PTH ameliorates acidosis-induced adverse effects in skeletal growth centers: the PTH-IGF-I axis

BACKGROUND: Chronic metabolic acidosis (CMA) exerts profound adverse effects on bone metabolism thereby leading to impaired skeletal linear growth. We have recently shown that CMA in vitro causes distinct morphological changes in skeletal growth centers along with inhibition of endochondral differentiation. In addition, CMA causes an end organ resistance to the anabolic effects of growth hormone (GH) and locally produced insulin-like growth factor-I (IGF-I) in skeletal growth centers. Given the effects of parathyroid hormone (PTH) and PTH related protein (PTHrP) on the development of cartilaginous bone, we sought to determine whether PTH has any effects on the changes induced by CMA in skeletal growth centers. The interaction between PTH and IGF-I in growth centers during neutral or acidic conditions were studied specifically. METHODS: An in vitro organ culture system using the murine mandibular condyle was employed as a model for endochondral active growth center. Condyles from six-day-old mice were cultured in BGJb medium of either neutral pH (pH approximately 7.4) or acidic pH (pH approximately 7.15) in the presence or absence of 10-10 mol/L [1-34] PTH. After 24, 48, 72 and 96 hours of culture, the condyles were washed, fixed in formaldehyde, and processed for paraffin embedding. Histologic markers of the growth center were assessed. In addition, the protein level and mRNA expression for various markers of cartilage differentiation were evaluated by immunohistochemistry and in situ hybridization, respectively. The abundance and expression levels of IGF-I and IGF-I receptor (IGF-I-R) were assessed also. RESULTS: Following incubation for 72 hours in acidic conditions, there was a marked attenuation of the chondroblastic zone, suggesting a defect in the process of cellular differentiation. Acidosis also down-regulated endochondral differentiation markers (cartilage specific proteoglycans, collagen type II). This was accompanied by a reduction in the expression of IGF-1, IGF-1 receptor and PTH receptors. PTH (10-10 mol/L) added to acidic cultures prevented the adverse effects of CMA on endochondral differentiation and increased the overall condylar growth, when compared to acidic conditions without PTH. PTH also up-regulated its own receptor in control as well as during acidic conditions, and increased the expression levels of IGF-1 and IGF-1 receptor in the acidotic condyle. Acidosis increased the expression of IGF-I binding protein-4 (IGFBP-4, an inhibitor of IGF-I activity), whereas coincubation with PTH during acidic conditions abrogated the up-regulation of IGFBP-4. Addition of a neutralizing antibody to IGF-I-R during PTH treatment under acidic conditions resulted in the abrogation of the ameliorative effect of PTH on endochondral differentiation. The protein kinase C (PKC) signaling pathway was modulated negatively by CMA. However, PTH activated PKC-alpha under both control and acidic conditions. The phorbol ester, PMA (phorbol 12-myristate 13-acetate), a PKC activator, mimicked the effect of PTH on chondrocyte differentiation. CONCLUSION: Parathyroid hormone at low concentration stimulates the differentiation and proliferation of cartilage cells and prevents the suppressive effect of acidosis on endochondral bone differentiation and on the IGF-I/IGF-I-R system in skeletal growth centers. Increased local production of IGF-I by PTH, which takes place even during acidotic conditions, mediates, at least in part, the ameliorative effect of PTH. Protein kinase C is probably one of the signaling pathways mediating the salutary effects of PTH on chondrocyte differentiation in growth centers. This study lends further credence to the notion that under certain conditions, PTH or PTHrP can exert anabolic effects in the skeleton. These findings may be of clinical-therapeutic significance in children and patients with CMA.     

Chronic acidosis-induced growth retardation is mediated by proton-induced expression of Gs protein.

