Insulin-like growth factor system abnormalities in hepatitis C-associated osteosclerosis. Potential insights into increasing bone mass in adults

A case of hepatitis C-associated osteosclerosis in an elderly Japanese man

Hepatitis C-Associated Osteosclerosis (HCAO) is characterized by a marked increase in bone mass with deep bone pain. Since 1992, eleven cases of HCAO have been reported. This report describes an elderly Japanese man with HCAO, whose clinical course we followed for 3 years. A 68-year-old man developed pain in both pretibial regions in June 2000, and he had frequent episodic loss of muscular strength in his hands. He had recieved blood transfusion for a bleeding ulcer 43 years before and was seropositive for hepatitis C virus. His serum alkaline phosphatase (ALP) level was markedly increased, while his serum calcium was slightly decreased and serum phosphate was normal. Skeletal radiographs of the lower extremities showed a progressive increase in skeletal density, but did not show any apparent deformity. Administration of nonsteroidal anti-inflammatory drugs led to a reduction in bone pain. Treatment with vitamin D3 and calcium decreased the number of episodes of sudden muscular weakness and maintained serum calcium within the normal range. Three years after the onset of the disease, bone mineral density of his lumbar vertebrae and left hip rose from 0.963 g/cm2 to 1.096 g/cm2, and from 0.938 g/cm2 to 1.383 g/cm2, respectively. His serum ALP level decreased from 2889 to 277 IU/L (normal range: 104-338) and serum calcium normalized. These findings were accompanied by a decrease in bone pain. This case and previous reports suggest that the skeletal tissue of this disease appears to be of good quality.

IGF-I secretion by prostate carcinoma cells does not alter tumor-bone cell interactions in vitro or in vivo

BACKGROUND

IGF-I is an important growth and differentiative factor for osteoblasts and may have a role in defining prostate cancer risk and skeletal metastases.

METHODS

Conditioned media (CM) from human prostate cancer (PC), C4-2 and C4-2B, which produce osteoblastic lesions, and PC-3, which causes osteolysis, was added to MC3T3-E1 bone cultures. SCID mice were injected intratibially with these engineered cells. Tumor bearing tibiae were analyzed by microCT and pQCT.

RESULTS

CM from PC cells increased osteoblast proliferation and differentiation and was unaltered by the type of PC cell, IGF-I antibodies, or exogenous IGF-I and IGFBP2. Study of intratibial PC tumors in SCID mice showed that C4-2 cells grew slowly preserving bone structure, while PC-3 tumors caused rapid osteolysis. Overexpression of IGF-I did not change either tumor progression or skeletal response.

CONCLUSIONS

IGF-I is neither necessary nor sufficient for the osteoblastic response to PC metastases.

Hepatitis C-associated osteosclerosis (HCAO): report of a new case with involvement of the OPG/RANKL system

We report a new case of hepatitis C-associated osteosclerosis (HCAO). The clinical presentation of the patient was an acquired deep severe bone pain with increased serum bone alkaline phosphatase activity (up to 12 times the upper limit of normal), and generalized bone sclerosis, temporally related to the hepatitis C-virus (HCV) infection. We documented in this patient an increase of circulating osteoprotegerin (OPG), and a concentration of circulating receptor activator for nuclear factor-kB ligand (RANKL) below the lower limit of the reference range. The observed abnormalities of the OPG/RANKL system may contribute to the maintenance of the positive balance of bone remodeling that characterizes patients with HCAO.

OPG/RANKL system imbalance in a case of hepatitis C-associated osteosclerosis: the pathogenetic key?

