Insulin-like growth factors (IGFs) and IGF binding proteins, serum acid-labile subunit and growth hormone binding protein in nephrotic children

Growth Hormone Treatment for Non-GHD Disorders: Excitement Tempered by Biology

The success of growth hormone (GH) replacement in children with classical GH deficiency has led to excitement that other causes of short stature may benefit similarly. However, clinical experience has shown less consistent and generally less dramatic effects on adult height, perhaps not surprising in light of increased understanding of GH and growth plate biology. Nonetheless, clinical demand for GH treatment continues to grow. Upon the 20th anniversary of the US Food and Drug Administration's approval of GH treatment for idiopathic short stature, this review will consider the factors underlying the expansion of GH treatment, the biological mechanisms of GH action, the non-GH-deficient uses of GH as a height-promoting agent, biological constraints to GH action, and future directions.

Renal effects of growth hormone in health and in kidney disease

Growth hormone (GH) and its mediator insulin-like growth factor-1 (IGF-1) have manifold effects on the kidneys. GH and IGF receptors are abundantly expressed in the kidney, including the glomerular and tubular cells. GH can act either directly on the kidneys or via circulating or paracrine-synthesized IGF-1. The GH/IGF-1 system regulates glomerular hemodynamics, renal gluconeogenesis, tubular sodium and water, phosphate, and calcium handling, as well as renal synthesis of 1,25 (OH)2 vitamin D3 and the antiaging hormone Klotho. The latter also acts as a coreceptor of the phosphaturic hormone fibroblast-growth factor 23 in the proximal tubule. Recombinant human GH (rhGH) is widely used in the treatment of short stature in children, including those with chronic kidney disease (CKD). Animal studies and observations in acromegalic patients demonstrate that GH-excess can have deleterious effects on kidney health, including glomerular hyperfiltration, renal hypertrophy, and glomerulosclerosis. In addition, elevated GH in patients with poorly controlled type 1 diabetes mellitus was thought to induce podocyte injury and thereby contribute to the development of diabetic nephropathy. This manuscript gives an overview of the physiological actions of GH/IGF-1 on the kidneys and the multiple alterations of the GH/IGF-1 system and its consequences in patients with acromegaly, CKD, nephrotic syndrome, and type 1 diabetes mellitus. Finally, the impact of short- and long-term treatment with rhGH/rhIGF-1 on kidney function in patients with kidney diseases will be discussed.

A review of renal GH/IGF1 family gene expression in chronic kidney diseases

Despite decades of study on the contribution of growth hormone (GH) to the development of kidney disease, there remains the question of the relative contribution of elevated levels of GH to kidney damage in humans, particularly in diabetic nephropathy occurring in type 1 patients. In this study, we reviewed several publicly available datasets to examine transcription of twelve genes associated with the GH/IGF1 axis in several types of human and rodent kidney diseases. Our analyses revealed downregulation of renal GHR and IGF1 gene expression in several different chronic human kidney diseases, including diabetic nephropathy, with general upregulation of IGFBP6 in the same tissues and diseases. These findings were generally supported by a review of studies in rodent models. In healthy and diseased human kidneys, increased GHR gene expression was associated with increases in glomerular filtration rate (GFR) and decreases in serum creatinine. IGFBP6 gene expression demonstrated the opposite clinical correlation. Our results suggest the kidney may exhibit GH insensitivity due to low GHR gene expression during most chronic kidney diseases.

Insulin-like growth factors in normal and diseased kidney

This article reviews the physiology of the insulin-like growth factor (IGF) system in the kidney and the changes and potential role of this system in selected renal diseases. The potential therapeutic uses of recombinant human IGF-I for the treatment of acute and chronic kidney failure are briefly discussed.