The etiology of skeletal growth retardation accompanying metabolic acidosis is not clear. Using ex vivo models for endochondral ossification, we showed that the cAMP/PKA pathway, probably triggered by proton sensitive G-protein-coupled receptors, is responsible for impaired skeletal growth in acidosis. INTRODUCTION: Chronic metabolic acidosis (CMA) is very often accompanied by skeletal growth retardation. We have previously shown in an ex vivo model of endochondral ossification that murine mandibular condyles subjected to acidic conditions exhibit growth retardation accompanied by a decline of insulin-like growth factor-I (IGF-I) and its receptors. PTH-induced ameliorative effects on the CMA-induced growth retardation of the mandibular condyle are partially mediated by protein kinase C (PKC). In this study we explored the mechanisms underlying the acidosis-induced growth retardation; in particular, the involvement of the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) cellular pathway in the process. MATERIALS AND METHODS: Mandibular condyles from neonatal mice or mandibular condyle derived chondrocytes (MCDCs) were incubated for 3 days under either control or acidic conditions or in the presence of cAMP-regulating factors (cAMPrf) such as forskolin, iso-butyl methyl xanthine (IBMX), or 8-Br cAMP. The effects on proliferation and differentiation of the cultures as well as on phosphorylation of cAMP responsive element binding protein (CREB) and increased expression of the alpha subunit, Gs were determined. The intracellular pH was detected using the acridine orange assay. RESULTS: Our results show that, under acidic conditions, PKA levels were increased. H89 abolished the adverse effects of acidosis on condylar development and restored IGF-I and IGF-I receptors (IGF-IR) levels. The inhibitory effects of acidosis on proliferation and differentiation of cartilaginous cells were mimicked by cAMPrf. We have also shown that acidosis stimulates activation of Gs trimeric protein and CREB phosphorylation. GDPbetaS--a Gs antagonist--abolished the acidosis-induced condylar growth arrest. Using an acridine orange assay, we showed that the intracellular environment is not acidified under acidic conditions. CONCLUSIONS: Our results indicate that the adverse effects of acidosis on skeletal growth centers are mediated at least in part by the cAMP/PKA cellular pathway. We speculate that high proton concentrations exerted by acidosis conditions stimulate proton sensitive G-protein-coupled receptors, which are mediated by the cellular cAMP/PKA pathway and induce skeletal growth retardation.     

Expression of osteotropic growth factors and growth hormone receptor in a canine distraction osteogenesis model

Osteotropic growth factors play an important role in bone metabolism. Nevertheless, knowledge about their expression in relation to distraction osteogenesis remains limited. The aim of the present study was to determine the expression of growth hormone (GH), growth hormone receptor (GHR), insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II), and bone morphogenetic protein 2 (BMP-2) in distraction-induced bone regeneration. Expression of these factors was assessed during the consolidation phase, comparing distraction osteogenesis with osteotomy-induced bone formation. Real-time PCR was performed as a semiquantitative measurement of mRNA, and the relative expression levels of these factors were determined. In addition, plasma GH profiles and plasma concentrations of IGF-I, IGF-II, and insulin-like growth factor-binding protein 4 and -6 (IGFBP-4 and -6) were measured to assess their potential systemic role during bone formation. Expression of GHR, IGF-I, and BMP-2 had significantly increased in comparison with the expression of these factors in mature bone. Expression of GHR was significantly higher in distraction-induced bone regenerate than in osteotomy-induced bone. No significant differences were found for the expression of IGF-I and BMP-2 between distraction and osteotomy. Plasma concentrations of GH, IGF-I, IGF-II, IGFBP-4, and IGFBP-6 did not demonstrate any significant differences between treatment groups and controls. Upregulation of GHR expression in distraction osteogenesis may enhance sensitivity to endogenous systemic GH and thus promote consolidation of the regenerated bone. Changes in the systemic osteotropic growth factors GH, IGF-I, IGF-II, IGFBP-4, and IGFBP-6 do not seem to be of importance during distraction osteogenesis.     

Growth hormone/insulin-like growth factor system in children with chronic renal failure