Hepatitis C-associated osteosclerosis (HCAO) is an impressive example of acquired diffuse osteosclerosis in adults, recently described in ten patients infected with hepatitis C virus (HCV). Its hallmark is a painful and generalized increase of bone mass. Bone biopsies show enhanced accretion rate, usually without histological abnormalities. The HCAO pathogenesis is hitherto unknown. HCV might induce a slow bone cell infection and the production of bone growth factors, such as insulin-like growth factors. Recently, receptor activator of nuclear factor-kappaB (RANK), its ligand (RANKL), and soluble decoy receptor osteoprotegerin (OPG) have been identified as a pivotal cytokine system in the bone remodeling control. We describe the 11th case of HCAO. Notably, the patient's bone biopsy showed the presence of a high number of OPG-positive osteoblasts, a slight increase of RANKL-positive stromal cells, and a dramatic reduction of the osteoclasts. Moreover, OPG serum levels were increased. These findings reported here for the first time are consistent with a pathogenetic role of the OPG/RANKL system imbalance in HCAO.

Circulating insulin-like growth factors in patients infected with Helicobacter pylori

OBJECTIVES

The level of insulin-like growth factors (IGFs) and their binding proteins may change in acutely ill humans. The aim of this work was to examine the changes in the IGF system in patients suffering from infection induced by Helicobacter pylori (H. pylori).

DESIGN AND METHODS

The serum concentrations of IGF-I, IGF-II and cortisol were measured by radioimmunoassay. IGFBP patterns were characterized by ligand-affinity blotting, and a lectin-binding assay was used to investigate the possible changes in the glycocomponent of IGFBP-3.

RESULTS

Both IGF-I and IGF-II concentrations were significantly lower in patients with H. pylori infection (P < 0.001 for IGF-I and P = 0.016 for IGF-II) compared to healthy individuals, whereas the level of cortisol was significantly elevated in analyzed patients (P < 0.001). Autoradiography demonstrated the increased presence of IGFBP-2 and IGFBP-1, together with a decreased level of IGFBP-3.

CONCLUSIONS

The circulating IGF/IGFBP system is altered in patients infected with H. pylori. The increased level of cortisol suggests the involvement of the hypothalamic/pituitary/adrenal axis that stimulates the elevation of blood glucose, probably in coordination with decreased IGF activity to minimize anabolic metabolism.

Distúrbios do eixo cálcio-PTH-vitamina D nas doenças hepáticas crônicas

Distúrbios no eixo cálcio-PTH-vitamina D são freqüentemente associados às doenças hepáticas crônicas (DHC). Já foi demonstrado que pacientes com DHC apresentam uma tendência à diminuição do cálcio e vitamina D, com aumento compensatório do PTH. Embora a diminuição da hidroxilação da vitamina D em 25 (OH) vitamina D fosse considerada o mecanismo principal destas alterações, estudos recentes vêm demonstrando que, mesmo nos estágios avançados de doença, o fígado ainda consegue manter níveis adequados de 25 (OH) vitamina D. Desta forma, outros fatores (ex: dieta inadequada, diminuição da exposição à luz solar) seriam os responsáveis pelas alterações no eixo cálcio-PTH-vitamina D. Além disso, o tratamento das DHC com glicocorticóides (fibrose cística) e ribavirina (Hepatite C) parece contribuir como agravante destes distúrbios. Por outro lado, parece ser a osteoporose, e não a osteomalácia ou o hiperparatireoidismo secundário, a principal alteração nas DHC. Assim, continua objeto de discussão o papel das alterações do eixo cálcio-PTH-vitamina D na osteodistrofia hepática.

A potentially deleterious role of IGFBP-2 on bone density in aging men and women

The role of the IGFs and IGFBPs on age-related changes in BMD in adult men and women is not well understood. Studying an age-stratified community based sample of 344 men and 276 women, we found higher IGFBP-2 levels to be associated with lower BMD. IGFBP-2, which increases with age in both men and women, was the strongest, most consistent predictor of BMD among the IGF/IGFBPs studied.

INTRODUCTION

Insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) are important regulators of tissue growth and metabolism, but their association with BMD in adult men and women is controversial.

MATERIALS AND METHODS

In an age-stratified, random sample of the community population, we examined the role of serum levels of IGF-I, IGF-II, and IGFBP-1, -2, and -3 on BMD of the proximal femur (total hip), lateral spine, midshaft, and ultradistal radius as measured by DXA. We explored the association before and after adjustment for potential confounders, including age, bioavailable estradiol and testosterone, sex hormone binding globulin (SHBG), and measures of total fat and skeletal muscle mass.