Cardiac dysfunction in HgCl2-induced nephrotic syndrome

The experimental model of HgCl2 injection is characterized by a systemic autoimmune disease which leads to the development of nephrotic syndrome (NS). NS seems to be accompanied by cardiovascular alterations, since patients with NS present an increased incidence in cardiac disease. The aim of our work was to study the effects of HgCl2-induced NS on myocardial function and morphometry. Normotensive Brown–Norway rats were injected with HgCl2 (1 mg/kg, HgCl2 group; n = 6, subcutaneous) or the vehicle (control group; n = 6, subcutaneous) on days 0, 2, 4, 7, 9 and 11. The animals were placed in metabolic cages for evaluation of urinary excretion of noradrenaline, sodium, total proteins, albumin and creatinine. Fourteen and 21 days after the first HgCl2 injection, left ventricle (LV) hemodynamics was evaluated through pressure micromanometers in basal and isovolumetric heartbeats. The heart and gastrocnemius muscle weights and tibial length were also examined. In an additional group of animals cardiac dimensions and ejection fraction were assessed by echocardiography and LV apoptosis and fibrosis were studied. HgCl2-injected rats presented proteinuria, albuminuria, hyperlipidemia, anemia, sodium retention and ascites at day 14. These alterations were accompanied by LV hemodynamic changes only in isovolumetric heartbeats. Similarly, on day 21, HgCl2-injected rats presented proteinuria, albuminuria, hyperlipidemia, anemia, but no sodium retention or ascites. These animals presented LV systolic and diastolic dysfunction in both basal and isovolumetric heartbeats, as well as cardiac atrophy, LV fibrosis and an increase in myocyte apoptosis. In conclusion, HgCl2-induced NS is accompanied by LV dysfunction and can be a promising model for studying the link between NS and cardiac disease.

Successful treatment of dwarfism secondary to long-term steroid therapy in steroid-dependent nephrotic syndrome

Prolonged steroid therapy is generally used for steroid-dependent nephrotic syndrome in pediatric patients. However, dwarfism secondary to a long-term regimen and its successful reverse is rarely reported. The underlying mechanism of dwarfism is still poorly understood, as both long-term steroid use and nephrotic syndrome may interact or independently interfere with the process of growth. Here, we present a 17-year-old patient with dwarfism and steroid-dependent nephrotic syndrome and the successful treatment by recombinant human growth factor and cyclosporine A with withdrawal of steroid. We also briefly review the current understanding and the management of dwarfism in pediatric patients with nephrotic syndrome.

Cardiac remodeling and dysfunction in nephrotic syndrome

There is an increased incidence of heart disease in patients with chronic nephrotic syndrome (NS), which may be attributable to the malnutrition and activated inflammatory state accompanying the sustained proteinuria. In this study, we evaluated renal function, cardiac morphometry, contractile function, and myocardial gene expression in the established puromycin aminonucleoside nephrosis rat model of NS. Two weeks after aminonucleoside injection, there was massive proteinuria, decreased creatinine clearance, and a negative sodium balance. Skeletal and cardiac muscle atrophy was present and was accompanied by impaired left ventricular (LV) hemodynamic function along with decreased contractile properties of isolated LV muscle strips. The expression of selected cytokines and proteins involved in calcium handling in myocardial tissue was evaluated by real time polymerase chain reaction. This revealed that the expression of interleukin-1beta, tumor necrosis factor-alpha, and phospholamban were elevated, whereas that of cardiac sarco(endo)plasmic reticulum calcium pump protein was decreased. We suggest that protein wasting and systemic inflammatory activation during NS contribute to cardiac remodeling and dysfunction.

Hyperphosphatemia is prevalent among children with nephrotic syndrome and normal renal function

The aim of the study was to analyze systematically our observation that children with severe nephrotic syndrome (NS) have hyperphosphatemia despite normal kidney function. Forty-seven children with NS and normal glomerular filtration rate (GFR) were studied [26 with steroid-sensitive nephrotic syndrome (SSNS) and 21 with persistent NS]. The plasma phosphate level was expressed as the number of standard deviations (SDs) from the mean levels in age- and gender-matched controls. In SSNS plasma phosphate concentration was elevated (+3.7+/-2.0 SDs) during relapse and normalized (-0.7+/-1.7 SDs) in remission. In persistent NS the phosphate level was +4.0+/-2.1 SDs. Patients with marked hyperphosphatemia (>4 SDs) were younger (p<0.001), had lower plasma albumin (p<0.001), and had higher urinary protein levels (p<0.05). Hyperphosphatemia did not correlate with GFR, plasma calcium, or urinary sodium levels. Children with persistent NS had decreased serum 25(OH)D(3) and insulin-like growth factor 1 (IGF-1) concentrations. Hyperphosphatemia is prevalent among children with persistent nephrotic syndrome and normal renal function, correlates with its severity, and may result from increased urinary IGF-1 wasting.