Disturbances of the somatotropic hormone axis play an important pathogenic role in growth retardation and catabolism in children with chronic renal failure (CRF). The apparent discrepancy between normal or elevated growth hormone (GH) levels and diminished longitudinal growth in CRF has led to the concept of GH insensitivity, which is caused by multiple alterations in the distal components of the somatotropic hormone axis. Serum levels of IGF-I and IGF-II are normal in preterminal CRF, while in end-stage renal disease (ESRD) IGF-I levels are slightly decreased and IGF-II levels slightly increased. In view of the prevailing elevated GH levels in ESRD, these serum IGF-I levels appear inadequately low. Indeed, there is both clinical and experimental evidence for decreased hepatic production of IGF-I in CRF. This hepatic insensitivity to the action of GH may be partly the consequence of reduced GH receptor expression in liver tissue and partly a consequence of disturbed GH receptor signaling. The actions and metabolism of IGFs are modulated by specific high-affinity IGFBPs. CRF serum has an IGF-binding capacity that is increased by seven- to tenfold, leading to decreased IGF bioactivity of CRF serum despite normal total IGF levels. Serum levels of intact IGFBP-1, -2, -4, -6 and low molecular weight fragments of IGFBP-3 are elevated in CRF serum in relation to the degree of renal dysfunction, whereas serum levels of intact IGFBP-3 are normal. Levels of immunoreactive IGFBP-5 are not altered in CRF serum, but the majority of IGFBP-5 is fragmented. Decreased renal filtration and increased hepatic production of IGFBP-1 and -2 both contribute to high levels of serum IGFBP. Experimental and clinical evidence suggests that these excessive high-affinity IGFBPs in CRF serum inhibit IGF action in growth plate chondrocytes by competition with the type 1 IGF receptor for IGF binding. These data indicate that growth failure in CRF is mainly due to functional IGF deficiency. Combined therapy with rhGH and rhIGF-I is therefore a logical approach.This work was presented in part at the IPNA Seventh Symposium on Growth and Development in Children with Chronic Kidney Disease: The Molecular Basis of Skeletal Growth, 1–3 April 2004, Heidelberg, Germany     

Insulin-like growth factor binding proteins as growth inhibitors in children with chronic renal failure

Children with chronic renal failure (CRF) often fail to attain an adult height consistent with their genetic potential. The growth hormone (GH)/insulin-like growth factor (IGF)/growth plate chondrocyte axis has been intensively studied in these children to determine the basis for this growth failure. Evidence suggests that hepatic GH resistance results in deficient expression of IGF-I. However, serum IGF-I levels are usually normal and it is IGF-I action on target tissues which is inhibited, possibly by the presence of excess high-affinity IGF binding proteins (IGFBPs) in CRF serum. In this paper we evaluate the roles of IGFBP-1, -2, and -3 as growth inhibitors in CRF children. The data support a role for each of these IGFBPs as growth inhibitors. Currently, IGFBP-1 meets most criteria expected of a growth inhibitor, but IGFBP-2 and -3 will likely also meet these criteria and may well be important contributors to the growth failure of CRF. Ultimately, many or all of the six IGFBPs may be found to contribute to the excess high-affinity IGF binding sites which are a hallmark of CRF serum and are possible contributors to the growth failure of CRF children.     

Expression of insulin-like growth factor-I and transforming growth factor-beta in hypokalemic nephropathy in the rat

BACKGROUND: Potassium deficiency (KD) in the rat retards body growth but stimulates renal enlargement caused by cellular hypertrophy and hyperplasia, which is most marked in the outer medulla. If hypokalemia persists, interstitial infiltrates appear and eventually fibrosis. Since early in KD insulin-like growth factor-I (IGF-I) levels in the kidney are elevated, suggesting that it may be an early mediator of the exaggerated renal growth, and as transforming growth factor-beta (TGF-beta) promotes cellular hypertrophy and fibrosis, we examined the renal expression of these growth factors in prolonged KD. METHODS: Rats were given a K-deficient diet or were pair fed or ad libitum fed a K-replete diet for 21 days. Growth factor mRNA levels were measured in whole kidney and protein expression localized by immunohistochemistry. RESULTS: KD rats weighed less than pair-fed controls, while the kidneys were 49% larger. Their serum IGF-I and kidney IGF-I protein levels were depressed, as were their IGF-I mRNA levels in liver, kidney, and muscle. These changes can largely be attributed to decreased food intake. In contrast, kidney IGF binding protein-1 (IGFBP-1) mRNA and TGF-beta mRNA levels were increased significantly. Histology of outer medulla revealed marked hypertrophy and adenomatous hyperplasia of the collecting ducts and hypertrophy of the thick ascending limbs of Henle with cellular infiltrates in the interstitium. Both nephron segments immunostained strongly for IGF-I and IGFBP-1, but only the nonhyperplastic enlarged thick ascending Henle limb cells immunostained for TGF-beta, which was strongly positive. Prominent interstitial infiltrates with ED1 immunostained monocytes/macrophages were present. CONCLUSIONS: These findings are consistent with a sustained role for IGF-I in promoting the exaggerated renal growth of KD and appear to be mediated through local trapping of IGF-I by the overexpressed IGFBP-1, which together with IGF-I can promote renal growth. The selective localization of TGF-beta to hypertrophied nonhyperplastic nephron segments containing IGF-I raises the possibility that TGF-beta may be serving to convert the mitogenic action of IGF-I into a hypertrophic response in these segments. It is also conceivable that TGF-beta may be a cause of the tubulointerstitial infiltrate. Finally, the low circulating IGF-I levels likely contribute to the impaired body growth.     