RESULTS

We studied 344 men (age, 23-90 years) and 276 women (age, 21-93 years; 166 postmenopausal) not on hormone replacement or oral contraceptives. In both men and women, IGF-I and IGFBP-3 levels fell with advancing age, whereas IGFBP-2 levels tended to rise with age. There was an inverse association of IGFBP-2 with BMD at most skeletal sites in men and both premenopausal and postmenopausal women, whereas lower IGF-I and IGFBP-3 were associated with lower BMD in men and postmenopausal women only. Lower IGF-II was associated with lower BMD in men only. There were no associations between IGFBP-1 and BMD in either sex. After adjustment for age, in most cases, we found no further associations between IGF-I, IGF-II, or IGFBP-3 and BMD. In contrast, after age adjustment, higher IGFBP-2 remained a predictor of lower BMD in men and postmenopausal women at all sites except for the lateral spine (for men: r = -0.21, -0.20, and -0.19, all p < 0.001; and for postmenopausal women: r = -0.34, -0.24, and -0.25, all p < 0.01, for the total hip, midshaft, and ultradistal radius, respectively). IGFBP-2 remained an independent negative predictor of BMD in men, postmenopausal women, and all women combined after additional adjustment for bioavailable sex steroids, but not at all sites after adjustment for SHBG and muscle mass. In premenopausal women, IGFBP-2 had similar associations as seen in postmenopausal women, but they were weaker and not statistically robust.

CONCLUSIONS

Among the IGF/IGFBPs in our study, IGFBP-2 was a key negative predictor of BMD among men and women, particularly postmenopausal women. Our findings suggest a potential role of the IGF/IGFBP system in regulating bone loss in aging men and women and identify a previously under-recognized, potentially deleterious role for IGFBP-2, a known inhibitor of IGF action that increases with age in both sexes. Whether the action of the IGF/IGFBP system on bone metabolism is mediated partly through its effects on muscle mass or SHBG deserves further study.

Potentiating role of IGFBP-2 on IGF-II-stimulated alkaline phosphatase activity in differentiating osteoblasts

The insulin-like growth factor (IGF) system plays an important role in the autocrine and paracrine regulation of bone formation and remodeling. The aim of this study was to evaluate the role of the autocrine IGF system during osteogenic differentiation in rat tibial osteoblasts (ROB) in culture. In this in vitro model, the stages of osteogenesis studied were S1, corresponding to the onset of alkaline phosphatase (AP) expression (days 0-3); S2, coincident with the peak of AP expression in differentiation culture conditions (days 4-6), and S3, corresponding to the onset of mineral deposition in the extracellular matrix (days 7-9). The results showed that conditioned medium of ROB contains greater amounts of IGF-II than IGF-I at all differentiation stages. Both peptides showed the highest concentrations on day 3 of differentiation (end of S1). All IGF-binding proteins (IGFBPs), except IGFBP-1 and -6, were detected, and IGFBP-2 was the most abundant IGFBP present in the conditioned media, and its degradation increased from S1 to S3. By semiquantitative RT-PCR, IGF-I and IGF-II were highly expressed on days 3 and 6, whereas IGFBP-2 was constantly expressed. We focused our study on the role of IGF-II and IGFBP-2 on the synthesis of AP, an early marker of osteoblast maturation. The results showed that a significant increase in AP expression was induced by IGF-II added to the differentiating osteoblasts continuously or in S1 but not in S2 or S3. IGFBP-2 was able to potentiate endogenous and exogenous IGF-II-dependent stimulation of AP activity, and its proteolytic degradation in late stages of osteogenesis (S2 and S3) was highly correlated with the increase of active matrix metalloproteinase-2 in the CM and with the decreased efficacy of IGF-II action. These data suggest that IGFBP-2, at nearly equimolar concentration with IGF-II, plays a potentiating role in IGF-II action on ROB differentiation in vitro.

