFBP-3 and profibrotic action of IGFBP-rP2/CTGF. These findings reinforce the concept in support of the clinical significance of the IGF-independent action of IGFBPs in the assessment of pathophysiology of kidney disease and its therapeutic potential for CKD. Further understanding of GH-IGF-IGFBP etiopathophysiology in CKD may lead to the development of therapeutic strategies for this devastating disease. It would hold promise to use of GH, somatostatin analogs, IGFs, IGF agonists, GHR and insulin-like growth factor-I receptor (IGF-IR) antagonists, IGFBP displacer, and IGFBP antagonists as well as a combination treatment as therapeutic agents for CKD.

The IGF/IGFBP system in relation to macroscopic bone architecture in pediatric renal transplant patients

The post-transplant bone disease of the peripheral skeleton in pediatric renal transplant recipients is characterized by an inadequately thin bone cortex in relation to muscular force. A major hormonal modulator of periosteal growth is the insulin-like growth factor (IGF)/IGF binding protein (IGFBP) system. We therefore hypothesized that the reduced cortical thickness in these patients may be due to functional IGF deficiency. To test this hypothesis, we investigated 55 patients (mean estimated glomerular filtration rate 86.3 +/- 30.0 ml/min/1.73 m(2)) in a cross-sectional study. Parameters of macroscopic bone architecture and forearm muscle size were analyzed by peripheral quantitative computed tomography (pQCT), and serum IGF/IGFBP system components were measured by specific radioimmunoassays. The mean (+/- standard deviation) standardized serum IGF-I (0.20 +/- 1.16 score) level was normal, while the mean IGF-II (1.16 +/- 0.11 score) level was significantly elevated. Serum IGFBP-1 and IGFBP-2 levels were not altered, whereas the IGFBP-3 (1.34 +/- 0.15 score) level was significantly increased. The serum IGFBP-4 level was slightly elevated (by 11%), the IGFBP-6 level was markedly (2.3-fold) elevated, while the IGFBP-5 level was comparable to that of the control. The respective age-adjusted cortical thickness at both the proximal (r = 0.407, P < 0.005) and distal (r = 0.383, P < 0.01) forearm was positively correlated with the standardized serum IGF-I level. In conclusion, the serum IGF/IGFBP system in pediatric renal transplant recipients is characterized by an increase in the levels of the inhibitory IGFBPs, IGFBP-3, -4 and -6, resulting in a functional IGF deficiency. The positive correlation of IGF-I with cortical thickness underlines the importance of this hormonal system in the modeling of bone, particularly periosteal growth.

The role of liver-derived insulin-like growth factor-I

IGF-I is expressed in virtually every tissue of the body, but with much higher expression in the liver than in any other tissue. Studies using mice with liver-specific IGF-I knockout have demonstrated that liver-derived IGF-I, constituting a major part of circulating IGF-I, is an important endocrine factor involved in a variety of physiological and pathological processes. Detailed studies comparing the impact of liver-derived IGF-I and local bone-derived IGF-I demonstrate that both sources of IGF-I can stimulate longitudinal bone growth. We propose here that liver-derived circulating IGF-I and local bone-derived IGF-I to some extent have overlapping growth-promoting effects and might have the capacity to replace each other (= redundancy) in the maintenance of normal longitudinal bone growth. Importantly, and in contrast to the regulation of longitudinal bone growth, locally derived IGF-I cannot replace (= lack of redundancy) liver-derived IGF-I for the regulation of a large number of other parameters including GH secretion, cortical bone mass, kidney size, prostate size, peripheral vascular resistance, spatial memory, sodium retention, insulin sensitivity, liver size, sexually dimorphic liver functions, and progression of some tumors. It is clear that a major role of liver-derived IGF-I is to regulate GH secretion and that some, but not all, of the phenotypes in the liver-specific IGF-I knockout mice are indirect, mediated via the elevated GH levels. All of the described multiple endocrine effects of liver-derived IGF-I should be considered in the development of possible novel treatment strategies aimed at increasing or reducing endocrine IGF-I activity.