Compensatory renal growth in uninephrectomized adult mice is growth hormone dependent

Compensatory renal growth in uninephrectomized adult mice is growth hormone dependent. BACKGROUND: Growth hormone (GH) and insulin-like growth factors (IGFs) have been implicated as pathogenic factors in compensatory renal growth (CRG) following unilateral nephrectomy in rodents. CRG in adult rats has been suggested to be GH dependent and GH independent in immature rats. However, the exact role of GH as a regulating or permissive factor in CRG in adult rodents has not been fully resolved to date. METHODS: To elucidate a possible direct, permissive role of GH in CRG, we examined the effect of a newly developed specific GH receptor (GHR) antagonist (G120K-PEG) on kidney IGF-I accumulation and renal/glomerular hypertrophy over seven days after uninephrectomy in adult mice. RESULTS: Placebo-treated uninephrectomized mice were characterized by a transient increase in kidney IGF-I concentration preceding CRG and an increase in glomerular volume. In G120K-PEG-treated uninephrectomized animals, increased kidney IGF-I levels, kidney weight, and glomerular volume were fully abolished. No differences were seen between the two uninephrectomized groups with respect to body weight, food intake, blood glucose, serum GH, IGF-I, or IGFBP-3 levels. CONCLUSIONS: The administration of a GHR antagonist in uninephrectomized adult mice has renal effects without affecting circulating levels of GH/IGFs, indicating that the effect of G120K-PEG may be mediated through a direct inhibitory effect on renal IGF-I accumulation through the renal GHR. This study shows, to our knowledge for the first time, that CRG in adult mice is strictly GH dependent.     

Leptin acts as a growth factor on the chondrocytes of skeletal growth centers.

Childhood obesity frequently is associated with an increase in height velocity and acceleration of epiphyseal growth plate maturation despite low levels of serum growth hormone (GH). In addition, obesity is associated with higher circulating levels of leptin, a 16-kDa protein that is secreted from the adipocytes. In this study, we evaluated the direct effect of leptin on the chondrocyte population of the skeletal growth centers in the mouse mandibular condyle, a model of endochondral ossification. We found that chondrocytes in the growth centers contain specific binding sites for leptin. Leptin, at a concentration of 0.5-1.0 microg/ml, stimulated in a dose-dependent manner the width of the chondroprogenitor zone (up to 64%), whereas higher concentrations had an inhibitory effect. Leptin induction of both proliferation and differentiation activities in the mandibular condyle was confirmed by our findings of an increase in bromodeoxyuridine (BrdU) incorporation into DNA and in (acidic) Alcian blue (AB) staining of the cartilaginous matrix. Leptin also increased the abundance of the insulin-like growth factor (IGF) I receptor and IGF-I receptor messenger RNA (mRNA) within the chondrocytes and the progenitor cell population. Our results indicate that leptin acts as a skeletal growth factor with a direct peripheral effect on skeletal growth centers. Some of its effects on the growing bone may be mediated by the IGF system via regulation of IGF-I receptor expression. We speculate that the high circulating levels of leptin in obese children might contribute to their growth.     