Prostate carcinoma cells that have resided in bone have an upregulated IGF-I axis

BACKGROUND

Prostate cancer (PC) has a propensity to metastasize to the skeleton, inducing an osteoblastic response in the host. Recent epidemiological studies have suggested that circulating IGF-I may be important for both the pathogenesis and dissemination of PC. We have postulated that tumor secreted IGF-I in conjunction with endogenous IGF-I contributes to the osteoblastic phenotype characteristic of metastatic PC.

METHODS

To test this thesis we studied the established LNCaP PC progression model consisting of three genetically related human PC cell lines.

RESULTS

Using RIA, we found serum-free conditioned media (CM) of LNCaP and C4-2 had no measurable IGF-I, whereas IGF-I was easily detected in CM from C4-2B cells at 24 hr (i.e., 1.8 +/- 0.53 ng/mg cell protein). Real-time PCR of IGF-I mRNA showed that C4-2B expressed 100-fold more IGF-I mRNA than LNCaP cells. In addition, C4-2B expression of IGF-I mRNA was substantially increased in the presence of exogenous IGF-I to nearly twofold. While IGFBP-3 and IGFBP-1 were not detectable in the CM of any PC line, all cells secreted IGFBP-2. C4-2B cells produced 40% more IGFBP-2 than LNCaP or C4-2 cells (C4-2B at 167 +/- 43 ng/mg cell protein). RANKL, a product of bone stromal cells, was also differentially expressed: LNCaP had threefold higher RANKL mRNA compared to C4-2 and C4-2B and at least equivalent protein expression.

CONCLUSIONS

Our results suggest that PC cells that have metastasized to bone have an upregulated IGF-I regulatory system. This suggests an activated IGF-I axis contributes to the host-PC interaction in promoting osteoblastic metastases.

Role of extracellular matrix in insulin-like growth factor (IGF) binding protein-2 regulation of IGF-II action in normal human osteoblasts

Insulin-like growth factor binding protein-2 (IGFBP-2) in its native form had little affinity for extracellular matrix (ECM) derived from human or rat osteoblastic cells. However, in the presence of IGFs, IGFBP-2 binding to ECM was markedly enhanced, with IGF-II being more effective than IGF-I. IGF-II-enhanced binding of IGFBP-2 to ECM was specific for IGFBP-2 of the six known IGFBPs. In the presence of IGF-II, IGFBP-2 bound with high affinity to heparin-Sepharose, but not to type I collagen, fibronectin, or laminin. Furthermore, heparin and heparan sulfate, but not chondroitin sulfate, inhibited IGFBP-2/IGF-II binding to ECM. High salt (100 mM NaCl) inhibited, while CaCl(2) enhanced binding of IGFBP-2/IGF-II to ECM. In the presence of ECM, IGFBP-2/IGF-II was as effective as IGF-II alone in stimulating [3H]thymidine and [3H]proline incorporation and in inhibiting apoptosis in cultured human osteoblasts. On the other hand, IGFBP-2 was a potent inhibitor of IGF-II action in human breast and ovarian carcinoma cells. There was no difference between soluble and ECM-associated IGFBP-2 in affinity for IGF-I and IGF-II. These data suggest a unique mechanism for targeting an anabolic IGFBP-2/IGF-II complex in bone.

Use of site-specific antibodies to characterize the circulating form of big insulin-like growth factor II in patients with hepatitis C-associated osteosclerosis