Growth hormone binding protein 2001

The present state of knowledge about growth hormone binding proteins (GHBP) is reviewed, with particular emphasis on the high affinity GHBP, which represents the circulating ectodomain of the growth hormone receptor (GHR). GHBP is conserved through vertebrate evolution, is produced in many tissues (especially liver) by either alternative GHR mRNA splicing (rodents) or by proteolytic cleavage from the GHR (humans, rabbits and several other species). The metalloprotease TACE (tumor necrosis factor-alpha converting enzyme) is the likely enzyme responsible for cleavage, but the structural requirements for TACE recognition or catalysis, and hence the precise cleavage point in the GHR, are unknown. GHBP is widely distributed in biological fluids, with marked concentration differences amongst them. GHBP binds about half of the circulating GH under basal conditions but is easily saturated at high GH levels; it subserves complex functions, including a circulating buffer/reservoir function for GH, prolongation of plasma GH half-life, competition with GHRs for GH, and probably unproductive heterodimer formation with the GHR. The net effect of these partly enhancing and partly inhibitory functions on GH action in vivo is complex and difficult to ascertain. Serum GHBP levels roughly parallel GHR expression (particularly in liver) through the life span, with very low levels in fetal life, upregulation to adult levels during childhood, and decline in senescence. Rodent pregnancy is associated with a massive increase in GHBP expression. Although the regulation of GHBP expression/production is not necessarily tightly linked to GHR expression, in general, low GHBP levels occur in conditions associated with GH resistance (e.g., malnutrition, uncontrolled diabetes, catabolic states, renal failure, hypothyroidism). Conversely, obesity, a condition with enhanced GH responsivity, is associated with elevated GHBP levels. This suggests that in many (but not all) instances of abnormal GH action, the GHBP level reflects GHR status. Laron syndrome (genetic GHR deficiency/dysfunction due to mutations in the GHR gene) is associated with low or undetectable GHBP in 75-80% of patients; GHBP measurement can therefore be used diagnostically. Depending on the design of assays for serum GH, endogenous GHBP may interfere to varying degrees, and GH assays should be individually validated and optimized in this regard. The ultimate biological role and physiological significance of the GHBP remain to be established.

Proteolysis of insulin-like growth factor-binding protein-3 is increased in urine from patients with diabetic nephropathy

The insulin-like growth factor (IGF) system has been implicated in the development of experimental diabetic nephropathy. IGF-binding protein-3 (IGFBP-3) modulates IGF actions, and proteolysis decreases its binding affinity for IGFs. The aim of this study was to explore the possibility that proteolysis of IGFBP-3 may be altered in diabetic nephropathy and may therefore modify the intrarenal effects of IGFs. IGFBP-3 proteolysis in urine from diabetic patients with normo- [albumin excretion rate (AER), <20 microg/min], micro- (AER, 20-200 microg/min), and macroalbuminuria (AER, >200 microg/min) was studied in 34 patients with noninsulin-dependent diabetes mellitus (NIDDM), 14 patients with insulin-dependent diabetes mellitus, and 9 controls. Urine samples were analyzed by Western ligand blotting and IGFBP-3 immunoblotting. Protease activity was quantitated using [125I]IGFBP-3 as a substrate. WLB showed three main bands (40-46, 35, and 26 kDa) in control urine and a fainter 18-kDa band. All but the 35-kDa band were immunoreactive with the IGFBP-3 antiserum. The same pattern of IGFBPs was seen in urine from normoalbuminuric diabetic patients. However, the urine of diabetic patients with micro- and macroalbuminuria contained little or no intact 40- to 46-kDa IGFBP-3. In patients with noninsulin-dependent diabetes mellitus, urinary IGFBP-3 protease activity in micro- (n = 13) and macroalbuminuric patients (n = 12; mean +/- SD[SCAP], 75 +/- 25% and 84 +/- 24%) was significantly higher than that in normoalbuminuric patients (29 +/- 9%; P = 0.0001). Similar results were observed in patients with insulin-dependent diabetes mellitus. Proteolytic activity in diabetic urine was due to a serine protease. In conclusion, diabetic nephropathy was associated with IGFBP-3 proteolysis in urine. As similar changes were not observed in patients' sera, this is likely to reflect changes in the kidney or urinary tract, resulting in increased local IGF bioavailability, and therefore may contribute to the structural changes of diabetic nephropathy.