Growth hormone aggravates renal abnormalities induced by neonatal enalapril treatment

Lack of neonatal angiotensin II type-1 receptor stimulation produces irreversible abnormalities of renal function and morphology, which can be prevented by simultaneous administration of insulin-like growth factor-I (IGF-I). Given the fact that growth hormone (GH) is the strongest secretagogue for IGF-I, we wanted to explore whether GH could reproduce the effect of IGF-I. Rats were treated from 3 to 13 days of age with the angiotensin-converting enzyme inhibitor enalapril (10 mg/kg/day) and GH (4 mg/kg/day), alone or in combination. Renal gene expression of IGF-I and IGF-binding proteins (IGFBP) was determined during and after treatment. Renal function and morphology were investigated at adult age. In contrast to the beneficial effect of IGF-I, GH treatment in combination with enalapril further deteriorated both renal function and morphology as compared with enalapril treatment alone, demonstrating: reduced glomerular filtration rate, increased tubular dilation and further expansion of the outer medulla. Enalapril decreased medullary expression of IGF-I and increased renal expression of IGFBP-1, changes that were not affected by concomitant GH treatment. These findings indicate that GH and IGF-I have different roles in the renin-angiotensin system-mediated kidney development.     

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.     

生长激素荷人结肠癌裸鼠GH/IGF-I/IGFBP-3轴的影响

目的：探讨外源性生长激素（GH）对荷瘤裸鼠GH/胰岛素样生长因子（IGF）/胰岛素样生长因子结合蛋白3（IGFBP-3）轴的影响。方法：采用人结肠癌细胞株（HCT116）建立人结肠癌细胞裸鼠移植瘤模型。取48只荷瘤裸鼠随机均分为生理盐水处理组（NS组）、氟尿嘧啶处理组（FU组）、GH处理组（GH组）,FU+GH处理组（FU+GH组）。每组连续给药6 d,在给药结束后24,72 h分别处死每组6只动物,取血及移植瘤标本,应用ELISA法检测血清GH,IGF-I,IGFBP-3含量和RT-PCR法检测移植瘤IGF-I,IGF-I受体（IGF-IR）,IGFBP-3的mRNA表达。结果：ELISA结果显示,给药结束后24 h,GH组和FU+GH组血清GH,IGF-I,IGFBP-3含量较NS组与FU组明显升高（均P<0.05）;给药结束后72 h,各组GH,IGF-I的水平无统计学差异（均P>0.05）,但GH组和FU+GH组IGFBP-3水平仍高于NS组和FU组（均P<0.05）。RT-PCR结果显示,给药结束后24 h,GH,FU,FU+GH组移植瘤组织IGF-I mRNA与IGF-IR mRNA的表达较NS组明显降低,而IGFBP-3 mRNA表达明显增加;给药结束后72 h,IGF-I mRNA与IGF-IR mRNA表达各组间无差别,但GH组,FU组和FU+GH组IGFBP-3 mRNA表达量仍明显高于NS组。结论：短期应用外源性GH所致GH/IGF/IGFBP-3轴的变化对人结肠癌移植瘤生长无促进作用。

     

Stimulatory effect of insulin-like growth factor binding protein-5 on mouse osteoclast formation and osteoclastic bone-resorbing activity.

Insulin-like growth factor binding protein-5 (IGFBP-5) stimulates osteoblast proliferation directly or indirectly through IGF-I action, but its effects on osteoclast formation and osteoclastic activity are unknown. We tested the effects of IGFBP-5 on osteoclastic activity and osteoclast formation. IGFBP-5 significantly stimulated pit formation by pre-existent osteoclasts in mouse bone cell cultures and its stimulatory effect was completely blocked by IGF-I antibody (Ab). However, IGFBP-5 did not affect the bone-resorbing activity of isolated rabbit osteoclasts. When IGFBP-5 was added to unfractionated bone cells after degeneration of pre-existent osteoclasts, IGFBP-5 (77 pM-7.7 nM) dose-dependently stimulated osteoclast-like cell formation, irrespective of the presence of IGF-I Ab. Moreover, osteoclast-like cells newly formed by IGFBP-5 from unfractionated bone cells possessed the ability to form pits on dentine slices. We next examined the direct effect of IGFBP-5 on osteoclast precursors in the absence of stromal cells, using hemopoietic blast cells derived from spleen cells. IGFBP-5 dose-dependently stimulated osteoclast-like cell formation from osteoclast precursors, irrespective of the presence of IGF-I Ab. Growth hormone (GH) as well as IGF-I significantly stimulated bone resorption by pre-existent osteoclasts in mouse bone cell cultures and these stimulatory effects were completely blocked by IGF-I Ab. GH as well as IGF-I stimulated osteoclast-like cell formation from unfractionated bone cells and this stimulatory effect of GH was significantly but partially blocked by IGF-I Ab. The direct stimulatory effect of GH on osteoclast-like cell formation from hemopoietic blast cells was not affected by IGF-I Ab. The present data indicate that IGFBP-5 stimulates bone resorption both by stimulation of osteoclast formation in an IGF-I-independent fashion and by IGF-I-dependent activation of mature osteoclasts, possibly via osteoblasts, in vitro.     