Hepatitis C-associated osteosclerosis (HCAO) is a rare syndrome of adult-onset osteosclerosis. An understanding of the factor(s) leading to the stimulation of bone formation in these patients may provide novel anabolic approaches for the treatment of osteoporosis. We have demonstrated that HCAO patients have a specific increase in circulating big IGF-II (IGF-IIE) and IGF-binding protein-2 (IGFBP-2) levels, and that IGF-IIE and IGFBP-2 circulate together in a bioavailable, 50-kDa complex. Patients with nonislet cell tumor hypoglycemia (NICTH) also have increased circulating IGF-IIE and IGFBP-2 levels. However, HCAO patients do not exhibit hypoglycemia, nor do NICTH patients exhibit obvious osteosclerosis. Thus, to better understand the reason(s) for the differing clinical manifestations of the IGF-IIE excess in the two syndromes, we characterized IGF-IIE in HCAO and NICTH sera using recently developed antibodies (Ab) recognizing either the full-length IGF-IIE 89-amino acid C-terminal extension peptide (IIE(138-156) Ab) or specific cleavage forms of IGF-IIE (IIE(78-88) Ab and IIE(89-101) Ab). The predominant IGF-IIE form in HCAO serum migrated on SDS-PAGE as a single band at approximately 18 kDa that reacted with the IIE(89-101) Ab. On the other hand, the predominant form in NICTH serum migrated as a doublet of 14 and 16 kDa that reacted with the IIE(78-88) Ab. There results are consistent with differential processing of the IGF-IIE precursor at predicted cleavage sites producing IGF-IIE(1-104) and IGF-IIE(1-88) in HCAO and NICTH, respectively. As these two forms may have differing biological activities and/or targeting properties, our findings may explain at least in part the different manifestations of IGF-IIE overproduction in the two syndromes.

Subcutaneous administration of insulin-like growth factor (IGF)-II/IGF binding protein-2 complex stimulates bone formation and prevents loss of bone mineral density in a rat model of disuse osteoporosis

Elevated serum levels of insulin-like growth factor binding protein-2 (IGFBP-2) and a precursor form of IGF-II are associated with marked increases in bone formation and skeletal mass in patients with hepatitis C-associated osteosclerosis. In vitro studies indicate that IGF-II in complex with IGFBP-2 has high affinity for bone matrix and is able to stimulate osteoblast proliferation. The purpose of this study was to determine the ability of the IGF-II/IGFBP-2 complex to increase bone mass in vivo. Osteopenia of the femur was induced by unilateral sciatic neurectomy in rats. At the time of surgery, 14-day osmotic minipumps containing vehicle or 2 microg IGF-II+9 microg IGFBP-2/100g body weight/day were implanted subcutaneously in the neck. Bone mineral density (BMD) measurements were taken the day of surgery and 14 days later using a PIXImus small animal densitometer. Neurectomy of the right hindlimb resulted in a 9% decrease in right femur BMD (P<0.05 vs. baseline). This loss in BMD was completely prevented by treatment with IGF-II/IGFBP-2. On the control limb, there was no loss of BMD over the 14 days and IGF-II/IGFBP-2 treatment resulted in a 9% increase in left femur BMD (P<0.05). Bone histomorphometry indicated increases in endocortical and cancellous bone formation rates and in trabecular thickness. These results demonstrate that short-term administration of the IGF-II/IGFBP-2 complex can prevent loss of BMD associated with disuse osteoporosis and stimulate bone formation in adult rats. Furthermore, they provide proof of concept for a novel anabolic approach to increasing bone mass in humans with osteoporosis.

Alterations of IGF-binding proteins in patients with alcoholic liver cirrhosis

The protein synthetic activity of the liver is diminished in cirrhosis. The aim of this study was to investigate possible changes in the serum IGF-IGFBP system among patients with alcoholic liver cirrhosis (ALC). The results obtained demonstrated that serum IGF-I and IGF-II concentrations were significantly lower in patients with ALC than in healthy persons (P=0.0008 for IGF-I and 0.0002 for IGF-II). The IGFBP profile was markedly altered and the 34 kDa IGFBP from patients had higher affinity towards 125I-IGF-II compared to the 34 kDa IGFBP of control individuals. Moreover, the 40-45 kDa IGFBP (in isolated complex with 125I-IGF-II) exhibited diminished interaction with concanavalin A, wheat germ, and breadfruit lectins. Modification of the glyco-component of the 40-45 kDa IGFBP seems to be an early event in ALC since change in reactivity towards lectins was noticed in patients with ALC classified as Child score A, whose serum IGF-I and IGF-II levels were within reference limits (the existence of carbohydrate microheterogeneity of this IGFBP was also assessed by lectin-affinity electrophoresis). It is possible that these biochemical alterations may affect the functional activity of the IGFs by changing the dynamics and distribution of these growth factors in the organism.