Serum-free insulin-like growth factor I correlates with clearance in patients with chronic renal failure

Serum-free insulin-like growth factor I correlates with clearance in patients with chronic renal failure.

BACKGROUND

Chronic renal failure (CRF) results in major changes in the circulating growth hormone (GH)/insulin-like growth factor (IGF) system. However, there are only limited data on changes in free IGF-I in CRF.

METHODS

Matched groups of nondiabetic, nondialyzed patients with CRF (N = 25) and healthy controls (N = 13) were compared. The creatinine clearance (CCr) based on a 24-hour urine collection ranged from 3 to 59 and 89 to 148 ml/min/1.73 m2 in patients and controls, respectively. Overnight fasting serum samples were analyzed for free and total IGF-I and -II, and IGF-binding protein (IGFBP)-1, -2, and -3. Additionally, intact as well as proteolyzed IGFBP-3 was determined.

RESULTS

The patients had reduced serum-free IGF-I (-53%) and increased levels of total IGF-II (40%), IGFBP-1 (546%), and IGFBP-2 (270%, P < 0.05). Serum total IGF-I and free IGF-II were normal. Also, serum levels of immunoreactive IGFBP-3 were elevated (33%, P < 0.05), but this could be explained by an increased abundance of IGFBP-3 fragments, as ligand blotting showed no difference in levels of intact IGFBP-3. Accordingly, patients had an increased proteolysis of IGFBP-3 in vivo (17%) and in vitro (7%, P < 0.05). In patients, free IGF-I levels correlated positively with CCr (r2 = 0.38, P < 0.002) and inversely with IGFBP-1 (r2 = 0.69, P < 0. 0001) and IGFBP-2 (r2 = 0.41, P < 0.0007), whereas CCr was inversely correlated with levels of IGFBP-1 (r2 = 0.48, P < 0.0001) and IGFBP-2 (r2 = 0.63, P < 0.0001).

CONCLUSIONS

These data strongly support the hypothesis that CRF-related growth failure and tissue catabolism are caused by an increased concentration of circulating IGFBP-1 and -2, resulting in low serum levels of free IGF-I and thus IGF-I bioactivity. In addition, low levels of free IGF-I may explain the increased secretion of GH in CRF.

Acquired growth hormone resistance in adults

Acquired growth hormone resistance (AGHR) may be defined as the combination of a raised serum growth hormone (GH) concentration, low serum insulin-like growth factor-1 (IGF-1) concentration and a reduced anabolic response to exogenous GH. A wide range of conditions exhibit the syndrome to a variable degree, including sepsis, trauma, burns, AIDS, cancer, and renal or liver failure. The primary defect seems to be a reduction in IGF-1 concentration which then leads to increased GH concentration by a loss of negative feedback. It is not clear whether IGF-1 concentration falls because of decreased production or increased clearance from the circulation, or both. Treatment to reverse the biochemical defect by restoring IGF-1 levels, either by the administration of GH or IGF-1, has resulted in improvements in a wide range of metabolic parameters and, more recently, to definite clinical benefit in well-defined groups, such as patients with AIDS. These results cannot be extrapolated to other groups with AGHR as a recent unpublished report suggested increased mortality in critically ill patients treated with GH. Research needs to focus on the molecular basis of AGHR if we are to develop therapies for catabolism.