Inhibitory effect of a growth hormone receptor antagonist (G120K-PEG) on renal enlargement, glomerular hypertrophy, and urinary albumin excretion in experimental diabetes in mice.

Growth hormone (GH) and IGFs have a long and distinguished history in diabetes, with possible participation in the development of renal complications. To investigate the effect of a newly developed GH receptor (GHR) antagonist (G120K-PEG) on renal/glomerular hypertrophy and urinary albumin excretion (UAE), streptozotocin-induced diabetic and nondiabetic mice were injected with G120K-PEG every 2nd day for 28 days. Placebo-treated diabetic and nondiabetic animals were used as reference groups. Placebo-treated diabetic animals were characterized by growth retardation, hyperphagia, hyperglycemia, increased serum GH levels, reduced serum IGF-I, IGF-binding protein (IGFBP)-3, and liver IGF-I levels, increased kidney IGF-I, renal/glomerular hypertrophy, and increased UAE when compared with nondiabetic animals. No differences were seen between the two diabetic groups with respect to body weight, food intake, blood glucose, serum GH, IGF-I, and IGFBP-3 levels or hepatic IGF-I levels. Kidney IGF-I, kidney weight, and glomerular volume were normalized, while the rise in UAE was partially attenuated in the G120K-PEG-treated diabetic animals. No effect of G120K-PEG treatment on any of the parameters mentioned above was seen in nondiabetic animals. In conclusion, administration of a GHR antagonist in diabetic mice has renal effects without affecting metabolic control and circulating levels of GH, IGF-I, or IGFBP-3, thus indicating that the effect of G120K-PEG may be mediated through a direct inhibitory effect on renal IGF-I through the renal GHR. The present study suggests that specific GHR blockade may present a new concept in the treatment of diabetic kidney disease.     

Paradoxical body and kidney growth in potassium deficiency

In the growing animal, K deficiency (KD) retards body growth, but paradoxically stimulates renal growth. If KD persists, interstitial infiltrates appear and eventually tubulointerstitial fibrosis develops. In patients with chronic KD, renal cysts may form and with time tubulointerstitial disease with renal failure develops. Since early in KD, kidney IGF-I levels increase and may be a cause of the renal hypertrophy, and as TGF-beta promotes hypertrophy and fibrosis, we examined the expression of these growth factors in chronic KD. Rats were given a KD diet or pair or ad-lib fed a normal K diet. After 21 days, KD rats weighed less than pair fed controls, while the kidneys were 49% larger Serum IGF-I and kidney IGF-I protein levels were depressed, as were IGF-I mRNA levels, and is largely attributable to decreased food intake. Kidney IGFBP-1 and TGF-beta mRNA levels were increased (p < 0.05). There was marked hypertrophy and adenomatous hyperplasia of outer medullary collecting ducts, hypertrophy of thick ascending limbs of Henle (TALH) and interstitial infiltrates. Both nephron segments stained strongly for IGF-I and IGFBP-1. Only the non-hyperplastic TALH was strongly TGF-beta positive. Interstitial infiltrates containing monocytes/macrophages were prominent. These findings are consistent with a sustained role for IGF-I in promoting the renal hypertrophy of KD and appear to be caused by local trapping of IGF-I by the over-expressed IGFBP-1. Localization of TGF-beta to the hypertrophied non-hypoplastic tubules containing IGF-I, suggests that TGF-beta may be acting to convert the proliferative action of IGF-I into a hypertrophic response. TGF-beta may also contribute to the genesis of the tubulointerstitial infiltrate. Finally, the reduced levels of serum IGF-1 levels may be a cause of the blunted body growth.     