The growth hormone-insulin-like growth factor-I axis in chronic kidney disease

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are important physiologic regulators of growth, body composition, and kidney function. Perturbations in the GH-IGF-I axis are responsible for many important complications seen in chronic kidney disease (CKD), such as growth retardation and cachectic wasting, as well as disease progression. Recent evidence suggests that CKD is characterized by abnormalities in GH and IGF-I signal transduction and the interaction of these pathways with those that involve other molecules such as ghrelin, myostatin, and the suppressor of cytokine signaling (SOCS) family. Further understanding of GH/IGF pathophysiology in CKD may lead to the development of therapeutic strategies for these devastating complications, which are associated with high rates of mortality and morbidity.

Recombinant insulin-like growth factor-1 as a therapy for IGF-1 deficiency in renal failure

Renal disease in children disrupts the growth hormone (GH) and insulin-like growth factor (IGF) axis and causes growth failure. Although GH therapy stimulates growth in these children, their short stature is likely due to a form of IGF-1 deficiency (IGFD) rather than GH deficiency. Recent experimental data have caused us to reconsider the importance of IGF-1 and IGFD to human growth. Pharmacology studies in rodents, as well as studies in patients with no functional GH receptors and primary IGFD, have shown that IGF-1 is an effective growth-promoting therapy. Gene knockout studies in mice have shown that IGF-1, rather than GH, is the major hormone controlling growth. In addition, both pharmacological and genetic studies have shown that there are effects of GH and IGF-1 that require their combined presence. In children with primary IGFD, where there is no GH signaling, recombinant human (rh)IGF-1 produces a large growth response, while in children who are GH and IGF-1 deficient, treatment with rhGH is the most-appropriate therapy. Children with short stature due to renal failure are GH sufficient and have some GH receptor signaling capacity, so that rhIGF-1, or rhIGF-1 plus rhGH, are logical therapeutic options and merit clinical testing.

Growth hormone therapy influences endothelial function in children with renal failure

Endothelial dysfunction, an early step in atherogenesis, is prevalent in children with renal insufficiency. Endothelial dysfunction in growth hormone deficiency is reversed by growth hormone (rhGH) therapy. Renal failure induces growth hormone resistance at the receptor and post-receptor level, which can be overcome by rhGH therapy. This study investigates the influence of rhGH therapy in children with renal failure on flow-mediated dilation (FMD) of the brachial artery, a marker of endothelial function. We studied 8 patients, who were on rhGH for at least 6 months, and 8 healthy children for comparison. FMD of the brachial artery was measured non-invasively as the percentage increase in diameter during post-ischemic hyperemia. Patients were studied at baseline, after 4 weeks interruption of rhGH therapy, and 4 weeks after resumption of therapy. FMD was significantly lower in patients (4.7%) than healthy controls (13.8%) ( P=0.01). During the administration of rhGH, FMD was significantly higher (3.9%) than during interruption of the treatment (1.4%) ( P=0.04). Our data support the theory that a disturbance in the GH-IGF axis contributes to the endothelial dysfunction of renal failure. Treatment with rhGH not only improves growth but may also favorably influence the risk for atherogenesis.