Increased marrow-derived osteoprogenitor cells and endosteal bone formation in mice lacking thrombospondin 2

The phenotype of thrombospondin 2 (TSP2)-null mice includes abnormalities in collagen fibrils and increases in ligamentous laxity, vascular density, and bleeding time. In this study, analyses by computerized tomography (CT) revealed that cortical density was increased in long bones of TSP2-null mice. Histomorphometric analysis showed that the mid-diaphyseal endosteal bone formation rate (BFR) of TSP2-null mice was increased in comparison with that of wild-type (WT) animals. Although microgeometric analysis showed that periosteal and endosteal radii were reduced, the mechanical properties of femurs from TSP2-null mice were not significantly different from those of controls, presumably because of the concomitant increase in endosteal bone mass. Bone loss in ovariectomized mice was equivalent for WT and mutant mice, a finding that indicates that TSP2-null animals are capable of normal bone resorption. To further explore the cellular basis for the increased endosteal BFR in TSP2-null mice, marrow stromal cells (MSCs) were isolated and examined in vitro. These cells were found to be present in increased numbers in a colony forming unit (CFU) assay and showed an increased rate of proliferation in vitro. We conclude that TSP2 regulates the proliferation of osteoblast progenitors, directly or indirectly, and that in its absence endosteal bone formation is increased.

Effects of androgens on the insulin-like growth factor system in an androgen-responsive human osteoblastic cell line

Although androgens have significant effects on bone metabolism, the mediators of their effects are still unclear. As the insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) have important effects on osteoblast proliferation and differentiation, we examined androgen effects on the IGF system in a conditionally immortalized human fetal osteoblastic cell line, hFOB/AR-6, which displays a mature osteoblastic phenotype and physiological levels of functional androgen receptors. The nonaromatizable androgen, 5alpha-dihydrotestosterone (5alphaDHT), and testosterone, but not dehydroepiandrosterone, increased IGF-I messenger RNA (mRNA) levels up to 4-fold in a dose (10(-12)-10(-6) M)- and time (2-72 h)-dependent fashion. These changes were prevented by the specific androgen receptor antagonist, hydroxyflutamide. In addition, 5alpha-DHT decreased IGFBP-4 mRNA and protein levels by 2- and 4-fold, respectively, and increased IGFBP-2 and -3 mRNA and protein levels by 6- and 7-fold (for mRNA) and 3- and 5-fold (for protein), respectively. hFOB/AR-6 cells expressed the type-I IGF receptor, but this was not regulated by 5alphaDHT. 5alphaDHT and IGFBP-3 specifically increased hFOB/AR-6 cell proliferation, and a monoclonal antibody specific for IGF-I blocked this effect. Thus, androgens increase the expression of IGF-I, IGFBP-2, and IGFBP-3, but decrease levels of the inhibitory IGFBP-4 in an androgen-responsive human osteoblastic cell line. Our data are consistent with the hypothesis that the effects of androgen on bone cells may be mediated at least in part by increases in IGF-I production and by differential regulation of IGFBPs.

Bone abnormalities in gastrointestinal and hepatic disease

Bone is a dynamic tissue that undergoes constant remodeling in response to local and environmental stimuli. Bone mass is maintained by this delicate equilibrium between bone formation and bone resorption. In growing children, the balance is tilted toward bone formation until peak bone mass is achieved in the second decade of life. Alterations in bone metabolism can result in decreased bone mass (osteopenia and osteoporosis) or impaired mineralization of the bone protein matrix (rickets and osteomalacia). Diseases of the alimentary tract such as celiac disease, inflammatory bowel diseases, gastrectomy, cholestatic liver diseases, liver transplantation, and hepatitis C can affect bone mineralization, remodeling, or bone mass. This article presents a summary of recent reports concerning bone disorders associated with disorders of the liver and gastrointestinal tract.