Correction of metabolic acidosis improves thyroid and growth hormone axes in haemodialysis patients.

BACKGROUND: Chronic metabolic acidosis (CMA) in normal adults results in complex endocrine and metabolic alterations including growth hormone (GH) insensitivity, hypothyroidism, hyperglucocorticoidism, hypoalbuminaemia and loss of protein stores. Similar alterations occur in chronic renal failure, a prototypical state of CMA. We evaluated whether metabolic acidosis contributes to the endocrine and metabolic alterations characteristic of end-stage renal disease. METHODS: We treated 14 chronic haemodialysis patients with daily oral Na-citrate for 4 weeks, yielding a steady-state pre-dialytic plasma bicarbonate concentration of 26.7 mmol/l, followed by 4 weeks of equimolar Na-chloride, yielding a steady-state pre-dialytic plasma bicarbonate of 20.2 mmol/l. RESULTS: Blood pressure, body weight and dialysis adequacy were equivalent in the two protocols. Na-citrate treatment corrected CMA, improved GH insensitivity, increased and normalized plasma free T(3) concentration, and improved plasma albumin. Correction of CMA had no significant effect on measured cytokines (interleukin-1 beta and -6, tumour necrosis factor-alpha) or acute phase reactants (C-reactive protein, serum amyloid A, alpha(2)-macroglobulin). CONCLUSION: CMA contributes to the derangements of the growth and thyroid hormone axes and to hypoalbuminaemia, but is not a modulator of systemic inflammation in dialysis patients. Correcting CMA may improve nutritional and metabolic parameters and thus lower morbidity and mortality.     

mRNA expression of the IGF system in the kidney of the hypersomatotropic rat

AIM: To examine the response of the insulinlike growth factor (IGF) system in the kidney during a state of extreme growth. METHODS: We studied the mRNA expression of IGF-I, IGF-I receptor, and IGF-binding proteins (BP) using sensitive RNase protection assays following subcutaneous implantation of growth hormone pituitary cells (GH(3)) in rats. RESULTS: Within 5 weeks, the serum GH levels increased from 18.0 +/- (SE) 5.0 ng/ml in control animals to 389.8 +/- 30.3 ng/ml in GH(3) rats (n = 5, p < 0.001). The circulating IGF-I levels were also elevated. The kidney weights increased from 0.74 +/- 0.01 g in controls to 1.06 +/- 0.03 g in GH(3) animals (n = 5, p < 0.001). Similar changes were observed at week 10. The renal IGF-I mRNA averaged 1.0 +/- (SD) 0.33 relative densitometry units in controls (n = 4) and increased to 2.11 +/- 0.13 relative densitometry units in GH(3) rats (n = 5, p < 0.001). On the other hand, mRNA for the type I IGF receptor decreased in hypersomatotropic rats. Messenger RNAs for IGFBP-1 and IGFBP-4, which have been localized to renal tubules, both decreased significantly following growth induction, while IGFBP-3, the mRNA of which has an interstitial localization, was increased at week 10. CONCLUSION: These data suggest that there is a dynamic relationship between tubular and interstitial compartments with regard to the IGF system in the kidney which may be important in the regulation of the cell mass.     

High-protein induced renal enlargement is growth hormone independent

BACKGROUND: Growth hormone (GH) and insulin-like growth factors (IGFs) have been postulated as pathogenic factors in several forms of renal growth, including that induced by high-protein (HP) diets. Compensatory renal growth (CRG) following renal uninephrectomy is strictly GH dependent, while the exact role of GH as a regulating factor in HP induced renal growth has not been fully clarified. METHODS: To elucidate a possible direct role for GH in HP-induced renal growth, we examined the effect of a newly developed specific GH-receptor (GHR) antagonist (B2036-PEG) on renal growth and renal GH/IGF-system expression in HP-fed mice. RESULTS: Mice fed a HP diet (45% protein) for one week demonstrated renal hypertrophy and increased renal IGF-I. GH receptor antagonist (GHRA) treatment neither modified renal IGF-I nor abolished the renal hypertrophy. In contrast, however, GHRA administration did modify renal mRNA expression of many members of the GH and IGF systems. CONCLUSIONS: The major new finding is that HP-induced renal growth in adult mice is GH independent.     