Neuroendocrine adaptations in renal disease

Chronic renal failure (CRF) disrupts the time-dependent secretion of multiple hormones. The present review focuses on altered pulsatile release of peptide hormones. CRF is marked by impaired tissue actions, disorderly release patterns, and relative [growth hormone (GH)] or absolute [luteinizing hormone (LH)] deficiency of secretion. At the hypothalamo-pituitary level, experimental evidence suggests that CRF reduces the synthesis and/or release of the cognate hypothalamic releasing factors, GHRH and LHRH, and enforces excessive inhibition by somatostatin. Parathyroid hormone (PTH) and insulin are secreted in both basal and pulsatile modes, wherein the latter is putatively coordinated by autonomic innervation. Amplitude and frequency-dependent adaptations of PTH and insulin outflow fail in CRF, as assessed under steady-state conditions and during metabolic drive (i.e., calcium for PTH and glucose for insulin). A common feature in CRF is a diminished mass of hormone released per burst, due in principle to attenuation of feedforward signals and/or accentuation of (unknown) feedback signals. Damping of neuronal control and/or prolonged network response times may contribute to aberrant pulse frequency, disproportionate basal (nonpulsatile) hormone release, and consistent erosion of secretory process regularity in the uremic state. The homeostatic consequences of distorted secretory dynamics, tissue resistance, impaired hormone clearance, and altered mean agonist concentrations are evident in certain therapeutic interventions, such as GH supplementation in CRF.

Impaired JAK-STAT signal transduction contributes to growth hormone resistance in chronic uremia

Chronic renal failure (CRF) is associated with resistance to the growth-promoting and anabolic actions of growth hormone (GH). In rats with CRF induced by partial renal ablation, 7 days of GH treatment had a diminished effect on weight gain and hepatic IGF-1 and IGFBP-1 mRNA levels, compared with sham-operated pair-fed controls. To assess whether GH resistance might be due to altered signal transduction, activation of the JAK-STAT pathway was studied 10 or 15 minutes after intravenous injection of 5 mg/kg GH or vehicle. Hepatic GH receptor (GHR) mRNA levels were significantly decreased in CRF, but GHR protein abundance and GH binding to microsomal and plasma membranes was unaltered. JAK2, STAT1, STAT3, and STAT5 protein abundance was also unchanged. However, GH-induced tyrosine phosphorylation of JAK2, STAT5, and STAT3 was 75% lower in the CRF animals. Phosphorylated STAT5 and STAT3 were also diminished in nuclear extracts. The expression of the suppressor of cytokine signaling-2 (SOCS-2) was increased twofold in GH-treated CRF animals, and SOCS-3 mRNA levels were elevated by 60% in CRF, independent of GH treatment. In conclusion, CRF causes a postreceptor defect in GH signal transduction characterized by impaired phosphorylation and nuclear translocation of GH-activated STAT proteins, which is possibly mediated, at least in part, by overexpression of SOCS proteins.

Short dialyzed children respond less to growth hormone than patients prior to dialysis. German Study Group for Growth Hormone Treatment in Chronic Renal Failure

Recombinant human growth hormone (rhGH) is a new treatment modality for short children with chronic renal failure (CRF) prior to and during dialysis. It is difficult to analyze whether dialysis patients respond less to rhGH than children with CRF on conservative treatment because they are older and often in a pubertal age range. One hundred and eight patients were treated with 28-30 IU rhGH/kg per week for at least 1 year. We analyzed the growth response to rhGH in 56 prepubertal patients aged less than 10 years at the start of rhGH treatment; 38 children with a mean age of 6.5 +/- 2.4 years were on conservative treatment (CT) and 18 patients with a mean age of 6.5 +/- 2 years on dialysis treatment (D). Mean height velocity was 4.9 +/- 2.3 cm/year in children on CT and 4.6 +/- 1.8 cm/year in children on D. During the 1st treatment year, height velocity was 9.5 +/- 3.8 cm/year in CT patients and 7.3 +/- 1.3 cm/year in D patients (P < 0.05). The change in height was +1.1 +/- 0.8 standard deviation (SD) in CT patients and +0.5 +/- 0.4 SD in D patients (P < 0.005). During the 2nd treatment year, the change in height was again greater in CT patients (0.5 +/- 0.4 SD vs. 0.2 +/- 0.4 SD; P < 0.05). The difference in height velocity and change in height standard deviation score was also significant when a subgroup of patients was matched for sex, age, height. Height velocity and the change in height velocity during rhGH treatment were not correlated with residual renal function, the degree of anemia, or metabolic acidosis. We conclude that short children on D respond less to rhGH than short children on CT, indicating a greater insensitivity to rhGH during D treatment.