Growth hormone,insulin growth factor-1, and igf binding protein-3 axis relationship with bone mineral density among healthy men

The aim of this study was to investigate serum levels of growth hormone (GH), insulin growth factor-I (IGF-I), and insulin growth factor binding protein-3 (IGFBP-3) in 363 healthy caucasian men with and without decreased bone density, who had never experienced fractures. Mean age was 51+/-8.7 years. Height and weight were measured and BMI was calculated using the formula weight (kg)/height (m(2)). Bone mineral density (BMD) was assessed: in 4 skeletal sites (lumbar spine [LS], femoral neck [FN], Ward's triangle [WT], and trochanter [T]) using dual-energy X-ray absorpsiometry (DEXA). After an overnight fasting, blood samples were taken at 8:00 a.m. Serum concentrations of GH, IGF-I, and IGFBP-3 were measured using the immunofunctional (GH) and IRMA (IGF-I and IGFBP-3) methods. The BMD at the 4 skeletal sites is expressed as mean value+/-SD in g/cm(2) and T score. Forty-four men (11%) had bone mineral density (BMD)<-2.5 SD (T score). Mean GH, IGF-I, and IGFBP-3 levels were 0.2+/-0.1, 186.1+/-177.3, and 4990+/-1460 ng/mL, respectively. There were no significant differences between men with normal BMD and men with reduced BMD concerning GH, IGF-I, and IGFBP-3 measurements. In normal men (319), mean GH, IGF-I, and IGFBP-3 levels were 0.4+/-0.1, 192+/-87, and 4960+/-1530 ng/mL, respectively. In the subgroup with reduced BMD (44), mean GH, IGF-I and IGFBP-3 levels were 0.2+/-0.1, 179+/-72 and 5230+/-1270 ng/mL, respectively. An age-dependent attenuation of GH, IGF-I, and IGFBP-3 levels was also found. No correlation was revealed between BMD and GH in the 4 skeletal sites tested. On the contrary, a positive correlation was established between BMD and IGF-I levels in 3 skeletal sites (LS, FN, T). The same was true between BMD and IGFBP-3 in 2 skeletal sites (LS, FN). In conclusion, 11% of Greek healthy males had decreased bone density. No fractures were demonstrated in any individuals. No significant differences were found between men with normal and reduced BMD, with regards to serum GH, IGF-I, and IGFBP-3, although these levels decreased with age. No correlation was found between BMD and GH levels in the 4 skeletal sites. A positive correlation was found between BMD and IGF-I levels in 3 skeletal sites and IGFBP-3 in 2 skeletal sites.     

Glomerulosclerosis in mice transgenic for human insulin-like growth factor-binding protein-1

BACKGROUND: The growth hormone (GH)/insulin-like growth factor (IGF) system is thought to participate in the glomerulosclerosis process. Because IGF-binding proteins (IGFBPs) modulate IGF actions and hence GH secretion, this study assessed whether mice transgenic for human IGFBP-1 have altered susceptibility to glomerulosclerosis. METHODS: A line of transgenic mice that express human IGFBP-1 mRNA in the liver under the control of the alpha1-antitrypsin promoter has been obtained, and morphological changes in the kidney tissue were assessed. Glomerulosclerosis was identified using light microscopy, light microscopic morphometry, and electron microscopy. Extracellular matrix components were analyzed by immunohistochemistry. RESULTS: There was a marked increase in mesangial extracellular matrix area in homozygous transgenic mice at three months of age as compared with heterozygous transgenic mice and nontransgenic littermates. These changes were not associated with alterations in glomerular volume or cellularity. The expansion of extracellular matrix area was related to a marked increase in laminin and type IV collagen and to the appearance of type I collagen. CONCLUSIONS: These observations indicate that the enhanced expression of IGFBP-1 may result in the development of glomerulosclerosis without glomerular hypertrophy. The changes are potentially related to a decrease in IGF-I availability and/or to an IGF-I-independent role of IGFBP-1.